Electrical Measurements Pune University MCQs

Electrical Measurements Pune University MCQs

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Introduction of Bridges”.

1. A bridge circuit is used for the measurement of which of the following components?

a) Resistance, capacitance, and inductance

b) Diode, triode, and thyristor

c) Transistor, thermistor, and antenna

d) LED, op amp, and transducer

Answer: a

Explanation: A bridge circuit is basically used for the measurement of basic electronic components such as resistance, capacitance, and inductance.

2. A simple bridge circuit consists of a network of __________

a) 3 resistance arms

b) 2 resistance arms

c) 4 resistance arms

d) 6 resistance arms

Answer: c

Explanation: A simple bridge circuit is made of a network consisting of 4 resistance arms. Usually a galvanometer is connected between the ends of the opposite two junctions in order to measure the flow of current.

3. What is applied to the two opposite junctions of a bridge circuit?

a) source of voltage

b) source of current

c) source of power

d) source of impedance

Answer: b

Explanation: A current source is connected between the two opposite junctions of a bridge circuit. Deflection of the galvanometer in the circuit indicates the flow of current.

4. A bridge circuit uses which method of measurement?

a) absolute

b) relative

c) differential

d) comparison

Answer: d

Explanation: A bridge circuit makes use of a comparison measurement method. In this method the bridge compares the value of an unknown component with a standard value of a given component.

5. Which principle operates a bridge circuit?

a) null indication

b) ampere’s rule

c) partial indication

d) kirchhoff’s laws

Answer: a

Explanation: A bridge circuit operates on the principle of null indication. Based on the deflection of the galvanometer, current flows between the two opposite junctions.

6. The accuracy of a bridge depends on the _________

a) null indicator

b) bridge components

c) current source

d) voltage source

Answer: b

Explanation: As a bridge circuit compares the value of an unknown component with the value of a standard, it’s accuracy depends on the bridge components.

7. When is the bridge circuit balanced?

a) When voltage is applied

b) When current flows through the opposite ends of the bridge circuit

c) When no current flows through the galvanometer

d) When impedance is minimum

Answer: c

Explanation: The bridge circuit is said to be balanced when no current flows through the null indicator which is generally a galvanometer.

8. Relationship at balance condition between the component values of the four arms of a bridge is known as _________

a) full load condition

b) open circuit condition

c) short circuit condition

d) balancing condition

Answer: d

Explanation: During balance condition or equilibrium there exists a certain relationship between the component values of the four arms of the bridge. This relationship is known as the balancing condition or balancing equation.

9. D.C. bridges are used for _________

a) measurement of resistance

b) measurement of capacitance

c) measurement of current

d) measurement of inductance

Answer: a

Explanation: Resistance measurements are done by making use of a suitable D.C. bridge.

10. What is used to characterize single port devices, multiport devices, etc?

a) current values

b) impedance values

c) voltage values

d) power values

Answer: b

Explanation: Impedance values are used to characterize one port devices, networks, multiport devices and other systems.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Advantages of Bridge Circuits”.

1. What is the relation between the balance equation and the magnitude of input voltage?

a) directly proportional

b) independent

c) inversely proportional

d) depends on the null indicator

Answer: b

Explanation: The input voltage does not appear in the expression for the balance equation. Thus balance equation is independent of the magnitude of input voltage.

2. Accuracy of bridge circuit depends on _________

a) component values

b) null detector

c) voltage source

d) current source

Answer: a

Explanation: The accuracy of the measurement of a bridge circuit depends on the values of the components used in it. Voltage source supplies dc bias to the circuit while the detector is used for balance condition.

3. What happens to the balance condition, if the source and detector are interchanged?

a) increases by a factor of 2

b) reduces to half

c) remains unchanged

d) independent of the type of source and detector

Answer: c

Explanation: The balance condition is independent of the positions of the source and the detector. Source and detector can be connected across any two sets of opposite arms of the bridge.

4. The simplest type of bridge used for the measurement of medium resistances is known as _________

a) Kelvin

b) Schering

c) Anderson

d) Wheatstone

Answer: d

Explanation: Wheatstone bridge is the simplest bridge that is used for the measurement of medium resistances. Kelvin bridge is used for the measurement of low resistance, whereas Schering bridge is used for the measurement of high voltages.

5. How is the measurement accuracy in a bridge circuit?

a) high

b) low

c) medium

d) inaccurate

Answer: a

Explanation: The measurement is done by comparing the unknown value with a standard known value. Thus the measurement accuracy is high in a bridge circuit.

6. The bridge circuit can be used in _________

a) high voltage circuits

b) low power circuits

c) control circuits

d) digital integrated circuits

Answer: c

Explanation: The bridge circuit is generally used in control applications. Control systems make use of bridge circuits for industrial applications.

7. Commonly used D.C. bridges are _________

a) Schering and Anderson

b) Maxwell inductance and capacitance

c) DeSauty and Wagner

d) Wheatstone and Kelvin

Answer: d

Explanation: Wheatstone and Kelvin are the commonly used bridges for the measurement of resistance. Wagner’s and De Sauty’s bridges are used for shielding the circuit.

8. In control applications, one arm of the bridge circuit contains a _________

a) capacitive element

b) resistive element

c) inductive element

d) impedance element

Answer: b

Explanation: One of the arms of a bridge circuit in general consists of a resistive element. Control systems employ resistive elements for industrial applications.

9. What are the physical parameters that are to be controlled when a bridge is used in control applications?

a) area and volume

b) mass and weight

c) pressure and temperature

d) current and voltage

Answer: c

Explanation: In control applications, when one of the arms of the bridge circuit consists of a resistance element, sensitive physical parameters such as pressure and temperature are to be controlled.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Wheatstone Bridge Balance Condition”.

1. Wheatstone bridge consists of _________

a) 4 resistive arms

b) 2 resistive arms

c) 6 resistive arms

d) 8 resistive arms

Answer: a

Explanation: A Wheatstone bridge essentially consists of 4 resistive arms. The arms are such that two resistances appear across each end.

2. A galvanometer is used as a _________

a) current source

b) voltage source

c) null detector

d) input impedance

Answer: c

Explanation: A galvanometer is used as a null detector to detect the flow of current across the ends of the two opposite junctions of the circuit. Voltage source is used for providing the required dc supply to the bridge.

3. The opposite two ends of a Wheatstone bridge consist of _________

a) voltage and current source

b) e.m.f and null detector

c) resistance and capacitance

d) inductance and impedance

Answer: b

Explanation: The two opposite ends of a Wheatstone bridge circuit consists of a source of e.m.f and a null detector. Four arms of a Wheatstone bridge consist of resistances. Inductance and capacitance do not appear in a Wheatstone bridge.

4. The arms consisting of the resistances R 1 and R 2 are called _________

a) resistance arms

b) impedance arms

c) source arms

d) ratio arms

Answer: d

Explanation: The arms consisting of the two resistances R 1 and R 2 are known as the resistance arms. Sources do not appear on the arms of the bridge and they are connected across opposite ends. Wheatstone bridge is purely resistive in nature.

5. The arm consisting of the standard known resistance R 3 is known as __________

a) standard arm

b) resistance arm

c) accurate arm

d) known arm

Answer: a

Explanation: The arm consisting of the standard known resistance R 3 is known as the standard arm. By making use of this resistance value the unknown resistance can be determined using the balance condition.

6. Resistance R 4 is known as ________

a) standard resistance

b) unknown resistance to be measured

c) resistance arm

d) input resistance

Answer: b

Explanation: R 4 is the unknown resistance whose value has to be found by comparison with a standard. R3 is known as the standard resistance. Resistance arm comprises of four resistances including R1, R2, R3, and R4.

7. What is connected between the two ends of a Wheatstone bridge?

a) current and voltage source

b) ammeter and voltmeter

c) battery and galvanometer

d) ohmmeter and wattmeter

Answer: c

Explanation: A battery is connected between the two ends of the Wheatstone bridge while a galvanometer is connected between the opposite two ends of the circuit. Ammeter is connected in series with the circuit.

8. Wheatstone bridge works on the principle of ________

a) full deflection

b) partial deflection

c) no deflection

d) null deflection

Answer: d

Explanation: The Wheatstone bridge works on the principle of null deflection. A galvanometer is usually used for measuring the flow of current in the bridge circuit.

9. The balance condition of a Wheatstone bridge depends on the _________

a) ratio of arms R 1 and R 1

b) ratio of arms R 3 and R 4

c) emf source and null detector

d) current source and power source

Answer: a

Explanation: The ratio of the arms R 1 and R 2 determines the balance condition of a Wheatstone bridge. The balance condition is given by the equation R 4 = R 3 R 1 ⁄ R 2 .

10. Balance condition can be obtained by _________

a) varying the standard resistance R 3

b) varying the resistance arms R 1 and R 2

c) keeping the unknown resistance R 4 constant

d) by making use of a null detector

Answer: b

Explanation: The balance condition in a Wheatstone bridge can be obtained by varying the resistances R 1 and R 2 . Null detector is used for determining balance condition.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Sensitivity of Wheatstone Bridge”.

1. When the bridge is balanced, what is the current flowing through the galvanometer?

a) 0

b) depends on the ratio arms R 1 and R 2

c) varies by a factor of 2

d) depends on the type of null detector used

Answer: a

Explanation: Under bridge balance condition, no current flows through the galvanometer. Current flow is independent of the values of ratio arms R 1 and R 2 .

2. Amount of deflection of the galvanometer depends on _________

a) resistance of the ratio arms

b) sensitivity

c) current flowing through the bridge

d) emf across the circuit

Answer: b

Explanation: The amount of deflection of the galvanometer depends upon its sensitivity. Resistance of the ratio arms does not affect the amount of deflection of the galvanometer.

3. Sensitivity is defined as _________

a) amount of voltage per unit current

b) amount of power per unit voltage

c) amount of resistance per unit voltage

d) amount of deflection per unit current

Answer: d

Explanation: Sensitivity is expressed as

electrical-measurements-questions-answers-sensitivity-wheatstone-bridge-q3

Thus sensitivity is defined as the amount of deflection per unit current.

4. Sensitivity is expressed in _________

a) cm/A

b) m/mA

c) mm/µA

d) inch/nA

Answer: c

Explanation:

electrical-measurements-questions-answers-sensitivity-wheatstone-bridge-q3

where, deflection is in mm and current is in µA.

So the unit of sensitivity is mm/ µA.

5. What is the relation between the sensitivity and deflection for a galvanometer?

a) directly proportional

b) inversely proportional

c) independant of each other

d) depends on the type of galvanometer used

Answer: a

Explanation:

electrical-measurements-questions-answers-sensitivity-wheatstone-bridge-q3

Thus we see that sensitivity is directly proportional to the deflection.

6. The voltage sensitivity of a galvanometer is given by _________

a) S v = e ⁄ θ

b) S v = θ ⁄ e

c) S v = 1 ⁄ e

d) S v = 1 ⁄ θ

Answer: b

Explanation:

electrical-measurements-questions-answers-sensitivity-wheatstone-bridge-q6

Voltage sensitivity is defined as the amount of deflection per unit voltage and is given by the relation

S v = θ ⁄ e .

7. Unit of voltage sensitivity is _________

a) volts per degrees

b) amps per ohms

c) degrees per volts

d) watts per amps

Answer: c

Explanation:

electrical-measurements-questions-answers-sensitivity-wheatstone-bridge-q6

So the unit of voltage sensitivity is degrees per volts as deflection is measured in degrees and voltage is in volts.

8. Bridge sensitivity is defined as _________

a) \

\(S_B=\frac{\theta}{\frac{\Delta R}{R}}\)

Answer: d

Explanation: The bridge sensitivity is defined as the amount of deflection of the galvanometer per unit fractional change in the unknown resistance.

\(S_B=\frac{\theta}{\frac{\Delta R}{R}}\)

Here ∆R/R denotes the fractional change in the unknown resistance.

9. Maximum sensitivity occurs when?

a) R 3 ⁄ R 4 = 1

b) R 2 ⁄ R 4 = 1

c) R 1 ⁄ R 2 = 1

d) R 3 ⁄ R 2 = 1

Answer: a

Explanation: Under a small unbalance condition, the bridge sensitivity equation becomes

electrical-measurements-questions-answers-sensitivity-wheatstone-bridge-q9

Here E is the emf of the circuit. For maximum bridge sensitivity, we get R 3 =R 4 .

This set of Electrical Measurements Assessment Questions and Answers focuses on “Measurement Errors in a Wheatstone Bridge”.

1. The Wheatstone bridge is used for the measurement of _________

a) 1ῼ to a few megaohms

b) 1kῼ to a few megaohms

c) 1Mῼ to a few gigaohms

d) 1mῼ to a few ohms

Answer: a

Explanation: A Wheatstone bridge is used for the measurement of medium resistance in the range of 1ῼ to a few megaohms. Kelvin bridge is used for the measurement of low resistance.

2. The source of error in a Wheatstone bridge is due to _________

a) range of galvanometer used

b) type of the source of emf used

c) limiting errors of the three known resistances

d) balance condition

Answer: c

Explanation: The main source of error in a Wheatstone bridge is because of the limiting errors of the three known resistances. As a result very precise resistances are required with 1 % tolerance.

3. What is the main source of error in a null detector?

a) lower current detection ability

b) insufficient sensitivity of the null detector

c) wiring resistance

d) power dissipation

Answer: b

Explanation: Resistance of contact wires and power dissipation are some of the causes for error in a null detector. But insufficient sensitivity is the major source of error in a null detector such as a galvanometer.

4. When current passes through the resistances in the Wheatstone bridge what happens?

a) voltage drop occurs

b) null detector burns

c) back emf is induced

d) temperature increases due to power dissipation

Answer: d

Explanation: Current flow through the resistances causes power dissipation i.e. I 2 R leading to an increase in the temperature. As the bridge consists of pure resistances, there is no back e.m.f induced.

5. What is the effect of the increase in temperature on the resistance elements?

a) directly proportional

b) independent

c) inversely proportional

d) changes by a factor of 10

Answer: a

Explanation: Temperature affects resistance of the circuit. Resistance has a positive temperature coefficient and increases linearly with rise in temperature.

6. Heating effect in the Wheatstone bridge can be avoided by _________

a) using an expensive emf source

b) limiting current to a safe value

c) using heating sinks

d) immersing the setup in ice

Answer: b

Explanation: Heating effect can be eliminated by limiting the current through the circuit to a safe value and by calculating the power dissipation in the arms. Heat sinks are typically used in power electronic applications.

7. The main error when measuring low resistances is _________

a) power dissipation of the arms

b) voltage drop across the emf source

c) lead and contact resistance

d) current flowing through the circuit

Answer: c

Explanation: Voltage drop across the circuit along with power dissipation lead to errors in the measurement of low resistances. The resistance of leads and contacts of the external circuit adds to the values in the circuit. This is the main source of error while measuring low resistances.

8. How is thermal emf generated?

a) when current flows

b) when voltage is applied

c) when the null detector is connected

d) when dissimilar metals come in contact

Answer: d

Explanation: When dissimilar metals come into contact with each other in a galvanometer circuit, thermal emf is generated. Null detector is used for detecting the balance condition.

9. Thermal emf can be prevented by _________

a) using more sensitive galvanometers

b) using similar metals

c) by separating the dissimilar metals

d) reducing the supply emf

Answer: a

Explanation: Thermal emf can be eliminated by making use of sensitive galvanometers consisting of copper coils and copper suspension systems. Dissimilar metals can’t be physically separated.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Applications of Wheatstone Bridge”.

1. Wheatstone bridge is a __________

a) a.c. bridge

b) d.c. bridge

c) high voltage bridge

d) power dissipation bridge

Answer: b

Explanation: The Wheatstone bridge is a d.c. bridge that is used for the measurement of medium resistance. Schering bridge is used for measurement of high voltages. AC bridges comprise of Anderson bridge, Maxwell Bridge, etc.

2. Wheatstone bridge is used to measure resistance in the range of ________

a) 1Ω to a few megaohms

b) 10kΩ to a few megaohms

c) 100MΩ to a few gegaohms

d) 100Ω to a few teraohms

Answer: a

Explanation: Wheatstone bridge is the simplest form of bridge circuit. It is basically used for the measurement of medium resistances in the range of 1Ω to a few megaohms.

3. Wheatstone bridge is used to measure the d.c. resistance of various types of wires for _________

a) determining their effective resistance

b) computing the power dissipation

c) quality control of wire

d) maintaining a source of constant e.m.f

Answer: c

Explanation: Wheatstone bridge is used to measure the d.c. resistance of various types of wires for controlling the quality of the wires. Voltage source maintains a constant e.m.f in the bridge circuit.

4. Telephone companies make use of the Wheatstone bridge for _________

a) measuring the telephone resistance

b) computing the line strength

c) maintaining dialtone

d) locating the cable faults

Answer: d

Explanation: Cable faults in telephones can be located by telephone companies by making use of a Wheatstone bridge. Telephonic resistances are determined using suitable techniques. Dialtone is maintained through optical fibre technology.

5. The types of faults in a telephone line are ________

a) line to line or line to ground

b) triple line to line or line to ground

c) open circuit and short circuit

d) symmetrical and unsymmetrical

Answer: a

Explanation: In a telephone line, line to line and line to ground faults occur. Symmetrical, unsymmetrical, open circuit, short circuit, triple line to line and line to ground faults occur in power systems.

6. How can a Wheatstone bridge be used for the measurement of physical parameters?

a) in conjunction with a rectifier

b) along with an op amp

c) by connecting it to a thermistor

d) by making use of a transducer

Answer: b

Explanation: A Wheatstone bridge can be used for the measurement of physical parameters such as temperature, strain, light, etc by making use of an operational amplifier. Rectifier circuits are used for the conversion of ac to dc.

7. By using the variations on a Wheatstone bridge we can _________

a) measure quantities such as voltage, current and power

b) measure high resistance values

c) measure quantities such as complex power

d) measure quantities such as capacitance, inductance and impedance

Answer: d

Explanation: In its simplest form a Whetstone bridge consists of resistive arms. A Wheatstone bridge is used for the measurement of quantities such as capacitance, inductance and impedance by making use of the variations.

8. One of the simplest applications of a Wheatstone bridge is ________

a) voltage measurement

b) current measurement

c) light measurement

d) power measurement

Answer: c

Explanation: Wheatstone bridge consists of simple resistances in the ratio arms. One of the simplest applications of a Wheatstone bridge is the measurement of light by making use of a photo resistive device.

9. Thermal compensation can be provided in a Wheatstone bridge by ________

a) using more than one resistive sensor

b) making use of a heat sink

c) using cooling fans

d) immersing the circuit into a liquid

Answer: a

Explanation: By making use of more than one resistive sensor within the four arms of a Wheatstone bridge we get a full bridge, half bridge or a quarter bridge setup with an automatic balancing effect.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Limitations of Wheatstone Bridge”.

1. Wheatstone bridge can’t be used for measurement of _________

a) high resistance

b) medium resistance

c) low resistance

d) accurate resistance

Answer: a

Explanation: Wheatstone bridge can be used for the measurement of medium resistances only. Kelvin bridge is used for the measurement of medium resistances.

2. Cost of maintenance of Wheatstone bridge is _________

a) low

b) high

c) depends on the components

d) depends on the source e.m.f

Answer: b

Explanation: As the resistance must have a tolerance of upto 1%, cost of maintenance of the Wheatstone bridge circuit is expensive. Voltage source does not add to the cost of maintenance of a Wheatstone bridge as it is uniform for all bridge circuits.

3. What is the effect of galvanometer on measurement of high resistance?

a) no effect

b) depends on the e.m.f source

c) galvanometer becomes insensitive to an imbalance

d) depends on the type of galvanometer used

Answer: c

Explanation: If the Wheatstone bridge is used for the measurement of high resistance, the galvanometer becomes insensitive and does not detect any imbalance.

4. What is the effect of heat on the resistances in a Wheatstone bridge?

a) no effect

b) increases the voltage drop across the circuit

c) decreases the current flowing through the circuit

d) causes a permanent change in the resistance values

Answer: d

Explanation: As the current flowing through the Wheatstone bridge circuit increases, the temperature of the resistance increases. As a result the resistance values are changed permanently.

5. Effect of high dc on Wheatstone bridge.

a) no effect

b) not susceptible

c) burns the circuit

d) increases the temperature

Answer: b

Explanation: A Wheatstone bridge is not susceptible to the flow of high dc current. A Wheatstone bridge in simplest form is used for the measurement of resistance with values in the medium resistance range.

6. A Wheatstone bridge may not give accurate readings if _________

a) it is not balanced

b) it is balanced

c) the voltage drop across the circuit is maximum

d) excessive current flows through the circuit

Answer: a

Explanation: A Wheatstone bridge circuit may give inaccurate measurement of resistance if it is not balanced properly. Current flow through a Wheatstone bridge circuit is fixed as the e.m.f source magnitude is constant.

7. What is the effect of lead wires on the Wheatstone bridge?

a) no effect

b) stabilizes the system

c) desensitizes the system

d) increases the resistance of the circuit

Answer: c

Explanation: The lead wires connecting the resistance arms of a Wheatstone bridge add to the existing values of resistances across the ratio arms. As a result the net value of resistance changes, thus destabilizing the system.

8. Why a Wheatstone bridge can’t be used for signal conditioning?

a) due to the galvanometer

b) due to excessive current flow

c) due to the e.m.f source used

d) due to lead wires

Answer: d

Explanation: Lead wires add to the resistance of the arms of the Wheatstone bridge. As a result the bridge circuit is destabilized and can’t be used for signal conditioning.

9. How to minimize the drift in the value of resistance measured using a Wheatstone bridge?

a) by using a high precision null detector

b) by keeping the lead wire resistances within 0.2 mΩ

c) by using a e.m.f source of minimum value

d) by minimizing the flow of current

Answer: b

Explanation: The drift in the measured value of resistance in a Wheatstone bridge can be minimized by maintaining the lead wire resistances within 0.2 mΩ. As a result, the effect of lead wire resistance gets removed in the output value of the bridge circuit.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Measurement of Low Resistance”.

1. Low resistance refers to _________

a) resistances of the order of 1ῼ

b) resistances of the order of 1kῼ

c) resistances of the order of 1mῼ

d) resistances of the order of 1Mῼ

Answer: a

Explanation: Low resistance refers to resistance of the order of 1ῼ or less than that. Medium resistances range from above 1ῼ to a few kῼ. Any resistance value greater than a few kῼ is known as high resistance.

2. What is the significance of measuring low resistances?

a) voltage drop across the circuit is high

b) contact and lead resistances are appreciable

c) there is no power loss

d) no current flows through the bridge circuit

Answer: b

Explanation: When measuring low resistances of the order of 1 ῼ or even less, lead and contact resistances of the order of even 0.002 ῼ cannot be neglected. High currents flow through low resistance circuits.

3. Fig 15.1 represents?

electrical-measurements-questions-answers-measurement-low-resistance-q3

a) construction of medium resistance

b) construction of high resistance

c) construction of low resistance

d) construction of very low resistance

Answer: c

Explanation: Fig 15.1, illustrates the construction of low resistance. A is an ammeter used to measure current through the circuit, while V is the voltmeter used to measure voltage.

4. How is the voltage drop across a low resistance related to lead resistance?

a) it contains contact resistance

b) it depends on the magnitude of voltage drop

c) it depends on the type of null detector used

d) It does not contain any contact resistance

Answer: d

Explanation: The voltage drop measured across a low resistance does not contain any contact and lead resistances of the components and is independent of it.

5. Which is not a source of error in the measurement of low resistance?

a) contact resistance drops at the leads

b) thermal e.m.f

c) temperature effect

d) power dissipation through the circuit

Answer: a

Explanation: As the current flowing through a low resistance circuit is low, the voltage drop across the terminals due to contact and lead resistances is negligible. Thermal e.m.f occurs in a circuit when its temperature increases due to high current flow.

6. Which is the most popular method for measuring low resistance?

a) ammeter-voltmeter method

b) potentiometer method

c) kelvin double bridge method

d) ducter ohmmeter method

Answer: c

Explanation: Kelvin’s double bridge is used for the measurement of low resistances of the order of 1ῼ or less. Ammeter voltmeter method is used for the measurement of current flowing through and the voltage across the circuit.

7. How is the contact resistance related to the circuit while measuring a low resistance?

a) independent of the type of resistance

b) it is negligible

c) depends on the e.m.f source

d) it is very high

Answer: b

Explanation: The contact and lead resistances form a part of the circuit whose resistance is very high. As a result the contact and lead resistances are usually neglected compared to the high resistance value.

8. In fig 15.1, the terminals aa’ are used for _________

electrical-measurements-questions-answers-measurement-low-resistance-q3

a) measuring the current flow through the circuit

b) measuring the power dissipation of the circuit

c) measuring the resistance of the circuit

d) measuring the voltage drop across the resistance

Answer: d

Explanation: The terminals aa’ are used for the measurement of the voltage drop across the resistance R. An voltmeter V is connected across the terminals aa’.

9. In the following figure, what is the value of I?

electrical-measurements-questions-answers-measurement-low-resistance-q9

a) I = I V + I r

b) I = I V – I r

c) I = I V I r

d) I = I V ⁄ I r

Answer: a

Explanation: By applying Kirchhoff’s current law at the node N from fig we get,

I = I V + I r

where,

I is the total series current flowing through the circuit

Iv is the current flowing through the voltmeter

Ir is the current flowing through the resistance R.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Kelvin Bridge”.

1. Kelvin’s bridge consists of _________

a) double bridge

b) single bridge

c) half bridge

d) three fourth bridge

Answer: a

Explanation: Kelvin’s bridge consists of two additional arms compared to a Wheatstone bridge. Hence it is also known as a double bridge.

2. The range of resistance measured in a Kelvin bridge is _________

a) 10Ω to 10 mΩ

b) 1Ω to 10 μΩ

c) 0.01Ω to 10 MΩ

d) 0.1Ω to 10 nΩ

Answer: b

Explanation: Kelvin bridge is used for the measurement of low resistances. Low resistances vary in the range of 1Ω to 10 μΩ.

3. Accuracy of Kelvin bridge is of the order of _________

a) ±0.5 to ±2 %

b) ±0.05 to ±0.02 %

c) ±0.05 to ±0.2 %

d) ±0.005 to ±0.02 %

Answer: c

Explanation: As Kelvin bridge is used for the measurement of low resistance values, the accuracy of measurement of low resistances in a Kelvin bridge is of the order of ±0.05 to ±0.2 %.

4. What is the balance equation of Kelvin bridge?

a) R x = \

R x = \

R x = \(\frac{R_1 R_3}{R_2}\)

Answer: d

Explanation: The balance equation in a Kelvin bridge is given by the relation R x = \(\frac{R_1 R_3}{R_2}\)

where,

R 1 , R 2 , R 3 , and R x form the ratio arms

Rx is the value of the unknown resistance.

5. What is the effect of load and contact resistance in Kelvin bridge?

a) independent

b) fully dependent

c) partially dependent

d) depends on the resistance value

Answer: a

Explanation: Effect of contact and lead resistances are completely eliminated in a Kelvin bridge as they don’t appear in the balance equation. Hence the Kelvin bridge is independent of the load and contact resistances.

6. The relation between ratio of resistance arms and ratio of resistance arms of second bridge is _________

a) unequal

b) equal

c) twice

d) one forth

Answer: b

Explanation: The relation between the ratio of the resistances of resistance arm and second resistance arm is equal for balance condition.

7. Why Kelvin bridge is used for measurement of low resistance?

a) due to e.m.f source used

b) due to a large current flow

c) due to contact and lead resistance

d) due to power dissipation across the circuit

Answer: c

Explanation: While measuring very low resistances the contact and lead resistances cause significant errors in the value of the measured resistance. As a result Kelvin bridge is used for measurement of low resistances.

8. What is the condition to achieve a high sensitivity in a Kelvin bridge?

a) low voltage

b) high power

c) medium resistance

d) high current

Answer: d

Explanation: The condition to achieve a high sensitivity in a Kelvin bridge is that the measuring current should be high enough so as to sensitize the null detector.

9. Kelvin bridge can be calibrated to read _________

a) inductance and Quality factor value

b) capacitance only

c) power and voltage

d) current and frequency

Answer: a

Explanation: In its basic form a Kelvin bridge is used for the measurement of low resistance. A Kelvin bridge can be used for the measurement of inductance and Quality factor value through calibration.

10. Why can’t a Kelvin bridge be used for the measurement of low Quality factor value?

a) due to thermoelectric effect

b) due to balance problem

c) due to the dull detector used

d) due to temperature

Answer: b

Explanation: A Kelvin bridge can be used for the measurement of high Quality factor values. Due to bridge imbalance problem, Kelvin bridge can’t be used for measuring low Quality factor values.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Megger”.

1. High resistances are of the order of __________

a) 0.1 Mῼ

b) 10 mῼ

c) 1 kῼ

d) 10 Gῼ

Answer: a

Explanation: Resistances of the order of 0.1 Mῼ and above are known as high resistances. Resistance values upto 1 ῼ are known as low resistances. Resistances upto a few kῼ are known as medium resistances.

2. Megger is a ________

a) source of e.m.f

b) source to measure high resistance

c) type of a null detector

d) current carrier

Answer: b

Explanation: Megger is a portable instrument to measure high resistances.

3. Megger is also used for ________

a) providing additional e.m.f

b) bridge balance

c) testing insulation resistance

d) controlling the temperature

Answer: c

Explanation: A null detector is used to balance the bridge. Additional e.m.f can be provided to a circuit by increasing the magnitude of the voltage source. Megger is used for testing the insulation resistance of cables.

4. Megger works on the principle of ________

a) kirchhoff’s current laws

b) ohm’s law

c) gauss’s law

d) electromagnetic induction

Answer: d

Explanation: Ohm’s law is applicable to only purely resistive circuits which are based on the linearity principle. Megger basically works on the principle of electromagnetic induction.

5. The role of the permanent magnet in a megger is to ________

a) provide field

b) provide voltage

c) generate power

d) balance the circuit

Answer: a

Explanation: Voltage can be provided by means of an e.m.f source. Power generation occurs when current flows through a circuit. Permanent magnet in a megger is used to provide a field for the generator as well as the ohmmeter.

6. A guard ring is provided in a megger to ________

a) protect the circuit

b) eliminate error

c) reduce current flow

d) limit the temperature rise

Answer: b

Explanation: Temperature rise can be prevented by reducing the flow of excessive current through the circuit. The role of a guard ring in a megger is to reduce the errors due to leakage current.

7. The supply to the megger is given by ________

a) ac motor

b) ac generator

c) permanent magnet dc motor

d) dc generator

Answer: c

Explanation: Megger works on the principle of electromagnetic induction. Supply can be given through a dc motor. A permanent magnet dc motor driven by hand is used as a source of supply to the megger.

8. The moving element of the ohmmeter in a megger consists of ________

a) 1 coil

b) 4 coils

c) 3 coils

d) 10 coils

Answer: c

Explanation: The moving element of an ohmmeter in a megger consists of three coils, namely current or deflection coil, pressure or control coil and compensating coil.

9. The role of the compensating coil in a megger is ________

a) reduce current

b) increase voltage

c) control temperature

d) scaling

Answer: d

Explanation: Temperature is controlled by minimising the flow of current through the circuit. Better scaling proportions can be achieved in a megger by making use of a compensating coil.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Applications of Megger”.

1. Why is the scale of a megger calibrated in megaohms?

a) to indicate resistance

b) to minimise the current flow

c) to increase the voltage drop

d) to reduce the temperature

Answer: a

Explanation: Current flow through the circuit depends on the magnitude of the e.m.f source. In order to indicate the resistance value indicated by the pointer, the scale of a megger is calibrated.

2. Megger can be used for verifying the electrical insulation level of ____________

a) passive components such as resistance, capacitor and inductance

b) devices such as motor, cable, etc

c) solid state devices

d) liquid crystal devices

Answer: b

Explanation: Solid state devices consist of power electronic components and drives. One of the applications of a Megger circuit is in verifying the electrical insulation levels of devices such as motor, cable, generator, etc.

3. Continuity between any two points can be measured using _________

a) ammeter

b) voltmeter

c) megger

d) galvanometer

Answer: c

Explanation: A galvanometer is used for detecting the balance condition in a bridge circuit. An ammeter measures the current flow through the circuit while the voltmeter is used for determining the voltage across the bridge circuit. A megger circuit can be used to determine the continuity between any two points.

4. Electrical continuity between any two points exists if _________

a) there is current flow through them

b) there is a wire connecting the points

c) there is sufficient voltage drop

d) pointer shows deflection

Answer: d

Explanation: Voltage drop across the circuit is measured by using a voltmeter. When the pointer displays full deflection, then there is an electrical continuity between the two points.

5. Megger is also known as _________

a) megohmmeter

b) multimeter

c) galvanometer

d) ammeter

Answer: a

Explanation: A galvanometer is used to detect the balance condition. A multimeter can be used for measurement of voltage, current, resistance and power. A megger is also known as a megohmmeter as it is used for the measurement of resistances in the order of Mῼ.

6. The application of a megger is _________

a) to measure resistance

b) to test for leakage

c) to limit the current

d) to increase the emf of the circuit

Answer: b

Explanation: Current flow through a circuit depends on the magnitude of the voltage source. Magnitude of the voltage source can be increased. A megger is mainly used for testing electrical leakages in wires.

7. What is the significance of a megger with respect to high resistance?

a) it is used to limit the current

b) it is used to provide stability

c) used for measuring high resistance with respect to ground

d) it is used for temperature protection

Answer: c

Explanation: Temperature protection can be provided to a bridge circuit by making use of heat sinks. Megger is used for determining very high resistances between the conducting part of a circuit and ground.

8. How is the megger calibrated?

a) in steps of 1 unit per division

b) based on the value of resistance to be measured

c) directly calibrated on the position of the pointer

d) reversely calibrated based on the pointer position

Answer: d

Explanation: The scale in a megger is calibrated such that normal position of a pointer indicates infinity while full scale corresponds to zero resistance.

This set of Electrical Measurements Questions and Answers for Aptitude test focuses on “Measurement of Earth Resistance”.

1. What is earthing?

a) connecting electrical machines to earth

b) providing a connection to the ground

c) connecting the electrical machines to source

d) providing a source of current

Answer: a

Explanation: Connecting electrical machines to the general mass of the earth by making use of a conducting material with very low resistance is known as earthing.

2. What is an earth electrode?

a) electrode that is connected to earth

b) material used for earthing

c) electrode connected to the circuit

d) electrode which is connected to the mains

Answer: b

Explanation: Electrode connected to the main is basically a source of e.m.f. Conducting material that is used for connecting electrical machinery to the earth is known as an earth electrode.

3. Earth electrode provides ____________

a) high resistance

b) medium resistance

c) low resistance

d) very high resistance

Answer: c

Explanation: In the case of occurrence of any leakage currents due to poor shielding of the apparatus, the earth electrode is used to provide a very low resistance path from the electrical appliances to the earth.

4. How is the condition of an earth electrode measured?

a) by measuring the voltage

b) by measuring the current

c) by measuring the power

d) by measuring resistance

Answer: d

Explanation: The resistance of the earth electrode is measured in order to check whether it is in a good condition or not.

5. In a three phase system, the neutral is _________

a) earthed

b) connected to low voltage

c) connected to high voltage

d) not connected

Answer: a

Explanation: Earthing can be used to maintain a constant line voltage in a three phase system. This is achieved by earthing the neutral.

6. Earthing is used as return conductor in telephone lines and for traction work.

a) True

b) False

Answer: a

Explanation: The complications involved in laying separate telephone cables and the cast used for traction work is minimised. As a result earthing is used as a return conductor in telephone lines and for traction work.

7. Earthing does not help in protecting the equipment.

a) True

b) False

Answer: b

Explanation: Spike voltages occurring as a result of lightning or any other fault can be dissipated to ground by earthing, thus protecting the equipment.

8. After earthing, the different parts of an electrical machinery are at _________

a) infinite potential

b) intermediate potential

c) zero potential

d) undefined potential

Answer: c

Explanation: After earthing, the various parts of electrical machinery such as casing, armoring of cables, etc are at zero potential.

9. Connection of the various parts of a circuit to earth has a _________

a) medium resistance

b) high resistance

c) very high resistance

d) very low resistance

Answer: d

Explanation: Once an electrical apparatus is grounded, most of its components are at ground potential. When the different parts of electrical machinery are connected to the ground, they possess very low resistance.

10. Specific resistance of soil is _________

a) changes from soil to soil

b) is constant

c) depends on the circuit connected to it

d) depends on the supply voltage

Answer: a

Explanation: Specific resistance depends on the nature and properties of a material. Specific resistance is different for various types of soils such as dry soil, rocky soil, wet soil, etc.

This set of Electrical Measurements Objective Questions & Answers focuses on “Advanced Problems on Measurement of Low Medium and High Resistance”.

1. Circuit shows the method of Measurement of low resistance by Ammeter-Voltmeter method. The measured resistance Rm for the given Circuit is _________

electrical-measurements-objective-questions-answers-q1

a) R x + R v

b) \

\(\frac{R_x R_v}{R_x + R_v}\)

Answer: d

Explanation: Measured resistance R m = \(\frac{V_x}{I_A} = \frac{V_x}{I_v + I_R}\)

\(\frac{I_v}{V_x} = \frac{1}{R_v}\) And \(\frac{I_R}{V_x} = \frac{1}{R_X}\)

So, R m = \(\frac{R_x R_v}{R_x+R_v}\).

2. Circuit shows the method of Measurement of low resistance by Ammeter-Voltmeter method. What is the percentage error?

electrical-measurements-objective-questions-answers-q1

a) Zero

b) \

\(– \frac{R_v}{R_x + R_v}\) × 100

Answer: c

Explanation: Percentage Error = \(\frac{R_m – R_x}{R_x}\) × 100

\(= \frac{R_x R_v – R_x

}{R_x

}\) × 100

∴ Percentage Error = \(– \frac{R_x}{R_x + R_v}\) × 100.

3. The readings of polar type potentiometer are I = 12.4∠27.5°, V = 31.5∠38.4°. Then, reactance of the coil will be ________

a) 2.51 Ω

b) 2.56 Ω

c) 2.54 Ω

d) 2.59 Ω

Answer: c

Explanation: Here, V = 31.5∠38.4°

I = 12.4∠27.5°

Z = \(\frac{31.5∠38.4°}{12.4∠27.5°}\) = 2.54∠10.9°

But Z = R + jX = 2.49 + j0.48

∴ Reactance X= 2.54 Ω.

4. The voltage drop across a standard resistor of 0.2 Ω is balanced at 83 cm. Find the magnitude of the current, if the standard cell emf of 1.53 V is balanced at 42 m.

a) 13.04 A

b) 10 A

c) 14.95 A

d) 12.56 A

Answer: c

Explanation: Voltage drop per unit length = \(\frac{1.53}{42}\) = 0.036 V/cm

Voltage drop across 83 cm length = 0.036 × 83 = 2.99 V

∴ Current through resistor, I = \(\frac{2.99}{0.2}\) = 14.95 A.

5. A resistance R is measured using the connection shown in the below figure.

electrical-measurements-objective-questions-answers-q1

The current measured is 10 A on ranges 100A and the voltage measured is 125 V on 150 V range. The scales of the ammeter and voltmeter are uniform. The total number of scale divisions of the ammeter is 100 and that of the voltmeter is 150. The scale division can be distinguished. The constructional error of the ammeter is ± 0.3% and that of voltmeter±0.4%. The resistance of the ammeter is 0.25 Ω.

The value of R is?

a) 12.75 Ω

b) 12.0 Ω

c) 12.25 Ω

d) 12.5 Ω

Answer: c

Explanation: Percentage error in ammeter = \

\) = 12.25 Ω.

6. A resistance R is measured using the connection shown in the below figure.

electrical-measurements-objective-questions-answers-q1

The possible error in the measurement of R is?

a) ±0.11 Ω

b) ±0.15 Ω

c) ±0.867 Ω

d) ±0.625 Ω

Answer: a

Explanation: Possible error is ± 0.867, so,

12.25 ± 0.867%

Or, 12.25 ± 0.11 Ω.

7. Low resistance is measured by ___________

a) De-Sauty’s bridge

b) Maxwell’s bridge

c) Kelvin double bridge

d) Wein’s bridge

Answer: c

Explanation: De-Sauty’s bridge is used for measurement of Capacitance; Maxwell’s bridge is used for measurement of Inductance and Wein Bridge for Frequency. Kelvin double bridge is used for measurement of Low resistance.

8. The resistance can be measured most accurately by _________

a) Voltmeter-Ammeter method

b) Bridge method

c) Multimeter

d) Megger

Answer: b

Explanation: Bridge method applies the concept of null point or bridge balance condition. Multimeter and Megger are used for measuring very high resistances and Voltmeter-Ammeter method is used for Low resistances. A null type instrument has higher accuracy as compared to a deflection type instrument.

9. A slide wire potentiometer has 10 wires of 2 m each. With the help of a standard voltage source of 1.045 V, it is standardized by keeping the jockey at 104.5 cm. If the resistance of potentiometer wires is 2000 Ω, then the value of working current is?

a) 1 mA

b) 10 mA

c) 0.1 mA

d) 0.5 mA

Answer: b

Explanation: Total length of the slide wire = 10 × 200

Total resistance of slide wire = 2000 Ω

∴ Resistance per cm = 1 Ω

Resistance of 104.5 cm = 104.5 Ω

This corresponds to a voltage of 1.045 V

∴ Current = \(\frac{1.045}{104.5}\) = 10 mA.

10. Which of the following method is used for the measurement of Medium Resistance?

a) Kelvin’s double bridge method

b) Carey-Foster bridge method

c) Anderson Bridge

d) Direct-Deflection method

Answer: b

Explanation: Kelvin’s double bridge method is used for measurement of Low Resistance, Anderson Bridge is not used for measurement of Resistance and Direct-Deflection method is used for Measurement of High Resistance.

11. In the Wheatstone bridge shown below, if the resistance in each arm is increased by 0.05%, then the value of Vout will be ________

electrical-measurements-objective-questions-answers-q11

a) 50 mV

b) Zero

c) 5mV

d) 0.1mV

Answer: b

Explanation: In Wheatstone bridge, balance condition is

R 1 R 3 = R 2 R 4

Here, R 1 = 5, R 2 = 10, R 3 = 16, R 4 = 8

And when the Wheatstone bridge is balanced then, at V out voltage will be Zero.

This set of Electrical Measurements Questions & Answers for Exams focuses on “Advanced Problems on Error Analysis in Electrical Instruments”.

1. A resistor of 10 kΩ with the tolerance of 5% is connected in parallel with 5 kΩ resistors of 10% tolerance. What is the tolerance limit for a parallel network?

a) 9%

b) 12.4%

c) 8.33%

d) 7.87%

Answer: c

Explanation: Here, R 1 and R 2 are in parallel.

Then, \(\frac{1}{R} = \frac{1}{R_1} + \frac{1}{R_2}\)

Or, R = \(\frac{50}{15}\) kΩ

∴\( \frac{△R}{R} = \frac{△R_1}{R_1^2} + \frac{△R_2}{R_2^2}\)

And △R 1 = 0.5×10 3 , △R 2 = 0.5×10 3

∴\( \frac{△R}{R} = \frac{10 × 10^3}{3 × 10 × 10^3} × \frac{0.5 × 10^3}{10 × 10^3} + \frac{10}{3} × \frac{10^3}{5 × 10^3} × \frac{0.5 × 10^3}{5 × 10^3}\)

= \( \frac{0.5}{30} + \frac{1}{15} = \frac{2.5}{30}\) = 8.33%.

2. A 0-400V voltmeter has a guaranteed accuracy of 1% of full scale reading. The voltage measured by this instrument is 250 V. Calculate the limiting error in percentage.

a) 4%

b) 2%

c) 2.5%

d) 1%

Answer: a

Explanation: The magnitude of limiting error of the instrument

ρA = 0.01 × 400 = 4 V

The magnitude of voltage being measured = 250 V

The relative at this voltage E r = \( \frac{4}{250}\) = 0.016

∴ Voltage measured is between the limits

A a = A s (1± E r )

= 250

= 250 ± 4 V.

3. The current flowing in a resistor of 1Ω is measured to be 25 A. But it was discovered that ammeter reading was low by 1% and resistance was marked high by 0.5%. Find true power as a percentage of the original power.

a) 95%

b) 101.5%

c) 100.1%

d) 102.4%

Answer: b

Explanation: True current = 25 = 25.25 A

True resistance R = 1 = 0.995Ω

∴ True power = I 2 R = 634.37 W

Measured power = 2 × 1 = 625 W

∴ \( \frac{True \,power}{Measured \,power}\) × 100 = \(\frac{634.37}{625}\) × 100 = 101.5%.

4. A resistor of 10 kΩ with the tolerance of 5% is connected in series with 5 kΩ resistors of 10% tolerance. What is the tolerance limit for a series network?

a) 9%

b) 12.04%

c) 8.67%

d) 6.67%

Answer: d

Explanation: Error in 10 kΩ resistance = 10 × \( \frac{5}{100}\) = 0.5 kΩ

Error in 5 kΩ resistance = 5 × \( \frac{10}{100}\) = 5 kΩ

Total measurement resistance = 10 + 0.5 + 5 + 0.5 = 16 kΩ

Original resistance = 10 + 5 = 15 kΩ

Error = \( \frac{16-15}{15}\) × 100 = \( \frac{1}{15}\) × 100 = 6.67%.

5. Two resistances 100 ± 5Ω and 150 ± 15Ω are connected in series. If the error is specified as standard deviations, the resultant error will be _________

a) ±10 Ω

b) ±10.6 Ω

c) ±15.8 Ω

d) ±20 Ω

Answer: c

Explanation: Given, R 1 = 100 ± 5 Ω

R 2 = 150 ± 15 Ω

Now, R = R 1 + R 2

The probable errors in this case, R = \

^{0.5}\) = ± 15.8 Ω.

6. Resistances R 1 and R 2 have respectively, nominal values of 10Ω and 5Ω and limiting error of ± 5% and ± 10%. The percentage limiting error for the series combination of R 1 and R 2 is?

a) 6.67%

b) 5.5%

c) 7.77%

d) 2.8%

Answer: a

Explanation: R 1 = 10 ± 5%

R 2 = 5 ± 10%

R 1 = 10 ± \( \frac{5}{100}\) × 10 = 10 ± 0.5Ω

R 2 = 5 ± \( \frac{5}{100}\) × 5 = 5 ± 0.5Ω

The limiting value of resultant resistance = 15 ± 1

Percentage limiting error of series combination of resistance = \( \frac{1}{15}\) × 100 = 6.67%.

7. A voltmeter has a sensitivity of 1000 Ω/V reads 200 V on its 300 V scale. When connected across an unknown resistor in series with a millimeter. When the milliammeter reads 10 mA. The apparent resistance of the unknown resistor will be?

a) 20 kΩ

b) 21.43 kΩ

c) 18.57 kΩ

d) 22.36 kΩ

Answer: a

Explanation: R T = \( \frac{V_T}{I_T}\)

V T = 200 V, I T = 10 A

So, 20 kΩ.

8. A voltmeter has a sensitivity of 1000 Ω/V reads 200 V on its 300 V scale. When connected across an unknown resistor in series with a millimeter. When the milliammeter reads 10 mA. The actual resistance of the unknown resistor will be?

a) 20 kΩ

b) 18.57 kΩ

c) 21.43 kΩ

d) 22.76 kΩ

Answer: c

Explanation: Resistance of voltmeter,

R V = 1000 × 300 = 300 kΩ

The Voltmeter is in parallel with an unknown resistor,

R X = \(\frac{R_T R_V}{R_T – R_V} = \frac{20 × 300}{280}\) = 21.43 kΩ.

9. A voltmeter has a sensitivity of 1000 Ω/V reads 200 V on its 300 V scale. When connected across an unknown resistor in series with a millimeter. When the milliammeter reads 10 mA. The error due to the loading effect of the voltmeter is ________

a) 3.33%

b) 6.67%

c) 13.34%

d) 13.67%

Answer: b

Explanation: R T = \( \frac{V_T}{I_T}\)

V T = 200 V, I T = 10 A

So, R T = 20 kΩ

Resistance of voltmeter,

R V = 1000 × 300 = 300 kΩ

Voltmeter is in parallel with unknown resistor,

R X = \( \frac{R_T R_V}{R_T – R_V} = \frac{20 × 300}{280}\) = 21.43 kΩ

Percentage error = \(\frac{Actual-Apparent}{Actual}\) × 100

= \(\frac{21.43-20}{21.43}\) × 100 = 6.67%.

10. A 500 A, 50 Hz current transformer has a bar primary. The secondary burden is a pure resistance of 1 Ω and it draws a current of 5 A. If the magnetic core requires 250 Ampere-turn for magnetization, the percentage ratio error is __________

a) 10.56%

b) -10.56%

c) 11.80%

d) -11.80%

Answer: b

Explanation: I M = 250/I = 250 A

I p Or, R = \

= ± 8%.

This set of Electrical Measurements Question Paper focuses on “Advanced Miscellaneous Problems on Measurement of Resistance”.

1. R a and R d are the opposite arms of a Wheatstone bridge as are R c and R b . The source voltage is applied across R a and R c . Then when the bridge is balanced which one of the following is true?

a) R a = R c R d /R b

b) R a = R b R c /R d

c) R a = R b Rd/R c

d) R a = R b + R c + R d

Answer: b

Explanation: At balance condition, Potential at B = Potential at D

∴ V A – I a R a = V A – I b R b

Or, \( \frac{I_a}{I_b} = \frac{R_b}{R_a}\)

Similarly, \( \frac{I_a}{I_b} = \frac{R_d}{R_c}\)

∴ R a = \( \frac{R_b R_c}{R_d}\).

2. A setup is used to measure resistance R. The ammeter and voltmeter resistance are 0.01 Ω and 2000 Ω respectively. Their readings are 2 A and 180 V respectively, giving a measured resistance of 90 Ω. The percentage error in the measurement is?

a) 2.25 %

b) 2.35 %

c) 4.5 %

d) 4.71 %

Answer: d

Explanation: Current through the voltmeter I v = \(\frac{180}{2000}\)

Current through R, I R = 2 – 9/100 = 1.91 A

Since, 1.91 R = 180

∴ R = 94.24

∴ Percentage error = \(\frac{94.24-90}{90}\) × 100 = 4.71 %.

3. A 35 V DC supply is connected across a resistance in series with an unknown resistance R. a voltmeter having a resistance of 1.2 kΩ is connected across 600 Ω resistance and reads 5 V. The value of the known resistance is 600 Ω. The value of resistance R will be?

a) 120 Ω

b) 400 Ω

c) 1.8 kΩ

d) 2.4 kΩ

Answer: d

Explanation: Voltage across R 1 , V 1 = 35 – 5 = 30 V

Current in the circuit, I = \(\displaystyle\frac{5}{\frac{600 ×1200}{600+1200}} = \frac{5}{400}\) A

∴ R = \(\frac{30 × 400}{5}\) = 2.4 kΩ.

4. A DC ammeter is rated for 15 A, 250 V. The meter constant is 14.4 A-s/rev. The meter constant at rated voltage may be expressed as __________

a) 3750 rev/kW-h

b) 3600 rev/kW-h

c) 1000 rev/kW-h

d) 960 rev/kW-h

Answer: c

Explanation: Meter constant is 14.1 A-s/rev

\(\frac{14.1}{3600}\) A-h/rev = \(\frac{14.4 × 250}{3600}\)

So, w = 1 W-h/rev

Hence, 1 rev/W-h = 1000 rev/kW-h.

5. A DC ammeter has a resistance of 0.1 Ω and its current range is 0-100 A. If the range is to be extended to 0-500 A, the meter requires which of the following shunt resistance?

a) 0.010 Ω

b) 0.011 Ω

c) 0.025 Ω

d) 1.0 Ω

Answer: c

Explanation: R sh = \( \frac{R_m}{m-1}\)

Where, m is the multiplication factor = 500/100 = 5

∴ R sh = 0.1/4 = 0.025 Ω.

6. A 100 μA ammeter has an internal resistance of 100 Ω. The range is to be extended to 500 μA. The shunt required is of resistance __________

a) 20.0 Ω

b) 22.22 Ω

c) 25.0 Ω

d) 50.0 Ω

Answer: c

Explanation: I sh R sh = I m R m

I sh = I – I m or, \(\frac{I}{I_m} – 1 = \frac{R_m}{R_{sh}}\)

Now, m = \(\frac{I}{I_m}\)

Or, m – 1 = \(\frac{R_m}{R_{sh}}\)

∴ R sh = 25 Ω.

7. Resistance is measured by the voltmeter-ammeter method employing DC excitation and a voltmeter is connected directly across the unknown resistance. If the voltmeter and ammeter readings are subject to maximum possible errors of ±2.4 % and ±1% respectively, then the magnitude of the maximum possible percentage error in the value of resistance deduced from the measurement is?

a) 1.4 %

b) 1.7 %

c) 2.4 %

d) 3.4 %

Answer: d

Explanation: Ammeter error ∆I = ± 1%

Voltmeter error ∆V = ± 2.4%

We know that \(\frac{∆R}{R} = \frac{∆V}{V} + \frac{∆I}{I}\)

∴ Maximum percentage error = 2.4% + 1% = 3.4%.

8. A galvanometer with a full-scale current of 10 mA has a resistance of 1000 Ω. The multiplying power of a 100 Ω shunt with this galvanometer is?

a) 110

b) 100

c) 11

d) 10

Answer: c

Explanation: Multiplying factor = m = \(\frac{I}{I_1} \)

Now, \(\frac{I_1}{I_2} = \frac{100}{1000} \)

∴ \(\frac{I_1}{100} = \frac{I_2}{1000} = \frac{I}{1000} \)

∴ \(\frac{I}{I_1}\) = 11.

a) 1 mA

b) 10 mA

c) 0.1 mA

d) 0.5 mA

Answer: b

Explanation: Total length of the slide wire = 10 × 200

Total resistance of slide wire = 2000 Ω

∴ Resistance per cm = 1 Ω

Resistance of 104.5 cm = 104.5 Ω

So, the current = \(\frac{1.045}{104.5}\) = 10 mA.

10. The simultaneous applications of signals x and y to the horizontal and vertical plates respectively, of an oscilloscope, produce a vertical figure of 8 displays. If P and Q are constants and x = P sin , then y is equal to _________

a) Q sin

b) Q sin

c) Q sin

d) Q sin

Answer: b

Explanation: \

= Q sin .

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Introduction to AC Bridges”.

1. In the simplest form, an AC bridge consists of ____________

a) arms, source and a detector

b) arms and source

c) source and detector

d) arms and detector

Answer: a

Explanation: In its simplest form, an AC bridge consists of four arms, a source for excitation and a null detector. The source is connected across a pair of arms while the detector is connected to the pair of opposite arms.

2. Source is ________

a) dc supply

b) ac supply

c) mixed mode supply

d) high voltage supply

Answer: b

Explanation: For an AC bridge we require an AC supply as the source of voltage. It supplies AC voltage at the required frequency.

3. At high frequency, source consists of ________

a) amplifiers

b) regulators

c) oscillators

d) op amps

Answer: c

Explanation: Op amps are basically differential amplifiers. Amplifiers are used in analog circuits for increasing the strength of the signal. Electronic oscillators form sources at high frequencies.

4. Commonly used balance detectors for AC bridges are headphones, tuned amplifiers and vibration galvanometers.

a) True

b) False

Answer: a

Explanation: Headphones, tuned amplifier circuits and vibration galvanometers are used for detecting the balance condition in AC bridges.

5. What is the frequency range for a headphone as a detector?

a) 20 Hz to 20 kHz

b) 10 kHz to 1 MHz

c) 10 MHz to 1 GHz

d) 250 Hz to 4 kHz

Answer: d

Explanation: Headphones can be used as detectors in AC bridges in the low audio frequency range. Low audio frequency range varies from 250 Hz to 4 KHz.

6. For single frequency value, the most sensitive detector is ________

a) tuned detector

b) vibration galvanometer

c) headphone

d) oscillator

Answer: a

Explanation: Vibration galvanometer is used for detecting the balance condition. Oscillator is used as a source of supply voltage. Tuned detector is the most sensitive detector for a single frequency value.

7. Tuned detectors are used in the frequency range of ________

a) 1 Hz to 100 Hz

b) 10 Hz to 100 Hz

c) 1 kHz to 100 kHz

d) 1 MHz to 100 MHz

Answer: b

Explanation: Tuned amplifier circuits are used as detectors in the low frequency range. Low frequency range usually ranges from 10 Hz to 100 Hz in AC bridges.

8. Vibration galvanometers are used for ________

a) very high frequency

b) very low frequency

c) low audio frequency

d) high audio frequency

Answer: c

Explanation: Vibration galvanometers are used as detectors in AC bridges for low audio frequency. Low audio frequency ranges from 5 Hz to 1000 Hz.

9. AC bridge is an outcome of ________

a) Kelvin bridge

b) Megger

c) De Sauty bridge

d) Wheatstone bridge

Answer: d

Explanation: Wheatstone bridge is the simplest form of bridge for the measurement of resistance and forms the basis for an AC bridge. Kelvin bridge is used for the measurement of low resistance and a megger is used for the measurement of high resistances.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Sources and Detectors”.

1. At very low frequencies in a AC bridge, the source is _________

a) power line

b) e.m.f

c) galvanometer

d) tuned circuit

Answer: a

Explanation: Galvanometer is used for detecting the balance condition. The power line acts as a source of supply for bridge measurements in an AC bridge circuit at very low frequencies.

2. At high frequencies in an AC bridge, the source is _______

a) tuned amplifiers

b) oscillators

c) vibration galvanometer

d) high voltage source

Answer: b

Explanation: Tuned amplifiers are used as a source of voltage in AC bridges. Electronic oscillators are used as a source of supply for bridge measurements in an AC bridge circuit at high frequencies.

3. The frequency range of a typical oscillator is _______

a) 1 Hz to 50 Hz

b) 1 kHz to 100 KHz

c) 40 Hz to 125 kHz

d) 1 MHz to 150 MHz

Answer: c

Explanation: An oscillator has a frequency range slightly above the audio frequency. A typical oscillator has a frequency range of 40 Hz to 125 kHz.

4. The power output for a typical oscillator is _______

a) 1 kW

b) 1 MW

c) 1 mW

d) 7 W

Answer: d

Explanation: Oscillator usually has a low power output. A typical oscillator has a power output of around 7 W.

5. The output waveform in an oscillator is _______

a) sinusoidal

b) cosinusoidal

c) tangential

d) logarithmic

Answer: a

Explanation: AC supply is generally in the form of sinusoidal signal. In an electronic oscillator, output waveform is very close to sinusoidal.

6. The output frequency of an oscillator is _______

a) unstable and fixed

b) stable and adjustable

c) stable and fixed

d) unstable and variable

Answer: b

Explanation: In an electronic oscillator, the output frequency is stable. It can be determined accurately and is also adjustable.

7. The output power of an oscillator is not enough to drive power circuits.

a) True

b) False

Answer: b

Explanation: Power circuits generally require a low output in order to function. An electronic oscillator provides sufficient output power to drive power circuits.

8. Tuned amplifiers can be set to _______

a) low frequencies

b) high frequencies

c) any frequency

d) audio frequencies

Answer: c

Explanation: Tuning refers to varying a parameter. Tuned amplifier circuits can be set to any desired frequency.

9. Tuned amplifier circuits respond to broad bandwidth at bridge frequency.

a) True

b) False

Answer: b

Explanation: Amplifiers can be used to detect the balance condition in AC bridges. Tuned amplifier circuits consist of transistors that respond to a narrow bandwidth at the bridge frequency.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Bridge Balance Equation”.

1. Bridge balance equation for magnitude is given by which of the following relation?

a) Z 1 Z 4 = Z 2 Z 3

b) Z 1 Z 2 = Z 3 Z 4

c) Z 2 Z 4 = Z 1 Z 3

d) Z 1 Z 3 = Z 2 Z 4

Answer: a

Explanation: In an AC bridge, the balance condition for magnitude is given by the equation

Z 1 Z 4 = Z 2 Z 3

where, Z 1 , Z 2 , Z 3 and Z 4 are the impedance arms of the AC bridge circuit.

2. Angular balance equation is given by which of the following relation?

a) θ 1 × θ 4 = θ 2 × θ 3

b) θ 1 + θ 4 = θ 2 + θ 3

c) θ 2 + θ 4 = θ 1 + θ 3

d) θ 2 × θ 4 = θ 1 × θ 3

Answer: b

Explanation: The angular balance condition in an AC bridge is given by the relation

θ 1 + θ 4 = θ 2 + θ 3

Where,

θ 1 , θ 2 , θ 3 and θ 4 are the phase angles of the impedances Z 1 , Z 2 , Z 3 and Z 4 .

3. Bridge must be balanced for ________

a) magnitude

b) angle

c) magnitude and angle

d) power

Answer: c

Explanation: The ratio arms consist of impedances which have magnitude as well as phase. In an AC bridge, balance condition implies magnitude balance as well as angular balance.

4. Phase angle is based on _______

a) source

b) detector

c) power

d) impedance

Answer: d

Explanation: The four ratio arms comprise of impedances which consist of not only magnitude but some phase as well. Value of the phase angles are based on the component of individual impedances.

5. For inductive impedances, the phase angle is _______

a) positive

b) negative

c) zero

d) exponential

Answer: a

Explanation: The current through an inductor does not increase instantaneously. For inductive impedances, the voltage leads the current and as a result the phase angle is positive.

6. For capacitive impedances, the phase angle is _______

a) tangential

b) negative

c) positive

d) logarithmic

Answer: b

Explanation: The voltage across a capacitor does not rise instantaneously. For capacitive impedances, the current leads the voltage and as a result the phase angle is negative.

7. Bridge balance equation for magnitude in terms of admittances is given by the relation.

a) Y 1 Y 3 = Y 2 Y 4

b) Y 1 Y 2 = Y 3 Y 4

c) Y 1 Y 4 = Y 2 Y 3

d) Y 1 Y 3 = Y 2 Y 4

Answer: c

Explanation: Admittance is the reciprocal of impedance. The balance condition for magnitude is given by the equation

electrical-measurements-questions-answers-bridge-balance-equation-q7

8. When a bridge is balanced?

a) no voltage drop across the circuit

b) power dissipation is high

c) temperature of the circuit is high

d) no current flows

Answer: d

Explanation: At balance condition, no current flows through the headphones present in the AC bridge circuit. As a result the detector indicates null deflection at balance condition.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Capacitance Comparison Bridge”.

1. In a capacitance bridge, the arms are _________

a) resistive

b) capacitive

c) inductive

d) mixture of resistance, capacitance and inductance

Answer: a

Explanation: The capacitance bridge is mainly used for the measurement of unknown capacitance. The ratio arms in a capacitance bridge are resistive in nature.

2. How is the bridge balanced?

a) using resistance R 1

b) using resistance R 3

c) through capacitance C 3

d) through capacitance C x

Answer: b

Explanation: Bridge balance is obtained by varying the resistance R 3 . At balance we get the value of the unknown resistance as R x = R 1 R 3 ⁄ R 2 .

3. Impedance Z 4 consists of _________

a) resistance R x

b) capacitance C x

c) combination of capacitance Cx and resistance Rx

d) consists of a detector

Answer: c

Explanation: Ratio arm Z 4 consists of the unknown impedance. Impedance Z 4 consists of capacitance C x in series with a leakage resistance R x .

4. Impedance Z 3 consists of_________

a) resistance R 3

b) capacitance C 3

c) vibration galvanometer

d) capacitance C 3 in series with resistance R 3

Answer: d

Explanation: Impedance usually refers to the combination of resistance and either capacitance or inductance. As we are considering the case of capacitance measurement, impedance Z 3 comprises capacitance C 3 in series with resistance R 3 .

5. Unknown capacitance value is obtained by _________

a) comparison with standard

b) using a tuned detector

c) using capacitance of other ratio arms

d) using a vibration galvanometer

Answer: a

Explanation: Tuned circuit is used for detecting balance condition. Vibration galvanometer is used for the same purpose. Unknown value of capacitance is obtained by comparing it with a standard value.

6. Unknown resistance is obtained by using which of the following relation?

a) R x = \

R x = \

R x = \(\frac{R_2}{R_1}\)

Answer: b

Explanation: The value of the unknown resistance is obtained by using the relation

R x = \(\frac{R_2 R_3}{R_1}\)

at balance condition.

7. Unknown capacitance is found by using which of the following relation?

a) C x = \

C x = \

C x = \(\frac{R_1}{R_2}\)

Answer: c

Explanation: The value of unknown capacitance is found using the relation C x = \(\frac{C_3 R_1}{R_2}\) at balance condition.

8. Actual balance condition can be obtained by _________

a) varying R 1

b) varying R 3

c) varying R 2

d) varying R 1 and R 3

Answer: d

Explanation: Resistances R 1 and R 3 are variable, while resistance R 2 is fixed. By varying the resistances R 1 and R 3 , we get the actual balance condition.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Inductance Comparison Bridge”.

1. Inductance comparison bridge is used to compute _________

a) unknown inductance and resistance

b) unknown resistance

c) unknown inductance

d) unknown capacitance

Answer: a

Explanation: By making use of an inductance comparison bridge, the values of unknown inductance and its internal resistance can be determined.

2. Ratio arms of the bridge consists of _________

a) pure inductances

b) pure resistances

c) pure capacitances

d) inductance and capacitance

Answer: b

Explanation: An inductance comparison bridge is basically used to compute the unknown resistance and inductance values. Ratio arms of an inductance bridge consists of pure resistances.

3. Value of unknown resistance is found by using which of the following relation?

a) R x = \

R x = \

R x = \(\frac{R_2}{R_1}\)

Answer: c

Explanation: The inductance comparison bridge mainly consists of pure resistances in its ratio arm. The value of unknown resistance is given by the relation R x = \(\frac{R_2 R_3}{R_1}\).

4. The value of unknown inductance is found by using which of the following relation?

a) L x = \

L x = \

L x = \(\frac{R_2 L_3}{R_1}\)

Answer: d

Explanation: At balance condition in an inductance comparison bridge, the value of unknown inductance is found by using the relation L x = \(\frac{R_2 L_3}{R_1}\).

5. Inductance control is obtained by _________

a) using R 2

b) using R 1

c) using R 3

d) using L x

Answer: a

Explanation: In an inductance comparison bridge, the resistance R 2 and R 3 are variable. The value of resistance R 2 is varied so as to control the inductance of the bridge.

6. Bridge depends on frequency.

a) True

b) False

Answer: b

Explanation: In an inductance comparison bridge, the balance equation is independent of frequency. As a result the bridge balance condition remains unaffected by variation in the value of frequency.

7. Bridge can be used at audio frequency.

a) True

b) False

Answer: a

Explanation: An inductance comparison bridge can be used for measurement of unknown inductance at a wide range of audio frequencies in the order of a few Hz to KHz.

8. Bridge is used for the measurement of _________

a) high Q factor

b) medium Q factor

c) low Q factor

d) very low Q factor

Answer: b

Explanation: The inductance comparison bridge is used for the measurement of low Q factor values of the order of 1 to 10. It cannot be used for the measurement of Q factors below 1. As a result, the bridge is used for the measurement of medium Q factor values.

This set of Electrical Measurements Interview Questions and Answers focuses on “Anderson Bridge, Advantages & Disadvantages of Anderson Bridge”.

1. Anderson bridge is used for _________

a) the measurement of self-inductance

b) the measurement of resistance

c) the measurement of capacitance

d) the measurement of impedance

Answer: a

Explanation: The Anderson bridge is one of the important bridges used for the measurement of self-inductances in terms of standard capacitance value. Resistance is usually measured by making use of a Wheatstone’s bridge or Kelvin’s double bridge.

2. Anderson bridge is a modified form of ________

a) Wheatstone’s bridge

b) Maxwell bridge

c) Kelvin double bridge

d) Schering bridge

Answer: b

Explanation: The Anderson’s bridge is a modified form of Maxwell’s bridge which is used for the measurement of self-inductances in terms of standard capacitance value. Wheatstone bridge and Kelvin bridge are used for the measurement of medium and low resistances respectively.

3. Anderson’s bridge is basically used for ________

a) measurement of capacitance

b) measurement of resistance

c) measurement of inductance

d) measurement of voltage

Answer: c

Explanation: Anderson’s bridge is used basically for the precise measurement of self-inductances in terms of a standard capacitance value over a wide range of values.

4. Balance equation for computing the inductance is ________

a) L x = R 3 R 5

b) L x = CR 5

c) L x = CR 3

d) L x = CR 3 R 5

Answer: d

Explanation: The balance equation for computing the self-inductance in an Anderson’s bridge is given by the equation, L x = CR 3 R 5 .

where, C is the standard capacitance

R 3 and R 5 are the known non-inductive resistances.

5. Which of the following is a balance equation for computing the resistance?

a) R 1 = R 2 R 3 ⁄ R 4

b) R 1 = R 2 ⁄ R 4

c) R 1 = R 3 ⁄ R 4

d) R 1 = R 2 R 3

Answer: a

Explanation: The balance equation for computing the resistance in an Anderson’s bridge is given by the equation R 1 = R 2 R 3 ⁄ R 4 .

where, R 2 , R 3 and R 4 are the known non-inductive resistances.

6. When the capacitor used is imperfect, the inductance value changes.

a) True

b) False

Answer: b

Explanation: For an imperfect capacitor used in the Anderson bridge, the value of inductance remains unaffected. The value of R 1 changes.

7. Anderson’s bridge is used for the measurement of capacitance.

a) True

b) False

Answer: a

Explanation: When a calibrated self-inductance is available, the value of unknown capacitance can be computed by making use of Anderson’s bridge.

8. Anderson’s bridge is used for the measurement of ________

a) capacitance

b) resistance

c) inductance

d) impedance

Answer: a

Explanation: Anderson’s bridge is used for the measurement of capacitance. Unknown capacitance value can be measured accurately in terms of the self-inductance of one of the ratio arms of the bridge.

9. Anderson’s bridge makes use of a variable capacitance.

a) True

b) False

Answer: b

Explanation: An Anderson’s bridge makes use of a fixed capacitance value. Most of the other AC bridges used for the measurement of either capacitance, inductance or impedance make use of a variable capacitance.

10. Anderson’s bridge is very basic.

a) True

b) False

Answer: b

Explanation: An Anderson’s bridge is basically used for the measurement of unknown capacitance value in terms of the self-inductance of one of the standard ratio arms. It is a complex bridge comprising of equivalent star-delta networks for computation of resistance and inductance.

11. Bridge balance equations are ________

a) easy to derive

b) independent of the components

c) complex in nature

d) real in nature

Answer: c

Explanation: An Anderson’s bridge is basically used for the measurement of unknown capacitance value in terms of the self-inductance of one of the ratio arms. It consists of real as well as complex terms. It also comprises of star-delta equivalent networks for impedance computations.

12. Components in an Anderson’s bridge are ________

a) less

b) zero

c) intermediate

d) more

Answer: d

Explanation: An Anderson’s bridge is a complex type of bridge used basically for the measurement of unknown capacitance. It consists of several resistances, inductances and capacitances in the ratio arms.

13. Anderson’s bridge ________

a) can’t be shielded

b) can be fully shielded

c) can be partially shielded

d) can be shielded based on the components used

Answer: a

Explanation: An Anderson’s bridge is a complex circuit and a modified form of the Maxwell bridge. An Anderson’s bridge cannot be shielded due to the presence of an additional junction point.

14. What is the significance of Anderson bridge with respect to Q factor?

a) difficult to balance the bridge

b) easy to balance the bridge

c) intermediate balance can be achieved

d) no balance can be done

Answer: b

Explanation: An Anderson’s bridge is a modified form of the Maxwell bridge and is used for the measurement of unknown capacitance in terms of self-inductance of standard value. It is easy to achieve balance condition in an Anderson bridge.

15. An Anderson’s bridge can be used to ________

a) measure mutual inductance

b) measure impedance

c) measure self inductance

d) measure stray capacitance

Answer: c

Explanation: An Anderson bridge can be used for the measurement of the self-inductance of a coil. A coil with unknown capacitance can be used to determine its self-inductance by making use of an Anderson bridge.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Schering Bridge”.

1. Schering bridge is one of the most widely used AC bridges.

a) True

b) False

Answer: a

Explanation: Schering bridge is an AC bridge used for the measurement of unknown capacitance, dielectric loss and power factor. It is one of the most commonly used AC bridges.

2. Schering bridge is used for _________

a) low voltages only

b) low and high voltages

c) high voltages only

d) intermediate voltages only

Answer: b

Explanation: Schering bridge is used for both low as well as high voltages. A particular bridge connection is used for low voltage. High voltages employ the use of a different type of Schering bridge.

3. Power factor of a Schering bridge is _________

a) p.f. = sin∅ x = Z x ⁄ R x

b) p.f. = cot∅ x = R x ⁄ Z x

c) p.f. = cos∅ x = R x ⁄ Z x

d) p.f. = tan∅ x = R x ⁄ Z x

Answer: c

Explanation: The power factor of the RC combination in a Schering bridge is given by the relation p.f. = cos∅ x = R x ⁄ Z x .

where,

R x is the series resistance

Z x is the series impedance comprising of Rx and C x .

4. For phase angles close to 90°, the power factor of the bridge is _________

a) p.f. = ωR x

b) p.f. = ωC x

c) p.f. = R x C x

d) p.f. = ωR x C x

Answer: d

Explanation: When phase angle reaches 90°, reactance equals the impedance and the power factor of the bridge is calculated using the relation,

electrical-measurements-questions-answers-schering-bridge-q4

5. For a series RC circuit, what is δ?

a) voltage between series RC combination and C

b) voltage between series RC combination

c) voltage across C

d) voltage across R

Answer: a

Explanation: In a series RC circuit, δ refers to the angle between the series combination of R x , C x and the voltage across the capacitance C x . δ is also known as the loss angle.

6. What is the expression for the loss angle?

a) tan⁡ δ = ωR 4

b) tan⁡ δ = ωR 4 C 4

c) tan⁡ δ = ωC 4

d) tan⁡ δ = R 4 C 4

Answer: b

Explanation: The expression for the loss angle can be computed as the ratio of the tangent of the voltage drop across resistance R x to the voltage drop across the capacitance C x .

electrical-measurements-questions-answers-schering-bridge-q6

7. Quality factor is given by which of the following expression?

a) Q = 1 ⁄ R

b) Q = R

c) Q = X ⁄ R

d) Q = XR

Answer: c

Explanation: The quality factor the Schering bridge circuit is defined as Q = X ⁄ R .

where, X = 1 ⁄ wC is the capacitive impedance.

8. Dissipation factor is the reciprocal of quality factor.

a) True

b) False

Answer: a

Explanation: Dissipation factor for a circuit is defined as the reciprocal of the quality factor.

It is given by the expression Q = 1 ⁄ wCR . It basically provides information about the quality of a capacitor.

9. Commercial Schering bridge can be used for the measurement of capacitances from _____________

a) 10pF to 0.1nF

b) 100pF to 1μF

c) 50nF to 10mF

d) 25mF to 5F

Answer: b

Explanation: Commercial Schering bridges are used for the measurement of capacitances in the range of a few pico farads to a few micro farads. Accuracy varies in the range of –2% to +2%.

10. A Schering bridge can be used for the ______________

a) measuring voltages

b) measuring currents

c) testing capacitors

d) protecting the circuit from temperature rises

Answer: c

Explanation: A Schering bridge can be used with both low voltage as well as high voltages. A Schering bridge is basically used for the measurement of small capacitances at low voltages with high precision.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “High Voltage Schering Bridge”.

1. A Schering bridge can be used for capacitance measurements at low voltages.

a) True

b) False

Answer: b

Explanation: When a Schering bridge is used for the measurement of small capacitances at low voltages, it comprises of errors. In order to avoid this a high voltage Schering bridge is used.

2. How is the high voltage obtained?

a) by using a step up transformer

b) by using a high voltage source

c) by using a step down transformer

d) by using a high current source

Answer: a

Explanation: High voltage supply for a Schering bridge is obtained by making use of a step up transformer. The frequency for the high voltage supply used in a Schering bridge is 50 Hz.

3. The detector used in a high voltage Schering bridge is _________

a) tunable circuit

b) e.m.f source

c) vibration galvanometer

d) headphone

Answer: c

Explanation: A high voltage Schering bridge is used for the measurement of low capacitance values at high voltages. A vibration galvanometer is used as a detector in a high voltage Schering bridge.

4. Detector is very sensitive in a high voltage Schering bridge.

a) True

b) False

Answer: a

Explanation: In a high voltage Schering bridge the ratio arms have high impedance values. As a result, a very small current is drawn by the ratio arms. Hence the detector must be very sensitive in a high voltage Schering bridge.

5. How are the inter-capacitance errors minimized?

a) by separating the plates of the capacitance

b) by using earthing

c) by reducing the area of cross section of the capacitors

d) by increasing the distance between the capacitor plates

Answer: b

Explanation: In a high voltage Schering bridge, errors due to inter-capacitance between the high and low impedance ratio arms can be eliminated through earthing screens.

6. How to minimize the effect of earth capacitance?

a) by increasing the supply voltage

b) by using a series resistance

c) by using a Wagner ground connection

d) by using an inductor across the circuit

Answer: c

Explanation: In a high voltage Schering bridge, the effect of earth capacitance on the circuit including the galvanometer and the contact leads is minimized by making use of a Wagner ground connection.

7. What is the effect of breakdown of high voltage capacitor?

a) No effect

b) voltage drop across the circuit reduces

c) circuit components rupture

d) a high voltage appears across the branches

Answer: d

Explanation: In a high voltage Schering bridge, a very high voltage appears across the branches when the breakdown of high voltage capacitor occurs. This is prevented by making use of a spark gap across the branches involved.

8. What is the dependence of frequency on the balance equation?

a) independent

b) varies by a factor of 2

c) depends on the supply magnitude

d) depends on the detector used

Answer: a

Explanation: In a high voltage Schering bridge, the balance equation does not depend on the frequency of operation of the circuit. A detector is only used for detecting the balance condition in a bridge circuit.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Maxwell’s Inductance Capacitance Bridge”.

1. Maxwell inductance capacitance bridge can be used for _________

a) measurement of inductance

b) measurement of capacitance and inductance

c) measurement of resistance

d) measurement of voltage and current

Answer: a

Explanation: A Maxwell inductance capacitance bridge is used for the measurement of inductance by making comparison with a standard capacitance value. Voltmeter is used to measure voltage, while an ammeter is used to measure current.

2. Balance equation for computing the unknown resistance is?

a) R x = \

R x = \

R x = \(\frac{1}{R_1}\)

Answer: b

Explanation: The balance condition for determining the value of the unknown resistance is given by the relation R x = \(\frac{R_2 R_3}{R_1}\)

where, R 1 and R 3 are variable resistances and R 2 is a fixed resistance.

3. Balance equation for computing the value of the unknown inductance is?

a) L x = R 2 R 3

b) L x = R 2 C 1

c) L x = R 2 R 3 C 1

d) L x = R 3 C 1

Answer: c

Explanation: The balance equation for determining the value of the unknown inductance is given by the relation L x = R 2 R 3 C 1 .

where,

C 1 is the capacitance across the resistance R 1

R 3 is a variable resistance and R 2 is a fixed resistance.

4. Quality factor of the circuit is given by _________

a) Q = ωC 1

b) Q = ωR 1

c) Q = ω

d) Q = ωR 1 C 1

Answer: d

Explanation: The quality factor of a Maxwell inductance capacitance bridge is given by the relation

electrical-measurements-questions-answers-maxwells-inductance-capacitance-bridge-q4

5. Standard inductor requires no shielding.

a) True

b) False

Answer: b

Explanation: Stray magnetic fields are present in a circuit consisting of inductances and capacitances. In order to eliminate the stray magnetic fields proper shielding is required for the standard inductance.

6. Standard inductor provides rated inductance directly.

a) True

b) False

Answer: b

Explanation: When the current flow through the standard inductance is adjusted precisely, it provides its rated value of inductance.

7. What is the significance of capacitors in a Maxwell bridge?

a) they are used to block dc

b) they are used to block ac

c) they are cheap

d) they are expensive

Answer: c

Explanation: In a Maxwell inductance capacitance bridge, the capacitors are cheaper when compared to a stable and accurate standard value of inductors.

8. The bridge balance equation can be written in _________

a) impedance form

b) resistance form

c) conductance form

d) admittance form

Answer: d

Explanation: The bridge balance equation for a Maxwell inductance capacitance bridge consists of admittances. This is due to the connection of capacitance in parallel across the resistance in one of the ratio arms.

This set of Electrical Measurements Questions and Answers for Campus interviews focuses on “Advantages and Limitations of Maxwell Bridge”.

1. What is the significance of the balance equation on losses?

a) independent of losses in inductance

b) independent of losses in capacitance

c) independent of losses in resistance

d) independent of losses in the circuit

Answer: a

Explanation: The balance equation in a Maxwell inductance capacitance bridge is independent of the losses associated with an inductance. According to the balance equation the unknown inductance is computed as L x = R 2 R 3 C 1 .

2. Balance equation is dependent on frequency.

a) True

b) False

Answer: b

Explanation: The balance equation in a Maxwell inductance capacitance bridge is independent on the measurement of frequency. The balance equation does not contain frequency terms such as ω and as a result, it is independent of frequency.

3. How can R 1 be scaled?

a) by using a scale

b) by using an ohmmeter

c) by calibration

d) by using a galvanometer

Answer: c

Explanation: The resistance R 1 in a Maxwell inductance capacitance bridge can be scaled through calibration. The value of the Quality factor Q can be read directly through calibration.

4. Scale of resistance can be calibrated.

a) True

b) False

Answer: a

Explanation: The resistance R 1 in a Maxwell inductance capacitance bridge can be calibrated directly. As a result the value of the unknown inductance can be read directly.

5. Bridge can be used for the measurement of _________

a) high Q values

b) intermediate Q values

c) very low Q values

d) low Q values

Answer: d

Explanation: A Maxwell inductance capacitance bridge can be used for the measurement of low Q values only of the order of 1 to 10. This is because at high Q factor values the angular balance condition is not satisfied.

6. The balance condition is _________

a) is easy to obtain

b) is difficult to obtain

c) can’t be obtained

d) exists always

Answer: b

Explanation: The balance condition in a Maxwell inductance capacitance bridge is difficult to obtain. This occurs due to an interaction between resistance and reactance components in the bridge circuit.

7. Commercial Maxwell bridges measures _________

a) inductances in the range of 1 to 1000H

b) capacitances in the range of 10mF to 1F

c) resistances in the range of 0.001 Ω to 1Ω

d) power in the range of 1W to 50MF

Answer: a

Explanation: Basically a Maxwell bridge is used for the measurement of inductance in terms of known standard capacitance value. Inductances in the range of 1 to 1000H with an accuracy range of ±2% can be measured.

8. At high Q values, the angular balance condition is _________

a) satisfied

b) not satisfied

c) independent of Q factor

d) partially affected

Answer: b

Explanation: For high Q factor values in a Maxwell inductance capacitance bridge, the angular balance condition is affected. The relation θ 1 + θ 4 = θ 2 + θ 3 is not satisfied at high Q factor values. This occurs as θ 4 reaches 90°. θ 1 must become –90° as per the angular balance condition. But for this the value of R 1 should be very high, which is not practically feasible.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Shielding and Grounding of Bridges”.

1. In general bridges consist of __________

a) lumped inductances

b) lumped resistances

c) distributed capacitance

d) distributed impedance

Answer: a

Explanation: AC bridges in general such as Maxwell, Anderson, Schering, etc consist of lumped components such as inductance.

2. Stray capacitance exists between the components.

a) True

b) False

Answer: a

Explanation: In general in AC bridges, stray capacitance exists between the components of the bridge with respect to the ground. These stray capacitances short the ratio arms and lead to errors in the measurement.

3. The magnitude of stray capacitances is fixed.

a) True

b) False

Answer: b

Explanation: Stray capacitances are uncertain in nature. Their magnitude depends on the adjustment of the bridge arms and the position of the operator.

4. Stray capacitance effects can be minimized by __________

a) making use of an inductance

b) connecting a resistance in series

c) shielding and grounding

d) using a galvanometer

Answer: c

Explanation: The stray capacitance effects in an AC bridge can be eliminated by shielding and grounding. This method helps in making the stray capacitances constant in value. They can be compensated.

5. Most popular method of avoiding the stray capacitance effects is __________

a) by grounding

b) by using guard rings

c) by using galvanometer

d) by using Wagner device

Answer: d

Explanation: A Wagner earthing device is used in general to eliminate the stray capacitance effects in AC bridges. The stray capacitance effects between the components in the ratio arms with respect to ground can be eliminated through this method.

6. Wagner device is a ____________

a) capacitance bridge

b) resistance bridge

c) inductance bridge

d) impedance bridge

Answer: a

Explanation: A Wagner earth device is generally used for shielding and grounding purpose. It consists of capacitances in the ratio arms along with a series RC combination connected across the ends of the bridge forming a potential divider.

7. Which is the guarding arm?

a) parallel RC combination

b) series RC combination

c) resistance R

d) capacitance C

Answer: b

Explanation: The series combination of R and C in a Wagner earth device forms a potential divider across the ratio arms. It is also known as the guard arm.

8. Bridge is suitable for _________

a) coils with high Q values

b) coils with low Q values

c) coils with intermediate Q values

d) coils with very high Q values

Answer: b

Explanation: The Maxwell inductance capacitance bridge is basically used for the measurement of quality factor of inductance coils with low Q values.

This set of Tough Electrical Measurements Questions and Answers focuses on “Advanced Problems on Measurement of Inductance using AC Bridges”.

1. In the Owen’s bridge shown in below figure, Z 1 = 200∠60°, Z 2 = 400∠-90°, Z 3 = 300∠0°, Z 4 = 400∠30°. Then the _______

tough-electrical-measurements-questions-answers-q1

a) Bridge is balanced with given impedance values

b) Bridge can be balanced, if Z 4 = 600∠60°

c) Bridge can be balanced, if Z 3 = 400∠0°

d) Bridge cannot be balanced with the given configuration

Answer: d

Explanation: For Bridge to be balanced, the product of impedances of the opposite arm should be equal in magnitude as well as phase angle. Here Z 3 Z 2 ≠ Z 1 Z 4 for whatever chosen value. Therefore the Bridge cannot be balanced.

2. In Maxwell’s capacitance bridge for calculating unknown inductance, the various values at balance are, R 1 = 300 Ω, R 2 = 700 Ω, R 3 = 1500 Ω, C 4 = 0.8 μF. Calculate R 1 , L 1 and Q factor, if the frequency is 1100 Hz.

a) 240 Ω, 0.12 H, 3.14

b) 140 Ω, 0.168 H, 8.29

c) 140 Ω, 0.12 H, 5.92

d) 240 Ω, 0.36 H, 8.29

Answer: b

Explanation: From Maxwell’s capacitance, we have

R 1 = \(\frac{R_2 R_3}{R_4} = \frac{300 × 700}{1500}\) = 140 Ω

L 1 = R 2 R 3 C 4

= 300 × 700 × 0.8 × 10 -6 = 0.168 H

Q = \(\frac{ωL_1}{R_1} = \frac{2 × π × 1100 × 0.168}{140}\) = 8.29.

3. In Wein’s bridge, the output frequency is determined by __________

a) RLC combination

b) LC combination

c) RC combination

d) RL combination

Answer: c

Explanation: The frequency of Wien Bridge is given by

f = \(\frac{1}{2π

^{0.5}}\) Hz

∴ The output frequency is determined by the RC combinations.

4. What is the disadvantage of Maxwell Bridge?

a) Inductance cannot be measured over a wide range

b) Measurement is not independent of frequency

c) Number of components is large

d) Inductance can be measured over a wide range

Answer: a

Explanation: Maxwell Bridge cannot be used for the measurement of high Q values.

We have, Q = \(\frac{1}{ωR_X C_X} = \frac{ωL_X}{R_X}\)

Hence, Q ∝ L X

∴ Inductance cannot be measured over a wide range.

5. The Bridge shown in the below figure is ______________

tough-electrical-measurements-questions-answers-q5

a) Maxwell’s Bridge

b) Wien’s Bridge

c) Anderson’s Bridge

d) Hay’s Bridge

Answer: a

Explanation: The given figure is Maxwell’s Bridge because it consists of two inductors. It is also used to measure the inductance of the inductor.

6. Hay’s Bridge is used for measuring __________

a) Resistance in the milliohm range

b) Low values of capacitance

c) Comparison of resistances which are nearly equal

d) The Inductance of a coil with a large time constant

Answer: d

Explanation: Carey – Foster slide-wire is suited for the comparison of resistances which are nearly equal. The Schering Bridge is suited for Low values of capacitance. The Kelvin double bridge is used for measuring resistance in the milliohm range. Hay’s Bridge is suited for the measurement of Inductance of a coil with a large time constant.

7. In Maxwell’s Bridge, as shown in the figure below, the values of the resistance R 1 and inductance L 1 of a coil are to be calculated after the bridge is balanced. The values are?

tough-electrical-measurements-questions-answers-q7

a) 375 Ω and 75 mH

b) 75 Ω and 150 mH

c) 37.5 Ω and 75 mH

d) 75 Ω and 75 mH

Answer: a

Explanation: Applying the usual balance condition relation,

Z 1 Z 4 = Z 2 Z 3

We have, (R 1 + jL 1 ω) \(\frac{R_4/jωC_4}{R_4+1/jωC_4}\) = R 2 R 3

Or, R 1 R 4 + jL 1 ωR 4 = R 2 R 3 + j R 2 R 3 R 4 C 4 ω

∴ R 1 = 2000 × \(\frac{750}{4000}\) = 375 Ω

∴ L 1 = 2000 × 750 × 0.5 × 10 -6

= 75 mH.

8. Maxwell’s Inductance Capacitance Bridge is used for measuring ___________

a) Inductance

b) Capacitance

c) Frequency

d) Mutual Inductance

Answer: a

Explanation: For measuring Capacitance De-Sauty’s Bridge and Schering Bridge should be used. For measuring Frequency Wien’s Bridge is used. For measuring Mutual Inductance Heaviside and Campbell’s Bridge are used.

9. The four arms of an AC bridge network are as follows:

Arm AB: unknown impedance

Arm BC: standard capacitor C2 of 1000pf

Arm CD: a non-inductive resistance of R of 100 Ω in parallel to a capacitor of 0.01 μF

Arm DA: a non-inductive resistance of 1000 Ω

The supply frequency is 50 Hz and connected across terminals B and D. If the bridge is balanced with the above value, determine the value of unknown Impedance.

a) 10 kΩ

b) 100 kΩ

c) 250 kΩ

d) 20 kΩ

Answer: a

Explanation: For the balance conditions,

Z 1 Z 3 = Z 2 Z 4

1000 × \

\(\frac{100}{1 + jω + 10^{-6}} \)

Or, \(\frac{- j10^{10}}{ω}\) – 10 4 = R + jX

Comparing the real part, we get,

R = 10 kΩ.

10. The four arms of an AC bridge network are as follows:

Arm AB: unknown impedance

Arm BC: standard capacitor C2 of 1000pf

Arm CD: a non-inductive resistance of R of 100 Ω in parallel to a capacitor of 0.01 μF

Arm DA: a non-inductive resistance of 1000 Ω

The supply frequency is 50 Hz and connected across terminals B and D. If the bridge is balanced with the above value, determine the value of unknown Capacitance.

a) 100 pf

b) 1000 pf

c) 500 pf

d) 10 pf

Answer: a

Explanation: For the balance conditions,

Z 1 Z 3 = Z 2 Z 4

1000 × \

\(\frac{100}{1 + jω + 10^{-6}} \)

Or, \(\frac{- j10^{10}}{ω}\) – 10 4 = R + jX

Comparing the imaginary part, we get,

\(\frac{1}{ωC} = \frac{10^{10}}{ω}\)

Or, C = 100 pf.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Shunts and Multipliers”.

1. Range of an electrical instrument depends on __________

a) current

b) voltage

c) power

d) resistance

Answer: a

Explanation: The amount of current safely passing through the coil of the instrument and the spiral springs. This acts as the leads of the current to the instrument. As a result, the range of an electrical instrument depends on the current.

2. Moving coil instruments have a current and voltage rating of __________

a) 100 A and 25 V

b) 50 mA and 50 mV

c) 75 nA and 100 μV

d) 25 μA and 75 V

Answer: b

Explanation: Moving coil instruments are designed to function as Ammeters and Voltmeters. They have a maximum current carrying capacity of 50 mA with a voltage rating of 50 mV.

3. A shunt is a __________

a) very high resistance

b) medium resistance

c) very low resistance

d) high resistance

Answer: c

Explanation: Usually shunt is a very low value of resistance. It is connected in parallel with the ammeter coil. Through this we can extend the range of an ammeter.

4. A shunt can be used to measure large currents.

a) True

b) False

Answer: a

Explanation: A shunt is normally a very low value of resistance, connected in parallel with the ammeter coil. By making use of a low range ammeter, large current values can be measured through a shunt.

5. Current terminals have a small current capacity.

a) True

b) False

Answer: b

Explanation: A shunt is normally a very low value of resistance, connected in parallel with the ammeter coil. In a shunt, the current terminals have a large current capacity and are connected in series.

6. Potential terminals have a __________

a) high current capacity

b) low voltage capacity

c) low current capacity

d) high voltage capacity

Answer: c

Explanation: A shunt is normally a very low value of resistance, connected in parallel with the ammeter coil. In a shunt, the potential terminals have a low current carrying capacity. As a result, a low range ammeter is used to measure the large current.

7. In case of AC ammeters, shunts consist of __________

a) impedance

b) capacitance

c) resistance

d) inductance

Answer: d

Explanation: AC ammeter shunts comprise of the inductances of the ammeter as well as the shunt. In order to extend the range of an AC ammeter, inductances of the ammeter and the shunt are taken into account.

8. What is the effect of the ammeter range on the shunt resistance?

a) no effect

b) varies by a factor of multiplying factor

c) varies by a factor of the resistance

d) varies by a factor of unity

Answer: b

Explanation: We know that

N = 1 + R a ⁄ R s

where, N is the multiplying factor

R a is the ammeter resistance

R s is the shunt resistance

It is clear from the above equation that in order to increase the ammeter range by N times, the shunt resistance is equivalent to 1 ⁄ N-1 .

9. A multiplier is __________

a) non-inductive

b) resistive

c) capacitive

d) non-capacitive

Answer: a

Explanation: A multiplier is basically a non-inductive, high resistance that is used to extend the range of a D.C. voltmeter. Multiplier consists of a low range D.C. voltmeter connected in series with it.

10. What is the condition for using a multiplier in A.C. voltmeters?

a) by using ac supply

b) by maintaining a uniform impedance

c) by maintaining a uniform frequency

d) by using a galvanometer

Answer: c

Explanation: A multiplier can be used for A.C. voltmeters. The condition to be satisfied is that the total impedance of the voltmeter and the multiplier circuit must be constant for a wide range of frequencies.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Instrument Transformers”.

1. What is the current transformer?

a) transformer used with an A.C. ammeter

b) transformer used with an D.C. ammeter

c) transformer used with an A.C. voltmeter

d) transformer used with an D.C. voltmeter

Answer: a

Explanation: A transformer used to extend the range of an A.C. ammeter is known as a current transformer. A current transformer is also abbreviated as C.T.

2. What is the potential transformer?

a) transformer used with an D.C. ammeter

b) transformer used with an A.C. voltmeter

c) transformer used with an D.C. ammeter

d) transformer used with an A.C. voltmeter

Answer: b

Explanation: A transformer used to extend the range of an A.C. voltmeter is known as a potential transformer. A potential transformer is also abbreviated as P.T.

3. C.T. and P.T. are used for _________

a) measuring low current and voltages

b) measuring very low current and voltages

c) measuring high currentsand voltages

d) measuring intermediate currents and voltages

Answer: c

Explanation: C.T. is basically used for the measurement of high currents. A P.T. is usually used for the measurement of high voltages. They are used with A.C. ammeters and voltmeters in order to extend their range.

4. The primary winding of a C.T. has _________

a) a larger number of turns

b) no turns at all

c) intermediate number of turns

d) a few turns

Answer: d

Explanation: The primary winding of a C.T. has a very few number of turns. It is connected in series with the load circuit through which the primary current flows.

5. The secondary winding of a C.T. has _________

a) a large number of turns

b) a few turns

c) no turns at all

d) intermediate number of turns

Answer: a

Explanation: Secondary winding of a C.T. has a large number of turns. It is connected in series to an ammeter through which a small portion of the current flows through.

6. Turns ration for a C.T. is _________

a) n = N p ⁄ N s

b) n = N s ⁄ N p

c) n = 1 ⁄ N p

d) n = N s

Answer: b

Explanation: The turns ratio for a C.T. is defined as the ratio of the number of turns in the secondary to the number of turns in the primary. It is given by the relation

n = N s ⁄ N p

7. The primary winding of a P.T. has _________

a) intermediate number of turns

b) no turns at all

c) a larger number of turns

d) a few turns

Answer: c

Explanation: The primary winding of a P.T. has a very large number of turns. It is connected in parallel with the load whose voltage is to be measured.

8. The secondary winding of a P.T. has _________

a) a large number of turns

b) intermediate number of turns

c) no turns at all

d) a few turns

Answer: d

Explanation: Secondary winding of a P.T. has a few number of turns. A low range voltmeter is connected in parallel with the secondary winding.

9. Turns ration for a C.T. is _________

a) n = N p ⁄ N s

b) n = N s ⁄ N p

c) n = 1 ⁄ N p

d) n = N s

Answer: a

Explanation: The turns ratio for a P.T. is defined as the ratio of the number of turns in the primary to the number of turns in the secondary. It is given by the relation

n = N p ⁄ N s .

This set of Electrical Measurements Problems focuses on “Advantages of Instrument Transformers”.

1. Instrument transformers can be easily replaced.

a) True

b) False

Answer: a

Explanation: The secondary windings of C.T. and P.T. are standardized. As a result, instruments can be standardized with the ratings of C.T. and P.T. Hence the instrument transformers can be replaced with ease.

2. Instrument transformers provide _________

a) electrical isolation from low rated winding

b) electrical isolation from high rated winding

c) electrical isolation from medium rated winding

d) no electrical isolation at all

Answer: b

Explanation: In an instrument transformer, the low rated secondary windings provide electrical isolation from the high rated primary windings.

3. Instrument transformers give same readings irrespective of number of other instruments connected.

a) True

b) False

Answer: a

Explanation: When instruments are used with instrument transformers, they provide consistent readings. It does not vary with the instrument constants and the number of instruments connected in the circuit.

4. C.T. and P.T. are standardized at _________

a) 50 A and 220 V

b) 25 mA and 2.2 kV

c) 5 A and 110 V

d) 75 nA and 1.1 MV

Answer: c

Explanation: Current transformers are standardized at 5 A of secondary winding current, whereas Potential transformers are standardized at 110 V of secondary winding voltage.

5. A 5A ammeter can measure a current of upto 1000 A using a _________

a) 5/1000A C.T.

b) 1000A C.T.

c) 5A C.T.

d) 1000/5A C.T.

Answer: d

Explanation: A 1000/5A current transformer can be used for measuring a current of upto 1000A by making use of an ammeter with 5A current reading.

6. A 110V voltmeter can measure a voltage of upto 110kV using a _________

a) 110000/110V P.T.

b) 110000V P.T.

c) 110V P.T.

d) 110/110000V P.T.

Answer: a

Explanation: An 110000/110V potential transformer can be used for measuring a voltage of upto 110000V by making use of a voltmeter with 110V voltage reading.

7. How can the meter circuit be isolated from the power circuit?

a) by grounding

b) through electrical isolation

c) by physical separation

d) through mechanical isolation

Answer: b

Explanation: Leads of the secondary winding transformer are brought to the switch board thus separating them from high voltage windings. In this way, the meter circuit is isolated from the high voltage power circuit.

8. How are instrument transformers different from shunts and multipliers?

a) they are all the same

b) they have transformers

c) readings are independent of component values

d) they can be used for high voltages and currents

Answer: c

Explanation: Instrument transformers can be used for extending the range of the A.C. instruments. In instrument transformers, readings are independent of the values of R, L, and C. But in the case of shunts and multipliers, the readings depend on the values of circuit constants.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Ratios of Instrument Transformers”.

1. Transformation ratio of an instrument is defined as ____________

a) ratio of primary to secondary phasor

b) ratio of secondary to primary phasor

c) reciprocal of the primary phasor

d) reciprocal of the secondary phasor

Answer: a

Explanation: For an instrument transformer, the transformation ratio is defined as the ratio of the magnitude of the actual primary phasor to the magnitude of the secondary phasor.

2. For a C.T. the transformation ratio is given by which of the following relation?

a) R = \

R = \

R = I p

Answer: b

Explanation: In a current transformer, the transformation ratio is given by the ratio of the magnitude of the actual primary current to the magnitude of the actual secondary current.

R = \(\frac{I_p}{I_s}\)

where, R is the transformation ratio

I p is the actual primary winding current

I s is the actual secondary winding current.

3. For a P.T. the transformation ratio is given by which of the following relation?

a) R = \

R = \

R = V p

Answer: c

Explanation: In a potential transformer, the transformation ratio is given by the ratio of the magnitude of the actual primary current to the magnitude of the actual secondary current.

R = \(\frac{V_p}{V_s}\)

where, R is the transformation ratio

V p is the actual primary winding voltage

V s is the actual secondary winding voltage.

4. Nominal ratio of an instrument transformer is defined as the __________

a) reciprocal of the rated primary value

b) ratio of rated secondary value to primary value

c) reciprocal of the rated secondary value

d) ratio of rated primary value to secondary value

Answer: d

Explanation: In an instrument transformer, nominal ratio is defined as the ratio of the rated primary current or voltage to the rated secondary winding current or voltage.

5. For a C.T. the nominal ratio is given by which of the following relation?

a) K n = \

K n = \

K n = I p

Answer: a

Explanation: In a current transformer, the transformation ratio is given by the ratio of the magnitude of the actual primary current to the magnitude of the actual secondary current.

K n = \(\frac{I_{p}}{I_{s}}\)

where, R is the transformation ratio

I p is the rated primary winding current

I s is the rated secondary winding current.

6. For a P.T. the nominal ratio is given by which of the following relation?

a) K n = \

K n = \

K n = V p

Answer: b

Explanation: In a potential transformer, the transformation ratio is given by the ratio of the magnitude of the actual primary voltage to the magnitude of the actual secondary voltage.

electrical-measurements-questions-answers-ratios-instrument-transformers-q6a

where, R is the transformation ratio

V p is the rated primary winding voltage

V s is the rated secondary winding voltage.

7. Ratio correction factor is defined as _________

a) reciprocal of nominal ratio

b) ratio of nominal ratio to transformation ratio

c) ratio of transformation ratio to nominal ratio

d) reciprocal of transformation ratio

Answer: c

Explanation: The ratio correction factor for an instrument transformer is defined as the ratio of the transformation ratio to the nominal ratio.

R.C.F = R ⁄ K n

where,

R.C.F is the ratio correction factor

R is the transformation ratio

K n is the nominal ratio.

8. For a C.T. the turns ratio is defined as the _________

a) n = N p ⁄ N s

b) n = 1 ⁄ N p

c) n = N s

d) n = N s ⁄ N p

Answer: d

Explanation: For a current transformer, the turns ratio is defined as the ratio of the number of turns in the secondary winding to the number of turns in the primary winding.

n = N s ⁄ N p

where, n is the turns ratio

N s is the secondary turns

N p is the primary turns.

9. For a P.T. the turns ratio is defined as the _________

a) n = N p ⁄ N s

b) n = 1 ⁄ N p

c) n = N s

d) n = N s ⁄ N p

Answer: a

Explanation: For a potential transformer, the turns ratio is defined as the ratio of the number of turns in the primary winding to the number of turns in the secondary winding.

n = N p ⁄ N s

where, n is the turns ratio

N p is the primary turns

N s is the secondary turns.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Errors in Current Transformers”.

1. Errors are introduced in Current Transformers.

a) True

b) False

Answer: a

Explanation: A current transformer is used for the measurement of very high currents. The use of a C.T. leads to the introduction of two errors in power measurement.

2. Ratio error is defined as ___________

a) Ratio error = K n ⁄ R

b) Ratio error = K n – R ⁄ R

c) Ratio error = K n – R

d) Ratio error = 1 ⁄ R

Answer: b

Explanation: Ratio error of a C.T. is defined as the ratio of the magnitude of the difference between the nominal and actual ratio with respect to the actual ratio.

electrical-measurements-questions-answers-errors-current-transformers-q2

3. Phase angle in a C.T. is defined as ____________

a) \

\(\frac{180}{π} [\frac{I_m sinδ – I_c cosδ}{nI_s}]\) degrees

Answer: c

Explanation: During power measurement, there exists phase angle error in a C.T. The phase angle is defined as

Phase angle = \(\frac{180}{π} [\frac{I_m cosδ – I_c sinδ}{nI_s}]\) degrees.

where. I m is the magnetising component of the excitation current

I c is the core loss component of the excitation current

I s is the secondary winding current.

4. Phase angle error is given by ____________

a) \

\(\frac{180}{π} [\frac{I_m}{nI_s}]\) degrees

Answer: d

Explanation: The power measurement in a C.T. leads to phase angle error. Phase angle error is given by the relation

θ = \(\frac{180}{π} [\frac{I_m}{nI_s}]\) degrees

where, θ is the phase angle error

I m is the magnetising component of the excitation current

I s is the secondary winding current.

5. Ratio error is due to _________

a) iron loss

b) C.T.

c) magnetising component

d) supply voltage

Answer: a

Explanation: We know that the ratio error in a C.T. is given by the relation

Ratio error = K n – R ⁄ R = n + I e ⁄ I s

where, I e is the iron loss component of the excitation current

n is the turns ratio.

6. Phase angle error is due to _________

a) C.T.

b) magnetising component

c) iron loss

d) supply voltage

Answer: b

Explanation: We know that the phase angle error in a C.T. is given by the relation

θ = \(\frac{180}{π} [\frac{I_m}{nI_s}]\) degrees

where, θ is the phase angle error

I m is the magnetising component of the excitation current

I s is the secondary winding current

It is observed from the equation for the phase angle error that it depends on the magnetising component of the excitation current.

7. In power measurements 180° phase shift is required.

a) True

b) False

Answer: a

Explanation: For eliminating errors in power measurement, there must be a phase difference of 180° between the primary and the secondary currents.

8. Errors in a C.T. can be minimised by _________

a) making use of laminations

b) having low reactance

c) increasing the secondary winding turns

d) decreasing the primary winding turns

Answer: b

Explanation: The excitation current Io can be minimised thus eliminating the errors in a C.T. by minimising the iron loss. The core must have a low iron loss and a minimum value of leakage reactance.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Design Features of Current Transformers”.

1. The secondary leakage reactance of a C.T. ____________

a) increases its ratio error

b) decreases its ratio error

c) has no effect on its ratio error

d) increases the impedance of the circuit

Answer: a

Explanation: The windings in a current transformer must be kept close so that the secondary leakage reactance is minimum. Secondary leakage reactance of a C.T. thus increases its ratio error.

2. Secondary and primary windings consist of ________

a) copper turns

b) 14 S.W.G copper wire and copper strip respectively

c) iron coils wound around

d) laminations

Answer: b

Explanation: For a current transformer the most popular form used is the bar primary and ring core construction. Hence 14 S.W.G copper wire is used for the secondary winding whereas a copper strip is used for the primary winding.

3. Coils of a C.T. are separately wound.

a) True

b) False

Answer: a

Explanation: A C.T. is used for the measurement of high magnitudes of current. In order to get lower line voltages, the coils of a C.T. are wound separately and insulated through tapes and varnish.

4. The windings of a C.T. are ________

a) tied together

b) shorted

c) wound over one another

d) grounded

Answer: c

Explanation: Using cylinders made of Bakelite, the windings of a C.T. are wound over one another. This setup is mounted on a steel tank sheet filled with transformer oil.

5. At high voltages, the current transformers are enclosed in a tank.

a) True

b) False

Answer: a

Explanation: The current transformers are enclosed in a tank at high voltages of the order of more than 7 kV. The tank consists of a solid insulating compound. Since the cooling is poor, the compound introduces difficulty.

6. Turns compensation is used to obtain ________

a) to compensate the turns

b) to equalise the turns on the windings

c) to protect the equipment

d) transformation ratio equal to nominal ratio

Answer: d

Explanation: In a C.T., the transformation ratio is given by

R = n + I e ⁄ I s

where, n is the turns ratio

I e is the core loss component of the excitation current

I s is the secondary winding current

Turns compensation is used to obtain the transformation ratio equal to the nominal ratio (K n ).

7. What is the effect of reducing the secondary turns in a C.T. by 1%?

a) transformation ratio reduces by the same value

b) no effect

c) nominal ratio increase by the same value

d) secondary current increases by the same value

Answer: a

Explanation: In a C.T., the transformation ratio is given by

R = n + I e ⁄ I s

where, n is the turns ratio

I e is the core loss component of the excitation current

I s is the secondary winding current

As the number of secondary turns is reduced by a factor of 1%, the transformation ratio is reduced by approximately the same percentage.

8. In a 1000/5 A C.T., the number of secondary turns would be ________

a) 200

b) 199 or 198

c) 5

d) 1000

Answer: b

Explanation: The optimum number of secondary turns in a C.T. is the value that makes the transformation ratio and nominal ratio (K n ) equal. It is usually one or two turns less than the actual value. Thus in a 1000/5 A, though the number of turns would be 200 ideally, it is considered as 198 or 199 in order to keep R and K n equal.

9. In the ring type of core, the secondary winding is ________

a) non-uniformly distributed over the core

b) shorted with the primary winding

c) uniformly distributed over the core

d) connected in the form of a ring

Answer: c

Explanation: The ring type of core used for a secondary winding is a jointless core. It has a very small leakage reactance. Hence in a ring type of core, the secondary winding is uniformly distributed over the core.

10. In a shell type of core, the windings are ________

a) in the form of the shell

b) shorted with the primary windings

c) not wound

d) placed on the central limb

Answer: d

Explanation: The windings in a shell type of core are placed in a central limb. It provides protection to the windings.

11. Mumetal has ________

a) low permeability, high loss

b) high permeability, medium loss

c) medium permeability, high loss

d) high permeability, low loss

Answer: c

Explanation: Mumetal is an alloy of nickel, iron and copper. It has a high permeability, low loss and small retentivity. It has a maximum permeability of 90,000 at a flux density of 0.35 W/m 2 .

12. Perminder has __________

a) medium saturation point of permeability

b) low saturation point of permeability

c) no saturation point of permeability

d) high saturation point of permeability

Answer: d

Explanation: Perminder is an alloy of iron, cobalt and vanadium. It has a high flux density of the order of 2.4 Wb/m 2 . It is very expensive.

This set of Electrical Measurements Questions and Answers for Freshers focuses on “Open Circuiting the Secondary Circuit of a Current Transformer”.

1. In a C.T., the primary ampere turns is variable.

a) True

b) False

Answer: b

Explanation: In a current transformer, the primary ampere turns is fixed. When the secondary circuit is opened, assuming a constant primary current we get a fixed number of primary ampere turns.

2. The secondary circuit of a C.T. is open when?

a) a very high flux density is produced

b) a very low flux density is produced

c) a moderate flux density is produced

d) no flux density is produced

Answer: a

Explanation: When current is flowing in the secondary circuit which is kept open in a C.T., a very high flux density is produced in the core as a result of the absence of demagnetizing ampere turns.

3. High flux density leads to _________

a) a decreased voltage in the secondary

b) a decreased voltage in the primary

c) a increased voltage in the secondary

d) a decreased voltage in the primary

Answer: c

Explanation: High flux density in the secondary winding of a C.T. leads to an increase in the induced voltage in the secondary winding. This may damage the insulation.

4. When primary current flows, secondary circuit should be open.

a) True

b) False

Answer: b

Explanation: In a current transformer, even when it is not in use for any measurement purposes, the secondary circuit must be closed when the primary current is flowing.

5. High magnetizing forces in the core when removed suddenly lead to ____________

a) no residue

b) partial residual magnetism

c) rupture of the device

d) residual magnetism

Answer: d

Explanation: In a C.T, the high magnetizing forces on the core may leave behind residual magnetism in the core and ratio and phase angle errors.

6. The secondary winding of a C.T. ____________

a) can be shorted

b) can’t be shorted

c) can be opened

d) can’t be opened

Answer: a

Explanation: When a C.T. is used in measurements, it acts as a short circuit. This is because the impedance of the load is negligible due to the ammeter or the wattmeter coil. Thus the secondary winding of a C.T. can be shorted.

7. The secondary winding of a C.T. is opened when?

a) C.T. is magnetised

b) C.T. is demagnetised

c) C.T. is shorted

d) C.T. is opened

Answer: b

Explanation: In a C.T., when the secondary winding is opened by mistake when the primary current is flowing, the C.T. must be demagnetized first fully and then only must be used again in the circuit for any measurements.

8. The rectangular type of C.T. is built of _________

a) L shaped windings

b) T shaped windings

c) A shaped windings

d) Z shaped windings

Answer: a

Explanation: In a rectangular type of C.T., the windings are placed on the shorter limbs. The primary winding is wound over the secondary. The rectangular type of C.T. is built of L shaped windings.

This set of Electrical Measurements Questions and Answers for Entrance exams focuses on “Differences between C.T. and P.T. “.

1. Potential transformers are used to measure _________

a) high voltages

b) low voltages

c) high currents

d) low currents

Answer: a

Explanation: Potential transformers are also known as P.T. and are used in the measurement of high magnitude of voltages.

2. Potential transformers are used with _________

a) high range voltmeter

b) low range voltmeter

c) intermediate range voltmeter

d) very high range voltmeter

Answer: b

Explanation: In general, potential transformers are used with low range voltmeters. They are also used for energizing the potential coils of low range energy meters and wattmeters.

3. Potential transformer is similar in design to a _________

a) C.T.

b) Step up transformer

c) Power transformer

d) Step down transformer

Answer: c

Explanation: In terms of design, the potential transformer resembles a power transformer. Potential transformers have a very low loading capacity of the order of a few volt amperes.

4. The secondary winding of a P.T. is designed for _________

a) 220 V

b) 2.2 kV

c) 1.1 kV

d) 110 V

Answer: d

Explanation: A potential transformer is generally used for the measurement of the very high magnitude of voltages in a circuit. But the secondary winding of a P.T. is designed for a capacity of 110 V.

5. The primary current in a C.T. is _________

a) independent of secondary circuit

b) dependent on the secondary circuit

c) depends on the transformation ratio

d) depends on the nominal ratio

Answer: a

Explanation: A C.T. is used for the measurement of high magnitude of currents in a circuit, while a P.T. is used for the measurement of high magnitude of voltages in a circuit. Primary current in a C.T. is independent of the secondary circuit conditions.

6. The excitation current of a C.T. _________

a) varies over a fixed range of operation

b) varies over a wide range of normal operation

c) is fixed over a range of operation

d) is fixed always

Answer: b

Explanation: In a potential transformer, the excitation current remains constant under normal operation. While in a current transformer, the excitation current varies over a wide range of operations.

7. Secondary of a P.T. can be open circuited.

a) True

b) False

Answer: a

Explanation: In a C.T., the secondary winding must never be open circuited when current is flowing in the primary winding. While in a P.T., the secondary winding can be open circuited without any damage to the circuit.

8. When C.T. is connected in series with a line, a large voltage exists across the primary.

a) True

b) False

Answer: b

Explanation: In a P.T., full voltage appears across the primary winding when it is connected across the line. While when a C.T. is connected in series with a line, a very small voltage appears across the primary winding.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Reduction of Errors in Potential Transformers”.

1. Winding resistance of a P.T. can be reduced by _________

a) using thick conductors

b) decreasing the length of the winding

c) shorting the primary and secondary windings

d) using thin conductors

Answer: a

Explanation: In a potential transformer, the winding resistance is usually minimised by using thick conductors and by making use of small length for the turns.

2. Leakage reactance is minimised by _________

a) using thin conductors

b) reducing leakage flux

c) increasing flux density

d) shorting the windings

Answer: b

Explanation: By maintaining the primary and secondary windings together in a P.T. and also by reducing the leakage flux, we can minimise the leakage reactance.

3. High flux density is due to less turns.

a) True

b) False

Answer: a

Explanation: In a P.T., a high flux density in the core, gives rise to a less number of turns. This in turn results in a lower leakage reactance.

4. Ratio error in a P.T. depends on _________

a) secondary current

b) primary voltage

c) secondary current

d) turns ratio

Answer: c

Explanation: In a P.T., the difference between actual ratio and turns ratio is given by the relation,

electrical-measurements-questions-answers-reduction-errors-potential-transformers-q4

where, R is the ratio error

n is the turns ratio

I s is the secondary winding current

I e is the iron loss component

I m is the magnetising component

It is seen from the above equation that the ratio error in a P.T. depends on the secondary current, magnetising and iron loss components of current.

5. In a P.T. values of components of currents are negligible.

a) True

b) False

Answer: b

Explanation: In a C.T. the various components of current such as magnetising current, iron loss component of current are almost comparable in magnitude with the value of the load current.

6. Ratio error can be minimised by _________

a) reducing the turns

b) reducing the current

c) increasing the voltage

d) using a good core material

Answer: d

Explanation: By making use of a good quality core material, low value of flux density and following required precautions in the core assembly we can minimise the value of the ratio error.

7. Another method of eliminating the ratio error is _________

a) by reducing secondary turns

b) by increasing the primary turns

c) by increasing secondary turns

d) by reducing the primary turns

Answer: a

Explanation: In a P.T., at no load, we get

electrical-measurements-questions-answers-reduction-errors-potential-transformers-q7

where, R is the ratio error

n is the turns ratio

I s is the secondary winding current

I e is the iron loss component

I m is the magnetising component

From the above equation it is seen that to reduce the ratio error, actual ratio and nominal ratio must be made equal. This can be done by reducing the secondary turns.

8. How is the voltage ratio dependent on the frequency?

a) they are independent of each other

b) they aid each other

c) they oppose each other

d) depends on the setup of the circuit

Answer: c

Explanation: As the voltage ratio changes, the frequency also changes. It depends on the relative value of the core loss component Io as well as the leakage reactance. The effects due to the voltage ratio and the change in frequency oppose each other.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Characteristics of Potential Transformers”.

1. Increasing secondary burden _____________

a) increases I s

b) decreases I s

c) keeps I s constant

d) decreases I p

Answer: a

Explanation: When the secondary burden of a potential transformer increases, it leads to an increase in the secondary current. As a result the primary current also increases.

2. For a given V p the V s __________

a) increases

b) decreases

c) remains constant

d) depends on the supply

Answer: b

Explanation: For a particular value of primary voltage V p , the value of the secondary voltage V s decreases. This leads to a decrease in the actual ratio.

3. What is effect of the secondary burden on the ratio error?

a) ratio error is constant with secondary burden

b) ratio error decreases with secondary burden

c) ratio error increases with secondary burden

d) depends on the supply voltage

Answer: c

Explanation: As the secondary burden is increased, the ratio error also increases and becomes more negative. Ratio error varies linearly with respect to the change in the secondary burden.

4. V p is leading in phase, while V s is lagging in phase.

a) True

b) False

Answer: a

Explanation: As the secondary burden is increased, winding voltage drop increases. Voltage V p is leading in phase while V s is lagging in phase. As a result the phase angle increases with the secondary burden.

5. What is the effect of p.f. on secondary burden?

a) I p shifts towards I o

b) I p deviates from I o

c) I p is independent of I o

d) I p and I o cancel eachother

Answer: a

Explanation: When the power factor of the secondary burden is reduced, I p shifts towards I o . Voltages V p and V s come closer to E p and E s .

6. How is the transformation ratio dependent on the secondary burden?

a) decreases

b) increases

c) remains constant

d) depends on the supply

Answer: b

Explanation: As the primary voltage V p is constant, the induced primary e.m.f E p is reduced. Similarly the secondary voltage V s is reduced with respect to E s . As a result the transformation ratio increases.

7. Decrease in p.f. makes V s to lead V p .

a) True

b) False

Answer: a

Explanation: As the power factor is decreased, Vs leads in phase while V p decreases in phase. Thus the phase angle reduces with the decrease in power factor .

8. At constant voltage how is frequency affected by flux?

a) decreases with an increase in flux

b) increases with a decrease in flux

c) remains constant

d) depends on the current

Answer: b

Explanation: When frequency is increased at a constant voltage, the flux decreases. Voltage ratio decreases as the magnetizing and iron loss components of current are reduced.

This set of Tricky Electrical Measurements Questions and Answers focuses on “Advanced Problems on C.T. and P.T.”.

1. A 50 Hz, bar primary CT has a secondary with 800 turns. The secondary supplies 7 A current into a purely resistive burden of 2 Ω. The magnetizing ampere-turns are 300. The phase angle is?

a) 3.1°

b) 85.4°

c) 94.6°

d) 175.4°

Answer: a

Explanation: Secondary burden is purely resistive and the resistance of burden is equal to the resistance of the secondary winding; the resistance of secondary winding = 1Ω. The voltage induced in secondary × resistance of secondary winding = 7 × 2 = 14V. Secondary power factor is unity as the load is purely resistive. The loss component of no-load current is to be neglected i.e. I e = 0. I M = 300 A.

Secondary winding current I S = 7 A

Reflected secondary winding current = n I S = 5600 A

∴ tan θ = \(\frac{I_M}{nI_S}\). So, θ = 3.1°.

2. A 50 Hz, bar primary CT has a secondary with 500 turns. The secondary supplies 5 A current into a purely resistive burden of 1 Ω. The magnetizing ampere-turns are 200. What is the ratio error at full load, if the iron loss is 1.5 W and magnetizing mmf is 100 A?

a) Zero

b) 45 μWb

c) 25.5 μWb

d) 100 μWb

Answer: b

Explanation: Voltage induced in the secondary,

E S = I S × Z S = 5 V

E S = 4.44 f ∅ N

∴ ∅ = \(\frac{E_S}{4.44 \,f \,N} = \frac{5}{4.44 \,f \,N}\) = 45 μWb.

3. A 1000/5 A, 50 Hz correct transformer has a secondary burden comprising a non-inductance of 1.6Ω. The flux in the core at full load is?

a) 160 μWb

b) 180 μWb

c) 200 μWb

d) 150 μWb

Answer: b

Explanation: Turn ratio = 1000/5 = 200

N P = 1

So, N S = 200

Secondary impedance = 1.6Ω

Secondary induced voltage, E S = 5 × 1.6 = 8 V

∴ E S = 4.44 f N ∅

So, ∅ = \(\frac{E_S}{4.44 \,f \,N} = \frac{8}{4.44 \,f \,N}\) = 180 μWb.

4. A 1000/5 A, 50 Hz correct transformer has a secondary burden comprising a non-inductance of 2Ω. What is the ratio error, if the iron loss is 3 W and magnetizing mmf is 250 A?

a) 4%

b) 5.7%

c) 3.6%

d) 4.8%

Answer: b

Explanation: E = \(\frac{10}{200}\) V

I = 60 A

I = \(\frac{mmf}{N_P}\) = 250 A

Actual rating R = 200 + \(\frac{60}{5}\) = 212

So, percentage ratio error = \(\frac{K_n-R}{R}\) × 100 = \(\frac{200-212}{212}\) × 100 = 5.7%.

5. A 200/1 Current Transformer is wound with 400 turns on the secondary on a toroidal core. When it carries a current of 180 A on the primary, the ratio is found to be -0.5%. If the number of secondary turns is reduced by 1, the new ratio error will be?

a) 0.0

b) -0.5

c) -1.0

d) -2.0

Answer: c

Explanation: Turn compensation only alters ratio error n=400

Ratio error = -0.5% = – \(\frac{0.5}{100}\) × 400 = -2

So, Actual ratio = R = n+1 = 401

Nominal Ratio K N = 400/1 = 400

Now, if the number of turns are reduced by one, n = 399, R = 400

Ratio error = \(\frac{K_N-R}{R} = \frac{200-200}{200}\) = 0.

6. A , 50 Hz current transformer has a primary bar. The secondary burden is a pure resistance of 1 Ω and it draws a current of 5 A. The magnetic core requires 350 AT for magnetization. Find the percentage ratio error.

a) 10.56

b) -28.57

c) 11.80

d) -11.80

Answer: b

Explanation: I m = 350/1 = 350 A

I p = \

^2 +

^2)^{0.5}\) = 490.05

n = 350/7 = 50

∴ R = \(\frac{I_P}{I_S} = \frac{490.05}{7}\) = 70

∴ Percentage ratio error = \(\frac{50-70}{70}\) × 100 = -28.57%.

7. The observation when the secondary winding of a current transformer is open-circuited is?

a) The whole of the primary current produces a large value of flux in the core thereby producing a large voltage in the secondary winding

b) The large voltage may act as a safety hazard for the operators and many even raptures the insulation

c) When the large magnetizing force is taken off, it leaves a large value of residual magnetism

d) When the large magnetizing force is taken off, it leaves a small value of residual magnetism

Answer: b

Explanation: Never open the circuit of the secondary winding of a current transformer while to the primary winding is energized. Failure to observe this precaution may lead to serious consequences both to the operating personnel and to the transformer.

8. Usually a CT has ____________

a) Power overload capacity than PT

b) The same overload capacity as a PT

c) A higher overload capacity than a PT

d) No overload capacity

Answer: c

Explanation: A CT cannot have greater or same power overload than PT. Also, it will be having some load on it. This load is a higher overload capacity than a PT.

9. A PT is a device which is ___________

a) Electrostatically coupled

b) Electrically coupled

c) Electromagnetically coupled

d) Conductively coupled

Answer: c

Explanation: A Potential Transformer cannot be electrostatically coupled since CRO are electrostatically coupled. Also, they cannot be conductively coupled. But since they are kind of electrically coupled hence electromagnetically coupled is the only correct option.

10. The CT supplies current to the current coil of a wattmeter power factor meter, energy meter and, an ammeter. These are connected as?

a) All coils in parallel

b) All coils in series

c) Series-parallel connection with two in each arm

d) Series-parallel connection with one in each arm

Answer: b

Explanation: Since the CT supplies the current to the current coil of a wattmeter, therefore the coils are connected in series so that the current remains the same. If they were connected in parallel then the voltages would have been the same but the currents would not be the same and thus efficiency would decrease.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Advanced Problems on Indicating Instruments – 1”.

1. In a moving iron meter, the deflection torque is proportional to?

a) Square of the current through the coil

b) Current through the coil

c) Sine of measurand

d) The Square root of the measurand

Answer: a

Explanation: We know that,

T d = \(\frac{1}{2} I^2 \frac{dl}{dθ} \)

∴ The deflection torque is proportional to the square of the current through the coil.

2. The full-scale deflection current of an ammeter is 4 mA and its internal resistance is 400Ω. If this meter is to have a full deflection of 10 A, what is the value of the shunt resistance to be used?

a) 49.99 Ω

b) 0.16 Ω

c) 1.5 Ω

d) 2.6 Ω

Answer: b

Explanation: Voltage across the meter = 4 × 10 -3 × 4 × 10 2 = 1.6 V

Current through the shunt = 10 – 0.004 = 9.996 A

∴ Shunt resistance = \(\frac{16}{10 × 9.996} \) = 0.16 Ω.

3. The full-scale deflection current of a meter is 4 mA and its internal resistance is 400Ω. This meter is to have full deflection when 400 V is measured. What is the value of the series resistor to be used?

a) 99.90 kΩ

b) 100 kΩ

c) 99.60 kΩ

d) 100 Ω

Answer: c

Explanation: (R S + 400) × 10 -3 × 4 = 400

Or, R S = 100000 – 400 = 99.6 kΩ.

4. Two ammeters, one with a full-scale current of 1 mA and internal resistance of 100 Ω and other a full-scale current of 10 mA and internal resistance of 25 Ω are in parallel. What is the total current, these two meters can carry without the reading out of scale in any meter?

a) 1 mA

b) 10 mA

c) 11 mA

d) 5 mA

Answer: d

Explanation: The lower current I l will decide the total current.

∴ T × \(\frac{25}{125}\) = 1 mA

Or, T = 5 mA.

5. A meter has a full scale of 90° at a current of 1 A. This meter has a perfect square law response. What is the current when the deflection angle is 45°?

a) 0.5 A

b) 0.25 A

c) 0.707 A

d) 0.67 A

Answer: c

Explanation: We know, T D = Cθ

Also, T D = KI 2

∴ I 2 = \(\frac{C}{K}\) θ = C’θ

Or, \(\frac{I^2}{I} = \frac{C’ π}{C’ \frac{\pi}{2}} = \frac{1}{2}\)

So, I = 0.707 A.

6. The scale of a dynamometer type instrument marked in terms of RMS value would be__________

a) Uniform throughout

b) Non-uniform and crowded near the full scale

c) Non-uniform and crowded at the beginning

d) Non-uniform and crowded around mid-scale

Answer: c

Explanation: We have deflection θ ∝ I 2 for an ammeter and θ ∝ V 2 for a voltmeter. We have assumed the value for the voltmeter to be constant but it is not true. The value is constant for a radical field but not for a voltmeter.

7. Moving Iron Instrument can be used as ____________

a) An ammeter for measuring DC as well as AC

b) For measuring DC current and voltages only

c) An ammeter and a voltmeter for measuring DC as well as AC

d) For measuring AC current and voltages only

Answer: c

Explanation: When the instrument is connected in the circuit, the current flows through the coil. These currents set up a magnetic field in the coil. The result is that the pointer attached to the moving system moves from zero position. If the current in the coil is reversed, the direction of deflecting torque remains unchanged. Therefore, these instruments can be used for both DC as well as AC measurements.

8. A 10 mA PMMC ammeter reads 4 mA in a circuit. Its bottom control spring snaps suddenly. The meter will now show __________

a) 10 mA

b) 8 mA

c) 2 mA

d) Zero

Answer: d

Explanation: The spring gives the controlling torque. It is connected in series with the coil. If the spring is cut open, there will be no deflection.

9. The standardization of AC potentiometer is done by ____________

a) Using a DC standard source and d’ Arsonval galvanometer

b) Using AC standard sources and transfer instruments

c) Using a standard AC voltage source

d) Using a DC standard source and transfer instruments

Answer: d

Explanation: Standardization of AC potentiometer is done with the help of standard DC source i.e., a standard cell or a Zener source and a transfer instrument where transfer instrument may be an electrodynamometer or a thermocouple instrument.

10. The inductance of a certain moving- iron ammeter is expressed as L = 10 + 3θ – \(\frac{θ^2}{4}\) μH, where θ is the deflection in radian from the zero position. The control spring torque is 25 × 10 -6 Nm/rad. The meter carries a current of 5 A. What is the deflection?

a) 2.4

b) 2.0

c) 1.2

d) 1.0

Answer: c

Explanation: At equilibrium,

Kθ = \(\frac{1}{2} I^2 \frac{dl}{dθ} \)

(25 × 10 -6 ) θ = \

\) × 10 -6

∴ 2 θ + \(\frac{θ}{2}\) = 3

Or, θ = 1.2.

This set of Electrical Measurements written test Questions & Answers focuses on “Advanced Problems on Indicating Instruments – 2”.

1. A current of – 8 + 6\) A is passed through three meters. The respective readings will be?

a) 8, 6 and 10

b) 8, 6 and 8

c) – 8, 10 and 10

d) -8, 2 and 2

Answer: c

Explanation: PMMC instrument reads only DC value and since it is a centre zero type, so it will give – 8 values.

So, rms = \(\sqrt{8^2 +

^2}\) = 10 A

Moving iron also reads rms value, so its reading will also be 10 A.

2. A rectifier type AC voltmeter consists of a series resistance R, an ideal full-wave rectifier bridge and a PMMC instrument. The internal resistance of the instrument is 100 Ω and a full- scale deflection is produced by a DC current of 1 mA. A voltage of 100 V is applied to the input terminals. The value of R required is?

a) 63.56 Ω

b) 89.83 Ω

c) 89.83 kΩ

d) 141.3 kΩ

Answer: c

Explanation: V OAverage = 0.636 × \(\sqrt{2}\) V rms = 0.8993 V rms

The deflection with AC is 0.8993 times that with DC for the same value of voltage V

S AC = 0.8993 S DC

S DC of a rectifier type instrument is \(\frac{1}{I_{fs}}\) where I fs is the current required to produce full scale deflection, I fs = 1 mA; R m = 100 Ω; S DC = 10 3 Ω/V

S AC = 0.8993 × 1000 = 899.3 Ω/V. Resistance of multiplier R S = S AC V – R m – 2R d , where R d is the resistance of diode, for ideal diode R d = 0

∴ R S = 899.3 × 100 – 100 = 89.83 kΩ.

3. A current of [2 + \ + 2\] is measured with a thermocouple type, 5A full scale, class 1 meter. The meter reading would lie in the range?

a) 5 A ± 1 %

b) A ± 1%

c) 3 A ± 1.7 %

d) 2 A ± 2.5 %

Answer: c

Explanation: I = [2 + \ + 2\] Thermocouple measure the rms value of current.

I rms = \

^2 +

^2]^{1/2} = \sqrt{9}\) = 3 A ± 1.7%.

4. A 50 Hz voltage is measured with a moving iron voltmeter and a rectifier type AC voltmeter connected in parallel. If the meter readings are V a and V b respectively. Then the form factor may be estimated as?

a) \

\(\frac{π V_a}{V_b}\)

Answer: b

Explanation: Form factor of the wave = \(\frac{RMS value}{Mean value}\)

Moving iron instrument will show rms value. Rectifier voltmeter is calibrated to read rms value of the sinusoidal voltage that is, with form factor of 1.11.

∴ Mean value of the applied voltage = \(\frac{V_b}{1.11}\)

∴ Form factor = \(\frac{V_a}{V_b/1.11} = \frac{1.11 V_a}{V_b}\)

5. A moving iron ammeter produces a full-scale torque of 240 μN-m with a deflection of 120° at a current of 10 A. the rate of change of self-inductance of the instrument at full scale is?

a) 2.0 μH/rad

b) 4.8 μH/rad

c) 12.0 μH/rad

d) 114.6 μH/rad

Answer: b

Explanation: At full scale position, \(\frac{1}{2} I^2 \frac{dL}{dθ}\) = T C

\(\frac{1}{2} 10^2 \frac{dL}{dθ}\) = 240 × 10 -6

∴ \(\frac{dL}{dθ}\) = 4.8 μH/rad.

6. A moving coil of a meter has 250 turns and a length and depth of 40 mm and 30 mm respectively. It is positioned in a uniform radial flux density of 450 mT. The coil carries a current of 160 mA. The torque on the coil is?

a) 0.0216 N-m

b) 0.0456 N-m

c) 0.1448 N-m

d) 1 N-m

Answer: a

Explanation: Given, N = 250, L = 40 × 10 -3 , d = 30 × 10 -3 m, I = 160 × 10 -3 A, B = 450 × 10 -3 T

Torque = 250 × 450 × 10 -3 × 40 × 10 -3 × 30 × 10 -3 × 160 × 10 -3 = 200 × 10 -6 N-m = 0.0216 N-m.

7. Two 100 μA full-scale PMMC meters are employed to construct a 10 V and a 100 V full-scale voltmeter. These meters will have figure of merit as?

a) 10 kΩ/V and 10 kΩ/V

b) 100 kΩ/V and 10 kΩ/V

c) 10 kΩ/V and 100 kΩ/V

d) 10 kΩ/V and 1 kΩ/V

Answer: a

Explanation: S V = \(\frac{1}{I_{SS}}\) = current required for full scale deflection

S V = \( \frac{1}{100 × 10^{-6}}\) = 10 kΩ/V.

8. A PMMC rated as 100 μA is used in a rectifier type of instrument which uses full wave rectification. What is the sensitivity on sinusoidal AC?

a) 4.5 kΩ/V

b) 18 kΩ/V

c) 10 kΩ/V

d) 9 kΩ/V

Answer: d

Explanation: Sensitivity = \(\frac{1}{100 × 10^{-6}}\) = 10 kΩ/V

For full-wave rectification S AC = 0.9 + S DC = 0.9 × 10 = 9kΩ/V.

9. The discharge of a capacitor through a ballistic galvanometer produces a damped frequency of 0.125 Hz and successive swings of 120, 96 and 76.8 mm. The damping ratio is?

a) 0.0568

b) 0.0887

c) 0.0357

d) 0.0441

Answer: c

Explanation: Logarithmic decrement, δ = \(ln \frac{x_1}{x_2} = ln \frac{120}{96}\) = 0.225

Now, δ is related to damping ratio K as, K = \(\frac{1}{

^2)^{0.5}}\)

K = \(\frac{1}{

^2)^{0.5}}\)

∴ K = 0.0357.

10. The discharge of a capacitor through a ballistic galvanometer produces a damped frequency of 0.125 Hz and successive swings of 120, 96 and 76.8 mm. The logarithmic decrement is?

a) 0.225

b) 0.565

c) 0.484

d) 0.7887

Answer: a

Explanation: Logarithmic decrement, δ = \(ln \frac{x_1}{x_2} = ln \frac{120}{96}\) = 0.225

Now, δ is related to damping ratio K as, K = \(\frac{1}{

^2)^{0.5}}\)

K = \(\frac{1}{

^2)^{0.5}}\)

∴ K = 0.0357.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Dynamometer Type Wattmeter”.

1. Power is ___________

a) rate of doing work

b) rate of producing voltage

c) rate of generating current

d) rate of overcoming friction

Answer: a

Explanation: Power is defined as the rate of doing work. The unit of power is watt. In D.C. circuits, power is the product of the voltage consumed and the current flowing through a circuit. P = VI watts.

2. In A.C. circuits, power consumed is ________

a) product of voltage and current

b) it depends on the p.f. of the circuit in addition to voltage and current

c) it depends on the supply voltage

d) it depends on the magnitude of the circuit current

Answer: b

Explanation: In a A.C. circuit, the power consumption is given by the expression,

P = VI cos∅

where, V is the voltage across the circuit

I is the current flowing through the circuit

cos∅ is the power factor of the circuit.

3. In D.C. circuits, power is measured using ________

a) ohmmeter and galvanometer

b) ohmmeter and voltmeter

c) ammeter and voltmeter

d) ammeter and galvanometer

Answer: c

Explanation: An ammeter is used to measure current flowing through a circuit, while a voltmeter is used to measure the voltage across the circuit. Hence in D.C. circuits, ammeter and voltmeter are used to measure power.

4. In A.C. circuits, power is measured using ________

a) voltmeter

b) ammeter

c) ohmmeter

d) wattmeter

Answer: d

Explanation: A.C. circuits make use of power factor of the circuit in addition to the current flowing through the circuit and the voltage across the circuit. As a result, a wattmeter is used to measure A.C. power.

5. A wattmeter consists of a current coil and a potential coil.

a) True

b) False

Answer: a

Explanation: Power in single phase A.C. circuits are measured by making use of a wattmeter. It consists of a current coil and a potential coil . Current coil is connected with the load while the potential coil is connected across the supply.

6. A dynamometer type wattmeter consists of ________

a) only potential coil

b) potential and current coils

c) only current coil

d) no coils

Answer: b

Explanation: Dynamometer type wattmeter is used for the measurement of A.C. as well as D.C. power. It consists of a fixed coil forming the current coil whereas the moving coil forms the potential coil.

7. Controlling torque is provided by gold springs.

a) True

b) False

Answer: b

Explanation: In a Dynamometer type wattmeter, controlling torque is provided by two phosphor bronze hair springs. They act as leads to the current flowing through the coil. Also air friction damping is used.

8. In a Dynamometer type wattmeter, the fixed coil is split into ________

a) 4

b) 3

c) 2

d) 1

Answer: c

Explanation: When a Dynamometer type wattmeter is used for the measurement of A.C. power, the fixed coil is split into two equal parts. The two parts are air-cored to avoid hysteresis loss.

9. When a current carrying coil is placed in the magnetic field?

a) no force is exerted

b) voltage is produced

c) power is generated

d) a force is exerted

Answer: d

Explanation: When the current carrying coil of a Dynamometer type wattmeter is placed in the magnetic field of another current carrying coil, the moving coil experiences a force. As a result a deflection torque is generated and the moving coil undergoes deflection.

10. When the moving coil in a Dynamometer type wattmeter deflects ________

a) pointer moves

b) pointer doesn’t move

c) current flows

d) voltage is generated

Answer: a

Explanation: In a Dynamometer type wattmeter, when the moving coil deflects the pointer moves over the scale. The pointer then comes back to rest at a point where the deflecting torque equals the controlling torque.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Errors in Dynamometer Wattmeter”.

1. Pressure coil of a wattmeter ________

a) has capacitance and inductance

b) has inductance and resistance

c) has resistance and capacitance

d) has only inductance

Answer: a

Explanation: Series resistance R consists of inter turn capacitance. As a result, the pressure coil of the wattmeter consists of capacitance in addition to inductance.

2. What is the effect of capacitance on wattmeter reading?

a) aiding the inductance

b) opposite to that of inductance

c) aiding the capacitance

d) opposite to that of resistance

Answer: b

Explanation: For lagging power factor of the load, the wattmeter reading is more. As a result, the wattmeter shows a reading opposite to that of the inductance.

3. Wattmeter reading is not affected by temperature.

a) True

b) False

Answer: b

Explanation: Wattmeter reading is affected by change in temperature. Resistance of the pressure coil and the spring stiffness are affected by the changes in temperature. Effects caused by these two effects oppose each other and neutralize.

4. Dynamometer type wattmeter has _________

a) strong magnetic field

b) intermediate magnetic field

c) weak magnetic field

d) no magnetic field

Answer: c

Explanation: Dynamometer type wattmeter consists of a weak magnetic field. It is affected by stray magnetic fields. As a result, wattmeters are shielded to offset effects of stray magnetic fields.

5. Wattmeter reading has errors induced by _________

a) resistance

b) self-capacitance

c) self-inductance

d) mutual inductance

Answer: d

Explanation: Due to mutual inductance between the current and pressure coil in a wattmeter, errors are introduced. Errors are negligible at power frequencies whereas they have a considerable value at higher frequencies.

6. Current in a pressure coil of the Dynamometer type wattmeter ________

a) lags the applied voltage

b) leads the applied voltage

c) is in phase with the applied voltage

d) there is a phase difference of 90 degrees

Answer: a

Explanation: The current through the pressure coil is in phase with the applied voltage in an ideal wattmeter. The pressure coil is assumed to be purely resistive. Practically, the pressure coil has a small inductance L. As a result the current lags the applied voltage by a certain angle.

electrical-measurements-questions-answers-errors-dynamometer-wattmeter-q6

where, R 2 = r 2 + R = total resistance of the pressure coil

r 2 = resistance of pressure coil

R = series resistance with the pressure coil

I1 = load current.

7. Wattmeters are compensated for errors due to inductance by _________

a) using a series capacitor

b) using a parallel capacitor

c) using a series resistance

d) using a parallel resistance

Answer: b

Explanation: Wattmeters are compensated for errors caused by the inductance of pressure coil through the connection of a suitable parallel capacitor with multiplier resistance R.

electrical-measurements-questions-answers-errors-dynamometer-wattmeter-q7

Fig illustrates that the total impedance of the pressure coil circuit Z 2 equals the total resistance of the pressure coil circuit namely R 2 .

8. Eddy currents are induced in solid metal parts within the thickness of the conductor.

a) True

b) False

Answer: a

Explanation: Eddy currents produce their own field. They affect the magnitude and phase of the current flowing through the current coil. This leads to errors. As a result, the wattmeter reads low values for lagging power factors and high values for leading power factors.

9. What is the effect of frequency on the torque of a moving system?

a) torque is half of the frequency

b) torque is twice the frequency

c) torque is thrice the frequency

d) torque is four times the frequency

Answer: b

Explanation: In a wattmeter, the torque of the moving system is affected by the frequency. Torque is twice the natural frequency with respect to the supply voltage. As a result of this, pointer in the measurement scale vibrates causing difficulty in reading.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Low Power Factor Wattmeter”.

1. In an ordinary dynamometer, the deflecting torque is _________

a) small

b) medium

c) large

d) very large

Answer: a

Explanation: The deflecting torque in an ordinary dynamometer is small. The current and pressure coils are excited. The measurement of power factor is inaccurate.

2. Errors are introduced by ________

a) capacitance

b) inductance

c) resistance

d) impedance

Answer: b

Explanation: At low power factors in an ordinary dynamometer type wattmeter, the errors are caused due to inductance of the pressure coil.

3. Power coil has a low value of ________

a) inductance

b) capacitance

c) resistance

d) impedance

Answer: c

Explanation: In a low power factor dynamometer type wattmeter, the pressure coil is designed in order to have a low value of resistance. The current flowing through the pressure coil is increased in order to raise the operating torque.

4. Resistance of pressure coil in a low power factor dynamometer type wattmeter is ________

a) once time

b) three times

c) hundred times

d) ten times

Answer: d

Explanation: In a low power factor dynamometer type wattmeter, pressure coil has a resistance value that is one tenth of the actual with respect to unity power wattmeters. This is done in order to ensure a reasonable amount of torque at low power factors.

5. Low power factor wattmeters are designed to ________

a) have a low torque

b) have a high torque

c) have a medium torque

d) have no torque

Answer: a

Explanation: Low power factor wattmeters have a low value of control torque. They provide full scale deflection for low values of power factors of the order of 0.1.

6. Power loss in the current coil is ________

a) less

b) more

c) intermediate

d) very less

Answer: b

Explanation: Low power factor circuits have low power. Current coil constitutes a high current. As a result, the power loss in the current coil is high. The reading obtained from the wattmeter is prone to errors.

7. Pressure coil has no error.

a) True

b) False

Answer: b

Explanation: Pressure coil has an error induced due to inductance. It is given by the relation EI sinΦ tanβ. As value of Φ is large for low value of power factor, the error is high in a pressure coil.

8. Error in a pressure coil can be compensated.

a) True

b) False

Answer: a

Explanation: In a low power factor wattmeter, by connecting a capacitor of value C across a portion of the resistance R in the circuit the error in the pressure coil can be compensated.

This set of Electrical Measurements Interview Questions and Answers for freshers focuses on “Induction Type Single Phase Energy Meter”.

1. Induction type instruments are used for ____________

a) A.C. measurements

b) D.C. measurements

c) Resistance measurements

d) Voltage measurements

Answer: a

Explanation: A.C. measurements are made using Induction type instruments. Induction type energy meter is used to measure the energy that is consumed in A.C. circuits only.

2. Driving system in an induction type single phase energy meter consists of _________

a) one magnet

b) two electromagnets

c) five electromagnets

d) ten magnets

Answer: b

Explanation: In an induction type single phase energy meter, the driving system consists of two electromagnets, namely series electromagnet and shunt electromagnet.

3. Series electromagnet consists of _________

a) L shaped laminations

b) T shaped laminations

c) U shaped laminations

d) Y shaped laminations

Answer: c

Explanation: The driving system of an induction type single phase energy meter consists of U shaped laminations made of silicon steel. The laminations are insulated from one another and pressed to form the core.

4. Shunt magnet consists of _________

a) N shaped laminations

b) E shaped laminations

c) S shaped laminations

d) M shaped laminations

Answer: d

Explanation: The driving system of an induction type single phase energy meter consists of M shaped laminations made of silicon steel. The laminations are insulated from one another and pressed to form the core of the shunt magnet.

5. Shunt magnet has _________

a) large turns of wire

b) small turns of wire

c) medium turns of wire

d) no turns or wires

Answer: a

Explanation: The central limb of the shunt magnet has a large number of turns. It connected across the supply and is known as the voltage coil or potential coil. It is excited using a current value that is proportional to the applied voltage.

6. Moving system of the induction type single phase energy meter has _________

a) heavy aluminium disc

b) light aluminium disc

c) medium aluminium disc

d) no aluminium disc

Answer: b

Explanation: Aluminium disc is provided in the air gap between the series and shunt magnets. Jewel bearings support the spindle. Hence the moving system in an induction type single phase energy meter consists of light aluminium disc.

7. Braking system consists of _________

a) bar magnet

b) temporary magnet

c) permanent magnet

d) super magnet

Answer: c

Explanation: In an induction type single phase energy meter, edge of the aluminium disc consists of a permanent magnet also known as a brake magnet. E.m.f is induced in the aluminium disc when it rotates as a result of the magnetic field produced by the brake magnet.

8. What is the effect of eddy currents in the aluminium disc?

a) varies by a factor of twice the disc length

b) independent of the disc speed

c) varies by a factor of four times the disc size

d) proportional to the disc speed

Answer: d

Explanation: The eddy currents induced in an aluminium disc vary in proportion to the speed of the disc. As a result the braking torque exerted on the disc varies in proportion to the speed.

9. An energy meter produces a flux of ∅ when connected to a supply V.

a) True

b) False

Answer: a

Explanation: Flux ∅ is produced in an energy meter when it is connected to a supply voltage of magnitude V volts. Since the potential coil is highly inductive, current and flux lag the voltage by 90°.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Lag Adjustment Devices”.

1. The energy meter always measures the load energy correctly.

a) True

b) False

Answer: b

Explanation: When the difference in phase angles between the shunt magnetic flux and the applied voltage is 90 degrees , the reading of the load energy obtained from an energy meter is correct.

2. Obtaining correct reading from the energy meter requires ______________

a) low resistance and iron losses

b) high resistance and iron losses

c) high resistance and low iron losses

d) low resistance and high iron losses

Answer: a

Explanation: In order to obtain an exact reading for the energy consumed by a load using an energy meter, we require the pressure coil to have a low value of resistance and low iron losses.

3. Phase angle can be made 90 degrees using ____________

a) lead circuit

b) lag circuit

c) special design

d) transformer

Answer: c

Explanation: Phase angle in an energy meter can be made approximately 90 degrees by making use of a special design in the energy meter.

4. Shading coil consists of many thick turns.

a) True

b) False

Answer: b

Explanation: On the central limb of a shunt magnet we can make use of a shading coil. The shading coil consists of a few fairly thick turns. The figure below shows a shading coil on the central limb of the shunt magnet.

electrical-measurements-questions-answers-lag-adjustment-devices-q4

5. Copper shading bands are _________

a) placed as resistance

b) placed as wire

c) placed outside the central limb

d) placed around central limb

Answer: d

Explanation: The central limb of a shunt magnet consists of copper shading bands. They can be moved up or down by making use of the central limb. Figure below illustrates the use of copper shading bands.

electrical-measurements-questions-answers-lag-adjustment-devices-q5

6. As copper shading bands move up ________

a) more flux is induced

b) less flux is induced

c) intermediate flux is induced

d) no flux is induced

Answer: a

Explanation: When the copper shading bands are moved up the central limb, more flux is induced. As a result the difference in angle between the phase and voltage increases. The angle can be made approximately equal to 90 degrees.

7. Shunt flux is made to lag the applied voltage using ________

a) lead circuit

b) lag adjustment

c) lead-lag circuit

d) transformer

Answer: b

Explanation: We make use of shading coil on the central limb of a shunt magnet and shading bands in order to make the shunt flux to lag the applied voltage by almost 90 degrees.

8. At overloads, magnetic shunt ________

a) aids the series flux

b) diverts series flux

c) maintains zero flux

d) disables the shunt flux

Answer: b

Explanation: As the magnetic shunt reaches saturation at overloads, magnetic shunt diverts the flux due to series magnet. As a result a large portion of the flux appears in the gap of the air disc. This compensates the self braking torque.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Friction and Overload Compensation”.

1. Energy meter reads correctly when the ___________

a) torque is small

b) torque is large

c) torque is medium

d) torque is zero

Answer: a

Explanation: The reading in an energy meter is obtained correctly when the torque value is small at low loads. It is independent of the load on the meter an acts in the same direction as the driving torque.

2. Small torque for energy meter is provided __________

a) by a supply

b) by a shading loop

c) by unshaded loop

d) by a transformer

Answer: b

Explanation: Friction can be compensated in an energy meter by making use of a shading loop. It is placed between the central limb of the shunt magnet and a disc. Figure below illustrates the same.

electrical-measurements-questions-answers-friction-overload-compensation-q2

3. Driving torque is small and is adjustable.

a) True

b) False

Answer: a

Explanation: Interaction between the parts of the shaded and unshaded fluxes, obtained through a shading loop leads to a small driving torque. The value of the torque can be adjusted through lateral movement of the loop.

4. Friction torque is eliminated by _________

a) using lubricating oil

b) by suspending the components in air

c) by adjusting the position of limb

d) by using steel alloy components

Answer: c

Explanation: We can eliminate the friction torque completely by adjusting the position of the shading loop. This enables in providing compensation for the frictional torque.

5. Frictional errors are dominant in an energy meter.

a) True

b) False

Answer: a

Explanation: Frictional errors exist in an energy meter at the top as well as bottom surfaces even at low value of loads. Even when the disc is rotating slowly errors due to friction exist in an energy meter.

6. At full load, disc __________

a) partially revolves and then stops

b) continuously revolves

c) does not revolve at all

d) revolves in an alternating fashion

Answer: b

Explanation: When an energy meter is operated in full load condition, disc revolves continuously due to the field of the series magnet. As a result, an e.m.f is induced in the disc.

7. Self braking torque is _________

a) proportional to cube of load current

b) proportional to load current

c) proportional to square of load current

d) proportional to reciprocal of load current

Answer: c

Explanation: In an energy meter, the self braking torque is dependent on the square of the load current. As a result the disc rotates at a slightly slower speed at high value of loads.

8. Self braking action is minimised by _________

a) maintaining high speed for disc

b) maintaining medium speed for disc

c) keeping the disc at rest

d) maintaining low speed for disc

Answer: d

Explanation: In an energy meter we can minimise or eliminate the self braking action by keeping the disc speed as low as possible at full load condition. This is achieved by maintaining the flux due to the current coil smaller than that due to the shunt coil. The figure below shows the compensating device.

electrical-measurements-questions-answers-friction-overload-compensation-q8

9. Overload compensating devices is _________

a) in the form of a magnetic shunt

b) in the form of a series magnet

c) in the form of a transformer

d) in the form of a supply

Answer: a

Explanation: Magnetic shunt reaches saturation at overloads. As a result, its permeability reduces. Hence the overload compensating device takes the form of a magnetic shunt.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Errors in Single Phase Energy Meters”.

1. Magnitude of flux in an energy meter varies __________

a) due to abnormal currents and voltages

b) due to high resistance and inductance values

c) due to changes in the transformer turns

d) due to the induced e.m.f in the windings

Answer: a

Explanation: In the driving system of an energy meter, magnitude of flux can be incorrect as a result of abnormal values of currents and voltages. This occurs due to a change in the resistance of the pressure coil circuit.

2. Phase angles in an energy meter cannot be incorrect.

a) True

b) False

Answer: b

Explanation: In an energy meter, phase angle errors occur as a result of improper adjustments of lag condition, abnormal frequencies etc. Due to temperature, changes in resistance values also lead to error in the phase angle.

3. Energy meter creeps __________

a) due to change in supply

b) due to reversal in polarity of voltage

c) due to asymmetry in magnetic circuit

d) due to turns ratio of transformer

Answer: c

Explanation: In an energy meter, when the magnetic circuit is asymmetrical, a driving torque is produced. As a result of this driving torque, the energy meter creeps.

4. Supply voltage in an energy meter is __________

a) constant always

b) zero always

c) depends on the load

d) can fluctuate

Answer: d

Explanation: Generally the supply voltage is constant in an energy meter. It can fluctuate as a result of unavoidable reasons leading to errors in the reading of the energy meter.

5. How is the flux of shunt coil related to voltage?

a) flux is proportional to square of voltage

b) directly proportional

c) inversely proportional

d) independent of each other

Answer: a

Explanation: In an energy meter, the supply voltage may fluctuate as a result of unavoidable reasons leading to errors in the reading. Supply voltage causes the shunt flux to induce an e.m.f in the disc. This is results in a self braking torque proportional to square of the voltage.

6. How can temperature effect be compensated in an energy meter?

a) through heat sinks

b) by a temperature shunt

c) by using resistance

d) by using a coolant

Answer: b

Explanation: The resistance of the copper and aluminium parts in an energy meter increase with an increase in the temperature. As a result the disc rotates with a speed that is higher than actual. Temperature effects can be compensated by making use of a temperature shunt on the brake magnet.

7. Disc rotates slowly in some energy meters.

a) True

b) False

Answer: a

Explanation: Even when there is no current flow through the energy meter, disc rotates slowly. This is known as creeping. This is occurs as a result of the over compensation provided for friction.

8. Creeping is avoided by __________

a) reversing the polarity of the voltage

b) drilling two diametrically opposite holes

c) holding the disc

d) increasing the friction

Answer: b

Explanation: In an energy meter, creeping causes the disc to rotate even when there is no current flowing. By drilling two diametrically opposite holes under the edge of the poles of a shunt magnet, rotation of the disc is limited to a minimum value.

9. In some energy meters, creeping can be avoided by __________

a) attaching small gold pieces

b) attaching small aluminium pieces

c) attaching small iron pieces

d) attaching small zinc pieces

Answer: c

Explanation: By attaching some iron pieces to the edge of the disc, creeping can be limited in some energy meters. Force of attraction that is experienced by the brake magnet as a result of the iron piece is enough to eliminate the creeping.

This set of Electrical Measurements Questions and Answers for Experienced people focuses on “Electronic Energy Meter, Adjustments in Single Phase Energy meters”.

1. An electronic energy meter makes use of ___________

a) IC

b) Transformer

c) CRO

d) Multimeter

Answer: a

Explanation: Basically, integrated circuits also known as IC’s are used for the operation of an electronic energy meter.

2. Measurement of energy involves _________

a) inductance and capacitance measurement

b) power consumption and time duration

c) resistance measurement and voltage drop

d) current consumption and voltage drop

Answer: b

Explanation: An electronic energy meter is used in two stages. Energy measurement basically involves the measurement of power and the time duration. In the first stage, it is used as a wattmeter while in the second stage it is used monitoring the power consumed in a time interval.

3. Average power is _________

a) product of voltage and current

b) product of average current and voltage

c) product of instantaneous voltage and current

d) product of absolute voltage and current

Answer: c

Explanation: The average power is computed as the product of the instantaneous voltage across the load and the instantaneous current flowing through the load. A scaling device is used to bring the supply voltage to a proper level.

4. What is the role of a multiplier?

a) it multiplies the voltage and current

b) divides the alternating voltage and current

c) supplies instantaneous voltage and current

d) multiplies alternating voltage and current

Answer: d

Explanation: A multiplier basically performs the multiplication of the alternating voltage and the current. Multiplier also provides the current in the form of instantaneous power to a voltage controlled oscillator.

5. Frequency of oscillation in an electronic energy meter depends on __________

a) output current of multiplier

b) output voltage of multiplier

c) output power of multiplier

d) input resistance of multiplier

Answer: a

Explanation: Oscillator used in an energy meter generates a square wave. The frequency of the this depends on the output current flowing through the multiplier.

6. Analog signal is converted _________

a) into oscillations

b) into digital

c) into pulses

d) into current

Answer: b

Explanation: The analog signal obtained in an electronic energy meter is converted into digital by making use of a digital circuit. By making use of a seven-segment display, energy is mentioned in watt-hours.

7. An electronic energy meter is advantageous compared to conventional ones.

a) True

b) False

Answer: a

Explanation: An electronic energy meter does not have frictional losses, creeping is not needed irrespective of the nature of the load such as low load, full load power factor, etc and the accuracy in the reading is of the order of ±1%.

8. Energy meter can be directly used in measurement.

a) True

b) False

Answer: b

Explanation: Adjustments need to be made in an energy meter before it is used for the measurement of energy. This is done in order to keep the errors due to measurement within allowable limits of ±5 %.

9. Creeping in an energy meter can be found using _________

a) creep adjustment

b) preliminary light load adjustment

c) full load u.p.f adjustment

d) light load adjustment

Answer: b

Explanation: Energy meter can be tested for creeping using preliminary light load adjustment. Disc holes are so positioned that they aren’t under the poles of a series magnet.

10. Preliminary light load adjustment involves _________

a) applying rated voltage across current coil

b) making use of a light load

c) applying rated voltage across pressure coil

d) adjusting the light load

Answer: c

Explanation: Rated voltage is applied across the pressure coil. No current flows through the current coil. Till the disc stops rotating, light load device or equipment is adjusted continuously.

11. Creep adjustment involves _________

a) adjusting the creep

b) exciting the current coil

c) adjusting the turns ratio

d) exciting the pressure coil

Answer: d

Explanation: The pressure coil is excited by 110% with respect to the rated voltage. Load current is zero. The meter will not creep provided the light load is adjusted correctly.

12. Light load adjustment involves _________

a) applying rated voltage across the pressure coil

b) adjusting a light load

c) applying rated current across the transformer

d) applying rated voltage across the current coil

Answer: a

Explanation: Disc rotation is adjusted in such a way that correct speed is maintained. The pressure coil is supplied with the rated voltage and the current coil is provided with only about 5 % of the full load at u.p.f.

13. Low power factor adjustment involves _________

a) adjusting the power factor at lower loads

b) applying rated voltage to pressure coil and a p.f. of 0.5 for current coil

c) only applying rated voltage to pressure coil

d) only a p.f. of 0.5 for the current coil

Answer: b

Explanation: Rated voltage is applied to the pressure coil. The current coil is provided with a current at 0.5 p.f. lagging. Till the disc rotates at correct speed, lag device is adjusted.

14. Full load u.p.f adjustment involves _________

a) adjusting the loads at unity power factor

b) applying rated voltage to pressure coil and a p.f. of unity for current coil

c) only applying rated voltage to pressure coil

d) only a p.f. of unity for the current coil

Answer: c

Explanation: Rated voltage is applied to the pressure coil. The current coil is provided with a current at unity p.f. Errors are kept minimum and the position of the brake magnet is so adjusted that disc rotates at the correct speed.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Phase Sequence Indicator”.

1. Phase sequence indicator gives the maximum value of phase voltages.

a) True

b) False

Answer: a

Explanation: The phase sequence for a three phase supply indicates the order in which maximum values of phase voltages E R , E Y , and E B occur. A three phase supply can be in either RYB or RBY configuration.

2. Synchronization of A.C. supply means __________

a) different phase sequence

b) same phase sequence

c) zero phase

d) using a transformer

Answer: b

Explanation: During synchronization, the phase sequences of any two given supplies are maintained equal. This is ensured by making use of a phase sequence indicator.

3. How many types of phase sequence indicators are there?

a) 1

b) 5

c) 2

d) 10

Answer: c

Explanation: Generally, two types of phase sequence indicators are used. The first one is the rotating type while the second type is the static type. Usually the rotating type of phase sequence indicator is used.

4. A rotating phase sequence indicator consists of ________

a) 1 coil

b) 2 coils

c) 5 coils

d) 3 coils

Answer: d

Explanation: A rotating type of phase sequence indicator basically consists of three coils. These are mounted at 120º to each other is space. The ends of the coils are connected to the terminals R, Y, and B respectively.

5. The three coils are ________

a) star connected

b) delta connected

c) not connected

d) shorted

Answer: a

Explanation: In a rotating type phase sequence indicator, the three coils are connected in the form of a star and excited by a three-phase supply.

6. Excitation of the three coils produces ________

a) a static magnetic field

b) a rotating magnetic field

c) a static electric field

d) a rotating electric field

Answer: b

Explanation: Aluminum disc is mounted on the top of the three coils. A rotating magnetic field is produced when the three coils are excited by a supply of three phase. As a result e.m.f with eddy current effects are induced in the coils.

7. Eddy e.m.f produces a torque.

a) True

b) False

Answer: a

Explanation: A rotating magnetic field is produced when the three coils are excited by a supply of three phase. As a result, eddy e.m.f circulates in the disc. A torque is produced as a result of the interaction between the eddy currents and the rotating magnetic field.

8. Disc rotation is determined by ________

a) the supply voltage

b) an arrow

c) the turns ratio

d) the load current

Answer: b

Explanation: Direction of rotation of the disc is determined by making use of an arrow that is marked on the disc. The phase sequence of the supply voltage is same as that mentioned on the terminals of the meter provided disc rotates in the same direction as the arrow head.

This set of Electrical Measurements Puzzles focuses on “Advanced Problems on Measurement of Power in Polyphase Circuit”.

1. In the Two wattmeter method of measuring power in a balanced three-phase circuit, one wattmeter shows zero and the other positive maximum. The load power factor is?

a) 0

b) 0.5

c) 0.866

d) 1.0

Answer: b

Explanation: The load power factor is = 0.5. Since at this power factor one wattmeter shows zero and the other shows a positive maximum value of power.

2. Two watt meters, which are connected to measure the total power on a three-phase system supplying a balanced load, read 10.5 kW and – 2.5 kW respectively. What is the total power?

a) 13.0 kW

b) 13.0 kW

c) 8.0 kW

d) 8.0 kW

Answer: d

Explanation: w1 = 10.5 kW

w2 = -2.5 kW

w = w1 + w2 = 8 kW

So, tan ∅ = \(\frac{1.732}{}\) = 2.81

Or, ∅ = 70.43

So, cos ∅ = 0.334.

3. Power flowing in 3-phase, 3-wire system is measured by two wattmeter whose readings are 7000 W and -2500 W. if the voltage of the circuit is 400 V, then what will be the value of capacitance introduced in each phase to make one wattmeter reads zero? The frequency is 50 Hz.

a) 500 μF

b) 668.6 μF

c) 1000 μF

d) 748.5 μF

Answer: b

Explanation: P = P 1 + P 2 = 7000 – 2500 = 4500 W

∴ Power in each phase = 1500 W

Voltage of each phase = 231 V

So, cos∅ = 0.264

∴ Current in each phase = 24.6 A

∴ Z of each phase = 9.39 Ω

∴ R of each phase = 2.48 Ω

Reactance of each phase = 9.056 Ω

For one watt-meter to read zero, power factor should be 0.5

Now, tan∅ = \(\frac{X}{R}\) or, X = 4.29 Ω

∴ Capacitance reactance required = 9.056 – 4.29 = 4.76 Ω

∴ Capacitance C = \(\frac{1}{2π × 50 × 4.76}\) F = 668.6 μF.

4. A single-phase load is connected between R and Y terminals of a 220 V, symmetrical, 3-phase, 4 wire systems with phase sequence RYB. A watt-meter is connected in the system. The watt-meter will read ?

a) – 795 W

b) – 168 W

c) + 597 W

d) + 795 W

Answer: b

Explanation: V RY = 220∠30°

I RY = \(\frac{220∠30°}{100∠36.86°}\) = 2.2∠-6.68° A

Power = V BN I RY = cos∅ = \

= -167.6 W ≈ – 168 W.

5. The two-wattmeter method is used to measure active power. The system is a 3-phase, 3- wire system. Then, the power reading is?

a) Affected by both negative sequence and zero sequence voltages

b) Affected by negative sequence voltages but not by zero sequence voltages

c) Affected by zero sequence voltages but not by negative sequence voltages

d) Not affected by negative or zero sequence voltages

Answer: d

Explanation: If the phase voltage is unbalanced, then the power reading is not affected by both negative as well as zero sequence voltages. This is a characteristic property of the 2 watt-meter meter since it measures the active power on a three phase three wire system.

6. The ratio of the reading of 2 watt-meters connected to measure power in a balanced 3-phase load is 2: 1 and the load is inductive. The power factor of load is?

a) 0.866 lag

b) 0.615 lead

c) 0.866 lead

d) 0.625 lag

Answer: a

Explanation: Power factor, cosθ = cos arc tan 0.5 \

0.5 \(\frac{2-1}{2+1}\)

= cos 30° = 0.866 lag.

7. Choose the correct statement regarding two watt-meter method for power measurements in 3-phase circuit.

a) When power factor is unity, one of the wattmeters reads zero

b) When the readings of the two watt-meters are equal but opposite sign, the power factor is zero

c) Power can be measured using two watt-meter method only for star connected 3-phase circuit

d) When two watt-meters show identical readings, the power factor is 0.5

Answer: b

Explanation: When power factor is 0, we have ∅ = 90°

P 1 = 0.5 VIcos = 0.5 VIcos = \(\frac{^{0.5}}{2}\) × VI

P 2 = 0.5 VIcos = 0.5 VIcos = \(– \frac{^{0.5}}{2}\) × VI

∴Total power P = 0

So, with zero power factor the readings of the two watt-meters are equal but of opposite sign.

8. The meter constant of a single-phase, 230 V induction watt-meter is 600 rev/kW-h. The speed of the meter disc for a current of 15 A at 0.8 power factor lagging will be?

a) 30.3 rpm

b) 25.02 rpm

c) 27.6 rpm

d) 33.1 rpm

Answer: c

Explanation: Meter constant = \(\frac{Number \,of\, revolution}{Energy} = \frac{600 × 230 × 15 × 0.8}{1000}\) = 1656

∴ Speed in rpm = \(\frac{1656}{60}\) = 27.6 rpm.

9. In the measurement of 3-phase power by 2 watt-meter method, if the 2 watt-meter readings are equal, the power factor of the circuit is?

a) 0.8 lagging

b) 0.8 leading

c) Zero

d) Unity

Answer: d

Explanation: Power factor, cosθ = cos arc tan 0.5 \(\frac{W_1-W_2}{W_1+W_2}\)

W 1 = W 2 = cos 0° = 1.

10. The figure shows a three-phase, delta connected load supplied from a 220 V, 50 Hz, 3-phase balanced source. The pressure Coil and Current Coil of a watt-meter are connected to the load as shown, with the coil polarities suitably selected to ensure a positive deflection. The watt-meter reading will be?

electrical-measurements-puzzles-q10

a) Zero

b) 1600 W

c) 242 W

d) 400 W

Answer: c

Explanation: Watt-meter reading = Current through CC × Voltage across PC × cos .

I BR = I CC = \(\frac{220∠120°}{100°}\) = 2.2∠120°

V YB = V PC = 220∠-120°

w = 2.2∠120°× 220∠-120° × cos 240° = 242 W.

This set of Advanced Electrical Measurements Questions and Answers focuses on “Advanced Miscellaneous Problems on Measurement of Power”.

1. A coil has been designed for high Q performance. The voltage is rated at and a specified frequency. If the frequency of operation is increased 10 times and the coil is operated at the same rated voltage. The new value of Q factor and the active power P will be?

a) P is doubled and Q is halved

b) P is halved and Q is doubled

c) P remains constant and Q is doubled

d) P decreases 100 times and Q is increased 10 times

Answer: d

Explanation: ω 2 L = 10 ω 1 LR will remain constant

∴ Q 2 = \(\frac{10 ω_1 L}{R}\) = 10 Q 1

That is Q is increased 10 times.

Now, I 1 = \(\frac{V}{ω_1 L}\)

For a high Q coil, ωL &Gt;> R,

I 2 = \(\frac{V}{10 ω_1 L} = \frac{I_1}{10}\)

∴ P 2 = \

^2 = \frac{P_1}{100}\)

Thus, P decreases 100 times and Q is increased 10 times.

2. Two watt-meters, which are connected to measure the total power on a three-phase system supplying a balanced load, read 20.5 kW and -3.5 kW respectively. The total power is?

a) 13.0 kW

b) 17 kW

c) 15 kW

d) 19 kW

Answer: d

Explanation: w 1 = 20.5 kW, w 2 = -3.5 kW

∴ w = w 1 + w 2 = 20.5 – 3.5 = 17 kW.

3. A circuit is used to measure the power consumed by the load. The current coil and the voltage coil of the watt-meter have 0.02 Ω and 1000 Ω resistances respectively. The measured power will be?

a) 0.4 % less

b) 0.2 % less

c) 0.2 % more

d) 0.4 % more

Answer: c

Explanation: Power indicated by watt-meter = 400 × 20 + 20 2 × 0.02 = 4008 W

Percentage increase = \(\frac{4008-4000}{4000}\) × 100 = 0.2 % more.

4. A sampling watt-meter is used to measure the average power of a load. The peak to peak voltage of the square wave is 10 V and the current is a triangular wave of 5A p-p. The reading in watt will be?

a) Zero

b) 25 W

c) 50 W

d) 100 W

Answer: a

Explanation: If we consider both the waves, we can see positive power and negative power in each case are equal. So, the net resultant power is zero.

5. The line to line input voltage to the 3-phase, 50 Hz, AC circuit, is 100 V rms. Assuming that the phase sequence is RYB; the watt-meters would read?

a) W 1 = 886 W and W 2 = 886 W

b) W 1 = 500 W and W 2 = 500 W

c) W 1 = 0 W and W 2 = 1000 W

d) W 1 = 250 W and W 2 = 750 W

Answer: c

Explanation: W 1 = 100 × 20 cos 90° = 0

W 2 = \(\frac{100 × 20 × \sqrt{3}}{\sqrt{3} × 2}\) = 1000 W.

6. The meter constant of a single-phase, 100 V induction watt-meter is 600 rev/kW-h. The speed of the meter disc for a current of 15 A at 0.8 power factor lagging will be?

a) 30.3 rpm

b) 16 rpm

c) 12 rpm

d) 33.1 rpm

Answer: c

Explanation: Meter constant = \(\frac{Number \,of\, revolution}{Energy}\)

Number of revolution = \(\frac{600 × 100 × 15 × 0.8}{1000}\) = 720

∴ Speed in rpm = \(\frac{720}{60}\) = 12 rpm.

7. A 3-phase, 600 V motor, the load having 0.6 power factor uses two watt-meter to measure the power. If the power measured be 45 kW, then the reading of each instrument will be?

a) P 1 = 35 kW, P 2 = 10 kW

b) P 1 = 47.25 kW, P 2 = -2.25 kW

c) P 1 = 39.82 kW, P 2 = 5.179 kW

d) P 1 = 45 kW, P 2 = 0 kW

Answer: c

Explanation: P 1 + P 2 = 45 kW

And, cos ∅ = 0.6

∴ tan ∅ = 1.33

Or, 1.33 = \(\sqrt{3} \frac{P_1 – P_2}{45} \)

∴ P 1 – P 2 = 34.64 kW

∴ P 1 = 39.82 kW

P 2 = 5.179 kW.

8. An average-reading digital Multimeter reads 10 V when fed with a triangular wave, symmetric about the time-axis. If the input is same, the rms reading meter will read?

a) 20/\ -10/\ -20/\ 10/\(\sqrt{3}\)

Answer: d

Explanation: For triangular wave- Average value = \(\frac{V_m}{3}\), rms value = \(\frac{V_m}{\sqrt{3}}\)

\(\frac{V_m}{3}\) = 10 V or, V m = 30 V

So, rms = \(\frac{30}{\sqrt{3}}\) = 10\(\sqrt{3}\).

9. In the Two wattmeter method of measuring power in a balanced three-phase circuit, one wattmeter shows zero and the other positive maximum. The load power factor is?

a) 0

b) 0.5

c) 0.866

d) 1.0

Answer: b

Explanation: The load power factor is = 0.5. Since at this power factor one wattmeter shows zero and the other shows a positive maximum value of power.

10. Two watt-meters connected to measure the total power on a three-phase system supplying a balanced load reads 10.5 kW and -2.5 kW respectively. Then the total power factor is?

a) 0.334

b) 0.684

c) 0.52

d) 0.334

Answer: d

Explanation: w 1 = 10.5 kW, w 2 = -2.5 kW

∴ w = w 1 + w 2 = 8 kW

Also, tan ∅ = 2.81

∴ ∅ = 70.43° or, cos ∅ = 0.3347.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Advantages of Electronic Instruments”.

1. Electronic voltmeters use electronic circuits.

a) True

b) False

Answer: a

Explanation: Voltmeters that make use of rectifiers, diodes, amplifiers, etc in order to produce a current that is in proportion to the quantity that is being measured is known as an electronic voltmeter.

2. In olden days voltmeters were __________

a) made of transistors

b) made of vaccum tubes

c) made of transformers

d) made of diodes

Answer: b

Explanation: Initially, voltmeters were made of vaccum tubes. These voltmeters were known as vaccum tube voltmeters .

3. Modern day voltmeters are made of __________

a) made of transformers

b) made of vaccum tubes

c) made of transistors and diodes

d) made of insulated iron coils

Answer: c

Explanation: Nowadays in voltmeters, transistors and semiconductor diodes are used. A transistor voltmeter makes use of transistor in a voltmeter.

4. FETVM is __________

a) an ammeter

b) a galvanometer

c) a multimeter

d) a voltmeter

Answer: d

Explanation: Field effect transistors can also be used at the input. Such voltmeters are known as FETVM .

5. Electronic voltmeters are __________

a) compact

b) large in size

c) not portable

d) difficult to use

Answer: a

Explanation: When compared to conventional analog voltmeters, electronic voltmeters are compact and also portable. This is due to the small size of the components.

6. Electronic voltmeters are not accurate.

a) True

b) False

Answer: b

Explanation: Compared to analog voltmeters, electronic voltmeters are very accurate and precise.

7. Electronic voltmeters are __________

a) dependent of frequency

b) dependent of voltage

c) independent of frequency

d) dependent of current

Answer: c

Explanation: Usually electronic voltmeters can measure frequency in the range of a few volts D.C. to frequencies of the order of hundreds of MHz. As a result, the effect of frequency on the response of electronic voltmeters is negligible.

8. Dynamic range of electronic voltmeter is __________

a) zero

b) limited

c) narrow

d) wide

Answer: d

Explanation: When compared to conventional analog voltmeters, the dynamic range is very wide and improved in electronic voltmeters. Very low as well as very high input signals can be measured using an electronic voltmeter.

9. Loading effect in electronic voltmeters is __________

a) nil

b) high

c) low

d) medium

Answer: a

Explanation: In an electronic voltmeter as the power is supplied by an external circuit, there is no loading effect. In a PMMC instrument, a minimum current of 50 µA is obtained from the signal that is to be measured and this leads to loading effect.

10. Electronic voltmeters are ____________

a) measure high level signals

b) measure low level signals

c) measure medium level signals

d) don’t measure any signal

Answer: b

Explanation: Electronic voltmeters make use of amplifier circuits. As a result they can be used for measuring low level signals.

This set of Electrical Measurements Question Bank focuses on “Consideration in Selecting Voltmeter”.

1. Input impedance of a voltmeter is ___________

a) high

b) low

c) medium

d) zero

Answer: a

Explanation: In order to prevent the loading effect in a voltmeter, the input impedance is maintained as high as possible. It must be maintained higher than the impedance of the circuit being used.

2. Input impedance depends on _________

a) resistance

b) capacitance

c) inductance

d) voltage

Answer: b

Explanation: Shunt capacitance appearing across the input terminals affects the input impedance. Capacitive reactance of the capacitance is inversely proportional to the frequency.

X c ∝ 1 ⁄ f

where, X c is the capacitive reactance

f is the frequency.

3. At high frequencies the capacitive reactance _________

a) is constant

b) increases

c) decreases

d) becomes zero

Answer: c

Explanation: We know that the capacitive reactance is inversely proportional to the frequency.

X c ∝ 1 ⁄ f

At high frequencies, the capacitive reactance becomes very small.

4. Voltage ranges in a meter are _________

a) 5-10-15

b) 20-50-100

c) 0.5-1-1.5

d) 1-3-10

Answer: d

Explanation: Meter scale will have a calibration of 1-3-10 for the voltage range with a separation of 10 dB. It can also be in the sequence of 1.5-5-15. We can also make use of a single scale.

5. Linear meter with 1% accuracy must have _________

a) 100 divisions

b) 50 divisions

c) 200 divisions

d) 500 divisions

Answer: a

Explanation: In order to recognize a reading with 1% accuracy it must have 100 divisions on the 1 V range.

6. Decibel covers a small range of values.

a) True

b) False

Answer: b

Explanation: As the unit decibel makes of the logarithmic scale, it covers a wide range of values of any given quantity.

7. Noise is a function of _________

a) voltage

b) current

c) bandwidth

d) frequency

Answer: c

Explanation: Noise in general depends on the value of the bandwidth. Voltmeter having a large bandwidth takes up more noise. Usually, the sensitivity of a voltmeter is 1mV for a bandwidth of 10Hz – 10MHz.

8. Current can be measured effectively by making use of _________

a) d.c. voltmeter

b) a.c. ammeter

c) d.c. ammeter

d) a.c. voltmeter

Answer: d

Explanation: By making use of an a.c. voltmeter in series with resistance we can obtain the current value. We can also make use of the current probe method to obtain the value of the current without effectively disturbing the circuit.

9. Average responding voltmeter is cheap and accurate.

a) True

b) False

Answer: a

Explanation: Average responding voltmeter is used for a.c. measurements for a sine wave with 10% distortion or less. Hence the average responding voltmeter is cheap and accurate.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Basic Electronic Voltmeter”.

1. Low voltage signals can be measured by ___________

a) amplifiers

b) transformers

c) transducers

d) voltmeters

Answer: a

Explanation: Electronic voltmeters make use of amplifiers to measure low voltage signals. It consists of two or more stages of D.C. amplifiers.

2. Input impedance of an electronic voltmeter is ________

a) low

b) high

c) medium

d) zero

Answer: b

Explanation: In an electronic voltmeter, the input impedance is maintained very high. This is achieved by making use of an FET at the input of an electronic voltmeter.

3. Meter can be isolated from the circuit in a basic D.C. electronic voltmeter.

a) True

b) False

Answer: a

Explanation: Field effect transistor acts as a source follower and provides very high input impedance. BJT along with resistors form a balanced bridge circuit. As a result the meter circuit can be isolated from the main circuit.

4. Bridge is balanced by ________

a) galvanometer

b) oscillator

c) zero adjustment resistor

d) head phone

Answer: c

Explanation: Bridge circuit in a basic D.C. electronic voltmeter is balanced by making use of a zero adjustment resistor such that the pointer shows zero deflection.

5. What is the effect of the input on the transistor Q 2 ?

a) bias on Q 2 decreases

b) bias on Q 2 is constant

c) bias on Q 2 is zero

d) bias on Q 2 increases

Answer: d

Explanation: The bias on the transistor Q 2 increases when the input voltage is applied. As a result a proportional amount of current flows through the meter. Hence the deflection of the meter is directly proportional to the applied voltage within the dynamic range.

6. What is basic range of a meter?

a) causes maximum deflection

b) causes minimum deflection

c) causes zero deflection

d) causes medium deflection

Answer: a

Explanation: The input voltage that causes maximum deflection of the meter is known as the basic range of a meter. It occupies the lowest range on the range switch in the unamplified circuits.

7. High range can be obtained in a basic D.C. electronic voltmeter by ________

a) a transformer

b) an attenuator

c) a transducer

d) a resistor

Answer: b

Explanation: By making use of an attenuator in a basic D.C. electronic voltmeter, we get high range of values for the voltage reading. Attenuator is basically a voltage divider circuit with a predefined front panel.

8. Sensitivity of electronic voltmeter is high.

a) True

b) False

Answer: a

Explanation: In a PMMC voltmeter , the sensitivity obtained is less and of the order of a few volts. In electronic voltmeters the sensitivity is very high and is of the order of at least 100 times as that compared to a PMMC voltmeter.

9. Overloading is ________

a) damages the meter

b) increases the temperature

c) doesn’t affect the meter

d) decreases the sensitivity

Answer: c

Explanation: As transistors saturate after a certain range of operating voltage and current, the value of the meter current is limited. As a result, overloading does not affect the meter and it remains safe.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “True RMS Responding Voltmeter”.

1. R.M.S value means _________

a) root mean square

b) rate mean second

c) root median second

d) rate mode second

Answer: a

Explanation: R.M.S value indicates the Root Mean Square. It is obtained by taking the square root of the average value of the square of the input signal. It is also known as the effective value.

2. Meter reading is obtained by ________

a) sensing voltage

b) sensing heat power

c) sensing current

d) sensing resistance

Answer: b

Explanation: In a true R.M.S responding voltmeter, the meter reading is obtained by sensing the heat power of the waveform. The heat power is directly proportional to the r.m.s value of the input.

3. Measurement of heat power ________

a) uses a heat sink

b) uses a thermometer

c) uses a thermocouple

d) uses a black body

Answer: c

Explanation: A thermocouple is used to measure the heat power in a true R.M.S responding voltmeter. Input voltage under measurement is applied to the heater to which a thermocouple is also attached.

4. Sufficient heating of the heater is ensured by ________

a) increasing the temperature

b) making use of induction coil

c) amplifying d.c. input

d) amplifying a.c. input

Answer: d

Explanation: Maximum heating of the heater is obtained by making use of an amplified a.c. input. As a result the thermocouple generates maximum voltage level in order to cause the meter deflection.

5. Power in a thermocouple is given by ________

a) Power = E 2 rms / R heater

b) Power = E 2 rms

c) Power = R heater

d) Power = E 2 rms × R heater

Answer: a

Explanation: The power consumed in a thermocouple is given by the relation

Power = E 2 rms ⁄ R heater

where, E rms is the r.m.s value of the a.c. input signal

R heater is the resistance of the heater.

6. What is the main disadvantage of a true r.m.s responding voltmeter?

a) presence of transducer

b) presence of thermocouple

c) presence of transformer

d) presence of oscillator

Answer: b

Explanation: Thermocouples have non-linear voltage and current characteristics. This is the major drawback of the true r.m.s responding voltmeter. This is overcome in some instruments by making use of an additional thermocouple in the same thermal environment.

7. What is the naming convention for the two thermocouples?

a) thermocouple 1 and thermocouple 2

b) input thermocouple and output thermocouple

c) measuring thermocouple and balancing thermocouple

d) internal thermocouple and external thermocouple

Answer: c

Explanation: The thermocouple used in the input section of the voltmeter is known as the measuring thermocouple whereas the thermocouple used in the feedback path is known as the balancing thermocouple.

8. Sensitivity is of the order of ________

a) MV

b) V

c) GV

d) mV

Answer: d

Explanation: By making use of true r.m.s responding voltmeter we get the sensitivity of the order of mV. The voltage ranges from 100 µV to 300 V with a frequency range of 10 Hz to 100 MHz.

9. Response of thermocouples is fast.

a) True

b) False

Answer: b

Explanation: Crest factor limits the meter reading in a true r.m.s responding voltmeter when complex signals are taken into consideration. Also, the meter costs higher compared to average and peak responding meters. As a result the response of the thermocouples is slow.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Electronic Multimeter”.

1. Electronic multimeter measures ________

a) voltage, current and resistance

b) voltage and current

c) current and power

d) energy and power

Answer: a

Explanation: A.C. as well as D.C. voltage, current and resistance can be measured by making use of an electronic multimeter. It is also known as a voltage-ohm meter.

2. Basic circuit of multimeter consists ________

a) of a.c. amplifier

b) of d.c. amplifier

c) operational amplifier

d) power amplifier

Answer: b

Explanation: A.C. as well as D.C. voltage, current and resistance can be measured by making use of an electronic multimeter. The basic circuit of a multimeter is made up of d.c. amplifier circuit in the form of a balanced bridge.

3. Input signal magnitude is limited by ________

a) button

b) resistance

c) attenuator

d) voltage

Answer: c

Explanation: A range switch is provided in an electronic multimeter in order to limit the input signal in terms of magnitude. We can adjust the input attenuator and limit the input signal in terms of magnitude.

4. Electronic multimeter consists of a rectifier.

a) True

b) False

Answer: a

Explanation: An electronic multimeter is used for the measurement of A.C. as well as D.C. voltage, current and resistance. It consists of a rectifier section that is used to convert the a.c. input signal to d.c. voltage.

5. Multimeter can be used as an ammeter by ________

a) connecting series resistances

b) making use of a transducer

c) making use of a transformer

d) connecting shunts

Answer: d

Explanation: An electronic multimeter can be used as an ammeter by making use of shunt resistances across the meter. This is achieved by range selecting switch.

6. Multimeter can be used for D.C. voltage measurement by ________

a) connecting series resistances

b) connecting shunt resistances

c) connecting star delta resistances

d) using a switch

Answer: a

Explanation: We can obtain a wide range of D.C. voltage from a multimeter by connecting various series resistances in the circuit through a range selection switch. By adjusting the value of the resistance we get the required D.C. voltage.

7. Multimeter can be used only for low resistance measurement.

a) True

b) False

Answer: b

Explanation: A multimeter is used for the measurement of A.C. as well as D.C. voltage, current and resistance. By manipulating the scale with a multiplication factor of 100 and 10, 000 we can make use of a multimeter for measuring high resistances.

8. What is the role of a rectifier in a multimeter?

a) bias purpose

b) thermal stability

c) rectification

d) inversion

Answer: c

Explanation: When the multimeter is used for the measurement of A.C. voltages, rectifier section is used. It mainly performs the conversion of the input A.C. voltage into D.C. for the measurement of A.C. voltage.

9. What is the initial setting made in a multimeter before it is used for measuring resistance?

a) fine adjustment

b) instrument is open circuited

c) voltage is applied

d) zero adjustment

Answer: d

Explanation: Initially the multimeter is short circuited and zero adjustment control is made. This is done till the meter reads zero resistance or in other words displays full scale current.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Digital Voltmeters”.

1. Digital voltmeters converts ________

a) analog to digital signal

b) digital to analog signal

c) current to voltage

d) resistance to voltage

Answer: a

Explanation: In general digital voltmeters are known as DVM. They convert analog signals into digital voltage. They also display the voltage to be measured in the form of discrete numerals in place of pointer deflection.

2. Digital voltmeters can be used to measure ________

a) voltage only

b) voltage, temperature, pressure, etc

c) voltage and current

d) voltage and resistance

Answer: b

Explanation: Digital voltmeters are used for the measurement of A.C. as well as D.C. voltages and also to measure physical quantities such as temperature, pressure, stress etc. through the use of appropriate transducer and signal conditioning circuits.

3. A digital voltmeter reduces parallax error.

a) True

b) False

Answer: a

Explanation: A digital voltmeter minimizes the errors due to human interference, interpolation mismatch and errors due to parallax. A digital display is used to show the output voltage on a front panel.

4. In a DVM, a transducer converts ________

a) input to a proportional current

b) input to a proportional power

c) input to a proportional voltage

d) input to a proportional resistance

Answer: c

Explanation: In a digital voltmeter, a transducer is used. In general a transducer converts a physical quantity into an electrical signal. In a DVM the transducer converts the input signal into a proportional voltage.

5. In a DVM, a signal conditioning circuit is used ________

a) to bring current to a suitable limit

b) to bring resistance to a suitable limit

c) to bring resistance to s suitable limit

d) to bring voltage to a suitable limit

Answer: d

Explanation: In a DVM, signal conditioning circuit is used. It converts the input signal into an voltage of suitable limit. This is done so that the voltmeter can read the magnitude of the signal correctly.

6. Input range of DVM is _________

a) 1 V to 1000 V

b) 0.1 V to 10 V

c) 0.01 V to 1 V

d) 0.001 V to 0.1 V

Answer: a

Explanation: In a DVM, the input voltage range is given as 1 V to 1000 V. It includes automatic range selection and overload indication.

7. Output in digital form can’t be used directly.

a) True

b) False

Answer: b

Explanation: The output obtained from a DVM can be used directly. It can be recorded and is also suitable for further processing.

8. What is the effect of IC chips on DVM?

a) increase in cost

b) increase in power

c) reduction in cost

d) increase in size

Answer: c

Explanation: Advancement in IC chips have ensured the reduction in the cost of the DVM’s. Size and power needs of DVM’s have been reduced by a huge margin.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Performance Parameters of Digital Voltmeters”.

1. Basic range of DVM is _________

a) 1 or 10 V

b) 0.1 or 1 V

c) 10 or 100 V

d) 100 or 1000 V

Answer: a

Explanation: In a DVM, the basic range is 1 V or 10 V. Range of a DVM can be extended from a few µV to kV. This is achieved by making use of an attenuator.

2. Accuracy of a DVM is ________

a) low

b) high

c) medium

d) zero

Answer: b

Explanation: Accuracy of a DVM is based on the resolution. Resolution depends on the number of digits. The more the number of digits, the higher is the accuracy. For a DVM, the accuracy is of the order of ±0.005 % of the reading.

3. Input impedance of a DVM is ________

a) low

b) zero

c) high

d) medium

Answer: c

Explanation: Typical input impedance of a DVM is usually very high. Typical value is of the order of 10 MΩ. This is usually done in order to reduce the loading effect.

4. In DVM the common mode rejection noise is eliminated by ________

a) increasing the signal amplitude

b) making use of a resistance

c) using a transformer

d) guarding

Answer: d

Explanation: In a DVM, common mode noise can be eliminated through guarding. A guard is basically a sheet metal box around the circuit. This is made available to the circuit being measured by making use of a terminal at the front panel.

5. Output of DVM needs ________

a) 4 lines

b) 2 lines

c) 8 lines

d) 16 lines

Answer: a

Explanation: Type of DVM used depends on the digital output lines. Four lines of BCD or a single line serial output may be provided so as to read the output from a DVM.

6. Normal mode noise can be eliminated through ________

a) attenuation

b) filtering

c) amplification

d) a transformer

Answer: b

Explanation: Filters can be used to eliminate the normal mode noise signals. When used for low voltage measurement, noise present at the input can cause errors in the analog to digital converter.

7. DVM has ________

a) 1-3 digits

b) 2-5 digits

c) 3-6 digits

d) 7-10 digits

Answer: c

Explanation: The DVM consists of 3 to 6 digits. As the number of digits are increased the resolution also increases. Thus, the resolution of a DVM is very high.

8. What is a digitizing circuit?

a) converts digital signal to analog

b) boosts the magnitude of a digital signal

c) attenuates a digital signal

d) converts analog signal to digital

Answer: d

Explanation: DVM converts analog signal to digital. The process is known as digitization and the circuit used to obtain the conversion is known as a digitizing circuit. Time needed for this conversion is known as digitizing period.

9. User must wait for a stable reading.

a) True

b) False

Answer: a

Explanation: Since it is difficult to follow the reading visually at high reading speeds, user has to wait till a stable reading is obtained. The digitizing period depends on the maximum speed at which the value is read from the meter.

This set of Electrical Measurements online quiz focuses on “Successive Approximation Type DVM”.

1. A successive approximation type DVM makes use _______

a) of a digital divider

b) of an analog divider

c) of an oscillator

d) of a transducer

Answer: a

Explanation: Servo balancing type DVM makes use of a linear divider in a potentiometer. In the case of a successive approximation type DVM we make use of a digital divider. A digital divider is basically a digital to analog converter.

2. Successive approximation type DVM is based on the principle of ______

a) acceleration of an object

b) weight of an object

c) velocity of an object

d) momentum of an object

Answer: b

Explanation: A successive approximation type DVM works on the principle of measuring the weight of an object. It consists of an object on one of the sides of the balance and an appropriate weight on the other side of the balance. The weight of the object is determined by successively adding and removing weights from the balance.

3. Which compares the output in a successive approximation type DVM?

a) op amp

b) diode

c) comparator

d) rectifier

Answer: c

Explanation: A comparator is used to compare the output of the digital to analog converter in a successive approximation type DVM. As a result the comparator provides high or low signals.

4. D/A converter generates the set pattern successively.

a) True

b) False

Answer: a

Explanation: If the output of the digital to analog converter becomes equal to the unknown voltage in terms of magnitude, the D/A converter generates the set pattern of voltages successively.

5. What is the role of logic control and sequencer in a successive approximation type DVM?

a) generate analog voltage

b) generate power

c) generate current through resistance

d) generate sequence code

Answer: d

Explanation: A comparator is used in a successive approximation type DVM so as to compare the output of the D/A converter with the unknown voltage. Logic control and sequencer takes the input from the comparator and generates the sequence code.

6. Resolution of a successive approximation type DVM is given by which of the following relation?

a) R = 1 ⁄ 10 n

b) R = 1 ⁄ 10

c) R =10 n

d) R = 10

Answer: a

Explanation: The resolution of a successive approximation type depends on the number of digits. It is given by the relation,

R = 1 ⁄ 10 n

where, R is the resolution

n is the number of digits.

7. Sensitivity of a successive approximation type DVM is given by which of the following relation?

a) S = fs min

b) S = fs min × R

c) S = R

d) S = fs min ⁄ R

Answer: b

Explanation: In a successive approximation type DVM, the sensitivity is given by the relation

S = fs min × R

where, S is the sensitivity

R is the resolution

fs min is the full scale reading when the range is minimum.

8. Speed of a successive approximation type DVM can be improved by making use of ______

a) electrical switches

b) mechanical devices

c) solid state devices

d) transformers

Answer: c

Explanation: Solid state devices can be used in order to increase the speed of operation in a successive approximation type DVM. Electromechanical switches provide a low speed of operation.

9. Accuracy depends on external supply.

a) True

b) False

Answer: b

Explanation: In a successive approximation type DVM, the accuracy is dependent on the internal reference supply. It also depends on the accuracy of the digital to analog converter that is used in the circuit.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Ramp Type DVM”.

1. Ramp type DVM uses ___________

a) a linear ramp technique

b) a non-linear ramp technique

c) an exponential ramp technique

d) an asymptotic ramp technique

Answer: a

Explanation: A ramp type DVM makes use of a staircase ramp technique or a linear ramp technique. Compared to the linear ramp technique, the staircase ramp technique is much simpler.

2. Linear ramp technique is based on __________

a) voltage measurement

b) time measurement

c) current measurement

d) resistance measurement

Answer: b

Explanation: Linear ramp technique works on the principle of measurement of time required by a linear ramp to rise from 0 V to the input voltage. It can also be the time required by the input voltage to fall to 0 V.

3. Time is measured using __________

a) clock

b) logic gates

c) counter

d) flip-flops

Answer: c

Explanation: An electronic counter is used for the measurement of time in the linear ramp technique. A digital display is used to show the numerical value of time.

4. Which is the main device used in the linear ramp technique?

a) exponential ramp

b) asymptotic ramp

c) non-linear ramp

d) linear ramp

Answer: d

Explanation: The linear ramp technique essentially consists of a linear ramp. It is either positive or negative going. Range of the linear ramp varies from –12 V to +12 V. Base range varies from –10 V to +10 V.

5. Resolution depends on __________

a) frequency

b) resistance

c) voltage

d) current

Answer: a

Explanation: In the linear ramp technique, resolution is dependent on the frequency of the local oscillator. By adjusting the frequency of the local oscillator the resolution of the linear ramp can be made higher.

6. How is input voltage measured?

a) by using a voltmeter

b) by counting the pulses

c) by using a multimeter

d) by using a transformer

Answer: b

Explanation: The electronic counter used in the linear ramp technique counts the definite number of pulses during the start and end pulse. This count is a measure of the input voltage signal.

7. Which determines the rate of measurement cycles?

a) oscillator

b) amplifier

c) mutivibrator

d) oscilloscope

Answer: c

Explanation: Initiation of the measurement cycles is taken care of by the sample rate multivibrator. This vibrator oscillates at the rate of 1000 cycles per second. It is adjusted by a front panel control.

8. What is the typical value of the multivibrator?

a) 10 cycles/second

b) 0.2 cycles/second

c) 50 cycles/second

d) 5 cycles/second

Answer: d

Explanation: A multivibrator has a typical value of 5 cycles/second. It has an accuracy of the order of ±0.005 %. The ramp generator starts the next ramp voltage based on the sample rate.

9. Swing of the ramp is __________

a) ±12 V

b) ±10 V

c) ±8 V

d) ±5 V

Answer: a

Explanation: In the linear ramp technique, a swing of ±12 V is produced by the ramp. This limits the effective voltage available to ±10 V considering the voltage drop across the components in the circuit.

This set of Electrical Measurements online test focuses on “Voltage to Frequency Converter Type Integrating DVM”.

1. In a voltage to frequency converter type integrated DVM _____________

a) voltage is converted to time

b) voltage is converted to frequency

c) frequency is converted to voltage

d) frequency is converted to time

Answer: a

Explanation: We know that the quantities time and frequency are related to each other. Voltage is converted into time in a voltage to frequency converter type integrating DVM.

2. Input voltage is measured by ____________

a) using a voltmeter

b) counting pulses

c) using a multimeter

d) using an ammeter

Answer: b

Explanation: A pulse train is generated. Their frequency depends on the frequency of the unknown voltage. Number of pulses present in a definite interval are counted. Unknown input voltage is a measure of the pulses generated.

3. What is the main component of an integrating type DVM?

a) diode

b) amplifier

c) op amp

d) oscillator

Answer: c

Explanation: An op amp forms the heart of the integrating type DVM. Op amp is used as an integrator. The input signal is integrated for a fixed interval giving rise to a ramp signal at the output.

4. When input is positive, then output is?

a) growing exponential signal

b) decaying exponential signal

c) positive going ramp

d) negative going ramp

Answer: d

Explanation: The op amp produces a negative going ramp signal for a positive input voltage. Capacitor is discharged after some time and the output returns to zero. The next cycle starts and the output is a sawtooth waveform. Figure shows the output sawtooth waveform. electrical-measurements-questions-answers-online-test-q4

5. What is the effect of the input signal on the output teeth?

a) directly proportional

b) inversely proportional

c) independent

d) square proportional

Answer: a

Explanation: When the input signal in a voltage to frequency conversion type integrated DVM is doubled, the number of tooth in the output signal is doubled per unit time. This doubles the frequency of the output signal.

6. Sawtooth pulses enter into a reversible counter.

a) True

b) False

Answer: a

Explanation: The sawtooth output signal obtained from the integrating type DVM is passed through a reversible counter. A digital readout displays the value measured by the reversible counter.

7. Application of an input voltage generates a ____________

a) linear signal at the output

b) ramp at the output

c) exponential signal at the output

d) unit step signal at the output

Answer: b

Explanation: When an input voltage of magnitude Vin is applied at the input, capacitor C is charged by the charging current Vin/R1. As a result a ramp signal is produced at the output.

8. Number of pulses is related to frequency.

a) True

b) False

Answer: a

Explanation: Each tooth in the sawtooth waveform produces a pulse at the output of the pulse generator. Hence the number of tooth i.e. the frequency is directly related to the number of pulses.

9. Accuracy depends on ____________

a) input voltage

b) drop across the capacitor

c) magnitude and stability of pulse generator

d) magnitude of the ramp

Answer: c

Explanation: Accuracy of the voltage to frequency conversion depends on the capacity of the pulse generator to produce an electric charge with a suitable magnitude and stability. Hence the accuracy depends on the precision of the charge feedback.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Potentiometric Integrating Type DVM”.

1. In a potentiometric DVM ________

a) voltage is compared

b) current is compared

c) resistance is compared

d) power is compared

Answer: a

Explanation: Potentiometric integrating type DVM employs voltage comparison. The unknown voltage is compared with a reference. The reference value is set by a calibrated potentiometer.

2. How to obtain balance?

a) by using a detector

b) by changing the pot setting

c) by supplying voltage

d) by using a transformer

Answer: b

Explanation: Balance is obtained in a potentiometric integrating type DVM by adjusting the settings of the potentiometer. The dial setting of the potentiometer gives the value of the unknown voltage.

3. In a potentiometric DVM, balance is obtained manually.

a) True

b) False

Answer: b

Explanation: Balance is obtained in a potentiometric integrating type DVM by adjusting the settings of the potentiometer. Hence in a potentiometric integrating type DVM, the balance is obtained automatically.

4. Unknown voltage is __________

a) converted to current

b) boosted

c) filtered

d) measured using a voltmeter

Answer: c

Explanation: In a potentiometric integrated type DVM, the unknown voltage is filtered. It is also attenuated to a suitable magnitude. This forms the input for the comparator. A chopper is usually used as an error detector.

5. How is the reference voltage obtained?

a) from a fixed current source

b) from a variable voltage source

c) from a variable current source

d) from a fixed voltage source

Answer: d

Explanation: Reference voltage is applied to the potentiometer. It is obtained from a source of fixed voltage. The position of the slider on the contact surface determines the value of the feedback voltage.

6. Feedback voltage is applied to the ________

a) comparator

b) error amplifier

c) potentiometer

d) sliding contact

Answer: a

Explanation: Comparator accepts the feedback voltage as an input. Comparator compares the values of the unknown voltage and the feedback voltage. Comparator then provides the difference between the feedback voltage and the unknown voltage as its output.

7. Output of the comparator is known as ________

a) amplified signal

b) error signal

c) feedback signal

d) attenuated signal

Answer: b

Explanation: Comparator then provides the difference between the feedback voltage and the unknown voltage as its output. This is also known as the error signal.

8. Slider movement depends on ________

a) current magnitude

b) resistance magnitude

c) voltage magnitude

d) power magnitude

Answer: c

Explanation: In a potentiometric integrating type DVM, the slider moves based on the magnitude of the feedback voltage with respect to the input voltage. Contact is pushed back to the place where the unknown voltage equals the feedback voltage.

9. Accuracy of a potentiometric DVM is ________

a) zero

b) medium

c) low

d) high

Answer: d

Explanation: In a potentiometric integrating type DVM, the accuracy is usually high. It generally depends on the reference of the digital to analog converter. Accuracy of the voltage to frequency converter is less important compared to that of the digital to analog converter.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Dual Slope Integrating Type DVM”.

1. Why is dual slope method preferred over ramp techniques?

a) no noise

b) partial noise

c) average noise

d) maximum noise

Answer: a

Explanation: During the process of integration, noise is canceled out by the positive and negative ramps in the dual slope method. The input signal is integrated only for a fixed interval of time and this is the basis for the dual slope method.

2. What is the significance of the name dual slope method?

a) it has two slopes

b) it integrates the input twice

c) it uses two inputs

d) it has two outputs

Answer: b

Explanation: The input signal is integrated only for a fixed interval of time and this is the basis for the dual slope method. Reference voltage is integrated with a negative slope. Hence the method is known as dual slope integrating type DVM.

3. What is the output voltage in a dual slope integrating type DVM?

a) differential of the input

b) multiple of the input

c) integral of the input

d) zero

Answer: c

Explanation: In a dual slope integrating type DVM, the output voltage is given by the integral of the input voltage.

electrical-measurements-questions-answers-dual-slope-integrating-type-dvm-q3

where, V in is the input voltage

R 1 is the series resistance

t 1 is the time for which the capacitor is charged.

4. Input voltage depends on ____________

a) resistance

b) capacitance

c) current

d) time-period

Answer: d

Explanation: The input voltage in a dual slope integrating type DVM is given by the relation,

V in = V ref t 2 ⁄ t 1

From the above equation it is seen that the input voltage in a dual slope integrating type DVM depends on the time periods t 1 for which the capacitor is charged and t 2 during which the capacitor is discharged.

5. Noise rejection is poor.

a) True

b) False

Answer: b

Explanation: In a dual slope integrating type DVM, the noise is cancelled out by the positive and negative ramps during the process of integration. As a result, the noise rejection is excellent.

6. What is the effect of the capacitor on the output?

a) no effect

b) charging effect

c) electrostatic effect

d) magnetic effect

Answer: a

Explanation: In the dual slope integrating type DVM method, the capacitor is connected through means of an electronic switch. As a result the effects due to offset voltage wherein there exists an output voltage without the application of any input are eliminated.

7. What is the effect of clock on the voltage?

a) voltage doubles with clock input

b) voltage halves with clock input

c) no effect

d) voltage becomes zero with clock input

Answer: c

Explanation: In a dual slope integrating type DVM, the value of the unknown voltage is independent of the frequency of the clock. It depends only on the number of counts read by the electronic counter.

8. What is the counter value at the beginning?

a) one

b) ten

c) three

d) zero

Answer: d

Explanation: In a dual slope integrating type DVM, the electronic counter is reset to 0 at the beginning of the measurement of voltage. Flip-flop output is also maintained at zero and is given to control logic.

9. What is the maximum count of the counter?

a) 9999

b) 0

c) 500

d) 1000

Answer: a

Explanation: In a dual slope integrating type DVM, the electronic counter reaches a maximum value of 9999 before resetting. A carry pulse is generating pulling down all the digits to zero. Flip-flop then activates the control logic.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Resolution and Sensitivity”.

1. Resolution of a DVM is given by ____________

a) R = 1 ⁄ 10 n

b) R = 1

c) R = 10 n

d) R = n ⁄ 10

Answer: a

Explanation: The resolution of a DVM is,

R = 1 ⁄ 10 n

where, n is the number of full digits

R is the resolution.

2. What is the resolution for a 3 digit display?

a) 1 %

b) 0.1 %

c) 0.001 %

d) 10 %

Answer: b

Explanation: The resolution of a DVM is,

R = 1 ⁄ 10 n

Here, n is 3. Substituting n=3 in the equation for resolution we get,

R = 1 ⁄ 10 3 = 10 -3 = 0.001 = 0.1 %.

3. Sensitivity is largest change in input.

a) True

b) False

Answer: b

Explanation: Sensitivity of any instrument is defined as the smallest hange in the input signal to which the output responds.

4. Sensitivity of a DVM is given by ______________

a) S = 1

b) S = min

c) S = min × R

d) S = R

Answer: c

Explanation: Sensitivity of the DVM is obtained from the relation,

S = min × R

where, S is the sensitivity

R is the resolution

min is the full scale value on minimum range.

5. What is the resolution of a 3 digit display on 1 V range?

a) 1 V

b) 0.1 V

c) 0.01 V

d) 0.001 V

Answer: d

Explanation: The resolution of a DVM is,

R = 1 ⁄ 10 n

Here, n is 3. Substituting n=3 in the equation for resolution we get,

R = 1 ⁄ 10 3 = 10 -3 = 0.001

For 1 V range, the resolution is,

R 1V = 1×0.001 = 0.001 V.

6. How is 11.87 V displayed on a 10 V range for a 4 digit display?

a) 11.870

b) 1.1870

c) 118.7

d) 0.1187

Answer: a

Explanation: The resolution of a DVM is,

R = 1 ⁄ 10 n

Here, n is 4. Substituting n=4 in the equation for resolution we get,

R = 1 ⁄ 10 4 = 10 -4 = 0.0001

Since there are 5 digit places in the resolution, 11.87 which already has four digits is represented as 11.870.

7. Consider a 3 digit display for a DVM with an accuracy of ± 0.5 % for a reading of ± 1 digit. Compute the error for 5 V reading on a 10 V range.

a) ± 10 V

b) ± 0.035 V

c) ± 0.05 V

d) ± 1 V

Answer: b

Explanation: The resolution of a DVM is,

R = 1 ⁄ 10 n

Here, n is 3. Substituting n=3 in the equation for resolution we get,

R = 1 ⁄ 10 3 = 10 -3 = 0.001

For 10 V range, the resolution is,

R 10V = 10 × 0.001 = 0.01 V

Consider the reading of 5 V.

Error = ± 0.5 % of 5 = 0.5 ⁄ 100 × 5 = ± 0.025 V

1 digit error = ± 0.01 V

Total error = ±=± 0.035 V.

8. Clock pulses are controlled ______

a) automatically

b) using microcontrollers

c) using valves

d) manually

Answer: d

Explanation: A manual range hold command is used to control the clock pulses and the autoranging. This is done through a signal that exceeds the maximum range for up counts by reaching the most sensitive range .

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Autoranging”.

1. Autoranging means __________

a) automatic ranging

b) fixed ranging

c) automobile ranging

d) constant ranging

Answer: a

Explanation: Autoranging refers to obtaining an automatic reading with optimum resolution under all operating conditions. Say for example, 155 mV is displayed as 155.0 and not 0.155.

2. A 3 digit display DVM with a maximum reading of 1999 indicates __________

a) increase by a factor

b) reduction by a factor

c) no change in value

d) depends on the circuit components

Answer: b

Explanation: A 3 digit display DVM with maximum reading capability indicates that any reading above the maximum set limit of 1999 will be reduced by a factor of 10.

3. For a value less than 0200, the instrument should ________

a) read values less than 0200 correctly

b) read values randomly

c) automatically switch range

d) should not respond at all

Answer: c

Explanation: The DVM should automatically switch its range when the display is greater than 1999 units as it is the maximum set limit for achieving a higher sensitivity.

4. ADC counter ________

a) attenuates the signal

b) converts digital to analog

c) converts analog to digital

d) contains information

Answer: d

Explanation: When the count produced by the ADC counter is less than 170, a control pulse is obtained for down ranging. Whereas the control pulse for up ranging is produced once the ADC counter exceeds 1999 units.

5. ADC gives polarity indication.

a) True

b) False

Answer: a

Explanation: ADC contains information required for polarity indication. The polarity of the signal that is integrated is of utmost importance.

6. Integration period is obtained by ________

a) using signal amplitude

b) counting the pulse

c) measuring time

d) by differentiating the signal

Answer: b

Explanation: By counting the pulses we obtain the integration period. Polarity measurement is obtained by making use of the last count or some of the last counts.

7. Integrator’s output is ________

a) attenuated through a filter

b) feedback to the input

c) stored in a flip-flop

d) differentiated

Answer: c

Explanation: The output from the integrator is used to set a polarity flip-flop. The flip-flop’s output is then stored in memory until the next measurement of voltage is obtained.

8. Old information is used to set range relays.

a) True

b) False

Answer: b

Explanation: Range relays are set through the decoder using the new information obtained with the help of a clock pulse. Decimal point is also changed as per the requirement of the new range.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Digital Multimeter”.

1. Digital multimeter is used for _________

a) measuring a.c. and d.c. current, voltage and resistance

b) measuring a.c. current and voltage

c) measuring d.c. current and resistance

d) measuring a.c. voltage and resistance

Answer: a

Explanation: Digital multimeter is usually used for the measurement of a.c. current, voltage and resistance. It is also used for the measurement of d.c. current, voltage and resistance as well over several range.

2. Current is converted to voltage __________

a) through a voltmeter

b) through a resistance

c) through an ammeter

d) through a galvanometer

Answer: b

Explanation: Current is passed through a low shunt resistance and is converted to voltage. A.C. quantities are converted to D.C. through various rectifier and filter circuits. Voltmeter and ammeter are used for voltage and current measurement respectively.

3. For resistance measurement, meter contains _________

a) high current source

b) medium current source

c) low current source

d) low voltage source

Answer: c

Explanation: Usually in the measurement of resistance, meter consists of a precision low current source applied across an unknown resistance which gives a d.c. voltage.

4. Quantities are digitised using _________

a) D/A converter

b) oscillator

c) amplifier

d) A/D converter

Answer: d

Explanation: Quantities such as current, voltage and resistance are digitised by making use of an A/D converter. They are then displayed on the screen by making use of a digital display.

5. Analog mulimeters require power supply.

a) True

b) False

Answer: b

Explanation: Analog multimeters are less affected by electric noise and isolation problems. As a result analog multimeters don’t require a power supply.

6. Output of a digital multimeter is _________

a) mechanical

b) optical

c) electrical

d) analog

Answer: c

Explanation: Digital multimeter gives an electrical signal as the output. A/D converter is employed for the conversion from analog to digital signal. This can be used for interfacing with external equipment.

7. Basic building blocks of digital multimeter are _________

a) oscillator, amplifier

b) diode, op amp

c) rectifier, schmitt trigger

d) A/D, attenuator, counter

Answer: d

Explanation: Usually dual slope integrating type ADC is preferred in multimeter. It basically consists of several A/D converters, counter circuits and an attenuation circuit.

8. Resistance is measured using _________

a) constant current source

b) constant voltage source

c) variable current source

d) variable voltage source

Answer: a

Explanation: Constant current source is used to measure resistance in a digital multimeter. Standard known value of current is passed through an unknown resistance and the drop in voltage across the resistance is measured.

9. A.C. voltages are measured using _________

a) oscillators and op amps

b) rectifiers and filters

c) resistor and capacitor

d) inductor and resistor

Answer: b

Explanation: Rectifiers and filter circuits with various configurations are employed for measuring A.C. voltages. A.C. is converted to D.C. and is applied to the A/D converter.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Qmeter”.

1. Q factor is called __________

a) Quality factor

b) Quantity factor

c) Queen factor

d) Quarter factor

Answer: a

Explanation: Q factor is also known as Quality factor or storage factor. It is basically a ratio of the power stored in an element to the power dissipated in that element.

2. Q factor is also defined as the ratio of _______

a) resistance to reactance

b) reactance to resistance

c) power to voltage

d) current to power

Answer: b

Explanation: Q factor can also be obtained as the ratio of reactance to resistance of an element. For inductive element it is the ratio of X L to R and for a capacitive element it is the ratio of X C to R.

3. What is a Q meter?

a) quality meter

b) quantity meter

c) instrument

d) detector

Answer: c

Explanation: Q meter is basically an instrument that is used for the measurement of electrical properties of capacitors and coils. It is also used as a laboratory instrument.

4. Q meter works on the principle of _______

a) barkhausen criterion

b) piezoelectric effect

c) parallel resonance

d) series resonance

Answer: d

Explanation: Q meter basically operates on the characteristics of a series resonant coil. In a series resonant circuit the voltage drop across the coil or a capacitor is equal to the applied voltage multiplied by its Q factor.

5. Q factor for a series resonant circuit is?

a) Q = \

Q = X L R = X C R

c) Q = \

Q = \(\frac{1}{R}\)

Answer: a

Explanation: Q factor in a series resonant circuit is given by the relation,

Q = \(\frac{X_L}{R} = \frac{X_C}{R}\)

where, R is resistance of the coil

X C is the capacitive reactance

X L is the inductive reactance.

6. What is the relation between Q factor and voltage?

a) Q = \

Q = \

Q = E

d) Q = \(\frac{R}{X_L}=\frac{R}{X_C}=\frac{E}{E_C}\)

Answer: b

Explanation: The applied voltage E is inversely proportional to the Q factor of a circuit and is given by the relation,

Q = \(\frac{X_L}{R}=\frac{X_C}{R}=\frac{E_C}{E}\).

7. A practical Q meter consists of __________

a) Wien bridge oscillator

b) AF oscillator

c) RF oscillator

d) Crystal oscillator

Answer: c

Explanation: Practically a Q meter consists of a wide range RF oscillator with a frequency range of 50 kHz to 50 MHz. Oscillator acts as a source and delivers current to a low shunt resistance.

8. Voltage across the shunt is measured by ________

a) voltmeter

b) multimeter

c) thermocouple

d) thermometer

Answer: c

Explanation: A thermocouple is used for measuring the voltage across a shunt resistance in a practical Q meter. Electronic voltmeter is used for the measurement of voltage across a resonant capacitor.

9. Inductance of the coil is ________

a) L = \

L = \

L = \(\frac{1}{^2 C}\)

Answer: d

Explanation: Coil inductance in a Q meter is given by the relation,

L = \(\frac{1}{^2 C}\)

where, f is the frequency in Hz

C is the capacitance in F.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Advanced Problems on Q Meter”.

1. Q meter operator is the principle of __________

a) Series resonance

b) Current resonance

c) Self-inductance

d) Eddy currents

Answer: a

Explanation: We know that Q = \(\frac{ωL}{R}\)

From the above relation, we can say that it works on series resonance.

2. In a Q Meter, the values of tuning capacitor are C 3 and C 4 for resonant frequencies f 3 and 2f 4 respectively. The value of distributed capacitance is?

a) \

\(\frac{C_3-3C_4}{2}\)

Answer: c

Explanation: Q X = \(\frac{R_P}{X_P} = \frac{

Q_3 Q_4}{Q_3 C_3 – Q_4 C_4}\)

The main error in the measurement of Q is due to the distribution. To check for this, the Q value is measured at two frequencies f 1 and 2f 2 . It should be same, if not then, \(\frac{C_3-4C_4}{3}\).

3. A circuit tuned to a frequency of 1.5 MHz and having an effective capacitance of 150 pF. In this circuit, the current falls to 70.7 % of its resonant value. The frequency deviates from the resonant frequency by 5 kHz. Q factor is?

a) 50

b) 100

c) 150

d) 200

Answer: c

Explanation: Q = \(\frac{ω}{ω1 – ω2} = \frac{f}{f2-f1}\)

Here, f = 1.5 × 10 6 Hz

f1 = (1.5 × 10 6 – 5 × 10 3 )

f2 = (1.5 × 10 6 + 5 × 10 3 )

So, f2 – f1 = 10 × 10 3 Hz

Q = \(\frac{1.5 × 10^6}{10 × 10^3}\) = 150.

4. A circuit tuned to a frequency of 1.5 MHz and having an effective capacitance of 150 pF. In this circuit, the current falls to 70.7 % of its resonant value. The deviates from the resonant frequency are 5 kHz. Effective resistance of the circuit is?

a) 2 Ω

b) 3 Ω

c) 5.5 Ω

d) 4.7 Ω

Answer: d

Explanation: R = \(\frac{f2-f1}{2πf^2 L}\)

Here, f = 1.5 × 10 6 Hz

f1 = (1.5 × 10 6 – 5 × 10 3 )

f2 = (1.5 × 10 6 + 5 × 10 3 )

So, f2 – f1 = 10 × 10 3 Hz

R = \(\frac{10 × 10^3}{2π

^2 L}\)

R = 4.7 Ω.

5. Q Meter is used to measure _________

a) Q factor of an inductive coil

b) Only the effective resistance

c) Only bandwidth

d) Q factor of an inductive coil, the effective resistance, and bandwidth

Answer: d

Explanation: Q meter can measure the Q factor of an inductive coil. It can also measure the effective resistance. Also, the bandwidth can be measured by the Q Meter. Therefore it can be used for all the above functions.

6. Q factor of a coil measured by the Q Meter is _________ the actual Q of the coil.

a) Equal to

b) Same but somewhat lesser than

c) Same but somewhat higher than

d) Not equal to

Answer: b

Explanation: The Q factor measured by the Q meter cannot be exactly equal to the actual Q of the coil because of the presence of errors. Also, it is not practically possible for the value to be higher than the actual one. But the value is somewhat lesser and almost equal to the actual value.

7. Consider a circuit consisting of two capacitors C 1 and C 2 . Let R be the resistance and L be the inductance which are connected in series. Let Q 1 and Q 2 be the quality factor for the two capacitors. While measuring the Q value by the Series Connection method, the value of the Q factor is?

a) Q = \

Q = \

Q = \( \frac{

C_1 C_2}{Q_1 C_1 – Q_2 C_2}\)

Answer: a

Explanation: ωL = \(\frac{1}{ωC}\)and Q 1 = \(\frac{ωL}{R} = \frac{1}{ωC_1 R}\)

X S = \(\frac{C_1-C_2}{ωC_1 C_2 }\), R S = \(\frac{Q_1 C_1 – Q_2 C_2}{ωC_1 C_2 Q_1 Q_2}\)

Q X = \(\frac{X_S}{R_S} = \frac{

Q_1 Q_2}{Q_1 C_1-Q_2 C_2}\).

8. Consider a circuit consisting of two capacitors C 1 and C 2 . Let R be the resistance and L be the inductance which are connected in series. Let Q 1 and Q 2 be the quality factor for the two capacitors. While measuring the Q value by the Parallel Connection method, the value of the Q factor is?

a) Q = \

Q = \

Q = \(\frac{

C_1 C_2}{Q_1 C_1 – Q_2 C_2}\)

Answer: b

Explanation: \(\frac{1}{R_P} = \frac{ωC_1}{Q_2} – \frac{1}{RQ_1^2}\), X P = \(\frac{1}{ω

}\)

Q = \(\frac{

Q_1 Q_2}{Q_1 C_1 – Q_2 C_2}\).

9. Consider the following statements regarding the sources of error in a Q Meter.

i) If a coil with a resistance R is connected in the direct measurement mode and

If the residual resistance of the Q Meter is 0.1 R,

Then the measured Q of the coil would be 1.1 times the actual Q.

ii) If the inductance to be measured is less than 0.1 μH.

The error due to the presence of residual inductance cannot be neglected.

iii) The presence of a distributed capacitance modifies the effective Q of the coil.

Which of the above statements are correct?

a) i, ii and iii

b) i and ii

c) ii and iii

d) i and iii

Answer: c

Explanation: We know that, Q = \

is incorrect. Hence, statements and are correct.

10. The function of the Q- Meter is to _________

a) Measure capacitance

b) Measure inductance

c) Measure quality factor of capacitor and inductor

d) Measure form factor of capacitor and inductor

Answer: c

Explanation: Q-Meters are intended to measure the quality factor of a capacitor and inductor. Q = \(\frac{Lω}{R} = \frac{1}{ωCR} = \frac{V_C}{V_A}\). They are not used for measuring capacitances and inductances, unlike AC Bridges.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Oscilloscope”.

1. CRO stands for __________

a) Cathode Ray Oscilloscope

b) Current Resistance Oscillator

c) Central Resistance Oscillator

d) Capacitance Resistance Oscilloscope

Answer: a

Explanation: Cathode Ray Oscilloscope is basically used for the measurement of the amplitude of periodic and non periodic signals as a function of time.

2. C.R.O gives __________

a) actual representation

b) visual representation

c) approximate representation

d) incorrect representation

Answer: b

Explanation: Cathode Ray Oscilloscope is used as universal laboratory equipment. It provides a visual representation of time varying signals. It is an important equipment in the development of electronic circuits.

3. Oscilloscope is __________

a) a ohmmeter

b) an ammeter

c) a voltmeter

d) a multimeter

Answer: c

Explanation: Oscilloscope is basically a voltmeter. It employs the movement of an electronic gun assembly with respect to a fluorescent screen. The screen produces the movement of the visible spot.

4. Electron beam is deflected in __________

a) 1 direction

b) 4 directions

c) 3 directions

d) 2 directions

Answer: d

Explanation: The electron beam in an oscilloscope can be deflected in two directions, namely the horizontal and the vertical . Two dimensional displays are produced as a result.

5. CRO is a __________

a) fast x-y plotter

b) slow x-y plotter

c) medium x-y plotter

d) not a plotter

Answer: a

Explanation: CRO is basically a fast x-y plotter. The x and y axes can be used to understand the variation in the magnitude of one voltage with respect to another voltage signal.

6. CRO can’t display microseconds time.

a) True

b) False

Answer: b

Explanation: CRO is a fast x-y plotter and displays periodic signals with time periods of the order of a few microseconds and even nanoseconds.

7. CRT is the heart of CRO.

a) True

b) False

Answer: a

Explanation: CRT stands for Cathode Ray Tube. It generates electron beam, accelerates and deflects the beam. It thus forms the heart of the CRO.

8. Typically oscilloscope represents __________

a) current and time

b) resistance and time

c) voltage and time

d) power and time

Answer: c

Explanation: In an oscilloscope typically the horizontal or x-axis represents the time while the vertical or y-axis represents the variation in the magnitude of the input signal.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Cathode Ray Tube”.

1. Electron gun section ________

a) provides sharp beam

b) provides poorly focussed beam

c) doesn’t provide any beam

d) provides electrons only

Answer: a

Explanation: In a cathode ray tube, the electron gun section gives a sharply focussed beam of electrons. They are focussed on the fluorescent coated screen.

2. Control grid is given ________

a) positive voltage

b) negative voltage

c) neutral voltage

d) zero voltage

Answer: b

Explanation: Grid controls the amount of electrons falling on the fluorescent screen of a cathode ray tube. Cathode ray tube is provided with a negative voltage with respect to the cathode as a reference.

3. What determines light intensity in a CRT?

a) voltage

b) current

c) momentum of electrons

d) fluorescent screen

Answer: c

Explanation: Momentum of the electrons gives the intensity or brightness of the light emitted from the fluorescent screen due to electron bombardment. It is given as the product of the no of electrons and their speed.

4. Effect of negative voltage to the grid is ________

a) no force

b) a gravitational force

c) an attractive force

d) a repulsive force

Answer: d

Explanation: Since the electron is negatively charged, application of a negative voltage to the control grid produces a repulsive force.

5. Electron beam diverges.

a) True

b) False

Answer: a

Explanation: Similar charges on electrons lead to a repulsion. As a result the electron beam diverges as it contains many electrons. Electrostatic force is applied between the focussing anodes in order to compensate the repulsive force.

6. Focusing and accelerating anodes are ________

a) rectangular

b) cylindrical

c) spherical

d) square

Answer: b

Explanation: Focussing and accelerating anodes in a cathode ray tube are essentially cylindrical in nature. Each electrode has a small opening at the centre with a co-axial tubular axis.

7. Deflection system of a CRT consists of ________

a) 4 plates

b) 6 plates

c) 2 plates

d) 8 plates

Answer: c

Explanation: Cathode ray tube consists of two sets of plates that are parallel in nature. They are referred to as horizontal and vertical deflection plates. One of the plates is set to ground potential.

8. Horizontal deflection is given by ________

a) x = K x

b) x = V x

c) x = 1

d) x = K x V x

Answer: d

Explanation: In a cathode ray tube the horizontal deflection is given by,

x = K x V x

where, K x is the constant of proportionality

x is the horizontal deflection

V x is the horizontal deflecting voltage.

9. Vertical deflection is given by ________

a) y = K y V y

b) y = K y

c) x = 1

d) y = V y

Answer: a

Explanation: In a cathode ray tube the vertical deflection is given by,

y = K y V y

where, K y is the constant of proportionality

y is the vertical deflection

V y is the vertical deflecting voltage.

This set of Basic Electrical Measurements Questions and Answers focuses on “Basic Principle of Signal Display”.

1. What provides a periodic voltage waveform?

a) sweep generator

b) voltmeter

c) oscillator

d) amplifier

Answer: a

Explanation: Sweep generator provides a periodic voltage waveform in an oscilloscope. As the waveform resembles the teeth of a hacksaw it is known as a sawtooth waveform.

2. Visible spot must be moved in _______

a) two directions

b) one direction

c) three directions

d) four directions

Answer: b

Explanation: Sweep voltage must be brought to zero once it reaches its maximum value. The visible spot must be moved in a single direction only. Return sweep will trace back the signal in a reverse direction.

3. Spot is displayed only when _______

a) frequencies are different

b) frequencies are zero

c) frequencies are same

d) voltage is high

Answer: c

Explanation: When the sweep frequency and the signal frequency are same or integral multiple of each other, visible spot is displayed on the screen of the cathode ray oscilloscope.

4. What is done to make the trace horizontal?

a) negative voltage is applied

b) positive voltage is applied

c) no voltage is applied

d) voltage is synchronised

Answer: d

Explanation: The trace is made stationary by synchronising the sawtooth voltage with the magnitude of the signal that is applied to the vertical input.

5. A single cycle appears on the screen when _______

a) sweep and signal frequencies are equal

b) sweep and signal frequencies are not equal

c) sweep and signal frequencies are zero

d) sweep frequency is greater than signal frequency

Answer: a

Explanation: Many cycles are present on the screen when the sweep frequency is lower than the signal frequency. Only a single cycle appears on the screen when the sweep and signal frequencies are equal.

6. Sinusoidal voltage is not observed on the screen.

a) True

b) False

Answer: b

Explanation: Application of a sinusoidal voltage to the y terminal and the internally produced sawtooth voltage to the x terminal results in the shifting of the sawtooth voltage in terms of magnitude. Finally a sinusoidal waveform is observed on the screen.

7. What is the flyback period?

a) voltage is very high

b) current is very low

c) voltage is zero

d) current is very high

Answer: c

Explanation: During the flyback period, voltage suddenly drops to zero from a certain value.

8. During trace time, voltage is decreasing with time.

a) True

b) False

Answer: b

Explanation: The electron beam moves linearly along the horizontal direction during the trace time. The voltage Vx increases linearly with respect to time Tr during the instant of the trace period.

9. Light produced in a screen is _______

a) disappears immediately

b) does not disappear at all

c) is not visible to the eye

d) disappears slowly

Answer: d

Explanation: When the magnitude of the applied voltage reduces to zero, the light produced on the screen due to the bombardment of electrons does not disappear immediately and reduces in terms of intensity slowly.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Simple Oscilloscope”.

1. What is the role of CRT?

a) to emit electrons

b) to emit protons

c) to emit neutrons

d) to emit alpha particles

Answer: a

Explanation: Cathode ray tube forms the heart of a C.R.O. It is used to emit electrons so as to strike the phosphor screen to produce a spot for the visual display of the signals.

2. Input signals are amplified using ___________

a) rectifier

b) amplifier

c) oscillator

d) op amp

Answer: b

Explanation: Vertical amplifier is used in a cathode ray tube to amplify the input signals. Magnitude of the input signal is weak and not sufficient enough to give deflection on the screen.

3. Amplifier stage is ___________

a) half band

b) full band

c) wide band

d) narrow band

Answer: c

Explanation: Wide band amplifiers are generally used to amplify the input signals. The whole band of frequency to be measured must be passed faithfully by making use of a wide band amplifier.

4. Role of an attenuator is ___________

a) to boost the signal

b) to distort the signal

c) to remove noise

d) to improve the operation

Answer: d

Explanation: When we need to measure very high voltage signals, attenuator stages are used. This is done in order to bring the signal level within the range of operation of the amplifier.

5. Amplifier is multiple stage in a CRO.

a) True

b) False

Answer: a

Explanation: A Cathode Ray Tube essentially consists of multiple stages of amplifiers with a overall fixed sensitivity. Amplifier is designed for stability and required bandwidth very easily due to the fixed gain.

6. Input stage in the amplifier consists of ___________

a) oscillator

b) attenuator

c) rectifier

d) op amp

Answer: b

Explanation: The amplifier stage of a Cathode Ray Tube essentially consists of an attenuator stage. It is followed by a FET source follower. The input impedance is very high.

7. Phase inverter is used in an amplifier in the CRO because ___________

a) phase inversion is needed

b) no phase inversion is needed

c) it is needed to operate a push pull

d) it provides voltage stability

Answer: c

Explanation: In a Cathode Ray Oscilloscope, phase inverter is typically used for operating a push pull amplifier. It provides two antiphase output signals in order to operate the push pull amplifier.

8. BJT is used in the amplifier stage.

a) True

b) False

Answer: a

Explanation: A BJT emitter follower is used in the amplifier stage after the FET in order to provide impedance matching to the output of the FET. With respect to the input of the phase-inverter.

9. Why is a delay line used in a CRO?

a) to boost the signal

b) to distort the signal

c) to provide signal delay

d) for stability

Answer: c

Explanation: Delay line is used in a Cathode Ray Oscilloscope so as to delay the signal for some time. If the delay line is not used then a part of the signal is lost. A delay line circuit is used for this purpose.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Delay Line”.

1. CRO uses __________

a) 2 delay lines

b) 3 delay lines

c) 4 delay lines

d) 5 delay lines

Answer: a

Explanation: Cathode Ray Oscilloscope uses two delay lines. They are as follows:

Lumped parameter delay line and

Distributed parameter delay line.

2. T section in a delay circuit of CRO acts as ________

a) high pass filter

b) low pass filter

c) band pass filter

d) band reject filter

Answer: b

Explanation: In the delay circuit of a CRO, T section is present in the lumped parameter delay line. The T section acts as a low pass filter having a cut off frequency as,

electrical-measurements-questions-answers-delay-line-q2 .

3. Lumped parameter delay line consists of________

a) RC networks

b) RL networks

c) LC networks

d) Resistive networks

Answer: c

Explanation: In the delay line circuit of a Cathode Ray Oscilloscope, the lumped parameter delay line is made of several cascaded LC networks. They are known as T sections.

4. Delay for the T section is given by ________

a) t s = 1 ⁄ f c

b) t s = 1

c) t s = 1 ⁄ π

d) t s = 1 ⁄ πf c

Answer: d

Explanation: In the T section of the lumped parameter delay in a delay line circuit of the CRO the delay is given by the relation

t s = 1 ⁄ πf c

t s = delay for a single circuit

t d = total delay

n = number of T sections.

5. Distributed parameter delay line is a transmission line.

a) True

b) False

Answer: a

Explanation: The delay line circuit consists of distributed parameter delay as well as lumped parameter delay. The distributed parameter delay is basically a transmission line with a coil wound on a helix mandrel.

6. Inductance does not affect a transmission line.

a) True

b) False

Answer: b

Explanation: The inductance of the transmission line in a distributed parameter delay line can be increased by winding the inner conductor of the helix onto a ferromagnetic core.

7. Typical values for a distributed parameter delay line are ________

a) Z o = 10 Mῼ and t d = 10 nsec/m

b) Z o = 1 kῼ and t d = 500 nsec/m

c) Z o = 1000 ῼ and t d = 180 nsec/m

d) Z o = 100 Gῼ and t d = 275 nsec/m

Answer: c

Explanation: For the distributed parameter delay line in a delay line circuit the typical parameters are the characteristic impedance which is Z o = 1000 ῼ and the delay time which is t d = 180 nsec/m.

8. What is the effect of the signal delay on the sweep generator?

a) no effect

b) input increases in magnitude

c) output doesn’t get any delay

d) output gets sufficient delay

Answer: d

Explanation: When the signal is delayed, the sweep generator’s output gets sufficient time in order to reach the horizontal plates before the signal passes over to the vertical deflection plates.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Front Panel Controls of CRO”.

1. Front panel of a CRO has _________

a) 4 sections

b) 8 sections

c) 15 sections

d) 20 sections

Answer: a

Explanation: A simple Cathode Ray Oscilloscope has the following four sections:

i) Basic controls

ii) Vertical section

iii) Horizontal section

iv) Z axis intensity control.

2. What is the role of the intensity section in a CRO?

a) decreases the light intensity

b) controls light intensity

c) increases the light intensity

d) keeps the light intensity zero

Answer: b

Explanation: In a Cathode Ray Oscilloscope the intensity section controls the brightness or intensity of the light beam produced by the bombardment of electrons on the fluorescent screen.

3. What is the role of the focus section in a CRO?

a) increases the focus

b) decreases the focus

c) controls sharpness

d) maintains the focus zero

Answer: c

Explanation: In a Cathode Ray Oscilloscope the focus section controls the sharpness of the visible spot on the screen. By varying the voltage applied to the focussing anodes, visible spot on the screen is focussed sharply.

4. What is the role of astigmatism in a CRO?

a) increases the intensity

b) used for voltage stability

c) diminishes the intensity

d) focus control

Answer: d

Explanation: In a Cathode Ray Oscilloscope the astigmatism forms another set of focus control. A sharp spot can be obtained by the combination of focus control and astigmatism.

5. What is the role of scale illumination in a CRO?

a) measurement

b) illumination

c) sharpness

d) stability

Answer: a

Explanation: In a Cathode Ray Oscilloscope the scale illumination is basically used for the purpose of measurement. It basically illuminates the scale and as a result the reading can be clearly seen.

6. What is the role of an invert in a CRO?

a) inverts the output

b) inverts the input

c) attenuates the input

d) magnifies the input

Answer: b

Explanation: In a Cathode Ray Oscilloscope the invert control section is used for the purpose of inverting the input signal. It basically multiplies the input signal by a factor of -1.

7. X10 in a CRO means ________

a) one tenth

b) control knob

c) 10 times as normal

d) attenuate the voltage by 10 times

Answer: c

Explanation: In a Cathode Ray Oscilloscope X10 indicates that gain of the vertical amplifier is made 10 times that of the normal value. When the X10 switch is turned ON, scope of the CRO is et to 0.05 V/cm.

8. Position knob in a CRO indicates ________

a) voltage position only

b) time position only

c) current position only

d) any pattern’s position

Answer: d

Explanation: In a Cathode Ray Oscilloscope the position knob is used for indicating the position of any pattern on the screen. The pattern can be shifted vertically upwards or downwards.

9. Alternate is used to shift the inputs.

a) True

b) False

Answer: a

Explanation: In a Cathode Ray Oscilloscope the alternate knob is used to transition between the two different input signals. Using the vertical position control, the traces of the two input signals are separated vertically.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Time Base”.

1. Time domain oscilloscopes require ___________

a) sweep generator

b) oscillator

c) amplifier

d) rectifier

Answer: a

Explanation: Time domain oscilloscopes need a sweep generator. The sweep generator must be a linear function of time for the x-axis display.

2. What is time base generator?

a) time measuring device

b) generator

c) voltage generation device

d) current generation device

Answer: b

Explanation: In a Cathode Ray Oscilloscope, a generator that produces a waveform required for the movement of the visible spot horizontally is known as the time base generator.

3. Linear sweep moves spot __________

a) top to bottom

b) right to left

c) left to right

d) bottom to top

Answer: c

Explanation: In a Cathode Ray Oscilloscope, a linear sweep is used to move the visible spot from left to right direction. The movement of the spot from right to left direction is not visible.

4. Time base generator controls __________

a) intensity of light

b) current direction

c) voltage magnitude

d) spot movement

Answer: d

Explanation: In a Cathode Ray Oscilloscope, the time base generator controls the rate at which the visible spot moves across the screen. Using the front panel controls this rate can be modified.

5. Time dependent waveforms need x-axis for calibration.

a) True

b) False

Answer: a

Explanation: In a Cathode Ray Oscilloscope, the time dependent waveforms need x-axis for calibration. It is calibrated as the time axis.

6. Sweep generator works on the principle of __________

a) inductor

b) capacitor

c) resistor

d) diode

Answer: b

Explanation: In a Cathode Ray Oscilloscope, the sweep generator basically works on the principle of a capacitor. It generates linear rise time voltages by making use of the charging characteristics of a capacitor.

7. Left to right visibility of the spot is ensured by __________

a) linear waveform

b) linear ramp waveform

c) sinusoidal waveform

d) unit step waveform

Answer: c

Explanation: In the time base generator, a linearly increasing ramp waveform that decreases to zero within a very short time span is used to make sure that the spot is only visible from left to right direction.

8. Time base generator circuit resembles a __________

a) regulator

b) rectifier

c) amplifier

d) oscillator

Answer: d

Explanation: The time base generator circuit is basically a relaxation oscillator. It generates a saw tooth waveform. A bootstrap technique allows linearity but is very expensive.

9. Sweep generator is a time base generator.

a) True

b) False

Answer: a

Explanation: In a Cathode Ray Oscilloscope the sweep base generator produces the movement of the spot on the screen. It acts as the time base for the waveforms and as a result it is known as a time base generator.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Principle of Time Base Generator”.

1. What is hold off time in a CRO?

a) time to start a ramp

b) time to end a ramp

c) time to start a unit step

d) time to end a unit step

Answer: a

Explanation: In a Cathode Ray Oscilloscope, the trigger circuit applies the pulse as soon as the cycle ends. The hold off time in a time base generator is defined as the time taken for the ramp signal so as to stabilise the flyback circuitry.

2. What is the wait time in a CRO?

a) time to deactivate time base generator

b) time to activate time base generator

c) time from input to output

d) time from output to input

Answer: b

Explanation: In a Cathode Ray Oscilloscope, the trigger circuit produces a trigger pulse. The pulse must exceed a certain reference threshold level in order to activate the time base generator. This is known as trigger threshold.

3. A trigger circuit is ___________

a) is used for triggering the input

b) is used for triggering the output

c) used with time base generator

d) used as a oscillator

Answer: c

Explanation: In a Cathode Ray Oscilloscope, the trigger circuit is basically used for triggering the time base generator. It triggers the time base generator and produces a ramp signal.

4. Time base generator takes certain time to begin a new cycle.

a) True

b) False

Answer: a

Explanation: After the end of a cycle of sweep and retrace, the time base generator takes certain amount of time to commence a new cycle. This time can be divided into two parts:

i) Hold off time and ii) Waiting time.

5. After hold off time, the time base generator is activated immediately.

a) True

b) False

Answer: b

Explanation: As a result of trigger threshold crossing the time base generator doesn’t immediately get activated after the hold off time. This time is known as the waiting time wherein the triggering pulses cross the trigger threshold.

6. A time base should have _________

a) non-linearity

b) ramp relationship

c) linearity

d) unit step relationship

Answer: c

Explanation: In a Cathode Ray Oscilloscope, a time base generator must have a linear relationship. Linearity of the order of more than 1 % across the cathode ray tube can be obtained by making use of a time base generator.

7. The horizontal amplifier in a CRO can be expanded by _________

a) 5 times

b) 15 times

c) 30 times

d) 10 times

Answer: d

Explanation: In a Cathode Ray Oscilloscope, the horizontal amplifier can be expanded by up to 10 times. This allows a division of 1nsec display for very high speed transient waveforms.

8. Sweep rate is controlled by a _________

a) capacitor

b) resistor

c) diode

d) inductor

Answer: a

Explanation: In a Cathode Ray Oscilloscope, the sweep rate is controlled by a capacitor. This is done through means of the charging current flowing through the capacitor.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “TTL Triggering”.

1. How many, time base generators are provided to a CRO?

a) 2

b) 4

c) 6

d) 8

Answer: a

Explanation: A Cathode Ray Oscilloscope has two time base generators. A time base generator has various sweep modes based on the complexity of the second time base generator.

2. TTL trigger mode is not used for any purpose.

a) True

b) False

Answer: b

Explanation: The TTL trigger mode in a Cathode Ray Oscilloscope is useful in the case of ringing effects. Ringing effects lead to the formation of unwanted oscillations due to switching transients.

3. CRO waveform is disturbed due to _____________

a) Capacitor banks

b) RTL triggering

c) TTL triggering

d) Voltage sources

Answer: c

Explanation: In a Cathode Ray Oscilloscope, the waveform is affected as a result of TTL trigger mode. The lead inductance of the ground along with probe capacitance results in a resonance circuit.

4. Ringing effects can cause false triggering.

a) True

b) False

Answer: a

Explanation: The TTL trigger mode in a Cathode Ray Oscilloscope is useful in the case of ringing effects. Ringing effects produce false triggering even though the trigger points may not be set.

5. How can false triggering be prevented?

a) using RTL logic

b) using TTL logic

c) using DTL logic

d) using flip flops

Answer: b

Explanation: In a Cathode Ray Oscilloscope, TTL trigger circuit is used for setting the correct trigger points. The trigger circuit acts in the same way as the input of a TTL circuit.

6. What is the significance of the TTL trigger mode?

a) initiates interference

b) attenuates the signal

c) prevents interference

d) boosts the signal

Answer: c

Explanation: In a Cathode Ray Oscilloscope, TTL trigger circuit prevents sweep signals that are below the trigger gap from getting triggered falsely.

7. TTL triggering gives a ____________

a) attenuated output

b) magnified output

c) unstable output

d) stable output

Answer: d

Explanation: TTL triggering circuit in a Cathode Ray Oscilloscope gives rise to a stable display. There is no necessity to check the TTL levels on the screen. The logic levels are also checked to be correct.

8. Switched sweep mode is also known as ____________

a) dual sweep mode

b) single sweep mode

c) quadruple sweep mode

d) triple sweep mode

Answer: a

Explanation: A switches sweep mode is used for displaying two independent variable sweep modes in an alternative fashion. Initially, waveform is displayed with a slow sweep rate and then with a fast sweep rate.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Dual Trace Oscilloscope”.

1. Why a dual slope oscilloscope is needed?

a) to compare more than two voltages

b) to measure the voltage

c) to measure the current

d) to measure the time

Answer: a

Explanation: A dual trace oscilloscope is required for comparison for two or more voltages in the analysis and study of electronic circuits and systems.

2. What is the problem with using more than one oscilloscopes?

a) measuring the signal’s parameters

b) triggering

c) supply voltage

d) errors in reading

Answer: b

Explanation: When one more than one oscilloscope is used, the trigger sweeps of each can’t be synchronized simultaneously. As a result dual trace oscilloscopes are used in order to save the cost.

3. Independent traces can be obtained using ____________

a) 4 methods

b) 6 methods

c) 2 methods

d) 8 methods

Answer: c

Explanation: In order to generate two independent traces in a oscilloscope, two methods are used. One method is known as the sweep method whereas the other is known as the chop method.

4. Two methods are used to generate independent traces.

a) True

b) False

Answer: a

Explanation: In a Cathode Ray Oscilloscope, two methods are used to generate two independent traces. The first method is an alternate sweep method while the second is the chop method.

5. How many vertical inputs exist in a dual trace oscilloscope?

a) 8

b) 6

c) 4

d) 2

Answer: d

Explanation: In a Dual Trace Oscilloscope, two vertical inputs exist. The two channels are known as A and B. A separate preamplifier and an attenuator stage exist for each channel. The amplitude of each input can be controlled separately.

6. After pre-amplification the signals are fed into ____________

a) an electronic switch

b) a signal generator

c) a rectifier

d) a regulator

Answer: a

Explanation: In a Dual Trace Oscilloscope, after the pre amplification process is done, the signals are fed into an electronic switch. The switch passes one channel at a time through the delay line.

7. X-Y mode means ____________

a) 2 modes

b) vertical and horizontal

c) x axis and y axis

d) ground and full line supply

Answer: b

Explanation: In a Dual Trace Oscilloscope, X-Y mode means the oscilloscope operates from the first channel A as a vertical signal and from the second channel B as a horizontal signal.

8. Electronic switch is controlled by ____________

a) D flip-flop

b) SR flip-flop

c) T flip-flop

d) JK flip-flop

Answer: c

Explanation: In the Dual Trace Oscilloscope, an electronic switch is controlled by making use of a T flip-flop which is also known as a toggle flip-flop. Switching occurs during the beginning of a new sweep.

9. Which technique of a Dual Trace Oscilloscope maintains the phase between the signals?

a) Analog mode

b) Mixed mode

c) Chop mode

d) Alternate mode

Answer: d

Explanation: In a Dual Trace Oscilloscope, the alternate mode of operation enables to maintain the correct phase relationship between the signals from the channels A and B.

This set of Electrical Measurements Interview Questions and Answers for Experienced people focuses on “Electronic Switch & Dual Beam Oscilloscope”.

1. Electronic switch is used in a dual trace oscilloscope.

a) True

b) False

Answer: a

Explanation: By using a single CRT gun, two signals can be displayed on the screen simultaneously by means of an electronic switch.

2. Signals are applied to ___________

a) input

b) gain control stage

c) output

d) capacitor

Answer: b

Explanation: In a dual trace oscilloscope, the signals are applied to the gain control as well as the gate control stage.

3. What adjusts the amplitudes of the signals A and B?

a) L 1 and L 2

b) C 1 and C 2

c) R 1 and R 2

d) Oscillator

Answer: c

Explanation: In a dual trace oscilloscope, the resistances R 1 and R 2 are used for adjusting the magnitudes of the amplitudes of the signals A and B of the two channels A and B.

4. What is the role of a square wave generator?

a) generates square waves

b) generates triangular waves

c) generates saw-tooth signals

d) generates alternate inputs

Answer: d

Explanation: A square wave generator in a dual trace oscilloscope provides alternate biasing signals to the switches Q 3 and Q 4 .

5. How many switches work at a time?

a) 1

b) 3

c) 2

d) 5

Answer: a

Explanation: In a dual trace oscilloscope, the square wave generator provides alternate bias signals to the switches Q 3 and Q 4 . When Q 3 is conducting, Q 4 remains off while Q 3 is off, Q 4 conducts.

6. Square wave generator doesn’t reproduce the signals on the screen.

a) True

b) False

Answer: b

Explanation: In a dual trace oscilloscope, the square wave generator reproduces two signals on the screen. When the switching frequency of the square wave generator is higher than that of the individual signals, the bits of each signal are provided alternately to the vertical inputs.

7. A multitrace oscilloscope makes use of __________

a) three traces

b) two traces

c) many traces

d) one trace

Answer: c

Explanation: In a multitrace oscilloscope, a signle electron beam is used. It makes use of several traces by switching the Y deflection plates from one input signal to the other.

8. A dual beam oscilloscope has __________

a) 2 beams

b) 4 beams

c) 6 beams

d) 8 beams

Answer: a

Explanation: In a dual beam oscilloscope, the beams are deflected horizontally by means of a common set of plates. Each electron beam has its own set of vertical deflection plates.

9. Two voltages can be studied simultaneously by making use of __________

a) single electron gun

b) two electron guns

c) four electron guns

d) six electron guns

Answer: b

Explanation: On the Cathode Ray Oscilloscope, two voltages can be studied simultaneously by means of two electron guns generating two separate beams through a special cathode ray tube.

10. A dual beam oscilloscope has __________

a) 8 vertical deflection plates

b) 6 vertical deflection plates

c) 2 vertical deflection plates

d) 4 vertical deflection plates

Answer: c

Explanation: In a dual beam oscilloscope, there are two vertical deflection plates and two separate channels. Each channel consists of a preamplifier and an attenuator stage.

11. Sweep generator is triggered by __________

a) oscillator

b) flip-flop

c) transformer

d) channel A or B

Answer: d

Explanation: In a dual beam oscilloscope, the sweep generator is triggered internally by means of either the channel A signal or the channel B signal.

12. A sweep generator can be triggered by an external switch as well.

a) True

b) False

Answer: a

Explanation: In a dual beam oscilloscope, the sweep generator can be triggered by means of an external switch or a line frequency signal. This is done through means of a trigger selector switch.

13. A dual beam oscilloscope has same sweep rates for different channels.

a) True

b) False

Answer: b

Explanation: In a dual beam oscilloscope, the sweep rates are different for different channels. As a result the size and weight of the oscilloscope is increased. A dual beam oscilloscope has a separate time-base for different channels.

14. In a multi-beam oscilloscope __________

a) single beam is produced

b) three beams are produced

c) many beams are produced

d) two beams are produced

Answer: c

Explanation: In a multi-beam oscilloscope, several beams are produced from a single tube. Each system is made up of a separate set of vertical deflection plates and a common time base system.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Digital Storage Oscilloscope”.

1. What is the main advantage of using a digital storage oscilloscope?

a) uses digital storage

b) uses analog storage

c) uses mixed mode storage

d) uses disc storage

Answer: a

Explanation: The disadvantage of a analog storage oscilloscope is overcome in a digital storage oscilloscope. The unreliable storage method in a analog storage oscilloscope is overcome in a digital storage oscilloscope. The digital storage oscilloscope makes use of digital storage for the memory.

2. The memory of a digital storage oscilloscope is limited.

a) True

b) False

Answer: b

Explanation: In a digital storage oscilloscope, the memory can store data as long as required without degradation. It makes use of complex signal processing techniques through high speed digital signal processing.

3. The waveform is stored in _________

a) compressed form

b) analog form

c) digital form

d) mixed form

Answer: c

Explanation: The waveform to be studied is stored in digital form in the digital storage oscilloscope. It is digitized and stored in a digital memory.

4. Which oscilloscope is used in a digital storage oscilloscope?

a) multi trace

b) dual trace

c) modern

d) conventional

Answer: d

Explanation: A digital storage oscilloscope makes use of a conventional cathode ray tube. As a result, the cost is reduced.

5. Power requirement is _________

a) low

b) high

c) medium

d) zero

Answer: a

Explanation: In a digital storage oscilloscope, the power required by the memory is less. It can be supplied through the means of a small battery.

6. The stored image can be displayed _________

a) for a limited time

b) for infinite time

c) for zero time

d) for an intermediate time

Answer: b

Explanation: In a digital storage oscilloscope, the stored image can be displayed for a long time as long as the power supply to the digital memory is kept intact without any kind of disruption.

7. The analog signal is digitized using _________

a) D/A converter

b) Oscillator

c) A/D converter

d) Rectifier

Answer: c

Explanation: In a digital storage oscilloscope, the analog signal is digitized by making use of an analog to digital converter. After digitizing the waveform is loaded into a computer and can be analyzed.

8. How is the data displayed?

a) through a screen

b) through a computer

c) through an FPGA

d) through a microprocessor

Answer: d

Explanation: In a digital storage oscilloscope, the data is displayed by passing it through a microprocessor which processes the data and displays the waveform onto a screen.

9. A digital storage oscilloscope has _________

a) 3 modes

b) 2 modes

c) 4 modes

d) 5 modes

Answer: a

Explanation: In a digital storage oscilloscope, there are three modes of operation. They are as follows:

• Store

• Roll

• Hold or Save.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “CRO Measurements”.

1. By making use of a CRO _________

a) many characteristics of a signal can be measured

b) only a few characteristics of a signal can be measured

c) no characteristics of a signal can be measured

d) signal can only be displayed

Answer: a

Explanation: Through the means of a Cathode Ray Oscilloscope, most of the characteristics of an input signal can be measured. Properties of a signal can be studied as well.

2. How is the waveform adjusted?

a) by adjusting the voltage

b) through shift controls

c) by reducing the current

d) by means of a galvanometer

Answer: b

Explanation: In a Cathode Ray Oscilloscope, the waveform can be adjusted by means of shift controls. As a result, the measurement of divisions corresponding to the amplitude becomes easy.

3. How is error in measurement reduced?

a) using r.m.s value

b) using absolute value

c) using peak to peak value

d) using a voltmeter

Answer: c

Explanation: In a Cathode Ray Oscilloscope, the error in measurement is reduced by making use of the peak to peak value.

4. Peak to peak voltage is given by ________

a) V p-p = number of units × \

b) V p-p = \

c) V p-p = number of units × volts

d) V p-p = number of units × \

Answer: d

Explanation: In a Cathode Ray Oscilloscope, the peak to peak voltage is given by the relation,

V p-p = number of units × \

where, V p-p is the peak to peak voltage.

5. The amplitude of voltage is given by which of the following relation?

a) V m = \

V m = \

V m = 2 × V p-p

d) V m = 4 × V p-p

Answer: a

Explanation: In a Cathode Ray Oscilloscope, the amplitude of voltage is given by the relation,

V m = \(\frac{V_{p-p}}{2}\)

where, V p-p is the peak to peak voltage

Vm is the amplitude.

6. The R.M.S voltage is given by which of the following relation?

a) V rms = \

V rms = \

V rms = \(\frac{V_m}{\sqrt{8}}\)

Answer: b

Explanation: The r.m.s value of voltage is given by the relation,

V rms = \(\frac{V_m}{\sqrt{2}}\)

where, V rms is the r.m.s value of voltage

V m is the amplitude of the voltage.

7. CRO is voltage measuring device.

a) True

b) False

Answer: a

Explanation: Generally, a CRO is a voltage measuring device. Current is measured by passing current through a known value of resistance. Voltage across the resistance is displayed on the screen of the CRO.

8. Period of a waveform is obtained by which of the following relation?

a) T = number of divisions occupied by 1 cycle×

b) T = number of divisions occupied by 1 cycle×( 1 ⁄ division )

c) T = number of divisions occupied by 1 cycle×( time ⁄ division )

d) T = number of divisions occupied by 1 cycle

Answer: c

Explanation: The time period of a waveform is obtained by using the relation,

T=number of divisions occupied by 1 cycle×( time ⁄ division ).

9. How is frequency related to time period?

a) square proportional

b) not related

c) directly proportional

d) inversely proportional

Answer: c

Explanation: Frequency is inversely proportional to the time period of any given signal.

f = 1 ⁄ t

where, f is the frequency

T is the time period.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Acquisition Methods”.

1. How many types of acquisition methods are there in a digital storage oscilloscope?

a) 3

b) 6

c) 2

d) 4

Answer: a

Explanation: In a digital storage oscilloscope, there are three methods in which a digital signal can be captured and stored. They are as follows:

i) Real time sampling

ii) Random repetitive sampling

iii) Sequential repetitive sampling.

2. An oscilloscope with 20 to 50 GHz needs a slow speed.

a) True

b) False

Answer: b

Explanation: For an oscilloscope with a bandwidth of 20 to 50 GHz, a high speed network setting is required. This is achieved through the means of the sequential repetitive sampling.

3. In which method of acquisition, pretrigger event is lost?

a) Real time sampling

b) Random repetitive sampling

c) Sequential repetitive sampling

d) Analog Sampling

Answer: c

Explanation: In Sequential repetitive sampling, pretrigger information cannot be captured. And the pretrigger view is lost. It can be used only in microwave digital oscilloscope as a result.

4. In Sequential repetitive sampling how many samples are captured?

a) ten

b) five

c) two

d) one

Answer: d

Explanation: In Sequential repetitive sampling, one sample is captured at a controlled time delay of t ds . After each point is captured, the delay is increased by a small amount t se/sub>.

5. In Real time sampling, bandwidth is limited.

a) True

b) False

Answer: a

Explanation: In Real time sampling, the bandwidth is only ¼ of the actual value. As a result to increase the bandwidth, fast sample rate digitizers and memory are required which are very expensive.

6. Nyquist criteria states that ______________

a) F s = f max /2

b) F s ≥ 2f max

c) F s = f max

d) F s = 2

Answer: b

Explanation: Nyquist criteria states that the sampling rate is twice the maximum frequency. It is given by the relation.

F s ≥2f max

where, F s is the sampling rate

f max is the maximum frequency.

7. What plays an important role in Real time sampling?

a) small memory and fast sampling

b) large memory and slow sampling

c) large memory and fast sampling

d) small memory and slow sampling

Answer: c

Explanation: In Real time sampling, a higher sampling rate is required to capture long time interval signal capturing. Large memory and a fast sampling rate are the characteristic feature of real time sampling.

8. A single trigger event can capture how many samples in Real time sampling?

a) 1

b) n m /2

c) 2n m

d) n m

Answer: d

Explanation: In Real time sampling, a trigger event can be used to capture as much as n m samples. The waveform is then displayed on a digital storage oscilloscope.

9. In Real time sampling what is the 3 dB bandwidth?

a) f s /4

b) f s /8

c) 2f s

d) f s

Answer: a

Explanation: In Real time sampling, the 3 dB bandwidth is set to f s /4 with an overshoot of 5%. Here f s is the sampling frequency.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Applications of CRO”.

1. CRO is used for measurement of __________

a) AC as well as DC current

b) AC current only

c) DC current only

d) AC power only

Answer: a

Explanation: A Cathode Ray Oscilloscope is used for the measurement of AC as well as DC current. It is used for the calculation peak to peak voltage, r.m.s value, duty cycle, etc.

2. CRO is used in a radar for __________

a) studying the pattern of flights

b) visualizing a target

c) measuring voltage

d) determining the distance between source and destination

Answer: b

Explanation: A Cathode Ray Oscilloscope is used in a radar for visualizing a target such as an aeroplane, ship, etc.

3. In radio applications, CRO is used for measuring __________

a) audio frequency range

b) a narrow range of frequencies

c) a wide range of frequencies

d) radio frequency range

Answer: c

Explanation: By making use of a Cathode Ray Oscilloscope, a wide range of frequencies can be measured. The radio frequency, audio frequency and intermediate frequency signals can be measured by making use of a CRO.

4. In medical applications CRO can be used for __________

a) measuring the heart beats

b) monitoring the brain

c) improving the nervous system functioning

d) displaying cardiograms

Answer: d

Explanation: A Cathode Ray Oscilloscope, can be used in medical applications for displaying cardiograms. Cardiograms are used for diagnosing the condition of heart of a patient. Electromyograms are used for studying the condition of a patient’s muscle.

5. CRO is used for many purposes in the industry.

a) True

b) False

Answer: a

Explanation: A Cathode Ray Oscilloscope, is used for observing B-H curves, P-V diagrams, etc. A CRO is also used in various transducers for the measurement of strain, pressure and temperature.

6. A CRO can’t be used in transmission lines.

a) True

b) False

Answer: b

Explanation: A Cathode Ray Oscilloscope, is used in transmission lines for the measurement of modulation characteristics. It is also used for detecting the standing waves in a transmission line.

7. Curve tracers use CRO in __________

a) diodes

b) passive devices

c) active devices

d) op amps

Answer: c

Explanation: Curve tracers in a Cathode Ray Oscilloscope are used for testing active devices such as vacuum tubes, transistors and integrated circuits.

8. A CRO is used in check __________

a) op amps

b) resistors

c) voltage

d) capacitance, inductance and diodes

Answer: d

Explanation: A Cathode Ray Oscilloscope is used for checking diodes. It is also used in the measurement of inductances and capacitances. A CRO can also be used for detecting the faults in a circuit.

9. A CRO is used in labs for __________

a) frequency measurement

b) voltage measurement

c) current measurement

d) resistance measurement

Answer: a

Explanation: A Cathode Ray Oscilloscope is used in the laboratory for the measurement of frequency, phase and period of a signal. Periodic as well as non-periodic relationships of signals can also be studied.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on ” Advanced Problems on CRT and CRO”.

1. A recorder is a device ________

a) An indicating instrument which displays a time-varying signal

b) Whose function is to record the value of the quantity as it is being measured

c) Which records electrical and non-electrical quantities or relates two signals to each other as a function of time

d) Which records the value of the quantity measured as well as the electrical and non-electrical quantities as a function of time

Answer: d

Explanation: A recorder is a device which record the value of quantity as it is being measured. It records electrical and non-electrical quantities or relates two signals to each other as a function of time.

2. In a dual slop integrating type digital voltmeter, the firs integrating is carried out for 10 periods of the supply frequency of 50 Hz. If the reference voltage used is 2 V, the total conversion time for an input of 1 V is?

a) 0.01 s

b) 0.05 s

c) 0.1 s

d) 1 s

Answer: c

Explanation: In a dual slope integrating digital voltmeter,

\) V in = V ref

Where, t 1 = first integration time = 10 × \(\frac{1}{50}\) = 0.25

But V in = 1 V and V ref = 2 V

∴ t 2 = \(\frac{V_in t_1}{V_{ref}}\) = 0.1 s.

3. The source of emission of electrons in a circuit is ______________

a) p-n junction diode

b) a barium and strontium oxide coated cathode

c) accelerating anode

d) post-accelerating anode

Answer: d

Explanation: The source of focused and the accelerated electron beam is the electron gun. The electron gun which emits electrons forms them into a beam consisting of a heater, a cathode, a grid, a pre-accelerating anode, a focusing anode and an accelerating anode.

4. A CRO can display _________

a) AC signals

b) DC signals

c) Both AC and DC signals

d) Time-invariant signals

Answer: c

Explanation: A Cathode Ray Oscilloscope cannot measure or display Time invariant signals. However, it can measure both AC and DC signals.

5. X and Y plates of a CRO are connected to unequal voltages of equal frequency with phase shift of 90°. The Lissajous figure on the screen will be?

a) Circle

b) Straight line

c) Ellipse

d) Figure of eight

Answer: c

Explanation: The pattern observed on the CRT, when two sinusoidal signals are applied to the X-X and Y-Y plates of the CRT are known as Lissajous pattern.

sin φ = \(\frac{y_1}{y_2} = \frac{X_1}{X_2}\)

Here, the voltages are unequal and frequencies are equal with a phase shift of 90°. Therefore the Lissajous figure on the screen will be an ellipse.

6. To the Y input of a CRO, we feed a signal defined by 10sin100t, to the X-input, we feed signal 10cos100t. The gain for both X channel and Y channel is the same, the screen will show?

a) Sinusoidal signal

b) A straight line

c) An ellipse

d) A circle

Answer: d

Explanation: The pattern observed on the CRT, when two sinusoidal signals are applied to the X-X and Y-Y plates of the CRT are known as Lissajous pattern.

sin φ = \(\frac{y_1}{y_2} = \frac{X_1}{X_2}\)

∴ Screen will show a circle.

7. A CRO uses _________

a) Electromagnetic focusing

b) Electrostatic focusing

c) Both Electrostatic and Electromagnetic focusing

d) No focusing technique

Answer: b

Explanation: A Cathode Ray Oscilloscope always using the focusing technique for its operation. Electromagnetic focusing is used by the Cathode Ray Tube. However, the Cathode Ray Oscilloscope employs Electrostatic focusing.

8. A CRO probe has an impedance of 500 kΩ in parallel with a capacitance of 10 pF. The probe is used to measure the voltage between P and Q as shown in the figure. The measured voltage will be?

electrical-measurements-questions-answers-advanced-problems-crt-cro-q8

a) 3.53 V

b) 3.47 V

c) 5.54 V

d) 7.00 V

Answer: b

Explanation: X C = \(\frac{1}{jCω} = \frac{-j}{2 × 3.14 × 100 × 10^3 × 10 × 10^{-12}}\)

Applying KCL at node,

\(\frac{V_a-10}{100} + \frac{V_a}{100} + \frac{V_a}{500} + \frac{V_a}{-j159}\)

∴ V a = 4.37∠-15.95°.

9. The two inputs of a CRO are fed with two stationary periodic signals. The figure changes from ellipse to circle and back to ellipse with its major axis changing orientation slowly and repeatedly. The following inference can be made from this.

a) The signals are not sinusoidal in nature

b) The amplitudes of the signals are very close but not equal

c) The signals are sinusoidal with their frequencies very close but not equal

d) There is a constant but small phase difference between the signals

Answer: d

Explanation: X = A sinωt

Y = A sin

Phase difference = ∅t

For ellipse, A 1 ≠ A 2

For circle, A 1 = A 2

Hence, there is a constant but small difference between the signals.

10. An oscilloscope indicates ___________

a) The peak to peak value of the voltage

b) DC value of the voltage

c) Rms value

d) Average value

Answer: a

Explanation: The oscilloscope can measure not only the DC value but also the AC value. The RMS value cannot be measured by the oscilloscope. Similarly, the average value is also not measured. Therefore the peak to peak value of the voltage is measured.

This set of Electrical Measurements test focuses on “Objectives of Data Acquisition System”.

1. What is a data acquisition system?

a) system used for data processing, conversion and transmission

b) accepts data as an input

c) removes noise

d) boosts the signal

Answer: a

Explanation: A data acquisition system basically is used for the processing of data. It is also used for data conversion, data transmission and storage of data.

2. A typical data acquisition system consists of __________

a) op amps

b) sensors

c) rectifiers

d) transistors

Answer: b

Explanation: Data acquisition system consists of sensors. It also consists of suitable signal conditioners, data converters, data processors, data handlers, storage and display systems.

3. The data acquisition system implies input data collection __________

a) in mixed signal form

b) in analog form

c) in digital form

d) in the form of binary codes

Answer: c

Explanation: In a data acquisition system, input data is collected in the form of digital signals. The digital signals are collected in a fast, economic, reliable and accurate manner.

4. Data measurement systems are __________

a) not flexible

b) rigid

c) less flexible

d) more flexible

Answer: d

Explanation: The data acquisition system are more flexible and easily programmable nowadays as a result of development in the automation field.

5. Modern electronic instrumentation system is not complex.

a) True

b) False

Answer: a

Explanation: Inspite of significant development in the field of electronic instrumentation systems with the advent of op amps, data converters, multiplexers, microprocessors and microcontrollers, they are not complicated.

6. The data acquisition system can have any speed.

a) True

b) False

Answer: b

Explanation: A data acquisition system must acquire the required speed at the correct time. It must also use the data efficiently to detect the status of the plant.

7. A data acquisition system provides __________

a) partial communication

b) ineffective communication

c) effective communication

d) complete communication

Answer: c

Explanation: The data acquisition system must be able to provide proper human communication to minimize the unit availability and maximize the unit output at a lower cost.

8. Data acquisition system can be used in __________

a) 10 ways

b) 8 ways

c) 4 ways

d) 2 ways

Answer: d

Explanation: A data acquisition system can be used to measure and record the signals in two ways. In the first method the signal can be directly measured from electrical quantities such as a.c., d.c. voltage or current. In the second case the signal originates from transducers such as pressure transducer, thermocouple, etc.

9. Data acquisition system is mainly classified into __________

a) 2 types

b) 4 types

c) 6 types

d) 8 types

Answer: a

Explanation: A data acquisition system is basically classified into two main types. They are analog and digital. While the analog data system deals with signals having analog input signals the digital data system consists of input signals in digital form.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Analog Data Acquisition System”.

1. Transducer is used to convert a _________

a) physical quantity into an electrical signal

b) electrical signal into a physical quantity

c) physical quantity into a mechanical quantity

d) physical quantity into a chemical quantity

Answer: a

Explanation: Transducer forms one of the most important components of an analog data acquisition system. It converts a physical quantity into an electrical signal. Strain gauge, thermocouples, piezoelectric devices are the most widely used transducers.

2. Transducer produces a _________

a) proportional current

b) proportional voltage

c) proportional resistance

d) proportional power

Answer: b

Explanation: A transducer generates a voltage proportional to the physical quantity that is being measured. The voltage output from a transducer forms the input to a data acquisition system.

3. Sensors produce frequency which is counted by _________

a) a chemical counter

b) a mechanical counter

c) an electronic counter

d) a basic counter

Answer: c

Explanation: Transducers consist of special sensors used to produce frequency that can be counted by means of an electronic counter. This frequency forms an integral part of the frequency measured.

4. Signal conditioner is used for _________

a) attenuating the voltage

b) maintaining a constant voltage

c) keeping the voltage zero

d) boosting the voltage

Answer: d

Explanation: Signal conditioner is an important part of an analog data acquisition system. A signal conditioner converts the output voltage to the desired form which is accepted by the next stage.

5. A multiplexer is used for _________

a) accepting multiple inputs

b) accepting single input

c) accepting multiple outputs

d) accepting single output

Answer: a

Explanation: A multiplexer forms an important constituent of an analog data acquisition system. It takes multiple analog inputs. By making use of a multiplexer many quantities can be transmitted.

6. Multiplexers are used when the distance between source and destination is less.

a) True

b) False

Answer: b

Explanation: Generally multiplexers are made use of only when the distance of separation between the transmitting end and the receiving end is more.

7. Output signal is captured using _________

a) CRO

b) plotter

c) recorder

d) voltmeter

Answer: c

Explanation: In an analog data acquisition system, the output signal is recorded by means of an analog recorder. It includes the likes of strip chart recorder, magnetic tape recorder, etc.

8. Analog computers have __________

a) zero cost

b) intermediate cost

c) more cost

d) less cost

Answer: d

Explanation: The accuracy of digital computers is more than that of analog computers. Analog computers are widely used when compared to digital computers because of their less cost.

9. Before and after each test, calibration is carried out.

a) True

b) False

Answer: a

Explanation: In an analog data acquisition system, calibration carried out before each test is known as pre-calibration. The test carried out after calibration is known as post-calibration.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Digital Data Acquisition System”.

1. A/D converter is used for __________

a) converting analog to digital

b) converting digital to analog

c) converting digital to mixed signal mode

d) converting analog to mixed signal mode

Answer: a

Explanation: In a digital data acquisition system, an A/D converter is used for the purpose of converting analog signals to digital.

2. Output of A/D converter is _________

a) given to an analog display

b) given to a digital display

c) given to a CRO

d) given to a voltmeter

Answer: b

Explanation: Output from the analog to digital converter is given to a digital display device or to a digital recorder for the purpose of displaying or recording.

3. What are auxiliary equipments?

a) equipment

b) guard rings

c) devices

d) voltage source

Answer: c

Explanation: Auxiliary equipments are basically devices used for system programming functions and digital data processing applications.

4. What is the main function of auxiliary equipment?

a) unit step response

b) ramp response

c) non-linear response

d) linear response

Answer: d

Explanation: The typical functions of auxiliary equipments include linearization and limit compression for the input signals. Individual instruments or a digital computer is used to perform these functions.

5. What is a digital recorder?

a) records digital data

b) records analog data

c) does not record data

d) records both analog and digital data

Answer: a

Explanation: A digital recorder is used for the purpose of recording the digital data. Punched cards, magnetic tape recorders, type written pages, etc make use of digital recorders.

6. Data acquisition systems are not widely used.

a) True

b) False

Answer: b

Explanation: In digital recorders, data acquisition systems are used widely in industries, space applications, medical and telephony.

7. For lower accuracies _________

a) digital acquisition system is used

b) both digital and analog acquisition systems are used

c) analog acquisition system is used

d) mechanical data acquisition system is used

Answer: c

Explanation: When low values of accuracy is required, analog data acquisition system is used. This includes a wide frequency bandwidth as well.

8. Digital acquisition systems are used when _________

a) bandwidth is high

b) bandwidth is medium

c) bandwidth is zero

d) bandwidth is low

Answer: d

Explanation: When the bandwidth required is low, usually digital acquisition systems are made use of. For higher accuracy and lower per channel cost, digital data acquisition systems are used.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Single Channel Data Acquisition System”.

1. A single channel data system consists of a signal conditioner, A/D converter and a buffer.

a) True

b) False

Answer: a

Explanation: The single channel data acquisition system consists of a signal conditioner, an analog to digital converter and a buffer circuitry.

2. A/D conversion rate is __________

a) variable

b) predefined

c) zero

d) constant

Answer: b

Explanation: In a single channel data acquisition system, the conversion rate of an analog to digital converter is predefined. A/D converter performs the conversions at a pre-determined rate.

3. The buffer output is ________

a) analog

b) zero

c) digital

d) mixed mode

Answer: c

Explanation: In a single channel data acquisition system, the output of the buffer circuitry is digital in nature. It is stored in a digital computer or a storage device or sometimes even a printer.

4. Which is the best example of a single channel data acquisition system?

a) CPM

b) BPM

c) APM

d) DPM

Answer: d

Explanation: A digital panel meter usually abbreviated as DPM is the best example of a single channel data acquisition system.

5. Digital outputs are obtained from _____________

a) A/D converter

b) D/A converter

c) Oscilloscope

d) Voltage source

Answer: a

Explanation: An analog to digital converter provides digital outputs. The A/D converters are designed in such a way that they accept external commands in order to convert and hold the operations.

6. A/D converters can’t be used for low frequency ranges.

a) True

b) False

Answer: b

Explanation: Analog to digital converters based on the dual slope techniques are usually used in the conversion of low frequency data coming from the thermocouples.

7. Which technique is most widely used in the single channel data acquisition system?

a) Counter type approximation

b) Flash approximation

c) Successive approximation

d) Delta Sigma approximation

Answer: c

Explanation: The successive approximation technique is most widely used in a single channel data acquisition system. This is due to the fact that it has a high value of resolution and high speed.

8. What is pre-amplification?

a) reducing the magnitude of a signal

b) making the magnitude of a signal zero

c) reducing the noise

d) boosting the signal

Answer: d

Explanation: To match the input needs, the level of an input signal is boosted. This is done as the magnitude of the input signal is sometimes very low. This is known as pre-amplification.

9. How can the input be isolated from the system?

a) using optocouplers

b) using op-amps

c) using a capacitor

d) using rectifiers

Answer: a

Explanation: By making use of an optocoupler, we can isolate the input signal from the system. Before processing the data, pre-amplifiers are fitted with active filters so as to eliminate the noise and boost the signal.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Multiple Channel Data Acquisition System”.

1. Multichannel data acquisition system has __________

a) multiple channels

b) single channel

c) two channels

d) five channels

Answer: a

Explanation: A multichannel data acquisition system has multiple channels. The various subsystems can be shared in terms of time by more than two or more input sources.

2. How many types of multiplexed system exist?

a) 2

b) 3

c) 5

d) 10

Answer: b

Explanation: In general there are three types of multiplexed systems. They are as follows:

• Multichannel Analog Multiplexed System

• Multiplexing Output of Sample/Hold Circuits

• Multiplexing after A/D Conversion.

3. Multichannel Analog Multiplexed System is __________

a) very fast

b) fast

c) slow

d) moderate

Answer: c

Explanation: The Multichannel Analog Multiplexed System is one type of multiplexed system. It is comparatively slow. As it shares more than one channel, the cost is less.

4. Multichannel Analog Multiplexed System utilises time __________

a) using a transformer

b) using a capacitor

c) using a flip-flop

d) using a mux

Answer: d

Explanation: Multichannel Analog Multiplexed System is one type of multiplexed system. It makes use of a multiplexer to utilise the time. The previous data stored in the sample and hold circuit gets converted into digital form.

5. In a Multichannel Analog Multiplexed System __________

a) A/D converter is used

b) D/A converter is used

c) Sigma delta converter is used

d) Modulator is used

Answer: a

Explanation: In a Multichannel Analog Multiplexed System, individual analog signals are applied directly. The signals are amplified and conditioned. An A/D converter then converts the signals into digital form.

6. In a Multichannel Analog Multiplexed System, data stored in sample and hold circuit is converted into analog form.

a) True

b) False

Answer: b

Explanation: The Multichannel Analog Multiplexed System, converts the previous data stored in the sample and hold circuit into digital form. Upon data collection, mode of the sample and hold circuit is changed to hold mode.

7. Many channels can be monitored at the same time by __________

a) Demultiplexing

b) A/D conversion

c) Multiplexing

d) D/A conversion

Answer: c

Explanation: Monitoring of a number of channels can be done at the same time by multiplexing the outputs of the sample and hold circuit.

8. Multiplexing after A/D conversion involves _____________

a) noisy data

b) mixed signal data

c) analog data

d) digital data

Answer: d

Explanation: Multiplexing after A/D conversion is also known as fast data acquisition. Digital data performs the logical operation and depending on the relative speed, the scan rate can be increased or decreased.

9. Multiplexing after A/D conversion provides immunity to noise.

a) True

b) False

Answer: a

Explanation: Multiplexing after A/D conversion involves the transformation of analog signal into digital form. Data transmission provides, immunity from line frequency and other interferences.

This set of Electrical Measurements Multiple Choice Questions & Answers focuses on “PC based Data Acquisition System”.

1. What led to the development of PC based transducers?

a) low cost

b) medium cost

c) high cost

d) zero cost

Answer: a

Explanation: Easy availability, low cost and large scale usage of Personal Computers have led to the development of interfaces between PC and the transducer outputs.

2. ADD ON card is used for _______

a) to reduce noise

b) communication

c) to boost the magnitude

d) to measure voltage

Answer: b

Explanation: PC based data acquisition system makes use of an ADD ON card for the purpose of communication and analysis of multiple measurement data.

3. PC based data acquisition system displays system parameters ____________

a) once in a while

b) intermittently

c) continuously

d) only at specific intervals

Answer: c

Explanation: A PC based data acquisition system displays the parameters of a system in a continuous manner. As a result all the parameters are monitored instantaneously and conveniently.

4. What are MIMIC displays?

a) man-material interface

b) man-made interface

c) man-machine interface

d) man-machine interface

Answer: d

Explanation: In a PC based data acquisition system, MIMIC displays are used for displaying the data measured at any part of a system on the screen. MIMIC stands for man-machine interface.

5. System parameters are distinguished by physical attributes.

a) True

b) False

Answer: a

Explanation: In a PC based data acquisition system, physical attributes such as blink, underline, inverse video, etc are used to display the system parameters.

6. Personal computer does not contain additional hardware in a PC based data acquisition system.

a) True

b) False

Answer: b

Explanation: In a PC based data acquisition system, the personal computer consists of additional hardware for data analysis and data acquisition. These are integrated through the means of software.

7. Data analysis hardware is used for _______

a) making the process independent

b) slowing the process

c) fastening the process

d) making the process constant

Answer: c

Explanation: In a PC based data acquisition system, data analysis software is used for the purpose of mainly fastening the computations and analysis in case of DSP applications.

8. Input signal range in a PC based data acquisition system is _______

a) 0.10 mV to 1 V

b) 1 mV to 100 V

c) 5 mV to 5 V

d) 10 mV to 10 V

Answer: d

Explanation: In a PC based data acquisition system, the input signal in the range of 10 mV to 10 V is amplified by means of a digital programmable gain amplifier to a particular level.

9. Amplified input signal is digitised through ________

a) A/D converters

b) D/A converters

c) Rectifiers

d) Sigma delta modulators

Answer: a

Explanation: In a PC based data acquisition system, the amplified input signal is converted to digital form by making use of high speed A/D converters. These are interfaced to the PC bus.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Process Control System”.

1. What is the main objective of process control?

a) to control physical parameters

b) to control mechanical parameters

c) to control optical parameters

d) to control electrical parameters

Answer: a

Explanation: A process control is mainly used in order to control the physical parameters including temperature, pressure, flow rate, force, etc.

2. What is a process control system?

a) system to keep the parameters at zero value

b) system to maintain the parameters constant

c) system to keep the parameters at highest value

d) system to check the voltage

Answer: b

Explanation: A process control system is generally used to maintain the parameters such as temperature, pressure, flow rate, force, etc constant in a system.

3. Physical parameters change due to ________

a) voltage

b) current

c) internal and external disturbances

d) power

Answer: c

Explanation: The physical parameters such as temperature, pressure, flow rate, force, etc in a process control system are affected due to both internal and external disturbances. As a result, constant corrective action is required to keep them at a constant value.

4. A process control system consists of ________

a) 10 elements

b) 6 elements

c) 2 elements

d) 4 elements

Answer: d

Explanation: A typical process control system consists of 4 elements. They are as follows:

• Process

• Measurement

• Controller

• Control element

The figure shown below illustrates the process control loop. electrical-measurements-questions-answers-process-control-system-q4

5. For proper feedback in a process control element, it is required to ________

a) measure P

b) measure set point

c) measure error

d) measure comparator

Answer: a

Explanation: In a process control element, proper feedback is obtained by measuring the parameter P. Electrical input is required in most of the process controllers as they are electronic in nature.

6. Feedback path element measure only input parameters.

a) True

b) False

Answer: b

Explanation: In a process control system, feedback path measures the output parameters. It also produces a proportional analog signal in electric form.

7. A transducer converts ________

a) mechanical quantity to electrical form

b) electrical quantity to physical form

c) physical quantity to electrical form

d) chemical quantity to physical form

Answer: c

Explanation: A transducer basically converts a physical quantity such as temperature, pressure, force, flow rate, etc into electrical form such as voltage and current.

8. An electrical transducer consists of ________

a) 4 parts

b) 6 parts

c) 8 parts

d) 2 parts

Answer: d

Explanation: An electrical transducer basically consists of 2 parts. The first is known as the sensing element while the second is known as the transduction element. The first element is also known as a sensor.

9. A transducer is part of a large circuit and produces the required output.

a) True

b) False

Answer: a

Explanation: A transducer basically converts a physical quantity such as temperature, pressure, force, flow rate, etc into an electrical forms such as voltage and current. A transducer is part of a large circuit. It produces the required output by operating along with several other elements.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Transducers”.

1. How many types of transducers are there?

a) 2

b) 4

c) 6

d) 8

Answer: a

Explanation: There are basically two types of transducers. They are as follows:

i) Mechanical

ii) Electrical.

2. Mechanical transducers sense __________

a) electrical changes

b) physical changes

c) chemical changes

d) biological changes

Answer: b

Explanation: A mechanical transducer senses the changes in a system’s physical condition and gives an output. When a bimetallic strip is subjected to changes in temperature, the output is the displacement of the strip mechanically.

3. Mechanical transducers generate ________

a) electrical signals

b) chemical signals

c) physical signals

d) biological signals

Answer: c

Explanation: Mechanical transducers in general portray physical or mechanical signals at the output in response to any physical changes in a system.

4. Electrical transducers generate ________

a) biological signals

b) chemical signals

c) physical signals

d) electrical signals

Answer: d

Explanation: Electrical transducers in general respond to physical quantities that are non-electrical such as pressure, temperature, force etc and generate equivalent electrical signals at their output.

5. Electrical signals are easy to amplify.

a) True

b) False

Answer: a

Explanation: Electrical signals are easier to either amplify or attenuate. By making use of static devices such as FGK, electrical signals can be brought to a suitable level.

6. The power needs of electrical transducers is ________

a) maximum

b) minimum

c) zero

d) infinite

Answer: b

Explanation: Electrical transducers have very minimum power requirements. Electrical transducer based systems are controlled with a small amount of power.

7. Electrical transducers are ________

a) small and non-portable

b) large and non-portable

c) small and compact

d) large and portable

Answer: c

Explanation: Electrical systems have integrated circuits that are small and compact. They can be easily ported as well.

8. Mechanical transducers cause ________

a) power loss

b) hysteresis loss

c) eddy current loss

d) frictional loss

Answer: d

Explanation: Mechanical transducer based systems are affected by the frictional loss of the rotating parts. In electrical transducers, there is no wear and tear due to non moving parts.

9. Electrical transducers are costly.

a) True

b) False

Answer: a

Explanation: Electrical transducers are very expensive in nature. The ageing and drift of the various electronic components act as an overhead in the use of electrical transducers on a large scale.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Classification of Transducers”.

1. Active transducers are classified into ____________

a) 4 types

b) 2 types

c) 6 types

d) 8 types

Answer: a

Explanation: Active transducers can be subdivided into four types. They are as follows:

• Photovoltaic

• Thermoelectric

• Piezoelectric

• Electromagnetic.

2. Active transducers develops ______________

a) mechanical parameter

b) electrical parameter

c) chemical parameter

d) physical parameter

Answer: b

Explanation: Active transducers are also known as self generating type of transducers. They develop an electrical voltage or current proportional to the quantity being measured.

3. How do passive transducers develop electrical signals?

a) using a transformer

b) using internal source

c) using external source

d) using a diode

Answer: c

Explanation: Passive transducers develop electrical signals by means of an external source. They are usually known as externally power driven sources.

4. Capacitive transduction involves ___________

a) change in resistance

b) change in inductance

c) change in resistance

d) change in capacitance

Answer: d

Explanation: In capacitive transduction, measurand involves the change in the capacitance. Capacitance changes when the distance between the plates is varied or by a change in the dielectric.

5. In electromagnetic based transduction measurand is ___________

a) converted into mechanical force

b) converted into electromotive force

c) converted into chemical force

d) converted into physical force

Answer: b

Explanation: Electromagnetic transduction involves the conversion of the measurand into electromotive force. Magnetic flux is produced as a result of the relative motion between the magnet and an electromagnet.

6. Inductive transduction involves ___________

a) change in self inductance

b) change in capacitance

c) change in mutual inductance

d) change in resistance

Answer: a

Explanation: In an inductive transduction based system, measurand involves change in the self inductance of the coil.

7. Photovoltaic transduction involves ___________

a) voltage generation heat

b) voltage generation through sound

c) voltage generation through light

d) voltage generation current

Answer: c

Explanation: In a photovoltaic transduction based system, measurand is converted into voltage when the junction between dissimilar elements is illuminated.

8. Analog transducers convert input into ___________

a) voltage

b) current

c) digital

d) analog

Answer: d

Explanation: The analog transducers convert input into analog signal. The output is a continuous function of time. Strain gauge, LVDT, thermistor etc are analog transducers as they produce outputs which are a continuous function of time.

9. Inverse transducer converts electrical into a physical quantity.

a) True

b) False

Answer: a

Explanation: An inverse transducer is used to convert an electrical quantity into a physical quantity. For example, loudspeaker converts electrical signal into sound signal.

10. Digital transducers produce analog output.

a) True

b) False

Answer: b

Explanation: Digital transducers produce digital output in response to an input signal. A unique code is generated for each discrete value sensed.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Characteristic of Transducers”.

1. Accuracy is defined as the closeness that a reading approaches with respect to a standard value.

a) True

b) False

Answer: a

Explanation: Accuracy in the measurement of a quantity is defined as the closeness that a reading approaches when it measured with a standard value.

2. The output of a transducer must ___________

a) be different at different environment conditions

b) be same at all environment conditions

c) be same at some environment conditions

d) be zero always

Answer: b

Explanation: Output of a transducer must be the same under various environmental conditions when same input is applied to it.

3. The output of a transducer must be __________

a) low

b) medium

c) high

d) zero

Answer: c

Explanation: Output of a transducer is usually high so that it can be easily measured and processed. The transducer output is generally higher than the noise. As a result most of the application makes use of digital outputs.

4. The size of a transducer must be __________

a) infinite

b) zero

c) large

d) small

Answer: d

Explanation: A transducer generally has a small size and shape. It occupies minimum volume and has a minimum weight. As a result the system being measured will become compact.

5. A transducer must be __________

a) quick in response

b) slow in response

c) medium in response

d) very slow in response

Answer: a

Explanation: The transducer is generally fast in response. Speed of response basically tells the time taken by the transducer to produce the output in a fast and efficient manner.

6. The output of a transducer must __________

a) be less reliable

b) be highly reliable

c) not be reliable

d) be of medium reliability

Answer: b

Explanation: Output of a transducer is generally high in reliability. Changes in the environment conditions should not affect the output of a transducer.

7. The range of a transducer is __________

a) medium

b) narrow

c) large

d) zero

Answer: c

Explanation: A transducer has a large range of operation. The operating range is set wide so that it is useful for a wide range of operating frequencies.

8. The transducer output is __________

a) exponential

b) unit step

c) non-linear

d) linear

Answer: d

Explanation: Transducer output varies linearly with the input quantity that is being measured. A transducer must have a linear input vs output characteristic response.

9. The sensitivity of an electrical transducer is obtained by dividing the electrical output with respect to a unit change in the physical quantity.

a) True

b) False

Answer: a

Explanation: Sensitivity of an electrical transducer is defined as the ratio of the electrical output to a unit change in the value of a physical quantity such as temperature, pressure, etc.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Transducer Selection Factors”.

1. Selection of a transducer depends on the quantity being measured.

a) True

b) False

Answer: a

Explanation: A transducer is selected based on the nature of the quantity that is being measured. For example temperature measurement involves the use of temperature sensors whereas measurement of stress involves a strain gauge.

2. A transducer must have _____________

a) maximum loading

b) minimum loading

c) zero loading

d) infinite loading

Answer: b

Explanation: A transducer in general should have a minimum amount of load. Minimum loading effect ensures that the transducer has minimal errors in the measurement of any quantity.

3. Transducers must operate under ___________

a) zero electromagnetic field

b) constant electromagnetic fields

c) varying electromagnetic fields

d) infinite electromagnetic field

Answer: c

Explanation: A transducer should operate under strong electromagnetic fields. Generally transducers with a low value of output impedance, high value of output voltage and shorter cable length are not susceptible to such interference.

4. Errors can be minimised in some transducers through ___________

a) power compensation

b) voltage compensation

c) resistance compensation

d) temperature compensation

Answer: d

Explanation: In some transducers errors occurring due to temperature changes can be minimized by providing temperature compensation. Operation and maintenance of transducers beyond 300°F is extremely difficult.

5. How can a transducer be used in the environment with vibrations?

a) using shock absorbers

b) using proper grounding

c) using effective voltage

d) using a transformer

Answer: a

Explanation: Transducers can be used effectively in an environment subjected to shock and vibrations by making use of dampers.

6. How many passive transducers are there?

a) 1

b) 3

c) 5

d) 7

Answer: b

Explanation: There are three passive transducers. They are as follows:

Resistor

Capacitor

Inductor.

7. Resistance of a metallic conductor is given by ___________

a) R = I ⁄ A

b) R = ρ ⁄ A

c) R = ρl ⁄ A

d) R = 1 ⁄ A

Answer: c

Explanation: The resistance of a metallic conductor is given by the relation

R = ρl ⁄ A

where, R is the resistance

l is the length

A is the area of cross-section

ρ is the resistivity of material of the conductor.

8. Passive transducers are described with their primary parameters.

a) True

b) False

Answer: a

Explanation: The passive transducers such as resistor, capacitor and inductor are described through the means of their primary parameters namely resistance, capacitance and self inductance.

9. Rotational potentiometers use ___________

a) capacitance

b) self inductance

c) mutual inductance

d) resistance

Answer: d

Explanation: Rotational potentiometers or translational potentiometers make use of the change in resistance as a result of the change in length of a conductor.

10. Temperature transducers make use of ___________

a) change in resistivity

b) change in length

c) change in area

d) change in capacitance

Answer: a

Explanation: The change in resistivity of the material of a conductor is used to measure the variation in temperature. Temperature is affected due to change in the resistance which in turn varies the resistivity.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Potentiometric Resistance Transducers”.

1. Potentiometric resistance transducer measures __________

a) linear displacement

b) rectangular displacement

c) square displacement

d) triangular displacement

Answer: a

Explanation: A Potentiometric resistance transducer measures linear displacement. It can also be used for measuring angular displacement.

2. Resistance potentiometer consists of _________

a) capacitive element

b) resistive element

c) inductive element

d) no elements

Answer: b

Explanation: A resistance potentiometer consists of a resistive element. It also has a sliding contact known as a wiper.

3. Resistance transducer has _________

a) medium efficiency

b) low efficiency

c) high efficiency

d) zero efficiency

Answer: c

Explanation: A resistance transducer has a high electrical efficiency. It provides a sufficient amount of output for further control operations.

4. What is a helipot?

a) inductive element

b) helicopter

c) helipad

d) resistive element

Answer: d

Explanation: A resistive transducer in the form of a helix is also known as a heliport. They are used for measuring linear as well as angular motion.

5. Resistance potentiometers convert mechanical displacement into _________

a) electrical signal

b) chemical signal

c) physical output

d) kinetic energy

Answer: a

Explanation: Resistive transducers are used for transforming the mechanical displacement into electrical signal. Linear displacement is applied to the sliding contact which then converts the change in resistance into voltage or current.

6. Strain gauge is a _________

a) inductive transducer

b) resistive transducer

c) capacitive transducer

d) mechanical transducer

Answer: b

Explanation: A strain gauge is a resistive transducer. It works on the principle of mechanical displacement into a change in resistance.

7. Strain is defined as _________

a) change in height per unit height

b) change in weight per unit weight

c) change in length per unit length

d) change in diameter per unit diameter

Answer: c

Explanation: Strain is defined as the ratio of two quantities as follows:

Strain = ∆l ⁄ l

where,

l is the length

∆l is the change in length.

8. Stress is defined as _________

a) diameter per unit area

b) length per unit area

c) weight per unit area

d) force per unit area

Answer: d

Explanation: Stress is defined as the ratio of two quantities as follows:

Stress = Force ⁄ Area

The unit of stress is N / m 2 .

9. Stress vs strain curve is always linear.

a) True

b) False

Answer: b

Explanation: Within the elastic limits, the curve of stress vs strain is linear. Strain measurements must be made on the free surface of any body. A strain gauge is usually used to measure the magnitude of strain.

10. Sensitivity is the smallest value of measurable strain.

a) True

b) False

Answer: a

Explanation: The smallest value of strain that can be measured is known as the sensitivity of the body. The type of strain gauge used dictates the maximum value of strain that can be measured.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Operation of Strain Gauges”.

1. Electrical strain gauge works on the principle of __________

a) variation of resistance

b) variation of capacitance

c) variation of inductance

d) variation of area

Answer: a

Explanation: An electrical strain gauge works on the basis of change in resistance as a function of strain. The wire resistance increases with tension and reduces with compression.

2. The strain gauge is not bonded to the specimen.

a) True

b) False

Answer: b

Explanation: The gauge is under the same strain as that the specimen under test. As a result the strain gauge is bonded to the specimen.

3. Bonding element in a strain gauge must have __________

a) zero insulation resistance

b) low insulation resistance

c) high insulation resistance

d) infinite insulation resistance

Answer: c

Explanation: In a strain gauge, the bonding element must have a high value of insulation resistance. It should be immune to effects of moisture and must also have the ability to transmit strain.

4. Dynamic strain measurements use __________

a) brass iron alloy

b) iron aluminium alloy

c) nickel cadmium alloy

d) nickel chromium alloy

Answer: d

Explanation: Nickel chromium alloy is also known as a nichrome alloy. It contains 80 % of Nickel and 20 % of Chromium. Platinum is used for the temperature compensation of nickel chromium alloys.

5. Commonly used elements for wire strain gauges are __________

a) nickel and copper

b) nickel and gold

c) gold and brass

d) silver and aluminium

Answer: a

Explanation: Nickel and copper are the most commonly used elements for wire strain gauges. They comprise of 45 % of Nickel and 55 % of Copper. They exhibit a high value of specific resistance.

6. Cement is classified under __________

a) 4 types

b) 2 types

c) 6 types

d) 8 types

Answer: b

Explanation: Cement can be divided into two broad categories. They are as follows:

i) Solvent setting cement

ii) Chemically reacting cement.

7. Proper functioning of a strain gauge depends on __________

a) strain

b) stress

c) bonding

d) length of wire

Answer: c

Explanation: A strain gauge works properly only if the bonding material used is durable and keeps the gauge together to the surface of the material that is being tested.

8. Gauge factor is given by which of the following relation?

a) S = \

S = \

S = \(\frac{\Delta R/R}{\Delta l/l}\)

Answer: d

Explanation: Gauge factor in a strain gauge is given by the relation

S = \(\frac{\Delta R/R}{\Delta l/l}\)

where, S is the gauge factor

R is the gauge wire resistance

∆R is the change in resistance

l is the length of the wire in unstressed condition

∆l is the change in length of the wire.

9. Poisson’s ratio is given by which of the following relation?

a) µ = –\

µ = –\

µ = –\(\frac{\Delta d/d}{\Delta l}\)

Answer: a

Explanation: Poisson’s ratio is given by the relation

µ = –\(\frac{\Delta d/d}{\Delta l/l}\)

where, d is the diameter of the cross-section of the wire

∆d is the change in the diameter of cross-section of the wire.

10. Proper bonding causes errors in strain gauges.

a) True

b) False

Answer: b

Explanation: Strain gauge is fixed onto the specimen by means of a bonding element. Cement is a commonly used adhesive. It transfers the strain from the specimen to the gauge sensing element.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Types of Strain Gauges”.

1. Strain gauges are classified into ________

a) 3 types

b) 5 types

c) 7 types

d) 9 types

Answer: a

Explanation: Strain gauges can be classified into three broad categories based on the principle of operation and construction. They are mechanical, optical, and electrical.

2. Resistance wire gauges come in _______

a) 4 forms

b) 2 forms

c) 6 forms

d) 8 forms

Answer: b

Explanation: Strain gauges made out of electrical wires come in two broad forms. They are as follows:

• Bonded

• Unbonded.

3. Bonded resistance wire strain gauge is of _______

a) 7 types

b) 5 types

c) 3 types

d) 9 types

Answer: c

Explanation: The bonded electrical wire resistance strain gauge is broadly classified into three main types. They are as follows:

• Flat grid

• Helical grid

• Thin foil.

4. Commonly used electrical strain gauge is _______

a) open type

b) closed type

c) unbounded type

d) bonded type

Answer: d

Explanation: Electrical strain gauges are a type of strain gauge. The commonly used electrical strain gauge is the bonded resistance type. Capacitance and inductance types are used in special types of applications.

5. Electrical strain gauges measure changes in _______

a) resistance, capacitance and inductance

b) resistance only

c) capacitance only

d) inductance only

Answer: a

Explanation: Strain is transferred between the specimen and the gauge element in a strain gauge. Electrical strain gauges measure the changes occurring in resistance, capacitance and inductance.

6. Mechanical gauges measure the _______

a) change in resistance

b) change in length

c) change in area

d) change in inductance

Answer: b

Explanation: A mechanical gauge is used to measure the change in length. They make use of gears. Mechanical gauges are used for static strain measurements only.

7. Optical gauges make use of _______

a) pulleys

b) electricity

c) mirrors

d) rack and pinion

Answer: c

Explanation: Optical gauges are similar to mechanical gauges. They make use of prisms and mirrors for obtaining magnification. A plain mirror is fixed onto a movable knife edge.

8. Tensile stress decreases the length.

a) True

b) False

Answer: b

Explanation: Tensile stress tends to elongate a wire. As a result its length increases and its area of cross-section decreases.

9. In a foil strain gauge, strain is detected through _______

a) a capacitance element

b) a resistance wire

c) a gold foil

d) a metal foil

Answer: d

Explanation: Strain is detected in a foil strain gauge by making use of a metal foil. The foil makes use of nickel, nichrome, constantan, isoelastic, and platinum.

10. Etched foil strain gauges are flexible.

a) True

b) False

Answer: a

Explanation: Etched foil strain gauges are a type of foil strain gauge. Compared to resistance wire gauges, they can be made thinner. They are also flexible. Etched foil strain gauges are made use o curved surfaces.

This set of Electrical Measurements MCQs focuses on “Characteristics of Resistance Wire Strain Gauge”.

1. Gauge factor in a strain gauge must be ________

a) high

b) low

c) medium

d) small

Answer: a

Explanation: The gauge factor in a strain gauge must be high. A large value of gauge factor indicates a large change in the value of resistance for a particular strain.

2. Strain gauges are used for _______

a) small scale measurements

b) dynamic measurements

c) static measurements

d) large scale measurements

Answer: b

Explanation: Strain gauges are used for dynamic measurements. The frequency response must be better. The characteristics must be linear over the entire frequency range.

3. Resistance of the strain gauge must be _______

a) zero

b) small

c) large

d) medium

Answer: c

Explanation: The resistance of a strain gauge must be large. Typical resistance values for a strain gauge are in the range of 120 ῼ, 350 ῼ, and 1000 ῼ.

4. Strain gauge has a _______

a) tangential

b) exponential

c) non-linear

d) linear

Answer: d

Explanation: The strain gauge has a linear characteristic. Variation in resistance must be a linear function of the strain.

5. Strain gauge has a _______

a) low temperature coefficient of resistance

b) high temperature coefficient of resistance

c) zero temperature coefficient of resistance

d) infinite temperature coefficient of resistance

Answer: a

Explanation: The strain gauge has a low temperature coefficient of resistance. Due to temperature variation, errors can be minimised in this way. In most of the strain gauges, temperature compensation is provided.

6. Semiconductor strain gauges are used for _______

a) low gauge factor values

b) high gauge factor values

c) zero gauge factor value

d) infinite gauge factor value

Answer: b

Explanation: The semiconductor strain gauges are generally used when high values of gauge factors are required. The gauge factor for semiconductor gauges is 50 times higher than that for wire gauges.

7. Strain gauge works on the principle of _______

a) piezo-electric effect

b) barkhausen criterion

c) piezo- resistive effect

d) feedback element effect

Answer: c

Explanation: A semiconductor strain gauge works on the principle of piezo-resistive effect. Piezo-resistive effect is the change in the value of the resistance due to a change in the resistivity of the semiconductor.

8. In metallic gauges resistance changes due to _______

a) temperature

b) current

c) voltage

d) dimension

Answer: d

Explanation: The resistance varies in metallic gauges due to a change in the dimensions of the metallic gauge. Germanium and silicon are the materials used in metallic gauges.

9. Gauge factor for a semiconductor strain gauge is _______

a) 130 ± 10%

b) 30 ± 10%

c) 200 ± 10%

d) 10 ± 10%

Answer: a

Explanation: The gauge factor for a typical semiconductor strain gauge is about 130 ± 10% for 350 ῼ. The gauge factor is measured at the room temperature. The gauge measures small strains from 0.1 to 500 microstrains.

10. Hysteresis characteristics of a semiconductor strain gauge are poor.

a) True

b) False

Answer: b

Explanation: The hysteresis characteristics for a semiconductor strain gauge are excellent. It is less than 0.05 %.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Strain Gauge Measurement Technique”.

1. Strain gauge measurement involves __________

a) Wheatstone bridge

b) Kelvin bridge

c) De Sauty’s bridge

d) Anderson bridge

Answer: a

Explanation: Strain gauge makes use of the practical form of Wheatstone’s bridge to measure the strain developed by an element.

2. Load cell is used for the measurement of _______

a) area

b) force

c) mass

d) length

Answer: b

Explanation: The load cell is used in a semiconductor strain gauge for the measurement of force. Load cells measure the deformation that is produced by force or weight.

3. Strain is a _______

a) fractional change in volume

b) fractional change in area

c) fractional change in length

d) fractional change in height

Answer: c

Explanation: Strain is defined as the fractional change in length of a body. A change in resistance of the element is reflected in the form of strain of the gauge as well as the element.

4. Semiconductor strain gauge uses _______

a) rectifier circuitry

b) power electronics circuitry

c) ordinary bridge circuit

d) bridge circuit with temperature compensation

Answer: d

Explanation: The semiconductor strain gauge makes use of a Wheatstone practical bridge circuit along with temperature compensation. Output is made linear as the resistance characteristics with respect to strain are non-linear.

5. A semiconductor strain gauge consists of how many dummy gauges?

a) 2

b) 4

c) 6

d) 10

Answer: a

Explanation: The semiconductor strain gauge consists of two dummy gauges in the form of two arms of the Wheatstone bridge circuit. Dummy gauges are used for temperature compensation.

6. Metals in strain gauge construction have _______

a) non-linear temperature coefficient

b) linear temperature coefficient

c) tangential temperature coefficient

d) exponential temperature coefficient

Answer: b

Explanation: The metals used in a strain gauge construction have a linear temperature coefficient. A change in the temperature affects the resistance and varies the value of strain.

7. A Wheatstone bridge has _______

a) low sensitivity

b) zero sensitivity

c) high sensitivity

d) infinite sensitivity

Answer: c

Explanation: A Wheatstone bridge circuit has a high sensitivity for detecting very small variation in the values of resistance. We can connect the strain gauge in one of the arms of a Wheatstone bridge and measure the strain in terms of variation in resistance.

8. Load cells are calibrated such that _______

a) force varies inversely with resistance

b) force varies as the square of resistance

c) force remains constant with resistance

d) force varies directly with resistance

Answer: d

Explanation: The load cells in a semiconductor strain gauge are calibrated in such a way that the force or weight varies directly as the resistance. The strain gauge is arranged in the form of a bridge.

9. Load cell is sensitive to minute strains.

a) True

b) False

Answer: a

Explanation: A load cell responds to very minute variation in the value of strain. It is sensitive to high values of the load.

10. Mass of only about 20 kg can be measured by a load cell.

a) True

b) False

Answer: b

Explanation: Using a load cell a mass or weight of the order of 20 kg to 20,000 kg can be measured. By making use of appropriate load cells we can measure forces as high as 5 MN.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Resistance Temperature Detector”.

1. Resistance temperature detector is ___________

a) a electrical transducer

b) a mechanical transducer

c) a chemical transducer

d) a physical transducer

Answer: a

Explanation: Resistance temperature detector is an electrical transducer. It is used for measuring the variation in temperature. It is also known as a resistance thermometer.

2. Relation between temperature and resistance of a conductor is ________

a) R t = R ref [1+t]

b) R t = R ref [1+α∆t]

c) R t = R ref [1-αt]

d) R t = R ref [1-t]

Answer: b

Explanation: The relationship between temperature and resistance of a conductor is given by

R t = R ref [1+α∆t]

where, R t is the resistance of the conductor at t°C.

R ref is the resistance of the conductor at reference temperature

α is the temperature coefficient of resistance

∆t is the difference between the temperature being measured and the reference temperature.

3. Sensing element in the thermometer must provide ________

a) small change in resistance

b) no change in resistance

c) large change in resistance

d) infinite change in resistance

Answer: c

Explanation: The sensing element in a thermometer must give a large change in the resistance for a given change in the temperature.

4. Platinum is used for industrial applications because ________

a) it is cheap

b) it is available readily

c) it is a noble metal

d) it gives accurate measurements

Answer: d

Explanation: In industrial applications, platinum is used due to its accuracy in providing measurements. It is also reproducible. Platinum element can be used for the measurement of temperatures of about 1000 K.

5. Resistance thermometer provides the change in electrical resistance.

a) True

b) False

Answer: a

Explanation: A resistance thermometer provides a change in the electrical resistance with respect to a variation in the temperature. Basically resistance thermometers work on the principle of change in the electrical resistance with variation in the temperature.

6. If the sensing element is large, then less amount of heat is required.

a) True

b) False

Answer: b

Explanation: When the sensing element in a resistance thermometer is small in size, then less quantity of heat is required to raise the temperature. Platinum, nickel and copper are the commonly used metals for measuring temperature.

7. Most metallic conductors have a ________

a) neutral temperature coefficient of resistance

b) negative temperature coefficient of resistance

c) positive temperature coefficient of resistance

d) zero temperature coefficient of resistance

Answer: c

Explanation: In general metallic conductors have a positive temperature coefficient of resistance. The resistance increases with an increase in temperature.

8. In a temperature sensing element ________

a) low value of α is required

b) infinite value of α is required

c) α must be zero

d) high value of α is required

Answer: d

Explanation: In order to achieve a large change in the value of resistance for a small change in the value of temperature, high value of α is required. Change in resistance is measured through a Wheatstone’s bridge.

9. Nickel and its alloys can be used over a temperature range of ________

a) 100 to 450 K

b) 10 to 50 K

c) 0 to 25 K

d) 5 to 15 K

Answer: a

Explanation: Temperature sensors constructed using nickel and its alloys can be used in the temperature range of 100 to 450 K. Compared to platinum, they are less expensive. They have a comparatively higher temperature coefficient that increases with temperature.

10. How can corrosion be prevented in a resistance thermometer?

a) by immersing the setup in oil

b) by enclosing the elements in a glass tube

c) by using guard rings

d) by painting the elements

Answer: b

Explanation: Corrosion can be eliminated in a resistance thermometer by enclosing the elements in a protective tubular glass made of pyrex, quartz or crystal depending upon the temperature range.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Thermistor”.

1. Thermistor is a contraction _________

a) thermal resistor

b) laser resistor

c) electric resistor

d) mechanical resistor

Answer: a

Explanation: Thermistor is basically the short form of a thermal resistor. Resistors which depend on temperature are known as thermal resistors.

2. Thermistors have ________

a) positive temperature coefficient

b) negative temperature coefficient

c) zero temperature coefficient

d) infinite temperature coefficient

Answer: b

Explanation: Thermistor generally has a negative temperature coefficient of resistance. With an increase in temperature, resistance of a thermistor decreases.

3. Thermistors ________

a) sense large changes in temperature

b) cannot sense any change in temperature

c) sense small changes in temperature

d) have a positive temperature coefficient of resistance

Answer: c

Explanation: Thermistors can sense very small changes in temperature. The negative temperature coefficient of thermistors can be a few percent/degree celcius change in temperature.

4. Thermistor has a resistance of ________

a) 250 ῼ to 500 kῼ

b) 50 ῼ to 10 kῼ

c) 1 ῼ to 1 kῼ

d) 100 ῼ to 100 kῼ

Answer: d

Explanation: Thermistor has a resistance range of 100 ῼ to 100 kῼ. Thermistor consists of a mixture of metallic oxides of manganese, nickel, cobalt, copper, iron and uranium.

5. Thermistors are suited for precision temperature measurements.

a) True

b) False

Answer: a

Explanation: Thermistors can be used for precision measurement of temperature, controlling g temperature and for temperature compensation due to a very large variation in resistance with temperature.

6. Change in resistance is measured using a ________

a) Anderson’s bridge

b) Wheatstone’s bridge

c) Hay’s bridge

d) Maxwell’s bridge

Answer: b

Explanation: The change in resistance in a thermistor is measured using a Wheatstone’s bridge. It is used for measurement of resistance in the range of -100°C to +200°C.

7. Thermistor material is pressed ________

a) under zero pressure

b) under low pressure

c) under high pressure

d) under low volume

Answer: c

Explanation: A thermistor material is usually pressed under high pressure to form a flat cylindrical shape. Disks and washers are placed in series or in parallel to increase the power dissipation.

8. Thermistor follows which law for small variations ________

a) Charle’s law

b) KVL

c) KCL

d) Ohm’s law

Answer: d

Explanation: For small changes in the values of current, voltage across a thermistor increases. It attains a peak value. Then the voltage across the thermistor decreases. As a result Ohm’s law is followed at small variations of current.

9. At small values of voltage, a thermistor ________

a) reaches peak current slowly

b) reaches peak current immediately

c) does not reaches peak current

d) reaches peak current intermediately

Answer: a

Explanation: For minute variations in voltage, thermistor reaches peak value of current slowly. As the magnitude of voltage is increased, less time is required to attain peak current.

10. Thermistor has low resistance.

a) True

b) False

Answer: b

Explanation: Thermistor generally has a very high value of resistance. Cables with shield are required to be used for minimising interference.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Pressure Sensor”.

1. Pressure is the _________

a) force per unit area

b) mass per unit area

c) force per unit volume

d) mass per unit volume

Answer: a

Explanation: Pressure at a point is defined as the force acting per unit area. It is measured at some given point over a surface.

2. Pressure measurement devices make use of ________

a) non-elastic member

b) elastic member

c) bendable member

d) non-bendable member

Answer: b

Explanation: Pressure sensors employ elastic member at the input stage to detect or sense the pressure variations. Elastic members are usually of various forms and convert the pressure into mechanical displacement.

3. Output of electrical transducer is ________

a) inversely proportional to displacement

b) proportional to square of displacement

c) proportional to displacement

d) constant

Answer: c

Explanation: The output of an electrical transducer is proportional to displacement. Displacement is measured using electrical transducers.

4. In general how many pressure sensitive devices are there?

a) 6

b) 20

c) 10

d) 4

Answer: d

Explanation: Usually there are four pressure sensitive devices. They are as follows:

• Diaphragms

• Capsule

• Bourdon tube

• Bellows.

5. Diaphragms in a pressure sensor are of ________

a) 2 types

b) 5 types

c) 10 types

d) 20 types

Answer: a

Explanation: Generally in a pressure sensor we have four pressure sensitive devices. Diaphragm is a type of a pressure sensitive device. They are of two types:

• Flat type

• Corrugated type.

6. Temperature is the only consideration while selecting a diaphragm.

a) True

b) False

Answer: b

Explanation: While selecting a suitable diaphragm for sensing the pressure the following factors are considered important.

• Temperature range

• Shock and vibration

• Frequency response requirements.

7. Capsule type of pressure sensor consists of ________

a) 6 dissimilar diaphragms

b) 4 identical diaphragms

c) 2 identical diaphragms

d) 8 dissimilar diaphragms

Answer: c

Explanation: Capsule is a type of a pressure sensor. It comprises of two identical annular corrugated metal diaphragms that are sealed together to form a shell like enclosure.

8. Bourdon tubes are ________

a) very highly sensitive to shock

b) not sensitive to shock

c) less sensitive to shock

d) more sensitive to shock

Answer: d

Explanation: Bourdon tube is one type of pressure sensor. It is more sensitive to shock and vibrations as compared to diaphragms. Bourdon tube can be used for precision measurements of pressure up to 3 MN/m 2 .

9. Bellows have 5 to 20 convolutions.

a) True

b) False

Answer: a

Explanation: Bellow is a type of pressure sensor. They have about 5 to 20 convolutions. The number of convolutions depends on the pressure range, displacement, and operating temperature.

10. Sensitivity in a capsule is increased ________

a) through parallel connection of capsules

b) through series connection of capsules

c) through series and parallel connection of capsules

d) by not connecting them at all

Answer: b

Explanation: Capsule is a type of pressure sensor. In a capsule, we can increase the sensitivity by connecting two or more capsules in series. The resultant displacement is equal to the number of capsules.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Inductive Transducer”.

1. Mutual inductance between two coils is given as _________

a) M = k\

M = k\

M = \(\sqrt{L_1 L_2}\)

Answer: a

Explanation: The mutual inductance between two coils is given by the relation

M = k\(\sqrt{L_1 L_2}\)

where, k is the coefficient of coupling

M is the mutual inductance between the coils.

2. Mutual inductance depends on _________

a) self-inductance

b) self-inductance and coefficient of coupling

c) coefficient of coupling

d) permittivity of air

Answer: b

Explanation: The mutual inductance of a pair of coils depends on the self-inductance of the individual coils and on the coefficient of coupling.

3. Self-inductance of an inductor is given by ________

a) L = N ⁄ S

b) L = 1 ⁄ S

c) L = N 2 ⁄ S

d) L = N 2

Answer: c

Explanation: The self-inductance of an inductor is obtained by making use of the relation

L = N 2 ⁄ S

where, N is the number of coil

S is the reluctance of the coil .

4. Reluctance of a coil is given by which of the following relation?

a) S = 1 ⁄ A

b) S = 1 ⁄ μ

c) S = a ⁄ μA

d) S = 1 ⁄ μA

Answer: d

Explanation: The reluctance of an inductance coil is given by the relation

S = 1 ⁄ μA

where, l is the length of the magnetic circuit

a is the area of the magnetic circuit which encloses the flux (m 2 )

µ is the permeability of the core .

5. Self-inductance depends on ________

a) permeability

b) permittivity

c) plank’s constant

d) rydberg constant

Answer: a

Explanation: The self-inductance of an inductor is obtained by making use of the relation

L = N 2 ⁄ S

where, N is the number of coil

S is the reluctance of the coil

As reluctance depends on the permeability, the self-inductance of a coil depends on the permeability.

6. What is the relation between the self-inductance and the reluctance of a coil?

a) directly proportional

b) inversely proportional

c) no relation

d) constant

Answer: b

Explanation: The self-inductance of an inductor is obtained by making use of the relation

L = N 2 ⁄ S

where, N is the number of coil

S is the reluctance of the coil

We observe from the above equation that the self-inductance of a coil is inversely proportional to its reluctance.

7. Based on self-inductance of a coil, how many types of inductive transducers are available?

a) 5

b) 10

c) 4

d) 20

Answer: c

Explanation: Based on the self-inductance of an inductive coil, there are four types of inductive transducers available. They are as follows:

i) Variable permeability inductive transducer

ii) Variable reluctance inductive transducer

iii) Eddy current inductive transducer

iv) Linear variable differential transducer.

8. In an eddy current transducer output depends on the variation in the eddy current.

a) True

b) False

Answer: a

Explanation: An eddy current transducer is a self-generating type of inductive transducer. In an eddy current transducer, output depends on the change in the value of the eddy current at the input.

9. An inductive transducer measures the variation in ________

a) reluctance

b) resistance

c) capacitance

d) self-inductance

Answer: d

Explanation: Inductive transducer measures the variation in the self-inductance and mutual inductance of an inductive coil. Variation in the inductance is measured as a change in the displacement.

10. Inductive transducer is used for the measurement of physical quantities.

a) True

b) False

Answer: a

Explanation: An inductive transducer is usually used for the measurement of physical quantities such as pressure, force, displacement, position, vibration, velocity, etc.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Capacitive Transducer”.

1. Capacitance of a parallel plate capacitor is ________

a) C = A∈ ⁄ d

b) C = ∈ ⁄ d

c) C = A ⁄ d

d) C = A

Answer: a

Explanation: The capacitance of a parallel plate capacitor is given by the relation,

C = A∈ ⁄ d

where,

A is the area of cross section of the plates

d is the distance of separation between the plates

∈ is the permittivity of space.

2. A capacitive transducer works on the principle of ________

a) inductance

b) capacitance

c) resistance

d) reluctance

Answer: b

Explanation: A capacitive transducer works on the principle of capacitance. The capacitance of a system depends on the dielectric used as well as the properties of a capacitive system.

3. Capacitance of a cylindrical capacitor is given by which of the following relation?

a) C = \

C = \

C = \(\frac{2π∈}{ln⁡

}\)

Answer: c

Explanation: The capacitance of a cylindrical capacitor is given by the relation

C = \(\frac{2π∈l}{ln⁡

}\)

where, l is the length of the cylinder

R is the inner radius of the external cylinder

r is the outer radius of the inner cylinder.

4. Capacitance can be varied in ________

a) 10 ways

b) 6 ways

c) 2 ways

d) 4 ways

Answer: d

Explanation: Capacitance is varied in four ways. They are as follows:

Change of distance

Change in dielectric

Change in common plate area

Using quartz diaphragms.

5. Capacitive pressure transducer uses distance of separation for sensing the capacitance.

a) True

b) False

Answer: a

Explanation: A capacitive pressure transducer is based on the principle of distance of separation between the plates of the capacitor. Capacitance of a parallel plate capacitor varies when the distance between the two parallel plates changes.

6. Capacitive transducer displays ________

a) linear behaviour

b) non-linear behaviour

c) exponential behaviour

d) tangential behaviour

Answer: b

Explanation: A capacitive transducer displays non-linear behaviour. This is due to stray electric fields. Guard rings are required to eliminate the edge effects and the parasitic electric field effects.

7. Frequency response of capacitive transducers is ________

a) high

b) medium

c) low

d) zero

Answer: c

Explanation: In a capacitive transducer, long leads and cables are used. Due to loading effect, frequency response is poor and the sensitivity reduces.

8. What is the relation between capacitance and output impedance?

a) proportional to square

b) constant

c) directly proportional

d) inversely proportional

Answer: d

Explanation: When the capacitance is low in the range of pico-farads, output impedance tends to a high value. This leads to loading effect.

9. What is the relation between capacitance and input impedance?

a) directly proportional

b) constant

c) proportional to square

d) inversely proportional

Answer: a

Explanation: Capacitive transducer has high input impedance. It also has a good frequency response. The loading effects are minimum.

10. Composite capacitance consists of _________

a) one dielectric medium

b) more than one dielectric medium

c) five dielectric media

d) ten dielectric media

Answer: b

Explanation: In a composite capacitance, there is more than one dielectric medium. The capacitance is given by

electrical-measurements-questions-answers-capacitive-transducer-q10

where, d 1 , d 2 and d 3 are the thicknesses

∈ 1 , ∈ 2 and ∈ 3 are the permittivities of the three different media.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Thermoelectric Transducer”.

1. Thermoelectric transducer is a __________

a) temperature transducer

b) pressure transducer

c) inductive transducer

d) capacitive transducer

Answer: a

Explanation: A thermoelectric transducer is a temperature transducer. It converts thermal energy into electrical energy.

2. Commonly used thermoelectric transducer is __________

a) thermometer

b) thermocouple

c) linear variable differential transducer

d) loud speaker

Answer: b

Explanation: The most commonly used thermoelectric transducer is a thermocouple. It measures the change in temperature and converts it into an electrical signal.

3. The algebraic sum of e.m.f.s in a circuit containing thermocouples is __________

a) infinite

b) hundred

c) zero

d) ten

Answer: c

Explanation: In a circuit consisting of many thermocouples, the algebraic sum of the e.m.f.s produced is zero. It remains constant with temperature.

4. What is a thermopile?

a) single thermocouple

b) series-parallel connection of thermocouples

c) parallel connection of thermocouples

d) series of thermocouples

Answer: d

Explanation: Thermopile is a series connection of thermocouples. By making use of thermopiles, a more sensitive element is obtained as compared to a single thermocouple.

5. Chromel-constantan thermopile consists of 25 thermocouples.

a) True

b) False

Answer: a

Explanation: A chromel-constantan thermopile provides a sensitivity of 1 mv/°F. It is made up of 25 thermocouples. Temperature variation as small as 0.001°F can be measured using this thermopile.

6. Thermocouple must provide ________

a) small thermo e.m.f

b) sufficient thermo e.m.f

c) no thermo e.m.f

d) infinite thermo e.m.f

Answer: b

Explanation: A thermocouple must be able to provide sufficient thermo e.m.f. This must be with respect to each degree variation in the temperature. It helps in detecting the temperature variation and in measurement.

7. Most suitable material for a thermocouple is ________

a) brass

b) gold

c) platinum

d) silver

Answer: c

Explanation: Platinum is the most suitable material for constructing thermocouples. It has a very high sensitivity. Constantan is the other material with a composition of 40 % of Ni and 60 % of Cu used in a thermocouple.

8. If two different metals are joined forming a closed circuit an electric current flows.

a) True

b) False

Answer: b

Explanation: When two different metals are joined together forming a closed circuit, if the temperatures of the two junctions are different then an electric current flows through the circuit.

9. Which of the following should satisfy for measuring higher temperatures using a thermocouple?

a) no wire is required

b) wire must be small

c) wire must be thin

d) wire must be heavy

Answer: d

Explanation: Higher temperatures can be measured using a thermocouple by making the wire heavy. Increase in size of the wire affects the response time of the thermocouple.

10. For accurate temperature measurement in a thermocouple the __________

a) cold compensation is needed

b) hot compensation is needed

c) no compensation is needed

d) hot and cold compensations are needed

Answer: a

Explanation: Temperature can be measured accurately by using a thermocouple with cold junction temperature compensation.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Piezoelectric Transducer”.

1. Piezoelectric transducer is used for measuring __________

a) non-electrical quantities

b) electrical quantities

c) chemical quantities

d) any quantity

Answer: a

Explanation: A piezoelectric transducer is used for measuring non-electrical quantities such as vibration, acceleration, pressure and the intensity of sound.

2. Piezoelectric crystals __________

a) float on water

b) dissolve in water

c) are not soluble in water

d) absorb water

Answer: b

Explanation: A piezoelectric crystal dissolves in water. It is fully soluble in water. When the temperature is humid, the piezoelectric crystals gets dissolved in water.

3. Piezoelectric crystals produce _________

a) no voltage

b) low voltage

c) high voltage

d) very high voltage

Answer: c

Explanation: Piezoelectric crystals can be used spark ignition engines. They are also used in electrostatic dust filters and produce high voltage at low current.

4. Piezoelectric transducer consists of _________

a) copper rod

b) aluminum wire

c) gold crystal

d) quartz crystal

Answer: d

Explanation: A piezoelectric transducer consists of a quartz crystal. It comprises of silicon and oxygen arranged in a crystal structure of SiO 2 .

5. When a compressive force is applied to a quartz crystal then ____________

a) positive charges are induced

b) negative charges are induced

c) no charge is induced

d) both positive and negative charges are induced

Answer: a

Explanation: When a quartz crystal is subjected to compressive stress, positive charges are induced in one side of the crystal while negative charges are induced on the other side of the crystal.

6. In kitchen applications a piezoelectric crystal is used for _________

a) skimming milk

b) lighting a gas stove

c) grinding

d) mixing

Answer: b

Explanation: A piezoelectric lighter is used for lighting a gas based stove in kitchen applications. The pressure induced on the piezoelectric sensor creates an electric signal leading to a spark.

7. A piezoelectric transducer has a _________

a) very high sensitivity

b) low sensitivity

c) high sensitivity

d) zero sensitivity

Answer: c

Explanation: The sensitivity is high in a piezoelectric transducer. A piezoelectric transducer can be used as a sensor. It can also be used in an accelerometer due to its good frequency response.

8. A piezoelectric transducer is used as an ignition source for a cigarette.

a) True

b) False

Answer: a

Explanation: Cigarettes use piezoelectric transducers as a source of ignition. They are also used in the measurement of sonar, microphone, pressure, displacement and force.

9. Microphone converts light into heat.

a) True

b) False

Answer: b

Explanation: A microphone is used to convert the pressure induced in the form of sound waves into electric signal. The electrical signal is then amplified to produce louder sound.

10. A quartz crystal is _________

a) a chemical transducer

b) a photoelectric transducer

c) not a self-generating transducer

d) a self-generating transducer

Answer: d

Explanation: The quartz crystal is a self-generating transducer. It does not need any electric voltage for operation. The quartz crystal becomes short in length due to an applied electric field in the opposite direction.

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers focuses on “Photoelectric Transducers”.

1. Optical radiations involve _________

a) optoelectric devices

b) biological devices

c) mechanical devices

d) chemical devices

Answer: a

Explanation: Emission and absorption of optical radiations are carried out by making use of optoelectric devices.

2. Photoelectric transducers consist of _______

a) 1 transducer

b) 3 transducers

c) 5 transducers

d) 10 transducers

Answer: b

Explanation: A photoelectric transducer consists of 3 transducers. They are as follows:

Photo-emissive

Photo-conductive

Photo-voltaic.

3. Photoconductive transducers produce output ________

a) due to change in inductance

b) due to change in light

c) due to change in resistance

d) due to change in temperature

Answer: c

Explanation: A photoconductive transducer produces an output due to a change in the resistance. Electrical output is produced due to a variation in the temperature.

4. Commonly used photoemissive material is _______

a) gold

b) opium

c) tellurium

d) cesium-antimony

Answer: d

Explanation: Cesium-antimony is the most commonly used photoemissive material. The photoemissive material is housed in a glass tube. Photoemissive devices are also called as phototubes.

5. Phototubes are very quick in response to light.

a) True

b) False

Answer: a

Explanation: Phototubes are quick in response to light. Phototubes are used in applications which require light pulses of very short durations to be observed.

6. Photoconductors are made of _______

a) thick layer of semiconductor

b) thin layer of semiconductor

c) capacitive substrate

d) inductive substrate

Answer: b

Explanation: Photoconductors comprise of a thin layer of semiconductor. Photoconductors not consisting of a junction are known as junction less detectors.

7. When an open circuited pn junction is illuminated then _________________

a) resistance increases

b) there is no effect

c) electron hole pairs are formed

d) capacitance increases

Answer: c

Explanation: Upon illumination of an open circuited pn junction, electron hole pairs are generated. A small voltage appears across the junction and as a result it acts as a voltae source.

8. Optocoupler consists of a phototransistor and a led.

a) True

b) False

Answer: a

Explanation: The optocoupler consists of a phototransistor and an infrared emitting diode. Wavelength of the emitting and receiving diodes must be matched in order to get a proper output.

9. Response time for gas-filled phototubes is _______

a) zero

b) intermediate

c) fast

d) slow

Answer: d

Explanation: Gas filled phototubes are generally very slow in response as compared to vacuum phototubes. This is due to the slow movement of ions towards the photocathode.

10. Reverse leakage current in a transistor _______

a) is affected by light

b) is not affected by light

c) increases with a decrease in pressure

d) decreases with increase in temperature

Answer: a

Explanation: The reverse leakage current in a transistor is directly proportional to the intensity of light. It increases with the increase in light intensity.

This set of Electrical Measurements Quiz focuses on “Objectives and Requirements of Recording Data”.

1. Electronic recorders are of __________

a) 2 types

b) 4 types

c) 10 types

d) 15 types

Answer: a

Explanation: Electronic recorders are of two types. They are as follows:

• Analog recorders

• Digital recorders.

2. Non-electrical quantities are measured directly.

a) True

b) False

Answer: b

Explanation: All non-electrical quantities are measured indirectly. The non-electrical quantities are converted into their equivalent voltages or currents using different transducers.

3. A physical quantity is recorded to preserve the details.

a) True

b) False

Answer: a

Explanation: Physical quantity is recorded so as to preserve some of the details of the quantity with time.

4. How many types of graphic recorders are there?

a) five

b) ten

c) three

d) one

Answer: c

Explanation: There are three types of graphic recorders. They are as follows:

• Strip chart recorder

• Circular chart recorder

• X-Y recorder.

5. Recorder is a ________

a) measuring instrument

b) voltage source

c) current divider

d) musical tool

Answer: a

Explanation: Recorder is a measuring equipment. A recorder is used to measure time varying quantities even if the quantity has stopped.

6. Efficiency of a recorder is determined using ________

a) paper

b) chart

c) voltmeter

d) oscilloscope

Answer: b

Explanation: The recorder efficiency is determined by means of a chart. Generally chart recorders are of three types. They are X-Y recorder, strip chart recorder and a circular chart recorder.

7. In a strip chart recorder ________

a) biological quantity is measured

b) chemical quantity is measured

c) physical quantity is measured

d) no quantity is measured

Answer: c

Explanation: A strip chart recorder measures a physical quantity by making use of a continuous roll of chart paper at a constant speed.

8. Basic elements of a strip chart recorder are ________

a) chalk and board

b) pen and pencil

c) pencil and paper

d) pen and chart paper

Answer: d

Explanation: The basic elements of a strip chart recorder are pen and chart paper for recording data. Input data is recorded on a chart paper through the following methods:

• Pen and ink stylus

• Impact printing

• Chopper bar printing

• Thermal writing

• Electric writing

• Optical writing.

9. How many types of tracing systems are used in graphical representation?

a) two

b) five

c) ten

d) one

Answer: a

Explanation: There are two types of tracing systems used in graphical representation. They are as follows:

• Curvilinear System

• Rectilinear System.

10. A galvanometer based recorder works on the principle of ________

a) Van der Wall’s effect

b) D’Arsonval movement

c) Paschen effect

d) Azhimuthal quatum number

Answer: b

Explanation: D’Arsonval movement forms the basis for the working of a galvanometer type recorder. When current passes through the coil, deflection is produced by the galvanometer.