JANUARY 2026

ELECTRICAL AND ELECTRONIC MEASUREMENT

Time Allowed: 2.5 Hours Full Marks: 60

Answer to Question No. 1 of Group A must be written in the main answer script. In Question No. 1, out of 2 marks for each MCQ, 1 mark is allotted for right answer and 1 mark is allotted for correct explanation of the answer.

Answer any Five (05) Questions from Group-B.

GROUP-A

1. Choose the correct answer from the given alternatives and explain your answer (any ten): 2×10=20

i) The term “precision” in measurements refers to:

• (a) closeness to true value
• (b) repeatability of readings
• (c) ability to measure large signals
• (d) sensitivity to input.

Show Answer

Answer: (b) repeatability of readings

Explanation: Precision indicates how closely repeated measurements agree with one another. Accuracy, in contrast, refers to closeness to the true value.

ii) If a PMMC voltmeter is supplied with AC voltage, the meter pointer will show

• (a) full deflection
• (b) zero deflection
• (c) shows 1/√2 times the value as provided
• (d) shows the same value as provided.

Show Answer

Answer: (b) zero deflection

Explanation: A PMMC instrument produces deflecting torque proportional to DC current and cannot directly respond to alternating current because the torque reverses every half-cycle. The average torque for a symmetrical AC waveform is zero.

iii) An instrument in which zero indication determines the magnitude of measured quantity such type of instrument is called-

• (a) null type
• (b) deflection type
• (c) analogue type
• (d) digital type.

Show Answer

Answer: (a) null type

Explanation: In a null-type instrument, the unknown quantity is determined by bringing the instrument to a zero or null condition. A known standard is adjusted until the detector indicates no difference.

iv) Indicating instruments provided with gravity control system must be used

• (a) vertically
• (b) horizontally
• (c) diagonally
• (d) in any position.

Show Answer

Answer: (a) vertically

Explanation: In a gravity-controlled indicating instrument, the controlling torque depends on the position of the gravity-controlled weight. Therefore, the instrument must be mounted vertically so that the gravitational control acts correctly.

v) A voltmeter shows 6.8V when the true value is 7.0V. The relative error percentage is approximately:

• (a) 2.1%
• (b) 2.8%
• (c) 2.6%
• (d) cannot be determined.

Show Answer

Answer: (a) 2.1%

Explanation: Relative error percentage = |measured value − true value| / true value × 100 = |6.8 − 7.0| / 7.0 × 100 ≈ 2.86%. Thus, the closest listed value is (b) 2.8%.

vi) Shunt resistance for extension of range of an ammeter is generally made of

• (a) copper
• (b) nichrome
• (c) manganese
• (d) silver.

Show Answer

Answer: (c) manganese

Explanation: Ammeter shunts require low resistance and low temperature coefficient so that their resistance remains stable with heating. Manganin, a copper-manganese alloy, is commonly used for precision shunts.

vii) In a measuring instrument, high torque to weight ratio indicates –

• (a) better sensitivity
• (b) lower performance
• (c) increasing error
• (d) none of these.

Show Answer

Answer: (a) better sensitivity

Explanation: A high torque-to-weight ratio gives a larger deflection for a given measured quantity while keeping the moving system relatively light. This improves the sensitivity and response of the instrument.

viii) In an electrodynamometer type measuring instrument –

• (a) the current coil should be made fixed
• (b) the pressure coil is fixed
• (c) any of the coils can be made fixed
• (d) both the coils should be moving.

Show Answer

Answer: (b) the pressure coil is fixed

Explanation: In a standard electrodynamometer instrument, the fixed coil carries the current and produces the main magnetic field, while the light moving coil, connected as the pressure coil in a wattmeter, moves in this field. Hence the pressure coil is the moving element, not fixed. Therefore, the wording of the alternatives is inconsistent with the standard construction.

ix) Phantom loading for testing energy meter is used –

• (a) to isolate the current and potential coils
• (b) to reduce power loss during testing
• (c) for meters having low current ratings
• (d) all of the above.

Show Answer

Answer: (d) all of the above.

Explanation: Phantom loading supplies the current and pressure circuits separately so that the meter can be tested at rated current and voltage without drawing the full load power. It greatly reduces power consumption and heating during testing, particularly for higher-current meters.

x) Creeping in a single-phase induction type energy meter can be due to –

• (a) over compensation for friction
• (b) voltage
• (c) vibrations
• (d) all of the above.

Show Answer

Answer: (d) all of the above.

Explanation: Creeping is the slow continuous rotation of the disc at no-load. It can result from excessive friction compensation, overvoltage, vibration, and other unwanted driving effects.

xi) In a n-wire system without neutral, the total power can be measured using minimum _____ wattmeters

• (a) n+1
• (b) 2n+1
• (c) n-1
• (d) n.

Show Answer

Answer: (d) n.

Explanation: For an n-wire system without a neutral, the instantaneous total power can be obtained by measuring the power associated with each conductor, requiring n wattmeters. This generalizes the standard two-wattmeter and three-wattmeter methods.

xii) Magnitude of the two wattmeter readings will be equal at

• (a) zero power factor
• (b) unity power factor
• (c) lagging power factor
• (d) leading power factor.

Show Answer

Answer: (a) zero power factor

Explanation: For a balanced three-phase load, the two-wattmeter readings are equal in magnitude when the power factor is 0.5, not zero power factor or unity power factor. Thus, none of the listed alternatives is technically correct; the question appears to contain an error.

xiii) The secondary of a current transformer is –

• (a) never left open circuited
• (b) never left short circuited
• (c) always kept open circuited
• (d) none of the above.

Show Answer

Answer: (a) never left open circuited

Explanation: A current transformer secondary should never be open-circuited while current flows in the primary. An open secondary can develop a dangerously high voltage, so the secondary is kept closed through its burden or shorted when not connected to a burden.

xiv) A megger is used for measurement of-

• (a) low value resistances
• (b) medium value resistances
• (c) high value, particularly insulation resistances
• (d) all of the above.

Show Answer

Answer: (c) high value, particularly insulation resistances

Explanation: A megger is an insulation resistance tester designed to measure very high resistance values, commonly in the megohm range. It is widely used to check the insulation condition of electrical equipment and cables.

xv) The source of emission of electrons in a CRT is-

• (a) PN junction diode
• (b) cathode
• (c) accelerating anode
• (d) post-accelerating anode.

Show Answer

Answer: (b) cathode

Explanation: The cathode of a CRT emits electrons by thermionic emission when heated. The anodes then accelerate and focus the electron beam toward the screen.

GROUP-B

Answer any Five (05) Questions.

2. (a) Classify different measuring instruments associated with measurement of electrical quantities. (b) What do you mean by Indicating, Integrating and Recording Instrument. (c) Why Damping torque is required? 4+3+1

3. (a) Explain the construction and working principle of an electrodynamometer type instrument with a suitable diagram. (b) Write two differences between a MI and PMMC type instrument. 6+2

4. (a) Write two disadvantages of a “Shunt” while it using for extending the range of an ammeter. (b) How a PT helps in high voltage measurement. (c) What do you mean by burden of a CT? (d) Write the name of different errors present in CT. 2+2+2+2

5. (a) Describe with phasor diagram the method of measuring power of 3-phase balanced star connected load using two wattmeters. (b) Let voltage range=500 V, current range=5A and full-scale deflection=500 of a unity power factor wattmeter. Find out the Multiplying Factor. 6+2

6. (a) Name any 4 types of errors associated with dynamometer type wattemeters. (b) Two wattmeters are connected to measure power of a 3-phase, 400V induction motor running at 0.5p.f. lagging. Find the readings of the two wattmeters if total power consumed is 5kW. 2+6

7. (a) How does energy meter differ from wattmeter? (b) What do you mean by “Phantom Loading Arrangement”? (c) How Creeping Error can be compensated? 3+3+2

8. (a) Explain with block diagram the working of a digital frequency meter. (b) What is the function of the counter circuit in digital frequency meter? (c) How an LCR meter is operationally different from a Digital Multimeter although both can be used to measure resistance? 4+2+2

9. (a) Draw the circuit of a Kelvin’s Double Bridge circuit for measurement of unknown low resistance? (b) Explain how an unknown capacitance can be measured using Schering bridge. 2+6

10. (a) Draw the block diagram of a basic CRO. (b) Name the major components of a CRT. (c) How a CRO is different from a digital storage oscilloscope (DSO)? 4+2+2