Electrical Measurements and Instrumentation MCQs 2026

Percentage error in a measurement equals

1. A measured value divided by full scale only without true reference ✓
2. B true value minus measured only without percentage ✓
3. C (measured value − true value) / true value × 100 ✓
4. D random scatter standard deviation only ✓

Sensitivity of a PMMC galvanometer increases with

1. A more turns on the moving coil and stronger permanent magnet ✓
2. B heavier pointer without coil change ✓
3. C higher control spring stiffness only ✓
4. D open-circuit damping vane only ✓

Thermocouple-type ammeter used for AC measurement relies on

1. A rectified PMMC torque on half cycles only ✓
2. B heating effect of current measured via thermocouple EMF ✓
3. C moving iron attraction on DC component only ✓
4. D Wheatstone bridge unbalance without heat ✓

Permanent magnet in PMMC provides

1. A damping torque directly without eddy currents ✓
2. B controlling torque replacing springs ✓
3. C AC rectification for the coil ✓
4. D strong uniform radial magnetic field across the air gap ✓

Moving iron instruments generally consume

1. A less power because iron is lighter ✓
2. B equal power at all frequencies by definition ✓
3. C more power than PMMC instruments for comparable range ✓
4. D no power because deflection is mechanical only ✓

PMMC meter cannot read AC mains directly because

1. A bidirectional torque averages to zero over a cycle ✓
2. B spring control fails on AC only ✓
3. C damping vane blocks AC deflection ✓
4. D permanent magnet demagnetizes on AC ✓

Full-scale deflection current of a sensitive PMMC movement may be as low as

1. A 50 A in standard panel meters always ✓
2. B 50 μA in laboratory galvanometers ✓
3. C 500 A without shunts always ✓
4. D 5 kA for moving coil only ✓

Electrodynamometer movement differs from PMMC in that it uses

1. A permanent magnet stronger than any electromagnet always ✓
2. B electromagnetic field from fixed coils instead of a permanent magnet ✓
3. C moving iron vanes only without coils ✓
4. D thermocouple heating without coils ✓

An electrodynamometer wattmeter has

1. A a fixed coil (current coil) and a moving coil (pressure coil) ✓
2. B only moving iron vanes without coils ✓
3. C only one permanent-magnet coil ✓
4. D only a thermocouple junction ✓

Current coil of a wattmeter is connected

1. A across the load voltage only ✓
2. B in parallel with supply bus only ✓
3. C in series with the load carrying line current ✓
4. D in the pressure coil circuit only ✓

Pressure coil of a wattmeter is connected

1. A in series with load current only ✓
2. B inside current coil only ✓
3. C to the watt-hour meter disc only ✓
4. D across the load voltage ✓

Wattmeter deflection indicates

1. A reactive power only ✓
2. B apparent power without angle ✓
3. C average real power over the meter time constant ✓
4. D peak instantaneous power only ✓

Wattmeter error at low power factor is mainly due to

1. A excessive current coil resistance only ✓
2. B braking magnet creep only ✓
3. C CT saturation in the voltage circuit ✓
4. D inductance of the pressure coil carrying current ✓

Compensating winding in a wattmeter is provided to

1. A reduce error caused by pressure coil inductance ✓
2. B increase creep on energy meters ✓
3. C replace the braking magnet ✓
4. D measure reactive power directly ✓

A low power factor wattmeter is designed with

1. A higher pressure coil inductance for lagging loads ✓
2. B no pressure coil at all ✓
3. C low inductance pressure coil and higher resistance ✓
4. D moving iron vanes instead of coils ✓

Electrodynamometer wattmeter can measure power on

1. A DC only like PMMC ammeters ✓
2. B AC only without DC ✓
3. C three-phase reactive power without any connection rule ✓
4. D both AC and DC circuits ✓

In the two-wattmeter method on a three-phase three-wire system, total power equals

1. A product of the two readings ✓
2. B difference only regardless of power factor ✓
3. C zero always for balanced load ✓
4. D algebraic sum of the two wattmeter readings ✓

Two-wattmeter method is applicable to

1. A only single-phase loads ✓
2. B only DC distribution ✓
3. C three-phase three-wire circuits balanced or unbalanced ✓
4. D four-wire systems without any modification ever ✓

For balanced lagging load, power factor angle φ is obtained from two wattmeters by

1. A cos φ = W1 × W2 only ✓
2. B sin φ = W1 + W2 only ✓
3. C tan φ = √3 (W1 − W2) / (W1 + W2) ✓
4. D φ = 0 whenever W1 equals W2 always ✓

One wattmeter in the two-wattmeter method reads zero when

1. A power factor is unity always for both meters ✓
2. B power factor angle is 60° lagging for balanced load ✓
3. C load is open circuit on all phases always ✓
4. D both wattmeters always read equal on lagging load ✓

Pressure coil of a wattmeter should have

1. A very low resistance to maximize coil current ✓
2. B same turns as current coil always ✓
3. C high resistance to limit current drawn from the circuit ✓
4. D zero inductance without any resistance ✓

Phantom loading during wattmeter calibration allows

1. A full rated voltage and current simultaneously always ✓
2. B testing at rated current with reduced voltage power ✓
3. C measurement without any coils energized ✓
4. D direct connection to PT secondary only ✓

Turns ratio of a CT is approximately inverse to

1. A burden volt-ampere rating only ✓
2. B wattmeter pressure coil resistance ✓
3. C current transformation ratio between primary and secondary ✓
4. D energy meter registration constant ✓

Accuracy class 0.5 on an indicating instrument means

1. A maximum error is ±0.5% of full-scale value at reference conditions ✓
2. B ±0.5% of reading at all points always without qualification ✓
3. C ±5% of full scale ✓
4. D zero error at half scale only ✓

Systematic measurement error is

1. A random scatter around mean only ✓
2. B error eliminated by averaging infinite readings without removing bias ✓
3. C always caused by quantization only ✓
4. D consistent deviation repeating under the same conditions ✓

Random measurement errors are reduced by

1. A using a lower accuracy class meter ✓
2. B opening CT secondary during test ✓
3. C taking multiple readings and averaging ✓
4. D increasing loading effect of the voltmeter ✓

Loading effect of a voltmeter is minimized by using

1. A very low input impedance ✓
2. B series connection in the line current path ✓
3. C very high input impedance ✓
4. D moving iron movement without springs ✓

Loading effect of an ammeter is minimized by using

1. A high series resistance in the coil ✓
2. B connection across the load terminals ✓
3. C open-circuit secondary of CT ✓
4. D very low voltage drop (low impedance) across the meter ✓

Calibration traceability ensures

1. A instruments never drift after calibration ✓
2. B measurement chain links to recognized national or international standards ✓
3. C random errors are eliminated permanently ✓
4. D CT secondary can be left open safely ✓

Resolution of a digital measuring instrument is

1. A maximum full-scale value only ✓
2. B accuracy class percentage only ✓
3. C smallest change in input that produces a discernible change in reading ✓
4. D hysteresis loop width on analog meters ✓

Standard secondary current for many CTs is

1. A 110 V always ✓
2. B 415 V line voltage ✓
3. C 5 A or 1 A depending on system design ✓
4. D 50 μA galvanometer level ✓

Protection CTs are designed to

1. A measure kWh only at light load ✓
2. B operate with secondary always open ✓
3. C replace fuses on distribution feeders ✓
4. D maintain defined performance up to high fault currents without excessive saturation ✓

Instrument CT accuracy class applies at

1. A any burden without limit always ✓
2. B rated burden and between stated percentage of rated current ✓
3. C primary voltage only ✓
4. D DC primary current only ✓

Knee-point voltage of a protection CT indicates

1. A rated secondary current only ✓
2. B meter accuracy class 0.2 only ✓
3. C point where CT begins to saturate significantly with increased voltage ✓
4. D primary conductor cross-section ✓

Ring-type (window) current transformer is installed by

1. A breaking the bus to insert series primary winding always ✓
2. B passing the primary conductor through the CT window ✓
3. C connecting only to PT secondary ✓
4. D mounting on the energy meter disc spindle ✓

Burden of a current transformer is

1. A primary line impedance only ✓
2. B ratio error in per unit only ✓
3. C magnetizing reactance of core alone ✓
4. D total impedance of secondary load including leads and relays ✓

Potential transformer (VT) is used to

1. A step up current for ammeters ✓
2. B measure frequency without voltage ✓
3. C replace energy meter disc ✓
4. D step down high system voltage to standard low voltage for instruments ✓

CT ratio is defined as

1. A secondary voltage to primary voltage ✓
2. B ratio of primary current to secondary current ✓
3. C primary turns to secondary turns squared ✓
4. D burden impedance to secondary current ✓

Current transformer secondary must never be left open while primary carries current because

1. A dangerous high voltage can appear across secondary terminals ✓
2. B primary current becomes zero automatically ✓
3. C meter reads high resistance only ✓
4. D disc creep increases on energy meters ✓

Power factor of load affects induction energy meter accuracy mainly through

1. A phase angle between voltage and current fluxes ✓
2. B frequency alone without phase ✓
3. C braking magnet strength only ✓
4. D disc material resistivity only ✓

Maximum demand indicator associated with energy metering records

1. A instantaneous peak current without averaging ✓
2. B highest average demand over a defined interval ✓
3. C total kWh only without demand ✓
4. D power factor minimum over a year only ✓

Electronic static energy meter computes energy by

1. A rotating aluminium disc without sensors ✓
2. B multiplying instantaneous voltage and current samples and integrating ✓
3. C moving iron attraction only ✓
4. D Fourier series of voltage without current ✓

Voltage element of an induction energy meter is connected

1. A across the supply voltage ✓
2. B in series with line current only ✓
3. C between CT secondary terminals only ✓
4. D only to the braking magnet poles ✓

Current element of an induction energy meter is connected

1. A across supply voltage only ✓
2. B in series with the line carrying load current ✓
3. C in the braking magnet circuit only ✓
4. D only to the potential coil without series path ✓

Registration constant of an energy meter specifies

1. A number of disc revolutions per unit energy (kWh) ✓
2. B watts per revolution only ✓
3. C maximum demand in kVA only ✓
4. D power factor at full load ✓

Light-load adjustment in an energy meter is intended to

1. A increase creep for testing ✓
2. B disable the braking magnet ✓
3. C improve accuracy at small fractions of rated current ✓
4. D raise rated voltage of the pressure coil ✓

Lag adjustment in an energy meter compensates for

1. A creep at zero load only ✓
2. B frequency variation above 60 Hz only ✓
3. C CT polarity reversal on three-phase ✓
4. D error due to lagging power factor of the load ✓

Creep in an energy meter refers to

1. A fast rotation at full load only ✓
2. B correct registration at unity power factor ✓
3. C disc stopping instantaneously at zero power ✓
4. D unwanted slow disc rotation with no load applied ✓

Braking magnet in an energy meter provides

1. A damping torque proportional to disc speed ✓
2. B additional driving torque at low power factor ✓
3. C series connection to the voltage coil ✓
4. D calibration of CT ratio only ✓

The rotating aluminium disc in a single-phase induction energy meter is driven by

1. A permanent magnet rotation without flux ✓
2. B spring control torque only ✓
3. C pressure coil inductance alone ✓
4. D interaction of eddy currents in the disc with crossing fluxes ✓

An induction-type energy meter is essentially

1. A an integrating wattmeter registering energy in kWh ✓
2. B a peak power indicator only ✓
3. C a frequency meter with drag magnets ✓
4. D a DC-only coulomb counter ✓

UPF error in electrodynamometer wattmeter is reduced by

1. A shorting the current coil for tests ✓
2. B removing the compensating winding ✓
3. C using moving iron instead of dynamometer coils ✓
4. D making pressure coil resistance large compared with its reactance ✓

Repulsion-type moving iron meter compared with attraction type has

1. A more uniform scale over a wider range ✓
2. B higher sensitivity at very low current always ✓
3. C DC-only operation ✓
4. D no iron vanes in the magnetic circuit ✓

Attraction-type moving iron instrument has scale that is

1. A perfectly linear throughout ✓
2. B cramped at the lower end and spread at the higher end ✓
3. C uniformly spaced at low current only ✓
4. D independent of current magnitude ✓

PMMC instrument scale is approximately linear because

1. A magnetic field is radial and coil turns are in uniform field ✓
2. B iron vane saturation shapes the scale ✓
3. C spring stiffness varies with angle only ✓
4. D damping magnet controls linearity ✓

Damping torque in a PMMC instrument is mainly produced by

1. A control springs only ✓
2. B eddy currents induced in the aluminum former ✓
3. C series resistance only ✓
4. D pressure coil inductance ✓

Controlling torque in PMMC and moving iron meters is provided by

1. A permanent magnet only ✓
2. B eddy current disc only ✓
3. C air friction vanes only ✓
4. D spiral springs attached to the moving system ✓

Deflection torque in a PMMC movement is proportional to

1. A square of voltage only ✓
2. B coil current in a uniform radial magnetic field ✓
3. C frequency only ✓
4. D power factor only ✓

A PMMC instrument can be used to measure

1. A DC only ✓
2. B AC only ✓
3. C both AC and DC equally ✓
4. D frequency only ✓

Moving iron instruments can measure

1. A both AC and DC ✓
2. B DC only ✓
3. C AC only without DC ✓
4. D frequency without current ✓

PMMC meter cannot read AC mains directly because

1. A bidirectional torque averages to zero over a cycle ✓
2. B spring control fails on AC only ✓
3. C damping vane blocks AC deflection ✓
4. D permanent magnet demagnetizes on AC ✓

Moving iron instruments generally consume

1. A less power because iron is lighter ✓
2. B equal power at all frequencies by definition ✓
3. C more power than PMMC instruments for comparable range ✓
4. D no power because deflection is mechanical only ✓

Permanent magnet in PMMC provides

1. A damping torque directly without eddy currents ✓
2. B controlling torque replacing springs ✓
3. C AC rectification for the coil ✓
4. D strong uniform radial magnetic field across the air gap ✓