gate-2014 electrical measurements

SITAMS

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

GATE-2014

ELECTRICAL AND ELECTRONIC MEASUREMENTS

Syllabus

Bridges and potentiometers; PMMC, moving iron, dynamometer and

induction type instruments; measurement of voltage, current, power,

energy and power factor; instrument transformers; digital voltmeters and

multi meters; phase, time and frequency measurement; Q-meters;

oscilloscopes; potentiometric recorders; error analysis.

Objective Questions with Solutions

1. A wattmeter is connected as shown in figure. The wattmeter reads.

(A) Zero always (B) Total power consumed by Z 1and Z2 (C) Power consumed by Z1 (D) Power consumed by Z2

SOL: - Since potential coil is applied across Z2 as shown below

Wattmeter read power consumed by Z2

2. An ammeter has a current range of 0-5 A, and its internal resistance is 0.2 . In

order to change the range to 0-25 A, we need to add a resistance of (A) 0.8 in series with the meter (B) 1.0 in series with the meter (C) 0.04 in parallel with the meter (D) 0.05 in parallel with the meter

SOL:- Given that full scale current is 5 A

Current in shunt I = IR Ifs = 25 5 = 20 A 20Rsh = 50.2 Rsh =1/20 = .05

3. As shown in the figure, a negative feedback system has an amplifier of gain 100 with 10% tolerance in the forward path, and an attenuator of value 9/100 in the

feedback path. The overall system gain is approximately :

(A) 101% (B) 102% (C) 105% (D) 1010%

4. The Maxwells bridge shown in the figure is at balance. The parameters of the

inductive coil are.

(A) R=R2R3/R4,L=C4R2R3 (B) L=R2R3/R4,R=C4R2R3 (C) R=R4/R2R3,L=1/(C4R2R3) (D) L=R4/R2R3,R=1/(C4R2R3)

5. Two 8-bit ADCs, one of single slope integrating type and other of successive

approximate type, take TA and TB times to convert 5 V analog input signal to equivalent digital output. If the input analog signal is reduced to 2.5 V, the approximate time taken by the two ADCs will respectively, be (A) TA,TB (B) TA/2,TB (C) TA,TB/2 (D) TA/2,TB/2

Sol:-

Conversion time does not depend on input voltage so it remains same for both type of ADCs. Hence (A) is correct option.

6. Two sinusoidal signals p(1,t)=Asin1t and q(2t) are applied to X and Y inputs of a dual channel CRO. The Lissajous figure displayed on the screen shown below : The signal q(2t) will be represented as

(A) q(2t)=Asin2t,2=21 (B) q(2t)=Asin2t,2=1/2 (C) q(2t)=Acos2t,2=21 (D) q(2t)=Acos2t,2=1/2

Sol:-

7. The ac bridge shown in the figure is used to measure the impedance Z . If the bridge is balanced for oscillator frequency f = 2 kHz, then the impedance Z will be

(A) (260 + j0) (B) (0 + j200) (C) (260 j200) (D) (260 + j200)

SOL:-

8. The probes of a non-isolated, two channel oscillocope are clipped to points A, B and C in the circuit of the adjacent figure. Vin is a square wave of a suitable low frequency. The display on Ch1 and Ch2 are as shown on the right. Then the Signal and Ground probes S1,G1 and S2,G2 of Ch1 and Ch2 respectively are connected to points :

(A) A, B, C, A (B) A, B, C, B (C) C, B, A, B (D) B, A, B, C SOL:- Since both the waveform appeared across resistor and inductor are same so the common point is B. Signal Probe S1 is connecte with A, S2 is connected with C and both the grount probes G1 and G2 are connected with common point B. Hence (B) is correct option.

9. A bridge circuit is shown in the figure below. Which one of the sequence given below is most suitable for balancing the bridge ?

(A) First adjust R4, and then adjust R1 (B) First adjust R2, and then adjust R3 (C) First adjust R2, and then adjust R4 (D) First adjust R4, and then adjust R2 SOL:-

10. The time/div and voltage/div axes of an oscilloscope have been erased. A

student connects a 1 kHz, 5 V p-p square wave calibration pulse to channel-1 of the scope and observes the screen to be as shown in the upper trace of the figure. An unknown signal is connected to channel-2(lower trace) of the scope. It the time/div and V/div on both channels are the same, the amplitude (p-p) and period of the unknown signal are respectively

(A) 5 V, 1 ms (B) 5 V, 2 ms (C) 7.5 V, 2 ms (D) 10 V, 1 ms

SOL:-

11. A sampling wattmeter (that computes power from simultaneously sampled values of voltage and current) 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 5 A p-p as shown in the figure. The period is 20 ms. The reading in W will be

(A) 0 W (B) 25 W (C) 50 W (D) 100 W

SOL:-

12. A current of 8 +6 2(sint+30%) A is passed through three meters. They are a

centre zero PMMC meter, a true rms meter and a moving iron instrument. The respective reading (in A) will be (A) 8, 6, 10 (B) 8, 6, 8 (C) 8,10,10 (D) 8,2,2 SOL:-

13. A variable w is related to three other variables x ,y ,z as w=xy/z. The variables are measured with meters of accuracy 0.5% reading, 1% of full scale value and 1.5% reading. The actual readings of the three meters are 80, 20 and 50 with 100 being the full scale value for all three. The maximum uncertainty in the measurement of w will be (A) 0.5% rdg (B) 5.5% rdg

(C) 6.7 rdg (D) 7.0 rdg

14. The simultaneous application of signals x(t) and y(t) to the horizontal and vertical plates, respectively, of an oscilloscope, produces a vertical figure-of-8 display. If P and Q are constants and x(t)=Psin(4t+30c) , then y(t) is equal to (A) Qsin(4t 30c) (B) Qsin(2t + 15c) (C) Qsin(8t + 60c) (D) Qsin(4t + 30c) SOL:-

15. A DC ammeter has a resistance of 0.1 and its current range is 0-100A. If the range is to be extended to 0-500 A, then meter required the following shunt resistance (A) 0.010 (B) 0.011 (C) 0.025 (D) 1.0

SOL:-

16. The set-up in the figure is used to measure resistance R .The ammeter and voltmeter resistances are 0.01 and 2000 , respectively. Their readings are 2 A and 180 V, respectively, giving a measured resistances of 90 The percentage

error in the measurement is

(A) 2.25% (B) 2.35% (C) 4.5% (D) 4.71%

17. A 1000 V DC supply has two 1-core cables as its positive and negative leads :

their insulation resistances to earth are 4 M and 6 M, respectively, as shown in the figure. A voltmeter with resistance 50 k is used to measure the insulation

of the cable. When connected between the positive core and earth, then voltmeter reads

(A) 8 V (B) 16 V (C) 24 V (D) 40 V

18. Two wattmeters, 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. The total power and the power factor, respectively, are (A) 13.0 kW, 0.334 (B) 13.0 kW, 0.684 (C) 8.0 kW, 0.52 (D) 8.0 kW, 0.334

19. A dc potentiometer is designed to measure up to about 2 V with a slide wire of

800 mm. A standard cell of emf 1.18 V obtains balance at 600 mm. A test cell is seen to obtain balance at 680 mm. The emf of the test cell is (A) 1.00 V (B) 1.34 V (C) 1.50 V (D) 1.70 V

20. The circuit in figure is used to measure the power consumed by the load. The

current coil and the voltage coil of the wattmeter have 0.02 and 1000 resistances respectively. The measured power compared to the load power will be

(A) 0.4 % less (B) 0.2% less (C) 0.2% more (D) 0.4% more

21. A galvanometer with a full scale current of 10 mA has a resistance of 1000 . The multiplying power (the ratio of measured current to galvanometer current) of 100 shunt with this galvanometer is

(A) 110 (B) 100 (C) 11 (D) 10

.

22. A CRO probe has an impedance of 500 k in parallel with a capacitance of 10

pF. The probe is used to measure the voltage between P and Q as shown in figure. The measured voltage will be

(A) 3.53 V (B) 4.37 V (C) 4.54 V (D) 5.00 V

23. A moving coil of a meter has 100 turns, and a length and depth of 10 mm and 20

mm respectively. It is positioned in a uniform radial flux density of 200 mT. The coil carries a current of 50 mA. The torque on the coil is (A) 200 Nm (B) 100 Nm (C) 2 Nm (D) 1 Nm

24. A dc A-h meter is rated for 15 A, 250 V. The meter constant is 14.4 A-sec/rev.

The meter constant at rated voltage may be expressed as (A) 3750 rev/kWh (B) 3600 rev/kWh (C) 1000 rev/kWh (D) 960 rev/kWh

25. A moving iron ammeter produces a full scale torque of 240 Nm with a deflection

of 120c at a current of 10 A . The rate of change of self induction (H/radian) of the instrument at full scale is (A) 2.0 H/radian (B) 4.8 H/radian (C) 12.0 H/radian (D) 114.6 H/radian

26. A single-phase load is connected between R and Y terminals of a 415 V,

symmetrical, 3-phase, 4-wire system with phase sequence RYB. A wattmeter is connected in the system as shown in figure. The power factor of the load is 0.8 lagging. The wattmeter will read

(A) 795 W (B) 597 W (C) +597 W (D) +795 W

27. The simplified block diagram of a 10-bit A/D converter of dual slope integrator

type is shown in figure. The 10-bit counter at the output is clocked by a 1 MHz clock. Assuming negligible timing overhead for the control logic, the maximum frequency of the analog signal that can be converted using this A/D converter is approximately

(A) 2 kHz (B) 1 kHz (C) 500 Hz (D) 250 Hz

28. The items in Group-I represent the various types of measurements to be made

with a reasonable accuracy using a suitable bridge. The items in Group-II represent the various bridges available for this purpose. Select the correct choice of the item in Group-II for the corresponding item in Group-I from the following List-I List-II P. Resistance in the milli- 1. Wheatstone Bridge ohm range Q. Low values of Capacitance 2. Kelvin Double Bridge R. Comparison of resistance 3. Schering Bridge which are nearly equal S. Inductance of a coil with 4. Wiens Bridge a large time-constant

5. Hays Bridge 6. Carey-Foster Bridge

Codes : (A) P=2, Q=3, R=6, S=5 (B) P=2, Q=6, R=4, S=5 (C) P=2, Q= 3, R=5, S=4 (D) P=1, Q=3, R=2, S=6

29. A rectifier type ac voltmeter of a series resistance Rs , an ideal fullwave rectifier

bridge and a PMMC instrument as shown in figure. The internal. resistance of the instrument is 100 and a full scale deflection is produced by a dc current of 1 mA. The value of Rs

required to obtain full scale deflection with an ac voltage of 100 V (rms) applied to the input terminals is

(A) 63.56 (B) 69.93 (C) 89.93 (D) 141.3 k

30. A wattmeter reads 400 W when its current coil is connected in the R-phase and

its pressure coil is connected between this phase and the neutral of a symmetrical 3-phase system supplying a balanced star connected 0.8 p.f. inductive load. This phase sequence is RYB. What will be the reading of this wattmeter if its pressure coil alone is reconnected between the B and Y phases, all other connections remaining as before ? (A) 400.0 (B) 519.6 (C) 300.0 (D) 692.8

31. The inductance of a certain moving-iron ammeter is expressed as 10 L= +3(2/4)H, where is the deflection in radians from the zero position. The control spring torque is 2510-6 - Nm/radian. The deflection of the pointer in radian when the meter carries a current of 5 A, is (A) 2.4 (B) 2.0 (C) 1.2 (D) 1.0

32. A 500A/5A, 50 Hz transformer has a bar primary. The secondary burden is a

pure resistance of 1 and it draws a current of 5 A. If the magnetic core requires 250 AT for magnetization, the percentage ratio error is (A) 10.56 (B) 10.56 (C) 11.80 (D) 11.80

33. The voltage-flux adjustment of a certain 1-phase 220 V induction watt-hour meter

is altered so that the phase angle between the applied voltage and the flux due to it is 85c(instead of 90c). The errors introduced in the reading of this meter when the current is 5 A at power factor of unity and 0.5 lagging are respectively (A) 3.8 mW, 77.4 mW (B) 3.8 mW, 77.4 mW (C) 4.2 W, 85.1 W (D) 4.2 W, 85.1 W

34. Group-II represents the figures obtained on a CRO screen when thevoltage signals Vx=Vxmsint and Vy=Vymsin(t+) are given to its X and Y plates respectively and is changed. Choose the correct value of from Group-I to

match with the corresponding figure of Group-II.

Group-I P. = 0 Q. = /2 R.

(A) P=1, Q= 3, R=6, S=5 (B) P=2, Q= 6, R=4, S=5 (C) P=2, Q= 3, R=5, S=4 (D) P=1, Q=5, R=6, S=4

35. Two in-phase, 50 Hz sinusoidal waveforms of unit amplitude are fed into channel-1 and channel-2 respectively of an oscilloscope. Assuming that the voltage scale, time scale and other settings are exactly the same for both the channels, what would be observed if the oscilloscope is operated in X-Y mode ? (A) A circle of unit radius (B) An ellipse (C) A parabola (D) A straight line inclined at 45c with respect to the x-axis.

36. Resistance R1 and R2 have, respectively, nominal values of 10 and 5 , and tolerance of 5% and 10%. The range of values for the parallel combination of R1 and R2 is (A) 3.077 to 3.636 (B) 2.805 to 3.371 (C) 3.237 to 3.678 (D) 3.192 to 3.435

SOL:-

For positive tolerance,

R1= 10+0.5=10.5

R2=5+0.5= 5.5

Req= R1 R2/( R1+ R2)=3.6

For negative tolerance,

R1= 10-0.5=9.5

R2=5-0.5= 4.5

Req= R1 R2/( R1+ R2)=3.07

Hence, range is 3.06 to 3.6.

Hence (A) is correct option.

37. The two wattmeter method is used to measure active power on a three-phase, three wire

system. If the phase voltage is unbalanced, 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.

SOL:-

In two wattmeter reading method, the power reading is independent of negative and zero sequence

voltages.

Hence (d) is correct option.

38. A 4 digit DMM has the error specification as 0.2% of reading+ 10 counts. If a DC voltage of

100V is read on its 200V full scale. The maximum error that can be expected in the reading is

(a) 0.1% (b) 0.2% (c) 0.3% (d) 0.4%

SOL:- 0.3%

39. An average reading digital multimeter reads 10V when fed with a triangular wave, symmetric

about the time axis. For the same input, an rms reading meter will read

(a)20/3 (b) 10/3 (c) 203 (d) 103

Sol: for triangular wave,

Average value = Vm/3

Rms = Vm/3

Vmm = 30

Rms = 30/3 = 103

40. For a step input ei, the overshoot in the output eo will be

(a) Step Function (b)square wave of frequency 50 Hz

(c) square wave of frequency 300 Hz (c) square wave of frequency 2.0 Hz

Sol: Step function

41. An energy meter connected to an immersion heater (resistive) operating on an AC 230V,50Hz,

AC single-phase source reads 2.3 unit (kWh) in 1h. the heater is removed from the supply and

now connected to a 400V peak to peak square wave source of 150Hz. The power in kW

dissipated by the heater will be

(a) 3.478 (b) 1.739 (c) 1.540 (d) 0.870

Sol:

Reading of energy meter

2.3 =V2/R *e = (230)2/R *1

R = 23

Power dissipated = V2/R = (200)2/23

= 1.739 kW

42. An ammeter has a current range of 0-5A and its internal resistance of 0.2. in order to change the

range of 0-25 A, we need to add a resistance of

(a) 0.8 in series with the ammeter

(b) 1.0 in series with the ammeter

(c) 0.04 in parallel with the ammeter

(d) 0.05 in parallel with the ammeter

Sol:

Multiplying power

m = I/Im = 25/5 = 5

Resistance of shunt

Rsh = Rm/m-1 = 0.2/5-1 = 0.05

43. A PMMC voltmeter is connected across a series combination of a dc voltage source V1 = 2V and

an AC voltage source V2(t) = 3sin(4t). the voltmeter reads

(a) 2V (b) 5V (c)(2+3/2)V (d) (17/2)V

Sol:

The permanent magnet moving coil measures the DC value only. The torque will be reversed

if the current is reversed. If the instrument is connected to AC, the deflection responds to the

mean torque which is zero. Hence, voltmeter reads 2V.

44. The effect of stray magnetic fields on the actuating torque of a portable instrument is maximum

when the operating field of the instrument and the stray fields are

(a) Perpendicular (b) parallel (c) inclined at 600 (d) inclined at 300

Sol:

Actuating torque cos (angle between operating field and magnetic field)

For maximum actuating torque both are parallel

45. A current of -8+62(si nwt+300) is passed through three meters. They are a centre zero PMMC

meter, a true rms meter and a moving iron instrument. The respective readings (in amphere) will

be

(a) 8,6.10 (b) 8,6,8 (c) -8,10,10 (d) -8,2,2

Sol:

PMMC reads only DC value and since, it is centre zero type so, it will give -8 value. RMS

meter will read rms value of the current

So, RMS = (82 +(62/2)) = 10A

Moving iron also read rms value, so its reading will also be 10A, hence ultimately it will be

(-8, 10, 10)

46. A variable w is related to three other variables x, y, z as w = xy/z. the variables are measured with

meters of accuracy 0.5% reading, 1% of full scale value and 1.5 reading. The actual readings

of the three meters are 80, 20 and 50 with 100 being the full scale value for all three. The

maximum uncertainty in the measurement of w will be

(a) 0.5% (b) 5.5% (c) 6.7% (d) 7.0%

Sol:

W=xy/z

Relative limiting error of w,

w/w = (w/x + w/y + w/z)

= (0.4/80 + 1/20 + 0.75/50 )

= 7% reading

47.The figure shows a three-phase delta connected load supplied from a 400V,50Hz,3-phase

balanced source. The pressure coil(PC) and current coil(CC) of a wattmeter are connected to

the load as shown,with the coil polarities suitably selected to ensure a positive deflection. The

wattmeter reading will be

A. 0 B. 1600Watt C. 800Watt D. 400Watt

Ans: C

48. An analog voltmeter uses external multiplier settings. With a multiplier setting of 20k, it reads

440V and-with a multiplier setting of 80k it reads 352V. For a multiplier setting of 40k,voltmeter

reads

A. 371V B. 383V C. 394V D. 406V Ans: D

49.the measurement of Hall coefficient of a semiconductor with one type of charge carrier gives the

information about

A. sign of charge carrier B. density of charge carrier C. both sign and density of charge carrier D. mass of the charge carrier Ans:C

50. The measurement system shown in the figure uses three sub systems in cascade whose gains are

specified as G1, G2 and 1/G3. The relative small errors associated with each respective subsystem

G1, G2,G3 are 1,2 and 3.The error associated with the output is

A.1+2+1/3 B.(1.2)3 C.1+2-3 D.1+2+3 Ans:C

51.

Ans. D

Sol:

52. Digital data acquisition systems are used

i. Only when the output of the transducers is in digital form

ii. When physical process being monitored is slowly varying (narrow bandwidth)

iii. When low accuracy can be tolerated

iv. When high accuracy and low per channel cost is required

Which of these statements are correct?

(a) 1, 2 and 3 (b) 1, 3 and 4 (c) 1 and 3 (d) 2 and 4

Sol: - Digital data acquisition systems can be used with analog output as well as digital output

Of the transducers. Analog data can be converted into digital data through A/D converter.

Further, Digital data acquisition systems are highly accurate due to better noise immunity.

So, (d) is the correct option.

53. Which one of the following statements correctly represents the post acceleration in a Cathode Ray

Tube?

(a) It provides deflection of the beam

(b) It increases the brightness of the trace if the signal frequency is higher than 10 MHz.

(c) It accelerates the beam before deflection

(d) It increases the brightness of the trace of low frequency signal.

Sol:- In an electrostatic system of deflection, a low value of accelerating voltage (Ea) should be used to give high deflection sensitivity (S1/ Ea). This voltage is usually kept below 4kV. Although This voltage gives good sensitivity but reduces brightness, which can be seriously impaired at high frequencies. If, signals of frequencies higher than 10 MHz are to be displayed, post deflection acceleration is necessary to increase the brightness of the trace which otherwise would be dim. Hence, option (b) is correct.

54. Consider the following statements:

The value of earth resistance depends upon 1. Shape of electrode 2. Depth to which the electrode is driven into earth 3. Specific resistance of soil 4. Material of electrode Which of the following statements is correct? (a) 1,2,3 and 4 (b) 2,3 and 4 (c) 1 and 2 (d) 1,3 and 4

Sol: - The resistance of earth electrode should be low to give good protection. An earth electrode will only be effective so long it has a low resistance to the earth and can carry large currents without deteriorating. Hence option (a) is correct.

55. Which of the following electronic instruments can be used to frequency component of a waveform and its higher harmonics?

1. CRO 2. Vacuum tube voltmeter 3. Spectrum Analyzer 4. Distortion factor meter

Select the correct answer using the codes given below:

(a) 1 and 2 (b) 2 and 3 (c) 3 and 4 (d) 1 and 4

Sol: - Both spectrum analyzer and distortion factor meter are signal analyzers. A spectrum

analyzer sweeps the signal frequency band and displays a plot of amplitude versus frequency.

Distortion factor meter tunes out the fundamental signal and gives an induction of the

harmonics.

Hence option is correct.

56. In a single phase power factor meter, controlling torque is (a) Provided by spring control (b) Provided by gravity control (c) Provided by stiffness of suspension (d) Not required

Sol: - There will be two deflecting torques, one acting on the coil A and the other on coil B. the coil windings are so arranged that the torques due to the two coils are opposite in direction. So, there is no controlling torque.

57. A dc circuit can be represented by an internal voltage source of 50V with an output resistance of 100k. In order to achieve accuracy better than 99% for voltage measurement across its terminals, the voltage measuring device should have a resistance of at least.

(a) 10 M (b) 1 M (c) 2 M (d) 1k Sol: - EL/E0 = 49.5/50 = 1/(1+100k/ZL) ZL = 10 M

Hence, option (a) is correct.

58. In Electrodynamometer watt meters, the inductance of pressure coil produces error. The error is (a) Constant irrespective of the power factor of the load (b) Higher at high power factor load (c) Higher at low power factor load (d) Highest at unity power factor load Sol: - the error caused by pressure coil inductance is VIsin tan. With low power factor, the value of is large and therefore, the error is correspondingly large. Hence, option is correct.

59. An analog voltage signal whose highest significant frequency is 1 kHz is to be coded with a resolution of 0.01 percent for a voltage range of 0-10 V. the minimum sampling frequency and the minimum number of bits should respectively be

(a) 1 kHz and 12 (b) 1kHz and 14 (c) 2 kHz and 12 (d) 2 kHz and 14

Sol: - Minimum sampling frequency = Nyquist sampling rate = 2 kHz and

Resolution = 0.01 = 1/(2n 1) 100 => n 14 60. An ac voltmeter using full-wave rectification and having a sinusoidal input has an ac

sensitivity equal to (a) 1.414 times dc sensitivity (b) Dc sensitivity (c) 0.9 times dc sensitivity (d) 0.707 times dc sensitivity Sol: - For full-wave rectifier type of instruments Vavg = 0.9V where V= Vm/2. Hence option is correct.

61. Consider the following statements in connection with measurement of temperature: 1. A thermistor is highly sensitive as compared with platinum resistance

thermometer. 2. The resistance of a thermistor is solely a function of its absolute temperature

whether the source of heat is external, internal or both. 3. A thermistor has linear resistance temperature characteristics 4. Most thermistors exhibit negative resistance temeperature coefficient

Which of these statements are correct?

(a) 1,2 and 3 (b) 1,2 and 4 (c) 2,3 and 4 (d) 1,3 and 4 Sol:- Thermistor is a semiconductor device which is non-linear andighly sensitive as well as exhibit negative resistance temperature coefficient. Thermistors having positive resistance temperature coefficient are not useful as temperature transducers. Hence (b) is correct option

62. If an induction type energy meter runs fast, it can be slowed down by (a) Lag adjustment (b) light load adjustment adjusting the position of braking magnet and moving it closer from the centre of the disc (d)adjusting the position of braking magnet and moving it away from the centre of the disc Sol:- braking torque, TD R2 where R is the radial position of braking magnet with respect to the centre of the disc. Hence (d) is correct option

63. Consider the following statements about the DArsonval Movement: 1. It is best suited for d.c. current measurement 2. It responds to the average value of current 3. It measures the r.m.s value of a.c. currents 4. It could be used for power measurements Which of these statements is/are correct? (a) Only 1 (b) 1 and 2 (c) 2 and 3 (d) 1,2,3 and 4 Sol:- dArsonval ammeter is PMMC ammeter which measures average value. Hence (b) is correct option

64. What is the correct sequence of the following types of ammeters and voltmeters with increasing accuracy?

1. Moving iron 2. Moving coil permanent magnet 3. Induction Select the correct answer using the codes given below:

(a) 1,3,2 (b) 1,2,3 (c) 3,1,2 (d)2,1,3 Sol:- induction principle is more generally used for watt-hour meter than for ammeters and voltmeters owing to their comparatively high cost, and inaccuracy of induction instruments of the latter types. Hence is correct option.

65. If a high frequency AC signal, whose r.m.s. value is 2V, is applied to a PMMC

Instrument, then the reading of the instrument will be

(a) 2 V (b) 2 V (c) 1 V (d) zero

Sol:- A PMMC instrument is used for measurement of dc voltages and currents. When it

is connected to an ac supply, the average torque produced in the instrument will be zero.

So, it will read zero.

Hence (d) is correct option

66. A single-phase energy meter having meter constant of 200 rev/kWh is operating on 230V, 50 Hz supply with a load of 10 A, and at unity power factor for three hours

continuously. The number of revolutions shown by the meter during this period is

(a) 13800 (b) 1380 (c) 276 (d) 138

Sol:- number of revolutions shown by the energy meter = meter constant * energy consumed

= 200 * (230*10*3)/1000

= 1380 revolutions

Hence (b) is correct option

67. In the circuit shown, when the current through the branch AD is zero, the battery current IB is

(a) 1 mA (b) 2 mA (c) 10 mA (d) 20 mA

A

Sol:- Given that current through the branch AD is zero. This implies the case of bridge balance. At the balance condition, voltage across AB will be equal to voltage across BD. Also RAB=RBD => R = 120 Battery current IB = 1/(120||120+80||80)

IB = 1/ 100 = 10 mA Hence, option is correct option

68. When a steady current is passed through a ballistic galvanometer, then the deflection will Be

(a) maximum

(b) zero

(c) twice the normal value as it depends on Hibbert magnetic standard

(d) None of the above

Sol:- when a steady current is passed through a ballistic galvanometer, then the deflection

will be zero because, the net deflecting torque will be zero.

Hence, option (b) is correct.

69. The measurement of frequency can be carried out with

(a) Owens bridge (b) Wiens bridge (c) Maxwells inductance-capacitance bridge (d) Scherings bridge

Sol:- measurement of frequency can be carried out with Wiens bridge Hence, (b) is correct option

70. An angular deflection type indicating PMMC meter is provided with spring control and

(a) damping by air dashpot

(b) electromagnetic damping in the aluminium former only

(c) electromagnetic damping in the aluminium former and the moving coil as well

(d) no damping

Sol:- Generally, electromagnetic damping in the aluminium former is provided for a PMMC

type instrument with spring control.

Hence, (b) is correct option.

71. An advantage of PMMC instrument is that it

(a) is free from friction error

(b) has high torque-to-weight ratio of moving parts

(c) has low torque-to-weight ratio

(d) can be used on both AC and DC

Sol:- In a PMMC instrument, the deflecting torque is provided by the movement of coil of light

weight. Hence the torque to weight ratio of the moving parts in the instrument is high due to

which the sensitivity of the instrument is high.

Hence, (b) is correct option

72. The following is not essential for the working of an indicating instrument

(a) Deflecting torque (b) Braking torque

(c) Damping torque (d) Controlling torque

Sol:- For the working of an indicating instrument, braking torque is not essential.


73. Systematic error of an instrument for measurement can be minimized by

(a) selecting a proper measuring device for the particular application

(b) calibrating the measuring device against a standard device

(c) applying correction factors for change of ambient conditions

(d) carrying out all of the above

Sol:-

Systematic error of an instrument for measurement can be minimized by selecting a proper

measuring device for the particular application, calibrating the measuring device against a

standard device, applying correction factors for change of ambient conditions.

Hence, (d) is correct option

74. The following material is not used for making a piezoelectric transducer

(a) Rochelle salt (b) Barium titanate

(c) Chromium sulphide (d) Quartz

Sol:-

Chromium sulphide is not used for making a piezoelectric transducer.

Hence, is correct option

75. An electronic voltmeter gives more accurate readings in high resistance circuits as

compared to a non-electronic voltmeter because of its

(a) low meter resistance (b) high k/V rating

(c) high V/krating (d) high resolution

Sol:- An electronic voltmeter has high k/V rating. So, it has high sensitivity. Hence it gives more accurate readings in high resistance circuits as compared to a non-electronic voltmeter.

Hence (b) is correct option.

76. By mistake, an ammeter is used as a voltmeter. In all probabilities, it will

(a) give much higher reading (b) give extremely low reading

(c) indicate no reading at all (d) get damaged

Sol:- For an ammeter, the overall resistance is minimum when compared to a voltmeter. When it

is used as a voltmeter, higher current will flow which will cause overheating of the parts of the

instrument and hence it gets damaged.


77. The meter constant of a single-phase energy meter is 500 rev/kWh. It is found that with a

load of 5 kW, it makes 40 revolutions in 50 sec. The percentage error is

(a) 5.25% (b)10.5% (c) 15.25% (d) 20%

Sol:-

Meter constant = 500 rev/kWh.

Actual energy consumed = 5 * 50/3600 = 25/360 kWh.

Energy consumption as per meter reading = 40/ 500 = 0.08 kWh.

% error = (actual energy consumption-energy consumption as per meter reading)/ actual energy

consumption *100

= (0.06944-0.080)/0.06944 *100%

= -15.2%


78. A shunt resistance of 25is required for extending the range of an ammeter from 100

A to 500 A. The value of internal resistance of this ammeter will be

(a) 25 (b) 50 (c) 100 (d) 1000

Sol:-

Shunt resistance for extending range of ammeter is Rsh = Rm / (m-1)

Where, m = I/Im = 500

Therefore, meter resistance Rm = Rsh * (m-1) = 25 * (5-1) = 100 Hence, is correct option

79. Two resistances R1= 100 10%and R2 = 300 5% are connected in series. The resulting limiting error of the series combination is

(a) 5 (b) 15 (c) 25 (d) 30

Sol:-

Error in R1 = 100 * 10/100 = 10 Error in R2 = 300 * 5/100 = 15 Total limiting error of the series combination of R1 and R2 is = 10+15 = 25 . Hence, is correct option

80. A frequency counter can be used for the measurement of

1. fundamental frequency of input signal

2. time interval between two pulses

Which of these is /are correct?

(a) 1 only (b) 2 only (c) Neither 1 nor 2 (d) Both 1 and 2

Sol:-

A frequency counter can be used for the measurement of both

1. fundamental frequency of input signal

2. time interval between two pulses


81. Modern electronic multimeters measure resistance by

(a) taking advantage of an electronic bridge compensator for nulling

(b) forcing a constant current and measuring the voltage across unknown resistance

(c) using a bridge circuit

(d) applying a constant voltage across the unknown resistance and measuring the current

through it.

Sol:-

Modern electronic multimeters measure resistance by forcing a constant current and measuring

the voltage across unknown resistance.


82. Guard circuits are used in insulation resistance measurements to

(a) increase the range of resistance values measured

(b) reduce the effect of leakage current on measurement

(c) protect against external electric fields

(d) protect against external magnetic fields

Sol:-

Guard circuits are used in insulation resistance measurements to reduce the effect of leakage

current on measurement.


83. Match List I with List II and select the correct answer using the code given below the

Lists:

List I List II

A. Mutual inductance 1. Wien bridge

B. High Q inductance 2. Schering bridge C. Audio frequency 3. Hay bridge

D. Dielectric loss 4. Heaviside-Campbell bridge

Code:

A B C D A B C D

(a) 4 1 3 2 (b) 2 3 1 4

(c) 4 3 1 2 (d) 2 1 3 4

Sol:-

Wien bridge is used for measurement of audio frequency. Heaviside-Campbell bridge is

used for measurement of mutual inductance. Dielectric loss of a capacitor can be measured by

using a schering bridge. Hays bridge is used for measurement of high-Q inductance.


84. The preferred methods of measuring low resistance and the resistance of cable insulation

are respectively.

(a) V/I method and loss-of-charge method

(b) Kelvins double bridge and Megger test (c) Wheatstone bridge and Kelvins double bridge

(d) potentiometer method and Wheatstone bridge

Sol:-

Kelvins double bridge method is normally used for measuring low resistance and Megger is used to measure resistance of a cable insulation which is of the order of Mega ohms.

Hence, correct option is (b).

85. A 50 A meter with an internal resistance of 1 kis to be used as a DC voltmeter of range 50V. Then the voltage multiplying factor n is

(a) 100 (b) 10 (c) 1000 (d) 10000

Sol:-

Multiplying factor, n = V / Vm

= 50/ (50 A*1k = 1000


86. The value of resistance Rs to be added in series with an ammeter whose full-scale

deflection is of 0.1 mA and internal resistance is of 500, to make it suitable to measure (0-10) V is

(a) 0.02 k (b) 99.5k (c) 500.02 (d) 499.98

Sol:-

Shunt resistance to be added to ammeter, Rs = Rm/ (m-1)

= 500/((10/500)/0.1m-1)

= 99.5 k ohms

Hence correct option is (b)

87. For low resistance (from few micro ohms to one ohm) measurement, Which bridge is used? (A) Wheatstone bridge (B) Kelvin bridge (C) Guarded Wheatstone bridge (D) Maxwell bridge Sol:- Kelvin bridge is used for measurement of low resistance. Hence, (b) is correct option 88. Which bridge is used to determine frequency ? (A) Anderson bridge (B) De Sauty bridge (C) Wien bridge (D) Campbell bridge Sol:- Wien bridge is used for measurement of frequency. Hence, is correct option

89. The dielectric loss of a capacitor can be measured by which one of the following ? (A) Wien bridge (B) Owen bridge (C) Schering bridge (D) Maxwell bridge Sol:- The dielectric loss of a capacitor can be measured by Schering bridge. Hence, is correct option. 90. Inductance is measured by which one of the following ? (A) Wien bridge (B) Schering bridge (C) Maxwell bridge (D) Owen bridge Sol:- Inductance is measured by Maxwell bridge. Hence, is correct option. 91.Schering bridge can be used to measure which one of the following? (A) Q of a coil (B) Inductance and its Q-value (C) Very small resistance (D) Capacitance and its power factor Sol:- Schering bridge can be used to measure Capacitance and its power factor.

92. Which one of the following is used for the measurement of 3-phase

power factor ? (A) Power factor meter (B) Crossed-coil power factor meter (C) Phase-angle watt hour meter (D) Polarised-vane power factor meter Sol:- Power factor meter is used for measurement of 3-phase power factor. Hence, (a) is correct option 93. What is the swamping resistance which is connected in series with the working coil of a voltmeter to drastically reduce the error in measurement caused due to variation in temperature, made of ? (A) Constant (B) Eureka (C) Manganin (D) Nichrome Sol:- Swamping resistance is made up of a material having high temperature coefficient of resistance so that increase in temperature cannot affect its characteristics. Manganin is generally used as swamping resistance which is connected in series with a voltmeter pressure coil. Hence, is correct option.

94. How can a milli-ammeter be used as a voltmeter? (A) By connecting a low resistance in parallel with the instrument (B) By connecting a high resistance in parallel with the instrument (C) By connecting a low resistance in series with the instrument (D) By connecting a high resistance in series with the instrument Sol:- a milli-ammeter be used as a voltmeter by connecting a high resistance in series with the instrument. Hence, (d) is correct option 95. Due to which one of the following reasons bearing of PMMC Instrument are made of Jewel ? (A) To avoid wear and tear of the moving system (B) To provide a small support (C) It can be easily replaced (D) To make the system robust Sol:- Bearing of PMMC Instrument are made of Jewel to avoid wear and tear of the moving system. Hence, (a) is correct option 96. The imperfect capacitance which is shunted by a resistance can be measured by which one of the following? (A) Carey Foster bridge (B) Owen bridge (C) Schering bridge (D) Wien bridge Sol:- The imperfect capacitance which is shunted by a resistance can be measured by Schering bridge. Hence, is correct option 97. Which of the following statements are correct in case of a power factor meter? 1. The deflection is proportional to the phase angle between field coil and crossed coil. 2. The restoring torque is provided by a controlling torque. 3. It consists of two coils mounted at right angles to each other. Select the correct answer using the code given below: (A) 1 and 2 (B) 2 and 3 (C) 1 and 3 (D) 1, 2 and 3 Sol:- A power factor meter the deflection is proportional to the phase angle between field coil and crossed coil. It consists of two coils mounted at right angles to each other. Hence, is correct option 98. In a low power factor wattmeter, why is a compensating coil employed? (A) To neutralize the capacitive effect of pressure coil (B) To compensate for inductance of pressure coil (C) To compensate for the error caused by power loss in the pressure coil

(D) To compensate for the error caused by eddy currents Sol:- In a low power factor wattmeter, why is a compensating coil employed to compensate for inductance of pressure coil. Hence, (b) is correct option 99. Which one of the following instruments is used for standardization of a Drysdale a.c. potentiometer ? (A) Rectifier type ammeter (B) PMMC ammeter (C) Precision type electrodynamometer ammeter (D) Thermocouple ammeter Sol:- Precision type electrodynamometer ammeter is used for standardization of a Drysdale a.c. potentiometer. Hence, is correct option 100. Match List I (Property) with List II (Type of the Instrument) and select the correct answer using the codes given below the lists :

List I List II A. Linear scale 1. Thermocouple type B. True r.m.s. up to RF Range 2. Rectifier type C. r.m.s. only for sinusoidal input 3. Moving iron type D. Reads r.m.s. value using square law scale 4. Permanent magnet moving coil type Codes :

A B C D A B C D

(A) 1 4 3 2 (B) 4 1 2 3 (C) 4 1 3 2 (D) 1 4 2 3 Sol:- Correct option is (b) 101. Flux meter is a special type of ballistic galvanometer provided with which one of the following ? (A) Heavy electromagnetic damping and very small controlling torque (B) Heavy electromagnetic damping and very large controlling torque (C) Small electromagnetic damping and small controlling torque (D) Large controlling torque and small electromagnetic damping

Sol:-

In a flux meter, a special type of ballistic galvanometer provided with very small controlling

torque and large electromagnetic damping.

Hence, (a) is correct option

102. Why is damping of a ballistic galvanometer kept small? (A) To get minimum overshoot (B) To make the system critically damped (C) To make the system oscillatory (D) To get first deflection large Sol:- To get minimum overshoot, damping of a ballistic galvanometer kept small. Hence, (a) is correct option 103. Match list I with list II and select the correct answer using the code given below the lists:

List I List II

(Type of Instrument) (Example)

A. Indicating 1. Wattmeter B. Absolute 2. Tangent galvanometer C. Recording 3. Aneroid barometer D. Integrating 4. Energy meter

Code:

A B C D

(a) 1 2 3 4 (b) 4 2 3 1 (c) 1 3 2 4 (d) 4 3 2 1

Sol:-

Wattmeter is an indicating instrument. Tangent galvanometer is an absolute instrument. Aneroid

barometer is a recording instrument. Energy meter is an integrating type instrument.


104. Dissipation factor, tan of a capacitor is measured by which bridge ? (a) Anderson bridge (b) Hay bridge {c) Schering bridge (d) Wien bridge

Sol:-

Dissipation factor is normally measured using Schering bridge.


105. A D'Arsonvnl galvanometer. 1 mA, 50 ohm is to be converted to a 5 Amp-ammeter. What

is the value of the shunt resistor, Rsh ?

(a) 10 ohm (b) 1 ohm (c) 001 ohm (d) 100 ohm

Sol:-

Shunt resistance to be connected, Rsh = Rm/(m-1)

Where, m = I/Im

Rsh = 50/(5/5m-1) = 0.01 ohm


106. A 0 to 300 V voltmeter has an error oft: 2% of fsd. What is the range of readings if true voltage is 30 V?

(a) 24V-36V (b) 20V-40V (c) 294 V - 306 V d) 20V-30V Sol:- % error on 0-300v scale = 2/100* 300 = 6V If the voltage is 30V, % error = 30+6 = 24 to 36V Hence, (a) is correct option 107. ln a digital voltmeter, the oscillator frequency is 400 kHz. The ramp voltage falls from 8 V to 0 V in 20 ms. what is the number of pulses counted by the counted? (a) 8000 (b) 4000 (c) 3200 (d) 1600

Sol:-

No. of pulses = 400 1032010-3

= 8000


108. Which one of the following is frequency sensitive bridge? (a) De-Sauty bridge (b) Schering bridge (c) Wiens bridge (d)Maxwell's bridge

Sol:-

Wiens bridge is frequency sensitive bridge. Hence, is correct option

109. If the bandwidth of an oscilloscope is given as direct current to 10 MHz, what is the fastest

rise time a sine wave can have to be produced accurately by the oscilloscope/

(a) 35 nsec (b) 10 nsec (c) 3.5 nsec (d) 0.035 nsec

Sol:-

Tr = 0.35/ B.W = 0.35/ (10106) = 35 nsec

Hence, (a) is correct option.

110. A 100 kV, 50 Hz supply is fed to a rectifier ammeter (using a bridge rectifier) through a

capacitor. The PMMC ammeter of the rectifier instrument reads 45 10-3 amp. What is the value

of the capacitor?

(a) 15.910-10 F (b) 15.910-12 F (c) 17.6610-9 F (d) 17.6610-11 F

Sol:-

Bridge rectifier output is, V0 = 2Vm/ V0 = I Xc

2 Vm/ = I/C 2100103 2/ = 4510-3/ (250C)

C = 15.910-9 F Hence, (a) is correct option

111. Which one of the following is not the criterion used to select potentiometer in a control

system?

(a) Accuracy (b) Noise (c) Time response (d) Frequency restiponse

Sol:-

Noise is not the criterion used to select potentiometer in a control system.


112. The resolution of DAC is governed by which one of the following (where n is the number

of digital inputs)?

(a)2n (b) 2/n (c) 2n (d) 2n

Sol:-

Resolution = Vmax/(2n-1)


113. Which one of the following statements is correct?

Spiral springs are used in instruments to

(a) Provide controlling torque (b) provide damping torque lead the current to moving coil as well as to provide the controlling torque

(d) Provide linear deflection

Sol:-

Spiral springs are used in instruments to lead the current to moving coil as well as to provide

the controlling torque.


114. Which one of the following decides the time of response of an indicating instrument?

(a) deflecting system (b) controlling system (c) damping system (d) pivot and jewel bearing

Sol:-

Damping system decides the time of response of an indicating instrument.


115. Which one of the following is measured by the loss of charge method?

(a) Low R (b) High R (c) Low L (d) High L

Sol:-

High R is measured by the loss of charge method.

Hence, (b) is correct method.

116. The power of a three phase, three wire balanced system was measured by two wattmeter

method. The reading of one of the watt meters was found o be double that of the other. What is

the power factor of the system?

(a) 1 (b) 0.866 (c) 0.707 (d) 0.5

Sol:-

Cos = cos (tan-1(3(2P-P)/(2P+p))) = 0.866


117. To measure 5 Volts, if one selects a 0-100 volt range voltmeter which is accurate within +

1%, then the error in this measurement may be up to

(a) + 1.5% (b) + 2.5% (c) + 7.5% (d) + 20%

Sol:-

Magnitude of error = 1*100/100 1V

% of error = 1*100/5 = + 20%


\

118. The voltage coil of a single-phase house service energy meter

(a) is highly resistive (b) is highly inductive (c) is highly capacitive (d) has

a phase angle equal to load power factor angle.

Sol:-

The voltage coil of a single-phase house service energy meter is highly inductive.


119. What is the series resistance required to extend the 0-100V range of a 20000/V meter to 0-1000 V?

(a) 10 M (b) 16 M (c) 18 M (d) 20 M

Sol:-

Initial resistance = 20000100 = 2 M Final resistance = 200001000 = 20 M Therefore, series resistance = 20-2 = 18 M Hence, is correct option

120. Hays bridge is suitable for the measurement of which one of the following?

(a) Inductance with Q10 (c) Capacitance with high dissipating

factors (d) capacitance with low dissipating factors

Sol:-

Hays bridge is suitable for the measurement of Inductance with Q>10 Hence, (b) is correct option

121. A 0-100V voltmeter has an accuracy of 1 percent at full-scale reading. What will be the

error if it reads 50V?

(a) 1% (b) 2% (c) 0.5% (d) 4%

Sol:-

Magnitude of limiting error = 0.01*100 = 1V

% error = 1*100/50 = 2%


122. The value of shunt resistance required to convert an ammeter of 1mA with 100 ohms

internal resistance into 0-100 mA ammeter is

(a) 2.2 ohm (b) 1.01 ohm (c) 1.2 ohm (d) 1.1 ohm

Sol:-

Shunt resistance, Rsh = Rm/m-1

Where, Rm = 100 ohm and m = 100/1 = 100

Therefore, Rsh = 100/99 = 1.01 ohm


123. when reading is taken at half scale in the instrument, the error is

(a) exactly equal to half of full-scale error

(b) equal to full-scale error

less than full-scale error

(d)More than full-scale error

Sol:-

Always the error is taken as % of true value.

Hence, is correct option.

124. Match the following:

List I List II

A. Average value of current 1. Self balancing bridge B. RMS value of current 2. Wien bridge C. Frequency of a wave 3. PMMC ammeter D. Strain gauge resistance 4. Moving iron ammeter

Codes:

A B C D A B C D

(a) 3 4 2 1 (b) 2 1 3 4

3 1 2 4 (d) 2 4 3 1

Sol:-

Average value of current is measured by PMMC ammeter.

RMS value of current is measured by Moving iron ammeter.

Frequency of a wave is measured by Wien bridge.

Strain gauge resistance is measured by Strain gauge resistance.


125. A rectifier instrument is used to measure an alternating square wave of amplitude 100V.

What is the meter reading?

(a) 100V (b) 70.7V (c) 111V (d) None of these

Sol:-

Meter reading, V0 = 0.707 Vdc = 0.707100 = 70.7V.


126. A single slide wire is used for the measurement of current in a circuit. The voltage drop

across a standard resistance of 1.0 ohm is balanced at 70 cm. What is the magnitude of the

current, if the standard cell having an emf of 1.45 volts is balanced at 50 cm?

(a) 3.09 A (b) 2.65 A (c) 2.03 A (d) 1.45 A

Sol:-

Voltage drop per unit length = 1.45/50 = 0.029 V/cm

Voltage drop across 70 cm length = 0.029 70 = 2.03 V

Therefore, current through resistor = 2.03/ 1 = 2.03 A


127. What is the range for a 3 digital meter?

(a) 0 to 1999 (b) 0 to 1500 (c) 0 to 999 (d) 0 to 19999

Sol:-

A three digit display on a digital voltmeter for 0-1V range will be able to indicate vales from

zero to 999 mV, with smallest increment or resolution of 1mV. In practice a fourth digit usually

capable of indicating either 0 or 1 only is placed to the left of active digits. This permits going

above 999 to 1999 to give overlap between ranges for convenience. This is called over ranging.

This type of display is known as a 3 digit display.


128. A moving coil instrument gives full scale deflection for 1 mA and has a resistance of 5 ohm.

If a resistance of 0.55 ohm is connected in parallel to the instrument, what is the maximum value

of current it can measure?

(a) 5 mA (b) 10 mA (c) 50 mA (d) 100 mA

Sol:-

V = 51 = 5V

New resistance = (555)/5.55 = 55/111 Therefore, Imax = (5111) / 55 = 10 mA


129. Data acquisition systems are usually of

(a) analog type (b) digital type (c) Integrating type (d) hybrid type

Sol:-

Data acquisition systems are usually of digital type.


130. what is clamp-on ammeter used for?

(a) low ac current (b) high ac current (c) low dc current (d) high dc current

Sol:-

Clamp on ammeter is used for high ac current.


131. which one of the following instrument is commonly used to measure primary current of a

transformer connected to mains?

(a) Electrostatic meter (b) Current transformer

(c) Moving coil type meter (d) moving iron meter

Sol:-

Moving iron ammeter is used to measure primary current of a transformer connected to mains.


132. The errors introduced by an instrument fall in which category?

(a) Systematic errors (b) random errors (c) Gross errors (d) Environmental errors

Sol:-

The errors introduced by an instrument fall in systematic errors category.


133. Which one of the following passive components has the most precise and accurate

standard?

(a) Resistance (b) Inductance (c) Capacitance (d) Conductance

Sol:-

Inductance has the most precise and accurate standard.


134. Which amplifier is used in an electronic multimeter?

(a) power amplifier (b) Buffer amplifier (c) Differential amplifier (d) Wideband

amplifier

Sol:-

Differential amplifier is used in an electronic multimeter.


135. What is the approximate input impedance of a CRO? (A) Zero (B) 1 M (C) 10 (D) 10

Sol:-

CRO has high i/p impedance.


136. Match List I (Type of Digital Voltmeter) with List II (It construction features) and select the correct answer using the codes given below the lists :

List I List II A. Basic ramp type DVM 1. Uses D/A converter B. Staircase-ramp type DVM 2. True average value of

Input voltage using voltage Frequency converter

C. Integrating type DVM 3. Servo-driven potentiometer Is commonly used D. Continuous balance type 4. Does not use D/A converter DVM Codes:

A B C D A B C D

(A) 1 2 3 4 (B) 4 1 2 3 (C) 1 2 4 3 (D) 4 1 3 2 Sol:- Integrating type DVM measure true average using voltage to conversion. Basic ramp type DVM does not use D/A converter. Staircase-ramp type DVM uses D/A converter. Continuous balance type DVM is used in servo-driven potentiometer. Hence, (b) is correct option 137. The measurement of very low and very high frequencies is invariably done using a frequency counter in which one of the following? (A) Frequency measurement mode only (B) Period measurement mode only (C) Frequency and period measurement modes, respectively (D) Period and frequency measurement modes, respectively Sol:- Low frequency measurement in frequency mode gives low-accuracy. So, period measurement is used. Hence, (d) is correct option.

138. Consider the following statements

(i) The compensating coil of a low power factor wattmeter compensates the effect of the impedance of the current coil.

(ii) The compensating coil of a low power factor wattmeter compensates the effect of the impedance of the voltage coil circuit.

(A) (i) is true but (ii) is false (B) (i) is false but (ii) is true (C) both (i) and (ii) are true (D) both (i) and (ii) are false Sol:- Compensating coil of a low power factor wattmeter compensates the effect of the impedance of pressure coil or voltage coil circuit. Hence, (b) is correct option 139. Match the following: List I (Instrument) List II (Damping)

A. Moving iron and hot wire type 1. Air friction B. Galvanometer 2. Electromagnetic C. PMMC type 3. Fluid friction D. Electrostatic type 4. Eddy current Codes: A B C D A B C D

(a) 1 4 2 3 (b) 3 4 2 1 1 2 4 3 (d) 3 1 2 4

Sol:- Air friction does not require the use of permanent magnet whose introduction may lead to distortion of operating field. This damping is used whose operating field is weak. It is generally used in moving iron, dynamometer, hotwire instruments. Galvanometer uses electromagnet damping. PMMC type instrument uses eddy current damping. Electrostatic instrument uses fluid friction damping. Hence, is correct option. 140. In a vibrating reed type frequency meter, all the reeds (a) are of identical dimensions and weight (b) have different natural frequencies have the same natural frequencies (d) are not placed closed to an

electromagnet Sol:- Vibrating reed frequency meter indicates the supply frequency by means of individual reeds. When rated voltage is applied across the terminals of the meter, the particular reed whose natural frequency of vibration coincides with the supply frequency, vibrate with full amplitude. Hence, (b) is correct option

141. The main function of a damping torque in an indicating electrical instrument is to

(a) Bring the pointer to rest quickly (b) Prevent sudden movement of the pointer (c) Make pointer deflection gradual (d) Provide friction Sol:- Due to moment of inertia present in the moving parts of the instrument, it cannot reach quickly to its steady state. To bring it to steady state position, damping torque is required. Hence, (a) is correct option 142. Electrostatic instruments are most commonly used as (a) Ammeters (b) Voltmeters (c) Watt meters (d) All of the above Sol:-

Electrostatic instruments are most commonly used as Voltmeters. Hence, (b) is correct option

143. Instrument transformers are known to introduce magnitude and phase errors in measurements. These are primarily due to (a) improper connections on the primary side (b) measurement errors inherent in the meter connected to the transformer secondary (c) open and short circuit parameters of the instrument transformers (d) None of the above Sol:-

Magnitude and phase errors in measurements of an instrument transformers are primarily due to open and short circuit parameters of the instrument transformers. Hence, option is correct. 144. If an energy meter disc makes 10 revolutions in 100 seconds when a load of 450 W is connected to it, the meter constant (in rev/kWh) is

(a) 1000 (b) 500 (c) 1600 (d) 800

gate-2014 electrical measurements

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