Electrical Measurements - 4 - PDF Flipbook
Electrical Measurements - 4
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GATE
EEE
Electrical
Measurements
Test-04Solutions
ELECTRICAL MEASUREMENTS
1. Two holes are drilled in the disc on a diameter of energy-meter
to
a) increase ventilation
b) reduce the weight of disc
c) eliminate creeping on no-load
d) increase deflecting torque
Answer: (c)
Solution:
To eliminate creeping on no-load condition two holes are drilled
in the disc on a diameter of energy meter
2. For measuring the signal level of individual harmonics in an
unknown waveform, which of the following instruments are
useful?
1. Distortion analyzer
2. Wave analyzer
3. Spectrum analyzer
Select the correct answer using the code given below:
a) 1 and 2 only
b) 2 and 3 only
c) 1 and 3 only
d) 1, 2 and 3
Answer: (d)
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Solution:
Spectrum analyzer: Portray amplitude as function of frequency.
Distortion analyzer: It analyses the distorted waveform by
analyzing frequency distortion, phase distortion.
3. In a semiconductor strain gauge, the change in resistance on
application of strain is mainly due to the change in its
a) Length
b) Diameter
c) Resistivity
d) Length and diameter
Answer: (d)
Solution:
Gauge factor, Gf = 1 + 2V
Gf = ∆R , V = − ∂D/D
R ∂L/L
∆L
L
4. A wheat stone bridge has ratio arm of 1000 Ω and 100 Ω
resistances, the standard resistance arm consists of 4-decade
resistance boxes of 1000, 100, 10, 1 Ω steps. The maximum and
minimum values of unknown, resistance that can be determined
with this setup are:
a) 111100 Ω, 10 Ω
b) 111100 Ω, 1 Ω
c) 11110 Ω, 10 Ω
d) 10000 Ω, 10 Ω
Answer: (a)
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5. Consider the following statement:
Dual – slope integration type Analog – to – Digital converters
provide
1. Higher speeds compared to all other types of A/D converters.
2. Very good accuracy without putting extreme requirements on
component stability.
3. Good rejection of power supply hum.
Which of the statements given above is/are correct?
a) 2 and 3
b) 1 and 2
c) 1 and 3
d) 3 only
Answer: (a)
Solution:
• Maximum speed is that of flash or parallel A/D converter.
• Noise immunity as noise rejected during integration
6. The slope and level detector circuit in a CRO has a delay of 100
ns. The start-stop sweep generator has a response time of 50 ns.
In order to display correctly, a delay line of
a) 150 ns has to be inserted into the y-channel
b) 150 ns has to be inserted into the x-channel
c) 150 ns has to be inserted into both x and y-channels
d) 100 ns has to be inserted into both x and y-channels
Answer: (a)
3
Solution:
In order to display correctly, a delay line of 150 ns has to be
inserted in to the Y-channel between output of vertical amplifier
and Y-input of CRT.
7. In a CRO, a sinusoidal waveform of a certain frequency is
displayed. The value of the quantity that can be made out by
observation is
a) rms value of the sine wave.
b) average value of the sine wave.
c) form factor of the sine wave.
d) peak-peak value of the sine wave.
Answer: (d)
Solution:
In a CRO, in sinusoidal waveform peak to peak value of the sine
wave can be observed.
8. If a dynamometer type wattmeter is connected in an AC circuit,
the power indicated by the wattmeter will be:
a) Peak power
b) Instantaneous power
c) Volt ampere product
d) Average power
Answer: (d)
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Solution:
Dynamometer type wattmeter measures active power (average
power) in an AC circuit given by
P = VI cosϕ
Here, V and I rms values
9. Which one of the following statements is correct?
In an energy meter, the braking device is provided produce
braking torque so that the
a) Energy meter can be brought to a standstill
b) Meter creeping be checked
c) Moving system of the instrument (disc) rotates at speed for a
particular rate of energy consumption any time
d) Shunt field flux lags behind voltage by exactly 900
Answer: (c)
Solution:
Braking system operates such that,
Braking torque = Driving torque
It will cause the disc of energy meter to rotate at
Constant speed for a particular energy input rate.
10. The controlling torque in a meager is provided by
a) spring
b) weights attached to the moving system
c) it does not need any controlling torque
d) none of these
Answer: (c)
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11. Match List-I (Bridges) with List-II (Measurements) and
select the correct answer using the code given below the lists:
List – I
A. Maxwell
B. Hay
C. Schering
D. Wien
List - II
1. Frequency
2. Capacitance
3. High ‘Q’ coil
4. Inductance
Codes:
A BC D
a) 4 3 2 1
b) 1 3 2 4
c) 4 2 3 1
d) 1 2 3 4
Answer: (a)
Solution:
Maxwell: inductance
Hay: High Q
Wein: Frequency
Scheming: Capacitance
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12. A dc electronic voltmeter using chopper stabilization is free
from errors due to
a) low CMRR
b) amplifier drift
c) source output impedance
d) interference
Answer: (c)
13. Wagner's Earth Devices are used for a.c. bridge circuits for
a) Eliminating the effect of earth capacitances
b) Eliminating the effect of line capacitances
c) Eliminating the effect of stray electrostatic fields
d) Shielding the bridge elements
Answer: (a)
Solution:
If earth capacitances are not eliminated, null point may not be
obtained correctly.
14. Two meters X and Y required 40 mA and 50 mA respectively
for full scale deflection. Then,
a) Both are equally sensitive.
b) Data are insufficient to comment.
c) X is more sensitive than Y
d) Y is more sensitive than X
Answer: (c)
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Solution:
Sensitivity = 1
= full scale current
Hence, X = 40 mA in more sensitive than Y = 50 mA
15. The ballistic galvanometer is usually lightly damped so that
a) It may oscillate.
b) It may remain stable.
c) Amplitude of the first swing is large.
d) Amplitude of the first swing is small.
Answer: (c)
Solution:
Ballistic galvanometer is used to measure the charge passing
through it Owing to transitory current, it oscillates. The
amplitude of first deflection is proportional to charge passing.
So first defection should be large. The damping of system must
be small, so as to have first large deflection.
16. In a moving-iron meter, the deflecting torque is proportional to
a) square of the current through the coil
b) current through the coil
c) sine the measurand
d) square-root of the measurand
Answer: (a)
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17. A transfer instrument employed in the standardization of a
polar type a.c potentiometer is
a) an electrostatic instrument
b) a thermal instrument
c) a dynamo meter instrument
d) a moving coil instrument
Answer: (b)
18. Glare is caused due to
a) none of (c) and (d)
b) both of (c) and (d)
c) excessive lighting contrast in the field of vision
d) excessive luminance
Answer: (b)
Solution:
Glare is caused due to excessive luminance and lighting contrast
in the field of vision.
19. 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
Answer: (c)
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Solution:
Meter constant is 14.4 A-sec/rev
= 14.4 A − h/rev
3600
and V(A − h/rev) = 250×14.4 = 1
3600
Wh = 1 rev
kWh/rev = 1000
∴ meter constant = 1000 rev/kWh
20. The current in a circuit consists of a DC component of 10A
superposed on a 50 Hz sinusoidal component of rms value of
10A. The reading shown by a PMMC ammeter will be
a) 10√2
b) 20
c) 10 A
d) 10 + 10
Answer: (c)
Solution:
PMMC meter responds only to dc component, hence reading of
the meter will be 10A.
21. The potential coil of a wattmeter is designed for minimum
inductance. Therefore, the current through it is
a) inversely proportional to the voltage and out of phase with it
b) proportional to the voltage and out of phase with it
c) proportional to the voltage and in phase with it
d) inversely proportional to the voltage and in phase with it
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Answer: (c)
22. Spectrum analyzer is a combination of which of the following?
a) Narrow band super heterodyne receiver and CRO
b) Signal generator and CRO
c) Oscillator and wave analyzer
d) VTVM and CRO
Answer: (a)
Solution:
Spectrum analyzer: Graphically plot amplitude vs frequency of
a Selected portion of frequency spectrum.
23. Among the measuring instruments for current and voltage the
instrument that can be used as a secondary standard is
a) Thermocouple
b) Electrodynamometer
c) Moving iron
d) Electrostatic
Answer: (b)
24. Creeping in energy-meters implies that
a) fast rotation of the rotor with current coil excited
b) slow rotation of the rotor with current coil excited
c) slow rotation of the rotor with only voltage coil excited
d) none of these
Answer: (c)
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25. Which of the following is/are essential sub-system(s) of a data
acquisition system?
1. ADC
2. DAC
3. RAM
4. Processor
5. Network card
Select the correct answer using the codes given below:
a) 1, 2, 3 and 4
b) 3 and 5
c) 4 only
d) 1, 3 and 4 only
Answer: (d)
Solution:
Network card may not be essential for data acquisition system.
It can also be a standalone system.
26. The following units are user in a data acquisition stem:
1. Central Processing Unit
2. Memory
3. Transducer
4. ADC
The sequence of placement of these units from input to output is
a) 4, 3, 1, 2
b) 3, 4, 1, 2
c) 3, 4, 2, 1
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d) 4, 3, 2, 1
Answer: (b)
Solution:
27. A very accurate voltmeter gives inaccurate readings when used
to measure voltage across a law resistance because
a) the sensitivity of the meter is high
b) the sensitivity of the meter is too low
c) the higher scale has been selected
d) the voltmeter is drawing too low current
Answer: (b)
28. Electro dynamic type watt meters have large errors while
measuring power in a.c circuits at low power factor conditions,
since the voltage across and the current though the
a) current coil is not in phase
b) current coil is not in quadrature
c) pressure coil is not in phase
d) pressure coil is not in quadrature
Answer: (c)
29. When using ohmmeter, applied voltage disconnected from the
circuit because
a) voltage source will increase resistance
b) current will decrease resistance
c) the ohmmeter has its own internal battery
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d) none of these
Answer: (c)
30. Two meters X and Y require 40 mA and 60 mA, respective to
give full-scale deflection, then
a) X is more sensitive
b) Y is more sensitive
c) both are equally sensitive
d) sensitivity cannot be judged with the given information
Answer: (a)
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