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6. Measurement
1. Errors in instruments 1.1 – 1.12
2. Measurement of R,L,C,F 2.1 – 2.18
3. Indicating instrument 3.1 – 3.21
4. Power & energy 4.1 – 4.18
5. Electronic instrument 5.1 – 5.12
6. Transducers 6.1 – 6.15
Measurement MASTERPLUS EDUCATION®|1.1
CHAPTER
ERRORS IN
INSTRUMENTS 1
Q.1 The use of electronic instruments is Q.6 A pressure gauge is calibrated from 0-50
becoming more extensive because they have kN/m². It has a uniform scale with 100 scale
(a) the capability to respond to signals from divisions. One fifth of a scale division can
remote places be read with certainty. The gauge has a
(b) a fast response and compatibility with (a) threshold of 0.1 kN/m²
digital computers (b) dead zone of 0.2 kN/m²
(c) both (a) and (b) (c) resolution of 0.1 kN/m²
(d) a high sensitivity but less reliability (d) both (a) and (b)
Q.2 A multimeter having a sensitivity of 2 kΩ/V Q.7 A resistance is determined by voltmeter-
is used for the measurement of voltage ammeter method. The voltmeter reads 100
across a circuit having an output resistance V with an uncertainty of ±12V and the
of 10 k. The open circuit voltage of the ammeter reads 10 A with an uncertainty of
circuit is 6 volts. The percentage error in ±2 A. The uncertainty in the measurement
multimeter reading when it is set to 10 volt of resistance is
is given by (a) 1.56 Ω (b) 0.26 Ω
(a) 33% low (b) 22% high (c) 3.25 Ω (d) 2.33 Ω
(c) 33% high (d) 22% low
Q.8 The resistance of an unknown resistor is
Q.3 A 50 V range voltmeter is connected across determined by Wheatstone bridge. The
the terminals X and Y of the circuit shown solution for the unknown resistance is stated
in figure below. The voltage across the as:
terminals are measured both under open R1 R2
circuit and loaded conditions. R4
R3
200 k
X where limiting values of various resistances
500V are:
100V 200 k Voltmeter R1 500 1%
1000 k
Y R2 615 1%
The accuracy in the measurement of voltage
across the terminals X and Yin percent is R3 100 0.5%
(a) 9.1% (b) 90.9% The limiting error of the unknown resistor in
(c) 45.45% (d) 4.54% ohm is
(a) 76.88 (b) 66.66
Q.4 The number of significant figures in the two (c) 3.07 (d) 98.76
resistors having resistances 4 106 k and
0.345 kΩ are respectively Q.9 Dynamic response consists of
(a) 6 and 3 (b) 2 and 4 (a) two parts, one steady state and the other
(c) 1 and 4 (d) 1 and 3 transient state response
(b) only transient state response
Q.5 An ammeter reads 6.7 A and the true value (c) only steady state response
of current is 6.5 A. The correction factor is (d) steady state and transient frequency
(a) 0.97 (b) 0.20 response.
(c) 0.03 (d) none of these
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Q.10 Match List-I (Quantity) with List-II Q.14 Match List-I (Dynamic characteristics of an
(Dimensions) and select the correct answer Instrument) with List-II (Definition) and
using the codes given below the lists: select the correct answer using the codes
List-I List-II given below the lists:
A. Emf 1. [MT 2 I 1 ] List-I
B. Magnetic flux density 2. [M 1L2T 2 I 2 ] A. Speed of response
B. Fidelity
C. Magnetizing force 3. [ML2T 3 I 1 ] C. Lag
D. Reluctance 4. [ L1 I ] D. Dynamic Error
Codes: List-II
A B C D 1. the delay in the response of an instrument
(a) 2 1 3 4 to changes in the measured variable.
(b) 3 1 2 4 2. the difference between the true value of a
(c) 3 2 4 1 quantity changing with time and the value
(d) 3 1 4 2 indicated by the instrument.
3. the degree to which an instrument
Q.11 Match List-I (Damping Mechanism) with indicates the changes in the measured
List-II (Applications) and select the correct variable.
answer using the codes given below the 4. the rapidity with which an instrument
lists: responds to changes in the measured
List-I quantity.
A. Fluid friction damping Codes:
B. Electromagnetic damping A B C D
C. Eddy current damping (a) 4 1 3 2
D. Air friction damping (b) 4 3 1 2
List-II (c) 4 2 1 3
1. Electrostatic instruments (d) 1 4 2 3
2. Galvanometers
3. PMMC instruments Q.15 The difference between the expected value
4. Moving iron instruments of the variable and the measured variable is
Codes: termed as
A B C D (a) absolute error (b) random error
(a) 1 2 3 4 (c) instrumental error (d) gross error
(b) 2 1 3 4
(c) 4 3 2 1 Q.16 Limiting errors are
(d) 4 2 3 1 (a) manufacturer's specifications of accuracy
(b) manufacturer's specifications of instrum-
Q.12 Assertion (A): The frictional torque exerts a ental error
considerable influence on the performance (c) environmental errors
of an indicating instrument. (d) random errors
Reason (R): If the weight of moving parts
is large, the frictional torque will be small. Q.17 Consider the following statements about the
(a) Both A and R are true and R is a correct null type instruments used in measurement
explanation of A. and instrumentation:
(b) Both A and R are true but R is not a 1. Null type instruments are more accurate
correct explanation of A. than deflection type instruments.
(c) A is true but R is false. 2. Null type instruments can be highly
(d) A is false but R is true. sensitive as compared with deflection types
instruments.
Q.13 Improper setting of range of multimeter 3. Null type instruments are more suited for
leads to an error called measurements under dynamic conditions.
(a) random error (b) limiting error 4. ADC potentiometer and a Wattmeter are
(c) instrumental error (d) observational error null type instruments.
Measurement MASTERPLUS EDUCATION®|1.3
Which of the above statements are correct? standard deviation. Current I is measured as
(a) 2, 3 and 4 (b) 1, 2, 3 and 4 (a) (400 ± 3) A (b) (400 ± 2.24) A
(c) 1 and 2 (d) 1, 2 and 3 (c) (400 ± 1/5) A (d) (400 ± 1) A
Q.18 Match List-I with List-II and select the Q.22 The dead tire an instrument refers to..........
correct answer using the codes given below (a) Large change of input quantity for which
the lists: there is no output
List-I List-II (b) The time encountered when the
A. Instrumental errors 1. Parallax error instrument has to wait for some reactions to
B. Observational 2. Human mistakes take place
error (c) The time before the instrument begins to
C. Residual error 3. Loading effect response after the quantity has altered.
D. Gross errors 4. Random error (d) Retardation or delay in the response of
Codes: an instrument to a change in the input
A B C D signal.
(a) 3 4 2 1
(b) 3 1 4 2 Q.23 What does zero adjustment on a meter
(c) 4 3 1 2 provide?
(d) 2 3 1 4 (a) Reading of the smallest change
(b) Adjustment of sensitivity
Q.19 A zero to 300 V voltmeter has an error of (c) Correction or drift
±2% of the full-scale deflection. If the true (d) Increase in power level.
voltage is 30 V, then the range of readings
on this voltmeter would be Q.24 To reduce the loading effect, an instrument
(a) 20 V to 40 V (b) 24 V to 36 V must possess :
(c) 29.4 V to 30.6 V (d) 29.94 V to 30.06 V (a) Zero input impedance
(b) Unit input impedance
Q.20 Match List-I with List-II and select the (c) High input impedance
correct answer using the codes given below (d) Low input impedance
the lists:
List-I Q.25 Perfect reproducibility means the instrument
A. Precision has:
B. Accuracy (a) Zero drift (b) High accuracy
C. Resolution (c) Maximum drift (d) Minimum accuracy
D. Static
List-II Q.26 Which of the following statements are
1. The smallest change in the input quantity correct?
which can be detected with its certainty. 1. Accuracy is the closeness with which an
2. Closeness of reading with its true value. instruments approaches the true value of the
3. Measure of reproducibility of the quantity being measured.
measurements. 2. Precision is a measure of the
4. Ratio of infinitesimal change sensitivity reproducibility of the measurement.
in output to infinitesimal change in input. 3. Precision of an instrument can be
Codes: improved upon by calibration.
A B C D 4. Accuracy may be specified in terms of
(a) 3 2 1 4 limits of errors.
(b) 2 3 1 4 (a) 1, 2 and 3 only (b) 1, 3 and 4 only
(c) 2 3 4 1 (c) 1, 2 and 4 only (d) 2, 3 and 4 only
(d) 3 2 4 1
Q.27 What is the meaning of accuracy of a
Q.21 The total current, I = I1 + I2 in a circuit is sensor?
measured as I1 = 150 ± 1 A, I2 = 250 ± 2 A, (a) Closeness of output to the true value
where the limits of error are given as (b) Change in output for every change in
1.4 | JE-AE Electrical MASTERPLUS EDUCATION®
input (a) smallest increment in the output that can
(c) Degree of freedom from random errors be detected with certainty.
(d) Dispersion of measurements (b) largest input change to which the
instrument fails to respond.
Q.28 Sensitivity and specificity are related to (c) ratio of the change in the magnitude of
(a) Accuracy of the instrument the output to the corresponding change in
(b) Precision of the instrument the magnitude of the input.
(c) Both accuracy of the instrument & (d) closeness of the output values for
precision of the instrument repeated applications of a constant input.
(d) None of these
Q.34 The degree of consistency and agreement
Q.29 In measurement system, which of the among independent measurements of the
following are undesirable static same quantity is known as.
characteristic? (a) accuracy (b) precision
(a) sensitivity and accuracy (c) correctness (d) uncertainty
(b) drift, static error and dead zone
(c) drift, static error, dead zone and non- Q.35 A 0-150 V has a guaranteed accuracy of 1
linearity percent full scale reading. The voltage
(d) reproducibility and non-linearity measured by the instrument is 83 V.
Calculate the limiting error in percentage
Q.30 Consider the following statements In value.
connection with deflection and null type (a) 1.5% (b) 1.81%
instruments: (c) 3% (d) 3.6%
1. Null type instrument is more accurate
than the deflection type one. Q.36 True value has been 50 whereas measured
2. Null type of instrument can be highly value is 40 then the percentage error in the
sensitive as compared with deflection type reading will be ______.
instrument. (a) 20% (b) 40%
3. Under dynamic conditions, null type (c) 50% (d) 30%
instrument is not preferred to deflection type
instrument Q.37 The resistance of a circuit is found by
4. Response is faster in null type instrument measuring current flowing and the power
as compared to deflection type instrument. fed into the circuit. If the limiting errors in
Which of the statements are correct? the measuring of power and current are
(a) 1, 2 and 3 only (b) 1, 2 and 4 only ±1.5% and ±1.0% respectively, the limiting
(c) 2, 3 and 4 only (d) 1, 2, 3 and 4 error in the measurement of resistance will
be
Q.31 The term _____ refers to measure the ability (a) ±1% (b) ±1.5%
of a measurement system to give the same (c) ±2.5% (d) ±3.5%
value for repeated measurements of the
same value of a variable. Q.38 The values of ammeter and voltmeter
(a) reliability (b) repeatability resistance are 0.1 and 2000 respectively
(c) stability (d) sensitivity as shown in the figure below. The
percentage error in the calculated value of R
Q.32 Repeatability and Reproducibility are = 100 (voltmeter reading 200V/ammeter
related to- reading 2A) is nearly
(a) Accuracy of the instrument
(b) Precision of the instrument
(c) Both accuracy of the instrument &
A
precision of the instrument R
RA 0.1
(d) None of these
V
Q.33 The sensitivity of an instrument is RV 2000
Measurement MASTERPLUS EDUCATION®|1.5
(a) -2% (b) -5% (a) 3.33% (b) 13.33%
(c) 2% (d) 5% (c) 98.67% (d) 96.67%
Q.39 The measured value of a capacitor is 205.5 Q.46 The static error band of an instrument
µF; where as its true value is 202.4 µF. The implies the-
relative error is (a) Accuracy of the instrument
(a) 1.87% (b) 1.94% (b) Difference between the measured value
(c) 1.53% (d) 1.73% and the true value of the quantity
(c) Error introduced in low varying inputs
Q.40 Which of the following types of errors come (d) Irreparability of the instrument
under systematic errors?
1. Irregular spring tension Q.47 In electronic measurements, when the
2. Improper readings of an instrument. quantity determined is the sum of two
3. Loading effects different measurements, the total possible
4. Error due to the presence of electric field error is the
or magnetic field. (a) difference of relative errors in each
(a) 1 and 2 (b) 2 and 3 measurement
(c) 3 and 1 (d) 4 and 1 (b) Sum of absolute values of each
individual error
Q.41 Determine the percentage voltage error of a (c) Net tolerance in each measurement
potential transformer with the system (d) Difference between absolute values of
voltage of 11,000 V and having a turn's ratio the two individual errors
of 104, if the measured secondary voltage is
98 V. Q.48 Which of the following errors occur(s) in a
(a) 7.35 (b) 5.75 moving iron instrument?
(c) 6.25 (d) 8.84 (a) Stray magnetic field error
(b) Hysteresis error
Q.42 To minimize the errors due to lead and (c) All of the options
contact resistances, low resistances used in (d) Temperature error
electrical measurement work are provided
with Q.49 Systematic errors in bourdon tube pressure
(a) guard rings (b) four terminals gauge may be caused by
(c) thick insulation (d) metal shields (a) friction in the pins and gears of the
amplifying mechanism.
Q.43 A meter reads 125 V and the true value (b) incorrect zero setting of the pointer.
of the voltage is 125.5 V. Find the static (c) variation of atmospheric pressure.
error of the instrument? (d) incorrect readings of the scale due to
(a) 125/0:5 V (b) 0.5/125 V parallax.
(c) 0.5 V (d) 125 V
Q.50 Systematic error of an instrument for
Q.44 The pressure in a tank varies from 20 psi to measurement can be minimized by
100 psi. Further pressure in the tank is (a) selecting a proper measuring device for
desired to be kept at 50 psi. The full scale the particular application
error, when pressure inside the tank is 30 (b) calibrating the measuring device against
psi, is given by a standard device
(a) -62.5% (b) 25% (c) applying correction factors for change of
(c) 80% (d) -2.5% ambient conditions.
(d) carrying out all of the above.
Q.45 A frequency counter needs to measure a
frequency of 15 Hz. Its signal getting time is Q.51 A resistance of 105 ohms is specified using
2s. What is the percentage accuracy of the significant figures as indicated below:
counter, taking into account the gating 1. 105 ohms
error? 2. 105.0 ohms
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3. 0.000105 ΜΩ Q.58 Two capacitance C₁ = 150 ± 2.4 µF and C2
Among these = 120 ± 1.5µF are connected in parallel.
(a) 1 represents greater precision than 2 and What is the limiting error of the resultant
3 capacitance C?
(b) 2 and 3 represent greater precision than (a) 0.9 µF (b) 1.9 µF
1 (c) 3.9 µF (d) 4.8 µF
(c) 1, 2 and 3 represent same precision
(d) 2 represents greater precision but 1 and 3 Q.59 Calculate the scale span of the instrument
represent same precision. that is calibrated between 20 bar and 200
bar and used for the measurement of
Q.52 The voltage of a circuit is measured by a pressure.
voltmeter having input impedance (a) 20 bar (b) 180 bar
comparable with the output impedance of (c) 190 bar (d) 220 bar
the circuit thereby causing error in voltage
measurement. This error may be called Q.60 A set of independent current measurements
as............. taken by four observers was recorded as:
(a) Gross error 117.02 mA, 117.11 mA, 117.08 mA and
(b) Random error 117.03 mA. What is the range of error?
(c) Error caused by misuse of instrument (a) ± 0.045 (b) ± 0.054
(d) Error caused by loading effect (c) ± 0.065 (d) ± 0.056
Q.53 Two resistance R1 = 100 ± 10% and R2 = Q.61 A 300 V voltmeter has an accuracy of ± 2%
300 ±5% are connected in series. The of full scale deflection. When the reading is
resulting limiting error of the series 222 V, the actual voltage?
combination is (a) Lies between 217.56 and 226.44 V
(a) 5 Ω (b) 15 Ω (b) Lies between 217.4 and 226.6 V
(c) 25 Ω (d) 30 Ω (c) Lies between 216 and 228 V
(d) Is exact 222 V
Q.54 In a current measurement exercise the
standard deviation is 4 mA. Calculate Q.62 Five observers have taken a set of
probable error. independent voltage measurements and
(a) 3.7 mA (b) 3 mA recorded as 110.10V, 110.20 V, 110.15 V,
(c) 4 mA (d) 2.7 mA 110.30 V and 110.25 V. Under the situation
mentioned above, the range of error is
Q.55 A 0-10 A ammeter has a guaranteed (a) ± 0.3 (b) ± 0.1
accuracy of 1% of full scale deflection, the (c) ± 0.2 (d) ± 1.0
limiting error while reading 2.5 A will be
(a) 1% (b) 2% Q.63 The unknown resistance R, measured in a
(c) 4% (d) None of these Wheatstone bridge by the formula
( R2 R3 )
Q.56 The accuracy of D' Arsonval movements R4 with
R1
used in common laboratory meters is about
the full-scale reading. of R₁ = 100 ± 0.5%Ω,
(a) 1% (b) 5% R2 = 1000 ± 0.5%Ω,
(c) 10% (d) 0.1% R3 = 842 ± 0.5%Ω,
resulting in R4
Q.57 The expected voltage value across an (a) 8420 ± 0.5% Ω (b) 8420 ± 1.0% Ω
element is 50V. However, a voltmeter reads (c) 8420 ± 1.5% Ω (d) 8420 ± 0.125% Ω
it as 48 V. Calculate the percentage error in
the measurement. Q.64 Observational error are called:
(a) 4% (b) 3% (a) Gross errors (b) Systematic errors
(c) 1% (d) 2% (c) Random errors (d) Instrumental errors
Measurement MASTERPLUS EDUCATION®|1.7
Answer Key: Errors in Instruments
1 C 2 A 3 B 4 D 5 A
6 C 7 D 8 A 9 A 10 D
11 A 12 C 13 D 14 B 15 A
16 A 17 C 18 B 19 B 20 A
21 B 22 C 23 C 24 C 25 A
26 C 27 A 28 A 29 C 30 A
31 B 32 B 33 C 34 B 35 B
36 A 37 D 38 B 39 C 40 C
41 A 42 B 43 C 44 B 45 D
46 B 47 B 48 C 49 B 50 D
51 D 52 D 53 C 54 D 55 C
56 A 57 A 58 C 59 B 60 A
61 C 62 B 63 C 64 B
Solution
1. (c) 6 6
4 volts
2. (a) 10 1.5
The circuit diagram for the measurement of voltage 1
20
using multimeter is shown below:
So, (VL)measured = 4 volts and (VL)True = 6 volts
IL R0
% error in voltage reading
(VL )measured (VL )True
V0 VL RL 100
(VL )True
46
Given, multimeter (voltage) rading = 10V 100 33.33%
Input resistance of voltmeter 6
RL = Sensitivity Voltmeter reading ≈ -33% ≈ 33% low
= 2 103 10 = 20k 3. (b)
Also, V0 = 6 volts The given circuit can be reduced to its Thevenin’s
= Open circuit voltage equivalent circuit as shown below.
And R0 = 10k R0 100kΩ X
= Output resistance of circuit
Let the current in the circuit be IL IL
Now, VL = ILRL and V0 = IL (R0 + RL) V0 50V VL RL 1000k
So, VL I L RL
V0 I L ( R0 RL )
Or, V0 Y
VL True value of voltage across terminals X-Y is
R0
1 (VL)True = V0 = 50 volt
RL
1.8 | JE-AE Electrical MASTERPLUS EDUCATION®
Measured value of voltage across terminals X-Y is 2 2
1 100
RL WR 122 4
(VL )measured V0 10
100
R0 RL 144 544
1000 WR 4 2.33
50 100 100
1000 100 8. (a)
1000 The limiting error in percentage for the unknown
50 45.45 volts resistor is
1100
(V ) (VL )True r (1 2 3 )
Loading error L measured 100
(VL )True r (1 1 0.5)% 2.5%
45.45 50 Also, true value of resistance
100 9.1% 500 615
50 R4 3075
Accuracy in measurement of voltage 100
= 100 – loading error (in %) So, limiting error of the unknown resistor in ohm
= 100 – 9.1 = 90.9% 2.5
3075
4. (d) 100
5. (a) 76.875 76.88
I m IT 9. (a)
Error in ammeter reading r 10. (d)
IT
Im Emf, e Work done F .x
Or, 1 r Charge q
IT [ MLT 2 ][ L]
[ e] [ ML2T 3 I 1 ]
I 1 [ IT ]
Or, T
Im 1 r
Magnetic flux density, B
6.5 A
= Correction factor 0.97
6.7 d
Now, eN
6. (c) dt
50 e. t
1 scale division kN/m2 0.5kN/m2
100 N
th
Resolution = 1/5 of scale division Or, [ ] [ML2T 3 I 1 ][T ] [ML2T 2 I 1 ]
1
0.5 0.1kN/m2 [ ] [ ML2T 2 I 1 ]
5 So, [ B]
7. (d) [ A] [ L2 ]
V [MT 2 I 1 ]
Resistance, R (Using V-I method)
I Also, magnetizing force,
R 1 R V mmf NI
and H
V I I I2 length l
Given WV 12V [I ]
[H ] [ IL1 ]
WI 2A [ L]
V = 100 volt mmf NI
And I = 10 A And, reluctance Rl
Uncertainty in the measurement of resistance is
Flux
[I ]
R
2
R
2
[ Rl ] [ M 1L2T 2l 2 ]
WR WV
2
WI
2 2 2 1
[ ML T I ]
V I
11. (a)
2 2
1 V 12. (c)
WR WV2 2 WI2 13. (d)
I I
Measurement MASTERPLUS EDUCATION®|1.9
The errors introduced by the observer are called Zero adjustment on a meter provide correction or
observational errors. Improper setting of range of drift. Zero drift or bias describes the effect where the
multimeter will lead to observational error. zero reading of an instrument is modified by a
14. (b) change in ambient conditions. This causes a constant
15. (a) error that exists over the full range of measurement
16. (a) of the instrument.
17. (c) 24. (c)
Since the response of null type instrument is slower, To reduce the loading effect, an instrument must
therefore they are not suited for dynamic conditions. have high input impedance.
Hence, statement-3 is false. The loading effect is the degree to which a
A wattmeter is an indicating type instrument while a measuring / instrument impacts electrical properties
DC potentiometer is a null type instrument. (voltage, current, resistance etc) of a circuit.
18. (b) 25. (a)
Loading effect is one of the cause of Perfect reproducibility means the instrument has
instrumental error. zero drift. Drift is a departure in the output of the
Parallax error fall in the category of instrument over the period of the time. An
observational error. instrument is said to have no drift if it produces
Residual error is also called random error. same reading at different times for the same
Gross error is mainly due to human mistakes in variation in the measured variable.
recording reading and calculating measurement 26. (c)
results. Accuracy- It is the closeness with which on
19. (b) instrument reading approaches the true value of the
V quantity being measured. It may be specified in
Given, 2% terms of limits of error.
V Precision- It is a measure of reproducibility of a
2 measurement i.e. it is degree of exactness.
V 300 6V
100 27. (a)
Hence, the range of reading Accuracy of a sensor is closeness of output to the
= 30 6 = 24 V to 36 V true value.
20. (a) Precision describe the reproducibility of the
21. (b) measurement
Since the limits of error are given as standard 28. (a)
deviation therefore error in current measure-ment is Sensitivity and specificity are related to an accuracy
given by of the instruments.
2 Sensitivity is the ratio of change in output (or
I I 2 response) of the instrument to change in input or
I . I1
2
. I2
I1 I2 measured variable. A higher sensitivity indicates
Now, I = I1 + I2 that the system can respond to even the smallest
input.
I I
1 and I 1, I 2 29. (c)
I1 I 2 1 2
In measurement system drift, static error, dead zone,
and non-linearity are undesirable.
I 12.12 12.22
30. (a)
5 2.24A Null type is more accurate as compare to deflection
Hence, I (400 2.24)A type instrument and its sensitivity is also high but it
is not suitable for dynamic condition because
22. (c)
measuring quantity is vary with time and multiple
Dead time of an instrument is defined as the time
value is available.
required by a measurement system to begin to
31. (b)
respond to a changed in the measured. It is basically
Repeatability is defined as the closeness of
the time before the instrument begins to respond
agreement between independent test result, obtained
after the measured (quantity) has been changed.
with the same method, on the same test material, in
23. (c)
the same laboratory, by the same operator, and using
1.10 | JE-AE Electrical MASTERPLUS EDUCATION®
the same equipments within short interval of time. (1.5%) 2(1.0%)
32. (b)
Repeatability and reproducibility are ways of R
100 3.5%
measuring precision, particularly in the fields of R
chemistry and engineering repeatability measures 38. (b)
the variation in measurements taken by a single Value of measured resistance
instrument or person under the same conditions, 200
while reproducibility measures whether an entire ( Rm ) 100
2
study or experiment can be reproduce in its entirely. In this case measured value is less than actual value.
33. (c) Actual value resistance = R
The sensitivity of an instrument is ratio of the
R 2000
change in the magnitude of the output to the Rm 100
corresponding change in the magnitude of the input. 2000 R
q 20R = R + 2000 2000
Static sensitivity out 2000
qin R 105.26
It is often offered to as incremental sensitivity or 19
gain as it relates to increments in the signals. Rm R 100 105.26
%error 100 100
I 1 R R 105.26
Sensitivity /V
I fsd V / R V 4.99% 5%
39. (c)
34. (b)
Given that,
The degree of consistency and agreement among
Measured value = 205.5 µF
independent measurements of the same quantity is
True value = 202.4 µF
known as precision.
35. (b) %Relative error = Measured value True value 100
% limiting error = True value
% full scale error × Full scale value
Measured value - True value = 205.5 - 202.4 = 3.1
3.1
Measured value % Relative error = 100 1.53%
1150 202.4
= 1.807% 1.81% 40. (c)
83 Irregular spring tension and loading effect comes
36. (a) under systematic error.
Measured value - True value 41. (a)
%error 100
True value
Nominal ratio = 11000 105.76
40-50 104
%error 100%
50 Nominal ratio - Actual ratio
Sign shows increased or decreased value of %error = 100
Actual ratio
measuring 6 of quantity.
37. (d) 105.76 98
100 7.9% 7.35%
Given data, 98
P 42. (b)
limiting error in power
100 1.5% To minimize the error due to lead and contact
P
resistance, low resistance used in electrical
I
Limiting error in current 100 1.0% measurement work are provided with four terminal
I sensing.
P = I2R A
P
R V
I2
1 2 3 4
limiting error in Resistance
R P I Four-point measurement of resistance between
100 100 2 100 voltage sense connection 2 & 3. Current is
R P I
supplied via force connection 1 & 4.
Measurement MASTERPLUS EDUCATION®|1.11
43. (c) Systematic error of an instrument for measurement
Static error measured value-actual value can be minimized by selecting a proper measuring
A Am At device, calibrating the measuring device against a
standard device and applying correction factors for
A 125 125.5 change of ambient conditions.
A 0.5Volt Systematic errors are:
Sign show the in decrease in measuring quantity. 1. Instrumental errors
44. (b) 2. Environmental error
Variation of pressure range is 20 psi to 100 psi 3. Observational errors
full scale range 80 psi Instrumental errors arise due to
Difference between measured value and actual value Inherent shortcomings in the instrument.
is (50-30) 20 psi Misuse of the instruments.
20 Loading effects of instruments.
The full scale error is 100 25% 51. (d)
80
45. (d) 2 is more precise as compare to 1 and 3 because its
Counter needs to measure i.e. true value of counter representation is given by upto one decimal point. It
15Hz. is more accurately measured (10 times better
measurement).
1
15 52. (d)
Percentage accuracy 2 100 96.67% Loading effect due to an improper way of using the
15 instrument causes. Serious error the best example of
46. (b) such a loading effect error in connecting a well-
The static error band of an instrument is defined as calibrated voltmeter across two point of high of
the difference between the measured value and the high-resistance.
true value of the quantity. 53. (c)
Static error A Am At Given, R₁ = 100 ± 10%
Am = measured value R2 = 300 ± 5%
At = true value R₁ = 100 ± 10%
47. (b) A1
Let q1, q2, q3…….qn outputs of each device and Q = % r 100
At
The final result;
Q q1 q2 q3 ........qn 10 100
A1 10
100
Q q q q q
1 1 2 2 ....... R2 = 300 ± 5%
Q Q q1 Q q2 A2
Resultant limiting error in this case is equal to the % r 100
At
sum of the products formed by multiplying the
individual relative errors by the ratio of each term to 5 300
A2 15
be function. 100
48. (c) So
The instrument in which the moving iron is used for R A1 A2 10 15 25
measuring the flow of current or voltage is known as
54. (d)
the moving iron instrument.
Standard deviation (S.D.) = 4 mA
The error occurs in a moving iron instrument
Probable error = ?
are-
formula-
Stray magnetic field error probable error = 0.6745 × S.D.
Hysteresis error = 0.6745 × 4 × 10-3
Temperature error. P.E. = 2.698
49. (b) P.E. = 2.7m A
Bourdon tube pressure gauge may be caused by 55. (c)
incorrect zero setting of the pointer. Given, % full scale deflection = 1%
50. (d) Im = 10A, I = 2.5 A
1.12 | JE-AE Electrical MASTERPLUS EDUCATION®
Limiting error = ? 110.10 110.20 110.15 110.30 110.25
% full scale deflection I m
Limiting error = 5
I = 110.20 V
110 100 (V Vavg ) (Vavg Vmin )
4% Range of error = max
2.5 25 2
56. (a) (110.30 110.20) (110.20 110.10)
The accuracy of D'Arsonval movements
(galvanometer) used in common laboratory meters is 2
about 1% of full scale reading. = ± 0.1
Alternate solution –
57. (a)
Given, expected voltage = 50V Max value Min value
Range of error =
Voltmeter reading = 48V 2
% error in measurement = 110.30 110.10
0.1
Measured value 2
100
expected true value 63. (c)
Measured value = expected true value - voltmeter ( R2 R3 )
Since, R4
reading R1
50 48 1000 842
% error in measurement 100 8420
50 100
%error = 4%
R4 R R R
58. (c) % % 2 % 3 % 1
Equivalent capacitance of the given parallel R4 R2 R3 R1
combination is C- = 0.5% + 0.5% + 0.5% = 1.5%
C = C1 + C2 64. (b)
So, Limiting error of C is- Observational error are called systematic errors.
= (2.4 + 1.5) = 3.9µF Type of errors
59. (b) (1) Gross error
In the measurement of pressure by an Instrument- (2) systematic error-
Lower calibration = 20 bar (i) Instrument Error
Higher calibration = 200 bar (ii) Environment Error
Scale span = 200 - 20 (iii) Observation Error
Scale span = 180 bar (3) Random Error
60. (a)
Given reading, 117.02 mA, 117.11 mA
117.08 mA, 117.03 mA
Max. value - Min. value
Range of error =
2
117.11 117.02
= 0.045
2
61. (c)
Given, Full scale deflection of voltmeter =
300 V, Accuracy ± 2%
Then, error ± 2% of 300 V = ± 6V
Measured value = 222 V
Actual voltage = 222 ± 6 V = lies between 216 and
228V
62. (b)
Given that,
Vmax = 110.30 V
Vmin = 110.10 V
Average value of voltage = Vavg =
Measurement MASTERPLUS EDUCATION®|2.1
CHAPTER
MEASUREMENT
OF R, L, C, F 2
Q.1 Frequency can be measured using: Q.7 In measuring resistance by voltmeter-
(a) Owen's bridge (b) Maxwell's bridge ammeter method, the voltmeter can be
(c) Wien's bridge (d) Schering's bridge connected either across supply or across the
resistance. If the resistance is low, the
Q.2 Vibration galvanometers, tune able voltmeter should be connected
amplifiers and head phones are used in (a) across the supply
(a) d.c. bridges (b) across the resistance
(b) a.c. bridges (c) either across the supply or across the
(c) Both d.c. and a.c. bridges resistance
(d) kelvin double bridge. (d) neither across the supply nor across the
resistance
Q.3 The mega ohmmeter is used for the
measurement of: Q.8 Kelvin double bridge is chosen to measure
(a) High value capacitance low resistance because
(b) Medium value resistance (a) it has high sensitivity
(c) High value resistance (b) thermoelectric emf's can be taken
(d) Low value resistance (c) resistance variation due to temperature
can be accounted for
Q.4 A standard resistance is made 'Bifilar' type (d) resistance variation due to contacts and
to eliminate leads can be eliminated
(a) Stray capacitance (b) Temperature effect
(c) Inductive effect (d) Skin effect Q.9 Which one of the following is measured by
the loss of charge method?
Q.5 The preferred methods of measuring low (a) Low R (b) High R
resistance and the resistance of cable (c) Low L (d) High L
insulation are respectively
(a) V/I method and loss-of-charge method Q.10 Schering bridge can be used to measure
(b) Kelvin's double-bridge and Megger test which one of the following?
(c) Wheatstone bridge and Kelvin's double (a) Q of a coil
bridge (b) Inductance and its Q-value
(d) potentiometer method and Wheatstone (c) Very small resistance
bridge (d) Capacitance and its power factor
Q.6 Which of the following bridges can be Q.11 Which of the following factors decide the
used for inductance measurement? accuracy in a bridge measurement?
1. Maxwell's bridge 1. Accuracy of the null indicator
2. Schering bridge 2. Accuracy of the bridge components
3. Wien bridge 3. Sensitivity of the null indicator to the
5. Wheatstone bridge bridge system
4. Hay's bridge 4. Applied voltage
Select the correct answer using the codes Select the correct answer using the codes
given below: given below:
(a) 1 and 2 (b) 2 and 3 (a) 1 and 2 (b) 2 and 3
(c) 3, 4 and 5 (d) 1 and 4 (c) 3 and 4 (d) 1 and 3
2.2 | JE-AE Electrical MASTERPLUS EDUCATION®
Q.12 Low resistance from few ohms down to one Ls
micro ohm is measured using which one of 30
Rs
the following instruments?
(a) Ohmmeter
(b) A series type ohmmeter 40μF
30
(c) A shunt type ohmmeter 40
(d) A voltmeter and an ammeter
Q.13 Identify the bridge shown in the circuit.
50Hz
B
R1 (a) 2 (b) 1
C2 (c) 0 (d) 4
I1
A I2 D C
Q.18 De Sauty's Bridge is most suitable for the
C3 measurement of .........
R2
I
(a) resistance (b) inductance
D (c) capacitance (d) frequency
(a) Wien series bridge Q.19 Calculate the value of unknown capacitance
(b) Wien parallel bridge C (in µF) for the circuit given below, when
(c) Schering bridge no current flows through the detector (D).
(d) From Sauty bridge Cx 20
Q.14 Which one of the following bridges is D
generally used for measurement of
60
frequency and also capacitance? 10μF
(a) Owen's bridge (b) Schering bridge
(c) Wien bridge (d) Hay's bridge
E
Q.15 A wheat stone bridge has ratio arm of 1000 (a) 30 (b) 40
Ω and 100 resistances, the standard (c) 50 (d) 60
resistance arm consist of 4 decade resistance
boxes of 1000,100,10,1 steps. The Q.20 Determine the value of unknown resistance
maximum and minimum value of unknown Rx (in k) and unknown capacitance Cx (in
resistance that can be determined with this µF) respectively for the circuit given below,
setup are: when no current flow through the detector
(a) 11110, 10 (b) 10000, 10 (D)?
(c) 111100, 10 (d) 111100Ω, 1Ω Cx 20
Q.16 Which of the following is NOT the correct D
representation of the balanced condition of
60
AC bridges? 10μF
(a) I1 I3 , I 2 I 4
(b) Z1 Z 4 Z 2 Z3 E
(c) 1 4 2 3 (a) 70, 60 (b) 80, 70
(c) 80, 60 (d) 60, 80
(d). Z1 Z 4 Z 2 Z3
Q.21 Inductance is measured by which one of the
Q.17 Determine the quality factor in Hay's bridge following?
given below, if the bridge is supplied by a (a) Wien bridge (b) Schering bridge
frequency of 50 Hz. (c) Maxwell bridge (d) Owen bridge
Measurement MASTERPLUS EDUCATION®|2.3
Q.22 Guard electrodes are used in capacitance about megger?
measurement to minimize (a) Megger is used to the measurement of
(a) fringing of electric field voltage.
(b) thermo-emf (b) Megger is used for the measurement of
(c) dielectric loss current.
(d) eddy current (c) Megger is used for the measurement of
insulation resistance.
Q.23 In the Maxwell bridge as shown in the (d) Megger is used for the measurement of
figure below the values of resistance Rx and breakdown voltage of insulation
inductance Lx of a coil are to be calculated
after balancing the bridge. The component Q.28 Determine the quality factor for Maxwell's
values are shown in 'the fig at balance. The inductance capacitance bridge given below
values of Rx and Lx will respectively be: when the bridge is supplied by a frequency
Lx of 50 Hz.
Rx 2000 Lx
50
Rx
0.05μF G
750 60
4000Ω 30
(a) 75 ohm, 150 mH (b) 75 ohm, 75mH 20μF
(c) 37.5 ohm, 75 mH (d) 375 ohm, 75mH
Q.24 Which of the following bridge is most (a) 0.3 (b) 0.4
suitable for the measurement of an unknown (c) 0.6 (d) 0.8
resistance?
(a) Hay's Bridge (b) Anderson Bridge Q.29 Calculate the value of quality factor in the
(c) Wein's Bridge (d) Wheatstone Bridge Hay's Bridge given below when supplied by
a frequency of 50 Hz?
Lx
Q.25 Which of the following is the CORRECT
50
expression for the quality factor of Rx
Maxwell's inductance-capaci-tance bridge? 10μF
1
(a) C4 R4 (b) 20
C4 R4 10
C4 R4 50Hz
(c) (d)
R4 C4
(a) 31.83 (b) 15.91
Q.26 Determine the value of the unknown
(c) 10.61 (d) 6.36
capacitance Cx (in µF) for the circuit given
below, when no current flows through the
Q.30 What is the value of unknown capacitance
detector (D).
Cx (in μF) and unknown resistance Rx
Cx 40 (ink) respectively, in the circuit given
below when no current flows through the
D
detector (D)?
Rx
20μF 80 80
Cx
D
25μF 20μF
E
(a) 20 (b) 40 R3
R4
160Ω
(c) 60 (d) 80
Q.27 Which of the following statement is TRUE e
2.4 | JE-AE Electrical MASTERPLUS EDUCATION®
(a) 25, 64 (b) 25, 100 (d) any of the above
(c) 50, 64 (d) 50, 100
Q.36 Relative permittivity can be measured by
Q.31 With Kelvin double bridge method for the _______ Bridge.
measurement of resistance, the accuracy can (a) Wheat stone (b) Hay’s
be expected around: (c) Schering (d) Desauty’s
(a) 20% (b) 10%
(c) 5% (d) 0.5% Q.37 Which part/phenomenon controls the
controlling torque in megger?
Q.32 In the circuit shown, when the current (a) earthing (b) leakage current
through the branch AD is zero, the battery (c) spring (d) coil
current IB is
A Q.38 What will be the reading of Megger, if the
R 80 measuring terminals are open circuited?
(a) Zero (b) Infinity
B G C (c) 500 Ω (d) 10,000 Ω
120 80 Q.39 The bridge shown in figure has Z1 =
D
5010°, Ζ2 = 100°Ω, Ζ3 = 150-10°
IB 1V
For what value of Z4 the bridge will be
(a) 1. mA (b) 2 mA balanced?
E1 E3
(c) 10 mA (d) 20mA
b
I3
Q.33 Determine the unknown resistance R in the Z1 Z3
given network, if the galvanometer reads
I1
zero.
d a D Detector C
P Q I2
a G b Z2 Z4
I4
d
R E2 E4
S
c
E Source
(a) 3010° (b) 30-20°
E
(c) 3020° (d) 300°
Q PQ
(a) R S (b) R
P S Q.40 Maxwell bridge is used to measure
P P Q (a) Inductance (b) Capacitance
(c) R S (d) R
Q S (c) Frequency (d) None of the above
Q.34 For measuring a very high resistance, we
should use Q.41 A bridge circuit works at a frequency of 2
kHz. The following can be used as detectors
(a) Wheat stone bridge
(b) Megger for detection of null conditions in the bridge
(c) Kelvin's double bridge (a) Vibration galvanometers and Head-
phones
(d) none of the above
(b) Headphones and Tunable amplifiers
Q.35 For measurement of inductance having high (c) Vibration galvanometers and Tunable
value, we should use amplifiers
(a) Hay's bridge (d) Vibration galvanometers, Head-phones
(b) Maxwell bridge and Tunable amplifiers
(c) Maxwell wien bridge
Measurement MASTERPLUS EDUCATION®|2.5
Q.42 A Wheatstone bridge requires a change of (b) Schering bridge, Anderson bridge
6 in the unknown arm of the bridge to (c) Desauty bridge, Schering bridge
produce a change in deflection of 3 mm of (d) Anderson bridge, Schering bridge
the galvanometer. The sensitivity of the
instrument is Q.48 Megger is a combination of-
(a) 3 /mm (b) 0.5 mm/ (a) Generator
(c) 1.5 mm/ (d) 0.2 /mm (b) Motor
(c) Generator and Ohmmeter
Q.43 A Wheatstone bridge has got three (d) Both Motor and Generator
resistances taken in clockwise direction as
120 Ω, 150 Ω, and 150 . The value of the Q.49 What type of a bridge circuit is used to
fourth resistance for null balance would be measure inductance and capacitance?
(a) 150 Ω (b) 120 Ω (a) Wheatstone bridge (b) DC bridge
(c) 300 Ω (d) 750 Ω (c) AC bridge (d) AC, DC bridge
Q.44 Schering bridge is a very versatile AC Q.50 Multiplication features are incorporated in
bridge and is used for capacitor testing in an ohmmeter to enable the meter to
terms of _______:
1. Capacitance value (magnitude) (a) measure very high resistance values
2. Loss angle measurement (b) measure values with the least error
3. Simple balance detector like PMMC (c) be multipurpose in its application
instrument (d) has less power consumption
4. Providing safety to operators by
incorporating Wagner earthing device Q.51 Bridge suited for measurement of low Q-
Which of the above are correct? factor inductance is:
(a) 1 and 3 only (b) 3 and 4 only (a) Hay's bridge (b) Maxwell's bridge
(c) 1, 2 and 4 only (d) 1, 2, 3 and 4 (c) Schering bridge (d) Anderson's bridge
Q.45 The figure show below an AC bridge Q.52 Resistance can be measured by-
which is balanced at 100 Hz. The quality 1. Ohmmeters
factor of the coil will be- 2. Resistance bridges
R 3. Wattmeters
1kΩ L 4. Ampere-hour meters
(a) only 2 and 3 (b) only 2, 3 and 4
0.1mF G (c) only 1 and 3 (d) only 1 and 2
Q.53 Insulation resistance of a cable can be
100 300 measured by which of the following?
i. Megger
ii. Galvanometer method
(a) Only (i) (b) Both (i) and (ii).
(a) 189 (b) 149 (c) Neither (i) nor (ii) (d) Only (ii)
(c) 159 (d) 169
Q.54
Q.46 Schering bridge can be used to measure
(a) Very small resistance R1
(b) Capacitance and its power factor R2
(c) 'Q' of a coil C1
(d) Inductance and its 'Q' value Detector
Q.47 The inductance and capacitance measu- R3
rement can be done by____ respectively. R4
(a) Schering bridge, Desauty bridge C3
2.6 | JE-AE Electrical MASTERPLUS EDUCATION®
Identify the bridge network shown above. Q.61 For the measurement of high resistances,
(a) Wein bridge (b) Schering bridge following method's are used:
(c) Wheatstone bridge (d) Maxwell bridge 1. Loss of Charge Method
2. Direct Deflection Method
Q.55 What is the balanced condition for the given 3. Substitution Method
bridge? Which of the following is/are correct?
B (a) 1 and 2 (b) 2 and 3
(c) 1 and 3 (d) Only 1
Z1
R1 R2
I1 Q.62 The circuit diagram shown in Figure is a:
I2
L1
A C R1
L4
R2
I4 C1
Z4
R4 R3 Detector
I3
Lx
D R3
Rx
V
(a) Owen's bridge (b) Schering bridge
(a) Z1 – R3 = R2 - Z4 (b) Z1 Z4 = R2 R3
(c) Hay's bridge (d) Maxwell-Wien bridge
(c) Z1 R3 = R2 Z4 (d) Z1 R2 = R3 Z4
Q.63 In the circuit, the galvanometer shows no
Q.56 A Ohmmeter is basically:
deflection. What is the value of 'X' ?
(a) A ammeter (b) A voltmeter
(c) A multimeter (d) None of these 50 0
0Ω Ω
50
20
Q.57 A megger indicates infinity when test 0Ω 0Ω
10
terminal are open-circuited. This is because:
(a) No current flows through the current coil
(b) No current flows through the pressure 2.5 1.5 X ?
coil
(c) No current flows through the 10V
compensating winding, (a) 1 Ω (b) 2 Ω
(d) Current does not flow through current (c) 3 Ω (d) 4 Ω
coil and pressure coil
Q.64 The precision measurement of resistance is
Q.58 Which of the following is NOT an AC generally carried out by-
bridge? (a) Potentiometer method
(a) Kelvin's bridge (b) CRO method
(b) Hay's bridge (c) Bridge method
(c) Capacitance comparison bridge (d) Voltmeter method
(d) Anderson's bridge
Q.65 In a balanced Wheatstone bridge, if the
Q.59 The bridge that is used to measure the positions of galvanometer and source are
resistance of motor winding is: interchanged, what will happen?
(a) Maxwell's bridge (b) Kelvin's bridge (a) Galvanometer will show positive
(c) Wheatstone bridge (d) De-Sauty's bridge deflection
(b) Galvanometer will show zero deflection
Q.60 A megger is to measure insulation resistance (c) Galvanometer will show negative
of a cable. The cable should be connected to deflection
(a) Battery (b) DC supply (d) Pointer will oscillate about zero position
(c) AC supply (d) No supply
Measurement MASTERPLUS EDUCATION®|2.7
Q.66 The role of the compensating coll in a P q
(c) X S
p q r
megger is
(a) reduce current (b) increase voltage Q
(c) control temperature (d) scaling P p
qr
(d) X P S Q q
Q.67 A guard ring is provided in a megger to Q pqr
(a) protect the circuit
(b) eliminate error
(c) reduce current flow
(d) limit the temperature rise Q.73 In the figure given below, R₁ = 10 ΚΩ, R2 =
15 k and R3 = 30 kΩ. Find Rx.
Q.68 In an electrometer, the movable plate is 11 A
I2
cm. in diameter. When 12 kV is applied I1
between the movable plate and the fixed R2
SW1 R1
plate, the force is 0.006 N. The change in
capacitance for 1.5 mm movement of the C G D
movable plate is E I1 I4
(a) 0.44 10-12 F (b) 0.37 × 10-6 F R3 R4
-12
(c) 0.125 × 10 F (d) 12.5 × 10-12 F
B
Q.69 Megger works on the principle of (a) 25 k (b) 30 k
(a) Kirchhoff's current laws (c) 45 k (d) 15 k
(b) Ohm's law.
(c) Gauss's law Q.74 For measurement of high resistance by loss
(d) Electromagnetic induction of charge method which graph be used for
more accurate results?
Q.70 Which of the following statements is
incorrect? v Vet/RC
v V
(a) The inductance of a coil can be increased
by adding a few more turns in the coil
(b) The inductive reactance varies directly
(a) t
as the frequency of the applied voltage
(c) Inductive reactance can be measured by
an ohmmeter loge V
(d) An inductance does not oppose direct loge v
currents
t
(b) t
Q.71 In a cross coil megger, when two currents
are passing through them the torque acting
up on the coil v V v Ve t/RC
(a) opposite direction (b) same direction
(c) Tan (d) none of the above
(c) t
Q.72 In Kelvin's double bridge, the unknown
resistance is given by:
P p V
qr
v
(a) X P S Q q
Q pqr t
(d) t
P q
(b) X S Q.75 Match List -I with List-II and select the
Q p q r correct answer using the codes given below:
2.8 | JE-AE Electrical MASTERPLUS EDUCATION®
List-I List-II at high frequencies because
A. Megger 1. Measurement of (a) They are likely to melt under excessive
loss angle in a eddy current
dielectric (b) They exhibit unwanted inductive and
B. Spectrum 2. Measurement of capacitive effects
Analyser frequency (c) They create more electrical noise.
C. Schering 3. Measurement of (d) They consume more power.
Bridge insulation
resistance Q.80 Consider the following equation which can
D. Digital 4. Measurement of be derived from the ac bridges shown in the
Counter harmonics fig. 1 and fig. 2 by assuming ∆L/L = 0.1 and
Codes R = ωL:
Codes: 1. V01 = V02 2. V01 = 0.05Vs
A B C D 3. V01 = 0.1 Vs 4. V02 = 0.05 Vs
(a) 1 2 3 4 5. V02 = 0.1 Vs
(b) 1 2 4 3 L
±
R ∆L
(c) 4 3 2 1
(d) 3 4 1 2 Vs V01
Q.76 Which of the following method is used to
R ∆L
measure medium value of resistances? ∓
L
(a) Loss of charge method Figure - 1
(b) Potentiometer method
(c) Kelvin double bridge method R
R
(d) Carey-foster slide wire bridge method
Vs V02
Q.77 Four arms of an AC bridge are arranged as L
follows to obtain the balance: ±
∆L ∆L
Arm PQ: R = 250; Arm QR: R = 500; L∓
Arm SP:C = 0.2 µF Arm; RS = an unknown Figure - 2
impedance. A source of 200V, 1kHz is The correct derived equations from these
applied between terminals P and R and fig. of ac bridges are
detector is connected between the terminals (a) 1, 2 and 4 (b) 2, 4 and 5
Q and S. The value of unknown parameter (c) 2 and 5 (d) 1, 3 and 5
of the Arm is ____.
(a) Capacitance of 0.3 µF Q.81 Consider the following statements:
(b) Capacitance of 0.4 µF The value of earth resistance depends upon
(c) Capacitance of 0.1 µF 1. shape of electrode
(d) Capacitance of 0.2 µF 2. depth to which the electrode is driven into
earth
Q.78 All the following statements are correct with 3. specific resistance of soil
respect to Wien bridge oscillator, except? 4. material of electrode
(a) Frequency f0 can be varied in the ratio of Which of the following statements are
3:1 correct?
(b) The expression for oscillation frequency, (a) 1, 2, 3 and 4 (b) 2, 3 and 4
1 (c) 1 and 2 (d) 1, 3 and 4
f=
2 RC
(c) Minimum gain of the amplifier must be Q.82 An inductance comparison bridge is used to
3 measure inductive Impedance at the
(d) It employs lead-lag network frequency of 5 kHz. The bridge constants at
balance are L3 = 10 mH, R1 = 10 ΚΩ, R2 =
Q.79 Wire-wound resistors are unsuitable for use 30 k and R3 = 100 k. Determine the
Measurement MASTERPLUS EDUCATION®|2.9
values of RX and LX respectively. (c) 2X (d) 8X
R1 R2
Detector
Rx Rx
Lx Lx
(a) 300 k, 10 mH (b) 300 k, 30 mH
(c) 100 k, 30 mH (d) 100 k, 10 mH
Q.83 During the measurement of resistance by
Carey
Foster bridge, no error is introduced due to
1. contact resistance
2. connecting leads
3. thermoelectric emf
Which of the above are correct?
(a) 1 and 2 only (b) 1 and 3 only
(c) 2 and 3 only (d) 1, 2 and 3
Q.84 The accuracy of Kelvin's double for the
measurements of low resistance is high
because the bridge
(a) uses two pairs of resistance arms
(b) has medium value resistance in the ratio
arms
(c) uses a low resistance link between
standard and test resistances
(d) uses a null indicating galvanometer.
Q.85 Which of the following statements is correct
regarding bridges available for inductance
measurement?
(a) Hay's bridge is used for coils having Q >
10, whereas Maxwell's bridge is used for
coils having 1 < Q < 10.
(b) Hay's bridge is used for coils having Q <
10, whereas Anderson's bridge is used for
very high Q coils.
(c) Hay's bridge is used for coils having Q <
10, whereas Anderson's bridge is used for
very high Q coils.
(d) Hay's bridge is used for coils having Q >
10, whereas Maxwell's bridge is used for
very high Q coils.
Q.86 Starting just after unknown resistance, if
three known resistance of Kelvin's bridge
are X, 2X and 4X, respectively, then the
value of unknown resistance is:
(a) X/2 (b) X
2.10 | JE-AE Electrical MASTERPLUS EDUCATION®
Answer Key: Measurement of R, L, C, F
1 C 2 B 3 C 4 C 5 B
6 D 7 B 8 D 9 B 10 D
11 B 12 D 13 D 14 C 15 C
16 B 17 A 18 C 19 A 20 B
21 C 22 C 23 D 24 D 25 A
26 B 27 C 28 B 29 A 30 C
31 D 32 C 33 C 34 B 35 A
36 C 37 D 38 B 39 B 40 A
41 B 42 B 43 B 44 C 45 C
46 B 47 D 48 C 49 C 50 B
51 D 52 D 53 B 54 A 55 C
56 A 57 A 58 A 59 C 60 A
61 A 62 C 63 B 64 C 65 B
66 D 67 B 68 C 69 D 70 C
71 A 72 A 73 C 74 A 75 D
76 D 77 C 78 A 79 B 80 A
81 A 82 B 83 D 84 A 85 A
86 D
Solution
1. (c) 1
b f
C1 I1 2 R1R2C1C2
If R1 = R2 = R, C1 = C2 = C
R1 R3 Then,
a c 1
D f
I2 2 RC
R2 R4 2. (b)
I3 Vibration galvanometers, tune able amplifiers and
C2
d head phones are used in a.c. bridges.
3. (c)
A Mega ohmmeter or insulator resistance Tester is a
E special type of ohmmeter used to measure the
Frequency can be measured by using Wien's bridge electrical resistance of Insulation.
Measurement MASTERPLUS EDUCATION®|2.11
It Measure 1 to 10 Mega ohm Resistance. V (t ) t
4. (c) log e
V0
A standard resistance is made 'Bifilar' type to
t
eliminate inductive effect.
5. (b) V (t )
log e
Methods for measurement of high resistance V0
Direct deflection method t
RC
Loss of charge method V (t )
log e
Mega ohm bridge V0
Mugger t 0.4343t
Measurement of low resistance R
V (t ) V (t )
Kelvin’s double bridge method C log e C log10
V
0 V0
Ammeter voltmeter method Where, V(t) is voltage after t time
Potentiometer V0 is initial voltage across resistance
Measurement of medium resistance R – High value unknown resistance.
Wheatstone bridge 10. (d)
Substitution method Schering bridge can be used to measure capacitance
Ohm-meter method dielectric loss and its power factor. It is one of the
6. (d) most commonly used AC bridge.
Maxwell's bridge and Hay's bridge can be use for Bridge Measurement
inductance measurement out of all five given points. (i) Wheatstone bridge Medium resistance
Instrument Measurement (ii) Kelvin double bridge Low resistance
Wien bridge Frequency (iii) Hay's bridge High Q-inductance
Wheatstone bridge Resistance (iv) Anderson's bridge Low Q-inductance
Schering bridge Capacitance (v) Schering bridge Capacitance
Maxwell's and Hay's bridge Inductance (vi) Vienna bridge Frequency
7. (b) 11. (b)
In measuring resistance by voltmeter- ammeter Accuracy of bridge measurement depends on
method, the voltmeter can be connected either accuracy of the bridge component & sensitivity of
across supply or across the resistance. If the the null detector.
resistance is low, the voltmeter should be connected 12. (d)
across the resistance. Low resistance from few ohms down to one micro
8. (d) ohm is measured using a voltmeter and an ammeter.
Kelvin double bridge is chosen to measure low 13. (d)
resistance because resistance variation due to The above bridge circuit is the example of De Sauty
contacts and leads can be eliminated. bridge circuit. It is used to measure unknown
As a result Kelvin double bridge is used for capacitance with respect to a variable capacitor.
measurements of low resistance. B
Bridge Measurement R1
C2
(i) Wheatstone bridge Medium resistance I1
(ii) Kelvin double bridge Low resistance
A I2 D C
(iii) Hay's bridge High Q-inductance
(iv) Anderson's bridge Low Q-inductance
R2 C3
(v) Schering bridge Capacitance
(vi) Vienna bridge Frequency I D
9. (b)
Loss of charge method is used to measurement high
value for resistance. At balance
V (t ) V0et / (during discharging) Z1Z 4 Z 2 Z3
V (t ) 1 1
et / R1 R2
V0 J C3 J C2
2.12 | JE-AE Electrical MASTERPLUS EDUCATION®
CR Q=2
C3 2 1 18. (c)
R2
De Sauty's Bridge is most suitable for the
14. (c) measurement of capacitance. It measures
Owen's Bridge used to measure unknown capacitance of a loss free capacitor by comparing
inductance with respect to known resistance and other standard capacitor.
capacitance respectively. 19. (a)
Schering Bridge used to measure dielectric Given, circuit is a De-shauty's bridge, so value R of
constant and unknown capacitance unknown capacitance
Wien's Bridge used to measure unknown R4
frequency and also capacitance (Cx ) C2
Hay's Bridge used to measure unknown R3
inductance of high Q coil. 60
15. (c) 10μF
20
Given
Cx 30μF
P = 1000, Q = 100, R = ?
Decade resistance box consist of 4 dials. The 20. (b)
respective step size are 1000, 100, 10 and 1 In balance condition
Dial Dial 1 Dial 2 Dial 3 Dial 4 R3 = 60kΩ C4 = 40µF
step size (1000) (100) (10) R4 = 140kΩ C₂ = 30µF
(1)
It is Schering bridge
Max. 10000 1000 100 10
Hence,
value
R3C4
Min. 1000 100 10 1 RX
value C2
Max. value of standard resistance (S) = 11110 60 103 40 106
Min, value of standard resistance (S) = 1 30 106
P R Rx = 80k
Q S R4 140k
For max value of resistance
Cx C2 30μF
R3 60k
1000 R
Cx = 70µF
100 11110 So Rx and Cx will be 80k, 70 µF
R 111100 21. (c)
For min. value of resistance Maxwell's and Owen's both bridges are suitable for
1000 R inductance measurement of coil but Maxwell’s
bridge gives more accurate result, hence Maxwell
100 1
R 10 bridge is preferable.
22. (c)
16. (b)
Guard electrodes are used in capacitance
The expression given below does not represent
measurement to minimize the dielectric loss.
balance condition of alternating current bridge:-
23. (d)
{ Z1 Z 4 Z 2 Z3 } In Maxwell Bridge -
17. (a) R2 R3
It is given, R4 40 R = Resistance R1
R4
C4 40 106 C = Capacitance R2 750
Quality factor of Hay’s bridge is given by R3 2000
1
Q R4 4000
R4C4
C4 0.05μF
2 f 2 3.14 50 314
750 2000
1 104 R1
Q 1.99 4000
314 40 40 106 314 16
Measurement MASTERPLUS EDUCATION®|2.13
R1 375 6
20 10 80
Cx 40μF
L1 R2 R3C4 40
L1 750 2000 0.05 106 Cx 40μF
L1 75mH Cx 40μF , Here {Cx = unknown capacitance}
24. (d) 27. (c)
Wheatstone bridge is the most suitable bridge for Megger is a measuring instrument used for the
measuring unknown resistance. We can measure measurement of insulation resistance of an electrical
medium resistance (order of 0.1 ΜΩ) with the help system. An electrical system degrades its quality of
of this bridge. insulation resistance with time and various
P S environmental conditions including temperature,
In Balance condition moisture dust particles and humidity. Its speed lies
R Q between 130 rpm to 170 rpm.
P S 28. (b)
Given that,
G R2 = 50, R3 = 30
R4 = 60, C4 = 20µF
R Q f = 50Hz
It is Maxwell inductance capacitance bridge-
Hence,
P, Q, R and S are resistive arms of the Wheatstone Quality factor (Q) = R4C4 2 fR4C4
bridge respectively. = 2 × 3.14 × 50 × 60 × 20 × 10-6
25. (a) = 0.376 = 0.4
Maxwell Inductance capacitance bridge is shown Q = 0.4
below:- 29. (a)
L1 It is given,
Frequency (f) = 50Hz
R1
R3 Lx
Rx 50
C4
R2 10μF
R4
20
10
50Hz
Supply
This bridge is used to measure inductance of coil
having medium factor (1< Q < 10). We measure by 1
Quality factor of coil (Q)
comparing to variable standard capacitor with the R4C4
help of this bridge. Here R4 = 10, C4 = 10F = 10 10-6F
Q factor = C4 R4 1
Q
Q = C4 R4 2 fR4C4
26. (b) 1
It is given Q
2 3.14 50 10 106
C4 20 106 F 100
Q Q 31.83
R3 80 3.14
R2 40 30. (c)
It is given
CR
Cx 4 3 C2 = 25F, R4 = 160, R3 = 80, C4 = 20F
R2 Where {R = Resistance, C = Capacitance}
It is schering bridge
2.14 | JE-AE Electrical MASTERPLUS EDUCATION®
Hence, It work on the principal of comparison.
R4 160 The accuracy of megger is high as compared to
Cx C2 Cx 25 106 other instrument.
R3 80
35. (a)
Cx 50μF Hay's bridge is used to determine the inductance of
R3C4 80 20 106 an inductor with a high Q factor. (Q > 10)
Since Rx Maxwell bridge is only appropriate for measuring
C2 25 106 the value for inductor with a medium quality factor.
Rx 64 (10 > Q > 1)
Note: The value of Resistance is in ohm in the given 36. (c)
circuit but the value of Resistance is asked in kilo Wheat stone Bridge-Medium Resistance (1 -
ohm in question. 105)
31. (d) Hays Bridge - Inductance
This bridge is a modified version of Desauty's Bridge - Capacitance
Wheatstone bridge and provides greatly increase Schering Bridge - Capacitance, Relative permittivity
accuracy in the measurement of low-value. 37. (d)
Resistances, generally below 1 to as low as Meggers are instruments which measure the
0.00001 Ω (accuracy varying from ± 0.05% to ± insulation resistance of electric circuits relative to
0.2%. earth and one another. The controlling torque in the
32. (c) meggar is moving coil. Like other instrument spring
A is not used for the production of controlling torque.
38. (b)
R 80 At open circuit condition the value of resistance
becomes infinite. Hence reading of megger gives
B C infinite resistance at open circuit condition.
39. (b)
120 80 Bridge balance condition states that;
D Z1Z 4 Z 2 Z3
Z1 5010, Z2 100, Z3 150 10
IB 1V 5010 Z4 100150 10
As IAD = 0 1500 10
At balance condition Z4 30(10 10)
R 80 = 120 80 5010
R = 120 Z 4 30 20
Hence total resistance across battery is 40. (a)
{(120 + 80) || (120 + 80)} Maxwell bridge is used to measure inductance.
= 100 The medium range inductance can be measured
Hence current, accurately by this method. In this method to measure
1 the value of self-inductance by comparison of
IB 10mA known self inductance.
100 41. (b)
33. (c) Headphones and Tunable amplifiers can be used as
Since the reading of galvanometer is zero, it is clear detectors for detection of null conditions in the
that the wheat stone bridge is balanced. bridge if a bridge circuit works at a frequency of 2
P R kHz.
Q S 0 Hz → D'Arsovnal Galvanometer
PS 5 Hz - 1000 Hz → Vibration Galvanometer
R 200 Hz - 5 KHz → Telephone detector
Q (Head phones)
34. (b) > 5 KHz → tunable detector
Megger is used for measuring high resistance. 42. (b)
It measure insulation resistance of cable.
Measurement MASTERPLUS EDUCATION®|2.15
Sensitivity- It is the ratio of deflection of the 1000
Galvanometer to that of the small change in the
2
value of the resistance.
Q 159.15 159
Change in output response
Sensitivity = 46. (b)
Change in input response The Schering bridge use for measuring the
3 capacitance of the capacitor, dissipation factor,
s mm/Ω
6 properties of an insulator, capacitor bushing,
s = 0.5mm/Ω insulating oil and other insulating materials. It is one
43. (b) of the most commonly used AC bridge. The
A Schering bridge works on the principle of balancing
R 120
the load on its arm.
47. (d)
B G C Anderson bridge-
Anderson bridge is one of the most common bridge
150 150 method for precise measurement of inductance over
D a wide range. In this bridge the unknown self-
inductance is measured in terms of a known
E capacitance and resistance by comparison.
For null balance condition Schering bridge-
R 150 = 150 × 120 Schering bridge is also used for measurement of
R = 120 capacitance and dissipation factor for insulation and
44. (c) in determining the general properties of condenser,
Capacitance, dielectric loss & D-factor can be bushings, insulation oil and other insulating
measured by Schering bridge and it provide safety to materials.
operators by Wagner earthling device. Schering
bridge is particularly suitable for small capacitance, 48. (c)
value of capacitor, generally high frequency or high Megger is a combination of generator and
voltage source a required for good accuracy. ohmmeter. This instrument used for measuring the
Capacitance measurement suffer with many high
Hand driven Supply DC
disadvantage with low voltage supply & frequency. generator
45. (c) Megger
Given circuit diagram- Supply
Battery operated
R Battery
1kΩ L Minimum voltage produce in megger is 40V-
500 V.
0.1mF G
Used for measurement of High resistance or
insulation resistance.
300
100 It is also called moving coil type instrument.
Megger works on faraday's law of
electromagnetic induction.
Given, C4 = 0.1 µF 49. (c)
R4 = 100 A.C. bridge is used to measure the value of
f = 100 Hz inductance and capacitance. Also, it can be used to
Quality factor (Q) =? find the unknown frequency and other parameters.
As we know that, 50. (b)
1 Multiplication features are incorporated in an
Quality factor (Q) =
C4 R4 ohmmeter to enable the meter to measure values
with the least error. An ohm meter is an instrument
1
( 2 f ) that measure the electrical resistance of a material.
2 fC4 R4 This instrument is connected with a battery, a series
1 adjustable resistor and an instrument that give the
reading.
2 100 0.1106 100
2.16 | JE-AE Electrical MASTERPLUS EDUCATION®
51. (d) At Balance condition Z1 R3 =Z2 Z4
Bridge suited for measurement of low Q- factor that is Z1 R3 = R2 Z4
inductance is Anderson's bridge. 56. (a)
Bridge suited for measurement of medium Q- An Ohm meter having a battery which is installed by
factor inductance is Maxwell's bridge. the manufacturer.
Bridge suited for measurement of high Q-factor It causes the flow of current through the unknown
inductance is Hay's bridge. resistance which is required to measure that is
Schering bridge is used to measure capacitance nothing but ammeter.
and dielectric loss. After applying that ohm's law = (V/I)
52. (d) V, is fixed so it is not required to measure, but
Resistance can be measured by ohm meter and current is required because of resistance value is
resistance bridge. Electrical power measured by unknown and this is varying according to resistance.
wattmeter and quantity of electricity measure by. 57. (a)
Ampere-hour meter. Meggers are instruments which measure the
53. (b) insulation resistance of electric circuits relative to
Insulation resistance of a cable can be measured earth and one another. A megger indicates infinity
with the help megger and galvanometer method. A when test terminals are open-circuited because no
"megger" or mega ohm meter (resistance meter) is a current flows through the current coil.
meter used for measuring large resistance values. 58. (a)
These meters are commonly used for measuring Kelvin's bridge is a bridge in which we used only
insulation resistance. resistor. It is a double bridge which is used to
54. (a) measure the low value of resistance it works on de
The bridge circuit shown by above figure is as well as ac.
epresented as Wein's bridge 59. (c)
Wheatstone bridge is mainly used to measurement
R1 of medium resistance. Hence to measure the value of
R2
C1 resistance of a motor, Wheatstone bridge is used.
Detector 60. (a)
R3
Measurement of high resistance megger can be used.
R4 Megger works on the principle of
C3 electrodynamometer. A megger is used to measure
the insulation resistance of cable. The cable should
1) This bridge measure frequency from 100 Hz to
be connected to battery.
100 kHz,
61. (a)
2) This bridge is also used for other applications like
For high resistance measurement Megger, Loss of
capacitance measurement, harmonic distortion
charge, Direct deflection method is used.
analysis and frequency
62. (c)
1 Given bridge is Hay's bridge-
3) The value of f
2 R1 R2C1C3
55. (c) R1
R2
B
C1
Z1
R1 R2 Detector
I1
L1
I2 Lx
R3
A C Rx
L4
I4
R4 R3
Hay's bridge is basically used for measurement of
Z4 high- Q inductance. It is the advanced form of
I3
Maxwell's bridge.
D
63. (b)
V
Measurement MASTERPLUS EDUCATION®|2.17
Q
0Ω =5 2 force displacment
50 0 0Ω So, C
P= q= V2
00 Ω 20
P=
1 0Ω 2 0.06 1.5 103
0.125 1012 F
(12 103 ) 2
R = 2.5 r =1.5 X ?
69. (d)
Ohm's law is applicable to only purely resistive
10V circuits, which are based on the linearity principle.
For zero galvanometer deflection Megger basically works on the principle on
electromagnetic induction.
P qr P p 70. (c)
R S ______(i)
Q p q r Q q Ohm-meter method is used for the measurement of
Put the value of above bridge in eq. (i) medium resistance, not inductive reactance.
500 200 1.5 500 100 71. (a)
2.5 X The torque acting on coils in crossed coil megger is
500 100 200 1.5 500 200 always in opposite direction.
300 1 72. (a)
2.5 X
301.5 2 In Kelvin double bridge unknown resistance is-
P p
X 2.0 qr
P Q q
64. (c) X S
a Q pqr
I1 I2
Z1 Z2 It’s used to measure lower than 1ohm resistance
V b D 73. (c)
I3 I4
R₁ = 10 ΚΩ, R2 = 15 k, R3 = 30 k, R4 = ?
Z3 Z4 At Balance Bridge condition
d A
I2
Bridge are often used for the precision measurement I1
of component values like resistance, inductance, R2
SW1 R1
capacitance etc. The simplest form of a bridge
circuit consists of a network of four resistance arms C G D
forming a closed circuit as shown in figure. E I1 I4
65. (b) R3 R4
If the galvanometer and source are interchanged,
B
there will be no deflection galvanometer as bridge is
at balance. This can be proof by reciprocity theorem. R1Rx = R2R3
66. (d) 10 Rx = 15 30
Temperature is control by minimising the flow of Rx = 45 k
current through the circuit. Better scaling properties 74. (a)
can be achieved in a megger by making use of a Loss of charge method:
compensating coil. It is used for measurement of high resistance
t=0
67. (b)
Temperature rise can be prevented by reducing the
flow of excessive current through the circuit. The V V R C
role of a guard ring in a megger is to reduce the
error due to leakage current.
(Circuit for loss of charge
68. (c)
method)
Given,
F = 0.006N v Vet / RC
Displacement = 1.5mm t 0.4343t
R
= 1.5×10-3 m V V
1 C n C log10
(C )V 2 F displacement v v
2
2.18 | JE-AE Electrical MASTERPLUS EDUCATION®
80. (a)
v Vet/RC
v V For balanced bridge
Vs L
V01 V02 .
t 2 L
75. (d) 81. (a)
Megger– Measurement of insulation resistance Earth resistance analysis is required during
Spectrum analyzer- Measurement of harmonics installation switch yard, generating station,
Schering bridge- Measurement of loss angle in a substation as well as industrial application.
dielectric. Earth resistance depends on-
Digital counter codes- Measurement of frequency 1. Shape of electrode
76. (d) 2. Depth to which the electrodes is driven into earth
Carey foster slide wire bridge method is used to 3. Specific resistivity of the soil
measure the medium value of resistance. In Carey 4. Material of electrode used.
foster slide wire bridge method there is a 82. (b)
comparison between standard resistor and unknown Given:
resistors. L3 = 10mH = 10 × 10-3 H
77. (c) R₁ = 10k = 10 × 103
Q R2 = 30k = 30 × 103
R3 = 100 KΩ = 100 × 103
R1 250 R2 500
R1 R2
P D R
C4 Detector
C3 0.2μF
S Rx Rx
Lx Lx
220 V, 1kHz R2 30
For balancing ac bridge- Rx R3 100
R1 10
Magnitude condition
R1 | X C 4 | R2 | X C 3 | Rx 300 k
1 1 R 30
R1 R2 Lx 2 L3 10
C4 C3 R1 10
R Lx 30 mH
C4 C3 1
R2 83. (d)
During the measurement of resistance by using
250
C4 0.2 Carey Foster bridge, no error introduced due to-
500 1. contact resistance
C4 0.1μF 2. connecting leads
78. (a) 3. Thermo electric emf.
For Wien’s bridge oscillator 84. (a)
1 The accuracy of Kelvin's double for the
(i) Frequency F measurements of low resistance is high because the
2 RC bridge uses two pairs of resistance arms.
(ii) A Wien bridge oscillator generates the 85. (a)
oscillation only if the gain of two stage amplifier is Bridge used for inductance measurement
more than 3. 1. Maxwell bridge – 1 < Q < 10
(iii) Wien bridge circuit employs lead-leg network 2. Hay bridge – Q > 10
79. (b) 3. Anderson Bridge – Precise measurement of
At high frequency, wire wound resistor show inductance
capacitive and inductive effect which deviate the 86. (d)
value of impedance (resistance) from actual value.
Measurement MASTERPLUS EDUCATION®|3.1
CHAPTER
INDICATING
INSTRUMENT 3
Q.1 In a permanent magnet moving coil 2. Permanent magnet moving- coil meter
instrument, which force is responsible to 3. Thermocouple meter
move the pointer from the zero position? 4. Rectifier type meter
(a) Deflecting force Select the correct answer using the code
(b) Controlling force given below
(c) Frictional force (a) Only 1 and 2 (b) Only 2 and 3
(d) Damping force (c) Only 3 and 4 (d) Only 2
Q.2 A current of i 6 8 2 sin(t 30) is Q.7 Consider the following instruments:
1. MI tool
pass through a centre zero PMMC meter and
2. Electrostatic instrument
a moving iron meter. The two meters will
3. Electrodynamometer instrument
read
Which of the above instrument is/are free
(a) 6 A, 10 A (b) -6A, 8A
from hysteresis and eddy-current losses?
(c) -6 A, 10 A (d) 6A, 8A
(a) 1 only (b) 2 only
(c) 3 only (d) 1, 2 and 3
Q.3 The damping provided in moving iron type
of instruments is of type:
Q.8 Which of the following factors limit the
(a) spring (b) air friction
deflection of the pointer of a PMMC
(c) oil friction (d) eddy current
instrument to about 90°?
1. Its damping mechanism
Q.4 Which one of the following instruments is
2. Linearity of the magnetic field in which
commonly used to measure primary current
the coil moves
of a transformer connected to mains?
3. Controls spring arrangement
(a) Electrostatic meter
4. Shape of the pole shoe of the horseshoe
(b)Current transformer
magnet
(c) Moving coil type meter
Select the correct answer using the code
(d) Moving iron meter
given below:
(a) Only 1 and 3 (b) Only 2 and 4.
Q.5 Which of the following are the
(c) Only 2 and 3 (d) Only 1 and 4
characteristics of a thermocouple type of
indicating instrument?
Q.9 If current through the operation coil of a
1. Its accuracy is very high, as high as about
moving iron instrument is doubled, the
1 percent.
operating force becomes-
2. It has linear scale because a D'Arsonval
(a) One and a half times (b) 2 times
movement is used for measuring the output.
(c) 3 times (d) 4 times
3. It is an RF instrument and can be used for
frequency up to about 50 MHz
Q.10 An advantage of PMMC instruments is that
4. It cannot be damaged by overloads.
it
(a) 1 and 2 (b) 2 and 3
(a) Is free from friction error
(c) 3 and 4 (d) 1 and 3
(b) Has high torque to weight ratio of
moving parts
Q.6 Which of the following indicating
(c) Has low torque to weight ratio
instruments. has/have linear scale?
(d) Can be used on both AC and DC
1. Moving-iron meter
3.2 | JE-AE Electrical MASTERPLUS EDUCATION®
Q.11 Which of the following is NOT essential for infinitely high.
working of an indicating instrument?
(a) Controlling torque (b) Deflecting torque D
8
(c) Damping torque (d) Braking torque 100V
ac
Q.12 The damping torque in a moving coil meter
instrument is caused by:
(a) eddy current (b) gravity friction A list consists of meters (List-I) and another
(c) fluid friction (d) copper losses list shows the meter readings (List-II).
List-I List-II
Q.13 The deflecting torque in analog (i) PMMC (a) 7.07 A
measurement device is: (ii) Hot wire (b) 4.5 A
(a) proportional to the resistance of the coil (c) 10 A
(b) proportional to the current through the (d) 12.5 A
coil (a) (i) → (a), (ii) → (c)
(c) inversely proportional to flux density (b) (i) → (b), (ii) → (d)
(d) inversely proportional to the current (c) (i) → (a), (ii) → (b)
through the coil (d) (i) → (b), (ii) → (a)
Q.14 Extension of moving iron ammeter range Q.20 In reference to the figure, the voltage
can be done by using waveform v(t) is measured by a PMMC, a
(a) Multiplier (b) Capacitor PMMC combined with bridge rectifier and a
(c) Shunt (d) Inductor moving iron (MI) instrument. Two lists are
prepared thereafter:
V(t)
Q.15 Which of the following is NOT an
advantage of PMMC type instruments? 10
(a) Frictional error is low
(b) Single instrument can be used for multi t
0 4ms
range measurements of voltage and current
(c) Uniformly divided scale 16ms
(d) Stray magnetic field error is small Instrument list/List of instrument reading
A. PMMC i. 5 V
Q.16 The controlling torque in gravity controlled B. PMMC rectifier ii. 2.75 V
method is proportional to- C. M.I. iii. 2.5 V
(a) cos (b) sin The correct option relating the instruments
(c) tan (d) and their reading is
(a) A - i, B - ii, C – iii (b) A - iii, B - ii, C - i
Q.17 What will happen to the operating torque of (c) A - ii, B - iii, C – i (d) A - iii, B - i, C - ii
moving iron instrument, if current through
the operating coil is halved? Q.21 What will be the deflection (in rad) of a
(a) Halved (b) Doubled moving iron instrument, when the
(c) Remain same (d) One-fourth inductance of the moving iron instrument is
(2 + 4)µH, where 0 is the deflection in
Q.18 A current of i = 6 + 10sin (100t) + 20sin radian from zero position and the deflection
(200t) is flowing through a series current is 5 A? Assuming spring constant K
combination of a PMMC and moving iron = 10 10-6 Nm/rad.
instrument. Ratio of the two currents as (a) 5 (b) 10
registered by the M.I. and PMMC meter is (c) 15 (d) 20
(a) 1.81 (b) 3.11
(c) 2.82 (d) 2.63 Q.22 The response time of an indicating
instrument is determined by its-
Q.19 In the circuit, forward resistance of the (a) deflecting system
diode D is 2 and its reverse resistance is (b) damping system
Measurement MASTERPLUS EDUCATION®|3.3
(c) controlling system Q.29 Which of the following produces breaking
(d) support type to the moving system torque in induction type energy meter?
(a) Air Dampers (b) Eddy current
Q.23 In a PMMC instrument, the final steady (c) Spring (d) Gravity
state deflection is:
(a) i 2 , where i is the current through the Q.30 A permanent magnet moving coil
coil instrument has a coil of dimension 10 mm x
(b) 1/ i , where i is the current through the 20 mm the flux density in the air gap is 2 x
coil 10-3 Wb/m² and the spring constant is 0.25 x
(c) i , where i is the current through the 10-6 Nm/rad. If the current of 10 mA is
flowing through the coil, then calculate the
coil
number of turns required to produce an
(d) 1/ i 2 , where i is the current through angular deflection of 60 degrees.
the coil/ 1/ i 2 (a) 50 (b) 55
(c) 60 (d) 65
Q.24 With respect to dynamometer type
measuring instruments, choose the incorrect Q.31 The instruments having gravity control can
statement be used in ______.
(a) They can be used to measure both AC & (a) vertical position (b) horizontal position
DC (c) any position (d) inclined position
(b) They are free from hysteresis and eddy
current losses Q.32 The spindle of the moving system in a
(c) They have a uniform scale PMMC instrument is supported at both ends
(d) They have Low torque/weight ratio with the help of-
(a) Bush bearings
Q.25 In a moving iron instrument, the deflecting (b) Jewelled bearings
torque is. (c) Gun metal bearings
(a) 1/ i 2 , where i is the current through (d) Steel bearings
the instrument
(b) i , where i is the current through the Q.33 In a DC/AC instrument the deflection is
instrument proportional to the:
1 (a) Square value of the DC current or DC
(c) , where i is the current through the voltage under measurement only
i (b) Square value of the current or voltage
instrument under measurement
(d) i 2 , where i is the current through the (c) Value of the current or voltage under
instrument measurement
(d) Value of the AC current AC voltage
Q.26 Hot wire instruments read under measurement only
(a) Peak values (b) R.M.S. values
(c) Average values (d) None of the above Q.34 In a hotwire instrument, which alloy is
used?
Q.27 If the instrument have a wide range, then (a) Platinum iridium (b) Platinum - Lead
instrument should have ______. (c) Zinc – Nickel (d) Platinum - Li
(a) Square-law scale (b) Linear scale
(c) Exponential scale (d) Logarithmic scale Q.35 A rectifier is used in an instrument for the
purpose of:
Q.28 Which of the following types of instruments (a) measuring high voltage values
is used to measure voltage only? (b) measuring high current values
(a) Moving-iron type (c) converting AC into DC
(b) Permanent- magnet moving coil type (d) making the instrument more stable
(c) Electrostatic type
(d) Induction type Q.36 The full scale deflection in an Induction
3.4 | JE-AE Electrical MASTERPLUS EDUCATION®
instruments is about: (a) Direct current only
(a) 180° (b) 270° (b) Alternating current only
(c) 300° (d) 360° (c) Both direct current and alternating
current
Q.37 Ballistic galvanometer is calibrated to (d) dc/ac voltage only
measure:
(a) Current (b) Voltage Q.45 The instrument which is cheapest for dc
(c) Resistance (d) Charge measurement is:
(a) Moving iron (b) PMMC
Q.38 Which of the following types of measuring (c) Hot-wire (d) Electro- dynamo
instrument is used in the measurement of
both ac and de quantities? Q.46 Electrostatic instruments are suitable for the
(a) Electrolytic type measurement of:
(b) Split-phase induction type (a) ac and de voltages
(c) Dynamometer type (b) ac voltage and current
(d) Shaded-pole induction type (c) de voltage and current
(d) ac and de current
Q.39 In Hot-wire instruments the deflection is __.
(a) Directly proportional to I Q.47 What happens when the shunt resistance of
(b) Inversely proportional to I a galvanometer circuit is increased?
(c) Inversely proportional to I2 (a) Its current sensitivity increases.
(d) Directly proportional to I2 (b) Its current sensitivity decreases.
(c) It's damping increases.
Q.40 For a rectifier type instrument, with (d) It's controlling torque increases.
sinusoidal input and with full wave rectifier,
the a.c. sensitivity (Sac) is Q.48 To get quick and reliable readings of
(a) Sac = 0.45 Sdc (b) Sac = Sdc indicating instrument those are to be
(c) Sac = 0.9 Sdc (d) Sac = 2 Sdc (a) Under damped
(b) Over damped
Q.41 If the current through a moving iron (c) Critically damped
instrument is increased by 20%, what is the (d) Slightly less than critical damped
percentage increase in the deflecting torque?
(a) 40 (b) 25 Q.49 Which of the following meters is the most
(c) 32 (d) 44 accurate instrument for measuring AC
signals with frequencies lower than 200 Hz?
Q.42 An electrodynamometer instrument can be (a) Electrodynamometer movement
used as (b) Clamp-on meter
1. Wattmeter and VAR meter. (c) Thermocouple meter
2. Power factor meter and Frequency meter. (d) Peak responding AC meter
3. Transfer instrument.
Which of the above statements are correct? Q.50 Thermocouple meters are AC meters that
(a) 1 and 2 only (b) 1 and 3 only respond to the of a signal.
(c) 2 and 3 only (d) 1, 2 and 3 (a) Average value (b) RMS value
(c) Instantaneous value (d) Peak value
Q.43 The ballistic galvanometer with high
oscillation period and high critical resistance Q.51 The disc of an instrument using eddy current
will be most suitable for the measurement damping should be of-
of: (a) conducting and magnetic material
(a) Inductance (b) Voltage (b) non-conducting and magnetic material
(c) Current (d) Capacitance (c) conducting and non-magnetic material
(d) non-conducting and non-magnetic
Q.44 A thermo-couple instruments can be used material
for the measurement of:
Measurement MASTERPLUS EDUCATION®|3.5
Q.52 Which of the following instruments totalize parallel to the instrument, what is the
events over a specified period of time? maximum values of current it can measure?
(a) Indicating instruments (a) 5 mA (b) 10 mA
(b) All the types of analog instruments (c) 50 mA (d) 100mA
(c) Recording instruments
(d) Integrating instruments Q.59 A 50 V range voltmeter has a sensitivity of
20k/V. The total resistance of the
Q.53 A PMMC type measuring instrument is not voltmeter is
provided with any controlling mechanism. If (a) 2.5 KΩ (b) 0.4 KΩ
a current of 1 Amp DC is passed through the (c) 10 K (d) 1 M
coil, what will be the reading of the
instrument? Q.60 If n= number of full digits, then the
(a) Pointer will not move resolution R of a digital voltmeter is given
(b) Pointer will move to full deflection by
(c) 1 Amp (a) 1/10n (b) 1/10n+1
(d) 10 Amp (c) 10 n-1
(d) 1/10n-1
Q.54 Which of the following instruments is Q.61 Determine the angle through which a coil
equally accurate on ac as well as de circuits? turns when a deflection of 42 mm is
(a) PMMC voltmeter observed on the scale of a galvanometer
(b) Dynamometer placed at a distance of 0.6 m from the
(c) Moving iron ammeter mirror.
(d) Induction wattmeter (a) 0.35 radians (b) 0.035 radians
(c) 35 radians (d) 3.5 radians
Q.55 The reflecting mirror mounted on the
moving coil of a vibration galvanometer is Q.62 A moving coil voltmeter has a uniform scale
replaced by a bigger size mirror. This will with 100 divisions and gives a full scale
result in reading of 200 V. The instrument can read
(a) Lower frequency of resonance and lower up to 1/5 of 1 a scale division with a fair
amplitude of vibration. degree of certainty. The resolution of the
(b) Lower frequency of resonance but the instrument in volt is:
amplitude of vibration is unchanged. (a) 400 V (b) 4 V
(c) Higher frequency of resonance and lower (c) 40 V (d) 0.4 V
amplitude of vibration.
(d) Higher frequency of resonance but the Q.63 A d'Arsonval movement with internal
amplitude of vibration is unchanged. resistance R = 100 and full scale current
of 1 mA is to be converted into (0-10) V
Q.56 If a voltmeter has a scale from -5 V to 15 V range what is the required resistance?
and can only read integer values of voltages, (a) 10 KΩ (b) 10100
its resolution is: (c) 9900 (d) 12000
(a) 15 V (b) -5 V
(c) 1 V (d) 20V Q.64 A current i = 5+14.14 sin(314t + 45°) is
passed through a centre-zero PMMC, hot-
Q.57 A dc voltmeter has a sensitivity of 1000 wire, and moving iron instrument, the
Ω/Μ. When it measures half full scale in respective readings are
100 V range, the current through the (a) -5, 15 and √125 (b) 5, √125 and √125
voltmeter is (c) -5, and 19.14 (d) 5, 10 and 10
(a) 100 mA (b) 50 mA
(c) 10 mA (d) 0.5mA Q.65 In the thermocouple ammeter the heat
produced is proportional to
Q.58 A moving-coil instrument gives full-scale (a) Current
deflection for 1 mA and has a resistance of 5 (b) Square root of current
. If a resistance of 0.55 is connected in (c) Square of current
3.6 | JE-AE Electrical MASTERPLUS EDUCATION®
(d) Voltage Q.73 A current i = (10 + 10 sint) amperes is
passed through moving iron type ammeter.
Q.66 A 1-mA meter movement with an internal Its reading will be
resistance of 100 is to be converted into a (a) zero (b) 10A
0 to 100 mA range. The value of shunt (c) √150A (d) √2A
resistance required is:
(a) 1.01 (b) 1.001 Q.74 A 10 mA meter having an internal resistance
(c) 10 Ω (d) 0.01 of 100 Ohms is to be converted to 0-200 mA
ammeter. What value of shunt resistance (in
Q.67 Two voltmeters of the same range, one M.I. ohms) is required?
type and the other M.C. type are connected (a) 5.26 (b) 5
in parallel for measuring a.c. supply voltage. (c) 10.52 (d) 10
If the reading of the M.I. type is 300 V the
reading of the M.C. type will be Q.75 Determine the full-scale reading (in V) of a
(a) Higher than M.I. type PMMC type voltmeter, when the internal
(b) Same as the M.I. type resistance of the voltmeter is 230 kild-ohms,
(c) Lower than M.I. type the series resistance connected with the
(d) Zero voltmeter is 70 kilo-ohms and the sensitivity
of the voltmeter is 3 kilo-ohms/Volt.
Q.68 A PMMC meter can be used as an ammeter (a) 200 (b) 150
using: (c) 100 (d) 250
(a) Series resistors (b) Shunt inductors
(c) Shunt resistors (d) Series inductors Q.76 Determine the value of current (in mA) for
the full-scale deflection of a voltmeter,
Q.69 What is the value of series resistance when the sensitivity of the voltmeter is 50
required to extend the 0-100 Volts range of ohm/Volt.
a 20,000Ω/V meter to 0-1000 volts? (a) 1 (b) 2
(a) 10 M (b) 18 M (c) 10 (d) 20
(c) 15 M (d) 20 M
Q.77 How will you convert galvanometer Into
Q.70 A galvanometer with a full scale current of ammeter?
10 mA has a resistance of 1000. Ω. The (a) low resistance parallel with galvano-
multiplying power (the ratio of measured meter
current to galvanometer current) of a 100 Ω (b) low resistance series with galvanometer
shunt with this galvanometer is: (c) high resistance parallel with
(a) 100 (b) 11 galvanometer
(c) 10 (d) 110 (d) high resistance series with galvanometer
Q.71 Meter A has a range of 0-100 V and a Q.78 An ac meter of resistance R.m and reactance
multiplier resistance of 28 k and an Xm is connected in series with a resistance
internal resistance of 2 ΚΩ. It's sensitivity Rs.A shunt of impedance (Rsh + JXsh) is
is: applied in parallel to the existing
(a) 0.6 kΩ/kV (b) 0.3 kΩ/V combination of meter and Rs. The current
division across the two branches will be
(c) 0.5 k/V (d) 3 kΩ/V
independent of frequency when
Meter
Q.72 What is the percentage voltage error of a Rm Xm Rs
potential transformer with system voltage of
11,000 V and having turns ratio of 100, if
the measured secondary side voltage is 105
V? Xsh
R sh
(a) 2.75 (b) 3.55
(c) 4.54 (d) 9.09
Measurement MASTERPLUS EDUCATION®|3.7
Xm X (b) connect a 10.012 resistance in parallel
(a) m with the meter
Rm Rs Rsh
(c) Connect a 1.01 Ω resistance in parallel
Rs R with the meter
(b) sh
Rm X m X sh
2 2 (d) Connect a 10.012 resistance in series
with the meter
X m X sh
(c)
Rm Rsh Q.84 The internal resistance of a voltmeter is
20,000 ohms. If this voltmeter is connected
(d) ( Rs Rm ) X R X
2 2 2 2
m sh sh
in series with a resistance and a 220 volt
supply is connected across the combination,
Q.79 Which one of the following is the the voltmeter reads 200 volts. The value of
CORRECT expression for voltmeter the resistance is
sensitivity of PMMC type instrument? (a) 200 Ω (b) 4000 Ω
Rm Rs Rm Rs (c) 2000 Ω (d) 20,000 Ω
(a) (b)
V V
Rm Rs Rm Rs Q.85 Of what material, Swamping resistance is
(c) (d) made up?
V2 V2 (a) Alloy of nickel and cobalt
(b) Alloy of manganin and aluminium
Q.80 Determine the value of current (in mA) (c) Alloy of manganin and copper
required for the full-scale deflection of a (d) None of these
voltmeter when the sensitivity of the
voltmeter is 125 Ohms/Volt. Q.86 In an ammeter, the deflecting torque is
(a) 2 (b) 4 proportional to the current passing through
(c) 8 (d) 10 it, and the instrument has full scale
deflection of 80° for a current of SA. What
Q.81 Determine the required value of series deflection will occur for a current of 2.5 A
resistance (in Ohms) to convert a when the instrument is spring controlled?
galvanometer into a voltmeter of reading 0.4 (a) 20° (b) 35°
volt range when the resistance of the (c) 45° (d) 40°
galvanometer is 40 ohms and the value of
current to full-scale deflection is 4 mA. Q.87 The meter element of a permanent-magnet
(a) 60 (b) 50 moving coil instrument has a resistance of
(c) 40 (d) 30
5 and requires 250 mA for full scale
deflection. Calculate the resistance to be
Q.82 Which of the following is TRUE in case of
connected to enable the instrument to read
current transformers? up to 1A.
(a) It helps in measuring high current using
(a) 5 resistor in series
high range ammeter.
(b) It helps in measuring high current using (b) 5/3 resistor in parallel
low range ammeter (c) 5 Ω resistor in parallel
(c) It helps in measuring high voltage using (d) 5/3Ω resistor in series
high range voltmeter.
(d) It helps in measuring low voltage using Q.88 The multiplying power of the shunt of a
high range ammeter. millimeter is 8. If the circuit current is 200
mA, then current through the meter is
Q.83 How to convert a (0 to 1) m A meter to (a) 25 mA (b) 200 mA
(c) 1600 mA (d) 3200mA
measure the current in the range of 0 to 100
mA? The internal resistance of the meter is
100 Ω Q.89 An analog voltmeter uses external multiplier
settings with a multiplier setting of 20 k
(a) Connect a 1.012 resistance in series with
meter ohm. It reads 440V and with a multiplier
setting of 80 k ohm it reads 352V. What will
3.8 | JE-AE Electrical MASTERPLUS EDUCATION®
be the voltmeter reading for a multiplier (c) A shunt should have a very low
setting of 40k. ohm? resistance
(a) 300 V (b) 320 V (d) An electronic voltmeter draws
(c) 250 V (d) 225 V appreciable current from source
(e) 412V
Q.95 Calculate the reading that will be given by a
Q.90 The current through a resistor has a hot-wire voltmeter it is connected across the
waveform as shown in figure. The reading terminal's of a generator whose voltage
shown by a moving coil ammeter will be waveform is represented by V = 400 sin t
amperes. + 300 sin 3t V.
i (a) 250/√2 V (b) 500/√2 V
5A (c) 400/√2 V (d) 300/ √2 V
Q.96 If V1 and V3 are the rms values of the
fundamental and third harmonics of an
ωt
π 2π 2π alternating quantity, then the rms value of
(a) 5/√2 (b) 2.5/√2 the alternative quantity is given as:
(c) 5/ (d) 0 (a) V1 / V3 (b) V1 V3
Q.91 A thermocouple having an internal (c) V1 V3 (d) V12 V32
resistance of 40 and lead resistance of
10 produce a voltage of 100mV. If the Q.97 To convert a galvanometer into
output is read by a voltmeter having an voltmeter, the value and type of connection
internal resistance of 150 what will be the of the resistance to be connected with
voltage indicated by the voltmeter? should be-
(a) 66.6 mV (b) 100 mV (a) Low and parallel (b) High and parallel
(c) 55.5 mV (d) 75 mV (c) Low and series (d) High and series
Q.92 A shunt, which is used to extend the range Q.98 A 100 kV, 50 Hz supply is fed to a rectifier
of ammeter is made of: ammeter (using a bridge rectifier) through a
(a) Cu (b) Al capacitor. The PMMC ammeter of the
(c) Nichrome (d) Manganese rectifier instrument reads 45 10-3 Amp.
What is the value of the capacitor?
Q.93 A moving iron instrument has full scale (a) 15.90 × 10-10 F (b) 15.90 × 10-12 F
-9
current of 100 mA. It is converted into a (c) 17.66 × 10 F (d) 17.66 × 10-11F
250V voltmeter by using a series resistance
made of a material having negligible Q.99 A dc circuit can be represented by an
resistance temperature coefficient. The internal voltage source of 50V with an
meter has a resistance of 320 at 20°C output resistance of 100k ohm. In order to
After carrying a steady current of 100 mA achieve 99 percent accuracy for voltage
for a long time, the resistance of the coil measurement across its terminals, the
increases to 369 due to self heating. When voltage measuring device should have-
a voltage of 250V is applied continuously, (a) A resistance of at least 10MΩ
the error due to self-heating will be nearly. (b) A resistance of 100K ohm
(a) -1.1% (b) -1.9% (c) A resistance of at least 10 Ω
(c) -2.5% (d) -3.3% (d) None of these
Q.94 Which of the following is not correct? Q.100 Two ammeters A and B both 0-10Amp have
(a) Voltmeter should have a very high internal resistance of 12 and 0.5
resistance respectively. They are connected in parallel.
(b) An ammeter should have a very low th If total current is 15A, then-
resistance (a) IA = IB = 7.5A (b) IA = 5A, IB = 10A
Measurement MASTERPLUS EDUCATION®|3.9
(c) IA = 10A, IB = 5A (d) IA = 9A, IB = 6A
Q.101 If one of the control springs of a permanent
magnet coil ammeter is broken, then on
being connected it will read
(a) Zero
(b) Half of the correct value
(c) Twice of the correct value
(d) An finite value
Q.102 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.
Q.103 The value of resistance R, to be added in
series with an ammeter whose full scale
deflection is of 0.1 mA and internal
resistance is of 500 Ω, to make it suitable to
measure (0-10) V is
(a) 0.02 KΩ (b) 99.5 KΩ
(c) 500.02 Ω (d) 499.98 Ω
Q.104 Voltmeter sensitivity is defined by :
(a) Volts/ohms (b) Volts/ohm²
(c) Ohms/volts (d) Ohm/volt²
3.10 | JE-AE Electrical MASTERPLUS EDUCATION®
Answer Key: Indicating Instrument
1 A 2 C 3 B 4 D 5 D
6 D 7 B 8 B 9 D 10 B
11 D 12 A 13 B 14 C 15 A
16 B 17 D 18 C 19 D 20 B
21 A 22 B 23 C 24 C 25 D
26 B 27 D 28 C 29 B 30 D
31 A 32 B 33 B 34 A 35 C
36 C 37 D 38 C 39 D 40 C
41 D 42 D 43 D 44 C 45 A
46 A 47 B 48 D 49 A 50 B
51 C 52 D 53 B 54 B 55 A
56 C 57 D 58 B 59 D 60 A
61 B 62 D 63 C 64 B 65 C
66 A 67 D 68 C 69 B 70 B
71 B 72 C 73 C 74 A 75 C
76 D 77 A 78 A 79 A 80 C
81 A 82 B 83 C 84 C 85 C
86 D 87 B 88 A 89 E 90 C
91 D 92 D 93 B 94 D 95 B
96 D 97 D 98 A 99 A 100 B
101 A 102 D 103 B 104 C
Solution
1. (a) PMMC always reads DC or average value. Hence,
The deflecting force is the force required for moving PMMC will read = -6A
the pointer from rest on the calibrated scale. Moving iron meter reads RMS value
Deflecting torque is proportional to quantity under Hence,
measurement- 2
Td measuring quantity 8 2
irms (6)
2
2. (c) 2
Given, i 6 8 2 sin(t 30)
irms 36 64 100 10A
Measurement MASTERPLUS EDUCATION®|3.11
3. (b) T
2
I 2I
2
The moving iron instrument uses the air friction Td I d 2 2 1
2
damping while moving coil instrument uses the eddy Td 1 I1 I1
current damping system. Td 2 4Td1
The Damping is the phenomenon through which 10. (b)
the amplitude of the oscillations decreases as Advantage of PMMC instruments-
quickly as possible. The PMMC instruments have high torque to
4. (d) weight ratio thus is has higher sensitivity and
When a transformer is connected to supply mains. It accuracy-
take AC on primary winding of transformer. We use The scale of the PMMC instruments is linear
such type instrument which can measure ac current. The power consumption of the PMMC
So from the given option we use moving iron instruments very less
instrument which
PMMC is used for DC only
5. (d)
11. (d)
The accuracy of thermocouple type instrument 1%
Indicating instrument indicates the value of the
limiting error which is very high accuracy for any
electrical quantity to be measured generally by the
instrument, thermocouple is a category of RF
deflection of the pointer on the calibrated scale.
instrument because it work upto very high frequency
Essential working torque in indicating instruments-
around upto 50 MHz. Its works on the principle
1. controlling torque
temperature difference between two junction of
2. Deflecting torque
special arrangement of two dissimilar metal and it
3. Damping torque.
can be damage due to over loading (overheating of
Thus the braking torque in an indicating instrument
junction) overheating of junction may be leads to
are not essential for working.
melt out the junction material which will destroy the
12. (a)
thermocouple arrangement, hence this instrument is
The damping torque in a moving coil instrument is
also affected by overloading criteria. Thermocouple
caused by eddy current. A moving coil instrument is
scale is non-linear scale because it is based on
operated only on DC and also known as "PMMC
thermal effect which is already non linear physical
instrument". It has high torque to weight ratio. And
quantity i.e. heating limit of used material.
scale also is uniform and linear. The deflecting
6. (d)
torque in a PMMC instrument can be given by-
Moving-iron meter and thermocouple meter have
square-law response so do not have linear scale. Td I
1 I 2 dL 13. (b)
Td The deflecting torque in analog instrument device is
2 K d proportional to the current through the coil.
But PMMC and rectifier type meter both have linear Deflecting torque can be given by-
scale.
7. (b)
TD NBAI
Electrostatic instrument is free from hysteresis and TD GI ( NBA = G)
eddy current losses. Eddy current is available where
TD I
relative motion is present between magnetic field
and conducting material or conducting material 14. (c)
experience variation of magnetic field with respect A shunt resistance can be used to extend the range
to time. of a moving iron type of Ammeter because it will
8. (b) reduce the voltage drop that occurs due to
Linearity of the magnetic field in which the coil instruments internal resistance.
moves and shape of pole shoe of the horseshoe 15. (a)
magnet limit the deflection of the pointer of a The permanent-magnet moving coil (PMMC) type
PMMC instrument. instruments have following advantages and
9. (d) disadvantages.
For moving iron type instrument Advantage-
1 dL (i) They have low power consumption
Td i 2 (ii) Their scales are uniform and can be designed to
2 d extend over an arc of 270°
3.12 | JE-AE Electrical MASTERPLUS EDUCATION®
(iii) They possess high (torque/weight) ratio. 1
(iv) They have no hysteresis loss. I rms 62 (102 202 )
(v) They have very effective and efficient eddy 2
current damping. = 16.91
Disadvantage - Ratio of MI to PMMC reading is
(i) Some errors are set is due to aging of control IMI 16.91
2.82
spring and assembly of various parts, such IPMMC 6
instruments are somewhat cost lies as compared to
19. (d)
moving iron.
For PMMC & hot wire-
(ii) It has friction loss due to jewel pivot suspension.
Vrms = 100V.
(iii) It is very costly due to delicate construction and
accurate machining. Peak voltage, Vm Vrms 2
16. (b) Vm 100 2 141.42V
Gravity Control:-
Scale V 141.42
Im m =14.14A
R (8 2)
O
RMS current of half wave rectifier is-
P P I m 14.14
I rms = 7.07
B 2 2
S PMMC type Ammeter average value are-
Im 14.14
I av
A A
B
d I av 4.5A
In the figure gravity control is shown is which two
20. (b)
masses A & B are attached to the spindle S of the
PMMC reads average value
moving system.
The basic function of mass A is to balance the 10 4 103
Vav 2.5V
weight of the pointer P. 16 103
17. (d) MI type Instrument Read R.M.S. value
Operating torque of moving Iron instrument:- 102 4 103 0 0 100 10
T1 I12 ______(i) Vrms 3
16 10 4 2
According to question Vrms = 5V
2
I PMMC half wave Rectifier measures
T2 1 = 1.11 Average Value of PMMC
2
= 1.11 2.5 = 2.775 Volt
I12 = 2.75 Vs
T2 ______(ii)
4 21. (a)
From (i) and (ii) It is given,
T1 Spring constant (K) = 10 10-6 Nm/rad
4 Deflection current = 5 A
T2
Inductance (L) = (20 + 4)μΗ
1 The rate of change of inductance with deflection is,
Or T2 T1
4 dL d
(20 4 )μH
18. (c) d d
i = 6 + 10sin (100t) + 20sin (200t) dL
PMMC read-only DC value. 4 106 H
d
I(PMMC) = 6 2
for M.I. instrument form torque equation, 1 I dL
2 K d
1 1 52
I rms I 02 ( I12 I 22 .....) 4 106
2 2 10 10 6
Measurement MASTERPLUS EDUCATION®|3.13
25 4 If the instrument have a wide range, then instrument
should have logarithmic scale. The logarithm
20
reduces this to a more manageable range.
= 5 radians
28. (c)
22. (b)
Electrostatic types of instrument is used to measure
Damping system determines the response time of an
voltage only. These instruments are based on the
indicting instrument.
fact that an electric force (attraction or repulsion)
If damping is not In indicating instrument provided
exists between charged plates or objects.
then pointer will oscillate due to inertia about it's
There are three types of electrostatic voltmeter-
final deflection position which is undesirable. The
(1) Attracted disc type- usual range from 500V to
damping force should be of such a force acting on
500 kV
the pointer of the moving system comes to its final
(2) Quadrant type - usual range from 250V to 10kV
steady state as quickly as possible without any
(3) Multicellular- usual range 30V to 300V
oscillation.
29. (b)
23. (c)
The movement of rotating disc in induction type
In PMMC instruments, final steady state is
energy meter through the magnetic field crossing the
proportional to the deflection current.
air gap sets up eddy currents in, disc that Reacts
Where, i = Current flowing through the coil.
with the magnetic field an exerts a braking torque.
Td = Deflection torque.
24. (c) spindle
Permanent
Dynamometer type instrument is a transfer device magnet
they have non-uniform scale. They can used both
AC and DC. eddy current
Advantages- Braking torque
The system is free from hysteresis and eddy current generation
error. Since we use air-core for both moving coil
and field coil. [Braking Torque (Tθ N ) ]
Disadvantages- 30. (d)
The heavier moving system causes low torque to Given,
weight ratio. Spring constant (K) = 0.25×10-6 Nm/rad
As the magnetic field operates the instrument,
we not utilize eddy current damping in 60 rad
3
dynamometer type instrument. I = 10 mA
25. (d) Flux Density (B) = 2 × 10-3 Wb/m²
In a moving iron instrument, the deflecting torque is
directly proportional to the square of current flowing Tc k
through the instrument. Tc 0.25 106 3.14 / 3 2.6 107 Nm
I 2 dL Td = NBIA
Td
2 K d In balance condition
Td I 2 Td Tc
Where, Td = Deflection torque. Td
26. (b) N BIA
Hot wire instruments read R.M.S. value.
The deflection produce in hot wire is directly 2.6 107
N
proportional to the wire extension due to the heat 2 103 10 103 10 20 106
produced in the wire. Hot wire instruments read rms 2.6 105
value of the current and the reading is independent N 65Turn
of the waveform and frequency. It has non-uniform 4000
scale. N = 65 Turn
27. (d) 31. (a)
Gravity control instruments must be used in vertical
position so that the control weight may operate and
must be loaded otherwise it will give error.
3.14 | JE-AE Electrical MASTERPLUS EDUCATION®
38. (c)
B Spindle Split phase Induction Used for measuring AC
Pointer type instrument measurement only
Shaded-pole used for AC only
BALANCE induction type
CONTROL weight
weight 39. (d)
Hot wire instruments read both AC and DC
32. (b) measurement.
The spindle of the moving system in a PMMC It is a transfer type instrument
instrument is supported at both ends with the help of It is free-from stray magnetic field and its deflection
jewelled bearings. Made-up of aluminium, the () is proportional to square of the current that is
rectangular block is called aluminium former passing through it I 2
pivoted to the jewelled bearing. When current is 40. (c)
passed through these coils, it receives a deflection in For a rectifier type instrument, with sinusoidal input
the field which is then used to determine and with full wave rectifier, the ac sensitivity (Sac) is
voltage/current magnitude 0.9 times of de sensitivity.
33. (b) Sac = 0.9 Sdc
In a DC/AC instrument the deflection is proportional 41. (d)
to the square value of the current or voltage under Deflecting torque in a moving iron instrument can
measurement. If a DC/AC instrument measure the be given by-
voltage then deflection
T1 I12
1 2 dc
Td V deflection V 2
T2 (1.2 I1 )2
2K d
If it is measure current the deflection can be given T2 1.44I12
by-
T2 T1
1 2 dL % Increase in torque (∆T) = 100
Td I deflection I 2
T1
2 K d
34. (a) 1.44 I12 I12
Hot wire Instrument: The instruments which uses T 100 0.44 100
I12
the heating effect for knowing the current and their
magnitude, such type of instrument is known as hot %T 44%
wire instrument. The best material used for the hot 42. (d)
wire instrument is the platinum-iridium alloy. Uses of electrodynamometer instruments-
35. (c) Frequency meter
A rectifier is used in an instrument for the purpose Power factor meter
of converting AC into DC. Wattmeter and VAR meter
36. (c) Transfer instruments
The full scale-deflection in an induction instruments Electro dynamo meter is a type of transfer
is about 300° instrument because this may calibrated with de and
Deflecting torque in the induction-instruments is then without modification this can be used for
directly proportional to the square of the measuring measure ac.
current. 43. (d)
37. (d) The ballistic galvanometer with high oscillation
Ballistic galvanometer are the measuring period and high critical resistance will be most
instruments which are used for measuring the suitable for the measurement of capacitance.
quantity of electric charges obtained from magnetic The ballistic galvanometer is used to measure
flux. the quantity of electricity.
C.V The eddy current damping is provided in
K
d ballistic galvanometer is very small.
Where, K = Ballistic galvanometer (Coulomb /cm) 44. (c)
Hence C.V = K.d = Q The instrument which uses see beck effect for the
Where Q = Charge. measurement of the temperature, current and voltage
Measurement MASTERPLUS EDUCATION®|3.15
such type of instrument is known as thermocouple instrument because it is adds the energy
instrument. It is used for both the AC and DC cumulatively over a period of time.
measurement. 53. (b)
45. (a) A PMMC type measuring instrument is not provided
Moving iron- with any controlling mechanism. If a current of 1
Cheaper to manufacture Amp DC is passed through the coil pointer will
Very accurate on AC or DC if properly move to full deflection.
designed. 54. (b)
Mostly used as an indicating instrument. Electro dynamometer type wattmeter used for
46. (a) the measurement of AC as well as DC power, it
Electrostatic instrument are suitable for the is equally accurate on AC & DC circuit.
measurement of ac and de voltages. These type of PMMC voltmeter is used for only DC circuit
instrument used for the measurement of high voltage whereas induction type wattmeter is used for
but in some cases, they can be used in measuring the only AC circuit.
lower voltage and power of a given circuit. Dynamometer type wattmeter has uniform scale.
47. (b) In Dynamometer type wattmeter we can
When the shunt resistance of a galvanometer circuit obtained high degree of accuracy through
is increased its current sensitivity decreases. careful design.
Because a galvanometer is calibrated by choosing 55. (a)
the correct shunt resistance. Reflecting mirror mounted on the moving coil of a
θ NAB vibration galvanometer is replaced by a bigger size
current sensitivity Si rad/A mirror then this will result in lower frequency of
I K
48. (d) resonance and lower amplitude of vibration.
Damping torque is provided in indicating type 1 K
instruments such that pointer gets damped out as fn
2 J
quick as possible. If we provide critically damped
GI m
response, instrument may get damaged due to very A
fast response and for over damped response, it may ( D )2 ( K J 2 )2
become a sluggish response. Thus system should be From the above formula, as J increases both fn and A
work in under damped response such that speed of decrease.
operation should be quite high. Hence instruments 56. (c)
response should be slightly less than critically Given that,
damped. Scale = -5 to 15V
49. (a) Minimum quantity that can be measure by
Electrodynamometer is the most accurate instrument equipment is called resolution.
for measuring AC signals with frequency lower than Resolution = IV
200Hz. 57. (d)
50. (b) 1
Thermocouple meter are AC meters that respond to I fsd
the RMS value of signal. sensitivity
Thermocouple is a kind of temperature sensor that is 1
used to measure the temperature on the surface in I fsd 1mA
1000 Ω/V
the form of emf or current.
51. (c) I
Ihalf fsd fsd 0.5mA
The disc of an instrument using eddy current 2
damping should be of conducting and non-magnetic 58. (b)
material. Given
52. (d) Im = 1mA
An instruments which is totalized the event over a Rm = 5
specified period of time is known as integrating type Rsh = 0.55
instrument. An energy meter is an integrating type I=?
3.16 | JE-AE Electrical MASTERPLUS EDUCATION®
R I 62. (d)
Rsh m Where m Voltmeter has 100 divisions with full scale
m 1 Im
deflection of 200V
R 200
m 1 m then one division = 2V
Rsh 100
5 1
m 1 Instrument reads of scale division with fair
0.55 5
100 1
m 1 degree it means 2 4 will be Resolution
11 5
111 Resolution is the minimum value of any
m instrument which can be measured by it
11
accurately.
I 111
63. (c)
I m 11 Given,
111 Rm = 100
I 1mA 10.09mA 10mA Im = 1mA
11
V = 10V
59. (d)
Given, sensitivity (S) = 20 ΚΩ/V, V
m
V = 50V, R = ? Vm
R 1 Vm = Im.Rm
Sensitivity or
V I fsd Vm = 1 10-3 100 = 0.1 V
Rs = Rm(m – 1)
R
20 103 = 100(100 – 1) = 100 99 = 9900
50 64. (b)
R 20 50 103 1000 103 i = 5 + 14.14 sin (314t + 45°)
R 1 MΩ PMMC will measure iavg = 5A
60. (a) Hot wire and moving iron instrument will measure
Digital Voltmeter:- Digital voltmeter measures the rms value Hence,
2
potential difference between two point. Digital 10 2
voltmeter displays the value of AC or DC Voltage irms 5
2
125
being measured directly as discrete numerical 2
instead of a pointer deflection on a continuous scale 65. (c)
as in analog instruments if n = number of full digits, Heat is produced in a thermocouple instruments due
then resolution R of a digital voltmeter is given by- to potential difference between hot junction and cold
1 junction and is directly proportional to the square of
R current. H = i2 Rt
10n 66. (a)
61. (b) Im = 1mA
42 mm 21 mm 21 mm
Rm = 100
Galvanometer I = 100 mA
Scale 600 mm
Mirror Ish = ?
I 100
m 100
Deflection of Galvanometer = 42 mm Im 1
Distance of the scale from Mirror = 0.6m = 600mm R
21 Rsh m
Then angle tan = m 1
600 100
21 1 7
Rsh
tan 1 tan 100 1
600 200 100
Rsh 1.01
0.035 radians 99
Measurement MASTERPLUS EDUCATION®|3.17
67. (d) 72. (c)
Moving iron instrument always measure rms value Vm = 105V, Primary Voltage = 11000 V.
while moving coil instrument always measure N1 V1
average value. So when ac applied on moving coil Turns Ratio 100
N 2 V2
instrument, the reading will be zero.
68. (c) 11000
V2 110
PMMC meter use only in DC supply. PMMC meter 100
can be used as ammeter with the help of shunt Measured value True value
resistor. The value of shunt resistor is very low. %Voltage error 100
True value
Shunt resistor increase the range of PMMC
Vm VT
ammeter. 100 If Vm VT
69. (b) VT
Rsc Rm (m 1) Here V m < VT
V Vm
V T 100
m VT
Vm
110 105 5
Given that 100 100 4.54%
110 110
V= 1000
73. (c)
Vm = 100, Sv = 20,000 /V (Sensitivity)
Since, MI instrument measures RMS value of the
1000 quantity therefore M.I. ammeter reading is-
m
100 2
10 100
m = 10 I rms (10)
2
A 100 2 A
Then 2
Rm 100 50A
Sv
V I rms 150 A
Rm Sv V 74. (a)
Rm = 20000 100 = 2 106 It is given:-
Then Resistance (Rm) = 100 Ω
Rsc = Rm(m – 1) Meter Current (Im) = 10 mA = 10 × 10-3 A = 0.01A
Rsc = 2 × 106 (10 – 1) Total current (I) = 200 mA = 200 × 10-3 A = 0.2A
Rsc = 18 M Shunt Resistance (Rsh) = ?
70. (b) I
Given : Rm = 1000, Rsh = 100 Ω Rm Rsh 1
Multiplying factor (m) = ? Im
Rm 0.2
Rsh 100 Rsh 1
(m 1) 0.01
1000 Rsh 5.26
100
(m 1) 75. (c)
1000 It is given. Rint = 230kΩ, Rs = 70kΩ
(m 1) Here, Rint = Internal Resistance
100 Rs = series Resistance sensitivity
m = 10 + 1
Sensitivity = 3k/V
m = 11
71. (b) R
Sensitivity of voltmeter Ω/volt
R R Rs V
Meter sensitivity / Volt m Rs 70
V V
28 2
kΩ/Volt
100 V Rint 230k
0.3 kΩ/Volt
3.18 | JE-AE Electrical MASTERPLUS EDUCATION®
R Rs Sensitivity = 125 = / ν
3 int 1
V I fsd 8 103 A
230 70 125
3 Ifsd = 8mA
V
V = 100 Volt 81. (a)
76. (d) Im = 4 10-3 Amp.
V = 0.4 volt
Sensitivity 1 R Rm = 40
I fsd Vm V
0.4
1 1 I 0.01 Amp
I fsd 0.02 40
sensitivity 50
I 0.01
Ifsd = 20 mA m 2.5
77. (a) I m 4 103
A galvanometer can be converted into ammeter by Rs Rm (m 1) 40(2.5 1) 40 1.5
connecting a low resistance called shunt in parallel
to the galvanometer. An ammeter is a device used to Rs 60
measure the current in the circuit. So, value of series resistance Rs = 60 Ω
78. (a) Alternate solution-
Voltage in two parallel branches are same- V 0.4
Rs Rm 40 100 40
V I m ( Rm Rs jxm ) Im 4 103
V I sh ( Rsh jxsh ) Rs 60
Im ( Rsh jX sh ) 82. (b)
Current transformer helps in measuring high current,
I sh ( Rm Rs jX m )
using low range ammeter. Secondary winding of
Performing rationalization and put the imaginary
current transformer is always short circuited.
part equal to zero as –
Current transformer is connected in series with the
( Rsh jX sh ) Rm Rs jX m electrical circuit.
Rm Rs jX m Rm Rs jX m 83. (c)
for frequency independency, the imaginary part is Internal resistance of ammeter
zero- (Rm) = 100
( Rm Rs ) X sh X m ( Rsh ) Ammeter measurement range (Im) = (0-1)mA
0 Required measurement range (I) = (0-100)mA
( Rm Rs )2 X m2 I 100
( Rm Rs ) X sh X m ( Rsh ) Ammeter coefficient (m) =
Im 1
Xm X 100 100
sh Shunt resistance ( Rsh )
( Rm Rs ) Rsh m 1 100 1
79. (a) Rsh 1.010
For voltmeter sensitivity of PMMC type instrument
84. (c)
Rm Rs
V
is correct equation. Rr = Rv (m - 1) m V
Vr
Where, Rm = Meter resistance
Rs = Series resistance connected with meter Where, m = Multiplying factor
Because internal resistance connected series in Rv = Resistance of voltmeter 20,000 Ω
voltmeter and multiplier resistance connected in Rr = Resistance of series resistor = ?
series. The value of voltmeter sensitivity ohm/volt. V = 220 Volts
80. (c) Vr = 200 Volts
We know that :- 220 20
Rr 20, 000 1 20, 000
1 200 200
Sensitivity full scale Deflection Rr 2,000
Measurement MASTERPLUS EDUCATION®|3.19
85. (c) 440
To reduce the temperature effect, swamping V 20 440 _______(i)
resistance made up of manganin (having Rm
temperature coefficient of practically zero) and 90. (c)
i
combined with copper in the ratio of 20:1 to 30:1.
86. (d) 5A
Given,
1 = 80°, 2 = ?
I1 = 5A, I2 = 2.5A
For spring control- π ωt
2π 2π
Tc = K Moving-coil ammeter reads only the average value-
I Area of one cycle
1 I1 I av
Total time period
2 I2 2I 0
I 80 2.5 I av m
2 1 2 2
I1 5 But given Im = 5 Amp
2 40 (2 5) 0
I av
87. (b) 2
Given, 5
I av
Im = 250mA, Rm = 5
I = 1A 91. (d)
Multiplying factor of shunt, Ri = 40 Ω, RLead = 10, V = 100 mV
I 1 Rv = 150, VV = ?
m
I m 250 103 Rv
VV Vt
m=4 Ri Rv RLead
Required shunt resistance 100mV 150
Rm 5 VV
Rsh 150 40 10
m 1 4 1 100mV 150 100 150
5 VV
Rsh in parallel 150 40 10 200
3 VV 75mV
88. (a)
Given 92. (d)
I = 200 mA, A shunt which is used to extend the range of
m=8 ammeter is made of manganin.
Im = ? The ammeter shunt is the device which provides the
I (total current) low resistance path to flow of current. It connects in
Multiplying factor (m) 8 parallel with ammeter. For measuring the heavy
I m (meter current) current, the shunt is connected in the parallel to the
200mA ammeter.
Im 25mA
8 Rm
Rsh
89. (e) m 1
Let resistance of voltmeter be R k 93. (b)
When, Rs1 = 20 ΚΩ, V = 440V Total resistance
20k 80 k 250
( Rse Rm ) 2500
100 103
R440V IA
Rse 2500 Rm 2500 320 2180
From the figure- Steady current of 100 mA meter resistance has
changed to 369
3.20 | JE-AE Electrical MASTERPLUS EDUCATION®
Rse + Rm = 2180 + 369 = 2549 This value of resistance should be connected in
I m2 series with galvanomenter
98. (a)
Rse 2180 Average output of bridge rectifier-
250
2Vm
Rm 369 V0
250 V0 I X c
Now I m 2 98.07mA
369 2180 1
%Error Xc
I m 2 I m1 (98.07 100) C
100 1.93% 2Vm I
I m1 100
C
94. (d)
Voltmeter is always connected in parallel with 2 100 10 2
3
45 103
circuit and want to flow minimum current from 2 50 C
meter. So electronic voltmeter does not draws C 15.90 1010 F
appreciable current from source. 99. (a)
95. (b) Given data, Eactual = 50C,
Given
Resistance (R) = 100 k
V = 400 sint + 300 sin 3t V Accuracy of voltmeter is 99%
Then
2 2
100kΩ
1 RMS value RMS value
Vrms
2 of first wave form of second wave form
1
Vrms 4002 3002 50V
2
1 V
Vrms 500 500 / 2V
2 Emeasured
0.99 Emeasured 0.99 50 49.5V
96. (d) Eactual
If V1 and V3 are the rms values of the fundamental
50
and third harmonies of an alternating quantity, then I actual 0.5mA
the rms value of the alternative quantity is 100k
I measured (49.5) /100K 0.495mA
V12 V32
97. (d)
I " I actual I measured 0.5 0.495) 0.005mA
To convert galvanometer into voltmeter a high This I' current flow through the voltmeter which has
resistance is connected in series with galvanometer 99% accuracy.
which is shown in figure below. Therefore, 50 = I' R = 0.005 × 10-3 × R
Voltmeter R = 10ΜΩ
Ig R 100. (b)
A G B Given,
Total current (I) = 15A
Internal resistance, RA = 1, RB = 0.5
V If they are connected in parallel-
V I g R I gG I IA IB
V I g ( R G)
RA RB
V
RG
Ig By current division rule-
V RB 0.5 7.5
R G IA I 15 5A
Ig RA RB 1 0.5 1.5
Measurement MASTERPLUS EDUCATION®|3.21
RA 1 15
And, I B I 15 10A
RA RB 1 0.5 1.5
101. (a)
In PMMC type instruments, spring carry the
measuring current and if break down occurs in
spring then no current flow through it and reading
will be zero
102. (d)
Ammeter has very low internal resistance and when
it connect across supply it will draw large current
which will leads to meter damage.
103. (b)
Given,
Im = 0.1 mA
Rm = 500
V = 10 V
Multiplying factor (m)
V 10
m
Vm 50 103
Vm I m .Rm 0.1103 500 50 103
10 1000
m
50
m = 200
Rs = Rm (m-1) = 500(200 – 1) = 99500 = 99.5k
104. (c)
1
1
Sensitivity = V
I fsd R
R
Sensitivity Ω/Volt
V
Measurement MASTERPLUS EDUCATION®|4.1
POWER CHAPTER
& 4
ENERGY
Q.1 In two wattmeter method of power CC 20A
calculation of a 3-phase balanced star
connected system, what is the power factor
of the system if one of the wattmeter shows PC Load
zero reading and the other shows a positive 10k
reading?
(a) 0 CC
(b) Greater than 0 but less than 0.5
(c) 0.5
(d) Greater than 0.5 but less than 1 PC 200V Load
10k
Q.2 In the measurement of 3-phase power by
two wattmeter method, the two wattmeters The value of the Wattmeter current coil
indicate equal readings if the power factor resistance r, which makes the connection
is- errors the same in the two cases is
(a) Zero lagging (b) Unity (a) 0.05 Ω (b) 0.1 Ω
(c) 0.5 lagging (d) 0.8 lagging (c) 0.01 Ω (d) 0.125 Ω
Q.3 A 400 V three phase 50 Hz balanced source Q.7 An induction watt meter consist of
is supplying power to a balanced three phase (a) series electromagnet
load. Line current flowing through the load (b) shunt electromagnet
is 5A at a power factor angle of 30 degrees (c) permanent magnet
lagging. Reading of two wattmeters, used to (d) series and shunt electromagnet
measure the load power are:
(a) 1000 W, 2000 W (b) 2000 W, 4000 W Q.8 In two watt meter method, when both the
(c) 2000 W, 3000 W (d) 1000 W, 3000 W meters shows equal magnitude then what is
the power factor angle of the load current
Q.4 Two wattmeters connected to measure the (a) 45° (b) 90°
power in a balanced three phase load reads. (c) 0° (d) less than 45°
1000 W and 250 W respectively. The later
reading has been taken after reversing the Q.9 In the method of measuring 3-phase power
connection of current coil. The total power using two wattmeter, the reading of
taken by the load is _______. wattmeter W₁ for a capacitive type of load
(a) 1000 W (b) 250 W is given by: (Note: Assume W, is connected
(c) 750 W (d) 500 W between lines R & Y and W2 is connected
between lines B and Y)
Q.5 In two wattmeter method of power (a) W1 3EL I L cos(30 )
measurement phase angle is above 60°, then
total power is: (b) W1 EL I L cos(30 )
(a) W₁ + W₂ (b) 2W2 (c) W1 3EL I L cos(30 )
(c) W2 (d) W₂ - W1
(d) W1 EL I L cos(30 )
Q.6 Two types of connection of Wattmeter
pressure coil are shown in the figures. Q.10 Which one of the following methods
4.2 | JE-AE Electrical MASTERPLUS EDUCATION®
decreases the error due to connections in a (b) load impedance is low
dynamometer type Wattmeter? (c) supply voltage is low
(a) Using bifilar compensating winding in (d) None of the above
place of current coil.
(b) Using non-inductive pressure coil Q.16. In a low power factor wattmeter, why is a
circuit. compensating coil employed?
(c) Using a capacitor across a part of high (a) To neutralize the capacitive effect of
resistance of pressure coil circuit. pressure coil
(d) Using a swamping resistance. (b) To compensate for inductance of
pressure coil
Q.11 While measuring power in a 3-phase load by (c) To compensate for the error caused by
2 wattmeter method the readings of two power loss in the pressure coil
wattmeters are equal and opposite when (d) To compensate for the error caused by
(a) Pf is unity eddy currents
(b) Load is balanced
(c) Phase angle is between 60° and 90° Q.17. The minimum number of wattmeters
(d) The load is pure inductive required to measure the real power in an N
phase system with unbalanced load is:
Q.12. The power of a three-phase, three-wire Or
balanced system was measured by two What is the number of watt-meters required
wattmeter method. The reading of one of the to measure the power of a poly phase
wattmeter was found to be double that of the system containing 'N' conductors?
other. What is the power factor of the (a) (N–1) (b) N
system? (c) (N+1) (d) None of these
(a) 1 (b) 0.866
(c) 0.707 (d) 0.5 Q.18. Consider the following statements regarding
measurement of 3-phase power by two-
Q.13. The current and potential coils of a wattmeter method; one of the wattmeter
dynamometer type wattmeter were reads negative implying:
accidentally interchanged while connecting. 1. Power factor is less than 0.5
After energizing the circuit, it was observed 2. Power flow is in the reverse direction.
that the wattmeter did not show the reading. 3. Load power factor angle is greater than
This could be due to the 60°.
(a) Damage to potential coil 4. Load is unbalanced.
(b) Damage to current coil Which of the above statements are correct?
(c) Damage to both the potential and current (a) 1 and 2 only (b) 2 and 3 only
coil (c) 1 and 3 only (d) 1, 2, 3 and 4
(d) Loose contacts
Q.19. The power in an unbalanced 3-phase 4-wire
Q.14. A wattmeter is reading back-wards in an circuit can be measured by using a______
experiment. Upscale reading can be method:
obtained by reversing- (a) 4 wattmeters (b) 3 wattmeters
(a) Pressure coil connection only (c) 2 wattmeters (d) 1 watt meter
(b) Current coil connection only
(c) Both pressure and current coil Q.20. Due to the effect of inductance in the
connection only pressure coil, a dynamometer type
(d) Either pressure or current coil wattmeter
connection (a) Reads low on lagging power factor and
high on leading power factor
Q.15. The pressure coil of a wattmeter should be (b) Reads high on lagging power factor and
connected on the supply side of the current low on leading power factor
coil when- (c) Reading is independent of the power
(a) load impedance is high factor
Measurement MASTERPLUS EDUCATION®|4.3
(d) Always reads lower than actual value Q.26. In a balanced 3-phase circuit, the line
current is 12 A. When the power is
Q.21. Z₁ and Z₂ are connected in series to form a measured by two wattmeter method, one
load. A wattmeter's current coil is connected meter reads 11 kW while the other reads
in series with the load, whereas its pressure zero. Power factor of the load is
coil is connected across Z2. The wattmeter (a) 0 (b) 0.5
reads. (c) 0.866 (d) 1.0
(a) zero always
(b) power consumed by Z₂ Q.27. In a low power factor wattmeter compens-
(c) power consumed by Z₁ ating coil is connected:
(d) power consumed by Z₁ and Z2 (a) In series with the current coil
(b) In series with the pressure coil
Q.22. Determine the reading (in kW) of both the (c) In parallel with the pressure coil
wattmeters used to measure the power of a (d) In parallel with the current coil
three-phase three-wire system having input
of 6 kW and power factor of 1. Q.28. In 'Two-wattmeter method' of power
(a) 4, 2 (b) 5, 1 calculation of a 3-phase balanced star
(c) 3, 3 (d) 6, 0 connected system, what is the power factor
of the system, if one of the wattmeter's
Q.23. Power consumed by a balanced star shows negative reading and the other shows
connected 3-phase load is measured using a positive reading?
two-wattmeter method. The phase voltage (a) Greater than or equal 0 but less than 0.5
and phase current in the load is 220 V and (b) 0.5
10A respectively. What will be difference in (c) Greater than 0.5 but less than equal to l
reading (in W) of the two wattmeter, if the (d) Greater than 1
power factor of the system is 0.8 lagging?
(a) 2286.3 (b) 2861.2 Q.29. What is the reading (in kW) of both the
(c) 3048.4 (d) 3810.5 wattmeter, when measuring the power of a
three-phase three wire system having an
Q.24. In two-wattmeter method of measuring input of 5 kW and power factor of 0.866?
power in a balanced 3-phase circuit the (a) 5, 0 (b) 3.33, 1.67
readings of the two wattmeters are in the (c) 2.5, 2.5 (d) 1, 4
ratio of 1: 2, the circuit power factor is
(a) (b) Q.30. In the measurement of 3 phase power by
√ two watt meter method, for an unbalanced
√
(c) (d) 1 load, the power factor of the load is
(a) cos tan 1 3(W2 W1 )
Q.25. Phasor diagram of load voltage (V), current
W2 W1
in pressure coil (Ip) and current in current
coil (Ic) is shown in the figure when an (b) cos tan 1 W2 W1
electrodynamic wattmeter is used to W2 W1
measure power. The reading of the (c) cos (W2 – W1)
wattmeter will be proportional to (d) None of the above
β V
ψ Q.31. In an electrodynamometer wattmeter
(a) The fixed coils providing magnetic flux
IP are connected across the power line.
(b) The compensated wattmeter improves its
accuracy by using windings with opposite
IC currents with respect to series windings
(a) cos (β + ψ) (b) cos ψ (c) If the full-scale power measured is 100
(c) cos β cos ψ (d) cos β cos (β + ψ) W, then the half-scale power will be 10 W
4.4 | JE-AE Electrical MASTERPLUS EDUCATION®
(d) It can measure a.c. power but is (b) tan 3 W1 W2
unsuitable for d.c. power
W1 W2
Q.32. The wattmeter readings by two-wattmeter (c) tan 3 W1 W2
W1 W2
methods of power measurement are given as
W1 100 kW, W₂ = 50 kW. Wattmeter W₂ (d) tan 3 W1 W2
gives the reading after reversing the W1 W2
connection of its current coil. What is the
power factor of load? Q.39. If a wattmeter is used in a circuit it is safe
(a) 1.0 (b) 0.655 voltage or current rating is exceeded, the
(c) 0.5 (d) 0.866 meter will ______.
(a) not be affected
Q.33. In electro dynamometer type wattmeter, a (b) operated erratically
high non inductive resistance is connected (c) immediately peg the pointer
in______. (d) not indicate the overload
(a) parallel with fixed coil
(b) parallel with moving coil Q.40 A 400 V, three-phase, rated frequency
(c) series with moving coil balanced source is supplying power to a
(d) series with fixed coil balanced three phase load carrying a line
current of 5 at an angle of 30° lagging. The
Q.34. For a balance three phase circuit, two readings of the two wattmeters W1 and W₂,
wattmeter are connected to measure the used for measuring the power drawn by the
input. The reading of two wattmeter is 2000 circuit, are respectively
W and 535.98 W respectively. Determine (a) 2000 W and 1000 W
the power factor of the circuit. (b) 1500 W and 1500 W
(a) 1.0 (b) 0.7 (c) 2000 W and 1500 W
(c) 0.34 (d) 0.051 (d) 1500 W and 1000 W
Q.35. A dynamometer wattmeter can't read _____ Q.41 Dynamometer type moving coil instruments
power. are provided with................
(a) AC (b) DC (a) Eddy current damping
(c) AC/DC (d) None of these (b) Pneumatic damping
(c) Fluid friction damping
Q.36. Which of the following effects is used in (d) Electrostatic damping
Wattmeter?
(a) Chemical effect Q.42 For a delta-connected load being measured
(b) Electrostatic effect for power by the two-wattmeter method, if
(c) Electrodynamic effect W₁=VLIL cos(30-) and
(d) Thermal effect W2 =VLIL cos(30 + ) .Then total 3-phase
power is:
Q.37. With which of the following is the one (a) 3Vph I ph sin(30 )
wattmeter method of three-phase power
measurement possible? (b) 3VL I L sin(30 )
(a) Star-connected balanced load (c) 3VL I L cos( )
(b) Delta-connected balanced load
(c) Star-connected unbalanced load (d) 3Vph I ph cos(30 )
(d) Delta-connected unbalanced load
Q.43 The two-wattmeter method is used to
Q.38 Measurement of power factor for balanced measure the power of a three-phase
load by two wattmeters for lagging power balanced system. powered by a 415 V,
factor is: three-phase, 50 Hz power supply. If the
(a) tan 3 W1 W2 reading on both wattmeters is 8.5 kW.
calculate the power factor.
W1 W2
Measurement MASTERPLUS EDUCATION®|4.5
(a) 0.98 lagging (b) 0.858 lagging (b) 25.60 kW and 23.23 kW
(c) 1 (d) 0.88 lagging (c) 23 kW and 23 kW
(d) 18.34 kW and 46 kW
Q.44 For a delta-connected load being measured
for power by the two-wattmeter method, if Q.50 The two-wattmeter method is used to
Iph will lead Vph by angle then it is the case measure a three-phase power supply. If the
of ______. two wattmeter readings are 2 kW and 500
(a) Leading power factor (b) Short circuit W, determine the input current drawn from
(c) Lagging power factor (d) Open circuit a 440 V, three-phase AC supply if the load
is delta connected.
Q.45 A 3-phase 10 kVA load has a power factor (a) 26.95 A (b) 25.86 A
of 0.342. The power is measured by the (c) 2.58 A (d) 5.2 A
two- wattmeter method. Find the reading of
each wattmeter when the power factor is Q.51 Two watt meter method for 3 phase circuit
leading. is preferred over other methods because
(a) W₁ = 1 kW and W₂ = 4.4 kW (a) Pf of the load can also be estimated
(b) W₁ = -4.4 kW and W₂ = 1 kW (b) it can be used for star or delta connected
(c) W₁= -1 kW and W₂ = 4.4 kW load
(d) W₁ = 4.4 kW and W₂ = 1 kW (c) it can be used for balanced or unbalanced
load
Q.46 A balanced three-phase star-connected load (d) all are correct
draws power from a 440 V supply. The two
connected wattmeters, W₁ and W₂ indicate Q.52 In 3-phase power measurement by two-
5 kW and 1200 W respectively. Calculate wattmeter method, the two wattmeters read
the power factor of the system. as W₁ = 300 W and W₂ = 300 W. Then the
(a) 0.75 (b) 0.69 load is said to be operating at _______.
(c) 0.98 (d) 0.54 (a) Lagging power factor
(b) Zero power factor
Q.47 The wattmeter method is used to measure (c) Unity power factor
the power in a three-phase load. The (d) Leading power factor
wattmeter readings are 400 W and -35 W.
What will be the total active power? Q.53 Consider the following statements regarding
(a) 360 W (b) 370 W power measurement of three-phase circuits
(c) 365 W (d) 375 W by two-wattmeter method
1. Total power can be measured if the three-
Q.48 A delta-connected balanced load is supplied phase load is balanced and can be
from a three-phase balanced 400 V, 50 Hz represented by an equivalent Y connection
AC supply. The readings on the two only
wattmeters are 970 W and 480 W 2. Total power can be measured for the
respectively. Each phase of load consists of three- phase load irrespective of, whether
resistance and inductance connected in the load is balanced or not and connected in
series. Calculate the total active power Y or A
consumed. 3. Power factor can be calculated only if the
(a) 1.45 kW (b) 14.5 kW three-phase load is balanced
(c) 145 kW (d) 1,450 kW Which of the above statements are correct?
(a) 1 and 2 only (b) 1 and 3 only
Q.49 A three-phase star-connected balanced load (c) 2 and 3 only (d) 1, 2 and 3
of (4+j3) per phase is connected across
three- phase, 50 Hz, 400 V AC supply. If Q.54 The one-wattmeter method of 3 power
the two- wattmeter method is used to measurement can only be used for:
determine input power. find each wattmeter (a) Balanced delta connected load
reading. (b) Balanced load
(a) 18.34 kW and 7.26 kW (c) Unbalanced load
4.6 | JE-AE Electrical MASTERPLUS EDUCATION®
(d) Balanced star connected load (a) kWh/Revolutions (b) Revolutions/kWh
(c) Revolutions /kW (d) kW/ Revolutions
Q.55 In 3- power measurement for a balanced
load using the two-wattmeter method, the Q.62 In phantom loading arrangement, energy
reactive power is given by: consumption in the calibration test of
(a) the sum of both the wattmeter readings wattmeter is reduced because of
(b) three times the difference of the readings (a) the separate application of low voltage
of the two wattmeters supply across current coil
(c) √3 times the sum of the readings of the (b) no common point between the two coils.
two wattmeters (c) the reduced loss in current coil and
(d) √3 times the difference of the readings of pressure coil
the two wattmeters (d) the absence of load in the test set.
Q.56 In the two-wattmeter method of 3-4 power Q.63 In an induction type energy meter,
measurement, if the phase sequence of the everything else remaining same, if the radial
supply is reversed: distance of the brake magnet poles from the
(a) there won't be a change in meter spindle is decreased by 10%, the rotational
readings speed of the disc will _____ approximately.
(b) the reading of wattmeters will be (a) increase by 23.5%
interchanged (b) decrease by 10.6%
(c) the meters will not read (c) decrease by 19.4%
(d) one of the meters will show a negative (d) increase by 11%
reading
Q.64 Creeping in a single phase induction type
Q.57 When the 3 phase power is measured by two energy meter may be due to?
wattmeter method, at what power factor, the (a) Over voltage
readings of both wattmeter (b) Over compensation for friction
will be positive but not equal? (c) Vibrations
(a) Between unity to 0.5 lag (b) At 0.5 Lag (d) All of the given options
(c) Between 0.5 lag to zero (d) At Unity
Q.65 Which of the following is the cause of meter
Q.58 An energy meter is designed to make 100. phase error in induction type energy meter?
revolutions for one unit of energy. the (a) Incorrect position of brake magnets.
number of revolutions when connected to a (b) Incorrect adjustment of the position of
load of 40A, at 230V and 0.95 power factor shading bands.
lagging for an hour is: (c) Slow but continuous rotation of
(a) 657 (b) 874 aluminum disc.
(c) 362 (d) 530 (d) Temperature variations
Q.59 Induction type single phase energy meter Q.66 An energy-meter having a meter constant of
measure electric energy in 1200 rev/kWh is found to make 5
(a) kW (b) Wh revolutions in 75s. The load power is
(c) kWh (d) VAR (a) 500 W (b) 100 W
(c) 200 W (d) 1000 W
Q.60 The energy meter used for measuring
energy of D.C. circuit is: Q.67 A domestic energy meter disc moves
(a) ampere hour type slowly, even when main switch is off the
(b) induction type reason is-
(c) electrostatic type (a) Speed error (b) Voltage error
(d) dynamometer type (c) Frequency error (d) Creep error
Q.61 The meter constant of an energy meter will Q.68 A 60A, 220V energy meter makes 51
be revolutions in 35 seconds on full load test.
Measurement MASTERPLUS EDUCATION®|4.7
Calculate the percentage error (in %) if (a) Applied voltage: marked value of
meter constant is 420 rev/kWh. voltage; Applied current: 0.5% of marked
(a) 4.23 (b) 5.13 value of current
(c) 7 (d) 8.93 (b) Applied voltage: 110% of marked value
of voltage; Applied current: open circuit
Q.69 The adjustment of position of shading (c) Applied voltage: marked value of
bands, in an energy meter is done to provide voltage; Applied current: open circuit
(a) friction compensation (d) Applied voltage: 110% of marked value
(b) creep compensation of voltage; Applied current: 0.5% of marked
(c) braking torque value of current
(d) none of these
Q.76 An energy meter connected to an immersion
Q.70 The voltage coil of a single-phase house heater (resistive) operating on an AC 230 V,
service energy meter 50 Hz, single phase source read 2.3 kWh in
(a) Is highly resistive 1 hour. The heater is removed from the
(b) Is highly inductive supply and now connected to a 400 V peak
(c) Is highly capacitive to peak square wave source of 150 Hz. The
(d) Has a phase angle equal to load power power in kW dissipated by the heater will be
factor angle (a) 3.478 (b) 1.739
(c) 2.100 (d) 0.870
Q.71 A house has 4kW connected loads and is fed
by single phase supply. What range energy Q.77 A meter whose constant is 600 revolutions/
meter is recommended for the house? kWh makes 5 revolutions in 20 seconds.
(a) 50 A (b) 15 A Calculate the load in kW.
(c) 30 A (d) 10 A (a) 0.5 kW (b) 1 kW
(c) 1.5 kW (d) 2 kW
Q.72 A 5A, 230V meter on full load unity power
factor test makes 60 revolutions in 360 Q.78 In an energy meter, braking torque is
seconds. If the normal disc speed is 520 produced to-
revolutions per kWh, what will be% error? (a) safe guard it against creep
(a) 0.42% (b) 0.33% (b) brake the instrument
(c) 0.10% (d) 0.98% (c) bring energy meter to stand still
(d) maintain steady speed and equal to
Q.73 The series magnet of a single phase Energy driving torque
meter consists of coil of.......
(a) Thin wire of few turns Q.79 A 230 V, 1-phase watt hour meter records a
(b) Thick wire of few turns constant load of 10 A for 10 hours at unity
(c) Thick wire of more turns p.f. If the meter disc makes 2300 revolutions
(d) Thin wire of more turns during this period, what is the meter
constant in revolutions/kWh?
Q.74 Creeping in energy meter can be avoided (a) 100 rev/kWh (b) 200 rev/kWh
by: (c) 300 rev/kWh (d) 400 rev/kWh
(a) Using shading bands around the central
limb of shunt magnet Q.80 An energy meter is designed to make 100
(b) Using adjustable resistance revolutions of disc for one unit of energy.
(c) Providing a small shading loop between The number of revolutions made by it when
the central pole of shunt magnet and the disc connected to a load carrying 40 A at 230 V
(d) Drilling two diametrically opposite holes and 0.4 pf for an hour is:
in the disc (a) 368 (b) 600
(c) 628 (d) 356
Q.75 During the testing of an energy meter, what
are the required voltage and current Q.81 Consider the following statements:
conditions for a creep test? Adjustment is required in an induction type
4.8 | JE-AE Electrical MASTERPLUS EDUCATION®
energy meter in the following manner so Q.87 Phantom loading for testing of energy
that it can be compensated for slowdown of meters is used:
speed on the specified load due to some (a) To isolate the current and potential
unspecified reason: circuits
1. Adjusting the position of breaking magnet (b) To reduce power loss during loading
and moving it away from the centre of the (c) For meters having low current ratings
disc. (d) To test meters having a large current
2. Adjusting the position of braking magnet rating
and moving it closer to the centre of the
disc.
3. Adjusting the load. 3.
Which of these statements are correct?
(a) 1, 2 and 3 (b) 1 only
(c) 2 only (d) 3 only
Q.82 A single phase energy meter has a constant
of 1200 revolution/kWh. When a load of
200 W is connected, the disc rotates at 4.2
revolutions per min. If the load is on for 10
hours, the meter records an excess of
(a) 0.1 kWh (b) 0.2 kWh
(c) 1.0 kWh (d) 2.0 kWh
Q.83 The constant of a given energy meter is 500
revolution/kWh. At the test 4.4 kW full
load, meter completes 50 revolutions in 86
seconds. The percentage error of the meter
is
(a) -4.86% (b) 4.86%
(c) 2.0% (d) 3.0%
Q.84 Two holes in die disc of energy meter are
drilled at opposite sides of the spindle to
(a) improve its ventilation
(b) eliminate creeping at no load
(c) increase its deflecting torque
(d) increase its braking torque
Q.85 The current coil of a single-phase energy
meter is wound on
(a) One limb of the laminated core
(b) Both the limbs of the laminated core
with same number of turns
(c) Both the limbs of the laminated core
with different number of turns
(d) The center of the limb on the laminated
core
Q.86 The pressure coil of an energy meter has
(a) few turns of thin wire
(b) few turns of thick wire
(c) many turns of thin wire
(d) many turns of thick wire
Measurement MASTERPLUS EDUCATION®|4.9
Answer Key: Power & Energy
1 C 2 B 3 A 4 C 5 D
6 C 7 D 8 C 9 B 10 A
11 D 12 B 13 B 14 D 15 A
16 B 17 A 18 C 19 B 20 B
21 B 22 C 23 A 24 C 25 C
26 B 27 B 28 A 29 B 30 A
31 B 32 D 33 C 34 D 35 D
36 C 37 A 38 C 39 D 40 A
41 B 42 C 43 C 44 A 45 C
46 B 47 C 48 A 49 A 50 D
51 D 52 C 53 C 54 B 55 D
56 B 57 A 58 B 59 C 60 A
61 B 62 D 63 D 64 D 65 B
66 C 67 D 68 B 69 A 70 B
71 C 72 B 73 B 74 D 75 B
76 B 77 C 78 D 79 A 80 A
81 C 82 A 83 A 84 B 85 B
86 C 87 D
Solution
1. (c) As we known that-
Let W1 = W, W2 = 0 3(W1 W2 )
(W W2 ) tan 1
tan 1 3 1
(W1 W2 )
(W1 W2 )
3(W1 W1 )
(W 0) W tan 1
tan 1 3 tan 1 3
W 0
W (W1 W1 )
tan 3 tan 1 30
60 tan 1 (0)
cos cos 60 0
cos 0.5 cos cos 0 1
2. (b) Hence, power factor will be unity
Given, W1 = W2, cos = ?
4.10 | JE-AE Electrical MASTERPLUS EDUCATION®
3. (a) W1 W1
Wattmeter reading are given as tan 1 3
W1 W1
W1 VL I L cos(30 )
tan 0 1
W2 VL I L cos(30 )
Power factor angle 0
Thus for 30,VL 400V and I L 5A 9. (b)
W1 400 5 cos(30 30) 2000W Given that,
Load capacitive nature
W2 400 5 cos(30 30) 1000W
Y-connection
4. (c)
Given,
VL 3Vph
W1 = 1000 watt IP IL
W2 = -250 watt (due to reading take after reversing W1 measured-
the connection of C.G.) VRY
We known that total power taken by load in 2- IR
wattmeter method W = W1 + W2 Angle
W = 1000 – 250 W₂ measured-
W = 750 watt VBY
5. (d) IB
When p.f. is less than 0.5 but greater than 0 Angle
(90 60) W1
IR
W2 = Positive reading R
W1 = Negative reading Z
The total power N
P = W 1 + W2 VB Y
= (-W1) + W2 Z Z
P = W 2 – W1
i.e. when phase greater than 600 or p.f. less than 0.5 Y
IY
then one wattmeter will read negative VBY
6. (c) B
For type-1 connection W2
IB
error = I2 RC Phasor diagram-
For type-2 connection
VB Y
V2 VYN VRY
error =
RP
If error is same in both connection- VBN 30 30 IR
V 2 (200) 2 IB
So, I 2 RC VRN
RP 10, 000
(200)2
RC 0.01 IY
10, 000 (20)2
VYN
7. (d)
An Induction wattmeter consist of series and shunt W1 = VRY IR cos(30 - )
electromagnet to work as a current coil and voltage W1 = VL IL cos(30 - )
coil respectively. W2 = VL IL cos(30 + )
8. (c) 10. (a)
In two watt meter method, we know- By using bifilar compensating winding in place of
W W2 current coil, error due to connection in a
tan 1 3 1 dynamometer type wattmeter decreases.
W1 W2 11. (d)
Both wattmeter shows equal magnitude hence, W1 = given, [W₂ = -W1]
W2
Measurement MASTERPLUS EDUCATION®|4.11
W W2 True power = WT = VLIL
We know that, tan 1 3 1 Measured power Wm = VaIa + VLIL
W1 W2 I a I L Wm I a (Va VL )
W W1
tan 1 3 1 error Va I L VL I L VL I L Va I L
W1 W1 Va I L
% error 100
2W VL I L
tan 1 3 1
0 V
tan 1 Or % error a 100
VL
tan tan 90
90 If load impedance () VL %error
So, the load is pure inductive. 16. (b)
While measuring power in a 3-phase load by 2 Pressure coil is connected across the load in case of
wattmeter method the reading of two wattmeters are low power factor for this case, generally LC
equal and opposite when phase angle is 90°. connection is used. The wattmeter measure
12. (b) V 2
Given, W₁ = 2P, W2 = P additional power loss in the pressure coil, to
Power factor formula given by- R p
W W2 reduces this error a compensating coil is employed
cos cos tan 1 3 1 in the pressure circuit.
W1 W2 17. (a)
2P P According to Blondel's theorem
cos cos tan 1 3 0.866
2P P If system in a phase (N + 1) wire then N wattmeter
13. (b) is needed.
Current coil is connected in series with the load and If system is N phase N wire the (N-1) wattmeter
carries the load current. If the coils are interchanged, is needed so in N phase unbalance load the
current coils gets directly connected across the number of wattmeter required
supply. Large current flows through the coil = (N-1)
resulting into damage to current coil. Total voltage 18. (c)
apply across current coil. Which has very less Reading of wattmeter W1 and W2
resistance which leads to damage the current coil W1 = VLIL cos(30 - )
14. (d) W2 = VLIL cos(30 + )
If wattmeter reading is back-ward in experiment If > 60 then cos < 0.5 then the reading of
then upscale reading can be obtained by reversing wattmeter W₂ is always negative.
either pressure or current coil connection. In general 19. (b)
wattmeter is an electro-dynamo meter type The power in an unbalanced 3-phase 4-wire circuit
instrument which current coil is in series of load and can be measured by using a 3 wattmeter method:
pressure coil is in parallel to supply. Used to Number of wattmeters = (n-1).
measure power of any circuit, Where n = Number of wires.
15. (a) 20. (b)
Pressure coil of wattmeter should be connected on Due to the effect of inductance in the pressure coil,
the supply side of the current coil when load deflecting torque in a dynamometer type wattmeter.
impedance is high to reduce % error in measurement (i) For lagging power factor,
because for power measurement % error of Td VI cos( ) {cos( ) cos }
wattmeter is as following- So wattmeter reads high.
Ia Va (ii) For leading power factor,
IV IL Td VI cos( ) {cos( ) cos }
So wattmeter reads low.
Vv 21. (b)
VL
4.12 | JE-AE Electrical MASTERPLUS EDUCATION®
Wattmeter CC 25. (c)
P V cos . I c cos
I
Z1 P VI c cos cos
PC
P cos cos
Z2 26. (b)
IL = 12A
W1 = 11kw
Wattmeter will read power consumed by Z2.
W2 = 0
Because in Load Z2 both current, from CC and
Power factor of the wattmeter is
voltage from PC are present while in Z1 only
current. Thus wattmeter will read Load of Z2. tan 3[(w1 w2 ) / (w1 w2 )]
22. (c)
tan 3[(11 0) / (11 0)]
It is given: cos = cos0° = 1
= 0° tan 3 60
W₁ = VLIL cos (30 + ) = VLIL (30 + 0°) cos 60 1/ 2 0.5
[W1 = VLIL cos30°] ............... (i) 27. (b)
In the same way, In a low power factor wattmeter compensating coil
W2 = VLIL cos (30 - ) is connected in series with the pressure coil.
W2 = VLIL cos (30 + 0°) The high value current causes the error in the
[W2 = VLIL cos30°] ............... (ii) wattmeter reading for reducing the error, the
from above relations shown in above equations. The compensation coil is used in the circuit. The
reading of both wattmeters is same positive since, compensating coil compensates the error in the
W1 + W₂ = 6 kW circuit which induces because of low power factor.
W+W=6 28. (a)
2W = 6, W = 3 When the value of angle is less than 60° greater than
W1 = 3kW W2 = 3kW 90° then the value of power factor is greater than
23. (a) zero and less then 0.5, So the reading of one
P 3Vph I ph cos wattmeter is positive and others is negative.
i.e. 0 cos 0.5
3 220 10 0.8 5280W
P = W 1 + W2 29. (b)
Given that
cos = 0.8, sin = 0.6
P = 5kW, cos = 0.866, = 300
W W2 P1 + P2 = 5kW ____(i)
tan 3 1
W1 W2 P P
We know that, tan 3 1 2
0.6 W W2 P1 P2
3 1
0.8 5280 P P 1 P P
5280 0.6 3168 tan 30 3 1 2 3 1 2
W1 W2 5 3 5
0.8 1.732 1.3856 5 3( P1 P2 )
W1 W2 2286.3W
5
24. (c) P1 P2 1.66
Let W1 = 2W 3
W2 = W P1 P2 1.66kW ____(ii)
W W2 2W W From equation (i) and (ii)
tan 3 1 3 P1 = 3.33 kW
W1 W2 2W W
P2 = 1.67 kW
1 30. (a)
tan 30
3 In the measurement of 3-o power by two watt meter
method, for an unbalanced load the power factor of
3
p.f. cos cos30 the load is-
2
Measurement MASTERPLUS EDUCATION®|4.13
35. (d)
Power factor = cos tan 1 3(W2 W1 ) A dynamometer wattmeter can read both AC and
W2 W1 DC power. Dynamometer type wattmeter works on
31. (b) the principle stated as when any current carrying
In electrodynometer watt meter fixed coil (field coil conductor is placed inside a magnetic field, hence
or current coil) are connected in series with load current carrying conductor experience a force which
which is carry load current. The compensating coil is given by-
is connected in series with pressure coil & it opposes F iB sin Newton
the field of, current coil. This type meter suitable for 36. (c)
both ae and de measurement, it measure average Electrodynamics effect is used in wattmeter. This
value of active power. effect is used in the electrodynamic or
32. (d) electrodynamometer type of instruments. This
Given W1 = 100 kW effect, which is basically a magnetic effect is
W2 = 50 kW produced in the form of force, when two current
W W2 carrying coils are placed near each other.
tan 3 1 Current
W1 W2 i coil ic
100 50
tan 3 ip L
150 Supply
O
Pressure A
1 1
tan 3 i.e. coil
R D
3 3
Thus, tan = tan 300 = = 300 37. (a)
The limitation of the one wattmeter method of three-
Hence power factor = cos = cos300
phase power measurement is that is not operate at
= 0.866
unbalanced load condition. Therefore the
33. (c)
measurement of 3-phase power by one wattmeter
A electrodynamometer type wattmeter consists of
method is possible only star-connected balanced
two coils called moving coil and fixed coil. A
load.
moving coil connected in parallel to the load. In
dynamometer type wattmeter a high non inductive P I1
resistance is connected in series with moving coil.
1
Moving coil is also known as pressure coil. I3 V1
An electrodyanometre type wattmeter shown in
2
figure given below. V2
Scale V3
C.C C.C 3
I1 I L I I2
L
V O Total power = P1 + P2 + P3 = 3P
P.C Re
A = 3 Vphase Iphase cos
D
38. (c)
34. (d) Measurement of power factor for balanced load by
Reading of 1st wattmeter (W₁) = 2000W two wattmeter for lagging power factor is-
Reading of 2nd wattmeter (W₂) = 535.98W Total power measured by two wattmeter is-
W1 = 2000W W₂ = 535.98W PT = W1 + W2 = √3VLIL cos _____(i)
3(W1 W2 ) 3(2000 535.98) Total reactive power measured by two wattmeter is-
tan QT = √3(W1 – W2) = √3VLIL sin ______(ii)
W1 W2 (2000 535.98)
By equation (i) and (ii) we get
3(1464.02) 2535.7546 3VL I L sin 3(W1 W2 )
tan 0.9987
2535.98 2535.98 3VL I L cos (W1 W2 )
tan 1 tan 45 45
3(W1 W2 )
The value of cos = cos 45° = 0.707 tan
(W1 W2 )
4.14 | JE-AE Electrical MASTERPLUS EDUCATION®
39. (d) 46. (b)
If a wattmeter is used in a circuit, it is safe voltage Given that-
or current rating is exceeded, the meter will not W1 = 5 kW = 5000 W
indicate the overload. W2 = 1200 W
Total Power = √3VLIL cos W W2
40. (a) tan 3 1
W1 W2
Reading of 1st wattmeter
W1 = VLIL cos (30 - ) 5000 1200
3
= 400 × 5 × cos (30 - 30) = 2000W 5000 1200
Reading of 2nd wattmeter, 3800
3 1.732 0.61 1.061
W₂ = VLIL cos (30 + ) 6200
= 400 × 5 × cos (30 + 30) = 1000 W tan 1.061
41. (b)
Pneumatic dampers provide speed and motion tan 1 (1.061)
control using gas damping in extension compression 46.69 47
or both direction. dynamometer type moving coil P. f . cos cos 47 0.6819
instrument are provided with pneumatic damping.
42. (c) cos 0.69
Total power (P) = W1 + W2 47. (c)
= VLIL cos (30 - ) + VLIL (30 + ) Given that-
W₁ = 400 W
3VL I L cos W₂ = -35 W
43. (c) Total Power (P) = W₁ + W₂ = 400 + (-35)
Given that- P = 365 W
W1 = W2 = 8.5 kW 48. (a)
W W2 8.5 8.5 Given that-
tan 3 1 3 W₁ = 970 W
W1 W2 8.5 8.5
W₂ = 480 W
tan = 0
Total power (P) = W₁ + W2
tan = tan00 P = 970 + 480
= 00 P = 1450 W
p.f. = cos = cos 00 = 1 P = 1.45 kW
44. (a) 49. (a)
When current lead to voltage by an angle of () Given that-
then the power factor will be leading. When current VL = 400V
lags to voltage by an angle of () then the power Z (4 j3)
factor will be lagging.
I ph
| Z | 16 9 25 5
R 4
cos 0.8
Z 5
cos (0.8) 36.869
1
V ph tan tan (36.869)
45. (c) = 0.7499 ≅ 0.75
Given that- For star connection -
Apparent power (S) = 10kVA VL
3VL I L 10kVA V ph
3
10 400
VL I L kVA V ph
3 3
cos = 0.342 V 400 / 3
= cos-1 0.342 I ph ph 46.2A
= 700 Z 5
Measurement MASTERPLUS EDUCATION®|4.15
Total power concerned by load (P) = W1
W1 W2 3I Rph
2
ph C.C i1
R
3 (46.2)2 4
P.C
= 25613.28 W v1
P = W1 + W2 = 25.6 kW ____(i)
W W2 v2
tan 3 1 i2
W1 W2 B v3
P.C
W W2
0.75 3 1 Y
C.C
25.6 i3
W2
25.6 0.75
W1 W2 Total power
1.732 W = W 1 + W2
W1 W2 11.08kW ____(ii)
3- active power P 3VL I L cos W1 W2
After solving equation (i) & (ii)
W1 = 18.34 kW 3- reactive power P 3VL I L sin 3(W1 W2 )
And, W2 = 25.6 – 18.43 3(W1 W2 )
W2 = 7.26 kW tan 1
50. (d) W1 W2
For delta connection load- By two wattmeter method we can measure both
VL = Vph balance & unbalance load condition.
IL = √3 Iph Neutral point for star connected load is not
Total Power (P) = W₁ + W₂ necessary to connect the wattmeter.
= 2000 + 500 52. (c)
P = 2500 W Power factor-
P 3VL I L cos W W2
tan 3 1
W W2
tan 3 1 W1 W2
W1 W2 Reading of wattmeter at different power factor-
S.No cos constant
2000 500
3 1 0 0
1 W1 = W 2
2000 500 2 300 0.86 W1 = 2W2
tan 1.039 3 600 0.5 W1 = 0,
tan 1 1.039 W2 = W
0
4 90 0 W1 = -W2
46 53. (c)
cos cos 46 0.694 Total power can be measured for three phase load
P 2500 irrespective of whether the load is balanced or not.
IL Total power = v1i1 + v2i2
3VL cos 3 440 0.6 = W1 = W 2
IL 5.2A = sum of two wattmeter readings,
51. (d) But in two wattmeter method, power factor can be
Two wattmeter method: In this method we have two calculated only when load is balanced.
type of connections Readings of wattmeter,
(1) Star connection of loads W1 3VI cos(30 )
(2) Delta connection of loads
When the load is star connected- W2 3VI cos(30 )
Total reactive power, Q 3(W1 W2 )
So, power factor of load,
4.16 | JE-AE Electrical MASTERPLUS EDUCATION®
3(W1 W2 ) 60. (a)
cos cos tan 1 The meter which is used for measuring the energy
(W1 W2 ) utilizes by the electric load is known as energy
54. (b) meter.
One wattmeter method can measure power only for 61. (b)
balanced load whether the load is delta connected or Energy meter constant
star connected. No. of revolutions
Power can be measured by one wattmeter method K
energy recorded
even if the neutral point is not available.
N N
Total power = 3 Vph Iph cos K
The two and three wattmeter method can be used for V .I .cos .t p.t
balanced and unbalanced load. 62. (d)
55. (d) In Phantom loading arrangement energy
In 3- power measurement for a balanced load using consumption in the calibration test of wattmeter is
the two wattmeter method, the reactive power is reduced because of the absence of load in the test
given by √3 times the difference of the readings of set.
the two wattmeters. 63. (d)
3(W1 W2 ) 3VL I L sin Braking torque of Induction type energy meter is
given by
56. (b)
Tb Km2 N .d
In the two wattmeter method of 3- power
measurement, if the phase sequence of the supply is 1
N
reversed the reading of wattmeter will be d
interchanged. Distance is decreased by 10%
57. (a) d2 0.9d1
When the 3- power is measured by two wattmeter
method, at between unity to 0.5 lag power factor, the N 2 d1
reading of both wattmeter N1 d 2
(i) At unity power factor cos = 1, = 0° N2 d
Power measured by first wattmeter 1
W1 = VLI cos (30 – 00) = 0.866 VLI N1 0.9d1
power measured by second wattmeter N2 = 1.11 N1
W₂ = VLI cos (30 + 0°) = 0.866 VLI Therefore speed increases by 11%
58. (b) 64. (d)
As given energy meter makes 100 Revolutions for The vibration, stray magnetic field and the extra
one unit of energy voltage across the potential coil are also responsible
So, according to question for the creeping. The creeping error occurs because
Energy consumed by energy meter of the excessive friction. The main driving torque is
230 40 0.95 absent at no load. Hence the disc rotates because of
8.74 unit the additional torque provided by the compensating
1000
Then number of revolutions by energy meter vane.
= 8.74 100 = 874 65. (b)
59. (c) Incorrect Adjustment of the position of shading
Induction type single phase energy meter measure bands is the cause of meter phase error in induction
electric energy in kWh. type energy meter. Phase error; it is necessary that
Induction type instruments are used for AC the energy meter should give correct reading on all
measurement. The induction principle find its power factors, which is only possible when field
widest application as an energy meter. Energy setup by shunt magnet lags behind the applied
meter is an integrating instrument which voltage by 90° so by adjusting the position of
measures the total quantity of electrical energy shading band placed round the lower port of control
supplied to the circuit in given period. limb of shunt magnet, it can made to lag.
66. (c)
The basic principle of induction type energy
meter is electromagnetic induction. Number of revolutions = K P t
Measurement MASTERPLUS EDUCATION®|4.17
75 72. (b)
5 1200 P Given,
3600
I = 5A, V = 230 V, N = 60 rev
75P
5 t = 360 sec k2 = 520 rev/kWh,
3 error = ?, cos = 1
1 N 3600 1000
P kWh k1
5 VIt cos
1 60 3600 1000
P 1000 k1
5 5 230 360 1
P = 200 W 12000 1000
67. (d) k1 521.73
The disc of domestic energy meter makes slow but 23
continuous rotation at no load, when potential coil is k k 521.73 520
% error 1 2 100 100
excited but with no current flowing in the load. This k1 521.73
is called creeping. This error may be caused due to
% error = 0.33%
overcompensation for friction, excessive supply
73. (b)
voltage, vibration, stray magnetic field etc.
Series magnet or current coil is of thick wire of few
68. (b)
turns where as shunt magnet or voltage coil is of
Given that: Current (I) = 60 A,
thin wire of more turns.
Volt (V) = 220V
74. (d)
Meter constant (K) = 420 rev/kWh, Time (t)= 35 sec
Creeping in energy meter can be avoided by drilling
Et = True Energy
two diametrically opposite holes in the disc.
= VI cos t = 220 60 1 35 = 462000 Joule Creeping error- Sometimes even when there is no
462000 charge on the energy meter, only the potential coil
Et 0.128 kWh
3600 10 3
keeps moving very slowly, only when the potential
No. of revolutions 51 coil is excited, this type of error in the meter is
Et 0.121 called creeping error. To remove this error two holes
K 420
are made on the disk on either side of the axis in
| E Et | | 0.121 0.128 |
%error r 100 100 such a way that the braking magnets pass thorough
Et 0.128 the magnetic field. At zero load state when any of
0.007 the holes come under the resistor coupler in this case
100 the disc stops.
0.128
%error 5.13% 75. (b)
During testing of an energy meter, applied voltage is
69. (a)
110% rated voltage and applied current is open
The adjustment of position of shading bands, in an
circuit. So at this time no current flow in energy
energy meter is done to provide friction
meter.
compensation.
76. (b)
70. (b)
Given, E = 2.3 kWh, t = 1 h, V = 400 V
Pressure coil of induction type energy meter is
highly inductive and has low resistance to make E 2.3 103
P 2300W
angle p is more with respect to V. t 1
71. (c) V 2 (230) 2 230 230
Given: load = 4kW R 23
P 2300 2300
Put cos = 1
Voltage supply = 230 volt (200)2 200 200
R 1.739kW
P 4000 23 23
Current( I ) 17.39 77. (c)
V cos 230 1 Given data,
17.39 A current flowing to load. So energy meter Meter constant = 600 revolution/kWh
current should be greater than 17.39A number of revolution = 5
Hence, further extension the range of energy meter
is recommended for the house is 30A.
4.18 | JE-AE Electrical MASTERPLUS EDUCATION®
1 Given, k₁ = 500 rev/kWh
time t = 20 seconds h P = 4.4 kW, t = 86 sec, N = 50 rev, error = ?
180
We known N 3600
k2
No. of revolution Pt
Meter constant K 50 3600
Power (kW) × time (h)
no of revolution 4.4 86
Power (kW) = 475.68 rev/kWh
meter constant (K) × time (h) k2 k1
5 5 180 % error 100
1.5 kW k1
1 600
600 475.68 500
180 100
78. (d)
500
In energy meter, breaking torque is produced to % error = -4.86%
maintain steady state speed and this torque is equal 84. (b)
to driving torque. The torque which is applied to Two holes are drilled in the disc of the energy meter
stop the motion of the moving equipment is called on the opposite side of the spindle to eliminate
braking torque. creeping on no load in energy meter.
79. (a) 85. (b)
Series magnet having two limbs, hence current coil
revolution
Meter constant is connected in two limbs with equal number of
kWh turns. Therefore option (b) is most suitable and
meter constant 2300 correct option.
100 rev/kWh
230 10 10 103 86. (c)
80. (a) A pressure coil of an energy meter has many turns
Total power = VIcos of thin wire. The conduction of energy meter
P = 40 230 0.4 consists of two electromagnetic whose cores are
P = 16 230 made of silicon steel lamination. An electromagnet
P = 3680 W made of two current coils is excited by a load
P = 3.68 kW current.
For 1 kW = 100 Rev 87. (d)
Hence for 3.68 kW = 100 3.68 Phantom loading- For calibration of wattmeter and
= 368 Revolution energy meter the current coil applied with small
81. (c) potential and variable resistor, to flow the current
For slowdown compensation in energy meter can equivalent to load current and potential coil is
avoid by moving brake magnet closer to centre of applies with supply voltage. This type of loading is
disk. called phantom loading or factious loading.
1 It is mainly used to test meters having a large
Speed of disc current rating.
d
82. (a)
Meter constant = 1200 revolution/kWh A
In 1 minute 4.2 revolution
In 1 hour 4.2 60 = 252 revolution
In 10 hour revolution 252 10 = 2520 revolution
2520
Measured value kWh 2.1 kWh
1200
200 10
True value kWh 2 kWh
1000
Meter read excess kWh = 2.1 – 2 = 0.1 kWh
True kWh = 0.1 kWh
83. (a)
Measurement MASTERPLUS EDUCATION®|5.1
CHAPTER
ELECTRONIC
INSTRUMENT 5
Q.1 Lissajous patterns of CRO depends on Q.7 Loading by the measuring instruments
which of following quantity of sine wave introduces an error in the measured
given to field- parameter. Which of the following devices
(a) Frequency (b) Amplitude gives the most accurate result?
(c) Phase relationship (d) All of these (a) PMMC (b) Hot-wire
(c) CRO (d) Electrodynamics
Q.2 If the bandwidth of an oscilloscope is given
as direct current to 10 MHz, what is the Q.8 In an oscilloscope, the observed Lissajous
fastest rise time a sine wave can have to be figure is shown below:
produced accurately by the oscilloscope?
(a) 35 ns (b) 10 ns
(c) 3.5 ns (d) 0.035 ns
What is the ratio of vertical input signal
Q.3 The signal generated by the time-base frequency to that of horizontal input
circuitry of the CRO is basically a: frequency?
(a) square waveform (a) 3/2 (b) 2/3
(b) saw-tooth waveform (c) 5/3 (d) 3/5
(c) sinusoidal waveform
(d) triangular waveform Q.9 Spectrum analyzer is a combination of
(a) narrow band super heterodyne receiver
Q.4 A digital voltmeter uses a 10MHz clock and and CRO
has a voltage controlled generator which (b) signal generator and CRO
provides a width of 10µ sec per volt of unit (c) oscillator and wave analyzer
signal. 10 volt of input signal would (d) VTVM and CRO
correspond to a pulse count of
(a) 500 (b) 750 Q.10 The CRT display is made up of small
(c) 1000 (d) 1500 picture elements called pixels. The _____
the _____ the pixels, the image clarity or
Q.5 The X and Y plates of a cathode ray resolution of the display.
oscilloscope are provided with sinusoidal (a) smaller, better
inputs of equal amplitude and frequency (b) smaller, poorer
which are 90° out of phase. The resulting (c) larger, better
Lissajous pattern will be a: (d) larger, poorer
(a) circle
(b) parabola Q.11 Which of the following materials when used
(c) horizontal straight line as the viewing surface of a CRO gives a
(d) vertical straight line bluish glow?
(a) Zinc sulfide with copper as impurity
Q.6 Multimeter can be used for measuring (b) Zinc sulfide with silver as impurity
(a) Both A.C. and D.C. (c) Yttrium oxide
(b) A.C only (d) Pure zinc sulfide
(c) D.C. only
(d) Half wave rectified A.C. Q.12 Which of the following materials when used
as the viewing surface of a CRO gives a
5.2 | JE-AE Electrical MASTERPLUS EDUCATION®
reddish glow? that of horizontal input frequency are
(a) Zinc Sulfide with copper as impurity
(b) Zinc Sulfide with silver as impurity
(c) Yttrium Oxide
(d) Pure Zinc Sulfide
1 (X) (Y)
Q.13 In a 3 digit voltmeter, the largest number (a) 5/3 for X and 3/2 for Y
2
(b) 3/2 for X and 5/3 for Y
that can be read is:
(c) 5/3 for X and 5/3 for Y
(a) 1999 (b) 5999
(d) 3/2 for X and 3/2 for Y
(c) 9999 (d) 0999
Q.19 Two meters X and Y required 40 mA and 50
Q.14 A screen pattern oscillogram, shown in the
mA respectively for full scale deflection.
given figure is obtained when a sine-wave
Then
signal of unknown frequency is connected
(a) Both are equally sensitive.
to the vertical input terminals, and at the
(b) Data are insufficient to comment
same time, a 600 Hz sine-wave voltage is
(c) X is more sensitive than
connected to the horizontal input terminals
(d) Y is more sensitive than
of an oscilloscope.
Q.20 A C.R.O. is operated with X and y settings
of 0.5 ms/cm and 100 mV/cm. The screen of
the C.R.O. is 10 cm x 8cm (X and Y). A
sine wave of frequency 200 Hz and r.m.s.
Vertical
axis amplitude of 300mV is applied to the Y-
input. The screen will show
Horizontal axis (a) one cycle of the undistorted sine wave.
What is the value of unknown frequency? (b) two cycles of the undistorted sine wave.
(a) 300 Hz. (b) 400 Hz (c) one cycle of the sine wave with clipped
(c) 600 Hz (d) 900 Hz amplitude.
(d) two cycles of the sine wave with clipped
Q.15 The deflection sensitivity of the CRO is 10 amplitude.
m/V. What is the value of deflection factor
(in V/m)? Q.21 In a standard multimeter for measuring AC
(a) 10 (b) 0.1 voltage, parameter of.........voltage is
(c) 1 (d) 0.01 measured:
(a) Peak-to-peak (b) Peak
Q.16 Calculate the fastest rise time (in ms) a sine (c) Average value (d) RMS
wave can have to be reproduced by a CRO,
if the bandwidth ranges from (0 to 10) Hz Q.22 A lissajous pattern on an oscilloscope has 5
(a) 17.5 (b) 0.35 horizontal tangencies and 2 vertical
(c) 35 (d) 1.75 tangencies. The frequency of the horizontal
input is 1000 Hz. The frequency of the
Q.17 Which of the following is NOT a vertical input will be:
component of a CRO? (a) 4000 Hz (b) 2500 Hz
(a) Electron gun (c) 40 Hz (d) 5000 Hz
(b) Deflection plate system
(c) Fluorescent screen Q.23 What is the phase shift (in degrees) between
(d) Motor the signals, which is indicated by the
Lissajous pattern given below?
Q.18 In an oscilloscope, two Lissajous figure (X)
and (Y) are observed. This indicates that
ratio of vertical input signal frequency to
Measurement MASTERPLUS EDUCATION®|5.3
on an oscilloscope is found to occupy 6cm
at a scale setting of 30µs/cm. What is the
signal frequency?
0
(a) 1.8 kHz (b) 5.55 kHz
0
(c) 18 kHz (d) 55.5 kHz
Q.30 In a CRO, a sinusoidal waveform of a
(a) 0 (b) 60 certain frequency is displayed. The value of
(c) 90 (d) 180 the quantity that can be made out by
observation is
Q.24 DVM meters are the of instrument? (a) RMS value of the sine wave
examples for which type (b) average value of the sine wave
(a) Integrating type (c) form factor of the sine wave
(b) Digital type (d) peak-peak value of the sine wave
(c) Indicating type
(d) Recording type Q.31 In a Cathode Ray Tube, the focusing anode
is located
Q.25 A 4-digit DVM (digital voltmeter) with a (a) after accelerating anode
100 mv lowest full-scale range would have a (b) between pre-accelerating and accele-
sensitivity of how much value while rating anodes
resolution of this of this DVM is 0.0001 ? (c) before pre-accelerating anode
(a) 0.1 mV (b) 10 mV (d) just after electron-gun
(c) 0.1 mV (d) 0.01 mV
Q.32 An integrator type DVM (digital voltmeter)
Q.26 The precision of a ramp type digital contains a 100 k 2 and 1 µF capacitor. If the
voltmeter depends on voltage applied to the integrator input is I
(a) frequency of the generator and slope of volt. What voltage will be present at the
the ramp output of the integrator after 1 second.
(b) frequency of the generator (a) 1.1 V (b) 1 V
(c) slope of the ramp (c) 10 V (d) 100 V
(d) switching time of the gate
Q.33 In a CRO astigmatism is
Q.27 In a digital voltmeter, the oscillator (a) a source of generating fast electrons
frequency is 400 kHz. A ramp voltage to be (b) a medium for absorbing secondary
measured by this voltmeter falls from 8 V to emission electrons
0V in 20 ms. The number of pulses counted (c) an additional focus control
by the counter is (d) a time-delay control in the vertical
(a) 8000 (b) 4000 deflection system
(c) 3200 (d) 1600
Q.34 The technique of adding a precise amount of
time between the trigger point and the
Q.28 Horizontal input to a scope is Em sin(t) V,
beginning of the scope sweep in a CRO is
vertical input to that scope is Em
known as ______.
sin(t+300)V. What is the Lissajous pattern
(a) Non-saw tooth sweep
in that CRO?
(b) Triggered sweep
(c) Free running sweep
(d) Delayed sweep
(a) (b)
Q.35 An oscilloscope shows peak-to-peak
amplitude of 8 cm for a measured sinusoidal
(c) (d) voltage waveform with vertical sensitivity
nob set to 8 V/cm. The average value of the
Q.29 One cycle of a square wave signal observed voltage is:
5.4 | JE-AE Electrical MASTERPLUS EDUCATION®
(a) 10.19 V (b) 20.37 V 2. It is used for precise measurement of
(c) 40.74 V (d) 2.55 V frequency of a voltage signal.
3. The ratio between frequencies of vertical
Q.36 The grid on the display screen of an and longitudinal voltage signals should be
oscilloscope that comprises the horizontal an integer to have a steady Lissajous
and vertical axes and used to visually pattern.
measure waveform parameters is called Which of the above statements is/are
_______. correct?
(a) Focus control (b) Graticule (a) 1 only (b) 2 only
(c) Intensity control (d) Aquadag (c) 3 only (d) 1, 2 and 3
Q.37 The oscilloscope has an input capacitance of Q.42 A CRT has an anode voltage of 2000 V and
50pF and a resistance of 2M and the parallel deflecting plates 2 cm long and 5
voltage divider ratio (k) of 10. What are the mm apart. The screen is 30 cm from the
parameters of a high-impedance probe? centre of the plates. If the input voltage is
(a) C₁= 5.55 pF and R₁ =9 ΜΩ applied to the deflecting plates gain of 100,
(b) C₁= 5.55 pF and R₁ =18 ΜΩ the input voltage required to deflect the
(c) C₁=3.33 pF and R₁ =9 ΜΩ beam through 3 cm will be
(d) C₁=1.11 pF and R₁ =18 ΜΩ (a) 1V (b) 3 V
(c) 5 V (d) 7V
Q.38 In a CRO, when set for internal trigger
(INT) ______: Q.43 A 2 cm long CRT has an anode voltage of 2
(a) trigger circuit input will vertical kV and parallel deflecting plates that are 5
amplifier mm to apart. The screen is 30 cm from the
(b) trigger circuit will input horizontal centre of the plates. if the input voltage
amplifier applied to the is a deflecting plates through
(c) trigger circuit receives input from the amplifiers has an overall gain of 100,
horizontal amplifier determine the input voltage required red to
(d) trigger circuit receives input from the deflect the beam through 3 cm.
vertical amplifier (a) 0.1 V (b) 1 V
(c) 10 V (d) 100 V
Q.39 In a two-channel oscilloscope operating in
x-y mode, two in phase 50 Hz sinusoidal Q.44 From the given Lissajous patterns obtained
waveforms of equal amplitude are fed to the while measuring frequency using a cathode-
two channel. What will be the resultant ray oscilloscope (CRO), select the pattern
pattern on the screen? which indicates the relationship f v 1 f h
(a) An ellipse 2
(b) A parabola
(c) Straight line inclined at 45° with respect
to x-axis (1) (2) (3) (4)
(d) A circle (a) 2 (b) 4
(c) 1 (d) 3
Q.40 Vertical delay line in CRO
(a) Gives proper time for thermionic Q.45 The measurement of very low and very high
emission of electrons frequencies is invariably done using a
(b) Delays the signal voltage by 200 ns frequency counter in which one of the
(c) Allows the horizontal sweep to start following?
prior the vertical deflection (a) Frequency measurement mode only
(d) Delays the generation of sweep voltage (b) Period measurement mode only
(c) Frequency and period measurement
Q.41 Consider the following statements with modes, respectively
regard to Lissajous pattern on a CRO: (d) period and frequency measurement
1. It is a stationary pattern on the CRO. modes, respectively.
Measurement MASTERPLUS EDUCATION®|5.5
1 setting of 5m sec/div, the number of cycles
Q.46 If a voltmeter uses 4 digit display, then of signal displayed on the screen will be
2 (a) 0.5 cycle (b) 2.5 cycles
its resolution is-
(c) 5 cycles (d) 10 cycles
(a) 0.0001 (b) 0.01
(c) 0.001 (d) 0.1
1
Q.53 The 3 digital voltmeter displays a
Q.47 A digital voltmeter has a read-out range 2
from 0 to 9999. When full scale reading is maximum value of _______ and has a
9.999 V, the resolution of the full scale resolution of _________ of the range
reading is respectively.
(a) 0.001 (b) 1000 (a) 999 and 1/2000th
(c) 3 digit (d) 1 mV (b) 1999 and 1/2000th
(c) 999 and 1/1000th
Q.48 When two frequencies F₁ & F₂ are applied (d) 1999 and 1/1000th
to the horizontal & vertical amplifiers
respectively of a CRO, a "circle" is appeared Q.54 In a CRT, the electrostatic deflection
on the CRT/CRO screen. With reference to sensitivity and magnetic deflection
the lissajous figures, the ratio of frequencies sensitivity are proportional ____ and _____
F₁ & F₂ is? with accelerating voltage (V) respectively
(a) 2:1 (b) 1:2 (a) 1/ Va and Va (b) Va and Va
(c) 1:1 (d) 3:1
(c) 1/ Va and 1/ Va (d) Va and 1/ Va
Q.49 In an oscilloscope, the sensitivity can be
increased by............ Q.55 Consider a measuring system consisting of a
(a) Decreasing the value of accelerating sensor, an amplifier and an oscilloscope.
voltage Ea The sensitivity of each equipment is as
(b) Increasing the value of accelerating follows: Sensor sensitivity: 0.4 mV/°C,
voltage Ea Amplifier gain: 5.0 V/mV, and Oscilloscope
(c) Increasing the separation between the sensitivity: 10mV/V. What is the sensitivity
deflecting plates of complete measurement system?
(d) None of these (a) 5.0 V/mV (b) 10 m V/V
(c) 15.4 mV/°C (d) 20 mV/°C
Q.50 Which one of the following statements
correctly represents the post acceleration in Q.56 The screen/display of oscilloscope is made
a Cathode- Ray Tube? of which of the following materials?
(a) It provides deflection of the beam. (a) Phosphor (b) Germanium
(b) It increases the brightness of the trace if (c) Carbon (d) Arsenic
the signal frequency is higher than 10 MHz.
(c) It accelerates the beam before deflection. Q.57 Study the Lissajous pattern shown below.
(d) It increases the brightness of the trace of 1
low frequency signal.
1
Q.51 In a CRO which of the following is not a
part of electron gun? 2
(a) X-Y Plates
(b) Grid 3
(c) Cathode
(d) Accelerating anode This pattern is obtained when which of the
below options holds true, where:
Q.52 A CRO screen has ten divisions on the fv = vertical signal frequency
horizontal scale. If a voltage signal 5 sin fh = horizontal signal frequency.
(314t+45°) is examined with a line base (a) fv = (3) fh (b) fv = (1/5) fh
(c) fv = (5) fh (d) fv = (1/3) fh
5.6 | JE-AE Electrical MASTERPLUS EDUCATION®
Q.58 In a cathode ray tube, the length of
deflecting plate of the direction of beam is
2cm, the spacing of the plate is 0.5 cm and
the distance of the fluorescent screen from
the centre of the plate is 18 cm. Calculate
deflection sensitivity if anode voltage is 400
V.
(a) 0.09 cm/volt (b) 0.9 cm/volt
(c) 0.18 cm/volt (d) 0.018 cm/volt
Measurement MASTERPLUS EDUCATION®|5.7
Answer Key: Electronic Instrument
1 D 2 A 3 B 4 C 5 A
6 A 7 C 8 A 9 A 10 A
11 B 12 C 13 A 14 B 15 B
16 C 17 D 18 D 19 C 20 C
21 D 22 B 23 D 24 D 25 D
26 A 27 A 28 A 29 B 30 D
31 B 32 C 33 C 34 D 35 B
36 B 37 B 38 D 39 C 40 C
41 D 42 A 43 B 44 A 45 D
46 A 47 D 48 C 49 A 50 B
51 A 52 B 53 D 54 C 55 D
56 A 57 D 58 A
Solution
1. (d) Given clock frequency is 10 × 106 Hz
Lissajous patterns of CRO depends on frequency, 1 1
tCL 0.1μsec
amplitude and phase relationship of sine waves clock frequency 10 106
given to fields. Number of clock pulses
2. (a)
time taken to generate 10V
Given,
Bandwidth 10 MHz clock frequency
Fastest rise time T(rise) 100μ 100
1000
0.35 0.35 0.1μ 0.1
Oscilloscope bandwidth 10MHz 5. (a)
7 Lissajous pattern with equal frequency voltage and
0.35 10 zero phase shift.
35 109 Thus when two equal voltage of equal frequency but
= 35 ns with 90° phase displacement are applied to a CRO.
3. (b) The trace on the screen is a circle.
Saw-tooth waveform: It is a kind of triangular 6. (a)
waveform which is generated by time-base circuitry Multimeter can be used for measuring both A.C.
of the CRO. and D.C.
(Amplitude)
A multimeter or a multitester also known as a
volt/ohm meter. It is measuring instrument that
combine several measurement function in one
(time)
unit.
4. (c) 7. (c)
To generate IV, the voltage controlled generator CRO gives more accurate result because there is no
takes 10µSec. loading effect rather than other instrument like as
So for 10V, it takes 100µSec.
5.8 | JE-AE Electrical MASTERPLUS EDUCATION®
PMMC, Hot wire & electrodynamometer type
instrument. 1
8. (a) 2
Y
Vertical
axis 3
1 2
X
Horizontal axis
fy No. of horizontal tengencies of associated lissajous pattern
From lissajous pattern – fx No. of vertical tengencies of associated lissajous pattern
f y Maximum cut point in horizontal axis (x) fy 2
fx Maximum cut point in vertical axis (y) 600 3
Then, x = 3 f y 400Hz
Y=2 15. (b)
fy 3 Deflection sensitivity = 10m/V
Deflection factor = ?
fx 2
1
9. (a) Deflection factor Deflection sensitivity
Spectrum analyzer is a combined setup of narrow
band super heterodyne receiver and CRO. CRO 1
Deflection factor 0.1
show the signal spectrum on the CRO screen. 10
10. (a) 16. (c)
The CRT display is made up of small picture Bandwidth (BW) = 10 Hz
elements called pixels. The smaller the pixels the Rise time of C.R.O. (tr) = ?
better the images clarity or resolution of the display. 0.35
11. (b) Formula: B.W
Zinc sulfide with silver metal as impurity gives a tr
bluish glow and with copper metal as an impurity a 0.35 0.35
greenish glow. The selection of phosphor to be used tr
B.W 10
in a cathode ray tube is very important.
tr 0.035 35ms
12. (c)
Yttrium oxide gives a reddish glow when used as the 17. (d)
viewing surface of a C.R.O (Cathode Ray Motor is not a part or component of CRO. CRO is a
Oscilloscope). A CRO is an instrument generally fast type X-Y plotter. It plots a given signal with
used in a laboratory to display and measure analyzes respect to other signal or time. Generally CRO is
various waveform of an electrical circuit. Yttrium used for 20Hz to 1MHz frequency but range of
oxide (Y2O3) nanoparticle is air stable, solid modern CRO is greater than 500 MHz.
substance white in color. 18. (d)
13. (a)
[0 to 9]
MSB
0/1
1
For 3 digital voltmeter, it has three full digit and
2 (X) (Y)
one half digit. Half digit (MSB) can have either 0 or fy No. of horizontal tengencies of associated lissajous pattern
1, while other three full digits can have digits from 0 fx No. of vertical tengencies of associated lissajous pattern
to 9. Hence voltmeter can vary from 0 to 1999 fy 3 fy 3
i.e. largest number is 1999 For (X); and for (Y );
14. (b) fx 2 fx 2
19. (c)
Sensitivity is defined as amount of deflction per unit
current-
Measurement MASTERPLUS EDUCATION®|5.9
D DVM is a digital type voltmeter which measures an
S analog input voltage by converting the voltage to a
I digital value and then displays the voltage
1 1000 25. (d)
SX 25Ω/V
40mA 40 Given, resolution = 0.0001
1 1000 Range = 100 mV
SY 20Ω/V Sensitivity = Resolution (minimum full scale
50mA 50
value)
Hence,
from the above solution it is clear that sensitivity of = Resolution Range
X is more then sensitivity of Y. = 0.0001 × 100 × 10-3 V
20. (c) = 0.0001 × 1 × 10-1 = 0.01 mV
Number of cycle display by the signal 26. (a)
In a ramp type DVM
f signal Tsweep
Vm = slope Pulse width final count
200 0.5 103 10 ( Tsweep 10 0.5 103 ) Slope
Vm final count ______(i)
= 1 cycle frequency
Peak to peak applied voltage on y-axis From equation (i) its clear that accuracy is decided
2 2Vrms 2 2 300 848.52mV by frequency & slope in ramp type DVM.
27. (a)
848.52
Required display =8.485cm Pulse width
100 Number of pulses
Oscillator time period
But screen is only 8 cm vertical so peak point will
be clipped 20 103
8000
21. (d) 1 3
10
A multimeter to measure an AC voltage or current 400
the reading on the meter is an rms" on root mean 28. (a)
square" reading the rms value also known as Horizontal input to a scope is Em sin (t) V, vertical
"effective value". input to that scope is Em sin (t + 300)V
22. (b) When 900 < < 1800 < < 2700 then lissajous
( f ) HL pattern in that CRO is
fy x
VL 90
f y Input Vertical Frequency 180 0
f x Horizontal frequency
270
VL Vertical tangencies 29. (b)
H L Horizontal tangencies Given,
Vertical Input frequency Scale setting = 30 µs/cm
1000 5 Distance 6 cm
fy Time period (T) = Scale setting distance
2 = 30 × 6
f y 2500Hz = 180 µs
23. (d) = 180×10-6 s
Phase shift between signal = 45 + 90 + 45 = 1800 1 1
frequency f = = 5.55kHz
T 180 106
30. (d)
45 0 CRO is a voltage dependent instruments and can be
90 used for the measurement of the voltages at any
45
frequency with in the range of the CRO. The CRO
measures peak to peak value of sine wave because
from the peak value of AC signal the RMS and other
24. (b) parameters can be determined such as distortion.
5.10 | JE-AE Electrical MASTERPLUS EDUCATION®
31. (b) 37. (b)
The cathode ray tube (CRT) focusing anode is Given,
located between preaccelerating anode and Cin = 50 pF
accelerating anode. The preaccelerating and Rin = 2M
accelerating anodes are applied with a common K = 10
voltage while focusing anode is connected to a High impedance probe resistance
lower voltage. R1 = Rin (k – 1)
32. (c) = 2(10 – 1) = 18M
Given, High impedance probe resistance
Resistance R = 100k = 100 103 Cin
Capacitance C = 1F = 1 10-6 F C1
Voltage V0 = 1V
k 1
Time t = 1second 50
C1 5.55pF
1
1 10 1
RC 0
V V0 dt 38. (d)
The trigger circuit may receive an input from one of
V0t 1 1 three sources depending on setting of the trigger
V selector switch.
RC 100 103 1106
V = 10V The input signal may come from an external
33. (c) source when the trigger selector switch is set to
This additional control arrangement is present in EXT.
modern oscilloscope. Astigmatism is an additional From a low amplitude ac voltage at line
focusing control and this is analogous to frequency when the switch is set to LINE.
astigmatism in optical lenses, its provide sharp focus When set for internal triggering (INT), the
on the entire screen. This control is affected by trigger circuit receives it input from the vertical
varying the potential plate and accelerating anode. amplifier.
34. (d) 39. (c)
The technique of adding a precise amount of time For same frequency with 0 phase difference, CRO
between the trigger point and the beginning of the screen shows straight line inclined at 45° with
scope sweep in a CRO iş known as delayed sweep. respect to x-axis.
When the scope is being used in the sweep mode, 40. (c)
the start of the horizontal sweep can be delayed, Vertical delay line in CRO allows the horizontal
typically from a few ps to 10 seconds or more. sweep to start prior to vertical deflection. A delay
35. (b) line placed in vertical signal path after the trigger
Given: Vp = 8cm, S = 8V/cm signal will result in the ability to display trigger
88 portion of the signal.
Amplitude of voltage (V) 32V 41. (d)
2 Lissajous pattern is a stationary pattern.
2Vm Ex.
Vavg Y Y Y
2 32
Average value of voltage (Vavg ) X X X
Vavg 20.37V
36. (b) All the patterns are independent of time.
Vertical axis Lissajoous pattern can be used for measuring of
frequency of an unknown signal
Horizontal axis
If fx = frequency of known signal
The grid on the display screen of an oscilloscope fy = frequency of unknown signal
that comprises the horizontal and vertical axes and then,
used to visually measure waveform parameters is f y no. of horizontal tangencies
called garticule fx no. of vertical tangencies
Measurement MASTERPLUS EDUCATION®|5.11
Ex. step size 0.01
1 1 2 resolution =
full scale reading 9.999
1 1 Resolution = 1mV
48. (c)
2
When two frequencies F₁ & F₂ are applied to the
horizontal & vertical of a CRO then the ratio of F1
fy 1 fy 2
, and F₂ is 1:1.
fx 2 fx 1 Y
42. (a)
Given, Va = 2000V X’ X
ld = 2cm
d = 5mm = 0.5 cm Y’
L = 20 cm F1 : F2 = 1 : 1 at x-axis intersection 1 times
D = 3 cm And y-axis intersection 1 times
Y
Vd = ?
43. (b)
Voltage applied to the deflecting plates is X’ X
2dEa D
Ed
L d Y’
F1 : F2 = 2 : 2 at x-axis intersection 2 times
2 5 103 2000 3 102 And y-axis intersection 2 times
100V
0.3 2 102 49. (a)
Input voltage required for a deflection of 3 cm Deflection sensitivity- The deflection sensitivity of
Ed 100 a cathode ray tube is defined as the deflection of the
Vi 1V screen per unit deflection voltage.
gain 100
D L d
44. (a) Deflection sensitivity, S m/V
f v Number of horizontal tangencies Ed 2dEa
Where,
fh Number of vertical tangencies
D = deflection of an electron beam on the screen in
fv 1 the Y direction in m
fh 2 Ed = potential between deflecting plates in V
1 L = distance between the screen and the center of
the deflecting plates in m
2 d length of the deflecting plates in M
d = distance between deflecting plates in m
45. (d) Ea = accelerating voltage in V
The measurement of very low and very high 1
frequencies is invariably done using a frequency S S Ea
Ea
counter period and frequency measurement modes,
respectively. 50. (b)
46. (a) For post acceleration in CRT if signal frequency is
higher than 10 MHz then it increases brightness of
1
Resolution = the trace.
10n 51. (a)
Where n = Number of full digit X-Y plates are not the part of electron gun in a
1 CRO. The electron gun emits electrons and forms
0.0001 them into a beam by the help of a heater, cathode,
104
47. (d) grid, pre- accelerating, accelerating and focusing
anode.
Output = (step size) decimal value.
52. (b)
9.999 (step size) 999
Given number of division = 10
step size = 0.01
5.12 | JE-AE Electrical MASTERPLUS EDUCATION®
Base setting = 5m sec/dive. Overall sensitivity = S1 S2 S3
n=? = 0.4 5 10 = 20 mV/0C
Tsweep = Base setting number of division 56. (a)
= 5 10-3 10 Screen/Display of oscilloscope is made of
Tsweep = 0.05 sec phosphorous which converts heat energy into light
2 energy. Some elements called activators are added
314 to the coating of phosphor in order to increase
Tsignal
luminous efficiency.
2 57. (d)
100
Tsignal Given Lissajous pattern
1
1
Tsignal sec 2
50 3
Tsweep 0.05 1 4 2
n
Tsignal 1 5
50 6
n = 0.050 50 No. of intersection of the horizontal line with the
n = 2.5 cycle curve = 2
53. (d) No. of intersection of the vertical line with the curve
1 =6
As given digital voltmeter has 3 digits
2 Formula:
So it has 3 full digits and 1 half digit f v No. of intersection of the horizontal line with the curve
fh No. of intersection of the vertical line with the curve
1
So, resolution R Range of voltmeter fv 2
10 N
Where N = Number of full digits = 3 fh 6
1 1 1
R Range of voltmeter = fv fh
10 3
1000th 3
Maximum value = 1 half digit 3 full digit 58. (a)
1 999 = 1999 Deflection sensitivity of a CRT is defined as the
full digit counts deflection of the screen per unit deflection voltage
From 0 to 9 and half digit counts L d
From 0 to 1 Deflection sensitivity (s) = (m/V) or cm/V
2dEn
54. (c)
Where,
We know that-
L = Distance between screen and the deflecting
LVd d
Electrostatic deflection D Where, plates (in m) = 18cm
2dVa
d Length of deflecting plates (in m) = 2cm
1 d = Distance between deflecting plates (in m) =
D
Va 0.5cm
Magnetic deflection sensitivity Ea = Voltage of pre-accelerating anode = 400 V
e 18 2
SL S cm/V
2mVa 2 0.5 400
S = 0.09 cm/V
1
S
Va
55. (d)
Given,
S₁ = 0.4mV/°c, S₂ = 5V/mV
S3 = 10 mV/V
Measurement MASTERPLUS EDUCATION®|6.1
CHAPTER
TRANSDUCERS 6
Q.1 A thermistor exhibits: (a) P-3; Q-2; R-4; S-1 (b) P-4; Q-3; R-2; S-1
(a) Only a negative change of resistance (c) P-2; Q-1: R-4; S-3 (d) P-1; Q-2; R-3; S-4
with increase in temperature
(b) Only a positive change of resistance with Q.6 An imperfect capacitor is represented by a
increase in temperature capacitance C in parallel with a resistance
(c) Can exhibits either a negative or positive R. The value of its dissipation factor tan is
change of resistance with increase (a) CR (b) 2CR
temperature depending upon the type of (c) 1/2CR (d) 1/CR
material
(d) None of these Q.7 Moire fringes are used to measüre rotary
displacement along with _______.
Q.2 Which of the following device is used to (a) contact type encoders only
measure flow of air around an aeroplane? (b) optical encoders only
(a) Venturimeter (b) Rotameter (c) contact type encoders and optical
(c) Orifice (d) Anemometer encoders.
(d) none of these
Q.3 Gauge factor of strain gauge is defined as
the ratio of per unit change in the............. Q.8 A LVDT produces as RMS output voltage
(a) conductive to the per unit change in of 2.6 V for displacement of 0.4 µm.
applied force action acting on the element Calculate the sensitivity of LVDT.
(b) resistance to the per unit change in the (a) 6.5 V/µm (b) 4.5V/µm
length of the element. (c) 8.5 V/µm (d) 12.5 V/µm
(c) stress to the per unit change in strain of
the element Q.9 Delay fuses are used for the protection of-
(d) current to the per unit change in the (a) Both motors and transformers
length of the element (b) Motors
(c) Transformers
Q.4 Dummy strain gauge is used in conjunction (d) Semiconductor devices
with the gain strain gauge to..............
(a) calibrate the system Q.10 Consider the signal, Vmsin100t +
(b) compensate temperature effects 2Vmsin200t to be sampled and stored in a
(c) improve sensitivity data acquisition system. The same is to be
(d) reduce strain on the gauge extracted off-line later on. In order to extract
the signal effectively, the original sampling
Q.5 Match List-1 (transducer) with List-2 frequency has to be
(characteristics) and select the correct (a) 100 rad/s (b) 200 rad/s
answer using codes given below the lists: (c) 210 rad/s (d) 1002 2002 rad/s
List-I List-II
P. Thermocouple 1 Modulated output
Q.11 Thermocouple is a device which converts-
Q. Thermistor 2 Resistance change with
(a) Kinetic energy to heat energy
pressure
(b) Mechanical energy to heat energy
R. Strain gauge 3 Negative temperature
(c) Heat energy to electric energy
coefficients
(d) Electric energy to heat energy
S. LVDT 4 Constant temperature one end
6.2 | JE-AE Electrical MASTERPLUS EDUCATION®
Q.12 Which curve in the given figure represents (b) coefficient of discharge which is
resistance temperature characteristics of a typically about 0.95 and loss of head of
thermistor? about 10%.
A (c) coefficient of discharge which is
typically about 0.6 and loss of head of about
Resistivity
10%.
Ωm
B
(d) None of these
C
D
Q.18 Which one of the following transmission
Temp. C systems for telemetry has largest
(a) Curve A (b) Curve B bandwidth?
(c) Curve C (d) Curve D (a) FM/FM radio transmission system
(b) Co-axial copper cables transmission
Q.13 A.1 cm piezoelectric transducer having a g- system
coefficient of 58 V/kg/m² is subjected to a (c) Fibre-optic data transmission system
constant pressure of 10-3 kg/m² for about (d) Synchro-position repeater system
minutes. The Piezo voltage developed by
the transducer will be 15 Q.19 The size of the venturimeter is expressed as
(a) 116 mV (b) 58 mV 200 x 100 mm². It means that the
(c) 29 mV (d) 0 mV (a) diameter of upstream pipe is 200 mm
and that of down-stream pipe is 100 mm.
Q.14 The output of LVDT is in the form of (b) diameter of the pipe is 200 mm and that
(a) Rotary movement of core of throat is 100 mm.
(b) Linear displacement of core (c) diameter of the pipe is 100 mm and that
(c) Pulses of throat is 200 mm.
(d) High frequency signals (d) None of these
Q.15 Which of the following devices is primarily Q.20 Thermocouples are ______.
used as resistive temperature sensors and (a) Active transducer only
current-limiting devices? (b) passive transducers only
(a) NTC thermistor (c) both active and passive transducers
(b) Rheostat (d) output transducers
(c) Light dependent resistor
(d) Preset resistor Q.21 A strain gauge with a resistance of 250
ohms undergoes a change of 0.150 ohm
Q.16 What is done to reduce the effect of fringing during a test. The strain is 1.5×10-4. Then
in a capacitive type transducer? the gauge factor is
(a) The transducer is shielded and the shield (a) 2.0 (b) 3.0
is kept at ground potential. (c) 4.0 (d) 100
(b) A guard rings is provided and is kept at
ground potential. Q.22 Which one of the following gives Gauge
(c) The transducer is shielded and the shield factor of a strain gauge?
is kept at the same potential as the moving L R R L
(a) / (b) /
plate.. L R R L
(d) A guard ring is provided and it is kept at R D R
the same potential as the moving plate. (c) / (d) /
R D R
Q.17 Orifice plates have ______.
(a) coefficient of discharge which is Q.23 Match List-1 (quantity) with List-2
typically about 0.6 and loss of head of about (transducer) and select the correct answer
60-70%. using the codes given below the list:
List-I List-II
P Force measurement 1Flat spiral spring
Measurement MASTERPLUS EDUCATION®|6.3
Q Torque measurement 2 Seismic mass (c) Exact cancellation of secondary voltages
R Acceleration measurement 3 Cantilever beam (d) Insulation used in the winding
(a) P-1; Q-2; R-3 (b) P-1; Q-3; R-2
(c) P-3; Q-1; R-2 (d) P-3; Q-2; R-1 Q.30 Resolution of a potentiometric transducer
depends on...........
Q.24 Which is the most suitable thermocouple (a) Diameter of wire (b) Length of wire
transducer for the measurement of (c) Material of wire (d) Excitation voltage
temperature in the range of 1300°C to
1500°C? Q.31 Self-generating type transducers are.......
(a) Chromel-alumel transducers.
(b) Platinum-rhodium (a) Active (b) Passive
(c) Iron-constantan (c) Secondary (d) Inverse
(d) Chromel-constantan
Q.32 Thermistors are essentially semiconduc-tors
Q.25 Consider the following statement: (a) Well suited to precision measurement of
A Linear Variable Differential Transformer temperature
(LVDT) has (b) Widely used in the lower temperature
i. One primary winding range of-100°C to 300°C
ii. Two exactly similar secondary windings (c) Which behave as resistors with a high
iii. A toroidal magnetic core negative temperature of resistance
Of these statements which is/are correct? (d) All of the above
(a) ii & iii (b) i & ii
(c) i & iii (d) i, ii & iii Q.33 Which of the following is not an advantage
of semiconductor as compared to
Q.26 Match List-1 (transducer) with List-2 conventional strain gauges?
(input/output variables) and select the (a) Excellent hysteresis characteristics
correct answer using the codes given below (b) Least sensitive to temperature changes
the list: (c) High fatigue life
List-1 List-1=2 (d) Smaller size
P. Electrodynamic 1. Gas pressure to
generator resistance change Q.34 T-type thermocouple is made of:
Q. Venturi meter 2 Force to displacement (a) Iron-Constantan
R. Pirani gauge 3 Motion to voltage (b) Copper-Constantan
S. Spring balance 4 Flow rate to pressure (c) Platinum-Rhodium
(a) P-2; Q-1; R-4; S-3 (b) P-2; Q-4; R-1; S-3 (d) Chromel-alumel
(c) P-3; Q-4; R-1; S-2 (d) P-3; Q-4; R-2; S-1
Q.35 Rochelle salt is used as a/an aids. in hearing
Q.27 Unbounded strain gauges are.............. (a) multivibrator (b) oscillator
(a) Exclusively used for transducer (c) strain gauge (d) transducer
applications
(b) Exclusively used for stress analysis Q.36 Which of the following is an essential
(c) Used for unbounded strains only condition for the transfer of heat from body
(d) None of these to another by means of conduction?
(a) Both the bodies must be at the same
Q.28 The instrumentation amplifiers are used temperature
principally to amplify signals from which of (b) Both the bodies must be metallic
the following? (c) One of the bodies must be a metal
(a) Transducers (b) Active filters (d) Both the bodies must be at different
(c) Choppers (d) D/A converters temperatures
Q.29 Sensitivity of LVDT is mainly due to Q.37 A thermometer is calibrated from 150° C to
(a) Magnetic shielding of the core 300° C. The accuracy is specified as ±0.2%
(b) Permeability of the core of span. What is the maximum static error?
6.4 | JE-AE Electrical MASTERPLUS EDUCATION®
(a) ±0.6 °C (b) ±0.3 °C to sensitivity of transducer to any plane
(c) ± 0.06 °C (d) ±0.03 °C other than the required plane is
(a) Cross sensitivity
Q.38 Which of the following can be (b) Sensitivity
used/modified for measurement of angular (c) Interference
speed? (d) Distributed sensitivity
(1) LVDT
(2) Magnetic pick-up Q.46 Light is capable of transferring electrons to
(3) Tacho-generator the free-state inside a material thus
(4) Strain gauge increasing the electrical conductivity of the
Select the correct answer using the code material. When the energy imparted to the
given. below: electrons is quite large, the latter may be
(a) Only 1 and 2 (b) Only 2 and 3 emitted from the material into the
(c) Only 3 (d) Only 2, 3 and 4 surrounding medium. This phenomenon is
known as
Q.39 Thermopile is a: (a) Photoemissive effect
(a) parallel connection of thermocou-ples. (b) Photovoltaic effect
(b) series connection of thermocouples (c) Photoconductivity effect
(c) series connection of RTDS (d) Photo absorptive effect
(d) series connection of thermistors
Q.47 For contactless body temperature measure-
Q.40 The change in resistance of an electrical ment, advanced thermometers are used.
strain gauge with a gauge factor of 2.0 and They are based on:
resistance of 50 when subjected to a strain (a) alpha particles
of 0.001 is. (b) infrared radiation
(a) 0.0001 Ω (b) 0.001 (c) ultra-violet radiation
(c) 0.1 Ω (d) 0.01 Ω (d) laser beams
Q.41 A fixed resistor of suitable value is usually Q.48 Which of the following is not a pressure
connected across a thermistor to ______. measurement transducer?
(a) compensate its self-heating effect (a) Thermocouple
(b) improve its linearity (b) Strain gauge
(c) decrease its resistance (c) LVDT
(d) Increase its sensitivity (d) Piezoelectric transducers
Q.42 Piezo-electric crystal is generally employed Q.49 The primary standard for calibrating
for the measurement of which one of the vacuum is:
following? (a) McLeod gauge
(a) Flow (b) Velocity (b) Dead weight tester
(c) Acceleration (d) Temperature (c) Thermocouple gauge
(d) Knudsen gauge
Q.43 Hall effect transducers can be used for
measurement of........... Q.50 Which displacement transducer is used for
(a) Power (b) Current accurate and linear measurement?
(c) Displacement (d) All of these (a) LVDT
(b) Strain gauge
Q.44 Piezoelectric crystal converts: (c) Potentiometer
(a) Acceleration to voltage (d) Capacitive displacement transducer
(b) Light to voltage
(c) Displacement to voltage Q.51 The measurement of the speed of a rotating
(d) Force to voltage shaft by means of an electric tachometer is
a:
Q.45 The variations in the measured quantity due (a) Direct Measurement
Measurement MASTERPLUS EDUCATION®|6.5
(b) Secondary Measurement (c) -444 pF/cm (d) +44.4 pF/cm
(c) Tertiary Measurements
(d) All of these Q.59 Consider the following regarding types of
strain gauges
Q.52 The gauge factor of a strain gauge is 1, A. Semiconductor strain gauges
stress is 1050 kg/cm2, Young's modulus of B. Conductor strain gauges
elasticity is 2.1 106 kg/cm2 and resistance C. Capacitive strain gauges
is 1000 Ω. The change in resistance of the The types of strain gauges are
strain gauge is (a) Only B (b) Only A and B
(a) 0.5 Ω (b) 1.0 (c) Only A and C (d) Only C.
(c) 1.5 (d) 2.0
Q.60 Thermocouple works on
Q.53 What is a load cell? (a) Thomson Effect (b) Seebeck Effect
(a) A strain gauge (c) Peltier Effect (d) Joule Effect
(b) A photo voltaic cell
(c) A thermistor Q.61 For a certain thermistor, the material
(d) A pressure pick up device constant () is 3000 kelvin and its resistance
at 270C is 1050 ohm. What is the
Q.54 The hall voltage, VH, for a thin copper plate temperature coefficient of resistances for
of 0.1 mm carrying a current of 100 A with this thermistor?
the flux density in the Z-direction, Bz = 1 (a) 0.033×10-3 ohm/ohm/°C
Wb/m² and the Hall coefficient, RH = (b) -0.033ohm/ohm/°C
7.4×10-11 m³/C, Is (c) -3.33 ohm/ohm/°C
(a) 148µV (b) 111µV (d) -3.0 ohm/ohm/°C
(c) 74µV (d) 37 µV
Q.62 Linear variable for differential transformer
Q.55 The thermocouple pair that gives the (LVDT) is used for measuring
maximum sensitivity around 273 °k is displacement. The principle of working of
(a) Platinum-Constantan LVDT is--
(b) Nichrome-Constantan (a) Magnetic reluctance (b) Permanence
(c) Nickel-Constantan (c) Mutual induction (d) Self induction
(d) Copper-Nickel
Q.63 The resistance of 125 strain gauge changes
Q.56 A strain gauge is a passive transducer and is by 1 for 4000 micro-strain. The gauge
employed for converting factor for strain gauge is
(a) Pressure into change in resistance (a) 1.5 (b) 2.0
(b) force into displacement (c) 2.5 (d) 3.0
(c) mechanical displacement into a change
of resistance Q.64 A microphone is classified as a
(d) None of the above (a) Optical transducer
(b) Thermal transducer
Q.57 The dynamic characteristics of capacitive (c) Magnetic transducer
transducer are similar to those of (d) Acoustical transducer
(a) Low-pass filter
(b) High-pass filter Q.65 Consider the following transducers:
(c) Notch filter (1) LVDT
(d) Band-stop filter (2) Piezoelectric
(3) Thermocouple
Q.58 A capacitive transducer consists of two (4) Photovoltaic cell
parallel plates of diameter 2 cm each and Which of the above are active transducers?
separated by an air gap of 0.25 mm. What is (a) 1, 2 and 3 (b) 1, 2 and 4
the displacement sensitivity: (c) 2 and 4 only (d) 2, 3 and 4
(a) +200 pF/cm (b) -300 pF/cm
6.6 | JE-AE Electrical MASTERPLUS EDUCATION®
Q.66 The Gauge factor of a resistance wire strain (c) 1, 3 and 4 (d) 2, 3 and 4
gauge, is a measure of
(a) Sensitivity of the gauge Q.73 Which of the following devices can measure
(b) Dynamic range of displacement measure pressure directly
(c) Resolution (a) Stain gauge (b) LVDT
(d) Resistivity (c) Rotameter (d) Bumblebee tube
Q.67 Pirani gauge is used for the measurement of Q.74 The expansion for the acronym LVDT, a
pressure in the range of- transducer used measurement, is for
(a) 10-8 mm to 10-5 mm of Hg displacement
(b) 10-3 mm to 10-1 mm of Hg (a) low voltage displacement transducer.
(c) 10 mm to 10-3 mm of Hg (b) light vision displacement transducer.
(d) 10-5 mm to 10-8 mm of Hg (c) linear variable displacement transducer.
(d) Linear variable differential transformer.
Q.68 A resistance strain gauge with a gauge
factor of 2.0 is fastened to a steel member Q.75 An LVDT is used to measure 1mm
subjected to a stress of 100 N/mm². The displacement for which a voltmeter of range
modulus of elasticity of steel is approx.- 0 to 2V through an amplifier having a gain
imately 2×105 N/mm². The percentage of 500 is connected at the output of the
change in resistance is LVDT. If the output of the LVDT is 2mV,
(a) 1.50 (b) 1.00 then the sensitivity of the instrument will be
(c) 0.15 (d) 0.10 (a) 1V/mm (b) 0.5V/mm
(c) 0.1V/mm (d) 0.05V/mm
Q.69 The gauge factor of a material of strain
gauge is such that the resistance changes Q.76 The output of a piezoelectric crystal has- (a)
from 2000 to 2009 when subjected to a Low amplitude and low impedance
strain of 0.0015. The Poisson's ratio of the (b) High amplitude and high impedance
material of gauge- (c) Low amplitude and high impedance
(a) 1.75 (b) 3.0 (d) High amplitude and low impedance
(c) 1.0 (d) 6
Q.77 In a transducer the observed output deviates
Q.70 The strain gauge with a resistance of 250 from the current value by a constant factor.
ohm undergoes a change of 0.15 ohm. The resulting error is called-
During a test the strain is 1.5×10-4. What is (a) Zero error
the gauge factor? (b) Non conformity error
(a) 4.7 (b) 4.0 (c) Sensitivity error
(c) 3.5 (d) 2.0 (d) Hysteresis error
Q.71 Which one of the following material is not a Q.78 A plezoelectric crystal has a thickness of 2.5
Piezoelectric Material? mm and a voltage sensitivity of 0.05 V/N.
(a) BaTiO3 (b) Quartz The piezoelectric crystal is subjected to an
(c) Rochelle Salt (d) Yttrium garnet external pressure of 1.6×10 N/m²,
corresponding output voltage is
Q.72 When compared with other transducers (a) 200 volts then the
measuring temperature, a four-lead platinum (b) 3.2×109 volts/m of thickness
RTD (c) 0.07×109 V/(m³/New)
(1) has better linearity over a wide operating (d) 200 m volts.
range.
(2) has better accuracy and precision. Q.79 Active transducer is:
(3) has better stability at high temperature. (a) Strain gauge transducer
(4) is inexpensive. (b) Photo voltaic transducer
Which of these are correct? (c) POT
(a) 1, 2 and 3 (b) 1, 2 and 4 (d) Company
Measurement MASTERPLUS EDUCATION®|6.7
Q.80 Photo conductive cell is used for- Q.87 Air cored inductive transducer are suitable
(a) High frequency application for use ______.
(b) Medium frequency application (a) At lower frequencies
(c) Low frequency application (b) At higher frequencies
(d) All of these (c) At equal frequencies
(d) As are employed for iron cored
Q.81 The instrumentation amplifiers are used transducer
principally to amplify from which of the
following? Q.88 Which one of the following statements is
(a) Transducers (b) Active filters NOT true?
(c) Choppers (d) D/A converters. (a) Potentiometric linear displacement can
give high output signal
Q.82 Consider the following units for the (b) Linear variable differential transformer
measurement of pressure directly: has low output impedance
(1) Rota meter (c) Synchros and resolvers have low
(2) Bumblebee tube accuracy
(3) Plani meter (d) Eddy current proximity transducers are
(4) Vanes non- contact type transducers
Of these, the pressure can be measured by
(a) 1 and 2 only (b) 3 and 4 only Q.89 The sensitivity factor of strain gauge is
(c) 2 only (d) 1, 2, 3 and 4 normally of the order of
(a) 1 to 1.5 (b) 1.5 to 2
Q.83 The commercial thermopiles are formed by (c) 0.5 to 1 (d) 5 to 10
(a) Series of Si-Al thermocouples in an IC
by doping Al layers on P-type Si on n-type Q.90 The commercial thermopiles are formed by
Si epitaxial layers (a) Series of Si-Al thermocouples in an IC
(b) Series of Cu-W thermocouples strips by doping Al layers on p-type Si on n-type
(c) Piezoelectric material strips piled Si epitaxial layers
together (b) Series of Cu-W thermocouples strips
(d) Series of bismuth-telluride couples (c) Piezoelectric material strips piled
together
Q.84 Which one of the following is not a self- (d) Series of bismuth-telluride couples
generating type transducer?
(a) Thermocouple and thermopile Q.91 Strain gauge is basically a
(b) Piezoelectric pick-up (a) Active device which converts
(c) Photovoltaic cell mechanical displacement into a change of
(d) Magnetostriction gauge resistance
(b) Passive device which converts electrical
Q.85 Which one of the following transducer is displacement into a change of resistance
made of semiconductor? (c) Passive device which converts
(a) Thermometer (b) Microphone mechanical displacement into a change of
(c) Thermocouple (d) Thermistor resistance
(d) Active device which converts electrical
Q.86 A thermistor exhibits displacement into a change of resistance
(a) only a negative change of resistance with
increase in temperature Q.92 Which of the following is a disadvantage of
(b) only positive change of resistance with using Linear Motion Variable Inductance
increase in temperature Transducer (LMVT)?
(c) can exhibit either a negative or positive (a) It responds to dynamic systems
change of resistance with increase in (b) It responds to static systems
temperature depending on the type of (c) It is free from mechanical hysteresis
material used problem
(d) none of these (d) It is affected by external magnetic field
6.8 | JE-AE Electrical MASTERPLUS EDUCATION®
Answer Key: Transducers
1 C 2 D 3 B 4 B 5 B
6 D 7 B 8 A 9 A 10 B
11 C 12 C 13 D 14 B 15 A
16 B 17 A 18 C 19 B 20 A
21 C 22 B 23 C 24 B 25 B
26 C 27 A 28 A 29 C 30 C
31 A 32 D 33 B 34 B 35 D
36 D 37 B 38 B 39 B 40 C
41 B 42 C 43 D 44 D 45 A
46 A 47 B 48 A 49 A 50 A
51 C 52 A 53 A 54 C 55 B
56 C 57 B 58 C 59 C 60 B
61 B 62 C 63 B 64 D 65 D
66 A 67 B 68 D 69 C 70 B
71 D 72 A 73 D 74 D 75 A
76 C 77 C 78 A 79 B 80 C
81 A 82 C 83 A 84 D 85 D
86 C 87 B 88 D 89 B 90 A
91 C 92 D
Solution
1. (c) Resistance increases (↓) with increase (↑)
A thermistor is defined as a type of resistor whose temperature depending upon material used.
electrical resistance varies with change in 2. (d)
temperature. Although all resistor's resistance will An Anemometer is a device used for measuring
fluctuate slightly with temperature, a thermistor is wind speed & direction. It is also a common weather
particularly sensitive to temperature changes. station instrument.
Thermistor is a passive transducer. 3. (b)
Types of thermistor- Gauge factor (GF) or strain factor of a strain gauge
1. Negative temperature coefficient thermistor- is the ratio of relative change in electrical resistance
Resistance decrease (↓) with increase (↑) to the change in length of the element.
temperature depending upon material used.
2. Positive temperature coefficient thermistor-
Measurement MASTERPLUS EDUCATION®|6.9
R 10. (b)
Using band pass sampling theorem rather than
GF R baseband (i.e. low pass) sampling theorem
100 100 50 50
fu Hz; f B Hz
GF ratio of p.u. change in resistance to p.u. change
in the length. fu
4. (b) 2k 2
fB
Strain gauge is used in conjunction with the gain
strain gauge to compensate temperature effects. The 2f 2 100
fs u
main strain gauge should have a lower resistance k 2
heat coefficient for best result. s 2 f s 200rad/s
5. (b)
Thermocouple - Constant temperature one end The minimum sampling rate, 2fm samples per
Thermistor - Negative temperature coefficients second is called the Nyquist rate. Which applies to
Strain gauge - The electrical resistance of the strain, baseband or lowpass signals. The bandpass sampling
gauge varies not only with strain but with theorem states that if a bandpass signal m(t) has
temperature as well spectrum of bandwidth B = 2fB and an upper
- Modulated output frequency limit u = 2fu then m(f) can be recovered
6. (d) 2 fu
from ms(t) by bandpass filtering if fs ,
An imperfect capacitor is represented by a k
capacitance C in parallel with a resistance R. The fu
value of its dissipation factor tan & is 1/CR. where k is the largest integer not exceeding , All
fB
C higher sampling rates are not necessarily usable
unless they exceed 2fu
R 11. (c)
Energy stored V2 / X A thermocouple is a transducer which depends on
Q 2 c CR see beck effect, that states when two dissimilar
Energy dissipated V / R
metals are joined together and two temperature
1 1 difference is maintained at two junctions, emf is
Dissipation factor tan
Q CR produced.
So, thermocouple is an active transducer which
C R converts heat energy to electric energy.
Dissipation factor (tan) = CR 12. (c)
7. (b) Thermistor is a semiconductor device which is non-
Moire fringes are used to measure rotary linear and highly sensitive as well as exhibit
displacement along with optical encoders only. negative resistance temperature coefficient.
An optical encoder is an electromechanical device 13. (d)
which has an electrical output in digital form It can't measure static pressure.
proportional to the angular position of input shaft. Piezo electric transducer response only dynamic
8. (a) pressure.
Given that, V = 2.6V So an induce voltage 0 mV.
Displacement = 0.4 µm 14. (b)
Output voltage 2.6 The output of LVDT is in the form of linear
Sensitivity 6.5V/μm
Displacement 0.4 displacement of core. This association of a single
9. (a) value to a position occurs through electromagnetic
A time delay fuse is a special kind of fuse that coupling of an AC excitation signal on the primary
allows electrical surge for a short time before it winding to the core.
actually blows. Due to its special design. it can bear 15. (a)
electricity overload in a repeated cycle for a short Negative temperature coefficient (NTC) resistor
period without blowing and used in motor and which means that the resistance decrease with
transformer. increasing temperature. They are primarily used as
6.10 | JE-AE Electrical MASTERPLUS EDUCATION®
resistive temperature sensors and current limiting 25. (b)
device. The linear variable differential transformer (LVDT)
16. (b) consists of a transformer with a single primary
To reduce the effect of fringing in a capacitive type winding and two secondary winding which are
transducer, a guard ring is provided and is kept at electrically out-of-phase from each other by 180°.
ground potential. The LVDT also consists of a movable core.
The capacitive transducer or sensor is nothing but 26. (c)
the capacitor with variable capacitance. The Electrodynamic generator – Motion to voltage
capacitive transducer comprises two parallel metal Venturi meter – Flow rate to pressure
plates that are separated by the material such as air, Pirani gauge – Gas pressure to resistance change
which is called as the dielectric material. Spring balance – Force to displacement
17. (a) 27. (a)
Orifice plates have coefficient of discharge which is Unbounded strain gauges are exclusively used for
typically about 0.6 and loss of head of about (60- transducer application is to detached and used again
70)%. and again. Unbounded strain gauges are used in
An orifice plate is a device used for measuring flow force, pressure and acceleration measurement.
rate, for reducing pressure or for restricting flow. 28. (a)
18. (c) A transducer is a device that converts one type of
Fibre-optic data transmission system for telemetry energy to another. The conversion can be from
has largest bandwidth electrical, electro - mechanical, electro-magnetic,
19. (b) photovoltaic or any other form of energy.
The size of the venturimeter is expressed as 200 While the term transducer commonly used as a
100 mm². It means that the "diameter of the pipe is sensor/detector, any device which converts energy
200 mm and that of throat is 100 mm." Venturimeter can be considered a transducer.
is a device that is used to measure the rate of flow of 29. (c)
fluid through a pipe. This device is based on the
grind principle of Bernoulli's equation. Primary Secondary Resultant
Diameter output
Diameter of throat
of pipe Secondary 2
20. (a) LVDT has one primary winding and two exactly
A Thermocouple is a sensor used to measure similar secondary winding. Both secondary
temperature. It is active transducer don't require windings are exactly same and connected opposite
auxiliary power source to produce output. induced polarity, core of transformer is free from
21. (c) linear motion, thus linear motion is converted into
Given, R = 250, R = 0.150 corresponding electrical signal.
Strain = 1.5 10-4 30. (c)
GF = ? Resolution of a potentiometric transducer depends
Gauge factor = change in resistance/ lateral strain on material of wire.
R / R 0.150 31. (a)
G.F . 4
/ 250 1.5 104 Active transducers are self generating type they
22. (b) don't require external power to work while passive
Gauge factor change in resistance/strain- transducers require external power to work.
R / R 32. (d)
G.F . Thermistor have very high and negative temperature
/
coefficient of resistance. It is used from -100°C to
23. (c)
300°C. It used for precision measurement.
Force measurement-cantilever beam
33. (b)
Torque measurement-Flat spiral spring Least sensitive to temperature changes is not an
Acceleration measurement-seismic mass. advantage of semiconductor as compared to
24. (b) conventional strain gauge.
Platinum-rhodium is the most suitable thermocouple 34. (b)
transducer for the measurement of temperature in
the range of 1300°C to 1500°C
Measurement MASTERPLUS EDUCATION®|6.11
T-type thermocouple is made of copper constantan. Thermistor generally has a negative temperature
It is very stable thermocouple and used in extremely coefficient of resistance with an increase in
low temperature. Such as cryogenics or ultra low temperature, resistance of a thermistor decreases. A
freezers. fixed resistor of suitable value is usually connected
Type of base metal thermocouple is - across a thermistor to improve its linearity.
T-type - Copper + Constantan. 42. (c)
J-type - Iron + Constantan. Piezo electric crystal usually employed for
K-type - Nickel + Cormium. measurement of acceleration and use as a
E-type - Nichrome + Constantan. measurement of pressure by developing emf as a
35. (d) function of the deformation.
Rochelle Salt is used a transducer in hearing aids 43. (d)
device. The hall effect element is a type of transducer used
36. (d) for measuring the power, current, displacement and
For transfer of the heat from one object to another it requires small space and also gives the continuous
object through conduction both bodies must be at signal concerning the magnetic field strength.
different temperature. 44. (d)
37. (b) Piezoelectric crystal is one of small scale energy
A thermometer is calibrated from 150°C to 300°C resource. A potential difference appears across the
Maximum value = 300°C opposite faces of the material as a result of
Minimum value = 150°C dimensional charges when a mechanical force is
Span = 300°C - 150°C = 150°C applied to it.
Static error = ±0.2% of span 45. (a)
= ± 0.2% of 150 The variation in the measured quantity due to
= ± 0.3°C sensitivity of transducer to any plane other than the
38. (b) required plane is called cross-sensitivity. sometimes
LVDT is linear variable transducer which is measure situation may occur where the equipment is very
linear displacement. sensitive to the plane perpendicular to the required
(1) Magnetic pick-up is related to attractive type plane and we have to abandon that equipment due to
relay which is used in circuit breaker erroneous result.
(2) Tacho-generator is related to measurement of 46. (a)
angular speed of alternator or any rotating machine. Photoemissive effect- Electrons or, charge carriers
39. (b) absorb light, get excited and ejected out of material.
A thermopile is an electronic device that converts Photovoltaic effect- Electrons on charge carriers
thermal energy into electrical energy. It is composed absorb light, get excited but still contain within
of several thermocouples connected usually in series material.
or rarely in parallel. Photoconductivity effect- After absorbing light, the
40. (c) number of free electrons or charge carrier increases
Given, and hence increases electrical conductivity.
L 47. (b)
Gr 2 0.001 For contactless body temperature measurement,
L advanced thermometers are used. They are based on
R 50 R = ? infrared radiation it is design to measurement of
R temperature measurement at a point on surface of a
machine.
Gr R 48. (a)
L
Measurement of thermocouple-
L By using a PMMC instrument i.e. a PMMC
R millivoltmeter.
2
0.001 50 After amplification, the output voltage can be
R = 100 0.001 measured.
R = 0.1 So, thermocouple is not a pressure measurement
41. (b) transducer.
49. (a)
6.12 | JE-AE Electrical MASTERPLUS EDUCATION®
McLeod gauge amplifies the low pressure and = 7.4 10-5 V
developed to extent the range of vacuum VH = 74 volt
measurement significantly. 55. (b)
50. (a) Material A is platinum. EAB and EAC are obtained
Secondary 1 from the given data from the law of intermediate
Primary Secondary Resultant metals
output EBC = EBA + EAC = -EAB + EAC
The thermo emf sensitivities of given pair in table.
Secondary 2
B C EAB EAC EBC |EBC|
LVDT has one primary winding and two exactly =
similar secondary winding. Both secondary EAC
windings are exactly same and connected opposite -
induced polarity, core of transformer is free from EAB
linear motion, thus linear motion is converted into Nichrome Constantan 25 -35 -60 60
corresponding electrical signal. Nickel Constantan -25 -35 -10 10
51. (c) Copper Constantan 6 -35 41 41
The measurement of speed of rotating shaft by an Copper Nickel 6 -25 41 31
electric transducers is the example of tertiary 56. (c)
measurement. When measuring process involves The strain gauge is one of the most important sensor
two conversion then its called tertiary measurement. of the electrical measurement technique applied to
52. (a) the measurement of technical quantities. It converts
Given that- force, pressure, tension, weight etc, into a change in
Resistance = 1000 electrical resistance which can then be measured.
Strain gauge = 1 57. (b)
Stress 1050 kg/cm² The capacitive transducer is used for measuring the
Young modulus of elasticity = 2.1 106 kg/cm2 displacement, pressure and other physical quantities
Stress it is a passive transducer that means it required
Strain ( )
young modulus of elasticity external power for operation. The capacitive
transducer work on the principle of variable
Strain gauge (G) R / R R / R A 0 r A
strain / Capacitance C
R /1000 d d
1 Where, A = Overlapping area of plates in m2
1050 / 2.1 106 d = Distance between two plates in meter
R 0.5 = Permittivity of the medium in F/m
53. (a) r = Relative permittivity
Load cell: A load cell is a force transducer. It 0 = The permittivity of free space
converts a force such as tension, compression, Dynamic characteristics of capacitive transducer are
pressure or torque into an electrical. signals that can high phase filter
measured and standardized. As the force applied to 58. (c)
load cell increases, the common type of load cell
A
used are, strain gauge. Pneumatic and hydraulic, Capacitance C
54. (c) d
Hall voltage VH = ? d A
Sensitivity s C 2
Thickness t = 0.1 mm dd d
Carrying current I = 100A 59. (c)
Magnetic flux density B = 1Wb/m2 A strain gauge is a sensor whose resistance varies
Hall coefficient RH = 7.4 10-11 m3/c with applied force. It converts force pressure,
BI 7.4 1011 1100 tension, weight etc. into a change in electrical
VH RH resistance which can then be measured.
t 0.1103
When external forces are applied to a stationary
7.4 109 object, stress and strain are the result. Stress is
104 defined as the object's internal resisting forces and
Measurement MASTERPLUS EDUCATION®|6.13
strain is defined as the displacement and Pirani gauge is used for the measurement of pressure
deformation that occur. in the range of 10 mm to 10 mm of Hg. Pirani gauge
60. (b) is a robust thermal conductivity gauge which is used
Thermocouple works on Seebeck effect a for the measurement of pressure.
thermocouple is a sensor for measuring temperature. 68. (d)
This sensor consisting of two dissimilar metal wire Given, Gauge factor (GF) = 2.0
joint at one end and connected to a thermocouple Stress 100N/mm²
meter. Modulus of elasticity = 2 105 N/mm²
61. (b) R / R
For Thermistor temperature coefficient of resistance G.F. _____(i)
/
is given as
3000 Stress
(TTCR) 2 0.0333 / / C Modulus of elasticity
T (273 27) Strain
62. (c) 100
2 105
A linear variable differential transformer or LVDT ( / )
is an electromechanical position transducer (sensor) 100
which provides accurate and frictionless positional 50 105
feedback information about the linear mechanical 2 105
position of an external force. It uses basic From equation (i)
transformer principles of mutual inductance to R / R
2
measure linear movement as in the working of 50 105
transformer. R
63. (b) 50 2 105 103
R
Given, R = 125
% change in resistance = 10-3 × 100 = 0.1
R = 1 69. (c)
Strain = 4000 10-6
R / R
R / R 1/125 GF
G.F . 2
strain 4000 106
= Strain
64. (d)
A microphones is classified as a acoustical 9
GF 3
transducer. Acoustical transducer is a non-contact 2000 0015
wave generation and reception in conducting GF = 1 + 2v (v = Poisson’s ratio)
material. 3 = 1 + 2v
65. (d) v=1
Piezoelectric, Thermocouple & photovoltaic cell are 70. (b)
active transducer. In other hand LVDT is passive Gauge factor is ratio of relative p.u. change in
transducer. Active transducers do not require an resistance to p.u. change in length.
auxiliary power source to produce their output. R / R
66. (a) Gauge factor
strain
The gauge factor of a resistance wire strain gauge, is
0.15 / 250
a measure of sensitivity of the gauge. This strain Gauge factor 4
gauge is a passive transducer. The resistance 1.5 104
coefficient of strain gauge should be low for good 71. (d)
magnitude. Piezoelectric material on crystal such as tourmaline,
dR / R topaz, quarts Rochelle salt and cane sugar, BaTiO3
G Where, G = Gauge factor mode.
d / Yttrium garnet is not a piezoelectric material. It is a
d / magnetic material.
G 1 2v
d / 72. (a)
dD / D RTD has better linearity, better accuracy and
v new v precision and at high temperature it has a better
d / stability.
67. (b)
6.14 | JE-AE Electrical MASTERPLUS EDUCATION®
Advantages: Sensitivity error- This type of error occurs
Most stable where the observed output deviates from the
Most accurate current value by a constant value.
More linear than thermocouple Non-conformity error- When experimentally
Disadvantages: obtained transfer function deviates from the
Expensive theoretical transfer function for almost every
Self-heating. input.
Current-source required Hysteresis error- The effect of hysteresis is
73. (d) obtained in all transducers. The output of a
Bourdon tube can be used to measure pressure transducer not only depends upon the input but
directly. also upon input quantities previously applied to
Bourdon tube- it. So, different output is obtained when the
same value of input quantity is applied,
depending upon whether it is increasing or
decreasing.
Vm 78. (a)
Given,
g = 0.05Vm/N
p = 1.6 106N/m2
P t = 2.5 mm = 2.5 10-3 m
Bourdon tube can be used to measures pressure Output voltage of piezoelectric crystal
directly. It is a primary transducer. e0 = g.p.t
The output of Bourdon tube is angular e0 = 0.05 1.6 106 2.5 10-3
displacement e0 = 200 V
The angular displacement of bourdon tube us up Where,
to 2700 g = voltage sensitivity
74. (d) P = Applied pressure
The most widely used inductive transducer to t = thickness of rystal
convert the linear motion into electrical signals. 79. (b)
LVDT stands for Linear Variable Differential The transducer which generate the output in the
Transformer. form of the voltage or current, without any external
75. (a) energy source is called active transducers. Photo
LVDT output voltage for displacement of 1 mm voltaic transducer is an active transducer.
(Vout) 2mV Strain gauge transducer is a passive transducer.
80. (c)
Sensitivity (s) Output voltage Photo conductive cell is used for low frequency
Displacement
application. It is referred to as light dependent
2 resistors (LDR). The photo conductive cell detects
2mV/mm
1 when light fall on it.
Entire sensitivity 81. (a)
= Amplification factor LVDT sensitivity Generally, transducer signal is very weak, its need to
= 500 2 10-3 = 1V/mm amplify upto measurable range.
76. (c) 82. (c)
A crystal, such as quartz, that produces a potential Bourdon tube is used to measure the pressure
difference across its opposite face when under directly.
mechanical stress is called piezoelectric crystal. The Rota meter is used to measure the flow.
output of a piezoelectric crystal has low amplitude 83. (a)
and high impedance. A thermocouple is an electronic device that converts
77. (c) thermal energy into electrical energy. A thermopile
Zero error- In such type of error, the output consists of a number of thermocouples connected in
deviates from the original value by a constant series. The thermopiles have a slow response and the
factor over the entire range of the transducer. sensitive to changes in ambient temperature. They
Measurement MASTERPLUS EDUCATION®|6.15
are used in radiation pyrometers and as infrared 3. Many other quantities such as torque, pressure,
detectors. weight & tension etc, which involve effects of force
Thermocouple are formed by Si-Al thermocouples or displacement,
in an IC by doping Al layers on P-type and Si layer 4. Gauge factor (G): It indicates the strain sensitivity
on N-type. of gauge.
84. (d) R / R Change in Resistance
Active transducer or self-generating transducers are G
l / l Change in length
devices that do not require any power supply for
92. (d)
their operation but passive transducer require
Disadvantage of LMVT-
external power source for their operation. eg.:
(i) Accuracy errors may occurs due to the
Photovoltaic cell, thermocouple and thermopile,
interference of external magnetic field.
piezoelectric crystals.
(ii) The frequency response is controlled by the
85. (d)
construction of force ring members.
Thermistor are semiconductor sensor which are
made from the sintered compound of metallic oxide
of Cu, Mn, Ni & Co form beads, rings and disc.
86. (c)
The word thermistor is formed by two words
thermal and resistor. It is a solid state device in
which resistance varies with the ambient
temperature. Most thermistor possess negative
temperature coefficient.
The thermistors are manufactured from the oxides of
metal such as cobalt, copper, iron, zinc, nickel,
manganese, titanium, magnesium etc.
87. (b)
Air core inductive transducer are used for-
Constructing RF tuning coils
High frequency applications including TV and
radio receivers.
To ensure a lower peak inductance
Snubber circuit.
88. (d)
Eddy current proximity transducers are contact type
transducers, hence option (d) is incorrect.
89. (b)
The sensitivity factor of a strain gauge is normally
greater then 1. The order of sensitivity factor is 1.5
to 2.
90. (a)
The commercial thermopiles are formed.by series of
Si-Al thermocouples in an IC by doping Al layers on
p-type Si and on n-type Si epitaxial layers.
91. (c)
1. The strain gauge is basically a passive transducer
used for measuring mechanical surface strain.
2. Strain gauge works on the principle of change in
resistance i.e. it converts mechanical displacements
into change in resistance.
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