JNTU Kakinada B-Tech 3-1 RT31021 I ELECTRICAL MEASUREMENTS R13 April 2018 Question Paper

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Code No: RT31021
III B. Tech I Semester Supplementary Examinations, May -2018
ELECTRICAL MEASUREMENTS (Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B) 2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PART ?A
1 a) Explain about transfer instruments. List out the features of indicating instruments. [3M]
b) List out the errors in electrodynamometer wattmeters. [4M]
c) Explain the process of standardization of potentiometer. [3M]
d) Classify sources of supply and detectors and briefly explain about each. [4M]
e) List out the principal requirements in magnetic measurements and reasons for
inaccuracies in measurement.
[4M]
f) List out the advantages and limitations of digital instruments over analog
instruments.
[4M]
PART -B
2 a) Explain about static calibration and list out the static characteristics with
necessary description.
[6M]
b) Write about multipliers, multi range voltmeters, multi range ammeters. [6M]
c) The coil of a moving coil voltmeter is 40 mm long and 30 mm wide and has 100
turns on it. The control spring exerts a torque of 240 x 10
-6
N-m when the
deflection is 100 divisions on full scale. If the flux density of the magnetic filed
in the air gap is 1.0 weber/m
2
, estimate the resistance that must be put in series
with the coil to give one volt per division. The resistance of the voltmeter coil
may be neglected.
[4M]
3 a) Describe the feature incorporated in an electro dynamometer wattmeter to make it
a low power factor type of wattmeter.
[6M]
b) Explain the procedure to measure power using instrument transformers with the
help of phasor diagrams and correction factors
[5M]
c) The constant for a three phase, 3 element integrating wattmeter is 0.12 revolution
of disc per kWh. If the meter is normally used with a potential transformer of
ratio 22000/110 V and a current transformer of ratio 500/5 A; find the error
expressed as a percentage of the correct reading from the following test figures
for the instrument only: Line voltage=100 V, current=5.25 A, power factor=1,
time to complete 40 revolutions=61 sec.

1 of 2

[5M]
R13
SET – 1
|”|”|||”|”’|||’|

Code No: RT31021
III B. Tech I Semester Supplementary Examinations, May -2018
ELECTRICAL MEASUREMENTS (Electrical and Electronics Engineering)Time: 3 hours Max. Marks: 70
Note: 1. Question Paper consists of two parts (Part-A and Part-B) 2. Answering the question in Part-A is compulsory
3. Answer any THREE Questions from Part-B
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PART ?A
1 a) Explain about transfer instruments. List out the features of indicating instruments. [3M]
b) List out the errors in electrodynamometer wattmeters. [4M]
c) Explain the process of standardization of potentiometer. [3M]
d) Classify sources of supply and detectors and briefly explain about each. [4M]
e) List out the principal requirements in magnetic measurements and reasons for
inaccuracies in measurement.
[4M]
f) List out the advantages and limitations of digital instruments over analog
instruments.
[4M]
PART -B
2 a) Explain about static calibration and list out the static characteristics with
necessary description.
[6M]
b) Write about multipliers, multi range voltmeters, multi range ammeters. [6M]
c) The coil of a moving coil voltmeter is 40 mm long and 30 mm wide and has 100
turns on it. The control spring exerts a torque of 240 x 10
-6
N-m when the
deflection is 100 divisions on full scale. If the flux density of the magnetic filed
in the air gap is 1.0 weber/m
2
, estimate the resistance that must be put in series
with the coil to give one volt per division. The resistance of the voltmeter coil
may be neglected.
[4M]
3 a) Describe the feature incorporated in an electro dynamometer wattmeter to make it
a low power factor type of wattmeter.
[6M]
b) Explain the procedure to measure power using instrument transformers with the
help of phasor diagrams and correction factors
[5M]
c) The constant for a three phase, 3 element integrating wattmeter is 0.12 revolution
of disc per kWh. If the meter is normally used with a potential transformer of
ratio 22000/110 V and a current transformer of ratio 500/5 A; find the error
expressed as a percentage of the correct reading from the following test figures
for the instrument only: Line voltage=100 V, current=5.25 A, power factor=1,
time to complete 40 revolutions=61 sec.

1 of 2

[5M]
R13
SET – 1
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Code No: RT31021

4 a) Explain about Gall-Tinsley AC potentiometer with necessary connection
diagram.
[8M]
b) In the measurement of power by a polar potentiometer, the following readings
were obtained: Voltage across a 0.2 ? standard resistance in series with the
load=1.46?32deg, Voltage across a 200:1 potential divider across the line =
1.37?56 degV. Estimate the current, voltage, power and power factor of the
load.
[8M]
5 a) Explain about the measurement of relative permittivity with necessary bridge
equations.
[5M]
b) Explain about measurement of mutual inductance in terms of standard
capacitance using Heydweiller Bridge with necessary equations.
[7M]
c) Explain the precautions and techniques used for reducing errors in bridges.
[4M]
6 Explain about ballistic tests for the determination of magnetic flux density,
magnetizing force, magnetic potentiometer, B-H curve and Hysteresis loop.
[16M]
7 a) Explain the basic circuitry of cathode ray oscilloscope. [8M]
b) Explain the procedure to measure angle of phase shift using Lissajous patterns. [8M]
*****

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