Categories: Third Year First Semester (3-1)

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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

|”|”|||”|”’|||’|

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]

*****

2 of 2

R13

SET – 1

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