Exercise: Measurements And Instrumentation

Questions for: Measurements And Instrumentation

Induction wattmeter can be used in
A:
ac circuit only
B:
dc circuit only
C:
both ac and dc circuit
D:
ac 3 phase only
Answer: A

Induction effect occurs with ac only.

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A moving iron instrument gives correct reading when used at
A:
low frequencies
B:
high frequencies
C:
only one frequency
D:
all frequencies upto a certain value
Answer: C

If frequency changes reactance of coil changes and reading is affected.

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In a thermocouple temperature transducer, the output voltage is usually measured by
A:
high resistance ammeter
B:
high resistance voltmeter
C:
high resistance milli-voltmeter
D:
none of the above
Answer: C

The output voltage is very small. So we need a milli voltmeter.

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Which of the following statement is correct for two wattmeters method of power measurement in 3 phase circuit?
A:
Power can be measured by this method only for star connected loads
B:
When two wattmeters have equal readings power factor is 0.5.
C:
When power factor is 1, one of the wattmeters readings is zero
D:
When the two wattmeter read equal and opposite, p.f. is zero.
Answer: D

When p.f. is zero, active power is zero and the two redaings are equal and opposite.

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Which of the following measurements using a dc potentiometer do not require standardisation of potentiometer?
A:
Measurement of unknown voltage
B:
Measurement of resistance
C:
Measurement of unknown current
D:
Calibration of voltmeter
Answer: B

Unknown resistance is compared with a standard resistance. Therefore standardisation of potentiometer is not necessary.

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