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Electronics and Communication Engineering - Measurements and Instrumentation

Exercise : Measurements and Instrumentation - Section 1
41.
Which of the following measurements using a dc potentiometer do not require standardisation of potentiometer?
Measurement of unknown voltage
Measurement of resistance
Measurement of unknown current
Calibration of voltmeter
Answer: Option
Explanation:

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

42.
Which of the following statement is correct for two wattmeters method of power measurement in 3 phase circuit?
Power can be measured by this method only for star connected loads
When two wattmeters have equal readings power factor is 0.5.
When power factor is 1, one of the wattmeters readings is zero
When the two wattmeter read equal and opposite, p.f. is zero.
Answer: Option
Explanation:

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

43.
In a thermocouple temperature transducer, the output voltage is usually measured by
high resistance ammeter
high resistance voltmeter
high resistance milli-voltmeter
none of the above
Answer: Option
Explanation:

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

44.
A moving iron instrument gives correct reading when used at
low frequencies
high frequencies
only one frequency
all frequencies upto a certain value
Answer: Option
Explanation:

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

45.
Induction wattmeter can be used in
ac circuit only
dc circuit only
both ac and dc circuit
ac 3 phase only
Answer: Option
Explanation:

Induction effect occurs with ac only.

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