Electrical Measurements Questions and Answers – True RMS Responding Voltmeter

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers (MCQs) focuses on “True RMS Responding Voltmeter”.

1. R.M.S value means _________
a) root mean square
b) rate mean second
c) root median second
d) rate mode second
View Answer

Answer: a
Explanation: R.M.S value indicates the Root Mean Square. It is obtained by taking the square root of the average value of the square of the input signal. It is also known as the effective value.

2. Meter reading is obtained by ________
a) sensing voltage
b) sensing heat power
c) sensing current
d) sensing resistance
View Answer

Answer: b
Explanation: In a true R.M.S responding voltmeter, the meter reading is obtained by sensing the heat power of the waveform. The heat power is directly proportional to the r.m.s value of the input.

3. Measurement of heat power ________
a) uses a heat sink
b) uses a thermometer
c) uses a thermocouple
d) uses a black body
View Answer

Answer: c
Explanation: A thermocouple is used to measure the heat power in a true R.M.S responding voltmeter. Input voltage under measurement is applied to the heater to which a thermocouple is also attached.

4. Sufficient heating of the heater is ensured by ________
a) increasing the temperature
b) making use of induction coil
c) amplifying d.c. input
d) amplifying a.c. input
View Answer

Answer: d
Explanation: Maximum heating of the heater is obtained by making use of an amplified a.c. input. As a result the thermocouple generates maximum voltage level in order to cause the meter deflection.

5. Power in a thermocouple is given by ________
a) Power = E2 rms / Rheater
b) Power = E2 rms
c) Power = Rheater
d) Power = E2 rms × Rheater
View Answer

Answer: a
Explanation: The power consumed in a thermocouple is given by the relation
Power = E2 rms ⁄ Rheater
where, Erms is the r.m.s value of the a.c. input signal
Rheater is the resistance of the heater.
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6. What is the main disadvantage of a true r.m.s responding voltmeter?
a) presence of transducer
b) presence of thermocouple
c) presence of transformer
d) presence of oscillator
View Answer

Answer: b
Explanation: Thermocouples have non-linear voltage and current characteristics. This is the major drawback of the true r.m.s responding voltmeter. This is overcome in some instruments by making use of an additional thermocouple in the same thermal environment.

7. What is the naming convention for the two thermocouples?
a) thermocouple 1 and thermocouple 2
b) input thermocouple and output thermocouple
c) measuring thermocouple and balancing thermocouple
d) internal thermocouple and external thermocouple
View Answer

Answer: c
Explanation: The thermocouple used in the input section of the voltmeter is known as the measuring thermocouple whereas the thermocouple used in the feedback path is known as the balancing thermocouple.

8. Sensitivity is of the order of ________
a) MV
b) V
c) GV
d) mV
View Answer

Answer: d
Explanation: By making use of true r.m.s responding voltmeter we get the sensitivity of the order of mV. The voltage ranges from 100 µV to 300 V with a frequency range of 10 Hz to 100 MHz.

9. Response of thermocouples is fast.
a) True
b) False
View Answer

Answer: b
Explanation: Crest factor limits the meter reading in a true r.m.s responding voltmeter when complex signals are taken into consideration. Also, the meter costs higher compared to average and peak responding meters. As a result the response of the thermocouples is slow.

Sanfoundry Global Education & Learning Series – Electrical Measurements.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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