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
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
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
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
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
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.
6. Main disadvantage of a true r.m.s responding voltmeter is ________
a) presence of transducer
b) presence of thermocouple
c) presence of transformer
d) presence of oscillator
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
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 ________
Explanation: By making use of true r.m.s responding voltmeter we get 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.
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.
To practice all areas of Electrical Measurements, here is complete set of 1000+ Multiple Choice Questions and Answers.