21. A multimeter is often called a VOM, which is an abbreviation of volt-ohm ________.
Meter
Mega ammeter
milliammeter
Microammeter
Answer.1. Meter
Explanation:
A multimeter or a multitester is also known as a VOM (volt-ohm-milliammeter)
It is an electronic measuring instrument that combines several measurement functions in one unit
A typical multimeter can measure voltage, current, and resistance.
22. The advantages of an Electronic voltmeter are
Low Power Consumption
Low-Level Signal Detection
High Accuracy
All of the above
Answer.4. All of the above
Explanation:
Low-level signal detection: The low-level signal cannot be detected by the analog meter but an electronic voltmeter can detect the low-level signal also
Low power consumption: In the case of an electronic voltmeter, the power required for the deflection is provided from the external circuit by the use of amplifiers and not from the signal to be measured.
High accuracy: The electronic voltmeters are precise and highly accurate as compared to the analog conventional voltmeters.
Compactness and portability: Due to the small size of electronic components, the electronic voltmeters are compact and hence portable as compared to the analog conventional voltmeters.
High sensitivity and high input impedance: The sensitivity is very high as much as 100 times the normal PMMC voltmeter.
Less loading effect: In the PMMC instrument, the minimum current of 50 µA is taken from the signal to be measured, and hence it produces a great loading effect. As the power is supplied by the external circuit in electronic voltmeters, there are no loading effects.
High-frequency range: The response of electronic voltmeters practically can be made independent of frequency. Some of the electronic voltmeters can measure the voltages from d.c. to the frequencies of the order of hundreds of MHz.
Improved dynamic range: The range over which the meter is able to detect the input under various measurement conditions is called its dynamic range. For an electronic voltmeter, the dynamic range is improved as compared to an analog conventional voltmeter. It can measure very low as well as very high input signals.
23. Which of the following statements is not correct for thermo-couple measuring instruments?
They are very useful as transfer instruments
They are incapable of taking any overload
Power losses are very low
Their calibration does not change with time or temperature
Answer.3. Power losses are very low
Explanation:
The instrument which uses the thermocouple for the measurement of the temperature, current, and voltage type of instrument is known as the thermocouple instrument. It is used for both the AC and DC measurement. The thermocouple is an electric device that uses two wires of different metals.
24. Measuring range of a voltmeter can be extended by using
High shunt resistance
High series resistance
Low shunt resistance
Low series resistance
Answer.2. High series resistance
Explanation:
To increase the ranges of a voltmeter, we need to connect a high series of multiplier resistance in series with voltmeters.
25. Electronic voltmeters using rectifiers are designed to have large negative feedback. This is done:
To improve stability
To improve sensitivity
To increase the overall gain
To overcome the non-linearity of the rectifier diodes
Answer.4. To overcome the non-linearity of the rectifier diodes
Explanation:
The effect of large negative feedback in an electronic voltmeter is to greatly increase the input resistance of the stage in which it is used. High input resistance is the most desirable feature in an electronic voltmeter to ensure that the circuit under test is unaffected by the addition of a voltmeter.
Another important effect of large negative feedback is that it improves the overall characteristics, thereby reducing harmonics and removing the non-linearity of the rectifier diode.
26. A thermocouple ammeter/voltmeter has _____
A logarithmic law response
A square-law response
A linear law response
None of these
Answer.2. A square-law response
Explanation:
In a thermocouple ammeter/voltmeter, the scale is directly proportional to the square of the current and hence it has a square law response.
27. A VTVM is never used to measure
Resistance
Volt
Current
Frequency
Answer.3. Current
Explanation:
The voltmeter which uses the vacuum tube for amplifying the measured AC and DC voltage is known as the vacuum tube voltmeter (VTVM). The vacuum tube increases the sensitivity of the voltmeter because of which it can detect the signal of very weak strength.
VTVM cannot measure current directly because of its high resistance.
28. V.T.V.M. is superior to conventional voltmeter because
It has a high input impedance
It enables the measurement of low a.c. and d.c. voltages
It enables the measurement of high-frequency voltages
All of the above
Answer.4. All of the above
Explanation:
The voltmeter which uses the vacuum tube for amplifying the measured AC and DC voltage is known as the vacuum tube voltmeter (VTM).
The vacuum tube increases the sensitivity of the voltmeter because of which it can detect the signal of very weak strength.
The vacuum tube has many advantages like they have high input impedance, wide frequency range, and high sensitivity.
The most significant advantage of the VTM is that it can draw very less current as compared to the other meter.
In VTM, the measuring signal is directly supplied to the vacuum tube of the meter. The vacuum tube is amplifying the signal and passes it to the deflecting meter.
29. Which of the following instrument will be used to measure a small current of very high frequency?
Electrodynamic ammeter
Moving coil galvanometer
Thermocouple type instrument
Induction type instrument
Answer.3. Thermocouple type instrument
Explanation:
A thermocouple is defined as a thermal junction that functions based on the phenomenon of the thermoelectric effect, i.e the direct conversion of temperature differences to an electric voltage.
Thermocouple instruments are RF (radio frequency) type indicating instruments.
These instruments can be used for the measurement of AC signals up to 50 MHz frequency.
30. The electronic voltmeter can measure the voltage level up to ___
More than 5 mV
More than 2 mV
Less than 2 mV
More than 10 mV
Answer.3. Less than 2 mV
Explanation:
An electronic voltmeter can measure very low voltage.
A PMMC instrument requires at least a few tens of microamperes to give full-scale deflection. Suppose the FSD current of the meter is 20 #A and the internal resistance R, of the meter, is 100 ohms. The full-scale voltage range of the instrument is 2 mV. This is the voltage drop across the meter. So, the meter cannot read any voltage lower than 2 mV.
But an electronic voltmeter with an amplifier with high voltage gain can be used for very low voltage measurement.
