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Electrical Measurements & Measuring Instruments Multiple Choice Questions on “Performance Parameters of Digital Voltmeters”.
1. Basic range of DVM is _________
a) 1 or 10 V
b) 0.1 or 1 V
c) 10 or 100 V
d) 100 or 1000 V
Answer: a
Clarification: In a DVM, the basic range is 1 V or 10 V. Range of a DVM can be extended from a few µV to kV. This is achieved by making use of an attenuator.
2. Accuracy of a DVM is ________
a) low
b) high
c) medium
d) zero
Answer: b
Clarification: Accuracy of a DVM is based on the resolution. Resolution depends on the number of digits. The more the number of digits, the higher is the accuracy. For a DVM, the accuracy is of the order of ±0.005 % of the reading.
3. Input impedance of a DVM is ________
a) low
b) zero
c) high
d) medium
Answer: c
Clarification: Typical input impedance of a DVM is usually very high. Typical value is of the order of 10 MΩ. This is usually done in order to reduce the loading effect.
4. In DVM the common mode rejection noise is eliminated by ________
a) increasing the signal amplitude
b) making use of a resistance
c) using a transformer
d) guarding
Answer: d
Clarification: In a DVM, common mode noise can be eliminated through guarding. A guard is basically a sheet metal box around the circuit. This is made available to the circuit being measured by making use of a terminal at the front panel.
5. Output of DVM needs ________
a) 4 lines
b) 2 lines
c) 8 lines
d) 16 lines
Answer: a
Clarification: Type of DVM used depends on the digital output lines. Four lines of BCD or a single line serial output may be provided so as to read the output from a DVM.
6. Normal mode noise can be eliminated through ________
a) attenuation
b) filtering
c) amplification
d) a transformer
Answer: b
Clarification: Filters can be used to eliminate the normal mode noise signals. When used for low voltage measurement, noise present at the input can cause errors in the analog to digital converter.
7. DVM has ________
a) 1-3 digits
b) 2-5 digits
c) 3-6 digits
d) 7-10 digits
Answer: c
Clarification: The DVM consists of 3 to 6 digits. As the number of digits are increased the resolution also increases. Thus, the resolution of a DVM is very high.
8. What is a digitizing circuit?
a) converts digital signal to analog
b) boosts the magnitude of a digital signal
c) attenuates a digital signal
d) converts analog signal to digital
Answer: d
Clarification: DVM converts analog signal to digital. The process is known as digitization and the circuit used to obtain the conversion is known as a digitizing circuit. Time needed for this conversion is known as digitizing period.
9. User must wait for a stable reading.
a) True
b) False
Answer: a
Clarification: Since it is difficult to follow the reading visually at high reading speeds, user has to wait till a stable reading is obtained. The digitizing period depends on the maximum speed at which the value is read from the meter.
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