Digital Voltmeter MCQ || Digital Voltmeter Questions and Answers

Measurement and Instrumentation, MCQ / April 19, 2022

11. The Input range of DVM is _______

  1. 1 V to 1000 V
  2. 0.1 V to 10 V
  3. 0.01 V to 1 V
  4. 0.001 V to 0.1 V

Answer:1.1 V to 1000 V

Explanation: 

Digital voltmeter have input range from +1.000 V to +1000 V with the automatic range selection and the overload indication.

 

12. An 8-bit successive approximation DVM of 5 V range is used to measure 1.2 V. The contents of the SAR after 5 clock is

  1. 01010000
  2. 00111100
  3. 00111000
  4. 00110111

Answer:2. 00111100

Explanation: 

An 8-bit successive approximation type DVM of 5 V range.

i.e. 5 V is the upper limit.

5 represents 11111111 = 255

To measure 1.2 V on 5 V range is,

1.2 V represent after 5 clock pulses = 255 × 1.2/5 = 61.5

The content of SAR after 5 clock pulses

= 60 = 00111100

 

13. A DVM has a 3 ½ digit display. The 1-volt range can read upon

  1. 9999
  2. 9.99
  3. 1.999
  4. 0.19999

Answer:3. 1.999

Explanation: 

The resolution (R) in an N bit DVM is given by:

R = Range of voltmeter/10N

Where N is the number of full digits.

The given DVM has 3 ½ digit display, i.e. it has 3 full digits and 1 half digit.

Resolution for the given DVM is = 1/103 = 0.001

Minimum count for the given DVM = 0.001

Maximum count = 1.999 V

 

14. Multiplication features are incorporated in an ohmmeter to enable the meter to ______

  1. Measure very high resistance values
  2. Measure values with the least error
  3. Be multipurpose in its application
  4. Has less power consumption

Answer:2. Measure values with the least error

Explanation: 

To enable the ohmmeter to indicate any value being measured, with the least error, scale multiplication features are used in most ohmmeters.

 

15. Which of the following is NOT true for an analog/digital multimeter?

  1. An increase or decrease in signal levels can be observed.
  2. A sudden change in signal can be detected by an analog multimeter more swiftly than a digital multimeter.
  3. All measurements are possible by using one meter only
  4. Digital meters are bulky and costly.

Answer:4. Digital meters are bulky and costly

Explanation: 

  • A multimeter is an electronic instrument. It is mainly used to measure the three basic electrical characteristics of voltage, current, and resistance.
  • It is a handheld device with a positive and negative indicator needle over a numeric LCD digital display.
  • An increase or decrease in signal levels can be observed. Hence option (1) is true.
  • Multimeters can be used for testing batteries, household wiring, electric motors, and power supplies.
  • All measurements are possible by using one meter only. Hence option (3) is true.
  • Digital multimeters are more accurate than analog multimeters.
  • The analog multimeter also exhibits low resistance and high sensitivity with scales down, hence a sudden change in the signal can be detected by an analog multimeter more swiftly than a digital multimeter. So option (2) is true.
  • Analog multimeters are more bulky and costly than digital multimeters, hence option(4) is not true.

 

16. A digital to analog converter with a full–scale output voltage of 3.5 V has a resolution close to 14 mV. Its bit size is

  1. 4
  2. 8
  3. 16
  4. 32

Answer:2. 8

Explanation: 

It is defined as the smallest change in the analog output voltage corresponding to a change of one bit in the digital output.

The percentage resolution (%R) of an n-bit DAC is:

Rn = 1/(2n − 1)

Calculation:

Resolution = analog value of LSB

= Full Scale/2n

14 mV = 3.5V/2n

2n = 250

n = 8

 

17. A variable reluctance tachometer has 180 teeth on rotor. The speed of shaft on which mounted in 1800. The frequency of output pulses is

  1. 1800 Hz
  2. 3600 Hz
  3. 4800 Hz
  4. 5400 Hz

Answer:4. 5400 Hz

Explanation: 

In variable reluctance tachometer,

Frequency of output pulse = (No. of teeth on the rotor) × (speed of shaft).

Calculation:

Given:

No. of teeth = 180, speed = 1800 rpm

So, the frequency of the output pulse will be:

= (180 × 1800)/60 = 5400 sec

 

18. An integrating digital voltmeters measures

  1. True average value
  2. RMS value
  3. Peak value
  4. None of the above

Answer:1. True average value

Explanation: 

Integrating type digital voltmeter (DVM) measures the voltage in the digital domain. It is possible to do so using voltage to frequency conversion.

The voltage measurement is proportional to frequency for a fixed reference value.

Since it reads a digital value from the converted actual analog voltage signal, the average value of the voltage signal is used for comparison.

Thus, DVM measures the true average value of the input voltage over a fixed measuring period.

 

19. Frequency counter can be used to measure

  1. Fundamental frequency of input signal
  2. Time interval between two pulses
  3. Pulse width
  4. All of the above

Answer:4. All of the above

Explanation: 

The frequency counter counts the number of times a signal passes a given voltage point or a zero-crossing point.

  • It usually measures the number of cycles of oscillation i.e. time interval between two pulses.
  • It also measures the pulse width of a signal.
  • It can only measure the fundamental component of a signal, not a harmonic component.

 

20. The Voltage Sensitivity of a multimeter is 10 mV, its internal resistance is 20 ohms. Then its current sensitivity is

  1. 1 mA
  2. 5 μA
  3. 500 μA
  4. 0.8 A

Answer:3. 500 μA

Explanation: 

Given:

Voltage Sensitivity = 10 mV

Internal Resistance = 20 ohms

Current sensitivity = voltage sensitivty/Internal Resistance

Current sensitivity = 10 × 10−3/20

Current sensitivity = 500 × 10-6

Current sensitivity = 500 μA 

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