Question

A 3 ½ digit voltmeter has an accuracy specification of ± 0.5% of reading ± one digit. What is the possible error in volts when the instrument displays 2.00 V on the 10 V scale?
1. 0.03 V
2. 0.02 V
3. 0.01 V
4. 0.005 V

Answer 1

Correct Answer - Option 2 : 0.02 V

Concept:

The resolution in an N digit DVM is given by \(= \frac{1}{{{{10}^N}}} × range\;of\;voltage\)

Where N is the number of full digits.

In a DVM, a full digit counts 0 to 9 and a half digit counts from 0 to 1.

The resolution indicates the voltage corresponding to one digit.

Calculation:

Voltmeter reading = 2 V

Full scale reading = 10 V

Number of full digits = 3

Full scale reading = 10 V

Resolution \( = \frac{1}{{{{10}^3}}} × 10 = 0.01\;V\)

The voltage corresponding to one digit = 0.01 V

Error in the voltmeter = ±0.5% of displaying 2.0 V reading ± 1 digit

= 0.005 × 2 + 0.01 = 0.02 V