Question

A 0-400V voltmeter has a guaranteed accuracy of 1% of full scale reading. The voltage measured by this instrument is 250 V. Calculate the limiting error in percentage.

(a) 4%

(b) 2%

(c) 2.5%

(d) 1%

The question was posed to me in an interview for job.

This is a very interesting question from Advanced Problems on Error Analysis in Electrical Instruments topic in chapter Measurement of Resistance of Electrical Measurements

Answer 1

The correct answer is (a) 4%

For explanation I would say: The magnitude of limiting error of the instrument

ρA = 0.01 × 400 = 4 V

The magnitude of voltage being measured = 250 V

The relative at this voltage Er = \( \frac{4}{250}\) = 0.016

∴ Voltage measured is between the limits

Aa = As(1± Er)

= 250(1 ± 0.016)

= 250 ± 4 V.