Question

In a dual slop integrating type digital voltmeter, the first integrating is carried out for 50 periods of the supply frequency of 50 Hz. If the reference voltage used is 10 V, the total conversion time for an input of 40 V is?

(a) 3 s

(b) 2 s

(c) 4 s

(d) 1 s

This question was addressed to me during an interview.

This key question is from Problems on Initial and Final Value Theorem in portion Application of the Laplace Transform in Circuit Analysis of Network Theory

Answer 1

The correct option is (c) 4 s

Explanation: In a dual slope integrating digital voltmeter,

\((\frac{t_1}{t_2})\) Vin = Vref

Where, t1 = first integration time = 50 × \(\frac{1}{50}\) = 1

But Vin = 40 V and Vref = 10 V

∴ t2 = \(\frac{V_{in} t_1}{V_{ref}}\) = 4 s.