Question

In a dual slop integrating type digital voltmeter, the firs integrating is carried out for 10 periods of the supply frequency of 50 Hz. If the reference voltage used is 2 V, the total conversion time for an input of 1 V is?

(a) 0.01 s

(b) 0.05 s

(c) 0.1 s

(d) 1 s

The question was asked in semester exam.

The origin of the question is Advanced Problems on CRT and CRO in portion Oscilloscopes of Electrical Measurements

Answer 1

Right answer is (c) 0.1 s

For explanation I would say: In a dual slope integrating digital voltmeter,

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

Where, t1 = first integration time = 10 × \(\frac{1}{50}\) = 0.25

But Vin = 1 V and Vref = 2 V

∴ t2 = \(\frac{V_in t_1}{V_{ref}}\) = 0.1 s.