Question

In a digital voltmeter, the oscillator frequency is 400 KHz. The Ramp voltage falls from 8V to 0V in 20 ms. what is the number of pulses Counted by counter?
1. 8000
2. 4000
3. 3200
4. 1600

Answer 1

Correct Answer - Option 1 : 8000

Concept:

The number of pulses counted by the counter is N = \(\frac{{pulse\;width\;}}{{time\;period\;of\;the\;oscillator}}\) = Tw / T

Where

Tw is the pulse width

T is the time period of the oscillator

Calculation:

Given that 

The oscillator frequency of the digital voltmeter f = 400 kHz

Then the time period of the oscillator is given by T = 1 / f  = 1 / 400 × 103 sec

The pulse width of the ramp voltage given by Tw = 20 ms

⇒ N = \(\frac{{20 \times {{10}^{ - 3}}}}{{\frac{1}{{400 \times {{10}^3}}}}}\) = 8000