While using a frequency counter for measuring frequency, two modes of measurement are possible. I) Period mode ii) Frequency mode. There is a ‘cross-over frequency’ below which the period mode is preferred. Assuming the crystal oscillator frequency to be 4 MHz the cross-over frequency is given by

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ESE Electrical 2013 Paper 1: Official Paper

Answer 1

Frequency meter:

Frequency meter is used to measure the frequency of periodic signals, by balancing two opposite forces.
Change in the frequency which is to be measured causes a change in the balance and measured by the deflection of pointer.
There are two modes of measurement that can be possible. Periodic mode and Frequency mode

Let f_x = unknown frequency, f_c = crystal frequency, f_o = crossover frequency

Then, If f_x < f_o periodic mode

And f_x > f_o frequency mode

Now crossover frequency

⇒ f_o = 2 kHz