Key Digital ES381 User Manual download pdf (Page 19)

2.5.2 Frequency Mode

The counter can be put into Frequency mode using the selection

button shown below. Note too that clicking on a new period

selection item will change to Frequency mode.

In this mode of operation, the counter will use an internally

generated gating period of 0.1s, 1s or 10s, to integrate (count) pulses

that arrive at the input during the period. Normally, the 1s period

will suffice for most readings from 50MHz

down, but if the input

frequency is slow (less than 1KHz), the 10s period may prove better

at the expense of a slower reading update time. The 0.1s period

offers faster reading update rates but is only useful for input

frequencies of greater than around 10KHz. Note that both of these

“limits” are simply the point at which one extra count during the

integration time has a 0.1% effect on the reading. You can of course

count lower frequencies if you don’t mind the resolution getting

worse than 0.1%.

If you have a slow input frequency, Period mode may be more

suitable.

Elan Digital Systems Ltd. 19 USBcount50 USER’S GUIDE Iss1

With favourable input drive (i.e. suitable amplitude to trigger the counter) the counter can reach

100MHz counting rates.

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Key Digital ES381 User Manual Page 19