signal frequency and duty cycle

hello.
suppose that we have a digital signal that come from a proximity sensor
and frequency of it is 50hz.
we have connected this sensor to one of normal digital inputs of s7-300 plc
and want to calculate frequency.

i am curious to know that if duty cycle of the signal is important or not?
i mean that does the cpu see the signal with duty cycle of 10% or etc?

best regards.

This will never work neither accurate nor reliably. Believe me, you are not the first optimist trying this. Use a counter module instead.

Kalle

Edit
A link to performance calculations: https://support.automation.siemens....136000&cspltfrm=0&cssw=0&csbinh=5&caller=view

thanks for your reply.

i told s7 plc as an example but my main question is:

The module specifications for a standard 16 channel 24VDC input module says:
input delay for 0-1: 1.2 to 4.8 ms.

what does mean "input delay"?
Does it mean that the cpu don't see signal if width of it be lower than 1.2ms?

best regards.

I go by - the time ON and the OFF time must be as long or longer than the worst input delay plus one scan time.

In your case the input module may not see the pulse if it is less than 4.8 ms. And the signal must be stable at the point in the cycle when it is sampled. Thus my rule above.