A good way to measure scan rate

[cch1955]

I have an application that is counting inputs from an optical sensor with a conventional input to a standard counter. I suspect I am loosing counts at higher rates. The On time is quite short.

What is a good way to measure the scan time so I can estimate the rate I should be a able to read.

I would use the fast counters, but they are tied up.

Thanks.

[support]

<tt>
construct a circuit:
     OUT1                 OUT1
|---|/|-----------------(OUT)
</tt>

Then use an oscilloscope to view the resulting wave form. The scan time is half the period.

However, if you have differentiated Custom Function running then the scan time varies widely depending on whether the Custom Function is executed. So you may need to use a second PLC with PULSEPERIOD monitoring and a comparison routine to capture the worst case pulsewidth/pulseperiod in order to find out the worst case scan time.