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Output pulse in msec timing

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I'm trying to create a series of pulses with high timing precision (2.5ms accuracy)

Using the internal timer function (10ms resolution) I got something to work but the timing of the actual pulses is not what I was hoping for

Set Actual

10ms 34-37

20ms 34-55

30ms 51-55

40ms 51-72

50ms 69-72

So the timing is offset by ~20ms and has high jitter in even timer setting (the timer is 10ms resolution)

The jitter looks like the pulses are either short by 10ms or off by 10ms but not the correct pulse length

Any ideas ?

I've changed the ladder a bit and that got me shorter "On" time but still the same issue with even timer setting and the "Off" time does not reach the same low limit (even with the same settting as the "On: time)



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  • MVP 2014

I would try the 2.509ms Interrupt function. Search "interrupt" in the helpfile.

You will never get what you want using the basic scan time of the PLC and the internal timers. You already know the internal timers are liited to 10ms resolution. The jitter you see is almost certinaly due to the scan time, which can be at least 10ms for a simple program. The timer output is only evaluated once per scan.

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  • MVP 2023

You didn't tell us about your hardware configuration, but your output address (O34) indicates that you are trying to get high speed from an output on an expansion I/O module so I'm guessing you have an M91. This will not work.

Search the Help for "immediate" and then look at "Immediate: Read Inputs...". You'll see that based on your model number there are system bits you can set to immediately write certain outputs on the main board.

Joe T.

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