Triggering events using a timer & counter combo

[OkiePC 14]

I know this is too late, but here's what I do to avoid accumulated errors with timers: In case the attachment doesn't show up: Put the TON on an unconditional rung with a preset that is much greater than the scan time. When the ACC is greater than or equal to the interval you want, (your normal preset...) subtract the interval from the ACC and set a bit to use as an alternative to the DN bit. The error or accumulator overrun is left in the ACC. Your interval may still vary up to the amount of the scan time (which was a huge part of the original poster's problem) but my solution will give you the correct average number of pulses over a long duration.