RS Logix 500 Counter won't reset

steelm · Oct 24, 2008

I am sure this has been covered, please direct if so.

Using the DN bit to energize an output then address a set of contacts the same as the output to reset the counter. Problem is the counter never resets to zero it goes to one instead. What causes this?
Thanks for your patience!
Matt

Tharon · Oct 24, 2008

It does go to 0, but it is counting to 1 right away, too fast for you to see.

Take a look at your logic that enables the counter. Or post it here for us to look at too.

Edit:
This is very common. Most of the time I'd rather just add one to the preset and then ignore the 1 that it resets to. It's usually faster for me than to modify my CTU rung to try and stop it from happening. And unless it's a value that an Operator has to see on an HMI, then who cares if it's counting 1 to 5 instead of 0 to 4?

Ron Beaufort · Oct 24, 2008

and if you want more detail, see if this post helps ...

http://www.plctalk.net/qanda/showthread.php?p=137158&postcount=15

actually the whole thread might be interesting ...

steelm · Oct 24, 2008

See attached. Thanks!!

tomalbright · Oct 24, 2008

I can barely make it out, but it looks like your input is still on. ?

bernie_carlton · Oct 24, 2008

The counter internally performs a one-shot on its count input. Thus if the input changes from OFF to ON it counts up 1. Unfortunately one of the effects of resetting the counter is also to reset the memory bit of the input. So just after the reset the counter has, as a memory, that the count input was OFF. But now it gets back to processing the counter instruction again and it sees the count input on and so it counts up 1. If you can, add a NC of the input condition after the DN contact of the counter before resetting the counter.

steelm · Oct 24, 2008

That makes sense. The processor is working in milli-seconds and the action on the input is in tenths.

Thanks soo much for the accurate, quick responses. Take the rest of the day off!

daba · Oct 26, 2008

Instead of the RES of the counter, you can - if you wish - just CLR the counter's .ACC, and OTU the .DN bit.

This will not reset the internal one-shot

jdbrandt · Oct 26, 2008

Speed has nothing (well, almost nothing) to do with it.

The fact is that the counter is still enabled when you try to reset it.

I almost always pre-condition the 'bit that counts', creating a one-shot action in front of the counter, and adding the reverse sense of the reset action to the count oneshot bit (ANDED). Its a bit more cumbersome, but I've never had anyone say to me: "I don't understand what you're trying to do here." When you write 'verbose' logic, it nearly always explains itself.
[FLAME_SUIT=.on.]

Roy Matson · Oct 27, 2008

Try using a transitional contact on your count input.
Roy

gravedigger02 · Oct 28, 2008

If you put a ONS after the input it should.

RS Logix 500 Counter won't reset

steelm

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Tharon

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Ron Beaufort

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steelm

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tomalbright

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bernie_carlton

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steelm

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Roy Matson

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