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Author Topic: E-Stopping a PLC  (Read 2382 times)

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E-Stopping a PLC
« on: November 19, 2013, 07:25:56 PM »
Hi PLC'ers,
I've written a little ladder program and it is working quite well.

How do you typically apply an E-Stop function into the logic ( or hardware) ?

Someone mentioned just killing the 24vdc to the unit but I'm wondering if there could be 1 control bit that would stop the scan and put the unit into STOP mode until it is reset.

Another thing I'd like is to be able to have 1 input to PAUSE the execution of the ladder at any point, then another to RESUME.
Or similarly, something like Mach's Single Step mode.

Thanks again,
Russ

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Re: E-Stopping a PLC
« Reply #1 on: November 21, 2013, 12:47:09 PM »
Hey RC, It all depends. Best to kill everything you can mechanically and in the ladder and make provisions in the PLC and Mach to recover from this. Most PLCs have something similar to a Master Control Relay you can use in the logic. Depending on what its doing you may want to build a flip-flop in the PLC and Macro pump so that if one isn't talking to the other each can throw an error and stop. You can use this and let one stop the other mechanically too. Lots of ways to do all of this. Best to just figure out exactly what needs to happen in all possible states and go from there.

Brett
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Re: E-Stopping a PLC
« Reply #2 on: November 22, 2013, 05:39:27 PM »
I've always had E-stop applied only to PLC outputs, as when there is a problem I still want to know what the inputs are, especially if they are analog.  So I usually kill the common supply to outputs.  Turning off the PLC will lose the status of any latch relays which may or may not be desired.