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snakes79 December 6th, 2017 03:22 PM

Intermittent fault AB -- L24ER-BB1B
Hello friends. I have a PLC in the field that intermittently faults out. Its a compact logix L24ER-BB1B. The status "OK" light blinks red, according to the customer. He toggled the switch from program mode to remote, to reset the fault, and the machine resumed operation. According to the customer, this has happened 2 or 3 times in a month.


Does toggling the switch erase the controller fault list in the properties window?

Has anybody ever dealt with something like this?

If there was a negative number in a counter or timer, (which I don't think happened) Toggling the reset wouldn't fix the problem, and it would fault out again instantly?



janner_10 December 6th, 2017 03:48 PM

You need to go online and see what the fault is.

Jeev December 6th, 2017 07:24 PM

Does this site have a lot of brown-outs, supply transients or do they have a habit of cycling power to fix things often?

GaryS December 6th, 2017 07:59 PM

The Micrologix and SL line will do that with a math overflow fault just going to program and back to run will reset it until the next time.
I don't know if the Logix processors still have that problem

ScottTheEngineer December 7th, 2017 09:11 AM

I had a couple that did that do to programming error. The SCP instruction I was using had indirect addresses and I was causing a divide by 0 error When I accessed the routine they were located in.

Ken Roach December 7th, 2017 11:12 AM

The ControlLogix/CompactLogix OS considers overflow and divide by zero to be minor faults, which will not stop the user program.

An out-of-bounds array index will definitely fault the controller, and that's the sort of thing that's very typically reset during an initialization routine.

I agree that OP needs to go online and look at the fault logs. I admit I don't remember if they are cleared by a keyswitch cycle or power cycle.

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