PLC5 and PID instruction - processor fault

I was wondering if anyone had experience with a PLC5/20 and the PID instruction faulting the processor while changing values in the setup screen.

I was programming online and I noticed that the PV for the PID loop was reading double what the instrument was. I figured it must be scaling so I opened the setup screen , and I changed the low raw value (from 0 to 819), then the processor went into fault.

The error was something like "illegal setpoint" or "setpoint out of range". I change the low value back to 0 and tried to go online again and it faulted again with the same error.

The only way to clear the fault was to delete the instruction and copy an existing PID controller.

Has anyone experienced this before?

Thanks.

It's been my experience that if the setpoint is outside the lower and upper limits, the processor will fault.

Yes,been there done that.There are wanings about this in the instruction set manual under PID instruction ( see Pic below)
It is good practice to check for limits before sending the PV value to the PID instruction.
You should not have to re-create the instruction to clear the fault. Just make sure the value is within limits and clear the fault. You will have to do this manually because the processor is not running while its faulted. Or disable the rung with the PID instruction, clear the fault, start the the processor running, make sure the value is within limits, then re-enable the PID rung.

I'm sure Ron will be along to give a much better understanding of all this.

I'm sure Ron will be along to give a much better understanding of all this.

Click to expand...

no, Mickey, my distinguished friend - it looks like you've nailed it down already ...