FAULT'ing

Hello,

An unusual problem for me...
I have always been able to connect or disconnect analog or digital inputs with no problem. This SLC5/04 objects to that by FAULT'ing...stopping dead in its tracks with the red FAULT light on. Yesterday I connected a perfectly fine 4-20mA input, the PLC FAULT'ed, I cleared the FAULT, Major 20H, which indicates a minor I/O fault occured and we're done. Why does this SLC care? Bad card? Once the FAULT is cleared, the input is, once again, perfectly happy and reads the 4-20mA input. Hmmm...

D. J-O

S:20 is a power loss sounds like you shorted out the processor momentarily via a ground short while you were hooking up by the way yuo should whenever possible disconnect all power to the SLC when hooking up new wire to prevent damage caused by this exact scenario

Yeah, I'm pretty sure the PLCs aren't really meant to be hot swapped...

nope not a good idea Dan one option you may want to look into is to set S:1/8 fault override on powerup to 1. The disadvantage of this is you would need a fault routine to record any errors that are being cleared up this is in the SLC 500 instruction set. However without that bit set any time to processor loses power through black outs etc this PLC will fault without that bit set

Are you checking the status of the math overflow bit (S:5/0) at the end of you program? Error Code 0020H could indicate a math overflow scenario, which if not handled properly will fault the processor. If this is the problem, add a rung at the end of your main routine, after you have called all of your subroutines, to watch for this bit to be set and unlatch if it is set. This should be the last rung executed before the program ends.

Are your I/O modules wired down to terminal blocks or are you landing these new wires directly on the PLC module terminal blocks? Typically we have each analog input device fused, and if new devices are landed while the processor is running the fuse is open. What order did you land the wires when you landed the new 4-20mA input? Did you land the return side first and then the signal? Is this analog device loop powered or does it source it's own power?