Welding

Any doubt remove the PLC, you may also have a problem with and sensors and motors.

I agree except I'd remove your first two words...

Del

true

We see a lot of maintenance around PLCs including welding--It is amazing how hardy and how few problems we have had--A couple of analog sizing eyes and optical encoders have been damaged from welding, but the damage is usually from feet and hammers and pry bars. It also depends on who is doing the welding and where--I've caught guys welding through bearings with bad ground placement(I suspect that is how the encoder went--I tore it open and there was a visible film from the shaft seal/heat that was getting smeared on the glass).

We hardly ever get notified of maintenance and welding on or around PLC equipment prior to it being done and we are purely reactive-BUT if it was up to me I would take the time to guarantee no damage to the processor or any I/O and cover or remove it(the only downside may be the disposition of the processor battery, but may give you a good chance to plan for, and change it).

The contract maintenance technicians on rolling stock/heavy equipment ALWAYS disconnects the ECM(s) prior to even simple service requests and an ounce of that prevention.........

You could remove the PLC but I wouldn't, turn them off instead nor would I remove grounds,the most important thing is to connect your welder ground in such a way as not to pass current through things that won't like it.Connect the welder ground as near to work as possible,Have welded on plc controlled equipment many times.