Siemens Analog Module Faults!!!

Hey guys, this is my first post here but I've gotten some answers from other posts already.
Here's my problem:
I have several machines using ALL Siemens PLCs, but I have very limited Siemens experience. Over the last several months, I've replaced about a dozen analog input modules (6ES7 331-7PF01-0AB0) for what appears to be the same reason. I'm getting the red light "SF" and my HMI shows no input signal. If I replace the card, the fault goes away so I know it's not a sensor issue. It has happened twice now during a power blink but several times with no cause that I can see. The problem is on the same type of module but in several different panels on at least three different machines. There's not a grounding issue that I can see.
Design flaw?
Dirty power?
Gremlins?
Any suggestions?

Check where the power is coming from, boards will fault if card power is on but PLC power is off.

lefthandedsquirrel said:

There's not a grounding issue that I can see.
Design flaw?
Dirty power?
Gremlins?
Any suggestions?

Click to expand...

Hi!

Could you please show how the card is wired?
There are alternative methods.

Kalle

lefthandedsquirrel said:

Design flaw?
Dirty power?
Gremlins?
Any suggestions?

Click to expand...

For Dirty Power you can use a vacuum cleaner.
For Gremlins you just have to keep them away from water.
Sorry but I could't help it.