Blown analogue input... Siemens cpu

Today I had a Siemens PLC 314C with an analogue input that was reading 32768 while having 4mA. So the input is defective. I connected on an other analogue input en all okay.

Several months ago it was the analogue output of the softstarter (same analogue signal that we're talking about) that was broke. We had to replace the softstarter because this analogue signal is a really important one that regulates conveyors.

This is not normal... analogue output and now the input on the other side...

The Altistart takes around 1000 AMPS at Start-U
The analogue signalcable is a shielded one, but the shield isn't connected on ground, normally it should on one side I think. Could that be the cause of blown up analogue inputs and outputs ?

How can I protect my analogue in and out ?

Thanks in fwd
regards,
Gerry

Perhaps a 4-20mA signal isolator / galvanic isolator would help?

Yes, ground the shield at the analog output side.

Does the softstarter supply the power necessary for the 4-20mA signal?


Or does power come from the Siemens AI connections?


Or is a separate power supply needed?


Is where the DC power for the analog output grounded at some point? Can the ground be lifted?