Analogue Reading Going To Zero

Dear Sirs,

This is my first posting on the forum so please forgive any mistakes or dim wittedness on my part.

I am using an anlogue input card (6ES7 331-7NF00-0ABO), 5 of the inputs are configured as 2 wire -10v / +10v the others are not used. This card is mounted in a remote rack via an IM361 (6ES7 361-3CA01-0AA0)this is connected to an 840D CNC controller over a 10 m cable(6ES7 368-3CB01-0AA0).

When a steady voltage is applied to any channel the reading at the relavent PIW is cycling from the correct value to zerothen back. When I cross refrence the PIW it is only read from not written too.

I have now changed the input, IM card and the connecting cable with new from Siemens and the problem remains.

Does anybody have any ideas of where to look next?

Kind Regards

Maintman