IO-ATC8 all inputs showing alarm, Possible reasons?

[Ladderlogic]

Hi,

Would someone have some clue to why all Inputs on the IO-ATC8 remote IO suddenly show alarm. Also had them showing 0 and switching to alarm without any obvious reason. What are the alarm triggers in the IO module?

Grateful for any help. 

[Ausman]

Have you done the obvious of checking all connections, power supply ok, earthing correct, commons ok etc?  And not just looking at them, disconnecting and measuring where applicable, at both the ATC8 and PLC end.   Measure resistances etc b/n relevant terminals before disassembly for later reference.

Some power supplies can indicate they are ok, but fail under load.  If all else appears ok after inspection, measure things carefully during use.

But to me it looks like you've got a connection problem, particularly earthing or 0.  Remember that you are talking very small voltages etc here, and the slightest upset in resistances can severely affect things.  I would initially start on all your common connections between the plc and IO.  Don't forget the module connector(s).

cheers, Aus