ControlLogix - Inhibit Module turning on

[gbeaker]

Hi,

I have a 1756-a17 rack with a 1756-L61 processer. There is three 1756-OB32 cards installed amongst various other cards. About twice a month one, two, or three of the OB32 cards stop working and the OK light is flashing. If I go online the "Inhibit module" box is checked in the module properties. If I uncheck the box, everything is ok again.

Does any one have any idea what could cause this? Is someone going online and checking the box or will it happen under a failure or fault of some kind? There is no errors listed under Module Fault.

Thanks

 

[Ken Roach]

Either somebody is going online and inhibiting the modules, or they are being inhibited by the program.

You can set the inhibit/enable property of an I/O module connection with the Set System Variable (SSV) instruction, or with a carefully configured MSG instruction. Check the program logic for an SSV that might be addressed to those modules.

 

[Anirban Hazra]

If not done by any person, then check whether it is being done in the program using a conditional SSV instruction which is changing the Inhibit bit in the Module object.