Troubleshooting
372 SPU 780 01EMAN May 2002 273
Isolating Faults

Isolating Faults Faults can fit into one of four categories:

Fault Possible Causes/Fixes
Input/Output Faults This is the most common type of fault. It occurs when an open,
short, or an electrical or mechanical malfunction happens.
Common locations for these faults are in the field devices and the
wiring between the I/O module that interfaces to the field device.
Controller Faults These faults include a faulty controller or improper ladder logic.
The Controller Manual Check helps isolate a faulty Controller.
Communication Faults Communication Faults: Modicon controllers communicate with the
I/O sub system through remote I/O processor communication
networks or within local drops on the Modbus subsystem. Faults
occur when two pieces of hardware unexpectedly stop
communicating or communications becomes unintelligible.
Invalid Command When the warning ’Command Not Valid Unless Logged In’
appears, check the following:
Ensure the cable is properly attached to the controller.
Ensure that the controller you’re connected to isn’t logged onto
by another user.
Ensure you’re using the correct cable.
Ensure the cable is connected to the correct controller port.
If the problem persists, contact Schneider Electric’s Customer
Support.