Detecting and Diagnosing Inoperative Components through Health Messages

Inoperative Components

An inoperative component causes system changes:

If...	Then...
A component of the Primary CPU becomes inoperative	Control shifts to Standby CPU
A component of the Standby CPU becomes inoperative	Standby CPU goes offline
Fiber optic sync-link cable link becomes inoperative	Standby CPU goes offline

Health Messages

The Primary CPU sends a health message to the Standby CPU over Copro sync-link every 10 milliseconds.

Health messages over the RIO link:

If...	Then Primary CPU Sends Health Message over RIO link...
No communication is required with any drop on RIO link	Every 5 ms
All systems are OK	Every scan

Lack of health messages over the RIO link:

If...	Then...
Standby CPU does not receive health messages on neither the Copro link nor the RIO link	Standby CPU determines the cause Standby CPU assumes control by becoming the Primary CPU
Primary CPU does not receive a valid response from the Standby CPU	Primary CPU operates as a non-redundant Standalone PLC.

Finding Diagnostic Information with Control Expert

Detected errors and Switchovers are logged in the diagnostic buffer. To view the buffer log select from the menu Tools → Diagnostic Viewer.