Allen-Bradley GuardLogix 5570, User Manual

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Rockwell Automation Publication 1756-UM022D-EN-P - May 2017 145
Monitor Status and Handle Faults Chapter 9
Controller Faults Faults in the GuardLogix system can be nonrecoverable controller faults,
nonrecoverable safety faults in the safety application, or recoverable safety
faults in the safety application.
Nonrecoverable Controller Faults
These occur when the controller’s internal diagnostics fail. If a nonrecoverable
controller fault occurs, safety task execution stops and safety I/O devices are
placed in the safe state. Recovery requires that you download the application
program again.
Nonrecoverable Safety Faults in the Safety Application
If a nonrecoverable safety fault occurs in the safety application, safety logic and
the safety protocol are terminated. Safety task watchdog and control
partnership faults fall into this category.
When the safety task encounters a nonrecoverable safety fault that is cleared
programmatically in the Controller Fault Handler, the standard application
continues to execute.
If a safety task signature exists, you can clear the fault to enable the safety task
to run. If no safety task signature exists, the safety task cannot run again until
the entire application is downloaded again.
Recoverable Faults in the Safety Application
If a recoverable fault occurs in the safety application, the system can halt the
execution of the safety task, depending upon whether or not the fault is
handled by the Program Fault Handler in the safety application.
When a recoverable fault is cleared programmatically, the safety task continues
without interruption.
When a recoverable fault in the safety application is not cleared
programmatically, a Type 14, Code 2 recoverable safety fault occurs. The safety
program execution is stopped, and safety protocol connections are closed and
reopened to re-initialize them. Safety outputs are placed in the safe state and
the producer of safety-consumed tags commands the consumers to place them
in a safe state, as well.
ATTENTION: Overriding a safety fault does not clear the fault. If you override
a safety fault it is your responsibility to prove that operation of your system is
still safe.
You must provide proof to your certifying agency that your system can continue
to operate safely after an override of a safety fault.