Fault handling

Join Date
Aug 2015
Location
Detroit, MI
Posts
177
So I am rewriting a messy program (which I wrote awhile back), adding some features and streamlining some security and decided to try my hand in fault handling. It's new to me but I am interested in learning it...

If there is a major controller fault, for example an I/O fault, is there a way to write logic to send the controller into programming mode?đź“š

Compactlogix 1769-L32E
v.20.14
 
I urge you to think about what you are wanting to do.

putting the machine into program mode while running may do more harm than good.

I have written several programs that monitor I/o for faults.
when the fault occurs, I fault out that station and stop the machine after the auto cycle is complete for the other stations.

I have a pv terminal with a multi message screen that will scroll through the faults.

I have a fault search routine that looks for the errors.

regards,
james
 
What is the advantage of going into program mode vs fault? Keeping your outputs in the last state? It's probably safer to let it fault.

I agree, you should "handle" the faults. We use the term "rack fault". We use GSV instructions to make sure the connection is good and all IO associated with the connection can be "trusted". If connection is bad then you can set your output states of the associated IO properly. If you logically handle the connection error, then you can disable major fault on connection error and let your logic handle it.
 
The default for CopactLogix I/O is for the controller to Major Fault if an I/O module loses its "connection" with the controller. You can change this on the module properties dialogs.

This is different to ControlLogix, where the default is to not Major Fault the controller.

Once you have stopped the controller major faulting, you can get module status, and shut your processes down in an orderly manner, just as if an alarm has occurred on a controlled device.
 

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