AB Fault Routine

[AMarks95]

I have a fault routine set up in my 1769-L36ERM. Is this routine called repeatedly when there's a fault, or is it only called once? It seems that it only calls once?

 

[Ken Roach]

You are correct: the fault routine is only called once when there is a Major Fault.

 

[alan_505]

Hi Ken, are you able to reset a watchdog fault within the fault routine?

 

[AMarks95]

You are correct: the fault routine is only called once when there is a Major Fault.

So I can't have a TON in the fault routine to automatically clear a specific fault? For instance, say an IO fault?

 

[Ken Roach]

No, you can't use logic that depends on multiple scans or the passage of time in a Fault Routine.

It is pretty common to have an IO module connection failure cause a Major Fault in ControlLogix, since some I/O devices are critical to the control process. Sometimes that default setting causes faults that the system designer did not intend.

What is the application where you need a time delay ? Are you trying to react to an I/O module connection failure, or a detected condition like an overload, short-circuit, or open-wire fault ?

 

[AMarks95]

No, you can't use logic that depends on multiple scans or the passage of time in a Fault Routine.

It is pretty common to have an IO module connection failure cause a Major Fault in ControlLogix, since some I/O devices are critical to the control process. Sometimes that default setting causes faults that the system designer did not intend.

What is the application where you need a time delay ? Are you trying to react to an I/O module connection failure, or a detected condition like an overload, short-circuit, or open-wire fault ?

Trying to react to a temporary AENT disconnect. I'm guessing I'll have to disable the option that halts the PLC when the fault occurs and handle the fault in a normal routine accordingly?

 

[ASF]

Trying to react to a temporary AENT disconnect. I'm guessing I'll have to disable the option that halts the PLC when the fault occurs and handle the fault in a normal routine accordingly?

Yes, that's how I generally do it. Monitor all ethernet devices and just alarm/program the system response in standard ladder logic.

Where you have a remote I/O rack, it's always ideal to monitor not only the network adaptor (your AENT) but also each module on the rack.

 

[JeremyM]

Have a look at the Pax interlock AOI. You can supply one of its inputs the connection status of a device to break its run command. It can be configured to remain tripped until reset, which could be the combined status of a) reconnection and b) an operator ack of some sort.