Reading when a PLC faults into Wonderware

Ones_Zeros · Jan 28, 2022

Hello,
I have a SLC500 Micrologix PLC that will sometimes go into a "Watchdog fault"
When it does this all the data on the wonderware screen is frozen and appears to be real until someone catches it on site.

My question is if the PLC is faulted is there a way that I can still read this fault into the wonderware so that a operator can catch it early or does a faulted PLC cut off all comminutions to the controller?

thanks,

plvlce · Jan 28, 2022

Your basic issue is that when the PLC faults, whether because of the watchdog or for other reasons, it continues to communicate but stops updating values (because the scan cycle is no longer running).

I've never dealt with Wonderware, but if you set up a constantly changing value in the PLC (such as a free running timer) and can implement on the Wonderware side a check that the value is not static, that would be a simple way to detect the issue.

iirc with newer Panelviews and the Logix platform it's possible to more directly check whether the PLC is in run, but I've never done it myself and only know about it from threads here, so no idea if it could be set up with a SLC/Wonderware.

Ones_Zeros · Jan 28, 2022

Thanks for the help.
What about also monitoring the $sys$status bit in each of the PLC's?
Would this bit be readable if a PLC faults?

I also have logix to monitor the S2 status file and reads the S:6 bits for the Major error fault code, but i was thnking if the plc faults would this be locked up and not read accurately?

thanks,

Operaghost · Jan 28, 2022

When the PLC has faulted, it stops scanning logic, but it does not stop communicating. WW can still talk with it.

The SLC sets a Major Error Halt (S:1/13) and stores the Major Error code S:6. I'm not sure if your WW system can read that processor status file. But if it can, then I would monitor S:1/13 and if it is on, pop up a message in WW to alert the operator. You could also display the fault code if you chose to do so.

If your WW cannot read the status information then you would want to have a fault routine in your SLC (LAD 8 here). This is a routine that executes automatically when the controller experiences a major fault. You can write logic in there to turn on a bit in a Binary file (B10:0/0 in my example). You can use a MOV to move the fault code into an integer (N11:0 in my example).

I would also include logic (not in the fault routine) to clear the integer value and unlatch the binary bit while the system is running normally.

OG

Ones_Zeros · Jan 28, 2022

awesome thanks for the help

lostcontrol · Jan 28, 2022

Ones_Zeros said:
Thanks for the help.
What about also monitoring the $sys$status bit in each of the PLC's?

Would this bit be readable if a PLC faults?

That bit is a IOServer status bit, not a bit that is read from then actual PLC. You can use that to
monitor the status of the IOServer, but not the PLC status.

As others have stated, the most bullet proof way to prove the PLC Comms are functional AND the plc is running is to monitor a changing value in the PLC, if it does not change for more than xx time, then there is an issue.
I often use the clock second for this.

Ones_Zeros · Jan 28, 2022

Hello Operaghost

Could you provide example logic on how to clear the integer and unlatch the bit to zero?

I would also include logic (not in the fault routine) to clear the integer value and unlatch the binary bit while the system is running normally.

thanks I appreciate it

Ones_Zeros · Jan 28, 2022

Sorry Operaghost
I figured it out. I mis-read your instructions
I was trying to add reset logix to the fault routine.

I have a question.
Before I clear the integer, how can i copy or move this fault value to a different integer before I clear the integer.
Reason is this would allow me to show the last known fault.

thanks,

lostcontrol · Jan 28, 2022

Ones_Zeros said:
Sorry Operaghost
I have a question.
Before I clear the integer, how can i copy or move this fault value to a different integer before I clear the integer.
Reason is this would allow me to show the last known fault.

thanks,

Use a one shot to move the fault value to your integer, then clear the value
I am not that good at posting images etc, but something like this

 XIC FAULT ONS ONSFAULT BST MOV FAULT N7:10 NXB CLR FAULT BND

If you copy that into RS500, it might make sense?

NetNathan · Jan 29, 2022

In the "heartbeat" I use.
I run a 30 sec timer in the PLC. I monitor this count in Intouch and write to the elapsed time every 15 sec, by setting it back to 1.
If I loose this reset, then I alarm in Intouch and the PLC.
Also if I loose monitoring of the changing number (it stops changing) in Intouch I alarm.
This is built in scripts.

Operaghost · Jan 29, 2022

Ones_Zeros;906061...Before I clear the integer said:
Here is an option for capturing the last ten faults. Hopefully this is readable. It has been ages since I wrote code for an SLC/Micro. But this should work. I didn't add it in the comment, but the Destination for the FFU is simply a place to unload the old fault code before they are lost for good.

Oh, and if you want the fault routine to actually clear the fault and prevent the shutdown from occurring, add an OTU for S:1/13 on the last rung all by itself. That will unlatch any fault and allow the system to continue to run. Just be aware, it faulted for a reason and clearing the fault does not fix the cause. It could just keep faulting again over and over. It might be unsafe to allow it to continue running when there is a fault.

OG

Ones_Zeros · Jan 30, 2022

@Operaghost
Perfect, thanks. And thanks also to everyone else for helping!!

Reading when a PLC faults into Wonderware

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