SLC 500 faulted.

[Conor 4]

Hi guys, I just had a SLC go into fault. When I went online the error was as follows: "The user watchdog scan time has been exceeded!" I cleared the fault and the PLC came back fine. Can anyone throw any light on this? See attached screendump Thanks, Conor blower_g_error_5_11_13.doc

[b_carlton 61]

Are you asking what a 'Watchdog Scan Timeout' is? Or what may cause it? It means the scan took longer than the set 'watchdog' time. Look for any kind of long file or looping code.

[Conor 4]

For some idea's that may have caused it. I have 9 of these machines, all with the same program in them. The only time before that I saw one of the PLC's faulting was when an Analogue Input card had gone faulty. So after that I put in watchdog code to monitor each of the PLC's.

[panic mode 246]

watchdog timer is used to get attention when something (program in this case) is not responding. this can be because you are using loops for example or alternating normal program flow in some other way (jump to label etc.). in PLC scan is used to process variety of tasks, not just user program. for PLC to function normally, it needs to return to those other tasks frequently enough. for example this is what allows PLC to communicate with outside world. but if you don't mind that your program tends to get 'preoccupied' and forgets to return to it's chores that run in the background, feel free to increase WDT preset.

[mhowasso 5]

What does this WatchDog code look like..?? Could you post an example..?? Thanks

[Conor 4]

Sorry I worded that wrong. I set up a watchdog timer in a remote PLC that triggers site alarms. I am looking at a bit coming on and off in each of the PLC's and triggering a "Watchdog" alarm on a PanelView that displays the site alarms. Basically I have nothing special in the PLC that faulted Sorry for the confusion Conor

[b_carlton 61]

Yet the error you posted shows a PLC watchdog error. Do you specifically trigger this error as your 'Communication Fault'? If so you might want to trigger a 'User Error' if possible rather than triggering this one and possibly masking a true PLC scan 'Watchdog Timeout'.