bhyde
Member
I’ve run into a strange situation that I’m struggling to explain. We have several AB-PLC5’s that have scan rates that “spikes” up for short periods of time. This usually causes the processor to fault because of a watchdog error (yes I know I can increase the watchdog value). The “spike” is typically about 800ms to 1200ms and the normal scan time is around 50ms. When the programs are fully loaded, we might see a normal scan rate of about 100ms.
The programs do contain several For/Next loops in high program numbers, but even if I force all the loops to execute on a single scan, I only see an increase of about 300ms max in the scan rate. In actual running conditions only one or two loops ever run on a single scan, so I’m not convinced the For/Next loops are the problem.
It’s a fairly typical PLC5 setup with RIO, Ethernet, and a couple of remote racks. There is also some HMI’s, a batch server, and a data logging system.
So the question is: Has anyone seen big jumps in scan rates that are not related to for/next loops? Maybe a communications problem or something related to I/O?
The programs do contain several For/Next loops in high program numbers, but even if I force all the loops to execute on a single scan, I only see an increase of about 300ms max in the scan rate. In actual running conditions only one or two loops ever run on a single scan, so I’m not convinced the For/Next loops are the problem.
It’s a fairly typical PLC5 setup with RIO, Ethernet, and a couple of remote racks. There is also some HMI’s, a batch server, and a data logging system.
So the question is: Has anyone seen big jumps in scan rates that are not related to for/next loops? Maybe a communications problem or something related to I/O?