CTU presets changing on their own and other weird events

I'm not sure if you read above/previous posts but we have changed the processor already. Shouldn't any corrupted memory areas be back to serviceable? The program that we dropped in was months old.

It really isn't a hardware issue. There is no mechanism by which such a thing as you describe can happen. "Corrupted memory" = faulted processor.


It is almost certainly a programming issue. Some instruction or outside device (the HMI - does it have any scripts running? Recipes installed?) is manipulating those registers.



If allowed, you can zip the PLC and HMI programs up and post them for us to look at (or PM me if you don't want them to be public).

To me this sound like a DC ground loop problem. I know you said you changed hardware and some wiring but I would check the DC common. Also check things like having only one shielding point.

I've never seen any Allen-Bradley PLC with a memory problem continue to run. In every case I have seen in almost 30 years, any problem with the PLC memory will result in the PLC shutting down and erasing its program. Post the code here if you are allowed (zip it and attache to a reply).

I just thought - do the counter presets actually get changed, or do the counter /DN bits come on way before they should?

Maybe an intermittent signal is causing the counter to count many times for one part. I had a similar situation years ago where a proxy at a line entrance sensed a circuit board entering, but the proxy after an acid wash only sensed the copper traces. 1 In = 250 Out.