Control Logix L73 running V19. For the third time a RTO (retentive timer on) has its preset changed to a large negative value on its own. there is NO code in the PLC any other PLC or any HMI that writes to this preset, the preset is "hard-coded" i.e. typed write in.

What's up?

 

I have never heard of this one..............I know you said none, is there any file instructions moving to the timer array, I have seen strange things like a plant wide system (recipe management) writing to the array without us knowing it (fat finger by IT) (I KNOW Ugh)..........try creating an entirely unrelated new timer, ie DAVE_TEST so that you are absolutely sure there is nothing doing some strange write to it.............

Have you talked to Rockwell? I was only on 19 for a short time and it did have some issues (didn't hear of this one).........

Sorry if I stated some obvious, just trying to help

Dave Ferguson
Control Systems Engineer

 

To make SURE that no one else is writing to it set the external access as "Read Only." Then, as Mr. Ferguson suggests, look for file instructions like COP, CPS, FLL, FAL, etc. Logix doesn't check boundaries when doing file operations, so doing a COP to a single DINT with a length of 1000 will nuke a bunch of stuff in your data table.

If neither of those two things are the issue, I would try a new processor, and if THAT doesn't fix it I would take it to Rockwell as a bug. (Updating the firmware might also be an option, but unless a problem is specifically mentioned in the release notes it probably didn't get fixed.)

Good luck.

-James Ingraham
Sage Automation, Inc.