Micrologix 1100 RTC disabling by itself

We have a system with a Micrologix 1100 in the field. Lately it's been driving me nuts and AB has been unable to help. The customer will call and report a loss of clock data (the month/day/year and hour/minute/second/dow values all go to 0). We replace the PLC and it runs for awhile, but then it will happen again.

This is a big issue since the only way to set the RTC values after this happens is by connecting to a PC. When we get the PLCs back and I go online, the RTC is disabled and can be reset.

Anyone seen this before or have any ideas on what's causing it?

I'll also add that we have over 100 of these machines in the field with the same program and have never had this problem.

Is there an HMI that might be writing to the RTC ?

Does your MicroLogix 1100 have a Memory Module installed ?

There's an HMI attached that has the ability to write to it, but it shouldn't be. There is no memory module installed.

Sorry to hijack, but i just had the same problem. ML1100 was running solidly for over 4 years, then RTC suddenly became disabled.

I tried a rung with an always-on OTU to set RTC:0/DS, but it won't accept it.

rguimond said:

Sorry to hijack, but i just had the same problem. ML1100 was running solidly for over 4 years, then RTC suddenly became disabled.

I tried a rung with an always-on OTU to set RTC:0/DS, but it won't accept it.

Click to expand...

Help file says RTC:n/DS is READ-ONLY