Micrologix 1100 question

[Michael Lloyd 85]

I added a timer to a Micrologix 1100 yesterday and it acted strangely. Initially it would not run no matter what. The preceding XIO and (2) XIC's were nothing fancy, just a couple of permissives anded together to tell the timer to run plus a NC Timer/DN contact to make the timer restart. It was a 60 second timer (1 sec time base). ** Every now and then the timer would run, time out, and then just sit there. Some period of time later, maybe 30-45 seconds, it would do the same thing. Logically speaking it should have run 60 seconds, reset, repeat. The first thing someone is going to say is that one of my preceding bits was cycling off an on. I checked that. All but one was latched. Here's the really interesting part. It didn't start the behavior that I put the ** in front of until I added a jumper around all of the inputs. If I remember correctly I have 19 timers configured and this one was #12. All of the other timers operate perfectly. Ultimately I rewrote the rung to use S:3/15 to toggle (I think it was S3... hard to remember as I have 2 active CLX projects starting up this week plus the little micrologix and I'm the only programmer.)

[b_carlton 61]

Can you post the program?

[Michael Lloyd 85]

Im traveling to another site at the moment. When I get there I'll post it if I have an Internet connection

[Ken Roach 194]

My strong suspicion is that there's additional logic in the program mis-addressed to the control bits of that timer that are interfering with it, or a mis-keying of an address in an HMI. I've never heard anyone suggest that a MicroLogix 1100 has some limit on the number of Timer instruction it can execute (other than 255 per data file, up to the memory limit of the controller). Do a careful cross-reference, and do a recompile and download of the whole program. I'm not ruling out some malfunction related to the OS of the controller or some failure of the online edit process, I'm just saying such a thing is extremely improbable.

[Michael Lloyd 85]

IO understand... however one of the first steps that I do when I encounter a problem is to cross reference the IO. 99% of the time I've used a one shot twice or something like that. Not this time. Apparently I didn't save a copy of the version with the timer that ran intermittentaly so post problem troubleshooting is going to be difficult. I appreciate the help though

[TConnolly 13]

Two possibilities that come to mind: 1) By chance was the timer in a conditional subroutine? If the subroutine logic is not being called then the timer instruction won't execute. 2)The same timer address is used in two different TON instructions in different parts of the program. A timer can be duplicated in the logic and you won't get any warnings about it.