Weird Allen Bradley coil issue...

Hi guys,

Can I firstly say that, apart from today that I havent had much to do with Allen Bradley software/hardware, and when I do it always seems to be quite glitchy. I deal with seimens alot more often.

The issue I had today which is yet to be resolved, was on a filler machine. Basically there is a reference point on the machine that makes a input high on every rev. This input directly switchs an output in the software, to trigger master card to begin a sync. (Still with me..?)

The issue is the input goes high on every rev, as it should but the out coil does nothing.. both the input and output are not called anywhere else just in that one network.

I still believe that the output is being switched from else where (conflict) but dont know where. I know in seimens you can have indirect addressing so wouldnt show up when you done a search but being such a virgin the allen bradley and PLC's in general, we have kinda hit a brick wall.

I have also re-download the program onto CPU as I thought the connection of the imagine table had got corupt some way...

The cause of this issue was a power cut earlier in the day, hope you guys can help in someway...

Which model of Allen-Bradley controller are you using ?

A power cycle may have caused the controller to re-load a copy of the application program that was saved in nonvolatile memory. Check the status of the battery backup and the nonvolatile memory, if they are installed.

The basic Allen-Bradley relay ladder execution model is to run the Main Program only. Any sub-routines have to be explicitly called by JSR or FOR instructions. Exceptions include interrupts, which your system might be using since it sounds like a fast input.

If an old copy of the program got loaded it's possible that the old copy lacked the proper configuration for an interrupt routine, or the proper Jumpt To Subroutine (JSR) instruction to execute the routine the affected rung is in.

Could offer you more help if you post up the program so we can take a look.

Otherwise, try right clicking the output and selecting Cross-Reference instead of Find All.

Cross-Reference includes indirect addressing and addressing at the word as well as bit levels.

errr yeah.

I find the "glitchyness" of either Siemens or AB (or most anything for that matter) to be directly related to the relative amount of experience and tact the guy who wrote the program had with that platform.

Software and controller? AB has many platforms dating back to the 70s. Most if not all still "in the wild".
Explain what you mean by "coil does nothing"
Is this code that up until now was otherwise working fine?
As others have said, check for interrupt/event driven functions, conditional subroutines, forcing enabled, etc.