I've got an AB PLC-5 rack set up as a remote rack. The first eight bigs of a sixteen bit isolated output card keep turning off by themselves. There is continuity throughout the rung all the way to the output, and suddenly after a while the output will just turn off. Here's the troubleshooting I've done so far.
1) Verified that I wasn't momentarily losing some other bit in the software rung. I am, indeed, just losing the output even though there's continuity.
2) Swapped out the output card with a brand new isolated output card.
3) Called Rockwell technical support, sat on hold for 10 minutes, and talked to a guy who said either my chassis is bad (not likely) or I've got a block transfer instruction that is for some reason writing to that card. The fact that the problem is limited only to the first 8 bits would seem to give credibility to the second possibility. There USED to be an analog output module in that rack, but it was taken out. As far as I can tell, all the code, including the BTR and BTW for it, have been removed from the software. Besides, the analog out was in slot 7, whereas my problematic card is in slot 0.
4) After finding no block transfer instructions in the code going to that rack at all, and after verifying that there are no conflicts between the integer files used in the block transfers (before or after the analog cards were removed) and any I/O, I replaced the chassis.
The problem still persists.
I've moved all the outputs over to a different isolated output card and they aren't having any problems. I'd like, however, to find the root cause of the problem in case we have future needs to use those outputs.
Any suggestions???
1) Verified that I wasn't momentarily losing some other bit in the software rung. I am, indeed, just losing the output even though there's continuity.
2) Swapped out the output card with a brand new isolated output card.
3) Called Rockwell technical support, sat on hold for 10 minutes, and talked to a guy who said either my chassis is bad (not likely) or I've got a block transfer instruction that is for some reason writing to that card. The fact that the problem is limited only to the first 8 bits would seem to give credibility to the second possibility. There USED to be an analog output module in that rack, but it was taken out. As far as I can tell, all the code, including the BTR and BTW for it, have been removed from the software. Besides, the analog out was in slot 7, whereas my problematic card is in slot 0.
4) After finding no block transfer instructions in the code going to that rack at all, and after verifying that there are no conflicts between the integer files used in the block transfers (before or after the analog cards were removed) and any I/O, I replaced the chassis.
The problem still persists.
I've moved all the outputs over to a different isolated output card and they aren't having any problems. I'd like, however, to find the root cause of the problem in case we have future needs to use those outputs.
Any suggestions???