We encountered a problem last night that I can’t explain. My suspicion is that a faulty output modules in a remote rack controlled by a SLC5/05 caused the problem, but I’m looking for validation. I've contacted our local Rockwell rep, but havent received a reply yet.
We had a few valves not open. These valves are all controlled from the same output card, controlled by a sequencer. A counter that controls the sequencer seems to have reset itself after only completing part of the cycle (about 20 steps into a 100-step cycle). The sequencer started working spontaneously at one point. My question is:
Could a faulty output card cause a PLC reset that would restart the counter?
There is no logic other than detection of a "reset" bit on the 100th step of the counter that should reset the counter, and there is nothing that MOVes a value into the .ACC of the counter in question. It has worked fine for years, until last night.
We had a few valves not open. These valves are all controlled from the same output card, controlled by a sequencer. A counter that controls the sequencer seems to have reset itself after only completing part of the cycle (about 20 steps into a 100-step cycle). The sequencer started working spontaneously at one point. My question is:
Could a faulty output card cause a PLC reset that would restart the counter?
There is no logic other than detection of a "reset" bit on the 100th step of the counter that should reset the counter, and there is nothing that MOVes a value into the .ACC of the counter in question. It has worked fine for years, until last night.