At shift change, I wrote a 1 back to an OPC tag to reset some timers and counters. I then have a handshake to acknowledge this at the PLC a set this bit low. I encountered a situation today where the controller was powered off when the tag went high, and when the controller came back on it did not change that bit.
I assume this is because the tag does not continuously write. Does antone have a suggestion for how to achieve this? Thanks!
I would assume that the tag status was bad at the time that the PLC was off, you can check that maybe.
I write out to UDT structures often, and when I do, I do a write for most of the data, then I read back the tags and wait until the values match what I sent, then I write out the trigger element that the PLC is waiting for. During the Read you do get back status for the tags indicating if they are valid or not.
You could do something with that information maybe
Bill S.