We lost power to the whole plant on Tuesday, about 20 minutes. When it came back the sump pump in the pit under press 2 ran on its own. No start from the HMI and nobody was down in the pit.
Controller's a 1769 L30ER with a PF525 on the pump. Start is an OTL on a run bit from the HMI start button, stop is an OTU from the stop button and from the high current alarm.
I checked the HMI log first and there's no start press anywhere after the restart, so then I pulled the drive fault log and that's empty as well, although the drive reckons it got a run command from the PLC.
Has the L30 got a battery in it that could be flat, or is the HMI firing a start when it reconnects? I've got to tell the safety guy on Monday why a pump started on its own, so any ideas which of the two it is?
Was the pump running when the power went off? If it was, the run bit was on, and an OTL bit keeps its value through a power cycle on Logix. No battery in a 1769 L30ER, the program and the tag values come back exactly as they were.
It was running, yes. It had just been started to empty the pit before the outage. So the bit sat there through 20 minutes of no power and the drive got a run command the second it had power back. We spent an hour looking at the HMI for a start that never happened.