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How do you record events prior to the start of an event frame

Question asked by caffreys_col on Jan 30, 2020
Latest reply on Feb 3, 2020 by Dan Fishman

Ok, the topic title might be a little but more scary than what I really mean. What we would like to do is record data for a specified period PRIOR to an event occuring. For example, if I have a valve trip closed, I would like to see what the plant was doing for 1 hour prior to the trip so we can investigate causes of the trip. We might associate 3 or 4 signals (pressures, temperatures, flows, etc.) to the valve that could initiate the trip, and we would like to see what they were all doing prior to the trip taking place. While the valve is shut we would record an event frame (pretty easy to do; Valve = closed, then start event frame. 30 minutes later, close event frame). But I don't know how to record the information prior to the trip. I've seen reference to child frames but would have thought they are only generated when the initial event frame is started and can only record events from that time period onwards. 


Also what version of PI Vision do you need to show event frames on top of each other (similar to what Batchview shows you)? Is there a PI Vision replacement for Batchview (Gantt chart layout, batch overlays, etc.)? 


All help greatly appreciated!