Calcs and Events - Latch value
I have a complex event trigger that I am having difficulty programming. I have a trigger that when the length has been reset (Previous length > current length - which we'll call A) and then the length is greater than 200 (where now the Previous length will not be > than current length). Is there a way to latch the first constraint to True when it becomes true (A) in order to use an and A with the second constraint?
so something like
A = if(PreviousValue('Length') or A, True, False) (But we can't use A where it is defined)
B = A and (Length > 200)
5 replies
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Hi ,
I'm having difficulty understanding what you're trying to accomplish. Could you provide some more detail or context?
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Thanks Steve
I'll try to be more specific. I have an event I would like to capture that requires:
1) The length to be reset - PreviousValue('Length') > Length
2) The Length needs to be greater than 200
3) Then when (1) and (2) are true I want to be able to create an event if another tag goes out of a calculated range.
(1) and (2) may not all be true at the same time, so I need the ability to hold a variable True when (1) happens, then (2) and (3) will always be True at the same time (if (3) happens at all). So my problem is being able to hold a value True even after PreviousValue('Length') > Length is no longer True.
I hope that helps make it a little more clear.
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Thanks for the clarification. I think I understand now, but I don't know if we have a way to handle this. Does the resetting of the Length happen at a set interval or set time of day?
If you had a Boolean tag that was set to True whenever the PreviousValue>CurrentValue, then used CountInStateNonZero when it exceeded 200, could you look back over a set amount of time to see if the Count = 1?
Scratching my head on this one.
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Thanks. I figured I may have to create another tag for this purpose. I was hoping to avoid that. To answer your question though - no the length reset can happen anytime during the day.
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Ok. You'll have to have a flag for the initial reset when the PreviousValue > CurrentValue. I can't think of a way to refer back to an "old" True state. Steps 1 and 2 from your previous message would have to be True at the same time. The tricky part might be determining when to reset Step 1 back to False. I thought if there was a predictable schedule of when this occurs, you could just do it based on a periodic calculation.
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