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finding value of tag when another tag changes state

Question asked by caffreys_col on Jan 21, 2020

Hello everyone,

I'm having a little difficulty in getting a performance equation to work properly. I need to freeze the value of tag when another tag changes state but I can't get the PE to work. The PE is as follows;

If 'AI-2025_Override' = "On" then tagval('AI-2025', findeq('AI-2025_Override', '*-8h', '*', Digstate("On"))) else 'AI-2025'

 

What I'm trying to do is hold the value of an analyser while it's override is on. We calibrate our analysers daily, but don't want to effect any of the mass balance calcs we have when that takes place. For some reason the above PE does not work. I've checked the digital set for the override tag, and its states are ON or OFF (they are not case sensitive are they?)

 

Anyone got any bright ideas why the above does not work?

 

Thanks

 

Col

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