I have an event frame that I'm trying to capture each time the supply source changes. When the supply changes I want to store the current value and the previous value which then gets sent in an email via a notification rule.
The tag 'Supply' is stored in Historian as a Int32
In Asset Framework the tag is an enumeration of the value
Here is trend of the data changes to the tag.
What I'm expecting that when the event frame triggers because the 'Supply' value changed, I should be able to capture the previous value. That doesn't appear to be what's happening and I'm bit perplexed as to what's going on.
Supply_Tank and Previous_Supply should not be = otherwise the event frame trigger would be false. My attempts to retrieve the previous 3 events don't make sense with regards to what I'm expecting. Based on the tag being a stepped tag I'm expecting the last value captured but it appears I'm getting an interpolated value. Is this perhaps due to compression and exception?
I could add a Boolean tag from the PLC to use as a trigger but I'd like to understand the "problem" more before I abandon the current solution.