I am trending a tag in Ignition and also separately recording it in a transaction group. While the value in the transaction group remains fixed, the historical value either grows or decays by about 1 per 90 minutes. The value is "Tare Weight" and does not change often. Here is an example of the dataset I am using.
and truncated using LAG(ScaleTareWeight) != ScaleTareWeight so that it only shows when the value changes
Here is what an easy chart shows for the same tag between those times:
I cropped off the top of the picture, but it does go to 97 and then 98 at the same time the transaction data does.
I can provide more details if necessary, but before I take the time to do that has anyone else encountered something like this before?
I posted this before looking at the historical data in the database. The historical data does not show it decaying or growing and is consistent with the transaction group data. The values between 44 and 33 must be the data points that the easy chart creates to interpolate the values between those 2 times. I was not expecting these values to be included in the chart when I was using X-trace.
On the tag that is being logged via the historian, what is the "Deadband Style" set for?
You may be getting into a situation where the data you are reading in the historian database is stored as an analog type which uses dead bands etc... vs discreet which is the actual value. Your transaction group will be logging the actual value. So you may not be able to directly compare those values from a database query.
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If you need to correlate with other values, just use the transaction group.
