I am seeing strange data values on my power chart when I change my time span for viewing. So far I have seen it happen most on setpoint values where I have a tag that doesn’t change very often. These are integer values that may get changed once or twice a week. I’ve set the data to collect “periodically” every 5 seconds. When I view the tag in a power chart at a recent time interval (before the last time it was changed) it shows an old value (example 515) that is incorrect from the actual value being read (example 520). When I zoom out and look at the last 72 hours I see the current value accurately displayed (example 520). It seems as though if I am far enough back to see the last data change that was made then the current value is correct, but if I don’t go far enough back to capture the moment when the data value changed then I see the old value. I’ve seen a table that is using the same tag to display values in tabular form and it is not giving this behavior.
Has anyone else experienced this problem or know a setting on the power chart that I am not aware of?
thanks!
Try setting the tag history binding to “AsStored” to get the actual values recorded in the historian.
Then on your chart set the pen’s Interpolation value to CurveStepAfter. You’ll get a stepped “curve” which makes it clear where the data changes were recorded.
Tip: create a view with a table component and copy the chart binding to the table so you can inspect the data returned by the tag history binding. It can be quite illuminating - particularly if you create a second one beside it, paste in the same binding and then modify the query mode to PointCount or Periodic.
Thanks for the response, Transistor!
The problem I’m experiencing is not that I cannot see when the data is stepping, but rather that the “current” value shown in the power chart changes depending on the time span I have my power chart range set to. It isn’t consistent (e.g. at 36 hours back the current value changes every tag or every time I look at the chart), but it does seem to correlate to the last time a change was made to the setpoint value. For example, the setpoint on 3/7 was changed from 515 to 520. If I looked at the power chart on 3/9 for the last 8 hours, it showed my current set point value as 515, which is incorrect. If I expand my time range to look back for 72 hours it would correct the current value to 520. This is happening on many of my tags and it should be noted that the value also shows up incorrectly when I use x-trace/look at the actual trend on the power chart.
thanks!
So what settings are you using for the tag history binding?
What do you see when you make the same binding to a table component?