Chart Dataset for Realtime Trend


I want to use a chart (and sometimes sparkline chart) to trend last 8 hours of a process value. When I bind the data to a historical tag should it automatically create a dataset for the last 8 hours? The datasets just have a few rows but definitely not enough for 8 hours of 60 second interval data. What am I missing here?


No, the chart timescale is configurable. What kind of chart is this? (And are you using Vision or Perspective? You didn't mark this post for either.)

Also, note that, by default, slowly changing analog values won't make many rows in the DB. Adjust the tag's deadband and min/max recording intervals if necessary.

I'm using the Chart (not Easy Chart) object in Vision.

Then you are responsible for setting appropriate time boundaries in your history binding. Be aware that the classic chart autoscales its domain axis, by default, to the min and max timestamp actually present in the data.

The images below show the setup for this chart and historical tags. If I unselect Auto Range the X axis changes to one month instead of 8 hours which seems backwards. The historical tag data is set to last 8 hours. However, the blue line on chart should be at 0 not 3000. The chart doesn't appear to be updating. I added a numeric display for this tag to see what the current value is reading which you can see in bottom right hand corner of screenshot (Test_FIT_101). Last screenshot is the Dataset bound to this chart.



Try using "Closest Value" instead of time-weighted averaging, along with "On Change" samples. This should show you what got recorded.

If you think it is still odd, go look at each tag's history recording constraints (and deadband).

{ With on-change samples, you might want to use four separate datasets, one per pen. }

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Thanks again for your reply. Changing "Closest Value" and "On Change" seemed to help at first but then the chart appears to stop updating. You can see how on the image below the live values don't match up with pens on right side.

In your screenshot, you have an absolute poll rate of 60 seconds. That means the query will run once per minute. Change that if you want faster updates.

Called tech support. They recommended using the settings below and changing the history deadband setting on each tag from Auto to Discrete and it started working. However, after talking to tech support and playing with the Easy Chart, I've decided to use this object instead since it is customizable enough to get the look I was after for the display. Thanks again for you help.


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