Avoid interpolation of "on-change" historical tags in chart (or table) - ie show a step change

[dean.mcclure]

So when I run a query on an on-change history tag with natural I will get:

and fixed with no interpolation I get what I expect

If I add another tag with “natural” “min/max” it adds in the extra lines as expected

but if I change this from natural to “fixed” “min/max” (which is what I use for charts in order to keep them reasonably responsive) it starts dropping the end values which shows up as missing data (note that the time is not across all values, it appears to have just ignored the end values before converting to “fixed” and using the truncated time range).

Now here is where it gets weird.

If I add in a fixed interval tag (shown below in realtime natural)

it actually starts interpolating even with the interpolation off (although it gives slightly different results)

“fixed” “min/max” with interpolation on

“fixed” “min/max” with interpolation off

This is causing havoc with my charts as well as analysing historical data which is pulled out as all of the step changes (setpoints for example) are shown with linear gradients and any calculations based on this historical data all comes out incorrect as it’s taking an interpolated datapoint.

Any idea on how to fix this?

[alexpavlic]

I am also unsure how to prevent this. A setpoint step change (e.g. instantaneous change from 20% to 50%) is shown as a linear gradient even though there is only a single record in historian. Ideally this would be depicted as a horizontal line from the last historian record to show the actual value.

[pturmel]

Have you tried discrete mode instead of analog mode for your tags?

[alexpavlic]

I've changed my tag's History -> Deadband style to Discrete and viewing the trend on an Easy Trend with Style = Digital is exactly what I'm looking for.

Is there any way to achieve this on a Sparkline Trend, or should I just use a real-time Easy Trend?