Easy Chart not trending properly

I have an Easy Chart setup for 5 PID loops. The SP and PV for these loops have been flat-lined for over 15 minutes, but Easy Chart shows the PV has been ramping. In other words, PV and SP have stayed constant the whole time but Easy Chart shows SP has been constant while PV has been moving in a straight line:

It almost looks like it is drawing the PV line from the highest to lowest value over the past hour instead of trending the actual value based on its timestamp. Any ideas what is happening here?

Set the chart mode to X-Trace and then move the mouse around on the chart.
It will tell you the exact values at each point in time.

The chart modes are Manual, Historical, Realtime. I don’t see X-Trace

Right click on the chart.

Got it. What is happening is the trace is drawing a straight line across instead of plotting it.

Are there actual values there? Or is it interpolating?

The value is being interpolated instead of plotting the actual value versus time.

I think your issue is there is no actual value for that time frame, so it is interpolating from the last value in the database? I can’t reproduce what you are seeing though.

There are values. MySQL is the datasource and I see good values with a timestamp for every second when I do SQL query in MySQL. On Easy Chart I see what appear to be interpolated values

In MySQL I see this data:

In Chart when I select the dataset I see that the data for SoftPLC_PD9_1_PV does not match the MySQL data source:

The data in MySQL is what I want to trend, but neither Chart nor Easy Chart are doing it. It seems to be deriving different data or doing some aggregation instead of showing the value from history

A clue: I put the data in a table and all the PV values seem to have a bad status or something. It is not clear to me what this means

FIXED! Ignition tech support is very good and they happened to check something I had taken for granted; the scan class. I had a scan class called FAST that somehow got set to a really big number. When I changed it to 1,000 msec things worked. That was the core problem. Other issues that had confused me:

  • The misleading history configuration Value Mode which intuitively would be Analog but should actually be Discrete; I think those enumerations should be changed to something like Interpolate/Actual.
  • I also had trouble pointing data to the Transaction Group versus the automatically created history table. To get data into Easy Chart from a Transaction Group it needs to be a Database Pen instead of a Tag History Pen.

Thanks tech support!