Easy Chart not plotting constant value

Ignition 7.9.14
Windows 10

I am trying to plot constant values on an Easy Chart because they are setpoint values that the customer wants to see when the measured values exceed the setpoints.

What confuses me is that sometimes the straight line of constant values is plotted, and sometimes it’s not.

I set the following properties for the Tag History for the setpoint tags:
Historical Deadband = 0.0
Historical Deadband Mode = Absolute
Value Mode = Discrete (tried Analog as well)
Max time between records = 1 Execution
Timestamp Source = Value

I would think with the Historical Deadband = 0.0 and Max time between records = 1 Execution, that I would always see a point plotted every 2 seconds (my scanclass interval). But I don’t, usually.

The Easy Chart properties are set as:
Tag History Resolution = 300
Tag History resolution Mode = Fixed
Allow Tag History Interpolation = True
Validate Scan Class Executions = True
Ignore Bad Quality Data = False
Bypass Tag History Cache = False

Any help is appreciated,

1 Like

Hi Bob

We had the same issue with some cool rooms.
We had to change the sample mode to periodic or tag group to make it record.
Otherwise you can set a constant Pen if the setpoint never changes.

The issue here is that the chart will not query for values that occur outside of the selected chart window, so if the value doesn’t change within your selected area and no historic value are recorded, then no line will be drawn. As @trentbliss said, you’ll need to start logging periodically. I’ve started setting my Max time between to 30s for all tags, or lower for more critical tags, to avoid this issue. Whatever value you set will determine the min chart window domain shown that will guarantee a trend line being shown

Thanks for this idea which does plot the value consistently.

But since this is a value that comes from an OPC server, now when connection to the OPC server is lost, the setpoint values continue to plot. For setpoints this isn’t a problem really. But even measured data that isn’t setpoints will have this issue when the data values don’t change for a long period of time. This is a problem to show the last measured value being still plotted as if new data is coming in even when the OPC server is no longer passing data.

Any thoughts on addressing that?

The quality should be bad in those cases, in which case I think there’s an option for how to show bad quality data :thinking:

Thank you for the suggestion.

Even when setting the property to ignore bad quality data (the quality is listed as “Uncertain” in this case) the values are still plotted.

I think I have found a solution that is not perfect, but the customer may be satisfied with.

1 Like

I hope IA put setting in chart that when we have bad quality the chart doesn’t draw anything.
We have same problem for perspective.