How to log and graph a variable only on specific conditions (non-periodic Tag Historian)

Ignition
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1

Hi all,

I’m using Ignition 8.1.48 with the Vision, Tag Historian and SQL Brigde modules, and I need help setting up historical logging for a tag only when a certain condition is true — for example, when a tag is 1..

Here’s what I need to do:

  • Start logging a tag value only while a condition is true.
  • Stop logging when the condition goes false.
  • Plot the logged values later in an Easy Chart.
  • Make sure the data is stored in the database, not just in memory.

I don’t want the tag to be logged continuously. I only want to store values while something is happening, like when a tag is ON, and stop when that tag is OFF.

What’s the best way to approach this in Vision?

Things I’ve considered:

  • Enabling/disabling the historian dynamically (not sure if that’s possible in Vision).
  • Using a memory tag with history enabled and writing to it conditionally.
  • Using system.tag.storeTagHistory() to manually push values into the historian.

Any examples or recommendations would be much appreciated!

Thanks!

2

The tag historian doesn't directly support this.

The SQL Bridge module is designed to do exactly this, with a suitable trigger and period.

You can also use a gateway timer event script to do this.

3

What if we toggle the Enabled property for Historian using scripting?

4

If you're okay with the tag not updating at all when the condition is not met, you could utilize a driven tag group, configured so that the tag only scans (and stores history) based on your condition. Follow the Driven Tag Group Examples, except set the Rate to 0 seconds.

5

That should work, with some changeover delay. But note that is a tag configuration property, and there is overhead and internal DB churn for doing that.

6

Seems to me it woud be better to do this at the tag value source level. If it's a PLC, clear the tag that's historized when the condition is false.