I have an ‘Off’ Scan class for preserving tags but not polling them. However, I’ve noticed that on gateway restart or OPC-UA module restart, the gateway will log the following message:
After this, that scan class will appear in the OPC-UA connections list with a polling rate of 100ms. In order to stop this, I have to go open the project that the scan class is associated with, adjust the polling rate to 1000ms, and then back to 0. After doing this, the scan class will return to ‘Closed’ and no longer poll, as intended.
A screen of the scan class’s settings:
Is there a better way to have a “No-Polling” scan class?
Is there a work around for this?
Why don’t you use a memory tag to hold the value instead?
I’m sorry, I should have expanded on that.
We are in the midst of an automation upgrade at a facility, that includes upgrading devices and restructuring ignition projects. These are old device tags, I am not keeping them for their current value. They are being kept during the migration for tag history, templates for rebuilds (how did we do it before?), etc. Many of them no longer reference the device they once polled, but still have some value.
That’s why I have an ‘Off’ scan class.
I was going off of this snippet from the user manual, which is why I was surprised it was not working, and posted it here.
Why not just Disable the tags?
This is for Driven or Leased scan classes, you are using Direct
@MMaynard - That’s so simple I feel kind of silly. Thank you.
@ethomason - Gotcha, I overlooked that detail.
If you don’t mind, what allows a Leased or Driven to accommodate a polling rate of 0, while Direct cannot? Is it just because it is a temporary / dynamic polling rate, rather than fixed at 0? Or a fundamental difference in the way the OPC-UA server handles the tag types?
Thank you both, I appreciate the assistance.