Is there a way to directly reference tags in devices without adding them as tags in the Ignition database first?
I’m working with AB PLC, and currently I’m dragging the whole controller tag folder from the PLC to Ignition to create tags and then building my displays, but if I change tags or add new ones in the controller, it’s a bit of a pain to have to re-create all the Ignition tags each time (Ignition is so fast with adding the tags that it’s quicker to delete and recreate them all rather than pick the ones I need). So I’m thinking maybe there’s a key piece of the puzzle I’m missing here in how to directly reference tags, so I don’t have that step in between. Do I need to create a new tag provider that is linked to the PLC directly?
Any assistance appreciated…
-Greg
No, you’re not missing anything, it works like you’re using it (minus the part where you delete all the tags instead of just finding the one you added or remove; that’s not what people usually do).
The only thing I might add is that you can read or write directly to tags in the OPC server using the system.opc.read/write scripting functions. These work on OPC addresses, so the tag doesn’t have to exist as an Ignition tag to read/write to it.
Let me add a little bit about what’s going on.
When you create an Ignition OPC tag (any tag you drag from the OPC browser, from any server, or tags that you create as an OPC tag) what you’re really doing is making a tag in Ignition and a subscription for that tag on the OPC server that tag is from.
Subscribing to an item is not free; typically it means that server now has to poll the PLC for that value along with any other values it’s already polling.
With that in mind, it should become immediately obvious that you do not want Ignition to auto-subscribe to every tag on every device on every server, as they get added or removed, simply on the off chance that you might want to use that tag in Ignition. (and that brushes over the fact that the OPC servers can’t/don’t indicate to us that a tag might have been added or removed).