OPC-UA server limit (Max PLC and Max tags) vs Kepserver

Hello Ignition’s passionated!

We have a KepServer connecting to 17 PLC. These PLC are running complex machine and have multiple tags. The most complicated one have more than 2 millions tags…

Now in Kep, we did “create tags” for all the PLC and we end up with a 800 MB config file. Also, Kep need about 4 minutes to start and almost the same to stop.

But in fact, we will read maximum 2000 tags per PLC. We could manually create only the required tags but it could become a nightmare to manage.

Let’s say I switch to the OPC-UA server of Ignition… How are managed the tags in it? Will I end-up with a ultra big gateway backup? Any other toughts?


It depends what kind of PLCs they are (and the driver you would use) and whether you actually tried to create 2 million tags in Ignition or just the ones you needed.

Hello Kevin,

We have almost exclusively ControlLogix PLC on version 32. And in the tag provider, we will create only the tags that are required.

I’m trying to understand how works OPC-UA under the hood.

With KEP, when I push the “create tags” button, it scan the memory of the PLC and all the tags in the PLC are created in KEP as static tags. It seems this is why my config file become so big (>800 MB). I could not push the “create tags” button, but then I would loose the possibility to browse the tags inside Ignition… So from the KEP point of view, my options are limited:
1- Avoid the create tags button: Config file will become much smaller, but I will not be able to browse the PLC tags in Ignition.
2- Continue to use the “create tags” buttons: Any config change in KEP become very slow due to the too big config file.

This is why I would like to know how Ignition’s OPC-UA driver works compare to KEP.

Thank you very much.

Ignition’s Logix driver scans the PLC’s tags on initial connect, and optionally monitors the PLC state change indicators to trigger rescan. This information is then presented to users on-demand in the Designer’s OPC Browser. There’s no equivalent to Kepware’s “create tags”, as it is handled automatically.

Ok. So Ignition create the tag list every time it connect to the PLC. That means the PLC tags are not created as static tags (and save in a file on disk) like in KEP. Am I right?

I don’t think the Logix driver keeps a copy on disk.

Beware of terminology, btw. Kepware may be a culprit here, but “Tags” can be an ambiguous term. A PLC has tags, which are named memory locations. An OPC server has items that typically point at a device’s tags. An OPC server may also have internal tags for its own status and metadata, also represented as items. Ignition has tags, which can contain internal data, various forms of calculated data, or data obtained from external sources via an OPC connection’s items.

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Thank you for the terminology lesson. I will take care. There a lot of confusion around that since even kep is using the term tag for the items.

The Logix driver browses every time it connects, and rebrowses any time it detects a program change.

Nothing is stored on disk. The symbols and template definitions are kept in memory. Browse structure is derived on demand from the symbol and template definitions.