Ignition tag/data subscription

Hi all,

I am building a historian and using the vision ad hoc trending tool for trending purposes. I do not have any other screens. The devices connected are two PLCs from Allenbradley.

I have imported around 8,000 tags in Ignition and only enabled historian on 700 of them. I am using the default tag group.
Default: Direct mode, Rate 1000, Subscribed

I can see the tags (historized and not historized) updating in real-time when I have Designer open. If I close Designer and only run the Vision client which has the adhoc trending tool for the purpose of trending the historized tags, will Ignition still request data for the tags that are not being historized?

Thanks in advance!

With direct mode, Ignition will poll the PLC tags with no client or designer open at all.

Thank you!

I am thinking to set mode to Leased and this is something I have to test. I am wondering if I am not showing the tags on the screen, will a leased tag that has historian/alarming enabled still request data from the PLC.

At the slow rate, or not at all if slow is disabled. Don’t use leased mode with tags you wish stored in history.

Also, avoid bringing OPC items into Ignition tags at all if you have no display or logic or history purpose–each adds communication load to the PLC.


If I am understanding this correctly, it makes for a complicated configuration as we will have to manage Tag Groups for tags to be historized differently from regular tags. Which implies that we need Direct Mode for Historian tags and Leased (to reduce OPC UA driver load) for non-historized tags (Vision/Perspective purposes). When a user wants to configure a “leased” Tag (Vision/Perspective) to be Historized they will need to remember to not only Enable History, but to put the tag in the correct Tag Group. Is this Correct? (Perhaps you some additional guidance on this as a best practice?)

Thanks in advance for your response.


I recently had a discussion with Inductive support about this. I managed to decrease my PLC communications load factor from >80% to <40% on a similar sized project by changing non-historized tags to a leased tag group, I only changed about 20% of the tags because I only set the tags I knew would be unlikely to ever be historized to the leased group.
Yes this means that every time you change a non-historized tag to be historized you will need to change the tag group as well.
When you generate your tags, you could set certain types of tags that you typically may want to historize to be direct and tags you don’t generally historize to be leased, that way you still make significant communications performance savings and you can still select what you want to historize without needing to change the tag group.
This was recommended by Inductive support so I assume it’s best practice.