Scann Classes Understanding

Hi everyone,
I’m trying to understand “Scan Classes” in order to achieve the following :

I have many tags which I’m not really interested on, so my aim is to set their “Direct” scan class slow polling rate to 0 seconds.

I’d like to put all those tags in a transaction group, and force there the “read” option, so when I’ll set a trigger, all those tags (“at least in my plans”) got forced to be read from the opc server, and then executing the transaction group.

When I started working on this, I noticed that when I was setting an amount of seconds higher than 5 to the “Direct” scan class, it would not be considered, and it would eventually poll value at 5 sec.

Looking everywhere to understand what I was doing wrong, I saw the same behavior in the Inductive University Video at the 0:50 time mark :

He is setting the polling rate at 30000 ms, but after 5 sec the values are getting updated.

I’d Like to understand what I’m doing wrong, and if I set a 0 sec scan class, if I can then force a poll from the transaction group options.


If you just need this data for a transaction group using OPC Read mode, don’t use Ignition tags. Just drag and drop directly from the OPC browser to the Transaction Group editor. Then you’ll get these items read from OPC precisely when your transaction group trigger becomes true. The OPC item that you use to trigger the rest will be subscribed at the base pace of the group.

Use Ignition’s OPC tags for user interface operations, tag history recording, and for event triggers. Only drag items from the OPC Browser to the Tag Browser for the data you actually need.

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OK, that’s is interesting, i never thought I could drop an opc item directly in the transaction group, and adding tags to the ignition tag system just for the ones i really need.

Thanks for the hint, I may need to go back to every project I developed until today I guess :slight_smile:

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