Subscribe OPC-DA Autosol vs Read

I have a connection to Autosol and can use scan class read to get data back. I am under the assumption that this is like a demand poll. Well, in Autosol we are using intervals, I would prefer to just subscribe to those tags and keep from double polling. My tags are structured like so connecting to a ROC800.


Example - EFM0000.69.3:0<TFLP>

When setting a scan class to subscribe, it does not show bad value, just null with unknown status.

Any ideas what I might be missing here?

I use a direct scan class set to slow rate of 1000 ms with OPC Data mode of subscribed. Then I just let Autosol handle when to poll.

Are your tags structured as shown above? Or are you defining the Interval at the tag level in Ignition?

I dont think I have any rocs but do have totalflow, controllogix, DF1, and various modbus devices. I dont see why the OPC Item would matter when it comes to the polling though, unless I am not understanding what you are trying to accomplish.

The way I look at it there are two methods:

#1 Let Ignition control the rate the tags are subscribed at.

#2 Let Autosol control the speed at which the tags are updated and have Ignition read the updates fast enough so that the user doesnt have to wait on an update.

I have always done #2.

Well I am fairly new to Autosol, we are migrating a system from IFIX to ignition that was using Autosol as OPC server. It has some tags setup with a <I1> for interval 1 at the end of the tag path from some of the IFIX exports. Such as this EFM0000.69.3:0<TFLP><I1>.

That is what I was referring too. In my case, I do want Autosol to handle the polling, as your #2 example. So, I should still get data whether I subscribe or read. So my tag path should be correct.

I have the scan class slow rate set to 30 minutes. I may just have it set too slow. I will try to speed up to 1 sec to see if I get better results.

Yeah I could see cases where you would want some tags at a certain interval and others at a separate interval. For instance, gas analysis tags on a roc meter run may only need to be pulled 1 time a day. I think the way I have it setup would be the way you would need it to be setup on the Ignition side to make use of that.

I played with the setting this morning. On the schedule you have setup for your devices you have multiple intervals. On mine, Interval 1 is what I use for my base polling. I added a interval 5 that was set to 1 hour. When I added to one of my tags the tag only updates 1 time per hour as opposed to the faster rate set in interval 1. I am assuming that Autosol is skipping those tags when doing its normal interval 1 poll so I guess the idea is that you can set different intervals for tags. Stuff that is important like flowrates, etc would be on the faster interval. Stuff that seldom changes, like gas analysis, can be on a slower interval, since it rarely changes. Assuming that Autosol is actually skipping those values when polling, this should save data and also make polling slightly faster. I am going to test it out more. In my brief test it appears that a demand poll would update all items.