Scanclass duration over an hour

I’m still new to Ignition and I am the only software developer at my company right now, so I have some questions. If you know the answers, I would be delighted to know.

On the gateway, it says one of my scan classes ‘Query’ has a rate of 1 minute and a duration of 1 hour (8,000 tags). There are other scan classes that seem like they can’t keep up either. ‘Default’ has a rate of 10 seconds and a duration of 5 minutes 10 seconds (62,000 tags).

Is it a bad thing that these take so long, and what type of problems could this cause?
If I do need to move thousands of tags to a scan class with a slower rate, how can I find a list of tags in a scan class?
If I need to keep the tags in Query at a rate of 1 minute, would splitting the tags into multiple scan classes (with rates of 1 minute) be more efficient?


Sounds like overloaded drivers. Common when a newbie drags everything from the OPC browser over into the tag browser. (Don’t do that!) Look at your driver diagnostics device by device to see what your load factor is. An overall subscription load over 75 or 80% leaves no room for writes or other on-demand access.

Drivers don’t lead to long scan class executions unless you’re using OPC Polled Read Mode instead of subscriptions.

It’s probably exactly what he described - a scan class full of way too many slow query tags. Sounds like they may have tried to do the right thing by putting the query tags in their own scan class but there are too many or the queries are too slow.

Need more info from OP to diagnose.

Thanks for the replies. When I look at Devices (under Status/Connections on the gateway, right?) I see 2 PLCs with 0% load factor. They both have under 100 tags.
We can’t use the OPC browser for anything but those 2 PLCs, they are just for utilities (One if for water and the other is electricity)

For tags monitoring the facility, we have to manually find the path for each tag in the process control system.

As Kevin noted, “Duration” isn’t going to be affected by OPC subscribed tags, which are the only items that are included in driver load factors. Query tags or OPC read tags are what you need to focus on.

External OPC Servers?

I am not totally sure. The gateway says it connects to the OPC-UA server on - which would mean its running in the same VM as the gateway?

Ignition is both an OPC-UA Server and an OPC-UA Client. Out of the box, it connects to itself for any devices managed by its own server. It can also connect to other OPC-UA servers. When connected to other servers, there are no corresponding devices in the status area. That area is only for Ignition’s own OPC-UA devices.

I think I’m following, what are the consequences of the scan classes having such long durations? I haven’t noticed any errors in our data collection and the window load times seem normal.

Without knowing what is running long, I have no way to advise you. Most likely you have somewhat stale data in your tags.

It’s been a while since I originally posted this thread, I was able to identify some tags that could be removed and a lot were moved to a slower scan class.
There is still a 35 minute duration… but at least it’s better

The reason I am coming back to this thread is that I was wondering what the difference in performance is between:
1 scan class with a 1 min rate and 2000 tags
2 different scan classes with 1 min rates and 1000 tags each