Hi all,
I'm running up against a problem with trying to communicate tags over OPC-UA between an Ignition Gateway and 4 Siemens S7-1500 series PLCs. At a small number of tags, I seem to have no issue, but once I add about 10 UDT instances, I start getting tag quality problems, ranging from GoodOverload to BadTimeout, even on tags that were previously alright.
I've thrown just about everything I can think of at this. I've split tags within a single PLC into separate tag groups, hoping that might alleviate some traffic. I've maxed out all the OPC-UA settings on the Siemens side. I've been meticulous about assigning tags to tag groups, even going as far as to place everything in driven tag groups that I drive based on the currently active page.
I don't really know what else to try. Does anyone have any experience using Ignition with Siemens S7 PLCs, and how do you optimize OPC-UA communication with it?
Are you subscribing to every tag within each structure individually, or are you subscribing to the structure values as a whole (ends up being a Document in Ignition)?
How big are these? You're not telling us much of anything without more detail about these UDTs.
Are you subscribing to every tag within each structure individually, or are you subscribing to the structure values as a whole (ends up being a Document in Ignition)?
I've tried both ways. With the individual tags method, I can interact with and monitor them how I want, but I have these quality problems.
With Document tags, I seem to be able to poll them better (though not fully tested yet), but I can't seem to write to an element of that Document at all. I kept getting the error:
Bad("Bad_TypeMismatch: The value supplied for the attribute is not of the same type as the attribute's value.")
I tried multiple ways around this, to no avail. But all of those have involved the use of system.tag.writeBlocking(), which may not be the right way to go about doing this.
How big are these? You're not telling us much of anything without more detail about these UDTs.
Forgive me for not providing much detail. I'm trying to juggle a lot right now, and after staring at this problem for a while, I'm no longer sure what information is relevant. Please ask me for clarification, and I'll provide what I can.
Here, the UDTs vary wildly from just a few bools and a string; to large, nested structures that can have several hundred tags inside. A mid-range UDT, which is what I had in mind, probably contains 100-150 base tags within it.
Here's an example of a mid-sized UDT that's currently working.
Well, the bottom line is that the Siemens server will perform drastically better if you read only the top level structures and use the derived tags with jsonGet/jsonSet strategy (described here and elsewhere) to read/write the tags. Unless the structures contain some kind of system type that results in a "swiss cheese" structure that can't be written to, writing should generally work.
The problem with this strategy is it's a real pain in the ass to set up and work with.
I've seen others do an end-run around the Monitored Item limitations in the Siemens server by just using dedicated Tag Groups set to OPC polled/read mode instead of subscribe mode.
