Any OPC UA server for Logix that "properly" supports Logix UDT tags

[dmroeder]

In theory you could have a top level UDT and all other scoped variables in the single UDT and then read the single UDT.

Exactly, and because you can, someone will
In fact, I did some work with Motoman's MLX platform and this is exactly what they did. A single tag that is made up of dozens of UDT's for a total of 386k bytes. The ultimate torture test for any driver handling UDT's.

 

[AlfredoQuintero]

This is curious. Have you set up the UDT read as an Ignition tag?

On assumption that the struct is <= 512 bytes, it ought to be reading the entire struct in one read.

I have not had time to test the ignition solution. Not sure I will. The customer is evaluating FactoryTalk and we found Keptware does the job.

 

[AlfredoQuintero]

It gets complicated because UDT supports nested UDT, with no limit on the levels allowed, that I can find.

In theory you could have a top level UDT and all other scoped variables in the single UDT and then read the single UDT.

What I have found is that the OPCUA servers for Rockwell that so far I have tested correctly detect the kind of nested UDT structures you mention. The problem is that it seems some of them (like Keptware) can replicate the same UDT Tag structure into the corresponding OPCUA address space (one OPCUA node per tag includig UDT based complex tags), whereas other OPCUA servers simply configure the OPCUA address space by adding one OPCUA node for each element of the PLC tag.



It is not a problem of the Logix client capability of the OPCUA server, rather it is the way in which the product maps the OPCUA address space into the PLC tags.

 

[Mark-]

...correctly detect the kind of nested UDT structures you mention

Sure, we do it (can fetch and parse all UDTs), we just do not create one giant tag. Our "point/tag" system is designed for all communication protocols we support.

 

[rwang0417]

The problem in our case is the OPC UA client and the OPC UA server (talking to Logix) are oceans and continents apart. So having the OPCUA client poll hundreds of tags (i.e. OPCUA nodes) per second is probably not realistic. I have one idea that might sound crazy at first but I think is doable. Since the customer has a secure VPN between the computer room in Japan and the different factories in different parts of the world, I will advice them to use a CompactLogix to poll the UDT tags with a simple Logix program which I was able to develop thanks to Ken and others on a different post.

Hi Alfredo, do you mind sharing the link to the post you mentioned above? I am facing a similar issue that I need to collect a batch of data from one tag at a certain rate. The time interval between two data points needs to be accurate. My current solution is to create a data buffer and add some code (basically a timer and a few MOV blocks) to the existing ControlLogix (which contains the tag I need to read). The problem is that the customer does not want us to change the existing code in the ControlLogix. The method you mentioned that uses an added CompactLogix might be a great option for me. Also, I am exploring if I can use OPC UA subscription to achieve that. Any guidance is greatly appreciated!

 

[AlfredoQuintero]

Hi rwang0417 and welcome to the forum.

I think I was referring to the post below.
http://www.plctalk.net/qanda/showthread.php?t=132145

Whatever it is you are trying to do, if it is not related to the original purpose of this one post, my suggestion is for you to start a new thread with a subject that summarizes tour situation. That way you can have higher probability that someone with the expertise in that subject can help you. Good luck.