OPC UA variable reset
I have noticed a issue with OPC UA variables running PLCNext Engineer 2020.LTS / FW 2020.LTS:
We have 6 variables (BOOL) for enabling functions that are set via a HMI (Visu+). Those are only written via the HMI as toggle function. But some how those variables are set from TRUE to FALSE without user input in the controller (AXC F2152).
To be sure, I have a added log function and added password protection to see when a user input has occurred. Today I was checking the system again and could see that no user input has been done, but the variables have been set to FALSE.
There has been no power failure and the PLC was not restarted. So why are the variables set to FALSE without command to do so?
Peter Paul
Comments
Hi Peter Paul,
If you run the PLC without any OPC UA client connections (including Visu+), does the problem still happen?
It would be interesting to know if an OPC UA client is resetting this flag somehow, or if the reset is originating from the PLC itself.
~ Martin.
Hi Martin,
I have just run some test. The variables are reset because the OPC UA client is dropping the connection. I have no indication why the communication is been dropped. The log on the FL Switch 2306 shows no problems, PLC log only indicates that the OPC UA communication dropped for around 1500ms. I have run a cross communication to an simens ET200SP CPU and there the indication is that the AXC F2152 is dropping the OPC UA. Again, for around 1500ms.
Wireshark does show the same. As a fix, I have rebuild the function with an ResetSet - there should be no problem.
What is irritating me, is the fact that the project was running without those issues when running FW 2019.9.
As it stands now, I can't trust the updates in Engineer or in the firmware. Some issues are solved and new one show up. In my opinion, the gain in functionality is no longer offsetting the problems.
It is nice that we gain the PLCNext functions but in the first place, would I like to see that the "standard" PLC functions are working. Remember, there are two side of the story: Must have / Nice to have
As long as the standard PLC functions are not working, PLCNext is in my opinion a nice to have option.
OK, just so I understand the OPC UA problem:
In your case it appears that the OPC UA server is dropping the connection to the client, and you know this because the behaviour is the same with two different OPC UA clients (Visu+ and an ET200SP). When the OPC UA server drops the connection - for about 1.5 seconds - the value of the boolean OPC UA tag(s) changes from True to False, and this value remains when the connection is re-established to the OPC UA client. There is only an FL Switch 2306 between the PLC and the OPC UA client, and this does not indicate any comms problems.
If this is what you are seeing, then we will try to reproduce the problem here and find the root cause.
This particular problem does not seem to relate to PLCnext Engineer, but I understand your more general point. This information is all available to the relevant product managers, and I am sure that they are taking it on board.
~ Martin.