Experimental Physics and
Industrial Control System

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<== Date ==>		<== Thread ==>

Subject:	Re: [EXTERNAL] Re: opc ua
From:	"Sinclair, John via Tech-talk" <tech-talk at aps.anl.gov>
To:	tech-talk <tech-talk at aps.anl.gov>
Date:	Fri, 26 May 2023 15:58:51 +0000

I have previously installed the python opcua (actually opcua-asyncio) for the server simulation. The server creates the object MyObject with a member variable MyVariable.

The opcua-asyncio python client reads this as follows:

# Get the variable node for read / write

var = await client.nodes.root.get_child(

["0:Objects", f"{nsidx}:MyObject", f"{nsidx}:MyVariable"]

)

value = await var.read_value()

As suggested below, I tried

field( INP, "@opcua1 str:123,\"MyObject\".\"MyVariable\"" )

I also tried

field( INP, "@opcua1 str:123,\"MyObject.MyVariable\"" )

field( INP, "@opcua1 str:123,\'MyObject\'.\'MyVariable\'" )
field( INP, "@opcua1 str:123,\'MyObject.MyVariable\'" )

In every case, I get the error message from the IOC:

Error reading from node: BadNodeIdUnknown

-----

In the server code, I can print the namespace index and node id which, for the above is 123 and 2 respectively.

Doing

field( INP, "@opcua1 num:123,2" )

does work and gets the correct value.

Thanks,

John

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Jörn Dreyer via Tech-talk <tech-talk at aps.anl.gov>
Sent: Friday, May 26, 2023 1:54 AM
To: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: [EXTERNAL] Re: opc ua

Am Freitag, 26. Mai 2023, 06:18:51 CEST schrieb Blomley, Edmund (IBPT) via
Tech-talk:
> Hey,
>
> > Saying:
> > field( INP, "@opcua1 str:123,MyObject.MyVariable" )
> >
> > does not work but I could find nothing in the documentation that describes
> > the syntax for this case.
> I think you are missing quotation marks around the strings. For your case I
> would try:
>
> field( INP, "@opcua1 str:123,\"MyObject\".\"MyVariable\"" )
>
> In general I find it helpful to use a OPC UA client to connect to the OPC
> server and look up the proper names of the relevant channels. For example
> this one: https://urldefense.us/v2/url?u=https-3A__www.unified-2Dautomation.com_downloads_opc-2Dua-2Dclients.html&d=DwIFaQ&c=v4IIwRuZAmwupIjowmMWUmLasxPEgYsgNI-O7C4ViYc&r=y1ySv2e6R1vXjM6-S-0q8nP52didqNXa2-iA6BX9G3w&m=jo1RgfpgortAIJVWuXWuI8DHNQ8N-IytVG--U3aloVKHHB650IhQAhzS0kLB_xzj&s=Apx5AxvkpcpVpVguN0iATlc-zoHyzlgDH5fRnexGdzk&e=
>
There is also a Python program called opcua-client that you can install via
pip.

Regards
Jörn

References:: Re: opc ua Blomley, Edmund (IBPT) via Tech-talk; Re: opc ua Jörn Dreyer via Tech-talk

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ANJ, 28 May 2023

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System