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Cannot view DeltaV in Connectivity Explorer

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20 Feb 2024 17:45 #12573 by support
Examples for OPC client and subscriber development in Python are now on GitHub: github.com/OPCLabs/Examples-QuickOPC-Python .

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21 Nov 2023 13:23 #12384 by support
Note: QuickOPC now supports Python in much better way, cleaner syntax, and public packages (pypi.org/project/opclabs-quickopc/) on Python Package Index . See What's new in QuickOPC 2023.2 for more information. And, over 270 examples are available in the User's Guide!

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18 Jun 2023 06:54 #11813 by support
Hello,

this may be because by default, QuickOPC reads ask the server to provide the value with "maximum age" of 1 second. In order to obtain the "absolutely latest" value, a read "from device" needs to be specified. opclabs.doc-that.com/files/onlinedocs/QuickOpc/Latest/User%2...m%20OPC%20Classic%20Items.html

Unfortunately the COM API does not support method overloads and this has to be done in more complicated manner than in .NET.

In short, you need to use ReadMultipleItemValues instead of ReadItemValue (even if it is with just one value), and pass in an array of parameter objects, and iniside these parameters, the "read from device" can be specified.

Please have a look at the following example - switch to the VBScript tab which is closer to Python code:
opclabs.doc-that.com/files/onlinedocs/QuickOpc/Latest/User%2...ems%20from%20the%20device.html

You will use this example (rewritten to Python) with following differences:
- one element in an array (and not 3), if you ae just reading 1 item
- call ReadMultipleItemValues and not ReadMultipleItems
- the result(s) will be of type ValueResult and not VtqResult (see e.g. opclabs.doc-that.com/files/onlinedocs/QuickOpc/Latest/User%2...0multiple%20item%20values.html )

Best regards

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16 Jun 2023 12:30 #11810 by Mattias
I created a 32 bit python driver and connection now works good. I never managed to set up a UA server as I am not in charge of the DeltaV system, only using it.

Anyway,
I am now using client.WriteItemValue and client.ReadItemValue to monitor, controle the deltaV system. I now realized that my read values are not always updated, and sometimes them are showing 0.0, even if i can verify updated (correct) values on the server using OPCWatchIt. Is there some way of refreshing values, ore possibly clearing cash to avoid this?

I am currently using the OPC da example for python with client = win32com.client.Dispatch('OpcLabs.EasyOpc.DataAccess.EasyDAClient').

Greatful for any help.
//Mattias

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09 Jun 2023 10:08 #11805 by support
Hello.
A demo would be truly helpful.

OPC UA is not based on COM and thus there won't be any 32/64 bit issues like this. And it is modern technology and a way forward. Sometimes it can be troublesome to do the security correctly (certificates), but if you are considering it, certainly there are no objections from our side.

Best regards

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09 Jun 2023 06:40 #11804 by Mattias
Ok, thanks anyway.
I am still hunting down a demo you can run for evaluation, I hope something can be solved there.

One additional question. Our DeltaV is currently set up as a DA server. Will anything improve if I set it up as a UA server instead? The reason for the current DA setup is to align to another lab we have, but if DA is causing problems I am happy to swap.

Mattias

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09 Jun 2023 06:09 #11803 by support
No, thank you. We would actually need to manipulate registry and possibly even install our development environment there. And a lengthy process indeed. Nothing that you or we want to happen on the actual computer used for anything else.

Regards

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08 Jun 2023 14:05 #11801 by Mattias
Re " if we got access to actually investigate in detail the computer":
The DeltaV system we are using is firewalled off, but if can be of any help I can set up a Teams meeting where we can poke around to identify any strange stuff on the computer.

//Mattias

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08 Jun 2023 13:27 #11800 by support
Hello,
what do you mean by "it still looks the same"? Are you referring to the bitness text in the About box, or to the "CoCreateInstanceEx: Class not registered", or both?

Re "Regarding the 32/64 bit thing! Will the win32com.client connect as 32 bit also if python is running 32bit?": Yes

Regards

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08 Jun 2023 13:23 #11799 by Mattias
I tried the -32BITREQ+ but it still looks the same.

Regarding the 32/64 bit thing! Will the win32com.client connect as 32 bit also if python is running 32bit?

//Mattias

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