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I can write to an OPC server but not read

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19 Sep 2019 18:46 #7748 by mikeboiko
Sure, I'll try that out and will get back to you.

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19 Sep 2019 18:12 #7746 by admin
My is that you make the code change I recommended.

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19 Sep 2019 16:20 #7745 by mikeboiko
Thank you for the quick reply.
I tried performing Synchronous and Asynchronous reads/writes using the Kepware OPC client and both were successful. I don't believe that is the issue.
I don't have msbuild on my work computer, so I can't test out the change on QuickOPC. I'll try it out when I get a chance though.
Do you have any other ideas?
Here is some more info on the server from the Browser:
OPC Server
Technology: OPC-COM
Implements: (OpcDataAccess10, OpcDataAccess20, OpcDataAccess30)
Vendor:
ProgID: Yokogawa.ExaopcDACS1.1
Version-independent ProgID: Yokogawa.ExaopcDACS1
CLSID: {c14d1400-d13a-11d2-93b9-0060b067c684}
URL: opcda://STN0447/Yokogawa.ExaopcDACS1.1/%7Bc14d1400-d13a-11d2-93b9-0060b067c684%7D

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19 Sep 2019 07:21 - 19 Sep 2019 07:21 #7737 by support
Although I cannot be sure, the problem might be related to asynchronous method calls, which QuickOPC uses by default. Other clients might be using synchronous. And, getting properties is also always synchronous, which might explain the difference in behavior.

Although you cannot do this directly form the pre-built demo app, a suggested workaround is to disable the asynchronous calls, by this setting:

client.InstanceParameters.Mode.AllowAsynchronousMethod = False
(where 'client' is your instance of the EasyDAClient object). If you wanted to still use the demo app for it, you can modify its source code - it is available in the Examples solutions for C# and VB.NET.

In this respect, it can still be a DCOM issue, because the backwards channel (for callbacks) is separate, and its configuration might not be OK while the config for normal calls still works.

Best regards
Last edit: 19 Sep 2019 07:21 by support.

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18 Sep 2019 23:51 #7736 by mikeboiko
Hi,

I'm not able to perform read/write operations to a Yokogawa ExaOPC.

I downloaded the latest QuickOPC library (2019.1) for this test. Then, I opened EasyOpcNetDemo.exe to perform a test on FCS0317!202PC01093B.MV
- I am able to retrieve the value property (2) without issues. When I clicked "Get property value", I got: 14.95476
- I am not able to read properly, when I clicked "Read Item", I got the following error after waiting for approximately for 30s "Read not completed. This error indicates that it could not be verified that the requested read operation was completed during the timeout period. It is possible that the read operation will actually succeed or fail, but later. Increase the timeout period if you want to obtain positive or negative indication of the operation outcome. Other reason for this error may be that under heavy loads, topic request or response queue is overflowing. Check the event log for queue overflow errors (if event logging is supported by the product and enabled)."
- I am somewhat able to write, but with an error. When I clicked "Write item value" and put a value of 20, the OPC server changed to 20 as expected, but I got the following error after approximately 30s: "Write not completed. This error indicates that it could not be verified that the requested write operation was completed during the timeout period. It is possible that the write operation will actually succeed or fail, but later. Increase the timeout period if you want to obtain positive or negative indication of the operation outcome. Other reason for this error may be that under heavy loads, topic request or response queue is overflowing. Check the event log for queue overflow errors (if event logging is supported by the product and enabled)."
- When I clicked on "Get property value" again, I got: 20

During some read operations, I would simply get the "Access is denied." error.

I'm pretty sure that it's not a DCOM permissions problem either because I was able to successfully perform the exact same read/write operations with the Matrikon Explorer and Kepware OPC clients.

Please let me know if the QuickOPC library can be patched somehow to rectify this issue.

Thank you!
Mike

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