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  5. QuickOPC-UA in COM
  7. Reading, Writing, Subscriptions
  9. Problems Writing and Reading Values

Problems Writing and Reading Values

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28 Oct 2018 06:40 #6799 by support
Replied by support on topic Problems Writing and Reading Values
Hello.

For reading: Normally, the read is performed with "maximum age" (defaults to 1 second), which can lead to reads from server cache or using client's memoized value. if you want to be sure that you are reading the most up-to-date value from the server, you need to specify a read from the Device. This can be done in DAReadParameters that are passed to the method; in COM, you will have to switch to the ReadMultipleItems method, because there are no method overloads, and the ReadValue COM method does not allow to pass DAReadParameters in.

For writing: Are you sure that you detect any possible errors thrown by the WriteValue call? QuickOPC always throws an error when the OPC Server returns a failure code from the OPC write operation. If no error is thrown (and you do not ignore them), then the problem is practically guaranteed to be on the server side.

Best regards

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26 Oct 2018 10:11 #6796 by Alessandro Tessari
Problems Writing and Reading Values was created by Alessandro Tessari
Hi,
i'm having problems reading and writing values in an application i've developed, seems like some values do not refresh.

The communication in the application is really simple, i use client.ReadValue and client.WriteValue calls only.
Sometime happens that the value returned by the ReadValue function is not what i see in the OPCserver and, similarly, the WriteValue function fails to update the value in the OPCserver.
The strange thing is that it happens only for some items, and not every time.
For reference i'm using version 5.51.465.1 in a vb6 application.

Am I missing something??
Could it be caused by a different configuration on the OPCserver items??
Any suggestion on how to solve the problem wuold be really appreciated. If more details are needed feel free to ask.

Thank you in advance!!
Alessandro

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  1. Forum
  3. Discussions
  5. QuickOPC-UA in COM
  7. Reading, Writing, Subscriptions
  9. Problems Writing and Reading Values
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