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03/03/2017
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The few 3rd part OPC UA Clients I have worked with do not set the Data Change Trigger to look for a change in timestamp by default so if I subscribe to a node who's data does not change often (air borne particle counts in a clean room) I will receive an initial data set and nothing after that. Our customers are interested in knowing the data value at regular intervals not only when it changes.
So I know how to change this in a Client but I am not in charge of the Clients they use. I am building a Server and am wondering of I can do anything to "push" this data to the Clients. Does anyone have any suggestions?
10/02/2014
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First, the UA Server you are using needs to support that specific DataChange filter and I am not sure how many do. Usually the timestamp changes when a value or quality changes. A very few servers will change the time stamp when a write occurs even if the value written is the same that is already there.
The simple solution would be to have the client set to get changes and to poll/read on a set interval. You will at least get a response to each request with the current value.
The next would be to set the client to request that the server sample multiple time in one publish interval and to respond with multiple samples. Some servers will provide those samples regardless of change. However, the client has to be able to handle a publish response with multiple sample values for each item. Each sample result will have a timestamp of when it was sampled.
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