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09/11/2015
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I have a UA DA client that subscribes to value changes on a UA server. The client sets the sampling interval for the monitored items to 500 ms. The publish interval for the subscription is set to 1000 ms. The server is not revising my sampling interval or publishing interval.
Since the values are changing constantly, what I am expecting to see is generally 2 values for each item in every notification where the source timestamps are about 500 ms apart. However, what I am really seeing is generally 2 values for each item in every notification but the source timestamps are 10-20 ms apart. For example, in one notification I get a value at 20:19:53.2456344 and another value at 20:19:53.3466316. Then the next notification skips 700 ms and I get value at 20:19:54.0486762 and 20:19:54.2496868. So I am only getting about 2 samples per second like my sampling interval specifies, but they are not “evenly” spaced.
Is the servers behavior valid for the UA specification? Thanks.
10/02/2014
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Well, the sample rate is the rate at which the device is polled, if it takes a while for the first poll request to be returned I would expect to see something like this but if you have been connected for a while then the following publish responses should contain data that is more evenly spread out around the 500 msec sample interval. You could try an experiment and set the sample rate to 1000 msec and the publish rate to 2000 msec and see what the result is. I would also contact the server manufacturer and ask them if this is expected behaviour.
09/11/2015
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Thanks for the response. I contacted the server vendor and it turns out it is just an oddity related to some simulation tags.
So, my understanding at this point is that the timestamp changes should not generally exceed the sample interval of the monitored items. This is the information I wanted to verify.
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