Page 1 of 1

Subscription to data change misses values

Posted: 23 Sep 2019, 15:33
by kube
Dear all,

We are testing the evaluation version of the C++ OPC UA SDK and our goal is to create a subscription to a series of nodes, whose value is changed by an OPC UA server each 100 ms.
The issue is that our client is missing some of the data changes performed by the OPC UA server.
So my questions are:

1. The OPC UA protocol actually supports working with real time applications? (Sorry for asking, but I am a novice in this field)
2. I have tested configuring the subscription with different values of SamplingInterval and QueueSize, but nothing seems to change the amount of data received by the client.
3. In our use case is correct to use the data change protocol instead of the event protocol? (I read something about this in other website). What is the difference between both?

Thank so much in advance,
Kube.

Re: Subscription to data change misses values

Posted: 03 Oct 2019, 10:13
by JohnWick
Hello,

1. Yes
I have tested configuring the subscription with different values of SamplingInterval and QueueSize, but nothing seems to change the amount of data received by the client.
2. The client is missing the data change notifications, because of the QueueOverflow (Generally, this happens when publishingInterval = 2 * samplingInterval (PS: just an example)). Try it by changing publishingInterval. make sure to have publishingInterval is a bit faster than the samplingInterval.
3. Yes, for the values you have to use dataChange and you are doing it right.