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DataChange Notification when value doesn't change
May 14, 2019
19:20, EEST
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kkettinger
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Hello,

is it normal to not receive DataChange notifications when the same value is written to the server?
When i’m writing the same value to a variable to the server, the source/server timestamp doesn’t update
and we can’t recgonize that the value was written. We don’t know if the client is still alive.

Is this expected behaviour?

I couldn’t find if that is normal, so any clarification on this would be of great help.
Thank you!

Best regards,
Kevin

May 15, 2019
9:55, EEST
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Bjarne Boström
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Hi,

That is the default behaviour of OPC UA, unless you have set a DataChangeFilter with DataChangeTrigger STATUS_VALUE_TIMESTAMP (1.04 Part 4 section 7.12.2). By default the SDK’s MonitoredDataItems do not set a filter, therefore you will get only “STATUS_VALUE” changes, i.e. only if the StatusCode or the actual Value changes.

You can set it via MonitoredDataItem.setDataChangeFilter(DataChangeFilter).

DataChangeFilter filter = new DataChangeFilter();
filter.setTrigger(DataChangeTrigger.StatusValueTimestamp);
filter.setDeadbandType(UnsignedInteger.valueOf(DeadbandType.None.getValue()));
May 15, 2019
11:24, EEST
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kkettinger
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Thanks Bjarne, that helps me!

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