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Expected behaviour of Historical Access for constant data values

Sricharan Andugulapati

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06/24/2021 - 00:20

Hi everyone,

Please help me understand how OPC UA Server should behave when a historical variable is written with the same data for constant intervals.

Usecase: In field, Temperature sensor logs data for every minute. If the temperature remains same for an hour, Is the server supposed to store 60 values or single value?

I tried testing the same with UAExpert. However, the interface doesn't allow me to log the same data.

Please let me know the expected behaviour of sever in such cases.

Thanks in advance.

Randy Armstrong

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06/24/2021 - 02:25

It depends on the historian.

Some only archive on change. Other allow this to be configured.

If your historian is a UA client you would need to set to DataChangeTrigger to StatusTimestamp if you wanted to log all data.

The specification does not mandate one way or the other since it is a design decision internal to the server.

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