Every attribute in OPC UA has a sourceTimestamp and a serverTimestamp as you see here for example for the “batteryVoltage” node.
The sourceTimestamp and the serverTimestamp are the two basic timestamps of OPC UA. This is standard OPC UA functionality. We refer you to the standards for more detailed information.
Some background information in relation to our system:
The sourceTimestamp indicates the time of the last change of the value or statusCode and it should always be generated by the same physical clock (cfr https://reference.opcfoundation.org/v104/Core/docs/Part4/7.7.3/).
In our case, the sourceTimestamp is the measurement timestamp that you also see in the iQunet Sensor Dashboard (the timestamps of the measurements are the timestamps of the moment when the data download is finished for that axis).
The serverTimestamp is used to reflect the time that the server received a variable value or knew it to be accurate (cfr https://reference.opcfoundation.org/v104/Core/docs/Part4/7.7.4/).
In our case the serverTimestamp will thus be the timestamp of the moment when the measurement is received by the OPC UA Server.
Remark: for historical data nodes the sourceTimestamp is used to determine which historical values are to be returned (cfr https://reference.opcfoundation.org/v104/Core/docs/Part11/4.3/).