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Who applies timestamp to sourceTimestamp parameters?

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Who applies timestamp to sourceTimestamp parameters?

Postby chrisfb » 02 Jan 2018, 16:41

Hi,

I'm working in a development of a method for time analysis of OPC UA services which main feature is realize data access in real time (operations like read, write and monitoring).

For this work I'm using the timestamp parameters available in services and shared between client and server in the execution of these services. One of these parameters is the souceTimestamp that is used to reflect the timestamp applied to a data by the data source.

In most of cases the data source is a device like a PLC that in conected to field devices like a sensor, for example (OPC UA Client -> OPC UA Server -> PLC -> Sensor). Considering here that the server is installed in a dedicated hardware separated from PLC.

My question is who applies the timestamp to the data, PLC or sensor?

In the case where the PLC applies the timestamp to the data, in order to determine the moment when the sensor has captured the read value, I have to consider the scan cycle, or am I wrong?

Thank you very much in advance and I'm sorry for any English mistake.
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Re: Who applies timestamp to sourceTimestamp parameters?

Postby Support Team » 11 Jul 2019, 09:44

Hello,

My question is who applies the timestamp to the data, PLC or sensor?

That depends on the PLC and the sensor, some manufacturers have sensor modules that have own clock inside and hence the sensor can timestamp directly. However, in most cases you will probably have the PLC stamping when receiving from the sensor. Typically the PLCs get the data from their IO modules (including the sensor) at a certain point in time, one time in the main loop (get inputs, run main loop, do outputs, get inputs again, run main loop, and so forth...). Therefore if the main loop runs 200ms the sensor data timestamp will not get more accurate than that.

I have to consider the scan cycle, or am I wrong?

Not sure what you mean, the time stamp is as accurate as it gets. So there is nothing you could do (consider) about that.
Best regards
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