Source TimeStamp

[Marco1982]

Hi All,
On the OPC UA Expert, I find "Source TimeStamp"and "Server Time Stamp" in the center of the screen.
On the right under section "Attributes" I also see "Source TimeStamp" and "Server TimeStamp".

The problem is that the "Source TimeStamp" that I see in the center of the screen is different from the "Source TimeStamp" that I see under Attributes.

Perhaps the two "timestamps" even though they are called the same show two different types of information?

I hope I've been able to explain myself, I couldn't attach an image

[Support Team]

Hi,

the source-timestamp and the server-timestamp are delivered by the server with each data-value. UaExpert just displays what it gets.

The DA-View represents a "subscription to the change of the value attribute", whenever the server delivers (new) value, the source and server timestamp will be updated as coming with the value. If the value does not change, the timestamp will not change. Transfer "value on change" will reduce (useless) traffic.

In contrast thereto the Attribute-Windows shows an explicite "Read" on all the attributes of a specific node "on click" (the node that you have selected in the browse tree). With clicking on the node in the tree, the explicite "read" call is performed, hence the timestamp may be different, because you read at a different point in time. You can permanentely click on the refresh/update button top of Attribute-Windows (manuell polling), and try to catch up with the "on-change" delivery of the DA-View.

[Marco1982]

Thank you very much for your reply.
In this specific case I think it is different, in the sense that
I have the stationary signal (in fact I see yesterday's date in the DA-View), but the Source timestamps between DA-View and the Attribute section are different

Thanks
Marco

[Support Team]

Hi,

If the value has "changed" last time yesterday and you explicitely "read" today this may be the case, yes.

In OPC UA (same as in classic OPC) you can read "from cache" and you can read "from device", depending on the "maxAge" parameter given in the explicite "Read" call. Most clients set maxAge to "0" (or forget to setit at all), meaning that they want the value from the device (but not from cache). Now, if the source has no own clock, this may lead to a new source timestamp (and of course a new server timestamp).

Furthermore in OPC UA you can subscribe for value/status change (default) but additionally for Timestamp change, which allows to deliver information on (short) value changes back and forth to the same value again. Looking from outside the "value has not changed", but the source timestamp has, indicating that the value was, at least for a short period, somewhat different in between internal scan cycle. The monitored items setting give clients the ability to ask server for data change filter individually for each monitored item (UaExpert has such ability too).

However, UaExpert is not touching the timestamps, just display what it gets.