History trend view

Questions regarding the use of the UaExpert.

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cesar
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Joined: 02 Sep 2021, 07:21

History trend view

Post by cesar »

Hi

I'm trying to retrieve a trend view from some variables, i see there are some historized values in the Log view, but i cant see any graphic. Also reset view seems doesn't work.

Is possible to set the Y-Axis to any automatic values ? or reset the view to the historized values?

Thx

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Support Team
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Joined: 18 Mar 2011, 15:09

Re: History trend view

Post by Support Team »

Hello,

the DataLogger-View is a simple data logger that subscribes for value changes of a given Node and logs the information into a comma separated file. This is what the document description says. However, this has nothing to do with UA-HistoricalAccess. The Client (UaExpert) is logging the data as it gets the data, if not connected, no data is logged. If you connect later, you can't get the data backwards in time, logging means just "logging current data".

The Histrory Trend View can be used for obtaining historical data for one or more OPC UA Nodes. The received values are displayed in a graphical trend view. This is what the document description says. However, such Nodes must have the "historizing" attribute set "true", indicating that the UA-Server has historic data for this particular node (and not only current data). A serverside history of values for some particular nodes is where "UA-HistoricalAccess" comes into play. For such nodes the client can request data backwards in time (and ask the server to aggregate, find min/max, calculate average or mean over a requested time interval, and much more). But the client (UaExpert) can only display such time series of data in a graphical trend view.

So we have two fundamentally different things here:
a) Data-Logger View (simple client-side recording of live data)
b) Hisorical Trend View (simple display of server-side historized values)

And as a side note: yes, in case of UaExpert it must be "scalar" values to be displayed, because a two-dimensional pane with time axis just can display scalar/numeric values. Because graphical display of multidimensional arrays, or nested structures, or arrays of matrix is not an easy task for graphic display. But remember, in general OPC UA would allow for historizing structures, multidimensional arrays and complex objects of all kinds, but just poor UaExpert can not graphically display them (log windows shows error: data type not supported to be displayed).
Best regards
Unified Automation Support Team

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