Creating and writing a tag for data created within LabVIEW

[Stuart Wilson]

I am recording times of a production sequence and trending them in the Historical Trend chart through the HMI Wizard in the DSC module. I am receiving each value from a Seimens plc through an OPC server. The trend alone doesn’t mean a lot for analysis, so I would like to add more data to the chart such as averages and targets which I have calculated in my block diagram. How can I create and write a tag for data (e.g. a calculated average) so that it appears on the graph with the historical data?

I have tried the write tag vi in the DSC palette, however it returns a "Tag Name is undefined" (see attached example). I can’t create the tag in the configuration editor because I have nothing to link it to apart from items on the OPC Server. If there is any other way of getting data from labview (not plc data) to appear on my historical trends then I would be extremely grateful for any input/examples.

Many thanks,

Stuart Wilson

[Donald]

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@Stuart Wilson wrote:

...How can I create and write a tag for data (e.g. a calculated average) so that it appears on the graph with the historical data?
I have tried the write tag vi in the DSC palette, however it returns a "Tag Name is undefined" (see attached example). I can’t create the tag in the configuration editor because I have nothing to link it to apart from items on the OPC Server ...

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Stuart,

You need to create the tag in the Tag Configuration Editor with tag access as Memory  (rather than Input, Output or In/Out).

As the LV DSC manual defines it, a memory tag is "a tag not connected to a real-world input/output point. Memory tags are used for user-defined calculation."  You don't need to link it to any OPC item and you just use the WriteTag.vi  to write a value to it programatically (I can't look at your attachment since I'm behind the times).