Download the Solution Example here: TagEstimatedValues.dbsln

  • Solution Name: Tag Estimated Values
  • Software Version: v10
  • Keywords: Tags. Tag Estimated Value. Tag Historian Value. Trend PlayBack. Display PlayBack.

Summary

Example showing the difference between DisplayValue and EstimatedValue in a solution.

Technical Information

DisplayValue Tag Property

The Tags are used on display, you use the syntax Tag.TagName. 

Each TagName has many properties like Quality, TimeStamp, Value, Min, Max and others. So in fact when you add Tag.TagName to a display, the system is selecting the Default Properties to the value, which is the property Value.

It is possible to customize that behavior, so the display instead of showing the Value of the tag, will show its estimated value, or historical data.

The DisplayValue field of that can  will show one of three options:

  • The Value tag property (the tag's current value),

  • The EstimatedValue tag property (which is a user-defined calculation).

  • The Historian Value of the tag at an specified DateTime

Using this infrastructure, you can calculate the EstimatedValue for any simulating, or process analysis reason,  and choose whether your display or another system will show the units dynamically.
The method to switch between multiple display values is through the "Client.Context.DisplayValueMode" property, where each given number changes its DisplayValue (i.e., if set to 0, it will show the original value; if set to 1, it will show the estimated value).
In the given example, the current estimation is done by obtaining the first three significant digits of your original number.

Client.Context.SetDisplayValueToEstimated(); // the DisplayValue will show the Tag EstimatedValue property

Client.Context.SetDisplayValueToCurrent(); // the DisplayValue will show the Tag Value property

Showing Tag Historian Value to PlayBack

You can also change the Client.Context.DisplayValueMode, to Historian information using the method:

Client.Context.SetDisplayValueToHistorian(DateTime selectedDateTime)

This command will set the DisplayValue property to the tags show the HistorianValue at the selected DateDate. 

This features can be used to PlayBack the contents of an HMI display. By calling the method to the desired date time. It can controlled by an operator input, scripts. it can be one specific time or playback at a give interval, your solution logic when control when new values shall be loaded.

In order to accomplish the task, the system will look for the Historian storage for that tag, therefore only tags that are enabled to Historian can play back. 

The system will run more efficiently if all tags of the display used for playback are in the Historian Table.

To make the HMI display to show again the current value for tag, use the command

Client.Context.SetDisplayValueToCurrent()

Reference Information

→ See Tags for more information.

In this section:

  • No labels