Rockwell Automation FactoryTalk View Site Edition Users Guide - Manual (Page 632)

F ACTORY T ALK V IEW S ITE E DITION U SER ’ S G UIDE
24–4
• •
•
•
•
These are the tasks involved in setting up derived tags for an application:
1. Create the derived tags in the Derived Tags editor in FactoryTalk View Studio.
2. Set the maximum update rate in the Derived Tag Setup dialog box.
3. Save the derived tags component and give it a name.
To create a derived tags component
1. In the Derived Tags editor, specify the tag that will hold the derived value and type a
description of the tag.
2. In the Expression box, create an expression that will determine the derived tag’s
value. For information about expressions, see Chapter 20, Creating expressions.
3. Click Accept.
4. If the derived tags component is to contain more than one derived tag, click Next to
create another derived tag.
5. Repeat steps 1 through 4 until all derived tags for the particular component are
defined.
6. From the Setup menu, select Derived Tag Setup.
7. In the Derived Tag Setup dialog box type a description of the component and specify
a maximum update rate, and then click OK.
8. In the Derived Tags editor, click Close.
9. Specify the name of the derived tags component and then click OK.
For details about options in the Derived Tags editor and in the Setup dialog box, click
Help.
About the maximum update rate
The maximum update rate is the fastest rate, at which the value of any derived tag in a
derived tag component can be updated.
The maximum update rate also determines the fastest rate, at which data servers can send
changes in tag values.
Set a maximum update rate separately, for each derived tag component you create.
Set the update rate as fast as, or faster than, the rate, at which the values of tags used in the
derived tags component change, unless it is desirable to miss changes in tag values.
Expressions containing derived tags are evaluated only when the value of a tag or function in the
expression changes.