Rockwell Automation FactoryTalk View Machine Edition Users Guide - Manual (Page 95)

6 • Work with tags
6-11
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Use expressions to manipulate tag values
In many of the places where you can assign a tag, you can also use expressions to perform
logical or mathematical calculations on tag values. If you assign an expression,
FactoryTalk View monitors the expression value rather than the original tag value. For
example, your machine might send values to the data source in the form of temperature in
degrees Celsius. You could use an expression to convert the value to degrees Fahrenheit,
and then monitor the expression result rather than the original tag value.
If you can assign an expression, a Browse button is present in the Exprn column in the
editor or Connections tab.
To assign an expression, do one of the following
 In the Exprn column, click the Browse button, and then create an expression in the
Expression editor. Use this method if you want to check the expression syntax.
 In the Tag or expression column, type the expression. The expression syntax is not
checked if you use this method.
For more information about expressions, see Chapter 23.
Substitute tag names used in graphic objects
You can use tag substitution or Find and Replace to replace tag names and expressions
assigned to the connections for graphic objects. For example, if you assign a tag to
multiple objects in a graphic display, and then decide to use a different name for the tag,
you can create a new tag and then use tag substitution or Find and Replace to search for all
tag references with the old name, and replace them with the new tag name.
You can also use tag substitution to replace the tags contained in embedded variables.
For more information about tag substitution and Find and Replace, see page 20-38.
Type the expression here... ...or click the Browse button to open the
Expression editor.