Rockwell-automation FactoryTalk View Site Edition Users Guide Instrukcja Użytkownika Pobierz pdf (Strona 565)

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20 • CREATING EXPRESSIONS

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20 • Placeholder

To examine multiple alarms at once (a set of alarms for a machine in a particular area, for

example) use a wildcard character in the expression argument.

For more information about using FactoryTalk alarm functions in expressions, and for

examples, see Chapter 12, Setting up FactoryTalk alarms.

About using FactoryTalk alarm names in expressions

To supply a FactoryTalk alarm name for an expression, type it in the Expressions box, or

click the Alarms button to browse for and select one or more tags in the Alarm Source

browser.

You must specify an alarm source when you use the built-in FactoryTalk alarm functions

in an expression. An alarm source might be a single alarm, or an area containing several

alarms.

When referring to an alarm source, you can use an absolute or relative reference.

Enclose alarm names that contain dashes or start with a number in brackets {} when you

use them in an expression. Also use brackets when using wildcard characters (* or ?) to

represent multiple alarms.

You can also use tag placeholders in alarm names, to substitute values for the placeholders

at run time. For more information about tag placeholders, see page 16-35.

Using if-then-else logic in expressions

Use if-then-else logic in an expression to carry out an action conditionally, or to branch

actions depending on the statements in the expression. You can also use if-then-else

statements to repeat actions until a condition changes.

To build conditional expressions, use the relational operators and the logical operators for

the statement, and values.

The if-then-else structure is:

If statement Then value1 Else value2

This wildcard character Does this

? Matches any single character.

* Matches any number of characters, including the

backslash (\) character.

Do not confuse the if-then-else expression with the If command. For details about the If

command, see the FactoryTalk View Site Edition Help.

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