Rockwell-automation FactoryTalk View Site Edition Users Guide Manual de usuario descargar pdf (Pagina 547)

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Creating expressions

This chapter describes:

 What expressions are and where you can use them.

 Working in the Expression editor.

 Using tag names and tag placeholders in expressions.

 Using constants in expressions.

 Using operators to modify values.

 Using built-in functions.

 Using if-then-else logic.

About expressions

Sometimes the data you gather from devices is only meaningful when you compare it to

other values, combine it with other values, or create a cause-effect relationship with other

values.

You can use expressions to create mathematical or logical combinations of data that return

more meaningful values.

Where you can use expressions in FactoryTalk View SE

In FactoryTalk View Studio, you can set up expressions in the following editors:

 In the

Graphics editor

, use an expression to control the appearance of a graphic

object, or to display the value of an expression in a numeric or a string display object.

You can also use expressions to set the value of a tag, using the If or Set command.

For details, see the FactoryTalk View Site Edition Help.

 In the

Derived Tags editor

, specify the name of a tag that will store the result of an

expression.

 In the

Events editor

, associate an expression with an action (a command or macro).

When the expression changes from false to true (from 0 to any non-zero value), the

action runs.

 In the

Data Log Models editor

, when setting up file management for a data log

model, use an expression to determine when log files are created.

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