User Manual

Ta g s
selection dialog is displayed. Select the expression in the drop-down list and click
OK.
If you have saved expressions to the library that you want to remove, click Delete
and select among the saved expressions in a dialog. Expressions included when
installing iX Developer are not listed, since these cannot be deleted.
4.11.4 Limitations
An expression is executed only on read, i.e. when the value is changed in the
controller.
When writing a value (from e.g. an analog numeric tag), the expression is not
executed.
If another tag than the original tag is used in the expression, the expression is not
triggered on its value change.
If an expression that is used in more than one location is either renamed or deleted,
references are not updated. A build error is given.
Expressions can be used for all data connections except for
• actions
• the Property grid
• recipe item tags
• current language tag in Multiple languages configuration
• trigger tags
• index tags
• scheduler tags
• dynamic text for alarm items
Expressions use explicit bool comparison.
Example:
Donot use: value;Globals.Tags.Tag1.Value
Use: value!=0; GlobalsTags.Tag1.Vaule==1
4.12 TagExpressions
Tag expressions are applied before reading o r writing a tag value. Tag expressions
should only be used on tags that have an associated address on a controller.
There are two different tag expressions, referred to as read expressions and write
expressions. A read expression is applied to a tag when the tag value is changed
from the controller. A write expression is applied to a tag when the tag value is
changed from the user interface or script. When both a read expression and a write
expression are assigned to a tag it is strongly recommended that the read expression
is the inverse of the write expression and vice versa.
When using a write express ion make sure the controller's data type matches any
possible result from the expression. For example, the data type float should be used
if the expression would multiply an integer value with 0.1.
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