Transition expressions
Transition expressions define the criteria to STOP, RESET, and detach all preceding steps and their associated
Equipment Phase
s and attach and START the Equipment Phase
s and steps. The expression must always evaluate to either TRUE or FALSE. Example 1
XFR_OUT_1.Complete
Example 2
Tank_Level > Add_Water:Dose_Amount.Value
Transition expressions are configured using the expression editor. A transition expression is structured text and is executed as structured text. Structured text is a text-based programming language that uses statements to define what to execute.
- Structured text is not case sensitive.
- Use tabs and carriage returns (separate lines) to make your expression easier to read. They have no effect on the execution of the structured text.
- Structured text is a text-based programming language that uses statements to define what to execute.
- Structured text is not case sensitive.
- Use tabs and carriage returns (separate lines) to make your expression easier to read. They have no effect on the execution of the structured text.
A transition expression is evaluated every scan of the sequence, and evaluates as either TRUE or FALSE. When an expression evaluates as TRUE, the transition is said to
fire
--stopping and resetting preceding steps and activating and starting following steps. If the expression is FALSE, no action is taken.Also, with every scan of the sequence, the
Valid
attribute (quality of data) of an expression is evaluated. If any term in the expression is invalid, the Valid
attribute is set as invalid, which causes the transition to evaluate as FALSE.Provide Feedback