Transition Element

Introduction

The Transition in a Sequential Function Chart are conditions that change the active steps in the flow chart.

Transition Element Syntax

The Transition Element has this syntax:

transition-element ::= TRANSITION [ transition-name ] FROM step-list TO step-list
:= condition
END_TRANSITION

step-list ::= [ step-name | ( step-name {, step-name} ) ]
condition ::= expression;

Where:

transition-name is an optional name for the Transition Element.
step-list is a list of references to Step Elements.
step-name is the name of the associated Step Element.
condition is the condition to test.

Remarks

A Transition Element passes control to the TO steps when the following conditions are met:

All of the FROM steps are all active.
The condition is TRUE.

Examples

A transition to transfer control from step Filling to Heating when a level is reached:
```
TRANSITION FROM Filling TO Heating
    := Level >= 4.0;
END_TRANSITION
```

A transition that uses the elapsed time of a step to transfer control:

TRANSITION FROM WarmUp TO Operational
    := WarmUp.T >= T#30s;
END_TRANSITION

Standards Compliance

IEC 61131-3 Second Edition: Table 41.

IEC 61131-3 Third Edition: Table 55.

Further Information

IEC 61131-3 Expressions

To learn about expressions to use as a transition condition.

Sequential Function Chart

For general information about Sequential Function Charts.

IEC 61131-3

For information about IEC 61131-3 scripts.

Glossary

For the meaning of terms used in Fernhill SCADA.