Sequential Function Chart (SFC)

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Introduction

A Sequential Function Chart (SFC) is a high level programming language that used Steps, Transitions and Actions to create a flow chart.

An SFC is one of the five programming languages defined in the IEC 61131-3 standard.

Elements of a Sequential Function Chart

A Sequential Function Chart is built from these elements:

ElementDescription
Step Element A Step Element represents the states in the flow chart. For example:
  • Stopped
  • Running
  • Heating
  • Cooling
  • Moving
Action Element An Action Element represents work to do when when a Step Element is active. For example:
  • Stop
  • Start
  • Turn heater on
  • Turn heater off
Transition Element A Transition Element is a condition that changes the active step.

A Sequential Function Chart is a natural choice for recipe management.

Example Chart

  1. Simple Chart with Two Steps:
    Program Test
    Var
    	PushButton : BOOL;
    	Run : BOOL;
    End_Var
    
    	Initial_Step Stopped:
    		Stop( P1 );
    	End_Step
    
    	Step Running:
    		Start( P1 );
    	End_Step
    
    	(* Transition from stopped to running when the push button is pressed *)
    	Transition FROM Stopped TO Running
    		:= PushButton;
    	End_Transition
    
    	(* Transition from running to stopped after running for 20 seconds *)
    	Transition FROM Running TO Stopped
    		:= Running.T >= T#20S;
    	End_Transition
    
    	Action Start :
    		Run := TRUE;
    	End_Action
    
    	Action Stop :
    		Run := FALSE;
    	End_Action
    End_Program

How to use an SFC in Fernhill SCADA

In Fernhill SCADA you can an SFC in:

Further Information

Common Elements

To learn about IEC 61131-3 Common Elements you can use in an SFC.

Glossary

For the meaning of terms used in Fernhill SCADA.