Sequential function charts

The Workflow module provides graphical views of flows, based on Sequential Function Chart (SFC) technology.

An SFC is a graphical programming language used for Programmable Logic Controllers (PLCs). It represents the sequential flow of steps in a process and supports the parallelization of actions with contingency for the completion of all parallel branches for forward flow to progress.

These are the main components of an SFC:

  • Steps with associated actions
  • Transitions with associated logic conditions
  • Directed links between steps and transitions

Steps in an SFC diagram can be active or inactive, with actions being executed for active steps only. A step can be active for one of these reasons:

  • It is an initial step as specified by the programmer
  • It was activated during a scan cycle and not deactivated since

Steps are activated when all steps above it are active and the associated condition of the connecting transition is true. When a transition is passed, all steps above are deactivated at once and after all steps below are activated at once.

From Action 1, there are 2 options; 2 or 3, with 3 looping around until Action 2 can be performed.

After Action 4, there is a split to perform Actions 5 and 6 in parallel, these then merge before Action 7.

Sequential function chart

The Workflow module enables these SFC charts to be defined at these levels:

  • A Routing level to view all operations and their sequence
  • An Operation level to see all the phases and their sequence
  • A Phase level to see all actions and their sequence