Industrial Engineer · phase 3 of 16
Sequential Function Chart (SFC)
IEC 61131-3 elements that organize programs and function blocks as steps, actions, and transitions.
The Explain card
- Plain English
- SFC lays a program out as steps, the actions that run inside each step, and the transitions that move from one step to the next. Only the active step's actions run.
- Example
- A wash cycle is Fill, Agitate, Drain, Spin. Each is a step, each transition is a condition like level reached or timer done, and the chart shows exactly where the machine is.
- Why it matters
- A machine that goes through phases is a state machine whether you draw it or not. SFC makes the states visible and stops two phases from fighting over the same outputs, which is the bug that hides in ladder sequencers.
- Hook
- The flowchart is the program.
Where it sits in the deck
Phase 3: PLC Program Organization and Execution
How the logic is arranged and how the scan actually runs it, which is the difference between code that works and code that works every time.
