Sequential function chart
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Sequential function chart (SFC) is a graphical programming language used for PLCs. It is one of the five languages defined by IEC 61131-3 standard. The SFC standard is defined in IEC 848, "Preparation of function charts for control systems", and was based on GRAFCET.
It can be used to program processes that can be split into steps.
Main components of SFC are:
- Steps with associated actions
- Transitions with associated logic condition
- Directed links between steps and transitions
Always starts in step 0. The blocks represent "actions" and the little crossing lines represent "conditions" eg. if the PLC was busy with step 13 and the leftmost condition is true then it goes back to the start (step 0). If the rightmost condition is true then jump back to step 11 and performs another cut. The programmer must make sure that conditions at the same level are exclusive as there must be only one active block at any moment. The "action" of the block is performed elsewhere in the program, e.g., for as long as step 13 is active then activate the cutting valve.
