SFC / GRAFCET Lab

The token, the guard and the scan cycle — how a chart actually executes.

• 1.1Your first step and transitionA chart is steps (what the machine is doing) joined by transitions (why it moves on).Belt conveyor starter, 1.5 kW motor on a DOL contactor60 XP
• Pass the previous lesson to unlock this one1.2Step time — the timer you never have to declareEvery step counts how long it has held the token. `Step.T` is that time, in milliseconds.Hot-melt glue dispenser, 400 ms bead then 200 ms string-break dwell70 XP
• Pass the previous lesson to unlock this one1.3Closing the loop — a repeating cycleA transition back to an earlier step turns a line of steps into a machine cycle.Rotary index table, 4 stations, pneumatic indexer with home proximity80 XP
• Pass the previous lesson to unlock this one1.4Guards and interlocks — permission to moveA transition guard is where machine permissives, not just sensors, belong.Hydraulic press, 250 kN, light-curtain guarded90 XP

All eleven IEC qualifiers — the difference between a command and a latch.

• Pass the previous lesson to unlock this one2.1N versus S and R — the valve that stayed openN drives an output only while its step is active; S latches it until an R clears it.CIP supply skid, caustic dosing valve plus a run-hours latch80 XP
• Pass the previous lesson to unlock this one2.2P — one shot on entryA pulse action executes on the single scan the step is entered, never again.Carton case-packer, part counter and recipe load per lane change85 XP
• Pass the previous lesson to unlock this one2.3L — time limited actionAn L action is active for the first <time> of the step, then drops while the step continues.Overhead gantry crane, 3 s pre-travel warning horn75 XP
• Pass the previous lesson to unlock this one2.4D — time delayed actionA D action stays off for the first <time> of the step, then energises for the remainder.Vacuum gripper end-effector, 200 ms vacuum settle before lift75 XP

Alternative branches, parallel branches, convergence and priority.

• Pass the previous lesson to unlock this one3.1Alternative branch — one road or the otherTwo transitions leaving the same step form a choice; exactly one of them takes the token.Vision reject station on a bottling line, accept lane vs reject chute95 XP
• Pass the previous lesson to unlock this one3.2Simultaneous branch — two things at onceOne transition with several targets splits the token: every branch runs in parallel.Batch reactor, agitator and jacket heating started together100 XP
• Pass the previous lesson to unlock this one3.3Convergence — the synchronisation pointA transition with several sources fires only when every source step holds a token.Twin-head filler, both heads must finish before the index moves100 XP
• Pass the previous lesson to unlock this one3.4Priority — when two guards are true at onceFireable transitions leaving the same step are resolved by declaration order.Palletiser infeed, jam abort branch above the normal pack branch90 XP

Complete sequences: batch, handshake, safe abort and CIP.

• Pass the previous lesson to unlock this one4.1Batch tank — fill, heat, mix, drainA full production sequence: analogue guards, parallel processing and a clean cycle end.2000 L jacketed batch tank, level transmitter + RTD, CIP-capable120 XP
• Pass the previous lesson to unlock this one4.2Pick and place with a robot handshakeA sequence that waits for another controller: request, acknowledge, release.4-axis SCARA feeding a tray sealer, digital I/O handshake120 XP
• Pass the previous lesson to unlock this one4.3Safe abort — E-stop, reset and re-homeAn abort chain drains the sequence to a known state and refuses to restart until re-homed.Bottle unscrambler with a category 3 safety circuit130 XP
• Pass the previous lesson to unlock this one4.4CIP wash — a recipe of timed phasesLong sequences stay readable when every phase carries its own time and confirmation.Dairy CIP set: pre-rinse, caustic, intermediate rinse, acid, final rinse130 XP