10 templates
Ladder logic (PLC) templates
IEC 61131-3 ladder diagrams: rungs of normally-open and normally-closed contacts, coils, set/reset latches, timers (TON/TOF/TP) and counters (CTU/CTD), drawn between the power rails with parallel branches for OR logic. The engine evaluates each rung against a declared input state, so the drawing can show which rungs are true — the industrial control diagram nothing else in a diagram tool renders.
Ladder - Motor Start/Stop Seal-In
Five rungs of a direct-on-line starter solved with the start button already released: the parallel Start_PB/Motor_Run branch seals the coil in through the healthy stop and overload contacts, the run-hours CTU sits at 412 of its 500-hour preset so the done bit stays low, and the engine reports the service lamp as the one output never energised in this state.
Operations & OpsLadder - Signalled Junction Sequence
Eight rungs freeze a junction two seconds into its four-second amber: the 30 s green TON is done, the amber TON is still timing, the 25 s red TON has never been enabled, so only the amber lamp is lit and the engine names the green lamp, the red lamp and the unstarted red timer as never energised at this instant.
Flow & ProcessLadder - Conveyor Jam Watchdog
Six rungs where the photo-eye has been blocked for 8 s against a 6 s TON preset, so the jam latches on rung 4 after the belt coil was already solved true on rung 2 -- the one-scan lag that makes a real controller keep the belt running for one more pass -- with the beacon and horn coils drawn in series off the same latched fault.
Lean & FlowLadder - Tank Fill on Level Switches
Seven rungs latch the fill valve on the low-level switch and leave the unlatch rung unpowered because the high-level switch has not made, run the 180 s overfill watchdog out to 96 s, and end on a deliberate interlock chain with no coil, so the engine reports both the never-energised overfill alarm and the rung whose logic is solved and thrown away.
Operations & OpsLadder - Two-Hand Press Anti-Tie-Down
Five rungs of two-hand control where both buttons are made inside the 500 ms concurrency window (a TP pulse at 180 ms) and the ram is correctly permitted on rung 4 -- then a maintenance mute rung writes Ram_Solenoid a second time and silently overrides it, the duplicate destination flagged alongside a light-curtain tag examined by a contact that nothing in the program writes.
Risk & ReliabilityLadder - Roller Door Open/Close Interlock
Eight rungs of a loading-bay roller door caught mid-travel with the close command sealed in: the open rung is held off by its own reverse interlock rather than by the buttons, the safety beam is clear so no reverse is latched, and the 180 s courtesy-light TOF is enabled by the moving door so its done bit keeps the bay lamp lit.
ArchitectureLadder - Packaging Line Fill and Cap
Ten rungs of a fill-and-cap machine frozen on the scan where the 1.2 s fill dwell has just timed out: the valve rung reads the timing bit and has already dropped, the capper fires off the done bit, and the batch CTU sits at 1,180 of 1,200 so the counter's done bit - and the batch lamp behind it - stay low.
Operations & OpsLadder - Duplex Pump Duty Alternation
Eight rungs of a duplex sump station with the duty selector on pump B: the same lead/lag branch pair drives both pumps from one alternation bit, so B runs and A stays standby on this scan, the duty counter has reached its 2,000-hour service preset, and the both-pumps-running alarm stays unlatched.
Chemistry & PhysicsLadder - Lift Hall Call and Door Dwell
Nine rungs of a three-storey lift with a registered level-3 hall call and the car standing at level 1: the call latches on rung 2, the clear rung stays unpowered because the car has not arrived, the up command and hoist motor follow, and the 8 s door dwell has never been enabled so the door-open command is dead.
ArchitectureLadder - Batch Mixer Charge and Soak
Nine rungs of a jacketed batch vessel caught 240 s into a 600 s soak: both charge valves have closed on their made weights, the agitator and its soak TON are running, and the batch-done latch on rung 7 is still unpowered - which is exactly why rung 2's seal-in reads that not-yet-written tag as zero and holds the batch on.
Chemistry & Physics