Lesson 5 — Seal-in Motor
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Briefing
The seal-in rung is the "aha!" moment of ladder logic. A momentary START press energises the MOTOR. A parallel branch using the MOTOR output itself keeps the rung energised after the START button is released — the coil "seals in" around the start contact. STOP breaks the circuit.
Objectives
- A momentary START pulse latches MOTOR on
- MOTOR stays on after START is released (seal-in)
- STOP de-energises MOTOR
Hints
- Put START and the MOTOR feedback contact in parallel, then put STOP (NC) in series.
- Think of it as: (START OR MOTOR) AND NOT STOP → MOTOR.
I/O Table
Inputs
STARTMomentary start push-button (NO)
BOOL · %I0.0
STOPMomentary stop push-button (NC wired)
BOOL · %I0.1
Outputs
MOTORMotor contactor coil
BOOL · %Q0.0
Your program will be tested against:
All test cases run automatically when you submit. Assertions are hidden until you pass.
- #1Momentary START pulse latches MOTOR
Brief START press → MOTOR stays on after release
- #2STOP de-energises MOTOR
While latched, pressing STOP drops MOTOR
- #3MOTOR stays off without START
After STOP, MOTOR remains off even when STOP is released
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