Two-Speed Motor Control

Briefing

A two-speed (Dahlander or separate windings) motor starter. HIGH_PB runs the motor at high speed; LOW_PB at low speed. The two contactors are interlocked — only one can be energised at a time. Changing speed requires pressing STOP_PB first (direct high-to-low or low-to-high switching is not permitted, preventing winding damage). ESTOP drops both contactors immediately.

Objectives

• HIGH_PB seals in HIGH_CONTACTOR (while stopped and no fault)
• LOW_PB seals in LOW_CONTACTOR (while stopped and no fault)
• STOP_PB de-energises the active contactor
• Direct speed change without STOP is inhibited — pressing HIGH while low is running does nothing
• ESTOP drops both contactors and latches FAULT_LAMP
• RUN_LAMP on while either speed is running

I/O Table

Your program will be tested against:

All test cases run automatically when you submit. Assertions are hidden until you pass.

1. #1HIGH_PB seals in HIGH_CONTACTOR

   Momentary HIGH_PB seals in high-speed contactor; STOP drops it

2. #2LOW_PB seals in LOW_CONTACTOR

   Momentary LOW_PB seals in low-speed contactor

3. #3Cannot switch from high to low without STOP first

   Pressing LOW_PB while HIGH is running is inhibited — must STOP first

4. #4ESTOP drops both contactors and latches fault

   E-stop de-energises all and latches fault; STOP_PB clears after ESTOP restored