VFD Fault Detection & Safe Reset

Briefing

The physics engine runs a VFD and trips it after 2 seconds of operation (simulating an overload / overcurrent fault). Your ladder must: 1. **3-wire seal-in** — START latches RUN_BIT; STOP or VFD_FAULTED resets it. 2. **VFD_RUN** follows RUN_BIT. 3. **FAULT_LAMP** mirrors VFD_FAULTED. 4. **Safe reset** — RESET_PB only issues a VFD_RESET pulse when the drive is stopped (RUN_BIT = 0). Use an **R_TRIG** one-shot so the reset is a single scan pulse, not a continuous command. Safety note: resetting a faulted drive while it is still in RUN command can cause the motor to restart unexpectedly. The interlock on the reset ensures the operator must stop first.

Objectives

• SET RUN_BIT on START; RESET on STOP or VFD_FAULTED
• VFD_RUN := RUN_BIT
• FAULT_LAMP := VFD_FAULTED
• VFD_RESET via R_TRIG one-shot — only when /RUN_BIT

I/O Table

Your program will be tested against:

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

1. #1Drive trips after 2 s → VFD_RUN drops, FAULT_LAMP on

   START the drive; physics trips it after 2 s; FAULT_LAMP must be on and VFD_RUN off.

2. #2RESET_PB ineffective while still in RUN state

   Immediately after START (before fault), pressing RESET_PB should NOT issue VFD_RESET — interlock requires drive stopped.

3. #3After STOP → RESET_PB clears fault (issues VFD_RESET pulse)

   Start drive, manually STOP it, then press RESET_PB — VFD_RESET pulse should fire.