VFD Conveyor Speed Control

Briefing

A Variable-Frequency Drive (VFD) controls the conveyor belt speed. The drive needs a **run command** (VFD_RUN) from the PLC and feeds back two status bits: - **VFD_AT_SPEED** — true when the drive has ramped up and actual speed is within 2 % of the setpoint. - **VFD_FAULTED** — true when the drive has tripped (overcurrent, overheat, etc.). Write the supervisory ladder to: 1. **3-wire seal-in**: START sets RUN_BIT; STOP or VFD_FAULTED resets it. 2. **VFD_RUN** follows RUN_BIT — send the run command to the drive. 3. **FEEDER_ENABLE** only when VFD_AT_SPEED — the upstream feeder must not dump product while the belt is still ramping. 4. **ALARM_LAMP**: use a TON of 5 seconds — if VFD_RUN is on but VFD_AT_SPEED never arrives within 5 s (stall / belt jam), light the alarm.

Objectives

• SET RUN_BIT on START; RESET on STOP or VFD_FAULTED
• VFD_RUN := RUN_BIT
• FEEDER_ENABLE := VFD_AT_SPEED
• ALARM_LAMP via TON(5 s) when VFD_RUN and NOT VFD_AT_SPEED

I/O Table

Your program will be tested against:

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

1. #1START → VFD_RUN on

   Pressing START latches RUN_BIT and drives VFD_RUN high; no alarm or feeder yet.

2. #2FEEDER_ENABLE only when VFD_AT_SPEED

   After START, drive physics ramps to speed at 8 %/s (~12.5 s) — FEEDER_ENABLE must stay off until VFD_AT_SPEED goes high.

3. #3Stall: VFD_RUN but no AT_SPEED for 5 s → ALARM_LAMP

   Drive ramps at 8 %/s — VFD_AT_SPEED stays false for ~12.5 s; TON fires ALARM_LAMP at 5 s.