PLC Simulator
Pro
20 min

VFD Conveyor Speed Control

vfdconveyordriveseal-inTONindustrial

Ready to build this?

Sign up free — no credit card required. This scenario requires the Pro plan.

Sign up to play this scenario →

Already have an account? Log in

Not ready for Pro? Try a free scenario like this →

VFD Conveyor Speed Control scenario preview

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

Hints

  • Use SET/RESET coils: | START AND /VFD_FAULTED | S= RUN_BIT ; | STOP OR VFD_FAULTED | R= RUN_BIT ;
  • Call the TON as a statement: TON_STALL(IN := VFD_RUN AND /VFD_AT_SPEED, PT := 5000); — when the IN condition goes false the timer auto-resets.

I/O Table

Inputs

START

Start push-button (momentary NO)

BOOL · %I0.0

STOP

Stop push-button (momentary NO)

BOOL · %I0.1

VFD_AT_SPEED

Physics: drive at reference speed (< 2 % error)

BOOL · %I0.2

VFD_FAULTED

Physics: drive fault / trip

BOOL · %I0.3

Outputs

VFD_RUN

Run command to VFD

BOOL · %Q0.0

FEEDER_ENABLE

Enable upstream feeder (only when at speed)

BOOL · %Q0.1

ALARM_LAMP

Stall / fault alarm lamp

BOOL · %Q0.2

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.

Related scenarios

basic

Sortation Diverter

conveyormaterial-handlingdiverter
basic

Case Packer

packagingcounterpusher
basic

Palletizer (Simple)

palletizerconveyorcounting

Ready to build this?

Sign up free — no credit card required. This scenario requires the Pro plan.

Sign up to play this scenario →

Already have an account? Log in

Not ready for Pro? Try a free scenario like this →

Runnable simulator field guide

VFD conveyor-speed PLC scenario: test checklist

Direct answer

The learner can distinguish run command, speed reference, drive ready or running state and actual conveyor response, then diagnose the first disagreeing boundary.

Written for pLC and drive learners controlling a conveyor with run permissives, a bounded speed reference and independent motion feedback.

a guarded motor-control and machine-safety training cell used to prove starter, drive, interlock, stop, feedback and restart behavior while studying conveyor VFD command, reference, acceleration and speed-feedback evidence
System map / 02

NODE 01observable

Scenario setup

Conveyor duty, guarding boundary, run permissives, drive ready, command source, frequency or speed reference, minimum and maximum, ramps, motor data, feedback, trip and restart policy.

NODE 02observable

I/O and state map

Operator or sequence demand through PLC interlocks, drive run command and reference to output frequency, motor torque, belt motion, measured speed and process result.

NODE 03observable

Normal run

A permitted start accelerates to the bounded reference and stop returns the conveyor to the declared state with coherent feedback.

NODE 04observable

Boundary run

Zero reference, minimum and maximum, reversed direction, missing feedback, overload, jam, trip, communication loss, stop demand and power return.

NODE 05observable

Injected fault

A permissive, ownership, command, reference, drive-state, motor, belt, feedback, trip or restart mismatch.

NODE 06observable

Target check

The application validated on guarded target equipment with current drive data, risk controls and supervised acceptance tests.

Answer surface / 07

Why can a VFD show running while a conveyor is stopped?

The drive command and output can exist while the motor, coupling, belt, load or speed-feedback path fails downstream.

Should conveyor speed be proved from the frequency reference?

No. A reference is a request; use drive output evidence and independent conveyor or process feedback for the required result.