PLC Simulator
Pro
10 min

Fault 02 — Broken Seal-in

fault-injectionlogicseal-in
Fault 02 — Broken Seal-in scenario preview

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Briefing

The motor starts when START_PB is held but drops out immediately when the button is released. Field wiring has been verified correct. Diagnose why the motor won't latch, then fix the ladder.

Objectives

  • Observe the momentary vs latching behaviour using slow-scan mode
  • Identify the missing seal-in branch
  • Add the correct parallel contact to create a latching (seal-in) rung
  • Verify the motor seals in and only stops on STOP_PB

Hints

  • Hold START_PB in the I/O tab — watch the scan-cycle highlight show the rung state
  • Release START_PB and watch what happens — does the rung stay true?
  • A latching circuit needs a path that stays closed after the start button opens

I/O Table

Inputs

START_PB

Start push-button (momentary)

BOOL · %I0.0

STOP_PB

Stop push-button (momentary NC)

BOOL · %I0.1

Outputs

MOTOR_CONTACTOR

Main motor contactor coil

BOOL · %Q0.0

RUN_LAMP

Running indicator lamp

BOOL · %Q0.1

Your program will be tested against:

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

  1. #1Motor seals in after START_PB released

    Momentary press — contactor stays energised after button releases

  2. #2STOP_PB drops the contactor

    While running, STOP_PB press drops the motor

Related scenarios

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Lesson 5 — Seal-in Motor

curriculumlessonseal-in
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Fault 01 — NO/NC Swap

fault-injectionlogicno-nc
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Fault 03 — Wrong Address

fault-injectionwiringaddress

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