Basic
12 min

Forward/Reverse Motor PLC Ladder Diagram (Run It Free)

This page walks through the complete forward/reverse motor control PLC program — the seal-in latches that hold each direction, the cross-interlock that stops the two contactors from ever pulling in together, the stop-before-reverse logic, and the auxiliary-feedback fault detection that catches a welded contactor. The ladder is grounded in a live scenario you can run right now in your browser: write the rungs, press the forward and reverse push-buttons, watch the motor spin each way, and get instant pass/fail feedback — no PLC hardware and no software to install.

motorforward-reverseinterlocksafety
Forward / Reverse Motor scenario preview

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Briefing

A reversible motor starter with electrical and mechanical interlocking. FWD_PB runs the motor forward (seals in); REV_PB reverses it. STOP_PB de-energises both contactors. A cross-interlock prevents both contactors from energising simultaneously. Auxiliary feedback contacts are used to detect a stuck (welded) contactor — a mismatch between the commanded contactor and its auxiliary latches FAULT_LAMP.

Objectives

  • FWD_PB energises FWD_CONTACTOR and seals in (while STOP_PB and no fault)
  • REV_PB energises REV_CONTACTOR and seals in; FWD_CONTACTOR is de-energised first
  • STOP_PB de-energises both contactors
  • Both contactors are interlocked — FWD inhibits REV and vice versa
  • ESTOP drops both contactors and latches FAULT_LAMP
  • AUX mismatch (contactor commanded off but AUX still on) latches FAULT_LAMP

Hints

  • FWD_BIT: S= by FWD_PB; R= by STOP_PB, ESTOP off, REV_PB (change direction), or fault
  • REV_BIT: S= by REV_PB; R= by STOP_PB, ESTOP off, FWD_PB, or fault
  • FWD_CONTACTOR := FWD_BIT AND /FAULT_BIT AND /REV_BIT (cross-interlock)
  • FAULT: S= by /ESTOP. Aux mismatch: FWD_AUX high when FWD_CONTACTOR de-energised (or REV_AUX similarly)

I/O Table

Inputs

FWD_PB

Forward push-button (momentary)

BOOL · %I0.0

REV_PB

Reverse push-button (momentary)

BOOL · %I0.1

STOP_PB

Stop push-button (momentary)

BOOL · %I0.2

ESTOP

E-stop (NC — true=healthy)

BOOL · %I0.3

FWD_AUX

Forward contactor auxiliary feedback

BOOL · %I0.4

REV_AUX

Reverse contactor auxiliary feedback

BOOL · %I0.5

Outputs

FWD_CONTACTOR

Forward motor contactor coil

BOOL · %Q0.0

REV_CONTACTOR

Reverse motor contactor coil

BOOL · %Q0.1

FWD_LAMP

Forward running indicator lamp

BOOL · %Q0.2

REV_LAMP

Reverse running indicator lamp

BOOL · %Q0.3

FAULT_LAMP

Fault indicator lamp

BOOL · %Q0.4

Your program will be tested against:

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

  1. #1FWD_PB seals in forward contactor

    Momentary FWD_PB energises FWD_CONTACTOR; STOP_PB drops it

  2. #2REV_PB seals in reverse contactor

    Momentary REV_PB energises REV_CONTACTOR; STOP_PB drops it

  3. #3REV_PB clears forward and energises reverse — never both on

    Pressing REV_PB while forward is running switches direction; both contactors never simultaneously energised

  4. #4E-stop latches fault and drops both contactors

    E-stop drops both contactors and latches fault

How forward/reverse motor control works

A reversing motor starter drives a three-phase motor in either direction by swapping two of the three supply phases. In the power circuit this is done with two contactors: the forward contactor connects the phases straight through, and the reverse contactor swaps L1 and L3. Energising the wrong pair — or both contactors at once — creates a phase-to-phase short across the swapped lines, so the single most important job of the PLC program is to guarantee the two contactors can never be energised at the same time.

The control logic is a pair of seal-in (latching) rungs, one per direction, tied together by a cross-interlock. Pressing FWD_PB energises FWD_CONTACTOR, which seals itself in through a holding contact so the motor keeps running after the button is released. Pressing REV_PB does the same for REV_CONTACTOR. STOP_PB and the E-stop drop both. The cross-interlock is the contact of each direction wired normally-closed into the other direction's rung, so whenever one contactor is in, the opposite rung is broken.

In this scenario six inputs are pre-wired for you: FWD_PB (%I0.0), REV_PB (%I0.1), STOP_PB (%I0.2), ESTOP (%I0.3, normally-closed — TRUE means healthy), and the two contactor auxiliary feedback contacts FWD_AUX (%I0.4) and REV_AUX (%I0.5). Five outputs are pre-wired: FWD_CONTACTOR (%Q0.0), REV_CONTACTOR (%Q0.1), FWD_LAMP (%Q0.2), REV_LAMP (%Q0.3), and FAULT_LAMP (%Q0.4).

The seal-in and cross-interlock rungs

Each direction is a memory latch. The cleanest way to build it is with SET/RESET coils on an internal bit, then drive the physical contactor from that bit through the interlock.

FWD_BIT is SET by a momentary press of FWD_PB and RESET by any of: STOP_PB, the E-stop dropping out, a fault, or — for stop-before-reverse safety — REV_PB. REV_BIT mirrors it: SET by REV_PB, RESET by STOP_PB, E-stop, fault, or FWD_PB. Because pressing the opposite direction button resets the running bit, the motor always coasts to stop before the other direction can take over, which protects the gearbox and the contactors from a plugging-style instant reversal.

The physical coils then carry the cross-interlock: FWD_CONTACTOR := FWD_BIT AND NOT FAULT_BIT AND NOT REV_BIT, and REV_CONTACTOR := REV_BIT AND NOT FAULT_BIT AND NOT FWD_BIT. The NOT REV_BIT term in the forward rung (and vice versa) is the software interlock — even if both bits were somehow set, neither contactor would energise. In a real panel this software interlock is backed up by a mechanical interlock on the contactors and by the normally-closed auxiliary contacts in the power-circuit wiring, giving three independent layers of protection.

Welded-contactor fault detection with auxiliary feedback

A contactor whose main contacts weld shut is one of the most dangerous failures in a reversing starter: the PLC commands the coil off, but the motor keeps running, and if the operator then selects the opposite direction the interlock in software is no longer enough. This scenario teaches the standard guard — auxiliary-contact feedback.

Each contactor carries a normally-open auxiliary contact wired back to an input: FWD_AUX and REV_AUX. When the program de-energises a contactor coil, its auxiliary should drop within one scan. If the coil is commanded OFF but the auxiliary is still reading ON, the main contacts are stuck (welded or mechanically jammed). The program latches FAULT_BIT, lights FAULT_LAMP, and forces both contactors off until the fault is cleared. The E-stop input does the same: losing ESTOP (it is normally-closed, so TRUE is healthy) drops both contactors and latches the fault.

This is exactly the kind of diagnostic logic the CCST and most maintenance roles expect you to be able to read and write. You can build it and watch the fault latch fire in the live scenario — toggle a contactor's auxiliary out of step with its coil and the fault lamp comes on.

Frequently asked questions

What does a forward/reverse motor PLC ladder diagram look like?

It is two seal-in (latching) rungs — one for forward, one for reverse — joined by a cross-interlock. Each rung latches its contactor on a momentary push-button and holds it through a seal-in contact; a normally-closed contact of the opposite direction is wired into each rung so the two contactors can never be energised together. Stop and E-stop drop both. You can run a complete working version free in the browser on this page.

How do you write a forward/reverse motor control PLC program?

Use SET/RESET on an internal bit per direction: FWD_BIT is set by FWD_PB and reset by STOP, E-stop, a fault, or REV_PB; REV_BIT mirrors it. Then drive the contactors with the interlock — FWD_CONTACTOR = FWD_BIT AND NOT REV_BIT AND NOT FAULT, and REV_CONTACTOR = REV_BIT AND NOT FWD_BIT AND NOT FAULT. Resetting the running bit when the opposite button is pressed gives you safe stop-before-reverse behaviour.

Why must forward and reverse contactors be interlocked?

A reversing starter swaps two supply phases to change direction. If the forward and reverse contactors energise at the same time, those two swapped phases are shorted together phase-to-phase, which trips protection at best and causes an arc-flash at worst. The interlock — a normally-closed contact of each direction in the other rung — guarantees only one contactor can ever be in. Real panels add a mechanical interlock on top of the software one.

What is stop-before-reverse (anti-plugging) in motor control?

Stop-before-reverse means the motor must come to rest before it can run the other way, instead of being instantly reversed (plugged) while still spinning. In ladder logic you achieve it by making the reverse button reset the forward latch (and vice versa) rather than directly starting the opposite contactor — the motor de-energises, coasts down, and only a second press starts it in the new direction. This protects the coupling, gearbox, and contactors from the huge current and torque of a plugging reversal.

How does a PLC detect a welded (stuck) motor contactor?

With auxiliary-contact feedback. Each contactor has a spare contact wired back to a PLC input. When the program commands a contactor off, that feedback input should drop within a scan. If the coil is off but the feedback is still on, the main contacts are welded shut — the program latches a fault, lights the fault lamp, and forces both directions off. This scenario includes that FWD_AUX / REV_AUX fault logic so you can see the fault latch fire.

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Runnable simulator field guide

Forward-reverse motor PLC scenario: implementation, evidence and troubleshooting

Direct answer

Forward-reverse motor PLC scenario becomes useful when it connects motor and load, forward and reverse requests, mode, permissives, stop priority, electrical and software interlocks, output ownership, auxiliary feedback, stopped condition, transition delay and restart policy with operator request through command arbitration and interlocks to one final direction output, contactor or drive state, motor motion and independent direction feedback, then proves forward and reverse each run separately, simultaneous requests produce the declared safe result and stop removes both commands under normal, boundary, fault and recovery conditions. The objective is a repeatable engineering or learning result, not merely activity inside a page or tool.

This guide is written for pLC and motor-control learners programming two mutually exclusive directions with contactor or drive feedback and deliberate direction changes. The intended result is specific: the learner can prove that forward and reverse commands never coexist, stop retains priority and changing direction follows the declared stopped-state and restart policy.

a guarded motor-control and machine-safety training cell used to prove starter, drive, interlock, stop, feedback and restart behavior while studying forward-reverse commands, mutual interlock, stop priority and feedback
The field scene connects forward-reverse commands, mutual interlock, stop priority and feedback to declared initial conditions, observable boundaries, safe limits and repeatable acceptance evidence.

System map / 02

Six concepts that control the result

Treat these as connected checkpoints. Each checkpoint has an expected state, an observable state and a boundary to the next part of the system. That structure prevents a software indication from being mistaken for physical proof.

NODE 01observable

Define the operating contract

motor and load, forward and reverse requests, mode, permissives, stop priority, electrical and software interlocks, output ownership, auxiliary feedback, stopped condition, transition delay and restart policy. For forward-reverse commands, mutual interlock, stop priority and feedback, record the initial condition, actor, requested change, observable result and stopping condition before selecting a tool or implementation.

NODE 02observable

Map the evidence path

operator request through command arbitration and interlocks to one final direction output, contactor or drive state, motor motion and independent direction feedback. Separate request, internal state, output or service, physical or user-visible result and independent feedback so each boundary can be inspected.

NODE 03observable

Prove normal operation

forward and reverse each run separately, simultaneous requests produce the declared safe result and Stop removes both commands. Run more than one cycle from a known state and retain the values, timings or artifacts that demonstrate repeatability.

NODE 04observable

Exercise a boundary case

both requests, direction change while moving, welded feedback, failed contactor, stopped feedback missing, overload, power loss, held start and restart. Choose minimum, maximum, simultaneous, delayed or restart conditions that reveal assumptions hidden by the happy path.

NODE 05observable

Diagnose a controlled fault

a request, priority, state, interlock, output-owner, contactor, drive, motor, feedback or restart mismatch. Preserve the first symptom, divide the system at a measurable boundary and change one condition only after predicting the result.

NODE 06observable

Transfer and hand over

the logic recreated on target equipment with hardware interlocks, protection, phase checks, motion risks and supervised acceptance tests. Restore normal state, remove temporary changes, repeat affected checks and document which claims remain limited to the learning environment.

Procedure / 03

A six-step practice and commissioning workflow

Run the steps in order the first time. Later, the same structure becomes a diagnostic loop: define the expected condition, observe the boundary, interpret the difference and choose one proving action.

  1. 01

    Write the acceptance case

    Convert motor and load, forward and reverse requests, mode, permissives, stop priority, electrical and software interlocks, output ownership, auxiliary feedback, stopped condition, transition delay and restart policy into initial conditions, one stimulus and observable pass criteria.

    Evidence: Another person can repeat the case without guessing the intended result.

    Avoid: Using page completion or an animation as the acceptance criterion.

  2. 02

    Build the map

    Document operator request through command arbitration and interlocks to one final direction output, contactor or drive state, motor motion and independent direction feedback and name who owns each state or decision.

    Evidence: Every request and result has a source, destination and useful inspection point.

    Avoid: Using the same value as command, status and independent feedback.

  3. 03

    Run the baseline

    Apply forward and reverse each run separately, simultaneous requests produce the declared safe result and stop removes both commands from a clean start and record the expected evidence.

    Evidence: Repeated runs produce the same bounded result.

    Avoid: Changing several parameters before a baseline exists.

  4. 04

    Challenge assumptions

    Test both requests, direction change while moving, welded feedback, failed contactor, stopped feedback missing, overload, power loss, held start and restart without changing the acceptance contract.

    Evidence: Limits, timing and restart behavior reach defined states.

    Avoid: Testing only one ideal sequence.

  5. 05

    Isolate one failure

    Introduce or analyse a request, priority, state, interlock, output-owner, contactor, drive, motor, feedback or restart mismatch and locate the first disagreement.

    Evidence: The proving action distinguishes the leading hypotheses.

    Avoid: Resetting, forcing or replacing before evidence is retained.

  6. 06

    Close the evidence loop

    Complete the logic recreated on target equipment with hardware interlocks, protection, phase checks, motion risks and supervised acceptance tests and repeat the affected regression cases.

    Evidence: A run is complete only when the requested behavior, stop behavior, fault response and recovery are observable from a fresh initial condition.

    Avoid: Treating an acknowledged message or one successful rerun as handover.

Diagnostic matrix / 04

Symptoms, proving points and next actions

The table is a reasoning aid, not a parts-replacement chart. Preserve the initial symptom, inspect the named boundary and use the interpretation to choose the next controlled test. Site safety procedures and equipment manuals remain authoritative.

Diagnostic symptoms, inspection points, interpretations and next actions for Forward-reverse motor PLC scenario: implementation, evidence and troubleshooting
Observed symptomInspectInterpretationNext proving action
The expected result is unclearRequirement, initial state, actor, stimulus, units and pass conditionThe operator, programmer and reviewer may be solving different versions of the task.Rewrite one observable acceptance case before continuing.
Internal state changes but the outcome does notRequest, final owner, output or service boundary and independent feedbackA software or interface indication proves intent at one layer, not the complete outcome.Trace the first boundary after the changing state.
Normal case passes but an edge case failsLimits, timing, simultaneous events, reset and restart assumptionsThe implementation contains a hidden assumption exposed by the changed condition.Add the failed boundary as a permanent regression case.
The failure disappears after resetOriginal symptom, histories, diagnostics, timestamps and active causeReset changed evidence or state without proving the initiating cause.Reproduce under a controlled condition and preserve pre/post-event data.
Simulator and target disagreeModel boundary, software version, task timing, I/O behavior, data types and configurationA learning model and the intended target do not share one of the recorded assumptions.Reduce the case and verify against current target documentation.
The result cannot be explainedPrediction, observation, proving action, alternative hypotheses and limitationsActivity occurred but the evidence is not yet transferable or reviewable.Have the learner defend the signal path and repeat a changed case.

Product evidence / 05

What the browser practice can actually demonstrate

The browser runtime joins editable control state to visible I/O and machine or process behavior, allowing the same initial conditions and stimuli to be replayed.

Where simulation stops

The scenario cannot validate a real reversing starter, phase sequence, braking, plugging, mechanical load, protection, guarding or functional safety.

Commissioning notebook / 06

Six cases that turn the concepts into evidence

Use these as written briefs rather than click-through instructions. For every case, state the expected condition before acting, retain the first useful observation and explain why the final result proves the requirement. A different program or component choice can still be correct when it produces the same bounded behavior and evidence.

Case 01

predict → observe → prove

Prove define the operating contract

Engineering context. motor and load, forward and reverse requests, mode, permissives, stop priority, electrical and software interlocks, output ownership, auxiliary feedback, stopped condition, transition delay and restart policy. For forward-reverse commands, mutual interlock, stop priority and feedback, record the initial condition, actor, requested change, observable result and stopping condition before selecting a tool or implementation. Begin with a written normal condition and identify which request, state, physical result or communication value will provide independent confirmation. Do not begin by changing the configuration; the initial state is part of the evidence and should remain reproducible.

Controlled setup. Use the “Write the acceptance case” stage of the workflow: convert motor and load, forward and reverse requests, mode, permissives, stop priority, electrical and software interlocks, output ownership, auxiliary feedback, stopped condition, transition delay and restart policy into initial conditions, one stimulus and observable pass criteria. The acceptance record should show this result: another person can repeat the case without guessing the intended result. Record initial conditions, the exact stimulus and the observation point so another learner can repeat the case without relying on your memory.

Fault challenge. Introduce or analyse “The expected result is unclear” as one bounded deviation. Inspect requirement, initial state, actor, stimulus, units and pass condition The working interpretation is that the operator, programmer and reviewer may be solving different versions of the task. The next proving action is to rewrite one observable acceptance case before continuing. Change only one condition before observing the result, and preserve timestamps or measurements where timing matters.

Review and recovery. The most common trap here is using page completion or an animation as the acceptance criterion. After restoring the cause, repeat the normal case and at least one stop, timeout, disconnect or restart boundary relevant to this topic. Remove temporary forces and bypasses, return the model to a known state and retain the evidence that both operation and recovery are deliberate.

Explain it aloud: How do you interlock forward and reverse motor outputs? A defensible short answer is: Use one explicit command owner plus mutual software conditions and the required hardwired or device interlocks so both direction outputs cannot energize together.

Case 02

predict → observe → prove

Prove map the evidence path

Engineering context. operator request through command arbitration and interlocks to one final direction output, contactor or drive state, motor motion and independent direction feedback. Separate request, internal state, output or service, physical or user-visible result and independent feedback so each boundary can be inspected. Begin with a written normal condition and identify which request, state, physical result or communication value will provide independent confirmation. Do not begin by changing the configuration; the initial state is part of the evidence and should remain reproducible.

Controlled setup. Use the “Build the map” stage of the workflow: document operator request through command arbitration and interlocks to one final direction output, contactor or drive state, motor motion and independent direction feedback and name who owns each state or decision. The acceptance record should show this result: every request and result has a source, destination and useful inspection point. Record initial conditions, the exact stimulus and the observation point so another learner can repeat the case without relying on your memory.

Fault challenge. Introduce or analyse “Internal state changes but the outcome does not” as one bounded deviation. Inspect request, final owner, output or service boundary and independent feedback The working interpretation is that a software or interface indication proves intent at one layer, not the complete outcome. The next proving action is to trace the first boundary after the changing state. Change only one condition before observing the result, and preserve timestamps or measurements where timing matters.

Review and recovery. The most common trap here is using the same value as command, status and independent feedback. After restoring the cause, repeat the normal case and at least one stop, timeout, disconnect or restart boundary relevant to this topic. Remove temporary forces and bypasses, return the model to a known state and retain the evidence that both operation and recovery are deliberate.

Explain it aloud: Can a motor reverse immediately while running? A defensible short answer is: The permitted policy depends on the motor, load and drive or starter; many systems require a proven stop and deliberate transition before the opposite direction.

Case 03

predict → observe → prove

Prove prove normal operation

Engineering context. forward and reverse each run separately, simultaneous requests produce the declared safe result and Stop removes both commands. Run more than one cycle from a known state and retain the values, timings or artifacts that demonstrate repeatability. Begin with a written normal condition and identify which request, state, physical result or communication value will provide independent confirmation. Do not begin by changing the configuration; the initial state is part of the evidence and should remain reproducible.

Controlled setup. Use the “Run the baseline” stage of the workflow: apply forward and reverse each run separately, simultaneous requests produce the declared safe result and stop removes both commands from a clean start and record the expected evidence. The acceptance record should show this result: repeated runs produce the same bounded result. Record initial conditions, the exact stimulus and the observation point so another learner can repeat the case without relying on your memory.

Fault challenge. Introduce or analyse “Normal case passes but an edge case fails” as one bounded deviation. Inspect limits, timing, simultaneous events, reset and restart assumptions The working interpretation is that the implementation contains a hidden assumption exposed by the changed condition. The next proving action is to add the failed boundary as a permanent regression case. Change only one condition before observing the result, and preserve timestamps or measurements where timing matters.

Review and recovery. The most common trap here is changing several parameters before a baseline exists. After restoring the cause, repeat the normal case and at least one stop, timeout, disconnect or restart boundary relevant to this topic. Remove temporary forces and bypasses, return the model to a known state and retain the evidence that both operation and recovery are deliberate.

Explain it aloud: What should I learn first about forward-reverse commands, mutual interlock, stop priority and feedback? A defensible short answer is: Start with the operating contract and evidence path: motor and load, forward and reverse requests, mode, permissives, stop priority, electrical and software interlocks, output ownership, auxiliary feedback, stopped condition, transition delay and restart policy, followed by operator request through command arbitration and interlocks to one final direction output, contactor or drive state, motor motion and independent direction feedback. Add advanced features only after the baseline is predictable.

Case 04

predict → observe → prove

Prove exercise a boundary case

Engineering context. both requests, direction change while moving, welded feedback, failed contactor, stopped feedback missing, overload, power loss, held start and restart. Choose minimum, maximum, simultaneous, delayed or restart conditions that reveal assumptions hidden by the happy path. Begin with a written normal condition and identify which request, state, physical result or communication value will provide independent confirmation. Do not begin by changing the configuration; the initial state is part of the evidence and should remain reproducible.

Controlled setup. Use the “Challenge assumptions” stage of the workflow: test both requests, direction change while moving, welded feedback, failed contactor, stopped feedback missing, overload, power loss, held start and restart without changing the acceptance contract. The acceptance record should show this result: limits, timing and restart behavior reach defined states. Record initial conditions, the exact stimulus and the observation point so another learner can repeat the case without relying on your memory.

Fault challenge. Introduce or analyse “The failure disappears after reset” as one bounded deviation. Inspect original symptom, histories, diagnostics, timestamps and active cause The working interpretation is that reset changed evidence or state without proving the initiating cause. The next proving action is to reproduce under a controlled condition and preserve pre/post-event data. Change only one condition before observing the result, and preserve timestamps or measurements where timing matters.

Review and recovery. The most common trap here is testing only one ideal sequence. After restoring the cause, repeat the normal case and at least one stop, timeout, disconnect or restart boundary relevant to this topic. Remove temporary forces and bypasses, return the model to a known state and retain the evidence that both operation and recovery are deliberate.

Explain it aloud: How do I practise forward-reverse commands, mutual interlock, stop priority and feedback effectively? A defensible short answer is: Use short cases with known initial conditions, a written prediction, one action and an observable result. Then alter a boundary or fault and explain why the evidence changed.

Case 05

predict → observe → prove

Prove diagnose a controlled fault

Engineering context. a request, priority, state, interlock, output-owner, contactor, drive, motor, feedback or restart mismatch. Preserve the first symptom, divide the system at a measurable boundary and change one condition only after predicting the result. Begin with a written normal condition and identify which request, state, physical result or communication value will provide independent confirmation. Do not begin by changing the configuration; the initial state is part of the evidence and should remain reproducible.

Controlled setup. Use the “Isolate one failure” stage of the workflow: introduce or analyse a request, priority, state, interlock, output-owner, contactor, drive, motor, feedback or restart mismatch and locate the first disagreement. The acceptance record should show this result: the proving action distinguishes the leading hypotheses. Record initial conditions, the exact stimulus and the observation point so another learner can repeat the case without relying on your memory.

Fault challenge. Introduce or analyse “Simulator and target disagree” as one bounded deviation. Inspect model boundary, software version, task timing, I/O behavior, data types and configuration The working interpretation is that a learning model and the intended target do not share one of the recorded assumptions. The next proving action is to reduce the case and verify against current target documentation. Change only one condition before observing the result, and preserve timestamps or measurements where timing matters.

Review and recovery. The most common trap here is resetting, forcing or replacing before evidence is retained. After restoring the cause, repeat the normal case and at least one stop, timeout, disconnect or restart boundary relevant to this topic. Remove temporary forces and bypasses, return the model to a known state and retain the evidence that both operation and recovery are deliberate.

Explain it aloud: What counts as proof of competence? A defensible short answer is: A repeatable artifact or system result plus an explanation of the signal path is stronger than time spent, screenshots or a copied answer. Physical competence requires separate supervised evidence.

Case 06

predict → observe → prove

Prove transfer and hand over

Engineering context. the logic recreated on target equipment with hardware interlocks, protection, phase checks, motion risks and supervised acceptance tests. Restore normal state, remove temporary changes, repeat affected checks and document which claims remain limited to the learning environment. Begin with a written normal condition and identify which request, state, physical result or communication value will provide independent confirmation. Do not begin by changing the configuration; the initial state is part of the evidence and should remain reproducible.

Controlled setup. Use the “Close the evidence loop” stage of the workflow: complete the logic recreated on target equipment with hardware interlocks, protection, phase checks, motion risks and supervised acceptance tests and repeat the affected regression cases. The acceptance record should show this result: a run is complete only when the requested behavior, stop behavior, fault response and recovery are observable from a fresh initial condition. Record initial conditions, the exact stimulus and the observation point so another learner can repeat the case without relying on your memory.

Fault challenge. Introduce or analyse “The result cannot be explained” as one bounded deviation. Inspect prediction, observation, proving action, alternative hypotheses and limitations The working interpretation is that activity occurred but the evidence is not yet transferable or reviewable. The next proving action is to have the learner defend the signal path and repeat a changed case. Change only one condition before observing the result, and preserve timestamps or measurements where timing matters.

Review and recovery. The most common trap here is treating an acknowledged message or one successful rerun as handover. After restoring the cause, repeat the normal case and at least one stop, timeout, disconnect or restart boundary relevant to this topic. Remove temporary forces and bypasses, return the model to a known state and retain the evidence that both operation and recovery are deliberate.

Explain it aloud: Why test faults and restart behavior? A defensible short answer is: Because a request, priority, state, interlock, output-owner, contactor, drive, motor, feedback or restart mismatch or both requests, direction change while moving, welded feedback, failed contactor, stopped feedback missing, overload, power loss, held start and restart can expose assumptions that never appear during ideal startup and steady operation.

Answer surface / 07

Questions people ask about Forward-reverse motor PLC scenario

These concise answers define the operating, training and product boundaries most often missed in broad summaries. The full workflow and diagnostic table above provide the evidence behind them.

How do you interlock forward and reverse motor outputs?

Use one explicit command owner plus mutual software conditions and the required hardwired or device interlocks so both direction outputs cannot energize together.

Can a motor reverse immediately while running?

The permitted policy depends on the motor, load and drive or starter; many systems require a proven stop and deliberate transition before the opposite direction.

What should I learn first about forward-reverse commands, mutual interlock, stop priority and feedback?

Start with the operating contract and evidence path: motor and load, forward and reverse requests, mode, permissives, stop priority, electrical and software interlocks, output ownership, auxiliary feedback, stopped condition, transition delay and restart policy, followed by operator request through command arbitration and interlocks to one final direction output, contactor or drive state, motor motion and independent direction feedback. Add advanced features only after the baseline is predictable.

How do I practise forward-reverse commands, mutual interlock, stop priority and feedback effectively?

Use short cases with known initial conditions, a written prediction, one action and an observable result. Then alter a boundary or fault and explain why the evidence changed.

What counts as proof of competence?

A repeatable artifact or system result plus an explanation of the signal path is stronger than time spent, screenshots or a copied answer. Physical competence requires separate supervised evidence.

Why test faults and restart behavior?

Because a request, priority, state, interlock, output-owner, contactor, drive, motor, feedback or restart mismatch or both requests, direction change while moving, welded feedback, failed contactor, stopped feedback missing, overload, power loss, held start and restart can expose assumptions that never appear during ideal startup and steady operation.

Can browser practice replace official software or hardware?

No. It can build concepts and diagnostic reasoning. Exact firmware, I/O electrical behavior, networking, safety and commissioning require current official tools, documentation and target equipment.

How should progress be documented?

Keep the requirement, initial state, program or configuration, observed values, fault hypothesis, proving action, recovery result and a concise limitations statement.

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Forward/Reverse Motor PLC Logic — Electrical and Logical Interlocks