PLC Ladder Logic Simulator

Run and step through ladder logic programs in the browser — toggle digital inputs, watch outputs and coils update rung-by-rung, trace the PLC scan cycle, and advance through Beginner, Intermediate, and Advanced scenarios.

AVAILABLEAUTOMATED CHECKS ONLYCONCEPTUAL ONLYINTERMEDIATEWHAT DO THESE STATUSES MEAN?

LIVE LADDER EXECUTION3 DIFFICULTY LEVELSSCAN CYCLE TRACEI/O MONITOR

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Overview

Ladder logic is the lingua franca of industrial control systems, and the scan-cycle model that governs it — evaluate inputs, execute rungs left-to-right top-to-bottom, update outputs — is the mental model every controls engineer and technician must internalize. This simulator runs an executable ladder logic engine in the browser: load a preset scenario, press Run, and watch inputs, rungs, and outputs evaluate in real time. Toggling a digital input immediately changes rung continuity and output state within the same scan. Single-step mode lets you advance one scan at a time and observe exactly which rungs changed and why. The Ladder Logic tab shows the live rung diagram with contact states highlighted. The Process Mimic tab shows a visual representation of the controlled process (conveyor, pump, motor) responding to PLC outputs. Three difficulty tiers — Beginner, Intermediate, and Advanced — control program complexity. Scenarios include seal-in (latching) circuits, interlocking, and the PLC scan cycle demonstration. A Quiz tab reinforces ladder logic concepts. The I/O Monitor panel shows real-time digital input and output states.

App preview

A live look at the app you'll launch — every control on the left drives the visualizations on the right in real time.

Inside the lab

Example data — not a real field report

Dashboard with Run/Step controls, difficulty tier, and live I/O monitor — Dashboard — the mission-control view. Press Run to start the scan cycle, Step to advance one scan at a time, and toggle Beginner / Intermediate / Advanced to change program complexity. The I/O monitor on the right shows every digital input and output updating in real time as rungs evaluate.

Ladder Logic tab showing live rung diagram with energized contacts highlighted — Ladder Logic — the full-height rung diagram. Contacts light up as continuity flows left-to-right, coils energize when their rung is true, and seal-in / latching branches are easy to spot. Toggle any input and watch the affected rungs re-evaluate on the very next scan.

Process Mimic tab showing the controlled process responding to PLC outputs — Process Mimic — a visual representation of the process being controlled (conveyor, pump, motor, lights) driven directly by PLC outputs. Great for connecting abstract ladder logic to a physical picture of what the program is actually doing on the plant floor.

Learn tab explaining scan cycle, contacts, coils, and seal-in circuits — Learn — plain-language reference cards covering the PLC scan cycle, normally-open vs normally-closed contacts, output coils, seal-in (latching) circuits, and interlocking. Use it as an in-context primer before jumping into a scenario.

Quiz tab with multiple-choice questions on ladder logic and scan cycle — Quiz — short multiple-choice checks on scan order, contact/coil behavior, and common latching patterns. A quick way to confirm the concepts stuck before moving to the Intermediate and Advanced scenarios.

What you'll do

01Describe the PLC scan cycle — input scan, program execution, output update — and explain why scan order matters
02Trace rung continuity through series and parallel contact configurations to predict output coil state
03Implement a seal-in (latching) circuit using a normally-open output contact in parallel with a start pushbutton
04Apply interlocking logic to prevent two outputs from being energized simultaneously
05Toggle digital inputs and observe the effect on rung continuity within the same scan cycle
06Interpret an I/O monitor table showing current input and output states during program execution

Try a guided scenario

Build a start/stop latch with an interlock.

Ladder logic · PLC & Controls

No sign-in required. Progress is saved on this device.

What this lab is not

Not a design document, stamped calculation, or approval record.
Not a substitute for engineering analysis by a licensed professional.
Not connected to live equipment and not a safety device.

Calculation basis

Results are computed from first-principles circuit relationships using the values you enter.

Simplifying assumptions are stated in the lab itself; where a model is intentionally conceptual, the lab says so rather than implying study-grade accuracy.

Standards basis: Conceptual only. Validation state: Automated checks only (last checked 2026-08-15).