PLC Ladder Logic Simulator

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.

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

• 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