Type or edit IEC 61131-3 Structured Text expressions on the left.
Click "⚡ Compile to Rust WASM" to translate assignments and boolean logic directly into native Rust bytecode evaluated deterministically on each scan cycle.
| Step | Operator | Operand | Accumulator (CR) Value | IEC Address Mapping |
|---|---|---|---|---|
| 001 | LD | %IX0.0 | FALSE (PB_START) | Pushbutton Start Contact |
| 002 | OR | %QX0.0 | FALSE (MOTOR_RUN) | Seal-in Auxiliary Contact |
| 003 | ANDN | %IX0.1 | TRUE (PB_STOP) | Normally Closed Stop PB |
| 004 | ANDN | %IX0.2 | TRUE (OVERLOAD) | Thermal Overload Relay |
| 005 | ST | %QX0.0 | FALSE | Store to Motor Run Contactor |
| 006 | LD | %IX0.3 | FALSE (PE_DETECT) | Conveyor PhotoEye Sensor |
| 007 | ST | %QX0.1 | FALSE (DIVERT_ACT) | Store to Diverter Actuator |
| # | Name | Class | Type | Initial Value | Documentation | Debug |
|---|---|---|---|---|---|---|
| 0 | State | Input | IRRIGATION STATE ▾ | 0 | Current operating sequencer state | 🐞 ON |
| 1 | Moisture | Input | BOOL ▾ | FALSE | Soil moisture sensor trip (%IX0.3) | 🐞 ON |
| 2 | T_Max | Input | TOD ▾ | TOD#18:00:00 | Time of Day irrigation lockout window | 🐞 OFF |
| 3 | Valve_Cmd | Output | BOOL ▾ | FALSE | Solenoid valve coil trigger (%QX0.1) | 🐞 ON |
Connect physical Modbus RTU slave devices (VFDs, energy meters, flow sensors) directly via USB-to-RS485 adapter using navigator.serial. If no physical USB adapter is plugged into your machine, use the Virtual Modbus RTU Loopback to simulate authentic 8-N-1 packet polling with CRC-16 validation.
Ingest agricultural and municipal wireless sensor telemetry from ChirpStack or TTN. Dynamic binary parser validates channels and sensor types, decoding real floating-point physical telemetry directly into PLC analog input registers (%IW0, %IW1, %IW2).
Discover and pair with industrial vibration accelerometers, bearing temperature sensors, and wireless flow transmitters using the native navigator.bluetooth API. (Requires compatible BLE GATT peripheral).
| Time | Dir | Trans ID | Function | Raw Hex Frame | Decoded Payload | Latency |
|---|
In strict compliance with our Zero Technical Fraud Mandate, this OpenPLC Web platform operates with 100% transparency regarding its computational and physical boundaries:
The IEC 61131-3 logic runs directly in your browser using safe Rust compiled to WebAssembly (openplc_rust_bg.wasm, 21.9 KB). It executes a simulated 10 ms (100 Hz) cyclic scan inside a dedicated browser Web Worker rather than a hard real-time RTOS (like VxWorks or Linux RT PREEMPT_RT). Observed cycle execution latency is typically sub-millisecond, but browser garbage collection and tab throttling mean this is an educational simulator, not a deterministically certified industrial runtime. Closing this tab stops execution.
There is no physical cast-iron centrifugal pump, copper wire, or pneumatic piston connected to your Mac. Field pressures, tank levels, and motor speeds are solved via real physical math models using affinity laws (\(H \propto N^2\)) and continuous dynamic differential equations.
Modbus TCP frames are processed by zero-copy byte buffers in WebAssembly memory without requiring root socket privileges or port 502 binding. This eliminates network stack overhead and guarantees instant zero-latency test feedback.
The Emergency Stop button models an interlock in software. Under international machinery safety standards (ISO 13850 / IEC 60204-1), a real emergency stop must be hardwired through safety relays directly to the drive's Safe Torque Off (STO) terminals to physically remove electrical power.
| Incident | Year | Root Cause | PLC / Safety Impact | Structural Insulation |
|---|---|---|---|---|
| Stuxnet | 2010 | Siemens S7-300 PLC rootkit intercepting OB1 cyclic scan | Over-speeded uranium enrichment centrifuges while reporting normal telemetry to WinCC SCADA | Cryptographic hash validation of ladder rungs; read-only PLC runtime integrity checks |
| Texas City Refinery | 2005 | Defective level transmitter float & manual bypass switch failure | Distillation tower overfilled with 52,000 gallons of hydrocarbons, vapor cloud ignited | Redundant high-high level switches (SIL-3) with independent physical shutdown circuit |
| Bellingham Olympic Pipeline | 1999 | SCADA database computer froze, preventing pressure relief valve actuation | Pipeline ruptured, releasing 277,000 gallons of gasoline into Whatcom Creek | Autonomous local soft-PLC interlock execution independent of supervisory HMI network |
| Triton / TRISIS | 2017 | Schneider Electric Triconex Safety Instrumented System (SIS) malware | Targeted industrial emergency shutdown controller at petrochemical facility | Physical keyswitch forced into RUN mode; air-gapped engineering workstation protocol |
Why does an automated factory look the way it does? Every industrial machine is engineered around a deterministic physical signal chain that connects the physical environment, logic computation, pneumatic power, and failsafe protection.
An optical retroreflective photo-eye shoots a 650nm infrared laser beam across the conveyor into a corner-cube reflector. When a cardboard carton intercepts the beam, the phototransistor turns OFF, switching 24V DC onto terminal %IX0.3. Optical sensing allows high-speed contactless detection of objects moving at >1.5 m/s.
Standard operating systems (Windows, generic Linux) introduce scheduling jitter. An industrial Programmable Logic Controller (PLC) executes a strict cyclic loop: 1. Read Inputs %IX → 2. Solve IEC 61131-3 Logic → 3. Write Outputs %QX with deterministic periodicity. In this browser lab, our Rust WebAssembly engine simulates this cyclic model at 10 ms (100 Hz), showing live measured execution latency without real-time RTOS guarantees.
A microchip cannot move a 10 kg box. The PLC output terminal (%QX0.1) switches a 24V DC transistor to energize an electromagnetic solenoid coil. This shifts a mechanical spool valve, routing 6-bar (87 psi) compressed air from the plant's pneumatic manifold directly into a double-acting cylinder.
The pneumatic cylinder piston extends linearly (+0.05m), pushing the package smoothly across the motorized conveyor belt onto the secondary unpowered roller spur line. When the box passes and the beam clears, a return spring or reverse air port retracts the pusher arm back to -0.45m.
Notice why Stop (%IX0.1) and Thermal Overload (%IX0.2) use Normally Closed (NC) contacts. In industrial electrical design, 24V DC must flow through the circuit when healthy. If a wire is severed, a fuse blows, or the motor bimetallic strip overheats, the circuit breaks open to 0V. The seal-in latch on Rung 1 instantly drops out, immediately stopping the motor contactor without relying on software to notice.
| Pin | Signal Type | IEC Address | Stable Alias (Cross-Validated) | Hardware Header | Live Electrical State / Simulation Contact |
|---|
| ADDR | TAG | VAL | ACTION |
|---|
| ADDR | TAG | VAL | STATUS |
|---|