What is a PLC simulator?
A PLC simulator runs a PLC program on an ordinary computer. It reads simulated inputs, solves your logic one scan at a time and writes simulated outputs, so you can write and test a program with no controller and no machine. FORGE is a free PLC simulator that runs in your browser.
What a PLC is
A PLC, or programmable logic controller, is the computer that runs a machine. It reads inputs such as buttons and sensors, runs a program, and turns outputs such as motors, valves and lamps on and off. It repeats this every few milliseconds. One round is one scan.
What the simulator does
The simulator does the same three steps in software. You set the inputs yourself, or a simulated machine sets them, and you watch the outputs change. This is the same seal-in rung run one scan at a time in FORGE:
1. Press Start. The StartPB branch passes power and StopPB is off, so Motor turns on at the end of the scan.
2. Release Start. Motor stays on. Its own contact on the lower branch now holds the rung.
3. Press Stop. The normally closed StopPB contact opens the rung, so Motor turns off.
4. Release Stop. Motor stays off until Start is pressed again.
| Step | StartPB | StopPB | Motor |
|---|---|---|---|
| 1. Press Start | 1 | 0 | 1 |
| 2. Release Start | 0 | 0 | 1 |
| 3. Press Stop | 0 | 1 | 0 |
| 4. Release Stop | 0 | 0 | 0 |
FORGE, the free PLC simulator in your browser
| In FORGE | Where to read more |
|---|---|
| Four languages: Ladder, Function Block Diagram, Sequential Function Chart and Structured Text | FBD, SFC, Structured Text |
| 90 instructions: contacts, coils, timers, counters, compare, math, text, arrays and more | Instructions |
| Run, Stop and Single Scan, with live tag values and forces | Test one scan at a time |
| Eight machine scenes to practise on | Simulators and scenes |
| Operator screens in HMI Studio | HMI Studio |
| Seven Link types to real devices and services | Links |
| FRC robot logic in Arena | Arena |
A simulator and a real PLC
| PLC simulator | Real PLC | |
|---|---|---|
| Inputs | Set by you, a forced value or a machine scene | Wired buttons, switches and sensors |
| Time | Simulated: each scan moves the clock by exactly the scan time | Real time |
| Mistakes | Free: press Reset and try again | Can damage a machine or hurt someone |
| Use | Learning, practice and testing logic | Running a machine |
FORGE is for learning and practice. It is not a safety system and must not run a real machine. A MicroController or network device you connect through a Link is for training setups.
Try it
- Open the free sandbox. No account is needed.
- It opens with Motor Starter Practice, a seal-in like the one above.
- Click Click to toggle bits, turn
StartPBon, then click Single Scan. - Read The scan cycle next, then open a scene from Simulators.