Why the Ladder Cannot Be Judged Yet
A ladder listing alone does not define the intended machine sequence. Without a control description, I/O expectations, or required state transitions, an engineer cannot determine whether the logic is correct. Add rung comments and document what each input, output, and internal condition must do before reviewing the program.
| Required evidence | Purpose |
|---|---|
| Control sequence | Defines the expected order of operations. |
| I/O behavior | Defines which conditions must turn each output on or off. |
| Rung comments | Makes intent traceable during review and simulation. |
Start the GX Works2 Simulator
- Press Alt+B, then S to start the simulator.
- Reset the simulator before testing.
- Place the simulated PLC in Run.
- Enter monitor mode.
If the shortcut does not open the expected command, use the equivalent simulator command available in the software interface; the evidence does not identify a software version or menu layout.
Test Inputs and Observe the Logic
In monitor mode, force the required simulated I/O or switch ladder contacts on and off. Exercise each documented operating condition and observe whether the rung states and outputs follow the intended sequence. Do not treat a successful Run state as proof of correct control behavior.
Record and Verify the Result
Compare every observed transition with the documented control requirement. A mismatch identifies either incorrect logic or an incomplete expectation. Remove forced states after each test so they do not affect the next condition, then add comments wherever the rung purpose remains unclear.
FAQ
How do I start the simulator in GX Works2?
Press Alt+B, then S. Reset the simulator, select Run, and enter monitor mode before testing contacts.
How can I test GX Works2 ladder logic without physical I/O?
Use the simulator and force simulated I/O or switch monitored contacts on and off. Confirm that each output and rung state matches the documented control sequence.
Can someone verify a PLC ladder program from the ladder alone?
Not reliably. The reviewer also needs the intended control sequence, expected I/O behavior, and rung comments to distinguish correct logic from unintended operation.