PLC Ladder Logic Practice Online: Free LADX Mini Simulator

The fastest way to learn ladder logic

Ladder logic makes sense only when something moves because of it. Reading about contacts and coils is slow. Writing a rung, pressing a button and seeing a pump respond is fast. That is the idea behind the PLC lab in the EDWartens Lab and its editor, LADX Mini.

The video above shows the whole loop in sixteen seconds. A blank network, a contact added for the start button, a coil added for the motor, and then the plant running.

What happens in the clip

The job is called motor start and stop with overload. In the program tab you choose a language. Ladder is selected, and Structured Text and SFC are there as well if you want to try the same job another way.

You open the instruction panel, pick a normally open contact and place it on Network 1. It is addressed as Start_PB on input I0.0. Then you add an output coil addressed as Motor on Q0.0. That is the first rung of nearly every motor starter ever written.

Press Simulate and the view changes to a 2D plant. There is an effluent transfer pump, a tank on each side, an operator panel with START, STOP and an emergency stop. Hold START and the pump runs and liquid moves toward the treatment tank. Switch to the 3D view and you see the same plant as a real room, with a motor, a pipe and the tank, which you can orbit and zoom.

What to try next

A rung that runs only while you hold the button is not how a pump is started in a real plant. The classic fix is a seal-in contact, where the motor output holds itself on until STOP is pressed. Add a STOP contact, add a parallel branch with the motor contact across START, and watch the difference. Then think about the overload input, because the job name says overload and the plant model heats the motor.

Try the same logic in Structured Text, and compare. Writing the same small program in two languages is a good way to learn the difference.

Who it helps

B.E. and B.Tech students who only did PLC theory, diploma students whose lab has two trainer kits for the whole class, freshers who were told to practise before an interview, and technicians who keep fixing other people's programs but have never written one. It does not replace a real PLC and a wired panel, so treat it as the first step, and use the Bangalore classroom if you want hands-on time with hardware.

Start writing rungs

Open the PLC lab, build the start rung, press Simulate and then add the stop and the overload. Open the free PLC practice in your browser.

It is free to start, and nothing needs to be installed.

To learn this with an instructor in a classroom, see classroom PLC training in Bangalore.