Worked examples with virtual plants
Real processes explained step by step, ordered by difficulty. Each example includes its input/output list, the Ladder program and an animated virtual plant. Open it in the simulator, run it and change it.
- 01Level 1Plant: Lamp
Turn on a lamp with a switch
The simplest program: one input and one output. Perfect for seeing power flow and the scan cycle for the first time.
- 02Level 1Plant: Motor with contactor and overload relay
Motor start and stop with seal-in
The most used circuit in industry: NO start button, NC stop button, contactor and thermal overload relay.
- 03Level 2Plant: Reversing motor
Reversing motor with electrical interlock
Two contactors run the motor in one direction or the other. An interlock prevents both from closing at once, which would cause a short circuit.
- 04Level 2Plant: Crossroad traffic lights
Crossroad traffic lights
Two coordinated traffic lights driven by a single cycle timer and compare contacts on its elapsed time.
- 05Level 2Plant: Automatic gate
Automatic gate
A gate that opens and closes with limit switches, stops and reopens if a photocell detects an obstacle, and warns with a flashing beacon while it moves.
- 06Level 2Plant: Tank with pump
Tank filling with level switches
A pump keeps the level between two switches: it starts at low level and stops at high level (hysteresis control).
- 07Level 3Plant: Star-delta motor starter
Star-delta starter with timer
The motor starts in star, with less current, and after a few seconds switches to delta. A timer marks the change and a short pause prevents a short circuit between contactors.
- 08Level 3Plant: Conveyor belt with boxes
Conveyor belt with box counter
A sensor counts the passing boxes. When a batch of 6 boxes is complete, the belt stops and a light turns on until the operator starts a new batch.
- 09Level 3Plant: Car park
Car park with space counter
An up/down counter keeps track of the cars inside. With all 10 spaces taken the FULL sign lights up and the entry barrier no longer opens.
- 10Level 4Plant: Sorting conveyor
Sorting parts by size
Two sensors at different heights tell the large parts apart. A timer waits for the part to reach the piston, which pushes it aside. Small parts continue to the end of the belt.
- 11Batch mixerComing soon
- 12Level 4Plant: Tank with two pumps
Two pumps with alternation and backup
Two pumps fill a tank. Each filling cycle uses a different one to share the wear, and if one fails the other takes over and an alarm lights up.
- 13Level 4Plant: Electric oven
On/off temperature control of an oven
A temperature transmitter gives an analog signal. The program scales it to degrees Celsius and switches the heater on and off with a ±5 °C hysteresis around 180 °C.
- 14Level 5Plant: Tank with proportional valve
Analog level control (introduction to PID)
A proportional valve opens more or less depending on how far the level is from 60 %. It is the P part of a PID, and shows its limitation: the steady-state error.