1. Direct-On-Line (DOL) Motor Starter

The Direct-On-Line (DOL) motor starter is one of the most basic and widely used applications of ladder logic. It provides a simple method for starting and stopping an electric motor.

Functionality: The DOL starter uses a start button to energize a motor starter coil, which then latches itself on to maintain power to the motor. A stop button breaks the circuit, de-energizing the coil and stopping the motor.

// Ladder Logic for DOL Motor Starter
// ---[ Start ]----[ Stop ]----( Motor )---
//       |
//       -----( Motor )-------------

2. Star-Delta Motor Starter

Star-Delta motor starters are used to reduce the inrush current during motor startup. This is particularly useful for large motors that can cause voltage dips in the power supply.

Functionality: The motor starts with the windings connected in a star configuration, which reduces the voltage applied to each winding. After a set time, the windings are switched to a delta configuration, providing full voltage to the motor.

3. Sequential Motor Start

In many industrial processes, motors need to be started in a specific sequence. This can be achieved using ladder logic to create a sequential motor start system.

Functionality: The first motor starts when a start button is pressed. After a set time delay, the second motor starts, and so on, until all motors are running.

// Ladder Logic for Sequential Motor Start
// ---[ Start ]----[ Timer1.DN ]----( Motor1 )---
// ---[ Timer1.EN ]----( Timer1 )---
// ---[ Timer1.DN ]----[ Timer2.DN ]----( Motor2 )---
// ---[ Timer2.EN ]----( Timer2 )---

4. Tank Level Control

Tank level control is a common application in process industries. Ladder logic can be used to maintain the liquid level within a specified range.

Functionality: Sensors monitor the tank level. When the level drops below a low threshold, a pump is activated to fill the tank. The pump is deactivated when the level reaches a high threshold.

5. Traffic Light Control

Traffic light control is a classic example of using ladder logic for sequential control. It involves cycling through different light phases in a specific order.

Functionality: The ladder logic controls the sequence of red, yellow, and green lights based on timers. The sequence typically includes a green phase, a yellow phase, and a red phase, repeated continuously.

6. Conveyor Belt System

Conveyor belt systems are widely used in manufacturing and logistics. Ladder logic can control the start, stop, and speed of the conveyor belt, as well as monitor for jams or obstructions.

7. Automatic Filling Machine

Automatic filling machines use sensors and actuators to fill containers with a specific amount of product. Ladder logic controls the filling process, ensuring accuracy and efficiency.

8. Temperature Control System

Temperature control systems are used in various industries to maintain a desired temperature within a process. Ladder logic can control heaters, coolers, and fans to regulate temperature based on sensor feedback.

9. Packaging Machine Control

Packaging machines automate the process of packaging products, including tasks such as wrapping, sealing, and labeling. Ladder logic can control the various components of the packaging machine, ensuring synchronized operation.

10. Elevator Control

Elevator control systems use ladder logic to manage the movement of the elevator car between floors, respond to call buttons, and ensure passenger safety.