PLC ladder diagram and circuit diagram

Ladder logic programming language (LAD) is the most commonly used graphic programming language of PLC, and it is called the first programming language of PLC.

Ladder diagram language follows the form of relay control circuit. Ladder diagram is evolved by simplifying symbols on the basis of logic control of common relays and contactors. It has the characteristics of image, intuition and practicality, and is easily accepted by electrical technicians. It is the most widely used PLC programming language.

In the PLC program diagram, the left and right buses are similar to relay and contactor control power lines, the output coils are similar to loads, and the input contacts are similar to buttons. The ladder diagram consists of several levels, arranged from top to bottom. Each stage starts from the left bus, passes through contacts and coils and ends at the right bus.