PLC ladder diagram programming methods and five principles

Ladder programming is a method of building process control programs based on logic components (AND gates, OR gates, NOT gates) and control elements (counters, timers, comparators, etc.). In PLCs, ladder diagrams are usually written in an integrated development environment (IDE), where PLC programmers use a graphical editor to create connections between logic and control elements.

The methods of PLC ladder diagram programming mainly include the following:

1. Contact input and output method: According to the input and output devices and control requirements in the actual control system, design the input and output signals required for each part, and then set these signals as the input and output of the PLC program.

2. Functional modular programming method: Design the program modularly according to the function, treat each functional module as an independent "small program", and then connect these small programs together as needed to form a complete PLC program.

3. Process control programming method: According to the actual control system process, the PLC program is divided into several levels to implement different process controls respectively, and different equipment is operated according to the needs of the control process.

4. Event-driven programming method: Design the PLC program according to the event sequence in the actual control system. When the PLC receives an event signal, it controls the equipment according to the judgment conditions and event processing procedures designed in advance.

5. Object-oriented programming method: According to the objects and relationships in the actual control system, the PLC program is decomposed into several objects, and then corresponding states and operation interfaces are established for different objects to realize the control of the objects.

The five principles of PLC ladder programming are:

1. Clear planning: Before programming, you should plan the structure of the entire program and divide the modules according to the needs in order to write specific programs.

2. Simple logic: The writing logic should be as simple as possible, while also considering the maintainability and readability of the program.

3. Reasonable functions: When writing a program, full consideration should be given to functional needs, and only necessary functions should be involved to avoid program redundancy and complexity.

4. Good comments: Before writing a program, each module in the program should be commented so that subsequent engineers can understand the meaning of the code.

5. Exception handling: In the actual operation of the program, there will always be exceptions in the system. Developers should be able to handle these exceptions accordingly to avoid problems such as system crashes or data loss.