PLC (Programmable Logic Controller) is widely used in the industrial automation field due to its high reliability, flexibility, and scalability. In PLC programming, using PLC symbols can replace complex textual descriptions and make the code more intuitive and easy to understand. This article will cover the following topics:
1. PLC Symbol Overview
- 1.1 Basic Structure of PLC
- 1.2 Purpose of PLC Symbols
- 1.3 Application of PLC Symbols
2. Common PLC Symbols and Their Meanings
- 2.1 Input/Output symbols
- 2.2 Connection symbols
- 2.3 Control symbols
- 2.4 Counter/timer symbols
- 2.5 Storage symbols
- 2.6 Operation symbols
- 2.7 Other symbols
3. Examples of Using PLC Symbols
- 3.1 Input/output symbol examples
- 3.2 Connection symbol examples
- 3.3 Control symbol examples
- 3.4 Counter/timer symbol examples
- 3.5 Storage symbol examples
- 3.6 Operation symbol examples
- 3.7 Other symbol examples
4. Precautions When Using PLC Symbols
- 4.1 Size and position of symbols
- 4.2 Color and line type of symbols
- 4.3 Naming and numbering of symbols
5. Methods for Creating PLC Symbols
- 5.1 Manual drawing
- 5.2 Software drawing
6. Conclusion
1. PLC Symbol Overview
1.1 Basic Structure of PLC
PLC consists of a central processing unit (CPU), input/output (I/O) modules, power supply, and communication modules.
1.2 Purpose of PLC Symbols
PLC symbols can replace detailed textual descriptions and enable programmers to create more intuitive and understandable codes.
1.3 Application of PLC Symbols
PLC symbols are widely used in various automation control fields, such as power, chemical, metallurgy, machinery, and construction industries.
2. Common PLC Symbols and Their Meanings
2.1 Input/Output symbols
Input/output symbols are used to represent digital input and output devices or modules in the PLC system. The commonly used input/output symbols include switches, sensors, relays, etc.
2.2 Connection symbols
Connection symbols represent various connection methods between elements in the PLC system, including parallel, series, reverse parallel, reverse series, etc.
2.3 Control symbols
Control symbols represent the control logic of the PLC system, including logical relationships such as AND, OR, NOT, and command symbols such as SET, RESET, etc.
2.4 Counter/timer symbols
Counter/timer symbols represent the counter and timer in the PLC system, including UP, DOWN, TON, TOF, etc.
2.5 Storage symbols
Storage symbols represent storage devices in the PLC system, including M, S, T, and other types of storage devices used to store variables in the PLC program.
2.6 Operation symbols
Operation symbols represent arithmetic and logical operations in the PLC system, including basic operations such as addition, subtraction, multiplication, division, AND, OR, NOT, etc.
2.7 Other symbols
Other symbols include comparison symbols, output port symbols, etc., used to realize comparison and output operations in the PLC program.
3. Examples of Using PLC Symbols
3.1 Input/output symbol examples: The schematic diagram includes symbols for sensors, relays, buttons, warning lights, etc., used to control and monitor the device status.
3.2 Connection symbol examples: The schematic diagram includes parallel, series, reverse parallel, reverse series, and other connection methods, used to describe the connection method between elements.
3.3 Control symbol examples: The schematic diagram includes logical relationships such as AND, OR, NOT, etc., used to describe the control logic.
3.4 Counter/timer symbol examples: The schematic diagram includes UP, DOWN, TON, TOF, and other types, used to describe the counter and timer.
3.5 Storage symbol examples: The schematic diagram includes M, S, T, and other types of storage devices used to store variables in the PLC program.
3.6 Operation symbol examples: The schematic diagram includes basic operations such as addition, subtraction, multiplication, division, AND, OR, NOT, and other arithmetic and logical operations in the PLC program.
3.7 Other symbol examples: The schematic diagram includes comparison symbols, output port symbols, and other symbols used to realize comparison and output operations in the PLC program.
4. Precautions When Using PLC Symbols
4.1 Size and position of symbols
When drawing PLC symbols, attention should be paid to the size and position of the symbols to ensure that they are in accordance with specifications and aesthetically pleasing.
4.2 Color and line type of symbols
When drawing PLC symbols, attention should be paid to the color and line type of the symbols to distinguish different types of symbols and lines.
4.3 Naming and numbering of symbols
When writing PLC programs, each symbol needs to be named and numbered for easy programming and debugging.
5. Methods for Creating PLC Symbols
5.1 Manual drawing
PLC symbols can be drawn manually, paying attention to the size, proportion, and position of the symbols.
5.2 Software drawing
PLC drawing software can be used to draw PLC symbols, and some software also provides symbol libraries and shortcut keys, making it easier to use and modify.
6. Conclusion
PLC symbols are an essential part of PLC programming. Understanding the knowledge of PLC symbols can greatly improve the efficiency and quality of PLC programming. When creating and using PLC symbols, attention should be paid to the specifications and techniques to ensure the stability and reliability of the PLC system.
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