PLC has the characteristics of strong versatility, convenient use, wide adaptability, high reliability, strong anti-interference ability, and simple programming.
The International Electrotechnical Commission (IEC) defines PLC in its standard as: "Programmable logic controller is an electronic system for digital operation, specially designed for application in industrial environment. It uses a type of programmable memory, It is used for its internal storage program to perform user-oriented instructions such as logic operations, sequence control, timing, counting and arithmetic operations, and to control various types of machinery or production processes through digital or analog input/output. Programmable logic controller And its related external devices are designed according to the principle of being easy to integrate with the industrial control system and easy to expand its functions.”
In 1968, General Motors of the United States proposed the famous "General Ten" bidding indicators, which are also the characteristics of the current PLC:
1. The programming is convenient, and the program can be modified on site;
2. Easy maintenance and modular structure;
3. The reliability is higher than that of the relay control device;
4. The volume is smaller than the relay control device;
5. The data can be directly sent to the computer;
6. The cost can be competitive with the relay control device;
7. The input can be AC 115V;
8. The output is AC 115V, above 2A, which can directly drive solenoid valves, contactors, etc.;
9. When expanding, the original system only needs minor changes;
10. The user program memory capacity can be expanded.
In 1978, NEMA defined the programmable controller as:
Programmable controller is an electronic device that operates digitally. It uses programmable memory to store instructions, perform functions such as logic, sequence, timing, counting, and arithmetic, and control it through digital or analog input and output modules. Various mechanical or work procedures.