A Programmable Logic Controller (PLC) is a digital operation electronic system specifically designed for industrial environments. It uses a programmable memory to store instructions for logic operations, sequence control, timing, counting, and arithmetic operations. Through digital or analog input and output, it controls various types of mechanical equipment or production processes.

Components of a PLC

• Power Supply Module: Provides power to the entire PLC, commonly using AC 220V or DC 24V.

• CPU Module: The "brain" of the PLC, similar to a computer's CPU, and is a high-end microcontroller chip.

• Analog Input Module: Receives external analog input signals, such as 4-20mA or 0-10V analog signals.

• Digital Input Module: Receives external digital signals, usually 24V signals, such as from buttons.

• Analog Output Module: Outputs analog signals such as 4-20mA or 0-10V.

• Digital Output Module: Outputs 24V digital signals to drive components like contactor coils and solenoid valves.

• High-Speed Counting Module: For receiving external high-speed PWM pulse signals.

• Communication Module: Facilitates communication with external devices, such as RS485 and Ethernet interfaces, as well as specific protocol communication modules like ProfiNet and EtherCat.

• Specialized Module: For example, a weighing module.

• Rack: Used to connect the various sub-modules of the PLC, enabling communication and control between the CPU module and the sub-modules (larger PLCs require dedicated racks, while small or integrated PLCs do not).

PLC Application Areas

✔ Production Line Control: Control of various production lines, such as automotive electronics and mechanical manufacturing, including automatic packaging, assembly, processing, handling, inspection, and more.

✔ Robot Control: In automotive factories (for example, hundreds of robots on the Jianghuai NIO automotive production line are almost entirely controlled by PLCs).

✔ Intelligent Building Control: Also known as building automation, where PLCs serve as the main controllers for systems like water supply, elevators, lighting, and surveillance in buildings.

✔ Energy System Control: For example, control of wind power generation, solar energy production, and generator sets.

✔ Precision Machine Tool Equipment: Control of inverters, servo motors, stepper motors, and more via PLCs.

✔ Traffic Light Control: Most traffic lights were previously controlled by small PLCs, with traffic light control being a classic example in PLC training materials.

Selecting a PLC

The selection of a PLC depends on the specific control requirements. The number of I/O points should be estimated based on the functional control needs. Most PLCs come with RS232 or RS485 interfaces and Ethernet interfaces. If special communication methods are needed, a PLC module with specific communication capabilities should be chosen.

For structure selection, PLCs come in two types: integrated and modular. Integrated PLCs are typically smaller, with the power supply, CPU, input/output modules, and communication modules all included in one unit, making them non-expandable. Modular PLCs typically require a rack, with each sub-module operating independently, allowing additional modules to be added as needed.