PLC controllers play a core role in the field of industrial automation, and their main functions can be summarized as follows:
Real time collection and processing of on-site signals (perception and input):
PLC continuously connects and monitors the status signals (such as temperature, pressure, position, switch on/off, flow, etc.) of various sensors, switches, buttons, and other devices from the field through its input module (I/O).
It converts various physical quantities (analog quantities such as 420mA, 010V) or switch states (digital quantities) into digital signals that can be processed internally by the PLC. This is equivalent to the "senses" of an automated system.
Execute user written control logic (brain and decision-making):
This is the most core and iconic role of PLC. Engineers use specialized programming languages (such as ladder diagrams, functional block diagrams, structured text, etc.) to write programs based on the process requirements and control logic of the controlled object.
The central processing unit (CPU) of PLC reads the input status at high speed and cyclically according to the set scanning cycle, and executes logical operations, sequential control, timing, counting, arithmetic operations, data processing and other instructions in the user program.
The result of program execution determines the state of the output signal. This is equivalent to the "brain" of an automated system, responsible for making decisions based on input information and preset rules.
Drive on-site actuator actions (output and execution):
PLC sends control signals to the on-site execution mechanism through its output module (I/O) based on the results of program calculations.
These signals drive the motor to start and stop, control valve opening and closing, adjust the speed of the frequency converter, light up indicator lights, start alarms, etc., thereby directly controlling mechanical equipment or production processes. This is equivalent to the "hands and feet" of an automation system.
Provide reliable and real-time automation control (core value):
Replacing complex relay logic: Compared to traditional relay control systems, PLC implements control logic through software programming, greatly simplifying hardware wiring and improving system flexibility and reliability. Modifying control logic only requires modifying the program without rewiring, significantly shortening the development, debugging, and maintenance cycle.
High reliability and stability: PLC is designed specifically for industrial environments, with characteristics such as anti-interference, resistance to harsh environments (temperature, humidity, dust, vibration), and long-term stable operation.
Strong real-time performance: The cyclic scanning mechanism of PLC (input sampling>program execution>output refresh) ensures control certainty and can respond to input changes and update outputs in milliseconds, meeting the real-time requirements of most industrial processes.
Sequential control, process control, and motion control: PLCs are adept at handling sequential logic based on time and events (such as pipeline workstation conversion), as well as basic analog process control (such as PID regulation). Some high-performance PLCs can also achieve complex motion control (such as positioning and interpolation).
Realize communication and data exchange between devices (information hub):
Modern PLCs typically have powerful communication capabilities and support multiple industrial communication protocols such as Modbus, Profibus, EtherNet/IP, CANopen, Profinet, EtherCAT, etc.
This enables PLC to:
Connect with human-machine interface (HMI) or monitoring and data acquisition (SCADA) system to provide operation interface and data monitoring.
Exchange data and collaborate with other PLCs or intelligent devices such as frequency converters, robots, and instruments.
Connect with the upper computer management system (such as MES, ERP), upload production data, receive production instructions, and achieve information integration at the workshop or factory level.
In summary, the main functions of PLC controllers are:
As the core control unit of industrial automation systems, it collects real-time input signals from the site, executes user written control program logic at high speed, and drives the actions of on-site execution mechanisms accordingly, achieving highly reliable, flexible, and real-time automation control of mechanical equipment or production processes. At the same time, as an information hub, it connects on-site devices with upper level management systems, building a complete automation and information network.
In short, PLC is the "intelligent switch" and "decision-making center" in industrial automation. It softens and modularizes complex control logic, greatly improving the efficiency, quality, and flexibility of industrial production.