The main function of a PLC controller is to realize industrial automation control. It is capable of accepting input signals, such as temperature, pressure, flow rate detected by sensors, processing them through internal program logic, and then generating output signals to control, for example, the operation of actuators such as motors, valves, and liquid levelers.PLC controllers can be programmed to meet a variety of automation control needs, and their programmability, stability, and reliability are among their greatest strengths. Due to their modular structure, PLC controllers can be expanded and upgraded according to specific control needs.
Specifically, the PLC controller consists of the following basic components:
CPU (Central Processing Unit): Responsible for controlling the operation of the entire system, executing user-written programs and handling input/output operations.
Input/Output Module (I/O Module): Receives input signals (e.g., sensors, pushbuttons, switches, etc.), converts them to digital signals, and transmits them to the CPU for processing. Similarly, output modules convert digital signals processed by the CPU into physical operations (e.g. motors, lights, buzzers, etc.).
Memory: PLC controllers use memory to store user-written information such as programs, data, variables, and status.
PROGRAMMERS: PLC controller programmers are used to write, modify and download programs into the PLC controller's memory.
Communication Interfaces: PLC controllers can also communicate with other devices (e.g. computers, sensors, actuators, etc.) through various communication interfaces.
In general, PLC controller realizes industrial automation control by processing input signals and output signals, and its programmability, modularity, scalability and other features make it an indispensable part of industrial automation control.
PLC's five functions explained
1. Switching logic control
This is the most basic and most widely used PLC, PLC input signals and output signals are only on / off state of the switching signal, this control is the closest to the relay control, you can use the lower price, only switching control function of the PLC as a relay control system alternatives. Switching logic control can be used for single equipment, can also be used in automatic production lines, such as a variety of relay control, stamping, casting machinery, transport belts, packaging machinery control, elevator control, chemical systems in a variety of pumps and solenoid valve control, metallurgical systems, blast furnace charging system, rolling mill, continuous casting machine, flying shear control, plating production line, beer filling production line, automobile assembly line, TV and Radio production line control, etc.
2. Motion control
PLC can be used for linear or circular motion control. Early direct switching I / O module connected to the position sensor and the actuator, now generally have a dedicated motion control module, the world's major PLC manufacturers produce PLC almost all have motion control functions.PLC motion control functions are widely used in a variety of machinery, such as metal cutting machine tools, metal molding machinery, assembly machinery, robots, elevators and so on.
3. Closed-loop process control
Process control refers to the closed-loop control of temperature, pressure, flow and other continuously changing analog quantities, PLC through the analog I / O module, analog (Analog) and digital (Digital) between the A/D conversion and D / A conversion. And the analog implement closed-loop PID control. Modern large and medium-sized PLC generally have PID closed-loop control function, this function can be realized with a dedicated intelligent PID module PID subroutine, you can also design the PID subroutine to complete, and more use of special PID function instruction to complete.PLC analog PID control function has been widely used in plastic extrusion molding machines, heating furnaces, heat-treatment furnaces, boilers and other equipment, as well as Light industry, chemical industry, machinery, metallurgy, electric power, building materials and other industries.
4. Data processing
Modern PLC has mathematical operations (including matrix operations, function operations, logic operations), data operations, conversion, sorting and table lookup, bit operation and other functions, can complete the data acquisition, analysis and processing. These data can be stored in memory with the reference value comparison, but also can use the communication function to other intelligent devices, or they will print tabulation, data processing is generally used for large-scale control systems, such as unmanned flexible manufacturing system, can also be used for process control systems, such as papermaking, metallurgy, the food industry, some of the large-scale control systems.
5. Communication
PLC communication includes communication between programmable controllers, programmable controllers and other intelligent control devices. With the development of computer control, in recent years the development of foreign factory automation communication network very quickly, the famous PLC manufacturers have launched a network system between the PLC.