What are the application areas of PLC?
PLC programmable controller is an electronic device specially designed for digital computing operation in industrial environments. It uses a memory that can be programmed to store instructions for performing logical operations, sequential operations, timing, counting and arithmetic operations in its interior, and can control various types of mechanical or production processes through digital or analog inputs and outputs. PLC and its related peripherals should be designed according to the principle of easy to form a whole with the industrial control system and easy to expand its functions.
At present, PLC programmable controllers have been widely used in various industries such as steel, petroleum, chemical, electric power, building materials, machinery manufacturing, automobiles, light textiles, transportation, environmental protection and culture and entertainment at home and abroad, and the use cases can be roughly summarized into the following categories.
1. Logic control of switch
This is the most basic and extensive application field of PLC, which replaces the traditional relay circuit to realize logic control and sequence control, which can be used for the control of a single device, as well as for multi-machine group control and automatic assembly line. Such as injection molding machines, printing machines, staple machinery, combination machine tools, grinding machines, packaging production lines, electroplating lines, etc.
2. Analog control
In industrial processes, there are many continuously varying quantities such as temperature, pressure, flow, level and velocity that are analog. In order for the programmable controller to process analog quantities, A/D conversion and D/A conversion between analog and digital must be realized. PLC manufacturers produce matching A/D and D/A conversion modules to enable programmable controllers for analog control.
3. Motion control
PLC can be used for the control of circular motion or linear motion. In terms of control mechanism configuration, in the early days, it was directly used to connect position sensors and actuators to switching I/O modules, and now dedicated motion control modules are generally used. For example, single-axis or multi-axis position control modules that can drive stepper motors or servo motors. Almost all the products of the world's major PLC manufacturers have motion control functions, which are widely used in various machinery, machine tools, robots, elevators and other occasions.
4. Process control
Process control refers to the closed-loop control of analog quantities such as temperature, pressure, and flow. As an industrial control computer, PLC can program a variety of control algorithms to complete closed-loop control. PID adjustment is a more commonly used adjustment method in general closed-loop control systems. Large and medium-sized PLCs have PID modules, and many small PLCs also have this function module. PID processing is generally done by running a dedicated PID subroutine. Process control has a wide range of applications in metallurgy, chemical industry, heat treatment, boiler control and other occasions.
5. Data processing
Modern PLC has mathematical operations (including matrix operations, function operations, logical operations), data transmission, data conversion, sorting, table lookup, bit operations and other functions, which can complete data collection, analysis and processing. This data can be compared with a reference value stored in memory to complete certain control operations, or it can be transmitted to other smart devices using communication functions, or they can be printed and tabulated. Data processing is generally used for large-scale control systems, such as unmanned flexible manufacturing systems; It can also be used for process control systems, such as some large control systems in the papermaking, metallurgy, and food industries.
6. Communication and networking
PLC communication includes communication between PLCs and communication between PLCs and other intelligent devices. With the development of computer control, factory automation networks have developed rapidly, and PLC manufacturers have attached great importance to the communication function of PLC and have launched their own network systems. The newly produced PLCs have communication interfaces, which is very convenient for communication.