What are the application fields of PLC?
May 26, 2022
A PLC programmable controller is an electronic device that performs digital operations specifically designed for use in industrial environments. It uses a programmable memory to store instructions for performing operations such as logical operations, sequential operations, timing, counting, and arithmetic operations, and can control various types of equipment through digital or analog inputs and outputs. machinery or production process. PLC and its related peripheral equipment should be designed according to the principle of easy integration with the industrial control system and easy expansion of its functions.
At present, PLC programmable controllers have been widely used in various industries such as steel, petroleum, chemical industry, electric power, building materials, machinery manufacturing, automobiles, textiles, transportation, environmental protection, culture and entertainment at home and abroad. The usage can be roughly summarized as follows Several categories.
1. Logic control of switching quantity
This is the most basic and extensive application field of PLC. It replaces traditional relay circuits to realize logic control and sequence control. It can be used for the control of single equipment, as well as for multi-machine group control and automated assembly lines. Such as injection molding machines, printing machines, stapling machinery, combination machine tools, grinders, packaging production lines, electroplating lines, etc.
2. Analog control
In the industrial production process, there are many continuously changing quantities, such as temperature, pressure, flow, liquid level and speed, etc., which are all analog quantities. In order for the programmable controller to process analog quantities, A/D conversion and D/A conversion between analog quantities (Analog) and digital quantities (Digital) must be implemented. PLC manufacturers all produce matching A/D and D/A conversion modules to enable programmable controllers to be used for analog control.
3. Motion control
PLC can be used to control circular motion or linear motion. In terms of control mechanism configuration, in the early days, switching I/O modules were directly used to connect position sensors and actuators. Nowadays, dedicated motion control modules are generally used. Such as single-axis or multi-axis position control modules that can drive stepper motors or servo motors. Almost all the products of major PLC manufacturers in the world have motion control functions and are widely used in various machinery, machine tools, robots, elevators, etc.
4. Process control
Process control refers to the closed-loop control of analog quantities such as temperature, pressure, flow, etc. As an industrial control computer, PLC can program various control algorithms to complete closed-loop control. PID adjustment is a 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 functional module. PID processing generally runs a dedicated PID subroutine. Process control is widely used in metallurgy, chemical industry, heat treatment, boiler control and other occasions.
5. Data processing
Modern PLC has functions such as mathematical operations (including matrix operations, function operations, and logical operations), data transmission, data conversion, sorting, table lookup, and bit operations, and can complete data collection, analysis, and processing. These data can be compared with the reference values stored in the memory to complete certain control operations. They can also be transmitted to other smart devices using the communication function, or they can be printed and tabulated. Data processing is generally used in large-scale control systems, such as unmanned flexible manufacturing systems; it can also be used in process control systems, such as some large-scale control systems in 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. All PLC manufacturers attach great importance to the communication function of PLC and have launched their own network systems. Newly produced PLCs all have communication interfaces, making communication very convenient.
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