PLC = Programmable, Logic, Controller, programmable logic controller, an electronic system for digital operation, designed for use in industrial environments. It uses a programmable memory, used in its internal storage procedures to perform the logic operation, sequence control, timing, counting and arithmetic operations such as user oriented instructions, and through digital or analog input / output control various types of machinery or production processes. It’s the core part of industrial control.
At present, PLC has been widely applied in iron and steel, petroleum, chemical, electric power, building materials, machinery manufacturing, automobile, textile, transportation, environmental protection, water treatment and cultural entertainment industries, using general can be summed up as follows.
1 、 logic control of switch quantity
This is the PLC the most basic and most widely used, it is replacing the traditional relay circuit, logic control, sequence control, which can be used for the control of a single device, can also be used for machine control and automation line. Such as injection molding
2 analog control
In the process of industrial production, there are many continuous changes, such as temperature, pressure, flow rate, liquid level and velocity, etc.. In order for the programmable controller to process analog quantities, the A/D conversion and D/A conversion between analog (Analog) and digital (Digital) quantities must be implemented. PLC manufactures both A/D and D/A conversion modules that allow programmable controllers to be used for analog control.
3, exercise control
PLC can be used for the control of circular motion or linear motion. From the configuration of the control mechanism, the former is used directly for the switch I/O module, the position sensor and the actuator. Now, the special motion control module is used. Such as the stepper motor or servo motor single axis or multi axis position control module. Almost all of the major PLC manufacturers in the world have motion control functions, which are widely used in various machines, machine tools, robots, elevators and so on.
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 work out a wide variety of control algorithms to complete closed-loop control. PID regulation is a widely used adjustment method in general closed loop control systems. Large and medium-sized PLC have PID modules, and many small PLC also have this function module. PID processing is typically running PID subroutines that are specific. Process control has a wide range of applications in metallurgy, chemical, heat treatment, boiler control and other occasions.
5, data processing
Modern PLC has the functions of mathematical operation (including matrix operation, function calculation and logic operation), data transfer, data conversion, sorting, table look-up, bit operation, etc. it can complete data collection, analysis and processing. These data can be compared with reference values stored in memory, complete a certain control operation, or can be transferred to other intelligent devices by communication function, or printed and recorded. Data processing is generally used in large-scale control systems, such as unmanned flexible manufacturing systems, and can also be used in process control systems, such as paper, metallurgy, and food industry.
6, communications and networking
PLC communication includes communication between PLC and communication between PLC and other intelligent devices. With the development of computer control, factory automation network is developing very fast, and all PLC vendors attach great importance to the communication function of PLC, and have launched their own network systems. The newly produced PLC have communication interface, and communication is very convenient.
In short, PLC is mainly used to achieve industrial automation control procedures, but now because of the development of the hardware and software function more and more powerful, and increasingly low cost, its application is not limited to industrial countries in recent years, in addition, vigorously promote industrial restructuring, so industrial automation is becoming more and more popular, so as to achieve the backbone PLC industrial automation control, PLC forward good.