PLC products a wide range of its specifications and performance are also different. The classification of PLC, usually according to its different forms of structure, functional differences and the number of I / O points, such as the general classification.
1. Sort by I / O points
(1) minicomputer. Small PLC input and output points are generally below 256 points, the function of the main switch control, the user program memory capacity below 4K words. Small PLC is characterized by small size, low price, suitable for controlling a single device, the development of mechanical and electrical integration products.
(2) medium machine. Medium PLC input and output of the total points are generally 256 ~ 2048 points, the user program storage capacity of 2 to 8K words. Medium PLC not only has the switch and analog control function, but also has a stronger digital computing power, its communication function and analog processing capacity is more powerful, suitable for complex logic control system and continuous production process control occasions.
(3) mainframe. Large PLC input and output of the total number of points in more than 2048 points, the user program storage capacity of 8 ~ 16K words, it has the calculation, control and regulation functions, but also has a strong network structure and communication networking capabilities. Its surveillance system uses CRT display, can represent the process of dynamic processes. The mainframe is suitable for equipment automation control, process automation control and process monitoring system.
2. Sorted by structure
According to the different PLC structure, PLC can be divided into two kinds of monolithic and modular.
(1) the overall structure. Overall, also known as unit or box type, its small size, low price, small PLC – like the use of the overall structure.
The integral structure is characterized by the basic components of the PLC, such as CPU modules, I / O modules and power supply, etc. installed in a standard cabinet, a PLC to form a basic unit or expansion unit. There is no expansion port on the base unit, connected to the expansion unit via the extension cable to form a different configuration for the PLC.
The integrated PLC is also equipped with a number of dedicated special function modules to extend the functionality of the PLC.
(2) modular structure. Modular structure of the PLC by a number of modular units, these modules can be inserted on the frame or the substrate can be. Each module function is independent, uniform size, according to the need to flexibly configure the inserted module. At present, large and medium-sized PLC to use this structure.
3. Sort by function
According to the PLC has different functions, can be divided into low-end PLC, mid-range, high-grade three categories.
(1) low-end PLC: a logical operation, timing, counting, shift and self-diagnosis, monitoring and other basic functions, but also a small amount of analog input / output, arithmetic, data transmission and comparison, communication and other functions. Mainly used for logic control, sequential control or a small amount of analog control single control system.
(2) mid-range PLC: In addition to the function of low-grade PLC, but also has a strong analog input / output, arithmetic operations, data transmission and comparison, digital conversion, remote I / O, subroutine, communication networking and other functions. Some can also add interrupt control, PID control and other functions, suitable for complex control systems.
(3) high-end PLC: In addition to the function of the mid-range machine, but also increased with the symbol arithmetic, matrix operations, bit logic operations, square root operations and other special functions of the operation, tabulation and table transfer function. High-end PLC machine has a stronger communication networking capabilities, can be used for large-scale process control or constitute a distributed network control system to achieve factory automation.

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