1. Classification by structure
According to the PLC‘s structure, PLC can be divided into two types of monolithic and modular.
(1) integrated PLC–PLC as a whole is the power supply, CPU, I/O interfaces and other components are collected in a single chassis, has the characteristic of compact structure, small size, low price. Small PLC uses this monolithic structure. Integrated PLC I/O points by different basic units (also known as a host) and expansion unit. Basic unit has CPU, I/O interfaces, and I/O expansion unit attached to the expansion port, and connected to the programmer or EPROM writer interface. Expansion units, only the I/O and power supply, no CPU. Basic flat cable connection between the unit and the extension unit. Overall PLC also can be equipped with special function units, such as analog unit, control unit, so that it functions to expand.
(2) modular modular PLC PLC PLC is the part were made into a separate module, CPU module, I/O modules, power supply module (included in the CPU module) and a variety of function modules. Modular PLC by a frame or base plate and a variety of modules. Module installed in the socket of the frame or substrate. This modular PLC is flexible, according to demand, systems of different sizes, and easy installation, easy to expand and repair. Large and medium PLC module structure is generally used.
Other PLC to combine monolithic and modular features, constitute the so-called stack–mounted PLC. Stack–mounted PLC CPU, power supplies, I/O interfaces such as separate modules, but by cables connected between them, and each module can assemble in the layer stack. In this way, not only the system can be flexibly configured, you can also do small.
2. Classification by function
According to the different functions of the PLC, PLC can be divided into low, mid-range, high-end class.
(1) low-grade PLC logic operations, timing and counting, shift and diagnostic, monitoring, and other basic functions, but also a small analog input/output, data transfer, arithmetic operations and compare, communications and other functions. Mainly used for logic control, order, control or a few analog control system.
(2) mid-range PLC in addition to the functions of low-grade PLC, also has a strong analog input/output, arithmetic, data transfer and comparison, conversion, remote I/O, subroutines, communication networks and other functions. There are also additional interrupt control, PID control functions such as applied to complex control systems.
(3) high PLC in addition to the functions of mid-range machines, increase of signed arithmetic operations, matrix operations, logical operations, square roots and other particular function of operations, tabulation and the transmission of the form function. High-end networking is more communication between PLC and can be used for large-scale or distributed network control system of process control and factory automation.
3. According to the I/O points classification
According to PLC I/O points, PLC can be divided into small, medium and large categories.
(1). small PLC–I/O points < 256; single–CPU, 8-bit or 16-bit processors, user memory capacity of 4K words.
For example: GE-I–United States General Electric (GE) company
TI100 United States Texas instruments company
F, F1, F2, Japan‘s Mitsubishi Electric Corporation
C20, C40 Japan stone companies (Omron)
S7-200 Germany Siemens company
EX20 EX40 Japan Toshiba
SR-20/21 joint venture Wuxi Hua Guang electronic industry Co Ltd
(2). medium–PLC–I/O point 256~2048 point dual CPU, user memory capacity 2~8K
For example: S7-300 Germany Siemens company
SR-400 joint venture Wuxi Hua Guang electronic industry Co Ltd
SU-5, SU-6, Germany Siemens company
C-500 Japan stone company
GE-III GE company
(3). large number PLC–I/O > 2048; CPU,16-bit, 32-bit processors, user memory capacity 8~16K
For example: S7-400 Germany Siemens company
GE-IV GE company
C-2000 stone company