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There are many kinds of PLC products,and their specifications and performances also vary.The classification of PLC is usually roughly classified according to the difference in its structure,the difference in function,and the number of I/O points.

Classification by structure

According to the structure of PLC,PLC can be divided into two types:integral type and modular type.

Integral PLC Integral PLC integrates the power supply,CPU,I/O interface and other components in one chassis,and has the characteristics of compact structure,small size and low price.Small PLC generally adopts this kind of integral structure.Integral PLC is composed of basic unit(also called host)and expansion unit with different I/O points.In the basic unit,there are CPU,I/O interface,expansion port connected with I/O expansion unit,and interface connected with programmer or EPROM writer.There are only I/O and power supply in the expansion unit,and there is no CPU.The basic unit and extension unit are generally connected by flat cables.Integral PLC can generally be equipped with special functional units,such as analog units,position control units,etc.,to expand its functions.

Modular PLC Modular PLC is to make each component of PLC into several separate modules,such as CPU module,I/O module,power supply module(some are included in CPU module)and various functional modules.Modular PLC consists of frame or base plate and various modules.The modules are mounted on the sockets of the frame or base plate.The characteristics of this modular PLC are flexible configuration,which can be selected according to the needs of different scale systems,and easy to assemble,easy to expand and maintain.Large and medium-sized PLCs generally adopt a modular structure.

There are also some PLCs that combine the characteristics of integral and modular to form a so-called stacked PLC.The CPU,power supply,I/O interface,etc.of the stacked PLC are also independent modules,but they are connected by cables,and each module can be stacked layer by layer.In this way,not only the system can be flexibly configured,but also can be made compact.

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