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PLC hardware and software

Classification of PLC

PLC has formed micro,small,medium,large and giant PLCs in the 1990s.According to the number of I/O points,it can be divided into:

l Micro PLC:32 I/O

l Small PLC:256 I/O

l Medium PLC:1024 I/O

l Large PLC:4096 I/O

l Giant PLC:8195 I/O

In recent years,there are large-scale systems that support 300 loops and 65,000 I/O points in a single machine,which correspond to medium-sized PLCs and above,all of which use 16-bit to 32-bit CPUs.Micro and small PLCs originally used 8-bit CPUs.Now,according to the requirements of communication and other aspects,some are also Use a 16-bit to 32-bit CPU instead.Due to I/O

The sales of PLCs below 64 points account for 47%of the entire PLC,and those from 64 points to 256 points account for 31%,which together account for 78%of the entire PLC sales.Therefore,more research should be done on micro and small PLCs.

Hardware of PLC

The hardware of the PLC controller itself adopts a building block structure,and the product structure of each manufacturer is similar.Taking Japan’s Omron C200HE as an example,it is a bus template frame structure.The basic frame(CPU motherboard)is equipped with a CPU template,and other slots are equipped with I/O templates;The O expansion cable is connected to the I/O expansion motherboard,and the I/O module is installed on it;another method is to equip the remote I/O slave station,etc.These all show that PLC manufacturers develop all hardware components to users,which is convenient for users to choose and configure them into PLCs of different scales.Moreover,the openness of this hardware configuration is beneficial for manufacturers,distributors(agents),and system integrators.,The end user brings a lot of convenience,and it brings a lot of convenience to the marketing supply chain,which is a great success experience.

In addition to the general DI/DO and AD/DA templates,the I/O templates in PLC have also developed a series of I/O templates with special functions,which opens a way for PLC to be used in all walks of life,such as for barcodes ASCII/BASIC template for identification,PID template for feedback control,high-speed counting template for operation control,machining,single-axis position control template,dual-axis position control template,cam positioner template,RFID interface template,etc.,This will be further developed in the future.In addition,the related components of input and output,input and output electrical isolation and ground isolation in strong interference situations will also be more perfect.

The CPU in the PLC cooperates with the memory to complete the control function.It is different from the DCS system that deals with parameters such as temperature,pressure,flow,etc.It adopts a fast circuit scan period,generally 0.1~0.2s,and a faster scan period of 50ms or less.It is a digital sampling control system.