Introduction to PLC required - — What is a PLC PLC known each other

Since the 1960 s the United States to launch a programmable logic controller ( 可编程序逻辑控制器,PLC) Since the device instead of traditional relay control, PLC controller got rapid development, has been widely used all over the world. At the same time, the function of PLC are continually improved. Along with the computer technology, signal processing technology, control technology, the development of network technology and the continuous improvement of user requirements, the PLC on the basis of switch process and increased the analog processing and motion control, and other functions. Today is no longer limited to the logic control of PLC, motion control, process control and other fields also plays a very important role. As the product of choice for discrete control system, PLC got rapid development in the ninety s and 1980 s, the world within the scope of the PLC controller annual growth rate of 20% ~ 30%. With the continuous improvement of factory automation and PLC the expansion of the base of market capacity, PLC in industrial developed countries in recent years growth speed slow. However, in developing countries such as China PLC is growing very quickly. Comprehensive related information, the sales revenue of 2004 global PLC for about $10 billion, occupies a very important position in the field of automation. PLC is developed by touch the imitation of the original relay control principle, PLC in the 1970 s only the switch quantity logic control, automobile manufacturing industry is the first application. It to store the execution logic operation, sequence control, timing, counting and arithmetic operations such as instruction; And through the digital input and output operations, to control various types of machinery or production process. User control program expressed the production process requirement, and advance in the PLC user program memory. Run time according to the content of the stored procedure to perform a detailed, to complete the process requirements of operation. PLC controller CPU contains instructions step program memory address of the program counter, in the process of program is running, each step this counter is automatically add 1, from initial step ( Step number zero) Executed in sequence to the final step ( Usually the END instruction) Step, and then return to the starting cycle operation. PLC every time required to complete a cycle operation is called a scan cycle. Different models of PLC, loop scan cycle between 1 millisecond to a few microseconds. PLC ladder diagram programming, in terms of solving logic, showing the advantages of quick, in microseconds level, solution 1 k logic program is less than 1 millisecond. It had all the input as a switch, and 16 ( There are also a 32-bit) As an analog. Use another large PLC CPU to complete the analogue calculation. Give the results to the PLC controller. The same I/O points system, PLC is much simpler to use than DCS, its cost is lower, Can save about 40% or so) 。 PLC no special operation station, it USES software and hardware is common, so the maintenance cost is much lower than DCS. A PLC controller, can receive thousands of I/O point ( Up to 8000 I/O) 。 If the object is mainly equipment chain, little circuit, PLC is more appropriate. PLC with general monitoring software, in terms of design management information system of enterprise, easier. In recent 10 years, as PLC prices falling and the expansion of the user requirements, more and more small and medium-sized equipment adopted PLC control, PLC application in our country is growing very quickly. As China's economy and the rapid development of basic automation level unceasing enhancement, the future for a period of PLC will continue to maintain rapid growth momentum in our country. General PLC is applied to special equipment can be thought of as it is an embedded controller, but relatively general embedded controller and PLC has higher reliability and better stability. Encountered in practical work of some user originally USES the embedded controller, are now gradually universal PLC or custom PLC to replace the embedded controller, PLC industry will have a bright future.
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