The development of PLC programmable controller

as the product of choice for discrete control, 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 controller to 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 controller is developed by imitation of the original relay control principle, PLC controller 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 controller in the 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 controller every time required to complete a cycle operation is called a scan cycle. Different models of PLC controller, 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. Large PLC controller using another CPU to complete the analogue calculation. Give the results to the PLC controller.

the same I/O points of the system, PLC controller 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, with the price of PLC controller and the decrease of the expansion of the user requirements, more and more small and medium-sized equipment adopted PLC controller to control, the application of PLC controller 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 controller will continue to maintain rapid growth momentum in our country.

general PLC controller is applied to special equipment can be thought of as it is an embedded controller, but relatively general embedded controller PLC controller has higher reliability and better stability. Encountered in practical work of some user originally USES the embedded controller, are now gradually universal PLC controller or custom PLC to replace the embedded controller.