Abstract: PLC is microprocessor-based, integrated computer, communications, networking, and automatic control technology and the development of a new generation of industrial control devices. PLC in China's development and application of some 30 years of history, now it has been widely used in the national economy in all areas of industrial production, raise a traditional industrial equipment and technical capacity of key equipment and a strong pillar. With the global integration of economic development, efforts to develop PLC in China's large-scale applications, with independent intellectual property rights form the PLC technology, should be a vast number of technical personnel to the direction. PLC is an industrial environment for the design and application of digital computing operating system. It uses programmable memory storage implementation logical, sequential control, timing counts and arithmetic operations, and other operational directives, through digital and analog input and output, the mechanical movement and control of the production process. Key words: PLC； digital computing operating system 1 The definition of a programmable logic controller Programmable logic controller, or PLC (Programmable logic Controller), refers to computer technology as the basis for the new industrial control devices. In 1987 the International Electrotechnical Commission draft standards promulgated by the PLC in the PLC to do the following definition:
