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1、 晋 中 学 院本科毕业设计英文参考资料题 目 Programmable Logic Controller PLC 院 系 机械学院 专 业 机械设计制造及其自动化 姓 名 学 号 1014312109 学习年限2010年09月至2012年07月 指导教师 职称 讲师 申请学位 学士学位 2012年05月20日l英文原文：Programmable Logic Controller PLC1 PLC IntroducePLC Introduction Programmable controller is the first in the late 1960s in the United Stat
2、es, then called PLC programmable logic controller (Programmable Logic Controller) is used to replace relays. For the implementation of the logical judgment, timing, sequence number, and other control functions. The concept is presented PLC General Motors Coroperation.PLC and the basic design is the
3、computer functional improvements, flexible, generic and other advantages and relay control system simple and easy to operate, such as the advantages of cheap prices combined controller hardware is standard and overall. According to the practical application of target software in order to control the
4、 content of the user procedures memory controller, the controller and connecting the accused convenient target. In the mid-1970s, the PLC has been widely used as a central processing unit microprocessor, import export module and the external circuits are used, large-scale integrated circuits even wh
5、en the PLC is no longer the only logical (IC) judgment functions also have data processing, PID conditioning and data communications functions. International Electro technical Commission (IEC) standards promulgated programmable controller for programmable controller draft made the following definiti
6、on: programmable controller is a digital electronic computers operating system, specifically for applications in the industrial design environment. It used programmable memory, used to implement logic in their internal storage operations, sequence control, timing, counting and arithmetic operations,
7、 such as operating instructions, and through digital and analog input and output, the control of various types of machinery or production processes. Programmable controller and related peripherals, and industrial control systems easily linked to form a whole, to expand its functional design. Program
8、mable controller for the user, is non-contact equipment, the procedures can be changed to change production processes. The programmable controller has become a powerful tool for factory automation, widely popular replication. Programmable controller is user-oriented industries dedicated control comp
9、uter, with many distinctive features.high reliability, anti-interference capability; programming visual, simple; adaptability good; functional improvements, strong functional interface.Programmable Logic Controllers (PLC), a computing device invented by Richard E. Morley, have been widely used in in
10、dustry including manufacturing systems, transportation systems, chemical process facilities, and many others. At that time, the PLC replaced the hardwired logic with soft-wired logic or so-called relay ladder logic (RLL), a programming language visually resembling the hardwired logic, and reduced th
11、ereby the configuration time from 6 months down to 6 days. Although PC based control has started to come into place, PLC based control will remain the technique to which the majority of industrial applications will adhere due to its higher performance, lower price, and superior reliability in harsh
12、environments. Moreover, according to a study on the PLC market of Frost and Sullivan, an increase of the annual sales volume to 15 million PLC per year with the hardware value of more than 8 billion US dollars has been predicted, though the prices of computing hardware is steadily dropping. The inve
13、ntor of the PLC, Richard E Morley, fairly considers the PLC market as a 5-billion industry at the present time. Though PLC are widely used in industrial practice, the programming of PLC based control systems is still very much relying on trial-and-error. Alike software engineering, PLC software desi
14、gn is facing the software dilemma or crisis in a similar way. Morley himself emphasized this aspect most forcefully by indicating: “If houses were built like software projects, a single woodpecker could destroy civilization.” Particularly, practical problems in PLC programming are to eliminate softw
15、are bugs and to reduce the maintenance costs of old ladder logic programs. Though the hardware costs of PLC are dropping continuously, reducing the scan time of the ladder logic is still an issue in industry so that low-cost PLC can be used. In general, the productivity in generating PLC is far behind compared to other domains, for instance, VLSI design, where efficient computer aided design tools are in practice. Existent software engineering methodologies are not necessarily applicable to the PLC based software design because PLC-programming requires a simultaneous consideration
