PLC英文文献+翻译

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PLC-english-wenxian-translate
ONE、PLC overview
　Programmable controller is the first in the late 1960s in the United States, 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 Corporation. Plc and the basic design is the 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 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 when 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 definition : 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, 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. Programmable controller for the user, is a 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 computer, with many distinctive features.
　First, high reliability, anti-interference capability;
　Second，programming visual, simple;
　Third, adaptability good;
　Fourth functional improvements, strong functional interface.
TWO、History of PLC
　Programmable Logic Controllers (PLC), a computing device invented by Richard E. Morley in 1968, have been widely used in industry 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 thereby the configuration time from 6 months down to 6 days [Moody and Morley, 1999].
　Although PC based control has started to come into place, PLC based control will remain the tec沈阳软件定制　Particularly,%20practical%20problems%20in%20PLC%20programming%20are%20to%20eliminate%20software%20bugs%20and%20to%20reduce%20the%20maintenance%20costs%20of%20old%20ladder%20logic%20programs.%20Though%20the%20hardware%20costs%20of%20PLCs%20are%20dropping%20continuously,%20reducing%20the%20scan%20time%20of%20the%20ladder%20logic%20is%20still%20an%20issue%20in%20industry%20so%20that%20low-cost%20PLCs%20can%20be%20used.
　In%20general,%20the%20productivity%20in%20generating%20PLC%20is%20far%20behind%20compared%20to%20other%20domains,%20for%20instance,%20VLSI%20design,%20where%20efficient%20computer%20aided%20design%20tools%20are%20in%20practice.%20Existent%20software%20engineering%20methodologies%20are%20not%20necessarily%20applicable%20to%20the%20PLC%20based%20software%20design%20because%20PLC-programming%20requires%20a%20simultaneous%20consideration%20of%20hardware%20and%20software.%20The%20software%20design%20becomes,%20thereby,%20more%20and%20more%20the%20major%20cost%20driver.%20In%20many%20industrial%20design%20projects,%20more%20than%20of%20the%20manpower%20allocated%20for%20the%20control%20system%20design%20and%20installation%20is%20scheduled%20for%20testing%20and%20debugging%20PLC%20programs.
　In%20addition,%20current%20PLC%20based%20control%20systems%20are%20not%20properly%20designed%20to%20support%20the%20growing%20demand%20for%20flexibility%20and%20reconfigurability%20of%20manufacturing%20systems.%20A%20further%20problem,%20impelling%20the%20need%20for%20a%20systematic%20design%20methodology,%20is%20the%20increasing%20software%20complexity%20in%20large-scale%20projects.

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