pc外文文献译文.doc

外文文献译文 设计(论文)题目: 可编程逻辑控制器 专业与班级: 学生姓名: 指导教师: 2010年3月18日 Programmable logic controller A programmable logic controller (PLC) or programmable controller is a HYPERLINK /wiki/Digital_computerdigital computer used for HYPERLINK /wiki/Automationautomation of HYPERLINK /wiki/Electromechanicalelectromechanical processes, such as control of machinery on factory HYPERLINK /wiki/Assembly_lineassembly lines, amusement rides, or lighting fixtures. PLCs are used in many industries and machines. Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery-backed or HYPERLINK /wiki/Non-volatile_memorynon-volatile memory. A PLC is an example of a HYPERLINK /wiki/Real-time_computingreal time system since output results must be produced in response to input conditions within a bounded time, otherwise unintended operation will result. 1.History The PLC was invented in response to the needs of the American automotive manufacturing industry. Programmable logic controllers were initially adopted by the automotive industry where software revision replaced the re-wiring of hard-wired control panels when production models changed. Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was accomplished using hundreds or thousands of HYPERLINK /wiki/Relayrelays, HYPERLINK /wiki/Cam_timercam timers, and HYPERLINK /wiki/Drum_sequencerdrum sequencers and dedicated closed-loop controllers. The process for updating such facilities for the yearly model HYPERLINK /wiki/Changeoverchange-over was very time consuming and expensive, as HYPERLINK /wiki/Electricianelectricians needed to individually rewire each and every relay. In 196