【正文】 , 1Network 17 LD S , 1Network 18 LD TON T39, 30Network 19 // 產(chǎn)生下一臺空壓機(jī)變頻運(yùn)行啟動信號LD T39EU= R , 1 R , 1 系統(tǒng)圖紙山東科技大學(xué)學(xué)士學(xué)位論文 外文文獻(xiàn)翻譯 外文文獻(xiàn)翻譯Programmable logic controller[11]A programmable logic controller (PLC) or programmable controller is a digital puter used for automation of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or lighting fixtures. PLCs are used in many industries and machines. Unlike generalpurpose puters, 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 batterybacked or nonvolatile memory. A PLC is an example of a real time system since output results must be produced in response to input conditions within a bounded time, otherwise unintended operation will result. 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 rewiring of hardwired control panels when production models changed. Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was acplished using hundreds or thousands of relays, cam timers, and drum sequencers and dedicated closedloop controllers. The process for updating such facilities for the yearly model changeover was very time consuming and expensive, as electricians needed to individually rewire each and every relay. In 1968 GM Hydramatic (the automatic transmission division of General Motors) issued a request for proposal for an electronic replacement for hardwired relay systems. The winning proposal came from Bedford Associates of Bedford, Massachusetts. The first PLC, designated the 084 because it was Bedford Associates39。 eightyfourth project, was the result. Bedford Associates started a new pany dedicated to developing, manufacturing, selling, and servicing this new product: Modicon, which stood for MOdular DIgital CONtroller. One of the people who worked on that project was Dick Morley, who is considered to be the father of the PLC. The Modicon brand was sold in 1977 to Gould Electronics, and later acquired by German Company AEG and then by French Schneider Electric, the current owner. One of the very first 084 models built is now on display at Modicon39。s headquarters in North Andover, Massachusetts. It was presented to Modicon by GM, when the unit was retired after nearly twenty years of uninterrupted service. Modicon used the 84 moniker at the end of its product range until the 984 made its appearance. The automotive industry is still one of the largest users of PLCs. Early PLCs were designed to replace relay logic systems. These PLCs were programmed in ladder logic, which strongly resembles a schematic diagram of relay logic. This program notation was chosen to reduce training demands for the existing technicians. Other early PLCs used a form of instruction list programming, based on a stackbased logic solver. Modern PLCs can be programmed in a variety of ways, from ladder logic to more traditional programming languages such as BASIC and C. Another method is State Logic, a very highlevel programming language designed to program PLCs based on state transition diagrams. Many early PLCs did not have acpanying programming terminals that were capable of graphical representation of the logic, and so the logic was instead represented as a series of logic expressions in some version of Boolean format, similar to Boolean algebra. As programming terminals evolved, it became more mon for ladder logic to be used, for the aforementioned reasons. Newer formats such as State Logic and Function Block (which is similar to the way logic is depicted when using digital integrated logic circuits) exist, but they are still not as popular as ladder logic. A primary reason for this is that PLCs solve the logic in a predictable and repeating sequence, and ladder logic allows the programmer (the person writing the logic) to see any issues with the timing of the logic sequence more easily than would be possible in other formats. Early PLCs, up to the mid1980s, were programmed using proprietary programming panels or specialpurpose programming terminals, which often had dedicated function keys representing the various logical elements of PLC programs. Programs were stored on cassette tape cartridges. Facilities for printing and documentation were very minimal due to lack of memory capacity. The very oldest PLCs used nonvolatile magnetic core memory. More recently, PLCs are programmed using application software on personal puters. The puter is connected to the PLC through Ethernet, RS232, RS485 or RS422 cabling. The programming software allows entry and editing of the ladderstyle logic. Generally the software provides functions for debugging and troubleshooting the PLC software, for example, by highlighting portions of the logic to show current status during operation or via simulation. The software will upload and download the PLC program, for backup and restoration purposes. In some models of programmable controller, the program is transferred from a personal puter to the PLC though a programming board which writes the program into a removable chip such as an EEPROM or EPROM. The functionality of the PLC has evolved over the years to include sequential relay control, motion control, process control, distributed control systems and networking. The data handling, storage, processing power and munication capabilities of some modern PLCs are approximately equivalent to desktop puters. PLClike programm