【精品文档】可编程控制器英文文献及其翻译.doc
《【精品文档】可编程控制器英文文献及其翻译.doc》由会员分享,可在线阅读,更多相关《【精品文档】可编程控制器英文文献及其翻译.doc(10页珍藏版)》请在三一办公上搜索。
1、Programmable Logic ControllerA programmable logic controller (PLC) or programmable controller is a digital computer 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
2、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 non-volatile
3、 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.1HistoryThe PLC was invented in response to the needs of the American automotive manufacturing industry. Programm
4、able 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 hun
5、dreds or thousands of relays, cam timers, and drum sequencers and dedicated closed-loop controllers. The process for updating such facilities for the yearly model change-over was very time consuming and expensive, as electricians needed to individually rewire each and every relay.In 1968 GM Hydramat
6、ic (the automatic transmission division of General Motors) issued a request for proposal for an electronic replacement for hard-wired relay systems. The winning proposal came from Bedford Associates of Bedford, Massachusetts. The first PLC, designated the 084 because it was Bedford Associates eighty
7、-fourth project, was the result. Bedford Associates started a new company 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 fa
8、ther 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 Modicons headquarters in North Andover, Massachusetts. It was presen
9、ted 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.2DevelopmentEarly PLCs were designed to
10、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 sta
11、ck-based 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 high-level programming language designed to program PLCs based on state transition diagrams.Many early PLCs
12、 did not have accompanying 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 commo
13、n 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
14、 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.3ProgrammingEarly PLCs, up to the mid-1980s, were programme
15、d using proprietary programming panels or special-purpose 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 lac
16、k of memory capacity. The very oldest PLCs used non-volatile magnetic core memory.More recently, PLCs are usually programmed using special application software written for use on desktop computers, and connecting between the desktop computer and the PLC such as via Ethernet or RS-232 cabling. Such s
17、oftware allows entry and editing of the ladder style logic, and then may provide additional functionality to assist debugging and troubleshooting the software, for example by highlights portions of the logic to show current status during operation or via simulation. Finally, the software may allow u
18、ploading and downloading of the program between the computer and the PLC, for backup and restoration purposes. Alternately, specific devices known as programming boards are used to hard wire the logic into the controller by the use of a removable chip, such as an EEPROM, where the program is transfe
19、rred to the programming board from the workstation via serial or other bus logic.4FunctionalityThe 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, process
20、ing power and communication capabilities of some modern PLCs are approximately equivalent to desktop computers. PLC-like programming combined with remote I/O hardware, allow a general-purpose desktop computer to overlap some PLCs in certain applications. Regarding the practicality of these desktop c
21、omputer based logic controllers, it is important to note that they have not been generally accepted in heavy industry because the desktop computers run on less stable operating systems than do PLCs, and because the desktop computer hardware is typically not designed to the same levels of tolerance t
22、o temperature, humidity, vibration, and longevity as the processors used in PLCs. In addition to the hardware limitations of desktop based logic, operating systems such as Windows do not lend themselves to deterministic logic execution, with the result that the logic may not always respond to change
23、s in logic state or input status with the extreme consistency in timing as is expected from PLCs. Still, such desktop logic applications find use in less critical situations, such as laboratory automation and use in small facilities where the application is less demanding and critical, because they
24、are generally much less expensive than PLCs.In more recent years, small products called PLRs (programmable logic relays), and also by similar names, have become more common and accepted. These are very much like PLCs, and are used in light industry where only a few points of I/O (i.e. a few signals
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- 精品文档 精品 文档 可编程控制器 英文 文献 及其 翻译
链接地址:https://www.31ppt.com/p-2392547.html