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1、英文参考文献原文复印件及译文专 业： 电气工程及其自动化 姓 名： 学 号： 指导教师： 刘增环 完成日期 2012 年 6 月1外文原文：PLCPLCs (programmable logical controller) face ever more complex challenges these days . Where once they quietly replaced relays and gave an occasional report to a corporate mainframe, they are now grouped into cells, given new jo
2、b and new languages, and are forced to compete against a growing array of control products. For this years annual PLC technology update ,we queried PLC makers on these topics and more .Programming languages Higher level PLC programming languages have been around for some time ,but lately their popul
3、arity has mushrooming. As Raymond Leveille, vice president Programmable controls are being used for more and more sophisticated operations, languages other than ladder logic become more practical, efficient, and powerful. For example, its very difficult to write a trigonometric function using ladder
4、 logic .Languages gaining acceptance include Boolean, control system flowcharting, and such function chart languages as Graphcet and its variation .And theres increasing interest in languages like C and BASIC.PLCs in process controlThus far, PLCs have not been used extensively for continuous process
5、 control .Will this continue? The feeling that Ive gotten, says Ken Jannotta, manger, product planning, series One and Series Six product ,at GE Fanuc North America ,is that PLCs will be used in the process industry but not necessarily for process control.Several vendors -obviously betting that the
6、opposite will happen -have introduced PLCs optimized for process application .Rich Ryan, manger, commercial marketing, Allen-bradley Programmable Controls Div., cites PLCss increasing use such industries as food ,chemicals ,and petroleum. Ryan feels there are two types of applications in which theyr
7、e appropriate. one, he says, is where the size of the process control system thats being automated doesnt justify DCSdistributed control system.With the starting price tags of chose products being relatively high, a programmable controller makes sense for small, low loop count application .The secon
8、d is where you have to integrate the loop closely with the sequential logical .Batch controllers are prime example ,where the sequence and maintaining the process variable are 2intertwined so closely that the benefits of having a programmable controller to do the sequential logical outweighs some of
9、 the disadvantages of not having a distributed control system.Bill Barkovitz, president of Triconex, predicts that all future controllers that come out in the process control system business will embrace a lot of more PLC technology and a lot more PLC functionality than they ever did before .Communi
10、cations and MAPCommunications are vital to an individual automation cell and to be automated factory as a whole. Weve heard a lot about MAP in the last few years ,and a lot of companies have jumped on the bandwagon.2Many, however, were disappointed when a fully-defined and completed MAP specificatio
11、n didnt appear immediately .Says Larry Komarek: Right now, MAP is still a moving target for the manufacturers, a specification that is not final .Presently, for example. people are introducing products to meet the MAP2.1standard .Yet2.1-based products will be obsolete when the new standard for MAP3.
12、0 is introduced.Because of this, many PLC vendors are holding off on full MAP implementations. Omron, for example, has an ongoing MAP-compatibility program;3but Frank Newburn, vice president of Omrons Industrial Division ,reports that because of the lack of a firm definition ,Omrons PLCs dont yet ta
13、lk to MAP.Since its unlikely that an individual PLC would talk to broad MAP anyway, makers are concentrating on proprietary networks. According to Sal Provanzano, users fear that if they do get on board and vendors withdraw from MAP, theyll be the ones left holding a communications structure thats n
14、ot supported.Universal I/OWhile there are concerns about the lack of compatible communications between PLCs from different vendors, the connection at the other end-the I/O-is even more fragmented .With rare exceptions, I/O is still proprietary .Yet there are those who feel that I/O will eventually b
15、ecome more universal .GE Fanuc is hoping to do that with its Genius smart I/O line. The independent I/O makers are pulling in the same direction. Many say that I/O is such a high-value item that PLC makers will always want to keep it proprietary .As Ken Jannotta, says: The I/O is going to be a dispr
16、oportionate amount of the hardware sale. Certainly each PLC vendor is going to try to protect that. For that reason, he says, PLC makers wont begin selling universal I/O system from other vendor. if we start selling that kind of product, says jannotta, what do we manufacture?3With more intelligent I/O appearing, Sal Provanzano feels this
