外文翻译PLC今天PLC (programmable logical controller)，可编程序逻辑控制器)面临着更为复杂的挑战。
当初，它们悄悄地取代了继电器、接触器并时不时见诸于公司主框架的报告。
而今，他们已经组成了各种单元、被赋予新的任务、使用新的语言，并面临着与各种新型控制产品竞争。
作为每年一度PLC技术最新报道，我们请教了PLC市场销售人员，制作了这个专刊。
编程语言高级PLC编程语言已经在有些方面很普及，但是最近高级编程语言已经迅速发展。
西门子的总经理兼生产部长指出：“可编程控制在被广泛的应用与于精密操作，除了梯形图逻辑以外的编程语言变得更加实用、有效和强大。
例如，用梯形图逻辑写一个三角函数公式是非常困难的。
”被接收的语言包括Boolean,控制系统流程图编制，和如公式编制语言Graphtec和与它类似的语言，并且还有增加的重要语言如C语言和BASIC语言。
过程控制中的PLCPLC还没有广泛的应用于过程控制中。
是否会一直这样下去呢？北美GE Fanuc一系列和六系列的生产企划经理Ken Jeannette说：“我觉得PLC将被用于过程控制但是对于过程控制又不是必须的。
”一些厂家十分确定PLC不会广泛用于过程控制。
Rich Ryan经理提到PLC 在食品、化学和石油等工业领域越来越多的应用。
他认为PLC适合应用于场合有两种，他说：“第一，过程控制系统的型号不适合离散控制系统，刚开始这些产品的价格非常的高。
而一个可编程控制器以它的体积小，价格低顺理成章的被应用。
第二，你必须把电路和逻辑紧密的结合起来。
例如，一组基本的控制器，连续的过程变量紧密的互相联系在一起，以至于用可编程控制器来完成一系列的逻辑胜过没有离散控制器的系统。
”Triconex 的总裁Bill Barkovitz预测:“今后所有的控制器在过程控制系统的业务将引用更多的PLC技术，PLC功能比以往任何时候都要多。
”通信和生产自动化协议（MAP）通信对于个人自动单元和自动化产业是很重要的。
在过去的几年里，我们听到许多关于生产自动化协议的事情，并且许多公司已经加入大有成功希望的事业。
然而，当一个完善的生产自动化协议说明书没有及时出现时许多公司都很失望。
Larry Kotare说:”现在，生产自动化协议仍然是生产中一个发展的对象，一个说明书并不是最终的结果。
例如，虽然当新的生产自动化协议MAP3.0版本使用之时以MAP2.1版本为基础的产品将会被汰，但是现在人们仍然将产品用于MAP2.1版。
由于这些原因，许多PLC厂家紧盯着MAP的最新成果。
如欧姆龙公司正在进行一个有关MAP兼容性的项目。
但是欧姆龙生产部门总经理Frank Newborn 说由于缺少一个固定的标准，欧姆龙的产品并不涉及到MAP。
由于个体PLC不可能无论何时广泛的涉及到MAP，生产厂家正在考虑专用网络。
根据Sal Probanzano的说法，用户担心如果他们广泛的应用生产厂家将会收回MAP，这样将会留下一个不支持通信的交流框架。
通用的I/O然而关于 PLC 的兼容问题不同厂商的仍有顾虑，在另一端连接的 I/O 问题，更是支离破碎的。
除了少数例外，I/O 仍然是专有技术。
然而，还是有那些觉得 I/O 最终将更普及。
GE Fanuc 希望用它的智能 I/O 线这么做。
各个独立 I/O 制造商都在向同一方向进发。
许多人说，I/O 是这样一个高价值项目， PLC 制造商将永远希望保持它的专有性。
就像Ken Jannotta说的：“ I/O 将在硬件销售中不成比例。
当然每个 PLC 供应商将试图保护这一点。
”出于这个原因，他说，PLC 的制造商将不会开始销售其他厂商的通用 I/O 。
“如果我们开始销售那种产品，那我们还有什么可生产的？” Jannotta 说道。
随着更多智能 I/O 出现，Sal Provanzano 认为在不同的制造商中间这将导致更多的分化。
“当 I/O 变得非常只能，并成为系统的一部分，到底哪个是I/O,哪个是CPU真的很难定义。
如果你愿意，CPU 也同样可以纳入 I/O 的系统”。
PLC的I/O和个人电脑的连接虽然不同的 PLC 厂商可能会继续用专有的 I/O，但一些厂商使 I/O 连接到 IBM PC 这样的兼容设备成为可能。
Alle - bradeley 和辛辛那提米拉克龙公司已经拥有，并有传言说，GE计划将沿着同样的思路。
Bill Ketelhut, GE Fanuc 北美的产品规划经理，认为是 I/O 的普及“我觉得多个主机接口将代替 I/O 。
”他说。
朱迪格洛尔，Square D 自动化产业市场经理，将 PLC 看做是工业电脑。
PLC和个人电脑如果 IBM 7552，行动仪器 BC22，和其他计算机出现在工厂，这难道不意味着对 PLC 的新竞争。
“有一些对于更有利于电脑的控制功能。
可编程程序控制器被迫适应的这些要求。
” Rich Ryan说。
然而，在我们调查的厂商多数不认为“个人电脑入侵”将对他们产生影响。
大多数人说，PLC和PC除架构之外，他们通常会做足够的控制。
他们认为PC会做PLC的工作紧紧是因为现在PLC I/O 模块能跟PC连接。
他们相信这只是意味着，PLC 和个人电脑将能够共享相同的数据。
富瑞恩说：“通用的计算机和可编程控制器内在结构不同，硬件结构有内置到几乎每一个制造商的可编程控制器。
如今定制的硬件来运行梯形逻辑，解决机器代码。
”他引用的一个根本的区别称呼为“机器状态”富瑞安说：“当你关闭机器，或中断周期，或者跳转到另一个周期，可编程控制器本身记得机器的状态：定时器状态是什么，计数器状态是什么，锁存的状态是什么,但计算机本身不这样做。
PLCPLCs(programmable logical controller) face ever more complex challengesthese days . Where once they quietly replaced relays and gave an occasiona l report to a corporate mainframe, they are now grouped into cells, given new job and new languages, and are forced to compete against a growing array of control products. For this year's annual PLC technology update ,we queried PLC makers on these topic s and more .Programming languagesHigher level PLC programming languages have been around for some time ,but l ately their popularity has mushrooming. "As Raymond Leveille, vice president & gen eral manager, Siemens Energy &Automation .inc; Programmable controls are being u sed for more and more sophisticated operations, languages other than ladder logic bec ome more practical, efficient, and powerful. For example, it's very difficult to write a t rigonometric function using ladder logic ."Languages gaining acceptance include Boo lean, control system flowcharting, and such function chart languages as Graphcet and its variation .And there's increasing interest in languages like C and BASIC.PLCs in process controlThus far, PLCs have not been used extensively for continuous process control .W ill this continue? "The feeling that I've gotten," says Ken Jannotta, manger, product pl anning, 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 opposite will happen -have introduce d PLCs optimized for process application .Rich Ryan, manger, commercial marketing, Allen-bradley Programmable Controls Div., cites PLCs's increasing use such industri es as food ,chemicals ,and petroleum. Ryan feels there are two types of applications in which they're appropriate. "one," he says," is where the size of the process control sys tem that's being automated doesn't justify DCS[distributed control system].With the st arting price tags of chose products being relatively high, a programmable controller m akes sense for small, low loop count application .The second is where you have to integrate the loop closely with the sequential logical .Batch controllers are prime example ,where the sequence and maintaining theprocess variable are intertwined so closely th at the benefits of having a programmable controller to do the sequential logical outwei ghs some of the disadvantages of not having a distributed control system."Bill Barkovitz, president of Triconex, predicts that "all future controllers that co me out in the process control system business will embrace a lot of more PLC technol ogy and a lot more PLC functionality than they ever did before ."Communications and MAPCommunications are vital to an individual automation cell and to be automated f actory as a whole. We've heard a lot about MAP in the last few years ,and a lot of com panies have jumped on the bandwagon.Many, however, were disappointed when a ful ly-defined and completed MAP specification didn't appear immediately .Says Larry K omarek: "Right now, MAP is still a moving target for the manufacturers, a specificatio n 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 MAP3.0 is introduced."Because of this, many PLC vendors are holding off on full MAP implementation s. Omron, for example, has an ongoing MAP-compatibility program;but Frank Newbu rn, vice president of Omron's Industrial Division ,reports that because of the lack of a firm definition ,Omron's PLCs don't yet talk to MAP.Since it's unlikely that an individual PLC would talk to broad MAP anyway, mak ers are concentrating on proprietary networks. According to Sal Provanzano, users fea r that if they do get on board and vendors withdraw from MAP, they'll be the ones left holding a communications structure that's not 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 fra gmented .With rare exceptions, I/O is still proprietary .Yet there are those who feel tha t I/O will eventually become 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 disproportionate amount of the hardware sale. Certainly each PLC vendor is going to try to protect that . "For that reason, he says, PLC makers won't begin selling universal I/O system from other vendor. "if we start selling that kind of product, "says jannotta, "what do we man ufacture?"With more intelligent I/O appearing, Sal Provanzano feels this will lead to more differentiation among I/O from different makers. "Where the I/O becomes extremely i ntelligent and becomes part of the system, "he says, "it really is hard to define which i s the I/O and which is CPU. It really CPU, if you will, is equally integrated into the sy stem as the I/O."Connecting PLC I/O to PCsWhile different PLCs probably will continue to use proprietary I/O, several vend ors make it possible to connect5 their I/O to IBM PC-compatible equipment. Alle-br adeley, Could, and Cincinnati Milacron already have, and rumor has it that GE is plan ning something along these same lines .Bill Ketelhut, manage of product planning at GE Fanuc North America ,sees this sort of thing as alternative to universal I/O."I thin k the trend ,instead of toward universal I/O, will be multiple host interface ," he says . Jodie Glore ,director of marking, Square D Automation Products, Views it as another i ndication that PLCs are, and have been for some time, industrial computers.PLCs and PCsIf the IBM 7552, the Action Instruments BC22,and other computers are appearin g on the factory floor, won't this mean new competition for PLCs? Rich Ryan: "There are some control functions that are better jobs for computers. Programmable controlle rs have been forced to fit into those applications. "Yet, the majority of vendors we sur veyed don't like the "PC invasion" will pose a problem for them .Most said that PLCs and PCs are enough apart in architecture that they will usually do the control. They do n't feel that PCs will take jobs from PLCs just because PLC I/O modules can now be connected to PCs; they believe this simply means that PLCs and PCs will be able to sh are the same data."There are inherent architectural differences between a general purpose computer ," says Rich Ryan, "and a programmable controller .There are hardware constructs bui lt into almost every manufacture's programmable controller today that customize the h ardware to run ladder logic and to solve machine code. "One fundamental difference h e cites is called state of the machine .Ryan: "When you shut the machine off, or interr upt the cycle, or you jump to another spot in the cycle, programmable controllers inhe rently remember the state of the machine: what the timers were, what the counters wer e ,what the states of all the latches were .Computers don't inherently do that."。
