PLC的介紹和應(yīng)用(外文翻譯)

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1、動(dòng)力
1968年，Richard E. Morley創(chuàng)造出了新一代工業(yè)控制裝置可編程邏輯控制器(PLC),現(xiàn)在，PLC已經(jīng)被廣泛應(yīng)用于工業(yè)領(lǐng)域，包括機(jī)械制造也、運(yùn)輸系統(tǒng)、化學(xué)過(guò)程設(shè)備、等許多其他領(lǐng)域。初期可編程控制器只是用一種類似于語(yǔ)言的軟件邏輯于代替繼電器硬件邏輯，并且使開(kāi)發(fā)時(shí)間由6個(gè)月縮短到6天。
雖然計(jì)算機(jī)控制技術(shù)已經(jīng)產(chǎn)生，但是PLC控制因?yàn)樗母咝阅?、成本低、并且?duì)惡劣的環(huán)境有很強(qiáng)的適應(yīng)能力而在工業(yè)控制的廣泛應(yīng)用中保持優(yōu)勢(shì)。而且，盡管硬件的價(jià)格在逐漸下跌，據(jù)估計(jì)，根據(jù)Frost和Sullivan對(duì)PLC市場(chǎng)的調(diào)查研究表明，每年銷售硬件的價(jià)格要比銷售PLC的價(jià)格（一千五百萬(wàn)）至少多出八十億美元。PLC的創(chuàng)造者Richard E. Morley十分肯定的認(rèn)為目前PLC市場(chǎng)是一個(gè)價(jià)值五十億的工業(yè)
雖然PLC廣泛應(yīng)用于工業(yè)控制中，PLC控制系統(tǒng)的程序依然和語(yǔ)法有關(guān)。和軟件過(guò)程一樣，PLC的軟件設(shè)計(jì)也以同樣的方式會(huì)遇到軟件錯(cuò)誤或危機(jī)。Morley在演講中著重強(qiáng)調(diào)了這個(gè)方面。
如果房子建造的像軟件過(guò)程一樣，那么僅僅一只啄木鳥(niǎo)就可以摧毀文明。特別的，PLC程序要解決的實(shí)際問(wèn)題是消除軟件錯(cuò)誤和減少老式梯形邏輯語(yǔ)言的花費(fèi)。盡管PLC的硬件成本在繼續(xù)下降，但是在工業(yè)控制上減少梯形邏輯的掃描時(shí)間仍然是一個(gè)問(wèn)題，以至于可以用到低耗時(shí)的PLC。
一般來(lái)說(shuō)，和其他領(lǐng)域相比生產(chǎn)PLC的周期要短很多。例如，在實(shí)踐中，VISI設(shè)計(jì)是一種有效的計(jì)算機(jī)輔助設(shè)計(jì)。PLC不需要使用目前的以軟件設(shè)計(jì)為基礎(chǔ)軟件工程方法論，因?yàn)镻LC程序要求對(duì)軟件和硬件搜都要考慮到。因此，軟件設(shè)計(jì)越來(lái)越成為花費(fèi)動(dòng)力。在許多的工業(yè)設(shè)計(jì)工程中 ......


The introduction and application of PLC

1.1Motivation

Programmable Logic Controllers (PLC), a computing device invented by Richard E. Morley in 1968, have been widely used in industry including manufacturing systems, transportation systems, chemical process facilities, and many others. At that time, the PLC replaced the hardwired logic with soft-wired logic or so-called relay ladder logic (RLL), a programming language visually resembling the hardwired logic, and reduced thereby the configuration time from 6 months down to 6 days [Moody and Morley, 1999].

Although PC based control has started to come into place, PLC based control will remain the technique to which the majority of industrial applications will adhere due to its higher performance, lower price, and superior reliability in harsh environments. Moreover, according to a study on the PLC market of Frost and Sullivan [1995], an increase of the annual sales volume to 15 million PLCs per year with the hardware value of more than 8 billion US dollars has been predicted, though the prices of computing hardware is steadily dropping. The inventor of the PLC, Richard E Morley, fairly considers the PLC market as a 5-billion industry at the present time ......