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2、從系統(tǒng)結(jié)構(gòu)來(lái)說(shuō):
PLC與DCS的基本結(jié)構(gòu)是一樣的。PLC發(fā)展到今天，已經(jīng)全面移植到計(jì)算機(jī)系統(tǒng)控制上了，傳統(tǒng)的編程器早就被淘汰。小型應(yīng)用的PLC一般使用觸摸屏，大規(guī)模應(yīng)用的PLC全面使用計(jì)算機(jī)系統(tǒng)。和DCS一樣，控制器與IO站使用現(xiàn)場(chǎng)總線（一般都是基于RS485或RS232異步串口通訊協(xié)議的總線方式），控制器與計(jì)算機(jī)之間如果沒(méi)有擴(kuò)展的要求，也就是說(shuō)只使用一臺(tái)計(jì)算機(jī)的情況下，也會(huì)使用這個(gè)總線通訊。但如果有不止一臺(tái)的計(jì)算機(jī)使用，系統(tǒng)結(jié)構(gòu)就會(huì)和DCS一樣，上位機(jī)平臺(tái)使用以太網(wǎng)結(jié)構(gòu)。這是PLC大型化后和DCS概念模糊的原因之一。
3、PLC和DCS的發(fā)展方向:
小型化的PLC將向更專業(yè)化的使用角度發(fā)展，比如功能更加有針對(duì)性、對(duì)應(yīng)用的環(huán)境更有針對(duì)性等等。大型的PLC與DCS的界線逐步淡化，直至完全融和。
DCS將向FCS的方向繼續(xù)發(fā)展。FCS的核心除了控制系統(tǒng)更加分散化以外，特別重要的是儀表。FCS在國(guó)外的應(yīng)用已經(jīng)發(fā)展到儀表級(jí)?？刂葡到y(tǒng)需要處理的只是信號(hào)采集和提供人機(jī)界面以及邏輯控制，整個(gè)模擬量的控制分散到現(xiàn)場(chǎng)儀表，儀表與控制系統(tǒng)之間無(wú)需傳統(tǒng)電纜連接，使用現(xiàn)場(chǎng)總線連接整個(gè)儀表系統(tǒng)。(目前國(guó)內(nèi)有橫河在中海殼牌石化項(xiàng)目中用到了FCS,儀表級(jí)采用的是智能化儀表例如:EJX等，具備先進(jìn)的控制水準(zhǔn))。
○如何正確對(duì)待PLC和DCS
我個(gè)人從不強(qiáng)調(diào)PLC和DCS之間孰優(yōu)孰劣，我把它們使用了一個(gè)新名詞“控制類產(chǎn)品”。我們提供給用戶的是適合用戶的控制系統(tǒng)。絕大多數(shù)用戶不會(huì)因?yàn)橄胧褂靡惶譊CS而去使用DCS，控制類產(chǎn)品必須定位在滿足用戶的工藝要求的基礎(chǔ)之上。其實(shí)提出使用DCS還是PLC的用戶大抵是從沒(méi)接觸過(guò)自控產(chǎn)品或有某種特殊需求的。過(guò)分強(qiáng)調(diào)這個(gè)東東只會(huì)陷入口舌之爭(zhēng)。
從PLC與DCS之間的區(qū)別和共同之處我們了解了控制類產(chǎn)品的大抵情況。注意，作為專業(yè)人士，我們自己不要為產(chǎn)品下PLC還是DCS的定義，自己的心理上更不能把產(chǎn)品這樣來(lái)區(qū)別對(duì)待。
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