一、PLC與DCS比較

    如果按從弱至強(qiáng)將PLC與DCS的性能劃分為1至10個(gè)等級(jí)，則可將它們的對(duì)比列于表1

    表1PLC與DCS的比較

    比較項(xiàng)目PLC控制DCS控制

    高速順序控制106

    復(fù)雜過(guò)程控制610

    硬件可靠性98

    聯(lián)網(wǎng)和通訊功能48

    管理能力39

    系統(tǒng)診斷和報(bào)警38

早期的PLC以數(shù)字量的順序控制為主。隨著PLC功能不斷擴(kuò)充，PLC增加了模擬量控制功能、PID調(diào)節(jié)功能、通訊聯(lián)網(wǎng)功能及分級(jí)控制功能等，在過(guò)去DCS占統(tǒng)治地位的化工、冶金等行業(yè)也可由PLC進(jìn)行控制。但PLC難以組成大型、復(fù)雜、綜合的系統(tǒng)，如果過(guò)多的PC企圖通過(guò)網(wǎng)絡(luò)與過(guò)多的PLC通訊，則可能導(dǎo)致瓶頸現(xiàn)象及計(jì)時(shí)上的困難。

    DCS是由模擬儀表控制系統(tǒng)發(fā)展而來(lái)，初期的功能以回路調(diào)節(jié)為主，之后又加入了順序控制的功能。DCS的設(shè)計(jì)思想是操作管理集中，控制分散以提高整個(gè)系統(tǒng)的可靠性及管理能力。DCS的上述優(yōu)勢(shì)使它在控制系統(tǒng)的高端市場(chǎng)仍占主流。但DCS比PLC價(jià)位高，對(duì)一些資金有限的中小型企業(yè)有時(shí)難以承受。

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