產(chǎn)品詳情
在PLC控制系統(tǒng)中,電源占有極重要的地位。電網(wǎng)干擾串入PLC控制系統(tǒng)主要通過PLC系統(tǒng)的供電電源(如電源、I/O電源等)、變送器供電電源和與PLC系統(tǒng)具有直接電氣連接的儀表供電電源等耦合進(jìn)入的?,F(xiàn)在,對于PLC系統(tǒng)供電的電源,一般都采用隔離性能較好電源,而對于變送器供電的電源和PLC系統(tǒng)有直接電氣連接的儀表的供電電源,并沒受到足夠的重視,雖然采取了一定的隔離措施,但普遍還不夠,主要是使用的隔離變壓器分布參數(shù)大,干擾能力差,經(jīng)電源耦合而串入共模干擾、差模干擾。所以,對于變送器和共用信號儀表供電應(yīng)選擇分布電容小、帶大(如采用多次隔離和屏蔽及漏感技術(shù))的配電器,以減少PLC系統(tǒng)的干擾。
位保證電網(wǎng)饋點不中斷,可采用在線式不間斷供電電源(UPS)供電,提高供電的安全可靠性。并且UPS還具有較強的干擾隔離性能,是一種PLC控制系統(tǒng)的理想電源。
2電纜選擇的敖設(shè)
為了減少動力電纜輻射電磁干擾,尤其是變頻裝置饋電電纜。筆者在某工程中,采用了銅帶鎧裝屏蔽電力電纜,從而降低了動力線生產(chǎn)的電磁干擾,該工程投產(chǎn)后取得了滿意的效果。
上世紀(jì)60年代后期,根據(jù)當(dāng)時汽車市場需求和計算技術(shù)的發(fā)展,在美國麻薩諸塞州Bedford的Bedford Associates,向美國汽車制造業(yè)提議開發(fā)一種Modular Digital Controller(MODICON)取代繼電控制盤。其它一些公司也建議以計算機為基礎(chǔ)的方案。其核心思想是采用軟件編程方法代替繼電控制的硬接線方式,并備有生產(chǎn)現(xiàn)場大量使用的輸入傳感器和輸出執(zhí)行器的接口,以便于進(jìn)行大規(guī)模生產(chǎn)線的流程控制。這就是以后被稱為Programmable Logic Controller的由來。MODICON 084是世界上種投入商業(yè)生產(chǎn)的PLC。
0年代是PLC崛起,首先在汽車工業(yè)獲得大量應(yīng)用,在其它產(chǎn)業(yè)部門也開始應(yīng)用的時期。80年代是它走向成熟,采用微電子及微處理器技術(shù);大量推廣應(yīng)用,并奠定其在工業(yè)控制中不可動搖地位的時期。在此階段PLC銷售始終以兩位數(shù)百分點的速度增長,前六年的增長率超過35%,后四年穩(wěn)定發(fā)展,年增長率約12%。90年代又開始了它的第三個發(fā)展時期。隨著PLC的IEC 61131的正式頒布,推動了PLC在技術(shù)上發(fā)動新的突破:在系統(tǒng)體系結(jié)構(gòu)上,從傳統(tǒng)的單機向多和分布式及遠(yuǎn)程控制系統(tǒng)發(fā)展;在編程語言上,文本化和圖形化的語言多樣性,創(chuàng)造了更具表達(dá)控制要求、文字處理、通信能力的編程環(huán)境。
從應(yīng)用范圍和應(yīng)用水平上,除了繼續(xù)發(fā)展機械加工自動生產(chǎn)線的控制系統(tǒng)外,則是發(fā)展以PLC為基礎(chǔ)的DCS系統(tǒng)、監(jiān)控和數(shù)據(jù)采SCADA系統(tǒng)、柔性制造系統(tǒng)(FMS)、安全聯(lián)鎖保護(hù)(ESD)系統(tǒng)、運動控制系統(tǒng)等,地產(chǎn)提高PLC的應(yīng)用范圍和水平。
進(jìn)入90年代后期,由于用戶對開放性的強烈要求和壓力,由于信息技術(shù)的大力推動,PLC如果還停留在原有的專用而又封閉的系統(tǒng)概念上,它將坐以待斃。于是PLC進(jìn)入了其發(fā)展的第四階段。其特征是:
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