6AR1508-0AB11-3AA0
6AR1508-0AB11-3AA0
6AR1508-0AB11-3AA0PLC的接地
良好的接地是保證PLC可靠作的重要條件,可以避免偶然發(fā)生的電壓沖擊危害。PLC的接地線與機(jī)器的接地端相接,接地線的截面積應(yīng)不小于2mm2 ,接地電阻小于100Ω;如果要用擴(kuò)展單元,其接地點(diǎn)應(yīng)與基本單元的接地點(diǎn)接在起。為了抑制加在電源及輸入端、輸出端的干擾,應(yīng)給PLC接上專用地線,接地點(diǎn)應(yīng)與動(dòng)力設(shè)備(如電機(jī))的接地點(diǎn)分開(kāi);若達(dá)不到這種要求,也必須做到與其它設(shè)備公共接地,禁止與其它設(shè)備串連接地。接地點(diǎn)應(yīng)盡可能靠近PLC。
RS485網(wǎng)絡(luò):RS485/MODBUS是現(xiàn)在流行的種布網(wǎng)方式,其特點(diǎn)是實(shí)施簡(jiǎn)單方便 ,而且現(xiàn)在支持RS485的儀表又特多,特別是在油品行業(yè)RS485/MODBUS簡(jiǎn)直是統(tǒng)天下,現(xiàn)在的儀表商也紛紛轉(zhuǎn)而支持RS485/MODBUS,原因很簡(jiǎn)單,象原來(lái)的 HART儀表想買個(gè)轉(zhuǎn)換口非常困難 而且價(jià)格昂貴,RS485的轉(zhuǎn)換接口就便宜的多而且種類繁多。至少在低端市場(chǎng)RS485/MODBUS還將是主要的組網(wǎng)方式,近兩三年內(nèi)不會(huì)改變。
初是數(shù)據(jù)模擬信號(hào)輸出簡(jiǎn)單過(guò)程量,后來(lái)儀表接口是RS232接口,這種接口可以實(shí)現(xiàn)點(diǎn)對(duì)點(diǎn)的通信方式,但這種方式不能實(shí)現(xiàn)聯(lián)網(wǎng)功能。隨后出現(xiàn)的RS485解決了這個(gè)問(wèn)題RS485采用差分信號(hào)負(fù)邏輯,+2V~+6V表示“0”,- 6V~- 2V表示“1”。RS485有兩線制和四線制兩種接線,四線制只能實(shí)現(xiàn)點(diǎn)對(duì)點(diǎn)的通信方式,現(xiàn)很少采用,現(xiàn)在多采用的是兩線制接線方式,這種接線方式為總線式拓樸結(jié)構(gòu)在同總線上多可以掛接32個(gè)結(jié)點(diǎn)。
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