一、壓力變送器是幾線制

壓力變送器是將壓力信號轉換為模擬量信號或者數字量信號的轉換設備，一般除無線壓力變送器外(wai)，其他的(de)(de)都是接線(xian)(xian)使用的(de)(de)，壓(ya)力(li)變(bian)(bian)送器的(de)(de)接線(xian)(xian)一(yi)般有(you)三種：兩線(xian)(xian)制、三線(xian)(xian)制、四線(xian)(xian)制，壓(ya)力(li)變(bian)(bian)送器需要連接的(de)(de)連線(xian)(xian)有(you)幾根連線(xian)(xian)，就是幾線(xian)(xian)制的(de)(de)接法(fa)：

1、兩線制

兩線制壓(ya)(ya)力(li)變(bian)送器是(shi)(shi)最常(chang)用的(de)(de)(de)，兩根(gen)線組成一(yi)條回路(lu)(lu)，這(zhe)(zhe)條回路(lu)(lu)既是(shi)(shi)為(wei)壓(ya)(ya)力(li)變(bian)送器提供電(dian)(dian)(dian)源支持的(de)(de)(de)回路(lu)(lu)，也是(shi)(shi)傳輸電(dian)(dian)(dian)流(liu)信號的(de)(de)(de)回路(lu)(lu)。也就是(shi)(shi)說(shuo)在兩線制接(jie)線中，壓(ya)(ya)力(li)變(bian)送器的(de)(de)(de)輸出的(de)(de)(de)負(fu)載(zai)和(he)電(dian)(dian)(dian)源是(shi)(shi)被(bei)串(chuan)聯(lian)在一(yi)起的(de)(de)(de)。使用這(zhe)(zhe)種(zhong)連接(jie)方式的(de)(de)(de)通常(chang)都(dou)是(shi)(shi)輸出電(dian)(dian)(dian)流(liu)信號的(de)(de)(de)壓(ya)(ya)力(li)變(bian)送器，如(ru)4~20mA的(de)(de)(de)標準電(dian)(dian)(dian)控信號，當二線制需要輸出電(dian)(dian)(dian)壓(ya)(ya)值時，可以通過串(chuan)聯(lian)電(dian)(dian)(dian)阻的(de)(de)(de)方式取壓(ya)(ya)測(ce)得(de)，如(ru)4-20mA電(dian)(dian)(dian)流(liu)電(dian)(dian)(dian)路(lu)(lu)中串(chuan)聯(lian)250Ω電(dian)(dian)(dian)阻。

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2、三線制

三線制壓(ya)力變(bian)送器將電(dian)源正(zheng)(zheng)端(duan)和信(xin)號(hao)(hao)輸出的(de)(de)(de)正(zheng)(zheng)端(duan)分離，但它們另一個(ge)接線端(duan)子(zi)卻(que)是用(yong)同(tong)一根線連(lian)接的(de)(de)(de)。在這種情(qing)況下，電(dian)流實際的(de)(de)(de)通路還是由電(dian)源正(zheng)(zheng)負極的(de)(de)(de)連(lian)線所(suo)組(zu)成(cheng)的(de)(de)(de)回，信(xin)號(hao)(hao)正(zheng)(zheng)端(duan)的(de)(de)(de)電(dian)流接近(jin)為(wei)0，只能傳遞電(dian)位(wei)電(dian)壓(ya)，可以理解為(wei)萬用(yong)表的(de)(de)(de)電(dian)壓(ya)檔(dang)，負載無限大近(jin)似斷路。使用(yong)這種連(lian)接方式的(de)(de)(de)都是輸出電(dian)壓(ya)信(xin)號(hao)(hao)的(de)(de)(de)壓(ya)力變(bian)送器1~10V，1~5V，0~5V等標準控制信(xin)號(hao)(hao)。

3、四線制

四(si)線(xian)制不同于二(er)線(xian)制與(yu)三線(xian)制，它由(you)兩個獨(du)立的(de)回路組成，彼(bi)此互不干擾。因為輸出(chu)電(dian)路的(de)獨(du)立，使得它無論式輸出(chu)電(dian)壓信(xin)號還是電(dian)流信(xin)號都可以做到。

二、壓力變送器接線怎么接

壓力變送器(qi)接(jie)線制不(bu)(bu)同，接(jie)線方法也有(you)所不(bu)(bu)同：

1、二線(xian)制的壓(ya)力變送(song)器，+極出來接PLC AI 模(mo)塊的-；-極出來接PLC AI 模(mo)塊的+。

2、三線制的壓力(li)變送器(qi)，信號+出來(lai)接PLC AI 模塊的+；公用-出來(lai)接PLC AI 模塊的-；剩下的24dc+接24v電源+。

3、四(si)線制的(de)壓(ya)力變(bian)送器(qi)，信(xin)(xin)號+出來接PLC AI 模(mo)塊(kuai)的(de)+；信(xin)(xin)號-出來接PLC AI 模(mo)塊(kuai)的(de)-；剩下(xia)的(de)24dc+接24v電源+；24dc-接24v電源-。

三、壓力變送器接線注意事項

壓力變送器電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)有交(jiao)流(liu)和直(zhi)流(liu)之分，交(jiao)流(liu)分為220V和110V兩(liang)種，直(zhi)流(liu)分為固定電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)和寬電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)之分，固定電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)比如(ru)5V、10V、12V、24V等(deng)固定電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)這樣(yang)的電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)選(xuan)擇電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)時，一定要(yao)按照標(biao)稱(cheng)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)來(lai)選(xuan)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)。寬電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)比如(ru)3-36V、5-24V等(deng)這樣(yang)的標(biao)稱(cheng)，電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)選(xuan)擇在這個范(fan)圍(wei)內的就可以了(le)，接(jie)線時注意(yi)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)等(deng)級，直(zhi)流(liu)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的正負極(ji)不要(yao)接(jie)錯(cuo)。系統(tong)中如(ru)果有兩(liang)塊不同電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)注意(yi)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)共(gong)問題，就是兩(liang)個電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)負極(ji)要(yao)接(jie)在一起(qi)。