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)都是(shi)接(jie)(jie)線(xian)(xian)使(shi)用的(de)，壓力變(bian)送(song)器的(de)接(jie)(jie)線(xian)(xian)一般(ban)有三種：兩線(xian)(xian)制、三線(xian)(xian)制、四(si)線(xian)(xian)制，壓力變(bian)送(song)器需要連(lian)接(jie)(jie)的(de)連(lian)線(xian)(xian)有幾根連(lian)線(xian)(xian)，就(jiu)是(shi)幾線(xian)(xian)制的(de)接(jie)(jie)法：

1、兩線制

兩線(xian)(xian)(xian)制(zhi)(zhi)壓(ya)(ya)力(li)變送(song)(song)器是(shi)最常用的，兩根線(xian)(xian)(xian)組成(cheng)一(yi)(yi)條(tiao)回(hui)路(lu)(lu)，這(zhe)條(tiao)回(hui)路(lu)(lu)既是(shi)為壓(ya)(ya)力(li)變送(song)(song)器提供電(dian)(dian)(dian)源支持的回(hui)路(lu)(lu)，也(ye)是(shi)傳輸電(dian)(dian)(dian)流(liu)信(xin)(xin)號的回(hui)路(lu)(lu)。也(ye)就是(shi)說在(zai)兩線(xian)(xian)(xian)制(zhi)(zhi)接線(xian)(xian)(xian)中，壓(ya)(ya)力(li)變送(song)(song)器的輸出的負載和(he)電(dian)(dian)(dian)源是(shi)被(bei)串(chuan)(chuan)聯(lian)在(zai)一(yi)(yi)起(qi)的。使用這(zhe)種連接方(fang)式的通常都是(shi)輸出電(dian)(dian)(dian)流(liu)信(xin)(xin)號的壓(ya)(ya)力(li)變送(song)(song)器，如(ru)(ru)4~20mA的標準電(dian)(dian)(dian)控(kong)信(xin)(xin)號，當二(er)線(xian)(xian)(xian)制(zhi)(zhi)需要輸出電(dian)(dian)(dian)壓(ya)(ya)值時(shi)，可以通過串(chuan)(chuan)聯(lian)電(dian)(dian)(dian)阻(zu)的方(fang)式取(qu)壓(ya)(ya)測得，如(ru)(ru)4-20mA電(dian)(dian)(dian)流(liu)電(dian)(dian)(dian)路(lu)(lu)中串(chuan)(chuan)聯(lian)250Ω電(dian)(dian)(dian)阻(zu)。

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2、三線制

三線(xian)(xian)制壓力變送器將電(dian)源正端(duan)(duan)和信(xin)號輸出(chu)的(de)正端(duan)(duan)分離，但它(ta)們另一個(ge)接(jie)線(xian)(xian)端(duan)(duan)子卻是(shi)用(yong)同一根線(xian)(xian)連(lian)接(jie)的(de)。在這種情況下，電(dian)流實際的(de)通路還是(shi)由(you)電(dian)源正負極的(de)連(lian)線(xian)(xian)所組成的(de)回，信(xin)號正端(duan)(duan)的(de)電(dian)流接(jie)近為(wei)0，只能傳遞電(dian)位電(dian)壓，可以(yi)理(li)解為(wei)萬用(yong)表的(de)電(dian)壓檔，負載無(wu)限(xian)大近似斷路。使用(yong)這種連(lian)接(jie)方式的(de)都是(shi)輸出(chu)電(dian)壓信(xin)號的(de)壓力變送器1~10V，1~5V，0~5V等標準控制信(xin)號。

3、四線制

四線(xian)制(zhi)不同于(yu)二線(xian)制(zhi)與三(san)線(xian)制(zhi)，它由兩個獨立(li)的回路(lu)組成，彼此互不干擾。因為輸(shu)出(chu)電(dian)路(lu)的獨立(li)，使得它無論式輸(shu)出(chu)電(dian)壓信(xin)號(hao)還是電(dian)流信(xin)號(hao)都可以做到。

二、壓力變送器接線怎么接

壓力(li)變(bian)送器接(jie)線(xian)制不(bu)同，接(jie)線(xian)方法也(ye)有所(suo)不(bu)同：

1、二線制的壓(ya)力變送器，+極(ji)出(chu)來(lai)接(jie)(jie)PLC AI 模(mo)塊的-；-極(ji)出(chu)來(lai)接(jie)(jie)PLC AI 模(mo)塊的+。

2、三線制的壓力(li)變送器，信(xin)號+出來接(jie)PLC AI 模塊(kuai)的+；公用-出來接(jie)PLC AI 模塊(kuai)的-；剩下的24dc+接(jie)24v電源+。

3、四(si)線制的(de)壓力變送(song)器，信號+出(chu)來接PLC AI 模塊(kuai)的(de)+；信號-出(chu)來接PLC AI 模塊(kuai)的(de)-；剩下的(de)24dc+接24v電源(yuan)+；24dc-接24v電源(yuan)-。

三、壓力變送器接線注意事項

壓力變送器電(dian)(dian)(dian)(dian)源(yuan)有交(jiao)流和(he)(he)直(zhi)流之(zhi)分，交(jiao)流分為220V和(he)(he)110V兩(liang)(liang)種，直(zhi)流分為固定電(dian)(dian)(dian)(dian)壓(ya)和(he)(he)寬電(dian)(dian)(dian)(dian)壓(ya)之(zhi)分，固定電(dian)(dian)(dian)(dian)壓(ya)比如5V、10V、12V、24V等(deng)固定電(dian)(dian)(dian)(dian)壓(ya)這樣的(de)(de)電(dian)(dian)(dian)(dian)壓(ya)選擇(ze)電(dian)(dian)(dian)(dian)源(yuan)時(shi)，一(yi)定要(yao)按(an)照標稱(cheng)(cheng)電(dian)(dian)(dian)(dian)壓(ya)來選電(dian)(dian)(dian)(dian)源(yuan)。寬電(dian)(dian)(dian)(dian)壓(ya)比如3-36V、5-24V等(deng)這樣的(de)(de)標稱(cheng)(cheng)，電(dian)(dian)(dian)(dian)源(yuan)選擇(ze)在這個(ge)(ge)范圍內的(de)(de)就可以了，接(jie)線(xian)時(shi)注(zhu)意電(dian)(dian)(dian)(dian)壓(ya)等(deng)級(ji)，直(zhi)流電(dian)(dian)(dian)(dian)源(yuan)的(de)(de)正負(fu)極(ji)不(bu)要(yao)接(jie)錯。系統中如果有兩(liang)(liang)塊不(bu)同電(dian)(dian)(dian)(dian)壓(ya)電(dian)(dian)(dian)(dian)源(yuan)注(zhu)意電(dian)(dian)(dian)(dian)源(yuan)共問題，就是兩(liang)(liang)個(ge)(ge)電(dian)(dian)(dian)(dian)源(yuan)負(fu)極(ji)要(yao)接(jie)在一(yi)起。