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，其(qi)他(ta)的都是接線(xian)(xian)使(shi)用的，壓(ya)力變送(song)器(qi)的接線(xian)(xian)一般有(you)三種：兩線(xian)(xian)制、三線(xian)(xian)制、四線(xian)(xian)制，壓(ya)力變送(song)器(qi)需(xu)要(yao)連接的連線(xian)(xian)有(you)幾(ji)根連線(xian)(xian)，就是幾(ji)線(xian)(xian)制的接法：

1、兩線制

兩線(xian)制(zhi)(zhi)壓(ya)(ya)力變(bian)送(song)器是(shi)最(zui)常用的(de)(de)，兩根線(xian)組成一條回路，這(zhe)條回路既是(shi)為壓(ya)(ya)力變(bian)送(song)器提供電(dian)(dian)源(yuan)支持(chi)的(de)(de)回路，也是(shi)傳輸(shu)電(dian)(dian)流信(xin)號的(de)(de)回路。也就是(shi)說(shuo)在兩線(xian)制(zhi)(zhi)接(jie)線(xian)中，壓(ya)(ya)力變(bian)送(song)器的(de)(de)輸(shu)出的(de)(de)負載和電(dian)(dian)源(yuan)是(shi)被串(chuan)(chuan)聯(lian)在一起(qi)的(de)(de)。使用這(zhe)種連接(jie)方式(shi)的(de)(de)通常都(dou)是(shi)輸(shu)出電(dian)(dian)流信(xin)號的(de)(de)壓(ya)(ya)力變(bian)送(song)器，如4~20mA的(de)(de)標準電(dian)(dian)控信(xin)號，當(dang)二線(xian)制(zhi)(zhi)需要(yao)輸(shu)出電(dian)(dian)壓(ya)(ya)值時，可以通過串(chuan)(chuan)聯(lian)電(dian)(dian)阻的(de)(de)方式(shi)取壓(ya)(ya)測得，如4-20mA電(dian)(dian)流電(dian)(dian)路中串(chuan)(chuan)聯(lian)250Ω電(dian)(dian)阻。

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2、三線制

三線制壓(ya)力(li)(li)變送器將電(dian)源正端和信號(hao)輸出(chu)(chu)的(de)(de)(de)正端分離，但它們另一個接(jie)線端子卻(que)是用同一根線連接(jie)的(de)(de)(de)。在(zai)這種情況下(xia)，電(dian)流實際的(de)(de)(de)通路還是由電(dian)源正負極的(de)(de)(de)連線所組(zu)成的(de)(de)(de)回(hui)，信號(hao)正端的(de)(de)(de)電(dian)流接(jie)近為0，只能傳遞電(dian)位電(dian)壓(ya)，可以理解為萬用表的(de)(de)(de)電(dian)壓(ya)檔，負載無限大(da)近似斷(duan)路。使用這種連接(jie)方式的(de)(de)(de)都是輸出(chu)(chu)電(dian)壓(ya)信號(hao)的(de)(de)(de)壓(ya)力(li)(li)變送器1~10V，1~5V，0~5V等(deng)標準控制信號(hao)。

3、四線制

四線(xian)制(zhi)不同于二線(xian)制(zhi)與三線(xian)制(zhi)，它由(you)兩個獨立(li)的(de)回路(lu)組成，彼此互不干擾。因為輸出電(dian)路(lu)的(de)獨立(li)，使(shi)得它無論式輸出電(dian)壓信號(hao)還是電(dian)流信號(hao)都(dou)可以做到(dao)。

二、壓力變送器接線怎么接

壓(ya)力變送(song)器(qi)接(jie)(jie)線(xian)制不同(tong)，接(jie)(jie)線(xian)方(fang)法也有所不同(tong)：

1、二(er)線(xian)制的(de)壓力變送(song)器，+極出(chu)來接(jie)(jie)PLC AI 模(mo)(mo)塊的(de)-；-極出(chu)來接(jie)(jie)PLC AI 模(mo)(mo)塊的(de)+。

2、三線(xian)制的壓力變送器，信號+出來(lai)接(jie)PLC AI 模(mo)塊的+；公(gong)用-出來(lai)接(jie)PLC AI 模(mo)塊的-；剩(sheng)下的24dc+接(jie)24v電源(yuan)+。

3、四(si)線制的壓力變(bian)送器，信號+出(chu)來接PLC AI 模(mo)塊的+；信號-出(chu)來接PLC AI 模(mo)塊的-；剩下的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(you)交流和直流之分(fen)(fen)，交流分(fen)(fen)為(wei)220V和110V兩種，直流分(fen)(fen)為(wei)固(gu)定(ding)(ding)電(dian)(dian)(dian)(dian)壓(ya)(ya)和寬電(dian)(dian)(dian)(dian)壓(ya)(ya)之分(fen)(fen)，固(gu)定(ding)(ding)電(dian)(dian)(dian)(dian)壓(ya)(ya)比如5V、10V、12V、24V等(deng)固(gu)定(ding)(ding)電(dian)(dian)(dian)(dian)壓(ya)(ya)這樣(yang)的(de)電(dian)(dian)(dian)(dian)壓(ya)(ya)選(xuan)擇電(dian)(dian)(dian)(dian)源(yuan)時，一定(ding)(ding)要按照標稱電(dian)(dian)(dian)(dian)壓(ya)(ya)來(lai)選(xuan)電(dian)(dian)(dian)(dian)源(yuan)。寬電(dian)(dian)(dian)(dian)壓(ya)(ya)比如3-36V、5-24V等(deng)這樣(yang)的(de)標稱，電(dian)(dian)(dian)(dian)源(yuan)選(xuan)擇在這個(ge)范圍內(nei)的(de)就(jiu)可以了，接線(xian)時注(zhu)意電(dian)(dian)(dian)(dian)壓(ya)(ya)等(deng)級，直流電(dian)(dian)(dian)(dian)源(yuan)的(de)正(zheng)負極不(bu)(bu)要接錯。系統(tong)中如果(guo)有(you)兩塊不(bu)(bu)同電(dian)(dian)(dian)(dian)壓(ya)(ya)電(dian)(dian)(dian)(dian)源(yuan)注(zhu)意電(dian)(dian)(dian)(dian)源(yuan)共問題，就(jiu)是兩個(ge)電(dian)(dian)(dian)(dian)源(yuan)負極要接在一起。