差壓變送器用于(yu)(yu)防止管道中的介(jie)質直(zhi)接進入變送器里，感壓膜(mo)片與變送器之間靠注滿流體的毛細管連(lian)接起來。它用于(yu)(yu)測量液體、氣體或蒸汽的液位、流量和壓力(li)，然后將其(qi)轉變成4～20mADC信(xin)號輸出。
    差壓變送器零(ling)位設置：
    變(bian)送(song)器(qi)測量液位時(shi)，零位的(de)(de)設(she)置是非常(chang)重要的(de)(de)環節(jie)。當變(bian)送(song)器(qi)的(de)(de)高(gao)壓（H）側(ce)、低(di)壓（L）側(ce)與(yu)(yu)就地(di)測量筒的(de)(de)高(gao)壓側(ce)、低(di)壓側(ce)連接一致時(shi)，高(gao)壓側(ce)導壓管始終(zhong)處于充滿(man)水狀態，變(bian)送(song)器(qi)高(gao)壓端測得壓力為(wei)(wei)P+kPa，變(bian)送(song)器(qi)的(de)(de)低(di)壓側(ce)與(yu)(yu)低(di)壓側(ce)導壓管相連，測得壓力為(wei)(wei)P-kPa，則變(bian)送(song)器(qi)測得實際差壓為(wei)(wei)（P+-P-）kPa。容器(qi)液位zui低(di)時(shi)，差壓值zui大，對應于變(bian)送(song)器(qi)內(nei)部設(she)置LRV，也(ye)就是變(bian)送(song)器(qi)的(de)(de)零位，此(ci)時(shi)變(bian)送(song)器(qi)輸(shu)出電(dian)流4mA，容器(qi)液位zui高(gao)時(shi)，差壓值為(wei)(wei)0，對應于變(bian)送(song)器(qi)內(nei)部設(she)置URV，也(ye)就是變(bian)送(song)器(qi)的(de)(de)滿(man)度，此(ci)時(shi)變(bian)送(song)器(qi)輸(shu)出電(dian)流20mA。
    當變(bian)(bian)送(song)(song)器(qi)的高(gao)(gao)(gao)壓(ya)(ya)(ya)（H）側(ce)、低壓(ya)(ya)(ya)（L）側(ce)與(yu)(yu)就(jiu)地測量筒(tong)的高(gao)(gao)(gao)壓(ya)(ya)(ya)側(ce)、低壓(ya)(ya)(ya)側(ce)連(lian)接相反時，需要對變(bian)(bian)送(song)(song)器(qi)內部設(she)置進行(xing)修改：即將變(bian)(bian)送(song)(song)器(qi)的LRV設(she)置為(wei)（P--P+）kPa（這個差值為(wei)負(fu)數(shu)），也就(jiu)是說，無(wu)論變(bian)(bian)送(song)(song)器(qi)與(yu)(yu)導壓(ya)(ya)(ya)管怎樣(yang)連(lian)接，變(bian)(bian)送(song)(song)器(qi)的滿(man)度(du)對應于(yu)測量容器(qi)的滿(man)水位，差壓(ya)(ya)(ya)始終為(wei)0，即變(bian)(bian)送(song)(song)器(qi)的滿(man)度(du)URV為(wei)0kPa，輸出電(dian)流20mA。當變(bian)(bian)送(song)(song)器(qi)的高(gao)(gao)(gao)壓(ya)(ya)(ya)側(ce)與(yu)(yu)導壓(ya)(ya)(ya)管高(gao)(gao)(gao)壓(ya)(ya)(ya)側(ce)相連(lian)時，變(bian)(bian)送(song)(song)器(qi)零位LRV設(she)置為(wei)zui大差壓(ya)(ya)(ya)值，當變(bian)(bian)送(song)(song)器(qi)的高(gao)(gao)(gao)壓(ya)(ya)(ya)側(ce)與(yu)(yu)導壓(ya)(ya)(ya)管低壓(ya)(ya)(ya)側(ce)相連(lian)時，變(bian)(bian)送(song)(song)器(qi)零位LRV設(she)置為(wei)zui大差壓(ya)(ya)(ya)值的負(fu)數(shu)。