壓力、差壓測量儀表的選型原則和方法

1、在(zai)諸類儀表中(zhong)，變(bian)(bian)送(song)(song)(song)(song)器(qi)的應用廣泛、普遍，變(bian)(bian)送(song)(song)(song)(song)器(qi)大體分為壓(ya)力變(bian)(bian)送(song)(song)(song)(song)器(qi)和差壓(ya)變(bian)(bian)送(song)(song)(song)(song)器(qi)。變(bian)(bian)送(song)(song)(song)(song)器(qi)常用來測量(liang)壓(ya)力、差壓(ya)、真空(kong)、液位、流量(liang)和密度等(deng)。變(bian)(bian)送(song)(song)(song)(song)器(qi)有(you)兩線(xian)制(zhi)和四線(xian)制(zhi)之分，兩線(xian)制(zhi)變(bian)(bian)送(song)(song)(song)(song)器(qi)尤(you)多(duo)；有(you)智能(neng)和非(fei)智能(neng)之分，智能(neng)變(bian)(bian)送(song)(song)(song)(song)器(qi)漸(jian)多(duo)；有(you)氣動和電動之分，電動變(bian)(bian)送(song)(song)(song)(song)器(qi)居多(duo)；另外，按應用場合有(you)本(ben)安(an)型(xing)（本(ben)質安(an)全型(xing)）和隔(ge)爆型(xing)之分；按應用工(gong)況，變(bian)(bian)送(song)(song)(song)(song)器(qi)的主要種類如下：

 

※ 低(di)（微(wei)）壓/低(di)（微(wei)）差壓變送器；   

※ 中壓/中差壓變送器；   

※ 高壓/高差(cha)壓變送器； 

※ 絕壓(ya)/真空(kong)/負壓(ya)差壓(ya)變送器(qi)；   

※ 高溫/壓力、差壓變送器；   

※ 耐腐(fu)蝕/壓力、差(cha)壓變送器；   

※ 易結晶(jing)/壓力、差(cha)壓變送器(qi)。 

 

   變(bian)(bian)(bian)送(song)(song)器的選(xuan)型通(tong)(tong)常(chang)根據安裝條件(jian)、環境條件(jian)、儀表性能、經濟性和(he)使用(yong)(yong)介質等方(fang)面考慮。實(shi)際(ji)應用(yong)(yong)中分為直接測(ce)量和(he)間接測(ce)量兩種；其用(yong)(yong)途有(you)過程(cheng)測(ce)量、過程(cheng)控制和(he)裝置(zhi)連鎖等。常(chang)見的變(bian)(bian)(bian)送(song)(song)器有(you)普通(tong)(tong)壓力變(bian)(bian)(bian)送(song)(song)器、差壓變(bian)(bian)(bian)送(song)(song)器、單發(fa)蘭(lan)變(bian)(bian)(bian)送(song)(song)器、雙發(fa)蘭(lan)變(bian)(bian)(bian)送(song)(song)器、插入(ru)式(shi)發(fa)蘭(lan)變(bian)(bian)(bian)送(song)(song)器等。

 

2． 壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)/差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)變(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)介(jie)(jie)(jie)紹     壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)變(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)和(he)(he)(he)差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)變(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)單從名稱(cheng)上(shang)(shang)講測(ce)(ce)(ce)(ce)量(liang)(liang)(liang)的(de)(de)是壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)和(he)(he)(he)差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)（兩(liang)(liang)個壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)的(de)(de)差(cha)(cha)(cha)），但它(ta)(ta)們可(ke)(ke)(ke)(ke)(ke)以(yi)(yi)(yi)間(jian)(jian)接(jie)測(ce)(ce)(ce)(ce)量(liang)(liang)(liang)的(de)(de)量(liang)(liang)(liang)卻很多。如壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)變(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)，除可(ke)(ke)(ke)(ke)(ke)以(yi)(yi)(yi)測(ce)(ce)(ce)(ce)量(liang)(liang)(liang)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)外(wai)，還可(ke)(ke)(ke)(ke)(ke)以(yi)(yi)(yi)測(ce)(ce)(ce)(ce)量(liang)(liang)(liang)設(she)備(bei)內的(de)(de)液(ye)位(wei)。在(zai)常壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)容器(qi)(qi)內測(ce)(ce)(ce)(ce)量(liang)(liang)(liang)液(ye)位(wei)時，需(xu)要(yao)一(yi)臺(tai)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)變(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)即可(ke)(ke)(ke)(ke)(ke)。當測(ce)(ce)(ce)(ce)量(liang)(liang)(liang)受(shou)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)容器(qi)(qi)的(de)(de)液(ye)位(wei)時，可(ke)(ke)(ke)(ke)(ke)考慮用(yong)(yong)兩(liang)(liang)臺(tai)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)/差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)變(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)，即測(ce)(ce)(ce)(ce)量(liang)(liang)(liang)下(xia)限(xian)一(yi)臺(tai)，測(ce)(ce)(ce)(ce)量(liang)(liang)(liang)上(shang)(shang)限(xian)一(yi)臺(tai)，它(ta)(ta)們的(de)(de)輸出(chu)(chu)(chu)信號(hao)進行(xing)減法運(yun)算，即可(ke)(ke)(ke)(ke)(ke)測(ce)(ce)(ce)(ce)出(chu)(chu)(chu)液(ye)位(wei)，這(zhe)時一(yi)般(ban)(ban)(ban)選(xuan)(xuan)用(yong)(yong)差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)變(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)。在(zai)容器(qi)(qi)內液(ye)位(wei)與壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)值(zhi)不(bu)變(bian)(bian)(bian)(bian)(bian)(bian)的(de)(de)情況下(xia)它(ta)(ta)還可(ke)(ke)(ke)(ke)(ke)以(yi)(yi)(yi)用(yong)(yong)來測(ce)(ce)(ce)(ce)量(liang)(liang)(liang)介(jie)(jie)(jie)質(zhi)(zhi)的(de)(de)密度(du)。壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)變(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)的(de)(de)測(ce)(ce)(ce)(ce)量(liang)(liang)(liang)范圍可(ke)(ke)(ke)(ke)(ke)以(yi)(yi)(yi)做的(de)(de)很寬(kuan)，從絕壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)0開(kai)始可(ke)(ke)(ke)(ke)(ke)以(yi)(yi)(yi)到(dao)(dao)(dao)一(yi)百多兆(zhao)帕（一(yi)般(ban)(ban)(ban)情況）。     差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)變(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)除了測(ce)(ce)(ce)(ce)量(liang)(liang)(liang)兩(liang)(liang)個被(bei)(bei)測(ce)(ce)(ce)(ce)量(liang)(liang)(liang)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)的(de)(de)差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)值(zhi)外(wai)，它(ta)(ta)還可(ke)(ke)(ke)(ke)(ke)以(yi)(yi)(yi)配(pei)合(he)各種(zhong)節流(liu)元件來測(ce)(ce)(ce)(ce)量(liang)(liang)(liang)介(jie)(jie)(jie)質(zhi)(zhi)流(liu)體的(de)(de)流(liu)量(liang)(liang)(liang)，可(ke)(ke)(ke)(ke)(ke)以(yi)(yi)(yi)直接(jie)測(ce)(ce)(ce)(ce)量(liang)(liang)(liang)受(shou)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)容器(qi)(qi)的(de)(de)液(ye)位(wei)和(he)(he)(he)常壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)容器(qi)(qi)的(de)(de)液(ye)位(wei)以(yi)(yi)(yi)及壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)和(he)(he)(he)負壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)。   2.1 制(zhi)作(zuo)     從壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)/差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)變(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)制(zhi)作(zuo)的(de)(de)結構上(shang)(shang)來分有普(pu)(pu)通(tong)型(xing)和(he)(he)(he)隔(ge)離型(xing)。普(pu)(pu)通(tong)型(xing)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)/差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)變(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)的(de)(de)測(ce)(ce)(ce)(ce)量(liang)(liang)(liang)膜(mo)(mo)(mo)(mo)盒為(wei)(wei)一(yi)個，它(ta)(ta)直接(jie)感受(shou)被(bei)(bei)測(ce)(ce)(ce)(ce)介(jie)(jie)(jie)質(zhi)(zhi)的(de)(de)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)或差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)；隔(ge)離型(xing)的(de)(de)測(ce)(ce)(ce)(ce)量(liang)(liang)(liang)膜(mo)(mo)(mo)(mo)盒接(jie)受(shou)到(dao)(dao)(dao)的(de)(de)是一(yi)種(zhong)穩定液(ye)（一(yi)般(ban)(ban)(ban)為(wei)(wei)硅油）的(de)(de)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)，而(er)這(zhe)種(zhong)穩定液(ye)是被(bei)(bei)密封在(zai)兩(liang)(liang)個膜(mo)(mo)(mo)(mo)片(pian)(pian)中間(jian)(jian)，直接(jie)接(jie)受(shou)被(bei)(bei)測(ce)(ce)(ce)(ce)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)的(de)(de)膜(mo)(mo)(mo)(mo)片(pian)(pian)為(wei)(wei)外(wai)膜(mo)(mo)(mo)(mo)片(pian)(pian)，原(yuan)(yuan)普(pu)(pu)通(tong)型(xing)膜(mo)(mo)(mo)(mo)盒的(de)(de)膜(mo)(mo)(mo)(mo)片(pian)(pian)為(wei)(wei)內膜(mo)(mo)(mo)(mo)片(pian)(pian)，當外(wai)膜(mo)(mo)(mo)(mo)片(pian)(pian)上(shang)(shang)接(jie)受(shou)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)信號(hao)時通(tong)過硅油的(de)(de)傳(chuan)遞原(yuan)(yuan)封不(bu)動的(de)(de)將外(wai)膜(mo)(mo)(mo)(mo)片(pian)(pian)的(de)(de)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)傳(chuan)遞到(dao)(dao)(dao)了普(pu)(pu)通(tong)膜(mo)(mo)(mo)(mo)盒上(shang)(shang)，從而(er)可(ke)(ke)(ke)(ke)(ke)以(yi)(yi)(yi)測(ce)(ce)(ce)(ce)出(chu)(chu)(chu)外(wai)膜(mo)(mo)(mo)(mo)片(pian)(pian)所(suo)感受(shou)到(dao)(dao)(dao)的(de)(de)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)。     隔(ge)離型(xing)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)/差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)變(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)主要(yao)是針對特殊(shu)的(de)(de)被(bei)(bei)測(ce)(ce)(ce)(ce)量(liang)(liang)(liang)介(jie)(jie)(jie)質(zhi)(zhi)設(she)計和(he)(he)(he)使用(yong)(yong)的(de)(de)，如果被(bei)(bei)測(ce)(ce)(ce)(ce)介(jie)(jie)(jie)質(zhi)(zhi)離開(kai)設(she)備(bei)后會(hui)產生結晶，而(er)使用(yong)(yong)普(pu)(pu)通(tong)型(xing)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)(li)(li)(li)/差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)變(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)需(xu)要(yao)取(qu)(qu)出(chu)(chu)(chu)介(jie)(jie)(jie)質(zhi)(zhi)，會(hui)將導壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)(ya)管膜(mo)(mo)(mo)(mo)盒室(shi)堵塞使其不(bu)能正(zheng)常工作(zuo)，所(suo)以(yi)(yi)(yi)必(bi)須選(xuan)(xuan)用(yong)(yong)隔(ge)離型(xing)。隔(ge)離型(xing)變(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)通(tong)常作(zuo)成(cheng)發蘭(lan)式安裝，即在(zai)被(bei)(bei)測(ce)(ce)(ce)(ce)設(she)備(bei)上(shang)(shang)開(kai)口使變(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)安裝后它(ta)(ta)的(de)(de)感應膜(mo)(mo)(mo)(mo)片(pian)(pian)是設(she)備(bei)壁(bi)的(de)(de)一(yi)部(bu)分，這(zhe)樣它(ta)(ta)不(bu)會(hui)取(qu)(qu)出(chu)(chu)(chu)被(bei)(bei)測(ce)(ce)(ce)(ce)介(jie)(jie)(jie)質(zhi)(zhi)，一(yi)般(ban)(ban)(ban)也不(bu)會(hui)造成(cheng)結晶和(he)(he)(he)堵塞。     當被(bei)(bei)測(ce)(ce)(ce)(ce)介(jie)(jie)(jie)質(zhi)(zhi)需(xu)求結晶溫度(du)較高時，可(ke)(ke)(ke)(ke)(ke)選(xuan)(xuan)用(yong)(yong)將膜(mo)(mo)(mo)(mo)片(pian)(pian)凸出(chu)(chu)(chu)的(de)(de)結構，這(zhe)樣可(ke)(ke)(ke)(ke)(ke)將傳(chuan)感膜(mo)(mo)(mo)(mo)片(pian)(pian)插入(ru)到(dao)(dao)(dao)設(she)備(bei)內部(bu)，從而(er)感應到(dao)(dao)(dao)的(de)(de)介(jie)(jie)(jie)質(zhi)(zhi)溫度(du)不(bu)會(hui)降低(di)，這(zhe)樣測(ce)(ce)(ce)(ce)量(liang)(liang)(liang)是有保障的(de)(de)，即選(xuan)(xuan)用(yong)(yong)插入(ru)式發蘭(lan)變(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)。     

隔離型(xing)(xing)變(bian)送(song)(song)器(qi)有(you)遠(yuan)傳型(xing)(xing)和一體型(xing)(xing)之(zhi)分。遠(yuan)傳型(xing)(xing)即外(wai)(wai)膜(mo)(mo)(mo)盒(he)(he)與測量膜(mo)(mo)(mo)盒(he)(he)之(zhi)間用(yong)加強(qiang)毛細管連(lian)接(jie)，一般(ban)毛細管為(wei)3~5米，這(zhe)樣(yang)外(wai)(wai)膜(mo)(mo)(mo)盒(he)(he)裝在(zai)設(she)備(bei)(bei)上(shang)(shang)，內膜(mo)(mo)(mo)盒(he)(he)及變(bian)送(song)(song)器(qi)可(ke)以安(an)裝在(zai)便于(yu)維護的安(an)裝支架上(shang)(shang)；另一種(zhong)形式是外(wai)(wai)膜(mo)(mo)(mo)盒(he)(he)與變(bian)送(song)(song)器(qi)做成一體直接(jie)由(you)發蘭安(an)裝在(zai)設(she)備(bei)(bei)上(shang)(shang)。對于(yu)隔離型(xing)(xing)壓(ya)力變(bian)送(song)(song)器(qi)它還可(ke)以作成螺紋連(lian)接(jie)型(xing)(xing)，即外(wai)(wai)膜(mo)(mo)(mo)盒(he)(he)或外(wai)(wai)彈性元件可(ke)在(zai)安(an)裝螺紋的前面，只(zhi)要(yao)在(zai)被(bei)測設(she)備(bei)(bei)上(shang)(shang)焊接(jie)上(shang)(shang)內螺紋凸臺，便可(ke)將變(bian)送(song)(song)器(qi)直接(jie)擰到設(she)備(bei)(bei)上(shang)(shang)，安(an)裝非常(chang)方便。    隔離型(xing)(xing)壓(ya)力/差壓(ya)變(bian)送(song)(song)器(qi)的制作復雜，材質要(yao)求也較高，所以它的價(jia)格通常(chang)是普通型(xing)(xing)的3~4倍。 

 

2.2 選型(xing)原則     

在(zai)(zai)壓力(li)(li)/差壓變(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)的(de)(de)(de)(de)(de)選(xuan)(xuan)(xuan)用(yong)(yong)(yong)上主要(yao)(yao)(yao)(yao)(yao)(yao)依據：以(yi)(yi)被測(ce)(ce)介質(zhi)(zhi)的(de)(de)(de)(de)(de)性質(zhi)(zhi)指標為準，以(yi)(yi)節約資金、便(bian)于(yu)(yu)安(an)裝(zhuang)和維(wei)(wei)護(hu)(hu)為參(can)考(kao)。如(ru)果(guo)被測(ce)(ce)介質(zhi)(zhi)為高黏度(du)(du)、易結晶、強腐蝕的(de)(de)(de)(de)(de)，必(bi)(bi)須選(xuan)(xuan)(xuan)用(yong)(yong)(yong)隔(ge)離(li)型(xing)(xing)(xing)(xing)(xing)(xing)(xing)變(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)。     在(zai)(zai)選(xuan)(xuan)(xuan)型(xing)(xing)(xing)(xing)(xing)(xing)(xing)時(shi)(shi)(shi)(shi)要(yao)(yao)(yao)(yao)(yao)(yao)考(kao)慮(lv)被測(ce)(ce)流體介質(zhi)(zhi)對(dui)膜盒(he)金屬的(de)(de)(de)(de)(de)腐蝕，一定(ding)(ding)要(yao)(yao)(yao)(yao)(yao)(yao)選(xuan)(xuan)(xuan)好膜盒(he)材(cai)質(zhi)(zhi)，否(fou)則(ze)使(shi)(shi)用(yong)(yong)(yong)后很短(duan)時(shi)(shi)(shi)(shi)間(jian)就會將外(wai)膜片腐蝕壞，法蘭(lan)也會被腐蝕壞造成設(she)(she)備(bei)或(huo)人身事故，所(suo)以(yi)(yi)膜盒(he)材(cai)質(zhi)(zhi)的(de)(de)(de)(de)(de)選(xuan)(xuan)(xuan)擇非(fei)常(chang)關鍵。變(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)的(de)(de)(de)(de)(de)膜盒(he)材(cai)質(zhi)(zhi)有(you)(you)普通(tong)不(bu)銹(xiu)鋼(gang)(gang)、304不(bu)銹(xiu)鋼(gang)(gang)、316/316L不(bu)銹(xiu)鋼(gang)(gang)、鉭(tan)材(cai)質(zhi)(zhi)等(deng)。     在(zai)(zai)選(xuan)(xuan)(xuan)型(xing)(xing)(xing)(xing)(xing)(xing)(xing)時(shi)(shi)(shi)(shi)要(yao)(yao)(yao)(yao)(yao)(yao)考(kao)慮(lv)到(dao)被測(ce)(ce)介質(zhi)(zhi)的(de)(de)(de)(de)(de)溫(wen)(wen)度(du)(du)，如(ru)果(guo)溫(wen)(wen)度(du)(du)高，達到(dao)200℃~400℃，要(yao)(yao)(yao)(yao)(yao)(yao)選(xuan)(xuan)(xuan)用(yong)(yong)(yong)高溫(wen)(wen)型(xing)(xing)(xing)(xing)(xing)(xing)(xing)，否(fou)則(ze)硅油(you)會產生(sheng)汽化膨脹，使(shi)(shi)測(ce)(ce)量(liang)不(bu)準確(que)。     在(zai)(zai)選(xuan)(xuan)(xuan)型(xing)(xing)(xing)(xing)(xing)(xing)(xing)時(shi)(shi)(shi)(shi)要(yao)(yao)(yao)(yao)(yao)(yao)考(kao)慮(lv)設(she)(she)備(bei)的(de)(de)(de)(de)(de)工(gong)作壓力(li)(li)等(deng)級，變(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)的(de)(de)(de)(de)(de)壓力(li)(li)等(deng)級必(bi)(bi)須與應(ying)用(yong)(yong)(yong)場(chang)合(he)相(xiang)符合(he)。從(cong)經濟(ji)角度(du)(du)上講(jiang)，外(wai)膜盒(he)及插入部分(fen)(fen)材(cai)質(zhi)(zhi)比(bi)較(jiao)重(zhong)要(yao)(yao)(yao)(yao)(yao)(yao)，要(yao)(yao)(yao)(yao)(yao)(yao)選(xuan)(xuan)(xuan)合(he)適，但(dan)連接(jie)發蘭(lan)可(ke)以(yi)(yi)降低材(cai)質(zhi)(zhi)要(yao)(yao)(yao)(yao)(yao)(yao)求，如(ru)選(xuan)(xuan)(xuan)用(yong)(yong)(yong)碳(tan)鋼(gang)(gang)、鍍(du)鉻等(deng)，這(zhe)樣(yang)(yang)會節約很多(duo)資金。     隔(ge)離(li)型(xing)(xing)(xing)(xing)(xing)(xing)(xing)壓力(li)(li)變(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)選(xuan)(xuan)(xuan)用(yong)(yong)(yong)螺紋連接(jie)形式，這(zhe)樣(yang)(yang)既節約資金，安(an)裝(zhuang)也方便(bian)。    對(dui)于(yu)(yu)普通(tong)型(xing)(xing)(xing)(xing)(xing)(xing)(xing)壓力(li)(li)和差壓變(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)選(xuan)(xuan)(xuan)型(xing)(xing)(xing)(xing)(xing)(xing)(xing)，也要(yao)(yao)(yao)(yao)(yao)(yao)考(kao)慮(lv)到(dao)被測(ce)(ce)介質(zhi)(zhi)的(de)(de)(de)(de)(de)腐蝕性問題，但(dan)使(shi)(shi)用(yong)(yong)(yong)的(de)(de)(de)(de)(de)介質(zhi)(zhi)溫(wen)(wen)度(du)(du)可(ke)以(yi)(yi)不(bu)予考(kao)慮(lv)，因(yin)為普通(tong)型(xing)(xing)(xing)(xing)(xing)(xing)(xing)是(shi)引壓到(dao)表(biao)內，長期(qi)工(gong)作時(shi)(shi)(shi)(shi)溫(wen)(wen)度(du)(du)是(shi)常(chang)溫(wen)(wen)，但(dan)普通(tong)型(xing)(xing)(xing)(xing)(xing)(xing)(xing)使(shi)(shi)用(yong)(yong)(yong)的(de)(de)(de)(de)(de)維(wei)(wei)護(hu)(hu)量(liang)要(yao)(yao)(yao)(yao)(yao)(yao)比(bi)隔(ge)離(li)型(xing)(xing)(xing)(xing)(xing)(xing)(xing)大。首(shou)先是(shi)保溫(wen)(wen)問題，氣(qi)溫(wen)(wen)零(ling)下時(shi)(shi)(shi)(shi)導壓管會結冰(bing)，變(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)無(wu)法工(gong)作甚(shen)至損(sun)壞，這(zhe)就要(yao)(yao)(yao)(yao)(yao)(yao)增加伴熱和保溫(wen)(wen)箱等(deng)裝(zhuang)置。     從(cong)經濟(ji)角度(du)(du)上來講(jiang)，選(xuan)(xuan)(xuan)用(yong)(yong)(yong)變(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)時(shi)(shi)(shi)(shi)，只要(yao)(yao)(yao)(yao)(yao)(yao)不(bu)是(shi)易結晶介質(zhi)(zhi)都可(ke)以(yi)(yi)采用(yong)(yong)(yong)普通(tong)型(xing)(xing)(xing)(xing)(xing)(xing)(xing)變(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)，而且對(dui)于(yu)(yu)低壓易結晶介質(zhi)(zhi)也可(ke)以(yi)(yi)加吹(chui)掃介質(zhi)(zhi)來間(jian)接(jie)測(ce)(ce)量(liang)（只要(yao)(yao)(yao)(yao)(yao)(yao)工(gong)藝允許用(yong)(yong)(yong)吹(chui)掃液或(huo)氣(qi)），應(ying)用(yong)(yong)(yong)普通(tong)型(xing)(xing)(xing)(xing)(xing)(xing)(xing)變(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)就是(shi)要(yao)(yao)(yao)(yao)(yao)(yao)求維(wei)(wei)護(hu)(hu)人員(yuan)多(duo)進行定(ding)(ding)時(shi)(shi)(shi)(shi)檢查，包括各種導壓管是(shi)否(fou)泄漏(lou)、吹(chui)掃介質(zhi)(zhi)是(shi)否(fou)正常(chang)、保溫(wen)(wen)是(shi)否(fou)良好等(deng)，只要(yao)(yao)(yao)(yao)(yao)(yao)維(wei)(wei)護(hu)(hu)好，大量(liang)使(shi)(shi)用(yong)(yong)(yong)普通(tong)型(xing)(xing)(xing)(xing)(xing)(xing)(xing)變(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)一次性投資會節約很多(duo)。維(wei)(wei)護(hu)(hu)時(shi)(shi)(shi)(shi)要(yao)(yao)(yao)(yao)(yao)(yao)注意硬件維(wei)(wei)護(hu)(hu)和軟維(wei)(wei)護(hu)(hu)相(xiang)結合(he)。     從(cong)選(xuan)(xuan)(xuan)用(yong)(yong)(yong)變(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)測(ce)(ce)量(liang)范(fan)(fan)(fan)圍(wei)(wei)上來說(shuo)，一般變(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)都具有(you)(you)一定(ding)(ding)的(de)(de)(de)(de)(de)量(liang)程可(ke)調(diao)(diao)范(fan)(fan)(fan)圍(wei)(wei)，將使(shi)(shi)用(yong)(yong)(yong)的(de)(de)(de)(de)(de)量(liang)程范(fan)(fan)(fan)圍(wei)(wei)設(she)(she)定(ding)(ding)在(zai)(zai)它量(liang)程的(de)(de)(de)(de)(de)1/4~3/4段，這(zhe)樣(yang)(yang)精(jing)度(du)(du)會有(you)(you)所(suo)保證(zheng)，對(dui)于(yu)(yu)微差壓變(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)來說(shuo)更(geng)是(shi)重(zhong)要(yao)(yao)(yao)(yao)(yao)(yao)。實踐中(zhong)有(you)(you)些應(ying)用(yong)(yong)(yong)場(chang)合(he)（液位測(ce)(ce)量(liang)）需要(yao)(yao)(yao)(yao)(yao)(yao)對(dui)變(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)的(de)(de)(de)(de)(de)測(ce)(ce)量(liang)范(fan)(fan)(fan)圍(wei)(wei)遷(qian)移(yi)(yi)，根據現場(chang)安(an)裝(zhuang)位置計算出測(ce)(ce)量(liang)范(fan)(fan)(fan)圍(wei)(wei)和遷(qian)移(yi)(yi)量(liang)進行遷(qian)移(yi)(yi)，遷(qian)移(yi)(yi)有(you)(you)正遷(qian)移(yi)(yi)和負遷(qian)移(yi)(yi)之(zhi)分(fen)(fen)。     目前，智能(neng)變(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)已相(xiang)當普及，它的(de)(de)(de)(de)(de)特(te)點是(shi)精(jing)度(du)(du)高、可(ke)調(diao)(diao)范(fan)(fan)(fan)圍(wei)(wei)大，而且調(diao)(diao)整非(fei)常(chang)方便(bian)、穩定(ding)(ding)性好，選(xuan)(xuan)(xuan)型(xing)(xing)(xing)(xing)(xing)(xing)(xing)時(shi)(shi)(shi)(shi)應(ying)多(duo)考(kao)慮(lv)。    按照設(she)(she)計規范(fan)(fan)(fan)，在(zai)(zai)工(gong)程設(she)(she)計選(xuan)(xuan)(xuan)型(xing)(xing)(xing)(xing)(xing)(xing)(xing)中(zhong)，究竟采用(yong)(yong)(yong)氣(qi)動變(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)還是(shi)電動變(bian)(bian)(bian)送(song)(song)(song)器(qi)(qi)，因(yin)其各有(you)(you)特(te)長，應(ying)該根據裝(zhuang)置的(de)(de)(de)(de)(de)具體條件進行綜合(he)考(kao)慮(lv)和分(fen)(fen)析。以(yi)(yi)下幾(ji)點可(ke)供選(xuan)(xuan)(xuan)型(xing)(xing)(xing)(xing)(xing)(xing)(xing)時(shi)(shi)(shi)(shi)參(can)考(kao)： 

※ 集中操作程度(du)及響應速度(du)；

※ 是否(fou)與DCS計算(suan)機操作相配合；    

※ 經濟性(xing)、可(ke)靠性(xing)及(ji)使用維護方面；   

 ※ 安全性（防爆、停(ting)電、氣源故(gu)障(zhang)等）；    

※ 環境條(tiao)件及傳輸(shu)距(ju)離。  一(yi)般來說，下(xia)列條(tiao)件以選(xuan)用氣(qi)動變(bian)送器為宜：     

※ 自變送器至顯示(shi)調節單元間的距離較短，通常以不超過150米為合適；    

※ 工(gong)藝物料是易燃易爆介質及相對濕(shi)度(du)很大的(de)場合；    

※ 要求(qiu)儀表(biao)投資少(shao)、響應速度要求(qiu)不快的場合；    

※ 一(yi)般中小型企業(ye)要求易維修，經濟可(ke)靠；    

※ 在以(yi)電(dian)動(dong)儀表為主的(de)大型裝(zhuang)置(zhi)里，有些現場調節回路不要求引入中央控制室集中操作(zuo)。  下列(lie)條件以(yi)選用電(dian)動(dong)變送器為宜：     

※ 變送器至(zhi)顯示調節單元間的距離超(chao)過(guo)150米(mi)以上；    

※ 大型企業要求高(gao)度集中管理的中央控制；   

 ※ 設置有DCS計算機(ji)進行控制(zhi)及管理的對象；    

 ※ 要求響(xiang)應速度快，信(xin)息處理(li)及運算復雜的(de)場合。     實(shi)際(ji)中，在現代化生產(chan)裝置中都(dou)是發揮它們各自的(de)特點進行混(hun)合選用(yong)的(de)。 

 

3． 壓力變(bian)送(song)器的選型    

從物理學角度來看，任何一個物體上受到的壓力都包括大氣壓力和被測介質的壓力（一般稱為表壓）兩部分。作用在被測物體上的這兩部分壓力總和稱為絕、對壓力。     P絕=P表 + 大氣壓     測量絕、對壓力的儀表稱為絕壓表。對于普通的工業壓力表測量的都是表壓值，也就是絕、對壓力與大氣壓的壓差值。當絕(jue)、對壓力大于大氣壓值時測得的表壓值為正值，稱為正表壓；當絕、對壓力小于大氣壓值時測得的表壓值為負值，稱為負表壓，即真空度。測量真空度的儀表稱為真空表。     

⑴ 為了保證壓力(li)測量(liang)精度，小壓力(li)測量(liang)值應高于壓力(li)表(biao)測量(liang)量(liang)程的1/3；     ⑵ 對需(xu)遠距離測量(liang)或測量(liang)精度要求較高的場合，應選用壓力(li)傳感器或壓力(li)變送器；    

 ⑶ 在(zai)測量精度要求(qiu)不(bu)高(gao)時，可(ke)選擇電阻(zu)式(shi)或(huo)電感式(shi)、霍爾效應式(shi)遠傳壓力變送(song)器；    

 ⑷ 氣動基地(di)式壓(ya)力(li)指示調節(jie)器適宜做(zuo)就地(di)壓(ya)力(li)指示調節(jie)；    

 ⑸ 壓力變(bian)送(song)器、壓力開(kai)關(guan)應(ying)根據安裝場所(suo)的防爆要求合理選擇。

 

 4．差(cha)壓變送(song)器(qi)的選(xuan)型(xing)     差(cha)壓變送(song)器(qi)根據以下幾點選(xuan)型(xing)：   

 ⑴ 測(ce)量(liang)范圍(wei)、需要的精(jing)度及測(ce)量(liang)功能(neng)；    

⑵ 測(ce)量儀表(biao)面對的(de)(de)環境，如石(shi)油化工(gong)的(de)(de)工(gong)業環境，有可熱（有毒）和爆(bao)炸危險(xian)氣氛(fen)的(de)(de)存在，    有較高的(de)(de)環境溫度等；   

 ⑶ 被測介質(zhi)(zhi)的物理化學性質(zhi)(zhi)和(he)狀態(tai)，如(ru)強酸(suan)、強堿、粘稠(chou)、易凝固結晶和(he)汽化等工況；    

⑷ 操作條(tiao)件的(de)變(bian)化，如(ru)介質溫度(du)、壓力、濃度(du)的(de)變(bian)化。有時還要考慮到(dao)從開(kai)車到(dao)參數(shu)達到(dao)正常生產時，氣相和液相濃度(du)和密度(du)的(de)變(bian)化；   

 ⑸ 被(bei)測(ce)對象容器的結構、形狀、尺寸、容器內(nei)的設備附(fu)件及各(ge)種(zhong)進出口(kou)料管口(kou)都要考慮，如(ru)    塔、溶液槽(cao)、反應器、鍋爐汽包、立(li)罐、球(qiu)罐等；   

⑹ 其它要(yao)求，如環保及衛生等要(yao)求；    

⑺ 工(gong)程(cheng)儀表選(xuan)型要有(you)統(tong)一的考慮，要求(qiu)盡可能地(di)減少規格品(pin)種，減少備品(pin)備件，以利管理(li)；   

 ⑻ 實(shi)際(ji)的工藝情況(kuang)：     

 ① 考(kao)慮(lv)被測(ce)(ce)對(dui)象(xiang)是屬(shu)于(yu)哪一(yi)類(lei)設備(bei)。如(ru)槽(cao)、罐類(lei)，槽(cao)的(de)(de)(de)(de)(de)容積較小(xiao)，測(ce)(ce)量(liang)的(de)(de)(de)(de)(de)范圍(wei)不(bu)會太大，罐的(de)(de)(de)(de)(de)容積較大，測(ce)(ce)量(liang)的(de)(de)(de)(de)(de)范圍(wei)可(ke)能較大；    ② 要(yao)(yao)看介質(zhi)(zhi)(zhi)的(de)(de)(de)(de)(de)物(wu)化性質(zhi)(zhi)(zhi)及(ji)潔凈(jing)程(cheng)度，常規的(de)(de)(de)(de)(de)差壓(ya)(ya)變(bian)送(song)器(qi)(qi)(qi)及(ji)浮筒式液位變(bian)送(song)器(qi)(qi)(qi)，還要(yao)(yao)對(dui)接觸介質(zhi)(zhi)(zhi)部分的(de)(de)(de)(de)(de)材質(zhi)(zhi)(zhi)進行選(xuan)擇；     ③ 對(dui)有些懸(xuan)浮物(wu)、泡沫等(deng)介質(zhi)(zhi)(zhi)可(ke)用(yong)單發蘭式差壓(ya)(ya)變(bian)送(song)器(qi)(qi)(qi)。有些易(yi)(yi)析出、易(yi)(yi)結晶的(de)(de)(de)(de)(de)用(yong)插入式雙發蘭差壓(ya)(ya)變(bian)送(song)器(qi)(qi)(qi)；     ④ 對(dui)高黏度介質(zhi)(zhi)(zhi)的(de)(de)(de)(de)(de)液位及(ji)高壓(ya)(ya)設備(bei)的(de)(de)(de)(de)(de)液位，由于(yu)設備(bei)無法開孔，可(ke)選(xuan)用(yong)放射(she)液位計來(lai)測(ce)(ce)量(liang)；     ⑤ 除了測(ce)(ce)量(liang)方(fang)法上和技術上問題以外，還有儀表的(de)(de)(de)(de)(de)投(tou)資問題。    綜上所述，變(bian)送(song)器(qi)(qi)(qi)的(de)(de)(de)(de)(de)選(xuan)型(xing)，技術上要(yao)(yao)可(ke)行，經(jing)濟上要(yao)(yao)合理(li)，管理(li)上要(yao)(yao)方(fang)便。

 

 

變送(song)器(qi)可以(yi)直接安(an)裝在測(ce)量點處，可以(yi)安(an)裝在墻上，或者使用安(an)裝板(變送(song)器(qi)附件)夾(jia)拼在管道上。

變送器壓力(li)容室上的(de)(de)導(dao)壓連接孔(kong)為(wei)螺(luo)紋孔(kong)，接頭上的(de)(de)導(dao)壓接孔(kong)為(wei)內錐(zhui)管(guan)螺(luo)紋(或外螺(luo)紋)，根據需要可選擇。

與引壓(ya)接頭(tou)(tou)錐管螺紋的過渡接頭(tou)(tou)。壓(ya)力變(bian)送器可以輕而易舉(ju)地從流程工藝管道上拆下，方法(fa)是擰下緊固接頭(tou)(tou)的兩個(ge)螺栓。轉動(dong)接頭(tou)(tou)，可以改變(bian)其接孔的中心距離。

 

 

3.壓力和差壓變送器(qi)安裝說明

*取壓點處應(ying)保證有直管(guan)段，兩(liang)邊各大于5D(管(guan)道通(tong)經)；

*在蒸(zheng)汽管道(dao)上取壓(ya)時，應在管道(dao)的側面(mian)安(an)裝(zhuang)引(yin)壓(ya)管；

*平衡罐應安裝在引壓管的高(gao)點處；

*排污管應在(zai)靠近變送(song)器引壓管連接處安裝(zhuang)；

*取壓點與變送器的(de)管道(dao)距離(li)應大于1米(mi)；

 

4.壓力變(bian)送器在(zai)工藝管道上(shang)的安裝位(wei)置(zhi)，與被測介質有關。

安裝時應(ying)注意考慮下(xia)面的情況(kuang):   ;    

1)盡量(liang)避免變送器與腐蝕(shi)性(xing)或過(guo)熱的被測介(jie)質直接接觸。      

 2)要防止渣滓在導壓管內沉積。       

3)導壓管要盡可能短(duan)一(yi)些(xie)。       

4)兩邊(bian)導壓(ya)管內的液(ye)柱壓(ya)力應(ying)保持平衡。       

5)導壓管應安裝(zhuang)在溫(wen)度梯度和溫(wen)度波動小的地方(fang)  

測量(liang)液體流(liu)量(liang)時，取壓口應開在流(liu)程管(guan)道的(de)(de)側(ce)面(mian)，以(yi)避免渣滓(zi)的(de)(de)沉(chen)淀。同(tong)時變送(song)器(qi)要安(an)裝在取壓口的(de)(de)旁邊或下面(mian)，以(yi)便氣泡排(pai)入(ru)流(liu)程管(guan)道之內(nei)。     

測量氣體流(liu)量時，取壓口應開在流(liu)程管道的(de)頂端或(huo)側面。并且變(bian)送器(qi)應裝(zhuang)在流(liu)程管道的(de)旁邊或(huo)上面，以便(bian)積聚的(de)液體容易(yi)流(liu)入流(liu)程管道之(zhi)中。 　　　

使(shi)用壓(ya)力(li)(li)(li)容(rong)室裝有側(ce)面(mian)泄(xie)(xie)放閥(fa)(fa)的變送器(qi)，取壓(ya)口要開在流程管(guan)道的側(ce)面(mian)。比如(ru)被測(ce)介(jie)質為液體(ti)時(shi)，3051智能壓(ya)力(li)(li)(li)變送器(qi)的泄(xie)(xie)放閥(fa)(fa)應(ying)安裝在上面(mian)，以便排除出滲在被測(ce)介(jie)質中的氣(qi)體(ti)。被測(ce)介(jie)質為氣(qi)體(ti)時(shi)，變送器(qi)的泄(xie)(xie)放閥(fa)(fa)應(ying)安裝在下(xia)面(mian)，以便排放積(ji)聚的液體(ti)(見下(xia)圖)。壓(ya)力(li)(li)(li)容(rong)室轉動180。，就可使(shi)其上面(mian)的泄(xie)(xie)放閥(fa)(fa)變到下(xia)面(mian)。