1、概述(shu)

在諸類儀(yi)(yi)表(biao)中(zhong)，變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)的(de)應用(yong)(yong)(yong)*為廣泛(fan)、普(pu)(pu)遍，變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)大體(ti)分為壓(ya)(ya)(ya)(ya)(ya)力(li)(li)變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)和(he)(he)差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)。變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)常(chang)用(yong)(yong)(yong)來(lai)測量壓(ya)(ya)(ya)(ya)(ya)力(li)(li)、差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)、真空、液位、流量和(he)(he)密度等。變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)有兩線(xian)制和(he)(he)四線(xian)制之(zhi)(zhi)(zhi)分，兩線(xian)制變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)尤多；有智(zhi)(zhi)能和(he)(he)非(fei)智(zhi)(zhi)能之(zhi)(zhi)(zhi)分，智(zhi)(zhi)能變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)漸(jian)多；有氣動和(he)(he)電(dian)動之(zhi)(zhi)(zhi)分，電(dian)動變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)居多；另(ling)外(wai)，按應用(yong)(yong)(yong)場(chang)合有本安型(xing)（本質(zhi)(zhi)**型(xing)）和(he)(he)隔爆型(xing)之(zhi)(zhi)(zhi)分；按應用(yong)(yong)(yong)工況(kuang)，變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)的(de)主要種(zhong)類有：低（微）壓(ya)(ya)(ya)(ya)(ya)/低（微）差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)；中(zhong)壓(ya)(ya)(ya)(ya)(ya)/中(zhong)差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)；高(gao)壓(ya)(ya)(ya)(ya)(ya)/高(gao)差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)；絕壓(ya)(ya)(ya)(ya)(ya)/真空/負壓(ya)(ya)(ya)(ya)(ya)差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)；高(gao)溫/壓(ya)(ya)(ya)(ya)(ya)力(li)(li)、差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)；耐腐(fu)蝕(shi)/壓(ya)(ya)(ya)(ya)(ya)力(li)(li)、差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)；易結晶/壓(ya)(ya)(ya)(ya)(ya)力(li)(li)、差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)。變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)的(de)選型(xing)通常(chang)根據(ju)安裝條件(jian)、環(huan)境條件(jian)、儀(yi)(yi)表(biao)性能、經(jing)濟性和(he)(he)使用(yong)(yong)(yong)介(jie)質(zhi)(zhi)等方面考慮。實際應用(yong)(yong)(yong)中(zhong)分為直接(jie)測量和(he)(he)間接(jie)測量兩種(zhong)；其用(yong)(yong)(yong)途有過程測量、過程控制和(he)(he)裝置連鎖等。常(chang)見的(de)變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)有普(pu)(pu)通壓(ya)(ya)(ya)(ya)(ya)力(li)(li)變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)、差(cha)(cha)(cha)壓(ya)(ya)(ya)(ya)(ya)變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)、單(dan)發蘭變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)、雙(shuang)發蘭變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)、插入式發蘭變(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)(bian)送(song)(song)(song)(song)器(qi)(qi)等。

2、壓(ya)力(li)/差壓(ya)變送器介紹

壓(ya)(ya)力(li)變(bian)(bian)送(song)(song)(song)(song)器(qi)和(he)(he)差(cha)(cha)(cha)(cha)壓(ya)(ya)變(bian)(bian)送(song)(song)(song)(song)器(qi)單從名(ming)稱(cheng)上講測(ce)(ce)(ce)量(liang)(liang)的(de)(de)是壓(ya)(ya)力(li)和(he)(he)差(cha)(cha)(cha)(cha)壓(ya)(ya)（兩個壓(ya)(ya)力(li)的(de)(de)差(cha)(cha)(cha)(cha)），但它們(men)(men)可(ke)以(yi)間接測(ce)(ce)(ce)量(liang)(liang)的(de)(de)量(liang)(liang)卻很(hen)多。如壓(ya)(ya)力(li)變(bian)(bian)送(song)(song)(song)(song)器(qi)，除可(ke)以(yi)測(ce)(ce)(ce)量(liang)(liang)壓(ya)(ya)力(li)外，還可(ke)以(yi)測(ce)(ce)(ce)量(liang)(liang)設備內的(de)(de)液(ye)位。在常壓(ya)(ya)容(rong)(rong)器(qi)內測(ce)(ce)(ce)量(liang)(liang)液(ye)位時，需要一(yi)(yi)(yi)臺(tai)(tai)壓(ya)(ya)力(li)變(bian)(bian)送(song)(song)(song)(song)器(qi)即可(ke)。當(dang)測(ce)(ce)(ce)量(liang)(liang)受壓(ya)(ya)容(rong)(rong)器(qi)的(de)(de)液(ye)位時，可(ke)考慮用兩臺(tai)(tai)壓(ya)(ya)力(li)/差(cha)(cha)(cha)(cha)壓(ya)(ya)變(bian)(bian)送(song)(song)(song)(song)器(qi)，即測(ce)(ce)(ce)量(liang)(liang)下(xia)(xia)限一(yi)(yi)(yi)臺(tai)(tai)，測(ce)(ce)(ce)量(liang)(liang)上限一(yi)(yi)(yi)臺(tai)(tai)，它們(men)(men)的(de)(de)輸出信號(hao)進行(xing)減法運(yun)算，即可(ke)測(ce)(ce)(ce)出液(ye)位，這時一(yi)(yi)(yi)般選用差(cha)(cha)(cha)(cha)壓(ya)(ya)變(bian)(bian)送(song)(song)(song)(song)器(qi)。在容(rong)(rong)器(qi)內液(ye)位與壓(ya)(ya)力(li)值不(bu)變(bian)(bian)的(de)(de)情況(kuang)下(xia)(xia)它還可(ke)以(yi)用來測(ce)(ce)(ce)量(liang)(liang)介質(zhi)的(de)(de)密(mi)度。壓(ya)(ya)力(li)變(bian)(bian)送(song)(song)(song)(song)器(qi)的(de)(de)測(ce)(ce)(ce)量(liang)(liang)范圍可(ke)以(yi)做的(de)(de)很(hen)寬，從絕壓(ya)(ya)0開始(shi)可(ke)以(yi)到一(yi)(yi)(yi)百多兆(zhao)帕(pa)（一(yi)(yi)(yi)般情況(kuang)）。

差壓(ya)(ya)變送器除(chu)了(le)測(ce)(ce)量兩個被測(ce)(ce)量壓(ya)(ya)力的差壓(ya)(ya)值(zhi)外，它還可(ke)以配合各種節流(liu)元件(jian)來測(ce)(ce)量介質流(liu)體(ti)的流(liu)量，可(ke)以直(zhi)接測(ce)(ce)量受壓(ya)(ya)容器的液位和(he)(he)常壓(ya)(ya)容器的液位以及壓(ya)(ya)力和(he)(he)負壓(ya)(ya)。

2.1 制作

從壓(ya)力/差(cha)壓(ya)變送器制作(zuo)的結構上來分有普(pu)通(tong)型(xing)和隔(ge)離(li)型(xing)。普(pu)通(tong)型(xing)壓(ya)力/差(cha)壓(ya)變送器的測(ce)(ce)量膜(mo)(mo)(mo)(mo)盒(he)為(wei)一(yi)個，它直接(jie)感受(shou)被測(ce)(ce)介質的壓(ya)力或差(cha)壓(ya)；隔(ge)離(li)型(xing)的測(ce)(ce)量膜(mo)(mo)(mo)(mo)盒(he)接(jie)受(shou)到的是(shi)一(yi)種穩定液（一(yi)般為(wei)硅(gui)油）的壓(ya)力，而這(zhe)種穩定液是(shi)被密封在兩個膜(mo)(mo)(mo)(mo)片中(zhong)間，直接(jie)接(jie)受(shou)被測(ce)(ce)壓(ya)力的膜(mo)(mo)(mo)(mo)片為(wei)外膜(mo)(mo)(mo)(mo)片，原普(pu)通(tong)型(xing)膜(mo)(mo)(mo)(mo)盒(he)的膜(mo)(mo)(mo)(mo)片為(wei)內膜(mo)(mo)(mo)(mo)片，當外膜(mo)(mo)(mo)(mo)片上接(jie)受(shou)壓(ya)力信號時通(tong)過硅(gui)油的傳遞原封不動的將外膜(mo)(mo)(mo)(mo)片的壓(ya)力傳遞到了普(pu)通(tong)膜(mo)(mo)(mo)(mo)盒(he)上，從而可以測(ce)(ce)出外膜(mo)(mo)(mo)(mo)片所感受(shou)到的壓(ya)力。

隔(ge)離型(xing)壓(ya)力/差壓(ya)變(bian)(bian)送(song)器(qi)(qi)主要是針對特(te)殊(shu)的(de)被測量介質(zhi)設計和(he)使用的(de)，如果被測介質(zhi)離開設備后(hou)會產生(sheng)結晶(jing)，而使用普通型(xing)壓(ya)力/差壓(ya)變(bian)(bian)送(song)器(qi)(qi)需要取(qu)出介質(zhi)，會將(jiang)導壓(ya)管膜(mo)(mo)盒室(shi)堵塞使其不(bu)能正常工作(zuo)(zuo)，所以必須(xu)選(xuan)用隔(ge)離型(xing)。隔(ge)離型(xing)變(bian)(bian)送(song)器(qi)(qi)通常作(zuo)(zuo)成發蘭式安裝，即在(zai)被測設備上開口使變(bian)(bian)送(song)器(qi)(qi)安裝后(hou)它(ta)的(de)感應膜(mo)(mo)片是設備壁的(de)一部分(fen)，這(zhe)樣它(ta)不(bu)會取(qu)出被測介質(zhi)，一般也不(bu)會造成結晶(jing)和(he)堵塞。

當被測(ce)介質需求結晶溫(wen)(wen)度(du)較高(gao)時，可選(xuan)用將(jiang)膜(mo)(mo)片(pian)凸出(chu)的(de)結構，這樣(yang)可將(jiang)傳感膜(mo)(mo)片(pian)插入到設備內部(bu)，從而感應到的(de)介質溫(wen)(wen)度(du)不會降低，這樣(yang)測(ce)量是有保障的(de)，即(ji)選(xuan)用插入式(shi)發蘭變(bian)送(song)器。

隔離(li)型變送(song)(song)器有遠傳型和一(yi)體(ti)型之分(fen)。遠傳型即外(wai)膜(mo)(mo)盒(he)(he)與(yu)測(ce)(ce)量膜(mo)(mo)盒(he)(he)之間(jian)用(yong)加(jia)強(qiang)毛(mao)細(xi)管連(lian)接(jie)(jie)(jie)，一(yi)般毛(mao)細(xi)管為3~5米(mi)，這(zhe)樣外(wai)膜(mo)(mo)盒(he)(he)裝(zhuang)在設(she)備(bei)(bei)上，內膜(mo)(mo)盒(he)(he)及變送(song)(song)器可以安(an)裝(zhuang)在便(bian)于維護的安(an)裝(zhuang)支架上；另(ling)一(yi)種形式是(shi)外(wai)膜(mo)(mo)盒(he)(he)與(yu)變送(song)(song)器做成一(yi)體(ti)直(zhi)接(jie)(jie)(jie)由發蘭安(an)裝(zhuang)在設(she)備(bei)(bei)上。對于隔離(li)型壓力(li)變送(song)(song)器它還可以作成螺(luo)紋連(lian)接(jie)(jie)(jie)型，即外(wai)膜(mo)(mo)盒(he)(he)或(huo)外(wai)彈性元件(jian)可在安(an)裝(zhuang)螺(luo)紋的前面，只要在被測(ce)(ce)設(she)備(bei)(bei)上焊接(jie)(jie)(jie)上內螺(luo)紋凸臺，便(bian)可將變送(song)(song)器直(zhi)接(jie)(jie)(jie)擰(ning)到(dao)設(she)備(bei)(bei)上，安(an)裝(zhuang)非(fei)常方(fang)便(bian)。

隔離型壓力/差壓變送器的制作復(fu)雜(za)，材質要求也(ye)較(jiao)高(gao)，所以它的價格通(tong)常是(shi)普通(tong)型的3~4倍(bei)。

2.2 選型原則(ze)

在(zai)壓力/差(cha)壓變送器(qi)的(de)選用(yong)(yong)上(shang)主要依據：以被(bei)測介質的(de)性質指標為準，以節(jie)約(yue)資金(jin)、便于安裝和維護為參考(kao)。如果被(bei)測介質為高黏度、易(yi)結晶、強腐(fu)蝕的(de)，必須選用(yong)(yong)隔(ge)離(li)型變送器(qi)。

在選(xuan)型時(shi)要考慮被測(ce)流體介質對膜盒金屬的(de)腐(fu)蝕(shi)，一定要選(xuan)好膜盒材質，否則使(shi)用(yong)后很短時(shi)間就會(hui)將外膜片腐(fu)蝕(shi)壞，發(fa)蘭也會(hui)被腐(fu)蝕(shi)壞造成(cheng)設備(bei)或人身事(shi)故(gu)，所以(yi)膜盒材質的(de)選(xuan)擇非(fei)常關鍵。變送器的(de)膜盒材質有普(pu)通不(bu)銹鋼、304不(bu)銹鋼、316/316L不(bu)銹鋼、鉭材質等。

在(zai)選型(xing)時要考慮到被測(ce)介質的溫度(du)，如果溫度(du)高(gao)(gao)，達到200℃~400℃，要選用高(gao)(gao)溫型(xing)，否(fou)則硅油會產生(sheng)汽化膨脹，使測(ce)量不(bu)準確。

在選(xuan)型時(shi)要(yao)(yao)考慮(lv)設(she)備(bei)的(de)工作壓力(li)(li)等級(ji)，變(bian)送(song)器(qi)的(de)壓力(li)(li)等級(ji)必須與應用場合(he)相符合(he)。從經濟(ji)角度上講，外膜盒及插入部分材質比較重要(yao)(yao)，要(yao)(yao)選(xuan)合(he)適(shi)，但連接(jie)發(fa)蘭可以降低材質要(yao)(yao)求，如選(xuan)用碳(tan)鋼、鍍鉻等，這樣會節(jie)約(yue)很(hen)多資(zi)金。隔離(li)型壓力(li)(li)變(bian)送(song)器(qi)*好選(xuan)用螺紋連接(jie)形式(shi)，這樣既節(jie)約(yue)資(zi)金，安裝也方便。

對于普(pu)通(tong)型壓力和(he)差(cha)壓變送(song)器選型，也要(yao)考慮(lv)到(dao)被(bei)測(ce)介質的(de)(de)腐蝕性問題，但(dan)(dan)使(shi)用(yong)的(de)(de)介質溫(wen)(wen)(wen)度(du)(du)可以不予考慮(lv)，因(yin)為普(pu)通(tong)型是引壓到(dao)表內(nei)，長(chang)期工作(zuo)時溫(wen)(wen)(wen)度(du)(du)是常溫(wen)(wen)(wen)，但(dan)(dan)普(pu)通(tong)型使(shi)用(yong)的(de)(de)維(wei)護(hu)量要(yao)比隔離(li)型大。首先是保溫(wen)(wen)(wen)問題，氣溫(wen)(wen)(wen)零下時導壓管會結冰(bing)，變送(song)器無(wu)法(fa)工作(zuo)甚(shen)至損壞，這就要(yao)增加(jia)伴熱和(he)保溫(wen)(wen)(wen)箱等(deng)裝置(zhi)。

從經濟角(jiao)度上(shang)來(lai)講(jiang)，選用(yong)(yong)變(bian)送(song)器(qi)時(shi)，只(zhi)要不是(shi)(shi)易結(jie)晶(jing)介(jie)質都可以采(cai)用(yong)(yong)普(pu)(pu)通(tong)型(xing)(xing)變(bian)送(song)器(qi)，而且對于低壓(ya)易結(jie)晶(jing)介(jie)質也(ye)可以加吹(chui)掃(sao)(sao)介(jie)質來(lai)間接(jie)測量(liang)（只(zhi)要工(gong)藝允許用(yong)(yong)吹(chui)掃(sao)(sao)液(ye)或氣），應用(yong)(yong)普(pu)(pu)通(tong)型(xing)(xing)變(bian)送(song)器(qi)就是(shi)(shi)要求(qiu)維(wei)(wei)護人(ren)員多(duo)進(jin)行定時(shi)檢(jian)查，包括各(ge)種導壓(ya)管是(shi)(shi)否(fou)泄漏、吹(chui)掃(sao)(sao)介(jie)質是(shi)(shi)否(fou)正常、保溫是(shi)(shi)否(fou)良好等，只(zhi)要維(wei)(wei)護好，大量(liang)使(shi)用(yong)(yong)普(pu)(pu)通(tong)型(xing)(xing)變(bian)送(song)器(qi)一次性投資會節約很多(duo)。維(wei)(wei)護時(shi)要注意硬件維(wei)(wei)護和軟維(wei)(wei)護相結(jie)合。

從選用變(bian)(bian)送(song)器測(ce)(ce)量(liang)(liang)范圍上來(lai)說(shuo)，一般變(bian)(bian)送(song)器都(dou)具有(you)一定(ding)的量(liang)(liang)程(cheng)可調范圍，*好將使(shi)用的量(liang)(liang)程(cheng)范圍設(she)定(ding)在(zai)它(ta)量(liang)(liang)程(cheng)的1/4~3/4段，這樣精度會(hui)有(you)所保(bao)證(zheng)，對于微差壓變(bian)(bian)送(song)器來(lai)說(shuo)更是重要(yao)。實踐中有(you)些應(ying)用場合(he)（液位測(ce)(ce)量(liang)(liang)）需要(yao)對變(bian)(bian)送(song)器的測(ce)(ce)量(liang)(liang)范圍遷(qian)(qian)(qian)移(yi)(yi)(yi)(yi)(yi)，根據現場安裝位置計算出測(ce)(ce)量(liang)(liang)范圍和遷(qian)(qian)(qian)移(yi)(yi)(yi)(yi)(yi)量(liang)(liang)進行遷(qian)(qian)(qian)移(yi)(yi)(yi)(yi)(yi)，遷(qian)(qian)(qian)移(yi)(yi)(yi)(yi)(yi)有(you)正遷(qian)(qian)(qian)移(yi)(yi)(yi)(yi)(yi)和負遷(qian)(qian)(qian)移(yi)(yi)(yi)(yi)(yi)之(zhi)分。

目(mu)前，智(zhi)能(neng)變送(song)器已相當普及，它的特(te)點是精(jing)度高(gao)、可調范圍大，而且調整非常(chang)方(fang)便、穩定性(xing)好，選型時應(ying)多考慮。

按照設計規范，在工程(cheng)設計選型中，究(jiu)竟采用(yong)氣動變(bian)送器(qi)還是(shi)電動變(bian)送器(qi)，因(yin)其(qi)各(ge)有特長，應該根據裝置的具體條件進行綜合考(kao)慮(lv)和分析。以(yi)下幾(ji)點(dian)可供(gong)選型時參考(kao)：

※ 集中操作程度及響應速度；

※ 是否與(yu)DCS計算機操(cao)作(zuo)相配合；

※ 經濟性(xing)、可靠性(xing)及使用維護(hu)方(fang)面；

※ **性(xing)（防爆(bao)、停電、氣源故障等）；

※ 環境條(tiao)件及傳輸距離(li)。

一(yi)般來說，下列(lie)條件以(yi)選(xuan)用氣動(dong)變送(song)器為宜：

※ 自變送器至顯(xian)示(shi)調節單(dan)元間的距離較短，通常以不超過150米(mi)較為合適；

※ 工藝物料是易燃(ran)易爆介質及相對濕度很大的場合(he)；

※ 要(yao)求(qiu)儀表投資少、響應(ying)速(su)度(du)要(yao)求(qiu)不快的場合；

※ 一般中小型企業要(yao)求易維修，經濟可靠；

※ 在以電動(dong)儀表為主(zhu)的大型裝置(zhi)里，有些現場調節回路不要求引入中(zhong)(zhong)央(yang)控制室集中(zhong)(zhong)操作。

下列(lie)條(tiao)件以(yi)選用電動變送器為宜：

※ 變送器(qi)至(zhi)顯(xian)示(shi)調節單元間的(de)距離(li)超過150米(mi)以上；

※ 大型企(qi)業要求高度集中(zhong)(zhong)管理的中(zhong)(zhong)央控制；

※ 設置有(you)DCS計算機進行控制(zhi)及(ji)管(guan)理(li)的對象；