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Technical articles法國KIMO凱茂差壓變送器如(ru)何(he)校準
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差壓(ya)變送器的現場校準方法
差壓(ya)變送器在工廠有廣泛的(de)應用(yong),為保證其正常運行及準確性,定期檢查、校準是(shi)很有必要的(de)。現介(jie)紹一種不用(yong)拆除導壓(ya)管就(jiu)進行現場校準的(de)方法。
一、準備工作:
我們(men)知道差(cha)(cha)壓(ya)(ya)變(bian)(bian)送(song)器(qi)在(zai)應用(yong)中是(shi)與(yu)導(dao)壓(ya)(ya)管(guan)(guan)(guan)相(xiang)連接(jie)的(de)(de),通(tong)常的(de)(de)做(zuo)法,需要把導(dao)壓(ya)(ya)管(guan)(guan)(guan)和差(cha)(cha)壓(ya)(ya)變(bian)(bian)送(song)器(qi)的(de)(de)接(jie)頭拆開,再接(jie)入壓(ya)(ya)力源進(jin)行(xing)校(xiao)準(zhun)。這樣是(shi)很(hen)麻煩的(de)(de),并(bing)且工作和勞動強度(du)大(da),最(zui)擔心的(de)(de)是(shi)拆裝接(jie)頭時(shi)(shi)把導(dao)壓(ya)(ya)管(guan)(guan)(guan)扳斷或(huo)(huo)出現泄漏問題(ti)。我們(men)知道不(bu)管(guan)(guan)(guan)什么型號的(de)(de)差(cha)(cha)壓(ya)(ya)變(bian)(bian)送(song)器(qi),其正(zheng)、負壓(ya)(ya)室都有排(pai)(pai)(pai)氣(qi)、排(pai)(pai)(pai)液閥(fa)(fa)或(huo)(huo)旋(xuan)(xuan)(xuan)塞(sai);這就為我們(men)現場校(xiao)準(zhun)差(cha)(cha)壓(ya)(ya)變(bian)(bian)送(song)器(qi)提(ti)供了方便,也(ye)就是(shi)說不(bu)用(yong)拆除導(dao)壓(ya)(ya)管(guan)(guan)(guan)就可校(xiao)準(zhun)差(cha)(cha)壓(ya)(ya)變(bian)(bian)送(song)器(qi)。對差(cha)(cha)壓(ya)(ya)變(bian)(bian)送(song)器(qi)進(jin)行(xing)校(xiao)準(zhun)時(shi)(shi),先把三閥(fa)(fa)組(zu)的(de)(de)正(zheng)、負閥(fa)(fa)門關(guan)閉(bi),打開平衡(heng)(heng)閥(fa)(fa)門,然(ran)后旋(xuan)(xuan)(xuan)松排(pai)(pai)(pai)氣(qi)、排(pai)(pai)(pai)液閥(fa)(fa)或(huo)(huo)旋(xuan)(xuan)(xuan)塞(sai)放空,然(ran)后用(yong)自(zi)制(zhi)的(de)(de)接(jie)頭來代替接(jie)正(zheng)壓(ya)(ya)室的(de)(de)排(pai)(pai)(pai)氣(qi)、排(pai)(pai)(pai)液閥(fa)(fa)或(huo)(huo)旋(xuan)(xuan)(xuan)塞(sai);而(er)負壓(ya)(ya)室則保持旋(xuan)(xuan)(xuan)松狀態,使其通(tong)大(da)氣(qi)。壓(ya)(ya)力源通(tong)過膠皮管(guan)(guan)(guan)與(yu)自(zi)制(zhi)接(jie)頭相(xiang)連接(jie),關(guan)閉(bi)平衡(heng)(heng)閥(fa)(fa)門,并(bing)檢查氣(qi)路(lu)密封情況,然(ran)后把電(dian)流(liu)表(biao)(電(dian)壓(ya)(ya)表(biao))、手操器(qi)接(jie)入變(bian)(bian)送(song)器(qi)輸出電(dian)路(lu)中,通(tong)電(dian)預熱后開始校(xiao)準(zhun)。
二、常規差壓(ya)變送器的校準(zhun):
先將(jiang)阻(zu)尼(ni)(ni)調(diao)(diao)(diao)至零(ling)(ling)狀態,先調(diao)(diao)(diao)零(ling)(ling)點(dian)(dian),然(ran)(ran)后加(jia)滿(man)度(du)(du)壓力調(diao)(diao)(diao)滿(man)量(liang)(liang)程(cheng)(cheng)(cheng),使輸出為(wei)(wei)(wei)20mA,在(zai)(zai)現場調(diao)(diao)(diao)校講的(de)是快(kuai)(kuai),在(zai)(zai)此(ci)介紹零(ling)(ling)點(dian)(dian)、量(liang)(liang)程(cheng)(cheng)(cheng)的(de)快(kuai)(kuai)速調(diao)(diao)(diao)校法。調(diao)(diao)(diao)零(ling)(ling)點(dian)(dian)時(shi)對滿(man)度(du)(du)幾乎(hu)沒有(you)影響(xiang),但調(diao)(diao)(diao)滿(man)度(du)(du)時(shi)對零(ling)(ling)點(dian)(dian)有(you)影響(xiang),在(zai)(zai)不帶遷(qian)移時(shi)其(qi)影響(xiang)約(yue)為(wei)(wei)(wei)量(liang)(liang)程(cheng)(cheng)(cheng)調(diao)(diao)(diao)整量(liang)(liang)的(de)1/5,即量(liang)(liang)程(cheng)(cheng)(cheng)向上調(diao)(diao)(diao)整1mA,零(ling)(ling)點(dian)(dian)將(jiang)向上移動約(yue)0.2mA,反(fan)之(zhi)亦然(ran)(ran)。例如:輸入(ru)滿(man)量(liang)(liang)程(cheng)(cheng)(cheng)壓力為(wei)(wei)(wei)100Kpa,該讀數為(wei)(wei)(wei)19.900mA,調(diao)(diao)(diao)量(liang)(liang)程(cheng)(cheng)(cheng)電位器(qi)使輸出為(wei)(wei)(wei)19.900+(20.000-19.900)×1.25=20.025mA.量(liang)(liang)程(cheng)(cheng)(cheng)增(zeng)加(jia)0.125mA,則零(ling)(ling)點(dian)(dian)增(zeng)加(jia)1/5×0.125=0.025.調(diao)(diao)(diao)零(ling)(ling)點(dian)(dian)電位器(qi)使輸出為(wei)(wei)(wei)20.000mA.零(ling)(ling)點(dian)(dian)和滿(man)量(liang)(liang)程(cheng)(cheng)(cheng)調(diao)(diao)(diao)校正常后,再檢查中(zhong)間各刻度(du)(du),看(kan)其(qi)是否超差?必要時(shi)進行微調(diao)(diao)(diao)。然(ran)(ran)后進行遷(qian)移、線性、阻(zu)尼(ni)(ni)的(de)調(diao)(diao)(diao)整工(gong)作。
三(san)、智能(neng)差壓(ya)變送(song)器的校準
用上(shang)述的常規(gui)方(fang)法(fa)對智能(neng)變(bian)(bian)(bian)(bian)(bian)送(song)(song)器(qi)(qi)進行校準(zhun)是(shi)不行的,因(yin)為這(zhe)(zhe)是(shi)由HART變(bian)(bian)(bian)(bian)(bian)送(song)(song)器(qi)(qi)結構(gou)原理(li)所(suo)(suo)決定(ding)了(le)。因(yin)為智能(neng)變(bian)(bian)(bian)(bian)(bian)送(song)(song)器(qi)(qi)在(zai)輸(shu)(shu)入(ru)(ru)壓(ya)力(li)(li)源和產生的4-20mA電流信號之(zhi)(zhi)間(jian),除機械(xie)、電路外,還(huan)有(you)微處理(li)芯片(pian)對輸(shu)(shu)入(ru)(ru)數(shu)據的運算(suan)工(gong)作(zuo)。因(yin)此調(diao)校與(yu)(yu)常規(gui)方(fang)法(fa)有(you)所(suo)(suo)區別。;V???_7@)m7v#F實(shi)(shi)際上(shang)廠家(jia)對智能(neng)變(bian)(bian)(bian)(bian)(bian)送(song)(song)器(qi)(qi)的校準(zhun)也是(shi)有(you)說明的,如ABB的變(bian)(bian)(bian)(bian)(bian)送(song)(song)器(qi)(qi),對校準(zhun)就(jiu)有(you):“設(she)(she)定(ding)量程(cheng)"、“重定(ding)量程(cheng)"、“微調(diao)"之(zhi)(zhi)分(fen)。其中“設(she)(she)定(ding)量程(cheng)"操作(zuo)主要是(shi)通(tong)(tong)過(guo)LRV.URV的數(shu)字(zi)設(she)(she)定(ding)來完成配置(zhi)工(gong)作(zuo),而“重定(ding)量程(cheng)"操作(zuo)則要求將變(bian)(bian)(bian)(bian)(bian)送(song)(song)器(qi)(qi)連接到(dao)(dao)標準(zhun)壓(ya)力(li)(li)源上(shang),通(tong)(tong)過(guo)一系(xi)列指令引(yin)導,由變(bian)(bian)(bian)(bian)(bian)送(song)(song)器(qi)(qi)直接感應實(shi)(shi)際壓(ya)力(li)(li)并對數(shu)值(zhi)進行設(she)(she)置(zhi)。而量程(cheng)的初始(shi)、最終(zhong)設(she)(she)置(zhi)直接取決于(yu)(yu)真實(shi)(shi)的壓(ya)力(li)(li)輸(shu)(shu)入(ru)(ru)值(zhi)。但(dan)(dan)要看到(dao)(dao)盡管變(bian)(bian)(bian)(bian)(bian)送(song)(song)器(qi)(qi)的模擬輸(shu)(shu)出與(yu)(yu)所(suo)(suo)用的輸(shu)(shu)入(ru)(ru)值(zhi)關系(xi)正確,但(dan)(dan)過(guo)程(cheng)值(zhi)的數(shu)字(zi)讀數(shu)顯(xian)示的數(shu)值(zhi)會(hui)略有(you)不同,這(zhe)(zhe)可(ke)(ke)通(tong)(tong)過(guo)微調(diao)項來進行校準(zhun)。由于(yu)(yu)各部分(fen)既要單獨調(diao)校又(you)必需要聯(lian)調(diao),因(yin)此實(shi)(shi)際校準(zhun)時可(ke)(ke)按以下步驟進行:
1.先做(zuo)一(yi)次4-20mA微調,用(yong)以校正變送(song)器(qi)內(nei)部的D/A轉換器(qi),由于其(qi)不(bu)涉及傳感部件,無需外部壓力信號源。
2.再(zai)做一次全程微調,使4-20mA、數字讀數與實際施加(jia)的壓力信號(hao)相吻合,因此(ci)需要壓力信號(hao)源。
3.最后做重定(ding)量(liang)程(cheng),通過調整(zheng)使模擬輸出(chu)4-20mA與外加的(de)壓(ya)力信號源相吻(wen)合(he),其作(zuo)用(yong)與變送器外殼上的(de)調零(Z)、調量(liang)程(cheng)(R)開關的(de)作(zuo)用(yong)*相同。