智能雙顯絕緣電阻測試儀工作原理

，通(tong)常被(bei)稱為數(shu)字兆歐表或高阻(zu)(zu)(zu)計，廣(guang)泛(fan)用(yong)于測量發電(dian)(dian)(dian)機(ji)、馬達、電(dian)(dian)(dian)源(yuan)變壓器、配線、電(dian)(dian)(dian)器和(he)其它電(dian)(dian)(dian)氣裝置（如控制(zhi)、信號(hao)、通(tong)信和(he)電(dian)(dian)(dian)源(yuan)的電(dian)(dian)(dian)纜）的絕(jue)緣電(dian)(dian)(dian)阻(zu)(zu)(zu)。它們往往被(bei)用(yong)于例行(xing)維護程序中來指示(shi)電(dian)(dian)(dian)機(ji)在數(shu)月或數(shu)年內絕(jue)緣電(dian)(dian)(dian)阻(zu)(zu)(zu)的變化。絕(jue)緣電(dian)(dian)(dian)阻(zu)(zu)(zu)發生大的變化，就可能(neng)預示(shi)著潛在的故障。所以(yi)，就需要對(dui)兆歐表進(jin)行(xing)定期校準(zhun)，以(yi)確保(bao)儀表本身沒(mei)有(you)隨(sui)時間發生變化。

兆(zhao)歐(ou)表通過用一個(ge)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)激(ji)勵被測(ce)裝置或(huo)網絡，然后(hou)測(ce)量(liang)(liang)激(ji)勵所(suo)產生(sheng)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)，利(li)(li)用歐(ou)姆定律測(ce)量(liang)(liang)出電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)。優良的(de)校(xiao)(xiao)(xiao)準(zhun)器(qi)(qi)(qi)包(bao)括各種可選(xuan)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器(qi)(qi)(qi)，這點(dian)與(yu)(yu)現代校(xiao)(xiao)(xiao)準(zhun)器(qi)(qi)(qi)利(li)(li)用合(he)成電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)功(gong)能提供(gong)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器(qi)(qi)(qi)差別(bie)不大。兆(zhao)歐(ou)表校(xiao)(xiao)(xiao)準(zhun)器(qi)(qi)(qi)與(yu)(yu)直流(liu)(liu)/低頻校(xiao)(xiao)(xiao)準(zhun)器(qi)(qi)(qi)的(de)不同(tong)之(zhi)處(chu)在(zai)于(yu)所(suo)需的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器(qi)(qi)(qi)范(fan)圍(wei)，以及耐受(shou)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)能力不同(tong)。例如，與(yu)(yu)數(shu)字多(duo)用表（DMM）上配(pei)備(bei)的(de)歐(ou)姆表功(gong)能相比，這些電(dian)(dian)(dian)(dian)(dian)(dian)(dian)氣測(ce)試器(qi)(qi)(qi)在(zai)進(jin)行電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)測(ce)量(liang)(liang)時施加的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)要(yao)(yao)高得多(duo)。兆(zhao)歐(ou)表采用的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)范(fan)圍(wei)通常從50V到(dao)高達5 kV；而典型數(shu)字多(duo)用表的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)一般(ban)小于(yu)10 V。對(dui)于(yu)絕緣測(ce)試來說，需要(yao)(yao)測(ce)量(liang)(liang)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)值范(fan)圍(wei)很大，其上限(xian)可達到(dao)10TΩ，所(suo)需的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)更高。

幾乎所(suo)有(you)的(de)(de)(de)都采用直(zhi)流(liu)電(dian)(dian)(dian)壓作為(wei)(wei)激勵，所(suo)以(yi)兆(zhao)歐表(biao)(biao)校準(zhun)器的(de)(de)(de)交流(liu)要(yao)求很少。許多兆(zhao)歐表(biao)(biao)為(wei)(wei)兩端設備，它提供一(yi)個電(dian)(dian)(dian)壓，并測量(liang)由被測設備所(suo)決(jue)定的(de)(de)(de)電(dian)(dian)(dian)流(liu)。量(liang)程達到1TΩ 以(yi)及(ji)更高的(de)(de)(de)兆(zhao)歐表(biao)(biao)通常具(ju)有(you)第三(san)個端子(zi)，稱為(wei)(wei)保(bao)護端（Guard），對于消除(chu)泄(xie)漏(lou)通路以(yi)及(ji)被測未知電(dian)(dian)(dian)阻(zu)Rx的(de)(de)(de)并聯元件(jian)非常有(you)用。保(bao)護端的(de)(de)(de)目的(de)(de)(de)是(shi)消除(chu)可(ke)能會(hui)產生的(de)(de)(de)泄(xie)漏(lou)電(dian)(dian)(dian)流(liu)來選(xuan)擇性地(di)將輸出寄生電(dian)(dian)(dian)阻(zu)性元件(jian)的(de)(de)(de)影響減小為(wei)(wei)零。

校準這些(xie)儀(yi)器時的一個主要(yao)問題是找到(dao)合適的電(dian)(dian)(dian)阻(zu)器，當然是首先要(yao)足夠(gou)精Q；還需要(yao)電(dian)(dian)(dian)阻(zu)值(zhi)足夠(gou)大，使其能(neng)夠(gou)承受高直流電(dian)(dian)(dian)壓。此外，對于(yu)應該采用什么樣的電(dian)(dian)(dian)阻(zu)值(zhi)來進行校準，兆歐表制造商并沒有統一的標(biao)準，所以就需要(yao)各(ge)種各(ge)樣的電(dian)(dian)(dian)阻(zu)值(zhi)。通過了解各(ge)種不(bu)同的絕緣測(ce)(ce)(ce)試(shi)(shi)儀(yi)，可以知道它(ta)們需要(yao)不(bu)同的性(xing)能(neng)檢(jian)查點(dian)。例如，某個測(ce)(ce)(ce)試(shi)(shi)儀(yi)需要(yao)測(ce)(ce)(ce)試(shi)(shi)50kΩ，而另一款測(ce)(ce)(ce)試(shi)(shi)儀(yi)則需要(yao)測(ce)(ce)(ce)試(shi)(shi)60kΩ，再一款又需要(yao)測(ce)(ce)(ce)試(shi)(shi)100 kΩ，等等。

“通(tong)用”的(de)(de)多功(gong)能(neng)電氣(qi)/電子校(xiao)準(zhun)器(qi)不能(neng)用于校(xiao)準(zhun)絕(jue)緣電阻(zu)(zu)測試儀，因為它們(men)的(de)(de)電阻(zu)(zu)器(qi)通(tong)常(chang)僅僅能(neng)夠(gou)處理有限的(de)(de)電壓，常(chang)常(chang)g不過20V。絕(jue)緣電阻(zu)(zu)校(xiao)準(zhun)器(qi)所面臨的(de)(de)挑戰(zhan)是將這些特殊需要集成(cheng)到一(yi)款(kuan)經濟、緊(jin)湊和(he)便攜(xie)的(de)(de)解決方案(an)中。

合成(cheng)(cheng)電(dian)阻的(de)(de)方法由于受到設(she)計成(cheng)(cheng)本和尺寸規格的(de)(de)限制被排除在(zai)外。采用的(de)(de)是分立式高壓電(dian)阻器矩陣的(de)(de)方法，組成(cheng)(cheng)一個陣列，能夠提供(gong)500,000多種(zhong)電(dian)阻值輸(shu)出。在(zai)這(zhe)種(zhong)校準器中，有(you)8個范(fan)圍的(de)(de)電(dian)阻值，覆蓋了10kΩ到10 GΩ的(de)(de)范(fan)圍，每個范(fan)圍均能提供(gong)4.5 位的(de)(de)穩定輸(shu)出。

收集合(he)適的(de)高壓(ya)電(dian)(dian)阻器并將其集成到一個儀(yi)器內又(you)存在另一項(xiang)挑戰。這(zhe)就是與(yu)歐(ou)盟CE認證的(de)一項(xiang)強制性要(yao)求(qiu)《低電(dian)(dian)壓(ya)指令》相(xiang)關的(de)安(an)全性標準挑戰。與(yu)儀(yi)器制造(zao)商相(xiang)關的(de)標準是EN 61010－測(ce)量、控制和實驗室用電(dian)(dian)氣設(she)備的(de)安(an)全要(yao)求(qiu)。

低(di)電(dian)(dian)(dian)壓指(zhi)(zhi)令(ling)要求(qiu)將校準(zhun)器(qi)電(dian)(dian)(dian)壓限制(zhi)為(wei)1,000Vrms。那么如何(he)校準(zhun)測(ce)試電(dian)(dian)(dian)壓高(gao)達5 kV 的(de)(de)兆歐表呢？這類儀器(qi)具有更寬的(de)(de)動態(tai)范(fan)圍，可測(ce)量高(gao)到10TΩ的(de)(de)電(dian)(dian)(dian)阻(zu)，并且提(ti)供了如上(shang)所(suo)(suo)述的(de)(de)保護(hu)端子，使其(qi)能夠準(zhun)確(que)測(ce)量非常(chang)高(gao)的(de)(de)電(dian)(dian)(dian)阻(zu)值。幸運的(de)(de)是，這樣的(de)(de)保護(hu)配置(zhi)可以使其(qi)本身形成(cheng)一個電(dian)(dian)(dian)阻(zu)倍(bei)(bei)增(zeng)器(qi)，能夠有效地將一個已知電(dian)(dian)(dian)阻(zu)倍(bei)(bei)增(zeng)為(wei)1000倍(bei)(bei)。同樣重要的(de)(de)是，由于倍(bei)(bei)增(zeng)器(qi)是一個分立(li)、隔離、獨(du)立(li)的(de)(de)設備，可以滿(man)足倍(bei)(bei)增(zeng)器(qi)所(suo)(suo)需的(de)(de)高(gao)電(dian)(dian)(dian)壓，它已經不(bu)是《低(di)電(dian)(dian)(dian)壓指(zhi)(zhi)令(ling)》所(suo)(suo)管轄的(de)(de)范(fan)圍。