【萬用表(biao)測(ce)電容(rong)】萬用表(biao)怎(zen)么測(ce)電容(rong) 怎(zen)樣用萬用表(biao)測(ce)電容(rong)

現在，數字(zi)(zi)式測量儀表(biao)已成為主流，有取代模(mo)擬(ni)式儀表(biao)的趨勢(shi)。與模(mo)擬(ni)式儀表(biao)相(xiang)比(bi)，數字(zi)(zi)式儀表(biao)靈敏度高，準確度高，顯示清晰，過載能力強，便(bian)于攜帶，使(shi)用(yong)更簡(jian)單。下面(mian)以VC9802型數字(zi)(zi)萬用(yong)表(biao)為例，簡(jian)單介紹其使(shi)用(yong)方法。

1、使用方法

（1）使用前，應(ying)認真閱讀有關(guan)的(de)使用說明(ming)書，熟悉電源開關(guan)、量(liang)程開關(guan)、插孔、特殊插口的(de)作用。

（2）將電源開關置于ON位置。

（3）交(jiao)直(zhi)流(liu)電壓的測(ce)量(liang)：根據需要將量(liang)程開關撥至DCV（直(zhi)流(liu)）或ACV（交(jiao)流(liu)）的合適量(liang)程，紅(hong)表筆插(cha)入V／Ω孔，黑表筆插(cha)入COM孔，并將表筆與被(bei)測(ce)線路并聯，讀數即顯(xian)示(shi)。

（4）交直(zhi)(zhi)流(liu)(liu)電(dian)流(liu)(liu)的測量(liang)：將量(liang)程(cheng)開關撥至DCA（直(zhi)(zhi)流(liu)(liu)）或ACA（交流(liu)(liu)）的合適量(liang)程(cheng)，紅表(biao)(biao)筆插入mA孔（＜200mA時(shi)）或10A孔（＞200mA時(shi)）,黑表(biao)(biao)筆插入COM孔，并將萬用(yong)(yong)表(biao)(biao)串聯在被測電(dian)路中即可。測量(liang)直(zhi)(zhi)流(liu)(liu)量(liang)時(shi)，數(shu)字(zi)萬用(yong)(yong)表(biao)(biao)能(neng)自動顯(xian)示(shi)極(ji)性。

（5）電(dian)阻(zu)的測量(liang)(liang)(liang)：將量(liang)(liang)(liang)程(cheng)(cheng)(cheng)開(kai)關撥至Ω的合適量(liang)(liang)(liang)程(cheng)(cheng)(cheng)，紅(hong)表(biao)筆(bi)(bi)插入(ru)(ru)V／Ω孔(kong)，黑(hei)表(biao)筆(bi)(bi)插入(ru)(ru)COM孔(kong)。如果被測電(dian)阻(zu)值超出所選擇量(liang)(liang)(liang)程(cheng)(cheng)(cheng)的最大值，萬用表(biao)將顯示“1”，這時應選擇更高(gao)的量(liang)(liang)(liang)程(cheng)(cheng)(cheng)。測量(liang)(liang)(liang)電(dian)阻(zu)時，紅(hong)表(biao)筆(bi)(bi)為正極(ji)，黑(hei)表(biao)筆(bi)(bi)為負(fu)極(ji)，這與(yu)指針式(shi)萬用表(biao)正好相(xiang)反。因此，測量(liang)(liang)(liang)晶體管、電(dian)解(jie)電(dian)容器等有(you)極(ji)性的元(yuan)器件時，必須注意表(biao)筆(bi)(bi)的極(ji)性。

2、使用注意事項

（1）如果無法預先估計被測電(dian)壓或(huo)電(dian)流的大小(xiao)，則應先撥(bo)至(zhi)最高(gao)量程擋(dang)測量一次，再視情況逐漸(jian)把(ba)量程減小(xiao)到合(he)適位置。測量完畢，應將量程開(kai)關(guan)(guan)撥(bo)到最高(gao)電(dian)壓擋(dang)，并關(guan)(guan)閉電(dian)源。

（2）滿量程(cheng)時，儀(yi)表僅在最高(gao)位(wei)顯(xian)示數字“1”，其它位(wei)均(jun)消失，這(zhe)時應選(xuan)擇更高(gao)的量程(cheng)。

（3）測量電(dian)壓時，應將數字萬用表與被測電(dian)路并聯(lian)。測電(dian)流時應與被測電(dian)路串聯(lian)，測直流量時不必考慮(lv)正、負(fu)極性。

（4）當誤用交(jiao)流電(dian)(dian)壓擋(dang)去測(ce)量(liang)直流電(dian)(dian)壓，或者誤用直流電(dian)(dian)壓擋(dang)去測(ce)量(liang)交(jiao)流電(dian)(dian)壓時(shi)，顯(xian)示屏將顯(xian)示“000”，或低位上(shang)的(de)數字出(chu)現跳動。

（5）禁止在測量高電(dian)壓(ya)（220V以上(shang)）或大電(dian)流（0.5A以上(shang)）時(shi)換量程，以防止產(chan)生電(dian)弧，燒毀開關觸點。

（6）當顯示“”、“BATT”或“LOWBAT”時，表示電池的(de)電壓(ya)低(di)于(yu)工作電壓(ya)。

怎樣用萬用表測電容可按以下方法進行：

1、用電容檔直接檢測

某些數(shu)(shu)字萬用表具有測(ce)量(liang)電容的(de)功能，其量(liang)程(cheng)分(fen)為2000p、20n、200n、2μ和20μ五檔。測(ce)量(liang)時(shi)可將已放電的(de)電容兩引腳直(zhi)接插(cha)入表板上的(de)Cx插(cha)孔，選(xuan)取適當的(de)量(liang)程(cheng)后(hou)就可讀取顯示數(shu)(shu)據。

000p檔，宜于(yu)(yu)測量小于(yu)(yu)2000pF的(de)電(dian)(dian)容(rong)；20n檔，宜于(yu)(yu)測量2000pF至(zhi)20nF之間的(de)電(dian)(dian)容(rong)；200n檔，宜于(yu)(yu)測量20nF至(zhi)200nF之間的(de)電(dian)(dian)容(rong)；2μ檔，宜于(yu)(yu)測量200nF至(zhi)2μF之間的(de)電(dian)(dian)容(rong)；20μ檔，宜于(yu)(yu)測量2μF至(zhi)20μF之間的(de)電(dian)(dian)容(rong)。

經驗(yan)證明，有(you)些(xie)型號的(de)數字萬(wan)(wan)用表(biao)（例如DT890B＋）在(zai)測(ce)(ce)量(liang)(liang)50pF以(yi)下的(de)小容(rong)(rong)(rong)量(liang)(liang)電(dian)(dian)容(rong)(rong)(rong)器(qi)時(shi)誤差較大，測(ce)(ce)量(liang)(liang)20pF以(yi)下電(dian)(dian)容(rong)(rong)(rong)幾乎(hu)沒(mei)有(you)參考價值。此(ci)時(shi)可采用串聯(lian)法(fa)測(ce)(ce)量(liang)(liang)小值電(dian)(dian)容(rong)(rong)(rong)。方法(fa)是(shi)：先找一只220pF左右的(de)電(dian)(dian)容(rong)(rong)(rong)，用數字萬(wan)(wan)用表(biao)測(ce)(ce)出(chu)其實(shi)際(ji)容(rong)(rong)(rong)量(liang)(liang)C1，然(ran)后(hou)把待(dai)測(ce)(ce)小電(dian)(dian)容(rong)(rong)(rong)與之并聯(lian)測(ce)(ce)出(chu)其總容(rong)(rong)(rong)量(liang)(liang)C2，則兩(liang)者之差（C1－C2）即是(shi)待(dai)測(ce)(ce)小電(dian)(dian)容(rong)(rong)(rong)的(de)容(rong)(rong)(rong)量(liang)(liang)。用此(ci)法(fa)測(ce)(ce)量(liang)(liang)1～20pF的(de)小容(rong)(rong)(rong)量(liang)(liang)電(dian)(dian)容(rong)(rong)(rong)很(hen)準(zhun)確。

2、用電阻檔檢測

實踐證(zheng)明，利用(yong)(yong)(yong)數(shu)(shu)(shu)字萬用(yong)(yong)(yong)表(biao)(biao)也可(ke)觀察(cha)(cha)電(dian)(dian)容(rong)(rong)(rong)(rong)器(qi)的(de)(de)充電(dian)(dian)過程，這(zhe)實際上是以離散的(de)(de)數(shu)(shu)(shu)字量(liang)反映充電(dian)(dian)電(dian)(dian)壓的(de)(de)變化情況。設數(shu)(shu)(shu)字萬用(yong)(yong)(yong)表(biao)(biao)的(de)(de)測(ce)(ce)量(liang)速率(lv)為n次/秒，則在(zai)觀察(cha)(cha)電(dian)(dian)容(rong)(rong)(rong)(rong)器(qi)的(de)(de)充電(dian)(dian)過程中，每(mei)秒鐘即可(ke)看到n個彼此獨立且依次增大(da)的(de)(de)讀數(shu)(shu)(shu)。根據數(shu)(shu)(shu)字萬用(yong)(yong)(yong)表(biao)(biao)的(de)(de)這(zhe)一顯示(shi)特點，可(ke)以檢測(ce)(ce)電(dian)(dian)容(rong)(rong)(rong)(rong)器(qi)的(de)(de)好壞和估測(ce)(ce)電(dian)(dian)容(rong)(rong)(rong)(rong)量(liang)的(de)(de)大(da)小。下面介紹的(de)(de)是使(shi)用(yong)(yong)(yong)數(shu)(shu)(shu)字萬用(yong)(yong)(yong)表(biao)(biao)電(dian)(dian)阻檔檢測(ce)(ce)電(dian)(dian)容(rong)(rong)(rong)(rong)器(qi)的(de)(de)方法，對于未設置電(dian)(dian)容(rong)(rong)(rong)(rong)檔的(de)(de)儀表(biao)(biao)很有實用(yong)(yong)(yong)價(jia)值(zhi)。此方法適用(yong)(yong)(yong)于測(ce)(ce)量(liang)0.1μF～幾千微法的(de)(de)大(da)容(rong)(rong)(rong)(rong)量(liang)電(dian)(dian)容(rong)(rong)(rong)(rong)器(qi)。

將數字萬用表(biao)撥至合適的電(dian)(dian)(dian)阻檔(dang)，紅(hong)(hong)表(biao)筆(bi)(bi)和(he)黑表(biao)筆(bi)(bi)分別接觸被測電(dian)(dian)(dian)容(rong)(rong)器(qi)(qi)Cx的兩極(ji)，這時(shi)顯(xian)示(shi)(shi)值將從“000”開始逐漸增加(jia)，直(zhi)至顯(xian)示(shi)(shi)溢(yi)出(chu)符號“1”。若始終顯(xian)示(shi)(shi)“000”，說明(ming)電(dian)(dian)(dian)容(rong)(rong)器(qi)(qi)內部(bu)短路；若始終顯(xian)示(shi)(shi)溢(yi)出(chu)，則可能(neng)時(shi)電(dian)(dian)(dian)容(rong)(rong)器(qi)(qi)內部(bu)極(ji)間開路，也可能(neng)時(shi)所選擇的電(dian)(dian)(dian)阻檔(dang)不合適。檢查電(dian)(dian)(dian)解電(dian)(dian)(dian)容(rong)(rong)器(qi)(qi)時(shi)需要注意，紅(hong)(hong)表(biao)筆(bi)(bi)（帶(dai)正電(dian)(dian)(dian)）接電(dian)(dian)(dian)容(rong)(rong)器(qi)(qi)正極(ji)，黑表(biao)筆(bi)(bi)接電(dian)(dian)(dian)容(rong)(rong)器(qi)(qi)負極(ji)。