萬用表功能及原理
時間:2019-11-25
作(zuo)者:化工(gong)儀(yi)器(qi)網
閱讀:9789
萬(wan)用(yong)表(biao)又(you)稱為復用(yong)表(biao)、多用(yong)表(biao)、三用(yong)表(biao)、繁(fan)用(yong)表(biao)等(deng),是電(dian)(dian)力電(dian)(dian)子等(deng)部門(men)不(bu)可(ke)缺少的(de)測量(liang)(liang)儀表(biao),一(yi)般(ban)以測量(liang)(liang)電(dian)(dian)壓、電(dian)(dian)流(liu)(liu)(liu)和(he)電(dian)(dian)阻為主要目的(de)。萬(wan)用(yong)表(biao)按顯(xian)示(shi)方式分為指針萬(wan)用(yong)表(biao)和(he)數字萬(wan)用(yong)表(biao)。是一(yi)種多功能、多量(liang)(liang)程(cheng)的(de)測量(liang)(liang)儀表(biao),一(yi)般(ban)萬(wan)用(yong)表(biao)可(ke)測量(liang)(liang)直(zhi)流(liu)(liu)(liu)電(dian)(dian)流(liu)(liu)(liu)、直(zhi)流(liu)(liu)(liu)電(dian)(dian)壓、交(jiao)(jiao)流(liu)(liu)(liu)電(dian)(dian)流(liu)(liu)(liu)、交(jiao)(jiao)流(liu)(liu)(liu)電(dian)(dian)壓、電(dian)(dian)阻和(he)音頻(pin)電(dian)(dian)平(ping)等(deng),有(you)的(de)還(huan)可(ke)以測交(jiao)(jiao)流(liu)(liu)(liu)電(dian)(dian)流(liu)(liu)(liu)、電(dian)(dian)容量(liang)(liang)、電(dian)(dian)感(gan)量(liang)(liang)及(ji)半導體的(de)一(yi)些參數(如β)等(deng)。
萬用表是一種帶有整流器的、可以測量交、直流電流、電壓及電阻等多種電學參量的磁電式儀表。對于每一種電學量,一般都有幾個量程。又稱多用電表或簡稱多用表。萬用表是由磁電系電流表(表頭),測量電路和選擇開關等組成的。通過選擇開關的變換,可方便地對多種電學參量進行測量。其電路計算的主要依據是閉合電路歐姆定律。萬用表種類很多,使用時應根據不同的要求進行選擇。
基本功用
萬(wan)(wan)用表(biao)(biao)不僅(jin)可(ke)(ke)以(yi)用來(lai)測量被測量物體的(de)電阻,交直流(liu)電壓還可(ke)(ke)以(yi)測量直流(liu)電壓。甚(shen)至(zhi)有(you)的(de)萬(wan)(wan)用表(biao)(biao)還可(ke)(ke)以(yi)測量晶體管的(de)主(zhu)要參數以(yi)及電容器的(de)電容量等。充分熟練(lian)掌(zhang)握萬(wan)(wan)用表(biao)(biao)的(de)使用方法是電子技(ji)術的(de)基(ji)本技(ji)能(neng)之一(yi)(yi)。常見的(de)萬(wan)(wan)用表(biao)(biao)有(you)指針式(shi)萬(wan)(wan)用表(biao)(biao)和數字(zi)式(shi)萬(wan)(wan)用表(biao)(biao)。指針式(shi)多用表(biao)(biao)是以(yi)表(biao)(biao)頭(tou)為核(he)心部件的(de)多功能(neng)測量儀表(biao)(biao),測量值由(you)(you)表(biao)(biao)頭(tou)指針指示(shi)讀(du)取。數字(zi)式(shi)萬(wan)(wan)用表(biao)(biao)的(de)測量值由(you)(you)液(ye)晶顯示(shi)屏(ping)直接以(yi)數字(zi)的(de)形式(shi)顯示(shi),讀(du)取方便,有(you)些還帶有(you)語音提示(shi)功能(neng)。萬(wan)(wan)用表(biao)(biao)是公(gong)用一(yi)(yi)個表(biao)(biao)頭(tou),集電壓表(biao)(biao)、電流(liu)表(biao)(biao)和歐(ou)姆表(biao)(biao)于一(yi)(yi)體的(de)儀表(biao)(biao)。
萬用(yong)(yong)表(biao)(biao)(biao)的(de)直流電(dian)(dian)(dian)流檔是多(duo)量(liang)程(cheng)的(de)直流電(dian)(dian)(dian)壓(ya)表(biao)(biao)(biao)。表(biao)(biao)(biao)頭并(bing)聯閉路(lu)式分壓(ya)電(dian)(dian)(dian)阻即(ji)可擴大(da)其電(dian)(dian)(dian)壓(ya)量(liang)程(cheng)。萬用(yong)(yong)表(biao)(biao)(biao)的(de)直流電(dian)(dian)(dian)壓(ya)檔是多(duo)量(liang)程(cheng)的(de)直流電(dian)(dian)(dian)壓(ya)表(biao)(biao)(biao)。表(biao)(biao)(biao)頭串(chuan)聯分壓(ya)電(dian)(dian)(dian)阻即(ji)可擴大(da)其電(dian)(dian)(dian)壓(ya)量(liang)程(cheng)。分壓(ya)電(dian)(dian)(dian)阻不同,相應(ying)的(de)量(liang)程(cheng)也(ye)不同。萬用(yong)(yong)表(biao)(biao)(biao)的(de)表(biao)(biao)(biao)頭為(wei)磁電(dian)(dian)(dian)系測量(liang)機構,它(ta)只能通過(guo)直流,利用(yong)(yong)二極管將交(jiao)流變為(wei)直流,從而(er)實現交(jiao)流電(dian)(dian)(dian)的(de)測量(liang)。
結構組成
萬用(yong)(yong)表(biao)(biao)(biao)(biao)由表(biao)(biao)(biao)(biao)頭、測量(liang)電(dian)(dian)(dian)(dian)路及(ji)轉換開關等三(san)個主(zhu)要(yao)部分(fen)(fen)組(zu)成(cheng)。萬用(yong)(yong)表(biao)(biao)(biao)(biao)是電(dian)(dian)(dian)(dian)子測試領域基本的(de)工具,也(ye)是一(yi)(yi)種(zhong)使用(yong)(yong)廣泛的(de)測試儀(yi)(yi)器。萬用(yong)(yong)表(biao)(biao)(biao)(biao)又叫多(duo)用(yong)(yong)表(biao)(biao)(biao)(biao)、三(san)用(yong)(yong)表(biao)(biao)(biao)(biao)(A,V,Ω也(ye)即電(dian)(dian)(dian)(dian)流,電(dian)(dian)(dian)(dian)壓(ya),電(dian)(dian)(dian)(dian)阻(zu)三(san)用(yong)(yong))、復(fu)用(yong)(yong)表(biao)(biao)(biao)(biao)、萬能表(biao)(biao)(biao)(biao),萬用(yong)(yong)表(biao)(biao)(biao)(biao)分(fen)(fen)為指針(zhen)式萬用(yong)(yong)表(biao)(biao)(biao)(biao)和數字萬用(yong)(yong)表(biao)(biao)(biao)(biao),還(huan)有一(yi)(yi)種(zhong)帶示波器功能的(de)示波萬用(yong)(yong)表(biao)(biao)(biao)(biao),是一(yi)(yi)種(zhong)多(duo)功能、多(duo)量(liang)程(cheng)的(de)測量(liang)儀(yi)(yi)表(biao)(biao)(biao)(biao)。一(yi)(yi)般萬用(yong)(yong)表(biao)(biao)(biao)(biao)可測量(liang)直流電(dian)(dian)(dian)(dian)流、直流電(dian)(dian)(dian)(dian)壓(ya)、交流電(dian)(dian)(dian)(dian)壓(ya)、電(dian)(dian)(dian)(dian)阻(zu)和音頻電(dian)(dian)(dian)(dian)平等,有的(de)還(huan)可以測交流電(dian)(dian)(dian)(dian)流、電(dian)(dian)(dian)(dian)容量(liang)、電(dian)(dian)(dian)(dian)感量(liang)、溫度及(ji)半導體(二(er)極(ji)管、三(san)極(ji)管)的(de)一(yi)(yi)些(xie)參數。數字式萬用(yong)(yong)表(biao)(biao)(biao)(biao)已成(cheng)為主(zhu)流,已經取代模擬(ni)式儀(yi)(yi)表(biao)(biao)(biao)(biao)。與模擬(ni)式儀(yi)(yi)表(biao)(biao)(biao)(biao)相比,數字式儀(yi)(yi)表(biao)(biao)(biao)(biao)靈(ling)敏度高(gao),精確度高(gao),顯示清晰,過載能力強,便(bian)于攜帶,使用(yong)(yong)也(ye)更方便(bian)簡單。
表頭
萬用表(biao)的(de)表(biao)頭是靈敏電(dian)(dian)流(liu)計。表(biao)頭上的(de)表(biao)盤印有(you)多種符(fu)(fu)號,刻(ke)(ke)度(du)(du)線(xian)(xian)(xian)和數值(zhi)。符(fu)(fu)號A一(yi)V一(yi)Ω表(biao)示(shi)這(zhe)只電(dian)(dian)表(biao)是可以測量電(dian)(dian)流(liu)、電(dian)(dian)壓(ya)和電(dian)(dian)阻(zu)的(de)多用表(biao)。表(biao)盤上印有(you)多條刻(ke)(ke)度(du)(du)線(xian)(xian)(xian),其中右端(duan)(duan)標有(you)"Ω"的(de)是電(dian)(dian)阻(zu)刻(ke)(ke)度(du)(du)線(xian)(xian)(xian),其右端(duan)(duan)為(wei)零,左端(duan)(duan)為(wei)∞,刻(ke)(ke)度(du)(du)值(zhi)分布是不(bu)均勻的(de)。符(fu)(fu)號"-"或(huo)"DC"表(biao)示(shi)直流(liu),"~"或(huo)"AC"表(biao)示(shi)交流(liu),"~"表(biao)示(shi)交流(liu)和直流(liu)共(gong)用的(de)刻(ke)(ke)度(du)(du)線(xian)(xian)(xian)。刻(ke)(ke)度(du)(du)線(xian)(xian)(xian)下的(de)幾行數字(zi)是與選擇開(kai)關(guan)的(de)不(bu)同(tong)檔位相對應的(de)刻(ke)(ke)度(du)(du)值(zhi)。
表頭上還設(she)有機械零位調整旋鈕,用以校正(zheng)指針在左端零位。
選擇開關
萬用表的(de)選擇開關是一個多(duo)檔位的(de)旋轉開關。用來選擇測量項目和量程。
一般的萬用表測量(liang)項(xiang)目包括:"mA";直(zhi)流(liu)電(dian)流(liu)、"V(-)":直(zhi)流(liu)電(dian)壓(ya)(ya)、"V(~)":交流(liu)電(dian)壓(ya)(ya)、"Ω":電(dian)阻(zu)。每個測量(liang)項(xiang)目又劃分(fen)為(wei)幾(ji)個不(bu)同的量(liang)程以(yi)供選擇。
表筆和表筆插孔
表筆分為紅、黑二只。使用時應將紅色表筆插入(ru)標有"+"號(hao)的(de)插孔,黑色表筆插入(ru)標有"-"號(hao)的(de)插孔。
表頭(指針式)
它(ta)是(shi)(shi)(shi)一只高靈(ling)敏度(du)(du)的(de)(de)(de)磁電(dian)(dian)(dian)式直(zhi)流(liu)(liu)(liu)電(dian)(dian)(dian)流(liu)(liu)(liu)表,萬用(yong)表的(de)(de)(de)主(zhu)要性(xing)能(neng)指(zhi)(zhi)標基本上(shang)取決于(yu)表頭(tou)的(de)(de)(de)性(xing)能(neng)。表頭(tou)的(de)(de)(de)靈(ling)敏度(du)(du)是(shi)(shi)(shi)指(zhi)(zhi)表頭(tou)指(zhi)(zhi)針滿刻(ke)度(du)(du)偏轉(zhuan)時流(liu)(liu)(liu)過表頭(tou)的(de)(de)(de)直(zhi)流(liu)(liu)(liu)電(dian)(dian)(dian)流(liu)(liu)(liu)值(zhi),這個值(zhi)越(yue)小,表頭(tou)的(de)(de)(de)靈(ling)敏度(du)(du)愈高。測(ce)電(dian)(dian)(dian)壓(ya)時的(de)(de)(de)內阻(zu)越(yue)大,其(qi)性(xing)能(neng)就越(yue)好。表頭(tou)上(shang)有(you)四(si)條(tiao)(tiao)刻(ke)度(du)(du)線(xian),它(ta)們的(de)(de)(de)功能(neng)如下:條(tiao)(tiao)(從上(shang)到下)標有(you)R或(huo)(huo)Ω,指(zhi)(zhi)示的(de)(de)(de)是(shi)(shi)(shi)電(dian)(dian)(dian)阻(zu)值(zhi),轉(zhuan)換(huan)開(kai)關(guan)在(zai)歐姆擋時,即讀此(ci)條(tiao)(tiao)刻(ke)度(du)(du)線(xian)。第(di)二條(tiao)(tiao)標有(you)∽和VA,指(zhi)(zhi)示的(de)(de)(de)是(shi)(shi)(shi)交(jiao)(jiao)、直(zhi)流(liu)(liu)(liu)電(dian)(dian)(dian)壓(ya)和直(zhi)流(liu)(liu)(liu)電(dian)(dian)(dian)流(liu)(liu)(liu)值(zhi),當(dang)轉(zhuan)換(huan)開(kai)關(guan)在(zai)交(jiao)(jiao)、直(zhi)流(liu)(liu)(liu)電(dian)(dian)(dian)壓(ya)或(huo)(huo)直(zhi)流(liu)(liu)(liu)電(dian)(dian)(dian)流(liu)(liu)(liu)擋,量(liang)程在(zai)除交(jiao)(jiao)流(liu)(liu)(liu)10V以外(wai)的(de)(de)(de)其(qi)它(ta)位置(zhi)時,即讀此(ci)條(tiao)(tiao)刻(ke)度(du)(du)線(xian)。第(di)三條(tiao)(tiao)標有(you)10V,指(zhi)(zhi)示的(de)(de)(de)是(shi)(shi)(shi)10V的(de)(de)(de)交(jiao)(jiao)流(liu)(liu)(liu)電(dian)(dian)(dian)壓(ya)值(zhi),當(dang)轉(zhuan)換(huan)開(kai)關(guan)在(zai)交(jiao)(jiao)、直(zhi)流(liu)(liu)(liu)電(dian)(dian)(dian)壓(ya)擋,量(liang)程在(zai)交(jiao)(jiao)流(liu)(liu)(liu)10V時,即讀此(ci)條(tiao)(tiao)刻(ke)度(du)(du)線(xian)。第(di)四(si)條(tiao)(tiao)標有(you)dB,指(zhi)(zhi)示的(de)(de)(de)是(shi)(shi)(shi)音頻電(dian)(dian)(dian)平。
表頭(數字式)
數字(zi)萬(wan)用(yong)(yong)表(biao)的(de)(de)(de)表(biao)頭一般(ban)由一只(zhi)A/D(模擬/數字(zi))轉(zhuan)換芯(xin)片(pian)(pian)+外圍元(yuan)件(jian)+液晶(jing)顯示器(qi)組成,萬(wan)用(yong)(yong)表(biao)的(de)(de)(de)精(jing)度受(shou)表(biao)頭的(de)(de)(de)影響(xiang),萬(wan)用(yong)(yong)表(biao)由于(yu)A/D芯(xin)片(pian)(pian)轉(zhuan)換出來的(de)(de)(de)數字(zi),一般(ban)也稱為3 1/2位(wei)(wei)數字(zi)萬(wan)用(yong)(yong)表(biao),4 1/2位(wei)(wei)數字(zi)萬(wan)用(yong)(yong)表(biao)等(deng)等(deng)。常用(yong)(yong)的(de)(de)(de)芯(xin)片(pian)(pian)是ICL7106(3位(wei)(wei)半LCD手(shou)動量(liang)程經典(dian)芯(xin)片(pian)(pian),后(hou)續版本(ben)為7106A,7106B,7206,7240等(deng)等(deng)),ICL7129(4位(wei)(wei)半LCD手(shou)動量(liang)程經典(dian)芯(xin)片(pian)(pian)),ICL7107(3位(wei)(wei)半LED手(shou)動量(liang)程經典(dian)芯(xin)片(pian)(pian))。
測量線路
測(ce)(ce)量(liang)(liang)線路是用來把各種被測(ce)(ce)量(liang)(liang)轉(zhuan)換(huan)到(dao)適合表頭測(ce)(ce)量(liang)(liang)的(de)微小直流電(dian)流的(de)電(dian)路,它(ta)由電(dian)阻、半導(dao)體(ti)元件及電(dian)池組成
它能將(jiang)各種不同(tong)(tong)的(de)(de)被測(ce)量(如(ru)電(dian)流(liu)、電(dian)壓(ya)、電(dian)阻等)、不同(tong)(tong)的(de)(de)量程(cheng),經(jing)過一系列的(de)(de)處理(如(ru)整(zheng)流(liu)、分(fen)流(liu)、分(fen)壓(ya)等)統(tong)一變成一定量限的(de)(de)微小直流(liu)電(dian)流(liu)送入表頭進行(xing)測(ce)量。
轉換開關
其作用是用來選擇各(ge)種(zhong)不同的(de)測量線路,以滿足不同種(zhong)類和不同量程(cheng)的(de)測量要求。轉換(huan)開關一般是一個(ge)圓形撥盤,在其周圍(wei)分別標有功能和量程(cheng)。
工作原理
萬用表的基本原理是利用一只靈敏的磁電式直流電流表(微安表)做表頭。
設計原理
數(shu)字(zi)萬用(yong)表的(de)測量過程(cheng)由轉(zhuan)換(huan)(huan)電路將(jiang)被測量轉(zhuan)換(huan)(huan)成直流電壓(ya)(ya)信號,再由模/數(shu)(A/D)轉(zhuan)換(huan)(huan)器(qi)將(jiang)電壓(ya)(ya)模擬量轉(zhuan)換(huan)(huan)成數(shu)字(zi)量,然后(hou)通(tong)過電子計數(shu)器(qi)計數(shu),最后(hou)把測量結果用(yong)數(shu)字(zi)直接顯示(shi)在顯示(shi)屏上(shang)。
萬用表(biao)測量電(dian)壓、電(dian)流(liu)和電(dian)阻(zu)功(gong)能是(shi)通(tong)過(guo)轉(zhuan)換電(dian)路(lu)部(bu)分實現的,而電(dian)流(liu)、電(dian)阻(zu)的測量都(dou)是(shi)基(ji)于電(dian)壓的測量,也(ye)就是(shi)說數字萬用表(biao)是(shi)在數字直流(liu)電(dian)壓表(biao)的基(ji)礎上擴展而成(cheng)的。
數(shu)字(zi)直流(liu)電(dian)壓(ya)表A/D轉換器將(jiang)隨時間(jian)連(lian)續(xu)變化的(de)(de)模擬電(dian)壓(ya)量變換成數(shu)字(zi)量,再由(you)電(dian)子計數(shu)器對(dui)數(shu)字(zi)量進行計數(shu)得到測(ce)量結(jie)(jie)果,再由(you)譯碼顯(xian)示(shi)電(dian)路(lu)將(jiang)測(ce)量結(jie)(jie)果顯(xian)示(shi)出(chu)來。邏輯控(kong)制電(dian)路(lu)控(kong)制電(dian)路(lu)的(de)(de)協調工作(zuo),在時鐘的(de)(de)作(zuo)用下(xia)按順(shun)序(xu)完(wan)成整個測(ce)量過程
當微小電(dian)流(liu)(liu)通(tong)過表(biao)(biao)頭,就會有電(dian)流(liu)(liu)指示。但表(biao)(biao)頭不能通(tong)過大電(dian)流(liu)(liu),所以(yi),必須(xu)在表(biao)(biao)頭上并聯(lian)(lian)與(yu)串聯(lian)(lian)一些電(dian)阻(zu)進行分流(liu)(liu)或降壓,從而測出電(dian)路中(zhong)的電(dian)流(liu)(liu)、電(dian)壓和電(dian)阻(zu)。