一、功率表的原理是什么

功率表的核心(xin)工作(zuo)原理基(ji)于(yu)電(dian)(dian)(dian)動(dong)系測(ce)量機(ji)構。在電(dian)(dian)(dian)動(dong)系測(ce)量機(ji)構中，定(ding)圈串聯接入(ru)被測(ce)電(dian)(dian)(dian)路，而動(dong)圈與附(fu)加電(dian)(dian)(dian)阻串聯后并聯接入(ru)被測(ce)電(dian)(dian)(dian)路。國家標準規定(ding)，在測(ce)量線(xian)路中，用一(yi)(yi)個(ge)圓加一(yi)(yi)條水平粗實線(xian)和一(yi)(yi)條豎(shu)直細實線(xian)來(lai)表示電(dian)(dian)(dian)壓(ya)與電(dian)(dian)(dian)流相乘的線(xian)圈。

1、直流電路的功率測量

當用于直流(liu)(liu)電(dian)(dian)(dian)(dian)路(lu)的(de)(de)(de)功(gong)(gong)(gong)率測量時，通(tong)過電(dian)(dian)(dian)(dian)流(liu)(liu)線圈(quan)(quan)的(de)(de)(de)電(dian)(dian)(dian)(dian)流(liu)(liu)與(yu)被測電(dian)(dian)(dian)(dian)路(lu)電(dian)(dian)(dian)(dian)流(liu)(liu)相等。電(dian)(dian)(dian)(dian)壓線圈(quan)(quan)中的(de)(de)(de)電(dian)(dian)(dian)(dian)流(liu)(liu)可以通(tong)過歐(ou)姆定律(lv)確定。由于電(dian)(dian)(dian)(dian)流(liu)(liu)線圈(quan)(quan)兩端的(de)(de)(de)電(dian)(dian)(dian)(dian)壓降(jiang)遠小于負(fu)載兩端的(de)(de)(de)電(dian)(dian)(dian)(dian)壓，因此(ci)可以認為(wei)電(dian)(dian)(dian)(dian)壓支路(lu)兩端的(de)(de)(de)電(dian)(dian)(dian)(dian)壓與(yu)負(fu)載電(dian)(dian)(dian)(dian)壓相等。電(dian)(dian)(dian)(dian)動系功(gong)(gong)(gong)率表可動部分的(de)(de)(de)偏轉角正比于被測負(fu)載功(gong)(gong)(gong)率。

2、交流電路的功率測量

在交(jiao)流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)路中，功率(lv)(lv)表的工作原(yuan)理(li)與(yu)直流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)路類似(si)，但由于交(jiao)流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)的特性，需要考(kao)慮電(dian)(dian)(dian)(dian)流(liu)(liu)(liu)與(yu)電(dian)(dian)(dian)(dian)壓之間的相位差。功率(lv)(lv)表可以測量(liang)出交(jiao)流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)路中的有(you)功功率(lv)(lv)，即實際功率(lv)(lv)，它等(deng)于電(dian)(dian)(dian)(dian)壓與(yu)電(dian)(dian)(dian)(dian)流(liu)(liu)(liu)有(you)效值(zhi)的乘積再乘以功率(lv)(lv)因數。

二、功率表的使用方法

1、正確選擇功率表的量程

選(xuan)擇(ze)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)表(biao)(biao)(biao)的(de)(de)量(liang)(liang)(liang)程(cheng)就是(shi)選(xuan)擇(ze)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)表(biao)(biao)(biao)中(zhong)的(de)(de)電(dian)(dian)流(liu)量(liang)(liang)(liang)程(cheng)和電(dian)(dian)壓(ya)量(liang)(liang)(liang)程(cheng)。使用時應使功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)表(biao)(biao)(biao)中(zhong)的(de)(de)電(dian)(dian)流(liu)表(biao)(biao)(biao)程(cheng)不(bu)小于負(fu)(fu)載(zai)(zai)電(dian)(dian)流(liu)，電(dian)(dian)壓(ya)量(liang)(liang)(liang)程(cheng)不(bu)低于負(fu)(fu)載(zai)(zai)電(dian)(dian)壓(ya)，而(er)不(bu)能(neng)僅從(cong)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)量(liang)(liang)(liang)程(cheng)來(lai)考慮。例如，兩只功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)表(biao)(biao)(biao)，量(liang)(liang)(liang)程(cheng)分(fen)別是(shi)ia、300v和2a、150v，由計算可(ke)知其功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)量(liang)(liang)(liang)程(cheng)均為30ow，如果要(yao)測量(liang)(liang)(liang)一負(fu)(fu)載(zai)(zai)電(dian)(dian)壓(ya)為220v、電(dian)(dian)流(liu)為ia的(de)(de)負(fu)(fu)載(zai)(zai)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)時應逸用ia、300v的(de)(de)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)表(biao)(biao)(biao)，而(er)2a、150v的(de)(de)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)表(biao)(biao)(biao)雖功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)量(liang)(liang)(liang)程(cheng)也大于負(fu)(fu)載(zai)(zai)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)，但(dan)是(shi)由于負(fu)(fu)載(zai)(zai)電(dian)(dian)壓(ya)高于功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)表(biao)(biao)(biao)所(suo)能(neng)承(cheng)受的(de)(de)電(dian)(dian)壓(ya)150v，故不(bu)能(neng)使用。所(suo)以，在(zai)測量(liang)(liang)(liang)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)前(qian)要(yao)根據負(fu)(fu)載(zai)(zai)的(de)(de)額定(ding)電(dian)(dian)壓(ya)和額定(ding)電(dian)(dian)流(liu)來(lai)選(xuan)擇(ze)功(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)表(biao)(biao)(biao)的(de)(de)量(liang)(liang)(liang)程(cheng)。

2、正確連接測量線路

電(dian)(dian)(dian)動(dong)系(xi)測量機構的(de)(de)轉動(dong)力(li)矩方向和兩線(xian)(xian)(xian)圈(quan)中的(de)(de)電(dian)(dian)(dian)流方向有(you)關(guan)，為了防止電(dian)(dian)(dian)動(dong)系(xi)功(gong)(gong)率表(biao)(biao)的(de)(de)指針反偏，接線(xian)(xian)(xian)時功(gong)(gong)率表(biao)(biao)電(dian)(dian)(dian)流線(xian)(xian)(xian)標有(you)“·”號的(de)(de)端(duan)(duan)鈕必須接到電(dian)(dian)(dian)源的(de)(de)正極端(duan)(duan)，而電(dian)(dian)(dian)流線(xian)(xian)(xian)圈(quan)的(de)(de)另一(yi)(yi)端(duan)(duan)則與負載(zai)(zai)相連，電(dian)(dian)(dian)流線(xian)(xian)(xian)圈(quan)以串聯形式接入(ru)電(dian)(dian)(dian)路中。功(gong)(gong)率表(biao)(biao)電(dian)(dian)(dian)壓線(xian)(xian)(xian)圈(quan)標有(you)“·”號的(de)(de)端(duan)(duan)鈕可以接到電(dian)(dian)(dian)源端(duan)(duan)鈕的(de)(de)任一(yi)(yi)端(duan)(duan)上，而另一(yi)(yi)電(dian)(dian)(dian)壓端(duan)(duan)鈕則跨接到負載(zai)(zai)的(de)(de)另一(yi)(yi)端(duan)(duan)。

3、正確讀數

一(yi)(yi)般安(an)裝式功(gong)率(lv)表(biao)(biao)為直讀(du)單量程(cheng)式，表(biao)(biao)上的(de)示(shi)數(shu)(shu)即為功(gong)率(lv)數(shu)(shu)。但便攜式功(gong)率(lv)表(biao)(biao)一(yi)(yi)般為多量程(cheng)式，在(zai)(zai)表(biao)(biao)的(de)標度尺上不直接標注示(shi)數(shu)(shu)，只標注分格(ge)。在(zai)(zai)選用不同的(de)電(dian)流與電(dian)壓量程(cheng)時，每一(yi)(yi)分格(ge)都可以(yi)表(biao)(biao)示(shi)不同的(de)功(gong)率(lv)數(shu)(shu)。在(zai)(zai)讀(du)數(shu)(shu)時，應(ying)先根據(ju)所選的(de)電(dian)壓量程(cheng)u、電(dian)流量程(cheng)i以(yi)及標度尺滿量程(cheng)時的(de)格(ge)數(shu)(shu)，求出每格(ge)瓦數(shu)(shu)（又稱功(gong)率(lv)表(biao)(biao)常數(shu)(shu)）c，然后再乘上指針(zhen)偏轉的(de)格(ge)數(shu)(shu)，就可得到所測功(gong)率(lv)p。

三、功率表使用注意事項

1、功率表在使(shi)用過程中應水平放置。

2、儀表指針如不在零(ling)位時，可利用(yong)表蓋上零(ling)位調(diao)整器調(diao)整。

3、測量時，如遇儀表(biao)指針(zhen)反向(xiang)偏轉，應改變(bian)儀表(biao)面扳(ban)上的“ ”、“-”換(huan)向(xiang)開關極(ji)性，切忌互換(huan)電壓接(jie)線(xian)，以免使儀表(biao)產生誤差。

4、功率表與其它指示儀表不同，指針偏轉大小只表明功率值，并不顯示儀表本身是否過栽，有時表針雖未達到滿度，只要U或I之一超過該表的量程就會損壞儀表。故在使用功率表時(shi)，通(tong)常需接入電壓表和電流表進行監控(kong)。

5、功率表所(suo)測(ce)功率值(zhi)包括了其本身電流線(xian)圈的功率損耗，所(suo)以(yi)在作(zuo)準確測(ce)量時，應從測(ce)得的功率中減(jian)去電流線(xian)圈消耗的功率，才(cai)是所(suo)求負(fu)載消耗的功率。