一、功率表的原理是什么

功率表的核(he)心工作原理基于電(dian)(dian)動系(xi)測(ce)量機構。在電(dian)(dian)動系(xi)測(ce)量機構中，定圈(quan)串聯(lian)接(jie)入被(bei)測(ce)電(dian)(dian)路，而動圈(quan)與附加電(dian)(dian)阻(zu)串聯(lian)后(hou)并聯(lian)接(jie)入被(bei)測(ce)電(dian)(dian)路。國家標準規定，在測(ce)量線路中，用一個圓加一條水平粗實線和(he)一條豎直細實線來表示電(dian)(dian)壓與電(dian)(dian)流(liu)相乘的線圈(quan)。

1、直流電路的功率測量

當用于(yu)直(zhi)流(liu)電(dian)(dian)(dian)路的(de)功率(lv)測(ce)量時，通(tong)過電(dian)(dian)(dian)流(liu)線圈的(de)電(dian)(dian)(dian)流(liu)與被測(ce)電(dian)(dian)(dian)路電(dian)(dian)(dian)流(liu)相(xiang)等(deng)。電(dian)(dian)(dian)壓(ya)(ya)線圈中的(de)電(dian)(dian)(dian)流(liu)可以通(tong)過歐姆定(ding)律確定(ding)。由于(yu)電(dian)(dian)(dian)流(liu)線圈兩端(duan)的(de)電(dian)(dian)(dian)壓(ya)(ya)降遠小于(yu)負(fu)載(zai)兩端(duan)的(de)電(dian)(dian)(dian)壓(ya)(ya)，因此可以認為電(dian)(dian)(dian)壓(ya)(ya)支路兩端(duan)的(de)電(dian)(dian)(dian)壓(ya)(ya)與負(fu)載(zai)電(dian)(dian)(dian)壓(ya)(ya)相(xiang)等(deng)。電(dian)(dian)(dian)動(dong)系功率(lv)表可動(dong)部分的(de)偏轉(zhuan)角正比于(yu)被測(ce)負(fu)載(zai)功率(lv)。

2、交流電路的功率測量

在交流(liu)(liu)(liu)電(dian)路中(zhong)，功(gong)率表的(de)工作(zuo)原理與(yu)(yu)直(zhi)流(liu)(liu)(liu)電(dian)路類(lei)似，但由于交流(liu)(liu)(liu)電(dian)的(de)特性，需(xu)要考慮(lv)電(dian)流(liu)(liu)(liu)與(yu)(yu)電(dian)壓(ya)之間(jian)的(de)相位差。功(gong)率表可以測量出(chu)交流(liu)(liu)(liu)電(dian)路中(zhong)的(de)有(you)(you)功(gong)功(gong)率，即實際(ji)功(gong)率，它等(deng)于電(dian)壓(ya)與(yu)(yu)電(dian)流(liu)(liu)(liu)有(you)(you)效(xiao)值(zhi)的(de)乘(cheng)(cheng)積再乘(cheng)(cheng)以功(gong)率因數。

二、功率表的使用方法

1、正確選擇功率表的量程

選擇功(gong)(gong)(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)(lv)(lv)(lv)表(biao)(biao)(biao)的(de)量(liang)(liang)程(cheng)(cheng)(cheng)(cheng)就是選擇功(gong)(gong)(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)(lv)(lv)(lv)表(biao)(biao)(biao)中的(de)電(dian)(dian)(dian)(dian)流(liu)(liu)量(liang)(liang)程(cheng)(cheng)(cheng)(cheng)和(he)電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)量(liang)(liang)程(cheng)(cheng)(cheng)(cheng)。使(shi)用時(shi)應使(shi)功(gong)(gong)(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)(lv)(lv)(lv)表(biao)(biao)(biao)中的(de)電(dian)(dian)(dian)(dian)流(liu)(liu)表(biao)(biao)(biao)程(cheng)(cheng)(cheng)(cheng)不(bu)小(xiao)于(yu)(yu)負載(zai)電(dian)(dian)(dian)(dian)流(liu)(liu)，電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)量(liang)(liang)程(cheng)(cheng)(cheng)(cheng)不(bu)低于(yu)(yu)負載(zai)電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)，而(er)不(bu)能僅從功(gong)(gong)(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)(lv)(lv)(lv)量(liang)(liang)程(cheng)(cheng)(cheng)(cheng)來考慮。例如，兩只功(gong)(gong)(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)(lv)(lv)(lv)表(biao)(biao)(biao)，量(liang)(liang)程(cheng)(cheng)(cheng)(cheng)分別(bie)是ia、300v和(he)2a、150v，由計算可知其功(gong)(gong)(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)(lv)(lv)(lv)量(liang)(liang)程(cheng)(cheng)(cheng)(cheng)均為(wei)30ow，如果要測(ce)量(liang)(liang)一負載(zai)電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)為(wei)220v、電(dian)(dian)(dian)(dian)流(liu)(liu)為(wei)ia的(de)負載(zai)功(gong)(gong)(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)(lv)(lv)(lv)時(shi)應逸(yi)用ia、300v的(de)功(gong)(gong)(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)(lv)(lv)(lv)表(biao)(biao)(biao)，而(er)2a、150v的(de)功(gong)(gong)(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)(lv)(lv)(lv)表(biao)(biao)(biao)雖功(gong)(gong)(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)(lv)(lv)(lv)量(liang)(liang)程(cheng)(cheng)(cheng)(cheng)也大(da)于(yu)(yu)負載(zai)功(gong)(gong)(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)(lv)(lv)(lv)，但是由于(yu)(yu)負載(zai)電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)高于(yu)(yu)功(gong)(gong)(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)(lv)(lv)(lv)表(biao)(biao)(biao)所(suo)能承受(shou)的(de)電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)150v，故不(bu)能使(shi)用。所(suo)以，在測(ce)量(liang)(liang)功(gong)(gong)(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)(lv)(lv)(lv)前要根據負載(zai)的(de)額定電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)和(he)額定電(dian)(dian)(dian)(dian)流(liu)(liu)來選擇功(gong)(gong)(gong)(gong)(gong)率(lv)(lv)(lv)(lv)(lv)(lv)(lv)(lv)表(biao)(biao)(biao)的(de)量(liang)(liang)程(cheng)(cheng)(cheng)(cheng)。

2、正確連接測量線路

電(dian)(dian)(dian)動(dong)系測(ce)量機(ji)構的(de)(de)轉動(dong)力矩(ju)方向和(he)兩線(xian)圈(quan)中(zhong)的(de)(de)電(dian)(dian)(dian)流方向有(you)關，為了防止(zhi)電(dian)(dian)(dian)動(dong)系功(gong)率表(biao)的(de)(de)指針反偏，接(jie)線(xian)時功(gong)率表(biao)電(dian)(dian)(dian)流線(xian)標有(you)“·”號的(de)(de)端(duan)(duan)鈕(niu)(niu)(niu)必(bi)須(xu)接(jie)到(dao)電(dian)(dian)(dian)源的(de)(de)正(zheng)極端(duan)(duan)，而電(dian)(dian)(dian)流線(xian)圈(quan)的(de)(de)另一(yi)端(duan)(duan)則與(yu)負載相連，電(dian)(dian)(dian)流線(xian)圈(quan)以串聯(lian)形(xing)式接(jie)入電(dian)(dian)(dian)路中(zhong)。功(gong)率表(biao)電(dian)(dian)(dian)壓(ya)線(xian)圈(quan)標有(you)“·”號的(de)(de)端(duan)(duan)鈕(niu)(niu)(niu)可以接(jie)到(dao)電(dian)(dian)(dian)源端(duan)(duan)鈕(niu)(niu)(niu)的(de)(de)任一(yi)端(duan)(duan)上，而另一(yi)電(dian)(dian)(dian)壓(ya)端(duan)(duan)鈕(niu)(niu)(niu)則跨接(jie)到(dao)負載的(de)(de)另一(yi)端(duan)(duan)。

3、正確讀數

一般安裝式(shi)功率(lv)(lv)表(biao)為(wei)(wei)直(zhi)讀(du)單量程式(shi)，表(biao)上的(de)示數(shu)(shu)(shu)即為(wei)(wei)功率(lv)(lv)數(shu)(shu)(shu)。但便攜式(shi)功率(lv)(lv)表(biao)一般為(wei)(wei)多量程式(shi)，在表(biao)的(de)標(biao)度尺(chi)上不直(zhi)接標(biao)注示數(shu)(shu)(shu)，只標(biao)注分(fen)格(ge)。在選用不同的(de)電(dian)流與電(dian)壓量程時(shi)(shi)，每一分(fen)格(ge)都可(ke)以表(biao)示不同的(de)功率(lv)(lv)數(shu)(shu)(shu)。在讀(du)數(shu)(shu)(shu)時(shi)(shi)，應先根據(ju)所(suo)選的(de)電(dian)壓量程u、電(dian)流量程i以及標(biao)度尺(chi)滿(man)量程時(shi)(shi)的(de)格(ge)數(shu)(shu)(shu)，求出每格(ge)瓦(wa)數(shu)(shu)(shu)（又(you)稱功率(lv)(lv)表(biao)常數(shu)(shu)(shu)）c，然后再乘(cheng)上指針偏轉(zhuan)的(de)格(ge)數(shu)(shu)(shu)，就可(ke)得到所(suo)測功率(lv)(lv)p。

三、功率表使用注意事項

1、功率表在使用過程中(zhong)應(ying)水平放置(zhi)。

2、儀(yi)表指針如不在零位時，可利用表蓋上零位調(diao)(diao)整(zheng)(zheng)器調(diao)(diao)整(zheng)(zheng)。

3、測量時(shi)，如遇(yu)儀表指針反向(xiang)偏轉，應改變儀表面扳上的(de)“ ”、“-”換向(xiang)開關極性，切忌互換電(dian)壓接線，以免使儀表產生誤差。

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，通常需接入電壓(ya)表和電流表進行監控(kong)。

5、功(gong)率(lv)(lv)(lv)表(biao)所測(ce)功(gong)率(lv)(lv)(lv)值包括(kuo)了其本身電流線圈的(de)功(gong)率(lv)(lv)(lv)損(sun)耗(hao)，所以在作準確測(ce)量時，應從測(ce)得的(de)功(gong)率(lv)(lv)(lv)中減去電流線圈消耗(hao)的(de)功(gong)率(lv)(lv)(lv)，才(cai)是所求負載消耗(hao)的(de)功(gong)率(lv)(lv)(lv)。