一、電阻壞了有什么現象
電阻是(shi)電(dian)(dian)(dian)器設備中數量最多的(de)元(yuan)件,但不是(shi)損壞(huai)(huai)率最高(gao)的(de)元(yuan)件。電(dian)(dian)(dian)阻(zu)(zu)損壞(huai)(huai)以開路最常見(jian),阻(zu)(zu)值(zhi)變(bian)大(da)較(jiao)少見(jian),阻(zu)(zu)值(zhi)變(bian)小(xiao)十分少見(jian)。常見(jian)的(de)有(you)碳膜電(dian)(dian)(dian)阻(zu)(zu)、金屬膜電(dian)(dian)(dian)阻(zu)(zu)、線繞電(dian)(dian)(dian)阻(zu)(zu)和合(he)金電(dian)(dian)(dian)阻(zu)(zu)等幾種,在這些電(dian)(dian)(dian)阻(zu)(zu)中如何判(pan)斷它們在電(dian)(dian)(dian)路中是(shi)否(fou)損壞(huai)(huai),它們損壞(huai)(huai)后又有(you)哪(na)些特征呢(ni)?
1、線繞電阻損壞的特征
線繞電阻一般(ban)用作大電流(liu)(liu)限(xian)流(liu)(liu),阻值(zhi)不大。
圓(yuan)柱形線繞電阻燒壞(huai)時(shi)有的會發黑或表面(mian)爆皮、裂紋,有的沒有痕跡。
水泥電阻是線繞電阻的一種(zhong),燒壞時可能(neng)會斷(duan)裂,否則(ze)也沒有(you)可見(jian)痕跡。
保險電阻燒壞時有的(de)表(biao)面會炸掉一塊皮,有的(de)也沒(mei)有什(shen)么痕(hen)跡,但絕不會燒焦發(fa)黑。
根據(ju)以上特點,在檢查電(dian)阻(zu)時可有所側重,快(kuai)速找出損壞的電(dian)阻(zu)。
2、金屬膜電阻和碳膜電阻損壞特征
金屬膜(mo)電(dian)(dian)阻(zu)(zu)(zu)和碳膜(mo)電(dian)(dian)阻(zu)(zu)(zu)應用是(shi)最廣,其損(sun)壞(huai)的(de)特(te)點:一是(shi)低(di)阻(zu)(zu)(zu)值(100Ω以(yi)下)和高(gao)阻(zu)(zu)(zu)值(100kΩ以(yi)上)的(de)損(sun)壞(huai)率(lv)較高(gao),中(zhong)間阻(zu)(zu)(zu)值(如幾百歐(ou)到幾十千歐(ou))的(de)極(ji)少損(sun)壞(huai);二是(shi)低(di)阻(zu)(zu)(zu)值電(dian)(dian)阻(zu)(zu)(zu)損(sun)壞(huai)時往往是(shi)燒焦發(fa)黑,很容易發(fa)現,而高(gao)阻(zu)(zu)(zu)值電(dian)(dian)阻(zu)(zu)(zu)損(sun)壞(huai)時很少有痕跡(ji)。
二、怎么測量電阻好壞
1、外觀檢查
對于(yu)固定(ding)電阻(zu)首先(xian)查看標(biao)志清晰,保護(hu)漆完好(hao),無(wu)燒焦,無(wu)傷痕,無(wu)裂痕,無(wu)腐(fu)蝕,電阻(zu)體(ti)與引腳緊密接觸等。對于(yu)電位器還應檢(jian)查轉(zhuan)軸靈(ling)活(huo),松緊適當,手(shou)感舒適。有開關的要(yao)檢(jian)查開關動作是否正常。
2、萬用表檢測
①固定電阻的檢測
用萬用表(biao)的電阻(zu)(zu)(zu)擋(dang)(dang)對(dui)電阻(zu)(zu)(zu)進行(xing)測量(liang),對(dui)于(yu)測量(liang)不同阻(zu)(zu)(zu)值(zhi)(zhi)的電阻(zu)(zu)(zu)選(xuan)擇萬用表(biao)的不同倍乘(cheng)擋(dang)(dang)。對(dui)于(yu)指(zhi)針式萬用表(biao),由于(yu)電阻(zu)(zu)(zu)擋(dang)(dang)的示(shi)(shi)數是非線性的,阻(zu)(zu)(zu)值(zhi)(zhi)越大(da),示(shi)(shi)數越密,所以選(xuan)擇合適(shi)的量(liang)程,應(ying)使(shi)表(biao)針偏轉角大(da)些,指(zhi)示(shi)(shi)于(yu)1/3~2/3滿量(liang)程,讀(du)數更為(wei)準確。若測得阻(zu)(zu)(zu)值(zhi)(zhi)超過該電阻(zu)(zu)(zu)的誤差范圍、阻(zu)(zu)(zu)值(zhi)(zhi)無限大(da)、阻(zu)(zu)(zu)值(zhi)(zhi)為(wei)0或阻(zu)(zu)(zu)值(zhi)(zhi)不穩,說明該電阻(zu)(zu)(zu)器已壞。
在測(ce)量中注意拿電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)的(de)手不要與電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器(qi)的(de)兩個引腳相接(jie)觸,這樣(yang)會使手所(suo)呈現(xian)的(de)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)與被測(ce)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)并(bing)聯,影響(xiang)測(ce)量準確。另外,不能帶電(dian)(dian)(dian)(dian)(dian)情(qing)況(kuang)下用(yong)萬用(yong)表電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)擋檢(jian)測(ce)電(dian)(dian)(dian)(dian)(dian)路中電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器(qi)的(de)阻(zu)(zu)值。在線(xian)檢(jian)測(ce)應首先斷(duan)電(dian)(dian)(dian)(dian)(dian),再將(jiang)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)從電(dian)(dian)(dian)(dian)(dian)路中斷(duan)開出來,然后進行(xing)測(ce)量。
②保險絲電阻和敏感電阻的檢測
保(bao)險絲電(dian)阻一(yi)般(ban)阻值(zhi)只有幾到幾十(shi)歐,若(ruo)測(ce)得阻值(zhi)為(wei)無限大,則已(yi)熔斷。也(ye)可在線(xian)檢測(ce)保(bao)險絲電(dian)阻的好壞,分別測(ce)量其(qi)兩端對地電(dian)壓(ya),若(ruo)一(yi)端為(wei)電(dian)源(yuan)電(dian)壓(ya),一(yi)端電(dian)壓(ya)為(wei)0伏,保(bao)險絲電(dian)阻已(yi)熔斷。
敏(min)感(gan)電(dian)阻(zu)種類(lei)較多,以熱(re)敏(min)電(dian)阻(zu)為例,又(you)分正溫(wen)(wen)度(du)系(xi)數和負溫(wen)(wen)度(du)系(xi)數熱(re)敏(min)電(dian)阻(zu)。對于正溫(wen)(wen)度(du)系(xi)(PTC)熱(re)敏(min)電(dian)阻(zu),在常(chang)溫(wen)(wen)下一般阻(zu)值不(bu)大,在測量中用(yong)燒熱(re)的電(dian)烙鐵靠近電(dian)阻(zu),這(zhe)時阻(zu)值應明(ming)顯增大,說(shuo)明(ming)該電(dian)阻(zu)正常(chang),若無變(bian)化說(shuo)明(ming)元(yuan)件損(sun)壞,負溫(wen)(wen)度(du)系(xi)熱(re)敏(min)電(dian)阻(zu)則相(xiang)反(fan)。
光敏電阻(zu)在無(wu)光照(zhao)(用(yong)手或物遮住光)的情況下萬(wan)用(yong)表測得(de)阻(zu)值大,有光照(zhao)表針(zhen)指示電阻(zu)值有明顯減小。若無(wu)變化,則元件損壞。
③可變電阻和電位器的檢測
首先測量兩固定端之間電(dian)阻(zu)值是否正(zheng)(zheng)常(chang),若為無(wu)限大或(huo)為零歐,或(huo)與標稱(cheng)相差較(jiao)大,超過(guo)誤差允許(xu)范圍(wei),都(dou)說明已損(sun)壞;電(dian)阻(zu)體(ti)阻(zu)值正(zheng)(zheng)常(chang),再(zai)將萬用(yong)表(biao)一(yi)只表(biao)筆接電(dian)位器滑(hua)動(dong)(dong)端,另一(yi)只表(biao)筆接電(dian)位器(可調(diao)電(dian)阻(zu))的(de)任一(yi)固定端,緩慢旋動(dong)(dong)軸(zhou)柄,觀察表(biao)針是否平(ping)穩變(bian)化,當從(cong)一(yi)端旋向另一(yi)端時,阻(zu)值從(cong)零歐變(bian)化到標稱(cheng)值(或(huo)相反(fan)),并(bing)且無(wu)跳(tiao)變(bian)或(huo)抖(dou)動(dong)(dong)等現象,則說明電(dian)位器正(zheng)(zheng)常(chang),若在旋轉的(de)過(guo)程中有跳(tiao)變(bian)或(huo)抖(dou)動(dong)(dong)現象,說明滑(hua)動(dong)(dong)點現電(dian)阻(zu)體(ti)接觸不良。
3、用電橋測量電阻
如果要求精確測量電阻器的(de)(de)阻(zu)(zu)(zu)(zu)(zu)值,可通過電(dian)(dian)橋(qiao)(數字式)進(jin)(jin)行(xing)測試。將電(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)插入電(dian)(dian)橋(qiao)元件測量端,選擇合適的(de)(de)量程,即可從顯示(shi)器(qi)(qi)上讀(du)出電(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)(qi)的(de)(de)阻(zu)(zu)(zu)(zu)(zu)值。例如,用電(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)絲自制電(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)或對固定電(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)(qi)進(jin)(jin)行(xing)處理來獲得(de)某一較為精確的(de)(de)電(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)值時,就必須用電(dian)(dian)橋(qiao)測量自制電(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)的(de)(de)阻(zu)(zu)(zu)(zu)(zu)值。