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(duo)的(de)元件,但(dan)不是(shi)損壞(huai)率最高的(de)元件。電(dian)(dian)(dian)阻(zu)損壞(huai)以開(kai)路(lu)最常見,阻(zu)值變大較少見,阻(zu)值變小十分少見。常見的(de)有(you)碳膜(mo)電(dian)(dian)(dian)阻(zu)、金屬膜(mo)電(dian)(dian)(dian)阻(zu)、線(xian)繞電(dian)(dian)(dian)阻(zu)和合金電(dian)(dian)(dian)阻(zu)等(deng)幾種,在這些電(dian)(dian)(dian)阻(zu)中如何判斷它們在電(dian)(dian)(dian)路(lu)中是(shi)否(fou)損壞(huai),它們損壞(huai)后又有(you)哪些特(te)征呢?
1、線繞電阻損壞的特征
線繞電阻一般用作(zuo)大(da)電流(liu)限流(liu),阻值不大(da)。
圓柱形線(xian)繞電阻燒(shao)壞時有(you)的會發黑或(huo)表面爆皮、裂紋,有(you)的沒有(you)痕跡(ji)。
水泥電阻是線繞電阻的一(yi)種,燒壞(huai)時可能會斷裂,否(fou)則(ze)也沒有(you)可見痕(hen)跡。
保險電(dian)阻燒(shao)壞時有(you)的表面會炸掉一(yi)塊皮,有(you)的也沒(mei)有(you)什(shen)么痕(hen)跡(ji),但絕(jue)不會燒(shao)焦發黑。
根據以上(shang)特點,在檢查電阻時可有所側重,快(kuai)速找出損(sun)壞(huai)的(de)電阻。
2、金屬膜電阻和碳膜電阻損壞特征
金屬膜電(dian)阻(zu)(zu)和(he)碳(tan)膜電(dian)阻(zu)(zu)應用是最廣,其損(sun)壞(huai)的特點:一是低(di)阻(zu)(zu)值(100Ω以下)和(he)高阻(zu)(zu)值(100kΩ以上(shang))的損(sun)壞(huai)率較高,中間阻(zu)(zu)值(如幾(ji)(ji)百歐到幾(ji)(ji)十千歐)的極少(shao)損(sun)壞(huai);二是低(di)阻(zu)(zu)值電(dian)阻(zu)(zu)損(sun)壞(huai)時往往是燒焦發黑,很(hen)容易發現,而高阻(zu)(zu)值電(dian)阻(zu)(zu)損(sun)壞(huai)時很(hen)少(shao)有痕(hen)跡。
二、怎么測量電阻好壞
1、外觀檢查
對于固(gu)定電阻首先查看(kan)標(biao)志(zhi)清晰,保護(hu)漆完(wan)好,無(wu)(wu)燒(shao)焦,無(wu)(wu)傷痕,無(wu)(wu)裂痕,無(wu)(wu)腐蝕,電阻體與(yu)引腳緊(jin)密接觸等。對于電位器還應檢(jian)查轉軸(zhou)靈(ling)活,松(song)緊(jin)適當,手感(gan)舒適。有(you)開關的要檢(jian)查開關動作是(shi)否正(zheng)常。
2、萬用表檢測
①固定電阻的檢測
用(yong)萬(wan)用(yong)表的(de)電(dian)(dian)阻(zu)(zu)(zu)擋對(dui)電(dian)(dian)阻(zu)(zu)(zu)進行測(ce)量(liang)(liang),對(dui)于測(ce)量(liang)(liang)不(bu)同阻(zu)(zu)(zu)值(zhi)的(de)電(dian)(dian)阻(zu)(zu)(zu)選擇(ze)萬(wan)用(yong)表的(de)不(bu)同倍乘擋。對(dui)于指(zhi)針(zhen)式萬(wan)用(yong)表,由于電(dian)(dian)阻(zu)(zu)(zu)擋的(de)示數是非線性的(de),阻(zu)(zu)(zu)值(zhi)越大,示數越密,所以(yi)選擇(ze)合適的(de)量(liang)(liang)程(cheng),應使表針(zhen)偏轉角大些(xie),指(zhi)示于1/3~2/3滿(man)量(liang)(liang)程(cheng),讀數更為準確。若測(ce)得阻(zu)(zu)(zu)值(zhi)超(chao)過該電(dian)(dian)阻(zu)(zu)(zu)的(de)誤差范圍、阻(zu)(zu)(zu)值(zhi)無限大、阻(zu)(zu)(zu)值(zhi)為0或阻(zu)(zu)(zu)值(zhi)不(bu)穩,說明(ming)該電(dian)(dian)阻(zu)(zu)(zu)器已壞。
在測量中(zhong)注意拿電(dian)(dian)阻(zu)(zu)的(de)(de)手不要與(yu)電(dian)(dian)阻(zu)(zu)器的(de)(de)兩個引(yin)腳相接(jie)觸(chu),這樣(yang)會(hui)使(shi)手所(suo)呈現(xian)的(de)(de)電(dian)(dian)阻(zu)(zu)與(yu)被測電(dian)(dian)阻(zu)(zu)并(bing)聯,影響測量準確。另(ling)外,不能帶電(dian)(dian)情況下用萬用表電(dian)(dian)阻(zu)(zu)擋檢(jian)測電(dian)(dian)路中(zhong)電(dian)(dian)阻(zu)(zu)器的(de)(de)阻(zu)(zu)值(zhi)。在線檢(jian)測應首先斷(duan)電(dian)(dian),再將電(dian)(dian)阻(zu)(zu)從電(dian)(dian)路中(zhong)斷(duan)開出(chu)來,然后進行測量。
②保險絲電阻和敏感電阻的檢測
保(bao)險(xian)絲(si)電阻一(yi)般阻值只(zhi)有(you)幾到幾十歐,若測得(de)阻值為無限大(da),則已(yi)熔(rong)斷。也(ye)可在(zai)線檢測保(bao)險(xian)絲(si)電阻的好壞,分別測量其兩端對地電壓,若一(yi)端為電源(yuan)電壓,一(yi)端電壓為0伏,保(bao)險(xian)絲(si)電阻已(yi)熔(rong)斷。
敏(min)(min)(min)感(gan)電(dian)(dian)(dian)阻(zu)(zu)種類較多(duo),以熱(re)(re)敏(min)(min)(min)電(dian)(dian)(dian)阻(zu)(zu)為例(li),又分正溫(wen)(wen)度(du)(du)系(xi)數(shu)(shu)和(he)負溫(wen)(wen)度(du)(du)系(xi)數(shu)(shu)熱(re)(re)敏(min)(min)(min)電(dian)(dian)(dian)阻(zu)(zu)。對于正溫(wen)(wen)度(du)(du)系(xi)(PTC)熱(re)(re)敏(min)(min)(min)電(dian)(dian)(dian)阻(zu)(zu),在(zai)常(chang)溫(wen)(wen)下一(yi)般(ban)阻(zu)(zu)值(zhi)(zhi)不大,在(zai)測量中(zhong)用燒熱(re)(re)的電(dian)(dian)(dian)烙鐵靠(kao)近(jin)電(dian)(dian)(dian)阻(zu)(zu),這時阻(zu)(zu)值(zhi)(zhi)應明(ming)(ming)顯增大,說明(ming)(ming)該電(dian)(dian)(dian)阻(zu)(zu)正常(chang),若(ruo)無變化說明(ming)(ming)元件損壞,負溫(wen)(wen)度(du)(du)系(xi)熱(re)(re)敏(min)(min)(min)電(dian)(dian)(dian)阻(zu)(zu)則(ze)相反(fan)。
光(guang)敏(min)電(dian)阻在無光(guang)照(用(yong)手或物遮住光(guang))的情(qing)況(kuang)下萬用(yong)表測得阻值大,有光(guang)照表針指(zhi)示電(dian)阻值有明顯減小。若無變化,則(ze)元(yuan)件損壞(huai)。
③可變電阻和電位器的檢測
首先測(ce)量兩固定端(duan)之間電(dian)阻(zu)值(zhi)是否正(zheng)常(chang)(chang),若為(wei)無(wu)限大或(huo)為(wei)零(ling)歐(ou),或(huo)與標稱(cheng)相(xiang)差(cha)較大,超(chao)過誤(wu)差(cha)允許范圍(wei),都說明(ming)(ming)(ming)已損壞(huai);電(dian)阻(zu)體(ti)阻(zu)值(zhi)正(zheng)常(chang)(chang),再將萬用(yong)表一(yi)只表筆接電(dian)位器(qi)(qi)滑動(dong)端(duan),另(ling)一(yi)只表筆接電(dian)位器(qi)(qi)(可調電(dian)阻(zu))的(de)(de)任一(yi)固定端(duan),緩慢(man)旋(xuan)動(dong)軸(zhou)柄,觀察(cha)表針是否平(ping)穩變(bian)(bian)化,當(dang)從一(yi)端(duan)旋(xuan)向另(ling)一(yi)端(duan)時,阻(zu)值(zhi)從零(ling)歐(ou)變(bian)(bian)化到標稱(cheng)值(zhi)(或(huo)相(xiang)反),并(bing)且無(wu)跳(tiao)(tiao)變(bian)(bian)或(huo)抖(dou)動(dong)等(deng)現(xian)(xian)象,則說明(ming)(ming)(ming)電(dian)位器(qi)(qi)正(zheng)常(chang)(chang),若在旋(xuan)轉的(de)(de)過程中(zhong)有跳(tiao)(tiao)變(bian)(bian)或(huo)抖(dou)動(dong)現(xian)(xian)象,說明(ming)(ming)(ming)滑動(dong)點(dian)現(xian)(xian)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)阻值,可(ke)通(tong)過電(dian)(dian)(dian)(dian)橋(qiao)(數(shu)字式)進(jin)行測試(shi)。將電(dian)(dian)(dian)(dian)阻插入電(dian)(dian)(dian)(dian)橋(qiao)元件(jian)測量端(duan),選(xuan)擇合適的(de)量程,即可(ke)從顯示(shi)器(qi)上讀出電(dian)(dian)(dian)(dian)阻器(qi)的(de)阻值。例如(ru),用(yong)電(dian)(dian)(dian)(dian)阻絲(si)自(zi)制電(dian)(dian)(dian)(dian)阻或(huo)對固定電(dian)(dian)(dian)(dian)阻器(qi)進(jin)行處理來獲得某一較為精確的(de)電(dian)(dian)(dian)(dian)阻值時(shi),就必須用(yong)電(dian)(dian)(dian)(dian)橋(qiao)測量自(zi)制電(dian)(dian)(dian)(dian)阻的(de)阻值。