一、電阻的種類有哪些
1、按伏安特性分類
可(ke)分(fen)為(wei)(wei)線(xian)性電阻和非(fei)線(xian)性電阻。對(dui)大多數導體來說,在一(yi)定的(de)溫度下,其(qi)電阻幾乎維(wei)持不變而為(wei)(wei)一(yi)定值,這類電阻稱為(wei)(wei)線(xian)性電阻。
有(you)些(xie)材料的電(dian)(dian)(dian)阻(zu)(zu)明(ming)顯地(di)隨著(zhu)電(dian)(dian)(dian)流(或電(dian)(dian)(dian)壓)而變化,其(qi)伏安特(te)性(xing)(xing)是(shi)一(yi)條曲(qu)線(xian),這類電(dian)(dian)(dian)阻(zu)(zu)稱為非線(xian)性(xing)(xing)電(dian)(dian)(dian)阻(zu)(zu)。非線(xian)性(xing)(xing)電(dian)(dian)(dian)阻(zu)(zu)在某一(yi)給定的電(dian)(dian)(dian)壓(或電(dian)(dian)(dian)流)作用下,電(dian)(dian)(dian)壓與電(dian)(dian)(dian)流的比值為在該工作點下的靜態電(dian)(dian)(dian)阻(zu)(zu),伏安特(te)性(xing)(xing)曲(qu)線(xian)上(shang)的斜率為動(dong)態電(dian)(dian)(dian)阻(zu)(zu)。表(biao)達非線(xian)性(xing)(xing)電(dian)(dian)(dian)阻(zu)(zu)特(te)性(xing)(xing)的方(fang)式比較(jiao)復雜,但這些(xie)非線(xian)性(xing)(xing)關系在電(dian)(dian)(dian)子電(dian)(dian)(dian)路(lu)中得到了廣泛的應用。
2、按材料分類
a.線(xian)繞電阻(zu)(zu)(zu)器(qi)由電阻(zu)(zu)(zu)線(xian)繞成電阻(zu)(zu)(zu)器(qi),用高(gao)(gao)阻(zu)(zu)(zu)合(he)金線(xian)繞在絕(jue)緣骨(gu)架上制成,外面涂有(you)耐(nai)熱的釉絕(jue)緣層或絕(jue)緣漆。繞線(xian)電阻(zu)(zu)(zu)具有(you)較低的溫度(du)系(xi)數,阻(zu)(zu)(zu)值(zhi)精度(du)高(gao)(gao),穩(wen)定性好,耐(nai)熱耐(nai)腐(fu)蝕,主要做精密大功(gong)率(lv)電阻(zu)(zu)(zu)使用,缺點是(shi)高(gao)(gao)頻性能差,時間常數大。
b.碳(tan)合(he)成(cheng)(cheng)電阻器由碳(tan)及合(he)成(cheng)(cheng)塑膠壓制成(cheng)(cheng)而成(cheng)(cheng)。
c.碳(tan)(tan)膜電(dian)阻器在(zai)瓷管上(shang)(shang)鍍上(shang)(shang)一層碳(tan)(tan)而成(cheng)(cheng),將(jiang)結晶碳(tan)(tan)沉積(ji)在(zai)陶瓷棒骨(gu)架(jia)上(shang)(shang)制成(cheng)(cheng)。碳(tan)(tan)膜電(dian)阻器成(cheng)(cheng)本低、性能穩定、阻值(zhi)范圍寬(kuan)、溫(wen)度系(xi)數(shu)和電(dian)壓系(xi)數(shu)低,是目前應用最廣泛(fan)的電(dian)阻器。
d.金(jin)(jin)屬(shu)膜(mo)電阻器在瓷(ci)管上鍍(du)上一層金(jin)(jin)屬(shu)而(er)成,用真空蒸發的(de)方法將合金(jin)(jin)材料蒸鍍(du)于陶瓷(ci)棒(bang)骨(gu)架表面。金(jin)(jin)屬(shu)膜(mo)電阻比碳膜(mo)電阻的(de)精度(du)高,穩定性(xing)好,噪聲(sheng),溫度(du)系數小。在儀器儀表及通訊設備中大量采用。
e.金(jin)屬氧化(hua)膜電阻(zu)器在瓷管上(shang)鍍上(shang)一層氧化(hua)錫而(er)成,在絕緣棒上(shang)沉積一層金(jin)屬氧化(hua)物(wu)。由于其本身(shen)即是氧化(hua)物(wu),所(suo)以高(gao)溫下(xia)穩定,耐熱沖擊,負載能力(li)強。按用途(tu)分,有通用、精密、高(gao)頻、高(gao)壓、高(gao)阻(zu)、大功率和電阻(zu)網絡等(deng)。
3、特殊電阻器
a.保(bao)(bao)險(xian)電(dian)阻(zu)(zu):又叫熔(rong)斷電(dian)阻(zu)(zu)器(qi),在(zai)正常情(qing)況下起著(zhu)電(dian)阻(zu)(zu)和保(bao)(bao)險(xian)絲(si)的雙重作(zuo)用,當電(dian)路出現故(gu)障而(er)使其(qi)功(gong)(gong)率(lv)超過額定功(gong)(gong)率(lv)時,它會像保(bao)(bao)險(xian)絲(si)一(yi)樣熔(rong)斷使連(lian)接電(dian)路斷開。保(bao)(bao)險(xian)絲(si)電(dian)阻(zu)(zu)一(yi)般電(dian)阻(zu)(zu)值都小(0.33Ω~10KΩ),功(gong)(gong)率(lv)也較小。保(bao)(bao)險(xian)絲(si)電(dian)阻(zu)(zu)器(qi)常用型(xing)號(hao)有:RF10型(xing)、RF111-5保(bao)(bao)險(xian)絲(si)電(dian)阻(zu)(zu)器(qi)的符號(hao)型(xing)、RRD0910型(xing)、RRD0911型(xing)等。
b.敏(min)(min)(min)感電(dian)阻器(qi)(qi)(qi):是(shi)指其電(dian)阻值對于(yu)某種物(wu)理(li)量(liang)(如溫度、濕(shi)度、光(guang)照(zhao)、電(dian)壓、機械(xie)力(li)、以及氣體(ti)濃(nong)度等)具有敏(min)(min)(min)感特性,當這(zhe)些(xie)物(wu)理(li)量(liang)發生變化時,敏(min)(min)(min)感電(dian)阻的阻值就(jiu)會(hui)隨物(wu)理(li)量(liang)變化而發生改變,呈現(xian)不同(tong)的電(dian)阻值。根據對不同(tong)物(wu)理(li)量(liang)敏(min)(min)(min)感,敏(min)(min)(min)感電(dian)阻器(qi)(qi)(qi)可分為熱(re)敏(min)(min)(min)、濕(shi)敏(min)(min)(min)、光(guang)敏(min)(min)(min)、壓敏(min)(min)(min)、力(li)敏(min)(min)(min)、磁敏(min)(min)(min)和氣敏(min)(min)(min)等類(lei)型敏(min)(min)(min)感電(dian)阻。敏(min)(min)(min)感電(dian)阻器(qi)(qi)(qi)所用的材料幾(ji)乎都是(shi)半導(dao)體(ti)材料,這(zhe)類(lei)電(dian)阻器(qi)(qi)(qi)也稱為半導(dao)體(ti)電(dian)阻器(qi)(qi)(qi)。
c.熱(re)敏(min)(min)電(dian)(dian)阻(zu)(zu)(zu)的(de)阻(zu)(zu)(zu)值(zhi)(zhi)隨溫度(du)變(bian)化(hua)而變(bian)化(hua),溫度(du)升高阻(zu)(zu)(zu)為負(fu)溫度(du)系(xi)(xi)數(shu)(NTC)熱(re)敏(min)(min)電(dian)(dian)阻(zu)(zu)(zu)。應用較多的(de)是負(fu)溫度(du)系(xi)(xi)數(shu)熱(re)敏(min)(min)電(dian)(dian)阻(zu)(zu)(zu),又可(ke)分為普通型(xing)負(fu)溫度(du)系(xi)(xi)數(shu)熱(re)敏(min)(min)電(dian)(dian)阻(zu)(zu)(zu);穩(wen)壓型(xing)負(fu)溫度(du)系(xi)(xi)數(shu)熱(re)敏(min)(min)電(dian)(dian)阻(zu)(zu)(zu);測溫型(xing)負(fu)溫度(du)系(xi)(xi)數(shu)熱(re)敏(min)(min)電(dian)(dian)阻(zu)(zu)(zu)等(deng)。光敏(min)(min)電(dian)(dian)阻(zu)(zu)(zu)是電(dian)(dian)阻(zu)(zu)(zu)的(de)阻(zu)(zu)(zu)值(zhi)(zhi)隨入(ru)射光的(de)強(qiang)弱變(bian)化(hua)而改變(bian),當入(ru)射光增(zeng)強(qiang)時(shi),光敏(min)(min)電(dian)(dian)阻(zu)(zu)(zu)的(de)減(jian)小,入(ru)射光減(jian)弱時(shi)電(dian)(dian)阻(zu)(zu)(zu)值(zhi)(zhi)增(zeng)大。
二、電阻器選用的方法
1、固定電阻器的選用
固定(ding)(ding)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi)有多種類(lei)型,選擇(ze)哪一種材料(liao)和結構的(de)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi),應(ying)根據應(ying)用(yong)電(dian)(dian)(dian)(dian)(dian)路的(de)具(ju)體要求而(er)(er)定(ding)(ding)。高(gao)(gao)頻電(dian)(dian)(dian)(dian)(dian)路應(ying)選用(yong)分布(bu)電(dian)(dian)(dian)(dian)(dian)感和分布(bu)電(dian)(dian)(dian)(dian)(dian)容小的(de)非線繞電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi),例如碳膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi)、金屬電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi)和金屬氧(yang)化(hua)膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi),薄膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi),厚膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi),合金電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi),防腐(fu)蝕鍍(du)膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi)等。高(gao)(gao)增(zeng)益小信號放大(da)電(dian)(dian)(dian)(dian)(dian)路應(ying)選用(yong)低噪聲電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi),例如金屬膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi)、碳膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi)和線繞電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi),而(er)(er)不能使(shi)用(yong)噪聲較(jiao)大(da)的(de)合成碳膜(mo)(mo)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi)和有機實心電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)器(qi)(qi)(qi)。
所選(xuan)(xuan)(xuan)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器的(de)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)值應接近(jin)應用電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)中計算(suan)值的(de)一個(ge)標稱值,應優先選(xuan)(xuan)(xuan)用標準系列的(de)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器。一般電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)使用的(de)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器允許(xu)誤(wu)差為±5%~±10%。精密(mi)儀器及特殊電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)中使用的(de)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器,應選(xuan)(xuan)(xuan)用精密(mi)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器,對精密(mi)度為1%以內的(de)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu),如(ru)0.01%,0.1%,0.5%這些量(liang)級(ji)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)應采用捷比信電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)。所選(xuan)(xuan)(xuan)電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器的(de)額定功率,要符合應用電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)中對電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器功率容量(liang)的(de)要求,一般不應隨(sui)意(yi)加(jia)大或減小電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)器的(de)功率。
若電路(lu)要求(qiu)是功(gong)率型(xing)電阻器,則其額定功(gong)率可高(gao)于實際應用電路(lu)要求(qiu)功(gong)率的(de)1~2倍。
2、熔斷電阻器的選用
熔斷電(dian)(dian)(dian)阻器具(ju)有保(bao)護(hu)功能的(de)電(dian)(dian)(dian)阻器。選用時應考(kao)慮其雙重性能,根據電(dian)(dian)(dian)路(lu)的(de)具(ju)體要求選擇其阻值(zhi)(zhi)和功率等參(can)數。既要保(bao)證它(ta)在過負荷時能快(kuai)速熔斷,又(you)要保(bao)證它(ta)在正(zheng)常條件下能長(chang)期穩定的(de)工作(zuo)。電(dian)(dian)(dian)阻值(zhi)(zhi)過大(da)或功率過大(da),均不(bu)能起(qi)到保(bao)護(hu)作(zuo)用。
三、電阻器選用的基本原則
1、選擇通過(guo)認證(zheng)機構(gou)認證(zheng)的(de)生產線制造出的(de)執行高水平標準的(de)電阻(zu)器。
2、選擇具備功能(neng)優(you)勢(shi)、質量優(you)勢(shi)、效率優(you)勢(shi)、功能(neng)價格比優(you)勢(shi)、服務優(you)勢(shi)的制造商生產(chan)的電(dian)阻器。
3、選擇能滿足上述要求的上型號目錄的制造商,并向其直接訂購電阻器。