一、什么是熱敏電阻
熱敏電阻器是敏感(gan)元件的(de)(de)一類,按照溫(wen)度(du)(du)系(xi)數(shu)不(bu)(bu)同(tong)分為正(zheng)溫(wen)度(du)(du)系(xi)數(shu)熱(re)敏電(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)(qi)(PTC)和負溫(wen)度(du)(du)系(xi)數(shu)熱(re)敏電(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)(qi)(NTC)。熱(re)敏電(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)(qi)的(de)(de)典型特點是對(dui)溫(wen)度(du)(du)敏感(gan),不(bu)(bu)同(tong)的(de)(de)溫(wen)度(du)(du)下(xia)表現出不(bu)(bu)同(tong)的(de)(de)電(dian)阻(zu)(zu)(zu)(zu)(zu)值(zhi)。正(zheng)溫(wen)度(du)(du)系(xi)數(shu)熱(re)敏電(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)(qi)(PTC)在(zai)溫(wen)度(du)(du)越(yue)(yue)高(gao)時電(dian)阻(zu)(zu)(zu)(zu)(zu)值(zhi)越(yue)(yue)大(da),負溫(wen)度(du)(du)系(xi)數(shu)熱(re)敏電(dian)阻(zu)(zu)(zu)(zu)(zu)器(qi)(qi)(NTC)在(zai)溫(wen)度(du)(du)越(yue)(yue)高(gao)時電(dian)阻(zu)(zu)(zu)(zu)(zu)值(zhi)越(yue)(yue)低,它們同(tong)屬于半導體器(qi)(qi)件。
二、熱敏電阻的工作原理
熱(re)敏(min)(min)電(dian)(dian)(dian)(dian)阻(zu)(zu)是(shi)(shi)一(yi)(yi)種(zhong)傳(chuan)感器(qi)電(dian)(dian)(dian)(dian)阻(zu)(zu),熱(re)敏(min)(min)電(dian)(dian)(dian)(dian)阻(zu)(zu)的(de)(de)電(dian)(dian)(dian)(dian)阻(zu)(zu)值,隨(sui)(sui)著(zhu)溫度(du)的(de)(de)變(bian)化而改(gai)變(bian),與一(yi)(yi)般的(de)(de)固(gu)定(ding)電(dian)(dian)(dian)(dian)阻(zu)(zu)不同。金屬的(de)(de)電(dian)(dian)(dian)(dian)阻(zu)(zu)值隨(sui)(sui)植度(du)的(de)(de)升(sheng)(sheng)高而增(zeng)大(da),但半(ban)導(dao)體則相反,它的(de)(de)電(dian)(dian)(dian)(dian)阻(zu)(zu)值隨(sui)(sui)溫度(du)的(de)(de)升(sheng)(sheng)高而急劇減小,并呈現非線(xian)性。在溫度(du)變(bian)化相同時,熱(re)敏(min)(min)電(dian)(dian)(dian)(dian)阻(zu)(zu)器(qi)的(de)(de)阻(zu)(zu)值變(bian)化約為鉛熱(re)電(dian)(dian)(dian)(dian)阻(zu)(zu)的(de)(de)10倍,因(yin)此可以說,熱(re)敏(min)(min)電(dian)(dian)(dian)(dian)阻(zu)(zu)器(qi)對溫度(du)的(de)(de)變(bian)化特別(bie)敏(min)(min)感。半(ban)導(dao)體的(de)(de)這種(zhong)溫度(du)特性.是(shi)(shi)因(yin)為半(ban)導(dao)體的(de)(de)導(dao)電(dian)(dian)(dian)(dian)方式是(shi)(shi)載流子(電(dian)(dian)(dian)(dian)子、空(kong)穴)導(dao)電(dian)(dian)(dian)(dian)。由于(yu)半(ban)導(dao)體中載流子的(de)(de)數(shu)目遠(yuan)比金屬中的(de)(de)自由電(dian)(dian)(dian)(dian)子少得(de)多,所以它的(de)(de)電(dian)(dian)(dian)(dian)阻(zu)(zu)率很大(da)。隨(sui)(sui)著(zhu)溫度(du)的(de)(de)升(sheng)(sheng)高,半(ban)導(dao)體中參加導(dao)電(dian)(dian)(dian)(dian)的(de)(de)載流子數(shu)目就(jiu)(jiu)會增(zeng)多,故(gu)半(ban)導(dao)體導(dao)電(dian)(dian)(dian)(dian)率就(jiu)(jiu)增(zeng)加,它的(de)(de)電(dian)(dian)(dian)(dian)阻(zu)(zu)率也就(jiu)(jiu)降低了(le)。
熱敏(min)(min)電阻(zu)器正是(shi)利用半導體的(de)(de)電阻(zu)值(zhi)(zhi)隨(sui)溫度(du)顯著變(bian)化(hua)這一特性制(zhi)成的(de)(de)熱敏(min)(min)元(yuan)件(jian)。它是(shi)由某(mou)些金(jin)屬氧化(hua)物按(an)不(bu)同的(de)(de)配方(fang)制(zhi)成的(de)(de)。在一定(ding)的(de)(de)溫度(du)范圍內,根(gen)據(ju)測(ce)量(liang)熱敏(min)(min)電阻(zu)阻(zu)值(zhi)(zhi)的(de)(de)變(bian)化(hua),便(bian)可(ke)知(zhi)被測(ce)介質的(de)(de)溫度(du)變(bian)化(hua)。
將熱(re)(re)敏(min)(min)電(dian)(dian)(dian)(dian)阻(zu)(zu)安裝在(zai)電(dian)(dian)(dian)(dian)路(lu)(lu)(lu)中(zhong)使用(yong)時(shi),熱(re)(re)敏(min)(min)電(dian)(dian)(dian)(dian)阻(zu)(zu)在(zai)環(huan)境溫(wen)(wen)度(du)相同時(shi),動(dong)作(zuo)時(shi)間隨著電(dian)(dian)(dian)(dian)流(liu)(liu)的增加而急劇縮短;熱(re)(re)敏(min)(min)電(dian)(dian)(dian)(dian)阻(zu)(zu)在(zai)環(huan)境溫(wen)(wen)度(du)相對較高(gao)時(shi)具有更短的動(dong)作(zuo)時(shi)間和較小的維持(chi)電(dian)(dian)(dian)(dian)流(liu)(liu)及動(dong)作(zuo)電(dian)(dian)(dian)(dian)流(liu)(liu)。當(dang)電(dian)(dian)(dian)(dian)路(lu)(lu)(lu)正(zheng)常工作(zuo)時(shi),熱(re)(re)敏(min)(min)電(dian)(dian)(dian)(dian)阻(zu)(zu)溫(wen)(wen)度(du)與室(shi)溫(wen)(wen)相近(jin)、電(dian)(dian)(dian)(dian)阻(zu)(zu)很小,串聯在(zai)電(dian)(dian)(dian)(dian)路(lu)(lu)(lu)中(zhong)不會阻(zu)(zu)礙電(dian)(dian)(dian)(dian)流(liu)(liu)通過;而當(dang)電(dian)(dian)(dian)(dian)路(lu)(lu)(lu)因故障(zhang)而出現過電(dian)(dian)(dian)(dian)流(liu)(liu)時(shi),熱(re)(re)敏(min)(min)電(dian)(dian)(dian)(dian)阻(zu)(zu)由于發熱(re)(re)功率增加導(dao)致(zhi)溫(wen)(wen)度(du)上升,當(dang)溫(wen)(wen)度(du)超過開關溫(wen)(wen)度(du)時(shi),電(dian)(dian)(dian)(dian)阻(zu)(zu)瞬(shun)間會劇增,回路(lu)(lu)(lu)中(zhong)的電(dian)(dian)(dian)(dian)流(liu)(liu)迅(xun)速減(jian)小到安全值。
三、熱敏電阻的作用
1、測(ce)溫。作為(wei)測(ce)量溫度的熱敏電阻傳(chuan)感器一般(ban)結構較(jiao)(jiao)簡單,價格較(jiao)(jiao)低廉;
2、溫度(du)補(bu)償。熱敏電阻傳感器可在(zai)一定的溫度(du)范圍內對某些元器件濕度(du)進行補(bu)償;
3、過熱保護。當溫度大于(yu)突變(bian)點時,電路中的(de)電流可以(yi)內十分之幾毫(hao)安突變(bian)為幾十毫(hao)安,因此繼電器動作(zuo),從(cong)而實現過熱保護;
4、液面測量。
四、熱敏電阻型號
熱敏電阻(zu)分別有三種型號:
1、PTC是指在某一(yi)溫(wen)度下電(dian)(dian)阻急劇增加(jia)、具有正溫(wen)度系數的熱敏電(dian)(dian)阻現象或材料。
2、NTC是指(zhi)隨溫度上升電阻(zu)(zu)呈(cheng)指(zhi)數(shu)關系(xi)減小、具(ju)有負溫度系(xi)數(shu)的(de)熱敏(min)電阻(zu)(zu)現(xian)象和材料。
3、CTR(臨(lin)界溫度熱敏(min)電阻(zu))具(ju)有負電阻(zu)突變特性。
五、熱敏電阻參數
1、標稱阻值Rc:一般指環境(jing)溫度為25℃時(shi)熱敏電阻器的實際(ji)電阻值。
2、實際阻值(zhi)RT:在一定的溫度條件下(xia)所(suo)測得的電阻值(zhi)。
3、材料常數(shu):它是(shi)一(yi)個描述熱敏電阻材料物(wu)理(li)特性的(de)參數(shu),也是(shi)熱靈敏度(du)指標,B值越大,表示(shi)熱敏電阻器的(de)靈敏度(du)越高(gao)。應注意的(de)是(shi),在實際工作時,B值并非一(yi)個常數(shu),而(er)是(shi)隨溫度(du)的(de)升(sheng)高(gao)略有增(zeng)加(jia)。
4、電阻(zu)溫度系數αT:它表(biao)示溫度變化1℃時的阻(zu)值變化率,單(dan)位(wei)為%/℃。
5、時間(jian)常數τ:熱敏電阻(zu)器是有(you)熱慣性(xing)(xing)的,時間(jian)常數,就是一(yi)個描述熱敏電阻(zu)器熱慣性(xing)(xing)的參(can)數。它(ta)的定(ding)義為,在(zai)無功耗的狀態下,當(dang)環境溫(wen)(wen)度由一(yi)個特(te)定(ding)溫(wen)(wen)度向另一(yi)個特(te)定(ding)溫(wen)(wen)度突然改變(bian)(bian)時,熱敏電阻(zu)體的溫(wen)(wen)度變(bian)(bian)化了兩個特(te)定(ding)溫(wen)(wen)度之差的63.2%所需的時間(jian)。τ越(yue)小,表明熱敏電阻(zu)器的熱慣性(xing)(xing)越(yue)小。
6、額(e)定功率(lv)PM:在規定的(de)技術條件下,熱敏(min)電阻(zu)器長期(qi)連(lian)續負載所允許的(de)耗散功率(lv)。在實際使用時不得超(chao)過額(e)定功率(lv)。若熱敏(min)電阻(zu)器工作的(de)環(huan)境溫度超(chao)過25℃,則必須相(xiang)應降低其(qi)負載。
7、額定工作電(dian)流(liu)IM:熱(re)敏電(dian)阻器在(zai)工作狀態下規定的名義電(dian)流(liu)值。
8、測(ce)(ce)量功率(lv)Pc:在規定的環(huan)境溫度(du)下(xia),熱敏電阻體受測(ce)(ce)試電流(liu)加熱而引起的阻值變化不超過0.1%時所消耗的電功率(lv)。
9、最(zui)大電(dian)(dian)壓:對于(yu)NTC熱敏(min)(min)電(dian)(dian)阻器(qi),是指在(zai)(zai)規定(ding)的(de)(de)環(huan)境溫度下,不使熱敏(min)(min)電(dian)(dian)阻器(qi)引起熱失(shi)控所允許(xu)(xu)連(lian)續(xu)(xu)施加的(de)(de)最(zui)大直流(liu)電(dian)(dian)壓;對于(yu)PTC熱敏(min)(min)電(dian)(dian)阻器(qi),是指在(zai)(zai)規定(ding)的(de)(de)環(huan)境溫度和靜止空氣中(zhong),允許(xu)(xu)連(lian)續(xu)(xu)施加到熱敏(min)(min)電(dian)(dian)阻器(qi)上并保證熱敏(min)(min)電(dian)(dian)阻器(qi)正常工(gong)作在(zai)(zai)PTC特性部(bu)分的(de)(de)最(zui)大直流(liu)電(dian)(dian)壓。
10、最高工作溫度Tmax:在規定的技術條件下,熱敏電(dian)阻(zu)器長期連續工作所允(yun)許(xu)的最高溫度。
11、開關溫度tb:PTC熱敏(min)電阻(zu)器的電阻(zu)值(zhi)開始發生躍(yue)增(zeng)時的溫度。
12、耗散系數H:溫度增加1℃時,熱敏電阻器所耗散的功率,單位(wei)為mW/℃。