兩(liang)(liang)種(zhong)不同成份的(de)導體（稱(cheng)為(wei)熱電(dian)偶(ou)絲(si)材或熱電(dian)極）兩(liang)(liang)端(duan)(duan)接(jie)合成回路，當接(jie)合點的(de)溫度(du)不同時，在回路中就會產生(sheng)電(dian)動(dong)勢，這種(zhong)現象稱(cheng)為(wei) 熱電(dian)效應，而這種(zhong) 電(dian)動(dong)勢稱(cheng)為(wei)熱電(dian)勢。熱電(dian)偶(ou)就是利用這種(zhong)原(yuan)理(li)進行溫度(du)測量(liang)(liang)的(de)，其中，直(zhi)接(jie)用作(zuo)(zuo)測量(liang)(liang)介質溫度(du)的(de)一(yi)端(duan)(duan)叫(jiao)做工作(zuo)(zuo)端(duan)(duan)（也稱(cheng)為(wei)測量(liang)(liang)端(duan)(duan)），另一(yi)端(duan)(duan)叫(jiao)做冷(leng)端(duan)(duan)（也稱(cheng)為(wei)補(bu)償端(duan)(duan)）；冷(leng)端(duan)(duan)與顯示儀表或配套儀表連(lian)接(jie)，顯示儀表會指出熱電(dian)偶(ou)所產生(sheng)的(de)熱電(dian)勢。
熱(re)(re)(re)電偶實際(ji)上是一種 能量(liang)(liang)轉換器(qi)，它將(jiang)熱(re)(re)(re)能轉換為 電能，用所產(chan)生的熱(re)(re)(re)電勢(shi)測量(liang)(liang)溫(wen)度，對于熱(re)(re)(re)電偶的熱(re)(re)(re)電勢(shi)，應注(zhu)意如(ru)下幾個問題(ti)：
1：熱電(dian)(dian)偶(ou)的(de)熱電(dian)(dian)勢是熱電(dian)(dian)偶(ou)工(gong)作端的(de)兩端溫度(du)函數(shu)的(de)差，而不是熱電(dian)(dian)偶(ou)冷端與工(gong)作端兩端溫度(du)函數(shu)的(de)差；
2 ：熱電(dian)(dian)偶所產生的(de)熱電(dian)(dian)勢的(de)大(da)小，當熱電(dian)(dian)偶的(de)材(cai)料(liao)是均勻時，與熱電(dian)(dian)偶的(de)長(chang)度和(he)直徑無關，只與熱電(dian)(dian)偶材(cai)料(liao)的(de)成份和(he)兩端(duan)的(de)溫差有關；
3：當熱(re)電(dian)(dian)(dian)(dian)(dian)偶(ou)的兩個熱(re)電(dian)(dian)(dian)(dian)(dian)偶(ou)絲材(cai)料成(cheng)份(fen)確(que)定后，熱(re)電(dian)(dian)(dian)(dian)(dian)偶(ou)熱(re)電(dian)(dian)(dian)(dian)(dian)勢(shi)的大小，只與熱(re)電(dian)(dian)(dian)(dian)(dian)偶(ou)的溫度差有關(guan)；若熱(re)電(dian)(dian)(dian)(dian)(dian)偶(ou)冷端的溫度保持一(yi)(yi)定，這(zhe)進(jin)熱(re)電(dian)(dian)(dian)(dian)(dian)偶(ou)的熱(re)電(dian)(dian)(dian)(dian)(dian)勢(shi)僅是工作端溫度的 單(dan)值函(han)數(shu)。將兩種不同材(cai)料的導(dao)體或 半導(dao)體A和B焊(han)接(jie)起來，構成(cheng)一(yi)(yi)個閉(bi)合回路(lu)，如圖所示。當導(dao)體A和B的兩個執著點(dian)1和2之(zhi)間存在溫差時，兩者(zhe)之(zhi)間便產生 電(dian)(dian)(dian)(dian)(dian)動勢(shi)，因而在回路(lu)中(zhong)形(xing)成(cheng)一(yi)(yi)個大小的電(dian)(dian)(dian)(dian)(dian)流,這(zhe)種現象稱為 熱(re)電(dian)(dian)(dian)(dian)(dian)效應。熱(re)電(dian)(dian)(dian)(dian)(dian)偶(ou)就是利用這(zhe)一(yi)(yi)效應來工作的。
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