超(chao)(chao)聲波(bo)(bo)是機(ji)械波(bo)(bo)的(de)(de)(de)一種，即是機(ji)械振動在(zai)彈(dan)性介質中(zhong)的(de)(de)(de)一種傳(chuan)播(bo)過程，它的(de)(de)(de)特征(zheng)是頻率高、波(bo)(bo)長短、繞射現象小，另(ling)外方向性好(hao)，能(neng)夠(gou)成為射線而(er)定向傳(chuan)播(bo)。超(chao)(chao)聲波(bo)(bo)在(zai)液體(ti)、固(gu)體(ti)中(zhong)衰減很(hen)小，因而(er)穿透(tou)(tou)能(neng)力強，尤其是在(zai)對(dui)光(guang)不透(tou)(tou)明的(de)(de)(de)固(gu)體(ti)中(zhong)，超(chao)(chao)聲波(bo)(bo)可穿透(tou)(tou)幾十米的(de)(de)(de)長度，碰到雜質或界面就會有顯著的(de)(de)(de)反射，超(chao)(chao)聲波(bo)(bo)液位計(ji)就是利用(yong)它的(de)(de)(de)這(zhe)一原理而(er)工作的(de)(de)(de)。
在超(chao)(chao)(chao)聲(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)波(bo)(bo)(bo)(bo)(bo)(bo)檢(jian)測技術(shu)中，不(bu)管那種超(chao)(chao)(chao)聲(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)波(bo)(bo)(bo)(bo)(bo)(bo)儀(yi)器(qi)(qi)，都必須把電能(neng)(neng)轉換(huan)(huan)(huan)超(chao)(chao)(chao)聲(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)波(bo)(bo)(bo)(bo)(bo)(bo)發(fa)(fa)射(she)(she)(she)(she)(she)出(chu)去(qu)，再接(jie)(jie)收(shou)回來變(bian)換(huan)(huan)(huan)成電信(xin)(xin)號，完成這項功能(neng)(neng)的(de)(de)(de)裝置(zhi)就叫超(chao)(chao)(chao)聲(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)波(bo)(bo)(bo)(bo)(bo)(bo)換(huan)(huan)(huan)能(neng)(neng)器(qi)(qi)，也被稱作為探頭(tou)。將超(chao)(chao)(chao)聲(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)波(bo)(bo)(bo)(bo)(bo)(bo)換(huan)(huan)(huan)能(neng)(neng)器(qi)(qi)置(zhi)于被測液(ye)體或(huo)(huo)物(wu)(wu)位上方(fang)，向下(xia)發(fa)(fa)射(she)(she)(she)(she)(she)超(chao)(chao)(chao)聲(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)波(bo)(bo)(bo)(bo)(bo)(bo)，超(chao)(chao)(chao)聲(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)波(bo)(bo)(bo)(bo)(bo)(bo)穿過(guo)(guo)空氣介質(zhi)(zhi)，在遇到(dao)水(shui)面(mian)或(huo)(huo)物(wu)(wu)體介面(mian)時(shi)被反射(she)(she)(she)(she)(she)回來，然后(hou)被換(huan)(huan)(huan)能(neng)(neng)器(qi)(qi)所(suo)接(jie)(jie)收(shou)并轉換(huan)(huan)(huan)為電信(xin)(xin)號，電子檢(jian)測部分檢(jian)測到(dao)這一(yi)信(xin)(xin)號后(hou)將其變(bian)成物(wu)(wu)位信(xin)(xin)號進行顯示并輸出(chu)標(biao)準信(xin)(xin)號,供其它儀(yi)表或(huo)(huo)控(kong)制裝置(zhi)使用(yong).由(you)超(chao)(chao)(chao)聲(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)波(bo)(bo)(bo)(bo)(bo)(bo)在介質(zhi)(zhi)中傳(chuan)播(bo)原理可知，若(ruo)介質(zhi)(zhi)壓力、溫度、密度、濕度等(deng)條件一(yi)定(ding)，則超(chao)(chao)(chao)聲(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)波(bo)(bo)(bo)(bo)(bo)(bo)在該(gai)介質(zhi)(zhi)中傳(chuan)播(bo)速(su)度是(shi)一(yi)個常(chang)數。因此，當測量(liang)出(chu)超(chao)(chao)(chao)聲(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)波(bo)(bo)(bo)(bo)(bo)(bo)由(you)發(fa)(fa)射(she)(she)(she)(she)(she)到(dao)遇到(dao)物(wu)(wu)面(mian)或(huo)(huo)液(ye)面(mian)反射(she)(she)(she)(she)(she)被接(jie)(jie)收(shou)所(suo)需要的(de)(de)(de)時(shi)間(jian)，則可換(huan)(huan)(huan)算出(chu)超(chao)(chao)(chao)聲(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)波(bo)(bo)(bo)(bo)(bo)(bo)通過(guo)(guo)的(de)(de)(de)路程，從而間(jian)接(jie)(jie)地(di)測量(liang)出(chu)物(wu)(wu)位或(huo)(huo)者液(ye)位數據。超(chao)(chao)(chao)聲(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)波(bo)(bo)(bo)(bo)(bo)(bo)液(ye)位計(ji)的(de)(de)(de)工作原理是(shi)由(you)換(huan)(huan)(huan)能(neng)(neng)器(qi)(qi)(探頭(tou))發(fa)(fa)出(chu)高頻超(chao)(chao)(chao)聲(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)波(bo)(bo)(bo)(bo)(bo)(bo)脈(mo)沖(chong)遇到(dao)被測介質(zhi)(zhi)表面(mian)被反射(she)(she)(she)(she)(she)回來，部分反射(she)(she)(she)(she)(she)回波(bo)(bo)(bo)(bo)(bo)(bo)被同一(yi)換(huan)(huan)(huan)能(neng)(neng)器(qi)(qi)接(jie)(jie)收(shou)，轉換(huan)(huan)(huan)成電信(xin)(xin)號。超(chao)(chao)(chao)聲(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)波(bo)(bo)(bo)(bo)(bo)(bo)脈(mo)沖(chong)以聲(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)波(bo)(bo)(bo)(bo)(bo)(bo)速(su)度傳(chuan)播(bo)，從發(fa)(fa)射(she)(she)(she)(she)(she)到(dao)接(jie)(jie)收(shou)到(dao)超(chao)(chao)(chao)聲(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)波(bo)(bo)(bo)(bo)(bo)(bo)脈(mo)沖(chong)所(suo)需時(shi)間(jian)間(jian)隔與(yu)換(huan)(huan)(huan)能(neng)(neng)器(qi)(qi)到(dao)被測介質(zhi)(zhi)表面(mian)的(de)(de)(de)距(ju)離成正比。此距(ju)離值S與(yu)聲(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)(sheng)速(su)C和傳(chuan)輸時(shi)間(jian)T之間(jian)的(de)(de)(de)關系(xi)可以用(yong)公式表示：
S=CxT/2。
由于發(fa)射的(de)(de)超(chao)聲波脈沖有一定的(de)(de)寬(kuan)度，使得距(ju)離換能器(qi)較近的(de)(de)小段(duan)區(qu)(qu)域(yu)(yu)內的(de)(de)反射波與發(fa)射波重迭，無法識別，不能測量(liang)其距(ju)離值(zhi)。這個區(qu)(qu)域(yu)(yu)稱為測量(liang)盲區(qu)(qu)。盲區(qu)(qu)的(de)(de)大小與超(chao)聲波物位計的(de)(de)型號有關。
超聲(sheng)波液(ye)位計安裝要求：
換能(neng)器(qi)發(fa)(fa)射超聲(sheng)波(bo)(bo)脈沖時(shi)，都有(you)一定(ding)的發(fa)(fa)射開角。從換能(neng)器(qi)下緣到被(bei)測(ce)介質表面(mian)之(zhi)間(jian)，由發(fa)(fa)射的超聲(sheng)波(bo)(bo)波(bo)(bo)束所輻射的區(qu)域(yu)內，不得(de)有(you)障礙物，因此安裝時(shi)應盡可能(neng)避開罐內舉措(cuo)措(cuo)施(shi)，如(ru)：人梯、限位開關(guan)、加熱設備、支架等。 另外須留意超聲(sheng)波(bo)(bo)波(bo)(bo)束不得(de)與加料料流相交。
安(an)裝儀(yi)表(biao)(biao)時(shi)還(huan)要留意：Z高料位不得進入丈(zhang)量盲(mang)區;儀(yi)表(biao)(biao)距罐壁必需(xu)保持(chi)一定的間隔;儀(yi)表(biao)(biao)的安(an)裝盡可(ke)能使換能器的發(fa)射方向與液面垂直。
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