射頻導納物位開關的運行原理

射頻導納物位開關控(kong)制(zhi)技(ji)術(shu)是一種電容式物位控(kong)制(zhi)技(ji)術(shu)發展起來的(de)，防掛料(傳(chuan)感(gan)器(qi)粘附之物料稱位掛料)性能(neng)更(geng)(geng)好，工作(zuo)更(geng)(geng)可靠，測量更(geng)(geng)準(zhun)確(que)，使(shi)用(yong)性更(geng)(geng)廣的(de)物位控(kong)制(zhi)技(ji)術(shu)，‘射頻(pin)(pin)導納’中 ‘射頻(pin)(pin)’既高(gao)頻(pin)(pin)，‘導納’的(de)含義為電學(xue)中阻(zu)抗(kang)的(de)倒(dao)數，它由阻(zu)性成份，容性成份，感(gan)性成份綜合而成，所(suo)以(yi)射頻(pin)(pin)導納技(ji)術(shu)可以(yi)理解為用(yong)高(gao)頻(pin)(pin)信(xin)號(hao)測量導納的(de)方法(fa)。

點位射頻導納技術與(yu)(yu)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)技術的(de)(de)重要區(qu)別是(shi)采用(yong)了三端技術和(he)測(ce)量參量的(de)(de)多樣性。電(dian)(dian)(dian)(dian)(dian)路單元中(zhong)心(xin)(xin)(xin)端測(ce)量信號(hao)與(yu)(yu)同(tong)(tong)軸(zhou)電(dian)(dian)(dian)(dian)(dian)纜(lan)中(zhong)心(xin)(xin)(xin)線連(lian)接(jie)，然后連(lian)接(jie)到(dao)傳(chuan)感(gan)器中(zhong)心(xin)(xin)(xin)端上(shang)。同(tong)(tong)時同(tong)(tong)軸(zhou)電(dian)(dian)(dian)(dian)(dian)纜(lan)屏蔽層(ceng)(ceng)懸浮在一個幅(fu)度(du)非常(chang)小(xiao)又非常(chang)穩定的(de)(de)，但與(yu)(yu)測(ce)量信號(hao)等(deng)電(dian)(dian)(dian)(dian)(dian)位，同(tong)(tong)相(xiang)位，同(tong)(tong)頻率，但又沒(mei)有(you)直接(jie)電(dian)(dian)(dian)(dian)(dian)氣(qi)關系既(ji)互相(xiang)隔(ge)離的(de)(de)電(dian)(dian)(dian)(dian)(dian)平上(shang)，其效果相(xiang)當于(yu)，測(ce)量信號(hao)經(jing)過(guo)(guo)一個增益為‘1’，驅動能力很(hen)強的(de)(de)同(tong)(tong)相(xiang)放大器，輸(shu)出(chu)(chu)與(yu)(yu)同(tong)(tong)軸(zhou)電(dian)(dian)(dian)(dian)(dian)纜(lan)屏蔽層(ceng)(ceng)相(xiang)連(lian)，然后再(zai)連(lian)到(dao)傳(chuan)感(gan)器的(de)(de)屏蔽層(ceng)(ceng)上(shang)。地線是(shi)電(dian)(dian)(dian)(dian)(dian)纜(lan)中(zhong)另一條(tiao)獨立的(de)(de)導線。由(you)于(yu)同(tong)(tong)軸(zhou)電(dian)(dian)(dian)(dian)(dian)纜(lan)的(de)(de)中(zhong)心(xin)(xin)(xin)線與(yu)(yu)屏蔽層(ceng)(ceng)存在上(shang)述關系，所(suo)以(yi)二者之間沒(mei)有(you)電(dian)(dian)(dian)(dian)(dian)位差，也就(jiu)沒(mei)有(you)電(dian)(dian)(dian)(dian)(dian)流流過(guo)(guo)，既(ji)沒(mei)有(you)電(dian)(dian)(dian)(dian)(dian)流從中(zhong)心(xin)(xin)(xin)線漏出(chu)(chu)來，相(xiang)當于(yu)二者之間沒(mei)有(you)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)或電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)等(deng)于(yu)零。因此(ci)電(dian)(dian)(dian)(dian)(dian)纜(lan)的(de)(de)溫度(du)效應，安裝電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)也就(jiu)不會產生影響。

對于(yu)傳(chuan)(chuan)感(gan)器(qi)(qi)(qi)(qi)上(shang)的(de)掛(gua)料(liao)(liao)影(ying)響(xiang)問題，采用一種新的(de)傳(chuan)(chuan)感(gan)器(qi)(qi)(qi)(qi)結構，五層(ceng)同(tong)心(xin)結構，見(jian)圖(tu)(tu)1.1傳(chuan)(chuan)感(gan)器(qi)(qi)(qi)(qi)結構：最里(li)層(ceng)是(shi)中心(xin)探桿，中間(jian)(jian)是(shi)屏(ping)蔽層(ceng)，最外面是(shi)接地(di)的(de)安裝(zhuang)螺紋，用絕緣層(ceng)將(jiang)其分(fen)別隔離起來(lai)。與(yu)同(tong)軸電(dian)(dian)纜(lan)的(de)情(qing)況是(shi)一樣的(de)，中心(xin)探桿與(yu)屏(ping)蔽層(ceng)之(zhi)間(jian)(jian)沒有(you)電(dian)(dian)勢(shi)差，即使傳(chuan)(chuan)感(gan)器(qi)(qi)(qi)(qi)上(shang)掛(gua)料(liao)(liao)阻抗(kang)較小，也不(bu)會有(you)電(dian)(dian)流(liu)(liu)(liu)(liu)流(liu)(liu)(liu)(liu)過(guo)，電(dian)(dian)子儀器(qi)(qi)(qi)(qi)測(ce)(ce)量(liang)(liang)(liang)(liang)的(de)僅僅是(shi)從傳(chuan)(chuan)感(gan)器(qi)(qi)(qi)(qi)中心(xin)到(dao)(dao)對面罐壁(bi)(地(di))的(de)電(dian)(dian)流(liu)(liu)(liu)(liu)，因為屏(ping)蔽層(ceng)能阻礙電(dian)(dian)流(liu)(liu)(liu)(liu)沿傳(chuan)(chuan)感(gan)器(qi)(qi)(qi)(qi)返回流(liu)(liu)(liu)(liu)向容(rong)(rong)器(qi)(qi)(qi)(qi)壁(bi)，因而對地(di)電(dian)(dian)流(liu)(liu)(liu)(liu)只(zhi)能經傳(chuan)(chuan)感(gan)器(qi)(qi)(qi)(qi)未端通(tong)過(guo)被測(ce)(ce)物(wu)料(liao)(liao)到(dao)(dao)對面容(rong)(rong)器(qi)(qi)(qi)(qi)壁(bi)。既UA=UB，IAB=(UA-UB)×Y=O見(jian)圖(tu)(tu)1.2測(ce)(ce)量(liang)(liang)(liang)(liang)的(de)等效(xiao)(xiao)圖(tu)(tu)。雖然屏(ping)蔽層(ceng)與(yu)容(rong)(rong)器(qi)(qi)(qi)(qi)壁(bi)之(zhi)間(jian)(jian)存在電(dian)(dian)勢(shi)差，兩者之(zhi)間(jian)(jian)有(you)電(dian)(dian)流(liu)(liu)(liu)(liu)流(liu)(liu)(liu)(liu)過(guo)，但(dan)該(gai)電(dian)(dian)流(liu)(liu)(liu)(liu)不(bu)被測(ce)(ce)量(liang)(liang)(liang)(liang)，不(bu)影(ying)響(xiang)測(ce)(ce)量(liang)(liang)(liang)(liang)結果。這樣就將(jiang)測(ce)(ce)量(liang)(liang)(liang)(liang)端保(bao)護起來(lai)，不(bu)受掛(gua)料(liao)(liao)的(de)影(ying)響(xiang)。只(zhi)有(you)容(rong)(rong)器(qi)(qi)(qi)(qi)中的(de)物(wu)料(liao)(liao)確實(shi)上(shang)升接觸(chu)到(dao)(dao)中心(xin)探桿時，通(tong)過(guo)被測(ce)(ce)物(wu)料(liao)(liao)，中心(xin)探桿與(yu)地(di)之(zhi)間(jian)(jian)才能形成被測(ce)(ce)電(dian)(dian)流(liu)(liu)(liu)(liu)，儀表檢測(ce)(ce)到(dao)(dao)該(gai)電(dian)(dian)流(liu)(liu)(liu)(liu)，產生(sheng)有(you)效(xiao)(xiao)輸出信號。射頻導納技術(shu)由于(yu)引入了(le)除電(dian)(dian)容(rong)(rong)以外地(di)測(ce)(ce)量(liang)(liang)(liang)(liang)參量(liang)(liang)(liang)(liang)，尤其是(shi)電(dian)(dian)阻參量(liang)(liang)(liang)(liang)，使得儀表量(liang)(liang)(liang)(liang)信號信噪比上(shang)升，大幅度的(de)提高了(le)儀表的(de)分(fen)辨力，準確性和可(ke)靠(kao)性；測(ce)(ce)量(liang)(liang)(liang)(liang)參量(liang)(liang)(liang)(liang)的(de)多(duo)樣性也有(you)力地(di)拓展(zhan)了(le)儀表的(de)可(ke)靠(kao)應用領域。

圖1.1傳(chuan)感器結構(gou)圖