產品列表
PROUCTS LIST
4-20mA電(dian)流(liu)本身就可(ke)以為變送(song)器(qi)供電(dian)。變送(song)器(qi)在電(dian)路中相當(dang)于(yu)一個特殊的(de)負載，特殊之處(chu)在于(yu)變送(song)器(qi)的(de)耗電(dian)電(dian)流(liu)在4~20mA之間根據傳感器(qi)輸出而(er)變化。顯示儀(yi)表(biao)只需要串(chuan)在電(dian)路中即可(ke)。這(zhe)種變送(song)器(qi)只需外接2根線(xian)，因而(er)被稱為兩線(xian)制變送(song)器(qi)。工(gong)業電(dian)流(liu)環標準下限(xian)為4mA，因此只要在量程范(fan)圍內，變送(song)器(qi)至少有4mA供電(dian)。這(zhe)使(shi)得兩線(xian)制傳感器(qi)的(de)設計成為可(ke)能。
在工業(ye)應用(yong)中(zhong)(zhong)，測量點一般在現場(chang)，而顯示設(she)備或者控制(zhi)設(she)備一般都在控制(zhi)室或控制(zhi)柜上。兩(liang)(liang)者之(zhi)間距離可能數十至數百(bai)米。按一百(bai)米距離計(ji)算，省去2根信號傳輸導線(xian)(xian)意味(wei)著成本(ben)降低近(jin)百(bai)元！另外(wai)四(si)線(xian)(xian)制(zhi)變(bian)送(song)(song)器和三線(xian)(xian)制(zhi)變(bian)送(song)(song)器因導線(xian)(xian)內電流不對稱(cheng)必須(xu)使用(yong)昂貴的屏蔽線(xian)(xian),而兩(liang)(liang)線(xian)(xian)制(zhi)變(bian)送(song)(song)器可使用(yong)非常便宜的的雙絞線(xian)(xian)導線(xian)(xian),因此(ci)在應用(yong)中(zhong)(zhong)兩(liang)(liang)線(xian)(xian)制(zhi)變(bian)送(song)(song)器必然是選擇。
差(cha)(cha)壓(ya)(ya)(ya)變(bian)送(song)(song)器(qi)(qi)是(shi)測量變(bian)送(song)(song)器(qi)(qi)兩(liang)端壓(ya)(ya)(ya)力之差(cha)(cha)的(de)變(bian)送(song)(song)器(qi)(qi)，輸出標準信號（如(ru) 4~20mA、0~5V）。差(cha)(cha)壓(ya)(ya)(ya)變(bian)送(song)(song)器(qi)(qi)與(yu)一(yi)般(ban)的(de)壓(ya)(ya)(ya)力變(bian)送(song)(song)器(qi)(qi)不同(tong)的(de)是(shi)它們均有2個壓(ya)(ya)(ya)力接口， 差(cha)(cha)壓(ya)(ya)(ya)變(bian)送(song)(song)器(qi)(qi)一(yi)般(ban)分(fen)為正(zheng)壓(ya)(ya)(ya)端和負壓(ya)(ya)(ya)端，一(yi)般(ban)情況下， 差(cha)(cha)壓(ya)(ya)(ya)變(bian)送(song)(song)器(qi)(qi)正(zheng)壓(ya)(ya)(ya)端的(de)壓(ya)(ya)(ya)力應大于負壓(ya)(ya)(ya)段(duan)壓(ya)(ya)(ya)力才能(neng)測量。
