返回系數為什么恒小于1？
電流(liu)繼電器是過流(liu)動(dong)作(zuo)，小于整定(ding)(ding)值后返(fan)(fan)回(hui)(hui)；為了避免電流(liu)在整定(ding)(ding)值附近時(shi)導致繼電器頻繁(fan)啟動(dong)返(fan)(fan)回(hui)(hui)，一般要設一個返(fan)(fan)回(hui)(hui)值，例如0.97，電流(liu)小于0.97才(cai)返(fan)(fan)回(hui)(hui)。因此返(fan)(fan)回(hui)(hui)值要小于1。
電流繼電器的功能及作用：
電(dian)(dian)(dian)流(liu)繼(ji)電(dian)(dian)(dian)器(qi)一般都(dou)有(you)能(neng)(neng)反映一定(ding)輸(shu)(shu)入(ru)變量（如電(dian)(dian)(dian)流(liu)、電(dian)(dian)(dian)壓、功率(lv)、阻抗、頻率(lv)、溫度、壓力(li)、速度、光等(deng)）的感(gan)應(ying)機構；有(you)能(neng)(neng)對被控(kong)(kong)(kong)(kong)電(dian)(dian)(dian)路實(shi)現(xian)通(tong)斷控(kong)(kong)(kong)(kong)制的執行機構；在(zai)電(dian)(dian)(dian)流(liu)繼(ji)電(dian)(dian)(dian)器(qi)的輸(shu)(shu)入(ru)部(bu)分(fen)和輸(shu)(shu)出部(bu)分(fen)之間(jian)，還(huan)有(you)對輸(shu)(shu)入(ru)量進行耦(ou)合隔離(li)，功能(neng)(neng)處(chu)理和對輸(shu)(shu)出部(bu)分(fen)進行驅動(dong)(dong)的中間(jian)機構。電(dian)(dian)(dian)流(liu)繼(ji)電(dian)(dian)(dian)器(qi)是(shi)具有(you)隔離(li)功能(neng)(neng)的自動(dong)(dong)開關(guan)元(yuan)件(jian)，廣泛應(ying)用(yong)于遙(yao)控(kong)(kong)(kong)(kong)、遙(yao)測(ce)、通(tong)訊、自動(dong)(dong)控(kong)(kong)(kong)(kong)制、 機電(dian)(dian)(dian)一體化(hua)及電(dian)(dian)(dian)力(li)電(dian)(dian)(dian)子設備中，是(shi)最重(zhong)要(yao)的控(kong)(kong)(kong)(kong)制元(yuan)件(jian)之一電(dian)(dian)(dian)流(liu)繼(ji)電(dian)(dian)(dian)器(qi)。作為(wei)控(kong)(kong)(kong)(kong)制元(yuan)件(jian)，概(gai)括起(qi)來(lai)，電(dian)(dian)(dian)流(liu)繼(ji)電(dian)(dian)(dian)器(qi)有(you)如下幾種作用(yong)：
（1）擴大(da)控(kong)制范圍：
繼(ji)電(dian)器目前已廣泛應(ying)用于計算機(ji)(ji)(ji)(ji)(ji)外圍接(jie)口設(she)備、恒溫(wen)系統(tong)、調(diao)(diao)溫(wen)、電(dian)爐(lu)加溫(wen)控(kong)(kong)(kong)制(zhi)(zhi)、電(dian)機(ji)(ji)(ji)(ji)(ji)控(kong)(kong)(kong)制(zhi)(zhi)、數控(kong)(kong)(kong)機(ji)(ji)(ji)(ji)(ji)械，遙控(kong)(kong)(kong)系統(tong)、工業自動(dong)化裝(zhuang)置；信號燈、調(diao)(diao)光、閃爍器、照(zhao)明舞臺燈光控(kong)(kong)(kong)制(zhi)(zhi)系統(tong)；儀器儀表、醫療器械、復印(yin)機(ji)(ji)(ji)(ji)(ji)、自動(dong)洗衣(yi)機(ji)(ji)(ji)(ji)(ji)；自動(dong)消防，保安系統(tong)，以及作(zuo)為電(dian)網功率因素補償的(de)(de)電(dian)力電(dian)容的(de)(de)切(qie)換開(kai)關等等，另外在化工、煤礦等需防爆(bao)、防潮(chao)、防腐蝕場合(he)中都有(you)大(da)量使用。例如，多觸(chu)點(dian)繼(ji)電(dian)器控(kong)(kong)(kong)制(zhi)(zhi)信號達到某一定值時， 可(ke)以按觸(chu)點(dian)組的(de)(de)不同形式，同時換接(jie)、開(kai)斷、接(jie)通(tong)多路電(dian)路。
（2）放大：
例(li)如，靈敏(min)型繼電器、等，用(yong)一個很(hen)微小的(de)控制量，可(ke)以控制很(hen)大功(gong)率的(de)電路。
（3）綜合信(xin)號：
例如，當(dang)多(duo)個控制信(xin)號按(an)規定(ding)的形式(shi)輸入多(duo)繞(rao)組繼(ji)電器時，經過比較綜合(he)， 達到預(yu)定(ding)的控制效果。
（4）自動、遙控、監(jian)測(ce)：
例如，自(zi)動裝置上的(de)電(dian)流繼(ji)電(dian)器(qi)(qi)與其他電(dian)器(qi)(qi)一起，可以組成程序控制(zhi)線路，從而實現自(zi)動化(hua)運(yun)行(xing)。
