不(bu)銹鋼管穿過磁(ci)(ci)化線圈(quan)時會發生如(ru)下(xia)兩種電磁(ci)(ci)感應現象：
1. 鋼管在橫向漏磁檢測磁化器內運動時，不銹(xiu)鋼管切割磁力線而在其內部形成感生渦流。
2. 不銹鋼管(guan)磁(ci)介質在(zai)管(guan)頭進入磁(ci)化(hua)(hua)線(xian)圈(quan)(quan)和(he)管(guan)尾離開磁(ci)化(hua)(hua)線(xian)圈(quan)(quan)時，由于磁(ci)化(hua)(hua)線(xian)圈(quan)(quan)的磁(ci)通(tong)總(zong)量發生(sheng)急劇變化(hua)(hua)，線(xian)圈(quan)(quan)中(zhong)會(hui)產生(sheng)感(gan)生(sheng)電流。
一、鋼管內產生的感生渦(wo)流(liu)
不銹鋼管橫向(xiang)缺(que)陷漏磁(ci)檢(jian)(jian)測方法采(cai)用穿過式線圈產生軸向(xiang)磁(ci)化場(chang)(chang)，并在磁(ci)化線圈內布置(zhi)檢(jian)(jian)測傳感器(qi)。當鋼管沿著軸向(xiang)移(yi)動(dong)時，處(chu)于磁(ci)化線圈內的不銹鋼管段被磁(ci)化至近(jin)飽和狀態，如存在缺(que)陷將在鋼管表面產生泄漏磁(ci)場(chang)(chang)，然后被磁(ci)敏(min)感元(yuan)件拾取(qu)并依(yi)次轉換為(wei)模擬信號和數字信號，最(zui)終由計(ji)算機信號處(chu)理(li)系統實施報(bao)警和分類。
如圖5-1所(suo)示，以鋼(gang)管(guan)(guan)軸線(xian)為中(zhong)(zhong)(zhong)心(xin)建(jian)立圓柱坐(zuo)標系。沿著鋼(gang)管(guan)(guan)運動(dong)方向，以磁(ci)化(hua)(hua)線(xian)圈為中(zhong)(zhong)(zhong)心(xin)將鋼(gang)管(guan)(guan)劃分為進入(ru)區(qu)(qu)和離(li)開區(qu)(qu)，在磁(ci)化(hua)(hua)線(xian)圈中(zhong)(zhong)(zhong)施(shi)加如圖所(suo)示的磁(ci)化(hua)(hua)電流，磁(ci)力線(xian)分布特征為：在進入(ru)區(qu)(qu)磁(ci)力線(xian)從空(kong)氣中(zhong)(zhong)(zhong)進入(ru)鋼(gang)管(guan)(guan)，并在磁(ci)化(hua)(hua)線(xian)圈中(zhong)(zhong)(zhong)部(bu)匯聚，然后在離(li)開區(qu)(qu)折射入(ru)空(kong)氣中(zhong)(zhong)(zhong)。
如圖(tu)5-1所(suo)示，將磁感應(ying)強(qiang)度矢量B(r,z)分解為軸向(xiang)分量和徑向(xiang)分量，即 B(r,z)=B2(r,z)+B,(r,z)
從圖(tu)5-1中(zhong)可以看出，軸(zhou)向(xiang)分量(liang)B2(r,z)在進入(ru)(ru)區和(he)離開區方(fang)(fang)向(xiang)一(yi)致，沿著鋼管前進方(fang)(fang)向(xiang)，其強度(du)在進入(ru)(ru)區逐(zhu)漸(jian)增大，并(bing)在磁(ci)(ci)化線圈中(zhong)部達到極大值，之后在離開區逐(zhu)漸(jian)減小(xiao)。徑(jing)向(xiang)分量(liang)B,(r,z)在進入(ru)(ru)區方(fang)(fang)向(xiang)指向(xiang)鋼管內部，并(bing)在磁(ci)(ci)化線圈中(zhong)部發生(sheng)轉變，在離開區方(fang)(fang)向(xiang)指向(xiang)鋼管外部。
為(wei)(wei)(wei)了研究與(yu)鋼管同軸圓(yuan)(yuan)環l(ro ,zo)的(de)渦流分布，設圓(yuan)(yuan)環半徑(jing)為(wei)(wei)(wei)ro，軸向位(wei)置(zhi)為(wei)(wei)(wei)200根(gen)據楞次定律(lv)，當圓(yuan)(yuan)環移動(dong)(dong)時，軸向分量B,(r,z)的(de)強度變(bian)化導致(zhi)圓(yuan)(yuan)環磁通(tong)量也發生改變(bian)，從而在圓(yuan)(yuan)環中產(chan)生感生電動(dong)(dong)勢(shi)。因磁化場為(wei)(wei)(wei)軸對稱，建立圓(yuan)(yuan)環感應電動(dong)(dong)勢(shi)方程為(wei)(wei)(wei)
根據(ju)式(shi)(shi)（5-3），沿(yan)鋼管前(qian)進方(fang)(fang)(fang)向(xiang)，在(zai)進入區(qu)，軸(zhou)向(xiang)分(fen)量強度(du)逐漸增強，感生(sheng)渦流方(fang)(fang)(fang)向(xiang)與(yu)原磁(ci)化電(dian)流方(fang)(fang)(fang)向(xiang)相反；在(zai)磁(ci)化線圈中(zhong)間位置，由(you)(you)于(yu)軸(zhou)向(xiang)分(fen)量變(bian)化率(lv)為零，故(gu)此部位無感生(sheng)流產(chan)生(sheng)；在(zai)離開區(qu)，軸(zhou)向(xiang)分(fen)量強度(du)由(you)(you)中(zhong)間最(zui)大值逐漸減小，于(yu)是(shi)形成與(yu)原磁(ci)化電(dian)流方(fang)(fang)(fang)向(xiang)相同(tong)的(de)感生(sheng)渦流，最(zui)終鋼管中(zhong)感生(sheng)渦流分(fen)布如圖5-2a所示。如果改變(bian)磁(ci)化電(dian)流方(fang)(fang)(fang)向(xiang)，根據(ju)式(shi)(shi)（5-3），同(tong)樣可(ke)得出鋼管內(nei)感生(sheng)渦流分(fen)布，如圖5-2b所示。
從圖5-2中(zhong)可(ke)以(yi)看出，鋼管中(zhong)感(gan)生電(dian)流(liu)(liu)(liu)分(fen)布方向(xiang)由(you)磁(ci)(ci)(ci)(ci)化(hua)電(dian)流(liu)(liu)(liu)方向(xiang)和鋼管運動方向(xiang)共同(tong)決(jue)定。在進入區，鋼管中(zhong)的(de)感(gan)生渦流(liu)(liu)(liu)J1與磁(ci)(ci)(ci)(ci)化(hua)電(dian)流(liu)(liu)(liu)方向(xiang)相反；在磁(ci)(ci)(ci)(ci)化(hua)線圈中(zhong)間位置無感(gan)生渦流(liu)(liu)(liu)產生；在離開區，感(gan)生渦流(liu)(liu)(liu)J2與磁(ci)(ci)(ci)(ci)化(hua)電(dian)流(liu)(liu)(liu)方向(xiang)相同(tong)。從而，在感(gan)生渦流(liu)(liu)(liu)產生的(de)磁(ci)(ci)(ci)(ci)場(chang)作用(yong)下(xia)，鋼管的(de)磁(ci)(ci)(ci)(ci)化(hua)狀態將發生變化(hua)。
建立如圖5-3所示的仿真模(mo)型。鋼(gang)管直(zhi)徑(jing)為(wei)400mm、壁厚為(wei)15mm、長度為(wei)3000mm，材質為(wei)25鋼(gang)（電(dian)導率為(wei)）。磁(ci)化(hua)線圈內徑(jing)為(wei)440mm、外徑(jing)為(wei)750mm、厚度為(wei)160mm，磁(ci)化(hua)電(dian)流(liu)密度iA／㎡，電(dian)流(liu)方向如圖5-3所示。
對(dui)(dui)不(bu)銹(xiu)(xiu)鋼(gang)管(guan)中(zhong)(zhong)(zhong)的(de)感(gan)生渦(wo)流(liu)(liu)(liu)(liu)分(fen)布(bu)(bu)進(jin)(jin)行(xing)仿(fang)(fang)真(zhen)(zhen)研(yan)究。磁(ci)化線圈固定不(bu)動(dong)，鋼(gang)管(guan)運行(xing)速度設置為(wei)1m／s，不(bu)銹(xiu)(xiu)鋼(gang)管(guan)從(cong)左端進(jin)(jin)人并(bing)向(xiang)(xiang)右端移(yi)動(dong)，當鋼(gang)管(guan)中(zhong)(zhong)(zhong)心與(yu)(yu)(yu)磁(ci)化線圈中(zhong)(zhong)(zhong)心重(zhong)合時獲(huo)取感(gan)生渦(wo)流(liu)(liu)(liu)(liu)分(fen)布(bu)(bu)云(yun)圖(tu)，如圖(tu)5-4所(suo)示。從(cong)圖(tu)中(zhong)(zhong)(zhong)可以看出，進(jin)(jin)入(ru)(ru)區的(de)感(gan)生渦(wo)流(liu)(liu)(liu)(liu)方(fang)向(xiang)(xiang)與(yu)(yu)(yu)磁(ci)化電流(liu)(liu)(liu)(liu)方(fang)向(xiang)(xiang)相(xiang)(xiang)反，離開(kai)(kai)區的(de)感(gan)生渦(wo)流(liu)(liu)(liu)(liu)方(fang)向(xiang)(xiang)與(yu)(yu)(yu)磁(ci)化電流(liu)(liu)(liu)(liu)方(fang)向(xiang)(xiang)相(xiang)(xiang)同，在線圈中(zhong)(zhong)(zhong)部感(gan)生渦(wo)流(liu)(liu)(liu)(liu)幾(ji)乎為(wei)零。進(jin)(jin)入(ru)(ru)區和(he)離開(kai)(kai)區的(de)渦(wo)流(liu)(liu)(liu)(liu)分(fen)布(bu)(bu)相(xiang)(xiang)對(dui)(dui)于線圈呈對(dui)(dui)稱分(fen)布(bu)(bu)，方(fang)向(xiang)(xiang)相(xiang)(xiang)反，強度基(ji)本相(xiang)(xiang)同，仿(fang)(fang)真(zhen)(zhen)結果(guo)與(yu)(yu)(yu)圖(tu)5-2所(suo)示的(de)渦(wo)流(liu)(liu)(liu)(liu)分(fen)布(bu)(bu)理論分(fen)析(xi)結論相(xiang)(xiang)同，其中(zhong)(zhong)(zhong)感(gan)生渦(wo)流(liu)(liu)(liu)(liu)最大值為(wei)1.4×105A/㎡。
為了研究感生(sheng)(sheng)(sheng)渦流(liu)(liu)與(yu)(yu)不(bu)銹鋼管(guan)(guan)運(yun)行速度(du)的(de)(de)關系(xi)(xi)，分(fen)別取(qu)速度(du)0.1m／s、1m/s、2m/s、5m/s、8m／s、10m／s、20m／s、30m／s、40m／s和50m／s進行仿真。當(dang)鋼管(guan)(guan)中部與(yu)(yu)磁化線圈重合時(shi)(shi)提取(qu)渦流(liu)(liu)密度(du)最(zui)大值和最(zui)小值，繪制成如(ru)圖5-5所示(shi)的(de)(de)渦流(liu)(liu)密度(du)與(yu)(yu)運(yun)行速度(du)關系(xi)(xi)曲線。從圖中可以看出，感生(sheng)(sheng)(sheng)渦流(liu)(liu)與(yu)(yu)不(bu)銹鋼管(guan)(guan)運(yun)行速度(du)成近似正比關系(xi)(xi)。鋼管(guan)(guan)低速運(yun)動時(shi)(shi)感生(sheng)(sheng)(sheng)渦流(liu)(liu)很小，可忽略不(bu)計(ji)；當(dang)運(yun)行速度(du)增至(zhi)50m／s時(shi)(shi)，渦流(liu)(liu)密度(du)為2。此時(shi)(shi)，感生(sheng)(sheng)(sheng)渦流(liu)(liu)已接近傳導(dao)電流(liu)(liu)密度(du)。因此，高(gao)速運(yun)動時(shi)(shi)，感生(sheng)(sheng)(sheng)渦流(liu)(liu)對鋼管(guan)(guan)漏(lou)磁檢測的(de)(de)影(ying)響不(bu)可忽視(shi)。
二、磁化線圈中(zhong)產生(sheng)的感(gan)生(sheng)電流
當(dang)不銹鋼管端部(bu)進入(ru)和離開磁(ci)化(hua)線(xian)圈(quan)(quan)(quan)時(shi)(shi)，線(xian)圈(quan)(quan)(quan)中(zhong)的(de)(de)磁(ci)通量(liang)發生(sheng)(sheng)變化(hua)而產(chan)生(sheng)(sheng)感生(sheng)(sheng)電(dian)(dian)流(liu)(liu)。設磁(ci)化(hua)電(dian)(dian)源提供的(de)(de)電(dian)(dian)壓(ya)為Uo，磁(ci)化(hua)線(xian)圈(quan)(quan)(quan)電(dian)(dian)阻為R，則磁(ci)化(hua)電(dian)(dian)源在線(xian)圈(quan)(quan)(quan)中(zhong)產(chan)生(sheng)(sheng)的(de)(de)初始傳(chuan)導(dao)(dao)電(dian)(dian)流(liu)(liu)為Io=Uo/RR。磁(ci)化(hua)線(xian)圈(quan)(quan)(quan)通過(guo)(guo)的(de)(de)磁(ci)通總量(liang)為Φ，當(dang)磁(ci)化(hua)線(xian)圈(quan)(quan)(quan)中(zhong)磁(ci)通總量(liang)發生(sheng)(sheng)變化(hua)時(shi)(shi)，根據楞次(ci)定(ding)律，線(xian)圈(quan)(quan)(quan)中(zhong)將產(chan)生(sheng)(sheng)感生(sheng)(sheng)電(dian)(dian)動(dong)勢，對應的(de)(de)感生(sheng)(sheng)電(dian)(dian)流(liu)(liu)磁(ci)化(hua)線(xian)圈(quan)(quan)(quan)中(zhong)通過(guo)(guo)的(de)(de)電(dian)(dian)流(liu)(liu)I為初始傳(chuan)導(dao)(dao)電(dian)(dian)流(liu)(liu)和感生(sheng)(sheng)電(dian)(dian)流(liu)(liu)之和，即(ji)
當(dang)(dang)線圈(quan)中沒有鋼管時，磁(ci)化(hua)(hua)線圈(quan)磁(ci)通總(zong)(zong)量為線圈(quan)自身產(chan)生(sheng)的(de)靜態磁(ci)通量，其與磁(ci)化(hua)(hua)電(dian)(dian)(dian)流強(qiang)度成正比，當(dang)(dang)磁(ci)化(hua)(hua)電(dian)(dian)(dian)流不(bu)變時，線圈(quan)磁(ci)通總(zong)(zong)量也不(bu)發生(sheng)變化(hua)(hua)。此(ci)時線圈(quan)中通過的(de)電(dian)(dian)(dian)流為磁(ci)化(hua)(hua)電(dian)(dian)(dian)源產(chan)生(sheng)的(de)初始磁(ci)化(hua)(hua)傳導電(dian)(dian)(dian)流
當管(guan)頭進(jin)入(ru)磁(ci)化(hua)線(xian)(xian)(xian)圈(quan)(quan)時，具有高磁(ci)導率的(de)鋼管(guan)磁(ci)介質進(jin)入(ru)磁(ci)化(hua)線(xian)(xian)(xian)圈(quan)(quan)內部(bu)，使得線(xian)(xian)(xian)圈(quan)(quan)內部(bu)的(de)磁(ci)通總量增大。根據式（5-4），磁(ci)化(hua)線(xian)(xian)(xian)圈(quan)(quan)中會產生(sheng)與初(chu)始磁(ci)化(hua)傳導電(dian)(dian)流方向相(xiang)反的(de)感生(sheng)電(dian)(dian)流，此(ci)時線(xian)(xian)(xian)圈(quan)(quan)中通過的(de)電(dian)(dian)流為，如圖5-6a所示。
當管(guan)體通(tong)過磁(ci)(ci)化(hua)(hua)線圈時(shi)，線圈內部磁(ci)(ci)介質總量(liang)及(ji)分布特性基本(ben)不變，從而(er)線圈內部的磁(ci)(ci)通(tong)總量(liang)也保持恒定(ding)。根據式(shi)（5-4），磁(ci)(ci)化(hua)(hua)線圈基本(ben)無感(gan)生電流產生，此時(shi)，磁(ci)(ci)化(hua)(hua)線圈中通(tong)過的電流與無鋼管(guan)時(shi)相同(tong)，為磁(ci)(ci)化(hua)(hua)電源(yuan)產生的初始磁(ci)(ci)化(hua)(hua)傳(chuan)導(dao)電流1＝，如圖5-6b所(suo)示。
當管(guan)尾離開磁(ci)化(hua)線圈(quan)(quan)時(shi)，由于線圈(quan)(quan)內部(bu)的高磁(ci)導率磁(ci)介質不斷減少，導致磁(ci)化(hua)線圈(quan)(quan)的磁(ci)通總(zong)量也不斷減少。根(gen)據式（5-4），磁(ci)化(hua)線圈(quan)(quan)中會(hui)產生與初始磁(ci)化(hua)傳導電流(liu)方向相(xiang)同的感生電流(liu)，此(ci)時(shi)線圈(quan)(quan)中通過(guo)的電流(liu)為，如圖5-6c所示(shi)。
不銹鋼(gang)(gang)管(guan)內(nei)的(de)(de)(de)磁(ci)(ci)場(chang)包括：磁(ci)(ci)化線(xian)圈通(tong)(tong)過電流I產生(sheng)(sheng)的(de)(de)(de)磁(ci)(ci)場(chang)和鋼(gang)(gang)管(guan)中(zhong)感生(sheng)(sheng)渦流J形成的(de)(de)(de)磁(ci)(ci)場(chang)。磁(ci)(ci)化線(xian)圈的(de)(de)(de)磁(ci)(ci)通(tong)(tong)總量包含了由感生(sheng)(sheng)渦流J產生(sheng)(sheng)的(de)(de)(de)部分磁(ci)(ci)通(tong)(tong)量，因此鋼(gang)(gang)管(guan)中(zhong)的(de)(de)(de)渦流效(xiao)應會對(dui)磁(ci)(ci)化線(xian)圈中(zhong)的(de)(de)(de)感生(sheng)(sheng)電流產生(sheng)(sheng)一定影響(xiang)。
采(cai)用如(ru)圖5-3所(suo)示(shi)模型，進一(yi)步研究磁化(hua)線(xian)(xian)(xian)圈中(zhong)產(chan)生的(de)感(gan)生電(dian)(dian)(dian)流(liu)變化(hua)規律(lv)。其中(zhong)，線(xian)(xian)(xian)圈匝數為(wei)(wei)600匝，磁化(hua)電(dian)(dian)(dian)流(liu)為(wei)(wei)5A。當鋼管(guan)(guan)(guan)(guan)(guan)管(guan)(guan)(guan)(guan)(guan)頭、管(guan)(guan)(guan)(guan)(guan)體和(he)管(guan)(guan)(guan)(guan)(guan)尾分(fen)別(bie)與(yu)磁化(hua)線(xian)(xian)(xian)圈耦合時(shi)(shi)提(ti)取(qu)磁化(hua)線(xian)(xian)(xian)圈內部產(chan)生的(de)感(gan)生電(dian)(dian)(dian)流(liu)，如(ru)圖5-7所(suo)示(shi)。仿真分(fen)兩種：一(yi)是考慮鋼管(guan)(guan)(guan)(guan)(guan)渦流(liu)效(xiao)應(ying)(ying)時(shi)(shi)分(fen)析線(xian)(xian)(xian)圈感(gan)生電(dian)(dian)(dian)流(liu)與(yu)運動速(su)(su)度的(de)關系，二是忽(hu)略(lve)(lve)鋼管(guan)(guan)(guan)(guan)(guan)渦流(liu)效(xiao)應(ying)(ying)而單(dan)獨(du)分(fen)析線(xian)(xian)(xian)圈感(gan)生電(dian)(dian)(dian)流(liu)與(yu)鋼管(guan)(guan)(guan)(guan)(guan)運動速(su)(su)度關系。分(fen)別(bie)取(qu)速(su)(su)度0.1m／s、1m／s、2m／s、5m／s、8m／s、10m／s、20m／s、30m／s、40m／和(he)50m／s進行仿真，獲得如(ru)圖5-8所(suo)示(shi)的(de)磁化(hua)線(xian)(xian)(xian)圈感(gan)生電(dian)(dian)(dian)流(liu)與(yu)運動速(su)(su)度關系曲線(xian)(xian)(xian)。其中(zhong)I1csI2cs和(he)I3cs分(fen)別(bie)為(wei)(wei)考慮鋼管(guan)(guan)(guan)(guan)(guan)渦流(liu)效(xiao)應(ying)(ying)時(shi)(shi)在管(guan)(guan)(guan)(guan)(guan)頭、管(guan)(guan)(guan)(guan)(guan)體和(he)管(guan)(guan)(guan)(guan)(guan)尾處(chu)線(xian)(xian)(xian)圈中(zhong)產(chan)生的(de)感(gan)生電(dian)(dian)(dian)流(liu)，11cI2c和(he)I3c分(fen)別(bie)為(wei)(wei)忽(hu)略(lve)(lve)不銹鋼管(guan)(guan)(guan)(guan)(guan)渦流(liu)效(xiao)應(ying)(ying)時(shi)(shi)磁化(hua)線(xian)(xian)(xian)圈中(zhong)產(chan)生的(de)感(gan)生電(dian)(dian)(dian)流(liu)。
圖5-8所(suo)示的(de)(de)(de)仿(fang)真(zhen)結果與(yu)圖5-6所(suo)示的(de)(de)(de)理論分(fen)析(xi)結論相同(tong)：當管(guan)頭進(jin)入磁(ci)(ci)化(hua)(hua)(hua)線(xian)(xian)圈(quan)(quan)(quan)時(shi)(shi)(shi)，線(xian)(xian)圈(quan)(quan)(quan)中(zhong)產(chan)生(sheng)(sheng)(sheng)(sheng)的(de)(de)(de)感(gan)生(sheng)(sheng)(sheng)(sheng)電流(liu)(liu)(liu)(liu)幅值為負，即(ji)與(yu)磁(ci)(ci)化(hua)(hua)(hua)電流(liu)(liu)(liu)(liu)方向(xiang)(xiang)相反；當管(guan)體(ti)通(tong)過磁(ci)(ci)化(hua)(hua)(hua)線(xian)(xian)圈(quan)(quan)(quan)時(shi)(shi)(shi)，線(xian)(xian)圈(quan)(quan)(quan)中(zhong)基(ji)本無(wu)感(gan)生(sheng)(sheng)(sheng)(sheng)電流(liu)(liu)(liu)(liu)產(chan)生(sheng)(sheng)(sheng)(sheng)；隨著(zhu)管(guan)尾離(li)(li)開磁(ci)(ci)化(hua)(hua)(hua)線(xian)(xian)圈(quan)(quan)(quan)，此(ci)時(shi)(shi)(shi)線(xian)(xian)圈(quan)(quan)(quan)中(zhong)產(chan)生(sheng)(sheng)(sheng)(sheng)與(yu)磁(ci)(ci)化(hua)(hua)(hua)電流(liu)(liu)(liu)(liu)方向(xiang)(xiang)相同(tong)的(de)(de)(de)感(gan)生(sheng)(sheng)(sheng)(sheng)電流(liu)(liu)(liu)(liu)。根(gen)據(ju)楞次定律，線(xian)(xian)圈(quan)(quan)(quan)中(zhong)產(chan)生(sheng)(sheng)(sheng)(sheng)的(de)(de)(de)感(gan)生(sheng)(sheng)(sheng)(sheng)電流(liu)(liu)(liu)(liu)會(hui)阻礙(ai)線(xian)(xian)圈(quan)(quan)(quan)磁(ci)(ci)通(tong)量(liang)的(de)(de)(de)變化(hua)(hua)(hua)：當管(guan)頭進(jin)入磁(ci)(ci)化(hua)(hua)(hua)線(xian)(xian)圈(quan)(quan)(quan)時(shi)(shi)(shi)，線(xian)(xian)圈(quan)(quan)(quan)中(zhong)會(hui)產(chan)生(sheng)(sheng)(sheng)(sheng)反向(xiang)(xiang)感(gan)生(sheng)(sheng)(sheng)(sheng)電流(liu)(liu)(liu)(liu)來阻礙(ai)磁(ci)(ci)通(tong)量(liang)的(de)(de)(de)增(zeng)大(da)；當管(guan)體(ti)與(yu)磁(ci)(ci)化(hua)(hua)(hua)線(xian)(xian)圈(quan)(quan)(quan)耦合時(shi)(shi)(shi)，由于線(xian)(xian)圈(quan)(quan)(quan)磁(ci)(ci)通(tong)量(liang)基(ji)本不變而(er)無(wu)感(gan)生(sheng)(sheng)(sheng)(sheng)電流(liu)(liu)(liu)(liu)產(chan)生(sheng)(sheng)(sheng)(sheng)；當管(guan)尾離(li)(li)開磁(ci)(ci)化(hua)(hua)(hua)線(xian)(xian)圈(quan)(quan)(quan)時(shi)(shi)(shi)，線(xian)(xian)圈(quan)(quan)(quan)中(zhong)會(hui)產(chan)生(sheng)(sheng)(sheng)(sheng)同(tong)向(xiang)(xiang)感(gan)生(sheng)(sheng)(sheng)(sheng)電流(liu)(liu)(liu)(liu)來阻礙(ai)磁(ci)(ci)通(tong)量(liang)的(de)(de)(de)減小。
另外，從圖5-8中可以看出，在(zai)運行速(su)度較低(di)時，磁(ci)化(hua)線圈(quan)(quan)中感生電流(liu)隨著速(su)度的增加(jia)而(er)快速(su)上升；當(dang)速(su)度達到一定幅值時，磁(ci)化(hua)線圈(quan)(quan)中的感生電流(liu)基本保(bao)持不變(bian)。因為感生電流(liu)只能減緩(huan)磁(ci)化(hua)線圈(quan)(quan)磁(ci)通量(liang)的變(bian)化(hua)速(su)度，而(er)不能改變(bian)磁(ci)通量(liang)的變(bian)化(hua)趨勢。
從圖5-8中還可以(yi)看出(chu)，鋼(gang)管中的渦流會削弱(ruo)磁(ci)化線圈中產生的感生電流，根據楞次定律，鋼(gang)管(guan)中的(de)渦流(liu)同(tong)(tong)(tong)樣會阻(zu)礙鋼(gang)管(guan)中磁通(tong)(tong)量(liang)的(de)變(bian)化(hua)。當(dang)不銹鋼(gang)管(guan)進入和離開磁化(hua)線(xian)圈時(shi)，鋼(gang)管(guan)中的(de)磁通(tong)(tong)量(liang)變(bian)化(hua)規律同(tong)(tong)(tong)樣先(xian)增大后(hou)減小。由于磁化(hua)線(xian)圈磁通(tong)(tong)總量(liang)包含了(le)不銹鋼(gang)管(guan)磁通(tong)(tong)量(liang)，所(suo)以，感生(sheng)(sheng)渦流(liu)在阻(zu)礙鋼(gang)管(guan)磁通(tong)(tong)量(liang)變(bian)化(hua)的(de)同(tong)(tong)(tong)時(shi)也(ye)阻(zu)礙了(le)線(xian)圈磁通(tong)(tong)量(liang)的(de)變(bian)化(hua)速率，最終削弱(ruo)了(le)線(xian)圈感生(sheng)(sheng)電(dian)流(liu)的(de)強度。
