不銹鋼管穿過(guo)磁化線圈時會發(fa)生如下兩(liang)種電(dian)磁感應現(xian)象：
1. 鋼管在橫向漏磁檢測磁化器內運動時，不銹鋼管切割磁力線而在其內部形成感生渦流。
2. 不銹(xiu)鋼管磁(ci)(ci)介(jie)質在管頭進入磁(ci)(ci)化線(xian)圈和管尾離開磁(ci)(ci)化線(xian)圈時(shi)，由于磁(ci)(ci)化線(xian)圈的(de)磁(ci)(ci)通總(zong)量發生(sheng)急劇變化，線(xian)圈中會產生(sheng)感生(sheng)電流。
一、鋼管內產生的感(gan)生渦流
不銹鋼管(guan)橫向(xiang)缺陷漏磁(ci)(ci)(ci)檢測(ce)方法采(cai)用穿過式線(xian)圈產生軸向(xiang)磁(ci)(ci)(ci)化(hua)場，并在磁(ci)(ci)(ci)化(hua)線(xian)圈內(nei)布(bu)置(zhi)檢測(ce)傳感器。當鋼管(guan)沿著(zhu)軸向(xiang)移動時，處于磁(ci)(ci)(ci)化(hua)線(xian)圈內(nei)的不銹鋼管(guan)段(duan)被磁(ci)(ci)(ci)化(hua)至(zhi)近(jin)飽和(he)狀態，如存(cun)在缺陷將在鋼管(guan)表(biao)面產生泄漏磁(ci)(ci)(ci)場，然后被磁(ci)(ci)(ci)敏感元件拾取并依次轉換為模(mo)擬信(xin)號和(he)數(shu)字信(xin)號，最終由計(ji)算機信(xin)號處理(li)系(xi)統實施報警和(he)分類。
如圖(tu)(tu)5-1所(suo)示，以鋼管(guan)(guan)(guan)軸線為(wei)中心建立圓柱坐標系。沿(yan)著鋼管(guan)(guan)(guan)運(yun)動方向，以磁(ci)化(hua)線圈為(wei)中心將鋼管(guan)(guan)(guan)劃分(fen)為(wei)進(jin)入(ru)(ru)區(qu)和離開(kai)區(qu)，在磁(ci)化(hua)線圈中施加(jia)如圖(tu)(tu)所(suo)示的磁(ci)化(hua)電(dian)流，磁(ci)力線分(fen)布特征為(wei)：在進(jin)入(ru)(ru)區(qu)磁(ci)力線從空氣(qi)中進(jin)入(ru)(ru)鋼管(guan)(guan)(guan)，并(bing)在磁(ci)化(hua)線圈中部匯聚(ju)，然(ran)后在離開(kai)區(qu)折射入(ru)(ru)空氣(qi)中。
如圖5-1所示，將磁感應強度矢量B(r,z)分解為軸向分量和徑向分量，即 B(r,z)=B2(r,z)+B,(r,z)
從圖5-1中(zhong)(zhong)可以看(kan)出，軸向分量B2(r,z)在(zai)進入(ru)區(qu)和離開(kai)區(qu)方(fang)向一致(zhi)，沿著鋼管(guan)前(qian)進方(fang)向，其強度(du)在(zai)進入(ru)區(qu)逐漸增大(da)，并在(zai)磁(ci)(ci)化線(xian)圈中(zhong)(zhong)部達(da)到極大(da)值，之后在(zai)離開(kai)區(qu)逐漸減(jian)小。徑向分量B,(r,z)在(zai)進入(ru)區(qu)方(fang)向指向鋼管(guan)內(nei)部，并在(zai)磁(ci)(ci)化線(xian)圈中(zhong)(zhong)部發生轉變，在(zai)離開(kai)區(qu)方(fang)向指向鋼管(guan)外部。
為(wei)了研(yan)究與鋼管同軸圓(yuan)(yuan)(yuan)環(huan)(huan)l(ro ,zo)的渦流分布，設圓(yuan)(yuan)(yuan)環(huan)(huan)半徑為(wei)ro，軸向(xiang)位置為(wei)200根據楞次定律，當圓(yuan)(yuan)(yuan)環(huan)(huan)移動時，軸向(xiang)分量(liang)B,(r,z)的強度變(bian)化導致圓(yuan)(yuan)(yuan)環(huan)(huan)磁通(tong)量(liang)也發生改變(bian)，從而在(zai)圓(yuan)(yuan)(yuan)環(huan)(huan)中產生感(gan)生電(dian)動勢。因磁化場為(wei)軸對稱，建立圓(yuan)(yuan)(yuan)環(huan)(huan)感(gan)應電(dian)動勢方(fang)程(cheng)為(wei)
根據式（5-3），沿鋼(gang)管(guan)前進(jin)方(fang)(fang)(fang)向(xiang)(xiang)，在(zai)(zai)進(jin)入區(qu)，軸向(xiang)(xiang)分(fen)(fen)量強(qiang)度逐漸增強(qiang)，感(gan)生(sheng)渦(wo)(wo)流(liu)(liu)方(fang)(fang)(fang)向(xiang)(xiang)與原磁(ci)化(hua)(hua)電流(liu)(liu)方(fang)(fang)(fang)向(xiang)(xiang)相反(fan)；在(zai)(zai)磁(ci)化(hua)(hua)線圈中間(jian)位置，由于軸向(xiang)(xiang)分(fen)(fen)量變化(hua)(hua)率為零，故此部位無感(gan)生(sheng)流(liu)(liu)產生(sheng)；在(zai)(zai)離開區(qu)，軸向(xiang)(xiang)分(fen)(fen)量強(qiang)度由中間(jian)最大值逐漸減小(xiao)，于是形成與原磁(ci)化(hua)(hua)電流(liu)(liu)方(fang)(fang)(fang)向(xiang)(xiang)相同的感(gan)生(sheng)渦(wo)(wo)流(liu)(liu)，最終(zhong)鋼(gang)管(guan)中感(gan)生(sheng)渦(wo)(wo)流(liu)(liu)分(fen)(fen)布(bu)如(ru)圖(tu)(tu)5-2a所示(shi)。如(ru)果改變磁(ci)化(hua)(hua)電流(liu)(liu)方(fang)(fang)(fang)向(xiang)(xiang)，根據式（5-3），同樣可得出鋼(gang)管(guan)內感(gan)生(sheng)渦(wo)(wo)流(liu)(liu)分(fen)(fen)布(bu)，如(ru)圖(tu)(tu)5-2b所示(shi)。
從圖5-2中可以(yi)看出，鋼管中感生(sheng)(sheng)電(dian)流(liu)(liu)分布方(fang)(fang)向(xiang)由磁(ci)化(hua)電(dian)流(liu)(liu)方(fang)(fang)向(xiang)和鋼管運動方(fang)(fang)向(xiang)共同決定(ding)。在(zai)(zai)進入區(qu)，鋼管中的(de)(de)感生(sheng)(sheng)渦流(liu)(liu)J1與磁(ci)化(hua)電(dian)流(liu)(liu)方(fang)(fang)向(xiang)相反；在(zai)(zai)磁(ci)化(hua)線(xian)圈中間位置無感生(sheng)(sheng)渦流(liu)(liu)產(chan)生(sheng)(sheng)；在(zai)(zai)離開區(qu)，感生(sheng)(sheng)渦流(liu)(liu)J2與磁(ci)化(hua)電(dian)流(liu)(liu)方(fang)(fang)向(xiang)相同。從而，在(zai)(zai)感生(sheng)(sheng)渦流(liu)(liu)產(chan)生(sheng)(sheng)的(de)(de)磁(ci)場作用下，鋼管的(de)(de)磁(ci)化(hua)狀態(tai)將發生(sheng)(sheng)變(bian)化(hua)。
建立如圖5-3所示(shi)的仿真模型。鋼(gang)管直徑為(wei)(wei)400mm、壁厚為(wei)(wei)15mm、長度(du)(du)為(wei)(wei)3000mm，材質(zhi)為(wei)(wei)25鋼(gang)（電導率為(wei)(wei)）。磁化(hua)(hua)線圈內(nei)徑為(wei)(wei)440mm、外徑為(wei)(wei)750mm、厚度(du)(du)為(wei)(wei)160mm，磁化(hua)(hua)電流(liu)密度(du)(du)iA／㎡，電流(liu)方向如圖5-3所示(shi)。
對(dui)不銹鋼管中(zhong)(zhong)的(de)感(gan)生(sheng)渦(wo)(wo)(wo)流(liu)(liu)(liu)(liu)分(fen)(fen)布(bu)進(jin)行仿真研究(jiu)。磁(ci)(ci)(ci)化(hua)(hua)線(xian)(xian)圈(quan)(quan)固定(ding)不動，鋼管運行速度(du)設置為(wei)1m／s，不銹鋼管從(cong)左端(duan)進(jin)人并向(xiang)右端(duan)移動，當鋼管中(zhong)(zhong)心(xin)與磁(ci)(ci)(ci)化(hua)(hua)線(xian)(xian)圈(quan)(quan)中(zhong)(zhong)心(xin)重合時獲(huo)取(qu)感(gan)生(sheng)渦(wo)(wo)(wo)流(liu)(liu)(liu)(liu)分(fen)(fen)布(bu)云圖(tu)，如圖(tu)5-4所示。從(cong)圖(tu)中(zhong)(zhong)可(ke)以(yi)看出，進(jin)入區的(de)感(gan)生(sheng)渦(wo)(wo)(wo)流(liu)(liu)(liu)(liu)方(fang)向(xiang)與磁(ci)(ci)(ci)化(hua)(hua)電流(liu)(liu)(liu)(liu)方(fang)向(xiang)相(xiang)(xiang)(xiang)(xiang)反，離(li)開(kai)區的(de)感(gan)生(sheng)渦(wo)(wo)(wo)流(liu)(liu)(liu)(liu)方(fang)向(xiang)與磁(ci)(ci)(ci)化(hua)(hua)電流(liu)(liu)(liu)(liu)方(fang)向(xiang)相(xiang)(xiang)(xiang)(xiang)同(tong)(tong)，在線(xian)(xian)圈(quan)(quan)中(zhong)(zhong)部感(gan)生(sheng)渦(wo)(wo)(wo)流(liu)(liu)(liu)(liu)幾(ji)乎為(wei)零。進(jin)入區和離(li)開(kai)區的(de)渦(wo)(wo)(wo)流(liu)(liu)(liu)(liu)分(fen)(fen)布(bu)相(xiang)(xiang)(xiang)(xiang)對(dui)于線(xian)(xian)圈(quan)(quan)呈對(dui)稱分(fen)(fen)布(bu)，方(fang)向(xiang)相(xiang)(xiang)(xiang)(xiang)反，強(qiang)度(du)基(ji)本相(xiang)(xiang)(xiang)(xiang)同(tong)(tong)，仿真結果與圖(tu)5-2所示的(de)渦(wo)(wo)(wo)流(liu)(liu)(liu)(liu)分(fen)(fen)布(bu)理論分(fen)(fen)析結論相(xiang)(xiang)(xiang)(xiang)同(tong)(tong)，其中(zhong)(zhong)感(gan)生(sheng)渦(wo)(wo)(wo)流(liu)(liu)(liu)(liu)最(zui)大值為(wei)1.4×105A/㎡。
為了研究感(gan)生(sheng)渦(wo)(wo)流(liu)與(yu)(yu)不(bu)銹鋼(gang)(gang)管(guan)運(yun)行(xing)速(su)(su)(su)度(du)(du)的(de)關系，分別取速(su)(su)(su)度(du)(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(xing)仿真。當鋼(gang)(gang)管(guan)中(zhong)部與(yu)(yu)磁化線圈重合時(shi)提取渦(wo)(wo)流(liu)密度(du)(du)最(zui)(zui)大值(zhi)和最(zui)(zui)小值(zhi)，繪制成(cheng)如圖5-5所示的(de)渦(wo)(wo)流(liu)密度(du)(du)與(yu)(yu)運(yun)行(xing)速(su)(su)(su)度(du)(du)關系曲線。從圖中(zhong)可以看(kan)出(chu)，感(gan)生(sheng)渦(wo)(wo)流(liu)與(yu)(yu)不(bu)銹鋼(gang)(gang)管(guan)運(yun)行(xing)速(su)(su)(su)度(du)(du)成(cheng)近似(si)正比關系。鋼(gang)(gang)管(guan)低(di)速(su)(su)(su)運(yun)動時(shi)感(gan)生(sheng)渦(wo)(wo)流(liu)很(hen)小，可忽略不(bu)計(ji)；當運(yun)行(xing)速(su)(su)(su)度(du)(du)增至(zhi)50m／s時(shi)，渦(wo)(wo)流(liu)密度(du)(du)為2。此時(shi)，感(gan)生(sheng)渦(wo)(wo)流(liu)已接近傳導電流(liu)密度(du)(du)。因此，高速(su)(su)(su)運(yun)動時(shi)，感(gan)生(sheng)渦(wo)(wo)流(liu)對鋼(gang)(gang)管(guan)漏磁檢(jian)測的(de)影響不(bu)可忽視。
二、磁化線圈中(zhong)產生的感生電流
當(dang)不銹鋼管端部進入和(he)(he)離(li)開磁化(hua)(hua)(hua)線(xian)圈(quan)時，線(xian)圈(quan)中(zhong)(zhong)的(de)(de)磁通(tong)(tong)量(liang)發生(sheng)變(bian)化(hua)(hua)(hua)而(er)產生(sheng)感(gan)生(sheng)電(dian)(dian)(dian)流(liu)。設磁化(hua)(hua)(hua)電(dian)(dian)(dian)源提供的(de)(de)電(dian)(dian)(dian)壓為(wei)Uo，磁化(hua)(hua)(hua)線(xian)圈(quan)電(dian)(dian)(dian)阻為(wei)R，則磁化(hua)(hua)(hua)電(dian)(dian)(dian)源在線(xian)圈(quan)中(zhong)(zhong)產生(sheng)的(de)(de)初始傳導電(dian)(dian)(dian)流(liu)為(wei)Io=Uo/RR。磁化(hua)(hua)(hua)線(xian)圈(quan)通(tong)(tong)過(guo)的(de)(de)磁通(tong)(tong)總量(liang)為(wei)Φ，當(dang)磁化(hua)(hua)(hua)線(xian)圈(quan)中(zhong)(zhong)磁通(tong)(tong)總量(liang)發生(sheng)變(bian)化(hua)(hua)(hua)時，根據楞次(ci)定(ding)律，線(xian)圈(quan)中(zhong)(zhong)將(jiang)產生(sheng)感(gan)生(sheng)電(dian)(dian)(dian)動勢，對應的(de)(de)感(gan)生(sheng)電(dian)(dian)(dian)流(liu)磁化(hua)(hua)(hua)線(xian)圈(quan)中(zhong)(zhong)通(tong)(tong)過(guo)的(de)(de)電(dian)(dian)(dian)流(liu)I為(wei)初始傳導電(dian)(dian)(dian)流(liu)和(he)(he)感(gan)生(sheng)電(dian)(dian)(dian)流(liu)之和(he)(he)，即
當線圈(quan)(quan)中沒有(you)鋼(gang)管時，磁(ci)(ci)(ci)化線圈(quan)(quan)磁(ci)(ci)(ci)通總(zong)量為線圈(quan)(quan)自身(shen)產(chan)生(sheng)的靜態磁(ci)(ci)(ci)通量，其與磁(ci)(ci)(ci)化電(dian)(dian)(dian)(dian)流(liu)強度成正比(bi)，當磁(ci)(ci)(ci)化電(dian)(dian)(dian)(dian)流(liu)不變(bian)時，線圈(quan)(quan)磁(ci)(ci)(ci)通總(zong)量也不發生(sheng)變(bian)化。此時線圈(quan)(quan)中通過的電(dian)(dian)(dian)(dian)流(liu)為磁(ci)(ci)(ci)化電(dian)(dian)(dian)(dian)源產(chan)生(sheng)的初始(shi)磁(ci)(ci)(ci)化傳導電(dian)(dian)(dian)(dian)流(liu)
當管頭進(jin)入(ru)磁化(hua)線圈時，具有高磁導率(lv)的(de)鋼管磁介質進(jin)入(ru)磁化(hua)線圈內(nei)(nei)部(bu)，使得線圈內(nei)(nei)部(bu)的(de)磁通(tong)總量增大(da)。根(gen)據式（5-4），磁化(hua)線圈中會(hui)產生與初始磁化(hua)傳(chuan)導電流(liu)方向相反(fan)的(de)感生電流(liu)，此(ci)時線圈中通(tong)過(guo)的(de)電流(liu)為，如圖5-6a所示。
當管體通過(guo)磁(ci)(ci)化(hua)線(xian)圈時，線(xian)圈內部磁(ci)(ci)介質總量及分(fen)布特性基本(ben)不變，從而線(xian)圈內部的(de)磁(ci)(ci)通總量也保(bao)持恒(heng)定。根據式（5-4），磁(ci)(ci)化(hua)線(xian)圈基本(ben)無感(gan)生(sheng)電(dian)流產生(sheng)，此(ci)時，磁(ci)(ci)化(hua)線(xian)圈中(zhong)通過(guo)的(de)電(dian)流與(yu)無鋼管時相同，為磁(ci)(ci)化(hua)電(dian)源產生(sheng)的(de)初始磁(ci)(ci)化(hua)傳導電(dian)流1＝，如圖5-6b所示。
當管(guan)尾離開磁(ci)(ci)化(hua)線(xian)(xian)(xian)圈(quan)(quan)時(shi)，由于線(xian)(xian)(xian)圈(quan)(quan)內部(bu)的高磁(ci)(ci)導率磁(ci)(ci)介質不(bu)斷(duan)減(jian)少，導致磁(ci)(ci)化(hua)線(xian)(xian)(xian)圈(quan)(quan)的磁(ci)(ci)通總量也(ye)不(bu)斷(duan)減(jian)少。根據式（5-4），磁(ci)(ci)化(hua)線(xian)(xian)(xian)圈(quan)(quan)中會產生與初始磁(ci)(ci)化(hua)傳導電流方向相同(tong)的感生電流，此時(shi)線(xian)(xian)(xian)圈(quan)(quan)中通過(guo)的電流為，如圖5-6c所示。
不銹(xiu)鋼(gang)管(guan)內的磁(ci)(ci)場包(bao)括：磁(ci)(ci)化(hua)(hua)線圈(quan)通過電(dian)流I產(chan)生的磁(ci)(ci)場和鋼(gang)管(guan)中(zhong)感生渦(wo)流J形成的磁(ci)(ci)場。磁(ci)(ci)化(hua)(hua)線圈(quan)的磁(ci)(ci)通總量(liang)包(bao)含了由(you)感生渦(wo)流J產(chan)生的部分磁(ci)(ci)通量(liang)，因此鋼(gang)管(guan)中(zhong)的渦(wo)流效(xiao)應會對磁(ci)(ci)化(hua)(hua)線圈(quan)中(zhong)的感生電(dian)流產(chan)生一定影(ying)響。
采用如圖(tu)5-3所(suo)示模型(xing)，進一步研究磁(ci)化(hua)(hua)線(xian)(xian)圈(quan)(quan)(quan)中(zhong)(zhong)產(chan)生(sheng)(sheng)(sheng)(sheng)的(de)感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流變化(hua)(hua)規律。其中(zhong)(zhong)，線(xian)(xian)圈(quan)(quan)(quan)匝數(shu)為(wei)600匝，磁(ci)化(hua)(hua)電(dian)流為(wei)5A。當鋼(gang)(gang)管(guan)(guan)(guan)管(guan)(guan)(guan)頭、管(guan)(guan)(guan)體(ti)和(he)管(guan)(guan)(guan)尾分(fen)別(bie)與磁(ci)化(hua)(hua)線(xian)(xian)圈(quan)(quan)(quan)耦合時(shi)(shi)提取磁(ci)化(hua)(hua)線(xian)(xian)圈(quan)(quan)(quan)內部產(chan)生(sheng)(sheng)(sheng)(sheng)的(de)感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流，如圖(tu)5-7所(suo)示。仿真分(fen)兩種(zhong)：一是考慮鋼(gang)(gang)管(guan)(guan)(guan)渦(wo)流效應(ying)(ying)時(shi)(shi)分(fen)析線(xian)(xian)圈(quan)(quan)(quan)感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流與運動(dong)速(su)度(du)(du)的(de)關系，二是忽(hu)略鋼(gang)(gang)管(guan)(guan)(guan)渦(wo)流效應(ying)(ying)而單獨(du)分(fen)析線(xian)(xian)圈(quan)(quan)(quan)感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流與鋼(gang)(gang)管(guan)(guan)(guan)運動(dong)速(su)度(du)(du)關系。分(fen)別(bie)取速(su)度(du)(du)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(huo)得如圖(tu)5-8所(suo)示的(de)磁(ci)化(hua)(hua)線(xian)(xian)圈(quan)(quan)(quan)感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流與運動(dong)速(su)度(du)(du)關系曲線(xian)(xian)。其中(zhong)(zhong)I1csI2cs和(he)I3cs分(fen)別(bie)為(wei)考慮鋼(gang)(gang)管(guan)(guan)(guan)渦(wo)流效應(ying)(ying)時(shi)(shi)在管(guan)(guan)(guan)頭、管(guan)(guan)(guan)體(ti)和(he)管(guan)(guan)(guan)尾處(chu)線(xian)(xian)圈(quan)(quan)(quan)中(zhong)(zhong)產(chan)生(sheng)(sheng)(sheng)(sheng)的(de)感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流，11cI2c和(he)I3c分(fen)別(bie)為(wei)忽(hu)略不銹鋼(gang)(gang)管(guan)(guan)(guan)渦(wo)流效應(ying)(ying)時(shi)(shi)磁(ci)化(hua)(hua)線(xian)(xian)圈(quan)(quan)(quan)中(zhong)(zhong)產(chan)生(sheng)(sheng)(sheng)(sheng)的(de)感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流。
圖5-8所示的(de)仿(fang)真結(jie)果與(yu)圖5-6所示的(de)理論(lun)分析結(jie)論(lun)相(xiang)(xiang)(xiang)同(tong)：當管(guan)頭進入磁(ci)(ci)化(hua)線(xian)(xian)圈(quan)(quan)(quan)(quan)(quan)時(shi)，線(xian)(xian)圈(quan)(quan)(quan)(quan)(quan)中(zhong)(zhong)(zhong)產(chan)(chan)(chan)生(sheng)(sheng)(sheng)(sheng)的(de)感(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)幅值為負，即與(yu)磁(ci)(ci)化(hua)電(dian)(dian)流(liu)(liu)方(fang)向相(xiang)(xiang)(xiang)反；當管(guan)體通過磁(ci)(ci)化(hua)線(xian)(xian)圈(quan)(quan)(quan)(quan)(quan)時(shi)，線(xian)(xian)圈(quan)(quan)(quan)(quan)(quan)中(zhong)(zhong)(zhong)基(ji)本無感(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)產(chan)(chan)(chan)生(sheng)(sheng)(sheng)(sheng)；隨(sui)著管(guan)尾(wei)離開(kai)磁(ci)(ci)化(hua)線(xian)(xian)圈(quan)(quan)(quan)(quan)(quan)，此(ci)時(shi)線(xian)(xian)圈(quan)(quan)(quan)(quan)(quan)中(zhong)(zhong)(zhong)產(chan)(chan)(chan)生(sheng)(sheng)(sheng)(sheng)與(yu)磁(ci)(ci)化(hua)電(dian)(dian)流(liu)(liu)方(fang)向相(xiang)(xiang)(xiang)同(tong)的(de)感(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)。根(gen)據楞次定律，線(xian)(xian)圈(quan)(quan)(quan)(quan)(quan)中(zhong)(zhong)(zhong)產(chan)(chan)(chan)生(sheng)(sheng)(sheng)(sheng)的(de)感(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)會(hui)阻(zu)礙線(xian)(xian)圈(quan)(quan)(quan)(quan)(quan)磁(ci)(ci)通量的(de)變(bian)化(hua)：當管(guan)頭進入磁(ci)(ci)化(hua)線(xian)(xian)圈(quan)(quan)(quan)(quan)(quan)時(shi)，線(xian)(xian)圈(quan)(quan)(quan)(quan)(quan)中(zhong)(zhong)(zhong)會(hui)產(chan)(chan)(chan)生(sheng)(sheng)(sheng)(sheng)反向感(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)來(lai)阻(zu)礙磁(ci)(ci)通量的(de)增(zeng)大；當管(guan)體與(yu)磁(ci)(ci)化(hua)線(xian)(xian)圈(quan)(quan)(quan)(quan)(quan)耦合時(shi)，由(you)于線(xian)(xian)圈(quan)(quan)(quan)(quan)(quan)磁(ci)(ci)通量基(ji)本不變(bian)而無感(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)產(chan)(chan)(chan)生(sheng)(sheng)(sheng)(sheng)；當管(guan)尾(wei)離開(kai)磁(ci)(ci)化(hua)線(xian)(xian)圈(quan)(quan)(quan)(quan)(quan)時(shi)，線(xian)(xian)圈(quan)(quan)(quan)(quan)(quan)中(zhong)(zhong)(zhong)會(hui)產(chan)(chan)(chan)生(sheng)(sheng)(sheng)(sheng)同(tong)向感(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)來(lai)阻(zu)礙磁(ci)(ci)通量的(de)減小。
另外(wai)，從圖5-8中可(ke)以看出，在運行速(su)度(du)較低(di)時(shi)(shi)，磁化(hua)線圈(quan)(quan)中感生電(dian)(dian)流隨著速(su)度(du)的(de)增(zeng)加(jia)而快(kuai)速(su)上升；當速(su)度(du)達(da)到一定幅(fu)值時(shi)(shi)，磁化(hua)線圈(quan)(quan)中的(de)感生電(dian)(dian)流基本(ben)保(bao)持不變。因為(wei)感生電(dian)(dian)流只能(neng)減緩磁化(hua)線圈(quan)(quan)磁通(tong)量的(de)變化(hua)速(su)度(du)，而不能(neng)改(gai)變磁通(tong)量的(de)變化(hua)趨勢。
從(cong)圖5-8中還(huan)可以看出，鋼(gang)管中的渦(wo)流會削弱(ruo)磁(ci)化(hua)線圈中產生的感生電流，根據楞次定(ding)律，鋼管中(zhong)(zhong)的(de)(de)渦(wo)流(liu)(liu)(liu)同(tong)樣會(hui)阻(zu)礙(ai)鋼管中(zhong)(zhong)磁通(tong)(tong)量(liang)的(de)(de)變化(hua)。當不銹鋼管進(jin)入和離(li)開(kai)磁化(hua)線(xian)(xian)圈(quan)時，鋼管中(zhong)(zhong)的(de)(de)磁通(tong)(tong)量(liang)變化(hua)規律同(tong)樣先增大后減小(xiao)。由(you)于磁化(hua)線(xian)(xian)圈(quan)磁通(tong)(tong)總量(liang)包(bao)含(han)了(le)不銹鋼管磁通(tong)(tong)量(liang)，所以(yi)，感(gan)(gan)生渦(wo)流(liu)(liu)(liu)在(zai)阻(zu)礙(ai)鋼管磁通(tong)(tong)量(liang)變化(hua)的(de)(de)同(tong)時也阻(zu)礙(ai)了(le)線(xian)(xian)圈(quan)磁通(tong)(tong)量(liang)的(de)(de)變化(hua)速率，最(zui)終削弱了(le)線(xian)(xian)圈(quan)感(gan)(gan)生電(dian)流(liu)(liu)(liu)的(de)(de)強度。
