不銹(xiu)鋼管(guan)穿(chuan)過磁化(hua)線圈時會發生如下(xia)兩種電磁感應現(xian)象(xiang)：

 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. 不銹鋼(gang)管磁(ci)(ci)介質(zhi)在管頭(tou)進(jin)入(ru)磁(ci)(ci)化線圈和管尾(wei)離開磁(ci)(ci)化線圈時，由于磁(ci)(ci)化線圈的磁(ci)(ci)通總量發(fa)生(sheng)急劇(ju)變化，線圈中會產生(sheng)感生(sheng)電流。

一、鋼管內產生(sheng)(sheng)的感生(sheng)(sheng)渦流

  不(bu)銹鋼管橫向(xiang)缺陷漏(lou)磁檢(jian)測方(fang)法采用(yong)穿過式線(xian)圈產生軸向(xiang)磁化(hua)場，并(bing)在磁化(hua)線(xian)圈內(nei)布置檢(jian)測傳感(gan)器。當鋼管沿著軸向(xiang)移動(dong)時(shi)，處(chu)于磁化(hua)線(xian)圈內(nei)的(de)不(bu)銹鋼管段被磁化(hua)至近飽和(he)狀態，如存在缺陷將在鋼管表(biao)面產生泄漏(lou)磁場，然(ran)后被磁敏(min)感(gan)元(yuan)件拾(shi)取并(bing)依次轉換為模(mo)擬信號(hao)(hao)(hao)和(he)數字信號(hao)(hao)(hao)，最終由(you)計算機信號(hao)(hao)(hao)處(chu)理系統(tong)實施報警和(he)分類。

  如圖5-1所示(shi)，以鋼管軸(zhou)線(xian)為(wei)中(zhong)(zhong)(zhong)(zhong)心建立圓柱坐標系。沿著鋼管運動(dong)方向，以磁(ci)(ci)化(hua)線(xian)圈(quan)為(wei)中(zhong)(zhong)(zhong)(zhong)心將鋼管劃分(fen)(fen)為(wei)進(jin)入區(qu)和(he)離開(kai)區(qu)，在(zai)磁(ci)(ci)化(hua)線(xian)圈(quan)中(zhong)(zhong)(zhong)(zhong)施加如圖所示(shi)的(de)磁(ci)(ci)化(hua)電流，磁(ci)(ci)力線(xian)分(fen)(fen)布特征為(wei)：在(zai)進(jin)入區(qu)磁(ci)(ci)力線(xian)從(cong)空氣中(zhong)(zhong)(zhong)(zhong)進(jin)入鋼管，并在(zai)磁(ci)(ci)化(hua)線(xian)圈(quan)中(zhong)(zhong)(zhong)(zhong)部匯聚，然后(hou)在(zai)離開(kai)區(qu)折(zhe)射(she)入空氣中(zhong)(zhong)(zhong)(zhong)。

  如圖(tu)5-1所(suo)示，將磁感應強度(du)矢量(liang)(liang)B(r,z)分(fen)解(jie)為軸向分(fen)量(liang)(liang)和徑向分(fen)量(liang)(liang)，即  B(r,z)=B2(r,z)+B,(r,z)

  從圖5-1中(zhong)可以(yi)看出，軸向(xiang)分量(liang)(liang)B2(r,z)在(zai)(zai)進(jin)入區和離(li)開(kai)區方向(xiang)一(yi)致(zhi)，沿(yan)著鋼(gang)(gang)管前進(jin)方向(xiang)，其強度在(zai)(zai)進(jin)入區逐漸(jian)增大，并在(zai)(zai)磁(ci)化(hua)線圈中(zhong)部達到(dao)極大值(zhi)，之后在(zai)(zai)離(li)開(kai)區逐漸(jian)減(jian)小。徑向(xiang)分量(liang)(liang)B,(r,z)在(zai)(zai)進(jin)入區方向(xiang)指向(xiang)鋼(gang)(gang)管內部，并在(zai)(zai)磁(ci)化(hua)線圈中(zhong)部發(fa)生(sheng)轉(zhuan)變，在(zai)(zai)離(li)開(kai)區方向(xiang)指向(xiang)鋼(gang)(gang)管外部。

  為(wei)了研究(jiu)與鋼管(guan)同軸(zhou)圓(yuan)(yuan)環(huan)l(ro ,zo)的渦流分布，設圓(yuan)(yuan)環(huan)半(ban)徑為(wei)ro，軸(zhou)向(xiang)位置為(wei)200根(gen)據楞次定律，當圓(yuan)(yuan)環(huan)移動(dong)時，軸(zhou)向(xiang)分量(liang)B,(r,z)的強度變化導致圓(yuan)(yuan)環(huan)磁通量(liang)也發生(sheng)改變，從而(er)在圓(yuan)(yuan)環(huan)中產生(sheng)感生(sheng)電(dian)動(dong)勢(shi)。因磁化場為(wei)軸(zhou)對稱，建立圓(yuan)(yuan)環(huan)感應電(dian)動(dong)勢(shi)方程為(wei)

  根據式（5-3），沿(yan)鋼(gang)管(guan)(guan)前進(jin)方(fang)向，在進(jin)入區(qu)(qu)，軸(zhou)向分量(liang)強度(du)逐(zhu)漸(jian)增強，感(gan)(gan)(gan)(gan)生(sheng)(sheng)渦(wo)(wo)流(liu)方(fang)向與原磁(ci)化(hua)電(dian)流(liu)方(fang)向相(xiang)反；在磁(ci)化(hua)線(xian)圈中(zhong)間位置(zhi)，由(you)于軸(zhou)向分量(liang)變化(hua)率為零，故(gu)此部位無感(gan)(gan)(gan)(gan)生(sheng)(sheng)流(liu)產生(sheng)(sheng)；在離開(kai)區(qu)(qu)，軸(zhou)向分量(liang)強度(du)由(you)中(zhong)間最(zui)大(da)值逐(zhu)漸(jian)減小，于是形成與原磁(ci)化(hua)電(dian)流(liu)方(fang)向相(xiang)同(tong)的感(gan)(gan)(gan)(gan)生(sheng)(sheng)渦(wo)(wo)流(liu)，最(zui)終(zhong)鋼(gang)管(guan)(guan)中(zhong)感(gan)(gan)(gan)(gan)生(sheng)(sheng)渦(wo)(wo)流(liu)分布如圖5-2a所示。如果改(gai)變磁(ci)化(hua)電(dian)流(liu)方(fang)向，根據式（5-3），同(tong)樣可(ke)得出鋼(gang)管(guan)(guan)內感(gan)(gan)(gan)(gan)生(sheng)(sheng)渦(wo)(wo)流(liu)分布，如圖5-2b所示。

  從(cong)圖5-2中可以看出，鋼(gang)(gang)(gang)管(guan)中感(gan)生(sheng)(sheng)電流(liu)分(fen)布方(fang)向由磁(ci)(ci)(ci)化(hua)電流(liu)方(fang)向和鋼(gang)(gang)(gang)管(guan)運動(dong)方(fang)向共(gong)同決(jue)定。在(zai)進入區(qu)，鋼(gang)(gang)(gang)管(guan)中的感(gan)生(sheng)(sheng)渦(wo)流(liu)J1與磁(ci)(ci)(ci)化(hua)電流(liu)方(fang)向相反；在(zai)磁(ci)(ci)(ci)化(hua)線圈中間位置無感(gan)生(sheng)(sheng)渦(wo)流(liu)產(chan)生(sheng)(sheng)；在(zai)離(li)開區(qu)，感(gan)生(sheng)(sheng)渦(wo)流(liu)J2與磁(ci)(ci)(ci)化(hua)電流(liu)方(fang)向相同。從(cong)而，在(zai)感(gan)生(sheng)(sheng)渦(wo)流(liu)產(chan)生(sheng)(sheng)的磁(ci)(ci)(ci)場作用下，鋼(gang)(gang)(gang)管(guan)的磁(ci)(ci)(ci)化(hua)狀態將(jiang)發生(sheng)(sheng)變化(hua)。

  建立(li)如(ru)圖5-3所(suo)示的仿真(zhen)模型。鋼管直(zhi)徑為(wei)400mm、壁(bi)厚(hou)為(wei)15mm、長度(du)為(wei)3000mm，材質為(wei)25鋼（電導率為(wei)）。磁化(hua)線(xian)圈內徑為(wei)440mm、外徑為(wei)750mm、厚(hou)度(du)為(wei)160mm，磁化(hua)電流(liu)密度(du)iA／㎡，電流(liu)方向如(ru)圖5-3所(suo)示。

  對不(bu)銹鋼(gang)管(guan)中(zhong)的(de)感(gan)(gan)生(sheng)渦(wo)(wo)流(liu)分(fen)(fen)布進(jin)行仿真研究。磁化(hua)(hua)線(xian)圈固定不(bu)動，鋼(gang)管(guan)運行速度(du)設置(zhi)為1m／s，不(bu)銹鋼(gang)管(guan)從(cong)左端進(jin)人并向(xiang)(xiang)(xiang)右端移動，當鋼(gang)管(guan)中(zhong)心與(yu)(yu)(yu)磁化(hua)(hua)線(xian)圈中(zhong)心重(zhong)合時(shi)獲取感(gan)(gan)生(sheng)渦(wo)(wo)流(liu)分(fen)(fen)布云圖(tu)(tu)，如圖(tu)(tu)5-4所(suo)示。從(cong)圖(tu)(tu)中(zhong)可(ke)以看出，進(jin)入區的(de)感(gan)(gan)生(sheng)渦(wo)(wo)流(liu)方(fang)向(xiang)(xiang)(xiang)與(yu)(yu)(yu)磁化(hua)(hua)電流(liu)方(fang)向(xiang)(xiang)(xiang)相(xiang)(xiang)反(fan)，離開區的(de)感(gan)(gan)生(sheng)渦(wo)(wo)流(liu)方(fang)向(xiang)(xiang)(xiang)與(yu)(yu)(yu)磁化(hua)(hua)電流(liu)方(fang)向(xiang)(xiang)(xiang)相(xiang)(xiang)同，在線(xian)圈中(zhong)部感(gan)(gan)生(sheng)渦(wo)(wo)流(liu)幾乎(hu)為零。進(jin)入區和離開區的(de)渦(wo)(wo)流(liu)分(fen)(fen)布相(xiang)(xiang)對于線(xian)圈呈對稱分(fen)(fen)布，方(fang)向(xiang)(xiang)(xiang)相(xiang)(xiang)反(fan)，強度(du)基本相(xiang)(xiang)同，仿真結(jie)果與(yu)(yu)(yu)圖(tu)(tu)5-2所(suo)示的(de)渦(wo)(wo)流(liu)分(fen)(fen)布理論分(fen)(fen)析結(jie)論相(xiang)(xiang)同，其(qi)中(zhong)感(gan)(gan)生(sheng)渦(wo)(wo)流(liu)最(zui)大(da)值為1.4×105A/㎡。

  為(wei)了研究感生(sheng)渦(wo)(wo)(wo)流(liu)與(yu)(yu)不銹鋼(gang)(gang)管(guan)運(yun)行速(su)度(du)的關(guan)(guan)系，分(fen)別取速(su)度(du)0.1m／s、1m/s、2m/s、5m/s、8m／s、10m／s、20m／s、30m／s、40m／s和(he)50m／s進行仿真。當(dang)鋼(gang)(gang)管(guan)中部(bu)與(yu)(yu)磁(ci)化線(xian)圈重(zhong)合時(shi)(shi)提取渦(wo)(wo)(wo)流(liu)密(mi)(mi)度(du)最大值和(he)最小值，繪制成如圖(tu)5-5所示的渦(wo)(wo)(wo)流(liu)密(mi)(mi)度(du)與(yu)(yu)運(yun)行速(su)度(du)關(guan)(guan)系曲線(xian)。從(cong)圖(tu)中可以(yi)看出，感生(sheng)渦(wo)(wo)(wo)流(liu)與(yu)(yu)不銹鋼(gang)(gang)管(guan)運(yun)行速(su)度(du)成近(jin)似(si)正比關(guan)(guan)系。鋼(gang)(gang)管(guan)低(di)速(su)運(yun)動(dong)時(shi)(shi)感生(sheng)渦(wo)(wo)(wo)流(liu)很小，可忽略不計；當(dang)運(yun)行速(su)度(du)增至50m／s時(shi)(shi)，渦(wo)(wo)(wo)流(liu)密(mi)(mi)度(du)為(wei)2。此時(shi)(shi)，感生(sheng)渦(wo)(wo)(wo)流(liu)已(yi)接近(jin)傳導電流(liu)密(mi)(mi)度(du)。因此，高速(su)運(yun)動(dong)時(shi)(shi)，感生(sheng)渦(wo)(wo)(wo)流(liu)對鋼(gang)(gang)管(guan)漏磁(ci)檢測的影響不可忽視。

二、磁化線圈中產生的(de)感生電流

  當不銹鋼(gang)管端部進入和(he)離開(kai)磁(ci)(ci)(ci)(ci)(ci)化線(xian)圈(quan)時(shi)，線(xian)圈(quan)中的(de)磁(ci)(ci)(ci)(ci)(ci)通(tong)量發生變化而產生感(gan)生電(dian)(dian)流(liu)。設磁(ci)(ci)(ci)(ci)(ci)化電(dian)(dian)源提供的(de)電(dian)(dian)壓為Uo，磁(ci)(ci)(ci)(ci)(ci)化線(xian)圈(quan)電(dian)(dian)阻為R，則磁(ci)(ci)(ci)(ci)(ci)化電(dian)(dian)源在線(xian)圈(quan)中產生的(de)初始傳導電(dian)(dian)流(liu)為Io=Uo/RR。磁(ci)(ci)(ci)(ci)(ci)化線(xian)圈(quan)通(tong)過(guo)的(de)磁(ci)(ci)(ci)(ci)(ci)通(tong)總(zong)量為Φ，當磁(ci)(ci)(ci)(ci)(ci)化線(xian)圈(quan)中磁(ci)(ci)(ci)(ci)(ci)通(tong)總(zong)量發生變化時(shi)，根據楞次(ci)定律，線(xian)圈(quan)中將產生感(gan)生電(dian)(dian)動勢，對應的(de)感(gan)生電(dian)(dian)流(liu)磁(ci)(ci)(ci)(ci)(ci)化線(xian)圈(quan)中通(tong)過(guo)的(de)電(dian)(dian)流(liu)I為初始傳導電(dian)(dian)流(liu)和(he)感(gan)生電(dian)(dian)流(liu)之和(he)，即

  當線(xian)(xian)(xian)圈中沒有鋼(gang)管時(shi)，磁(ci)(ci)化(hua)線(xian)(xian)(xian)圈磁(ci)(ci)通(tong)總量為線(xian)(xian)(xian)圈自身產生(sheng)的靜態(tai)磁(ci)(ci)通(tong)量，其與磁(ci)(ci)化(hua)電流(liu)強度成正(zheng)比，當磁(ci)(ci)化(hua)電流(liu)不(bu)變(bian)時(shi)，線(xian)(xian)(xian)圈磁(ci)(ci)通(tong)總量也不(bu)發(fa)生(sheng)變(bian)化(hua)。此時(shi)線(xian)(xian)(xian)圈中通(tong)過的電流(liu)為磁(ci)(ci)化(hua)電源產生(sheng)的初(chu)始磁(ci)(ci)化(hua)傳(chuan)導電流(liu)

  當管(guan)頭進入磁(ci)化(hua)線(xian)圈(quan)(quan)時，具(ju)有高磁(ci)導率的(de)鋼管(guan)磁(ci)介質進入磁(ci)化(hua)線(xian)圈(quan)(quan)內(nei)部(bu)，使得線(xian)圈(quan)(quan)內(nei)部(bu)的(de)磁(ci)通(tong)總量增大。根據式（5-4），磁(ci)化(hua)線(xian)圈(quan)(quan)中(zhong)會產生與(yu)初始磁(ci)化(hua)傳導電流(liu)方向相反的(de)感生電流(liu)，此時線(xian)圈(quan)(quan)中(zhong)通(tong)過(guo)的(de)電流(liu)為，如圖5-6a所(suo)示。

  當管體通過(guo)磁(ci)(ci)化(hua)線(xian)圈時(shi)(shi)，線(xian)圈內部磁(ci)(ci)介(jie)質總量及分布特性基本不變(bian)，從而線(xian)圈內部的(de)磁(ci)(ci)通總量也保(bao)持恒定。根據式（5-4），磁(ci)(ci)化(hua)線(xian)圈基本無感生(sheng)電流產生(sheng)，此時(shi)(shi)，磁(ci)(ci)化(hua)線(xian)圈中通過(guo)的(de)電流與無鋼(gang)管時(shi)(shi)相同，為磁(ci)(ci)化(hua)電源產生(sheng)的(de)初始磁(ci)(ci)化(hua)傳導(dao)電流1＝，如(ru)圖5-6b所示。

  當管尾(wei)離開磁化線(xian)(xian)圈(quan)時，由(you)于線(xian)(xian)圈(quan)內部的(de)高磁導(dao)率磁介質不斷減少(shao)，導(dao)致(zhi)磁化線(xian)(xian)圈(quan)的(de)磁通總量也不斷減少(shao)。根據(ju)式（5-4），磁化線(xian)(xian)圈(quan)中會(hui)產生(sheng)與初始磁化傳(chuan)導(dao)電(dian)(dian)流(liu)(liu)方向相同的(de)感(gan)生(sheng)電(dian)(dian)流(liu)(liu)，此時線(xian)(xian)圈(quan)中通過的(de)電(dian)(dian)流(liu)(liu)為，如圖5-6c所示。

  不銹(xiu)鋼管(guan)內(nei)的磁(ci)(ci)場(chang)包括：磁(ci)(ci)化(hua)(hua)線(xian)圈(quan)(quan)通(tong)過電流I產(chan)(chan)生(sheng)(sheng)的磁(ci)(ci)場(chang)和鋼管(guan)中(zhong)(zhong)感生(sheng)(sheng)渦流J形成的磁(ci)(ci)場(chang)。磁(ci)(ci)化(hua)(hua)線(xian)圈(quan)(quan)的磁(ci)(ci)通(tong)總(zong)量包含(han)了由感生(sheng)(sheng)渦流J產(chan)(chan)生(sheng)(sheng)的部分磁(ci)(ci)通(tong)量，因(yin)此鋼管(guan)中(zhong)(zhong)的渦流效(xiao)應會對磁(ci)(ci)化(hua)(hua)線(xian)圈(quan)(quan)中(zhong)(zhong)的感生(sheng)(sheng)電流產(chan)(chan)生(sheng)(sheng)一(yi)定影響(xiang)。

  采用如圖(tu)5-3所示(shi)模(mo)型，進一步研(yan)究磁(ci)化(hua)線(xian)(xian)圈(quan)(quan)中(zhong)(zhong)(zhong)產(chan)生(sheng)的(de)(de)感(gan)(gan)(gan)生(sheng)電(dian)(dian)流(liu)(liu)(liu)(liu)變化(hua)規律。其中(zhong)(zhong)(zhong)，線(xian)(xian)圈(quan)(quan)匝數為600匝，磁(ci)化(hua)電(dian)(dian)流(liu)(liu)(liu)(liu)為5A。當鋼(gang)(gang)(gang)管(guan)(guan)管(guan)(guan)頭、管(guan)(guan)體(ti)和(he)管(guan)(guan)尾分別與(yu)磁(ci)化(hua)線(xian)(xian)圈(quan)(quan)耦合時(shi)提取磁(ci)化(hua)線(xian)(xian)圈(quan)(quan)內(nei)部產(chan)生(sheng)的(de)(de)感(gan)(gan)(gan)生(sheng)電(dian)(dian)流(liu)(liu)(liu)(liu)，如圖(tu)5-7所示(shi)。仿真分兩種(zhong)：一是考慮(lv)鋼(gang)(gang)(gang)管(guan)(guan)渦流(liu)(liu)(liu)(liu)效應時(shi)分析(xi)線(xian)(xian)圈(quan)(quan)感(gan)(gan)(gan)生(sheng)電(dian)(dian)流(liu)(liu)(liu)(liu)與(yu)運動(dong)速(su)度的(de)(de)關系(xi)，二是忽(hu)略鋼(gang)(gang)(gang)管(guan)(guan)渦流(liu)(liu)(liu)(liu)效應而單(dan)獨(du)分析(xi)線(xian)(xian)圈(quan)(quan)感(gan)(gan)(gan)生(sheng)電(dian)(dian)流(liu)(liu)(liu)(liu)與(yu)鋼(gang)(gang)(gang)管(guan)(guan)運動(dong)速(su)度關系(xi)。分別取速(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，獲得如圖(tu)5-8所示(shi)的(de)(de)磁(ci)化(hua)線(xian)(xian)圈(quan)(quan)感(gan)(gan)(gan)生(sheng)電(dian)(dian)流(liu)(liu)(liu)(liu)與(yu)運動(dong)速(su)度關系(xi)曲線(xian)(xian)。其中(zhong)(zhong)(zhong)I1csI2cs和(he)I3cs分別為考慮(lv)鋼(gang)(gang)(gang)管(guan)(guan)渦流(liu)(liu)(liu)(liu)效應時(shi)在管(guan)(guan)頭、管(guan)(guan)體(ti)和(he)管(guan)(guan)尾處(chu)線(xian)(xian)圈(quan)(quan)中(zhong)(zhong)(zhong)產(chan)生(sheng)的(de)(de)感(gan)(gan)(gan)生(sheng)電(dian)(dian)流(liu)(liu)(liu)(liu)，11cI2c和(he)I3c分別為忽(hu)略不銹鋼(gang)(gang)(gang)管(guan)(guan)渦流(liu)(liu)(liu)(liu)效應時(shi)磁(ci)化(hua)線(xian)(xian)圈(quan)(quan)中(zhong)(zhong)(zhong)產(chan)生(sheng)的(de)(de)感(gan)(gan)(gan)生(sheng)電(dian)(dian)流(liu)(liu)(liu)(liu)。

  圖(tu)5-8所(suo)(suo)示的(de)(de)(de)仿真結(jie)果與(yu)(yu)圖(tu)5-6所(suo)(suo)示的(de)(de)(de)理(li)論(lun)分(fen)析結(jie)論(lun)相同(tong)：當(dang)管(guan)頭(tou)進入磁(ci)(ci)(ci)(ci)化(hua)線(xian)(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)時(shi)(shi)，線(xian)(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)中(zhong)(zhong)(zhong)(zhong)產(chan)(chan)生(sheng)(sheng)(sheng)(sheng)(sheng)的(de)(de)(de)感生(sheng)(sheng)(sheng)(sheng)(sheng)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)幅值(zhi)為負，即(ji)與(yu)(yu)磁(ci)(ci)(ci)(ci)化(hua)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)方向相反(fan)；當(dang)管(guan)體通過(guo)磁(ci)(ci)(ci)(ci)化(hua)線(xian)(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)時(shi)(shi)，線(xian)(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)中(zhong)(zhong)(zhong)(zhong)基本無感生(sheng)(sheng)(sheng)(sheng)(sheng)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)產(chan)(chan)生(sheng)(sheng)(sheng)(sheng)(sheng)；隨著管(guan)尾(wei)離開(kai)磁(ci)(ci)(ci)(ci)化(hua)線(xian)(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)，此(ci)時(shi)(shi)線(xian)(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)中(zhong)(zhong)(zhong)(zhong)產(chan)(chan)生(sheng)(sheng)(sheng)(sheng)(sheng)與(yu)(yu)磁(ci)(ci)(ci)(ci)化(hua)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)方向相同(tong)的(de)(de)(de)感生(sheng)(sheng)(sheng)(sheng)(sheng)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)。根據楞(leng)次定律，線(xian)(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)中(zhong)(zhong)(zhong)(zhong)產(chan)(chan)生(sheng)(sheng)(sheng)(sheng)(sheng)的(de)(de)(de)感生(sheng)(sheng)(sheng)(sheng)(sheng)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)會(hui)阻礙線(xian)(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)磁(ci)(ci)(ci)(ci)通量(liang)(liang)的(de)(de)(de)變化(hua)：當(dang)管(guan)頭(tou)進入磁(ci)(ci)(ci)(ci)化(hua)線(xian)(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)時(shi)(shi)，線(xian)(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)中(zhong)(zhong)(zhong)(zhong)會(hui)產(chan)(chan)生(sheng)(sheng)(sheng)(sheng)(sheng)反(fan)向感生(sheng)(sheng)(sheng)(sheng)(sheng)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)來(lai)阻礙磁(ci)(ci)(ci)(ci)通量(liang)(liang)的(de)(de)(de)增大(da)；當(dang)管(guan)體與(yu)(yu)磁(ci)(ci)(ci)(ci)化(hua)線(xian)(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)耦合(he)時(shi)(shi)，由于線(xian)(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)磁(ci)(ci)(ci)(ci)通量(liang)(liang)基本不(bu)變而無感生(sheng)(sheng)(sheng)(sheng)(sheng)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)產(chan)(chan)生(sheng)(sheng)(sheng)(sheng)(sheng)；當(dang)管(guan)尾(wei)離開(kai)磁(ci)(ci)(ci)(ci)化(hua)線(xian)(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)時(shi)(shi)，線(xian)(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)中(zhong)(zhong)(zhong)(zhong)會(hui)產(chan)(chan)生(sheng)(sheng)(sheng)(sheng)(sheng)同(tong)向感生(sheng)(sheng)(sheng)(sheng)(sheng)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)來(lai)阻礙磁(ci)(ci)(ci)(ci)通量(liang)(liang)的(de)(de)(de)減小。

  另外，從(cong)圖5-8中(zhong)可以(yi)看出，在運行速(su)度較低時，磁化(hua)線(xian)圈中(zhong)感(gan)生(sheng)電流隨著速(su)度的增加而(er)快速(su)上升；當速(su)度達到(dao)一定幅值時，磁化(hua)線(xian)圈中(zhong)的感(gan)生(sheng)電流基本保持(chi)不變。因為感(gan)生(sheng)電流只能減(jian)緩(huan)磁化(hua)線(xian)圈磁通量的變化(hua)速(su)度，而(er)不能改(gai)變磁通量的變化(hua)趨勢。

  從(cong)圖5-8中還(huan)可以看出，鋼管中的(de)(de)渦流會削弱磁化(hua)線(xian)圈(quan)中產生的(de)(de)感生電(dian)流，根據楞(leng)次定(ding)律，鋼(gang)管(guan)中(zhong)的(de)渦流同(tong)樣會阻礙(ai)(ai)鋼(gang)管(guan)中(zhong)磁(ci)通量的(de)變(bian)化(hua)(hua)。當不銹鋼(gang)管(guan)進入(ru)和離(li)開磁(ci)化(hua)(hua)線圈(quan)時，鋼(gang)管(guan)中(zhong)的(de)磁(ci)通量變(bian)化(hua)(hua)規(gui)律同(tong)樣先增大后減小。由于磁(ci)化(hua)(hua)線圈(quan)磁(ci)通總量包(bao)含了不銹鋼(gang)管(guan)磁(ci)通量，所以，感(gan)生(sheng)渦流在阻礙(ai)(ai)鋼(gang)管(guan)磁(ci)通量變(bian)化(hua)(hua)的(de)同(tong)時也(ye)阻礙(ai)(ai)了線圈(quan)磁(ci)通量的(de)變(bian)化(hua)(hua)速(su)率，最(zui)終削弱了線圈(quan)感(gan)生(sheng)電流的(de)強度。