不銹(xiu)鋼管穿過磁(ci)化線圈時(shi)會發生(sheng)如下兩(liang)種電磁(ci)感應現象：
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. 不銹鋼管(guan)磁(ci)(ci)介(jie)質在(zai)管(guan)頭進(jin)入磁(ci)(ci)化線圈(quan)和管(guan)尾離(li)開磁(ci)(ci)化線圈(quan)時，由于磁(ci)(ci)化線圈(quan)的(de)磁(ci)(ci)通總量發生(sheng)急劇(ju)變化，線圈(quan)中會產生(sheng)感(gan)生(sheng)電流。
一、鋼管內產(chan)生(sheng)的感生(sheng)渦流
不(bu)(bu)銹鋼管(guan)橫向(xiang)缺陷漏(lou)磁(ci)(ci)(ci)檢測方法(fa)采用(yong)穿過式線圈(quan)產生軸向(xiang)磁(ci)(ci)(ci)化場，并(bing)在(zai)(zai)磁(ci)(ci)(ci)化線圈(quan)內布(bu)置檢測傳(chuan)感器。當鋼管(guan)沿著軸向(xiang)移動時，處于磁(ci)(ci)(ci)化線圈(quan)內的不(bu)(bu)銹鋼管(guan)段被(bei)磁(ci)(ci)(ci)化至近飽和狀態，如(ru)存(cun)在(zai)(zai)缺陷將在(zai)(zai)鋼管(guan)表面產生泄(xie)漏(lou)磁(ci)(ci)(ci)場，然后被(bei)磁(ci)(ci)(ci)敏(min)感元(yuan)件拾取并(bing)依次轉(zhuan)換為模擬信(xin)號(hao)和數字信(xin)號(hao)，最(zui)終由(you)計算機信(xin)號(hao)處理(li)系統實施報警和分類(lei)。
如(ru)(ru)圖5-1所(suo)(suo)示(shi)，以(yi)鋼(gang)(gang)管軸線為中(zhong)心建立(li)圓柱坐(zuo)標系(xi)。沿著鋼(gang)(gang)管運動方向，以(yi)磁(ci)(ci)(ci)化線圈(quan)(quan)(quan)為中(zhong)心將(jiang)鋼(gang)(gang)管劃分為進(jin)(jin)入(ru)區和離開區，在(zai)(zai)(zai)磁(ci)(ci)(ci)化線圈(quan)(quan)(quan)中(zhong)施加如(ru)(ru)圖所(suo)(suo)示(shi)的磁(ci)(ci)(ci)化電流(liu)，磁(ci)(ci)(ci)力線分布特征為：在(zai)(zai)(zai)進(jin)(jin)入(ru)區磁(ci)(ci)(ci)力線從空氣(qi)(qi)中(zhong)進(jin)(jin)入(ru)鋼(gang)(gang)管，并在(zai)(zai)(zai)磁(ci)(ci)(ci)化線圈(quan)(quan)(quan)中(zhong)部匯聚，然后在(zai)(zai)(zai)離開區折射入(ru)空氣(qi)(qi)中(zhong)。
如(ru)圖(tu)5-1所示，將磁感應強度矢(shi)量B(r,z)分(fen)解為軸向分(fen)量和(he)徑向分(fen)量，即 B(r,z)=B2(r,z)+B,(r,z)
從(cong)圖5-1中可以看出，軸向(xiang)分(fen)(fen)量(liang)B2(r,z)在(zai)(zai)(zai)進(jin)(jin)入區和離開(kai)(kai)區方向(xiang)一致，沿著(zhu)鋼(gang)管前進(jin)(jin)方向(xiang)，其強(qiang)度在(zai)(zai)(zai)進(jin)(jin)入區逐(zhu)漸增大(da)，并(bing)在(zai)(zai)(zai)磁(ci)化線圈中部達到極大(da)值(zhi)，之后(hou)在(zai)(zai)(zai)離開(kai)(kai)區逐(zhu)漸減小。徑向(xiang)分(fen)(fen)量(liang)B,(r,z)在(zai)(zai)(zai)進(jin)(jin)入區方向(xiang)指(zhi)向(xiang)鋼(gang)管內部，并(bing)在(zai)(zai)(zai)磁(ci)化線圈中部發生轉變(bian)，在(zai)(zai)(zai)離開(kai)(kai)區方向(xiang)指(zhi)向(xiang)鋼(gang)管外部。
為了研究與(yu)鋼(gang)管(guan)同軸(zhou)圓(yuan)(yuan)(yuan)環l(ro ,zo)的渦流分(fen)布，設圓(yuan)(yuan)(yuan)環半徑為ro，軸(zhou)向位置為200根據楞(leng)次定律，當圓(yuan)(yuan)(yuan)環移(yi)動時，軸(zhou)向分(fen)量B,(r,z)的強(qiang)度變化導致圓(yuan)(yuan)(yuan)環磁通量也(ye)發生改變，從而在圓(yuan)(yuan)(yuan)環中產(chan)生感生電(dian)動勢(shi)。因(yin)磁化場為軸(zhou)對(dui)稱，建立圓(yuan)(yuan)(yuan)環感應電(dian)動勢(shi)方程為
根(gen)據(ju)式（5-3），沿鋼管前進(jin)方(fang)向(xiang)，在(zai)進(jin)入區，軸(zhou)(zhou)向(xiang)分量(liang)強(qiang)度(du)逐(zhu)漸增強(qiang)，感生(sheng)(sheng)渦流(liu)(liu)方(fang)向(xiang)與原磁化(hua)電流(liu)(liu)方(fang)向(xiang)相(xiang)反(fan)；在(zai)磁化(hua)線圈中(zhong)間位(wei)置，由(you)于軸(zhou)(zhou)向(xiang)分量(liang)變(bian)化(hua)率為(wei)零，故此(ci)部位(wei)無感生(sheng)(sheng)流(liu)(liu)產生(sheng)(sheng)；在(zai)離開區，軸(zhou)(zhou)向(xiang)分量(liang)強(qiang)度(du)由(you)中(zhong)間最大值逐(zhu)漸減小(xiao)，于是(shi)形成與原磁化(hua)電流(liu)(liu)方(fang)向(xiang)相(xiang)同的感生(sheng)(sheng)渦流(liu)(liu)，最終鋼管中(zhong)感生(sheng)(sheng)渦流(liu)(liu)分布如圖(tu)5-2a所示。如果改變(bian)磁化(hua)電流(liu)(liu)方(fang)向(xiang)，根(gen)據(ju)式（5-3），同樣可得出鋼管內(nei)感生(sheng)(sheng)渦流(liu)(liu)分布，如圖(tu)5-2b所示。
從(cong)圖5-2中(zhong)(zhong)可以看出(chu)，鋼(gang)管(guan)中(zhong)(zhong)感(gan)生電(dian)流(liu)(liu)分布方(fang)(fang)向(xiang)由磁化(hua)(hua)電(dian)流(liu)(liu)方(fang)(fang)向(xiang)和鋼(gang)管(guan)運動方(fang)(fang)向(xiang)共同(tong)(tong)決定。在(zai)進入區(qu)，鋼(gang)管(guan)中(zhong)(zhong)的(de)感(gan)生渦(wo)(wo)流(liu)(liu)J1與磁化(hua)(hua)電(dian)流(liu)(liu)方(fang)(fang)向(xiang)相反；在(zai)磁化(hua)(hua)線圈(quan)中(zhong)(zhong)間位置無感(gan)生渦(wo)(wo)流(liu)(liu)產生；在(zai)離開區(qu)，感(gan)生渦(wo)(wo)流(liu)(liu)J2與磁化(hua)(hua)電(dian)流(liu)(liu)方(fang)(fang)向(xiang)相同(tong)(tong)。從(cong)而，在(zai)感(gan)生渦(wo)(wo)流(liu)(liu)產生的(de)磁場作(zuo)用下，鋼(gang)管(guan)的(de)磁化(hua)(hua)狀態將發(fa)生變(bian)化(hua)(hua)。
建立如(ru)圖5-3所示(shi)的仿真模(mo)型。鋼管(guan)直徑為(wei)(wei)(wei)400mm、壁厚為(wei)(wei)(wei)15mm、長度為(wei)(wei)(wei)3000mm，材質為(wei)(wei)(wei)25鋼（電(dian)導率為(wei)(wei)(wei)）。磁化(hua)線圈內徑為(wei)(wei)(wei)440mm、外徑為(wei)(wei)(wei)750mm、厚度為(wei)(wei)(wei)160mm，磁化(hua)電(dian)流密度iA／㎡，電(dian)流方向如(ru)圖5-3所示(shi)。
對不(bu)(bu)銹(xiu)(xiu)鋼(gang)管中(zhong)(zhong)的(de)(de)(de)感(gan)生(sheng)渦(wo)(wo)(wo)流(liu)(liu)(liu)分(fen)(fen)布進行仿真研究。磁(ci)化線圈(quan)(quan)(quan)固(gu)定不(bu)(bu)動，鋼(gang)管運行速(su)度(du)設置為(wei)1m／s，不(bu)(bu)銹(xiu)(xiu)鋼(gang)管從(cong)(cong)左端進人并向右端移動，當鋼(gang)管中(zhong)(zhong)心(xin)與(yu)磁(ci)化線圈(quan)(quan)(quan)中(zhong)(zhong)心(xin)重合時獲(huo)取感(gan)生(sheng)渦(wo)(wo)(wo)流(liu)(liu)(liu)分(fen)(fen)布云(yun)圖(tu)(tu)(tu)，如圖(tu)(tu)(tu)5-4所示(shi)。從(cong)(cong)圖(tu)(tu)(tu)中(zhong)(zhong)可以看出，進入(ru)區(qu)的(de)(de)(de)感(gan)生(sheng)渦(wo)(wo)(wo)流(liu)(liu)(liu)方(fang)向與(yu)磁(ci)化電流(liu)(liu)(liu)方(fang)向相(xiang)(xiang)反，離開區(qu)的(de)(de)(de)感(gan)生(sheng)渦(wo)(wo)(wo)流(liu)(liu)(liu)方(fang)向與(yu)磁(ci)化電流(liu)(liu)(liu)方(fang)向相(xiang)(xiang)同，在線圈(quan)(quan)(quan)中(zhong)(zhong)部(bu)感(gan)生(sheng)渦(wo)(wo)(wo)流(liu)(liu)(liu)幾乎(hu)為(wei)零。進入(ru)區(qu)和離開區(qu)的(de)(de)(de)渦(wo)(wo)(wo)流(liu)(liu)(liu)分(fen)(fen)布相(xiang)(xiang)對于線圈(quan)(quan)(quan)呈(cheng)對稱分(fen)(fen)布，方(fang)向相(xiang)(xiang)反，強度(du)基本相(xiang)(xiang)同，仿真結果與(yu)圖(tu)(tu)(tu)5-2所示(shi)的(de)(de)(de)渦(wo)(wo)(wo)流(liu)(liu)(liu)分(fen)(fen)布理(li)論(lun)分(fen)(fen)析結論(lun)相(xiang)(xiang)同，其中(zhong)(zhong)感(gan)生(sheng)渦(wo)(wo)(wo)流(liu)(liu)(liu)最大值為(wei)1.4×105A/㎡。
為(wei)了(le)研究(jiu)感生(sheng)渦(wo)(wo)流(liu)(liu)(liu)(liu)與(yu)不銹(xiu)鋼(gang)管(guan)運(yun)(yun)行速(su)(su)(su)度的關系，分別取(qu)速(su)(su)(su)度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(fang)真。當鋼(gang)管(guan)中部與(yu)磁化(hua)線(xian)圈(quan)重(zhong)合時(shi)提(ti)取(qu)渦(wo)(wo)流(liu)(liu)(liu)(liu)密(mi)(mi)(mi)度最大(da)值和最小值，繪制成如圖5-5所示的渦(wo)(wo)流(liu)(liu)(liu)(liu)密(mi)(mi)(mi)度與(yu)運(yun)(yun)行速(su)(su)(su)度關系曲線(xian)。從圖中可以看出，感生(sheng)渦(wo)(wo)流(liu)(liu)(liu)(liu)與(yu)不銹(xiu)鋼(gang)管(guan)運(yun)(yun)行速(su)(su)(su)度成近(jin)似正比(bi)關系。鋼(gang)管(guan)低速(su)(su)(su)運(yun)(yun)動時(shi)感生(sheng)渦(wo)(wo)流(liu)(liu)(liu)(liu)很(hen)小，可忽(hu)略不計(ji)；當運(yun)(yun)行速(su)(su)(su)度增至50m／s時(shi)，渦(wo)(wo)流(liu)(liu)(liu)(liu)密(mi)(mi)(mi)度為(wei)2。此時(shi)，感生(sheng)渦(wo)(wo)流(liu)(liu)(liu)(liu)已接近(jin)傳導電流(liu)(liu)(liu)(liu)密(mi)(mi)(mi)度。因此，高速(su)(su)(su)運(yun)(yun)動時(shi)，感生(sheng)渦(wo)(wo)流(liu)(liu)(liu)(liu)對鋼(gang)管(guan)漏磁檢測的影響不可忽(hu)視。
二、磁化線圈中產生的(de)感生電流
當(dang)不(bu)銹鋼(gang)管端部進入和(he)(he)(he)離開磁化(hua)(hua)線(xian)(xian)(xian)(xian)圈時，線(xian)(xian)(xian)(xian)圈中的(de)磁通量(liang)發生變化(hua)(hua)而產(chan)生感生電(dian)(dian)(dian)(dian)(dian)流。設(she)磁化(hua)(hua)電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)提供的(de)電(dian)(dian)(dian)(dian)(dian)壓為(wei)(wei)Uo，磁化(hua)(hua)線(xian)(xian)(xian)(xian)圈電(dian)(dian)(dian)(dian)(dian)阻為(wei)(wei)R，則磁化(hua)(hua)電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)在線(xian)(xian)(xian)(xian)圈中產(chan)生的(de)初(chu)始(shi)傳(chuan)導(dao)電(dian)(dian)(dian)(dian)(dian)流為(wei)(wei)Io=Uo/RR。磁化(hua)(hua)線(xian)(xian)(xian)(xian)圈通過(guo)的(de)磁通總(zong)量(liang)為(wei)(wei)Φ，當(dang)磁化(hua)(hua)線(xian)(xian)(xian)(xian)圈中磁通總(zong)量(liang)發生變化(hua)(hua)時，根(gen)據(ju)楞(leng)次(ci)定律，線(xian)(xian)(xian)(xian)圈中將產(chan)生感生電(dian)(dian)(dian)(dian)(dian)動勢，對應(ying)的(de)感生電(dian)(dian)(dian)(dian)(dian)流磁化(hua)(hua)線(xian)(xian)(xian)(xian)圈中通過(guo)的(de)電(dian)(dian)(dian)(dian)(dian)流I為(wei)(wei)初(chu)始(shi)傳(chuan)導(dao)電(dian)(dian)(dian)(dian)(dian)流和(he)(he)(he)感生電(dian)(dian)(dian)(dian)(dian)流之和(he)(he)(he)，即(ji)
當(dang)(dang)線(xian)(xian)(xian)圈(quan)(quan)中沒有鋼管(guan)時，磁(ci)(ci)(ci)化線(xian)(xian)(xian)圈(quan)(quan)磁(ci)(ci)(ci)通總量(liang)為線(xian)(xian)(xian)圈(quan)(quan)自(zi)身產生的靜(jing)態磁(ci)(ci)(ci)通量(liang)，其與磁(ci)(ci)(ci)化電流強度成正(zheng)比，當(dang)(dang)磁(ci)(ci)(ci)化電流不變(bian)時，線(xian)(xian)(xian)圈(quan)(quan)磁(ci)(ci)(ci)通總量(liang)也不發生變(bian)化。此時線(xian)(xian)(xian)圈(quan)(quan)中通過的電流為磁(ci)(ci)(ci)化電源產生的初始磁(ci)(ci)(ci)化傳導電流
當管(guan)頭進入磁化(hua)(hua)線(xian)圈時，具有高(gao)磁導率的(de)鋼管(guan)磁介質進入磁化(hua)(hua)線(xian)圈內部，使得線(xian)圈內部的(de)磁通總量增大。根據式（5-4），磁化(hua)(hua)線(xian)圈中會產生與初(chu)始(shi)磁化(hua)(hua)傳導電流(liu)(liu)方(fang)向(xiang)相反的(de)感生電流(liu)(liu)，此時線(xian)圈中通過的(de)電流(liu)(liu)為(wei)，如(ru)圖5-6a所(suo)示(shi)。
當管(guan)體通(tong)過磁(ci)化(hua)(hua)(hua)線(xian)圈時(shi)，線(xian)圈內部磁(ci)介質總(zong)(zong)量(liang)及分布(bu)特性(xing)基(ji)本不(bu)變(bian)，從而線(xian)圈內部的磁(ci)通(tong)總(zong)(zong)量(liang)也(ye)保持恒定(ding)。根據式（5-4），磁(ci)化(hua)(hua)(hua)線(xian)圈基(ji)本無(wu)感生電(dian)流產生，此(ci)時(shi)，磁(ci)化(hua)(hua)(hua)線(xian)圈中(zhong)通(tong)過的電(dian)流與無(wu)鋼管(guan)時(shi)相同，為磁(ci)化(hua)(hua)(hua)電(dian)源產生的初始(shi)磁(ci)化(hua)(hua)(hua)傳(chuan)導電(dian)流1＝，如圖5-6b所示。
當管尾離開磁(ci)化(hua)線(xian)圈時(shi)，由(you)于線(xian)圈內部(bu)的(de)高(gao)磁(ci)導(dao)率(lv)磁(ci)介質不斷減少，導(dao)致(zhi)磁(ci)化(hua)線(xian)圈的(de)磁(ci)通(tong)總量也(ye)不斷減少。根據式（5-4），磁(ci)化(hua)線(xian)圈中會產生(sheng)(sheng)與初始磁(ci)化(hua)傳(chuan)導(dao)電流(liu)方向相同的(de)感生(sheng)(sheng)電流(liu)，此時(shi)線(xian)圈中通(tong)過的(de)電流(liu)為，如圖5-6c所示(shi)。
不銹鋼管(guan)內的磁(ci)(ci)(ci)場包括(kuo)：磁(ci)(ci)(ci)化(hua)(hua)線圈通(tong)過電流I產生的磁(ci)(ci)(ci)場和鋼管(guan)中(zhong)感(gan)生渦(wo)(wo)流J形(xing)成的磁(ci)(ci)(ci)場。磁(ci)(ci)(ci)化(hua)(hua)線圈的磁(ci)(ci)(ci)通(tong)總量包含了由感(gan)生渦(wo)(wo)流J產生的部(bu)分磁(ci)(ci)(ci)通(tong)量，因此鋼管(guan)中(zhong)的渦(wo)(wo)流效應會(hui)對磁(ci)(ci)(ci)化(hua)(hua)線圈中(zhong)的感(gan)生電流產生一定影響。
采用如(ru)圖(tu)5-3所(suo)示模型(xing)，進一步研究磁(ci)化(hua)線(xian)(xian)(xian)(xian)圈(quan)中產(chan)(chan)(chan)生(sheng)(sheng)(sheng)的感生(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)(liu)(liu)變化(hua)規律。其中，線(xian)(xian)(xian)(xian)圈(quan)匝數為(wei)600匝，磁(ci)化(hua)電(dian)(dian)流(liu)(liu)(liu)(liu)為(wei)5A。當鋼(gang)管(guan)(guan)(guan)管(guan)(guan)(guan)頭(tou)、管(guan)(guan)(guan)體和管(guan)(guan)(guan)尾分(fen)(fen)別(bie)與(yu)磁(ci)化(hua)線(xian)(xian)(xian)(xian)圈(quan)耦合時提取磁(ci)化(hua)線(xian)(xian)(xian)(xian)圈(quan)內部產(chan)(chan)(chan)生(sheng)(sheng)(sheng)的感生(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)(liu)(liu)，如(ru)圖(tu)5-7所(suo)示。仿(fang)真分(fen)(fen)兩種(zhong)：一是(shi)考慮鋼(gang)管(guan)(guan)(guan)渦流(liu)(liu)(liu)(liu)效(xiao)應(ying)時分(fen)(fen)析線(xian)(xian)(xian)(xian)圈(quan)感生(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)(liu)(liu)與(yu)運(yun)(yun)動(dong)速(su)度的關(guan)系，二是(shi)忽略鋼(gang)管(guan)(guan)(guan)渦流(liu)(liu)(liu)(liu)效(xiao)應(ying)而單獨分(fen)(fen)析線(xian)(xian)(xian)(xian)圈(quan)感生(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)(liu)(liu)與(yu)鋼(gang)管(guan)(guan)(guan)運(yun)(yun)動(dong)速(su)度關(guan)系。分(fen)(fen)別(bie)取速(su)度0.1m／s、1m／s、2m／s、5m／s、8m／s、10m／s、20m／s、30m／s、40m／和50m／s進行(xing)仿(fang)真，獲得如(ru)圖(tu)5-8所(suo)示的磁(ci)化(hua)線(xian)(xian)(xian)(xian)圈(quan)感生(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)(liu)(liu)與(yu)運(yun)(yun)動(dong)速(su)度關(guan)系曲線(xian)(xian)(xian)(xian)。其中I1csI2cs和I3cs分(fen)(fen)別(bie)為(wei)考慮鋼(gang)管(guan)(guan)(guan)渦流(liu)(liu)(liu)(liu)效(xiao)應(ying)時在管(guan)(guan)(guan)頭(tou)、管(guan)(guan)(guan)體和管(guan)(guan)(guan)尾處(chu)線(xian)(xian)(xian)(xian)圈(quan)中產(chan)(chan)(chan)生(sheng)(sheng)(sheng)的感生(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)(liu)(liu)，11cI2c和I3c分(fen)(fen)別(bie)為(wei)忽略不銹鋼(gang)管(guan)(guan)(guan)渦流(liu)(liu)(liu)(liu)效(xiao)應(ying)時磁(ci)化(hua)線(xian)(xian)(xian)(xian)圈(quan)中產(chan)(chan)(chan)生(sheng)(sheng)(sheng)的感生(sheng)(sheng)(sheng)電(dian)(dian)流(liu)(liu)(liu)(liu)。
圖5-8所(suo)示的(de)(de)仿真結果與圖5-6所(suo)示的(de)(de)理論(lun)(lun)分析結論(lun)(lun)相(xiang)同：當管頭進(jin)入磁(ci)(ci)(ci)化(hua)線(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)時(shi)(shi)，線(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)中(zhong)產生(sheng)(sheng)(sheng)的(de)(de)感(gan)(gan)(gan)生(sheng)(sheng)(sheng)電(dian)流幅值(zhi)為負，即(ji)與磁(ci)(ci)(ci)化(hua)電(dian)流方向(xiang)相(xiang)反；當管體(ti)通(tong)過磁(ci)(ci)(ci)化(hua)線(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)時(shi)(shi)，線(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)中(zhong)基(ji)本(ben)無(wu)感(gan)(gan)(gan)生(sheng)(sheng)(sheng)電(dian)流產生(sheng)(sheng)(sheng)；隨著管尾離(li)開磁(ci)(ci)(ci)化(hua)線(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)，此時(shi)(shi)線(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)中(zhong)產生(sheng)(sheng)(sheng)與磁(ci)(ci)(ci)化(hua)電(dian)流方向(xiang)相(xiang)同的(de)(de)感(gan)(gan)(gan)生(sheng)(sheng)(sheng)電(dian)流。根(gen)據(ju)楞次定律，線(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)中(zhong)產生(sheng)(sheng)(sheng)的(de)(de)感(gan)(gan)(gan)生(sheng)(sheng)(sheng)電(dian)流會(hui)阻(zu)礙線(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)磁(ci)(ci)(ci)通(tong)量(liang)的(de)(de)變化(hua)：當管頭進(jin)入磁(ci)(ci)(ci)化(hua)線(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)時(shi)(shi)，線(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)中(zhong)會(hui)產生(sheng)(sheng)(sheng)反向(xiang)感(gan)(gan)(gan)生(sheng)(sheng)(sheng)電(dian)流來(lai)(lai)阻(zu)礙磁(ci)(ci)(ci)通(tong)量(liang)的(de)(de)增大；當管體(ti)與磁(ci)(ci)(ci)化(hua)線(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)耦合時(shi)(shi)，由(you)于線(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)磁(ci)(ci)(ci)通(tong)量(liang)基(ji)本(ben)不變而無(wu)感(gan)(gan)(gan)生(sheng)(sheng)(sheng)電(dian)流產生(sheng)(sheng)(sheng)；當管尾離(li)開磁(ci)(ci)(ci)化(hua)線(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)時(shi)(shi)，線(xian)(xian)(xian)(xian)圈(quan)(quan)(quan)中(zhong)會(hui)產生(sheng)(sheng)(sheng)同向(xiang)感(gan)(gan)(gan)生(sheng)(sheng)(sheng)電(dian)流來(lai)(lai)阻(zu)礙磁(ci)(ci)(ci)通(tong)量(liang)的(de)(de)減小。
另(ling)外，從圖5-8中(zhong)(zhong)可以看出，在運行速(su)(su)度(du)(du)較低時(shi)，磁化(hua)(hua)線(xian)圈(quan)中(zhong)(zhong)感生(sheng)(sheng)電(dian)(dian)流隨著速(su)(su)度(du)(du)的增(zeng)加而快速(su)(su)上升；當速(su)(su)度(du)(du)達到一定(ding)幅值(zhi)時(shi)，磁化(hua)(hua)線(xian)圈(quan)中(zhong)(zhong)的感生(sheng)(sheng)電(dian)(dian)流基本保持不變。因為感生(sheng)(sheng)電(dian)(dian)流只能(neng)減緩磁化(hua)(hua)線(xian)圈(quan)磁通(tong)量的變化(hua)(hua)速(su)(su)度(du)(du)，而不能(neng)改變磁通(tong)量的變化(hua)(hua)趨勢。
從圖5-8中(zhong)還(huan)可(ke)以(yi)看(kan)出，鋼管中(zhong)的渦流會削弱磁化線圈(quan)中(zhong)產(chan)生(sheng)的感生(sheng)電流，根據楞次定律(lv)，鋼管中的(de)(de)渦流(liu)(liu)同(tong)樣會(hui)阻礙鋼管中磁(ci)(ci)通(tong)(tong)量(liang)的(de)(de)變化(hua)(hua)。當不銹鋼管進入和離開磁(ci)(ci)化(hua)(hua)線(xian)圈(quan)時(shi)(shi)，鋼管中的(de)(de)磁(ci)(ci)通(tong)(tong)量(liang)變化(hua)(hua)規律(lv)同(tong)樣先增大后減小(xiao)。由于磁(ci)(ci)化(hua)(hua)線(xian)圈(quan)磁(ci)(ci)通(tong)(tong)總量(liang)包含了不銹鋼管磁(ci)(ci)通(tong)(tong)量(liang)，所以，感生渦流(liu)(liu)在阻礙鋼管磁(ci)(ci)通(tong)(tong)量(liang)變化(hua)(hua)的(de)(de)同(tong)時(shi)(shi)也阻礙了線(xian)圈(quan)磁(ci)(ci)通(tong)(tong)量(liang)的(de)(de)變化(hua)(hua)速率，最(zui)終削弱(ruo)了線(xian)圈(quan)感生電流(liu)(liu)的(de)(de)強度。
