不銹鋼管穿過磁(ci)化線圈時會發生(sheng)如(ru)下兩種電(dian)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(guan)切割磁力線而在其內部形成感生渦流。
2. 不(bu)銹(xiu)鋼管磁(ci)(ci)(ci)介質在管頭(tou)進入磁(ci)(ci)(ci)化線圈(quan)和(he)管尾(wei)離開磁(ci)(ci)(ci)化線圈(quan)時(shi)，由于磁(ci)(ci)(ci)化線圈(quan)的磁(ci)(ci)(ci)通總量發(fa)生急(ji)劇變化，線圈(quan)中會產生感(gan)生電流。
一、鋼(gang)管內產(chan)生的感生渦流
不銹(xiu)鋼管橫向缺(que)陷(xian)漏磁(ci)(ci)檢(jian)測方法采用(yong)穿過(guo)式線圈產(chan)生軸(zhou)向磁(ci)(ci)化場(chang)，并在(zai)磁(ci)(ci)化線圈內(nei)布置(zhi)檢(jian)測傳(chuan)感器。當(dang)鋼管沿著軸(zhou)向移(yi)動時，處于磁(ci)(ci)化線圈內(nei)的不銹(xiu)鋼管段被磁(ci)(ci)化至近飽(bao)和狀態，如存在(zai)缺(que)陷(xian)將(jiang)在(zai)鋼管表面產(chan)生泄漏磁(ci)(ci)場(chang)，然后(hou)被磁(ci)(ci)敏感元件(jian)拾取并依(yi)次轉(zhuan)換為(wei)模(mo)擬信(xin)號和數字(zi)信(xin)號，最(zui)終由計算機(ji)信(xin)號處理系統(tong)實施報警和分類。
如(ru)圖5-1所示，以(yi)鋼管軸線(xian)為(wei)中心建(jian)立圓柱坐標(biao)系(xi)。沿著鋼管運動方向(xiang)，以(yi)磁(ci)化(hua)線(xian)圈為(wei)中心將鋼管劃分(fen)為(wei)進(jin)入區(qu)和離開區(qu)，在(zai)磁(ci)化(hua)線(xian)圈中施加如(ru)圖所示的磁(ci)化(hua)電(dian)流，磁(ci)力線(xian)分(fen)布特征為(wei)：在(zai)進(jin)入區(qu)磁(ci)力線(xian)從空(kong)(kong)氣中進(jin)入鋼管，并在(zai)磁(ci)化(hua)線(xian)圈中部(bu)匯聚，然后在(zai)離開區(qu)折射(she)入空(kong)(kong)氣中。
如圖5-1所示(shi)，將磁感應強(qiang)度矢量B(r,z)分解為軸向分量和徑向分量，即(ji) B(r,z)=B2(r,z)+B,(r,z)
從圖(tu)5-1中可以(yi)看出，軸向(xiang)(xiang)(xiang)分量B2(r,z)在(zai)(zai)(zai)進(jin)入(ru)區(qu)(qu)和(he)離(li)開區(qu)(qu)方(fang)向(xiang)(xiang)(xiang)一致，沿著(zhu)鋼(gang)管(guan)(guan)前(qian)進(jin)方(fang)向(xiang)(xiang)(xiang)，其強度(du)在(zai)(zai)(zai)進(jin)入(ru)區(qu)(qu)逐漸增(zeng)大，并在(zai)(zai)(zai)磁(ci)化線(xian)圈中部(bu)達(da)到(dao)極大值，之后在(zai)(zai)(zai)離(li)開區(qu)(qu)逐漸減小。徑向(xiang)(xiang)(xiang)分量B,(r,z)在(zai)(zai)(zai)進(jin)入(ru)區(qu)(qu)方(fang)向(xiang)(xiang)(xiang)指向(xiang)(xiang)(xiang)鋼(gang)管(guan)(guan)內部(bu)，并在(zai)(zai)(zai)磁(ci)化線(xian)圈中部(bu)發生轉變，在(zai)(zai)(zai)離(li)開區(qu)(qu)方(fang)向(xiang)(xiang)(xiang)指向(xiang)(xiang)(xiang)鋼(gang)管(guan)(guan)外部(bu)。
為(wei)了研究與鋼管同軸圓環l(ro ,zo)的(de)渦流分(fen)布，設圓環半徑為(wei)ro，軸向(xiang)位置為(wei)200根據楞次定律，當圓環移動(dong)時，軸向(xiang)分(fen)量(liang)B,(r,z)的(de)強度(du)變化(hua)導致圓環磁通量(liang)也發生改變，從而在圓環中產生感生電動(dong)勢。因(yin)磁化(hua)場為(wei)軸對(dui)稱，建立圓環感應電動(dong)勢方程為(wei)
根據(ju)式(shi)（5-3），沿鋼管(guan)前(qian)進方(fang)向(xiang)，在(zai)進入區，軸(zhou)向(xiang)分(fen)(fen)量強度逐(zhu)漸增強，感生(sheng)渦流(liu)方(fang)向(xiang)與(yu)原磁(ci)(ci)化電(dian)流(liu)方(fang)向(xiang)相(xiang)反；在(zai)磁(ci)(ci)化線(xian)圈中(zhong)(zhong)間(jian)位置，由于軸(zhou)向(xiang)分(fen)(fen)量變化率為(wei)零，故此部位無感生(sheng)流(liu)產(chan)生(sheng)；在(zai)離開(kai)區，軸(zhou)向(xiang)分(fen)(fen)量強度由中(zhong)(zhong)間(jian)最大值逐(zhu)漸減(jian)小，于是形成與(yu)原磁(ci)(ci)化電(dian)流(liu)方(fang)向(xiang)相(xiang)同(tong)(tong)的感生(sheng)渦流(liu)，最終鋼管(guan)中(zhong)(zhong)感生(sheng)渦流(liu)分(fen)(fen)布如圖5-2a所示。如果改變磁(ci)(ci)化電(dian)流(liu)方(fang)向(xiang)，根據(ju)式(shi)（5-3），同(tong)(tong)樣可得出鋼管(guan)內(nei)感生(sheng)渦流(liu)分(fen)(fen)布，如圖5-2b所示。
從(cong)圖5-2中(zhong)可以看出(chu)，鋼管中(zhong)感(gan)(gan)生(sheng)(sheng)(sheng)電(dian)流(liu)(liu)分布(bu)方向(xiang)由磁(ci)化(hua)電(dian)流(liu)(liu)方向(xiang)和(he)鋼管運(yun)動方向(xiang)共同決(jue)定。在進入區(qu)，鋼管中(zhong)的感(gan)(gan)生(sheng)(sheng)(sheng)渦(wo)流(liu)(liu)J1與(yu)磁(ci)化(hua)電(dian)流(liu)(liu)方向(xiang)相(xiang)反；在磁(ci)化(hua)線圈中(zhong)間位置(zhi)無感(gan)(gan)生(sheng)(sheng)(sheng)渦(wo)流(liu)(liu)產生(sheng)(sheng)(sheng)；在離開區(qu)，感(gan)(gan)生(sheng)(sheng)(sheng)渦(wo)流(liu)(liu)J2與(yu)磁(ci)化(hua)電(dian)流(liu)(liu)方向(xiang)相(xiang)同。從(cong)而，在感(gan)(gan)生(sheng)(sheng)(sheng)渦(wo)流(liu)(liu)產生(sheng)(sheng)(sheng)的磁(ci)場作用下，鋼管的磁(ci)化(hua)狀態(tai)將發生(sheng)(sheng)(sheng)變化(hua)。
建(jian)立如圖5-3所示的仿(fang)真模型。鋼管直徑為(wei)(wei)400mm、壁厚為(wei)(wei)15mm、長度為(wei)(wei)3000mm，材質為(wei)(wei)25鋼（電(dian)導率為(wei)(wei)）。磁化線圈內徑為(wei)(wei)440mm、外(wai)徑為(wei)(wei)750mm、厚度為(wei)(wei)160mm，磁化電(dian)流密(mi)度iA／㎡，電(dian)流方向如圖5-3所示。
對不(bu)銹鋼管(guan)(guan)中(zhong)(zhong)(zhong)的感(gan)生(sheng)(sheng)渦(wo)(wo)流(liu)(liu)分(fen)(fen)布進行仿真(zhen)(zhen)研究。磁(ci)化(hua)線(xian)圈(quan)固定(ding)不(bu)動(dong)，鋼管(guan)(guan)運(yun)行速度(du)設(she)置為(wei)1m／s，不(bu)銹鋼管(guan)(guan)從左端進人并向(xiang)右端移動(dong)，當鋼管(guan)(guan)中(zhong)(zhong)(zhong)心與(yu)磁(ci)化(hua)線(xian)圈(quan)中(zhong)(zhong)(zhong)心重合(he)時獲取感(gan)生(sheng)(sheng)渦(wo)(wo)流(liu)(liu)分(fen)(fen)布云圖(tu)，如圖(tu)5-4所示。從圖(tu)中(zhong)(zhong)(zhong)可以(yi)看出，進入區的感(gan)生(sheng)(sheng)渦(wo)(wo)流(liu)(liu)方(fang)向(xiang)與(yu)磁(ci)化(hua)電流(liu)(liu)方(fang)向(xiang)相反，離開區的感(gan)生(sheng)(sheng)渦(wo)(wo)流(liu)(liu)方(fang)向(xiang)與(yu)磁(ci)化(hua)電流(liu)(liu)方(fang)向(xiang)相同(tong)，在(zai)線(xian)圈(quan)中(zhong)(zhong)(zhong)部感(gan)生(sheng)(sheng)渦(wo)(wo)流(liu)(liu)幾乎(hu)為(wei)零。進入區和離開區的渦(wo)(wo)流(liu)(liu)分(fen)(fen)布相對于線(xian)圈(quan)呈對稱分(fen)(fen)布，方(fang)向(xiang)相反，強度(du)基本相同(tong)，仿真(zhen)(zhen)結(jie)果與(yu)圖(tu)5-2所示的渦(wo)(wo)流(liu)(liu)分(fen)(fen)布理(li)論(lun)(lun)分(fen)(fen)析結(jie)論(lun)(lun)相同(tong)，其中(zhong)(zhong)(zhong)感(gan)生(sheng)(sheng)渦(wo)(wo)流(liu)(liu)最(zui)大值為(wei)1.4×105A/㎡。
為了研究感(gan)生(sheng)渦(wo)流(liu)與(yu)不銹鋼(gang)管(guan)(guan)運(yun)(yun)行(xing)速(su)(su)度(du)(du)的(de)(de)(de)關系，分別取速(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(dang)鋼(gang)管(guan)(guan)中部與(yu)磁化(hua)線(xian)圈重(zhong)合時(shi)提取渦(wo)流(liu)密(mi)(mi)度(du)(du)最大值和最小值，繪(hui)制成(cheng)如(ru)圖5-5所示的(de)(de)(de)渦(wo)流(liu)密(mi)(mi)度(du)(du)與(yu)運(yun)(yun)行(xing)速(su)(su)度(du)(du)關系曲線(xian)。從圖中可以看出，感(gan)生(sheng)渦(wo)流(liu)與(yu)不銹鋼(gang)管(guan)(guan)運(yun)(yun)行(xing)速(su)(su)度(du)(du)成(cheng)近似正(zheng)比關系。鋼(gang)管(guan)(guan)低速(su)(su)運(yun)(yun)動時(shi)感(gan)生(sheng)渦(wo)流(liu)很(hen)小，可忽略不計；當(dang)運(yun)(yun)行(xing)速(su)(su)度(du)(du)增至50m／s時(shi)，渦(wo)流(liu)密(mi)(mi)度(du)(du)為2。此時(shi)，感(gan)生(sheng)渦(wo)流(liu)已接近傳導電流(liu)密(mi)(mi)度(du)(du)。因此，高速(su)(su)運(yun)(yun)動時(shi)，感(gan)生(sheng)渦(wo)流(liu)對鋼(gang)管(guan)(guan)漏磁檢測(ce)的(de)(de)(de)影響不可忽視。
二、磁化線圈中產生的感生電流
當不銹鋼管端部進入和(he)(he)離開磁(ci)(ci)化(hua)(hua)線(xian)圈時(shi)，線(xian)圈中(zhong)的(de)磁(ci)(ci)通(tong)量發生(sheng)(sheng)(sheng)(sheng)變化(hua)(hua)而產生(sheng)(sheng)(sheng)(sheng)感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)(dian)流。設磁(ci)(ci)化(hua)(hua)電(dian)(dian)源(yuan)提供的(de)電(dian)(dian)壓為Uo，磁(ci)(ci)化(hua)(hua)線(xian)圈電(dian)(dian)阻為R，則磁(ci)(ci)化(hua)(hua)電(dian)(dian)源(yuan)在線(xian)圈中(zhong)產生(sheng)(sheng)(sheng)(sheng)的(de)初(chu)始傳(chuan)導(dao)電(dian)(dian)流為Io=Uo/RR。磁(ci)(ci)化(hua)(hua)線(xian)圈通(tong)過(guo)的(de)磁(ci)(ci)通(tong)總量為Φ，當磁(ci)(ci)化(hua)(hua)線(xian)圈中(zhong)磁(ci)(ci)通(tong)總量發生(sheng)(sheng)(sheng)(sheng)變化(hua)(hua)時(shi)，根據楞次定律，線(xian)圈中(zhong)將產生(sheng)(sheng)(sheng)(sheng)感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)(dian)動勢，對(dui)應的(de)感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)(dian)流磁(ci)(ci)化(hua)(hua)線(xian)圈中(zhong)通(tong)過(guo)的(de)電(dian)(dian)流I為初(chu)始傳(chuan)導(dao)電(dian)(dian)流和(he)(he)感(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)(dian)流之和(he)(he)，即
當(dang)線圈(quan)中(zhong)沒有鋼管時，磁(ci)化(hua)(hua)(hua)線圈(quan)磁(ci)通(tong)總量(liang)為(wei)線圈(quan)自(zi)身產(chan)生的靜(jing)態磁(ci)通(tong)量(liang)，其(qi)與(yu)磁(ci)化(hua)(hua)(hua)電(dian)(dian)(dian)流強度成正比，當(dang)磁(ci)化(hua)(hua)(hua)電(dian)(dian)(dian)流不變時，線圈(quan)磁(ci)通(tong)總量(liang)也不發生變化(hua)(hua)(hua)。此時線圈(quan)中(zhong)通(tong)過的電(dian)(dian)(dian)流為(wei)磁(ci)化(hua)(hua)(hua)電(dian)(dian)(dian)源產(chan)生的初始磁(ci)化(hua)(hua)(hua)傳導電(dian)(dian)(dian)流
當管頭進入磁(ci)化(hua)(hua)線圈(quan)(quan)時(shi)，具有(you)高磁(ci)導(dao)率的(de)鋼管磁(ci)介質進入磁(ci)化(hua)(hua)線圈(quan)(quan)內部(bu)，使(shi)得線圈(quan)(quan)內部(bu)的(de)磁(ci)通(tong)總量增大。根據式(shi)（5-4），磁(ci)化(hua)(hua)線圈(quan)(quan)中(zhong)(zhong)會產生(sheng)與初始磁(ci)化(hua)(hua)傳導(dao)電流方向(xiang)相反的(de)感生(sheng)電流，此時(shi)線圈(quan)(quan)中(zhong)(zhong)通(tong)過的(de)電流為，如(ru)圖5-6a所示。
當管(guan)體通(tong)(tong)過(guo)磁化(hua)線(xian)圈(quan)時(shi)，線(xian)圈(quan)內部磁介質總量(liang)及分布特性基本(ben)不(bu)變，從而線(xian)圈(quan)內部的磁通(tong)(tong)總量(liang)也保持恒定。根據式（5-4），磁化(hua)線(xian)圈(quan)基本(ben)無感(gan)生(sheng)電(dian)流產生(sheng)，此時(shi)，磁化(hua)線(xian)圈(quan)中通(tong)(tong)過(guo)的電(dian)流與無鋼(gang)管(guan)時(shi)相同，為磁化(hua)電(dian)源(yuan)產生(sheng)的初始磁化(hua)傳導電(dian)流1＝，如圖5-6b所示。
當管尾離開磁化(hua)線(xian)圈(quan)時，由于(yu)線(xian)圈(quan)內部(bu)的高磁導(dao)率(lv)磁介質不斷減少，導(dao)致(zhi)磁化(hua)線(xian)圈(quan)的磁通(tong)總量也不斷減少。根據式（5-4），磁化(hua)線(xian)圈(quan)中(zhong)會(hui)產生與初始磁化(hua)傳導(dao)電流(liu)方向(xiang)相同的感(gan)生電流(liu)，此時線(xian)圈(quan)中(zhong)通(tong)過的電流(liu)為，如(ru)圖5-6c所示。
不銹(xiu)鋼(gang)管內(nei)的(de)磁(ci)場包括：磁(ci)化線圈通過電流(liu)I產生的(de)磁(ci)場和(he)鋼(gang)管中(zhong)(zhong)感(gan)生渦流(liu)J形成的(de)磁(ci)場。磁(ci)化線圈的(de)磁(ci)通總量包含了(le)由感(gan)生渦流(liu)J產生的(de)部(bu)分磁(ci)通量，因此鋼(gang)管中(zhong)(zhong)的(de)渦流(liu)效應會對磁(ci)化線圈中(zhong)(zhong)的(de)感(gan)生電流(liu)產生一定影響。
采用如(ru)(ru)圖(tu)5-3所示(shi)模型，進(jin)一(yi)步研究磁(ci)(ci)化線(xian)(xian)圈(quan)(quan)中(zhong)(zhong)產生的(de)感(gan)(gan)生電(dian)(dian)流(liu)變化規律。其中(zhong)(zhong)，線(xian)(xian)圈(quan)(quan)匝數為(wei)(wei)600匝，磁(ci)(ci)化電(dian)(dian)流(liu)為(wei)(wei)5A。當鋼管(guan)(guan)管(guan)(guan)頭、管(guan)(guan)體和管(guan)(guan)尾分(fen)(fen)(fen)別(bie)與(yu)磁(ci)(ci)化線(xian)(xian)圈(quan)(quan)耦合時(shi)提取磁(ci)(ci)化線(xian)(xian)圈(quan)(quan)內(nei)部產生的(de)感(gan)(gan)生電(dian)(dian)流(liu)，如(ru)(ru)圖(tu)5-7所示(shi)。仿真分(fen)(fen)(fen)兩種：一(yi)是(shi)考慮鋼管(guan)(guan)渦流(liu)效(xiao)應(ying)時(shi)分(fen)(fen)(fen)析線(xian)(xian)圈(quan)(quan)感(gan)(gan)生電(dian)(dian)流(liu)與(yu)運動(dong)速(su)(su)度的(de)關(guan)系，二是(shi)忽(hu)略鋼管(guan)(guan)渦流(liu)效(xiao)應(ying)而單獨分(fen)(fen)(fen)析線(xian)(xian)圈(quan)(quan)感(gan)(gan)生電(dian)(dian)流(liu)與(yu)鋼管(guan)(guan)運動(dong)速(su)(su)度關(guan)系。分(fen)(fen)(fen)別(bie)取速(su)(su)度0.1m／s、1m／s、2m／s、5m／s、8m／s、10m／s、20m／s、30m／s、40m／和50m／s進(jin)行仿真，獲(huo)得如(ru)(ru)圖(tu)5-8所示(shi)的(de)磁(ci)(ci)化線(xian)(xian)圈(quan)(quan)感(gan)(gan)生電(dian)(dian)流(liu)與(yu)運動(dong)速(su)(su)度關(guan)系曲(qu)線(xian)(xian)。其中(zhong)(zhong)I1csI2cs和I3cs分(fen)(fen)(fen)別(bie)為(wei)(wei)考慮鋼管(guan)(guan)渦流(liu)效(xiao)應(ying)時(shi)在管(guan)(guan)頭、管(guan)(guan)體和管(guan)(guan)尾處線(xian)(xian)圈(quan)(quan)中(zhong)(zhong)產生的(de)感(gan)(gan)生電(dian)(dian)流(liu)，11cI2c和I3c分(fen)(fen)(fen)別(bie)為(wei)(wei)忽(hu)略不銹(xiu)鋼管(guan)(guan)渦流(liu)效(xiao)應(ying)時(shi)磁(ci)(ci)化線(xian)(xian)圈(quan)(quan)中(zhong)(zhong)產生的(de)感(gan)(gan)生電(dian)(dian)流(liu)。
圖5-8所示的(de)(de)(de)仿真結果與(yu)圖5-6所示的(de)(de)(de)理論(lun)分析結論(lun)相同(tong)：當管(guan)頭(tou)進入磁(ci)化(hua)線(xian)(xian)(xian)圈(quan)(quan)(quan)(quan)時，線(xian)(xian)(xian)圈(quan)(quan)(quan)(quan)中(zhong)產(chan)(chan)生(sheng)(sheng)(sheng)(sheng)的(de)(de)(de)感(gan)(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)幅(fu)值為負，即與(yu)磁(ci)化(hua)電(dian)流(liu)方向(xiang)相反；當管(guan)體通(tong)(tong)過(guo)磁(ci)化(hua)線(xian)(xian)(xian)圈(quan)(quan)(quan)(quan)時，線(xian)(xian)(xian)圈(quan)(quan)(quan)(quan)中(zhong)基(ji)本無感(gan)(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)產(chan)(chan)生(sheng)(sheng)(sheng)(sheng)；隨著管(guan)尾離開磁(ci)化(hua)線(xian)(xian)(xian)圈(quan)(quan)(quan)(quan)，此(ci)時線(xian)(xian)(xian)圈(quan)(quan)(quan)(quan)中(zhong)產(chan)(chan)生(sheng)(sheng)(sheng)(sheng)與(yu)磁(ci)化(hua)電(dian)流(liu)方向(xiang)相同(tong)的(de)(de)(de)感(gan)(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)。根據楞次定(ding)律(lv)，線(xian)(xian)(xian)圈(quan)(quan)(quan)(quan)中(zhong)產(chan)(chan)生(sheng)(sheng)(sheng)(sheng)的(de)(de)(de)感(gan)(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)會阻(zu)礙線(xian)(xian)(xian)圈(quan)(quan)(quan)(quan)磁(ci)通(tong)(tong)量(liang)的(de)(de)(de)變化(hua)：當管(guan)頭(tou)進入磁(ci)化(hua)線(xian)(xian)(xian)圈(quan)(quan)(quan)(quan)時，線(xian)(xian)(xian)圈(quan)(quan)(quan)(quan)中(zhong)會產(chan)(chan)生(sheng)(sheng)(sheng)(sheng)反向(xiang)感(gan)(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)來(lai)阻(zu)礙磁(ci)通(tong)(tong)量(liang)的(de)(de)(de)增大(da)；當管(guan)體與(yu)磁(ci)化(hua)線(xian)(xian)(xian)圈(quan)(quan)(quan)(quan)耦合時，由于線(xian)(xian)(xian)圈(quan)(quan)(quan)(quan)磁(ci)通(tong)(tong)量(liang)基(ji)本不變而無感(gan)(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)產(chan)(chan)生(sheng)(sheng)(sheng)(sheng)；當管(guan)尾離開磁(ci)化(hua)線(xian)(xian)(xian)圈(quan)(quan)(quan)(quan)時，線(xian)(xian)(xian)圈(quan)(quan)(quan)(quan)中(zhong)會產(chan)(chan)生(sheng)(sheng)(sheng)(sheng)同(tong)向(xiang)感(gan)(gan)(gan)(gan)生(sheng)(sheng)(sheng)(sheng)電(dian)流(liu)來(lai)阻(zu)礙磁(ci)通(tong)(tong)量(liang)的(de)(de)(de)減小。
另外，從圖5-8中(zhong)可以看出，在運行速(su)(su)度(du)較低時(shi)(shi)，磁(ci)化線圈(quan)中(zhong)感(gan)(gan)生(sheng)電(dian)流隨著速(su)(su)度(du)的增(zeng)加而快速(su)(su)上(shang)升；當速(su)(su)度(du)達到一(yi)定幅值(zhi)時(shi)(shi)，磁(ci)化線圈(quan)中(zhong)的感(gan)(gan)生(sheng)電(dian)流基本(ben)保持不變。因(yin)為(wei)感(gan)(gan)生(sheng)電(dian)流只能減緩磁(ci)化線圈(quan)磁(ci)通量的變化速(su)(su)度(du)，而不能改變磁(ci)通量的變化趨(qu)勢。
從圖(tu)5-8中(zhong)(zhong)還可以看(kan)出，鋼管(guan)中(zhong)(zhong)的(de)渦流會削弱(ruo)磁化線(xian)圈中(zhong)(zhong)產生的(de)感(gan)生電流，根據楞次定(ding)律(lv)，鋼(gang)(gang)管(guan)中的渦流(liu)同樣會阻礙鋼(gang)(gang)管(guan)中磁(ci)(ci)通(tong)(tong)量的變(bian)化(hua)(hua)。當(dang)不銹(xiu)鋼(gang)(gang)管(guan)進入和離開(kai)磁(ci)(ci)化(hua)(hua)線(xian)(xian)圈時，鋼(gang)(gang)管(guan)中的磁(ci)(ci)通(tong)(tong)量變(bian)化(hua)(hua)規律(lv)同樣先增大后減小。由(you)于磁(ci)(ci)化(hua)(hua)線(xian)(xian)圈磁(ci)(ci)通(tong)(tong)總量包(bao)含了不銹(xiu)鋼(gang)(gang)管(guan)磁(ci)(ci)通(tong)(tong)量，所以，感生渦流(liu)在(zai)阻礙鋼(gang)(gang)管(guan)磁(ci)(ci)通(tong)(tong)量變(bian)化(hua)(hua)的同時也阻礙了線(xian)(xian)圈磁(ci)(ci)通(tong)(tong)量的變(bian)化(hua)(hua)速率(lv)，最(zui)終(zhong)削弱了線(xian)(xian)圈感生電(dian)流(liu)的強度。
