攝(she)像機要求(qiu)的(de)(de)(de)供(gong)(gong)(gong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)源一(yi)般有三(san)種：直流12V、交流24V或220V，大多數(shu)工程應用中不從電(dian)(dian)(dian)(dian)(dian)梯(ti)轎(jiao)廂(xiang)(xiang)的(de)(de)(de)供(gong)(gong)(gong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)源上取，而(er)是另外(wai)布設供(gong)(gong)(gong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)源給(gei)攝(she)像機供(gong)(gong)(gong)電(dian)(dian)(dian)(dian)(dian)，攝(she)像機輸出圖像經(jing)過(guo)一(yi)條軟性的(de)(de)(de)視(shi)頻(pin)(pin)(pin)(pin)(pin)電(dian)(dian)(dian)(dian)(dian)纜(lan)從井道(dao)的(de)(de)(de)止方或下方送出，視(shi)頻(pin)(pin)(pin)(pin)(pin)電(dian)(dian)(dian)(dian)(dian)纜(lan)和(he)供(gong)(gong)(gong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)纜(lan)與轎(jiao)廂(xiang)(xiang)的(de)(de)(de)動(dong)(dong)力線(xian)(xian)捆綁(bang)在一(yi)起，當電(dian)(dian)(dian)(dian)(dian)梯(ti)運行時牽引電(dian)(dian)(dian)(dian)(dian)機運行產生的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)磁場(chang)沿照明(ming)動(dong)(dong)力線(xian)(xian)傳播，顯然會(hui)影響攝(she)像機供(gong)(gong)(gong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)纜(lan)和(he)視(shi)頻(pin)(pin)(pin)(pin)(pin)電(dian)(dian)(dian)(dian)(dian)纜(lan)，當視(shi)頻(pin)(pin)(pin)(pin)(pin)電(dian)(dian)(dian)(dian)(dian)纜(lan)的(de)(de)(de)屏蔽層不夠嚴密時，高頻(pin)(pin)(pin)(pin)(pin)干(gan)擾就(jiu)經(jing)視(shi)頻(pin)(pin)(pin)(pin)(pin)電(dian)(dian)(dian)(dian)(dian)纜(lan)傳回監(jian)視(shi)器。而(er)對于50Hz的(de)(de)(de)橫(heng)紋滾動(dong)(dong)根據電(dian)(dian)(dian)(dian)(dian)磁學理論知道(dao)視(shi)頻(pin)(pin)(pin)(pin)(pin)電(dian)(dian)(dian)(dian)(dian)纜(lan)的(de)(de)(de)屏蔽層可(ke)完(wan)全消除50Hz工頻(pin)(pin)(pin)(pin)(pin)干(gan)擾。由此可(ke)以推斷這(zhe)部分干(gan)擾不是通過(guo)視(shi)頻(pin)(pin)(pin)(pin)(pin)電(dian)(dian)(dian)(dian)(dian)纜(lan)耦合過(guo)來(lai)(lai)，而(er)是來(lai)(lai)自電(dian)(dian)(dian)(dian)(dian)源線(xian)(xian)和(he)不合理的(de)(de)(de)視(shi)頻(pin)(pin)(pin)(pin)(pin)線(xian)(xian)聯結。

　　對于圖像中的(de)(de)(de)高(gao)頻干擾，因它的(de)(de)(de)頻帶仍在8MHz以(yi)內，采用空(kong)隙率(lv)為50%左右的(de)(de)(de)屏(ping)蔽網(wang)可基(ji)本(ben)消防高(gao)頻干擾，但(dan)要達到50%的(de)(de)(de)空(kong)隙率(lv)屏(ping)蔽網(wang)根數(shu)需每個波長長度有(you)60根以(yi)上，這(zhe)樣高(gao)的(de)(de)(de)密度又會使電纜(lan)的(de)(de)(de)柔韌性(xing)下降，比(bi)較好的(de)(de)(de)方法是采用帶有(you)雙層(ceng)屏(ping)蔽的(de)(de)(de)視頻電纜(lan)，信號的干擾問題分析在我們日常生活中使(shi)用(yong)的時(shi)候是經常遇到的問題。

　　視頻電纜屏(ping)蔽(bi)層是接地的，如果視頻信號“地”與顯示器的“地”相對“電網地”的電位不同，那么通過電源在攝像機與顯示器之間形成電源回路，這樣50Hz的工頻干擾進入顯示器中，消除50Hz工頻干擾方法有兩種，一是想辦法使各處的“地”電位與“電網地”的電位差完全相同，或者切斷形成地環流的路徑。由于工程環境比較復雜，使各處“地”完全等電位比較困難，只能通過加大攝像機供電線纜的線徑，盡可能降低地回路的電阻。或者采用切斷地環流回路的方法，在攝像機或顯示器端有一端不接地，通常在顯示器端不接供電電源的地，這樣雖不能完全消除干擾但可大減少50Hz的干擾。

　　那么從上(shang)(shang)面對監控(kong)視(shi)頻的(de)(de)信號干擾問(wen)題的(de)(de)分析來看，如果(guo)電源線上(shang)(shang)耦(ou)合上(shang)(shang)高頻噪聲(sheng)(sheng)，即使(shi)視(shi)頻電纜的(de)(de)屏(ping)蔽電纜的(de)(de)屏(ping)蔽再好，也會(hui)將(jiang)(jiang)噪聲(sheng)(sheng)送至(zhi)顯(xian)示器(qi)，因此攝像(xiang)機(ji)的(de)(de)供電電源線最好也要屏(ping)蔽，上(shang)(shang)述措施需(xu)要在(zai)(zai)工程設計和(he)施工時就要全(quan)面考(kao)慮才(cai)能實現，若到(dao)(dao)了系(xi)統(tong)調試時發現干擾存在(zai)(zai)可采(cai)用調制和(he)解調的(de)(de)方(fang)法(fa)將(jiang)(jiang)噪聲(sheng)(sheng)濾(lv)除，在(zai)(zai)攝像(xiang)機(ji)端設一調制器(qi)將(jiang)(jiang)視(shi)頻信號搬移到(dao)(dao)幾十兆赫茲的(de)(de)頻度段上(shang)(shang)，在(zai)(zai)顯(xian)示器(qi)端設一低(di)通(tong)濾(lv)波器(qi)將(jiang)(jiang)低(di)于8MHz的(de)(de)信號全(quan)部濾(lv)除，再經過解調將(jiang)(jiang)視(shi)頻圖(tu)像(xiang)還原。

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編輯：梁靜茹