點解「閉路電視」叫「閉路」牙？

閉路電視是指播送的訊號只有在固定的迴路設備裡播放，例如以前的錄影機，或是一般大樓的監視器。這類的播放模式就被稱作閉路電視。（不對外播放）
以前的人都會稱錄影機播放節目這類叫做閉路電視。不過等到錄影機比較普遍後，就很少人說錄影機叫做閉路電視。反倒是大樓的監視系統，目前也還會被稱作閉路監視系統。

圖片參考：http://upload.wikimedia.org/wikipedia/en/thumb/8/8b/CCTVinopperation.jpg/180px-CCTVinopperation.jpg


The graphic for a CCTV Camera

圖片參考：http://upload.wikimedia.org/wikipedia/commons/thumb/a/a1/Three_Surveillance_cameras.jpg/180px-Three_Surveillance_cameras.jpg


Surveillance cameras.

圖片參考：http://upload.wikimedia.org/wikipedia/commons/thumb/c/c5/Closed.circuit.camera.arp.750pix.jpg/180px-Closed.circuit.camera.arp.750pix.jpg



Surveillance camera at London (Heathrow) Airport

Closed Circuit Television (CCTV) is the use of video cameras to transmit signal to a specific, limited set of monitors. It differs from broadcast television in that the signal is not openly transmitted, though it may employ point to point wireless links. CCTV is often used for surveillance in areas which need monitoring, such as banks, casinos, airports, military installations and convenience stores. Increasing use of CCTV in public places has caused debate over public surveillance versus privacy. In industrial plants, CCTV equipment may be used to observe parts of a process that are remote from a control room, or where the environment is not comfortable for humans. CCTV systems may operate continuously or only as required to monitor a particular event.

因為電線的電路不會外露出來以達至不容易被發現的攝影裝置.
叫做閉路(close-circuit)，係因為呢d訊號只會o係一個細o既範圍度發放，例如一棟大廈、一個商場，而唔係好似我地平日睇o既電視咁作公開o既廣播。
閉路電視是指播送的訊號只有在固定的迴路設備裡播放，例如以前的錄影機，或是一般大樓的監視器。這類的播放模式就被稱作閉路電視。


以前的人都會稱錄影機播放節目這類叫做閉路電視。不過等到錄影機比較普遍後，就很少人說錄影機叫做閉路電視。反倒是大樓的監視系統，目前也還會被稱作閉路監視系統。

圖片參考：http://hk.wrs.yahoo.com/_ylt=A8tU327UUs1HVGEBjTm.ygt./SIG=127rr12at/EXP=1204724820/**http%3A//www.mandom5354.com/treasure/017cam/cam06.JPG