CLOSED CIRCUIT TELEVISION
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15-10-2010, 05:10 PM
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CLOSED CIRCUIT TELEVISION
ELECTRONICS AGAINST TERRORISM
As the name implies, Closed Circuit Television (CCTV) is a system in which the circuit is closed and all the elements are directly Connected. Directly connected in this context includes systems linked by (CCTV) is the use of video cameras to transmit a signal to a specific place, limited set of monitors
This is unlike broadcast television where any receiver that is correctly tuned can pick up the signal from the airwaves. 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 that may need monitoring such as banks, casinos, airports, military installations and convenience stores
The first CCTV system was installed by Siemens AG at Test Stand VII in Peenemünde, Germany in 1942, for observing the launch of V2-rockets.The noted German engineer Walter Bruch was responsible for the design and installation of the system. CCTV recording systems are still often used at modern launch sites to record the flight of the rockets, in order to find the possible causes of malfunctions, while larger rockets are often fitted with CCTV allowing pictures of stage separation to be transmitted back to earth by radio link. In September 1968, Olean, NY was the first city in the United States to install video cameras along its main business street in an effort to fight crime. The use of closed-circuit TV cameras piping images into the Olean Police Department propelled Olean to the forefront of crime-fighting technology. The use of CCTV later on became very common in banks and stores to discourage theft, by recording evidence of criminal activity. Their use further popularised the concept. The first place to use CCTV in the United Kingdom was King's Lynn, Norfolk. In recent decades, especially with general crime fears growing in the 1990s and 2000s, public space use of surveillance cameras has taken off, especially in some countries such as the United Kingdom
A monitor and a camera are the two prerequiste devices required to build up a CCTV network or a system.
The starting point for any CCTV system must be the camera. The camera creates the picture that will be transmitted to the control position. Apart from special designs CCTV cameras are not fitted with a lens. The lens must be provided separately and screwed onto the front of the camera. There is a standard screw thread for CCTV cameras, although there are different types of lens mounts.
Not all lenses have focus and iris adjustment. Most have iris adjustment. Some very wide angle lenses do not have a focus ring.
The 'BNC' plug is for connecting the coaxial video cable. Line powered cameras do not have the mains cable. Power is provided via the coaxial cable.
The picture created by the camera needs to be reproduced at the control position. A CCTV monitor is virtually the same as a television receiver except that it does not have the tuning circuits.
SIMPLE CCTV SYSTEMS:
The simplest system is a camera connected directly to a monitor by a coaxial cable with the power for the camera being provided from the monitor. This is known as a line powered camera. Diagram 3 shows such a system. Probably the earliest well-known version of this was the Pye Observation System that popularised the concept of CCTV, mainly in retail establishments. It was an affordable, do-it-yourself, self-contained system.