Closed Circuit TV Technology Page
 

Closed circuit simply means that the signal is not being broadcastanywhere, but rather is travelling by wire from the source to thereceiver. Usually a closed-circuit television (CCTV) system uses a stand-mounted or hand-held video camera to project a magnified image onto a video monitor or a television (TV) screen. Advances in CCTV technology are turning video surveillance into one of the most valuable loss prevention, safety/security and management tools available today. Retailers use CCTV to monitor for shoplifters and dishonest employees, compile recorded evidence against bogus accident claims and monitor merchandising displays in stores that may be hundreds of miles away. Manufacturers, governments, hospitals and universities use CCTV to identify visitors and employees, monitor hazardous work areas, thwart theft and ensure the security of the premises and parking facilities.

Closed circuit television (CCTV) originated in the 1950s and consisted of two low-resolution black and white cameras. Its main objective was to replace humans for visual security surveillance. In the 1980s, solid state cameras and VCRs were introduced. The resolution was better, but the pictures were still in black and white. In the 1990s, came the transformation to color, and eventually digital video recorders (DVRs) were introduced. Security has become an important part of most of our lives. Today there are still applications where black&white cameras are used, because they perform much better in low light and IR illuminated applications than the color cameras.

Today we can install miniature security cameras everyhwere(such cameras can even include infra-red illumination which enables us to see in the dark). The security camera in the local store or bank, that feeds to a monitorand a tape machine, is closed circuit television. Also, some sportsvenues will have closed circuit video support - TV that isn't broadcastanywhere, but just gives the people in the cheap seats a better view ofthe action. Since the events of September 11, many companies are increasingly concerned about building security and have started to investigate the functionality of their security systems. With the use of a Closed Circuit Television (CCTV) system (i.e., security cameras), the pictures taken could prevent many threats to public and private establishments.

Traditionally video transmission in CCTV is done using 75 ohm coaxial cables. The video signal transmitted is generally normal composite video signal, although some systems use RF signals. The camera is usually powered by low voltage (typically 12V or 24V) through a local power supply near camera or separate power cable fed together with the coaxial cable. There are also some systems which feed the power to the camera through the same coaxial cable where to picture is transported. Nowadays the use of UTP cabling (usually CAT5 cable as used in structured cabling systems) in CCTV systems has increased. Using suitable video signal converter video signals can be transportedmore or less well through unshielded twisted pair wiring. Twisted pair wiring method is used in many CCTV applications nowadays to use existing in-house twisted pair wiring instead ofinstalling new coaxial cable for the CCTV camera. For at least 20 years products have been available capable of transmitting video using UTP wire. There is a wide variety of systems from simple passive balun transformers to complicated active systems. Generally the better UTP cable you have and shorter distance, the simpler approach will work well. Generally if you run picture up to 100 meters or so using CAT5, simple passive baluns will do well. If you plans to transport the picture through lower quality "telephone cable" for many hunreds of meters, you need very good active adapters on the both ends of the cable to get good results.

Typical connections found on CCTV camera:

  • BNC connector and separate power connector: The BNC connector gives out standard composite video (1Vpp to 75 ohms, PAL or NTSC standard) and the power connector accepts the camera power (typically 12V or 24V). The Video signal on BNC connector is standard video signal that can be wired to almost any monitor or TV with video input.
  • Just BNC connector: In this kind of camera system the camera power is fed to the came through the ciaxial cable (fed to it by the monitor or video switcher). The same cable also transports the video from the camera to the monitor. The transported video can be either normal composite video or video signal modulated to RF carrier. This kind of systems are manufacturer specific and the camera works only with the monitor/switcher from the same manyfacturer.
  • RJ-11E connector: Some security cameras use similar connector as normal telephone connectors. Depending the camera either 4 or 6 connectors are used. This connecotr is generally used to connect power, video and audio signals. Different manufacturers can use different pinouts. The signals are typically normal composite video signal, analogue audio (line or mic level), power (12-15V often) and ground.

There are many standards in CCTV field. In Europe some CCTV system characteristics are standardized in EN 50132-2-1: Alarm systems - CCTV surveillance systems for use in security applications -- Part 2-1: Black and white cameras.

The CCTV field is changing with the expansion of network connections all around. More and more traditional composite CCTV installers and systems integrators are waking up to the fact that networked CCTV has significant benefits either integrated with existing equipment or as a stand-alone surveillance solution. Those who have yet to embrace these benefits run the risk of being left behind.


 
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