CCTV system plays a special role in modern architecture. The reason why it is widely applied is that it can real-time, visually and truly display images, and it has already become a very effective tool in modern monitoring management. CCTV system includes four parts: camera, transmission & distribution, control, image process & display. This system is a bidirectional, multi transmission system which not only transmits video signal to receiver, but also transmits controlling signal & power to camera.

1.Control mode & control signal transmission

CCTV system control motorized pan / tilt, motorized zoom lens, housing and power supply. Distance between control center and controlled center and quantity of controlled device determines CCTV control mode.
(1)With few cameras and no more than 500m distance, we can adopt directly control mode which transmits controlling signal by poly-core cable. This mode control line is with numerous control lines and heavy construction.

(2)With few cameras, few controlling items and no more than 1000m distance, we can adopt indirectly control mode which is with numerous controlling lines also.

(3)As PC technology is developing fast, digital skill has been widely applied in traditional analog CCTV field, which is so called digital control. Digital control mode adopts serial code for transmitting controlling signal. It only needs two controlling lines, suitable for controlling large and medium system and long distance transmission; even can connect monitoring with alarm system by software.

(4)When controlling distance is between 300m and 500m, video signal and controlling signal can use same coaxial cable, which is called coaxial control. Save controlling lines as this mode could, it costs too much at present. We should carefully consider for design.

2.Video signal distribution & transmission

Video signal distribution
With no more than 5 monitors and proximal settings, adopt bridging distribution pattern; with one channel signal transmitting to remote multi monitors, adopt video distributor.
Video signal transmission
Video transmission cables include coaxial cable (unbalanced cable), balanced cable (telephone cable) and optical cable. Balanced cable and optical cable mainly apply in long distance transmission. In hotel suchlike buildings, it is usual to adopt coaxial cable transmitting video signal. With 75-5 coaxial cable and 300m distance, adopt cable compensator; with 75-9 coaxial cable and no more than 500m distance from camera to monitor, do not adopt cable compensator.

3.Camera & accessories selection

Divided by picture pickup device, CCTV camera includes electro-vacuum device (vidicon) camera and solid picture pickup device (CCD device, MOS device) camera. Electro-vacuum vidicon develops earlier and has numerous kinds, having been displaced by solid vidicon which is applied in common CCTV systems by now; the former is a new kind of picture pickup device developed latest years. Solid pickup device has features of slight inertia, high sensitivity, anti intensive light, low geometric distortion, good equilibrium, anti shock, no microphony effect, and smart, slight and long expectancy. CCTV camera is trending to small size, slight weight, and low price, enhancing image quality and increasing functions.
Housing selection
At first, camera should be selected according to working environment. Different environments require different functions for cameras. For example rainproof, dustproof, even radiation-proof and waterproof; outdoor environment requires automatic temperature adjustment function and remote control wiper function. These functions are realized by housings.
Illumination selection
When selecting camera, we should ensure that min illumination of environment is 10 times more than that of camera. Usually with black & white monitor, objects illumination should be no less than 10lux; with color monitor, objects illumination should be no less than 50lux. In 0lux environment, we should adopt IR LED or other light sources.
Lens selection
In order to display image on monitor, even reach optimum requirement. Generally speaking, for the environments with large scope, macro & micro monitoring, repeated & non-synchronous monitoring, it is suitable for adopting zoom lens and remote control pan / tilt. Other environments should adopt mono-focal lens. In backlight recording, we should select camera with backlight compensation function; for the camera with more than 100 times luminance difference or day / night camera, we should adopt automatic aperture lens or motorized aperture lens; when remote control is necessary, we should adopt remote control lens with light focus, adjustable aperture and varifocal; for concealed camera, we should adopt pinhole lens or prism lens; for elevator camera, we should adopt wide angle lens with more than 70° horizontal angle.
Black & white camera and color camera selection
Color camera is higher than black & white camera in price and repair cost. So if objects have no obvious mark or difference in color, we had better adopt black & white camera.

Pan / tilt selection
Pan / tilt voltage includes AC and DC. We should select them according to controller model and other devices in system. AC pan / tilt suits constant speed. DC pan / tilt suits changeable speed, which is with fast speed and suits preset system.

4.Camera installation

Indoor camera height ranges from 2.5m to 5m; outdoor camera height ranges from 3.5m to 10m. Inner-elevator installation should choose top section which is diagonal with elevator keyboard; even camera optic-axle forms 45° with both-sides of inner-elevator and ceiling.

5.Image process & display

Image process
CCTV system can record, switch, replay, process and copy image data. Video switcher supports manually program and auto program, displaying all video signals on appointed monitor with fixed or timed mode, besides, video switcher supports image mixing, image partition and caption overlay. In CCTV system, video switcher should have port connecting with alarm controller. Once alarm happens, video switcher instantly switches related image, record and replay in order to analyze & process accidents.
Image record & replay
CCTV system adopts video recorder realizing record and replay function. The features of such kind recorder lie in long time recording (24h recording is popular nowadays), quick and static replay images with remote control function. System can remotely manage recorder or auto manage recorder with control signal.
Image display
Monitor is the terminal display device in CCTV system. Monitor selection should determined by system skill performance index and usage. Monitor should accord with camera in color or black & white. Screen size should be chosen according to control center area and managers quantity. Monitor resolution should no less than that of camera in order to show camera performance thoroughly. Monitor quantity should according to practical requirement, make differing matters’ priority and ensuring main parts as the principle, besides, monitor should be appropriate proportion with camera in quantity. In my opinion, in main part, proportion between monitor and camera should be no less than 1:3; other part proportion should be no less than 1:8.

6.Power supply & grounding

CCTV system should be supplied power by stable AC circuit. Camera should be supplied power by control center to avoid sudden power-off affecting entire system, as well as to create condition for later project repair & management.
System grounding should adopt one point grounding mode with 4Ω or less resistance; or joint grounding with 1Ω or less resistance.