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A camera, for example, collects reflected images from objects in the environment and then converts them into electronic signals. Cameras require more knowledge and skill to install than any other part of a CCTV system. For example, installers must consider such things as light sensitivity, lines of horizontal and vertical resolution, available light at the target, and the technology behind the imager. All of these things are important because they help determine how well a camera performs in an environment.
Assuming that the installer installed the right camera for the job, the collected images are converted from visible light into invisible electronic signals inside a solid-state imager. These signals then are transported by one of many transmission media to the monitor, where these signals are converted back to visible light in a CCTV monitor. In addition, these video signals are commonly routed to other devices designed to manipulate and/or process these images in a variety of ways. These devices are usually referred to as peripherals. After installing the right camera and picking the right video signal transmission technology for a CCTV installation, it's integral that an adequate video monitor be picked. Although video monitors are not usually as complicated as cameras, they are important enough for us to take the time to study.
CCTV "peripherals" are also important, as mentioned earlier, although they are often overlooked. They can also be the most difficult part of a CCTV installation to get right.
For example, a camera will operate without a lens (the lens is a peripheral) because it will still produce a 1 Vpp video signal-- which fits the classical definition of a video signal. However, the images reproduced by such a monitor will not be usable for identification purposes or visual recognition of others. In fact, without a lens, it's unlikely that there will be an image at all.
Pan-and-tilt mechanisms are another important peripheral that provides camera scanning and panning capabilities. In fact, camera housings, switchers, splitters, distribution amplifiers, time- lapse tape recorders, and others are all considered as peripherals.
A camera is designed to collect the reflected light from objects around them and then to convert them into a usable video signal that measures 1 Vpp (Volt, peak to peak). This video signal then is transmitted to a monitor or some other piece of equipment using any one of several transmission medias.
Selection of cameras
Tthe selection criteria should take into consideration the following factors:
- camera set should fulfill functional requirements in all demanded environmental conditions;
- it should fulfill all safety requirements ruling in the country and those specific for the application (e.g. in industrial plant)
The main points that should be considerate when selecting CCTV cameras:
- white balance for color cameras;
- electronic iris - important in changeable lighting conditions;
- long exposition times - in the connection with " multiplying " moving objects edges;
- spectral sensitivity - in connection with illumination type;
- external synchronization;
- back-up powering (especially in remote sites).
Selection of optimum kind of cameras requires consideration of many factors, such as: environmental conditions during all seasons, sizes of objects in the field of view, and others, listed above. The choice of color or B/W type is connected with the use of the camera. More detailed information is provided by color image, as it allows to distinguish details that are also easier to remember; the differences are noted faster, and, in some cases, viewing the color picture is the only way to estimate preciously the situation. Disadvantages of color cameras are higher price and lower sensitivity. We should choose B/W kind when information about intrusion is enough. In low light, only B/W camera with high sensitivity can ensure right surveillance qualities. |
