CCTV cameras use an internal generator or AC power to synchronize their processes of creating motion video. In countries like the United States that use alternating current of 60 Hz. (Cycles), each second of video contains 60 fields, which are 30 pictures. In Europe and other regions use 50 cycles so there are 50 fields and 25 frames of video per second. To the human eye, these video frames appear as moving images.
The total voltage produced video is measured from the bottom of the sync pulse to the top of the white level, thus generating a peak to peak (w / w) of a volt voltage. The luminance signal starts from 0.3 volts to 0.7 volts maximum voltage. This complex signal is known as a composite video signal since video information and synchronization is combined into a single signal.
CCD Image size
Based on DELUXESURVEILLANCE, the first CCTV cameras had a circular tube as a sensor. The image size was determined by the pipe diameter, which is the diagonal measure of the picture.
Although today the sensor CCD are flat silicon chips rectangular, this method of measurement it is still used.
Larger CCDs capture more light, and therefore tend to be more sensitive than CCDs in smaller format.
The prices of cameras increase with the size of the sensor. Therefore, the selection of the sensor size should suit both your budget and application.
Please note size sensor shown in the diagram should be considered in relation to the selected since the lenses are also designed for specific sensor lens sizes.
The lenses are the “eyes” of a CCTV system. They are essential for creating functions of video. The lenses perform two main functions. First, determine the scene can be displayed on the monitor – this is a function of the focal length. Second, they control the amount of light reaching the sensor – this is a function of the iris. The focal length can be fixed or variable (eg. A lens with zoom). The iris can be adjusted manually or camera can do it automatically.
How can you determine the best lens for every situation?
The lenses have many features that should be compatible with your requirements.
Fixed focal length lenses
Fixed lenses are the simplest type of lens, and thus are less expensive. Your default focal length requires a precise calculation for the selection of the lens that is best suited to the location. This decision should be based on the desired size of the display area and its distance from the camera. The size of the lenses can vary from a narrow field of view 30 degrees to allow more detail to a given wider 90 degree field of view known as one wide angle distance.
The varifocal lenses offer more flexibility, enabling adjustment of field of view in the form manually . Although they are a little more expensive, these lenses are very popular because you can get a more accurate setting of the scene.
Also, they simplify the specification process, since a flexible view field means that you can select only a single lens for all cameras in a complete system.
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