The role of security cameras for monitoring the imaging region and converts it into an electrical signal , according to the specification can be divided into 1/ 3 “, 1 / 2″ and 2/ 3 ” and other types of installation with two kinds of fixed and PTZ while in the purchase of such security products to the attention of its argument , the following are the parameters for the purchase of the camera should be noted that some of the problems :
1 , sensor parameters
At present , the mainstream security cameras with CCD sensor element , in fact, a photoelectric conversion element . And compared to the previous CMOS sensor , CCD sensitivity is 3 to 10 multiples more than the CMOS , CCD chips thus can receive more light signals converted into electrical signals by the video processing circuit filter , amplified video signal output form . The stronger the received optical signal , the greater the amplitude of the video signal . Video signal is connected to a monitor or TV’s video input terminal can see video images. Improve image clarity simply is to improve the camera’s photographic capabilities.
2 , the parameters of the lens
Aperture : Aperture installed in the rear of the lens , the larger the aperture opening , the amount of light passing through the lens , the greater , the higher the sharpness of the image ; aperture opening as small , the amount of light passing through the lens smaller , more clarity of the image low . Usually F ( flux) to represent. F = focal length (f) / aperture . Technical specifications of the camera , we can often see 6mm/F1.4 such parameter , which indicates the lens focal length is 6mm, the luminous flux is 1.4 , then we can easily calculate the aperture of 4.29mm. In the case of the same focal length f , F value is smaller, the larger the aperture , the luminous flux reaching the CCD chip is larger , the lens the better.
FOV parameters: In engineering practice , we used horizontal field angle of the screen to reflect the shooting range . The larger the focal length f , the smaller the field of view , the photosensitive member formed on a screen smaller range ; the contrary, the smaller the focal length f , the field angle, the photosensitive member formed on the larger the screen .
Focal length (f) parameters: a focal length of the lens and the distance between the photosensitive member , by changing the focal length of the lens , the lens magnification can be changed , changing the size of the captured image . When the distance between the object and the lens is very far away , we can express the following formula : ≈ magnification lens focal length / object distance . Increase the focal length of the lens , magnification increases , you can narrow the vision , the picture smaller scope , the vision to see more clearly the details ; if the focal length of the lens to reduce the magnification is reduced, expanding the scope of the screen and can see the bigger scene .
Security cameras pixels and resolution than the computer’s video head to be high, but can not keep up professional digital camera or dv. security cameras just a single video capture device, it does not have the data storage function .
The installation of security cameras
Here I will introduce a security cameras installation method:
1 ) , to meet the monitoring requirements of the target field of view under the conditions of its installation height : Interior from the ground should not be less than 2.5m; outdoor ground should not be less than 3.5m.
2 ) , security cameras and supporting devices such as lenses, protective cover, bracket, wipers , etc., should be firmly installed , running should be flexible , should pay attention to anti-sabotage, and coordinate with the surrounding environment .
3 ) , in the strong electromagnetic interference environment , security cameras should be installed with the insulation isolation.
4 ) , the signal lines and power lines should be introduced separately , the exposed part of the hose protection, does not affect the PTZ rotation.
5 ) , the elevator car security cameras inside the car door should be installed in the top of the left or right , and can effectively monitor the elevator occupant compartment facial features.