How to choose surveillance camera and installation and debugging precautions
Tag: Camera CCD This article refers to the address: http:// In a closed-circuit monitoring system, a camera is also called a camera or a CCD or a charge coupled device. Strictly speaking, the camera is a general term for cameras and lenses. The main sensing component of the camera is CCD, which has the characteristics of high sensitivity, small distortion, long life, anti-vibration, anti-magnetic field, small volume and no residual image. CCD is an electric coupling device, which can turn light into electric charge and can By storing and transferring the charge, it is also possible to take out the stored charge and change the voltage, so it is an ideal imaging element. It is a new device that replaces the camera sensor. The working principle of the CCD is that the object reflects light, propagates to the lens, and focuses on the CCD chip through the lens. The CCD accumulates the corresponding charge according to the intensity of the light, and periodically discharges to generate an electrical signal representing a picture. After filtering and amplifying processing, a standard composite video signal is output through the output terminal of the camera. This standard video signal is the same as the video output of a home video recorder, VCD player, and home video camera, so it can be viewed on a TV. First, the selection and classification of CCD camera The CCD chip is like the human retina and is the core of the camera. At present, China is not capable of manufacturing. Most of the cameras on the market use chips produced by Japanese companies such as SONY, SHARP, Panasonic, South Korea's Samsung, and LG. Because the chip produces different grades, different manufacturers obtain different ways, etc., resulting in CCD acquisition effects are also very different. At the time of purchase, you can take the following methods: connect the power supply, connect the video cable to the monitor, see if there is a bright spot when the image is black, and the snow on the screen is not big. These are the simplest and direct methods for detecting the CCD chip, and Need special equipment. Then you can open the aperture and see a still life. If it is a color camera, it is best to take a colorful object and check whether the image on the monitor is color cast, distorted, and the color or gray level is smooth. A good CCD can restore the color of the scene well, making the object look clear and natural; and the image of the defective product will have a color cast, even if it faces a piece of white paper, the image will show blue or red. Individual CCDs have impurities on the CCD target surface due to dust in the production workshop. In general, impurities do not affect the image, but in low light or microscopic imaging, fine dust can also cause adverse consequences if used. Such work must be carefully selected. 1, according to the image color division Color camera: It is suitable for detailing of scenes, such as distinguishing the color of clothing or scenery. Black and white camera: Suitable for areas with insufficient light and areas where lighting cannot be installed at night. Black and white cameras can be used when monitoring only the position or movement of the scene. 2, according to the size of the CCD target CCD chips have been developed in a variety of sizes: Most of the chips currently used are 1/3" and 1/4". When purchasing a camera, especially when the camera angle is relatively strict, the size of the CCD target surface, the cooperation of the CCD and the lens will directly affect the angle of view and the sharpness of the image. 1 inch - the target size is 12.7mm wide by 9.6mm high and 16mm diagonal. 2/3 inch - the target size is 8.8mm wide by 6.6mm high and 11mm diagonal. 1/2 inch - the target size is 6.4mm wide by 4.8mm high and 8mm diagonal. 1/3 inch - the target size is 4.8mm wide by 3.6mm high and 6mm diagonal. 1/4 inch - the target size is 3.2mm wide by 2.4mm high and 4mm diagonal. 3 according to the power supply 110VAC (NTSC is mostly of this type), 220VAC, 24VAC. 12VDC or 9VDC (most of these are miniature cameras). 4, divided by synchronization Internal synchronization: The synchronization signal generated by the synchronization signal generation circuit in the camera is used to complete the operation. External synchronization: An external sync signal generator is used to feed the sync signal to the external sync input of the camera. Power synchronization (linear lock, linelock): Vertical push synchronization with the camera AC power. External VD synchronization: The VD sync pulse input on the camera signal cable completes the external VD synchronization. Multi-camera external synchronization: fixed external synchronization for multiple cameras, so that each camera can work under the same conditions, because each camera is synchronized, so even if one of the cameras is switched to For other scenes, the picture of the synchronous camera will not be distorted. 5, illuminance division, CCD is divided into: Normal type of illumination required for normal work 1~3LUX Moonlight type normal work required illumination of about 0.1 LUX The starlight type requires illuminance below 0.01 LUX for normal operation. The infrared type is illuminated by infrared light and can be imaged in the absence of light (common type) Main technical indicators of CCD color camera (1) CCD size, which is the camera surface. Originally more than 1/2 inch, now 1/3 inch has become popular, 1/4 inch and 1/5 inch have also been commercialized. (2) CCD pixels, which are the main performance indicators of CCD, determine the clarity of the displayed image. The higher the resolution, the better the image details. The CCD is composed of area array photosensitive elements, each of which is called a pixel. The more pixels, the clearer the image. Most of the market is currently delimited by 250,000 and 380,000 pixels, and more than 380,000 pixels are high-definition cameras. (3) Horizontal resolution. The typical resolution of color cameras is between 320 and 500 TV lines, mainly 330 lines, 380 lines, 420 lines, 460 lines, 500 lines and other different grades. The resolution is represented by a TV line (referred to as the line TVLINES), and the resolution of the color camera is between 330 and 500 lines. The resolution is related to the CCD and the lens, and is also directly related to the bandwidth of the camera circuit channel. The usual rule is that the bandwidth of 1 MHz corresponds to a resolution of 80 lines. The wider the band, the clearer the image and the larger the line value. (4) Minimum illumination, also known as sensitivity. It is the sensitivity of the CCD to ambient light, or the darkest light required for normal CCD imaging. The unit of illuminance is lux. The smaller the value, the less light is needed and the more sensitive the camera. Moonlight and star-level high-sensitivity cameras can work in very dark conditions, 2~3lux is a general illumination, and now there are less than 1lux ordinary cameras. . (5) Camera power supply. The AC has 220V, 110V, 24V, and the DC is 12V or 9V. (6) Signal to noise ratio. The typical value is 46db. If it is 50db, the image has a small amount of noise, but the image quality is good. If it is 60db, the image quality is excellent and no noise occurs. (7) Video output. Mostly 1Vp-p, 75Ω, all use BNC connectors. (8) Lens mounting method. There are C and CS modes, the difference between the two is that the sensing distance is different. Second, the adjustable function of CCD color camera (1) Choice of synchronization method A. For a single camera, the main synchronization methods are as follows: Internal synchronization - The synchronization signal is generated by the crystal oscillation circuit inside the camera to complete the operation. External synchronization - Synchronization is generated by the synchronization signal generated by an external synchronization signal generator being sent to the external synchronization input of the camera. Power Synchronization - Also known as linear or line lock - is the use of the camera's AC power to complete the vertical push synchronization, that is, the camera and power neutral synchronization. B. For multi-camera systems, it is hoped that all video input signals are vertically synchronized, so that when the camera output is changed, no image distortion will occur, but power is supplied from each camera in the multi-camera system. It may be taken from different phases in the three-phase power supply, or even the entire system is out of sync with the AC power supply. The measures that can be taken at this time are: The synchronization signals generated by the same external synchronizing signal generator are sent to the external synchronizing input terminals of each camera to adjust the synchronization.
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