Modern security monitoring equipment are microelectronic products, these monitoring equipment has a high density, high speed, low voltage and low power consumption and other characteristics. Because of the precision of the security monitoring electronic equipment, overvoltage resistance to decline in its ability to a variety of overvoltage such as lightning, power system operation overvoltage, electrostatic discharge, electromagnetic radiation and other electromagnetic interference is very sensitive to make the monitoring system equipment is very susceptible to lightning overvoltage damage, resulting in the paralysis of the entire monitoring system.
In order to be able to accurately and effectively provide security monitoring system lightning solutions, first of all, should accurately analyze the security monitoring system suffered lightning damage to the main causes and possible lightning overvoltage intrusion path. On this basis, the selection of suitable lightning protection devices, research and explore reasonable signal, power line wiring, clear shielding and grounding methods, before you can give accurate, systematic lightning protection solutions.
The main reason for the damage caused by lightning direct lightning protection device in guiding the powerful lightning current into the earth, in its lead, grounding body and connected to them on the metal conductor generates a very high transient voltage, and they are close to the surrounding metal objects, equipment, lines, and they are not connected to the human body to generate a huge potential difference between the potential difference caused by the shock is the ground, the lightning protection device is the main reason for the damage caused by lightning. Potential counterattack.
Security monitoring system lightning solutions
4-1 direct lightning protection direct lightning protection, lightning protection is an indispensable and important basis for protection, is an important part of the lightning protection system.
4-1-1 front-end equipment direct lightning protection
Security monitoring system front-end equipment outdoor and indoor two kinds of equipment installed in the indoor equipment is generally not subject to direct lightning, can not consider direct lightning protection. Installed in outdoor equipment, most of which are in a relatively open area, the risk of direct lightning is greater, it must consider the issue of direct lightning protection. Security monitoring system front-end equipment, such as cameras, should be placed within the effective protection of the lightning. In order to prevent electromagnetic induction, the camera's power and signal lines should be laid through the metal pipe, the metal pipe should be reliably grounded.
4-1-2 Transmission lines of direct lightning protection
In order to make the transmission line from direct lightning, the transmission line should try to avoid overhead erection, it is best to wear a metal pipe laid in the ground, the ends of the metal pipe should be reliably grounded.
4-1-3 Terminal equipment direct lightning protection
Terminal equipment room (monitoring room) should be taken in the building to protect against direct lightning protection measures should meet the "Building Lightning Protection Design Code" GB50057294 (2000 edition) requirements.
4-2 Lightning protection and grounding system
All lightning protection systems should be reliable and effective grounding. Grounding system is one of the necessary components of the lightning protection system. Security monitoring system front-end, terminal equipment should be a good lightning grounding, grounding system should meet the specification requirements. Generally independent of the monitoring room where the building's front-end equipment must be equipped with independent grounding. But here we need to point out in particular: If you do not meet the independent grounding requirements, you should do *** with grounding.
4-3 wiring should pay attention to the problem
In order to reduce the risk of lightning, any wire, metal lines should be avoided as far as possible and direct lightning protection devices parallel bundled, and should be in accordance with the relevant specification requirements wiring, reserved a certain safety distance.
4-4 AC power surge protector selection
For security monitoring system, all AC power supply into the end of the effective lightning protection. Front-end equipment should be installed at the front-end AC power supply into the corresponding power surge protector. Into the monitoring room of the power line should be considered as a three-tier protection, can be installed in the building's power distribution room of the power inlet a power surge protector, in the monitoring room where the floor distribution box of the power inlet to the installation of two power surge protector, in the monitoring of the power inlet to the room of the important equipment to install a three-tier power surge protector.
4-5 Transmission line protection
The safest way of wiring, should be taken throughout the buried metal pipe laying, at the same time, the metal pipe must be done at both ends of the effective grounding. In the actual project, in many cases the conditions do not allow, you can wear the whole metal pipe overhead line; or not wear the whole metal pipe, but in the cable into the monitoring room and the front-end equipment must be worn before the metal pipe buried laying, buried length should not be less than 15m, in the household end of the cable metal jacket, metal pipe and lightning grounding effective connection. All transmission lines should be installed at both ends of the corresponding surge protector.
4-6 Fiber optic communication line protection
Generally speaking, fiber optic lines do not have to be retrofitted with lightning surge protection devices, because the fiber optic line itself does not belong to the conductor, it will not inductance, transfer of overvoltage surge. However, it should be noted that the fiber optic cable generally have metal reinforcement core and metal armor layer for the protection of fiber optic cable, then the fiber optic into the home must be well protected by grounding.
4-7 video signal lightning protection precautions
Video signal lightning protection, the concept is relatively simple, but there are often due to negligence in the work of the link leading to the failure of lightning protection, while leading to the video lightning itself was damaged. Most of the signal lightning protection products on the market, generally using two-level protection, the first level as a coarse protection, generally using gas discharge tubes as a protection device, after a fine protection, generally using TV S as a protection device.
4-8 DC power protection, control line signal protection
DC power protection, control line signal protection and video signal protection of the same common problems, the connection is generally crimped. Field engineers must pay attention to the correct connection of such lightning protection.
5, the daily maintenance requirements
(1) lightning rods, lightning straps, brackets, grounding lead wires, grounding bodies, connecting lines and other components, should be hot-dip galvanized and other methods to effectively prevent corrosion, daily use of the rust corrosion should be frequently removed.
(2) should regularly check the use of lightning arrester, found to be damaged, aging should be replaced in a timely manner.
In the closed-circuit monitoring system, the camera, also known as the camera or CCD (Charge Coupled Device) that is, charge-coupled device. Strictly speaking, the camera is the camera and the lens of the general term, but in fact, most of the camera and lens are purchased separately, the user according to the size of the target object and the distance between the camera and the object, through the calculation of the focal length of the lens, so each user needs the lens is based on the actual situation, do not think that the camera (head) on the lens is already there to meet all the needs.
The main sensing component of the camera is the CCD, which has high sensitivity, small distortion, long life, anti-vibration, anti-magnetic field, small size, no residual shadow, etc., the CCD is an electrically coupled device (Charge Couple Device) for short, which can change the light into a charge and can be stored and transferred, but also can be stored out of the charge so that the voltage changes, so it is the ideal camera component. Therefore, it is an ideal camera element. It is a new type of device that replaces the camera tube sensor.
The working principle of the CCD is: the photographed object reflects the light, spread to the lens, the lens focuses on the CCD chip, the CCD according to the intensity of the light accumulates the corresponding charge, by the periodic discharge, resulting in the production of a picture of a picture of the electrical signals, filtering, amplification, through the camera's output terminals output a standard composite video signal. This standard video signal with home video recorders, VCD players, home video cameras, the video output is the same, so you can also record or receive a TV set to watch.
CCD camera selection and classification CCD chip is like the human retina, is the core of the camera. At present, our country is not yet capable of manufacturing, most of the cameras on the market are used in Japan SONY, SHARP, Panasonic, LG and other companies to produce the chip, South Korea also has the ability to produce, but the quality will be a little inferior. Because of the chip produced by different levels of production, each manufacturer to obtain different ways and other reasons, resulting in CCD acquisition effect is also very different. At the time of purchase, you can take the following methods of detection: turn on the power, connect the video cable to the monitor, close the lens aperture, see if the image is completely black when there are bright spots, the screen snowflake big or not, these are the detection of the CCD chip is the most simple and direct method, and does not require other specialized instruments. Then you can open the aperture, look at a still life, if it is a color camera, it is best to ingest a brightly colored object, to see whether the image on the monitor is off-color, distorted, color or gray scale is smooth. A good CCD can well restore the color of the scene, so that the object looks clear and natural; while the image of the defective product will have a color deviation phenomenon, even if the face of a piece of white paper, the image will show blue or red. Individual CCD due to the dust of the production plant, CCD target surface will have impurities, in general, the impurities will not affect the image, but in low light or microscopic camera, fine dust can also cause adverse consequences, if used for this type of work, be sure to carefully select.
1, according to the imaging color division Color camera: applicable to the scene of fine discrimination, such as identification of clothing or the color of the scene. Black-and-white cameras: for poorly lit areas and areas where lighting can not be installed at night, only to monitor the location or movement of the scene, black-and-white cameras can be used.
2, according to the resolution of sensitivity and other divisions Image pixels in the 380,000 or less for the general type, especially 250,000 pixels (512 * 492), the resolution of 400 lines of the most common products. The high resolution type with more than 380,000 pixels.
3, divided by the size of the CCD target CCD chip has been developed in a variety of sizes: most of the chips used for 1/3 "and 1/4". In the purchase of the camera, especially on the camera angle has more stringent requirements, the size of the CCD target surface, CCD and the lens with the situation will directly affect the size of the field of view and the clarity of the image. 1 inch - the target size of 12.7mm wide * 9.6mm high, 16mm diagonal. 2/3 inch - the target size of 8.8mm wide * 6.6mm high, 11mm diagonal. 1/2 inch - the target size of 8.8mm wide * 6.6mm high, 11mm diagonal. 11mm. 1/2 inch - target surface size of 6.4mm wide * 4.8mm high, diagonal 8mm. 1/3 inch - target surface size of 4.8mm wide * 3.6mm high, diagonal 6mm. 1/4 inch - target surface size of 3.2mm wide * 2.4mm high, diagonal 4mm.
4, according to the scanning system PAL system. NTSC. China's use of interlaced (PAL) system (black and white for CCIR), the standard is 625 lines, 50 fields, only medical or other specialized areas to use some non-standard system. In Japan, the standard is NTSC, 525 lines and 60 fields (EIA in black and white).
5, according to the power supply 110VAC (NTSC is mostly such), 220VAC, 24VAC, 12VDC or 9VDC (miniature cameras are mostly such).
6, according to the synchronization method is divided into internal synchronization: the synchronization signal generated by the camera within the synchronization signal generation circuit to complete the operation. External synchronization: the use of an external synchronization signal generator, the synchronization signal into the camera's external synchronization input. Power synchronization (linear lock, line lock): with the camera AC power to complete the vertical push synchronization. External VD Sync: Input the VD sync pulse from the camera's signal cable to complete the external VD sync. Multi-camera external synchronization: Fixed external synchronization of multiple cameras, so that each camera can operate under the same conditions, due to the synchronization of the cameras, so that even if one of the cameras converted to other scenes, the synchronization of the camera's picture will not be distorted.
7, in accordance with the degree of division, CCD is divided into:
Ordinary type of illumination required for normal operation 1 ~ 3LUX
Moonlight type of illumination required for normal operation 0.1LUX or so
Starlight type of illumination required for normal operation 0.01LUX or less
Infrared type of illumination using infrared lamps, in the absence of light can also be Imaging
8, according to the appearance: organic plate type, pinhole type, hemispherical type.
CCD color camera main technical indicators
(1) CCD size, that is, the camera target surface. The original more than 1/2 inch, 1/3 inch has been popularized, 1/4 inch and 1/5 inch has also been commercialized.
(2) CCD pixels, is the main performance indicator of the CCD, which determines the degree of clarity of the display image, the higher the resolution, the better the performance of the image details.CCD is composed of a surface array of light-sensitive elements, each element is called a pixel, the more pixels, the more clear the image. Most of the market is demarcated by 250,000 and 380,000 pixels, and those with more than 380,000 pixels are considered 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. Resolution is expressed in terms of television lines (referred to as lines TVLINES), the resolution of the color camera is between 330 and 500 lines. Resolution and CCD and lens-related, but also with the camera circuit channel bandwidth is directly related to the usual law is 1MHz bandwidth equivalent to the clarity of 80 lines. The wider the bandwidth, the clearer the image, the greater the relative value of the line.
(4) minimum illumination, also known as sensitivity. Is the degree of sensitivity of the CCD to ambient light, or the CCD normal imaging needs the darkest light. The unit of illumination is lux (LUX), the smaller the value, indicating that less light is needed, the more sensitive the camera. Moonlight level and starlight level and other high sensitivity cameras can work in very dark conditions, 2 ~ 3lux is a general illumination, there are less than 1lux of ordinary cameras introduced.
(5) scanning system. There are PAL and NTSC system.
(6) camera power supply. AC 220V, 110V, 24V, DC 12V or 9V.
(7) Signal-to-noise ratio. Typical value of 46db, if 50db, the image has a small amount of noise, but the image quality is good; if 60db, the image quality is excellent, no noise.
(8) video output. Mostly 1Vp-p, 75Ω, all using BNC connectors.
(9) lens mounting method. There are C and CS mode, the difference between the two is that the light-sensitive distance is different.
2, CCD color camera can be adjusted
(1) the choice of synchronization
A, for a single camera, the main synchronization methods are the following three:
Internal synchronization - the use of the camera's internal crystal oscillator circuit to generate synchronization signals to complete the operation. External synchronization - using an external synchronization signal generator to generate a synchronization signal sent to the camera's external synchronization input to achieve synchronization.
Power synchronization - also known as linear lock or line lock, uses the camera's AC power supply to accomplish vertical push synchronization, i.e., the camera is synchronized with the power supply zero line.
B, for multi-camera system, I hope that all the video input signal is vertically synchronized, so that in the change of the camera output, will not cause picture distortion, but because of the multi-camera system, the camera power supply may be taken from the three-phase power supply in different phases, or even the whole system is not synchronized with the AC power supply, at this time, measures can be taken to: are using the same external synchronization signal generator Synchronization signal generated into the camera's external synchronization input to adjust the synchronization. Adjust the camera's "phase adjustment" potentiometer, because the camera in the factory, its vertical synchronization is the same phase with the rising edge of the AC power positive zero, so the use of phase delay circuit can make each camera has a different phase shift, so as to obtain the appropriate vertical synchronization, phase adjustment range of 0 ~ 360 degrees.
(2) automatic gain control All cameras have a signal from the CCD will be amplified to the level of video amplifier can be used, the amplification of a large number of that is the gain, the equivalent of a high sensitivity, which can be made to be sensitive in low light, however, in the bright light of the environment will be overloaded amplifier, so that the video signal distortion. For this reason, the need to use the camera's automatic gain control (AGC) circuit to detect the level of the video signal, switch AGC at the right time, so that the camera can work in a larger range of light, which is the dynamic range, that is, in low light automatically increase the sensitivity of the camera, thereby increasing the intensity of the image signal to obtain a clear image.
(3) background light compensation Usually, the camera's AGC operating point is determined by the average of the contents of the entire field of view to determine, but if the field of view contains a very bright background area and a very dark foreground target, it is possible to determine the AGC operating point of the foreground target is not enough to be appropriate, the background light compensation is likely to improve the foreground target display conditions. When the background light compensation is on, the camera averages only a sub-area of the entire field of view to determine its AGC working point, and then if the foreground target is located in this sub-area, the visibility of the foreground target is expected to improve.
(4) electronic shutter in the CCD camera, is used to optically control the image surface charge accumulation time to manipulate the shutter. The electronic shutter controls the accumulation time of the camera's CCD, when the electronic shutter is closed, for NTSC cameras, its CCD accumulation time of 1/60 seconds; for PAL cameras, 1/50 seconds. When the electronic shutter of the camera is open, for NTSC cameras, its electronic shutter covers the range from 1/60 second to 1/10,000 second in 261 steps; for PAL cameras, its electronic shutter covers the range from 1/50 second to 1/10,000 second in 311 steps. When the electronic shutter speed increases, in the time allowed for each video field, the light focused on the CCD is reduced, the result will be a reduction in the sensitivity of the camera, however, higher shutter speeds for the observation of moving images will produce a "stop-motion" effect, which will greatly increase the dynamic resolution of the camera.
(5) white balance white balance is used only for color cameras, its purpose is to achieve the camera image can accurately reflect the scene conditions, there are manual white balance and automatic white balance two ways.
A, automatic white balance Continuous mode - this time the white balance settings will be continuously adjusted as the scene color temperature changes, the range of 2800 ~ 6000 K. This way for the scene of the color temperature during the shooting of the occasions is the most appropriate, so that the color performance of the natural, but for the scene of very little white or even no white, continuous white balance can not produce the best color! effect. Push-button mode - Aim the camera at a white target such as a white wall, white paper, etc., then flip the AUTO mode switch from the manual to the set position and hold it there for a few seconds or until the image appears white. After the white balance has been executed, flip the AUTO mode switch back to the manual position to lock in the white balance setting, which is then retained in the camera's memory until it is executed again and changed. The white balance setting will remain in the camera's memory until it is changed by another execution, which is in the range of 2300~10000K, during which the setting will not be lost even if the camera is powered off. Setting the white balance in the push-button mode is the most accurate and reliable, and is suitable for most applications.
B, manual white balance on manual white balance will turn off the automatic white balance, this time to change the image of the red or blue condition has up to 107 levels for adjustment, such as increasing or decreasing the red level, increasing or decreasing the blue level. In addition to this, some cameras have a white balance will be fixed at 3200K (incandescent level) and 5500K (daylight level) and other gear commands.
(6) color adjustment For most applications, there is no need for the camera color adjustment, such as the need to adjust the need to carefully adjust so as not to affect the other colors, adjustable color: red - yellow color increase, the red to magenta move one step. Red - yellow color decreases, then move the red to yellow one step. Orchid - yellow color increase, at this time the orchid color to the blue orchid color to move a step. Orchid-yellow color decreases, at this point move the orchid color one step towards magenta.
3, digital adjustment and control method
The new camera on the foregoing optional parameters of the adjustment of digital adjustment and control, this time do not have to manually adjust the potentiometer but the use of auxiliary control code, and these adjustments are stored in the digital memory unit, increasing the stability and reliability.
DSP camera in the analog system on the basis of the introduction of some digital processing technology, called digital signal processing (DSP, DIGITAL SIGNAL PROCESSOR) camera. The camera has the following advantages:
1, due to the use of digital detection and digital computing technology with intelligent background light compensation. Conventional cameras require the scene to be photographed in the center of the screen and to occupy a large area in order to have a better background light compensation, otherwise too bright background light may reduce the transparency of the image center. The DSP camera is divided into 48 small processing areas to effectively detect the target, so that even a small, thin or not in the center of the screen area of the scene can be clearly rendered.
2, due to the DSP technology and can automatically track the white balance, that is, in any conditions to detect and track the "white", and digital computing processing functions to reproduce the original color. The traditional camera because of the system of all the colors on the screen for the average processing, so that if the color objects on the screen occupies a large area, then the color reproduction will not be balanced, that is, can not reproduce the original color. DSP camera is a screen is divided into 48 small processing area, so that the effective detection of white, even if the screen is only a very small piece of white, the camera is also able to track it so that the original color reproduction. The camera is able to track even a small piece of white on the screen to reproduce the original color. When photographing grid-like objects, image aliasing caused by camera color noise is minimized