Modern monitoring and security 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 solutions.
Monitoring security system suffered lightning damage to the main reasons
(1) direct lightning. Directly hit the open-air camera, direct damage to the equipment; direct hit on the cable, resulting in cable fusion, damage.
(2) Lightning intrusion wave. Security monitoring system power lines, signal transmission lines or other metal cables into the monitoring room was struck by lightning or lightning induction, lightning waves along these metal wires, conductors into the equipment, resulting in a high potential difference in equipment damage.
(3) Lightning induction. Electromagnetic induction: When the nearby area has a lightning flash, in the lightning strike around the landing channel will produce a strong transient electromagnetic field. In the electromagnetic field in the monitoring equipment and transmission lines will be induced by a large electric potential, so that damage, destruction of equipment. Electrostatic induction: When a charged thundercloud appears, in the thundercloud below the building and transmission lines will be induced with the thundercloud opposite of the bound charge. Once the thundercloud is discharged, the bound charge spreads rapidly, causing an induced lightning strike. Electromagnetic induction and electrostatic induction triggered by the phenomenon of lightning are known as induction lightning, also known as secondary lightning, the chance of occurrence of large, according to statistics, induction lightning accidents accounted for more than 80% of lightning accidents.
(4) ground potential counterattack. Direct lightning protection device in guiding the powerful lightning current into the earth, in its lead wires, grounding bodies and metal conductors connected to them to produce a very high instantaneous voltage, and they are close to the surrounding but not connected to them metal objects, equipment, lines, the human body to produce a huge potential difference between the potential difference caused by the electric shock is the ground potential counterattack.
Monitoring security system lightning protection solution points, common problems and precautions
3-1 direct lightning protection direct lightning protection, lightning protection is an indispensable and important basis for the whole lightning protection system is an important part.
3-1-1 front-end equipment direct lightning protection
Security monitoring system front-end equipment outdoor and indoor two kinds of equipment, installed in the indoor equipment will not be subjected to direct lightning strikes, can not be considered 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.
3-1-2 Transmission lines of direct lightning protection
In order to make the transmission line from direct lightning, transmission lines should try to avoid overhead erection, preferably through the metal pipe buried laying, the ends of the metal pipe should be reliably grounded.
3-1-3 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.
3-2 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 good lightning protection 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 requirements of independent grounding, you should do *** with grounding.
3-3 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 bundles, and should be in accordance with the relevant specification requirements wiring, reserved a certain safety distance.
3-4 AC power surge protector selection
For monitoring the security system of all AC power supply into the end of the effective lightning protection. Front-end equipment should be installed at the 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 the second 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.
3-5 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.
3-6 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 sense, transfer overvoltage surge. However, it should be noted that the fiber optic cable generally have a metal reinforced 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.
3-7 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 lightning protection failure, while leading to the video of the lightning itself was damaged. At present, most of the signal lightning protection products on the market, generally using two levels of 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.
3-8 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.
Four, the daily maintenance of the rules
(1) lightning rod, lightning belt, bracket, grounding lead, grounding body, connecting line and other components, should be hot-dip galvanized and other methods to effectively prevent rust and corrosion, the daily use of the rust corrosion should be carried out frequently.
(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 the 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 to get 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 camera already has a lens.
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, and now 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 will also cause adverse consequences, if used for such work, must be carefully selected.
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 currently used 1/3 and 1/4. In the purchase of the camera, especially for the camera angle has a more stringent requirements of the time, the size of the CCD target, the CCD and the lens with the situation will have a direct impact on the size of the field of view angle and the clarity of the image. 1 inches - the target size of the width of 12.7mm * height 9.5mm. 1 inch - target surface size for the width of 12.7mm * height 9.6mm, diagonal 16mm. 2/3 inch - target surface size for the width of 8.8mm * height 6.6mm, diagonal 11mm. 1/2 inch - target surface size for the width of 6.4mm * height 4.8mm, diagonal 8mm. 1/3 inch - target surface size for the width of 4.8mm * height 3.6mm, diagonal 6mm. 1/4 inch - target surface size for the width of 3.2mm * height 4.8mm, diagonal 6mm. 1/4 inch - target surface size for the width of 3.2mm * height 3.6mm, diagonal 6mm. Target surface size is 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. Original more than 1/2 inch, now 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. Nowadays, the market is mostly demarcated by 250,000 and 380,000 pixels, and those with more than 380,000 pixels are high-definition cameras.
(3) horizontal resolution. The typical resolution of the color camera 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 TV LINES), 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 camera can work in very dark conditions, 2 ~ 3lux is the general illumination, now also has less than 1lux of the ordinary camera came out.
(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 The synchronization signal generated by the camera into the external synchronization input to adjust the synchronization. Adjust the phase adjustment potentiometer of each camera, because the camera in the factory, its vertical synchronization is in phase with the rising edge of the AC power positive zero point, so the use of phase delay circuit can make each camera has a different phase shift, so as to obtain the appropriate vertical synchronization, the 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 is increased, less light is focused on the CCD in the time allowed for each video field, and as a result, the sensitivity of the camera will be reduced, however, higher shutter speeds produce a stop-motion effect for the observation of moving images, 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 to avoid affecting other colors, adjustable color ways: red - yellow color increase, this time the red to magenta to move a 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 based on the introduction of part of the 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 it can effectively detect the 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 shooting grid-like objects, the image aliasing caused by the camera color noise can be reduced to a minimum
Six, monitoring security system performance layer:
For the monitoring security system, according to the different functions of the various parts of the system, we will be the entire monitoring security system is divided into seven layers - performance layer, control layer, Processing layer, transmission layer, execution layer, support layer, acquisition layer. Of course, due to the increasing integration of equipment, for some of the system, some equipment may exist in the system at the same time as more than one layer.
1. Performance layer
The performance layer is the most intuitive to us, it shows the quality of the whole security monitoring system. Such as monitoring video walls, monitors, tweeting alarm speakers, alarms, etc. belong to this layer.
2. Control layer
The control layer is the core of the entire security monitoring system, it is the most clear embodiment of the level of system technology. Usually we have two types of control - analog control and digital control. Analog control is an early control method, its console is usually composed of controllers or analog control matrix, applicable to small local security monitoring system, this control method is less costly, the failure rate is small. But for medium and large security monitoring system, this approach appears to be complex and no price advantage, then we are more sensible choice should be digital control. Digital control is an industrial computer as the control core of the monitoring system, it will be a complex analog control operation into a simple mouse click operation, the huge stack of analog controllers down to an industrial computer, the complexity and the huge number of control cables into a serial telephone line. It will be in the remote monitoring into a fact, for the Internet remote monitoring possible. But the digital control is not so perfect, control the price of the host is very expensive, module waste, the system may be a total collapse of the crisis, the control of the more lagging and so on the problem still exists.
3. Processing layer
Processing layer may be called the audio and video processing layer, it will have the transmission layer to send over the audio and video signals to be distributed, amplification, segmentation and so on, organic performance layer and control layer to be connected. Audio-video distributor, audio-video amplifier, video splitter, audio-video switcher and other equipment belongs to this layer.
4. Transmission layer
Transmission layer is equivalent to the blood of the security monitoring system. In the small security monitoring system, we are the most common transmission layer equipment is the video cable, audio cable, for the middle and long-distance monitoring system, we often use the radio frequency line, microwave, for remote monitoring, we usually use the Internet as a cheap carrier. It is worth mentioning that the emerging transmission layer medium - network cable / fiber optic. Most people in the digital security monitoring there is a misunderstanding, they think that the control layer using digital control of the security monitoring system is a digital security monitoring system, in fact, not. The transmission medium of a purely digital security monitoring system must be network cable or optical fiber. Signal from the acquisition layer out, it has been modulated into a digital signal, digital signals in the network has become mature run, theoretically non-attenuation, which ensures that the remote monitoring of the image without loss of display, which is incomparable to analog transmission. Of course, the return of high performance also requires high-cost investment, which is purely digital security monitoring system can not be popularized one of the most important reasons.
5. Execution layer
Execution layer is the command object of our control instructions, at some point, it is not very good with what we said later to support the sincerity of the acquisition layer is not very separate, we believe that the controlled object that is the implementation of the layer of equipment. For example: PTZ, lens, decoder, ball and so on.
6. support layer
As the name suggests, the support layer is used to support the back-end equipment to protect and support the acquisition layer, the implementation layer equipment. It includes brackets, shields, and other ancillary equipment.
7. Acquisition layer
Acquisition layer is the key factor in the quality of the entire security monitoring system, but also the largest cost of the system. It includes lenses, cameras, alarm sensors and so on.