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Position:IcFull.com » IC Electronic information » Category: I

IC Electronic information

IR infrared LED light source used in security surveillance camera project

In Electronic Infomation Category: I | on April 18,2011

We all know the night vision technology in military applications for a long time, as technology development, video surveillance in the civilian also was widely used. In fact, the night vision technology is achieved by means of optical imaging device of a night observation optical technology. It includes two types of night vision and NS8250AV datasheet and infrared night vision: Night Vision technology is through the image intensifier tube with a night vision technology, it is actually light up the night sky as to enhance the weak targets for observation optical imaging.

Night vision devices, is the amount of foreign production and NS8250AV price and equipment, the largest and NS8250AV suppliers and most versatile night vision equipment, which can be divided into direct observation (such as night vision instruments, weapons sights, night driving device, the night as glasses) and indirect observation (such as low light level television) two; and infrared night vision technology is divided into active and passive infrared night vision technology infrared night vision technology. Passive infrared night vision technology is the goal of their own means of infrared radiation emitted to achieve the observed infrared technology, which according to the target or target and background temperature difference between the various parts or poor thermal radiation to find the target, the corresponding equipment for the thermal imager. Speaking here mainly active infrared night vision technology, it is through active use of targets reflected infrared light and infrared light source to observe the implementation of a night vision technology, which corresponds to active infrared night vision equipment, the actual core of the infrared camera.


Infrared light source, by a non-direct-optical imaging device CCD or CMOS image sensor at the core of the camera lens and the imaging screen, etc. with the necessary choice is the dominant effect of infrared cameras at night to monitor the merits of the three major factors. To get a good night to monitor the quality of this article will focus on the infrared camera in its infrared light source, camera and lens and other options for deals on a few key points should be noted that, for business users such as selection of reference works.

An infrared light source of choice

Infrared light is a wavelength greater than 780nm is not visible. General, resulting in visible ways that do not have the following three.

. Direct use of incandescent or xenon lamp infrared light. That is installed in both the visible light filter, filter out visible light, invisible infrared radiation only to injection;

. Use infrared light-emitting diode LED or LED array to generate infrared light. This device is through the gallium arsenide (GaAs) semiconductors in the electronic and hole recombination to produce infrared light;

. Using infrared laser diode LD, but also can be used for infrared light. But it should at a low energy state of the electronic excited or pumped up to a higher energy state, a large number of particle distribution by inversion, resonance and infrared light to maintain stimulated emission.

First light source is infrared light source, its biggest advantage is that power can be made larger and large irradiation angle, the exposure distance. The biggest downside is that contains the visible components, namely, red bursts, and short life, working 10 hours a day, 5,000 hours a year can only be used if the heat is not enough to consider life even shorter. Infrared light to increase the life of thermal radiation, the use must also be controlled by light switch circuit to reduce their working hours. In addition, increased the delay switch circuit to prevent interference from ambient light.

Second is to use light-emitting diode arrays, the semiconductor gallium arsenide infrared light, especially now with the new technology development and production of integrated LED array chip LEDArray. One of its optical output of LED-Array reached 800mw-1000mw, and become the replacement for an ordinary LED, LED-Array-emitting half-power angle of 10-120 (Variable angle). The LED-Array is a highly integrated LED, while the volume is only one penny coin the size of the room can be uniformly illuminated all the space, its life of 50,000 hours. It was originally used in aviation aircraft above, in recent years, civil night monitoring the development of the market, LED-Array was gradually moving towards civilian market as a high ideal for night surveillance.

Although infrared LED and LED-Array out of the thermal infrared light source, but for more than 1km long distance monitoring of the scene, or to select the infrared light source LD. Than the LED semiconductor lasers for high brightness, direction and other characteristics.

Usually, the choice of infrared light sources note the following several points.

A, selected according to infrared light from the monitor

By infrared light-emitting diode LED can be mounted on the lens, equipped with infrared cameras and a sense of, or directly mounted around the camera and lens mount chassis. Obviously, these two assembly less infrared LED, and its certainly not as separate from the exposure to the infrared LED light irradiation far. General, 50m or more, the best selection of separate infrared light as well, the other LD used for more than 1km away from the scene of the night vision to monitor lighting, but the LD beam thin and strong, the infrared beam to illuminate a range of scenarios, the use of will also be required through a beam expander lens beam expander Caixing.

B, infrared light from the left margin to select

Select infrared light, special attention to the nominal distance and the distance between the actual radiation. Because some of the visual distance of the nominal plant is often too large, so the infrared light irradiation in the choice of the actual distance to the test, and to leave enough margin to make the observation of the scene illumination and reliable.

C, to use a good heat source

Because both heating and cooling LED, in particular, large power distance of the light source heat, it is necessary to use a good heat source, in order to ensure stable and reliable.

D, should use the source-driven steady flow of light

Is the current drive for LED devices, the LED brightness and power is proportional to the same drive current, not voltage. Therefore, in order to maintain the same luminous intensity, we must choose the steady flow of light source driver.

E, light control switch to select automatic control circuit of the power supply circuit board with separate infrared light source

Because infrared light lamp power supply circuit board and not separated, it will be the work of the heat generated by the LED power supply circuit components affect performance, leading to instability in LED light, with such light control switch circuit , can make the infrared light during the day and closed at night open.

Second, the choice of camera

Current CMOS camera and CCD light-sensitive devices have two. As with the CCD, CMOS image sensor chip also respond to infrared light, but it is 890-980nm range of sensitivity than the CCD image sensor chips to be much higher, and the increase of attenuation with wavelength gradient is also slower. With the rapid development of CMOS imaging chip, further reducing the noise signal, and the Star-class CMOS camera has also been available. Therefore, not necessarily confined to the CCD camera choice to make full use of their advantages selected. General, infrared cameras are the choice of points.

A, should be selected low-light cameras, the illumination requirements are generally 0.02Lux

Some camera manufacturer or distributor false minimum illumination, so that greatly reduce the effective distance night vision, it is best to be more specific test. Moon-and star-level cameras such as increased sensitivity can work in very dark conditions, but some reflection coefficient of the place or fail to meet requirements, such as deserts, green space, forests, etc.. In this case, you need to use the high-performance image intensifier and CCD CCIR standard black and white cone of light through the fiber panel and direct coupling from the night vision camera. In short, the illumination as low as possible, as there is still not standardized, can not believe that the nominal plant of the most illumination to be tested in practical conditions, as well, usually illumination requirements are generally 0.02Lux.

B, use the infrared camera image sensor size the better Can not be used for 1/4CCD

infrared night vision 15m effective range of the above, because the flux is only 1/3CCD 1/4CCD 50%. The CCD size large, luminous flux received large; CCD is small, the flux received little. So, night vision cameras multiple choice 1 / 2 CCD, 1 / 3 of the can to test possible, but we can not choose 1 / 4.

C, infrared cameras have automatic electronic shutter and automatic gain control (AGC) function

Because of these features can be adjusted to better the signal state to meet the observed effects.

D, to be ultra-miniature CMOS hidden camera selected occasions

Due to low power, high integration, small size CMOS image sensors can only be done, thus made his shirt, suit the size of the CMOS camera button. With the corresponding more small infrared light source, and the introduction of high-performance batteries, so that third eye will be everywhere. In this way, bring a pair of night vision glasses and an infrared light source with ultra-miniature CMOS camera and a hat, and the night will be as light as day. Obviously, this will change our entire social life.

E, matching well the camera supporting small power regulator

Selected to power the cameras attention to the following two points

1. Select power supply. AC220V instability due to electricity, such as the election only a 12V AC-DC voltage transformer and not the circuit would make the camera work in unstable, so that the camera work of instability, the required performance to fail to meet requirements; < / P>

2. The current election is bigger than the camera nearly doubled over the small power supply as well. If the current is 200mA camera or 250mA, 500mA is enough general election. If the election is too large for a camera such as the 1A to the volume is too large and the price of your side; too small as to be equal to the current camera fever (due to continuous long working hours) while the impact of reliability and working life and so on.

Third, the choice of lens, etc.

Infrared camera camera lens is the key equipment, its quality (indicators) directly affect the systems imaging results, therefore, choose the lens that is related to the adequacy of system quality, but also related to the project cost. Therefore, the choice of lens to note the following points:

A, preferably infrared lens

By conventional optical lens, the object of the infrared light reflected back to the lens to the CCD can not be effectively focused on the target surface, infrared night vision will be greatly reduced at this time, so the best selection of infrared camera. Especially the color to black camera, do not use infrared surveillance camera focal plane will not make the same night, resulting in both day and night to maintain a clear image can not.

B, choose the best size of the imaging lens and the camera image sensor the same size

Imaging lens selection and camera size should be the same size image sensor, such as the image sensor size is 1 / 2 ", the cameras image size must be 1 / 2". When the image size than the camera lens the size of large photosensitive surface will not affect the image, but the actual image field of view than the nominal field angle lens is small, and when the size of the lens than the cameras photosensitive imaging surface Size hours, it will affect the image and performance of the screen image is surrounded by tube block, the four corners of the screen will appear dark corner.

Can be seen on the 1 / 3 "camera, you can use 1 / 3", 1 / 2 "and 2 / 3" lens; to 1 / 2 "camera, optional 1 / 2", 2 / 3 "lens, rather than using 1 / 3 of the lens. because the CCD is like the human eye, the lens just like people with glasses, glasses are too small, the eyes will not see the things around.

C, preferably with the camera lens line interface installation

Lens and camera interface with C-mount installation and the installation of two CS-type, the best agreement between the two. If you use the C-type lens, you need to 5mm thick, then add a circle can be. If not add up lap the interface to the camera directly to the CS, you can make the lens after the mirror surface touch sensitive CCD protective glass, the damage caused by CCD camera, which is in need of special attention in the practical.

D, preferably auto-iris lens, day and night illumination to meet the great changes

The day and night surveillance, the illumination varies greatly, which can automatically select the best auto iris lens illumination changes, so images remain clear.

E, resolution and light transmittance of the lens to achieve the required

With the resolution of the imaging lens must be greater than the resolution of the camera, or fail to clear the required results. And lens opacity in the lens is better, that is, the attenuation of light to be very small.

F, monitor the distance of 1 km or more, need to expand the use of laser beam collimation lens

Want to observe the scene, according to the size and distance select the appropriate laser beam expander collimator lens, the laser beam to illuminate the scene monitoring required in order to monitor the scene of the reflected light can be received by the camera.

G, pay attention to selecting a good performance window glass shield

Addition to election of infrared light, camera, lens, but also pay attention to protective cover, power supply, etc. sets considered. Because the guard had the effect of infrared light effects, such as infrared light through different media, transmittance and reflectance is different. For example, a different window glass, coated glass in particular, automatic defrost, the attenuation of infrared light are also different, so pay attention to choose a good performance window glass shield.

Conclusion

From the foregoing, three infrared light sources have their advantages and disadvantages, but the basic light source is infrared thermal infrared LED and LED-Array light source eliminated. Because the use of LED-Array also fully control exposure to hundreds of meters away from the scene. For more than 1km long distance monitoring of the scene, or LD should be used infrared light as well. Because of its high brightness, a lot of LD top LED, so the infrared light source LD small size, light weight, is the best choice for long distance.

Infrared camera to select the most important sets of problems. In addition to selecting infrared light source, the camera, lens, protective cover, power supply and other supporting comprehensive consideration. Described only by the choice of elements of the text took into account in order to get to the multiplier effect.

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