With the growing demand for night vision surveillance in security video surveillance systems engineering, infrared cameras have entered the mainstream market of cameras, sales are increasing day by day, and problems in the application of infrared night vision technology are gradually exposed. This article briefly discusses the technical problems of the infrared camera and the precautions for selection, so as to share and communicate with the people in the industry.
We all understand that the application of night vision technology in the military has been a long time. With the development of technology, it has also been widely used in civil video surveillance. In fact, night vision technology is an optoelectronic technology that uses photoelectric imaging devices to achieve night observation. It includes low-light night vision and infrared night vision. Low-light night vision technology is a kind of night vision technology with an image enhancement tube. It actually enhances the weak target image lit by night sky for observation. Photoelectric imaging technology. The low-vision night vision instrument is the night vision equipment with the largest amount of foreign production and equipment, and the most widely used night vision equipment. It can be divided into direct observation (such as night vision observer, weapon sight, nighttime pilot, night vision glasses). And indirect observation (such as low light television) two kinds; and infrared night vision technology is divided into active infrared night vision technology and passive infrared night vision technology. Passive infrared night vision technology is an infrared technology that uses the infrared radiation emitted by the target itself to achieve observation. It finds the target according to the difference in temperature or thermal radiation between the target and the background or parts of the target. The corresponding equipment is a thermal imager. The active infrared night vision technology is mainly discussed here. It is a kind of night vision technology that performs observation by actively irradiating and using the infrared light of the target reflective infrared source. The corresponding equipment is an active infrared night vision device, and the actual core is the infrared camera.
Infrared light sources, cameras composed of non-directly-photoelectric imaging device CCD or CMOS image sensor, and lenses required for imaging are the three major factors that dominate the effectiveness of infrared cameras at night. In order to obtain a good night surveillance quality, this article will focus on the application of infrared cameras, the infrared light source, the camera and its lens, etc. should pay attention to a few points that should be noted for the selection of engineering companies and other users reference.
First, the choice of infrared light source Infrared light is a wavelength greater than 780nm invisible light. In general, there are the following three methods for generating such invisible light.
1. Direct infrared light from incandescent or xenon lamps. That is, a visible light filter is installed on these two lamps to filter out visible light and only invisible infrared rays are emitted.
2. Infrared light is generated using infrared LEDs or LED arrays. The device generates infrared light by recombination of electrons and holes in gallium arsenide (GaAs) semiconductors;
3. Using an infrared laser diode LD can also be used as an infrared light source. However, it is required to excite or pump the electrons in the lower energy state to the higher energy state, and to maintain the stimulated radiant infrared light through a large number of particle distribution inversions and resonances.
The first type of light source is a thermal infrared light source, and its greatest advantage is that it can be made with relatively large power and a large irradiation angle, so the distance of irradiation is far. The biggest drawback is that it contains visible light components, that is, there is a red storm, and the service life is short. If you work 10 hours a day, 5000 hours can only be used for more than a year. If you consider that the heat is not enough, the life expectancy is shorter. In order to increase the life of heat-radiating infrared lamps, light-controlled switch circuits must also be used to reduce their operating time. In addition, a delay switch circuit is added to prevent ambient light interference.
The second type is an infrared lamp that uses an array of semiconductor gallium arsenide light-emitting diodes. In particular, an array-type integrated light-emitting diode (LED) Array has been developed and produced using new technologies. The LED-Array has an optical output of 800mW-1000mw, which has become a replacement for ordinary LEDs. The LED-Array has a luminous half-power angle of 10-120° (variable angle). Since the LED-Array is a highly integrated LED and has the size of only a penny coin, it can evenly illuminate the entire space in the room, and its lifetime is 50,000 hours. It was originally used in aviation aircraft. In recent years, due to the development of the civilian night surveillance market, LED-Array has gradually become a civilian market and has become an ideal choice for high-quality night surveillance.
Although infrared LEDs and LED-Arrays eliminate thermal infrared light sources, infrared LD light sources must be selected for super-long-distance scene monitoring above 1 km. Because the semiconductor laser has higher brightness and directional characteristics than the LED.
In general, the following points should be noted when selecting an infrared light source.
A, infrared light distance to choose to leave a margin to choose infrared light, pay special attention to the distance between the nominal distance and the actual irradiation distance. Because the nominal visible distance of some manufacturers is often too large, practical tests must be performed when selecting the irradiation distance of the infrared lamp, and sufficient margin is left to make the illumination of the observed scene reliable.
B. The light source driven by a steady current source should be selected because the LED is a current-driven device, and its light emission luminance and power are proportional to the drive current, rather than the voltage. Therefore, in order to keep the luminous intensity unchanged, it is necessary to choose a steady-current source-driven light source.
C, to choose a good heat source because the light emitting tube has a fever and heat problems, especially the power of a large distance light source heat, so you must choose a good heat source to ensure that the work is stable and reliable.
D. The infrared light source separated from the lamp board by the power supply circuit of the light control switch automatic control circuit should be selected. Because the power supply circuit and the light board of the infrared lamp are not separated, the heat generated by the work of the light tube will affect the performance of the components of the power supply circuit. As a result, the light emission of the light emitting tube is unstable. With this circuit of the light control switch, the infrared light can be turned off during the day and turned on at night.
E. The infrared lamp should be selected according to the monitoring distance. The infrared LED can be mounted on the lens, used with the infrared camera, or directly on the casing around the camera and lens interface. Obviously, these two types of assembled infrared LEDs are less, and the irradiated distance is certainly not as far away as the individual infrared LED lights. Generally, 50m or more, it is better to use a separate infrared lamp, and the other LD is used for night vision lighting of a monitoring scene of distance of more than 1km, but the LD beam is thin and strong, in order to make the infrared beam illuminate a certain range of scenes, use It also needs to be expanded by a beam expander lens.
Second, the choice of camera The current camera's photosensitive devices are CMOS and CCD. Like the CCD, the CMOS image sensor chip also responds to infrared light waves, but its sensitivity is much higher than the CCD image sensor chip in the 890-980 nm range, and the attenuation gradient is also slower as the wavelength increases. With the rapid development of CMOS image chips, the noise signal is further reduced, and star-class CMOS cameras are also available. Therefore, it is not necessarily limited to the CCD camera selection, but can fully utilize their respective advantages. In general, the main points of infrared camera selection are as follows.
A. Low-light camera should be selected, and its illuminance requirement is generally ≤ 0.02 Lux
Some camera manufacturers or vendors falsely report the minimum illumination, which greatly reduces the effective distance of night vision. Therefore, it is better to be able to test it. Moonlight-level and star-level sensitization cameras can work in very dark conditions, but some places with low reflectance factors can not meet the requirements, such as deserts, green areas, forest areas. In this case, it is necessary to use a low-light-level night-vision camera that is directly coupled with a fiber panel and a light cone by a black and white CCD of a high-performance image intensifier and a CCIR system. In short, the lower the illuminance the better, because the current is still not standardized, can not believe the minimum illuminance of the production plant, it is better to test under practical conditions, usually illuminance requirements are generally ≤ 0.02Lux.
B. The larger the size of the infrared camera image sensor chosen, the better because the 1/4 CCD cannot be used for an effective distance of 15m or more infra-red night vision, because the 1/4 CCD light flux is only 50% of the 1/3 CCD. The CCD has a large size and receives a large luminous flux; the CCD has a small size and receives less luminous flux. Therefore, the night vision camera selects 1/2 of the CCDs. One-third of the CCDs can be tested, but it is absolutely impossible to select 1/4.
C. Infrared cameras must have automatic electronic shutter and automatic gain control (AGC) function. Because of these features, the signal can be adjusted to a better state to meet the observation effect.
D. CMOS ultra-miniature cameras that need to be concealed on the occasion Because of low power consumption, high integration, and small size, only CMOS image sensors can do it. Thus, shirt buttons and suit button-sized CMOS cameras can be made. With the corresponding miniaturization of infrared light sources, and the introduction of high-performance batteries, the third eye will be everywhere. In this way, bring a night-vision goggles and a hat with an infrared light source and CMOS ultra-micro camera, the night will be like day. Obviously, this will change the face of our entire social life.
E. The matching of the power supply of the camera with a matching voltage regulator and a small power supply must be selected as follows.
· Select regulated power supply. Because the AC220V of the mains is unstable, if only a transformer with an AC-to-DC 12V is selected and the voltage is not stabilized, the circuit work in the camera will be unstable. As a result, the camera will be unstable and the required performance will not meet the requirements.
• It is better to choose a small power supply that is more than twice the current of the camera. If the camera's current is 200mA or 250mA, 500mA is generally sufficient. If the selection is too large, such as 1A for a camera, the volume is too large and the price is too expensive; if the current is too small, the current of the camera may heat up (because the continuous working time is too long) and affect the reliability and the working life.
Third, the choice of lens, etc. Camera lens is the key equipment of the infrared camera, its quality (index) has a direct impact on the quality of the system's imaging results, therefore, the lens is appropriate whether it is related to the quality of the system, but also related to the project cost. Therefore, when selecting a lens, pay attention to the following points:
A, the best choice for the infrared lens due to ordinary optical lens, the infrared light reflected from the object back to the lens can not be effectively focused on the CCD target surface, infrared night vision effect will be greatly reduced, so the best choice for infrared lenses. In particular, color-to-black cameras cannot use the infrared lens to make the day-night surveillance focal plane consistent, resulting in the inability of the day-night images to remain clear.
B. Selecting the imaging size of the lens is the same as the size of the image sensor in the camera. The imaging size of the selected lens should be the same as the size of the image sensor in the camera. If the size of the image sensor is 1/2, the imaging size of the lens must be It is 1/2". When the imaging size of the lens is larger than the size of the camera's photosensitive surface, it will not affect the imaging, but the actual imaging field of view is smaller than the lens's nominal angle of view, and when the lens imaging size than the camera's photosensitive surface When the size is small, the imaging will be affected, and the imaging frame will be surrounded by the lens barrel. Black corners will appear on the four corners of the screen. It can be seen that for 1/3 "cameras, 1/3", 1/2" and 2/3" lenses can be selected; for 1/2" cameras, 1/2" and 2/3" can be selected. The lens can't use 1/3 of the lens, because the CCD is like the human eye, the lens is like people's glasses, the glasses are too small, the eyes can not see the surrounding things.
C, the best choice for the lens and camera interface installation method The lens and camera interface installation methods are C-type installation and CS-type installation of the two, the best of both. If you choose a C-type lens, you need to add a 5mm thick ring. If it is directly connected to the CS interface camera without a collar, it may cause the rear mirror surface of the lens to collide with the protective glass of the sensitive surface of the CCD, resulting in damage of the CCD camera. This needs special attention in practical use.
D, the best choice for automatic iris lens, to adapt to changes in day and night illumination due to day and night monitoring, the illuminance range is very large, so it is best to use automatic iris lens can automatically change according to the illuminance, so that the image remains clear.
E. Resolution and Transmittance of the Lens The resolution of the imaging lens used to achieve the required resolution must be greater than the resolution of the camera. Otherwise, the required clearness cannot be achieved. In addition, the transmittance of the lens in the lens is better, that is, the attenuation of light is very small.
F. If the monitoring distance is more than one kilometer, laser beam expanding and collimating lens must be used to select the appropriate laser beam expanding and collimating lens according to the size and distance of the scene to be observed, so that the laser beam can illuminate the scene to be monitored for monitoring. The reflected light of the scene can be received by the camera.
G, pay attention to the selection of a good performance window glass protective cover in addition to infrared light, camera, lens, but also pay attention to the protective cover, power supply and other comprehensive considerations. Because the protective cover has an effect on the effect of infrared light, such as infrared light through different media, the transmittance and reflectivity are different. For example, different window glasses, especially automatic defrosting coated glass, have different attenuation of infrared light, so care should be taken to choose a protective cover with good window glass.
It can be seen from the above that the three infrared light sources have their advantages and disadvantages, but the thermal infrared light source is basically eliminated by the infrared LED and the LED-Array light source. Because with the LED-Array is also fully exposed to the distance of a few hundred meters monitoring the scene. As for super-long-distance monitoring scenes above 1km, infrared LD light sources should be used as well. Because of its high brightness, a lot of LD LED top, so the infrared LD light source is small, light weight, is the best choice for ultra-long distance.
The most important issue for the selection of infrared cameras is the set of features. In addition to selecting the infrared light source, the camera, lens, protective cover, power supply, etc. must be comprehensively considered. Only by taking into account the selection points outlined in the article, can we get a multiplier effect.
We all understand that the application of night vision technology in the military has been a long time. With the development of technology, it has also been widely used in civil video surveillance. In fact, night vision technology is an optoelectronic technology that uses photoelectric imaging devices to achieve night observation. It includes low-light night vision and infrared night vision. Low-light night vision technology is a kind of night vision technology with an image enhancement tube. It actually enhances the weak target image lit by night sky for observation. Photoelectric imaging technology. The low-vision night vision instrument is the night vision equipment with the largest amount of foreign production and equipment, and the most widely used night vision equipment. It can be divided into direct observation (such as night vision observer, weapon sight, nighttime pilot, night vision glasses). And indirect observation (such as low light television) two kinds; and infrared night vision technology is divided into active infrared night vision technology and passive infrared night vision technology. Passive infrared night vision technology is an infrared technology that uses the infrared radiation emitted by the target itself to achieve observation. It finds the target according to the difference in temperature or thermal radiation between the target and the background or parts of the target. The corresponding equipment is a thermal imager. The active infrared night vision technology is mainly discussed here. It is a kind of night vision technology that performs observation by actively irradiating and using the infrared light of the target reflective infrared source. The corresponding equipment is an active infrared night vision device, and the actual core is the infrared camera.
Infrared light sources, cameras composed of non-directly-photoelectric imaging device CCD or CMOS image sensor, and lenses required for imaging are the three major factors that dominate the effectiveness of infrared cameras at night. In order to obtain a good night surveillance quality, this article will focus on the application of infrared cameras, the infrared light source, the camera and its lens, etc. should pay attention to a few points that should be noted for the selection of engineering companies and other users reference.
First, the choice of infrared light source Infrared light is a wavelength greater than 780nm invisible light. In general, there are the following three methods for generating such invisible light.
1. Direct infrared light from incandescent or xenon lamps. That is, a visible light filter is installed on these two lamps to filter out visible light and only invisible infrared rays are emitted.
2. Infrared light is generated using infrared LEDs or LED arrays. The device generates infrared light by recombination of electrons and holes in gallium arsenide (GaAs) semiconductors;
3. Using an infrared laser diode LD can also be used as an infrared light source. However, it is required to excite or pump the electrons in the lower energy state to the higher energy state, and to maintain the stimulated radiant infrared light through a large number of particle distribution inversions and resonances.
The first type of light source is a thermal infrared light source, and its greatest advantage is that it can be made with relatively large power and a large irradiation angle, so the distance of irradiation is far. The biggest drawback is that it contains visible light components, that is, there is a red storm, and the service life is short. If you work 10 hours a day, 5000 hours can only be used for more than a year. If you consider that the heat is not enough, the life expectancy is shorter. In order to increase the life of heat-radiating infrared lamps, light-controlled switch circuits must also be used to reduce their operating time. In addition, a delay switch circuit is added to prevent ambient light interference.
The second type is an infrared lamp that uses an array of semiconductor gallium arsenide light-emitting diodes. In particular, an array-type integrated light-emitting diode (LED) Array has been developed and produced using new technologies. The LED-Array has an optical output of 800mW-1000mw, which has become a replacement for ordinary LEDs. The LED-Array has a luminous half-power angle of 10-120° (variable angle). Since the LED-Array is a highly integrated LED and has the size of only a penny coin, it can evenly illuminate the entire space in the room, and its lifetime is 50,000 hours. It was originally used in aviation aircraft. In recent years, due to the development of the civilian night surveillance market, LED-Array has gradually become a civilian market and has become an ideal choice for high-quality night surveillance.
Although infrared LEDs and LED-Arrays eliminate thermal infrared light sources, infrared LD light sources must be selected for super-long-distance scene monitoring above 1 km. Because the semiconductor laser has higher brightness and directional characteristics than the LED.
In general, the following points should be noted when selecting an infrared light source.
A, infrared light distance to choose to leave a margin to choose infrared light, pay special attention to the distance between the nominal distance and the actual irradiation distance. Because the nominal visible distance of some manufacturers is often too large, practical tests must be performed when selecting the irradiation distance of the infrared lamp, and sufficient margin is left to make the illumination of the observed scene reliable.
B. The light source driven by a steady current source should be selected because the LED is a current-driven device, and its light emission luminance and power are proportional to the drive current, rather than the voltage. Therefore, in order to keep the luminous intensity unchanged, it is necessary to choose a steady-current source-driven light source.
C, to choose a good heat source because the light emitting tube has a fever and heat problems, especially the power of a large distance light source heat, so you must choose a good heat source to ensure that the work is stable and reliable.
D. The infrared light source separated from the lamp board by the power supply circuit of the light control switch automatic control circuit should be selected. Because the power supply circuit and the light board of the infrared lamp are not separated, the heat generated by the work of the light tube will affect the performance of the components of the power supply circuit. As a result, the light emission of the light emitting tube is unstable. With this circuit of the light control switch, the infrared light can be turned off during the day and turned on at night.
E. The infrared lamp should be selected according to the monitoring distance. The infrared LED can be mounted on the lens, used with the infrared camera, or directly on the casing around the camera and lens interface. Obviously, these two types of assembled infrared LEDs are less, and the irradiated distance is certainly not as far away as the individual infrared LED lights. Generally, 50m or more, it is better to use a separate infrared lamp, and the other LD is used for night vision lighting of a monitoring scene of distance of more than 1km, but the LD beam is thin and strong, in order to make the infrared beam illuminate a certain range of scenes, use It also needs to be expanded by a beam expander lens.
Second, the choice of camera The current camera's photosensitive devices are CMOS and CCD. Like the CCD, the CMOS image sensor chip also responds to infrared light waves, but its sensitivity is much higher than the CCD image sensor chip in the 890-980 nm range, and the attenuation gradient is also slower as the wavelength increases. With the rapid development of CMOS image chips, the noise signal is further reduced, and star-class CMOS cameras are also available. Therefore, it is not necessarily limited to the CCD camera selection, but can fully utilize their respective advantages. In general, the main points of infrared camera selection are as follows.
A. Low-light camera should be selected, and its illuminance requirement is generally ≤ 0.02 Lux
Some camera manufacturers or vendors falsely report the minimum illumination, which greatly reduces the effective distance of night vision. Therefore, it is better to be able to test it. Moonlight-level and star-level sensitization cameras can work in very dark conditions, but some places with low reflectance factors can not meet the requirements, such as deserts, green areas, forest areas. In this case, it is necessary to use a low-light-level night-vision camera that is directly coupled with a fiber panel and a light cone by a black and white CCD of a high-performance image intensifier and a CCIR system. In short, the lower the illuminance the better, because the current is still not standardized, can not believe the minimum illuminance of the production plant, it is better to test under practical conditions, usually illuminance requirements are generally ≤ 0.02Lux.
B. The larger the size of the infrared camera image sensor chosen, the better because the 1/4 CCD cannot be used for an effective distance of 15m or more infra-red night vision, because the 1/4 CCD light flux is only 50% of the 1/3 CCD. The CCD has a large size and receives a large luminous flux; the CCD has a small size and receives less luminous flux. Therefore, the night vision camera selects 1/2 of the CCDs. One-third of the CCDs can be tested, but it is absolutely impossible to select 1/4.
C. Infrared cameras must have automatic electronic shutter and automatic gain control (AGC) function. Because of these features, the signal can be adjusted to a better state to meet the observation effect.
D. CMOS ultra-miniature cameras that need to be concealed on the occasion Because of low power consumption, high integration, and small size, only CMOS image sensors can do it. Thus, shirt buttons and suit button-sized CMOS cameras can be made. With the corresponding miniaturization of infrared light sources, and the introduction of high-performance batteries, the third eye will be everywhere. In this way, bring a night-vision goggles and a hat with an infrared light source and CMOS ultra-micro camera, the night will be like day. Obviously, this will change the face of our entire social life.
E. The matching of the power supply of the camera with a matching voltage regulator and a small power supply must be selected as follows.
· Select regulated power supply. Because the AC220V of the mains is unstable, if only a transformer with an AC-to-DC 12V is selected and the voltage is not stabilized, the circuit work in the camera will be unstable. As a result, the camera will be unstable and the required performance will not meet the requirements.
• It is better to choose a small power supply that is more than twice the current of the camera. If the camera's current is 200mA or 250mA, 500mA is generally sufficient. If the selection is too large, such as 1A for a camera, the volume is too large and the price is too expensive; if the current is too small, the current of the camera may heat up (because the continuous working time is too long) and affect the reliability and the working life.
Third, the choice of lens, etc. Camera lens is the key equipment of the infrared camera, its quality (index) has a direct impact on the quality of the system's imaging results, therefore, the lens is appropriate whether it is related to the quality of the system, but also related to the project cost. Therefore, when selecting a lens, pay attention to the following points:
A, the best choice for the infrared lens due to ordinary optical lens, the infrared light reflected from the object back to the lens can not be effectively focused on the CCD target surface, infrared night vision effect will be greatly reduced, so the best choice for infrared lenses. In particular, color-to-black cameras cannot use the infrared lens to make the day-night surveillance focal plane consistent, resulting in the inability of the day-night images to remain clear.
B. Selecting the imaging size of the lens is the same as the size of the image sensor in the camera. The imaging size of the selected lens should be the same as the size of the image sensor in the camera. If the size of the image sensor is 1/2, the imaging size of the lens must be It is 1/2". When the imaging size of the lens is larger than the size of the camera's photosensitive surface, it will not affect the imaging, but the actual imaging field of view is smaller than the lens's nominal angle of view, and when the lens imaging size than the camera's photosensitive surface When the size is small, the imaging will be affected, and the imaging frame will be surrounded by the lens barrel. Black corners will appear on the four corners of the screen. It can be seen that for 1/3 "cameras, 1/3", 1/2" and 2/3" lenses can be selected; for 1/2" cameras, 1/2" and 2/3" can be selected. The lens can't use 1/3 of the lens, because the CCD is like the human eye, the lens is like people's glasses, the glasses are too small, the eyes can not see the surrounding things.
C, the best choice for the lens and camera interface installation method The lens and camera interface installation methods are C-type installation and CS-type installation of the two, the best of both. If you choose a C-type lens, you need to add a 5mm thick ring. If it is directly connected to the CS interface camera without a collar, it may cause the rear mirror surface of the lens to collide with the protective glass of the sensitive surface of the CCD, resulting in damage of the CCD camera. This needs special attention in practical use.
D, the best choice for automatic iris lens, to adapt to changes in day and night illumination due to day and night monitoring, the illuminance range is very large, so it is best to use automatic iris lens can automatically change according to the illuminance, so that the image remains clear.
E. Resolution and Transmittance of the Lens The resolution of the imaging lens used to achieve the required resolution must be greater than the resolution of the camera. Otherwise, the required clearness cannot be achieved. In addition, the transmittance of the lens in the lens is better, that is, the attenuation of light is very small.
F. If the monitoring distance is more than one kilometer, laser beam expanding and collimating lens must be used to select the appropriate laser beam expanding and collimating lens according to the size and distance of the scene to be observed, so that the laser beam can illuminate the scene to be monitored for monitoring. The reflected light of the scene can be received by the camera.
G, pay attention to the selection of a good performance window glass protective cover in addition to infrared light, camera, lens, but also pay attention to the protective cover, power supply and other comprehensive considerations. Because the protective cover has an effect on the effect of infrared light, such as infrared light through different media, the transmittance and reflectivity are different. For example, different window glasses, especially automatic defrosting coated glass, have different attenuation of infrared light, so care should be taken to choose a protective cover with good window glass.
It can be seen from the above that the three infrared light sources have their advantages and disadvantages, but the thermal infrared light source is basically eliminated by the infrared LED and the LED-Array light source. Because with the LED-Array is also fully exposed to the distance of a few hundred meters monitoring the scene. As for super-long-distance monitoring scenes above 1km, infrared LD light sources should be used as well. Because of its high brightness, a lot of LD LED top, so the infrared LD light source is small, light weight, is the best choice for ultra-long distance.
The most important issue for the selection of infrared cameras is the set of features. In addition to selecting the infrared light source, the camera, lens, protective cover, power supply, etc. must be comprehensively considered. Only by taking into account the selection points outlined in the article, can we get a multiplier effect.