[Summary] This article analyzes the working principle of infrared integrated camera and several existing technical difficulties from a technical point of view, and proposes some feasible solutions; It is helpful for the security industry personnel in product selection and use.
[Keywords] Infrared integrated camera Infrared utilization rate Reddish storm technology Constant current power supply Anti-fog defrosting constant temperature control Automatic cooling and heating air conditioning fully enclosed
In the security TV monitoring system, with the improvement of people's awareness of security, the need for 24 hours continuous monitoring of TV monitoring in important places and the maturity of infrared imaging technology, the use rate of infrared integrated cameras is getting higher and higher, and has gradually developed into A trend that is not only used in important departments such as banks, treasuries, museums, archives, libraries and prisons, but also in general TV monitoring projects such as residential quarters.
1. The principle characteristics of infrared and infrared lamps
Light is an electromagnetic wave and has the same essence as radio waves. Its wavelength range is from a few nanometers (1nm = 10-9m) to about one millimeter (mm). Only part of it is visible to the human eye. We call it visible light. The wavelength of visible light ranges from 380nm to 780nm. The wavelength of visible light is divided into red, orange, yellow, green, blue, blue, and purple light from long to short. It is called ultraviolet light, and the wavelength longer than infrared light is called infrared light. The wavelength of infrared light is between 780nm ~ 1000μm, located between radio waves and visible light.
Infrared lamps are divided into semiconductor solid light emitting according to their infrared radiation mechanism (infrared emitting diode IR LED)
There are two types of infrared lamps and thermal radiation infrared lamps. At present, the former is often used in CCTV infrared cameras.
The principle of infrared emitting diode (IR LED) infrared lamp is: the luminous body is composed of a matrix of infrared light emitting diodes. The infrared emitting diode is made of a material with high infrared radiation efficiency (usually gallium arsenide GaAs), and a forward bias voltage is applied to inject current into the PN junction to excite infrared light. The spectral power distribution is the center wavelength of 830-950nm, and the half-peak bandwidth is about 40nm. It is a narrow-band distribution, which is the range that can be felt by ordinary CCD black and white cameras.
The emission power of the infrared light emitting diode is expressed by the irradiance μW / m2. The maximum radiation intensity of the infrared diode is generally directly in front of the optical axis, and decreases as the angle between the radiation direction and the optical axis increases. The angle at which the radiation intensity is 50% of the maximum value is called the half intensity radiation angle, that is, the half power angle. The infrared angles of infrared light emitting diodes of different packaging process models are different.
Second, the infrared integrated camera imaging principle
In the night vision monitoring system, the conventional method is to use visible light illumination, but this method has the disadvantages of not being concealed and easy to expose the monitoring target, so it is used less; the current hidden and scientific night vision monitoring uses infrared camera technology. Infrared camera technology is divided into passive and active. Passive infrared camera technology uses any substance to have infrared radiation above absolute zero (-273 ° C). The higher the temperature of the object, the more infrared radiation is emitted. The most typical camera made by this principle is an infrared camera. However, this special infrared camera is expensive, so it is limited to military or special occasions. The active infrared camera technology uses infrared lamps to radiate "illumination" (mainly infrared light), using ordinary low-illumination black-and-white cameras, color-to-black-and-white cameras, or infrared low-illumination color cameras to feel the infrared light reflected from the surrounding scenery and the environment. Night vision monitoring. Active infrared camera technology is mature and stable, becoming the mainstream of night vision monitoring.
The infrared integrated camera is a camera device that integrates the camera, protective cover, infrared lamp, power supply and heat dissipation unit into one. The basic principle of night vision is to use ordinary CCD black and white cameras to feel the spectral characteristics of infrared light (that is, you can feel visible light and infrared light), and use infrared lights as "illumination sources" to image night vision. The power and angle of the infrared lamp, the configuration of the camera, the infrared lens with a certain focal length, and whether there is good power supply and heat treatment are important parameters to judge the performance of the integrated infrared camera.
At present, there are many products on the market that are separated from the camera and the infrared projector. This requires users to have sufficient understanding of the performance of the infrared lamp and the camera, and can make a reasonable match according to the angle of the infrared lamp and the camera lens parameters.
3. Performance analysis of infrared integrated camera
Infrared integrated cameras have outstanding advantages such as long night vision distance, strong concealment, and stable performance among surveillance cameras, so they occupy most of the market in CCTV night vision monitoring. How to distinguish the advantages and disadvantages in the complicated infrared integrated camera market? The infrared integrated camera with excellent performance must have the following performance:
1. Working conditions of infrared lamps
In general, the radiant power of the infrared lamp is proportional to the forward operating current, but when the maximum rating of the forward current is approached, the temperature of the device rises due to the heat consumption of the current, causing the light emission power to decrease. Infrared diode current is too small, it will affect the performance of its radiated power, but too large operating current will affect its life, and even burn the infrared diode.
When the voltage crosses the positive threshold voltage (about 0.8V), the current starts to flow, and it is a very steep curve, indicating that its working current requirement is very sensitive. Therefore, the working current is required to be accurate and stable, otherwise it will affect the performance of the radiated power and its reliability. The increase in radiant power with ambient temperature (including the increase in ambient temperature due to its own heat) will cause its radiant power to decrease. Infrared lamps, especially long-distance infrared lamps, heat consumption is a problem that should be noted when designing and selecting.
Therefore, the use of infrared lamps must have a good constant current power supply and a good heat dissipation design. ZOOM's zoom MCD, MDD, MED, MBB series cameras are equipped with high-power infrared lamps (up to 24), and use a high-power constant current power supply, internal circulation heat dissipation design, which can achieve long-distance night Sight (up to 220 meters away) and the long life of infrared lamps.
2. Infrared light utilization and red storm
What is a red storm? Red storms are caused by the visible infrared light contained in the emitted infrared light.
Infrared lamps can be completely free of red bursts (using 940-950nm wavelength infrared tubes) or only weak red bursts. Zhonglu Communication Company adopts American AUCSITER infrared technology. By ensuring the infrared lamp power, the infrared lamp's own heat consumption is reduced, the infrared light angle is adjusted, and the effective utilization rate of the infrared lamp reaches 90%. In the choice of infrared lamps, choose infrared lamps with a larger wavelength (910nm) to strictly reduce red bursts and achieve the effect of red bursts.
3. The fog and frost problem of infrared camera
The formation of fog and frost is caused by the condensation of saturated water vapor in the air, which is condensed into frost and fog due to the strength and weakness of the cold environment. During the work of infrared cameras, especially outdoor cameras, fog or frost is often formed on the window glass of the protective cover due to seasonal changes, day-night temperature differences, and rain and snow environments, which causes the camera to be unable to see clearly and directly affects the monitoring effect. By adopting advanced electronic defrosting circuit, Zhonglu Communication Company can effectively control the concentration of saturated water vapor in the cavity to achieve automatic defrosting and defrosting.
4. Window glass cleaning of infrared camera
The camera works in a rainy, snowy or dusty environment, and the window glass of the protective cover is prone to dirt, causing the camera's sight to be blocked. The solution is usually to add a wiper on the protective cover and clean the glass by controlling the wiper; another method is to use an invisible wiper window glass. Compared with ordinary window glass, invisible wiper window glass has the function of repelling water, dust and snowflakes.
5. Constant temperature of infrared camera
Due to the configuration of the infrared lamp with large heat generation, after the infrared lamp is started, it will be in front of the infrared camera during the entire working period (in 12 hours)
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