Passive infrared detectors do not require additional infrared radiation sources, and do not emit any energy to the outside world. Instead, the detectors directly detect infrared radiation from moving targets, and thus have a passive name.
Passive infrared detector basic composition
It is composed of optical system, thermal sensor (also called infrared sensor) and alarm controller. Also known as passive infrared alarm.
Passive infrared detector working principle
The core component of the passive infrared device is an infrared detector (infrared sensor). Through the cooperation of the optical system, it can detect the change of thermal radiation in a certain stereoscopic space. When there are no moving objects such as human bodies in the prevention area, since all the background objects (such as walls, furniture, etc.) have relatively small infrared radiation energy at room temperature and are basically stable, all of them cannot trigger an alarm. When the human body walks in the detection area, it will cause changes in the infrared thermal radiation energy. The infrared sensor converts the change in the infrared thermal radiation energy received between the active human body and the background object into a corresponding electrical signal. After appropriate processing, it sends it to the alarm controller and issues an alarm signal. The infrared sensor's detection wavelength range is 8~14μm. Since the human body's infrared radiation wavelength is within this detection wavelength range, it can better detect the active human body. The optical system in front of the infrared sensor can reflect the infrared radiation energy from multiple directions through the reflector or the special lens and all concentrate on the infrared sensor. In this way, on the one hand, the thermoelectric conversion efficiency of the infrared sensor can be improved, and on the other hand it also has the effect of lengthening the detection distance and enlarging the vigilance field of view.
Infrared radiation characteristics of natural objects
Any object in nature can be considered as an infrared radiation source. This is because when the temperature of the surface of the object is higher than the absolute zero temperature of 0 K (ie, -273° C.), heat radiation is generated, and the spectrum generated by the heat radiation is mainly located in the infrared band. For example, when an incandescent light bulb is commonly seen, about 10% of the light is visible light, and the remaining 90% is almost infrared light. Our body is also an infrared radiation source. The ability to radiate varies from person to person, and the ability to radiate in different parts of the human body is also different. The higher the surface temperature of the object, the shorter the wavelength of infrared radiation it radiates. That is, the absolute temperature of the surface of the object determines the peak wavelength of its infrared radiation. The amount of infrared energy radiated by an object depends on the absolute temperature of the object, which increases with the fourth power of the absolute temperature of the object, and the energy intensity at the peak wavelength of the radiation increases with the fifth power of the absolute temperature. This means that if the temperature of an object is twice as high as that of another object, the infrared energy of the object radiating at all wavelengths is 16 times larger than that of another object, and the infrared energy radiated at the peak wavelength is 32 times bigger. In addition, the infrared energy emitted by the object is also related to the color of the object and the surface finish. At the same temperature, the cleaner and smoother the surface of the object, the less infrared energy is radiated. From the above analysis, we can see that the human body and other background objects in the room are not only different in the infrared radiation energy, but also the peak wavelength of the infrared radiation radiated from them is not the same, and the infrared peak wavelength of the human radiation is about 10 μm.
Passive infrared detector installation and use of points
1. Passive infrared detectors are space-controlled detectors. It does not radiate any energy to the outside world itself. Its power consumption is small, and ordinary batteries can maintain long-term work.
2. Due to the poor penetration of infrared rays, there should be no obstructions in the monitoring area, otherwise it will cause a "blind area" to be detected.
3. In order to prevent false alarms, the passive infrared detector probe should not be aimed at any object whose temperature will change rapidly, especially the heating element.
4, in the choice of installation location, the detector should have the maximum range of alert, so that all possible intruders can be in the alert range, so that all possible intruders can be in the infrared alert beam range. The activity of the intruder is conducive to laterally crossing the beam zone, which can increase the detection sensitivity.
5. The product types include wall-mounted and ceiling-mounted passive infrared detectors.
6. Since the passive infrared detector works in a passive manner, several installations in the same room will not generate interference.
Passive infrared detector basic composition
It is composed of optical system, thermal sensor (also called infrared sensor) and alarm controller. Also known as passive infrared alarm.
Passive infrared detector working principle
The core component of the passive infrared device is an infrared detector (infrared sensor). Through the cooperation of the optical system, it can detect the change of thermal radiation in a certain stereoscopic space. When there are no moving objects such as human bodies in the prevention area, since all the background objects (such as walls, furniture, etc.) have relatively small infrared radiation energy at room temperature and are basically stable, all of them cannot trigger an alarm. When the human body walks in the detection area, it will cause changes in the infrared thermal radiation energy. The infrared sensor converts the change in the infrared thermal radiation energy received between the active human body and the background object into a corresponding electrical signal. After appropriate processing, it sends it to the alarm controller and issues an alarm signal. The infrared sensor's detection wavelength range is 8~14μm. Since the human body's infrared radiation wavelength is within this detection wavelength range, it can better detect the active human body. The optical system in front of the infrared sensor can reflect the infrared radiation energy from multiple directions through the reflector or the special lens and all concentrate on the infrared sensor. In this way, on the one hand, the thermoelectric conversion efficiency of the infrared sensor can be improved, and on the other hand it also has the effect of lengthening the detection distance and enlarging the vigilance field of view.
Infrared radiation characteristics of natural objects
Any object in nature can be considered as an infrared radiation source. This is because when the temperature of the surface of the object is higher than the absolute zero temperature of 0 K (ie, -273° C.), heat radiation is generated, and the spectrum generated by the heat radiation is mainly located in the infrared band. For example, when an incandescent light bulb is commonly seen, about 10% of the light is visible light, and the remaining 90% is almost infrared light. Our body is also an infrared radiation source. The ability to radiate varies from person to person, and the ability to radiate in different parts of the human body is also different. The higher the surface temperature of the object, the shorter the wavelength of infrared radiation it radiates. That is, the absolute temperature of the surface of the object determines the peak wavelength of its infrared radiation. The amount of infrared energy radiated by an object depends on the absolute temperature of the object, which increases with the fourth power of the absolute temperature of the object, and the energy intensity at the peak wavelength of the radiation increases with the fifth power of the absolute temperature. This means that if the temperature of an object is twice as high as that of another object, the infrared energy of the object radiating at all wavelengths is 16 times larger than that of another object, and the infrared energy radiated at the peak wavelength is 32 times bigger. In addition, the infrared energy emitted by the object is also related to the color of the object and the surface finish. At the same temperature, the cleaner and smoother the surface of the object, the less infrared energy is radiated. From the above analysis, we can see that the human body and other background objects in the room are not only different in the infrared radiation energy, but also the peak wavelength of the infrared radiation radiated from them is not the same, and the infrared peak wavelength of the human radiation is about 10 μm.
Passive infrared detector installation and use of points
1. Passive infrared detectors are space-controlled detectors. It does not radiate any energy to the outside world itself. Its power consumption is small, and ordinary batteries can maintain long-term work.
2. Due to the poor penetration of infrared rays, there should be no obstructions in the monitoring area, otherwise it will cause a "blind area" to be detected.
3. In order to prevent false alarms, the passive infrared detector probe should not be aimed at any object whose temperature will change rapidly, especially the heating element.
4, in the choice of installation location, the detector should have the maximum range of alert, so that all possible intruders can be in the alert range, so that all possible intruders can be in the infrared alert beam range. The activity of the intruder is conducive to laterally crossing the beam zone, which can increase the detection sensitivity.
5. The product types include wall-mounted and ceiling-mounted passive infrared detectors.
6. Since the passive infrared detector works in a passive manner, several installations in the same room will not generate interference.
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