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Passive infrared detectors do not require an additional infrared radiation source. This projector does not emit any energy to the outside world. Instead, the detector directly detects the infrared radiation from the moving target. Therefore, it is passive.
The basic components of passive infrared detectors :
It consists of an optical system, a thermal sensor (also called an infrared sensor), and an alarm controller.
The working principle of passive infrared detector :
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.