Passive infrared detector principle

Passive pyroelectric infrared detectors are referred to as passive infrared detectors. In the field of electronic anti-theft and human body detectors, passive infrared detectors (PIR, Passive infra-red Detectors) are widely used because of their low price and stable technical performance. And applied to various fields.

In theory, all objects in nature, as long as its temperature is higher than absolute zero (-273.15 ° C), its surface will constantly radiate infrared rays. Objects of different temperatures have different wavelengths of infrared energy released, so the infrared wavelength is related to the temperature. According to the difference in thermal irradiance of various parts of the human body (including the body), the peak value is between 8-12 μm.

Passive infrared probes work by detecting infrared rays of around 10 UM emitted by the human body. The 10 UM infrared rays emitted by the human body are enhanced by the Finnel filter and collected on the infrared sensing source. The infrared sensing source usually adopts a pyroelectric element, which loses the charge balance when receiving the temperature change of the infrared radiation of the human body, and discharges the charge outward, and the subsequent circuit can generate an alarm signal after being detected and processed.