Any object whose temperature exceeds 0°C can generate thermal radiation, and the spectrum of thermal radiation generated by objects whose temperature is lower than 1725°C is concentrated in the infrared region. Therefore, all objects in the natural world can radiate infrared heat outward. The wavelength and distance of infrared radiation generated by any object due to its own physical and chemical properties and its own temperature are not the same, generally the higher the temperature, the stronger the infrared radiation. People are warm-blooded animals and infrared radiation is also the most stable. Infrared alarm detectors are divided into passive infrared detectors and active infrared detectors .
Passive infrared detectors , that is, the detector itself does not emit any energy but only passively receives and detects infrared radiation from the environment. A few seconds after installation, the detector has been adapted to the environment. When nobody or animals enter the detection area, the infrared radiation at the scene remains stable. Once the human body's infrared radiation comes in, the pyroelectric device generates an abrupt electrical signal when focused by the optical system. And send an alert. The warning line formed by passive infrared intrusion detectors can generally reach tens of meters.
The active infrared detector is composed of two parts: transmitting or receiving device. The principle: infrared transmitters drive infrared light emitting diodes emit a noisy modulated infrared beam. At a distance from the infrared transmitter, an infrared receiver is placed in alignment with it. It receives the infrared radiation energy discovered by the transmitter through a phototransistor and converts it into an electrical signal through photoelectric conversion. This electrical signal is sent to the alarm controller circuit after appropriate processing.
The optical systems that are placed on the receiving and transmitting sides are generally optical lenses. It plays a role of gathering infrared light into a relatively thin beam of light so that the energy of infrared light can be transmitted in a concentrated manner. The infrared light emitting tube is placed at the focal point of the emitting optical lens, and the photosensitive crystal agro-pastoralists are placed at the focus of the receiving optical lens.
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