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Basic concepts of infrared detection by passive infrared detectors

Dec 16, 2019

Basic concepts of infrared detection by passive infrared detectors

Passive infrared detectors are a type of detector that is extremely common in security engineering. However, for its normal use, it is necessary to prevent false alarms and reduce false alarms. In particular, how to minimize false alarms is a topic facing the majority of engineering designers. To do this, we must first understand some basic concepts and technical characteristics of passive infrared detectors, so that we can follow these basic technical characteristics from installation, commissioning, use, etc., and according to the basic technical characteristics of the detector. This can maximize the effectiveness of the detector.


Within the alert range, why can a passive infrared detector generate an alarm signal when people are moving?

In nature, any object above the absolute temperature (-273 degrees) will produce an infrared spectrum. Objects with different temperatures will have different wavelengths of infrared energy, so the infrared wavelength is related to the temperature.

There are two key components in a passive infrared detector. One is a pyroelectric infrared sensor (PIR), which can transform infrared signals with wavelengths between 8 and 12um into electrical signals. The white light signal has a suppressing effect. Therefore, in the guard zone of the passive infrared detector, when no human body moves, the pyroelectric infrared sensor only senses the background temperature. When the human body enters the guard zone, the Fresnel lens, the heat The electric discharge infrared sensor detects the difference signal between the human body temperature and the background temperature. Therefore, the basic concept of the infrared detection of the infrared detector is to sense the difference between the temperature of the moving object and the background object. Another device is a Fresnel lens. Fresnel lenses come in two forms, refractive and reflective. The Fresnel lens has two functions: one is focusing, which is to refract (reflect) the thermally-released infrared signal on the PIR, and the second is to divide the warning zone into several bright and dark zones to enter the warning zone. Moving objects in the zone can generate a changing pyroelectric infrared signal on the PIR in the form of temperature changes, so that the PIR can generate a changing electrical signal.