What is a passive movement detector?

Passive movement detector is a device that detects movable objects by infrared light detection that emit. They use the fact that all objects emit infrared radiation in the amount that differs depending on their temperatures. Like all passive detectors, the detector of passive infrared movement only works by detection of emissions produced from other objects and does not use its own emissions for this purpose, unlike active microwave -based movement or ultrasonic pulses. These detectors are often used in safety systems to detect intruders.

The infrared area of ​​the electromagnetic spectrum includes radiation with wavelengths between 0.7 and 300 micrometers, shorter than the wavelength of visible light, but longer than the microwave. Infrared light with a relatively short wavelength close to the visible light, called "near the infrared", cannot be detected by human senses. "Far infrared," with longer wavelengthsKami, can not be seen by the human eye, but feels like warm.

The heat of the object causes to emit part of this energy in the form of electromagnetic radiation, with higher temperatures creating greater emissions. At high temperatures, some of these emissions are in a visible spectrum, as shown in the fiber of the bulb or the glow of metal, which is processed by a blacksmith. All objects, however, emit at least some thermal radiation on infrared wavelengths, and because regardless of this, the temperature has absolute zero, even extremely cold objects have infrared emissions.

When objects close to the passive infrared detector of movement move with respect to the detector, the infrared radiation reaching the detector from the direction of movement changes. If the intruder enters the scope of the detector, the change of emissions caused by the presence of his body will be recorded. Since the detector is running by changes in the infrared light thatThey achieve a specific direction rather than its absolute amount, moving low emissions objects start the detector as well as a moving high -emission object. Hiding the body heat of the intruder therefore does not hide the intruder.

The detector sensor of passive infrared movement is made of pyroelectric crystals, which are substances that create temporary electrical voltage when their temperatures change due to fine shifts, the causes of changes in their crystalline structures. The commonly used pyroelectric materials include nitrate cesia (CSNO _{3 ) and nitrid Gallia (GAN). Changes in the incoming infrared light caused by moving objects change the temperature of the pyroelectric crystals and create electrical signals that are accepted and interpreted by the sensor electronics to trigger the alarm. These components are placed in a plastic window housing that maintains the most visible light, but is transparent to infrared light. The sensor may also contain a cutOutline, such as parabolic mirrors or specialized lenses called Fresnel lenses that focus infrared light on the way to the pyroelectric crystal.}