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A passive infrared sensor (PIR sensor) is an electronic sensor that measures infrared (IR) light radiating from objects in its field of view. They are most often used in PIR-based motion detectors . PIR sensors are commonly used in security alarms and automatic lighting applications.
A passive infrared detector mounted on circuit board (right), along with photoresistive detector for visible light (left). This is the type most commonly encountered in household motion sensing devices and is designed to turn on a light only when motion is detected and when the surrounding environment is sufficiently dark.
Passive infrared systems do not use an infrared light source, instead they capture thermal radiation already emitted by the objects, using a thermographic camera. Pros: greater range of about 300 meters or 1,000 feet, higher contrast for living objects [3] Cons: grainy, lower resolution image, works poorly in warmer weather conditions, larger ...
Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequencies between 300 MHz and 300 GHz, broadly construed.
An infrared detector is a detector that reacts to infrared (IR) radiation. The two main types of detectors are thermal and photonic ( photodetectors ). The thermal effects of the incident IR radiation can be followed through many temperature dependent phenomena. [ 2 ]
A microwave oven or simply microwave is an electric oven that heats and cooks food by exposing it to electromagnetic radiation in the microwave frequency range. [1] This induces polar molecules in the food to vibrate [ 2 ] and produce thermal energy in a process known as dielectric heating .
This is also why you can take a piece of paper from a desk that is the same, exact, temperature as everything in the room, attach it to a stick (also the same exact temperature as the room) and wave it slowly in front of a sensor (at any range within the limit of the sensor) and it will activate the sensor."
There can be a variety of sources for a passive instrument, including scattered radiation, light emitted directly from the sun, moon or stars—both more appropriate in the visual or ultra-violet range—as well light emitted from warm objects, which is more appropriate in the microwave and infrared.
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