How does a motion detector work?
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A PIR sensor usually contains two sensors (sometimes more), which look at different parts of the room through a multifaceted lens. The sensors readings are fed into a difference amplifier. If a person is stationary in the room each of the sensors will have a particular reading. If the person moves the lens will project the radiation differently onto the sensors, so that the difference amplifier's output will change. A differentiator will detect changes in the sensors' readings and switch the output. In the past I've used Panasonic's NaPiOn PIR sensor, which has a quad-type sensor, which, combined with the multifaceted lens divides the room in 64 detection zones.
Even small movements will cause a difference in the quad sensor, which will activate the output signal. |
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