A Short Note On Passive Infrared Sensor ( Pir Sensor ) Essay

800 Words Jun 2nd, 2016 4 Pages
A Passive InfraRed sensor (PIR sensor) is an electronic device which measures IR light radiating from objects in its field of view. Apparent motion is detected when an infrared source with one temperature, such as a human, passes in front of an infrared source with another temperature, such as a wall. All objects emit what is known as black body radiation. This energy is invisible to the human eye but can be detected by electronic devices designed for such a purpose. The term 'passive ' in this instance means the PIR does not emit energy of any type but merely accepts incoming infrared radiation. A person entering the monitored area is detected when the infrared energy emitted from the intruder 's body is focused by a Fresnel lens or a mirror segment and overlaps a section on the chip which had previously been looking at some much cooler part of the protected area. That portion of the chip is now much warmer than when the intruder wasn 't there. As the intruder moves, so does the hot spot on the surface of the chip. This moving hot spot causes the electronics connected to the chip to de-energize the relay, operating its contacts, thereby activating the detection input on the alarm control panel. Conversely, if an intruder were to try to defeat a PIR perhaps by holding some sort of thermal shield between himself and the PIR, a corresponding 'cold ' spot moving across the face of the chip will also cause the relay to de-energize — unless the thermal shield…

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