Passive infrared intrusion detector and its use
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United States of America Patent
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Aug 24, 1999
Grant Date -
N/A
app pub date -
Nov 1, 1996
filing date -
Nov 3, 1995
priority date (Note) -
Expired
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Abstract
A passive infrared intrusion detector for the detection of infrared body radiation includes a sabotage detector, in particular for detecting spraying of the entrance window of the intrusion detector. The sabotage detector includes a light source, a corresponding light sensor, and an optical diffraction grating structure on the outside of the entrance window. The light source and the light sensor can be on the same or on opposite sides of the entrance window. By first- or higher-order diffraction, light from the light source is focused onto the sensor, and a resulting electrical signal from the sensor is evaluated by an evaluation circuit. In case of sabotage, the focusing effect of the optical diffraction grating structure vanishes, so that the light intensity at the detector is reduced. The drop in light intensity triggers a sabotage alarm signal.
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