Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1997-01-13
1998-10-06
Swann, Glen
Communications: electrical
Condition responsive indicating system
Specific condition
250340, 250342, 250395, G08B 13191, G08B 13193
Patent
active
058183370
ABSTRACT:
A passive infrared intrusion detection device uses a dual element pyroelectric detector and a housing for surrounding and containing the dual element pyroelectric detector. The housing has a plurality of Fresnel lens elements for gathering infrared radiation from a "look down" volume of space and for focusing the gathered infrared radiation onto the pyroelectric detector. A mask positioned between the plurality of Fresnel lens elements and the detector partially occludes the gathered infrared radiation from the Fresnel lens elements to one of the elements of the dual element pyroelectric detector creating an imbalance in the signal thereby preventing common mode rejection.
REFERENCES:
patent: 4841284 (1989-06-01), Biersdorff
C & K Systems Inc.
Swann Glen
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