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Passive infrared detector

  • US 4,321,594 A
  • Filed: 11/01/1979
  • Issued: 03/23/1982
  • Est. Priority Date: 11/01/1979
  • Status: Expired due to Term
First Claim
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1. A passive infrared intrusion detection system comprising:

  • a sheet of material transmissive to infrared radiation in a predetermined infrared range and having at least one Fresnel lens formed therein, said lens being disposed to receive and to focus incident infrared radiation from a protected area, said sheet being translucent to light outside of said infrared range such that visible light is diffused by said sheet; and

    a blanced detector disposed at the focus of said lens, said detector having two sensing elements electrically connected in series opposition and operative to provide an electrical output signal in response to the infrared radiation focused thereon, and substantially no output signal in response to diffused non-focused visible light transmitted by said sheet.

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