Passive infra-red sensor

• US 4,734,585 A
• Filed: 07/16/1986
• Issued: 03/29/1988
• Est. Priority Date: 07/17/1985
• Status: Expired due to Fees

• Current Assignee: Racal-Guardata Limited
• Original Assignee: Racal-Guardata Limited
• Inventors: Owers, Ian A.
• Primary Examiner(s): Fields, Carolyn E.
• Application Number:
  US06/886,038
• Time in Patent Office: 622 Days
• Field of Search: 250/342, 250/353, 250/349
• US Class Current: 250/353
• CPC Class Codes: G08B 13/19 using infrared-radiation detection systems G08B13/194 takes precedence
• CPC Class Codes: Y10S 250/01 Passive intrusion detectors

Abstract

A passive infra-red sensor includes a window in a housing which also houses an infra-red detector. The window defines a plurality of infra-red transmitting strips which are separated by Fresnel lens segments or infra-red opaque strips. The infra-red transmitting strips provide short range sensitivity. The Fresnel lens segments where provided give longer range sensitivity.

Claims

1. A passive infra-red sensor including

a housing

a window defined in said housing, and

an infra-red detector mounted within said housing behind said window,

said window defining an alternating sequence of infra-red transmitting strips which allow infra-red radiation to pass unfocused onto the detector, and lens segments positioned for focusing infra-red radiation onto said detector.

2. A sensor according to claim 1, in which the housing defines slots which provide continuations of at least some of said strips.

3. A sensor according to claim 2, in which at least some of said slots extend into a portion of the housing which faces downwardly when the sensor is in a mounted position.

4. A sensor according to claim 1, in which the lens segments are Fresnel lens segments.

5. A sensor according to claim 1, in which said window is bowed in transverse cross-section.

6. A sensor according to claim 1, in which said window further defines at least one row of adjacent Fresnel lens segments above said alternating sequence of infra-red transmitting strips and lens segments.