Arrangement in order to prevent false alarms of a passive infrared motion alarm
AssigneeHeimann GmbH
InventorsGerhard Doenges, Thomas Herwig
Life of this patent
Estimating the term…
Abstract
In an infrared motion alarm an optical filter arranged in front of an input of an infrared detector is attached to a heat sink in the form of a solid metal crucible in order to reduce the sensitivity to glass-penetrating electromagnetic radiation. Changes in radiation absorbed in the optical filter are either captured in the thermal sink or decelerated at least as to the characteristic thermal radiation of the optical filter and no longer fall within the characteristic range of change of the motion alarm.
Claims14
An arrangement for preventing false alarms of a passive infrared motion alarm, comprising:
- (a) means for focusing electromagnetic radiation coming from at least one angle onto an infrared detector means;
- (b) in front of the infrared detector means optical filter means for withholding electromagnetic radiation having a wavelength less than approximately 4.5 .mu.m from the infrared detector means;
- (c) the infrared detector means producing an electric signal from the received radiation and transmitting it to an analysis means for analyzing characteristic time changes of the electric signal for alarm purposes;
- (d) said optical filter means resting on a solid metal plate in highly thermal conductive fashion at a side which faces towards the infrared detector means;
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- (e) the metal plate having a central opening whose inner surface is mirror-coated to reflect the radiation passing through the opening and directed onto the infrared detector means.
An arrangement for preventing false alarms of a passive infrared motion alarm, comprising:
- an infrared detector means for producing an electric signal from incident electromagnetic radiation and transmitting it to an analysis means for analyzing characteristic changes of the electric signal for alarm purposes;
- in front of the infrared detector means optical filter means for filtering out electromagnetic radiation having a wavelength less than approximately 4.5 .mu.m from the infrared detector;
- said optical filter means resting on a solid metal surface in highly thermal conductive fashion;
- and the metal surface having a central opening positioned for transmission of the radiation therethrough and onto the infrared detector.
Dependencies are inferred from the claim text.