| 摘要 |
A passive infrared alarm device evaluates the changes in infrared radiation level of a monitored room or a monitored portion of a room for alarm purposes. In accordance with the invention, an infrared sensing element is employed toward which an optical reflector directs infrared radiation emanating from one or more angles in a room to be monitored. An infrared filter is mounted in the path of the reflected infrared radiation before such radiation reaches the sensing element. The infrared filter is designed to absorb infrared radiation below a predetermined minimum wavelength, and additional means is provided for partially absorbing infrared radiation below the predetermined minimum at the reflector.
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