Fire detector system and method
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United States of America Patent
Stats
-
Sep 7, 1993
Grant Date -
N/A
app pub date -
Dec 2, 1991
filing date -
Dec 4, 1990
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
A fire detector system including ionization smoke detectors (7) is provided with improved false-alarm protection. The system includes an ionization chamber (1) with a radioactive source (10), connected in series with a resistor (2) between power supply lines (8, 9), and circuitry (11, 28) for switching the operating voltage of the ionization chamber between a normal operating value (Ut) chosen for maximized detector sensitivity, and an elevated value (Uh) for operation at current saturation. Comparisons involving the ionization currents through the ionization chamber at the two operating voltages are used not only to recognize a condition of partial shielding of the radio-active source (due to condensation, for example), but also to detect smoke under such conditions.
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Cited Art Landscape
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