Optical smoke detector with active self-monitoring
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United States of America Patent
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-
Jan 10, 1995
Grant Date -
N/A
app pub date -
Sep 8, 1992
filing date -
Sep 6, 1991
priority date (Note) -
Expired
status (Latency Note)
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Abstract
In a scattered-light smoke detector, for preventing false alarms due to extraneous matter in a measurement chamber (1), a radiation source (2) and two radiation detectors (7, 8) are included. An evaluation circuit is provided for comparing the two detector signals, and an alarm signal is triggered if at least one of the detector signals exceeds a predetermined threshold, and if the two detector signals are at least approximately equal. In another embodiment, a scattered-light smoke detector includes two radiation sources (2, 22), a radiation detector (7), and circuitry for alternatively activating one (2) or the other (22) radiation source. For comparison, corresponding detector signals are stored in sample-and-hold circuits, and an alarm signal can be triggered depending on the same tests. Furthermore, in both cases, a trouble signal can be produced if the two signals are significantly different.
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