Optical particle detector

Details Optical particle detector Optical particle detector

1978-03-13

1980-12-30

Caldwell, Sr., John W.

Communications: electrical

Condition responsive indicating system

Specific condition

250574, 356439, G08B 1710

Patent

active

042426731

ABSTRACT:
A photoelectronic smoke detector has walls around a dark chamber to which smoke, but not light, is admitted, and through which light is directed from a source on a path to a limited area of a chamber wall. A first photocell views light scattered from the through path by particles in the path primarily and also receives background light scattered from the chamber wall outside the limited area. A second photocell is disposed to receive background light substantially only from the limited area and other areas outside the source light path. The first cell produces a first signal in response to background and particle-scattered light. The second cell produces a second signal corresponding to background scatter. The first and second cells, preferably photovoltaic photodiodes, are coupled in opposition in a circuit whose output consequently is substantially independent of the background light.

REFERENCES:
patent: 1877279 (1932-09-01), Dawson
patent: 2640123 (1953-05-01), Cahusal et al.
patent: 2712643 (1955-07-01), Hall
patent: 3444544 (1969-05-01), Pearson et al.
patent: 3881112 (1975-04-01), Roberts
patent: 3922655 (1975-11-01), Lecuver
patent: 4021792 (1977-05-01), Ludt et al.

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