Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1991-12-02
1993-09-07
Mullen, Thomas
Communications: electrical
Condition responsive indicating system
Specific condition
250381, 340511, 340661, G08B 1710
Patent
active
052433307
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.
REFERENCES:
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patent: 3964036 (1976-06-01), Adachi et al.
patent: 4041479 (1977-08-01), Miyabe
patent: 4288694 (1981-09-01), Ahrons
patent: 4300133 (1981-11-01), Solomon
patent: 4364031 (1982-12-01), Scheidweiler et al.
patent: 4401978 (1983-08-01), Solomon
patent: 4455553 (1984-06-01), Johnson
patent: 4459583 (1984-07-01), van der Walt et al.
Abstract of Japanese Appln. No. 47-93018; title--Ionization Smoke Detector. Published May 1974.
Cerberus AG
Mullen Thomas
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