Ionization-type fire sensing system

Details Ionization-type fire sensing system Ionization-type fire sensing system

1976-11-15

1978-08-22

Caldwell, Sr., John W.

Communications: electrical

Condition responsive indicating system

Specific condition

250381, 331 65, 331113R, G08B 1710

Patent

active

041092406

ABSTRACT:
An ionization chamber is exposed to the atmosphere to be supervised, the ionization chamber being so constructed that the electrical resistance thereof changes in the presence of fire particles or aerosols upon occurrence of a fire; to improve reliability of detection, the ionization chamber is connected as a resistance element in a free-running multivibrator oscillator circuit, which includes a pair of cross-coupled field effect transistors (FET's) so that, upon change of the atmosphere to which the ionization chamber is exposed, the pulse frequency of the oscillator changes, which change is detected by a pulse rate detector. If the detector has upper and lower threshold levels, deviation of pulse rate in one direction may be used to sense presence of a fire, and in the other direction may be used to sense incipient trouble in the circuit itself.

REFERENCES:
patent: 3253153 (1966-05-01), Stoddard
patent: 3308667 (1967-03-01), Pearlman
patent: 3375716 (1968-04-01), Hersch
patent: 3559196 (1971-01-01), Scheidweiler
patent: 3775616 (1973-11-01), Tagashira et al.
patent: 3821699 (1974-06-01), Marus et al.

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