Ionization-type fire or smoke sensing system

Radiant energy – Invisible radiant energy responsive electric signalling – Including a radiant energy responsive gas discharge device

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250385, 307310, 340237S, G08C 100

Patent

active

040371069

ABSTRACT:
To render an ionization-type sensing element essentially immune to changes in ambient conditions, principally temperature or operating voltage, while still using low-current draining circuits to sense response of the ionization chamber of the sensor, the threshold response level of a field effect transistor (FET) is arranged to have approximately the same temperature response characteristic, within the range of ambient temperature considered, as the ionization cell so that the overall circuit or system combination of the cell and FET amplifier will have a response which is essentially independent of ambient temperature or similar conditions. The source path of the FET is connected to a voltage divider which is so dimensioned that the voltage division ratio (R.sub.2 /R.sub.1) is related to the temperature coefficient (.alpha.) of the base-emitter voltage of the FET and the temperature coefficient (.beta.) of the measuring ionization cell chamber:

REFERENCES:
patent: 3701004 (1972-10-01), Tuccinardi et al.
patent: 3718919 (1973-02-01), Sasaki et al.
patent: 3728706 (1973-04-01), Tipton et al.
patent: 3742262 (1973-06-01), Ichinohe et al.
patent: 3760199 (1973-09-01), Graeme
patent: 3899693 (1975-08-01), Gaudreault
patent: 3909815 (1975-09-01), Gacogne
patent: 3946374 (1976-03-01), McMillian

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