Output circuit of an ionization smoke sensor

Details Output circuit of an ionization smoke sensor Output circuit of an ionization smoke sensor

1976-02-09

1977-08-09

Caldwell, John W.

Communications: electrical

Systems

Call station

250381, G08B 2100

Patent

active

040414795

ABSTRACT:
An ionization smoke sensor including a pair of ionization chambers normally biased to maintain an ionic current which varies in response to smoke particles within one of the chambers. A normally non-conductive transistor is biased to conduct when an impedance change of the combination of ionization chambers, caused by the smoke, exceeds a certain amount. The conductive transistor in turn biases a thyristor to conduct to actuate an alarm circuit. A comparator circuit is connected between the transistor and the thyristor for providing a biased signal therebetween. The biased signal is not applied by the comparator until the current through the conductive transistor exceeds a certain threshold value. Consequently, leakage currents of the transistor when it is non-conductive are isolated from the thyristor to prevent erroneous triggering of the same.

REFERENCES:
patent: 3717862 (1973-02-01), Sasaki
patent: 3728703 (1973-04-01), Burnett
patent: 3906474 (1975-09-01), Lehsten

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