Abstract: In a storage type smoke detector which requires a predetermined time after an ionization smoke sensor detects a fire before a fire warning is issued, a charging circuit including a capacitor connected to a power supplying line is coupled with a discharging circuit for periodically discharging a voltage charged in the capacitor, and the discharging circuit is periodically closed by a P-channel type field effect transistor which is connected to an output end the ionization smoke sensor and which is supplied with a series of oscillating pulse.

Abstract: A smoke detector comprising a smoke detection cell of the ionization type and an electrical network which provides for ac operation of the detection cell. The impedance of the smoke detection cell is very high (40,000 megohms) and changes in the presence of airborne combustion products. The network senses the impedance change by a measurement of the current through the chamber assuming an ac source under a short circuit load condition, a technique facilitating the use of bipolar transistors.

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.

Abstract: A smoke detector comprising a smoke detection cell of the ionization type and an electrical network providing for a.c. operation of the detection cell. The impedance of the detection cell changes in the presence of airborne combustion products and alters the operating frequency of the network. The frequency change is sensed to actuate an alarm. A.C. operation avoids the problem of d.c. instability in the high impedance detection cell circuit and simplifies sensing the electrical condition of the detection cell. The electrical network typically uses MOS-FET devices as the active circuit elements.