Patent Development & Management Company

Fyrnetics, Inc.

Larry D Larsen

Richard C Yung

Wing K Leung

Joseph E Hogel

Weight scales and strain gauge assemblies useable therein

A battery-powered fire alarm including a smoke detector circuit, a controllable horn circuit and a battery monitoring circuit. The smoke detector employs a pair of complementary field-effect transistor switches with gates respectively connected to an ionization chamber and a potentiometer of a Wheatstone bridge circuit connected across the battery. The field-effect transistors are biased off to minimize standby power consumption and are connected such that the threshold voltages thereof are offsetting to minimize supply voltage sensitivity of the detector. When the voltage from the ionization chamber assumes a value approximately equal to a preselected alarm voltage at the potentiometer, both field-effect transistors turn on to energize an alarm circuit to sound an alarm. Hysteresis circuitry is provided to ensure that the complementary switches, once turned on, will not turn off and thereby terminate the alarm until after the alarm condition has terminated. In one embodiment, a feedback signal causes the preselected alarm voltage to increase in response to alarm activation. In other embodiment, hysteresis is achieved by means of a feedback signal proportionately lowering the sensing voltage from the ionization chamber in response to alarm activation. A test switch and associated circuitry is also provided to manually lower the sensing voltage below the preselected alarm voltage to test the detection circuitry in addition to the battery and alarm horn.

Detection circuit with hysteresis

A battery-powered fire alarm including a smoke detector, a controllable horn circuit and a battery monitoring circuit. The smoke detector employs a pair of complementary field-effect transistor switches with gates respectively connected to an ionization chamber and a potentiometer of a Wheatstone bridge circuit connected across the battery. The field-effect transistors are biased off to minimize standby power consumption and are connected such that the threshold voltages thereof are offsetting to minimize supply voltage sensitivity of the detector. When the voltage from the ionization chamber assumes a value approximately equal to the potentiometer voltage, both field-effect transistors turn on to energize an alarm circuit to sound an alarm. The switching circuit is provided with hysteresis through positive feedback. The battery monitoring circuit employs a pair of complementary field-effect transistors connected with each other to establish a reference voltage to which the battery voltage is compared. The reference voltage is a function of both the threshold characteristics of the field-effect transistors and the magnitude of a preselected control voltage. Both field-effect transistors remain off until a low battery voltage condition is sensed to minimize standby power consumption.

Detection circuit

Fire alarm housing

Two cup-shaped electrodes respectively defining outer walls of a closed and an open ionization chamber and an insulator wall sandwiched therebetween defining an interior wall of both chambers and carrying both an electrode common to both chambers and at least one circuit element of a sensing circuit responsive to the relative impedances of the two chambers for indicating the presence of smoke in the open chamber. Minimizing leakage current-increasing factors as moisture, dust, etc., the body of the circuit element is protectively mounted to the insulator wall within the closed chamber by means of a plurality of leads extending through mating holes in the insulator wall with a header surface of the body pressed against the wall. One of the leads is folded around the edge of a hole in the wall wherein the common electrode is mounted and is squeezed between the insulator wall and a part of the common electrode to make electrical contact therewith. Some of the leads which extend out of the chamber for connection with external circuitry are sandwiched between an insulator member and the wall and thereby insulated against electrical contact with either of the cup-shaped electrodes. The insulator member is integrally formed with the insulator wall by cutting a portion thereof away from the wall to form the electrode mounting hole and folding it to overlie the leads and the wall.

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Elgin, IL, United States of America

Larry D Larsen