Abstract: A smoke detector of the type utilizing a photo-responsive device to detect light reflected from smoke particles illuminated by a light source and actuate an alarm, in which a second photo-responsive device is utilized to control the intensity of the light source so that it is continuously exposed to a light intensity from the light source such that its thermal co-efficient of resistance is maintained at a value substantially equal to that of the first photo-resistive device when said first photo-resistive device is exposed to the amount of light that causes an alarm. In one embodiment of the invention identical photo-cells are connected into circuitry which includes two level detectors with the same transfer curve and voltage gain, and means causing the two photo-responsive devices to have the desired resistance at the alarm point. Changes in ambient temperature and line voltage are therefore prevented from affecting the alarm point.

Abstract: A fire detection system of the type utilizing an optical detector with discriminating photo-cells connected in series to form a voltage divider, with the rise in voltage at the junction of the photo-cells being utilized as the input to an amplifier to energize an alarm or actuate an extinguishing system, in which the ground wire to the remote optical detectors is also used as the ground wire between the amplifier and the actuating means for the alarm or the extinguishing system, whereby a break in the ground wire, which causes a rise in voltage at the junction, is prevented from causing a false alarm, since said break also breaks the circuit between the amplifier and the actuating means.

Abstract: A detector system particularly adapted for use in installation where the supply voltage is subject to wide variations comprises a detector which produces a voltage in response to a condition to be detected, a supervisory circuit, and an alarm actuator, in which the voltage signal produced by the detector when the predetermined condition exists, varies in proportion to line voltage, the alarm actuating means produces an alarm when the input signal rises to a predetermined percentage of the line voltage, and the supervisory circuit applies to the signal lead a supervisory voltage which also varies in proportion to the variation of line voltage.

Abstract: A detector of the type utilizing photo-electric detection of reflected light which is almost completely immune to false alarms from changing ambient light and random electrical noise, with a sensitivity that is independent of ambient light, with a power consumption low enough to permit battery operation for a period of over 12 months. The light source is a light emitting diode which is pulsed at a low repetition rate, such as one pulse every two seconds, by an extremely short pulse, such as 20 microseconds. Voltage pulses generated when the reflected pulsed light is received by the photo-generative cell is amplified and applied to a level detector, the output of which is applied to the "set" terminal of a flip-flop circuit. The amplifier is on continuously, however the level detector is pulsed to the on condition simultaneously with the on pulse to the light emitting diode, and for the same period of time.

Abstract: A portable fire alarm device comprising fire detecting means and alarm means powered from a self-contained power supply. The power to the detector and alarm is through a normally closed switch of the type such as a mercury switch which may be opened by tilting the device to a predetermined angle from the vertical so that the alarm may be shut off.A second normally open switch of the mercury type connects the power supply directly to the alarm device and is so oriented that tilting the device to a predetermined angle from the vertical closes said switch and energizes the alarm to test the condition of the battery.