Smoke detector with means for compensating for variations in light source brightness due to line voltage variations

Claim 2

In a smoke detector of the type designed to be energized from an A.C. source and having a photo-resistive cell positioned to view smoke particles illuminated by the light source, the improvement comprising means for varying the effective voltage applied to the photo-resistive cell inversely with variations in voltage applied to the Light source, whereby the increase or decrease in brightness of the light source with increase or decrease in supply voltage does not appreciably change the alarm point of the detector due to the compensating decrease and increase of voltage across the photo-cell with the increase and decrease respectively of the brightness of the light source.

Claim 3

In a smoke detector of the type designed to be energized from an A.C. source and having a light source, a photocell positioned to view smoke particles illuminated by the light source, and an alarm actuating circuit responsive to an increase in voltage resulting from a drop in resistance of the photocell to actuate an alarm, the improvement comprising means for causing the voltage at the alarm actuating circuit to decrease when the supply voltage increases and vice-versa, said means including a capacitor connected to serve as a D.C. voltage supply for the alarm actuating circuit, means for applying a D.C. charging voltage to said capacitor from the supply voltage, and means for reducing the effective D.C. voltage applied to the capacitor during each half cycle with increases in supply voltage.

Claim 4

In a smoke detector of the type designed to be energized from an A.C. source and having a light source, a photocell positioned to view smoke particles illuminated by the light source, and an alarm actuating circuit responsive to an increase in voltage resulting from a drop in resistance of the photocell to actuate an alarm, the improvement comprising means for causing the voltage at the alarm actuating circuit to decrease when the supply voltage increases and vice-versa, said means including a capacitor connected to serve as a D.C. voltage supply for the alarm actuating circuit, means for applying a D.C. charging voltage to said capacitor from the supply voltage, and means for reducing the effective D.C. voltage applied to the capacitor during each half cycle with increases in supply voltage.

Claim 5

In a smoke detector of the type adapted to be energized from an A.C. source and having a light source, a photo-cell positioned to view smoke particles illuminated by the light source, and means responsive to change in D.C. voltage drop across the photo-cell to actuate an alarm, wherein a change in the supply voltage will cause a change in the brightness of the light source and a consequent change in the light received by the photo-cell at a given smoke concentration, the improvement comprising means for causing the D.C. voltage across the photo-cell to decrease when the supply voltage increases and vice-versa, said means including a capacitor connected to serve as the voltage supply for the cell, means charging said capacitor with half-wave current from the same source that supplies the light source, a neon bulb connected across said capacitor to control the effective charge applied thereto, whereby as the supply voltage increases, the neon goes into conduction at an earlier point in the charging half cycle and the high frequency voltage spike formed by the clipping action of the neon bulb filters through the capacitor more readily than the spike formed by the neon bulb at a lower line voltage, and the maximum voltage acquired by the capacitor decreases.

Claim 6

In a smoke detector of the type adapted to be energized from an A.C. source and having a light source, a photo-cell positioned to view smoke particles illuminated by the light source, and means responsive to change in D.C. voltage drop across the photo-cell to actuate an alarm, wherein a change in the supply voltage will cause a change in the brightness of the light source and a consequent change in the light received by the photo-cell at a given smoke concentration, the improvement comprising means for causing the D.C. voltage across the photo-cell to decrease when the supply voltage increases and vice-versa, said means including a capacitor connected to serve as the voltage supply for the cell, means charging said capacitor with half-wave current from the same source that supplies the light source, a neon bulb connected across said capacitor to control the effective charge applied thereto, whereby as the supply voltage increases, the neon goes into conduction at an earlier point in the charging half cycle and the high frequency voltage spike formed by the clipping action of the neon bulb filters through the capacitor more readily than the spike formed by the neon bulb at a lower line voltage, and the maximum voltage acquired by the capacitor decreases.

Claim 7

In a smoke detector of the type designed to be energized from an A.C. source and having a light source, a photo-resistive cell positioned to view smoke particles illuminated by the light source, means for supplying a D.C. voltage across the cell, and means responsive to a change in drop in voltage across the cell to actuate an alarm, the improvement comprising means for compensating for a change in brightness of the light due to a change in supply voltage, said means causing a decrease in voltage applied to the photo-cell when the supply voltage to the light increases, and vice-versa.

Claim 8

In a smoke detector of the type designed to be energized from an A.C. source and having a light source, a photo-resistive cell positioned to view smoke particles illuminated by the light source, means for supplying a D.C. voltage across the cell, and means responsive to a change in drop in voltage across the cell to actuate an alarm, the improvement comprising means for compensating for a change in brightness of the light due to a change in supply voltage, said means causing a decrease in voltage applied to the photo-cell when the supply voltage to the light increases, and vice-versa.

Claim 9

A smoke detector as set out in claim 4 in which said means for supplying voltage across said cell and for compensating for a change in the brightness of the light comprises a capacitor and a diode in series across a neon voltage regulator bulb, the voltage supply to the cell being taken from the junction between the diode and the capacitor.