Patent US3725660A successfully refreshed from Google Patents.
US3725660A
Expired / Lapsed
US
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Fire detector with red and blue responsive photocells and regenerative feedback
Assignee: Kidde Technologies Inc
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Filing: 1971-05-13
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Granted: 1973-04-03
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Expires: 1991-05-13
Abstract
Abstract A fire detector in which a pair of photo-resistive cells which respond differently to radiation from a fire and a pair of fixed resistors are connected in voltage divider circuits across a common source, with an alarm actuating device connected between the junction of the cells and the junction of the fixed resistors. The alarm actuating device responds to a reversal of relative polarity of said junctions to actuate the alarm. In one embodiment of the invention the portion of the alarm actuation means connected between the junctions is the base-emitter circuit of the first transistor of a transistor amplifier. In a modified form of the invention, on actuation of the alarm, additional resistance is connected into the circuit to shift the drop-out point of the alarm actuator to a desired point.
Inventors
- 👤 W Doherty
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 19:07
CPC Classifications
G; G08; G08B; G08B17/00; G08B17/12
Claims Analysis
Total Claims: 4
Claim 1
Independent Claim
293 words
A fire detector, comprising a transistor amplifier, alarm actuating means, and a power source, said amplifier triggering said alarm actuating means when the input transistor thereof conducts in the collector-emitter path, the emitter of said input transistor being connected to opposite poles of the power source by a pair of resistors to provide a predetermined voltage at the emitter, the base of said input transistor being connected to opposite sides of the power source by a pair of photo-cells, said cells being so associated that they view the same space, one of said cells being responsive by a decrease in resistance to light in the red to infra-red band, the other cell being responsive by a decrease in resistance to light in the blue band, whereby a change from ordinary ambient light to raDiation from a fire will cause a change in voltage at said base in relation to the voltage at the emitter, the value of the resistors connected to the emitter being such that during normal standby conditions, a reverse bias is applied to the base, and when the voltage at the base changes due to the change in resistance of the photo-cells due to radiation from a fire, a forward bias is applied to the base to allow conduction in the emitter collector path to trigger said alarm actuating device, and means responsive to energization of the alarm actuating means for changing the value of the resistance between one pole of the power source and the emitter of said input transistor in such a manner as to increase the forward bias on the base, whereby the level of radiation from a fire at which the alarm actuating means is de-energized is less than the level at which it was energized.
Claim 2
Dependent Claim
293 words
A fire detector, comprising a transistor amplifier, alarm actuating means, and a power source, said amplifier triggering said alarm actuating means when the input transistor thereof conducts in the collector-emitter path, the emitter of said input transistor being connected to opposite poles of the power source by a pair of resistors to provide a predetermined voltage at the emitter, the base of said input transistor being connected to opposite sides of the power source by a pair of photo-cells, said cells being so associated that they view the same space, one of said cells being responsive by a decrease in resistance to light in the red to infra-red band, the other cell being responsive by a decrease in resistance to light in the blue band, whereby a change from ordinary ambient light to raDiation from a fire will cause a change in voltage at said base in relation to the voltage at the emitter, the value of the resistors connected to the emitter being such that during normal standby conditions, a reverse bias is applied to the base, and when the voltage at the base changes due to the change in resistance of the photo-cells due to radiation from a fire, a forward bias is applied to the base to allow conduction in the emitter collector path to trigger said alarm actuating device, and means responsive to energization of the alarm actuating means for changing the value of the resistance between one pole of the power source and the emitter of said input transistor in such a manner as to increase the forward bias on the base, whereby the level of radiation from a fire at which the alarm actuating means is de-energized is less than the level at which it was energized.
Claim 3
Dependent Claim
169 words
A fire detector, comprising a pair of photo-cells so associated that they view the same space, one of said cells being responsive by a decrease in resistance to light in the red to infra-red band, the other cell being responsive by a decrease in resistance to light in the blue band, said cells being connected in series across a power source through a first junction, a pair of resistors connected in series across said power source through a second junction, whereby radiation from a fire received by said photo-cells will cause a change in voltage between said junctions, means responsive to said change in voltage to actuate an alarm energizing means, and means responsive to the actuation of said alarm energizing means to further change the voltage between said junctions in a direction such that on decrease of the amount of radiation from a fire, the alarm will continue to be energized at a level of fire radiation less than the level of radiation at which it was energized.
Claim 4
Dependent Claim
169 words
A fire detector, comprising a pair of photo-cells so associated that they view the same space, one of said cells being responsive by a decrease in resistance to light in the red to infra-red band, the other cell being responsive by a decrease in resistance to light in the blue band, said cells being connected in series across a power source through a first junction, a pair of resistors connected in series across said power source through a second junction, whereby radiation from a fire received by said photo-cells will cause a change in voltage between said junctions, means responsive to said change in voltage to actuate an alarm energizing means, and means responsive to the actuation of said alarm energizing means to further change the voltage between said junctions in a direction such that on decrease of the amount of radiation from a fire, the alarm will continue to be energized at a level of fire radiation less than the level of radiation at which it was energized.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-04-02 | 1976-10-02 | 1977-04-03 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-04-02 | 1980-10-02 | 1981-04-03 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-04-02 | 1984-10-02 | 1985-04-03 | $7700.00 | Window Closed / Lapsed |