Patent US3846772A successfully refreshed from Google Patents.
US3846772A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Fire detector responsive to amplitude modulation of a pulsed em beam
Assignee: Chubb Fire Ltd
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Filing: 1973-08-06
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Granted: 1974-11-05
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Expires: 1993-08-06
Abstract
Abstract In fire-detection apparatus of the kind in which a radiation receiver is exposed to a source of radiation through an intervening gaseous medium, the beam of radiation overlaps the receiver so that the beam continues to cover the receiver despite minor changes in beam direction due, for example, to movement of the surfaces supporting the emitter and receiver. Discrimination against ambient radiation is improved by causing the source, which is a solid-state emitter, to emit pulses of radiation and by having a frequency-selective circuit for selecting from the output of the radiation-sensitive device in the receiver a pulse signal resulting from the received pulses of radiation; an alarm circuit is responsive to an amplitude modulation in this pulse signal at a frequency which is typical of the modulation produced by a fire heating the gaseous medium between the source and the receiver.
Inventors
- 👤 W Peberdy
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 16:01
CPC Classifications
G; G08; G08B; G08B17/00; G08B17/10; G08B17/103
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
129 words
Fire-detecting apparatus comprising: a source of radiation including a solid-state emitter emitting a beam of radiation in a series of pulses; radiation-receiving means positioned to receive radiation which has passed through an intervening gaseous medium from the said source and including a device sensitive to the received radiation to produce a corresponding electric signal, the beam of radiation, where incident on the radiation-receiving means, overlapping the radiation-receiving means around the whole of its perimeter; a frequency-selective circuit for selecting from the output of the radiation-sensitive device a pulse signal resulting from the pulses of radiation from the said source; and an alarm circuit connected to receive this pulse signal and responsive to an amplitude modulation thereof indicative of the effect of a fire on the said intervening gaseous medium.
Claim 2
Dependent Claim
129 words
Fire-detecting apparatus comprising: a source of radiation including a solid-state emitter emitting a beam of radiation in a series of pulses; radiation-receiving means positioned to receive radiation which has passed through an intervening gaseous medium from the said source and including a device sensitive to the received radiation to produce a corresponding electric signal, the beam of radiation, where incident on the radiation-receiving means, overlapping the radiation-receiving means around the whole of its perimeter; a frequency-selective circuit for selecting from the output of the radiation-sensitive device a pulse signal resulting from the pulses of radiation from the said source; and an alarm circuit connected to receive this pulse signal and responsive to an amplitude modulation thereof indicative of the effect of a fire on the said intervening gaseous medium.
Claim 3
Dependent Claim
23 words
Fire-detecting apparatus in accordance with claim 1, in which the source of radiation is an infra-red light source of the gallium arsenide kind.
Claim 4
Dependent Claim
15 words
Fire-detecting apparatus in accordance with claim 1, in which the radiation-sensitive device is a photo-transistor.
Claim 5
Dependent Claim
18 words
Fire-detecting apparatus in accordance with claim 3, including means whereby the photo-transistor is given a constant forward bias.
Claim 6
Dependent Claim
35 words
Fire-detecting apparatus in accordance with claim 4, in which the forward biasing means is a subsidiary source of radiation, located at the radiation-receiving means, and arranged to irradiate the photo-transistor at a substantially constant level.
Claim 7
Dependent Claim
30 words
Fire-detecting apparatus in accordance with claim 1, in which the frequency response of the frequency-selective circuit is substantially greater than the pulse repetition frequency of the emitted pulses of radiation.
Claim 8
Dependent Claim
18 words
Fire-detecting apparatus in accordance with claim 1, in which the alarm circuit includes a frequency-selective audio frequency circuit.
Claim 9
Dependent Claim
29 words
Fire-detecting apparatus in accordance with claim 7, in which the maximum response of the said audio frequency circuit occurs in the frequency range of 2 Hz to 25 Hz.
Claim 10
Dependent Claim
36 words
Fire-detecting apparatus in accordance with claim 1, including a further alarm circuit responsive to a reduction in the amplitude of the said pulse signal indicative of at least a partial obscuration of the said emitted radiation.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-11-04 | 1978-05-06 | 1978-11-05 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-11-04 | 1982-05-06 | 1982-11-05 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-11-04 | 1986-05-06 | 1986-11-05 | $7700.00 | Window Closed / Lapsed |