Patent US3874795A successfully refreshed from Google Patents.
US3874795A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Smoke detector
Assignee: Commonwealth Scientific and Industrial Research Organisation
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Filing: 1973-06-05
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Granted: 1975-04-01
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Expires: 1993-06-05
Abstract
Abstract A smoke monitoring instrument having first and second chambers, each with a respective photodetector means, a light source common to both chambers and positioned to illuminate part of the interior of each chamber, means for conveying a first air sample from the space to be monitored into said part of the first chamber, means for conveying a second air sample from outside the space into said part of the second chamber, each photodetector means being arranged to receive light from the source which is scattered by its respective air sample but not to receive light directly from the source whereby the effects of suspended material in the first sample originating from outside the space to be monitored can be observed or removed from the output of the instrument.
Inventors
- 👤 David Roy Packham
- 👤 Leonard Gibson
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-06 17:42
CPC Classifications
G; G01; G01N; G01N21/00; G01N21/17; G01N21/47; G01N21/49; G01N21/53; G08; G08B; G08B17/00; G08B17/10; G08B17/103; G08B17/107; G08B17/11; G08B17/113
Claims Analysis
Total Claims: 22
Claim 1
Independent Claim
101 words
A smoke monitoring instrument having first and second chambers, each with a respective photodetector means, a light source common to both chambers and positioned to simultaneously illuminate part of the interior of each chamber, means for conveying a first air sample from the space to be monitored into said part of the first chamber, means for conveying a second air sample from outside the space into said part of the second chamber, each photodetector means being arranged to simultaneously receive light from the source which is scattered by its respective air sample but not to receive light directly from the source.
Claim 2
Dependent Claim
101 words
A smoke monitoring instrument having first and second chambers, each with a respective photodetector means, a light source common to both chambers and positioned to simultaneously illuminate part of the interior of each chamber, means for conveying a first air sample from the space to be monitored into said part of the first chamber, means for conveying a second air sample from outside the space into said part of the second chamber, each photodetector means being arranged to simultaneously receive light from the source which is scattered by its respective air sample but not to receive light directly from the source.
Claim 3
Dependent Claim
28 words
An instrument as claimed in claim 1 wherein the light source comprises a flash tube and the instrument includes an energizing circuit to operate the flash tube periodically.
Claim 4
Dependent Claim
41 words
An instrument as claimed in claim 2 wherein each photodetector means comprises a light sensitive element and a detector circuit responsive thereto and operable to produce an output signal representative of the amount of light received by the light sensitive element.
Claim 5
Dependent Claim
30 words
An instrument as claimed in claim 3 including means to produce a differential output signal, being a signal derived from the difference of the output signals of the detector circuits.
Claim 6
Dependent Claim
110 words
An instrument as claimed in claim 3 wherein each detector circuit includes first and second storages, the first storage being operable to store a signal representative of the light received by its associated light sensitive element during the time the flash tube is operated and during the time the flash tube is not operated, the second storage being operable to store a signal representative of the light received by its associated light sensitive element during the time the flash tube is not operated, said output signal of the detector circuit being derived from the difference of the signals stored in the first and second storages, whereby noise signals are reduced.
Claim 7
Dependent Claim
38 words
An instrument as claimed in claim 1 wherein the means for conveying a first air sample from the space to be monitored is coupled to an exhaust duct of an airconditioning system for the space to be monitored.
Claim 8
Dependent Claim
30 words
An instrument as claimed in claim 6 wherein the means for conveying a second air sample from outside the space is coupled to an inlet duct of the airconditioning system.
Claim 9
Dependent Claim
18 words
An instrument as claimed in claim 3 including means to record the output signals of the detector circuits.
Claim 10
Dependent Claim
22 words
An instrument as claimed in claim 8 wherein the means to record is operable to record the difference between the output signals.
Claim 11
Dependent Claim
32 words
An instrument as claimed in claim 3, including alarm circuitry operable to produce alarm signals which are dependent upon the output signal levels of the detector circuit associated with the first chamber.
Claim 12
Dependent Claim
27 words
An instrument as claimed in claim 8 wherein the means to record is located remote from the detector circuits and is coupled thereto by a telecommunications link.
Claim 13
Dependent Claim
45 words
An instrument as claimed in claim 3 wherein the first and second chambers comprise a pair of spaced elongate chambers, the interiors of which are optically black, and said source of light is positioned between chambers, each chamber including a window adjacent to the source.
Claim 14
Dependent Claim
22 words
An instrument as claimed in claim 12 wherein the instrument includes opal glass diffusing surfaces interposed between the windows and the source.
Claim 15
Dependent Claim
24 words
An instrument as claimed in claim 13 wherein the opal glass diffusing surfaces are planar and their normals are inclined toward respective photodetector means.
Claim 16
Dependent Claim
36 words
An instrument as claimed in claim 12 wherein the chambers and the diffusing surfaces are mounted upon a removable housing for the instrument and the source and photodetectors are mounted on a base of the instrument.
Claim 17
Independent Claim
74 words
A method of detecting the generation of smoke associated with a fire hazard in a space to be monitored, comprising the steps of drawing a first sample of air from the space to be monitored, drawing a second sample of air from outside said space, exposing both samples simultaneously to a source of light and generating two signals simultaneously, each related to the amount of light scattered by a respective one of said samples.
Claim 18
Independent Claim
74 words
A method of detecting the generation of smoke associated with a fire hazard in a space to be monitored, comprising the steps of drawing a first sample of air from the space to be monitored, drawing a second sample of air from outside said space, exposing both samples simultaneously to a source of light and generating two signals simultaneously, each related to the amount of light scattered by a respective one of said samples.
Claim 19
Dependent Claim
27 words
A method as claimed in claim 16 wherein the first sample is drawn from an exhaust duct of an airconditioning system for the space to be monitored.
Claim 20
Dependent Claim
21 words
A method as claimed in claim 17 wherein the second sample is drawn from an inlet duct of the airconditioning system.
Claim 21
Dependent Claim
22 words
A method as claimed in claim 16 including the step of storing a record of the signals over a period of time.
Claim 22
Dependent Claim
25 words
A method as claimed in claim 19 wherein the storing of a record is performed at a location remote from the space to be monitored.
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) | 1978-03-31 | 1978-09-30 | 1979-04-01 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-03-31 | 1982-09-30 | 1983-04-01 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-03-31 | 1986-09-30 | 1987-04-01 | $7700.00 | Window Closed / Lapsed |