US3676681A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Ionization smoke detector
Assignee: Nittan Co Ltd
•
Filing: 1970-07-17
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Granted: 1972-07-11
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Expires: 1990-07-17
Abstract
Abstract An ionization smoke detector having an open and a closed chamber, each including a pair of electrodes, the electrodes in the chambers being connected in series across a voltage supply. A field effect transistor interconnected with the chambers and the voltage supply to sense a change in impedance in the open chamber upon the admission of smoke and sensitivity controlling means interconnected with the field effect transistor to prevent the production of an erroneous signal from the transistor as a result of momentary increases of smoke concentrations in the ambient air.
Inventors
- 👤 Akihiro Kobayashi
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 10:34
CPC Classifications
G; G08; G08B; G08B17/00; G08B17/10; G08B17/11
Claims Analysis
Total Claims: 4
Claim 1
Independent Claim
119 words
An ionization smoke detector, comprising a closed ionization chamber including a pair of electrodes and a radioactive source, an open ionization chamber having similarly a pair of electrodes and a radioactive source and connected in series with said closed ionization chamber, a voltage source for supplying a voltage to saId series connection of said both ionization chambers, a field effect transistor having a gate electrode connected to the junction between said both ionization chambers and a source-drain conduction path connected through a load resistor to said voltage source for detecting a voltage at said junction between said both ionization chambers, and a sensitivity reducing capacitor connected between the gate electrode and the source electrode of said field effect transistor.
Claim 2
Dependent Claim
119 words
An ionization smoke detector, comprising a closed ionization chamber including a pair of electrodes and a radioactive source, an open ionization chamber having similarly a pair of electrodes and a radioactive source and connected in series with said closed ionization chamber, a voltage source for supplying a voltage to saId series connection of said both ionization chambers, a field effect transistor having a gate electrode connected to the junction between said both ionization chambers and a source-drain conduction path connected through a load resistor to said voltage source for detecting a voltage at said junction between said both ionization chambers, and a sensitivity reducing capacitor connected between the gate electrode and the source electrode of said field effect transistor.
Claim 3
Dependent Claim
22 words
An ionization smoke detector, according to claim 1 characterized in that said sensitivity reducing capacitor is contained in said closed ionization chamber.
Claim 4
Dependent Claim
163 words
An ionization smoke detector, according to claim 1 characterized in that one of said pair of electrodes of said open ionization chamber is formed as a housing of the device in which a number of windows are bored for allowing smoke to come in, the other electrode of said open ionization chamber and one of said pair of electrodes of said closed ionization chamber are integrally formed as a single cup-shaped conductor whose open end is closed by an insulating plate and whose outer and inner surfaces serve functions of said other electrode of said open ionization chamber and said one electrode of said closed ionization chamber respectively, said radioactive sources of said open and closed ionization chambers are respectively arranged on said outer and inner surfaces of said cup-shaped conductor, the other electrode of said closed ionization chamber is located in said cup-shaped conductor and insulated from said conductor, and at least said sensitivity reducing capacitor is contained in said cup-shaped conductor.
References Cited (Backward Citations)
US3516083A
Cited
US3500368A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1975-07-11 | 1976-01-10 | 1976-07-11 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1979-07-11 | 1980-01-10 | 1980-07-11 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1983-07-11 | 1984-01-10 | 1984-07-11 | $7700.00 | Window Closed / Lapsed |