US3718919A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Ionization smoke detector
Assignee: Nittan Co Ltd
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Filing: 1970-03-17
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Granted: 1973-02-27
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Expires: 1990-03-17
Abstract
Abstract An ionization smoke detector having an open and a closed chamber each including a pair of electrodes and a radioactive source. The chambers are connected in series across a power supply and the gate electrode of a junction type field effect transistor is connected to the junction of said chambers. The drain-source circuit of the field effect transistor includes means for limiting the current in that circuit to maintain the gate leakage current below a predetermined minimum and thereby avoid erroneous indications of the presence and absence of smoke.
Inventors
- 👤 K Sasaki
- 👤 A Kobayashi
- 👤 N Takahashi
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 11:10
CPC Classifications
G; G08; G08B; G08B17/00; G08B17/10; G08B17/11
Claims Analysis
Total Claims: 3
Claim 1
Independent Claim
191 words
An ionization smoke detector comprising a series circuit of a closed ionization chamber and an open ionization chamber each including a pair of electrodes and a radioactive source, the interconnection of said chambers one to the other forming a junction therebetween, a field effect transistor having the source-drain path connected to the power supply and the gate electrode connected to the junction of said both ionization chambers, alarm activating means interconnected with said transistor, and a second circuit interconnected with said sourcedrain path of said field effect transistor to maintain the source-drain current below a predetermined minimum value during normal operation to minimize affects of the gate leakage current and maintain the total current drain of the detector at a minimum, said second circuit being responsive to a selected increase in gate voltage to cause said transistor to operate said alarm activating means, the drain electrode circuit of said field effect transistor including the emitter-collector path of a transistor, the last said transistor having a base electrode and a zener diode connected between said base electrode and the source electrode to maintain the source drain current below said predetermined minimum value.
Claim 2
Dependent Claim
191 words
An ionization smoke detector comprising a series circuit of a closed ionization chamber and an open ionization chamber each including a pair of electrodes and a radioactive source, the interconnection of said chambers one to the other forming a junction therebetween, a field effect transistor having the source-drain path connected to the power supply and the gate electrode connected to the junction of said both ionization chambers, alarm activating means interconnected with said transistor, and a second circuit interconnected with said sourcedrain path of said field effect transistor to maintain the source-drain current below a predetermined minimum value during normal operation to minimize affects of the gate leakage current and maintain the total current drain of the detector at a minimum, said second circuit being responsive to a selected increase in gate voltage to cause said transistor to operate said alarm activating means, the drain electrode circuit of said field effect transistor including the emitter-collector path of a transistor, the last said transistor having a base electrode and a zener diode connected between said base electrode and the source electrode to maintain the source drain current below said predetermined minimum value.
Claim 3
Dependent Claim
20 words
An ionization smoke detector according to claim 1 wherein said field effect transistor is a junction type field effect transistor.
References Cited (Backward Citations)
No citation records indexed.
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-02-27 | 1976-08-28 | 1977-02-27 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-02-27 | 1980-08-28 | 1981-02-27 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-02-27 | 1984-08-28 | 1985-02-27 | $7700.00 | Window Closed / Lapsed |