US3781841A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Load resistance change alarm
Assignee: Trident Engineering Co
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Filing: 1972-05-04
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Granted: 1973-12-25
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Expires: 1992-05-04
Abstract
Abstract A load resistance change alarm in which the magnitude and frequency of an audio signal are increased in proportion to an increase or decrease in resistance of the load. The load is connected in one branch of a bridge circuit. Any imbalance across the bridge circuit caused by a change in the load resistance is applied to an amplifier having a feedback circuit. The oscillations of the amplifier circuit turn on an electronic switch which allows unilateral current flow through the speaker. The current applied to the speaker is supplied through a step down transformer from the same power supply supplying current to the load.
Inventors
- 👤 J Hughes
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 06:55
CPC Classifications
G; G08; G08B; G08B21/00; G08B21/18; G08B21/185
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
120 words
Apparatus for detecting a change in resistance of a load and providing an alarm, comprising: a bridge circuit having a first and a second pair of terminals connected across opposite ends thereof, said load being connected in one branch of said bridge circuit; means for applying electrical power across said first pair of terminals of said bridge circuit; amplifier means connected across said second pair of terminals of said bridge circuit, said amplifier means being provided with positive feedback means including a diode to control oscillation of said amplifier in response to an unbalanced bridge condition causing a voltage of predetermined polarity across said second pair of terminals; and alarm means energized in response to oscillation by said amplifier means.
Claim 2
Dependent Claim
120 words
Apparatus for detecting a change in resistance of a load and providing an alarm, comprising: a bridge circuit having a first and a second pair of terminals connected across opposite ends thereof, said load being connected in one branch of said bridge circuit; means for applying electrical power across said first pair of terminals of said bridge circuit; amplifier means connected across said second pair of terminals of said bridge circuit, said amplifier means being provided with positive feedback means including a diode to control oscillation of said amplifier in response to an unbalanced bridge condition causing a voltage of predetermined polarity across said second pair of terminals; and alarm means energized in response to oscillation by said amplifier means.
Claim 3
Dependent Claim
18 words
Apparatus in accordance with claim 1 wherein said bridge circuit includes means for initially balancing said bridge circuit.
Claim 4
Dependent Claim
18 words
Apparatus in accordance with claim 1 wherein said positive feedback means of said amplifier means includes a capacitor.
Claim 5
Dependent Claim
41 words
Apparatus in accordance with claim 1 wherein said alarm means comprises a speaker and a source of alternating current connected to said speaker through an electronic switch, said electronic switch being turned on in response to oscillations by said amplifier means.
Claim 6
Dependent Claim
210 words
Apparatus for detecting successive changes in resistance of a load supplied with an alternating current and providing an indication which varies with the changes in resistance of said load, comprising: a bridge circuit having a first pair of terminals connected across one pair of opposite ends of said bridge circuit and a second pair of terminals connected across the other pair of opposite ends of said bridge circuit, said load being connected in one branch of said bridge circuit; means for applying an alternating current across said first pair of terminals of said bridge circuit; amplifier means connected across said second pair of terminals of said bridge cicruit, said amplifier means being provided with positive feedback means including a diode iN order to enable oscillation in response to an unbalanced bridge condition of a predetermined voltage polarity across said second pair of terminals; an acoustical transducer; means for applying said alternating current to said acoustical transducer; and electronic switch means connected in series with said acoustical transducer and said means for applying said alternating current to said acoustical transducer, said electronic switch means allowing unilateral current flow, during half waves of a predetermined polarity of said alternating current, through said acoustical transducer in response to oscillation of said amplifier means.
Claim 7
Dependent Claim
210 words
Apparatus for detecting successive changes in resistance of a load supplied with an alternating current and providing an indication which varies with the changes in resistance of said load, comprising: a bridge circuit having a first pair of terminals connected across one pair of opposite ends of said bridge circuit and a second pair of terminals connected across the other pair of opposite ends of said bridge circuit, said load being connected in one branch of said bridge circuit; means for applying an alternating current across said first pair of terminals of said bridge circuit; amplifier means connected across said second pair of terminals of said bridge cicruit, said amplifier means being provided with positive feedback means including a diode iN order to enable oscillation in response to an unbalanced bridge condition of a predetermined voltage polarity across said second pair of terminals; an acoustical transducer; means for applying said alternating current to said acoustical transducer; and electronic switch means connected in series with said acoustical transducer and said means for applying said alternating current to said acoustical transducer, said electronic switch means allowing unilateral current flow, during half waves of a predetermined polarity of said alternating current, through said acoustical transducer in response to oscillation of said amplifier means.
Claim 8
Dependent Claim
17 words
Apparatus in accordance with claim 5 wherein said bridge circuit includes means for initially balancing said circuit.
Claim 9
Dependent Claim
14 words
Apparatus in accordance with claim 5 wherein said positive feedback means includes a capacitor.
Claim 10
Dependent Claim
13 words
Apparatus in accordance with claim 5 wherein said acoustical transducer is a speaker.
Claim 11
Dependent Claim
23 words
Apparatus in accordance with claim 5 wherein said means for applying said alternating current to said acoustical transducer is a step down transformer.
Claim 12
Dependent Claim
14 words
Apparatus in accordance with claim 5 wherein said load is a plurality of lights.
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) | 1976-12-24 | 1977-06-25 | 1977-12-25 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-12-24 | 1981-06-25 | 1981-12-25 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-12-24 | 1985-06-25 | 1985-12-25 | $7700.00 | Window Closed / Lapsed |