US3781571A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Loop current detector
Assignee: International Standard Electric Corp
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Filing: 1971-12-06
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Granted: 1973-12-25
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Expires: 1991-12-06
Abstract
Abstract A detector is provided for unidirectional currents flowing in a loop circuit. A dc amplifier coupled to a resistor in the loop provides an output signal proportional to the loop current. A voltage drop across a second resistor in the loop is supplied to the input of a voltage threshold detector and to the output of said amplifier. Means are provided to indicate when said input is less or greater than a reference voltage.
Inventors
- 👤 M Lord
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 16:58
CPC Classifications
H; H04; H04M; H04M3/00; H04M3/22; H04M3/2272
Claims Analysis
Total Claims: 7
Claim 1
Independent Claim
190 words
A detector for detecting unidirectional loop currents while provIding compensation to avoid measuring longitudinal currents flowing through a closed circuit formed to include first and second legs terminating respectively at ground potential and at d.c. potential, said detector comprising a first resistor coupled in the first leg of the circuit between a first terminal and ground potential, a second resistor coupled in the second leg of the circuit, a third resistor coupled to the first resistor via said first terminal to provide a path for a first output current proportional to current in the first leg of the closed circuit, a d.c. amplifier coupled to the second resistor to provide a second output current proportional to current in the second leg of the circuit, a voltage threshold detector, means coupling said first output current from said third resistor and said second output current from said d.c. amplifier to the input terminal of said threshold detector, said threshold detector responding to said first and second output currents to provide an output potential proportional to the loop currents flowing in the loop and independent of any longitudinal currents flowing in the loop.
Claim 2
Dependent Claim
190 words
A detector for detecting unidirectional loop currents while provIding compensation to avoid measuring longitudinal currents flowing through a closed circuit formed to include first and second legs terminating respectively at ground potential and at d.c. potential, said detector comprising a first resistor coupled in the first leg of the circuit between a first terminal and ground potential, a second resistor coupled in the second leg of the circuit, a third resistor coupled to the first resistor via said first terminal to provide a path for a first output current proportional to current in the first leg of the closed circuit, a d.c. amplifier coupled to the second resistor to provide a second output current proportional to current in the second leg of the circuit, a voltage threshold detector, means coupling said first output current from said third resistor and said second output current from said d.c. amplifier to the input terminal of said threshold detector, said threshold detector responding to said first and second output currents to provide an output potential proportional to the loop currents flowing in the loop and independent of any longitudinal currents flowing in the loop.
Claim 3
Dependent Claim
22 words
A detector as claimed in claim 1 in which the direct current amplifier and the voltage threshold detector each include transistor circuits.
Claim 4
Dependent Claim
35 words
A detector as claimed in claim 1 in which the ratio of the voltage drop across said first resistor to the output current of the amplifier is equal to the value of said coupling resistor.
Claim 5
Dependent Claim
44 words
A detector as claimed in claim 3 in which the amplifier includes a transistor, the input circuit to the transistor includes a biasing resistor of value equal to said third resistor, the former being connected in series with the emitter electrode of the transistor.
Claim 6
Dependent Claim
31 words
A detector as claimed in claim 4 in which a source of bias potential is provided in series with the emitter electrode of the transistor acting as a voltage threshold detector.
Claim 7
Dependent Claim
39 words
A detector as claimed in claim 5 in which the source of bias potential to the emitter of the voltage threshold detector is a voltage drop derived from a potential divider connected across the battery supplying the loop current.
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) | 1976-12-24 | 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 |