US4939451A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Wide dynamic range a.c. current sensor
Assignee: Proxim Wireless Corp
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Filing: 1989-01-06
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Granted: 1990-07-03
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Expires: 2009-01-06
Abstract
Abstract Various combinations of three elements are disclosed for use in accurate measurement of power through current measurement over a wide dynamic range, namely, a current shunt which is preferably an isothermal current shunt, a current transformer, which is preferably a high initial permeability current transformer, and a low-impedance burden load, which in the preferred embodiment includes an active negative impedance element which causes the removal of the effects of excitation current by canceling secondary winding resistance of the current transformer. In a specific embodiment of an isothermal current shunt according to the invention, a very linear device is achieved by construction out of copper in such a manner that the poor resistance versus temperature coefficient of copper does not affect the accuracy of measurement. Specifically, the shunt is constructed in an unbalanced isothermal bridge configuration, so that heat-induced variations are suppressed. Further, a very small current transformer is used having a core optimized for high initial permeability.
Inventors
- 👤 Paul Baran
- 👤 Timothy J. Knutson
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-31 18:00
CPC Classifications
G; G01; G01R; G01R15/00; G01R15/14; G01R15/18; G01R15/183; G01R1/00; G01R1/20; G01R1/203
Claims Analysis
Total Claims: 11
Claim 1
Independent Claim
207 words
An apparatus for providing an isothermal current shunt, said isothermal current shunt comprising: a current transformer having a primary and a secondary; separate first and second solid conductive bars of equal length, said first and second bars being electrically and thermally coupled at a first or current input node and at a second or current output node; and a separate third round solid conductive bar electrically and thermally coupled to said first bar at a first hole at a third node and to said second bar at a second hole at a fourth node to form the primary of said current transformer, said third bar being constructed of the same material as said first and second bars, the length between said input current node and said third node being different than the length between said input current node and said fourth node, and the length between said output current node and said third node being equal to the length between said input current node and said fourth node, and wherein said current transformer comprises a core formed of a toroid mounted around said third bar and between said first bar and said second bar; thereby to form an unbalanced bridge with a current transformer at the shunt.
Claim 2
Independent Claim
207 words
An apparatus for providing an isothermal current shunt, said isothermal current shunt comprising: a current transformer having a primary and a secondary; separate first and second solid conductive bars of equal length, said first and second bars being electrically and thermally coupled at a first or current input node and at a second or current output node; and a separate third round solid conductive bar electrically and thermally coupled to said first bar at a first hole at a third node and to said second bar at a second hole at a fourth node to form the primary of said current transformer, said third bar being constructed of the same material as said first and second bars, the length between said input current node and said third node being different than the length between said input current node and said fourth node, and the length between said output current node and said third node being equal to the length between said input current node and said fourth node, and wherein said current transformer comprises a core formed of a toroid mounted around said third bar and between said first bar and said second bar; thereby to form an unbalanced bridge with a current transformer at the shunt.
Claim 3
Dependent Claim
63 words
The apparatus according to claim 1 further including an electronic amplifying means comprising a first operational amplifier and a first impedance means in a negative feedback loop for said first operational amplifier wherein amplification of said amplifying means is substantially equal to the ratio of the impedance value of said first impedance means and the impedance value of winding resistance of said secondary.
Claim 4
Dependent Claim
54 words
The apparatus according to claim 1 wherein said burden load impedance is formed by a series connection of said secondary, a first electronic amplifying means and a second electronic amplifying means, said first electronic amplifying means having an amplification factor at least in part determined by the value of winding resistance of said secondary.
Claim 5
Dependent Claim
129 words
The apparatus according to claim 3 wherein said secondary has a first terminal and a second terminal and wherein said first electronic amplifying means is coupled to present as a load to said secondary at said first terminal a high impedance at a first input terminal of said first electronic amplifying means, and further wherein said first electronic amplifying means is coupled in series with a second input terminal of said second electronic amplifying means, the output terminal of said second electronic amplifying means being coupled to said second terminal, said second electronic amplifying means having an amplification factor equal to the complement of the amplification factor of said first electronic amplifying means, thereby to present a negative impedance to said secondary removing effects of said secondary winding resistance.
Claim 6
Dependent Claim
78 words
The apparatus according to claim 4 wherein said second electronic amplifying means comprises a second operational amplifier and a second impedance means in a negative feedback loop for said second operational amplifier, said second impedance means being formed of a material having a temperature to resistance coefficient equal to said secondary winding and is disposed in isothermal relationship to said secondary winding thereby to minimize heat-induced differences in resistance between said secondary winding resistance and said second impedance.
Claim 7
Dependent Claim
22 words
The apparatus according to claim 4 wherein said current transformer further comprises a core formed of a material having high initial permeability.
Claim 8
Independent Claim
377 words
An apparatus for providing an osothermal current shunt, said isothermal current shunt comprising: a current transformer having a primary and a secondary; first and second solid conductive bars of equal length, said first and second bars being electrically and thermally coupled t a first or current input node and at a second or current output node; and a third round solid conductive bar electrically and thermally coupled to said first bar at a first hole at a third node and to said second bar at a second hole at a fourth node to form the primary of said current transformer, said third bar being constructed of the same material as said first and second bars, the length between said input current node and said third node being different than the length between said input current node and said fourth node, and the length between said output current node and said third node being equal to the length between said input current node and said fourth node, and wherein said current transformer comprises a core formed of a toroid mounted around said third bar and between said first bar and said second bar; wherein a burden load impedance is formed by a series connection of said secondary, a first electronic amplifying means and a second electronic amplifying means, said first electronic amplifying means having an amplification factor at least in part determined by the value of winding resistance of said secondary; thereby to form an unbalanced bridge with a current transformer at the shunt; and wherein said secondary has a first terminal and a second terminal and wherein said first electronic amplifying means is coupled to present as a load to said secondary at said first terminal a high impedance at a first input terminal of said first electronic amplifying means, and further wherein said first electronic amplifying means is coupled in series with a second input terminal of said second electronic amplifying means, the output terminal of said second electronic amplifying means being coupled to said second terminal, said second electronic amplifying means having an amplification factor equal to the complement of the amplification factor of said first electronic amplifying means, thereby to present a negative impedance to said secondary removing effects of said secondary winding resistance.
Claim 9
Independent Claim
377 words
An apparatus for providing an osothermal current shunt, said isothermal current shunt comprising: a current transformer having a primary and a secondary; first and second solid conductive bars of equal length, said first and second bars being electrically and thermally coupled t a first or current input node and at a second or current output node; and a third round solid conductive bar electrically and thermally coupled to said first bar at a first hole at a third node and to said second bar at a second hole at a fourth node to form the primary of said current transformer, said third bar being constructed of the same material as said first and second bars, the length between said input current node and said third node being different than the length between said input current node and said fourth node, and the length between said output current node and said third node being equal to the length between said input current node and said fourth node, and wherein said current transformer comprises a core formed of a toroid mounted around said third bar and between said first bar and said second bar; wherein a burden load impedance is formed by a series connection of said secondary, a first electronic amplifying means and a second electronic amplifying means, said first electronic amplifying means having an amplification factor at least in part determined by the value of winding resistance of said secondary; thereby to form an unbalanced bridge with a current transformer at the shunt; and wherein said secondary has a first terminal and a second terminal and wherein said first electronic amplifying means is coupled to present as a load to said secondary at said first terminal a high impedance at a first input terminal of said first electronic amplifying means, and further wherein said first electronic amplifying means is coupled in series with a second input terminal of said second electronic amplifying means, the output terminal of said second electronic amplifying means being coupled to said second terminal, said second electronic amplifying means having an amplification factor equal to the complement of the amplification factor of said first electronic amplifying means, thereby to present a negative impedance to said secondary removing effects of said secondary winding resistance.
Claim 10
Dependent Claim
78 words
The apparatus according to claim 7, wherein said second electronic amplifying means comprises a second operational amplifier and a second impedance means in a negative feedback loop for said second operational amplifier, said second impedance means being formed of a material having a temperature to resistance coefficient equal to said secondary winding and is disposed in isothermal relationship to said secondary winding thereby to minimize heat-induced differences in resistance between said secondary winding resistance and said second impedance.
Claim 11
Dependent Claim
22 words
The apparatus according to claim 7, wherein said current transformer further comprises a core formed of a material having high initial permeability.
References Cited (Backward Citations)
US31613A
Cited
US1084721A
Cited
US2818544A
Cited
US2831164A
Cited
US2915707A
Cited
US3372334A
Cited
US3815013A
Cited
US3815011A
Cited
US4506214A
Cited
USRE31613E
Cited
US4182982A
Cited
US4240059A
Cited
US4626778A
Cited
US4492919A
Cited
US4580095A
Cited
US4513273A
Cited
US4628251A
Cited
US4652810A
Cited
US4659981A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1993-07-02 | 1994-01-01 | 1994-07-03 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1997-07-02 | 1998-01-01 | 1998-07-03 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2001-07-02 | 2002-01-01 | 2002-07-03 | $7700.00 | Window Closed / Lapsed |