US3842344A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Bridge circuit for measuring dielectric properties of insulation
Assignee: Doble Engineering Co
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Filing: 1974-01-10
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Granted: 1974-10-15
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Expires: 1994-01-10
Abstract
Abstract A precision bridge for measuring the dielectric properties, such as capacitance and power factor, of an electrically insulating specimen. The standard branch comprises a high voltage resistor in series with a phase balancing network consisting of a variable capacitor and voltage follower shunted across a fixed resistor, and with the primary of a mutual inductor. The secondary of the mutual inductor provides a voltage which is in quadrature with the in-phase current through the high-voltage resistor, except for any phase shift introduced by the phase balancing network. The quadrature voltage excites a current source circuit to produce a quadrature current which is adjustable in magnitude by a variable resistor. This quadrature current energizes a first winding in a ratio transformer. The current in the specimen branch energizes a second winding in the ratio transformer, opposing the magnetic action of the first winding. A third winding responsive to the difference in the magnetic actions of the two opposing windings is connected to a detector. When the bridge is balanced as shown by a null reading of the detector, the power factor of the specimen is derived from the setting of the variable capacitor in the phase balancing circuit, and the capacitance of the specimen is derived from the setting of the variable resistor in the current source circuit and from the ratio of turns in the first and second transformer windings.
Inventors
- 👤 E Povey
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-29 16:37
CPC Classifications
G; G01; G01R; G01R17/00
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
216 words
Apparatus to be used in conjunction with a source of alternating test voltage for measuring the capacitance and power factor of a test specimen, said apparatus comprising: a standard resistor, a mutual inductor having first and second windings, said first winding being connected in series with said standard resistor such that the current through said first winding, resulting from application of said test voltage to said apparatus, is substantially determined by said standard resistor and is in phase with said test voltage, said mutual inductor constructed such that the voltage induced in said second winding is substantially in quadratUre phase relation with said test voltage, a current source responsive to the voltage induced in the second winding of said mutual inductor, which produces an output current substantially in phase with said induced voltage, means for controlling the magnitude of the current output of said current source with no significant effect on the current in the first winding of said mutual inductor, terminal means for connecting said test specimen across said source of test voltage, and detection means responsive to the difference in phase and magnitude between the output current of said current source and that of the current through said specimen resulting when said specimen is connected to said terminal means with said test voltage applied.
Claim 2
Dependent Claim
216 words
Apparatus to be used in conjunction with a source of alternating test voltage for measuring the capacitance and power factor of a test specimen, said apparatus comprising: a standard resistor, a mutual inductor having first and second windings, said first winding being connected in series with said standard resistor such that the current through said first winding, resulting from application of said test voltage to said apparatus, is substantially determined by said standard resistor and is in phase with said test voltage, said mutual inductor constructed such that the voltage induced in said second winding is substantially in quadratUre phase relation with said test voltage, a current source responsive to the voltage induced in the second winding of said mutual inductor, which produces an output current substantially in phase with said induced voltage, means for controlling the magnitude of the current output of said current source with no significant effect on the current in the first winding of said mutual inductor, terminal means for connecting said test specimen across said source of test voltage, and detection means responsive to the difference in phase and magnitude between the output current of said current source and that of the current through said specimen resulting when said specimen is connected to said terminal means with said test voltage applied.
Claim 3
Dependent Claim
120 words
Apparatus as claimed in claim 1 wherein said detection means is comprised of a transformer having two windings of known turns ratio plus a third winding, the first winding of said transformer, when connected in series with the test specimen across the source of test voltage, producing a magnetomotive force depending on the specimen current and the number of turns in said first winding, the second winding connected to said current source and producing an opposing magnetomotive force depending upon the output current of said current source and the number of turns in said second winding, and the third winding connected to an indicating device sensitive to any imbalance in the magnetomotive forces produced by the first and second windings.
Claim 4
Dependent Claim
50 words
Apparatus as claimed in claim 1 wherein said current source includes an operational amplifier connected to act as a voltage follower, said operational amplifier having two input terminals drawing no significant current and having an output current determined by the voltage induced in the second winding of said mutual inductor.
Claim 5
Dependent Claim
37 words
Apparatus as claimed in claim 3 wherein said means for controlling the magnitude of the current output of said current source is a variable resistor connected between the output of said operational amplifier and said detection means.
Claim 6
Dependent Claim
49 words
Apparatus as claimed in claim 1 further including means for controlling the phase relation of the current flowing through the first winding of said mutual inductor as a result of application of said test voltage, said means being connected in shunt across the first winding of said mutual inductor.
Claim 7
Dependent Claim
80 words
Apparatus as claimed in claim 5 wherein said means for controlling the phase relation includes a fixed resistor connected in series with the first winding ofsaid mutual indictor, a variable capacitor, and an operational amplifier connected as a follower to keep the voltage across said variable capacitor equal to the voltage across said fixed resistor, said variable capacitor and said operational amplifier connected in series as a shunt across aid fixed resistor and said first winding of the mutual inductor.
Claim 8
Dependent Claim
193 words
Apparatus to be used in conjunction with a source of alternating test voltage for measuring the capacitance and power factor of a test specimen, said apparatus comprising a standard resistor, a mutual inductor having first and second windings, said first winding being connected in series with said standard resistor such that the current through said first winding, resulting from application of said test voltage to said apparatus, is substantially determined by said standard resistor, said mutual inductor constructed such that the voltage induced in such second winding is substantially in quadrature phase relation with said test voltage, means for controlling the phase relation of the current flowing through the first winding of said mutual inductor as a result of application of said test voltage, said means being connected in shunt across the first winding of said mutual inductor, terminal means for connecting said test specimen across said source of test voltage, and detection means responsive to the difference in phase and magnitude between the output current of said curRent source and that of the current through said specimen resulting when said specimen is connected to said terminal means with said test voltage applied.
Claim 9
Dependent Claim
193 words
Apparatus to be used in conjunction with a source of alternating test voltage for measuring the capacitance and power factor of a test specimen, said apparatus comprising a standard resistor, a mutual inductor having first and second windings, said first winding being connected in series with said standard resistor such that the current through said first winding, resulting from application of said test voltage to said apparatus, is substantially determined by said standard resistor, said mutual inductor constructed such that the voltage induced in such second winding is substantially in quadrature phase relation with said test voltage, means for controlling the phase relation of the current flowing through the first winding of said mutual inductor as a result of application of said test voltage, said means being connected in shunt across the first winding of said mutual inductor, terminal means for connecting said test specimen across said source of test voltage, and detection means responsive to the difference in phase and magnitude between the output current of said curRent source and that of the current through said specimen resulting when said specimen is connected to said terminal means with said test voltage applied.
Claim 10
Dependent Claim
81 words
Apparatus as claimed in claim 7 wherein said means for controlling the phase relation includes a fixed resistor connected in series with the first winding of said mutual inductor, a variable capacitor, and an operational amplifier connected as a follower to keep the voltage across said variable capacitor equal to the voltage across said fixed resistor, said variable capacitor and said operational amplifier connected in series as a shunt across said fixed resistor and said first winding of the mutual inductor.
Claim 11
Dependent Claim
36 words
Apparatus as claimed in claim 7 further including a current source responsive to the voltage induced in the second winding of said mutual inductor, which produces an output current substantially in phase with said induced voltage.
Claim 12
Dependent Claim
50 words
Apparatus as claimed in claim 9 wherein said current source includes an operational amplifier connected to act as a voltage follower, said operational amplifier having two input terminals drawing no significant current and having an output current determined by the voltage induced in the second winding of said mutual inductor.
Claim 13
Dependent Claim
27 words
Apparatus as claimed in claim 10 wherein said current source is further comprised of a variable resistor connected in series with the output of said operational amplifier.
Claim 14
Dependent Claim
119 words
Apparatus as claimed in claim 5 wherein said detection means is comprised of a transformer having two windings of known turns ratio plus a third winding, the first winding of said transformer, when connected in series with the test specimen across the source of test voltage, producing a magnetomotive force depending on the specimen current and the number of turns of said first winding, the second winding connected to said current source producing an opposing magnetomotive force depending upon the output current of said current source and the number of turns in said second winding, and the third winding connected to an indicating device sensitive to any imbalance in the magnetomotive forces produced by the first and second windings.
Claim 15
Dependent Claim
81 words
Apparatus as claimed in claim 11 wherein said means for controlling the phase relation includes a fixed resistor connected in series with the first winding of said mutual inductor, a variable capacitor, and an operational amplifier connected as a follower to keep the voltage across said variable capacitor equal to the voltage across said fixed resistor, said variable capacitor and said operational amplifier connected in series as a shunt across said fixed resistor and said first winding of the mutual inductor.
Claim 16
Dependent Claim
116 words
Apparatus as claimed in claim 13 wherein said detection means includes a transformer having two windings of known turns ratio plus a third winding, the first winding of said transformer, when connected in series with the test specimen across the source of test voltage, producing a magnetomotive force depending on the specimen current and the number of turns in said first winding, the second winding connected to said current source producing an opposing magnetomotive force depending upon the output current of said current source and the number of turns in said second winding, and the third winding connected to a device sensitive to any imbalance is the magnetomotive forces produced by the first and second windings.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-10-14 | 1978-04-15 | 1978-10-15 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-10-14 | 1982-04-15 | 1982-10-15 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-10-14 | 1986-04-15 | 1986-10-15 | $7700.00 | Window Closed / Lapsed |