US3764897A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Electromagnetic thickness gauging using a transmitting coil shaped to provide a constant field over a range of measuring distances
Assignee: Singer Co
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Filing: 1971-12-28
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Granted: 1973-10-09
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Expires: 1991-12-28
Abstract
Abstract In an electromagnetic thickness gauge a transmitting coil induces eddy currents in a conducting sheet the thickness of which is to be measured. The phase angle of the magnetic field generated by the eddy currents relative to the field generated directly by the transmitting coil provides the measure of thickness. The magnetic field generated by the transmitting coil is shaped so that the phase angle measurement is substantially constant as the distance between the sheet and the transmitting coil changes. This constant phase angle is achieved by designing the coil to produce an electromagnetic field in which the scalar magnetic potential varies as a single exponential over a selected range of distances from the transmitting coil. Two eddy current measurements in which the phase angles are different functions of the thickness and conductivity are taken so that both the thickness and conductivity can be determined from the two measurements by solving simultaneous equations.
Inventors
- 👤 I Greenwood
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 22:53
CPC Classifications
G; G01; G01B; G01B7/00; G01B7/02; G01B7/06; G01B7/10; G01B7/107
Claims Analysis
Total Claims: 25
Claim 1
Independent Claim
107 words
An eddy current thickness gauge for measuring the thickness of an electrically conducting sheet comprising transmitting means for generating a magnetic field to induce eddy currents in said sheet, and receiving means for detecting the phase of the magnetic field generated by the eddy currents induced in said sheet, said transmitting means generating a magnetic field shaped to approximately simulate single mode operation in which the field is characterized by a single separation constant whereby the phase angle of the field generated by said eddy currents detected by said receiving means does not vary substantially with variations in the distance between said transmitting means and said sheet.
Claim 2
Dependent Claim
107 words
An eddy current thickness gauge for measuring the thickness of an electrically conducting sheet comprising transmitting means for generating a magnetic field to induce eddy currents in said sheet, and receiving means for detecting the phase of the magnetic field generated by the eddy currents induced in said sheet, said transmitting means generating a magnetic field shaped to approximately simulate single mode operation in which the field is characterized by a single separation constant whereby the phase angle of the field generated by said eddy currents detected by said receiving means does not vary substantially with variations in the distance between said transmitting means and said sheet.
Claim 3
Dependent Claim
45 words
An eddy current thickness gauge as recited in claim 1 wherein said transmitting means comprises a plurality of windings spaced from one another in a predetermined geometric pattern, said windings being connected in series and having turn ratios selected to generate said shaped magnetic field.
Claim 4
Dependent Claim
49 words
An eddy current thickness gauge as recited in claim 1, wherein said transmitting means comprises a plurality of low reluctance concentric sleeves, a winding wound on each of said sleeves, the ratio of the ampere turns of each of said windings being selected to generate said shaped magnetic field.
Claim 5
Dependent Claim
17 words
An eddy current thickness gauge as recited in claim 3, wherein the windings are connected in series.
Claim 6
Dependent Claim
53 words
An eddy current thickness gauge as recited in claim 3, wherein said sleeves are sized to have radii which occur at the peaks of the Bessel function Jo (qr) in which q is said separation constant and r is the radius from the center of said concentric sleeves to one of said sleeves.
Claim 7
Dependent Claim
27 words
An eddy current thickness gauge as recited in claim 3, wherein said receiving means comprises a plurality of windings identical to the windiNgs of said transmitting means.
Claim 8
Dependent Claim
140 words
An eddy current thickness gauge for measuring the thickness of a conducting sheet comprising transmitting means for generating a magnetic field to induce eddy currents in said sheet, and receiving means for detecting the phase of the magnetic field generated by the eddy currents induced in said sheet, said transmitting means generating a magnetic field shaped so that the scalar magnetic potential without said sheet being present would vary as a single exponential along an axis perpendicular to said sheet over a range centered at a distance selected to be twice the nominal distance said sheet is to be spaced from said transmitting means whereby the phase angle of the field generated by said eddy currents detected by said receiving means does not vary substantially with variations in the distance between said transmitting means and said sheet, within said range.
Claim 9
Dependent Claim
140 words
An eddy current thickness gauge for measuring the thickness of a conducting sheet comprising transmitting means for generating a magnetic field to induce eddy currents in said sheet, and receiving means for detecting the phase of the magnetic field generated by the eddy currents induced in said sheet, said transmitting means generating a magnetic field shaped so that the scalar magnetic potential without said sheet being present would vary as a single exponential along an axis perpendicular to said sheet over a range centered at a distance selected to be twice the nominal distance said sheet is to be spaced from said transmitting means whereby the phase angle of the field generated by said eddy currents detected by said receiving means does not vary substantially with variations in the distance between said transmitting means and said sheet, within said range.
Claim 10
Dependent Claim
82 words
A transmitter for an eddy current thickness gauge comprising a plurality of concentric cylindrical sleeves of low reluctance material, and a plurality of windings each wound on one of said cylinders, said sleeves being sized to have radii which occur at the peaks of the bessel function Jo (qr) in which q is a selected separation constant characterizing the field to be generated by said transmitter r is the radius from the center of said concentric sleeves to one of said sleeves.
Claim 11
Dependent Claim
82 words
A transmitter for an eddy current thickness gauge comprising a plurality of concentric cylindrical sleeves of low reluctance material, and a plurality of windings each wound on one of said cylinders, said sleeves being sized to have radii which occur at the peaks of the bessel function Jo (qr) in which q is a selected separation constant characterizing the field to be generated by said transmitter r is the radius from the center of said concentric sleeves to one of said sleeves.
Claim 12
Dependent Claim
50 words
A transmitter for an eddy current thickness gauge as recited in claim 8, wherein said windings are connected in series and have turn ratios selected to generate a magnetic field shaped to simulate single mode operation in which said field is characterized by a single operation constant which is q.
Claim 13
Dependent Claim
61 words
A transmitter for an eddy current thickness gauge comprising a plurality of concentric cylinders of low reluctance material, a plurality of windings connected in series each wound on one of said cylinders, the turn ratios of said windings being selected to simulate single mode operation in which the magnetic field generated by said windings is characterized by a single separation constant.
Claim 14
Dependent Claim
61 words
A transmitter for an eddy current thickness gauge comprising a plurality of concentric cylinders of low reluctance material, a plurality of windings connected in series each wound on one of said cylinders, the turn ratios of said windings being selected to simulate single mode operation in which the magnetic field generated by said windings is characterized by a single separation constant.
Claim 15
Independent Claim
119 words
A method of measuring the thickness of a conducting metal sheet comprising inducing eddy currents at a first frequency in said sheet to generate with said eddy currents a first magnetic field having a phase depending upon both the parameters, thickness and conductivity of said sheet, in accordance with a first functional relationship and inducing eddy currents at a second frequency to generate with said eddy currents a second magnetic field having a phase depending upon only one of said parameters in accordance with a second functional relationship, detecting the phases of said first and second magnetic fields whereby the thickness and conductivity of said sheet can be determined by simultaneous solution of said first and second functional relationships.
Claim 16
Independent Claim
119 words
A method of measuring the thickness of a conducting metal sheet comprising inducing eddy currents at a first frequency in said sheet to generate with said eddy currents a first magnetic field having a phase depending upon both the parameters, thickness and conductivity of said sheet, in accordance with a first functional relationship and inducing eddy currents at a second frequency to generate with said eddy currents a second magnetic field having a phase depending upon only one of said parameters in accordance with a second functional relationship, detecting the phases of said first and second magnetic fields whereby the thickness and conductivity of said sheet can be determined by simultaneous solution of said first and second functional relationships.
Claim 17
Dependent Claim
55 words
A method as recited in claim 11, wherein said eddy currents of said first frequency are induced in said sheet by a magnetic field characterized predominantly by a first low separation constant and wherein eddy currents of said second frequency are induced by a magnetic field characterized predominantly by a second substantially higher separation constant.
Claim 18
Dependent Claim
45 words
A method as recited in claim 12, wherein said first frequency is less than 50 kilohertz, said second frequency is 1 to 5 megahertz, said first separation constant is less than 500 meter 1 and said second separation constant is greater than 500 meter 1.
Claim 19
Dependent Claim
67 words
A method as recited in claim 11, wherein said eddy currents of said first frequency are induced by a magnetic field shaped to simulate single mode operation in which said field is characterized by a single separation constant and wherein said eddy currents of said second frequency are induced by a magnetic field characterized predominantly by a second separation constant substantially longer than said first separation constant.
Claim 20
Dependent Claim
119 words
An eddy Current thickness gauge for measuring the thickness of a conducting sheet comprising means to induce eddy currents in said sheet to generate with said eddy currents a first magnetic field having a phase depending on both parameters, thickness and conductivity of said sheet, in accordance with a first equation and to generate with said eddy currents a second magnetic field having a phase depending upon only one of said parameters in accordance with a second equation, means to detect the phase of said first magnetic field, means to detect the phase of said second magnetic field, whereby the thickness and conductivity of said sheet can be determined by a simultaneous solution of said first and second equations.
Claim 21
Dependent Claim
119 words
An eddy Current thickness gauge for measuring the thickness of a conducting sheet comprising means to induce eddy currents in said sheet to generate with said eddy currents a first magnetic field having a phase depending on both parameters, thickness and conductivity of said sheet, in accordance with a first equation and to generate with said eddy currents a second magnetic field having a phase depending upon only one of said parameters in accordance with a second equation, means to detect the phase of said first magnetic field, means to detect the phase of said second magnetic field, whereby the thickness and conductivity of said sheet can be determined by a simultaneous solution of said first and second equations.
Claim 22
Dependent Claim
131 words
An eddy current thickness gauge for measuring the thickness of a conducting sheet comprising first transmitting means for inducing eddy currents in said sheet to generate with said eddy currents a first magnetic field having a phase depending upon both the parameters, thickness and conductivity of said sheet, in accordance with a first equation, second transmitting means for inducing eddy currents in said sheet to generate with said eddy currents a second magnetic field having a phase depending upon only one of said parameters in accordance with a second equation, means to detect the phase of said first magnetic field, and means to detect the phase of said second magnetic field, whereby the thickness and conductivity of said sheet can be determined by simultaneous solution of said first and second equations.
Claim 23
Dependent Claim
131 words
An eddy current thickness gauge for measuring the thickness of a conducting sheet comprising first transmitting means for inducing eddy currents in said sheet to generate with said eddy currents a first magnetic field having a phase depending upon both the parameters, thickness and conductivity of said sheet, in accordance with a first equation, second transmitting means for inducing eddy currents in said sheet to generate with said eddy currents a second magnetic field having a phase depending upon only one of said parameters in accordance with a second equation, means to detect the phase of said first magnetic field, and means to detect the phase of said second magnetic field, whereby the thickness and conductivity of said sheet can be determined by simultaneous solution of said first and second equations.
Claim 24
Dependent Claim
33 words
An eddy current thickness gauge as recited in claim 16 wherein said first and second detecting means are on the same side of said sheet as said first and second transmitting means respectively.
Claim 25
Dependent Claim
46 words
An eddy current thickness gauge as recited in claim 16 wherein said first detecting means is on the same side of said sheet as said first transmitting means and said second detecting means is on the opposite side of said sheet from said second transmitting means.
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) | 1976-10-08 | 1977-04-09 | 1977-10-09 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-10-08 | 1981-04-09 | 1981-10-09 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-10-08 | 1985-04-09 | 1985-10-09 | $7700.00 | Window Closed / Lapsed |