Patent US5017869A successfully refreshed from Google Patents.
US5017869A
Expired / Lapsed
US
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Swept frequency eddy current system for measuring coating thickness
Assignee: General Electric Co
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Filing: 1989-12-14
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Granted: 1991-05-21
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Expires: 2009-12-14
Abstract
Abstract An apparatus for measuring the thickness of a coating on a substrate has a bridge circuit including four coils. One coil is placed near the coated substrate and another placed near an uncoated substrate of the same material. An oscillator is connected to the bridge circuit and frequency sweeps, e.g. from 10 KHz to 10 MHz. Phase differences between the voltages induced in the coils are detected to determine conductivity changes with frequency. A method for measuring coating thickness comprises generating variable frequency eddy current in coated and uncoated substrates of the same material and comparing the generated eddy current.
Inventors
- 👤 David W. Oliver
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-03 18:27
CPC Classifications
G; G01; G01B; G01B7/00; G01B7/02; G01B7/06; G01B7/10; G01B7/105
Claims Analysis
Total Claims: 36
Claim 1
Independent Claim
94 words
Apparatus for measuring the thickness of a coating on a substrate having a given substrate material, said apparatus comprising: means for generating variable frequency eddy currents in the coated substrate, the coating, and an uncoated substrate of the given material; and means for comparing conductivity changes of the coating and the coated substrate with the uncoated substrate with changes in frequency and for determining a transition frequency, the transition frequency being related to the coating thickness and being a frequency at which current flow transitions substantially between penetration and no penetration into the substrate.
Claim 2
Dependent Claim
94 words
Apparatus for measuring the thickness of a coating on a substrate having a given substrate material, said apparatus comprising: means for generating variable frequency eddy currents in the coated substrate, the coating, and an uncoated substrate of the given material; and means for comparing conductivity changes of the coating and the coated substrate with the uncoated substrate with changes in frequency and for determining a transition frequency, the transition frequency being related to the coating thickness and being a frequency at which current flow transitions substantially between penetration and no penetration into the substrate.
Claim 3
Dependent Claim
19 words
The apparatus of claim 1 wherein said comparing means comprises means for detecting phase differences between said eddy currents.
Claim 4
Dependent Claim
29 words
The apparatus of claim 1 wherein said generating means comprises a pair of probe first and second coils adapted to be respectively disposed proximate the coated and uncoated substrates.
Claim 5
Dependent Claim
19 words
The apparatus of claim 3 wherein said generating means comprises a bridge circuit including said first and second coils.
Claim 6
Dependent Claim
15 words
The apparatus of claim 4 wherein said bridge circuit further includes third and fourth coils.
Claim 7
Dependent Claim
23 words
The apparatus of claim 3 wherein said comparing means includes a difference amplifier having a pair of inputs respectively coupled to said coils.
Claim 8
Dependent Claim
21 words
The apparatus of claim 1 wherein said generating means includes an oscillator that sweeps between about 10 KHz to 10 MHz.
Claim 9
Dependent Claim
15 words
The apparatus of claim 1 further comprising a display means coupled to said comparing means.
Claim 10
Dependent Claim
27 words
The apparatus of claim 1 further comprising a regression analysis circuit coupled to said comparing means, and a thickness versus frequency memory coupled to said analysis circuit.
Claim 11
Dependent Claim
14 words
The apparatus of claim 9 wherein said analysis circuit is a least squares circuit.
Claim 12
Dependent Claim
14 words
The apparatus of claim 9 wherein said analysis circuit is a maximum likelihood circuit.
Claim 13
Dependent Claim
33 words
The apparatus of claim 1 further comprising a first differentiator coupled to said comparing means, a second differentiator coupled to said first differentiator, and a ratio circuit coupled to both of said differentiators.
Claim 14
Dependent Claim
114 words
Apparatus or measuring the thickness of a coating on a substrate having a given substrate material, said apparatus comprising: a pair of probe first and second coils adapted to be disposed respectively proximate the coated substrate and an uncoated substrate of the given material; a swept frequency oscillator coupled to said coils; and means coupled to said coils and to said oscillator, for comparing conductivity changes of the coating and the coated substrate with the uncoated substrate with changes in frequency and for determining a transition frequency, the transition frequency being related to the coating thickness and being a frequency at which current flow substantially transitions between penetration and no penetration into the substrate.
Claim 15
Dependent Claim
114 words
Apparatus or measuring the thickness of a coating on a substrate having a given substrate material, said apparatus comprising: a pair of probe first and second coils adapted to be disposed respectively proximate the coated substrate and an uncoated substrate of the given material; a swept frequency oscillator coupled to said coils; and means coupled to said coils and to said oscillator, for comparing conductivity changes of the coating and the coated substrate with the uncoated substrate with changes in frequency and for determining a transition frequency, the transition frequency being related to the coating thickness and being a frequency at which current flow substantially transitions between penetration and no penetration into the substrate.
Claim 16
Dependent Claim
13 words
The apparatus of claim 13 further comprising the coated and the uncoated substrates.
Claim 17
Dependent Claim
17 words
The apparatus of claim 14 wherein each of said substrates comprises zircalloy, and said coating comprises zirconium.
Claim 18
Dependent Claim
14 words
The apparatus of claim 13 further comprising a bridge circuit including said probe coils.
Claim 19
Dependent Claim
22 words
The apparatus of claim 16 wherein said bridge circuit includes third and fourth coils respectively coupled to said first and second coils.
Claim 20
Dependent Claim
18 words
The apparatus of claim 13 wherein said swept frequency oscillator sweeps between about 10 KHz to 10 MHz.
Claim 21
Dependent Claim
26 words
The apparatus of claim 13 wherein said comparison means comprises a first phase detector coupled to said coils, said first detector being coupled to said oscillator.
Claim 22
Dependent Claim
29 words
The apparatus of claim 19 further comprising a second phase detector coupled to said coils, and a 90 degree phase shifter coupled between said oscillator and said second detector.
Claim 23
Dependent Claim
30 words
The apparatus of claim 20 further comprising a phase adjustment means having an input coupled to said oscillator and an output coupled to said first detector and said phase shifter.
Claim 24
Dependent Claim
26 words
The apparatus of claim 20 further comprising a servo circuit coupled to said second detector and mechanically coupled to said coil disposed proximate said coated substrate.
Claim 25
Dependent Claim
23 words
The apparatus of claim 13 wherein said comparison means comprises a differential amplifier having a pair of inputs respectively coupled to said coils.
Claim 26
Independent Claim
92 words
A method for measuring the thickness of a coating on a substrate having a give substrate material, said method comprising: generating variable frequency eddy currents in the coated substrate, the coating, and an uncoated substrate of the given material; and comparing changes in conductivity of the coating and the coated substrate with the uncoated substrate with changes in frequency in order to determine a transition frequency, the transition frequency being related to coating thickness and being a frequency at which current flow substantially transitions between penetration and no penetration into the substrate.
Claim 27
Independent Claim
92 words
A method for measuring the thickness of a coating on a substrate having a give substrate material, said method comprising: generating variable frequency eddy currents in the coated substrate, the coating, and an uncoated substrate of the given material; and comparing changes in conductivity of the coating and the coated substrate with the uncoated substrate with changes in frequency in order to determine a transition frequency, the transition frequency being related to coating thickness and being a frequency at which current flow substantially transitions between penetration and no penetration into the substrate.
Claim 28
Dependent Claim
17 words
The method of claim 24 wherein said comparing step comprises detecting phase differences between said eddy currents.
Claim 29
Dependent Claim
22 words
The method of claim 24 wherein said generating step comprises generating a frequency that sweeps between about 10 KHz to 10 MHz.
Claim 30
Dependent Claim
12 words
The method of claim 24 further comprising displaying the compared eddy currents.
Claim 31
Dependent Claim
19 words
The method of claim 24 further comprising calculating a transition frequency, and determining the thickness from said transition frequency.
Claim 32
Dependent Claim
14 words
The method of claim 28 wherein said calculating step comprises the least squares method.
Claim 33
Dependent Claim
14 words
The method of claim 28 wherein said calculating step comprises the maximum likelihood method.
Claim 34
Dependent Claim
36 words
The method of claim 24 further comprising calculating the first derivative of a signal representing the compared conductivity changes, calculating second derivative of said signal, and calculating the ratio of the first to the second derivatives.
Claim 35
Dependent Claim
14 words
The method of claim 24 further comprising performing a phase adjustment for maximum sensitivity.
Claim 36
Dependent Claim
19 words
The method of claim 24 further comprising performing a calibration using a substrate having a coating of known thickness.
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| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
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| 3.5 Years (Year 4) | 1994-05-20 | 1994-11-19 | 1995-05-21 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1998-05-20 | 1998-11-19 | 1999-05-21 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2002-05-20 | 2002-11-19 | 2003-05-21 | $7700.00 | Window Closed / Lapsed |