US4467281A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Multi frequency eddy current test apparatus with intermediate frequency processing
Assignee: Electric Power Research Institute
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Filing: 1980-02-29
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Granted: 1984-08-21
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Expires: 2000-02-29
Abstract
Abstract An eddy current test apparatus and method in which multiple sequential test frequencies are employed. The voltage induced in a sensing coil at said test frequencies are multiplexed and frequency translated to provide a single frequency for processing. The apparatus employs a single channel to process the induced voltages.
Inventors
- 👤 Thomas J. Davis
- 👤 Charles B. Perry
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 18:04
CPC Classifications
G; G01; G01N; G01N27/00; G01N27/72; G01N27/82; G01N27/90; G01N27/9046; G01N27/9053
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
162 words
Eddy current test apparatus including inducing coil means adapted to be coupled to an object to be tested to induce eddy currents in said object which currents induce voltages in sensing coil means, said induced voltages containing certain phase and amplitude information; means for sequentially providing at least two test frequencies, one at a time, to said inducing coil means; means for receiving and converting the induced voltages in said sensing coil means by said induced eddy currents to an intermediate frequency having a fixed predetermined frequency value independent of the frequency value of each test frequency selected while preserving said phase and amplitude information of said induced voltages, said converting means including first and second choppers and means for driving said first and second choppers at IF∠0° and at IF∠90°, respectively, where IF is the intermediate frequency; and means for sequentially processing said intermediate frequency to provide in-phase and quadrature components, A i B i for each of the test frequencies.
Claim 2
Dependent Claim
162 words
Eddy current test apparatus including inducing coil means adapted to be coupled to an object to be tested to induce eddy currents in said object which currents induce voltages in sensing coil means, said induced voltages containing certain phase and amplitude information; means for sequentially providing at least two test frequencies, one at a time, to said inducing coil means; means for receiving and converting the induced voltages in said sensing coil means by said induced eddy currents to an intermediate frequency having a fixed predetermined frequency value independent of the frequency value of each test frequency selected while preserving said phase and amplitude information of said induced voltages, said converting means including first and second choppers and means for driving said first and second choppers at IF∠0° and at IF∠90°, respectively, where IF is the intermediate frequency; and means for sequentially processing said intermediate frequency to provide in-phase and quadrature components, A i B i for each of the test frequencies.
Claim 3
Dependent Claim
55 words
Eddy current test apparatus as in claim 1 including first and second modulators connected to receive the outputs of the first and second choppers and means for driving the first one of modulators with a signal F T ∠0° and the second with a signal F T ∠90° where F T is the test frequency.
Claim 4
Dependent Claim
47 words
Eddy current test apparatus as in claim 2 including a resonant circuit connected to receive the output of said first and second modulators and to eliminate all but the fundamental components of these outputs said fundamental components being the in-phase and quadrature components of the intermediate frequency.
Claim 5
Dependent Claim
38 words
Eddy current test apparatus as in claim 3 including multiplex means responsive to control signals connected to said resonant circuit and serving to sequentially apply signals corresponding to each of the test frequencies to a signal processing circuit.
Claim 6
Dependent Claim
17 words
Eddy current test apparatus as in claim 4 wherein said signal processing apparatus includes phase sensitive detectors.
Claim 7
Dependent Claim
70 words
Eddy current test apparatus as in claim 5 wherein said phase sensitive detectors include third and fourth choppers driven at IF∠0° and IF∠90° where IF is the intermediate frequency to provide inverted and non-inverted signals and sample and hold circuits connected to receive the outputs of the choppers, one such sample and hold circuit for each test frequency to provide the in-phase and quadrature outputs A i B i .
Claim 8
Dependent Claim
30 words
Eddy current test apparatus as in claim 3 including means connected to receive said in-phase and quadrature outputs and serving to derive nulling signals for application to said resonant circuit.
Claim 9
Dependent Claim
30 words
Eddy current test apparatus as in claim 6 including means connected to receive said in-phase and quadrature outputs and serving to derive nulling signals for application to said resonant circuit.
Claim 10
Dependent Claim
110 words
Eddy current test apparatus as in claims 7 or 8 wherein said means connected to receive the in-phase and quadrature outputs and provide autonull signals to the resonant circuit comprises switching means serving to connect said outputs to the resonant circuit responsive to a command, integrators serving to receive said outputs and apply the same to first and second multiplexers, means for applying signals to said multiplexers to sequentially switch the signals A i and B i , fifth and sixth choppers, connected to receive said signals, means for driving said choppers at IF∠0° and IF∠90° and amplifiers serving to apply the output of the choppers to the resonant circuit.
Claim 11
Dependent Claim
157 words
Eddy current test apparatus including inducing coil means adapted to be coupled to an object to be tested to induce eddy currents in said object which currents induce voltages in sensing coil means said induced voltages containing certain phase and amplitude information; means for sequentially providing at least one test frequency to said inducing coil means; means for receiving and converting the induced voltages in said sensing coil means by said induced eddy currents to an intermediate frequency having a predetermined fixed frequency value independent of the frequency value of the test frequency selected while preserving phase and amplitude information of said induced voltages, said converting means including first and second choppers and means for driving said first and second choppers at IF∠0° and at IF∠90°, respectively, where IF is the intermediate frequency; and means for sequentially processing said intermediate frequency to provide in-phase and quadrature components, A i B i for each of the test frequencies.
Claim 12
Dependent Claim
157 words
Eddy current test apparatus including inducing coil means adapted to be coupled to an object to be tested to induce eddy currents in said object which currents induce voltages in sensing coil means said induced voltages containing certain phase and amplitude information; means for sequentially providing at least one test frequency to said inducing coil means; means for receiving and converting the induced voltages in said sensing coil means by said induced eddy currents to an intermediate frequency having a predetermined fixed frequency value independent of the frequency value of the test frequency selected while preserving phase and amplitude information of said induced voltages, said converting means including first and second choppers and means for driving said first and second choppers at IF∠0° and at IF∠90°, respectively, where IF is the intermediate frequency; and means for sequentially processing said intermediate frequency to provide in-phase and quadrature components, A i B i for each of the test frequencies.
Claim 13
Dependent Claim
55 words
Eddy current test apparatus as in claim 10 including first and second modulators connected to receive the outputs of the first and second choppers and means for driving the first one of modulators with a signal F T ∠0° and the second with a signal F T ∠90° where F T is the test frequency.
Claim 14
Dependent Claim
34 words
Eddy current test apparatus as in claim 11 including a circuit connected to receive the output of said first and second modulators and serving to eliminate all but the fundamental components of the outputs.
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) | 1987-08-21 | 1988-02-20 | 1988-08-21 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1991-08-21 | 1992-02-20 | 1992-08-21 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1995-08-21 | 1996-02-20 | 1996-08-21 | $7700.00 | Window Closed / Lapsed |