US4667149A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Precision nondestructive testing of metals
Assignee: Nokia Bell Labs
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Filing: 1983-05-31
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Granted: 1987-05-19
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Expires: 2003-05-31
Abstract
Abstract A large number of applications exists for measuring the resistivity or other properties of ferrous and nonferrous metals, including matching alloys to ensure weld compatibility and measuring weld size to estimate weld strength. In the present invention, a DC current-reversal technique allows for accurate electrical measurement with a 4-point probe, alleviating problems due to surface potentials, thermal effects, and eddy currents that previously rendered such measurements inaccurate. Estimates of thermal conductivity, flaw size and location, among others, can also be obtained.
Inventors
- 👤 Richard L. Cohen
- 👤 Kenneth W. West
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 16:07
CPC Classifications
G; G01; G01R; G01R27/00; G01R27/02; G01N; G01N25/00; G01N25/18; G01N27/00; G01N27/02; G01N27/04; G01N27/041
Claims Analysis
Total Claims: 24
Claim 1
Independent Claim
100 words
A method of testing an article characterized by contacting metal having a volume resistivity of less than 200 microhm-cm by means of at least four spaced probes; passing a current in a first direction between two of said probes and integrating the voltage produced thereby across another two of said probes; thereafter reversing said current while again integrating said voltage produced thereby; and combining the magnitudes of the integrated voltages; wherein the duration of the flow of said current is in the range of 0.1 to 2 seconds and wherein said reversing of said current is performed once per test.
Claim 2
Independent Claim
100 words
A method of testing an article characterized by contacting metal having a volume resistivity of less than 200 microhm-cm by means of at least four spaced probes; passing a current in a first direction between two of said probes and integrating the voltage produced thereby across another two of said probes; thereafter reversing said current while again integrating said voltage produced thereby; and combining the magnitudes of the integrated voltages; wherein the duration of the flow of said current is in the range of 0.1 to 2 seconds and wherein said reversing of said current is performed once per test.
Claim 3
Dependent Claim
17 words
The method of claim 1 wherein all of said probes contact the same surface of said metal.
Claim 4
Dependent Claim
34 words
The method of claim 1 wherein at least two of said probes contact a first surface of said metal, and at least another two of said probes contact an opposite surface of said metal.
Claim 5
Dependent Claim
13 words
The method of claim 1 wherein said current is less than 10 amperes.
Claim 6
Dependent Claim
20 words
The method of claim 1 wherein said metal is a magnetic metal having a magnetic permeability of greater than 1.05.
Claim 7
Dependent Claim
20 words
The method of claim 1 wherein said metal is a nonmagnetic metal having a magnetic permeability of less than 1.05.
Claim 8
Dependent Claim
28 words
The method of claim 1 wherein a resistivity value is obtained from the combined integrated voltages that is within 5% of the actual resistivity value of said metal.
Claim 9
Dependent Claim
46 words
The method of claim 1 wherein said probes are placed in the vicinity of a weld in said metal, whereby at least a portion of said current flows through at least a portion of said weld, thereby obtaining a measurement of the strength of said weld.
Claim 10
Dependent Claim
65 words
The method of claim 1 wherein the total time of said passing a current is sufficiently short so that heating effects in said metal do not substantially limit the accuracy of said testing, and wherein the time of said passing a current in a given direction is sufficiently long so that eddy currents in said metal do not substantially limit the accuracy of said testing.
Claim 11
Independent Claim
138 words
An apparatus for testing an article characterized by means for contacting a metallic portion of said article with at least four probes; means for causing a current to flow in a first direction between two of said probes for a first time period; means for causing a current to flow in the opposite direction between said two probes for a second time period; means for integrating the voltages produced by said currents across another two of said probes; and means for combining the magnitudes of the integrated voltages; wherein said apparatus is adapted for testing a metallic portion having a volume resistivity of less than 200 microhm-cm, and adapted to flow said current once in each direction per test, with the total duration of the flows being in the range of from 0.1 to 2 seconds per test.
Claim 12
Independent Claim
138 words
An apparatus for testing an article characterized by means for contacting a metallic portion of said article with at least four probes; means for causing a current to flow in a first direction between two of said probes for a first time period; means for causing a current to flow in the opposite direction between said two probes for a second time period; means for integrating the voltages produced by said currents across another two of said probes; and means for combining the magnitudes of the integrated voltages; wherein said apparatus is adapted for testing a metallic portion having a volume resistivity of less than 200 microhm-cm, and adapted to flow said current once in each direction per test, with the total duration of the flows being in the range of from 0.1 to 2 seconds per test.
Claim 13
Dependent Claim
30 words
The apparatus of claim 10 wherein said apparatus provides a resistivity measurement of said metallic portion that is accurate to within ±5% of the actual volume resistivity of said portion.
Claim 14
Dependent Claim
26 words
The apparatus of claim 10 wherein said apparatus is adapted for testing a weld, whereby the combined integrated voltages provide a measurement of approximate weld strength.
Claim 15
Dependent Claim
13 words
The apparatus of claim 10 wherein said current is less than 10 amperes.
Claim 16
Dependent Claim
84 words
The apparatus of claim 10 wherein said means for causing a current to flow in said first direction and said second direction provide for a total time of current flow that is sufficiently short so that heating effects in said metallic portion do not substantially limit the accuracy of said testing, and provide for a time of current flow in a given direction to be sufficiently long so that eddy currents in said metallic portion do not substantially limit the accuracy of said testing.
Claim 17
Independent Claim
139 words
A method of testing an article characterized by contacting a metal substantially comprising iron and having a volume resistivity of less than 200 microhm-cm by means of at least four spaced probes; passing a current in a first direction between two of said probes and integrating the voltage produced thereby across another two of said probes; thereafter reversing the direction of said current and integrating the voltage produced thereby; and combining the magnitudes of the integrated voltages; wherein the total time of the passing of the current is sufficiently short so that heating effects in said metal do not substantially limit the accuracy of said testing, and wherein the time of the passing of the current in a given direction is sufficiently long so that eddy currents in said metal do not substantially limit the accuracy of said testing.
Claim 18
Independent Claim
139 words
A method of testing an article characterized by contacting a metal substantially comprising iron and having a volume resistivity of less than 200 microhm-cm by means of at least four spaced probes; passing a current in a first direction between two of said probes and integrating the voltage produced thereby across another two of said probes; thereafter reversing the direction of said current and integrating the voltage produced thereby; and combining the magnitudes of the integrated voltages; wherein the total time of the passing of the current is sufficiently short so that heating effects in said metal do not substantially limit the accuracy of said testing, and wherein the time of the passing of the current in a given direction is sufficiently long so that eddy currents in said metal do not substantially limit the accuracy of said testing.
Claim 19
Dependent Claim
30 words
The method of claim 15 wherein said testing provides a resistivity measurement of said metal that is accurate to within ±5 percent of the actual volume resistivity of said metal.
Claim 20
Dependent Claim
13 words
The method of claim 15 wherein the current is less than 10 amperes.
Claim 21
Dependent Claim
17 words
The method of claim 15 wherein the current is passed only once in each direction per test.
Claim 22
Dependent Claim
18 words
The method of claim 18 wherein the total time of passing the current is less than 2 seconds.
Claim 23
Dependent Claim
18 words
The method of claim 19 wherein the total time of passing the current is at least 0.05 seconds.
Claim 24
Dependent Claim
20 words
The method of claim 15 wherein said metal is a magnetic metal having a magnetic permeability of greater than 1.05.
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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) | 1990-05-18 | 1990-11-17 | 1991-05-19 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1994-05-18 | 1994-11-17 | 1995-05-19 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1998-05-18 | 1998-11-17 | 1999-05-19 | $7700.00 | Window Closed / Lapsed |