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US4481471A
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Method and apparatus for the detection of anomalies in rotating members
Assignee: Siemens Energy Inc
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Filing: 1981-08-14
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Granted: 1984-11-06
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Expires: 2001-08-14
Abstract
Abstract A detector operable to detect cracks in a rotating member generates an alternating eddy current in the rotating member with an external coil surrounding the rotating member. A pick-up coil senses changes in the magnetic field of the eddy current due to a crack. The frequency of the excitation current is very much lower than the frequency of rotation of the rotating member and a plurality of samples are taken for each degree location. The output signal of the pick-up coil is comprised of both the crack indicative component and a residual or induced magnetism component. The signal is processed so as to extract the desired crack indicative component.
Inventors
- 👤 Robert C. Miller
- 👤 Walter J. Carr, Jr.
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 20:31
CPC Classifications
G; G01; G01N; G01N27/00; G01N27/72; G01N27/82; G01N27/90; G01N27/9046
Claims Analysis
Total Claims: 22
Claim 1
Independent Claim
128 words
Apparatus for detecting anomalies in an electrically conducting rotating member comprising: (A) current conducting means contiguous said rotating member operable to establish a circumferential alternating eddy current therein, and a corresponding external magnetic field, as said member rotates; (B) means for providing said current conducting means with an AC excitation current having a frequency f; (C) the period of said excitation current being orders of magnitude greater than the period of rotation of said rotating member; (D) sensing means contiguous said rotating member for detecting any changes in said magnetic field caused by said anomalies and operable to provide an output signal indicative thereof; (E) signal processing means operable in response to said output signal to provide an indication of anomaly and anomaly location within said rotating member.
Claim 2
Dependent Claim
128 words
Apparatus for detecting anomalies in an electrically conducting rotating member comprising: (A) current conducting means contiguous said rotating member operable to establish a circumferential alternating eddy current therein, and a corresponding external magnetic field, as said member rotates; (B) means for providing said current conducting means with an AC excitation current having a frequency f; (C) the period of said excitation current being orders of magnitude greater than the period of rotation of said rotating member; (D) sensing means contiguous said rotating member for detecting any changes in said magnetic field caused by said anomalies and operable to provide an output signal indicative thereof; (E) signal processing means operable in response to said output signal to provide an indication of anomaly and anomaly location within said rotating member.
Claim 3
Dependent Claim
16 words
Apparatus according to claim 1 wherein: (A) said frequency f is a fraction of a Hertz.
Claim 4
Dependent Claim
34 words
Apparatus according to claim 1 wherein: (A) said output signal of said sensing means is periodically sampled by said signal processing means at least several hundred times during said period of said excitation current.
Claim 5
Dependent Claim
27 words
Apparatus according to claim 1 wherein: (A) said output signal of said sensing means is sampled at least once during each complete rotation of said rotating member.
Claim 6
Dependent Claim
20 words
Apparatus according to claim 1 wherein: (A) said current conducting means is a coil which uninterruptedly surrounds said rotating member.
Claim 7
Dependent Claim
20 words
Apparatus according to claim 5 wherein: (A) said sensing means is a pick-up coil disposed adjacent said current conducting means.
Claim 8
Dependent Claim
37 words
Apparatus according to claim 1 wherein: (A) said current conducting means is a multipart coil each part of which does not surround said rotating member but all the parts of which collectively substantially surround said rotating member.
Claim 9
Dependent Claim
32 words
Apparatus according to claim 1 wherein: (A) said signal processing means is operable to eliminate the undesired effects that any residual magnetism of said rotating member may have on said output signal.
Claim 10
Dependent Claim
82 words
Apparatus according to claim 8 wherein: (A) said signal processing means is operable to sample said output signal of said sensing means a predetermined number of times, for each of a predetermined number of degree locations around said rotating member, to compute in a first time period, for each said degree location, an average value of said output signal (E i ) and to subtract, in a subsequent time period, said average value from said output signal to obtain an anomaly signal.
Claim 11
Dependent Claim
27 words
Apparatus according to claim 9 wherein: (A) said output signal is sampled a predetermined number of times for each of 360 degree locations around said rotating member.
Claim 12
Dependent Claim
26 words
Apparatus according to claim 9 wherein: (A) said signal processing means is operable to further process said anomaly signal to obtain in-phase and quadrature components thereof.
Claim 13
Dependent Claim
19 words
Apparatus according to claim 1 wherein: (A) said signal processing means controls the generation of said AC excitation current.
Claim 14
Dependent Claim
22 words
Apparatus according to claim 1 wherein: (A) said sensing means includes a plurality of pick-up coils angularly disposed about said rotating member.
Claim 15
Dependent Claim
51 words
Apparatus according to claim 13 which includes: (A) a plurality of signal-processing means each connected to a respective one of said pick-up coils and each operable in response to the output signal provided by the respective pick-up coils to provide an indication of anomaly and anomaly location within said rotating member.
Claim 16
Dependent Claim
36 words
Apparatus according to claim 13 wherein: (A) said pick-up coils are electrically connected in signal opposition so as to tend to cancel any signals caused by an external magnetic field acting simultaneously on said pick-up coils.
Claim 17
Independent Claim
81 words
A method of detecting anomalies in an electrically conducting rotating member comprising the steps of: (A) establishing, in said member as it rotates, a circumferential alternating eddy current having a period which is orders of magnitude greater than the period of rotation of said rotating member; (B) detecting the resultant magnetic field due to said eddy current and providing a signal indicative thereof; and (C) processing said signal to obtain an indication of anomaly and anomaly location within said rotating member.
Claim 18
Independent Claim
81 words
A method of detecting anomalies in an electrically conducting rotating member comprising the steps of: (A) establishing, in said member as it rotates, a circumferential alternating eddy current having a period which is orders of magnitude greater than the period of rotation of said rotating member; (B) detecting the resultant magnetic field due to said eddy current and providing a signal indicative thereof; and (C) processing said signal to obtain an indication of anomaly and anomaly location within said rotating member.
Claim 19
Dependent Claim
24 words
A method according to claim 16 wherein: (A) said signal is processed to eliminate the effects of any residual magnetism of said rotating member.
Claim 20
Dependent Claim
27 words
A method according to claim 16 wherein: (A) said signal is processed to obtain a first component indicative of permeability and a second component indicative of conductivity.
Claim 21
Dependent Claim
25 words
A method according to claim 16 wherein: (A) said signal is sampled at least hundreds of times in one period of said alternating eddy current.
Claim 22
Dependent Claim
24 words
A method according to claim 18 which includes the step of: (A) providing a graphic printout of at least one of said component indications.
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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) | 1987-11-06 | 1988-05-07 | 1988-11-06 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1991-11-06 | 1992-05-07 | 1992-11-06 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1995-11-06 | 1996-05-07 | 1996-11-06 | $7700.00 | Window Closed / Lapsed |