Title: Omnidirectional eddy current probes, array probes, and inspection systems
Abstract: An omnidirectional eddy current probe includes a number of sense coils arranged in a stack having a principal axis. At least two of the sense coils are rotationally skewed about the principal axis relative to one another. The sense coils are operatively connected to each other and a drive coil is also positioned in the stack. An impulse through the drive coil induces a magnetic influx through a conducting material specimen having a surface, thereby generating eddy currents on the surface. Secondary magnetic field generated from the eddy currents produces corresponding signals in the sense coils, and the signals are then analyzed for the possibility of surface flaw in the conducting material.
Patent Number: 6,888,347 Issued on 05/03/2005 to Batzinger, et al.
| Inventors:
|
Batzinger; Thomas James (Burnt Hills, NY);
Nath; Shridhar Champaknath (Niskayuna, NY);
Rose; Curtis Wayne (Mechanicville, NY)
|
| Assignee:
|
General Electric Company (Niskayuna, NY)
|
| Appl. No.:
|
662681 |
| Filed:
|
September 12, 2003 |
| Current U.S. Class: |
324/242; 324/240; 324/243 |
| Intern'l Class: |
G01N 027/82 |
| Field of Search: |
324/222,228,232,234,238-240,242,243,244,256-257,260-262
|
References Cited [Referenced By]
U.S. Patent Documents
| 3876932 | Apr., 1975 | Domon et al.
| |
| 5006801 | Apr., 1991 | Young.
| |
| 5182513 | Jan., 1993 | Young et al.
| |
| 5262722 | Nov., 1993 | Hedengren et al.
| |
| 5334934 | Aug., 1994 | Viertl.
| |
| 5345514 | Sep., 1994 | Mahdavieh et al.
| |
| 5389876 | Feb., 1995 | Hedengren et al.
| |
| 5418547 | May., 1995 | Mizukata et al.
| |
| 5430376 | Jul., 1995 | Viertl.
| |
| 5442286 | Aug., 1995 | Sutton, Jr. et al.
| |
| 5659248 | Aug., 1997 | Hedengren et al.
| |
| 5903147 | May., 1999 | Granger, Jr. et al.
| |
| 6175234 | Jan., 2001 | Granger, Jr. et al.
| |
| 6414483 | Jul., 2002 | Nath et al.
| |
| 6456066 | Sep., 2002 | Burd et al.
| |
| Foreign Patent Documents |
| 0518635 | Dec., 1992 | EP.
| |
| 2109112 | May., 1983 | GB.
| |
Other References
Patent Abstract of Japan, 2003240762A, H. Tatsuo, "Probe for Eddy Current Flaw
Detection and Eddy Current Flaw Detecting Apparatus Using The Same", vol. 2003,
No. 12, Aug. 27, 2003.
European Search Report, EP04255457, D. Joyce, Nov. 12, 2004.
|
Primary Examiner: LeDynh; Bot
Attorney, Agent or Firm: Clarke; Penny A., Patnode; Patrick K.
Claims
1. An omnidirectional eddy current probe comprising:
a plurality of sense coils arranged in a stack having a principal axis, wherein
at least two of said sense coils are rotationally skewed about the principal axis
relative to one another;
electrical connections operatively connecting said sense coils; and
a drive coil positioned in the stack.
2. The omnidirectional eddy current probe of claim 1, wherein said sense coils
are electrically insulated from each other.
3. The omnidirectional eddy current probe of claim 2 further comprising at least
one substrate positioned between a pair of said sense coils, said substrate electrically
insulating the pair of said sense coils.
4. The omnidirectional eddy current probe of claim 3, wherein said at least one
substrate is flexible.
5. The omnidirectional eddy current probe of claim 4, wherein at least one of
said sense coils in the pair is formed on said at least one substrate.
6. The omnidirectional eddy current probe of claim 5, wherein two of said sense
coils are formed on said at least one substrate.
7. The omnidirectional eddy current probe of claim 3, comprising a plurality
of substrates, said substrates being stacked.
8. The omnidirectional eddy current probe of claim 7, wherein said substrates
are bonded to maintain alignment of the stack.
9. The omnidirectional eddy current probe of claim 1, wherein at least two of
said sense coils have a common geometry.
10. The omnidirectional eddy current probe of claim 1, wherein at least two of
said sense coils have a different geometry.
11. The omnidirectional eddy current probe of claim 1, wherein said drive coil
is one of said sense coils.
12. The omnidirectional eddy current probe of claim 1, wherein said drive coil
(
120) is not one of said sense coils.
13. An omnidirectional eddy current array probe comprising:
a plurality of sense coils arranged in a plurality of stacks, each of the stacks
having a principal axis, wherein at least two of said sense coils in the stack
are rotationally skewed about the respective principal axis;
a plurality of electrical connections operatively connecting said sense coils
within the respective stacks; and
a plurality of drive coils, each of said drive coils being positioned in a respective
one of said stacks.
14. The omnidirectional eddy current array probe of claim 13 further comprising
at least one substrate positioned between at least one pair of said sense coils
in each of the stacks, said substrate electrically insulating said at least one
pair of said sense coils.
15. The omnidirectional eddy current array probe of claim 14, wherein said at
least one substrate is flexible.
16. The omnidirectional eddy current array probe of claim 14, comprising a plurality
of substrates arranged in a global stack, each of said substrates being positioned
between a respective pair of said sense coils in each of the stacks.
17. The omnidirectional eddy current array probe of claim 13, wherein at least
two of said sense coils within a respective one of said stacks have a common geometry.
18. The omnidirectional eddy current array probe of claim 13, wherein at least
two of said sense coils within a respective one of said stacks have a different geometry.
19. The omnidirectional eddy current array probe of claim 13, wherein at least
two of said stacks have a common geometry.
20. The omnidirectional eddy current array probe of claim 13, wherein at least
two of said stacks have a different geometry.
21. The omnidirectional eddy current array probe of claim 13, wherein a corresponding
sense coil of each stack defines a level, and at least two of said sense coils
in a respective one of the levels have a common geometry.
22. The omnidirectional eddy current array probe of claim 13, wherein none of
said drive coils is one of said sense coils.
23. The omnidirectional eddy current array probe of claim 13, wherein at least
one of said drive coils is one of said sense coils.
24. The omnidirectional eddy current array probe of claim 16, wherein a center
of one of said sense coils is offset with respect to a center of another of said
sense coils within the respective stack, resulting in a staggered arrangement of
said sense coils.
25. An omnidirectional eddy current inspection system comprising:
an eddy current probe comprising:
a plurality of sense coils arranged in a stack having a principal axis, wherein
at least two of said sense coils are rotationally skewed about the principal axis
relative to one another,
a drive coil positioned in the stack, and
a plurality of electrical connections connecting said sense coils; and
an eddy current instrument connected to said probe.
26. The omnidirectional eddy current inspection system of claim 25, wherein each
of said sense coils is individually monitored by said eddy current instrument.
27. The omnidirectional eddy current inspection system of claim 25, wherein said
sense coils are monitored simultaneously through a single channel by said eddy
current instrument.
28. An omnidirectional eddy current inspection system comprising:
an eddy current array probe comprising:
a plurality of sense coils arranged in a plurality of stacks, each of the stacks
having a principal axis, wherein at least two of said sense coils in a respective
one of the stacks are rotationally skewed about the respective principal axis,
a plurality of drive coils, each of said drive coils being positioned in a respective
one of the said stacks, and
a plurality of electrical connections connecting said sense coils; and
an eddy current instrument connected to said probe.
29. The omnidirectional eddy current inspection system of claim 28, wherein each
of said sense coils in said probe is individually monitored by said eddy current instrument.
30. The omnidirectional eddy current inspection system of claim 28, wherein each
of said sense coils within a respective one of said stacks is monitored simultaneously
through a single channel by said eddy current instrument.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to eddy current inspection and, more
specifically, to eddy current probes for non-destructive testing of conductive materials.
Eddy current inspection is a commonly used technique for non-destructive testing
of conductive materials for surface flaws. Eddy current inspection is based on
the principle of electromagnetic induction, wherein a drive coil carrying currents
induces eddy currents within a test specimen, by virtue of generating a primary
magnetic field. The eddy currents so induced in turn generate a secondary magnetic
field, which induces a potential difference in the sense coils, thereby generating
signals, which may be further analyzed for flaw detection. In case of a flaw in
the test specimen, as for example, a crack or a discontinuity, the eddy current
flow within the test specimen alters, thereby altering the signals induced in the
sense coils. This deviation in the signals may be used to indicate the flaws.
Existing systems, such as those described in commonly assigned U.S. Pat.
No. 5,389,876, Hedengren et al, "Flexible Eddy Current Surface Measurement Array
for Detecting Near Surface Flaws in a Conductive Part," function on the above-mentioned
principle. However, because magnetic fields are directional in nature, the eddy
current probes described above are limited in their utility by the fact that a
prior knowledge of crack orientation is required. This is also referred to as the
directionality of eddy current probes.
Compensation for the directionality of conventional eddy current probes
has been performed previously by repeatedly scanning a test specimen, with the
eddy current probes being rotated slightly between each scan, in order to inspect
the specimen for flaws along a number of orientations. However, this process is
laborious and time consuming. Another possible approach would be to use an array
probe designed to include number of elements formed on a substrate and slightly
rotated. However, the latter arrangement would be inconvenient, in that it would
either require a great deal of equipment or allow for a smaller scan.
Accordingly, there exists a need for an improved eddy current probe,
array probe, and inspection system that overcomes the abovementioned problems inherent
to compensating for the directionality of conventional eddy current probes.
BRIEF DESCRIPTION OF THE INVENTION
An omnidirectional eddy current probe includes a number of sense coils arranged
in a stack having a principal axis. At least two of the sense coils are rotationally
skewed about the principal axis relative to one another. The sense coils are operatively
connected to each other, and a drive coil is also positioned in the stack.
Operationally, an impulse through the drive coil induces a magnetic
influx through a conducting material specimen having a surface, thereby generating
eddy currents on the surface. Secondary magnetic field generated from the eddy
currents produces corresponding signals in the sense coils, and the signals are
then analyzed for the possibility of surface flaw in the conducting material.
According to another embodiment of the present invention, an array of stacks
as described above, forms a probe.
According to another embodiment of the invention, an omnidirectional eddy
current inspection system includes an eddy current probe. The eddy current probe
has a number of sense coils arranged in a stack, which has a principal axis. At
least two of the sense coils are rotationally skewed about the principal axis relative
to one another. A drive coil is positioned in the stack, and a number of electrical
connections connect the sense coils. The inspection system also includes an eddy
current instrument connected to the probe.
According to yet another embodiment of the invention, an omnidirectional
eddy current array probe inspection system includes an eddy current array probe.
The eddy current array probe includes multiple sense coils arranged in a number
of stacks, and each of the stacks has a principal axis. At least two of the sense
coils in a respective one of the stacks are rotationally skewed, relative to one
another, about the respective principal axis. The eddy current probe also includes
a number of drive coils, and each of the drive coils is positioned in a respective
one of the stacks. The eddy current probe also includes a number of electrical
connections, which connect the sense coils. The eddy current system also includes
an eddy current instrument connected to the eddy current probe.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other advantages and features of the invention will become
apparent upon reading the following detailed description and upon reference to
the drawings in which:
FIG. 1 illustrates an omnidirectional eddy current inspection system embodiment
of the invention;
FIG. 2 is a perspective, blown-up view of an omnidirectional eddy current probe
having a single eddy current stack;
FIG. 3 is a top view of the single eddy current stack of FIG. 2;
FIG. 4 illustrates a diamond shaped eddy current coil;
FIG. 5 depicts a rectangular eddy current coil;
FIG. 6 is a perspective, blown-up view of an omnidirectional eddy current array
probe embodiment that includes a number of eddy current stacks;
FIG. 7 is a perspective, blown-up view of another omnidirectional eddy current
array probe embodiment; and
FIG. 8 is a perspective, blown-up view of another omnidirectional eddy current
array probe, with a number of staggered layers.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
FIG. 1 shows an omnidirectional eddy current inspection system
10 including
an omnidirectional eddy current probe
100 in communication with an eddy
current instrument
130, in accordance with an embodiment of the present
invention. The omnidirectional eddy current array probe
100 is positioned
over an object to be inspected
12 having a surface
14. Exemplary
test objects
12 include conductive materials.
Referring now to FIGS. 2 and 3, an omnidirectional eddy current probe
100
is shown. A number of sense coils (or sense coil elements)
110 are positioned
on top of each other and centered about a straight line, which is called the principal
axis
114, to form a stack
112. At least two of the sense coils
110
in the stack
112 are rotated with respect to each other, resulting in a
rotationally skewed arrangement of the sense coils
110 within the stack
112, as illustrated by FIG.
3. It is noted here that an arrangement
in which a group of consecutive sense coils are not rotationally skewed with respect
to each other, but at least one of the sense coils external to the group is skewed
with respect to that group, lies within the scope of the present invention. A (meaning
at least one) drive coil
120 is positioned in the stack
112. More
particularly, the drive coil
120 is disposed about the principal axis
114.
According to a particular embodiment, the sense coils
110 are interconnected
using electrical connections (or circuitry)
124 and are further connected
to an eddy current instrument (ECI)
130. For this embodiment, the drive
coil
120 is also connected by circuitry
126 to the eddy current instrument
130, which monitors the sense coils
110 and drives the drive coils
120. Eddy current instruments are known and, hence, will not be discussed
in detail. It should be appreciated that the coils
110 and
120, and
circuitry
124 and
126 shown in the figure are merely representational,
and do not attempt to depict accurately, the coil shapes or electrical connections
formed by the circuitry.
Operationally, the eddy current instrument
130 generates a
current in the drive coil
120, which generates a magnetic flux. The magnetic
field influx into the conducting material
12 generates eddy currents on
the surface
14, which in turn generate a secondary magnetic field. In case
of a surface flaw (not shown), the secondary magnetic field generated is deviant
from its normal orientation when no flaw is present, to a direction corresponding
to the flaw orientation. This deviant secondary magnetic field induces corresponding
signals in the sense coils
110 thereby indicating the presence of the surface
flaw. A potential difference induced in each sense coil
110 is added up
by the virtue of interconnecting circuitry
124, and thereafter sensed by
the eddy current instrument
130. Due to the rotational skewing, the sense
coils
110 advantageously detect the directional deviation in the secondary
magnetic flux corresponding to any crack orientation, thereby imparting an omnidirectional
sensitivity to the probe
100.
Insulating substrate layers
116, which may desirably be flexible
substrates (also indicated by reference numeral
116), are positioned between
the sense and/or drive coils
110,
120. An exemplary flexible material
for such layers is polyimide, one example of which is Kapton™, a registered
trademark of E.I. du Pont de Nemours and Company of Wilmington, Del. More particularly,
the sense and/or drive coils
110,
120 are formed on the flexible
substrate(s)
116. To fix the flexible substrates
116 relative to
one another, the flexible substrates
116 are bonded to each other, for example
by a flexible adhesive layer (not shown), or otherwise held together in a physically
stable arrangement to form the coil stack
112.
FIGS. 4 and 5 show a few exemplary shapes of sense coils
110 or drive
coils
120, as for example, a diamond shaped coil
400 or rectangular
coil
500. It may be further appreciated that the stack
112 may include
sense coils
110 having an identical (common) geometry, as for example, diamond
shaped coils. In an alternate embodiment, one or more of the sense coils
110
within the stack
112 may have a different geometry than do the other sense
coils
110, for example, some sense coils
110 may be diamond shaped
and some maybe rectangular.
Further, according to an embodiment of the present invention, the drive
coil
120 may be one of the sense coils
110. For example, the drive
coil
120 may be selected from the sense coils
110 based on the geometry
of the sense coil
110, in order to generate a particular, desired magnetic
field. Alternatively, the drive coil
120 may be distinct from the sense
coils
110 as shown, for example, in FIG.
2.
In addition to an omnidirectional eddy current probe
100 comprising a
single
stack
112 of eddy current coils
110,
120, an omnidirectional
eddy current array probe
600 is disclosed and illustrated in FIGS. 6-8.
As shown, for example, in FIG. 6, a number of stacks
112 are arranged to
form the omnidirectional eddy current array probe
600. The probe
600
may be connected to an eddy current instrument
130, as discussed above.
The stacks
112 are described above with respect to FIGS. 2 and 3. A number
of electrical connections
124 operatively connect the eddy current coils
110,
120 within the respective stacks
112. It is appreciated
here that as shown in FIG. 6, the circuitry
124 is merely representative
of the electric connections within a stack
112.
According to a particular embodiment, each of the stacks
112 in
the probe
600 is similar, with the same number of sense coils
110
and a drive coil
120 in each of the stacks
112. More particularly,
each of the coils
110 and
120 are placed at a corresponding positional
order (level) in a stack
112. According to a more particular embodiment,
each of the coils
110,
120 has the same geometry as a respective
coil at the same level in another stack
112. The probe
600 illustrated
in FIG. 6 also includes a number of substrates
116, each of the substrates
116 being positioned between at least one pair of sense coils
110.
As noted above, the substrates
116 electrically insulate the pair of sense
coils
110. For the exemplary embodiment of FIG. 7, a number of coils (sense
110 and drive
120) are formed on a single extended insulating substrate
layer
116 which may be a flexible layer. As noted above, the extended layers
116 may be adhesively bonded to, or otherwise held in a physically stable
arrangement over similar substrate layers to form a global stack
712. As
used here, the term "global stack" refers to a stack of substrate layers
116.
Because a number of coils (sense
110 and drive
120) are formed on
each of the substrate layers, the global stack
712 encompasses a number
of individual stacks
112, as shown in FIG. 7, for example. For the exemplary
embodiment of FIG. 7, the substrates
116 are positioned on top of one another,
such that the respective sense coils
110 and drive coil
120 are aligned
along respective principal axes
114, as shown. As shown in FIG. 7, the sense
coils
110 in each of the stacks
112 are rotationally skewed with
respect to each other. Circuitry (not shown) interconnects the sense coils
110
within a stack
112. According to a particular embodiment, the circuitry
further links array probe
600 to outside instrumentation, such as an eddy
current instrument (not shown). Similarly, circuitry (not shown) connects the drive
coils
120 of the stacks
112 to exterior instrumentation, such as
an eddy current instrument. It will be appreciated that the coils
110,
120
may have identical or dissimilar geometries within a given stack
112 and
further, that the coils
110 or
120 within a particular layer of the
global stack
712 may also have identical or dissimilar geometries.
Another embodiment of the omnidirectional eddy current array probe
600
is illustrated in FIG.
8. As shown, the substrates
116, which are
desirably flexible insulating layers, are staggered with respect to adjacent layers,
so that the centers
802,
804 of the coils
110,
120
in adjacent layers are offset. Consequently, principal axes
114 of the coil
stacks
112 are inclined with respect to the substrates
112. Such
staggering of the layers advantageously affords a greater coverage to the probe
600.
It should be appreciated that in the embodiments illustrated by FIGS. 6-8, the
omnidirectional eddy current array probe
600 may also include circuitry
that connects sense coils
110 within a given level
616 or layers
716 across the coil stacks
112, in addition to connecting the coils
110 within a given coil stack
112. Similarly, the drive coils
120
may also be connected across the stacks
112. Additionally, for the embodiments
illustrated in FIGS. 6-8, a coil stack
112 may have coils
110,
120
geometrically similar or dissimilar from the respective coils
110,
120
in other coil stacks
112 in the probe
600. It should also be appreciated
that in this and related embodiments as illustrated by FIGS. 6,
7 and
8,
the drive coil
120 of a particular stack
112 may be at positioned
at a different layer than the drive coil
120 of another stack
112.
The abovementioned embodiments and equivalents thereof advantageously provide
for an omnidirectional surface flaw detection system. Although the invention may
be susceptible to various modifications and alternative forms, specific embodiments
have been shown by way of example in the drawings and have been described in detail
herein. However, it should be understood that the invention is not intended to
be limited to the particular forms disclosed. Rather, the invention is to cover
all modifications, equivalents, and alternatives falling within the spirit and
scope of the invention as defined by the following appended claims.
*
