# US 8,274,282 B2 · Method for assembling a high-dynamic and high-spatial resolution eddy current testing head

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- Number: US 8,274,282 B2
- Document ID: US8274282B2
- Status: Granted
- Kind: B2
- Application number: 11/815,293
- Filed: 2006-01-27
- Published: 2010-06-10
- Granted: 2012-09-25
- Earliest claimed: 2005-02-04
- Assignees: Commissariat a l'Energie Atomique
- Inventors: Jean-Marc Decitre; Thierry Sollier
- Web page: https://patentgrep.com/patent/US8274282B2

## CPC

- G01N 27/9046: {by analysing electrical signals}
- Y10T 29/49007: Indicating transducer
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

The invention concerns a method for producing an assembly of at least one transmission coil (B1) and one reception coil (B2) for eddy current testing, the reception coil receiving in the absence of fault a complex amplitude signal VR, subject to a variation δVR in the presence of a characteristic fault to be detected. The method consists in selecting the distance ΔER between the axes of the transmission coil and the reception coil so as to maximize the ratio IδVR/VRI.

## Claims

### Claim 1

A method for assembling an assembly of at least one transmission coil and one receiving coil for eddy current testing, the receiving coil receiving, in the absence of a flaw, a complex amplitude signal, VR, subjected to a variation in the presence of a standard flaw to be detected, δVR, the method including selecting a distance ΔER between respective axes of the transmission and receiving coils that maximizes an absolute value of a ratio of (a) the variation (δVR) in the presence of the standard flaw to be detected to (b) the complex amplitude (VR) in the absence of the flaw.

### Claim 2 (depends on 1)

A method according to claim 1, in which R is a greatest distance between a baric centre of one of the coils having a dimension larger than the dimension of any other of the coils and a point furthest away from a largest wire winding of the one coil, such method comprising:
a—determining a frequency value of an exitation current running along the transmission coil;
b—determining a further value representing a standard flaw to be detected, characterised by an average size and depth of the standard flaw in relation to a surface to be tested;
c—using the values determined in steps a and b, determining values representing three flaw sizes, either through modelling or by experiment:
i) determining the VR emf complex induced inside the receiving coil when a distance, ΔER, between the axes of the transmission and receiving coils varies at least within a {0; 3R} gap,
ii) determining the δVR variation of the VR emf complex induced inside the receiving coil for the ΔER distance variation within the gap of at least {0; 3R},
iii) determining the variation of the ratio |δVR/VR| for the values obtained in ii) and i), for the ΔER distance variation within the gap of at least {0; 3R},
d—determining a course of the |δVR/VR| ratio curve depending on the ΔER distance variation within the gap of at least {0; 3R}, and then determining a maximal |δVR/VR|0 ordinate and of the ΔERO abscissa of this maximum, such value constituting an optimal operating point;
e—as an optimal and sub-optimal solution, determining a range of {Δmin; ΔMax} distances on either side of ΔERO, for which the |δVR/VR| ratio corresponds to one third of its maximal value;
f—if the ΔER values found during the optimal step d or during the sub-optimal step e are not considered acceptable, then modifying the parameters obtained in steps a and b;
g—adjusting the coils or assembly of the coils, in such a manner that the operating point of each receiving coil corresponds to either the optimal criteria of step d or the sub-optimal criteria of step e.

### Claim 3 (depends on 2)

A method according to claim 2, wherein the distance between the respective axes of each transmission/receiving coil combination is fixed and the frequency of the excitation current is adjusted in accordance with a minimal dimension and the average depth of the standard flaws to be detected.

### Claim 4 (depends on 2)

A method according to claim 2, wherein the excitation frequency is constant, the method further including the step of determining, according to the minimal dimension and the average depth of the standard flaws to be detected, a value, either optimal (step d) or sub-optimal (step e), of the ΔER distance between the respective axes of each transmission/receiving coil combination.

### Claim 5 (depends on 2, 3, 4)

A method according to one of the claims 2 to 4, wherein the ΔER distance between the respective axes (A1 and A2) of two coils, respectively (B1) transmitter and (B2) receiver, varies within a {0; 3R} gap.

### Claim 6 (depends on 2, 3, 4)

A method according to one of the claims 2 to 4, wherein the ΔER distance between the respective axes (A1 and A2) of two coils, respectively (B1) transmitter and (B2) receiver, varies within a gap exceeding {0; 3R}, and the method further includes the step of determining for an upper abscissa at 3R a second maximum of the |δVR/VR| ratio obtained during step d, such second maximum being associated with a second range of values {Δmin; ΔMax}2 on either side of ΔERO2, obtained during step e, for which the |δVR/VR| ratio corresponds to one third of its maximal |δVR/VR|2 value.

### Claim 7 (depends on 2)

A method according to claim 2, further including the step of adjusting the ΔER distance between the respective axes (A1 and A2) of two coils, respectively (B1) transmitter and (B2) receiver.

### Claim 8 (depends on 7)

A method according to claim 7, wherein the step of adjusting the ΔER distance includes using mechanical and passive means.

### Claim 9 (depends on 7)

A method according to claim 7, wherein the step of adjusting the ΔER distance includes using at least one micro-actuator.

### Claim 10 (depends on 2, 3, 4, 7, 8, 9)

A method according to any one of the claims 2 to 4 and 7 to 9, wherein the coils have an elongated axial section, a widest wire winding having a big radius RM and a small radius RM, and wherein, within the plane including the coil's axis and the big axis RM define a first optimal distance (ΔERO)Max and a range of associated values {Δmin; ΔMax}Max, while within the plane including the coil's axis and the small axis Rm defines a second associated optimal distance (ΔERO)min and a second range of values {Δmin; ΔMax}min.

### Claim 11

A method according to any one of the claims to 4 and 7 to 9, wherein the assembly of at least one transmission coil and one receiving coil comprises an elementary pattern constituted of three coils, one transmission coil (B1), located in a central position, and two receiving coils (B2) and (B3), located on either side of the transmission coil and distant from the transmission coil by a value within a range {Δmin; ΔMax}.

### Claim 12

A method according to any one of the claims to 4 and 7 to 9, wherein the assembly of at least one transmission coil and one receiving coil comprises an elementary pattern constituted of three coils, one receiving central coil (B1) and two transmission coils (B2) and (B3), located on either side and distant from the transmission coil by a value within a range {Δmin; ΔMax}.

### Claim 13 (depends on 2, 3, 4, 7, 8, 9)

A method according to any one of the claims 2 to 4 and 7 to 9, wherein the assembly of at least one transmission coil and one receiving coil comprises an elementary pattern constituted of three coils, one receiving central coil (B1) and two transmitter coils (B2) and (B3), located on either side of the receiving coil.

### Claim 14 (depends on 13)

A method according to claim 13, wherein the elementary pattern further comprises two other receiving coils (B4 and B5), respectively associated with each transmission coil (B2 and B3), at a distance within the distance range {Δmin; ΔMax} located around ΔERO and in a direction approximately perpendicular to a plane passing through the axes of the transmitter coils.

### Claim 15 (depends on 2, 3, 4, 7, 8, 9)

A method according to one of the claims 2 to 4 and 7 to 9 and wherein, with reference to step e, the transmission and receiving coils have an elongated axial section, a widest wire winding having, on either side, a small radius Rm, determining, in accordance with its orientation, a {Δmin; ΔMax} distance range equal to {Δmin; ΔMax}min in which is chosen a distance between the wire winding axes in accordance with such orientation, and on the other side a big radius RM, determining a {Δmin; ΔMax} distance range equal to {Δmin; ΔMax}max, in which is chosen the distance between the wire winding axes in accordance with such orientation.

### Claim 16 (depends on 1, 2, 3, 4, 7, 8, 9)

A method according to one of claims 1 to 4 and 7 to 9, wherein the transmission and the receiving coils constitute a pattern, repeated several times over in such a manner as to create a detection matrix, wherein the assembly is associated with electronic means for excitation and for processing the signals, the excitation and processing comprising multiplexing the signals to the transmitter coils and demultiplexing the signals from the receiving coils.

### Claim 17 (depends on 1, 2, 3, 4, 7, 8, 9)

A method according to any one of claims 1 to 4 and 7 to 9, wherein, in the vicinity of the coils and on a side opposite a part to be controlled, exists soft magnetic material serving to reduce the reluctance of the magnetic circuit of each transmission/receiving coil combination.

### Claim 18 (depends on 2)

A method according to claim 2, further including the step of, after obtaining a first optimal or sub-optimal value of the ΔER distance, readjusting such value according to a plurality of parameter variations by respectively replacing steps c, d and e by the following steps c′, d′ and e′:
c′—using the values obtained during steps a and b, determining, either by modelling or by experiment, the δVR variation of the VR emf complex induced inside a receiving coil when the ΔER distance between the axes of the transmission and receiving coils varies at least within the {0; 3R} gap;
d′—tracing a curve of the |δVR| values according to the ΔER distance variation within the gap of at least {0; 3R}, then determining the maximal |δVR|0 ordinate and the ΔERO abscissa of this maximum, such value constituting the optimal operating point;
e′—determining a range of {Δmin; ΔMax} distances on either side of ΔERO, for which the |δVR| ratio corresponds to one third of its maximal value.