Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
  • G01N27/82—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws
  • G01N27/90—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents
  • G01N27/9073—Recording measured data
  • G01N27/9086—Calibrating of recording device

Definitions

• the present invention relates to an eddy current control method with separate emission / reception functions, with a high dynamic range of operation. It also makes it possible to carry out checks with a set of coils of emission and reception very compact. Therefore, it is particularly advantageous for the detection of small defects, in particular for the non-destructive testing (NDT) of conductive mechanical parts.
• NDT non-destructive testing
• fem abbreviated electromotive force
• a defect can significantly alter the mechanical strength of a thin part, even if it is small.
• the principle of defect detection by Eddy currents in a conductive part consists in emitting in the vicinity of this part, using a transmitting coil, an electromagnetic field of frequency adapted to the conductivity of this material and to the depth of the desired defects.
• an electromotive force is measured at the terminals of the receiver coil due to the direct coupling of the magnetic field lines between the transmitting coil and the receiver coil in the presence of the conductive part and, secondly, a small electromotive force variation. which is superimposed on it when there is a defect in the material.
• the invention is limited to processes using at least one coil assigned to the emission of the electromagnetic signal capable of generating eddy currents in the material to be tested, and at least one coil assigned to the reception of the signals induced by the eddy currents (configuration called with separate functions).
• the electromotive force V R induced at the terminals of each receiving coil is obviously at the same frequency as the current I E sent into the associated transmitting coil, and requires demodulation to obtain the wanted signal.
• this induced electromotive force V R varies very strongly when approaching a faultless part at the working distance. In the presence of a fault, the complex induced electromotive force V R becomes V R ⁇ ⁇ V R , and only the variation ⁇ V R , very small in front of V R , carries information.
• determines the quality of the measurement and the sensitivity of the process.
• the detection electronics must therefore have a very great dynamic of operation. Given the technological possibilities, this constraint very strongly limits, in the prior art, the possibility of detecting defects of small dimensions, especially when they are badly oriented. Any defects in the material to be tested are all the easier to detect as they further modify the flow of eddy currents. These circulate in the thickness of the test material along a path comparable to the current lines of the inductor coil, but in the opposite direction. It is easier to detect the defects extending in the plane formed by the axes of the transmitting coil and the receiver coil, and placed between them (type I defects). Conversely, it is difficult to detect defects extending in the mediating plane to the plane formed by the axes of the two coils (so-called type II defects).
• Foucault leads to the detection of very small complex variations ⁇ V R of V R , around the much larger value of V R , which varies in large proportions with the distance from the coils to the part to be controlled, as well as their relative orientation; it also varies, to a lesser extent, with the conductivity of this part, a high conductivity being more favorable. This difficulty, aggravated by the small size of the defects to be detected, is also due to their orientation.
• small-size fault detection is the small size of the transducer coils (small patterns), which leads to detected signals of very low amplitude.
• Eddy current probe arrays a device using matrices or eddy-current sensor arrays, whose coils are made on flexible support to remain as close as possible to the defects when the test piece is of curved geometry, and are further spatially correlated.
• the inductors consist of two rectangular coils very elongated in the direction orthogonal to the scan. Faced with these two inductors, two rows of receiver coils are arranged staggered vis-à-vis the first row of coils.
• any fault located between two receiving coils of the first row is located above the coils of the second row in the preferred direction of scanning, and vice versa. Nevertheless, despite the cost and heaviness of such a device, the defects difficult to detect because of their orientation relative to the first row of coils keep this same orientation, and therefore this same difficulty of detection, compared to the second row of receiver coils. Finally this document specifies several embodiments of the coils and the methods of adding a shield. The receiver coils all receive on their entire surface the field lines immediately emerging from the corresponding transmitter coil (large mutual inductance).
• Apparatus for near surface nondestructive eddy current scanning of a conductive part using a multi-layer eddy current probe array discloses a device, similar to the previous one, but implemented in a multiplexed manner.
• the current state of the eddy current control methods and devices does not make it possible to be certain of the detection of dimensional defects detrimental to the strength of certain mechanical parts, in particular when the size of the defects or their orientation. is unfavorable to their detection.
• the invention relates to a method of producing an assembly of at least one transmitting coil and a receiving coil for an eddy current control, the receiving coil receiving in the absence of defect a complex amplitude signal V R , subjected to a variation ⁇ V R in the presence of a standard defect to be detected, characterized in that one chooses the distance ⁇ ER between the axes of the coils of emission and reception of to maximize the ratio
• Each coil is composed of turns, generally of several dimensions.
• the widest turn describes a loop which is called R the greatest distance from its center of gravity.
• R R M along the axis of maximum dimension
• R m R M along the minimum dimension axis.
• the method according to the invention aims to perform the eddy current control by placing and maintaining between the respective axes Ai and A 2 of two transmitting flat coils Bi and B 2 receiver, a distance comparable or equal to ⁇ ERO which optimizes the ratio
• the process according to the invention is involved in the design and the realization of the transducer head, after the characteristics of the material to be controlled, the value of the air gaps e and e 'between this piece and each of the coils, made it possible to determine the working frequency, the shape and the size of the coils whose largest radius is R.
• the greatest distance between the center of gravity of the largest dimension coil and the point farthest from the largest turn of this coil is called R, the following steps: a- determining a value of the frequency of the excitation current flowing through the transmission coil, this frequency being determined in a conventional manner; b- determining a standard defect to be detected, characterized by its size and average depth relative to the surface of the part to be controlled; c- from the values obtained in steps a and b to determine, either by modeling or experimentally, the following three variables: i) the complex V R emf induced in the receiver coil when the distance ⁇ E R between the coil axes of transmission and reception varies at least in the interval ⁇ 0; 3R ⁇ , ii) change .DELTA.V R, the complex V R emf induced in a receiver coil for the same change in distance ⁇ E R in the range of at least ⁇ 0; 3R ⁇ , iii) the variation
• the distance between the respective axes of each pair of transmit / receive coils is fixed and the frequency of the excitation current is adjusted according to the minimum dimension and the mean depth of the standard defects to be detected.
• the excitation electronics it is necessary for the excitation electronics to be capable of modifying the working frequency of the electronic means associated with the coils, for example whenever the size of the standard defects to be detected is modified, or else if changes the material of the part to be controlled.
• electronic associated with the coils is meant electronic means for supplying current to the transmission coil (s), for demodulating and processing the signals of the reception coil (s), and possibly for adding, subtracting or multiplex signals from several coils.
• the excitation frequency is constant, and the method according to the invention makes it possible to determine, as a function of the minimum dimension and the mean depth of the standard defects to be detected, an optimum value (step d). or suboptimal (step e) of the distance e ⁇ R between the respective axes of each pair of transmitting and receiving coils.
• the distance ⁇ E R between the respective axes Al and A2 of the two coils Bi respectively transmitting and receiving B 2 varies in the range ⁇ 0; 3R ⁇ .
• This first variant is particularly advantageous for the detection of small defects.
• the distance ⁇ ER between the respective axes Ai and A 2 of two coils respectively transmitting Bi and B 2 receiver varies in a range greater than ⁇ 0; 3R ⁇ , and preferably equal to ⁇ 0; 9R ⁇ . In this case, there is generally, for abscissa greater than 3R, a second maximum of the ratio
• the distance ⁇ ER between the respective axes Ai and A 2 of two coils respectively transmitting Bi and B 2 receiver is carried out in step g adjustably.
• the transmitting coils are on a first support, for example a first printed circuit
• the receiving coils are on a second support, for example a second printed circuit
• the two supports can move relative to each other. the other through sliding means.
• These means allow not only an adjustable sliding of the relative position of the two supports, but also its maintenance during the measurement phases, once the control head is made. They can be passive of the mechanical type (for example with screw and / or slide), or active comprising at least one micro-actuator (for example piezoelectric).
• the coils have an axial section of elongate shape, the widest turn having a large radius R M and a small radius Rm, it is possible to apply to each of the embodiments described above the variant below.
• the application of the invention makes it possible to define a first optimum distance ( ⁇ E Ro) Ma ⁇ and an associated range of values ⁇ min; ⁇ Max ⁇ Ma ⁇ / whereas in the plane comprising the axis of the coil and the small radius R m .
• the invention makes it possible to define a second optimal distance ( ⁇ ER0 ) associated min and a second range of values ⁇ min; ⁇ Max ⁇ min ..
• the existence of several optimal distances along several axes thus makes it possible to produce patterns where the coils are not necessarily at the vertices of squares or lozenges. Such a variant will be further illustrated by FIGS. 7b, 7c and 8b.
• Step c of the process can be determined either by modeling or experimentally using a device similar to that described below by way of example.
• the two flat coils Bi for the emission and B 2 for the reception are each made on a thin kapton printed circuit, of identical dimensions: 6 spiral plane spirals, the widest of which has a radius R of 0.5 mm and the smaller one has the diameter of the central metallized hole used to pass the connection. They can slide against each other.
• the respective axes A 1 and A 2 of Bi and B 2 can thus have a variable distance ⁇ ER between them.
• a standard defect is fixed corresponding to either the type of defect the smallest that one wishes to detect, or to a defect considered representative.
• a parallelepipedal defect elongated in a main direction we choose a parallelepipedal defect elongated in a main direction, and measuring in this direction 0.4 mm, and in other directions 0.1 mm wide (parallel to the surface) and 0.2 mm deep . It is flush with the surface of the room to be controlled.
• the orientation used for the modelizations or the experiments is that which maximizes the probability of detection: the length of 0.4 mm is centered on the axis connecting the centers of the coils.
• the part to be tested has a conductivity ⁇ of 1 MS / m and a thickness of 3 mm.
• the working frequency is chosen equal to 2 MHz.
• the pair of transmitting / receiving coils is then placed in front of the part to be inspected, at a distance e from the nearest coil (for example the receiving coil) and e 'of the other coil, the distance e. e being the sum of the axial length of the nearest coil and the thickness of the support.
• This distance e is chosen with the help of the usual practice of eddy current checks.
• the transmitter coil is excited by a current I E at a frequency adequate to induce eddy currents.
• the receiver coil is then the seat of an electromotive force V R induced at its terminals.
• the phase ⁇ that presents V R with respect to I E changes between the position where the axes Ai and A 2 are almost identical, and the position where these axes are separated by about two times R or slightly more. Between these two positions, there is an intermediate position where the phase ⁇ varies very suddenly and where the module of
• the modulus of the electromotive force increases again without reaching a value as high as that of the first maximum, then decreases, but with a phase which varies more slowly.
• Figure la shows the module
• the phase variation is less abrupt, according to a profile depending on the values of ⁇ and e, and the modulus of the complex amplitude of V R passes through a minimum which is no longer equal to zero, and whose position and value depend in particular on the values of ⁇ , gaps e and frequency.
• the modulus of the complex amplitude of V R passes through a minimum which is no longer equal to zero, and whose position and value depend in particular on the values of ⁇ , gaps e and frequency.
• it is the appearance of an imaginary component, not canceling for the same abscissa as the real component, which has the effect of shifting the position of this minimum and making its non-zero value.
• the method according to the invention for producing a set of transducer coils allows numerous variants and combinations, provided that for each pair of transmission coils / reception, their axes Ai and A 2 are separated by a distance ⁇ ER within the range of distances ⁇ min, ⁇ Max ⁇ .
• the coils are flat, that is to say that their axial length is more weak than the largest radius of their largest turn.
• Figures 3a, 3b and 3c are similar to Figures Ic Ic, but the main length of the defect here is 2 mm; and Figures 4a, 4b and 4c are similar to the previous ones with a main defect length of 3 mm.
• the method inherently allows each pair of transmit / receive coils a virtual cancellation of the electromotive force V R induced at the terminals of the receiving coil, it is possible to choose to use, according to a first variant, a transmission coil and two reception coils located symmetrically and connected in opposition, or two emission coils located symmetrically with respect to the same receiving coil and connected in opposition. This produces a differential device, but free from the main defect of the differential devices not implement the process.
• the electromotive force V R induced at the terminals of each receiver coil is intrinsically very close to zero and the slope of the curve representing
• the steps c, d and e of the method can be written in an equivalent manner: - c'- from the values obtained in steps a and b to determine, either by modeling or experimentally, the variation ⁇ V R , of the a complex emf V R induced in a receiver coil when the distance ⁇ ER between the axes of the transmitting and receiving coils varies at least in the interval ⁇ 0; 3R ⁇
• -e'- optionally, determine a range of distances ⁇ min; ⁇ Max ⁇ on both sides of ⁇ ER0 , for which the ratio
• a preferred application of this variant is to determine as previously the optimal value ⁇ ER0 of ⁇ ER or a suboptimal value in the range ⁇ min; ⁇ Max ⁇ and vary when certain use conditions such as the nature of the part to be inspected or the size of defects, using the present embodiment for adjusting the distance ⁇ E R. More elaborate combinations will be discussed later in the detailed description.
• FIGS. 2a, 2b and 2c are similar to FIGS. 1a, 1b and 1c, but for a defect of 1 mm in length
• FIGS. 3a, 3b and 3c are similar to FIGS. 1a, 1b and 1c, but for a defect 2 mm long
• FIGS. 4a, 4b and 4c are similar to FIGS. 1a, 1b and 1c, but for a defect 3mm long
• FIG. 5a and 5b show schematically the two coils of a basic system for measuring eddy currents according to the invention
• FIG. 6 shows the variations required for the excitation frequency to keep the same optimum distance ⁇ ER o when the main dimension of the defect varies
• FIGS. 7a, 7b and 7c schematize the three coils of an alternative embodiment of an eddy current measuring system according to the invention
• FIGS. 8a and 8b schematize the five coils of an alternative embodiment of an eddy current measuring system according to the invention
• FIG. 9 schematizes a variant of the system presented in FIG. 5a including the addition of a ferromagnetic strip which channels the magnetic field lines between the transmitter and the receiver.
• FIGS. 10a and 10b schematize two embodiments in which the distance ⁇ ER between the coils is adjustable mechanically (FIG. 10a) or by piezoelectric micro-actuator (FIG. 10b)
• FIG. 11 schematizes an example of matrix association according to the method of the invention of several couples of transmit / receive coils.
• the main parameters are those exposed in the explanation of step c.
• the part to be tested has a conductivity ⁇ of 1 MS / m and a thickness of 3 mm.
• the coils are on air, directly etched on both sides of the same kapton flexible printed circuit 50 ⁇ m thick.
• a 100 ⁇ m thick Teflon protective film is applied to the kapton face in contact with the target, providing electrical insulation and mechanical protection.
• the same pattern is chosen for the transmit and receive coils, composed of a planar spiral whose largest diameter is 1 mm, and comprising 6 turns etched in copper of thickness 5 ⁇ m, the smallest turn having the diameter of the metallized hole providing the electrical connection, ie approximately 0.25 mm.
• the corresponding working frequency is around 2 MHz.
• Is considered in the transmitter coil an inductor current I E taken equal to 20mA; the module
• Modeling in the first variant of the second preferred embodiment leads to the drawn curves, Ib and Ic for a distance ⁇ R E between the axes of the transmitting and receiving coils varying in the range ⁇ 0; 3R ⁇ , i.e. ⁇ 0; 1.5 mm ⁇ .
• the transmitter coil B1 is shown at the top, and the receiver coil B2 is shown at the bottom, but the invention would not be changed by inverting them.
• the insulating support 1 is a soft kapton film 50 ⁇ m thick.
• the coil connections 4 use metallized holes whenever necessary to pass from one side to the other of the dielectric support. Thus all the connections are brought to a single face of the printed circuit.
• the working frequency can be adjusted when the characteristics of the defects or the nature of the piece to be controlled vary.
• the initial frequency of 2 MHz must increase to approximately 2.45 MHz to maintain the same optimum distance ⁇ ER0 .
• the operating frequency is fixed, and the optimum ⁇ ER0 distance ⁇ R E between the axes of the transmitter and receiver coils is determined as described above in the case of the first variant in which the distance ⁇ E R between the respective axes Al and A2 of the two coils Bi respectively transmitting and receiving B 2 varies in the range ⁇ 0; 3R ⁇ .
• the distance between the respective axes of each pair of transmit / receive coils is fixed and the frequency of the excitation current is adjusted according to the dimension. minimum and the average depth of the standard defects to be detected.
• the part to be tested has a conductivity ⁇ of 1 MS / m and a thickness of 3 mm
• the coils are on air, directly etched on both sides of the same flexible kapton circuit of 50 ⁇ m. thickness.
• the most frequent defects being generally very long elongated in a main direction, they are classified into different types according to the inclination of their largest axis with the plane formed by the axes Al and A2 of a pair of coils of transmission / reception.
• they are said to be of type I, when their largest axis is in the plane defined by the axes Al and A2, or at the parallel rigor and situated at a short distance in front of the radius R.
• a receiver coil arranged at a location such that the electromagnetic field produced by the two transmitting coils is canceled at this receiver coil, the distance between the receiver coil and each transmitting coils being around the range of distances ⁇ min; ⁇ Max ⁇ located around ⁇ ERO -
• this configuration makes it difficult to detect so-called type II defects.
• FIG. 7a represents an implementation variant, mainly intended to overcome the edge effects of the parts to be controlled, and possibly to improve slightly the detection of type II defects. It comprises a pattern of three coils, a priori a central transmitting coil B1 and two receiving coils B2 and B3 situated on either side and distant from that of transmitting a value lying in the range ⁇ ⁇ min; ⁇ Max ⁇ . But we would not change the performance by assigning a reception function to the central coil, and a transmission function to the two side coils. We thus obtain a basic pattern consisting of three coils, one of reception located in the center and two of emission, located on both sides, and distant from that of emission of a value included in the range ⁇ min; ⁇ Max ⁇ . The windings are in the same direction.
• the scanning direction is orthogonal to a direction passing through the axes A2 and A3, and the asymmetry of the mutual introduced by the edge of the part does not affect in the same manner the two receiving coils B2 and B3.
• it is important to correct it by introducing, for example at the level of the demodulation means of the signals coming from the coils B2 and B3, an offset (offset) of amplitude and / or phase.
• offset offset of amplitude and / or phase
• FIG. 7b represents another variant, similar to that of FIG. 7a, but in the particular case where the coils have an axial section of elongate shape, the widest turn having a large radius R M and a small radius R m .
• the application of the invention allows to define a first maximum distance ( ⁇ E Ro) mm and a range of values associated ⁇ min; ⁇ Max ⁇ min .
• the plane comprising the axis of the coil and the large radius R M / the invention makes it possible to define a second optimum distance ( ⁇ E Ro) ma ⁇ associated and a second range of values ⁇ min; ⁇ Max ⁇ max .
• the operation is equivalent by choosing the receiver coil B1 and the two emitter coils B2 and B3.
• the proximity of a coin edge inducing a mutual difference between the pairs of coils B1 / B2 and B1 / B3 can be compensated at the supply means of the coils B2 and B3 in alternating current, in generating signals of different amplitudes and / or phases, able to compensate for this asymmetry.
• a lack of symmetry between these coils (systematic error) can also be corrected in this way.
• This second embodiment with a pattern with three coils makes it possible to increase the density of the patterns when scanning in a direction orthogonal to the plane containing the three axes, and thus improves the detection of type I defects. On the other hand, it does not improve the detection of the defects of type II.
• the plane comprising the three axes of the coils is placed parallel to the edge of the part. It is then possible to wire the two receiving coils in differential mode, which makes it possible to eliminate the disturbance induced by the proximity of the edge of the part. More generally, such a differential configuration minimizes the effects of distance variation between the transmitting coil and the receiver, which allows less sensitivity to distance differences when producing coils.
• the detection of Type II defects is improved by a refinement of the pattern comprising a receiving central coil B1 and the two coils B2 and B3 emitting on either side.
• This improvement is characterized in that two additional receiver coils B4 and B5 (FIG. 8a) associated respectively with each transmitting coil B2 and B3 are added at a distance in the range of distances ⁇ min; ⁇ Max ⁇ located around ⁇ ERO / and in a direction substantially perpendicular to the plane passing through the axes of these transmitting coils.
• These second and third receiver coils make it possible to detect elongated defects in this perpendicular direction (of type II), the distance between each transmitting coil and the receiver coil being optimized for the detection of these defects in this direction.
• FIG. 8a which represents a third embodiment.
• the coils B2 (20) and B3 (30) of axes A2 and A3, located on a first face of a printed circuit, are emitter coils, receiving electronic excitation means 34 an alternating current at the frequency of chosen excitation.
• the detection is ensured by a set of three receiving coils B1 (10), B4 (40) and B5 (50) of axes A1, A4 and A5, situated on the second face of the printed circuit and connected to preamplification and detection means 35.
• the axes A2, A3, Al, A4, A5 are parallel to each other.
• the coil B1 has its axis Al located preferentially in the plane defined by A2 and A3 and necessarily equidistant from these two axes by a distance d belonging to the range of distances ⁇ d.
• the signal it delivers is applied to the input of a first measurement channel.
• the coil B4 has its axis A4 located at a distance d, belonging to the range of distances ⁇ d, of A2 and defining with A2 a plane orthogonal to the plane defined by A2 and A3.
• the coil B5 has its axis A5 located at a distance d from A3, d belonging to the range of distances ⁇ d, and defining with A3 a plane orthogonal to the plane defined by A2 and A3.
• the two coils B4 and B5 are connected in series or in opposition, to form the same signal source, applied to a second measurement channel of an amplifier 40.
• FIG. 8b shows a variant of the coils of FIG. 8a in the particular case where the coils have an axial section of elongate shape, the widest turn having a large radius R M and a small radius Rm.
• the application of the invention makes it possible to define a first optimum distance ( ⁇ E Ro) Ma ⁇ and an associated range of values ⁇ min; ⁇ Max ⁇ Ma ⁇ / whereas in the plane comprising the axis of the coil and the small radius R m .
• the invention allows defining a second maximum distance ( ⁇ E Ro) mm and associated a second range of values ⁇ min; ⁇ Max ⁇ min ..
• this variant which can be cumulated with all the preceding and following embodiments, is characterized in that the emission and reception coils have an elongate axial section, the widest coil having on the one hand a small radius Rm, determining in its orientation a range of distance ⁇ min; ⁇ Max ⁇ equal to ⁇ min; ⁇ Max ⁇ min in which is chosen the distance between the axes of turns in this orientation, and secondly a large radius R M determining a range of distance ⁇ min; ⁇ Max ⁇ equal to ⁇ min; ⁇ Max ⁇ Ma ⁇ - in which is chosen the distance between the axes of the turns according to this orientation.
• the preamplification and detection means (35) comprise a first preamplifier receiving the signals from the measuring channel coming from the coil B1, a first preamplifier receiving the signals from the measuring channel coming from the coils B4 and B5, and electronic means of demodulation and processing. They are designed to determine the difference between the peak values of the emf. existing between the two measurement channels.
• the resulting information possibly improved by corrections or filtering known to those skilled in the art, provides good detection of all defects, regardless of their orientation. If the test area is close to the edge of the test piece, playing on the intensity of the currents and their phase eliminates the mutual for each line of movement along the edge of the room.
• Providing two transmitting coils B2 and B3 also makes it possible to compensate, by a control electronics, the symmetry defects between the coils B2 and B3. For this purpose, this compensation is performed by phase and / or amplitude variations.
• the magnetic field lines are channeled and improves the signal-to-noise ratio of the device by implanting, in the vicinity of the coils and on the side opposite the part to be controlled, a soft magnetic material (weak hysteresis), for example ferromagnetic.
• a soft magnetic material weak hysteresis
• the magnetic material may for example consist of ferrite plates.
• Figure 9 shows a variant of the system shown in Figure 5a including the addition of a ferromagnetic tape (9) as described above. It channels the magnetic field lines between the transmitter and the receiver.
• a ferromagnetic tape 9 as described above. It channels the magnetic field lines between the transmitter and the receiver.
• an insulating layer 8 is inserted between the ribbon and the printed circuit engraved on the kapton 1.
• FIGS. IQa and IQb schematically a variant combinable with all other variants.
• the transmission coils are located on a first insulating support 1
• the receiver coils (not shown) are located on a second insulating support 11 in contact with the first, and at least one device to change the distance ⁇ E between R coils or pairs of transmitting / receiving coils.
• this device is mechanical.
• the ends of the first insulating support 1 are glued to an end support 2 having two threaded holes, while the ends of the second insulating support 11 are glued to an end support 12 having two holes of diameter greater than the threads of the support 2.
• between the parts 2 and 12 are interposed elastic strips 13 made of elastomer, more or less compressed by the screw 14 so as to change the distance ⁇ R E between the axes of each pair of transmitting / receiving coils.
• the device for changing the distance ⁇ E R between the pairs of coils transmitting / receiving comprises at least one active mechanical device (micro actuator) that allows to change the distance ⁇ E between R coils of at least one transmitting torque.
• FIG. 10b is therefore identical to FIG. 10a, except the elastic bands 13 which are here replaced by piezoelectric micro-actuators 14 fed by electrical conductors 15.
• the invention can be combined with the known technique of associating a plurality of transmit and receive coils into a matrix of transducer coils.
• Each of the above embodiments, or a combination of these modes may thus be reproduced a plurality of times in one or two dimensions, each representing a step of measurement.
• the two receiver coils mounted to detect the second type of fault are arranged in series or in opposition.
• the method according to the invention is implemented by coils on air, etched on a flexible double-sided printed circuit, one of which the faces carrying the transmitting coils, and the other the receiving coils.
• a spatial resolution of the defects substantially greater than the resolution obtained with the devices operating in separate functions as they exist according to the prior state of the art is obtained.
• the gain is noticeable on the parameter
• a printed circuit technology for producing the coils is advantageous for the implementation of the invention.
• This printed circuit is advantageously flexible, like those that can be achieved with kapton, for certain types of parts to control, given the importance of maintaining a constant very small air gap.
• the present invention may be advantageously combined with a matrix structure for the transmitting and / or receiving coils.
• the eddy current measuring device comprises a pattern of at least two flat coils Bi, B 2 according to the invention, this pattern being repeated a plurality of times so as to constitute a detection matrix
• the associated electronics include means for multiplexing the transmitting coils and demultiplexing the receiver coils.
• FIG. 11 An embodiment of this type (matrix or bar configuration) is shown schematically in FIG. 11. The succession of transmission / reception coil pairs is organized on two lines, orthogonal to the direction of displacement, and offset laterally. half a step to improve the probability of detection.
• the electronic processing means of the signals from the receiver coils can be constituted by any type of circuit for measuring the fem of a coil at its terminals.
• This circuit optionally includes one (or more) amplification stage (s) followed by a demodulation stage intended to suppress the excitation frequency of the inductor coil or coils.
• the invention is compatible with all existing electronic supply of the transmitting coils and signal processing from the receiving coils. It is simply necessary to ensure, if one wishes to invert the transmission and reception functions of certain coils, that the used electronics accept coils of the same impedance for these two functions.

Landscapes

• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Physics & Mathematics (AREA)
• Health & Medical Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Analytical Chemistry (AREA)
• Biochemistry (AREA)
• General Health & Medical Sciences (AREA)
• General Physics & Mathematics (AREA)
• Immunology (AREA)
• Pathology (AREA)
• Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=36390271

Family Applications (1)

Country Status (2)

Families Citing this family (1)

Citations (2)

Family Cites Families (5)

• 2006
  • 2006-01-27 EP EP06709453A patent/EP1848989A1/de not_active Ceased
  • 2006-01-27 WO PCT/FR2006/050069 patent/WO2006082334A1/fr active Application Filing

Patent Citations (2)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events