NO20211546A1

NO20211546A1 -

Info

Publication number: NO20211546A1
Application number: NO20211546A
Authority: NO
Priority date: 2021-12-20
Filing date: 2021-12-20
Publication date: 2023-04-24
Also published as: WO2023121475A1; NO347046B1

Description

Eddy current sensor

The present invention is related to an eddy current sensor according to the preamble of claim 1.

Background

For eddy current measurements one and the same coil with only one winding can be used as both transmitter (magnetizer) and receiver, because it is possible to make impedance measuring instruments that separate the electromagnetic wave that is transmitted into the coil from the backscattered wave returning from the coil. The signal sent into the coil is normally much stronger than the signal returning. Both signals must be measured at the same time, which according to prior art has been done by using linear receivers. For such an absolute coil arrangement, it is thus high demands for dynamic range on the measurement equipment. In such a measurement, the strong transmitter signal into the coil will have to be withdrawn with high precision to find the actual signal returning from a metallic measurement object.

The use of ACFM (alternating current field measurement) has been established as a standard for detecting and measurement of a defect, such as cracks, in different metallic measurement objects, such as surfaces, welding seams, etc.

For ACFM, two magnetic flux components are measured. One is Bx, which lies in longitudinal direction of the defect, in the same direction as the magnetization, and the second one is Bz, perpendicularly to the surface and thus perpendicular to the magnetization. A common solution for ACFM sensor probes is to use a magnetizer coil in longitudinal direction and then two different receivers, one for the Bx, and another receiver for the orthogonal Bz magnetic flux component.

Bz is therefore measured by means of a differential technique where it is established a balance such that strong signals from the magnetizer is nulled as a consequence of orthogonal orientation by the Bz sensor in relation to magnetizing flux in X-direction.

From US5068608 A it is known a multiple coil eddy current probe system and method for determining the length of a discontinuity. The probe system makes use of a plurality of eddy current coils mutually separated at known distances with respect to each other along the longitudinal axis of the probe, and an eddy current coil actuating device for separately and independently actuating each of the coils to provide an adjustable electromagnetic sensing field.

In US7489129 BB is disclosed a method and system for the detection of surface defects on a metal product as it is being continuously casted. The solution makes use of a sensor consisting of a matrix comprising at least two rows of at least three adjoining measuring cells that can be controlled by a multiplexing control unit. Each cell can generate eddy currents at the surface of the product and, alternately, detect eddy currents in said surface. The measurement principle is based on controlling a first transmitting cell and a second receiving cell from the same row, but which are separated from one another by at least one inactive cell.

From US8269489 BB is known a system and method for eddy current inspection of parts with complex geometries. The system includes a multi-dimensional array of eddy current sensors that conforms to a contour of a three dimensional shape of the part. The system also includes a controller coupled to the multi-dimensional array, wherein the controller is configured to electronically scan the part via an electrical connection of the eddy current sensors to an eddy current instrument.

In US2015177191 AA is disclosed a high resolution eddy current array probe. The eddy current array probe comprises a probe body adapted to be displaced along a scan direction and a plurality of coils arranged in a linear configuration on the surface of the probe body. The coils being adapted to be operated in one mode among a transmit mode, an inactive mode and a receive mode at each of a plurality of time-spaced instances. At least two adjacent coils of the plurality being adapted to be operated in the inactive mode between a coil adapted to be in transmit mode and a coil adapted to be in receive mode in the linear configuration at each of the time-spaced instances.

From US10794864 BB is known an eddy current array probe for detection and depth sizing of a surface-breaking defect in a metallic material. The eddy current array probe comprises a probe body comprising a plurality of probe elements arranged in a linear configuration, wherein the probe elements each comprising at least one coil. The probe body is adapted to be displaced along a surface of the metallic material so that a longitudinal axis of the coil is parallel to the surface of the metallic material. Further, the coil, when in use, being adapted to induce an eddy current within the metallic material to detect the eddy current. A set of active elements of the plurality of probe elements being adapted to be selectively operated at a plurality of time-spaced instances.

A disadvantage with the mentioned prior art solutions is that the coils are linearly distributed, something which makes the solutions unsuitable for use in corners.

Another disadvantage with the prior art solutions is that the solutions are configured for changing the receiving coils between active and passive mode. The mentioned changing between active and passive mode can result in variating impedance on the receiver coils making calibration of the system difficult.

A further disadvantage with the prior art solutions is that they are configured for switching the transmitter coils in time-spaced instances, which has been considered as an essential method for impedance measurement. The switching will reduce the active duty cycle and SNR (Signal-to-Noise-Ratio).

Object

The main object of the present invention is to provide an eddy current sensor partly or entirely solving the mentioned drawbacks of prior art.

An object of the present invention is to provide an eddy current sensor capable of performing detection and measurement at corners and/or curved surfaces.

It is an object of the present invention to provide an eddy current sensor enabling measurement at many frequencies to generate a rich data foundation for machine learning purposes.

An object of the present invention is to provide an eddy current sensor enabling measurement around and even behind the eddy current sensor independent of the number of sensor probe pairs.

It is an object of the present invention to provide an eddy current sensor enabling measurement in vicinity of all coils of each sensor probe pair at all time.

A further object of the present invention is to provide an eddy current sensor providing higher signal-to-noise-ratio compared to prior art solutions.

An object of the present invention is to provide an eddy current sensor capable of using all magnetic or nonmagnetic materials included ferrite to generate a large magnetic field for the transmitter maximizing the range/detection.

A further object of the present invention is to provide an eddy current sensor enabling bending or arrangement of the sensor probe pairs along a curvature.

An object of the present invention is to reduce manufacturing cost, physical size and power consumption compared to prior art.

Further objects of the present invention will appear from the following description, claims and attached drawings.

The invention

An eddy current sensor according to the present invention is defined by the technical features of the independent claim 1. Preferable features of the eddy current are described in the respective dependent claims.

An eddy current sensor according to the present invention is suitable for detection and measurement of a defect in a metallic measurement object. A defect will be a discontinuity in the surface of the metallic measurement object, also known as a surface-breaking defect.

The eddy current sensor according to the present invention comprises at least one sensor probe pair formed by two coils oriented after one another in axial direction. According to the present invention, each coil has at least one winding for transmitting and measuring magnetic flux by induction.

According to one embodiment of the present invention the mentioned two coils together constitute an axial length that is at least 1.5 times the length, more preferably at least twice the length, of each coil. If one of the coils are shorter than the other, this will be related to the shortest coil.

According to one embodiment of the present invention, the mentioned coils of each sensor probe are similar as regards size and shape, but may also be of different size and shape. If they are too different in size or shape, the accuracy of the measurement will be reduced, so that it will be preferable that the coils are as close to similar as possible. In a preferred embodiment, the mentioned coils are as close to identical in shape and size as possible. The more different in shape and/or size the mentioned coils are, the more compensation and corrections of the measurement result is required.

In accordance with a further embodiment of the present invention, the eddy current sensor further comprises a control and processing unit configured to calculate magnetic flux components from the measuring object when each of the coils of the at least one sensor probe pair is used as transmitter and receiver.

The eddy current sensor according to the present invention thus realizes ACFM by using the same sensor probe pair to excite the magnetic flux component Bx and detect the back scattered magnetic flux components Bx and Bz, further described below.

According to a further embodiment of eddy current sensor according to the present invention, the eddy current sensor comprises multiple sensor probe pairs.

According to a further embodiment of the eddy current sensor according to the present invention, the measured flux components from the coils are used for ACFM analysis.

In accordance with one embodiment of the eddy current sensor according to the present invention, the two coils of each sensor probe pair are spaced apart with a distance being similar to or larger than zero. This spacing reduces the magnetic coupling between the coils that must be less than 1.

In accordance with a further embodiment of the eddy current sensor according to the present invention, the control and processing unit is configured to carry out impedance measurements on the two coils of the at least one sensor probe pair where the impedance is found by the ratio between voltage and current at each coil terminal.

According to a one embodiment of the eddy current sensor according to the present invention, the two coils of each sensor probe pair are electrically connected in series to allow for equal current but individual voltage measurement of each coil.

In an alternative embodiment of the eddy current sensor according to the present invention, the mentioned coils of each sensor probe pair are electrically connected in parallel to allow for equal voltage but individual current measurement of each coil.

In accordance with a further embodiment of the present invention, the mentioned coils of the sensor probe pairs are arranged in a combination of series and parallel connection.

By arranging a measurement point (center tap) between the coils arranged in series, also the magnetic flux component Bz can be detected/measured by the same coil. This measurement point is also referred to as a center tap.

The Bz sensor is according to the present invention realized by combining two coils with different winding direction, where both the coils are oriented in the X-direction. Such a sensor probe pair oriented in the X-direction becomes sensitive to magnetic fields orthogonal to the X-direction that includes the Bz magnetic flux component that is orthogonal to the surface of the metallic measurement object. If the surface of the metallic measurement object is curved or bent the Bz sensor even becomes sensitive to all magnetic fields perpendicular to the curved surface.

The Bz sensor may according to an alternative embodiment of the present invention be realized by combining two coils with same winding direction, and then subtracting their measured backscattered magnetic flux.

The Bz sensor according to the present invention, weather realized by opposite winding directions or by subtracting measurements, will be a “self-nulling” or differential probe that becomes sensitive to magnetic anomalies like surface breaking cracks in the longitudinal direction of the sensor probe. A differential sensor probe is detecting a signal when the balanced geometry is broken. For ACFM this means that normal magnetic flux Bz, which lies in the symmetric plane dividing right and left side of an ACFM probe, is zero as long as right and left side is exposed to the same symmetric signals. This symmetry is broken if one side of the sensor probe is presented to a defect, such as a crack.

The eddy current sensor according to the present invention may be configured in different settings to perform a number of measurements.

In accordance with one configuration embodiment of the eddy current sensor according to the present invention, the control and processing unit is configured to emit the same transmitter signal on the two coils of each sensor probe pair at the same time as two different signals are received by the two coils of each sensor probe pair enabling two different measurements.

In another configuration embodiment of the eddy current sensor according to the present invention, the control and processing unit is configured to perform individual measurements for all coils of each sensor probe pair by using the same transmitter signal on all coils of each sensor probe pair and wherein at the same time receiving signals from all coils of each sensor probe pair.

In accordance with one embodiment of the eddy current sensor according to the present invention, the multiple sensor probe pairs are oriented in transversal direction of the measurement direction and metallic measurement object.

According to one embodiment of the present invention, the multiple sensor probe pairs oriented in transversal direction are arranged along a predefined curved path.

According to one embodiment of the eddy current sensor according to the present invention, multiple probe pairs are oriented in transversal direction are arranged along a flexible path. This embodiment enables adaption of the eddy current sensor according to the shape of the metallic measurement object to be inspected.

In accordance with a further embodiment of the eddy current sensor according to the present invention, the mutual distance and mutual inductivity between two adjacent sensor probe pairs are maintained constant.

According to one embodiment of the present invention, the multiple sensor probe pairs are arranged on a solid or flexible probe body.

In accordance with one embodiment of the present invention, the probe body is a solid or flexible circuit card.

According to a further embodiment of the present invention, multiple sensor probe pairs are arranged symmetrically on both sides the solid or flexible probe body.

In an alternative embodiment of the present invention, the multiple sensor probe pairs are arranged unsymmetrically by arranging sensor probe pairs at only one side of the probe body, such that the other side forms a natural surface against the metallic measurement object.

In a further alternative embodiment of the present invention, the flexible probe body is designed for high bending and wherein fewer sensor probe pairs (or a smaller number of) are arranged on the inside, i.e. the concave side of the curvature.

According to a further embodiment of the eddy current sensor according to the present invention, the control and processing unit is configured to calculate calibrated magnetic flux components for use for defect analysis.

In a further embodiment of the present invention, the control and processing unit is configured to calculate magnetic flux components over a wide frequency range to generate a rich data foundation for machine learning purposes.

In accordance with one configuration embodiment of the eddy current sensor according to the present invention, only one coil of each sensor probe pair is activated at a time. In this manner, it will be possible to perform N<2 >(N=number of coils, integer number larger than 1) measurements where one subsequently transmits on one coil at time of each sensor probe pair and measures on all coils N of all sensor probe pairs. This configuration embodiment will provide full measurement flexibility.

According to a further configuration embodiment of the eddy current sensor according to the present invention, all coils of all sensor probe pairs are activated for transmitting and receiving at the same time on all coils of all sensor probe pairs. This configuration embodiment will provide a plain set-up while simplifying and improving the measurements.

In a further configuration embodiment of the eddy current sensor according to the present invention, the coils of a chosen/desired section of sensor probe pairs are activated for transmitting and receiving at the same time on all coils of all sensor probe pairs.

In accordance with a further embodiment of the eddy current sensor according to the present invention, the control and processing unit is configured to magnetize different groups of sensor probe pairs with different settings.

According to a further embodiment of the eddy current sensor according to the present invention, the control and processing unit is configured to simultaneously magnetize only every third or more sensor probe pairs.

The latter embodiments, in addition to enabling measurements of magnetic flux components Bx and Bz near to each sensor probe pair, also enables calculations of other magnetic flux components Bx and Bz located in the area between the sensor probe pairs.

The choice of configuration embodiment of the eddy current sensor according to the present invention can accordingly be adapted to the desires of the user and/or application area, and is not restricted to the use of only one configuration.

In accordance with one embodiment of the eddy current sensor according to the present invention, the at least one sensor probe pair is rotational symmetric about the X-axis. Coils with, e.g. a cylindrical shape, is a preferred shape to achieve constant magnetic coupling even when the probe body is dynamically curved/bent. The rotational symmetric nature of the sensor probe pair also imply that the sensor probe pair do not need to be tilted or rotated around the longitudinal X-axis. The rotational symmetric sensor probe pair is therefore able to detect flaws 360 degrees around its shape and preferable inside tight corners.

In accordance to one embodiment of the eddy current sensor according to the present invention, systematic measurement errors are removed/corrected for by performing measurements on one or more calibration objects.

According to one embodiment of the eddy current sensor according to the present invention, the metallic measurement object is used as the calibration object.

In accordance with one embodiment of the eddy current sensor according to the present invention, measurements performed on one coil of a sensor probe pair or different sensor probe pair are used to remove/correct for systematic measurement error on another coil of the same and/or different sensor probe pair.

By the present invention the eddy current sensor is capable of measuring on a wide range of frequencies.

The eddy current sensor according to the present invention, due to being able to provide flexibility or a curved patch with distributed sensor probe pairs/coils, will provide improved measurements, compared to prior art solutions, in connection with tight corners and practical use.

An advantage with the eddy current sensor according to the present invention is that it is easily scalable, due to the eddy current sensor is able to measure around the coils independent if it comprises only one sensor probe pair or multiple sensor probe pairs. Accordingly, the eddy current sensor according to the present invention will have a wide range of application areas.

A further advantage with the eddy current sensor according to the present invention is that it is capable of performing measurements in the vicinity of the coils of each sensor probe pair at all times, i.e. over, under as well as around them.

By the eddy current sensor according to the present invention a higher signal-to-noise-ratio is achieved, compared to the prior art solutions, due to the opportunity for long calculation of average without disruption.

The eddy current sensor according to the present invention enables utilization of all magnetic or nonmagnetic materials included ferrite to create a large magnetic field for the transmitter maximizing the range/detection.

By the present invention is provided an eddy current sensor wherein the sensor probe pairs are magnetically coupled in a manner allowing bending to deviate from an initial curved path used during calibration.

The present invention is applicable for detection and measurement of a defect in a metallic measurement object in air and in submerged applications. The eddy current sensor according to the present invention is applicable for both manual and automated guidance over a metallic measurement object.

The present invention is especially suitable for detection and measurement of cracks in welding seams, hereunder also over and under water, as well as in the splash zone.

Further preferable features and advantageous details of the present invention will appear from the following example description, claims and attached drawings.

Example

The present invention will below be described in further details with references to the attached drawings, where:

Fig.1a-c are principle drawings of various embodiments of an eddy current sensor according to the present invention,

Fig.2 is a principle drawing of a further embodiment of the eddy current sensor according to the present invention, and

Fig.3a-b are principle drawings of further embodiments of the present invention.

Reference is now made to Figures 1a-c showing principle drawings of different embodiments of an eddy current sensor 10 according to the present invention. The eddy current sensor 10 according to the present invention comprises at least one sensor probe pair 20a-n formed by two coils 21a-b, i.e. first 21a and second 21b coils, oriented after one another in axial direction, wherein each coil 21a-b has at least one winding for transmitting and measuring magnetic flux by induction.

Fig. 1a shows a non-limiting example embodiment with one sensor probe pair 20a connected in series, Fig.1b shows a non-limiting example embodiment with multiple (three) sensor probe pairs 20a-c connected in parallel, and Fig. 1c shows a non-limiting embodiment with multiple (six) sensor probe pairs 20a-f, connected in parallel.

According to one embodiment of the present invention the coils 21a-b constitute an axial length that is at least 1.5 times the length, more preferably at least twice the length, of each coil 21a-b or shortest coil 21a-b if one of the coils 21a-b is shorter than the other.

According to the present invention, the properties of the two coils 21a-b of each sensor probe pair 20a-n are similar or equal, and wherein the magnetic flux B1 and B2 of the first 21a and second 21b coil, respectively, can be measured by performing voltage measurements.

In an alternative embodiment the properties of the two coils 21a-b of each sensor probe pair 20an are slightly different, something that is compensated for both in calibration and in calculation of measurement results.

According to one embodiment of the present invention, the mentioned two coils 21a-b are wound around separate cores 22 (Fig.1c, 2, 3a-b) or the same core (not shown).

The eddy current sensor 10 according to the present invention further comprises a control and processing unit 30 configured (provided with means and/or software) for controlling each sensor probe pair 20a-n as regards transmitting or receiving mode, hereunder synchronization, performing magnetic flux measurement by the two coils 21a-b of each sensor probe pair 20a-n, and performing sampling and decimation of the magnetic flux measurements.

According to one embodiment of the present invention the control and processing unit 30 comprises at least one magnetizer 31a-c enabling transmitting mode of the coils 21a-b of each sensor probe pair 20a-n. The at least one magnetizer 31a-c is preferably a controllable pulse source transmitting pulses with a desired/controllable frequency to the respective coil 21a-b of each sensor probe pair 20a-n to make the coils 21a-b of the respective sensor probe pair 20a-n magnetic, i.e. generating a magnetic field.

To be able to measure the mentioned magnetic flux, the eddy current sensor 10 comprises at least one resistor 32 arranged in series with the mentioned coils 21a-b, in front of the first coil 21a, and a ground point 33 arranged in series after the second coil 21b.

The eddy current sensor 10, in the shown embodiment, further comprises a first measurement point 34, arranged in front of the at least one resistor 32 enabling a reference measurement, a second measurement point 35 arranged after the at least one resistor 32 and in front of the first coil 21a enabling measurement of magnetic flux B1 over the first coil 21a, and a third measurement point 36 arranged after the first coil 21a and in front of the second coil 21b enabling measurement of magnetic flux B2 over the second coil 21b. The mentioned third measurement point 36 may be center tap arranged between the two coils 21a-b.

The control and processing unit 30 is according to one embodiment configured to perform three synchronous measurements of the voltages in the first 34, second 35 and third 36 measurement point.

The control and processing unit 30 is further configured for ACFM analysis (provided with means and/or software) to calculate the magnetic flux components Bx and Bz based on the mentioned measured voltages. In more detail, the magnetic flux component Bx = B1 B2 and the magnetic flux component Bz = B1 - B2.

A challenge with ACFM is that detection of defects in the metallic measurement object is only performed effective in vicinity of the coils 21a-b and if the coils 21a-b are too large to cover a large measurement area, the detection of small defects is reduced.

It is thus useful to use multiple smaller sensor probe pairs 20a-n in vicinity of each other to be able to detect both smaller defects and at the same time a larger area of the metallic measurement object, as e.g. shown in Fig.1b-c.

By using multiple sensor probe pairs 20a-n one according to the present invention achieves a large enough and sensitive enough eddy current sensor 10 for ACFM.

In Figure 1b is shown a second embodiment of the eddy current sensor 10 comprises multiple sensor probe pairs 20a-c, exemplified by three sensor probe pairs 20a-c, and wherein there are two measurement points 35-36 for each of the sensor probe pairs 20a-c, in addition to the reference measurement 34. In this embodiment, one will accordingly have a total of six magnetic flux measurements in addition.

Reference is now made to Figure 1c showing a further embodiment of the eddy current sensor 10 according to the present invention. According to the present invention, the at least one sensor probe pair 20a-n is arranged on a probe body 40 for fixation of the at least one sensor probe pair 20a-n.

In accordance with one embodiment of the present invention the probe body 40 is a circuit board enabling easy connection of the coils 21a-b of the sensor probe pair(s) 20a-n, as well as arrangement of ground 33 and the measurement points 34-36. According to the present invention, the circuit board 40 may be planer or exhibit a desired curvature, as shown in Figure 1c.

According to one embodiment of the present invention the probe body 40 is a flexible circuit board enabling bending of the eddy current sensor 10 to adapt to a curvature of a metallic measurement object, such as a weld seam. The flexible circuit 40 according to one embodiment is flexible from an initial curvature or flexible from a mainly planar initial shape.

When arranging some or all of the sensor probe pairs 20a-n of the eddy current sensor in parallel along a curved path it is required to apply a constant voltage to the mentioned sensor probe pairs 20a-n. According to one embodiment of the present invention, this is achieved by arranging at least one low-pass filter 50 arranged in series between the at least one magnetizer 31a-c and the at least one resistance 32. The mentioned at least one low-pass filter 50 in addition provides a common anti-aliasing filter for all the sensor probe pairs 20a-n. The implementation of the lowpass filter 50 is within the knowledge of a skilled person, such as by capacitors and coils, and needs no description in detail herein. The at least one low-pass filter 50 may be a fixed filter or controllable filter, such that the properties of the at least one low-pass filter 50 may be altered depending on the application.

The at least one low-pass filter 50 is according to the present invention also used for matching inductive loads from the at least one sensor probe pair 20a-n to achieve higher output.

To achieve a curvature of the sensor probe pair 20a-n distribution, the coils 21a-b should be enclosed in a non-conductive material. The insulation between the respective sensor probe pairs 20a-n should further preferably be neither electric nor magnetic conductive.

Reference is now made to Fig. 2 and 3a-b showing principle drawings of further embodiments of the eddy current sensor 10 according to the present invention. According to a further embodiment of the present invention the eddy current sensor 10 comprises sensor probe pairs 20a-n symmetrically arranged on both sides, i.e. upper and lower sides, of the probe body 40. In Fig.2 is shown an embodiment with a mainly planer probe body 40, while in Figs. 3a-b are shown an embodiment of two different curvatures of the probe body 40 and thus sensor probe pair 20a-n distribution.

By arranging the sensor probe pairs 20a-n on both sides of the probe body 40, a constant magnetic coupling is achieved even when the probe body 40 is dynamically curved/bent.

In one embodiment of the present invention the coils 21a-b are realized by multiple sub coils, wherein some of these multiple sub coils of the respective coil 21a-b are arranged below the probe body 40 and others of these multiple sub coils of the respective coils 21a-b are arranged above the probe body 40. All sub coils of the respective coil 21a-b are elctrically connected. When bending the probe body 40, the sum unwanted change in magnetic copling between the sensor probe pairs 20a-n from sub coils placed below and above the probe body 40 in this manner is significantly reduced.

The coils 21a-b may have any shape and cross-section, such as, but not limited to, circle, rectangle, square, ellipse, trapes, trapezoid, triangle, rhombus, pentagon, hexagon, octogon, etc. A skilled person in the area will recognize that the coils in different embodiments can have any of these cross-sections and variants of these. The cross-section and distance between the sensor probe pairs 20a-n will affect how step curvature that can be achieved for the eddy current sensor 10. The choise of cross-section will also be relevant for maintaining mutual distance and mutual inductivity between two adjacent sensor probe pairs constant during bending to a curvature, further described below.

In many embodiments there will be preferably to use sensor probe pairs 20a-n being cylindershaped, further discussed below. By using a cylinder-shape and constant distance, the sensor probe pairs 20a-n will be rotational symmetric and provide a constant magnetic coupling to nighbour objects and neighbour coils at constant distance. By that the sensor probe pairs 20a-n are rotational symmetric one can measure all around the senor probe as well as all sensor probe paris 20a-n can rotate all the way around themselves without being affected by adjacent sensor probe pairs 20a-n.

The sensor probe pairs 20a-n are thus arranged to the probe body 40 such that the probe body 40, and thus sensor probe pair 20a-n distribution, can be bent to exhibit a curved shape. According to one embodiment of the present invention, the probe body 40 has an initial curvature, e.g. as shown in Fig.3a, used for calibration, and wherein the probe body 40 and thus sensor probe 20a-n distribution can be bent to a deviating curvature, as e.g. shown in Fig. 3b without loosing the calibration. The deviating curvature may be both a steeper curvature or slacker curvature.

The possible curvature will depend on the properties (flexibility/elasticity) of the probe body 40 and the distance between the sensor probe pair 20a-n, as well as the size and shape of the sensor probe pairs 20a-n. The longer distance between the sensor probe pairs 20a-n, the steeper curvature can be achieved. However, with a long distance, the sensitivity of the total eddy current sensor 10 will be reduced. The distance will thus be a middle course between desired curvature properties, range and bandwidth.

As shown in Fig. 1c, the control and processing unit 30 is provided with one or more connection interfaces for power and wired or wireless communication with external units 100 for further processing of the measurement data and metallic measurement object defect analysis. The eddy current sensor 10 can be powered via wire and/or by energy storages, such as batteries or similar. According to one embodiment, the eddy current sensor 10 is provided with an umbilical interface, enabling both power and communication with external units 100 via one cable.

The control and processing unit 30 is configured (provided with means and/or software) to perform sampling and decimation of the magnetic flux measurements from the sensor probe pair(s) 20a-n for transfer to the mentioned external unit 100 for further processing. In this manner, the control unit 30 is configured to increase the resolution of the measurement data.

The external unit 100 is according to a further embodiment comprising a user interface for controlling the settings of the eddy current sensor 10 via the control and processing unit 30.

In accordance with a further embodiment of the present invention, the control and processing unit 30 is further provided with means and/or software for performing machine learning of the measurement data from the sensor probe pairs 20a-n. In an alternative embodiment, the machine learning is implemented on an external unit 100. By means of machine learning, one can make predictions or calculations based on large amounts of data. Machine learning can be divided in several methods, which is known as e.g. supervised learning, unsupervised learning, semisupervised learning and reinforcement learning that enable different approaches for processing of the measurement data depending on the result to be achieved. Accordingly, by providing the control and processing unit 30 with means and/or software for machine learning the control and processing unit 30, alternatively the external unit 100, is configured to improve the defect detection of the eddy current sensor 10 by collecting and producing training data usable for machine learning.

The eddy current sensor 10 according to the present invention is also capable of performing magnetic flux measurement by additional virtual sensor probes, i.e. by calculating magnetic flux in the spacing between the sensor probe pairs 20a-n. This is achieved by providing the control and processing unit 30 with multiple magnetizers 31a-c, configured to magnetize every third sensor or more probe pairs 20a-n. In this manner, Bx and Bz in the area between the sensor probe pairs 20an will be detected.

Accordingly, if one consider the embodiment of Fig.1c, and six probe pairs 20a-f, a first magnetizer 31a could be used to magnetize a first group of non-adjacent sensor probe pairs 20a and 20d and wherein a second magnetizer 31b could be used to magnetize a second group of sensor probe pairs 20b and 20e and the third magnetizer 31c could be used to magnetize a third group of sensor probe pairs 20c and 20f.

In an alternative embodiment, the same magnetizer 31a is used to magnetize several times with different settings.

In this manner, it will be possible to measure Bx and Bz in the area between sensor probe pairs 20a and 20b, between sensor probe pairs 20b and 20c, between sensor probe pairs 20c and 20d, between sensor probe pairs 20d and 20e and between sensor probe pairs 20e and 20f.

The above describe control and processing unit 30 may be divided in several units. Further, if appropriate for the application, the control and processing unit 30 may be arranged exterior/remote of the at least one sensor probe pair 20a-n and probe body 40.

Features of the above described embodiments may be combined to form modified embodiments within the scope of the attached claims.

Claims

1. Eddy current sensor (10) for detection and measurement of a defect in a metallic measurement object, said eddy current sensor (10) comprising at least one sensor probe pair (20a-n) formed by two coils (21a-b) oriented after one another in axial direction, wherein each coil (21a-b) has at least one winding for transmitting and measuring magnetic flux by induction.

2. Eddy current sensor (10), according to claim 1, wherein the coils (21a-b) constitute an axial length that is at least 1.5 times the length, more preferably at least twice the length, of each coil (21a-b) or shortest coil (21a-b).

3. Eddy current sensor (10) according to claim 1, wherein comprising a control and processing unit (30) configured to calculate magnetic flux components from the metallic measuring object when the at least one sensor probe pair (20a-n) is used as transmitter and receiver.

4. Eddy current sensor (10) according to any preceding claim, wherein comprising multiple sensor probe pairs (20a-n).

5. Eddy current sensor (10), according to claim 1, wherein measured flux components from the coils (21a-b) are used for alternating current field measurement analysis.

6. Eddy current sensor (10) according to any preceding claim, wherein the two coils (21a-b) of each sensor probe pair (20a-n) are spaced apart with a distance being similar to or larger than zero.

7. Eddy current sensor (10) according to any preceding claim, wherein the two coils (21a-b) of each sensor probe pair (20a-n) are electrically connected in series or parallel.

8. Eddy current sensor (10) according to any preceding claim 3-7, wherein the control and processing unit (30) is configured to emit a signal alternating on the two coils (21a-b) of each sensor probe pair (20a-n) at the same time as signals are received on the two coils (21a-b) of each sensor probe pair (20a-n) enabling four different measurements.

9. Eddy current sensor (10) according to any preceding claim 3-7, wherein the control and processing unit (30) is configured to emit the same transmitter signal on the two coils (21a-b) of each sensor probe pair (20a-n) at the same time as two different signals are received by the two coils (21a-b) of each sensor probe pair (20a-n) enabling two different measurements for each sensor probe pair (20a-n).

10. Eddy current sensor (10) according to claim 3-7, wherein the control and processing unit (30) being configured to perform individual measurements for all coils (21a-b) of each sensor probe pair (20a-n) by using the same transmitter signal on all coils (21a-b) of each sensor probe pair (20a-n) and wherein at the same time receiving signals from all coils (21a-b) of each sensor probe pair (20a-n).

11. Eddy current sensor (10) according to any preceding claim, wherein the at least one sensor probe pair (20a-n) is oriented in transversal direction of the measurement direction and metallic measurement object.

12. Eddy current sensor (10) according to claim 4 and 11, wherein the multiple sensor probe pairs (20a-n) are arranged along a predefined curved path.

13. Eddy current sensor (10) according to claim 4 and 11, wherein the multiple sensor probe pairs (20a-n) are arranged along a flexible path.

14. Eddy current sensor (10) according to any preceding claim 11-13, wherein the mutual distance between two adjacent sensor probe pairs (20a-n) are maintained constant.

15. Eddy current sensor (10) according to any preceding claim, wherein the at least one sensor probe pair (20a-n) is arranged on a solid or flexible probe body (40).

16. Eddy current sensor (10) according to any preceding claim 15, wherein the multiple sensor probe pairs (20a-n) are arranged symmetrically on both sides of the solid or flexible probe body (40).

17. Eddy current sensor (10) according to claim 15, wherein the probe body (40) is a solid or flexible circuit card.

18. Eddy current sensor (10) according to any preceding claim, wherein shape of the sensor probe pairs (20a-n) are cylindrical.

19. Eddy current sensor (10) according to any preceding claim, wherein each coil (21a-b) is formed by multiple sub coils electrically connected.

20. Eddy current sensor (10) according to any preceding claim 3-19, wherein the control and processing unit (30) being configured to calculate calibrated flux components for use for defect detection and analysis.

21. Eddy current sensor (10) according to any preceding claim 4-20, wherein the control and processing unit (30) is configured to magnetize different groups of sensor probe pairs (20a-n) with different settings.

22. Eddy current sensor (10) according to claim 21, wherein the control and processing unit (30) is configured to simultaneously magnetize only every third or more sensor probe pairs (20a-n).