JP2019020320A - probe - Google Patents

Abstract

To cause more magnetic fluxes to pass through an object.SOLUTION: A probe 2, which generates an eddy current in a measurement object 9, has a first pole P1 and a second pole P2, and the poles are opposed to the measurement object 9 and are excited to be oppositely magnetic. The probe includes: a core 3 for causing a magnetic flux which exits from one of the first pole P1 and the second pole P2 and enter the other to pass through the measurement target 9; and an excitation coil 41 wound around the core 3 to excite the core. The first pole P1 and the second pole P2 are tapered.SELECTED DRAWING: Figure 1

Description

  The technique disclosed here relates to a probe.

  Conventionally, a probe, particularly a probe used for flaw detection using eddy current is known. For example, Patent Document 1 discloses a probe including a core made of a magnetic material and a coil wound around the core. The core is excited by applying a pulsed voltage to the coil. Both ends of the core are arranged so as to face the pipe that is the object of flaw detection. Therefore, an eddy current is generated in the pipe by the magnetic field generated by the coil. By detecting this eddy current, flaw detection such as a thinning inspection of pipes is performed.

JP 2008-145137 A

  By the way, in the probe as described above, it may be desired to pass more magnetic flux through the object. For example, in flaw detection, the larger the eddy current, the easier it is to determine the change in eddy current due to the presence or absence of the flaw, and the measurement accuracy improves. For this purpose, it is preferable to pass more magnetic flux through the object.

  The technology disclosed herein has been made in view of such a point, and an object thereof is to pass more magnetic flux through the object.

  The technique disclosed herein is a probe that generates an eddy current in an object. The probe has a first pole and a second pole that are arranged so as to face the object and are excited by opposite magnetism, and exits from one of the first pole and the second pole to the other. A core for passing an incoming magnetic flux through an object and a coil wound around the core and exciting the core are provided, and the first pole and the second pole have a tapered shape.

  According to the probe, more magnetic flux can be passed through the object.

FIG. 1 is a block diagram of a thickness measuring apparatus. FIG. 2 is a front view of the probe. FIG. 3 is an enlarged perspective view of the first and second poles of the core. FIG. 4 is a graph showing a time change of the voltage signal V (t). FIG. 5 is a front view of a probe according to a comparative example, in which the first pole and the second pole are not cut away.

  Hereinafter, exemplary embodiments will be described in detail with reference to the drawings. FIG. 1 is a block diagram of the thickness measuring apparatus 100.

  The thickness measuring device 100 generates the eddy current in the measuring object 9 and detects the generated eddy current, and obtains the thickness of the measuring object 9 based on the transient change of the detected eddy current. And an arithmetic device 6. The thickness measuring apparatus 100 measures the thickness of the measuring object 9 by pulsed eddy current flaw detection (PEC: Pulsed Eddy Current). The measurement object 9 is, for example, a metal pipe.

  The sensor device 10 includes a probe 2 that generates an eddy current in the measurement object 9 and detects the generated eddy current, and a device body 5 that controls the probe 2.

  The probe 2 includes a core 3, an excitation coil 41 and a reception coil 42 wound around the core 3. The probe 2 is a non-contact type probe and is disposed in the vicinity of the measurement object 9. The “non-contact type” means that it can be used without contact, and does not exclude use in a contact state. The probe 2 generates an eddy current in the measurement object 9 by generating a variable magnetic field. The probe 2 detects a change in eddy current generated in the measurement object 9 as an induced voltage. For example, the probe 2 is installed on the measurement object 9 via a spacer (not shown) having heat insulation properties.

  The apparatus body 5 includes an excitation unit 51 that applies an excitation current to the excitation coil 41, a detection unit 54 that detects a transient change in eddy current of the measurement target 9, a communication unit 56 that communicates with an external device, and various types of information. And a control unit 58 that controls at least the excitation unit 51, the detection unit 54, the communication unit 56, and the storage unit 57.

  The excitation unit 51 supplies a pulsed excitation current to the excitation coil 41. The excitation unit 51 includes a pulse generator 52 that generates a pulse signal, and a transmission amplifier 53 that amplifies the pulse signal from the pulse generator 52 and outputs the amplified signal as an excitation current.

  The detection unit 54 detects an induced electromotive force generated in the reception coil 42 in accordance with the eddy current of the measurement object 9. The transient change of the induced electromotive force generated in the receiving coil 42 is related to the transient change of the eddy current generated in the measurement object 9. The detection unit 54 has at least a reception amplifier 55 that amplifies the voltage generated in the reception coil 42. The detection unit 54 may further include a filter that performs a filtering process on the voltage signal.

  The communication unit 56 performs wireless communication with an external device. For example, the communication unit 56 transmits the voltage signal detected by the detection unit 54 to the arithmetic device 6.

  The control unit 58 is formed by a processor. For example, the control unit 58 causes the excitation unit 51 to output an excitation current only for a predetermined period, and acquires a detection signal from the detection unit 54 after stopping the excitation current output. The control unit 58 stores the acquired detection signal in the storage unit 57 and transmits the detection signal stored in the storage unit 57 to the arithmetic device 6 via the communication unit 56 at a predetermined timing.

  The arithmetic device 6 is formed of a computer or a computer network (so-called cloud). The calculation device 6 includes a communication unit 61 that communicates with an external device, a storage unit 62 that stores various types of information, a calculation unit 63 that obtains the thickness of the measurement object 9 based on the detected transient change in eddy current, have.

  The communication unit 61 performs wireless communication with an external device. For example, the communication unit 61 receives a voltage signal from the sensor device 10.

  The storage unit 62 stores a voltage signal from the sensor device 10 and information necessary for calculating the thickness of the measurement target 9.

  The calculation unit 63 is formed by a processor. The computing unit 63 computes the thickness of the measurement object 9 based on the voltage signal from the sensor device 10 (specifically, a transient change in the voltage signal).

  Subsequently, the probe 2 will be described in detail. FIG. 2 is a front view of the probe 2. FIG. 3 is an enlarged perspective view of the first pole P1 and the second pole P2 of the core 3.

  The core 3 includes a first straight portion 31, a second straight portion 32, and a connecting portion 33 that connects the first straight portion 31 and the second straight portion 32, and is formed in a substantially U shape as a whole. Yes. More specifically, the core 3 is formed by laminating a plurality of substantially U-shaped thin plates made of permalloy (see FIG. 3). Permalloy sheets are subjected to hydrogen annealing.

  The core 3 has two end portions, a first end portion 34 that is an end portion of the first straight portion 31 and a second end portion 35 that is an end portion of the second straight portion 32. When the core 3 is excited by the excitation coil 41, opposite poles are formed at the first end portion 34 and the second end portion 35. The pole formed at the first end 34 is referred to as a first pole P1, and the pole formed at the second end 35 is referred to as a second pole P2. That is, the core 3 has a first pole P1 and a second pole P2 that are excited by opposite magnetism. The core 3 is arranged so that the first pole P1 and the second pole P2 face the measurement object 9. A magnetic flux (a two-dot chain line arrow in FIG. 2) that exits from one of the first pole P <b> 1 and the second pole P <b> 2 and enters the other passes through the measurement object 9. At this time, the connecting portion 33 functions as a yoke, and a closed circuit is formed by the core 3 and the measurement object 9.

  The first pole P1 and the second pole P2 have a tapered shape. More specifically, a portion near the second pole P2 in the end edge of the first pole P1 is notched, and a notch 36 is formed. Similarly, the portion of the edge of the second pole P2 that is close to the first pole P1 is notched, and a notch 37 is formed.

  The exciting coil 41 is wound around the first straight part 31 and the second straight part 32. In this example, the first excitation coil 41A wound around the first straight portion 31 and the second excitation coil 41B wound around the second straight portion 32 are formed by a single electric wire. Hereinafter, when the first excitation coil 41A and the second excitation coil 41B are not distinguished, they are simply referred to as “excitation coil 41”. The first excitation coil 41 </ b> A and the second excitation coil 41 </ b> B generate magnetic fields having the same direction in the longitudinal direction of the core 3. Therefore, when the first pole P1 is an N pole, the second pole P2 is an S pole. Conversely, when the first pole P1 is the S pole, the second pole P2 is the N pole.

  The reception coil 42 is wound around the first straight part 31 and the second straight part 32. In this example, the first receiving coil 42A wound around the first straight portion 31 and the second receiving coil 42B wound around the second straight portion 32 are formed of electrically separated electric wires. Hereinafter, when the first receiving coil 42A and the second receiving coil 42B are not distinguished, they are simply referred to as “receiving coil 42”. The first receiving coil is formed by changing the magnetic flux that is formed by the eddy current generated in the portion of the measuring object 9 that faces the first pole P1 and passes through the first receiving coil 42A via the first linear portion 31. An induced electromotive force is generated at 42A. The first receiving coil is formed by changing the magnetic flux that is formed by the eddy current generated in the portion of the measuring object 9 that faces the second pole P2 and passes through the second receiving coil 42B via the second linear portion 32. An induced electromotive force is generated at 42A. The first receiving coil 42A and the second receiving coil 42B detect these induced electromotive forces.

  Subsequently, a thickness measurement process performed by the thickness measuring apparatus 100 will be described.

  First, the control unit 58 causes the excitation unit 51 to output an excitation current to the excitation coil 41. Next, the control unit 58 stops the output of the excitation current and causes the detection unit 54 to detect the eddy current generated in the measurement object 9. The control unit 58 continues the detection of the voltage signal via the detection unit 54 for a predetermined period, and stores the detected electrical signal in the storage unit 57. As a result, the control unit 58 acquires a transient change (time-dependent change) in the dielectric electromotive force of the receiving coil 42, that is, a transient change in eddy current generated in the measurement object 9. Thereafter, the control unit 58 transmits the voltage signal stored in the storage unit 57 to the calculation unit 63 via the communication unit 56.

  The control unit 58 acquires the transient change of the eddy current as described above in a state where the thickness d of the measurement object 9 is known. Thereafter, the control unit 58 periodically acquires transient changes in eddy currents. Thereby, the transient change of the eddy current of the measuring object 9 whose thickness d has changed is continuously acquired. Note that the magnitude of the exciting current applied to the exciting coil 41 is constant when acquiring periodic eddy current transient changes.

  The arithmetic device 6 calculates the thickness d of the measurement object 9 based on the voltage signal acquired from the sensor device 10.

  FIG. 4 is a graph showing a time change of the voltage signal V (t). The graph of FIG. 4 is a log-log graph. In FIG. 4, a voltage signal V0 (t) is a voltage signal of the measurement object 9 having a thickness d0, and a voltage signal V1 (t) is a measurement object 9 having a thickness d1 smaller than the thickness d0. Voltage signal.

  The eddy current attenuates as it penetrates into the measuring object 9. The eddy current is gradually attenuated until it reaches the back surface from the surface of the measurement object 9 (the surface on which the probe 2 is opposed), and rapidly attenuates when it reaches the back surface. The voltage signal V (t) also shows the same change as the eddy current. That is, the transient change of the voltage signal V (t) corresponds to the transient change of the eddy current. The change of the voltage signal V (t) until the eddy current reaches the back surface of the measuring object 9 is expressed linearly (linearly) on the log-log graph. Thereafter, the voltage signal V (t) is rapidly attenuated. The voltage signal V (t) changing in this way is expressed by the following equation (1).

ここで、Ａは、受信アンプ５５の増幅率である。ｎは、電圧信号Ｖ（ｔ）の減衰の程度に関連する定数であり、−ｎは、両対数グラフにおける電圧信号Ｖ（ｔ）の傾きを表す。

Here, A is the amplification factor of the reception amplifier 55. n is a constant related to the degree of attenuation of the voltage signal V (t), and −n represents the slope of the voltage signal V (t) in the log-log graph.

  As can be seen from Equation (1), the change mode of the voltage signal V (t) is switched at time τ. Hereinafter, for convenience of explanation, τ is referred to as “attenuation time”. The decay time τ is expressed by the following equation (2).

τ = σμd ² (2)
Here, σ is the conductivity of the measurement object 9, μ is the magnetic permeability of the measurement object 9, and d is the thickness of the measurement object 9.

That is, when the thickness d of the measurement object 9 changes, the decay time τ changes. In this case, since the electrical conductivity σ and the magnetic permeability μ of the measurement object 9 are constant, the decay time τ changes depending only on the thickness d of the measurement object 9. Further, even if the decay time τ and the thickness d change, τ / d ² is constant. Therefore, if the decay time τ0 with respect to the known thickness d0 and the decay time τx with respect to the unknown thickness dx are known, the unknown thickness dx can be obtained based on the following equation (3).

例えば、図４において電圧信号Ｖ０（ｔ），Ｖ１（ｔ）を比較すると、厚さｄ０の測定対象物９の電圧信号Ｖ０（ｔ）の変化態様は、減衰時間τ０で切り替わる。測定対象物９の厚さｄがｄ０からｄ１に減少すると、減衰時間τは、τ０からτ１に減少する。尚、電圧信号Ｖ（ｔ）のうち両対数グラフで直線状の部分の変化態様は、式（１）からわかるように厚さｄに依存しないので、電圧信号Ｖ０（ｔ），Ｖ１（ｔ）で実質的に同じである。厚さｄ０及び減衰時間τ０，τ１を式（３）に代入することによって、厚さｄ１を求めることができる。

For example, when the voltage signals V0 (t) and V1 (t) are compared in FIG. 4, the change mode of the voltage signal V0 (t) of the measurement object 9 having the thickness d0 is switched at the decay time τ0. When the thickness d of the measurement object 9 decreases from d0 to d1, the decay time τ decreases from τ0 to τ1. In addition, since the change mode of the linear portion in the logarithmic graph of the voltage signal V (t) does not depend on the thickness d as can be seen from the equation (1), the voltage signals V0 (t), V1 (t) Is substantially the same. The thickness d1 can be obtained by substituting the thickness d0 and the decay times τ0 and τ1 into the equation (3).

  The calculation device 6 sets the known thickness of the measurement object 9 as the reference thickness d0, and acquires a transient change in the voltage signal V0 (t) at the reference thickness d0. Hereinafter, the voltage signal V0 (t) is referred to as a reference voltage signal V0 (t). Thereafter, when the arithmetic device 6 obtains the voltage signal Vx (t) regarding the unknown thickness dx, the arithmetic device 6 measures the transient change of the voltage signal Vx (t) with the transient change of the reference voltage signal V0 (t). The thickness dx of the object 9 is obtained. Specifically, the arithmetic unit 6 obtains the changed thickness dx from the reference thickness d0, the reference decay time τ0, and the decay time τx using Equation (3).

  Thus, in the thickness measuring apparatus 100 for determining the thickness d of the measurement object 9, the measurement accuracy of the thickness d can be improved by using the probe 2 as described above. Hereinafter, the reason will be described by taking an example in which the first pole P1 is an N pole and the second pole P2 is an S pole as shown in FIG. The same explanation holds true when the first pole P1 is the S pole and the second pole P2 is the N pole.

  Most of the magnetic flux emitted from the first pole P1 of the probe 2 exits in the normal direction of the end face of the first pole P1 and enters the measurement object 9, passes through the measurement object 9 in a substantially arc shape, The second pole P2 enters the normal direction of the end face of the second pole P2. However, a part of the magnetic flux passes from the first pole P1 through the surface layer of the measuring object 9 to the second pole P2, or from the first pole P1 through the air to the second pole P2. Or For example, FIG. 5 is a front view of a probe 2 ′ having a core 3 ′ having a first pole P <b> 1 ′ and a second pole P <b> 2 ′ in which notches 36 and 37 are not formed. In such a configuration, since the distance between the first pole P1 'and the second pole P2' is narrow, the magnetic flux that generates a magnetic field only on the surface layer of the measurement object 9 increases.

  On the other hand, the first pole P1 and the second pole P2 of the core 3 of the probe 2 have a tapered shape as described above. The magnetic flux exits from the end of the first pole P1 in the longitudinal direction of the core 3, and the part of the second pole P2 that is closest to the measuring object 9, that is, the end of the core 3 in the longitudinal direction. There is a tendency to enter from the part. Therefore, the magnetic flux density emitted from the first pole P1 or the second pole P2 and the magnetic flux density entering the second pole P2 are improved. When the magnetic flux density is improved, the magnetic flux exiting in the normal direction of the end face of the first pole P1 and the magnetic flux entering in the normal direction of the end face of the second pole P2 increase. Such a magnetic flux not only passes through a deep part (non-surface layer) of the measurement object 9 but also has a long distance to pass through the measurement object 9, so that the magnetic field acting on the measurement object 9 is large. Become. As a result, a larger eddy current is generated in the measurement object 9.

  When the eddy current generated in the measurement object 9 increases, the time from when the excitation by the probe 2 is stopped until the eddy current of the measurement object 9 is completely attenuated becomes longer. That is, the decay time τ becomes longer. When the decay time τ is short, it is required to measure the decay time τ with high accuracy. In other words, if the decay time τ is increased, the measurement accuracy of the decay time τ is improved. As can be seen from Equation (3), the thickness dx of the measurement object 9 is obtained based on the ratio between the reference decay time τ0 and the decay time τx. When the measurement accuracy of the decay time τ is improved, the accuracy of the ratio between the reference decay time τ0 and the decay time τx is naturally improved. As a result, the measurement accuracy of the thickness dx is improved.

  Furthermore, a portion near the second pole P2 in the end edge of the first pole P1 is cut out, and similarly, a portion near the first pole P1 in the end edge of the second pole P2 is cut out. As a result, the magnetic flux emitted from the notch 36 of the first pole P1 is reduced, and the magnetic flux emitted from the end of the first pole P1 in the longitudinal direction of the core 3, that is, the end face closest to the measuring object P is reduced. To increase. The same applies to the magnetic flux entering the second pole P2. The magnetic flux entering the notch 37 of the second pole P2 is reduced, and the most end portion in the longitudinal direction of the core 3 in the second pole P2, that is, the measurement object P and the most. Magnetic flux entering the approaching end face increases. As a result, the interval between the first pole P1 and the second pole P2 is expanded as compared with the case where the notches 36 and 37 are not formed. As a result, the magnetic flux that enters the second pole P2 through the surface layer of the measurement object 9 from the first pole P1 and the magnetic flux that enters the second pole P2 through the air from the first pole P1. The magnetic flux that decreases and emerges in the normal direction of the end face of the first pole P1 and enters the deep part (the part that is not the surface layer) of the measurement object 9 increases. As a result, the magnetic field acting on the measurement object 9 increases, and a larger eddy current is generated in the measurement object 9.

  By simply separating the first pole P1 and the second pole P2, the magnetic flux passing through the surface layer of the measurement object 9 from the first pole P1 and entering the second pole P2 or the first pole P1 can be obtained. It may be possible to reduce the magnetic flux entering the second pole P2 from the pole P1 through the air. However, in that case, the dimensions of the core 3 and thus the dimensions of the probe 2 are increased. When the probe 2 becomes large, not only the handling of the probe 2 becomes complicated, but also the size of the measurement location of the thickness d in the measurement object 9 becomes large. That is, by forming the notches 36 and 37 as described above in the first pole P1 and the second pole P2, it is possible to generate a large eddy current in the measurement object 9 while reducing the size of the core 3. By reducing the size of the core 3, the probe 2 can be easily handled and the thickness d of the local portion of the measurement object 9 can be measured.

  As described above, the probe 2 that generates an eddy current in the measurement object 9 (object) is disposed so as to face the measurement object 9 and is excited by the opposite magnetism to each other. A core 3 having a pole P2 and passing a magnetic flux coming out of one of the first pole P1 and the second pole P2 and entering the other into the measurement object 9, and an exciting coil 41 wound around the core 3 and exciting the core (The coil), and the first pole P1 and the second pole P2 have a tapered shape.

  According to this configuration, the magnetic flux density of the first pole P1 and the second pole P2 can be improved. Thereby, the magnetic flux which enters into the other from the one of the 1st pole P1 and the 2nd pole P2 in the air or through the surface layer of the measuring object 9 can be reduced, and the magnetic flux which penetrates deeply into the measuring object 9 can be increased. . As a result, a larger eddy current can be generated in the measurement object 9 by passing more magnetic flux through the measurement object 9.

  Further, a portion near the second pole P2 in the edge of the first pole P1 and a portion near the first pole P1 in the edge of the second pole P2 are cut out.

  According to this configuration, the inner edge of each of the first pole P1 and the second pole P2 that are arranged side by side is cut out, so that one of the first pole P1 and the second pole P2 is in the air or the measurement object. The magnetic flux that enters the other through the surface layer of 9 can be reduced, and the magnetic flux that enters deeply into the measuring object 9 can be increased. In addition, the interval between the first pole P1 and the second pole P2 can be increased without increasing the size of the core 3.

  The probe 2 is for measuring the thickness d of the measuring object 9.

  In the thickness measurement using the eddy current, it is desired to generate a large eddy current in the measurement object 9. Therefore, the probe 2 is particularly effective.

  Furthermore, the core 3 is made of permalloy.

  According to this configuration, since permalloy is a highly magnetically permeable material, the tendency for magnetic flux to be emitted from the end portion in the longitudinal direction of the core 3 is increased. Therefore, even if the notches 36 and 37 are formed in the first pole P1 and the second pole P2 as described above, the magnetic flux from the notches 36 and 37 does not increase, and the first pole P1 or the second pole P2 does not increase. It is possible to increase the magnetic flux coming out of the earliest part or entering the earliest part.

  The core 3 is formed of a laminated plate.

  According to this configuration, the magnetic field generated in the core 3 can be strengthened.

<< Other Embodiments >>
As described above, the embodiment has been described as an example of the technique disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can also be applied to an embodiment in which changes, replacements, additions, omissions, and the like are appropriately performed. Moreover, it is also possible to combine each component demonstrated by the said embodiment and it can also be set as a new embodiment. In addition, among the components described in the attached drawings and detailed description, not only the components essential for solving the problem, but also the components not essential for solving the problem in order to illustrate the technology. May also be included. Therefore, it should not be immediately recognized that these non-essential components are essential as those non-essential components are described in the accompanying drawings and detailed description.

  About the said embodiment, it is good also as following structures.

  For example, the probe 2 is applied to the thickness measuring apparatus 100, but is not limited thereto. If it is an apparatus which needs to generate an eddy current in a target object, the above-mentioned probe 2 can be applied.

  Furthermore, the probe 2 is not limited to the above-described configuration. For example, the probe 2 may not include the reception coil 42. In that case, the eddy current of the measuring object 9 may be detected by a receiving coil physically separated from the probe 2. Moreover, the eddy current of the measuring object 9 can also be detected by a Hall element or the like.

  Moreover, although the core 3 is formed in the substantially U shape which has the 1st linear part 31, the 2nd linear part 32, and the connection part 33, it is not restricted to this. For example, the core 3 only needs to have the first pole P1 and the second pole P2, and for example, the first straight part 31 and the second straight part 32 may be physically separated. However, since the connecting portion 33 acts like a yoke by connecting the first straight portion 31 and the second straight portion 32 with the connecting portion 33 as described above, the magnetic field formed in the core 3 becomes stronger. .

  Further, the first excitation coil 41A and the second excitation coil 41B may be formed of separate electric wires that are electrically separated. The exciting coil 41 may be provided in only one place instead of the two places of the first straight portion 31 and the second straight portion 32. The exciting coil 41 may be wound around the connecting portion 33.

  Furthermore, the thickness measurement by the thickness measuring apparatus 100 is only an example. Since there are various methods for measuring the thickness by PEC, any measurement method can be adopted.

  Moreover, the structure of the thickness measuring apparatus 100 is only an example. The sensor device 10 and the arithmetic device 6 may be integrally configured. Further, the probe 2, the excitation unit 51, and the detection unit 54 of the sensor device 10 may be housed in separate housings and separated. Further, the sensor device 10 and the arithmetic device 6 may be connected by wire. A plurality of sensor devices 10 may be connected to one arithmetic device 6. In addition, the calculation device 6 may transmit data regarding the calculated thickness to another device connected wirelessly or by wire.

  As described above, the technique disclosed herein is useful for probes.

2 Probe 3 Core 41A First exciting coil (coil)
41B Second excitation coil (coil)
9 Measurement object (object)
P1 1st pole P2 2nd pole

Claims (5)

A probe for generating an eddy current in an object,
A first magnetic pole and a second magnetic pole that are arranged so as to face the object and are excited by opposite magnetism, and the magnetic flux that exits from one of the first and second poles and enters the other A core to be passed through,
A coil wound around the core and exciting the core;
The probe characterized in that the first pole and the second pole have a tapered shape. The probe according to claim 1, wherein
2. The probe according to claim 1, wherein a portion near the second pole in the edge of the first pole and a portion near the first pole in the edge of the second pole are cut out. The probe according to claim 1 or 2,
The probe is for measuring the thickness of an object. The probe according to any one of claims 1 to 3,
The probe is characterized in that the core is made of permalloy. The probe according to any one of claims 1 to 4,
The probe is characterized in that the core is formed of a laminated plate.

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