Eddy current electromagnetic sensors and non-destructive testing equipment

Abstract

This invention provides an eddy current type electromagnetic sensor with improved signal strength. [Solution] The eddy current electromagnetic sensor 1 comprises a first coil unit 2A having a first excitation coil 21 and a first measurement coil set 24 consisting of first and second measurement coils 22 and 23, a second measurement coil set 28 consisting of a second excitation coil 25 and third and fourth measurement coils 26 and 27, a power supply unit 3, and a signal output unit 4 that outputs a signal of the difference between the first and second measurement coil sets 24 and 28. The first and second excitation coils 21 and 25 are connected in series with both ends connected to the power supply unit 3. The first and second measurement coil sets 24 and 28 are connected such that the first measurement coil 22 and the third measurement coil 26, and the second measurement coil 23 and the fourth measurement coil 27, are connected in a direction in which their excitation voltages cancel each other out.

Description

[Technical Field]

[0001] The present invention relates to an eddy current electromagnetic sensor capable of generating a magnetic field and detecting eddy currents generated by magnetic field changes with high sensitivity, and to a non-destructive inspection apparatus using said sensor. [Background Art]

[0002] For example, when performing inspections such as characteristic analysis of soil and evaluation of welding strength, non-destructive inspection apparatuses capable of non-destructively inspecting an inspection target are used, which are equipped with an eddy current electromagnetic sensor that generates a magnetic field and detects, with high sensitivity, eddy currents secondarily generated by a magnetic field changed by the influence of a measurement object (hereinafter referred to as "magnetic field change"), and perform signal processing on the detection signal of said eddy current electromagnetic sensor.

[0003] Figures 17 to 19 are schematic diagrams for explaining the structure of a conventionally known eddy current electromagnetic sensor. First, a conventional eddy current electromagnetic sensor will be described with reference to these figures.

[0004] As shown in Figure 17, the basic structure of the eddy current electromagnetic sensor comprises an excitation coil (EC) and a measurement coil (SC) disposed overlapping the excitation coil (EC) in the magnetic field direction; an AC power supply is applied to the excitation coil (EC) to generate a magnetic field, and eddy currents generated in the measurement coil (SC) due to a magnetic field change caused by the influence of a measurement object (M) are detected by an ammeter or voltmeter connected to the measurement coil (SC).

[0005] Furthermore, a common structure of an eddy current electromagnetic sensor used for surface flaw detection and the like is shown in Figure 18, which comprises one excitation coil (EC) and a pair of measuring coils (SC) consisting of a first measuring coil (SC1) and a second measuring coil (SC2) arranged superimposed on the excitation coil (EC) in the direction of the magnetic field and connected in series. An AC power supply is applied to the excitation coil (EC) to generate a magnetic field, and the eddy currents generated in each measuring coil (SC1, SC2) due to the change in the magnetic field caused by the influence of the object being measured (M) are detected by an ammeter or voltmeter connected to the pair of measuring coils (SC). The first measuring coil (SC1) and the second measuring coil (SC2) are coils of similar form, arranged side by side in the radial direction of the coil, and connected in a direction in which their excitation voltages cancel each other out. In an eddy current electromagnetic sensor equipped with such a pair of measuring coils (SC), when measuring an object with a uniform surface, opposing voltages are generated between the first measuring coil (SC1) and the second measuring coil (SC2). These voltages cancel each other out, resulting in no potential difference and no current flow, thus the detected combined current is zero. However, when measuring an object with an uneven surface due to scratches or other defects, different voltages are generated between one coil and the other. This potential difference causes current to flow, which can then be used as a signal to detect scratches or other defects.

[0006] Furthermore, as an applied structure of the eddy current electromagnetic sensor, as shown in Figure 19, there is a known type that comprises one excitation coil (EC), one measurement coil (SC) superimposed on the excitation coil (EC) in the direction of the magnetic field, and one reference measurement coil (SC') superimposed on the excitation coil (EC) on the opposite side from the measurement coil (SC) in the direction of the magnetic field. An AC power supply is applied to the excitation coil (EC) to generate a magnetic field, and the difference in eddy currents generated in the measurement coil (SC) and the reference measurement coil (SC') due to the change in the magnetic field caused by the influence of the object being measured (M) is detected by an ammeter or voltmeter connected between the measurement coil (SC) and the reference measurement coil (SC') (see also Patent Document 1). Such an eddy current electromagnetic sensor equipped with a reference measurement coil (SC') is also based on the idea of ​​amplifying the signal by obtaining the difference in signals from the two measurement coils, the measurement coil (SC) and the reference measurement coil (SC'). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 6283965 [Overview of the project] [Problems that the invention aims to solve]

[0008] Conventional eddy current electromagnetic sensors with general and applied structures, and non-destructive testing equipment equipped with these eddy current electromagnetic sensors, can perform well for inspection targets where strong signal differences can be obtained. However, there were cases where it was not possible to obtain sufficient signal differences for evaluating trace elements in soil or for inspecting differences in the internal structure of metal materials, which inherently produce strong signals. To explain this in more detail, the signals due to differences in soil or material structure are only slightly different from the basic signals of each material. On the other hand, in ordinary electromagnetic coils, variations occur due to the state of the windings, and weak signals generated by induced currents between windings and from the coil itself become measurement noise. As a result, the ratio of the target signal to the noise (hereinafter referred to as the "S / N ratio") becomes small, making it difficult to measure weak signal differences.

[0009] In view of these points, an object of the present invention is to provide an eddy current electromagnetic sensor that further improves signal strength by improving the signal-to-noise ratio. Another object of the present invention is to provide a non-destructive testing apparatus equipped with such an eddy current electromagnetic sensor with improved signal strength. [Means for solving the problem]

[0010] To solve the above problems, the eddy current type electromagnetic sensor according to the present invention is A first coil unit having a first excitation coil that generates a magnetic flux when power is applied, and a first measuring coil set consisting of a first measuring coil and a second measuring coil, each of which is wound in a spiral or helical shape, coaxial with the first excitation coil and positioned on the magnetic flux generated by the first excitation coil, and connected in series with each other, A second coil unit having a second excitation coil that generates a magnetic flux when power is applied, and a second measuring coil set consisting of a third measuring coil and a fourth measuring coil, each coaxial with the second excitation coil, positioned on the magnetic flux generated by the second excitation coil, wound in a spiral or helical shape, and connected in series with each other. A power supply unit that applies AC power to the first excitation coil and the second excitation coil, A signal output unit is connected between the first measuring coil and the second measuring coil, and between the third measuring coil and the fourth measuring coil, and outputs a signal that is the difference between the first signal obtained from between the first measuring coil and the second measuring coil and the second signal obtained from between the third measuring coil and the fourth measuring coil. Equipped with, The first coil unit and the second coil unit are coil units that are electrically connected to each other. The first measurement coil set and the second measurement coil set are connected such that the excitation voltage of the first measurement coil set caused by the change in the magnetic flux of the first excitation coil cancels out the excitation voltage of the second measurement coil set caused by the change in the magnetic flux of the second excitation coil, with the first measurement coil connected to the third measurement coil and the second measurement coil connected to the fourth measurement coil. It is characterized by the following.

[0011] In this eddy current electromagnetic sensor, the first excitation coil and the second excitation coil may be connected in series with one end of the first excitation coil and the other end of the second excitation coil connected to a power supply unit to which power is applied.

[0012] In this eddy current electromagnetic sensor, the first and second excitation coils are formed with the same outer diameter and the same number of windings so that their inductances are matched, and the first to fourth measuring coils are formed with the same outer diameter and the same number of windings so that their inductances are matched.

[0013] Furthermore, in this eddy current electromagnetic sensor, one example of an arrangement is to use a straight-shaped yoke in which the first coil unit and the second coil unit are positioned close to each other with their coil centers aligned in a straight line, and the straight-shaped yoke is arranged in a straight line so as to pass through the coil centers of the first coil unit and the second coil unit, or to use a bent-shaped yoke that is bent in the middle, with one end of the bent-shaped yoke passing through the coil center of the first coil unit and the other end of the bent-shaped yoke passing through the coil center of the second coil unit, thereby causing magnetic repulsion or coupling.

[0014] Furthermore, in this eddy current electromagnetic sensor, as another example of an arrangement, there is a type in which the first coil unit and the second coil unit are arranged in a straight line with a predetermined distance between them, so that the object to be inspected can be placed in between.

[0015] Furthermore, in this eddy current electromagnetic sensor, as another example of an arrangement, there is a type in which the first coil unit and the second coil unit are arranged side by side at a distance from each other, thereby being magnetically independent.

[0016] Furthermore, in this eddy current type electromagnetic sensor, A voltage adjustment unit that applies voltage to output lines that output the first signal and the second signal, A voltage adjustment control unit controls the applied voltage value output by the voltage adjustment unit, Furthermore, The output line that outputs the first signal and the second signal is branched into two parts: one part that goes towards the first output terminal to which the signal output section is connected, and the other part that goes towards the second output terminal to which the adjustment voltage application section is connected. Resistors are placed at the position before each branch and at a position along the way to the second output terminal after the branch. The adjustment voltage control unit controls the applied voltage value output by the adjustment voltage applying unit so as to suppress variations among the first to fourth measurement coils for each frequency based on measurement results of the first signal and the second signal acquired in advance for each frequency, it is also preferable to configure the signal processing unit as such.

[0017] Further, in order to solve the above problem, a nondestructive inspection apparatus according to the present invention mounts an eddy current electromagnetic sensor that generates a magnetic field and detects secondary eddy currents generated by magnetic field changes with high sensitivity, and detects the state of the inspection target by causing the eddy current electromagnetic sensor to face the inspection target, thereby enabling nondestructive inspection of the inspection target, wherein the above-described eddy current electromagnetic sensor according to the present invention is mounted as the eddy current electromagnetic sensor.

Effects of the Invention

[0018] According to the present invention, by improving the S / N ratio, an eddy current electromagnetic sensor with further improved signal intensity can be provided. Further, according to the present invention, a nondestructive inspection apparatus equipped with such an eddy current electromagnetic sensor with further improved signal intensity can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] [Figure 1] It is a circuit diagram of the eddy current electromagnetic sensor of Embodiment 1. [Figure 2] It is a schematic diagram showing an arrangement form of coil units in the eddy current electromagnetic sensor of Embodiment 1. [Figure 3] It is a diagram showing the arrangement form of FIG. 2 as a circuit diagram. [Figure 4] It is a schematic diagram showing a modification of an arrangement form in which coil units are magnetically coupled to each other. [Figure 5] It is a schematic diagram showing an arrangement form of coil units in the eddy current electromagnetic sensor of Embodiment 2. [Figure 6] It is a diagram showing the arrangement form of FIG. 5 as a circuit diagram. [Figure 7]This is a schematic diagram showing the arrangement of the coil unit in the eddy current type electromagnetic sensor of Embodiment 3. [Figure 8] Figure 7 shows the arrangement configuration as a circuit diagram. [Figure 9] This is a schematic diagram showing variations in the method of using the eddy current type electromagnetic sensor according to Embodiment 3. [Figure 10] This is a circuit diagram of the eddy current type electromagnetic sensor of Embodiment 4. [Figure 11] This graph shows the measurement results of a metal sample when using the eddy current type electromagnetic sensor of Embodiment 1 in Example 1. [Figure 12] This graph shows the background measurement results when using the eddy current type electromagnetic sensor of Embodiment 1 in Example 1. [Figure 13] For comparison with Figure 11, this graph shows the measurement results of a metal sample using a conventional applied eddy current electromagnetic sensor. [Figure 14] This graph shows the background measurement results when using a conventional applied eddy current electromagnetic sensor, for comparison with Figure 12. [Figure 15] This graph shows the background measurement results and soil measurement results when using the eddy current type electromagnetic sensor of Embodiment 1 in Example 2. [Figure 16] For comparison with Figure 15, this graph shows the background measurement results and soil measurement results when using a conventional applied-type eddy current electromagnetic sensor. [Figure 17] This is a schematic diagram showing the basic structure of a conventionally known eddy current electromagnetic sensor. [Figure 18] This is a schematic diagram showing the general structure of a conventionally known eddy current electromagnetic sensor. [Figure 19] This is a schematic diagram showing an applied structure of a conventionally known eddy current type electromagnetic sensor. [Modes for carrying out the invention]

[0020] The following describes, with reference to the drawings, an eddy current electromagnetic sensor as one embodiment to which the present invention is applied, and a non-destructive testing apparatus equipped with the eddy current electromagnetic sensor. Note that the drawings do not necessarily strictly reflect all actual configurations.

[0021] [Embodiment 1] (Basic configuration of eddy current electromagnetic sensor 1) Figure 1 is a circuit diagram of the eddy current electromagnetic sensor 1 of Embodiment 1. First, the basic configuration of the eddy current electromagnetic sensor 1 of Embodiment 1 will be explained with reference to Figure 1.

[0022] The eddy current electromagnetic sensor 1 is a sensor that generates a magnetic field and detects eddy currents secondarily generated by changes in the magnetic field with high sensitivity. As shown in Figure 1, it comprises a coil unit 2 composed of multiple coils connected to each other in a so-called bridge type, a power supply unit 3 that applies AC power to the coil unit 2, and a signal output unit 4 that acquires signals from the coil unit 2.

[0023] The coil unit 2 consists of two sets, a first coil unit 2A and a second coil unit 2B, which are electrically connected to each other. Each set consists of one excitation coil that generates magnetic flux when power is applied, and two measuring coils that measure the change in the magnetic field caused by the magnetic flux generated in the excitation coil.

[0024] The first coil unit 2A consists of a first excitation coil 21 as an excitation coil, and a first measurement coil 22 and a second measurement coil 23 as measurement coils. The first excitation coil 21 is a spirally or helical coil, with one end connected to the second excitation coil 25 of the second coil unit 2B (described later) and the other end connected to the power supply unit 3 (described later). The first excitation coil 21 is supplied with AC power by the power supply unit 3 (described later) and can generate a magnetic field that passes through the center of the coil in a direction corresponding to the direction of the flowing current. The first measurement coil 22 and the second measurement coil 23 are spirally or helically wound coils, each positioned coaxially with the first excitation coil 21 and on the magnetic flux generated by the first excitation coil 21. They are formed with the same outer diameter, the same number of windings, and the same winding direction to match their inductances. Furthermore, the first measuring coil 22 and the second measuring coil 23 are electrically connected in series with the same excitation direction, thereby constituting the first measuring coil set 24. The first measuring coil set 24 has both ends connected in parallel (connected in a loop) to the second measuring coil set 28, which will be described later. In the first coil unit 2A, as an example, the first measuring coil 22 and the second measuring coil 23 are arranged superimposed on both sides of the first excitation coil 21 in the direction of the magnetic field, so that the first measuring coil 22 and the second measuring coil 23 sandwich the first excitation coil 21.

[0025] The second coil unit 2B consists of a second excitation coil 25 as an excitation coil, and a third measurement coil 26 and a fourth measurement coil 27 as measurement coils. The second excitation coil 25 is a spirally or helical coil, with one end connected to the first excitation coil 21 of the first coil unit 2A and the other end connected to the power supply unit 3 described later. The second excitation coil 25 is supplied with AC power by the power supply unit 3 described later, and can generate a magnetic field that passes through the center of the coil in a direction corresponding to the direction of the flowing current. The third measurement coil 26 and the fourth measurement coil 27 are spirally or helically wound coils, each positioned coaxially with the second excitation coil 25 and on the magnetic flux generated by the second excitation coil 25, and are formed with the same outer diameter, the same number of windings, and the same winding direction to match their inductances. Furthermore, the third measuring coil 26 and the fourth measuring coil 27 are electrically connected in series with the same excitation direction, thereby constituting the second measuring coil set 28. As mentioned above, both ends of the second measuring coil set 28 are connected in parallel to the first measuring coil set 24 (connected in a loop). In the second coil unit 2B, as an example, the third measuring coil 26 and the fourth measuring coil 27 are arranged superimposed on both sides of the second excitation coil 25 in the direction of the magnetic field, with the third measuring coil 26 and the fourth measuring coil 27 sandwiching the second excitation coil 25.

[0026] Here, the first coil unit 2A and the second coil unit 2B have similar configurations. More specifically, the first excitation coil 21 and the second excitation coil 25 correspond to each other in the first coil unit 2A and the second coil unit 2B, the first measurement coil 22 and the third measurement coil 26 correspond to each other, and the second measurement coil 23 and the fourth measurement coil 27 correspond to each other. Corresponding coils have the same outer diameter, the same number of windings, and the same winding direction so that their inductances are matched. In other words, the first excitation coil 21 and the second excitation coil 25 have similar configurations, and the first to fourth measurement coils (22, 23, 26, 27) have similar configurations. Furthermore, the first coil unit 2A and the second coil unit 2B are electrically connected to each other by the connections between the first measuring coil 22 and the third measuring coil 26, and between the second measuring coil 23 and the fourth measuring coil 27, so that the excitation voltage of the first measuring coil set 24 caused by the change in magnetic flux of the first excitation coil 21 and the excitation voltage of the second measuring coil set 28 caused by the change in magnetic flux of the second excitation coil 25 cancel each other out. As a specific example, in the coil unit 2 of Embodiment 1 shown in Figure 1, all coils are wound in the same direction, and the first measuring coil set 24 and the second measuring coil set 28 are connected at the beginning of the winding of the first measuring coil 22 and the beginning of the winding of the third measuring coil 26, and at the end of the winding of the second measuring coil 23 and the end of the winding of the fourth measuring coil 27. Furthermore, in the coil unit 2 of Embodiment 1, the first excitation coil 21 is positioned with the same winding direction as the first measurement coil set 24, and the second excitation coil 25 is positioned with the same winding direction as the second measurement coil set 28, and the end of the winding of the first excitation coil 21 and the beginning of the winding of the second excitation coil 25 are connected. The specific arrangement of the first coil unit 2A and the second coil unit 2B will be described later.Furthermore, in the coil unit according to the present invention, the first measurement coil set and the second measurement coil set are connected such that the excitation voltage of the first measurement coil set caused by the change in magnetic flux of the first excitation coil and the excitation voltage of the second measurement coil set caused by the change in magnetic flux of the second excitation coil cancel each other out. The first measurement coil and the third measurement coil, and the second measurement coil and the fourth measurement coil are connected in such a way. The winding direction of each coil, the direction of connection, and the arrangement of the excitation coil and the measurement coil are not limited to the winding direction of each coil, the direction of connection, and the arrangement of the excitation coil and the measurement coil in the coil unit 2 as a specific example, but various patterns can be selected.

[0027] The power supply unit 3 includes equipment that generates AC power and, as described above, is connected to one end of the first excitation coil 21 and the other end of the second excitation coil 25, which are connected in series. The power supply unit 3 applies AC power to the first excitation coil 21 and the second excitation coil 25, which are connected in series.

[0028] The signal output unit 4 is connected between the first measuring coil 22 and the second measuring coil 23 in the first coil unit 2A, and between the third measuring coil 26 and the fourth measuring coil 27 in the second coil unit 2B. It acquires the first signal from between the first measuring coil 22 and the second measuring coil 23, and the second signal from between the third measuring coil 26 and the fourth measuring coil 27. The signal output unit 4 also has a function to calculate the difference between the acquired signals by processing with an electronic circuit or by software, and outputs the difference signal between the first signal and the second signal as a detected value. The signal output unit 4 may output the difference signal as is, but it is also preferable that it has a function to process the signal, such as by amplification, before outputting it.

[0029] In an eddy current electromagnetic sensor with this basic configuration, various arrangements of coil units are possible. However, in Embodiment 1, the coil unit 2 is arranged such that the first coil unit 2A and the second coil unit 2B repel each other magnetically (see Figure 3). This arrangement will be explained next.

[0030] (Arrangement configuration of coil unit 2) Figure 2 is a schematic diagram showing the arrangement of the coil unit 2 in the eddy current electromagnetic sensor 1, Figure 3 is a circuit diagram showing the arrangement in Figure 2, and Figure 4 is a schematic diagram showing a modified arrangement in which the coil units are magnetically coupled. The arrangement of the coil unit 2 in the eddy current electromagnetic sensor 1 will be described below with reference to Figures 2 to 4.

[0031] In the eddy current electromagnetic sensor 1, as shown in Figure 2, the first coil unit 2A and the second coil unit 2B are positioned close to each other with their coil centers aligned in a straight line. More specifically, in the eddy current electromagnetic sensor 1 as an example, the first measuring coil 22 is used when it is placed in relation to the object to be measured M to directly detect the change in the magnetic field caused by the object to be measured M. The first coil unit 2A and the second coil unit 2B are arranged in the following order from the object to be measured M side: first measuring coil 22, first excitation coil 21, second measuring coil 23, fourth measuring coil 27, second excitation coil 25, and third measuring coil 26. In this configuration, as shown in Figure 3, the first measuring coil set 24 and the second measuring coil set 28 repel each other magnetically (the magnets in the hatched areas of Figure 3 are opposite), and the influence of the magnetic field from the first excitation coil 21 is transmitted to the second measuring coil set 28 side in the form of a change in repulsion.

[0032] In addition, depending on the measurement purpose, it may be desirable to increase the excitation force. In such cases, the connection method, winding direction, etc., can be appropriately changed to select an arrangement that aligns the direction of the magnetic flux generated by the second coil unit 2B with that of the first coil unit 2A in the same configuration (the "S / N" and "N / S" markings on the second coil unit 2B in Figure 3 will be reversed). As a result, the magnetic field generated by the first excitation coil 21 and the magnetic field generated by the second excitation coil 25 are superimposed, enabling evaluation with increased excitation force.

[0033] Furthermore, in order to magnetically couple the first coil unit 2A and the second coil unit 2B as shown in Figure 3, the first coil unit 2A and the second coil unit 2B may be arranged in a configuration where their coil centers are aligned in a straight line and close to each other, as shown in Figure 2 above. In addition, for example, the following configurations may also be used. For example, as shown in Figure 4(a), a straight-shaped yoke (Y1) may be used, and the first coil unit 2A and the second coil unit 2B may be arranged in a configuration where the yoke (Y1) passes through the coil centers and they are aligned in a straight line. Alternatively, as shown in Figure 4(b), a bent-shaped yoke (Y2) may be used, and the first coil unit 2A and the second coil unit 2B may be arranged in a configuration where each end of the bent-shaped yoke (Y2) passes through the respective coil centers and they are not aligned in a straight line. Even in this configuration, if it is desired to increase the excitation force for measurement purposes, an arrangement can be selected in which the direction of the magnetic flux generated by the second coil unit 2B is aligned with that of the first coil unit 2A, as described above.

[0034] (Detection of the state of the object M using eddy current electromagnetic sensor 1) Next, the detection of the state of the object to be measured M using the eddy current electromagnetic sensor 1 will be explained. To detect the state of the object to be measured M using the eddy current electromagnetic sensor 1, first, the power supply unit 3 is turned on and AC power is supplied from the power supply unit 3 to the coil unit 2. When this is done, current flows through the first excitation coil 21 and the second excitation coil 25, generating magnetic flux and a magnetic field. At this time, each time the direction of the current is repeatedly switched by the AC power supply, the resulting change in the magnetic field generates an excitation voltage in the first measurement coil set 24, which is positioned in the magnetic field of the first excitation coil 21, according to the direction of the magnetic flux of the first excitation coil 21. On the other hand, an excitation voltage is also generated in the second measurement coil set 28, which is positioned in the magnetic field of the second excitation coil 25, according to the direction of the magnetic flux of the second excitation coil 25. Here, in the eddy current electromagnetic sensor 1, the first measurement coil set 24 and the second measurement coil set 28 have the same inductance and are connected so that the directions of the excitation voltages are opposite. Therefore, when there is no object to be measured M, and the sensor is in the background, there is no difference in the disturbances between the magnetic field of the first excitation coil 21 and the magnetic field of the second excitation coil 25. The magnitudes of the excitation voltage generated in the first measurement coil set 24 and the excitation voltage generated in the second measurement coil set 28 are the same and cancel each other out, so theoretically no current flows through the measurement coils. As a result, the first signal and the second signal are both zero, and the output of the signal output unit 4, which outputs the difference between the two, is also zero. In other words, the eddy current electromagnetic sensor 1 can reduce background noise by canceling it out with the first coil unit 2A and the second coil unit 2B. On the other hand, as shown in Figure 2, when the first coil unit 2A is brought closer to the object to be measured M, the magnetic field of the first excitation coil 21 fluctuates more than the magnetic field of the second excitation coil 25 due to the influence of the object to be measured M. As a result, the difference between the excitation voltage generated in the first measurement coil set 24 and the excitation voltage generated in the second measurement coil set 28 becomes larger. As a result, the difference in current flows through the measuring coil, the magnitudes of the first signal and the second signal also become different, and the signal output unit 4 outputs a value greater than or equal to zero. This output value is a signal mainly influenced by the object being measured M, with background noise removed as much as possible.As a result, the eddy current electromagnetic sensor 1 detects a signal with a good signal-to-noise ratio.

[0035] (Use of eddy current electromagnetic sensor 1 in non-destructive testing equipment) The eddy current electromagnetic sensor 1 configured in this way is a sensor that generates a magnetic field and detects eddy currents secondarily generated by changes in the magnetic field with high sensitivity. For example, it is suitable for use in non-destructive testing equipment used for inspections such as soil characteristic analysis and welding strength evaluation, and is ideal for non-destructive testing that requires the measurement of weak signal differences, such as the evaluation of trace elements in soil or differences in the internal structure of metal materials that originally produce strong signals. Such a non-destructive testing equipment can inspect the object M non-destructively by placing the eddy current electromagnetic sensor 1 in front of the object M and detecting the state of the object M.

[0036] (Effects / Actions) The eddy current electromagnetic sensor 1 of Embodiment 1 includes a first coil unit 2A having a first excitation coil 21 and a first measurement coil set 24 consisting of a first measurement coil 22 and a second measurement coil 23, each positioned on the magnetic flux generated by the first excitation coil 21 and connected in series with each other; and a second coil unit 2B having a second excitation coil 25 and a second measurement coil set 28 consisting of a third measurement coil 26 and a fourth measurement coil 27, each positioned on the magnetic flux generated by the second excitation coil 25 and connected in series with each other. The eddy current electromagnetic sensor 1 also includes a power supply unit 3 that applies AC power to the first excitation coil 21 and the second excitation coil, and a signal output unit 4 that outputs a signal that is the difference between a first signal obtained from between the measurement coils (22, 23) of the first coil unit 2A and a second signal obtained from between the measurement coils (26, 27) of the second coil unit 2B. In the eddy current electromagnetic sensor 1 configured in this way, the first coil unit 2A and the second coil unit 2B are electrically connected coil units 2. The first measurement coil set 24 and the second measurement coil set 28 are connected such that the excitation voltage of the first measurement coil set 24, caused by the change in magnetic flux of the first excitation coil 21, and the excitation voltage of the second measurement coil set 28, caused by the change in magnetic flux of the second excitation coil 25, cancel each other out. The first measurement coil 22 and the third measurement coil 26, and the second measurement coil 23 and the fourth measurement coil 27 are connected in this manner. In other words, the eddy current electromagnetic sensor 1 has an applied structure of an eddy current electromagnetic sensor as shown in Figure 19 for each of the first coil unit 2A and the second coil unit 2B. By obtaining the difference between the signals from the two measurement coils, noise can be greatly reduced, and the signals from each are amplified.Furthermore, in the eddy current electromagnetic sensor 1, the measurement coils (22, 23) in the first coil unit 2A and the measurement coils (26, 27) in the second coil unit 2B are connected in a manner similar to a so-called bridge circuit, and the signal is output to the signal output unit 4. The sensitivity of the first measurement coil 22, which is the measurement coil for the object to be measured M, is improved compared to when it is composed of a single coil unit, and the signal strength is increased. Therefore, with the eddy current electromagnetic sensor 1, the signal strength can be further improved by improving the signal-to-noise ratio.

[0037] In the eddy current electromagnetic sensor 1, the first excitation coil 21 and the second excitation coil 25 are connected in series, and both ends are connected to the power supply unit 3 to apply power. In this case, if the same excitation voltage is applied to a conventional excitation coil as to a single eddy current electromagnetic sensor, the current flowing through each excitation coil will be halved compared to a conventional excitation coil, and the sensor output will also be halved. However, with the eddy current electromagnetic sensor 1, the output is obtained by taking the difference between the first measurement coil set 24 and the second measurement coil set 28, so the noise is greatly reduced and the sensitivity is improved compared to a conventional eddy current electromagnetic sensor, and sufficient signal strength can be obtained. In other words, power consumption can be reduced.

[0038] Furthermore, in the eddy current electromagnetic sensor 1, the first and second excitation coils (21, 25) are formed with the same outer diameter and the same number of windings so that their inductances are matched, and the first to fourth measurement coils (22, 23, 26, 27) are formed with the same outer diameter and the same number of windings so that their inductances are matched. As a result, in the eddy current electromagnetic sensor 1, the first coil unit 2A and the second coil unit 2B become equivalent, the ratio of the signal to noise (S / N ratio) is increased, and even weak signal differences can be captured, resulting in high accuracy.

[0039] Furthermore, in the eddy current electromagnetic sensor 1, the first coil unit 2A and the second coil unit 2B are arranged close to each other with their coil centers aligned in a straight line using a straight-shaped yoke Y1, or a bent-shaped yoke Y2 is used, where one end of the bent-shaped yoke Y2 pierces the coil center of the first coil unit 2A and the other end pierces the coil center of the second coil unit 2B, thereby causing them to repel or be coupled magnetically. By configuring the first coil unit 2A and the second coil unit 2B to repel or be coupled magnetically in this way, the first measurement coil set 24 and the second measurement coil set 28 are affected by each other's magnetism, and the signal-to-noise ratio can be reduced according to the measurement purpose to evaluate the object being measured.

[0040] A non-destructive testing device equipped with an eddy current electromagnetic sensor 1 can take advantage of the effects of the eddy current electromagnetic sensor 1 and can be effectively used for non-destructive testing that requires the measurement of weak signal differences, such as the evaluation of trace elements in soil or differences in the internal structure of metal materials that originally produce strong signals.

[0041] [Embodiment 2] Figure 5 is a schematic diagram showing the arrangement of the coil unit 102 in the eddy current electromagnetic sensor 101 of Embodiment 2, and Figure 6 is a diagram showing the arrangement of Figure 5 as a circuit diagram. The eddy current electromagnetic sensor 101 is similar to the eddy current electromagnetic sensor 1 of Embodiment 1 in terms of its circuit configuration and the fact that the first coil unit 2A and the second coil unit 2B are arranged in a straight line. However, in order to distinguish the number of coils that detect changes caused by the measurement target M in relation to the measurement target M, the position and orientation of the second coil unit 2B relative to the first coil unit 2A are different. That is, in the coil unit 2 of the eddy current electromagnetic sensor 1 of Embodiment 1, the coil that detects changes caused by the measurement target M in relation to the measurement target M is the first measurement coil 22, and the first coil unit 2A and the second coil unit 2B are magnetically repelled by bringing the second measurement coil 23 and the fourth measurement coil 27 close together. However, the coil unit 102 of the eddy current electromagnetic sensor 101 differs in that this is not the case. The eddy current electromagnetic sensor 101 of Embodiment 2 will be described below with reference to Figures 5 and 6, but only the differences from Embodiment 1 will be described. Components similar to those in Embodiment 1 will be denoted by the same reference numerals as in Figures 1 to 4 in Figures 5 and 6, and their description will be omitted.

[0042] In the eddy current electromagnetic sensor 101, as shown in Figure 5, the first coil unit 2A and the second coil unit 2B are positioned opposite each other at a predetermined distance apart. More specifically, as an example, the eddy current electromagnetic sensor 101 has a first measuring coil 22 and a third measuring coil 26 that are placed in opposition to the object to be measured M during use to detect changes caused by the object to be measured M. The first coil unit 2A consists of the first measuring coil 22, the first excitation coil 21, and the second measuring coil 23, arranged in that order from one side of the object to be measured M, and the second coil unit 2B consists of the third measuring coil 26, the second excitation coil 25, and the fourth measuring coil 27, arranged in that order from the other side opposite the one side of the object to be measured M. The first measuring coil 22 and the third measuring coil 26 are positioned opposite each other at a predetermined distance apart and aligned in a straight line. In other words, the eddy current electromagnetic sensor 101 measures by placing coils that detect changes caused by the object to be measured M on either side of the object to be measured M, so as to sandwich the object to be measured M.

[0043] The eddy current electromagnetic sensor 101 has basically the same circuit configuration as the eddy current electromagnetic sensor 1 of Embodiment 1, and therefore, like the eddy current electromagnetic sensor 1 of Embodiment 1, it can increase the measured signal strength. Furthermore, with the eddy current electromagnetic sensor 101, by measuring the thickness direction of the object to be measured M from different directions using the first coil unit 2A and the second coil unit 2B, it becomes possible to measure the component distribution in the thickness direction, etc.

[0044] [Embodiment 3] Figure 7 is a schematic diagram showing the arrangement of the coil unit 202 in the eddy current electromagnetic sensor 201 of Embodiment 3, Figure 8 is a circuit diagram showing the arrangement of Figure 7, and Figure 9 is a schematic diagram showing variations in the usage method of the eddy current electromagnetic sensor 201. The eddy current electromagnetic sensor 201 has the same circuit configuration as the eddy current electromagnetic sensor 1 of Embodiment 1 as shown in Figure 1, but the magnetic relationship between the coil units differs from that of the eddy current electromagnetic sensor 1. Specifically, in the coil unit 2 of the eddy current electromagnetic sensor 1 of Embodiment 1, the first coil unit 2A and the second coil unit 2B were magnetically repelled or coupled, whereas the coil unit 202 of the eddy current electromagnetic sensor 201 differs in that the first coil unit 2A and the second coil unit 2B are magnetically separated. The eddy current electromagnetic sensor 201 of Embodiment 3 will be described below with reference to Figures 7 to 9, but only the differences from Embodiment 1 will be described. Components similar to those in Embodiment 1 will be denoted by the same reference numerals as in Figures 1 to 4 in Figures 7 to 9, and their description will be omitted.

[0045] In the eddy current electromagnetic sensor 201, as shown in Figure 7, the first coil unit 2A and the second coil unit 2B are arranged side by side at a distance from each other. More specifically, as an example, the eddy current electromagnetic sensor 201 has a first measuring coil 22 which is placed in relation to the object to be measured M during use to detect changes caused by the object to be measured M. The first coil unit 2A consists of the first measuring coil 22, the first excitation coil 21, and the second measuring coil 23, while the second coil unit 2B consists of the third measuring coil 26, the second excitation coil 25, and the fourth measuring coil 27. The first measuring coil 22 and the third measuring coil 26 are oriented in the same direction, and the coils are spaced apart in the radial direction. As shown in Figure 8, in the eddy current electromagnetic sensor 201, the second measuring coil 23 and the fourth measuring coil 27 are connected, but since the first coil unit 2A and the second coil unit 2B are located at different positions, they are magnetically independent of each other.

[0046] Furthermore, in the eddy current electromagnetic sensor 201, since the first coil unit 2A and the second coil unit 2B are aligned in the coil radial direction, as shown in Figure 7, it is possible to use the sensor not only by facing only the first measuring coil 22 of the first coil unit 2A toward the object to be measured M to detect the state of the object to be measured M, but also by simultaneously facing the third measuring coil 26 of the second coil unit 2B toward a reference object to be measured M', as shown in Figure 9, to detect the degree of deviation of the object to be measured M relative to the reference object to be measured M'.

[0047] The eddy current electromagnetic sensor 201 has basically the same circuit configuration as the eddy current electromagnetic sensor 1 of Embodiment 1, and therefore, like the eddy current electromagnetic sensor 1 of Embodiment 1, it can increase the measured signal strength. Furthermore, because the first coil unit 2A and the second coil unit 2B of the eddy current electromagnetic sensor 201 are arranged side by side at a distance from each other and are magnetically independent, it can be used for measurements in which one coil unit is used as a reference unit that is not affected by the measurement, or for comparative measurements with a reference of the object to be measured by measuring a reference sample with one coil unit.

[0048] [Embodiment 4] Figure 10 is a circuit diagram of the eddy current electromagnetic sensor 301 of Embodiment 4. The eddy current electromagnetic sensor 301 has the same basic configuration as the eddy current electromagnetic sensor 1 of Embodiment 1, but the circuit configuration connected to the coil unit is different from that of the eddy current electromagnetic sensor 1. That is, in the eddy current electromagnetic sensor 1 of Embodiment 1, the signal output unit 4 performs signal processing that outputs the difference between the first signal obtained from the first coil unit 2A and the second signal obtained from the second coil unit 2B, while the eddy current electromagnetic sensor 301 differs in that it is further equipped with a coil characteristic variation reduction adjustment function. The eddy current electromagnetic sensor 301 of Embodiment 4 will be described below with reference to Figure 10, but only the differences from Embodiment 1 will be described, and the same parts configuration as in Embodiment 1 will be denoted in Figure 10 with the same reference numerals as in Figure 1, and their description will be omitted.

[0049] The eddy current electromagnetic sensor 301 further includes an adjustment voltage application unit 305 connected to the output lines that output the first signal and the second signal, and an adjustment voltage control unit 306 electrically connected to the adjustment voltage application unit 305. In the eddy current electromagnetic sensor 301, the output lines that output the first signal and the second signal branch into two: one leading towards the first output terminal to which the signal output unit 4 is connected, and the other leading towards the second output terminal to which the adjustment voltage application unit 305 is connected. The output lines that output the first signal and the second signal each have resistors 351a and 351b before the branching point, and resistors 351c and 351d located midway along the line towards the second output terminal after the branching point.

[0050] The adjustment voltage application unit 305 includes a voltage generator that applies voltage to output lines that output a first signal and a second signal based on the command of 306 described later.

[0051] The adjustment voltage control unit 306 controls the applied voltage value output by the adjustment voltage application unit 305. More specifically, the adjustment voltage control unit 306 controls the applied voltage value output by the adjustment voltage application unit 305 to suppress variations in the first to fourth measuring coils 22, 23, 26, and 27 for each frequency, based on the measurement results of the first and second signals acquired in advance for each frequency.

[0052] According to the eddy current electromagnetic sensor 301 of Embodiment 4, by further suppressing the variation of the measuring coils 22, 23, 26, and 27 compared to the eddy current electromagnetic sensor 1 of Embodiment 1, the background noise components of the first signal from the first measuring coil set 24 and the second signal from the second measuring coil set 28 become more equal and cancel each other out more effectively, thus further improving the signal-to-noise ratio compared to the eddy current electromagnetic sensor 1 of Embodiment 1.

[0053] [Other forms] Although the present invention has been described above based on the above embodiments, the present invention is not limited to the above embodiments. It can be implemented in various forms without departing from the spirit of the invention, and for example, the following modifications are also possible.

[0054] (1) The number of components, specific placement and orientation, wiring method, circuit configuration, etc. described in the above embodiment are illustrative examples and can be changed within the scope that does not impair the effects of the present invention.

[0055] (2) In the embodiments described above, the eddy current electromagnetic sensor 1 was described as having the same shape for the first and second excitation coils 21 and 25, and the same shape for the first to fourth measurement coils 22, 23, 26 and 27. However, the present invention is not limited to this. The concept of the present invention also includes cases where the coils are not formed in the same shape as described above, but the first coil unit 2A and the second coil unit 2B are configured to cancel out background noise as much as possible.

[0056] (3) In the embodiments described above, the first and second excitation coils 21, 25 and the first to fourth measurement coils 22, 23, 26, 27 were each formed as a single coil with a winding start and winding end unit, but the present invention is not limited thereto. The first and second excitation coils 21, 25 and the first to fourth measurement coils 22, 23, 26, 27 may each be formed by combining multiple coils with a single winding start and winding end unit.

[0057] (4) In the above-described embodiment 1, the first excitation coil 21 and the second excitation coil 25 were described as being connected in series and both ends were connected to the power supply unit 3 to apply power. However, the present invention is not limited to this, as long as each excitation coil and the corresponding measurement coil set are connected in a direction that cancels out the excitation voltages of each other. For example, the first excitation coil and the second excitation coil may be connected in parallel and both ends of each may be connected to the power supply unit. In this case, at the same excitation voltage, the current flowing through each coil will be double that of embodiment 1, and the power consumption will be higher, but the resolution will be increased as the sensor output will be doubled. [Examples]

[0058] (Example 1) Figure 11 is a graph showing the measurement results of a metal sample when using the eddy current electromagnetic sensor 1, and Figure 12 is a graph showing the background measurement results in this measurement. Figure 13 is a graph showing the measurement results of a metal sample when using a conventional applied-type eddy current electromagnetic sensor for comparison, and Figure 14 is a graph showing the background measurement results in this measurement. Below, the results of a test conducted as Example 1 to confirm the effect of improving the signal-to-noise ratio of the eddy current electromagnetic sensor 1 according to the present invention are shown.

[0059] In Example 1, a comparative test was conducted between the eddy current electromagnetic sensor 1 of Embodiment 1 according to the present invention (see Figures 1 and 2) and a conventional eddy current electromagnetic sensor with an applied structure (see Figure 19). The coils of both were manufactured under the same conditions. That is, while the coil units are equivalent in both cases, the eddy current electromagnetic sensor 1 differs from the conventional eddy current electromagnetic sensor with an applied structure, which is composed of a single coil unit, in that it is composed of two coil units 2A and 2B.

[0060] In the comparative test of Example 1, to evaluate the differences in metal structures that produce stronger signals but show less signal difference between samples, comparative measurements were performed on six types of stainless steel thin sheets with different grain sizes ranging from 0.3 μm to 9.0 μm, using each eddy current electromagnetic sensor. Background measurements were also performed without the object being measured. Figure 11 shows the measurement results for stainless steel thin sheets using eddy current electromagnetic sensor 1, Figure 12 shows the measurement results for stainless steel thin sheets using a conventional applied eddy current electromagnetic sensor, Figure 13 shows the background measurement results using eddy current electromagnetic sensor 1, and Figure 14 shows the background measurement results using a conventional applied eddy current electromagnetic sensor. In each figure, the horizontal axis represents frequency, and the vertical axis represents the signal amplitude ratio (detection voltage divided by excitation voltage), showing the average value of 10 measurements.

[0061] In Example 1, when using the eddy current electromagnetic sensor 1, as shown in Figure 11, the results differed significantly only for a particle size of 0.3 μm. This is because, as the crystal grain size decreases, the microstructure changes from face-centered cubic to body-centered cubic, thus capturing a significant change in the microstructure. From particle sizes 0.5 μm to 9.0 μm, differences between the results became apparent at high frequencies, and the amplitude ratio also increased at high frequencies, reaching a maximum of approximately 0.15. Furthermore, as shown in Figure 12, the background noise at this time showed a decreasing amplitude ratio as the frequency increased, reaching a maximum of 0.000008.

[0062] On the other hand, in Example 1, when using a conventional applied eddy current electromagnetic sensor, as shown in Figure 13, the results differed significantly for a particle size of 0.3 μm, similar to the case when using eddy current electromagnetic sensor 1. This is because, as the crystal grain size decreases, the microstructure changes from face-centered cubic to body-centered cubic, thus capturing a significant change in the microstructure. Also, similar to the case when using eddy current electromagnetic sensor 1, differences between the two values ​​become apparent at high frequencies between particle sizes of 0.5 μm and 9.0 μm, and the amplitude ratio increases at high frequencies, but not as large as when using eddy current electromagnetic sensor 1, reaching a maximum of about 0.06. Furthermore, as shown in Figure 14, the background noise at this time showed an amplitude ratio that increased with increasing frequency, reaching 0.00012 at its highest point.

[0063] Comparing the two, in metal sample measurement, the amplitude ratio when using eddy current electromagnetic sensor 1 was approximately 0.15 at its maximum, which is 2.5 times higher than when using a conventional applied-type eddy current electromagnetic sensor. On the other hand, in background measurement, the amplitude ratio when using eddy current electromagnetic sensor 1 was 0.000008 at its highest point, which is less than 1 / 15 times lower than when using a conventional applied-type eddy current electromagnetic sensor. As a result, using eddy current electromagnetic sensor 1 resulted in a signal-to-noise ratio improvement of more than 10 times compared to using a conventional applied-type eddy current electromagnetic sensor, demonstrating a significant improvement.

[0064] (Example 2) Figure 15 is a graph showing the background measurement results and soil measurement results when using the eddy current electromagnetic sensor 1, and Figure 16 is a graph showing the background measurement results and soil measurement results when using a conventional applied structure eddy current electromagnetic sensor for comparison. Below, the results of a test conducted as Example 2 to confirm the effect of improving the S / N ratio of the eddy current electromagnetic sensor 1 according to the present invention are shown.

[0065] In Example 2, as in Example 1, a comparative test was conducted between the eddy current electromagnetic sensor 1 of Embodiment 1 according to the present invention (see Figures 1 and 2) and a conventional applied-type eddy current electromagnetic sensor (see Figure 19).

[0066] In the comparative test of Example 2, measurements were taken using each eddy current electromagnetic sensor in two different conditions: with no object to be measured for background measurement, with a plastic case placed in the sensor, and with two different types of soil. The measurement results when using eddy current electromagnetic sensor 1 are shown in the graph in Figure 15, and the measurement results when using a conventional applied structure eddy current electromagnetic sensor are shown in the graph in Figure 16. In both figures, the horizontal axis is frequency and the vertical axis is the amplitude ratio of the signal (the value obtained by dividing the detection voltage by the excitation voltage), and the average value of 10 measurements is shown.

[0067] In Example 2, when using the eddy current electromagnetic sensor 1, as shown in Figure 15, when measuring without the object to be measured, the amplitude ratio is small, less than 0.00002 across the entire frequency range, and is almost zero. When measuring with the plastic case in place, the amplitude ratio is approximately 0.00008 across the entire frequency range. Furthermore, when measuring soil, the amplitude ratio is slightly less than 0.0002 across the entire frequency range.

[0068] On the other hand, in Example 2, when using a conventional applied eddy current electromagnetic sensor, as shown in Figure 16, when measuring without a target object, the amplitude ratio fluctuates with frequency, ranging from 0.0002 or higher to approximately 0.0003 at certain frequencies. Furthermore, when measuring with a plastic case placed, the amplitude ratio fluctuates with frequency, ranging from 0.0002 or higher to approximately 0.0003 at certain frequencies, and at some frequencies it is higher than the background measurement. In addition, when measuring soil, the amplitude ratio fluctuates with frequency, ranging from approximately 0.0003 to 0.0004.

[0069] Comparing the two, the eddy current electromagnetic sensor 1 exhibits less variation in the amplitude-to-frequency ratio, while the conventional applied-type eddy current electromagnetic sensor exhibits greater variation in the amplitude-to-frequency ratio. In the conventional applied-type eddy current electromagnetic sensor, the background noise itself fluctuates significantly, making it difficult to determine whether fluctuations in soil measurements are due to noise or the actual signal. This problem is improved in the eddy current electromagnetic sensor 1. Furthermore, the eddy current electromagnetic sensor 1 yields a signal value approximately four times that of the background noise for a plastic case with a small signal, improving the signal-to-noise ratio compared to the conventional applied-type eddy current electromagnetic sensor, which sometimes exceeded the background measurement at certain frequencies. Additionally, while the soil measurement values ​​of the eddy current electromagnetic sensor 1 are slightly lower than those of the conventional applied-type eddy current electromagnetic sensor in some areas, the signal-to-noise ratio is more than 10 times better.

[0070] From the above test results, it was confirmed that the eddy current electromagnetic sensor to which the present invention is applied is able to further improve signal strength by improving the signal-to-noise ratio. [Explanation of Symbols]

[0071] 1, 101, 201, 301…Eddy current electromagnetic sensor, 2, 102, 202…Coil unit, 2A…First coil unit, 2B…Second coil unit, 3…Power supply unit, 4…Signal output unit, 21…First excitation coil, 22…First measurement coil, 23…Second measurement coil, 24…First measurement coil set, 25…Second excitation coil, 26…Third measurement coil, 27…Fourth measurement coil, 28…Second measurement coil set, 305…Adjustment voltage application unit, 306…Adjustment voltage control unit, 351…Resistor, M…Measurement target (inspection target), M'…Reference measurement target

Claims

1. A first coil unit having a first excitation coil that generates a magnetic flux when power is applied, and a first measuring coil set consisting of a first measuring coil and a second measuring coil, each of which is wound in a spiral or helical shape, coaxial with the first excitation coil and positioned on the magnetic flux generated by the first excitation coil, and connected in series with each other, A second coil unit having a second excitation coil that generates a magnetic flux when power is applied, and a second measuring coil set consisting of a third measuring coil and a fourth measuring coil, each coaxial with the second excitation coil, positioned on the magnetic flux generated by the second excitation coil, wound in a spiral or helical shape, and connected in series with each other; A power supply unit that applies AC power to the first excitation coil and the second excitation coil, A signal output unit is connected between the first measuring coil and the second measuring coil and between the third measuring coil and the fourth measuring coil, and outputs a signal which is the difference between the first signal obtained from between the first measuring coil and the second measuring coil and the second signal obtained from between the third measuring coil and the fourth measuring coil. Equipped with, The first coil unit and the second coil unit are coil units that are electrically connected to each other. The first measuring coil set and the second measuring coil set are connected such that the excitation voltage of the first measuring coil set caused by the change in magnetic flux of the first excitation coil and the excitation voltage of the second measuring coil set caused by the change in magnetic flux of the second excitation coil cancel each other out, with the first measuring coil connected to the third measuring coil and the second measuring coil connected to the fourth measuring coil. An eddy current type electromagnetic sensor characterized by the following features.

2. In the eddy current type electromagnetic sensor according to claim 1, The first excitation coil and the second excitation coil are connected in series with respect to each other, and one end of the first excitation coil and the other end of the second excitation coil are connected to the power supply unit to which power is applied. Eddy current type electromagnetic sensor.

3. In the eddy current type electromagnetic sensor according to claim 1, The first and second excitation coils are formed with the same outer diameter and the same number of windings so that their inductances are matched. The first to fourth measuring coils are formed with the same outer diameter and the same number of windings so that their inductances are matched. Eddy current type electromagnetic sensor.

4. In the eddy current type electromagnetic sensor according to claim 1, The first coil unit and the second coil unit are arranged close to each other with their coil centers aligned in a straight line, using a straight-shaped yoke, wherein the straight-shaped yoke is arranged in a straight line so as to penetrate the coil centers of the first coil unit and the second coil unit, or, a bent-shaped yoke is used, wherein one end of the bent-shaped yoke penetrates the coil center of the first coil unit and the other end of the bent-shaped yoke penetrates the coil center of the second coil unit, thereby causing magnetic repulsion or coupling. Eddy current type electromagnetic sensor.

5. In the eddy current type electromagnetic sensor according to claim 1, The first coil unit and the second coil unit are arranged in a straight line with a predetermined distance between them so that an object to be inspected can be placed between them. Eddy current type electromagnetic sensor.

6. In the eddy current type electromagnetic sensor according to claim 1, The first coil unit and the second coil unit are arranged side by side at a distance from each other, thereby being magnetically independent. Eddy current type electromagnetic sensor.

7. In the eddy current type electromagnetic sensor according to any one of claims 1 to 6, An adjustment voltage application unit that applies voltage to the output lines that output the first signal and the second signal, The adjustment voltage control unit controls the applied voltage value output by the adjustment voltage application unit, Furthermore, The output line that outputs the first signal and the second signal is branched into two parts: one part that goes toward the first output terminal to which the signal output unit is connected, and the other part that goes toward the second output terminal to which the adjustment voltage application unit is connected. Resistors are placed at the position before each branch and at a position midway along the path toward the second output terminal after the branch. The adjustment voltage control unit controls the applied voltage value output by the adjustment voltage application unit to suppress variations in the first to fourth measuring coils for each frequency, based on the measurement results of the first and second signals acquired in advance for each frequency. Eddy current type electromagnetic sensor.

8. A non-destructive testing apparatus that generates a magnetic field and is equipped with an eddy current type electromagnetic sensor that detects eddy currents secondarily generated by changes in the magnetic field with high sensitivity, and measures the state of the object to be inspected by facing the object to be inspected, thereby enabling non-destructive inspection of the object, A non-destructive testing apparatus characterized in that the eddy current type electromagnetic sensor is mounted as the eddy current type electromagnetic sensor described in any one of claims 1 to 6.

9. A non-destructive testing apparatus that generates a magnetic field and is equipped with an eddy current type electromagnetic sensor that detects eddy currents secondarily generated by changes in the magnetic field with high sensitivity, and by placing the eddy current type electromagnetic sensor in front of the object to be inspected and detecting the state of the object to be inspected, the apparatus is capable of non-destructively inspecting the object to be inspected, A non-destructive testing apparatus characterized in that the eddy current type electromagnetic sensor described in claim 7 is mounted as the eddy current type electromagnetic sensor.

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