阅读说明：本技术 一种提高涡流检测线圈分辨能力的方法和装置 (Method and device for improving resolution capability of eddy current detection coil ) 是由 林俊明 沈功田 卢超 郭奇 付刚强 沈淮 于 2021-04-25 设计创作，主要内容包括：本发明一种提高涡流检测线圈分辨能力的方法和装置,用于航空飞机发动机涡轮叶片(1)等的通气孔(11)的裂纹缺陷(12)的无损检测技术,通过引线(21)连接于检测仪器(2),传感器装置(3)包括控制器(31)、检测线圈(32)以及磁屏蔽装置(33),其特征在于所述磁屏蔽装置(33)包括屏蔽片(331)和移动装置(332),所述屏蔽片(331)覆盖检测线圈(32)的检测面设置。实现检测传感器的小型化,解决了精小的传感器不容易制作的难题,提高了金属材料的小孔边缘细小裂纹检测的分辨能力。(The invention provides a method and a device for improving resolution capability of an eddy current detection coil, which are used for a nondestructive detection technology of crack defects (12) of vent holes (11) of turbine blades (1) and the like of an aircraft engine, and are connected to a detection instrument (2) through leads (21), a sensor device (3) comprises a controller (31), the detection coil (32) and a magnetic shielding device (33), and the method and the device are characterized in that the magnetic shielding device (33) comprises a shielding sheet (331) and a moving device (332), and the shielding sheet (331) is arranged to cover a detection surface of the detection coil (32). The miniaturization of the detection sensor is realized, the difficult problem that the small sensor is difficult to manufacture is solved, and the resolution capability of small crack detection of the edge of the small hole of the metal material is improved.)

1. A method for improving resolution capability of an eddy current detection coil is used for nondestructive detection technology of crack defects (12) of vent holes (11) of turbine blades (1) and the like of an aircraft engine, and is characterized in that a detection surface of a detection sensor device covers a movable magnetic shielding sheet, and the magnetic shielding sheet is provided with detection holes smaller than the detection surface, and the specific method comprises the following steps:

a. magnetic shielding piece selection: according to specific detection requirements, the shape and material properties of the detection coil and the magnetic shielding sheet and other conditions, selecting a proper magnetic shielding sheet to cover and install on the detection surface of the coil of the eddy current detection sensor;

b. adjusting and selecting the detection period: setting the moving speed of the shielding plate according to the size and shape of the selected detection hole, and selecting and adjusting a detection surface of a detection period;

c. adjusting the position of the detection hole: extracting the position information of the detection hole, and adjusting the detection hole to a corresponding position;

d. collecting detection data: collecting detection signal data of one period, wherein each period is concentrated into a detection signal data combination;

e. and (3) combined data analysis: analyzing and processing each detection signal data combination as a single data combination, wherein one combination is used as a detection signal;

f. and detection signal imaging processing: combining and synthesizing single detection signal data into a holographic image;

g. image data synthesis: a plurality of detection signal data detected in sequence are combined into a holographic image and combined into integral detection signal data.

2. The method as claimed in claim 1, wherein the step b of adjusting the detection period further comprises the step of obtaining the position information of the detection hole, and the period of movement is set such that the detection hole sequentially moves all positions of the complete detection surface of all eddy current detection sensing coils in turn.

3. A system for improving the resolution capability of an eddy current detection coil is used for the nondestructive detection technology of crack defects (12) of vent holes (11) of turbine blades (1) and the like of an aircraft engine, a detection surface of a detection sensor device covers a movable magnetic shielding sheet, and the magnetic shielding sheet is provided with detection holes smaller than the detection surface, and is characterized in that a detection system controller module (5) comprises a power supply module (51), an encoder linkage module (52), a signal combination processing module (53) and an image processing module (54);

the encoder linkage module (52) comprises a detection hole position information acquisition module (521), a detection period setting module (522), a detection hole selection module (523) and a detection hole movement sequence setting module (524);

the signal combination processing module (53) comprises a period detection signal data combination collection module (531), a detection signal data combination sequence setting module (532) and a combination data storage module (533);

the image processing module (54) comprises a single detection signal data combination holographic imaging module (541), a periodic image synthesis module (542) and an image storage module (543).

4. A sensor device for improving the resolution of an eddy current detection coil is used for the nondestructive detection technology of crack defects (12) of vent holes (11) of turbine blades (1) and the like of an aircraft engine, and is connected to a detection instrument (2) through a lead (21), the sensor device (3) comprises a controller (31), the detection coil (32) and a magnetic shielding device (33), and the sensor device is characterized in that the magnetic shielding device (33) comprises a shielding sheet (331) and a moving device (332), and the shielding sheet (331) is arranged to cover the detection surface of the detection coil (32);

wherein, the shielding sheet (331) is provided with a detection hole (333), the detection coil (32) detects the eddy current detection signal of the detected object through the detection hole (333), and the moving device (332) moves the detection hole (333) of the shielding sheet (331) to align with different positions of the detection coil (32).

5. The sensor device of claim 4, wherein the detecting coil (32) is a hollow spiral coil structure, the shielding plate (331) is a disk structure covering the detecting surface of the detecting coil (32), the moving device (332) comprises a rotating shaft (3321) having an end portion fixed to the shielding plate (331) through the detecting coil (32), the rotating shaft (3321) rotates the disk-shaped shielding plate (331), and the position of the detecting hole (333) in the disk-shaped shielding plate (331) is adjusted.

6. The sensor device for improving the resolution of the eddy current detection coil according to claim 5, wherein the detection hole (333) is formed around a sector-shaped small hole of the rotary collar, and the radius of the sector-shaped ring of the ring is larger than or equal to that of the ring of the hollow disc detection coil (32).

7. The sensor device for improving the resolution of the eddy current detection coil according to claim 5, wherein the detection hole (333) is a circular hole having a diameter equal to or smaller than the radius of the ring body of the hollow disc detection coil (32).

8. The sensor device for improving the resolution of the eddy current detection coil according to claim 4, wherein the shielding plate (331) is configured as a square plate structure covering the detection surface of the detection coil (32), the square shielding plate completely covers the planar spiral coil, the moving device (332) drives the shielding plate (331) to move in parallel along the length or width direction of the shielding plate (331), and the position of the detection hole (333) on the shielding plate (331) is adjusted.

9. The sensor device for improving the resolution of the eddy current detection coil according to claim 8, wherein the detection hole (333) is a small square hole having a length and a width parallel to the shielding plate (331), one side of the small square hole is smaller than the planar spiral detection coil, and the other side is smaller than or equal to the planar spiral detection coil.

10. The sensor device for improving the resolution of the eddy current detection coil according to claim 8, wherein the detection hole (333) is provided as a circular hole having a diameter equal to or smaller than the length and width in the moving direction of the detection surface of the detection coil (32) of the planar spiral coil.

Technical Field

The invention relates to the technical field of nondestructive testing, in particular to a method and a technology of an eddy current testing sensor, and particularly relates to a method and a device for improving the resolution capability of an eddy current testing coil.

Background

As is known, the aircraft engine is the core of the whole aircraft, and its performance directly determines the overall performance of the aircraft, while the most severe working environment and most complicated stress in the aircraft gas turbine engine are the turbine blades, and the turbine blades are also the key points for achieving high performance under the condition of small size and light weight of the aircraft engine, so the turbine blades are the core of the whole aircraft. The requirement of an aviation gas turbine engine also makes the operating temperature and the bearing temperature of the turbine blade very high, the cooling technology of the turbine blade also gives great attention to, through designing a cooling channel and a cooling hole on the blade, then leading the low-temperature gas in the compressor to the inside of the turbine blade, and then spraying the low-temperature gas from the cooling hole on the surface of the blade to form an air film, so as to isolate the turbine blade with lower temperature from the high-temperature gas in the working environment, namely the air film cooling technology.

As shown in the attached figure 1, the air hole (11) on the hollow turbine blade (1) is extremely small, usually about 1um, the hole diameter shape direction is also special and different, the crack (12) on the periphery of the hole (11) is extremely small, so that the nondestructive detection is quite difficult, the eddy current detection probe is made to be small, the process is not easy to reach, and the defect part is quite difficult to align during the detection.

Aiming at the problems of the defects, the invention adopts the following technical scheme.

Disclosure of Invention

The invention aims to provide a method and a device for improving the resolution capability of an eddy current detection coil, and the disclosed technical scheme is as follows:

the method for improving the resolution capability of the eddy current detection coil is used for the nondestructive detection technology of crack defects (12) of vent holes (11) of turbine blades (1) and the like of an aircraft engine, and is characterized in that a detection surface of a detection sensor device covers a movable magnetic shielding sheet, and the magnetic shielding sheet is provided with detection holes smaller than the detection surface, wherein the magnetic shielding sheet is a replaceable device, and the magnetic shielding sheets with different apertures and detection holes of different shapes are selected, and the specific method comprises the following steps:

a. magnetic shielding piece selection: according to specific detection requirements, the shape and material properties of the detection coil and the magnetic shielding sheet and other conditions, selecting a proper magnetic shielding sheet to cover and install on the detection surface of the coil of the eddy current detection sensor;

b. adjusting and selecting the detection period: setting the moving speed of the shielding plate according to the size and shape of the selected detection hole, and selecting and adjusting a detection surface of a detection period;

c. adjusting the position of the detection hole: extracting the position information of the detection hole, and adjusting the detection hole to a corresponding position;

d. collecting detection data: collecting detection signal data of one period, wherein each period is concentrated into a detection signal data combination;

e. and (3) combined data analysis: analyzing and processing each detection signal data combination as a single data combination, wherein one combination is used as a detection signal;

f. and detection signal imaging processing: combining and synthesizing single detection signal data into a holographic image;

g. image data synthesis: a plurality of detection signal data detected in sequence are combined into a holographic image and combined into integral detection signal data.

And c, adjusting and selecting the detection period in the step b, wherein the step b further comprises the step of acquiring the position information of the detection hole, and one period is set to be moved so that the detection hole sequentially moves all the positions of the complete detection surface of one eddy current detection sensing coil in turn.

Furthermore, a complete detection surface of the coil of the eddy current detection sensor is set and detected in one period through the linkage of the encoder.

The invention also discloses a system for improving the resolution capability of the eddy current detection coil, which is used for the nondestructive detection technology of crack defects (12) of vent holes (11) of turbine blades (1) and the like of an aircraft engine, wherein the detection surface of a detection sensor device covers a movable magnetic shielding sheet, and a detection hole smaller than the detection surface is arranged on the magnetic shielding sheet, and the system is characterized in that a detection system controller module (5) comprises a power supply module (51), an encoder linkage module (52), a signal combination processing module (53) and an image processing module (54); the encoder linkage module (52) comprises a detection hole position information acquisition module (521), a detection period setting module (522), a detection hole selection module (523) and a detection hole movement sequence setting module (524); the signal combination processing module (53) comprises a period detection signal data combination collection module (531), a detection signal data combination sequence setting module (532) and a combination data storage module (533); the image processing module (54) comprises a single detection signal data combination holographic imaging module (541), a periodic image synthesis module (542) and an image storage module (543).

The invention also discloses a sensor device for improving the resolution capability of the eddy current detection coil, which is used for the nondestructive detection technology of crack defects (12) of vent holes (11) of turbine blades (1) and the like of an aircraft engine, and is connected to a detection instrument (2) through a lead (21), the sensor device (3) comprises a controller (31), the detection coil (32) and a magnetic shielding device (33), and the sensor device is characterized in that the magnetic shielding device (33) comprises a shielding sheet (331) and a moving device (332), and the shielding sheet (331) is arranged to cover the detection surface of the detection coil (32);

wherein, the shielding sheet (331) is provided with a detection hole (333), the detection coil (32) detects the eddy current detection signal of the detected object through the detection hole (333), and the moving device (332) moves the detection hole (333) of the shielding sheet (331) to align with different positions of the detection coil (32).

And, an embodiment, the detection coil (32) set up to hollow plane spiral coil structure, shielding piece (331) set up to cover the disc structure of detection coil (32) detection face, mobile device (332) include one end pass detection coil (32) be fixed in rotation axis (3321) of shielding piece (331), by rotation axis (3321) drive disc-shaped shielding piece (331) rotatory, adjust the position of detection hole (333) on disc-shaped shielding piece (331).

The detection holes (333) are arranged to surround the rotary collar sector-shaped small holes, and the radius of the sector ring of the ring is larger than or equal to that of the ring of the hollow disc detection coil (32). When the rotation detection is performed, the ring sector-shaped detection holes (333) rotate around the rotating shaft (3321) for one circle to be set as one detection period, namely, one period is a detection surface for sequentially detecting one eddy current detection sensor coil in turn.

Or the detection hole (333) is a circular hole with the diameter smaller than or equal to the radius of the ring body of the hollow disc detection coil (32).

In another embodiment, the shielding plate (331) is a square plate structure covering the detection surface of the detection coil (32), the square shielding plate completely covers the planar spiral coil, and the moving device (332) drives the shielding plate (331) to move in parallel along the length or width direction of the shielding plate (331) to adjust the position of the detection hole (333) in the shielding plate (331).

The detection hole (333) is a square small hole with the length and the width parallel to the shielding sheet (331), one side of the square hole is far smaller than the plane spiral detection coil, and the other side of the square hole is smaller than or equal to the plane spiral detection coil. Each time the shielding sheet (331) is moved, one detection hole is set to be switched, and one movement switching period is just to rotate all detection surface positions of the detection coil (32) of the square plane spiral coil. If the shielding plate drives the detection hole to move in the length or width direction (the x-axis direction or the y-axis direction) of the detection surface of the square plane spiral coil, a rotating shaft (3321) arranged on one outer side of the shielding plate (331) of the moving device (33) drives the shielding plate (331) to translate along the side direction, the length a of the square detection hole (333) in the moving direction of the shielding plate is smaller than or equal to the length or width A of the detection surface of the detection coil (32) of the square plane spiral coil, and a is a multiple of A. The other side length B of the square detection hole (333) is far smaller than the length or width B of the same side of the detection surface, and the B is a multiple of the B and is at least more than two times. If a = A, the magnetic shielding sheet (331) drives the detection hole (333) to move once in one direction, namely a period, and the movement of one period is just one detection surface of one eddy current detection sensor; when a =2A, the magnetic shielding sheet (331) drives the detection hole (333) to move back and forth once in one direction, namely a period, and the movement of the magnetic shielding sheet is just one detection surface of one eddy current detection sensor after the movement of one period; when a =4A, the magnetic shielding sheet (331) drives the detection hole (333) to move back and forth twice in one direction, namely a period, and the movement of the magnetic shielding sheet is just one detection surface of one eddy current detection sensor after the movement of one period, and so on.

Alternatively, the detection hole (333) is a circular hole having a diameter not larger than the length and width of the detection coil (32) of the planar spiral coil in the direction of movement of the detection surface. Or in another embodiment, the magnetic shielding sheet is arranged into a strip-shaped flexible strip-shaped structure, the strip-shaped flexible strip-shaped magnetic shielding sheet is provided with circular detection holes, the circular detection holes can be arranged into a plurality of detection holes distributed at regular positions and a plurality of detection holes with different sizes and diameters, and the strip-shaped magnetic shielding sheet (331) is moved to different positions around the detection surface of the eddy current detection sensor coil (32) to switch different circular detection holes (333); or the detection hole on the long-strip-shaped flexible strip-shaped magnetic shielding sheet (331) is of a square structure, the long-strip-shaped flexible strip-shaped magnetic shielding sheet (331) is moved to switch different square detection holes (333) to align with the detection surface of the eddy current detection sensor coil (32), or the square detection holes (333) with a plurality of structures of different sizes are arranged, and the long-strip-shaped flexible strip-shaped magnetic shielding sheet (331) is moved to switch the square detection holes (333) with structures of different sizes.

According to the technical scheme, the invention has the following beneficial effects:

the invention shields part of the detection surface of the eddy current detection coil through the magnetic shielding sheet with the detection hole, accurately detects the detection position of the probe, realizes the miniaturization of the detection sensor, solves the difficult problem that the small sensor is difficult to manufacture, and improves the resolution capability of small hole edge fine crack detection of the metal material;

the position of the switching detection hole is adjusted by moving the magnetic shielding sheet, and different positions on the detection surface of the eddy current sensor are detected in turn in sequence, so that the purpose of expanding the detection range is achieved;

the invention takes the coil detection surface of the eddy current detection sensor as a detection period by periodically setting different positions of the movable detection holes of the magnetic shielding sheets and completely and sequentially rotating the detection holes, thereby realizing the purpose of improving the detection accuracy, realizing the data comprehensive analysis of the detection surface of the whole eddy current detection sensor and realizing the small-range detection data analysis;

and thirdly, combining a periodic detection signal into a complete detection image by synthesizing the holographic image, so that the detected image is more complete, the complete image forming of micro air holes with different shapes and different apertures in the turbine blade of the aircraft engine is more facilitated, and the integral presentation of the detection signal image is more facilitated.

Drawings

FIG. 1 is a schematic diagram of an application scenario of the preferred embodiment of the present invention;

FIG. 2 is a schematic flow chart of a method according to a preferred embodiment of the present invention;

FIG. 3 is a schematic diagram of a system and method according to the preferred embodiment of the present invention;

FIG. 4 is a schematic structural diagram of a preferred embodiment of the present invention;

FIG. 5 is a schematic top view of a structural detection sensor apparatus in accordance with a preferred embodiment of the present invention;

FIG. 6 is a schematic bottom view of a structural detection sensor device in accordance with a preferred embodiment of the present invention;

FIG. 7 is a schematic bottom view of another exemplary configuration of a structural detection sensor device in accordance with the present invention;

FIG. 8 is another schematic structural view of the preferred embodiment of the present invention;

FIG. 9 is a schematic view of different detection apertures of another configuration of magnetic shield sheets in accordance with a preferred embodiment of the present invention;

FIG. 10 is a schematic diagram of different inspection hole shapes of the square planar spiral coil in accordance with the preferred embodiment of the present invention;

FIG. 11 is a schematic diagram of different inspection hole shapes of another square planar spiral coil in accordance with the preferred embodiment of the present invention;

FIG. 12 is a schematic view of another circular inspection hole shape according to the preferred embodiment of the present invention;

FIG. 13 is a schematic structural view of an elongated flexible strip-shaped magnetic shielding sheet according to the preferred embodiment of the present invention;

FIG. 14 is a schematic view of another structure of an elongated flexible magnetic shielding strip according to the preferred embodiment of the present invention;

fig. 15 is a schematic view of another structure of an elongated flexible strip-shaped magnetic shielding sheet according to the preferred embodiment of the present invention.

Detailed Description

The invention is further described with reference to the following drawings and detailed description.

As shown in fig. 1 and 2, a method for improving the resolution capability of an eddy current detection coil, which is used for the nondestructive detection technology of crack defects 12 of vent holes 11 of turbine blades 1 and the like of an aircraft engine, is characterized in that a detection surface of a detection sensor device is covered with a movable magnetic shielding sheet, the magnetic shielding sheet is provided with detection holes smaller than the detection surface, wherein the magnetic shielding sheet is a replaceable device, and the magnetic shielding sheets with different apertures and detection holes of different shapes are selected, and the specific method comprises the following steps:

a. magnetic shielding piece selection: according to specific detection requirements, the shape and material properties of the detection coil and the magnetic shielding sheet and other conditions, selecting a proper magnetic shielding sheet to cover and install on the detection surface of the coil of the eddy current detection sensor;

b. adjusting and selecting the detection period: setting the moving speed of the shielding plate according to the size and shape of the selected detection hole, and selecting and adjusting a detection surface of a detection period;

c. adjusting the position of the detection hole: extracting the position information of the detection hole, and adjusting the detection hole to a corresponding position;

d. collecting detection data: collecting detection signal data of one period, wherein each period is concentrated into a detection signal data combination;

e. and (3) combined data analysis: analyzing and processing each detection signal data combination as a single data combination, wherein one combination is used as a detection signal;

f. and detection signal imaging processing: combining and synthesizing single detection signal data into a holographic image;

g. image data synthesis: a plurality of detection signal data detected in sequence are combined into a holographic image and combined into integral detection signal data.

And c, adjusting and selecting the detection period in the step b, wherein the step b further comprises the step of acquiring the position information of the detection hole, and one period is set to be moved so that the detection hole sequentially moves all the positions of the complete detection surface of one eddy current detection sensing coil in turn.

Furthermore, a complete detection surface of the coil of the eddy current detection sensor is set and detected in one period through the linkage of the encoder.

As shown in fig. 3, the present invention also discloses a system for improving the resolution of the eddy current detection coil, which is used in the nondestructive detection technology of crack defects 12 of vent holes 11 of turbine blades 1 of aero-aircraft engines, etc., the detection surface of the detection sensor device is covered with a movable magnetic shielding sheet, and the magnetic shielding sheet is provided with detection holes smaller than the detection surface, and is characterized in that the detection system controller module 5 comprises a power module 51, an encoder linkage module 52, a signal combination processing module 53 and an image processing module 54; the encoder linkage module 52 includes a detection hole position information obtaining module 521, a detection period setting module 522, a detection hole selecting module 523, and a detection hole movement sequence setting module 524; the signal combination processing module 53 comprises a period detection signal data combination collection module 531, a detection signal data combination sequence setting module 532 and a combination data storage module 533; the image processing module 54 includes a single detection signal data combination holographic imaging module 541, a periodic image synthesis module 542, and an image storage module 543.

As shown in fig. 4 to 11, the present invention also discloses a sensor device for improving the resolution of an eddy current detection coil, which is used in the nondestructive detection technology of crack defects 12 in ventholes 11 of turbine blades 1 of aircraft engines and the like, and is connected to a detection instrument 2 through a lead wire 21, the sensor device 3 comprises a controller 31, a detection coil 32 and a magnetic shielding device 33, and is characterized in that the magnetic shielding device 33 comprises a shielding sheet 331 and a moving device 332, and the shielding sheet 331 is arranged to cover the detection surface of the detection coil 32;

the shielding plate 331 is provided with a detection hole 333, the detection coil 32 detects an eddy current detection signal of the detected object through the detection hole 333, and the moving device 332 moves the detection hole 333 of the shielding plate 331 to align with different positions of the detection coil 32.

And as shown in fig. 4 to fig. 7, in one embodiment, the detecting coil 32 is a hollow plane spiral coil structure, the shielding plate 331 is a disk structure covering the detecting surface of the detecting coil 32, the moving device 332 includes a rotating shaft 3321 having an end portion passing through the detecting coil 32 and fixed to the shielding plate 331, the rotating shaft 3321 rotates the disk-shaped shielding plate 331, and the position of the detecting hole 333 on the disk-shaped shielding plate 331 is adjusted.

The detection holes 333 are arranged around a sector-shaped small hole of the rotary collar, and the radius of the sector-shaped ring of the ring is larger than or equal to that of the ring of the hollow disc detection coil 32. When the rotation is detected, the ring-sector-shaped detection holes 333 are rotated around the rotation shaft 3321 by one circumference to be set as one detection period, that is, one period is a period in which the detection surfaces of one eddy current detection sensor coil are sequentially detected in turn.

Alternatively, the detection hole 333 is a circular hole having a diameter smaller than or equal to the radius of the ring body of the hollow disc detection coil 32.

As shown in fig. 8 to 11, in another embodiment, the shielding plate (331) is configured as a square plate structure covering the detection surface of the detection coil (32), the square shielding plate completely covers the planar spiral coil, and the moving device (332) drives the shielding plate (331) to move in parallel along the length or width direction of the shielding plate (331), so as to adjust the position of the detection hole (333) on the shielding plate (331).

The detection hole (333) is a square small hole with the length and the width parallel to the shielding sheet (331), one side of the square hole is far smaller than the plane spiral detection coil, and the other side of the square hole is smaller than or equal to the plane spiral detection coil. Each time the shield plate 331 is moved to switch one detection hole, one movement switching period is just rotating all the detection surface positions of the detection coil 32 of the square planar spiral coil. As shown in fig. 9, the movement of the shielding plate drives the detection hole to move on the detection surface of the circular planar spiral coil, and when the length of the square detection small hole is equal to the diameter D of the circular planar spiral coil (i.e. a = D), the magnetic shielding plate 331 drives the detection hole 333 to move in one direction once, which is a period; when 2a = D, the magnetic shielding sheet 331 drives the detection hole 333 to move back and forth in one direction once, which is a period, and the movement of the magnetic shielding sheet is exactly a detection surface of an eddy current detection sensor after the movement of one period; when 4a = D, the magnetic shielding sheet 331 drives the detecting hole 333 to move back and forth twice in one direction, which is a period, and the movement of the detecting hole is exactly a detecting surface of an eddy current detecting sensor after the movement of the detecting hole is completed, and so on.

As shown in fig. 10 and 11, the shielding plate drives the detecting hole to move in the length or width direction (x-axis direction or y-axis direction) of the detecting surface of the square planar spiral coil, the rotating shaft 3321 disposed on one outer side of the shielding plate 331 drives the shielding plate 331 to translate along the side direction by the moving device 33 shown in fig. 10, the length a of the square detecting hole 333 in the moving direction of the shielding plate is less than or equal to the length or width a on the same side of the detecting surface of the detecting coil 32 of the square planar spiral coil, and a is a multiple of a. The other side length B of the square detection hole 333 is far smaller than the length or width B of the same side of the detection surface, and B is a multiple of B and is at least more than two times. As shown in fig. 11 and 12, when a = a, the magnetic shielding sheet 331 drives the detecting hole 333 to move in one direction once, which is a cycle, and after moving one cycle, it is exactly one detecting surface of one eddy current detecting sensor; when 2a = a, the magnetic shielding sheet 331 drives the detection hole 333 to move back and forth in one direction once, which is a period, and the movement of the magnetic shielding sheet is exactly a detection surface of an eddy current detection sensor after the movement of one period; when 4a = a, the magnetic shielding sheet 331 drives the detection hole 333 to move back and forth twice in one direction, which is a period, and the movement of the magnetic shielding sheet is exactly a detection surface of an eddy current detection sensor after the movement of the detection hole is completed, and so on.

Alternatively, as shown in fig. 12, the detection hole (333) is a circular hole having a diameter equal to or smaller than the length and width in the moving direction of the detection surface of the detection coil (32) of the planar spiral coil.

As shown in fig. 13 to 15, or in another embodiment, the magnetic shielding sheet is configured as an elongated flexible strip-shaped structure, and the elongated flexible strip-shaped magnetic shielding sheet is configured with circular detection holes, which may be configured as a plurality of pieces distributed at regular positions, and a plurality of pieces with different sizes and diameters, and the elongated magnetic shielding sheet 331 is moved to surround the detection surface of the eddy current detection sensor coil 32 at different positions, so as to switch different circular detection holes 333; or the detection hole on the strip-shaped flexible strip-shaped magnetic shielding sheet 331 is in a square structure, and the strip-shaped flexible strip-shaped magnetic shielding sheet 331 is moved to switch different square detection holes 333 to align with the detection surface of the eddy current detection sensor coil 32, or as shown in fig. 14, the strip-shaped flexible strip-shaped magnetic shielding sheet 331 is moved to switch the square detection holes 333 with different size structures; the magnetic shielding sheets are selectively moved, and different shapes and different positions of the switching detection holes are adjusted.

The above is one embodiment of the present invention. Furthermore, it is to be understood that all equivalent or simple changes in the structure, features and principles described in the present patent concepts are included in the scope of the present patent.