An eddy current testing sensor with adjustable resolution and a testing method thereof

Abstract

The present application relates to the technical field of eddy current testing, in particular to a resolution-adjustable eddy current testing sensor for identifying and detecting the depth of cracks on the tread of a steel rail, comprising a probe rod, a detection assembly and a magnetic shielding cover, the detection assembly is embedded at the end of the probe rod and can be bounced up and down, the magnetic shielding cover is sleeved outside the detection assembly and is screwed on the probe rod, the magnetic shielding cover is a double-layer sleeve structure, comprising a first magnetic shielding cover and a second magnetic shielding cover which can rotate relative to each other, the first magnetic shielding cover and the second magnetic shielding cover are respectively provided with a through hole and a detection window in the form of a screen, and the through hole and the detection window can be corresponded when the two are rotated relative to each other; the magnetic shielding cover of the present application focuses the overflow magnetic field of the detection assembly on the surface of the workpiece to be detected, and the switching of the detection window is realized by rotating the magnetic shielding cover to control the magnetic shielding ability, so as to realize the adjustment of the crack detection resolution of the eddy current testing sensor, improve the detection sensitivity, and effectively avoid the misjudgment during detection.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electromagnetic nondestructive testing, and particularly relates to a resolution-adjustable eddy current sensor and a detection method thereof. BACKGROUND

[0002] In-service equipment is prone to surface cracks due to metal fatigue, for example, rail and wheel tread, if the surface cracks are not treated in time, they will expand into large defects, causing component failure and safety accidents. In order to quickly polish and process, modern technology adopts eddy current depth measurement technology, that is, when polishing the rail or wheel tread, the eddy current detection is carried out immediately behind, so as to control the polishing depth in time, avoid excessive polishing and cause waste, or the crack still exists due to insufficient polishing. However, in reality, the detection accuracy of the eddy current method corresponding to a single crack can completely meet the requirements of the site. However, when encountering dense cracks of two or more, the error is large, because the eddy current probe cannot be too small, and the eddy current field has an "overflow" effect. In practice, two 1mm cracks with a spacing of 1mm are detected by a conventional eddy current probe, and the effect is equivalent to a 2mm deep crack, although the phase angle is slightly different, but the amplitude is roughly equivalent, which makes it difficult to distinguish in engineering application, and easy to cause misjudgment. Based on this, the present application improves the prior art to solve the above problems. SUMMARY

[0003] To solve the above problems, the present application provides a resolution-adjustable eddy current detection sensor and a detection method for crack type and depth discrimination using the sensor, and the present application is implemented as follows:

[0004] A resolution-adjustable eddy current detection sensor for crack detection on a rail tread, in particular, by adjusting the resolution of the detection sensor to identify single cracks and dense cracks and detect crack depth, comprising a probe rod, a detection assembly, and a magnetic shielding cover sleeved outside the detection assembly.

[0005] The detection assembly can be embedded at the end of the probe rod and can be up and down micro-jointed and pressed, comprising a coil framework, and a first detection coil and a second detection coil arranged side by side on the coil framework, wherein the first detection coil is arranged at the center position of the coil framework.

[0006] The magnetic shielding cover is a double-layer cylindrical sleeve structure that can rotate relative to each other, comprising a first magnetic shielding cover as the inner layer and a second magnetic shielding cover as the outer layer, the first magnetic shielding cover is provided with through holes corresponding to the two detection coils respectively, the second magnetic shielding cover is provided with a first detection window corresponding to the first detection coil at the center position, a plurality of second detection windows with different sizes and shapes are arranged annularly around the first detection window, and the second detection windows can correspond to the second detection coil, and rotating the second magnetic shielding cover can center the first detection window and the second detection window with the through hole and form a detection channel.

[0007] During detection, the detection assembly is pressed towards the detection surface, the magnetic shielding cover focuses the overflow magnetic field of the detection assembly on the surface of the workpiece being detected, the switching of the detection channel is performed by rotating the second magnetic shielding cover to control the magnetic shielding ability of the magnetic shielding cover, and the crack detection resolution of the eddy current detection sensor is adjusted.

[0008] As a further improvement, the detection sensor is a pen-type detection sensor, the side wall of the probe rod is provided with a sliding control for controlling the up-and-down pressing of the detection assembly, and the magnetic shielding cover is arranged outside the detection assembly and is screwed to the outer side wall of the end of the probe rod.

[0009] As a further improvement, the first detection coil is in a planar square spiral shape, and the second detection coil is in a planar circular spiral shape.

[0010] As a further improvement, the first detection window is in a circular hole shape, and the second detection window is provided in different sizes as circular holes or square holes or long strips.

[0011] When the second magnetic shielding cover is rotated, the first detection coil is always in a fixed high detection resolution, the resolution of the second detection coil can be varied and adjusted, and the two detection coils form a contrast detection with different detection resolutions.

[0012] As a further improvement, the outer side wall of the first magnetic shielding cover is provided with a raised guide ring along its outer periphery, the inner side wall of the second magnetic shielding cover is recessed with a guide groove matched with the guide ring, and the first magnetic shielding cover and the second magnetic shielding cover are connected in relative rotation.

[0013] As a further improvement, the inner side wall of the first magnetic shielding cover is provided with an internal thread, and the outer side wall of the end of the probe rod is provided with an external thread matched with the internal thread.

[0014] As a further improvement, the first magnetic shielding cover is made of a composite material composed of metal fibers, copper foil, and polyimide film, and the second magnetic shielding cover is made of copper, aluminum, steel, or ferrite material; the lower bottom surface of the first magnetic shielding cover is film-shaped or sheet-shaped, and the lower bottom surface of the second magnetic shielding cover is sheet-shaped.

[0015] The application also discloses a method for detecting dense cracks by adjusting the resolution of a sensor, which adopts the eddy current detection sensor as described above to detect cracks on the rail tread, and the detection steps are as follows:

[0016] a. Setting of the detection sensor: a special pen-type eddy current detection sensor is adopted, and the detection assembly thereof comprises a coil framework and first and second detection coils arranged side by side on the coil framework; the first detection coil is planar square spiral-shaped, and the second detection coil is planar circular spiral-shaped; further, a double-layer cylindrical sleeve-type magnetic shielding cover with switchable detection windows is sleeved outside the detection assembly to focus the overflow electromagnetic field of the detection assembly to different degrees;

[0017] b. Adjustment of the crack resolution of the sensor: the first magnetic shielding cover is fixed relative to the detection assembly, the second magnetic shielding cover is rotated, the detection window on the second magnetic shielding cover is centered with the through hole on the first magnetic shielding cover, a through detection channel is formed, and the detection coil can detect through the detection channel; the sizes and shapes of different detection windows are different, the corresponding magnetic shielding effects are different, further, the crack detection resolution under different magnetic shielding effects is different, and the second magnetic shielding cover is rotated to adjust the crack resolution;

[0018] c. Acquisition of the contrast signals of the detection coils: through the special structural design of the magnetic shielding cover, the first detection coil always maintains the highest detection resolution, the first detection coil is adopted to detect the cracks on the rail tread and distinguish single cracks or dense cracks; the resolution of the second detection coil is changeable and adjustable, the second detection coil is adopted to detect the crack depth through the switchable detection windows to form different detection channels, and the two detection coils form contrast detection with different detection resolutions;

[0019] d. Rapid identification of the number of cracks and the crack depth: when the detection coil with the fixed high detection resolution is adopted for detection, a fixed detection time base range is set, within the time base range, when the detection image is a complete defect waveform, it is determined as a single crack; within the time base range, when the detection image presents two and more than two obviously spaced defect waveforms, it is determined as dense cracks;

[0020] Further, the detection images under multiple detection resolutions are comprehensively analyzed and compared, the amplitude and depth of the defect waveform within the detection time base range are converted by the computer, and the crack depth is obtained.

[0021] Compared with the prior art, the application can obtain the following technical effects:

[0022] First, the detection assembly of the application is embedded in the end of the probe rod and can be pressed up and down, including a coil framework and first and second detection coils arranged side by side on the coil framework, two groups of detection coils are designed and the structure of the detection coils is optimized to form a contrast; the detection assembly that can be pressed up and down can minimize the distance between the detection assembly and the magnetic shielding cover, improve the magnetic shielding effect, and reduce the distance to the detection surface to overcome the lift-off.

[0023] Second, a magnetic shielding cover with a special structure is designed to be sleeved on the outside of the detection assembly to shield the overflow magnetic field of the detection assembly, so that the overflow magnetic field is focused on the specific part to be detected on the surface of the workpiece to be detected, the resolution of the metal surface dense cracks is improved, and the confidence and reliability of the detection structure are improved.

[0024] Third, further, the magnetic shielding cover is a double-layer cylindrical sleeve structure, including a first magnetic shielding cover and a second magnetic shielding cover that can rotate relative to each other, the lower surface of the first magnetic shielding cover is provided with through holes corresponding to the two detection coils, the lower surface of the second magnetic shielding cover is provided with a plurality of detection windows with different sizes and shapes, the detection windows are arranged in sequence along an annular path, the through holes are arranged at positions corresponding to the annular path on the first magnetic shielding cover, and the detection windows can be corresponded to the through holes by rotating the second magnetic shielding cover to form detection channels; the detection windows are switched by rotating the second magnetic shielding cover to control the magnetic shielding capacity of the magnetic shielding cover and further adjust the crack detection resolution of the eddy current detection sensor. By adjusting different crack detection resolutions, a comprehensive judgment is made on the type and depth of the crack, the crack defect is accurately distinguished, and false judgment is effectively prevented. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the application examples or the prior art or the descriptions in the prior art, it is obvious that other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0026] Figure 1 The figure is a schematic diagram of the use of the eddy current detection sensor of the application.

[0027] Figure 2 The figure is a schematic diagram of the overall structure of the eddy current detection sensor of the application.

[0028] Figure 3 The figure is an exploded structural schematic diagram of the magnetic shielding cover of the eddy current detection sensor of the application.

[0029] Figure 4 The figure isFigure 3 Enlarged view of the middle C region.

[0030] Figure 5 For Figure 3 Schematic view from another perspective.

[0031] Figure 6 For Figure 5 Enlarged view of the middle D region.

[0032] Figure 7 Structure exploded view of the magnetic shielding cover of the present application.

[0033] Figure 8 For Figure 7 Schematic view from another perspective.

[0034] In the figure:

[0035] A - Steel rail tread;

[0036] B - Detection sensor;

[0037] 10 - Probe, 11 - External thread, 12 - Slotted guide;

[0038] 20 - Detection assembly, 21 - Coil former, 22 - First detection coil, 23 - Second detection coil;

[0039] 30 - Sliding control;

[0040] 40 - Magnetic shielding cover, 41 - First magnetic shielding cover, 411 - Through hole, 412 - Guide ring, 413 - Internal thread; 42 - Second magnetic shielding cover, 421 - First detection window, 422 - Second detection window, 423 - Guide slot. DETAILED DESCRIPTION

[0041] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but only represents selected embodiments of the application.

[0042] In the description of the present application, the terms "first", "second" are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features.

[0043] According to the current railway maintenance track standard, for the crack with a depth greater than 3mm, polishing treatment must be carried out, and the rail with excessive wear and deep crack must be scrapped in the next stage, however, in engineering practice, it is found that when two cracks are close to each other, although they are not over-standard, they are easy to cause misjudgment, leading to excessive polishing or early rail scrapping, which consumes time, effort and material, and brings huge economic loss. The uncertainty of detection is very unfavorable to the health maintenance of the rail.

[0044] Reference drawings Figures 1-8 The present application designs a resolution-adjustable eddy current detection sensor for rail tread A crack detection, especially for single crack and dense crack identification and depth detection, and the detection sensor B structure comprises a probe rod 10, a detection assembly 20 and a magnetic shielding cover 40 sleeved outside the detection assembly 20 connected in sequence.

[0045] The detection assembly 20 can be embedded in the end of the probe rod 10 and can be up and down, and it comprises a coil skeleton 21, the coil skeleton 21 is provided with a first detection coil 22 and a second detection coil 23, the first detection coil 22 is arranged at the center position of the coil skeleton 21, and the second detection coil 23 is arranged at any side of the first detection coil, wherein the first detection coil 21 is a planar square spiral, and the second detection coil 22 is a planar circular spiral. Under the same conditions, the detection sensitivity of the planar square spiral coil to the micro crack is higher, and the planar circular spiral has larger detection range, more optional modes and better flexibility. The magnetic shielding cover 40 is a double-layer cylindrical sleeve structure, comprising a first magnetic shielding cover 41 and a second magnetic shielding cover 42 sleeved and relatively rotatable, the lower surface of the first magnetic shielding cover 41 is provided with a through hole 411 corresponding to the detection assembly,

[0046] The center position of the second magnetic shielding cover 42 is provided with a first detection window 421 corresponding to the first detection coil 22, a plurality of second detection windows 422 with different sizes and shapes are arranged around the first detection window 421 in a ring shape, and the second detection window 422 can correspond to the second detection coil 23, and rotating the second magnetic shielding cover 42 can make the first detection window 421 and the second detection window 422 correspond to the center of the through hole 411 and form a detection channel;

[0047] During detection, the detection assembly 20 is pressed towards the detection surface, the magnetic shielding cover 40 focuses the overflow magnetic field of the detection assembly 20 on the surface of the workpiece to be detected, the detection channel is switched by rotating the second magnetic shielding cover 42 to control the magnetic shielding ability of the magnetic shielding cover 40, and the crack detection resolution of the eddy current detection sensor is adjusted.

[0048] The detection sensor B is a pen-type detection sensor. A groove 12 is formed on the side wall of its probe 10. A sliding control 30, which can slide up and down, is provided within the groove 12. A spring is hung on the sliding control, and the other end of the spring presses against the coil frame 211. By sliding the sliding control 30 up and down, the spring bounces and presses the detection component, causing it to bounce up and down at the end of the probe 10. This minimizes the distance between the sensor and the magnetic shielding cover 40, reducing the magnetic shielding effect, while simultaneously reducing the distance to the detection surface, thus preventing the sensor from lifting off. The magnetic shielding cover 40 covers the outside of the detection component 20. In conjunction with the detection coils, the first magnetic shielding cover 41 has through holes 411 corresponding to the first detection coil 22 and the second detection coil 23. In this embodiment, the through holes 411 are circular.

[0049] Reference Appendix Figure 8 The first detection window 421 is circular, and the second detection window 422 is set as a circular hole, square hole, or strip of different size.

[0050] Rotate the second magnetic shielding cover 42. The first detection coil 22 always corresponds to the first detection window 421 with a fixed small diameter. The first detection window 421 is designed as a round hole to ensure that the first detection coil 22 is always at a fixed detection resolution and has a high detection resolution when rotated. The second detection coil 23 corresponds to the second detection window 422 with a different size and shape. That is, the resolution of the second detection coil 23 can be varied and adjusted. The two detection coils form a comparison detection with different detection resolutions.

[0051] As a further improvement, a raised guide ring 412 is provided along the outer periphery of the outer side wall of the first magnetic shielding cover 41, and a guide groove 422 adapted to the guide ring 412 is recessed on the inner side wall of the second magnetic shielding cover 42. The first magnetic shielding cover 41 and the second magnetic shielding cover 42 are rotatably connected relative to each other through the cooperation of the guide ring 412 and the guide groove 422. An internal thread 413 is provided on the inner side wall of the first magnetic shielding cover 41, and an external thread 11 adapted to the internal thread 413 is provided on the outer side wall of the end of the probe rod 10. The magnetic shielding cover 40 is integrally screwed onto the outer side wall of the probe rod 10 through the cooperation of the internal and external threads. In other testing conditions, the magnetic shielding cover 40 can be disassembled and used separately, or the magnetic shielding cover 40 can be replaced.

[0052] As a further improvement, the first magnetic shielding cover 41 adopts a composite material composed of metal fibers, copper foil, polyimide film, the second magnetic shielding cover 42 adopts copper or aluminum or steel or ferrite material; the lower bottom surface of the first magnetic shielding cover 41 is film-shaped or sheet-shaped, and the lower bottom surface of the second magnetic shielding cover 42 is sheet-shaped. The material adopted has good magnetic shielding effect and can be made into film-shaped or sheet-shaped, small thickness, ensuring that the lift-off between the detection surface of the probe and the workpiece to be detected is within a reasonable range, avoiding affecting the detection.

[0053] The application also discloses a vortex detection method for adjusting sensor resolution to detect dense cracks, which adopts the vortex detection sensor as described above to detect cracks on a rail tread, and the detection steps are as follows:

[0054] a. Setting of the detection sensor: a special pen-type vortex detection sensor is adopted, and a detection assembly of the vortex detection sensor comprises a coil framework and first and second detection coils arranged side by side on the coil framework; the first detection coil is planar square spiral-shaped, and the second detection coil is planar circular spiral-shaped; further, a double-layer cylindrical sleeve type magnetic shielding cover with switchable detection windows is sleeved outside the detection assembly to focus the overflow electromagnetic field of the detection assembly to different degrees;

[0055] b. Adjustment of crack resolution of the sensor: the first magnetic shielding cover is fixed relative to the detection assembly, the second magnetic shielding cover is rotated, the detection window on the second magnetic shielding cover is centered on the through hole on the first magnetic shielding cover, a detection channel is formed, and the detection coil can be detected through the detection channel; the size and shape of different detection windows are different, the corresponding magnetic shielding effect is different, further, the crack detection resolution under different magnetic shielding effects is different, and the second magnetic shielding cover is rotated to adjust the crack resolution;

[0056] c. Acquisition of contrast signals of the detection coils: through special structural design of the magnetic shielding cover, the first detection coil always maintains the highest detection resolution, the first detection coil is adopted to detect cracks on the rail tread and distinguish single cracks or dense cracks; the resolution of the second detection coil can be changed and adjusted, the second detection coil is adopted to detect the depth of the cracks through different detection channels formed by switching the detection windows, and the two detection coils form contrast detection with different detection resolutions;

[0057] d. Rapid identification of the number of cracks and the depth of the cracks: when the detection coil with fixed high detection resolution is adopted for detection, a fixed detection time base range is set, when the detection image is a complete defect waveform within the time base range, it is determined as a single crack; when the detection image presents two and more than two obviously interval-changed defect waveforms within the time base range, it is determined as dense cracks;

[0058] Further, the detection images at multiple detection resolutions are comprehensively analyzed and compared, the conversion of the amplitude and depth of the defect waveform in the detection time base range is performed by the computer, and the crack depth is obtained.

[0059] Generally, the detection depth and the detection sensitivity of the probe to short defects are greatly related to the diameter of the detection surface. In order to increase the detection depth, the diameter of the probe can be increased, and the magnetic flux is improved. However, the diameter of the probe is increased, and the detection sensitivity of the probe to short defects is inevitably reduced. In the present application, the double detection coils are used to cooperate with the special magnetic shielding structure for contrast detection. The first detection coil in a planar square spiral shape is designed. Under the same detection condition, the detection sensitivity is higher. Further optimization is performed. The double-layer magnetic shielding cover is designed, and the small-diameter square detection window is arranged at the corresponding position of the coil. The first detection coil is kept in a high detection resolution, and is used for rapid detection and resolution of the dense cracks on the surface of the metal workpiece. The second detection coil in a planar circular spiral shape is designed. The planar circular spiral coil has high flexibility. The magnetic shielding effect is adjusted by switching the detection window. A plurality of sets of contrast data are formed. The metal surface crack condition is comprehensively evaluated by analyzing and comparing the plurality of sets of data. The confidence and reliability of the detection are improved.

[0060] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A resolution-adjustable eddy current detection sensor for detecting cracks in rail treads, particularly for identifying single cracks and dense cracks and detecting crack depth by adjusting the resolution of the detection sensor, characterized in that... Includes a probe, a detection assembly, and a magnetic shielding cover fitted over the detection assembly; The detection component is spring-loaded and can be slightly moved up and down to be embedded at the end of the probe. It includes a coil frame and a first detection coil and a second detection coil disposed on the coil frame. The first detection coil is disposed at the center of the coil frame, and the second detection coil is disposed on either side of the first detection coil. The magnetic shielding cover is a double-layer cylindrical sleeve structure that can rotate with each other, including an inner first magnetic shielding cover and an outer second magnetic shielding cover. The first magnetic shielding cover has through holes corresponding to two detection coils respectively. The second magnetic shielding cover has a first detection window corresponding to the first detection coil at its center. Several second detection windows of different sizes and shapes are arranged in a ring around the first detection window. The second detection windows can correspond to the second detection coil. Rotating the second magnetic shielding cover can center the first detection window and the second detection window with the through hole to form a detection channel. The detection sensor is a pen-type detection sensor, and the outer wall of the probe is provided with a sliding control for controlling the up and down springing of the detection component; the magnetic shielding cover is placed on the outside of the detection component and screwed onto the outer wall of the end of the probe. During testing, the testing component is pressed towards the testing surface, and the magnetic shielding cover focuses the overflow magnetic field of the testing component onto the surface of the workpiece being tested. The detection channel is switched by rotating the second magnetic shielding cover to control the magnetic shielding capability of the magnetic shielding cover and adjust the crack detection resolution of the eddy current detection sensor.

2. The resolution-adjustable eddy current detection sensor according to claim 1, characterized in that, The first detection coil is a planar square spiral, and the second detection coil is a planar circular spiral.

3. The resolution-adjustable eddy current detection sensor according to claim 2, characterized in that, The first detection window is circular, and the second detection window is set as a circular hole, square hole, or strip of different sizes. When the second magnetic shielding cover is rotated, the first detection coil is always at a fixed high detection resolution, while the resolution of the second detection coil can be adjusted. The two detection coils form a comparison detection with different detection resolutions.

4. The resolution-adjustable eddy current detection sensor according to claim 1, characterized in that, The first magnetic shielding cover has a raised guide ring on its outer periphery, and the second magnetic shielding cover has a recessed guide groove that matches the guide ring on its inner side wall. The first magnetic shielding cover and the second magnetic shielding cover are rotatably connected to each other.

5. The resolution-adjustable eddy current detection sensor according to claim 4, characterized in that, The inner wall of the first magnetic shielding cover is provided with an internal thread, and the outer wall of the end of the probe is provided with an external thread that matches the internal thread.

6. The resolution-adjustable eddy current detection sensor according to claim 1, characterized in that, The first magnetic shielding cover is made of a composite material composed of metal fibers, copper foil, and polyimide film, while the second magnetic shielding cover is made of copper, aluminum, steel, or ferrite material. The bottom surface of the first magnetic shielding cover is in the form of a film or sheet, and the bottom surface of the second magnetic shielding cover is in the form of a sheet.

7. An eddy current detection method for detecting dense cracks by adjusting sensor resolution, characterized in that, The eddy current detection sensor as described in any one of claims 1-6 is used to detect cracks in the rail tread. The detection steps are as follows: a. Sensor setup: A special pen-type eddy current sensor is used. Its detection components include a coil frame and a first detection coil and a second detection coil arranged in parallel on the coil frame. The first detection coil is a planar square spiral, and the second detection coil is a planar circular spiral. A double-layer cylindrical sleeve magnetic shielding cover with switchable detection windows is fitted outside the detection components to focus the overflow electromagnetic field of the detection components to different degrees. b. Adjustment of the crack resolution capability of the sensor: The first magnetic shielding cover is fixed relative to the detection component. Rotate the second magnetic shielding cover to align the detection window on the second magnetic shielding cover with the through hole on the first magnetic shielding cover, forming a through detection channel, so that the detection coil can pass through the detection channel for detection. Different detection windows have different sizes and shapes, corresponding to different magnetic shielding effects. The crack detection resolution capability is different under different magnetic shielding effects. Rotate the second magnetic shielding cover to adjust the crack resolution capability. c. Acquisition of the reference signal of the detection coil: Through the special structural design of the magnetic shielding cover, the first detection coil always maintains a fixed highest detection resolution. The first detection coil is used to detect cracks on the rail tread and distinguish between single cracks and dense cracks. The resolution of the second detection coil can be adjusted. The second detection coil is used to form different detection channels by switching detection windows to detect crack depth, and the two detection coils form a comparison detection with different detection resolutions. d. Rapid determination of the number and depth of cracks: When using a detection coil with a fixed high detection resolution for detection, a fixed detection time base range is set. Within this time base range, if the detection image is a complete defect waveform, it is determined to be a single crack; within this time base range, if the detection image shows two or more defect waveforms with obvious interval changes, it is determined to be a dense crack. By comprehensively analyzing and comparing detection images at multiple detection resolutions, and using a computer to convert the amplitude and depth of the defect waveform within the detection time base range, the crack depth can be obtained.

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