Magnetic flux leakage detection sensor capable of resisting strong electromagnetic interference and transformer welding seam detection method

Abstract

The invention provides an anti-strong electromagnetic interference magnetic flux leakage detection sensor and a transformer welding seam detection method, and belongs to the technical field of electrical equipment detection. According to the magnetic flux leakage detection sensor capable of resisting strong electromagnetic interference, the tunnel magnetoresistive magnetosensitive element arrays are arranged according to the orthogonal differential layout, an N * N array structure is formed and used for detecting a leakage magnetic field generated by weld defects, and the polarities of the adjacent tunnel magnetoresistive magnetosensitive elements are arranged in the opposite directions; and the output ends of the adjacent tunnel magnetoresistive magnetosensitive elements are connected with a differential amplifier to form a differential detection circuit which is used for suppressing common-mode interference. The multiple layers of electromagnetic shielding shells wrap the tunnel magnetoresistive magnetosensitive element array. The equipotential grounding system comprises an equipotential grounding terminal, a potential difference monitoring module and a potential difference compensation module. The problem that in the prior art, a magnetic flux leakage detection sensor is not high in transformer welding seam tiny defect detection precision under the strong electromagnetic interference environment of a transformer substation is solved.

Description

Technical Field

[0001] This invention belongs to the field of electrical equipment testing technology, specifically relating to a leakage magnetic flux detection sensor resistant to strong electromagnetic interference and a method for detecting transformer weld seams. Background Technology

[0002] With the continuous expansion of power system scale and the sustained growth of grid load, transformers, as key equipment in the power system, have a significant impact on the reliability of the power grid due to their safe and stable operation. The quality of transformer welds is directly related to the safe operation of the equipment, and flux leakage detection technology, as a non-destructive testing method, is widely used in the detection of transformer weld defects. However, the strong electromagnetic interference present in the substation environment poses a severe challenge to the accuracy and reliability of flux leakage detection.

[0003] Currently, magnetic flux leakage detection technology mainly relies on magnetic sensing elements to detect the magnetic flux leakage generated by surface and near-surface defects in ferromagnetic materials.

[0004] For example, patent application CN120254037A discloses a magnetic flux leakage detection sensor based on a T-shaped magnetization field. This magnetic flux leakage detection sensor uses a T-shaped magnetic yoke structure and multiple magnetic sensitive elements to achieve cross-inspection of crack defects, thereby improving the detection accuracy.

[0005] Patent application CN119901805A discloses a defect detection system for ferromagnetic metal devices. This system combines leakage magnetic field detection and eddy current detection methods and uses a tunneling effect magnetoresistive sensor array to improve the detection capability of buried defects.

[0006] To improve detection efficiency and accuracy, composite detection technology has gradually become a research hotspot.

[0007] For example, patent application CN108226277A discloses a composite external pipe inspection probe that combines magnetic flux leakage, electromagnetic ultrasound, and eddy current. This probe solves the problem that a single inspection method is difficult to identify different types of defects by integrating multiple inspection methods.

[0008] Patent application CN118759037A discloses an electromagnetic composite sensor that combines a triaxial integrated magnetic imaging array chip and a low-temperature co-fired ceramic eddy current chip to achieve comprehensive and high-precision detection of surface / deep defects and cracks in pipelines.

[0009] To address the unique environment of transformers, patent application CN118883705A discloses a transformer casing leakage magnetic flux detection device and method. This device includes a magnetic field detection sensor, a main unit, and a data transmission line, enabling timely detection of internal transformer defects. However, the anti-interference capability of this technology in environments with strong electromagnetic interference still needs improvement.

[0010] Despite some progress in existing technologies, leakage flux detection in the strong electromagnetic environment of substations still faces the following technical challenges: 1. Traditional magnetic flux leakage sensors suffer severe signal-to-noise ratio degradation in strong electromagnetic environments, leading to a significant decrease in defect detection rate. This is especially true in substation environments, where power frequency electromagnetic fields and high-frequency electromagnetic interference coexist, causing the detection signal to be submerged in noise.

[0011] 2. Existing single shielding structures are insufficient to effectively suppress both low-frequency magnetic fields and high-frequency electromagnetic interference simultaneously. While μ-metals can shield low-frequency magnetic fields, their effectiveness against high-frequency electromagnetic interference is limited; and conductive materials have good shielding effects against high-frequency electromagnetic interference, but their shielding ability against low-frequency magnetic fields is insufficient.

[0012] 3. In substation environments, a potential difference exists between the sensor and the transformer, which can easily create ground loop currents, generating additional electromagnetic interference and affecting detection accuracy. Current technologies lack effective equipotential bonding solutions, making it difficult to eliminate this interference.

[0013] 4. In order to improve anti-interference capabilities, existing technologies often adopt heavy shielding structures, which increases the size and weight of the equipment, affecting the flexibility of on-site operation, especially in the detection of complex structural areas of transformers.

[0014] 5. The power industry has an increasing demand for the detection of minute defects (below 0.5mm) in transformer welds, but existing leakage flux detection technology is difficult to meet this requirement in environments with strong electromagnetic interference, which limits its application in high-reliability applications.

[0015] Therefore, there is an urgent need to develop a leakage magnetic flux detection sensor that can accurately detect minute defects in transformer welds under strong electromagnetic interference environments in substations, so as to improve the reliability of transformer safe operation. Summary of the Invention

[0016] The purpose of this invention is to provide a leakage magnetic flux detection sensor and a method for detecting transformer welds that are resistant to strong electromagnetic interference, in order to solve the problem that the leakage magnetic flux detection sensor in the prior art has low accuracy in detecting small defects in transformer welds under strong electromagnetic interference environment in substations.

[0017] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a leakage magnetic flux detection sensor resistant to strong electromagnetic interference, comprising a tunnel magnetoresistive magnetic sensitive element array, a differential amplifier, several layers of electromagnetic shielding shell and an equipotential grounding system; The tunnel magnetoresistive magnetic sensitive element array is arranged in an orthogonal differential layout to form an N×N array structure, which is used to detect the leakage magnetic field generated by the transformer weld defects. The polarities of adjacent tunnel magnetoresistive magnetic sensitive elements are arranged in opposite directions, and the output terminals of adjacent tunnel magnetoresistive magnetic sensitive elements are connected to differential amplifiers to form a differential detection circuit, which is used to suppress common-mode interference. The tunnel magnetoresistive magnetic sensitive element array is enclosed by several layers of electromagnetic shielding shell; The equipotential grounding system includes an equipotential grounding terminal, a potential difference monitoring module, and a potential difference compensation module. The equipotential grounding terminal is connected to the transformer housing. The potential difference monitoring module is used to dynamically monitor changes in potential difference, and the potential difference compensation module is used to dynamically compensate for changes in potential difference.

[0018] A further improvement of the present invention is that the plurality of electromagnetic shielding shells, from the inside out, include a μ alloy layer, an insulating dielectric layer, a copper-based conductive coating, and an aluminum alloy protective shell.

[0019] A further improvement of the present invention is that it also includes a signal conditioning module, which is connected to the tunnel magnetoresistive magnetic sensitive element array and is used to condition the signal output by the tunnel magnetoresistive magnetic sensitive element array. The signal conditioning module includes an instrumentation amplifier and a bandpass filter.

[0020] A further improvement of the present invention is that the instrumentation amplifier is model AD8421.

[0021] A further improvement of the present invention is that the bandwidth of the bandpass filter is 1kHz-10MHz.

[0022] A further improvement of the present invention is that the spacing between adjacent tunnel magnetoresistive magnetic sensitive elements is less than or equal to a first set threshold.

[0023] A further improvement of the present invention is that the equipotential grounding terminal is connected to the transformer housing via a braided copper strip.

[0024] Secondly, the present invention provides a method for inspecting transformer welds, using the aforementioned anti-strong electromagnetic interference leakage magnetic flux detection sensor, comprising the following steps: A static magnetic field is applied to the weld area to be inspected; The electromagnetic interference-resistant magnetic flux leakage detection sensor is used to scan at a constant speed along the weld seam direction. The defect leakage magnetic field signal is extracted by differential detection circuit to suppress power frequency electromagnetic interference; Based on the defect leakage magnetic field signal, the width-to-depth ratio threshold of the defect is determined; Based on the width-to-depth ratio threshold of the defect, the defect level is determined, and the transformer weld inspection results are obtained.

[0025] A further improvement of the present invention is that the width-to-depth ratio threshold of the defect is set according to the type of defect.

[0026] A further improvement of the present invention is that the width-to-depth ratio threshold range for crack-type defects is 0.1-0.2, and the width-to-depth ratio threshold range for porosity-type defects is set to 0.3-0.5.

[0027] Compared with the prior art, the present invention has the following beneficial effects: The proposed electromagnetic interference (EMI) leakage magnetic flux leakage sensor features a tunnel magnetoresistive magnetic sensing element array and several layers of electromagnetic shielding. This design significantly improves EMI resistance and addresses the signal-to-noise ratio degradation under strong electromagnetic conditions. Furthermore, it overcomes the problem of low accuracy in detecting minute defects in transformer welds under strong electromagnetic interference in substation environments, a common issue in existing EMI leakage sensors. Additionally, an equipotential grounding system ensures that the grounding resistance does not exceed 0.1Ω and the potential difference between the EMI leakage magnetic flux leakage sensor and the transformer body is controlled within 10mV.

[0028] Furthermore, the present invention discloses that the bandpass filter has a frequency range of 1kHz-10MHz. The 1kHz-10MHz frequency band design can effectively filter out low-frequency power frequency interference and high-frequency electromagnetic noise in the substation environment, and only retain the characteristic signal frequency band generated by weld defects, thereby improving the accuracy of subsequent weld inspection. Attached Figure Description

[0029] Figure 1 This is a flowchart of the transformer weld inspection method of the present invention. Detailed Implementation

[0030] To further understand the content of this invention, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments are merely illustrative and not limiting of the invention.

[0031] Example 1: This embodiment discloses a strong electromagnetic interference leakage magnetic flux detection sensor for transformer weld inspection in substation environments. The sensor employs multiple protection measures to ensure reliable operation under strong electromagnetic interference conditions. The following is a detailed description of the strong electromagnetic interference leakage magnetic flux detection sensor: The electromagnetic interference leakage magnetic field detection sensor of the present invention includes a tunnel magnetoresistive magnetic sensitive element array (in this embodiment, the tunnel magnetoresistive magnetic sensitive element is a TMR (Tunneling Magnetoresistance) 2305 magnetic sensitive element, which has a sensitivity of 20mV / V / Oe and can accurately capture weak leakage magnetic field signals), a differential amplifier, several layers of electromagnetic shielding shells, and an equipotential grounding system.

[0032] The tunnel magnetoresistive magnetic sensitive element array is arranged in an orthogonal differential layout to form an N×N array structure (in this embodiment, a 4×4 array structure is formed, and the value of N can be set according to actual needs). It is used to detect the leakage magnetic field generated by the transformer weld defect. The polarities of adjacent tunnel magnetoresistive magnetic sensitive elements are arranged in opposite directions. The output terminals of adjacent tunnel magnetoresistive magnetic sensitive elements are connected to differential amplifiers to form a differential detection circuit, which is used to suppress common-mode interference and improve the signal-to-noise ratio.

[0033] The tunnel magnetoresistive magnetic sensing element array is enclosed by several layers of electromagnetic shielding shell.

[0034] The equipotential grounding system includes an equipotential grounding terminal, a potential difference monitoring module, and a potential difference compensation module (the potential difference monitoring module and the potential difference compensation module are implemented based on the ADuCM360 microcontroller). The equipotential grounding terminal is connected to the transformer shell. The potential difference monitoring module is used to dynamically monitor changes in potential difference, and the potential difference compensation module is used to dynamically compensate for changes in potential difference. The design of the potential difference monitoring module and the potential difference compensation module can ensure that the sensor maintains a stable grounding potential in the complex electromagnetic environment of the substation, and avoid the interference current caused by the ground potential difference from affecting the detection accuracy.

[0035] The design of the equipotential grounding system can ensure that the grounding resistance does not exceed 0.1Ω, and the potential difference between the leakage magnetic flux detection sensor and the transformer body is controlled within 10mV.

[0036] The electromagnetic shielding enclosure consists of several layers, from the inside out: a μ alloy layer, an insulating dielectric layer, a copper-based conductive coating, and an aluminum alloy protective shell. The μ alloy layer, insulating dielectric layer, copper-based conductive coating, and aluminum alloy shell are described in detail below: The electromagnetic shielding shell consists of several layers from the inside out, including: an inner layer of 0.5-1mm thick μ alloy with a relative permeability ≥50,000 and a saturation magnetic induction intensity ≥0.8T; a middle layer of insulating dielectric layer and a 50-100μm thick copper-based conductive coating with a surface resistance ≤0.05Ω / m; and an outer layer of aluminum alloy protective shell for providing mechanical protection and auxiliary electromagnetic shielding.

[0037] Specifically, in this embodiment, the electromagnetic shielding shell comprises four layers from the inside out: the first layer is a μ alloy layer with a thickness of 0.8 mm, a relative permeability of 55,000, and a saturation magnetic induction intensity of 0.85 T, which is mainly used to shield against external magnetic field interference; the second layer is a 0.2 mm thick epoxy insulating dielectric layer, used to isolate the magnetic shielding layer from the conductive layer; the third layer is a copper-based conductive coating with a thickness of 80 μm and a surface resistance of 0.03 Ω / m, mainly used to shield against high-frequency electromagnetic interference; and the fourth layer is a 2 mm thick 6061 aluminum alloy protective shell, providing mechanical protection and auxiliary electromagnetic shielding. This multi-layer shielding structure design can effectively block strong electromagnetic interference in the substation environment and ensure the normal operation of the sensor's internal circuitry.

[0038] The electromagnetic interference leakage magnetic field detection sensor of the present invention also includes a signal conditioning module. The signal conditioning module is connected to the tunnel magnetoresistive magnetic sensitive element array and is used to condition the signal output by the tunnel magnetoresistive magnetic sensitive element array. The signal conditioning module includes an instrumentation amplifier and a bandpass filter.

[0039] The instrumentation amplifier is model AD8421.

[0040] The bandpass filter has a frequency range of 1kHz-10MHz. The 1kHz-10MHz frequency band design can effectively filter out low-frequency power frequency interference and high-frequency electromagnetic noise in the substation environment, and only retain the characteristic signal frequency band generated by weld defects, thereby improving the accuracy of transformer weld inspection.

[0041] The spacing between adjacent tunnel magnetoresistive magnetic sensitive elements is less than or equal to a first set threshold (in this embodiment, the first set threshold is 5mm, and the first set threshold can be set according to actual needs) to ensure the sensitivity of detecting minute defects.

[0042] The equipotential grounding terminal is connected to the transformer housing through a braided copper strip with a cross-sectional area of ​​≥25mm² (0.8m in length) to achieve equipotential connection between the sensor and the transformer body.

[0043] In practical applications, the electromagnetic interference-resistant leakage magnetic field detection sensor of this invention is placed at the transformer weld. The tunnel magnetoresistive magnetic sensitive element array can detect changes in the leakage magnetic field caused by weld defects. The signal output by the tunnel magnetoresistive magnetic sensitive element array is processed by the signal conditioning module to output a clear defect characteristic signal. Several layers of electromagnetic shielding shell and equipotential grounding system ensure that the entire detection process is not affected by external electromagnetic interference, thereby realizing reliable non-destructive testing of transformer welds in a strong electromagnetic interference environment.

[0044] Compared with the prior art, the electromagnetic interference leakage magnetic flux detection sensor of the present invention has the following beneficial effects: 1. Significantly improved anti-interference performance: Through a multi-layer electromagnetic shielding system (several layers of electromagnetic shielding shell) and differential detection circuit, the power frequency magnetic field interference suppression is >100dB and the high frequency electromagnetic wave shielding effectiveness is ≥70dB, reducing the false alarm rate from >30% of traditional sensors to <3%, effectively solving the problem of signal-to-noise ratio degradation in strong electromagnetic environments.

[0045] 2. Breakthrough in detection accuracy: Using a TMR magnetic sensitive element array and signal conditioning module, it can detect micro-defects as small as 0.3mm×5mm, with a width-to-depth ratio resolution of 0.05. The detection rate of 0.5mm×5mm defects is >95%, meeting the stringent requirements of the power industry for micro-defect detection.

[0046] 3. Significantly enhanced field adaptability: Through compact integrated design, the total weight is <1.5kg, the size is ≤150×100×50mm, it supports wide temperature range of -40℃ to +85℃, and achieves IP67 protection level, overcoming the disadvantages of traditional anti-interference solutions that are large in size and heavy in weight.

[0047] 4. Significantly improved ease of maintenance: The modular design (tunnel magnetoresistive magnetic sensitive element array, differential amplifier, several layers of electromagnetic shielding shell and equipotential grounding system) makes probe replacement time less than 5 minutes, reducing maintenance costs. The self-diagnostic function monitors the system status in real time, improving the reliability and service life of the equipment.

[0048] Example 2: This embodiment discloses a method for inspecting transformer welds, and the flowchart of the inspection method is as follows: Figure 1 As shown, the following steps are included when using the electromagnetic interference-resistant leakage magnetic flux detection sensor described above: A static magnetic field with a strength of 200-500 Oe is applied to the weld area to be inspected. The electromagnetic interference leakage magnetic field detection sensor is used to scan along the weld seam at a uniform speed of ≤10mm / s. The defect leakage magnetic field signal is extracted by differential detection circuit to suppress power frequency electromagnetic interference; Based on the defect leakage magnetic field signal, the width-to-depth ratio threshold of the defect is determined; Based on the width-to-depth ratio threshold of the defect, the defect level is determined, and the transformer weld inspection results are obtained.

[0049] The aspect ratio threshold for defects is set according to the type of defect.

[0050] The width-to-depth ratio threshold range for crack-type defects is 0.1-0.2, and the width-to-depth ratio threshold range for porosity-type defects is set to 0.3-0.5.

[0051] Example 3: The transformer weld inspection method of the present invention will be described in detail below: Step 1: Applying a magnetic field A static magnetic field with a strength of 350 Oe is applied to the weld area to be inspected. The static magnetic field is generated by a permanent magnet array made of neodymium iron boron material, and the magnetic field strength can be adjusted within the range of 200-500 Oe to meet the inspection needs of welds of different thicknesses and materials.

[0052] Step 2: Scanning with a high-electromagnetic-interference leakage magnetic flux detection sensor A high-magnetic-interference (HEMI) leakage magnetic flux leakage sensor is used to scan at a constant speed along the weld seam, with the scanning speed set to 8 mm / s. During the scanning process, the HEMI leakage magnetic flux leakage sensor maintains a fixed distance of 1-2 mm from the weld seam surface, and a precision guide rail ensures the stability of the scanning path. The scanning speed of the HEMI leakage magnetic flux leakage sensor can be adjusted within the range of 0.5-10 mm / s according to the required detection accuracy; the lower the speed, the higher the detection resolution.

[0053] Step 3: Signal Processing The defect leakage magnetic field signal is extracted by a differential detection circuit to suppress power frequency electromagnetic interference. The differential detection circuit utilizes the reverse polarity arrangement of adjacent tunnel magnetoresistive magnetic sensitive elements to send the output signals of adjacent tunnel magnetoresistive magnetic sensitive elements to an AD8421 differential amplifier for processing, effectively eliminating common-mode interference. The signal output from the tunnel magnetoresistive magnetic sensitive element array is further filtered by a bandpass filter (1kHz-10MHz) to remove power frequency electromagnetic interference and improve the signal-to-noise ratio.

[0054] Step 4: Defect Identification Based on the width-to-depth ratio threshold of the defect, the defect level is determined, and the transformer weld inspection results are obtained. Specifically, the width-to-depth ratio parameter of the defect is calculated by analyzing the amplitude and spatial distribution characteristics of the defect leakage magnetic signal. The width-to-depth ratio threshold is set to 0.1-0.5 to distinguish defects of different severity.

[0055] Furthermore, the aspect ratio threshold for defects is set differently based on the type of defect: 0.15 for crack-type defects and 0.4 for porosity-type defects. This differentiated setting takes into account the differences in magnetic field distribution characteristics of different types of defects, improving the accuracy of detection. When a defect with an aspect ratio less than 0.05 is detected, an audible and visual alarm is automatically triggered and the defect is marked as a major defect in the detection results, reminding the inspection personnel to pay close attention.

[0056] The transformer weld inspection method of this invention demonstrates excellent performance in practical applications. In verification tests conducted in a substation environment, the method operated stably in a 50Hz / 100μT power frequency magnetic field interference environment without affecting detection accuracy. For crack defects with a width of 0.2mm and a depth of 1mm, the detection success rate reached 98%; for porosity defects with a diameter of 0.5mm, the detection success rate reached 95%.

[0057] This invention provides a transformer weld inspection method that combines the advantages of a leakage magnetic flux detection sensor that resists strong electromagnetic interference. Through reasonable detection parameter settings and signal processing strategies, it achieves high-precision detection of transformer weld defects in the complex electromagnetic environment of substations, providing a reliable guarantee for the safe operation of transformers.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A leakage magnetic flux detection sensor resistant to strong electromagnetic interference, characterized in that, It includes a tunnel magnetoresistive magnetic sensitive element array, a differential amplifier, several layers of electromagnetic shielding shell, and an equipotential grounding system; The tunnel magnetoresistive magnetic sensitive element array is arranged in an orthogonal differential layout to form an N×N array structure, which is used to detect the leakage magnetic field generated by the transformer weld defects. The polarities of adjacent tunnel magnetoresistive magnetic sensitive elements are arranged in opposite directions, and the output terminals of adjacent tunnel magnetoresistive magnetic sensitive elements are connected to differential amplifiers to form a differential detection circuit, which is used to suppress common-mode interference. The tunnel magnetoresistive magnetic sensitive element array is enclosed by several layers of electromagnetic shielding shell; The equipotential grounding system includes an equipotential grounding terminal, a potential difference monitoring module, and a potential difference compensation module. The equipotential grounding terminal is connected to the transformer housing. The potential difference monitoring module is used to dynamically monitor changes in potential difference, and the potential difference compensation module is used to dynamically compensate for changes in potential difference.

2. The electromagnetic interference leakage magnetic flux detection sensor according to claim 1, characterized in that, The electromagnetic shielding shell consists of, from the inside out, a μ alloy layer, an insulating dielectric layer, a copper-based conductive coating, and an aluminum alloy protective shell.

3. The electromagnetic interference leakage magnetic flux detection sensor according to claim 1, characterized in that, It also includes a signal conditioning module, which is connected to the tunnel magnetoresistive magnetic sensitive element array and is used to condition the signal output by the tunnel magnetoresistive magnetic sensitive element array. The signal conditioning module includes an instrumentation amplifier and a bandpass filter.

4. The electromagnetic interference leakage magnetic flux detection sensor according to claim 3, characterized in that, The instrumentation amplifier is model AD8421.

5. The electromagnetic interference leakage magnetic flux detection sensor according to claim 3, characterized in that, The bandpass filter has a frequency range of 1kHz-10MHz.

6. The electromagnetic interference leakage magnetic flux detection sensor according to claim 1, characterized in that, The spacing between adjacent tunnel magnetoresistive magnetic sensitive elements is less than or equal to a first set threshold.

7. The electromagnetic interference leakage magnetic flux detection sensor according to claim 1, characterized in that, The equipotential grounding terminal is connected to the transformer housing via a braided copper strip.

8. A method for inspecting transformer welds, using the anti-strong electromagnetic interference leakage magnetic flux detection sensor as described in claims 1-7, characterized in that, Includes the following steps: A static magnetic field is applied to the weld area to be inspected; The electromagnetic interference-resistant magnetic flux leakage detection sensor is used to scan at a constant speed along the weld seam direction. The defect leakage magnetic field signal is extracted by differential detection circuit to suppress power frequency electromagnetic interference; Based on the defect leakage magnetic field signal, the width-to-depth ratio threshold of the defect is determined; Based on the width-to-depth ratio threshold of the defect, the defect level is determined, and the transformer weld inspection results are obtained.

9. The transformer weld inspection method according to claim 8, characterized in that, The aspect ratio threshold of the defect is set according to the type of defect.

10. The transformer weld inspection method according to claim 9, characterized in that, The width-to-depth ratio threshold range for crack-type defects is 0.1-0.2, and the width-to-depth ratio threshold range for porosity-type defects is set to 0.3-0.5.

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