An eddy current flaw detector and method capable of detecting extremely fine cracks in a conductor wire

Abstract

This invention discloses an eddy current flaw detector and method for detecting extremely fine wire cracks in conductors, comprising: the output end of a resonant generator is connected to the transmitting end of a detection probe to form a 1-40MHz resonant frequency detection source; when the detection source approaches the material under test, it induces a current on the surface of the material under test; the receiving end of the detection probe is connected to the input end of a signal conversion module to receive the resonant frequency signal returned by the material under test; the detection probe generates a change in resonant frequency based on the change in the induced current of the material under test; the signal conversion module converts the resonant frequency signal generated by the detection probe into a voltage signal; the output end of the signal conversion module is connected to a recording and analysis module for real-time recording and analysis of the voltage signal to achieve flaw detection of the material under test. This method can detect extremely fine wire cracks.

Description

Technical Field

[0001] This invention relates to the field of eddy current flaw detection technology, and in particular to an eddy current flaw detector and method for detecting cracks in extremely fine conductor wires. Background Technology

[0002] Eddy current flaw detector is a device that uses the eddy current detection principle to detect defects such as cracks and pores in steel bars and plates. It has the functions of suppressing interference signals and picking up useful information. The instrument consists of an oscillation generator, a detection probe, a signal conversion module, a recording and analysis module, etc., and is mainly used for non-destructive testing of metallic materials.

[0003] Eddy current testing utilizes the principle of electromagnetic induction. When alternating current is applied to a coil, if the voltage and frequency remain constant, the current through the coil will also remain constant. If a conductor is present near the coil, an induced current is generated on the conductor's surface. Because this induced current flows in a circular motion, much like a vortex in water, it is called an eddy current. The direction of the eddy current magnetic field is opposite to the direction of the applied current, thus causing changes in the coil's impedance, the magnitude of the current, and its phase. If other factors remain constant, the presence of defects on the conductor's surface or subsurface will affect the changes in the coil's current, impedance, and other parameters. Amplifying the signal caused by these defects allows for flaw detection.

[0004] The detection probe contains a coil that functions as a sensing element. When the sensor probe scans the workpiece, any defects will modulate the high-frequency carrier (excitation) signal. Ultimately, any characteristics that affect the eddy current state within the metal workpiece (such as material conductivity or magnetic permeability) or any existing defects will be displayed on the eddy current signal curve. For example, as... Figure 1 As shown, when a crack appears, the magnitude of the AC voltage across the detection probe coil will temporarily increase.

[0005] Traditional flaw detectors obtain their results by outputting a certain excitation frequency signal and then analyzing the impedance changes of the signal. However, their frequency is limited and usually does not exceed 10MHz, making them inadequate for detecting extremely fine wire cracks. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide an eddy current flaw detector and method for detecting cracks in extremely fine conductor wires, which can solve the above-mentioned problems.

[0007] One aspect of the present invention provides an eddy current flaw detector capable of detecting cracks in extremely fine conductor wires, comprising: a resonant generator, a detection probe, a signal conversion module, and a recording and analysis module;

[0008] The output of the resonant generator is connected to the transmitting end of the detection probe to form a 1-40MHz resonant frequency detection source. When the detection source is close to the material under test, it induces a current on the surface of the material under test.

[0009] The receiving end of the detection probe is connected to the input end of the signal conversion module to receive the resonant frequency signal returned by the material under test. The detection probe generates a change in resonant frequency based on the change in the induced current of the material under test. The detection probe includes: a flaw detection signal acquisition coil, an interference signal compensation coil, and a comparator I1. The flaw detection signal acquisition coil is connected to the positive terminal of the comparator I1 to transmit and acquire the resonant frequency. The interference signal compensation coil is connected to the negative terminal of the comparator I1 to generate a differential compensation signal, thereby canceling external interference signals when receiving the resonant frequency signal. The output end of the comparator I1 is connected to the input end of the signal conversion module.

[0010] The signal conversion module converts the resonant frequency signal generated by the detection probe into a voltage signal. The signal conversion module includes a frequency divider circuit and a frequency-to-voltage conversion circuit. The input terminal of the frequency divider circuit is connected to the receiving terminal of the detection probe and is used to divide the resonant frequency signal. The output terminal of the frequency divider circuit is connected to the input terminal of the frequency-to-voltage conversion circuit and is used to convert the resonant frequency signal into a voltage signal. The output terminal of the signal conversion module is connected to the recording and analysis module and is used to record and analyze the voltage signal in real time to achieve flaw detection of the material under test.

[0011] Furthermore, it includes: a zero-point compensation circuit and a digital DC voltmeter;

[0012] The zero-point compensation circuit is connected to the output terminal of the signal conversion module and is used to adjust the output voltage and calibrate the reference voltage; the input terminal of the digital display DC voltmeter is connected to the output terminal of the signal conversion module and is used to display the current output voltage and calibrate the reference voltage in conjunction with the zero-point compensation circuit.

[0013] Furthermore, it includes: DC amplifier circuits;

[0014] The output of the zero-point compensation circuit is connected to the input of the DC amplifier circuit to amplify the voltage signal.

[0015] Furthermore, it includes: a voltage follower circuit;

[0016] The input terminal of the voltage follower circuit is connected to the output terminal of the DC amplifier circuit, and the output terminal of the voltage follower circuit is connected to the input terminal of the recording and analysis module, which is used to buffer and isolate the input voltage of the DC amplifier circuit.

[0017] Furthermore, it includes: a roller-type meter counter;

[0018] The output of the roller-type meter counter is connected to the input of the recording and analysis module, and is used to calculate the length of the material to be measured and send it to the recording and analysis module and the voltage signal for synchronous recording.

[0019] Another aspect of the present invention provides an eddy current flaw detection method for detecting cracks in extremely fine conductor filaments, comprising:

[0020] The resonant frequency signal generated by the resonant generator is sent to the material under test through the detection probe.

[0021] The detection probe generates a change in resonant frequency based on the change in the induced current of the material under test, thereby obtaining the resonant frequency signal;

[0022] The signal conversion module converts all the resonant frequency signals into voltage signals.

[0023] The recording and analysis module records the voltage signal according to the length of the material under test.

[0024] The voltage signal is analyzed and calculated by the recording and analysis module to obtain the crack depth at different locations in the material under test.

[0025] Furthermore, the step of converting all the resonant frequency signals into voltage signals through the signal conversion module includes:

[0026] The frequency-divided signal is obtained by performing a frequency-dividing process of six times on all the resonant frequency signals through the frequency division circuit.

[0027] The frequency-divided signal is converted into the voltage signal by the frequency-to-voltage conversion circuit.

[0028] Furthermore, the step of recording the voltage signal according to the length of the material under test by the recording and analysis module includes:

[0029] The roller-type meter counter moves along with the detection probe;

[0030] The number of meters moved is synchronously sent to the recording and analysis module via the roller-type meter counter.

[0031] The voltage signal is synchronously sent to the recording and analysis module through the signal conversion module.

[0032] Furthermore, the step of analyzing and calculating the crack depth L at different locations of the material under test using the recording and analysis module includes:

[0033] Obtain the diameter D, full-range voltage U, and amplified voltage signal Uo of the material under test;

[0034] The crack depth L is calculated using the diameter D of the material under test, the full-range voltage U, and the amplified voltage signal Uo. The crack depth satisfies L=DхUo / U.

[0035] Furthermore, before the resonant frequency signal is generated by the resonant generator and sent to the material under test through the detection probe, the following steps are included:

[0036] The zero-point compensation circuit is used to zero-calibrate the voltage signal output by the signal conversion module.

[0037] The beneficial effects of this invention are:

[0038] First, a sine wave with a frequency of 1-40MHz is generated by a resonant generator. Then, in conjunction with a frequency divider circuit, a frequency-to-voltage conversion module, and a DC amplifier circuit, the resonant frequency signal of 1-40MHz and above is divided and converted to amplify the weak signal, thereby improving the detection sensitivity and enabling the detection of cracks smaller than 10µm.

[0039] Secondly, a self-excited oscillation signal is generated by a common-base transformer feedback LC oscillator, breaking through the original fixed signal excitation frequency. The flaw detection signal is obtained by analyzing the impedance change signal. The flaw detection signal is obtained by using the resonant circuit principle to obtain the frequency change signal caused by the impedance change.

[0040] Third, by setting up a flaw detection signal acquisition coil and an interference signal compensation coil in the detection probe, the flaw detection signal is acquired in the same detection coil, avoiding the error caused by the difference between the two probes in the standard comparison method. At the same time, with the two coils in the same probe, the interference signals obtained are definitely consistent. The two coils form a differential compensation system to cancel the interference signals in real time, which significantly enhances the anti-interference capability. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of the flaw detector principle in the background technology of this invention.

[0043] Figure 2 This is a schematic diagram of the composition and structure of the flaw detector in this invention.

[0044] Figure 3 This is the LC parallel resonant circuit diagram in this invention.

[0045] Figure 4 This is a circuit diagram of a common-base transformer feedback LC oscillation circuit in this invention.

[0046] Figure 5 This is a schematic diagram of the standard comparative detection probe structure in this invention.

[0047] Figure 6 This is a schematic diagram of the traditional absolute detection probe structure in this invention.

[0048] Figure 7 This is a schematic diagram of the improved detection probe structure of the present invention.

[0049] Figure 8 This is a circuit diagram of the frequency-to-voltage conversion circuit in this invention.

[0050] Figure 9 This is the zero-point compensation circuit diagram in this invention.

[0051] Figure 10 This is a diagram of the DC amplifier circuit in this invention.

[0052] Figure 11 This is the voltage follower circuit diagram in this invention.

[0053] Figure 12 This is the voltage spectrum of the flaw detection results in this invention.

[0054] Figure 13 This is a comparison diagram of the flaw detection results and metallographic examination results under the condition of cracks in this invention.

[0055] Figure 14 This is a comparison chart of the flaw detection results and metallographic examination results under the condition of no cracks in this invention. Detailed Implementation

[0056] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0057] like Figure 2 As shown, this embodiment of the invention provides an eddy current flaw detector capable of detecting cracks in extremely fine conductor wires, comprising: a resonant generator, a detection probe, a signal conversion module, and a recording and analysis module;

[0058] The output of the resonant generator is connected to the transmitting end of the detection probe to form a 1-40MHz resonant frequency detection source. When the detection source is close to the material under test, it induces a current on the surface of the material under test.

[0059] In this embodiment, there are four commonly used design schemes for the signal source:

[0060] 1. Direct generation using a dedicated DDS chip; Advantages of this method: It can output signals with high stability and high precision, easily generate sine waves with a frequency range of 0Hz to 10MHz, and easily change the frequency; Disadvantages of this method: It is difficult to generate sine waves with frequencies above 10MHz.

[0061] 2. Using integrated chips such as FPGAs to synthesize via DDS technology; Advantages of this scheme: It can output a frequency source with high stability and high precision, easily achieve sine wave output, and easily change the frequency; Disadvantages of this scheme: It is difficult to generate sine waves with frequencies above 100kHz.

[0062] 3. Using a resonant circuit to generate the frequency; Advantages of this method: simple circuit structure, easy to generate sine waves in the frequency range of 0Hz to 50MHz; Disadvantages of this method: relatively difficult to change the frequency.

[0063] 4. Use a crystal oscillator and frequency divider to generate a square wave of the required frequency, and then convert it into a sine wave through a filter. Advantages of this method: It is easy to generate sine waves with a frequency range of 0Hz to 10MHz. Disadvantages of this method: It is difficult to generate sine waves with frequencies above 10MHz, and it is difficult to change the frequency.

[0064] Since this design has high requirements for the frequency of the signal source, Scheme 3 is more likely to achieve a frequency of 40MHz, so Scheme 3 is selected and the signal source is implemented using a resonant generator.

[0065] like Figure 3 As shown, the LC parallel resonant circuit is an oscillating circuit composed of an inductor L, a capacitor C, and an external signal source connected in parallel. Under signal excitation at different operating frequencies, the LC parallel resonant circuit exhibits different impedance amplitude-frequency characteristics and phase-frequency characteristics. Here, r represents the equivalent loss resistance of the coil L. Based on the fact that the equivalent impedance of the circuit at resonance is a pure resistance, the resonance value can be obtained... The resonant frequency is thus obtained. or .

[0066] Furthermore, such as Figure 4As shown, this invention uses a common-base transformer feedback LC oscillator as the resonant generator. In this type of feedback oscillator circuit, the feedback voltage is used as the input voltage, and the LC parallel resonant circuit is mainly used as a frequency-selective feedback network. The output signal is fed back to the input, and the feedback signal is in phase with the input signal, forming a closed-loop positive feedback. Therefore, an output signal can be generated without external signal excitation, resulting in self-excited oscillation.

[0067] The receiving end of the detection probe is connected to the input end of the signal conversion module to receive the resonant frequency signal returned by the material under test. The detection probe generates a change in resonant frequency based on the change in the induced current of the material under test. The detection probe includes: a flaw detection signal acquisition coil, an interference signal compensation coil, and a comparator I1. The flaw detection signal acquisition coil is connected to the positive terminal of the comparator I1 to transmit and acquire the resonant frequency. The interference signal compensation coil is connected to the negative terminal of the comparator I1 to generate a differential compensation signal, thereby canceling external interference signals when receiving the resonant frequency signal. The output end of the comparator I1 is connected to the input end of the signal conversion module.

[0068] In this embodiment, in eddy current testing, an alternating magnetic field is established by a detection probe (detection coil) to transfer energy to the conductor under test; simultaneously, the alternating magnetic field established by the eddy current is used to obtain mass information of the conductor under test. Therefore, the detection coil is essentially a transducer.

[0069] Standard comparison formula (e.g.) Figure 5 (As shown) It can identify continuous cracks and through cracks, but its anti-interference ability is poor. Analysis revealed that because its two probes are relatively independent, when one probe receives an interference signal while the other does not, the bridge becomes unbalanced, causing inspection errors. Therefore, this scheme requires high consistency between the two probes, the probe wires, and shielding, which is quite difficult in actual operation.

[0070] Traditional absolute terms (such as) Figure 6 The probe shown has only one coil. While it can identify continuous and through cracks, its anti-interference capability is relatively poor. Analysis revealed that because it only has one probe, when it receives an interference signal, the bridge circuit becomes unbalanced, causing inspection errors. Therefore, this solution requires extremely high shielding, which is quite difficult in actual operation.

[0071] Therefore, this invention comprehensively improves upon the absolute method by placing two coils within the same probe: one for flaw detection signal acquisition and one for interference signal compensation (e.g., ...). Figure 7 (As shown). This type of probe has two characteristics:

[0072] 1. The flaw detection signal is acquired in the same detection coil, avoiding the error caused by the difference between the two probes in the standard comparison method.

[0073] 2. When two coils are placed in the same probe, the interference signals obtained will definitely be the same. The two coils form a differential compensation type, which cancels the interference signals in real time, thus significantly enhancing the anti-interference ability.

[0074] The signal conversion module converts the resonant frequency signal generated by the detection probe into a voltage signal. The signal conversion module includes a frequency divider circuit and a frequency-to-voltage conversion circuit. The input terminal of the frequency divider circuit is connected to the receiving terminal of the detection probe and is used to divide the resonant frequency signal. The output terminal of the frequency divider circuit is connected to the input terminal of the frequency-to-voltage conversion circuit and is used to convert the resonant frequency signal into a voltage signal. The output terminal of the signal conversion module is connected to the recording and analysis module and is used to record and analyze the voltage signal in real time to achieve flaw detection of the material under test.

[0075] In this embodiment, the signal output by the resonant generator, as detected by flaw detection, causes a slight change in the resonant frequency, which increases with the size of the defect. This indicates a correlation between the changing frequency signal and the defect. Therefore, this invention only needs to extract the frequency signal. Since the change ratio of the frequency signal is constant, it remains unchanged after frequency division. Because this invention requires a conversion frequency as high as 40MHz, and the highest frequency of commercially available frequency-to-voltage conversion chips is 2MHz (AD652), special processing is required to resolve 40MHz. Furthermore, since the change ratio of the frequency signal is constant and remains unchanged after frequency division, this invention performs frequency division on the high-frequency signal. Using a frequency divider chip CD4024, it performs six 2-divisions, dividing 40MHz into 0.625MHz. This allows for direct signal conversion using a mature frequency-to-voltage conversion chip. Figure 8 As shown.

[0076] Furthermore, it includes: a zero-point compensation circuit and a digital DC voltmeter;

[0077] The zero-point compensation circuit is connected to the output terminal of the signal conversion module and is used to adjust the output voltage and calibrate the reference voltage; the input terminal of the digital display DC voltmeter is connected to the output terminal of the signal conversion module and is used to display the current output voltage and calibrate the reference voltage in conjunction with the zero-point compensation circuit.

[0078] In this embodiment, the present invention uses a small three-and-a-half-digit LCD digital display DC voltmeter to directly display the voltage value, which is more intuitive and convenient for reading the voltage value directly during calibration. The zero-point compensation circuit uses an addition and subtraction circuit to make the output voltage approach zero. Figure 9 As shown, its output voltage Uo = Ui1 - Ui2.

[0079] Furthermore, the calibration steps for the flaw detector using a zero-point compensation circuit and a digital DC voltmeter are as follows:

[0080] 1. First, select a standard sample. This sample can be chosen from actual material or laser-engraved from crack-free material. The standard sample should be approximately 200mm in length, with 100mm being a crack-free section and the other 100mm being a cracked section. The crack depth in the actual material can be obtained through metallographic observation, while the crack depth in the laser-engraved sample can be measured using a microscope.

[0081] 2. Once the depth of the crack segment is determined, the corresponding standard voltage value can be calculated using the following formula:

[0082] Standard voltage value = 5V × crack depth ÷ wire diameter;

[0083] For example: If a wire with a diameter of 0.2mm has a crack depth of 0.04mm, then the standard voltage value = 5V × 0.04 ÷ 0.2 = 1V;

[0084] 3. Insert the crack-free section of the standard sample into the testing probe, rotate the "zeroing" knob to adjust the voltage value to around 0V, then insert the cracked section into the testing probe and read the voltage value. If the voltage value is lower than the standard value, rotate the "zeroing" knob clockwise to adjust it to the standard value; if the voltage value is higher than the standard value, rotate the "zeroing" knob counterclockwise. After calibrating the voltage value, test the crack-free section again to confirm that the voltage value is near 0V. If it is, the calibration is complete.

[0085] Furthermore, it includes: DC amplifier circuits;

[0086] The output of the zero-point compensation circuit is connected to the input of the DC amplifier circuit to amplify the voltage signal.

[0087] In this embodiment, due to the small defect, the converted voltage signal is extremely weak, requiring amplification. Zero-point compensation is also necessary to ensure the amplified signal does not exceed limits. This invention directly uses the AD620 DC amplifier chip for DC signal amplification. The AD620 DC amplifier chip is developed from a traditional three-operational amplifier (such as...). Figure 10(As shown), but some key performance characteristics are superior to those of instrumentation amplifiers composed of three operational amplifiers, such as a wide power supply range (±2.3~±18V), small design size, and very low power consumption (maximum supply current of only 1.3mA), making it suitable for low-voltage, low-power applications. The monolithic structure and laser crystal tuning of the AD620 DC amplifier chip allow for tight matching and tracking of circuit components, thus ensuring the inherent high performance of the circuit. The AD620 DC amplifier chip is an instrumentation amplifier structure with three operational amplifiers integrated. To protect the high precision of gain control, its input transistors provide simple differential bipolar inputs and use β technology to obtain lower input bias current. Through feedback from the internal operational amplifiers of the input stage, the collector current of the input transistors is kept constant, and the input voltage is applied to the external variable gain resistor RG.

[0088] Furthermore, it includes: a voltage follower circuit;

[0089] The input terminal of the voltage follower circuit is connected to the output terminal of the DC amplifier circuit, and the output terminal of the voltage follower circuit is connected to the input terminal of the recording and analysis module, which is used to buffer and isolate the input voltage of the DC amplifier circuit.

[0090] In this embodiment, as Figure 11 As shown, the voltage follower circuit acts as a buffer and isolation mechanism. The output impedance of DC amplifier circuits is generally quite high, typically ranging from several thousand ohms to tens of thousands of ohms. If the input impedance of the subsequent stage is relatively low, a significant portion of the signal will be lost in the output resistance of the preceding stage. In this case, a voltage follower is needed to buffer the signal, acting as a bridge between the preceding and following stages. Another advantage of using a voltage follower is that it increases the input impedance, allowing for a significant reduction in the input capacitor's capacitance, thus providing a prerequisite for using high-quality capacitors.

[0091] Furthermore, it includes: a roller-type meter counter;

[0092] The output of the roller-type meter counter is connected to the input of the recording and analysis module, and is used to calculate the length of the material to be measured and send it to the recording and analysis module and the amplified voltage signal for synchronous recording.

[0093] In this embodiment, the recording and analysis module is used to record the detection results. A paper-based printer / recorder can be purchased directly, or an AD acquisition card can be used to convert analog signals into digital signals and transmit them to computer software to form the recording and analysis module, where the computer software collects and saves the data. In this invention, Advantech's PCI-1710UL-DE AD acquisition card is used for data conversion, and then the computer software collects and saves the signals. The saved voltage spectrum is as follows: Figure 12As shown, the voltage spectrum can record not only the magnified voltage waveform but also the corresponding meter readings. Specifically, the dashed lines in the figure represent 0.25V, 0.75V, and 1.5V, respectively, with a reference voltage of 5V, corresponding to crack depths of 5%, 15%, and 30%. This invention utilizes a roller-type meter counter to obtain corresponding meter readings as the detection probe rolls during flaw detection, and then uploads these data to the recording and analysis module.

[0094] Furthermore, it includes: an audible and visual alarm module;

[0095] The input terminal of the audible and visual alarm module is connected to the detection probe and is used to automatically trigger an audible and visual alarm when the flaw detector malfunctions.

[0096] In this embodiment, the audible and visual alarm is used to detect whether the flaw detector is malfunctioning. When the flaw detector malfunctions, the audible and visual alarm is automatically triggered, prompting the operator to stop the machine for maintenance. This design uses an AD16-16SM electronic buzzer and a 12-volt high-decibel speaker audible and visual alarm module. Since the detection probe is a consumable part, the main focus is on monitoring whether the detection probe is damaged. A normal detection probe outputs a signal to the audible and visual alarm module, while a damaged probe will not output a signal. When the audible and visual alarm module detects that the probe has no signal, it triggers the audible and visual alarm through a relay switch.

[0097] This invention provides an eddy current flaw detection method for detecting cracks in extremely fine conductor filaments, comprising:

[0098] S1 generates the resonant frequency signal through the resonant generator and sends it to the material under test through the detection probe;

[0099] Furthermore, before the resonant frequency signal is generated by the resonant generator and sent to the material under test through the detection probe, the following steps are included:

[0100] The zero-point compensation circuit is used to zero-calibrate the voltage signal output by the signal conversion module.

[0101] In this embodiment, the zero-adjustment calibration process can be found in the calibration process of the flaw detector using a zero-point compensation circuit and a digital DC voltmeter.

[0102] The detection probe described in S2 generates a change in resonant frequency based on the change in the induced current of the material under test, thereby obtaining the resonant frequency signal.

[0103] S3 converts all the resonant frequency signals into voltage signals through the signal conversion module;

[0104] Furthermore, the step of converting all the resonant frequency signals into voltage signals and amplifying them through the signal conversion module to obtain the voltage signals includes:

[0105] S301 performs a frequency division process of six times on all the resonant frequency signals through the frequency division circuit to obtain the frequency-divided signal;

[0106] S302 converts the frequency-divided signal into the voltage signal through the frequency-to-voltage conversion circuit.

[0107] S4 records the voltage signal according to the length of the material under test using the recording and analysis module;

[0108] Furthermore, the step of recording the voltage signal according to the length of the material under test by the recording and analysis module includes:

[0109] S401 follows the movement of the detection probe via the roller-type meter counter;

[0110] S402 synchronously sends the distance traveled to the recording and analysis module via the roller-type meter counter.

[0111] S403 synchronously sends the voltage signal to the recording and analysis module through the signal conversion module.

[0112] S5 uses the recording and analysis module to analyze and calculate the voltage signal to obtain the crack depth at different locations in the material under test.

[0113] Furthermore, the step of analyzing and calculating the crack depth L at different locations of the material under test using the recording and analysis module includes:

[0114] S501 acquires the diameter D, full-range voltage U, and amplified voltage signal Uo of the material under test;

[0115] S502 calculates the crack depth L using the diameter D of the material under test, the full-range voltage U, and the amplified voltage signal Uo. The crack depth satisfies L=DхUo / U.

[0116] The detection results of the present invention will be further explained by combining the test results with analysis.

[0117] The identification of 10µm deep cracks had not been verified before, therefore metallographic analysis of the flaw detection results was necessary to verify their accuracy. Here, a 0.1mm diameter tungsten wire was selected for flaw detection and sampling for metallographic analysis. Figure 13 and Figure 14 As shown in the image, this eddy current flaw detector can detect cracks up to 10 μm deep. Figure 13 and Figure 14 The images above are voltage spectra obtained from flaw detectors, while the images below are from metallographic examinations.

[0118] It should be noted that metallographic examination mainly uses quantitative metallography principles, employing the measurement and calculation of the metallographic microstructure of two-dimensional metallographic specimens (ground surfaces or thin films) to determine the three-dimensional spatial morphology of the alloy structure, thereby establishing a quantitative relationship between alloy composition, microstructure, and properties. This design primarily analyzes crack depth; therefore, the evaluation is performed by observing the cross-section of the specimen using a metallographic microscope and measuring the radial depth of the crack from the surface.

[0119] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0120] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0121] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0122] It should be noted that any reference signs placed between parentheses in the claims should not be construed as limiting the claims. The word "comprising" does not exclude the presence of components or steps not listed in the claims. The word "a" or "an" preceding a component does not exclude the presence of a plurality of such components. The invention can be implemented by means of hardware comprising several different components and by means of a suitably programmed computer. In a unit claim enumerating several means, several of these means may be embodied by the same item of hardware. The use of the words first, second, and third, etc., does not indicate any order. These words can be interpreted as names.

[0123] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0124] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

[0125] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0126] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

Claims

1. An eddy current flaw detector capable of detecting extremely fine wire cracks in conductors, characterized in that, include: Resonant generator, detection probe, signal conversion module, recording and analysis module, zero-point compensation circuit and DC amplifier circuit; The output of the resonant generator is connected to the transmitting end of the detection probe to form a 1-40MHz resonant frequency detection source. When the detection source is close to the material under test, it induces a current on the surface of the material under test. The receiving end of the detection probe is connected to the input end of the signal conversion module to receive the resonant frequency signal returned by the material under test. The detection probe generates a change in resonant frequency based on the change in the induced current of the material under test. The detection probe includes: a flaw detection signal acquisition coil, an interference signal compensation coil, and a comparator I1. The flaw detection signal acquisition coil is connected to the positive terminal of the comparator I1 to transmit and acquire the resonant frequency. The interference signal compensation coil is connected to the negative terminal of the comparator I1 to generate a differential compensation signal, thereby canceling external interference signals when receiving the resonant frequency signal. The output end of the comparator I1 is connected to the input end of the signal conversion module. The signal conversion module converts the resonant frequency signal generated by the detection probe into a voltage signal. The signal conversion module includes a frequency divider circuit and a frequency-to-voltage conversion circuit. The input terminal of the frequency divider circuit is connected to the receiving terminal of the detection probe for frequency division of the resonant frequency signal. The output terminal of the frequency divider circuit is connected to the input terminal of the frequency-to-voltage conversion circuit for converting the resonant frequency signal into a voltage signal. The output terminal of the signal conversion module is connected to the recording and analysis module for real-time recording and analysis of the voltage signal to achieve flaw detection of the material under test. The zero-point compensation circuit is connected to the output terminal of the signal conversion module and is used to adjust the output voltage and calibrate the reference voltage. The output of the zero-point compensation circuit is connected to the input of the DC amplifier circuit to amplify the voltage signal.

2. The eddy current flaw detector capable of detecting extremely fine wire cracks in conductors as described in claim 1, characterized in that, include: Digital DC voltmeter; The input terminal of the digital DC voltmeter is connected to the output terminal of the signal conversion module to display the current output voltage and to calibrate the reference voltage in conjunction with the zero-point compensation circuit.

3. The eddy current flaw detector capable of detecting extremely fine wire cracks in conductors as described in claim 1, characterized in that, include: Voltage follower circuit; The input terminal of the voltage follower circuit is connected to the output terminal of the DC amplifier circuit, and the output terminal of the voltage follower circuit is connected to the input terminal of the recording and analysis module, which is used to buffer and isolate the input voltage of the DC amplifier circuit.

4. The eddy current flaw detector capable of detecting extremely fine wire cracks in conductors as described in claim 1, characterized in that, include: Roller-type meter counter; The output of the roller-type meter counter is connected to the input of the recording and analysis module, and is used to calculate the length of the material to be measured and send it to the recording and analysis module and the voltage signal for synchronous recording.

5. An eddy current flaw detection method for detecting extremely fine wire cracks in conductors, characterized in that, An eddy current flaw detector for detecting extremely fine wire cracks in conductors, based on any one of claims 1-4, comprises: The resonant frequency signal generated by the resonant generator is sent to the material under test through the detection probe. The detection probe generates a change in resonant frequency based on the change in the induced current of the material under test, thereby obtaining the resonant frequency signal; The signal conversion module converts all the resonant frequency signals into voltage signals. The recording and analysis module records the voltage signal according to the length of the material under test. The voltage signal is analyzed and calculated by the recording and analysis module to obtain the crack depth at different locations in the material under test.

6. The eddy current flaw detection method for detecting extremely fine wire cracks in conductors as described in claim 5, characterized in that, The step of converting all the resonant frequency signals into voltage signals through the signal conversion module includes: The frequency-divided signal is obtained by performing a frequency-dividing process of six times on all the resonant frequency signals through the frequency division circuit. The frequency-divided signal is converted into the voltage signal by the frequency-to-voltage conversion circuit.

7. The eddy current flaw detection method for detecting extremely fine wire cracks in conductors as described in claim 5, characterized in that, The step of recording the voltage signal according to the length of the material under test by the recording and analysis module includes: The roller-type meter counter moves along with the detection probe; The number of meters moved is synchronously sent to the recording and analysis module via the roller-type meter counter. The voltage signal is synchronously sent to the recording and analysis module through the signal conversion module.

8. The eddy current flaw detection method for detecting extremely fine wire cracks in conductors as described in claim 5, characterized in that, The step of analyzing and calculating the crack depth L at different locations of the material under test by the voltage signal through the recording and analysis module includes: Obtain the diameter D, full-range voltage U, and amplified voltage signal Uo of the material under test; The crack depth L is calculated using the diameter D of the material under test, the full-range voltage U, and the amplified voltage signal Uo. The crack depth satisfies L=DхUo / U.

9. The eddy current flaw detection method for detecting extremely fine wire cracks in conductors as described in claim 5, characterized in that, Before the resonant frequency signal is generated by the resonant generator and sent to the material under test by the detection probe, the following steps are included: The zero-point compensation circuit is used to zero-calibrate the voltage signal output by the signal conversion module.

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