Frequency selection method of eddy current probe

Abstract

The invention provides a frequency selection method of an eddy current probe, which comprises the following steps: S100, performing impedance analysis on the eddy current probe through an impedance analyzer to obtain a resonant frequency point f of the eddy current probe; and S200, by taking the resonant frequency point f of the eddy current probe as a center, respectively carrying out scanning analysis on two states of the eddy current probe in the air and on the carbon fiber material to obtain the optimal frequency of the eddy current probe during nondestructive testing of the carbon fiber material. And the detection frequency of the eddy current probe can be accurately selected, so that the detection efficiency is improved, and the detection precision and the detection sensitivity can be ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of eddy current nondestructive testing of carbon fiber composite materials, and particularly relates to a frequency selection method of an eddy current probe. BACKGROUND

[0002] At present, the eddy current nondestructive testing technology is a convenient, fast and reliable detection method for carbon fiber composite materials. The detection frequency of the earliest used eddy current nondestructive testing technology is generally low (lower than 500 kHz), and with the continuous improvement of the technology, the eddy current nondestructive testing technology has been widely used, and the requirement for the frequency of the eddy current nondestructive testing is gradually improved. It is found that when the eddy current detection is performed at a low frequency stage, the receiving signal of the induction coil has more burrs and smaller amplitude. When the eddy current detection is performed at a low frequency stage, the sensitivity and gain of the signal processing circuit in the system, that is, the lock-in amplifier, need to be high enough and the anti-interference performance needs to be good, so that the useful information related to the damage can be extracted from the weak coil signal. Within a certain range, when the frequency of the eddy current nondestructive testing is improved, the induced voltage value of the detection coil will also be larger, and the signal-to-noise ratio will also be higher. At this time, the sensitivity of the eddy current nondestructive testing will be higher, and the detection effect will be better.

[0003] At present, many practices show that the detection frequency has a great influence on the detection effect and sensitivity in the eddy current nondestructive testing. Especially in the process of the eddy current detection of the carbon fiber composite material, since the carbon fiber composite material has the characteristics of weak conductivity, the improvement of the signal-to-noise ratio and the sensitivity of the detection signal is crucial to the optimization of the detection effect, and at present, there is still no specific frequency selection method for the eddy current detection of the carbon fiber composite material. Therefore, it is necessary to propose a detection frequency selection method for the eddy current detection, especially for the eddy current detection of the carbon fiber composite material. SUMMARY

[0004] The purpose of the present application is to provide a frequency selection method of an eddy current probe, which can accurately select the detection frequency of the eddy current probe, so as to not only improve the detection efficiency, but also ensure the detection accuracy and detection sensitivity.

[0005] To achieve the above purpose, the technical scheme adopted by the present application is:

[0006] A frequency selection method of an eddy current probe, comprising the steps that: S100, impedance analysis is performed on the eddy current probe by an impedance analyzer to obtain a resonance frequency point f of the eddy current probe;

[0007] S200, scanning analysis is performed on two states of the eddy current probe in the air and on the carbon fiber material respectively with the resonance frequency point f of the eddy current probe as the center to obtain the best frequency when the eddy current probe performs nondestructive detection on the carbon fiber material.

[0008] Preferably, the eddy current probe comprises a first circuit and a second circuit;

[0009] The first circuit has a first inductor capable of being electrically connected with an external signal generator, and the second circuit has a second inductor, and the first inductor and the second inductor correspond to each other.

[0010] Preferably, the first circuit further comprises a first capacitor C1 connected in parallel with the first inductor and a first resistor connected in series with the first inductor.

[0011] Preferably, the capacitance value of the first capacitor C1 is

[0012]

[0013] Wherein, N1 is the number of turns of each layer of the first inductor coil, l1 is the average length of turns of the first inductor coil, n1 is the number of layers of the first inductor coil, D1 is the cross-sectional diameter of the wire of the first inductor coil, d1 is the interlayer distance of the first inductor coil, ε1 is the relative dielectric constant of the first inductor coil, and ε0 is the material dielectric constant of the first inductor coil. r And ε0 are the relative dielectric constant and the material dielectric constant respectively.

[0014] Preferably, the second circuit comprises a second capacitor and a second resistor connected in series with the second inductor.

[0015] Preferably, the capacitance value of the second capacitor is

[0016]

[0017] Wherein, N2 is the number of turns of each layer of the second inductor coil, l2 is the average length of turns of the second inductor coil, n2 is the number of layers of the second inductor coil, D2 is the cross-sectional diameter of the wire of the second inductor coil, d2 is the interlayer distance of the second inductor coil, ε2 is the relative dielectric constant of the second inductor coil, and ε0 is the material dielectric constant of the second inductor coil. r And ε0 are the relative dielectric constant and the material dielectric constant respectively.

[0018] Preferably, in step S100, an impedance analysis diagram of the eddy current probe is drawn, and a resonance frequency point f of the eddy current probe is obtained in the impedance analysis diagram;

[0019] The first circuit further comprises a first capacitor connected in parallel with the first inductor and a first resistor connected in series with the first inductor

[0020] And the capacitance value of the first capacitor is

[0021]

[0022] The second circuit comprises a second capacitor and a second resistor connected in series with the second inductor, and the capacitance value of the first capacitor is

[0023]

[0024] In step S100, the impedance calculation formula of the whole of the first circuit and the second circuit is

[0025]

[0026] Plot the impedance analysis diagram of the eddy current probe;

[0027] Wherein, k is the coupling coefficient of the first circuit and the second circuit, Δ a , Δ b The whole impedance of the first circuit and the second circuit network respectively, has:

[0028]

[0029]

[0030] Wherein, R1 is the first resistance, L1 is the first inductance, C1 is the first capacitance, R2 is the second resistance, L2 is the second inductance, C2 is the second capacitance, and ω is the eddy current probe excitation frequency. Preferably, step S200 includes steps:

[0031] S210, with the resonance frequency point f of the eddy current probe as the center, voltage scanning analysis is respectively performed on the two states of the eddy current probe in air and on the carbon fiber material to obtain the voltage peak-peak value Vpp_air of the eddy current probe in air and the voltage peak-peak value Vpp_cfrp of the eddy current probe on the carbon fiber;

[0032] S220, plot f-Vpp_air diagram according to the voltage peak-peak value Vpp_air of the eddy current probe in air, and plot f-Vpp_cfrp diagram according to the voltage peak-peak value Vpp_cfrp of the eddy current probe on the carbon fiber;

[0033] S230, select the frequency when the difference between Vpp_airf and Vpp_cfrp is maximum as the optimal frequency of the eddy current probe.

[0034] Preferably, in step S210, the frequency range and step length of voltage scanning are f-1000KHz, 50KHz, f+1000KHz.

[0035] Preferably, in step S230, according to Vpp_max=|Vpp_airf-Vpp_cfrp|, plot Vpp_max diagram, and obtain the optimal frequency of the eddy current probe in the Vpp_max diagram.

[0036] The frequency selection method of the eddy current probe of the present invention adopts a technical solution of obtaining the optimal frequency of the eddy current probe for non-destructive testing of the carbon fiber material by scanning and analyzing the two states of the eddy current probe in the air and on the carbon fiber material with the resonant frequency point f of the eddy current probe as the center. The method can accurately select the detection frequency of the eddy current probe, which not only improves the detection efficiency, but also ensures the detection accuracy and detection sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a flow chart of the frequency selection method of the eddy current probe of the present invention;

[0038] Figure 2 This is the circuit diagram of the eddy current probe;

[0039] Figure 3 for Figure 2 Overall impedance diagram of the eddy current probe;

[0040] Figure 4 for Figure 1 Flow chart of step S200 in FIG.

[0041] Figure 5 This is the impedance analysis diagram of the eddy current probe in Example 3;

[0042] Figure 6 The f-Vpp_air diagram and f-Vpp_cfrp diagram in Example 4 are shown;

[0043] Figure 7 This is the Vpp_max diagram in Example 5.

[0044] Among them, 1-first circuit; 2-second circuit; 3-signal generator; 4-first inductor; 5-second inductor; 6-first capacitor; 7-first resistor; 8-second capacitor; 9-second resistor. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the frequency selection method of the eddy current probe of the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0046] Example 1

[0047] like Figure 1 As shown, a frequency selection method for an eddy current probe includes the steps of: S100, performing impedance analysis on the eddy current probe by an impedance analyzer to obtain a resonant frequency point f of the eddy current probe;

[0048] S200, with the resonance frequency point f of the eddy current probe as the center, scanning and analyzing two states of the eddy current probe in the air and on the carbon fiber material respectively, and obtaining the best frequency of the eddy current probe for nondestructive testing of the carbon fiber material.

[0049] By adopting the technical scheme, the detection efficiency is improved, and the detection precision and sensitivity are ensured.

[0050] Embodiment two

[0051] Based on the frequency selection method of the eddy current probe in embodiment one, as shown in the figure, Figure 2 the eddy current probe includes a first circuit 1 and a second circuit 2. The first circuit 1 has a first inductor 4 capable of being electrically connected with an external signal generator 3, and the second circuit 2 has a second inductor 5 corresponding to the first inductor 4. By adopting such a structural mode, the eddy current probe can select the eddy current nondestructive testing frequency based on the resonance theory. In turn, the signal-to-noise ratio and sensitivity of the detection signal are improved, which is helpful for field application and greatly improves the detection efficiency and precision.

[0052] Specifically, as shown in the figure, Figure 2 the first circuit 1 further includes a first capacitor 6C1 connected in parallel with the first inductor 4 and a first resistor 7 connected in series with the first inductor 4.

[0053] In actual use, the capacitance value of the first capacitor 6 is

[0054]

[0055] Wherein, N1 is the number of turns of each layer of the first inductor 4 coil, l1 is the average length of turns of the first inductor 4 coil, n1 is the number of layers of the first inductor 4 coil, D1 is the cross-sectional diameter of the wire of the first inductor 4 coil, d1 is the interlayer distance of the first inductor 4 coil, ε r and ε0 are the relative dielectric constant and the material dielectric constant respectively.

[0056] Further, as shown in the figure, Figure 2 the second circuit 2 includes a second capacitor 8 and a second resistor 9 connected in series with the second inductor 5.

[0057] In actual use, the capacitance value of the second capacitor 8 is

[0058]

[0059] Wherein, N2 is the number of turns of each layer of the second inductor 5 coil, l2 is the average length of turns of the second inductor 5 coil, n2 is the number of layers of the second inductor 5 coil, D2 is the cross-sectional diameter of the wire of the second inductor 5 coil, d2 is the interlayer distance of the second inductor 5 coil, ε r and ε0 are the relative dielectric constant and the material dielectric constant respectively.

[0060] Example 3

[0061] Based on Example 2, Figure 5 As shown, in step S100, an impedance analysis diagram of the eddy current probe is drawn, and the resonant frequency point f of the eddy current probe is obtained from the impedance analysis diagram. This allows the frequency corresponding to the resonant frequency point f to be quickly found in the impedance analysis diagram, thereby ensuring accurate acquisition of the resonant frequency point f.

[0062] Specifically, when the first circuit further includes a first capacitor connected in parallel with the first inductor and a first resistor connected in series with the first inductor

[0063] And the capacitance value of the first capacitor is

[0064]

[0065] At the same time, the second circuit includes a second capacitor and a second resistor connected in series with the second inductor, and the capacitance value of the first capacitor is

[0066]

[0067] When, in step S100, Figure 3 As shown, according to the impedance calculation formula of the first circuit and the second circuit as a whole

[0068]

[0069] Draw the impedance analysis diagram of the eddy current probe;

[0070] Where k is the coupling coefficient between the first circuit and the second circuit, Δ a , Δ b The overall impedance of the mesh loop of the first circuit and the second circuit respectively is:

[0071]

[0072]

[0073] Wherein, R1 is the first resistor, L1 is the first inductor, C1 is the first capacitor, R2 is the second resistor, L2 is the second inductor, C2 is the second capacitor, and ω is the excitation frequency of the eddy current probe.

[0074] Example 4

[0075] Based on Example 1, Figure 4 As shown, step S200 includes the following steps:

[0076] S210, centering on the resonant frequency point f of the eddy current probe, voltage scanning analysis is respectively performed on two states of the eddy current probe in air and on the carbon fiber material to obtain a voltage peak-peak value Vpp_air of the eddy current probe in air and a voltage peak-peak value Vpp_cfrp of the eddy current probe on the carbon fiber material;

[0077] S220, an f-Vpp_air graph is drawn according to the voltage peak-peak value Vpp_air of the eddy current probe in air, and an f-Vpp_cfrp graph is drawn according to the voltage peak-peak value Vpp_cfrp of the eddy current probe on the carbon fiber material;

[0078] S230, the frequency at which the difference between Vpp_airf and Vpp_cfrp is maximum is selected as the optimal frequency of the eddy current probe.

[0079] In the drawings, Figure 6 are the f-Vpp_air graph and the f-Vpp_cfrp graph in step S220, so in step S230, the peak value of the change curve in Figure 5 appears at f = 2100 kHz, and fbest = 2100 kHz is selected as the optimal frequency of the eddy current probe.

[0080] Specifically, in actual operation, in step S210, the frequency range and step length of voltage scanning are f-1000KHz, 50KHz, f+1000KHz.

[0081] Example Five

[0082] Based on example four, as shown in Figure 7 , in step S230, a Vpp_max graph is drawn according to Vpp_max = |Vpp_airf-Vpp_cfrp|, and the optimal frequency of the eddy current probe is obtained in the Vpp_max graph.

[0083] The above examples make the present application have the following advantages:

[0084] (1) The rapid and accurate working frequency selection of the carbon fiber composite material eddy current nondestructive testing can be realized, a large number of experiments are not needed, and the detection efficiency of the eddy current nondestructive testing is improved.

[0085] (2) The precision and detection sensitivity of the carbon fiber composite material eddy current nondestructive testing can be increased, and the method is also applicable to other conductor materials.

[0086] (3) Under the detection frequency selected by the method of the present application, the eddy current probe has strong anti-interference ability, high reliability, and strong field adaptability, and can effectively reduce the misjudgment rate of defect detection.

[0087] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the patent scope of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A frequency selection method for an eddy current probe, characterized in that: The method comprises the following steps: S100, performing impedance analysis on the eddy current probe by using an impedance analyzer to obtain a resonant frequency point f of the eddy current probe; S200 , taking the resonant frequency point f of the eddy current probe as the center, scanning and analyzing the eddy current probe in two states, in the air and on the carbon fiber material, respectively, to obtain the optimal frequency of the eddy current probe for nondestructive testing of the carbon fiber material.

2. The frequency selection method of the eddy current probe according to claim 1, characterized in that: The eddy current probe comprises a first circuit (1) and a second circuit (2); The first circuit (1) has a first inductor (4) that can be electrically connected to an external signal generator (3), and the second circuit (2) has a second inductor (5), and the first inductor (4) and the second inductor (5) correspond to each other.

3. The frequency selection method of the eddy current probe according to claim 2, characterized in that: The first circuit (1) further includes a first capacitor (6) connected in parallel with the first inductor (4) and a first resistor (7) connected in series with the first inductor (4).

4. The frequency selection method of the eddy current probe according to claim 3, characterized in that: Capacitance value of the first capacitor (6) Wherein, N1 is the number of turns of each layer of the first inductor (4) coil, l1 is the average turn length of the first inductor (4) coil, n1 is the number of layers of the first inductor (4) coil, D1 is the cross-sectional diameter of the wire of the first inductor (4) coil, d1 is the distance between the layers of the first inductor (4) coil, ε r and ε0 are the relative dielectric constant and material dielectric constant, respectively.

5. The frequency selection method of the eddy current probe according to claim 4, characterized in that: The second circuit (2) comprises a second capacitor (8) and a second resistor (9) connected in series with the second inductor (5).

6. The frequency selection method of the eddy current probe according to claim 5, characterized in that: The capacitance value of the second capacitor (8) Wherein, N2 is the number of turns of each layer of the second inductor (5) coil, l2 is the average turn length of the second inductor (5) coil, n2 is the number of layers of the second inductor (5) coil, D2 is the cross-sectional diameter of the wire of the second inductor (5) coil, d2 is the distance between the layers of the second inductor (5) coil, ε r and ε0 are the relative dielectric constant and material dielectric constant, respectively.

7. The frequency selection method of an eddy current probe according to any one of claims 1 to 6, characterized in that: In step S100, the process includes drawing an impedance analysis diagram of the eddy current probe, and obtaining a resonant frequency point f of the eddy current probe from the impedance analysis diagram; The first circuit (1) further includes a first capacitor (6) connected in parallel with the first inductor (4) and a first resistor (7) connected in series with the first inductor (4). And the capacitance value of the first capacitor (6) is The second circuit (2) includes a second capacitor (8) and a second resistor (9) connected in series with the second inductor (5), and the capacitance value of the first capacitor (6) is In step S100, the impedance of the first circuit (1) and the second circuit (2) is calculated according to the formula Draw an impedance analysis diagram of the eddy current probe; Where k is the coupling coefficient between the first circuit and the second circuit, Δ a , Δ b The overall impedance of the mesh loop of the first circuit and the second circuit respectively is: Wherein, R1 is the first resistor, L1 is the first inductor, C1 is the first capacitor, R2 is the second resistor, L2 is the second inductor, C2 is the second capacitor, and ω is the excitation frequency of the eddy current probe.

8. The frequency selection method of an eddy current probe according to any one of claims 1 to 6, characterized in that: Step S200 includes the following steps: S210, taking the resonant frequency point f of the eddy current probe as the center, performing voltage scanning analysis on the eddy current probe in the air and on the carbon fiber material, respectively, to obtain a peak-to-peak value of the voltage Vpp_air of the eddy current probe in the air and a peak-to-peak value of the voltage Vpp_cfrp on the carbon fiber; S220, plotting an f-Vpp_air graph based on the peak-to-peak voltage Vpp_air of the eddy current probe in the air, and plotting an f-Vpp_cfrp graph based on the peak-to-peak voltage Vpp_cfrp of the eddy current probe on the carbon fiber; S230 , selecting the frequency at which the difference between Vpp_airf and Vpp_cfrp is the largest as the optimal frequency of the eddy current probe.

9. The frequency selection method of the eddy current probe according to claim 8, characterized in that: In step S210 , the frequency range and step size of the voltage scan are f-1000 KHz, 50 KHz, and f+1000 KHz.

10. The frequency selection method of the eddy current probe according to claim 8, characterized in that: Step S230 includes drawing a Vpp_max graph according to Vpp_max=|Vpp_airf-Vpp_cfrp|, and obtaining the optimal frequency of the eddy current probe from the Vpp_max graph.

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