Eddy current detection circuit, method, system, storage medium and terminal

Abstract

The present invention discloses an eddy current detection circuit, method, system, storage medium and terminal, which belong to the field of eddy current non-destructive detection technology. The invention mainly utilizes a differential bridge and a transformer conditioning circuit to form a dual-path differential probe, and utilizes the signal parameters generated by the first differential signal and the second differential signal under their respective alternating magnetic fields to analyze the relationship between the amplitude, phase parameters and lift-off respectively generated under the alternating magnetic field, and performs multi-parameter signal fusion, which can suppress lift-off. The dual-path differential output has a high detection capability for defects when the lift-off changes greatly.

Description

Technical Field

[0001] The present invention relates to the technical field of eddy current nondestructive testing, and in particular to an eddy current testing circuit, method, system, storage medium and terminal. Background Art

[0002] Nondestructive testing technology is based on the premise of not destroying the internal structure of the object being tested, and uses physical methods to detect and evaluate possible discontinuities inside the object. Eddy current is an important method among many nondestructive testing methods. Its principle is to apply an alternating current to the end of the excitation coil to generate an alternating magnetic field. This magnetic field interacts with the test piece to generate alternating eddy currents in the test piece. The eddy currents in the test piece generate secondary magnetic fields. The detection sensor detects the superposition field of the source magnetic field and the secondary magnetic field, and the detection and identification of defects in the test piece are achieved by analyzing the detection signal. Therefore, the structure of the coil determines the distribution and coupling relationship of the magnetic field, which is closely related to the detection performance. Most of the existing eddy current array sensors are designed and optimized from the structure and manufacturing process of the eddy current sensor to improve the detection capability of defects.

[0003] When conducting eddy current testing, there is a lift-off distance in the non-contact detection between the sensor probe and the pipe wall, and the randomness of the detection conditions often makes the lift-off not constant (such as pipeline detection and rail detection). Therefore, as the lift-off changes, the distance changes the mutual inductance of the circuit formed by the probe and the metal conductor, which will cause the lift-off waveform signal to be mistaken for a defect signal, thereby affecting the qualitative judgment of whether the defect exists or not. In addition, the original defect signal will be affected by the interference of lift-off, resulting in changes in parameters such as amplitude and phase, which will bring challenges to the quantitative analysis of defects and make it impossible to accurately quantify the size of the defect and assess the damage state. Therefore, the lift-off problem is a key issue in eddy current testing, and its interference effect must be suppressed to improve the detection accuracy and reliability. In order to eliminate lift-off noise and increase the ability to detect defects, relevant scholars have carried out a number of research works. The prior art CN111398413A discloses a detection sensor, which detects defect information by detecting changes in the amplitude and phase of the induction coil output. It can perform defect detection under large lift-off, but does not consider the impact of the lift-off on the excitation coil. When the lift-off is constantly changing, the detection accuracy cannot be guaranteed.

[0004] In addition, the prior art also proposes the characteristic research of the transient response of the lift-off point intersection (LOI) of the pulse eddy current, the lift-off suppression method based on signal processing technology, the slope fitting method, the data-driven method such as artificial neural network and wavelet transform, the multi- / dual-frequency excitation method, the design and optimization method of the sensor probe, etc. Although they all have a certain immunity effect to lift-off, the defect information is still easily concealed in the fluctuation under random conditions such as railway or pipeline inspection or high lift-off noise, and the parameters need to be adjusted and set, and the modulation and demodulation of the system are complicated, making it difficult to realize engineering application. Summary of the invention

[0005] The purpose of the present invention is to suppress the interference of lift-off and enhance the detection capability of defects. An eddy current detection circuit, method, system, storage medium and terminal are proposed. A dual-path differential probe is formed by using a differential bridge and a transformer-type conditioning circuit structure. The relationship between the amplitude, phase parameters and lift-off generated by the dual-path differential probe under an alternating magnetic field is constructed based on an equivalent circuit model, and a method for multi-parameter signal fusion is proposed.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] In one embodiment, an eddy current detection circuit is provided, comprising:

[0008] The probe comprises an excitation unit and an induction unit, wherein the excitation unit forms a differential bridge for receiving an excitation signal and outputting a first differential signal, and the induction unit is coupled with the excitation unit to form a transformer conditioning circuit and output a second differential signal;

[0009] The differential signal processing unit is used to receive the first differential signal and the second differential signal, analyze the relationship between the parameters of the first differential signal, the parameters of the second differential signal and the lift-off under the alternating magnetic field, and merge the parameters of the first differential signal with the parameters of the second differential signal to eliminate the influence of the lift-off on the signal.

[0010] In a further solution, the excitation unit is composed of a plurality of excitation coils arranged in a row, and the induction unit is composed of a plurality of induction coils placed in a one-to-one correspondence with the excitation coils, wherein the coil winding directions of the induction coils and the excitation coils are opposite;

[0011] The input end of the excitation coil is connected to the output end of the signal generator, a plurality of the excitation coils are connected in parallel, and the output end of the excitation coil is connected to a capacitor or a resistor; the output ends of two adjacent excitation coils are connected to a first differential amplifier; the output ends of two adjacent induction coils are connected to a second differential amplifier.

[0012] In a further solution, the excitation coil and the induction coil are placed side by side, and two adjacent excitation coils serve as two arms of an AC bridge, and the corresponding two capacitors or resistors are connected to the remaining two arms of the AC bridge.

[0013] In another embodiment, an eddy current detection method is provided, comprising the following steps:

[0014] S1. In the case of lift-off variation, obtaining a first differential signal and a second differential signal output by the probe, wherein the first differential signal is output by an excitation unit of the probe, and the second differential signal is output by a sensing unit of the probe;

[0015] S2. analyzing the relationship between the parameters of the first differential signal, the parameters of the second differential signal and lift-off under the alternating magnetic field;

[0016] S3. Merge the parameters of the first differential signal and the parameters of the second differential signal to eliminate the influence of lift-off on the signal.

[0017] In a further embodiment, an eddy current detection method, said S2 comprises:

[0018] Calculating the amplitude and phase parameters of the first differential signal, and calculating the amplitude and phase parameters of the second differential signal;

[0019] The relationship between the amplitude of the first differential signal, the phase of the first differential signal, the amplitude of the second differential signal, the phase of the second differential signal and the lift-off is analyzed respectively.

[0020] In a further embodiment, an eddy current detection method, said S3 comprises:

[0021] fusing the amplitude of the first differential signal with the amplitude of the second differential signal;

[0022] performing linear processing on phase parameters of the first differential signal and / or the second differential signal;

[0023] The fused amplitude is fused with the phase parameter after linear processing to obtain the final detection signal.

[0024] As a preferred option, in an eddy current detection method, the effect of lift-off on two differential signal amplitude parameters is negatively correlated.

[0025] In a further embodiment, an eddy current detection method, the linear processing of the phase parameters of the first differential signal and / or the second differential signal comprises:

[0026] A differential operation is performed using the phase parameters of the first differential signal and / or the second differential signal to remove the nonlinearity thereof.

[0027] In another embodiment, based on the same inventive concept as the detection method, an eddy current detection system is provided, the system comprising:

[0028] A differential signal acquisition module, used to acquire a first differential signal and a second differential signal output by the probe when the lift-off changes, wherein the first differential signal is output by the excitation unit of the probe, and the second differential signal is output by the sensing unit of the probe;

[0029] A parameter calculation module, used for analyzing the relationship between the parameters of the first differential signal, the parameters of the second differential signal and lift-off under the alternating magnetic field;

[0030] The multi-parameter fusion module is used to fuse the parameters of the first differential signal with the parameters of the second differential signal to eliminate the influence of lift-off on the signal.

[0031] In another embodiment, a storage medium is provided, on which computer instructions are stored, and when the computer instructions are executed, the eddy current detection method is executed.

[0032] In another solution, a terminal is provided, including a memory and a processor, wherein the memory stores computer instructions that can be executed on the processor, and the processor executes the eddy current detection method when executing the computer instructions. It should be further explained that the technical features corresponding to the above options can be combined or replaced with each other to form a new technical solution if there is no conflict.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) In the detection circuit of the present invention, the excitation unit of the probe forms a differential bridge, and the induction unit is coupled with the excitation unit to form a transformer conditioning circuit. The entire probe adopts a combination of a differential bridge and a transformer conditioning circuit, wherein the induction unit outputs a first differential signal, and the excitation unit outputs a second differential signal to form a dual-path differential output circuit. The dual-path differential output has a high defect detection capability when the lift-off changes. When the lift-off changes, under an alternating magnetic field, the differential signal processing unit obtains the first differential signal and the second differential signal respectively generated by the induction unit and the excitation unit. The dual-path differential output has a high defect detection capability when the lift-off changes; at the same time, the signal parameters of the two differential signals are fused. Since the lift-off change will affect the first differential signal and the second differential signal at the same time, the lift-off can be suppressed by mathematically changing the two signals to eliminate the common influence of the lift-off on the two signals. The defect detection capability can be improved when the lift-off changes, and no parameter adjustment operations are required, which is simple and practical.

[0035] (2) The present invention fuses the amplitude of the first differential signal with the amplitude of the second differential signal. The change in the amplitude after fusion is only related to the coupling coefficient between the induction coil and the eddy current, which can reflect more information about the test piece and improve the detection capability. The phase parameters of the first differential signal and the second differential signal are linearly processed and fused with the fused amplitude. The fusion of multiple parameters can further enhance the defect information.

[0036] (3) The output end of the excitation coil of the present invention is connected to a first differential amplifier, and the output end of the induction coil is connected to a second differential amplifier. The differential amplifier can be used to differentiate the signal in the input amplifier, thereby suppressing common-mode signals such as (temperature, humidity, etc.), amplifying the differential-mode signal caused by the defect, and increasing the detection sensitivity of the defect.

[0037] (4) The excitation coil and the induction coil of the present invention are placed side by side. When this placement is adopted, the induction coil receives less magnetic flux generated by the excitation coil, so the background signal is small, and it can receive more information about the test piece, which can have a better lift-off suppression effect than placing it up and down. Secondly, the decay rate of eddy current in the test piece is negatively correlated with the radius of the coil. When placed horizontally, the excitation coil can be regarded as the center of the circle, and the distance from the excitation coil to the induction coil can be regarded as the radius. Therefore, the larger the radius, the slower the decay rate of the eddy current, so that deeper defects can be detected in theory. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The specific implementation methods of the present invention are further described in detail below in conjunction with the accompanying drawings. The accompanying drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The same reference numerals are used in these drawings to represent the same or similar parts. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0039] Figure 1 It is a schematic diagram of the structure of the eddy current detection probe shown in the present invention;

[0040] Figure 2 The structure of the excitation coil and the connection schematic diagram of the differential bridge shown in the present invention;

[0041] Figure 3 A connection diagram of an equivalent transformer shown in the present invention;

[0042] Figure 4 The probe structure corresponding to more than two groups of excitation coils shown in the present invention;

[0043] Figure 5 A schematic diagram of the probe structure in which one set of excitation coils corresponds to two sets of induction coils according to the present invention;

[0044] Figure 6The present invention is a schematic diagram of the operation of an eddy current probe based on a differential bridge and a transformer conditioning circuit;

[0045] Figure 7 A circuit diagram corresponding to the first differential signal during modeling shown in the present invention;

[0046] Figure 8 An equivalent circuit diagram corresponding to the first differential signal shown in the present invention;

[0047] Fig. 9 A circuit diagram corresponding to the second differential signal during modeling shown in the present invention;

[0048] Fig.10 is an equivalent circuit diagram corresponding to the second differential signal shown in the present invention;

[0049] Fig.11 The graph of the amplitude variation of the bridge output when the lift-off increases is shown in the present invention;

[0050] Fig.12 The transformer output amplitude variation curve diagram shown in the present invention when the lift-off increases;

[0051] Fig.13 The phase change curve diagram of the bridge output when the lift-off increases shown in the present invention;

[0052] Fig.14 The phase change curve diagram of the transformer output when the lift-off increases is shown in the present invention;

[0053] Fig.15 The processing result of the lift-off change curve using the fusion model shown in the present invention;

[0054] Fig.16 The present invention shows the detection results and signal fusion results of different defects when the lift-off gradually increases;

[0055] Fig.17 The present invention shows the crack detection results and signal fusion results along the weld;

[0056] Fig.18 The pipeline defect detection result and signal fusion result shown in the present invention. DETAILED DESCRIPTION

[0057] The technical solution of the present invention is described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0058] In the description of the present invention, it should be noted that the directions or positional relationships indicated by "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. are directions or positional relationships based on the drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0059] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0060] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0061] The present invention mainly performs multi-parameter measurement of amplitude and phase by combining a differential bridge and a transformer conditioning circuit. The dual-channel differential output has a high defect detection capability when the lift-off changes greatly. At the same time, a fusion model is proposed using the measured multiple parameters to suppress lift-off. The defect detection capability can be improved when the lift-off changes. There is no need to adjust parameters and the like, so the invention is simple and practical.

[0062] Example 1

[0063] Because physical information can be converted into circuit parameters, different signal conditioning circuits can measure different physical parameters, so conditioning circuits are also important in parameter measurement of nondestructive testing and evaluation technology. For example, low-frequency components are detected in pulsed eddy currents by inductive coupling methods, and magnetic fields or magnetic field change rates are measured by magnetic sensors (such as Hall, AMR, GMR, TMR) or induction coils. Peak amplitude, zero-crossing time, phase, peak arrival time, and rise time reflect the magnetic flux generated by eddy currents, which carry the information of the sample. From the perspective of power transmission, magnetic coupling has the greatest energy transfer and maintains constant efficiency within a certain range. It uses swept frequency excitation with multiple resonant frequencies to obtain different defect information and parameter acquisition. In addition, the real and imaginary parts of the impedance are usually extracted. Under this effect, the signal conditioning circuits in traditional eddy current testing are resonant circuits, bridge circuits, and inductively coupled transformers. The classic resonant circuit contains a parallel inductor and capacitor, in which the peak voltage appears at the resonant frequency. When a defect exists, the frequency change of the resonant frequency will cause the voltage to drop sharply. The bridge circuit uses an inductor and a resistor as the bridge arm to convert the impedance change into a voltage. The inductive coupling system refers to a transformer in which two or more coils are coupled to each other. However, these characteristics vary depending on the coupling parameters (such as discontinuities, cracks or peeling, etc.). Therefore, the design and selection of appropriate sensor probes and conditioning circuits are particularly critical in eddy current testing.

[0064] In an exemplary embodiment, an eddy current detection circuit is provided, comprising:

[0065] The probe comprises an excitation unit and a sensing unit, wherein the excitation unit forms a differential bridge for receiving an excitation signal and outputting a first differential signal, that is, an output signal U of the bridge in the figure. o1 The induction unit is coupled with the excitation unit to form a transformer conditioning circuit and output a second differential signal, that is, the output signal U of the transformer. o2 ;

[0066] A differential signal processing unit, configured to receive the first differential signal U o1 , the second differential signal U o2 , analyze the first differential signal U under the alternating magnetic field o1 Parameters of the second differential signal U o2 The relationship between the parameters and the lift-off, and the first differential signal U o1 The parameters and the second differential signal U o2 The parameters of the image are fused to eliminate the influence of lift-off on the signal.

[0067] The excitation unit is composed of a plurality of excitation coils arranged in a row, and the induction unit is composed of a plurality of induction coils placed one-to-one with the excitation coils, wherein the coil winding directions of the induction coils and the excitation coils are opposite;

[0068] The eddy current detection circuit also includes a first differential amplifier and a second differential amplifier. The input end of the excitation coil is connected to the output end of the signal generator. A plurality of the excitation coils are connected in parallel. The output end of the excitation coil is connected to a capacitor or a resistor. The output ends of two adjacent excitation coils are connected to a first differential amplifier. The first differential amplifier is used to amplify and output a first differential signal U o1 The output ends of the two adjacent induction coils are connected to a second differential amplifier, and the second differential amplifier is used to amplify and output a second differential signal U o2 .

[0069] Specifically, Figure 1-Figure 5 As shown, the probe structure consists of two groups of horizontally placed planar square spiral coils, each group of coils contains two square coils of equal size, one group is the excitation coil, and the other group is the induction coil. The excitation coil is connected in parallel, and the winding direction of the induction coil is opposite to that of the excitation coil. The excitation coil and the induction coil are placed side by side in the same plane. The winding method of the coil determines the difference in the conditioning circuits of the two groups of coils, which is a combination of a differential bridge and a transformer conditioning circuit. It should be noted that in other embodiments, the excitation coil and the induction coil can be placed vertically, and the actual number of excitation coils can be an even number greater than 2.

[0070] Furthermore, the excitation coil and the induction coil are placed side by side in the same plane, and the total magnetic flux received by the induction coil is the sum of the magnetic field generated by the excitation coil and the magnetic field generated by the eddy current on the specimen. When placed up and down, the magnetic flux generated by the excitation coil directly penetrates more into the induction coil (direct coupling between coils), so the background signal is strong. When placed relatively horizontally, the coupling vector distance between the coils is large and the coupling coefficient is small, so the induction coil receives less magnetic flux generated by the excitation coil, so the background signal is small, and it can receive more information about the specimen, and can have a better lift-off suppression effect than placing it up and down. Secondly, the decay rate of eddy current in the specimen is negatively correlated with the radius of the coil. When placed horizontally, the excitation coil can be regarded as the center of the circle, and the distance from the excitation coil to the induction coil can be regarded as the radius. Therefore, the larger the radius, the slower the decay rate of the eddy current, so theoretically deeper defects can be detected.

[0071] Furthermore, in one example, a differential bridge is provided, wherein the excitation unit includes two excitation coils, and two adjacent excitation coils serve as two arms of the AC bridge, and the corresponding two capacitors or resistors are connected to the other two arms of the AC bridge. Specifically, Figure 2 As shown, L1 and L2 of the excitation coil serve as the two arms of the AC bridge, and the remaining two arms are two capacitors with equal capacitance C. Therefore, the differential voltage of the two capacitors is the output of the AC bridge, which we call U o1 The excitation coil consists of two coils of exactly the same size and parameters placed horizontally. The common ends of the two coils are connected in parallel to the signal generator, and the remaining ends are connected in series with capacitors of equal capacitance. The other ends of the two capacitors are grounded. The voltage across the capacitors is passed into the differential amplifier, so that the current direction of the entire excitation coil is the same, and the two coils and the two capacitors form a bridge connection.

[0072] Furthermore, based on the probe, a transformer is provided, wherein the induction coil is formed by two coils connected in series, the two coils are equal in size and wire diameter, and one end of each coil is connected to a differential amplifier to increase the defect detection capability. Therefore, the two excitation coils are regarded as a whole, and the differential induction coil is regarded as a whole, such as Figure 3 As shown, the excitation coil L1 and the excitation coil L2 constitute the primary side of the transformer, and the induction coil L3 and the induction coil L4 constitute the secondary side of the transformer. Therefore, we can obtain the differential voltage U from the differential induction coil composed of the induction coil L3 and the induction coil L4. o2 .

[0073] Furthermore, if Figure 6 As shown, the parallel input end of the excitation coil is connected to the signal generator, and the output end of each excitation coil is connected to the first differential amplifier after being connected in series with a capacitor. The first differential amplifier is used to output the first differential signal U o1 The output end of the induction coil is connected to the second differential amplifier, and the second differential amplifier is used to output a second differential signal U o2 Specifically, the signal generator generates a sine wave signal of a specific frequency, which is injected into the power amplifier to increase the load capacity of the probe. The excitation coil receives the amplified AC signal, and the probe interacts with the conductor under the alternating electromagnetic field to generate eddy current. The excitation coil outputs a first differential signal U through the first differential amplifier. o1 , the induction coil outputs a second differential signal U under the mutual influence of the excitation coil and the conductor being measured. o2 , Both signals are output to the signal conditioning circuit, further collected by the data acquisition unit, and finally analyzed by the differential signal processing unit.

[0074] Furthermore, during the test, as the lifting distance changes, the eddy current intensity on the conductor specimen under test also changes, so the amplitude and phase of the two outputs change, and the acquisition circuit collects data of the changed amplitude and phase.

[0075] The probe of the present invention adopts a combination of a differential bridge and a transformer conditioning circuit to perform multi-parameter measurements of the amplitude and phase of the outputs of the excitation unit and the induction unit respectively. The dual-channel differential output has a high defect detection capability when there is a high lift-off change. At the same time, the signal parameters of the two differential signals are fused to suppress lift-off, and no operations such as parameter adjustment are required. The probe is simple and practical.

[0076] In another example, Figure 4 As shown, two adjacent excitation coils are taken as a group, the excitation unit includes multiple groups of excitation coils, and the corresponding induction unit includes multiple groups of induction coils. The working principle of each group of coils is as follows Figure 1 Implementation method of the middle coil. In which all coils are located in the same horizontal plane. By performing fusion measurement of more sets of differential output signal parameters, defects can be detected more accurately.

[0077] In another example, Figure 5 As shown, one set of excitation coils can correspond to two sets of induction coils, wherein all coils are located in the same horizontal plane, and the two sets of induction coils are located on both sides of the excitation coils. Similarly, more sets of differential output signal parameter fusion measurements can more accurately detect defects. It should be noted that other arrays or changes based on the same principle of the probe are still within the scope of protection of this application.

[0078] Example 2

[0079] Based on embodiment 1, a method for eddy current detection is provided, comprising the following steps:

[0080] S1. Under the condition of lift-off change, obtain the first differential signal U output by the probe o1 and the second differential signal U o2 , where the first differential signal U o1 The second differential signal U is output by the excitation unit of the probe. o2 Output by the sensing unit of the probe;

[0081] S2. Analyze the first differential signal U under the alternating magnetic field o1 Parameters of the second differential signal U o2 The relationship between the parameters and lift-off;

[0082] S3, the first differential signal U o1 The parameters and the second differential signal U o2 The parameters of the image are fused to eliminate the influence of lift-off on the signal.

[0083] Further, the S2 includes:

[0084] Calculate the first differential signal U o1The amplitude and phase parameters of the second differential signal U are calculated o2 The amplitude and phase parameters of

[0085] Analyze the first differential signal U respectively o1 The amplitude of the first differential signal U o1 The phase of the second differential signal U o2 The amplitude of the second differential signal U o2 The relationship between phase and lift-off.

[0086] Further, the S3 includes:

[0087] The first differential signal U o1 The amplitude of the second differential signal U o2 The amplitude of is fused;

[0088] The first differential signal U o1 and / or the second differential signal U o2 The phase parameters are processed linearly;

[0089] The fused amplitude is fused with the phase parameter after linear processing to obtain a final detection signal. The defects of the test piece are analyzed according to the final detection signal.

[0090] Specifically, see Figure 7-10 In order to analyze the mapping relationship between the signal characteristics and the lift-off of the proposed probe under the change of lift-off, we establish the system output response based on the equivalent circuit model. For the excitation coil, since the excitation current directions of the two coils are the same, the magnetic field directions in the middle area of ​​the two coils are opposite. Therefore, the magnetic field area composed of the excitation coil L1 and the excitation coil L2 can be regarded as the mutual inductance M 12 If we regard the conductor under test and the coil as a whole as a system, then the output of the bridge is the whole L formed by this pair of parallel coils (i.e. L1, L2). v It generates electromagnetic coupling with the conductor under test. Although the output of the differential bridge is a differential signal, it is used to amplify the external input differential signal that may destroy the balance of the bridge and suppress common-mode signals such as (temperature, etc.), but when the lift-off changes, no amount that destroys the balance is generated. Therefore, as long as the lift-off changes, the output of the bridge is the result of the lift-off change. If the defect is located below the single-coil bridge arm, the balance of the bridge will be broken, and the differential mode output will be a defect response signal. As for the transformer induction coil, it not only receives the magnetic field directly coupled by the excitation coil, but also receives the reflected magnetic field of the eddy current on the conductor under test (the magnetic field of the induction coil itself and the conductor under test can be ignored). From the results, the output of the differential coil is the result of the difference between the two, and the differential coil (ie L3, L4) is also regarded as a whole L r .

[0091] Further, the first differential signal U is obtained respectively o1 , the second differential signal U o2 ,include:

[0092] The conductor under test is equivalent to a coil with inductance and resistance, and the first differential signal U o1 , the second differential signal U o2 The corresponding equivalent circuit is constructed and modeled based on the equivalent circuit. The conductor under test is equivalent to an inductor with inductance L t and resistor R t The coil can be modeled according to Kirchhoff's law, so the two signals can be modeled based on the equivalent circuit under the lift-off change:

[0093]

[0094] Where R v， L v It means that under the action of the magnetic field, two parallel excitation coils form equivalent resistance and equivalent inductance. v is the equivalent current flowing into the excitation coil, U p refers to the voltage of the sinusoidal signal passed to the coil. f refers to the frequency of the excitation signal passed, and I e It is the eddy current generated on the conductor. vt is the mutual inductance between the excitation coil and the conductor being measured and is related to the lift-off distance x, k vt is the coupling coefficient between the excitation coil and the conductor being measured.

[0095]

[0096] Among them, 0 <k vt (x)<1, from (1) we can get the current I v and impedance Z v change:

[0097]

[0098]

[0099] For the bridge output U o1 , mainly outputs the change of current in two circuits, and the change of current ΔI v Mainly depends on the change in impedance ΔZ v , so there are the following two formulas:

[0100]

[0101]

[0102] Among them, C s is the capacitance of the capacitor connected in series with the coil, and we can get U o1 Amplitude of change |ΔU O1 | and phase parameters

[0103]

[0104] Similarly, for the change in the output of the second-stage differential transformer |ΔU 02 |For:

[0105]

[0106] where k rt (x) refers to the mutual inductance coefficient between the induction coil and the conductor being measured, which is also related to the lift-off distance x.

[0107] Phase change of the output of the second differential transformer for:

[0108]

[0109] Furthermore, the amplitude of the first differential signal |ΔU O1 | and the amplitude of the second differential signal |ΔU O2 |Fusion, including:

[0110] Using the first differential signal U o1 The amplitude of the second differential signal U o2 The relationship between the amplitudes of the two output channels is eliminated by removing the common influence of lift-off on the amplitude parameters of the two differential signals. From the model, it can be found that lift-off has a common influence on the amplitude parameters of the two output channels, that is, k vt , and their influence is negatively correlated. Therefore, we propose to use their amplitude relationship to eliminate k vt Impact:

[0111]

[0112] The first differential signal U o1 and / or the second differential signal U o2 The phase parameters are linearly processed, including:

[0113] Using the first differential signal U o1 and / or the second differential signal U o2The phase parameter is differentiated to remove its nonlinearity. From formula (10), it can be obtained that the change after amplitude fusion is only related to the coupling coefficient between the induction coil and the eddy current, which reflects more information about the specimen. Formula (7) reflects that the phase of the signal has nothing to do with the lift-off, but there is nonlinearity. Therefore, we can use the differential operation of the phase to remove its nonlinearity and fuse it with the existing amplitude signal to enhance the defect information. That is:

[0114]

[0115] The final fusion detection signal for specimen defect detection is:

[0116]

[0117] This method uses a combination of a differential bridge and a transformer conditioning circuit to perform multi-parameter measurements of amplitude and phase. The dual-channel differential output has a high defect detection capability when the lift-off changes. At the same time, a fusion calculation is proposed using the measured multiple parameters to suppress the lift-off and improve the defect detection capability when the lift-off changes. It does not require parameter adjustment and is simple and practical.

[0118] Example 3

[0119] Based on the same inventive concept as that of Example 2, an eddy current detection system is provided, the system comprising:

[0120] The differential signal acquisition module is used to obtain the first differential signal U output by the probe when the lift-off changes. o1 and the second differential signal U o2 , where the first differential signal U o1 The second differential signal U is output by the excitation unit of the probe. o2 Output by the sensing unit of the probe;

[0121] Parameter calculation module, used to analyze the first differential signal U under the alternating magnetic field o1 Parameters of the second differential signal U o2 The relationship between the parameters and lift-off;

[0122] A multi-parameter fusion module is used to transform the first differential signal U o1 The parameters and the second differential signal U o2 The parameters of the image are fused to eliminate the influence of lift-off on the signal.

[0123] The multi-parameter fusion module is used to transform the first differential signal U o1 The amplitude of the second differential signal U o2 The amplitude of the first differential signal U o1 and / or the second differential signal Uo2 The phase parameter of the linear processing is linearly processed; and the fused amplitude is fused with the phase parameter after the linear processing to obtain the final detection signal;

[0124] The defect analysis module is used to analyze the defects of the test piece according to the final detection signal.

[0125] Among them, the multi-parameter fusion module uses the first differential signal U o1 The amplitude of the second differential signal U o2 The relationship between the amplitudes of the first differential signal U is eliminated, and the common influence of the lift-off on the amplitude parameters of the two differential signals is eliminated. The change in amplitude after fusion is only related to the coupling coefficient between the induction coil and the eddy current, which reflects more information about the specimen. o1 and / or the second differential signal U o2 The phase parameter is differentiated to remove its nonlinearity. By using the differential operation of the phase to remove its nonlinearity and fusing it with the existing amplitude signal, the defect information can be enhanced.

[0126] Example 4

[0127] Based on Example 3, in this example, the detection effect and detection method of the probe are verified by example. Specifically, the changes of the two output signals when the lift-off increases are first verified. Figure 11-Figure 14 As shown in the figure, when the probe is lifted up from one point, the changes in the two output signals are different, such as Fig.11 As shown in Figure 2, for the output of the bridge, as the lift-off increases, the amplitude of the output signal first increases and then decreases, as shown in Figure 2. Fig.12 As shown, for the output of the transformer, under the same conditions, the amplitude of the output signal first decreases and then increases, which reflects that the parameters measured by the two outputs for the same change are different, which also lays the foundation for the proposal of the lift-off fusion suppression method.

[0128] Furthermore, the effect of parameter fusion detection method is verified, such as Fig.15 As shown in the figure, after parameter fusion, the originally nonlinear curve changes relatively slowly overall, which shows that with the change of lift-off, the final change is not large, and it also verifies that the fusion method has the effect of lift-off suppression.

[0129] Furthermore, the detection effect and signal fusion results of the probe sensor on different defects when the lift-off gradually increases are verified, such as Fig.16As shown in the figure, a specimen with different types of defects is tested, including circular size change defects, depth change defects, directional defects and width change defects. After the flat specimen is raised for a certain distance, the probe is used to scan the same type of defects to simulate the defect detection process when the lift-off is continuously increased. From the figure, we can see that the fused signal can easily distinguish the defects.

[0130] Furthermore, the effect of the probe sensor on the detection of cracks along the weld and the signal fusion results are verified. In order to verify the adaptability of this method in complex environments, such as Fig.17 As shown in the figure, considering the irregular lift-off variation, three groups of low-carbon X70 steel (conductivity is 7.77·) were tested with bent pipes with cracks along the weld. The bent pipes determine that the lift-off distance always changes irregularly during the detection process. In addition, the rough surface and material accumulation at the weld cause lift-off variation, which also brings difficulties to the detection. Unlike the continuous lift-off variation process, in this nonlinear lift-off variation process, it is difficult to identify the defect information from the original signal, and the number of defects cannot be directly determined from the original signal. However, all defects can be clearly obtained from the proposed parameter fusion response model.

[0131] Furthermore, the effect of the probe sensor on pipeline defect detection and the signal fusion results were verified. When detecting defects on the inner wall of the pipeline, it was difficult to distinguish the number of defects from the original signal, but from the fused data, such as Fig.18 As shown, all defects can be clearly displayed, indicating that fusion can increase the detection capability of defects and has a good signal-to-noise ratio.

[0132] Example 5

[0133] This embodiment has the same inventive concept as that of Embodiment 2. On the basis of Embodiment 2, a storage medium is provided, on which computer instructions are stored. When the computer instructions are executed, the eddy current detection method is executed.

[0134] Based on this understanding, the technical solution of this embodiment, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the methods of various embodiments of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM), random access memory (RAM), disk or optical disk, etc., various media that can store program codes.

[0135] Example 6

[0136] This embodiment has the same inventive concept as Embodiment 1, and provides a terminal including a memory and a processor. The memory stores computer instructions that can be executed on the processor, and the processor executes the eddy current detection method when executing the computer instructions.

[0137] The processor may be a single-core or multi-core central processing unit or a specific integrated circuit, or one or more integrated circuits configured to implement the present invention.

[0138] Embodiments of the subject matter and functional operations described in this specification may be implemented in: tangibly embodied computer software or firmware, computer hardware including the structures disclosed in this specification and their structural equivalents, or a combination of one or more of them. Embodiments of the subject matter described in this specification may be implemented as one or more computer programs, i.e., one or more modules of computer program instructions encoded on a tangible, non-transitory program carrier to be executed by a data processing device or to control the operation of the data processing device. Alternatively or additionally, the program instructions may be encoded on an artificially generated propagated signal, such as a machine-generated electrical, optical, or electromagnetic signal, which is generated to encode and transmit information to a suitable receiver device for execution by the data processing device.

[0139] The processes and logic flows described in this specification can be performed by one or more programmable computers executing one or more computer programs to perform corresponding functions by operating on input data and generating output. The processes and logic flows can also be performed by special purpose logic circuits, such as FPGAs (field programmable gate arrays) or ASICs (application-specific integrated circuits), and the apparatus can also be implemented as special purpose logic circuits.

[0140] Processors suitable for executing computer programs include, for example, general and / or special microprocessors, or any other type of central processing unit. Typically, the central processing unit will receive instructions and data from a read-only memory and / or a random access memory. The basic components of a computer include a central processing unit for implementing or executing instructions and one or more memory devices for storing instructions and data. Typically, the computer will also include one or more large-capacity storage devices for storing data, such as magnetic disks, magneto-optical disks, or optical disks, or the computer will be operably coupled to this large-capacity storage device to receive data from it or to transmit data to it, or both. However, the computer does not necessarily have such a device. In addition, the computer can be embedded in another device, such as a mobile phone, a personal digital assistant (PDA), a mobile audio or video player, a game console, a global positioning system (GPS) receiver, or a portable storage device such as a universal serial bus (USB) flash drive, just to name a few.

[0141] Although this specification includes many specific implementation details, these should not be interpreted as limiting the scope of any invention or the scope of protection claimed, but are mainly used to describe the features of the specific embodiments of specific inventions. Certain features described in multiple embodiments in this specification may also be implemented in combination in a single embodiment. On the other hand, the various features described in a single embodiment may also be implemented separately in multiple embodiments or in any suitable sub-combination. In addition, although features may work in certain combinations as described above and even initially claim protection, one or more features from the claimed combination may be removed from the combination in some cases, and the claimed combination may point to a sub-combination or a variation of a sub-combination.

[0142] Similarly, although operations are depicted in a particular order in the accompanying drawings, this should not be understood as requiring that these operations be performed in the particular order shown or performed sequentially, or requiring that all illustrated operations be performed to achieve the desired results. In some cases, multitasking and parallel processing may be advantageous. In addition, the separation of various system modules and components in the above-described embodiments should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product, or packaged into multiple software products.

[0143] The above specific implementation methods are detailed descriptions of the present invention. It cannot be determined that the specific implementation methods of the present invention are limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions and substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. An eddy current detection circuit, characterized in that: include: The probe comprises an excitation unit and an induction unit, wherein the excitation unit forms a differential bridge for receiving an excitation signal and outputting a first differential signal, and the induction unit is used to couple with the excitation unit to form a transformer conditioning circuit and output a second differential signal; A differential signal processing unit, configured to receive the first differential signal and the second differential signal, analyze the relationship between the parameters of the first differential signal and the parameters of the second differential signal and lift-off under the alternating magnetic field, and fuse the parameters of the first differential signal with the parameters of the second differential signal to eliminate the influence of lift-off on the signal; The fusing the parameters of the first differential signal with the parameters of the second differential signal includes: fusing the amplitude of the first differential signal with the amplitude of the second differential signal; performing linear processing on phase parameters of the first differential signal and / or the second differential signal; The fused amplitude is fused with the phase parameter after linear processing to obtain the final detection signal.

2. An eddy current detection circuit according to claim 1, characterized in that: The excitation unit is composed of a plurality of excitation coils arranged in a row, and the induction unit is composed of a plurality of induction coils placed one-to-one corresponding to the excitation coils, wherein the winding directions of the induction coils and the excitation coils are opposite; The input end of the excitation coil is connected to the output end of the signal generator, a plurality of the excitation coils are connected in parallel, and the output end of the excitation coil is connected to a capacitor or a resistor; the output ends of two adjacent excitation coils are connected to a first differential amplifier; the output ends of two adjacent induction coils are connected to a second differential amplifier.

3. An eddy current detection circuit according to claim 1, characterized in that: The excitation coil and the induction coil are placed side by side, and two adjacent excitation coils serve as two arms of an AC bridge, and the corresponding two capacitors or resistors are connected to the remaining two arms of the AC bridge.

4. An eddy current detection method, characterized in that: The following steps are involved: S1. In the case of lift-off variation, obtaining a first differential signal and a second differential signal output by the probe, wherein the first differential signal is output by an excitation unit of the probe, and the second differential signal is output by a sensing unit of the probe; S2. analyzing the relationship between the parameters of the first differential signal, the parameters of the second differential signal and lift-off under the alternating magnetic field; S3, fusing the parameters of the first differential signal with the parameters of the second differential signal to eliminate the influence of lift-off on the signal; The fusing the parameters of the first differential signal with the parameters of the second differential signal includes: fusing the amplitude of the first differential signal with the amplitude of the second differential signal; performing linear processing on phase parameters of the first differential signal and / or the second differential signal; The fused amplitude is fused with the phase parameter after linear processing to obtain the final detection signal.

5. An eddy current detection method according to claim 4, characterized in that: The S2 includes: Calculating the amplitude and phase parameters of the first differential signal, and calculating the amplitude and phase parameters of the second differential signal; The relationship between the amplitude of the first differential signal, the phase of the first differential signal, the amplitude of the second differential signal, the phase of the second differential signal and the lift-off is analyzed respectively.

6. An eddy current detection method according to claim 4, characterized in that: The linear processing of the phase parameters of the first differential signal and / or the second differential signal comprises: A differential operation is performed using the phase parameters of the first differential signal and / or the second differential signal to remove the nonlinearity thereof.

7. An eddy current detection system, characterized in that: The system comprises: A differential signal acquisition module, used to acquire a first differential signal and a second differential signal output by the probe when the lift-off changes, wherein the first differential signal is output by the excitation unit of the probe, and the second differential signal is output by the sensing unit of the probe; A parameter calculation module, used for analyzing the relationship between the parameters of the first differential signal, the parameters of the second differential signal and lift-off under the alternating magnetic field; A multi-parameter fusion module, used to fuse the parameters of the first differential signal with the parameters of the second differential signal to eliminate the influence of lift-off on the signal; The fusing the parameters of the first differential signal with the parameters of the second differential signal includes: fusing the amplitude of the first differential signal with the amplitude of the second differential signal; performing linear processing on phase parameters of the first differential signal and / or the second differential signal; The fused amplitude is fused with the phase parameter after linear processing to obtain the final detection signal.

8. A storage medium having computer instructions stored thereon, characterized in that: When the computer instructions are executed, the eddy current detection method described in any one of claims 4 to 6 is executed.

9. A terminal comprising a memory and a processor, wherein the memory stores computer instructions that can be executed on the processor, characterized in that: When the processor runs the computer instructions, the eddy current detection method according to any one of claims 4 to 6 is executed.

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