CN112666395A - Non-contact metal material conductivity measurement method and system - Google Patents
Non-contact metal material conductivity measurement method and system Download PDFInfo
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Abstract
The present disclosure provides a non-contact method for measuring electrical conductivity of a metal material, the method comprising: measuring eddy magnetic field delta B corresponding to tested metal piece0(z), wherein the measurement system is an axisymmetric structure or equivalent axisymmetric structure; establishing a relational expression of the eddy magnetic field and the conductivity of the tested metal piece; and acquiring the conductivity of the tested metal piece according to the relation between the eddy magnetic field and the conductivity of the tested metal piece measured by the measuring system. According to the invention, the eddy magnetic field corresponding to the tested metal piece is tested by building the testing system, and the conductivity of the metal is obtained by pre-storing the established relationship between the eddy magnetic field and the conductivity of the tested metal piece, so that equivalent comparison is not needed, and the measurement is not needed to be realized by identifying the difference between the tested metal piece and the standard block. Therefore, the method is a more convenient and non-contact direct measurement method.
Description
Technical Field
The disclosure relates to the technical field of conductivity measurement methods, and in particular relates to a non-contact metal conductivity measurement method and system.
Background
Most of the traditional metal conductivity measurement adopts a method of applying current signals at two ends of a conductor, measuring voltage signals at the two ends and calculating conductor resistance by using ohm's law. Since the resistance is related to the length and cross-sectional area of the conductor in addition to the material conductivity, the conductivity of the conductor needs to be calculated based on the size of the conductor and the boundary conditions of the applied current signal. The disadvantage of this calculation and measurement method is that it depends on the dimensions of the conductor and that it is necessary to pass a current signal through the conductor, which is a contact measurement. The measurement accuracy of the method is greatly influenced by the electrode contact mode and the magnitude of the conductivity of the conductor, and particularly under the condition that the conductivity of the measured conductor is very high, the voltage signals generated by the applied current signals at two ends of the conductor are very weak, so that the measurement error is large.
The eddy current detection is a nondestructive detection technology based on the electromagnetic induction principle, and compared with the traditional metal conductivity measurement method analyzed in the prior art, although the current application mode is different between the eddy current detection and the metal conductivity measurement method, the detection of the eddy current in the conductor is also influenced by factors such as the electrode contact mode, and the detection process is extremely inconvenient and still belongs to contact measurement. The method has the biggest defects of complex circuit, multiple interference factors of measurement results, easy parameter drift, frequent calibration and incapability of realizing automatic and continuous measurement of the conductivity. Meanwhile, the coil is used as an intermediate physical link to convert the magnetic field signal affected by the eddy current into a voltage signal, namely the voltage signal contains other non-useful signals except the conductivity of the measured material. This entails a lot of unnecessary disturbances and is influenced by the frequency and magnitude of the excitation current. Therefore, the accurate non-contact measurement of the conductivity of the metal material can be really realized only by completely removing the constraint of the detection coil. On the other hand, if the relationship between the eddy magnetic field and the metal conductivity is established, and the relationship is established by an experimental method, a very large sample database must be established, and the requirements on an experimental device are very high. If the accurate mathematical relation expression of the electromagnetic principle equation and the electromagnetic principle equation is established, very complicated mathematical derivation and calculation are involved.
Disclosure of Invention
The present disclosure provides a non-contact method for measuring the conductivity of a metal material.
In order to solve at least one of the above technical problems, the present disclosure proposes the following technical solutions:
first aspectThe non-contact type metal material conductivity measuring method comprises the following steps: s101, measuring an eddy current magnetic field delta B corresponding to a tested metal piece through a measuring system0(z), wherein the measurement system is an axisymmetric structure or equivalent axisymmetric structure;
s102, the data processing module stores a relational expression between the eddy current magnetic field in the corresponding measuring system and the conductivity of the tested metal piece;
s103, measuring the eddy current magnetic field delta B according to the measuring system0And (z) acquiring the conductivity of the metal piece to be tested by combining the relation between the eddy magnetic field and the conductivity of the metal piece to be tested.
In some embodiments, an eddy current magnetic field Δ B is acquired0(z) a step comprising:
before measurement, a source field B corresponding to the measuring probe is obtained0(z) comprising: putting the corresponding measuring probe into the space region independently and ensuring no metal substances around, wherein the output value of the magnetic field sensor is the source field B0(z)；
In the measuring process, the measuring probe is placed on the surface of the tested metal piece, the output value of the magnetic field sensor at the moment is recorded, and the output value of the magnetic field sensor at the moment is the sum B (z) of the source field and the eddy current magnetic field.
Subtracting the source field B obtained before from the measured record value B (z)0(z) obtaining the eddy magnetic field delta B corresponding to the tested metal piece0(z)。
In some embodiments, the relationship between the eddy current magnetic field and the electrical conductivity of the metal piece to be tested is established for analyzing the measurement signal fed back by the measurement probe and applying a prestored algorithm, and the method comprises the following steps:
acquiring mathematical expressions of all components of magnetic induction intensity in an area of a measuring system;
performing a modulus operation by using eddy magnetic fields corresponding to different metal materials according to a mathematical expression, and performing least square fitting on the obtained result to obtain a relation curve between the axial eddy magnetic field and the conductivity;
through curve fitting, the following relational expression of the axial eddy magnetic field and the conductivity is established:
y＝－0.01375098369612x2+0.24014968145481x+0.11463161109536
wherein y in the expression represents the strength value of the axial eddy magnetic field and has the unit of 10-3T, x is the conductivity value of the tested metal piece and has the unit of 107S/m；
And by adopting a polynomial root function roots, the conductivity of the tested metal piece can be obtained according to the measured eddy magnetic field.
In some embodiments, obtaining a mathematical expression of components of magnetic induction in a region of a measurement system comprises:
wherein
J1Representing a class of first-order Bessel functions, Y1Representing a class two first order Bessel function, Ai、Bi、CiAnd DiIs an unknown coefficient;
wherein A isSMagnetic vector potential of source field generated for exciting coil, AeRepresenting magnetic vector potential caused by eddy current in the tested metal part;
Can obtain a region (z is more than or equal to 0 and less than or equal to z)1) An analytical expression of each component of the magnetic induction intensity:
wherein the characteristic value alphai J1(αih) 0 is true root, B0(r) and B0(z) represents the radial and axial magnetic field, Δ B, respectively, of the area above the conductive test piece under the action of the exciting coil alone0(r) and. DELTA.B0(z) represents the radial and axial eddy magnetic fields, respectively, caused by induced eddy currents inside the test piece.
In a second aspect, a conductivity testing system is provided for performing the above non-contact method for measuring conductivity of a metal material, including:
the excitation device is used for generating an excitation signal, processing the excitation signal and transmitting the processed excitation signal to the test probe;
the test probe is used for generating a magnetic field signal for detecting the surface of a tested piece, converting the magnetic field signal into a voltage signal and sending the voltage signal to the data processing module;
and the data processing module is used for analyzing the measurement signals fed back by the measurement probe and applying a prestored solving algorithm to obtain the conductivity value of the tested metal piece.
In some embodiments, the test probe comprises an excitation coil and a magnetic field sensor;
the excitation coil is used for generating a magnetic field signal for detecting the surface of the tested metal piece;
the magnetic field sensor is used for detecting a magnetic field signal above the metal test piece to be detected and converting the magnetic field signal into a voltage signal.
In some embodiments, the excitation device comprises a signal generator and a power amplifier connected to each other,
a signal generator for generating an excitation signal:
and the power amplifier is used for amplifying the excitation signal, and the output end of the power amplifier is connected with the excitation coil.
In some embodiments, an isolation layer is disposed between the magnetic field sensor and the excitation coil for separation, and a protective layer is disposed below the magnetic field sensor. Therefore, the protective layer can protect the magnetic sensor and ensure that a certain lifting height is kept between the protective layer and the surface of the tested metal piece.
The method has the advantages that the eddy current magnetic field corresponding to the tested metal piece is tested by building the testing system, and the conductivity of the metal is obtained by calling the relational expression of the eddy current magnetic field and the conductivity of the tested metal piece in combination with the processing in the data processing module. The invention does not need to adopt equivalent comparison and does not need to identify the difference between the tested metal piece and the standard block to realize measurement. Therefore, the method is a more convenient and non-contact direct measurement method.
In addition, in the technical solutions of the present disclosure, the technical solutions can be implemented by adopting conventional means in the art, unless otherwise specified.
Drawings
In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the drawings used in the following description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the following description are some embodiments of the present disclosure, and other drawings can be obtained by those skilled in the art without creative efforts.
Fig. 1 is a flowchart of a non-contact type method for measuring conductivity of a metal material according to an embodiment of the present disclosure;
FIG. 2 is a schematic diagram of a relationship between an eddy current magnetic field and an electrical conductivity of a metal part under test according to another embodiment of the present disclosure;
FIG. 3 is a schematic diagram of a conductivity testing system provided in accordance with an embodiment of the present disclosure;
FIG. 4 is a block diagram of a data processing module of a conductivity testing system provided in one embodiment of the present disclosure;
FIG. 5 is a schematic structural diagram of a test probe provided in one embodiment of the present disclosure;
fig. 6 is a schematic diagram of a fitting curve of a test probe provided by an embodiment of the present disclosure.
Detailed Description
In order to make the objects, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below with reference to the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of some, but not all embodiments of the disclosure, and are not to be construed as limiting the disclosure. All other embodiments, which can be derived by a person skilled in the art from the embodiments disclosed herein without making any creative effort, shall fall within the protection scope of the present disclosure.
It should be noted that the terms "comprises" and "comprising," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or server that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
Example 1:
referring to the specification and the accompanying fig. 1, a non-contact type metallic material conductivity measurement method provided by an embodiment of the present application is shown, which may include the following steps:
s101: measuring eddy magnetic field delta B corresponding to tested metal piece0(z) whereinThe measuring system is of an axisymmetric structure and comprises an excitation probe and a tested metal piece;
s102: establishing a relational expression of the eddy magnetic field and the conductivity of the tested metal piece;
s103: and acquiring the conductivity of the tested metal piece according to the relation between the eddy magnetic field and the conductivity of the tested metal piece measured by the measuring system.
Specifically, an eddy magnetic field Δ B is acquired0(z) a step comprising:
s301: before measurement, a source field B corresponding to the type of measuring probe is obtained in advance0(z)；
In an alternative embodiment, the corresponding measuring probe is placed separately in the spatial region and ensures that there is no metallic material around, when the output value of the magnetic field sensor, i.e. the source field B0(z)。
S302: in the measuring process, a measuring probe is placed on the surface of a tested metal piece, and the output value of the magnetic field sensor at the moment is recorded;
in particular, in practical measurements, the magnetic field sensor obtains a spatial magnetic induction value, i.e. the source field B0(z) and eddy magnetic field Δ B0(z) when the magnetic field sensor output is the sum of the source field and the eddy current magnetic field, B (z).
From this, the previously obtained source field B is subtracted from the measurement record B (z)0(z) an eddy magnetic field DeltaB corresponding to the metal material can be obtained0(z)。
In an alternative embodiment, the source field B0(z) in addition to being influenced by the excitation coil parameters, the source field values at different locations are different. Thus, assuming that the magnetic field measurement position is unchanged, i.e. the magnetic field sensor is fixed at a relatively unchanged position of the excitation coil, the source field B is for the same type of excitation probe0(z) is unchanged. And for axial eddy magnetic field Δ B0(z), in addition to being influenced by spatial position, is also related to the metal conductivity of the metallic article being tested. Thus, for a metal with a relative permeability of typically 1, the electrical conductivity of the metal piece under test and the axial eddy magnetic field Δ B can be established0(z) betweenThe variation relationship of (a).
In an alternative embodiment, to avoid a slight difference in the electrical conductivity at different positions of the metal, if the measured object is the electrical conductivity of the entire metal material, the average value of the eddy magnetic field may be obtained by averaging multiple measurements at different positions.
In the traditional method for measuring the conductivity by using the eddy current, the eddy current is a comprehensive action effect of the action of the exciting coil on the metal surface, and a plurality of adverse influence factors exist. Therefore, the measuring method is not influenced by a source field, meanwhile, the influences of unstable factors such as geometric errors of a detection probe, excitation current parameters and the like are avoided, and the measuring accuracy and stability are improved to a certain extent.
In an alternative embodiment, the relationship between the eddy magnetic field and the electrical conductivity of the metal piece to be tested is established for analyzing the measurement signal fed back by the measurement probe and applying a pre-stored algorithm, and the method comprises the following steps:
acquiring mathematical expressions of all components of magnetic induction intensity in an area of a measuring system; in this embodiment, a mathematical expression of the axial eddy magnetic field and the electrical conductivity is adopted, or a mathematical expression of the radial eddy magnetic field and the electrical conductivity is adopted;
performing a modulus operation by using eddy magnetic fields corresponding to different metal materials according to a mathematical expression, and performing least square fitting on the obtained result to obtain a relation curve between the axial eddy magnetic field and the conductivity;
through curve fitting, the following relational expression of the axial eddy magnetic field and the conductivity is established:
y＝－0.01375098369612x2+0.24014968145481x+0.11463161109536
wherein y in the expression represents the strength value of the axial eddy magnetic field and has the unit of 10-3T, x is the conductivity value of the tested metal piece and has the unit of 107S/m；
And by adopting a polynomial root function roots, the conductivity of the tested metal piece can be obtained according to the measured eddy magnetic field.
As a preferable mode in the present embodiment: establishing a relational expression of the eddy magnetic field and the electrical conductivity of the tested metal piece, as shown in fig. 2, constructing a test schematic diagram by combining a test system, wherein the test system comprises a test probe and the tested metal piece, the test probe comprises a magnetic field sensor and an exciting coil, and the established relational expression comprises the following steps:
a cylindrical coordinate system is adopted, and the magnetic vector potential A only has a circumferential component at the moment, so that a function of a radial position r and an axial position z is obtained; because the measurement system satisfies the following electromagnetic equation:
wherein k is2J ω μ σ, σ is the electrical conductivity of the metallic piece under test.
Let the solution area be radially finite (0 ≦ r ≦ h) and apply a Dirichlet boundary condition at r ≦ h. According to the variable separation method, the general solution of formula (1-1) has the following form:
wherein
J1Representing a class of first-order Bessel functions, Y1Representing a class two first order Bessel function, Ai、Bi、CiAnd DiAre unknown coefficients.
Therefore, the magnetic vector potential a obtained by the formula (1-2) is expressed as the series and form of the feature function.
In an alternative embodiment, the air space used between the exciting coil and the metal piece to be tested is the function Y1Diverge, thus Bi0. Considering that the electrical conductivity of the air domain is 0, the magnetic vector potential (k ═ 0) in this domain has the following form:
in addition, in order to ensure the magnetic vector potential of the region 1 to be limited, as shown in the figure, the region 1 refers to the interior of the tested metal piece, and D in the formula (1-2) is seti0. Thus, the magnetic vector potential of the conductive region has the following form:
the unknown coefficients in equations (1-3) and (1-4) can be determined by applying the boundary condition (1-5) between the two regions.
Substituting equations (1-3) and (1-4) into equations (1-5) can obtain two unknown coefficients
Coefficient C0iThe parameters, which are dependent only on the excitation coil and not on the physical properties of the test piece, are called source field coefficients and have the following form:
wherein i ═ NcI/[(r2-r1)(z2-z1)]Is the source current density of the coil, Nc is the number of turns of the coil, I is the current amplitude, and equation χ (α r)1,αr2) Calculated by the following formula.
Therefore, the analytic expression of the magnetic vector potential of the air domain between the exciting coil and the tested metal piece is as follows
Wherein A isSMagnetic vector potential of source field generated for exciting coil, AeIs expressed as the magnetic vector potential caused by the eddy current in the tested metal piece.
In an alternative embodiment, the formula is calculated according to
Can obtain a region (z is more than or equal to 0 and less than or equal to z)1) An analytical expression of each component of the magnetic induction intensity:
wherein the characteristic value alphaiIs J1(αih) 0 for true root. B is0(r) and B0(z) represents the radial and axial magnetic fields, respectively, of the area above the conductive specimen under the action of the exciting coil alone. Delta B0(r) and. DELTA.B0(z) represents the radial and axial eddy magnetic fields, respectively, caused by induced eddy currents inside the test piece.
Specifically, the symbols of the formula in the present application are shown in table 1 below:
TABLE 1
Specifically, according to the mathematical expression of the acquired metal conductivity and the axial eddy current field, the numerical value of the axial eddy current field under typical common metal conditions is solved through calculation, and since the eddy current field obtained through solving is in a complex form, modulo operation needs to be performed. As a result of the calculations shown in Table 2, it can be found that the axial source field remains constant all the time, and the metal conductivity changes only the magnitude of the eddy current field.
TABLE 2 magnetic field calculation results for different metal materials
Based on the numerical values obtained by the calculation, a least square fitting is utilized to obtain a relation curve of the axial eddy current magnetic field and the conductivity, as shown in a graph 6 in the attached drawing of the specification, the abscissa of the graph 6 is the conductivity of the metal material and has a unit of 107S/m, and the ordinate is the axial eddy current magnetic field value and has a unit of 10-3T.
Through curve fitting, the following relational expression of the axial eddy magnetic field and the conductivity is established:
y＝-0.01375098369612x2+0.24014968145481x+0.11463161109536
in the expression, y represents the strength value of the axial eddy magnetic field and has the unit of 10-3T, x is the conductivity value of the metal piece to be tested and has the unit of 107S/m。
In an optional embodiment, a polynomial root function roots in Matlab software is adopted, and the conductivity value of the tested metal piece can be obtained according to the measured eddy current magnetic field. Because of the quadratic polynomial fitting, the roots function usually has two roots, and a smaller value is generally taken as the conductivity value of the tested metal piece.
By way of example, the accuracy of the conductivity obtained by the above measurement method was verified using metallic chromium as an example. The conductivity of metallic chromium is 3.8X 107S/m, where the calculated value of the formula (1-11) is used as the actually measured eddy magnetic field value, moduloHas a size of 0.82921410671475 × 10-3And T. According to the eddy magnetic field value, combining the established relation expression of the axial eddy magnetic field and the conductivity and the root function, calculating to obtain the material conductivity corresponding to the time being 13.65991957035989 multiplied by 107S/m and 3.80426239376905X 107And (5) S/m. Taking a small rule according to the equation root, the material conductivity should be 3.80426239376905 × 107And (5) S/m. Therefore, the metal conductivity error obtained by the method is 0.11%, and the method completely meets the requirement of measurement accuracy.
In an alternative embodiment, a temperature sensor is arranged in the test system for compensating the effect of temperature on the conductivity of the material. Since the metal conductivity is significantly affected by the temperature, and the material conductivity is usually measured at a temperature of 20 ℃, a temperature sensor needs to be arranged in the measuring system to compensate the effect of the temperature on the material conductivity if the conductivity of the tested metal piece is to be accurately evaluated.
The invention can also be applied to the occasion that the material of the metal is judged, the conductivity is an inherent attribute of the metal, and the material of the tested metal piece can be determined by a method of a lookup table according to the measured conductivity value. Of course, the conductivity of a certain metal material should be in a range and not be considered to be a fixed value. Therefore, the range of conductivity for each metal material should be predetermined.
In this embodiment, the eddy magnetic field Δ B corresponding to the tested metal piece is measured0(z) and establishing a relation between the eddy magnetic field and the conductivity of the metal piece to be tested to obtain the conductivity, and finding out from the acquisition process of the conductivity that the invention also has the advantages that equivalent comparison is not needed, and the difference between the metal piece to be tested and the standard block is identified to realize measurement. Therefore, the method is a more convenient and non-contact direct measurement method.
Example 2:
referring to the accompanying fig. 3-5, a test system for performing any one of the above test methods according to an embodiment of the present application is shown, including:
the excitation device is used for generating an excitation signal, processing the excitation signal and transmitting the processed excitation signal to the test probe for alternating current excitation;
the test probe is used for generating a magnetic field signal for detecting the surface of the tested metal piece, converting the magnetic field signal into a voltage signal and sending the voltage signal to the data processing module;
and the data processing module is used for analyzing the measurement signal fed back by the test probe and applying a prestored solving algorithm to obtain the conductivity value of the tested metal piece.
The test probe comprises an exciting coil and a magnetic field sensor; the excitation coil is used for generating a magnetic field signal for detecting the surface of the tested metal piece, and the magnetic field sensor is used for detecting the magnetic field signal above the tested metal test piece and converting the magnetic field signal into a voltage signal.
The data processing module comprises a signal acquisition processing unit, a data processing unit, a verification unit and a storage unit, wherein the storage unit is stored with a relation between the conductivity of the tested metal piece and the eddy magnetic field and a step algorithm in advance;
the signal acquisition and processing unit is used for acquiring and amplifying the acquired measurement signal fed back by the test probe to acquire a required voltage signal;
the data processing unit is used for processing according to the acquired voltage signal and calling a step algorithm stored in the storage unit in advance to acquire an output conductivity value;
and the checking unit is used for trimming and verifying the acquired conductivity value and feeding back a checking result to the data processing unit.
As shown in fig. 3, the driving device includes a signal generator for generating a driving signal and a power amplifier for amplifying the driving signal, which are connected, and the output terminal of the power amplifier is connected to the driving coil. The data acquisition in the figure is a data processing module in the application, the data processing module processes a measurement signal fed back by a test probe and then sends the measurement signal to a computer for display, the data processing module comprises a signal amplification unit, a signal processing unit and a data processing unit in the figure, the signal acquisition processing unit in the application refers to the signal processing and signal amplification in figure 3, the data processing unit in the application refers to the data processing in figure 3, specifically, a weak signal measured by the test probe is firstly subjected to signal amplification processing and passes through a signal processing circuit to obtain a voltage signal which can be directly processed, then the voltage signal is processed by means of data processing such as a single chip microcomputer, the conductivity value of a tested piece is obtained according to a prestored step algorithm, and finally, the direct display and storage are realized.
Specifically, the signal generator is used for generating a sinusoidal alternating current signal with a certain frequency, for example, the signal generator may use a luoyang YB1602 type function signal generator to generate a sinusoidal alternating current signal with a frequency of 1kHz, and the periodic sinusoidal signal amplified by the power amplifier generates an alternating magnetic field in the exciting coil and is applied to the tested metal piece.
Specifically, the exciting coil 1 and the magnetic field sensor 2 are packaged in the shell 3 of the test probe together, the magnetic field sensor 2 is placed at the axis position of the coil framework 4, the vertical distance between the magnetic field sensor 2 and the exciting coil 1 is kept at a fixed value, and an isolation layer 5 is arranged between the magnetic field sensor 2 and the exciting coil 1 for separation. The input current of the exciting coil 1 and the output voltage of the magnetic field sensor 2 exchange information with the outside through the leading terminal 6 and the signal line 7. The design of the test probe thus makes it possible to keep the magnetic field sensor 2 and the excitation coil 1 at a fixed value.
Specifically, the exciting coil 1 is formed by winding an enameled wire, the inner radius of the coil is 2mm, the outer radius of the coil is 4mm, the total number of turns of the coil is 800 turns, and the length of the probe is 3 mm.
The magnetic field sensor 2 can adopt a high-sensitivity magnetic sensor TMR2905 based on a tunneling magneto-resistance technology, and the size of the high-sensitivity magnetic sensor is 3mm x 3mm x 0.75 mm. When being installed, the magnetic field sensor 2 needs to place the sensitive direction thereof in the measuring direction of the measured magnetic field.
Specifically, an isolation layer 5 is arranged between the magnetic field sensor 2 and the excitation coil 1 for separation, and a protective layer 8 is arranged below the magnetic field sensor 2. The protective layer 8 can protect the magnetic sensor 2 and ensure that a certain lift-off height is kept between the protective layer and the surface of the tested metal piece. The isolation layer 5 and the protection layer 8 are made of non-conductive and non-magnetic materials.
Specifically, when the test probe is used, the test probe is placed above a tested metal part, firstly, the output end of the signal generator is connected with the input end of the power amplifier through a lead, then, the output end of the power amplifier is connected with the exciting coil of the test probe through a lead, and the periodic sinusoidal signal generated by the signal generator is amplified by the power amplifier and then is input to the exciting coil of the test probe, so that the periodic sinusoidal signal is used for driving the exciting coil of the test probe to generate an alternating magnetic field required for detecting the tested metal test piece.
It should be noted that, in the system provided in the foregoing embodiment, when the functions of the system are implemented, only the division of the functional modules is illustrated, and in practical applications, the functions may be distributed by different functional modules according to needs, that is, the internal structure of the device is divided into different functional modules, so as to complete all or part of the functions described above. In addition, the system and method embodiments provided by the above embodiments belong to the same concept, and specific implementation processes thereof are described in the method embodiments for details, which are not described herein again.
It should be noted that: the sequence of the embodiments in this specification is merely for description, and does not represent the advantages or disadvantages of the embodiments. And specific embodiments thereof have been described above. Other embodiments are within the scope of the following claims. In some cases, the actions or steps recited in the claims may be performed in a different order than in the embodiments and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In some embodiments, multitasking and parallel processing may also be possible or may be advantageous.
The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, as for the apparatus embodiment, since it is substantially similar to the method embodiment, the description is relatively simple, and for the relevant points, reference may be made to the partial description of the method embodiment.
It will be understood by those skilled in the art that all or part of the steps for implementing the above embodiments may be implemented by hardware, or may be implemented by a program instructing relevant hardware, and the program may be stored in a computer-readable storage medium, and the above-mentioned storage medium may be a read-only memory, a magnetic disk or an optical disk, etc.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, but rather as the subject matter of the invention is to be construed in all aspects and as broadly as possible, and all changes, equivalents and modifications that fall within the true spirit and scope of the invention are therefore intended to be embraced therein.
Claims (9)
1. The non-contact metal material conductivity measurement method is characterized by comprising the following steps:
s101, measuring an eddy current magnetic field delta B corresponding to a tested metal piece through a measuring system0(z), wherein the measurement system is an axisymmetric structure or equivalent axisymmetric structure;
s102, the data processing module stores a relational expression between the eddy current magnetic field in the corresponding measuring system and the conductivity of the tested metal piece;
s103, measuring the eddy current magnetic field delta B according to the measuring system0And (z) obtaining the conductivity of the tested metal piece by combining the relation between the eddy magnetic field and the conductivity of the tested metal piece.
2. The method as claimed in claim 1, wherein the eddy magnetic field Δ B is obtained0(z) a step comprising:
before measurement, a source field B corresponding to the measuring probe is obtained0(z) comprising: putting the corresponding measuring probe into the space region independently and ensuring no metal substances around, wherein the output value of the magnetic field sensor is the source field B0(z)；
In the measuring process, the measuring probe is placed on the surface of the tested metal piece, the output value of the magnetic field sensor at the moment is recorded, and the output value of the magnetic field sensor at the moment is the sum B (z) of the source field and the eddy current magnetic field.
Subtracting the source field B obtained before from the measured record value B (z)0(z) obtaining the eddy current magnetic field delta B corresponding to the tested metal piece0(z)。
3. The method as claimed in claim 1, wherein the relationship between the eddy magnetic field and the electrical conductivity of the metal piece under test is established for analyzing the measurement signal fed back by the measurement probe and applying a pre-stored algorithm, and the method comprises the following steps:
acquiring mathematical expressions of all components of magnetic induction intensity in an area of a measuring system;
performing modular operation by using eddy magnetic fields corresponding to different metal materials according to a mathematical expression, and performing least square fitting on the obtained result to obtain a relation curve between the axial eddy magnetic field and the conductivity;
through curve fitting, the following relational expression of the axial eddy magnetic field and the conductivity is established: -0.01375098369612 x2+0.24014968145481x+0.11463161109536
Wherein y in the expression represents the strength value of the axial eddy magnetic field and has the unit of 10-3T, x is the conductivity value of the tested metal piece and has the unit of 107S/m；
And by adopting a polynomial root function roots, the conductivity of the tested metal piece can be obtained according to the measured eddy magnetic field.
4. The method of claim 3, wherein obtaining a mathematical representation of each component of magnetic induction in the region of the measurement system comprises:
step 1, adopting a cylindrical coordinate system, wherein the magnetic vector potential A only has a circumferential component, obtaining a function of a radial position r and an axial position z, and obtaining the magnetic vector potential A according to an electromagnetism equation satisfied by a variable separation method and a test system, wherein A is expressed as the series and form of a characteristic function:
wherein
J1Representing a class of first-order Bessel functions, Y1Representing a class two first order Bessel function, Ai、Bi、CiAnd DiIs an unknown coefficient, r is a circumferential radial position, and z is a circumferential axial position;
step 2, adopting an air domain between the exciting coil and the tested metal part, and adopting a function Y1Diverge, thus Bi0, according to the electromagnetic boundary conditions satisfied between different media of the test system, obtaining a magnetic vector potential analytic expression of an air domain between the exciting coil and the tested metal piece as follows:
wherein A isSExpressed as the magnetic vector potential of the source field, A, produced by the excitation coileRepresenting magnetic vector potential caused by eddy current inside a tested metal piece;
step 3, combining the acquired magnetic vector potential of the upper space region of the exciting coil according to the following calculation formula
Can obtain a region (z is more than or equal to 0 and less than or equal to z)1) An analytic mathematical expression of each component of the magnetic induction intensity:
wherein the characteristic value alphaiIs J1(αih) 0 true root, B0(r) and B0(z) represents the radial and axial magnetic fields, Δ B, respectively, of the region above the conductive 10 test piece under the influence of the excitation probe alone0(r) and. DELTA.B0(z) represents the radial and axial eddy magnetic fields, respectively, caused by induced eddy currents inside the test piece.
5. The conductivity testing system for performing the non-contact type metal material conductivity measuring method of any one of claims 1 to 4, comprising:
the excitation device is used for generating an excitation signal, processing the excitation signal and transmitting the processed excitation signal to the test probe for alternating current excitation;
the test probe is used for generating a magnetic field signal for detecting the surface of the tested metal piece, converting the magnetic field signal into a voltage signal and sending the voltage signal to the data processing module;
and the data processing module is used for analyzing the measurement signal fed back by the measurement probe and applying a prestored algorithm to obtain the conductivity value of the tested metal piece.
6. The conductivity testing system according to claim 5, wherein the data processing module comprises a signal acquisition processing unit, a data processing unit, a verification unit and a storage unit, and the storage unit stores a relational expression of the conductivity of the tested metal piece and the eddy current magnetic field and a step algorithm in advance;
the signal acquisition and processing unit is used for acquiring and amplifying the acquired measurement signal fed back by the test probe to acquire a required voltage signal;
the data processing unit is used for processing according to the acquired voltage signal and calling a step algorithm stored in the storage unit in advance to acquire an output conductivity value;
and the checking unit is used for trimming and verifying the acquired conductivity value and feeding back a checking result to the data processing unit.
7. The conductivity test system of claim 5, wherein the test probe comprises an excitation coil and a magnetic field sensor;
the excitation coil is used for generating a magnetic field signal for detecting the surface of the tested metal piece;
the magnetic field sensor is used for detecting a magnetic field signal above the metal test piece to be detected and converting the magnetic field signal into a voltage signal.
8. The conductivity test system according to claim 5, wherein the excitation means comprises a signal generator and a power amplifier connected to each other,
a signal generator for generating an excitation signal;
and the power amplifier is used for amplifying the excitation signal, and the output end of the power amplifier is connected with the excitation coil.
9. The conductivity test system according to claim 5, wherein the magnetic field sensor is separated from the exciting coil by an isolating layer, and a protective layer is disposed under the magnetic field sensor.
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