CN112666395B - Non-contact metal material conductivity measurement method and system - Google Patents
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Abstract
The disclosure provides a non-contact metal material conductivity measurement method, which comprises the following steps: measuring an eddy current magnetic field delta B 0 (z) corresponding to the tested metal piece, wherein the measuring system is of an axisymmetric structure or an equivalent axisymmetric structure; establishing a relation between an eddy current magnetic field and the conductivity of the tested metal piece; and obtaining the conductivity of the tested metal piece according to the relation between the eddy current magnetic field and the conductivity of the tested metal piece, which is measured by the measuring system. According to the invention, the eddy current magnetic field corresponding to the tested metal piece is tested by building the test system, and the relation between the built eddy current magnetic field and the conductivity of the tested metal piece is stored in advance to obtain the conductivity of the metal, 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. Thus, the method is essentially a more convenient, 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 material conductivity measurement method and system.
Background
The conventional metal conductivity measurement mostly adopts a method of applying current signals to two ends of a conductor and calculating to obtain the resistance of the conductor by measuring voltage signals of the two ends and utilizing ohm's law. Since the resistance is related to the length and cross-sectional area of the conductor in addition to the conductivity of the material, it is necessary to calculate the conductivity of the conductor based on the dimensions of the conductor and the boundary conditions under which the current signal is applied. The disadvantage of this calculation and measurement method is that it depends on the dimensions of the conductor and that a current signal must be fed to the conductor, which is a contact measurement. The measurement accuracy of the method is greatly influenced by the electrode contact mode and the conductivity level of the conductor, and particularly under the condition that the conductivity of the conductor to be measured is very high, the voltage signals generated by the applied current signals at the two ends of the conductor are very weak, so that the measurement error is larger.
Compared with the traditional metal conductivity measurement method analyzed before, the eddy current detection is based on the electromagnetic induction principle, and the current application mode is different between the two, but the detection of the eddy current in the conductor is also influenced by factors such as an electrode contact mode, and the like, so that 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 conductivity. Meanwhile, the coil serves as an intermediate physical link to convert a magnetic field signal influenced by eddy current into a voltage signal, namely the voltage signal contains a plurality of other non-useful signals except the conductivity of the measured material. This entails a lot of unnecessary disturbances and is influenced by the excitation current frequency and amplitude. Therefore, only completely getting rid of the constraint of the detection coil can the accurate non-contact measurement of the conductivity of the metal material be truly realized. On the other hand, if the relation between the eddy magnetic field and the metal conductivity is established purely by an experimental method, a very large sample database must be established, and the requirement on experimental equipment is very high. If the electromagnetic principle equation is simply adopted, the accurate mathematical relation expression of the two is established, and very complex mathematical derivation and calculation are involved.
Disclosure of Invention
The present disclosure provides a non-contact metal conductivity measurement method for the above problems.
In order to solve at least one of the above technical problems, the present disclosure proposes the following technical solutions:
In a first aspect, a method for measuring conductivity of a metal material in a non-contact manner is provided, including the following steps: s101, measuring an eddy current magnetic field delta B 0 (z) corresponding to a tested metal piece through a measuring system, wherein the measuring system is of an axisymmetric structure or an equivalent axisymmetric structure;
S102, the data processing module stores the established relation between the eddy current magnetic field in the corresponding measuring system and the conductivity of the tested metal piece;
S103, measuring an eddy current magnetic field delta B 0 (z) according to a measuring system, and combining a relation between the eddy current magnetic field and the conductivity of the tested metal piece to obtain the conductivity of the tested metal piece.
In some embodiments, the step of obtaining the eddy current magnetic field Δb 0 (z) comprises:
Before measurement, a source field B 0 (z) corresponding to a measurement probe is obtained, including: the corresponding measuring probes are independently placed in the space area, and no metal substances are ensured to be arranged around the measuring probes, and the output value of the magnetic field sensor is the source field B 0 (z);
In the measuring process, a measuring probe is placed on the surface of a 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 a source field and an eddy current magnetic field.
Subtracting the previously obtained source field B 0 (z) from the measured recorded value B (z) to obtain the eddy current magnetic field Δb 0 (z) corresponding to the metal piece under test.
In some embodiments, establishing a relation between the eddy current magnetic field and the electrical conductivity of the metal piece to be tested is used for analyzing the measurement signal fed back by the measurement probe and applying a pre-stored algorithm, and includes the following steps:
Acquiring mathematical expressions of components of the magnetic induction intensity in the area of the measurement system;
Performing modular operation by using eddy current magnetic fields corresponding to different metal materials according to a mathematical expression, and performing least square fitting on the obtained result to obtain an axial eddy current magnetic field and conductivity relation curve;
through curve fitting, the following relation expression of axial eddy magnetic field and conductivity is established:
y＝－0.01375098369612x2+0.24014968145481x+0.11463161109536
wherein, y represents the axial eddy current magnetic field intensity value, the unit is 10 -3 T, x represents the conductivity value of the tested metal piece, and the unit is 10 7 S/m;
The conductivity of the tested metal piece can be obtained according to the measured eddy magnetic field by adopting a polynomial root function roots.
In some embodiments, obtaining a mathematical expression of components of magnetic induction in a region of a measurement system comprises the steps of:
Step1, adopting a cylindrical coordinate system, wherein the magnetic vector potential A only has circumferential components, obtaining a function at a radial position r and an axial position z, and obtaining the magnetic vector potential A according to a variable separation method and an electromagnetic equation met by a test system, wherein the magnetic vector potential A is expressed as the series and the form of a characteristic function:
Wherein the method comprises the steps of J 1 represents a first-order Bessel function, Y 1 represents a second-order Bessel function, and A i、Bi、Ci and D i are unknown coefficients;
Step 2, an adopted air domain is arranged between the excitation coil and the tested metal piece, and a function Y 1 diverges, so that B i =0, and according to electromagnetic boundary conditions met between different media of the test system, a magnetic vector potential analysis expression of the air domain between the excitation coil and the tested metal piece is obtained:
wherein, A S is the magnetic vector of the source field generated by the exciting coil, and A e is the magnetic vector caused by the eddy current in the tested metal piece;
step 3, combining the acquired magnetic vector potential of the space region above the exciting coil according to the following calculation formula
The analytical expression of each component of the magnetic induction intensity at the region (0.ltoreq.z.ltoreq.z 1) can be obtained:
Wherein, eigenvalue α i J1(αi h) =0 is positive, B 0 (r) and B 0 (z) represent radial and axial magnetic fields of the area above the conductive test piece under the separate action of the exciting coil, and Δb 0 (r) and Δb 0 (z) represent radial and axial eddy current magnetic fields caused by eddy currents induced inside the test piece.
In a second aspect, a conductivity testing system is provided, for performing the above-mentioned non-contact metal conductivity measurement method, including:
The excitation device is used for generating excitation signals, processing and transmitting the excitation signals to the test probe;
The test probe is used for generating a magnetic field signal for detecting the surface of the 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 obtaining the conductivity value of the tested metal piece by applying a prestored solving algorithm.
In some embodiments, the test probe includes an excitation coil and a magnetic field sensor;
The exciting 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 tested metal test piece and converting the magnetic field signal into a voltage signal.
In some embodiments, the excitation device includes a signal generator and a power amplifier connected,
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 provided between the magnetic field sensor and the excitation coil for separation, and a protective layer is provided below the magnetic field sensor. Therefore, the protective layer can protect the magnetic sensor and ensure that a certain lifting height is kept with the surface of the tested metal piece.
The method has the beneficial effects that the eddy current magnetic field corresponding to the tested metal piece is tested by building the test system, and the relation between the eddy current magnetic field and the conductivity of the tested metal piece is called by combining the processing in the data processing module, so that the conductivity of the metal is obtained. The invention does not need to adopt equivalent comparison, and does not need to realize measurement by identifying the difference between the tested metal piece and the standard block. Thus, the method is essentially a more convenient, non-contact, direct measurement method.
In addition, in the technical solutions of the present disclosure, the technical solutions may be implemented by adopting conventional means in the art, which are not specifically described.
Drawings
In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the drawings that are required in the description of the embodiments or the prior art will be briefly described, and it is apparent that the drawings in the following description are some embodiments of the present disclosure, and other drawings may be obtained according to the drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a non-contact metal conductivity measurement method according to an embodiment of the present disclosure;
FIG. 2 is a schematic diagram of establishing a relationship between eddy current magnetic fields and 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 according to 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 view of a test probe provided in one embodiment of the present disclosure;
Fig. 6 is a schematic diagram of a fitted curve of a test probe provided in one embodiment of the present disclosure.
Detailed Description
In order to make the objects, technical solutions and advantages of the present disclosure more apparent, the present disclosure will be further described in detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are illustrative of some, but not all embodiments of the disclosure and are not intended to limit the disclosure. All other embodiments, which can be made by one of ordinary skill in the art without inventive effort, based on the embodiments in this disclosure are intended to be within the scope of this disclosure.
It should be noted that the terms "comprises" and "comprising," along with 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 or inherent to such process, method, article, or apparatus, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
Example 1:
Referring to fig. 1 of the specification, there is shown a non-contact metal material conductivity measurement method according to an embodiment of the present application, which may include the following steps:
S101: measuring an eddy current magnetic field delta B 0 (z) corresponding to the tested metal piece, wherein the measuring system is of an axisymmetric structure and comprises an excitation probe and the tested metal piece;
S102: establishing a relation between an eddy current magnetic field and the conductivity of the tested metal piece;
S103: and obtaining the conductivity of the tested metal piece according to the relation between the eddy current magnetic field and the conductivity of the tested metal piece, which is measured by the measuring system.
Specifically, the step of obtaining the eddy current magnetic field Δb 0 (z) includes:
S301: before measurement, source field B 0 (z) corresponding to the type of measuring probe is obtained in advance;
In an alternative embodiment, the corresponding measurement probe is placed in the spatial region alone and ensures that there is no metallic material around, at which time the magnetic field sensor output value, i.e. source field B 0 (z), is located.
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 is recorded;
Specifically, in actual measurement, the magnetic field sensor obtains a spatial magnetic induction intensity value, that is, the sum of the source field B 0 (z) and the eddy current magnetic field Δb 0 (z), and the output value of the magnetic field sensor is the sum of the source field and the eddy current magnetic field B (z).
From this, it is known that the eddy current magnetic field Δb 0 (z) corresponding to the metal material can be obtained by subtracting the previously obtained source field B 0 (z) from the measurement recorded value B (z).
In an alternative embodiment, the source field B 0 (z) is also different in source field values at different locations, in addition to being affected by the excitation coil parameters. Thus, assuming that the magnetic field measurement location is unchanged, i.e., the magnetic field sensor is fixed at some relatively constant position of the excitation coil, the source field B 0 (z) is unchanged for the same type of excitation probe. And for axial eddy current magnetic field Δb 0 (z), it is also related to the metal conductivity of the metal piece under test, in addition to being affected by the spatial position. Thus, for metals having a relative permeability of typically 1, a changing relationship between the electrical conductivity of the metal piece under test and the axial eddy current magnetic field ΔB 0 (z) can be established.
In an alternative embodiment, to avoid possible slight differences in conductivity at different locations of the metal, if the measured object is the conductivity of the entire metal material, multiple measurements at different locations may be used to average the eddy current magnetic fields.
Because eddy current is a comprehensive effect of the action of the exciting coil on the metal surface in the traditional eddy current implementation conductivity measurement method, adverse influence factors are many. Therefore, the measuring method is not influenced by a source field, meanwhile, the influence of unstable factors such as geometric errors of a detection probe and excitation current parameters is avoided, and the measuring accuracy and stability are improved to a certain extent.
In an alternative embodiment, establishing a relation between the eddy current magnetic field and the electrical conductivity of the metal piece to be tested is used for analyzing the measurement signal fed back by the measurement probe and applying a pre-stored algorithm, and includes the following steps:
Acquiring mathematical expressions of components of the magnetic induction intensity in the area of the measurement system; in this embodiment, a mathematical expression of an axial eddy magnetic field and conductivity is adopted, or a mathematical expression of a radial eddy magnetic field and conductivity is also adopted;
Performing modular operation by using eddy current magnetic fields corresponding to different metal materials according to a mathematical expression, and performing least square fitting on the obtained result to obtain an axial eddy current magnetic field and conductivity relation curve;
through curve fitting, the following relation expression of axial eddy magnetic field and conductivity is established:
y＝－0.01375098369612x2+0.24014968145481x+0.11463161109536
wherein, y represents the axial eddy current magnetic field intensity value, the unit is 10 -3 T, x represents the conductivity value of the tested metal piece, and the unit is 10 7 S/m;
The conductivity of the tested metal piece can be obtained according to the measured eddy magnetic field by adopting a polynomial root function roots.
As a preferable mode in this embodiment: establishing a relation between an eddy current magnetic field and the conductivity of a metal piece to be tested, as shown in fig. 2, and constructing a test schematic diagram by combining a test system, wherein the test system comprises a test probe and the metal piece to be tested, the test probe comprises a magnetic field sensor and an exciting coil, and the established relation comprises the following steps:
a cylindrical coordinate system is adopted, and at the moment, the magnetic vector A only has a circumferential component, and a function at a radial position r and an axial position z is obtained; because the measurement system satisfies the following electromagnetic equation:
where k 2 =jωμσ, σ is the electrical conductivity of the metal piece being tested.
Let the solution area be finite in the radial direction (0. Ltoreq.r.ltoreq.h) and apply the Dirichlet boundary condition at r=h. According to the variable separation method, the general solution of equation (1-1) has the form:
Wherein the method comprises the steps of J 1 denotes a class of first-order Bessel functions, Y 1 denotes a class of first-order Bessel functions, A i、Bi、Ci and D i are unknown coefficients.
Thus, the magnetic vector potential A obtained by the formula (1-2) is expressed as the number of steps and form of the characteristic function.
In an alternative embodiment, the air field used between the excitation coil and the metal piece under test is the function Y 1 diverges, so B i = 0. Considering that the conductivity of the air domain is 0, this region magnetic sagittal potential (k=0) has the following form:
in addition, in order to ensure that the magnetic vector potential of the region 1 is limited, as shown in the figure, the region 1 refers to the inside of the metal piece to be tested, and D i =0 in the formula (1-2) is set. Thus, the magnetic sagittal 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 yield two unknown coefficients
The coefficient C 0i is related only to the parameters of the excitation coil and is independent of the physical properties of the test piece, called the source field coefficient, and has the following form:
Where i=n cI/[(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 formula χ (αr 1,αr2) is calculated using 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 S is the magnetic vector of the source field generated by the exciting coil, and A e is the magnetic vector caused by eddy currents in the tested metal piece.
In an alternative embodiment, the following calculation formula is used
The analytical expression of each component of the magnetic induction intensity at the region (0.ltoreq.z.ltoreq.z 1) can be obtained:
Wherein the eigenvalue α i is the positive root of J 1(αi h) =0. B 0 (r) and B 0 (z) represent the radial and axial magnetic fields, respectively, of the region above the conductive test piece under the action of the excitation coil alone. Δb 0 (r) and Δb 0 (z) represent the radial and axial eddy current magnetic fields, respectively, caused by induced eddy currents inside the test piece.
Specifically, the symbols of the formulas in the present application are shown in the following table 1:
TABLE 1
Specifically, according to the obtained mathematical expression of the metal conductivity and the axial vortex field, the numerical value of the axial vortex field is calculated under the typical common metal condition, and the obtained vortex field is in a complex form, so that the modular operation is needed. As the calculations shown in table 2, it can be found that the axial source field remains unchanged all the time and that the metal conductivity only changes the magnitude of the vortex field.
TABLE 2 magnetic field calculation results for different metallic materials
Based on the numerical values obtained by calculation, a least square method is used for fitting to obtain a relation curve of axial eddy magnetic field and conductivity, as shown in a curve of an attached drawing figure 6 of the specification, the abscissa of figure 6 is the conductivity of metal materials, the unit is 107S/m, and the ordinate is the axial eddy magnetic field value, and the unit is 10-3T.
Through curve fitting, the following relation expression of axial eddy magnetic field and conductivity is established:
y＝-0.01375098369612x2+0.24014968145481x+0.11463161109536
In the expression, y represents the axial eddy current magnetic field intensity value, the unit is 10 -3 T, and x represents the conductivity value of the tested metal piece, and the unit is 10 7 S/m.
In an alternative embodiment, the polynomial root function roots in Matlab software is used to obtain the conductivity value of the metal part under test based on the measured eddy current magnetic field. Since a quadratic polynomial fit is used, there are typically two roots using the roots function, and typically a smaller value is taken as the conductivity value of the metal part being tested.
By way of example, using metallic chromium as an example, the accuracy of the conductivity obtained by the above measurement method was verified. The conductivity of the chromium metal was 3.8X10 7 S/m, and the calculated value of the formula (1-11) was used as the actual measured eddy current magnetic field value, and the mode size was 0.82921410671475X 10 -3 T. According to the eddy current magnetic field value, the corresponding material conductivity is 13.65991957035989 multiplied by 10 7 S/m and 3.80426239376905 multiplied by 10 7 S/m by combining the established relation expression of the axial eddy current magnetic field and the conductivity and the root function. The rule is followed by equation root, at which time the material conductivity should be 3.80426239376905 X10 7 S/m. Therefore, the metal conductivity error obtained by the method is 0.11%, and the requirement of measurement accuracy is completely met.
In an alternative embodiment, a temperature sensor is arranged in the test system for compensating the influence of temperature on the conductivity of the material. Since the conductivity of metals is significantly affected by temperature, and the conductivity of materials is generally given as a value measured at a temperature of 20 ℃, it is necessary to arrange a temperature sensor in the measuring system to compensate for the effect of temperature on the conductivity of the materials in order to accurately evaluate the conductivity of the metal piece under test.
The invention can also be applied to the extended application occasions, namely judging the material quality of the metal, wherein the conductivity is an inherent attribute of the metal, and the material quality of the tested metal piece can be determined by a lookup table method according to the measured conductivity value. Of course, the conductivity of a metal material should be in a range and not considered a fixed value. Therefore, the conductivity range of each metal material should be predetermined.
In this embodiment, the eddy current magnetic field Δb 0 (z) corresponding to the metal piece to be tested is measured, and the electrical conductivity is obtained by establishing a relation between the eddy current magnetic field and the electrical conductivity of the metal piece to be tested. Therefore, the method is a more convenient and non-contact direct measurement method.
Example 2:
referring to fig. 3-5 of the drawings, there is shown a test system for performing any of the above test methods according to an embodiment of the present application, including:
the excitation device is used for generating excitation signals, processing and transmitting the excitation signals 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 transmitting the voltage signal to the data processing module;
And the data processing module is used for analyzing the measurement signals fed back by the test probe and obtaining the conductivity value of the tested metal piece by applying a prestored solving algorithm.
The test probe comprises an excitation coil and a magnetic field sensor; the exciting 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 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 checking unit and a storage unit, wherein the storage unit stores the relation between the conductivity of the tested metal piece and the eddy magnetic field and a step algorithm in advance;
the signal acquisition processing unit is used for acquiring and amplifying the acquired measurement signals fed back by the test probe to acquire required voltage signals;
the data processing unit is used for processing according to the acquired voltage signals and calling a step algorithm stored in the storage unit in advance to acquire an output conductivity value;
and the verification unit is used for trimming and verifying the acquired conductivity value and feeding back a verification result to the data processing unit.
As shown in fig. 3, the excitation device comprises a signal generator connected to generate an excitation signal and a power amplifier for amplifying the excitation signal, wherein the output end of the power amplifier is connected to an excitation coil. The data acquisition in the figure is the data processing module in the application, the data processing module processes the measurement signal fed back by the test probe and sends the measurement signal to the computer for display, the data processing module comprises signal amplification, signal processing and data processing units in the figure, the signal acquisition processing units in the application are the signal processing and signal amplification indicated in the figure 3, the data processing units in the application are the data processing indicated in the figure 3, specifically, the weak signal measured by the test probe is firstly subjected to signal amplification processing and is subjected to a signal processing circuit to obtain a voltage signal which can be directly processed, and then the voltage signal is processed by means of data processing such as a singlechip and the like, and the conductivity value of the tested piece is obtained according to a pre-stored 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 can use a model YB1602 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 together in the shell 3 of the test probe, the magnetic field sensor 2 is placed at the axial position of the coil frame 4, the vertical distance between the magnetic field sensor 2 and the exciting coil 1 is kept at a fixed value, and the isolating 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 lead 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 excitation coil 1 is formed by winding enamelled wires, 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 3mm.
The magnetic field sensor 2 may employ a high-sensitivity magnetic sensor TMR2905 based on tunnel magnetoresistance technology, which has a size 3mm x 3mm x 0.75mm. When installed, the magnetic field sensor 2 needs to place its sensitive direction in the measurement direction of the measured magnetic field.
Specifically, an isolation layer 5 is provided between the magnetic field sensor 2 and the exciting coil 1 to separate, and a protection layer 8 is provided under the magnetic field sensor 2. The protective layer 8 can protect the magnetic sensor 2 and ensure that a certain lifting height is kept from the surface of the tested metal piece. Wherein the isolating layer 5 and the protecting layer 8 are made of non-conductive and non-magnetic materials.
Specifically, when in use, the test probe is arranged above the tested metal piece, firstly the output end of the signal generator is connected with the input end wire of the power amplifier, then the output end of the power amplifier is connected with the exciting coil wire of the test probe, and the periodic sine signal generated by the signal generator is amplified by the power amplifier and then is input to the exciting coil of the test probe for driving the exciting coil of the test probe to generate an alternating magnetic field required by the detection of the tested metal piece.
It should be noted that, in the system provided in the foregoing embodiment, when implementing the functions thereof, only the division of the foregoing functional modules is used as an example, in practical application, the foregoing functional allocation may be implemented by different functional modules, that is, the internal structure of the device is divided into different functional modules, so as to implement all or part of the functions described above. In addition, the system and the method embodiments provided in the foregoing embodiments belong to the same concept, and specific implementation processes of the system and the method embodiments are detailed in the method embodiments and are not repeated herein.
It should be noted that: the embodiment sequence of the present disclosure is only for description, and does not represent the advantages and disadvantages of the embodiments. And the foregoing description has described specific embodiments of this specification. Other embodiments are within the scope of the following claims. In some cases, the actions or steps recited in the claims can 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 are also possible or may be advantageous.
In this specification, each embodiment is described in a progressive manner, and identical and similar parts of each embodiment are all referred to each other, and each embodiment mainly describes differences from other embodiments. In particular, for the device embodiments, since they are substantially similar to the method embodiments, the description is relatively simple, and reference is made to the description of the method embodiments in part.
It will be appreciated by those of ordinary skill in the art that all or part of the steps of implementing the above embodiments may be implemented by hardware, or may be implemented by a program to instruct related hardware, and the program may be stored in a computer readable storage medium, where the storage medium may be a read-only memory, a magnetic disk or an optical disk, etc.
The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (6)
1. The non-contact metal material conductivity measurement method is characterized by comprising the following steps:
S101, measuring an eddy current magnetic field corresponding to the tested metal piece through a measuring system Wherein the measurement system is of an axisymmetric structure or an equivalent axisymmetric structure, and eddy magnetic field/>, is obtainedComprises the steps of:
Before measurement, obtaining a source field corresponding to a measurement probe Comprising: the corresponding measuring probes are independently placed in the space area, and no metal substances are ensured to be arranged around the measuring probes, and the output value of the magnetic field sensor is the source field/>, at the moment；
In the measuring process, a measuring probe is placed on the surface of a tested metal piece, the output value of the magnetic field sensor is recorded, and the output value of the magnetic field sensor is the sum of a source field and an eddy current magnetic field;
Record the measured valuesSubtracting the previously obtained source field/>Obtaining the eddy current magnetic field corresponding to the tested metal piece；
S102, a data processing module stores a relation between an eddy current magnetic field and the conductivity of a tested metal piece in a corresponding established measurement system, wherein the relation between the eddy current magnetic field and the conductivity of the tested metal piece is used for analyzing a measurement signal fed back by a measurement probe and applying a prestored algorithm, and the method comprises the following steps of:
Acquiring mathematical expressions of components of the magnetic induction intensity in the area of the measurement system;
Performing modular operation by using eddy current magnetic fields corresponding to different metal materials according to a mathematical expression, and performing least square fitting on the obtained result to obtain an axial eddy current magnetic field and conductivity relation curve;
through curve fitting, the following relation expression of axial eddy magnetic field and conductivity is established:
wherein in the expression Represents the axial eddy current magnetic field intensity value with the unit of/>，/>The conductivity value expressed as the tested metal piece is expressed as/>S/m；
A polynomial root function roots is adopted, and the conductivity of the tested metal piece is obtained according to the measured eddy magnetic field;
s103, measuring an eddy current magnetic field according to a measuring system Combining the relation between the eddy current magnetic field and the conductivity of the tested metal piece to obtain the conductivity of the tested metal piece;
Obtaining a mathematical expression of each component of the magnetic induction in the region of the measurement system, comprising the steps of:
Step 1, adopting a cylindrical coordinate system, wherein the magnetic vector potential is With only circumferential components, giving radial position/>And axial position/>And obtaining magnetic vector/> according to a variable separation method and an electromagnetic equation satisfied by a test system，/>Expressed as a series and form of feature functions:
Wherein the method comprises the steps of ，/>Representing a class of first order Bessel functions,/>Representing class II first order Bessel functions,/>、/>、/>And/>Is of unknown coefficient,/>Is the circumferential radial position,/>Is the circumferential axial position;
Step 2, an adopted air domain and a function are adopted between the exciting coil and the tested metal piece Diverges, thus/>According to electromagnetic boundary conditions satisfied among different media of the test system, the magnetic vector potential analysis expression of the air domain between the exciting coil and the tested metal piece is obtained as follows:
wherein, Expressed as the magnetic sagittal potential of the source field generated by the excitation coil,/>Expressed as eddy currents in the metal part under test
Magnetic vector potential;
step 3, combining the acquired magnetic vector potential of the space region above the exciting coil according to the following calculation formula
The obtained region (0.ltoreq.2)≤/>) Analytical mathematical expression for each component of magnetic induction:
Wherein the characteristic value For/>Positive root of =0,/>And/>Represents the radial and axial magnetic fields, respectively,/>, of the region above the conductive 10 test piece under the separate action of the excitation probeAnd/>Representing the radial and axial eddy current magnetic fields, respectively, caused by induced eddy currents within the test piece.
2. A conductivity testing system for performing the non-contact metal conductivity measurement method according to claim 1, comprising:
The excitation device is used for generating an excitation signal, processing and transmitting the 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 transmitting 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 obtaining the conductivity value of the tested metal piece by applying a prestored algorithm.
3. The conductivity test system according to claim 2, wherein 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 stores a relation between the conductivity of the tested metal piece and the eddy magnetic field and a step algorithm in advance;
The signal acquisition processing unit is used for acquiring and amplifying the acquired measurement signals fed back by the test probe to acquire required voltage signals;
The data processing unit is used for processing according to the acquired voltage signals and calling a step algorithm stored in the storage unit in advance to acquire an output conductivity value;
The verification unit is used for trimming and verifying the acquired conductivity value and feeding back a verification result to the data processing unit.
4. The conductivity test system of claim 2, wherein said test probe includes an excitation coil and a magnetic field sensor;
The exciting 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 tested metal test piece and converting the magnetic field signal into a voltage signal.
5. The conductivity test system according to claim 2, wherein the excitation means comprises a signal generator and a power amplifier connected,
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.
6. The conductivity test system according to claim 2, wherein a magnetic field sensor is provided between the excitation coil and the excitation coil
The isolating layers are separated, and a protective layer is arranged below the magnetic field sensor.
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