CN108051648B - A kind of material electromagnetic attributes measurement method based on DC potential and detection method of eddy - Google Patents

Abstract

A method for measuring electromagnetic properties of materials based on DC potential and eddy current detection methods. The experimental device of the method is composed of a DC potential method device and an eddy current detection method device; Apply constant current excitation to the test piece, collect the voltage signal with a nanovolt meter, and obtain the conductivity of the test piece through calculation; then apply excitation to the test piece through the excitation coil in the eddy current testing device, and then use the detection coil to detect the voltage signal; Since the voltage signal of the detection coil is related to the conductivity and magnetic permeability of the test piece, the eddy current detection signal can be inverted by the conjugate gradient method on the premise that the conductivity of the test piece is measured by the DC potentiometric method. The magnetic permeability of the material is obtained; compared with the traditional measurement method of the electrical conductivity and magnetic permeability of the test piece, the method of the present invention can achieve the purpose of simultaneously measuring the electrical conductivity and magnetic permeability of the magnetic material, and the excitation frequency is adjustable. application prospects.

Description

A Method for Measuring Electromagnetic Properties of Materials Based on DC Potential and Eddy Current Testing

technical field

The invention relates to the fields of electrical conductivity measurement and magnetic permeability measurement of magnetic materials based on electromagnetic methods, in particular to a method for measuring electromagnetic properties of materials based on DC potential and eddy current detection methods.

Background technique

Magnetic materials are one of the main pillar materials of modern industrial and agricultural production. The products of magnetic materials are indicators of a country's economic development, and their demand can roughly reflect the national living standards of a country. As a basic functional material, magnetic materials are used in all aspects of life. At present, magnetic materials are mainly used in telecommunications, motors, televisions, and computer storage devices. It has gradually become a key material to promote social development. Therefore, its electromagnetic The measurement of parameters is particularly important. At present, the measurement methods of the electrical conductivity of magnetic materials mainly include the DC potentiometric method and the AC bridge method, and the magnetic permeability measurement methods mainly include the impact galvanometer method, the fluxmeter method, the nuclear magnetic resonance method, and the Hall effect method.

DC potentiometric method is one of the most commonly used methods to measure the electrical conductivity of materials. It is widely used in plastic deformation detection, fatigue damage detection, macro crack detection and so on. The DC potentiometric method has the advantages of simple system construction, simple operation, high sensitivity and short measurement time, so it can accurately measure the conductivity of magnetic materials conveniently and quickly.

During eddy current testing, the coil does not need to be in direct contact with the object to be tested, and high-speed testing can be performed, which is easy to realize automation. In addition, the voltage signal of the coil detected in eddy current testing is related to the electrical conductivity and magnetic permeability of the tested material. After research, it is found that after the electrical conductivity of the material is measured by the DC potentiometric method, the magnetic permeability of the material can be obtained from the voltage signal of the eddy current detection coil by the inversion method of the conjugate gradient method, and finally the measurement of the magnetic material is achieved. The purpose of electrical conductivity and magnetic permeability.

Contents of the invention

In order to achieve the above-mentioned purpose of measuring the electrical conductivity and magnetic permeability of magnetic materials, the object of the present invention is to provide a method for measuring electromagnetic properties of materials based on DC potential and eddy current detection methods. device composition. The DC potentiometric device consists of a constant current source, a nanovoltmeter, a scanning platform, a data acquisition device and four probes, in which the constant current source is connected to the two probes (1) and (4), and a constant current is applied to them. For the electric current, the nanovoltmeter is connected to the two probes (2) and (3) to measure the voltage between them, and the data acquisition device is connected to the scanning platform and the nanovoltmeter. The eddy current detection method device is composed of a signal generator, a power amplifier, a lock-in amplifier, a data acquisition device, an excitation coil and a detection coil, wherein the signal generator is connected to the power amplifier and the lock-in amplifier, and the excitation coil is connected to the power amplifier. The coil is connected to the lock-in amplifier, and the data acquisition device is connected to the lock-in amplifier. A sinusoidal signal is applied to the excitation coil through a signal generator and a power amplifier, and then the voltage signal of the detection coil is collected by the lock-in amplifier. When implementing this method, first place the test piece on the scanning table, place four probes on the upper surface of the test piece, apply a constant current to two of the probes with a constant current source, and measure the remaining two probes with a nanovoltmeter. The voltage between two probes, the voltage signal collected by the data acquisition device, the current signal output by the constant current source and the size of the test piece can be calculated to obtain the conductivity of the test piece; then the excitation coil is given by the signal generator and power amplifier. Apply sinusoidal signal excitation, and then use the lock-in amplifier to collect the voltage signal of the detection coil; since the voltage signal of the detection coil is related to the conductivity and magnetic permeability of the test piece, the conductivity of the test piece measured by the DC potentiometric method Under the premise of the eddy current detection signal, the magnetic permeability of the material can be obtained through the inversion of the conjugate gradient method. Compared with the traditional measurement method of the electrical conductivity and magnetic permeability of the test piece, the method of the present invention can achieve the purpose of simultaneously measuring the electrical conductivity and magnetic permeability of the magnetic material, and the detection sensitivity of the inventive method is high, the excitation frequency is adjustable, and the detection The system is easy to build, mature and reliable, and has broad application prospects.

To achieve the above object, the present invention adopts the following technical solutions:

A method for measuring electromagnetic properties of materials based on DC potential and eddy current testing, comprising the steps of:

Step 1: Build the experimental device. The experimental device consists of a DC potentiometric device and an eddy current detection device. The DC potentiometric device consists of a constant current source, a nanovoltmeter, a scanning table, a data acquisition device, and four Probe composition, the four probes are respectively No. 1 probe, No. 2 probe, No. 3 probe and No. 4 probe, in which the constant current source is connected to No. 1 probe and No. 4 probe, and the Constant current, the nanovoltmeter is connected with No. 2 probe and No. 3 probe, and the voltage between them is measured, and the data acquisition device is connected with the scanning table and the nanovoltmeter; the eddy current detection method device is composed of a signal generator, a power amplifier, a lock Phase amplifier, data acquisition device, excitation coil and detection coil, in which the signal generator is connected to the power amplifier and lock-in amplifier, the excitation coil is connected to the power amplifier, the detection coil is connected to the lock-in amplifier, and the data acquisition device is connected to the lock-in amplifier. The amplifier is connected, and the excitation coil is given a sinusoidal signal excitation through a signal generator and a power amplifier, and then the voltage signal of the detection coil is collected by a lock-in amplifier;

Step 2: First process the test piece into a plate-shaped test piece whose length is greater than its thickness, and fix the processed plate-shaped test piece on the scanning table; Four probes, and ensure that the distance between the probes is greater than the width and thickness of the plate-shaped test piece; then use a constant current source to apply a constant current to probe No. 1 and probe No. 4, and at the same time use a nanovoltmeter Record the change of the voltage between No. 2 probe and No. 3 probe; finally use the data acquisition device to collect n sets of data and use the formula (1-1) to calculate the conductivity of the plate-shaped test piece;

In the formula: σ is the conductivity of the plate-shaped test piece, ρ is the resistivity of the plate-shaped test piece, I is the current output by the constant current source, S is the distance between No. 2 probe and No. 3 probe, U _i is the voltage between No. 2 probe and No. 3 probe collected by the data acquisition device for the ith time, W and H are the width and thickness of the plate-like specimen respectively, n is the number of data sets collected, and i represents the current data collection The group number of data collected by the device;

Step 3: First place the excitation coil and detection coil of the eddy current detection method above the plate-shaped test piece, and use the signal generator to generate a sinusoidal excitation signal with a preset frequency, amplify the sinusoidal excitation signal through a power amplifier and apply it to the excitation coil; Then use the data acquisition device to collect the voltage signal of the detection coil amplified by the lock-in amplifier. The calculation formula of the voltage signal V of the detection coil is shown in formula (1-2),

In the formula, J _e is the eddy current density in the plate-like specimen, E _s is the electric field intensity of the source current field, which are calculated by formula (1‐3) and formula (1‐4) respectively; I _p is the current flowing through the detection coil The current, cond. indicates the spatial area where the detection coil is located;

J _e ＝-jωσA _r (1-3)

where ω is the angular frequency of the sinusoidal excitation signal, σ is the conductivity of the plate-like specimen, and A _r is the vector magnetic potential related to the eddy current field;

Where σ is the electrical conductivity of the plate-like test piece, μ is the magnetic permeability of the plate-like test piece, A _s is the vector magnetic potential related to the excitation current in the excitation coil;

Step 4: The voltage signal V of the detection coil measured by the eddy current testing device in step 3 is related to the conductivity σ and magnetic permeability μ of the plate-shaped test piece, and the conductivity σ of the plate-shaped test piece can be determined by the Measured by the DC potentiometric method, the magnetic permeability μ of the plate-like specimen is obtained by inverting the voltage signal V of the detection coil by the conjugate gradient method.

Compared with the prior art, the present invention has the following advantages:

1) The present invention proposes a method for measuring electromagnetic properties of materials based on DC potential and eddy current detection. Compared with traditional measurement methods, the method of the present invention can simultaneously measure the electrical conductivity and magnetic permeability of magnetic materials;

2) Compared with the electrical conductivity and magnetic permeability measuring methods of traditional magnetic materials, the excitation frequency of the excitation coil of the inventive method is adjustable, especially when the magnetic characteristic parameters of ferromagnetic materials change with the excitation frequency, this method can measure Magnetic permeability characteristics of ferromagnetic materials at different frequencies; in addition, the detection sensitivity of the method of the invention is high, the experimental system is easy to build and easy to operate, and has wide application prospects.

Description of drawings

Fig. 1 is the schematic diagram of the connection of each component of the DC potentiometric system and the eddy current detection system used in the present invention;

Fig. 2 is a schematic diagram of the test piece used in the present invention and a schematic diagram of the positions of the excitation coil and the detection coil in the eddy current test.

Detailed ways

Below in conjunction with accompanying drawing and specific embodiment the present invention is described in further detail:

For the tested piece as shown in Figure 2, the detection steps of the method of the present invention are as follows: as shown in Figure 1, the experimental device used in the method is composed of a DC potentiometric device and an eddy current testing device. The DC potentiometric device consists of a constant current source, a nanovoltmeter, a scanning platform, a data acquisition device and four probes. Connect the constant current source to No. 1 probe and No. 4 probe according to the connection method shown in Figure 1. A constant current is applied to it, the nanovoltmeter is connected to No. 2 probe and No. 3 probe, and the voltage between them is measured, and the data acquisition device is connected to the scanning table and the nanovoltmeter. The eddy current detection method device is composed of a signal generator, a power amplifier, a lock-in amplifier, a data acquisition device, an excitation coil and a detection coil, wherein the signal generator is connected to the power amplifier and the lock-in amplifier, and the excitation coil is connected to the power amplifier. The coil is connected to the lock-in amplifier, and the data acquisition device is connected to the lock-in amplifier. A sinusoidal signal is applied to the excitation coil through a signal generator and a power amplifier, and then the voltage signal of the detection coil is collected by the lock-in amplifier.

When implementing this method, first place the test piece on the scanning table, place four probes on the upper surface of the test piece, apply a constant current to the No. 1 probe and No. 4 probe with a constant current source, and use nanometer The voltmeter measures the voltage between No. 2 probe and No. 3 probe, and the conductivity of the test piece can be calculated through the voltage signal collected by the data acquisition device, the current signal output by the constant current source and the size of the test piece; The signal generator and power amplifier apply sinusoidal signal excitation to the excitation coil, and then use the lock-in amplifier to collect the voltage signal of the detection coil; since the voltage signal of the detection coil is related to the conductivity and magnetic permeability of the test piece, so in On the premise of measuring the conductivity of the test piece by the DC potentiometric method, the magnetic permeability of the material can be obtained by inverting the eddy current detection signal through the conjugate gradient method. The present invention will be further described in detail below in conjunction with the specific embodiments shown in FIG. 1 and FIG. 2 .

A method for measuring electromagnetic properties of materials based on DC potential and eddy current testing, comprising the steps of:

Step 1: Build the experimental device. The experimental device consists of a DC potentiometric device and an eddy current detection device. The DC potentiometric device consists of a constant current source, a nanovoltmeter, a scanning table, a data acquisition device, and four Probe composition, the four probes are respectively No. 1 probe, No. 2 probe, No. 3 probe and No. 4 probe, in which the constant current source is connected to No. 1 probe and No. 4 probe, and the Constant current, the nanovoltmeter is connected with No. 2 probe and No. 3 probe, and the voltage between them is measured, and the data acquisition device is connected with the scanning table and the nanovoltmeter; the eddy current detection method device is composed of a signal generator, a power amplifier, a lock Phase amplifier, data acquisition device, excitation coil and detection coil, in which the signal generator is connected to the power amplifier and lock-in amplifier, the excitation coil is connected to the power amplifier, the detection coil is connected to the lock-in amplifier, and the data acquisition device is connected to the lock-in amplifier. The amplifier is connected, and the excitation coil is given a sinusoidal signal excitation through a signal generator and a power amplifier, and then the voltage signal of the detection coil is collected by a lock-in amplifier;

Step 2: First process the test piece into a plate-shaped test piece whose length is greater than its thickness, and fix the processed plate-shaped test piece on the scanning table; Four probes, and ensure that the distance between the probes is greater than the width and thickness of the plate-shaped test piece; then use a constant current source to apply a constant current to probe No. 1 and probe No. 4, and at the same time use a nanovoltmeter Record the change of the voltage between No. 2 probe and No. 3 probe; finally use the data acquisition device to collect n sets of data and use the formula (1-1) to calculate the conductivity of the plate-shaped test piece;

In the formula: σ is the conductivity of the plate-shaped test piece, ρ is the resistivity of the plate-shaped test piece, I is the current output by the constant current source, S is the distance between No. 2 probe and No. 3 probe, U _i is the voltage between No. 2 probe and No. 3 probe collected by the data acquisition device for the ith time, W and H are the width and thickness of the plate-like specimen respectively, n is the number of data sets collected, and i represents the current data collection The group number of data collected by the device;

Step 3: First place the excitation coil and detection coil of the eddy current detection method above the plate-shaped test piece, and use the signal generator to generate a sinusoidal excitation signal with a preset frequency, amplify the sinusoidal excitation signal through a power amplifier and apply it to the excitation coil; Then use the data acquisition device to collect the voltage signal of the detection coil amplified by the lock-in amplifier. The calculation formula of the voltage signal V of the detection coil is shown in formula (1-2),

In the formula, J _e is the eddy current density in the plate-shaped specimen, E _s is the electric field intensity of the source current field, which are calculated by formula (1‐3) and formula (1‐4) respectively; I _p is the current flowing through the detection coil The current, cond. indicates the spatial area where the detection coil is located;

J _e ＝-jωσA _r (1-3)

where ω is the angular frequency of the sinusoidal excitation signal, σ is the conductivity of the plate-like specimen, and A _r is the vector magnetic potential related to the eddy current field;

Where σ is the electrical conductivity of the plate-like test piece, μ is the magnetic permeability of the plate-like test piece, A _s is the vector magnetic potential related to the excitation current in the excitation coil;

Step 4: The voltage signal V of the detection coil measured by the eddy current testing device in step 3 is related to the conductivity σ and magnetic permeability μ of the plate-shaped test piece, and the conductivity σ of the plate-shaped test piece can be determined by the Measured by the DC potentiometric method, the magnetic permeability μ of the plate-like specimen is obtained by inverting the voltage signal V of the detection coil by the conjugate gradient method.

Claims (1)

1. a kind of material electromagnetic attributes measurement method based on DC potential and detection method of eddy, it is characterised in that: including as follows Step:

Step 1: building experimental provision, which is made of DC potential subtraction unit and EDDY CURRENT subtraction unit, direct current Position subtraction unit is made of constant-current source, nanovoltmeter, scan table, data acquisition device and four probes being arranged on scan table, and four A probe respectively is No. 1 probe, No. 2 probes, No. 3 probes and No. 4 probes, wherein constant-current source and No. 1 probe and No. 4 probes It is connected, applies constant current to it, nanovoltmeter is connected with No. 2 probes and No. 3 probes, measures the voltage between it, data acquisition Device is connected with scan table, nanovoltmeter；Eddy current detection method device is by signal generator, power amplifier, lock-in amplifier, number According to acquisition device, excitation coil and detection coil composition, wherein signal generator is connected with power amplifier and lock-in amplifier, Excitation coil is connected with power amplifier, and detection coil is connected with lock-in amplifier, data acquisition device and lock-in amplifier phase Even, sinusoidal signal excitation is applied to excitation coil by signal generator, power amplifier, then is acquired and is detected with lock-in amplifier The voltage signal of coil；

Step 2: test specimen being processed into the plate test coupon that length is greater than thickness first, and the plate test coupon processed is fixed On scan table；Four probes of dc-bit method are equidistantly fixed on the central axes of plate test coupon, and ensure probe and probe The distance between be greater than plate test coupon width and thickness；Then apply constant electricity to No. 1 probe and No. 4 probes with constant-current source It flows, while recording the variation of voltage between No. 2 probes and No. 3 probes with nanovoltmeter；Finally n group data are acquired with data acquisition device And the conductivity for obtaining plate test coupon is calculated with formula (1-1)；

In formula: σ is the conductivity of plate test coupon, and ρ is the resistivity of plate test coupon, and I is the electric current of constant-current source output, and S is No. 2 spies The distance between needle and No. 3 probes, U_iThe voltage between No. 2 probes and No. 3 probes acquired for data acquisition device i-th, W, H is respectively the width and thickness of plate test coupon, and n is the data group number of acquisition, and i indicates that Current data acquisition device acquires data Group number number；

Step 3: placing the excitation coil and detection coil of detection method of eddy first above plate test coupon, and utilize signal Device generates the sinusoidal excitation signal of predeterminated frequency, amplifies the sinusoidal excitation signal by power amplifier and is applied to excitation line Circle；Then line is detected by the voltage signal of the amplified detection coil of lock-in amplifier locking phase with data acquisition device acquisition Shown in the calculation formula such as formula (1-2) of the voltage signal V of circle,

J in formula_eFor the vortex density in plate test coupon, E_sFor the electric field strength of ource electric current field, respectively by formula (1-3) and formula (1-4) It is calculated；I_pFor the electric current for flowing through detection coil, cond. indicates area of space locating for detection coil；

J_e=-j ω σ A_r (1-3)

ω is the angular frequency of sinusoidal excitation signal in formula, and σ is the conductivity of plate test coupon, A_rIt is vector magnetic relevant to vortex field Position；

Wherein σ is the conductivity of plate test coupon, and μ is the magnetic conductivity of plate test coupon, A_sIt is related to the exciting current in excitation coil Vector magnetic potential；

Step 4: in step 3 by eddy current testing device measure detection coil voltage signal V and plate test coupon conductivityσ and Magnetic permeability μ is related, and the conductivityσ of plate test coupon can be measured by the dc-bit method in step 2, then the magnetic conductivity of plate test coupon μ is obtained by the voltage signal V to detection coil using conjugate gradient method inverting.