CN102445493B - Modulation multifrequency eddy current testing method - Google Patents

Abstract

The invention relates to a modulation multifrequency eddy current testing method, comprising the following steps: generate a frequency modulation excitation signal, amplify the frequency modulation excitation signal, drive an eddy current sensor, and respectively test a benchmark testing piece and an object to be tested; collect response signals of the eddy current sensor when testing the benchmark testing piece and the object to be tested, perform an FFT (Fast Fourier Transformation) transformation to the response signals of the eddy current sensor to obtain a frequency spectrum of the response signals of the eddy current sensor, and then analyze the frequency spectrum of the response signals of the eddy current sensor and respectively calculate total spectrogram energy, spectrogram center-of-gravity shift, spectrogram kurtosis and spectrogram skewness of each frequency spectrum of the response signals of the eddy current sensor; finally, perform threshold value judgment to the total spectrogram energy, spectrogram center-of-gravity shift, spectrogram kurtosis and spectrogram skewness of the frequency spectrum of the response signals of the eddy current sensor of the object to be tested and the frequency spectrum of the response signals of the eddy current sensor of the benchmark testing piece to judge whether the object to be tested has defects and the defect location or other parameters or not. The modulation multifrequency eddy current testing method can effectively reduce peak factors of the excitation signal and the response signal of an eddy current testing system and increase the testing speed.

Description

Modulation multifrequency eddy current testing method

Technical field

The present invention relates to multifrequency eddy current testing method, particularly a kind of modulation multifrequency eddy current testing method that a kind of field of non destructive testing adopts, be applicable to the interference inhibition of testing process or the multiparameter of checked object and detect.

Background technology

Eddy detection technology is safeguarded at nuclear power station steam pipe, Aero-Space equipment maintenance, advantages such as the industries such as pipe, line, bar production have vital role, and that eddy detection technology has is contactless, easily realize robotization, detectability is strong and obtained application more and more widely.

Conventional eddy current detection method adopts single frequency sinusoidal signal excitation eddy current sensor, and the quantity of information of obtaining is limited, is difficult to adapt to more and more higher Non-Destructive Testing demand.1970, first American scientist Libby H L proposed multifrequency eddy current testing method, in order to the multiparameter that realizes interference inhibition in EDDY CURRENT process and checked object, detected.Multifrequency eddy current testing method adopts several different frequency sinusoidal signal excitation eddy current sensors, utilizes under different frequency, and parameter has the different principles that change to realize.The testing result obtaining under different frequency, carries out analyzing and processing by certain method, extracts multiple desired parameters, or suppresses undesired signal.

The pumping signal mode that existing multifrequency eddy current testing method adopts has two kinds, and the first is synchronous synthesis mode, as shown in Fig. 1 a and Fig. 1 b; The second is asynchronous synthesis mode, as shown in Fig. 2 a and Fig. 2 b.

In the multifrequency eddy current testing method of synchronous synthetic energisation mode, pumping signal adopts the sinusoidal signal stack of multiple frequency components, and the peak value of pumping signal is higher, and peak factor is larger, to the voltage range of driving circuit and rear end amplifying circuit, requires wider.

In the multifrequency eddy current testing method of asynchronous synthetic energisation mode, pumping signal adopts the sinusoidal signal of multiple frequency components to drive successively eddy current sensor, needs constantly to switch exciting signal frequency, and detection time is longer.

Summary of the invention

Technical matters to be solved by this invention is, for the deficiency of existing multifrequency eddy current testing method, provides a kind of modulation multifrequency eddy current testing method, and it can effectively reduce the peak factor of eddy detection system pumping signal and response signal, improves detection speed.

For solving the problems of the technologies described above, the technical solution adopted in the present invention is: a kind of modulation multifrequency eddy current testing method, it comprises the following steps:

The first step, preparation benchmark test specimen;

Second step, generation one fm exciter signal, and after this fm exciter signal is amplified, drive eddy current sensor, benchmark test specimen is detected;

The response signal of eddy current sensor when the 3rd step, acquisition testing benchmark test specimen, and this eddy current sensor response signal is carried out to FFT conversion obtain benchmark test specimen eddy current sensor response signal frequency spectrum, obtain detecting required benchmark response signal frequency spectrum;

The 4th step, benchmark response signal frequency spectrum is analyzed, and calculated spectrogram gross energy, spectrogram centre-of gravity shift, spectrogram kurtosis, the spectrogram degree of bias of this benchmark response signal frequency spectrum;

The 5th step, adopt aforesaid fm exciter signal, and after this fm exciter signal is amplified as described in second step, drive aforementioned eddy current sensor, checked object is detected;

The response signal of eddy current sensor when the 6th step, acquisition testing checked object, and this eddy current sensor response signal is carried out to FFT conversion obtain checked object eddy current sensor response signal frequency spectrum;

The 7th step, checked object eddy current sensor response signal frequency spectrum is analyzed, and calculated spectrogram gross energy, spectrogram centre-of gravity shift, spectrogram kurtosis, the spectrogram degree of bias of this checked object eddy current sensor response signal frequency spectrum;

The 8th step, according to the spectrogram gross energy of benchmark response signal frequency spectrum, spectrogram centre-of gravity shift, spectrogram kurtosis, the spectrogram degree of bias, spectrogram gross energy, spectrogram centre-of gravity shift, spectrogram kurtosis, the spectrogram degree of bias of the above-mentioned checked object eddy current sensor response signal frequency spectrum detecting are carried out to threshold decision: if the spectrogram gross energy of the checked object eddy current sensor response signal frequency spectrum detecting is greater than the spectrogram gross energy of benchmark response signal frequency spectrum, prove to exist on checked object defect; If the spectrogram centre-of gravity shift of the checked object eddy current sensor response signal frequency spectrum detecting is greater than the spectrogram centre-of gravity shift of benchmark response signal frequency spectrum, or the spectrogram kurtosis of the checked object eddy current sensor response signal frequency spectrum detecting is less than the spectrogram kurtosis of benchmark response signal frequency spectrum, or the spectrogram degree of bias of the checked object eddy current sensor response signal frequency spectrum detecting is greater than the spectrogram degree of bias of benchmark response signal frequency spectrum, proves that on checked object, defect is surface imperfection; If the spectrogram centre-of gravity shift of the checked object eddy current sensor response signal frequency spectrum detecting is less than the spectrogram centre-of gravity shift of benchmark response signal frequency spectrum, or the spectrogram kurtosis of the checked object eddy current sensor response signal frequency spectrum detecting is greater than the spectrogram kurtosis of benchmark response signal frequency spectrum, or the spectrogram degree of bias of the checked object eddy current sensor response signal frequency spectrum detecting is less than the spectrogram degree of bias of benchmark response signal frequency spectrum, proves that on checked object, defect is inherent vice.

This fm exciter signal is linear frequency modulation pumping signal.The optimized frequency scope of this linear frequency modulation pumping signal is 1kHz～20kHz; Time span is unsuitable long, guarantees that FFT requires preferably to count simultaneously, elects 4096us as.

The sample frequency that gathers eddy current sensor response signal is 5-10 times of fm exciter signal highest frequency.

Compared with the conventional method, the beneficial effect that the present invention has is: the present invention adopts the pumping signal of modulation multifrequency mode as eddy detection system, the discrete spectrum of conventional multifrequency Eddy method response signal frequency domain is become to continuous spectrum, by calculating the characteristic quantity of spectrogram, and then realize disturbing and suppress or multiparameter detection.With synchronize synthesis mode multifrequency eddy current testing method and compare, advantage of the present invention is: adopt a FM signal, effectively reduce the peak factor of multi-frequency excitation signal and eddy current response signal, be conducive to the design of eddy current sensor pumping signal driving circuit and response signal rear end amplifying circuit.Compare with asynchronous synthesis mode multifrequency eddy current testing method, advantage of the present invention is: FM signal is the pumping signal of a continuous change frequency in short-term, without switching, has reduced detection time, thereby has improved detection defect speed.

Accompanying drawing explanation

Below in conjunction with drawings and Examples, invention is described in further detail; But modulation multifrequency eddy current testing method of the present invention is not limited to embodiment.

The time domain waveform of the existing synchronous synthesis mode multi-frequency excitation signal of Fig. 1 a;

The spectrogram of the existing synchronous synthesis mode multi-frequency excitation signal of Fig. 1 b;

The time domain waveform of the existing asynchronous synthesis mode multi-frequency excitation signal of Fig. 2 a;

The spectrogram of the existing asynchronous synthesis mode multi-frequency excitation signal of Fig. 2 b;

The workflow diagram of Fig. 3 modulation multifrequency eddy current testing method of the present invention;

The benchmark test specimen adopting in Fig. 4 embodiment of the present invention;

Fig. 5 a is the linear FM signal figure that the embodiment of the present invention adopts;

Fig. 5 b is the linear FM signal spectrogram that the embodiment of the present invention adopts;

Fig. 6 a is the eddy current sensor response signal that embodiment of the present invention detection reference test specimen obtains;

Fig. 6 b is the response signal spectrogram of embodiment of the present invention detection reference test specimen eddy current sensor;

Fig. 7 is the checked object adopting in the embodiment of the present invention;

Fig. 8 is the eddy current sensor response signal spectrogram while detecting checked object surface imperfection in the embodiment of the present invention;

Fig. 9 is the eddy current sensor response signal spectrogram while detecting checked object inherent vice in the embodiment of the present invention;

Figure 10 is the spectrogram gross energy obtaining in the embodiment of the present invention;

Figure 11 is the spectrogram centre-of gravity shift obtaining in the embodiment of the present invention;

Figure 12 is the spectrogram kurtosis obtaining in the embodiment of the present invention;

Figure 13 is the spectrogram degree of bias obtaining in the embodiment of the present invention.

Embodiment

Modulation multifrequency eddy current testing method workflow of the present invention as shown in Figure 3.

Refer to Fig. 3 to Figure 11 below, with the defects detection of aluminum flat board be categorized as example and illustrate modulation multifrequency eddy current testing method workflow of the present invention:

The first step, preparation benchmark test specimen, this benchmark test specimen is flawless test specimen: in the present embodiment, as shown in Figure 4, this benchmark test specimen adopts flawless aluminum flat board 1, and it is of a size of 200mm × 200mm × 2mm.

Second step, generation one fm exciter signal, and after this fm exciter signal is amplified, drive eddy current sensor, benchmark test specimen is detected: in the present embodiment, what this fm exciter signal adopted is linear frequency modulation pumping signal 5, as shown in Figure 5 a, horizontal ordinate represents the time, unit is us, and ordinate represents amplitude, and unit is V.This linear frequency modulation pumping signal is the linear FM signal with rectangle envelope, and its time-domain expression is

$S\left(t\right)=A\·\mathrm{rect}(t/T)\·\cos \left[2\mathrm{\π}(f_{0}t+\frac{1}{2}{\mathrm{Kt}}^2)\right]$

In formula: S (t) is linear FM signal, the amplitude that A is linear FM signal, t is time variable, the time width that T is linear FM signal, f ₀for the centre frequency of linear FM signal, K is chirped slope, and rect (t/T) is rectangular function.

The frequency range of this linear frequency modulation pumping signal 5 is 1kHz～20kHz, and time span is 4096us.Linear frequency modulation pumping signal 5 is carried out to FFT conversion and can obtain linear FM signal frequency spectrum 6, as shown in Figure 5 b, horizontal ordinate represents frequency, and unit is kHz, and ordinate represents FFT amplitude, without unit.After this linear frequency modulation pumping signal 5 is amplified, drive eddy current sensor, flawless aluminum flat board 1 is detected.

The 3rd step, according to time domain sampling theorem, determine sample frequency.Generally, sample frequency be fm exciter signal highest frequency 5-10 doubly.The response signal of eddy current sensor during acquisition testing benchmark test specimen, and this eddy current sensor response signal is carried out to FFT conversion obtain benchmark test specimen eddy current sensor response signal frequency spectrum, obtain detecting required benchmark response signal frequency spectrum.Fig. 6 a is the detection reference test specimen collecting in the present embodiment, i.e. the dull and stereotyped 1 o'clock eddy current sensor response signal 7 of flawless aluminum, and its horizontal ordinate represents the time, and unit is us, and ordinate represents amplitude, and unit is mV.By finding out in figure, the frequency range of eddy current sensor response signal 7 and time span identical with linear frequency modulation pumping signal 5.This eddy current sensor response signal 7 is carried out to FFT conversion and can obtain benchmark test specimen eddy current sensor response signal frequency spectrum 8, as shown in Figure 6 b, horizontal ordinate represents frequency, and unit is kHz, and ordinate represents FFT amplitude, without unit.

The 4th step, benchmark response signal frequency spectrum is analyzed, and calculated spectrogram gross energy, spectrogram centre-of gravity shift, spectrogram kurtosis, the spectrogram degree of bias of this benchmark response signal frequency spectrum.Each characteristic quantity calculating formula is as follows:

Spectrogram gross energy is

$\mathrm{Energy}=\frac{1}{N_2-{\mathrm{<figure-callout\; id="1"\; label="N"\; filenames="HDA0000028150910000012.png,HDA0000028150910000041.png"\; state="\{\{state\}\}">N</figure-callout>}}_1+1}\underset{k=N_1}{\overset{N_2}{\mathrm{\&Sigma;}}}X{\left(k\right)}^2$

In formula: Energy is spectrogram gross energy result of calculation, the Fourier transform that X (k) is detection signal, the horizontal ordinate variable that k is Fourier transform, N ₁for Fourier transform point horizontal ordinate corresponding to linear frequency modulation initial frequency, N ₂for linear frequency modulation stops Fourier transform point horizontal ordinate corresponding to frequency.In the present embodiment, calculate the spectrogram gross energy of this benchmark response signal frequency spectrum, thereby while obtaining test specimen zero defect, the i.e. spectrogram gross energy 16 of this benchmark response signal frequency spectrum, as shown in figure 10, horizontal ordinate represents defect, without unit, ordinate represents spectrogram gross energy, without unit.

Spectrogram centre-of gravity shift is

$\mathrm{Barycenter}=\frac{\underset{k=N_1}{\overset{{\mathrm{<figure-callout\; id="2"\; label="N"\; filenames="HDA0000028150910000053.png,HDA0000028150910000072.png"\; state="\{\{state\}\}">N</figure-callout>}}_2}{\mathrm{\&Sigma;}}}\mathrm{kX}\left(k\right)}{\underset{k=N_1}{\overset{N_2}{\mathrm{\&Sigma;}}}X\left(k\right)}$

In formula: Barycenter is spectrogram centre-of gravity shift result of calculation, the Fourier transform that X (k) is detection signal, the horizontal ordinate variable that k is Fourier transform, N ₁for Fourier transform point horizontal ordinate corresponding to linear frequency modulation initial frequency, N ₂for linear frequency modulation stops Fourier transform point horizontal ordinate corresponding to frequency.In the present embodiment, calculate the spectrogram centre-of gravity shift of this benchmark response signal frequency spectrum, thereby while obtaining test specimen zero defect, the i.e. spectrogram centre-of gravity shift 19 of this benchmark response signal frequency spectrum, as shown in figure 11, horizontal ordinate represents defect, without unit, ordinate represents spectrogram barycentre offset, without unit.

Spectrogram kurtosis is

$\mathrm{Kurtosis}=\frac{1}{N_2-{\mathrm{<figure-callout\; id="1"\; label="N"\; filenames="HDA0000028150910000012.png,HDA0000028150910000041.png"\; state="\{\{state\}\}">N</figure-callout>}}_1+1}\underset{k=N_1}{\overset{N_2}{\mathrm{\&Sigma;}}}{[X\left(k\right)-\stackrel{\&OverBar;}{X}]}^4/{\mathrm{<figure-callout\; id="4"\; label="SD"\; filenames="HDA0000028150910000071.png,HDA0000028150910000072.png"\; state="\{\{state\}\}">SD</figure-callout>}}^4$

Wherein

$\stackrel{\&OverBar;}{X}=\frac{1}{N_2-{\mathrm{<figure-callout\; id="1"\; label="N"\; filenames="HDA0000028150910000012.png,HDA0000028150910000041.png"\; state="\{\{state\}\}">N</figure-callout>}}_1+1}\underset{k=N_1}{\overset{N_2}{\mathrm{\&Sigma;}}}X\left(k\right),$ $\mathrm{SD}={\left(\frac{1}{N_2-{\mathrm{<figure-callout\; id="1"\; label="N"\; filenames="HDA0000028150910000012.png,HDA0000028150910000041.png"\; state="\{\{state\}\}">N</figure-callout>}}_1}\underset{k=N_1}{\overset{N_2}{\mathrm{\&Sigma;}}}{[X\left(k\right)-\stackrel{\&OverBar;}{X}]}^2\right)}^{\frac{1}{2}}$

In formula: Kurtosis is spectrogram kurtosis result of calculation, the Fourier transform that X (k) is detection signal, the horizontal ordinate variable that k is Fourier transform, N ₁for Fourier transform point horizontal ordinate corresponding to linear frequency modulation initial frequency, N ₂for linear frequency modulation stops Fourier transform point horizontal ordinate corresponding to frequency.

for the average of X (k), SD is the standard variance of X (k).In the present embodiment, calculate the spectrogram kurtosis of this benchmark response signal frequency spectrum, thereby while obtaining test specimen zero defect, the i.e. spectrogram kurtosis 22 of this benchmark response signal frequency spectrum, as shown in figure 12, horizontal ordinate represents defect, without unit, ordinate represents spectrogram kurtosis, without unit.

The spectrogram degree of bias is

$\mathrm{Skenwness}=\frac{1}{N_2-{\mathrm{<figure-callout\; id="1"\; label="N"\; filenames="HDA0000028150910000012.png,HDA0000028150910000041.png"\; state="\{\{state\}\}">N</figure-callout>}}_1+1}\underset{k=N_1}{\overset{N_2}{\mathrm{\&Sigma;}}}{[X\left(k\right)-\stackrel{\&OverBar;}{X}]}^3/{\mathrm{<figure-callout\; id="3"\; label="SD"\; filenames="HDA0000028150910000053.png,HDA0000028150910000072.png"\; state="\{\{state\}\}">SD</figure-callout>}}^3$

Wherein

$\stackrel{\&OverBar;}{X}=\frac{1}{N_2-{\mathrm{<figure-callout\; id="1"\; label="N"\; filenames="HDA0000028150910000012.png,HDA0000028150910000041.png"\; state="\{\{state\}\}">N</figure-callout>}}_1+1}\underset{k=N_1}{\overset{N_2}{\mathrm{\&Sigma;}}}X\left(k\right),$ $\mathrm{SD}={\left(\frac{1}{N_2-{\mathrm{<figure-callout\; id="1"\; label="N"\; filenames="HDA0000028150910000012.png,HDA0000028150910000041.png"\; state="\{\{state\}\}">N</figure-callout>}}_1}\underset{k=N_1}{\overset{N_2}{\mathrm{\&Sigma;}}}{[X\left(k\right)-\stackrel{\&OverBar;}{X}]}^2\right)}^{\frac{1}{2}}$

In formula: Skewness is spectrogram degree of bias result of calculation, the Fourier transform that X (k) is detection signal, the horizontal ordinate variable that k is Fourier transform, N ₁for Fourier transform point horizontal ordinate corresponding to linear frequency modulation initial frequency, N ₂for linear frequency modulation stops Fourier transform point horizontal ordinate corresponding to frequency.

for the average of X (k), SD is the standard variance of X (k).In the present embodiment, calculate the spectrogram degree of bias of this benchmark response signal frequency spectrum, thereby while obtaining test specimen zero defect, the i.e. spectrogram degree of bias 25 of this benchmark response signal frequency spectrum, as shown in figure 13, horizontal ordinate represents defect, without unit, ordinate represents the spectrogram degree of bias, without unit.

The 5th step, adopt aforesaid fm exciter signal, and after this fm exciter signal is amplified as described in second step, drive aforementioned eddy current sensor, checked object is detected.In the present embodiment, as shown in Figure 7, checked object still adopts aluminum flat board 1, but in the middle of aluminum dull and stereotyped 1 defect 2,3,4 of uniform three kinds of different depths, wherein, defect 2 is of a size of 10mm × 1.0mm × 0.5mm, defect 3 is of a size of 10mm × 1.0mm × 1.0mm, and defect 4 is of a size of 10mm × 1.0mm × 1.5mm, and depth of defect increases successively, and agreement: when dull and stereotyped 1 upper surface of aluminum detects, defect all represents surface imperfection; When dull and stereotyped 1 lower surface of aluminum detects, defect all represents inherent vice.

The response signal of eddy current sensor when the 6th step, acquisition testing checked object, and this eddy current sensor response signal is carried out to FFT conversion obtain checked object eddy current sensor response signal frequency spectrum.In the present embodiment, respectively defect 2,3,4 is detected, eddy current sensor response signal while gathering respectively each detection, and those eddy current sensor response signals are carried out to FFT conversion obtain corresponding response signal frequency spectrum.In in this enforcement, when checked object upper surface is detected, the response signal frequency spectrum 10 of defect 2, the response signal frequency spectrum 11 of defect 3, the response signal frequency spectrum 12 of defect 4 have been obtained, as shown in Figure 8, horizontal ordinate represents frequency, and unit is kHz, ordinate represents FFT amplitude, without unit.When checked object lower surface is detected, obtain the response signal frequency spectrum 13 of defect 2, the response signal frequency spectrum 14 of defect 3, the response signal frequency spectrum 15 of defect 4, as shown in Figure 9, horizontal ordinate represents frequency, unit is kHz, and ordinate represents FFT amplitude, without unit.

The 7th step, checked object eddy current sensor response signal frequency spectrum is analyzed, and calculated spectrogram gross energy, spectrogram centre-of gravity shift, spectrogram kurtosis, the spectrogram degree of bias of this checked object eddy current sensor response signal frequency spectrum.Each characteristic quantity calculating method is identical with aforementioned the 4th step.

By checked object surface imperfection and the spectrum analysis of inherent vice eddy current sensor response signal that the 6th step is obtained, calculate: 1, the spectrogram gross energy 18 of the eddy current sensor response signal frequency spectrum of the spectrogram gross energy 17 of each surface imperfection response signal frequency spectrum and each inherent vice, as shown in figure 10, horizontal ordinate represents defect, without unit, ordinate represents spectrogram gross energy, without unit; 2, the eddy current sensor response signal spectrogram centre-of gravity shift 21 of the eddy current sensor response signal spectrogram centre-of gravity shift 20 of each surface imperfection and inherent vice, as shown in figure 11, horizontal ordinate represents defect, without unit, ordinate represents spectrogram barycentre offset, without unit; 3, the eddy current sensor response signal spectrogram kurtosis 23 of the eddy current sensor response signal spectrogram kurtosis 24 of each surface imperfection and inherent vice, as shown in figure 12, horizontal ordinate represents defect, without unit, ordinate represents spectrogram kurtosis, without unit; 4, the eddy current sensor response signal spectrogram degree of bias 27 of the eddy current sensor response signal spectrogram degree of bias 26 of surface imperfection and inherent vice, as shown in figure 12, horizontal ordinate represents defect, without unit, ordinate represents the spectrogram degree of bias, without unit.

The 8th step, according to the spectrogram gross energy of benchmark response signal frequency spectrum, spectrogram centre-of gravity shift, spectrogram kurtosis, the spectrogram degree of bias, spectrogram gross energy, spectrogram centre-of gravity shift, spectrogram kurtosis, the spectrogram degree of bias of the above-mentioned checked object eddy current sensor response signal frequency spectrum detecting are carried out to threshold decision: if the spectrogram gross energy of the checked object eddy current sensor response signal frequency spectrum detecting is greater than the spectrogram gross energy of benchmark response signal frequency spectrum, prove to exist on checked object defect; If the spectrogram centre-of gravity shift of the checked object eddy current sensor response signal frequency spectrum detecting is greater than the spectrogram centre-of gravity shift of benchmark response signal frequency spectrum, or the spectrogram kurtosis of the checked object eddy current sensor response signal frequency spectrum detecting is less than the spectrogram kurtosis of benchmark response signal frequency spectrum, or the spectrogram degree of bias of the checked object eddy current sensor response signal frequency spectrum detecting is greater than the spectrogram degree of bias of benchmark response signal frequency spectrum, prove that the defect on checked object is surface imperfection; If the spectrogram centre-of gravity shift of the checked object eddy current sensor response signal frequency spectrum detecting is less than the spectrogram centre-of gravity shift of benchmark response signal frequency spectrum, or the spectrogram kurtosis of the checked object eddy current sensor response signal frequency spectrum detecting is greater than the spectrogram kurtosis of benchmark response signal frequency spectrum, or the spectrogram degree of bias of the checked object eddy current sensor response signal frequency spectrum detecting is less than the spectrogram degree of bias of benchmark response signal frequency spectrum, prove that the defect on checked object is inherent vice.As can be seen from Figure 10, the spectrogram gross energy 18 of the eddy current sensor response signal frequency spectrum of the spectrogram gross energy 17 of each surface imperfection response signal frequency spectrum and each inherent vice is all greater than the spectrogram gross energy 16 of benchmark response signal frequency spectrum, and the spectrogram gross energy obtaining by detection thus just can judge whether to exist defect.As can be seen from Figure 11, the spectrogram centre-of gravity shift 20 of each surface imperfection response signal frequency spectrum is positioned on the spectrogram centre-of gravity shift 19 of benchmark response signal frequency spectrum, the spectrogram centre-of gravity shift 21 of each inherent vice response signal frequency spectrum is positioned under the spectrogram centre-of gravity shift 19 of benchmark response signal frequency spectrum, and the spectrogram centre-of gravity shift obtaining by detection computations thus just can judge the residing diverse location of defect.As can be seen from Figure 12, the spectrogram kurtosis 24 of each surface imperfection response signal frequency spectrum is positioned under the spectrogram kurtosis 22 of benchmark response signal frequency spectrum, the spectrogram kurtosis 23 of each inherent vice response signal frequency spectrum is positioned on the spectrogram kurtosis 22 of benchmark response signal frequency spectrum, and the spectrogram kurtosis obtaining by detection computations thus just can judge the residing diverse location of defect.As can be seen from Figure 13, the spectrogram degree of bias 26 of each surface imperfection response signal frequency spectrum is positioned on the spectrogram degree of bias 25 of benchmark response signal frequency spectrum, the spectrogram degree of bias 27 of each inherent vice response signal frequency spectrum is positioned under the spectrogram degree of bias 25 of benchmark response signal frequency spectrum, and the spectrogram degree of bias obtaining by detection computations thus just can judge the residing diverse location of defect.

Above-described embodiment is only used for further illustrating modulation multifrequency eddy current testing method of the present invention and application; but the present invention is not limited to embodiment; every foundation technical spirit of the present invention, to any simple modification made for any of the above embodiments, equivalent variations and modification, all falls in the protection domain of technical solution of the present invention.

Claims (4)

1. a modulation multifrequency eddy current testing method, is characterized in that comprising the following steps:

The first step, preparation benchmark test specimen;

Second step, generation one fm exciter signal, and after this fm exciter signal is amplified, drive eddy current sensor, benchmark test specimen is detected;

The response signal of eddy current sensor when the 3rd step, acquisition testing benchmark test specimen, and this eddy current sensor response signal is carried out to FFT conversion obtain benchmark test specimen eddy current sensor response signal frequency spectrum, obtain detecting required benchmark response signal frequency spectrum;

The 4th step, benchmark response signal frequency spectrum is analyzed, and calculated spectrogram gross energy, spectrogram centre-of gravity shift, spectrogram kurtosis and the spectrogram degree of bias of this benchmark response signal frequency spectrum;

The 5th step, adopt aforesaid fm exciter signal, and after this fm exciter signal is amplified as described in second step, drive aforementioned eddy current sensor, checked object is detected;

The response signal of eddy current sensor when the 6th step, acquisition testing checked object, and this eddy current sensor response signal is carried out to FFT conversion obtain checked object eddy current sensor response signal frequency spectrum;

The 7th step, checked object eddy current sensor response signal frequency spectrum is analyzed, and calculated spectrogram gross energy, spectrogram centre-of gravity shift, spectrogram kurtosis and the spectrogram degree of bias of this checked object eddy current sensor response signal frequency spectrum;

The 8th step, according to the spectrogram gross energy of benchmark response signal frequency spectrum, spectrogram centre-of gravity shift, spectrogram kurtosis and the spectrogram degree of bias, spectrogram gross energy, spectrogram centre-of gravity shift, spectrogram kurtosis and the spectrogram degree of bias of the above-mentioned checked object eddy current sensor response signal frequency spectrum detecting are carried out to threshold decision: if the spectrogram gross energy of the checked object eddy current sensor response signal frequency spectrum detecting is greater than the spectrogram gross energy of benchmark response signal frequency spectrum, prove to exist on checked object defect; If the spectrogram centre-of gravity shift of the checked object eddy current sensor response signal frequency spectrum detecting is greater than the spectrogram centre-of gravity shift of benchmark response signal frequency spectrum, or the spectrogram kurtosis of the checked object eddy current sensor response signal frequency spectrum detecting is less than the spectrogram kurtosis of benchmark response signal frequency spectrum, or the spectrogram degree of bias of the checked object eddy current sensor response signal frequency spectrum detecting is greater than the spectrogram degree of bias of benchmark response signal frequency spectrum, prove that the defect on checked object is surface imperfection; If the spectrogram centre-of gravity shift of the checked object eddy current sensor response signal frequency spectrum detecting is less than the spectrogram centre-of gravity shift of benchmark response signal frequency spectrum, or the spectrogram kurtosis of the checked object eddy current sensor response signal frequency spectrum detecting is greater than the spectrogram kurtosis of benchmark response signal frequency spectrum, or the spectrogram degree of bias of the checked object eddy current sensor response signal frequency spectrum detecting is less than the spectrogram degree of bias of benchmark response signal frequency spectrum, prove that the defect on checked object is inherent vice.

2. modulation multifrequency eddy current testing method according to claim 1, is characterized in that, this fm exciter signal is linear frequency modulation pumping signal.

3. modulation multifrequency eddy current testing method according to claim 2, is characterized in that, the optimized frequency scope of this linear frequency modulation pumping signal is 1kHz～20kHz, and preferably time span is 4096us.

4. modulation multifrequency eddy current testing method according to claim 1, is characterized in that, the sample frequency that gathers eddy current sensor response signal is 5-10 times of fm exciter signal highest frequency.

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