CN103336049A - Pulsed eddy current detection method and device for eliminating lift-off effect - Google Patents
Pulsed eddy current detection method and device for eliminating lift-off effect Download PDFInfo
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Abstract
The invention discloses a pulsed eddy current detection method and a pulsed eddy current detection device for eliminating a lift-off effect. The detection method specifically comprises the following steps of: 1, acquiring detection signal time domain curves of a tested part under different lift-off heights at different known defect depth positions, acquiring a reference signal time domain curve without lift-off height at a non-defect position of the tested part, and performing differential processing and characteristic value extraction processing on the time domain curves of a detection signal and a reference signal to acquire a relation curve of the differential peak voltage fitting straight line slope and the defect depth; and 2, performing quantitative evaluation on an unknown defect depth of the tested part, acquiring the detection signal time domain curves under different lift-off heights at the unknown defect depth positions, performing differential processing and characteristic value extraction on the time domain curves of the detection signal and the reference signal, and substituting the processing result into a solved expression to acquire the unknown defect depth of the tested part. According to the method, the influence of the lift-off effect in a pulsed eddy current detection system is eliminated.
Description
Technical field
The invention belongs to technical field of nondestructive testing, be specifically related to a kind of impulse eddy current detection method and Design of device of eliminating Lift-off effect.
Background technology
The impulse eddy current detection technique is a new application of EDDY CURRENT, and it determines defective locations with the time that the maximum value of magnetic field that records occurs, thereby has realized Non-Destructive Testing and the quantification description of defective.The reliability that this technology is usually used in transport pipelines such as safety detection, the jet chimney in the nuclear power installation and oil, the rock gas of aircraft fuselage structure and engine detects the quality monitoring in the metal parts production runes such as various plates, rod, pipe etc.The impulse eddy current Dynamic Non-Destruction Measurement is changed the mode that adopts the sinusoidal signal excitation coil in traditional EDDY CURRENT, multifrequency Eddy detection and the frequency sweep EDDY CURRENT, adopts the pulse signal drive coil with certain dutycycle.Because pulse signal can be expressed as the summation of flip-flop, first-harmonic and a series of odd harmonics, therefore the electromagnetic signal that produces by pulse excitation is loaded with abundanter characteristic information.
According to the EDDY CURRENT principle, when popping one's head near metallic conductor, the coil that is loaded with pulse signal can go out eddy current in the conductor induced inside, and any factor that causes eddy current to change all can influence testing result.Because the coefficient of mutual inductance between coil and measured body reduces rapidly to the increase of lifting from measured body surface with probe coil, marked change also takes place with the subtle change of lifting from the vortex density in the measured body, and this effect is called Lift-off effect.The expanding with heat and contract with cold of the coating thickness on measured body surface, irregular measured body surface, operator's minute movement and measured body all can cause lifts from variation, thereby covers real detection information.Therefore, suppress and elimination to lift from interference be a very important link in the research of impulse eddy current detection technique always.
When industrial practice, when popping one's head in the process that test specimen scans, because the other reasonses such as out-of-flatness of structure produce in the process of scanning and lift from, the signal that Lift-off effect produces may flood useful signal, becomes present research focus by adopting new probe designs or advanced signal processing software algorithm to eliminate Lift-off effect.
At this problem, the J ﹒ Chinese is gloomy to be used for the automatic lift-off compensation that impulse eddy current detects with tall proposition of X ﹒, and publication number is CN101413923A, and the known reference signal of lifting from the place can be used the ratio parameter weighting of corresponding calculating, and deduct from test signal, lift from compensation.The a plurality of reference signals of preferred acquisition, and preferably determine the amplitude peak gradient of each reference signal, identification has the corresponding reference signal near the amplitude peak gradient of test signal, and in the correlative compensation program, select this corresponding reference signal, but there is following problem in this method: 1. this scheme need obtain many group reference datas in order to improve accuracy of detection, each measurement all needs measuring reference signals, and the lift-off value of reference signal is known lifting from, also to select to have the reference data near the gradient of test signal, determine the reference signal selected and the difference between the test signal; 2. this method computing more complicated also needs signal is differentiated to determine gradient; 3. this scheme is used and is had whole emitter coil and the probe of receiver array, and typical receiver array has 16 or 32 sensors, the device more complicated; 4. in follow-up AD-LOC method compensation program, also to judge lifting from whether to exist, determine lifting from of existence, need to select to lift from reference after existing determining to lift from, calculate the compensation ratio, the reference data compensation of lifting from that deducts weighting from test data is lifted from.
Summary of the invention
Technical matters to be solved by this invention provides a kind of impulse eddy current detection method and device of eliminating Lift-off effect, and it can eliminate Lift-off effect to EDDY CURRENT result's influence, improve accuracy of detection, and processing procedure is easy.
The technical scheme that the present invention solves its technical matters employing is: a kind of impulse eddy current detection method of eliminating Lift-off effect specifically comprises:
S1, test specimen is obtained the detection signal time-domain curve under the different lift off was more and obtains the reference signal time-domain curve of no lift off was more in test specimen zero defect position at different known defect depth location places, and the time-domain curve of detection signal and reference signal is made difference processing handle with the extraction eigenwert, obtain the relation curve of difference crest voltage fitting a straight line slope and depth of defect, specifically comprise step by step:
S11, produce all adjustable pulse excitation signals of frequency and dutycycle;
S12, incentive probe coil produce excitation field, and probe coil is placed the test specimen top, obtain the time-domain curve of the response signal of different situations, comprising:
1, obtains the time-domain curve of the reference signal of no lift off was more in test specimen zero defect position;
2, at test specimen known defect degree of depth A at least everywhere
1, A
2, A
3, A
4The place obtains the time-domain curve of the detection signal under the different lift off was more, described A
1, A
2, A
3, A
4Be respectively different depth of defects;
S13, at known defect degree of depth A
1The time-domain curve of the detection signal that the place obtains and the time-domain curve of reference signal are made difference processing, obtain at known defect degree of depth A
1Locate the differential signal curve under the different lift off was more;
S14, repeating step S13 obtain at known defect degree of depth A
2, A
3, A
4Locate the differential signal curve under the different lift off was more;
The known defect degree of depth A that obtains among S15, the described step S13 of extraction and the S14
1, A
2, A
3, A
4The crest voltage of the differential signal curve under different lift off was more is obtained at different known defect degree of depth A
1, A
2, A
3, A
4Allowance below nominal size divides the relation curve of crest voltage with different lift off was more, and described relation curve is corresponding to different known defect degree of depth A respectively
1, A
2, A
3, A
4Under difference crest voltage fitting a straight line slope: K
1, K
2, K
3, K
4
S16, the difference crest voltage fitting a straight line slope K that obtains according to described step S15
1, K
2, K
3, K
4With corresponding known defect degree of depth A
1, A
2, A
3, A
4, it is fitted to a cubic function curve, described cubic function curve is: h=aK
3+ bK
2+ cK+d, wherein, described h is corresponding known defect degree of depth A
1, A
2, A
3, A
4, K is described difference crest voltage fitting a straight line slope K
1, K
2, K
3, K
4, a, b, c, d are respectively the coefficient of described cubic function curve, with described A
1, A
2, A
3, A
4And K
1, K
2, K
3, K
4The described cubic function curve of substitution obtains corresponding a, b, the value of c, d, with a, the b that obtains, the value substitution cubic function curve of c, d, obtains difference crest voltage fitting a straight line slope and depth of defect relation: h=aK again
3+ bK
2+ cK+d;
S2, the unknown depth of defect of test specimen is carried out qualitative assessment, the detection signal time-domain curve of acquisition under the different lift off was more in unknown depth of defect position, and the time-domain curve of detection signal and reference signal made difference processing and extract eigenwert, with the expression formula h=aK that tries to achieve among the described step S16 of result substitution
3+ bK
2Among+the cK+d, obtain the unknown depth of defect of test specimen, specifically comprise step by step:
S21, produce all adjustable pulse excitation signals of frequency and dutycycle;
S22, incentive probe coil produce excitation field, and probe coil is placed the test specimen top, obtain detection signal B at a certain unknown lift off was more place at unknown depth of defect Ax place
1Time-domain curve; On the basis of unknown lift off was more, increase △ x more respectively successively, the detection signal B of the different lift off was more at least three places of reentrying
2, B
3, B
4Time-domain curve;
S23, the detection signal B that described step S22 is obtained
1, B
2, B
3, B
4Time-domain curve and described step S12 in the time-domain curve of the reference signal that obtains make difference processing, obtain the differential signal curve under the different lift off was more, extract the crest voltage of differential signal curve, obtain the relation curve of different lift off was more and corresponding difference crest voltage, extract the difference crest voltage fitting a straight line slope K of described relation curve, and with the relation curve h=aK of gained among the described step S16 of K substitution
3+ bK
2+ cK+d obtains unknown depth of defect h, i.e. A among the step S22
xDepth value.
Further, the described degree of depth of known defect at least everywhere A
1, A
2, A
3, A
4In, the depth of defect value that a place is wherein arranged is 0.
Further, before described step S13, also comprise the amplification filtering of detection signal and reference signal is handled.
Further, before described step S23, also comprise the amplification filtering of the detection signal that obtains is handled.
Further, described △ x is 0.6mm.
Based on said method, the present invention solves its technical matters a kind of impulse eddy current pick-up unit of eliminating Lift-off effect, pulse excitation signal source, sensor probe, data acquisition module, lift-off compensation module and depth of defect computing module also is provided;
Described pulse signal source is for generation of pulse excitation signal;
The Hall element that described sensor probe comprises drive coil and is positioned at coil, drive coil is used at the inner eddy current that produces of test specimen conductor, Hall element is used for field signal is converted into electric signal, described electric signal is response signal, and described response signal is reference signal and detection signal;
Described data acquisition module is used for response signal is extracted and preserved, and extracts reference signal and detection signal under different depth of defects, different lift off was more, and described reference signal and detection signal are carried out record;
Described lift-off compensation module is used for reference signal and the detection signal of the transmission of data acquisition module are carried out difference processing, the relation curve of acquisition lift off was more and difference crest voltage under the different known defect degree of depth, and described relation curve is extracted eigenwert handle, obtain the relation curve at different depth of defects and difference crest voltage fitting a straight line slope;
Described depth of defect computing module is used for obtaining unknown depth of defect according to the relation curve of the resulting different depth of defects of lift-off compensation module and difference crest voltage fitting a straight line slope.
Further, also comprise the signal condition module, described signal condition module is used for the electric signal of Hall element output is carried out the amplification filtering processing, and outputs to data acquisition module.
Further, described signal condition module comprises amplifier AD620, operational amplifier OP07.
Further, described pulse excitation signal source employing SPF40 type numeral composite function signal generator is realized.
The invention has the beneficial effects as follows: the present invention is a kind of to eliminate the impulse eddy current detection method of Lift-off effect and device by the result's that produces processing under the different lift off was more of different known defect depth locations, eliminated the influence of Lift-off effect in the impulse eddy current detection system, system can quantitatively detect the depth of defect of test specimen more accurately, compared with prior art, pick-up unit is simple, algorithm is simple and clear, the influence of not only having eliminated Lift-off effect also can quantitatively detect depth of defect, promoted the safety detection of impulse eddy current detection technique at aircraft fuselage structure and engine, jet chimney in the nuclear power installation and oil, the reliability of transport pipelines such as rock gas detects, various plates, rod, the market competitiveness in the industrial applicability such as quality monitoring in metal parts such as pipe production run, thereby bring huge economic benefit, solved impulse eddy current detection technique development key problem for many years.
Description of drawings
Fig. 1 is a kind of FB(flow block) of eliminating the impulse eddy current detection method of Lift-off effect of the embodiment of the invention;
Fig. 2 is a kind of structured flowchart of eliminating the impulse eddy current pick-up unit of Lift-off effect of the embodiment of the invention;
Fig. 3 is that 4mm place lift off was more is respectively 0.2mm, lifts from 0.8mm, lifts from 1.4mm, lifts from the time-domain curve of the detection signal under the 2.0mm for the time-domain curve of the reference signal under zero defect, the no lift off was more when test specimen is aluminium alloy 7075 materials and depth of defect;
Fig. 4 is the differential signal curve of the time-domain curve of 4mm place detection signal and reference signal for depth of defect when test specimen is aluminium alloy 7075 materials;
Fig. 5 is known defect depth location place's lift off was more different when test specimen is aluminium alloy 7075 materials and the graph of relation of difference crest voltage;
Fig. 6 is the difference crest voltage fitting a straight line slope of different depth of defects when test specimen the is aluminium alloy 7075 materials relation curve with corresponding depth of defect;
Fig. 7 is that 4mm place lift off was more is respectively 0.2mm, lifts from 0.8mm, lifts from 1.4mm, lifts from the time-domain curve of the detection signal under the 2.0mm for the time-domain curve of the reference signal under zero defect, no lift off was more when test specimen is aluminium alloy 2024 materials and depth of defect;
Fig. 8 is the differential signal curve of the time-domain curve of 4mm place detection signal and reference signal for depth of defect when test specimen is aluminium alloy 2024 materials;
Fig. 9 is known defect depth location place's lift off was more different when test specimen is aluminium alloy 2024 materials and the graph of relation of difference crest voltage;
Figure 10 is the difference crest voltage fitting a straight line slope of different depth of defects when test specimen the is aluminium alloy 2024 materials relation curve with corresponding depth of defect;
Accompanying drawing curve description of symbols: 31-reference signal (zero defect do not have lift from), 32-lift from 0.2mm, 33-and lift from that 0.8mm, 34-lift from 1.4mm, 35-lifts from 2.0mm;
41-lifts from 0.2mm, 42-and lifts from that 0.8mm, 43-lift from 1.4mm, 44-lifts from 2.0mm;
51-zero defect, the dark 2mm of 52-, the dark 3mm of 53-, the dark 4mm of 54-, the dark 5mm of 55-, the dark 6mm of 56-, the dark 7mm of 57-, the dark 8mm of 58-;
71-reference signal (zero defect do not have lift from), 72-lift from 0.2mm, 73-and lift from that 0.8mm, 74-lift from 1.4mm, 75-lifts from 2.0mm;
81-lifts from 0.2mm, 82-and lifts from that 0.8mm, 83-lift from 1.4mm, 84-lifts from 2.0mm;
91-zero defect, the dark 2mm of 92-, the dark 4mm of 93-, the dark 6mm of 94-, the dark 8mm of 95-.
Embodiment
Below in conjunction with accompanying drawing embodiments of the invention are further described.
Be illustrated in figure 1 as a kind of FB(flow block) of eliminating the impulse eddy current detection method of Lift-off effect of the embodiment of the invention, its step specifically comprises:
S1, test specimen is obtained the detection signal time-domain curve under the different lift off was more and obtains the reference signal time-domain curve of no lift off was more in test specimen zero defect position at different known defect depth location places, and the time-domain curve of detection signal and reference signal is made difference processing handle with the extraction eigenwert, obtain the relation curve of difference crest voltage fitting a straight line slope and depth of defect, specifically comprise step by step:
S11, produce all adjustable pulse excitation signals of frequency and dutycycle;
S12, incentive probe coil produce excitation field, and probe coil is placed the test specimen top, obtain the time-domain curve of the response signal of different situations, comprising:
1, obtains the time-domain curve of the reference signal of no lift off was more in test specimen zero defect position;
2, at test specimen known defect degree of depth A at least everywhere
1, A
2, A
3, A
4The place obtains the time-domain curve of the detection signal under the different lift off was more, described A
1, A
2, A
3, A
4Be respectively different depth of defects;
Wherein the time-domain curve of the time-domain curve of reference signal and detection signal obtain the common practise that is those skilled in the art, in the present patent application scheme, no longer be described in detail.
In order to realize that test specimen is had flawless judgement, also should measure the detection signal under the different lift off was more in zero defect position, concrete to increase the accuracy of testing result, in embodiments of the present invention, the described degree of depth of known defect at least everywhere A
1, A
2, A
3, A
4In, the depth of defect value that a place is wherein arranged is 0, also can be described after having measured everywhere the detection signal of the known defect degree of depth, to the detection signal under its different lift off was more of zero defect position independent measurement.
S13, at known defect degree of depth A
1The time-domain curve of the detection signal that the place obtains and the time-domain curve of reference signal are made difference processing, obtain at known defect degree of depth A
1Locate the differential signal curve under the different lift off was more;
S14, repeating step S13 obtain at known defect degree of depth A
2, A
3, A
4Locate the differential signal curve under the different lift off was more;
The known defect degree of depth A that obtains among S15, the described step S13 of extraction and the S14
1, A
2, A
3, A
4The crest voltage of the differential signal curve under different lift off was more is obtained at different known defect degree of depth A
1, A
2, A
3, A
4Allowance below nominal size divides the relation curve of crest voltage with different lift off was more, and described relation curve is corresponding to different known defect degree of depth A respectively
1, A
2, A
3, A
4Under difference crest voltage fitting a straight line slope: K
1, K
2, K
3, K
4
S16, the difference crest voltage fitting a straight line slope K that obtains according to described step S15
1, K
2, K
3, K
4With corresponding known defect degree of depth A
1, A
2, A
3, A
4, it is fitted to a cubic function curve, described cubic function curve is: h=aK
3+ bK
2+ cK+d, wherein, described h is corresponding known defect degree of depth A
1, A
2, A
3, A
4, K is described difference crest voltage fitting a straight line slope K
1, K
2, K
3, K
4, a, b, c, d are respectively the coefficient of described cubic function curve, with described A
1, A
2, A
3, A
4And K
1, K
2, K
3, K
4The described cubic function curve of substitution obtains corresponding a, b, the value of c, d, with a, the b that obtains, the value substitution cubic function curve of c, d, obtains difference crest voltage fitting a straight line slope and depth of defect relation: h=aK again
3+ bK
2+ cK+d;
S2, the unknown depth of defect of test specimen is carried out qualitative assessment, the detection signal time-domain curve of acquisition under the different lift off was more in unknown depth of defect position, and the time-domain curve of detection signal and reference signal made difference processing and extract eigenwert, with the expression formula h=aK that tries to achieve among the described step S16 of result substitution
3+ bK
2Among+the cK+d, obtain the unknown depth of defect of test specimen, specifically comprise step by step:
S21, produce all adjustable pulse excitation signals of frequency and dutycycle;
S22, incentive probe coil produce excitation field, probe coil are placed the test specimen top, at unknown depth of defect A
xThe a certain unknown lift off was more place at place obtains detection signal B
1Time-domain curve; On the basis of unknown lift off was more, increase △ x more respectively successively, the detection signal B of the different lift off was more at least three places of reentrying
2, B
3, B
4Time-domain curve;
S23, the detection signal B that described step S22 is obtained
1, B
2, B
3, B
4Time-domain curve and described step S12 in the time-domain curve of the reference signal that obtains make difference processing, obtain the differential signal curve under the different lift off was more, extract the crest voltage of differential signal curve, obtain the relation curve of different lift off was more and corresponding difference crest voltage, extract the difference crest voltage fitting a straight line slope K of described relation curve, and with the relation curve h=aK of gained among the described step S16 of K substitution
3+ bK
2+ cK+d obtains unknown depth of defect h, i.e. A among the step S22
xDepth value.
In the prior art, impulse eddy current detects that general to use more be detection to the space flight equipment, when adopting the detection method of elimination Lift-off effect of the present invention that test specimen is detected, only need under for the first time to test specimen the known defect degree of depth of material to carry out Measurement and analysis, obtain the relation curve of difference crest voltage fitting a straight line slope and depth of defect, eliminate different lift off was more to the influence of testing result, the result that detection is obtained is more accurate, and algorithmic procedure wherein is easy, be easy to operate in practice, the instrument that need not use huge precision can be finished the detection to unknown depth of defect, eliminates Lift-off effect to the influence of testing result.
Wherein, because the response signal of output is comparatively faint, in order to obtain better testing result, need do the amplification filtering processing to detection signal and the reference signal of output, so before described step S13, also comprise the amplification filtering of detection signal and reference signal handled, same, before described step S23, also comprise the amplification filtering processing to the detection signal that obtains.
Be illustrated in figure 2 as a kind of structured flowchart of eliminating the impulse eddy current pick-up unit of Lift-off effect of the invention process, it comprises: pulse excitation signal source, sensor probe, data acquisition module, lift-off compensation module and depth of defect computing module;
Described pulse signal source is for generation of pulse excitation signal;
The Hall element that described sensor probe comprises drive coil and is positioned at coil, drive coil is used at the inner eddy current that produces of test specimen conductor, Hall element is used for field signal is converted into electric signal, described electric signal is response signal, and described response signal is reference signal and detection signal;
Described data acquisition module is used for response signal is extracted and preserved, and extracts reference signal and detection signal under different depth of defects, different lift off was more, and described reference signal and detection signal are carried out record;
Described lift-off compensation module is used for reference signal and the detection signal of the transmission of data acquisition module are carried out difference processing, the relation curve of acquisition lift off was more and difference crest voltage under the different known defect degree of depth, and described relation curve is extracted eigenwert handle, obtain the relation curve at different depth of defects and difference crest voltage fitting a straight line slope;
Described depth of defect computing module is used for obtaining unknown depth of defect according to the relation curve of the resulting different depth of defects of lift-off compensation module and difference crest voltage fitting a straight line slope.
Wherein, also comprise the signal condition module, described signal condition module is used for the electric signal of Hall element output is carried out the amplification filtering processing, and outputs to data acquisition module.Described signal condition module comprises amplifier AD620, operational amplifier OP07.Described pulse excitation signal source adopts SPF40 type numeral composite function signal generator to realize.
Can understand and implement the present invention program for the ease of those skilled in the art, below a kind of impulse eddy current detection method and device of eliminating Lift-off effect of the present invention is elaborated:
Obtaining of pumping signal described in above-mentioned steps S11 and the step S21 can utilize SPF40 type numeral composite function signal generator, directly obtain frequency, the duty equal adjustable high precision stable pulse signal f (t) of amplitude when by it, its available formula (1) is carried out Fourier expansion:
In the formula, A
0Be DC component, A
nBe the amplitude of each harmonic component of correspondence, ω
1Be the first-harmonic angular frequency,
Be the pulsating wave initial phase.
Described sensor probe is made up of drive coil and Hall element.Drive coil is the excitation field source, produces a magnetic field that constitutes eddy effect by it; Hall element places centre position, drive coil bottom, as the test section of probe, is used for obtaining the size in coil stimulating magnetic field and magnetic field, eddy current feedback magnetic field stack back, and is translated into voltage signal and feeds back to the subsequent treatment part.But because excitation field is fainter, therefore, the voltage signal that Hall element is exported is smaller equally, often have only tens millivolts, and the inside a lot of high-frequency interferencing signals that also mixed, therefore, need carry out amplification filtering to the signal of sensor probe output handles, just the reference signal that obtains and the detection signal that obtains are carried out the amplification filtering processing under the different lift off was more in each different known defect depth locations place, noise jamming signal in the filtered signal also amplifies it, makes it reach the measurement range of follow-up data acquisition module.For realizing this function, can use in embodiments of the present invention with instrument amplifier AD620 and realize the amplification of signal as the amplifying circuit of core, and utilize high precision operating amplifier OP07 to form the second-order low-pass filter filtering interference signals.
Finish after the obtaining of reference signal and the detection signal that under the different lift off was more in each different known defect depth locations place, obtains, resulting data need be extracted and preserved, with convenient the result is analyzed contrast, for realizing being connected of detection system and host computer, can utilize the PC control data collecting card to realize collection and storage to signal in embodiments of the present invention.By follow-up lift-off compensation module and depth of defect computing module the signal that obtains is carried out difference processing and extracts eigenwert again, obtain corresponding relation curve.
Below will obtaining and the process of the extraction of the difference processing of data and eigenwert be described in detail reference signal and various detection signals:
At first choosing test specimen is aluminium alloy 7075 materials, the zero defect position and at least everywhere known defect depth location place detect, having chosen the different known defect degree of depth in eight places in an embodiment of the present invention detects, depth of defect is followed successively by 0mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, obtain the detection signal under different lift off was more more respectively at difference known defect depth locations place, eight places, in the eddy detection technology field, by discovering, lift off was more is in certain variation range, its testing result that draws is effective sensing range, valid analysing range can be according to the geometry of impulse eddy current detection system probe, physical dimension and electrical specification change, described valid analysing range is that lift off was more is when changing between 0mm to 2mm in the present invention, choose different lift off was more in embodiments of the present invention everywhere, be respectively and lift from 0.2mm, lift from 0.8mm, lift from 1.4mm, lift from 2.0mm, be illustrated in figure 3 as at the test specimen zero defect, the time-domain curve of the reference signal under the no lift off was more and depth of defect are the 4mm place, lift off was more is respectively 0.2mm, lift from 0.8mm, lift from 1.4mm, lift from the time-domain curve of the detection signal under the 2.0mm, the signal curve at other known defect depth location places is also similarly listed in embodiments of the present invention no longer one by one.Respectively the time-domain curve of the detection signal that obtains and the time-domain curve of reference signal are made difference processing again, obtain differential signal curve as shown in Figure 4, extract crest voltage wherein, obtaining at depth of defect is 4mm place lift off was more and difference crest voltage curve, other known defect depth location places also make same treatment, obtain as shown in Figure 5 at different known defect depth location place's lift off was more and the graph of a relation of difference crest voltage.
Can be found when depth of defect one timing by Fig. 5, crest voltage and the lift off was more of the detection signal that obtains under different lift off was more and the differential signal of reference signal are linear, i.e. U=Kx+n, and wherein said U is crest voltage, x is lift off was more, and K is straight slope; And same depth of defect, the rate of change of the crest voltage of the differential signal of different lift off was more is certain, and namely K is certain, and is irrelevant with the situation of change of lifting from, thereby in the calculating of testing result and the influence of having eliminated lift off was more in analyzing.
Extract among Fig. 5 lift off was more and difference crest voltage corresponding relation slope of a curve K under the different known defect degree of depth at last
1, K
2, K
3, K
4, K
5, K
6, K
7, K
8, the slope that obtains is fitted to cubic function curve: h=aK with the corresponding known defect degree of depth
3+ bK
2+ cK+d, be illustrated in figure 6 as the relation curve of difference peak fitting straight slope and corresponding depth of defect, obtaining the value of coefficient a, b, c, d, is the measurement of difference peak fitting straight slope and the depth of defect relation curve of aluminium alloy 7075 materials thereby finished test specimen.
When test specimen is aluminium alloy 2024 materials, method and the test specimen handled are that aluminium alloy 7075 is similar, when the test result that obtains was illustrated in figure 7 as test specimen and is aluminium alloy 2024, the time-domain curve of the reference signal of its zero defect, no lift off was more and depth of defect were the time-domain curve of 4mm position lift off was more detection signal when being respectively 0.2mm, 0.8mm, 1.4mm, 2.0mm; Figure 8 shows that the differential signal curve based on the time-domain curve of the detection signal among Fig. 7 and reference signal; Figure 9 shows that the relation curve of lift off was more and difference crest voltage under different depth of defects, the depth of defect of choosing is respectively 0mm, 2mm, 4mm, 6mm, 8mm; Figure 10 shows that the cubic function curve of difference peak fitting straight slope among Fig. 9 and corresponding depth of defect.
Be fitting a straight line slope and depth of defect relation curve: the h=aK of aluminium alloy 7075 materials according to the test specimen of trying to achieve again
3+ bK
2+ cK+d is that the unknown depth of defect of aluminium alloy 7075 materials detects to test specimen, and concrete operation steps is as follows:
The position of step 1, a certain unknown lift off was more above unknown depth of defect obtains detection signal B
1Time-domain curve after, increase the at interval position of △ x=0.6mm of lifting from of known altitude on this basis, obtain detection signal B
2Time-domain curve; Obtaining detection signal B
2After, increase the at interval position of △ x=0.6mm of lifting from of known altitude more on this basis again, detect and obtain signal B
3Obtaining detection signal B at last
3After, increase the at interval position of △ x=0.6mm of lifting from of known altitude more on this basis again, obtain detection signal B
4Time-domain curve.Determine the validity of four detection signals, if detection signal can use, if not in effective range then must remeasure and then obtain effective detection signal in valid analysing range;
Wherein the value of △ x can artificially define according to determined effective range;
Step 3, simulate straight line at interval according to four that obtain in the step 2 effective difference crest voltage and known lifting from, obtain the slope K value of fitting a straight line;
Can try to achieve depth of defect h value in step 4, the cubic function relational expression with the different depth of defect h of resulting straight slope K value substitution in the step 3 and the existence of fitting a straight line slope K, thereby eliminate the influence of the unknown lift off was more of initial position to testing result.
Claims (9)
1. an impulse eddy current detection method of eliminating Lift-off effect is characterized in that, specifically comprises:
S1, test specimen is obtained the detection signal time-domain curve under the different lift off was more and obtains the reference signal time-domain curve of no lift off was more in test specimen zero defect position at different known defect depth location places, and the time-domain curve of detection signal and reference signal is made difference processing handle with the extraction eigenwert, obtain the relation curve of difference crest voltage fitting a straight line slope and depth of defect, specifically comprise step by step:
S11, produce all adjustable pulse excitation signals of frequency and dutycycle;
S12, incentive probe coil produce excitation field, and probe coil is placed the test specimen top, obtain the time-domain curve of the response signal of different situations, comprising:
1, obtains the time-domain curve of the reference signal of no lift off was more in test specimen zero defect position;
2, at test specimen known defect degree of depth A at least everywhere
1, A
2, A
3, A
4The place obtains the time-domain curve of the detection signal under the different lift off was more, described A
1, A
2, A
3, A
4Be respectively different depth of defects;
S13, at known defect degree of depth A
1The time-domain curve of the detection signal that the place obtains and the time-domain curve of reference signal are made difference processing, obtain at known defect degree of depth A
1Locate the differential signal curve under the different lift off was more;
S14, repeating step S13 obtain at known defect degree of depth A
2, A
3, A
4Locate the differential signal curve under the different lift off was more;
The known defect degree of depth A that obtains among S15, the described step S13 of extraction and the S14
1, A
2, A
3, A
4The crest voltage of the differential signal curve under different lift off was more is obtained at different known defect degree of depth A
1, A
2, A
3, A
4Allowance below nominal size divides the relation curve of crest voltage with different lift off was more, and described relation curve is corresponding to different known defect degree of depth A respectively
1, A
2, A
3, A
4Under difference crest voltage fitting a straight line slope: K
1, K
2, K
3, K
4
S16, the difference crest voltage fitting a straight line slope K that obtains according to described step S15
1, K
2, K
3, K
4With corresponding known defect degree of depth A
1, A
2, A
3, A
4, it is fitted to a cubic function curve, described cubic function curve is: h=aK
3+ bK
2+ cK+d, wherein, described h is corresponding known defect degree of depth A
1, A
2, A
3, A
4, K is described difference crest voltage fitting a straight line slope K
1, K
2, K
3, K
4, a, b, c, d are respectively the coefficient of described cubic function curve, with described A
1, A
2, A
3, A
4And K
1, K
2, K
3, K
4The described cubic function curve of substitution obtains corresponding a, b, the value of c, d, with a, the b that obtains, the value substitution cubic function curve of c, d, obtains difference crest voltage fitting a straight line slope and depth of defect relation: h=aK again
3+ bK
2+ cK+d;
S2, the unknown depth of defect of test specimen is carried out qualitative assessment, the detection signal time-domain curve of acquisition under the different lift off was more in unknown depth of defect position, and the time-domain curve of detection signal and reference signal made difference processing and extract eigenwert, with the expression formula h=aK that tries to achieve among the described step S16 of result substitution
3+ bK
2Among+the cK+d, obtain the unknown depth of defect of test specimen, specifically comprise step by step:
S21, produce all adjustable pulse excitation signals of frequency and dutycycle;
S22, incentive probe coil produce excitation field, probe coil are placed the test specimen top, at unknown depth of defect A
xThe a certain unknown lift off was more place at place obtains detection signal B
1Time-domain curve; On the basis of unknown lift off was more, increase △ x more respectively successively, the detection signal B of the different lift off was more at least three places of reentrying
2, B
3, B
4Time-domain curve;
S23, the detection signal B that described step S22 is obtained
1, B
2, B
3, B
4Time-domain curve and described step S12 in the time-domain curve of the reference signal that obtains make difference processing, obtain the differential signal curve under the different lift off was more, extract the crest voltage of differential signal curve, obtain the relation curve of different lift off was more and corresponding difference crest voltage, extract the difference crest voltage fitting a straight line slope K of described relation curve, and with the relation curve h=aK of gained among the described step S16 of K substitution
3+ bK
2+ cK+d obtains unknown depth of defect h, i.e. A among the step S22
xDepth value.
2. a kind of impulse eddy current detection method of eliminating Lift-off effect as claimed in claim 1 is characterized in that, the described degree of depth of known defect at least everywhere A
1, A
2, A
3, A
4In, the depth of defect value that a place is wherein arranged is 0.
Further, comprised also that before described step S13 it is 0 that detection signal and reference signal are had the depth of defect value at a place.
3. a kind of impulse eddy current detection method of eliminating Lift-off effect as claimed in claim 1 or 2 is characterized in that, also comprises the amplification filtering of detection signal and reference signal is handled before described step S13.
4. a kind of impulse eddy current detection method of eliminating Lift-off effect as claimed in claim 1 or 2 is characterized in that, also comprises the amplification filtering processing to the detection signal that obtains before described step S23.
5. as the described a kind of impulse eddy current detection method of eliminating Lift-off effect of each claim of claim 1 to 4, it is characterized in that described △ x is 0.6mm.
6. an impulse eddy current pick-up unit of eliminating Lift-off effect is characterized in that, pulse excitation signal source, sensor probe, data acquisition module, lift-off compensation module and depth of defect computing module;
Described pulse signal source is for generation of pulse excitation signal;
The Hall element that described sensor probe comprises drive coil and is positioned at coil, drive coil is used at the inner eddy current that produces of test specimen conductor, Hall element is used for field signal is converted into electric signal, described electric signal is response signal, and described response signal is reference signal and detection signal;
Described data acquisition module is used for response signal is extracted and preserved, and extracts reference signal and detection signal under different depth of defects, different lift off was more, and described reference signal and detection signal are carried out record;
Described lift-off compensation module is used for reference signal and the detection signal of the transmission of data acquisition module are carried out difference processing, the relation curve of acquisition lift off was more and difference crest voltage under the different known defect degree of depth, and described relation curve is extracted eigenwert handle, obtain the relation curve at different depth of defects and difference crest voltage fitting a straight line slope;
Described depth of defect computing module is used for obtaining unknown depth of defect according to the relation curve of the resulting different depth of defects of lift-off compensation module and difference crest voltage fitting a straight line slope.
7. a kind of impulse eddy current pick-up unit of eliminating Lift-off effect as claimed in claim 6, it is characterized in that, also comprise the signal condition module, described signal condition module is used for the electric signal of Hall element output is carried out the amplification filtering processing, and outputs to data acquisition module.
8. a kind of impulse eddy current pick-up unit of eliminating Lift-off effect as claimed in claim 7 is characterized in that described signal condition module comprises amplifier AD620, operational amplifier OP07.
9. a kind of impulse eddy current pick-up unit of eliminating Lift-off effect as claimed in claim 6 is characterized in that, described pulse excitation signal source adopts SPF40 type numeral composite function signal generator to realize.
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