CN103336049B - A kind of pulse eddy current detection method and device eliminating Lift-off effect - Google Patents
A kind of pulse eddy current detection method and device eliminating Lift-off effect Download PDFInfo
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Abstract
The invention discloses a kind of pulse eddy current detection method and the device of eliminating Lift-off effect, described detection method specifically comprises: step 1, to obtain the detection signal time-domain curve under different lift off was more at different known defect depth location places and the reference signal time-domain curve obtained in test specimen zero defect position without lift off was more to test specimen, and the time-domain curve of detection signal and reference signal is made to difference processing and extracted eigenwert process, obtain the relation curve of differential peak voltage fitting a straight line slope and depth of defect; Step 1, qualitative assessment is carried out to the unknown depth of defect of test specimen, obtain the detection signal time-domain curve under the different lift off was more in unknown depth of defect position, and the time-domain curve of detection signal and reference signal is made difference processing and extracted eigenwert, result is substituted in the expression formula of trying to achieve, obtain the unknown depth of defect of test specimen.This method eliminates the impact of Lift-off effect in Pulsed Eddy Current Testing System.
Description
Technical field
The invention belongs to technical field of nondestructive testing, be specifically related to a kind ofly eliminate the pulse eddy current detection method of Lift-off effect and the design of device.
Background technology
Pulsed eddy current testing technology is the new application of of EDDY CURRENT, and the time that it occurs with the maximum value of magnetic field recorded determines defective locations, thus achieves Non-Destructive Testing and the quantitative description of defect.The reliability that this technology is usually used in jet chimney in the safety detection of aircraft fuselage structure and engine, nuclear power installation and the transport pipeline such as oil, rock gas detects, the quality monitoring etc. in the metal parts production runes such as various plate, rod, pipe.Pulsed Eddy Current Nondestructive Testing Technology changes the mode adopting sinusoidal signal excitation coil in traditional EDDY CURRENT, multi frequency detection and 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 harmonic, the electromagnetic signal therefore produced by pulse excitation is loaded with abundanter characteristic information.
According to EDDY CURRENT principle, can induce eddy current at conductor when the close metallic conductor of the coil probe being loaded with pulse signal, any factor causing eddy current to change all can affect testing result.Because the coefficient of mutual inductance between coil and measured body reduces rapidly to the increase of the lift-off on measured body surface with probe coil, also there is marked change in the vortex density in measured body, this effect is called Lift-off effect with the subtle change of lift-off.Minute movement and the expanding with heat and contract with cold of measured body of the coating thickness on measured body surface, irregular measured body surface, operator all can cause lift-off to change, thus cover real Detection Information.Therefore, suppress and eliminate lift-off interference is a very important link in Pulsed eddy current testing technical research always.
When industrial practice, when probe carries out in the process scanned at test specimen, because the other reasons such as out-of-flatness of structure produces lift-off in the process of scanning, the signal that Lift-off effect produces may flood useful signal, and eliminating Lift-off effect by adopting the signal processing software algorithm of new probe designs or advanced person becomes current study hotspot.
For this problem, the J ﹒ Chinese is gloomy and X ﹒ is tall proposes the automatic lift-off compensation being used for Pulsed eddy current testing, and publication number is CN101413923A, and the reference signal of known lift-off place can use the ratio parameter weighting of corresponding calculating, and deduct from test signal, to compensate lift-off.The multiple reference signal of preferred acquisition, and preferably determine the amplitude peak gradient of each reference signal, identify the corresponding reference signal of the amplitude peak gradient had closest to test signal, and in correlative compensation program, select the reference signal of this correspondence, but there is following problem in the method: 1. the program needs acquisition to organize reference data to improve accuracy of detection more, each measurement all needs measuring reference signals, and the lift-off value of reference signal is known lift-off, also to select the reference data of the gradient had closest to test signal, determine the difference between the reference signal of selection and test signal, 2. the method computing more complicated, also needing differentiates to signal determines gradient, 3. the program use there is overall emitter coil and the probe of receiver array, typical receiver array has 16 or 32 sensors, device more complicated, 4. also whether to exist lift-off in follow-up AD-LOC method compensation program and judge, determine the lift-off existed, determining to need to select lift-off reference, calculation compensation ratio after lift-off exists, the lift-off reference data deducting weighting from test data compensates lift-off.
Summary of the invention
Technical matters to be solved by this invention is to provide a kind of pulse eddy current detection method and the device of eliminating Lift-off effect, and it can eliminate the impact of Lift-off effect on EDDY CURRENT result, improve accuracy of detection, and processing procedure is easy.
The technical scheme that the present invention solves the employing of its technical matters is: a kind of pulse eddy current detection method eliminating Lift-off effect, specifically comprises:
S1, the detection signal time-domain curve under different lift off was more is obtained and the reference signal time-domain curve obtained in test specimen zero defect position without lift off was more to test specimen at different known defect depth location places, and the time-domain curve of detection signal and reference signal is made to difference processing and extracted eigenwert process, obtain the relation curve of differential peak voltage fitting a straight line slope and depth of defect, specifically comprise step by step:
The pulse excitation signal that S11, generation frequency and dutycycle are all adjustable;
S12, incentive probe coil, produce excitation field, be placed in by probe coil above test specimen, obtains the time-domain curve of the response signal of different situations, comprising:
1, the time-domain curve without the reference signal of lift off was more is obtained 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
4place obtains the time-domain curve of the detection signal under 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 detection signal that place obtains and the time-domain curve of reference signal make difference processing, obtain at known defect degree of depth A
1locate the differential signal curve under different lift off was more;
S14, repetition step S13, obtain at known defect degree of depth A
2, A
3, A
4locate the differential signal curve under different lift off was more;
S15, extract the known defect degree of depth A obtained in described step S13 and S14
1, A
2, A
3, A
4the crest voltage of the differential signal curve under different lift off was more, obtains 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 from 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 differential peak voltage fitting a straight line slope: K
1, K
2, K
3, K
4;
S16, the differential peak voltage fitting a straight line slope K obtained 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, 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 differential peak 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, by described A
1, A
2, A
3, A
4and K
1, K
2, K
3, K
4substitute into described cubic function curve, obtain the value of corresponding a, b, c, d, then the value of a, b, c, d of obtaining is substituted into cubic function curve, obtain differential peak voltage fitting a straight line slope and depth of defect relation: h=aK
3+ bK
2+ cK+d;
S2, qualitative assessment is carried out to the unknown depth of defect of test specimen, obtain the detection signal time-domain curve under the different lift off was more in unknown depth of defect position, and the time-domain curve of detection signal and reference signal is made difference processing and extracted eigenwert, result is substituted into the expression formula h=aK tried to achieve in described step S16
3+ bK
2in+cK+d, obtain the unknown depth of defect of test specimen, specifically comprise step by step:
The pulse excitation signal that S21, generation frequency and dutycycle are all adjustable;
S22, incentive probe coil, produce excitation field, be placed in by probe coil above test specimen, obtains detection signal B at a certain unknown lift off was more place at unknown depth of defect Ax place
1time-domain curve; △ x is increased successively respectively again, the detection signal B of the different lift off was more at least three places of reentrying on the basis of unknown lift off was more
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 reference signal that obtains make difference processing, obtain the differential signal curve under 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 differential peak voltage, extract the differential peak voltage fitting a straight line slope K of described relation curve, and K is substituted into the relation curve h=aK of gained in described step S16
3+ bK
2+ cK+d, obtains unknown depth of defect h, the A namely in step S22
xdepth value.
Further, the described degree of depth A of known defect at least everywhere
1, A
2, A
3, A
4in, wherein there is the depth of defect value at a place to be 0.
Further, before described step S13, also comprise the amplification filtering process to detection signal and reference signal.
Further, before described step S23, also comprise the amplification filtering process to obtained detection signal.
Further, described △ x is 0.6mm.
Based on said method, the present invention solves its technical matters and additionally provides a kind of Pulsed eddy current testing device eliminating Lift-off effect, 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;
Described sensor probe comprises drive coil and is positioned at the Hall element of coil, drive coil is used for producing eddy current at test specimen conductor, Hall element is used for field signal to be 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 extracting response signal and preserving, and extracts reference signal and the detection signal under different depth of defect, different lift off was more, and carries out record to described reference signal and detection signal;
Described lift-off compensation module be used for data acquisition module transmission reference signal and detection signal carry out difference processing, obtain the relation curve of lift off was more and differential peak voltage under the different known defect degree of depth, and eigenwert process is extracted to described relation curve, obtain the relation curve at different depth of defect and differential peak voltage fitting a straight line slope;
The relation curve that described depth of defect computing module is used for different depth of defect and the differential peak voltage fitting a straight line slope obtained according to lift-off compensation module obtains unknown depth of defect.
Further, also comprise Signal-regulated kinase, the electric signal that described Signal-regulated kinase is used for Hall element exports carries out amplification filtering process, and outputs to data acquisition module.
Further, described Signal-regulated kinase comprises amplifier AD620, operational amplifier OP07.
Further, described pulse excitation signal source adopts SPF40 type digit synthesis function signal generator to realize.
The invention has the beneficial effects as follows: the present invention is a kind of eliminates the process of result by producing under the different lift off was more of different known defect depth location of the pulse eddy current detection method of Lift-off effect and device, eliminate the impact of Lift-off effect in Pulsed Eddy Current Testing System, system quantitatively can 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 impact not only eliminating Lift-off effect also quantitatively can detect depth of defect, improve the safety detection of Pulsed eddy current testing technology at aircraft fuselage structure and engine, jet chimney in nuclear power installation and oil, the reliability of the transport pipelines such as rock gas detects, various plate, rod, the market competitiveness in the industrial applicability such as the quality monitoring in the metal parts production runes such as pipe, thus bring huge economic benefit, solve Pulsed eddy current testing technical development key problem for many years.
Accompanying drawing explanation
Fig. 1 is a kind of FB(flow block) eliminating the pulse eddy current detection method of Lift-off effect of the embodiment of the present invention;
Fig. 2 is a kind of structured flowchart eliminating the Pulsed eddy current testing device of Lift-off effect of the embodiment of the present invention;
Fig. 3 be when test specimen is aluminium alloy 7075 material zero defect, be the time-domain curve that 4mm place lift off was more is respectively the detection signal under 0.2mm, lift-off 0.8mm, lift-off 1.4mm, lift-off 2.0mm without the time-domain curve of the reference signal under lift off was more and depth of defect;
Fig. 4 is that depth of defect is the differential signal curve of the time-domain curve of 4mm place detection signal and reference signal when test specimen is aluminium alloy 7075 material;
Fig. 5 is the known defect depth location place lift off was more different when test specimen is aluminium alloy 7075 material and the graph of relation of differential peak voltage;
Fig. 6 is the different differential peak voltage fitting a straight line slope of depth of defect and the relation curve of corresponding depth of defect when test specimen is aluminium alloy 7075 material;
Fig. 7 be when test specimen is aluminium alloy 2024 material at zero defect, be the time-domain curve that 4mm place lift off was more is respectively the detection signal under 0.2mm, lift-off 0.8mm, lift-off 1.4mm, lift-off 2.0mm without the time-domain curve of the reference signal under lift off was more and depth of defect;
Fig. 8 is that depth of defect is the differential signal curve of the time-domain curve of 4mm place detection signal and reference signal when test specimen is aluminium alloy 2024 material;
Fig. 9 is the known defect depth location place lift off was more different when test specimen is aluminium alloy 2024 material and the graph of relation of differential peak voltage;
Figure 10 is the different differential peak voltage fitting a straight line slope of depth of defect and the relation curve of corresponding depth of defect when test specimen is aluminium alloy 2024 material;
Accompanying drawing curve description of symbols: 31-reference signal (zero defect is without lift-off), 32-lift-off 0.2mm, 33-lift-off 0.8mm, 34-lift-off 1.4mm, 35-lift-off 2.0mm;
41-lift-off 0.2mm, 42-lift-off 0.8mm, 43-lift-off 1.4mm, 44-lift-off 2.0mm;
The dark 8mm of 51-zero defect, 52-dark 2mm, 53-dark 3mm, 54-dark 4mm, 55-dark 5mm, 56-dark 6mm, 57-dark 7mm, 58-;
71-reference signal (zero defect is without lift-off), 72-lift-off 0.2mm, 73-lift-off 0.8mm, 74-lift-off 1.4mm, 75-lift-off 2.0mm;
81-lift-off 0.2mm, 82-lift-off 0.8mm, 83-lift-off 1.4mm, 84-lift-off 2.0mm;
The dark 8mm of 91-zero defect, 92-dark 2mm, 93-dark 4mm, 94-dark 6mm, 95-.
Embodiment
Below in conjunction with accompanying drawing, embodiments of the invention are further described.
Be illustrated in figure 1 a kind of FB(flow block) eliminating the pulse eddy current detection method of Lift-off effect of the embodiment of the present invention, its step specifically comprises:
S1, the detection signal time-domain curve under different lift off was more is obtained and the reference signal time-domain curve obtained in test specimen zero defect position without lift off was more to test specimen at different known defect depth location places, and the time-domain curve of detection signal and reference signal is made to difference processing and extracted eigenwert process, obtain the relation curve of differential peak voltage fitting a straight line slope and depth of defect, specifically comprise step by step:
The pulse excitation signal that S11, generation frequency and dutycycle are all adjustable;
S12, incentive probe coil, produce excitation field, be placed in by probe coil above test specimen, obtains the time-domain curve of the response signal of different situations, comprising:
1, the time-domain curve without the reference signal of lift off was more is obtained 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
4place obtains the time-domain curve of the detection signal under different lift off was more, described A
1, A
2, A
3, A
4be respectively different depth of defects;
Wherein the acquisition of the time-domain curve of reference signal and the time-domain curve of detection signal is the common practise of those skilled in the art, is no longer described in detail in the present patent application scheme.
In order to realize there is flawless judgement to test specimen, the detection signal under the different lift off was more in zero defect position also should be measured, to increase the accuracy of testing result, concrete, in embodiments of the present invention, the described degree of depth A of known defect at least everywhere
1, A
2, A
3, A
4in, wherein there is the depth of defect value at a place to be 0, also can be described after the detection signal measuring the known defect degree of depth everywhere, 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 detection signal that place obtains and the time-domain curve of reference signal make difference processing, obtain at known defect degree of depth A
1locate the differential signal curve under different lift off was more;
S14, repetition step S13, obtain at known defect degree of depth A
2, A
3, A
4locate the differential signal curve under different lift off was more;
S15, extract the known defect degree of depth A obtained in described step S13 and S14
1, A
2, A
3, A
4the crest voltage of the differential signal curve under different lift off was more, obtains 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 from 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 differential peak voltage fitting a straight line slope: K
1, K
2, K
3, K
4;
S16, the differential peak voltage fitting a straight line slope K obtained 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, 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 differential peak 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, by described A
1, A
2, A
3, A
4and K
1, K
2, K
3, K
4substitute into described cubic function curve, obtain the value of corresponding a, b, c, d, then the value of a, b, c, d of obtaining is substituted into cubic function curve, obtain differential peak voltage fitting a straight line slope and depth of defect relation: h=aK
3+ bK
2+ cK+d;
S2, qualitative assessment is carried out to the unknown depth of defect of test specimen, obtain the detection signal time-domain curve under the different lift off was more in unknown depth of defect position, and the time-domain curve of detection signal and reference signal is made difference processing and extracted eigenwert, result is substituted into the expression formula h=aK tried to achieve in described step S16
3+ bK
2in+cK+d, obtain the unknown depth of defect of test specimen, specifically comprise step by step:
The pulse excitation signal that S21, generation frequency and dutycycle are all adjustable;
S22, incentive probe coil, produce excitation field, be placed in by probe coil above test specimen, at unknown depth of defect A
xthe a certain unknown lift off was more place at place obtains detection signal B
1time-domain curve; △ x is increased successively respectively again, the detection signal B of the different lift off was more at least three places of reentrying on the basis of unknown lift off was more
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 reference signal that obtains make difference processing, obtain the differential signal curve under 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 differential peak voltage, extract the differential peak voltage fitting a straight line slope K of described relation curve, and K is substituted into the relation curve h=aK of gained in described step S16
3+ bK
2+ cK+d, obtains unknown depth of defect h, the A namely in step S22
xdepth value.
In the prior art, it is detection to space flight equipment that Pulsed eddy current testing is generally applied more, when adopting the detection method of elimination Lift-off effect of the present invention to detect test specimen, only need carry out Measurement and analysis in first time to the known defect degree of depth of test specimen said material, obtain the relation curve of differential peak voltage fitting a straight line slope and depth of defect, eliminate different lift off was more to the impact of testing result, the result that just detection can be made to obtain is more accurate, and algorithmic procedure is wherein easy, be easy to operate in practice, do not need the instrument using huge precision can complete detection to unknown depth of defect, eliminate Lift-off effect to the impact of testing result.
Wherein, because the response signal exported is comparatively faint, in order to obtain better testing result, need to do amplification filtering process to the detection signal exported and reference signal, so also comprised the amplification filtering process to detection signal and reference signal before described step S13, same, before described step S23, also comprise the amplification filtering process to obtained detection signal.
Be illustrated in figure 2 a kind of structured flowchart eliminating the Pulsed eddy current testing device 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;
Described sensor probe comprises drive coil and is positioned at the Hall element of coil, drive coil is used for producing eddy current at test specimen conductor, Hall element is used for field signal to be 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 extracting response signal and preserving, and extracts reference signal and the detection signal under different depth of defect, different lift off was more, and carries out record to described reference signal and detection signal;
Described lift-off compensation module be used for data acquisition module transmission reference signal and detection signal carry out difference processing, obtain the relation curve of lift off was more and differential peak voltage under the different known defect degree of depth, and eigenwert process is extracted to described relation curve, obtain the relation curve at different depth of defect and differential peak voltage fitting a straight line slope;
The relation curve that described depth of defect computing module is used for different depth of defect and the differential peak voltage fitting a straight line slope obtained according to lift-off compensation module obtains unknown depth of defect.
Wherein, also comprise Signal-regulated kinase, the electric signal that described Signal-regulated kinase is used for Hall element exports carries out amplification filtering process, and outputs to data acquisition module.Described Signal-regulated kinase comprises amplifier AD620, operational amplifier OP07.Described pulse excitation signal source adopts SPF40 type digit synthesis function signal generator to realize.
Can understand for the ease of those skilled in the art and implement the present invention program, below to the present invention a kind of eliminate Lift-off effect pulse eddy current detection method and device be described in detail:
The acquisition of the pumping signal described in above-mentioned steps S11 and step S21 can utilize SPF40 type digit synthesis function signal generator, directly obtain frequency, duty high-accuracy stable pulse signal f (t) that when amplitude is all adjustable by it, its available formula (1) carries out Fourier expansion:
In formula, A
0for DC component, A
nfor the amplitude of each harmonic component of correspondence, ω
1for first-harmonic angular frequency,
for pulsating wave initial phase.
Described sensor probe is made up of drive coil and Hall element.Drive coil is excitation field source, produces by it the Primary field forming eddy effect; Hall element is placed in centre position bottom drive coil, as the detecting portion of probe, for obtaining the size in magnetic field after coil stimulating magnetic field and the superposition of eddy current feedback magnetic field, and is translated into voltage signal and feeds back to subsequent processing section.But because excitation field is fainter, therefore, the voltage signal that Hall element exports is smaller equally, often only have tens millivolts, and the inside is also doped with a lot of high-frequency interferencing signal, therefore, the signal to sensor probe exports is needed to carry out amplification filtering process, namely amplification filtering process is carried out to obtained reference signal and the detection signal that obtains under the different lift off was more in each different known defect depth location places, noise jamming signal in filtered signal also amplifies it, it is made to reach the measurement range of subsequent data acquisition module.For realizing this function, the amplifying circuit that can to use with instrument amplifier AD620 be in embodiments of the present invention core realizes the amplification of signal, and utilizes high precision operating amplifier OP07 to form second-order low-pass filter filtering interference signals.
After completing reference signal and the acquisition of detection signal that obtains under the different lift off was more in each different known defect depth location places, obtained data are needed to carry out extracting and preserving, to facilitate, analysis contrast is carried out to result, for realizing the connection of detection system and host computer, PC control data collecting card can be utilized realize the collection to signal and storage in embodiments of the present invention.By follow-up lift-off compensation module and depth of defect computing module, difference processing and extraction eigenwert are carried out to the signal obtained again, obtain corresponding relation curve.
Below by the acquisition to reference signal and various detection signal and be described in detail the process of the difference processing of data and the extraction of eigenwert:
First choosing test specimen is aluminium alloy 7075 material, zero defect position and at least everywhere known defect depth location place detect, have chosen the eight different known defect degree of depth in places in an embodiment of the present invention and detect, depth of defect is followed successively by 0mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, at eight places, different known defect depth location place obtains the detection signal under different lift off was more respectively again, in eddy detection technology field, found by research, lift off was more is in certain variation range, its testing result drawn is effective sensing range, and valid analysing range can according to the geometry of Pulsed Eddy Current Testing System probe, physical dimension and electrical specification change, and valid analysing range described is in the present invention lift off was more when changing between 0mm to 2mm, chooses different lift off was more in embodiments of the present invention everywhere, is respectively lift-off 0.2mm, lift-off 0.8mm, lift-off 1.4mm, lift-off 2.0mm, is illustrated in figure 3 at test specimen zero defect, be 4mm place without the time-domain curve of the reference signal under lift off was more and depth of defect, lift off was more is respectively 0.2mm, lift-off 0.8mm, lift-off 1.4mm, the time-domain curve of the detection signal under lift-off 2.0mm, the signal curve at other known defect depth location places is also similar, lists no longer one by one in embodiments of the present invention.Respectively difference processing is done to the time-domain curve of obtained detection signal and the time-domain curve of reference signal 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 differential peak voltage curve, other known defect depth location places also make same treatment, obtain the graph of a relation as shown in Figure 5 at different known defect depth location place's lift off was more and differential peak voltage.
Can find when depth of defect one timing by Fig. 5, crest voltage and the lift off was more of the detection signal obtained 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, has nothing to do with the situation of change of lift-off, thus eliminates the impact of lift off was more in the calculating and analysis of testing result.
Finally to extract in Fig. 5 lift off was more and differential peak voltage corresponding relation slope of a curve K under the different known defect degree of depth
1, K
2, K
3, K
4, K
5, K
6, K
7, K
8, the slope obtained is fitted to cubic function curve with the corresponding known defect degree of depth: h=aK
3+ bK
2+ cK+d, be illustrated in figure 6 the relation curve of differential peak fitting a straight line slope and corresponding depth of defect, obtain the value of coefficient a, b, c, d, thus to complete test specimen be the differential peak fitting a straight line slope of aluminium alloy 7075 material and the measurement of depth of defect relation curve.
When test specimen is aluminium alloy 2024 material, method and the test specimen of process are that aluminium alloy 7075 is similar, the test result obtained is illustrated in figure 7 test specimen when being aluminium alloy 2024, its zero defect, is the time-domain curve of 4mm position lift off was more detection signal when being respectively 0.2mm, 0.8mm, 1.4mm, 2.0mm without the time-domain curve of the reference signal of lift off was more and depth of defect; Figure 8 shows that the differential signal curve of the time-domain curve based on the detection signal in Fig. 7 and reference signal; Figure 9 shows that the relation curve of lift off was more and differential peak voltage under different depth of defect, the depth of defect chosen is respectively 0mm, 2mm, 4mm, 6mm, 8mm; Figure 10 shows that the cubic function curve of differential peak fitting a straight line slope and corresponding depth of defect in Fig. 9.
Be fitting a straight line slope and depth of defect relation curve: the h=aK of aluminium alloy 7075 material again according to the test specimen of trying to achieve
3+ bK
2+ cK+d, detect the unknown depth of defect that test specimen is aluminium alloy 7075 material, 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 position of the lift-off interval △ x=0.6mm of known altitude on this basis, obtain detection signal B
2time-domain curve; Obtaining detection signal B
2after, then increase again the position of lift-off interval △ x=0.6mm of known altitude on this basis, detect and obtain signal B
3; Finally obtaining detection signal B
3after, then increase again the position of lift-off interval △ x=0.6mm of known altitude on this basis, obtain detection signal B
4time-domain curve.Determine the validity of four detection signals, if detection signal can use in valid analysing range, if not in effective range, must remeasure and then obtain effective detection signal;
Wherein the value of △ x artificially can define according to determined effective range;
Step 2, by four detected above detection signal B
1, B
2, B
3, B
4time-domain curve carry out calculus of differences with the time-domain curve of reference signal respectively, obtain four differential signals, extract the crest voltage U of four differential signals
1, U
2, U
3, U
4;
Step 3, simulate straight line according to four that obtain in step 2 effective differential peak voltages and known lift-off interval, obtain the slope K value of fitting a straight line;
Step 4, the straight slope K value obtained substituted in cubic function relational expression that different depth of defect h and fitting a straight line slope K exist and can try to achieve depth of defect h value in step 3, thus eliminate initial position the unknown lift off was more to the impact of testing result.
Claims (9)
1. eliminate a pulse eddy current detection method for Lift-off effect, it is characterized in that, specifically comprise:
S1, the detection signal time-domain curve under different lift off was more is obtained and the reference signal time-domain curve obtained in test specimen zero defect position without lift off was more to test specimen at different known defect depth location places, and the time-domain curve of detection signal and reference signal is made to difference processing and extracted eigenwert process, obtain the relation curve of differential peak voltage fitting a straight line slope and depth of defect, specifically comprise step by step:
The pulse excitation signal that S11, generation frequency and dutycycle are all adjustable;
S12, incentive probe coil, produce excitation field, be placed in by probe coil above test specimen, obtains the time-domain curve of the response signal of different situations, comprising:
1, the time-domain curve without the reference signal of lift off was more is obtained 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
4place obtains the time-domain curve of the detection signal under 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 detection signal that place obtains and the time-domain curve of reference signal make difference processing, obtain at known defect degree of depth A
1locate the differential signal curve under different lift off was more;
S14, repetition step S13, obtain at known defect degree of depth A
2, A
3, A
4locate the differential signal curve under different lift off was more;
S15, extract the known defect degree of depth A obtained in described step S13 and S14
1, A
2, A
3, A
4the crest voltage of the differential signal curve under different lift off was more, obtains 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 from 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 differential peak voltage fitting a straight line slope: K
1, K
2, K
3, K
4;
S16, the differential peak voltage fitting a straight line slope K obtained 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, fitted to a cubic function curve, described cubic function curve is: h=aK
3+ bK
2+ cK+d, wherein, described h is depth of defect, and K is differential peak voltage fitting a straight line slope, and a, b, c, d are respectively the coefficient of described cubic function curve, by described A
1, A
2, A
3, A
4and K
1, K
2, K
3, K
4substitute into described cubic function curve, obtain the value of corresponding a, b, c, d, then the value of a, b, c, d of obtaining is substituted into cubic function curve, obtain differential peak voltage fitting a straight line slope and depth of defect relation: h=aK
3+ bK
2+ cK+d;
S2, qualitative assessment is carried out to the unknown depth of defect of test specimen, obtain the detection signal time-domain curve under the different lift off was more in unknown depth of defect position, and the time-domain curve of detection signal and reference signal is made difference processing and extracted eigenwert, result is substituted into the expression formula h=aK tried to achieve in described step S16
3+ bK
2in+cK+d, obtain the unknown depth of defect of test specimen, specifically comprise step by step:
The pulse excitation signal that S21, generation frequency and dutycycle are all adjustable;
S22, incentive probe coil, produce excitation field, be placed in by probe coil above test specimen, at unknown depth of defect A
xthe a certain unknown lift off was more place at place obtains detection signal B
1time-domain curve; Δ x is increased successively respectively again, the detection signal B of the different lift off was more at least three places of reentrying on the basis of unknown lift off was more
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 reference signal that obtains make difference processing, obtain the differential signal curve under different lift off was more, extract the crest voltage of differential signal curve, obtain different lift off was more and the relation curve of corresponding differential peak voltage, extract the differential peak voltage fitting a straight line slope K of described relation curve
x, and by K
xsubstitute into the relation curve h=aK of gained in described step S16
3+ bK
2+ cK+d, obtains unknown depth of defect h
x, the A namely in step S22
xdepth value.
2. a kind of pulse eddy current detection method eliminating Lift-off effect as claimed in claim 1, is characterized in that, the described degree of depth A of known defect at least everywhere
1, A
2, A
3, A
4in, wherein there is the depth of defect value at a place to be 0.
3. a kind of pulse eddy current detection method eliminating Lift-off effect as claimed in claim 1 or 2, is characterized in that, also comprises the amplification filtering process to detection signal and reference signal before described step S13.
4. a kind of pulse eddy current detection method eliminating Lift-off effect as claimed in claim 1 or 2, is characterized in that, also comprises obtained detection signal B before described step S23
1, B
2, B
3, B
4amplification filtering process.
5. a kind of pulse eddy current detection method eliminating Lift-off effect as claimed in claim 1 or 2, is characterized in that, described Δ x is 0.6mm.
6. eliminate a Pulsed eddy current testing device for Lift-off effect, it is characterized in that, comprise pulse excitation signal source, sensor probe, data acquisition module, lift-off compensation module and depth of defect computing module;
Described pulse excitation signal source is for generation of pulse excitation signal;
Described sensor probe comprises drive coil and is positioned at the Hall element of coil, drive coil is used for producing eddy current at test specimen conductor, Hall element is used for field signal to be 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 extracting response signal and preserving, and extracts reference signal and the detection signal under different depth of defect, different lift off was more, and carries out record to described reference signal and detection signal;
Described lift-off compensation module be used for data acquisition module transmission reference signal and detection signal carry out difference processing, obtain the relation curve of lift off was more and differential peak voltage under the different known defect degree of depth, the straight slope extracting described relation curve is differential peak voltage fitting a straight line slope, obtains the relation curve of different depth of defect and differential peak voltage fitting a straight line slope;
The relation curve that described depth of defect computing module is used for different depth of defect and the differential peak voltage fitting a straight line slope obtained according to lift-off compensation module obtains unknown depth of defect.
7. a kind of Pulsed eddy current testing device eliminating Lift-off effect as claimed in claim 6, it is characterized in that, also comprise Signal-regulated kinase, the electric signal that described Signal-regulated kinase is used for Hall element exports carries out amplification filtering process, and outputs to data acquisition module.
8. a kind of Pulsed eddy current testing device eliminating Lift-off effect as claimed in claim 7, it is characterized in that, described Signal-regulated kinase comprises amplifier AD620, operational amplifier OP07.
9. a kind of Pulsed eddy current testing device eliminating Lift-off effect as claimed in claim 6, is characterized in that, described pulse excitation signal source adopts SPF40 type digit synthesis function signal generator to realize.
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