CA1070766A - Process and apparatus for non-destructive eddy current testing - Google Patents
Process and apparatus for non-destructive eddy current testingInfo
- Publication number
- CA1070766A CA1070766A CA260,058A CA260058A CA1070766A CA 1070766 A CA1070766 A CA 1070766A CA 260058 A CA260058 A CA 260058A CA 1070766 A CA1070766 A CA 1070766A
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- probe
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-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/72—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables
- G01N27/82—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws
- G01N27/90—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents
- G01N27/9046—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating magnetic variables for investigating the presence of flaws using eddy currents by analysing electrical signals
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
- F28F2265/00—Safety or protection arrangements; Arrangements for preventing malfunction
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- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)
Abstract
ABSTRACT
A process of and apparatus for non-destructive eddy current testing involves the suppression of displayed lobes corresponding to fault parameters to be eliminated from the display. Elimination circuits are provided for operating on the measurement signal to remove the undesirable parameters from the signal by compensation of the effects produced by the parameters at different frequencies.
A process of and apparatus for non-destructive eddy current testing involves the suppression of displayed lobes corresponding to fault parameters to be eliminated from the display. Elimination circuits are provided for operating on the measurement signal to remove the undesirable parameters from the signal by compensation of the effects produced by the parameters at different frequencies.
Description
6 Ei The present invention is concerned with a non-destructive testing process employing eddy currents and with an apparatus for carrying out this process. One application is in the testing of metallic workpieces, particularly tubular bundles intended for heat exchangers, condensers or steam generators.
It is known that testing by eddy currents consists of the study of variations of currents induced in a metal workpiece by the magnetic field of a coil carrying an alternating exciting current. Such currents produce, in turn, a fleld which opposes the lnducing field, and consequently modifies the impedance of the excitation coil. This coil is disposed in a probe which moves along the workpiece to be tested. Any defect of the workpiece being examined, which is present at the level of the probe (change in dimension, variation of electric conductivity, cracks, etcO) modifies the flow or the intensity of the eddy currents and consequently the impedance of the coil.
The probe is usually made of two adjacent coils9 energized in oppositlon and placed in the two ad~acent branches of a measuring bridge. ~he passage of a fault in the field of the probe unbalances the bridge twice, first in one direction and then in the other. The voltage generated by the probe t~6~
is amplified and~ after analysis, may be represented on the screen of a cathode ray tube. This representation is effected by displaying the resistive (or reaL) component ~ of the voltage measured and the reactive (or imaginary~
component Y. The complex voltage provided by the probe is thus represented by a point having the co-ordinates X and Y. When a fault passes into the field of the probe, the representative point describes a curve which is generally in the form of a figure of eight. Each fault can, therefore, be identified with reference to the phase of the lobe of the figure of eight (inclination relative to a reference axis) and by its amplitude.
Known techniques of testing by means of eddy currents, which utilize a single excitation frequency are not well suited to certain problems in which it is desired to test a workpiece which possesses either known or acceptable deformation, or discontinuities resulting for example from the presence of massive metallic bodies in the neighbourhood of the workpiece. This is the case, for example, with tubes intended for heat exchangers which are joined to a tubular plate~ to a cross-piece or to anti-vibration bars.
These discontinuities show themselves on the test apparatus 3 _ ~ 07 ~7 by extremely important signals which could mask possible signals corresponding to faults being sought.
Techniques are known for eliminating parameters thought undesirable and for only retaining in the curve repre-senting the variations of the signal produced by the probe theparts representative of the faults to be discovered. In this kind of technique multiple frequency excitation signals are used and the representative curve is successively rotated in such a way that the signals corresponding to the undesirable parameters disappear. Reference may be made, for example, to U.S. patent No. 3,706,029 issued on 12th December, 1972 to Wandling et al.
The present invention is concerned with a process and an apparatus in which the excitation is also effected at different frequencies and in which the contribution of one or more parameters is eliminated from the measurement signal.
The originality of the invention resides in the manner in which this elimination is effected.
According to the invention use is made of the fact that the appearance of curves representing the excitation signal depends on the frequency of examination. It is consequently possible to eliminate the contribution of a parameter by judicious combination of the curves obtained 76~;
at different frequencies, in such a way that the contribu~ion of the undesirable parameter is compensated for by the contribution of the same parameter at a different frequency.
The invention is not restricted to the elimination of a single parameter; it also covers the case where n~l parameters are eliminated with the assistance of an excitation signal composed of n differeat frequencles.
Nore particularly, the invention is concerned with a process of non-destructive testing using eddy currents, of the kind in which:
- a probe is displaced in the proximity of a workpiece to be tested, - said probe is supplied with an excitation surrent of n different frequencies, - the components of each of the n frequencies of the signal produced by the probe are analysed, characterized in that:
- there are ~etermined, for each component9 its re~lstive part X in phase with the excitation current at the same frequency and its reactive part Y in quadraturey - the parts Xl and Yl of one ~omponent at a first frequency are modified so that they coinc~de, in the zone correspol1dillg to a fault o.E a parc~neter to be eliminated, with the parts Xz and Y2 ~ a component at a second freq~iency, - from the parts Xl and Yl thus modlfied there are remot7ed the parts X2 and Y2, which provides a new set of resistive and reactive parts X' and Yi, permitting a representative curve to be obtained in which the contribution of the undesirable par~neter has been eliminated, ~ there is displayed on a plane the signal of the components ~ and YJ.
~he eLirnlllation of several parameters may be effected as just clescribed, by combining judi.cious.~yi the parts X and Y charac-erizing the components at two different freqllencies, or ~y combining the parts X' and Y' resulting ~5 :E~:om cl irst elimination with the parts characterizing a component at another frequency.
The in~ention is also concerned with an apparatus ` which carries out the process which has been described and which is of the kind comprising:
- a probe disposed in the proximity of the workpiece .
to be tested, the probe and the workpiece being displaced one in relation to the other in the course of testing,-"' ' ' ~ 70 ~
- means for su~p:Lying said probe ~7ith an e~citation current resulting ~rom the superposition. o n currents of excitation at n different frequencies, - means for extracting from the measuring signal provided by the probe the components of each of said n frequencies, said means being constituted by n analysing circuits giving, for each frequency, the resistive part X in phase with the excitation current at the same frequency and the reactive part Y in quadrature, - means for representing a measurement signal, in a plane marked with two rectangular axes, one carrying the parts X and the other the parts Y of the components o the measurement signal, in such a way that, for each frecluency, the point of said plane having the co-ordinates X and Y described during kesting of the workpiece~ a curve generally in the form of lobes~ each Iobe correspo~ding to a :Eault of a parameter o-f the worlcpiece to be tested, th~ apparatus according to the invention is characterized in that it ;Eurther includes means for eliminating, in the representation of the measurement signal, the parts of the curve corresponding to faults affecting certain undesirable parameters, said means comprising as many elimination circuits 71:~71~6 as there are p~r~neters to be elirninated, each elimination circui.t cornprising:
- means for modifying the resistive and reactive parts Xl and Y1 of a component at a first frequency so that they coincide in the zone corresponding to a fault of the parameter to be eliminated, with the parts X2 and Y2 of a component at a second frequency, - means for removing from the modi.fied parts Xl and Yl the parts X2 and Y2 which provides a new set of resistive and reactive parts X' and Y~, applied thereafter to display rneans for the measurement signal, and which lead to a curve devoid o the lobe corresponding to the parameter tc) be ellrninated~
In ally case, the characteristics and advantages of the present invention will emerge better after the following description of embodiments given by way of explanation and in no way limiting the invention, with reference to the attached drawings, in which:
- E`igure 1 shows the known principle oE:, representlng one component of the measurement voltage, by displaying~
on a screen, a point the co-ordinates o which are equal respectively to the parts of the sai.d component in phase .
--"
: :
'1~7~7~6 and in phase quadrat~lre ~lth the exc:itation;
- Eigure 2 illustrates diE:Eerent fo:rms which the representative curve can take, for the samP worl~piece, ~hcn the excitati.on frequency is modi.fied;
- Figure 3 illustrates the principle of elimination of a paramete., according to the invention, by compensation o the effects produced by this parameter at two different frequencies;
- Figure 4 represents a block diagram of a circuit or two requencies, which allows the parts X and Y of each oE the two components o~ the measurernent signal to be obtained;
- Figure S represents a block diagr~m of a circuit per~itting the elimination, according to the invention, o.~ a par~neter starting with two components of different fre~lencies;
- Figure 6 represents a block diagram o a circuit permitt:ing the elimination oE two parameters between signals . at three different requencies. . .~ ~ c .
Figure 1 illustrates the kno~n principle of representing the measurement voltage issuing from a probe by eddy currents.
The plane is marked with two rectangular axes Ox - Oy, on _ g _ . ~ :
~ 7~7~6 which are carried the part X of the measurement signal in phase with the excitation signal and the part Y in phase quadrature with the excitation signal. In such a complex representation, the point M having the co-ordinates X and Y therefore represents, at any instant, the measurement voltage at one of the excitation frequencies, and the curve traced by this point illustrates the variations of the component at this frequency when the probe and the work-piece to be tested are displaced one in relation to the other. The curve described by the point M is usually in the form of a figure of eight, as is known. This curve carries the reference 10 and is only shown on this Figure 1.
As is knowng the amplitude and the inclination of the curve obtained depend on the examination frequency.
This dependence is illustrated in Figure 2, in the case where the workpiece is a tube made of a material, such as the one known under the trademark INCONFL, having the diameters 22.2 x 20.7 mm, in the interior of which the probe is displaced. For the purposes of the description it is assumed that this tube has an internal surface fault marked by the reference Dj, an external surface fault marked by the reference De and an intermediate metallic plate fixed to the said tube, which introduces a discontinuity '.'- 1 ~ 7 ~ ~ ~ 6 P. ~;`igure 2 repx~esents the cur~es obtained for these ~hree alloml~ies, at t:hree cli.Eferent frequencies, respectively equal to 20 kHz~ 100 k~lz and 240 kHz.
For the frequency of 20 kHz, the internal and external aults have the s~ne phase and are of small amplitude comparec] to the one which corresponds to the existence of the int2nmediate plate P0 This is explained by the fact tha~ at this low frequency the penetration of the magnetic field is important, which permits the field to reach the plate.
~ or the intermediate frequency oE 100 kHz, the amplitude ra~:Lo is a li.ttle less impo~tant and the appearance of dephasing between the internal and external faults may be noted.
lS The frequency of 240 kH~ corresponds to the case where dephasing between the interna.l and external faults is of the order of 90 . It is ~nown, in fact, that there is a frequency for whi.ch dephasing between the faults situated on the inside of a tube and the faults situated on the outside of the tube takes this special value. On this po.int ~ reference may be made, for example, to the report No. R4073 of the Commissariat à l'~nergie Atomique, entitled , ' , 7~`6 "Contribution to the study of eddy currerlts and application to the rnultipara1ne-ter testing of tubes" by ~Iichel Pigeon, published :in Octob~r, 1970. In the present ex~nple, at this frequency o~ 240 kHz, the depth of penetration of the eddy currents is of the order of the thickness of th~
tube wall; there exists9 therefore, only a weak field on the outside of the said tube, which explains the diminution of the amplitude of the signal corresp~nding to the existence of the intermediate plate. The ratio between the amplitudes of che internal and external aults is o the order oE 0.4.
If it were required to eliminate entirely the ault correspollcl:ing to the plate P, i.t would be necessary then to continue to increase the requency, but this would inevitably lead to the elimination of the external ~ ~;
lS f~lu1ts. This malmer of proceeding would, therefore, not be judici.ous. By avoiding this disadvantage the invention permits jllSt this elimination by a process the principle o~ which is illustrated schematically in Figure 3.
In Figure 3a, these.faults correspond to a irst.
frequency A and in Figure 3b, to a frequency Bo The frequency A is, for example9 lOO kHz and the frequency B is 2~0 kHz. Each representation of a fault is affected ~17~7~6 by the indicatlon A or B accordillg to the frequency. Thus, the not~tion D ~ corresponds to the representation of the e~ternal fault for the frequency A.
E~igure 3c sho~7s the ~au]ts obtai.ned from Figure 3a by S a homothesis of ratio k, k being chosen in such a way that the ampl.itude of the vector kPA at the frequency A, corresponding to the plate P, becomes equal to the amplitude - of the vector PB obtained at the frequency B. It ~oes without saying that the amplitudes of the vec~ors DeA and .
DiA for the frequency A undergo the same homothesis and become equal to kDeA and kDiA. It is only by way o explarlation that the co-ordinates X and ~ had been supposed to 'be mod.Lfied :in the same ratio 'k; it would not be departing rom the -fr~nework of the invention by multiplying the co-ordinal:es X by a first coefficient kx and the co~ordinates Y by a second coefficient ky.
Figure 3d shows the modification given to Figure 3c when the said Figure is t~lrned through an angle such that the vector kPA becomes parallel to the vect,or PB characterizing t'he same fault at the frequency B. In the effected rotation, the vectors kDeA and kDiA of course undergo the same rotation and become kD'eA and kD'iA.
~L~76~7~6 Figure 3e sho~s the result obtainecl by subtracting the diagram of Fi~ure 3d from the di.agrarn of Figure 3b.
As the vectors characterizing the discontinuity due to . the presence of the plate have the same amplitude and the same phase in the di.agrams 3b and 3d, these vectors disappear in the operation of subtraction, and there only subsist, in the diagram of Figure 3e, the vectors characterizing the internal and external faults, thatOis to sc~y a vector :-.
DiB-kD iA and DeB-~D eA~
100f course the simplified representation used in Figure 3 wh:ich assimilates one lobe of a vector does not necessarily ;mply that the said lobe only ~mdergoes a homothe~ic rotation, because in the multiplication by kx arl(l ky, t.he lobe can be deformed if kx ~ ky. . ~ :
15By these transformations which characterize the process according to the invention, the curve representing the variations o the measurement signal has had removed the contribution made by the undesirable parameter P. This process is useEul when the lobe corresponding to the undesirable parameter is well detached from the other lobes as is the case in Figure 2, but, even more, it is useful : when a fault which is to be detected is situated in the ' ~:D7~17~6 neighbourhood of the workpiece corresponding to the undesirable parameter; this is the case, for example, when a fault affecting the tube to be tested is situated in the neighbourhood of the plate. In this case, two lobes corresponding to the plate (an undesirable parameter to be eliminated) and to the fault (to be detected) are mixed and the second, if it is weak, can be swamped by the first. When the adjustment of the apparatus has been effected so that the lobe corresponding to the plate has been eliminated, according to the process of the invention, the lobe characterizing the fault then appears clearly and the fault can be analysed and identified.
The transformations characterizing the process of the invention are preferably effected on the resistive part X and reactive part Y of each component of the measurement signal. These parts can be obtained by effecting an analysis of the signal provided by the measuring probe, according to known methods. Reference may be made, for example, to the report already mentioned, and to the U.S.
patent No. 3,229,198 of 11th January, 1966 to Libby. By way of explanation, Figure 4 shows the block diagram of a circuit for two frequencies, which allows the obtaining of these ~ , ~
~7 ~ ~ ~ 6 ' parts X and Y, for each of tlle two cornponents of the measurement signal.
On Figure ~, the probe carries the reference 12 and it comprises a first coil 14 coupled to a second coil 16, in a balanced bridge arrangement comprising two resistances 18 and two inductances 20. This probe has an input ter~inal 22 and an output terminal 24. The excitation means of such a probe include a first oscillatoO 26, providing a current at the frequency A and a second oscillator 28, providing a current of frequency B. The currents provided by these two oscillators are superimposed in a sur~mation circuit 30, followed by an ampliEier 32. The output of the sald amplifier is connected to the input 22 of the pL vl~e .
The measurement signal provided by the probe is delivered by the output 24. This signal may be preamplified ~y the preamplification circuit 34, for example by a gain o~ 10 ' dec;.bels, in order that the measurement si.gnals may have a level sufficient for them to effect the balancing operation.~, These operations consist in compensating the imbalance of the construction of the probe and they are effected in a circuit refere~ced 36 and which is connected to the ~- - 16 -, '~ ' ' ~ ~' ' , ~'' ' ,.
~ 7 ~ ~
oscillators 26 ~nd 28 respectively by the connexions 38 and 40 ~hich carry the signals ~7hich are in phclse an~ in phase quadrature with the currents provided by the oscillators. ~le measurement signal is am21ified a~ter balancing in an amplifying circuit 42, for example of a gain of 30 decibels, the said amplification being such that the signal does not undergo any saturation.
The measurement signal provided by the amplifier 42 comprises signals in two frequencies A and B which are separately filtered by means of a first band-pass filter 44, centred on the frequency A, and by a band-pass filter 46, centred o~ the frequency B. These filters are advantageo-lsly of strong slope, for example 24 decibels per octave. The signals thus filtered are then amplified 'oy ampliEying circuits 48 and 50 and then analysed by memory sampling circuits 52 an~ 54. These circuits receive by the connections 56 and 58, t~o reference signals at the ~`
requencies A and B respectively in phase and in phase quadrature with the currents provided by the oscillators. , l~ese memory sampling circuits provide at their two output leads respectively 60-62 and 64-66 the parts X in phase and ~ in phase quadrature with the excitation currents.
.. ' .
.
.
~97~7~;G ' !
'~ ' .
These samplinO circuits may be ~ollo~ed by loi~-pass filters 68 and 70, wh;ch permit eliminatiorl of residual base noise due to sampling. The entire circuit, therefore, delivers, deEini~ively, the resistive and reactive parts X~ and YA
for the components at the frequency A, and XB and YB for the colnponents at the frequency B. These signals X and Y are continuous voltages, which are variable with the displacement o~ the probe.
It goes wlthout saying that this circuit is only described by way o example and that any other known means permitting the determination oE the said resistive and re~c~ive parts at each frequency may be associated with the elimination circuit such as wi.ll now be described ~ith ref~rence to Figure 5.
The ci.rcuit of Figure 5 is connected to the output o~
the analysis circuit represented in Figure 4 and it, therefore, receives at its inputs the resistive and reactive parts XA and Y~ correspondi.ng to the frequency A and ~
ancl YB corresponding to the requency B. This elimination circuit comprises a weighting circuit 807 on the path corresponding to the requency A, formed by two multipliers 80x and 80yO This circuit multiplies the parts X~ and YA
- 18 ~
.
~(3 7~7~6 respectively by the coe~ icients ~x and ky, ~hich are possibly equal, and supplies the parts X'~ and Y'A which are such that the arnplitude ~ ~ for the signal corresponding to the parameter to be eli.mi.nated is equal to the am.plitude ~X~ -~ YB of the signal corresponding to the same parc~meter for the frequency B. In other words, the weighting circuit 80 effects that which corresponds to the operation illustrated in Figure 3 in the case where kx ~ y. This operation of weightin8 can also be effected sim~lltaneously on the path E, if a second weighting circuit 82 is used on this path, comprising two multipliers 82x and 82y. The multiplier 80 is followed by a dephasing ci.rcuit 84, which modifies the parts X'A and Y'A and plovides the new parts X"~ and Y"~ such that for the faulk of the parameter to be eliminated, these new parts are equal to the corresponding parts XB and YB at the ire~uency B. In othe-r words, the dephasing circuit 84 effects the . .
operation of rotation illustrated in Figure 3d. Subtraction ~:
circuits 86 and 88 thereafter effect the ~ifference between J' the resistive parts XB and Xl'A and YB and Y"A. At the output of the circuits 86 and 88 there are avai]able two new resistive and reactive parts X' and Y' in which the . .
~'7~ 6 unc1esirable parclmeter has been eliminated. These are the pa.~s ~/hich are applied to the d:isplay means 90, possibly after passing through a dephasing circui~. 92, which permits the orientation of the curves ob-tained on the screen of the means 90.
The display system 90 is advantageously associated' with an electronic switch 94 which allows display on the screen the curve representing the component at the frequency A aEter the opera~ions o~ weighting and rotation, which is obtainecl by apply,ing to the means 90 the parts X"~ and Y"A s~lpplled by the dephaser 84. These switching means 94 also allow display on the screen of the curve corresponding to l:he frequency B. If the switch 94 comprises electronic c1lt-of:E, it is possible -to show alternatively these two curves and so to regulate the weighting circuits 80 and df~2'hasing circuit.s 84 so that after the opera.tion of s~btraction, the undesirable parameter will be conveniently el:Lmlnated. The switch 94 also permits the connection , ' of the display means 90 to the output of the dephasing circuit 92 in order to show the curve obtained after elimination of the undesirable parameter~ The circuit 84 allowing dephasing of the parts ~ and Y in relation to one ' 20 - ,, . . ~
~ C~7~66 another in such a way that the representative curve undergoes a rotat;on around the OrigiLI, is kno~n to t:he expert in the art. Reference may be macle on this subject to U,S.
Patent No. 3,706,02~, already ~entioned, where such circuits S are described.
Of course the switching means 94 are only shown schematically in Figure 5: they may be partially incorporated in the display means, particularly when these comprise a double beam cathode ray tube. These switching means may also be associated with a device for effacing the luminous spot: on the screen when moving from one curve to the other.
'~lese me.ms are well known and hence not shown, and may possibly be lncluded in the displa~ system 90.
The elirnination of several parameters may be effected 5 iTl a successlve manner as shown schematically in Figure 6.
In this flgure there is shown a circuit allowing the elimination of two parameters between three signals at three different frequencies. The circuit 100 supplies the parts XA and YA of one component at the frequency A~ XB and YB
of a component at the frequency B and Xc and YC of a component at the frequency C. These components depend on three parameters ~, ~ and ~. A third elimination circuit ~ 7 ~ 6 1.06 elimi.llates the parameters ~ by us:ing the parts X' and Y' on one hand, a.nd ~" c~nd Y~7 on the otLler han~l. This elimination circuit :lO6 provides the parts X" ' and Y'7 7 ~hich only clepencl OTI the parameter ~. The paramete,rs S and ~ have, there~ore, thus been eliminated.
.
.... . ... , . _.. . _. _. .___ .. _.. _ . .. . . .. _ .. ~.. ... , .. ~ .. , .. ....... ,.. ~ _ _. ,., . _ ._, . _ _ _ __. _ .
It is known that testing by eddy currents consists of the study of variations of currents induced in a metal workpiece by the magnetic field of a coil carrying an alternating exciting current. Such currents produce, in turn, a fleld which opposes the lnducing field, and consequently modifies the impedance of the excitation coil. This coil is disposed in a probe which moves along the workpiece to be tested. Any defect of the workpiece being examined, which is present at the level of the probe (change in dimension, variation of electric conductivity, cracks, etcO) modifies the flow or the intensity of the eddy currents and consequently the impedance of the coil.
The probe is usually made of two adjacent coils9 energized in oppositlon and placed in the two ad~acent branches of a measuring bridge. ~he passage of a fault in the field of the probe unbalances the bridge twice, first in one direction and then in the other. The voltage generated by the probe t~6~
is amplified and~ after analysis, may be represented on the screen of a cathode ray tube. This representation is effected by displaying the resistive (or reaL) component ~ of the voltage measured and the reactive (or imaginary~
component Y. The complex voltage provided by the probe is thus represented by a point having the co-ordinates X and Y. When a fault passes into the field of the probe, the representative point describes a curve which is generally in the form of a figure of eight. Each fault can, therefore, be identified with reference to the phase of the lobe of the figure of eight (inclination relative to a reference axis) and by its amplitude.
Known techniques of testing by means of eddy currents, which utilize a single excitation frequency are not well suited to certain problems in which it is desired to test a workpiece which possesses either known or acceptable deformation, or discontinuities resulting for example from the presence of massive metallic bodies in the neighbourhood of the workpiece. This is the case, for example, with tubes intended for heat exchangers which are joined to a tubular plate~ to a cross-piece or to anti-vibration bars.
These discontinuities show themselves on the test apparatus 3 _ ~ 07 ~7 by extremely important signals which could mask possible signals corresponding to faults being sought.
Techniques are known for eliminating parameters thought undesirable and for only retaining in the curve repre-senting the variations of the signal produced by the probe theparts representative of the faults to be discovered. In this kind of technique multiple frequency excitation signals are used and the representative curve is successively rotated in such a way that the signals corresponding to the undesirable parameters disappear. Reference may be made, for example, to U.S. patent No. 3,706,029 issued on 12th December, 1972 to Wandling et al.
The present invention is concerned with a process and an apparatus in which the excitation is also effected at different frequencies and in which the contribution of one or more parameters is eliminated from the measurement signal.
The originality of the invention resides in the manner in which this elimination is effected.
According to the invention use is made of the fact that the appearance of curves representing the excitation signal depends on the frequency of examination. It is consequently possible to eliminate the contribution of a parameter by judicious combination of the curves obtained 76~;
at different frequencies, in such a way that the contribu~ion of the undesirable parameter is compensated for by the contribution of the same parameter at a different frequency.
The invention is not restricted to the elimination of a single parameter; it also covers the case where n~l parameters are eliminated with the assistance of an excitation signal composed of n differeat frequencles.
Nore particularly, the invention is concerned with a process of non-destructive testing using eddy currents, of the kind in which:
- a probe is displaced in the proximity of a workpiece to be tested, - said probe is supplied with an excitation surrent of n different frequencies, - the components of each of the n frequencies of the signal produced by the probe are analysed, characterized in that:
- there are ~etermined, for each component9 its re~lstive part X in phase with the excitation current at the same frequency and its reactive part Y in quadraturey - the parts Xl and Yl of one ~omponent at a first frequency are modified so that they coinc~de, in the zone correspol1dillg to a fault o.E a parc~neter to be eliminated, with the parts Xz and Y2 ~ a component at a second freq~iency, - from the parts Xl and Yl thus modlfied there are remot7ed the parts X2 and Y2, which provides a new set of resistive and reactive parts X' and Yi, permitting a representative curve to be obtained in which the contribution of the undesirable par~neter has been eliminated, ~ there is displayed on a plane the signal of the components ~ and YJ.
~he eLirnlllation of several parameters may be effected as just clescribed, by combining judi.cious.~yi the parts X and Y charac-erizing the components at two different freqllencies, or ~y combining the parts X' and Y' resulting ~5 :E~:om cl irst elimination with the parts characterizing a component at another frequency.
The in~ention is also concerned with an apparatus ` which carries out the process which has been described and which is of the kind comprising:
- a probe disposed in the proximity of the workpiece .
to be tested, the probe and the workpiece being displaced one in relation to the other in the course of testing,-"' ' ' ~ 70 ~
- means for su~p:Lying said probe ~7ith an e~citation current resulting ~rom the superposition. o n currents of excitation at n different frequencies, - means for extracting from the measuring signal provided by the probe the components of each of said n frequencies, said means being constituted by n analysing circuits giving, for each frequency, the resistive part X in phase with the excitation current at the same frequency and the reactive part Y in quadrature, - means for representing a measurement signal, in a plane marked with two rectangular axes, one carrying the parts X and the other the parts Y of the components o the measurement signal, in such a way that, for each frecluency, the point of said plane having the co-ordinates X and Y described during kesting of the workpiece~ a curve generally in the form of lobes~ each Iobe correspo~ding to a :Eault of a parameter o-f the worlcpiece to be tested, th~ apparatus according to the invention is characterized in that it ;Eurther includes means for eliminating, in the representation of the measurement signal, the parts of the curve corresponding to faults affecting certain undesirable parameters, said means comprising as many elimination circuits 71:~71~6 as there are p~r~neters to be elirninated, each elimination circui.t cornprising:
- means for modifying the resistive and reactive parts Xl and Y1 of a component at a first frequency so that they coincide in the zone corresponding to a fault of the parameter to be eliminated, with the parts X2 and Y2 of a component at a second frequency, - means for removing from the modi.fied parts Xl and Yl the parts X2 and Y2 which provides a new set of resistive and reactive parts X' and Y~, applied thereafter to display rneans for the measurement signal, and which lead to a curve devoid o the lobe corresponding to the parameter tc) be ellrninated~
In ally case, the characteristics and advantages of the present invention will emerge better after the following description of embodiments given by way of explanation and in no way limiting the invention, with reference to the attached drawings, in which:
- E`igure 1 shows the known principle oE:, representlng one component of the measurement voltage, by displaying~
on a screen, a point the co-ordinates o which are equal respectively to the parts of the sai.d component in phase .
--"
: :
'1~7~7~6 and in phase quadrat~lre ~lth the exc:itation;
- Eigure 2 illustrates diE:Eerent fo:rms which the representative curve can take, for the samP worl~piece, ~hcn the excitati.on frequency is modi.fied;
- Figure 3 illustrates the principle of elimination of a paramete., according to the invention, by compensation o the effects produced by this parameter at two different frequencies;
- Figure 4 represents a block diagram of a circuit or two requencies, which allows the parts X and Y of each oE the two components o~ the measurernent signal to be obtained;
- Figure S represents a block diagr~m of a circuit per~itting the elimination, according to the invention, o.~ a par~neter starting with two components of different fre~lencies;
- Figure 6 represents a block diagram o a circuit permitt:ing the elimination oE two parameters between signals . at three different requencies. . .~ ~ c .
Figure 1 illustrates the kno~n principle of representing the measurement voltage issuing from a probe by eddy currents.
The plane is marked with two rectangular axes Ox - Oy, on _ g _ . ~ :
~ 7~7~6 which are carried the part X of the measurement signal in phase with the excitation signal and the part Y in phase quadrature with the excitation signal. In such a complex representation, the point M having the co-ordinates X and Y therefore represents, at any instant, the measurement voltage at one of the excitation frequencies, and the curve traced by this point illustrates the variations of the component at this frequency when the probe and the work-piece to be tested are displaced one in relation to the other. The curve described by the point M is usually in the form of a figure of eight, as is known. This curve carries the reference 10 and is only shown on this Figure 1.
As is knowng the amplitude and the inclination of the curve obtained depend on the examination frequency.
This dependence is illustrated in Figure 2, in the case where the workpiece is a tube made of a material, such as the one known under the trademark INCONFL, having the diameters 22.2 x 20.7 mm, in the interior of which the probe is displaced. For the purposes of the description it is assumed that this tube has an internal surface fault marked by the reference Dj, an external surface fault marked by the reference De and an intermediate metallic plate fixed to the said tube, which introduces a discontinuity '.'- 1 ~ 7 ~ ~ ~ 6 P. ~;`igure 2 repx~esents the cur~es obtained for these ~hree alloml~ies, at t:hree cli.Eferent frequencies, respectively equal to 20 kHz~ 100 k~lz and 240 kHz.
For the frequency of 20 kHz, the internal and external aults have the s~ne phase and are of small amplitude comparec] to the one which corresponds to the existence of the int2nmediate plate P0 This is explained by the fact tha~ at this low frequency the penetration of the magnetic field is important, which permits the field to reach the plate.
~ or the intermediate frequency oE 100 kHz, the amplitude ra~:Lo is a li.ttle less impo~tant and the appearance of dephasing between the internal and external faults may be noted.
lS The frequency of 240 kH~ corresponds to the case where dephasing between the interna.l and external faults is of the order of 90 . It is ~nown, in fact, that there is a frequency for whi.ch dephasing between the faults situated on the inside of a tube and the faults situated on the outside of the tube takes this special value. On this po.int ~ reference may be made, for example, to the report No. R4073 of the Commissariat à l'~nergie Atomique, entitled , ' , 7~`6 "Contribution to the study of eddy currerlts and application to the rnultipara1ne-ter testing of tubes" by ~Iichel Pigeon, published :in Octob~r, 1970. In the present ex~nple, at this frequency o~ 240 kHz, the depth of penetration of the eddy currents is of the order of the thickness of th~
tube wall; there exists9 therefore, only a weak field on the outside of the said tube, which explains the diminution of the amplitude of the signal corresp~nding to the existence of the intermediate plate. The ratio between the amplitudes of che internal and external aults is o the order oE 0.4.
If it were required to eliminate entirely the ault correspollcl:ing to the plate P, i.t would be necessary then to continue to increase the requency, but this would inevitably lead to the elimination of the external ~ ~;
lS f~lu1ts. This malmer of proceeding would, therefore, not be judici.ous. By avoiding this disadvantage the invention permits jllSt this elimination by a process the principle o~ which is illustrated schematically in Figure 3.
In Figure 3a, these.faults correspond to a irst.
frequency A and in Figure 3b, to a frequency Bo The frequency A is, for example9 lOO kHz and the frequency B is 2~0 kHz. Each representation of a fault is affected ~17~7~6 by the indicatlon A or B accordillg to the frequency. Thus, the not~tion D ~ corresponds to the representation of the e~ternal fault for the frequency A.
E~igure 3c sho~7s the ~au]ts obtai.ned from Figure 3a by S a homothesis of ratio k, k being chosen in such a way that the ampl.itude of the vector kPA at the frequency A, corresponding to the plate P, becomes equal to the amplitude - of the vector PB obtained at the frequency B. It ~oes without saying that the amplitudes of the vec~ors DeA and .
DiA for the frequency A undergo the same homothesis and become equal to kDeA and kDiA. It is only by way o explarlation that the co-ordinates X and ~ had been supposed to 'be mod.Lfied :in the same ratio 'k; it would not be departing rom the -fr~nework of the invention by multiplying the co-ordinal:es X by a first coefficient kx and the co~ordinates Y by a second coefficient ky.
Figure 3d shows the modification given to Figure 3c when the said Figure is t~lrned through an angle such that the vector kPA becomes parallel to the vect,or PB characterizing t'he same fault at the frequency B. In the effected rotation, the vectors kDeA and kDiA of course undergo the same rotation and become kD'eA and kD'iA.
~L~76~7~6 Figure 3e sho~s the result obtainecl by subtracting the diagram of Fi~ure 3d from the di.agrarn of Figure 3b.
As the vectors characterizing the discontinuity due to . the presence of the plate have the same amplitude and the same phase in the di.agrams 3b and 3d, these vectors disappear in the operation of subtraction, and there only subsist, in the diagram of Figure 3e, the vectors characterizing the internal and external faults, thatOis to sc~y a vector :-.
DiB-kD iA and DeB-~D eA~
100f course the simplified representation used in Figure 3 wh:ich assimilates one lobe of a vector does not necessarily ;mply that the said lobe only ~mdergoes a homothe~ic rotation, because in the multiplication by kx arl(l ky, t.he lobe can be deformed if kx ~ ky. . ~ :
15By these transformations which characterize the process according to the invention, the curve representing the variations o the measurement signal has had removed the contribution made by the undesirable parameter P. This process is useEul when the lobe corresponding to the undesirable parameter is well detached from the other lobes as is the case in Figure 2, but, even more, it is useful : when a fault which is to be detected is situated in the ' ~:D7~17~6 neighbourhood of the workpiece corresponding to the undesirable parameter; this is the case, for example, when a fault affecting the tube to be tested is situated in the neighbourhood of the plate. In this case, two lobes corresponding to the plate (an undesirable parameter to be eliminated) and to the fault (to be detected) are mixed and the second, if it is weak, can be swamped by the first. When the adjustment of the apparatus has been effected so that the lobe corresponding to the plate has been eliminated, according to the process of the invention, the lobe characterizing the fault then appears clearly and the fault can be analysed and identified.
The transformations characterizing the process of the invention are preferably effected on the resistive part X and reactive part Y of each component of the measurement signal. These parts can be obtained by effecting an analysis of the signal provided by the measuring probe, according to known methods. Reference may be made, for example, to the report already mentioned, and to the U.S.
patent No. 3,229,198 of 11th January, 1966 to Libby. By way of explanation, Figure 4 shows the block diagram of a circuit for two frequencies, which allows the obtaining of these ~ , ~
~7 ~ ~ ~ 6 ' parts X and Y, for each of tlle two cornponents of the measurement signal.
On Figure ~, the probe carries the reference 12 and it comprises a first coil 14 coupled to a second coil 16, in a balanced bridge arrangement comprising two resistances 18 and two inductances 20. This probe has an input ter~inal 22 and an output terminal 24. The excitation means of such a probe include a first oscillatoO 26, providing a current at the frequency A and a second oscillator 28, providing a current of frequency B. The currents provided by these two oscillators are superimposed in a sur~mation circuit 30, followed by an ampliEier 32. The output of the sald amplifier is connected to the input 22 of the pL vl~e .
The measurement signal provided by the probe is delivered by the output 24. This signal may be preamplified ~y the preamplification circuit 34, for example by a gain o~ 10 ' dec;.bels, in order that the measurement si.gnals may have a level sufficient for them to effect the balancing operation.~, These operations consist in compensating the imbalance of the construction of the probe and they are effected in a circuit refere~ced 36 and which is connected to the ~- - 16 -, '~ ' ' ~ ~' ' , ~'' ' ,.
~ 7 ~ ~
oscillators 26 ~nd 28 respectively by the connexions 38 and 40 ~hich carry the signals ~7hich are in phclse an~ in phase quadrature with the currents provided by the oscillators. ~le measurement signal is am21ified a~ter balancing in an amplifying circuit 42, for example of a gain of 30 decibels, the said amplification being such that the signal does not undergo any saturation.
The measurement signal provided by the amplifier 42 comprises signals in two frequencies A and B which are separately filtered by means of a first band-pass filter 44, centred on the frequency A, and by a band-pass filter 46, centred o~ the frequency B. These filters are advantageo-lsly of strong slope, for example 24 decibels per octave. The signals thus filtered are then amplified 'oy ampliEying circuits 48 and 50 and then analysed by memory sampling circuits 52 an~ 54. These circuits receive by the connections 56 and 58, t~o reference signals at the ~`
requencies A and B respectively in phase and in phase quadrature with the currents provided by the oscillators. , l~ese memory sampling circuits provide at their two output leads respectively 60-62 and 64-66 the parts X in phase and ~ in phase quadrature with the excitation currents.
.. ' .
.
.
~97~7~;G ' !
'~ ' .
These samplinO circuits may be ~ollo~ed by loi~-pass filters 68 and 70, wh;ch permit eliminatiorl of residual base noise due to sampling. The entire circuit, therefore, delivers, deEini~ively, the resistive and reactive parts X~ and YA
for the components at the frequency A, and XB and YB for the colnponents at the frequency B. These signals X and Y are continuous voltages, which are variable with the displacement o~ the probe.
It goes wlthout saying that this circuit is only described by way o example and that any other known means permitting the determination oE the said resistive and re~c~ive parts at each frequency may be associated with the elimination circuit such as wi.ll now be described ~ith ref~rence to Figure 5.
The ci.rcuit of Figure 5 is connected to the output o~
the analysis circuit represented in Figure 4 and it, therefore, receives at its inputs the resistive and reactive parts XA and Y~ correspondi.ng to the frequency A and ~
ancl YB corresponding to the requency B. This elimination circuit comprises a weighting circuit 807 on the path corresponding to the requency A, formed by two multipliers 80x and 80yO This circuit multiplies the parts X~ and YA
- 18 ~
.
~(3 7~7~6 respectively by the coe~ icients ~x and ky, ~hich are possibly equal, and supplies the parts X'~ and Y'A which are such that the arnplitude ~ ~ for the signal corresponding to the parameter to be eli.mi.nated is equal to the am.plitude ~X~ -~ YB of the signal corresponding to the same parc~meter for the frequency B. In other words, the weighting circuit 80 effects that which corresponds to the operation illustrated in Figure 3 in the case where kx ~ y. This operation of weightin8 can also be effected sim~lltaneously on the path E, if a second weighting circuit 82 is used on this path, comprising two multipliers 82x and 82y. The multiplier 80 is followed by a dephasing ci.rcuit 84, which modifies the parts X'A and Y'A and plovides the new parts X"~ and Y"~ such that for the faulk of the parameter to be eliminated, these new parts are equal to the corresponding parts XB and YB at the ire~uency B. In othe-r words, the dephasing circuit 84 effects the . .
operation of rotation illustrated in Figure 3d. Subtraction ~:
circuits 86 and 88 thereafter effect the ~ifference between J' the resistive parts XB and Xl'A and YB and Y"A. At the output of the circuits 86 and 88 there are avai]able two new resistive and reactive parts X' and Y' in which the . .
~'7~ 6 unc1esirable parclmeter has been eliminated. These are the pa.~s ~/hich are applied to the d:isplay means 90, possibly after passing through a dephasing circui~. 92, which permits the orientation of the curves ob-tained on the screen of the means 90.
The display system 90 is advantageously associated' with an electronic switch 94 which allows display on the screen the curve representing the component at the frequency A aEter the opera~ions o~ weighting and rotation, which is obtainecl by apply,ing to the means 90 the parts X"~ and Y"A s~lpplled by the dephaser 84. These switching means 94 also allow display on the screen of the curve corresponding to l:he frequency B. If the switch 94 comprises electronic c1lt-of:E, it is possible -to show alternatively these two curves and so to regulate the weighting circuits 80 and df~2'hasing circuit.s 84 so that after the opera.tion of s~btraction, the undesirable parameter will be conveniently el:Lmlnated. The switch 94 also permits the connection , ' of the display means 90 to the output of the dephasing circuit 92 in order to show the curve obtained after elimination of the undesirable parameter~ The circuit 84 allowing dephasing of the parts ~ and Y in relation to one ' 20 - ,, . . ~
~ C~7~66 another in such a way that the representative curve undergoes a rotat;on around the OrigiLI, is kno~n to t:he expert in the art. Reference may be macle on this subject to U,S.
Patent No. 3,706,02~, already ~entioned, where such circuits S are described.
Of course the switching means 94 are only shown schematically in Figure 5: they may be partially incorporated in the display means, particularly when these comprise a double beam cathode ray tube. These switching means may also be associated with a device for effacing the luminous spot: on the screen when moving from one curve to the other.
'~lese me.ms are well known and hence not shown, and may possibly be lncluded in the displa~ system 90.
The elirnination of several parameters may be effected 5 iTl a successlve manner as shown schematically in Figure 6.
In this flgure there is shown a circuit allowing the elimination of two parameters between three signals at three different frequencies. The circuit 100 supplies the parts XA and YA of one component at the frequency A~ XB and YB
of a component at the frequency B and Xc and YC of a component at the frequency C. These components depend on three parameters ~, ~ and ~. A third elimination circuit ~ 7 ~ 6 1.06 elimi.llates the parameters ~ by us:ing the parts X' and Y' on one hand, a.nd ~" c~nd Y~7 on the otLler han~l. This elimination circuit :lO6 provides the parts X" ' and Y'7 7 ~hich only clepencl OTI the parameter ~. The paramete,rs S and ~ have, there~ore, thus been eliminated.
.
.... . ... , . _.. . _. _. .___ .. _.. _ . .. . . .. _ .. ~.. ... , .. ~ .. , .. ....... ,.. ~ _ _. ,., . _ ._, . _ _ _ __. _ .
Claims (4)
1. Process for non-destructive testing by eddy currents of the kind in which:
- a probe is displaced in the proximity of the workpiece to be tested, - said probe is supplied by an excitation current of n different frequencies, - the components of each of the n frequencies in the measurement signal are analysed, characterized in that:
- there are determined, for each component, its resistive part X in phase with the excitation current at the same frequency, and its reactive part Y in quadrature, - the parts X1 and Y1 of a component at a first frequency are modified so that they coincide, in the zone corresponding to a fault of a parameter which is to be eliminated, with the parts X2 and Y2 of a component at a second frequency, - the parts X2 and Y2 are removed from the parts X1 and Y1 thus modified, which provides a new set of resistive and reactive parts X' and Y', permitting to be obtained a representative curve for which the contribution of the undesirable parameter has been eliminated, - the signal of the components X' and Y' are displayed on a plan.
- a probe is displaced in the proximity of the workpiece to be tested, - said probe is supplied by an excitation current of n different frequencies, - the components of each of the n frequencies in the measurement signal are analysed, characterized in that:
- there are determined, for each component, its resistive part X in phase with the excitation current at the same frequency, and its reactive part Y in quadrature, - the parts X1 and Y1 of a component at a first frequency are modified so that they coincide, in the zone corresponding to a fault of a parameter which is to be eliminated, with the parts X2 and Y2 of a component at a second frequency, - the parts X2 and Y2 are removed from the parts X1 and Y1 thus modified, which provides a new set of resistive and reactive parts X' and Y', permitting to be obtained a representative curve for which the contribution of the undesirable parameter has been eliminated, - the signal of the components X' and Y' are displayed on a plan.
2. Process according to Claim 1, characterized in that having eliminated a first parameter in accordance with the process of Claim 1, a second undesirable parameter is eliminated by effecting the operations of Claim 1 between the parts X' and Y' obtained after elimination of the first parameter, and the parts X3 and Y3 of a third component at a third frequency.
3. Apparatus for non-destructive eddy current testing for carrying out the process of Claim 1, of the kind comprising:
- a probe disposed in the proximity of a workpiece to be tested, the probe and the workpiece moving one in relation to the other in the course of testing, - means for supplying said probe with an excitation current resulting from the superposition of n alternating excitation currents at n different frequencies, - means for extracting from the measurement signal provided by the probe the components of each of said n frequencies, said means comprising n analysing circuits giving, for each frequency, the resistive part X in phase with the excitation current at the same frequency and the reactive part Y in quadrature, - means for representing the measurement signal, in a plane marked by two axes at right angles to one another one carrying the parts X and the other the parts Y of the components of the measurement signal, in such a way that, for each frequency, the point of said plan having X and Y
as co-ordinates, describes in the course of testing of said workpiece, a curve generally in the form of lobes, each lobe corresponding to a fault of a parameter of the workpiece under test, characterized in that it comprises in addition means for eliminating, in the representation of the measurement signal, the parts of the curve corresponding to the faults affecting certain undesirable parameters, said means comprising as many elimination circuits as there are parameters to be eliminated, each elimination circuit comprising:
- means for modifying the resistive and reactive parts X1 and Y1 of a component at a first frequency so that they coincide, in the zone corresponding to a fault of the parameter to be eliminated, with the parts X2 and Y2 of a component at a second frequency, - means for removing from X1 and Y1 as modified the parts X2 and Y2, which provides a new set of resistive and reactive parts X' and Y', applied thereafter to display means for the measurement signal and which lead to a curve devoid of the lobe corresponding to said eliminated parameter.
- a probe disposed in the proximity of a workpiece to be tested, the probe and the workpiece moving one in relation to the other in the course of testing, - means for supplying said probe with an excitation current resulting from the superposition of n alternating excitation currents at n different frequencies, - means for extracting from the measurement signal provided by the probe the components of each of said n frequencies, said means comprising n analysing circuits giving, for each frequency, the resistive part X in phase with the excitation current at the same frequency and the reactive part Y in quadrature, - means for representing the measurement signal, in a plane marked by two axes at right angles to one another one carrying the parts X and the other the parts Y of the components of the measurement signal, in such a way that, for each frequency, the point of said plan having X and Y
as co-ordinates, describes in the course of testing of said workpiece, a curve generally in the form of lobes, each lobe corresponding to a fault of a parameter of the workpiece under test, characterized in that it comprises in addition means for eliminating, in the representation of the measurement signal, the parts of the curve corresponding to the faults affecting certain undesirable parameters, said means comprising as many elimination circuits as there are parameters to be eliminated, each elimination circuit comprising:
- means for modifying the resistive and reactive parts X1 and Y1 of a component at a first frequency so that they coincide, in the zone corresponding to a fault of the parameter to be eliminated, with the parts X2 and Y2 of a component at a second frequency, - means for removing from X1 and Y1 as modified the parts X2 and Y2, which provides a new set of resistive and reactive parts X' and Y', applied thereafter to display means for the measurement signal and which lead to a curve devoid of the lobe corresponding to said eliminated parameter.
4. Apparatus according to Claim 3, characterized in that each elimination circuit comprises:
- a weighting circuit connected to the analysis circuit corresponding to the first frequency, said weighting circuit multiplying the parts X1 and Y1 supplied by said analysis circuit, by coefficients, and providing new co-ordinates X'1 and Y'1 such that the amplitude for the signal at the first frequency-corresponding to the parameter to be eliminated is equal to the amplitude of the same signal for the parameter, at the second frequency.
- a dephaser, disposed at the output of the weighting means, modifying the parts X1 and Y1 supplied by the weighting means and supplying new parts X1 and Y1 equal to the parts X2 and Y2 corresponding to the second frequency, - a subtracter receiving on the one hand the set of parts X? and Y? corresponding to the first frequency and outputs of the dephaser and the set of parts X2 and Y2 corresponding to the second frequency and outputs of the analysis circuit at the second frequency, and effecting the difference between these parts, which provides two new parts X' and Y' in which said parameter has been eliminated.
- a weighting circuit connected to the analysis circuit corresponding to the first frequency, said weighting circuit multiplying the parts X1 and Y1 supplied by said analysis circuit, by coefficients, and providing new co-ordinates X'1 and Y'1 such that the amplitude for the signal at the first frequency-corresponding to the parameter to be eliminated is equal to the amplitude of the same signal for the parameter, at the second frequency.
- a dephaser, disposed at the output of the weighting means, modifying the parts X1 and Y1 supplied by the weighting means and supplying new parts X1 and Y1 equal to the parts X2 and Y2 corresponding to the second frequency, - a subtracter receiving on the one hand the set of parts X? and Y? corresponding to the first frequency and outputs of the dephaser and the set of parts X2 and Y2 corresponding to the second frequency and outputs of the analysis circuit at the second frequency, and effecting the difference between these parts, which provides two new parts X' and Y' in which said parameter has been eliminated.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR7527615A FR2324003A1 (en) | 1975-09-09 | 1975-09-09 | NON DESTRUCTIVE EDD CURRENT CONTROL PROCESS AND CORRESPONDING DEVICE, USING MULTI-FREQUENCY EXCITATION AND ALLOWING THE ELIMINATION OF CERTAIN PARAMETERS |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1070766A true CA1070766A (en) | 1980-01-29 |
Family
ID=9159766
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA260,058A Expired CA1070766A (en) | 1975-09-09 | 1976-08-27 | Process and apparatus for non-destructive eddy current testing |
Country Status (14)
| Country | Link |
|---|---|
| JP (1) | JPS602619B2 (en) |
| BE (1) | BE845928A (en) |
| BR (1) | BR7605858A (en) |
| CA (1) | CA1070766A (en) |
| DD (1) | DD126270A5 (en) |
| DE (1) | DE2637201A1 (en) |
| ES (1) | ES451374A1 (en) |
| FI (1) | FI59302C (en) |
| FR (1) | FR2324003A1 (en) |
| GB (1) | GB1521203A (en) |
| IT (1) | IT1074264B (en) |
| NL (1) | NL184387C (en) |
| SE (1) | SE418905B (en) |
| ZA (1) | ZA764982B (en) |
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| FR2443682A1 (en) * | 1978-12-07 | 1980-07-04 | Commissariat Energie Atomique | CIRCUIT FOR AUTOMATIC CORRECTION OF A SIGNAL TRANSMITTED BY AN IMBALANCE DIFFERENTIAL SENSOR |
| US4292589A (en) * | 1979-05-09 | 1981-09-29 | Schlumberger Technology Corporation | Eddy current method and apparatus for inspecting ferromagnetic tubular members |
| US4303885A (en) * | 1979-06-18 | 1981-12-01 | Electric Power Research Institute, Inc. | Digitally controlled multifrequency eddy current test apparatus and method |
| US4467281A (en) * | 1980-02-29 | 1984-08-21 | Electric Power Research Institute, Inc. | Multi frequency eddy current test apparatus with intermediate frequency processing |
| US4424486A (en) * | 1980-10-14 | 1984-01-03 | Zetec, Inc. | Phase rotation circuit for an eddy current tester |
| JPS5791058U (en) * | 1980-11-25 | 1982-06-04 | ||
| JPS5817354A (en) * | 1981-06-12 | 1983-02-01 | Kobe Steel Ltd | Inspection of pipe material by multifrequency eddy current flaw detection |
| JPS58137748A (en) * | 1982-02-12 | 1983-08-16 | Ishikawajima Harima Heavy Ind Co Ltd | Eddy current examination method |
| DE3313820A1 (en) * | 1983-04-16 | 1984-10-18 | Institut Dr. Friedrich Förster Prüfgerätebau GmbH & Co KG, 7410 Reutlingen | DEVICE FOR TESTING THE SURFACE OF A METAL TEST PART |
| CA1212997A (en) * | 1983-12-16 | 1986-10-21 | Gerard Durou | Frequency scanning eddy current non destructive testing method and system |
| FR2562668B1 (en) * | 1984-04-05 | 1987-11-27 | Sncf | DEVICE FOR TRACKING DEFECTS OF RAILWAY RAILS BY EDGE CURRENTS, CAPABLE OF DISCRIMINATING DEFECTS OF CERTAIN DISCONTINUITIES IN RAIL CONSTRUCTION |
| JPS60262052A (en) * | 1984-06-08 | 1985-12-25 | Sumitomo Metal Ind Ltd | Heterogeneous material discrimination |
| JPS6273158A (en) * | 1985-09-27 | 1987-04-03 | Daizaburo Iwasaki | Signal processing method and apparatus in eddy current flaw detection test |
| JPS62255863A (en) * | 1986-04-28 | 1987-11-07 | Furukawa Electric Co Ltd:The | Eddy current flaw detector |
| SE456864B (en) * | 1986-08-27 | 1988-11-07 | Toernbloms Kvalitetskontroll | DEVICE FOR DETECTING AND SUPPRESSING THE IMPACT OF INTERNATIONAL MAGNETIC FIELD DURING THE VERTICAL FLOW TEST OF OMAGNETIC PROVOBJECTS |
| FR2627862A1 (en) * | 1988-02-26 | 1989-09-01 | Commissariat Energie Atomique | IMPULSIVE FOUCAULT CURRENT MONITORING METHOD AND DEVICE FOR IMPLEMENTING THE SAME |
| US5017869A (en) * | 1989-12-14 | 1991-05-21 | General Electric Company | Swept frequency eddy current system for measuring coating thickness |
| FR2724019B1 (en) * | 1994-08-31 | 1997-04-30 | Intercontrole Sa | METHOD OF DIGITAL ANALYSIS OF A SIGNAL, IN PARTICULAR FOR EDGE CURRENT CONTROL |
| FR2758882B1 (en) * | 1997-01-27 | 1999-04-09 | Intercontrole Sa | METHOD OF NON-DESTRUCTIVE MONITORING BY EDGE CURRENTS OF NUCLEAR REACTOR CONTROL CLUSTERS IN THE PRESENCE OF DISTURBING ELEMENTS |
| WO2003036287A1 (en) * | 2001-09-24 | 2003-05-01 | Alstom Technology Ltd | Method and device for controlling laminated steel sheet stacks of electrical machines in a view to detect steel sheet short-circuits |
| US6815957B2 (en) | 2001-09-24 | 2004-11-09 | Alstom (Switzerland) Ltd | Method and device for inspecting laminated iron cores of electrical machines for interlamination shorts |
| JP4762672B2 (en) * | 2005-10-27 | 2011-08-31 | 非破壊検査株式会社 | Magnetic material bending portion fracture inspection method and inspection apparatus |
| CZ306012B6 (en) * | 2014-09-03 | 2016-06-22 | Vysoké Učení Technické V Brně | Non-destructive indicator of local subsurface non-homogeneities |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3706029A (en) * | 1971-11-16 | 1972-12-12 | Atomic Energy Commission | Multiple parameter eddy current nondestructive testing device using plural transformation rotators to resolve each parameter |
-
1975
- 1975-09-09 FR FR7527615A patent/FR2324003A1/en active Granted
-
1976
- 1976-08-18 DE DE19762637201 patent/DE2637201A1/en active Granted
- 1976-08-19 ZA ZA764982A patent/ZA764982B/en unknown
- 1976-08-27 CA CA260,058A patent/CA1070766A/en not_active Expired
- 1976-08-30 IT IT69113/76A patent/IT1074264B/en active
- 1976-08-31 NL NLAANVRAGE7609666,A patent/NL184387C/en not_active IP Right Cessation
- 1976-09-03 BR BR7605858A patent/BR7605858A/en unknown
- 1976-09-08 BE BE170414A patent/BE845928A/en not_active IP Right Cessation
- 1976-09-08 FI FI762581A patent/FI59302C/en not_active IP Right Cessation
- 1976-09-08 GB GB37174/76A patent/GB1521203A/en not_active Expired
- 1976-09-08 SE SE7609913A patent/SE418905B/en not_active IP Right Cessation
- 1976-09-09 JP JP51108390A patent/JPS602619B2/en not_active Expired
- 1976-09-09 ES ES451374A patent/ES451374A1/en not_active Expired
- 1976-09-09 DD DD194716A patent/DD126270A5/xx unknown
Also Published As
| Publication number | Publication date |
|---|---|
| DE2637201C2 (en) | 1987-10-08 |
| JPS5233791A (en) | 1977-03-15 |
| NL184387C (en) | 1989-07-03 |
| ZA764982B (en) | 1977-07-27 |
| GB1521203A (en) | 1978-08-16 |
| FR2324003B1 (en) | 1979-03-02 |
| BE845928A (en) | 1976-12-31 |
| DE2637201A1 (en) | 1977-03-17 |
| BR7605858A (en) | 1977-08-16 |
| FI762581A (en) | 1977-03-10 |
| FI59302C (en) | 1981-07-10 |
| IT1074264B (en) | 1985-04-20 |
| DD126270A5 (en) | 1977-07-06 |
| SE418905B (en) | 1981-06-29 |
| ES451374A1 (en) | 1977-12-16 |
| SE7609913L (en) | 1977-03-10 |
| FI59302B (en) | 1981-03-31 |
| NL7609666A (en) | 1977-03-11 |
| JPS602619B2 (en) | 1985-01-23 |
| FR2324003A1 (en) | 1977-04-08 |
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