EP1943477A1 - Dispositif d'examen non destructeur d'un objet - Google Patents

Dispositif d'examen non destructeur d'un objet

Info

Publication number
EP1943477A1
EP1943477A1 EP05797956A EP05797956A EP1943477A1 EP 1943477 A1 EP1943477 A1 EP 1943477A1 EP 05797956 A EP05797956 A EP 05797956A EP 05797956 A EP05797956 A EP 05797956A EP 1943477 A1 EP1943477 A1 EP 1943477A1
Authority
EP
European Patent Office
Prior art keywords
magnet
magnetic field
sensor
analogue
signal
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP05797956A
Other languages
German (de)
English (en)
Inventor
Pieter Bestebreurtje
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Sonimex BV
Original Assignee
Sonimex BV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sonimex BV filed Critical Sonimex BV
Publication of EP1943477A1 publication Critical patent/EP1943477A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/02—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness
    • G01B7/023—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring distance between sensor and object
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
    • G01B7/02—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness
    • G01B7/06—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness
    • G01B7/10—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness using magnetic means, e.g. by measuring change of reluctance
    • G01B7/105—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness using magnetic means, e.g. by measuring change of reluctance for measuring thickness of coating
    • 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

Definitions

  • the present invention relates in general to measuring layer thicknesses, although the present invention is also usable in other fields, for example in examining whether a material contains cracks.
  • the present invention relates to non- destructively measuring the thickness of a non-ferromagnetic layer on a ferromagnetic material, for example iron, steel, etc.
  • the layer may be an oxide skin, a paint layer, a metal layer such as chrome, gold, etc.
  • a change of a measuring signal corresponds to a change in distance, which, when the coil/sensor combination is pressed against the surface of the object to be examined, corresponds to a change in the thickness of the layer.
  • the sensitivity of the sensor used may drift as function of the time and function of the temperature.
  • the measurement is sensitive to external magnetic fields, and variations therein (as function of location, time, temperature, etc.) again cause measuring errors.
  • the German patent 101.45.657 describes a method to reduce such measuring errors. To that end, two measurements are performed, at two different current magnitudes of the coil current, and the two measuring results obtained therein are compared with each other. Temperature influences are compensated by measuring the electric resistance of the sensor, as measure for the temperature.
  • Performing a continuous measurement is desired in particular if one wants to quickly examine a large part of the surface of the object to be examined, for example if one wants to examine a rail for the presence of cracks. It is an object of the present invention to overcome or at least reduce said disadvantages.
  • the present invention aims at providing a measuring device that can be built in a compact way, can measure continuously, and provides precise and reproducible measuring results .
  • a measuring device comprises a constant magnetic field and two magnetic field sensors, arranged at different positions, wherein the measuring signals obtained from both sensors are compared in order to eliminate variations in environmental factors.
  • figure 1 schematically shows a measuring device according to the present invention
  • figure 2 is a block diagram schematically illustrating a preferred embodiment of a control member
  • figure 3 illustrates several construction details of a probe
  • figure 4 schematically illustrates a probe with pole shoes
  • figure 5 is a graph illustrating a measurement signal obtained, as function of the time.
  • Figure 1 schematically shows a measuring device 100 according to the present invention for non-destructively examining an object 3.
  • the object 3 comprises a ferromagnetic body 1 with a layer 2 of a non-ferromagnetic material on it.
  • the body is a steel beam
  • the layer 2 is an oxide layer with a thickness D in the order of 0-10 ⁇ m
  • the measuring device 100 is used to measure the thickness D of the layer 2.
  • the measuring device 100 comprises a magnet 20, with an axis 21 which is directed substantially perpendicular to the surface to be examined.
  • the magnet 20 may be implemented as a permanent magnet, or, as illustrated, as a magnet coil energized with a direct current; a combination is also possible.
  • the axial length of the magnet 20 may be in the order of several millimetres.
  • the magnet 20 generates a primary magnetic field that, inside the magnet, is substantially directed according to the axis 21.
  • the exact shape of the magnetic field lines is influenced by the ferromagnetic body 1, in particular by the permeability thereof.
  • the influence is strongest in a space near the magnet axis 21 and near the surface of the layer 2; in this space, the field lines are concentrated more due to the presence of the ferromagnetic body 1.
  • the amount of influence depends inter alia on the distance between the magnet 20 and the ferromagnetic body 1: as this distance increases, the amount of influence decreases.
  • the measuring device 100 further comprises a first magnetic field sensor 30 and a second magnetic field sensor 40.
  • Each magnetic field sensor 30, 40 may be implemented as a Hall-sensor, but other embodiments of the magnetic field sensor are also possible.
  • the two magnetic field sensors 30, 40 are mutually identical Hall-sensors, but it is not essential that the sensors are mutually identical.
  • the magnetic field sensors will be indicated as Hall-sensors for the sake of convenience.
  • each Hall-sensor 30, 40 is fixed.
  • each Hall-sensor 30, 40 is fastened to the magnet 20, for example by gluing, clamping, or the like, or for example because these parts are cast together in a synthetic material, a resin or the like (see also figure 3) .
  • the combination of magnet 20 and both sensors 30, 40 will be indicated as probe 50.
  • the first Hall-sensor 30 is arranged at a position where the influence of the ferromagnetic body 1 is as large as possible.
  • the first Hall-sensor 30 is therefore arranged near the magnet axis 21, at the side of the magnet 20 directed toward the ferromagnetic body 1.
  • the first Hall-sensor 30 may be located at an axial distance below the magnet 20, closer to the object 3, as shown in figure 1. It is also possible that the magnet 20 is provided with an accommodation space for the first Hall-sensor 30 at its bottom end directed toward the object 3. In the case of a permanent magnet 20, however, it is preferred that the first Hall-sensor 30 is attached to the head end of the magnet 20. In the case of a magnet coil 20, the first Hall-sensor 30 may be arranged inside the interior space 23 enclosed by the coil windings 22, but preferably just outside the bottom end of the coil. In the case of a magnet coil 20, it is however preferred that the coil is provided with a coil core, as is known per se and not shown for the sake of simplicity; in that case, it is preferred that the first Hall-sensor 30 is attached to the head end of the coil core.
  • the bottom end of the magnet 20 or the sensor 30 touches the top surface of the layer 2.
  • a wear plate or slide plate is arranged between the layer 2 on the one hand and the magnet 20 (and the first sensor 30) on the other hand, which is also fastened to the magnet 20. Since such wear plates are known per se, this one is not shown for the sake of simplicity.
  • the second Hall-sensor 40 is preferably arranged at the opposite side of the magnet 20, near the magnet axis 21. Depending on the specific design, the second Hall-sensor 40 may be located at an axial distance above the magnet 20, further away from the object 3, as shown in figure 1.
  • the second sensor may be arranged inside the magnet 20, in a special accommodation space or inside the interior space 23 enclosed by the coil windings 22, near the top end of the coil, preferably aligned with the first Hall-sensor 30.
  • the second Hall-sensor 40 is attached to the upper head end of the magnet 20.
  • the coil is provided with a coil core, and that the second Hall- sensor 40 is attached to the head end of the coil core.
  • the device 100 further comprises a control member 10 that may for example be implemented as a suitably programmed microprocessor.
  • the control member 10 has inputs and outputs coupled with the probe 50.
  • control member 10 has a first control output 11 for supplying a first operating current Cl to the first Hall-sensor 30, and a first measuring input 12 for receiving a first measuring voltage Sl from the first Hall-sensor 30. Further, the control member 10 has a second control output 13 for supplying a second operating current C2 to the second Hall-sensor 40, and a second measuring input 14 for receiving a second measuring voltage Sl from the second Hall-sensor 40. In the case of a magnet coil 20, the control member 10 may have a third control output 15 for supplying a third operating current C3 for the coil 20.
  • control member 10 has a measuring output 19, and is adapted, based on the two received sensor signals Sl and S2, to generate a measuring signal M at this measuring output 19, which is representative for the thickness D of the layer 2 in a reliable way.
  • each sensor 30 and 40 issues a sensor signal, the precise magnitude of which depends on the circumstances. If the permeability of the ferromagnetic body 1 changes, this has an almost equally large influence on both sensors.
  • a suitable processing of both sensor signals it is possible to obtain two processed signals that are sensitive substantially to the same extent to variations in permeability; the difference between both processed signals is then substantially insensitive to variations in permeability.
  • the difference between both processed signals is thus sensitive to such distance variations, which may for example arise as a result of variations in the thickness of the layer 2 when the probe 50 is in contact with (or is kept at constant distance to) the layer 2.
  • the relation between this difference signal and the distance variations can be examined and stored in a calibration table or represented by a calibration line.
  • FIG. 2 is a block diagram schematically illustrating a preferred embodiment of the control member 10.
  • the control member 10 comprises a first analogue amplifier 61 and a second analogue amplifier 62.
  • the first sensor signal Sl is fed to an input of the first amplifier 61
  • the second sensor signal S2 is fed to an input of the second amplifier 62.
  • Both amplifiers 61 and 62 are mutually substantially identical (in particular, they have mutually substantially equal amplification factors ⁇ ) , and are thermally coupled well to each other.
  • both amplifiers are part of a same semiconductor body.
  • the analogue output signal of the first amplifier 61 is converted into a digital signal Sl' by a first analogue/ digital converter 71.
  • the analogue output signal of the second amplifier 62 is converted into a digital signal by a second analogue/digital converter 72, which signal is subsequently multiplied by a factor ⁇ by a digital multiplier 73.
  • control member 10 may be provided with a digital/analogue converter (not shown) in order to convert the output signal M to an analogue signal, but this is not shown for the sake of simplicity.
  • Figure 3 is a schematic cross section of the probe 50 illustrating a construction detail.
  • the sensors 30 and 40 are pressed and/or glued on both sides against the magnet 20.
  • the combination of magnet 20 with the sensors 30 and 40 is, at least partly, embedded in a moulding material 80, for example an epoxy or a paste, which material is electrically insulating and thermally conducting. Since such material is known per se, a further explanation thereof is not necessary.
  • the moulding material has as a result that the parts of the probe 50 are held together, are protected, and that there is a good thermal coupling between the two sensors 30 and 40.
  • Figure 4 is a schematic cross section of another embodiment of the probe 50.
  • a possible moulding material is not shown in figure 4.
  • a first pole shoe 91 is arranged between the magnet 20 and the first sensor 30, and a second pole shoe 92 is arranged between the magnet 20 and the second sensor 40.
  • the pole shoes 91 and 92 are made of a well magnetizable material, for example soft iron, as known per se.
  • the pole shoes 91 and 92 have a contour adapted to the contour of the magnet 20.
  • the magnet 20 has a cylinder shape with a circular cross section, and the pole shoes 91 and 92 have the shape of circular discs with preferably mutually equal diameters.
  • the pole shoes may have an axial dimension of several millimetres. Thanks to such pole shoes, there is a better coupling between the magnetic field of the magnet 20 and the ferromagnetic material 1.
  • the second sensor 40 is provided with a closing plate 94 at its top surface directed away from the magnet 20, as is also illustrated in figure 4.
  • the closing plate 94 is also made of a well magnetizable material, for example soft iron, and may be identical to the pole shoes 91 and 92.
  • the present invention also provides a method for detecting cracks in the material 1.
  • an alternating current can be passed through a magnet coil, generating an alternating magnetic field causing an eddy current to be generated in the material 1.
  • This eddy current in turn, generates a secondary magnetic field.
  • the strength of the eddy current, and thus the strength of the secondary magnetic field, and thus the magnitude of the measuring signal depends on the electrical conducting properties of the material 1. If a crack is present in the material, perpendicular to the material surface, the eddy current is broken up into two (or more) separate eddy currents, resulting in a much lower measuring signal.
  • an alternating magnetic field with a fairly high frequency is needed, typically in the order of 0,5 MHz.
  • the eddy currents typically occur close to the material surface, so that a measuring signal contains little information about the extent (depth) of the crack.
  • the known method is sensitive to surface defects such as local burnings, fluctuations in permeability, etc.
  • the present invention provides a crack detection method based on another measuring principle.
  • a probe 50 as discussed in the preceding, which is displaced over the surface of the object 3, wherein the distance to the object 3 is kept constant.
  • the probe 50 can be displaced over the surface of the object 3 in a sliding or rolling way.
  • the probe 50 is mounted to a measuring train, at small distance above a rail, in order to trace cracks in that rail.
  • Figure 5 is a graph illustrating the obtained measuring signal M (vertical axis) as function of the time (horizontal axis) .
  • the measuring signal M is almost constant in time, as the line part 5.1 illustrates.
  • the probe 50 approaches a crack, an edge effect occurs: the magnetic field lines have preference to remain in the ferromagnetic body 1, and can thus cross the crack only with difficulty or not at all. Because of this, the symmetry of the magnetic field lines is disturbed, and the number of magnetic field lines that the lower sensor 30 "feels" will reduce. This effect does not, or at best to a reduced extent, occur at the upper sensor 40. As a result, the measuring signal M decreases, as the line part 5.2 illustrates.
  • the magnetic field lines can "spread" themselves on both sides of the crack, so that the disturbance at the position of the lower sensor 30 is less and the measuring signal M is again somewhat larger, as the line part 5.6 illustrates.
  • the disturbance decreases and the measuring signal increases again, as the line part 5.3 illustrates.
  • the measuring signal M again remains almost constant in time, as the line part 5.5. illustrates.
  • the measuring signal M shows a minimum 5.7, wherein the distance X of this minimum to the normal level 5.1, 5.5 depends on the depth of the crack concerned and the mutual velocity between probe and crack: in case of a small and/or shallow crack, the magnetic field can virtually bend around the crack, and the disturbance is less than in the case of a large and deep crack.
  • the magnet 20 comprises two or more magnet segments, arranged axially in each others extension.
  • the closing plate 94 is a magnet.
  • the reaction of the measuring signal M to the presence of a crack is explained.
  • the measuring signal M is obtained by subtracting the second sensor signal from the first sensor signal.
  • the first sensor signal is subtracted from the second sensor signal, in which case the behaviour of the measuring signal M when approaching a crack is mirrored relative to the behaviour illustrated in figure 5, as will be clear to a person skilled in the art.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
  • Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)

Abstract

L'invention concerne un dispositif (100) permettant d'engendrer un signal de mesure (M) indicatif des propriétés surfaciques d'un objet (3) qui est essentiellement fabriqué à partir d'une matière ferromagnétique. Ce dispositif comprend au moins un aimant (20) pourvu d'un axe d'aimant (21), deux détecteurs de champ magnétique (30, 40) disposés à des positions axiales mutuellement différentes par rapport à l'axe d'aimant (21), un élément de commande (10) pourvu d'entrées (12, 14) couplées aux détecteurs de champ magnétique (30, 40) de manière à recevoir des signaux de détecteur (S1, S2) engendrés par les détecteurs de champ magnétique (30, 40) et d'une sortie (19) conçue pour émettre le signal de mesure (M). L'élément de commande (10) est élaboré pour engendrer le signal de mesure (M) en fonction des signaux de détecteur (S1, S2) reçus des détecteurs de champ magnétique (30, 40) selon la formule M = αS1 - αS2, où α et β sont des facteurs de multiplication.
EP05797956A 2004-10-29 2005-10-24 Dispositif d'examen non destructeur d'un objet Withdrawn EP1943477A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NL1027373A NL1027373C2 (nl) 2004-10-29 2004-10-29 Werkwijze en inrichting voor het niet-destructief onderzoeken van een voorwerp.
PCT/NL2005/000760 WO2006046859A1 (fr) 2004-10-29 2005-10-24 Dispositif d'examen non destructeur d'un objet

Publications (1)

Publication Number Publication Date
EP1943477A1 true EP1943477A1 (fr) 2008-07-16

Family

ID=34974304

Family Applications (1)

Application Number Title Priority Date Filing Date
EP05797956A Withdrawn EP1943477A1 (fr) 2004-10-29 2005-10-24 Dispositif d'examen non destructeur d'un objet

Country Status (3)

Country Link
EP (1) EP1943477A1 (fr)
NL (1) NL1027373C2 (fr)
WO (1) WO2006046859A1 (fr)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2601158A (en) * 2020-11-20 2022-05-25 Elcometer Ltd Coating thickness measurement instrument
CN115372458A (zh) * 2022-09-01 2022-11-22 国家石油天然气管网集团有限公司 用于动态检测裂纹的装置及方法

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1130870A (en) * 1966-10-20 1968-10-16 Nat Res Dev Method and apparatus for detecting and measuring cracks in metal structures
DE2345848C3 (de) * 1973-09-12 1986-06-19 ELEKTRO-PHYSIK Hans Nix & Dr.-Ing. E. Steingroever GmbH & Co KG, 5000 Köln Elektromagnetischer Schichtdickenmesser
EP0305591A3 (fr) * 1982-05-13 1992-03-25 C.A. Weidmüller GmbH & Co. Capteur inductif et dispositif de mesure utilisant ce capteur
JPS6114501A (ja) * 1984-06-30 1986-01-22 Nippon Kokan Kk <Nkk> 渦流式距離計
GB2306009B (en) * 1995-10-05 1999-06-16 Elcometer Instr Ltd A coating thickness measuring probe
GB0016591D0 (en) * 2000-07-06 2000-08-23 Elcometer Instr Ltd Dual mode coating thickness measuring instrument

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO2006046859A1 *

Also Published As

Publication number Publication date
WO2006046859A1 (fr) 2006-05-04
NL1027373C2 (nl) 2006-05-03

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