EP1828811A2 - Dispositif et procede pour reperer des objets magnetiques ou magnetisables - Google Patents

Dispositif et procede pour reperer des objets magnetiques ou magnetisables

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Publication number
EP1828811A2
EP1828811A2 EP05823413A EP05823413A EP1828811A2 EP 1828811 A2 EP1828811 A2 EP 1828811A2 EP 05823413 A EP05823413 A EP 05823413A EP 05823413 A EP05823413 A EP 05823413A EP 1828811 A2 EP1828811 A2 EP 1828811A2
Authority
EP
European Patent Office
Prior art keywords
magnetic field
magnetic
arrangement according
objects
field
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Withdrawn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
EP05823413A
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German (de)
English (en)
Inventor
Wilfried ANDRÄ
Holger Lausch
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.)
Individual
Original Assignee
Individual
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 Individual filed Critical Individual
Publication of EP1828811A2 publication Critical patent/EP1828811A2/fr
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices

Definitions

  • the invention relates to an arrangement and a method for locating magnetic or magnetizable objects, according to the preamble of the claims, wherein the objects are in non-magnetic media and, for example, are neither optically nor mechanically accessible.
  • This locating concerns for example, the determination of the position, shape and orientation of steel reinforcements in concrete as well as in the exploration of steel beams in masonry or soil or as the finding of ship anchors in the seabed, to name just a few applications.
  • the force measuring method either the force acting between the reinforcement and a permanent magnet outside the concrete is measured, or the stray magnetic field of the reinforcement magnetized by a permanent magnet is measured, see [1] in the list of references at the end of the description.
  • the disadvantage of the force measuring method is that the force decreases sharply with the distance and therefore low-lying reinforcements can not be detected.
  • the magnetic stray field of the reinforcement is superimposed on the magnetic field of the permanent magnet, which is generally much stronger than the stray field and therefore can only be eliminated from the stray field to be measured with a relatively large error. Both DC field methods are therefore used only for the relatively coarse location of magnetic objects [I].
  • the reinforcement is magnetized by an alternating magnetic field.
  • an alternating magnetic field is generated which starts from the reinforcement and, for example, changes the inductance of a coil generating the alternating field.
  • the location of the reinforcement is generally carried out by evaluating the changed complex impedance of an electrical circuit containing the generator coil for the primary magnetic field [1-5].
  • the alternating field offers the possibility of locating non-magnetic reinforcements (eg made of stainless steel).
  • non-magnetic reinforcements eg made of stainless steel
  • the invention is therefore based on the object not only to increase the depth of detection for ferromagnetic objects in non-magnetic media, but also their shape, position and structures in individual detection levels and detection levels separated, clearly detect.
  • the magnetic field generators may be coils of different shape and size traversed by variable electric currents, or differently shaped permanent magnets, or a combination of both.
  • the objects to be detected are magnetized by the generated primary magnetic field of predetermined field distribution and variable strength including polarity.
  • the then generated by the respective object Magnetic stray field is measured during the acting primary field or after elimination of the primary field by means of a magnetic sensor which is arranged at least with a magnetic field sensitive part in the stray field.
  • This part can be a small magnetic measuring body on which the stray magnetic field has a force (in the order of ⁇ N) and therefore displaces it in the direction of the field lines.
  • the adjustment can be measured electrically (inductive, capacitive), optically (eg interferometrically), acoustically or mechanically (pointer system with scale). If the measurement is made during the action of the primary magnetic field, the measuring body (s) must be arranged in the homogeneous region of the primary magnetic field in order to eliminate its force effect on the measuring body.
  • a system of magnetic field generators preferably electric coils, is used which generates a primary magnetic field whose maximum lying on the common coil axis is set at a variable distance from the center plane of the coil system and can be changed.
  • the planar detection of magnetic objects in a non-magnetic medium is possible by a cluster or matrix-like multiple arrangement of measuring bodies next to one another, lying in one surface.
  • the existing of a soft or hard magnetic material measuring body is advantageously each elastically connected to the magnetic field generator so that it can move at least substantially small amounts at right angles to the center plane of the magnetic field generator.
  • the elastic attachment has favorably at least one mechanical natural frequency, in whose excitation a significant increase in amplitude of the excited vibrations of the measuring body occurs.
  • a surface of the measuring body may be formed as a capacitor electrode.
  • the magnetic sensor may also be a mono-, di- or triaxial magnetometer with which the stray magnetic field of the magnetic object is determined with respect to characteristic parameters of its spatial distribution.
  • the optimum type of magnetometer used depends on the required measuring accuracy and the permissible technical expenditure. It can be one SQUID (Superconducting Quantum Interference Device) are basically used as well as a fluxgate or a magnetoresistive or a Hall effect working magnetometer. It is important that the required for stray field measurements magnetometer volume is small in relation to the required positioning accuracy. Therefore, magnetoresistive magnetometers or Hall effect magnetometers are advantageously usable.
  • characteristic parameters of the stray field are the direction and field strength of the stray field measured at one or more locations having a known spatial relationship with each other while the magnetized object is in different states of magnetization.
  • the measurements in the different magnetization state allow the elimination of magnetic background fields, eg. B. of the earth field.
  • the magnetic field components of the stray field measured after magnetization with opposite signs are subtracted from one another by means of at least one magnetometer in order to eliminate the influence of a background field.
  • the background field itself can be determined by adding the magnetic field components measured after magnetization with opposite signs. Since the spatial distribution of the stray field is determined by the location, the shape and the magnetization state of the object, in principle, from the complete measurement of the field distribution, these initially unknown data can be determined. With limitations, these data can also be determined if measurements are taken only in a sub-volume or even in a single location. For simple shapes of the object, such as spheres or very long rods, few measurements are sufficient at certain points because of the symmetry of the magnetic field distribution. The method is particularly simple in the case when the object is homogeneously magnetized and as a result has a calculable distribution of surface magnetic charges, from which the Stray field distribution can be derived theoretically.
  • an inhomogeneous magnetization distribution in the object can be tolerated if it can be approximated sufficiently close to the measuring points by a homogeneous distribution or if the local course of the inhomogeneity is known.
  • the local distribution of primary magnetic fields generated by current-carrying coils can be calculated as accurately as desired using the law of Biot and Savart. This simple computability is beneficial for this type of field generation. Another advantage is that by switching off the currents, the primary magnetic field can be completely switched off. It is also favorable that the local distribution of the primary magnetic field can be changed by varying the strength of the electric currents flowing in a plurality of coils. For example, the maximum or zero crossing of the primary magnetic field may be placed at different locations on the common coil axis of two concentric coils.
  • a useful property of coil fields is also that by special coils (compensation coils), which are mounted close to the magnetometer, the magnetic primary field compensated at the location of the magnetometer and thereby the measurement accuracy can be significantly increased.
  • permanent magnets For permanent magnets, the electrical power required to magnetize an object is generally needed only once and for a short period of time. The energy used is not needed again later. If the permanent magnets move in the application for the location, for example, have to be rotated to eliminate the background field, a much smaller power is required.
  • the magnetization distribution in objects can be calculated arbitrarily accurate when certain parameters, such. B. the distribution of the primary field, the location of the objects and the magnetic susceptibility of the objects are known.
  • the primary field is known in principle.
  • the susceptibility of the objects is generally unknown.
  • the magnetization distribution is determined by the so-called magnetic shape anisotropy, in which magnetic fields in which the objects sufficiently far from the state of the magnetic Saturation are removed, there is a nearly constant ratio between the magnetization of the object and the strength of the primary field whose value is determined by the shape of the object.
  • the magnetic shape anisotropy is determined by the so-called demagnetization factor, which is 1/3 for spheres, 1/2 (for magnetization perpendicular to the cylinder axis), and 0 (for magnetization parallel to the cylinder axis) for long cylinders.
  • the demagnetization factor is calculable from the three axes of the ellipsoids. The calculation becomes particularly simple if the primary field at the location of the object is homogeneous, ie with regard to direction and field strength, regardless of the location. Then results for the above simple object forms a homogeneous distribution of the object magnetization. For practical application, the primary field need not be completely homogeneous.
  • the primary field in a partial volume of the object used for the calculation of the stray field can be approximately described by a homogeneous field. This is generally the case as soon as the partial volume in question is smaller in all three dimensions than the diameter of the coils, which determine the primary field at the location of the object by more than 50%, or when generating with permanent magnets, if the partial volume in question is smaller as the volume of the field-generating permanent magnets.
  • An essential prerequisite for the calculation of the magnetization distribution is that the stray fields of neighboring objects are much weaker than the primary field. This condition is usually met when the distances between adjacent Objects are at least twice larger than the smallest dimension of the objects.
  • the distribution of the stray field resulting from the magnetic poles present in the objects by a current primary field or by the remanent magnetization after switching off the primary field can be calculated by known mathematical methods in principle for arbitrary pole distributions.
  • Particularly simple local distributions in the stray fields result in the cases represented by a magnetic monopole or a magnetic dipole or by simple dipole distributions (eg line dipole).
  • the special locating task z For example, the calculation of a field component (eg, the component parallel to a primary field coil) as a function of the location on an axis of symmetry of this coil is sufficient to determine the distance between the object and the magnetometer.
  • Another simple case is when the direction from the magnetometer to an object is to be determined. In this case, the measurement of the stray field components in a plane perpendicular to the connection axis between magnetometer and object is advantageous.
  • Stray field distributions each consist of a basic distribution and some characteristic parameters with which the basic distribution can be varied. For most locating tasks, the basic distribution can be assumed to be known. A typical one
  • Example is the task of one or more cylindrical
  • Parameters are the thickness of the bars, the distance from the concrete surface, the direction of the bars and the mutual distance of the bars.
  • a software that manages a parameter library allows the comparison of the stray field values measured at certain positions with the values available in the library. The characteristic parameters are varied and those parameter values are output that achieve the best match between measured values and library values. It is essential that the functional dependence of the library values of the various parameters, such. B. of the rod thickness and the distance between the rod and magnetometer, is different. In order to avoid possible ambiguity that, for example, a deeper lying thick rod generates the same stray field values in the sensor (magnetometer), such as a closer thin rod, several sensors, for example. Magnetometer, can be used with defined mutual positioning.
  • a method for locating magnetic or magnetizable objects that are in non-magnetic media is characterized by the generation of a primary magnetic field by means of coils, electromagnets or permanent magnets to which the objects are exposed. Thereafter, the spatial distribution of the stray magnetic field of the objects is determined and the magnitude and the direction of the stray magnetic field are measured at defined locations by means of sensors. Finally, a comparison of the measured values takes place with values determined in advance. This comparison can be made electronically with storeduploadssstreufeldern. The spatial distribution of the magnetic stray field of the objects can also be made by determining the gradient of this stray field.
  • Fig. 1 shows a first embodiment of the invention with a
  • FIG. 2 shows the basic arrangement of measuring bodies and capacitors of a second embodiment of the invention
  • Fig. 3 shows a net-like arrangement of measuring bodies of a third
  • FIG. 4 shows the use of only one sensor for a plurality of measuring bodies in a fourth embodiment of the invention
  • FIG. 5 shows an embodiment with rectangular coils and a magnetometer
  • FIG. 6 shows a diagram of the position of the maximum
  • Fig. 7 is a diagram of the position of the maximum
  • FIG. 8 shows a diagram for the influence of the displacement of the sensor against a magnetic object on the stray field components at the location of the magnetometer.
  • Fig. 1 shows a rod-shaped reinforcing element (object) 10 within a concrete body (non-magnetic medium) 12 having a concrete surface 13.
  • the primary magnetic field 14 of a coil for example, copper wire wound current-carrying coil 15 magnetizes the rod 10 in accordance with the magnetic field strength.
  • the bar magnetization 16 indicated by arrows generates a stray field which is superimposed on the primary field 14. With the arrow representing the primary field 14, the geometric axis ZZ of the coil 15 coincides. Both magnetic fields act on a magnetic measuring body 17 in different ways.
  • the strongly inhomogeneous stray field produces an attractive force on the measuring body 17 magnetized in the primary field 14, whose magnetization 18 indicated by arrows is parallel to the primary field 14 is directed.
  • the attractive force causes a displacement of the measuring body 17 fastened to the coil housing with a flexible holder 19, the magnitude of which is measured, for example, by the change in the electrical capacitance of a capacitor 11 consisting of a counter-electrode 20 and the surface 17 'of the measuring body 17.
  • the strength of Displacement has its maximum as soon as the distance between the rod 10 and the measuring body 17 has its minimum.
  • the bar 10 can be located and made visible with a display, registration and evaluation device 22.
  • This displacement can be measured both electrically and by other physical methods (eg, optically or acoustically with ultrasound, etc.).
  • the measuring body 17 can also be located in a fluid.
  • the magnetic field 14 generating coil 15 may have a round or advantageously rectangular shape and a corresponding magnetic field distribution. In the latter case, it is favorable if the longer edge of the coil 15 extends parallel to the rod 10.
  • the detection sensitivity of the displacement of the measuring body 17 can be increased, that the measuring body consists of a permanent magnetic material whose magnetization, for example., As shown in Fig. 1, pointing to the left.
  • the remanent magnetization of the permanent magnet material can be much larger than the magnetization of the soft magnetic measuring body generated in the primary field 14, the force acting on the measuring body can be much stronger. It is also possible, by reversing the polarity of the primary field 14, to reverse the direction of the force exerted on the permanent-magnetic measuring body 17.
  • the detection sensitivity can be further increased by periodically switching the primary field 14 on and off, changing it, or periodically reversing it, choosing the number of periods per second to be close to half or all of the mechanical natural frequency of the holder 19 and / or the natural electrical frequency of the circuit for measuring the capacitance change is.
  • the measurement of the concrete cover is also improved by using a system of coils which generates a primary field 14 whose maximum lying on the coil axis ZZ or the zero crossing at a variable distance from a perpendicular to the coil axis directed center plane of the coil assembly is adjustable and changeable.
  • a system of coils which generates a primary field 14 whose maximum lying on the coil axis ZZ or the zero crossing at a variable distance from a perpendicular to the coil axis directed center plane of the coil assembly is adjustable and changeable.
  • a plurality of sensors comprising the elements 17, 17 ', 19, 20 and 11 in FIG. 1 are shown in a linear arrangement, so that in each case the measuring bodies 171 to 175 face the electrodes 201 to 205.
  • the mating, opposing measuring body and electrodes can be arranged both within a single coil and each pair for themselves in an associated coil.
  • the measuring body 171 to 175 are shown without stray field influence and on the right side under the influence of a stray field, the measuring body 172, 173, 174 can detect a significant shift relative to the electrodes 202, 203, 204. Since the local distribution of the stray field depends on the shape of the magnetic object to be located, it can be concluded by separate measurement of the displacements of the individual measuring bodies on the shape of the object to be located.
  • the arrangement of the measuring body 170 is made like a matrix, so that all the effects of the stray field can be detected in a plane.
  • no stray field acts on the left side, while a clear influence of an acting stray field can be recognized on the right side.
  • a plurality of juxtaposed measuring body 170 act on a common sensor 21.
  • This sensor can be designed both as a condenser and as an optical or acoustic sensor.
  • Fig. 5 coaxially to an axis ZZ three rectangular coils 151, 152, 153 are arranged one inside the other.
  • a magnetometer 23 is provided in a plane parallel to the coil planes and perpendicular to the axis ZZ center plane 24 .
  • a reinforcing bar 10 which is parallel to the long edges of the rectangular coils and the outer surface 13 of the concrete body 12.
  • a primary field is formed, which magnetizes the rebar 10 and forms a stray field.
  • Fig. 6 shows, for an example of two coaxially arranged circular coils having a radius of 30 cm for the larger and 10 cm for the smaller coil, as by the change of this product NI the smaller coil, the maximum of the total magnetic field on the common coil axis ZZ is moved. Further, Fig. 6 shows how the position is shifted on the axis at which the total field is practically zero (zero crossing).
  • the curves 0; 0.2; 0.4; 0.6; 0.8 and 1.0 represent the changes that occur at 0%, 20%, 40%, 60%, 80% and 100% in the product for the small coil 152.
  • the zero crossings of the curves 0.4; 0.6; 0.8 and 1.0 are correspondingly at a distance of about 3.8 cm; 7.5 cm; 10 cm and 12 cm on the ZZ axis. All positions are measured from the lying in the median plane 24 coil center, which is also the location of the magnetometer 23.
  • FIG. 7 shows, analogously to FIG. 6, the course of a primary field on the common coil axis Z-Z as a function of the distance Z from the coil center.
  • the coil combination consists of three coaxial circular coils. The largest of these coils has, for example, a radius of 20 cm, the central coil a radius of 10 cm and the smallest coil, which is provided as a compensation coil, a radius of 1.5 cm.
  • FIG. 7 shows that by adjusting the product N-I of the compensation coil, the total primary field at the location of the magnetometer 23 can always be made to disappear.
  • the ratio of the products N-I of the two larger coils is chosen so that further zero crossings of the total primary field on the axis Z-Z are at different distances from the coil center 0.
  • the curves 0; 0.2; 0.4; 0.6; 0.8; 1.0; 1,2 represent the changes that result when the ratio of the products N-1 of the two larger coils changes to the maximum of the total primary field.
  • FIG. 8 shows, as in a movement of the magnetometer 23 parallel to the concrete surface 13, with the
  • Magnetometer 23 measured stray field components change.
  • the magnetometer 23 is arranged in the center of the coil combination.
  • the abscissa is the distance x of the rod from
  • Primary field is assumed a single rectangular coil whose long edge is parallel to the rod-shaped object 10 and has an edge length of 50 cm. The length of the shorter edge is
  • the rod-shaped object 10 has a diameter of 1 cm.
  • the coordinate which is perpendicular to both the ZZ axis and the axis of the rod-shaped object 10 is called X-axis.
  • the parallel to the X axis component of the stray field at the location of the magnetometer 23 is zero when the object lies on the axis ZZ. Then, from the amount of the Z component of the stray field, the distance a and the diameter of the object 10 can be determined, if the strength of the primary magnetic field at the location of the object 10 is changed in a controlled manner.
  • An approximate calculation shows that the Z component of the stray field is proportional to the product of the square of the object diameter and the primary field strength and decreases with a numerically calculable function of the distance a.
  • the primary field strength at the location of the object can be changed while the object diameter remains constant, (eg, by varying the zero crossing of the primary field), first the distance a and then determined with ititem a the object diameter. If the zero crossing of the primary field is appropriately set, the effect is that an object at a certain depth produces virtually no stray field, while a lower-lying object has a measurable stray field.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Remote Sensing (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Electromagnetism (AREA)
  • Environmental & Geological Engineering (AREA)
  • Geology (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Geophysics (AREA)
  • Geophysics And Detection Of Objects (AREA)
  • Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)

Abstract

La présente invention concerne un dispositif et un procédé pour repérer des objets magnétiques ou magnétisables qui se trouvent dans des milieux non magnétiques. Pour augmenter la profondeur de détection de tels objets, et pour permettre une détection univoque de leur forme, emplacement et structures dans des plans de détection individuels, au moins un détecteur est disposé dans un champ magnétique primaire d'un dispositif de production de champ magnétique, la répartition de magnétisation du champ magnétique au voisinage du détecteur respectif étant homogène ou connue du point de vue de son allure locale.
EP05823413A 2004-12-20 2005-11-29 Dispositif et procede pour reperer des objets magnetiques ou magnetisables Withdrawn EP1828811A2 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
DE102004062181 2004-12-20
DE102005026676 2005-06-07
PCT/DE2005/002167 WO2006066529A2 (fr) 2004-12-20 2005-11-29 Dispositif et procede pour reperer des objets magnetiques ou magnetisables

Publications (1)

Publication Number Publication Date
EP1828811A2 true EP1828811A2 (fr) 2007-09-05

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EP05823413A Withdrawn EP1828811A2 (fr) 2004-12-20 2005-11-29 Dispositif et procede pour reperer des objets magnetiques ou magnetisables

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US (1) US20080136408A1 (fr)
EP (1) EP1828811A2 (fr)
WO (1) WO2006066529A2 (fr)

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Publication number Priority date Publication date Assignee Title
WO2008049156A1 (fr) * 2006-10-24 2008-05-02 Andrew Duncan Détecteur de métaux
US7919962B2 (en) * 2007-11-20 2011-04-05 Xerox Corporation Magnet scanning device that scans a cylindrical magnet along a helical path
DE102008009360A1 (de) * 2008-02-14 2009-08-20 Bilfinger Berger Ag Vorrichtung zur Durchführung von Materialuntersuchungen und/oder -bearbeitungen an einem Bauwerk
US7919964B2 (en) * 2008-06-02 2011-04-05 Geonics Limited Combined electromagnetic sensor and magnetometer
FR2987680B1 (fr) * 2012-03-05 2014-03-14 Smartfuture Procede de mesure de courant dans un reseau electrique
GB201911009D0 (en) * 2019-08-01 2019-09-18 Matrasens Ltd Ferrmagnetic Sensing

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US5073858A (en) * 1984-12-10 1991-12-17 Mills Randell L Magnetic susceptibility imaging (msi)
SE9403188D0 (sv) * 1994-09-22 1994-09-22 Siemens Elema Ab Magnetfältsdetektor vid ett medicinskt implantat
DE4436078A1 (de) * 1994-10-10 1996-04-11 Dornier Gmbh Bildgebendes hochauflösendes Sensorsystem zu Detektion, Ortung und Identifizierung von metallischen Objekten
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Publication number Publication date
WO2006066529A2 (fr) 2006-06-29
WO2006066529A3 (fr) 2006-11-02
US20080136408A1 (en) 2008-06-12

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