DEVICE AND METHOD FOR DETECTING AN ARTICLE

Abstract

The invention relates to a device having, as a sensor for detecting an object arranged behind an article that is transparent to electromagnetic radiation, a coil assembly having a first transmitting coil (1.1) and a first receiving coil (2.1) arranged orthogonally with respect to the first transmitting. An evaluation unit evaluates the output signals from the coil assembly. The fact that the coil assembly comprises the first transmitting coil (1.1) and at least one further transmitting coil (1.2, 1.3, 1.4), and the first receiving coil (2.1) and at least one further receiving coil (2.2, 2.3, 2.4), wherein axes (1.5, 1.6) of the first and of the at least one further transmitting coil are orthogonal to each other, and the axes (1.5, 1.6) of the first and second transmitting coil intersect the axis (2.5) of the first receiving coil (2.1) that is orthogonal to the first and second transmitting coils (1.1, 1.2), means that a device is provided that reduces or even eliminates the grating effect. According to the method, for this purpose, the electromagnetic fields emitted by the transmitting coils as a result of a periodic AC signal during a first half period are each directed in the direction of the first receiving coil (2.1) and, during the second half period, are directed away from the first receiving call (2.1), wherein the first receiving coil (2.1) is wired and operated in series with at least one further receiving coil (2.2, 2.3, 2.4). An electromagnetic field which penetrates the coil assembly, generates mutually opposed voltages in the receiving coils (2.1, 2.3; 2.2, 2.4).

Claims

1. Device for detecting an object (9.1) arranged behind an article (12) that is transparent to an electromagnetic radiation, comprising a coil arrangement with a first transmitting coil (1.1) and a first receiving coil (2.1) arranged orthogonally to the first transmitting coil, wherein the coil arrangement forms a sensor for detecting the object (9.1) on a relative movement between the device and the article (12), a control circuit for driving the at least one transmitting coil (1.1) and for evaluating the output signals of the sensor, characterised in that the coil arrangement comprises the first transmitting coil (1.1) and at least one further transmitting coil (1.2, 1.3, 1.4) and the first receiving coil (2.1) and at least one further receiving coil (2.2, 2.3, 2.4), in that axes (1.5, 1.6) of the first (1.1) and the at least one further transmitting coil (1.2) are arranged orthogonally to one another, and in that the axes (1.5, 1.6) of the first (1.1) and the at least one further transmitting coil (1.2) intersect an axis (2.5) of the first receiving coil (2.1) orthogonally.

2. Device according to claim 1, characterised in that the axes (1.5, 1.6) of the first and the at least one further transmitting coil (1.1, 1.2) intersect the axis (2.5) of the first receiving coil (2.1) at one point.

3. Device according to claim 1 or 2, characterised in that the axes (1.5, 1.6) of the transmitting coils (1.1, 1.2) lie in the plane in which the receiving coils (2.1, 2.2, 2.3, 2.4) are arranged.

4. Device according to one of the claims 1 to 3, characterised in that the spacing between the at least one further transmitting coil (1.2) and the first receiving coil (2.1) is the same size as the spacing between the first transmitting coil (1.1) and the first receiving coil (2.1).

5. Device according to one of the preceding claims, characterised in that in a Cartesian coordinate system, the origin of which lies in the middle between the first receiving coil (2.1) and the further receiving coils (2.2, 2.3, 2.4) and the Z-axis of which points in the direction of the object (9.1) to be detected, the receiving coils (2.1, 2.2, 2.3, 2.4) are arranged in the XY plane, whilst at least one of the transmitting coils (1.1) is arranged in the XZ plane and at least one further of the transmitting coils (1.2) is arranged in the YZ plane.

6. Device according to one of the preceding claims, characterised in that at least one resonance capacitor (3.1) is connected in parallel with the first receiving coil (2.1) and with the at least one further receiving coil (2.2, 2.3, 2.4) and together with the receiving coils (2.1, 2.2, 2.3, 2.4) forms a resonant circuit.

7. Device according to one of the preceding claims, characterised in that the coil arrangement has a first configuration comprising the first transmitting coil (1.1) and the at least one further transmitting coil (1.2) as well as the first receiving coil (2.1) and the at least one further receiving coil (2.2, 2.3, 2.4), and has a second configuration comprising at least a third transmitting coil (1.3) and a fourth transmitting coil (1.4) as well as the first receiving coil (2.1) and the at least one further receiving coil (2.2, 2.3, 2.4), wherein the axes (1.7, 1.8, 1.5) of the third and fourth transmitting coils (1.3, 1.4) and of the first transmitting coil (1.1) lie in one plane, wherein the control circuit is intended and adapted for adding an amplitude response (8.1) of the first configuration to an amplitude response (8.2) of the second configuration for a measurement signal (8.3), said amplitude responses (8.1, 8.2) each occurring along a movement path (x) of the sensor on a relative movement between the device and the article (12).

8. Device according to claim 7, characterised in that the coil arrangement comprises at least two further receiving coils, in particular a third receiving coil (2.2) and a fourth receiving coil (2.3), and in that the coil arrangement has a third configuration comprising the at least one further transmitting coil (1.2) and the third transmitting coil (1.3) as well as the third receiving coil (2.2) and the fourth receiving coil (2.4), and has a fourth configuration comprising the first transmitting coil (1.1) and a fourth transmitting coil (1.4) as well as the third receiving coil (2.2) and the fourth receiving coil (2.4), wherein the axes (1.5, 1.7, 1.8) of the first, third and fourth transmitting coils (1.1, 1.3, 1.4) lie in one plane, wherein the control circuit is intended and adapted for evaluating the movement path two-dimensionally.

9. Method for detecting an object (9.1) arranged behind an article (12) that is transparent to an electromagnetic radiation, wherein a coil arrangement with a first transmitting coil (1.1) and a first receiving coil (2.1) arranged orthogonally to the first transmitting coil is provided and wherein the coil arrangement forms a sensor for detecting the object on a relative movement between the device and the article (12), wherein the at least one transmitting coil (1.1) is driven with a signal and wherein an output signal of the sensor influenced by this signal is evaluated, characterised in that the first transmitting coil (1.1) and at least one further transmitting coil (1.2, 1.4) are arranged orthogonally to one another and are driven with a periodic alternating voltage signal (5.1, 5.2), wherein axes (1.5, 1.6, 1.8) of the first (1.1) and the at least one further transmitting coil (1.2, 1.4) lie in a plane of the first (2.1) and of at least one further receiving coil (2.3; 2.2, 2.4), wherein the electromagnetic fields emitted by the transmitting coils as a result of the periodic alternating voltage signal during a first half-period of the periodic alternating voltage transmitting signal (5.1, 5.2), are each directed in the direction of the first receiving coil (2.1) and during the second half-period of the periodic alternating voltage transmitting signal, are each directed away from the first receiving coil (2.1), in that the first receiving coil (2.1) is connected and operated in series with the at least one further receiving coil (2.2, 2.3, 2.4), and in that a preferably homogeneous electromagnetic field which permeates the coil arrangement, generates mutually opposingly directed voltages in the receiving coils (2.1, 2.3; 2.2, 2.4).

10. Method according to claim 9, characterised in that the coil arrangement has a first configuration comprising the first transmitting coil (1.1) and the at least one further transmitting coil (1.2) as well as the first receiving coil (2.1) and the at least one further receiving coil (2.2, 2.3, 2.4), and has a second configuration comprising at least a third transmitting coil (1.3) and a fourth transmitting coil (1.4) as well as the first receiving coil (2.1) and the at least one further receiving coil (2.2, 2.3, 2.4), wherein the axes (1.5, 1.7, 1.8) of the first, third and fourth transmitting coils (1.1, 1.3, 1.4) lie in one plane, and in that on relative movement between the device and the article (12) along a movement path (x) of the sensor, an amplitude response (8.1) that is detected with the first configuration is added to an amplitude response (8.2) that is detected with the second configuration, for a measurement signal (8.3).

11. Method according to claim 10, characterised in that the coil arrangement comprises at least two further receiving coils, in particular a third receiving coil (2.2) and a fourth receiving coil (2.3), and in that the coil arrangement has a third configuration comprising the at least one further transmitting coil (1.2) and the third transmitting coil (1.3) as well as the third receiving coil (2.2) and the fourth receiving coil (2.4), and has a fourth configuration comprising the first transmitting coil (1.1) and a fourth transmitting coil (1.4) as well as the third receiving coil (2.2) and the fourth receiving coil (2.2, 2.3, 2.4), wherein the axes (1.5, 1.7, 1.8) of the first, third and fourth transmitting coils (1.1, 1.3, 1.4) lie in one plane, and in that the amplitude responses of the first and second configurations are added together for a measurement signal along the movement path (x) and in that the amplitude responses of the third and fourth configurations are added together for a measurement signal transverse to the movement path (x).

12. Method according to claim 10 or 11, characterised in that the quantitative sum of the amplitudes obtained from two of the configurations which lie opposing one another is greatest precisely when the origin of an imaginary Cartesian coordinate system of the coil arrangement, said origin lying in the middle between the first receiving coil (2.1) and the further receiving coils (2.2, 2.3, 2.4), the XY plane of said coordinate system lying in the receiving coils (2.1, 2.2, 2.3, 2.4) and its Z axis pointing in the direction of a grid segment (9.1) to be detected, lies exactly centrally over the grid segment (9.1) which separates two electrically conductive closed circuits of a grid structure from one another.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0021] The invention will now be described in greater detail making reference to exemplary embodiments illustrated in the accompanying Figures. In the drawings:

[0022] FIG. 1 shows a plan view of a simple geometrical coil arrangement,

[0023] FIG. 2 shows a lateral phantom view through the coil arrangement of FIG. 1,

[0024] FIG. 3 shows a plan view of a coil arrangement duplicated in relation to FIG. 1 for two-dimensional movement paths,

[0025] FIG. 4 shows a lateral phantom view through the duplicated coil arrangement of FIG. 3,

[0026] FIG. 5 shows a parallel driving of the transmitting coils with the transmitting signals,

[0027] FIG. 6 shows the electronic circuit of the receiving coils,

[0028] FIG. 7 shows schematically the signal shape occurring on moving over a metallic, electrically conductive grid with a simple coil arrangement,

[0029] FIG. 8 shows schematically the signal shapes occurring on moving over a metallic, electrically conductive grid with a duplicated coil arrangement for symmetrical one-dimensional measurements,

[0030] FIG. 9 shows schematically the signal shapes of the four possible configurations occurring on moving over a metallic, electrically conductive grid with a duplicated coil arrangement for symmetrical two-dimensional measurements,

[0031] FIG. 10 shows the relationship between the magnetic field direction and the current direction, as they occur in a grid.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0032] The invention will now be described in greater detail making reference to the accompanying drawings. However, the exemplary embodiments concern only examples which are not intended to restrict the inventive concept to a particular arrangement. Before the invention is described in detail, it should be noted that the invention is not restricted to the various components of the device and the various method steps, since these components and method can vary. The expressions used here are intended merely to describe particular embodiments and are not used restrictively. If, furthermore, the singular or the indefinite article are used in the description or the claims, this also relates to a plurality of these elements, provided the overall context does not clearly reveal otherwise.

[0033] The drawings show a device for detecting an object arranged behind a preferably planar or flat article 12 that is transparent to an electromagnetic radiation, said object being in the exemplary embodiment a grid segment 9.1 of a reinforcing grid in a wall. However, the device is also suitable fundamentally for detecting changes due to an object which influences the electromagnetic field that is generated by transmitting coils by means of the alternating voltage transmitting signal 5.1. Such objects can be hidden behind any articles or materials in a floor, a ceiling or a wall.

[0034] For this purpose, the device has a coil arrangement consisting of at least a first transmitting coil 1.1 and a second transmitting coil 1.2 arranged orthogonally to the first transmitting coil, as well as at least a first receiving coil 2.1 arranged orthogonally to the first and second transmitting coil and a second receiving coil 2.3 arranged orthogonally to the first and second transmitting coil. The coil arrangement thus forms a sensor for detecting the object on a relative movement between the device and a flat article 12. By means of a control circuit, the at least one transmitting coil 1.1, 1.2 is driven or controlled and the output signals of the sensor are evaluated.

[0035] The coils described in this application can be any desired coils, in particular coils printed onto a conducting track. A spatial position of the coils relative to one another is described in the following by means of imaginary coil planes and/or by means of imaginary axes of the coils. The geometric details serve only to illustrate the arrangement and do not need to be mathematically exactly configured. Rather, these can have a certain degree of imprecision, provided the effect and the measurement accuracy described is achievable. In particular, if these are attributable to tolerances and/or are easily compensatable by the circuit illustrated in FIG. 6 in the sense, in particular, of a calibration and/or an adjustment of the arrangement, in particular, in the sense of a virtual spatial adjustment and/or orientation of the coils and/or their fields achieved by electronic means.

[0036] A coil plane can be understood as an imaginary plane which lies orthogonally to a central flux occurring in an eye and in an energised state of the coil, wherein the central flux extends, in particular, through a centre point of the eye.

[0037] An axis of the coil can be understood as a straight line extending through the eye, through the central flux and in the direction of the central flux. The imaginary axis therefore lies orthogonally to the respective imaginary coil plane. In particular, a direction of a field generated by a coil can be understood as the direction of the central flux occurring in the eye. Depending on the energization, therefore, two directions mutually opposed by 180 along the imaginary axis are conceivable.

[0038] In the case of a coil with a round winding, the imaginary axis and the imaginary coil plane extend through a centre point of a circle or circular cylinder bordered by the winding and representing the eye of the coil.

[0039] In the case of a printed-on coil, the coil plane can be understood as being a plane spanned by a surface onto which the coil is printed, wherein the eye of such a coil can be assumed to be two-dimensional and also lies on the surface.

[0040] The eye of the coil can be understood, with a flat coil, as being an area enclosed by the winding or, with a spatially expanded coil, a body enclosed by the winding.

[0041] According to FIGS. 1, 2, the axes 1.5, 1.6 of the first and second transmitting coils 1.1, 1.2 lie orthogonally to one another and ideally intersect the axis 2.5 of the first receiving coil 2.1 at one point, in particular, orthogonally. The axes 1.5, 1.6 of the transmitting coils therefore lie in the plane in which the receiving coils 2.1, 2.2, 2.3, 2.4 are arranged. The spacing between the second transmitting coil 1.2 and the first receiving coil 2.1 is the same size as the spacing between the first transmitting coil 1.1 and the first receiving coil 2.1. These spacings are selected as small as possible.

[0042] In an exemplary embodiment not shown in FIGS. 1 and 2, the axes 1.5, 1.6 of the first and second transmitting coils 1.1, 1.2 are arranged orthogonally skewed to one another and intersect the axis 2.5 of the first receiving coil 2.1 at two points, in particular, each orthogonally.

[0043] If further transmitting coils are provided as a third transmitting coil 1.3 and a fourth transmitting coil 1.4, in accordance with FIGS. 3, 4, the axes 1.5, 1.7 of the first transmitting coil 1.1 and the third transmitting coil 1.3 and the axes 1.6, 1.8 of the second transmitting coil 1.2 and the fourth transmitting coil 1.4 extend parallel to one another in each case. The axes 1.5, 1.6, 1.7, 1.8 of adjacent transmitting coils 1.1, 1.2, 1.3, 1.4 in the plan view of FIG. 3 are arranged orthogonally to one another and intersect ideally at one point the axes 2.5, 2.6, 2.7, 2.8 of the receiving coils 2.5, 2.6, 2.7, 2.8, said receiving coils each being arranged between two of the transmitting coils 1.1, 1.2, 1.3, 1.4, said axes 2.5, 2.6, 2.7, 2.8 being orthogonal to the axes 1.5, 1.6, 1.7, 1.8 of the transmitting coils 1.1, 1.2, 1.3, 1.4, in particular at two points if the axes 1.5, 1.6, 1.7, 1.8 of the respective transmitting coils 1.5, 1.6, 1.7, 1.8 are arranged orthogonally skewed to one another. Thus, for example, the first transmitting coil 1.1 and the fourth transmitting coil 1.4 are adjacent to one another and enclose between them the fourth receiving coil 2.4. Thus the first transmitting coil 1.1 and the fourth transmitting coil 1.4 and their axes 1.5 and 1.8, respectively, are arranged orthogonally to one another and intersect ideally at one point the axis 2.8 of the receiving coil 2.4, said receiving coil being arranged between these transmitting coils 1.1 and 1.4, said axis 2.8 being orthogonal to the axes 1.5, 1.6, 1.7, 1.8 of the transmitting coils 1.1, 1.2, 1.3, 1.4. Here also, therefore, the axes 1.5, 1.6, 1.7, 1.8 of the transmitting coils 1.1, 1.2, 1.3, 1.4 lie in the plane in which the receiving coils 2.1, 2.2, 2.3, 2.4 are arranged. However, the spacings, in particular within the configurations of the coil arrangement described below, between the cooperating transmitting coils and the associated receiving coils are equal-sized and are also selected as small as possible.

[0044] In an imaginary Cartesian coordinate system of the coil arrangement of FIG. 3, the origin of which lies in the middle between the receiving coils 1.1, 1.3 and the Z-axis of which points in the direction of the object to be detected, the receiving coils 2.1, 2.2, 2.3, 2.4 are arranged in the XY plane. If the first transmitting coil 1.1 lies, for example, in the XZ plane, then the second transmitting coil 1.2 lies in the YZ plane. The origin of this Cartesian coordinate system can be understood as being the centre point of the coil arrangement or can define said centre point.

[0045] During operation of the coil arrangement, the grid structure to be detected preferably lies parallel to the XY plane of the imaginary coordinate system and to the plane spanned by the receiving coils 2.1, 2.2, 2.3, 2.4. For detection, the receiving coils 2.1, 2.2, 2.3, 2.4 of the coil arrangement can be positioned parallel to the grid structure and accordingly displaced parallel thereto. By this means, all the receiving coils 2.1, 2.2, 2.3, 2.4 and also all the transmitting coils 1.1, 1.2, 1.3, 1.4, the axes 1.5, 1.6, 1.7, 1.8 of which lie, in particular, in the XY plane, and the plane of the receiving coils 2.1, 2.2, 2.3, 2.4 are inductively coupled equally strongly to the target, that is, the grid structure.

[0046] The conceptuality, the spatial arrangement and the electronic significance associated therewith of transmitting coil and receiving coil can also be interchanged and the same advantages arise therefrom. For illustration, only the variant in which all the receiving coils are arranged in one plane and the transmitting coils are arranged orthogonally to one another will now be considered. The use and also the calculation take place similarly when all the transmitting coils are arranged in one plane and the receiving coils are arranged orthogonally thereto.

[0047] The coil arrangement can be driven or controlled as follows in order to achieve said advantages:

[0048] The first and second transmitting coils are driven with an AC signal 5.1, 5.2 in accordance with FIG. 5 so that the electromagnetic fields emitted by the transmitting coils 1.1, 1.2 during a half period of the periodic alternating voltage transmitting signal 5.1, 5.2 are both directed in the direction of the first receiving coil 2.1, and during the other half period of the periodic alternating voltage transmitting signal are both directed away from the first receiving coil 2.1. Due to the orthogonal arrangement of the transmitting coils 1.1, 1.2, the transmitting signals are also arranged orthogonally to one another and extend in the direction of the corresponding axis and thus, in particular, in the direction of the plane of the receiving coil(s) 2.1, 2.2, 2.3, 2.4. The first receiving coil 2.1 can be operated in series with the second receiving coil 2.3. The receiving coils 2.1, 2.3 are thus connected to one another so that a preferably homogeneous electromagnetic field which permeates the structure, generates mutually opposingly directed voltages in the two receiving coils 2.1, 2.3.

[0049] A resonance capacitor 3.1 can be connected in parallel with the receiving coil pair 2.1, 2.3. Together with the receiving coils 2.1, 2.3, the resonance capacitor forms a resonant circuit which amplifies and smooths the induced AC signal.

[0050] Voltages induced in the receiving coils are amplified and measured by means of a suitable amplifier circuit. With an ideal geometric arrangement of the coils, the measured signal without the presence of a metallic, conductive object is a zero signal without AC components. Tolerances, in particular, manufacturing-related tolerances of the coil arrangement and/or relatively small deviations of the geometrical arrangement of the coils relative to one another can be compensated for with the aid of an alternating voltage compensation signal 6.1 having a defined phase and a defined amplitude, which is fed via a compensation impedance 7.1 to the resonant circuit.

[0051] FIG. 1 shows the plan view, FIG. 2 shows the lateral phantom view of a simple construction of the coil arrangement. FIGS. 5 and 6 show the associated electrical connection of the coils. This arrangement of the components with the connection shown forms a first configuration which enables the detection of grid segments with a one-dimensional movement path x in accordance with FIG. 7. The amplitude response of the first configuration 8.1, which arises along the movement path x of the sensor parallel to a grid structure, is shown in FIG. 7. The signal shows a certain asymmetry, dependent upon the geometry of the coil system.

[0052] Through the addition of two further transmitting coils 1.3, 1.4, a second configuration in accordance with FIGS. 3, 4 is enabled. In this configuration, in place of the first and second transmitting coils 1.1, 1.2, the third and fourth transmitting coils 1.3, 1.4 are driven with the alternating voltage transmitting signal 5.1. Furthermore, the first and second receiving coils 2.1, 2.3 are used as the receiver. The amplitude responses 8.1, 8.2 of the first and second configurations 8.1, 8.2, which occur along the movement path x of the sensor parallel to a grid structure, are shown in FIG. 8. By addition of the first and second amplitude responses 8.1, 8.2, a symmetrical measurement signal 8.3 arises. By means of time multiplexing of a plurality of configurations, a plurality of measurement signals can be recorded with only one evaluating unit (not shown) of the control circuit.

[0053] By means of the addition of a third and fourth receiving coil 2.2, 2.4, two further configurations are enabled. In the third configuration, the second and third transmitting coils 1.2, 1.3, and in a fourth configuration the first and fourth transmitting coils 1.1, 1.4, can serve as the transmitter, whereas the third and fourth receiving coils 2.2, 2.4 can serve as the receiver. FIG. 3 shows a plan view of such a coil arrangement and FIG. 4 shows a lateral phantom view of such a coil arrangement with four transmitting coils 1.1, 1.2, 1.3, 1.4 and four receiving coils 2.1, 2.2, 2.3, 2.4.

[0054] For the first configuration, the axes 1.5, 1.6 of the first transmitting coil 1.1 and the second transmitting coil 1.2 are arranged orthogonally to one another and intersect the axis 2.5 of the first receiving coil 2.1, in particular, orthogonally, in particular, ideally in each case orthogonally and at one point, as shown in the exemplary embodiments of FIGS. 1 and 3. As a further receiving coil, the first configuration comprises, for example, the second receiving coil 2.3.

[0055] For the second configuration, the axes 1.7 and 1.8 of the third transmitting coil 1.3 and the fourth transmitting coil 1.4 are arranged orthogonally to one another and intersect the axis 2.7 of the second receiving coil 2.3, in particular, orthogonally, in particular, ideally in each case orthogonally and at one point, as shown in the exemplary embodiment of FIG. 3. As a further receiving coil, the second configuration comprises, for example, the first receiving coil 2.1.

[0056] For the third configuration, the axes 1.6 and 1.7 of the second transmitting coil 1.2 and the third transmitting coil 1.3 are arranged orthogonally to one another and intersect the axis 2.6 of the third receiving coil 2.2, in particular, orthogonally, in particular, ideally in each case orthogonally and at one point, as shown in the exemplary embodiment of FIG. 3. As a further receiving coil, the second configuration comprises, for example, the fourth receiving coil 2.4.

[0057] For the fourth configuration, the axes 1.8 and 1.5 of the fourth transmitting coil 1.4 and the first transmitting coil 1.1 are arranged orthogonally to one another and intersect the axis 2.8 of the fourth receiving coil 2.4, in particular, orthogonally, in particular, ideally in each case orthogonally and at one point, as shown in the exemplary embodiment of FIG. 3. As a further receiving coil, the fourth configuration comprises, for example, the third receiving coil 2.2.

[0058] This construction permits the measurement of the grid segments on two-dimensional movement of the sensor parallel to a grid structure.

[0059] FIG. 10 shows a portion of a grid with two closed electrically conducting segments through which electromagnetic fields of opposing directions flow. Due to the different directions of the electromagnetic fields, ring currents with different rotation senses form. In two receiving coils which lie spatially separated in the different electromagnetic fields, voltages of different polarity are induced.

[0060] Due to the coupling of the receiving coils shown in FIG. 6, the quantitative sum of the signal amplitudes obtained from two opposing configurations is greatest precisely when the centre point of the coil arrangement is situated exactly under a grid segment 9.1 which separates two closed circuits from one another. If the grid segment has an appreciable areal and/or spatial extent, then exactly under can be understood as meaning that the centre point lies centrally under the grid segment 9.1 and/or that the Z-axis of the imaginary Cartesian coordinate system of the coil arrangement intersects the grid segment 9.1 centrally.

[0061] It is self-evident that this description can be subject to a wide variety of modifications, amendments and adaptations, which belong within the scope of equivalents to the accompanying claims.

REFERENCE NUMERALS

[0062] 1.1 First transmitting coil [0063] 1.2 Second transmitting coil [0064] 1.3 Third transmitting coil [0065] 1.4 Fourth transmitting coil [0066] 1.5 to 1.8 Axes of the first to fourth transmitting coils [0067] 2.1 First receiving coil [0068] 2.3 Second receiving coil [0069] 2.2 Third receiving coil [0070] 2.4 Fourth receiving coil [0071] 2.5 to 2.8 Axes of the first to fourth receiving coils [0072] 3.1 Resonance capacitor [0073] 4.1 Amplifier circuit [0074] 5.1 Alternating voltage transmitting signal [0075] 5.2 Inverted alternating voltage transmitting signal [0076] 6.1 Alternating voltage compensation signal [0077] 7.1 Compensation impedance [0078] 8.1 Amplitude response of first configuration [0079] 8.2 Amplitude response of second configuration [0080] 8.3 Addition of amplitude responses of first and second configurations [0081] 9.1 Grid segment [0082] 9.2 Hollow locations of grid [0083] 11.1 Direction of current flowing through grid [0084] 11.2 Direction of electromagnetic field lines penetrating grid [0085] Article [0086] x Movement path of sensor