Metal detector for determining the position of conductive objects, method for determining the position of conductive objects using a metal detector, and measuring station for discovering conductive objects in a medium

Abstract

The invention relates to a metal detector, comprising: a measuring and operating circuit (MB) with an input (E); a primary coil (PS) which is supplied with an alternating current by the measuring and operating circuit (MB) and generates a primary magnetic field (PF) which can excite an electrically conductive object (G) to generate a secondary magnetic field; at least one coil arrangement (SA) having at least two secondary coils (SS1, SS2) with identical magnetic couplings to the primary coil (PS); wherein the coil arrangement (SA) has at least two gaps (SP1, SP2) between the secondary coils (SS1, SS2); wherein the voltages induced in the secondary coils (SS1, SS2) by a magnetic field have opposite signs and are processed to form at least one signal; characterised in that the metal detector is designed to check different locations (x1; x2; xn) for the secondary magnetic fields at different times by means of the at least one signal.

Description

[0001] Metal detector for determining the position of conductive objects, method for determining the position of conductive objects with a metal detector, measuring point for detecting conductive objects in a medium

[0002] The invention relates to a metal detector for classifying hidden electrically conductive objects, a method for classifying hidden electrically conductive objects using a metal detector, and further to a measuring device for detecting and classifying hidden electrically conductive objects in a medium.

[0003] A metal detector is a device for locating hidden metallic objects. It is used, for example, to locate pipelines, conductive objects in containers, especially foreign bodies in media, electrical conductors, electrically conductive objects, or objects concealed on people. In light of current events, the use of metal detectors for locating munitions such as mines, munitions, and unexploded ordnance is of particular interest. Common metal detectors consist of a transmitting coil, or primary coil, which is fed with an alternating current by an electronic circuit to generate the widest possible primary magnetic field, as well as one or more receiving coils, or secondary coils.

[0004] The document US2011241687A1 teaches a method for detecting metallic or other electrically conductive objects in flat search areas. This method uses at least one search probe that generates search signals. The probe is guided by a vehicle parallel to the surface of the search area along a search path located within a search area. The search signals are evaluated by at least one analysis unit coupled to the search probe.

[0005] Document BG3298U1 teaches a production line for filling and dosing a product in the confectionery industry, including, among other things, a metal detector. This document describes a mechanism connected to the metal detector, which is partly responsible for removing part of the product from the production line, for example, to prevent contamination of the product with metallic objects.

[0006] State-of-the-art metal detectors usually provide no, or at best very inaccurate, information about the type and size of a detected electrically conductive object, and they also provide, at best, inaccurate information about the object's position relative to the metal detector. A metal detector is often adapted to the search conditions, for example, by varying the properties and arrangement of the secondary coils.

[0007] In particular, the size of the receiving coils is adjusted to the distance between the object and the metal detector in order to maximize the voltage induced in the secondary coils by the secondary magnetic field. Consequently, to detect hidden electrically conductive objects at an unknown distance, it is sometimes necessary to replace the receiving coils. Furthermore, conventional metal detectors typically have only two receiving coils and can therefore only generate limited information about an object.

[0008] The invention is based on the object of providing a metal detector that can determine a position of a detected electrically conductive object within the primary magnetic field and that is light enough to be carried by an aerial drone.

[0009] The invention solves the problem by a metal detector according to independent claim 1.

[0010] The metal detector according to the invention comprises: a measuring and operating circuit with an input; a primary coil, configured to be supplied with an alternating current by the measuring and operating circuit and configured to generate a primary magnetic field; wherein the primary magnetic field serves, in use, to excite an electrically conductive object to generate a secondary magnetic field; at least one coil arrangement comprising a first secondary coil and a second secondary coil; wherein the at least one coil arrangement has at least two gaps between the first and the second secondary coil; wherein the first secondary coil and the second secondary coil are connected to the input such that voltages of the two secondary coils induced by a magnetic field and applied to the input have opposite signs;wherein the measuring and operating circuit is configured to process the sum of voltages present at the input into at least one signal; characterized in that the metal detector is configured to test different locations for the secondary magnetic fields at different times using the at least one signal.

[0011] In one embodiment of the metal detector according to the invention, the first secondary coil has a first magnetic coupling to the primary coil; the second secondary coil has a second magnetic coupling to the primary coil; the first magnetic coupling and the second magnetic coupling are identical except for tolerances.

[0012] In one embodiment of the metal detector according to the invention, the primary coil is symmetrical, in particular circularly symmetrical.

[0013] In one embodiment of the metal detector according to the invention, at least one secondary coil of the coil arrangement has one or more loops; wherein the one or more loops have the shape of a segment of a circle; wherein a magnetic coupling of the at least one secondary coil is given by a sum of the magnetic couplings of the one or more loops. One embodiment of the metal detector according to the invention comprises: a carrier; a rotator configured to rotate relative to the carrier; wherein the measuring and operating circuit and the primary coil are arranged on the carrier or on the rotator; wherein the coil arrangement is arranged on the rotator.

[0014] In one embodiment of the metal detector according to the invention, the coil arrangements are designed to generate, by rotation, a modulation, in particular a coding, of the temporal profile of the sum of the voltages present at the input and of the at least one signal.

[0015] In one embodiment of the metal detector according to the invention, the measuring and operating circuit is configured to modulate an angular velocity of the rotator continuously or adaptively between a minimum value and a maximum value.

[0016] In one embodiment of the metal detector according to the invention, the at least one coil arrangement consists of a plurality of secondary coils arranged around the center of the primary coil; wherein the measuring and operating circuit is configured to process the sum of the voltages of different secondary coils present at the input at different times.

[0017] In one embodiment of the metal detector according to the invention, the metal detector is attached to an aircraft, or to a vehicle, or to a swimming device.

[0018] In one embodiment of the metal detector according to the invention, the rotation is generated by the aircraft, the vehicle, or the floating device.

[0019] A method according to the invention for detecting a hidden electrically conductive object using a metal detector according to the invention comprises at least the following steps: generating a primary magnetic field with the primary coil of the metal detector for generating a secondary magnetic field by eddy currents induced in the electrically conductive object; detecting voltages induced by the secondary magnetic field in the coil arrangements and present at the input by means of the measuring and operating circuit; processing the voltages present at the input into at least one signal by means of the measuring and operating circuit; generating at least one signal curve by storing the at least one signal as at least one ordered time series; and evaluating the at least one time series.

[0020] An embodiment of the method according to the invention for determining location information of an electrically conductive object comprising an angular position and a radial distance further comprises at least the following steps: generating a signal curve with at least two features, wherein the at least two features include, for example, a minimum, a maximum, an inflection point, a rate of change, or a zero crossing; determining the angular position of the conductive object based on a first feature of the at least one time series of the signal curve; determining a radial distance to a center point of the primary coil based on at least one second feature of a time series of the signal curve.

[0021] In one embodiment of the method according to the invention for determining an angular position and a radial distance of an electrically conductive object, the at least one signal comprises a voltage amplitude; wherein the at least one signal curve comprises a voltage amplitude curve; wherein a first feature is given by a local minimum of the voltage amplitude curve having a time point; wherein a second feature is given by a global minimum of the voltage amplitude curve having a change duration; wherein the angular position is determined based on the time point of the local minimum and a rotation angle of the rotator; wherein the radial distance is determined based on the time period of the change.

[0022] In one embodiment of the method according to the invention for determining an angular position and a radial distance of an electrically conductive object, the at least one signal comprises a voltage amplitude and a function of a phase angle difference (S) formed by a difference between the phase angle of the primary magnetic field and the phase angle of the induced voltages applied to the input; wherein a signal curve comprises the product of the time curve of the voltage amplitude and the time curve of the function of the phase angle difference (S), for example sign δ~), sin(δ), cos(δ); wherein the first feature comprises a first zero crossing of the signal curve comprising a first point in time, and the second feature comprises a second zero crossing of the signal curve comprising a second point in time; wherein the signal curve has a change duration and a change rate at that point in time;wherein the signal curve has a change duration and a change rate at a time; where ZR2 < ZR1 and ZD2 > ZD1 ; wherein the angular position is determined based on the time of the first zero crossing and a rotation angle of the rotator; wherein the radial distance is determined based on the change duration of the second zero crossing or based on the change rate of the signal curve at the time of the second zero crossing.

[0023] A measuring point according to the invention, configured to detect an electrically conductive object in a medium (M), comprises: a metal detector according to the invention; a device guiding the medium; wherein the primary coil and the coil arrangement of the metal detector are arranged on the device; wherein the measuring and operating circuit is configured to enable derivation of location information of an electrically conductive object in the medium.

[0024] The invention is explained using the following figures.

[0025] Fig. 1 shows an embodiment of the metal detector according to the invention.

[0026] Fig. 2a shows an embodiment of the processed signal.

[0027] Fig. 2b shows an alternative embodiment of the processed signal. Fig. 3a shows an alternative embodiment of the processed signal. Fig. 3b shows an alternative embodiment of the processed signal. Fig. 4 shows an alternative embodiment of the coil arrangement according to the invention. Fig. 5 shows an embodiment of the processed signal of the coil arrangement of Fig. 4. Fig. 6 shows an embodiment of the metal detector according to the invention as part of a UAV. Fig. 7 shows an embodiment of the measuring point according to the invention.

[0028] The embodiment of the metal detector according to the invention shown in Fig. 1 shows the primary coil PF, which is fed with an alternating current by the measuring and operating circuit MB and is designed to generate a high-frequency primary magnetic field, which in turn excites a conductive object G, G', located, for example, at a location x1, x2, xn, to generate a secondary magnetic field. The coil arrangement SA is designed to test the location x1; x2; xn for the presence of a secondary magnetic field. This is done by the voltage induced by secondary magnetic fields in the secondary coils SS1, SS2 being fed via the input E into the measuring and operating circuit MB, where it is processed into a signal. The signal can comprise a voltage amplitude and / or a phase difference angle and / or a function of the phase difference angle of the voltages applied to the input and / or of the primary magnetic field PF.

[0029] In this embodiment, the coil arrangement SA consists of two sector-shaped and / or approximately semicircular secondary coils SS1, SS2, which are arranged around the center point MP of the primary coil PS. Two gaps SP1, SP2 spatially separate the secondary coils SS1, SS2, wherein the angular distance measured from the center point of the primary coil MP between the first secondary coil SS1 at the first gap SP1 is smaller than the angular distance between the first secondary coil SS1 and the second secondary coil SS2 at the second gap SP2. The coil arrangement SA is designed to rotate around a center point of the primary coil MP, resulting in a rotation angle of the coil arrangement that changes over time and can be defined, for example, via the position of the gap SP1. Due to a rotation, the location x1, x2, xn of different secondary coils SS1, SS2 is checked for the presence of secondary magnetic fields at different times.The voltages induced in the secondary coils SS1, SS2 are processed into a signal by the measuring and operating circuit MB. If an object G, G' is located at the location x1, x2, xn, location information Ol, Ol' of the object G, G' is derived from the processed signal. The derivable location information Ol, Ol' includes an angular position 0, 0' of the object G, G' with respect to a reference plane RE, and a radial distance A, A' of the object G, G' from the center of the primary coil PS.

[0030] The embodiment of the signal curve U according to the invention shown in Fig. 2a shows the temporal course of the signal processed by the measuring and operating circuit over a rotation period TO of the rotator.

[0031] The voltages applied to input E are induced in the secondary coils SS1, SS2 by a secondary magnetic field generated by object G.

[0032] In this embodiment, the signal waveform U is the product of a voltage amplitude applied to the input E and a function of a phase angle difference θ formed by a difference between the phase angle of the primary magnetic field PF and the phase angle of the induced voltages, where the function here is sign<5, but can also include sinθ, cosθ, for example, so that a change in sign of the signal waveform occurs. The features N1, N2 are a first zero crossing N1 with associated time t1 and rate of change ZR1, and a second zero crossing N2 with associated time t2 and rate of change ZR2, so that U(t=t1) = U(t=t2) = 0. The first zero crossing N1 and the second zero crossing N2 can be differentiated by the respective rate of change ZR1, ZR2 at the associated time t1, t2. The rate of change ZR1 of the zero crossing N1 is greater than the rate of change ZR2 of the zero crossing N2 because the gap SP1 has a smaller opening angle than the gap SP2.The angular position <p des Gegenstands G entspricht damit dem Rotationswinkel des Spalts SP1 zum selben Zeitpunkt. Der radiale Abstand des Gegenstands G zum Mittelpunkt MP der Primärspule PS kann aus den Änderungsraten ZR1 , ZR2 abgeleitet werden.

[0033] The embodiment of a signal curve U' shown in Fig. 2b is analogous to the signal curve U shown in Fig. 2, with the difference that the signal-generating electrically conductive object G' has a different angular position cf>' and a larger radial distance A'. The angular position cf>' of the object G' can be derived from the angle of rotation of the gap SP1 at time t1 '. The radial distance can be derived from the rates of change ZR1, ZR2 of the signal curve U' at the zero points N1, N2 at time t1 ', t2'. The shape of the gap SP1, SP2 determines the relationship between the rate of change ZR1, ZR2 and the radial distance A'. In general, a rate of change ZR1, ZR2 is smaller if the associated gap SP1, SP2 occupies a larger angular range and vice versa.For example, the rate of change ZR1, ZR2 for a pie-shaped gap SP1, SP2 is independent of the radial distance A', whereas the rate of change ZR1, ZR2 for a cup-shaped gap SP1, SP2 decreases with increasing radial distance A'. For a gap SP1, SP2 that has a constant width parallel to the radial direction, the rate of change ZR1, ZR2 increases with increasing radial distance A'. The embodiment illustrated in Fig. 3a shows the signal curve U formed by processing the voltages applied to the input E, wherein the voltages are induced in the secondary coils SS1, SS2 by a secondary magnetic field generated by the electrically conductive object G.

[0034] The signal curve U is given by the time course of the amplitude of the voltages applied to the input E, referred to as the voltage amplitude. The characteristics N1 , N2 are a local minimum N1 with the associated time t1 and temporal change duration ZDI , and a global minimum N2 with the associated time t2 and temporal change duration ZD2. The angular position of the object G is determined using the angle of rotation at the associated time t1. The radial distance A of the object G to the center MP of the primary coil PS is determined from the temporal change durations ZD1 , ZD2, which are given by t1 and t4-t3 if t4>t3, otherwise by t1 and T0-t3+t4, where T0 corresponds to one period of rotation.

[0035] The embodiment shown in Fig. 3b represents a signal curve U' analogous to the signal curve U shown in Fig. 2, wherein the signal-generating electrically conductive object G' has a different angular position cf>' and a larger radial distance A' compared to the angular position <p und dem Radialen Abstand A von dem Gegenstand G aufweist. Der radiale Abstand A‘ ergibt sich aus der zeitlichen Änderungsdauer ZD1 , ZD2 des Signalverlaufs U‘ zum Zeitpunkt t1 ‘, t2‘, welche einen vergleichsweise größeren Wert aufweist als die korrespondierende zeitliche Änderungsdauer ZD2 in Fig. 3a.

[0036] Fig. 4 shows an alternative embodiment of the coil arrangement SA according to the invention, which is arranged within the circularly symmetrical primary coil PS and around its center point MP. Here, the first secondary coil SS1 is formed by two essentially sector-shaped loops SS11, SS12, and the second secondary coil SS2 is formed by two essentially sector-shaped loops SS21, SS22. In this embodiment, two loops SS11, SS21; SS12, SS22 are symmetrical to one another by reflection at a mirror plane SE.

[0037] The embodiment shown in Fig. 5 shows the signal curve U formed by processing voltages applied to the input E, wherein the voltages are induced by a secondary magnetic field generated by the object G in the loops SS11, SS12, SS21, SS22 of the secondary coils SS1, SS2.

[0038] The signal curve U is the product of a voltage amplitude applied to the input E and a function of a phase angle difference δ formed by a difference between the phase angle of the primary magnetic field PF and the phase angle of the induced voltages, where the function here includes signδ, alternatively also sinδ or cosδ, so that a change of sign of the signal curve occurs. The features NO, N1, N2, N3 are zero crossings of the signal curve with associated times t=0, t1, t2, t3, such that U(0) = U(t1) = U(t2) = U(t3) = 0. The first zero crossing NO with associated time t=0 has the greatest rate of change and thus determines the angular position of the object G through the rotation angle of the slit SP1 at the same time. Additional information about the position and possibly also the shape of the object G can be obtained from the further zeros, associated times, and rates of change.

[0039] The embodiment of the metal detector according to the invention shown in Fig. 6 is a part of an unmanned aerial vehicle (UAV), for example a drone for mine detection and clearance.

[0040] In this embodiment, the carrier T is the body of the unmanned aerial vehicle, which has a rotary drive DA, which is connected by means of a rotator suspension SSA to the rotator R, which can be set in rotation by means of the rotary drive DA.

[0041] The rotator R comprises at least the primary coil PS for emitting a primary magnetic field PF and the coil arrangement SA for testing the locations x1, x2, xn for secondary magnetic fields.

[0042] The embodiment of the measuring point according to the invention shown in Fig. 7 shows a device V carrying a medium M, and an embodiment of the metal detector according to the invention, comprising a coil arrangement SA arranged relative to the device V, a primary coil PS and the measuring and operating circuit MB.

[0043] The primary coil PS generates a primary magnetic field PF, which excites an electrically conductive object G contained in the medium M to generate a secondary magnetic field, which in turn generates voltages in the coil arrangement SA, which in turn is processed into a signal in the measuring and operating circuit. In one embodiment of the invention, the measuring point can be arranged on a flow meter or on a conveyor belt that is part of a production line for filling and dosing a product, wherein the measuring point is at least partially responsible for removing products from the production line if they are contaminated with metallic objects.

[0044] List of reference symbols

[0045] MB measuring and operating circuit

[0046] E Entrance

[0047] PS primary coil

[0048] MP center point

[0049] PF primary magnetic field

[0050] G Object

[0051] SA coil arrangement

[0052] SS1. SS2 secondary coil

[0053] SP1. SP2 column x1 ,x2,xn locations

[0054] SS11, SS12, SS21, SS22 loops

[0055] T carrier

[0056] R Rotator

[0057] U Signal curve

[0058] <p Winkelposition

[0059] A radial distance

[0060] Ol local information

[0061] N1. N2 Feature t1 , t2 Time

[0062] ZD1. ZD2 change duration

[0063] ZR1. ZR2 rate of change

[0064] 6 Phase angle difference

[0065] SSA sensor suspension

[0066] M Medium

[0067] V device

Claims

Patent claims 1. Metal detector, comprising: • A measuring and operating circuit (MB) with one input (E); • a primary coil (PS) adapted to be supplied with an alternating current by the measuring and operating circuit (MB) and adapted to generate a primary magnetic field (PF); • wherein the primary magnetic field (PF) is used in the application to excite an electrically conductive object (G) to generate a secondary magnetic field; • at least one coil arrangement (SA) comprising a first secondary coil (SS1) and a second secondary coil (SS2); • wherein the at least one coil arrangement (SA) has at least two gaps (SP1, SP2) between the first and the second secondary coil (SS1, SS2); • wherein the first secondary coil (SS1) and the second secondary coil (SS2) are connected to the input (E) in such a way that voltages of the two secondary coils (SS1, SS2) induced by a magnetic field and applied to the input (E) have opposite signs; • wherein the measuring and operating circuit (MB) is designed to process the sum of voltages present at the input (E) into at least one signal; • characterized in that the metal detector is designed to check different locations (x1; x2; xn) for the secondary magnetic fields at different times by means of the at least one signal.

2. Metal detector according to claim 1, • wherein the first secondary coil (SS1) has a first magnetic coupling to the primary coil (PS); • wherein the second secondary coil (SS2) has a second magnetic coupling to the primary coil (PS); • where the first magnetic coupling and the second magnetic coupling are identical except for tolerances.

3. Metal detector according to one of claims 1 or 2, • wherein the primary coil (PS) is symmetrical, in particular circularly symmetrical.

4. Metal detector according to one of claims 1 to 3, • wherein at least one secondary coil (SS1; SS2) of the coil arrangement (SA) has one or more loops (SS11, SS12, SS21, SS22); • wherein the one or more loops (SS11, SS12, SS21, SS22) have the shape of a segment of a circle; wherein a magnetic coupling of the at least one secondary coil (SS1; SS2) is given by a sum of the magnetic couplings of the one or more loops (SS11, SS12; SS21, SS22).

5. Metal detector according to one of claims 1 to 4, further comprising: • A carrier (T); • a rotator (R) arranged to rotate relative to the support (T); • wherein the measuring and operating circuit (MB) and the primary coil (PS) are arranged on the carrier (T) or on the rotator (R); • wherein the coil arrangement (SA) is arranged on the rotator (R).

6. Metal detector according to claim 5, • wherein the coil arrangements (SA) are designed to generate, by rotation, a modulation, in particular a coding, of the temporal profile of the sum of the voltages and of the at least one signal present at the input (E).

7. Metal detector according to one of claims 5 or 6, • wherein the measuring and operating circuit (MB) is configured to continuously or adaptively modulate an angular velocity of the rotator (R) between a minimum value and a maximum value.

8. Metal detector according to one of claims 1 to 3, • wherein the at least one coil arrangement (SA) consists of a plurality of secondary coils arranged around the center point (MP) of the primary coil (PS); • wherein the measuring and operating circuit (MB) is designed to process the sum of the voltages of different secondary coils present at the input (E) at different times.

9. Metal detector according to one of claims 1 to 8, • the metal detector is attached to an aircraft, a vehicle or a floating device.

10. Metal detector according to claim 9, • where the rotation is generated by the aircraft, the vehicle, or the floating device.

11. A method for detecting a hidden electrically conductive object with a metal detector according to any one of claims 1 to 10, comprising at least the following steps: • generating a primary magnetic field (PF) with the primary coil (PS) of the metal detector, for generating a secondary magnetic field by eddy currents induced in the electrically conductive object (G); • Detecting voltages induced by the secondary magnetic field in the coil arrangements (SA) and present at the input (E) by means of the measuring and operating circuit (MB); • Processing the voltages applied to the input (E) into at least one signal by means of the measuring and operating circuit (MB); • Generating at least one signal curve (U) by storing the at least one signal as at least one ordered time series; and • Evaluate at least one time series.

12. A method for determining location information (Ol) of an electrically conductive object (G) comprising an angular position ( ) and a radial distance (A) according to claim 11, further comprising at least the following steps: • Generating a signal curve (U) with at least two features (N1, N2), wherein the at least two features (N1, N2) include, for example, a minimum, a maximum, an inflection point, a rate of change, or a zero crossing; • Determining the angular position ( ) of the conductive object (G) based on a first feature (N1) of the at least one time series of the signal curve (U); • Determining a radial distance (A) to a center point (MP) of the primary coil (PS) based on at least one second feature (N2) of a time series of the signal curve (U).

13. A method for determining an angular position ( ) and a radial distance (A) of an electrically conductive object (G) according to claim 12, • wherein the at least one signal comprises a voltage amplitude; • wherein the at least one signal curve (U) comprises a voltage amplitude curve; • wherein a first feature (N1) is given by a local minimum of the voltage amplitude curve having a time (t1); • wherein a second feature (N2) is given by a global minimum of the voltage amplitude curve having a change duration (ZD2); • wherein the angular position ( ) is determined based on the time (t1) of the local minimum and a rotation angle of the rotator (R); • where the radial distance (A) is determined based on the time period of change (ZD2).

14. A method for determining an angular position ( ) and a radial distance (A) of an electrically conductive object (G) according to claim 12, • wherein the at least one signal has a voltage amplitude and a function of a voltage determined by a difference between the phase angle of the primary magnetic field (PF) and the phase angle of the phase angle difference (5) formed by the induced voltages applied to the input (E); • wherein a signal curve (U) comprises the product of the time curve of the voltage amplitude and the time curve of the function of the phase angle difference (5), for example sign(3), sin(5), cos(5); • wherein the first feature (N1) comprises a first zero crossing of the signal curve (U) comprising a first time (t1), and the second feature (N2) comprises a second zero crossing of the signal curve (U) comprising a second time (t2); • wherein the signal curve (U) at the time (t1) has a change duration (ZD1) and a change rate (ZR1); • wherein the signal curve (U) has a change duration (ZD2) and a change rate (ZR2) at a time (t2); • where ZR2 < ZR1 and ZD2 > ZD1 ; • wherein the angular position ( ) is determined based on the time (t1) of the first zero crossing (N1) and a rotation angle of the rotator (R); • wherein the radial distance (A) is determined based on the time period of change (ZD2) of the second zero crossing (N2) or based on the rate of change (ZR2) of the signal curve (U) at the time of the second zero crossing (N2).

15. Measuring point, designed to detect an electrically conductive object (G) in a medium (M), comprising: • A metal detector according to one of claims 1 to 10; • a device (V) for conveying the medium; • wherein the primary coil (PS) and the coil arrangement (SA) of the metal detector are arranged on the device (V); • wherein the measuring and operating circuit (MB) is designed to enable derivation of location information (Ol) of an electrically conductive object (G) in the medium (M).

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