Measuring sensor for metal detector, method for detecting hidden electrically conductive objects using a measuring sensor for a metal detector, and method for producing a measuring sensor for a metal detector

Abstract

The invention relates to a measuring sensor, comprising: a primary coil (1) for generating a primary magnetic field in order to excite electrically conductive objects to generate secondary magnetic fields; a measuring and operation circuit (2) which supplies the primary coil with alternating current, having an amplifier (3) with amplifier input (4), amplification factor, and value of the saturation voltage; a first secondary coil (5), having a main loop (51), and having a first subsidiary loop (52), coupled to the main loop (51); a second secondary coil (6); wherein the magnetic couplings of the main loop (51) and the second secondary coil to the primary coil deviate from one another by less than 10%; wherein the magnetic coupling of the first subsidiary loop (52) to the primary coil is less than the magnetic coupling to the primary coil of the main loop (51); wherein the first secondary coil (5) and the second secondary coil (6) are coupled to the amplifier (3) such that the voltages, induced by the primary magnetic field in the first secondary coil (5) and in the second secondary coil (6), at the amplifier input (4) of the amplifier (3) have different signs.

Description

[0001] Sensor for metal detector, method for detecting hidden electrically conductive objects with a sensor for metal detector, and method for producing a sensor for a metal detector

[0002] The invention relates to a measuring sensor for a metal detector with special sensitivity, a method for detecting concealed electrically conductive objects using a measuring sensor for a metal detector with special sensitivity. Furthermore, the invention relates to a method for producing a measuring sensor for a metal detector with special sensitivity.

[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] US 10056186B2 describes a metal detector as a device for detecting electrically conductive materials, comprising multiple electromagnetic coils and circuit boards. The circuit boards are positioned so that their metallic surfaces and layers reduce or eliminate the influence of the coils on the detection of electrically conductive materials.

[0005] Document WO0225318A1 teaches a device and method for detecting electrically conductive materials, comprising a primary coil, referred to as an excitation coil, which is operated with alternating voltage, a secondary coil, referred to as a detection coil, which detects output signals, and a subtraction unit that subtracts one detected signal from the other. The invention makes it possible to eliminate a background signal and enables the detection of metal particles. Document US2022107439A1 teaches a device for detecting objects concealed on persons, consisting of a metal detector with at least three transducers or coils arranged around a passage, such that a combination of an induced voltage enables approximate localization of the object.

[0006] 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 device 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.

[0007] The document CN213800188U teaches a landmine detection device mounted on an unmanned aerial vehicle. The device includes, among other components, a microcontroller, a metal detector, and a GPS positioner. Due to its flies and unmanned nature, the device can help ensure the safety of deminers, reduce detection times, and improve the efficiency of mine clearance.

[0008] The sensitivity of a metal detector can be defined as the ratio of the field strength of a just-detectable secondary field to the field strength of the primary field. A metal detector with high sensitivity is desirable because this means that the metal detector can detect particularly weak secondary fields. In an alternating current operated metal detector, the sensitivity is limited by the magnetic coupling of the receiving coils to the primary coil, as described below. Coils printed on circuit boards have inductances that can be precisely adjusted down to a relative tolerance value. The voltages induced by the primary field in two secondary coils can be reduced to the relative tolerance value by connecting the coils in a specific way. This means that secondary magnetic fields can be detected with field strengths at the secondary coils that are comparable to the reduced field strength of the primary coil.Consequently, smaller tolerances in the secondary coils correspond to weaker detectable secondary fields. According to the state of the art, the tolerance value is usually in the percentage or per mille range.

[0009] The invention is based on the object of providing a measuring sensor for an alternating current operated metal detector which is particularly sensitive.

[0010] The invention solves the problem by a measuring sensor for a metal detector according to independent claim 1.

[0011] The measuring sensor according to the invention comprises: a primary coil, configured to generate a primary magnetic field, wherein the primary magnetic field serves in the application to excite electrically conductive objects to generate secondary magnetic fields; a measuring and operating circuit, configured to supply the primary coil with an alternating current, having an amplifier, an amplifier input, a gain factor, and a value of the saturation voltage; a first secondary coil, having a main loop, and having a first secondary loop coupled to the main loop; a second secondary coil; wherein the main loop has a magnetic coupling with the primary coil M 1 H and the second secondary coil has a magnetic coupling with the primary coil M2, so that < 0.05; wherein the first secondary loop has a magnetic coupling with the primary coil that is smaller than the magnetic coupling with the primary coil of the main loop; wherein the first secondary coil and the second secondary coil are coupled to the amplifier such that the electrical voltages induced by the primary magnetic field in the first secondary coil and in the second secondary coil have different signs at the amplifier input of the amplifier.

[0012] In a further development of the measuring sensor according to the invention, the magnetic coupling to the primary coil, the first secondary coil, and the second secondary coil is tuned such that the amplitude of the voltage induced by the primary magnetic field and present at the amplifier input is smaller than—preferably smaller than half of—the saturation voltage of the amplifier divided by the gain factor. In a further development of the measuring sensor according to the invention, the relative arrangement of the first secondary coil to the primary coil and the relative arrangement of the second secondary coil to the primary coil are substantially symmetrical, in particular mirror-symmetrical, to one of the symmetry planes or symmetry axes of the primary coil.

[0013] In a further development of the measuring sensor according to the invention, the first secondary loop is part of a plurality of secondary loops; wherein each secondary loop from the plurality of secondary loops has a magnetic coupling with the primary coil that is smaller than the magnetic coupling with the primary coil of the main loop; wherein any number of secondary loops from the plurality of secondary loops can be coupled to the main loop.

[0014] In a further development of the measuring sensor according to the invention, the first secondary coil comprises conductor tracks on a printed circuit board, in particular is formed by conductor tracks on a printed circuit board; and the second secondary coil comprises conductor tracks on a printed circuit board, in particular is formed by conductor tracks on a printed circuit board.

[0015] In a further development of the measuring sensor according to the invention, the primary coil comprises conductor tracks on a printed circuit board, in particular is formed by conductor tracks on a printed circuit board.

[0016] In a further development of the measuring sensor according to the invention, the first secondary coil, the second secondary coil, and the primary coil are arranged on separate levels of a printed circuit board.

[0017] A further development of the measuring sensor according to the invention comprises: a further main loop; a further plurality of secondary loops; wherein the second secondary coil comprises the further main loop; wherein the second secondary coil is configured to be coupled to one of the secondary loops from the further plurality of secondary loops. In a further development of the measuring sensor according to the invention, the gain factor with which the amplifier amplifies a voltage signal from the secondary coils is at least 1000—preferably at least 10,000.

[0018] A further development of the measuring sensor according to the invention further comprises a housing; wherein the primary coil, the first secondary coil, the second secondary coil and the amplifier have a fixed connection to the housing, which determines their relative position to one another.

[0019] A method according to the invention for detecting metal objects moving relative to a measuring sensor according to the invention, comprising at least the following steps: generating a primary field with the measuring sensor by means of the primary coil; wherein eddy currents in a metal object moving relative to the measuring sensor generate a secondary magnetic field; inducing electrical voltages in the secondary coils of the measuring sensor by means of the secondary magnetic field; amplifying the electrical voltages induced in the measuring sensor in the amplifier; evaluating the induced electrical voltages amplified by the amplifier.

[0020] A method for producing a metal detector according to the invention comprises at least the following steps: symmetrically arranging two secondary coils, each arranged on a plane of a circuit board, with respect to a plane of symmetry or axis of symmetry of the primary coil; arranging a plurality of secondary loops on a plane of the circuit board; connecting the first secondary coil and the second secondary coil to the amplifier; generating a primary magnetic field through the primary coil; measuring the voltage induced by the primary magnetic field in the first secondary coil and in the second secondary coil and amplified by the amplifier; comparing the amplified voltage with the value of the saturation voltage of the amplifier; and coupling at least one secondary loop from the plurality of secondary loops to one of the secondary coils, in particular by using at least one short-circuit bridge, so that the amplified voltage is minimized.and that the amplified voltage is less than, in particular half, the value of the saturation voltage. The invention has the advantage that secondary coils with a conventional tolerance, for example in the percentage range or in the per mille range, can be used, and secondary fields whose field strength at the secondary coils is less than one per mille of the field strength of the primary magnetic field can still be detected by means of the secondary loops. The invention further has the advantage that the measuring sensor according to the invention is compatible with conventional metal detectors and can be used widely. The invention further has the advantage that the secondary coils can be arranged on multiple levels of a circuit board, whereby the space required for and the overall weight of the measuring sensor are particularly low, so that the measuring sensor according to the invention is well suited for small, particularly unmanned, aircraft, vehicles, and floating devices.to be installed.,

[0021] The invention is explained using the following figures.

[0022] Fig. 1 shows a circuit diagram of an embodiment of the measuring sensor according to the invention.

[0023] Fig. 2 shows a circuit diagram of a further embodiment of the measuring sensor according to the invention.

[0024] Fig. 3 shows a schematic cross-section of an embodiment of the arrangement of primary coil and secondary coils on a circuit board.

[0025] Fig. 4 shows a flowchart of an embodiment of the method according to the invention for detecting a metal object.

[0026] Fig. 5 shows a flow chart of an embodiment of the method according to the invention for producing the measuring sensor according to the invention.

[0027] The circuit diagram of an embodiment of the measuring sensor according to the invention shown in Fig. 1 comprises a primary coil 1 with a plane of symmetry 7, which is supplied with alternating current by a measuring and operating circuit 2. A first secondary coil 5 consists of a main loop 51, which is connected to a plurality of secondary loops 53, wherein, in particular, the coupling of secondary loop 52 and main loop 51 is provided by a short-circuit bridge 54. In this embodiment of the invention, the main loops have 60 turns and an active area of ​​220 x 160 mm 2 and the multitude of secondary loops has an active area between 90 and 5400 mm 2 The coupling of the multitude of

[0028] The connection of the secondary loops with the main loop is such that the voltages induced by a magnetic field can be added or subtracted. The first secondary coil 5 is connected in series with the second secondary coil 6 and connected to the amplifier input 4 in such a way that the voltage generated by the primary coil

[0029] The voltages generated by the magnetic field in the secondary coils and those applied to the amplifier input have opposite signs. The switching elements are housed in a housing 8. In this embodiment, with magnetic coupling of the first main loop 51 M 1 H and magnetic coupling of the secondary coil 6 M2

[0030] M 1,H~ M2 < 0.005. The circuit suppresses the voltage applied to the amplifier input induced by the magnetic field of the primary coil, so that the voltages induced by external magnetic fields, in particular secondary magnetic fields generated by the magnetic field of the primary coil in electrically conductive objects through eddy currents, produce larger or at least comparable amplitudes at the amplifier input to those of the primary magnetic field. The amplifier 3 has a saturation voltage of 1 V, amplifies the applied total voltage with a gain factor of 10000, and passes this on to the measuring and operating circuit 2 as a signal for evaluation. Evaluation can be performed, for example, by an acoustic and / or optical signal to alert a user to a change in a secondary magnetic field.An evaluation may also include the storage and / or transmission of data to an evaluation unit, whereby the data may include, among other things, a signal transmitted by the amplifier, a spatial and / or a temporal coordinate.

[0031] The sketch shown in Fig. 2 of an embodiment of the first secondary coil 5 and the second secondary coil 6 according to the invention shows the first secondary coil 5 described in Fig. 1, as well as the second secondary coil 6 comprising a main loop 61. Furthermore, a further plurality of further secondary loops 62 are shown, of which a further first secondary loop 61 can be coupled to the main loop 61 by a short-circuit bridge 64.

[0032] Fig. 3 shows a schematic cross-section of an arrangement of coils according to one embodiment of the measuring sensor according to the invention. Several planes are arranged on the circuit board L. Here, EP denotes a set of planes comprising the primary coil 1, ES denotes the set of planes, each of which comprises the first secondary coil 5 and the second secondary coil 6 on one half. The one or more planes EN comprise the plurality of secondary coils 53. In this embodiment of the invention, all coils are planar, and all planes EP, ES, EN, and the circuit board L are parallel to a common orientation plane.

[0033] Fig. 4 shows a flowchart of an embodiment of the method for detecting electrically conductive objects using the measuring sensor according to the invention. For this purpose, a primary magnetic field is first generated using the primary coil 1. The metal detector with the measuring sensor according to the invention is moved over an electrically conductive object, inducing eddy currents in the object, which generate a secondary magnetic field that induces voltages in the first secondary coil 5 and in the second secondary coil 6 of the measuring sensor. These induced voltages are amplified by the amplifier 3 and forwarded as a signal to the measuring and operating circuit 2, where they are evaluated accordingly. An evaluation can be performed, for example, using an acoustic and / or optical signal to alert a user to a change in a secondary magnetic field.An evaluation may also include the storage and / or transmission of data to an evaluation unit, whereby the data may include, among other things, a signal transmitted by the amplifier, a spatial and / or a temporal coordinate.

[0034] Fig. 5 shows a flowchart of an embodiment of the method for manufacturing the measuring sensor according to the invention. Two secondary coils 5, 6 are arranged symmetrically to an axis of symmetry and / or plane of symmetry 7 of the primary magnetic field, for example, on two sides of a plane ES of a printed circuit board L. The first secondary coil 5 is defined by the secondary coil of the secondary coils 5, 6 in which a voltage with the lowest amplitude is generated by the primary magnetic field. A plurality of secondary loops 53 are arranged on one or more planes EN of the printed circuit board L such that they can be coupled to the first secondary coil 5. The first secondary coil 5 and the second secondary coil 6 are connected according to the invention to the input 4 of the amplifier 3. The primary coil 1 is supplied with alternating voltage by the measuring and operating circuit 2, and the voltage signal amplified by the amplifier 3 is measured.If the amplitude of the voltage signal corresponds to the value of the saturation voltage, a secondary loop 52 is selected and connected to the main loop 51 of the first secondary coil 5 via the short-circuit bridge 54 such that the amplitude of the voltage signal is minimized, wherein the minimized voltage signal is smaller than the value of the saturation voltage, preferably smaller than half of this value. With regard to minimizing the voltage signal, it may be advantageous for the plurality of secondary loops 53 to be coupled to both the first secondary coil 5 and the second secondary coil 6.In order to avoid having to determine in advance in which secondary coil 5; 6 a voltage with the lowest amplitude is generated by the primary magnetic field, it is advantageous if both the main loop 51 of the first secondary coil 5 is coupled to a secondary loop 52 from the plurality of secondary loops 53, and the further main loop 62 of the second secondary coil 6 is coupled to a further secondary loop 62 from a further plurality of secondary loops 63.

[0035] List of reference symbols

[0036] 1 primary coil

[0037] 2 Measuring and operating circuit

[0038] 3 amplifiers

[0039] 4 amplifier input

[0040] 5 First secondary coil

[0041] 51 Main loop

[0042] 52 First sub-loop

[0043] 53 Numerous sub-loops

[0044] 54 short-circuit bridge

[0045] 6 Second secondary coil

[0046] 61 Additional main loop

[0047] 62 Further First Sub-Loop

[0048] 63 Further variety of secondary loops

[0049] 64 Additional jumper

[0050] 7 plane of symmetry or axis of symmetry

[0051] 8 housings

[0052] L circuit board

[0053] EP primary coil comprehensive circuit board levels

[0054] ES secondary coils comprehensive circuit board levels

[0055] EN Large number of sub-loops comprising circuit board levels

Claims

Patent claims 1. Measuring sensor, comprising: • a primary coil (1 ) arranged to generate a primary magnetic field, the primary magnetic field being used in the application to excite electrically conductive objects to generate secondary magnetic fields; • a measuring and operating circuit (2) arranged to supply the primary coil with an alternating current, with an amplifier (3), an amplifier input (4), a gain factor, and a value of the saturation voltage; • a first secondary coil (5) having a main loop (51) and a first secondary loop (52) coupled to the main loop (51); • a second secondary coil (6); • wherein the main loop (51) has a magnetic coupling with the primary coil M 1 H and the second secondary coil has a magnetic coupling with the primary coil M2, so that < 0.05; • wherein the first sub-loop (52) has a magnetic coupling with the primary coil that is smaller than the magnetic coupling with the primary coil of the main loop (51); • wherein the first secondary coil (5) and the second secondary coil (6) are coupled to the amplifier (3) in such a way that the electrical voltages induced by the primary magnetic field in the first secondary coil (5) and in the second secondary coil (6) have different signs at the amplifier input (4) of the amplifier (3).

2. Sensor according to claim 1, • wherein the magnetic coupling with the primary coil of the first secondary coil (5) and the magnetic coupling with the primary coil of the second secondary coil (6) is tuned such that an amplitude of the voltage induced by the primary magnetic field and applied to the amplifier input (4) is smaller than - preferably smaller than half of - the saturation voltage of the amplifier (3) divided by the gain factor.

3. Sensor according to one of claims 1 or 2, • wherein the relative arrangement of the first secondary coil (5) to the primary coil (1) and the relative arrangement of the second secondary coil (6) to the primary coil is substantially symmetrical, in particular mirror-symmetrical, to one of the symmetry planes or symmetry axes (7) of the primary coil (1).

4. Sensor according to one of claims 1 to 4, • wherein the first sub-loop (52) is part of a plurality of sub-loops (53); • wherein each sub-loop of the plurality of sub-loops (53) has a magnetic coupling with the primary coil that is smaller than the magnetic coupling with the primary coil of the main loop (51); • wherein any number of secondary loops from the plurality of secondary loops (53) can be coupled to the main loop (51); • whereby the coupling of secondary loops (52) can increase or decrease the magnetic coupling of the main loop (51) with the primary magnetic field.

5. Sensor according to one of claims 1 to 4, • wherein the first secondary coil (5) comprises conductor tracks on a printed circuit board, in particular is formed by conductor tracks on a printed circuit board, and • wherein the second secondary coil (6) comprises conductor tracks on a printed circuit board, in particular is formed by conductor tracks on a printed circuit board.

6. Sensor according to one of claims 1 to 5, • wherein the primary coil (1) comprises conductor tracks on a printed circuit board, in particular is formed by conductor tracks on a printed circuit board.

7. Sensor according to one of claims 1 to 6, • wherein the first secondary coil (5), the second secondary coil (6), and the primary coil (1) are arranged on separate levels of a circuit board.

8. Sensor according to one of claims 1 to 7, further comprising: • another main loop (61 ); • a further plurality of secondary coils (63); • wherein the second secondary coil (6) comprises the further main loop (61); wherein the second secondary coil (6) is adapted to be coupled to a further sub-loop (62) from the further plurality of sub-loops (63).

9. Sensor according to one of claims 1 to 8, • wherein the amplification factor with which the amplifier (3) amplifies a voltage signal from the secondary coils (5, 6) is at least 1000 - preferably at least 10000.

10. Sensor according to one of claims 1 to 9, further comprising: • a housing; • wherein the primary coil (1), the first secondary coil (5), the second secondary coil (6) and the amplifier (3) have a fixed connection to the housing, which determines their relative position to one another.

11. A method for detecting hidden electrically conductive objects, comprising at least the following steps: • generating a primary field by means of a primary coil (1) of a measuring sensor according to one of claims 1 to 10; • Wherein eddy currents in a metal object moving relative to the primary coil (1) generate a secondary magnetic field; • Inducing electrical voltages in the secondary coils (5, 6) of the measuring sensor by the secondary magnetic field; • Amplifying the electrical voltages induced in the sensor in the amplifier; • Evaluate the induced electrical voltages amplified by the amplifier.

12. A method for manufacturing a sensor for a metal detector according to one of claims 1 to 10, comprising at least the following steps: • Symmetrical arrangement of two secondary coils (5, 6) arranged on one level of a printed circuit board with respect to a plane of symmetry or axis of symmetry of the primary coil (1); • Arranging a plurality of sub-loops (53) on one plane of the circuit board; • Connecting the first secondary coil (5) and the second secondary coil (6) to the amplifier (3); • Generating a primary magnetic field by the primary coil (1); • Measuring the voltage induced by the primary magnetic field in the first secondary coil (5) and in the second secondary coil (6) and amplified by the amplifier (3); • comparing the amplified voltage with the value of the saturation voltage of the amplifier (3); and • Coupling at least one secondary loop (52) from the plurality of secondary loops (53) to one of the secondary coils (5; 6), in particular by using at least one short-circuit bridge (54), so that the amplified voltage is minimized, and that the amplified voltage is less than, in particular half, the value of the saturation voltage.

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