WO2012113361A1

WO2012113361A1 - Inductive sensor

Info

Publication number: WO2012113361A1
Application number: PCT/DE2011/000178
Authority: WO
Inventors: Jörg GROSS
Original assignee: Balluff Gmbh
Priority date: 2011-02-24
Filing date: 2011-02-24
Publication date: 2012-08-30
Also published as: DE112011104961B4; DE112011104961A5; DE112011104961B8

Abstract

The invention relates to an inductive sensor (10), comprising a coil arrangement (18), which contains at least one exciting coil (20) and at least one detecting coil (22, 24), wherein the coil arrangement (18) can be influenced by an electromagnetic interaction with a target (40) to be detected. The inductive sensor (10) according to the invention is characterized in that an electrical conductor (12), which is arranged in the excitation field of the at least one exciting coil (20), is provided. The electrical conductor has at least two regions (16a, 16b, 16c, 16d) in the circumferential direction of the exciting coil (20), which regions each conduct an eddy current in the presence of an excitation field. The at least one electrical conductor (12) having the regions (16a, 16b, 16c, 16d) that conduct eddy currents leads to a concentration of the alternating magnetic field produced by the at least one exciting coil (20), wherein substantially axial flux density components having positive and negative amplitudes pass through essentially only one area extending orthogonally to the axial sensor direction. Thus high insensitivity to electromagnetically active material outside the inductive sensor (10) according to the invention and a greater detection region (A) are achieved.

Description

Description title

Inductive sensor

The invention is based on an inductive sensor according to the preamble of the independent claim.

In the case of an inductive sensor, a comparatively high field amplitude of at least one exciter coil occurs in comparison with an extremely small field amplitude resulting from the retroactivity of a target to be detected. A detection of the change of the field amplitude by the influence of the target to be detected by the inductive sensor requires a resolution of the measuring system of several orders of magnitude. Larger detection ranges can not be easily achieved with a cost-effective measuring system. It should be noted that an increase in the detection range from, for example, two times to three times, requires approximately a tenfold increase in the resolution of the measurement system.

With an inductive sensor designed as a gradiometer, a very high suppression of the exciter field can in principle be achieved if the detection coils are arranged in such a way that the flux components respectively encompassed by the coils are almost identical. An inductive sensor, the one

CONFIRMATION COPY pronounced sensitivity in the direction of the target, ie in the detection direction of the inductive sensor, and at the same time as possible no sensitivity to an electromagnetically active material in his

To have a direct environment requires in principle a very effective orientation of the magnetic field.

In an alternative embodiment of the inductive sensor, in which two coils are connected as excitation coils and a receiving coil is provided, the same problem occurs. Also in this case, electrically conductive or magnetizable material in the region of the inductive sensor should have as little influence as possible on the measurement result and ultimately on the achievable safe detection range.

State of the art

In principle, an alignment of a magnetic field can be achieved by means of an eddy current shield, which encloses a coil system in the shape of a cup. This solution has two significant disadvantages. On the one hand, a considerable wall thickness of the eddy current shielding is required for a sufficient shielding effect, which is difficult to accommodate in small designs. On the other hand, the eddy current shield causes a distortion of the excitation field symmetry, so that the suppression of the exciter field can no longer be ensured by a differential arrangement of detection coils.

A device for aligning a magnetic field is described, for example, in US Pat. No. 5,248,989. The alignment is done with an eddy-current-carrying conductor, which is made as a metal plate with a slot. The eddy current is generated as a counterreaction to an exciter field, which generates an exciting coil, which leads from the eddy current Head is surrounded.

Furthermore, US Pat. No. 6,057,683 describes an inductive sensor which has an exciter coil which is arranged within an electrically conductive sensor housing. The sensor housing is designed as a field concentrator, which has a slotted cylinder wall and a slotted bottom.

The patent DE 10 2006 053 222 B4 describes an inductive sensor designed as an inductive proximity switch, which has a transmitting coil arranged on a coil carrier and at least one detection coil. A coil designated as a supplementary coil, which is intended to build up a compensation field proportional to the excitation field generated by the at least one transmitting coil of the coil arrangement, is likewise arranged on a coil carrier, on whose rear side an electrically conductive screen is provided.

An orientation of a magnetic field by means of ferromagnetic material is generally customary. For this purpose ferromagnetic shell cores are used. In practice, this must be expected in some cases considerable batch deviations in the production of ferromagnetic materials, which are indeed specified in the data sheets in the context of tolerance ranges, but make an adjustment of each sensor in the manufacture of an inductive proximity sensor. Equally, it is necessary to react to geometry tolerances. The most serious disadvantage of a ferromagnetic flux guide, however, is the dependence of its permeability on the (DC) bias. In industrial use of inductive proximity sensors must with such external

Magnetic fields in the range of equipment, such as welding systems that generate strong magnetic fields are always calculated. Inductive proximity sensors used in the present patent application are described in the internet under the applicant's link: http://www.balluff.com. The inductive proximity sensors provide a switching signal that signals the presence of a target within a specified detection range.

The invention has for its object to provide an inductive sensor with the largest possible detection range.

The object is achieved by the features specified in the independent claim.

Disclosure of the invention

The invention is based on an inductive sensor with a coil arrangement which contains at least one exciter coil and at least one detection coil, wherein the coil arrangement can be influenced by an electromagnetic interaction with a target to be detected. The invention is characterized in that an electrical conductor arranged in the exciting field of the at least one exciter coil is provided, which has at least two regions in the circumferential direction of the exciter coil, which each lead to an eddy current in the presence of an exciter field.

The electrical conductor with the regions which in each case have an eddy current in the presence of an exciting field is also referred to below as the eddy currents of leading conductors.

The arrangement of at least one eddy-current-carrying conductor in the spool lenanordnung of the invention, for example, designed as a gradiometer inductive sensor leads to a bundling of the exciter field, without further stress radial space of the sensor housing. The emanating from an example toroidal exciter coil

magnetic field can be shaped such that substantially only one orthogonal to the axial sensor direction spanned surface of substantially axial flux density components with positive and negative amplitudes is interspersed.

The magnetic alternating field is thus shaped such that it has predominantly axially parallel flux density components of positive and negative amplitudes in the axial direction, which are rotationally symmetrical, but not coaxial, in a rotationally symmetrical inductive sensor, for example. This means that the output surface of the inductive sensor is interspersed alternately by positive and negative flux density components which lie on a coaxial ring.

The magnetic flux is bundled by the at least one eddy currents leading conductor in a comparable manner in the direction of the target to be detected, as determined by the known ferromag netic

Fluxing devices is achieved, but without their disadvantages, which are particularly in the influence of external magnetic fields. The absence of break-prone ferrite flux conductors also increases mechanical robustness.

The symmetry of the gradient of the axial flux density component of a cylindrical exciter coil is significantly disturbed by a one-sided shield in the axial direction. Coils of an axial gradiometer arranged in the axial direction above and below an exciter coil are therefore penetrated by flux density components which vary in magnitude and in particular significantly differentiate between phases. Here, the use according to the invention of the at least one electrical conductor with the at least two regions which each lead to an eddy current in the presence of a field exciter, a shaping of the geometry of the exciter field, so that its symmetry with respect to the at least one receiving coil of the inductive sensor is achieved in the required manner where optimization can be made in terms of both the amount of the field and its phase.

The measures according to the invention enable the realization of a sensor housing of the inductive sensor with a small housing diameter. The achievable field concentration is advantageous for a flush installation of the inductive sensor according to the invention in a sensor holder.

The measures according to the invention furthermore make it possible to minimize the sensitivity of the overall system to electromagnetically active objects in the immediate vicinity of the inductive sensor. The at least one eddy currents leading conductor is to be designed such that the eddy currents distributed over the circumference of the at least one exciter coil, resulting in extinction of the exciter field in individual areas. This requirement is achieved by the realization of the electrical conductor with the leading in the circumferential direction of the exciting coil at least two each an eddy current areas.

The resulting axial component of the magnetic flux density then has, distributed over the circumference of the coil system, alternately positive and negative components. The constellation of the magnetic flux achieved with the measures according to the invention thus alternates outside the inductive sensor and in optionally present electromagnetically active materials surrounding the inductive sensor Distributed regions of induced eddy currents with alternating current direction are distributed over the circumference, so that overall the influence on the coil system of the inductive sensor according to the invention is largely eliminated.

Advantageous developments and refinements of the inductive sensor according to the invention are objects of the dependent claims.

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description.

Brief description of the figures

FIG. 1 shows a sectional view through a sensor according to the invention with electrical conductors which have eddy-current-carrying regions,

FIG. 2 shows an isometric view of eddy current-carrying regions of the electrical conductor,

3 shows the axial component of a magnetic flux density distribution in a plan view of an inductive sensor according to the invention, FIG. 4 shows an isometric view of the upper side of a two-part eddy-current-carrying conductor,

FIG. 5 shows an isometric view of the underside of the two-part eddy current conductor shown in FIG. 4,

FIG. 6 shows a sectional view of the two-part eddy current conductor shown in FIGS. 4 and 5,

FIG. 7 shows an isometric view of the upper side of a one-piece conductor, which is arranged in a housing and carries eddy currents according to an alternative embodiment,

FIG. 8 shows an isometric view of the underside of the conductor shown in FIG. 7,

FIG. 9 shows a sectional view of the vortex shown in FIGS. 7 and 8. currents of the leading conductor,

FIG. 10 shows an isometric view of the underside of a two-part eddy-current-carrying conductor according to a further embodiment,

FIG. 11 shows an isometric view of the top side of the conductor carrying eddy currents shown in FIG. 10,

FIG. 12 shows a sectional view of the conductor carrying eddy currents shown in FIGS. 10 and 11,

FIG. 13 shows a sectional view of a two-part eddy-current-carrying conductor according to yet another embodiment,

FIG. 14 shows an isometric view of the underside of the conductor carrying eddy currents shown in FIG. 13,

Figure 15 shows an alternative embodiment of an inductive sensor according to the invention with two differently configured eddy currents leading conductors and three coils and

FIG. 16 shows a further embodiment of an inductive sensor according to the invention with two coils.

Detailed description of the embodiments

FIG. 1 shows a sectional view through an inductive sensor 10 according to the invention with two electrical conductors 12, each of which contains a plurality of regions 16a, 16b, 16c which, in the presence of an excitation field, each lead to an eddy current. The inductive sensor 10 contains a coil arrangement 18, which in the exemplary embodiment shown comprises an exciter coil 20 and two detection coils 22, 24. In the detection direction 26 of the inductive sensor 10, which points away from the inductive sensor 10, an eddy currents leading conductor 12 is disposed in front of and an eddy currents of leading conductors 12 behind the excitation coil 20. The eddy currents leading conductor 12 and the coil assembly 18 are arranged in a sensor housing 28, which has an inner housing 30 and an outer housing 32 in the illustrated embodiment. The sensor housing 28 is cylindrical in the embodiment shown with a sensor axis 34. Preferably, the inner housing 30 is electrically conductive. Usually, the outer housing 32 is made of metal. The sensor housing 28 is closed on its rear side and closed on its front side in the detection direction 26 with a protective cover 38.

An embodiment provides that the protective cover 38 is realized as a metallic, ie electrically conductive protective cover 38.

The inductive sensor 10 according to the invention provides a switching signal obtained by means of an electronic circuit, not shown in more detail, when a target 40 located within a detection range A is detected. For this purpose, an alternating magnetic field is generated by means of the at least one exciter coil 20, which in the detection direction 26 of the inductive

Sensor 10 occurs outside in the detection direction 26 before the protective cover 38. The target 40 must have magnetic field-influencing properties, so that a change of the magnetic field can occur on the basis of the voltage induced in at least one detection coil 22, 24, which is evaluated.

1, two detection coils 22, 24 are provided, so that the inductive sensor 10 can be operated as a gradiometer. The coil arrangement 18 with the three coils 20, 22, 24 is to be tuned in such a way that the two detection coils 22, 24 are adjusted without the presence of a target 40 and no difference signal occurs. The reverse function is also realizable, so that the gradiometer is matched with the present target 40 in the switching point.

A target 40 within the detection area A results in a difference of the induced voltages due to the difference in the distance of the detection coils 22, 24 from the target 40, which is detected and evaluated.

With the arrangement shown by way of example in FIG. 1, in principle a very high suppression of the excitation field with respect to the detection coils 22, 24 can be achieved.

A suppression of the field of excitation with respect to the detection coil 24 in front of the detection direction 26 also results from the fact that the positive and negative axial flux density components of the exciter field alternating over the circumference of the coil arrangement 18 are integrated over the cross section of the front detection coil 24 , largely cancel. By contrast, the flux density component passing through the front detection coil 24 and resulting from the influence of the target 40 is distributed coaxially. As a result, a directional separation between the exciter field and the field reaction of the target 40 to be detected results, so to speak. Because of this effect, the rear detection coil 22, as seen in the detection direction 26, can be dispensed with in principle. A corresponding embodiment will be shown in more detail below in connection with FIG. 16.

In order to achieve the largest possible detection range A of the inductive sensor 10, a pronounced sensitivity in the direction of the target 40, ie in the detection direction 26 of the inductive sensor 10, and at the same time no sensitivity to an electromagnetically active material in the vicinity of the inductive sensor 10 is required. For this purpose, a very effective alignment of the magnetic field is required. Ideally, in the outer region of the inductive sensor 10, except in the detection direction 26, no magnetic field at all.

An increase in the detection range A of the inductive sensor 10 is achieved by the inventively provided at least one electrical conductor 12, the at least two circumferentially arranged in the circumferential direction of the exciter coil 20 areas 16a, 16b, 16c, which in the presence of an exciter field each carry an eddy current.

In principle, only one eddy currents of leading conductors 12 may be present in the inductive sensor 10 according to the invention, which is preferably arranged in front of the at least one exciter coil 20 with respect to the detection direction 26. Alternatively, however, the eddy-current-carrying conductor 12 may also be positioned behind the at least one exciter coil 20. In the exemplary embodiment shown in FIG. 1, an eddy current of leading conductors 12 in the detection direction 26 in front of the excitation coil 20 and a further eddy current of leading conductors 12 are arranged behind the exciter coil 20 by way of example.

The at least one eddy currents leading conductor 12 leads in the circumferential direction of the inductive sensor 10 to alternately oppositely directed magnetic flux density components, which largely cancel out in the vicinity of the inductive sensor 10 outside the sensor housing 28, so that the resulting magnetic field is at least approximately zero. As a result, electromagnetically active material in the outer region of the inductive sensor 10 according to the invention (except in the detection direction 26) can not affect the magnetic flux in the at least one detection coil 22, 24. The sensitivity in the detection direction 26 can be significantly increased, so that the Detection area A is larger.

The use according to the invention of the at least one electrical conductor 12 with the at least two regions 16a, 16b, 16c, which in each case lead to an eddy current in the presence of an excitation field, makes possible a

Forming the geometry of the magnetic excitation field, so that its symmetry with respect to the at least one detection coil 22, 24 is achieved. The optimization can be done in terms of both the amount of the field and its phase.

If the protective cover 38 is realized with electrically conductive material, the alternating directions of the axial flux density components that enforce the protective cover 38 cause the influence of the detection signal by the eddy currents induced by the excitation field in the protective cover 38 to be comparatively small.

FIG. 2 shows an isometric view of an electrical conductor 12 used in the exemplary embodiment according to FIG. 1 with the regions 16a, 16b, 16c, 16d, which each lead to an eddy current in the presence of an exciter field. The optimization of the magnetic field is preferably carried out on the basis of experiments or calculations which leads to a specification of the shape of the eddy-current-carrying conductor 12 and its geometrical arrangement in the inductive sensor 10.

The respective one eddy current leading portions 16a, 16b, 16c, 16d are characterized in particular by the respectively formed surface, which is penetrated by the field lines of the exciter field of the excitation coil 20. The area of the eddy-current-carrying regions 16a, 16b, 16c, 16d effective in relation to the exciting field is to be matched to the desired intensity of the eddy currents. The eddy currents cause caused field lines are directed opposite to the field lines of the exciter field.

For example, the unspecified distances of an eddy-current-carrying conductor 12 to individual coils 20, 22, 24 can be varied. The embodiment shown in FIG. 2 is cylindrical regions 16a, 16b, 16c, 16d, which have a predetermined thickness D. exhibit.

The thickness D can be determined based on calculations and / or on experiments. The thickness D of the regions 16a, 16b, 16c, 16d is preferably selected as a function of the frequency of the magnetic exciter field, which may be in the range of, for example, 5 kHz to 10 MHz. The thickness D is in the range of a few 10 m to a few millimeters, for example, at 5 mm.

The eddy currents leading conductor 12 can also be replaced by a

layered structure, for example, be realized within a preferably multi-layer printed circuit board. Likewise, at least individual coils of the coil assembly 18 may be realized as printed structures on a printed circuit board.

FIG. 3 shows a field distribution 50 in a plan view in the direction of the protective cover 38 of the inductive sensor 10 according to the invention. The reproduced field distribution 50 is based on eight regions 16 of an eddy-current-carrying conductor 12 which have eight partial regions 52 with respect to the circumference of the inductive sensor 10. in which the magnetic field with respect to the sensor axis 34 points perpendicularly out of the plane of the drawing and alternately corresponding to eight subregions 54, in which the magnetic field with respect to the sensor axis 34 perpendicular to the Pointing into the drawing plane. It is also essential that outside the dashed line indicated circumference 56 of the sensor housing 28 almost no magnetic field occurs more.

FIG. 4 shows an isometric view of the upper side of a two-part eddy-current-carrying conductor 12. In the radial direction of the inductive sensor 10, an inner first part 60 of the eddy-current-carrying conductor 12 and a radially adjacent inner part 60 an outer second part 62 of FIG Eddy currents leading conductor 12 is arranged. In such a realization, the excitation coil 20 is positioned at least approximately in the radial direction at the transition between the inner first and outer second part 60, 62 of the eddy-current-carrying conductor 12.

The outer second part 62 of the eddy-current-carrying conductor 12 has, with respect to the circumferential direction, a plurality of rotationally symmetrically arranged regions 16a, 16b, 16c, 16d, which are bevelled with respect to the sensor axis 34, the bevels 64a, 64b, 64c, 64d in the detection direction 26 are inclined inwards to the front.

The inner first part 60 of the eddy-current-carrying conductor 12 has recesses 66a, 66b which lie opposite the segments 16a, 16b, 16c, 16d of the outer part 62. Preferably, the recesses 66a, 66b are chamfered in the radial sensor direction, wherein the bevels 68a, 68b correspond to the slopes 64a, 64b, 64c, 64d of the outer second part 62. Viewed in the detection direction 26, the bevels 68a, 68b are chamfered to the rear outside.

In addition, it can be provided that the tangential boundaries of the recesses 66a, 66b of the inner part 60 tilted in the axial direction become. The tilt may also be such that opposite boundary surfaces are tilted at different angles to tilt the direction of the magnetic flux in the tangential direction.

FIG. 5 shows an isometric view of the underside of the two-part eddy-current-carrying conductor 12 according to FIG. 4, matching parts of FIGS. 4 and 5 being denoted the same. This also applies to the following figures.

FIG. 6 shows a sectional view of the two-part eddy current-carrying conductor 12 according to FIGS. 4 and 5 with a view of the underside.

Figure 7 shows an isometric view of the top of a one-piece, arranged in the inner housing 30 eddy currents leading conductor 12. The eddy currents leading conductor 12 is realized as an electrically conductive disk 70, which is positioned in the detection embodiment 26 seen in the embodiment shown in front of the exciting coil 20.

The disc 70 has channels 72 in the axial direction, which are provided in a radius which is greater than the radius of the excitation coil 20 and alternate with further, tilted to the axial direction of channels 74, which on the front side with respect to the detection direction 26 in a radius larger than the radius of the excitation coil 20, but on the side of the exciting coil 20 but have a radius which is smaller than the radius of the exciting coil 20. The channels 72, 74 are arranged in the embodiment shown rotationally symmetrical with respect to the sensor axis 34.

The channels 72 and / or the tilted channels 74 may additionally be tilted in the tangential direction. Furthermore, the channels 72 and / or the tilted channels 74 may have a cross-section that is in relation to the Sensor direction 26 increases or decreases.

The axial channels 72, optionally in conjunction with the tilted channels 74, each form a region 16a, 16b. The regions 16a, 16b are rotationally symmetrical with respect to the sensor axis 34 in the exemplary embodiment.

FIG. 8 shows an isometric view with a view of the underside of the eddy current 12 shown in FIG. 7 and FIG. 9 shows a sectional view of a side view of the eddy current 12 shown in FIGS. 7 and 8.

FIG. 10 shows an isometric view of the underside of a two-part eddy-current-carrying conductor 12 according to a further embodiment. The two parts 60, 62 of the eddy-current-carrying conductor 12 have wavy boundaries 80, 82 with respect to the circumferential direction. In the radial sensor direction, the wave peaks of one part 60 of the eddy-current-carrying conductor 12 are opposite the troughs of the other part 62.

With a corresponding embodiment of the waveform, in particular in the case of a sawtooth-shaped cross section of the gap in the tangential direction, a balancing possibility for balancing the positive and negative axial flux density components can be created by the two parts 60, 62 being rotated against one another. The wave-shaped boundaries 80, 82 in this case have a sawtooth-shaped course in a cylindrical sectional area.

Here, too, the second outer part 62 preferably has slopes 84, in particular in the region of the wave crests, which are inclined inwards with respect to the detection direction 26. Accordingly, the first inner part 60 also have bevels 86 on its wave crests which are inclined outwards in relation to the detection direction 26.

A wave crest in conjunction with the adjacent wave trough, in particular of the outer part 62 of the electrical conductor 12, form the eddy current-carrying regions 16a, 16b, which are again rotationally symmetrically positioned about the sensor axis 34.

Figure 1 1 shows an isometric view of the top of the eddy current conductor 12 shown in Figure 10 and Figure 12 shows a cross-sectional view of the eddy currents shown in Figures 10 and 11 leading conductor 12 in which the ramps 84, 86 stand out clearly.

FIG. 13 shows a sectional view of a two-part electrical conductor 12 with regions 16a, 16b, 16c, 16d, which in each case lead to an eddy current in the presence of an exciter field, according to yet another embodiment. The at least one excitation coil 20 is arranged in a gap 90 between the inner and outer part 60, 62 of the electrical conductor 12.

The at least one excitation coil 20 can be arranged generally at the transition between the inner first and outer second part (60, 62) of the electrical conductor (12) viewed in the radial direction, so that the at least one exciter coil 20, as seen in the detection direction 26, also before or can be arranged behind the gap 90.

Furthermore, the at least one exciter coil 20 can be arranged according to an embodiment with appropriate isolation even within the electrical conductor 12. Another difference is that, according to the exemplary embodiment shown in FIG. 13, the outer part 62 of the electrical conductor 12 is integrated into the inner housing 30. With this measure, the

Positioning tolerance in the production of the two components minimized.

FIG. 14 shows an isometric view of the underside of the eddy current conductor 12 shown in FIG. 13, which provides a complete view of the at least one exciter coil 20 positioned in the gap 90.

Figure 15 shows an alternative embodiment of the inductive sensor 10 according to the invention with two eddy currents leading conductors 12 and three coils 20, 22, 24. The structure corresponds essentially to the reproduced in Figure 1 structure, but the two eddy currents leading conductors 12 are designed differently. The arranged between the excitation coil 20 and the rear detection coil 22 eddy currents leading conductor 12 is configured as shown in Figure 2, while arranged between the excitation coil 20 and the front detection coil 24 eddy currents leading conductor 12 as shown in Figures 10-12 configured is.

FIG. 16 shows a further embodiment of the inductive sensor 10 according to the invention, in which apart from the excitation coil 20 only one detection coil 24 positioned in the detection direction 26 and positioned in front of the exciter coil 20 is provided. The eddy currents leading conductor 12 is disposed between the two coils 20, 24. In the exemplary embodiment shown, the eddy-current-carrying conductor 12 is configured as shown in FIGS. 10 to 12.

Claims

claims

An inductive sensor comprising a coil assembly (18) including at least one excitation coil (20) and at least one detection coil (22, 24), the coil assembly (18) being formed by an electromagnetic coil

Interaction with a target to be detected (40) can be influenced, characterized in that in the excitation field of the at least one excitation coil (20) arranged electrical conductor (12) is provided, in the circumferential direction of the excitation coil (20) at least two regions (16a, 16b , 16c, 16d), which each lead to an eddy current in the presence of a field exciter.

2. Inductive sensor according to claim 1, characterized in that the at least one electrical conductor (12) with the respective one eddy current leading portions (16a, 16b, 16c, 16d) in the detection direction (26) of the inductive sensor (10) before at least an excitation coil (20) is arranged.

3. Inductive sensor according to claim 1, characterized in that the at least one electrical conductor (12) with the respective one eddy current leading portions (16a, 16b, 16c, 16d) in the detection direction (26) of the inductive sensor (10) behind the at least an excitation coil (20) is arranged.

4. Inductive sensor according to claim 1, characterized in that the at least one electrical conductor (12) with the respective one eddy current leading areas (16a, 16b, 16c, 16d) in the detection direction (26) of the inductive sensor (10) in front of and behind the at least one exciter coil (20) are arranged.

5. Inductive sensor according to claim 4, characterized in that the electrical conductors (12) with the respective one eddy current leading portions (16a, 16b, 16c, 16d) are designed differently.

6. Inductive sensor according to claim 1, characterized in that the at least one electrical conductor (12) is formed in two parts, such that in the radial direction of the inductive sensor (10) an inner first part (60) of the electrical conductor (12) and an outer second part (62) of the electrical conductor (12) is arranged in the radial direction adjacent to the inner first part (60).

7. Inductive sensor according to claim 6, characterized in that the at least one excitation coil (20) viewed in the radial direction at the transition between the inner first and outer second part (60, 62) of the electrical conductor (12) is arranged.

8. Inductive sensor according to claim 7, characterized in that the at least one exciter coil (20) in a gap (90) between the two parts (60, 62) of the electrical conductor (12) is arranged.

9. Inductive sensor according to one of claims 1 to 6, characterized in that the at least one excitation coil (20) within at least one electrical conductor (12) is arranged.

10. Inductive sensor according to claim 6, characterized in that the outer second part (62) of the electrical conductor (12) in the circumferential direction a plurality of rotationally symmetrically arranged regions (16a, 16b, 16c, 16d) and in that the regions (16a, 16b, 16c, 16d) are chamfered against the sensor axis (34), such that the slopes (64a, 64b, 64c, 64d) are inclined inwards in the detection direction (26).

11. Inductive sensor according to claim 6, characterized in that the inner part (60) of the electrical conductor (12) has recesses (66a, 66b, 66c, 66d) which are opposite to the areas (16a, 16b, 16c, 16d) of the outer part (62) of the electrical conductor (12) lie.

12. Inductive sensor according to claim 11, characterized in that the recesses (66a, 66b, 66c, 66d) are chamfered in the radial direction, such that the bevels (68a, 68b, 68c, 68d) with the bevels (64a, 64b , 64c, 64d) of the outer first part (62) of the electrical conductor (12) and are bevelled in the detection direction (26) to the rear outside.

13. Inductive sensor according to claim 11, characterized in that the tangential boundaries of the recesses (66a, 66b, 66c, 66d) of the inner part (60) are tilted in the axial direction.

14. Inductive sensor according to claim 1, characterized in that the electrical conductor (12) is integrally formed as a disc (70) and that a plurality of rotationally symmetrically arranged channels (72, 74) in the disc (70) are provided which in a radius positioned larger than the radius of the exciting coil (20).

15. Inductive sensor according to claim 14, characterized in that

Channels (72) are provided axially in the direction of the sensor axis (34) and that alternately further, with respect to the sensor axis (34) tilted channels (74) are provided, which on the front in detection seen direction (26) start in a radius which is greater than the radius of the exciting coil (20), and on the side of the exciting coil (20) have a radius which is smaller than the radius of the exciting coil (20).

16. Inductive sensor according to claim 15, characterized in that the channels (72) and / or the axially tilted channels (74) are tilted in the tangential direction.

17. Inductive sensor according to claim 15 or 16, characterized in that the cross section of the channels (72) and / or the tilted channels (74) in the detection direction (26) increases or decreases.

18. Inductive sensor according to one of claims 15 to 17, characterized in that the axial and the tilted channels (72, 74) open into one another and intersect.

19. Inductive sensor according to one of claims 15 to 18, characterized in that the channels (72, 74) are realized as bores.

20. Inductive sensor according to claim 6, characterized in that the two parts (60, 62) of the electrical conductor (12) in the circumferential direction wavy boundaries (80, 82).

21. Inductive sensor according to claim 20, characterized in that in the radial direction, the wave crests of one part (60) of the electrical conductor (12) opposite the wave troughs of the other part (62) of the eddy current leading conductor (12).

22. Inductive sensor according to claim 20 or 21, characterized in that the wave-shaped boundaries (80, 82) have a sawtooth-shaped profile in a cylindrical sectional area.

23. Inductive sensor according to claim 20, characterized in that the wave-shaped boundaries (80, 82) are designed to rotate against each other.

24. Inductive sensor according to one of claims 20 to 23, characterized in that the wave-shaped boundaries (80, 82) in the detection direction (26) are chamfered, such that the bevels (84, 86) in the detection direction (26 ) are inclined inwards towards the front.

25. Inductive sensor according to one of the preceding claims, characterized in that the material thickness (D) of the at least one electrical conductor (12) in dependence on the frequency of the excitation coil (20) generated magnetic exciter field is fixed.

26. Inductive sensor according to one of the preceding claims, characterized in that the coil arrangement (18) and / or the at least one electrical conductor (12) is at least partially realized by means of a printed circuit board.

27. Inductive sensor according to one of the preceding claims, characterized in that the inductive sensor (10) in a sensor housing (28) is arranged and that the at least one electrical conductor (12) in a sensor housing (28) containing the inner housing (30 ) is integrated.

28. Inductive sensor according to one of the preceding claims, characterized in that the inductive sensor (10) in a sensor housing (28) is arranged and that the sensor housing (28) has an electrically conductive protective cover (38).