INDUCTIVE SENSOR DEVICE FOR DETERMINING A LONGITUDINAL POSITION OF A MOVEABLE OBJECT ALONG A SENSITIVE AXIS OF THE SENSOR DEVICE AND METHOD FOR OPERATING A SENSOR DEVICE OF THIS KIND

Abstract

An inductive sensor device has a coil arrangement and sensor electronics for determining a longitudinal position of an at least partially electrically conductive and/or magnetically polarizable object moveable at a distance from a device end face along a device sensitive axis. The arrangement has a substantially planar exciting coil for producing an alternating magnetic field for inducing eddy currents and/or magnetic polarization in the object and a first substantially planar receiving coil substantially parallel to and overlapping the exciting coil. The coils are substantially parallel to the end face. The sensor electronics determine at least one parameter of an exciting coil electrical signal, which is variable owing to an inductive backward effect of the object, at least one parameter of a voltage inducible in the at least first receiving coil based on this effect, and the longitudinal position from the determined signal parameter and the determined voltage parameter.

Claims

1. An inductive sensor device (10) for determining a longitudinal position (P) of an object (11) which is moveable at a distance from an end face (12) of the sensor device (10) and which is at least partially electrically conductive and/or magnetically polarizable, along a sensitive axis (S1) of the sensor device (10), wherein the sensor device (10) has a coil arrangement (14) and sensor electronics (30), wherein the coil arrangement (14) has a substantially planar exciting coil (16), by means of which an alternating magnetic field is producible for inducing eddy currents and/or magnetic polarization in the object (11), and a first substantially planar receiving coil (18; 18a-18b), which is arranged substantially parallel to and overlapping the exciting coil (16), wherein the exciting coil (16) and the first receiving coil (18; 18a-18b) are arranged substantially parallel to the end face (12) of the sensor device (10), and wherein the sensor electronics (30) are configured to determine at least one parameter (DSS) of an electrical signal of the exciting coil (16), which is variable owing to an inductive backward effect of the object (11), and at least one parameter (PSS) of a voltage inducible in the at least first receiving coil (18; 18a-18b) owing to the inductive backward effect of the object (11) and to determine the longitudinal position (P) from the determined parameter (DSS) of the electrical signal of the exciting coil (16) and the determined parameter (PSS) of the inducible voltage in the first receiving coil (18; 18a-18b).

2. A sensor device according to claim 1, wherein the sensor electronics (30) are configured to determine a vertical distance (D) of the object (11) between the end face (11) of the sensor device (10) and the object (11) from the at least one parameter determined (DSS) of the electrical signal of the exciting coil (16) and the at least one parameter determined (PSS) of the inducible voltage of the receiving coil (18; 18a-18b).

3. The sensor device according to claim 1, wherein the first receiving coil (18; 18a-18b) is of anti-symmetrically polarizable configuration along the sensitive axis (S1).

4. The sensor device (10) according to claim 1, wherein the coil arrangement (14) has a second substantially planar receiving coil (18b), which is arranged substantially parallel to and overlapping the exciting coil (16), and wherein the second receiving coil (18b) overlaps the first receiving coil (18a) in the end regions thereof and is connected electrically in series with the first receiving coil (18a).

5. The sensor device (10) according to claim 1, wherein the coil arrangement (14) has at least a third substantially planar receiving coil (68), which is arranged substantially parallel to and overlapping the exciting coil (16) and which defines an additional sensitive axis (S2) of the sensor device (10), which extends substantially perpendicular to or in the sensitive axis (S1) of the first receiving coil (18; 18a, 18b), and wherein the sensor electronics (30) are configured to determine at least one parameter (LSS) of a voltage inducible in the third receiving coil (68) due to the inductive backward effect of the object (11) and for determining the lateral position (L) of the object (11) along the additional sensitive axis (S2) from the determined at least one parameter (DSS) of an electrical signal of the exciting coil (16) and the determined at least one parameter (LSS) of the inducible voltage of the third receiving coil (68).

6. The sensor device (10) according to claim 5, wherein the coil arrangement (14) has a fourth substantially planar receiving coil, which is arranged substantially parallel to and overlapping the exciting coil (16), and wherein the fourth receiving coil overlaps the third receiving coil (68) in the end regions thereof and is connected electrically in series with the third receiving coil (68).

7. The sensor device (10) according to claim 1, wherein the exciting coil (16), the first receiving coil (18; 18a), the second receiving coil (18b), the third receiving coil (68) and/or the fourth receiving coil are arranged on or in one or more layers (50, 52, 60, 62) of a printed-circuit board (38).

8. The sensor device (10) according to claim 1, wherein the exciting coil (16), the first receiving coil (18; 18a), the second receiving coil (18b), the third receiving coil (68) and/or the fourth receiving coil are made by a wire-wrapping technique.

9. The sensor device (10) according to claim 7, wherein windings (56, 58) of coil segments (21a, 21b; 40a, 40b) of the receiving coil (18; 18a-18b; 68) are oppositely directed, viewed along their respective sensitive axis (S1, S2).

10. The sensor device (10) according to claim 8, wherein the receiving coil (18; 18a-18b; 68), viewed along their respective sensitive axis (S1, S2), has substantially centrally crossed windings (20a, 20b).

11. The sensor device (10) according to claim 1, wherein the sensor device (10) further comprises a first electrically conductive shielding element (22a), which surrounds the coil arrangement (14) laterally, in particular completely.

12. The sensor device (10) according to claim 1, wherein the sensor device (10) further comprises a second electrically conductive, planar shielding element (22b), which is arranged on a side of the coil arrangement (14) that is turned away from the object (11).

13. The sensor device (10) according to claim 11, wherein, viewed in a direction perpendicular to the sensitive axis (S1, S2), symmetrically and on either side of the coil arrangement (14), in each case a coil-free region (66) is provided adjacent to the first shielding element (22a), whose width (d) is at least 10% of a width (b) of an opening (64) of the first shielding element (22a).

14. The sensor device (10) according to claim 1, wherein the exciting coil (16) is excitable substantially with a periodic, in particular a substantially sinusoidal, current or a periodic, in particular a substantially sinusoidal, voltage.

15. The sensor device (10) according to claim 1, wherein the exciting coil (16) is a part of an oscillating circuit (80) of the sensor electronics (30).

16. The sensor device (10) according to claim 1, wherein the exciting coil (16), as an inductive element of an LC circuit, is a part of a self-oscillating LC oscillating circuit (80).

17. The sensor device (10) according to claim 1, wherein the at least one parameter (DSS) determined from the electrical signal of the exciting coil is a frequency (f.sub.OSC), or an amplitude (U.sub.D).

18. The sensor device (10) according to claim 1, wherein the sensor electronics (30) are configured for determining a proximity signal (S.sub.N) from the changes of the determinable parameter of the electrical signal of the exciting coil (16) caused by the presence of the object (11), which is indicative of the change of the at least one parameter (DSS) caused by the presence of the object (11).

19. The sensor device (10) according to claim 1, wherein the sensor electronics (30) are configured for determining at least one reference signal (PHA; I.sub.ref, Q.sub.ref; φ.sub.ref) from an electrical signal of the exciting coil (16), whose phase has a predetermined ratio to a phase of the electrical signal of the exciting coil (16).

20. The sensor device (10) according to claim 19, wherein the sensor electronics (30) are configured for determining the at least one parameter (PSS, LSS) of the inducible voltage by means of a synchronous demodulation from the inducible voltage using the reference signal (PHA; φ.sub.ref).

21. The sensor device (10) according to claim 20, wherein the at least one parameter (PSS, LSS) is an amplitude (U.sub.φ) of a phase-sensitive demodulated inducible voltage, and wherein the phase of the phase-related phase reference signal has a predetermined ratio to the phase of an electrical signal of the exciting coil (16).

22. The sensor device (10) according to claim 19, wherein the sensor electronics (30) are configured for determining the at least one parameter (U.sub.I, U.sub.Q) of the inducible voltage by quadrature demodulation of the inducible voltage using the reference signal (PHA; I.sub.ref, Q.sub.ref).

23. The sensor device (10) according to claim 22, wherein the at least one parameter (PSS, LSS) of the inducible voltage is a phase-related amplitude (U.sub.I, U.sub.Q) of a quadrature-demodulated inducible voltage.

24. The sensor device (10) according to claim 1, wherein the sensor electronics (30) are configured for determining a longitudinal position signal (S.sub.p) from the at least one parameter (PSS, LSS) of the inducible voltage, and wherein the longitudinal position signal (S.sub.p) is based on the at least one parameter (PSS, LSS) of the inducible voltage.

25. The sensor device (10) according to claim 18, wherein the sensor electronics (30) are configured for determining a reduced longitudinal position signal (V.sub.M) as a ratio of the longitudinal position signal (S.sub.p) and the proximity signal (S.sub.N), in order to determine the longitudinal position (P) from the reduced longitudinal position signal (V.sub.M).

26. The sensor device (10) according to claim 25, wherein the sensor electronics (30) are configured to determine the longitudinal position (P) from the reduced longitudinal position signal (V.sub.M) by means of a linearization function.

27. The sensor device (10) according to claim 18, wherein the sensor electronics (30) are configured for determining a mechanical phase (P.sub.M) as arctan 2 from the reduced longitudinal position signal (V.sub.P) and the proximity signal (S.sub.N) multiplied by a scaling factor (B) determined in a prior learning process, in order to determine the longitudinal position (P) from the mechanical phase (P.sub.M).

28. The sensor device (10) according to claim 27, wherein the sensor electronics (30) are configured for linearizing the mechanical phase (V.sub.P).

29. The sensor device (10) according to claim 26, wherein the linearization is to be carried out in relation to the type of material of the object.

30. The sensor device (10) according to claim 1, wherein the sensor electronics (30) are configured for determining a type of an object material of the object (11) based on a typical phase of the voltage inducible by the object (11) with respect to the phase of an electrical signal of the exciting coil (16) or wherein the sensor electronics (30) are configured for determining the type of object material of the object (11) based on a typical ratio of the amplitude change and frequency change of the oscillator voltage (U.sub.OSC) caused by the presence of the object (11).

31. The sensor device (10) according to claim 1, wherein the sensor electronics (30) implement a self-parameterizing evaluation algorithm.

32. The sensor device (10) according to claim 1, wherein the sensor electronics (30) are configured for self-adaptively parameterizing an evaluation algorithm, self-adaptively determining a type of the object material of the object (11) and/or self-adaptively recognizing a change of a measuring arrangement.

33. The sensor device (10) according to claim 32, wherein the sensor electronics (30) are configured, for self-adaptive parameterization of the evaluation algorithm, to determine one or more values of the at least one parameter (DSS, PSS, LSS) and store them temporarily or permanently.

34. A method for operating an inductive sensor device (10) for determining a longitudinal position (P) of an object (11) which is moveable at a distance from an end face (12) of the sensor device (10) and which is at least partially electrically conductive and/or magnetically polarizable, along a sensitive axis (S1) of the sensor device (10), wherein the method comprises: producing an alternating magnetic field of a substantially planar exciting coil (16) of a coil arrangement (14) of the sensor device (10) for inducing eddy currents and/or magnetic polarization in the object (11), determining, by means of sensor electronics (30) of the sensor device (10), at least one parameter (DSS) of an electrical signal of the exciting coil (16), which is altered by an inductive backward effect of the object (11), and at least one parameter (PSS) of a voltage induced in a first receiving coil (18; 18a-18b) of the coil arrangement (14) owing to the inductive backward effect of the object (16), wherein the first receiving coil (18; 18a-18b) is of substantially planar configuration and is arranged substantially parallel to and overlapping the exciting coil (16), wherein the exciting coil (16) and the first receiving coil (18; 18a-18b) are arranged substantially parallel to the end face (12) of the sensor device (10), and determining, by means of the sensor electronics (30), the longitudinal position (P) based on the at least one parameter (DSS) of the electrical signal of the exciting coil (16) and the at least one parameter (PSS) of the induced voltage of the first receiving coil (18; 18a, 18b).

35. A program for data processing equipment, which is configured for carrying out steps of the method according to claim 34, when it is executed by the data processing equipment.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Other objects and features of the invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention.

[0072] In the drawings,

[0073] FIG. 1 shows schematically a sensor device and an object in accordance with embodiment examples;

[0074] FIGS. 2A-2C show an embodiment example of a coil system and a shielding element of the sensor device in FIG. 1 in an exploded view, in a perspective view and in a sectional view;

[0075] FIGS. 3A, 3B show a further embodiment example of the sensor device in FIG. 1 in an exploded view and in a sectional view;

[0076] FIGS. 4A-4D show an implementation of an exciting coil and a first receiving coil of the sensor device in FIGS. 3A, 3B;

[0077] FIG. 5 shows schematically an arrangement of a coil arrangement of the sensor device 10 in FIG. 1 inside a first shielding element of the sensor device;

[0078] FIGS. 6A-6B show a coil arrangement for a further embodiment example of the sensor device in FIG. 1 in an exploded view, in perspective view and in a top view;

[0079] FIG. 7 shows a schematic view of the sensor electronics of the sensor device in FIG. 1, which is connected electrically to the exciting coil and the receiving coil of the sensor device in FIG. 2, FIG. 3 or FIG. 6;

[0080] FIG. 8 shows an embodiment example of the sensor electronics in FIG. 7;

[0081] FIG. 9 shows a further embodiment example of the sensor electronics in FIG. 7;

[0082] FIG. 10 shows schematically a correlation between a quadrature-phase component and an in-phase component of a voltage induced in the receiving coil; and

[0083] FIGS. 11A-11E show diagrams which show a demodulation voltage, a proximity signal, a quadrature-phase component of the voltage induced in the receiving coil, a relationship between the quadrature-phase component and the proximity signal, and the mechanical phase as a function of a longitudinal object position for different object distances.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0084] Identical or similar components or elements are designated with the same reference symbol.

[0085] FIG. 1 shows a sensor device 10 in accordance with embodiment examples, which is configured for determining a longitudinal position of a moveable object 11 along a first sensitive axis S1 of the sensor device 10. The object 11 is moveable along a trajectory at a vertical distance from an end face 12 of the sensor device 10. The distance D is measured between the end face 12 of the sensor device 10 and a surface 13 of the object 11 facing the sensor device 10. The sensor device 10 may further optionally be configured for determining a position L along a second sensitive axis S2, which extends perpendicularly to the first sensitive axis S1. The first and the second sensitive axis S1, S2 are oriented perpendicular to one another. The sensor device 10 may additionally optionally be configured for determining the distance D.

[0086] The sensor device 10 is made with a coil arrangement and optionally a shield made of electrically conductive material, for example metal, which are illustrated in FIGS. 2A to 6B. The coil arrangement and the shield are arranged on a side of the end face of the sensor device 10 that is directed away from the object 11.

[0087] As shown in FIGS. 2A-2C, in a first embodiment example the sensor device 10 has the coil arrangement 14, which has a planar, rectangular exciting coil 16 and a planar, butterfly-shaped receiving coil 18, both of which are configured as wound wire conductor loops and are overlapping. Opposite winding segments 20a, 20b of the receiving coil 18, which are oriented along the sensitive axis S1, are crossed in the middle of a coil, so that the receiving coil 18 is configured as a butterfly coil and coil segments 21a, 21b, i.e., half-coils 21a, 21b, are anti-symmetrically polarizable. A first shielding element 22a of the shield 22 surrounds the coil arrangement 14 on all sides. The receiving coil 18 is arranged with its surface extension in its coil plane parallel to the rectangular surface of the exciting coil 16 and directed towards the end face 12 of the sensor device 10 and therefore to the end face 13 of the object 11. The exciting coil 16, the receiving coil 18 and the first shielding element 22a form a “head” of the sensor device 10. Alternatively, the exciting coil 16 may also be arranged towards the end face 12 of the sensor device 10 and therefore towards the end face 13 of the object 11, or the exciting coil 16 may surround the receiving coil 18 substantially in its own coil plane, or both coils 16, 18 may be wound on the same coil former (not shown).

[0088] As shown in FIG. 2C, a printed-circuit board 24 is arranged on a side of the first shielding element 22a turned away from the end face 12. Connections 26a, 26b of the exciting coil 16 and connections 28a, 28b of the receiving coil 18 are connected electrically to the printed-circuit board 24. Sensor electronics 30 are arranged on the side of the printed-circuit board 24 turned away from the coil arrangement 14. Alternatively, this surface may only have soldering points for contacting to the sensor electronics provided on a further printed-circuit board. A second shielding element 22b of the shield 22 may optionally be configured as a layer of copper on at least one layer of the printed-circuit board 24. The shielding element 22a and, if present, the shielding element 22b, the exciting coil 16, the receiving coil 18 and the sensor electronics 30 are enclosed in a housing 34. A connecting cable 36 extends through the housing 34 to the outside and is connectable to a power supply. The connecting cable 36 may furthermore comprise leads for one or more output signals. The end face 12 of the sensor device 10 corresponds to an end face of the housing 34 that is directed towards the object 11.

[0089] The sensor device 10 according to a second embodiment example, shown in FIGS. 3A, 3B, is configured in printed-circuit board technology, i.e., as a multilayer printed-circuit board 38. The coils 16, 18a, 18b are depicted as rectangular surface regions (FIG. 3A) or as a dotted line (FIG. 3B). For clarity, windings of the coils 16, 18a, 18b are not shown. A planar, rectangular exciting coil 16 and a first and second planar, rectangular receiving coil 18a, 18b are made overlapping in mutually parallel printed-circuit board layers. Viewed along the axis S1, the first and second receiving coil 18a, 18b have in each case oppositely directed windings. Coil segments 21a, 21b of the first receiving coil 18a and coil segments 40a, 40b of the second receiving coil 18b overlap, so that the coil segments 40a or 40b are parallel to an edge region of the coil segments 21a or 30b. Polarization of the coil segments 21a, 40a and of the coil segments 21b, 40b is the same in each case and is designated with “+” or “−”. In other words, the receiving coils 18a, 18b are of anti-symmetrically polarizable configuration. The first and second receiving coil 18a, 18b are connected electrically in series, and in circuit engineering terms may be treated electrically as a single receiving coil.

[0090] A first shielding element 22a of the shield 22 is made as a layer of metal on an internal surface of a housing 34 of the sensor device 10. The metal layer surrounds the coil arrangement 14 completely. A second shielding element 22b of the shield 22 is configured as a metallization layer between the layers of the coil arrangement 16, 18a, 18b and the layers of the sensor electronics 30. The exciting coil 16, the receiving coils 18a, 18b and the shielding elements 22a, 22b form a “head” of the sensor device 10. The end face 12 of the sensor device 10 corresponds to an end face of the housing 34 that is directed towards the object 11. Sensor electronics 30 have a first and second printed-circuit board layer 42, 44, on or in which one or more circuits and/or logic components for excitation of the receiving coil 16 and signal conditioning and signal processing of a signal or several signals of the exciting coil 16 and the first and second receiving coil 18a, 18b are mounted.

[0091] FIGS. 4A-4D show an implementation of the coil arrangement 14 in FIGS. 3A-3C. The exciting coil 16 shown in FIGS. 4A, 4B is arranged in two superposed layers 46, 48 of the printed-circuit board 38, the edges of which are shown as dashed lines. Windings 46 or 48 of the exciting coil 14 in the two layers 50 or 52 are in each case connected together by means of a via hole 54. Windings 56 and 58 of the receiving coil 18a or 18b are formed by circuit-board conductors in two layers 60 or 62 of the printed-circuit board 24 and are connected together with a via hole 63. On both layers 60, 62, the windings 56, 58 of the coil segments 21a or 40a and 21b or 40b are in each case configured in opposition, whereas the windings 56, 58 of the coil segments 21a, 21b and 40a, 40b shown in the drawing plane both on the left and on the right are directed in the same direction on both layers 60, 62. Connections 26a, 26b of the receiving coil 16 and connections 28a, 28b of the first and second receiving coil 18a, 18b for connecting to sensor electronics are in each case configured as via holes, onto which leads for the sensor electronics may also be soldered.

[0092] FIG. 5 shows a top view of the coil arrangement 14, which is arranged within the first shielding element 22a. The coil arrangement 14 may for example be one of the coil arrangements 14 in FIGS. 2A-2C, 3A, 3B. The coil arrangement 14 is spaced away from the lateral shielding element 22a so that there is a distance d between a region in which the coil arrangement 14 extends, and the lateral shielding element 22a, which is at least 10% of the width b of an internal opening 64 of the first shielding element 22a, measured perpendicularly to the sensitive axis A1, and a corresponding coil-free region 66 is formed.

[0093] FIGS. 6A, 6B show a coil arrangement 14 for a sensor device 10 according to a fourth embodiment example, which is configured similarly to the coil arrangement in FIGS. 3A, 3B. Coils 16, 18a, 18b of the coil arrangement 14 are depicted as rectangular surface regions. For clarity, windings of the coils 16, 18, 68 are not shown. However, a second receiving coil 68, turned through 90 degrees to the first receiving coil 18, is arranged so that the sensor device 10 has two sensitive axes S1, S2 instead of one sensitive axis S1. Half-coils of the receiving coil 68 have the reference symbols 69a, 69b. The receiving coil 18 may for example be configured like the coils 18a, 18b in FIGS. 3A, 3B. The sensor device 10 is therefore configured for determining the longitudinal position P of the object 11 along the sensitive axis S1 and the lateral position L of the object 11 along the sensitive axis S2. Moreover, all coils 16, 18, 68 have a square cross-section. A coil-free region 66 between a first shielding element 22a and the coil arrangement 14 is therefore provided adjacent to edges of the respective coil 16, 18, 68. A distance d may be selected, as shown in FIG. 5. A second shielding element (not shown) and the printed-circuit boards of the sensor electronics are of rectangular configuration. The first and second receiving coil 18a, 68 are connected electrically independently of one another.

[0094] The coil arrangement 14 may, just as in FIGS. 3A, 3B, further comprise an additional receiving coil in the end region of the first receiving coil 18 and an additional receiving coil in the end region of the receiving coil 68, which in each case increase the sensitivity in the end region of the respective receiving coil 18, 68.

[0095] The sensor electronics 30 shown in FIG. 7 have an oscillation unit 70, which is connected electrically via a capacitor 71 to the exciting coil 16 from FIGS. 2A-2C, FIGS. 3A, 3B or FIGS. 6A-6B. A demodulation unit 72 of the sensor electronics 30 in the form of a demodulator is connected electrically to the receiving coil(s) 18, 68 of the coil arrangement 14. Since the coils 18a and 18b are connected in series, and electrically do not have to be connected separately to the electronic circuit of the demodulation unit 72, in the following the receiving coil for the longitudinal sensitive axis S1 is designated, with reference to FIGS. 7-9, as the receiving coil 18.

[0096] Moreover, an evaluation unit 74 is coupled to the oscillation unit 70 and the demodulation unit 72.

[0097] The oscillation unit 70 is configured for determining and emitting, from an electrical signal of the exciting coil 16, which is either a voltage or a current, a first parameter DSS that is indicative of the presence of the object 11 in the vicinity of the coil arrangement 14, in particular in a fixed longitudinal position, at a vertical distance D between the sensor end face 12 and the object 11. The first parameter DSS further depends on the longitudinal position P and, if a lateral displacement of the object 11 is possible, on the lateral position L of the object 11. It is also possible for the oscillation unit 70 to be configured so that not one, but several signal parameters are determined from the electrical signal of the exciting coil 16 and emitted. In this case DSS denotes a first group of the parameters. The oscillation unit 70 is further configured to determine a reference signal PHA, whose phase is in a predetermined relationship with a phase of the voltage or the current in the exciting coil 16, and to output it to the demodulation unit 72.

[0098] The demodulation unit 72 is configured to determine a second parameter PSS from the voltage induced in the receiving coil 18 and output it to the evaluation unit 74. The second parameter PSS depends moreover on the distance D, and, provided a lateral displacement of the object 11 is possible, on the lateral position L of the object 11. The demodulation unit 72 is configured to determine the parameter PSS on the basis of the reference signal PHA. The demodulation unit 72 may also be configured so that not one, but several signal parameters are determined from the induced voltage of the receiving coil 18, and are output. In this case PSS denotes a second group of the parameters.

[0099] The evaluation unit 74 is configured for jointly evaluating the first and second parameters DSS, PSS or the first and second group of parameters DSS, PSS and for determining the longitudinal position P of the object 11 and optionally the vertical distance D of the object 11.

[0100] It is noted that for making a second sensitive axis S2 through the receiving coil 68 in FIGS. 6A-6B and for determining a third parameter LSS (not shown), either a second demodulation unit is necessary, or the first demodulation unit 72 is usable for demodulating the voltage of both receiving coils 18, 68 in time-division multiplex operation. The third parameter LSS is determinable from the induced voltage of the third receiving coil 68 similarly to the parameter PSS from the induced voltage of the receiving coil 18, and is processable for determining the lateral position L similarly to the first parameter PSS for determining the longitudinal position P.

[0101] In the first embodiment example of the sensor electronics 30 shown in FIG. 8, the oscillation unit 70 is formed as oscillation circuit 80 in FIG. 7, which is configured for supplying energy to the exciting coil 16 so that the exciting coil 16 is operable self-oscillating as inductive element of an LC circuit and the capacitor 71 is operable self-oscillating as capacitive element of the LC circuit. A demodulator 82 of the oscillation unit 70 is formed as a circuit and is configured, as amplitude detector of the oscillator voltage U.sub.OSC, to output a demodulation voltage U.sub.D that is characteristic of the oscillator amplitude, and/or as frequency detector, to output an oscillation frequency f.sub.OSC of the oscillator voltage U.sub.OSC as the first parameter or the first group of parameters DSS. Moreover, there is a linear relationship between the demodulation voltage and the oscillator amplitude. It is also possible for an oscillator current to be used instead of the oscillator voltage U.sub.OSC, and for the demodulation voltage U.sub.D to be replaced with another that characterizes the amplitude of the oscillator current. The demodulator 82 is in this case also configured as amplitude detector. Alternatively, the demodulator 82 may be configured as frequency detector of an oscillation frequency of the oscillator current.

[0102] A quadrature-phase detector 84 of the oscillation unit 70 is formed as a circuit and is configured to output binary signals, i.e., square-wave signals, I.sub.ref, Q.sub.ref, which correspond to an in-phase reference signal I.sub.ref or a quadrature phase reference signal Q.sub.ref with respect to a phase of the oscillator voltage U.sub.OSC. These two signals I.sub.ref, Q.sub.ref together form the reference signal PHA.

[0103] The demodulation unit 72 is configured as a phase-sensitive demodulator 86, which, using I.sub.ref, Q.sub.ref, performs a quadrature demodulation, and has a corresponding circuit. One input signal of the demodulator 86 is the voltage induced in the receiving coil 18, which is amplified by an amplifier 88. A further input signal of the phase-sensitive demodulator 86 is the output signal of the quadrature-phase detector 64, namely I.sub.ref, Q.sub.ref. One output signal of the demodulator 86 is the second parameter PSS or the second group of parameters PSS, which represents a demodulated voltage. The demodulated voltage may either have two components, namely an in-phase component U.sub.I and quadrature-phase component U.sub.Q, of the amplified induced voltage.

[0104] The second embodiment example of the sensor electronics 30 shown in FIG. 9 is configured in FIG. 7 similarly to the sensor electronics in FIG. 8. However, the quadrature-phase detector 84 is configured as phase detector 85, whose output signal is a phase reference signal φ.sub.ref, which has a predetermined relationship with the phase of the oscillator voltage U.sub.OSC. Instead of the two-channel phase-sensitive demodulator 86, a phase-sensitive demodulator 87 is provided, which performs a synchronous demodulation using the phase reference signal φ.sub.ref and instead of the in-phase or the quadrature-phase component U.sub.I, U.sub.Q, outputs a phase-related amplitude U.sub.φ as the second parameter PSS.

[0105] In operation of the sensor device 10, the oscillation circuit 70 of the sensor device 10 is supplied with a sinusoidal current. A magnetic field forms in the exciting coil 16, producing eddy currents and magnetic polarization in the object 11. Owing to the backward effect of the object 11 on the exciting coil 16, an electrical signal in the exciting coil is altered. Additionally, owing to the backward effect of the object 11, a voltage is induced in the receiving coil 18, 68. The first parameter DSS or the first group DSS and the phase reference signal PHA are determined by means of the oscillation unit 70. The phase reference signal PHA is output to the demodulation unit 72, which determines, using the phase reference signal PHA, a second parameter PSS from the amplified induced voltage of the receiving coil 18 and optionally a third parameter LSS from the amplified induced voltage of the receiving coil 68. The signal DSS and the signal PSS, LSS are output to the evaluation unit 74.

[0106] For determining the position P and the distance D, an algorithm implemented in the evaluation unit 74 of the sensor electronics 30 is executed, with which a dimensionless proximity signal S.sub.N is formed from the first parameter DSS. The proximity signal S.sub.N may be defined in particular as S.sub.N=a(U.sub.D0−U.sub.D) or S.sub.N=b(f.sub.OSC0−f.sub.OSC) or S.sub.N=a(U.sub.D0−U.sub.D)+b(f.sub.OSC0−f.sub.OSC). In the foregoing, a and b denote scaling factors, and U.sub.D0 and f.sub.OSC0 denote the object-free value of the demodulation voltage U.sub.D and the oscillation frequency f.sub.OSC in each case.

[0107] Furthermore, a dimensionless longitudinal position signal S.sub.P is formed from the second parameter PSS, which is determined in particular as S.sub.P=c*U.sub.I, S.sub.P=d*U.sub.Q, S.sub.P=c*U.sub.I+d*U.sub.Q, S.sub.P=e*U.sub.φ with scaling factors c, d and e. It is assumed that a possible background signal of the voltages U.sub.I, U.sub.Q or U.sub.φ has already been subtracted at this point.

[0108] A reduced longitudinal position signal V.sub.P is then formed as a relationship between the longitudinal position signal S.sub.P and the proximity signal S.sub.N in the form V.sub.P═S.sub.P/S.sub.N.

[0109] Additionally, a mechanical phase P.sub.M may optionally be formed by an arctan 2-function, defined as P.sub.M=arctan 2(V.sub.P, B*S.sub.N) with a scaling factor B.

[0110] The ratio V.sub.P and the mechanical phase P.sub.M may further optionally be scaled and linearized, in order to determine the longitudinal position P.

[0111] The scaling factor B may either be established beforehand, for example at the factory, if it is known at what vertical distance D the object 11 is expected to move. Alternatively or additionally, B may have been determined by means of a learning process, carried out before the method, in which the object 11 moves at least through the middle of the longitudinal measuring range of the sensor device 10 and an absolute quantity S.sub.NL is detected from the proximity signal S.sub.N, for example its maximum value, or its value at the point where the longitudinal position signal V.sub.P is zero. B may be inversely proportional to S.sub.NL, i.e., B=k/S.sub.NL, wherein k is a further scaling factor, with the result that the arctan 2 function represents a monotonic function, in particular a property that is as linear as possible over a certain range of the movement of the object.

[0112] As both the variation of the oscillation parameter, and therefore the proximity signal S.sub.N, as well as the induced voltage of the receiving coils 18, and therefore the longitudinal position signal S.sub.P are determined by the inductive backward effect of the same object 11, the reduced longitudinal position signal V.sub.P is “relatively” independent of the distance D. The precondition for position determination by calculating the mechanical phase P.sub.M is that the distance D between the object 11 and the end face 12 of the sensor device 10 does not deviate markedly from the distance at which the scaling factor B was determined.

[0113] For determining the lateral position L, the third parameter LSS, instead of PSS, may be examined and evaluated in exactly the same way.

[0114] For determining the distance, a prior calibration of the sensor device with respect to the longitudinal position P and optionally the lateral position L may be carried out for various distances D.

[0115] In a further method of evaluation, which can be implemented by the evaluation unit 74, it is possible to use a multi-variant, non-linear function of one or more of the aforementioned parameters DSS, PSS and LSS. For example, an artificial neural network may be used, which has previously been trained to determine the position P and optionally the lateral position L and/or optionally the distance D. The training of the artificial neural network may necessitate a prior learning process, which is carried out either for the type of sensor device 10 (for example for its size or its design) or for the environment of the sensor device in which it is used, for example at the factory at the design stage or individual production thereof.

[0116] FIG. 11 shows for example the relationship for the correlation between U.sub.I (x-axis 90 in arbitrary units) and U.sub.Q (y-axis 92 in arbitrary units) for the different materials structural steel, stainless steel and aluminium (curves 94a-9c) as the object 11 travels through the middle of the longitudinal measuring range. By comparing the parameter determined PSS, here U.sub.I, U.sub.Q, with varying object position, it is possible to draw conclusions about the type of material. Alternatively or additionally, the type of material of the object can be determined on the basis of a typical phase of the voltage induced by the object 11 in one or more receiving coils 18, 68. A typical phase may be defined in a time period as the most frequently occurring phase value (or mean value) of the inducible voltage, if it can be assumed that determination of the phase cannot be prevented by excessively narrow amplitudes. It may be necessary to take into account that the sign of the inducible voltage also depends on the object position, and a corresponding phase shift can be corrected before determining the mean value. Alternatively or additionally, the type of material of the object can be determined from a typical relationship between the change in amplitude and change in phase of the oscillator voltage U.sub.OSC. In this connection, the typical ratio can be regarded as constant and assumed to be known beforehand. Owing to the possible measurement inaccuracies, it is advantageous or necessary to determine the relations described above at larger values of the proximity signal or longitudinal position signal or over a period of time.

[0117] FIGS. 11A-11E show various quantities in the steps of the signal evaluation described above. The quantities are functions of the object position P (x-axes 96a-96e, in units of millimeters (mm)) for different vertical object distances D=0.25 mm (curves 98a, 100a, 102a, 104a, 106a; solid lines), D=0.50 mm (curves 98b, 100b, 102b, 104b, 106b; dashed lines) and D=0.75 mm (curves 98c, 100c, 102c, 104c, 106c; dotted lines), when the object 11 moves along the sensitive axis S1 of the sensor device 10 in FIG. 1. The y-axes 108a-108e are given in arbitrary units in each case for the corresponding quantity.

[0118] FIG. 11A and FIG. 11B show in each case the quantities U.sub.D and S.sub.N, wherein in this special case the proximity signal is formed as S.sub.N=(U.sub.D0−U.sub.D). U.sub.D0 and U.sub.D are digital values of the corresponding voltages, and may be regarded as dimensionless values. FIG. 11C shows the variation of the quadrature component U.sub.Q of the induced voltage. In FIGS. 11A, 11B and 11C it is to be noted that the shapes of the curves depend on the distance D. In contrast, as shown in FIG. 11D, the ratio V.sub.L substantially does not have any dependence on the object position P. Determination of the ratio V.sub.L does not require a learning process, but determination of the mechanical phase P.sub.M shown in FIG. 11E is only possible if in each case a learning operation has been carried out beforehand at each object distance D. However, determination of the longitudinal position P by determining the mechanical phase P.sub.M offers a larger measuring range or linearization range of about 18 mm compared to a linearizable measuring range of about 10 mm of the V.sub.M curves in FIG. 11D, if a total length of the coil arrangement 14 of 12.5 mm is assumed for a housing with 15 mm longitudinal extension. Each curve 106a-106c shown in FIG. 11E was calculated after the corresponding individual learning operations with the distance-specific B values, so that the B values were calculated as B=k/S.sub.NL with the same object-specific k-factor.

[0119] Although only a few embodiments of the present invention have been shown and described, it is to be understood that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention.