AU2015246241B2

AU2015246241B2 - Sensor device for detecting a change in a magnetic field and track-bound transportation system having at least one such sensor device

Info

Publication number: AU2015246241B2
Application number: AU2015246241A
Authority: AU
Inventors: Rainer Freise
Original assignee: Siemens Mobility GmbH
Current assignee: Siemens Mobility GmbH
Priority date: 2014-04-17
Filing date: 2015-03-30
Publication date: 2017-06-01
Anticipated expiration: 2035-03-30
Also published as: DE102014207409A1; NO2710153T3; WO2015158538A1; ES2662411T3; AU2015246241A1; PL3107791T3; DK3107791T3; EP3107791A1; CN106232452A; EP3107791B1; CN106232452B; HUE038475T2

Abstract

The present invention relates to a particularly efficient sensor device (1) for detecting a change in a magnetic field, which change is caused by an object approaching the sensor device (1) in a direction of movement (5) or moving past the sensor device (1) in the direction of movement (5). The sensor device (1) according to the invention has two sensor units (10, 20), wherein each of the sensor units (10, 20) comprises two receiver coils (12, 13; 22, 23) and an alternating-current-fed transmitter coil (11; 21) which is arranged between the receiver coils (12, 13; 22, 23) with respect to the direction of movement (5), wherein the longitudinal axes (12a, 13a; 22a 23a) of the receiver coils (12, 13; 22, 23) of the two sensor units (10, 20) are oriented essentially perpendicularly with respect to the direction of movement (5), wherein the longitudinal axes (11a; 21a) of the transmitter coils (11; 21) of the two sensor units (10, 20) are oriented essentially parallel to the direction of movement (5), wherein the transmitter coils (11; 21) of the two sensor units (10, 20) are arranged one behind the other with respect to the direction of movement (5), and wherein the sensor device (1) is embodied in such a way that the transmitter coils (11; 21) of the two sensor units (10, 20) generate magnetic fluxes (60, 70) which are opposed to one another. The invention also relates to a track-bound transportation system having at least one sensor device (1) according to the invention.

Description

PCT/EP2015/056917 / 2014P08271WOAU 1

Description

Sensor device for detecting a change in a magnetic field and track-bound transportation system having at least one such sensor device

Sensor devices for detecting changes in a magnetic field are employed in different areas of technology, such as for example industrial automation or railroad automation. For example, corresponding sensor devices are used in railroad automation in the form of wheel sensors or axle-counter sensors working in accordance with an inductive active principle in particular in the field of track vacancy detection systems. Thus for instance from German published patent application DE 10 2012 212 939 A1 a wheel sensor is known which comprises two receiver coils and an alternating-current-fed transmitter coil arranged between the receiver coils with respect to the rail longitudinal direction.

In sensor devices for detecting a change in a magnetic field in the form of wheel sensors used for axle counting, dual sensor systems, i.e. sensor devices having two sensor units, are normally used for detecting the direction of travel. In this case the received signals detected by the two sensor units overlap in terms of time during a wheel passage, such that the direction of travel can be determined from the sequence of signals in an evaluation unit. In the case of a corresponding dual system the overlap of the received signals is therefore of great importance in connection with detecting the direction of travel. It should be borne in mind here that corresponding dual systems are normally arranged in a common housing one behind the other in the rail longitudinal direction on the track, which means that for physical reasons 2 2015246241 10 May 2017 during a wheel passage only a limited signal overlap occurs, the characteristics of which depend in particular on the diameter of the relevant wheel to be detected. Thus the overlap of received signals in the case of wheels with a small diameter or else generally in the case of a comparatively minor effect on the respective received signals by a wheel approaching or moving past the sensor device normally diminishes. This can ultimately lead to interference in that an evaluation unit linked to the two sensor units can no longer reliably assign the signals of the two sensor units, for instance because a minimum overlap time is not reached, and as a result it is no longer possible reliably to detect the direction of travel.

It is the object of the present invention to substantially overcome or at least ameliorate one or more disadvantages of known arrangements.

The object of the present invention is to specify a sensor device for detecting a change in a magnetic field, which change is caused by an object approaching the sensor device in a direction of movement or moving past the sensor device in the direction of movement, said sensor device being particularly powerful and in particular enabling a particularly reliable identification of the direction of movement of the object.

This object is inventively achieved by a sensor device for detecting a change in a magnetic field, which change is caused by an object approaching the sensor device in a direction of movement or moving past the sensor device in the direction of movement, wherein the sensor device has two sensor units, wherein each of the sensor units has two receiver coils and an altemating-current-fed transmitter coil arranged between the receiver coils with respect to the direction of movement, wherein the longitudinal axes of the receiver coils of both sensor units are oriented essentially perpendicular to the

AH26( 12949847 1 ):SXY

PCT/EP2015/056917 / 2014P08271WOAU 3 direction of movement, wherein the longitudinal axes of the transmitter coils of both sensor units are oriented essentially parallel to the direction of movement, wherein the transmitter coils of the two sensor units are arranged one behind the other with respect to the direction of movement, and wherein the sensor device is embodied such that the transmitter coils of the two sensor units generate magnetic fluxes which are opposed to one another.

The inventive sensor device for detecting a change in a magnetic field, which change is caused by an object approaching the sensor device in a direction of movement or moving past the sensor device in the direction of movement, is initially characterized in that it has two sensor units. The sensor device is thus embodied as a dual sensor system suitable for identifying the direction of movement of the object approaching or moving past the sensor device.

Inventively each of the sensor units here comprises two receiver coils and an alternating-current-fed transmitter coil arranged between the receiver coils with respect to the direction of movement. Thanks to the respective alternating-current-fed transmitter coil a magnetic field or a magnetic flux is therefore generated, a change in which is detected by the approaching or passing object by means of the receiver coils .

The inventive sensor device is further characterized in that the longitudinal axes of the receiver coils of both sensor units are arranged perpendicular or at least essentially perpendicular to the direction of movement. This means that the sensor device, for its correct operation, is arranged or mounted such that the longitudinal axes of the receiver coils

PCT/EP2015/056917 / 2014P08271WOAU 4 of both sensor units are oriented such that the object to be detected approaches or passes the sensor device in the direction of movement perpendicular to the longitudinal axes of the receiver coils.

Inventively the longitudinal axes of the transmitter coils of both sensor units are oriented parallel or at least essentially parallel to the direction of movement.

Consequently the longitudinal axes of the transmitter coils and of the receiver coils are in particular also perpendicular or at least essentially perpendicular to one another.

The transmitter coils of the two sensor units of the inventive sensor device are arranged one behind the other with respect to the direction of movement. In addition, the inventive sensor device is embodied such that the transmitter coils of the sensor units generate magnetic fluxes which are opposed to one another.

The inventive sensor device is advantageous, since because of the arrangement and orientation of the transmitter and receiver coils and the opposing magnetic fluxes of the transmitter coils there is a particularly distinct temporal overlap of the received signals of the two sensor units detected by means of the respective receiver coils. This is advantageous in particular in the case of low signal levels, in that interference caused by overly short overlap times of the received signals of the two sensor units in connection with identification of the direction of movement of the object to be detected are prevented or at least reduced in comparison to previously known sensor devices. In addition, thanks to the influence of the adjacent sensor units the deflection of or change in the magnetic field or magnetic flux caused by the

PCT/EP2015/056917 / 2014P08271WOAU 5 approaching or passing object is advantageously exploited such that the inventive sensor device has particularly high sensitivity in respect of detection of the object.

According to a particularly preferred embodiment of the inventive sensor device the transmitter coils and the receiver coils of both sensor units are arranged one behind the other with respect to the direction of movement. This means that all six coils of the sensor device are arranged one behind the other in the direction of movement. The advantage of this is that interference between the two sensor units or their coil systems is prevented and a reliable detection of the object and its direction of movement is enabled.

Advantageously the inventive sensor device can also be developed such that for each of the two sensor units the receiver coils are arranged such that the longitudinal axis of the transmitter coil of the respective sensor unit intersects the receiver coils of the relevant sensor unit outside the transmitter coil. In other words this means that the receiver coils and the transmitter coil of the respective sensor unit are arranged essentially in a plane. In the case of a sensor device in the form of a wheel sensor mounted on a rail this means that the receiver coils and the transmitter coil of the respective sensor units are arranged horizontally at the same height.

According to a further particularly preferred embodiment of the inventive sensor device, for each of the two sensor units the receiver coils are connected in series inversely to one another in each case. The advantage of this is that the inverse connection of the receiver coils and their arrangement in respect of the respective transmitter coil mean that signal

PCT/EP2015/056917 / 2014P08271WOAU 6 voltages caused by a passing or approaching object are added up, whereas receiving interference voltages caused by an external magnetic interference field are subtracted thanks to the inverse connection of the receiver coils and thus completely or at least largely offset or eliminate one another. It should be borne in mind here that inductively working sensor devices are normally comparatively sensitive to interference which has a frequency corresponding to the working frequency of the respective sensor device. In the case of sensor devices in the form of wheel sensors corresponding interference voltages can arise for example because of rail currents. In this case the return conductor current (or the harmonic content thereof) of a locomotive which flows though the rail generates an interference signal which is received by the sensor device in the form of oscillations. Corresponding oscillations can normally not readily be separated or distinguished from signals caused by the influence of a passing wheel of a rail vehicle. Furthermore, interference can also be caused for example by adjacent sensor devices with the same working frequency. Regardless of the nature and origin of the respective interference signals the aforementioned preferred development of the inventive sensor device is characterized by a particularly distinct sensitivity to interference because of the inverse connection of the respective receiver coils of the two sensor units. Advantageously the two receiver coils are in this case constructed identically for each of the two sensor units in order to achieve optimum interference field offset, in that they correspond for instance in respect of their geometry and their number of windings.

Preferably the inventive sensor device can also be developed such that with respect to the direction of movement in each

PCT/EP2015/056917 / 2014P08271WOAU 7 case one of the two receiver coils of the two sensor units is arranged between the transmitter coils of the two sensor units and the relevant receiver coils have the same winding direction. This is advantageous, since as a result in particular in the overlap region of the two sensor units, i.e. for those positions of the object to be detected that exert a significant influence on the two relevant receiver coils, a particularly favorable signal characteristic is produced in particular in respect of a reliable identification of the direction of movement of the object.

According to a further particularly preferred embodiment of the inventive sensor device the receiver coils of the respective sensor unit are arranged, with respect to the direction of movement, symmetrically to the transmitter coil of the respective sensor unit for each of the two sensor units. A corresponding symmetrical arrangement in respect of the transmitter coil is advantageous in that as a result a particularly simple and space-saving structure of the sensor device is produced, which because of the symmetry can furthermore be employed particularly flexibly.

Preferably the inventive sensor device can also be developed such that the transmitter coils of the two sensor units are fed with alternating current of identical frequency. The advantage of this is that it avoids the necessity of providing alternating current or alternating voltage of different frequency and at the same time ensures that the amounts of magnetic flux generated by the transmitter coils correspond, giving a symmetrical configuration in this respect, which is particularly favorable in respect of reliable detection of the object and its direction of movement. Advantageously the inventive sensor device can furthermore be configured in this

PCT/EP2015/056917 / 2014P08271WOAU 8 case such that it has a generator feeding the transmitter coils of both sensor units with alternating current.

According to a further particularly preferred embodiment of the inventive sensor device it has a housing enclosing both sensor units. This is advantageous, since as a result costs and space are saved in comparison with a likewise conceivable embodiment in which each of the sensor units has a separate housing.

According to a further preferred development of the inventive sensor device it comprises an evaluation unit linked to the receiver coils of both sensor units. The evaluation unit thus enables the received signals of the two sensor units to be evaluated both individually and in combination with one another. This results in advantages in respect of the reliability both of the detection of the respective object as such and also the identification of the direction of movement of the object.

Essentially it is conceivable for the evaluation unit to be arranged in one housing together with the two sensor units. This is recommended in particular in cases in which as a result no disadvantages arise for the operation and if appropriate the maintenance of the evaluation unit, for instance because of initial or ambient conditions.

Preferably the inventive sensor device can also be developed such that the evaluation unit is arranged in a housing separate from the sensor units. As a function of the respective application this may give rise to advantages in particular in respect of the effect of mechanical or electrical interference on the evaluation unit, in respect of

PCT/EP2015/056917 / 2014P08271WOAU 9 the space available for the evaluation unit and/or in respect of the accessibility of the evaluation unit. Thus for example in the case of sensor devices in the form of wheel sensors it is frequently favorable to arrange the evaluation unit at a distance from the sensor units mounted directly on the track. Thus corresponding evaluation units are in this case normally accommodated in a trackside connection box which is generally a few meters away from the sensor units. This results firstly in advantages in respect of the space available for the evaluation device and protection against mechanical or electrical interference impacting directly in the region of the rails. Secondly the evaluation unit is advantageously accessible in the case or maintenance or repair work, without personnel having to be deployed directly on the track in the hazardous region.

According to a further particularly preferred embodiment of the inventive sensor device the transmitter coil and/or the receiver coil are each part of an oscillating circuit for each of the two sensor units. This is advantageous in respect of the provision of sufficient magnetic flux in particular in respect of the transmitter coils.

Preferably the inventive sensor device can also be developed such that for each of the two sensor units the transmitter coil and/or the receiver coil are designed to be free from ferromagnetic materials. Making the respective coils free from ferromagnetic materials has the advantage that as a result inductive interference can be reduced or prevented.

In principle the inventive sensor device can be employed for any purpose, i.e. in particular for detecting objects of any kind. This for example includes use in the field of industrial

PCT/EP2015/056917 / 2014P08271WOAU 10 automation

According to a further particularly preferred embodiment the inventive sensor device is designed as a wheel sensor for detecting a change in a magnetic field caused by an object in the form of a wheel approaching on a track in the direction of movement in the form of the rail longitudinal direction or moving past the wheel sensor in the rail longitudinal direction. This is advantageous, since corresponding wheel sensors are frequently employed in the field of railroad automation and because of the arrangement of the sensor units of the sensor device on the track are normally exposed to considerable interference. In addition, in particular when using corresponding wheel sensors for detecting track vacancy a reliable detection of an approaching or passing wheel and also its direction of movement or travel are of great importance. Thus the advantages of the inventive sensor device come to bear especially in the case of a sensor device designed as a wheel sensor.

The invention further comprises a system of the track-bound transportation system, in particular a track vacancy detection system, having at least one inventive sensor device or at least one sensor device according to one of the previously described preferred developments of the inventive sensor device.

The invention is further explained below on the basis of an exemplary embodiment, in which

Figure 1 shows a schematic sketch of a lateral perspective representation of an arrangement with an exemplary embodiment of the inventive sensor device and

PCT/EP2015/056917 / 2014P08271WOAU 11

Figure 2 shows a further schematic sketch of a plan view of a representation with a section of the inventive sensor device according to the exemplary embodiment of Figure 1.

For reasons of clarity the same reference characters are used in the figures for identical or identically working components .

Figure 1 shows a schematic sketch of a lateral perspective representation of an arrangement with an exemplary embodiment of the inventive sensor device. A sensor device 1 is represented in the form of a wheel sensor arranged in the region of a rail 100. The sensor device 1 is arranged on the inside of the rail and in respect of its detection range is oriented upward such that it detects the wheel flange or the running surface of iron wheels of rail vehicles approaching the sensor device 1 or moving past the sensor device 1.

The sensor device 1 comprises two sensor units 10 and 20, which each have two receiver coils 12, 13 or 22, 23. In respect of a direction of movement 5 given by the rail longitudinal direction, an alternating-current-fed transmitter coil 11 or 21 is arranged between the receiver coils 12, 13 or 22, 23 in each case.

In accordance with the representation in Figure 1 the longitudinal axes 12a, 13a, 22a, 23a of the receiver coils 12, 13 or 22, 23 of the two sensor units 10, 20 are oriented perpendicular to the direction of movement 5 in the form of the rail longitudinal direction. In contrast, the transmitter coils 11, 21 are arranged such that their longitudinal axes

PCT/EP2015/056917 / 2014P08271WOAU 12 11a, 21a are oriented parallel to the direction of movement 5 and thus perpendicular to the longitudinal axes 12a, 13a, 22a, 23a of the receiver coils 12, 13, 22, 23. It is further apparent that the transmitter coils 11, 21 and the receiver coils 12, 13, 22, 23 of both sensor units 10, 20 are each arranged spaced apart one behind the other with respect to the direction of movement 5, i.e. "in series" when viewed in the rail longitudinal direction.

Because of the orientation and arrangement of the transmitter coils 11, 21 these generate magnetic fields or magnetic fluxes 60, 70, which run essentially horizontally along the rail 100. Because of the orientation, perpendicular to the direction of movement 5, of the longitudinal axes 12a, 13a, 22a, 23a of the receiver coils 12, 13, 22, 23 the transmitter coils 11, 21 thus induce voltages in the respective receiver coils 12, 13 or 22, 23, which in the absence of field-distorting materials would be extremely small because of the position of the receiver coils 12, 13, 22, 23 in the center of the magnetic fields or magnetic fluxes 60, 70. However, the railhead 110 of the rail 100 causes field distortion, thereby producing a field asymmetry which even without influence by a passing wheel results in received signals of the receiver coils 12, 13, 22, 23 in the form of a signal open-circuit voltage.

According to the magnetic fluxes 60, 70 indicated in Figure 1 this means, with respect to each of the two sensor units 10, 20, that the magnetic field lines flow through the respective two receiver coils 12, 13 or 22, 23 of said sensor units 10, 20 in the inverse direction in each case, so that because of the symmetrical structure in principle identically high signal voltages with an opposing phase position would result for the two receiver coils 12, 13 of the left sensor unit 10. The same

PCT/EP2015/056917 / 2014P08271WOAU 13 applies analogously in respect of the two receiver coils 22, 23 of the right sensor unit 20. As will be explained in more detail below on the basis of Figure 2, the receiver coils 12 and 13 or 22 and 23 of each of the sensor units 10, 20 are however advantageously connected to one another inversely in series. This means that the signal voltages detected by the receiver coils 12, 13 or 22, 23 and brought about by the magnetic fluxes 60, 70 are advantageously added up. In contrast an external magnetic interference field, which is indicated in Figure 1 in the region of the left sensor unit 10 by the reference character 80 and which for example can be caused by rail currents, penetrates the receiver coils 12, 13 of the relevant sensor unit 10 such that the receiving interference voltages are subtracted by the inverse connection of the receiver coils 12, 13, in other words are completely or at least essentially eliminated.

The sensor device 1 represented in Figure 1 is further characterized in particular in that the transmitter coils 11, 21 of the two sensor units 10, 20 generate magnetic fluxes 60, 70 which are opposed to one another. Advantageously the sensor units 10, 20, which jointly form a dual system, here have the identical working frequency, in that the transmitter coils 11, 21 of the two sensor units 10, 20 are fed with alternating current of an identical frequency. This can be achieved for example by the transmitter coils 11, 21 of both sensor units 10, 20 each being connected to a generator feeding the transmitter coils 11, 21 with alternating current, said generator not being represented in Figure 1 for reasons of clarity.

When a wheel passes or transits in the direction of movement 5, i.e. in the present case from left to right, the left

PCT/EP2015/056917 / 2014P08271WOAU 14 sensor unit 10 will initially generate a received signal. If the wheel rolls further, the field of the transmitter coil 21 of the right sensor unit 20 is in consequence distorted more and more. However, this field distortion additionally affects the received signal or the received voltage in the right receiver coil 13 of the left sensor unit 10, in that the amplitude of the received signal, i.e. the received voltage, rises and the received signal as such is thus retained longer in total during a wheel passage or decreases comparatively slowly. This effect is advantageously symmetrical, in that an object moving past the sensor device 1 in the form of the wheel in the center of the sensor device 1 in each case results in an increase in the received voltages of the center receiver coils 13, 22 with the involvement of the magnetic fields or magnetic fluxes 60, 70 of both transmitter coils 11, 21. The result is thus an increase in the signal overlap during a wheel passage in conjunction with an increase in the received signal. This is advantageous especially with low signal levels, since as a result interference caused by overly short overlap times are prevented. Finally this means that the sensor device 1 can, by means of the two sensor units 10, 20, detect approaching or passing wheels particularly reliably, even under difficult conditions, and in particular the direction of movement 5 of the relevant wheels.

It is further apparent from Figure 1 that for each of the two sensor units 10, 20 the receiver coils 12, 13 or 22, 23 are arranged such that the longitudinal axes 11a, 21a of the transmitter coils 11 or 21 of the sensor units 10, 20 intersect the receiver coils 12, 13 or 22, 23 of the sensor units 10, 20 outside the respective transmitter coil 11 or 21. In other words this means that the transmitter coils 11, 21 and the receiver coils 12, 13, 22 and 23 are arranged

PCT/EP2015/056917 / 2014P08271WOAU 15 essentially horizontally at the same height.

Advantageously the sensor device 1 is further designed such that with respect to the direction of movement 5 in each case one of the two receiver coils 13 or 22 is arranged between the transmitter coils 11, 21 of the sensor units 10, 20 and the relevant receiver coils 13, 22 have the same winding direction. As a result a further increase in the signal overlap of the two sensor units 10, 20 is achieved.

In accordance with the representation in Figure 1 the receiver coils 12, 13 or 22, 23 of the respective sensor unit 10 or 20 are arranged symmetrically to the transmitter coil 11 or 21 of the respective sensor unit 10 or 20 with respect to the direction of movement 5. A corresponding symmetrical arrangement is advantageous both in respect of the space requirement of the sensor device and also in respect of the flexible deployability thereof.

In the illustrated exemplary embodiment the sensor device 1 has a housing 30 enclosing both sensor units 10, 20.

In respect of the receiver coils 13 and 22 arranged between the transmitter coils 11, 21 of the two sensor units 10, 20 it should be noted that in principle the position of these two receiver coils 13, 22 could be interchanged. In respect of the representation in Figure 1 the sensor unit 10 would in this case thus comprise the receiver coils 12 and 22 and the sensor unit 20 would comprise the receiver coils 13 and 23, i.e. the two sensor units 10, 20 would "overlap" in respect of the direction of movement 5, i.e. in the present case the rail longitudinal direction. A corresponding interchange of the position of the receiver coils 13, 21 is possible, since the

PCT/EP2015/056917 / 2014P08271WOAU 16 opposite orientation of the magnetic fluxes 60, 70 of the transmitter coils 11, 21 for the relevant receiver coils 13, 22 produces received signals in the form of voltages with the same sign. Thus it is advantageously possible, as a function of the respective circumstances and requirements, to vary the overlap of the received voltages of the receiver coils 12, 13, 22, 23.

It should further be noted that the sensor units 10 and 20 can, alternatively to the representation in Figure 1, also be arranged inclined or tilted in respect of the rail 100. In this case the entire system comprising the transmitter coils 11, 21 and the receiver coils 12, 13, 22, 23 would thus be arranged rotated about an axis parallel to the rail longitudinal direction.

The transmitter coils 11, 21 and the receiver coils 12, 13, 22, 23 are advantageously structured to be completely free from ferromagnetic materials, i.e. as air coils. In addition the aforementioned coils can advantageously be embodied as a component of oscillating circuits, thereby producing an increase in sensitivity depending on the respective circumstances .

In a further schematic sketch Figure 2 shows a plan view of a representation with a section of the inventive sensor device according to the exemplary embodiment of Figure 1. In contrast to Figure 1 only the left sensor unit 10 of the transmitter device 1 is shown for reasons of clarity. Regardless of this, the sensor device 1 according to the representation in Figure 1 has a further corresponding sensor likewise arranged in the region of the railhead 110.

PCT/EP2015/056917 / 2014P08271WOAU 17

The sensor unit 10 comprises, analogously to the representation in Figure 1, a transmitter coil 11 and two receiver coils 12 and 13. According to the representation in Figure 2 the receiver coils 12, 13 are connected inversely to one another in series, so that the individual received signals of the two receiver coils 12, 13 are subtracted and can be tapped as a signal voltage U. According to the exemplary embodiment in Figure 2 the signal voltage U is fed to an evaluation unit 40 which is arranged at a distance from the sensor unit 10 in a separate housing 50, which for example can be a component of a trackside connection box. As already explained in connection with Figure 1, thanks to the inverse connection of the two receiver coils 12, 13 an extensive offset of interference fields is produced, which for example can be caused by rail currents.

According to the explanations above, the exemplary embodiment of the inventive sensor device 1 explained on the basis of the figures has the advantage that in particular the opposing magnetic fluxes 60, 70 generated by the transmitter coils 11, 21 result in an increase in the signal overlap of the receiver coils 12, 13 or 22, 23, which especially in the case of low signal levels is favorable in respect of the prevention of interference because of overly small overlap times.

Furthermore the field deflection caused by a passing or approaching object is utilized multiple times advantageously by the subtraction of two received signals or voltages with different signs per sensor unit 10, 20 and the additional influence of the adjacent sensor unit 10 or 20 on the respective received voltage. This impacts advantageously on the overall signal characteristic of the sensor device 1, in that the latter has an increased sensitivity. In addition the field-compensating structure of the sensor device 1 with

PCT/EP2015/056917 / 2014P08271WOAU 18 transmitter coils 11, 21 and receiver coils 12, 13, 22, 23 also advantageously increases the interference resistance against external sources. As a result the previously described sensor device 1 is thus especially powerful and in particular enables especially reliable identification of the direction of movement of the objects to be detected.

Claims

1. A sensor device for detecting a change in a magnetic field which is caused by an object approaching the sensor device in a direction of movement of the sensor device or moving past the sensor device in the direction of movement, - wherein the sensor device has two sensor units, - wherein each of the sensor units comprises two receiver coils and an alternating-current-fed transmitter coil arranged between the receiver coils with respect to the direction of movement, - wherein the longitudinal axes of the receiver coils of both sensor units are oriented essentially perpendicular to the direction of movement, - wherein the longitudinal axes of the transmitter coils of both sensor units are oriented essentially parallel to the direction of movement, - wherein the transmitter coils of the two sensor units are oriented one behind the other with respect to the direction of movement, - and wherein the sensor device is embodied such that the transmitter coils of the two sensor units generate magnetic fluxes which are opposed to one another.

2. The sensor device as claimed in claim 1, wherein the transmitter coils and the receiver coils of both sensor units are arranged one behind the other with respect to the direction of movement.

3. The sensor device as claimed in claim 1 or 2, wherein for each of the two sensor units the receiver coils are arranged such that the longitudinal axis of the transmitter coil of the respective sensor unit intersects the receiver coils of the relevant sensor unit outside the transmitter coil.

4. The sensor device as claimed in any one of the preceding claims, wherein for each of the two sensor units the receiver coils are connected in series inversely to one another in each case.

5. The sensor device as claimed in any one of the preceding claims, wherein with respect to the direction of movement in each case one of the two receiver coils of the two sensor units is arranged between the transmitter coils of the two sensor units and the relevant receiver coils have the same winding direction.

6. The sensor device as claimed in any one of the preceding claims, wherein for each of the two sensor units the receiver coils of the respective sensor unit are arranged symmetrically to the transmitter coil of the respective sensor unit with respect to the direction of movement.

7. The sensor device as claimed in any one of the preceding claims, wherein the transmitter coils of the two sensor units are fed with alternating current of identical frequency.

8. The sensor device as claimed in claim 7, wherein the sensor device has a generator feeding the transmitter coils of both sensor units with alternating current.

9. The sensor device as claimed in any one of the preceding claims, wherein the sensor device has a housing enclosing both sensor units.

10. The sensor device as claimed in any one of the preceding claims, wherein the sensor device comprises an evaluation unit linked to the receiver coils of both sensor units.

11. The sensor device as claimed in claim 10, wherein the evaluation unit is arranged in a housing separate from the sensor units.

12. The sensor device as claimed in any one of the preceding claims, wherein for each of the two sensor units the transmitter coil and/or the receiver coils are in each case a component of an oscillating circuit.

13. The sensor device as claimed in any one of the preceding claims, wherein for each of the two sensor units the transmitter coil and/or the receiver coils are designed to be free from ferromagnetic materials.

14. The sensor device as claimed in any one of the preceding claims, wherein the sensor device is designed as a wheel sensor for detecting a change in a magnetic field, which change is caused by an object in the form of a wheel approaching the wheel sensor on a rail in the direction of movement in the form of the rail longitudinal direction or moving past the wheel sensor in the rail longitudinal direction.

15. A system of the track-bound transportation system, in particular a track vacancy detection system, having at least one sensor device as claimed in any one of the preceding claims.