WO2018041734A1

WO2018041734A1 - Device with an encoder and a sensor

Info

Publication number: WO2018041734A1
Application number: PCT/EP2017/071423
Authority: WO
Inventors: Armin Meisenberg; Axel Bartos
Original assignee: TE Connectivity Sensors Germany GmbH
Priority date: 2016-08-29
Filing date: 2017-08-25
Publication date: 2018-03-08
Also published as: DE102016010332A1

Abstract

The invention relates to a device comprising an encoder and a sensor, the position of the encoder relative to the sensor being changeable by rotation about a rotation axis, the encoder having a magnet, the direction of magnetisation of which points in the direction of the rotation axis, the sensor having four magnetoresistive resistors which are connected to form a Wheatstone bridge and which are arranged in a plane perpendicular to the rotation axis, the four magnetoresistive resistors being arranged around a centre point of the sensor which is located on the rotation axis.

Description

"Device with an encoder and a sensor"

The invention relates to a device with an encoder, which has a magnet, and a sensor which has four magnetoresistive resistors connected to a form Wheatstone bridge, the position of the encoder relative to the sensor being changeable by rotation about a rotation axis.

A variety of fields of application are known from practice in which the position of an encoder relative to a sensor must be determined, the position of the encoder relative to the sensor being changeable by rotation about a rotation axis. Adjusting knobs, for example, are known as an area of application for such devices, wherein an adjustment is carried out by rotating a knob, and how the position of the knob relative to a stationary base has changed must be determined with a device. Such adjusting knobs are used, for example, in cars, for air conditioning systems, for example, or for other control systems of the vehicle. Another area of application of such devices is determining the position of valve bodies in a valve housing if the position of the valve body can be changed by rotation. Determining the position of a float can also be considered to be an area of application if the position of the float is determined by determining the position of a bar which is rotatably arranged at a fixed location and connected to the float. An often safety-critical application is the determination of the angle of steering in motor vehicles.

In many areas of application of such devices, a magnet is used as an encoder. Weak magnets are generally used in order to keep the influence on the environment and costs for the magnetic material as low as possible. Furthermore, the problem that arises with strong magnets is that they attract ferromagnetic particles and this can consequently result in a blockage.

With such devices, in particular with those which use a weak magnet as an encoder, the problem is that determining the position of the encoder can be disrupted by an intermittent external magnetic field.

In this context, the problem of the invention was to provide a device with an encoder and a sensor in which the position of the encoder relative to the sensor can be reliably determined even if an external magnetic field is acting intermittently.

This problem is solved by the subject-matter of the main claim. Advantageous embodiments are set out in the subclaims and the following description.

The basic concept of the invention is to form the sensor with four magnetoresistive resistors which are connected to form a Wheatstone bridge and to arrange the magnet and the resistors of the sensor such that the magnetic field generated by the magnet is orientated at least substantially, in the case of the two resistors, antiparallel in the resistors of a first group which includes two of the four resistors, and is likewise orientated at least substantially antiparallel in the resistors of a second group, which includes the remaining two of the four resistors. According to the invention, the magnetic field generated by the magnet of the encoder is not intended to act substantially homogeneously on the four magnetoresistive resistors of the sensor. Instead, the magnet of the encoder is intended to generate a magnetic field which is particularly preferably split into two in the region of the resistors of the sensor, i.e. in a first part of the resistors it points in a first direction and in a second part of the resistors it points in a second direction. The concept of the invention is that applying an external magnetic field in such an arrangement leads to the change of direction of the magnetic field in the resistors of the sensor, caused by said application, being entirely cancelled out, such that the signal generated by the sensor remains uninfluenced by the effect of an external magnetic field.

For this purpose, the invention envisages that the encoder has a magnet, the direction of magnetisation of which points in the direction of the rotation axis. The invention further envisages that the sensor has four magnetoresistive resistors which are connected to form a Wheatstone bridge or a half bridge and which are arranged in a plane perpendicular to the rotation axis, wherein the four magnetoresistive resistors are arranged around a centre point of the sensor which is located on the rotation axis. The four resistors can also be interconnected to form an individual voltage divider, wherein then, however, either the advantages of the measurement of differential voltage typical for Wheatstone bridges are abandoned or a separate reference voltage is required. An advantage of a half bridge circuit is the quadrupled connecting resistance relative to a Wheatstone bridge, which reduces the energy consumption of the sensor fourfold.

This arrangement can be used to arrange the sensor above a pole of the magnet of the encoder. As is known, the projection of the respective field direction of a magnetic field generated by a magnet points, at different locations on a plane which is located above the pole and which is perpendicular to the direction of magnetisation of the magnet, in numerous directions. It can even be said that in the plane the magnetic field radiates outwards in a beam-like manner from the centre point of the pole. This effect may be able to be used for the desired circumstance of the invention to orientate the magnetic field generated by the magnet at least substantially antiparallel in the resistors of a first group, which includes two of the four resistors, and also to orientate it at least substantially antiparallel in the resistors of a second group, which includes the remaining two of the four resistors. The term "antiparallel" is intended to be understood to be an orientation of two directions to one another which run parallel to one another or on the same straight line, but point in opposite directions. In a preferred embodiment, two opposing resistors in relation to the centre point of the Wheatstone bridge are part of the first group and the two remaining opposing resistors, also in relation to the centre point of the Wheatstone bridge, are part of the second group.

Additionally or alternatively, the magnet and the resistors of the sensor are arranged such that the magnetic field generated by the magnet runs not radially but pivoted by an angular amount relative to the centre point of the Wheatstone bridge in two adjacent resistors, depending on the angular position between the magnet and sensor, wherein in the case of the one resistor the field direction is pivoted clockwise by the angular amount and in the adjacent resistor the field direction is pivoted anticlockwise by the angular amount. The magnetic field generated by the magnet particularly preferably does not run radially relative to the centre point of the Wheatstone bridge in all adjacent resistors, but pivoted by an angular amount, wherein in the case of the one resistor the field direction is pivoted clockwise by the angular amount and in the adjacent resistor the field direction is pivoted anticlockwise by the angular amount. This deviation of the field direction from the radial direction particularly preferably exhibits behaviour which is dependent on the angular position between the magnet and resistor, is 180 ° periodic and as a first approximation sinusoidal. The magnetic field generated by the magnet does not run radially relative to the centre point of the Wheatstone bridge in the resistors due to the fact that the magnet is a bar magnet in a preferred embodiment. For implementing the basic concept according to the invention, it is helpful to change the shape of the magnetic field in the sensor plane to be mirror- symmetrical by using a modified, e.g. rectangular, elongate shape of the magnet. In the event of a magnet being a round disk, the magnetic field is invariant relative to a rotation about the centre axis of the disk and is not suitable for an angle measurement.

For implementing the basic concept according to the invention, it is particularly helpful if the extent of the magnet of the encoder is greater, in a direction perpendicular to the rotation axis, than the maximum distance between a first point on a first of the four resistors of the sensor, which point is furthest from the centre point of the sensor, and a point on another of the four resistors of the sensor, which point is furthest from the first point. The longer the extent of the magnet of the encoder in a direction perpendicular to the rotation axis, the stronger is the arising effect that the magnetic field generated by the magnet points substantially homogeneously in a first direction in a plane above the pole of the magnet in a first region and points substantially homogeneously in a direction which is offset therefrom by 180 degrees in a second region.

In a preferred embodiment, the magnet is a bar magnet. The bar magnet particularly preferably extends in a direction perpendicular to the rotation axis. The bar magnet is particularly preferably cuboid. The cuboid is particularly preferably not a cube. In a preferred embodiment, the length of the bar magnet which points perpendicular to the rotation axis is more than 1 .5 times greater and/or less than 10 times greater than the width of the bar magnet which points perpendicular to the rotation axis and perpendicular to the length of the bar magnet. In the event of such a configuration of the bar magnet, the preferred effect of the invention can be adequately achieved without the device having to be made particularly bulky in a direction perpendicular to the rotation axis.

It is advantageous for the device according to the invention if the region in which the field direction of the magnetic field generated by the magnet extends in the direction of the rotation axis in the region of the sensor can be kept small. Sensors with magnetoresistive resistors can often detect the presence of a magnetic field in only one or two directions of a linear orthogonal coordinate system, but not in the third direction of the linear orthogonal coordinate system.

It has been found that the effect desired according to the invention that the projection of the field direction of the magnetic field generated by the magnet in a plane which is located above the pole and which is perpendicular to the magnetisation direction of the magnet is orientated, in the resistors, arranged in this plane, of a first group, which includes two of the four resistors, at least substantially antiparallel in the case of the two resistors and in the resistors, arranged in this plane, of a second group, which includes the remaining two of the four resistors, is also orientated at least substantially antiparallel, can be particularly effectively achieved if the magnet has a given extent along a longitudinal axis perpendicular to the rotation axis. It has at the same time been found that in the event of a very large extent of the magnet in a direction perpendicular to the rotation axis, the region in which the field direction of the magnetic field generated by the magnet extends in the direction of the rotation axis in the region of the sensor becomes large. In this region above the longitudinal axis of the magnet, only a very low field strength occurs in the sensor plane at the location of the sensor resistors, which, in the case of sensors which use a magnetoresistive effect, can lead to signal behaviour which is unreproducible, hysteretic and powerfully determined by interference fields. In the event of a configuration of the bar magnet in which the length of the bar magnet which points perpendicular to the rotation axis is more than 1 .5 times greater and/or less than 10 times greater than the width of the bar magnet which points perpendicular to the rotation axis and perpendicular to the length of the bar magnet, a good compromise should be reached for these two mutually conflicting effects.

In a preferred embodiment, the distance from the surface of the magnet associated with the sensor to the plane in which the four magnetoresistive resistors are arranged corresponds to 0.25 to 2 times the width of the magnet. In general, the width and length of the magnet and the distance from the sensor surface should be selected such that strong horizontal field components develop at the sensor resistors.

In a preferred embodiment, the centre of gravity and/or the centre of volume of the magnet is located on the rotation axis.

The four magnetoresistive resistors which are connected to form a Wheatstone bridge are arranged in a plane perpendicular to the rotation axis. Magnetoresistive resistors naturally have not only a length and width but also a height. The wording "arranged in a plane perpendicular to the rotation axis" should thus be understood to mean that the length direction and the width direction of the resistors do not point in the direction of the rotation axis. Magnetoresistive resistors are produced with a height of approximately 0.02-0.2 micrometres but often have a length of 100-1000 micrometres and a width of 2-20 micrometres, such that the height is virtually infinitesimally small in relation to the length and width of the resistor, such that it is appropriate to say that the resistors are arranged in a plane perpendicular to the rotation axis. The phrase "arranged in a plane perpendicular to the rotation axis" is also in particular intended to be understood to mean that the centres of gravity of the four resistors are arranged in a plane and/or the centres of volume of the four resistors are arranged in a plane. This also applies to resistors which are in each case formed by a series connection of resistive strips.

In a preferred embodiment, the resistors of the sensor are arranged in a point- symmetrical manner around the centre point of the sensor. In an alternative embodiment, the geometric configuration of the sensor is selected such that the resistors of the sensor can be mapped to each other by a rotation through at least one angle about the rotation axis.

In a preferred embodiment, an auxiliary magnet is provided, the position of which relative to the sensor is unchangeable. Such an auxiliary magnet enables the magnetic field generated by the magnet, in particular when using a very elongate encoder magnet, to be tilted by an offset amount above the longitudinal axis of the magnet in the region of the sensor, such that the regions, in which the field direction of the magnetic field generated by the magnet extends substantially in the direction of the rotation axis, do not arise in the region of the sensor resistors. In this manner, a radial field portion can be additionally generated over the sensor, which modifies the almost parallel mirror-symmetrical field distribution but also generates a field which is sufficient for stable sensor operation in the zone which is almost field-free with regard to the component in the chip plane. The auxiliary magnet is particularly preferably axially magnetised and arranged such that it generates a practically radial field over the sensor. Using a very elongate encoder magnet has the advantage that the field distribution at the sensor location becomes more robust in the longitudinal direction of the magnet relative to adjustment errors.

In a preferred embodiment, the sensor exhibits the "anisotropic" magnetoresistive effect (AMR effect) or the "giant" magnetoresistive effect (GMR effect) or the TMR effect (tunnel magnetoresistive effect). An essential feature of AMR (but also GMR and TMR) sensors is that these sensors primarily measure magnetic field angles and not field strengths like, for example, Hall sensors.

In a preferred embodiment, a resistor of the sensor is formed by a plurality of resistive strips. In a preferred embodiment, the resistive strips of a resistor can be arranged radially relative to the centre point of the sensor. In an alternative embodiment, the resistive strips of a sensor can be arranged parallel to each other. In a particularly preferred embodiment, each AMR-resistive strip has the geometric shape of a portion of a geometric spiral, the point of origin of which is located at the centre point of the sensor. It is evident that such arrangements are particularly suitable for compensating for harmonics.

Due to the fact that when using the GMR or TMR effect the resistance-determining reference direction of the signal behaviour is not determined by the current direction, as is the case with the AMR effect, but by the direction of magnetisation of a "pinned layer" in the sensor layer system, the described variations of the directions of the AMR resistive strips can be replaced therein with similar orientations of the magnetisation of the "pinned layer", having a comparable effect.

In order to achieve in AMR sensors as linear a conversion of the local field angle to a sensor signal as possible, the current direction in the AMR resistive strips of a resistor should be tilted by approx. 45 degrees in relation to the radial orientation. This can be achieved, for example, by using radially orientated resistors or possibly also resistors which are tangentially orientated and provided with barber's pole structures. Another method involves tilting the AMR strips themselves by 45 degrees in relation to the local radial direction, which leads to resistive strips in the form of a portion of a logarithmic spiral.

In a preferred embodiment, the four resistors and their reference directions are radially symmetrically distributed around the sensor centre point. In the field of an axial disk magnet with a completely radial field, all the resistors would generate the same signal independently of the magnet angle. In the field of a rotating, elongate magnet, however, the field direction would fluctuate periodically around the radial direction for each of the resistors concerned. The amplitude of this fluctuation of the field direction can be up to 90°, wherein when using AMR sensors, in order to prevent overloading, the amplitude of the fluctuations of the field direction should not substantially exceed the range of +/- 45°. The fields at diametrically opposed sensors are in this case always orientated antiparallel, whereas resistors which are in each case rotated by 90 ° relative to one another in sensor symmetry are subjected to fields which oscillate in opposite directions with the magnet rotation and which ultimately generate a periodic output signal of the sensor with an encoder magnet rotation of 180 ° in the Wheatstone bridge.

The direction in which the magnetoresistive resistor has its maximum resistance is understood to be the reference direction of a magnetoresistive resistor, if a magnetic field acting thereon points in this direction. In the case of AMR sensors this is normally the direction of current flow. In the case of GMR or TMR sensors this is often the direction of magnetisation of a layer with fixed magnetisation.

In a preferred embodiment, the device has a first sensor with four magnetoresistive resistors which are connected to form a Wheatstone bridge and which are arranged in a plane perpendicular to the rotation axis, wherein the four magnetoresistive resistors are arranged around a centre point of the sensor which is located on the rotation axis, wherein the device further has a second sensor with four magnetoresistive resistors which are connected to form a Wheatstone bridge and which are arranged in a plane perpendicular to the rotation axis, wherein the four magnetoresistive resistors are arranged around a centre point of the second sensor which is located on the rotation axis. In a particularly preferred embodiment, the resistors of the first sensor and the resistors of the second sensor are arranged in the same plane. In a preferred embodiment, the orientation of the resistors of the first sensor is rotated by 45 degrees to the orientation of the respectively corresponding resistors of the second sensor.

In a preferred embodiment, the distance of the centre of mass, the centre of gravity or the distance of the centre of volume of a resistor of the sensor from the centre point of the sensor is greater than 0.5 mm. The magnet of the encoder only generates a perpendicular field on the rotation axis itself without any component in the plane of the sensor. Rapidly increasing opposing fields on both sides of the longitudinal axis of the magnet are obtained in the plane of the sensor as the distance in the transverse direction from the longitudinal axis of the magnet increases. Along the longitudinal axis of the magnet (the extent of the magnet perpendicular to the rotation axis) there are significantly smaller field portions in the plane of the sensor than in the transverse direction. It is therefore recommended to arrange the resistors at a distance from the centre point of the sensor (at a distance from the rotation axis). In this manner, the resistors in the plane of the sensor are arranged predominantly in a region in which the strong field orientated on both sides of the longitudinal axis of the magnet in opposing directions is prevalent.

The resistors of the sensor are particularly preferably arranged in a circle around the centre point of the sensor. This is intended to be understood to mean in particular that the centres of mass, centres of gravity or centres of volume of the resistors are arranged in a circle around the centre point of the sensor. Sensor elements which are opposite in the circle are always subjected to a 180 degree opposing field in such an arrangement, such that, in the event of an interconnection between such resistor pairs in a bridge, the desired interference field compensation is achieved.

The invention enables the measurement of rotor angles in an "end of shaft" arrangement with extensive elimination of the influence of external, homogeneous magnetic interference fields. The sensor output signal can consist of a sine and a cosine analogue signal, whereby the signal evaluation can be carried out with one of the numerous commercially available IC solutions. A sine-shaped and a cosine- shaped signal can be generated using two separate Wheatstone bridges which are identically constructed in terms of shape and relative position of the sensitive resistors and which are constructed to be rotated by a quarter of the signal period, i.e. 45°, relative to each other about the rotation axis or the axis of symmetry of the sensor system. The encoder magnet can be made small. The invention enables the specific advantages of magnetoresistive technology (temperature stability, robustness also in terms of magnet ageing) to be harnessed, even in environments exposed to interference fields, without the hitherto unavoidable losses in measurement accuracy.

The invention can be used in particular for motor feedback systems, for starter generators, for electric motors and for establishing steering angles.

The invention will be explained below with reference to drawings which merely depict exemplary embodiments of the invention in greater detail. In the drawings:

Fig. 1 : shows a schematic side view of the device according to the invention,

Fig. 2: shows a schematic top view of a device according to the invention,

Fig. 3: shows a schematic top view of a device according to the invention when an external magnetic field is acting on the device,

Fig. 4: shows a schematic top view of a device according to the invention, in which the resistors of the sensor are formed by resistive strips, the geometric shape of which corresponds to a portion of a logarithmic spiral

Fig. 5: shows a schematic top view of a device according to the invention, in which the resistors of a sensor are formed by resistive strips, the geometric shape of which corresponds to a portion of a logarithmic spiral, and in which two sensors which are rotated by 45° are provided,

Fig. 6: shows a schematic, perspective view of a device according to the invention with an auxiliary magnet,

Fig. 7a,b,c: shows the superimposition of the magnetic fields as occurs when the magnetic field of the magnet (Fig. 7a) is superimposed with the magnetic field of the auxiliary magnet (Fig. 7b) to form a superimposition field (Fig. 7c) and Fig. 8: shows a schematic top view of a device according to the invention, in which the resistors of the sensor are formed by resistive strips, the geometric shape of which corresponds to a portion of a logarithmic spiral and which are interconnected to form a half bridge as a voltage divider.

The device illustrated in Figure 1 has a magnet 2 as an encoder. The magnet 2 is constructed to be rotatable about the rotation axis A. Four magnetoresistive resistors 3, which are connected to form a Wheatstone bridge, of a sensor 4 of the device are arranged in a plane E which is perpendicular to the rotation axis, only two of which resistors 3 are illustrated in the view of Figure 1 .

Figure 1 illustrates, by way of example, on two field lines how the field direction of the magnetic field generated by the magnet 2 changes. A third field line located on the rotation axis A shows that the magnet 2 of the encoder only generates a perpendicular field on the rotation axis A itself without any component in the plane E of the sensor 4.

The top view of Figure 2 shows that the magnet 2 takes the form of a bar magnet, the longitudinal extent of which points in the direction perpendicular to the rotation axis A. In Figure 2, eight field direction arrows are marked in the plane E for visualising the field directions of the magnetic field generated by the magnet 2. It is apparent that, due to the length of the magnet 2 in the plane E, two adjacent regions arise such that the magnetic field generated by the magnet 2 points substantially homogeneously in a first direction in a plane E above the pole of the magnet 2 in a first region and points substantially homogeneously in a direction which is offset thereto by 180 degrees in a second region which is adjacent to the first region.

In Fig. 2, the four resistors 3 and their interconnection to form a Wheatstone bridge are illustrated. It is apparent that pairs of resistors 3 have the same reference direction, that is, the resistors 3 which are arranged on opposite sides of the centre point of the sensor. It is further apparent that the magnetic field generated by the magnet 2 is orientated at least substantially antiparallel in the resistors 3 of a first group, which includes two of the four resistors, and is also orientated at least substantially antiparallel in the resistors 3 of a second group, which includes the remaining two of the four resistors. Two opposing resistors 3 in relation to the centre point of the Wheatstone bridge are part of the first group and the two remaining opposing resistors 3 also in relation to the centre point of the Wheatstone bridge are part of the second group.

Additionally, the magnet 2 and the resistors 3 of the sensor are arranged such that the magnetic field generated by the magnet 2 runs, in two adjacent resistors 3, not radially to the centre point of the Wheatstone bridge, but pivoted by an angular amount, wherein in the case of the one resistor 3 the field direction is pivoted clockwise by the angular amount and in the adjacent resistor 3 the field direction is pivoted anticlockwise by the angular amount.

Figure 3 shows the field direction M of a homogeneous, external magnetic field. By comparing Figure 2 with Figure 3, it is apparent how the effect of the external magnetic field changes the direction of the magnetic field generated by the magnet 2 in the plane E. The interference field rotates the opposing fields in respectively opposing directions (clockwise - anticlockwise). Since the resistors 3 are distributed inside the measuring bridge such that two resistors are always subjected to a field at 180 degrees relative to one another, in the event of the two individual resistance signals being combined, the influence of the interference field compensates for an overall signal which is dependent on field direction.

The embodiment illustrated in Figure 4 shows that the magnets 3 of the sensor 4 can in each case be composed of resistive strips, wherein each resistive strip has the geometric shape of a portion of a geometric spiral, the point of origin of which is located in the centre point of the sensor 4. The individual resistive strips which form a resistor are connected to each other at their ends (for the sake of clarity, not illustrated in greater detail in Fig. 4) to form the resistor, and one end of a resistive strip is connected to the respective opposite end of an adjacent resistive strip. Moreover, Fig. 4 shows that the geometric configuration of the sensor 4 is selected such that the resistors 3 of the sensor 4 can be mapped to each other by a rotation through at least one angle about the rotation axis A, here through 3 angles, that is, 90 °, 180⁰ and 270 °.

Figure 4 further shows connection faces 5 which are suitable for connecting the resistors 3 to an electronic evaluation unit.

The embodiment illustrated in Fig. 5 is based on the embodiment known from Fig. 4. The resistors 3 of the sensor 4 illustrated in Fig. 4 are marked as resistors 3A, the connection faces 5 illustrated in Fig. 4 as connection faces 5A. In addition, in the case of the embodiment of Fig. 5, a further sensor with resistors 3B and connection faces 5B is provided. As is apparent from Fig. 5, the arrangement of the resistors 3B relative to one another corresponds to the arrangement of the resistors 3A to one another, wherein, however, the resistors 3B are arranged in a state rotated by 45° to the resistors 3A with respect to the centre axis of the sensor.

Figure 6 shows the arrangement of an auxiliary magnet 6 on the sensor 4. The auxiliary magnet 6 is axially magnetised and arranged such that, in the substantially bidirectional field of the elongate magnet (Fig. 7a), it superimposes a practically radial field (Fig. 7b) over the sensor and thus ensures that a field 8, albeit weaker but sufficient for ensuring a defined magnetisation of all the sensor strips, is also present (Fig. 7c) in the regions of the sensor which are located over the longitudinal axis of the magnet.

It is also apparent from Fig. 7c) that the magnetic field generated by the magnet 2 and the auxiliary magnet 6 is orientated at least substantially antiparallel in the resistors 3 of a first group, which includes two of the four resistors, and is also orientated at least substantially antiparallel in the resistors 3 of a second group, which includes the remaining two of the four resistors. Two opposing resistors 3 in relation to the centre point of the Wheatstone bridge are part of the first group and the two remaining resistors 3 also opposing each other in relation to the centre point of the Wheatstone bridge are part of the second group.

Additionally, the magnet 2 and the auxiliary magnet 6 and the resistors 3 of the sensor are arranged such that the magnetic field generated by the magnet 2 and the auxiliary magnet 6 runs, in two adjacent resistors 3, not radially to the centre point of the Wheatstone bridge, but pivoted by an angular amount, wherein in the case of the one sensor 3 the field direction is pivoted clockwise by the angular amount and in the adjacent sensor 3 the field direction is pivoted anticlockwise by the angular amount.

Fig. 8 shows a resistor arrangement which, in relation to the shape and arrangement of the resistors 3, corresponds to the arrangement in Fig. 4, in the case of which the individual resistors 3 are not interconnected to form a Wheatstone bridge but to form a half bridge or a simple voltage divider, in the case of which two respectively opposing resistors 3, which act in phase, are directly series-connected and together form one of the two resistors of the voltage divider. Therefore, with this type of circuit, in contrast to the Wheatstone bridge, only three connection faces 5 are also required.

Claims

"Claims:"

1 . A device with an encoder, which has a magnet (2), and a sensor (4), which has four magnetoresistive resistors (3) connected to form a Wheatstone bridge or a half bridge, the position of the encoder relative to the sensor being changeable by rotation about a rotation axis (A),

characterised in that

- the direction of magnetisation of the magnet (3) points in the direction of the rotation axis (A) and

- the resistors (3) of the sensor (4) are arranged in a plane (E) perpendicular to the rotation axis (A) and around a centre point of the sensor (4), which is located on the rotation axis (A).

2. The device according to Claim 1 , characterised in that the magnet (2) is a bar magnet.

3. The device according to Claim 2, characterised in that the length of the bar magnet which points perpendicular to the rotation axis (A) is more than 1 .5 times greater and/or less than 10 times greater than the width of the bar magnet which points perpendicular to the rotation axis (A) and perpendicular to the length of the bar magnet.

4. The device according to any one of Claims 1 to 3, characterised in that the distance from the surface of the magnet (2) which faces the sensor (4) to the plane (E) in which the four magnetoresistive resistors (3) are arranged corresponds to 0.1 times to 2 times the width of the magnet.

5. The device according to any one of Claims 1 to 4, characterised in that the resistors of the sensor are arranged in a point-symmetrical manner around the centre point of the sensor or the geometric configuration of the sensor (4) is selected such that the resistors (3) of the sensor (4) can be mapped to each other by a rotation through at least one angle about the rotation axis (A).

6. The device according to any one of Claims 1 to 5, characterised by an auxiliary magnet (6), the position of which relative to the sensor (4) is unchangeable.

7. The device according to any one of Claims 1 to 6, characterised in that the sensor (4) exhibits the AMR, GMR or TMR effect.

8. The device according to any one of Claims 1 to 7, characterised in that a

resistor (3) of the sensor (4) is formed by a plurality of resistive strips and in that each resistive strip has the geometric shape of a portion of a geometric spiral, the point of origin of which is located at the centre point of the sensor.

9. The device according to any one of Claims 1 to 8, characterised in that the magnet (2) and the resistors (3) of the sensor are arranged such that the magnetic field generated by the magnet (2) is orientated at least substantially antiparallel in the resistors (3) of a first group, which includes two opposing resistors of the four resistors (3), and is also orientated at least substantially antiparallel in the resistors (3) of a second group, which includes the remaining two of the four resistors (3).