Method for calibrating a magnetic field sensor

Abstract

Method for calibrating a magnetic field sensor (1) with a permanent magnet, comprising the steps of: applying a first magnetic field with a first strength (B1) to a magnetic field probe (10) of the magnetic field sensor (1) and reading a first response voltage; applying a second magnetic field with a second strength (B2) to the magnetic field probe (10) of the magnetic field sensor (1) and reading a second response voltage; determining the sensitivity (S) of the magnetic field sensor (1) based on the difference between the first (B1) and the second magnetic field strength (B2) and the difference between the first and the second response voltage; and determining the useful field strength (BH) of the permanent magnet based on the determined sensitivity (S).

Description

[0001] The present invention relates to a method for calibrating magnetic field sensors, in particular magnetic field sensors with permanent magnets. State of the art

[0002] Magnetic field sensors are used in many applications, for example as current sensors, angle sensors, speed sensors, and in similar fields. Because magnetic field sensors are very sensitive, their measurement sensitivity can easily change with temperature, external interference fields, mechanical stress, radiation, and aging effects. Therefore, high measurement accuracy over the lifetime of magnetic field sensors is preferably ensured through individual calibration procedures during operation.

[0003] Magnetic field sensors in the automotive industry typically include Hall effect sensors and magnetoresistive sensors. Permanent magnets are frequently used, for example, to generate a bias voltage for the magnetic field sensors. Permanent magnets can change their field strength over the lifespan of a magnetic field sensor. Therefore, to calibrate magnetic field sensors, it is advantageous to determine and compensate for these changes.

[0004] The publication EP 2 063 229 A1 discloses a magnetic field sensor arrangement with a magnetic field source and a plurality of calibration coils for calibrating the magnetic field sensors.

[0005] The publication DE 10 2004 047 770 A1 discloses a method for calibrating a sensor element by superimposing an external magnetic field to set the optimal operating point of the sensor element.

[0006] Document US 7,746,065 discloses a magnetic field sensor with a magnetic field generator for generating a reference magnetic field. Disclosure of the invention

[0007] A fundamental idea of ​​the invention according to claim 1 is to provide a method for calibrating a magnetic field sensor with a permanent magnet. The method comprises the steps of applying a first magnetic field of a first strength to the magnetic field sensor and reading a first response voltage, and applying a second magnetic field of a second strength to the magnetic field sensor and reading a second response voltage. Furthermore, the sensitivity of the magnetic field sensor is determined based on the difference between the first and second magnetic field strengths and the difference between the first and second response voltages. Subsequently, the useful field strength of the permanent magnet is determined based on the determined sensitivity. This offers the advantage that the useful field strength of the permanent magnet can be easily determined during operation of the magnetic field sensor.

[0008] Further developments and variations of the invention are specified in the dependent claims.

[0009] The above embodiments and further developments can be combined with one another as appropriate. Further possible embodiments, further developments, and implementations of the invention also include combinations of features of the invention described previously or subsequently with regard to the exemplary embodiments, even if not explicitly mentioned. Brief description of the drawings

[0010] Embodiments of the invention are explained below with reference to the accompanying drawings, in which

[0011] Fig. 1 a magnetic field sensor according to an embodiment of the present invention;

[0012] Fig. 2 a diagram for a current ramp according to an embodiment of the present invention; and

[0013] Fig. Figure 3 shows a schematic illustration of a method according to an embodiment of the present invention.

[0014] In the figures, identical and functionally equivalent elements, features, and components are identified by the same reference symbols, unless otherwise stated. It is understood that, for the sake of clarity and comprehensibility, components and elements in the drawings are not necessarily shown to scale.

[0015] Fig. Figure 1 shows a magnetic field sensor 1 according to one embodiment of the present invention. The magnetic field sensor 1 includes a Hall probe 10 and a full bridge circuit with switches 11 , 12 , 13 and 14, which can include, for example, field-effect transistors, although any other type of switch is also possible for forming the full bridge circuit. Depending on the transistor configuration 11 , 12 , 13 and 14 can a Hall current I H different current directions into the Hall probe 10 to be imprinted. In the present example, a Hall current I flows. H from the drain and source terminals of the transistors 11 and 13 through the Hall probe 10 in the direction of the drain or source terminals of the transistors 12 and 14 .

[0016] If the Hall probe 10 When a magnetic field B is applied, a Lorentz force acts on the Hall current I. H mediating charge carriers, and a charge distribution is established that creates a potential difference, the so-called Hall voltage U. H, in a direction perpendicular to the Hall current I H and generated by the magnetic field B. In the present example, there is a magnetic field B 15 perpendicular to the drawing plane of the Fig. 1, which extends out of the plane of the drawing and which represents a potential difference U H mediated from a negatively charged area (indicated by the minus signs) to a positively charged area (indicated by the plus signs).

[0017] The Hall voltage U H can be used as a response voltage to a measuring magnetic field B H through the magnetic field sensor 1 The output is derived from the following relationship: U H (I H ) = S·B H ·I H + U off , where S is the sensitivity of the magnetic field sensor 1 and U off a voltage offset of the Hall probe 10 represents.

[0018] Calibrating an analog magnetic field sensor 1 The task now consists of determining the sensitivity S and the offset voltage U. off to determine.

[0019] The offset voltage U off can be determined, for example, by the direction of the Hall current I H in the Hall probe 10 This is reversed. This results in a Hall voltage U. H The following connection: U H (–I H ) = –S·B H ·I H + U off .

[0020] By adding the determined response voltages for different current directions, but equal magnitudes of the Hall current I H The offset voltage U is determined off to: U off = 0.5·[U H (I H ) + U H (–I H )].

[0021] The change in current direction in the magnetic field sensor 1This can be achieved, for example, by appropriately wiring the transistors. 11 , 12 , 13 and 14 in the full bridge circuit in Fig. 1 can be achieved. However, it is also clear that any other circuit is possible to change the direction of the Hall current I. H in the Hall probe 10 to reverse.

[0022] It may be possible to use the Hall current I H to change the field strength of the measuring magnetic field B H to roughly calculate, thereby allowing conclusions to be drawn about the state of the measuring magnetic field B H The change in the Hall current I can be deduced from the permanent magnet generating it, for example, by its demagnetization. H This can be achieved, for example, by modulating a current ramp for the Hall current I H This can be done. It may also be possible to apply the voltage to the Hall probe. 10for example, to control the Hall current I via charge pumps H to modify. Via the modulation of the Hall current I H will the Hall voltage U H amplified, so that the hysteresis of the Hall probe 10 related to the measuring magnetic field B H is reduced. In particular, it is possible to reduce the Hall current I. H to choose a size large enough that the Hall probe 10 leaves the range of hysteresis, so that its influence on the determination of the measuring magnetic field B H disappears.

[0023] Determining the offset voltage U off and the rough determination of the field strength B H This advantageously occurs without requiring a change in the orientation of the permanent magnet. This offers the advantage that the permanent magnet's configuration can be adjusted instantaneously during operation of the magnetic field sensor. 1 does not need to be changed.

[0024] To calibrate the magnetic field sensor 1 An external known magnetic field B is applied. E via the measuring magnetic field B H superimposed. For this, it is necessary to compare the external magnetic field B. E to imprint with at least two different field strengths, for example with field strengths B1 and B2, in order to determine the sensitivity S of the magnetic field sensor. 1 to determine.

[0025] When an external known magnetic field B is superimposed E via the measuring magnetic field B H The following relationship results for the response voltage: U H (B E , I H ) = S·(B H + B E )·I H + U off .

[0026] External magnetic fields can be generated, for example, by internal coils adjacent to the magnetic field sensor, by external conductor arrangements such as external coils, or by other components carrying high currents. If the magnetic field sensor1 For example, when used in an electric drive, the inverter can be used to generate an external magnetic field. The current applied to the inverter can be controlled in such a way that it produces neither torque nor noise.

[0027] For a coil, the generated magnetic field B E for example proportional to the current I kal in the coil: B E = m·I kal .

[0028] This results in the following for the change in response voltage with a change in the magnetic field B E generating electricity I kal the following connection: you H / dI kal = ΔU H / ΔI kal = S·I H ·m.

[0029] If m is known as the proportionality constant, that is, if the calibration current I can be changed, it can be determined by the change in the calibration current I. kal unambiguously referring to the generated magnetic field B EIt can be deduced by determining the difference in response voltages at two different field strengths B1 and B2 of the external magnetic field B. E It is possible to determine the sensitivity S. From the sensitivity S, the field strength B can then be determined. H Determine the measuring magnetic field: B H = (U H (0, I H ) – U off )·(S·I H ) –1 .

[0030] Determining the instantaneous measuring magnetic field B H , which may be altered, for example, by the aging of the permanent magnet, can be measured in the Hall probe 10 For example, compensation for magnetic interference fields can be carried out.

[0031] For digital magnetic field sensors, it is necessary to know the magnetic field strength B. dThe goal is to determine at which point the digital magnetic field sensor, for example a digital Hall sensor, switches. Reaching the magnetic switching points, for example when used as a current measuring sensor, also depends on the magnetic field strength of a permanent magnet used to operate the digital Hall sensor.

[0032] Fig. Figure 2 shows a diagram for a current ramp according to an embodiment of the present invention. Up to time t1, the response voltage U is d a digital magnetic field sensor at a logically low level 22 When passing through a power ramp I c to generate an external magnetic field B E The field strength of the external magnetic field increases linearly until time t1. At time t1, the first magnetic switching point of the digital magnetic field sensor is reached when the sum of the measuring magnetic field B H and the external magnetic field BE (I c1 ) a first switching magnetic field strength B d1 exceeds this value. At this point, the digital magnetic field sensor switches and outputs the response voltage U. d at a logically high level 21 out of.

[0033] Between times t1 and t2, the current ramp for the current I can be c Conversely, the field strength of the external magnetic field B E decreases until time t2. Due to the hysteresis of the magnetic field probe of the digital magnetic field sensor, the second magnetic switching point at time t2 is only reached when the sum of the measuring magnetic field B H and the external magnetic field B E (I c2 ) a second switching magnetic field strength B d2 The voltage falls below this threshold. At this point, the digital magnetic field sensor switches again and outputs the response voltage U. d back to the logically low level 22 out of.

[0034] By determining the current strengths I c1 and I c2 Knowing the nominal magnetic switching points of the digital magnetic field sensor, the field strength B can be determined. H The measuring magnetic field can be deduced. Advantageously, a rough determination of the measuring magnetic field B is carried out first. H via a variation of the Hall current I described above H , so that calibration of the digital magnetic field sensor can be performed near the magnetic switching points, with the switching of the digital signal consuming the least amount of power.

[0035] Fig. Figure 3 shows a schematic illustration of a method according to an embodiment of the present invention.

[0036] In a first step 31A first magnetic field of initial strength is applied to a magnetic field probe of a magnetic field sensor. A first response voltage from the magnetic field sensor is then read. In a second step... 32 A second magnetic field of a second strength is applied to the magnetic field probe of the magnetic field sensor, and a second response voltage is read out accordingly.

[0037] In a third step 33 A difference between the first and second response voltages, as well as a difference between the first and second magnetic field strengths, is calculated to determine the sensitivity of the magnetic field sensor based on these differences. It may be possible to derive the difference between the first and second magnetic field strengths from a difference between the first and second currents used to generate the first and second magnetic field strengths in a conductor arrangement.

[0038] In a fourth step 34 The usable field strength of the permanent magnet is determined based on the measured sensitivity. This measured field strength can then be used to calibrate the magnetic field sensor, for example by compensating for external interference fields or by adjusting the sensor's operating parameters.

[0039] It may also be possible to calibrate sensor configurations with different magnetic field sensors using the methods described above. For example, a sensor configuration might include a magnetoresistive sensor and one or more digital Hall sensors. The digital Hall sensors can be used in conjunction with the magnetic field sensors described above. Fig.The calibration described in section 2 can be performed. In particular, it is then possible to determine during operation how the hysteresis of the digital Hall sensor relates to the magnetic switching points. This also allows conclusions to be drawn about the aging of a permanent magnet used in the operation of the sensor configuration.

[0040] Furthermore, magnetoresistive magnetic field sensors, such as AMR (anisotropic magnetic resistance), TMR (tunnel magnetic resistance), GMR (gigantic magnetic resistance), or CMR (colossal magnetic resistance) sensors, can also be calibrated using the method described above. Superposition of an external magnetic field over the useful magnetic field of such sensors causes a rotation of the entire magnetic field and thus a change in the response signals of the magnetoresistive magnetic field sensors. If the disturbance is sufficiently known, i.e., its direction and field strength, the useful field strength of a permanent magnet used to operate the magnetoresistive magnetic field sensors can be deduced. QUOTES INCLUDED IN THE DESCRIPTION

[0041] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0042] EP 2063229 A1

[0004] DE 102004047770 A1

[0005] US 7746065

[0006]

Claims

[1] Method for calibrating a magnetic field sensor ( 1 ) with a permanent magnet, using the following steps: Applying a first magnetic field with a first strength (B1) to a magnetic field probe ( 10 ) of the magnetic field sensor ( 1 ) and reading out an initial response voltage; Applying a second magnetic field with a second strength (B2) to the magnetic field probe ( 10 ) of the magnetic field sensor ( 1 ) and reading out a second response voltage; Determining the sensitivity (S) of the magnetic field sensor ( 1 ) based on the difference between the first (B1) and the second magnetic field strength (B2) and the difference between the first and second response voltage; and Determining the usable field strength (B H ) of the permanent magnet based on the determined sensitivity (S). [2] Method according to claim 1, wherein the application of the first and the second magnetic field causes the imprinting of a current (I kal ) in a ladder arrangement. [3] Method according to claim 2, wherein the magnetic field sensor ( 1 ) a digital Hall sensor, with the step: Generating a current ramp (I c ) in the conductor arrangement for calibrating the magnetic switching points ( 21 ; 22 ) of the digital Hall sensor.

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