Device for calibrating a three-dimensional magnetic field sensor and / or for verifying the calibration of a three-dimensional magnetic field sensor

Abstract

Device (100) for calibrating a three-dimensional magnetic field sensor (5) and / or for verifying a calibration of a three-dimensional magnetic field sensor (5), comprising: at least a first receiving device (4) configured to receive at least one magnetic field sensor (5) to be calibrated or checked; at least a second receiving device, configured to receive at least one reference magnetic field sensor (6); at least one measuring section (1) in which several magnets, in particular permanent magnets (8) and / or electric magnets, are arranged such that their magnetic fields (11) are at least partially located in the measuring section (1); at least a drive device (2) which is configured to move the receiving devices (4) and / or the magnets (8) relative to each other along the measuring section (1), and wherein the receiving devices (4) are configured to receive the magnetic field sensors (5, 6) such that the magnetic field sensors (5, 6) are moved on the same trajectory along the measuring section (1).

Description

[0001] The present invention relates to a device for calibrating a three-dimensional magnetic field sensor and / or for checking a calibration of a three-dimensional magnetic field sensor and a corresponding method.

[0002] Three-dimensional magnetic field sensors, especially 3D Hall sensors, are generally known in the state of the art. Before their use, they must be calibrated and the response voltage U H for a respective dimension of a three-dimensional magnetic field sensor for a measuring magnetic field B HIn addition, previously calibrated magnetic field sensors must be checked before use to determine whether the calibration performed was sufficiently accurate for the respective application. Checking the quality of the calibration essentially involves the same steps as for the calibration itself. The magnetic field sensors must be exposed to a defined magnetic field, and it must be checked and compared to what extent the measured / recorded magnetic field values ​​deviate from the actual magnetic field values. The quality of the calibration is considered sufficient if the deviations between the measured magnetic field values ​​and the actual magnetic field values ​​for different magnetic field vectors do not exceed a specified threshold.

[0003] Calibration can be performed, for example, using so-called 3D Helmholtz coils, which can generate defined 3D magnetic field vectors. Without the use of superconductors and helium cooling, however, only low magnetic field strengths of up to approximately 100 mT can be achieved. While significantly higher magnetic fields could be achieved using superconductors and helium cooling, such devices are comparatively expensive and impractical to use.

[0004] In this context, it has become apparent that there is a need to provide a further solution for calibrating and / or verifying the calibration of a three-dimensional magnetic field sensor. In particular, there is a further need to provide a solution that allows high calibration quality and a simple way to verify the calibration of a three-dimensional magnetic field sensor without the need for superconductors or helium cooling.

[0005] It is therefore an object of the present invention to provide a solution for calibrating a three-dimensional magnetic field sensor and / or verifying the calibration of a three-dimensional magnetic field sensor. Furthermore, it is an object of the present invention to provide a solution that allows high calibration quality and a simple way to verify the calibration of a three-dimensional magnetic field sensor without having to use superconductors or helium cooling.

[0006] These and other objects, which will be mentioned upon reading the following description or which may be recognized by a person skilled in the art, are achieved by the subject matter of the independent claims. The dependent claims develop the central idea of ​​the present invention in a particularly advantageous manner.

[0007] A first aspect of the present invention relates to a device for calibrating a three-dimensional magnetic field sensor, in particular a 3D Hall sensor, and / or for checking a calibration of a three-dimensional magnetic field sensor, also in particular a 3D Hall sensor, comprising: at least one first receiving device configured to receive at least one magnetic field sensor to be calibrated or checked; at least one second receiving device configured to receive at least one reference magnetic field sensor; at least one measuring section on which a plurality of magnets, in particular permanent magnets and / or electric magnets, are arranged such that their magnetic fields are at least partially arranged in the measuring section; at least one drive device which is configured to move the receiving devices and / or the magnets relative to one another along the measuring path, and wherein the receiving devices are configured to receive the magnetic field sensors such that the magnetic field sensors are moved on the same trajectory along the measuring path.

[0008] In other words, the present invention proposes using a pre-calibrated reference magnetic field sensor to detect the actual magnetic field values ​​and compare these values ​​with the measured / detected magnetic field values ​​of the additional magnetic field sensors to be calibrated / tested. Preferably, the reference magnetic field sensor has a comparatively high calibration quality, as this determines the calibration quality or testing quality of the device proposed here. To further reduce errors, it is also possible to use multiple reference magnetic field sensors to detect the actual magnetic field values.

[0009] In one embodiment of the device, the first receiving device and second receiving device can be provided on a common holder. The first receiving device can, for example, comprise several fastening and connection options for 3D Hall sensors. For example, the first receiving device can comprise a PCI card (Peripheral Component Interconnect) that can accommodate several magnetic field sensors to be calibrated or tested. Alternatively or additionally, other receiving devices can also be used, for example adapted slots with spring contacts. In addition to the first receiving device, a second receiving device is provided that is configured to accommodate the at least one reference magnetic field sensor. The first and second receiving devices can be designed as separate receiving devices or as a common receiving device.In one embodiment of the device, the common holder / receiving device can be designed as a movable unit that is operatively connected to the drive device and by means of which the receiving devices can be moved along the measuring path. In one example, the receiving devices can be arranged in a carriage that can be moved along the measuring path by the drive device.

[0010] With regard to the arrangement of the magnetic field sensor and the reference magnetic field sensor, it is only important that the magnetic field sensors are arranged in such a way that they are exposed to the same magnetic field lines during the measurement, so that the measured values ​​of the reference magnetic field sensor can be used for calibration or to check the calibration of the other magnetic field sensors.

[0011] As an alternative to the use of 3D Helmholtz coils, which require cooling to generate the magnetic fields, the present proposal is to provide the magnetic fields with permanent magnets and / or electric magnets. This makes it possible to provide the device disclosed here in a comparatively inexpensive and compact manner. Furthermore, the device disclosed here has a comparatively low power requirement, which in practice is in the range of 5 to 30 W. The power requirement for operating devices with 3D Helmholtz coils, however, is significantly higher, amounting to several kW in practice.

[0012] The use of permanent magnets is fundamentally problematic, as it is difficult to provide a homogeneous magnetic field for calibration using permanent magnets. However, this problem is solved by the device disclosed here by mechanically ensuring that the X, Y, Z positions and the orientations (yaw, pitch, roll) of the magnetic field sensors relative to the magnetic field lines are known with a high degree of repeatability. In itself, it is not necessary for the provided magnetic fields to be homogeneous. It is only necessary to record as accurately as possible which magnetic field vectors (B x , B y , B z) the magnetic field sensors are exposed to at the moment of measurement, which can be determined more easily in the case of homogeneous magnetic fields. By using at least one reference magnetic field sensor, which is exposed to the same magnetic field vectors, it is also known which magnetic field vectors (B x , B y , B z ) the magnetic field sensors are exposed to at the moment of measurement. The magnets are preferably arranged along the measuring section in such a way that their magnetic field lines are oriented differently from each other.

[0013] In one embodiment of the device, the magnets can be arranged stationary along the measuring section, forming a gap through which the measuring section passes. In this embodiment, the holding devices are moved along the measuring section by means of the drive device, and thus also through the gap. Alternatively, the holding devices can be arranged stationary, and the magnets are moved along the measuring section by means of the drive device. The only decisive factor is that the magnetic field sensors are moved relative to the magnetic fields of the magnets.

[0014] In one embodiment of the device, the measuring section can be designed as a straight section, as a horizontally arranged circular section or as a vertically arranged circular section or as a combination thereof.

[0015] The magnets can be of different sizes and shapes, thus generating different magnetic field patterns in their local environment. Horseshoe magnets, for example, can also be used here. Additionally, the magnets can be arranged in rotatable holders. The exact position of the magnets can be detected, for example, using a stepper motor and an encoder. This makes it possible to make the device even more compact and, for example, reduce the length of the measuring section / linear guide.

[0016] In one embodiment of the device, the device can further comprise a heating device, wherein the heating device is preferably provided by one or more infrared heaters arranged along the measuring section. This makes it possible to set a defined and constant temperature along the measuring section. This is advantageous because the magnetic fields of the permanent magnets are temperature-dependent. Furthermore, in practice, the calibration should cover a temperature range between 18° and 50° C. Such temperature differences can occur, for example, during longer MR measurements. Furthermore, magnetic field sensors can exhibit temperature-related drift, which can also be corrected. The heating device can be used to set the temperature required for the measurements.In one embodiment of the device, the device can further comprise a temperature-insulating housing in which at least the measuring section is arranged. This allows the device or the heating device to be shielded from the environment. Furthermore, this can reduce the energy consumption for the heating device.

[0017] In one embodiment of the device, the device can further comprise at least one interface configured to acquire sensor data / values ​​of the at least one magnetic field sensor to be calibrated or tested and of the at least one reference magnetic field sensor, while the recording devices and / or the magnets are moved relative to one another along the measuring path. This interface is preferably a PCI interface, with which the measured values ​​of the magnetic field sensors can be read out. In one embodiment, the PCI interface is used as a mechanical holder with the spring-loaded galvanic contacts. The use of a PCI interface is particularly advantageous because, once arranged on a common PCI comb, the magnetic field sensors can be held mechanically very stably and with high precision.Furthermore, a PCI interface provides sufficient contact points. Regarding communication, the present invention is not limited to the use of the PCI protocol; the I2C (Inter-Integrated Circuit) protocol can be used, for example.

[0018] In one example, the device further comprises a control unit, for example in the form of a computer unit, which is preferably configured to control the drive device, acquire, store, and / or evaluate the sensor data. Furthermore, it is possible for the control unit / computer unit to transfer calibration parameters or changed / new calibration parameters to a storage device of the magnetic field sensors.

[0019] In one embodiment of the device, the measuring section can have a length between 1.0 and 4.0 m, preferably between 1.5 and 2.5 m and particularly preferably 2 m.

[0020] In one embodiment of the device, the device can further comprise a glass scale, preferably with a digital readout, which is configured to detect the position of the receiving devices and / or the magnets. In one embodiment of the device, the drive device can comprise at least one stepper motor or a servo motor. By using such a glass scale, it is possible to detect the position of the receiving devices and / or the magnets relative to one another with high accuracy. High accuracy in detecting the position of the receiving devices and / or the magnets relative to one another also ensures that the measured values ​​detected by the at least one reference magnetic field sensor correspond to the measured values ​​of the magnetic field sensors for the same position.In the example where the recording devices are arranged in a movable carriage, the glass scale can detect the carriage position with a very high repeatability.

[0021] A further aspect of the present invention relates to a method for calibrating a three-dimensional magnetic field sensor and / or a method for checking a calibration of a three-dimensional magnetic field sensor, comprising: Providing a device as described herein for calibrating a three-dimensional magnetic field sensor or for checking the calibration of such a magnetic field sensor; Arranging at least one magnetic field sensor to be calibrated or checked in the first receiving device; Arranging at least one reference magnetic field sensor in the second receiving device; Moving the receiving devices and / or the magnets relative to one another along the measuring section by means of the at least one drive device; Detecting sensor values ​​of the at least one magnetic field sensor and the at least one reference magnetic field sensor while moving the receiving devices and / or the magnets relative to each other; Checking the calibration or calibrating the at least one magnetic field sensor based on the sensor values ​​of the at least one reference magnetic field sensor.

[0022] In one embodiment of the method, the step of checking the calibration of the magnetic field sensor or calibrating the magnetic field sensor may further comprise: Output of difference values ​​of corresponding sensor values ​​of the at least one magnetic field sensor and of sensor values ​​of the at least one reference magnetic field sensor.

[0023] For example, an error sum can be derived from the difference values ​​to evaluate the calibration quality. The error sum is calculated from a standardized number of measurement positions or measurements. The calibration quality can then be specified, for example, by the following relationship: KG=1 / FS where: K G the calibration quality; F S an error sum for a standardized number of measuring positions is

[0024] If it is determined that the calibration quality of a magnetic field sensor is below a specified minimum value for the calibration quality, and the magnetic field sensor is therefore not calibrated with sufficient accuracy, the magnetic field sensor can be rejected or the measured values ​​can be used to adjust the calibration. For example, a suitable calibration algorithm can be used here. Optimization algorithms that maximize the calibration quality by adjusting the parameter values ​​or minimize the error sums, such as a simplex algorithm or a Levenberg-Marquardt algorithm, are particularly suitable for this purpose. However, the present invention is not limited to the use of these algorithms; other algorithms can also be used.

[0025] The calibration quality can be further improved by using the measurements to optimize the parameter values ​​of the magnetic field sensors and, for example, by determining an optimum for the 3 offset values, the 3 scaling values ​​and the 3 orthogonality factors by determining at which parameter values ​​the error sum is minimal.

[0026] The device and method proposed here provide a comparatively inexpensive, energy-efficient, compact, and thus easily applicable solution for calibrating and / or verifying the calibration of a three-dimensional magnetic field sensor. In particular, this solution does not require the use of superconductors or helium cooling.

[0027] All embodiments described herein can be combined with one another, unless explicitly stated otherwise. Further features, advantages, and possible applications of the present invention will become apparent from the following description, the exemplary embodiment, and the figures. These show: Fig. 1 shows a side view of a device according to the invention for calibrating a three-dimensional magnetic field sensor and / or for checking a calibration of a three-dimensional magnetic field sensor; Fig. 2 shows a plan view of the Fig. 1 shown device; and Fig. 3 shows a schematic representation of a method according to the invention for calibrating a three-dimensional magnetic field sensor and / or for checking a calibration of a three-dimensional magnetic field sensor.

[0028] The Fig. 1 shows a side view of a device 100 for calibrating three-dimensional magnetic field sensors. Fig. 2 shows a plan view of the Fig. 1. Identical parts are therefore provided with the same reference numerals.

[0029] The device 100 comprises a measuring section 1, here in the form of a linear axis 1. The linear axis 1 is operatively engaged with a stepper motor 2, which is configured to move a carriage 3 along the linear axis 1. The device 100 further comprises a first receiving device 4, here in the form of a PCI card 4, which accommodates several magnetic field sensors 5 to be calibrated or tested. Furthermore, a slot (not shown) is provided to accommodate a reference magnetic field sensor 6 as a second receiving device. The magnetic field sensors 5, 6 are preferably 3D Hall sensors.

[0030] The device further comprises a holding device 7 with which various permanent magnets 8 are held. As shown in the Fig. 1 and Fig. 2, the carriage 3 with the magnetic field sensors 5 and the reference magnetic field sensor 6 can be guided along the linear axis 1 in such a way (indicated by the arrow 9) that the magnetic field sensors 5 and the reference magnetic field sensor 6 can be guided through a gap 10 between the halves of the permanent magnets 8. As shown in Fig. As can be clearly seen in Figure 2, the permanent magnets 8 are arranged such that their magnetic field lines 11 are oriented differently from one another. The device 100 further comprises a glass scale 12 provided with a digital readout. In particular, the use of such a glass scale 12 makes it possible to detect the position of the carriage 3 with high accuracy, so that the measured values ​​of the reference magnetic field sensor 6 can be assigned to the measured values ​​of the magnetic field sensors 5 with high positional accuracy.

[0031] In the example shown, the reference magnetic field sensor 6 is the first to be guided through the gap 10 between the permanent magnets 8 along the linear axis 1. The reference magnetic field sensor 6 measures the magnetic flux density in the three spatial directions at the respective position, which can be determined with high accuracy by the glass scale 12. These reference measured values ​​can, for example, be stored as a continuously growing reference table, wherein the reference table contains corresponding entries for B x , B y , B z and the assigned position may include.

[0032] Due to their spatial arrangement on the PCI card 4, the magnetic field sensors 5 are slightly delayed, but due to the same spatial position as the reference magnetic field sensor 6, they are guided along the linear axis 1 through the gap 10 between the permanent magnets 8. Corresponding measured values ​​to the reference measured values ​​are recorded there. These measured values ​​can in turn be stored in a continuously growing measured value table, with the measured value table containing corresponding entries for B x , B y , B z and the assigned position may include.

[0033] Using the reference table and the measured value table, differential values ​​can be determined for the respective measuring positions by subtracting the measured values ​​of the reference magnetic field sensor 6 from the measured values ​​of a respective magnetic field sensor 5. From these differential values, an error sum can then be derived, for example, in order to evaluate the calibration quality of a magnetic field sensor 5. The error sum is calculated, for example, from a standardized number of measuring positions or measurements. The calibration quality can then be specified, for example, by the following relationship: KG=1 / FS where: K G the calibration quality; F S an error sum for a standardized number of measuring positions is

[0034] If it is determined that the calibration quality of a magnetic field sensor 5 is below a predetermined minimum value for the calibration quality, and the magnetic field sensor 5 is therefore not calibrated with sufficient accuracy, the magnetic field sensor 5 can be rejected or the measured values ​​can be used to adjust the calibration of the magnetic field sensor 5. For example, a suitable calibration algorithm can be used here. Optimization algorithms that maximize the calibration quality by adjusting the parameter values ​​or minimize the error sums, such as a simplex algorithm or a Levenberg-Marquardt algorithm, are particularly suitable for this purpose. However, the present invention is not limited to the use of these algorithms; other algorithms can also be used.It is also possible to improve the calibration quality by using the measurements to optimize the parameter values ​​of the magnetic field sensors 5. For example, an optimum for the three offset values, the three scaling values, and the three orthogonality factors can be determined by determining the parameter values ​​at which the error sum is minimal. Essentially the same steps are necessary when calibrating a magnetic field sensor 5. Here, too, a comparison is made of the values ​​recorded by a magnetic field sensor 5 compared to the reference magnetic field sensor 6. Based on the recorded deviations, a calibration or adjustment of the parameter values ​​of a magnetic field sensor 5 can be performed.

[0035] Fig. 3 shows a schematic representation of a method for calibrating a three-dimensional magnetic field sensor 5 and / or for checking a calibration of a three-dimensional magnetic field sensor 5, wherein the method is described with reference to the method described in the Fig. 1 and Fig. 2 shown embodiment is explained.

[0036] In a first step 20, the device 100 for calibrating a three-dimensional magnetic field sensor 5 and / or for checking a calibration of a three-dimensional magnetic field sensor 5 is provided. In a further step 21, at least one magnetic field sensor 5 to be calibrated or checked is arranged in a first receiving device 4. In a further step 22, at least one reference magnetic field sensor 6 is arranged in a second receiving device (not shown). In a further step 23, the receiving devices 4 and / or the magnets 8 are moved relative to one another along a measuring path / linear axis 1 by means of the at least one drive device 2. During the movement of the receiving devices 4 and / or the magnets 8, sensor values ​​of the at least one magnetic field sensor 5 and the at least one reference magnetic field sensor 6 are recorded in a step 24.The recorded sensor values ​​of the magnetic field sensor 5 and the at least one reference magnetic field sensor 6 are used in a step 25 to check the calibration of the magnetic field sensor 5 or to calibrate the at least one magnetic field sensor 5. Optionally, in addition to checking the calibration of the magnetic field sensor or the calibration of the magnetic field sensor, step 25 further comprises the output 26 of difference values ​​of corresponding sensor values ​​of the at least one magnetic field sensor 5 and the reference magnetic field sensor 6.

[0037] The present invention is not limited to the embodiment described above as long as it is encompassed by the subject matter of the following claims.

[0038] Additionally, it should be noted that the terms "comprising" and "having" do not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. Furthermore, it should be noted that features or steps described with reference to the above embodiments may also be used in combination with other features.

[0039] Furthermore, it is pointed out that regardless of the grammatical gender of a particular term, persons with male, female or other gender identity are included.

Claims

[1] Device (100) for calibrating a three-dimensional magnetic field sensor (5) or for checking a calibration of a three-dimensional magnetic field sensor (5), comprising: at least one first receiving device (4) configured to receive at least one magnetic field sensor (5) to be calibrated or checked; at least one second receiving device, configured to receive at least one reference magnetic field sensor (6); at least one measuring section (1) on which a plurality of magnets (8), in particular permanent magnets (8) and / or electric magnets, are arranged such that their magnetic fields (11) are at least partially arranged in the measuring section (1); at least one drive device (2) which is designed to move the receiving devices (4) and / or the magnets (8) relative to one another along the measuring section (1), and wherein the receiving devices (4) are designed to receive the magnetic field sensors (5, 6) in such a way that the magnetic field sensors (5, 6) are moved on the same trajectory along the measuring section (1). [2] Device (100) according to claim 1, wherein the first receiving device (4) and second receiving device are provided on a common holder (3). [3] Device (100) according to claim 1, wherein the common holder (3) is designed as a movable unit which is operatively connected to the drive device (2) and is movable along the measuring section (1) by the drive device (2). [4] Device (100) according to one of the preceding claims, wherein the magnets (8) are arranged on the measuring section (1) in such a way that their magnetic field lines (11) are oriented differently from one another. [5] Device (100) according to one of the preceding claims, wherein the magnets (8) are arranged stationary on the measuring section (1) and form a gap (10) through which the measuring section (1) leads. [6] Device (100) according to one of the preceding claims, wherein the measuring section (1) is designed as a straight section (1), as a horizontally arranged circular section or as a vertically arranged circular section or as a combination thereof. [7] Device (100) according to one of the preceding claims, wherein the device (100) further comprises a heating device, wherein the heating device is preferably provided by one or more infrared heaters arranged along the measuring section (1). [8] Device (100) according to one of the preceding claims, wherein the device (100) further comprises a temperature-insulating housing in which at least the measuring section (1) is arranged. [9] Device (100) according to one of the preceding claims, wherein the device (100) further comprises at least one interface which is configured to acquire sensor data / values ​​of the at least one magnetic field sensor (5) to be calibrated or checked and of the at least one reference magnetic field sensor (6) while the receiving devices (4) and / or the magnets (8) are moved relative to one another along the measuring path (1). [10] Device (100) according to one of the preceding claims, wherein the measuring section (1) has a length between 1.0 and 4.0 m, preferably between 1.5 and 2.5 m and particularly preferably 2 m. [11] Device (100) according to one of the preceding claims, wherein the device (100) further comprises a glass scale (12) which is configured to detect the position of the receiving devices (4) and / or the magnets (8) directly or indirectly. [12] Device (100) according to one of the preceding claims, wherein the drive device (2) comprises at least one stepper motor (2) or a servo motor. [13] Device (100) according to one of the preceding claims, wherein the device (100) does not comprise superconductors or helium cooling. [14] Method for calibrating a three-dimensional magnetic field sensor (5) and / or for checking a calibration of a three-dimensional magnetic field sensor (5), comprising: Providing (20) a device (100) according to one of claims 1 to 13; Arranging (21) at least one magnetic field sensor (5) to be calibrated or checked in the first receiving device (4); Arranging (22) at least one reference magnetic field sensor (6) in the second receiving device; Moving (23) the receiving devices and / or the magnets relative to one another along the measuring section (1) by means of the at least one drive device (2); Detecting (24) sensor values ​​of the at least one magnetic field sensor (5) and the at least one reference magnetic field sensor (6) while moving the receiving devices (4) and / or the magnets (8) relative to one another; Checking (25) the calibration or calibrating the at least one magnetic field sensor (5) based on the sensor values ​​of the at least one reference magnetic field sensor (6). [15] The method of claim 14, wherein the step (25) of checking the calibration of the magnetic field sensor or calibrating the magnetic field sensor further comprises: Output (26) of difference values ​​of corresponding sensor values ​​of the at least one magnetic field sensor (5) and sensor values ​​of the at least one reference magnetic field sensor (6).

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