Method for determining the magnetization direction of a Wiegand wire and Wiegand sensor device

Abstract

The present invention relates to a method for determining the magnetization direction (M) of a Wiegand wire (11), wherein a test current (Ip) that increases with time (t) is applied to a sensor coil (12) surrounding the Wiegand wire (11), a sensor coil voltage (US) applied to the sensor coil (12) is detected during the application of the test current (Ip), and the magnetization direction (M) is determined by comparing the sensor coil voltage (US) detected during the application of the test current (Ip) with a reference voltage (UR) that increases simultaneously with the test current (Ip), the reference voltage (UR) increasing from a defined start reference voltage value (URa) to a defined end reference voltage value (URe). ​​The present invention also relates to a Wiegand sensor device (100) comprising a Wiegand wire (11) and a sensor coil (12) surrounding the Wiegand wire (11), and having a magnetization direction determination unit (3) configured to perform the method for determining the magnetization direction (M) of a Wiegand wire (11) according to the present invention.

Description

[Technical Field]

[0001] The present invention relates to a method for determining the magnetization direction of a Wiegand wire by applying a test current that increases with time to a sensor coil surrounding the Wiegand wire and detecting a sensor coil voltage appearing in the sensor coil during application of the test current.The present invention also relates to a Wiegand sensor device comprising a Wiegand wire and a sensor coil surrounding the Wiegand wire. [Background technology]

[0002] Wiegand wires in the sense of this application, also known as impulse wires, generally have a hard magnetic sheath and a soft magnetic core, or vice versa. Under the influence of an external magnetic field, the magnetization direction of the Wiegand wire suddenly reverses, thereby generating a short Wiegand voltage pulse in a sensor coil radially surrounding the Wiegand wire, which can be detected via the two ends of the sensor coil. This effect is called the Wiegand effect and is well known in the prior art.

[0003] Knowing the magnetization direction of the Wiegand wire is important for performing synchronization between a Wiegand-sensor-based revolution counter sensor unit, also known as a multi-turn sensor unit, and a fine position sensor unit, also known as a single-turn sensor unit, e.g. in a rotary encoder.

[0004] Against this background, EP 1 565 755 B1 discloses a method for determining the magnetization direction of a Wiegand wire, in which an increasing test current is applied to a sensor coil surrounding the Wiegand wire, and the sensor coil voltage appearing in the sensor coil during the application of the test current is detected and evaluated. Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to enable a relatively simple and reliable determination of the magnetization direction of a Wiegand wire. [Means for solving the problem]

[0006] This object is achieved by a method for determining the magnetization direction of a Wiegand wire having the features of claim 1.

[0007] In the method for determining the magnetization direction of a Wiegand wire according to the present invention, a test current that increases over time is applied to a sensor coil surrounding the Wiegand wire to generate a test magnetic field acting on the Wiegand wire. Preferably, the test current increases continuously, i.e., continuously, from zero according to a defined test current curve. It is particularly preferred that the test current increase linearly with a defined gradient. The test current curve can be defined, for example, based on the results of laboratory tests. It is also conceivable to define different test current curves for different measurement conditions, for example, different temperatures.

[0008] If the magnetization direction is reversed by the generated test magnetic field, a so-called Wiegand voltage pulse is induced in the sensor coil by the Wiegand wire. The occurrence or non-occurrence of the Wiegand voltage pulse can therefore be used to determine whether the magnetization direction of the Wiegand wire was in the same direction as the test magnetic field or in the opposite direction to the test magnetic field before the test current was applied.

[0009] Therefore, in the method for determining the magnetization direction of a Wiegand wire according to the invention, the sensor coil voltage appearing in the sensor coil is detected and evaluated during application of the test current.

[0010] To determine whether a Wiegand voltage pulse is induced in the sensor coil and, therefore, the Wiegand magnetization direction, the sensor coil voltage detected during the application of the test current is compared with a reference voltage that preferably increases uniformly simultaneously with the test current, increasing from a defined start reference voltage value to a defined end reference voltage value. The start and end reference voltage values ​​can be determined directly or indirectly, for example, via a predetermined mathematical relationship. Preferably, the reference voltage increases continuously, particularly preferably linearly. For example, the end reference voltage value can be defined indirectly via a predetermined slope of the reference voltage. The comparison of the sensor coil voltage with the reference voltage is preferably performed by suitable hardware, for example, by a comparator that compares the sensor coil voltage detected at the sensor coil with a reference voltage signal that increases simultaneously with the test current. However, the comparison of the sensor coil voltage with the reference voltage can also, in principle, be performed by software, where a sensor coil voltage variable representing the detected sensor coil voltage is compared with a reference voltage variable that increases simultaneously with the test current.

[0011] The magnetization direction is determined depending on whether the sensor coil voltage exceeds the reference voltage during the application of the test current, i.e., whether it is greater in magnitude than the reference voltage. If the sensor coil voltage exceeds the reference voltage, a Wiegand voltage pulse is induced, and the Wiegand wire is therefore assumed to have had a magnetization direction opposite to the test magnetic field before the test current was applied. In this case, the magnetization direction is set to the first magnetization direction value. On the other hand, if the sensor coil voltage does not exceed the reference voltage, no Wiegand voltage pulse is induced, and the Wiegand wire is therefore assumed to have had a magnetization direction in the same direction as the test magnetic field before the test current was applied. In this case, the magnetization direction is set to the second magnetization direction value. To avoid erroneous determination of the magnetization direction due to voltage fluctuations, it may be advantageous to provide a specified minimum exceedance time as the criterion for exceeding the reference voltage, i.e., to set the magnetization direction to the first magnetization direction value only if the sensor coil voltage exceeds the reference voltage for the minimum exceedance time. The determined magnetization direction value is typically stored in memory. However, it is also conceivable that the magnetization direction values ​​are not stored but merely processed, for example, the rotation count value can be determined or corrected based on the determined magnetization direction value.

[0012] The method according to the invention therefore allows a simple and reliable determination of the magnetization direction of a Wiegand wire.

[0013] The electrical properties of the sensor coil, in particular its electrical resistance, are generally temperature dependent, and as a result, the voltage drop across the sensor coil caused by applying a test current to the sensor coil is also temperature dependent according to Ohm's law. Therefore, in the method according to the present invention, the temperature is preferably detected and a start reference voltage value and / or a stop reference voltage value are defined based on the detected temperature, in order to enable reliable determination of the magnetization direction of the Wiegand wire independently of the current temperature.

[0014] In a preferred embodiment of the method according to the present invention, calibration is performed before applying a test current. A calibration current, preferably increasing with time, is applied to the sensor coil, the calibration current having a maximum calibration current value corresponding to 1 / N times the maximum test current value of the test current, during which the sensor coil voltage is detected. The end reference voltage value until which the reference voltage is increased is defined as the sum of the start reference voltage value and N times the maximum sensor coil voltage value detected during the application of the calibration current. Therefore, the end reference voltage value is always greater than the maximum voltage drop caused by the test current in the sensor coil, thereby reliably preventing the sensor coil voltage caused by the test current alone from exceeding the reference voltage, regardless of the current measurement conditions.

[0015] Preferably, the sensor coil voltage detected during application of the calibration current is compared to a constant calibration reference voltage value, preferably slightly greater than the product of the maximum calibration current value and the electrical resistance of the sensor coil, to determine whether a Wiegand voltage pulse was induced in the sensor coil during calibration. If the sensor coil voltage detected during application of the calibration current exceeds the calibration reference voltage value, a Wiegand voltage pulse is induced, and the magnetization direction is assumed to be set to the first magnetization direction value. To avoid erroneous determination of the magnetization direction due to voltage fluctuations, it may also be advantageous to specify a specified minimum exceedance time as the criterion for exceeding the value. To avoid so-called incomplete pulses, a test current is preferably applied to the sensor coil after calibration to fully magnetize the Wiegand wire, even though the magnetization direction is already known.

[0016] The above-mentioned object is also achieved by a Wiegand sensor device having the features of claim 5.

[0017] The Wiegand sensor device according to the invention comprises a Wiegand wire and a sensor coil radially surrounding the Wiegand wire. Such an arrangement of a Wiegand wire and a sensor coil is known from the prior art and is also called a Wiegand sensor.

[0018] According to the invention, the Wiegand sensor device comprises a magnetization direction determining unit electrically connected to the sensor coil and configured to perform the method for determining the magnetization direction of a Wiegand wire according to the invention.

[0019] In particular, the magnetization direction determining unit is configured to apply a test current to the sensor coil that increases over time and detect a sensor coil voltage appearing in the sensor coil during this time, To this end, the magnetization direction determining unit typically comprises a controllable current source designed in any known manner as well as a voltage measuring device designed in any known manner.

[0020] Furthermore, the magnetization direction determination unit is configured to determine the magnetization direction of the Wiegand wire by comparing the sensor coil voltage detected during the application of the test current with a reference voltage that increases simultaneously with the test current and that increases from a defined start reference voltage value to a defined end reference voltage value, as already described above for the method according to the invention.

[0021] The magnetization direction determination unit may generally be implemented using any combination of hardware and / or software, however, the magnetization direction determination unit is preferably implemented entirely in a single appropriately structured and programmed integrated circuit (IC), in particular in a so-called application specific integrated circuit (ASIC).

[0022] The Wiegand sensor device according to the invention allows for a simple and reliable determination of the magnetization direction of a Wiegand wire by means of a magnetization direction determination unit adapted to carry out the method according to the invention.

[0023] In a preferred embodiment, the Wiegand sensor device according to the invention comprises a temperature sensor, and the magnetization direction determining unit comprises a temperature compensation module configured to define the start reference voltage value and / or the end reference voltage value based on the temperature detected by the temperature sensor.

[0024] Preferably, the temperature compensation module comprises a reference value memory, also known as a look-up table, in which several temperature-specific start and / or end reference voltage values ​​assigned to different temperatures are stored, which allows for a simple temperature-dependence definition of the start and / or end reference voltage values, without requiring a particularly powerful calculation unit for this.

[0025] Alternatively or additionally, the temperature compensation module may also include a calculation algorithm for the temperature-dependent calculation of the start and / or end reference voltage values ​​by the calculation unit, which allows the start and / or end reference voltage values ​​to be defined in dependence on temperature, without requiring a particularly large memory. In this case, it is conceivable, for example, that the calculation algorithm for calculating the start and / or end reference voltage values ​​uses one or more reference voltage values ​​stored in the reference value memory.

[0026] In order to enable a particularly reliable determination of the magnetization direction of the Wiegand wire, in a preferred embodiment of the Wiegand sensor device according to the invention, the magnetization direction determination unit comprises a calibration module configured to perform a calibration before the application of the test current, as described above. In particular, the calibration module is configured to apply a calibration current to the sensor coil, which preferably increases with time, with a maximum calibration current value corresponding to 1 / N times the maximum test current value, detect the sensor coil voltage during the application of the calibration current, and define an end reference voltage value as the sum of a start reference voltage value and a maximum sensor coil voltage value detected during the application of the calibration current.

[0027] Preferably, the calibration module is configured to compare the sensor coil voltage detected during application of the calibration current with a constant calibration reference voltage value that is preferably slightly greater than the product of the maximum calibration current value and the electrical resistance of the sensor coil, and is configured to prevent the test current from being applied and to set the magnetization direction to the first magnetization direction value if the sensor coil voltage detected during application of the calibration current exceeds the calibration reference voltage value.

[0028] Embodiments of the present invention are described below with reference to the accompanying drawings. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a schematic diagram of a Wiegand sensor device according to the present invention; [Figure 2] FIG. 2 is a schematic diagram of a magnetization direction determination unit of the Wiegand sensor device shown in FIG. 1; [Figure 3] 2 is an exemplary time curve of a test current applied to a sensor coil of the Wiegand sensor device shown in FIG. 1 when a Wiegand voltage pulse is induced in the sensor coil, the sensor coil voltage detected during application of the test current, and a reference voltage. [Figure 4] 4 shows a time curve of the test current, the sensor coil voltage detected during application of the test current, and the reference voltage, corresponding to FIG. 3, when no Wiegand voltage pulse is induced in the sensor coil. [Figure 5] FIG. 2 is a schematic diagram of an alternative magnetization direction determination unit of the Wiegand sensor arrangement shown in FIG. 1; [Figure 6] 2 is an exemplary time curve of a calibration current applied to a sensor coil of the Wiegand sensor device shown in FIG. 1, a sensor coil voltage detected during application of the calibration current, and a calibration reference voltage value when no Wiegand voltage pulse is induced in the sensor coil. [Figure 7] 10 shows time curves of the calibration current and sensor coil voltage detected during application of the calibration current, as well as the calibration reference voltage value, when a Wiegand voltage pulse is induced in the sensor coil. DETAILED DESCRIPTION OF THE INVENTION

[0030] 1 shows a Wiegand sensor device 100 having a Wiegand sensor 1, which comprises a Wiegand wire 11, a sensor coil 12 radially surrounding the Wiegand wire 11, and a circuit device 2 electrically connected to the sensor coil 12. The circuit device 2 comprises an ASIC (Application Specific Integrated Circuit) 21, a microcontroller 22, and a memory 23, which together constitute a magnetization direction determination unit 3.

[0031] The ASIC 21 includes a temperature sensor 211, a controlled current source circuit 212, a reference voltage generating circuit 213, and a comparison circuit 214. The microcontroller 22 includes a software-implemented temperature compensation module 221 that includes the temperature T detected by the temperature sensor 211.

[0032] The temperature compensation module 221 is configured to define a current start reference voltage value URa and a current end reference voltage value URe based on the temperature T.

[0033] The temperature compensation module 221 includes a reference value memory 2211 that stores several temperature-specific start reference voltage values ​​URa(T1) to URa(Tn) assigned to several different temperatures T1 to Tn, and several temperature-specific end reference voltage values ​​URe(T1) to URe(Tn) assigned to several different temperatures T1 to Tn. The temperature compensation module 221 further includes a calculation algorithm 2212 that is configured to calculate a current start reference voltage value URa and a current end reference voltage value URe based on the temperature T and the temperature-specific start reference voltage value URa(T1)-URa(Tn) and the temperature-specific end reference voltage value URe(T1)-URe(Tn) stored in the reference value memory 2211.

[0034] It should be noted at this point that the temperature compensation module 221 can alternatively comprise only the reference value memory 2211 or only the calculation algorithm 2212. In a first case, the temperature compensation module 221 is configured to determine the current start reference voltage value URa and the current end reference voltage value URe by reading a temperature-specific start reference voltage value URa(T) assigned to a temperature T and a temperature-specific end reference voltage value URe(T) assigned to a temperature T from the reference value memory 2211. In a second case, the calculation algorithm 2212 is configured to calculate the current start reference voltage value URa and the current end reference voltage value URe based on the temperature T only.

[0035] It should also be noted that the temperature compensation module 221 may also be configured to define only the current start reference voltage value URa or only the current end reference voltage value URe, in which case the respective other reference voltage values ​​URa and URe are constants.

[0036] The reference voltage generation circuit 213 has a current start reference voltage value URa and a current end reference voltage value URe, and is configured to generate a reference voltage UR that increases linearly with time t from the current start reference voltage value URa to the current end reference voltage value URe.

[0037] The controlled current source circuit 212 is configured to apply a test current Ip to the sensor coil 12 that increases linearly with time t, with a maximum test current value Ip-max specified via a maximum test current parameter PIp-max.

[0038] The comparison circuit 214 is provided with a sensor coil voltage US and a reference voltage UR. The comparison circuit 214 compares the sensor coil voltage US with the reference voltage UR to determine a magnetization direction value M indicating the magnetization direction of the Wiegand wire 11, and writes the magnetization direction value M to the memory 23. In particular, the comparison circuit 214 is configured to write a first magnetization direction value M=1 to the memory 23 if the sensor coil voltage US exceeds the reference voltage UR for a specified minimum exceedance time, and to write a second magnetization direction value M=0 to the memory 23 if not.

[0039] Figure 3 shows, as an example, the time curves of the test current Ip, the sensor coil voltage US, and the reference voltage UR when a Wiegand voltage pulse WP is induced in the sensor coil 12. Figure 4 shows the time curves of the test current Ip, the sensor coil voltage US, and the reference voltage UR from Figure 3, but without the Wiegand voltage pulse WP induced in the sensor coil 12.

[0040] Figure 5 shows an alternative magnetization direction determination unit 3' according to the invention, which is constituted by an alternatively configured microcontroller 22' for the circuit arrangement 2 of Figure 1. The microcontroller 22' differs from the microcontroller 22 of Figure 2 mainly in that, instead of the temperature compensation module 221, the microcontroller 22 comprises a calibration module 222 for defining the current start reference pressure value URa and the current end reference pressure value URe.

[0041] The calibration module 222 includes a calibration coefficient memory 2221 in which a calibration coefficient N is stored, a software-implemented calibration parameter determination module 2222, a software-implemented calibration sensor coil detection module 2223, and a software-implemented calibration evaluation module 2224.

[0042] The calibration parameter determination module 2222 is configured to determine a maximum calibration current parameter PIk-max corresponding to 1 / N times the maximum test current parameter PIp-max based on the calibration factor N, and the calibration parameter determination module 2222 is further configured to determine a calibration reference voltage value URk that is preferably slightly greater than the product of the maximum calibration current parameter PIk-max and the electrical resistance of the sensor coil 12. The calibration parameter determination module 2222 is configured to provide the maximum calibration current parameter PIk-max to the controlled current source circuit 212, such that the controlled current source circuit applies to the sensor coil 12 a calibration current Ik that increases linearly with time t up to a maximum calibration current value Ik-max specified by the maximum calibration current parameter PIk-max.

[0043] The calibration sensor coil detection module 2223 is configured to detect the calibration sensor coil voltage USk during application of the calibration current Ik.

[0044] The calibration evaluation module 2224 is configured to compare the calibrated sensor coil voltage USk with a calibrated reference voltage value URk, determine a maximum calibrated sensor coil voltage value USk-max if the calibrated sensor coil voltage USk does not exceed the calibrated reference voltage value URk, define the current start reference voltage value URa as the calibrated reference voltage value URk, and define the current end reference voltage value URe as the sum of the current start reference voltage value URa and N times the maximum calibrated sensor coil voltage value USk-max, and write a first magnetization direction value M=1 to the memory 23 if the calibrated sensor coil voltage USk exceeds the calibrated reference voltage value URk.

[0045] Figure 6 shows, by way of example, the time curves of the calibration current Ik and the calibration sensor coil voltage USk as well as the calibration reference voltage value URk when no Wiegand voltage pulse WP is induced in the sensor coil 12. Figure 7 shows the time curves of the calibration current Ik and the calibration sensor coil voltage USk as well as the calibration reference voltage value URk from Figure 6, but when a Wiegand voltage pulse WP is induced in the sensor coil 12.

[0046] The magnetization direction determination unit 3' is configured to, after the current start reference voltage value URa and the current end reference voltage value URe are defined by the calibration module 222, generate a reference voltage UR by the reference voltage generation circuit 213 as described above, apply a test current Ip to the sensor coil 12 by the controlled current source circuit 212, and determine the magnetization direction value M by comparing the sensor coil voltage US with the reference voltage UR by the comparison circuit 214 during the application of the test current Ip. [Explanation of symbols]

[0047] 100 Wiegand sensor device 1 Wiegand sensor 11 Wiegand Wire 12 Sensor coil 2 circuit device 21 Application Specific Integrated Circuits (ASICs) 211 Temperature Sensor 212 Controlled Current Source Circuit 213 Reference voltage generation circuit 214 Comparison circuit 22;22' microcontroller 221 Temperature Compensation Module 2211 Reference value memory 2212 Computational Algorithms 222 Calibration Module 2221 Calibration Coefficient Memory 2222 Calibration Parameter Determination Module 2223 Calibrated Sensor Coil Detection Module 2224 Calibration Evaluation Module 23 Memory 3;3' magnetization direction determination unit Ik Calibration Current Ik-max Maximum calibrated current value Ip test current Ip-max Maximum test current value M Magnetization direction value N calibration factor PIk-max Maximum calibrated current parameter PIp-max Maximum test current parameter S stop signal t time T Detected temperature T1-Tn temperature UR Reference Voltage URa start reference voltage value URa(T1-Tn) Temperature-specific starting reference voltage value URe end reference voltage value URe(T1-Tn) Temperature specific termination reference voltage value URk Calibration reference voltage value US sensor coil voltage USk Calibration Sensor Coil Voltage USk-max Maximum calibrated sensor coil voltage value WP Wiegand voltage pulse

Claims

1. A method for determining the magnetization direction (M) of a Wiegand wire (11), comprising the steps of: A test current (Ip) that increases with time (t) is applied to a sensor coil (12) surrounding the Wiegand wire (11); During application of the test current (Ip), a sensor coil voltage (US) appearing in the sensor coil (12) is detected; The magnetization direction (M) is determined by comparing the sensor coil voltage (US) detected during application of the test current (Ip) with a reference voltage (UR) that increases simultaneously with the test current (Ip); The method, characterized in that the reference voltage (UR) increases from a defined start reference voltage value (URa) to a defined end reference voltage value (URe).

2. Temperature (T) is detected, The method of claim 1 , wherein the start reference voltage value (URa) and / or the end reference voltage value (URe) are defined based on the detected temperature (T).

3. Before applying the test current (Ip), a calibration current (Ik) is applied to the sensor coil (12), and a maximum calibration current value (Ik-max) corresponds to 1 / N times the maximum test current value (Ip-max); During application of the calibration current (Ik), the sensor coil voltage (USk) is detected; 3. The method according to claim 1, wherein the end reference voltage value (URe) is defined as the sum of the start reference voltage value (URa) and N times the maximum sensor coil voltage value (USk-max) detected during application of the calibration current.

4. The sensor coil voltage (USk) detected during application of the calibration current (Ik) is compared with a calibration reference voltage value (URk) that is greater than the product of the maximum calibration current value (Ik-max) and the electrical resistance of the sensor coil (12); 4. The method of claim 3, wherein the magnetization direction (M) is set to a first magnetization direction value (M=1) if the sensor coil voltage (USk) detected during application of the calibration current (Ik) exceeds a calibration reference voltage value (URk).

5. Wiegand wire (11) and a sensor coil (12) surrounding the Wiegand wire (11), applying a test current (Ip) that increases with time (t) to the sensor coil (12); Detecting a sensor coil voltage (US) appearing in the sensor coil (12) while the test current (Ip) is being applied; The magnetization direction (M) of the Wiegand wire (11) is determined by comparing the sensor coil voltage (US) detected during application of the test current (Ip) with a reference voltage (UR) that increases simultaneously with the test current (Ip). A magnetization direction determination unit (3) configured as follows is provided: The reference voltage (UR) increases from a specified start reference voltage value (URa) to a specified end reference voltage value (URe). A Wiegand sensor device (100).

6. 6. The Wiegand sensor device (100) according to claim 5, further comprising a temperature sensor (211), wherein the magnetization direction determination unit (3) comprises a temperature compensation module (221) configured to define the start reference voltage value (URa) and / or the end reference voltage value (URe) based on a temperature (T) detected by the temperature sensor (211).

7. 7. The Wiegand sensor device according to claim 6, wherein the temperature compensation module comprises a reference value memory in which several temperature-specific start reference voltage values ​​(URa(T1) to URa(Tn)) assigned to different temperatures (T1 to Tn) and / or several temperature-specific end reference voltage values ​​(URe(T1) to URe(Tn)) assigned to different temperatures (T1 to Tn) are stored.

8. 8. The Wiegand sensor device (100) according to claim 6 or 7, wherein the temperature compensation module (221) comprises a calculation algorithm (2212) for calculating the start reference voltage value (URa) and / or the end reference voltage value (URe) as a function of temperature.

9. The magnetization direction determination unit (3) a calibration current (Ik) is applied to the sensor coil (12) before the application of the test current (Ip), and a maximum calibration current value (Ik-max) corresponds to 1 / N times the maximum test current value (Ip-max); Detecting the sensor coil voltage (USk) during application of the calibration current (Ik); defining an end reference voltage value (URe) as the sum of the start reference voltage value (URa) and N times the maximum sensor coil voltage value (USk-max) detected during application of the calibration current (Ik); 6. The Wiegand sensor device (100) of claim 5, comprising a calibration module (222) configured to:

10. The calibration module (222) comparing the sensor coil voltage (USk) detected during application of the calibration current (Ik) with a calibration reference voltage value (URk) greater than the product of the maximum calibration current value (Ik-max) and the electrical resistance of the sensor coil (12); If the sensor coil voltage (USk) detected during application of the calibration current (Ik) exceeds the calibration reference voltage value (URk), the magnetization direction (M) is set to a first magnetization direction value (M=1); 10. The Wiegand sensor device (100) of claim 9, configured as follows:

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