Test circuit for testing a magnetic sensor element

Abstract

Test circuit for testing a magnetic sensor element (2) with a current source (3) for applying a test current to the sensor element (2), characterized by a freewheeling path (4) for draining the storage current stored in the sensor element (2) after switching off the test current and a measuring device (5) for detecting the storage current.

Description

[0001] The present invention relates to a test circuit for testing a magnetic sensor element with a current source for applying a test current to the sensor element. The invention further relates to a position measuring device for determining angular or linear positions with a magnetic sensor element, as well as a method for testing a magnetic sensor element.

[0002] Position measuring devices are used in many areas of technology, for example, in industry, medical technology, and the like to detect the movements of a wide variety of objects. The position measuring devices can detect rotational and / or translational movements of an object. In magnetic position measuring devices, it is known to arrange an excitation magnet, such as a permanent magnet, on the object whose movement is to be detected.

[0003] To detect the movement of the excitation magnet, the position measuring device has a sensor element. Such a sensor element can be a magnetic sensor element such as a Wiegand sensor and / or a pulsed wire sensor. Due to the movement of the excitation magnet relative to the sensor element, a spontaneous remagnetization occurs in the sensor element at a specific point of the magnetic field strength. This remagnetization leads to a voltage pulse in the sensor element, which can then be detected by a corresponding detection circuit. This detection signal is digitally recorded and provides information about the current state of the position measuring device. A magnetic field sensor with a coil, a magnetic element, and pulsed wires is known from DE 199 25 884 A1.

[0004] Such a magnetic position measuring device is also known, for example, from DE 10 2012 102 308 A1. In the position measuring device described therein, voltage pulses are detected, evaluated, and stored in a counter using the detection circuit. To avoid false detections, the steepness of the voltage curve of the individual voltage pulses is evaluated. By evaluating the steepness, it can be determined whether the voltage pulse is a voltage pulse caused by the sensor element or a voltage pulse with a gentle rise, which is referred to therein as an interference pulse. It is described that such a voltage pulse with a gentle rise can be generated, for example, by applying a test current to the sensor element.

[0005] Such a test current can be generated by a current source and impressed into the sensor element to determine the current state of the position measuring device, for example, after a standstill. Similar to the movement of the excitation magnet, the test current can cause a spontaneous remagnetization and thus a regular voltage pulse to be evaluated.

[0006] Although testing the sensor element using a test current offers advantages by determining the magnetization within the sensor element, other interference can occur, particularly when the test current is switched off, which can impair the position measurement. Such interference can have any slope and cannot be reliably distinguished from regular voltage pulses using the conventional slope analysis.

[0007] The present invention therefore has the object of providing a test circuit with lower interference.

[0008] The task is solved in a test circuit of the type mentioned at the beginning by a test circuit with a freewheeling path for diverting the storage current stored in the sensor element after the test current has been switched off and with a measuring device that detects the storage current.

[0009] With the help of a test circuit according to the invention, the interference caused by the current source can be reduced. By applying a test current to a sensor element, a spontaneous remagnetization can be induced in the sensor element, by means of which the condition of the sensor element can be checked. The impressed test current can generate a changing magnetic field, which can cause the remagnetization and thus the induction of a voltage pulse in the sensor element. Due to the inductance of the sensor element, energy can be stored in the sensor element, for example in the form of a storage current. This storage current can be monitored and dissipated using the test circuit according to the invention. In this way, the sensor element can be transferred to a defined state with known magnetization.

[0010] After the test current is switched off, the stored current in the sensor element can be discharged via the freewheeling path. Any remaining energy in the sensor element can thus be easily dissipated. Any parameter fluctuations of the sensor element are negligible and do not negatively influence the measurement results of the position measuring device.

[0011] A measuring device that detects the stored current can be used to monitor the current flow from the sensor element. This allows the point in time at which the energy from the sensor element has been sufficiently dissipated to be determined. The information thus obtained can provide insight into the condition of the sensor element, thus reducing false detections of voltage pulses and other disturbances. Preferably, the measuring device can be used to define a switching point at which the power source and the measuring device can be disconnected from the sensor element.

[0012] For this purpose, it is advantageous if at least one switch for disconnecting the power source and the measuring device is provided in the test circuit. The test circuit can be disconnected from the remaining elements of the position measuring device via the switch in order to reduce interference. The switch can be arranged between the sensor element and between the other elements of the test circuit. Alternatively, the switch can also be arranged between the freewheeling path and the other elements of the test circuit. However, at least two switches are preferred, which can be arranged on either side of the sensor element. The power source and the measuring device can preferably be disconnected from the remaining elements of the position measuring device at the time at which the storage current falls below a certain threshold value. It is particularly advantageous if disconnection occurs at the time at which the storage current crosses zero.

[0013] An advantageous embodiment provides that the freewheeling path has a freewheeling diode, which can in particular be connected in the reverse direction. The freewheeling diode in the freewheeling path can ensure that the energy stored in the sensor element can be dissipated after the power source is switched off. It can also serve as protection against overvoltage. Due to operation in the reverse direction, the current flow of the stored current generated by the self-induction of the sensor element can continue to flow via the freewheeling diode in the original direction without generating voltage peaks that could lead to incorrect detection of voltage pulses. With a freewheeling diode, any voltage peaks can be limited to the forward voltage of the freewheeling diode and the current flow can be diverted safely and without influencing the measurement result.Alternatively, a Zener diode, a varistor or an active circuit can be used instead of a freewheeling diode.

[0014] In this context, it is also advantageous if the freewheeling path is connected in parallel with the sensor element and / or the power source. By connecting the freewheeling path in parallel, the flow of the stored current from the sensor element can be diverted via the freewheeling path. Switching off the test current can reverse the polarity of the self-induction voltage, whereby the parallel connection allows the stored current to be diverted via the then permeable freewheeling path.

[0015] It is further preferred if the measuring device is designed as a current measuring device and connected in series with the sensor element. A measuring device designed as a current measuring device can monitor the current flow of the stored current in the sensor element after the test current has been switched off. The series connection with the sensor element can ensure that the stored current flows through the current measuring device. The measuring device can be used to detect the point in time at which the current flow of the stored current from the sensor element has been sufficiently reduced, thus enabling a suitable switching point for opening the switch to be determined. Potential disturbances such as oscillations can thus be reduced.

[0016] Alternatively or additionally, the measuring device can also be designed as a voltage measuring device and connected in parallel with the sensor element. In this case, there is no direct current measurement of the stored current in the sensor element, but rather an indirect current measurement via the voltage tap, for example, across the sensor element. The corresponding stored current can then be determined in the measuring device. This offers the advantage that a direct current measurement is not necessarily required; voltage measuring devices can also be used. This allows for a wide variety of different measuring devices to be used.

[0017] According to a further preferred embodiment, the test current of the current source is ramp-shaped. Preferably, the current ramp of the test current is triangular overall, with a rising and a falling edge. The ramp-shaped curve can influence the magnetic field induced in the sensor element. The impressed current can be built up and down again according to the set ramp shape, which in turn is reflected in the build-up and down of the generated magnetic field.

[0018] In this context, it is advantageous if the edges of the ramp-shaped current curve of the current source are adjustable. In this way, the impressed current can be adjusted according to the parameters of the sensor element. The impressed current can advantageously be built up and reduced again according to a programmable slew rate. In this way, it can be ensured that the impressed current is not reduced too quickly, which could lead to undesirable interference or oscillations. The edges of the current curve can preferably be adjusted according to the self-discharge of the sensor element so that as little energy as possible is stored in the sensor element at the end of the current ramp. The inductance and the ohmic resistance of the sensor element can influence the choice of edge steepness. This enables the applicability of a wide variety of sensor elements.

[0019] In a position measuring device of the type mentioned above, the problem is solved by having a test circuit of the type already described. This results in the same advantages as those already described in connection with the test circuit.

[0020] An advantageous embodiment of the position measuring device provides that the sensor element comprises a hysteresis element, in particular a Wiegand wire or a pulse wire, and an induction coil wound around the hysteresis element. The combination of the two elements provides a magnetic sensor element that can convert the movement of an excitation magnet into a detection signal.

[0021] A hysteresis element within the meaning of the invention is an element that has a magnetic hysteresis curve similar to that of a ferromagnetic material. Hysteresis elements are preferably used in which, due to a shape or crystal anisotropy, only a single Weiss domain, i.e., a single magnetic domain, can form. Such hysteresis elements preferably have a nearly rectangular hysteresis curve. The hysteresis element can be spontaneously remagnetized by the magnetic field of the moving excitation magnet, whereby it is necessary that the magnetic field of the excitation magnet exceeds the coercive field strength of the hysteresis element. In a hysteresis element with a nearly rectangular hysteresis curve, the remagnetization occurs abruptly and thus independently of the rate of change of the magnetic field of the excitation magnet.

[0022] The hysteresis element can advantageously be magnetically coupled to the induction coil, in which a voltage pulse can be induced when the hysteresis element is remagnetized. By wrapping the induction coil around the hysteresis element, good magnetic coupling can be achieved.

[0023] The advantage of Wiegand sensors and / or pulse wire sensors as magnetic sensing elements is that they can exhibit a hysteresis curve with two distinct jump points where spontaneous remagnetization can occur. This makes it easy to induce defined voltage pulses in the induction coil. The size and shape of the voltage pulses are independent of the temporal change in the magnetic field.

[0024] A preferred embodiment further provides that the position measuring device has a detection circuit for detecting voltage pulses generated in the sensor element. With such a detection circuit, the voltage pulses induced in the sensor element can be detected and further processed. Thus, the detected voltage pulses can serve as counting pulses of the position measuring device. These provide information about the current counter reading of the position measuring device.

[0025] It is further preferred if the sensor element can be remagnetized by an excitation magnet that is movable relative to the sensor element. This remagnetization can induce voltage pulses in the induction coil of the sensor element. This remagnetization generates a voltage pulse, which can then be detected, thus triggering a counting process. The counter value of the position measuring device can be changed and written to a memory of the position measuring device. The counter value can then be read out by a user.

[0026] A further preferred embodiment provides that the test circuit and / or the detection circuit are implemented as integrated circuits, in particular as a common integrated circuit. The integrated circuit design allows the size of a position-measuring device to be reduced. It is particularly advantageous if the test circuit and / or the detection circuit are implemented as a common integrated circuit, thereby achieving a further reduction in size compared to individual elements. With an integrated design of the circuit, energy efficiency can be increased by reducing the size of parasitic elements and couplings.

[0027] In a method of the type mentioned above, the problem is solved by diverting the stored current in the sensor element via a freewheeling path after the test current is switched off and detecting it using a measuring device. This also results in the advantages already described in connection with the test circuit and the position measuring device.

[0028] An advantageous embodiment of the method provides that the test circuit is disconnected from the sensor element after the storage current falls below a predetermined threshold. The threshold can be selected depending on the self-discharge of the sensor element and the properties of the freewheeling path. By disconnecting the test circuit from the sensor element at a predetermined threshold, it can be ensured that the energy stored in the sensor element can be completely dissipated via the freewheeling path. The sensor element then has a defined state, based on which the individual voltage pulses can be counted.

[0029] It is also advantageous if a detection circuit is connected to the sensor element after the test circuit has been separated from the sensor element. Since the sensor element has a defined state at the time of separation, the sensor element can be connected to a detection circuit for detecting voltage pulses as counting pulses without false detections occurring. The detection circuit has the necessary components with which the voltage pulses can be detected, further processed, and displayed. Possible false detections caused by disturbances such as oscillations can thus be easily avoided.

[0030] It is further advantageous if the sensor element is subjected to a ramp-shaped, in particular adjustable, test current from the current source. The adjustable test current can generate a variable magnetic field, which can cause spontaneous remagnetization of the position measuring device, for example, for testing and / or synchronization purposes. The state of the position measuring device can be determined through the spontaneous remagnetization. In this case, it is preferred if the current profile of the test current builds up and decays in a ramp-like manner in the form of a triangle with a rising and a falling edge, which can avoid oscillations. The ramp shape of the test current is adjustable, and the parameters of the sensor element, such as the inductance and resistance, can serve as the basis.

[0031] A further preferred embodiment of the method provides that the energy required for the test circuit and / or the detection circuit is generated by the sensor element. For this purpose, the sensor element can be part of a so-called "energy harvesting" application. The voltage pulses generated in the induction coil of the sensor element provide sufficient energy, particularly for signal processing.

[0032] The advantageous embodiments of the invention described above can be used in the same way both in the test circuit and in the position measuring device and the corresponding method for operating a test circuit.

[0033] Further advantages and details will be explained in more detail below using the exemplary embodiments shown in the figures. Herein: Fig. 1 a schematic block diagram of a position measuring device, Fig. 2 a schematic block diagram of a first embodiment of a test circuit with sensor element, Fig. 3 a schematic block diagram of a second embodiment of a test circuit, Fig. 4 a schematic block diagram of a third embodiment of a test circuit, Fig. 5 is a schematic block diagram of a fourth embodiment of a test circuit, Fig. 6 a schematic representation of a current ramp, Fig. 7 a schematic representation of an exemplary voltage curve without disturbances, Fig. 8 a schematic representation of an exemplary voltage curve with disturbances and Fig. 9 a schematic representation of an exemplary voltage curve with test circuit.

[0034] In the Fig. 1 shows a schematic block diagram of an embodiment of the position measuring device 9 according to the invention, in which the test circuit 1 according to the invention is used to test a magnetic sensor element 2.

[0035] The position measuring device 9 can be used to determine angular or linear positions in order to detect rotational and / or translational movements of objects. Such positioning devices 9 have a magnetic sensor element 2 and a detection circuit 10 to detect these movements. The detection circuit 10 can detect voltage pulses induced in the sensor element 2 and subsequently evaluate, count, and display them.

[0036] Upon detection of a voltage pulse, the detection circuit 10 generates a pulse detection signal, which can be fed to a counter, preferably designed as a memory, of the detection circuit 10. The counter can be used to count the number of detected voltage pulses. The counter can then be read by a user via an output circuit, providing information about the current state of the position measuring device 9.

[0037] In addition to the detection circuit 10 and the sensor element 2, the position measuring device 9 includes an excitation magnet 12, which can be designed as a permanent magnet. To detect the movement of an object (not shown), the excitation magnet 12 is arranged on the object itself and thus moves with the object. The excitation magnet 12 can be mounted around a rotational axis.

[0038] The sensor element 2 is arranged in direct proximity to the excitation magnet 12. The movements of the excitation magnet 12 can generate voltage pulses in the sensor element, which can then be converted into a digital signal by the detection circuit 10. The sensor element 2 is a magnetic, in particular ferromagnetic, sensor element 2. The sensor element 2 essentially consists of a hysteresis element 7 and an induction coil 8.

[0039] The hysteresis element 7 can be alternately remagnetized by the rotational movement of the excitation magnet 12. The magnetic hysteresis element 7 can be designed, for example, as a Wiegand wire or as a pulse wire, through which the magnetic field of the excitation magnet 12 passes. Such hysteresis elements 7 have the advantage of having a nearly rectangular hysteresis curve, resulting in two distinct jumps. When the coercive field strength of the hysteresis element 7 is exceeded, the hysteresis element 7 is suddenly remagnetized, generating voltage pulses in the induction coil 8, which can then be digitally detected by the detection circuit 10. In the position measuring device 9 of the exemplary embodiment, the remagnetization occurs with every half rotation of the excitation magnet 12.For example, a rotating diametrical magnet 12 can be used to generate a voltage pulse that repeats every 180°.

[0040] The second component of the sensor element 2 is an induction coil 8 wound around the hysteresis element 7. The remagnetization of the hysteresis element 7 induces a voltage pulse in the induction coil 8, which can be detected and processed by a detection circuit 10. The hysteresis element 7 and the induction coil 8 are arranged in such a way that a good magnetic coupling between the two elements 7, 8 is achieved.

[0041] As shown in the Fig. As can be further seen in Figure 1, the sensor element 2 can be connected at the connection points 11 to the test circuit 1 according to the invention for testing the magnetic sensor element 2 and / or to the detection circuit 10, by means of which the voltage pulses generated in the induction coil 8 can be detected and counted. The detection circuit 10 detects the state of the magnetization of the sensor element 2.

[0042] Test circuit 1 can be used to check the state of magnetic sensor element 2, for example, for testing or synchronization purposes. Such a check is useful, for example, when the object, and thus the excitation magnet 12, has come to a standstill and is to be started again. This is generally referred to as power-on. However, a continuous check of the state of sensor element 2 is not practical, which is why test circuit 1 can be disconnected from the sensor element 2 after the test has been completed.

[0043] To perform the test, the sensor element 2 is subjected to a test current generated by a current source 3. The applied test current generates a variable magnetic field, which, similar to the excitation magnet 12, can cause a spontaneous remagnetization in the sensor element 2. The ferromagnetic hysteresis element 7 can thus be specifically remagnetized, with the test current generating a suitable magnetic field, also in combination with the external field of the movable excitation magnet 12.

[0044] The test current generated by current source 3 preferably has a ramp-like shape, with the edges being adjustable according to the test conditions. An example of such a "current ramp" is shown in Fig. 6. The current curve I(t) is plotted over time. As can be seen from the diagram, the current ramp has a roughly triangular shape with a rising and a falling edge.

[0045] By means of a ramp-shaped test current, a variable magnetic field can be built up and then dissipated in the induction coil 8, which generates a voltage pulse in the induction coil 8 of the sensor element 2. The impressed test current is built up and then dissipated according to a programmable slew rate, resulting in a current-induced magnetic field change. The magnetic field should be built up in such a way that no interference occurs. This can be achieved by selecting the edge steepness of the test current. An example of such a voltage curve without interference is shown in the Fig. 7, where the voltage shown was tapped across sensor element 2. The heights of the jumps are determined by the finite quality of induction coil 8.

[0046] If the applied test current is reduced faster than the self-discharge of the induction coil 8 allows, residual energy is still stored in the induction coil 8 at the end of the test cycle, for example in the form of a storage current in the sensor element 2. This storage current then flows out of the sensor element 2 after the test current is switched off and leads to undesirable disturbances such as oscillations. An exemplary voltage curve in which these disturbances occur in the form of oscillations is shown in the Fig. 8. Point A corresponds to the point in time at which the current ramp ends.

[0047] The self-discharge of the sensor element 2 is determined by the inductance and the ohmic resistance. In previous applications, the magnetic sensor elements 2 were therefore adapted to the specified or parametrically adjusted current ramps of the test current in order to minimize unwanted interference associated with the residual energy remaining in the sensor element 2. However, this severely limits the usability of available coil designs, the choice of the number of turns and / or the choice of inductance and ohmic resistance, and the temperature range. For example, in an induction coil 8 made of copper wire, the ohmic resistance can change by approximately 60% in the temperature range from -40°C to +125°C.

[0048] In order to open up the application area for various sensor elements 2 and extended temperature ranges without the undesirable interference and the associated false detections occurring, the test circuit 1 according to the invention includes a freewheeling path 4 for diverting the stored current in the sensor element 2 after the test current is switched off, as well as a measuring device 5 for detecting the stored current. The freewheeling path 4 serves to divert the inductive stored current.

[0049] The freewheeling path 4 has a freewheeling diode 6, which is connected in particular in the reverse direction and is connected in parallel with the sensor element 2 and / or the current source 3. Residual energy in the induction coil 8 can be dissipated in the form of the stored current via the freewheeling diode 6 in the freewheeling path 4, thereby ensuring that the energy stored in the sensor element 2 is reliably dissipated after the test current is switched off, without leading to interference. Such an exemplary voltage curve is shown in Fig. 9. It can also serve as protection against potentially occurring overvoltages. With the help of the freewheeling diode 6, voltage peaks can be reduced and limited to the forward voltage of the freewheeling diode 6. Instead of the freewheeling diode 6, a Zener diode, a varistor, or an active circuit can also be used in the freewheeling path 4.

[0050] In order to detect the storage current flowing from the sensor element 2, and in particular the current flow through the freewheeling diode 6, the test circuit 1 according to the invention includes a measuring device 5 that can measure the storage current. The measuring device 5 is used in particular to monitor the current flow from the sensor element 2 after the test current has been switched off.

[0051] The measuring device 5 is used in particular to detect a switch-off time B. This switch-off time B can be either a threshold value or a current zero crossing. At this time B, the test circuit 1 is disconnected from the current source 3 and the measuring device 5 via the switches S1, S2. At the switch-off time B, no residual energy is stored in the sensor element 2 and it is in a defined state from which a position measurement can then be carried out. By disconnecting the test circuit 1 or in particular by disconnecting the current source 3 from the sensor element 2, residual currents and interactions can be avoided. Monitoring the stored current is of particular importance here because, on the one hand, interference can be reduced and, on the other hand, it is possible to begin the actual measurement process of the meter reading more quickly.

[0052] The measuring device 5 detecting the storage current can be designed as a current measuring device and connected in series with the sensor element 2 or as a voltage measuring device and connected in parallel with the sensor element 2. Design variants in which the measuring device 5 is designed as a current measuring device are described in the Fig. 4 and Fig. 5. Variants in which the measuring device 5 is designed as a voltage measuring device are shown in the Fig. 2 and Fig. 3 represents.

[0053] First, we will take a closer look at the Fig. 2 and Fig. 3, in which the measuring device 5 of the test circuit 1 is designed as a voltage measuring device. These test circuits 1 can be used when direct current measurement is not desired. The storage current can be determined and further processed indirectly via the forward voltage of the freewheeling diode 6.

[0054] The Fig. Figure 2 shows a test circuit 1, which is connected to the induction coil 8 as part of the sensor element 2 at the connection points 11. In this exemplary embodiment, the freewheeling diode 6, the current source 3, and the measuring device 5 are each connected in parallel with the sensor element 2 and connected to ground. If the sensor element 2 is now subjected to a ramp-shaped test current generated by the current source 3, it can be seen that the freewheeling diode 6 is operated in the reverse direction. A current flow through the freewheeling diode 6 is therefore not possible at this time.

[0055] The measuring device 5 monitors the current flow from the sensor element 2 in order to determine whether a certain threshold value has been undershot and / or whether a current zero crossing has occurred. This measurement is necessary in order to define a suitable switch-off time B of the test circuit 1. If, after the switch-off time A of the test current, a threshold value has been undershot and / or the storage current has a zero crossing, the test circuit 1 can be separated from the sensor element 2 without causing any faults. If the switch-off time B, i.e. either the threshold value or the current zero crossing, has been reached, the Fig. The switches S1, S2 shown in Figure 2 must be opened, ensuring that no more energy is stored in the sensor element 2. Disconnecting the test circuit 1 is advisable to prevent interference, for example, due to interactions during ongoing measurement operation and thus to avoid generating interference. The test circuit 1, and thus in particular the current source 3, can be connected to the sensor element 2 for testing and disconnected again after the test is completed.

[0056] Similar to Fig. 2 also shows Fig. 3 a test circuit 1 with a measuring device 5, which is designed as a voltage measuring device. The essential difference to Fig. 2 is that the sensor element 2, the freewheeling diode 6, the current source 3 and the measuring device 5 are not connected to ground. However, they have a common potential. Fig. The variant shown in Figure 3 is therefore an alternative design to the one shown in Fig. 2 shown variant.

[0057] Based on the Fig. 4 and Fig. 5 will now discuss design variants in which the measuring device 5 is designed as a current measuring device.

[0058] The Fig. Figure 4 shows a test circuit 1 in which a direct current measurement can be carried out using the measuring device 5. The test procedure is carried out analogously to the Fig. 2 and Fig. 3 described procedure.

[0059] The measuring device 5 is connected in series with the sensor element 2 and the current source 3. In the present case, the current measuring device 5 is arranged in the circuit between the current source 3 and the sensor element 2. Fig. Figure 5, on the other hand, shows a test circuit 1 in which the measuring device 5 is arranged between the sensor element 2 and the current source 3. In principle, the position of the measuring device 5 in the circuit is of secondary importance. However, it is essential to ensure that the current flow from the sensor element 2 flows through the measuring device 5 so that the stored current can be measured.

[0060] Since the freewheeling diode 6 is connected as parallel as possible to the sensor element 2 and the current source 3, the current flow across the diode 6 can also be tapped using the measuring device 5. The position of the freewheeling path 4 is therefore fundamentally unimportant; however, it must be ensured that the stored current flowing from the sensor element 2 flows via the current measuring device 5 and the freewheeling path 4.

[0061] Another difference between the two test circuits 1 in the Fig. 4 and Fig. 5 also shows the potential against which the circuits 1 are connected. Thus, in the Fig. 4 the test circuit 1 is connected to ground, whereas the test circuit 1 according to Fig. 5 against a fixed common potential.

[0062] If the test circuit 1 has been separated from the sensor element 2 by means of the switches S1, S2, the detection circuit 10, provided that it was not already connected to the sensor element 2 during the test, can be connected to the connection points 11, which can then detect, process and display the voltage pulses induced by the excitation magnet 12 in the induction coil 8.

[0063] The voltage pulses can also be used as an energy source for signal processing. Such systems are also referred to as energy harvesting applications. Particularly in standard operation, in which voltage pulses are induced in the sensor element 2 by means of the excitation magnet 12, the energy thus obtained can be used to operate the detection circuit 10. To ensure reliable operation of such an energy harvesting application, an energy storage device (not shown), for example in the form of a capacitor, is arranged in the detection circuit 10, which can store the energy generated by the voltage pulses. The energy can then in turn be drawn from the energy storage device, for example, for signal processing.

[0064] The test circuit 1 and / or the detection circuit 10 are further each designed as an integrated circuit, wherein the test circuit 1 and the detection circuit 10 are in particular designed as a common integrated circuit.

[0065] With the position measuring device 9 according to the invention and with the test circuit 1 according to the invention, false detections caused by faulty voltage pulses can be minimized. To test the condition of the sensor element 2, a test current can be impressed into the sensor element 2 via a current source 3. Any residual energy remaining in the sensor element 2 can be detected by the test circuit 1 and dissipated via a freewheeling path 4. The current flow from the sensor element 2 is monitored via a measuring device 5, whereby a suitable switch-off time B can be defined. The energy from the sensor element 2 can thus be reliably dissipated, whereby parameter fluctuations of the sensor element 2 become negligible. Reference symbol: 1 test circuit 2 sensor element 3 Power source 4 free-wheeling path 5 Measuring device 6 freewheeling diode 7 Hysteresis element 8 Induction coil 9 Position measuring device 10 Detection circuit 11 Connection point 12 Excitation magnet S1, S2 switch A End point of the current ramp B Switch-off time

Claims

[1] Test circuit for testing a magnetic sensor element (2) with a current source (3) for applying a test current to the sensor element (2), characterized by a freewheeling path (4) for diverting the storage current stored in the sensor element (2) after the test current has been switched off and a measuring device (5) detecting the storage current. [2] Test circuit according to claim 1, characterized by at least one switch (S1, S2) for separating the power source (3) and the measuring device (5). [3] Test circuit according to one of the preceding claims, characterized by that the freewheeling path (4) has a freewheeling diode (6). [4] Test circuit according to one of the preceding claims, characterized by that the freewheeling path (4) is connected in parallel to the sensor element (2) and / or the current source (3). [5] Test circuit according to one of the preceding claims, characterized bythat the measuring device (5) is designed as a current measuring device and is connected in series with the sensor element (2). [6] Test circuit according to one of claims 1 to 4, characterized by that the measuring device (5) is designed as a voltage measuring device and is connected in parallel to the sensor element (2). [7] Test circuit according to one of the preceding claims, characterized by that the test current of the current source (3) is ramp-shaped. [8] Position measuring device for determining angular or length positions with a magnetic sensor element (2), characterized by a test circuit (1) according to one of the preceding claims. [9] Position measuring device according to claim 8, characterized by that the sensor element (2) has a hysteresis element (7), in particular a Wiegand wire or a pulse wire, and an induction coil (8) wound around the hysteresis element (7). [10] Position measuring device according to one of claims 8 or 9, characterized by a detection circuit (10) for detecting voltage pulses generated in the sensor element (2). [11] Method for testing a magnetic sensor element (2) with a test circuit (1), wherein a current source (3) applies a test current to the sensor element (2), characterized by that the storage current stored in the sensor element (2) is diverted via a freewheeling path (4) after the test current has been switched off and is detected by means of a measuring device (5). [12] Method according to claim 11, characterized by that the test circuit (1) is separated from the sensor element (2) after the storage current falls below a predetermined threshold value. [13] Method according to one of claims 11 or 12, characterized by that a detection circuit (10) is connected to the sensor element (2) after the test circuit (1) has been separated from the sensor element (2).

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