Magnetic sensor

Abstract

This magnetic sensor comprises: a shaft body that includes an excitation body (21A) and a magnetic body (21B); a coil (22) that is wound around the shaft body in a helical shape; an electricity conducting portion; and a measuring unit. The orientation of a magnetic moment (M) of the magnetic body (21B) is oriented in a predetermined direction (Y1). When an external magnetic field (Bex) is applied, the orientation of the magnetic moment (M) is inclined with respect to the predetermined direction (Y1). When the excitation body (21A) is energized, the orientation of the magnetic moment (M) is aligned in the predetermined direction (Y1) by a magnetic field generated from the excitation body (21A) as a result of the energization, and a magnetic field (Be) is generated in the process of aligning the orientation of the magnetic moment (M). A voltage is generated between the two ends of the coil (22) by means of the magnetic field (Be) generated by the magnetic body (21B). The measuring unit measures the magnitude of the external magnetic field (Bex) by measuring the voltage generated between the two ends of the coil (22).

Description

magnetic sensor

[0001] The present invention relates to a magnetic sensor.

[0002] Magnetic sensors that detect magnetism based on changes in the magnetic moment of a magnetic material have been proposed (see, for example, Patent Documents 1 and 2). Patent Document 3 discloses a magnetic sensor including a probe unit and a circuit. The probe unit includes a conductor having a soft magnetic material and a coil. The soft magnetic material has magnetic moments whose orientations are opposite to each other in the circumferential direction. When an external magnetic field is applied to the probe unit, the orientation of the magnetic moment of the soft magnetic material tilts depending on the strength and direction of the external magnetic field. When current is passed through the conductor from the circuit in this state, an applied magnetic field is applied to the soft magnetic material, and the magnetic moment aligns in the same direction as the applied magnetic field. When current is passed through the conductor periodically, the magnetic moment of the soft magnetic material repeatedly changes between an aligned state and an unaligned state. At this time, a minute magnetic field that changes over time is generated from the soft magnetic material. The circuit measures the magnitude of the external magnetic field by detecting this minute magnetic field with the coil.

[0003] JP 5-222493, JP 6-45145, JP 2018-189591

[0004] When the direction of the magnetic moment of a soft magnetic material changes, it is accompanied by precession. The greater the change in the direction of the magnetic moment, the greater the degree of precession. The magnetic field generated in response to the precession of the magnetic moment acts as noise on the magnetic field generated in response to the passage of a periodic current. Here, the soft magnetic material in the magnetic sensor includes magnetic moments whose directions are opposite to each other. Therefore, the change in the direction of the magnetic moment in response to the passage of a periodic current is greater than when the magnetic moments are in the same direction, and the degree of precession that occurs is also greater. Therefore, the magnetic sensor has a problem in that the noise associated with the precession of the magnetic moment reduces the accuracy of measuring the external magnetic field.

[0005] An object of the present invention is to provide a magnetic sensor that can measure an external magnetic field with high accuracy.

[0006] The magnetic sensor according to the present invention is a magnetic sensor comprising: a shaft body having an elongated exciter made of a non-magnetic material having electrical conductivity, and a magnetic body made of a magnetic material covering the exciter; a coil in which an insulating coated conductor is wound spirally around the shaft body and whose direction of travel is along the longitudinal direction of the exciter; a current conductor that applies current to the exciter on the shaft body; and a measurement unit that measures a voltage generated across both ends of the coil when current is applied to the exciter by the current conductor; and when no external magnetic field is applied and no current is passed through the exciter by the current conductor, the magnetic body has a magnetic moment that is oriented in an orthogonal direction perpendicular to the longitudinal direction along the circumferential direction of the shaft body. When an external magnetic field is applied, the magnetic moment is oriented in a predetermined direction, which is one of the directions of the magnetic moment, and the magnetic moment is tilted with respect to the predetermined direction. When the current is passed through the exciter by the current-carrying unit while the external magnetic field is applied, the magnetic field generated from the exciter by the current-carrying unit aligns the magnetic moment with the predetermined direction, and a magnetic field is generated in the process of aligning the magnetic moment. A voltage is generated at both ends of the coil due to the magnetic field generated in the magnetic body during the process of aligning the magnetic moment, and the measurement unit measures the voltage generated at both ends of the coil to measure the magnitude of the external magnetic field.

[0007] The magnetic sensor has a magnetic body whose magnetic moment is oriented in a predetermined direction when no external magnetic field is applied and no current is passed through the exciter. In this case, the degree of change in the direction of the magnetic moment in response to current being passed through the exciter can be suppressed. Therefore, the magnetic sensor can suppress precession caused by the change in the direction of the magnetic moment. Therefore, the magnetic sensor can measure the magnitude of the magnetic field generated by the change in magnetic moment that occurs when current is passed through the exciter while an external magnetic field is applied, in an environment where noise associated with precession is suppressed. Therefore, the magnetic sensor can accurately measure the magnitude of the external magnetic field based on this measurement result.

[0008] In the present invention, the current supplying section may supply a pulse current to the exciter, so that the magnetic sensor can measure the magnitude of the external magnetic field with even greater accuracy.

[0009] In the present invention, the current supply unit may supply the pulse current including a DC component to the exciter. The magnetic sensor can precisely orient the magnetic moment of the magnetic body in a predetermined direction by using the DC component of the pulse current. Therefore, the magnetic sensor can minimize noise caused by precession in response to changes in the magnetic moment, thereby enabling more accurate measurement of the external magnetic field.

[0010] In the present invention, the magnetic substance may be an iron-nickel alloy containing 19 to 23 wt % of iron. The magnetic sensor can suppress the influence of noise while maintaining sensitivity when measuring an external magnetic field.

[0011] In the present invention, the magnetic material may be formed on the surface of the exciter by electrolytic plating, and the direction of the current passed through the exciter during electrolytic plating may be the same as the direction of the current passed through the exciter by the current-carrying unit. In this case, a film-like magnetic material capable of precisely orienting the magnetic moment in a predetermined direction can be formed on the exciter. Therefore, when no external magnetic field is applied and no current is passed through the exciter, the inclination of the magnetic moment relative to the predetermined direction can be suppressed, thereby minimizing noise associated with precession in response to changes in the magnetic moment, and enabling the manufacture of a magnetic sensor capable of measuring external magnetic fields with even greater accuracy.

[0012] In the present invention, the current passed through the magnetic exciter when electrolytic plating is performed includes a plating current required to perform plating by applying a voltage between the magnetic exciter as a plating cathode and a plating anode, and a bias current for aligning the magnetic moments in the magnetic material, and the direction of the bias current may be the same as the direction of the plating current. In this case, tilt of the magnetic moment relative to a predetermined direction can be suppressed.

[0013] 1 is a diagram showing a magnetic sensor 1. FIG. 2 is a diagram showing a probe 2. FIG. 3 is a diagram for explaining the operating principle of the magnetic sensor 1. FIG. 4 is a diagram showing a manufacturing apparatus 6. FIG. 5 is a graph showing the relationship between the average iron content ratio in the magnetic body 21B and sensitivity (A), and the relationship between the average iron content ratio in the magnetic body 21B and linearity (B). FIG. 6 is a table showing the relationship between the DC component of the pulse current Ie and sensitivity and noise. ０ 10 is a graph showing the relationship between the magnetic moment M and normalized noise Vn / N. FIG. 11 is a diagram for explaining the operating principle when the magnetic moment M is not oriented.

[0014] <Outline of Magnetic Sensor 1> An embodiment of the present invention will be described with reference to the drawings. The drawings are used to explain technical features that can be adopted by the present invention, and the configuration of the device described is not intended to be limiting, but is merely an illustrative example.

[0015] The magnetic sensor 1 is a device for measuring the magnitude of an external magnetic field. As shown in FIG. 1, the magnetic sensor 1 includes a probe 2, a current-carrying unit 3, and a measuring unit 4.

[0016] 2, the probe 2 is cylindrical and includes a shaft 21 and a coil 22. Hereinafter, the direction extending along the center of the shaft 21 will be referred to as the longitudinal direction.

[0017] The shaft 21 includes an exciter 21A and a magnetic body 21B. The exciter 21A is a long, cylindrical body made of a non-magnetic material with electrical conductivity. A material with good electrical conductivity can be used for the exciter 21A. In this embodiment, the exciter 21A is made of copper. The diameter of the exciter 21A is, for example, 10 to 500 μm, preferably 30 to 100 μm. A conductor 20A is connected to one longitudinal end (hereinafter referred to as "end 211") of the exciter 21A, and a conductor 20B is connected to the other longitudinal end (hereinafter referred to as "end 212"). Both longitudinal ends of the exciter 21A are connected to a power supply unit 31 (see FIG. 1) of the current-carrying unit 3, which will be described later, via the conductors 20A and 20B.

[0018] The magnetic body 21B is made of a magnetic material and coats the side surface of the exciter 21A. An iron-nickel alloy is used as the material for the magnetic body 21B. An iron-nickel alloy containing 19 to 23 wt% iron is more preferably used as the material for the magnetic body 21B. The thickness of the magnetic body 21B is, for example, 1 to 50 μm, and preferably 1 to 15 μm. The shaft 21 may have various elongated shapes, but a cylindrical shape is preferable because a closed magnetic flux circuit in the circumferential direction of the magnetic body 21B can suppress the generation of a demagnetizing field. The probe 2 is not limited to extending linearly and may be bent.

[0019] In FIG. 3A, the magnetic moment of the magnetic body 21B when no external magnetic field is applied is indicated by an arrow labeled M. Thus, the magnetic moment M of the magnetic body 21B is oriented in a specific direction (hereinafter referred to as the "predetermined direction Y1"). The predetermined direction Y1 indicates a direction perpendicular to the longitudinal direction along the side surface of the shaft body 21 (hereinafter referred to as the "orthogonal direction"), in other words, a direction on one side of the circumferential direction. More specifically, the predetermined direction Y1 corresponds to the clockwise direction when viewing the magnetic body 21B from the end 211 of the exciter 21A to which the conductor 20A is connected toward the end 212 to which the conductor 20B is connected. The magnetic body 21B is formed on the surface of the exciter 21A by electrolytic plating. A method for forming the magnetic body 21B on the exciter 21A will be described later.

[0020] As shown in Fig. 2, the coil 22 is wound spirally around the shaft body 21. The wire of the coil 22 is a conductor with an insulating coating. The spiral of the coil 22 extends along the longitudinal direction of the shaft body 21. The coil 22 is a Helmholtz coil. The center positions of the coil 22 and the shaft body 21 are approximately the same. As shown in Fig. 1, one end 221 of the coil 22 is connected to a sample-and-hold circuit 41 of the measurement unit 4, which will be described later. The other end 222 of the coil 22 is grounded.

[0021] <Current Conductor 3, Measurement Unit 4> As shown in FIG. 1 , the current conductor 3 is a circuit provided to conduct current to the exciter 21A of the shaft 21 of the probe 2. The current conductor 3 includes a power supply 31 and a clock unit 32. The clock unit 32 is connected to the inputs of the power supply 31 and a sample-and-hold circuit 41 (described later), and outputs clock signals to the power supply 31 and the sample-and-hold circuit 41. The power supply 31 is connected to the exciter 21A of the probe 2 via conductors 20A and 20B. The power supply 31 applies a voltage between the conductors 20A and 20B in synchronization with the clock signal output by the clock unit 32, and supplies a periodically changing pulse current Ie to the exciter 21A. The pulse current Ie flows in the directions of the conductor 20A, the exciter 21A, and the conductor 20B.

[0022] The measurement unit 4 is a circuit provided to measure the voltage generated across the coil 22 of the probe 2 (described later). The measurement unit 4 includes a sample-and-hold circuit 41, a filter 42, an amplifier 43, and a calculation unit 44. The sample-and-hold circuit 41 detects the peak value of the amplitude of the voltage Ecoil induced in the coil 22 of the probe 2. The sample-and-hold circuit 41 detects the peak value at a predetermined phase in synchronization with the clock signal output from the clock unit 32. The filter 42 removes high- and low-frequency components from the peak value signal output from the sample-and-hold circuit 41 to extract only the desired frequency component. The amplifier 43 amplifies the signal output from the filter 42 and outputs the amplified signal Eout to the input of the calculation unit 44. The calculation unit 44 calculates the external magnetic field Bex (see FIG. 3 ) applied to the probe 2 based on the signal Eout and outputs the result to a display unit (not shown).

[0023] <Operating Principle> The operating principle of the magnetic sensor 1 will be described with reference to Fig. 3. Hereinafter, a state in which no external magnetic field is applied to the probe 2 and no current is passed through the exciter 21A of the shaft 21 of the probe 2 (the state shown in Fig. 3(A)) will also be referred to as a "non-voltage applied state."

[0024] 3A illustrates a case where an external magnetic field is applied to the probe 2 in an unloaded state. The component of the applied external magnetic field that is in the same direction as the longitudinal direction of the probe 2 is referred to as the "external magnetic field Bex." In this case, as shown in FIG. 3B, the magnetic moment M of the magnetic body 21B is affected by the external magnetic field Bex and tilts in a direction inclined relative to the predetermined direction Y1 (referred to as the "inclined direction Y2"). The magnitude of the inclination of the inclined direction Y2 relative to the predetermined direction Y1 increases as the magnitude of the external magnetic field Bex increases.

[0025] In the state shown in Fig. 3(B), a voltage is applied between the conductors 20A and 20B connected to both ends of the exciter 21A by the current-carrying unit 3 (see Fig. 1). As a result, a pulse current Ie containing a DC component flows in the current-carrying direction. At this time, as shown in Fig. 3(C), the pulse current Ie flows in the exciter 21A from the end 211 connected to the conductor 20A to the end 212 connected to the conductor 20B. Hereinafter, the direction in which the pulse current Ie flows is referred to as the current-carrying direction.

[0026] The exciter 21A generates a magnetic field Be in response to the pulse current Ie. The direction of the magnetic field Be coincides with the direction of the magnetic moment M (predetermined direction Y1) in the absence of applied current. Therefore, the direction of the magnetic moment M of the magnetic body 21B changes from the inclined direction Y2 to the predetermined direction Y1 due to the influence of the magnetic field Be. Furthermore, as the direction of the magnetic moment M aligns with the predetermined direction Y1, a change in magnetic flux occurs within the coil 22 in the longitudinal direction of the coil 22. This change in magnetic flux causes a current to flow through the coil 22, generating a voltage Ecoil at both ends of the coil 22, as shown in FIG. 3(D).

[0027] 1, the measurement unit 4 measures the voltage Ecoil generated in the coil 22 using a sample-and-hold circuit 41, a filter 42, and an amplifier 43. The calculation unit 44 of the measurement unit 4 measures the magnitude of the external magnetic field Bex based on the signal Eout output from the amplifier 43.

[0028] <Manufacturing Method> A method for manufacturing the shaft body 21 of the probe 2 will be described with reference to Fig. 4. The manufacturing apparatus 6 for manufacturing the shaft body 21 has a front-end process 6A, a middle process 6B, and a back-end process 6C.

[0029] A bobbin 5A wound with a busbar (hereinafter referred to as "exciter 51A") made of copper wire is prepared at the most upstream portion. The exciter 21A of the probe 2 is finally produced by cutting the exciter 51A to an appropriate length. The exciter 51A is unwound from the bobbin 5A by the rotation of the most downstream drive silicon roller 80. The unwound exciter 51A comes into contact with a guide roller 60 and a power supply roller 61, is guided, and is transported toward the previous process 6A downstream of the power supply roller 61. The transport direction of the exciter 51A is opposite to the current-carrying direction of the exciter 21A produced by cutting the exciter 51A (see Figures 3(C) and (D)).

[0030] The pre-process 6A includes an electrolytic degreasing process 62, water-washing processes 63A and 63B, a pickling process 64, and a water-washing process 65. In the electrolytic degreasing process 62, a voltage is applied between the exciter 51A and the power supply roller 61 via the exciter 51A, thereby performing electrolytic degreasing of the exciter 51A. When a voltage is applied via the exciter 51A, the side of the electrolytic degreasing process 62A on the downstream side in the conveyance direction is set as the positive side, and the power supply roller 61 on the upstream side in the conveyance direction is set as the negative side. The direction of the current 62A flowing through the exciter 51A during electrolytic degreasing is opposite to the conveyance direction of the exciter 51A, in other words, the same direction as the current flow direction of the exciter 21A produced by cutting the exciter 51A (see FIGS. 3(C) and 3(D)).

[0031] The electrolytically degreased magnetic body 51A is washed with water in water washing processes 63A and 63B, washed with strong acid in pickling process 64, and washed with water in water washing process 65. The magnetic body 51A washed in the water washing processes 63A and 63B, pickling process 64, and water washing process 65 comes into contact with the power supply roller 71, is guided, and is transported toward the intermediate process 6B downstream of the power supply roller 71.

[0032] In the intermediate process 6B, a coating of magnetic material 51B is formed on the surface of the magnetic exciter 51A by electrolytic plating. The formed magnetic material 51B corresponds to the magnetic material 51B in the probe 2. The intermediate process 6B includes six plating processes (plating processes 72A, 72B, 72C, 72D, 72E, and 72F). In each of the plating processes 72A to 72F, a voltage is applied between the magnetic exciter 51A and the power feed roller 71 via the magnetic exciter 51A, and the magnetic material 51B, which is a coating of magnetic material, is electrolytically plated on the side surface of the magnetic exciter 51A. When a voltage is applied via the magnetic exciter 51A, the plating processes 72A to 72F on the downstream side in the conveyance direction are set as the positive side, and the power feed roller 71 on the upstream side in the conveyance direction is set as the negative side. In other words, the magnetic exciter 51A corresponds to the plating cathode, and the power feed roller 71 corresponds to the plating anode.

[0033] During electroplating, the voltage applied between the plating cathode (exciter 51A) and the plating anode (power supply roller 71) is adjusted so that the plating current Ip and bias current Ib flow in the same direction. The plating current Ip is the current required to apply a voltage between the plating cathode (exciter 51A) and the plating anode (power supply roller 71) to perform electroplating, and is, for example, 25 mA [Inayama 1]. The bias current Ib is the current required to align the magnetic moment M in the magnetic material 51B in a predetermined direction Y1, and is, for example, 75 mA [Inayama 2]. The direction of the current 73A flowing through the exciter 51A during electroplating is opposite to the transport direction of the exciter 51A, in other words, the same direction as the current flow direction of the exciter 21A produced by cutting the exciter 51A (see Figures 3(C) and (D)). The magnetic exciter 51A, on which the magnetic material 51B is formed as a coating, comes into contact with the preliminary roller 81, is guided, and is transported toward the subsequent process 6C downstream of the preliminary roller 81.

[0034] The subsequent process 6C includes water washing processes 82A and 82B and a draining process 83. The produced shaft 21 is washed with water in the water washing processes 82A and 82B. Water remaining in the magnetic body 51A washed in the water washing processes 82A and 82B is removed in the draining process 83. The drained magnetic body 51A is guided by a guide roller 84 toward the drive silicon roller 80. The magnetic body 51A that has passed through the drive silicon roller 80 is wound onto the take-up bobbin 5B.

[0035] The exciter 51A wound around the take-up bobbin 5B is cut to an appropriate length. This forms a shaft 21 including the exciter 21A coated with the magnetic material 21B. As shown in FIG. 2, conductors 20A and 20B are connected to both ends of the exciter 21A of the shaft 21. At this time, the end of the exciter 21A located downstream in the conveying direction during the manufacturing process is the end 211 to which the conductor 20A is connected. On the other hand, the end of the exciter 21A located upstream in the conveying direction during the manufacturing process is the end 212 to which the conductor 20B is connected. As a result, the current flow direction shown in FIG. 3C coincides with the direction of the current 73A flowing through the exciter 51A in the plating processes 72A to 72F. Furthermore, the coil 22 is wound around the shaft 21, completing the manufacture of the probe 2.

[0036] Example 1 Figure 5 is a graph showing the results of measurements carried out to optimize the iron-nickel alloy used as the material for the magnetic body 21B in the shaft 21 of the probe 2. The results shown in Figure 5(A) are a graph showing the relationship between the average iron content ratio in the iron-nickel alloy and the sensitivity of the magnetic sensor 1. From the results shown in Figure 5(A), it was found that the sensitivity tends to increase as the iron content in the iron-nickel alloy used as the material for the magnetic body 21B decreases.

[0037] The results shown in Figure 5(B) are graphs illustrating the relationship between the average iron content in the iron-nickel alloy and the linearity of the voltage Ecoil generated at both ends of the coil 22 of the magnetic sensor 1. Linearity indicates the linearity of the voltage Ecoil relative to the external magnetic field Bex, and is calculated as "linearity = standard deviation of the sensitivity of the magnetic sensor 1 / average sensitivity." The smaller the linearity value, the more accurate the external magnetic field Bex measured based on the voltage Ecoil. The results shown in Figure 5(B) indicate that by setting the average iron content in the range of at least 19% to 23% by weight, the linearity value can be suppressed to a range of 0% to 15%, enabling highly accurate measurement of the external magnetic field Bex. The results shown in Figures 5(A) and 5(B) indicate that by setting the average iron content in the range of at least 19% to 23% by weight, a magnetic sensor 1 can be obtained that can measure the external magnetic field Bex with high sensitivity and accuracy.

[0038] Example 2 FIG. 6 is a graph showing the results of measurements conducted to optimize the method of supplying the pulse current Ie to the probe 2. The results shown in FIG. 6 are a table showing the relationship between the magnitude of the DC component of the pulse current Ie and the sensitivity and noise of the magnetic sensor 1. The maximum value of the pulse current Ie was set to 0.6 A. The effective noise value was obtained through a bandpass filter with a frequency of 1 Hz to 10 Hz (bandwidth 9 Hz). As shown in FIG. 6, by increasing the DC component of the pulse current Ie, the sensitivity was slightly reduced, but the noise was significantly reduced. This demonstrates that superimposing a DC component on the pulse current Ie can improve the resolution of the measured external magnetic field Bex.

[0039] 7 is a graph showing the results of measurements carried out to clarify that orienting the probe 2 so that the inclination of the magnetic moment M relative to the predetermined direction Y1 in the circumferential direction is small in a no-voltage state can suppress noise. The results shown in FIG. 7 are obtained by adjusting the offset angle θ ０ 10 is a graph showing the relationship between the offset angle θ and the normalized noise Vn / N. ０ indicates the tilt of the magnetic moment from the circumferential direction. Offset angle θ０ is calculated by the following formula based on the maximum value Vp1m of the voltage Ecoil generated in the coil 22 when the external magnetic field Bex is applied, and the maximum value Vp10 of the voltage Ecoil generated in the coil 22 in an environment where the external magnetic field Bex = 0 μT. Note that it is assumed that the magnetic moment is aligned in the longitudinal direction of the probe 2 when an external magnetic field Bex is applied such that the peak of the voltage Ecoil of the coil 22 is maximized. θ ０ = sin ―１ (Vp1m / Vp10) The normalized noise Vn / N was calculated by dividing the effective value Vn of the noise measured with the bandwidth set to 9 Hz (1 Hz to 10 Hz) by the number of turns N of the coil 22.

[0040] The graph shown in Fig. 7 was obtained by measuring noise when a pulse current Ie was applied with the maximum pulse current set to 0.23 A and the DC component current values ​​set to 15 mA, 30 mA, and 45 mA. From the results shown in Fig. 7, it can be seen that the offset angle θ ０ There is a correlation between the voltage of the normalized noise Vn / N and the offset angle θ ０ The larger the offset angle θ, the larger the normalized noise Vn / N. ０ Therefore, it is presumed that by orienting the magnetic moment of the magnetic body 21B in the predetermined direction Y1 in the no-voltage state as in this embodiment, the noise associated with the precession can be suppressed and the external magnetic field Bex can be measured with high accuracy.

[0041] <Actions and Effects of the Present Embodiment> In the magnetic sensor 1, when no external magnetic field Bex is applied and no current is applied to the exciter 21A of the shaft 21 of the probe 2 (non-voltage applied state), the magnetic moment M of the magnetic body 21B is oriented in a predetermined direction Y1 (see FIG. 3A). In this case, the degree of change in the direction of the magnetic moment M in response to current application to the exciter 21A can be suppressed compared to when the magnetic moment M is not oriented in the predetermined direction Y1 (e.g., as in FIG. 8A). (See FIGS. 3B → 3C and 8B → 8C). Therefore, the magnetic sensor 1 can suppress precession caused by the change in the direction of the magnetic moment M. Therefore, the magnetic sensor 1 can measure the magnitude of the magnetic field Be generated by the change in the magnetic moment M when current is applied to the exciter 21A while the external magnetic field Bex is applied, in an environment where noise associated with precession is suppressed (FIG. 3D). Therefore, based on this measurement result, the magnetic sensor 1 can accurately measure the magnitude of the external magnetic field Bex. Furthermore, by preferably making the shape of the shaft body 21 cylindrical, the magnetic flux path in the circumferential direction of the magnetic body 21B is closed, and the generation of a demagnetizing field can be suppressed.

[0042] The power supply unit 31 of the current supply unit 3 supplies a pulse current Ie containing a DC component to the exciter 21A (see FIG. 3C). In this case, the magnetic sensor 1 can precisely orient the magnetic moment M of the magnetic body 21B in the predetermined direction Y1 by using the DC component of the pulse current Ie. Therefore, the magnetic sensor 1 can minimize noise caused by precession in response to changes in the magnetic moment M, thereby enabling even more accurate measurement of the external magnetic field Bex.

[0043] The magnetic sensor uses an iron-nickel alloy containing 19 to 23 wt % of iron as the material of the magnetic body 21B, thereby making it possible to suppress noise while maintaining sensitivity when measuring the external magnetic field Bex.

[0044] During the manufacturing process of the shaft 21 of the probe 2, the magnetic material 51B is formed on the surface of the exciter 51A by electrolytic plating. Here, the direction of the current 73A passed through the exciter 51A during electrolytic plating is set to the same direction as the pulse current Ie passed through the exciter 21A by the current conductor 3 (see FIG. 4). In this case, a coated magnetic material 21B can be formed on the exciter 21A, which can precisely orient the magnetic moment M in the predetermined direction Y1. Therefore, tilt of the magnetic moment M relative to the predetermined direction Y1 in the unenergized state can be suppressed. This minimizes noise associated with precession in response to changes in the magnetic moment M, enabling the manufacture of a magnetic sensor 1 capable of measuring the external magnetic field Bex with even greater precision.

[0045] When electrolytic plating is performed during the manufacturing process of the shaft 21 of the probe 2, the current passed through the exciter 51A includes a plating current Ip required to perform plating by applying a voltage between the plating cathode (exciter 51A) and the plating anode (power feed roller 71), and a bias current Ib for aligning the magnetic moment M in the magnetic body 21B in the predetermined direction Y1. Note that the direction of the plating current Ip and the direction of the bias current Ib are the same. In this case, in the manufactured magnetic sensor 1, it is possible to suppress the tilt of the direction of the magnetic moment M with respect to the predetermined direction Y1 in the no-voltage state.

[0046] <Modifications> The present invention is not limited to the above embodiment and various modifications are possible. The pulse current Ie passed from the current conductor 3 to the exciter 21A of the probe 2 does not need to have a DC component. The current conductor 3 may pass a current having a waveform other than a pulse current (for example, a square wave or a triangular wave) to the exciter 21A of the probe 2.

[0047] The materials of the excitation body 21A and the magnetic body 21B constituting the shaft body 21 of the probe 2 are not limited to those in the above embodiment and may be other materials. The iron content ratio contained in the iron-nickel alloy constituting the magnetic body 21B is not limited to 19 to 23 wt % and may be other content ratios.

[0048] The power supply unit 3 may have only the power supply unit 31, and may not have the clock unit 32. The measurement unit 4 may have only the amplifier 43 and the calculation unit 44, without having the sample-and-hold circuit 41 and the filter 42.

Claims

1. A magnetic sensor comprising: a shaft body having a long exciter made of a conductive non-magnetic material and a magnetic body made of a magnetic material covering the exciter; a coil in which an insulating conductor is wound spirally around the shaft body and whose direction of travel is along the longitudinal direction of the exciter; a current-carrying unit that passes current through the exciter on the shaft body; and a measurement unit that measures the voltage generated at both ends of the coil when current is passed through the exciter by the current-carrying unit, wherein when no external magnetic field is applied and no current is passed through the exciter by the current-carrying unit, the magnetic body has a magnetic moment oriented in a predetermined direction that is one of the orthogonal directions perpendicular to the longitudinal direction along the circumferential direction of the shaft body; and when an external magnetic field is applied, the magnetic moment is tilted with respect to the predetermined direction, When an external magnetic field is applied and current is applied to the exciter by the current-carrying unit, the magnetic field generated from the exciter by the current-carrying unit aligns the magnetic moment in the predetermined direction, and a magnetic field is generated in the process of aligning the magnetic moment, and a voltage is generated at both ends of the coil due to the magnetic field generated in the magnetic body in the process of aligning the magnetic moment, and the measurement unit measures the magnitude of the external magnetic field by measuring the voltage generated at both ends of the coil.

2. The magnetic sensor according to claim 1, wherein the current-carrying section applies a pulse current to the exciter.

3. The magnetic sensor according to claim 2, wherein the current-carrying section applies the pulse current containing a DC component to the exciter.

4. A magnetic sensor according to any one of claims 1 to 3, wherein the magnetic material is an iron-nickel alloy containing 19 to 23 wt % iron.

5. A magnetic sensor as described in any one of claims 1 to 4, characterized in that the magnetic material is formed on the surface of the exciter by electrolytic plating, and the direction of the current passed through the exciter when the electrolytic plating is performed is the same as the direction of the current passed through the exciter by the current-carrying unit.

6. The magnetic sensor described in claim 5, characterized in that the current passed through the magnetic exciter when the electrolytic plating is performed includes a plating current required to perform plating by applying a voltage between the magnetic exciter as a plating cathode and a plating anode, and a bias current for aligning the magnetic moment in the magnetic material, and the direction of the bias current is the same as the direction of the plating current.

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