JP2005315812A - Magnetic field sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic field sensor capable of detecting weak magnetic fields with high precision despite of its simple configuration. <P>SOLUTION: The magnetic field sensor is configured such that , while exciting current i consisting of pulsating flow biased to, at least, either of positive or negative is electrified toward a magnetic core 1 winded by detecting coils 21 and 22, and the induced voltages V1 and V2 generated in detecting coils 21 and 22 are offset when the detected magnetic field Hex does not exist to be impressed in the magnetic core 1 and, on the other hand, the induced voltages V1 and V2 induced in detected magnetic field Hex generated in detecting coils 21 and 22 are outputted when the aforementioned detected magnetic field Hex exists. Therefore, weak magnetic fields, the true object to be detected, can be detected without the influence of an unnecessary induced voltage generated depending on property and constitution of the magnetic core and detecting coils, resulting in enhancement of detecting precision and implement of more stable detection. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an orthogonal fluxgate type magnetic sensor that detects a magnetic field by passing an electric current through a magnetic body around which a detection coil is wound, and in particular, prevents a decrease in detection accuracy based on the magnetic anisotropy of the magnetic body. The present invention relates to a magnetic sensor that detects a magnetic field with high sensitivity and high stability.

  In general, a magnetic sensor is a basic component of sensing technology that uses research fields as an information medium. Active magnetic shield, detection of foreign matter by magnetism, environmental magnetic assessment, traffic measurement by magnetism, magnetic nondestructive inspection, magnetic motion capture Etc. are used.

  Conventionally, this type of background art is disclosed in Japanese Patent Application Laid-Open No. 2003-215220, and this is shown in FIG. 11 as a principle circuit configuration diagram of a conventional magnetic field sensor. In the figure, the conventional magnetic sensor has a magnetic wire 101 and a detection coil 201 wound around the magnetic wire 101, and a bias current from a DC power source 501 is added to a current in which the polarity output from the oscillator 401 is alternated on the magnetic wire 101. The bias current is supplied from a series power source 501, the polarity of this bias current is periodically switched by the first switch 601, and the sensitivity is reversed. By obtaining the circuit configuration, an output from which the offset is almost completely removed is obtained. The excitation current is a pulse train including a direct current, and the polarity of the pulse train is periodically inverted.

The conventional magnetic sensor based on the above configuration has a detection coil 201 wound around a magnetic wire 101 made of an elongated magnetic material, and superimposes a bias current on a current whose polarity is alternated on the magnetic wire 101 made of an elongated magnetic material. By using a magnetic flux sensor with an orthogonal flux gate and switching the polarity of the bias current so that the polarity of the sensitivity can be reversed, the sensitivity retains its magnitude and reverses its polarity, but the offset polarizes while maintaining its magnitude. Also keep unchanged. Thereby, the polarity of the DC bias current is set to be positive and the polarity of the DC bias current is inverted while the excitation magnetic field Hex is not changed, and the output obtained in the same way is obtained. Thus, an output from which the offset is almost completely removed is obtained.
JP 2003-215220 A

  Since the conventional magnetic field sensor according to the background art is configured as described above, even when the detected magnetic field does not exist, an induced voltage appears in the detection coil 201 when the exciting magnetic field due to the exciting current exists, In addition to causing an offset of the magnetic field sensor, there is a problem that drift occurs if it fluctuates with temperature.

  That is, FIG. 12 is a diagram for explaining the induced voltage of the detection coil in the conventional magnetic field sensor, where Ku is the magnitude of magnetic anisotropy, Js is the magnetization of the amorphous wire, Hdc is the DC component of the excitation magnetic field, and Hac is Each AC component is represented. Here, when Ku = 0 or the angle α = 0 between this Ku and the external magnetic field Hdc + Hacsin (2πft), even if the detected magnetic field Hex = 0, Js is inclined by the angle θ from the circumferential direction and excited. When the magnetic field is maximized, the angle θ is minimum, and when the excitation magnetic field is minimum, the angle θ is maximized and vibrates as shown in (1) and (2) in FIG. .

  Even in the absence of the detected magnetic field Hex, when an exciting current is passed, the exciting magnetic field is generated in the circumferential direction of the magnetic wire 101. Therefore, the magnetization in the magnetic wire 101 has the same period as the alternating current and the easy axis of magnetization. Vibrates between the direction and the circumferential direction. As a result of this vibration, the magnetization component projected in the longitudinal direction of the magnetic wire 101 also changes periodically, giving the detection coil 201 a periodically varying magnetic flux linkage, and its time derivative becomes an induced voltage of the detection coil 201. Appears between both terminals.

  In particular, when the DC bias reverses the polarity, a large magnetization reversal is induced and a spike-like transient voltage is generated. In the conventional techniques so far, there has been a problem that the induced voltage having information on the detected magnetization Hex cannot be separated from the induced voltage generated when the detected magnetization Hex is 0 and the spike-like voltage. As a result, when a high gain amplifier is connected to the subsequent stage of the detection coil 201, there are problems such as not only saturating the high gain amplifier but also generating an offset, increasing drift, and causing switching noise. It was.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a magnetic field sensor that can detect a weak magnetic field with high accuracy with a simple configuration.

  A magnetic field sensor according to the present invention includes a magnetic core made of a magnetic material having a predetermined length and a detection coil wound around the magnetic core, and an induced current is passed through the magnetic core to induce an induced voltage in the detection coil. In a magnetic field sensor based on an orthogonal fluxgate that detects a minute magnetic field, an excitation current consisting of a pulsating current biased with a direct current is applied to at least one of positive and negative in the magnetic core, and the detection coil is applied to the magnetic core. There is no detected magnetic field, and there is an detected voltage applied to the magnetic core that cancels the induced voltage generated when the exciting magnetic field due to the exciting current exists, and there is an exciting magnetic field due to the exciting current. Sometimes an induced voltage induced by the detected magnetic field is output.

  As described above, in the present invention, when an excitation current consisting of a pulsating current biased to at least one of positive and negative is supplied to the magnetic core around which the detection coil is wound, and there is no detected magnetic field applied to the magnetic core. Since the induced voltage generated in the detection coil is canceled when the induced voltage generated in the detection coil is canceled and the detected magnetic field is present, it is a true detection target. A weak magnetic field can be detected without being affected by an unnecessary induced voltage generated depending on the characteristics and configuration of the magnetic core and the detection coil, so that detection accuracy can be improved and more stable detection can be performed.

The magnetic field sensor according to the present invention reverses the excitation direction at a cycle in which the excitation current flowing in the magnetic core is longer than the fluctuation cycle of the pulsating flow as necessary.
In this way, in the present invention, the excitation current flowing in the magnetic core is reversed in the excitation direction at a period longer than the fluctuation period of the pulsating flow, so that a plurality of detections are detected from the detection coil by the pulsating flow in the period in which the excitation direction is reversed. In this way, the induced voltage is averaged, and the spike voltage can be suppressed and the offset can be prevented from being generated, so that the weak magnetic field can be detected more stably.

  In the magnetic field sensor according to the present invention, if necessary, the excitation current flowing in the magnetic core reverses the excitation direction in a cycle longer than the fluctuation cycle of the pulsating flow, and the polarity of the induced voltage induced in the detection coil is in the magnetic core. It reverses in synchronization with the long period of the exciting current that flows.

  Thus, in the present invention, the excitation direction of the excitation current is reversed at a period longer than the fluctuation period of the pulsating current, and the polarity of the induced voltage is reversed in synchronization with the period of the excitation current. The induced voltage detected from the detection coil can be averaged and output by the pulsating current during the period of reversing the current. If an amplifier that amplifies the induced voltage is provided immediately after the output of the detection coil, offset by this amplifier is prevented. Therefore, a weak magnetic field can be detected more stably.

  In the magnetic field sensor according to the present invention, if necessary, the magnetic core is formed by arranging even number of magnetic bodies in parallel and the detection coil is formed by winding the even number of magnetic bodies. The magnetic bodies are divided into two sets, and the detection coils wound around the two sets of magnetic bodies are connected so as to cancel the induced voltage generated when there is no exciting magnetic field due to the exciting current.

  As described above, in the present invention, an even number of magnetic bodies each having a detection coil wound thereon are arranged in parallel, and the even number of magnetic bodies are divided into two sets, and the detection coils of each group are excited magnetic fields generated by an excitation current. Because it is connected so as to cancel the induced voltage generated when there is no current, the magnetic flux interlinked by each magnetic material arranged in parallel is transmitted evenly under the same conditions, and the excitation magnetic field due to the excitation current Can suppress the induced voltage generated as much as possible and perform highly accurate and stable detection.

In the magnetic field sensor according to the present invention, if necessary, a magnetic core is formed by bending a magnetic body having a predetermined length into a substantially U shape, and a detection coil is wound around each parallel portion of the substantially U-shaped magnetic body. Is.
Thus, in the present invention, a magnetic body having a predetermined length is bent into a substantially U shape to form a magnetic core, and the detection coils are wound around the parallel portions of the U shape magnetic body. Since it can be formed by a pair of magnetic bodies having similar magnetic anisotropy characteristics, the induced voltage generated when there is no exciting magnetic field can be canceled more reliably, and highly accurate and stable detection can be performed.

In the magnetic field sensor according to the present invention, if necessary, a magnetic core is formed by bending a magnetic body having a predetermined length into a substantially U shape, and a detection coil is wound around a parallel portion of the substantially U-shaped magnetic body. It is to be turned.
In this way, in the present invention, the magnetic body forming the magnetic core is bent into a substantially U shape, and the U-shaped magnetic body is commonly wound around the detection coil. The exciting currents flowing in opposite directions flow through the magnetic bodies and the detected magnetic field is transmitted in the same direction, so that the exciting magnetic field due to the exciting current can be canceled more reliably, and the detection accuracy can be improved with a simple configuration.

  In the magnetic field sensor according to the present invention, the magnetic core is formed of a magnetic body having a circular cross section as necessary. As described above, in the present invention, the cross section of the magnetic material forming the magnetic core is circular, so that the outer periphery of the magnetic material is evenly magnetized, and the residual magnetic hysteresis is prevented, thereby improving the detection accuracy. Can be made.

  In the magnetic field sensor according to the present invention, the current value of the DC current to be biased is larger than the amplitude of the pulsating current as necessary. As described above, in the present invention, by making the bias direct current larger than the amplitude of the superimposed pulsating current, the exciting current of the pulsating current does not zero-cross, and the weak magnetic field is detected at a cycle twice that of the pulsating current. Therefore, the detection accuracy can be improved more reliably.

  The magnetic field sensor according to the present invention is formed by connecting detection coils wound around two sets of magnetic bodies in series with opposite polarities as necessary. As described above, in the present invention, the detection coils wound around the two sets of magnetic bodies are connected so as to be connected in series with the magnets reversed, so that when an excitation current is passed through the magnetic bodies, the excitation magnetic field Even if this occurs, it is possible to cancel the excitation magnetic field and suppress the induced voltage in the detection coil, and the detection accuracy can be improved with only a simple circuit configuration.

  The magnetic field sensor according to the present invention includes a magnetic core made of a magnetic material having a predetermined length and a plurality of detection coils wound around the magnetic core as needed, and an excitation current is passed through the magnetic core to the detection coil. In the magnetic field sensor based on an orthogonal fluxgate that detects a minute magnetic field by an induced voltage, an excitation current consisting of a pulsating current biased with a direct current is applied to the magnetic core at least one of positive and negative, and the plurality of detections Each coil outputs an induced voltage generated when there is no magnetic field to be detected applied to the magnetic core and there is an exciting magnetic field due to an exciting current, and a difference is obtained based on a signal corresponding to the induced voltage. The difference based on the signal corresponding to the induced voltage induced in the detected magnetic field when the detected magnetic field applied to the magnetic core exists and the excited magnetic field due to the excitation current exists. And outputs a.

  As described above, in the present invention, when an excitation current consisting of a pulsating current biased to at least one of positive and negative is supplied to the magnetic core around which the detection coil is wound, and there is no detected magnetic field applied to the magnetic core. A signal corresponding to the induced voltage induced by the detected magnetic field generated in the detection coil when the difference is obtained based on the signal corresponding to the induced voltage caused by the excitation current generated in the detection coil and the detected magnetic field exists. Therefore, the weak magnetic field that is the true detection target can be detected without being affected by the unnecessary induced voltage generated depending on the characteristics and configuration of the magnetic core and the detection coil. The detection accuracy can be improved and more stable detection can be performed.

(First embodiment of the present invention)
Hereinafter, a magnetic field sensor according to a first embodiment of the present invention will be described with reference to FIGS. 1 is a circuit configuration diagram of the magnetic field sensor according to the present embodiment, FIG. 2 is a diagram of each magnetic field vector when there is no detected magnetic field of the magnetic field sensor in FIG. 1, and FIG. 3 is an induced voltage of the magnetic field sensor in FIG. FIG. 4 is a magnetic field vector diagram in the case where the detected magnetic field of the magnetic field sensor in FIG. 1 is present, and FIG. 5 is an induced voltage cancellation timing chart of the magnetic field sensor in FIG.

  In each of the drawings, the magnetic field sensor according to the present embodiment is formed by arranging two magnetic bodies 11 and 12 having a predetermined length in parallel, and connecting these magnetic bodies 11 and 12 in series with an electric wire 13. And the detection coils 21 and 22 wound around the magnetic bodies 11 and 12 of the magnetic core 1 with different polarities. The detection coils 21 and 22 are connected in series, and the series connection is made. The detection output unit 2 having each end as an output terminal 23, 24 is connected in series to the series circuit of the magnetic bodies 11, 12, and the magnetic body 11, 12 is biased with an alternating current AC by a direct current DC. And a power supply unit 3 for supplying the exciting current i.

  Next, the operation of the present embodiment based on the above configuration will be described. First, when the detected magnetic field Hex, which is a weak magnetic field, does not exist, when the excitation current i is supplied to the series circuit of the magnetic bodies 11 and 12, each magnetic field vector form as shown in FIG.

  In the figure, Hexc is the direction of the exciting magnetic field induced by the exciting current i, Ku is the magnitude of the assumed uniaxial magnetic anisotropy, the line segment of the arrowhead on both sides is its easy axis direction, Js is the magnetic body 11, 12 magnetization directions are shown. This magnetization Js has the lowest energy state when it is parallel to the direction of Ku, that is, it tries to be parallel. These magnetic field direction aspects have 180 degree symmetry.

The winding direction of the detection coils 21 and 22 is counterclockwise on the right side and counterclockwise on the left side in the direction of the excitation current i flowing through the magnetic bodies 11 and 12 which are magnetic wires. It is in the clockwise direction.
When the detected magnetic field Hex = 0, the direction components Jso of the magnetization Js in the magnetic line direction are opposite in the magnetic bodies 11 and 12, respectively. The magnitude of the directional component Jso represents the axial magnetic flux component of the magnetic bodies 11 and 12 in the magnetic bodies 11 and 12. It can be seen that these polarities are in the same direction as the excitation current i. In this way, when the induced voltage is observed in the direction shown in the figure, the result is as shown in FIG.

  As shown in FIGS. 3A and 3B, the induced voltage V 1 is induced from the detection coil 21, and the induced voltage V 2 is induced from the detection coil 22. When the characteristics of the magnetic bodies 11 and 12 of the magnetic core 1 and the winding conditions of the detection coils 21 and 22 match, the detection coils 21 and 22 are added by connecting them in series, and from the output terminals 23 and 24, The induced voltages V1 and V2 cancel each other, and the output becomes “0” (see FIG. 3C).

Further, when the detected magnetic field Hex, which is a weak magnetic field, is present, if the exciting current i is supplied to the series circuit of the magnetic bodies 11 and 12, each magnetic field vector form as shown in FIG. In the figure, when a detected magnetic field Hex is applied and transmitted through the magnetic bodies 11 and 12, the magnetization Js of the magnetic bodies 11 and 12 is affected by the detected magnetic field Hex. Further, when the axial direction (longitudinal direction) of the magnetic bodies 11 and 12 is the Z-axis, the magnetization components in the Z-axis direction of the magnetization Js are Js21 and Js22. Since the magnetic field Hexc is substantially perpendicular, and the magnitude Ku of the uniaxial magnetic anisotropy is located outside this substantially perpendicular range, it changes at a small angle θ1 with respect to the exciting magnetic field Hexc. On the other hand, in the magnetic body 12, the detected magnetic field Hex and the excitation magnetic field Hexc are substantially perpendicular, and the magnitude Ku of uniaxial magnetic anisotropy is located within the substantially perpendicular range. It changes with a large angle θ2 (θ2> θ1).

  Due to the difference between the angle θ1 and the angle θ2 at which the magnetization Js changes, an induced voltage V1 corresponding to the angle θ1 is output from the detection coil 21 as shown in FIG. 5 (see FIG. 5A) and detected. An induced voltage V2 corresponding to the angle θ2 is output from the coil 22 (see FIG. 5B). These induced voltages V1 and V2 are added because the detection coils 21 and 22 are connected in series, and are output from the output terminals 23 and 24 as addition results as shown in FIG.

(Second embodiment of the present invention)
The magnetic field sensor according to the present embodiment will be described with reference to FIGS. FIG. 6 is an overall circuit configuration diagram of the magnetic field sensor according to this embodiment, and FIG. 7 is an induced voltage cancellation timing chart in the magnetic field sensor shown in FIG.
In each of the drawings, the magnetic field sensor according to the present embodiment is the same as the magnetic field sensor according to the first embodiment shown in FIG. 1, but the detection output including the magnetic core 1 including the magnetic bodies 11 and 12 and the detection coils 21 and 22. Unit 2 and a power source unit 3, and the detection coils 21 and 22 of the detection output unit 2 have output terminals 23 a and 23 b and 24 a and 24 b without being connected in series, and the output terminals 23 a and 23 b , 24a and 24b are connected to amplifiers 41 and 42 and envelope calculation units 51 and 52, and a subtracter 6 for obtaining a difference between outputs of the envelope calculation units 51 and 52 is connected.

  Next, the operation of the present embodiment based on the above configuration will be described. First, as in the first embodiment, the induced voltages V1 and V2 are output from the detection coils 21 and 22 both when the detected magnetic field Hex is present and when it is not present (FIG. 7A). (See (B)).

  The output induced voltages V1 and V2 are input to the amplifiers 41 and 42 and amplified with a predetermined amplification factor, and the envelope calculation units 51 and 52 perform half-wave rectification on the amplified induced voltages V1 and V2, respectively. The DC induced voltages V1d and V2d of the envelope are calculated (see FIGS. 7C and 7D). A difference between the DC induced voltages V1d and V2d is obtained by the subtractor 6, and the value of the detected magnetic field Hex can be detected as a DC output.

  In each of the above embodiments, the detection coils 21 and 22 are not connected in series, and the output terminals 23a, 23b, 24a, and 24b are connected to the amplifiers 41 and 42, the envelope calculation units 51 and 52, and the subtractor 6 are connected to the direct current. Although the configuration is obtained by output, the detection coils 21 and 22 are connected in series as in the first embodiment, and the AC output output from the terminal of this series circuit is synchronized with the AC excitation frequency of the excitation current i. It can also be set as the structure which detects the to-be-detected magnetic field Hex by performing a rectification (phase detection).

(Third embodiment of the present invention)
The magnetic field sensor according to this embodiment will be described with reference to FIGS. 8 is a circuit configuration diagram of the magnetic field sensor according to the present embodiment, FIG. 9 is an output waveform diagram of induced voltage in the magnetic field sensor described in FIG. 8, and FIG. 10 is an output waveform of output induced voltage in the magnetic field sensor described in FIG. A noise characteristic diagram is shown.

  In each of the drawings, the magnetic field sensor according to the present embodiment includes a magnetic core 1 having a U-shape having a linear portion 10a, 10b parallel to one magnetic body 10 evenly bent in two, and the magnetic core 1 A detection output unit 2 formed by connecting detection coils 21 and 22 wound in the opposite directions around the straight portions 10a and 10b in series, and a power source for directly supplying an excitation current i to the magnetic body 10 of the magnetic core 1 It is a structure provided with the part 3.

  The magnetic core 1 has a configuration in which a magnetic body 10 is formed of a Co-based amorphous magnetic wire having a circular cross section, and glass pipes 10c and 10d are attached to linear portions 10a and 10b of the magnetic body 10. The detection coils 21 and 22 of the detection output unit 2 are configured to be wound around the straight portions 10a and 10b via the glass pipes 10c and 10d. The power source unit 3 is configured to generate and output an excitation current i by superimposing a direct current DC having a current value sufficiently larger than the alternating current AC on the alternating current AC.

  Next, the operation of the magnetic field sensor according to this embodiment based on the above configuration will be described. First, when an excitation current i is supplied from the power supply unit 3 to the magnetic body 10, the excitation current i flowing through the magnetic core 1 generates an excitation magnetic field. This excitation magnetic field is linked to the detection coils 21 and 22 to generate the induced voltages V1 and V2 in the detection coils 21 and 22 (in the direction of solid arrows in FIG. 8). And the induced voltages V1 and V2 cancel each other and cancel each other.

  On the other hand, when a detected magnetic field Hex exists outside and this detected magnetic field Hex passes through the magnetic bodies 11 and 12, induced voltages V1H and V2H induced by the detected magnetic field Hex are respectively generated (broken arrows in FIG. 8). The induced voltages V1H and V2H are added and output, but this output does not include the induced voltage when the detected magnetic field Hex does not exist (Hex = 0), and the weak magnetic field is not included. The detected magnetic field Hex can be detected with high accuracy.

  Further, the operation of the magnetic field sensor according to the present embodiment will be described in detail with reference to FIG. In the relationship shown in FIG. 12, the induced voltages V1 and V2 generated when the detected magnetic field Hex = 0 is substantially equal and can be substantially canceled by subtraction. FIG. 9 shows the result of examining the induced voltage by reducing the external magnetic field in the simple magnetic shield. FIG. 2A shows an observation of the induced voltage V1 output from one of the detection coils 21, with the detection coils 21 and 22 being separated without being connected. FIG. 5B shows the observations made by connecting the wires so that V1 + V2. In this observation, the exciting current i is a case where a rectangular wave current having a large amplitude of 1 kHz is superimposed on an alternating current of 50 kHz, and the biased direct current DC is switched. It can be seen that the significant reduction of the sine wave-like induced voltage cancels the induced voltage when the detected magnetic field Hex = 0 described with reference to FIG. Moreover, the reduction of the spike voltage shows the effect of suppressing the transient phenomenon accompanying the bias switching.

  Next, it will be described that the response to the detected magnetic field Hex is not canceled by the connection relationship between the detection coils 21 and 22. It is already known in the prior art that the positive / negative sensitivity to the detected magnetic field Hex has a one-to-one correspondence with the direction of the DC current DC to be biased. Since it has magnetic sensitivity with respect to the detected magnetic field Hex parallel to the linear portions 10a and 10b on which the detection coils 21 and 22 of the magnetic core 1 bent in a U-shape are provided, the direction of the detected magnetic field Hex is the linear portion 10a. 10b. If the direction of the detected magnetic field Hex is the same as the direction of the direct current DC of the bias in the right straight portion 10a around which the detection coils 21 and 22 are wound, the left straight portion 10b is opposite.

  Therefore, if the sensitivity is positive in the right straight portion 10a, the sensitivity is negative in the left straight portion 10b.

  As a result, the detection coils 21 and 22 are connected in series with their polarities reversed, so that it is possible to obtain an output twice that of the single detection coil 21 (or 22). That is, the influence of unnecessary magnetic flux linkage that adversely affects the operation of the magnetic field sensor is canceled, and only a useful magnetic flux change caused by the detected magnetic field Hex can be detected with double sensitivity. .

  Furthermore, in the present embodiment, when a high gain amplifier that amplifies the induced voltage induced by the detection coils 21 and 22 is provided in the subsequent stage, saturation of the high gain amplifier can be avoided, so that the magnetic field sensor is highly sensitive and low. Noise can be generated, and the induced voltage when the detected magnetic field Hex = 0, which causes an offset, can be suppressed, so that high stabilization can be achieved. Such effects are shown in FIG. 9 and FIG. 10 as characteristic diagrams based on the test data. FIG. 9 is an output waveform diagram in which the induced voltage is examined by reducing the external magnetic field within the simple magnetic shield. In FIG. 6A, a magnetic material is separated, and a detection coil is wound around each of the magnetic materials, and an induced voltage V1 (or V2) output from the detection coil is shown in FIG. . In FIG. 2B, each detection coil is wound around a magnetic material arranged in parallel, and the detection coils are connected in series with opposite polarities, and the induced voltage (V1 + V2) from each detection coil is the same. The waveform is shown in FIG. When the output waveforms of (A) and (B) are compared, it is apparent that the effects of the noise voltage level and the spike voltage are attenuated.

  FIGS. 10A and 10B show noise characteristics when the sensitivity is about 1 mV / 1 nT, and the drift is 0.5 nT or less in 4 hours of observation as shown in FIG. 9B. . Thus, a highly sensitive and highly stable magnetic field sensor can be realized by this embodiment.

(Other embodiments of the present invention)
A magnetic core of a magnetic field sensor according to another embodiment of the present invention is formed by rolling a thin plate-like magnetic body (for example, an amorphous magnetic ribbon) into a cylindrical shape, and providing a conductive wire on the rolled cylindrical body of the magnetic body. It can also be configured by inserting a filler (for example, epoxy resin) between the cylindrical body and the conductive wire.

  In addition, the magnetic core of the magnetic field sensor according to another embodiment can be formed by plating a magnetic body (for example, permalloy) around a conductive wire (for example, a cylindrical copper wire). In addition to the plating of the magnetic material, a magnetic material such as permalloy can be formed in advance into a hollow cylindrical shape and integrated with the conductive wire to form a magnetic core.

  Furthermore, in a magnetic field sensor according to another embodiment of the present invention, an even number of magnetic cores composed of an elongated ferromagnetic body and one detection coil wound around the ferromagnetic body are arranged in parallel with each other (for convenience, parallel to the Z axis), A common exciting current is passed through the magnetic bodies, the magnetic cores are divided into two groups, an exciting current is passed through the magnetic bodies in one group in the positive direction of the Z axis, and the magnetic bodies in the other group are passed through. A configuration may also be adopted in which an excitation current is passed in the negative direction of the Z-axis and the polarity of the bypass current is periodically switched by periodic switching. An amorphous magnetic wire can be used for the elongated magnetic body. This elongated magnetic body can be divided into two groups so that the size and magnetic properties are paired.

It is a circuit block diagram of the magnetic field sensor which concerns on the 1st Embodiment of this invention. It is each magnetic field vector mode figure in case the to-be-detected magnetic field of the magnetic field sensor in FIG. 1 does not exist. 3 is a timing chart for canceling an induced voltage of the magnetic field sensor in FIG. 2. It is each magnetic field vector mode diagram in case the to-be-detected magnetic field of the magnetic field sensor in FIG. 1 exists. 5 is an induced voltage cancellation timing chart of the magnetic field sensor in FIG. 4. It is a whole circuit block diagram of the magnetic field sensor which concerns on the 2nd Embodiment of this invention. 7 is an induced voltage canceling timing chart in the magnetic field sensor shown in FIG. 6. It is a circuit block diagram of the magnetic field sensor which concerns on the 3rd Embodiment of this invention. It is an output waveform figure of the induced voltage in the magnetic field sensor described in FIG. The upper figure in Fig. 10 shows the noise characteristics of a conventional magnetic field sensor. The figure below is this time. Both vertical axes are nT / √Hz, and are the effective values of noise output per 1 Hz. The horizontal axis is frequency. It is a noise characteristic figure of the output induced voltage in the magnetic field sensor described in FIG. It is a principle circuit block diagram of the conventional magnetic field sensor. It is explanatory drawing of the induced voltage of the detection coil in the conventional magnetic field sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetic core 2 Detection output part 3 Power supply part 6 Subtractor 10, 11, 12 Magnetic body 10a, 10b Linear part 10c, 10d Glass pipe 21, 22 Detection coil 23, 24, 23a * 23b, 24a * 24b Output terminal 41,42 Amplifier 51, 52 Envelope calculation unit 101 Magnetic wire 201 Detection coil 401 Oscillator 501 DC power supply 601 Switch i Excitation current V1, V2, V1H, V2H Induced voltage (V1H, V2H not shown)
V1d, V2d DC induced voltage

Claims (10)

An orthogonal flux gate comprising a magnetic core made of a magnetic material having a predetermined length and a detection coil wound around the magnetic core, and detecting a minute magnetic field by an induced voltage induced in the detection coil by passing an excitation current through the magnetic core In a magnetic field sensor based on
An excitation current consisting of a pulsating current biased with a direct current is applied to at least one of positive and negative in the magnetic core,
The detection coil cancels the induced voltage generated when there is no detected magnetic field applied to the magnetic core and there is an excited magnetic field due to an excitation current, and there is a detected magnetic field applied to the magnetic core. A magnetic field sensor that outputs an induced voltage induced by the detected magnetic field when an exciting magnetic field due to an exciting current is present. The magnetic field sensor according to claim 1,
A magnetic field sensor, wherein an excitation current flowing in the magnetic core reverses an excitation direction at a period longer than a fluctuation period of a pulsating flow. The magnetic field sensor according to claim 1,
The excitation current flowing in the magnetic core reverses the excitation direction in a cycle longer than the fluctuation cycle of the pulsating flow, and the polarity of the induced voltage induced in the detection coil is reversed in synchronization with the long cycle of the excitation current flowing in the magnetic core. A magnetic field sensor characterized by The magnetic field sensor according to any one of claims 1 to 3,
The magnetic core is formed by arranging an even number of magnetic bodies in a parallel state,
The detection coil is formed by winding an even number of magnetic bodies,
The even number of magnetic bodies are divided into two sets, and a detection coil wound around the two sets of magnetic bodies is connected so as to cancel an induced voltage generated by an exciting magnetic field caused by an exciting current. Sensor. The magnetic field sensor according to claim 4, wherein
A set of magnetic bodies of the magnetic core is formed by bending a magnetic body having a predetermined length into a substantially U shape, and a detection coil is wound around each parallel portion of the substantially U-shaped magnetic body. Magnetic field sensor. The magnetic field sensor according to claim 4, wherein
A magnetic field sensor, wherein the magnetic core is formed by bending a magnetic body having a predetermined length into a substantially U shape, and a detection coil is wound around a parallel portion of the substantially U-shaped magnetic body. The magnetic field sensor according to any one of claims 1 to 6,
The magnetic core is formed of a magnetic body having a circular cross section. The magnetic field sensor according to any one of claims 1 to 7,
A magnetic field sensor, wherein a current value of the biased direct current is larger than the amplitude of the pulsating current. The magnetic field sensor according to any one of claims 4, 5, 7, and 8,
A magnetic field sensor, wherein the detection coils wound around the two sets of magnetic bodies are formed in series with opposite polarities. A quadrature that includes a magnetic core made of a magnetic material of a predetermined length and a plurality of detection coils wound around the magnetic core, and detects a minute magnetic field by an induced voltage induced in the detection coil by passing an excitation current through the magnetic core. In magnetic field sensors based on fluxgates,
An excitation current consisting of a pulsating current biased with a direct current is applied to at least one of positive and negative in the magnetic core,
The plurality of detection coils each output an induced voltage generated when there is no magnetic field to be detected applied to the magnetic core and there is an exciting magnetic field due to an exciting current, and based on a signal corresponding to the induced voltage When the detected magnetic field applied to the magnetic core exists and the excitation magnetic field due to the excitation current exists, the difference is output based on the signal corresponding to the induced voltage induced in the detected magnetic field. Magnetic field sensor characterized by this.

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