JP2020122691A - Orthogonal fluxgate sensor - Google Patents

Abstract

To provide an orthogonal fluxgate sensor with reduced noise.SOLUTION: An orthogonal fluxgate sensor 1 comprises: an elongated ferromagnetic core 2; excitation units 4, 5 that makes an exciting current in which a bias current having a magnitude equal to or greater than the amplitude of an alternating current is superimposed on the alternating current of a predetermined cycle pass in the axial direction of the core 2, to excite the core; a detection coil 3 wound around the core 2; and magnetization promoting units 4, 5, 7, 8 that magnetize the core 2 with larger magnetizing force than those of the excitation units 4, 5.SELECTED DRAWING: Figure 1

Description

The present invention relates to an orthogonal fluxgate sensor.

A fluxgate sensor is known as one of magnetic sensors. In this flux gate sensor, the exciting current is used to excite the core of the ferromagnetic material, and the strength of the magnetic field applied to the core is obtained from the induced voltage generated in the detection coil wound around the core. One of such fluxgate sensors is the orthogonal fluxgate sensor described in Patent Document 1. In this orthogonal fluxgate sensor, the core is excited with an exciting current in which an alternating current component of frequency f and a bias current larger than the amplitude of this alternating current component are superposed, and the component of frequency f generated from the detection coil can be used for the calculation. it can.

JP, 2002-277522, A

In the orthogonal fluxgate sensor described in the cited document 1, when a magnetic field is applied to the core, a component having the same frequency as the AC component of the exciting current is output as the induced voltage in the detection coil. Therefore, in obtaining the strength of the magnetic field applied to the core, a component having the same frequency as the AC component of the exciting current in the induced voltage of the detection coil can be used, and the configuration can be simplified. In addition, since the direction of the magnetic field excited by the core is not reversed (excitation becomes unipolar) due to the superposition of the bias current, noise caused by magnetization reversal is compared to the configuration in which the magnetic field excited by the core is reversed Occurrence can be suppressed.

However, depending on the magnetism of the core before sensing, noise (Barkhausen noise) due to magnetization reversal may occur during sensing.

The present invention has been made in view of the above problems, and an object thereof is to provide an orthogonal fluxgate sensor with reduced noise.

An embodiment of the orthogonal fluxgate sensor of the present invention for solving the above-mentioned problems is
An elongated ferromagnetic core,
An exciting current in which a bias current having a magnitude equal to or larger than the amplitude of the alternating current is superimposed on the alternating current of a predetermined cycle, and an exciting portion for flowing the axial direction of the core to excite the core,
A detection coil wound around the core,
A magnetization promoting section that magnetizes the core with a larger magnetizing force than the exciting section;
It is characterized by having.

According to the above orthogonal fluxgate sensor, Barkhausen noise at the start of sensing can be reduced by promoting magnetization of the core related to sensing by the magnetization promoting unit and aligning magnetic domains in one direction.

Also, in the orthogonal fluxgate sensor described above,
The magnetization promoting unit,
A magnetization promoting current having the same polarity as the bias current and larger than the exciting current may flow to magnetize the core.

According to the above orthogonal fluxgate sensor, the magnetization of the core can be promoted by using the magnetization promoting current, and Barkhausen noise at the start of sensing can be reduced.

According to the embodiment of the orthogonal fluxgate sensor of the present invention, it is possible to provide an orthogonal fluxgate sensor with reduced noise.

It is a schematic diagram showing composition of orthogonal type flux gate sensor 1 of this embodiment. It is a model figure which shows an example of the change of the state of the core 2 of the orthogonal type flux gate sensor 1. FIG. 4 is a diagram showing an example of an exciting current of only an alternating current, and a change of the magnetic flux in the axial direction of the core 2 and the output voltage of the detection coil 3 accompanying the exciting current. FIG. 6 is a diagram showing an exciting current in which an alternating current is biased, and accompanying changes in the axial magnetic flux of the core 2 and the output voltage of the detection coil 3. 6 is a model diagram showing an example of changes in the direction of magnetization J at a point P on the peripheral surface of the core 2. FIG. It is a figure which shows the initial magnetization curve when magnetizing the ferromagnetic material in a demagnetized state.

Hereinafter, an example of the orthogonal fluxgate sensor of the present embodiment will be described with reference to the drawings.

FIG. 1 is a schematic diagram showing the configuration of an orthogonal fluxgate sensor 1 of this embodiment.

The fluxgate sensor 1 according to the present embodiment includes a core 2 made of a ferromagnetic material (for example, supermalloy, amorphous, etc.), a detection coil 3 wound around the core 2, and an AC power source connected in series to the core 2. 4 and a DC power supply 5. The core 2 is excited by an exciting current obtained by superimposing a bias current from the DC power supply 5 on an AC current having a frequency fHz from the AC power supply 4. Here, the magnitude of the bias current from the DC power supply 5 is set to be larger than the amplitude of the AC current from the AC power supply 4. Further, the detection coil 3 is connected to a detection circuit 6 that extracts a fHz component of the voltage induced in the detection coil 3 by applying an external magnetic field and outputs a voltage corresponding to the magnitude of the external magnetic field. ..

Although the core 2 has a cylindrical shape, a thin plate shape or a wire shape may be used as long as it has an elongated shape. Further, the bias current from the DC power source 5 has a positive polarity, but the polarity may be a negative polarity, and it is sufficient if the entire excitation current has a positive or negative polarity.

A time constant circuit 7 and a start-up detection circuit 8 for detecting power-on are connected to the DC power supply 5. When the activation detection circuit 8 detects that the power supply is turned on, the time constant circuit 7 outputs a signal to the DC power supply 5 for a fixed time (for example, 1 second). When this signal is input, the DC power supply 5 supplies a DC current larger than the DC bias current at the time of sensing to the core 2. As a result, a configuration is adopted in which a large current (for example, 2 to 5 times the maximum value of the exciting current) is passed through the core 2 at the start of sensing.

In the following description, the relationship of B=μ ₀ H+J between the magnetic flux density B and the magnetic field H and the magnetization J is used (where μ ₀ is the magnetic permeability of vacuum). The magnetic flux is an area integral of the magnetic flux density on a specific surface. For example, when the magnetic flux density in the core is integrated over the cross section of the core, the magnetic flux passing through the core can be obtained.

[When the exciting current is AC component only]
Before explaining the operation principle of the orthogonal fluxgate sensor 1, the operation when an exciting current of only an alternating current is used without superimposing a bias current will be described. FIG. 2 is a model diagram showing an example of changes in the state of the core 2 of the orthogonal fluxgate sensor 1. Further, FIG. 3 is a diagram showing an example of an exciting current of only an alternating current, and accompanying changes in the axial magnetic flux of the core 2 and the output voltage of the detection coil 3. In the following description, it is assumed that an external magnetic field is applied along the axial direction of the core 2 (the direction from left to right in FIG. 1, the direction from bottom to top in FIG. 2).

When the exciting current Id to the core 2 is 0, the core 2 is magnetized only by the external magnetic field. Here, it is assumed that the magnetic flux in the axial direction inside the core 2 is maximum (the magnetic flux of the external magnetic field is most attracted to the core 2) in this state. FIG. 2A shows that when the exciting current Id to the core 2 is 0, the magnetic flux of the external magnetic field is attracted to the core 2 and passes through the inside of the core 2 by a magnetic flux line indicated by a broken line. Is shown in.

From here, when the exciting current Id increases, the core 2 is magnetized by the magnetic field generated by the external magnetic field and the exciting current Id. In this state, as the exciting current Id increases, the magnetization direction of the core 2 is oriented in the circumferential direction, which is the exciting direction, and the magnetic flux in the axial direction inside the core 2 decreases (the magnetic flux attracted to the core 2 decreases). .. The arrow (1) shown in FIG. 2 indicates a period in which the magnetic flux in the axial direction inside the core 2 decreases as the exciting current Id increases in the positive direction. When the exciting current Id further increases and the magnetization direction of the core 2 is oriented in the most circumferential direction, the magnetic flux in the axial direction inside the core 2 becomes the minimum (the magnetic flux of the external magnetic field is most attracted to the core 2). No state). FIG. 2B qualitatively shows that the magnetic flux in the axial direction of the core 2 is smaller than that in FIG. 2A by the magnetic flux lines shown by broken lines.

Subsequently, when the exciting current Id starts to decrease, the force for orienting the magnetization direction of the core 2 in the circumferential direction weakens accordingly, and the magnetic flux in the axial direction inside the core 2 increases (the magnetic flux attracted to the core 2 increases. To). The arrow (2) shown in FIG. 2 indicates a period during which the magnetic flux in the axial direction inside the core 2 increases as the exciting current Id decreases from plus to zero. Then, when the exciting current Id becomes 0, the core 2 is again magnetized only by the external magnetic field (FIG. 2A), and the axial magnetic flux inside the core 2 becomes maximum (the magnetic flux of the external magnetic field is the core). 2 is the most attracted state).

Furthermore, when the exciting current Id decreases (increases to the minus side), the core 2 is magnetized by the magnetic field generated by the external magnetic field and the exciting current Id. In this state, as the absolute value of the exciting current Id increases, the magnetization direction of the core 2 is directed in the circumferential direction which is the exciting direction (direction opposite to the case where the exciting current Id is positive), and The magnetic flux in the axial direction is reduced (the magnetic flux attracted to the core 2 is reduced). The arrow (3) shown in FIG. 2 indicates a period during which the magnetic flux in the axial direction inside the core 2 decreases as the exciting current Id increases in the negative direction. When the exciting current Id further decreases (increases to the minus side) and the magnetization direction of the core 2 is oriented in the most circumferential direction, the magnetic flux in the axial direction inside the core 2 becomes the minimum (the magnetic flux of the external magnetic field is The state that is the least attracted to the core 2). In FIG. 2C, the magnetic flux in the axial direction of the core 2 is smaller than that in FIG.

Subsequently, when the exciting current Id starts to increase from minus to 0, the force for orienting the magnetization direction of the core 2 in the circumferential direction weakens accordingly, and the magnetic flux in the axial direction inside the core 2 increases (in the core 2). Magnetic flux attracted increases). The arrow (4) shown in FIG. 2 indicates a period during which the magnetic flux in the axial direction inside the core 2 increases as the exciting current Id increases from minus to zero. Then, when the exciting current Id becomes 0, the core 2 is again magnetized only by the external magnetic field (FIG. 2A), and the above-described change is repeated.

FIG. 3 shows that the change of the magnetic flux in the axial direction of the core 2 is for two cycles with respect to the change of the exciting current Id for one cycle described in FIG. Moreover, although the output of the detection coil 3 is shown in FIG. 3, this cycle is the same as the cycle of the change of the magnetic flux in the axial direction of the core 2. That is, when an external magnetic field is applied along the axial direction of the core 2, the detection coil 3 outputs an induced voltage having a frequency twice the frequency of the exciting current Id.

[When an exciting current with a bias current larger than the amplitude of the AC component is used]
Next, based on the above description, the operation principle of the orthogonal fluxgate sensor 1 of the present embodiment will be described. FIG. 4 is a diagram showing an exciting current in which an alternating current is biased, and accompanying changes in the axial magnetic flux of the core 2 and the output voltage of the detection coil 3.

As described above, in the orthogonal fluxgate sensor 1 of this embodiment, the magnitude of the bias current from the DC power supply 5 is set to be larger than the amplitude of the AC current from the AC power supply 4. Therefore, as shown in FIG. 4, the polarity of the exciting current is not reversed, and the core 2 is magnetized only in one direction. In this process, the magnetization direction does not reverse to the opposite direction on the circumferential surface, and Barkhausen noise accompanying the magnetization reversal does not occur. In FIG. 4, the exciting current is always positive, and the increase/decrease from the average value is periodically repeated. The period in which the magnetic flux in the axial direction inside the core 2 decreases as the exciting current Id increases from the average value (the period indicated by arrow (1)), and the axis inside the core 2 decreases as the exciting current Id decreases from the average value. It is shown that the period in which the magnetic flux in the direction increases (the period indicated by the arrow (2)) is repeated. In addition, in the present embodiment, in order to suppress Barkhausen noise, a configuration in which the minimum value of the exciting current does not become 0 is adopted as shown in FIG. 4, but even the configuration in which the minimum value of the exciting current becomes 0. Good.

In the example of FIG. 3, the magnetization in the circumferential direction of the core 2 is maximized twice during one cycle of the exciting current, and thus the magnetic flux in the axial direction of the core 2 is minimized twice (in FIG. 3, the period ( Twice between 1) and 2) and during periods (3) and (4)). However, in the orthogonal fluxgate sensor 1 of the present embodiment, unlike the example of FIG. 3, the cycle in which the core 2 is maximized only once during one cycle of the exciting current, the axial direction of the core 2 is reduced. The magnetic flux is also minimized only once (only when the period (1) shown in FIG. 4 changes to the period (2)). Along with this, the excitation current and the output frequency of the detection coil 3 become the same.

FIG. 4 shows a change of one cycle of the exciting current Id used in the present embodiment, and the change of the magnetic flux in the axial direction of the core 2 is one cycle with respect to this exciting current. It is shown. Moreover, although the output of the detection coil 3 is shown in FIG. 4, this cycle is the same as the cycle of the change of the magnetic flux in the axial direction of the core 2. That is, in the orthogonal fluxgate sensor 1 of the present embodiment, when the external magnetic field is applied along the axial direction of the core 2, the detection coil 3 outputs an induced voltage having the same frequency as the frequency of the exciting current Id. become.

Further, with respect to the above operation, a change in the direction of magnetization on the peripheral surface of the core 2 will be described with reference to FIG. This figure is a model diagram showing an example of changes in the direction of the magnetization J at a point P on the peripheral surface of the core 2. As shown in FIG. 5, at the point P, the magnetization is magnetized by the magnetic field generated in the circumferential direction by the external magnetic field and the exciting current Id (the arrow starting from the point P in FIG. 5 indicates the magnetization J). In the present embodiment, since the polarity of the exciting current Id is not reversed, the direction of the magnetic field in the circumferential direction generated by this exciting current Id does not reverse but remains in one direction (in the right direction in FIG. 5). When the strength of the magnetic field due to the exciting current Id changes, the angle of the magnetization J with respect to the circumferential direction increases or decreases accordingly. In FIG. 5, at a point P, when the circumferential magnetic field is strong, the direction of the magnetization J is tilted in the circumferential direction (arrow (1)), and when it is weak, the direction of the magnetization J is tilted axially ((2)). (Arrow) is shown. At this time, as the direction of the magnetization J is inclined in the circumferential direction, the magnetic flux in the axial direction inside the core 2 decreases. By this operation, when the external magnetic field is applied in the axial direction of the core 2, the detection coil 3 outputs an induced voltage having the same frequency as the frequency of the exciting current Id. The orthogonal fluxgate sensor 1 of the present embodiment is characterized in that the magnetization direction of the core 2 is less likely to be reversed as compared with the configuration in which the magnetic field that excites the core 2 is reversed.

As described above, in the orthogonal fluxgate sensor 1 of the present embodiment, when the magnetic field is applied to the core 2, the component of the same frequency as the AC component of the exciting current becomes the induced voltage of the detection coil 3 and is output. To be done. Therefore, in obtaining the strength of the magnetic field applied to the core 2, the component of the induced voltage of the detection coil 3 having the same frequency as the AC component of the exciting current can be used, and the configuration can be simplified. Further, since the direction of the magnetic field that excites the core 2 is not reversed (excitation becomes unipolar), the occurrence of Barkhausen noise due to the reversal of magnetization can be suppressed as compared with the configuration in which the magnetic field that excites the core 2 is reversed. it can.

[Regarding the configuration in which a large current is passed through the core when sensing starts]
Next, a configuration in which a large current is passed through the core 2 at the start of sensing will be described.

FIG. 6 shows the initial magnetization curve when the demagnetized ferromagnetic material is magnetized. First, in the initial magnetization range, the magnetization gradually increases with the magnetic field. Then, in the discontinuous magnetization range, the domain wall moves and the magnetic domain having the directional component of the external magnetic field increases. Note that this change is an irreversible change. Furthermore, in the rotating magnetization range, the magnetic moment in the magnetic domain rotates in the direction of the external magnetic field, and the magnetization reaches saturation.

In the orthogonal fluxgate sensor 1 of this embodiment, the direction of the magnetic field that excites the core 2 is not reversed. Therefore, the magnetization of the core 2 can be operated in a state of being in the rotational magnetization range, and Barkhausen noise can be suppressed. However, at the start of sensing, the magnetic domain may be reversed in the opposite direction to the desired direction depending on the initial conditions. In addition, some magnetic domains are hard to rotate (require more excitation energy). Therefore, it takes time for the core 2 to operate in a state of being in the rotational magnetization range, and Barkhausen noise may occur during that time. In some cases, there remain magnetic domains that do not shift to the rotating magnetization range.

Therefore, the orthogonal fluxgate sensor 1 of the present embodiment adopts a configuration in which a DC current larger than the DC bias current used during sensing is applied to the core 2 at the start of sensing (when the sensor is activated). There is. In this configuration, the core 2 is magnetized by a larger magnetizing force than during sensing, so that the magnetization of the core 2 during sensing can be brought into a state of being in the rotational magnetization range, and Barkhausen noise can be suppressed. .. The large current at the start of sensing is referred to as a magnetization promoting current because of its role.

The magnitude and time of the magnetization promoting current described above are not limited in any way. However, if a too large current continues to flow, the core 2 may generate heat and a problem may occur, so the magnitude of the magnetization promoting current is about 2 to 5 times the maximum value of the exciting current (or the bias current). And the time is preferably about 1 second.

Further, when the supply of the magnetization promoting current to the core 2 is stopped (or the magnetization promoting current is changed to the exciting current), the current may be gradually decreased (for example, in 1 second). In this case, since the magnetizing force of the core 2 does not change rapidly, it is possible to prevent a situation where the state of the core 2 suddenly changes.

Further, in the present embodiment, a configuration is adopted in which the DC power source 5 is controlled to allow the magnetization promoting current to flow in the core 2, but the present invention is not limited to this configuration, and the core is formed in a path different from the exciting current at the time of sensing. You may make it supply a magnetization promotion current with respect to 2. Further, the magnetizing of the core 2 is not limited to the configuration in which the current is directly supplied to the core 2, and a configuration may be provided in which the core 2 is magnetized in the circumferential direction from the outside. That is, it is sufficient that the core 2 is magnetized with a larger magnetizing force as compared with the case where the core 2 is excited by the exciting current.

[Other]
The configuration of the invention described above will be described below. The configuration of the above embodiment corresponding to the configuration of the invention will be described in parentheses.

In the above explanation,
An elongated ferromagnetic core (eg, core 2),
An exciting portion in which a bias current having a magnitude equal to or larger than the amplitude of the alternating current is superimposed on the alternating current of a predetermined cycle is passed in the axial direction of the core to excite the core (for example, the alternating current power source 4 and DC power supply 5 combination),
A detection coil (for example, the detection coil 3) wound around the core,
A magnetization promoting unit that magnetizes the core with a larger magnetizing force than the exciting unit (for example, a combination of an AC power supply 4, a DC power supply 5, a time constant circuit 7, and a start detection circuit 8);
An orthogonal fluxgate sensor, characterized by comprising:

Also, in the orthogonal fluxgate sensor described above,
The magnetization promoting unit,
A magnetizing promoting current having the same polarity as the bias current and larger than the exciting current is supplied to magnetize the core (refer to the description of [Structure in which large current is supplied to core at the start of sensing]).
An orthogonal fluxgate sensor characterized by the above is described.

1 Fluxgate Sensor 2 Core 3 Detection Coil 4 AC Power Supply 5 DC Power Supply 6 Detection Circuit 7 Time Constant Circuit 8 Startup Detection Circuit

Claims (2)

An elongated ferromagnetic core,
An exciting current in which a bias current having a magnitude equal to or larger than the amplitude of the alternating current is superimposed on the alternating current of a predetermined cycle, and an exciting portion for flowing the axial direction of the core to excite the core,
A detection coil wound around the core,
A magnetization promoting section that magnetizes the core with a larger magnetizing force than the exciting section;
An orthogonal fluxgate sensor characterized by comprising: The orthogonal fluxgate sensor according to claim 1, wherein
The magnetization promoting unit,
Magnetizing the core by flowing a magnetization promoting current having the same polarity as the bias current and larger than the exciting current.
An orthogonal fluxgate sensor characterized by the above.

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