JP7002112B2 - Sensor head module and magnetic sensor - Google Patents

Description

The present invention relates to a sensor head module of a fundamental wave magnetic field sensor.

The configuration of the fundamental wave type orthogonal fluxgate sensor is disclosed in, for example, Patent Document 1. FIG. 20 is a diagram showing a configuration of a fundamental wave type orthogonal fluxgate sensor disclosed in Patent Document 1. In FIG. 20, by superimposing a DC current I _dc larger than the amplitude of the AC exciting current I _ac on the AC exciting current I _ac that energizes the magnetic core, the output of the detection coil is the same fundamental wave as the AC exciting frequency f [Hz]. A fundamental wave type orthogonal flux gate magnetic field meter that can obtain the output of It consists of a hollow small diameter detection coil arranged so as to wrap the magnetic core.

Further, the fundamental wave type orthogonal flux gate magnetic field meter of FIG. 20 is connected to the terminal of the detection coil in the subsequent stage via the capacitor C as a basic configuration realized by the negative feedback type, and is a preamplifier that amplifies the input signal. : Preamplifier) and a synchronous rectifier (phase-sensitive detection: PSD) that is connected to the rear stage of the preamplifier and performs synchronous rectification using the AC excitation frequency f [Hz] as a synchronous pulse for the input signal, and is connected to the rear stage of the synchronous rectifier. A low-pass filter (low-pass filter) that removes high frequencies and an inverting input terminal (-input terminal, minus terminal) are connected to the subsequent stage of the low-pass filter, and the output terminal has a resistor Rf. It is configured to include an error amplifier connected to the terminal of the detection coil via.

Further, Non-Patent Document 1 discloses an orthogonal fluxgate magnetic field sensor using a magnetic strip in the core of the sensor head. Here, as-cast products of Mtglass2714A (reference: Metgals Technical Bulletin ref: 2714A04202011), which is an amorphous magnetic strip having a typical Co-based magnetostrictive composition (after production, heat treatment is performed to modify the magnetic properties). By using a product that does not exist) for the core of the sensor head, high-sensitivity and low-noise magnetic field sensor characteristics are realized.

In each of the technologies shown in Patent Document 1 and Non-Patent Document 1, for example, as shown in FIG. 21, an electronic circuit having functions such as excitation, detection, output / amplification is standardized into a drive / detection circuit, and is driven. -It is known that the detection circuit and the sensor head are connected by a shielded cable.

Japanese Unexamined Patent Publication No. 2013-57645

K.Goleman and I.Sasada, “High Sensitive Orthogonal Fluxgate Magnetometer Using a Metglas Ribbon”, IEEE TRANSACTIONS ON MAGNETICS, VOL.42, NO.10, OCTOBER 2006

However, in the case of the configuration as shown in FIG. 21, it is necessary to adjust the parameters related to excitation and detection according to the characteristics of the sensor head. For example, the magnetic wire sensor head shown in Patent Document 1 and Non-Patent Document 1 There is a big difference in the bias DC current between the magnetic thin band sensor heads shown in (1), and when using or replacing these sensor heads properly, prepare a drive / detection circuit suitable for each, or use each sensor head. The parameters will be adjusted individually on the drive / detection circuit side accordingly.

It is not practical to prepare a drive / detection circuit suitable for each sensor head because it is too wasteful. In addition, when adjusting the parameters according to each sensor head, if dozens of channels of sensors such as magnetocardiographic measurement are required, it is necessary to adjust excitation and detection from those channels. It is a very time-consuming task because you have to select and adjust various parts.

The present invention is a sensor head module that can improve usability by adding a function for adjusting parameters related to excitation and detection to the sensor head and modularizing it, thereby eliminating parameter adjustment for each sensor head in the drive / detection circuit. I will provide a.

The sensor head module according to the present invention is connected to the magnetic core with a magnetic core to which an exciting current consisting of an alternating current and a bias direct current is input, and a sensor head composed of a detection coil wound around the magnetic core. It is provided with a DC exciting current generating means for generating a bias DC current in the exciting current by a DC power supply.

As described above, in the sensor head module according to the present invention, a magnetic core having an exciting current composed of an AC current and a bias DC current, a sensor head composed of a detection coil wound around the magnetic core, and the magnetic field. Since it is provided with a DC exciting current generating means connected to the core and generating a bias DC current in the exciting current by a DC power supply, the bias DC current according to the characteristics of each sensor head can be individually adjusted by the sensor head module. This has the effect of minimizing the time and effort required to replace the sensor head and significantly improving work efficiency.

The sensor head module according to the present invention is connected to the magnetic core and includes an AC exciting current generation means that phase-adjusts and / or amplifies the AC current in the exciting current to generate an AC exciting current.

As described above, the sensor head module according to the present invention is provided with an AC exciting current generating means that phase-adjusts and / or amplifies the AC current in the exciting current to generate the AC exciting current, so that it depends on the characteristics of each sensor head. The parameters of the AC exciting current can be individually adjusted with the sensor head module, which has the effect of minimizing the time and effort required to replace the sensor head and significantly improving work efficiency.

The sensor head module according to the present invention includes a switching means for switching the energizing direction of the exciting current energized in the magnetic core.

As described above, the sensor head module according to the present invention is provided with the switching means for switching the energizing direction of the exciting current energized in the magnetic core, so that the offset value different depending on the energizing direction of the exciting current can be set in the dominant direction. It has the effect of being able to be switched and used.

That is, although the inventor has found that the offset value differs depending on the energization direction of the exciting current energized in the magnetic core, it is impossible to make a judgment from the appearance of the sensor head. Therefore, by actually switching the energizing direction of the exciting current by the switching means and calibrating, it is possible to set the energizing direction so that higher performance sensing is possible.

The sensor head module according to the present invention includes a control means for controlling the connection relationship of the switching means based on the respective results measured by the switching means by switching the energization direction of the exciting current.

As described above, in the sensor head module according to the present invention, since the switching means includes a control means for controlling the connection relationship of the switching means based on the respective results measured by switching the energization direction of the exciting current, it is magnetic. It is possible to automatically switch between different offset values according to the energization direction of the exciting current flowing through the core in the dominant direction, and it is possible to save the trouble of calibration.

The sensor head module according to the present invention uses the DC power supply of the DC excitation current generating means as a battery.

As described above, in the sensor head module according to the present invention, by performing the bias DC current generated by the DC excitation current generation means by the battery, the power supply becomes completely independent, and unnecessary noise and disturbance are suppressed. It has the effect of being able to achieve higher performance sensing.

In the sensor head module according to the present invention, a plurality of the sensor heads are arranged, the AC exciting current generating means is connected corresponding to the magnetic core of each sensor head, and a plurality of DC exciting current generating means are provided. It is connected in series or in parallel to all or some of the magnetic cores of the sensor head.

As described above, in the sensor head module according to the present invention, a plurality of sensor heads are arranged, and the AC exciting current generating means is connected corresponding to the magnetic core of each sensor head, and the DC exciting current generating means is connected. However, since it is connected in series or in parallel to all or some of the magnetic cores of the plurality of sensor heads, it may require dozens of channels of sensors such as magnetic field measurement. However, it is not necessary to prepare a DC exciting current generation means according to the number of sensors, and if there is at least one DC power supply, it is possible to supply a bias DC current to a plurality of sensor heads. Play.

In the sensor head module according to the present invention, the DC excitation current generating means is connected to the positive electrode of the DC power supply and one end of the magnetic core, and the negative electrode of the DC power supply and the other end of the magnetic core are connected to the DC power supply. It has a first coil between the positive electrode and one end of the magnetic core.

As described above, in the sensor head module according to the present invention, the DC exciting current generating means connects the positive electrode of the DC power supply and one end of the magnetic core, and connects the negative electrode of the DC power supply and the other end of the magnetic core. Since the first coil is provided between the positive electrode of the DC power supply and one end of the magnetic core, the impedance in the DC exciting current generation means can be increased to prevent deterioration of the detection accuracy due to the inflow of AC current. It plays the effect.

The sensor head module according to the present invention has a second coil that is magnetically coupled to the first coil between the negative electrode of the DC power supply and the other end of the magnetic core.

As described above, in the sensor head module according to the present invention, since the second coil magnetically coupled to the first coil is provided between the negative electrode of the DC power supply and the other end of the magnetic core, the first coil is provided. A large impedance can be obtained by the magnetic coupling between the second coil and the second coil, and the effect that the alternating current can be prevented from flowing into the DC exciting current generating means and the alternating current can flow only to the magnetic core part can be obtained. Play.

The sensor head module according to the present invention has a buffer circuit connected to the subsequent stage of the detection coil and negative feedback connected to the detection coil via the buffer circuit when measuring a signal detected by the detection coil. It is provided with a feedback current input terminal for inputting a current fed back by the circuit.

As described above, since the sensor head module according to the present invention includes a buffer circuit connected to the subsequent stage of the detection coil, it has an effect that noise resistance and disturbance resistance to the detection signal can be improved.
The magnetic field sensor according to the present invention includes a drive circuit that supplies an exciting current consisting of at least an alternating current to the sensor head module according to any one of the above.

As described above, since the magnetic field sensor according to the present invention includes a drive circuit that supplies an exciting current consisting of at least an alternating current to the sensor head module according to any one of the above, an alternating current is supplied from the drive circuit. , The effect is that a high-performance magnetic field sensor can be realized by supplying a bias DC current with the sensor head module.

In the magnetic field sensor according to the present invention, the drive circuit supplies an exciting current composed of an alternating current and a bias direct current to the sensor head module, and the sensor head module extracts only an alternating current component from the exciting current. It is provided with a means for extracting an alternating current component.

As described above, in the magnetic field sensor according to the present invention, the drive circuit supplies an exciting current composed of an alternating current and a bias DC current to the sensor head module, and the sensor head module makes an alternating current from the exciting current. Since it is equipped with an AC component extraction means that extracts only the components, it is possible to extract only the AC components from the current supplied from the drive circuit with the sensor head module and adjust the phase, without having to spend time on the sensor head alone. It has the effect of being able to be exchanged.

It is a functional block diagram which shows the structure of the magnetic field sensor which concerns on 1st Embodiment. It is a circuit block diagram of the drive part of the magnetic field sensor which concerns on 1st Embodiment. It is a circuit block diagram of the sensor head module which concerns on 1st Embodiment. It is a functional block diagram which shows the structure of the magnetic field sensor which concerns on 2nd Embodiment. It is a circuit block diagram of the sensor head module which concerns on 2nd Embodiment. It is a figure which shows the difference of the offset according to the polarity of the exciting current. It is a 1st circuit block diagram of the sensor head module which concerns on 3rd Embodiment. It is a 2nd circuit block diagram of the sensor head module which concerns on 3rd Embodiment. It is a 1st circuit block diagram of the drive part of the magnetic field sensor which concerns on 4th Embodiment. It is a 1st circuit block diagram of the sensor head module which concerns on 4th Embodiment. It is a 2nd circuit block diagram of the sensor head module which concerns on 4th Embodiment. It is a 3rd circuit block diagram of the sensor head module which concerns on 4th Embodiment. It is a 4th circuit block diagram of the sensor head module which concerns on 4th Embodiment. It is a 5th circuit block diagram of the sensor head module which concerns on 4th Embodiment. It is a 2nd circuit block diagram of the drive part of the magnetic field sensor which concerns on 4th Embodiment. It is a circuit block diagram of the sensor head module which concerns on other embodiment. It is a figure which shows the result of having measured the noise spectral density when the bias DC current was changed in an Example. It is a figure which shows the result of having measured the offset with respect to the change of a bias DC current after the adjustment of a switching part. It is a figure which shows the noise characteristic with respect to the frequency change in the comparative example and the magnetic field sensor which concerns on this invention. It is a figure which shows the circuit structure of the fundamental wave type orthogonal fluxgate sensor known conventionally. It is a figure which shows the apparatus structure of the fundamental wave type orthogonal fluxgate sensor which is known conventionally.

Hereinafter, embodiments of the present invention will be described. In addition, the same elements are designated by the same reference numerals throughout the present embodiment.

(First Embodiment of the present invention)
The sensor head module according to the present embodiment and the magnetic field sensor using the sensor head module will be described with reference to FIGS. 1 to 3. As the magnetic field sensor according to the present embodiment, for example, the fundamental wave type orthogonal fluxgate sensor shown in FIG. 20 can be used, and by modularizing the sensor head portion, the sensor head replacement work and the like are remarkably efficient. It is something that becomes.

FIG. 1 is a functional block diagram showing the configuration of the magnetic field sensor according to the present embodiment, FIG. 2 is a circuit configuration diagram of a drive unit of the magnetic field sensor according to the present embodiment, and FIG. 3 is a sensor head module according to the present embodiment. It is a circuit block diagram of. In FIG. 1, the magnetic field sensor 1 includes a drive unit 10 and a sensor head module 20. The drive unit 10 includes an output unit 11 that outputs at least an alternating current supplied to the sensor head 23, and a detection unit 12 that detects a magnetic field measured by the sensor head 23. Further, the sensor head module 20 includes a sensor head 23 that detects a magnetic field and a DC excitation current generation unit 22 that supplies a bias DC current to the sensor head 23.

First, the configuration of the drive unit 10 will be described in detail with reference to FIG. The output unit 11 in the drive unit 10 outputs an alternating current by the oscillator 11a, which is an alternating current power source, and the alternating current output here is preliminarily adjusted to a phase according to the type and characteristics of the sensor head 23. do. At the same time, the oscillator 11a transmits a synchronization signal to the synchronization detection circuit of the detection unit 12.

The detection unit 12 has the same configuration as the detection circuit in FIG. 20, and is connected to one end side of the detection coil 23b wound around the magnetic core 23a of the sensor head 23, and has a preamplifier, a synchronous rectifier, a low-pass filter, and a low-pass filter. It has an error amplifier to form a negative feedback circuit. The output V of the detection coil from the sensor head 23 is sent to the error amplifier as a predetermined voltage corresponding to the output V through the capacitor C, the preamplifier, the synchronous rectifier, and the low-pass filter. After that, the feedback current if flows to the detection coil 23b through the feedback resistor Rf so that the input to the error amplifier becomes zero. At this time, the voltage generated in the feedback resistor Rf gives the sensor output V.

Next, the configuration of the sensor head module 20 will be described in detail with reference to FIG. As described above, the sensor head module 20 includes a sensor head 23 and a DC excitation current generation unit 22.

The sensor head 23 includes a magnetic core 23a and a detection coil 23b wound around its extending direction (Z axis) so as to wrap around the magnetic core 23a. The magnetic core 23a is composed of, for example, a U-shaped (or hairpin-shaped) or W-shaped magnetic wire or magnetic strip, and the detection coil 23b has, for example, about 1000 turns. ..

The magnetic core 23a may be I-shaped (rod-shaped) in addition to the U-shaped and W-shaped. In that case, the folded portion may be configured by wiring such as a conducting wire. Further, as the material used for the magnetic core 23a, for example, an amorphous magnetic strip or wire or a permalloy strip or wire having a Co-based magnetostrictive composition with small magnetostriction may be used.

The DC exciting current generation unit 22 includes a battery 22a as a DC power source, a variable resistor 22b for adjusting a bias DC current flowing by the voltage of the battery 22a, and an inductor for preventing AC current from flowing from the drive unit 10. It is provided with a coil 22c. The inductance of the coil 22c may be, for example, about 1 mH or more.

The bias DC current idc2 is, for example, a value of about 40 mA in the case of a cobalt-based amorphous magnetic wire core having a diameter of about 120 μm, and a value of about 200 mA in the case of a cobalt-based amorphous magnetic thin band core having a width of 1 mm and a thickness of about 20 μm. Become.

Further, although the battery 22a is shown as the direct current power source in FIG. 3, it is not limited to the battery, and the alternating current may be converted into the direct current and supplied. The battery may be a rechargeable battery, and the connection with the AC power supply may be disconnected when the sensor is operating in order to prevent an increase in noise due to the connection with the AC power supply.

With the above configuration, the sensor head module 20 is integrally equipped with a bias DC current generator that needs to be adjusted according to the characteristics of the sensor head 23, so that the sensor head 23 can be replaced with a sensor head 23 having different characteristics. In this case, no adjustment is required in the drive unit 10, and the adjustment can be performed only by the sensor head module 20, so that the burden on the operator can be significantly reduced. Especially when a sensor with dozens of channels is required such as magnetocardiographic measurement, the effect is tremendous. Further, by energizing the bias DC current using a DC power supply independent of the AC power supply, unnecessary noise can be eliminated.

(Second Embodiment of the present invention)
The sensor head module according to the present embodiment and the magnetic field sensor using the sensor head module will be described with reference to FIGS. 4 and 5. The magnetic field sensor according to the present embodiment is provided with a function of further adjusting the AC exciting current in the sensor head module according to the first embodiment. In this embodiment, the description overlapping with the first embodiment will be omitted.

FIG. 4 is a functional block diagram showing the configuration of the magnetic field sensor according to the present embodiment, and FIG. 5 is a circuit configuration diagram of the sensor head module according to the present embodiment. In this embodiment, the circuit configuration of the drive unit 10 is the same as that of FIG. 2 in the first embodiment, but the alternating current output here depends on the type and characteristics of the sensor head 23. It is output in any phase.

In FIG. 4, the difference from the case of FIG. 1 in the first embodiment is that the sensor head module 20 performs phase adjustment and amplification with respect to the alternating current output from the output unit 11 of the drive unit 10. The sensor head 23 is provided with an AC exciting current generation unit 21 that supplies an AC exciting current.

The AC exciting current generation unit 21 amplifies the phase adjustment circuit 21a that adjusts the phase of the AC current iac1 oscillated from the drive unit 10 according to the characteristics of the sensor head 23, and the phase-adjusted AC current. It is provided with an amplification circuit 21b that outputs an AC exciting current iac2. As the phase adjustment circuit 21a, for example, an operational amplifier (operational amplifier) that operates at a low voltage source of about ± 2.5 V suitable for battery drive may be used. Further, as the amplifier circuit 21b, an operational amplifier having a high current supply capacity can be used.

When a frequency of, for example, about 100 kHz is used as the AC exciting current, the capacitor 21c inserted between the magnetic core 23a of the sensor head 23 and the amplifier circuit 21b may be 1 μF or more. Since the voltage applied to the capacitor 21c is at most several hundred millivolts, it can be realized by a general-purpose ceramic capacitor.

With the above configuration, the sensor head module 20 is integrally equipped with an AC exciting current generator that needs to be adjusted according to the characteristics of the sensor head 23, so that the sensor head 23 can be replaced with a sensor head 23 having different characteristics. In this case, no adjustment is required in the drive unit 10, and the adjustment can be performed only by the sensor head module 20, so that the burden on the operator can be significantly reduced. Especially when a sensor with dozens of channels is required such as magnetocardiographic measurement, the effect is tremendous.

(Third Embodiment of the present invention)
The sensor head module according to the present embodiment and the magnetic field sensor using the sensor head module will be described with reference to FIGS. 6 to 8. The magnetic field sensor according to the present embodiment is an improvement of the sensor head module according to the first embodiment, and has a switching means for switching the energization direction of the exciting current (idc + iac), thereby lowering the offset of the sensor. A higher performance magnetic field sensor is realized (by setting it to 0 in some cases). In this embodiment, the description overlapping with each of the above embodiments will be omitted.

From the inventor's experiment, it was found that the offset differs depending on the direction in which the DC bias magnetic field is applied with respect to the energization direction of the exciting current connected to both ends of the magnetic core 23a, that is, the width direction of the magnetic core 23a. Was done. FIG. 6 shows an example of a graph of the experimental results at this time. In the experiment of FIG. 6, the output when a sensor head (length 40 mm) using a magnetic strip with a width of 1 mm of Metaglass2714A was installed in a magnetic shield and excited with an alternating current of 100 kHz and an effective value of 24 mA was biased DC. This is an investigation of how it changes depending on the magnitude of the current. As shown in FIG. 6, it can be confirmed that there is a large difference in the offset depending on the polarity of the bias DC current.

It should be noted that the graph missing near the central axis is a region that does not correspond to | idc |> iac, which is a condition for becoming a fundamental wave type orthogonal flux gate.

As shown in the experimental results of FIG. 6, the reason why the offset value differs greatly due to the difference in the polarity of the bias DC current is that the magnetic anisotropy of the magnetic core 23a is not a little dispersed in each place, and the coercive force is held. However, when viewed microscopically, it fluctuates from place to place, and since there is magnetic hysteresis in the case where it magnetizes in one direction in the width direction and the case where it magnetizes in the opposite direction, all the magnetizations are reversed by 180 °. It doesn't become. That is, there is no perfect symmetry. Therefore, the occurrence of the offset differs depending on the polarity of the bias DC current.

In addition to the experiment shown in FIG. 6, even under other conditions (for example, when the magnetic core 23a is made of a wire or the length is changed), the polarity of the bias DC current is similarly adjusted. It has been confirmed that the expression of offset is different.

From such experimental results, it was clarified that the offset of the sensor head 23 used in the present embodiment has different properties depending on the polarity of the bias DC current, but the offset becomes smaller from the appearance of the sensor head 23. It is impossible to identify the polarity. Therefore, in the present embodiment, a switching means for switching the energization direction of the exciting current energized in the magnetic core 23a is provided so that the offset becomes smaller according to the result of actual sensing in each energization direction in the calibration. Determine the direction of energization.

FIG. 7 is a first circuit configuration diagram of the sensor head module 20 according to the present embodiment. As shown in FIG. 7, a switching unit 24 is provided between the DC exciting current generation unit 22 and the AC exciting current generation unit 21 and the magnetic core 23a. The switching unit 24 includes a switch 24a and a switch 24b, and each of the switches 24a and 24b is configured to switch between connecting to the contact (1) and connecting to the contact (2). When connected to the contact (1), an exciting current idc + iac flows through the magnetic core 23a, and when connected to the contact (2), an exciting current − (idc + iac) flows through the magnetic core 23a.

At the time of calibration, the offset is measured when the switch 24a and the switch 24b are connected to the contact (1) and the contact (2), respectively, and connected to the contact having a smaller offset. , It is possible to realize a high-performance magnetic field sensor.

FIG. 8 is a second circuit configuration diagram of the sensor head module 20 according to the present embodiment. Here, in addition to the circuit configuration of FIG. 7, a switching control unit 25 for controlling the switching unit 24 is provided. The switching control unit 25 measures the offset between the case where the switch 24a and the switch 24b are connected to the contact (1) and the case where the switch 24b is connected to the contact (2) at the time of calibration from the drive unit 10. The operation of the switch 24a and the switch 24b is controlled so that the switch 24a and the switch 24b are connected to the contact which is acquired and the offset is smaller. By doing so, it is possible to automatically control the switching unit 24 in the calibration, and it is possible to reduce the time and effort of the user.

In this embodiment, the sensor head module 20 may not be provided with the AC excitation current generation unit 21.

(Fourth Embodiment of the present invention)
The sensor head module according to the present embodiment and the magnetic field sensor using the sensor head module will be described with reference to FIGS. 9 to 15. In this embodiment, the description overlapping with each of the above embodiments will be omitted.

FIG. 9 is a first circuit configuration diagram of a drive unit of a magnetic field sensor according to the present embodiment, and FIG. 10 is a first diagram showing a circuit configuration of a sensor head module according to the present embodiment. As shown in FIG. 9, here, in the drive unit 10, a current of a DC component + an AC component is generated by an adder, and the configuration of the sensor head module 20 adapted to the drive unit of FIG. 9 is shown in FIG. There is. That is, as shown in FIG. 9, when the drive unit 10 that outputs the current of the DC component + the AC component is used, only the AC component is extracted on the sensor head module 20 side of FIG. 10 and the AC exciting current is used. Must be. Therefore, in FIG. 10, an AC component that extracts only the AC component current from the DC component + AC component current supplied from the drive unit 10 between the drive unit 10 and the drive unit 10 in the previous stage of the phase adjustment circuit 21a. It is configured to include an extraction circuit 21d.

That is, by configuring the sensor head module as shown in FIG. 10, even when the drive unit 10 is supplied with the current of the DC component + AC component as shown in FIG. 9, the drive unit 10 It is possible to set parameters according to the characteristics of the sensor head 23 only in the sensor head module 20 without depending on the structure.

The AC component extraction circuit 21d may be configured to be selectively connectable according to the structure of the drive unit 10. That is, when the drive unit 10 supplies only the current of the AC component as shown in FIG. 2, the terminals are connected so as to have the circuit configuration of FIG. 5, and the drive unit 10 has the DC component + as shown in FIG. When supplying the current of the AC component, the structure may be selective so that the terminals can be connected so as to have the circuit configuration of FIG.

FIG. 11 is a second diagram showing a circuit configuration of the sensor head module according to the present embodiment. In FIG. 11, the configuration of the AC exciting current generation unit 21 may be either the configuration of FIG. 5 or the configuration of FIG. 10, and the DC exciting current generation unit 22 includes the coil 22d so as to be magnetically coupled to the coil 22c. It has become.

That is, the coil 22c connected in series between the positive side of the battery 22a and the magnetic core 23a prevents the AC exciting current iac2 from flowing in, but further, between the negative side of the battery 22a and the magnetic core 23a. By connecting and arranging the coil 22d magnetically coupled to the coil 22c in series, a larger impedance can be obtained and the inflow of an alternating current can be prevented more reliably.

12 and 13 are the third and fourth views showing the circuit configuration of the sensor head module according to the present embodiment. The sensor head module 20 shown in FIGS. 12 and 13 has a configuration (sensor head modules 20-1 to 20-n) including a plurality of sensor head modules 20 shown in FIG. 11, but serves as a power source for a DC exciting current. The battery 22a is single and has a common connection to each sensor head module 20-1 to 20-n. In the case of FIG. 12, the battery 22a is connected in series to each of the plurality of sensor head modules 20-1 to 20-n, and in the case of FIG. 13, the plurality of sensor head modules 20-1 to 20 are connected in series. The battery 22a is connected in parallel to −n.

As described above, for example, when performing magnetocardiographic measurement, sensors having dozens of channels are required, and a plurality of sensor head modules 20 may be replaced at once. Even in such a case, by adopting the structure of the sensor head module 20 as shown in FIG. 12 or 13, it is possible to replace a plurality of sensor heads at once and bias DC for excitation. Since the current sources can be shared into one, it can be integrated very compactly.

Although the single battery 22a is arranged for the plurality of sensor head modules 20 in FIGS. 12 and 13, the battery 22a does not have to be a single battery and may be a plurality of batteries 22a. That is, it is not necessary that the sensor head module 20 and the battery 22a are arranged in a one-to-one correspondence with each other.

FIG. 14 is a fifth diagram showing the circuit configuration of the sensor head module according to the present embodiment, and FIG. 15 is a second circuit configuration diagram of the drive unit of the magnetic field sensor according to the present embodiment. As shown in FIG. 14, here, the buffer circuit 26 is provided after the detection coil 23b. By providing the buffer circuit 26, it is possible to lower the output impedance and improve the noise resistance and disturbance resistance to the signal detected by the detection coil 23b. That is, it is effective, for example, when the cable between the drive unit 10 and the sensor head module 20 is extended long (for example, when the cable length is about 10 m).

Further, by including the buffer circuit 26, the terminal (c2) for inputting the feedback current if fed back from the detection unit 12 is provided. This is because when the sensor head module 20 is configured as shown in FIG. 14, only the feedback current from the detection unit 12 is directly applied to the detection coil 23b.

On the other hand, in the circuit configuration of the drive unit 10, as shown in FIG. 15, the terminal (c2) is separated according to the circuit configuration of FIG. In this way, by directly applying only the feedback current from the detection unit 12 to the detection coil 23b, it becomes possible to realize a high-performance magnetic field sensor 1.

In this embodiment, the configuration without the switching unit 24 described in the third embodiment has been described as an example, but in each circuit configuration, the switching unit 24 and / or the switching control unit 25 is provided. May be good.

Further, in the present embodiment, the sensor head module 20 may be configured not to include the AC excitation current generation unit 21.

(Other Embodiments of the present invention)
A sensor head module according to the present embodiment and a magnetic field sensor using the sensor head module will be described with reference to FIG. In this embodiment, the description overlapping with each of the above embodiments will be omitted.

The magnetic field sensor according to the present embodiment is a gradient magnetic field sensor using a gradiometer that detects a local magnetic field (gradient magnetic field) using two sensor heads constituting a fundamental wave type orthogonal fluxgate sensor, and each sensor head. It is possible to easily and highly accurately adjust the difference in characteristics due to manufacturing errors and the like with the sensor head module, and to detect a local magnetic field such as an extremely minute foreign substance with high sensitivity.

FIG. 16 is a circuit configuration diagram of the sensor head module according to the present embodiment. Here, the sensor heads 231 and 232 are arranged so that the extending directions of the respective magnetic cores (magnetic cores 231a and 232a are parallel, but the extending directions of the respective magnetic cores are coaxial). It can also be placed.

In FIG. 16, one end of each of the detection coil 231b and the detection coil 232b is connected by electrical wiring so as to be connected in series. Further, the other end side of the detection coil 231b is connected to the detection unit 12, and the other end side of the detection coil 232b is connected to the ground. Further, the detection coil 231b and the detection coil 232b are connected so that the induced voltages (detection voltages V1 and V2) generated for the magnetic field in the same direction cancel each other out (so that their polarities are opposite to each other). To. As a result, for the magnetic field in the same direction, the difference between the detection voltages output from the respective sensor heads is taken as the combined voltage (sensor output) of the detection voltages V1 and V2 of the respective sensor heads 231 and 232. (V2-V1) appears. By doing so, a uniform magnetic field that arrives from a distance is similarly picked up by both the sensor heads 231 and 232 and does not appear in the sensor output. However, for a local magnetic field, it is picked up by only one sensor head (for example, sensor head 231), so that it is observed as a sensor output. As a result, it becomes possible to detect a signal related to a local magnetic field by removing noise having a uniform magnetic field property coming from a distance, and it becomes possible to detect a local magnetic field with high sensitivity.

The adjusting unit 27 includes a first adjusting unit 271 composed of an adjusting coil 271a and a variable resistor 271b connected in series to the drive unit 10 and connected in parallel to the magnetic core 231a, and an adjusting coil 272a connected in parallel to the magnetic core 232a. A second adjusting unit 272 including a variable resistor 272b is provided. By having the adjusting coils 271a and 272a, respectively, the first adjusting unit 271 and the second adjusting unit 272 increase the impedance with respect to the alternating current from the driving unit 10, and direct current to the first adjusting unit 271 and the second adjusting unit 272. It is configured so that only current flows. The impedance of the sensor heads 231 and 232 is based on the resistance value of the amorphous wire, and is, for example, about 10Ω. Therefore, it is desirable that the impedances of the adjusting coils 271a and 272a are 10 times or more, that is, about 100Ω or more. At this time, it is desirable that the maximum resistance value of the variable resistors 271b and 272b is 1 kΩ to 50 kΩ (that is, about 0 kΩ to 1 kΩ to 0 kΩ to 50 kΩ).

As described above, in the magnetic field sensor according to the present embodiment, the direct current energized in the first adjusting unit 271 and the direct current energized in the second adjusting unit 272 are adjusted by the variable resistors 271b and 272b. By doing so, the amount of direct current energized in each of the magnetic cores 231a and 232b can be adjusted, and the sensitivity of each of the sensor heads 231 and 232 can be adjusted. That is, for the sensor head with higher sensitivity, increase the DC current in the circuit on the sensor head module 20 side to reduce the sensitivity, and for the sensor head with lower sensitivity, decrease the DC current to increase the sensitivity. , Adjust the variable resistors 271b and 272b.

By making such adjustments, it becomes possible to flexibly adjust the sensitivity of the sensor heads 231 and 232 in the sensor head module 20.

In this embodiment, the sensor head module 20 may not be provided with the AC excitation current generation unit 21.

The following experiments were conducted on the sensor head module according to the present invention and the magnetic field sensor using the sensor head module.

(1) Adjustment of Bias DC Current Using a magnetic field sensor using the sensor head module according to the present invention, the noise spectral density when the bias DC current was changed was measured. A sensor head 23 having a length of 30 mm was manufactured and used by using a thin band having a width of 1 mm and a Metglass 2714A as the magnetic core 23a. The AC exciting current was set to 24 mA (effective value) at a frequency of 100 kHz. Here, the circuit configuration of the drive unit 10 shown in FIG. 9 and the sensor head module 20 shown in FIG. 10 is used.

FIG. 17 is a diagram showing the results of measuring the noise spectral density when the bias DC current is changed. The bias DC current Idc is changed from Idc = 40mA to around 200mA, and the results are shown when Idc = 40mA, 130mA and 200mA. As shown in the figure, there is a difference in noise characteristics depending on the magnitude of Idc, and in the case of this experiment, the noise characteristics are the best at Idc = 200 mA. That is, it can be seen that it is very important to adjust the Idc according to the characteristics of the sensor head.

According to previous research by the inventors, it is already known that when a magnetic wire is used as the magnetic core 23a, the noise characteristics are improved at around Idc = 40 mA. Therefore, for example, when the sensor head 23 is replaced with one using a magnetic wire and a magnetic thin band, the Idc can be adjusted in the sensor head module 20 as in the present invention, so that the drive unit 10 can be used. It is not necessary to operate and adjust the circuit on the side, and the burden on the operator can be significantly reduced.

(2) Measurement of offset according to the polarity of the exciting current Using a magnetic field sensor using the sensor head module according to the present invention, the change in offset when the polarity of the exciting current energized in the magnetic core 23a was changed was measured. .. A sensor head 23 having a length of 40 mm was produced by using a thin band having a width of 1 mm and a Metglass 2714A as the magnetic core 23a, and was arranged in a magnetic girade for use. The AC exciting current was set to 24 mA (effective value) at a frequency of 100 kHz. Here, the circuit configuration of the drive unit 10 shown in FIG. 9 and the sensor head module 20 shown in FIG. 7 is used.

The output results when the bias DC current is changed from −0.15 A to 0.15 A using the magnetic field sensor are already shown in FIG. As shown in FIG. 6, the output behavior is clearly different between the current region on the negative electrode side and the current region on the positive electrode side. Here, FIG. 18 shows the result of adjusting the switching unit 24 in the direction in which the offset becomes smaller and measuring the offset with respect to the change in the bias DC current. As shown in FIG. 18, when the bias DC current is 206 mA, the offset is 0. This shows the feasibility of a very sensitive magnetic field sensor.

When the bias DC current is connected to the opposite polarity, the offset is -2.03 μT when the bias DC current is -211 mA, and the offset is -2.33 μT when the bias current is -120 mA. There was a difference of 10 times or more as compared with the result in the case of FIG.

Further, such a difference in offset occurs even when a magnetic wire whose output characteristics change according to the polarity of the exciting current is used for the sensor head, and a switching unit is also used when the magnetic wire is used for the sensor head. The composition of can be very important.

(3) Performance improvement by modularization of the sensor head It was measured how much the noise characteristics differ between the case where the magnetic field sensor using the sensor head module according to the present invention is used and the case where the sensor head is not used. The comparison target is described in the reference (Mattia Butta and Ichiro Sasada, “Effect of Terminations in Magnetic Wire on the Noise of Orthogonal Fluxgate Operated in Fundamental Mode”, IEEE TRANSACTIONS ON MAGNETICS, VOL. 48, NO. 4, APRIL 2012). It is a magnetic field sensor using the above-mentioned magnetic field sensor and the sensor head module of the present invention. In the reference, the excitation current is all controlled on the same substrate as the drive circuit. On the other hand, in the experiment using the sensor head module according to the present invention, the same magnetic wire as above was used as the magnetic core, and the measurement was performed under the conditions of Iac = 12mA and Idc = 40mA at a frequency of 100 kHz.

FIG. 19 is a diagram showing noise characteristics with respect to frequency changes in each magnetic field sensor. FIG. 19A is the result of the magnetic field sensor of the reference, and FIG. 19B is the result of the magnetic field sensor using the sensor head module according to the present invention. As shown in FIG. 19, it can be seen that the magnetic field sensor according to the present invention has improved noise characteristics as compared with the magnetic field sensor in the reference. In the present invention, the sensor head module 20 is made independent from the drive unit 10, and the bias direct current is generated by the electrically independent battery in the sensor head module 20, so that there is no disturbance and a clean direct current. This is because it is possible to energize.

Note that similar results are the same even when a magnetic strip is used for the sensor head, and performance improvement can be realized by using the sensor head module of the present invention.

1 Magnetic field sensor 10 Drive unit 11 Output unit 11a Oscillator 12 Detection unit 20 Sensor head module 21 AC exciting current generator 21a Phase adjustment circuit 21b Amplification circuit 21c Condenser 21d AC component extraction circuit 22 DC exciting current generator 22a Battery 22b Variable resistance 22c , 22d Coil 23 Sensor head 23a Magnetic core 23b Detection coil 24 Switching unit 24a, 24b Switch 25 Switching control unit 26 Buffer circuit 27 Adjustment unit 231,232 Sensor head 231a, 232a Magnetic core 231b, 232b Detection coil 271 First adjustment unit 272 2nd adjustment unit 271a, 272a Adjustment coil 271b, 272b Variable resistor

Claims (3)

A magnetic core to which an exciting current consisting of an alternating current and a bias direct current is input, and a sensor head consisting of a detection coil wound around the magnetic core.
It is provided with a DC exciting current generating means connected to the magnetic core and generating a bias DC current in the exciting current by a DC power supply .
In the DC excitation current generating means, the positive electrode of the DC power supply and one end of the magnetic core are connected, the negative electrode of the DC power supply and the other end of the magnetic core are connected, and the positive electrode of the DC power supply and one end of the magnetic core are connected. A sensor head module characterized by having a first coil between the two . In the sensor head module according to claim 1,
A sensor head module having a second coil magnetically coupled to the first coil between the negative electrode of a DC power supply and the other end of the magnetic core . A drive circuit for supplying an exciting current consisting of at least an alternating current to the sensor head module according to claim 1 or 2 is provided.
The drive circuit supplies the sensor head module with an exciting current consisting of an alternating current and a bias direct current.
A magnetic field sensor in which the sensor head module includes an alternating current component extracting means for extracting only an alternating current component from the exciting current .

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