Gradient magnetic field sensor and magnetic object detection device

Abstract

The present application provides a kind of gradient magnetic field sensor, wherein: with: alternating current power connection terminal, it is connected with the 1st power terminal that alternating current power has;1st magnetic core, it is connected between the alternating current power connection terminal and ground wire;2nd magnetic core, it is connected in parallel with the 1st magnetic core between the alternating current power connection terminal and ground wire;Alternating current control unit, it is connected between the alternating current power connection terminal and at least one of the 1st magnetic core and the 2nd magnetic core, controls the alternating current that flows through at least one of the 1st magnetic core and the 2nd magnetic core;1st detection coil, it is wound in the 1st magnetic core;2nd detection coil, it is wound in the 2nd magnetic core, and is differentially connected with the 1st detection coil;And detection circuit, it detects the voltage corresponding to the difference between the 1st voltage output from the 1st detection coil and the 2nd voltage output from the 2nd detection coil.

Description

Technical Field

[0001] This invention relates to gradient magnetic field sensors and magnetic object detection devices.

[0002] This application claims priority based on Japanese Patent Application No. 2020-122886 filed on July 17, 2020, the contents of which are incorporated herein by reference. Background Technology

[0003] A gradient magnetic field sensor was researched and developed to detect the gradient of the magnetic field strength at two different locations. Here, the gradient is the difference in the magnetic field strength at the two different locations.

[0004] A gradient magnetic field sensor has two sensor heads to detect the strength of the magnetic field at two different locations. One sensor head detects the magnetic field strength at one of the two locations, while the other detects the magnetic field strength at the other location. Furthermore, the gradient magnetic field sensor detects the gradient of the magnetic field strength at the two locations based on the signals output from the two sensor heads. This gradient varies depending on the presence or absence of an object that can change the magnetic field. Utilizing this, the gradient magnetic field sensor can detect such objects as detection targets.

[0005] Here, as described above, the gradient magnetic field sensor detects the gradient of the magnetic field strength at two different locations. On the other hand, within a uniform magnetic field region, the magnetic field strength is equal at any location at the same time. Therefore, the gradient magnetic field sensor should not detect a gradient in the magnetic field strength within this region. Furthermore, in this specification, a uniform magnetic field region is a region where a uniform magnetic field is applied, and also a region where no magnetic field other than a uniform magnetic field is applied. Additionally, in this specification, a uniform magnetic field applied within a region refers to a magnetic field whose strength varies uniformly within that region regardless of location.

[0006] However, the two sensor heads of a gradient magnetic field sensor vary considerably, often resulting in different sensitivities. Therefore, even within a uniform magnetic field region, a gradient magnetic field sensor may sometimes detect gradients in magnetic field strength. This difference in sensitivity reduces the accuracy of detecting the presence or absence of an object, making it an undesirable option.

[0007] In this regard, a gradient magnetic field sensor is known, which has two sensor heads with DC excitation current and AC excitation current flowing in series respectively. By adjusting the amount of DC excitation current flowing in the two sensor heads respectively, the sensitivity of each of the two sensor heads can be adjusted (see Patent Document 1).

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2019-002688 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] Here, the gradient magnetic field sensor described in Patent Document 1 comprises two sensor heads, each consisting of a magnetic core through which an alternating current flows along with a DC excitation current, and a detection coil that senses a voltage through a magnetic field generated from the magnetic core. Furthermore, the detection coils of the two sensor heads are differentially connected. Therefore, in a uniform magnetic field region, when the sensitivities of the two sensor heads are equal, the amplitudes of the voltages sensed by the two detection coils are equal. Consequently, in this region, under these conditions, if the phases are opposite, the voltages sensed by the two detection coils cancel each other out.

[0013] However, even when the sensitivities of the two sensor heads in the gradient magnetic field sensor described in Patent Document 1 are equal, the voltages induced by the two detection coils in a uniform magnetic field region may not be out of phase. That is, even in this case, the voltages induced by the two detection coils in this region may not cancel each other out. This means that even in this region, the gradient magnetic field sensor will detect the gradient of the magnetic field strength, which is not preferable. Furthermore, the reasons why the phases of the voltages induced in each of the two detection coils are not out of phase can be attributed to the influence of magnetic coupling in the magnetic circuit containing the two sensor heads, and the deviation of the magnetic properties of the magnetic cores of the two sensor heads.

[0014] The present invention was made in consideration of such circumstances, and its objective is to provide a gradient magnetic field sensor and a magnetic object detection device that can improve the detection accuracy of objects using magnetic fields.

[0015] Methods for solving problems

[0016] One aspect of the present invention is a gradient magnetic field sensor comprising: an AC power connection terminal connected to a first power terminal of an AC power source; a first magnetic core connected between the AC power connection terminal and a ground wire; a second magnetic core connected in parallel with the first magnetic core between the AC power connection terminal and the ground wire; an AC current control unit connected between the AC power connection terminal and at least one of the first and second magnetic cores, controlling the AC current flowing through at least one of the first and second magnetic cores; a first detection coil wound around the first magnetic core; a second detection coil wound around the second magnetic core and differentially connected to the first detection coil; and a detection circuit that detects a voltage corresponding to the difference between a first voltage output from the first detection coil and a second voltage output from the second detection coil.

[0017] Invention Effects

[0018] According to the present invention, the detection accuracy of objects using magnetic fields can be improved. Attached Figure Description

[0019] Figure 1 This is a diagram showing an example of the structure of the magnetic material detection device 1.

[0020] Figure 2 This is a diagram illustrating an example of the circuit structure of the gradient magnetic field sensor 12.

[0021] Figure 3 This is a diagram illustrating an example of the time variations of the first induced voltage, the second induced voltage, the differential signal, the detector signal, and the detection signal before and after AC current adjustment of the gradient magnetic field sensor 12.

[0022] Figure 4 This is a diagram illustrating the time variations of the detection signal, differential signal, and detector signal when the gradient magnetic field sensor 12 detects the magnetic moment generated by a coil with one turn before and after the alternating current is adjusted.

[0023] Figure 5 It is about Figure 4 The two graphs of the detection signal shown are enlarged portions of each.

[0024] Figure 6 This is a diagram illustrating an example of the circuit structure of the gradient magnetic field sensor 12A.

[0025] Figure 7 This is a diagram showing an example of the circuit structure of the AC current control unit CC3.

[0026] Figure 8This diagram illustrates an example of a circuit structure that also includes a detection circuit DT with a high-pass filter (HF).

[0027] Figure 9 This is a diagram illustrating an example of the circuit structure of a gradient magnetic field sensor 12D.

[0028] Figure 10 This is a diagram illustrating an example of the configuration of a first magnetic core CR1 containing multiple magnetic bodies. Detailed Implementation

[0029] <Implementation Method>

[0030] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0031] <Overview of Magnetic Detection Device>

[0032] First, an overview of the magnetic material detection device of this embodiment will be described.

[0033] The magnetic object detection device of this embodiment includes the gradient magnetic field sensor of this embodiment. The gradient magnetic field sensor of this embodiment includes an AC power connection terminal, a first magnetic core, a second magnetic core, an AC current control unit, a first detection coil, a second detection coil, and a detection circuit. Here, the AC power connection terminal is a terminal connected to a first power terminal of an AC power source. The first magnetic core is a magnetic core connected between the AC power connection terminal and a ground wire. The second magnetic core is a magnetic core connected in parallel with the first magnetic core between the AC power connection terminal and the ground wire. The AC current control unit is connected between the AC power connection terminal and at least one of the first and second magnetic cores. Furthermore, the AC current control unit controls the AC current flowing through at least one of the first and second magnetic cores. The first detection coil is a coil wound around the first magnetic core. The second detection coil is a coil wound around the second magnetic core. Moreover, the second detection coil is differentially connected to the first detection coil. The detection circuit is a circuit that detects the voltage corresponding to the difference between the first voltage output from the first detection coil and the second voltage output from the second detection coil.

[0034] Therefore, the gradient magnetic field sensor of the embodiment and the magnetic object detection device of the embodiment can suppress the gradient of the intensity of the detected magnetic field in a uniform magnetic field region, and as a result, the detection accuracy of the object being detected using the magnetic field can be improved.

[0035] The structures of the magnetic object detection device and the gradient magnetic field sensor of the embodiment will be described in detail below.

[0036] <Structure of Magnetic Detection Device>

[0037] Hereinafter, taking magnetic object detection device 1 as an example, the structure of the magnetic object detection device of the embodiment will be described. In this embodiment, the conductor that transmits an electrical signal corresponding to direct current or alternating current will be referred to as the transmission path. The transmission path may be, for example, a conductor printed on a substrate, a wire formed as a line, or other conductors. Furthermore, in this embodiment, when referred to as voltage, it refers to the potential difference from a predetermined reference potential; illustrations and explanations regarding the reference potential are omitted. Here, the reference potential can be any potential. In this embodiment, as an example, the case where the reference potential is a ground potential will be described. Furthermore, in this embodiment, when referred to as ground, it means the same ground.

[0038] Figure 1 This is a diagram showing an example of the structure of the magnetic material detection device 1.

[0039] The magnetic object detection device 1 is a device that detects an object by means of a magnetic field. However, the object to be detected is an object that can cause a change in the magnetic field, such as a magnetic material.

[0040] The magnetic material detection device 1 includes, for example, a frame CS, a first roller RL1, a second roller RL2, a magnetization device 11, a gradient magnetic field sensor 12 equipped with two sensor heads, a first sensor head S1 and a second sensor head S2, and an information processing device 20. Additionally, in Figure 1 To avoid complicating the accompanying drawings, the cables connecting the information processing device 20 to other components in the magnetic object detection device 1 are omitted. Alternatively, the magnetic object detection device 1 may be a structure excluding some or all of the frame CS, the first roller RL1, the second roller RL2, the magnetizing device 11, and the information processing device 20. Alternatively, the magnetic object detection device 1 may be configured to replace some or all of the frame CS, the first roller RL1, the second roller RL2, the magnetizing device 11, and the information processing device 20, and include other components and devices along with the gradient magnetic field sensor 12. Alternatively, the magnetic object detection device 1 may also have a structure that, in addition to all of the frame CS, the first roller RL1, the second roller RL2, the magnetizing device 11, and the information processing device 20, also includes the gradient magnetic field sensor 12 and other components and devices.

[0041] The frame CS houses the components of the magnetic object detection device 1. The frame CS mainly consists of a top plate (not shown), a bottom plate (not shown), and multiple support columns connecting the top and bottom plates. Figure 1 In the example shown, the outer shape of the frame CS is approximately a cuboid. However, the outer shape of the frame CS can be any shape.

[0042] Inside the frame CS, there are roller RL1 and roller RL2.

[0043] The first roller RL1 is a roller in which a thin sheet member ST, which will be used to check the presence or absence of an object to be inspected, is wound into a roller shape. The second roller RL2 is a roller that winds up the thin sheet member ST pulled out from the first roller RL1 along a predetermined path. The second roller RL2 is rotated by a servo motor (not shown) or the like. Thus, the second roller RL2 can wind up the thin sheet member ST pulled out from the first roller RL1. That is, the second roller RL2 is a drive roller. Moreover, the first roller RL1 is a driven roller that rotates while winding the thin sheet member ST in response to the rotation of the second roller RL2. In addition, this servo motor is controlled, for example, by the information processing device 20 described later.

[0044] The sheet component ST is conveyed in a magnetic field generated by the magnetization device 11 during the period from being pulled out from the first roller RL1 to being wound up by the second roller RL2. As a result, the object to be detected attached to the sheet component ST is magnetized. After being conveyed in this magnetic field, the sheet component ST is conveyed within a predetermined detection area where the gradient magnetic field sensor 12 can detect the presence or absence of the object to be detected. Furthermore, the sheet component ST is wound around the second roller RL2.

[0045] Here, the magnetizing device 11 is a device that generates a magnetic field of a specified intensity within a specified magnetizing region, thereby magnetizing a magnetic body that enters the magnetizing region. Since the magnetizing device 11 is a known device, a more detailed description is omitted.

[0046] The gradient magnetic field sensor 12 detects the gradient of the magnetic field strength at two different locations within the aforementioned detection area, namely, the first sensor head S1 and the second sensor head S2. Thus, the information processing device 20, which obtains the detection signal output from the gradient magnetic field sensor 12, can determine whether the object being detected is attached to the sheet member ST being transported in the detection area based on the detection signal. Furthermore, for ease of explanation, the gradient of the magnetic field strength at the locations where the first sensor head S1 and the second sensor head S2 are located will be referred to simply as the gradient.

[0047] The information processing device 20 is connected to the gradient magnetic field sensor 12 in a communicative manner. Then, as described above, the information processing device 20 determines whether the object to be detected is attached to the sheet member ST being transported in the detection area based on the detection signal output from the gradient magnetic field sensor 12.

[0048] For example, if the information processing device 20 determines that a target object is attached to the sheet member ST being conveyed in the detection area, it controls the aforementioned servo motor to stop the second roller RL2 from winding the sheet member ST, and performs a notification process to indicate that the target object is attached to the sheet member ST. The notification process may involve displaying information indicating that a target object is attached to the sheet member ST on the display of the information processing device 20. Thus, the user of the magnetic material detection device 1 can remove the target object from the sheet member ST, identify the sheet member ST as a defective product, etc. Alternatively, the notification process can replace such a display process by outputting sound, vibration, light, or other means to indicate the information.

[0049] Information processing device 20 may be, for example, a notebook PC (Personal Computer), a tablet PC, a desktop PC, a workstation, a multi-functional mobile phone terminal (smartphone), a mobile phone terminal, a PDA (Personal Digital Assistant), etc. Alternatively, information processing device 20 may also be a microcomputer or other information processing device.

[0050] Furthermore, in the magnetic material detection device 1, some or all of the magnetization device 11, gradient magnetic field sensor 12, and information processing device 20 may be integrated into one unit.

[0051] Alternatively, the object that the magnetic material detection device 1 checks for the adhesion of the target object can be another object capable of checking for the presence or absence of the target object, instead of the thin sheet member ST. For example, a magnetic material detector including a gradient magnetic field sensor 12 detects the presence or absence of magnetic materials underground. In this case, the magnetic material detector is an example of the magnetic material detection device 1. Furthermore, underground magnetic materials are an example of the target object in this case.

[0052] <Circuit Structure of Gradient Magnetic Field Sensor>

[0053] The following is for reference Figure 2 The circuit structure of the gradient magnetic field sensor 12 is described. Figure 2 This is a diagram illustrating an example of the circuit structure of the gradient magnetic field sensor 12.

[0054] The gradient magnetic field sensor 12 includes an AC power connection terminal CT1, a first sensor head S1, a second sensor head S2, a zero phase shift circuit PS0, an AC current control unit CC1, a detection circuit DT, and a detection signal output terminal CT2. The first sensor head S1 includes a first magnetic core CR1 and a first detection coil CL1. The second sensor head S2 includes a second magnetic core CR2 and a second detection coil CL2. The zero phase shift circuit PS0 has two terminals: an input terminal PS01 and an output terminal PS02. The AC current control unit CC1 has a first input terminal CC11, a second input terminal CC12, a first output terminal CC13, and a second output terminal CC14. The AC current control unit CC1 also includes a first phase shift circuit PS1, a first variable resistor VR11, a first capacitor C1, a second phase shift circuit PS2, a second variable resistor VR12, and a second capacitor C2. The detection circuit DT has a first input terminal DT1, a second input terminal DT2, and an output terminal DT3. In addition, the detection circuit DT includes a phase detector circuit PD, a low-pass filter LF, an error amplifier EA, a resistor R1, and a third capacitor C3. Furthermore, the phase detector circuit PD has a first input terminal PD1, a second input terminal PD2, and an output terminal PD3.

[0055] Furthermore, the gradient magnetic field sensor 12 is connected to the AC power supply P1 via a transmission path. More specifically, the AC power connection terminal CT1 of the gradient magnetic field sensor 12 is connected via the transmission path to the first power terminal P11, which is one of the two power terminals of the AC power supply P1. The second power terminal P12, which is the other of the two power terminals of the AC power supply P1, is grounded via the transmission path. Here, the AC power supply P1 can be any AC power supply. Alternatively, other circuit elements or other devices can be connected between the AC power connection terminal CT1 and the first power terminal P11 without impairing the function of the gradient magnetic field sensor 12. Alternatively, other circuit elements or other devices can be connected between the second power terminal P12 and the ground wire without impairing the function of the gradient magnetic field sensor 12.

[0056] Furthermore, the gradient magnetic field sensor 12 is connected to the information processing device 20 via a transmission path. More specifically, the detection signal output terminal CT2 of the gradient magnetic field sensor 12 is connected to the information processing device 20 via a transmission path. Alternatively, other circuit elements, other devices, etc., can be connected between the detection signal output terminal CT2 and the information processing device 20 without impairing the functionality of the gradient magnetic field sensor 12.

[0057] Furthermore, the AC power connection terminal CT1 is connected via a transmission path to the input terminal PS01 of the 0th phase shift circuit PS0 and the first input terminal DT1 of the detection circuit DT. The output terminal PS02 of the 0th phase shift circuit PS0 is connected via a transmission path to the first input terminal CC11 and the second input terminal CC12 of the AC current control unit CC1. Alternatively, other circuit elements or devices may be connected between the AC power connection terminal CT1 and the input terminal PS01 without impairing the function of the gradient magnetic field sensor 12. Similarly, other circuit elements or devices may be connected between the AC power connection terminal CT1 and the first input terminal DT1 without impairing the function of the gradient magnetic field sensor 12. Finally, other circuit elements or devices may be connected between the output terminal PS02 and the first input terminal CC11 without impairing the function of the gradient magnetic field sensor 12. Alternatively, other circuit elements or devices can be connected between the output terminal PS02 and the second input terminal CC12 without compromising the functionality of the gradient magnetic field sensor 12.

[0058] Furthermore, in the AC current control unit CC1, a first phase shift circuit PS1, a first variable resistor VR11, and a first capacitor C1 are connected in series via a transmission path between the first input terminal CC11 and the first output terminal CC13. Additionally, in the AC current control unit CC1, a second phase shift circuit PS2, a second variable resistor VR12, and a second capacitor C2 are connected in series via a transmission path between the second input terminal CC12 and the second output terminal CC14. Furthermore, between the first input terminal CC11 and the first output terminal CC13, without impairing the functionality of the gradient magnetic field sensor 12, other circuit elements or devices can be connected together with the first phase shift circuit PS1, the first variable resistor VR11, and the first capacitor C1. Moreover, between the first input terminal CC11 and the first output terminal CC13, the first phase shift circuit PS1, the first variable resistor VR11, and the first capacitor C1 can be connected in series in any order. Furthermore, between the second input terminal CC12 and the second output terminal CC14, without impairing the functionality of the gradient magnetic field sensor 12, other circuit elements or devices can be connected together with the second phase shift circuit PS2, the second variable resistor VR12, and the second capacitor C2. Additionally, between the second input terminal CC12 and the second output terminal CC14, the second phase shift circuit PS2, the second variable resistor VR12, and the second capacitor C2 can also be connected in series in any order.

[0059] Furthermore, the first magnetic core CR1 of the first sensor head S1 is connected via a transmission path between the first output terminal CC13 of the AC current control unit CC1 and the ground wire. Additionally, the second magnetic core CR2 of the second sensor head S2 is connected via a transmission path between the second output terminal CC14 of the AC current control unit CC1 and the ground wire. Hereinafter, for ease of explanation, as follows... Figure 2 As indicated by the arrow, the alternating current flowing from the first output terminal CC13 to the first magnetic core CR1 will be referred to as the first AC excitation current AC1. Furthermore, for ease of explanation, the following will use... Figure 2 As indicated by the arrow, the alternating current flowing from the second output terminal CC14 to the second magnetic core CR2 will be referred to as the second alternating current excitation current AC2. Alternatively, other circuit elements or devices may be connected between the first output terminal CC13 of the alternating current control unit CC1 and the ground wire, without impairing the function of the gradient magnetic field sensor 12. Similarly, other circuit elements or devices may be connected between the second output terminal CC14 of the alternating current control unit CC1 and the ground wire, without impairing the function of the gradient magnetic field sensor 12.

[0060] Furthermore, in the detection circuit DT, the first input terminal DT1 is connected to the first input terminal PD1 of the phase detector circuit PD via a transmission path. Additionally, the output terminal PD3 of the phase detector circuit PD is connected to an input terminal (not shown) of the low-pass filter LF via a transmission path. Furthermore, the output terminal (not shown) of the low-pass filter LF is connected to the inverting input terminal of the error amplifier EA via a transmission path. Additionally, the non-inverting input terminal of the error amplifier EA is grounded via a transmission path. Furthermore, the output terminal of the error amplifier EA is connected via a transmission path to one of the output terminal DT3 of the detection circuit DT and one of the two terminals of the resistor R1. Additionally, the other of the two terminals of the resistor R1 is connected via a transmission path to one of the second input terminal DT2 of the phase detector circuit PD and one of the two terminals of the third capacitor C3. Furthermore, the other of the two terminals of the third capacitor C3 is connected via a transmission path to the second input terminal PD2 of the phase detector circuit PD. Furthermore, the transmission path connecting resistor R1 and the third capacitor C3 is connected to the second input terminal DT2 of the detection circuit DT via another transmission path. Thus, the detection circuit DT is a PSD (Phase Sensitive Detector) circuit. Alternatively, other circuit elements or devices can be connected between the first input terminal DT1 and the first input terminal PD1, without impairing the functionality of the detection circuit DT. Alternatively, other circuit elements or devices can be connected between the output terminal PD3 and the input terminal of the low-pass filter LF, without impairing the functionality of the detection circuit DT. Alternatively, other circuit elements or devices can be connected between the output terminal of the low-pass filter LF and the inverting input terminal of the error amplifier EA, without impairing the functionality of the detection circuit DT. Alternatively, other circuit elements or devices can be connected between the non-inverting input terminal of the error amplifier EA and ground, without impairing the functionality of the detection circuit DT. Alternatively, other circuit elements or devices can be connected between the output terminals of the error amplifier EA and the output terminal DT3, without impairing the function of the detection circuit DT. Alternatively, other circuit elements or devices can be connected between the output terminals of the error amplifier EA and the resistor R1, without impairing the function of the detection circuit DT. Alternatively, other circuit elements or devices can be connected between the resistor R1 and the third capacitor C3, without impairing the function of the detection circuit DT.Alternatively, other circuit elements or devices can be connected between the third capacitor C3 and the second input terminal PD2, without impairing the function of the detection circuit DT. Alternatively, other circuit elements or devices can be connected between the transmission path connecting the resistor R1 and the third capacitor C3 and the second input terminal DT2, without impairing the function of the detection circuit DT.

[0061] Furthermore, the second input terminal DT2 of the detection circuit DT is connected to one of the two terminals of the first detection coil CL1 via a transmission path. The other of the two terminals of the first detection coil CL1 is connected to one of the two terminals of the second detection coil CL2 via a transmission path. The other of the two terminals of the second detection coil CL2 is grounded via a transmission path. However, the second detection coil CL2 and the first detection coil CL1 are differentially connected. Alternatively, other circuit elements or devices may be connected between the second input terminal DT2 and the first detection coil CL1 without impairing the function of the gradient magnetic field sensor 12. Alternatively, other circuit elements or devices may be connected between the first detection coil CL1 and the second detection coil CL2 without impairing the function of the gradient magnetic field sensor 12. Alternatively, other circuit elements or devices may be connected between the second detection coil CL2 and the ground wire without impairing the function of the gradient magnetic field sensor 12.

[0062] <Operation of the gradient magnetic field sensor in the implementation method>

[0063] Next, the operation of the gradient magnetic field sensor 12 will be explained.

[0064] In the gradient magnetic field sensor 12 with the circuit structure described above, AC power supply P1 inputs AC current to AC power supply connection terminal CT1. The AC current input to AC power supply connection terminal CT1 is branched into two. One of the two branched AC currents is input as AC excitation current to the 0th phase shift circuit PS0. The other branched AC current is input as a reference signal to the first input terminal DT1 of the detection circuit DT.

[0065] The AC excitation current input to the 0th phase shift circuit PS0 is phase shifted by the 0th phase shift circuit PS0 and then branches into two AC excitation currents: the 1st AC excitation current AC1 and the 2nd AC excitation current AC2.

[0066] The first AC excitation current AC1 flows to the first magnetic core CR1 via the first phase shift circuit PS1, the first variable resistor VR11, and the first capacitor C1. Therefore, the first AC excitation current AC1 is phase-shifted by the first phase shift circuit PS1, and its amplitude is adjusted by the first variable resistor VR11. Consequently, a voltage corresponding to the strength of the first AC excitation current AC1 flowing through the first magnetic core CR1 and the magnetic field applied to the first detection coil CL1 is induced in the first detection coil CL1. That is, this voltage varies according to the strength of the magnetic field applied externally to the first detection coil CL1. Hereinafter, for ease of explanation, the voltage induced in the first detection coil CL1 will be referred to as the first induced voltage. Furthermore, the first capacitor C1 is a capacitor used for AC (Alternating Current) coupling. Due to the presence of the first capacitor C1, in the gradient magnetic field sensor 12, the flow of DC current from the first output terminal CC13 to the first input terminal CC11 can be suppressed.

[0067] On the other hand, the second AC excitation current AC2 flows to the second magnetic core CR2 via the second phase shift circuit PS2, the second variable resistor VR12, and the second capacitor C2. Therefore, the second AC excitation current AC2 is phase-shifted by the second phase shift circuit PS2 and its amplitude is adjusted by the second variable resistor VR12. Consequently, a voltage corresponding to the strength of the second AC excitation current AC2 flowing through the second magnetic core CR2 and the magnetic field applied to the second detection coil CL2 is induced in the second detection coil CL2. That is, this voltage varies according to the strength of the magnetic field applied externally to the second detection coil CL2. Hereinafter, for ease of explanation, the voltage induced in the second detection coil CL2 will be referred to as the second induced voltage. Furthermore, the second capacitor C2 is a capacitor used for AC coupling. Due to the presence of the second capacitor C2, in the gradient magnetic field sensor 12, the flow of DC current from the second output terminal CC14 to the second input terminal CC12 can be suppressed.

[0068] In the gradient magnetic field sensor 12, the signals corresponding to the first and second induced voltages are input as a differential signal Vout to the second input terminal DT2 of the detection circuit DT. The phase detection circuit PD of the detection circuit DT inputs a signal corresponding to the deviation between the input differential signal Vout and the reference signal input from the AC power supply P1 as a detection signal to the low-pass filter LF. The low-pass filter LF outputs the output signal from the detection signal input from the phase detection circuit PD after removing components above a predetermined first frequency to the inverting input terminal of the error amplifier EA. The error amplifier EA outputs a signal corresponding to the potential difference between the potential of the output signal input to the inverting input terminal of the error amplifier EA and the ground potential as a detection signal to the detection signal output terminal CT2 and the resistor R1, respectively. In addition, the third capacitor C3 is a capacitor for AC coupling. Furthermore, a buffer circuit (e.g., a voltage follower) is connected to the terminal opposite to the terminal connected to the phase detection circuit PD in the terminals of the third capacitor C3. The buffer circuit is omitted from the figure for simplicity.

[0069] Due to the presence of a buffer circuit (not shown), the detection signal input to resistor R1 is not input to the third capacitor C3, but flows as feedback current from the second input terminal DT2 to the first detection coil CL1.

[0070] In the detection circuit DT that performs this operation, by adjustment, a detection signal with a signal level of 0V is output from the detection signal output terminal CT2 when the differential signal Vout signal level is 0V, and a detection signal with a signal level not of 0V is output from the detection signal output terminal CT2 when the differential signal Vout signal level is not 0V. Furthermore, since the adjustment of the detection circuit DT is known, further detailed explanation is omitted.

[0071] Through the actions described above, the gradient magnetic field sensor 12 detects a gradient. However, without adjusting the first and second sensing voltages separately, the gradient magnetic field sensor 12 sometimes detects a gradient even within a uniform magnetic field region. This leads to false detection of a target object even when it is not present, which is undesirable. Therefore, by adjusting the gradient magnetic field sensor 12 using the adjustment method specified below, the detection accuracy of the target object using the magnetic field can be improved. Therefore, the adjustment methods for the first and second sensing voltages in the gradient magnetic field sensor 12 will be described below.

[0072] <Regarding the adjustment methods for the first and second induced voltages in the gradient magnetic field sensor>

[0073] The adjustment methods for the first and second induced voltages in the gradient magnetic field sensor 12 are described below.

[0074] First, the relationship between the strength of the magnetic field detected by the gradient magnetic field sensor 12 and the detection signal output from the gradient magnetic field sensor 12 will be explained.

[0075] Consider the following situation: the intensity B1(t) of the magnetic field applied to the first sensor head S1 at a certain time t is represented by the following equation (1), and the intensity B2(t) of the magnetic field applied to the second sensor head S2 at time t is represented by the following equation (2). However, here, as an example, consider the case where a uniform magnetic field is applied to the gradient magnetic field sensor 12, and the magnetized detection object is transported within the detection area of ​​the gradient magnetic field sensor 12. Furthermore, for ease of explanation, the magnetic field applied to the first sensor head S1 from the detection object will be referred to as the first magnetic field. Furthermore, for ease of explanation, the magnetic field applied to the second sensor head S2 from the detection object will be referred to as the second magnetic field.

[0076] B1(t)=B 01 (t)+B cos(ω n t)···(1)

[0077] B2(t)=B 02 (t)+B cos(ω n t)···(2)

[0078] Here, B in equation (1) above 01 (t) is a function representing the strength of the first magnetic field at time t. Additionally, B in equation (2) 02 (t) is a function representing the strength of the second magnetic field at time t. Furthermore, Bcos(ω) in equations (1) and (2) n ω is a function representing the strength of the uniform magnetic field at time t. n This represents the angular frequency of the time-varying change in the strength of the uniform magnetic field. Additionally, B represents the maximum strength of the uniform magnetic field.

[0079] Furthermore, consider the magnitude of the reference signal at time t as shown in the following equation (3): V r (t) represents the case. In equation (3) below, A represents the amplitude of the reference signal. In addition, ω in equation (3) below represents the angular frequency of the reference signal used as the AC signal.

[0080] V r (t)=Acos(ωt)···(3)

[0081] Furthermore, consider the magnitude of the differential signal Vout at time t as shown in the following equation (4). i (t) represents the case.

[0082] V i (t)=a{1+k1B1(t)}cos(ωt+θ+α)+b{1+k2B2(t)}cos(ωt+θ+β)

[0083] ···(4)

[0084] Here, θ in Equation (4) above represents the phase shift of the AC excitation current based on the 0th phase shift circuit PS0. Additionally, α in Equation (4) represents the phase shift of the 1st AC excitation current AC1 of the 1st phase shift circuit PS1. Furthermore, β in Equation (4) represents the phase shift of the 2nd AC excitation current AC2 of the 2nd phase shift circuit PS2. Furthermore, a in Equation (4) represents the adjustment amount of the amplitude of the 1st AC excitation current AC1 based on the 1st variable resistor VR11. Furthermore, b in Equation (4) represents the adjustment amount of the amplitude of the 2nd AC excitation current AC2 based on the 2nd variable resistor VR12. Additionally, the differential signal Vout is obtained by the difference between the 1st induced voltage induced as a result of AM modulation of the 1st magnetic field and the 2nd induced voltage induced as a result of AM modulation of the 2nd magnetic field. The modulation indices (i.e., magnetic sensitivity) of these AM modulations are k1 and k2 as shown in Equation (4). Furthermore, k1 is the modulation index of AM modulation of the 1st magnetic field. In addition, k2 is the modulation index of AM modulation of the second magnetic field.

[0085] The phase detection circuit PD is based on the magnitude V of the reference signal expressed by equation (3) above. r (t) and the magnitude V of the differential signal Vout as expressed by equation (4) above. i (t), the signal as shown in equation (5) below is output as the magnitude V0(t) of the detector signal at time t.

[0086] V0(t)=V r (t)·V i (t)

[0087] =A cos(ωt)·a{1+k1B1(t)}cos(ωt+θ+α)+A cos(ωt)·b{1+k2B2(t)}cos(ωt+θ+β)···(5)

[0088] The right side of the bottom part of the above equation (5) can be transformed using the addition theorem as shown in the following equation (6).

[0089]

[0090] The terms cos(θ+α) and cos(θ+β) on the right-hand side of equation (6) above are terms that do not change with time t, i.e., DC components. These DC components can be removed by a low-pass filter (LF). Therefore, the equation (7) is obtained by removing these DC components from equation (6).

[0091]

[0092] Here, in equation (7) above, it is required that the sum of the phase shift θ of the 0th phase shift circuit PS0 and the phase shift α of the 1st phase shift circuit PS1, i.e., (θ+α), and the difference (α-β) between the sum of the phase shift θ of the 0th phase shift circuit PS0 and the phase shift β of the 2nd phase shift circuit PS2, i.e., (θ+β), be -π. This requirement is to ensure that the phase of the 1st induced voltage is opposite to the phase of the 2nd induced voltage. Moreover, this requirement can be achieved by adjusting at least one of the phase shift α of the 1st phase shift circuit PS1 and the phase shift β of the 2nd phase shift circuit PS2. In addition, in equation (7) above, it is required that the product of the adjustment amount a based on the 1st variable resistor VR11 and the modulation index k1, and the product of the adjustment amount b based on the 2nd variable resistor VR12 and the modulation index k2 are equal (i.e., ak1=bk2). This requirement is to ensure that the amplitude of the 1st induced voltage is equal to the amplitude of the 2nd induced voltage. Moreover, this requirement can be achieved by adjusting at least one of the adjustment amount a of the first variable resistor VR11 and the adjustment amount b of the second variable resistor VR12 (in addition, it is not necessary to know the values ​​of the modulation index k1 and the modulation index k2 in order to implement this adjustment). If these two requirements are applied to equation (7), then equation (7) is transformed as in equation (8).

[0093]

[0094] According to equation (8) above, by making the two adjustments mentioned above, the component of the uniform magnetic field Bcos(ω) can be offset according to the magnitude of the detection signal V0(t). nt). Hereinafter, for ease of explanation, these two adjustments will be referred to as alternating current adjustments. That is, by performing alternating current adjustments, the gradient magnetic field sensor 12 can detect gradients without detecting the strength of a uniform magnetic field. As a result, the gradient magnetic field sensor 12 can improve the detection accuracy of objects using magnetic fields. Furthermore, the second term within the curly braces on the right side of the above equation (8) is an offset component. This offset component is included in the detection signal as an error. To know the magnitude of this offset component, it is necessary to know the values ​​of modulation index k1 and modulation index k2, or to know the ratio of modulation index k1 to modulation index k2. However, as described later, this offset component can be removed by signal processing. When the offset component is removed by signal processing, it is not necessary to know the values ​​of modulation index k1 and modulation index k2, or to know the ratio of modulation index k1 to modulation index k2. Furthermore, this offset component is generally smaller than the first term within the curly braces on the right side of the above equation (8). Therefore, in the embodiment, the case where this offset component is not removed and is treated as an error will be explained.

[0095] Here, Figure 3 This is a diagram illustrating an example of the time variations of the first induced voltage, the second induced voltage, the differential signal, the detector signal, and the detection signal before and after AC current adjustment of the gradient magnetic field sensor 12.

[0096] Figure 3 The two left-hand graphs, surrounded by labels such as "Before Adjustment," show the time variations of the first induced voltage, second induced voltage, differential signal, detection signal, and detection signal in the gradient magnetic field sensor 12 before AC current adjustment. The two right-hand graphs, surrounded by labels such as "After Adjustment," show the time variations of the first induced voltage, second induced voltage, differential signal, detection signal, and detection signal in the gradient magnetic field sensor 12 after AC current adjustment. The upper two graphs are those obtained when a magnetic moment generated by a coil with one turn is detected within a uniform magnetic field region where the intensity varies sinusoidally at 50Hz. The lower two graphs show the time variations of the first induced voltage, second induced voltage, differential signal, detection signal, and detection signal in the gradient magnetic field sensor 12 located in an area where no magnetic field is applied. The horizontal axis of all four graphs represents elapsed time. In addition, the vertical axis of these four graphs represents voltage.

[0097] When observing Figure 3When plotting the curve below the "before adjustment" setting, the phases of the first and second induced voltages are not opposite to each other, so even though the gradient magnetic field sensor 12 is positioned in the region where no magnetic field is applied, the signal level of the differential signal is not 0 [V]. Therefore, in Figure 3 In the lower curve of the "before adjustment" graph, the signal level of the detector signal is not 0 [V], resulting in the signal level of the detection signal also not being 0 [V]. In this case, the gradient magnetic field sensor 12 cannot cancel the component of the uniform magnetic field Bcos(ω) according to the magnitude V0(t) of the detection signal in the above equation (8). n Therefore, if it is configured within a uniform magnetic field region, a uniform magnetic field will be detected. Based on this, in the gradient magnetic field sensor 12 before alternating current adjustment, such as... Figure 3 As shown in the upper curve of the "before adjustment" graph, the detection signal when the gradient magnetic field sensor 12 is placed in an area without an applied magnetic field overlaps with the detection signal when a magnetic moment generated by a coil with one turn is detected in a uniform magnetic field area. As a result, in Figure 3 In the upper curve of the "before adjustment" graph, for example, in the range of -40ms to -20ms, or in the range of 20ms to 40ms, the signal level of the detection signal is not 0 [V], but fluctuates around 0.1 [V]. Moreover, such fluctuation of the detection signal becomes an error in the gradient detection performed by the gradient magnetic field sensor 12. Therefore, in the gradient magnetic field sensor 12 before the AC current adjustment, if the detected gradient is small, there is a high possibility that the detection signal will be buried in the error caused by such fluctuation and will not be seen.

[0098] On the other hand, if we observe Figure 3 The lower curve of the "adjusted" graph shows that the phases of the first induced voltage and the second induced voltage are opposite to each other. Therefore, when the gradient magnetic field sensor 12 is placed in the area where no magnetic field is applied, the signal level of the differential signal becomes 0 [V]. Therefore, in Figure 3 In the lower curve of the "adjusted" graph, the signal level of the detector signal is approximately 0 [V] (in reality, it is not exactly 0 [V] due to slight vibrations caused by noise, etc.), resulting in a signal level of the detection signal of approximately 0 [V]. In this case, the gradient magnetic field sensor 12 can cancel the component of the uniform magnetic field Bcos(ω) according to the magnitude V0(t) of the detection signal in the above equation (8). n Therefore, even when configured within a uniform magnetic field region, a uniform magnetic field is not detected. Based on this, in the gradient magnetic field sensor 12 after alternating current adjustment, as... Figure 3As shown in the upper curve of the "adjusted" graph, the detection signal when the gradient magnetic field sensor 12 is positioned in an area without an applied magnetic field does not overlap with the detection signal when a magnetic moment generated by a coil with one turn is detected in a uniform magnetic field area. As a result, in Figure 3 In the upper curve of the "adjusted" graph, for example, in the range of -40msec to -20msec and the range of 20msec to 40msec, the signal level of the detected signal is approximately 0 [V]. As a result, in the gradient magnetic field sensor 12 after AC current adjustment, even if the detected gradient is small, the detection signal representing the gradient will not be buried by error. In other words, the gradient magnetic field sensor 12 after AC current adjustment can detect the gradient without detecting the strength of the uniform magnetic field. That is, the gradient magnetic field sensor 12 after AC current adjustment can detect the object with high precision.

[0099] in addition, Figure 4 This is a diagram illustrating the time variations of the detection signal, differential signal, and detector signal when the gradient magnetic field sensor 12 detects the magnetic moment generated by a coil with one turn before and after the alternating current is adjusted.

[0100] Figure 4 The rightmost of the two graphs shown above, surrounded by labels such as "Before Adjustment," represents the temporal changes of the differential signal and the detection signal in the gradient magnetic field sensor 12 before AC current adjustment. Additionally, this graph represents the temporal changes of the differential signal and the detection signal when the gradient magnetic field sensor 12 is positioned in a region where no magnetic field is applied. On the other hand, Figure 4 The rightmost of the two graphs shown, surrounded by labels such as "Adjusted," represents the temporal changes of the differential signal and the detection signal in the gradient magnetic field sensor 12 after AC current adjustment. This graph shows the temporal changes of the differential signal and the detection signal when the gradient magnetic field sensor 12 is positioned in an area without an applied magnetic field. Comparing these two graphs, it can be seen that the amplitude of the differential signal after AC current adjustment is reduced by approximately two decimal places compared to the differential signal before AC current adjustment. As a result, the amplitude of the detection signal after AC current adjustment is also approximately two decimal places smaller than the detection signal before AC current adjustment. Based on this, when the scale interval of the vertical axis of the rightmost graph in the two lower graphs surrounded by labels such as "Before Adjustment" is changed to the same scale interval as the scale interval of the vertical axis of the rightmost graph in the two upper graphs surrounded by labels such as "Before Adjustment," the vibrations of the differential signal and the detection signal after AC current adjustment are as follows: Figure 3The vibrations of the differential signal and the detector signal in the lower right curve are not visible.

[0101] Figure 4 The left graph in the two graphs shown above, surrounded by labels such as "Before Adjustment," represents the time-varying change of the detection signal in the gradient magnetic field sensor 12 before AC current adjustment. The other graph represents the time-varying change of the detection signal when a magnetic moment generated by a coil with one turn is detected in a uniform magnetic field region. On the other hand, Figure 4 The left graph in the two graphs shown below, surrounded by labels such as "Adjusted," represents the time-varying change of the detection signal in the gradient magnetic field sensor 12 after AC current adjustment. The other graph represents the time-varying change of the detection signal when a magnetic moment generated by a coil with one turn is detected in a uniform magnetic field region. Comparing these two graphs, it can be seen that the noise in the detection signal output from the gradient magnetic field sensor 12 is reduced by AC current adjustment. This is because, as... Figure 4 As shown in the lower right curve, by adjusting the alternating current, the amplitudes of the differential signal and the detection signal decrease when the gradient magnetic field sensor 12 is configured in an area where no magnetic field is applied. As a result, the gradient magnetic field sensor 12 does not detect a uniform magnetic field.

[0102] Here, Figure 5 It is about Figure 4 The images show magnified portions of each of the two curves representing the detected signal. Figure 5 The graph shown above, surrounded by labels such as "Before Adjustment," is a graph representing the time-varying signal in the gradient magnetic field sensor 12 before AC current adjustment. On the other hand, by... Figure 5 The graph shown below, surrounded by labels such as "Adjusted," represents the time-varying signal in the gradient magnetic field sensor 12 after AC current adjustment. Comparing these two graphs clearly shows the difference between... Figure 4 Compared to the curve shown, the noise of the detection signal output from the gradient magnetic field sensor 12 is reduced by adjusting the alternating current.

[0103] Thus, based on these Figures 3-5 As shown in the graph, the gradient magnetic field sensor 12, by adjusting the alternating current, can detect gradients without detecting the strength of a uniform magnetic field. As a result, it can improve the detection accuracy of objects using magnetic fields. Furthermore, an example of the circuit structure that enables this is... Figure 2 The circuit structure shown is shown.

[0104] Furthermore, the gradient magnetic field sensor 12 in this embodiment may also be structured without the 0th phase shift circuit PS0. This is because, as described above, the phase shift θ of the 0th phase shift circuit PS0 does not matter what value it is in the two requirements mentioned above. However, by including the 0th phase shift circuit PS0 in this gradient magnetic field sensor 12, the amplitude of the detection signal can be adjusted while maintaining the relationship α based on the phase shift α of the 1st phase shift circuit PS1 and the phase shift β based on the 2nd phase shift circuit PS2, where α - β = -π.

[0105] Alternatively, the gradient magnetic field sensor 12 in this embodiment may also be structured without either the first phase shift circuit PS1 or the second phase shift circuit PS2. This is because, in the two requirements mentioned above, it is important that the difference between the phase shift α of the first phase shift circuit PS1 and the phase shift β of the second phase shift circuit PS2 is -π. This is also evident from the fact that the gradient magnetic field sensor 12 without either the first phase shift circuit PS1 or the second phase shift circuit PS2 is equivalent to making either the phase shift α or the phase shift β zero.

[0106] Alternatively, the gradient magnetic field sensor 12 in this embodiment may also be structured without either the first variable resistor VR11 or the second variable resistor VR12. This is because, among the two requirements mentioned above, it is important that the product of the adjustment amount a of the first variable resistor VR11 and the modulation index k1 and the product of the adjustment amount b of the second variable resistor VR12 and the modulation index k2 are equal. This is also evident from the fact that the gradient magnetic field sensor 12 does not have either the first variable resistor VR11 or the second variable resistor VR12, which is equivalent to setting either the adjustment amount a or the adjustment amount b to 1.

[0107] Alternatively, the gradient magnetic field sensor 12 of the embodiment may also be structured without at least one of the first capacitor C1 and the second capacitor C2. However, as mentioned above, these are capacitors used for AC coupling. Therefore, it is preferable that the gradient magnetic field sensor 12 includes both the first capacitor C1 and the second capacitor C2.

[0108] In addition, in the gradient magnetic field sensor 12 of the embodiment, the AC current control unit CC1 may be configured to replace the first variable resistor VR11, or in addition to the first variable resistor VR11, it may also have a first amplifier circuit that amplifies the amplitude of the first AC excitation current AC1.

[0109] In addition, in the gradient magnetic field sensor 12 of the embodiment, the AC current control unit CC1 may be configured to replace the second variable resistor VR12, or in addition to the second variable resistor VR12, it may also have a second amplifier circuit that amplifies the amplitude of the second AC excitation current AC2.

[0110] As described above, the gradient magnetic field sensor 12 of the embodiment includes: an AC power connection terminal CT1 connected to a first power terminal P11 of an AC power supply P1; a first magnetic core CR1 connected between the AC power connection terminal CT1 and a ground wire; a second magnetic core CR2 connected in parallel with the first magnetic core CR1 between the AC power connection terminal CT1 and the ground wire; an AC power connection terminal CT1; an AC current control unit CC1 connected between at least one of the first magnetic core CR1 and the second magnetic core CR2, controlling the AC current flowing through at least one of the first magnetic core CR1 and the second magnetic core CR2; a first detection coil CL1 wound around the first magnetic core CR1; a second detection coil CL2 wound around the second magnetic core CR2 and differentially connected to the first detection coil CL1; and a detection circuit DT that detects a voltage corresponding to the difference between a first induced voltage output from the first detection coil CL1 and a second induced voltage output from the second detection coil CL2 as a detection signal. Therefore, the gradient magnetic field sensor 12 can improve the detection accuracy of objects that use magnetic fields.

[0111] In addition, the gradient magnetic field sensor 12 can also use an AC power supply P1 with a grounded second power terminal P12.

[0112] Furthermore, in the gradient magnetic field sensor 12, the AC current control unit CC1 may also use a phase-shifting unit structure that includes a phase shift of at least one of the first AC excitation current AC1 flowing from the AC power connection terminal CT1 to the first magnetic core CR1 and the second AC excitation current AC2 flowing from the AC power connection terminal CT1 to the second magnetic core CR2. The aforementioned first phase-shifting circuit PS1 and second phase-shifting circuit PS2 are examples of this phase-shifting unit.

[0113] Furthermore, in the gradient magnetic field sensor 12, the AC current control unit CC1 may also use a structure that includes an amplitude adjustment unit that adjusts the amplitude of at least one of the first AC excitation current AC1 and the second AC excitation current AC2. The aforementioned first variable resistor VR11 and second variable resistor VR12 are examples of such an amplitude adjustment unit.

[0114] Furthermore, in the gradient magnetic field sensor 12, the AC current control unit CC1 can also be structured as an amplitude adjustment unit, comprising at least one of a first amplifier circuit and an eleventh variable resistor connected between the AC power connection terminal CT1 and the first magnetic core CR1, and at least one of a second amplifier circuit and a twelfth variable resistor connected between the AC power connection terminal CT1 and the second magnetic core CR2. The aforementioned first variable resistor VR11 is an example of this eleventh variable resistor. Similarly, the aforementioned second variable resistor VR12 is an example of this twelfth variable resistor.

[0115] <Modification 1 of the Implementation Method>

[0116] The following is for reference Figure 6 The following describes a variation of the embodiment 1. Furthermore, in variation 1, the same reference numerals are used for structural parts identical to those in the embodiment, and descriptions are omitted. Additionally, for ease of explanation, the gradient magnetic field sensor 12 of variation 1 will be referred to as gradient magnetic field sensor 12A. Furthermore, the matters described in variation 1 can be applied not only to the embodiment but also to any of the other variations of the embodiments described later.

[0117] Figure 6 This is a diagram illustrating an example of the circuit structure of the gradient magnetic field sensor 12A.

[0118] In addition to having an AC power connection terminal CT1, a first sensor head S1, a second sensor head S2, a zero phase shift circuit PS0, an AC current control unit CC1, a detection circuit DT, and a detection signal output terminal CT2, the gradient magnetic field sensor 12A also has a DC power connection terminal CT3 and a DC current control unit CC2. Furthermore, the DC current control unit CC2 has an input terminal CC21, a first output terminal CC22, and a second output terminal CC23. Additionally, the DC current control unit CC2 includes a first variable resistor VR21, a first inductor L1, a second variable resistor VR22, and a second inductor L2.

[0119] In addition, the gradient magnetic field sensor 12A is connected to both AC power supply P1 and DC power supply P2 via the transmission path. More specifically, the DC power supply connection terminal CT3 of the gradient magnetic field sensor 12A is connected to the positive power supply terminal of the DC power supply P2 via the transmission path. Furthermore, the negative power supply terminal of the DC power supply P2 is grounded via the transmission path. Here, the DC power supply P2 can be any DC power supply. Alternatively, other circuit elements or devices can be connected between the DC power supply connection terminal CT3 and the positive power supply terminal without impairing the function of the gradient magnetic field sensor 12A. Similarly, other circuit elements or devices can be connected between the negative power supply terminal and the ground wire without impairing the function of the gradient magnetic field sensor 12A.

[0120] Additionally, the DC power supply connection terminal CT3 is connected to the input terminal CC21 of the DC current control unit CC2 via a transmission path. Alternatively, other circuit elements or devices can be connected between the DC power supply connection terminal CT3 and the input terminal CC21 without impairing the functionality of the gradient magnetic field sensor 12A.

[0121] Furthermore, in the DC current control unit CC2, a first variable resistor VR21 and a first inductor L1 are connected in series via a transmission path between the input terminal CC21 and the first output terminal CC22. Additionally, in the DC current control unit CC2, a second variable resistor VR22 and a second inductor L2 are connected in series via a transmission path between the input terminal CC21 and the second output terminal CC23. Furthermore, between the input terminal CC21 and the first output terminal CC22, without impairing the function of the gradient magnetic field sensor 12A, other circuit elements or devices may be connected together with the first variable resistor VR21 and the first inductor L1. Alternatively, between the input terminal CC21 and the second output terminal CC23, without impairing the function of the gradient magnetic field sensor 12A, other circuit elements or devices may be connected together with the second variable resistor VR22 and the second inductor L2. Furthermore, the first variable resistor VR21 and the first inductor L1 can be connected in series in any order between the input terminal CC21 and the first output terminal CC22. Similarly, the second variable resistor VR22 and the second inductor L2 can be connected in series in any order between the input terminal CC21 and the second output terminal CC23.

[0122] Furthermore, the first output terminal CC22 of the DC current control unit CC2 is connected via another transmission path to the transmission path that connects the first output terminal CC13 of the AC current control unit CC1 and the first magnetic core CR1. Alternatively, other circuit elements, other devices, etc., can be connected between the first output terminal CC22 and the transmission path connecting the first output terminal CC13 of the AC current control unit CC1 and the first magnetic core CR1, without impairing the function of the gradient magnetic field sensor 12A.

[0123] Furthermore, the second output terminal CC23 of the DC current control unit CC2 is connected via another transmission path to the transmission path that connects the second output terminal CC14 of the AC current control unit CC1 and the second magnetic core CR2. Alternatively, other circuit elements, other devices, etc., can be connected between the second output terminal CC23 and the transmission path connecting the second output terminal CC14 of the AC current control unit CC1 and the second magnetic core CR2, without impairing the function of the gradient magnetic field sensor 12.

[0124] Next, the operation of the gradient magnetic field sensor 12A will be explained.

[0125] In the gradient magnetic field sensor 12A with the circuit structure described above, DC power supply P2 inputs DC current to DC power supply connection terminal CT3. The DC current input to DC power supply connection terminal CT3 is input to DC current control unit CC2 as DC excitation current.

[0126] The DC excitation current input to the DC current control unit CC2 is branched into two DC excitation currents: the first DC excitation current DC1 and the second DC excitation current DC2.

[0127] In the DC current control unit CC2, the magnitude of the first DC excitation current DC1 is adjusted by the first variable resistor VR21. Furthermore, the first DC excitation current DC1 is input to the first magnetic core CR1 from the first output terminal CC22. As a result, a voltage corresponding to the first AC excitation current AC1 flowing in the first magnetic core CR1, the first DC excitation current DC1 flowing in the first magnetic core CR1, and the strength of the magnetic field applied to the first detection coil CL1 is induced in the first detection coil CL1. That is, in the gradient magnetic field sensor 12A, this voltage also varies according to the strength of the magnetic field applied externally to the first detection coil CL1. Hereinafter, for ease of explanation, this voltage will be referred to as the third induced voltage. Furthermore, the first inductor L1 is an inductor for DC (Direct Current) coupling. Due to the presence of the first inductor L1, in the gradient magnetic field sensor 12A, the flow of AC current from the first output terminal CC22 to the input terminal CC21 can be suppressed.

[0128] On the other hand, in the DC current control unit CC2, the magnitude of the second DC excitation current DC2 is adjusted by the second variable resistor VR22. Furthermore, the second DC excitation current DC2 is input to the second magnetic core CR2 from the second output terminal CC23. As a result, a voltage corresponding to the second AC excitation current AC2 flowing in the second magnetic core CR2, the second DC excitation current DC2 flowing in the second magnetic core CR2, and the strength of the magnetic field applied to the second detection coil CL2 is induced in the second detection coil CL2. That is, in the gradient magnetic field sensor 12A, this voltage also varies according to the strength of the magnetic field applied externally to the second detection coil CL2. Hereinafter, for ease of explanation, this voltage will be referred to as the fourth induced voltage. Furthermore, the second inductor L2 is an inductor used for DC coupling. Due to the presence of the second inductor L2, in the gradient magnetic field sensor 12A, the flow of AC current from the second output terminal CC23 to the input terminal CC21 can be suppressed.

[0129] In the gradient magnetic field sensor 12A, the signals corresponding to the induced third and fourth induced voltages are input as differential signals Vout2 to the second input terminal DT2 of the detection circuit DT. The phase detection circuit PD of the detection circuit DT inputs a signal corresponding to the deviation between the input differential signal Vout2 and the reference signal input from the AC power supply P1 as a detection signal to the low-pass filter LF. The low-pass filter LF outputs the output signal from the detection signal input from the phase detection circuit PD after removing components above a predetermined first frequency to the inverting input terminal of the error amplifier EA. The error amplifier EA outputs a signal corresponding to the potential difference between the potential of the output signal input to the inverting input terminal of the error amplifier EA and the ground potential as a detection signal to the detection signal output terminal CT2 and the resistor R1, respectively.

[0130] Due to the presence of a buffer circuit (not shown), the detection signal input to resistor R1 is not input to the third capacitor C3, but flows as feedback current from the second input terminal DT2 to the first detection coil CL1.

[0131] In the detection circuit DT that performs such an action, by adjustment, a detection signal with a signal level of 0 [V] can be output from the detection signal output terminal CT2 when the signal level of the differential signal Vout2 is 0 [V], and a detection signal with a signal level of non-0 [V] can be output from the detection signal output terminal CT2 when the signal level of the differential signal Vout2 is not 0 [V].

[0132] Through the aforementioned actions, the gradient magnetic field sensor 12A detects a gradient. However, similar to the gradient magnetic field sensor 12 of the embodiment, if the third and fourth induced voltages are not adjusted separately, the gradient magnetic field sensor 12A sometimes detects a gradient even within a uniform magnetic field region. This leads to false detection of a target object even when it is not present, which is undesirable. Therefore, the gradient magnetic field sensor 12A is adjusted using the aforementioned alternating current and then using direct current. As a result, the gradient magnetic field sensor 12A can more reliably improve the detection accuracy of targets using magnetic fields.

[0133] DC current adjustment is the adjustment that makes the magnitude of the current flowing through the first magnetic core CR1 the same as the magnitude of the current flowing through the second magnetic core CR2. In other words, DC current adjustment is the adjustment that makes the magnitude of the first DC excitation current DC1 equal to the magnitude of the second DC excitation current DC2. Such DC current adjustment can be performed by adjusting at least one of the resistance values ​​of the first variable resistor VR21 and the second variable resistor VR22.

[0134] Furthermore, the gradient magnetic field sensor 12A of Embodiment Modification 1 may also be structured without either the first variable resistor VR21 or the second variable resistor VR22. Alternatively, the gradient magnetic field sensor 12A of Embodiment Modification 1 may be structured with a resistive element whose resistance value cannot be changed, replacing either the first variable resistor VR21 or the second variable resistor VR22. This is because DC current adjustment can be performed by adjusting the magnitude of at least one of the first DC excitation current DC1 and the second DC excitation current DC2.

[0135] Furthermore, based on the results of prior experiments, etc., the gradient magnetic field sensor 12A of the modified embodiment can also be configured to have a resistive element with the same resistance value as the first variable resistor VR21 and the second variable resistor VR22 described above, in order to replace either or both of the first variable resistor VR21 and the second variable resistor VR22, provided that the resistive element with the same resistance value as each of the first variable resistor VR21 and the second variable resistor VR22 can be prepared.

[0136] Alternatively, the gradient magnetic field sensor 12A of the embodiment may also be structured without at least one of the first inductor L1 and the second inductor L2. However, as mentioned above, they are capacitors used for DC coupling. Therefore, it is preferable that the gradient magnetic field sensor 12A includes both the first inductor L1 and the second inductor L2.

[0137] As described above, the gradient magnetic field sensor 12A of Embodiment Variation 1, in addition to having the components of the gradient magnetic field sensor 12 of Embodiment Variation 1, also includes: a DC power supply connection terminal CT3, which is connected to the positive power supply terminal of the DC power supply P2; a first variable resistor VR21, which is connected between the DC power supply connection terminal CT3 and the first magnetic core CR1; a first inductor L1, which is connected in series with the first variable resistor VR21 between the DC power supply connection terminal CT3 and the first magnetic core CR1; a second variable resistor VR22, which is connected between the DC power supply connection terminal CT3 and the second magnetic core CR2; and a second inductor L2, which is connected in series with the second variable resistor VR22 between the DC power supply connection terminal CT3 and the second magnetic core CR2. Therefore, the gradient magnetic field sensor 12A can more reliably improve the detection accuracy of objects using magnetic fields.

[0138] Alternatively, the gradient magnetic field sensor 12A can also use a structure that has a DC power supply P2 with its negative power terminal grounded.

[0139] <Modification 2 of the Implementation Method>

[0140] The following is for reference Figure 7 Modification 2 of the embodiment will be described below. Furthermore, in Modification 2 of the embodiment, the same reference numerals are used for structural parts identical to those in the embodiment, and descriptions are omitted. Additionally, for ease of explanation, the gradient magnetic field sensor 12 of Modification 2 of the embodiment will be referred to as gradient magnetic field sensor 12B below. Furthermore, the matters described in Modification 2 of the embodiment can also be applied to Modification 1 of the embodiment. Furthermore, the matters described in Modification 2 of the embodiment can be applied not only to the embodiment but also to other modifications of the embodiments described later.

[0141] The gradient magnetic field sensor 12B has an AC current control unit CC3 instead of an AC current control unit CC1.

[0142] Figure 7 This is a diagram illustrating an example of the circuit structure of the AC current control unit CC3. Additionally, in Figure 7 In order to clearly show the connection method of the AC current control unit CC3 and other components, the AC power supply P1, AC power supply connection terminal CT1, the 0th phase shift circuit PS0, the 1st magnetic core CR1, and the 2nd magnetic core CR2 are shown together with the AC current control unit CC3.

[0143] The AC current control unit CC3 has an input terminal CC31, a first output terminal CC32, and a second output terminal CC33. Additionally, the AC current control unit CC3 includes an inverting circuit RVC, a first switching circuit SWC1, a first phase shifting circuit PS1, a first variable resistor VR11, a first capacitor C1, a second switching circuit SWC2, a second phase shifting circuit PS2, a second variable resistor VR12, and a second capacitor C2. Furthermore, the inverting circuit RVC has an input terminal RVC1 and an output terminal RVC2. The first switching circuit SWC1 has a first input terminal SWC11, a second input terminal SWC12, and an output terminal SWC13. The second switching circuit SWC2 has a first input terminal SWC21, a second input terminal SWC22, and an output terminal SWC23.

[0144] The input terminal CC31 of the AC current control unit CC3 is connected to the output terminal PS02 of the 0th phase shift circuit PS0 via a transmission path. Alternatively, other circuit elements or other devices may be connected between the input terminal CC31 and the output terminal PS02 without impairing the functionality of the gradient magnetic field sensor 12B.

[0145] Furthermore, in the AC current control unit CC3, the input terminal CC31 is connected via a transmission path to the input terminal RVC1 of the inverting circuit RVC, the second input terminal SWC12 of the first switching circuit SWC1, and the second input terminal SWC22 of the second switching circuit SWC2. Alternatively, other circuit elements or devices may be connected between the input terminal CC31 and the input terminal RVC1, without impairing the function of the gradient magnetic field sensor 12B. Similarly, other circuit elements or devices may be connected between the input terminal CC31 and the second input terminal SWC12, without impairing the function of the gradient magnetic field sensor 12B. Finally, other circuit elements or devices may be connected between the input terminal CC31 and the second input terminal SWC22, without impairing the function of the gradient magnetic field sensor 12B.

[0146] Furthermore, the output terminal RVC2 of the inverting circuit RVC is connected via a transmission path to the first input terminal SWC11 of the first switching circuit SWC1 and the first input terminal SWC21 of the second switching circuit SWC2, respectively. Alternatively, other circuit elements or devices may be connected between the output terminal RVC2 and the first input terminal SWC11 without impairing the functionality of the gradient magnetic field sensor 12B. Also, other circuit elements or devices may be connected between the output terminal RVC2 and the first input terminal SWC21 without impairing the functionality of the gradient magnetic field sensor 12B.

[0147] Furthermore, a first phase shift circuit PS1, a first variable resistor VR11, and a first capacitor C1 are connected in series between the output terminal SWC13 of the first switching circuit SWC1 and the first output terminal CC32 of the AC current control unit CC3. Moreover, the first magnetic core CR1 of the first sensor head S1 is connected via a transmission path between the first output terminal CC32 and the ground wire. In this case, the first AC excitation current AC1 is an AC current flowing from the first output terminal CC32 to the first magnetic core CR1. Alternatively, other circuit elements or devices can be connected together with the first magnetic core CR1 between the first output terminal CC32 of the AC current control unit CC3 and the ground wire, without impairing the function of the gradient magnetic field sensor 12B. Furthermore, the first phase shift circuit PS1, the first variable resistor VR11, and the first capacitor C1 can be connected in series in any order between the output terminal SWC13 and the first output terminal CC32.

[0148] Furthermore, a second phase-shifting circuit PS2, a second variable resistor VR12, and a second capacitor C2 are connected in series between the output terminal SWC23 of the second switching circuit SWC2 and the second output terminal CC33 of the AC current control unit CC3. Moreover, the second magnetic core CR2 of the second sensor head S2 is connected via a transmission path between the second output terminal CC33 and the ground wire. In this case, the second AC excitation current AC2 is an AC current flowing from the second output terminal CC33 to the second magnetic core CR2. Alternatively, other circuit elements or devices can be connected together with the second magnetic core CR2 between the second output terminal CC33 of the AC current control unit CC3 and the ground wire, without impairing the function of the gradient magnetic field sensor 12B. Furthermore, the second phase-shifting circuit PS2, the second variable resistor VR12, and the second capacitor C2 can be connected in series in any order between the output terminal SWC23 and the second output terminal CC33.

[0149] Next, the operation of the AC current control unit CC3 will be explained.

[0150] In the AC current control unit CC3 with the circuit structure described above, the AC current input from the input terminal CC31 is branched into two.

[0151] One of the two branched AC currents is input to the inverting circuit RVC as the 11th AC magnetizing current AC11. Thus, the phase of the 11th AC magnetizing current AC11 is reversed by the inverting circuit RVC. Furthermore, the 11th AC magnetizing current AC11 output from the inverting circuit RVC is input to the first input terminal SWC11 of the first switching circuit SWC1 and the first input terminal SWC21 of the second switching circuit SWC2.

[0152] On the other hand, the other of the two AC currents, as the 12th AC excitation current AC12, is input to the second input terminal SWC12 of the first switching circuit SWC1 and the second input terminal SWC22 of the second switching circuit SWC2.

[0153] Here, the first switching circuit SWC1 outputs either the input 11th AC excitation current AC11 or the input 12th AC excitation current AC12 as the first AC excitation current AC1 to the first phase shift circuit PS1. Conversely, the second switching circuit SWC2 outputs either the input 11th AC excitation current AC11 or the input 12th AC excitation current AC12 as the second AC excitation current AC2 to the second phase shift circuit PS2.

[0154] That is, in the gradient magnetic field sensor 12B, the inverting circuit RVC, the first switching circuit SWC1, and the second switching circuit SWC2 can be used to switch whether the first AC excitation current AC1 and the second AC excitation current AC2 are set to currents with opposite phases or currents with the same phase. As a result, the gradient magnetic field sensor 12B, as each of the first phase shift circuit PS1 and the second phase shift circuit PS2, can be a structure with phase shift circuits that mutually lead each other in phase, a structure with phase shift circuits that mutually delay each other in phase, or a structure with both phase shift circuits that delay each other in phase and phase shift circuits that lead each other in phase. In other words, by including the AC current control unit CC3 in the gradient magnetic field sensor 12B, the gradient magnetic field sensor 12B can improve the degree of freedom in circuit design.

[0155] Furthermore, the gradient magnetic field sensor 12B may also be a structure that does not include at least one of the first switching circuit SWC1 and the second switching circuit SWC2.

[0156] As described above, in the gradient magnetic field sensor 12B of the modified embodiment 2, the AC current control unit CC3 may also use a structure that includes an inverting circuit RVC that reverses the phase of at least one of the first AC excitation current AC1 and the second AC excitation current AC2.

[0157] Alternatively, in the gradient magnetic field sensor 12B, the AC current control unit CC3 may also use the following structure: at least one of the following: a first switching circuit SWC1 that switches the AC current flowing to the first magnetic core CR1 as the first AC excitation current AC1 to either an AC current whose phase is reversed by the inverting circuit RVC or an AC current whose phase is not reversed by the inverting circuit; and a second switching circuit SWC2 that switches the AC current flowing to the second magnetic core CR2 as the second AC excitation current AC2 to either an AC current whose phase is reversed by the inverting circuit RVC or an AC current whose phase is not reversed by the inverting circuit RVC.

[0158] Therefore, the gradient magnetic field sensor 12B can improve the freedom of circuit design.

[0159] <Modification 3 of the Implementation>

[0160] The following is for reference Figure 8 Modification 3 of the embodiment will be described below. Furthermore, in Modification 3, the same reference numerals are used for structural parts identical to those in the embodiment, and descriptions are omitted. Additionally, for ease of explanation, the gradient magnetic field sensor 12 of Modification 2 will be referred to as gradient magnetic field sensor 12C below. Furthermore, the matters described in Modification 3 can also be applied to Modification 1 and Modification 2 of the embodiment, respectively. Furthermore, the matters described in Modification 3 can be applied not only to the embodiment but also to any of the other modifications of the embodiments described later.

[0161] The detection circuit DT of the gradient magnetic field sensor 12C also features a high-pass filter HF.

[0162] Figure 8 This diagram illustrates an example of a circuit structure that also includes a detection circuit DT with a high-pass filter (HF).

[0163] exist Figure 8In the example shown, in the detection circuit DT, a high-pass filter HF is connected via the transmission path between the error amplifier EA and resistor R1 and the output terminal DT3. Alternatively, other circuit elements or devices can be connected between the transmission path between the error amplifier EA and resistor R1 and the high-pass filter HF, without impairing the functionality of the detection circuit DT. Similarly, other circuit elements or devices can be connected between the high-pass filter HF and the output terminal DT3, without impairing the functionality of the detection circuit DT.

[0164] The high-pass filter HF removes components below a specified second frequency from the detection signal output from the error amplifier EA, and outputs the resulting signal as a new detection signal to the output terminal DT3. Thus, the gradient magnetic field sensor 12C can remove the aforementioned offset components. As a result, the gradient magnetic field sensor 12C can more reliably improve the detection accuracy of objects using magnetic fields.

[0165] As described above, in the gradient magnetic field sensor 12C, the detection circuit DT can also use a structure that includes a PSD (Phase Sensitive Detector) circuit. Furthermore, the gradient magnetic field sensor 12C can also use a structure that includes a high-pass filter HF that removes components below a predetermined second frequency from the signal output by the PLL circuit. Therefore, the gradient magnetic field sensor 12C can more reliably improve the detection accuracy of objects using magnetic fields.

[0166] <Modification 4 of the Implementation Method>

[0167] The following is for reference Figure 9 Modification 4 of the embodiment will be described below. Furthermore, in Modification 4 of the embodiment, the same reference numerals are used for structural parts that are the same as in the embodiment, and descriptions are omitted. Additionally, for ease of explanation, the gradient magnetic field sensor 12 of Modification 4 of the embodiment will be referred to as gradient magnetic field sensor 12D below. Furthermore, the matters described in Modification 4 of the embodiment can also be applied to Modification 1, Modification 2, and Modification 3 of the embodiment, respectively.

[0168] In Modification 4 of the Embodiment, similarly to Modification 2 of the Embodiment, the DC excitation current flows to the first magnetic core CR1 and the second magnetic core CR2. However, the gradient magnetic field sensor 12D of Modification 4 of the Embodiment differs from the gradient magnetic field sensor 12A of Modification 1 of the Embodiment in that it does not have a DC current control unit CC2.

[0169] Figure 9This is a diagram illustrating an example of the circuit structure of a gradient magnetic field sensor 12D.

[0170] In addition to having an AC power connection terminal CT1, a first sensor head S1, a second sensor head S2, a zero phase shift circuit PS0, an AC current control unit CC1, a detection circuit DT, and a detection signal output terminal CT2, the gradient magnetic field sensor 12D also has a DC power connection terminal CT3, a resistor R2, a third inductor L3, a fourth inductor L4, and a fourth capacitor C4.

[0171] In addition, the gradient magnetic field sensor 12D is connected to both AC power supply P1 and DC power supply P2 via a transmission path. More specifically, the DC power supply connection terminal CT3 of the gradient magnetic field sensor 12D is connected to the positive power supply terminal of the DC power supply P2 via the transmission path. Furthermore, the negative power supply terminal of the DC power supply P2 is grounded via the transmission path. Here, the DC power supply P2 can be any DC power supply. Alternatively, other circuit elements or devices can be connected between the DC power supply connection terminal CT3 and the positive power supply terminal without impairing the functionality of the gradient magnetic field sensor 12D. Similarly, other circuit elements or devices can be connected between the negative power supply terminal and the ground wire without impairing the functionality of the gradient magnetic field sensor 12D.

[0172] Furthermore, the DC power supply connection terminal CT3 is connected to one of the two terminals of resistor R2 via a transmission path. The other of the two terminals of resistor R2 is connected to one of the two terminals of the third inductor L3 via a transmission path. The other of the two terminals of the third inductor L3 is connected via another transmission path to the transmission path connecting the first output terminal CC13 of the AC current control unit CC1 and the first magnetic core CR1. Alternatively, other circuit elements or devices may be connected between the DC power supply connection terminal CT3 and resistor R2 without impairing the function of the gradient magnetic field sensor 12D. Similarly, other circuit elements or devices may be connected between resistor R2 and the third inductor L3 without impairing the function of the gradient magnetic field sensor 12D. Alternatively, other circuit elements or devices can be connected between the third inductor L3 and the transmission path connecting the first output terminal CC13 of the AC current control unit CC1 and the first magnetic core CR1, without impairing the functionality of the gradient magnetic field sensor 12D. Furthermore, the third inductor L3 is an inductor used for DC coupling. Due to the presence of the third inductor L3, the gradient magnetic field sensor 12D can suppress the flow of AC current from the transmission path connecting the first output terminal CC13 of the AC current control unit CC1 and the first magnetic core CR1 to the DC power supply connection terminal CT3.

[0173] Furthermore, between the first output terminal CC13 of the AC current control unit CC1 and ground, the first magnetic core CR1 and the fourth capacitor C4 are connected in series from the first output terminal CC13 side toward the ground side, in the order of the first magnetic core CR1 and the fourth capacitor C4. This fourth capacitor C4 is an AC coupling capacitor. Additionally, between the transmission path connecting the first magnetic core CR1 and the fourth capacitor C4 and the transmission path connecting the second output terminal CC14 of the AC current control unit CC1 and the second magnetic core CR2, a fourth inductor L4 is connected via another transmission path. This fourth inductor L4 is a DC coupling inductor. Furthermore, without impairing the function of the gradient magnetic field sensor 12D, it is also possible to connect other circuit elements or other devices between the first magnetic core CR1 and the fourth capacitor C4. Alternatively, without impairing the function of the gradient magnetic field sensor 12D, it is also possible to connect other circuit elements or other devices between the fourth capacitor C4 and the ground wire. Alternatively, other circuit elements or devices can be connected between the transmission path connecting the first magnetic core CR1 and the fourth capacitor C4 and the fourth inductor L4, without impairing the function of the gradient magnetic field sensor 12D. Alternatively, other circuit elements or devices can be connected between the fourth inductor L4 and the transmission path connecting the second output terminal CC14 and the second magnetic core CR2, without impairing the function of the gradient magnetic field sensor 12D.

[0174] Next, the operation of the gradient magnetic field sensor 12D will be explained.

[0175] In the gradient magnetic field sensor 12D with the circuit structure described above, a DC power supply P2 inputs a DC current to the DC power supply connection terminal CT3. This DC current input to the DC power supply connection terminal CT3 is fed into the first magnetic core CR1 as a DC excitation current DC3 via resistor R2 and the third inductor L3. Therefore, in the first magnetic core CR1, the DC excitation current DC3 flows together with the first AC excitation current AC1. Furthermore, the DC excitation current DC3 input to the first magnetic core CR1 is also fed into the second magnetic core CR2 via the fourth inductor L4. Therefore, in the second magnetic core CR2, the DC excitation current DC3 flows together with the second AC excitation current AC2. Additionally, through the fourth capacitor C4 and the fourth inductor L4, the first AC excitation current AC1 hardly flows from the first magnetic core CR1 to the second magnetic core CR2. Similarly, through the fourth inductor L4, the second AC excitation current AC2 hardly flows from the second magnetic core CR2 to the first magnetic core CR1.

[0176] Thus, in the gradient magnetic field sensor 12D, the same magnitude of DC current, i.e., DC excitation current DC3, can flow through the first magnetic core CR1 and the second magnetic core CR2 respectively. Therefore, the gradient magnetic field sensor 12D, using a simpler circuit structure than the modified embodiment 2, can more reliably improve the detection accuracy of the object being detected using the magnetic field.

[0177] Furthermore, the first magnetic core CR1 described above can also be a structure comprising two or more magnetic bodies connected in series. In this case, the first magnetic core CR1 can also be a structure in which some or all of these two or more magnetic bodies are connected in series by a non-magnetic conductor. Here, Figure 10 This is a diagram illustrating an example of the structure of the first magnetic core CR1, which contains multiple magnetic elements. Figure 10 In the example shown, the first magnetic core CR1 comprises two magnetic bodies. More specifically, in this example, the first magnetic core CR1 has a magnetic body CR1A, a magnetic body CR1B, a non-magnetic conductor CR1C, a terminal CR1D, and a terminal CR1E. Furthermore, magnetic bodies CR1A and CR1B are connected via conductor CR1C. Additionally, a terminal CR1D is provided at the end of magnetic body CR1A opposite to the end connected to conductor CR1C. Terminal CR1D is, for example, located at... Figure 2 The terminal is connected to the first output terminal CC13 of the AC current control unit CC1. Additionally, a terminal CR1E is provided on the opposite side of the end of the magnetic body CR1B that is connected to the conductor CR1C. For example, in... Figure 2 In the middle, terminal CR1E is the grounding terminal.

[0178] Furthermore, the second magnetic core CR2 described above can also be a structure comprising two or more magnetic bodies connected in series. In this case, the second magnetic core CR2 can also be a structure in which some or all of these two or more magnetic bodies are connected in series by a non-magnetic conductor. Moreover, regarding the structure of the second magnetic core CR2 comprising multiple magnetic bodies, since it is the same structure as the structure of the first magnetic core CR1 comprising multiple magnetic bodies, a description based on the illustrations is omitted.

[0179] As described above, the gradient magnetic field sensor of the embodiment (in the examples described above, gradient magnetic field sensor 12, gradient magnetic field sensor 12A, gradient magnetic field sensor 12B, gradient magnetic field sensor 12C, and gradient magnetic field sensor 12D) includes: an AC power connection terminal (in the examples described above, AC power terminal P11) connected to a first power terminal (in the examples described above, AC power terminal P11); a first magnetic core (in the examples described above, first magnetic core CR1) connected between the AC power connection terminal and the ground wire; a second magnetic core (in the examples described above, second magnetic core CR2) connected in parallel with the first magnetic core between the AC power connection terminal and the ground wire; an AC power connection terminal; and a connection between the first magnetic core and the second magnetic core. The sensor comprises at least one of the following: an AC current control unit (CC1 and CC3 in the above-described example) that controls the AC current (first AC excitation current AC1 in the example described above) flowing in at least one of the first and second magnetic cores; a first detection coil (CL1 in the above-described example); a second detection coil (CL2 in the above-described example) wound around the second magnetic core and differentially connected to the first detection coil; and a detection circuit (DT in the above-described example) that detects the voltage corresponding to the difference between a first voltage (first induced voltage and third induced voltage in the above-described example) output from the first detection coil and a second voltage (second induced voltage and fourth induced voltage in the above-described example) output from the second detection coil. Thus, the gradient magnetic field sensor can improve the detection accuracy of objects using magnetic fields.

[0180] Alternatively, the gradient magnetic field sensor can also use an AC power supply structure that grounds the second power terminal of the AC power supply.

[0181] Alternatively, in the gradient magnetic field sensor, the AC current control unit may also use a phase shifting unit (at least one of the first phase shifting circuit PS1 and the second phase shifting circuit PS2 in the above-described example) that shifts at least one of the first AC current (first AC excitation current AC1 in the example described above) flowing from the AC power connection terminal to the first magnetic core and the second AC current (second AC excitation current AC2 in the example described above) flowing from the AC power connection terminal to the second magnetic core.

[0182] Alternatively, in the gradient magnetic field sensor, the AC current control unit may also use a structure that includes an amplitude adjustment unit (in the example described above, at least one of the first variable resistor VR11 and the second variable resistor VR12) that adjusts the amplitude of at least one of the first AC current flowing from the AC power connection terminal to the first magnetic core and the second AC current flowing from the AC power connection terminal to the second magnetic core.

[0183] Alternatively, in the gradient magnetic field sensor, the AC current control unit may also use a structure that includes at least one of a first amplifier circuit and an 11th variable resistor (in the example described above, the first variable resistor VR11) connected between the AC power connection terminal and the first magnetic core, and at least one of a second amplifier circuit and a 12th variable resistor (in the example described above, the second variable resistor VR12) connected between the AC power connection terminal and the second magnetic core as the amplitude adjustment unit.

[0184] Alternatively, in the gradient magnetic field sensor, the AC current control unit may also use a structure that includes an inverting circuit (in the example described above, an inverting circuit RVC) that reverses the phase of at least one of the first AC current flowing from the AC power connection terminal to the first magnetic core and the second AC current flowing from the AC power connection terminal to the second magnetic core.

[0185] Alternatively, in the gradient magnetic field sensor, the AC current control unit may also use a structure including at least one of the following circuits: a first switching circuit (in the example described above, the first switching circuit SWC1), which switches the AC current flowing through the first magnetic core as the first AC current to either an AC current whose phase is reversed by an inverting circuit (in the example described above, the 11th AC excitation current AC11) or an AC current whose phase is not reversed by an inverting circuit (in the example described above, the 12th AC excitation current AC12); and a second switching circuit (in the example described above, the second switching circuit SWC2), which switches the AC current flowing through the second magnetic core as the second AC current to either an AC current whose phase is reversed by an inverting circuit or an AC current whose phase is not reversed by an inverting circuit.

[0186] Alternatively, in the gradient magnetic field sensor, the AC current control unit may also use a structure that includes a first capacitor (first capacitor C1 in the example described above) for AC coupling connected between the AC power connection terminal and the first magnetic core, and a second capacitor (second capacitor C2 in the example described above) for AC coupling connected between the AC power connection terminal and the second magnetic core.

[0187] Alternatively, the gradient magnetic field sensor may also use the following structure: It further includes: a DC power supply connection terminal (CT3 in the example above) connected to the positive power supply terminal of the DC power supply connection terminal (DC power supply P2 in the example above); a 21st resistor (VR21 in the example above) connected between the DC power supply connection terminal and the first magnetic core; a first inductor (L1 in the example above) connected in series with the 21st resistor between the DC power supply connection terminal and the first magnetic core; a 22nd resistor (VR22 in the example above) connected between the DC power supply connection terminal and the second magnetic core; and a second inductor (L2 in the example above) connected in series with the 22nd resistor between the DC power supply connection terminal and the second magnetic core.

[0188] Alternatively, in a gradient magnetic field sensor, at least one of the 21st and 22nd resistors can be a variable resistor.

[0189] Alternatively, gradient magnetic field sensors can also use a DC power supply structure with a grounded negative power terminal, as is common in DC power supplies.

[0190] Alternatively, in gradient magnetic field sensors, the detection circuit can also use a structure that includes a PSD (Phase Sensitive Detector) circuit.

[0191] Alternatively, in a gradient magnetic field sensor, the detection circuit may also use a structure that includes a low-pass filter (in the example described above, a low-pass filter LF) that removes components of a predetermined first frequency or higher from the signal output by the PSD circuit.

[0192] Alternatively, in a gradient magnetic field sensor, the detection circuit may also use a structure that includes a high-pass filter (in the example described above, a high-pass filter HF) that removes components below a predetermined second frequency from the signal output by the PSD circuit.

[0193] Furthermore, the magnetic object detection device of the embodiment (magnetic object detection device 1 in the example described above) includes the gradient magnetic field sensor described above. Therefore, the magnetic object detection device can improve the detection accuracy of objects that utilize magnetic fields.

[0194] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the specific structure is not limited to these embodiments. As long as the spirit of the present invention is not departed, changes, substitutions, deletions, etc., can be made.

[0195] Explanation of reference numerals in the attached figures

[0196] 1…Magnetic object detection device; 11…Magnetic device; 12, 12A, 12B, 12C, 12D…Gradient magnetic field sensor; 20…Information processing device; AC1…First AC excitation current; AC2…Second AC excitation current; AC11…Eleventh AC excitation current; AC12…Twelfth AC excitation current; C1…First capacitor; C2…Second capacitor; C3…Third capacitor; C4…Fourth capacitor; CC1, CC3…AC current control unit; CC2…DC current control unit; CL1…First detection coil; CL2…Second detection coil; CR1…First magnetic core; CR2…Second magnetic core; CS…Frame; CT1…AC power connection terminal; CT2…Detection signal output terminal; CT3…DC power connection terminal; DT…Detection circuit; DC1…First DC excitation current; DC2… …Second DC excitation current; DC3…DC excitation current; EA…error amplifier; HF…high-pass filter; L1…first inductor; L2…second inductor; L3…third inductor; L4…fourth inductor; LF…low-pass filter; P1…AC power supply; P2…DC power supply; PD…phase detector circuit; PS0…0th phase shift circuit; PS1…1st phase shift circuit; PS2…2nd phase shift circuit; R1, R2…resistors; RL1…1st roller; RL2…2nd roller; RVC…inverting circuit; S1…1st sensor head; S2…2nd sensor head; ST…sheet component; SWC1…1st switching circuit; SWC2…2nd switching circuit; Vout…differential signal; Vout2…differential signal; VR11, VR21…1st variable resistor; VR12, VR22…2nd variable resistor

Claims

1. A gradient magnetic field sensor, wherein: have: AC power connection terminal, which is connected to the first power terminal of the AC power supply; The first magnetic core is connected between the AC power connection terminal and the ground wire; The second magnetic core is connected in parallel with the first magnetic core between the AC power connection terminal and the ground wire; An AC current control unit is connected between the AC power supply connection terminal and at least one of the first magnetic core and the second magnetic core, and controls the AC current flowing through at least one of the first magnetic core and the second magnetic core; The first detection coil is wound around the first magnetic core; The second detection coil is wound around the second magnetic core and is differentially connected to the first detection coil; and The detection circuit detects the voltage corresponding to the difference between a first voltage output from the first detection coil and a second voltage output from the second detection coil. The AC current control unit includes a phase shifting unit that shifts at least one of the first AC current flowing from the AC power connection terminal to the first magnetic core and the second AC current flowing from the AC power connection terminal to the second magnetic core.

2. The gradient magnetic field sensor according to claim 1, wherein: It includes: the AC power supply, wherein the second power terminal of the AC power supply is grounded to the ground wire.

3. The gradient magnetic field sensor according to claim 1, wherein: The alternating current control unit includes an amplitude adjustment unit that adjusts the amplitude of at least one of a first alternating current flowing from the alternating power connection terminal to the first magnetic core and a second alternating current flowing from the alternating power connection terminal to the second magnetic core.

4. The gradient magnetic field sensor according to claim 3, wherein: The AC current control unit includes at least one of a first amplifier circuit and an eleventh variable resistor connected between the AC power connection terminal and the first magnetic core, and at least one of a second amplifier circuit and a twelfth variable resistor connected between the AC power connection terminal and the second magnetic core, serving as the amplitude adjustment unit.

5. A gradient magnetic field sensor, wherein: have: AC power connection terminal, which is connected to the first power terminal of the AC power supply; The first magnetic core is connected between the AC power connection terminal and the ground wire; The second magnetic core is connected in parallel with the first magnetic core between the AC power connection terminal and the ground wire; An AC current control unit is connected between the AC power supply connection terminal and at least one of the first magnetic core and the second magnetic core, and controls the AC current flowing through at least one of the first magnetic core and the second magnetic core; The first detection coil is wound around the first magnetic core; The second detection coil is wound around the second magnetic core and is differentially connected to the first detection coil; and The detection circuit detects the voltage corresponding to the difference between a first voltage output from the first detection coil and a second voltage output from the second detection coil. The AC current control unit includes an inverting circuit that reverses the phase of at least one of a first AC current flowing from the AC power connection terminal to the first magnetic core and a second AC current flowing from the AC power connection terminal to the second magnetic core.

6. The gradient magnetic field sensor according to claim 5, wherein: The AC current control unit includes either a first switching circuit or a second switching circuit. The first switching circuit switches the AC current flowing through the first magnetic core as the first AC current to either an AC current whose phase is reversed by the inverting circuit or an AC current whose phase is not reversed by the inverting circuit. The second switching circuit switches the AC current flowing through the second magnetic core as the second AC current to either an AC current whose phase is reversed by the inverting circuit or an AC current whose phase is not reversed by the inverting circuit.

7. The gradient magnetic field sensor according to any one of claims 1 to 6, wherein: The AC current control unit includes: a first capacitor for AC coupling, which is connected between the AC power connection terminal and the first magnetic core; and a second capacitor for AC coupling, which is connected between the AC power connection terminal and the second magnetic core.

8. A gradient magnetic field sensor, wherein: have: AC power connection terminal, which is connected to the first power terminal of the AC power supply; The first magnetic core is connected between the AC power connection terminal and the ground wire; The second magnetic core is connected in parallel with the first magnetic core between the AC power connection terminal and the ground wire; An AC current control unit is connected between the AC power supply connection terminal and at least one of the first magnetic core and the second magnetic core, and controls the AC current flowing through at least one of the first magnetic core and the second magnetic core; The first detection coil is wound around the first magnetic core; The second detection coil is wound around the second magnetic core and is differentially connected to the first detection coil; A detection circuit that detects the voltage corresponding to the difference between a first voltage output from the first detection coil and a second voltage output from the second detection coil; DC power supply connection terminal, which is connected to the positive power supply terminal of the DC power supply; The 21st resistor is connected between the DC power supply terminal and the 1st magnetic core; The first inductor is connected in series with the second 21 resistor between the DC power supply connection terminal and the first magnetic core; The 22nd resistor is connected between the DC power supply terminal and the 2nd magnetic core; and The second inductor is connected in series with the second resistor between the DC power supply connection terminal and the second magnetic core.

9. The gradient magnetic field sensor according to claim 8, wherein: At least one of the 21st resistor and the 22nd resistor is a variable resistor.

10. The gradient magnetic field sensor according to claim 8, wherein: The gradient magnetic field sensor includes: a DC power supply, wherein the negative power terminal of the DC power supply is grounded to a ground wire.

11. The gradient magnetic field sensor according to claim 9, wherein: The gradient magnetic field sensor includes: a DC power supply, wherein the negative power terminal of the DC power supply is grounded to a ground wire.

12. The gradient magnetic field sensor according to any one of claims 1 to 11, wherein: The detection circuit includes a PSD circuit, where PSD stands for Phase Sensitive Detector.

13. The gradient magnetic field sensor according to claim 12, wherein: The detection circuit includes a low-pass filter that removes components of a predetermined first frequency or higher from the signal output by the PSD circuit.

14. A gradient magnetic field sensor, wherein: have: AC power connection terminal, which is connected to the first power terminal of the AC power supply; The first magnetic core is connected between the AC power connection terminal and the ground wire; The second magnetic core is connected in parallel with the first magnetic core between the AC power connection terminal and the ground wire; An AC current control unit is connected between the AC power supply connection terminal and at least one of the first magnetic core and the second magnetic core, and controls the AC current flowing through at least one of the first magnetic core and the second magnetic core; The first detection coil is wound around the first magnetic core; The second detection coil is wound around the second magnetic core and is differentially connected to the first detection coil; and The detection circuit detects the voltage corresponding to the difference between a first voltage output from the first detection coil and a second voltage output from the second detection coil. The detection circuit includes a PSD circuit, whereby the PSD is a Phase Sensitive Detector. The detection circuit includes a high-pass filter that removes components below a predetermined second frequency from the signal output by the PSD circuit.

15. A magnetic material detection device, wherein: The gradient magnetic field sensor as described in any one of claims 1 to 14.

Images