JP7365915B2 - measuring device - Google Patents

Description

The present invention relates to a measuring device.

Conventionally, sensors that detect weak magnetic fields of about 10 pT have been known, and have been used in magnetocardiographs and the like that measure magnetocardial signals caused by electrical polarization of organs such as the heart (for example, Patent Document 1 (See ~4). It has also been known that in a current sensor using a magnetoresistive element, a feedback coil is used to cancel the influence of an environmental magnetic field (for example, see Patent Document 5).
[Prior art documents]
[Patent document]
[Patent Document 1] JP-A-2000-217798 [Patent Document 2] JP-A-2012-152515 [Patent Document 3] US Pat. No. 5,642,045 [Patent Document 4] JP-A-2000-284032 [Patent Document 5] US Patent Application Publication No. 2015/0253412

For example, a SQUID sensor that uses the Josephson effect can detect weak magnetic fields, but it requires expensive liquid helium and a large magnetically shielded room, making it difficult to install equipment equipped with the sensor. It wasn't easy. Further, current sensors using magnetoresistive elements are small and have high magnetic sensitivity, but have poor linearity in input/output characteristics. Furthermore, due to sensitivity errors and variations in sensor characteristics, it has been difficult to accurately detect weak magnetic fields using such current sensors.

In order to solve the above problems, a first aspect of the present invention provides a measuring device. The measuring device may include a magnetic sensor array configured by three-dimensionally arranging a plurality of magnetic sensor cells each including a magnetic sensor, and capable of detecting input magnetic fields in three axial directions. The measurement device may include a measurement data acquisition unit that acquires a plurality of measurement values based on the input magnetic field detected by the magnetic sensor array. The measuring device may include a magnetic field calculation unit that calculates an input magnetic field based on a plurality of measured values. The measuring device may include an error calculation unit that calculates a detection error of the magnetic field based on a plurality of measurement values and a calculation result of the input magnetic field. The measuring device may include a measurement data selection section that selects a plurality of measurement values to be used by the magnetic field calculation section to calculate the input magnetic field from among the plurality of measurement values based on the detection error.

The error calculation unit may calculate a detection error for each of the plurality of measurement values, and the measurement data selection unit may select the plurality of measurement values by excluding measurement values in which the detection error exceeds a predetermined range. .

The magnetic field calculation unit may recalculate the input magnetic field after excluding measurement values in which the detection error exceeds a predetermined range.

The magnetic field calculation section recalculates the input magnetic field at the location where the plurality of measurement values are measured based on the plurality of measurement values selected by the measurement data selection section, and the error calculation section recalculates the input magnetic field at the location where the plurality of measurement values are measured. The detection error may be calculated based on the detection result of the input magnetic field at the measured location.

The magnetic field calculation section calculates the input magnetic field at the location where the excluded measurement value was measured based on the coefficient related to the calculation result of the input magnetic field calculated from the plurality of measurement values selected by the measurement data selection section. good.

Each of the plurality of magnetic sensor cells includes a magnetic field generation section that provides the magnetic sensor with a feedback magnetic field that reduces the input magnetic field detected by the magnetic sensor, and an output signal that corresponds to the current that the magnetic field generation section flows to generate the feedback magnetic field. The output unit may further include an output unit.

In a second aspect of the invention, a measuring device is provided. The measuring device may include a magnetic sensor array that is configured by arranging a plurality of magnetic sensor cells in three dimensions and can detect input magnetic fields in three axial directions. The measurement device may include a measurement data acquisition unit that acquires a plurality of measurement values based on the input magnetic field detected by the magnetic sensor array. The measuring device may include a magnetic field calculation unit that calculates an input magnetic field based on a plurality of measured values. The measuring device may include an error calculation unit that calculates a detection error of the magnetic field based on a plurality of measurement values and a calculation result of the input magnetic field. The measuring device may include a determining unit that determines whether to reset at least one of the plurality of magnetic sensor cells based on the detection error. Each of the plurality of magnetic sensor cells includes a magnetic sensor, a magnetic field generating section that provides the magnetic sensor with a feedback magnetic field that reduces an input magnetic field detected by the magnetic sensor, and a magnetic field generating section that applies a feedback magnetic field to the magnetic sensor that reduces an input magnetic field detected by the magnetic sensor, and a magnetic field generating section that responds to the current that the magnetic field generating section sends to generate the feedback magnetic field. The magnetic sensor may include an output section that outputs an output signal, and a magnetic reset section that applies a reset magnetic field to the magnetic sensor to magnetically saturate the magnetic sensor when resetting the magnetic sensor cell.

The error calculation unit calculates a detection error for each of the plurality of measured values, and the determination unit determines to reset a magnetic sensor cell including a magnetic sensor used to obtain a measurement value in which the detection error exceeds a predetermined range. You may do so.

The magnetic field calculation unit may recalculate the input magnetic field after the magnetic sensor used to obtain the measurement value whose detection error exceeds a predetermined range is magnetically reset.

The magnetic reset section includes a switching section that switches whether or not to supply a feedback current that generates a feedback magnetic field to the magnetic field generation section, and in a state where the feedback current is not supplied to the magnetic field generation section, the reset current is supplied to the magnetic field generation section. The reset magnetic field may be supplied to the magnetic field generator to generate a reset magnetic field.

The magnetic field calculation unit may calculate the input magnetic field so that the square of the detection error is minimized.

The magnetic field calculation unit converts the spatial distribution of the input magnetic field indicated by the plurality of measured values into a signal whose components are signals output by each magnetic sensor when the magnetic sensor array detects a magnetic field having a spatial distribution of an orthonormal function. The signal may be separated using the vector as a basis vector, and the error calculation section may calculate the detection error based on the result of signal separation by the magnetic field calculation section.

The image forming apparatus may further include a basis vector updating section that updates the basis vectors based on the detection error.

The magnetic sensor may include a magnetoresistive element.

Each of the magnetic sensors may further include two magnetic convergence plates arranged at both ends of the magnetoresistive element, and the magnetoresistive element may be disposed at a position sandwiched between the two magnetic convergence plates.

A coil for generating a feedback magnetic field may be wound around the magnetoresistive element and the two magnetic convergence plates.

The device further includes a plurality of AD converters that convert the outputs of the plurality of magnetic sensor cells from analog to digital and output a plurality of measured values, and the plurality of AD converters may perform AD conversion in accordance with a common sampling clock. .

The cardiac magnetism generated by the electrical activity of the animal's heart may be the object of measurement, and the cardiac magnetism may be measured based on the calculation result of the magnetic field calculation unit.

Note that the above summary of the invention does not list all the necessary features of the invention. Furthermore, subcombinations of these features may also constitute inventions.

1 shows the configuration of a measuring device 10 according to this embodiment. 1 shows a configuration of a magnetic sensor unit 110 according to this embodiment. The configuration and arrangement of magnetic sensor cells 220 in the magnetic sensor array 210 according to the present embodiment are shown. An example of input/output characteristics of a magnetic sensor having a magnetoresistive element according to the present embodiment is shown. A configuration example of a sensor section 300 according to the present embodiment is shown. An example of input/output characteristics of the sensor section 300 according to the present embodiment is shown. A configuration example of a magnetic sensor 520 according to this embodiment is shown. The magnetic flux distribution when a feedback magnetic field is generated in the magnetic sensor 520 according to this embodiment is shown. The configuration of a magnetic sensor array 210, a sensor data collection section 230, and a sensor data processing section 900 according to this embodiment is shown. An example of a flow is shown in which the measuring device 10 according to the present embodiment excludes measured values from defective sensors as a preprocess for detecting a magnetic field to be measured. The configuration of a sensor unit 300 according to a modification of the present embodiment is shown. An example of the flow of magnetic reset in the reset phase by the sensor unit 300 according to this modification is shown. This shows magnetization curves of common magnetic materials. The characteristics of the voltage Vopen with respect to the input magnetic field Bin to the magnetic sensor 520 in the sensor unit 300 according to the present modification are shown. The configuration of a magnetic sensor array 210, a sensor data collection unit 230, and a sensor data processing unit 900 is shown in a case where each of a plurality of magnetic sensor cells 220 has a sensor unit 300 according to this modification. An example of a flow is shown in which a defective sensor is reset as pre-processing for the measuring device 10, each of which has a sensor section 300 according to the present modification, to detect a magnetic field to be measured. 22 illustrates an example computer 2200 in which aspects of the invention may be implemented, in whole or in part.

Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the invention according to the claims. Furthermore, not all combinations of features described in the embodiments are essential to the solution of the invention.

FIG. 1 shows the configuration of a measuring device 10 according to this embodiment. The measuring device 10 measures a magnetic field using a magnetoresistive element. The measuring device 10 is an example of a magnetocardial measuring device, and measures a magnetic field (referred to as "magnetocardial") generated by the electrical activity of a human heart. Alternatively, the measuring device 10 may be used to measure the magnetocardial field of a living body other than a human, or may be used to measure a biomagnetic field other than the magnetocardial field, such as a brain magnetic field. The measuring device 10 may also be used for magnetic flaw detection to detect surface and subsurface flaws of steel materials and welded parts.

The measuring device 10 includes a main body section 100 and an information processing section 150. The main body section 100 is a component for sensing the subject's magnetocardial field, and includes a magnetic sensor unit 110, a head 120, a drive section 125, a base section 130, and a pole section 140.

The magnetic sensor unit 110 is placed at a position facing the heart in the chest of the subject during magnetocardial measurement, and senses the subject's magnetism. The head 120 supports the magnetic sensor unit 110 and makes the magnetic sensor unit 110 face the subject. The drive unit 125 is provided between the magnetic sensor unit 110 and the head 120, and changes the orientation of the magnetic sensor unit 110 with respect to the head 120 when performing calibration. The drive unit 125 according to the present embodiment includes a first actuator that can rotate the magnetic sensor unit 110 360 degrees around the Z-axis in the figure, and an axis perpendicular to the Z-axis (in the state in the figure, the X-axis ), and the azimuth and zenith angle of the magnetic sensor unit 110 are changed using these actuators. As shown as a drive unit 125 in the figure, the drive unit 125 has a Y-shape when viewed from the Y-axis direction in the figure, and the second actuator moves the magnetic sensor unit 110 360 degrees around the X-axis in the figure. It can be rotated.

The base portion 130 is a base that supports other components, and in this embodiment serves as a platform on which a subject stands during magnetocardial measurement. The pole section 140 supports the head 120 at the level of the subject's chest. The pole section 140 may be expandable and retractable in the vertical direction to adjust the height of the magnetic sensor unit 110 to the height of the subject's chest.

The information processing section 150 is a component that processes measurement data from the main body section 100 and outputs it by displaying, printing, or the like. The information processing unit 150 may be a computer such as a PC (personal computer), a tablet computer, a smartphone, a workstation, a server computer, or a general-purpose computer, or may be a computer system in which a plurality of computers are connected. Alternatively, the information processing unit 150 may be a dedicated computer designed for information processing of magnetocardiometry, or may be dedicated hardware realized by a dedicated circuit.

FIG. 2 shows the configuration of the magnetic sensor unit 110 according to this embodiment. The magnetic sensor unit 110 includes a magnetic sensor array 210 and a sensor data collection section 230. The magnetic sensor array 210 is configured by arranging a plurality of magnetic sensor cells 220 in three dimensions, and is capable of detecting input magnetic fields in three axial directions. In this figure, the magnetic sensor array 210 includes a plurality of magnetic sensor cells 220 in each of the X direction, Y direction, and Z direction (for example, 8 in the X direction, 8 in the Y direction, and 2 in the Z direction, 128 in total). magnetic sensor cells 220) are arranged in a plane.

The sensor data collection unit 230 is electrically connected to the plurality of magnetic sensor cells 220 included in the magnetic sensor array 210 (not shown), collects sensor data (detection signals) from the plurality of magnetic sensor cells 220, and collects information. It is supplied to the processing section 150.

FIG. 3 shows the configuration and arrangement of the magnetic sensor cells 220 in the magnetic sensor array 210 according to this embodiment. Each of the plurality of magnetic sensor cells 220 has at least one sensor section 300 each having a magnetoresistive element. In this figure, an example is shown in which each of the plurality of magnetic sensor cells 220 has three sensor sections 300x to 300z (collectively referred to as "sensor sections 300") and can detect input magnetic fields in three axial directions. Shown as However, each of the plurality of magnetic sensor cells 220 is not limited to having the three sensor sections 300x to 300z, and as long as at least a portion of the magnetic sensor array 210 can detect input magnetic fields in three axial directions. good. The sensor unit 300x is arranged along the X-axis direction and can detect a magnetic field in the X-axis direction. Further, the sensor unit 300y is arranged along the Y-axis direction and can detect a magnetic field in the Y-axis direction. Further, the sensor unit 300z is arranged along the Z-axis direction and can detect a magnetic field in the Z-axis direction. As shown in the enlarged view indicated by the dashed line in this figure, in this embodiment, each sensor section 300 has magnetic convergence plates arranged at both ends of the magnetoresistive element. Therefore, each sensor section 300 samples the spatial distribution of the magnetic field using magnetoresistive elements placed in narrow positions sandwiched between magnetic convergence plates, thereby clearly identifying sampling points in space in each axial direction. can do. Details of the configuration of each sensor section 300 will be described later.

In this figure, the three axial directions of the magnetic fields detected by the sensor sections 300x, 300y, and 300z are the same as the three-dimensional direction in which the magnetic sensor cells 220 are arranged. This makes it easy to understand each component of the distribution of the measured magnetic field. Furthermore, the three sensor sections 300x, 300y, and 300z are provided within each magnetic sensor cell 220 so that they do not overlap with each other when viewed from each of the three-dimensional directions in which the magnetic sensor cells 220 are arranged, and are provided between the three sensor sections 300. It is preferable that one end is provided on the gap side, and the other end extends in each of the three axial directions so as to be away from the gap. However, the three axial directions of the magnetic field to be detected and the three-dimensional direction in which the magnetic sensor cells 220 are arranged may be different. For example, instead of the X-axis, Y-axis, and Z-axis as the three axial directions of the magnetic field to be detected, the r-axis, θ-axis, and φ-axis of a polar coordinate system may be used. Moreover, as the three-dimensional direction in which the magnetic sensor cells 220 are arranged, the r-axis, theta-axis, and the phi-axis of a polar coordinate system may be used instead of the x-axis, y-axis, and z-axis. When the three-axis directions of the magnetic field to be detected are different from the three-dimensional direction in which the magnetic sensor cells 220 are arranged, there are no restrictions on the arrangement of the sensor section 300 within the magnetic sensor cell 220 or the arrangement direction of the magnetic sensor cells 220, and the magnetic field is The degree of freedom in designing the sensor array 210 can be increased.

FIG. 4 shows an example of input/output characteristics of a magnetic sensor having a magnetoresistive element according to this embodiment. In this figure, the horizontal axis indicates the magnitude B of the input magnetic field input to the magnetic sensor, and the vertical axis indicates the magnitude V_xMR0 of the detection signal of the magnetic sensor. The magnetic sensor has, for example, a giant magneto-resistance (GMR) effect element or a tunnel magneto-resistance (TMR) effect element, and controls the magnitude of a magnetic field in a predetermined uniaxial direction. To detect.

Such a magnetic sensor has high magnetic sensitivity, which is the slope of the detection signal V_xMR0 with respect to the input magnetic field B, and can detect a minute magnetic field of about 10 pT. On the other hand, in the magnetic sensor, for example, the detection signal V_xMR0 is saturated when the absolute value of the input magnetic field B is about 1 μT, and the range in which the linearity of the input/output characteristics is good is narrow. Therefore, by adding a closed loop that generates a feedback magnetic field to such a magnetic sensor, the linearity of the magnetic sensor can be improved. Such a magnetic sensor will be explained next.

FIG. 5 shows a configuration example of the sensor section 300 according to this embodiment. The sensor section 300 is provided inside each of the plurality of magnetic sensor cells 220 and includes a magnetic sensor 520, a magnetic field generation section 530, and an output section 540. Note that a part of the sensor section 300, for example, the first amplifier circuit 532 and the output section 540, may be provided on the sensor data collection section 230 side instead of on the magnetic sensor cell 220 side.

The magnetic sensor 520 includes a magnetoresistive element such as a GMR element or a TMR element, similar to the magnetic sensor described with reference to FIG. Further, each of the magnetic sensors 520 includes a magnetoresistive element and two magnetic convergence plates arranged at both ends of the magnetoresistive element, and the magnetoresistive element is located at a position sandwiched between the two magnetic convergence plates. Placed. When the positive direction of the magnetic sensing axis is the +X direction, the magnetoresistive element of the magnetic sensor 520 increases its resistance when a magnetic field in the +X direction is input, and decreases when a magnetic field in the -X direction is input. It may be formed to decrease. That is, by observing changes in the resistance value of the magnetoresistive element included in the magnetic sensor 520, the magnitude of the magnetic field B input to the magnetic sensor 520 can be detected. For example, if the magnetic sensitivity of the magnetic sensor 520 is S, the detection result for the input magnetic field B of the magnetic sensor 520 can be calculated as S×B. Note that the magnetic sensor 520 is connected to, for example, a power source, and outputs a voltage drop corresponding to a change in resistance value as a detection result of an input magnetic field. Details of the configuration of the magnetic sensor 520 will be described later.

The magnetic field generation section 530 generates a feedback magnetic field that reduces the input magnetic field detected by the magnetic sensor 520 with a magnitude corresponding to the output signal output by the output section 540, and provides the feedback magnetic field to the magnetic sensor 520. For example, the magnetic field generation unit 530 operates to generate a feedback magnetic field B_FB having a direction opposite to the magnetic field B input to the magnetic sensor 520 and having substantially the same absolute value as the input magnetic field, thereby canceling the input magnetic field. Magnetic field generation section 530 includes an amplifier circuit 532 and a coil 534.

The amplifier circuit 532 outputs a current according to the detection result of the input magnetic field of the magnetic sensor 520 as a feedback current I_FB. When the magnetoresistive element included in the magnetic sensor 520 is configured by a bridge circuit including at least one magnetoresistive element, the outputs of the bridge circuit are connected to the input terminal pair of the amplifier circuit 532, respectively. Then, the amplifier circuit 532 outputs a current according to the output of the bridge circuit as a feedback current I_FB. The amplifier circuit 532 includes, for example, a transconductance amplifier, and outputs a feedback current I_FB according to the output voltage of the magnetic sensor 520. For example, if the voltage/current conversion coefficient of the amplifier circuit 532 is G, the feedback current I_FB can be calculated as G×S×B.

Coil 534 generates a feedback magnetic field B_FB according to feedback current I_FB. The coil 534 is wound along the axial direction of the magnetic field to be detected by the magnetic sensor 520 so as to surround the magnetoresistive element of the magnetic sensor 520 and the two magnetic convergence plates arranged at both ends of the magnetoresistive element. It's dark. Coil 534 preferably generates a uniform feedback magnetic field B_FB across magnetic sensor 520. For example, if the coil coefficient of the coil 534 is β, the feedback magnetic field B_FB can be calculated as β×I_FB. Here, since the feedback magnetic field B_FB is generated in a direction that cancels the input magnetic field B, the magnetic field input to the magnetic sensor 520 is reduced to BB_FB. Therefore, the feedback current I_FB is expressed as follows.

When formula (1) is solved for the feedback current I_FB, the value of the feedback current I_FB in the steady state of the sensor section 300 can be calculated. Assuming that the magnetic sensitivity S of the magnetic sensor 520 and the voltage/current conversion coefficient G of the first amplifier circuit 532 are sufficiently large, the following equation is calculated from equation (1).

The output section 540 outputs an output signal V_xMR according to the feedback current I_FB that the magnetic field generation section 530 sends to generate the feedback magnetic field B_FB. The output unit 540 includes, for example, a resistive element having a resistance value R, and outputs a voltage drop caused by the feedback current I_FB flowing through the resistive element as an output signal V_xMR. In this case, the output signal V_xMR is calculated from equation (2) as shown in the following equation.

As described above, since the sensor unit 300 generates a feedback magnetic field that reduces the magnetic field input from the outside, it substantially reduces the magnetic field input to the magnetic sensor 520. As a result, the sensor section 300 uses, for example, a magnetoresistive element having the nonlinearity shown in FIG. Also, it is possible to prevent the detection signal V_xMR from becoming saturated. The input/output characteristics of such a sensor section 300 will be explained next.

FIG. 6 shows an example of input/output characteristics of the sensor section 300 according to this embodiment. In this figure, the horizontal axis indicates the magnitude B of the input magnetic field input to the sensor section 300, and the vertical axis indicates the magnitude V_xMR of the detection signal of the sensor section 300. The sensor unit 300 has high magnetic sensitivity and can detect a minute magnetic field of about 10 pT. Further, the sensor unit 300 can maintain good linearity of the detection signal V_xMR even if the absolute value of the input magnetic field B exceeds 100 μT, for example.

That is, in the sensor unit 300 according to the present embodiment, the detection result for the input magnetic field B has linearity within a predetermined range of the input magnetic field B, for example, where the absolute value of the input magnetic field B is several hundred μT or less. It is configured as follows. By using such a sensor unit 300, weak magnetic signals such as magnetocardial signals can be easily detected.

FIG. 7 shows a configuration example of the magnetic sensor 520 according to this embodiment. In this figure, the magnetic sensor 520 includes a magnetoresistive element 710 and magnetic convergence plates 720 and 730 arranged at both ends of the magnetoresistive element 710. The magnetic convergence plates 720 and 730 are arranged at both ends of the magnetoresistive element 710 so as to sandwich the magnetoresistive element 710 therebetween. In this figure, a magnetic convergence plate 720 is provided on the negative side of the magnetoresistive element 710 along the magnetically sensitive axis, and a magnetic convergent plate 730 is provided on the positive side of the magnetoresistive element 710 along the magnetically sensitive axis. It is being Note that here, the magnetically sensitive axis may be along the direction of magnetization fixed in the magnetization fixed layer forming the magnetoresistive element 710. Furthermore, when a magnetic field is input from the negative side to the positive side of the magnetically sensitive axis, the resistance of the magnetoresistive element 710 may increase or decrease. The magnetic convergence plates 720 and 730 are made of a material with high magnetic permeability, such as permalloy. When the magnetic sensor 520 is configured as shown in this figure, the coil 534 surrounds the cross section of the magnetoresistive element 710 and the magnetic convergence plates 720 and 730 arranged at both ends of the magnetoresistive element 710. The magnetic sensor 520 is wound along the axial direction of the magnetic field to be detected. Furthermore, when one magnetic sensor 520 includes a plurality of magnetoresistive elements 710, the magnetic sensor 520 may have a plurality of sets including a magnetoresistive element and magnetic convergence plates arranged at both ends thereof. In that case, the coil 534 may be wound so that one coil surrounds a set including the magnetoresistive element and the magnetic convergence plates disposed at both ends thereof.

In such a magnetic sensor 520, when a magnetic field is input from the negative side to the positive side of the magnetically sensitive axis, the magnetic convergence plates 720 and 730 formed of a material with high magnetic permeability are magnetized, so that as shown in this figure, A magnetic flux distribution as shown by the broken line occurs. Then, the magnetic flux generated by magnetizing the magnetic convergence plates 720 and 730 passes through the position of the magnetoresistive element 710 sandwiched between the two magnetic convergence plates 720 and 730. Therefore, the magnetic flux density at the position of the magnetoresistive element 710 can be significantly increased by arranging the magnetic convergence plates 720 and 730. In addition, as shown in this figure, by sampling the spatial distribution of the magnetic field using the magnetoresistive element 710 placed in a narrow position between the magnetic convergence plates 720 and 730, the sampling point in space can be clarified. be able to.

FIG. 8 shows a magnetic flux distribution when a feedback magnetic field is generated in the magnetic sensor 520 according to this embodiment. In FIG. 8, members having the same functions and configurations as those in FIG. 7 are denoted by the same reference numerals, and description thereof will be omitted except for differences. In the magnetic sensor 520 according to this embodiment, when a feedback current is supplied to the coil 534, the coil 534 generates a feedback magnetic field, thereby generating a magnetic flux distribution as shown by the dashed line in the figure. The magnetic flux generated by this feedback magnetic field is spatially distributed so as to cancel the spatial distribution of the magnetic field input to the magnetoresistive element 710 and magnetically amplified by the magnetic convergence plates 720 and 730. For this reason, the magnetic sensor 520 includes magnetic convergence plates 720 and 730 arranged at both ends of the magnetoresistive element 710 as shown in this figure, and includes the magnetoresistive element and the magnetic convergence plates disposed at both ends thereof. When the coil 534 is wound so as to surround the set with one coil, the magnetic field distribution at the position of the magnetoresistive element 710 can be accurately canceled by the feedback magnetic field, so that the difference between the input magnetic field and the output voltage is It is possible to realize a sensor with high linearity between.

FIG. 9 shows the configuration of the magnetic sensor array 210, sensor data collection section 230, and sensor data processing section 900 according to this embodiment.

Magnetic sensor array 210 has a plurality of magnetic sensor cells 220. Each of the plurality of magnetic sensor cells 220 may have a plurality of sensor sections 300x to 300z, as described above. In this figure, among the plurality of magnetic sensor cells 220 that the magnetic sensor array 210 has in each dimension direction, positions [i, j, k], [i+1, j, k], [i, j+1, k], and The part related to [i, j, k+1] is shown.

The sensor data collection unit 230 includes a plurality of AD converters 232 and a clock generator 234. The plurality of AD converters 232 are provided corresponding to each of the plurality of sensor sections 300x to 300z of the magnetic sensor cell 220, and the analog detection signals (sensor output signal V_xMR in FIG. 6 ) into digital measurement values V (Vx, Vy, Vz) and outputs a plurality of measurement values. Here, Vx, Vy, and Vz are measured values (for example, digital voltage values) obtained by converting detection signals from the sensor units 300x, 300y, and 300z into digital values, respectively.

The clock generator 234 generates a sampling clock and supplies a common sampling clock to each of the plurality of AD converters 232. Each of the plurality of AD converters 232 performs AD conversion in response to a common sampling clock supplied from the clock generator 234. Therefore, all of the plurality of AD converters 232 that perform AD conversion on the outputs of the plurality of sensor units 300x to 300z provided at different positions operate synchronously. Thereby, the plurality of AD converters 232 can simultaneously sample the detection results of the plurality of sensor units 300x to 300z provided in different spaces.

The sensor data processing section 900 includes a measurement data acquisition section 910, a measurement data selection section 920, a magnetic field calculation section 930, a basis vector storage section 940, and an error calculation section 950.

The measurement data acquisition unit 910 acquires a plurality of measurement values based on the input magnetic field detected by the magnetic sensor array 210. The measurement data acquisition section 910 is connected to the plurality of AD converters 232 and obtains a plurality of measurement values measured by the sensor sections 300x to 300z in the plurality of magnetic sensor cells 220 forming the magnetic sensor array 210. Specifically, the measurement data acquisition unit 910 is configured using a flip-flop or the like that latches the measurement values V (Vx, Vy, Vz) digitally converted by the plurality of AD converters 232 at a predetermined timing T. good. The measurement data acquisition section 910 supplies the plurality of acquired measurement values to the measurement data selection section 920 as measurement data Φ _All .

The measurement data selection unit 920 selects a plurality of measurement values used for calculating an input magnetic field by the magnetic field calculation unit 930 from among a plurality of measurement values supplied from the measurement data acquisition unit 910 based on a magnetic field detection error described later. Select a value. Then, the measurement data selection section 920 supplies the selected plurality of measurement values to the magnetic field calculation section 930 as measurement data Φ _Select .

The magnetic field calculation section 930 calculates an input magnetic field based on the plurality of measurement values selected as the measurement data Φ _Select by the measurement data selection section 920. When the measurement target is magnetocardial magnetism generated by the electrical activity of the heart of an animal, the magnetocardial magnetism may be measured based on the calculation result of the magnetic field calculation unit 930. At this time, the magnetic field calculation unit 930 may calculate the input magnetic field so that the square of the magnetic field detection error is minimized. The magnetic field calculation unit 930 also converts the spatial distribution of the input magnetic field indicated by a plurality of measurement values into a signal output by each of the magnetic sensors 520 when the magnetic sensor array 210 detects a magnetic field having a spatial distribution of an orthonormal function. The signals may be separated using a signal vector whose components are as base vectors. This will be discussed later. The magnetic field calculation section 930 supplies the calculation result of the input magnetic field to the error calculation section 950 together with a plurality of measured values.

The basis vector storage section 940 stores basis vectors used when the magnetic field calculation section 930 separates the spatial distribution of the input magnetic field into signals, and supplies the stored basis vectors to the magnetic field calculation section 930. The magnetic field calculation section 930 may use the basis vectors supplied from the basis vector storage section 940 when separating the spatial distribution of the input magnetic field into signals.

The error calculation unit 950 calculates the detection error ε of the magnetic field based on the plurality of measurement values supplied from the magnetic field calculation unit 930 and the calculation result of calculating the input magnetic field. This will also be discussed later. The error calculation unit 950 supplies the calculated magnetic field detection error ε to the measurement data selection unit 920. Then, as described above, the measurement data selection section 920 selects a magnetic field calculation section from among the plurality of measurement values supplied from the measurement data acquisition section 910 based on the detection error ε of the magnetic field supplied from the error calculation section 950. 930 selects a plurality of measured values to be used to calculate the input magnetic field.

FIG. 10 shows an example of a flow in which the measuring device 10 according to the present embodiment excludes measured values from defective sensors as a preprocess for calculating the magnetic field to be measured.

In step 1010, the measuring device 10 performs initial settings. For example, let N be the total number of multiple sensor units 300x to 300z in multiple magnetic sensor cells 220 constituting the magnetic sensor array 210, that is, the total number of multiple measured values included in the measured data Φ _All , and M be the measured data Φ Assuming that the total number of multiple measurement values included in _Select is the total number, the measuring device 10 sets M=N. That is, the measuring device 10 is initially set so that all of the plurality of measured values become the measured data Φ _Select .

Next, in step 1020, the measuring device 10 calculates the input magnetic field. For example, the measurement data acquisition unit 910 acquires a plurality of measurement values (measurement data Φ _All ) based on the input magnetic fields measured by the sensor units 300x to z in the plurality of magnetic sensor cells 220 forming the magnetic sensor array 210. Then, in step 1020 following step 1010, the measurement data selection unit 920 selects all of the plurality of measurement values as measurement data Φ _Select ( Φ _Select =Φ _All ). Then, the magnetic field calculation unit 930 calculates the input magnetic field based on the plurality of measurement values selected as the measurement data Φ _Select .

In calculating the input magnetic field, the magnetic field calculation unit 930 calculates the spatial distribution of the input magnetic field indicated by a plurality of measured values, for example, when the magnetic sensor array 210 detects a magnetic field having a spatial distribution of an orthonormal function. The signals are separated using a signal vector whose components are the signals output by each of 520 as a base vector. Note that the orthonormal function may be, for example, a spherical harmonic function. As an example, before measuring the magnetic field to be measured, the basis vector storage unit 940 stores, as a basis vector, a magnetic field signal vector obtained by spatially sampling a spherical harmonic when a predetermined point in space is specified as the coordinate origin. Remember. Here, the spherical harmonic function is a function obtained by restricting a homogeneous polynomial that is a solution of the n-dimensional Laplace equation to a unit sphere, and has orthonormality on the sphere. Note that the base vector storage unit 940 may store signal vectors that are predetermined based on simulation results or the like as base vectors.

The magnetic field calculation unit 930 acquires the signal vector stored as a basis vector by the basis vector storage unit 940 from the basis vector storage unit 940. Then, the magnetic field calculation unit 930 expands the spatial distribution of the input magnetic field indicated by the plurality of measured values into a series using the signal vector as a basis vector. Then, the magnetic field calculation unit 930 separates the spatial distribution of the magnetic field into a measurement target magnetic field and a disturbance magnetic field from the vector obtained by series expansion.

Then, as a result of signal separation, the magnetic field calculation unit 930 suppresses the disturbance magnetic field and calculates and outputs only the magnetic field to be measured. This will be explained in detail below using mathematical formulas.

Regarding the position where each sensor constituting the magnetic sensor array 210 is arranged, when the current i(r) = 0 at the position of the position vector r representing the position from the coordinate origin, the static magnetic field B(r) is Using the potential V(r) that satisfies the equation Δ·V(r)=0, it is determined as a spatial gradient of the potential V(r) as shown in the following equation. Here, Δ is the Laplacian, μ is the magnetic permeability, and ∇ is an operator representing vector differential operation.

The solution to Laplace's equation generally has a solution in the form of a series expansion using the spherical harmonics Yl,m(θ,φ), which is an orthonormal function system, so the potential V(r) is calculated by the following equation. can be expressed. Here, |r| is the absolute value of the position vector r (distance from the coordinate origin), θ and φ are the two argument angles in spherical coordinates, l is the azimuthal quantum number, and m is the magnetic quantum number , α and β are multipolar moments, and Lin and Lout are the numbers of series for the space in front and the space behind the magnetic sensor array 210, respectively, as seen from the coordinate origin and the measurement target, respectively. The azimuthal quantum number l takes a positive integer, and the magnetic quantum number m takes an integer from −1 to +1. That is, for example, when l is 1, m is -1, 0, and 1; for example, when l is 2, m is -2, -1, 0, 1, and 2. Note that since there is no single magnetic pole in a magnetic field, the azimuth quantum number l starts from 1 instead of 0 in (Equation 5). The first term in (Equation 5) is a term that is inversely proportional to the distance from the coordinate origin, and indicates the potential that exists in the space in front of the magnetic sensor array 210 when viewed from the coordinate origin and the measurement target. Furthermore, the second term in (Equation 5) is a term proportional to the distance from the coordinate origin, and indicates the potential that exists in the space behind the magnetic sensor array 210 when viewed from the coordinate origin and the measurement target.

Therefore, according to (Equation 4) and (Equation 5), the static magnetic field B(r) can be expressed by the following equation. Here, the first term in (Equation 6) is a magnetic field source that exists in the space in front of the magnetic sensor array 210 when viewed from the coordinate origin and the measurement target, such as a magnetocardiogram (measurement target magnetic field) generated by the electrical activity of the heart. It shows. Furthermore, the second term in (Equation 6) indicates a disturbance magnetic field generated by a magnetic field source that exists in the space behind the magnetic sensor array 210 when viewed from the coordinate origin and the measurement target.

When the solution to Laplace's equation is expressed in the form of a series expansion using spherical harmonics, the general solution becomes an infinite series. It is sufficient to obtain the ratio of the magnetic field signal to be measured to the magnetic field and sensor noise, and in fact, it is said that it is sufficient to express it as a series of about 10 terms. Furthermore, it is said that the series for signal space separation in a magnetoencephalograph may be approximately Lin=8 and Lout=3. Therefore, in the measuring device 10 of this embodiment, which may be used as a magnetocardiograph, for example, the case where Lin=8 and Lout=3 will be described as an example. However, the values of Lin and Lout are not limited to these, and may be any numerical values that are sufficient to sufficiently suppress the disturbance magnetic field and calculate only the magnetic field to be measured.

Here, al,m and bl,m are defined as shown below, where K is a calibration coefficient matrix representing the error of each sensor included in the magnetic sensor array 210. That is, al,m and bl,m are defined as M-dimensional vectors having M components equal to the number of sensors included in the magnetic sensor array 210 obtained from the gradient of the spherical harmonic function Yl,m(θ,φ). , is multiplied by a calibration coefficient matrix K that corrects the magnetic sensitivity error of the magnetic sensor 520 included in the magnetic sensor array 210, thereby obtaining a base vector with the magnetic sensitivity error of the magnetic sensor array 210 corrected.

Then, the measurement data Φ _Select at a certain time can be expressed by the following equation.

Furthermore, Sin, Sout, Xin, and Xout are each defined as follows. In other words, Sin is a vector with a total of Lin・(Lin+2) columns, in which each vector a is arranged in a column in order from l=1 to l=Lin, and for each l an integer from m=-l to l. It is defined as Also, Sout is a vector with a total of Lout・(Lout+2) columns, in which each vector b is arranged in columns in order from l=1 to l =Lout, and for each l an integer from m=-l to l. It is defined as In addition, Xin is the total Lin・Define it as a vector with (Lin+2) rows. In addition, Xout is the total Lout obtained by transposing the vectors in which each multipolar moment β is arranged in a column in order from l=1 to l=L out , and for each l an integer from m=-1 to l. - Define as a vector of (Lout+2) rows.

Then, the effective measurement data Φ _Select can be expressed in the form of an inner product of the matrix S and the vertical vector X, as shown in the following equation. Here, the matrix S indicates a matrix obtained by arranging a total of Lin.(Lin+2)+Lout.(Lout+2) basis vectors in the horizontal direction. It is something. Further, a vertical vector X of (Lin·(Lin+2)+Lout·(Lout+2)) dimension indicates a coefficient of a linear combination related to the base vectors.

The magnetic field calculation unit 930 calculates the vertical _vector ^X (here, "^X" is the left side in (11) , which means the hat (estimated value) of X).

At this time, the magnetic field calculation unit 930 uses the least squares method to determine the vertical vector ^X so as to minimize the cost function F shown in the following equation. Thereby, the magnetic field calculation unit 930 can solve the spatial distribution of the magnetic field.

Here, with respect to the vertical vector ^X determined by the magnetic field calculation unit 930 using (Equation 11) and (Equation 12), ^Xin and Sin represent the magnetic field component to be measured (magnetic core), and ^Xout and Sout represent the disturbance Represents the magnetic field component. Therefore, in order to eliminate the disturbance magnetic field component and extract only the magnetic field component to be measured, it is sufficient to extract only ^Xin and Sin from the magnetic field detection results ^X and S.

Thereby, the magnetic field calculation unit 930 is configured by arranging a plurality of magnetic sensor cells 220 three-dimensionally and is indicated by the measurement data Φ _Select measured using the magnetic sensor array 210 that is capable of detecting input magnetic fields in three axial directions. It is possible to separate the spatial distribution of the magnetic field generated by the magnetic field into the magnetic field to be measured and the disturbance magnetic field. In this way, the measuring device 10 can suppress the disturbance magnetic field component and extract only the component of the magnetic field to be measured, and therefore can measure the magnetic field to be measured with higher precision. Furthermore, since each of the plurality of sensor sections 300 has a magnetic convergence plate, it is possible to increase the magnetic sensitivity of the sensor section 300 and to clarify the spatial sampling point, thereby further increasing compatibility with signal space separation technology. can. The magnetic field calculation section 930 supplies the calculation result of the input magnetic field to the error calculation section 950 together with a plurality of measured values.

In step 1030, the error calculation section 950 calculates the detection error ε of the magnetic field based on the plurality of measurement values supplied from the magnetic field calculation section 930 and the calculation result of calculating the input magnetic field. The error calculation unit 950 may calculate the detection error ε by subtracting the inner product of the matrix S and the vertical vector ^X from the measurement data Φ _Select , for example, as shown in the following equation. As a result, the error calculation unit 950 calculates the error when mapping the measurement data Φ _Select at a certain time to the subspace spanned by the base vector S = [Sin, Sout] using the least squares method for each component of the vector. This is calculated as the detection error ε. Therefore, the error calculation unit 950 calculates the detection error ε for each of the plurality of measured values. Then, the error calculation unit 950 supplies the calculated detection error ε of the magnetic field to the measurement data selection unit 920. Note that since the number of measured values is M, the detection error ε is a vertical vector of M rows.

In step 1040, the measurement data selection unit 920 determines whether the average value of the detection errors ε in the entire magnetic sensor array 210, that is, the average value of the detection errors ε for each of the plurality of measurement values, is less than or equal to a predetermined threshold value. Determine. The measurement data selection unit 920 calculates the average value avg(ε) of the detection error ε using the following equation, for example, and determines whether the average value avg(ε) of the detection error ε is less than or equal to a predetermined threshold value Avg_E_Th. may be determined.

If it is determined in step 1040 that the average value of the detection error ε is less than or equal to the predetermined threshold value, the measuring device 10 ends the process of excluding the measured value by the defective sensor.

On the other hand, if it is determined in step 1040 that the average value of the detection error ε exceeds the predetermined threshold, in step 1050 the measurement data selection unit 920 selects the detection error ε from among the plurality of measurement values. Select the measured values that exceed the specified range as the measured values to be excluded. As an example, the measurement data selection unit 920 may select the measurement value i for which the absolute value of the detection error ε is the maximum from the magnetic sensor array 210 as the measurement value to be excluded.

Next, in step 1060, the measurement data selection unit 920 selects a plurality of measurement values by excluding the measurement value i for which the detection error ε exceeds a predetermined range. That is, the measurement data selection unit 920 reconstructs the plurality of measurement values excluding the measurement value i as measurement data Φ _Select .

Then, in step 1070, the measurement data selection unit 920 decrements the dimension of M by one as a result of excluding the measurement value i, and returns the process to step 1020. Then, the magnetic field calculation unit 930 recalculates the input magnetic field in step 1020 after excluding the measurement value i for which the detection error ε exceeds a predetermined range. At this time, the magnetic field calculation unit 930 may re-obtain a new measurement value using the magnetic sensor array 210, or may reuse an already obtained measurement value. The measuring device 10 repeats this process until it is determined in step 1040 that the average value of the detection errors ε is less than or equal to a predetermined threshold.

In addition, in the above description, when the measuring device 10 determines that the average value of the detection error ε exceeds a predetermined threshold value, the measuring device 10 selects one measurement value i having the relatively largest absolute value of the detection error ε. The case where the flow is repeated with exclusion has been described as an example. However, it is not limited to this. The measuring device 10 first selects one measurement value i with the relatively largest absolute value of the detection error ε, and sets the detection error ε of the measurement value i, that is, the maximum absolute value of the detection error ε, in advance. If it is determined that the measured value i exceeds a predetermined threshold, the flow may be repeated by excluding the measured value i. Furthermore, the measuring device 10 may select a plurality of valid measurement values by excluding one or more measurement values i for which the absolute value of the detection error ε exceeds a predetermined threshold value.

In this way, before calculating the magnetic field to be measured, the measuring device 10 excludes the measured value i with a large absolute value of the detection error ε, and calculates the measured data Φ used by the magnetic field calculation unit 930 to calculate the input magnetic field. Update _Select . A measurement value i with a large absolute value of detection error ε corresponds to a sensor in which large noise has occurred. According to the measuring device 10 of the present embodiment, since such defective sensors with large noise are excluded before detecting the magnetic field to be measured, it is possible to improve the detection accuracy of the magnetic field to be measured.

FIG. 11 shows the configuration of a sensor section 300 according to a modification of this embodiment. In this figure, members having the same functions and configurations as those in FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted except for differences.

In this modification, the magnetic sensor 520 has at least one magnetoresistive element. In this figure, as an example, the magnetic sensor 520 includes a first magnetoresistive element 710a and a second magnetoresistive element 710b connected in series between the power supply voltage Vcc and the ground GND, and It has a third magnetoresistive element 710c and a fourth magnetoresistive element 710d connected in series between the ground GND. Although not shown in this figure, the first to fourth magnetoresistive elements 710a to 710d (collectively referred to as "magnetoresistive elements 710") each have a magnetic field as shown in FIG. The resistive effect element 710 may include magnetic convergence plates 720 and 730 arranged at both ends. The magnetoresistive element 710 and the magnetic convergence plate may be located so as to be included in the coil 534. The magnetic sensor 520 outputs the voltage between the first magnetoresistive element 710a and the second magnetoresistive element 710b, and the voltage between the third magnetoresistive element 710c and the fourth magnetoresistive element 710d, respectively. . Note that in this figure, a bridge circuit is configured by a first magnetoresistive element 710a, a second magnetoresistive element 710b, a third magnetoresistive element 710c, and a fourth magnetoresistive element 710d. However, instead of this, the magnetic sensor 520 may include at least one of the first magnetoresistive element 710a, the second magnetoresistive element 710b, the third magnetoresistive element 710c, and the fourth magnetoresistive element 710d. is composed of a fixed resistance, or one of the first magnetoresistive element 710a, the second magnetoresistive element 710b, the third magnetoresistive element 710c, and the fourth magnetoresistive element 710d is fixed. It may be configured with a voltage source, and includes various modes of outputting a voltage according to a magnetic field input to at least one magnetoresistive element.

The magnetic sensor 520 includes at least a first magnetoresistive element 710a and a second magnetoresistive element 710b, which are connected in series and have opposite polarities. If the configuration is configured to output a voltage between the two, it is possible to reduce characteristic fluctuations such as offset and sensitivity due to temperature. Here, the term "reverse polarity" means that the direction of increase/decrease in resistance of the magnetoresistive element is opposite to the input magnetic field in the same direction. In this figure, the third magnetoresistive element 710c has a polarity opposite to that of the first magnetoresistive element 710a, the fourth magnetoresistive element 710d has a polarity opposite to that of the second magnetoresistive element 710b, and the first An example will be shown in which, in addition to the magnetoresistive element 710a and the second magnetoresistive element 710b, the third magnetoresistive element 710c and the fourth magnetoresistive element 710d have opposite polarities.

In this modification, the amplifier circuit 532 connects two differential input terminals to the output terminals of the magnetic sensor 520, respectively. Then, the amplifier circuit 532 generates a feedback current according to the difference between the output voltages of the magnetic sensors 520, and supplies this to the coil 534. Here, the difference between the respective output voltages of the magnetic sensors 520 is defined as Vopen.

In this modification, the output section 540 includes a current-voltage conversion resistor 542 and an operational amplifier 544.

The current-voltage conversion resistor 542 has one end connected to the coil 534 and the other end connected to a fixed voltage, converts the feedback current into a voltage, and has a voltage based on the feedback current (feedback current × current-voltage conversion resistance) at both ends. 542 resistance value). Here, the voltage based on the feedback current generated by the current-voltage conversion resistor 542 is defined as Vclosed.

The operational amplifier 544 connects both ends of the current-voltage converting resistor 542 to differential input terminals, and outputs a voltage corresponding to the voltage across the current-voltage converting resistor 542, that is, the voltage Vclosed.

Moreover, in this modification, the sensor section 300 further includes a magnetic reset section 1110. The magnetic reset unit 1110 applies a reset magnetic field to the magnetic sensor 520 to magnetically saturate the magnetic sensor 520 in the reset phase. Magnetic reset section 1110 includes a reset current supply section 1120 and a switching section 1130.

In the reset phase, the reset current supply unit 1120 supplies a reset current to the coil 534 to cause the coil 534 to generate a reset magnetic field that magnetically saturates each magnetoresistive element included in the magnetic sensor 520. Note that magnetic saturation indicates that a certain amount of magnetic field is input to the magnetoresistive element so that the output of the magnetoresistive element no longer varies with respect to the magnetic field. In this way, the magnetic field that magnetically saturates the magnetoresistive element is defined as a reset magnetic field, and the current that generates the reset magnetic field is defined as a reset current.

The switching unit 1130 switches whether or not to supply a feedback current that generates a feedback magnetic field to the magnetic field generation unit 530. Then, the reset current supply section 1120 supplies a reset current to the magnetic field generation section 530 to cause the magnetic field generation section 530 to generate a reset magnetic field while the feedback current is not supplied to the magnetic field generation section 530. For example, the switching unit 1130 is provided between the amplifier circuit 532 and the coil 534, and connects the coil 534 to the reset current supply unit 1120 when the feedback current generated by the amplifier circuit 532 is not supplied to the coil 534. Then, the reset current supply unit 1120 may supply a reset current to the coil 534 to generate a reset magnetic field in the coil 534 in a state where the feedback current is not supplied to the coil 534.

As described above, in the present modification, when the input magnetic field to the sensor unit 300 is input to the magnetic sensor 520, the amplifier circuit 532 adjusts the output voltage of each of the magnetic sensors 520 according to the input magnetic field. A feedback current corresponding to the difference (that is, voltage Vopen) is generated and supplied to the coil 534. The coil 534 then generates a feedback magnetic field that cancels out the input magnetic field input to the magnetic sensor 520 according to the supplied feedback current. Then, in the measurement phase, the output unit 540 outputs a measured value according to the feedback current generated with respect to the input magnetic field, specifically, a voltage value according to the voltage Vclosed. Here, this series of control is defined as closed loop control. Note that under closed loop control, the value of the voltage Vopen is controlled to be 0, that is, so that a feedback magnetic field that cancels out the input magnetic field is generated.

In addition, in the above description, although the case where the coil 534 is shared as a coil for generating a feedback magnetic field and a reset magnetic field was shown as an example, it is not limited to this. The sensor unit 300 may include a coil different from the coil 534 for generating the feedback magnetic field as a coil for generating the reset magnetic field. Further, in the above description, the case where the sensor section 300 includes all of the magnetic reset section 1110 was shown as an example, but the present invention is not limited to this. A part of the magnetic reset unit 1110, for example, the reset current supply unit 1120, may not be provided in the sensor unit 300, and may be provided in the sensor data collection unit 230, for example.

FIG. 12 shows an example of the flow of magnetic reset in the reset phase by the sensor section 300 according to this modification. Here, a state in which closed loop control is not performed is defined as an open loop. In step 1210, the switching unit 1130 switches from closed loop control to a state in which no feedback current is supplied to the coil 534, that is, to an open loop. Furthermore, the switching unit 1130 connects the coil 534 to the reset current supply unit 1120.

Next, in step 1220, the reset current supply unit 1120 supplies a reset current to the coil 534, causing the coil 534 to generate a reset magnetic field. Here, the reset current supply unit 1120 may generate a reset magnetic field in the coil 534 by supplying a predetermined and sufficient current to magnetically saturate each magnetoresistive element included in the magnetic sensor 520. good. Instead, the reset current supply unit 1120 monitors the output voltage of the magnetic sensor 520 and supplies the reset current until the output voltage of the magnetic sensor 520 reaches a value indicating that each magnetoresistive element is magnetically saturated. The reset magnetic field may be generated in coil 534 with gradually increasing strength. The reset magnetic field is set, for example, in a state where the magnetic field is 0, so that the magnetoresistive element can be magnetically saturated regardless of the orientation of the sensor unit 300, that is, regardless of the orientation of the earth's magnetism. The magnitude may be greater than or equal to the magnitude of the magnetic field that magnetically saturates the magnetoresistive element plus the earth's magnetic field.

Next, in step 1230, the reset current supply section 1120 stops supplying the reset current to the coil 534. Here, the reset current supply section 1120 causes the coil 534 to generate a reset magnetic field to magnetically saturate each magnetoresistive element, and then gradually reduces the magnitude of the reset current supplied to the coil 534. The intensity of the reset magnetic field generated may be gradually reduced. Generally, in a magnetoresistive element, when a magnetic field is applied, the domain walls (boundaries between magnetic domains) move, then rotation of magnetization occurs within the magnetic domains, and eventually the whole becomes one magnetic domain. It becomes a single magnetic domain state covered by . This corresponds to magnetic saturation. When the magnetic field of a magnetoresistive element is decreased from a state of magnetic saturation, domain walls with various magnetization directions are generated to minimize the energy of the magnetoresistive element, and as the magnetic field decreases, the domain walls are Moving on. According to the reset current supply section 1120 of the sensor section 300 according to the present modification, in step 1230 after magnetically saturating each magnetoresistive element, the reset magnetic field supplied to the coil 534 is gradually reduced. The resistance effect element can always be brought close to the same magnetization state. As a result, the magnetoresistive element is in a similar state every magnetic reset, so that variations in the magnetization state of the magnetoresistive element after each magnetic reset can be made relatively small.

Then, in step 1240, the switching unit 1130 connects the coil 534 to the amplifier circuit 532, switches from open loop to closed loop control, and ends the magnetic reset process. Thereafter, the output unit 540 outputs a measured value according to the feedback current generated for the input magnetic field under closed-loop control in the measurement phase.

FIG. 13 shows a magnetization curve of a general magnetic material. In the initial magnetized state, the magnetic material has zero magnetization when the magnetic field is zero, as shown at a point 1310. When the magnetic field is increased from this state to the positive side, the magnetization increases along a curve 1350 and reaches a point 1312. This curve 1350 is called an initial magnetization curve. Once point 1312 is reached, the magnetization will not change even if the magnetic field is increased further in the positive direction. At this time, the magnetic material is in a magnetically saturated state. Thereafter, as the magnetic field is decreased, the magnetization decreases following curve 1360 instead of curve 1350 and reaches point 1314. At point 1314, magnetization remains even if the magnetic field is 0, and this is called residual magnetization. Further, as the magnetic field is increased to the negative side, the magnetization decreases following curve 1360 and reaches point 1316. Once point 1316 is reached, the magnetization will no longer change with further negative increases in the magnetic field. At this time, the magnetic material becomes magnetically saturated again. Thereafter, when the magnetic field is increased again to the positive side, the magnetization increases along a curve 1370 instead of a curve 1360, and reaches a point 1312 via a point 1318. Magnetic materials generally have such magnetic hysteresis characteristics. Here, the largest loop consisting of the curve 1360 and the curve 1370 passing through the points 1312 and 1316 where the magnetic material becomes magnetically saturated is called a major loop.

On the other hand, for example, if the magnetic field is increased to the negative side from the state at point 1318, the magnetization decreases following a curve 1380. From this state, when the magnetic field is increased again to the positive side at point 1320, before the magnetic material is magnetically saturated, the magnetization increases not along curve 1380 but along curve 1390, and reaches point 1318. In this way, a loop consisting of, for example, curve 1380 and curve 1390 that does not pass through points 1312 and 1316 where the magnetic material becomes magnetically saturated is called a minor loop.

FIG. 14 shows the characteristics of the voltage Vopen with respect to the input magnetic field Bin to the magnetic sensor 520 in the sensor section 300 according to this modification. In this modification, the characteristics of the voltage Vopen with respect to the input magnetic field Bin to the magnetic sensor 520 are the first magnetoresistive element 710a, the second magnetoresistive element 710b, the third magnetoresistive element 710c, and According to the magnetic hysteresis characteristics of the fourth magnetoresistive element 710d, the fourth magnetoresistive element 710d has characteristics as shown in the figure. Reference numeral 1410 indicates a minor loop, and reference numeral 1420 indicates a major loop.

In the sensor unit 300 according to this modification, when a magnetic field is measured under closed loop control in a state before magnetic reset, the magnetic operating point of each magnetoresistive element of the magnetic sensor 520 is above the minor loop 1410. The magnetic field will be measured at point 1430. However, as a general phenomenon of magnetic materials, each magnetoresistive element of the magnetic sensor 520 has a higher magnetic sensitivity (Bin) when operated on a minor loop than when operated on a major loop. (rate of change of voltage Vopen), and the weak magnetic field to be measured cannot be detected. Therefore, in the measuring device 10 in which each of the plurality of magnetic sensor cells 220 includes the sensor unit 300 according to the present modification, the magnetic sensor 520 that has a large noise and is detected as a defective sensor is magnetically reset before detecting the magnetic field to be measured.

FIG. 15 shows the configuration of the magnetic sensor array 210, the sensor data collection section 230, and the sensor data processing section 900 in a case where each of the plurality of magnetic sensor cells 220 has the sensor section 300 according to this modification. In this figure, members having the same functions and configurations as those in FIG. 9 are denoted by the same reference numerals, and description thereof will be omitted except for differences. In this modification, the plurality of magnetic sensor cells 220 included in the magnetic sensor array 210 include, for example, a sensor section 300 shown in FIG. 11. That is, each of the sensor units 300 included in the plurality of magnetic sensor cells 220 is configured to be able to magnetically reset the magnetic sensor 520 in the reset phase. Furthermore, in this modification, the sensor data processing section 900 further includes a determining section 1510 and a base vector updating section 1520.

The determining unit 1510 determines whether to reset at least one of the plurality of magnetic sensor cells 220 based on the magnetic field detection error ε supplied from the error calculating unit 950. More specifically, the determining unit 1510 determines to reset the magnetic sensor cell 220 including the magnetic sensor 520 used to obtain the measured value in which the magnetic field detection error ε exceeds a predetermined range. In this case, the determining unit 1510 may decide to reset only the magnetic sensor 520 used to obtain the measurement value for which the detection error ε exceeds a predetermined range, or may decide to reset only the magnetic sensor 520 that was used to obtain the measurement value in which the detection error ε exceeds a predetermined range, or It may be determined that all 220 magnetic sensors 520 are reset.

The base vector updating unit 1520 updates the base vector based on the detection error ε. Then, the magnetic field calculation unit 930 recalculates the input magnetic field after the magnetic sensor 520 used to obtain the measurement value in which the detection error ε exceeds a predetermined range is magnetically reset. At this time, the magnetic field calculation section 930 uses the basis vector updated by the basis vector updating section 1520. This will be explained in detail.

FIG. 16 shows an example of a flow in which the measuring device 10, each of which has a sensor unit 300 according to the present modification, resets a defective sensor as a preprocess for calculating a magnetic field to be measured. In step 1610, the measuring device 10 acquires measurement data. For example, the measurement data acquisition unit 910 acquires a plurality of measurement values (measurement data Φ _All ) based on the input magnetic fields measured by the sensor units 300x to z in the plurality of magnetic sensor cells 220 forming the magnetic sensor array 210.

In step 1620, the measurement device 10 calculates the input magnetic field. In this flow, the measurement data selection unit 920 selects all of the plurality of measurement values as measurement data Φ _Select ( Φ _Select =Φ _All ). Then, the magnetic field calculation unit 930 calculates the input magnetic field based on the measurement data Φ _All using the same method as in step 1020.

In step 1630, the measuring device 10 calculates the detection error ε. For example, the error calculation unit 950 calculates the detection error ε using a method similar to step 1030.

Then, in step 1640, the measuring device 10 updates the base vectors. For example, the base vector updating unit 1520 updates the base vector using the method of least squares so as to minimize the detection error ε calculated in step 1630. Specifically, for example, the basis vector is determined by executing an algorithm that minimizes ε defined by (Equation 13) based on optimization theory, and updating the calibration coefficient matrix K in (Equation 7). Update. Note that the calibration coefficient matrix K includes vectors representing the magnetic sensitivity axis directions and magnetic sensitivities in the sensor units 300x, y, and z of the plurality of magnetic sensor cells 220. Therefore, the basis vector updating unit 1520 can correct the magnetic sensitivity (principal axis sensitivity and other axis sensitivity) of each magnetic sensor cell 220 by updating the calibration coefficient matrix K.

In step 1650, the measuring device 10 calculates the input magnetic field using the updated basis vectors updated in step 1640. For example, the magnetic field calculation unit 930 calculates the input magnetic field using the updated basis vector using a method similar to step 1020.

In step 1660, the measuring device 10 calculates the detection error ε. For example, the error calculation unit 950 calculates the detection error ε using a method similar to step 1030.

In step 1670, the measuring device 10 selects the maximum error sensor with the maximum absolute value of the detection error ε (maximum error). For example, the determining unit 1510 identifies a measurement value with the maximum absolute value of the detection error ε based on the detection error ε for each measurement value supplied from the error calculation unit 950, and determines which measurement value is used to obtain the measurement value. 520 is selected as the maximum error sensor.

In step 1680, the measuring device 10 determines whether the maximum error is less than or equal to a predetermined threshold. For example, the determining unit 1510 may determine whether the absolute value of the detection error ε of the maximum error sensor selected in step 1670 is less than or equal to a predetermined threshold Max_E_Th.

If it is determined in step 1680 that the maximum error is less than or equal to the predetermined threshold, the measuring device 10 ends the process of resetting the defective sensor.

On the other hand, if it is determined in step 1680 that the maximum error exceeds the predetermined threshold, in step 1690 the determining unit 1510 determines to reset the magnetic sensor 520 selected as the maximum error sensor in step 1670. In this case, the determining unit 1510 may decide to reset only the magnetic sensor 520 used to obtain the measurement value for which the detection error ε exceeds a predetermined range, or may decide to reset only the magnetic sensor 520 that was used to obtain the measurement value in which the detection error ε exceeds a predetermined range, or It may be determined that all 220 magnetic sensors 520 are reset. Then, the determining unit 1510 instructs the magnetic sensor cell 220 including the magnetic sensor 520 determined to be reset to be reset. The magnetic sensor cell 220 that has been instructed to reset switches the magnetic sensor 520 to be reset from closed loop control to open loop control, transitions to the reset phase, and magnetically resets the magnetic sensor 520 to be reset, according to the flow shown in FIG.

In step 1690, after the magnetic sensor 520 used to acquire the measurement value in which the detection error ε exceeds the predetermined range is magnetically reset, the process returns to step 1610, and the magnetic field calculation unit 930 calculates the newly acquired value. The input magnetic field is recalculated using the measured data. The measuring device 10 repeats this process until it is determined in step 1680 that the maximum error is less than or equal to a predetermined threshold. Note that at this time, the measuring device 10 repeats the process (under closed loop control) without turning off the feedback current for the magnetic sensors other than the magnetic sensor that performs the magnetic reset.

In this way, the determining unit 1510 determines whether to reset at least one of the plurality of magnetic sensor cells 220 based on the magnetic field detection error ε supplied from the error calculating unit 950. More specifically, the determining unit 1510 determines to reset the magnetic sensor cell 220 including the magnetic sensor 520 used to obtain the measured value in which the magnetic field detection error ε exceeds a predetermined range.

In addition, in the above description, when the measuring device 10 first selects one maximum error sensor with the relatively largest detection error ε, and determines that the maximum error exceeds a predetermined threshold, The case where the error sensor is magnetically reset has been described as an example. However, it is not limited to this. The measuring device 10 may magnetically reset one or more magnetic sensors 520 for which the absolute value of the detection error ε exceeds a predetermined threshold.

In addition, if the absolute value of the detection error ε does not fall below the predetermined threshold even after magnetic resetting a predetermined number of times or more, the magnetic sensor 520 used to obtain the measurement value is It may be determined not to use it for detection and the process may be terminated.

In this way, the measuring device 10 magnetically resets the magnetic sensor 520 used to obtain the measurement value with the large absolute value of the detection error ε, and redetects the input magnetic field. The magnetic sensor 520 used to obtain the measurement value with a large absolute value of the detection error ε may be a defective sensor whose magnetic sensitivity has decreased or noise has increased due to magnetic history. According to the measuring device 10 of this modification, the magnetic sensitivity of a defective sensor with decreased magnetic sensitivity or increased noise is reset before detecting the magnetic field to be measured to increase the magnetic sensitivity, so calculation of the magnetic field to be measured is performed. Accuracy can be increased.

Note that the present embodiment and the other embodiments described above may function independently, or may function in combination. That is, for example, as preprocessing before detecting the magnetic field to be measured, the flow for resetting a defective sensor according to FIG. 16 may be executed, and then the flow for excluding a defective sensor according to FIG. 10 may be executed. By combining both embodiments, the detection accuracy of the magnetic field to be measured can be further improved.

Furthermore, in the present embodiment described above, the case where the measuring device 10 calculates the input magnetic field while excluding the measured value i with a large absolute value of the detection error ε was shown as an example. However, it is not limited to this.

For example, the magnetic field calculation section 930 solves the spatial distribution of the magnetic field using (Equation 11), and calculates, based on the plurality of measurement values selected by the measurement data selection section 920, the location where the plurality of measurement values are measured. The input magnetic field can be recalculated. In that case, the error calculation unit 950 may calculate the detection error based on the detection result of the input magnetic field at the location where the plurality of recalculated measurement values were measured.

As an example, the magnetic field calculation unit 930 solves the spatial distribution of the magnetic field using (Equation 11), and uses the coefficients related to the calculation result of the input magnetic field, that is, ^Xin and ^Xout in (Equation 11), to calculate the signal space. The magnetic field vector B(r) at the coordinates of the sensor that measured the measurement value i excluded from the separation calculation (position vector = r, coordinates expressed in polar coordinates = (r, θ, φ)) can be expressed by the following formula. can.

That is, the magnetic field calculation unit 930 calculates the input at the location where the excluded measurement value i was measured based on the coefficient related to the calculation result of the input magnetic field calculated from the plurality of measurement values selected by the measurement data selection unit 920. Magnetic field can be calculated. As a result, the measuring device 10 reconstructs the magnetic field at the defective sensor using (Equation 15), so it is possible to suppress a decrease in magnetic field measurement accuracy due to missing measurement values at the location of the defective sensor. Therefore, the measuring device 10 can perform highly accurate magnetic field detection.

Various embodiments of the invention may be described with reference to flowcharts and block diagrams, where the blocks represent (1) a stage in a process at which an operation is performed, or (2) a device responsible for performing the operation. may represent a section of Certain steps and sections may be implemented by dedicated circuitry, programmable circuitry provided with computer-readable instructions stored on a computer-readable medium, and/or a processor provided with computer-readable instructions stored on a computer-readable medium. It's fine. Specialized circuits may include digital and/or analog hardware circuits, and may include integrated circuits (ICs) and/or discrete circuits. Programmable circuits include logic AND, logic OR, logic Reconfigurable hardware circuits may include reconfigurable hardware circuits, including, for example.

A computer-readable medium may include any tangible device capable of storing instructions for execution by a suitable device, such that the computer-readable medium having instructions stored thereon is illustrated in a flowchart or block diagram. An article of manufacture will be provided that includes instructions that can be executed to create a means for performing the operations. Examples of computer readable media may include electronic storage media, magnetic storage media, optical storage media, electromagnetic storage media, semiconductor storage media, and the like. More specific examples of computer readable media include floppy disks, diskettes, hard disks, random access memory (RAM), read only memory (ROM), erasable programmable read only memory (EPROM or flash memory), Electrically Erasable Programmable Read Only Memory (EEPROM), Static Random Access Memory (SRAM), Compact Disc Read Only Memory (CD-ROM), Digital Versatile Disk (DVD), Blu-ray (RTM) Disc, Memory Stick, Integrated Circuit cards etc. may be included.

Computer-readable instructions include assembler instructions, Instruction Set Architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state configuration data, or object-oriented programming such as Smalltalk, JAVA, C++, etc. language, and either source code or object code written in any combination of one or more programming languages, including traditional procedural programming languages such as the "C" programming language or similar programming languages. good.

Computer-readable instructions may be implemented on a processor or programmable circuit of a general purpose computer, special purpose computer, or other programmable data processing device, either locally or over a wide area network (WAN), such as a local area network (LAN), the Internet, etc. ), computer-readable instructions may be executed to create a means for performing the operations specified in the flowchart or block diagrams. Examples of processors include computer processors, processing units, microprocessors, digital signal processors, controllers, microcontrollers, and the like.

FIG. 17 illustrates an example computer 2200 in which aspects of the invention may be implemented, in whole or in part. A program installed on computer 2200 may cause computer 2200 to function as an operation or one or more sections of an apparatus according to an embodiment of the present invention, or to perform one or more operations associated with an apparatus according to an embodiment of the present invention. Sections and/or computer 2200 may be caused to perform a process or a step of a process according to an embodiment of the invention. Such programs may be executed by CPU 2212 to cause computer 2200 to perform certain operations associated with some or all of the blocks in the flowcharts and block diagrams described herein.

Computer 2200 according to this embodiment includes a CPU 2212, RAM 2214, graphics controller 2216, and display device 2218, which are interconnected by host controller 2210. The computer 2200 also includes input/output units such as a communication interface 2222, a hard disk drive 2224, a DVD-ROM drive 2226, and an IC card drive, which are connected to the host controller 2210 via an input/output controller 2220. There is. The computer also includes legacy input/output units, such as ROM 2230 and keyboard 2242, which are connected to input/output controller 2220 via input/output chip 2240.

CPU 2212 operates according to programs stored in ROM 2230 and RAM 2214, thereby controlling each unit. Graphics controller 2216 obtains image data generated by CPU 2212, such as in a frame buffer provided in RAM 2214 or itself, and causes the image data to be displayed on display device 2218.

Communication interface 2222 communicates with other electronic devices via a network. Hard disk drive 2224 stores programs and data used by CPU 2212 within computer 2200. DVD-ROM drive 2226 reads programs or data from DVD-ROM 2201 and provides the programs or data to hard disk drive 2224 via RAM 2214. The IC card drive reads programs and data from and/or writes programs and data to the IC card.

ROM 2230 stores therein programs that are dependent on the computer 2200 hardware, such as a boot program that is executed by the computer 2200 upon activation. Input/output chip 2240 may also connect various input/output units to input/output controller 2220 via parallel ports, serial ports, keyboard ports, mouse ports, etc.

A program is provided by a computer readable medium such as a DVD-ROM 2201 or an IC card. The program is read from a computer readable medium, installed on hard disk drive 2224, RAM 2214, or ROM 2230, which are also examples of computer readable media, and executed by CPU 2212. The information processing described in these programs is read by the computer 2200 and provides coordination between the programs and the various types of hardware resources described above. An apparatus or method may be configured to implement the manipulation or processing of information according to the use of computer 2200.

For example, when communication is performed between the computer 2200 and an external device, the CPU 2212 executes a communication program loaded into the RAM 2214 and sends communication processing to the communication interface 2222 based on the processing written in the communication program. You can give orders. The communication interface 2222 reads transmission data stored in a transmission buffer processing area provided in a recording medium such as a RAM 2214, a hard disk drive 2224, a DVD-ROM 2201, or an IC card under the control of the CPU 2212, and transmits the read transmission data. Data is transmitted to the network, or received data received from the network is written to a reception buffer processing area provided on the recording medium.

Further, the CPU 2212 causes the RAM 2214 to read all or a necessary part of a file or database stored in an external recording medium such as a hard disk drive 2224, a DVD-ROM drive 2226 (DVD-ROM 2201), an IC card, etc. Various types of processing may be performed on data on RAM 2214. The CPU 2212 then writes back the processed data to the external recording medium.

Various types of information, such as various types of programs, data, tables, and databases, may be stored on a recording medium and subjected to information processing. The CPU 2212 performs various types of operations, information processing, conditional determination, conditional branching, unconditional branching, and information retrieval on the data read from the RAM 2214 as described elsewhere in this disclosure and specified by the instruction sequence of the program. Various types of processing may be performed, including /substitutions, etc., and the results are written back to RAM 2214. Further, the CPU 2212 may search for information in a file in a recording medium, a database, or the like. For example, if a plurality of entries are stored in the recording medium, each having an attribute value of a first attribute associated with an attribute value of a second attribute, the CPU 2212 search the plurality of entries for an entry that matches the condition, read the attribute value of the second attribute stored in the entry, and thereby associate it with the first attribute that satisfies the predetermined condition. The attribute value of the second attribute may be acquired.

The programs or software modules described above may be stored on computer readable media on or near computer 2200. Also, a recording medium such as a hard disk or RAM provided in a server system connected to a dedicated communication network or the Internet can be used as a computer-readable medium, thereby providing the program to the computer 2200 via the network. do.

Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the range described in the above embodiments. It will be apparent to those skilled in the art that various changes or improvements can be made to the embodiments described above. It is clear from the claims that such modifications or improvements may be included within the technical scope of the present invention.

The order of execution of each process, such as the operation, procedure, step, and stage in the apparatus, system, program, and method shown in the claims, specification, and drawings, is specifically defined as "before" or "before". It should be noted that they can be implemented in any order unless the output of the previous process is used in the subsequent process. Even if the claims, specifications, and operational flows in the drawings are explained using "first," "next," etc. for convenience, this does not mean that it is essential to carry out the operations in this order. It's not a thing.

10 Measuring device 100 Main body part 110 Magnetic sensor unit 120 Head 130 Base part 140 Pole part 150 Information processing part 210 Magnetic sensor array 220 Magnetic sensor cell 230 Sensor data collection part 232 AD converter 234 Clock generator 300 Sensor part 520 Magnetic sensor 530 Magnetic field Generation section 532 Amplification circuit 534 Coil 540 Output section 542 Current-voltage conversion resistor 544 Operational amplifier 710 Magnetoresistive elements 720, 730 Magnetic convergence plate 900 Sensor data processing section 910 Measurement data acquisition section 920 Measurement data selection section 930 Magnetic field calculation section 940 Base Vector storage section 950 Error calculation section 1110 Magnetic reset section 1120 Reset current supply section 1130 Switching section 1510 Determining section 1520 Base vector updating section 2200 Computer 2201 DVD-ROM
2210 Host controller 2212 CPU
2214 RAM
2216 Graphic controller 2218 Display device 2220 Input/output controller 2222 Communication interface 2224 Hard disk drive 2226 DVD-ROM drive 2230 ROM
2240 Input/output chip 2242 Keyboard

Claims (18)

A magnetic sensor array configured by three-dimensionally arranging a plurality of magnetic sensor cells each including a magnetic sensor, and capable of detecting input magnetic fields in three axial directions;
a measurement data acquisition unit that acquires a plurality of measurement values based on the input magnetic field detected by the magnetic sensor array;
a magnetic field calculation unit that calculates the input magnetic field based on the plurality of measured values;
an error calculation unit that calculates a magnetic field detection error based on the plurality of measured values and the calculation result of the input magnetic field;
a measurement data selection unit that selects a plurality of measurement values to be used by the magnetic field calculation unit to calculate the input magnetic field from among the plurality of measurement values based on the detection error;
Equipped with
The error calculation unit calculates the detection error for each of the plurality of measured values,
The measurement data selection unit selects the plurality of measurement values by excluding measurement values in which the detection error exceeds a predetermined range;
The magnetic field calculation section is configured to calculate the plurality of measurement values based on the plurality of measurement values selected by the measurement data selection section after excluding the measurement values in which the detection error exceeds a predetermined range. recalculate the input magnetic field at the location where
The error calculation unit calculates the detection error based on the detection result of the input magnetic field at the location where the plurality of measurement values are measured.
measuring device. A magnetic sensor array configured by three-dimensionally arranging a plurality of magnetic sensor cells each including a magnetic sensor, and capable of detecting input magnetic fields in three axial directions;
a measurement data acquisition unit that acquires a plurality of measurement values based on the input magnetic field detected by the magnetic sensor array;
a magnetic field calculation unit that calculates the input magnetic field based on the plurality of measured values;
an error calculation unit that calculates a magnetic field detection error based on the plurality of measured values and the calculation result of the input magnetic field;
a measurement data selection unit that selects a plurality of measurement values to be used by the magnetic field calculation unit to calculate the input magnetic field from among the plurality of measurement values based on the detection error;
Equipped with
The error calculation unit calculates the detection error for each of the plurality of measured values,
The measurement data selection unit selects the plurality of measurement values by excluding measurement values in which the detection error exceeds a predetermined range;
The magnetic field calculation unit recalculates the input magnetic field after excluding measurement values in which the detection error exceeds a predetermined range,
The magnetic field calculation unit is configured to calculate the magnetic field at the location where the excluded measurement value was measured, based on a coefficient related to the calculation result of the input magnetic field calculated from the plurality of measurement values selected by the measurement data selection unit. Calculate the input magnetic field ,
measuring device. A magnetic sensor array configured by three-dimensionally arranging a plurality of magnetic sensor cells each including a magnetic sensor, and capable of detecting input magnetic fields in three axial directions;
a measurement data acquisition unit that acquires a plurality of measurement values based on the input magnetic field detected by the magnetic sensor array;
a magnetic field calculation unit that calculates the input magnetic field based on the plurality of measured values;
an error calculation unit that calculates a magnetic field detection error based on the plurality of measured values and the calculation result of the input magnetic field;
a measurement data selection unit that selects a plurality of measurement values to be used by the magnetic field calculation unit to calculate the input magnetic field from among the plurality of measurement values based on the detection error;
Equipped with
Each of the plurality of magnetic sensor cells includes a magnetic field generating section that provides the magnetic sensor with a feedback magnetic field that reduces an input magnetic field detected by the magnetic sensor, and a magnetic field generating section that responds to the current that the magnetic field generating section sends to generate the feedback magnetic field. and an output section for outputting the output signal .
measuring device. The error calculation unit calculates the detection error for each of the plurality of measured values,
The measurement device according to claim 3, wherein the measurement data selection unit selects the plurality of measurement values by excluding measurement values in which the detection error exceeds a predetermined range. The measuring device according to claim 4, wherein the magnetic field calculation unit recalculates the input magnetic field after excluding measured values in which the detection error exceeds a predetermined range. A magnetic sensor array configured by arranging a plurality of magnetic sensor cells in three dimensions and capable of detecting input magnetic fields in three axial directions;
a measurement data acquisition unit that acquires a plurality of measurement values based on the input magnetic field detected by the magnetic sensor array;
a magnetic field calculation unit that calculates the input magnetic field based on the plurality of measured values;
an error calculation unit that calculates a magnetic field detection error based on the plurality of measured values and the calculation result of the input magnetic field;
a determining unit that determines whether to reset at least one of the plurality of magnetic sensor cells based on the detection error;
Equipped with
Each of the plurality of magnetic sensor cells includes:
magnetic sensor;
a magnetic field generation unit that provides the magnetic sensor with a feedback magnetic field that reduces the input magnetic field detected by the magnetic sensor;
an output unit that outputs an output signal according to a current that the magnetic field generation unit flows to generate the feedback magnetic field;
a magnetic reset unit that applies a reset magnetic field to the magnetic sensor to magnetically saturate the magnetic sensor when resetting the magnetic sensor cell;
Measuring equipment, including: The error calculation unit calculates the detection error for each of the plurality of measured values,
The measuring device according to claim 6 , wherein the determining unit determines to reset a magnetic sensor cell including a magnetic sensor used to obtain a measured value in which the detection error exceeds a predetermined range. The magnetic field calculation unit recalculates the input magnetic field after the magnetic sensor used to obtain the measurement value in which the detection error exceeds a predetermined range is magnetically reset. measuring device. The magnetic reset unit includes a switching unit that switches whether or not to supply a feedback current that generates the feedback magnetic field to the magnetic field generation unit, and in a state where the feedback current is not supplied to the magnetic field generation unit, the magnetic field The measuring device according to any one of claims 6 to 8 , wherein a reset current is supplied to the generating section to cause the magnetic field generating section to generate the reset magnetic field. The magnetic field calculation unit converts the spatial distribution of the input magnetic field indicated by the plurality of measurement values into a signal output by each of the magnetic sensors when the magnetic sensor array detects a magnetic field having a spatial distribution of an orthonormal function. Separate the signal using a signal vector with components as a basis vector,
The measuring device according to any one of claims 1 to 9 , wherein the error calculation unit calculates the detection error based on a result of signal separation by the magnetic field calculation unit. A magnetic sensor array configured by three-dimensionally arranging a plurality of magnetic sensor cells each including a magnetic sensor, and capable of detecting input magnetic fields in three axial directions;
a measurement data acquisition unit that acquires a plurality of measurement values based on the input magnetic field detected by the magnetic sensor array;
a magnetic field calculation unit that calculates the input magnetic field based on the plurality of measured values;
an error calculation unit that calculates a magnetic field detection error based on the plurality of measured values and the calculation result of the input magnetic field;
a measurement data selection unit that selects a plurality of measurement values to be used by the magnetic field calculation unit to calculate the input magnetic field from among the plurality of measurement values based on the detection error;
Equipped with
The magnetic field calculation unit converts the spatial distribution of the input magnetic field indicated by the plurality of measurement values into a signal output by each of the magnetic sensors when the magnetic sensor array detects a magnetic field having a spatial distribution of an orthonormal function. Separate the signal using a signal vector with components as a basis vector,
The error calculation unit calculates the detection error based on the result of signal separation by the magnetic field calculation unit .
measuring device. The measuring device according to any one of claims 1 to 11 , wherein the magnetic field calculation unit calculates the input magnetic field so that the square of the detection error is minimized. The measuring device according to claim 10 or 11 , further comprising a base vector updating unit that updates the base vector based on the detection error. The measuring device according to any one of claims 3 to 9 , wherein the magnetic sensor includes a magnetoresistive element. Each of the magnetic sensors further includes two magnetic convergence plates arranged at both ends of the magnetoresistive element, and the magnetoresistive element is disposed at a position sandwiched between the two magnetic convergence plates. , the measuring device according to claim 14. The measuring device according to claim 15, wherein a coil for generating the feedback magnetic field is wound so as to surround the magnetoresistive element and the two magnetic convergence plates. Further comprising a plurality of AD converters that convert the outputs of the plurality of magnetic sensor cells from analog to digital and output the plurality of measured values,
The measuring device according to any one of claims 1 to 16, wherein the plurality of AD converters perform AD conversion according to a common sampling clock. The object of measurement is the cardiac magnetism generated by the electrical activity of the animal's heart.
The measuring device according to any one of claims 1 to 17, wherein the magnetic field is measured based on a calculation result of the magnetic field calculating section.

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