JPS594671B2 - Magnetic field vector detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic field measurement method for precisely measuring a uniform magnetic field vector in the vicinity of a local magnetic field generator such as a magnetized body.

When measuring a uniformly distributed magnetic field vector at a location where a local magnetic field exists, such as near a magnetized object, generally speaking, if the vector of the local magnetic field at the measurement point is not known, the influence of the local magnetic field cannot be calculated from the measured value. It cannot be deleted.

Therefore, when measuring a uniform magnetic field, it is necessary to separate the local magnetic field beforehand and measure it, or to select a location sufficiently distant from the local magnetic field generator as the measurement point. However, both of these methods are often difficult to achieve, and it has been considered impossible to accurately measure magnetic field vectors under these conditions. The present invention enables accurate measurement of a uniform magnetic field vector under the above conditions regardless of the magnitude of the local magnetic field, and will be described in detail below with reference to the drawings.

Figure 1 is a sketch showing the positional relationship between a magnetized body or a local magnetic field generating body generated by magnetic induction, current, etc. (hereinafter simply referred to as a magnetized body) and a plurality of magnetic field detection points in the vicinity. Cartesian coordinate system for indicating the position of the detection point, 3, 4
, 5 indicates an arbitrary number of detection points (the case of three points will be explained below), and 6, 7, and 8 indicate magnetic field vectors caused by the magnetized body 1 at each detection point.

Here, if we consider the magnetized body 1 as a collection of magnetic dipoles, the nearby magnetic field due to the magnetized body 1 generally shows a complicated distribution, so in order to make the magnetic fields at all nearby points equal, Although an infinite number of pairs of magnetic dipoles are required, by limiting the number of detection points, the number of equivalent magnetic dipoles can also be limited. Figure 2 is a perspective view showing the limited equivalent magnetic dipole and the position of the magnetic field detection point to explain the above.
, y are the X component magnetic dipoles with sizes +mx, -mx and located symmetrically to the Z axis in the XY plane, 10, 1σ are the sizes +mY, -mY and symmetrically to the X axis in the YZ plane The Y-component magnetic dipoles 11 and 11' located at the position have a size of +m2
, -m2 indicate a Z component magnetic dipole located symmetrically to the Y axis in the ZX plane.

The X-direction component of the magnetic field vector at each detection point by the magnetic dipoles arranged in this way is determined only by the X-component magnetic dipole, and similarly, the Y- and Z-direction components are separated by the Y- and Z-component magnetic dipoles, respectively. Determined by Therefore, one of these components will be explained in detail below. Figure 3 shows the X-direction magnetic field vector due to the X-component magnetic dipole, and 1
2, 13, and 14 are the X of magnetic field vectors 6, 7, and 8, respectively.
is the component magnetic field vector.

Let each detection point be A, b, c, respectively, and the distance from A, b, c to each magnetic pole is 1x, n, x1x, n, x1, respectively.
x, the distance from the origin to a is Z, and the distance from the origin to the magnetic pole is X, the magnitude of the X-direction magnetic field EaX, ebX, and ecx due to the equivalent magnetic pole at each detection point is given by each.

However, the distances from a to b and c are D1 and D,
shall be. If the X-direction magnetic fields given by the actual magnetized body 1 to each detection point are Hax, hbx, and hcx, respectively, then the positions X and Z of the magnetic poles and their size Mx are such that EaX:HaX9ebXゞHbXPeCXゞHcx. If this can be determined, the magnetized body 1 can be replaced with the above magnetic dipole pair.

Here 1haX/HbXゝn'1x3! Hax/Hc
x n'2
X/EbX=NlX3, [1] From formula [3], EaX
/ECX=N2X3, so N,X=n'IX,
If there exists a magnetic pole position where n,X=n'2X, the above replacement becomes possible.

FIG. 4 is an explanatory diagram to clarify these relationships. As is clear from the figure, when n'IX is given to detection points A and b, n'IX becomes two points A and B. Since it is the ratio of the distance from Ab, the position of the magnetic pole is the locus of the point where the ratio of the distance from Ab is a constant value n/IX, that is, the center is A
, b, and on the circumference of circle 15 passing through the two points that divide A and b internally and externally. From the above, it can be seen that the intersection point 1T of both circles is the position of the equivalent magnetic pole with respect to the detection points A, b, and c.

The same holds true for the positions of the Y and Z component magnetic poles. For example, in the case of the Z component, the distances from points A, b, and c to the center of the Z component magnetic dipole are Z, Z + D, respectively.
.
, the Z-direction magnetic fields eo, EbZ, eCZ due to the Z-component magnetic dipole at point c are respectively, and if the magnetic fields at each point due to the magnetized body 1 are Haz, hbz, hcz, then 1eaZゞHaZPebZゞHbZ! The Z-component equivalent magnetic dipole is given as the values of NlZ, Z, and Mu that simultaneously satisfy ECZ:Hcz.

Also, the size m of the magnetic pole is calculated from the formula [1], Mx=Eaxl3x
/ 2 = Haxl3x/2. It has been shown above that the equivalent magnetic dipole can be determined when the magnetic field is applied by the magnetized body 1 at each detection point, but when a magnetic field detector is placed at each detection point, the output of the detector is equal to the magnetic field caused by the magnetized body 1. Since it is the sum of the magnetic fields to be measured, it is not possible to separate and detect only the magnetic field caused by the magnetized body 1. In order to separate this, it is necessary to have at least three observed values for the three unknowns Mx, X, and Z under conditions that do not include the uniform magnetic field component. Figure 5 shows an example of separating the two.
Shows the arrangement of a magnetic field detector to find the differential coefficient of the magnetic field,
3 indicates the position of the magnetic field detection point a, and 18 and 19 indicate the positions of the magnetic field detectors 1 and a', respectively, which are placed a distance Z apart from the point a.

I, a' are magnetic field detectors that provide outputs proportional to each axial component (in this case, the X axis) of the magnetic field vector at that point. By arranging the detectors in this way, the magnetic field vector at point a can be calculated from the sum of the output signals of both detectors.
The differential coefficient of the magnetic field at point a in the Z-axis direction can be determined from the difference signal and the magnitude of 8Z. [1], [2], [3]
] When the equation is differentiated, it becomes, and given the differential coefficient of the magnetic field at each detection point, M, X, Z or NlX, n,
Also, from equations [1], [2], and [3], EaX, ebX
, eCX can be obtained.

If the uniform magnetic field to be measured is Hx, the values of Eax+Hx, ebx+Hx, and ecx+Hx are measured at each detection point, so by subtracting the local magnetic field component obtained by the above method from these arbitrary measured values, , the uniform magnetic field component can be determined. In addition, the magnetic field components are determined using the same method for the Y-direction component and the Z-direction component of the magnetic field, that is, the three equations obtained by differentiating equations [4], [5], and [6] are obtained at the three detection points. Substituting the differential coefficient obtained by R
By determining r]Z, Z, and mu, a three-dimensional magnetic field vector is determined.

In addition, instead of placing two detectors at each of the three detection points as shown in Figure 5 and finding the differential coefficient of the magnetic field at each point, three detectors are placed at each detection point, By approximating as (D,,Dl《holds when Z)
By finding the ratio of the difference Ab between the detector outputs at points A and b and the difference Ac between the detector outputs at points A and c, NlX, n, and X can be determined directly from the equations be able to.

The method for detecting a uniform magnetic field when both the local magnetic field distribution and its magnitude are unknown has been described above, but when the magnetic field distribution is fixed and only its magnitude is unknown, 1
The local magnetic field can be easily canceled using a set of magnetic field detectors.

In Fig. 3, if magnetic field detectors are placed at detection points A and b,
The difference between the outputs (Eax+Hx) and (EbX+Hx) of both detectors is obtained from formulas [1] and [2], and if the magnetic field distribution is fixed, the value of NlX will be a constant value, so this value is known. In this case, Hx can be obtained from the magnetic field detector output (Eax+Hx) at point a by subtracting Eax by 1 as Eax=mu/(1-NlX-).

The same applies to the Y and Z components. As explained above, according to the method of the present invention, it is possible to measure magnetic fields near local magnetic field generators whose magnetic field distribution and magnitude are unknown. Even in places where magnetic bodies or electric currents exist, precise three-dimensional orientation can be determined using the geomagnetic vector as a standard.

[Brief explanation of the drawing]

Figure 1 is a perspective view of a three-dimensional coordinate system showing a magnetized body, multiple magnetic field detection points, and the magnetic field vector at each detection point by the magnetized body, and Figure 2 is a perspective view of a three-dimensional coordinate system showing the position of an equivalent magnetic dipole. A perspective view, Figure 3 is an XZ plan view of Figure 2, Figure 4 is an explanatory diagram for determining the position of the equivalent magnetic dipole, and Figure 5 is an explanatory diagram showing the positional relationship between the magnetic field detection point and the magnetic field detector. It is. 1... Magnetized body, 2... Three-dimensional rectangular coordinate system, 3, 4, 5... Magnetic field detection point, 6, 7,
8...Magnetic field vector due to magnetized body 1, 9,9'
...X component equivalent magnetic dipole, 10,10'...
...Y component equivalent magnetic dipole, 11,11/... ・
・Z component equivalent magnetic dipole, 12, 13, 14...
・X component magnetic field vector due to equivalent magnetic dipole, 15...
... Locus of an equivalent magnetic dipole that satisfies the conditions of detection points 3 and 4, 16... Locus of an equivalent magnetic dipole that satisfies the conditions of detection points 3 and 5, 17... ...Detection point 3,
The position of the equivalent magnetic dipole that satisfies the conditions of 4 and 5, 18,
19...Position of the magnetic field detector with respect to detection point 3.

Claims (1)

[Claims] 1. In the measurement of a uniform magnetic field in the vicinity of a local magnetic field generator, a method having a plurality of magnetic field detection points constituted by a plurality of magnetic field detectors and using the difference in the output signals of the detectors. A magnetic field vector detection method characterized by determining the position and size of a magnetic dipole equivalent to a local magnetic field generator and eliminating the local magnetic field component. 2. In the case where the magnetic field distribution is fixed and only its magnitude is unknown, the local magnetic field component is canceled by using the difference between the output signals of a pair of magnetic field detectors. The magnetic field vector detection method described in item 1.