JPH02218979A - Measuring apparatus for magnetic field - Google Patents

Abstract

PURPOSE:To enable removal of a noise component due to a uniform magnetic field by providing a first magnetic-field measurer, a mechanism for setting a correction coil and the inclination to the plane thereof, a second magnetic-field measurer, an output amplifier therefor and a comparing-subtracting means for first and second outputs. CONSTITUTION:A first magnetic-field measurer 10 using a differential-type coil LD as a pickup coil, measuring a magnetic field to be measured and outputting a signal proportional to a magnetic flux intersecting said magnetic field, a mechanism 30 for setting a correction coil Lc and the inclination of the plane thereof rotatably, a second magnetic-field measurer 20 using the coil Lc as the pickup coil and outputting a signal proportional to a magnetic flux intersecting this coil and an amplifier 1 setting an output of this measurer at a prescribed value, and also a means 2 for subtracting an output of the amplifier 1 from the output of the measurer 10, are provided. The direction of the normal line of the plane of the coil Lc is aligned with the direction of the normal line of the plane of an equivalent coil in respect to a uniform magnetic field of the coil LD by the mechanism 30, and thereafter the coil LD is disposed near a magnetic field source to be measured, while the coil Lc is disposed apart from the source. Then the magnetic field to be measured is hardly inputted to the coil Lc and only a component obtained by removing a noise component due to the uniform magnetic field from the output of the measurer 10 can be outputted.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a magnetic field measuring device, and the present invention relates to a magnetic field measuring device that uses a differential pickup coil, with the purpose of removing noise components due to a uniform magnetic field. - A first magnetic field measuring device that uses a coil, a correction coil, a setting mechanism that freely sets the inclination of the surface of the correction coil, and a second magnetic field measuring device that uses the correction coil as a pickup coil. and an amplifier for setting the output of the second magnetic field measuring device to a predetermined value;
subtracting means for subtracting the output of the amplifier from the output of the magnetic field measuring device, and setting the slope of the surface of the correction coil to the slope of the equivalent coil surface with respect to the uniform magnetic field of the differential coil,
The amplifier is set so that the outputs of the first and second magnetic field measuring devices for a uniform magnetic field are the same, and the noise component due to the uniform magnetic field is extracted from the measured value of the magnetic field to be measured obtained by the differential coil. Configure to remove.

[Industrial application field]

The present invention relates to an improvement in a magnetic field measuring device that removes external magnetic field noise components.

In recent years, SQUID (
Highly sensitive magnetic field measuring devices using superconducting quantum interferometers (superconducting quantum interferometers) are in use, but because they measure extremely small magnetic fields, the influence of external magnetic fields has become a problem.

The main sources of external magnetic field noise include geomagnetism, trains, elevators, computers, and other electrical equipment, but these sources are located much further away than the source of the magnetic field to be measured. Therefore, the external magnetic field noise can be regarded as a uniform magnetic field whose magnitude and direction hardly change depending on the location near the magnetic field source to be measured.

Taking advantage of this, in order to remove external magnetic field noise components, a first-order differential coil or a second-order differential coil or a second
Differential type coils such as second-order differential type coils are used, but there remains the problem that noise components caused by a uniform magnetic field cannot be sufficiently removed due to manufacturing errors in the pickup coil.

[Conventional technology]

FIG. 8 is a block diagram of a conventional magnetic field measuring device, and FIG. 9 is an explanatory diagram of a conventional noise removal method.

In the conventional magnetic field measurement apparatus, a first-order differential coil as shown in FIG. 8 is used as the pick amplifier coil L1 in order to remove noise caused by an external uniform magnetic field.

Although not shown, various types of differential coils, such as a second-order differential coil and a third-order differential coil, are used to remove noise caused by a uniform gradient magnetic field.

These pickup coils and the input coil L2, which is magnetically coupled to the SQUID S1, which is a highly sensitive magnetic sensor, are made of superconducting material and constitute a superconducting loop.

In Fig. 8, the magnetic field H is a first-order differential type pickup.
When input to coil L1, a current proportional to Φ cancels out the magnetic flux Φ flowing through pickup coil L1 and input coil L2.
A positive magnetic flux Φ proportional to the magnetic flux Φ flows from the input coil L2 to the Squid S.

The magnetic flux Φ□ applied to the SQUID S1 is detected by the SQUID S, and its output is processed by the magnetic field measuring circuit 11 to output a signal v0 corresponding to the SQUID magnetic flux Φ. This signal ■. ■ in the current conversion circuit 12. The feedback coil 3 is converted into a current proportional to and is magnetically coupled to the SQUID S1.
from input coil L2 to SQUID S1.
The magnetic flux is fed back in the direction of canceling the magnetic flux Φ1 input to the magnetic flux Φ1, and the magnetic flux Φi1 and therefore the magnetic field H are measured using the null method, and a signal proportional to the magnetic field H is output to the output terminal of the magnetic field measuring circuit 11. .

Here, using a −th order differential pickup coil as an example,
An equivalent coil for a uniform magnetic field of a differential type pickup coil (hereinafter referred to as a differential type coil) will be explained.

A H
, n 1 and Az, nz&, the magnetic flux Φ that the uniform magnetic field ■ intersects with the -th differential type coil is Φ-(A+n+・H
) + (A2 stone: >> (1). Here, the value in parentheses represents the scalar product.

In order for this Φ to become zero, At jl, =-Az nz
(2) is sufficient. That is, it is sufficient if the two coils have the same area and the normal directions of the surfaces are exactly opposite.

However, since the actually manufactured one includes manufacturing errors, the equation (2) is not satisfied and an output is output from the first-order differential coil even in response to a uniform magnetic field. Now A z = A + +ΔAX nz= (n++A
n), Bunraku magnetic flux Φ is Φ=(At n+・T) −((AI +ΔA)[n,+τn]・■)=(A
τn+ΔA n +An ・T) (3
). Since the underlined part in equation (3) indicates one vector quantity, if the magnitude of this vector is A and the unit vector in that direction is Wo, equation (3) can be written as follows.

Φ=(A, Ding.・H) (4)
This is equal to the magnetic flux produced by a uniform magnetic field in a coil whose area is A and whose normal direction is oriented in the -b-0 direction.

Therefore, for a uniform magnetic field, if the two coils that make up the −th differential type coil do not satisfy equation (2), the area will be 80, and the normal to that surface will be in the direction −n, It is equivalent to a coil oriented in the direction of , and is sensitive to a uniform magnetic field.

For other types of differential coils, if there is a manufacturing error, they will be equivalent to one coil having a certain area and a certain plane orientation, as described above.

The area A of the actually manufactured coil usually has an error of about 0.1% or more, and there is also an error in the parallelism between each coil surface, so noise due to these external magnetic fields is It can be reduced only to about 1/1000 at most.

Therefore, as shown in Figure 9 (1), the sensitivity of each of the three superconducting tabs 7 (thin plates with small area) changes only in one of the three axial directions perpendicular to each other. The position of these superconducting tabs 7 can be adjusted to change the magnetic field distribution, or the magnetic field distribution can be changed as shown in FIG. 9 (II).
As shown in FIG. 2, by providing three correction loops 9 whose surfaces are perpendicular to each other and shifting the position of the superconducting tab 8 to adjust the amount of magnetic shielding of that surface by the superconducting tab 8, The unbalance of the coil due to this manufacturing error is corrected.

[Problem to be solved by the invention]

In the conventional method shown in Figure 9N)(n), a uniform alternating current magnetic field is applied from the outside in each axis along the normal direction of each surface of the three superconducting tabs and the three correction loops. In addition, since adjustments are made sequentially to minimize the magnetic field measuring device, there is a problem in that the adjustment is quite troublesome.

In addition, the normal directions of the surfaces of the three superconducting tabs and the three correction loops must be exactly perpendicular to each other, but since manufacturing errors still exist, it is necessary to If you adjust so that there is no output in response to a uniform magnetic field, the output may increase in response to uniform magnetic fields in other axial directions.
Although the same adjustment is repeated to minimize the noise output, there is still a drawback that the noise component caused by the uniform magnetic field cannot be sufficiently removed.

In addition, the normals of the three correction coils are X and Y, respectively.
A method has been devised (Japanese Unexamined Patent Publication No. 63-32384) to eliminate noise caused by a uniform magnetic field by arranging the magnetic field so as to face the Z direction.
The normal lines of the surfaces of the three correction coils are exactly orthogonal to each other, and the direction of the uniform magnetic field applied from the outside during adjustment is
Although it is necessary to accurately match one of the normal directions, errors are likely to occur in the direction of the coil surface and the direction of the uniform magnetic field, and even if the same adjustment is repeated many times, It has the disadvantage that noise caused by a uniform magnetic field cannot be sufficiently removed.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a method that can more easily and reliably remove noise caused by a uniform magnetic field caused by unbalance of a differential pickup coil.

[Means to solve the problem]

FIG. 1 is a diagram explaining the principle of the present invention. In the figure, 10 is a first magnetic field measuring device that measures the magnetic field to be measured using a differential coil L as a pickup coil, which outputs a signal proportional to the magnetic flux applied to LI, and L is a correction coil. , 30 is a correction coil, and a setting mechanism for rotatably setting the inclination of the surface of the magnetic field, 20 is a second magnetic field measuring device in which the correction coil Lc is a pink amplifier coil, and a signal proportional to the magnetic flux to be sent to Lc is 1 is an amplifier that sets the output of the second magnetic field measuring device 20 to a predetermined value; 2 is a subtracting means that subtracts the output of the amplifier 1 from the output of the first magnetic field measuring device 10. It is something to do.

Weight→[Effect] The setting mechanism 30 sets the normal direction of the plane of the correction coil L to the equivalent coil (
LD) to match the normal direction of the surface.

This normal direction is determined as follows. (See Figure 3) In other words, a uniform alternating current magnetic field H is applied sequentially in the three orthogonal directions of X, Y, and Z.
, H, and H yo are added, the outputs of the first magnetic field measuring device 10 using the differential coil LD as a pickup coil are V, , Va, and ■2, respectively.

The unit vector in the normal direction of the surface of the equivalent coil L0 is -
Then, a (n-iHx) = VX a (n-Hy) = Vy a (n-kH,) = V,
(5) becomes. Here, a is a constant determined by the degree of manufacturing error of the differential coil Lo and the circuit characteristics of the magnetic field measuring device 10, and V and V represent unit vectors in the x, y, and z axis directions, respectively. Also, the number in parentheses represents a scalar product. Therefore, the X below
, each component nX in the Y and Z axis directions.

n,, n, becomes ・ ・ ・ (6). Correction coil L in the direction of T shown by equation (6)
When the cO normal direction is set, the output of the second magnetic field measuring device 20, which uses the correction coil Lc as a pickup coil, is the differential coil L for a uniform magnetic field. is multiplied by a coefficient of the output of the first magnetic field measuring device 10 caused by manufacturing errors.

For this reason, a correction coil and a differential coil LD are used.
A uniform magnetic field is applied to the magnetic field, and the gain of the amplifier 1 is adjusted so that the output of the second magnetic field measuring device 20 after amplification by the amplifier 1 is equal to the output of the first magnetic field measuring device 10.

After making the settings as described above, place the differential coil near the magnetic field source to be measured, the correction coil and place it at a position optically separated from the magnetic field source to be measured compared to the differential coil LD. Almost no measured magnetic field (Hs) is input to the correction coil Lc, and only the measured magnetic field component from which the noise component due to the uniform magnetic field has been removed from the output of the first magnetic field measuring device 10 is outputted from the subtraction means 2. .

〔Example〕

Figure 2 is a block diagram of the magnetic field measuring device of the first embodiment;
5 is a diagram showing an example of a setting mechanism, FIG. 5 is a diagram showing a second embodiment, FIG. 6 is a diagram showing a third embodiment, and FIG. 7 is a diagram showing a fourth embodiment.

(First Embodiment) In FIG. 2, Lc is a correction coil, 20 is a second magnetic field measuring device (hereinafter referred to as magnetic field measuring device 20), and magnetic field measuring circuit 21. It is equipped with a current conversion circuit 22 and a SQUID S2, and outputs a signal proportional to the magnetic flux crossing the correction coil Lc in the same manner as the conventional example, Lo is a differential type coil, and 10 is a first magnetic field measuring device ( Hereinafter, the magnetic field measuring device 10) will be referred to as the magnetic field measuring circuit 11. Current conversion circuit 12 and SQUID S
1 is an amplifier with variable gain, and 4 is a differential amplifier (corresponding to the subtracting means 2). So, magnetic field measuring device 1
30 is a setting mechanism that sets the slope of the correction coil L.

As shown in FIG. 4, the setting mechanism 30 includes a circular ring 3 having its center at the origin of the coordinate axes and rotating around the Z axis.
1, and a circular ring whose center is at the origin of the coordinate axes, rotates around a straight line passing through two points A and B where the xY plane intersects the circular ring 31, and whose diameter is smaller than the diameter of the circular ring 31. 32, circular scale plates 33 and 34 having a diameter slightly larger than the diameter of the circular ring 31 and the circular ring 32 and fixed on the xY plane and the Xz plane, respectively, and a correction coil, is circular ring 3
It is fixed in a plane parallel to the plane of 1.

The circular ring 32 is rotatably fixed to the circular ring 31 at point AB, and after the rotation is set, the relative positions of the circular rings 31 and 32 are maintained by friction or a fixing mechanism.

Further, the setting mechanism 30 provided with the correction coil Lc and the differential type coil L are fixed at intervals such that the magnetic field to be measured hardly acts on the correction coil, and so that their relative positions do not change.

In the magnetic field measuring device having the above configuration, first, the unit vector T in the normal direction to the surface of the equivalent coil L0 with respect to the uniform magnetic field of the differential coil LD is determined by the following method.

With the coordinate axes of the setting mechanism 30 as a reference, uniform magnetic fields H, H, , H, are sequentially applied in the orthogonal three axes directions of x, y, and z, and the output of the magnetic field measuring device 10 in each direction is measured. VX, V,,
Measure V.

By substituting these values into the above equation (6), the x, y, and z axis components nx + "V + n* of the unit vector T are determined.

Next, as shown in Figure 3, if the angle formed by the plane containing the 7 and Z axes and the plane containing the X and Z axes is φ, and the angle between n- and the Z axis is θ, then the direction of i is is n8nV + nt
can be represented by φ and θ instead.

φ and θ can be determined from the values of n, , n, :n, using equation (7).

To set the normal direction of the correction coil to the direction shown by equation (7), first set the circular ring 31 on the YZ plane and the circular ring 32 on the XY plane, and then set the circular ring 32 on the YZ plane. While looking at the circular scale plate 34, it is rotated by an angle θ around the AB axis (at this time, the AB axis overlaps with the Y axis). Next, while maintaining the relative positions of the circular rings 31 and 32, the rotation is completed by rotating around the Z-axis by an angle Φ while looking at the circular scale plate 33.

After setting Lc, make the equivalent coil again as much as possible,
The adjustment is completed by setting the gain of the amplifier 1 so that the output of the differential amplifier 4 becomes zero while applying an alternating current uniform magnetic field in a direction close to the normal direction of the plane.

As a result of the above, the differential type coil is created. As long as the relative position between and the correction coil Lc is maintained, a value obtained by removing the noise component of the uniform magnetic field from the measurement value obtained by the differential coil L0 will be obtained from the output of the differential amplifier 4. .

(Second example) FIG. 5 shows a second embodiment of the invention.

A correction coil is used, and the normal direction of the surface is differentiated by a differential coil L.
Set in the direction opposite to the normal direction of the plane of the equivalent coil with respect to the uniform magnetic field D, so that the polarity of the output of the magnetic field measuring device 10 and the output of the magnetic field measuring device 20 is opposite to the uniform magnetic field,
Both outputs are connected to perform addition by an adder consisting of an operational amplifier 5 and resistors R, , R2, and R8, and R is varied to remove noise components due to the uniform magnetic field.

(Third example) FIG. 6 shows a third embodiment of the present invention.

The correction coil Lc is set in the same manner as in the first embodiment, and a current proportional to the output of the amplifier 1 flows into the coil L4, which is magnetically coupled to the differential coil L0, through a resistor R4, and a uniform magnetic field is applied to L. The noise component due to the uniform magnetic field is removed by adjusting the gain of the amplifier 1 so that the magnetic flux of .

(Fourth example) FIG. 7 shows a fourth embodiment of the present invention.

A current proportional to the output of the amplifier 1 is caused to flow from the current converter 6 into the feedback coil L3 of the magnetic field measuring device 10,
By adjusting the gain of the amplifier 1, the uniform magnetic field cancels out the magnetic flux flowing from R3 to SQUID S1, and removes the noise component due to the uniform magnetic field.

Although the setting mechanism 30 has a circular ring that rotates around the Z-axis and the Y-axis, it goes without saying that the circular ring may rotate around other axes.

〔Effect of the invention〕

As explained above, according to the present invention, adjustment is performed only by setting the direction of the surface of one correction coil and setting the amplification degree of the amplifier. Adjustment imperfections caused by manufacturing errors such as superconducting tabs, three correction rings or three correction coils are eliminated. Further, there is no need to go back to the adjustment, and it is possible to eliminate noise caused by a uniform magnetic field by adjusting only once according to the adjustment procedure.

4 shows an example of a setting mechanism, FIG. 5 shows a second embodiment, FIG. 6 shows a third embodiment, and FIG. 7 shows a fourth embodiment. 8 is a block diagram of a conventional magnetic field measuring device, and FIG. 9 is an explanatory diagram of a conventional noise removal method.

In the figure, 1 is an amplifier, 2 is a subtraction means, 4 is a differential amplifier, and 5
is an operational amplifier, 6 is a current conversion circuit, 7 and 8 are superconducting tabs, 9 is a correction loop, 10 is a first magnetic field measuring device, 20
12. is a second magnetic field measuring device; IL21 is a magnetic field measuring circuit; 12.
22 is a current conversion circuit, SL and SZ are SQUIDs, LD is a differential type coil, L is a correction coil, L+ is a pickup coil, 30 is a setting mechanism, 31.32 is a circular ring,
33 and 34 are circular scale plates, and R2-R4 are resistors.

[Brief explanation of the drawing]

Fig. 1 is a principle diagram of the present invention, Fig. 2 is a block diagram of a magnetic field measuring device according to an embodiment, Fig. 3 is an explanation of the equivalent coil surface. Fig. 1 is an illustration of the equivalent coil surface. Block diagram of an example magnetic field measuring device FIG. 2, FIG. 4, and FIG. 5 W. Conventional magnetic field 4 anti-corrosion W block diagram Figure 8 (n) Illustration of conventional noise removal method

Claims (1)

[Claims] A first magnetic field measuring device (10) using a differential coil (L_D) as a pickup coil, a correction coil (L_C), and a surface inclination of the correction coil that is freely set. Setting mechanism (
30), a second magnetic field measuring device (20) that uses the correction coil as a pickup coil, and an amplifier (1) that sets the output of the second magnetic field measuring device (20) to a predetermined value; From the output of the first magnetic field measuring device (10) to the amplifier (1
), the inclination of the surface of the correction coil (L_C) is set to the inclination of the equivalent coil surface with respect to the uniform magnetic field of the differential coil (L_D), and the uniform magnetic field is said first and second
the amplifier (1) so that the outputs of the magnetic field measuring instruments are the same.
1. A magnetic field measuring device characterized in that a noise component due to a uniform magnetic field is removed from a measured value of a magnetic field to be measured obtained by the differential coil by setting the differential coil.