JPS6293675A - Apparatus for compensating magnetism - Google Patents

Abstract

PURPOSE:To measure a compensated external magnetic field without using a compensating coil,by providing a subtraction circuit and compensating the induction magnetic field, permanent magnetic field and eddy current magnetic field generated from a vehicle itself according to a predetermined vector formula. CONSTITUTION:Three low sensitivity fluxmeters 1 detect an external magnetic field E in formula. Herein, HP, A and B in the formula are a constant and stored in a constant memory part 2. A noise quantity calculation circuit 3 takes in the value of the external magnetic field E and calculates the value D represented by the above mentioned formula. A subtraction circuit 5 takes in the output signal of a high sensitivity magnetometer and subtracts the calculated noise quantity to output a compensated magnetometer signal. By this constitution, a compensating coil is not required and an axial alignment process in the compensating coil becomes unnecessary.

Description

[Detailed description of the invention] Natsushina Nagibun by Shuawa ■ This invention detects disturbances in the earth's magnetic field by installing a magnetic detector on an aircraft, thereby compensating for disturbances in the earth's magnetic field caused by the aircraft itself when searching for shipwrecks, etc. The present invention relates to a magnetic compensation device used for the purpose of

In general, noise magnetic fields generated from the vehicle itself include permanent magnetic fields, induced magnetic fields, and eddy current magnetic fields.

Permanent magnetic fields are generated by steel parts of the vehicle itself, induced magnetic fields by soft iron parts, and eddy current fields by electrical conductors.

Therefore, the noise magnetic field from the vehicle itself sensed by a highly sensitive magnetometer mounted on the vehicle to measure the magnetic field is expressed as follows.

First, it is assumed that the permanent magnetic field in the magnetometer detection section is Hp, the induced magnetic field is H4, and the eddy current magnetic field is He. Here, the permanent magnetic field H
p, the induced magnetic field Hi, and the eddy current magnetic field He are all three-dimensional vector quantities.

Since the permanent magnetic field is generated because the vehicle itself is semi-permanently magnetized, ■■p is constant.

The induced magnetic field is such that when an object that is easily magnetized is placed in an external magnetic field, it will be magnetized in that direction in proportion to the magnitude of the external magnetic field, so Hi = AE
It is expressed as ・ ・ ・■. Here, E is a three-dimensional vector representing the external magnetic field, and A is the vehicle-specific 3×
It is a 3 constant matrix. In addition, an eddy current magnetic field is one in which a current flows in a conductor in response to a change in an external magnetic field, generating a secondary magnetic field, and its magnitude is proportional to the rate of change over time of the external magnetic field. It is expressed as He=B・dE/dL −・−■. Here, dE/dt is the time differential of the external magnetic field E,
B is a vehicle-specific 3×3 constant matrix.

Therefore, if the noise magnetic field of the vehicle itself in the magnetometer detection section is Hn, In is expressed as Hn=I(p + AE + B - d E/di...■. Here, Hn is a three-dimensional vector. .

In the conventional system, a compensating coil generates a magnetic field of the same magnitude as Hn and in the opposite direction, and the magnetic field is applied to the magnetometer detection section to compensate for the noise of the vehicle itself.

The above conventional method will be explained with reference to the drawings.

In Figure 2, ■ indicates three orthogonal low-sensitivity magnetometers, 2
3 is a constant storage unit, 3 is a noise magnetic field calculation circuit that calculates a noise magnetic field based on the output of the low-sensitivity magnetometer 1 and the output of the constant storage unit 2, 4 is a compensation coil drive circuit, and 5 is 3 ([1i1
6 is a high-sensitivity magnetometer.

Here, the low-sensitivity magnetometer 1 detects the external magnetic field E in equation 0. However, Hp, A, and B in the formula 0 are constants and are stored in the constant storage section 2.

The noise magnetic field calculation circuit 3 takes in the output of the low-sensitivity magnetometer 1, that is, the value of the external magnetic field E, and calculates H n expressed by the formula (2). The compensation coil drive circuit 4 converts this value into a current, and the compensation coil 5 generates a magnetic field. High sensitivity magnetometer 6
detects the vector sum of the magnetic field generated by the vehicle itself and this compensation magnetic field, so it measures the compensated external magnetic field.

In the conventional method, it is necessary to align the three low-sensitivity magnetometers and the compensation coil with each other, and the accuracy of this alignment is limited by the performance of noise compensation. There is a problem in that while it has a direct effect on the alignment, it is difficult to ensure the accuracy of the axis alignment.

The present invention was devised in view of the above-mentioned circumstances, and an object of the present invention is to provide a magnetic compensation device that does not use the conventionally required compensation coil and therefore does not require axis alignment or the like.

The present invention is a magnetic compensation device that includes a subtraction circuit and compensates for an induced magnetic field Hi, a permanent magnetic field Hp, and an eddy current magnetic field He generated from a vehicle itself, in which a 3×3 constant matrix is , B. This magnetic compensation device performs compensation by electrically subtracting the value calculated when a three-dimensional vector is E from the signal of the high-sensitivity magnetometer using the subtraction circuit. .

A dish subtraction circuit subtracts the above D from the signal of the high-sensitivity magnetometer.

Since the high-sensitivity magnetometer detects the absolute value of the magnetic field, if the amount of noise from the vehicle itself detected by this magnetometer without compensation is D, then D=E-Hn/E.
...■That is, it is expressed as.

Here, . is an inner product, E is an absolute value of E, and D is a scalar quantity. The present invention compensates for the vehicle's own noise by subtracting the above values from a sensitive magnetometer. A detailed explanation will be given below based on a circuit diagram.

In Figure 1, 1 indicates three orthogonal low-sensitivity magnetometers, 2
3 is a constant storage unit, 3 is a noise amount calculation circuit, 4 is a high-sensitivity magnetometer, and 5 is a subtraction circuit.

The low sensitivity magnetometer 1 of the 3111i1 detects the external magnetic field E in the 0 type. Further, Hp, A, and B in the formula 0 are constants, and these are stored in advance in part 9 2 where the constants are written. The noise amount calculation circuit 3 takes in the value of the external magnetic field E and sets it to 0.
Calculate D expressed by the formula. - The subtraction circuit 5 takes in the output signal of the high-sensitivity magnetometer, subtracts the calculated amount of noise, and outputs a compensated magnetometer signal. With the configuration described above, a compensated external magnetic field can be measured.

As described above, according to the present invention, Hp, A, and B are stored in the constant storage section in advance, and after the noise amount calculation circuit takes in the value of the external magnetic field, the output is input to the subtraction circuit, the output signal of the high-sensitivity magnetometer is taken into the -yen subtraction circuit, the amount of noise is subtracted, and the output is output as a compensated magnetometer signal, so ? 1li (does not require an R coil. Therefore, of course, the process of aligning the axis of the compensation coil is not required, and as a result, a magnetic compensator with high compensation performance can be obtained.

Furthermore, since there is no compensation coil, it is possible to reduce the weight and size of the entire magnetic compensation device.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the system according to the present invention, and FIG. 2 is a block diagram of the conventional system. 1...Low sensitivity magnetometer, 2...Constant storage unit, 3...
Noise amount calculation circuit, 4...high sensitivity magnetometer 5...subtraction circuit. Patent applicant: Toru Ryoshita, Director General, Technology Research Headquarters, Defense Agency

Claims (1)

[Claims] (1) Induced magnetic field Hi, permanent magnetic field H generated from the vehicle itself
p, a magnetic compensation device for compensating an eddy current magnetic field He,
If A and B are 3×3 constant matrices and E is a three-dimensional vector, then D=1/|E|{E・[Hp+AE+B(dB/dt)
]} A magnetic compensation device characterized in that compensation is performed by electrically subtracting a value D calculated from a signal of a high-sensitivity magnetometer.