JPH07229955A - Increment magnetic permeability measuring apparatus for magnetic steel plate - Google Patents

Abstract

PURPOSE:To measure an increment magnetic permeability of a larger magnetic steel plate, for example, a PC parmaloy plate used for a magnetic shielding room in the form of an original plate. CONSTITUTION:This apparatus is provided with a coil 2 for excitation which is inserted into a magnetic steel plate 1 to generate a magnetic field with the energization of an alternating current, at least two magnetic field detectors 4a and 4b arranged between the magnetic steel plate and the coil 2 for excitation at different distances from one face of the magnetic steel plate 1, a coil 3 for detecting magnetic flux arranged crossing the magnetic steel plate 1 to detect a magnetic flux passing through the magnetic steel plate 1 and an arithmetic device which determines the intensity of the magnetic filed in the magnetic steel plate 1 from output signals of the plurality of magnetic field detectors 4a and 4b and obtains an increment magnetic permeability of the magnetic steel plate 1 from the value and the flux density of a magnetic flux passing through the magnetic steel plate 1 gained from the output signal of the coil 3 for detecting the magnetic flux.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for measuring the incremental magnetic permeability of a large magnetic steel plate, which is capable of measuring the incremental magnetic permeability of a large magnetic steel plate such as a PC permalloy plate used in a magnetically shielded room as it is. It relates to the device.

[0002]

2. Description of the Related Art The shielding performance of a magnetically shielded room against fluctuating magnetic fields is determined by the incremental permeability of magnetic steel sheets used for the side walls. Therefore, it is extremely important to measure and control the incremental magnetic permeability in the steel plate manufacturing process. On the contrary,
The measurement and management of the magnetic permeability of a steel sheet have been conventionally performed by the method specified in JISC2531. This is to measure the initial permeability by a small ring piece that follows the same manufacturing process of the product steel sheet.

However, the method of JIS C2531 has the following problems. 1) This is a measurement method of the initial magnetic permeability that determines the DC magnetic shield performance, not a quantitative evaluation of the incremental magnetic permeability. 2) The small ring pieces may have different magnetic permeability from the large steel plate due to different atmospheric conditions during heat treatment. On the other hand, as a method for measuring a small steel plate, there are conventionally an apstein test method and a b single plate test method. However,
This method is premised on the measurement of a small steel plate sample, and has the following problems when measuring a large steel plate. The method of a) requires a large space to measure a plurality of steel plate samples by forming them in a well shape, and thus individual management of steel plates cannot be performed. In the method of b), since the measurement is performed by combining the yokes, the apparatus becomes heavy, and it becomes difficult to manage the gap between the large steel plate and the yokes.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and a magnetic steel sheet is inserted into an exciting coil to energize an alternating current, and the surface of the magnetic steel sheet is different from each other. The strength of the magnetic field is measured by at least two magnetic field detectors arranged at different distances, and the magnetic flux that passes through the steel plate is detected by the magnetic flux detection coil. By utilizing the fact that it is a linear function of the distance, the incremental magnetic permeability is obtained based on the output signal of the magnetic field detector and the output signal of the magnetic flux detection coil. It is an object of the present invention to obtain an incremental magnetic permeability measuring device for a magnetic steel sheet capable of measuring the incremental magnetic permeability of the magnetic steel sheet as it is.

[0005]

SUMMARY OF THE INVENTION An incremental magnetic permeability measuring apparatus for a magnetic steel sheet according to the present invention includes an exciting coil for inserting a magnetic steel sheet inside to energize an alternating current to generate a magnetic field, a magnetic steel sheet and an exciting coil. Between the coils, at least two magnetic field detectors are arranged at different distances from one surface of the magnetic steel plate, and are arranged so as to intersect with the magnetic steel plate to detect the magnetic flux passing through the magnetic steel plate. Magnetic flux detection coil,
Obtain the strength of the magnetic field in the magnetic steel sheet from the output signals of the plurality of magnetic field detectors, from the value and the magnetic flux density of the magnetic flux passing through the magnetic steel sheet obtained from the output signal of the magnetic flux detection coil of the magnetic steel sheet And an arithmetic unit for obtaining the incremental magnetic permeability.

Further, at least two magnetic field detectors are arranged on each side of the magnetic steel plate.

Further, a magnetic steel plate is inserted inside to energize an alternating current to generate a magnetic field, and between the magnetic steel plate and the exciting coil is arranged so as to be vertically movable from the surface of the magnetic steel plate. The magnetic field detector, the magnetic flux detecting coil arranged to intersect with the magnetic steel plate to detect the magnetic flux passing through the magnetic steel plate, and the distance from the surface of the magnetic steel plate by moving the magnetic field detector. At least two different
The strength of the magnetic field in the magnetic steel sheet is obtained from the output signal of the magnetic field detector obtained at the location, and the magnetic field is determined from the value and the magnetic flux density of the magnetic flux passing through the magnetic steel sheet obtained from the output signal of the magnetic flux detection coil. This is to obtain the incremental magnetic permeability of the steel sheet.

The strength of the magnetic field generated by the exciting coil is set to 10 ^-2 Oe or less.

Further, the length of the exciting coil is made equal to or longer than the length of the magnetic steel plate, and the magnetic field detector and the magnetic flux detecting coil are arranged in the central portion of the magnetic steel plate divided into three equal parts in the longitudinal direction. However, the magnetic field detector is arranged in the space of one-third of the magnetic steel sheet side between the magnetic steel sheet and the exciting coil.

[0010]

According to the present invention, the magnetic steel sheet is inserted into the exciting coil, an alternating current is applied to generate a magnetic field, and at least two magnetic fields are arranged at different distances from one surface of the magnetic steel sheet. The strength of the magnetic field in the magnetic steel sheet is calculated from the output signal of the detector or the output signal of the magnetic field detector obtained by moving the magnetic field detector at at least two locations at different distances from the surface of the magnetic steel sheet. Since the incremental magnetic permeability is obtained from the value and the magnetic flux density of the magnetic flux passing through the magnetic steel sheet obtained from the output signal of the magnetic flux detecting coil, the incremental magnetic permeability of a large magnetic steel sheet can be measured as the original plate.

Further, by arranging at least two magnetic field detectors on each side of the magnetic steel plate, when a magnetic field distribution deviation occurs in the thickness direction of the magnetic steel plate, the deviation can be detected.

Further, by setting the strength of the magnetic field generated by the exciting coil to 10 ^-2 Oe or less, the characteristics against weak magnetic noise in a place where a magnetic shield room is installed, for example, in a hospital in a big city can be known. .

Further, the magnetic field detector and the magnetic flux detecting coil are arranged in the central portion of the magnetic steel plate which is divided into three equal parts in the longitudinal direction, and the magnetic field detector is located on the magnetic steel plate side between the magnetic steel plate and the exciting coil. By arranging it in the space of 1/3 of
Even if the position where the magnetic field detector is installed is displaced from the longitudinal center of the magnetic steel sheet, the incremental permeability can be measured.

[0014]

【Example】

Example 1. First, the principle of the present invention will be described. 1 is a front view showing an exciting unit and a sensor unit in Embodiment 1 of the present invention, and FIG. 2 is a sectional view taken along line AA of FIG. In the figure, 1 is a large magnetic steel plate (hereinafter, simply referred to as a steel plate) whose incremental magnetic permeability is measured, and is, for example, a PC permalloy original plate. Reference numeral 2 denotes an exciting coil that excites a steel sheet as a material to be tested with an alternating current, and has a transverse section (cross section orthogonal to the longitudinal direction) and a length that are sufficient for exciting the steel sheet 1 by inserting it inside, and The coil has a rectangular cross section. The rectangular coil is used to generate a uniform magnetic field in the width direction of the steel plate 1. Therefore, the steel plate 1 is inserted and measured in the center of the inside of the rectangular coil so that the conductor in the width W direction of the rectangular coil is parallel to the steel plate 1. Reference numeral 3 denotes a magnetic flux detecting coil arranged to intersect with the steel plate 1 to detect the magnetic flux passing through the steel plate, and 4a and 4b are magnetic field detectors, which are magnetometers such as Gauss meters. The two magnetometers measure the strength of the magnetic field at different positions from the surface of the steel plate 1, that is, one surface. The exciting coil 2 constitutes an exciting section, and the magnetic flux detecting coil 3 and the magnetometers 4a and 4b constitute a sensor section.

Magnetometers 4a and 4b and magnetic flux detecting coil 3
Is arranged at the center in the longitudinal direction of the steel plate 1 inserted in the exciting coil 2, and the magnetometers 4a and 4b are the surface of the steel plate 1,
That is, they are arranged at different distances from one surface.
The exciting coil 1, the magnetic flux detecting coil 3, and the magnetometers 4a and 4b are fixed by known means while maintaining the above positions. The exciting coil 2 is wound on a winding frame, and the outer dimensions thereof are length L = 1800 mm and width W = 8.
The height is 50 mm and the height H is 400 mm. Steel plate 1 has a width W
= 600 mm, thickness T = 1.2 mm, and length L is equal to or smaller than the length of the exciting coil 2.

With the above construction, the steel plate 1 is inserted into the exciting coil 2 to pass an alternating current to generate a weak magnetic field, and the magnetic field is measured by the magnetometers 4a and 4b to detect the magnetic flux. The magnetic flux density is calculated based on the output signal of No. 3, and the incremental magnetic permeability is measured. Occurs, and the strength of the magnetic field differs between the inside of the steel sheet including the surface and the vicinity of the surface of the steel sheet (hereinafter referred to as the steel sheet surface). Therefore, the inventor confirmed the following facts by magnetic field analysis and experiments. That is, "the strength of the magnetic field in the vicinity of the steel plate surface at the center of the exciting coil is a linear function of the distance from the steel plate surface and is minimum on the steel plate surface and inside the steel plate."

Hereinafter, this fact will be clarified by a magnetic field analysis calculation using a large-scale computer. The analysis is based on the model of 1/10 of the apparatus shown in FIGS. 1 and 2, and the vector potential method (A-φ method) of the integral element method analysis calculation assuming that the magnetic field distribution in the width direction of the steel sheet is almost uniform. Two-dimensional linear static magnetic field analysis was used. Considering the symmetry, 1 of the model shown in FIG.
The / 4 portion (first quadrant) was analyzed. Coil 2a
In the (first quadrant), an electric current flows from the top to the bottom of the drawing. The target axis X is a fixed boundary of the magnetic potential, the target axis Z is a free boundary of the magnetic potential, and the other boundaries (portions indicated by-) are integration boundaries. FIG. 4 shows the result of calculation of μΔ (relative magnetic permeability) at 10,000. As can be seen from FIG. 4, the strength of the magnetic field (X-direction component) changes linearly from the surface of the steel plate (PC permalloy) 1a and has a constant value within the steel plate. In addition,
The length L direction of the steel sheet 1 is the X axis, the width W direction is the Y axis, and the direction perpendicular to the steel sheet is the Z axis. The experimental results will be described later.

Then, based on the above analysis results, the magnetic field strength (AC component) at two points near the steel plate surface is measured while changing the distance from the steel plate surface, and the value and the distance between the two points are used to measure the steel plate surface. The method of calculating the above magnetic field strength is derived. FIG. 5 is an explanatory view for explaining the principle of the method for obtaining the strength of the magnetic field on the steel plate surface and inside, and FIG. 5 (a) is a view showing the positions where the magnetometers 4a, 4b are arranged on the steel plate 1, FIG. 5B is a graph showing that the magnetic field strength (X-direction component) near the steel plate surface based on the above analysis results is a linear function of the distance from the steel plate surface. The position Z ₁ of the magnetometers 4a and 4b in FIG.
Z ₂ corresponds to Z ₁ and Z _{2 on} the vertical axis in FIG.
Here, Z ₁ : distance between the steel plate surface and the magnetometer 1 Z ₂ : distance between the steel plate surface and the magnetometer 2 H ₁ : measurement data of the magnetometer 1 (magnetic field strength) H ₂ : measurement of the magnetometer 2 Given the data (magnetic field strength), the magnetic field strength H at the point z from the steel plate
(Z) can be expressed by _{(H (z) -H 1)} / (z-z 1) = (H 2 -H 1) / (z 2 -z 1) ... (1). The strength of the magnetic field on the steel plate surface (z = 0) is H (0) = (− z ₁ · H ₂ + z ₂ · H ₁ ) / (z ₂ −z ₁ ) ... (2). On the other hand, τ is the thickness of the steel plate, w is the width of the steel plate, V is the output of the coil for detecting magnetic flux, and n is the number of turns of the coil for detecting magnetic flux.

[0019]

[Equation 1] From this, the incremental magnetic permeability μΔ is obtained by μΔ = B / H (0) (4). From the above, the present invention measures the strength of the magnetic field at two points near the steel plate with at least two magnetometers and processes the information by a computing device to determine the strength of the magnetic field in the steel plate, that is, in the steel plate. The incremental magnetic permeability is measured by calculating the ratio with the magnetic flux density of the steel sheet obtained and measured at the same time.

FIG. 6 is a block diagram of an incremental magnetic permeability measuring apparatus according to Embodiment 1 of the present invention. In FIG. 6, 2 is an exciting coil, 3 is a magnetic flux detecting coil, 4a and 4b are magnetometers, and the one shown in FIGS. 1 and 2 is shown as a configuration diagram. The steel plate 1 is not shown. Reference numeral 5 is an oscillator that generates an alternating current for excitation, 6 is an amplifier that amplifies the output of the oscillator 5 and outputs it to the excitation coil 2, 7 is a proportional / integral arithmetic processor, and 8 is an add / subtract / multiply / divide arithmetic processor.

Next, the operation will be described. Excitation coil 2
Excites with the output of the amplifier 6. The frequency is the range where eddy current is not generated in the steel plate 1 as the material under test, and is 1 m.
In the case of PC permalloy having a thickness of m, the frequency is about 0.1 to 10 Hz. The lower limit of the frequency is 0.1 Hz. This is to provide a place to measure the strength of the magnetic field generated by the human body for medical purposes as the main application of the magnetically shielded room.To evaluate the materials used in such a shielded room, 0.1 corresponding to the frequency band of the magnetic field generated from
This is because it is sufficient to know the incremental magnetic permeability at about Hz. In addition, from the current performance of measuring instruments, etc., 0.01
It is possible to measure in the range up to Hz. The strength of the magnetic field is 1
Measurement is performed at 0 ^-2 Oe or less. This is because the level of magnetic fluctuations in cities is on the order of 10 ^-3 Oe.
That is, considering the case where the above-mentioned magnetic shield room for measuring the strength of the magnetic field generated from the human body is installed in a city hospital, it is necessary to shield the magnetic noise of 10 ⁻³ Oe class. . Therefore, it is necessary to evaluate the characteristics of PC permalloy as a material in a weak magnetic field of 10 ⁻³ Oe class. From the above, the magnetic field strength is 10 ^-2 O
e or less. On the other hand, in order to completely excite the steel sheet 1, the length of the exciting coil 2 should not be smaller than the length of the steel sheet.

The frequency and the strength of the magnetic field are adjusted by the oscillator 5 in front of the amplifier 6. The output signals of the magnetometers 4a and 4b and the magnetic flux detecting coil 3 are proportional / integral arithmetic processors 7
Is processed in. The two signals of the magnetometers 4a and 4b are converted into the values of the magnetic field strengths H ₁ and H ₂ by the proportional calculation and sent to the addition / subtraction / multiplication / division calculation processor 8. The output signal of the magnetic flux detecting coil 3 is converted into a value of the magnetic flux density B by integral calculation and sent to the addition / subtraction / multiplication / division calculation processor 8. Information on the positions Z ₁ and Z ₂ of the magnetometers 4a and 4b is input to the addition / subtraction / multiplication / division calculation processor 8 in advance, and the strength of the magnetic field on the steel plate surface is calculated based on the equation (2) to obtain the equation ( Based on 4), the incremental magnetic permeability μΔ is calculated and output.

Example 2. In the first embodiment, the magnetometer 4a,
4b and the magnetic flux detecting coil 3 are arranged at the center of the steel plate 1 in the longitudinal direction, but measurement is possible even if they are arranged at positions deviated from the center. In the second embodiment, the magnetometer and the magnetic flux detecting coil are arranged in the central portion of the steel plate which is divided into three equal parts in the longitudinal direction, and the magnetometer is provided on the steel plate side between the steel plate and the exciting coil.
It is to be placed in one-half the space. Hereinafter, a description will be given with reference to FIG. 7 which is a cross section at the same position as in FIG. FIG. 7 is an explanatory diagram for explaining an experiment for knowing the magnetic field distribution in the height direction inside the exciting coil, that is, in the direction perpendicular to the steel plate surface. FIG. 7A shows the strength of the magnetic field by changing the position of one magnetometer 4. The figure which shows the structure which measures height, (b) shows the state which takes out a part of steel plate 1 from the coil 2 for excitation, and (c) puts the steel plate 1 in the center of the coil 2 for excitation, and shows the steel plate 1. FIG. 5 is a diagram showing a state in which a magnetic field near the end in the longitudinal direction of is measured.

In Experiment 1, as shown in FIG. 2 (b), the steel plate 1 was moved out from the exciting coil 2 by 250 mm, and one magnetometer 4 was positioned in the Z direction at a position 200 mm from the end of the exciting coil. I changed and measured. The result is shown in FIG. Experiment 2
Was measured by changing the position of one magnetometer in the Z direction at the position indicated by Z at the end of the steel plate 1 as shown in FIG. The measurement result is shown in FIG. In both Experiments 1 and 2, the magnetic field distribution has linearity up to a distance of 90 mm from the steel plate 1, but becomes non-linear at a location of 90 to 200 mm. Based on this result, the distance from the steel plate 1 is 90 mm
It is understood that if the magnetometer is placed in the range up to, linearity can be obtained even if the position of the magnetometer with respect to the longitudinal direction of the steel plate 1 deviates from the center.

Therefore, in the second embodiment, in consideration of safety,
Magnetometers 4a and 4b are arranged at positions within a third space between the steel plate 1 and the excitation coil 2 on the steel plate side, and the longitudinal position is the center of the longitudinal direction of the steel plate divided into three equal parts. It is to be placed in the department. According to the second embodiment, in disposing the magnetometer, the longitudinal direction of the steel plate does not necessarily have to be arranged in the center, which is advantageous in manufacturing the device.

Example 3. According to the experimental result of the above-mentioned Example 2, the number of magnetic field detectors may be one. In this case, the surface of the steel sheet 1 and the magnetic field detector, i.e. is moved in a vertical direction from the one surface, and an output signal obtained at a distance from the steel plate 1 of Z _1, the output signal obtained at a distance from the steel plate 1 Z ₂ Based on the above, if the proportional / integral calculation processor 7 calculates proportionally the magnetic field strengths H ₁ and H ₂ , the incremental magnetic permeability can be calculated as in the first embodiment.

Example 4. In Examples 1 and 2, two magnetometers are arranged on one side of the steel plate. However, if two magnetometers are arranged on both sides of the steel plate, the magnetic field strengths _Hu (0) on both sides of the steel plate, H _d (0) can be measured. According to the third embodiment, when there is a deviation in the magnetic field distribution in the thickness direction of the steel sheet, it can be detected and corrected (average processing).

Example 5. In Examples 1 to 3, a magnetometer is used as the magnetic field detector. However, instead of the magnetometer, a pickup coil (air core coil) is used, and the proportional / integral calculation processor 7 performs integration processing to obtain H ₁ , H 2. You may calculate ₂ .

[0029]

As described above, according to the present invention, a magnetic steel plate is inserted into an exciting coil, an alternating current is applied to generate a magnetic field, and the magnetic steel plates are arranged at different distances from one surface of the magnetic steel plate. Output signals of at least two magnetic field detectors,
Alternatively, by moving the magnetic field detector, the strength of the magnetic field in the magnetic steel plate is obtained from the output signal of the magnetic field detector obtained at at least two locations at different distances from the surface of the magnetic steel plate, and the value and the coil for magnetic flux detection are obtained. Since the incremental magnetic permeability is obtained from the magnetic flux density of the magnetic flux that passes through the magnetic steel plate obtained from the output signal of, the incremental magnetic permeability of the large magnetic steel plate can be measured as the original plate. Therefore, 1) In particular, it becomes possible to measure the incremental permeability of a large magnetic plate used in a magnetically shielded room, etc., and the deviation of the alternative measurement in the measurement by the conventional test sample piece, that is, the characteristic between the sample and the actual product. The difference between 2) The problems of large size, heavy weight, and difficulty of gap management such as the single plate test method and the Epstein test method are solved.

Further, by disposing at least two magnetic field detectors on each side of the magnetic steel sheet, when the magnetic field distribution has a deviation in the thickness direction of the magnetic steel sheet, the deviation can be detected. Therefore, it is possible to evaluate whether or not there is a deviation in the magnetic field distribution in the thickness direction.

Further, by setting the strength of the magnetic field generated by the exciting coil to 10 ^-2 Oe or less, the characteristics against a weak magnetic noise in a place where the magnetic shield room is installed, for example, in a hospital in a city can be known. Therefore, it is possible to evaluate whether or not it is suitable as a material for a magnetically shielded room that shields weak magnetic noise.

Further, the magnetic field detector and the magnetic flux detecting coil are arranged in the central portion of the magnetic steel plate, which is divided into three equal parts in the longitudinal direction, and the magnetic field detector is located on the magnetic steel plate side between the magnetic steel plate and the exciting coil. By arranging in the space of 1/3, the incremental magnetic permeability can be measured even if the position where the magnetic field detector is installed deviates from the longitudinal center of the magnetic steel sheet. Therefore, there is a dimensional margin in arranging the magnetic field detector, which is advantageous in manufacturing the device.

[Brief description of drawings]

FIG. 1 is a front view showing an excitation unit and a sensor unit according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is an explanatory diagram showing a model for analysis.

FIG. 4 is a diagram showing an example of an analysis result.

FIG. 5 is an explanatory diagram illustrating the principle of a method for obtaining the strengths of magnetic fields on and inside a steel plate.

FIG. 6 is a configuration diagram of an incremental magnetic permeability measuring apparatus according to the first embodiment of the present invention.

FIG. 7 is an explanatory diagram illustrating an experiment for knowing a magnetic field distribution in a direction perpendicular to a steel plate surface.

FIG. 8 is a diagram showing the results of Experiment 1.

9 is a diagram showing the results of Experiment 2. FIG.

[Explanation of symbols]

 1 Magnetic Steel Plate 2 Excitation Coil 3 Magnetic Flux Detection Coil 4a, 4b Magnetic Field Detector 5 Oscillator 6 Amplifier 7 Proportional / Integral Calculation Processor 8 Addition / Decrement / Division Calculation Processor

Claims (5)

[Claims] 1. An exciting coil that inserts a magnetic steel sheet inside to pass an alternating current to generate a magnetic field, and between the magnetic steel sheet and the exciting coil, different distances from one surface of the magnetic steel sheet. At least two magnetic field detectors arranged on the magnetic steel plate, a magnetic flux detecting coil arranged so as to intersect with the magnetic steel plate for detecting a magnetic flux passing through the magnetic steel plate, and outputs of the plurality of magnetic field detectors. The strength of the magnetic field in the magnetic steel sheet is obtained from the signal, and the incremental magnetic permeability of the magnetic steel sheet is obtained from the value and the magnetic flux density of the magnetic flux passing through the magnetic steel sheet obtained from the output signal of the magnetic flux detection coil. An incremental magnetic permeability measuring device for magnetic steel sheets, which comprises a computing device. 2. The incremental magnetic permeability measuring apparatus for a magnetic steel sheet according to claim 1, wherein at least two magnetic field detectors are arranged on each side of the magnetic steel sheet. 3. A magnetic steel sheet is inserted inside to energize an alternating current to generate a magnetic field, and between the magnetic steel sheet and the exciting coil, the magnetic steel sheet is movable vertically from the surface of the magnetic steel sheet. A magnetic field detector arranged, a magnetic flux detecting coil arranged so as to intersect with the magnetic steel plate in order to detect a magnetic flux passing through the magnetic steel plate, and a surface of the magnetic steel plate by moving the magnetic field detector. From the output signal of the magnetic field detector obtained at least at two different distances from the magnetic steel sheet, and the magnetic steel sheet obtained from the value and the output signal of the magnetic flux detecting coil. An incremental magnetic permeability measuring apparatus for a magnetic steel sheet, comprising: an arithmetic unit for obtaining the incremental magnetic permeability of the magnetic steel sheet from the magnetic flux density of the magnetic flux passing through the inside. 4. The incremental magnetic permeability measuring device for a magnetic steel sheet according to claim 1, wherein the strength of the magnetic field generated by the exciting coil is 10 ⁻² Oe or less. . 5. The length of the exciting coil is made equal to or longer than the length of the magnetic steel plate, and the magnetic field detector and the magnetic flux detecting coil are divided into three parts in the longitudinal direction of the magnetic steel plate. The magnetic field detector is arranged in a portion, and the magnetic field detector is a third of the magnetic steel sheet side between the magnetic steel sheet and the exciting coil.
It arrange | positions in the space of Claim 1, 2, 3 characterized by the above-mentioned.
Or the incremental magnetic permeability measuring apparatus of the magnetic steel plate in any one of 4.