JP5293755B2 - Apparatus for measuring complex permeability of magnetic material and method for measuring crystal grain size of magnetic material using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for accurately and stably measuring local complex permeability and local crystal grain size of a magnetic body to be measured, even when a measuring object moves relatively with respect to a sensor section. <P>SOLUTION: This magnetic characteristic measuring device winds a coil for alternating current excitation and a coil for detection on a ferromagnetic body core with a U-shaped cross section, closely faces the tip of the leg of the core with the U-shaped cross section to the magnetic body to be measured, and measures the complex permeability of the magnetic body to be measured. In the complex permeability measuring device, leg interval A is determined to establish the equation A&ge;v/f+2&times;C and C&gt;0, where v is moving speed of the magnetic body to be measured moving relatively in the arrangement direction of the leg, f is application frequency to the alternating current exciting coil, C is width of a detection sensitivity reduction region between the legs expressed as a function of the predetermined lift off and the leg interval A. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to an apparatus for measuring the local complex permeability of a magnetic material and a crystal grain size measuring method using the same.

  For magnetic products with important electromagnetic characteristics used in an alternating magnetic field, physical properties expressed by complex permeability such as differential permeability, eddy current loss, and iron loss are very important for quality control. It is. The complex magnetic permeability mentioned here is expressed using complex magnetic permeability as described in Non-Patent Document 1, for example. The complex permeability μ is expressed as follows, assuming that the AC magnetic field applied from the outside is H, the magnetic flux density is B, and the phase delay is δ.

  The real part μ ′ in the above equation indicates the normally non-complex magnetic permeability, and μ ″ is associated with the loss. Also, since there is a correlation between the iron loss and the particle size, or the permeability and the particle size, By measuring the complex permeability of the magnetic material, it is possible to measure the crystal grain size averaged in the measurement region.

  This complex permeability can be generally determined by a laboratory measurement method (Epstein test, SST test, etc.) using a strip-shaped cut plate, but this method (a) takes time to measure, (b ) It is necessary to arrange the materials to be measured to a predetermined size. (C) Especially in the Epstein test, it is necessary to assemble the cut plate samples in a cross-beam shape. In the case of movement, there is a problem that it is not possible to simply measure the shape as it is.

  Therefore, as a method for easily measuring the iron loss which is one of the complex magnetic permeability, for example, in Patent Document 1, a large excitation coil and a detection coil for iron loss measurement are installed in the production line. A technique for measuring through a steel plate in a coil is disclosed. In the case of this technique, (1) since the entire coil is wound around the width direction of the steel sheet and the entire magnetic field is measured, only average characteristics can be measured in the width direction of the steel sheet. (2) Also in the rolling direction Since the magnetic flux has spread, the measurement has become a wide range. (3) Since the coil covers the steel strip, the sensor cannot be repaired by moving it outside the line. There is a problem that is bad.

  As a technique that can solve these problems, Patent Document 2 discloses that a sensor unit is formed by winding a primary coil and a secondary coil around a U-shaped core, and outputs from both the primary coil and the secondary coil are wattmeters. The technology of connecting to and investigating iron loss has been released. In this case, the magnetic field from the sensor unit is concentrated in a narrow range of the material to be measured around the core legs determined by the core size. Although the magnetic field spreads beyond the core size, the measurement target range is the size in the width direction of the core in the width direction and the distance between both legs in the rolling direction. In this configuration, in terms of local measurement, an appropriate measurement method can be used in both the width direction and the rolling direction of the steel sheet, the measuring device can be made compact, and the cost and maintenance are good.

JP-A 49-006961 Japanese Patent Laid-Open No. 03-115876

Keizo Ota, “Basics of Magnetic Engineering II”, Kyoritsu Shuppan, 1973, p. 304

  The technique of Patent Document 2 is a technique based on the premise of lab measurement in which there is no relative displacement between the sensor unit and the measurement object. Etc. were also confirmed. However, on the other hand, in the on-line test that measures iron loss in the actual magnetic steel sheet production line where the object to be measured moves, there are problems such as the output of the sensor unit becoming unstable and the measurement accuracy being bad depending on the production conditions. It turned out that it is not applicable.

  Therefore, the present invention solves the above-described problems, and even when the measurement object moves relative to the sensor unit, the local complex permeability and crystal grain size of the magnetic substance to be measured can be stably stabilized with high accuracy. The purpose is to provide technology that can be measured.

  The gist of the present invention is as follows.

In the first invention, an AC excitation coil and a detection coil are wound around a U-shaped ferromagnetic core, and a predetermined lift-off is applied to the magnetic material to be measured that moves the leg end of the U-shaped core. In the magnetic property measuring apparatus for measuring the complex permeability of the magnetic substance to be measured by making them close to each other, the moving velocity v of the magnetic substance to be moved relatively in the direction in which the legs are aligned, the AC excitation coil Frequency f, a width C of the detection sensitivity reduction region between the legs expressed as a function of a predetermined lift-off and the leg interval A, and the leg interval A satisfy the following expression: The complex permeability measuring device is characterized in that the leg interval A is determined.

A ≧ v / f + 2 × C
However, C> 0
According to a second aspect of the invention, the leg permeability A is determined so that n is an integer equal to or greater than 1, and the following formula is satisfied: It is.

A ≧ n × v / f + 2 × C
However, C> 0
According to a third invention, from the measurement result of the complex permeability using the complex permeability measurement device according to the first invention or the second invention, the measurement result of the complex permeability and the crystal grain size of the magnetic substance to be measured The average crystal grain size of the magnetic substance to be measured in the measurement region is obtained using the correlation between the magnetic substance and the crystal grain size of the magnetic substance.

  According to a fourth aspect of the present invention, the measured magnetic body is an electromagnetic steel plate in a production line passing plate, and the magnetic steel sheet measures the iron loss of the electromagnetic steel plate in the line passing plate. It is a complex permeability measuring device of a magnetic substance given in the 2nd invention.

  A fifth invention is a method for manufacturing an electromagnetic steel sheet using the magnetic permeability measuring device for magnetic material according to the first or second invention, wherein the measurement result of the complex permeability measuring device and the crystal of the electromagnetic steel plate Obtaining an average crystal grain size in the measurement region of the electrical steel sheet from the correlation with the grain size, and comprising the steps of controlling production conditions based on the obtained average crystal grain size Is the method.

  The first related art in this case is to wind an AC excitation coil and a detection coil around a U-shaped ferromagnetic core, and make the tip of the leg of the U-shaped core close to and face the magnetic material to be measured. A magnetic characteristic measuring apparatus for measuring a complex magnetic permeability in a local region of the magnetic substance to be measured, the moving speed v of the magnetic substance to be moved relatively in the direction in which the legs are arranged, and the alternating current From the frequency f applied to the exciting coil, the leg interval A satisfies the following formula.

A ≧ v / f
The second related art is characterized in that n is an integer of 1 or more and the leg interval A satisfies the following formula.

      A = n × v / f

  According to the present invention, even when the object to be measured moves relative to the sensor unit, the local complex permeability can be measured accurately and stably. For this reason, for example, the complex permeability distribution in the rolling direction of a magnetic material can be measured easily and accurately during continuous full length measurement, and high quality (high accuracy, full length continuous information) feedback to manufacturing condition control is provided in near real time. Realize and contribute to stable manufacturing. It can also contribute to advanced quality assurance.

  In addition, the sensor unit of the present invention has a simple configuration comprising a U-shaped core in cross section, and an AC excitation coil and a detection coil wound around the back of the core, so it is compact and inexpensive to manufacture. Maintenance is also easy. Therefore, it becomes easy to incorporate in the production line.

The schematic diagram which showed the basic composition of the magnetism measuring method concerning the present invention. The schematic diagram which showed this invention including the sensitivity fall area | region of the leg part 31 vicinity. The figure which showed the sensitivity distribution between both legs. The figure which showed the measuring method for obtaining the result of FIG. The figure which shows the relationship between the width C of a sensitivity fall area | region, the leg part space | interval A, and the lift-off L. FIG. The figure which showed the example of a measurement of the iron loss of an electromagnetic steel plate. The figure which showed the change loop of BH in a subject by the externally applied alternating current magnetic field. The schematic diagram which showed the measurement accuracy change at the time of changing only leg space | interval A among measurement conditions.

  When applying the magnetic characteristic measuring apparatus of Patent Document 2 to a magnetic substance to be measured that moves relatively, it was examined what measurement conditions would cause a problem.

  In the examination, an example of a basic embodiment of the magnetic property measuring apparatus according to the present invention is shown in FIG. 1 as a schematic diagram.

  The sensor unit 2 of the magnetic characteristic measuring apparatus is wound around a U-shaped ferromagnetic core 3 having two legs 31 and a back 32 connecting the legs, and the back 32 of the core 3. The excitation coil 4 and the detection coil 5 are configured as follows. The distance between the two legs 31 (that is, the effective measurement range) is A. In the present embodiment, the direction in which the two leg portions are aligned substantially coincides with the direction in which the magnetic substance to be measured moves, and in the width direction of the magnetic substance to be measured (direction perpendicular to the paper surface) perpendicular to that direction. The ferromagnetic core has the shape of a sensor unit having a core with a thickness corresponding to the required measurement accuracy and resolution in the width direction. In addition, when it is desired to measure a plurality of positions in the width direction of the magnetic substance to be measured, a plurality of sensor units 2 may be installed at each position in the width direction. The complex magnetic permeability distribution in the orthogonal width direction can be continuously and accurately measured during production in a simple and accurate manner. Although Patent Document 2 is different in that an exciting coil is wound around the core leg and FIG. 1 is wound around the back of the core, either configuration is possible in principle, and either configuration is used in the present invention. It is not limited to.

  The measured magnetic body 1 moves relative to the sensor portion 2 at a speed v in the direction in which the leg portions 31 of the U-shaped core 3 are arranged, that is, in the direction of the arrow. In addition, the distance (hereinafter referred to as lift-off) between the tip of the leg portion 31 of the U-shaped core 3 and the surface of the measured magnetic body 1 is L.

  The complex permeability of the magnetic body 1 to be measured is measured by making the tip of the leg 31 of the U-shaped core close to the magnetic body 1 to be measured and probing the tip of the leg 31 of the U-shaped core. Then, an alternating current is supplied to the exciting coil 4 at the frequency f by the oscillator 6, and then the output from the detection coil 5 is synchronously detected by the lock-in amplifier 7 to obtain the in-phase or phase component, and the result is calculated by 8 The required complex permeability is calculated by converting with an apparatus.

  The iron loss value can be obtained by measuring the synchronous detection in-phase component (COS component) with the lock-in amplifier 7. Furthermore, since the iron loss value is approximately obtained by a linear relationship with the crystal grain size, the crystal grain size can be obtained from the iron loss. Further, by measuring the SIN component of the synchronous detection, a value corresponding to the differential permeability (the real part of the complex permeability) can be measured. Furthermore, since the differential magnetic permeability and the crystal grain size have a correlation, the crystal grain size can also be measured.

In the configuration of FIG. 1, the tendency of the measurement accuracy when only one specific measurement condition is changed and the other measurement conditions are made constant is as follows.
(A) The leg portion interval A of the U-shaped core 31 constituting the sensor unit 2 is preferably large.
(B) The relative moving speed v of the magnetic substance 1 to be measured with respect to the sensor unit 2 is preferably small.
(C) The higher the frequency f, the more stable the characteristics can be measured.
(D) The distance L (lift-off) between the leg part 31 of the sensor part 2 (or the U-shaped core 3 in cross section) and the magnetic substance 1 to be measured should be small.
FIG. 8 shows a schematic diagram of the measurement accuracy changing tendency when only the leg interval A of the U-shaped core 3 is changed.

  As described in the above (a), it can be seen that the larger the leg interval A of the U-shaped core 3 is, the smaller the error is (the measurement accuracy is improved). It can be seen that there is a feature that there is a point (p) where the error is greatly improved. As described above, the characteristics that the error greatly changes in the vicinity of a certain value of the measurement condition can be seen in the above (b), (c), and (d). Therefore, it is assumed that there is a common physical situation in the background. The

  As a result of the investigation as described above, as a result of considering the reason why the measurement cannot be stably performed or the proper measurement result cannot be obtained, the following has been found. In order to measure the magnetic characteristics related to a specific frequency f, a magnetic loop of B and H as shown in FIG. 7 generated by an alternating magnetic field applied from the outside is sufficiently provided for each measurement point as much as possible. Need to experience. However, when the frequency is lowered (or the leg interval A of the U-shaped core 3 is reduced), the measurement site on the measured magnetic body 1 is measured by the sensor unit 2 while the applied AC magnetic field is changing. The phenomenon of moving out of the range, in other words, deviating from the central portion between the leg portions 31 that can be measured with high accuracy occurs.

When continuously measuring along the relative displacement between the magnetic substance 1 to be measured and the sensor unit 2, the state of the magnetic field change that one point of the measurement point experiences as it moves is considered to be the following two factors: There is. (A) Change in excitation magnetic flux (excitation frequency).
(B) Sensitivity distribution of the sensor unit 2 in the moving direction.

  In accordance with the above-described consideration regarding the measurement accuracy, the condition relating to (A) for accurate measurement is obtained as follows. The measured part needs to experience as many cycles as possible, not just a part of the period of the externally applied magnetic field, but it is sufficient that at least one cycle can be passed through the loop. Specifically, in order to investigate the characteristics at the frequency f [Hz] when the relative speed changes in the direction of arrangement of the leg portions 31 of the U-shaped core 3 at the speed v [mm / s], an alternating magnetic field is used. The length in the moving direction that can be applied and can be measured stably is equal to or longer than the length (v / f) corresponding to one cycle. This is an important condition for determining the leg interval A of the U-shaped sensor section, and is expressed as follows.

A ≧ v / f (1)
However, there are cases where it is not sufficient to satisfy this condition. This is the case when the factor (B) acts greatly. Since the magnetic substance 1 to be measured moves relative to the sensor unit 2, as shown in (B), as the measured part of the magnetic substance 1 to be measured moves, regions having different sensitivities within the measurement range of the sensor unit 2 are displayed. Will experience. As illustrated in FIG. 3, this sensitivity distribution is greatest at the center between both leg portions of the U-shaped core 3 and decreases as the center portion is separated. Among these, a region where the normalized sensitivity is 0.8 or less is set as a sensitivity reduction region. FIG. 3 shows the results of measurement with the configuration shown in FIG. That is, an electromagnetic steel plate is used as the magnetic body 1 to be measured, and the electromagnetic steel plate 1 provided with a defect 9 smaller than the size of the electromagnetic steel plate 1 or the sensor unit 2 is moved in the direction in which the legs 31 are arranged (the direction of the arrow). The measurement was performed with the sensor unit 2. At this time, a position r was set in the horizontal direction away from the center (g-g 'axis) of the leg interval A of the sensor unit 2, and the left direction toward the negative was negative, and the right direction toward the right was positive. Further, the position of the inner end of the leg portion 31 of the sensor unit 2 is E1 on the negative side and E2 on the positive side. The measurement result was plotted as a change from the measurement result when there was no defect 9 in the electromagnetic steel sheet 1 with respect to the position r.

  As described above, a sensitivity reduction region exists with a width C on the center side of the U-shaped core 3 in section from the inner end of the leg portion 31. A case where this sensitivity reduction region is considered will be described with reference to FIG. The same components as those in FIGS. 1 and 4 are denoted by the same reference numerals, and detailed description thereof is omitted.

  This sensitivity reduction region is a region in which the amplitude of the applied magnetic field is small in AC magnetic measurement, which is far from the amplitude condition to be originally measured, and the signal level is small compared to the intermediate portion because the amplitude is small. The width C of this region varies depending on factors such as the leg interval A of the sensor unit 2 and the lift-off L between the leg unit 31 and the measured magnetic body 1. Since the sensitivity reduction region on the central side of the U-shaped core 3 with respect to the leg portion 31 is small as a signal output as described above, if the contribution to the measurement values in other portions is sufficiently large, the entire measurement is performed. There is no adverse effect. Therefore, considering that the leg spacing A is such that each measurement target part experiences a magnetic field change of one period (v / f) or more, it is possible to exclude the sensitivity reduction area from the leg spacing A. That's fine. In other words, the portion of D, excluding the width C of the sensitivity reduction region from the leg interval A (the total is 2 × C because there are two legs), should be larger than v / f. Specifically, it is as schematically shown in FIG.

That is, when the mutual position of the sensor unit 2 and the magnetic substance 1 to be measured changes at a velocity v [mm / s] relative to the arrangement direction of the leg portions 31 of the U-shaped core 3 in cross section, the lift-off L [ mm], in order to investigate the characteristics at the frequency f [Hz], the leg spacing A [mm] of the leg 31 of the U-shaped core 3 in cross section, the width of the sensitivity reduction region of the sensor section C (total 2) × C) When [mm]
A ≧ v / f + 2 × C (3)
However, C> 0
Set to satisfy the relationship. C is almost determined by A and L.

  Specifically, the above C can be determined as follows, for example. In Fig. 2, the range of up to 80% (20% reduction) of the maximum sensitivity value at the center (position r = 0mm in Figs. 2 to 4) between the legs 31 indicated by the gg 'axis can be measured. It is assumed that it can be used if the magnetic loop is sufficiently experienced within the range. Under this premise, a graph is created by obtaining the sensitivity reduction region width C [mm] with respect to the lift-off L when the leg interval A is changed (see FIG. 5). If this data is arranged, C is expressed as follows.

C = q (L, A) (when q (L, A)> 0)
C = 0 (when q (L, A) ≤ 0)
here,
q (L, A) = (0.0043 × A + 0.29) × (L + 0.076 × A−10) (5)
Note that C = 0 when q (L, A) ≦ 0 because it is not necessary to substantially consider that the measurement region is widened beyond the leg interval A.

  Further, when the above equation (5) is substituted into the above equation (3) that defines the leg interval A, the equation (3) is displayed as a quadratic function of A and becomes an equation independent of C. In other words, since A is a finite length exceeding zero, it is a numerical value set according to the measurement object and the required measurement accuracy within this numerical range. And if the numerical value of A is decided, C will be decided by (5) Formula. By repeating this process several times, the leg interval A having a small ratio of the reduced sensitivity region width C can be obtained.

  In the lift-off range (up to about 20mm) suitable for measurement in terms of accuracy, the above equation (3) is considered from the three leg spacings (locality required for measurement, etc.) as shown in FIG. An approximate straight line of measured values is obtained for an appropriate range), and the approximate straight line group is generally expressed.

  In addition, when q (L, A) ≦ 0, C = 0 means that C is negative means that the measurement area extends more than the leg interval A, but in reality the measurement area This is because the maximum value of is considered to be the leg interval A, in which case C is not q (L, A), and it is appropriate to set it to zero.

  In the present embodiment, the relative movement direction of the magnetic substance 1 to be measured with respect to the sensor unit 2 and the arrangement direction of the leg portions 31 of the U-shaped core 3 in section are the same for stable measurement. Although various conditions were clarified, the present invention is not limited to this. A similar idea is that the direction in which the leg portions 31 of the U-shaped core are perpendicular to the relative movement direction of the magnetic substance 1 to be measured with respect to the sensor portion 2, or the intermediate direction (leg portion) of the above two examples. This can also be applied to the case where the direction of is a direction oblique to the steel plate moving direction. That is, regardless of the arrangement direction of the leg portions 31, it is possible to determine various measurement conditions including the shape of the sensor portion 2 for realizing accurate measurement.

  For example, in order to measure under conditions that do not include eddy currents, it is possible to measure at high frequencies and evaluate and remove the eddy current contribution in some way, but this takes time and accuracy. In the following examples, it will be described that measurement is possible even in such a case.

  As an example, a method for measuring the iron loss of a grain-oriented electrical steel sheet on the production line of the electrical steel sheet will be described with reference to FIG.

  Consider the case of measuring iron loss values (such as 50 Hz) in a low frequency range that is relatively close to direct current. In order to evaluate the iron loss value in the low-frequency region, if measurement is performed under measurement conditions with large eddy current loss, the measurement accuracy will not be improved even if correction is performed by any method, causing measurement accuracy to deteriorate. It is necessary to measure under low eddy current loss conditions (low frequency). However, the present inventors do not need to perform measurement at exactly the same excitation frequency as the frequency of the characteristic value to be obtained, and the iron loss at the frequency used for measurement and the iron loss value to be obtained are at a level required for accuracy. In the present example, it was decided to measure at the same 50 Hz by obtaining the knowledge that they should match.

  The tip of the leg 31 of the sensor unit 2 is disposed so as to face the electromagnetic steel plate 1 that is the measurement target. The arrangement direction of the two leg portions 31 coincides with the moving direction of the electromagnetic steel sheet 1, that is, the rolling direction, and as a result, the measured magnetic properties are those when a magnetic field is applied in the rolling direction.

  The moving speed (rolling line speed) v of the electromagnetic steel sheet 1 was 2000 mm / s, and the lift-off L was 10 mm. Accordingly, the leg interval A (inner distance between the leg portions) of the sensor unit 2 is 2000 [mm / s] / 50 [Hz] = 40 [mm] or more according to the equation (1).

  On the other hand, whether or not the expression (3) needs to be applied is related to the required measurement accuracy and the width C of the sensitivity reduction region.

  The width C of the sensitivity reduction region may be obtained by actual measurement in the manner as shown in FIGS. 3 and 4, or may be obtained by using equation (5). Assuming that A = 40 mm and calculating based on equation (5), 2 × C = 2.8 [mm].

  Then, 40 mm of the leg interval A is sufficiently larger than 2.8 mm which is the entire width 2C of the sensitivity reduction region. In this case, there is no problem even if the leg interval A is determined from the equation (1).

  If the conditions are better, it is sufficient to solve the inequality from the expression (3), and the leg interval A should be 43 mm or more. If it is an integral multiple of the period (v / f), it corresponds to an integral multiple of the magnetic loop of B and H described above, so each part of the measurement region experiences a magnetic loop of B and H evenly. Conditions are desirable, but if there is a certain number of periods, the influence of non-integer multiples can be minimized by the effect of averaging.

  For example, when the leg interval A is set to 283 mm, the effective measurement range D excluding the sensitivity reduction region is increased, and data can be collected for almost seven cycles of applied magnetization, so that accuracy is improved. However, on the other hand, the measurement range in the steel sheet rolling direction and the width direction is expanded, in other words, only an average value in a wider range can be measured as compared with the case of the small sensor unit, the size of the sensor unit 2 is large and the weight In addition, an undesirable point such as a point that the handling of the sensor unit 2 becomes more difficult occurs.

  Therefore, in this embodiment, the leg interval A is set to 123 mm. This corresponds to a measurement range D corresponding to three periods of applied magnetization.

  An alternating current having a frequency of 50 Hz is supplied to the exciting coil 4 by the oscillator 6, and a magnetic flux is caused to flow through the steel plate 1 along the core by the exciting 4 coil, and the reaction is measured by the detection coil 5. Synchronous detection was performed with the lock-in amplifier 7 to obtain an in-phase component (because the phase rotates 90 degrees with the detection coil). This in-phase component result is related to the imaginary component (loss) of the complex permeability. Accordingly, the iron loss value was calculated by the arithmetic unit 8 from the conversion coefficient obtained in advance from the measurement results of the plurality of standard samples. The obtained iron loss value is shown in FIG. The vertical axis indicating the sensor output in FIG. 6 is a.u. (abbreviation of arbitrary unit), which is a relative unit based on an arbitrary value. From this result, it can be seen that measurement is possible even when the measurement object is moving. And the iron loss calculated | required in this way becomes the measured value of a local area | region since the range which a sensor part measures is limited spatially (in a width direction and a moving direction). Yes.

  From the above results, it became clear that the application of the present invention makes it possible to accurately measure local magnetic characteristics while the measurement target is moving.

1 Magnetic material to be measured (Electromagnetic steel plate)
2 Sensor section 3 U-shaped core 31 Cross section U-shaped core (or sensor section) leg section 32 Back section of U-shaped core 4 Primary (excitation) coil 5 Secondary (detection) coil 6 Oscillator 7 Lock-in Amplifier 8 Arithmetic unit 9 Defect A Distance between leg portions of U-shaped core (or sensor part) B Magnetic flux density applied from outside C Width of sensitivity reduction region of sensor part D Sensitivity reduction region is excluded from leg interval A Part E End of the leg of the U-shaped core in the cross section f Measurement frequency H AC magnetic field applied from the outside L Distance between the leg of the U-shaped core in the cross section and the magnetic material (lift-off)
v Relative velocity of the magnetic body with respect to the sensor unit r Position away from the center of the leg interval A of the sensor unit in the horizontal direction (the center is 0)
δ Phase lag of AC magnetic field H and magnetic flux density B

Claims (5)

An AC excitation coil and a detection coil are wound around a U-shaped ferromagnetic core, and a magnetic material to be measured that moves the tip of the leg of the U-shaped core is placed in close proximity to each other with a predetermined lift-off. In the magnetic characteristic measuring apparatus for measuring the complex magnetic permeability of the magnetic material to be measured, the moving speed v of the magnetic material to be measured relatively moving in the direction in which the legs are arranged, and the frequency f applied to the AC excitation coil The leg spacing is such that the width C of the detection sensitivity reduction region between the legs expressed as a function of a predetermined lift-off and the leg spacing A, and the leg spacing A satisfies the following equation: A complex permeability measuring device, wherein A is determined.
A ≧ v / f + 2 × C
However, C> 0 The apparatus of claim 1, wherein the leg interval A is determined so that n is an integer equal to or greater than 1, and the following formula is satisfied.
A ≧ n × v / f + 2 × C
However, C> 0   From the measurement result of the complex permeability using the complex permeability measurement device according to claim 1 or 2, a measurement region is obtained by using a correlation between the measurement result of the complex permeability and the crystal grain size of the magnetic substance to be measured. A method for measuring a crystal grain size of a magnetic material, comprising: obtaining an average crystal grain size of a magnetic material to be measured in   The magnetic body according to claim 1 or 2, wherein the magnetic body to be measured is an electromagnetic steel plate in a production line passing plate, and the iron loss of the electromagnetic steel plate is measured by the electromagnetic steel plate in the line passing plate. Complex permeability measuring device.   It is a manufacturing method of the magnetic steel sheet using the complex permeability measuring device of the magnetic substance according to claim 1 or 2, Comprising: From the correlation between the measurement result of the complex permeability measuring device and the crystal grain size of the magnetic steel plate, A method for producing an electrical steel sheet, comprising: obtaining an average crystal grain size in a measurement region of the electrical steel sheet, and controlling production conditions based on the obtained average crystal grain size.

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