JPH02103485A - Magnetic characteristic measuring method of soft magnetic material - Google Patents

Abstract

PURPOSE:To improve accuracy when a sample having a small cross sectional area is measured and under a relatively low exciting condition by providing an amplifier having a variable amplification ratio thereby to automatically control the amplification ratio. CONSTITUTION:An amplifier which can vary its amplification ratio is placed between a magnetic flux detecting coil, a magnetic field detecting coil or an exciting current shunt and its detector. The amplification ratio is automatically controlled such that an output voltage of the amplifier is within 50-100% of the input voltage range of the detector. At an early stage of measurement, an applying voltage to the exciting coil which satisfies predetermined setting conditions for excitation is learned from the correlation among the applying voltage to the exciting coil, magnetic flux density and magnetic field strength. After demagnetization, the learned exciting voltage is used for setting. Thereafter, magnetic characteristic is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for measuring the magnetic properties of soft magnetic materials.

[Conventional technology] Soft magnetic materials include pure iron, grain-oriented electrical steel sheets, and non-oriented
``There are many types such as magnetic steel sheets, amorphous magnetic materials, ferrite, permalloy, permendur, etc., and they are used in power transformer cores, motor cores, high-frequency transformer cores, magnetic shielding materials, etc. It is a material for which magnetic properties such as iron loss and magnetization characteristics are most important.

The measurement of the magnetic properties of these soft magnetic materials is basically the same; a soft magnetic material sample is excited by passing a current through an excitation coil, and the magnetic field strength at this time is determined by the excitation current or by placing it near the sample. It is detected from the electromotive force of the air-core magnetic field coil, and the magnetic flux passing through the sample is detected from the electromotive force of the magnetic flux coil wound around the sample. The magnetic properties of the above-mentioned soft magnetic material can be determined from the correlation between the magnetic field strength and the magnetic flux density, which is the magnetic flux divided by the cross-sectional area of the sample. That is, magnetic permeability is the ratio of magnetic flux density to magnetic field strength, iron loss is determined from the hysteresis characteristic of magnetic flux density and magnetic field strength, and magnetization characteristic is a correlation curve between magnetic field strength and magnetic flux density.

The excitation coil is wound directly around the sample or around a yoke close to both ends of the sample, and the excitation current is either direct current or alternating current depending on the purpose, and in the case of alternating current, sinusoidal alternating current is mainly used. When detecting the magnetic field strength H from the excitation current I, it is determined from the number of turns Ni of the excitation coil and the length of the magnetic flux passing through the sample, that is, the magnetic path length, as H=kNil/L. k is a constant. In addition, when calculating the magnetic field strength H from the electromotive force Eh of the magnetic field coil, H
= kEh/(f Nh Ah). The magnetic flux density B is the electromotive force Eb of the magnetic flux coil, ! ! Number of magnetic flux coil turns Nb, cross-sectional area of the sample A to B = k Eb/(f N
b Determined by A). Furthermore, in many cases, the excitation current is measured by inserting a minute resistance (shunt) into the current path and measuring the electromotive force generated across the resistance. Therefore, the measurement accuracy of magnetic properties largely depends on the detection accuracy of the electromotive force of the shunt or the magnetic field coil and the magnetic flux coil. In addition, since these electromotive forces are proportional to the magnetic field strength and magnetic flux, respectively, when measuring the magnetic properties between a state of low excitation, that is, a state of small magnetic field strength or magnetic flux, to a state of high excitation, that is, a state of large magnetic field strength or magnetic flux, The manual ranges of these electromotive force detectors are usually tuned to a high excitation state to avoid overflow. For this reason, when measuring magnetic properties in a low excitation state, a lower electromotive force is measured than in the manual range of the detector, resulting in a low S/N ratio (signal/noise ratio) and low detection accuracy. There was a problem. For this reason, in the conventional measurement method, it is necessary to appropriately switch the range of the electromotive force detector depending on the excitation state, making it difficult to achieve both automatic measurement and high-precision measurement.

Further, the magnetic properties of soft magnetic materials are usually measured as characteristic values when the magnetic field strength or magnetic flux density is set under several conditions in order to make comparisons between materials. However, as is well known, magnetic materials have hysteresis characteristics between magnetic field strength and magnetic flux density.
The magnetic property value depends on the excitation history up to the measurement. For this reason, it is customary to first excite the measurement sample to near the saturation magnetization state at the beginning of the measurement of magnetic properties, perform so-called demagnetization to erase the previous excitation history, and then set the excitation conditions.

However, the conventional measurement method (T, YaaIaa+oto a
nd Y, 0hya; IEEE Trans, Mag,
MAG-10, 157 (1974) describes a method of setting the excitation condition after demagnetization by feeding back the magnetic field strength or magnetic flux density signal to the input of the excitation voltage amplifier to achieve the set value of the magnetic field strength or magnetic flux density. I'm taking it. For this reason, when excitation settings are made in a short period of time, a so-called overshoot occurs, which causes the magnetization to return past the set value and deviate from the ideal magnetization state, resulting in an error in the measured values of magnetic properties.

[Problems to be Solved by the Invention] The present invention aims to realize a high-precision automatic measurement method for the magnetic properties of soft magnetic materials, and solves the problem that measurement accuracy deteriorates under low excitation conditions with conventional magnetic property measurement methods. This is an attempt to solve the problem. For example, in the conventional method for measuring iron loss of grain-oriented electrical steel sheets, the measurement error increases as the sheet thickness and excitation magnetic flux density decrease, and the measurement error increases to 0. :The error in measuring the iron loss at 1°7 for a grain-oriented electrical steel sheet with a thickness of 1ml11 is less than ±1, whereas the magnetic flux density of a grain-oriented Mi plate with a thickness of 0.17mm is 1. The iron loss measurement error at .3T is ±496 or more. Considering that the typical difference in iron loss between grades of grain-oriented electrical steel sheets is about 396, the measured iron loss value needs to be ±196.

[Means for Solving the Problems] An object of the present invention is to provide a method that eliminates and improves the above-mentioned problems and makes it possible to automatically measure the magnetic properties of a soft magnetic material with high precision. To this end, we investigated in detail the causes of errors in measuring the magnetic properties of soft magnetic materials. As a result, it was found that there are two main types of measurement errors. One system is a detection error due to noise in the shunt or the circuit that detects the electromotive force of the magnetic field coil and magnetic flux coil, and the other system is a setting error in the excitation state due to the excitation setting at the time of measurement not being ideal. be. The causes of these errors and the improvement measures according to the present invention will be explained in detail below.

A detailed investigation into the state and location of noise in the electromotive force detection circuit revealed that there are three main types of noise. One type is Barkhausen noise, which is closely related to the magnetic properties of the measurement sample and cannot be avoided because it has a woody quality. However, Barkhausen noise is smaller than the other two noises, so it has little effect on measurement errors. The second type of noise is electromagnetic induction noise, which is generated by magnetic field coils and magnetic flux coils acting as antennas and picking up electromagnetic waves from surrounding motors, transformers, fluorescent lights, etc., and by taking shielding measures at the source of the electromagnetic waves, as well as shielding the coils and coils. This can be reduced by shielding the connected signal lines. The third type of noise is noise generated from the detector itself, and is one of the objects of improvement in the present invention. Causes of this noise include fluctuations of electrons in electronic devices, intrusion from power lines, and intrusion from earth lines, but it is normal for some noise to be superimposed on the output of the measuring equipment.

Therefore, it is necessary to take measures to reduce these noises and to improve the noise resistance of the detection signal.

For this purpose, the ratio of signal strength to noise strength, S
/N ratio had to be kept high. In the conventional measurement method, the manual range of the detector is adjusted to the highest excitation condition to be measured, so the S/N ratio is high under high excitation conditions, but the S/N ratio is extremely low under low excitation conditions. The electromotive force of magnetic field coils, etc. was detected. For example, when measuring the magnetic properties of grain-oriented electrical steel sheets, the magnetic field strength is 2500 A/m.
When measuring the magnetic flux density at a magnetic flux density of 0.5T and the iron loss at a magnetic flux density of 0.5T, the S/N ratio in the latter measurement is approximately 17250 due to the detection of the electromotive force of the shunt or magnetic field coil, and the electromotive force of the magnetic flux coil is In the detection of , it becomes about genus. For this reason, conventional measurement methods have low measurement accuracy under low excitation conditions.

In order to solve this problem, the present invention has devised a method of constantly maintaining the S/N ratio at a high value. That is, an amplifier with a variable amplification factor is inserted between the shunt, magnetic field coil, magnetic flux coil, and electromotive force detector, and the amplification factor is adjusted so that the output voltage of the amplifier becomes a voltage higher than 50 of the human power range of the detector. By automatically adjusting, S regardless of high or low excitation conditions.
/N ratio is kept high. Since this amplification factor is given back when calculating the measured value, accuracy can be improved without affecting the true value of the measurement result.

According to the method of the present invention, it is possible to easily improve the accuracy of measuring equipment using conventional measuring methods by adding an amplifier with a variable amplification factor, a calculation circuit for the measurement results, and a control circuit for controlling these. In addition, since this method uses only one range of the detector, there is no need to switch ranges, so by combining it with an excitation control circuit, it is easy to automatically measure the magnetic properties of soft magnetic materials without sacrificing accuracy. It can be achieved without any problems.

Next, we investigated the setting error of the excitation state.

The error in setting the excitation state is due to the bisteresis characteristic, which is a characteristic of magnetic materials, and ideally, after demagnetization, it is desirable to asymptotize to an excitation state that achieves the magnetic field strength or magnetic flux density of the excitation condition. Since the excitation conditions are normally controlled by the excitation voltage applied to the excitation coil,
In practice, the magnetic field strength or magnetic flux density is measured while gradually increasing the excitation voltage at a constant speed from a state without excitation after demagnetization, or gradually decreasing the excitation voltage at a constant speed from a demagnetized state, and when a predetermined excitation condition is reached. It is desirable to maintain the excitation voltage. However, in order to shorten the measurement time, it is usual to increase the rate of increase in the excitation voltage within a range where the influence is small.

However, in the conventional method, the signal strength of magnetic field strength or magnetic flux density is compared with the signal strength achieved under predetermined excitation conditions and fed back to the excitation voltage control circuit. ! The rate of increase in voltage is not constant and is particularly steep at the initial stage of excitation. Furthermore, depending on the material to be measured, feedback matching deteriorates, resulting in the so-called overshoot phenomenon.

These steep excitations and overshoots cause errors in the excitation state, resulting in errors in the measured values of magnetic properties. An error in the excitation state is a non-equilibrium state of the magnetic domain structure inside a magnetic material, and the change in the magnetic domain structure is non-uniform in each part due to the eddy current effect in response to a rapid change in magnetic field strength, and the change in the magnetic domain structure is non-uniform. This is because it is a reversible phenomenon.

In the present invention, a method is devised to reduce the increase rate of the excitation voltage and shorten the setting time, thereby improving the setting error of the excitation state. That is, as shown in FIG. 1, a method was devised in which the rate of increase in excitation is kept almost constant and the excitation condition is achieved in the same or shorter time than the time required for the excitation state to converge using the conventional method. In order to perform this excitation method, the excitation pressure that achieves the predetermined excitation conditions must be known.For this reason, we investigated the relationship between the excitation voltage, magnetic flux density, and magnetic field strength, and found that Fig. 2 found a correlation as shown in the example of grain-oriented electrical steel sheets.However, parameters such as the slope of this correlation could not be used uniformly because they varied depending on the material being measured.

In order to solve this problem, the present invention has devised a method of determining the correlation between the excitation voltage, magnetic flux density, and magnetic field strength at the beginning of each measurement and predicting the excitation voltage that will achieve a predetermined excitation condition. That is, from the magnetic flux density when a relatively small excitation voltage was applied at the beginning of the measurement, the increase ratio of the magnetic flux density with respect to the increase in the excitation voltage was determined, and the value of the excitation voltage that achieved the predetermined excitation magnetic flux density was calculated. The set value of the excitation voltage is corrected from the value of the magnetic flux density when the excitation voltage is set, and the correction ratio of the excitation voltage when the set magnetic flux density deviates is determined. Repeat this operation starting from the lowest excitation of the predetermined magnetic flux density and magnetic field strength to learn each excitation '1π pressure setting value, and after demagnetizing, set the excitation voltage from the low excitation condition or the high excitation condition. Take measurements. By the excitation method of the present invention, the accuracy of setting the excitation state can be significantly improved.

In the present invention, by improving the method of improving the S/N ratio and the method of setting the excitation state described above, the accuracy of measuring the magnetic properties of soft magnetic materials has been significantly improved. Measurement accuracy can be improved by adopting either of these two improvement measures, but
It is desirable to adopt two improvement measures simultaneously for the purpose of improving measurement granularity.

[Example 1] Amplifiers with variable amplification factors were inserted into the human power section of the magnetic field coil signal and the magnetic flux coil signal of a single-sheet magnetic measurement device (SST) according to the conventional method for grain-oriented electrical steel sheets, and the output voltage of each amplifier was The input range of the electromotive force detector of the magnetic field coil and the manual range of the electromotive force detector of the magnetic flux coil are 50 to 100t.
We have added a function to automatically adjust the amplification factor so that An excitation control function has been added to make excitation settings. Figure 3 shows the change in excitation voltage over time, and automatic measurements are performed according to the measurement flowchart shown in Figure 4, and the accuracy of measuring iron loss values in high and low magnetic fields of grain-oriented electrical steel sheets of various thicknesses is determined by the method according to the present invention. (new method) and conventional measurement method (old method).

As shown in Table 1, in the method of the present invention, high excitation, that is, plate thickness < (12 mil), high magnetic field (1,7 T
), low excitation means that the plate thickness is thin (4mi
l) Measurement accuracy was significantly improved even in the case of low magnetic fields (1,37). In particular, the accuracy improvement in low magnetic fields is large.
With the conventional method, it was not possible to achieve the required measurement accuracy of ±1t, but with the method of the present invention, an accuracy of ±0.4 or less could be achieved.

[Effects of the Invention] As explained above, according to the present invention, the accuracy of measuring the magnetic properties of a soft magnetic material can be significantly improved compared to the conventional method. In particular, accuracy can be significantly improved in measurements of samples with small cross-sectional areas and measurements under relatively low excitation conditions.

[Brief explanation of the drawing]

FIG. 1 compares changes in excitation voltage in excitation settings between a conventional method (old method) and a method according to the present invention (new method). FIG. 2 shows an example of the correlation between excitation voltage, magnetic flux density, and magnetic field strength. FIG. 3 shows the measurement procedure in the example in terms of changes in excitation voltage over time. FIG. 4 is a flowchart showing the measurement procedure in the example.

Claims (1)

[Claims] 1. In a method for measuring magnetic properties of a soft magnetic material, an amplifier with a variable amplification factor is placed between a magnetic flux detection coil, a magnetic field detection coil, or an exciting current shunt and these detectors, and the amplifier A magnetic measurement method characterized by automatically controlling an amplification factor so that the output voltage falls within a voltage range of 50 to 100% of the input voltage range of the detector. 2. In the method of measuring the magnetic properties of soft magnetic materials, the excitation coil applied voltage that satisfies predetermined excitation setting conditions is learned from the correlation between the excitation coil applied voltage, magnetic flux density, and magnetic field strength at the beginning of the measurement, and the demagnetization A magnetic measurement method characterized by measuring magnetic properties by making settings using excitation voltages learned later.