JPS6341033B2 - - Google Patents

Description

Detailed Description of the Invention The present invention utilizes the fact that when stress acts on a magnetic material, the core loss of the magnetic material changes in relation to the stress, and a magnetic sensor is brought into contact with the surface of the magnetic material. When the magnetic material is placed with
The present invention relates to a stress measurement method for determining stress from the measured iron loss.

For magnetic materials such as steel used in assembled structures, there is generally a relationship between stress and iron loss acting on the magnetic material, or between stress and iron loss change rate, as shown in Figure 1 or Figure 2. .

That is, FIG. 1 shows the relationship between the stress acting on the magnetic material and iron loss, and FIG. 2 shows the relationship between the stress acting on the magnetic material and the rate of change in iron loss.

Here, the rate of change in iron loss is defined as (W _i − W _p )/where W is the iron loss when no stress is applied to the magnetic material, and W _i is the iron loss when a certain amount of stress is applied. It is expressed as W _p ×100 (%).

Therefore, from the relationship shown in FIG. 1 or 2, by measuring the core loss of the magnetic material, the stress acting on the magnetic material can be determined.

The magnetic sensor 2 for measuring iron loss in this case includes a primary coil (excitation coil) 3 in a magnetic core 5 having a substantially U-shaped cross section, as shown in FIG. 4, which is an enlarged view of the AA cross section in FIG. It is constructed by winding a secondary coil (output secondary voltage coil) 4.

Note that a magnetic element such as a Hall element H may be used instead of the secondary coil 4 of the magnetic sensor 2. In this case, as shown in FIGS. 5b and 5c, a Hall element H is provided on the end face of the magnetic core of the magnetic sensor, which has a substantially U-shaped cross section, or in the middle of the magnetic core. In the following description, a case will be described in which the secondary coil 4 is used.

As shown in FIG. 3, measurement points 30 of the magnetic material 1
The magnetic sensor 2 is brought into close contact with the surface of the magnetic material 1, with the center of the magnetic sensor 2 aligned with the longitudinal direction or the center line perpendicular to the longitudinal direction with the direction in which the stress is to be measured. Deploy.

FIG. 5a shows a conventional stress measuring device in block diagram form. As mentioned above, the magnetic sensor 2 is placed in close contact with the magnetic material 1, the iron loss is measured, and the measured iron The iron loss change rate is determined from the loss, and the stress is converted from the relationship shown in FIG. 2 to determine the stress acting on the magnetic material 1.

This conventional stress measuring device for magnetic materials using iron loss includes an iron loss measuring device 28, an A/D converter 12,
Iron loss indicator 13, initial value setter 14, calculator 1
5. Consists of a stress indicator 16 and an indicator 17.

The iron loss measuring device 28 also includes an AC power supply 6, a magnetic sensor 2, a first amplifier 7, a second amplifier 8, a wattmeter 11, an output secondary voltage setting device 9, and an operational amplifier 1.
Consists of 0.

That is, the primary coil 3 of the magnetic sensor 2 is connected to the AC power supply 6 and the current terminal of the wattmeter 11 via the first amplifier 7, and the secondary coil 4 is connected to the current terminal of the wattmeter 11 via the rectifier (not shown). They are connected to voltage terminals of a power meter 11 via an amplifier 10 and a second amplifier 8, respectively.

Further, the output secondary voltage setter 9 is connected to the first operational amplifier 10.

The output side of this first operational amplifier 10 is an AC power supply 6
It is connected to the.

Further, the wattmeter 11 is connected to an A/D converter 12 , and the output side of the A/D converter 12 is connected to an iron loss indicator 13 and a calculator 15 .

It is obvious that if digital calculations are not to be performed, the wattmeter 11 may be connected directly to the calculator 15 instead of to the A/D converter 12.

An initial value setter 14 and a stress indicator 16 are connected to this calculator 15 .

The indicator 17 is connected to the output sides of the first amplifier 7 and the second amplifier 8 via a switch 18.

Now, when the primary coil 3 of the magnetic sensor 2 is excited by the AC power supply 6, the magnetic flux from the magnetic core 5 flows in the magnetic material 1 parallel to the direction of stress as shown by the arrow, as shown in FIG. A closed magnetic path returning to the magnetic core 5 is formed again.

At this time, the output secondary voltage induced in the secondary coil 4 of the magnetic sensor 2 is compared and subtracted from the voltage set in the output secondary voltage setting device 9 in the first operational amplifier 10, and the subtraction result is 6 will be fed back.

Then, the excitation current of the primary coil 3 is controlled so that the output secondary voltage of the second amplifier 8 is always kept constant, that is, equal to the set voltage of the output secondary voltage setting device 9.

Therefore, the output secondary voltage and the excitation current of the primary coil are introduced into the wattmeter 11 from the voltage terminal and current terminal of the wattmeter 11 via the first amplifier 7 and the second amplifier 8, respectively, and the voltage and current are The average value of the values multiplied by the value at the time of rest is displayed as the iron loss value.

Therefore, the iron loss of the magnetic material 1 can be accurately measured from the display on the wattmeter 11.

The iron loss measured in this way is converted into a numerically displayed iron loss W _i by the A/D converter 12, and in the case of an analog display, it is directly indicated to the iron loss indicator 13, and the arithmetic unit 15 sent to.

The calculator 15 calculates the iron loss W _p of the magnetic material 1 when the stress is 0, which is sent by the initial value setter 14, and
From the above iron loss W _i , from the formula for iron loss change rate mentioned above,
Calculate the rate of change in iron loss, convert the rate of change in iron loss to stress using the relationship shown in Figure 2, and convert the stress to stress indicator 1.
6.

The value of iron loss Wo set in the initial value setting device 14 is
The iron loss when no stress is applied to the magnetic material 1 can be read using the iron loss indicator 13.

In addition, the indicator 17 indicates the exciting current of the primary coil 3 of the magnetic sensor 2 or the output secondary voltage of the secondary coil 4 by switching the switch 18 to the exciting current side 26 or the output secondary voltage side 27. ,
If necessary, it can be used to check the set voltage of the output secondary voltage setting device 9, etc.

Since the conventional stress measuring device has the above-mentioned configuration, when the magnetic sensor 2 is placed in close contact with the surface of the magnetic material 1 so that the space is minimized, the primary If the excitation current of the coil 3 is controlled to keep the output secondary voltage induced in the secondary coil 4 of the magnetic sensor 2 constant and equal to the set voltage of the output secondary voltage setting device 9, the magnetic material 1 Since the magnetic flux flowing through the material is kept constant, the magnetic material 1
By measuring the iron loss, the stress acting on the magnetic material 1 can be accurately determined.

However, if the surface of the magnetic material 1 is uneven and the space in contact with the magnetic sensor 2 placed on the surface of the magnetic material 1 changes, the magnetic resistance increases in proportion to the size of the space. Therefore, a large magnetomotive force is required, and a large excitation current flows through the primary coil 3 of the magnetic sensor 2.

Moreover, as mentioned above, since the output secondary voltage of the magnetic sensor 2 is kept constant, a constant magnetic flux is generated in the magnetic core 5 of the magnetic sensor 2, but this magnetic flux is Proportionally, it leaks from the empty part,
The magnetic flux flowing through the magnetic material 1 decreases.

Therefore, the iron loss measured by the wattmeter 11 is
is smaller than the minimum case.

FIG. 6 is a diagram showing the above state.

In the figure, the horizontal axis represents the air current and excitation current, and the vertical axis represents the output secondary voltage and iron loss.

Now, the magnetic sensor 2 is placed on the surface of the magnetic material 1 on which no stress is applied so that the void is minimized (in Fig. 6, the minimum value of the void is shown as 0), and the primary The coil 3 is excited, and the exciting current is controlled so that the output secondary voltage becomes the set voltage _E2.When the exciting current is _I1 , the iron loss is _Wp , then when the air is 0,
A certain amount of stress is applied to the magnetic material 1, and the excitation current of the primary coil 3 is controlled so that the stress secondary voltage of the secondary coil 4 of the magnetic sensor 2 becomes the set voltage E2, and the current value is The iron loss when I _i1 (not shown) is Wi, and the vertical line 19 shows this relationship.

Next, the air in the contact area between the magnetic material 1 and the magnetic sensor 2 is
is increased, the air value is changed from 0 to a, and the excitation current of the primary coil is controlled so that the output secondary voltage of the secondary coil 4 of the magnetic sensor ₂ becomes the set voltage E2. Curves 20 and 21 show the measurement results of iron loss when no stress is applied and iron loss when a certain amount of stress is applied.
The iron loss decreases as the air space becomes larger, and when the air space is 0, the iron loss W _p and W _i are W ₀ ′ and W i when the air space is 0, respectively.
W _i ′.

Since the sky 〓a is usually small, the curves 20 and 21 can be regarded as straight lines.

Therefore, even if the same amount of stress is acting on the magnetic material 1, the larger the void, the smaller the iron loss, so the stress calculated from the iron loss will be smaller than the actual stress, and it is difficult to calculate the correct stress. The drawback was that it was not possible.

In view of the above points, the present invention provides a stress measuring method that can always accurately measure the stress of a magnetic material when a magnetic sensor is placed on the magnetic material, regardless of the size of the void in the contact area. .

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 7 is a block diagram of a stress measuring device for magnetic materials using the iron loss measuring device used in one method of measuring iron loss of the present invention, and FIG. FIG. 2 is a block diagram of a stress measuring device for magnetic materials using the iron loss measuring device.

In FIGS. 3 to 8, the same numbers represent the same members.

As mentioned above, when a magnetic sensor is placed on a magnetic material, as the contact area becomes larger, the excitation current of the primary side of the magnetic sensor, that is, the primary coil, increases and the iron loss decreases. .

Therefore, in response to an increase in the excitation current of the primary coil of the magnetic sensor, the secondary side, that is, the output secondary voltage of the secondary coil is increased to increase the magnetic flux generated in the magnetic core of the magnetic sensor, thereby reducing leakage from the air. If we compensate for the magnetic flux flowing through the magnetic material and make the magnetic flux flowing through the magnetic material the same as when the void is at a minimum, the iron loss will be constant regardless of the size of the void.

That is, as shown in Fig. 6, when no stress is acting on the magnetic material and there is an air gap a between the magnetic material and the magnetic sensor, the iron loss W _p when the air air is zero is
decreases to W ₀ ′, but the output secondary voltage of the magnetic sensor is increased along curve 25, and when the air gap becomes a, the output secondary voltage E ₂ when the air gap is 0 is increased to E ₂ ′. , the iron loss W ₀ ' can be made equal to W _p .

Curve 25 shows that the iron loss is always increased while increasing the air at the contact area between the magnetic material and the magnetic sensor from 0 to a.
The excitation current and output secondary voltage of the magnetic sensor can be measured so that W _p and can be expressed as a function of the output secondary voltage and excitation current.

Now, let 〓 be any value between 0 and a, and when the iron loss is held at W _p , the excitation current of the magnetic sensor is I, the output secondary voltage at that time is E (function of excitation current I), The sky where no stress is acting on the magnetic material is 0
When the excitation current is I ₁ and the output secondary voltage is E ₂ , the following relational expression is established: E=E2+∫ ^I _I1 dE/dI (1).

However, in reality, the sky 〓a is very small and the curve 25 can be regarded as almost a straight line, so (1)
dE/dI in the equation can be considered constant.

Therefore, by setting dE/dI=α, equation (1) becomes E=E ₂ +α(I-I ₁ )...(2).

The value of the constant α becomes a constant value once the type of magnetic sensor and the quality of the magnetic material are determined.

Next, when a certain stress is applied to the magnetic material, the output secondary voltage is increased in proportion to the increase in the excitation current of the magnetic sensor due to the air, in the same way as when no stress is applied to the magnetic material. Then, the iron loss that decreases due to the empty space is always made to be the same as the iron loss W _i when the empty space is 0.

In this case, a certain stress acts on the magnetic material, and the excitation current I _i1 of the magnetic sensor when the contact part with the magnetic sensor is zero, and the stress does not act on the magnetic material,
If the relationship with the excitation current I ₁ of the magnetic sensor when the contact portion of the magnetic sensor is empty = 0 is experimentally determined, I _i1 can be determined from I ₁ .

Therefore, the contact area between the magnetic material and the magnetic sensor is
Let I _i be the excitation current of the magnetic sensor when is an arbitrary value between 0 and a, and let the empty value from 0 to a be
Since the change in the excitation current of the magnetic sensor with respect to the change in can be considered to be linear as in the case where stress does not act, the voltage E _i required to compensate for the decrease in iron loss at that time can be expressed as Equation (2). Similarly, it can be obtained from E _i = E ₂ + α (I _i − I _i1 ) (3).

Here, in the present invention, if the material of the magnetic material and the type of magnetic sensor are the same, α will be the same value both when no stress is acting on the magnetic material and when stress is acting on the magnetic material. discovered this through experiments.

Therefore, regardless of the presence or absence of stress, when a magnetic sensor is placed on a magnetic material, the maximum void that can occur in the contact area is a, and the distance between void = 0 and a is always the same as when void = 0. In order to maintain iron loss,
The output secondary voltage E ₂ when the magnetic sensor is empty = 0 is,
A correction voltage obtained by multiplying the amount of increase in the excitation current due to the gap by the gain α may be added to obtain the output secondary voltage when the gap is greater than 0.

One method is to set the excitation current of the primary coil of the magnetic sensor when the contact area between the magnetic sensor and the surface of the magnetic material is minimum, and the air gap at the contact area between the magnetic sensor and the surface of the magnetic material to be The voltage obtained by adding the correction voltage corresponding to the difference in the excitation current of the primary coil of the magnetic sensor when 〓 is larger than the minimum value to the set voltage _E2 is the output secondary voltage induced in the secondary coil of the magnetic sensor. Control the excitation current of the primary coil so that it is equal to the voltage, and introduce the output secondary current of the secondary coil of the excitation current of the primary coil of the magnetic sensor into a wattmeter to measure the iron loss of the magnetic material. do it.

FIG. 7 shows a block diagram of a stress measuring device for magnetic materials using an iron loss measuring device using one of the stress measuring methods of the present invention described above. In the block diagram of the stress measuring device for magnetic materials using
Instead of 8, an iron loss measuring device 29 is used,
The iron loss measuring device 29 is the same as the iron loss measuring device 2 in FIG. 5a.
8 first operational amplifier 10 and output secondary voltage setting device 9
A first adding mechanism 31 is connected between the first amplifier 7 and
The input side of is connected to the input side of a second operational amplifier 22, and the excitation current setting device 23 is connected to the input side of this second operational amplifier 22.

Further, a gain setter 24 is connected in parallel to the second operational amplifier 22, and the output side of the second operational amplifier 22 is connected to the first addition mechanism 31.

The configuration other than this is the same as in FIG. 5.

Now, as shown in Fig. 3, the magnetic sensor 2 is placed on the surface of the magnetic material 1 so that the air space is minimized, and the output secondary voltage is adjusted so that no stress is applied to the magnetic material 1. When the set voltage _E2 is set on the setting device 9, the primary coil 3 of the magnetic sensor 2 is excited by the AC power supply 6, and the output secondary voltage induced in the secondary coil 4 becomes equal to the set voltage _E2. The current I ₁ is read by the indicator 17, the iron loss W _p at that time is read by the iron loss indicator 13, and the current I ₁ is read by the excitation current setting device 23.
Then, set the iron loss W _p in the initial value setting device 14, and set the iron loss in the gain setting device 24, which has been determined in advance by experiment, taking into consideration the material of the magnetic material and the type of magnetic sensor whose iron loss is to be measured. Set the value of constant α.

By making the settings as described above, you can correctly measure the magnetic material iron loss of the same material for which the above setting values were measured using the same type of magnetic sensor, regardless of the size of the air gap. Therefore, the correct stress acting on the magnetic material can be determined. That is, as shown in FIG. 3, when the magnetic sensor 2 is placed on the magnetic material 1 and the primary coil of the magnetic sensor 2 is excited by the AC power source 6, the exciting current I or I _i is introduced into the second operational amplifier 22. , is compared and subtracted from I _i or I _i1 set in the excitation current setting device 23, and multiplied by gain α to obtain α(I-I ₁ ) or α(I _i −I _i1 ).
Then, the addition mechanism 31 adds it to the voltage E2 set in the output secondary voltage setting device 9 to obtain E ₂ +α(I-I ₁ ) or E ₂ +α(I _i -I _i1 ), and then the first operational amplifier 10
will be introduced in In this first operational amplifier 10, this introduced E ₂ + α (I - I ₁ ) or E ₂ + α (I _i + I _i1 )
is compared with and subtracted from the induced voltage E or E ₁ of the secondary coil of the magnetic sensor 2 introduced separately, and the result of the subtraction is fed back to the AC power supply 6, so that E=E ₂
+ α (I - I ₁ ) or E _i = E ₂ + α (I _i - I _i1 ), that is, the output secondary voltage of the magnetic sensor is controlled so that the above formula (2) or (3) is satisfied. be done. Therefore, the exciting current I or I _i of the magnetic sensor 2 introduced into the wattmeter 11 via the first amplifier 7 and the second amplifier 8 and the output secondary voltage E = E ₂ + α (I - I _i ) or E _i = E ₂ + α (I _i − I _i1 )
Therefore, as described above, the measured value of the iron loss W _p or W _i can always be obtained regardless of the size of the void. Thereafter, the process of determining the stress acting on the magnetic material 1 from the measured iron loss is the same as that described in the conventional example shown in FIG. 5a.

Further, as another method of the present invention, the excitation current of the primary coil of the magnetic sensor when the contact area between the magnetic sensor and the surface of the magnetic material is minimum, and the The correction voltage corresponding to the difference in the excitation current of the primary coil of the magnetic sensor when the contact area is larger than the minimum value is equal to the set voltage E ₂ and the voltage of the magnetic sensor is kept constant. The output secondary voltage of the magnetic material is added to the output secondary voltage of the secondary coil, and this is introduced into the wattmeter together with the excitation current of the primary coil of the magnetic sensor as the output secondary voltage of the secondary coil of the magnetic sensor. There are ways to measure losses. Strictly speaking, this cannot be called an iron loss, but the inventor confirmed that it can be compensated for using this method as well.

Figure 8 shows a block diagram of a stress measuring device for magnetic materials using an iron loss measuring device that utilizes the iron loss measurement method described above. In the block diagram of the stress measuring device for magnetic materials, an iron loss measuring device 32 is used instead of the iron loss measuring device 28, and the iron loss measuring device 32 is the same as the iron loss measuring device 28 in FIG. 5a. the second of
A second addition mechanism 33 is connected between the amplifier 8 and the wattmeter 11, and the input side of the first amplifier 7 is connected to the input side of the second operational amplifier 22.
An excitation current setting device 23 is connected to the input side of 2. Further, a gain setter 24 is connected in parallel to the second operational amplifier 22.
The output side of 2 is connected to a second addition mechanism 33. The configuration other than this is the same as that in FIG. 5a. Now, as shown in Fig. 3, the magnetic sensor 2 is arranged so that the void on the surface of the magnetic material 1 is minimized, and the output secondary voltage setting device is set with no stress acting on the magnetic material 1. 9, the primary coil 3 of the magnetic sensor ₂ is excited by the AC power supply 6, and the current I when the output secondary voltage induced in the secondary coil 4 becomes equal to the set voltage _E2 . ₁ to indicator 17
Then, read the iron loss W _p at that time from the iron loss indicator 13, and input the current I ₁ to the exciting current setting device 23 to set the iron loss W _p
are respectively set in the initial value setter 14, and the value of α, which has been determined in advance through experiments, is set in the gain setter 24, taking into consideration the material of the magnetic material and the type of magnetic sensor whose iron loss is to be measured. do.

With the above settings, you can use the same type of magnetic sensor to accurately measure the iron loss of the same magnetic material used to measure the above settings, regardless of the size of the air. , therefore the correct stress acting on the magnetic material can be determined. That is, as shown in FIG. 3, when a magnetic sensor 2 is placed on a magnetic material 1 and the primary coil 3 of the magnetic sensor 2 is excited by an alternating current 6, the output voltage induced in the secondary coil 4 of the magnetic sensor 2 is The secondary voltage is compared and subtracted from a set voltage E ₂ introduced into the first operational amplifier 10 and set in the output secondary voltage setter 9. The subtraction result is fed back to the AC power supply 6, and the second
The output secondary voltage of the amplifier 8 is always a constant voltage, that is,
The excitation current of the primary coil 3 is controlled so as to be equal to the set voltage E ₂ of the output secondary voltage setting device 9.
Further, the excitation current I or I _i is introduced into the second operational amplifier 22, and the excitation current set in the excitation current setting device 23 is
It is compared with and subtracted from the current _Ii1 that can be calculated from the current _I1 based on _I1 or data obtained by experiment, and then multiplied by the gain α, resulting in α(I- _I1 ) or α( _Ii - _Ii1 ), The output secondary voltage E2 of the second amplifier 8 is added to this by the addition mechanism 33, and E= _E2 +α(I- _I1 )
Or, E _i = E ₂ + α (I _i − I _i1 ), and the above formula (2) or
The same value as in equation (3) is introduced into the wattmeter 11 as the output secondary voltage of the magnetic sensor 2. Also, magnetic sensor 2
The exciting current I or I _i is introduced into the power meter 11 via the first amplifier 7, and as mentioned above, it is possible to always obtain the measured value of the iron loss W _p or W _i regardless of the size of the air. can. Thereafter, the process of determining the stress acting on the magnetic material 1 from the measured iron loss is the same as that described in the conventional example shown in FIG. 5a.

As described above, when measuring stress in a magnetic material using the stress measurement method of the present invention, once the material of the magnetic material and the type of magnetic sensor whose stress is to be measured are determined, the output secondary voltage of the magnetic sensor is determined in advance. Set it on the output secondary voltage setting device, first, with no stress acting on the magnetic material, attach the magnetic sensor to the magnetic material so that the gap is minimized, and excite the primary coil of the magnetic sensor with the AC power supply. , confirm with the indicator that the output secondary voltage induced in the secondary coil is equal to the set voltage, read the excitation current of the primary coil at that time with the indicator, and set it in the excitation current setting device. After that, regardless of whether stress is acting on the magnetic material or not, the output secondary voltage will automatically increase in response to the increase in the excitation current of the magnetic sensor due to the air (Figure 7), or the output The secondary voltage is held constant and the increase in the output secondary voltage corresponding to the increase in the excitation current is added (Figure 8) to compensate for the decrease in iron loss due to the air flow. Regardless of the size of 〓, it is possible to always measure the iron loss that is equal to the iron loss of the magnetic material when 〓 is at its minimum, so it is possible to determine the correct stress acting on the magnetic material. Furthermore, the measured values of the embodiment shown in FIG. 7 are more accurate than those of the embodiment shown in FIG. On the other hand, since the embodiment shown in FIG. 8 is of a simple type, it has the advantage that the device does not become complicated.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between stress acting on magnetic material and iron loss, Figure 2 is a diagram showing the relationship between stress acting on magnetic material and iron loss change rate, and Figure 3 is a diagram showing the relationship between stress acting on magnetic material and iron loss change rate. The arranged plan view, Figure 4 is A in Figure 3.
- An enlarged cross-sectional view of A; Figure 5a is a block diagram of a stress measuring device for magnetic materials using a conventional iron loss measuring device; Figures 5b and c are front views of a magnetic sensor using a Hall element; FIG. 6 is an explanatory diagram of the principle of the present invention, FIG. 7 is a block diagram of a stress measuring device for magnetic materials using an iron loss measuring device using one method of the present invention, and FIG. FIG. 2 is a block diagram of a stress measuring device for magnetic materials using an iron loss measuring device using another method. DESCRIPTION OF SYMBOLS 1...Magnetic material, 2...Magnetic sensor, 3...Primary coil, 4...Secondary coil, 5...Magnetic core, 6...
...AC power supply, 7...First amplifier, 8...Second amplifier, 9...Output secondary voltage setter, 10...First operational amplifier, 11...Power meter, 22...Second operational amplifier, 23... Excitation current setting device, 24... Gain setting device, 29, 32... Iron loss measuring device, 31...
First addition mechanism, 33...Second addition mechanism, H...Hall element.

Claims (1)

[Claims] 1. A magnetic sensor is placed in contact with the surface of a magnetic material, and an excitation current on the primary side of the magnetic sensor is measured when no stress is acting on the magnetic material,
This measured value is set in the excitation current setting device, and when the contact area between the magnetic sensor and the surface of the magnetic material changes, the excitation current on the primary side and the setting value set in the excitation current setting device are calculated. Calculate the difference, and add the correction voltage obtained by multiplying the calculated excitation current difference by a constant determined by the type of magnetic sensor and the material of the magnetic material to the set voltage of the output secondary voltage setting device. , the excitation current on the primary side of the magnetic sensor is adjusted so that the output secondary voltage induced on the secondary side of the magnetic sensor is equal to the value obtained by adding the correction voltage to the set voltage of the output secondary voltage setting device. A stress measurement method that measures iron loss by controlling iron loss, and calculates stress from this iron loss. 2. Arranging a magnetic sensor in contact with the surface of a magnetic material, and measuring the excitation current on the primary side of the magnetic sensor when no stress is acting on the magnetic material,
This measured value is set in the excitation current setting device, and when the contact area between the magnetic sensor and the surface of the magnetic material changes, the excitation current on the primary side and the setting value set in the excitation current setting device are calculated. The difference is calculated, and the correction voltage obtained by multiplying the calculated excitation current difference by a constant determined by the type of magnetic sensor and the quality of the magnetic material is applied to the output secondary of the secondary side of the magnetic sensor. A stress measurement method in which iron loss is measured by adding this to a voltage and using this as an output secondary voltage on the secondary side of the magnetic sensor, and an exciting current on the primary side of the magnetic sensor, and calculating stress from this iron loss.