JPH05126798A - Method and device for measuring transformation rate - Google Patents

Abstract

PURPOSE:To precisely and simply measure a transformation rate in electric and magnetic characteristics accompanying heat treatment and the like on a metal plate of a steel plate and the like by bringing the device into contact therewith. CONSTITUTION:With a magnetizer 22 near the one hand face of an inspectionintended metal plate 25, the magnetizer 22 producing a magnetic flux for magnetizing the metal plate is arranged so that a pair of magnetic poles 23a, 23b may be opposed to each other. A pair of magnetic sensors 26a, 26b are arranged at right angles with the metal plate sandwiched at each opposed position of each magnetic pole in the direction of each magnetic induction and a subtraction magnetic flux DELTAPHI between each magnetic flux penetrating the metal plate detected with the magnetic sensors is found to measure a transformation rate of the metal plate by means of the subtraction magnetic flux value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transformation rate measuring method and a transformation rate measuring apparatus for measuring a transformation rate in a metal sheet such as a steel sheet using a mutual induction method.

[0002]

2. Description of the Related Art Maintaining a final structure that has a great influence on various mechanical properties and physical properties of steel sheets manufactured in steel mills in a constant state is a very important matter for maintaining high quality. Is.

For example, magnetic permeability among magnetic characteristics has a high correlation with mechanical characteristics such as hardness and grain size. Therefore, if the correlation between magnetic permeability and mechanical properties is measured in advance, the mechanical properties of the steel sheet can be estimated to some extent by measuring the magnetic permeability.

Also in the control of the manufacturing process, the austenite phase transforms to the ferrite phase during the heat treatment process of hot steel. If the transformation timing and transformation rate can be accurately monitored,
In the field of manufacturing various steel products using a hot rolling line and a heat treatment line, an extremely large effect on manufacturing quality can be expected. Further, in order to measure the magnetic properties of a steel sheet that actually flows continuously in the manufacturing process, it is necessary to perform these measurements in a non-contact and online state.

In the measurement of this phase transformation, the magnetic characteristics naturally change, so this magnetic change may be detected. Conventionally, when the magnetic characteristics of such a steel sheet are measured in a non-contact and online state, the property that the attenuation rate of the magnetic flux passing through the steel sheet to be inspected changes depending on the magnetic characteristics of the steel sheet is shown in FIG. The transformation rate measuring device shown below has been proposed (JP-A-56-82443).

That is, a magnetized iron core 2 and an excitation coil 3 are provided with a predetermined distance d ₁ on one side of a steel plate 1 to be inspected.
The magnetizer 4 made of is arranged so that the pair of magnetic poles 4a and 4b face the steel plate 1. An exciting current is applied to the exciting coil 3 of the magnetizer 4 from the magnetizing power supply 5. And
A magnetic detecting element 6 is arranged on the other side of the steel plate 1 with a distance d ₂ between them. The surface temperature of the steel sheet 1 is measured by the thermometer 7. The magnetic flux detected by the magnetic detection element 6 is transmitted to the arithmetic unit 8.

According to the transformation rate measuring device having such a configuration, most of the magnetic flux output from one magnetic pole 4a of the magnetizer 4 passes through the steel plate 1 and is input to the other magnetic pole 4b. When the magnetic field generated by the magnetizer 4 is large, a part of the magnetic flux 9 output from the one magnetic pole 4 a of the magnetizer 4 is part of the steel plate 1.
Through the space on the opposite side, the steel plate 1 is again penetrated in the opposite direction and input to the other magnetic pole 4b.

When the transformation rate of the steel sheet 1 changes, the magnetic characteristics such as the magnetic permeability of the steel sheet 1 change, and the strength Φ of the magnetic flux 9 penetrating the steel sheet 1 changes. Therefore, the transformation rate can be obtained by previously obtaining the reference magnetic flux strength of the test steel sheet having the known transformation rate and comparing the measured magnetic flux strength Φ with the reference flux strength. Further, while moving the steel sheet 1 in a certain direction, the strength Φ of the magnetic flux 9 leaked to the opposite side of the steel sheet 1 is continuously measured by the magnetic detection element 6, and the point at which the magnetic flux strength Φ largely changes is transformed on the steel sheet. It can be considered as a rate change point.

[0009]

However, the conventional transformation rate measuring apparatus shown in FIG. 6 still has the following problems.

That is, in addition to the magnetic flux 9 output from the magnetic poles 4a and 4b of the magnetizer 4 and penetrating the steel plate 1, the magnetic detection element 6 detects stray magnetic flux output from peripheral equipment. In particular, when this transformation rate measuring device is installed in the production line of the above-mentioned steel manufacturing plant, since many motors and various electric devices are arranged in the surroundings,
The magnetic flux leaking from these devices to the surroundings is large. When these magnetic fluxes intersect with the magnetic detection element 6, the signals caused by these floating magnetic fluxes are superimposed as noise components on the signal components caused by the regular magnetic flux 9 detected by the magnetic detection element 6.

Therefore, the signal component ratio of the normal magnetic flux 9 in the output signal of the magnetic detection element 6 is reduced, the S / N of the entire output signal is reduced, and the magnetic flux intensity Φ of the magnetic flux 9 is minutely changed. Cannot be detected accurately. Therefore, the measurement accuracy of the transformation rate of the steel sheet 1 is reduced.

In order to eliminate such an inconvenience, the distance d ₂ between the magnetic detection element 6 and the steel plate 1 may be set short and the number of magnetic fluxes 9 intersecting the magnetic detection element 6 may be increased. However, since the steel plate 1 is moving at a considerable speed while vibrating, there is a concern that a contact accident or the like may occur if the magnetic detection element 6 is brought too close. Further, when the temperature of the steel sheet 1 is high, there is a concern that the magnetic detection characteristics of the magnetic detection element 6 may change or the signal level of the detection signal may change if the steel plate 1 is brought too close.

The present invention has been made in view of the above circumstances, and a pair of magnetic poles of a magnetizer and a pair of magnetic sensors are arranged so as to face each other with a metal plate to be inspected interposed therebetween. It is possible to cancel the noise component caused by the stray magnetic flux of, can accurately detect the intensity of the magnetic flux penetrating the metal plate, and to provide a transformation rate measuring method and its device, which can significantly improve the transformation rate measurement accuracy. To do.

[0014]

In order to solve the above-mentioned problems, according to the transformation rate measuring method of the present invention, the magnetization for generating a magnetic flux that magnetizes the metal plate to be inspected is close to one surface of the metal plate to be inspected. A pair of magnetic sensors are arranged so that the pair of magnetic poles face the metal plate, and the pair of magnetic sensors are arranged at the respective facing positions of the respective magnetic poles with the metal plate sandwiched therebetween and in the directions in which the respective magnetically sensitive directions are orthogonal to the metal plate. The subtraction magnetic flux between the magnetic fluxes penetrating the metal plate detected by the pair of magnetic sensors is obtained, and the transformation rate of the metal plate is measured by the subtraction magnetic flux value.

Further, the transformation rate measuring apparatus of the present invention is provided with a magnetizer, which is provided with a pair of magnetic poles facing one surface of a metal plate to be inspected, and which generates a magnetic flux for magnetizing the metal plate, and a metal plate. A pair of magnetic sensors for detecting magnetic flux penetrating the metal plate, which are arranged at opposite positions of each magnetic pole with the magnetic poles sandwiched therebetween and in a direction in which each magnetic sensitive direction is orthogonal to the metal plate, and each detection of the pair of magnetic sensors. It is provided with a subtraction circuit for subtracting a signal, and a signal processing unit for obtaining the transformation rate of the metal plate based on the subtraction magnetic flux value obtained by the subtraction circuit.

[0016]

The operation principle of the transformation rate measuring method and apparatus thus constructed will be described with reference to FIG.

In FIG. 2, each magnetic pole 10 of the magnetizer 10 is shown.
a and 10b face one surface of the metal plate 12 to be inspected. Then, the magnetic poles 10a and 10 with the metal plate 11 sandwiched therebetween.
A pair of magnetic sensors 13a and 13b are arranged at positions facing each other. The magnetic sensitive direction of each magnetic sensor 13a, 13b is set to the direction orthogonal to the metal plate 11 shown by the Y direction in the drawing. Then, for example, most of the magnetic flux output from one magnetic pole 10a of the magnetizer 10 is input to the other magnetic pole 10b via the inside of the metal plate 11. However, a part of the magnetic flux output from the magnetic pole 10a of the magnetizer 10 is part of the metal plate 1.
Penetrate 1 The magnetic flux 14 penetrating the metal plate 11 passes through the space on the opposite side of the metal plate 11 and again penetrates the metal plate 11 in the opposite direction and is input to the other magnetic pole 10b.

Each magnetic sensor 13a, 13b is a metal plate 11
Intensity of the Y direction component of the magnetic flux 14 penetrating the
To detect. If there is stray magnetic flux output from equipment around the transformation rate measuring device, the magnetic flux intensity Φn of the stray magnetic flux in the Y direction is detected by the magnetic sensors 13a and 13b. Therefore, the magnetic flux intensities Φ _A and Φ _B in the Y direction detected by the magnetic sensors 13a and 13b are as follows. Φ _A = Φa + Φn Φ _B = Φb + Φn Therefore, when the magnetic flux intensity difference ΔΦ between the magnetic flux intensities Φ _A and Φ _B detected by the magnetic sensors 13a and 13b is calculated, the stray magnetic flux intensity Φn is offset. ΔΦ = Φa−Φb

The magnetic sensors 13a and 13b are magnetizers 10, respectively.
Since the magnetic fluxes Φa and Φb of the magnetic flux 14 have the same value and the polarities are opposite to each other (Φb = −Φa), since the magnetic poles 10a and 10b are arranged at opposite positions. Therefore, by calculating the magnetic flux intensity difference ΔΦ between the magnetic flux intensities Φ _A and Φ _B detected by the magnetic sensors 13a and 13b, it is possible to measure the correct magnetic flux intensity including no stray magnetic flux. ΔΦ = −Φb = 2Φa In this way, the stray magnetic flux detected by each magnetic sensor can be canceled out, so that the transformation rate of the metal plate can be measured with a high S / N.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a schematic configuration of a transformation rate measuring device to which the transformation rate measuring method of the embodiment is applied. The transformation rate measuring apparatus of this example is incorporated in a heat treatment line in a steelmaking factory and used to measure the transformation rate of a steel sheet continuously moved at high speed.

The magnetizing power source 21 outputs an alternating exciting current I having a constant frequency f ₁ . The exciting current I output from the magnetizing power source 21 is applied to the exciting coil 24 wound around the magnetized iron core 23 of the magnetizer 22. The magnetizer 22 includes magnetic poles 23a and 23b of a magnetized iron core 23 having a substantially U shape.
Is a distance La to the lower surface of the steel plate 25 as the metal plate to be inspected.
They are arranged so as to face each other apart by (lift-off). The steel plate 25 is conveyed in a direction orthogonal to the paper surface.

A pair of magnetic sensors 26a and 26b having the same structure are provided on the upper surface of the steel plate 25 at a position separated by a distance Lb and at positions facing the magnetic poles 23a and 23b of the magnetizer 22. The output signals a ₁ and a ₂ of the magnetic sensors 26a and 26b are input to the magnetic detection circuits 27a and 27b, respectively. The output signals a ₁ and a ₂ of the magnetic sensors 26a and 26b are strengths Φ _A and Φ _{B of} magnetic fluxes that intersect the magnetic sensors 26a and 26b in the magnetic detection circuits 27a and 27b.
Are converted into detection signals b ₁ and b ₂ . Each detection signal b ₁ output from each magnetic detection circuit 27a, 27b,
b ₂ is input to the next differential amplifier 28. The differential amplifier 28 detects the difference signal c between the detection signals b ₁ and b ₂ and sends it to the next signal processing unit 29.

The signal processing unit 29 is composed of, for example, an amplifier and a recorder, and the transformation rate A is calculated by using a calibration curve which is experimentally obtained in advance from the magnetic flux intensity ΔΦ contained in the input difference signal c. Is output to the recorder. The recorder records the change in the transformation rate A over time.

As the magnetic sensors 26a and 26b, the supersaturation type magnetic sensor described in Japanese Patent Laid-Open No. 1-308982 is adopted. That is, this magnetic sensor 26
In a and 26b, detection coils 31a and 31b are wound around rod-shaped cores 30a and 30b made of a ferromagnetic material. Further, high-frequency exciting currents are continuously applied to the detection coils 26a and 26b from the high-frequency power sources 32a and 32b having the same structure via the resistors 33a and 33b. Each of the rod-shaped cores 30a and 30b is in a state of being excited to a supersaturation region. Therefore, each detection coil 31
The amplitude value of the output voltage waveform across a and 31b is constant.

The rod-shaped core 3 excited by such supersaturation
When the external magnetic flux approaches 0a and 30b, the amplitude value of the voltage waveform at both ends does not change, but the positive and negative peak values Va and -V are obtained.
b changes. Therefore, the magnetic detection circuits 27a, 27
In b, each of the peak values Va and -Vb is detected by a detector, converted into direct current, and added by an adder to obtain a differential voltage (Va-Vb). That is, the difference voltage (Va-Vb) corresponds to the external magnetic flux applied to the magnetic sensors 26a and 26b. Therefore, from the magnetic detection circuits 27a and 27b to the magnetic sensors 26a and 2b, respectively.
The detection signals b ₁ and b ₂ corresponding to the magnetic flux intensities Φ _A and Φ _B of the magnetic fluxes applied to 6b are output. The magnetic detection circuits 27a, 2 in the magnetic sensors 26a, 26b.
The frequency response performance of each of the detection signals b ₁ and b ₂ output from 7b is sufficiently higher than the frequency f _{1 of the} exciting current I. Therefore, the difference signal c output from the differential amplifier 28 indicates the magnetic flux intensity ΔΦ which is the difference between the magnetic flux intensities Φ _A and Φ _B. ΔΦ = Φ _A −Φ _B

In the transformation rate measuring device having such a structure, when the magnetizing power supply 21 is activated, the magnetizer 22 magnetizes the steel plate 25. Then, for example, one magnetic pole 23
Most of the magnetic flux output from a is input to the other magnetic pole 23b passing through the steel plate 25, but a part of the magnetic flux is applied to the steel plate 2.
5 is passed through and passes through the space of the steel plate 25 on the side of the magnetic sensors 26a and 26b and again penetrates the steel plate 25 in the opposite direction and is input to the other magnetic pole 23b.

Since the magnetic sensitive directions of the magnetic sensors 26a and 26b are orthogonal to the steel plate 25, the magnetic sensors 26a and 26b have the magnetic flux of the steel plate 2 which penetrates the steel plate 25.
The respective strengths Φa and Φb in the direction orthogonal to 5 and the magnetic flux strength Φn in the direction orthogonal to the steel plate 25 among the stray magnetic fluxes output from the surrounding electric devices are detected. Therefore, as described above, the magnetic flux intensities Φ _A and Φ _B detected by the magnetic sensors 26a and 26b are as follows. Φ _A = Φa + Φn Φ _B = Φb + Φn

Therefore, the component of the stray magnetic flux intensity Φn can be removed from the magnetic flux intensity difference (subtraction magnetic flux) ΔΦ (= Φa−Φb) obtained by the differential amplifier 28. In addition, each magnetic sensor 26
Since a and 26b are arranged at the opposite positions of the magnetic poles 23a and 23b of the magnetizer 22, the magnetic flux intensities Φa and Φb have the same value and the polarities are opposite to each other (Φb = -Φa). Therefore, by calculating the magnetic flux intensity difference ΔΦ between the magnetic fluxes Φ _A and Φ _B detected by the magnetic sensors 26a and 26b,
It is possible to measure the correct magnetic flux strength that does not include stray magnetic flux. ΔΦ = Φa−Φb = 2Φa

Therefore, this magnetic flux intensity difference ΔΦ is the steel plate 2
The value corresponds to the transformation rate A of 5. The signal processing unit 29 records the time conversion of the transformation rate A converted from this magnetic flux intensity difference ΔΦ using a calibration curve.

FIG. 3 shows a difference corresponding to the magnetic flux intensity difference ΔΦ of the differential amplifier 27 when the transformation rate is measured by the apparatus of the embodiment for a large number of test steel sheets having a known transformation rate A of 0 to 100%. It is a characteristic view of the relationship between the output level (mV) of the signal c and the transformation A. However, the thickness T of the test steel plate is 5.6 mm, the distance B from each magnetic pole 23a, 23b to each magnetic sensor 26a, 26b is 500 mm, and the magnetizing frequency f ₁ of the magnetizer 22 is set to 10 Hz. ing. The average voltage e _m of the high-frequency signal outputted high-frequency power source 32a, from 32b is 3 mV. The characteristics indicated by the solid line in the figure are characteristics under the condition that the lift-off La is 100 mm, and the characteristics indicated by broken lines are characteristics under the condition that the lift-off La is 100 mm. Therefore, the characteristic of FIG. 3 becomes the calibration characteristic.

As shown in the characteristics of FIG. 3, the transformation rate is 0 to 1
Output voltage is 83-240mV for the range of change of 00%
And a very wide measurement range was obtained. Therefore, the distance Lb between the magnetic sensors 26a and 26b and the steel plate 25 is
Even if it is set large, a sufficiently high detection level can be secured. The lift-off La is 100 to 125 mm (25
%), The output signal level converted to the transformation rate A was less than 5%, and a very good value was obtained.
Further, although not shown in the graph of FIG. 3, since the component of the stray magnetic flux is removed as described above, high repeatability measurement accuracy can be secured.

In FIG. 4, the exciting coil 2 of the magnetizer 22
Change of the output level of the differential amplifier 28 of the apparatus of the embodiment when the excitation frequency f ₁ of the excitation current I applied to 4 is changed from 0 Hz (DC) to 240 Hz, and the supersaturated magnetic sensors 26a and 26b of the embodiment. Instead of, a comparison with the output level change when using a conventional ordinary search coil type magnetic sensor that is not a supersaturation type magnetic sensor is shown. In addition,
A conventional search coil type magnetic sensor is a magnetic sensor in which a coil is wound around a ferrite core and an induced voltage generated in the search coil by an external magnetic field is detected. As shown in FIG. 4, in the search coil type magnetic sensor, the detection sensitivity largely depends on the frequency of the measured magnetic flux, and at a frequency of about 220 Hz or less, the detection sensitivity is much lower than that of the supersaturation type magnetic sensor. In addition,
The number of coil turns in this search coil type magnetic sensor is 15
It is 00 times.

On the other hand, the detection sensitivity of the oversaturated magnetic sensor of the present embodiment does not depend on the number of turns, and the number of coil turns is far smaller than that of the conventional search coil type magnetic sensor (200 turns in this example). I'm done.

Generally, the excitation frequency f ₁ is determined by the inspection purpose and the steel plate 2
The optimum frequency is set according to the thickness T of 5. And
The inspection purpose is transformation rate measurement, and the thickness T of the steel plate 25 is 1 to
In the range of 10 mm, the excitation frequency f ₁ is often set in the range of several Hz to several tens of Hz. Therefore, as shown in the frequency characteristic diagram of FIG. 4, the magnetic sensors 26a and 26b are
By using a supersaturation type magnetic sensor, a constant output signal level can be obtained in a wide frequency range. FIG. 5 is a schematic configuration diagram of a transformation rate measuring device according to another embodiment of the present invention. The same parts as those in the embodiment of FIG. 1 are designated by the same reference numerals.

In this embodiment, the detection coils 36a and 36b are wound around the rod-shaped cores 35a and 35b of the magnetic sensors 34a and 34b, which are arranged to face the magnetic poles 23a and 23b of the magnetizer 22, respectively. Has been done. The winding directions of the detection coils 36a and 36b are the same. The high frequency signal output from the high frequency power supply 32 is applied to the winding start terminal St of the detection coil 36a of the one magnetic sensor 34a via the resistor 33. The winding terminator En of the detection coil 36a is connected to the winding terminator En of the detection coil 36b of the detection coil 34b of the other magnetic sensor 36b. Then, the winding start terminal S of the detection coil 36b
t is grounded.

The output signal a extracted from the winding start terminal St of the magnetic sensor 34a is input to the magnetic detection circuit 27. The magnetic detection circuit 27 detects the magnetic flux intensity from the output signal a and sends it to the next signal processing unit 29.

In the transformation rate measuring device having such a structure, the magnetic sensors 34a and 34b act so that the signal levels shift in opposite directions with respect to the external magnetic field.
Therefore, the stray magnetic flux intensities Φn detected by the magnetic sensors 34a and 34b have opposite polarities. Therefore, the stray magnetic flux intensities Φn cancel each other out in the output signals a of the magnetic sensors 34a, 34b connected in series. Also,
Since the magnetic flux penetrating the steel plate 25 from the magnetizer 22 acts on the magnetic sensors 36a and 36b in opposite directions, the output signal a includes information on the added intensity 2Φa of each magnetic flux.

Therefore, in this embodiment, the detection coils 36a and 36b of the magnetic sensors 34a and 34b are detected.
The wiring between and forms a subtraction circuit. Therefore, it becomes possible to remove the differential amplifier 28 of FIG. 1 and directly apply the output signal g of the magnetic detection circuit 27 to the signal processing unit 29.

Therefore, it is possible to obtain substantially the same effect as that of the embodiment of FIG. Further, in this embodiment, as compared with the embodiment of FIG. 1, the high frequency power source 32 can be implemented by one unit and the differential amplifier 28 can be removed, so that the entire device can be made small and lightweight and at low manufacturing cost. Can be manufactured.

The present invention is not limited to the above embodiment. In the apparatus of the embodiment, the magnetic sensor 2
A supersaturation type magnetic sensor having excellent temperature characteristics and detection sensitivity characteristics is used as 6, but a semiconductor magnetic sensor using a Hall element with a temperature guarantee circuit may be used, for example. Further, the effect of the present invention can be sufficiently achieved even if the detection sensitivity is low or an ordinary search coil type magnetic sensor is used.

[0041]

As described above, according to the transformation rate measuring method and transformation rate measuring apparatus of the present invention, the pair of magnetic poles of the magnetizer and the pair of magnetic sensors are opposed to each other with the metal plate to be inspected interposed therebetween. Are arranged. Therefore, by taking the difference between the outputs of the magnetic sensors, the noise component caused by the external stray magnetic flux can be canceled. In addition, since the magnetic flux penetrating the metal plate acts on each magnetic sensor in opposite directions,
By taking the difference, the magnetic flux penetrating the metal plate can be detected with twice the sensitivity. Therefore, the intensity of the magnetic flux penetrating the metal plate can be accurately detected with a high S / N ratio, and as a result, the transformation rate of the metal plate can be more accurately measured.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a schematic configuration of a transformation rate measuring apparatus to which a transformation rate measuring method according to an embodiment of the present invention is applied,

FIG. 2 is a diagram showing the operating principle of the present invention,

FIG. 3 is a diagram showing a relationship between a transformation rate of a sample steel sheet and an output voltage level measured by an apparatus of Example,

FIG. 4 is a diagram showing frequency characteristics of different types of magnetic sensors used in the embodiment apparatus;

FIG. 5 is a schematic diagram showing a schematic configuration of a transformation rate measuring apparatus according to another embodiment of the present invention,

FIG. 6 is a schematic diagram showing a schematic configuration of a conventional transformation rate measuring device.

[Explanation of symbols]

21 ... Magnetization power source, 22 ... Magnetizer, 23 ... Magnetized iron core, 23
a, 23b ... magnetic pole, 24 ... exciting coil, 25 ... steel plate, 2
6a, 26b, 34a, 34b ... Magnetic sensor, 27, 2
7a, 27b ... Magnetic detection circuit, 28 ... Differential amplifier, 29
... Signal processing unit, 32, 32a, 32b ... High-frequency power source.

Claims (2)

[Claims] 1. A magnetizer for generating a magnetic flux that magnetizes the metal plate in close proximity to one surface of the metal plate to be inspected is arranged such that a pair of magnetic poles face the metal plate, and the metal plate is attached to the metal plate. A pair of magnetic sensors are arranged at opposite positions of the magnetic poles and in a direction in which each magnetic sensitive direction is orthogonal to the metal plate.
A transformation rate measuring method for obtaining a subtraction magnetic flux between the respective magnetic fluxes penetrating the metal plate detected by the pair of magnetic sensors and measuring the transformation rate of the metal plate with the subtraction magnetic flux value. 2. A magnetizer, which is arranged so that a pair of magnetic poles face each other on one surface of a metal plate to be inspected, and which generates a magnetic flux that magnetizes the metal plate, and each of the magnetic poles sandwiching the metal plate. A pair of magnetic sensors, which are arranged at opposite positions and in which magnetic sensitive directions are orthogonal to the metal plate, detect magnetic flux penetrating the metal plate, and subtract each detection signal of the pair of magnetic sensors. A transformation rate measuring device comprising: a subtraction circuit; and a signal processing unit that obtains a transformation rate of the metal plate based on a subtraction magnetic flux value obtained by the subtraction circuit.