JPH10332433A - Magnetostrictive displacement detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetostrictive displacement detector that solves such a problem as influence of amplitude fluctuation of a twist elastic wave caused by the position of a permanent magnet and temperature change and can detect the axial direction displacement of magnetostrictive line given to the permanent magnet with precision. SOLUTION: By allowing a current pulse to flow in axial line direction or a magnetostractive line 1, a twist elastic wave is generated at such part of the magnetostrictive line 1 as close to a permanent magnet 9 movable along the magnetostrictive line 1, and by measuring a propagation time of the twist elastic wave to receiver 7, a mechanical displacement given to the permanent magnet 9 is detected. A peak hold value of a detected waveform of the receiver 7 is held by a peak hold circuit 11, and an amplification degree of a variable gain amplifier 12 is varied by a deviation between the peak value and a reference value, so that a detection waveform of almost constant level is obtained regardless of change in position of the permanent magnet 9 or ambient temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetostrictive displacement detecting device for detecting a mechanical displacement of an object or a displacement of a liquid surface by using a magnetostrictive phenomenon.

[0002]

2. Description of the Related Art Conventionally, as a magnetostrictive displacement detecting device, FIG.
As shown in (1), by applying a current pulse from the pulse generation circuit 31 to the magnetostrictive wire 30, a torsional elastic wave (ultrasonic wave) is generated at a portion of the magnetostrictive wire close to the permanent magnet 32 movable along the magnetostrictive wire 30. Is known to detect the mechanical displacement applied to the permanent magnet 32 by measuring the propagation time of the torsional elastic wave to the receiver 33 provided on the starting end side of the magnetostrictive wire 30. (For example, JP-A-61-1129
No. 23). Both ends of the magnetostrictive wire 30 are made of damping materials 34 and 35 such as rubber for suppressing the reflection of torsional elastic waves.
Is held in.

FIG. 2 is a waveform diagram showing a method of detecting the displacement of the permanent magnet 32. A is a current pulse, B is a receiver 33
And C is a waveform obtained by shaping the waveform B.
By measuring the time t from the supply of current pulses A to reach the waveform C _1, the following equation can be measured the displacement x given to the permanent magnet 32. x = v · t Here, v is the propagation speed of the torsional elastic wave.

[0004]

By the way, the permanent magnet 3
The torsional elastic wave generated at the portion 2 reaches the receiver 33 through the magnetostrictive wire 30, but has a property of being attenuated while propagating through the magnetostrictive wire 30. The attenuation increases as the distance between the permanent magnet 32 and the receiver 33 increases.
In the case of the displacement detection device using the magnetostrictive wire 30 of m, the receiver 3
3, the amplitude of the torsional elastic wave generated at the farthest position is attenuated to about half depending on the material of the magnetostrictive wire. Therefore, a displacement detection device that can obtain a detection waveform of a substantially constant level regardless of the position of the magnetostrictive wire 30 of the permanent magnet 32 in the axial direction by changing the amplification degree together with the propagation time of the torsional elastic wave is proposed. (JP-A-5-187854).

When the permanent magnet 32 is inserted through the magnetostrictive wire 30 as shown in FIG. 1, the distance between the permanent magnet 32 and the magnetostrictive wire 30 in the direction perpendicular to the axis is substantially constant.
However, when the permanent magnet 32 is not inserted through the magnetostrictive wire 30, the permanent magnet 32 may move far away from the magnetostrictive wire 30 in a direction perpendicular to the axis thereof. Permanent magnet 3
When 2 is far away from the magnetostrictive wire 30, the torsional elastic wave becomes smaller than when it is close to the magnetostrictive wire 30. For example, when the axial distance of the magnetostrictive line between the permanent magnet 32 and the receiver 33 is constant, compared to a torsional elastic wave generated when the vertical distance between the permanent magnet 32 and the magnetostrictive line 30 is 18 mm.
The amplitude of the torsional elastic wave generated at a vertical distance of 28 mm is about half under certain conditions. However, even if the permanent magnet 32 moves away from the magnetostrictive wire 30, the propagation time of the torsional elastic wave is almost the same as when it is close to the magnetostrictive wire 30, so that the amplification changes with the propagation time of the torsional elastic wave. With this method, a detection waveform of a substantially constant level cannot be obtained.

Further, since the magnetostrictive displacement detecting device is a detecting device using magnetism, the magnetic transformation point of the magnetostrictive wire cannot be ignored. Although the magnetic transformation point depends on the material of the magnetostrictive wire, it is about 150
When the ambient temperature exceeds the magnetic transformation point, the magnetostriction phenomenon disappears and the device does not function as a displacement detection device. Further, even if the ambient temperature does not exceed the magnetic transformation point, the amplitude of the generated torsional elastic wave is reduced only by approaching the magnetic transformation point.

Here, the amplitude change of the torsional elastic wave depending on the position and temperature of the permanent magnet will be described with reference to FIG. The waveform Xa is a detection waveform when the permanent magnet is close to the receiver and approaches the magnetostriction line, and the waveform Xb is a detection waveform when the distance in the axial direction of the magnetostriction line is the same as the waveform Xa, and is a detection waveform when the distance is away from the magnetostriction line. Ya is a detection waveform when the permanent magnet moves away from the receiver and approaches the magnetostriction line, and waveform Yb is a detection waveform when the distance in the axial direction of the magnetostriction line is the same as the waveform Ya and moves away from the magnetostriction line. Further, the solid line is at normal temperature, and the broken line is at the time of temperature rise.

In general, peaks xa1, xb1, which are originally required peaks, are generated in a torsional elastic wave generated at a portion of a permanent magnet.
Unnecessary mountains xa2, xb2, ya before ya1, yb1
2, yb2. When the ambient temperature is constant and the distance between the permanent magnet and the magnetostrictive wire is constant, the reference level (trigger point) T for detecting the arrival of the torsional elastic wave is higher than the peak xa2 of the waveform Xa at the nearest point. In addition, if the peak is set to a value lower than the peak ya1 of the waveform Ya at the farthest point, the peaks xa1 and ya1 of the waveforms Xa and Ya can always be detected. However, when the permanent magnet moves away from the magnetostriction line, the torsional elastic wave is attenuated, so that not only the peak yb1 but also the peak xb1 at the trigger point T.
Even cannot be detected. Further, since the attenuation occurs as shown by the broken line even when the temperature rises, it becomes more difficult to set the trigger point T.

Therefore, an object of the present invention is to eliminate the influence of the amplitude fluctuation of the torsional elastic wave due to the change in the position and temperature of the permanent magnet, and to make the permanent magnet extend over a wide range in the axial direction of the magnetostrictive wire and in the direction perpendicular to the axial line. It is an object of the present invention to provide a magnetostrictive displacement detection device which can detect a mechanical displacement of a magnetostrictive wire applied to a permanent magnet in the axial direction even if it moves, and can widen a usable temperature range.

[0010]

In order to achieve the above-mentioned object, the present invention provides a method in which a current pulse is applied in the axial direction of a magnetostrictive wire so that a permanent magnet that can move along the magnetostrictive wire is moved in proximity to the magnetostrictive wire. A device that generates a torsional elastic wave at a site and measures the mechanical displacement applied to the permanent magnet by measuring the propagation time of the torsional elastic wave to a receiver provided at a specific portion of the magnetostrictive wire A variable gain amplifier circuit, which changes the amplification degree according to the maximum value of the detected waveform of the torsional elastic wave and obtains a substantially constant level detection waveform regardless of the change of the position of the permanent magnet and the ambient temperature, is provided in the receiver. Connected.

For example, assuming that a current pulse is applied directly to the magnetostrictive wire, the application of the current pulse generates a torsional elastic wave at a portion of the magnetostrictive wire close to the permanent magnet. And is detected by the receiver. When the permanent magnet approaches the magnetostriction line, a large detection waveform is obtained, but when it is far away, a small detection waveform is obtained even if the axial distance of the magnetostriction line of the permanent magnet is the same. In the present invention, since the amplification degree is changed according to the maximum value of the torsional elastic wave detected by the receiver, if the permanent magnet is far from the magnetostriction line, the detection waveform is greatly amplified, When approaching, the waveform is amplified at a small level, thereby obtaining a waveform having a substantially constant level. Therefore, the detection can be reliably performed regardless of the change in the position of the permanent magnet or the ambient temperature, and the setting of the trigger point is simplified.

The variable gain amplifying circuit includes, for example, a peak hold circuit for holding a peak value of a torsional elastic wave detection waveform, and amplifying degree is varied by a deviation between the peak value and a reference value to amplify the detection waveform. Variable gain amplifier. In this case, the variable gain amplifier circuit can be constituted by a simple and inexpensive circuit.

[0013]

FIG. 4 shows an example of a magnetostrictive displacement detecting device according to the present invention. The start end of the magnetostrictive wire 1 is clamped by a clamp member 3 fixed on a base 2, and the end is supported by a support member 5 via a spring 4. Therefore, a constant tension is always applied to the magnetostrictive wire 1. Note that a damping material 6 such as silicon rubber is applied to the end of the magnetostrictive wire 1 so as to suppress the influence of the reflected wave from the spring 4 or the support member 5. Receiver 7
Is disposed near the clamp member 3, and the magnetostrictive wire 1 penetrates the center of the built-in coil 7a in a non-contact manner.
The coil 7a detects the arrival of a torsional elastic wave propagating through the magnetostrictive wire 1 using the inverse magnetostriction effect. The negative electrode of the coil 7a is grounded, and the positive electrode is connected to the pre-amplifier 8. In the vicinity of the magnetostrictive wire 1, a permanent magnet 9 movable in the axial direction (x direction) of the magnetostrictive wire 1 and in the direction perpendicular to the axis (y direction) is arranged. Although the permanent magnet 9 of this embodiment has an annular shape, it is not inserted through the magnetostrictive wire 1.

At the beginning of the magnetostrictive wire 1 protruding from the clamp member 3, a current pulse A is supplied periodically (for example, 100 Hz to 1 kHz) from the pulse generation circuit 10, and the magnetostrictive wire 1
Is returned to the ground of the pulse generating circuit 10 via the spring 4 from the end of the pulse generating circuit 10. When the current pulse A is supplied, a torsional elastic wave is generated at the portion of the magnetostrictive wire 1 close to the permanent magnet 9 due to the Biedemann effect, and is detected by the receiver 7. The detected torsional elastic wave is amplified by the pre-amplifier 8. The output B of the pre-amplifier 8 is input to the peak hold circuit 11 and also to the variable gain amplifier 12 via the masking circuit 17. The masking circuit 17 removes the electromagnetic noise B ₀ appearing in the detection waveform when the current pulse is applied, and is operated only for a certain period from the time when the current pulse A is applied.

The peak hold circuit 11 detects the peak value of the amplified detection waveform B, and outputs a current pulse A
Is reset immediately after the application of the clock signal (time t ₁ ). Therefore, a reset signal is sent from the pulse generation circuit 10 to the peak hold circuit 11 via the delay circuit 18. The output D of the peak hold circuit 11 is input to the sample hold circuit 13, where the detected peak value is sampled and held. Note that the sampling signal is also supplied to the sample and hold circuit 13 from the pulse generation circuit 10 via the delay circuit 18 and, of the peak value D detected by the peak hold circuit 11, immediately before the application of the next current pulse A (at time The peak value at t ₂ ) is sampled. The reason is that sampling can be performed even when the permanent magnet 9 is farthest from the receiver 7 in the x direction. The output E of the sample and hold circuit 13 is
Is compared with the reference signal G. The difference between the two is input to the gain adjustment circuit 15, and the gain of the variable gain amplifier 12 is determined. The output B of the pre-amplifier 8 is amplified by the determined gain, and a detection waveform having a constant peak value regardless of the position of the permanent magnet 9 in the x direction or the y direction or the fluctuation of the ambient temperature. F can always be obtained. Note that an integration element 16 or the like may be inserted to make the deviation between the reference signal G and the peak value E of the amplified detection waveform zero.

Referring now to the waveform diagram of FIG.
The operation of the displacement detection device will be described. First, when a current pulse A is supplied from the pulse generation circuit 10 to the magnetostrictive wire 1, a torsional elastic wave is generated at the portion of the magnetostrictive wire 1 close to the permanent magnet 9. This torsional elastic wave is detected by the receiver 7 and amplified by the pre-amplifier 8 as a waveform B. In this waveform B,
In addition to the required detection waveforms B ₁ and B ₂ , an electromagnetic noise B ₀ accompanying the application of the current pulse A is also included. The noise is removed by the masking circuit 17 to obtain a waveform C. Among the detected waveforms C, the amplitudes a ₁ and a ₂ of the waveforms C ₁ and C ₂ corresponding to the displacement of the permanent magnet 9
Of the magnetostrictive wire 1 in the x and y directions and temperature changes. Therefore, the peak value of the detected waveform B is held by the peak hold circuit 11, and a waveform like D is obtained. Then, the value of the waveform D immediately before the application of the current pulse A (time t ₂ ) is sampled by the sample and hold circuit 13 to obtain a sample and hold signal such as E. In the signal E, a ₀ is a voltage corresponding to the amplitude of the waveform one time before the waveform C ₁ .

Next, the sample hold signal E is compared with the reference signal G, and the difference is input to the variable gain amplifier 12 via the gain adjustment circuit 15 and the integration element 16. When the level of the sample hold signal E is high, the reference signal G
When the level of the sample hold signal E is low, the difference from the reference signal G is large, and the gain is also large. As a result, the output waveforms F ₁ and F ₂ of the variable gain amplifier 12 can obtain a substantially constant amplitude regardless of the levels of the detection waveforms C ₁ and C ₂ .
By detecting the waveforms F ₁ and F ₂ at the trigger point T, the mechanical displacement of the permanent magnet 9 can be easily detected based on the time t.

In the example of FIG. 5, the amplitude a of the previous detected waveform C ₁
And amplifies the next detection waveform C ₂ with a gain corresponding to _1. Therefore, the amplitude a ₁ of the detection waveform C _1, C _2, a ₂
Are substantially constant, the detected waveforms F ₁ , F
₂ cannot be obtained, but the sampling cycle (application cycle of the current pulse A) of the apparatus of the present invention is, for example, 1/10
Since it is about 0 to 1/1000 second, it is unlikely that the amplitudes a ₁ and a ₂ of the detected waveforms C ₁ and C ₂ change greatly (displace in the x and y directions) in such a short time. ,
There is actually no problem. Similarly, since the temperature does not greatly change in such a short period of time as described above, there is no practical problem.

In FIG. 5, as shown by a waveform B, an electromagnetic noise B ₀ accompanying the application of the current pulse A is included.
To remove the influence of this noise, a masking circuit 1
7, and the peak hold signal D is reset immediately after the application of the current pulse A.
The method of removing ₀ is not limited to the above method, and various methods can be considered. For example, the output C of the masking circuit 17
May be used as an input signal of the peak hold circuit 11, and the peak hold signal D may be reset immediately before the application of the current pulse A. Further, it is also possible to substantially eliminate the influence of the noise B ₀ without using a masking circuit.

In the case of FIG. 5, the sampling timing is set immediately before the application of the next current pulse A (time t ₂ ) so that the sample and hold can be performed even when the permanent magnet 9 is at the farthest point of the magnetostrictive wire 1. However, if the period Δta from the start of the peak hold to the start of the sample hold is long, the peak hold value may droop (indicated by the broken line in the waveform D in FIG. 6), and the sampling value may be an incorrect value.

[0021] As a countermeasure, detected at the level T 'as the waveform C ₁ can trigger even the smallest waveform as shown in FIG. 6, the first peak from the signal H ₁ after a short period Δtb than Δta of the detected waveform H The hold value may be sampled. By using this method, the influence of the droop on the peak hold value can be eliminated, and the peak hold value with a small error can be sampled.

FIG. 7 shows a specific example in which the displacement detecting device of FIG. 4 is used for a control rod driving device of a nuclear reactor. Reference numeral 20 denotes a magnetostrictive displacement detecting device, 21 denotes a control rod drive shaft, and 22 denotes a drive shaft housing. The control rod drive shaft 21 is vertically movably inserted into the drive shaft housing 22, a control rod (not shown) is connected to a lower end of the drive shaft 21, and an annular permanent shaft is connected to an upper end of the drive shaft 21. The magnet 23 is fixed. The magnetostrictive displacement detecting device 20 is mounted outside the drive shaft housing 22, and detects the axial position of the control rod drive shaft 21 by detecting the axial position of the permanent magnet 23, and thus the position of the control rod. be able to.

The control rod position indicating device used in the conventional control rod driving device has a poor position detection accuracy and cannot detect the position continuously. Further, when the conventional magnetostrictive displacement detecting device is applied to the control rod driving device, the distance between the magnetostrictive wire and the permanent magnet 23 fluctuates greatly due to the large deflection of the tip of the control rod driving shaft 21. Depending on the position, the position of the drive shaft 21 cannot be detected.

On the other hand, in the present invention, the position of the permanent magnet 23 can be detected with high accuracy even when the permanent magnet 23 moves over a wide range in the axial direction and the vertical direction of the magnetostrictive line by the variable gain amplifier circuit. Therefore, the position of the control rod can always be stably detected, and continuous detection of a position that was impossible in the related art is possible.

The above embodiment is merely an example of the present invention, and can be modified without departing from the gist of the present invention.
For example, in the above embodiment, a current pulse is applied to the magnetostrictive wire,
The torsional elastic wave propagating through the magnetostrictive wire is detected. However, as described in Japanese Patent Application Laid-Open No. 59-162412, the magnetostrictive wire is formed into a tube and a current pulse is supplied into the tube. A conductor may be inserted. The receiver is not limited to a coil.For example, a contact is made to contact a magnetostrictive wire almost orthogonally, a torsional elastic wave is converted to an axial force of the contact, and the end of the contact is applied to the end of the contact. The arrival of the torsional elastic wave may be detected by a piezoelectric element or a coil attached thereto. Although the N and S poles are magnetized on both end faces of the permanent magnet, the magnetizing direction is not limited to the axial direction but may be the radial direction. The shape of the permanent magnet need not be annular, but may be any shape such as a rectangular parallelepiped or a U-shape.

[0026]

As is apparent from the above description, according to the present invention, since the variable gain amplifier circuit for making the detected waveform a substantially constant level irrespective of the position and temperature of the permanent magnet is connected to the receiver, Damping due to the axial distance between the magnet and the receiver,
And eliminates the effect of attenuation due to the distance between the permanent magnet and the axis of the magnetostrictive wire in the direction perpendicular to the axis, and accurately detects the position of the permanent magnet even when the permanent magnet moves over a wide range in the axial direction of the magnetostrictive wire and in the direction perpendicular to the axis. can do. At the same time, the effect of attenuation due to an increase in ambient temperature can be eliminated, so that there is a feature that the operating temperature range can be expanded as compared with the conventional case.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a general magnetostrictive displacement detection device.

FIG. 2 is a waveform diagram of the displacement detection device of FIG.

FIG. 3 is a waveform diagram of a torsional elastic wave depending on the position of a permanent magnet.

FIG. 4 is a configuration diagram of an example of a magnetostrictive displacement detection device according to the present invention.

5 is a waveform chart of each part of the magnetostrictive displacement detecting device of FIG.

FIG. 6 is a waveform diagram of another example of the sampling method.

FIG. 7 is a partial perspective view of an example in which the displacement detection device according to the present invention is used in a control rod driving device of a nuclear reactor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetostrictive wire 7 Receiver 9 Permanent magnet 10 Pulse generation circuit 11 Peak hold circuit 12 Variable gain amplifier 13 Sample hold circuit 14 Reference signal generation circuit 15 Gain adjustment circuit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kozo Izumi Koizumi-ku, Osaka, Japan 1-1-60 Tsuneyoshi, Suntest Co., Ltd. (72) Inventor Hideyuki Takeuchi 1-1-60, Tsuneyoshi, Konohana-ku, Osaka City Suntest Co., Ltd.

Claims (2)

[Claims] 1. A torsional elastic wave is generated at a portion of a magnetostrictive wire adjacent to a permanent magnet movable along the magnetostrictive wire by flowing a current pulse in an axial direction of the magnetostrictive wire, and a specific portion of the magnetostrictive wire is generated. In the device that detects the mechanical displacement applied to the permanent magnet by measuring the propagation time of the torsional elastic wave to the receiver provided in, the amplification is performed according to the maximum value of the detected waveform of the torsional elastic wave A magnetostrictive displacement detecting device, wherein a variable gain amplifier circuit for changing the degree and obtaining a detection waveform of a substantially constant level irrespective of changes in the position of the permanent magnet and the ambient temperature is connected to a receiver. 2. A variable gain amplifier circuit comprising: a peak hold circuit for holding a peak value of a detected waveform of a torsional elastic wave; The magnetostrictive displacement detecting device according to claim 1, further comprising: a variable gain amplifier for amplifying.