JP3799416B2 - Magnetostrictive displacement detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetostrictive displacement detection apparatus that detects a mechanical displacement of an object, a displacement of a liquid surface, and the like using a magnetostriction phenomenon.
[0002]
[Prior art]
Conventionally, as a magnetostrictive displacement detection device, as shown in FIG. 1, by passing a current pulse from a pulse generation circuit 31 to a magnetostrictive wire 30, a magnetostrictive wire adjacent to a permanent magnet 32 that can move along the magnetostrictive wire 30 is used. A mechanical displacement applied to the permanent magnet 32 is detected by generating a torsional elastic wave (ultrasonic wave) at the site and measuring the propagation time of the torsional elastic wave to the receiver 33 provided on the starting end side of the magnetostrictive wire 30. Are known (see, for example, JP-A-61-112923). Both ends of the magnetostrictive wire 30 are supported with tension by support members 34 and 35.
[0003]
FIG. 2 is a waveform diagram showing a method for detecting the displacement of the permanent magnet 32. A is a current pulse, B is a waveform received by the receiver 33, and C is a waveform obtained by shaping the waveform B. If the time t from the supply of the current pulse A to the arrival of the waveform C ₁ is measured, the displacement x given to the permanent magnet 32 can be measured by the following equation.
x = v · t
Note that v is the propagation velocity of the torsional elastic wave.
[0004]
The torsional elastic wave includes a longitudinal wave that is a component in the axial direction and a transverse wave that is a component in the circumferential direction, but the propagation speed differs between the longitudinal wave and the transverse wave. Longitudinal wave propagation velocity v _L, respectively propagation velocity v _T of transverse waves is given by the following equation.
v _L = √ (E / ρ)
v _T = √ (G / ρ)
E is the longitudinal elastic modulus of the magnetostrictive wire, G is the rigidity, and ρ is the density.
[0005]
[Problems to be solved by the invention]
In a constant elastic material such as Ni-SpanC, the longitudinal elastic modulus E and the rigidity G are constant regardless of the temperature. However, in a material such as NS-1, the longitudinal elastic modulus E and the rigidity G are considerably different depending on the temperature. It changes a lot. For example, when the magnetostrictive displacement detection device is used for detecting the position of the control rod drive shaft of a nuclear reactor control rod drive device, the ambient temperature reaches about 350 ° C., so the fluctuation in propagation speed due to temperature change cannot be ignored. .
[0006]
Although it is possible to provide a temperature sensor separately from the displacement detection device and correct the propagation speed based on the detection signal of this temperature sensor, this requires a special temperature detection means such as a temperature sensor. Not only does it become high, but the temperature sensor cannot always accurately detect the temperature of the magnetostrictive wire.
[0007]
SUMMARY OF THE INVENTION An object of the present invention is to provide an inexpensive magnetostrictive displacement detector that can compensate for fluctuations in the propagation velocity of a torsional elastic wave due to temperature changes and can detect displacement with high accuracy.
[0008]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the invention described in claim 1 is a method in which a magnetostrictive wire adjacent to a permanent magnet for detection that can move along the magnetostrictive wire by flowing a current pulse in the axial direction of the magnetostrictive wire. In the apparatus for detecting a mechanical displacement applied to a permanent magnet for detection by generating a torsional elastic wave and measuring a propagation time of the torsional elastic wave to a receiver provided at a specific part of the magnetostrictive wire, the current pulse A reference signal generating means for applying a reference signal to the magnetostrictive line at a timing different from the application of the magnetic field; a resistance detecting means for detecting a resistance value of the magnetostrictive line from a signal change between the reference signal generating means and the magnetostrictive line; And a compensation means for compensating for the mechanical displacement applied to the permanent magnet for detection corresponding to the ambient temperature from the resistance value.
[0009]
In the present invention, the resistance value of the magnetostrictive wire is detected in order to detect the temperature. For example, when an alloy of 50% Ni and 50% Fe (NS-1 (trade name)) is used as the magnetostrictive wire, its resistance value changes almost linearly with the ambient temperature as shown in FIG. On the other hand, the propagation speed also changes almost linearly with the ambient temperature as shown in FIG. Therefore, if the resistance value of the magnetostrictive wire is detected, the ambient temperature, that is, the propagation velocity can be known almost accurately. If the torsional elastic wave propagation velocity is compensated in accordance with the ambient temperature in this way, accurate displacement measurement can always be performed even if the temperature changes greatly.
[0010]
The temperature compensation method is not limited to the case where the propagation velocity of the torsional elastic wave is compensated from the detected resistance value corresponding to the ambient temperature. For example, in the case of using a detection method in which a fixed permanent magnet is provided at a specific part of the magnetostrictive line in addition to the detection permanent magnet and the propagation velocity is canceled using the received waveform from the permanent magnet (for example, Japanese Patent Laid-Open No. 61-61). 226615), the distance between the fixed permanent magnet and the receiver may be temperature compensated. In addition, when a current pulse is passed, a longitudinal wave is generated at the end of the magnetostrictive line, so it is possible to cancel the influence of the propagation velocity using this longitudinal wave. In this case, too, the length of the magnetostrictive line is reduced. What is necessary is just temperature compensation.
[0011]
As in claim 2, a fixed resistor is connected between the reference voltage generating means and the magnetostrictive wire, and the divided voltage between the fixed resistor and the magnetostrictive wire is detected, so that the resistance value of the magnetostrictive wire is reduced. It is desirable to detect. Since the end portion of the magnetostrictive wire is returned to the ground of the pulse generation circuit, the resistance value of the magnetostrictive wire can be easily detected. It is desirable to use a fixed resistor that is stable with respect to temperature change, that is, with a resistance value that hardly changes even when the temperature changes.
Note that the resistance value of the magnetostrictive wire may be detected by using a constant current source as the reference signal generating means and detecting a voltage change between the constant current source and the magnetostrictive wire. In this case, no fixed resistor is required.
[0012]
Thus, in the present invention, a special detection device such as a temperature sensor is unnecessary, and the cost can be reduced. In addition, since the temperature of the magnetostrictive line itself affected by the temperature change is detected, the temperature can be detected more accurately than when a temperature sensor or the like is used.
[0013]
A torsional acoustic wave receiving coil inserted and disposed in a magnetostrictive wire as a receiver as in claim 3, a biasing permanent magnet for providing an axial deflection magnetic field is disposed in the vicinity of the coil, and the magnetostrictive wire is formed by the coil. It is desirable to detect a longitudinal wave out of the components of the torsional elastic wave propagating through.
That is, when a current pulse is applied to the magnetostrictive wire, a torsional elastic wave is generated at a portion of the magnetostrictive wire adjacent to the detection permanent magnet, and this torsional elastic wave propagates through the magnetostrictive wire and is detected by the receiver. The torsional elastic wave has a circumferential transverse component and an axial longitudinal component. When a torsional acoustic transverse wave is detected, the amplitude increases as the distance between the receiver and the permanent magnet for detection increases. Will be greatly attenuated. On the other hand, when the longitudinal wave of the torsional elastic wave is detected, the attenuation due to the propagation distance is less than that of the transverse wave, and a clear detection waveform can be obtained even if the permanent magnet for detection moves in a wide range in the axial direction of the magnetostrictive line.
[0014]
FIG. 5 shows a comparison of the attenuation of torsional elastic waves depending on the distance between the receiver and the permanent magnet when NS-1 is used as the magnetostrictive line and the transverse wave of the torsional elastic wave is detected and when the longitudinal wave is detected. is there. It can be seen that the longitudinal wave is less attenuated than the transverse wave, and even if the distance between the receiver and the permanent magnet is 4 m, the attenuation of the longitudinal wave can be suppressed to about 20%.
[0015]
By the way, the magnetostrictive displacement detecting device does not function when the ambient temperature exceeds the magnetic transformation point of the magnetostrictive wire and the magnetic phenomenon disappears. Further, even if the ambient temperature does not exceed the magnetic transformation point, the amplitude of the torsional elastic wave that is generated is attenuated only by approaching the same point, so that the usable ambient temperature range is limited. As a material of the magnetostrictive wire, a Ni—Cr—Fe—Ti—Al alloy (for example, Ni—SpanC (trade name)), which is a constant elastic material, is generally used, but the magnetic transformation point of Ni—SpanC is 150 ° C. Because of the attenuation of torsional elastic waves due to an increase in ambient temperature, it can be used only in an environment where the ambient temperature is about 100 ° C. in practice. When the magnetostrictive displacement detection device is used for detecting the position of the control rod drive shaft of the control rod drive device of the nuclear reactor, the ambient temperature reaches about 350 ° C., so Ni-SpanC cannot be used as the magnetostriction line.
[0016]
Therefore, as a result of trying various materials as the magnetostriction line so that the magnetostrictive displacement detection device can be used also for the control rod driving device of the nuclear reactor, for example, when the above NS-1 is used, It was discovered that even when the ambient temperature rises from room temperature to 350 ° C., the attenuation due to the temperature change of the torsional elastic wave amplitude is small.
[0017]
FIG. 6 shows attenuation of torsional elastic waves due to changes in ambient temperature of Ni-SpanC and NS-1. In NS-1, even if the ambient temperature is raised from room temperature to 350 ° C., the attenuation due to the temperature change of the torsional elastic wave is about 40%.
[0018]
Therefore, in claim 4, the present invention is applied to a displacement detection apparatus using NS-1 as a magnetostrictive wire. As a result, a high-performance displacement detection device is obtained in which the amount of attenuation of the torsional elastic wave is small, and the fluctuation of the propagation velocity due to the temperature change is small.
[0019]
When NS-1 is used as the material of the magnetostrictive wire, there is an advantage that the amount of attenuation due to the temperature change of the torsional elastic wave is small even when the ambient temperature rises. There is a property that the amount of attenuation between propagation of the line and arrival at the receiver, that is, the amount of attenuation due to the length of the propagation distance of the torsional elastic wave is larger than that of Ni-SpanC. Therefore, it is more effective if NS-1 is used as the material of the magnetostrictive wire and the longitudinal wave of the torsional elastic wave is detected.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 7 shows an example of a magnetostrictive displacement detector according to the present invention, and FIG. 8 is a signal waveform diagram of each part thereof.
The magnetostrictive wire 1 uses an alloy of 50% Ni and 50% Fe (NS-1 (trade name)) by weight. NS-1 has little attenuation due to temperature change of the amplitude of the torsional elastic wave even when the ambient temperature rises from room temperature to 350 ° C. The magnetostriction wire 1 is clamped by a clamp member 3 fixed on the base 2 and a terminal end of the magnetostrictive wire 1 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 silicone rubber that absorbs torsional elastic waves is applied to the start end of the magnetostrictive wire 1 to absorb reflected waves from the clamp member 3 and the like. The receiver 7 is disposed on the start end side of the magnetostrictive wire 1, and the magnetostrictive wire 1 passes through the central portion of the built-in coil 7 a without contact. The coil 7a detects the arrival of a torsional elastic wave propagating through the magnetostrictive wire 1 using the Villary effect. The negative electrode of the coil 7 a is grounded, and the positive electrode is connected to the amplifier 8.
[0021]
In the vicinity of the magnetostrictive wire 1, a detection permanent magnet 9 that is movable in the axial direction (x direction) of the magnetostrictive wire 1 is disposed. The permanent magnet 9 of this embodiment is annular and magnetized in the axial direction. However, the present invention is not limited to this, and any permanent magnet can be used as long as it can generate a torsional elastic wave in the magnetostrictive wire 1 by the Wiedemann effect. The shape and the magnetization direction are not limited. Further, the annular permanent magnet 9 may be inserted through the magnetostrictive wire 1.
[0022]
A biasing permanent magnet 10 that applies an axial deflection magnetic field is disposed in the vicinity of the coil 7a near the starting end of the magnetostrictive wire 1 located behind the receiver 7, particularly in the vicinity of the damping material 6. In this embodiment, the N and S poles are magnetized on both end faces of the disk-shaped permanent magnet 10. However, as long as an axial deflection magnetic field is applied, the shape, magnetization direction, and mounting of the permanent magnet The position is not limited. For example, a rod-shaped biasing permanent magnet 10 magnetized in the axial direction may be arranged on the outer side in the radial direction of the coil 7a.
[0023]
A current pulse is periodically (for example, 100 Hz to 1 kHz) supplied from the current pulse generation circuit 11 to the start end of the magnetostriction line 1 protruding from the clamp member 3, and the pulse generation circuit 11 passes through the spring 4 from the end of the magnetostriction line 1. Returned to earth. When a current pulse is supplied, a torsional elastic wave is generated at a portion of the magnetostrictive line 1 close to the permanent magnet 9 due to the Wiedemann effect and detected by the receiver 7. The detected torsional elastic wave is amplified by the amplifier 8 and sent to the detection circuit 12. The detection circuit 12 shapes the input signal and performs predetermined signal processing to detect the mechanical displacement x applied to the permanent magnet 9. The method for detecting the mechanical displacement x by the detection circuit 12 is known, for example, from Japanese Patent Laid-Open Nos. 61-112923 and 5-187854, and will not be described here.
[0024]
A first switch 13 is connected between the current pulse generation circuit 11 and the start end of the magnetostrictive wire 1, and the current pulse A of the current pulse generation circuit 11 is also input to the delay circuit 14. The delay circuit 14 generates timing signals C ₁ and C ₂ with a certain time delay from the generation of the current pulse A. The first switch 13 is turned OFF by a timing signal C ₁ of the delay circuit 14, second switch 15 is turned ON by the timing signal C _2. The timing signals C ₁ and C ₂ may be the same or different timings, but may be controlled so that the second switch 15 is not turned on when the current pulse A is applied. One end of the second switch 15 is connected to the reference voltage generation circuit 16 via the fixed resistor 17, and the other end is connected to the start end of the magnetostrictive wire 1. Therefore, the reference voltage Vs from the reference voltage generation circuit 16 is divided by the fixed resistor 17 and the magnetostrictive wire 1. The divided voltage Va is sampled and held by the sample and hold circuit 18. The sampling and holding circuit 18 receives the sampling signal D from the delay circuit 14 with a slight delay from the timing signals C ₁ and C ₂ , and performs sampling and holding in synchronization with the sampling signal D. The sampled and divided voltage Va is input to the detection circuit 12, and temperature compensation is performed.
[0025]
Note that two switches 13 and 15 may be provided, and one switch that selectively switches between the current pulse generation circuit 11 side and the reference voltage generation circuit 16 side may be provided, and the switch 13 is omitted. It is also possible. As the switches 13 and 15, known switching means such as relays and transistors can be used.
[0026]
Here, the operation of the displacement detection device of FIG. 7 will be described with reference to the waveform diagram of FIG. First, when a current pulse A is supplied from the pulse generation circuit 11 to the magnetostrictive wire 1, a torsional elastic wave is generated at a portion of the magnetostrictive wire 1 adjacent to the permanent magnet 9. This torsional elastic wave is detected by the receiver 7 and amplified by the amplifier 8 as waveform B. This waveform B includes electromagnetic noise B ₀ accompanying application of the current pulse A in addition to the required detection waveforms B ₁ and B ₂ , but this noise can be easily removed by a masking circuit or the like. be able to. Immediately before the next current pulse A is generated, timing signals C ₁ and C ₂ are generated from the delay circuit 14, and a sampling signal D is generated with a slight delay from the timing signal C ₂ . The reason why the sampling signal D is delayed from the timing signal C ₂ is that it takes a certain time until the voltage drop due to the magnetostrictive wire 1 occurs after the second switch 15 is turned on and the reference voltage Vs is applied. . The first switch 13 is turned off by the timing signal C ₁ and the second switch 15 is turned on by the timing signal C ₂ . As a result, the potential E at the intermediate portion between the fixed resistor 17 and the magnetostrictive wire 1 drops from the reference voltage Vs to Va. The sample and hold circuit 18 samples and holds the divided voltage Va in synchronization with the sampling signal to obtain a signal such as F. In the sample hold signal F, Va ₁ is the previous divided voltage, and Va ₂ is the current divided voltage.
The sample hold signal F is input to the detection circuit 12, whereby the torsional elastic wave propagation velocity is temperature compensated, and an accurate detection value x with little variation due to temperature change can be obtained.
[0027]
In order to know the resistance value Rm of the magnetostrictive wire 1 from the sampled and divided voltage Va, the following may be performed. That is, when the resistance value of the magnetostrictive wire 1 is Rm, the resistance value of the fixed resistor 17 is Rc, the reference voltage is Vs, and the divided voltage is Va, the resistance value Rm can be obtained by the following equation.
Rm = Va · Rc / (Vs−Va)
[0028]
As shown in FIG. 3, since the relationship between the resistance value Rm of the magnetostrictive wire 1 and the ambient temperature is known, the ambient temperature can be known from the divided voltage signal Va. Further, since the relationship between the propagation speed of the torsional elastic wave and the temperature is also known from FIG. 4, the propagation speed at the temperature at that time can be known from the divided voltage Va.
[0029]
As described above, if the divided voltage Va is sampled and held every time a current pulse is applied and the propagation velocity is temperature compensated, the displacement can always be detected with high accuracy even when the temperature changes suddenly.
Further, if the displacement detection device is constituted by analog circuits such as the detection circuit 12, the pulse generation circuit 11, the delay circuit 14, the reference voltage generation circuit 16, the fixed resistor 17, the sample hold circuit 18, etc., the displacement detection device can be configured extremely inexpensively. Easy to adjust.
[0030]
In the case of the above displacement detection device, the torsional elastic wave generated in the vicinity of the detection permanent magnet 9 is detected by the receiving coil 7a. At this time, a biasing magnetic field that applies an axial deflection magnetic field in the vicinity of the coil 7a. Since the permanent magnet 10 is disposed, the transverse wave component of the torsional elastic wave is suppressed and only the longitudinal wave component is emphasized. As shown in FIG. 5, since the longitudinal wave is less attenuated by the propagation distance than the transverse wave, even if the permanent magnet 9 moves over a wide range of, for example, 0 m to 4 m, a clear detection waveform is generated by the coil 7a. Can be received.
[0031]
Further, by using NS-1 as the magnetostrictive wire 1, as shown in FIG. 6, even if the ambient temperature rises from room temperature to 350 ° C., the attenuation due to the temperature change of the amplitude of the torsional elastic wave is small. However, when NS-1 is used as the magnetostrictive wire 1, the temperature change of the amplitude becomes small, but the temperature change of the propagation speed becomes 40 ppm / ° C. However, by using the present invention, the influence of the fluctuation of the propagation speed is reduced. It can be reduced to almost negligible level.
Therefore, by detecting the longitudinal wave of the torsional elastic wave, using NS-1 as the magnetostriction line, and compensating the temperature of the propagation speed of the torsional elastic wave, the temperature change is large as in the control rod driving device of the nuclear reactor, An optimum displacement detection device can be obtained for a device having a large amount of displacement.
[0032]
In addition, the said Example is only an example of this invention and can be changed in the range which does not deviate from the summary of this invention.
In the above embodiment, the relationship between the magnetostrictive wire resistance value and the temperature, and the relationship between the torsional elastic wave propagation velocity and the temperature, as shown in FIGS. Although it used, it is not restricted to this, You may use the material which has a nonlinear relationship.
Further, in the above embodiment, a current pulse is passed through the magnetostrictive line and a torsional elastic wave propagating through the magnetostrictive line is detected. However, as described in Japanese Patent Application Laid-Open No. 59-164212, the magnetostrictive line is It is also possible to insert a conducting wire for supplying a current pulse therein.
Although one coil is used as the receiving coil, two coils may be arranged in the axial direction, and the outputs of these coils may be taken out differentially. In this case, noise common to the two coils can be canceled out.
The method of detecting torsional elastic waves is not limited to using a coil in the receiver as described above and detecting torsional elastic waves by the Villary effect, but the contact is made almost perpendicular to the magnetostrictive line. Alternatively, the torsional elastic wave may be converted into the axial force of the touch element, and the arrival of the torsional elastic wave may be detected in the form of the axial displacement of the touch element with a piezoelectric element or a coil attached to the end of the touch element.
Therefore, not only the longitudinal wave of the torsional elastic wave but also the transverse wave may be detected.
[0033]
【The invention's effect】
As is apparent from the above description, according to the present invention, the reference signal generating circuit for applying the reference signal to the magnetostrictive wire at a timing different from the application of the current pulse, and the signal change between the reference signal generating means and the magnetostrictive wire. Since the resistance detecting means for detecting the magnetostriction wire resistance value is provided, the ambient temperature can be known almost accurately by detecting the magnetostriction wire resistance value. Compensation means compensates for the torsional elastic wave propagation velocity in response to the ambient temperature determined in this way, so that the mechanical displacement is compensated for temperature, so accurate displacement measurement is always possible even if the temperature changes greatly. Can be performed.
[0034]
Further, in the present invention, a special sensor such as a temperature sensor is unnecessary, and the cost can be reduced. In addition, since the temperature of the magnetostrictive line itself affected by the temperature change is detected, the temperature can be detected more accurately than when a temperature sensor or the like is used.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a general magnetostrictive displacement detection apparatus.
FIG. 2 is a waveform diagram of the displacement detection apparatus of FIG.
FIG. 3 is a diagram illustrating a relationship between a resistance value of a magnetostrictive wire and a temperature.
FIG. 4 is a diagram illustrating a relationship between a propagation speed of a torsional elastic wave and temperature.
FIG. 5 is a comparison diagram showing the relationship between the amplitude of torsional elasticity (longitudinal wave and transverse wave) and the axial distance between the receiver and the permanent magnet for detection.
FIG. 6 is a comparison diagram showing the relationship between the amplitude of torsional elasticity and temperature.
FIG. 7 is a configuration diagram of an example of a magnetostrictive displacement detector according to the present invention.
8 is a waveform diagram of each part of the magnetostrictive displacement detecting device of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Magnetostriction wire 7 Receiver 9 Permanent magnet 11 for detection 11 Pulse generation circuit 12 Detection circuit 14 Delay circuit 16 Reference voltage generation circuit 17 Fixed resistor 18 Sample hold circuit

Claims (4)

A receiver provided at a specific part of the magnetostriction line by generating a torsional elastic wave at the part of the magnetostriction line adjacent to the permanent magnet for detection movable along the magnetostriction line by passing a current pulse in the axial direction of the magnetostriction line In the device for detecting the mechanical displacement given to the permanent magnet for detection by measuring the propagation time of the torsional elastic wave up to,
A reference signal generating means for applying a reference signal to the magnetostrictive wire at a timing different from the application of the current pulse;
A resistance detecting means for detecting a resistance value of the magnetostrictive wire from a signal change between the reference signal generating means and the magnetostrictive wire;
A magnetostrictive displacement detecting device, comprising: compensation means for compensating for a mechanical displacement given to the permanent magnet for detection corresponding to the ambient temperature from the detected resistance value. The reference signal generating means is a reference voltage generating means for generating a reference voltage signal,
A fixed resistor is connected between the reference voltage generating means and the magnetostrictive wire,
2. The magnetostrictive displacement detecting apparatus according to claim 1, wherein the resistance detecting means detects a resistance value of the magnetostrictive wire from a divided voltage between the fixed resistor and the magnetostrictive wire. The receiver is a torsional elastic wave receiving coil inserted through a magnetostrictive wire, a permanent magnet for bias that provides an axial deflection magnetic field is disposed in the vicinity of the coil, and a torsion that propagates the magnetostrictive wire through the coil. 3. A magnetostrictive displacement detecting apparatus according to claim 1, wherein a longitudinal wave is detected among elastic wave components. 4. The magnetostrictive displacement detecting device according to claim 1, wherein the magnetostrictive wire is made of an alloy having a substantial weight ratio of Ni 50% and Fe 50%.

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