JPH06147873A - Noise eliminator for displacement detector - Google Patents

Abstract

PURPOSE:To provide a noise eliminator for displacement detector which can eliminate noise effectively regardless of the arriving time of noise. CONSTITUTION:Current pulse is fed periodically in the axial direction of magnetostriction lines 1 to generate torsional elastic wave at a part of the magnetostriction line 1 where a movable permanent magnet 2 approaches along the magnetostriction line 1. Propagation time of the torsional elastic wave required for arriving at a receiver 5 disposed at a specified part of the magnetostriction line 1 is measured in order to detect the mechanical displacement of the permanent magnet 2. Only a signal arrived first at the receiver 5 is detected among receiving signals having different periods. The propagation time difference between preceding and following signals is then compared with a predetermined value and if the difference 15 larger than the set value, subsequent signals are removed. Consequently, final output signal is proportional to the propagation time of essentially required ultrasonic signal and noise is eliminated effectively.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, as a magnetostrictive displacement detecting device, the present applicant has been
A torsional elastic wave (ultrasonic wave) is generated at the part of the magnetostrictive line that is adjacent to the permanent magnet that can move along the magnetostrictive line, and the propagation time of the torsional elastic wave to the receiver provided at the specific part of the magnetostrictive line is measured Accordingly, a device for detecting the mechanical displacement applied to the permanent magnet has been proposed (Japanese Patent Laid-Open Nos. 61-112923 and 63-217224).

In the case of this type of displacement detector, it is inevitable that the receiver receives various noises in addition to the torsional elastic wave originally required. Moreover, since such noise is in the same frequency band as the torsional elastic wave, it is difficult to distinguish the two. In order to deal with such a problem, a noise eliminator disclosed in Japanese Patent Laid-Open No. 62-14596 has been proposed. This noise removing device generates a prohibition signal in a predetermined period from the start pulse to prohibit noise reception.

[0004]

However, in the case of this noise removing device, reception of the noise is prevented if the noise is within the prohibited time, but if the noise is outside the prohibited time, the noise is not removed and the arrival of the noise is prevented. There is a risk of erroneous detection as arrival of a torsional elastic wave. As a result, an output fluctuation corresponding to the time from the arrival of noise to the arrival of the torsional elastic wave signal will occur. Then, the objective of this invention is providing the noise removal apparatus of the displacement detector which can remove noise effectively regardless of the arrival time of noise.

[0005]

In order to achieve the above object, the present invention provides a magnetostrictive magnetostrictive coil which is movable along a magnetostrictive line in proximity to a magnetostrictive line by causing a periodic current pulse to flow in the axial direction of the magnetostrictive line. A displacement detector that detects a mechanical displacement given to a permanent magnet by generating a torsional elastic wave at a line part and measuring the propagation time of the torsional elastic wave to a receiver installed at a specific part of the magnetostrictive line. Of the received signals received by the receiver, arrival signal detection means for detecting only the signal that arrives first after each current pulse is supplied, and arrival signal is detected by the arrival signal detection means from the supply of the current pulse. And a level difference comparison means for comparing the level difference between the two front and rear signals output from the proportional signal output means with a predetermined set value. It is obtained and a signal removing means for removing the compared level difference is at larger than the set value, after the signal by the level difference comparing means.

[0006]

When a current pulse is periodically passed in the axial direction of the magnetostrictive line, a torsional elastic wave is generated at a portion of the magnetostrictive line adjacent to the permanent magnet, and this elastic wave is received by the receiver. At this time, noise other than the torsional elastic wave may be received by the receiver. If the noise reaches the receiver before the torsional elastic wave,
In that cycle, only noise is detected by the arrival signal detecting means. On the other hand, in other cycles, the torsional elastic wave is detected by the arrival signal detecting means. Both of these signals are converted by proportional signal output means into signals proportional to the time required to reach the receiver. Among the signals output from the proportional signal output means, the level difference between the two signals of adjacent front and rear periods is compared with the set value by the level difference comparison means. This set value is set based on the maximum value of the normal moving speed of the permanent magnet.
When the previous signal level is higher than the latter signal level by the set value or more, that is, when it is recognized that the permanent magnet approaches the receiver faster than the preset speed during the two adjacent cycles, the signal removing means performs the rearward removal. It is determined that the signal of 1 is a signal due to noise, and the subsequent signal is removed. Therefore, only the signal due to the torsional elastic wave is output, and the position of the permanent magnet can be accurately detected. As described above, the noise removing device of the present invention does not prohibit the reception of noise for a predetermined period as in the conventional case, but also receives a signal due to noise and determines the arrival time of a correct signal (a signal due to a torsional elastic wave). And outputs the correct signal only.

[0007]

1 is a circuit diagram of an example of a displacement detector according to the present invention, and FIG. 2 is a signal waveform diagram of each part thereof. Reference numeral 1 is a magnetostrictive wire such as Ni, 2 is a cylindrical permanent magnet movable along the magnetostrictive wire 1, and the permanent magnet 2 has N on both end surfaces thereof.
The pole and the S pole are magnetized. The permanent magnet 2 may be magnetized in the radial direction. A current pulse B is applied from the pulse generation circuit 3 to the beginning of the magnetostrictive line 1, and the end of the magnetostrictive line 1 is grounded. The pulse generation circuit 3 is based on the rectangular wave signal A input from the rectangular wave generation circuit 4,
A short width current pulse B synchronized with the rising edge is generated. A receiver 5 is provided near the beginning of the magnetostrictive wire 1,
A signal propagating through the magnetostrictive line 1 is received. As the receiver 5, the contactor crosses the magnetostrictive wire 1 and is brought into contact therewith, and the torsional elastic wave propagating in the magnetostrictive wire 1 is converted into an axial force of the contactor, and a piezoelectric element attached to the end of the contactor. Detecting the arrival of torsional elastic waves in the detection part such as an element, or the inverse magnetostriction effect (Villari effect)
There is a coil or the like that detects the arrival of a torsional elastic wave that has propagated through the magnetostrictive wire 1 by utilizing the.

[0008] Voltage signal D received at the receiver 5 is compared with the constant voltage d ₁ by the waveform shaping circuit 6, which exceeds a predetermined voltage d ₁ is shaped into a pulse signal E. At this time, in addition to the ultrasonic wave (torsional elastic wave) signal U, the received signal D also includes noise S induced by the current pulse B and noise T invading from the outside. These signals U, S, T Waveform shaping circuit 6
Is similarly molded.

The rectangular wave signal A output from the rectangular wave generating circuit 4 is, in addition to the pulse generating circuit 3, a masking circuit 7, a sample hold pulse generating circuit 8 and a triangular wave generating circuit 9.
Is also entered. The masking circuit 7 outputs a masking signal C for removing the noise S induced by the current pulse B from the received signal D, and this signal C becomes L level for a certain time after the generation of the current pulse B. . Received signal E formed in a pulse shape by the waveform shaping circuit 6
Is input to the first AND circuit 10 together with the masking signal C. As described above, the masking signal C is the current pulse B.
Since the L level is maintained for a certain period of time after the occurrence of, the noise S existing in that period is removed, and the output signal F of the first AND circuit 10 includes the ultrasonic signal U and the noise T.

The output signal F of the first AND circuit 10 and the rectangular wave signal A of the rectangular wave generating circuit 4 are input to the sample hold pulse generating circuit 8. Inside the circuit 8, a rectangular wave signal G which becomes H level by the signal of the output signal F which arrives first in one cycle and becomes L level at the same time when the rectangular wave signal A falls is generated. Then, the circuit 8 outputs a sample hold pulse signal H synchronized with the rising edge of the signal G.

The triangular wave generating circuit 9 generates a triangular wave voltage I which rises at a constant gradient in synchronization with the rising of the rectangular wave signal A and is reset at the same time as the rising of the rectangular wave signal A. The triangular wave voltage I and the sample hold pulse signal H are input to the first sample hold circuit 11. The first sample-hold circuit 11 outputs a signal J obtained by sample-holding the triangular wave voltage I when the sample-hold pulse signal H is input. In the example of FIG. 2, the first
The output J of the cycle is sampled and held by the ultrasonic signal U at the voltage V ₁ , and the voltage V ₁ is sampled and held by the noise T in the second cycle.
_The voltage drops to ₂ and returns to the voltage V ₁ again by the ultrasonic signal U in the third cycle. These voltages V ₁ and V ₂ are proportional to the propagation time of the signal that first reaches the receiver 5 in each cycle.

Output J of the first sample hold circuit 11
And the output N of the second sample hold circuit 12 described later are input to the voltage comparison circuit 13. The voltage comparison circuit 13 compares the outputs J and N, and outputs an L level signal L when the voltage level of the output J is lower than the output N by a set value or more, and outputs an H level signal L otherwise. In the example of FIG. 2, when the noise T existing in the second period arrives, the output J
Suddenly drops from V ₁ to V ₂ , the output L of the voltage comparison circuit 13 changes from H level to L level at this moment,
When the ultrasonic signal U of the third cycle arrives, it changes to the H level again.

On the other hand, the sample hold pulse signal H is also input to the pulse delay circuit 14 and outputs a pulse signal K delayed from the pulse signal H by a minute time t ₁ . The pulse signal K includes an ultrasonic signal U'and noise T '. The output L of the voltage comparison circuit 13 and the output K of the pulse delay circuit 14 are input to the second AND circuit 15. The AND circuit 15 outputs the output signal M only when both input signals are at the H level, and in the example of FIG. 2, only the ultrasonic signal U ′ of the first cycle and the third cycle is output.

Finally, the output J of the first sample hold circuit 11 and the output M of the second AND circuit 15 are input to the second sample hold circuit 12. The second sample-and-hold circuit 12 outputs the signal N obtained by sampling and holding the output J in response to the input of the output M. In the example of FIG. 2, since the signal M is not output from the second AND circuit 15 in the second cycle in which the noise T ′ exists, the noise T ′ is removed and the voltage signal V corresponding to the propagation time of the ultrasonic signal U ′. Only ₁ is second
It is output from the sample hold circuit 12.
The output N of the second sample hold circuit 12 is fed back to the voltage comparison circuit 13 as described above.

The mechanical displacement x given to the permanent magnet 2 can be easily obtained by a known method. That is, the time t from the supply of the current pulse B to the arrival of the torsional elastic wave at the receiver 5 is calculated from the voltage signal V _{1, and} from this time t and the propagation velocity v of the torsional elastic wave of the magnetostrictive wire 1, The displacement x of the permanent magnet 2 can be calculated by the following equation. x = v · t

FIG. 2 shows the case where the permanent magnet 2 is stopped for easy understanding. In fact, the permanent magnet 2
Moves, so it is necessary to determine the set value so that the normal change in the voltage V ₁ due to the movement (however, only in the direction in which the voltage drops below V ₁ ) is not mistaken for noise.
In FIG. 2, the output J of the first sample and hold circuit 11 has a notch P due to a transient phenomenon of sample and hold.
Appears. However, by delaying the sample hold pulse signal H by the pulse delay circuit 14 and operating the second sample hold circuit 12 by this delay pulse, a DC signal without a notch can be obtained in the final output N.

In the conventional case (Japanese Patent Laid-Open No. 62-14596), a DC pulse train relating to the position of the permanent magnet is produced and averaged to obtain a DC (DC) output. Therefore, in order to create an accurate DC pulse train proportional to the position of the permanent magnet, it is necessary to output current pulses at accurate intervals, which requires an effective timepiece such as a crystal oscillator. Further, since a DC signal is obtained by averaging the DC pulse train, a sufficiently large filter is required for smoothing, and there is a drawback that the responsiveness deteriorates. On the other hand, in the case of the above embodiment, since it is not necessary to create an accurate DC pulse train proportional to the position of the permanent magnet, an inexpensive oscillator is sufficient and a DC signal is obtained by the sample hold method. The advantage is that the responsiveness is good.

The above embodiment is merely an example of the present invention and can be modified within the scope of the present invention. In the above embodiment, the solid line is used as the magnetostrictive line, and the current pulse is directly supplied to this magnetostrictive line.
As described in Japanese Patent No. 412, the magnetostrictive wire may have a tubular shape, and a conductor for passing a current pulse may be inserted through the center of the magnetostrictive wire. The permanent magnet used in the present invention is not limited to the annular shape as in the embodiment, and may have any shape such as a rectangular parallelepiped shape and a U shape, and the direction of its magnetic field is not limited.

[0019]

As is apparent from the above description, according to the present invention, only the first arriving signal of the received signals in each period received by the receiver is detected, and two signals of the preceding and following periods are detected.
The propagation time difference of two signals is compared with a preset value, and when this difference is larger than the set value, the latter signal is removed. Only a signal proportional to is obtained and noise is effectively removed. Therefore, there is an effect that the displacement of the permanent magnet can be accurately and stably measured even when used in a noisy environment.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an example of a displacement detector according to the present invention.

FIG. 2 is a signal waveform diagram of each part of FIG.

[Explanation of symbols]

 1 Magnetostrictive Wire 2 Permanent Magnet 3 Pulse Generation Circuit 8 Sample Hold Pulse Generation Circuit 9 Triangular Wave Generation Circuit 11 First Sample Hold Circuit 12 Second Sample Hold Circuit 13 Voltage Comparison Circuit 14 Pulse Delay Circuit 15 Second AND Circuit

Claims (1)

[Claims] 1. A torsional elastic wave is generated at a portion of a magnetostrictive line that is adjacent to a permanent magnet movable along the magnetostrictive line by causing a periodic current pulse to flow in the axial direction of the magnetostrictive line to identify the magnetostrictive line. In the displacement detector that detects the mechanical displacement given to the permanent magnet by measuring the propagation time of the torsional elastic wave to the receiver installed in the part, each current among the received signals received by the above receiver Arrival signal detection means for detecting only the signal that arrives first after the pulse is supplied, and proportional signal output means for outputting a signal proportional to the time from the arrival of the current pulse until the arrival signal is detected by the arrival signal detection means. A level difference comparing means for comparing the level difference between the two signals before and after outputted from the proportional signal output means with a predetermined set value, and a level difference compared by the level difference comparing means. When the signal is larger than the set value, a signal removing means for removing the subsequent signal,
A noise removal device for a displacement detector, comprising: