JP2017207426A - Acoustic wave propagation length measurement method, and acoustic wave propagation length measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To transmit and receive an acoustic wave in a flow duct and to reduce the influence of noises generated in the flow duct when measuring a propagation length of the acoustic wave based on a transmitted acoustic wave and a received acoustic wave.SOLUTION: An acoustic wave propagation length measurement method measures a propagation length of an acoustic wave by transmitting and receiving the acoustic wave via a fluid inside a fluid duct in the inner part of which a fluid is distributed, and includes a waveform generation process for generating a signal of a predetermined frequency band; an acoustic sound transmission process for reducing the noise included in the acoustic wave based on a signal; a noise reduction process for reducing the noise included in the acoustic wave based on the signal; and a measurement process for measuring a propagation length of the acoustic wave propagating in the fluid based on the signal where the noise is reduced in a noise reduction process and the signal generated in the waveform generation process.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a sound wave propagation length measurement method and a sound wave propagation length measurement device.

  2. Description of the Related Art Conventionally, a technique for transmitting and receiving sound waves in a fluid conduit and measuring the propagation length of sound waves based on the transmitted sound waves and the received sound waves is known (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 2002-196074

  However, in the conventional technique described in Patent Document 1, a waveform of noise generated in the fluid conduit may be superimposed on the received sound wave waveform. In this case, the propagation length of the sound wave There is a problem in that the measurement accuracy is reduced.

  Accordingly, an object of the present invention is to provide a wave propagation length measurement method and a sound wave propagation length measurement apparatus that can reduce the influence of noise generated in a fluid conduit in order to solve the above-described problem. .

  One aspect of the present invention is a sound wave propagation length measuring method for measuring the propagation length of a sound wave by transmitting and receiving sound waves via the fluid in a fluid conduit through which the fluid flows, and having a predetermined frequency A waveform generating procedure for generating a signal in a band; and the fluid pipe is formed by converting a signal generated in the waveform generating procedure into a sound wave having a frequency lower than a primary cutoff frequency when the fluid conduit is regarded as a waveguide. Sound wave transmission procedure for transmitting to the fluid in the path, sound wave reception procedure for receiving the sound wave transmitted in the sound wave transmission procedure, and noise included in the sound wave received in the sound wave reception procedure Based on a noise reduction procedure that reduces based on a signal generated in the procedure, a signal in which noise has been reduced in the noise reduction procedure, and a signal generated in the waveform generation procedure A sound wave propagation measurement method and a measurement procedure for measuring the propagation length of a sound wave propagating through the fluid.

  According to one aspect of the present invention, in the noise reduction procedure, noise included in the sound wave received in the sound wave reception procedure is reduced by a lock-in detection method based on the signal generated in the waveform generation procedure.

  One aspect of the present invention generates a burst signal of a predetermined frequency band as the signal in the waveform generation procedure.

  In one aspect of the present invention, in the waveform generation procedure, a continuous signal of a predetermined frequency band is generated as the signal.

  In one aspect of the present invention, in the sound wave reception procedure, the sound wave transmitted in the sound wave transmission procedure receives a reflected wave reflected by a measurement object, and the sound wave reception procedure receives the reflected wave in the measurement procedure. Based on the change in the reflected wave, a change in the position of the measurement object is measured.

  One aspect of the present invention is a sound wave propagation length measuring device that measures the propagation length of a sound wave by transmitting and receiving sound waves through the fluid in a fluid conduit through which the fluid flows, and has a predetermined frequency. A waveform generator for generating a signal in a band, and a signal generated by the waveform generator as a sound wave having a frequency lower than a primary cutoff frequency when the fluid conduit is regarded as a waveguide. The waveform generator generates sound included in the sound wave received by the sound wave transmitter, the sound wave receiver that receives the sound wave transmitted by the sound wave transmitter, and the sound wave received by the sound wave receiver. The propagation length of the sound wave propagating in the fluid is measured based on a noise reduction unit that is reduced based on a signal to be generated, a signal in which noise is reduced by the noise reduction unit, and a signal generated by the waveform generation unit With the measuring unit It is obtain acoustic propagation length measuring device.

  When the sound wave is transmitted and received in the fluid conduit and the propagation length of the sound wave is measured based on the transmitted sound wave and the received sound wave, the influence of noise generated in the fluid conduit can be reduced.

It is a figure which shows an example of a structure of the sound wave propagation length measuring apparatus of 1st Embodiment. It is a figure which shows an example of the signal waveform of 1st Embodiment. It is a figure which shows an example of a structure of the sound wave propagation length measuring apparatus of 2nd Embodiment. It is a figure which shows an example of the signal waveform of 2nd Embodiment.

[First embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. First, the outline of the sound wave propagation length measuring apparatus 1 will be described with reference to FIG.

  FIG. 1 is a diagram illustrating an example of a configuration of a sound wave propagation length measuring apparatus 1 according to the present embodiment. The sound wave propagation length measuring device 1 measures the propagation length of the sound wave W by transmitting and receiving the sound wave W via the fluid Fd in the fluid pipe Fp through which the fluid Fd flows. Specifically, the sound wave propagation length measurement device 1 includes a waveform generation unit 10, an amplification unit 20, a transmission unit 30, a reception unit 40, a lock-in detection unit 50, and a measurement unit 60.

  The waveform generator 10 generates a burst signal BtS and a reference signal RfS. The waveform generation unit 10 supplies the generated burst signal BtS to the amplification unit 20 and the measurement unit 60. The burst signal BtS is, for example, a burst waveform signal of 10 [kHz]. The waveform generator 10 supplies the generated reference signal RfS to the lock-in detector 50. The reference signal RfS is, for example, a continuous waveform signal of 10 [kHz].

  The amplification unit 20 amplifies the burst signal BtS supplied from the waveform generation unit 10 and supplies the amplified signal to the transmission unit 30 as the transmission signal TxS.

  The transmission unit 30 includes, for example, an underwater speaker, and outputs the supplied transmission signal TxS as a sound wave W to the fluid Fd in the fluid conduit Fp. Hereinafter, the property of the sound wave W will be described on the assumption that the fluid pipe line Fp is a parallel flat plate wall facing at an interval d.

  Consider a case where a wave with a wavelength λ = d / 4 propagates between flat plates facing each other at a distance d. In this case, the zero-order wave propagates straight between the flat plates. In this case, the primary wave, the secondary wave, and the tertiary wave propagate, and the wave of the 4th and higher order cannot propagate. Higher-order waves such as the first-order wave, the second-order wave, and the third-order wave travel obliquely with respect to the flat plate surface, undergo multiple reflection on the wall surface, and travel after the 0th-order wave. For this reason, the arrival of the high-order wave at the receiving unit 40 is delayed as compared with the zero-order wave. Therefore, a higher-order wave than the 0th-order wave has a waveform received by the receiving unit 40 that blurs and extends in the direction along the time axis. For this reason, it is difficult to determine the arrival time of the high-order wave compared to the zero-order wave at the receiving unit 40. Therefore, it is preferable that the transmission unit 30 outputs a 0th-order wave as the sound wave W in the fluid conduit Fp.

  Here, when the fluid conduit Fp is considered as a so-called waveguide, and the concept of the cutoff frequency of the waveguide is applied to the sound wave W, it can be explained as follows. That is, if the sound wave W has a frequency smaller than the primary cutoff frequency when the fluid pipe Fp is regarded as a waveguide, the higher-order boundary such as the primary wave, the secondary wave, the tertiary wave,. It can be said that no wave can exist and only the 0th-order wave can exist. In other words, if the sound wave has a wavelength longer than the wavelength corresponding to the primary cutoff frequency when the fluid conduit Fp is regarded as a waveguide, the first wave, the second wave, the third wave, ... It can be said that high-order boundary waves such as cannot exist, and only the 0th-order wave can exist.

The primary cutoff frequency of the sound wave W is the same as the cutoff frequency of the electromagnetic wave waveguide, and the cross-sectional shape of the tube, the speed of sound in the fluid (for example, the speed of sound in normal temperature water is 1500 m / s, 1513 m / s, etc.), and it is well known that the analysis can be performed mathematically in consideration of the boundary condition at the pipe wall. As is well known in the wave analysis of plate waves and the waveguide analysis of electromagnetic waves, it is also mathematically obvious that the wavelength order of the cut-off frequency waves hardly depends on the boundary conditions.
Further, it is known that the wavelength λ corresponding to the primary cutoff frequency of the sound wave W when the water path between the flat plates facing each other with a distance d is regarded as a waveguide is approximately λ = d.

If the waveform generator 10 outputs a burst signal BtS that can generate a sound wave W having a frequency lower than the primary cutoff frequency when the fluid pipe line Fp is regarded as a waveguide, the sound wave W in the fluid pipe line Fp is generated. It becomes 0th order wave. In other words, the burst signal BtS generated by the waveform generator 10 is a signal that can generate a sound wave W having a frequency lower than the primary cutoff frequency when the fluid conduit Fp is regarded as a waveguide.
That is, the transmitter 30 changes the signal generated by the waveform generator 10 into a sound wave W having a frequency lower than the primary cutoff frequency when the fluid pipeline Fp is regarded as a waveguide, and the fluid in the fluid pipeline Fp. Send to Fd.

  The receiving unit 40 includes, for example, an underwater microphone, receives the sound wave W output from the transmission unit 30 to the fluid Fd, and outputs the received sound wave W as a reception signal RxS. Here, the sound wave W received by the receiving unit 40 may include noise N. Here, the noise N is a component other than the component of the sound wave W transmitted by the transmission unit 30 among the components of the sound wave W received by the reception unit 40. For example, the noise N is a vibration component added in the fluid pipe line Fp to the sound wave W transmitted by the transmission unit 30. As a specific example, the fluid pipe line Fp may be placed in an environment where vibration occurs, such as a factory. In such a case, when vibration is applied to the fluid pipeline Fp, the vibration is transmitted from the wall surface of the fluid pipeline Fp to the fluid Fd, and vibration is generated in the fluid Fd. When vibration is generated in the fluid Fd, the sound wave W received by the receiving unit 40 includes noise N corresponding to the vibration. An example of the received signal RxS including the noise N is shown in FIG.

  FIG. 2 is a diagram illustrating an example of a signal waveform according to the first embodiment. The waveform generator 10 outputs a burst signal BtS shown in FIG. The transmission unit 30 outputs a transmission signal TxS obtained by amplifying the burst signal BtS as a sound wave W. That is, the waveform of the burst signal BtS generated by the waveform generator 10 is similar to the waveform of the sound wave W output from the transmitter 30. The receiving unit 40 receives the sound wave W and outputs a reception signal RxS shown in FIG. As shown in this example, the waveform of the reception signal RxS is deformed with respect to the waveform of the burst signal BtS. That is, the received signal RxS includes noise N.

Returning to FIG. 1, the lock-in detection unit 50 detects the received signal RxS by a known lock-in detection method based on the reference signal RfS. The lock-in detection unit 50 outputs the detection result of the received signal RxS to the measurement unit 60 as the lock-in output signal LiS. An example of the waveform of the lock-in output signal LiS is shown in FIG. Here, when the received signal RxS shown in FIG. 2B is compared with the lock-in output signal LiS, the lock-in output signal LiS has a rectangular waveform with a reduced noise N component included in the received signal RxS. Have. That is, the lock-in output signal LiS has a reduced noise N component contained in the received signal RxS.
That is, the lock-in detection unit 50 reduces the noise N included in the sound wave W received by the reception unit 40 based on the signal generated by the waveform generation unit 10.

  Here, in the known lock-in detection method, it is preferable to use a continuous signal of a predetermined frequency order as the reference signal. Here, the predetermined frequency is, for example, 100 kHz or less, or 1 kHz to 100 kHz. The burst signal BtS and the reference signal RfS generated by the waveform generator 10 are both signals of a predetermined frequency (for example, 100 kHz or less, or 1 kHz to 100 kHz). That is, the waveform generator 10 generates a signal in a predetermined frequency band. The reference signal RfS is a continuous wave having a predetermined frequency (for example, 100 kHz or less, or 1 kHz to 100 kHz) order. Therefore, the burst signal BtS and the reference signal RfS generated by the waveform generator 10 have a frequency band and a waveform suitable for a known lock-in detection method.

The measurement unit 60 propagates the sound wave W between the transmission unit 30 and the reception unit 40 based on the burst signal BtS output from the waveform generation unit 10 and the lock-in output signal LiS output from the lock-in detection unit 50. Measure the length l. Specifically, the measurement unit 60 acquires the burst signal BtS output from the waveform generation unit 10. The burst signal BtS is a signal whose burst waveform rises at time t1, as shown in FIG. The measurement unit 60 acquires the lock-in output signal LiS output from the lock-in detection unit 50. The lock-in output signal LiS is a signal whose rectangular waveform rises at time t2 as shown in FIG. The measuring unit 60 measures the propagation length l of the sound wave W based on the time difference Δt of the rise of these two signals and the sound velocity WS of the sound wave W propagating in the fluid Fd.
That is, the measurement unit 60 measures the propagation length l of the sound wave W propagating in the fluid Fd based on the signal whose noise is reduced by the lock-in detection unit 50 and the signal generated by the waveform generation unit 10.

As described above, in the sound wave propagation length measuring apparatus 1 of the present embodiment, the waveform generator 10 is a signal having a frequency band and waveform suitable for the detection method of the lock-in detector 50, that is, the burst signal BtS and the reference signal. RfS is output. Further, in the sound wave propagation length measuring device 1, the lock-in detector 50 reduces the noise N included in the received signal RxS based on the reference signal RfS output from the waveform generator 10. In other words, the sound wave propagation length measuring apparatus 1 measures the propagation length l of the sound wave W using a frequency band and a waveform that can employ a lock-in detection method having a noise N reduction effect.
That is, according to the sound wave propagation length measuring apparatus 1 of the present embodiment, the sound wave W is transmitted and received in the fluid conduit Fp, and the propagation length l of the sound wave W is based on the transmitted sound wave W and the received sound wave W. Can be reduced, the influence of the noise N generated in the fluid line Fp can be reduced. This method can also be applied to the second embodiment shown below by replacing the transmission unit 30 and the reception unit 40 with transmission / reception devices.

[Second Embodiment]
A second embodiment of the present invention will be described with reference to FIGS. First, with reference to FIG. 2, the outline | summary of the sound wave propagation length measuring apparatus 2 of this embodiment is demonstrated. In the following description, the same components as those of the first embodiment described above are denoted by the same reference numerals as those of the first embodiment, and description thereof is omitted.

  FIG. 3 is a diagram illustrating an example of the configuration of the sound wave propagation length measuring apparatus 2 according to the second embodiment. The sound wave propagation length measuring apparatus 2 includes a waveform generating unit 15 instead of the waveform generating unit 10, a transmitting / receiving unit 35 instead of the transmitting unit 30 and the receiving unit 40, and a lock-in detecting unit 55 instead of the lock-in detecting unit 50. Instead of the measuring unit 60, a measuring unit 65 is provided. It should be noted that the transmission / reception unit 35 does not necessarily have to be integrated and may be installed separately. The sound wave propagation length measuring device 2 is different from the first embodiment described above in that the position of the measuring object Obj in the fluid pipe line Fp is measured using the phase delay due to the reflection of the sound wave W. Here, the measurement object Obj is, for example, an inspection robot that moves in the fluid pipeline Fp, a foreign matter in the fluid pipeline Fp, or the like. In this example, the measuring object Obj is moving at a speed in the moving direction Dm shown in FIG. The case where the moving speed of the measuring object Obj is sufficiently lower than the sound speed WS of the sound wave W propagating in the fluid Fd (for example, the moving speed of the measuring object Obj is about 10 [km / h]) will be described. .

  The waveform generator 15 outputs a continuous signal CtS to the amplifier 20. The continuous signal CtS is, for example, a signal having a continuous waveform of 10 [kHz].

  The transmission / reception unit 35 includes, for example, an underwater speaker, and outputs the supplied transmission signal TxS as a sound wave W to the fluid Fd in the fluid conduit Fp. The sound wave W output from the transmission / reception unit 35 to the fluid Fd is also referred to as an incident wave Wi of the measurement object Obj or simply as an incident wave Wi. In addition, the transmission / reception unit 35 includes, for example, an underwater microphone, and receives the sound wave W reflected by the measurement object Obj, that is, the reflected wave Wr, which is output to the fluid Fd, and receives the received reflected wave Wr. The received signal RxS is output. The received signal RxS includes noise N corresponding to the vibration of the fluid Fd. An example of the received signal RxS including the noise N is shown in FIG.

  FIG. 4 is a diagram illustrating an example of a signal waveform according to the second embodiment. The waveform generator 15 outputs a continuous signal CtS shown in FIG. The transmission / reception unit 35 outputs the transmission signal TxS obtained by amplifying the continuous signal CtS as the sound wave W. That is, the waveform of the continuous signal CtS generated by the waveform generation unit 15 and the waveform of the sound wave W output by the transmission / reception unit 35 are similar.

  The lock-in detection unit 55 detects the received signal RxS by a known lock-in detection method based on the reference signal RfS. The lock-in detection unit 55 outputs the detection result of the reception signal RxS to the measurement unit 65 as the lock-in output signal LiS. An example of the waveform of the lock-in output signal LiS is shown in FIG. The lock-in output signal LiS is a signal in which the noise N component included in the reception signal RxS received by the transmission / reception unit 35 is reduced. The mechanism for reducing this noise N component is the first implementation described above. Since it is the same as that of the form, the description is omitted.

  The lock-in output signal LiS of the present embodiment is a signal having a rectangular waveform that rises and falls according to the distance l2 between the transmission / reception unit 35 and the measurement object Obj. Specifically, the lock-in output signal LiS rises and falls every time it moves in the movement direction Dm by a length of ¼ of the wavelength λ of the sound wave W in the fluid Fd, that is, the distance (λ / 4). Will occur. In the specific example shown in FIG. 4, the measurement object Obj moves in the moving direction Dm by a distance (λ / 4) from time t1 to time t2. The measurement object Obj moves in the moving direction Dm by a distance (λ / 4) from time t2 to time t3 and by a distance (λ / 4) from time t3 to time t4.

  Returning to FIG. 3, the measurement unit 65 measures the change in the distance l2 between the transmission / reception unit 35 and the measurement target Obj by counting the number of rising and falling times of the waveform of the lock-in output signal LiS. Here, if the distance between the transmission / reception unit 35 and the measurement object Obj at the time t1 illustrated in FIG. 4 is known, the measurement unit 65 performs transmission / reception based on the count result of the waveform change of the lock-in output signal LiS. It is also possible to measure the distance l2 between the unit 35 and the measurement object Obj. The measuring unit 65 can also measure the moving speed of the measurement object Obj based on the counting result of the waveform change of the lock-in output signal LiS per unit time.

  As described above, according to the sound wave propagation length measuring apparatus 2 of the present embodiment, the position and moving speed of the measurement object Obj in the fluid pipe line Fp are reduced while reducing the influence of the noise N generated in the fluid pipe line Fp. Can be measured. That is, according to the sound wave propagation length measuring device 2, when measuring the position and moving speed of the measurement object Obj in the fluid pipeline Fp, the influence of the noise N generated in the fluid pipeline Fp can be reduced.

  Note that the configurations in the above-described embodiment and each modification may be combined as appropriate as long as they do not contradict each other.

  DESCRIPTION OF SYMBOLS 1, 2 ... Sound wave propagation length measuring apparatus 10, 15 ... Waveform generation part, 20 ... Amplification part, 30 ... Transmission part (Sound wave transmission part), 35 ... Transmission / reception part (Sound wave transmission part, Sound wave reception part), 40 ... Reception Unit (sound wave receiving unit), 50, 55 ... lock-in detection unit (noise reduction unit), 60, 65 ... measurement unit, Fp ... fluid conduit, Obj ... measurement object

Claims (6)

A sound wave propagation length measuring method for measuring a propagation length of the sound wave by transmitting and receiving sound waves through the fluid in a fluid conduit through which the fluid flows,
A waveform generation procedure for generating a signal of a predetermined frequency band;
A sound wave that is transmitted to the fluid in the fluid line by converting the signal generated in the waveform generation procedure into a sound wave having a frequency lower than a primary cutoff frequency when the fluid line is regarded as a waveguide. Sending procedure,
A sound wave reception procedure for receiving the sound wave transmitted in the sound wave transmission procedure;
A noise reduction procedure for reducing noise included in the sound wave received in the sound wave reception procedure based on the signal generated in the waveform generation procedure;
A sound wave propagation length measurement method comprising: a measurement procedure for measuring a propagation length of a sound wave propagating in the fluid based on a signal in which noise is reduced in the noise reduction procedure and a signal generated in the waveform generation procedure . In the noise reduction procedure,
The sound wave propagation length measurement method according to claim 1, wherein noise included in the sound wave received in the sound wave reception procedure is reduced by a lock-in detection method based on a signal generated in the waveform generation procedure. In the waveform generation procedure,
The sound wave propagation length measuring method according to claim 1 or 2, wherein a burst signal of a predetermined frequency band is generated as the signal. In the waveform generation procedure,
The sound wave propagation length measuring method according to any one of claims 1 to 3, wherein a continuous signal of a predetermined frequency band is generated as the signal. In the sound wave receiving procedure,
The sound wave transmitted in the sound wave transmission procedure receives the reflected wave reflected by the measurement object,
In the measurement procedure,
The sound wave propagation length measurement method according to claim 4, wherein a change in the position of the measurement object is measured based on a change in the reflected wave received in the sound wave reception procedure. A sound wave propagation length measuring device that measures the propagation length of the sound wave by transmitting and receiving sound waves through the fluid in a fluid conduit through which the fluid flows;
A waveform generator for generating a signal of a predetermined frequency band;
A sound wave transmission in which the signal generated by the waveform generator is a sound wave having a frequency lower than a primary cutoff frequency when the fluid line is regarded as a waveguide, and is transmitted to the fluid in the fluid line. And
A sound wave receiver for receiving sound waves transmitted by the sound wave transmitter;
A noise reduction unit that reduces noise included in the sound wave received by the sound wave reception unit based on a signal generated by the waveform generation unit;
A sound wave propagation length measurement device comprising: a measurement unit that measures a propagation length of a sound wave propagating in the fluid based on a signal whose noise is reduced by the noise reduction unit and a signal generated by the waveform generation unit.

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