JP2010249637A - Method for detecting state of fluid and state detecting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for detecting the state of a fluid and a state detecting device for acquiring the state of a fluid even in the presence of external noise. <P>SOLUTION: When an ultrasonic wave from an ultrasonic vibrator 21 is given to cavitation arising on the downstream side of an orifice 11, nonlinear vibrations are repeated in response to the ultrasonic wave to generate sound waves of high-frequency components each having a frequency n times (n is an integer equal to or more than two) as large as the fundamental frequency of the ultrasonic wave, or of subharmonic components each having a 1/n frequency thereof. These sound waves similarly propagate through a process fluid to reach a hydrophone 31. The sound waves having reached the hydrophone 31 are converted into electric signals and captured in an oscilloscope 33 via an amplifier 32. By a personal computer 4, the waveforms of the electric signals are captured from the oscilloscope 33, and the waveforms are Fourier-transformed and decomposed into frequency spectra. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fluid state detection method and a state detection device that detect a fluid state using sound waves.

  In the plant piping, bubbles (cavitation) may be generated due to local negative pressure downstream of the orifice. Cavitation is a factor that promotes erosion of pipes, and the state of occurrence affects the life of pipes.

  Conventionally, a method using an acceleration sensor has been proposed as a method for detecting cavitation (Nuclear Safety System Laboratory, Ltd. LOUTNAL VOL.11 P129). This method converts the shock wave accompanying the collapse of cavitation due to pressure recovery in the pipe into an electrical signal. When cavitation occurs, a voltage value about 10 times higher than normal is observed, so based on the voltage value. Cavitation can be detected.

  In addition, as another method for detecting cavitation, a method using a microphone has been proposed (Nuclear Safety Systems Laboratories, Ltd. LOUTNAL VOL.12 P160). In this method, the shock wave is captured by a microphone, and the frequency spectrum of the shock wave is obtained by Fourier transform. Since cavitation-specific peaks appear in the vicinity of a specific frequency when cavitation occurs, cavitation can be detected.

JP 2007-170981 A

Nuclear Safety Systems Laboratory LOUTNAL VOL.11 P129 Nuclear Safety Systems Laboratory LOUTNAL VOL.12 P160 Flow 24 (2005) 405-412

  In an actual plant, there are many vibration sources and acoustic noise sources such as pumps and turbines. However, the conventional method has a problem that it is difficult to detect cavitation in an environment where external noise is large, and cavitation cannot be detected effectively during operation of the plant. In particular, it is difficult to apply to plants operating continuously.

  An object of the present invention is to provide a fluid state detection method and a state detection device that can grasp the state of a fluid even in the presence of external noise.

The fluid state detection method of the present invention is a fluid state detection method for detecting a fluid state using sound waves, the step of giving sound waves of a predetermined frequency to the fluid, and the waveform of the sound waves after propagating through the fluid And a step of analyzing a frequency component included in the waveform.
According to this fluid state detection method, a sound wave having a predetermined frequency is given to the fluid, and the frequency component included in the waveform of the sound wave after propagating in the fluid is analyzed, so that the fluid state can be obtained even in the presence of external noise. Can be grasped.

  In the analyzing step, the analysis may be performed based on a high frequency component or a divided frequency component of the predetermined frequency included in the waveform.

  In the analyzing step, the analysis may be performed based on a ratio between a high frequency component or a divided frequency component of the predetermined frequency included in the waveform and another frequency component.

  In the analyzing step, the analysis may be performed with reference to a state where the sound wave is not applied to the fluid.

  The analysis target in the analyzing step may be cavitation in the fluid.

The fluid state detection device according to the present invention is a fluid state detection device that detects a fluid state using sound waves. The fluid state detection device provides a sound wave having a predetermined frequency to the fluid, and the sound wave after propagating through the fluid. An acquisition means for acquiring a waveform, and an analysis means for analyzing a frequency component included in the waveform are provided.
According to this fluid state detection device, a sound wave of a predetermined frequency is given to the fluid, and the frequency component contained in the waveform of the sound wave after propagating through the fluid is analyzed, so that the state of the fluid can be detected even in the presence of external noise. Can be grasped.

  The applying unit and the acquiring unit may be attached to a flange that holds an orifice.

  According to the fluid state detection method of the present invention, a sound wave having a predetermined frequency is given to the fluid, and the nonlinear component included in the waveform of the sound wave after propagating in the fluid is analyzed. Therefore, the fluid is detected even in the presence of external noise. You can grasp the state of.

  According to the fluid state detection device of the present invention, a sound wave having a predetermined frequency is given to the fluid, and a nonlinear component included in the waveform of the sound wave after propagating in the fluid is analyzed. Therefore, the fluid is detected even in the presence of external noise. You can grasp the state of.

The figure which shows an example of the fluid state detection method by this invention. The figure which illustrates the frequency spectrum at the time of cavitation generation | occurrence | production. It is a figure which shows the example which generates the burst wave of an ultrasonic wave, (a) is a figure which shows the waveform of an ultrasonic burst wave, (b) shows the waveform obtained with an oscilloscope, respectively. The figure which shows the method of extracting the frequency component resulting from a cavitation by removing a fundamental frequency component with external noise. It is a figure which shows the frequency spectrum obtained by Fourier transformation, (a) is a figure which shows the frequency spectrum of the area | region without a cavitation, (b) is the frequency spectrum of the area | region where a cavitation exists, and subtracts the frequency spectrum of an area | region without a cavitation The figure which shows the frequency spectrum obtained by doing.

  Hereinafter, an embodiment of a fluid state detection method according to the present invention will be described.

  FIG. 1 is a diagram showing an example of a fluid state detection method according to the present invention.

  As shown in FIG. 1, an orifice is provided inside a throttle mechanism flange 1 that connects between the pipes 5 of the plant. The orifice 11 is fixed by fastening a screw 12.

  An ultrasonic vibrator 21 is attached to the outer surface of the diaphragm mechanism flange 1 by welding or the like. A hydrophone 31 having a frequency characteristic in the 20 kHz-100 kHz region is attached to the diaphragm mechanism flange 1 by welding or screwing.

  As shown in FIG. 1, the process fluid flows from right to left in FIG. 1, and the ultrasonic vibrator 21 and the hydrophone 31 are provided on the downstream side of the orifice 11.

  A function generator 22 is connected to the ultrasonic transducer 21 via an amplifier 23. The output signal of the hydrophone 31 is given to the oscilloscope 33 via the amplifier 32. The waveform obtained by the oscilloscope 33 can be taken into the personal computer 4.

  Next, the state detection procedure will be described.

First, a continuous wave having a fundamental frequency within a frequency range of 20 kHz-100 kHz is output from the function generator 22, and the ultrasonic transducer 21 is driven via the amplifier 23. As a result, the ultrasonic transducer 21 radiates ultrasonic waves having the above fundamental frequency, and ultrasonic waves are applied to the downstream side of the orifice 11. The amplitude of the ultrasonic wave at this time is set to a value smaller than the cavitation threshold value. For example, when the frequency of the ultrasonic wave is 100 kHz and the process fluid is saturated water, the amplitude becomes a power lower than the cavitation threshold value of 0.2 W / cm ⁻² .

  This ultrasonic wave propagates through the process fluid and reaches the hydrophone 31. Further, when the cavitation generated on the downstream side of the orifice 11 receives the ultrasonic wave, it repeats non-linear vibration in response to the ultrasonic wave, and a high frequency having a frequency n times (n is an integer of 2 or more) the basic frequency of the ultrasonic wave. A sound wave having a component or a frequency component having a frequency of 1 / n is generated. Similarly, these sound waves propagate through the process fluid and reach the hydrophone 31.

  The sound wave that has reached the hydrophone 31 is converted into an electric signal and is taken into the oscilloscope 33 via the amplifier 32.

  The personal computer 4 takes in the waveform of the electrical signal from the oscilloscope 33, and Fourier transforms the waveform to decompose it into a frequency spectrum.

  FIG. 2 is a diagram illustrating the obtained frequency spectrum.

  In the frequency spectrum shown in FIG. 2, a peak is observed in the high frequency component of the frequency f that is twice, three times, and four times the basic frequency f0 in addition to the divided frequency component of the frequency f that is 0.5 times the basic frequency f0. Since the frequency spectrum resulting from cavitation strongly includes high frequencies and split frequencies, the presence or absence of cavitation and the amount of generation can be measured from the intensity of these frequency components.

  In the example of FIG. 2, for example, the amplitude intensity of the frequency component (measurement point A) that does not correspond to either the high frequency or the split frequency of the fundamental frequency and the split frequency component (measurement) of the frequency f that is 0.5 times the fundamental frequency f0. Based on the ratio of the amplitude of point B) to the amplitude intensity (intensity at measurement point B / intensity at measurement point A), the presence / absence of cavitation and the amount of generation can be evaluated. Instead of the frequency component, an evaluation based on the amplitude intensity of the high frequency component may be performed. Note that it is desirable to select a frequency range where the measurement point B is not affected by external noise as much as possible.

  As described above, in the state detection method of the present embodiment, ultrasonic waves having a predetermined frequency (fundamental frequency) are irradiated on the fluid to induce non-linear vibration specific to cavitation, and the high frequency and the sub-frequency of the basic frequency caused by the non-linear vibration. Analysis based on the strength of For this reason, it is possible to increase the SN ratio at the time of measurement, and the influence of external noise can be greatly reduced. Moreover, the S / N ratio can be maximized by optimizing the intensity of the ultrasonic wave (closer to the cavitation threshold).

  Further, in the state detection method of the present embodiment, the ultrasonic transducer 21 and the hydrophone 31 are fixed to the diaphragm mechanism flange 1 so that the positions of the ultrasonic transducer 21 and the hydrophone 31 with respect to the orifice 11 are in an optimum state. Can be fixed. For this reason, it is difficult to be affected by external noise, and the cavitation occurrence state can be detected with high accuracy.

  FIG. 3 is a diagram showing an embodiment in which an ultrasonic burst wave is generated from the ultrasonic transducer 21 instead of a continuous wave. FIG. 3A shows a waveform of a burst wave of a function generator, and FIG. Shows the waveforms obtained with an oscilloscope.

  In the embodiment shown in FIG. 3, the function generator 22 generates a burst wave shown in FIG. The generation period of the burst wave is set to a time during which the period P and the period Q can be separated in the waveform of the oscilloscope. The frequency (fundamental frequency) of the ultrasonic wave is the same as that in the above example.

  In this case, the waveform in period P (FIG. 3B) is captured as the burst wave generation period. The waveform in the period P is the same as that in the above-described embodiment, and the same frequency spectrum as in FIG. 2 is obtained by performing Fourier transform in the personal computer 4. In addition to the fundamental frequency component of the ultrasonic wave, this frequency spectrum includes a frequency component based on nonlinear vibration of cavitation and an external noise component.

  On the other hand, in the present embodiment, the waveform in period Q (FIG. 3B) is captured as the burst wave stop period. The waveform in the period Q indicates external noise. A frequency spectrum of external noise can be obtained by Fourier transforming this waveform in the personal computer 4.

  As shown by the dotted lines in FIG. 1, the timing for capturing the waveforms in the period P and the period Q is based on the output timing of the burst wave obtained from the function generator 22, and the ultrasonic wave from the ultrasonic transducer 21 to the hydrophone 31 is used as a reference. Determined in consideration of propagation time. It is also possible to determine the timing for capturing the waveform while actually measuring the output signal waveform of the function generator 22 and the output signal waveform of the hydrophone 31 with the oscilloscope 33.

  Next, the frequency spectrum based on the external noise is removed by subtracting the frequency spectrum obtained from the waveform in the period Q from the frequency spectrum obtained from the waveform in the period P.

  Next, the presence / absence and generation amount of cavitation are analyzed based on the frequency spectrum from which the frequency component based on external noise has been removed. For example, as shown in FIG. 2, the amplitude intensity of the frequency component (measurement point A) not corresponding to the high frequency and the divided frequency of the fundamental frequency and the divided frequency component (measurement) of the frequency f 0.5 times the fundamental frequency f0. Based on the ratio of the amplitude of point B) to the amplitude intensity (intensity at measurement point B / intensity at measurement point A), the presence / absence of cavitation and the amount of generation can be evaluated.

  In this embodiment, the state (period Q) in which no ultrasonic wave is applied to the fluid is used as a reference, and the presence / absence and generation amount of cavitation are evaluated based on the frequency spectrum from which the influence of external noise has been removed. The influence can be effectively eliminated, and the fluid state can be analyzed more accurately.

  FIG. 4 is a diagram illustrating a method for extracting a frequency component caused by cavitation by removing a fundamental frequency component together with external noise.

  In the example shown in FIG. 4, an ultrasonic transducer 21 </ b> A and a hydrophone 31 </ b> A are provided on the upstream side of the orifice 11. The ultrasonic transducer 21A and the hydrophone 31A are the same devices as the ultrasonic transducer 21 and the hydrophone 31. These are fixed to the mechanism flange 1, and the positional relationship between the ultrasonic transducer 21A and the hydrophone 31A is substantially the same as that of the ultrasonic transducer 21 and the hydrophone 31.

  Next, the state detection procedure will be described.

First, a continuous wave having a fundamental frequency within a frequency range of 20 kHz-100 kHz is output from the function generator 22 to drive the ultrasonic transducer 21 and the ultrasonic transducer 21A simultaneously. As a result, the ultrasonic transducer 21 and the ultrasonic transducer 21 </ b> A radiate ultrasonic waves having the above fundamental frequency, and ultrasonic waves are applied to the downstream side and the upstream side of the orifice 11, respectively. The amplitude of the ultrasonic wave at this time is set to a value smaller than the cavitation threshold value. For example, when the frequency of the ultrasonic wave is 100 kHz and the process fluid is saturated water, the amplitude becomes a power lower than the cavitation threshold value of 0.2 W / cm ⁻² .

  The ultrasonic waves from the ultrasonic vibrator 21 propagate through the process fluid and reach the hydrophone 31. Further, when the cavitation generated on the downstream side of the orifice 11 receives the ultrasonic wave, it repeats non-linear vibration in response to the ultrasonic wave, and a high frequency having a frequency n times (n is an integer of 2 or more) the basic frequency of the ultrasonic wave. A sound wave having a component or a frequency component having a frequency of 1 / n is generated. Similarly, these sound waves propagate through the process fluid and reach the hydrophone 31.

  On the other hand, the ultrasonic wave from the ultrasonic transducer 21A propagates through the process fluid and reaches the hydrophone 31A. However, since there is no cavitation in this region, a sound wave having a high frequency component or a divided frequency component based on the non-linear vibration of cavitation is not generated.

  The sound wave that has reached the hydrophone 31 and the sound wave that has reached the hydrophone 31 </ b> A are each converted into an electrical signal and captured by the oscilloscope 33.

  The personal computer 4 takes in the waveform of the electric signal from the oscilloscope 33, and Fourier transforms each waveform to decompose it into a frequency spectrum.

  The frequency spectrum based on the sound wave reaching the hydrophone 31 is the same as that shown in FIG. On the other hand, FIG. 5A shows a frequency spectrum based on a sound wave reaching the hydrophone 31A. As shown in FIG. 5A, the frequency spectrum does not include a high frequency component and a divided frequency component based on the non-linear oscillation of cavitation.

  Next, the frequency spectrum based on the sound wave reaching the hydrophone 31A is subtracted from the frequency spectrum based on the sound wave reaching the hydrophone 31 to calculate the difference of the frequency spectrum.

  FIG. 5B is a diagram illustrating the frequency spectrum obtained in this way.

  As shown in FIG. 5B, in the frequency spectrum, in addition to the divided frequency component of the frequency f that is 0.5 times the basic frequency f0, the high frequency component of the frequency f that is twice, three times, and four times the basic frequency f0. A peak is observed. Further, the frequency components of the fundamental frequency and the external noise are effectively canceled by the frequency spectrum subtraction operation, and only the frequency components based on cavitation are extracted.

  In the present embodiment, the occurrence state of cavitation is analyzed based on the levels of the sub-frequency component and the high-frequency component that appear in the difference frequency spectrum (FIG. 5B). Similarly to the case of FIG. 2, the occurrence of cavitation may be evaluated based on the ratio (relative intensity) between the intensity of the divided frequency component or high frequency component and the intensity of other frequency components.

  As described above, in the state detection method according to the present embodiment, the fundamental frequency component and the external noise component can be effectively canceled by subtracting the frequency spectrum acquired in the area where there is no cavitation. State detection is possible.

  Further, in the state detection method of the present embodiment, the ultrasonic vibrator 21, the ultrasonic vibrator 21 </ b> A, the hydrophone 31, and the hydrophone 31 </ b> A are fixed to the diaphragm mechanism flange 1, so that the ultrasonic vibrator for the orifice 11 and The hydrophone position can be fixed in an optimum state. For this reason, it is difficult to be affected by external noise, and the cavitation occurrence state can be detected with high accuracy.

  As described above, according to the fluid state detection method and state detection device of the present invention, a sound wave having a predetermined frequency is given to the fluid, and a nonlinear component included in the waveform of the sound wave after propagating through the fluid is analyzed. Therefore, the fluid state can be grasped even in the presence of external noise.

  The scope of application of the present invention is not limited to the above embodiment. The present invention can be widely applied to a fluid state detection method and a state detection device that detect a fluid state using sound waves.

1 Flange for diaphragm mechanism 4 Personal computer (analysis means)
21 Ultrasonic vibrator (applying means)
31 Hydrophone (Acquisition means)
11 Orifice

Claims (7)

In a fluid state detection method for detecting a fluid state using sound waves,
Applying a sound wave of a predetermined frequency to the fluid;
Obtaining a waveform of the sound wave after propagating in the fluid;
Analyzing a frequency component contained in the waveform;
A fluid state detection method comprising: 2. The fluid state detection method according to claim 1, wherein in the analyzing step, the analysis is performed based on a high frequency component or a divided frequency component of the predetermined frequency included in the waveform. 3. The fluid state according to claim 2, wherein in the analyzing step, the analysis is performed based on a ratio between a high-frequency component or a divided-frequency component of the predetermined frequency included in the waveform and another frequency component. Detection method. 3. The fluid state detection method according to claim 2, wherein in the analyzing step, the analysis is performed with reference to a state where the sound wave is not applied to the fluid. The fluid state detection method according to claim 1, wherein the analysis target in the analyzing step is cavitation in the fluid. In a fluid state detection device that detects a fluid state using sound waves,
Applying means for applying a sound wave of a predetermined frequency to the fluid;
Obtaining means for obtaining a waveform of the sound wave after propagating in the fluid;
Analyzing means for analyzing a frequency component included in the waveform;
A fluid state detection apparatus comprising: The fluid state detection device according to claim 6, wherein the applying unit and the acquiring unit are attached to a flange that holds an orifice.

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