JP2006138638A - Noise removal method in leak detection - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a noise removal method capable of removing effectively external noise other than a leakage sound regardless of a working time or a place, when performing leak detection. <P>SOLUTION: The leakage sound by a vibration sensor 1 installed on the ground or the wall surface, a signal wherein the external noise is mixed, and a signal mainly composed of the external noise by a microphone 2 installed on a proper position on the ground are subjected respectively to fast Fourier transform, to thereby convert them into signals S1, S2 comprising frequency components. The signals S1, S2 comprising each frequency component are subjected to operation processing, to thereby generate a composite signal S3 wherein an external noise component is attenuated. The composite signal S3 is subjected to fast inverse Fourier transform, to thereby convert it into an output signal wherein the external noise is removed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is designed to detect the presence of leakage of water, gas, etc. from buried pipes such as water pipes and gas pipes on the ground and wall surfaces, traffic noise of automobiles, pedestrians, etc. The present invention relates to a noise removal method for effectively removing noise such as daily noise from a machine.

Conventionally, bandpass has been used as a method for removing noise other than water and gas leaks when detecting the presence or absence of water or gas leaks from buried pipes such as water pipes and gas pipes on the ground or wall surfaces. A method using a filter, a low-pass filter, a high-pass filter, or the like is known.
Here, the band-pass filter passes only signals in a specific range of frequencies and attenuates signals in other frequencies, and the low-pass filter passes only signals of frequencies below a specified frequency, and the others The high-pass filter is a filter that passes only signals having a frequency higher than a specific frequency and attenuates signals having other frequencies.

  In addition, a method of removing noise by installing a large number of vibration sensors on the ground or wall where a water pipe or the like is buried and comparing the output signals of the vibration sensors, as described in Patent Document 1 The method of doing is also known.

JP 2000-230879 A

  However, the method of using a bandpass filter or the like allows a signal in a specific frequency band to pass and attenuates a signal in other frequency bands. The noise that affects the entire frequency band cannot be identified at which frequency, and cannot be effectively removed. Similarly, daily noise from stores operating at midnight and vending machines could not be effectively removed.

  Also, the method of installing a large number of vibration sensors and comparing the output signals is difficult to implement by one worker because the use of a large number of vibration sensors increases the system scale and takes time and labor. Met.

  The present invention has been made to solve such problems in the prior art, and the object of the present invention is to detect leaks when detecting the presence or absence of leakage of water, gas, etc. from the buried pipe. Provide a noise removal method that can effectively remove traffic noise, daily noise, etc. other than leaked sound to reliably extract leaked sounds of water, gas, etc. regardless of the time and place There is to do.

  In order to achieve the above object, a noise removal method in leak detection according to the present invention converts a signal in which leaked sound and external noise are mixed and a signal mainly composed of external noise into signals each composed of frequency components, and each frequency component. A composite signal in which the external noise component is attenuated is generated by performing arithmetic processing on the signal consisting of the above and converted into an output signal from which the external noise has been removed.

  Here, a signal in which leakage sound and external noise are mixed is output by a vibration sensor installed on the ground or a wall surface, and a signal mainly consisting of external noise is output by a microphone installed at an appropriate position on the ground. Good.

  In order to generate a composite signal in which the external noise component is attenuated by performing arithmetic processing on the signal composed of each frequency component, (signal S1 in which leakage sound and external noise are mixed) and (signal S1 in which leakage sound and external noise are mixed) May be multiplied by each frequency component of the signal S1 to generate a composite signal in which the external noise component is attenuated.

  Alternatively, a signal S2 mainly composed of external noise may be subtracted from the signal S1 in which leakage sound and external noise are mixed to generate a composite signal in which the external noise component is attenuated.

Hereinafter, the noise removal method in the leak detection of the present invention will be specifically described with reference to the drawings.
FIG. 1 is an explanatory diagram showing a noise removal method in leak detection according to the present invention, and FIG. 2 is an explanatory diagram when the noise removal method according to the present invention is carried out for water leak detection in a water pipe.

  The noise detection method in the leak detection according to the present invention includes a first vibration capturing unit that captures leaked sound and external noise, and a second vibration capturing unit that mainly captures only the external noise. This is implemented by providing leakage sound extraction means for removing the external noise from the output signal by the second vibration capturing means and the output signal by the second vibration capturing means to extract only the leakage sound.

As shown in FIGS. 1 and 2, a vibration sensor 1 or the like installed on the ground or a wall surface can be employed as the first vibration capturing unit that supplements leakage sound and external noise.
Also, as the second vibration capturing means that mainly captures only external noise, a microphone 2 or the like installed at an appropriate position on the ground can be employed.

As the leakage sound extraction means for extracting only the leaked sound by removing the external noise from the output signals from the first and second vibration capturing means, the output signals from the first and second vibration capturing means are subjected to fast Fourier transform. Fast Fourier transform processing units 4 and 5 that convert frequency components, a noise component attenuation processing unit 6 that attenuates external noise components by performing arithmetic processing on signals that are frequency components, and a high-speed inverse signal that attenuates external noise components A leak detection apparatus 3 is configured which includes a high-speed inverse Fourier transform processing unit 7 that performs Fourier transform and converts it into an output signal.

In the noise removal method in the leak detection according to the present invention, first, as shown in FIG. 1, the fast Fourier transform processing unit 4 applies a fast Fourier transform processing unit 4 to a signal mixed with the leaked sound and the external noise captured by the first vibration capturing means. The signal is converted into a signal S1 composed of frequency components.
Similarly, a signal mainly composed of external noise captured by the second vibration capturing means is also subjected to fast Fourier transform by the fast Fourier transform processing unit 5 and converted to a signal S2 composed of frequency components.

  Next, as shown in FIG. 1, the signal S1 converted into the frequency component and the signal S2 converted into the frequency component are subjected to arithmetic processing by the noise component attenuation processing unit 6, and the external noise component is attenuated to produce the combined signal. S3 is generated.

When a Wiener filter is applied as the noise component attenuation processing unit 6, (output signal S1 from the first vibration capturing means) and (output signal S1 from the first vibration capturing means and output from the second vibration capturing means) The combined signal S3 in which the external noise component is attenuated can be generated by multiplying each frequency component of the signal S1 by the square root of the ratio to the signal (cross spectrum with the signal S2).
The cross spectrum is obtained by multiplying the frequency components of the spectrum of the two signals and averaging them. The cross spectrum shows a large value at a certain frequency. The correlation between the frequency components of the two signals at that frequency is shown. Means that both components are large.

  Instead of applying the Wiener filter as the noise component attenuation processing unit 6, the external noise component is attenuated by simply subtracting the output signal S2 from the second vibration capturing means from the output signal S1 from the first vibration capturing means. The synthesized signal S3 may be generated.

  Then, the synthesized signal S3 in which the external noise component is attenuated is subjected to high-speed inverse Fourier transform by the high-speed inverse Fourier transform processing unit 7, and is converted into an output signal including only the leaked sound from which the external noise is removed.

  Next, a case where the noise removal method of the present invention is implemented for water pipe leak detection will be described with reference to FIG.

In this embodiment, the vibration sensor 1 is installed on the ground where the water pipe 11 is embedded, and the microphone 2 is installed at an appropriate position on the ground.
The output cords of the vibration sensor 1 and the microphone 2 were connected to the leak detection device 3, and the input cord of the headphones 8 was connected to the leak detection device 3.

The water pipe 11 has a water leakage point 11a, and the water leakage sound generated at the water leakage point 11a propagates through the ground and is captured by the vibration sensor 1.
In addition, traffic noise such as automobiles and pedestrians traveling on the ground propagates through the ground and is captured by the vibration sensor 1, and also propagates through the air and is captured by the microphone 2.

  The water leakage sound and traffic noise captured by the vibration sensor 1 are input to the leak detection device 3 as electrical signals, and the traffic noise captured by the microphone 2 is also input to the leak detection device 3 as electrical signals.

As described above, the leak detection apparatus 3 includes the fast Fourier transform processing units 4 and 5, the noise component attenuation processing unit 6, and the fast inverse Fourier transform processing unit 7.
Therefore, the output signals from the vibration sensor 1 and the microphone 2 are converted into signals S1 and S2 each composed of frequency components by the fast Fourier transform processing units 4 and 5, and the external noise component is attenuated by the noise component attenuation processing unit 6. The synthesized signal S3 is generated and converted by the fast inverse Fourier transform processing unit 7 into an output signal consisting only of the water leakage sound from which the external noise has been removed.

The output signal waveform of the vibration sensor 1 is as shown in FIG. 3 (A), and the output signal waveform of the microphone 2 is as shown in FIG. 3 (B).
The output signal waveform after applying the noise removal method of the present invention to remove noise is as shown in FIG.

On the other hand, instead of using the microphone 2, a bandpass filter is used instead of the leak detection device 3, and noise is similarly removed from the output signal from the vibration sensor 1.
The output signal waveform obtained as a result was as shown in FIG.

  Comparing FIG. 4 and FIG. 5, it can be seen that the external noise is largely removed by the noise removal method in the leak detection of the present invention.

  Thus, since the headphone 8 outputs a signal consisting only of the water leakage sound from which the external noise has been removed, the operator can easily and reliably detect the water leakage point 11a in the water pipe 11.

  As described above, according to the noise removal method of the leak detection of the present invention, when detecting the presence or absence of leakage of water, gas, etc. from the buried pipe, external noise such as traffic noise and living noise other than leaked sound is detected. Because it can be effectively removed, it is possible to easily and reliably detect leakage points in buried pipes by reliably extracting leakage sounds of water, gas, etc. regardless of the time and place of leakage detection work. it can.

It is explanatory drawing which shows the noise removal method in the leak detection of this invention. It is explanatory drawing at the time of implementing the noise removal method in the leak detection of this invention about the leak detection of a water pipe. (A) is an output signal waveform diagram and spectrogram of a vibration sensor installed on the ground, and (B) is an output signal waveform diagram and spectrogram of a microphone installed on the ground. It is the output signal waveform figure and spectrogram after removing noise using a band pass filter. It is the output signal waveform figure and spectrogram after applying the noise removal method of this invention, and removing a noise.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vibration sensor 2 Microphone 3 Leak detection device 4,5 Fast Fourier transform processing part 6 Noise component attenuation processing part 7 Fast inverse Fourier transform processing part 8 Headphone

Claims (5)

  A signal containing both leaked sound and external noise and a signal composed mainly of external noise are converted into signals composed of frequency components, and a signal composed of each frequency component is arithmetically processed to generate a composite signal in which the external noise components are attenuated. A method for removing noise in leak detection, wherein the output signal is converted into an output signal from which extraneous noise has been removed.   2. The method of removing noise in leak detection according to claim 1, wherein a signal in which leaked sound and external noise are mixed is output by a vibration sensor installed on the ground or a wall surface.   3. The noise removal method for leak detection according to claim 1, wherein a signal mainly composed of external noise is output by a microphone installed at an appropriate position on the ground.   In order to generate a composite signal in which the external noise component is attenuated by performing arithmetic processing on the signal composed of each frequency component, (signal S1 in which leakage sound and external noise are mixed) and (signal S1 in which leakage sound and external noise are mixed) And a frequency spectrum of the signal S1 is multiplied by the square root of the ratio between the signal and the signal S2 mainly composed of external noise to generate a composite signal in which the external noise component is attenuated. 4. A noise removal method in leak detection according to 3.   In order to generate a composite signal in which the external noise component is attenuated by calculating and processing the signal composed of each frequency component, the signal S2 mainly composed of the external noise is subtracted from the signal S1 in which the leaked sound and the external noise are mixed, and the external noise 4. The method of removing noise in leak detection according to claim 1, wherein a composite signal with attenuated components is generated.

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