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JP2006138880

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DESCRIPTION JP2006138880
PROBLEM TO BE SOLVED: To provide a noise removal method capable of effectively removing
extraneous noise other than leaked sound regardless of working time and place in leak detection.
SOLUTION: A signal in which leaked sound and external noise are mixed by a vibration sensor 1
installed on the ground or a wall is subjected to fast Fourier transform to be converted into a
signal S1 composed of frequency components. The appearance frequency of the frequency
component having the largest power among the frequency components is counted, and the
frequency of the frequency component having the highest appearance frequency in a
predetermined time is determined as the central frequency F of the leaked sound. A pass
frequency k × F is selected with reference to the center frequency F, and a filter X in which a
predetermined bandwidth W is set for the center frequency F and each pass frequency k × F is
created. An output signal S1 consisting of frequency components is applied to this filter X to
generate a composite signal S2 in which frequency components of leaked sound are passed. The
synthesized signal S2 is subjected to high-speed inverse Fourier transformation to convert it into
an output signal consisting only of leaked sound from which extraneous noise has been removed.
[Selected figure] Figure 1
Noise removal method in leak detection
[0001]
The present invention detects traffic noise from cars, pedestrians, etc., stores operating at
midnight, and stores for auto sales when detecting the presence or absence of leakage of water,
gas, etc. from buried pipes such as water pipes and gas pipes on the ground or wall. The present
invention relates to a noise removal method for effectively removing noises such as noises from
machines and the like.
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[0002]
Conventionally, when detecting the presence or absence of leakage of water, gas, etc. from buried
pipes such as water pipes and gas pipes on the ground or wall, etc., a band pass is used as a
method of removing noise other than leaked sound such as water, gas etc. Methods using filters,
low pass filters, high pass filters, etc. are known.
Here, a band pass filter passes only signals of a specific range of frequencies and attenuates
signals of other frequencies, and a low pass filter passes only signals of frequencies below a
specific frequency, The signal of the frequency of is attenuated, the high pass filter is the one of
passing only the signal of the frequency higher than the specific frequency and the signal of
other frequencies is attenuated.
[0003]
In addition, many vibration sensors are installed on the ground or wall where water pipes and the
like are embedded, and the output signals of these vibration sensors are compared to remove
noise, as described in Patent Document 1, to remove noise. Also known are methods of
[0004]
Unexamined-Japanese-Patent No. 2000-230879
[0005]
However, the method of using a band pass filter or the like passes signals in a specific frequency
band and attenuates signals in other frequency bands, so sudden noise such as traffic noise of
cars, pedestrians, etc. The noise that affects the entire frequency band can not be identified at
which frequency and can not be removed effectively.
Similarly, life noises from late-night stores and vending machines could not be removed
effectively.
[0006]
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Also, the method of installing a large number of vibration sensors and comparing the output
signals is difficult to carry out by a single worker because the system scale becomes large due to
the use of a large number of vibration sensors, and the work personnel and time are required.
Met.
[0007]
The present invention has been made to solve the problems in the prior art, and the object of the
present invention is a leak detection operation when detecting the presence or absence of
leakage of water, gas, etc. from a buried pipe. We provide a noise removal method that can
effectively remove noises such as traffic noises and living noises other than leaked noises in
order to reliably extract leaked noises such as water and gas regardless of the time and place of
It is to do.
[0008]
In order to achieve the above object, the noise removal method in leak detection of the present
invention converts a signal in which leaked sound and extraneous noise are mixed into a signal
S1 consisting of frequency components, and the frequency having the largest power among the
frequency components The frequency of occurrence of the component was counted, and the
frequency in the frequency component at which the frequency of occurrence in a predetermined
time was maximum was determined as the center frequency F of the leaked sound, and a
predetermined bandwidth was set for the obtained center frequency F A filter is created, and an
output signal S1 consisting of frequency components is applied to the filter to generate a
combined signal S2 passing the frequency components of the leaked sound, and converted into
an output signal from which extraneous noise is removed. .
[0009]
Here, the signal in which the leaked sound and the external noise are mixed may be output by a
vibration sensor installed on the ground or a wall surface.
[0010]
Also, a pass frequency k × F is selected based on the obtained center frequency F, and a filter in
which a predetermined bandwidth is set for the center frequency F and each pass frequency k ×
F is created, and an output signal S1 consisting of frequency components May be applied to this
filter to generate a synthetic signal S2 in which the frequency component of the leaked sound
passes.
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[0011]
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 view showing a noise removal method in leak detection of the present
invention, and FIG. 2 is an explanatory view in the case where the noise removal method of the
present invention is implemented for water leak detection in a water pipe.
[0012]
The noise removal method in leak detection according to the present invention comprises:
vibration capture means for capturing leaked sound and extraneous noise; and leaked sound
extraction means for removing extraneous noise from the output signal from the vibration
capture means and extracting only leaked sound. It is carried out by providing.
[0013]
As shown in FIG. 2, a vibration sensor 1 or the like installed on the ground or a wall surface can
be adopted as a vibration capturing means for supplementing the leaked sound and the external
noise.
[0014]
As a leaked sound extraction unit that removes extraneous noise from the output signal from the
vibration capture unit and extracts only the leaked sound, a fast Fourier transform processing
unit 3 that converts the output signal from the vibration capture unit into a frequency
component by fast Fourier transform The center frequency determination unit 4 uses the
frequency of the frequency component having the largest power among the frequency
components of the output signal as the center frequency of the leaked sound, and determines the
frequency component to be passed by appropriately multiplying the center frequency by a
coefficient The filter creation unit 5, the leaked sound extraction processing unit 6 for extracting
the leaked sound by applying a filter to the output signal composed of frequency components,
and the output signal composed of the passed frequency components are subjected to high-speed
inverse Fourier transform to output signals A leak detection apparatus 2 is configured, which
includes a high-speed inverse Fourier transform processing unit 7 to be converted.
[0015]
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In the noise removal method for leak detection according to the present invention, first, as shown
in FIG. 1, the signal in which the leaked sound and the external noise are mixed by the vibration
capturing means such as the vibration sensor 1 is mixed by the fast Fourier transform processing
unit 3 The signal is fast Fourier transformed and converted into a signal S1 consisting of
frequency components.
Then, the signal S 1 composed of frequency components is transmitted to the center frequency
determination unit 4.
[0016]
The center frequency determination unit 4 searches the frequency component having the largest
power among the frequency components every time the output signal is subjected to fast Fourier
transform, counts the frequency of appearance of the frequency component, and displays the
frequency within a predetermined time. It is determined that the frequency of the frequency
component at which is the maximum is the center frequency F of the leaked sound.
[0017]
Sound from leaked water, gas, etc. from underground pipes such as water pipes and gas pipes is
constantly generated, while traffic noise from cars, pedestrians, etc., stores operating at midnight,
vending machines Because external noises such as living noises are generated non-stationarily, if
the frequency of appearance of the frequency component with the largest power is counted, the
frequency of the frequency component whose appearance frequency becomes the largest within
a predetermined time Can be determined as the center frequency of the leaked sound.
[0018]
Based on the obtained center frequency F, the filter generation unit 5 appropriately multiplies
the center frequency F by a coefficient k to select the pass frequency k × F, and the
predetermined frequency is selected for the center frequency F and each pass frequency k × F.
Set the bandwidth W of to create the filter X.
[0019]
Since it is empirically known that the frequency component of the leaked sound usually exhibits
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a maximum value at a frequency Fn obtained by appropriately multiplying the central frequency
F by the coefficient k, the central frequency F is appropriately multiplied by the coefficient k to
be a passing frequency. This is to select k × F and create a filter.
FIG. 1 shows the filter X created by setting k1 = 0.4, k2 = 1.4, and k3 = 2.0.
[0020]
The leaked sound extraction processing unit 6 applies the output signal S1 consisting of
frequency components to the filter X created as described above to attenuate the frequency
components other than the center frequency F and each passing frequency k × F, and the leaked
sound frequency The component is passed to generate a combined signal S2.
[0021]
Then, the synthesized signal S2 composed of the selected frequency components is subjected to
the fast inverse Fourier transform by the fast inverse Fourier transform processing unit 7 and
converted into an output signal composed only of the leaked sound in which extraneous noise is
attenuated.
[0022]
Next, the case where the noise removal method of the present invention is implemented for water
leakage detection of a water pipe will be described with reference to FIG.
[0023]
In the present embodiment, the vibration sensor 1 is installed on the ground where the water
pipe 11 is embedded, the output cord of the vibration sensor 1 is connected to the leak detection
device 2, and the input cord of the headphones 8 is connected to the leak detection device 2. .
[0024]
A water leak point 11 a exists in the water pipe 11, and a water leak sound generated at the
water leak point 11 a propagates in the ground and is captured by the vibration sensor 1.
In addition, traffic noises of vehicles, pedestrians, etc. traveling on the ground are also
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propagated through the ground and captured by the vibration sensor 1.
[0025]
Then, the water leakage noise and the traffic noise captured by the vibration sensor 1 are input
to the leak detection device 2 as an electrical signal.
[0026]
As described above, the leak detection device 2 includes the fast Fourier transform processing
unit 3, the center frequency determination unit 4, the filter creation unit 5, the leaked sound
extraction processing unit 6, and the fast inverse Fourier transform processing unit 7.
Therefore, the output signal from the vibration sensor 1 is converted by the fast Fourier
transform processing unit 3 into a signal S 1 composed of frequency components, and
transmitted to the center frequency determination unit 4.
[0027]
The center frequency determination unit 4 counts the appearance frequency of the frequency
component having the largest power among the frequency components, and the frequency
component of the frequency component whose appearance frequency becomes maximum in a
predetermined time is the central frequency F of the leaked sound It is determined, the pass
frequency k × F is selected based on the obtained center frequency F by the filter creating unit
5, and the filter X in which a predetermined bandwidth W is set for the center frequency F and
each pass frequency k × F is created Be done.
[0028]
Next, the leaked sound extraction processing unit 6 applies the filter X to the output signal S1
consisting of frequency components to generate a composite signal S2 in which the frequency
component of the leaked sound is passed, to the high speed inverse Fourier transform processing
unit 7 , And a synthetic signal in which extraneous noise components are attenuated is
generated.
[0029]
The output signal waveform diagram and spectrogram of the vibration sensor 1 are as shown in
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FIG. 3, and the output signal waveform diagram and spectrogram after noise removal by applying
the noise removal method of the present invention are as shown in FIG. The
[0030]
On the other hand, in place of the leak detection device 2, a band pass filter is used to similarly
remove noise from the output signal from the vibration sensor 1.
The resulting output signal waveform diagram and spectrogram were as shown in FIG.
[0031]
Comparing FIG. 4 with FIG. 5, the power difference between the extraneous noise and the leaked
sound is about 17 dB according to the noise removal method in the leak detection of the present
invention and the method using the band pass filter. It is understood that the noise removal
method in the leak detection of the invention has the same noise reduction effect as the method
using the band pass filter.
[0032]
However, the intrinsic effect of noise removal is determined by the size of the Signal to Noise
Ratio (SNR).
That is, even if the noise reduction effect is the same degree, the degree of the essential effect of
the noise removal is judged by whether or not the signal (leakage sound) is reliably captured, and
the higher the SNR, the more essential the noise removal. It can be said that the effect is high.
[0033]
An output signal waveform diagram and a spectrogram of the vibration sensor 1 at the water
leakage site A are shown in FIG. 6A, and an output signal waveform diagram and a spectrogram
after noise removal using a band pass filter are shown in FIG. An output signal waveform
diagram and a spectrogram after noise removal by applying the noise removal method of the
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invention are shown in FIG. 8 (A).
Also, FIG. 6 (B) shows the output signal waveform diagram and spectrogram of the vibration
sensor 1 at the water leakage site B, and FIG. 7 (B) shows the output signal waveform diagram
and spectrogram after noise removal using a band pass filter. An output signal waveform
diagram and a spectrogram after noise removal by applying the noise removal method of the
present invention are shown in FIG. 8 (B).
Here, the mark ▲ indicates the center frequency of the water leakage sound at the water leakage
site A, and the mark は indicates the center frequency of the water leakage sound at the water
leakage site B.
[0034]
If FIG. 7 (B) and FIG. 8 (B) are contrasted and a band pass filter is used as the same setting in the
water leak site A, the water leak sound can be reliably caught in the water leak site B. On the
other hand, it can be seen that when the noise removal method of the present invention is
applied, the leak noise can be reliably captured even at the leak site B.
[0035]
Therefore, since the headphone 8 outputs a signal consisting of only the water leakage sound
from which the extraneous noise has been removed, the worker can detect the water leakage
point 11 a in the water pipe 11 easily and reliably.
[0036]
As described above, according to the noise removal method in leak detection of the present
invention, when detecting the presence or absence of leak of water, gas and the like from the
buried pipe, extraneous noise such as traffic noise and life noise other than leak noise is detected.
Because it can be removed effectively, regardless of the time and place where the leak detection
work is performed, the leak sound of water, gas, etc. can be reliably extracted to detect the leak
point in the buried pipe easily and reliably it can.
[0037]
Also, according to the noise removal method of the present invention, the center frequency of the
leaked sound can be determined regardless of the presence or absence of extraneous noise, so as
in the case of using a band pass filter, the pass frequency band is set for each leak site. There is
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no need to do this, so the passband may be set improperly to avoid the risk of not being able to
capture leaked sound.
[0038]
Furthermore, according to the noise removal method of the present invention, the center
frequency F is appropriately multiplied by the coefficient k to select the pass frequency k × F,
and a filter is created. Therefore, as in the case of using a band pass filter, a constant frequency It
is possible to extract a spectrum close to the actual leaked sound, not the spectrum of the band
alone.
[0039]
It is explanatory drawing which shows the noise removal method in the leak detection of this
invention.
It is explanatory drawing in the case where the noise removal method in leak detection of this
invention is implemented about the leak detection of a water pipe.
It is an output signal waveform figure and a spectrogram of the vibration sensor installed in the
ground.
It is an output signal waveform figure and spectrogram after denoising using a band pass filter.
It is an output signal waveform figure and spectrogram after denoising by applying the noise
removal method of this invention.
It is an output signal waveform diagram and a spectrogram which show the output signal of the
vibration sensor installed in the ground, (A) is a leak site A, and (B) is a leak site B.
It is an output signal waveform diagram and spectrogram after noise removal using a band pass
filter, Comprising: (A) is a leak site A, and (B) is a leak site B.
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It is an output signal waveform figure and spectrogram after noise removal using the noise
removal method of this invention, Comprising: (A) is a leak site A, and (B) is a leak site B.
Explanation of sign
[0040]
Reference Signs List 1 vibration sensor 2 leak detection device 3 fast Fourier transform
processing unit 4 center frequency determination unit 5 filter creation unit 6 leaked sound
extraction processing unit 7 fast inverse Fourier transform processing unit
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