JPH0754245B2 - In-pipe condition inspection method using sound waves - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for investigating the internal condition of a pipe, and more particularly to a method for inspecting the internal condition of a pipe using sound waves.

[0002]

2. Description of the Related Art Conventionally, as a method for investigating the condition inside a tube using sound waves, there is a method for investigating the condition inside a tube using reflected sound waves, which is disclosed in Japanese Patent Application Laid-Open No. 61-29757. In this investigation method, a sound wave transmitter and a sound wave receiver are installed at one end of the tube, and a sound wave pulse is irradiated from the sound wave transmitter into the tube. The situation inside the pipe is investigated by measuring in.

According to this investigation method, it is possible to know the position where the internal cross-sectional area of the pipe is changing by measuring the elapsed time from the emission of the irradiation sound wave to the return of the reflected wave. By comparing the phases of the sound wave and the reflected wave, it is possible to know whether the internal air cross-sectional area inside the pipe is larger or smaller than the internal air cross-sectional area before and after it at the reflection position. By measuring the amplitude of, the amount of change in the hollow cross-sectional area in the pipe can be estimated.

[0004]

However, since the above-mentioned conventional investigation method is a method of measuring a reflected wave, the reflected wave has a bend that returns even when there is no particular change in the internal cross-sectional area of the pipe. There is a problem that it cannot be applied to a pipe, and the pipe to be measured is limited to a straight pipe, which is not practical. Further, although it is possible to substantially know the position where the in-pipe air cross-sectional area changes, there is a problem that it is not possible to quantitatively estimate the continuous change in the in-pipe air cross-sectional area in the pipe axis direction.

The present invention takes into consideration the above-mentioned problems of the conventional method for investigating the situation inside a pipe using a sound wave, and a sound wave that can quantitatively measure the hollow cross-sectional area in the pipe even for a bent pipe. The purpose is to provide a method for in-service condition inspection.

[0006]

According to the present invention, a predetermined sound wave signal is input from one end of a pipe whose both ends are open, and the other sound wave signal is received at the other end. Of the sampled x _i value obtained from the received sound wave signal, the autocorrelation coefficient v _i at a different time is obtained, and the linear prediction coefficient α _i is used based on the autocorrelation coefficient v _i. to 'seek further its partial correlation coefficient k _i' partial correlation coefficients k _i are the reflection coefficients k _i regarding sound waves of the tube
It is assumed that the hollow cross-sectional area in the pipe at each position in the axial direction of the pipe is obtained based on the recurrence formula established between the reflection coefficient k _i and the measured value A of the opening cross-sectional area. This is a method for inspecting a situation inside a tube using a characteristic sound wave.

[0007]

According to the present invention, when a predetermined sound wave signal is inputted from one end of the pipe to be measured whose both ends are open, the sound wave signal which has passed through the pipe is received at the other end, and the received sound wave signal is received. A sample value is extracted from the waveform of, the autocorrelation coefficient v _i is calculated, and the partial correlation coefficient k _i ′ is calculated based on the autocorrelation coefficient v _i using the linear prediction coefficient α _i. considers partial correlation coefficients k _i 'and the reflection coefficient k _i, further its reflection coefficient k _i, by being assigned to the opening cross-sectional area a transgressions recurrence formula which has been previously measured, corresponding to the i-th position The in-pipe air cross-sectional area is sequentially calculated, and thereby the distribution of the in-pipe air cross-sectional area in the pipe axis direction can be measured.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an apparatus for carrying out a method for inspecting a condition inside a tube using sound waves according to the present invention. In the figure, 1 is a gas conduit as an object to be measured, which is open at both ends. A speaker 2 for inputting a predetermined sound wave signal into the tube 1 is attached to one end of the tube 1, and the speaker 2 is connected to a sound generator 4 via a signal line 3. Driven by the sonic signal to enter the tube 1. In this embodiment, impulse sound or white noise is used as the sound source for the sound wave signal and is determined in advance.

A receiver 5 for receiving a sound wave signal passing through the pipe 1 is attached to the other end of the pipe 1, and the sound wave signal received by the receiver 5 passes through a signal line 6. And is sent to the data processor 7. The data processor 7 extracts sample values { _xn }, n = 0, 1, ..., N-1 from the waveform x (t) of the sound wave signal, and processes the extracted sample values according to a flowchart described later. . Then, the processing result is printed as a distribution diagram of the in-pipe air cross-sectional area corresponding to the axial position of the pipe 1. In addition, 8 is a foreign substance such as rust generated in the pipe 1.

An outline of data processing in the data processor 7 is performed according to the following procedure. That is,
(1) A sample value is extracted from the waveform of the sound wave signal received by the receiver 5. (2) Calculate autocorrelation coefficients v _i at different times in the waveform. (3) Its autocorrelation coefficient v _i
Based on the above, the partial correlation coefficient k _i ′ is calculated using the linear prediction coefficient α _i . (4) Based on a recurrence formula established between the partial correlation coefficient k _i ′ and the reflection coefficient k _i and the value A of the opening cross-sectional area of one of the tubes 1 (measured in advance). , The in-pipe air cross-sectional area distribution at each axial position of the pipe 1 is calculated.

The respective data processes (1) to (4) described above will be described in detail below. It should be noted that in the description, the principle diagrams shown in FIGS. 2 and 3 are referred to.

FIG. 2 is a schematic view showing the approximation of the inner diameter of an arbitrary tube. In the figure, A (x) indicates the cross-sectional area at the position of the distance x in the pipe, and in reality, the cross-sectional area A (x)
Is continuously changing, but for convenience of calculation, A
FIG. 3 is an approximation of the shape of (x) with a connection of a slightly elongated right circular cylinder having a length Δ.

When expressed as shown in FIG. 3, the ith cross-sectional area A (i) is expressed by the reflection coefficient k _i in the recurrence formula as follows.

[0015]

[Equation 5]

Therefore, if only the value of A _p or A ₀ at the end of the tube is known, the cross-sectional area A _i (i = 0, 1, 2, ... P at the i-th position is obtained by calculating the reflection coefficient k _i . −
1) can be obtained. The cross-sectional area A ₀ or A _{p at} the end should be known in advance by actual measurement. Here, p is the number of divisions in the tube axis direction by the elongated cylinder.

In this embodiment, this idea is applied to a gas conduit which is an object to be measured, and FIGS. 4 to 6 show an image of a measurement system when applied to an actual pipe, an image of calculation results, An example of the waveform x (t) obtained by the receiver is shown.

In FIG. 6, when the sample values {x _n }, n = 0, ..., N-1 of the waveform x (t) are given, the autocorrelation coefficient v _i is defined as follows.

[0019]

[Equation 6]

Further, the linear prediction coefficients are α _i , i = 1, 2,
, N, the sample value x _n is expressed as follows.

[0021]

[Equation 7]

With the above definition, the linear prediction coefficient α _i is given by the solution of the following equation.

[0023]

[Equation 8]

At this time, the partial correlation coefficient k _i ′ is incidentally calculated when the linear prediction coefficient α _i is obtained (see the flowchart described later).

By considering the partial correlation coefficient k _i ′ as the reflection coefficient k _i and substituting it in the recurrence formula, the area A _{i of the} inner diameter of the pipe is successively obtained from the sample value of the waveform x (t). .

Next, a specific algorithm executed inside the data processor 7 will be described with reference to the flowchart shown in FIG.

First, when the sample value x _n is given, the autocorrelation coefficient v _i is calculated (step 20) and the initial value is set (step 21). Next, n is set to "0" (step 22), k _{n + 1} and u _{n + 1} are calculated (step 23), and then the linear prediction coefficient α _i is calculated (step 2).
4), it is determined whether or not n has become p-1 (step 25). If yes, the process returns to the start of data processing and no
If so, w _{n + 1} is calculated (step 26), n is incremented by 1 (step 27), and the process returns to step 23.
Then, the partial correlation coefficient k _i ′ is obtained by repeatedly executing the processing of steps 23 to 27. The partial correlation coefficient k _i ′ is regarded as the reflection coefficient k _i, and the reflection coefficient k _i
By calculating _i and A ₀ or A _p while applying it to the recurrence formula, the empty cross-sectional area A _{i in the} pipe is sequentially obtained in the axial direction.

The pipe to which the present invention is applied is a gas pipe in the above embodiment, but the pipe to be measured is not limited to this, and electric pipes and fluid pipes may be used if both ends are open. The pipe may be used for any purpose such as.

The pipe need not be a straight pipe, but may be a curved pipe or a meandering pipe.

The sound wave of the present invention can use not only white noise but also an impulse sound source, but it is preferable that the energy density distribution is substantially constant in the frequency domain.

[0031]

As is apparent from the above description,
According to the in-pipe condition inspection method using the sound wave of the present invention, it is possible to quantitatively estimate the in-pipe air cross-sectional area corresponding to the pipe axis direction, and therefore, it is not limited to the measurement of the in-pipe air cross-sectional area, and the joint, It is possible to quantitatively inspect the change status of the internal cross-sectional area of the pipe, such as the detection of the position of foreign matter and dents, while the pipe is buried.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an apparatus used in an embodiment of the present invention.

FIG. 2 is a principle diagram for explaining calculation of a hollow area in a pipe in the same embodiment.

FIG. 3 is a principle diagram for explaining calculation of an in-tube air cross-sectional area in the example.

FIG. 4 is an explanatory diagram showing an image of a measurement system in the example.

FIG. 5 is an explanatory diagram showing an image of a calculation result in the example.

FIG. 6 is an explanatory diagram showing an example of waveforms obtained by the receiver in the embodiment.

FIG. 7 is a flowchart showing data processing of the same example.

[Explanation of symbols]

 1 tube 2 speaker 3 signal line 4 sound generator 5 receiver 6 signal line 7 data processor 8 foreign matter

Claims (2)

[Claims] 1. A predetermined sound wave signal is input from one end of a pipe whose both ends are open, the sound wave signal is received at the other end, and an opening cross-sectional area A of either one of the ends is measured. , the autocorrelation coefficients of the received acoustic signal different from the samples x _i values sampled from a time v _i look, the autocorrelation coefficients v partial correlation coefficients using the linear prediction coefficients alpha _i based on the _i k _i ′ Is determined, and the partial correlation coefficient k _i ′ is regarded as a reflection coefficient k _i related to the sound wave in the tube, and a graduation that is established between the reflection coefficient k _i and the measured value A of the opening cross-sectional area is calculated. An in-pipe condition inspection method using a sound wave, characterized in that the in-pipe air cross-sectional area at each axial position of the pipe is obtained based on a chemical formula. 2. The autocorrelation coefficient v _i is (Where N is the number of samples from the received waveform), and the linear prediction coefficient is α _i (i = 1, 2, ...,
n), the sample value x _n is The linear prediction coefficient α _i is expressed by The partial correlation coefficient k _i ′ is calculated in the process of obtaining α _i, and the recurrence formula is (Here, p is the number of divisions in the tube axis direction by the elongated cylinder.) The in-pipe condition inspection method according to claim 1, wherein