JPS5825225B2 - Sound wave propagation time measurement method and position locating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the propagation time of a sound wave and a method for locating the position of a sound wave source.

In this specification, "sound waves" include not only ultrasonic waves but also low frequency waves and audio frequency waves.

When a material breaks, elastic waves are generated when strain energy is released as a result of crack propagation or plastic deformation that occurs over a very short period of time.

This elastic wave is an acoustic emission
(abbreviated as AE) waves are ultrasonic waves.

By continuously monitoring AE waves, it is possible to predict the location of destruction of tanks, etc.

Conventionally, the AE wave is received and converted into an electrical signal, and this electrical signal is level-discriminated using a predetermined threshold value to measure the time from the generation of the AE wave to the threshold value. In addition, the AE wave generation position is located by detecting the time difference between level discrimination times at a plurality of reception points.

In such prior art, the level discrimination time varies depending on the received sound wave level, reception sensitivity, threshold value, etc., and therefore the measurement accuracy is very poor.

The main object of the present invention is to provide a method for measuring the propagation time of a sound wave and a method for locating the position of a sound wave generation source with improved measurement accuracy.

FIG. 1 is an overall system diagram of an embodiment of the present invention, showing a configuration for measuring the propagation time of an ultrasonic wave through a thin iron plate 1, for example.

An ultrasonic generator 2 provided on a thin iron plate 1 generates ultrasonic waves using pulses from a pulse generator 3 that generates sudden pulses.

A microphone 4 as a sound wave receiver is provided on the thin iron plate 1 at a distance from the ultrasonic generator 2.

The electrical signal output waveform from the microphone 4 is as shown in FIG. 2, and it is assumed that an ultrasonic wave is generated from the ultrasonic generator 2 at time O.

In FIG. 2, waveform 5 is noise, and waveform 6 is obtained when receiving ultrasonic waves.

As is clear from the waveform 6, even if the ultrasonic wave generator 2 generates an impulse-like ultrasonic wave, the received waveform becomes wider in time with the propagation distance.

The output from the microphone 4 is subjected to envelope detection by an envelope detection circuit 7.

The envelope detection output is given to a peak detection circuit 8 and a level discrimination circuit 9.

This envelope detection output waveform is shown by a broken line in FIG.

The peak detection circuit 8 detects the peak value vrry'2 of the envelope.

The level discrimination circuit 9 discriminates the level of the envelope using a preset threshold value S smaller than the peak value.

Outputs from the peak detection circuit 8, level discrimination circuit 9, and pulse oscillator 3 are provided to an arithmetic circuit 10.

The inventor of the present invention proposed that the longitudinal wave (
Considering that the velocity V (5000rrV/s) arrives as point 11, and the transverse wave (its velocity V 3000rrV/s) arrives at the peak detection point 12 after time t3, this longitudinal wave arrives. The point 11 was considered to be the point where the straight line 14 connecting the peak detection point 12 and the level discrimination point 13 intersects the zero level reference line 15.

Therefore, the longitudinal wave propagation time t1 is calculated by the arithmetic circuit 10 according to the actual measurement time t2 that is level-discriminated after the ultrasonic wave is generated.
It is calculated from the correction value Δt according to the following equation.

S Δ1=-(13-11) 7m 2sL 1 1 = -(---) ...... (1)vm V
3 Vl t1 = t2 - Δt (2) Therefore, L indicates the distance between the ultrasonic generator 2 and the micrometer/4.

The time t1 is visually displayed on the display 16.

In this way, the propagation time t1 of the longitudinal wave can be accurately calculated without depending on the magnitude of the waveform of the received ultrasonic wave and the threshold value S.

According to the experiment of inventor J of the present invention, as mentioned above, the first arriving wave is a longitudinal wave with a velocity of 5,000 rIN/s, and the arriving wave that reaches the peak value is a longitudinal wave with a velocity of V3: 3,000 rIN/s.
's, then the first equation and the second equation
It was confirmed that the calculated results of the formula were in good agreement with the actual results.

As another embodiment of the invention, speed V1. V3 may be changed to another value, and the arrival point 11 of the first arriving wave may be calculated based on a curve other than the straight line approaching the peak point 12 and the level discrimination point 13.

In the above embodiment, the peak value of the envelope waveform having a single peak was detected by the peak detection circuit 8, but according to the concept of the present invention, in the case of an envelope waveform having multiple peaks, In this case, it is preferable to detect the maximum peak value from the viewpoint of improving accuracy, or alternatively, it may be the value of the first peak among the plurality of peaks or the local maximum value of other peaks.

FIG. 4 is an overall system diagram of another embodiment of the present invention, in which one-dimensional positional locating of all AE wave sources 18 is performed.

A pair of microphones 19, 20 are arranged facing each other.

The distance between both microphones 19°20 is 2a, and AE
It is assumed that the wave source 18ν is shifted from the central origin 21 by a distance
Arrival time when level discrimination is performed using the aforementioned threshold value S to 9, ot2A, and aforementioned threshold value s5 to the microphone 20.
If the arrival time when the level is discriminated is t2C, then the following equation holds true.

Vs x= (t2C-t2A) ...... (3
) Distance L1.) from the microphone 19.20 to the total AE wave generation source 18. L2 is Ll ``”a x Vs = a (t 2 Ct 2 A) ”” (
4) Vs s I, 2== a + (t2 c t2 A
) "" (5) From the above-mentioned 4th and 5th equations and the 1st equation, the correction value for the arrival times t2A and t2C is ΔtA.

If Δtc and the peak value are vmV2 * vmC/2, then 2s 1 1 Vs ΔtA=-(--)(a -(t2C- vrnA Vs Vt 2 t2A)) ...... (6) 2s 1 1 Vs Δtc= −−(−−)(a+−(t2C−vrnCV
a Vl 2 t2A)) (7) Microphone 1 after AE wave generation until receiving the first arriving wave
The times t1A and t1C corresponding to 9 and 20 are calculated from the second equation as follows: tIA = t2A - ΔtA - 1 - (8) tIC = t2C - ΔtC...Song (9) Up to this point, the speed of sound obtained by the ■s■ (according to the inventor's experiments, in the case of a thin iron plate, it is about 4500 to 5000 m/s), then the orientation value X1 to be found is x, = M! −
L(tlC-tlA) =-(L.

The sound velocity Vsl obtained by single-statement correction is the value of the sound velocity at the point 11 where the straight line 14 connecting the peak detection point 12 and the level discrimination point 13 intersects the reference line 15 in Fig. 3, which was obtained by experiment. It is a value.

Substituting the 8th and 9th equations into the 10th equation, we get
”x
1=Ha1(t2C-t2A)-"(t2C-2 111 t2A)・[Vs-5・(-111)(--Vs V
lvrnC + '-)]-Vs8. a, 5 (''-single) 'vmA
Vs V11 (□-・-) . . . αυ vmCvmA The speeds Vs and Vs1 are experimentally selected to values such that Equation 11 matches the actual value.

Referring to FIG. 4, the outputs from the microphones 19 and 20 are transmitted to the envelope detection circuit 2 in the same manner as in the embodiment shown in FIG.
2.23 to the peak detection circuit 24.25 to obtain the peak value VmV2. wmC/2 is detected.

Outputs from the envelope detection circuits 22.23 are given to level discrimination circuits 26.27.

The level discrimination circuits 26 and 27 are connected to the microphone 19°20
The two envelope waveforms corresponding to the above are level-discriminated using the same threshold value S.

Time difference detection circuit: 281, level discrimination circuit 26.27
The difference in level discrimination time (t2C
−t2A).

The arithmetic circuit 29 receives the outputs from the peak detection circuit 24, 25 and the time difference detection circuit 28, performs the calculation of equation 11, and causes the display 30 to display the standard constant value X1.

As yet another embodiment of the present invention, in the case of two-dimensional positioning, in addition to the embodiment of FIG. What is necessary is to arrange the elements located on the diagonal line to form a pair, and such a modification is easy for those skilled in the art.

There may be five or more microphones.

Two-dimensional position localization can still be achieved with a minimum of three microphones.

As described above, according to the present invention, the maximum value of the received waveform of a sound wave, the threshold value for level discrimination, the propagation velocity of the first arriving wave, and the propagation velocity of the arriving wave forming the maximum value are used. Then, the propagation time from the sound wave generation to the reception of the first arriving wave is calculated by correcting the time that changes depending on the size of the received waveform and the threshold value from the time the sound wave is generated to the level discrimination time. As a result, accurate propagation time can be measured regardless of the size of the received waveform or the threshold value.

In addition, the time difference between the level discrimination times of electrical signals from multiple sound wave receivers is corrected to the time difference between each sound wave receiver of the first arriving wave, which does not depend on the magnitude of the received waveform or the threshold value. Therefore, the accuracy of positioning is improved.

[Brief explanation of drawings]

FIG. 1 is an overall system diagram of an embodiment of the present invention, FIG. 2 is an output waveform diagram from the microphone 4, FIG. 3 is an output waveform diagram from the envelope detection circuit 7, and FIG. 4 is a diagram of the output waveform from the envelope detection circuit 7. FIG. 7 is an overall system diagram of another embodiment. 2...Ultrasonic source, 4,19.20...
...Microphone, 3...Pulse transmitter, 7,
22.23... Envelope detection circuit, 8, 24.2
5...Peak detection circuit, 9,26.27...
...Level discrimination circuit, 10.29...Arithmetic circuit, 16,30...Display unit, 28...Time difference detection circuit, S...Threshold value.

Claims (1)

[Claims] 1. Receive the generated sound waves and convert them into electrical signals, and determine the maximum value of the amplitude distribution, the speed of the first arriving wave of the sound wave, and the speed of the arriving wave forming the maximum value. A method for measuring the propagation time of a sound path, characterized in that the propagation time of the first arriving wave of the received sound wave is calculated by correcting the time it takes for the sound wave to reach a threshold after it is generated, based on . 2. Sound waves are simultaneously received by sound wave receivers installed at multiple locations with known mutual distances and converted into electrical signals, and the maximum value of the amplitude distribution of the electrical signal obtained by the electrical signals from each sound wave receiver is determined. , a threshold value smaller than its local maximum, the speed of the first arriving wave of the sound wave, and the speed of the arriving wave forming the local maximum, A position locating method characterized by locating a sound wave generation position by correcting a mutual time difference in reaching a threshold value.