JPS58156854A - Detector for acoustic signal due to cracking - Google Patents

Abstract

PURPOSE:To detect an acoustic signal due to cracking generated from an object to be detected discriminately from noise easily and accurately by measuring the two of the rise period, holding period and fall time of the isolated wave where the electrically converted signal of said acoustic signal presents. CONSTITUTION:A sensor 21 is held in contact with an object to be examined, not shown in the figure, and the acoustic signal due to cracking generated from said object is converted to an electric signal which is drawn out. When the isolated wave which presents in this electrically converted signal is on the rise (rise period), that is, when the leading edge of the isolated wave is under inputting, the current output of a peak holding circuit 31 is larger than the output of the peak holding circuit 31 of one clock before, and the output of a comparator 32 goes to a high level. However, if the isolated wave is on the fall (fall period), the output of the circuit 31 of one clock before attains the value larger than the current output and the output of a comparator 33 goes to a high level. In the period except either of these two periods, the outputs of the comparators 32, 33 are the low level. The acoustic signal due to cracking is detected discriminately from noise by measuring these periods.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crack acoustic detection device that detects crack sounds generated when a crack occurs in an object to be detected or when a crack existing in the object propagates.

By detecting and analyzing the crack acoustic signal, it is extremely convenient to know when a crack has occurred in the object to be detected, or how the crack has propagated until then. However, in detecting the crack sound signal No. 41, various noises may be mixed in with the solitary wave of crack sound No. 41 depending on the setting location of the sensor, making it difficult to accurately detect the solitary wave of the crack sound signal.

In other words, the crack acoustic signal is an attenuated solitary wave, as shown as waveform 11 in Figure 1A, and in order to remove noise, a portion larger than the general threshold value, that is, the noise level, must be removed. It is also practiced to take out large parts. However, as shown in FIG. 1A, for example, if electrical pulse noise 12 is mixed in, the threshold value will be exceeded, and the noise cannot be removed by the threshold value alone.

For example, when the object to be detected is a pressure vessel, its outer surface becomes rusty and the rust peels off, producing a pulsed acoustic noise as shown at number 13 in Figure 1A. This noise 13 exceeds the threshold value.
It becomes impossible to distinguish between the crack acoustic signal 11 and the crack acoustic signal 11.

Therefore, conventionally, in order to distinguish between such pulse-like noise and the crack acoustic signal, the width of the solitary wave of the crack acoustic signal is measured, and if the width exceeds a predetermined value, that is, the bt gas pulse 1
It has been proposed to detect pulsed sonic noise 13 generated when peeling of rust or rust on a width plate as a crack acoustic signal. However, there are various types of acoustic noise. For example, the noise generated when solid matter is mixed into the fluid supplied to a container and the solid matter collides with the container is as shown in Figure 1B. Long duration range.

In addition, when a pipe connected to a container is held by a belt, the noise generated when the belt and pipe rub against each other due to expansion, contraction, etc. also lasts for a long time, as shown in Figure 1C. It was not possible to distinguish between the solitary wave 11 and the crack acoustic signal.

In order to distinguish between noise and crack acoustic signals, we magnetically record the waveform of the electrically converted output of the detected crack acoustic signal, reproduce it and observe the waveform as a still image, and determine whether it is a crack acoustic signal or noise. It is also possible to make a distinction. However, for example, in a case where several hundred deer solitary waves 11 are generated in 10 minutes, it is necessary to check whether each solitary wave 11 is a correct crack acoustic signal or noise. Distinguishing by observing waveforms takes a very long time and is not practical.

SUMMARY OF THE INVENTION An object of the present invention is to provide a crack Jinq1 signal detection device that can easily and accurately detect a crack acoustic signal by distinguishing it from noise.

According to the present invention, at least two of the rise time, retention time, and fall time of each solitary wave present in the crack acoustic signal generated from the detected object are measured, and The maximum amplitude value of the isolated waveform is measured. By doing this, it is determined whether the rise time, retention time, and fall time of the solitary waveform are within the predetermined ranges, which are the typical values of the attenuated solitary wave of the crack acoustic signal. For example, as shown in Figure 2, the sensor 21 detects the detected object ( A crack acoustic signal generated from the detected object (not shown) is converted into an electrical signal and taken out. The sensor 21 is, for example, a PZ
It is composed of a piezoelectric element such as T. This sensor 21
The electrical conversion output is amplified by an amplifier 22, and only the required frequency band components of the output are extracted by a wave oven 23, and further amplified by an amplifier 24 as required.

The output of this amplifier 24 is detected by an envelope detector 25,
The envelope detection output is compared with a reference value, that is, a certain threshold value, in a comparator 26, and an output is generated from the comparator 26 in a portion exceeding the threshold value. The output of this comparator 26 is given as a gate signal to a gate circuit 27, and a clock is given to the gate circuit 27 from a terminal 28.

The output of the amplifier 24 is also supplied to a full-wave rectifier circuit 29, and the output of the full-wave rectifier circuit 29 is supplied to a peak holding circuit 31. The peak holding circuit 31 is supplied with a clock that has passed through the gate circuit 27, and its holding output is reset every time this clock passes. The output of the peak holding circuit 31 is applied to the non-inverting input side of the comparator 32, the inverting input side of the comparator 330, and further to the buffer circuit 34. Buffer El;! The output of the l path 34 is supplied through a delay circuit 35 to an inverting input of a comparator 32 and a non-inverting input of a comparator 33. The delay time of the delay circuit 35, for example, coincides with the clock cycle of the terminal 28, and therefore, in the comparators 32 and 33, the output of the peak holding circuit 31 one clock ago and the current peak holding (low) ) is compared with the output of path 31.

Therefore, when the input solitary wave is rising, that is, when the leading edge of the solitary wave is being input, the current output of the peak holding circuit 31 is larger than the output of the peak holding circuit 31 one clock ago. , the output of the comparator 32 becomes high level. However, when the solitary wave is falling, the output of the peak holding circuit 31 one clock ago is larger than the current output, and the output of the comparator 33 becomes high level.

During the rising period (rising period) of the isolated waveform, the output of the comparator 32 is at a high level, and during the falling period (falling period) of the isolated wave, the output of the comparator 33 is at the sieve level.
If none of these periods, comparator 32.33
Each output is at a low level.

Therefore, during the holding time during which the peak value is held between the rising period and the falling period of the solitary wave, both the outputs of the comparators 32 and 33 are at a low level, which means that the outputs of the comparators 32 and 33 are By inverting it with inverters 36 and 37 and supplying it to the AND circuit 38, the holding period can be adjusted to the AND circuit 38.
The output is detected at daytime level.

The outputs of the comparator 32, AND circuit 38, and comparator 33 are supplied to gates 41, 42, and 43, respectively. The output clock of the gate circuit 27 is applied to these gates 41, 42, and 43. The clocks passing through gates 41, 42, 43 are counted by counters 44, 45, 46, respectively.

Further, the count values of the counters 44, 45, and 46 are respectively given to the printer 47 as a signal to be recorded. Further, the output of the peak holding circuit 31 is converted into a digital signal by the FiAD converter 48, and this is also input to the printer 47 as a signal to be recorded.

In order to issue a recording command to the printer 47, the outputs of the comparator 32, ANDLO1 path 38, and comparator 33 are input to an OR circuit 49 through an inverter, and the output of the OR circuit 49 is given to the printer 47 as a print command. , and the command is sent to the counter 44 which is slightly delayed by the delay circuit 51.
, 45, 46 as a reset signal.

For example, when a solitary wave is input from the sensor 21 as shown in FIG. 3A, it is detected by the envelope detection circuit 25, and the detection output is higher than the threshold value Es, and the period when it is large is 1h as shown in FIG. 3B. As shown in FIG. 2, the output of the comparator 26 becomes a high level trap and the gate [circuit 27 is opened. Therefore, the peak holding circuit 31 starts operating, and as a result, the voltage of the comparator 32 becomes high level as shown in FIG. During the holding period Tb0 in which the same value is held, the ANDL-path 3
The output of No. 8 is at the cylinder level as shown in Group 3 (Figure 1). When the output of the comparator 32 becomes low level, a print command is generated from the OR circuit 49 and the contents of the count of the counter 44.degree. 45.46 are printed on the printer 47. In this case, since only the cage 41 is opened, only the counter 44 counts, and the counted value corresponds to the rising period Ta.

Similarly, when the holding period Tb ends, a print command is generated from the OR circuit 49 at the falling edge of the hold period Tb, and in this case, only the counter 45 counts, and this counted value corresponds to the period Ta and is recorded.

When the holding period Tb ends and the solitary wave falls, the output of the comparator 33 becomes a high level as shown in FIG. 3E, and the gate 43 opens and the counter 46 counts the clocks. When this falling period Tc ends, a print command is issued and the count value of the counter 46 corresponding to this period is printed. Resetting the counter 44°45.46 is
A print command is generated and the count contents of the counter are sent to the printer 47.
This is done until the next clock is input. Note that the comparators 26, 32, 33, etc. are desirably provided with hysteresis characteristics because the level of the input electrical signal fluctuates frequently. The frequency of each issue of crack sound is 250+(z
The period is approximately 4 microseconds, and the terminal 2
The period of the clock supplied to 8 is 50 to 100 microseconds.

The attenuated solitary wave of crack sound 41I@ generally has a rising period Ta of 50 to 500 microseconds, a holding period Tb of 0 to 200 microseconds, and a falling period Tc of about 500 to 4000 microseconds. Therefore, by looking at the results recorded on the printer 47, those within these ranges are determined to be correct crack acoustic signal solitary waves.

On the other hand, the rise period Ta in the noise shown in FIG. 1B
is 2000 microseconds or more, the holding period Tb is 4 microseconds or more, and the falling period Tc is 4000 microseconds or more. In other words, since the rising period Ta is much longer than the solitary wave of each crack sound, it can be easily distinguished from the solitary wave of crack sound (N).The falling period is also longer than that of each crack sound. The noise shown in FIG.
b is too microseconds or more, falling period Tc is 1000
More than a microsecond. Therefore, in this case, the rising period Ta is longer than that of each crack sound, and in particular, the holding period Tb is much longer than that of each crack sound, thereby making it possible to distinguish this noise from the crack sound signal.

Distinguishing noise based on the rising period, holding period, and falling period is not only carried out by looking at the recording by the printer 47, but also can be done automatically. For this purpose, processing may be performed by, for example, a microcomputer. As a process, OR circuit 49
When an output print command is generated, the microcomputer is notified as an interrupt as shown in step S+ in FIG. Load. After that, in step Ss, the comparator 2
Check the output of step 6 to see if the envelope of the input signal at that time is above the threshold. If it is above the threshold, return to step Sl, wait for the next interrupt, and wait for the next interrupt. In the case of the lower case, the three counts (il) taken so far in S step S4 are different from the preset value, i.e., 50 to 500 of the rise period Ta as crack sound 1M.
Compare whether microseconds, retention period Tb00 to 200 microseconds, and Shimotsuguma Tc 500 to 4000 microseconds are within the range of values, respectively, and in step SL+, the relative softness in step S4 is all within the range. If there is one, it is considered to be a crack sound signal, and if there is a match this year, it is judged to be noise other than a crack sound signal. The maximum amplitude of the data determined to be a crack acoustic signal, a value obtained by subtracting the output of the ADf unit 48 in FIG. 2, can be used to analyze the crack acoustic signal.

In the above, the noise and the crack acoustic signal were distinguished based on whether or not each of the rising period, holding period, and falling period of the solitary wave was within a predetermined range. For example, the distinction may be made by determining whether the rising period and the holding period are within a predetermined value.

As described above, according to the present invention, it is possible to correctly detect a crack acoustic signal by distinguishing it from noise, and it is also possible to easily distinguish the crack acoustic signal by printing it on a printer, and of course automatically distinguish it by a microcomputer. By doing this, even if a large number of noises are mixed into the solitary waves of a large number of crack acoustic signals, it can be distinguished and processed in a short time. It becomes possible to analyze the propagation state correctly and in a short time.

[Brief explanation of drawings]

FIG. 1 is a diagram showing various waveforms of crack acoustic signals and noise, Stripe 2 is a block diagram showing an example of a crack acoustic signal detection device according to the present invention, and FIG. 3 is a waveform diagram for explaining its operation. FIG. 4 is a flowchart illustrating an example of a process for automatically distinguishing crack acoustic signals. 21: Sensor, 23: P wave detector, 25: Envelope detector, 2
6, 32, 33: Comparator, 28: Clock terminal, 29:
Full wave flow circuit, 31: Peak holding circuit, 34: Buffer circuit, 44, 45. 46 two digits, 47: printer, 48: AD converter. Patent applicant: Asahi Kasei Koka Co., Ltd. Agent: Hiao Kusano 3 Figure E'. Appearance>1. figure

Claims (1)

[Claims] (1) Means for measuring at least two of the rising period, holding period, and falling period of an isolated waveform in an electrical signal obtained by converting a crack acoustic signal generated from an object to be detected, and the maximum amplitude of the isolated waveform of the electrical signal. A crack acoustic signal detection device comprising means for detecting.