JPH0113534B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crack sound detection device that detects crack sound 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 whether a crack has occurred in the object to be detected or how the crack has propagated until then. However, in detecting a crack acoustic signal, depending on the location where the sensor is set, various types of noise may be mixed together with the solitary wave of the crack acoustic signal, making it difficult to accurately detect the solitary wave of the crack acoustic signal. When envelope detection is performed on (high frequency) signals that occur intermittently or suddenly on the time axis, each signal is converted into a signal having a certain amplitude and time width.
Since each of these events occurs independently and in isolation, they are called solitary waves to distinguish them from so-called continuous signal waves.

That is, the crack acoustic signal has the waveform 11 in FIG. 1A.
This is a damped solitary wave, as shown in FIG. 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 only by the threshold value. 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. In order to exceed the threshold, this noise 13 and the crack acoustic signal 1
It becomes impossible to distinguish between 1 and 1.

Therefore, conventionally, in order to distinguish between such pulse-like noise and crack acoustic signals, the width of the solitary wave of the crack acoustic signal is measured, and if the width is greater than a predetermined value,
In other words, it has been proposed that when the width of the electrical pulse 12 is greater than or equal to the width of the pulsed acoustic noise 13 generated when rust is peeled off, it is detected 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. , its duration range is long.
Furthermore, when a pipe connected to a container is held by a belt, the noise generated by rubbing between the belt and the pipe due to expansion and contraction, etc., has a long duration as shown in Figure 1C. It was not possible to distinguish between these noises and the solitary wave 11 of 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, several 100 in 10 minutes.
In such cases, it is very difficult to distinguish whether each solitary wave 11 is a correct crack acoustic signal or noise by observing the waveform. It takes a long time and is impractical.

An object of the present invention is to provide a crack acoustic 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 existing in the electrical conversion signal of the crack acoustic signal generated from the detected object are measured, and the solitary waveform to measure the maximum amplitude value. By doing this, the rise time, retention time, and
It is determined whether at least two of the fall times are within a predetermined range, that is, a range of typical values of the attenuated solitary wave of the crack acoustic signal to distinguish it as a crack acoustic signal or noise, and In the case of a crack acoustic signal, its peak value is detected in order to know the magnitude of its energy.

For example, as shown in FIG. 2, when the sensor 21 is brought into contact with a detected object (not shown), a crack acoustic signal generated from the detected object is converted into an electrical signal and extracted. The sensor 21 is composed of a piezoelectric element such as PZT. The electrically converted output of this sensor 21 is amplified by an amplifier 22, and only the required frequency band components of the output are extracted by a wave generator 23, and further amplified by an amplifier 24 as required.
The output of this amplifier 24 is detected by an envelope detector 25, and the envelope detection output is compared with a reference value, that is, a certain threshold value, in a comparator 26, and the portion exceeding the threshold value is output from the comparator 26. is caused to occur. The output of the comparator 26 is applied as a gate signal to a gate circuit 27, and a clock is applied 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 the 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 the comparator 3
2, an inverting input of comparator 33, and a buffer circuit 34. The output of the buffer circuit 34 is supplied to the inverting input side of the comparator 32 and the non-inverting input side of the comparator 33 through a delay circuit 35. The delay time of the delay circuit 35 is, for example, almost the same as the clock cycle of the terminal 28, so in the comparators 32 and 33, the output of the peak holding circuit 31 one clock before and the current peak holding circuit The output of No. 31 is compared.

Therefore, when the input solitary wave is rising,
That is, when the leading edge of a 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, and 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. In other words, the output of the comparator 32 is at a high level during the rising period (rising period) of the isolated waveform, and the output of the comparator 32 is at a high level during the falling period (falling period) of the isolated waveform.
The output of the comparators 32 and 33 is at a high level, and when it is not during any of these periods, the outputs of the comparators 32 and 33 are at a low level.

Therefore, the holding time during which the solitary wave maintains almost the peak value between the rising period and the falling period is the comparator 3.
The outputs of comparators 2 and 33 are both at low level, which means that the outputs of comparators 32 and 33 are connected to inverter 3, respectively.
By inverting the signal at 6 and 37 and supplying it to the AND circuit 38, the output of the AND circuit 38 becomes high level and detected during the holding period.

The outputs of the comparator 32, the AND circuit 38, and the 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 an AD converter 48, and this is also input to the printer 47 as a signal to be recorded.

The comparator 3 is used to issue a recording command to the printer 47.
2. Each output of the AND circuit 38 and the comparator 33 is inputted to an OR circuit 49 through an inverter.
The output of the OR circuit 49 is given to the printer 47 as a print command, and the command is sent to the delay circuit 51.
It is given as a reset signal to the counters 44, 45, and 46 which are slightly delayed.

For example, as shown in Figure 3A, a solitary wave is transmitted to sensor 2.
1, the signal is detected by the envelope detection circuit 25, and during a period when the detected output is larger in absolute value than the threshold value ± _E1 , the comparator 2 is detected as shown in FIG. 3B.
6 becomes high level and the gate circuit 27 is opened. Therefore, the peak holding circuit 31 starts operating, and as a result, the rising period of the solitary wave,
In other words, during the rising period Ta, the output of the comparator 32 is at a high level as shown in FIG. The level becomes high as shown in D. 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 counts of the counters 44, 45, 46 are sent to the printer 47.
is printed on. In this case, since only the gate 41 is opened, only the counter 44 counts, and the counted value becomes a value corresponding to the rising period Ta.

Similarly, when the holding period Tb ends, a print command is generated from the OR circuit 49 due to the fall of the holding period Tb, and in this case, only the counter 45 counts, and this counted value corresponds to the period Ta, and this is recorded. Ru. 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. This falling period Tc
When the period ends, a print command is issued and the count value of the counter 46 corresponding to this period is printed.
Resetting the counters 44, 45, 46 is as follows:
A print command is generated, the count contents of the counter are supplied to the printer 47, and the print command is executed until the next clock is input. Note that the comparators 26, 32, 33, etc. have many fluctuations in the level of the input electrical signal, so
It is desirable to have hysteresis characteristics. The frequency of the crack acoustic signal is about 250 KHz, and the period is about 4 microseconds, and the period of the clock supplied to terminal 28 is 50 to 100 microseconds.

The attenuated solitary wave of the crack acoustic signal is generally during the rising period
Ta is 50 to 500 microseconds, retention period Tb is 0 to 200
The falling period Tc is 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, in the noise shown in Figure 1B, the rise period Ta is 2000 microseconds or more, and the holding period Tb is 4
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 the crack acoustic signal, this can be easily distinguished from the crack acoustic signal. The falling period is also longer than that of the crack acoustic signal. The noise shown in Figure 1C is during the rising period.
Ta is 600 microseconds or more, holding period Tb is 1000 microseconds or more, and falling period Tc is 1000 microseconds or more. Therefore, in this case, the rising period Ta is longer than that of the crack acoustic signal, and in particular the holding period Tb is much longer than that of the crack acoustic signal, which makes it possible to distinguish this noise from the crack acoustic signal. .

Distinguishing noise based on the rising period, holding period, and falling period is not only carried out by observing the recording by the printer 47, but also can be done automatically. For this purpose, processing may be performed, for example, by a microcomputer. As for the processing, when an output print command from the OR circuit 49 occurs, it is notified to the microcomputer as an interrupt as shown in step _S1 in FIG. Read the count value in step _S2 . After that, in step _S3 , the output of the comparator 26 is checked to see if the envelope of the input signal at that time is above the threshold value, and if it is above the threshold value, the process returns to step _S1 and the next interrupt is executed. Wait, if below threshold, step S ₄
, the three counts taken so far and the preset values, namely, the rising period Ta of 50 to 500 microseconds, the holding period Tb of 0 to 200 microseconds, and the falling period Tc of the crack acoustic signal.
500 to 4000 microseconds are compared to see if they are within the range of each value, and in step _S5 , if all three values compared in step _S4 are within the range, it is considered a crack acoustic signal, and if there is even one discrepancy. If so, it is determined that the noise is other than a crack acoustic signal. Maximum amplitude of the data determined to be the crack acoustic signal, AD in Figure 2
The value taken from the output of the transducer 48 can be used to analyze the crack acoustic signal.

In the above, the noise and the crack acoustic signal were distinguished by whether or not each of the rising period, holding period, and falling period of the solitary wave was within a predetermined range. The distinction may be made by determining whether the period and the retention 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 from the printer's embossing. By distinguishing between solitary waves of a large number of crack acoustic signals, even if a large number of noises are mixed in, it can be distinguished and processed in a short time. It becomes possible to accurately analyze crack propagation conditions in a short time.

[Brief explanation of drawings]

FIG. 1 is a diagram showing various waveforms of crack acoustic signals and noise, FIG. 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: Transmitter, 25: Envelope detector, 26, 32, 33: Comparator, 28: Clock terminal, 29: Full wave rectifier circuit, 31: Peak holding circuit, 34: Buffer circuit, 44, 45, 46:
Counter, 47: Printer, 48: AD converter.

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 converted from a crack acoustic signal generated from the detected object, and at least two of the rising period, holding period, and falling period. A crack acoustic signal detection device, comprising means for determining whether the two are within a predetermined value, and means for detecting the maximum amplitude of the isolated waveform of the electric signal.