JPH0481633A - Leak detector - Google Patents

Abstract

PURPOSE:To detect a leak with high sensitivity by calculating the difference between a detected acoustic signal and the representative signal of environmental noise at every frequency and judging the presence of a leak from the magnitude of the effective value of the difference signal. CONSTITUTION:The frequency distribution of the detected acoustic signal of a microphone 1 is calculated in a frequency analyzing part 31 and the difference between the frequency distribution of detected sound and the representative frequency distribution of environmental noise at the time of normal operation is taken by a spectrum subtracting part 32 and the effective value of the frequency distribution of the difference between the representative value of the environmental noise and the detected sound is operated by an effective value operation part 33. A spectrum cumulation part 34 measures the average frequency distribution of the environmental noise at the time of normal operation and cumulation is stopped by detecting the generation of a leak. Since the signal of frequency enhanced in leak detection sensitivity is automatically detected to make it possible to detect a leak, it becomes unnecessary to alter the setting of the frequency of a filter at each time when the noise generating state or acoustic propagation characteristic in a plant is changed and the maintenance work of a leak detector can be reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a signal processing method for reducing noise mixed in a detection signal and noise in the signal to relatively increase a signal component. The present invention relates to a leak detector suitable for detecting sound accompanying leaks with high sensitivity in an environment with large background noise.

[Conventional technology]

As a conventional leakage detection means, a method of detecting sound accompanying leakage has been proposed. In particular, the method of detecting sound propagating through space has advantages such as relatively no restrictions on the sensor mounting position and fast response. For this reason,
An acoustic leak detector has been realized that determines that a leak has occurred when the detected sound exceeds a certain set value. In order to reduce noise in leakage detection, methods have also been implemented that selectively monitor frequencies at which leakage sounds are relatively loud. Such devices include Japanese Patent Application Laid-Open No. 62-43535, Sensor Technology, vol. 7. Nnl 1 (October 1987
There is a leak detector described on pages 18 to 20 of ``Month''.

[Problem to be solved by the invention]

The above conventional technology does not sufficiently consider the frequency distribution at the detection point of leakage sound due to acoustic propagation attenuation and the local noise near the detection point. There was a possibility that the sensitivity would decrease.

For example, the frequency components of leaked sound are distributed over a relatively wide range, but during propagation, the high frequency range is particularly attenuated.

Furthermore, in plants, there are equipment, piping, and other structures between the leak point and the detection point, so reflected waves are often detected in addition to direct waves. Environmental noise is usually dominated by low-frequency sounds emitted from high-power machines such as compressors and pumps, but locally there may also be sounds with relatively high-frequency components emitted from low-power sound sources. Furthermore, the acoustic propagation characteristics change due to movement of the device between the leakage point and the acoustic detection point. Environmental noise also changes due to periodic inspections that include the disassembly of major equipment. In other words, in the conventional leakage detection method using a bandpass filter, the performance as designed could not be ensured unless the above-mentioned factors were always taken into account and the leakage detector was maintained.

Therefore, it is an object of the present invention to maintain noise control even when changes occur in the noise generation situation within the plant or changes in the propagation characteristics up to the leak detection point.
Accordingly, it is an object of the present invention to provide a leakage detection means that captures signals in a frequency range that is sensitive to leakage detection.

[Means to solve the problem]

In order to achieve the above object, the present invention calculates the difference between a detected acoustic signal and a representative signal of environmental noise for each frequency, and determines whether there is a leakage based on the magnitude of the effective value of the difference signal.

The representative signal of environmental noise described below is a signal having an average frequency distribution of environmental noise in a state where no leakage occurs.

[Effect]

The effective value of an AC signal is a representative value representing the magnitude of its amplitude, and is determined as the square root of the sum of squares of the amplitudes of each frequency component. Therefore, the magnitude of the effective value is dominated by the component with a large amplitude among the frequency components of the signal.

When no leakage occurs, the detected sound signal is almost equal to the environmental noise signal, so the effective value of the difference signal from the environmental noise signal is a value that does not depend on any particular frequency component. On the other hand, when leakage occurs, the frequency components of the difference signal are only those newly increased due to the leakage, and the effective value is dominated by the frequency component with a large amplitude among the newly increased components.

In other words, take the difference between the detection signal and the representative signal of the environmental noise,
By taking the effective value of the difference signal, the same effect as the conventional method of selecting and monitoring the optimum frequency using a bandpass filter can be obtained. By timely measuring representative values of environmental noise, the optimum frequency can be automatically set.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is an example in which the signal processing device of the present invention is applied to a reactor coolant leak detector. When high-temperature, high-pressure coolant passing through the coolant pipe 101 spouts out from the leak point 102, the leakage sound accompanying the jet is detected by the microphone 1, the detected signal is amplified by the amplifier 2, and the spectrum subtractor 3 performs steady operation. Outputs the effective value of the signal obtained by removing the environmental noise in the detected sound from the detected sound. In the abnormality determiner 4, the spectrum subtractor 3
If the effective value output exceeds the set value, it is determined to be abnormal, and
Generates an abnormal signal. In this way, by subtracting the representative value of environmental noise during normal operation from the detected sound, it is possible to detect the occurrence of leakage sound that is smaller than the environmental noise.

Next, details of the configuration of the spectrum subtractor 3, which is the main element of the present invention, will be explained. The spectrum subtractor 3 is
As shown in FIG. 1, the frequency analysis section 31. Spectral subtraction section 32. It consists of an effective value calculation section 33 and a spectrum accumulation section 34. The frequency distribution of the acoustic signal detected by the microphone 1 is determined by the frequency analysis section 31. The spectrum subtraction unit 33 has a function of calculating the difference between the frequency distribution of the detected sound and the typical frequency distribution of environmental noise during normal operation. The effective value calculation section 33 has a function of calculating the effective value of the frequency distribution of the difference between the representative value of the environmental noise obtained by the spectrum calculation section 32 and the detected sound. The spectrum accumulator 34 has a function of measuring the average frequency distribution of environmental noise during normal operation, and calculates the environmental noise frequency for each operating condition, such as cumulative stoppage due to detection of leakage, whether pumps, etc. are in operation, etc. It is now possible to accumulate distributions and manually control the execution and stopping of accumulation.

Next, the operation will be explained with reference to FIG. Figure 2 (a
) is the frequency distribution of detected sounds during normal plant operation. Further, FIG. 2(b) shows the frequency distribution of the detected sound when a leak occurs, and it can be seen that the amplitude is partially increased in the high frequency region compared to the environmental noise. FIG. 2(c) shows the difference in frequency distribution between the detected sounds (a) and (b) and the representative value of the environmental noise. In this case, when monitoring with the effective value of the detected sound, the effective value is dominated by the amplitude of low frequencies, so there is no big difference between the effective values of the detected sound in (a) and (b), and the normal sound It is hidden by pressure fluctuations.

However, as can be seen from the frequency distribution of the difference signal in (c), in the case of the solid line where no leakage occurs, there is no main component that dominates the effective value. In other words, by subtracting the environmental noise from the detected sound, the environmental noise characteristics specific to the detection point are canceled.

On the other hand, if leakage occurs, the difference signal will have a frequency distribution of only components that exceed the environmental noise due to leakage, as shown by the dotted line in (c). Since the effective value in the case of the dotted line in (c) is dominated by its maximum amplitude, the same sensitivity as in the case where the optimal frequency of the bandpass filter is selected is ultimately obtained.

To realize the spectrum subtractor 3, a DSP (digital signal processor) is used in the frequency analysis section 31 due to the necessity of real-time processing.

It is also possible to employ other frequency analysis hardware, such as a system using a CCD (charge coupled device).

The spectral subtraction section only needs to be able to calculate the difference between two frequency distributions, and although a DSP is used here, it is also possible to use other general-purpose processors. Although the effective value calculator obtains the effective value from the integral value of the frequency distribution of the difference, it is also possible to apply other calculation methods such as a calculation method based on autocorrelation. Although the spectrum accumulator 34 performs digital processing using DSP to calculate the average value of the environmental noise, it can also be realized by a combination of other digital arithmetic elements.

The unique effects of this embodiment are as follows: (1) In determining the measurement points of the leak detector, there is no need to measure noise or evaluate the leak sound for each leak position in detail, which reduces the cost of the leak detector. reduction is possible.

(2) Measure the frequency distribution of environmental noise for each operating condition,
Since the representative value of the environmental noise under the operating conditions corresponding to the detected sound is subtracted, the sensitivity of leak detection can be improved compared to the case where the environmental noise does not depend on the operating conditions, and the malfunction of the equipment can be reduced. This has the effect of improving equipment performance.

(3) Since there is no need to limit the signal frequency band and noise frequency band, the detection performance will not be greatly affected by changes in environmental noise due to periodic inspections, etc., so the detection performance of the leak detector will be stable over the long term. and be able to maintain it.

〔Effect of the invention〕

According to the present invention, it becomes possible to automatically select and detect signals in a frequency range with high leakage detection sensitivity, so there is no need to change the filter frequency setting every time the noise generation state or acoustic propagation characteristics in the plant changes. Therefore, maintenance work for leak detectors can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a leak detector according to an embodiment of the present invention;
FIG. 2 is a frequency distribution diagram of the detected sound and the difference signal.

Claims (1)

[Claims] 1. In a leak detector equipped with means for detecting sound and means for determining that a leak has occurred when the signal level changes beyond a set value, the leak determination signal is a detected sound signal. A leakage detector characterized in that the frequency distribution is the difference between the noise signal and an environmental noise signal in a normal state where no leakage occurs. 2. The leak detector according to claim 1, which uses a noise signal measured in advance for each operating condition of the plant as the environmental noise during normal operation.