# Research on Leakage Location of Pipeline Based on Module Maximum Denoising
###### Abstract  
Leak detection and location of water supply pipelines is an important area of research, and it is especially important to find the leakage location in time and repair them. In view of the problem, that a large amount of noise is mixed in the detection signal when the pipeline leaks, it will inevitably affect the detection and positioning effect. In this paper, a denoising algorithm based on improved module maximum is proposed. Firstly, a discrete binary wavelet transform is carried out on the noisy signal, and the module maximum point corresponding to the wavelet transform coefficients, on each scale, is obtained. Secondly, different thresholds are used for the module maximum of different scale layers and the wavelet coefficients are reconstructed according to the retained module maximum and their extremums. Thirdly, the alternative projection algorithm is used to effectively suppress the false oscillations in the reconstructed signal, improve the quality of the reconstructed signal, and obtain the noise reduction signal. Finally, according to the theory of the negative pressure wave, the inflection point of the negative pressure wave is identified by the wavelet decomposition method, and the location of leakage point is determined. In order to verify the effectiveness of the proposed algorithm, a leakage simulation experiment system of water supply pipeline is built. The analysis of the results shows that, compared with the wavelet denoising method and the EMD-based method, the method proposed in this paper achieves a better denoising effect, obtains a smoother pressure signal, retains the signal waveform characteristics, and identifies the obvious inflexion point of the negative pressure wave. The minimum relative error of leakage point location is 0.9%, and the maximum relative error is 2.5%. water supply pipeline; leakage location; denoising; module maximum +
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the flow downstream of the leakage point will be significantly smaller than that upstream, so by calculating the change in the flow of the pipeline section, it can be judged whether there is leakage. However, the method cannot locate the pipeline leakage point [5]. The second method is the infrared thermal imaging method. When the water supply pipeline is damaged, the water flow in the pipeline will spread to the soil around the leakage point. As the wet soil heat dissipation speed is faster, the heat contained in the soil around the pipeline leakage point will be significantly different from the heat contained in other soils. However, the infrared thermal imaging method requires relatively high theoretical knowledge by staff, who must master the infrared spectrum analysis technology skillfully, and the cost of the instruments required for detection is also very high. These shortcomings make it difficult for infrared spectrum thermal imaging to be popularized in China [6]. The basic principle of the pressure gradient method is that when the water supply pipeline is operating normally, the pressure in the pipeline usually changes linearly along the pipeline. But when the pipeline leaks and reaches a stable state again over time, the pressure signal at the leakage point of the pipeline will have an obvious change. By comparing the difference of the pressure gradient curve before and after leakage, the extent of pipeline leakage and the location of pipeline leakage point can be determined. This method is usually greatly affected by the accuracy of the instrument and the environment in which the measuring instrument is located. The method of leak location based on the negative pressure wave (NPW) has become one of the research hotspots [7; 8; 9]. When the pipeline leaks, the pressure at the leakage point will drop rapidly, and this pressure drop named the NPW inflection point will propagate to both sides of the leakage point in the form of a negative pressure wave. The leakage can be detected by installing pressure sensors on both sides of the pipeline to obtain changes in the pressure signal in the pipe.