Research On Signal Acquisition System For Leak Detection Of Water Supply Pipelines

In order to reduce water loss and improve the detection efficiency, specific leak detection and location instruments are needed in the water distribution system leakage control engineering. A leak detection and location instrument system is built based on embedded technology and virtual instrument technology; and it incorporates modern sensor technology, signal conditioning technology, and signal processing technology. Due to the flexibility and openness of the water pipeline leak detection instrument system, it can satisfy various practical engineering applications, and its performance is highly improved compared with the traditional ones.The leak signals have low amplitude, wide dynamic range, and frequency contents vary with the pipe materials and the practical settings. Meanwhile, the leak signals are mixed with ambient noises. Confronted with these challenges, a leak signal acquisition system which should have low noise, low power consumption and be adjustable according to the practical settings is analyzed and designed in this dissertation. The MCU based data acquisition system comprises six modules: acceleration sensors embedded with ICs, signal conditioning, data acquisition, data transmission, LCD display, and power management. The signal conditioning parameters can be adjusted relative to the characteristics of leak signals. A band-pass filter is designed to suppress noises. A programmable gain amplifier is adopted to widen the system dynamic range. Low noise resisters and amplifiers are selected to reduce the noises of signal conditioning circuits. Low power consumption design is adopted to meet the demand of in situ operation of water pipeline leak detection.In order to improve leak location accuracy, it is necessary to increase the data length and bits, which leads to a sharp rise of data amount. An error constrained data compression algorithm for sensing signal acquisition is proposed to solve the problem. To accord with the varying characteristics of leak signal, the coefficients of the gradient predictor are dynamically adjusted relative to the correlation coefficients of data segments; the uniform residue quantizer is improved to reduce quantization noise; and the Golomb-Rice coding algorithm is adopted to encode the quantized prediction residual sequence. The upper bounds of compression error and compression rate are determined in terms of the noise level of the system front end. Applications on leak detection and location show that, at a compression rate of 2.63, the additional leak location error to the reconstructed signals is less than 0.2 m.With sufficient analysis of leak signals, this thesis designs the leak signal acquisition system based on embedded micro processor. The dynamic range of the data acquisition unit is 70 dB. The pass-band of the filter is 200-2000 Hz, hence the noises at 50 and 2500 Hz are rejected to -35 dB and -60 dB respectively. Error constrained data compression during leak signal acquisition is proposed, the upper bounds of compression error and compression rate are determined. Lots of leak detection experiments show that, the signal acquisition system for leak detection of water supply pipelines works efficiently, stably, and reliably. It satisfies the demands of leak detection and location with its low-noise, low power consumption, and portable features.