Reasch Of Detect The Status Of Underground Metal Pipeline's Anticorrosive Layer By The Technique Of Pseudo Random Code

Detection of underground pipelines is of great significance in normal activities. Regular nondestructive detection of such pipes and analysis of anticorrosive layer are quite necessary to reduce the possibility of fetal accidents and large economic losses resulted from the damages of the anticorrosive layer of underground metal pipes.In the early 1990's, the studies upon measuring the anticorrosive isolated resistor of unit pipeline and further estimating the status of anticorrosive layer have been done in the nation. In this method an electronic signal with a variable frequency is applied to one end of the pipeline, then detect the attenuated amplitude of the signal at the other end. When the signal is attenuated within a certain range through adjusting its frequency, the parameter of isolated resistor in the anticorrosive layer could be estimated based on the value of signal frequency. However, a serious drawback exists. The receiver can track the measurement only if the used frequency is given every time. Furthermore, many frequency points need to be employed in measuring a piece of pipe. Due to the different conditions of different pipes, sometimes the used frequencies may cover the whole frequency range. Therefore, it is quite time-consuming and labor-consuming and not convenient in the detection. A valid and efficient method is presented in this thesis. The technique of pseudo random code is introduced into this field and applied to the above measurement. Data of all frequency range can be achieved only through several transmitting and receiving. Therefore, the measurement is relatively easy and resolution is improved. In this thesis, the system model is constructed based on measurement principle and the function of transmitting/receiving unit module is determined. The following units in the transmitting device have been developed: generation of pseudo random code, precise phase shift of carrier wave, carrier's modulation by pseudo random code, amplification of amplitude and power of modulated signal and matched load. In addition, experiments have been done for the practical pipes using example transmission machine. As a result, the signals can be transmitted to the load and power can be as high as 10 W through different pipes. With regard to the receiving device, a general principle frame is designed and system is simulated. The result shows that the design is reasonable. Further, pre-amplifier, double frequency phase lock pulse generator, demodulator, step controller and phase detector have been tested for hardware devices.