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  • 1
    ISSN: 0168-9002
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 6029-6029 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic detection has been investigated for use in detecting the location of underground pipelines, such as gas and water lines, by inputting a signal current into a pipeline and detecting magnetic field ((approximately-less-than)100 μG) generated by that current. Measurement factors necessary for accurate detection have been experimentally determined and are discussed. From measurements made on signal current distribution (the current flowing in pipes and leaking from them to ground), it has been concluded that detection error is caused by the leakage current, namely, the current to ground. The detection error is due to the noncenter symmetric distribution of the ground current flowing around a pipe. Even though the ground current is inevitable when flowing a signal current into pipes, it is possible to reduce the error by reducing the nonsymmetry by lowering the signal frequency below 10 kHz in this work. The ground current distribution was obtained by measuring the potential difference between two electrodes, both of which were rod shaped and inserted in the ground to the same depth. At low frequencies below 10 kHz, the ground current distribution in a cross section perpendicular to the pipe showed a rather center symmetry around the pipe, while at high frequencies the distribution changed to a noncenter symmetry with a significant current increase in a region near the ground surface. The drastic change in the distribution of the ground current was also confirmed by magnetic field distribution measurements conducted on the ground using three orthogonally arranged magnetic sensors, each with a sensitivity of 1 μG.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 6030-6030 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recently, it becomes more important to locate the complex piping patterns such as tee, bend, riser, and the others with high accuracy for maintenance and protection of city gas pipelines. Hence, we have developed a new pipe locator system for imaging the complex underground pipelines using magnetic remote sensing techniques. The main framework of this development is the application of the pattern recognition of the magnetic field distribution to the location of buried pipelines in urban areas. The first step for imaging the complex pipelines is to measure the three-dimensional magnetic field distribution with high accuracy which is generated by the passage of the alternating signal current through buried pipeline. For this purpose a portable trolley unit which is capable of scanning the ground to collect data, the 10 three-axes coil sensors with a sensitivity of 1 μG which are aligned in the unit, and a filter system using a FFT signal processor which eliminates urban magnetic noise as high as 10 mG in some cases, were developed. The second step is to process the magnetic field distribution data, to extract the feature of the underground pipeline using the contour diagram and the three-dimensional drawing of the magnetic field, and to identify the complex piping patterns. Further, we recognized that a nonlinear least-square method algorithm for calculation of the pipeline's position was useful to improve the location accuracy.
    Type of Medium: Electronic Resource
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