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Magnetic Object Locating System.

A magnetic locator system has been built for detecting pipeline pigs, for determining the position and velocity vector of underground moving drill heads, and for possibly determining the position of personnel moving in radio-dead areas. In this technique, continuous low energy magnetic pulses are produced by a transmitter located on the moving object. The system has several types of receivers depending upon the application. The transmitter magnet, which is a small Archimedian Spiral magnet approximately 3 inches in diameter and .25 inches thick, can generate approximately one Tesla (10,000 gauss) of power in a millisec pulse. The receiver is a simple detector with a magnetic pickup coil for the pig locator and a more complex three-axis gradiometer for determining position, velocity, and direction of a free-moving object.

By combining the features of detection and tracking, the layout of buried pipes, both metallic and non-metallic, can be determined. Multiple targets can be tracked by timed responses to a single forward link interrogation pulse. Simulations of moving targets under various conditions, i.e., soil, wet sand, sea water, metallic and non-metallic pipelines, etc., have indicated detection ranges of hundreds of feet may be achievable. These long ranges have not, however, been field-tested yet. Because of the properties of magnetic pulse propagation, the path losses for air, soil, and salt water are similar. The shielding loss through a .4-inch steel pipeline wall thickness is only about 13 dB for the magnetic pulse characteristics of the transmitter.

Simulations have also been made of the tracking accuracies expected from a single gradiometer. The mean direction error from source to one receiver was 7 degrees and a mean relative range error of 1.6%. When two or more receivers are used, these accuracies should be greatly improved. The status of this project by midsummer was that the transmitter and receiver have been built and tested individually. Simulations for the tracking and direction-finding is continuing for two receivers. Field testing of the system is scheduled for this fall.
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Publication:Pipeline & Gas Journal
Article Type:Brief Article
Geographic Code:1USA
Date:Nov 1, 1998
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