The first public trials of an automated highway system (AHS) in Japan demonstrated the technical issues involved in the use of magnetic sensors. The main problem in connection with the application of magnetic sensors concerns with separating the sensor signals from extraneous magnetic fields. We have developed a magnetic sensor, consisting of three pairs of In-Sb Hall devices spaced 25 cm apart, that is designed to address the technical issues. The sensor is capable of removing the influence of terrestrial magnetism and other extraneous magnetic fields through real-time adjustment of the reference magnetic intensity level. The adjustment in based on the relationship between the peak and bottom magnetic flux densities as the vehicle travelling along. Additionally, the signal processing parameters have been optimally tuned for use on the test course at the Public Works Research institute. The authors discuss the technical issues involved in the development of the magnetic sensor for future AHS application.
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