Accurate Measurement Method of the Position of a Buried Line

Abstract

A conventional method to measure the position of a buried line has been used. This method is based on the measurements of magnetic field around a line which conducts a current. However, the pitfall is that the magnetic field generated by an induced current in a secondary line affords considerable measurement errors. This paper describes a novel method to exclude such errors caused by the induced current. While the magnetic field generated by the current in the primary line is in phase with the current, that generated by the induced current delays more than 90° compared to that of the current in the primary line because of a reluctance component of the secondary line. Hence, the 90° component of the magnetic field results from the induced current. This component is measured by a solenoid coil and a lock-in amplifier; the 0° component is measured also and corrected by using the 90° component. Thus, the net magnetic field generated by the current in the primary line is calculated; it is used to determine the correct position of the primary line. The new method is tested by using two buried lines and is proved to be useful.