MEASURING METHOD OF POSITION OF UNDERGROUND BODY

摘要

PURPOSE:To measure the position of the underground body with high precision by switching and supplying AC currents of <=2 frequencies to a magnetic field producing means and finding each inflection point of the induced voltage characteristic of each frequency of a magnetic field detecting means. CONSTITUTION:Alternating currents from an oscillator 5 of frequency f1 and an oscillator 6 of f2 are switched through a switch 7 and supplied to the oscilla tion coil 2 of a tunnel digging machine 1. The induced voltage across a receiving coil 3 is inputted to a voltage measuring instrument 13 through a BPF11 of frequency f1 or BPF12 of frequency f2 by a switch 10. Then when the induced voltage characteristic of the coil 3 is denoted as F1 when the frequency f1 is selected through the associative switching of the switches 7 and 10 or as F2 when the frequency f2 is selected, distances Y1 and Y2 between inflection points of both characteristics and a reference point P are found. Then, the real distance after the influence of a nearby metallic body 4 is removed is calculated from a specific expression.