Patent ID: 6369574
Filing Date: 2002-04-09
Classification: G01V

Abstract:
A method for electromagnetically probing drill holes in geological investigations, wherein a ground-located conductor loop forming part of a transmitter arrangement is placed in the vicinity of the drill hole and a current source in the transmitter arrangement is supplied with a periodically varying electric alternating current of predetermined wave shape, and wherein a probe that has at least one sensing coil is lowered into the drill hole in order to sense signals at different levels and therewith detect variations in magnetic fields correlated with the alternating current delivered to the conductor loop, comprising the steps of:controlling the periodicity of the electric alternating current through the conductor loop by means of a clock signal from a first clock circuit, said clock circuit being stabilized to time signals obtained from a radio connection; the probe is electrically dependent and battery powered and includes a second, accurate clock circuit for time-bound sensing by sampling signals from said at least one sensing coil, wherewith the sampled signals are stored in a memory in the probe; establishing the reading of the accurate clock mounted in the probe relative to the reading of the clock in the transmitter arrangement at frequent intervals, and preferably before and after each probing process, so as to take the time run by the probe clock into account; and for each level where a measurement has been made, correcting the second clock circuit to a calculated clock reading relative to the transmitter clock circuit for normalization of time to the clock of the transmitter arrangement, therein obtaining a defined phase relationship between the periodically varying alternating current in the transmitter arrangement and signals corresponding to magnetic field variations sensed in the probe.