System for determining electric geophysical prospecting work using synchronized clocks and direct coupled comparison means

Claim 1

A geophysical prospecting system comprising a portable current generator having at least two electrodes insertable into the ground and arranged to feed an input AC current into the ground via said electrodes to generate a complex electric low frequency field in the ground; a portable measuring means arranged to determine voltage differences with respect to their phase and amplitude in said complex electric field and comprising a compensating voltage generating means, a comparator direct coupled to said compensating voltage generating means, and a first precision clock, and wherein said compensating voltage generating means is arranged to generate a compensating voltage which comprises firstly a variable AC voltage having the same phase position as said input AC current, secondly a variable AC voltage being shifted 90* out of phase in relation to said input AC current, said AC voltages both having the same frequency as said input AC current, and thirdly a variable compensating DC voltage, said comparator being provided with at least two electrodes insertable into the ground, and being arranged to compare said compensating voltage with the voltage difference which owing to the influence of said complex electric field prevails between said last mentioned at least two electrodes when these are inserted in the ground, said first precision clock being pre-synchronized with said input AC current generated by said current generator to operate at a predetermined phase difference thereto, and being arranged to synchronize said compensatIng voltage generating means with said input AC current; and a second precision clock pre-synchronized with said first precision clock to operate at a predetermined phase difference thereto, and connected to said current generator to control the generation of said input AC current thereby.