Patent GB-378056-A (GB)
Title: A new method of electrical geophysical prospecting and surveying and apparatus for use therein
IPC: G01V3/06
Filed: 1931-03-26
Abstract: 378,056. Prospecting for minerals ; phase-difference measurements. TINSLEY, H., GALL, D. C., Werndee Hall, South Norwood, and EDGE, A. B. BROUGHTON-, Australia House, Strand, both in London. March 26, 1931, Nos. 9245 and 14449. [Class 37.] A method of determining the nature of the subsoil and detecting the presence of metalliferous deposits consists in supplying alternating current through ground electrodes or current carrying loops or both, together with means for determining and plotting the lines of equal in-phase potential and equal quadrature potential with respect to the main surface potential distribution. In one arrangement, Fig. 4, electrodes f are placed in the excited ground on two lines EP of equal in-phase potential the probes being connected by a variable resistance g. An amplifier A and detector D with the inducing coil e are connected to the resistance g and to a third electrode h. By moving the third electrode and keeping the balance between the lines EP, equal quadrature lines EQ can be plotted. The coil e can be orientated and may be provided with means for varying the number of its turns. Instead of the resistance g, a transformer or differential condenser may be employed. The ratio bridge described in Specification 364,085 may be employed for locating the EQ lines after the EP lines have been plotted from a baseline, the bridge arms having particular resistance and capacitance relationship. In addition to the probes a, Fig. 8, the area under investigation may be covered by a loop m fed from a source ml having the same frequency as the source b supplying the electrodes a. If the phase relation of the two current supplies is varied slowly, the EQ lines can be rotated and information obtained as to the shape or inclination of a deposit. Further modifications consist in substituting a variable mutual inductance for the coil e, Fig. 4, or utilizing a two-phase output amplifier A and connecting thereto potentiometer resistances which can be adjusted to balance directly the surface potentials. Potentiometer resistances connected through transformers to the EP and EQ lines with one moving and three fixed, or two moving and four fixed electrodes, may also be employed. Differential condensers may replace the potentiometer resistances. Fig. 13 shows another means for obtaining the EP and EQ balancing potentials, the inducing coil u or electrodes u<1> being connected to a resistance v and to one coil of a variable mutual inductance v<1>, v<2>, the EP and EQ values being obtained on the resistance and inductance respectively. Two electrodes on an EP line may be connected to one pair of plates of a cathode ray or other oscillograph and two electrodes on an EQ line connected to another pair of plates, the screen figure being a circle or ellipse depending upon the relative intensity of the line potentials. If the electrodes are not on true lines, the ellipse will be inclined. Differences in potential between pairs of points on the surface may be obtained by employing two variable mutual inductances. A further modification utilizes the electromagnetic field above the ground surface and provides a box inductance consisting of three coils in planes at right-angles, the EP and EQ values in vertical planes being balanced against the potentials induced in the horizontal coil.