Patent GB-659458-A (GB)
Title: Intensity, intensity ratio and phase difference measuring system for geophysical prospecting
IPC: G01R1/28
Filed: 1949-05-13
Abstract: 659,458. Apparatus for geophysical prospecting; potentiometric voltage measurements; phase differences measuring; magnetic tests and measurements. LUNDBERG EXPLORATIONS, Ltd. May 13, 1949, No. 12889. [Class 37] Relates to apparatus intended for use in geophysical prospecting and designed for measuring and comparing the magnitude and phase relationship of alternating potentials and the intensity, phase relationship and relative positioning of alternating magnetic fields. Essentially the apparatus is adapted to present a picked-up potential in phase opposition to another potential and includes (1) a variablegain amplifier; (2) first and second phase shifting networks; (3) a potentiometer resistance across the output of the second phase shifting network; (4) a second amplifier connected to the potentiometer resistance; (5) a plurality of potential pick-ups and means for connecting the pick-ups with the amplifiers. In Fig. 1 the phase-shifting networks 15, 16 are of the constant potential amplitude type and comprise phase control rheostats 18, 22 and the variable gain control is a rheostat 9 whose adjustment fixes screen potential and thus gain of pentode amplifier 7 and correspondingly the current flow in potentiometer resistance 35 connected across the output of the second phase-shifting network 16. To measure the alternating potential between ground located pick-ups 1 and 3 the operator places D.P. switch 5, 25 and S.P. switch 27 to positions shown, whereupon this potential is applied simultaneously to pentode 7 and fixed gain amplifier 30. The phase control 18 in network 15 is then adjusted together with control or tap 36 on potentiometer resistance 35 until zero or minimum response in indicator 33 shows that potential across potentiometer resistance section 64 is equal in magnitude and opposite in phase to that between pick-ups 1 and 3. The reading on the potentiometer control dial 45, Fig. 3, multiplied by the reading of milliameter 39 (in series with potentiometer 35) gives the magnitude and absolute value of the potential with reference to the standard current established for the milliameter. To compare the magnitude and phase of the potential between pick-ups 2 and 3 with that between pick-ups 1 and 3 the phase dial 44, Fig. 2, on phase control 22 is set to zero and the dial 45 is set to 1.0. The amplifier gain control 9 and phase control 18 are then adjusted until the indicator 33 again reacts with zero signal. The switch 27 is then thrown to the right and dial 44 on phase control 22 and the dial 45 on control 36 are both adjusted to further reinstate the null condition at 33. The reading on dial 45 is the ratio of the two voltages, i.e. 2-3/1-3 and the reading on dial 44 is the phase difference between them. The milliameter 39 may be shunted out and the voltage ratio 2-3/1-3 obtained without regard to absolute values. In modifications, Figs. 4 and 5 (not shown), induction pick-ups are utilized and voltage measurements made for determination of (1) the magnitudes of the horizontal and vertical components and the intensities of alternating magnetic fields at two selected points of observation; (2) the phase relationships between the horizontal and vertical components respectively at the two points; (3) relative positions in space, i.e. phase relationships, of the intensities at the two points. The Fig. 4 (not shown) equipment is arranged for induction pick-ups only and the Fig. 5 (not shown) equipment for selectively using both induction and contact pick-ups. In Fig. 5 (not shown), an amplifier is included in the first phaseshifting networks.