US1794666A - Apparatus for use in discovering and determining ore bodies - Google Patents

Description

March 3, 1931. E. s. BIELER ET AL 1,794,666

APPARATUS FOR USE IN DISCQVERING AND DETERMINING ORE BODIES Filed Dec. 12, 1927 2 Sheets-Sheet 1 Emwu: Snnun 3min, Home: Gums: lsals rm hlnroou,

Iuvnvrnns.

A TTORNEY March 3, 1931. E. s. BIELER ET AL 1,794,666

APPARATUS FOR USE IN DISCOVERING AND DETERMINING ORE BODIES Filed Dec. 12, 1927 2 Sheets-Sheet 2 ETIENNE 5. BIELER' Home: 6.1. wnrsonl,

INVENTORS.

A TTORNEY Patented Mar. 3, 1931 ETIENNE SAMUEL IBIELER AND UNITED STATES PATENT OFFICE HORACE GEORGE ISBISTER WATSON, OF MONTREAL,

QUEBEC, CANADA APPARATUS FOR USE IN DISCOVERING AND DETERMINING ORE BODIES Application filed December 12, 1927, Serial No. 239,572, and in Canada September 10, 1927.

This invention relates to an apparatus for discovering and determining ore bodies and maybe used in combination with other apparatus, electrodes or electric loops.

The'principal feature of our invention is the provision of two fiat coils of wire permanently fixed at right angles to each other,

but which may be tilted or turned in any desired direction so as to obtain the desired information relative to the location of any ore body in the vicinity.

With the foregoing and other objects in view, as will appear as the description proceeds, the invention consists of the novel construction, combination and arrangement of co-operating elements as hereinafter more specifically set forth, claimed and shown in the accompanying drawings forming a part of the present application, in which:

Fig. 1 is a perspective view ofthe preferred embodiment of our detector.

Fig. 2 is a diagrammatical View of the preferred embodiment of our invention, showing the detector coupled to a pair of telephone receivers. I

Fig. 3 is a ground cross sectional view illustrating the example of the elliptical polarization.

Fig. 4 is a schematic view illustrating the ratio of the minor to the major axes of the polarization ellipse.

' Fig. 5 is an elevation view and a corresponding plan view illustrating how the device would be set up to examine the ellipse illustrated in Fig. 4.

Figs. 6, 7 and 8 are diagrammatical views of the elliptic measurments and their relationship to each other.

Fig. 9 illustrates a plotting off of aparticular reading.

Fig. 10 illustrates a curvature diagonally indicating the resistance of the conducting b0 Various methods have been used for the detection of ore bodies by means of alternating'electric currents. They all depend on the fact that-metallic ores are in general much better electrical conductors than the surrounding rock. These methods may be sub-divided into two classes, the potential methods and electro-magnetic methods, according'as the ore is detected through the disturbance it causes in the lines of equal potential of the electric circuit, or through the disturbance it causes in the magnetic field of the current. They may also be sub-divided into galvanic and induction methods, according as the current is led directly into the ground or allowed to flow in a circuit entirely insulated from the ground. In the latter case, secondary currents are induced in any ore bodies that may be present in the area being investigated.

In the electro-magnetic method, whether the current from the alternating current generator is led directly into the ground or allowed to flow in a circuit insulated therefrom, it is usual to determine the direction and strength of the magnetic field as afiected by any ore bodies that may be present. This is done by means of a flat coil of wire wound on a suitable frame and connected to some alternating current detector or measuring instrument. When the axis of the coil is turned in any'particular direction, the measuring apparatus will give a reading proportional to the component of the oscillating magnetic field in that direction. When the axis of the coil is turned so that its plane includes that of the oscillating magnetic field, the measuring apparatus will give notreading. A pair of telephone receivers may be used to replace the measuring apparatus and if such pair of telephone receivers are used, there will be no sound in the receivers when the coil is turned so that its plane includes that of the oscillating magnetic field.

The objection to this method of measuring is that, in the neighbourhood of ore bodies,

when the coil is gradually rotated around a fixed line in its plane, there is generally no position at which the pair of telephone receivers are perfectly silent. The-reason for this is that the currents induced in any conducting bodies present are not in general, in time phase with the primary current inducing them, whether it goes through the ground or through an insulated circuit. Inconsequence, in the neighbourhood of conducting bodies, the oscillating magnetic field always has a component out-of-time phase with the primary field. As a result, the magnetic field in the neighbourhood of the conducting bodies is elliptically polarized, and hence,-

there is always a component of this oscillating'magnetic field along the axis of the exploring coil and a sound in the telephone receiver, except in the particular case where the plane of the exploring coil and the above polarization ellipse are coincident. Thus, an elliptically polarized magnetic field is an indication of the presence of a conducting body.

The purpose of the detector disclosed in this application is to enable the person using the same to determine at any point the direction and ratio of the magnitude of the minor'axis of this ellipse of polarization relative to the major axis of the same. The secondary current elfects are generally much smaller than that of the primary current with the result that the major axis of this ellipse consists almost entirely of the primary field,

while the minor axis'consists almost entirely of the secondary fields. Since the sec,- ondary fields are out-of-time phase with the primary fields, it is usual to refer to the minor axis as being the out-of-phase component of the field. Thus the ratio of the magnitude of the minor axis relative to the major axis is a measure of a secondary or out-of-phase componentof the resultant field relative to the primary field at the point being examined. This ratio is nil at any point which is not in the neighbourhood of a conducting body such as an ore deposit, and increases as the detector is moved closer tothe conducting body. In addition, the direction of the out-of-phase component (minor axis) which is determined simultaneously with the above ratio, points in general, towards the centre of the conduct ing body.

Our detector consists essentially of the two flat coils of wire A and B, whose planes are permanently fixed preferably at right angles to each other. The forms on which these coils are wound are secured together by means of brackets K or by any other suitable means so that the fixed position at right angles to each other may be maintained. The frame holding the coils A and B may be turned and tilted in any desired direction. The coil A is wound with a fixed number of turns of wire and, when used with other apparatus for this purpose, is connected across a condenser C, having a capacity such as to make the natural frequency. of the coil A equal to that of the primary alternating current used. The coil B is connected between one of the terminals A ofthe coil A and the detecting apparatus D, which may be 1; pair of telephone receivers, with or without an intermediate am lifier. The other terminal from the coil is connected direct to the other side of the detector.

The number of turns on the coil B may be The detector is used in the following man- The frame, on which the coils A and B ner. are wound, is moved with the ground end of the Jacobs stafi J as a pivotal point, until a minimum amount of sound is heard in the pair of telephone receivers D. W'hatever sound then remains is due to the fact that-the magnetic field is elliptically polarized and owes its existence to the component of the oscillating magnetic field along the minor axis of the ellipse of polarization. The intensity of the sound is therefore a measure of the component of the secondary field at the point being examined. This may be balanced by movement of the sliding contact S, which varies the number of turns of the coil Bincluded in the circuit, until the sound entirely disappears. The variation of the number of turns of the coil B included in the circuit, causes a variation of the share of the, induced potential created in coil B by the component of the oscillating magnetic field along its axis, which is included in the detector circuit. Since the coil B is supported in the frame at right angles to the coil A and the axis of the coil A lies along that part of the minor axis of the polarization ellipse in the plane containing the axes of the coils A and B, the axis of the coil B will lie along the major axis of this polarization ellipse. Hence the potential induced in the coil B is proportional to the major axis of the polarization ellipse and the potential induced in the coil A is proportional to that part of the minor axis lying in the plane containing the axes of coils A and B. By use of any suitable time phase shifting device, these potentials may be made 180 out of time phase. By varying .one of the potentials produced by the coils A or B (that in coil B being varied in this case) they can be made to completely nullify each other. The number of turns being used on the coil B is a measure of the ratio of magnitude of the major and minor axes of the polarization ellipse in the plane containing the axes of the coils A and B. The direction of this minor axis is determined from the knowledge of the manner in which the coil B is included in the circuit.

Since the actual direction of the minor axis (secondary field) at any point isoriginally unknown, it is found advisable to determine the ratio (as referred to in the preceding tent of any conducting body in the area can be deduced from such a map.

To illustrate the principle of the elliptical polarization let us consider a relatively simple case where the energizing (primary) field is created by a large insulated loop placed horizontally on the ground and where the conducting body, in which the secondary currents are induced, is so situated that only one part of these currents in the conducting are the cross-section of two sides of the loop through which the alternating current flows producing the primary field, which, at the surface of the ground, is practically vertical as indicated. 0 0 represents a conducting body as shown and having the greater part of the current induced in it concentrated about the extremity G, with the resultant magnetic field'as shown. The return current in the ore-body is so far removed that it has no practical efiect on the detecting device. Both ,the conducting body and the loop are considered as infinite in extent perpendicular to the plane of the figure, so that the representation of the magnetic field already given is complete. Therefore at any point P in the plane of the figure, the primary and secondary fields may be represented each by a vector which'varies periodically in magnitude between certain limits but always has a fixeddirection in space.

Now, since the secondary (ore-body) circuit has no inductance or capacitance, the

secondary current induced therein will be in phase with the induced secondary voltage and therefore by the elementary law of induced currents, 90 degrees behind the primary field in phase. This being the case the vectors representing the primary and secondary fields at any point are 90 degrees out of phase.

Elementary considerations show us that the resultant of any two harmonically varying-vectors is a single vector which rotates about a point and whose extremity traces out an ellipse. This ellipse will degenerate into astraight line either when the two original vectors are directed along the same I straight line, or when their phase displacement is 0, 180 or some integral multiple of 1809. Ingeneral, neitlier of these conditions is fulfilled as in the particular case outlined above. The resultant vector at any point P, P, P, traces an ellipse and the magnetic field is said to be elliptically polarized.

Several properties of these polarization ellipses should be noted. First, since in general the secondary fields at a point are Weaker than the primary field, it will be seen that the minor axisof the polarization ellipse is due mainly to the secondary (ore-body) currents and the major axisto the primary field. Secondly, since the secondary field is at right .angles to the current producing it, it (the secondary field) and hence the minor axis of the ellipse, points either towards the inside of the conducting body or in the opposite direction depending on which direction is chosen as standard. For example, if the dia- T represents the relative primary and secondary field directions at a point over one side of the conducting body then the diagram l r 4 must represent the relative field directions on the other side of the body for the relative direction of the secondary current, and hence its field, has changed, while that of the primary field has remained unaltered. A little study Will show that the rotating vector pre viously described would rotate in a clockwise direction in one case and an anti-clockwise direction in the other. By distinguishing between these two cases one can determine the location of the conducting body relative to the point of observation. Thirdly, it will be noticed that the ellipse flattens out as the point P moves away from the conducting body, both because the secondary current becomes weaker as we move away from the conductor, while the primary field remains relatively constant, and because the direction of the two fields become more nearly the same. From these properties one is able to determine the location and extent of the conducting body producing them. It must be understood that the above description applies only to a particular case in which the method and device may be used. Any method which results in a primary and secondary field, in general differently directed and phase displaced but of the same frequency will ive rise to an elliptically polarized magnetic eld which can be investigated by the device in I ing linear fields in various combinations.

Particularly this ellipse may be resolved into linear fields along its major and minor axes. When such is the case fields are at right angles and phase displaced 90?. Moreover in this respect such a resolution is unique. Referring to Figure 5 it will be noticed that, since J J lies in the plane of coil A any magnetic component lying along it cannot afiect coil A and will have a maximum effect on coil B. Similarly any magnetic component along I I efiects coil A only. Thus coil A' is affected by the minor axis and coil B by the major axis of the ellipse.

Consider Figure 6. Let 0 S represent the phase of the field along the minor axis of the ellipse. Then the phase of the E. M. in-

duced in coil A by it is represented by 0 S being 90 behind O S. Now coil A is connected across a condenser C of such capacity that the circuit so formed has a natural period equal to that of the current used. Such being the case the reactance of the circuit is zero, and the fiow of current in coil A is governed by the resistance of the coil A alone,

and is, therefore, in phase with the E. M. F. induced in A. Thus 0 S will also represent the phase relation of the current in coil A.' Now the property of a pure capacity is that the potential across it ,is 90 behind the current flOWiIlg through it, so that the potential across the tuning condenser C is represented in phase by 0 S Now consider Figure 7. Q, P represents the phase relation of the field along the major axis of the ellipse, proper regard being given to the phase relation of the field along the minor axis as represented in Figure 6. It will be noticed that Q P differs in phase from O S by 90. As in the above case of coil A, the potential setup in coil B by the field along the major axis is phase displaced 90 and is represented by Q, P It will thus be seen that the potential across condenser C and that 'set up in coil B are always opposite in sign so that, if they can be made equal in magnitude they can be made to balance each other completely. This is accomplished by varying the proportion of the voltage set up in B which is used to balance that set up across condenser C. In the particular form of the device submitted this is accomplished by a multicontact switch and taps.

Now the voltage tapped ofi in B isproportional to the number of turns of B included between the taps and hence this number as a measure of the potentialproduced across C by the current in coil A. Now we have the potential across 0 proportional to the current through it which is, in turn, proportional to the E. M. F. set up in A which is proportional to the field strength perpendicular to the axis of coil A. Therefore the potential across C is a constant multiple of the field'strength perpendicular to coil A. Likewise the potentlal set up in a single turn of B is proportional to the field strength along its axis. I

Suppose H =the Virtual field-strength along the minor axis which is also that along the axis of coil A.

H =the virtual field strength along the major axis which is also that along the axis of coil B.

N =No. of turns on coil A.

N =No. of turns between taps of coil B.

A =the average area of a turn on coil A.

A =the average area of a turn on coil B.

R =the resistance of the coil A.

C=the capacity of the condenser tuning coil A.

Then we have the coil A.

E -N H A A with a resulting current flow of N AHAAA E1 7 R R A This results in a potential of potential induced in or N (the number of turns tapped oif from coil B) gaa.

ABRA HB HE where K is a constant. But H is the minor axis field strength and H the major axis axes of the polarization ellipse. Thus N is a measure of this ratio.

It should be remarked here that, depending whether our ellipse is formed by a field strength so that is the ratio of the counter-clockwise or clockwise rotation of the vector described previously, the field along the minor axis will be represented in phase by O S or 0 S with resultant potentials across condenser 0 represented in phase by 0 S or O S respectively. Therefore if B is permanently connected across O we,will have the potential set up in B opposing or assisting that set up across C. But, if thatE. M. F. in B assist that across C, by reversing the manner in which B is connected'across C, they can be made to oppose each other. Thus, b knowing which way B is connected across C we can distin uish between counter-clockwise and clockwlse rotation of the vector and hence determine the direction of the conducting body relative to the point of 'observation.

Also, if the apparatus be set up so thatthe major and minor axes of the ellipse do not lie in theplane of the coils A and B respec-' tively, then the potentials set up in A and B will not differ in phase by 90, and hence they cannot be balanced since the construction of the device is such that it can only balance potentials phase displaced 90. This the particular set up of the device as described above is unique and can be determined without difficulty.

To illustrate the principle of compounding two readings at right angles to one another to get the resultant reading let us consider Figure 8. It represents a plan at a point of observation in the plane perpendicular to the major axis of the polarization ellipse. O V represents the direction and magnitude of the minor axis at the point, ma ng an angle with the direction of traverse O X. If readings aretaken perpendicular and parallel to O X we will get values which represent the resolved parts 0 V on. O Y and O X respectively, i. e., O B and O A respectively. Then, by compounding these by the parallelogram law we get 0 V.

Figure 9 gives an illustrative example of such a survey. L, L, L, L represents the emergizmg loop, G the source of power, 0, O, Q, 0 the ore-body, N 8,; N S N 8,; etc. hues of traverse with readings taken at known intervals along each line at A B C D A B C D etc. Readings are taken along and perpendicular to the N S lines, and the results compounded and plotted as shown. It willbe seen that the resultant arrows point in general towards the centre of the ore-body and also that they increase in size as they approach the edge of the ore-body. If one draws a graph plotting the resolved part of each vectoralong the N S lines for the dif-- ferent points, A, B, C, D, etc., a curved such as in Figure 10 will result; This represents the results along N 4 S The projections E E of the peaks indicate the limits of conducting body. A closer study of such curves will yield information asto depth and dip of i 05 the conducting body so located.

The foregoing specification and annexed drawings disclose the referred embodiment of our invention, but'lt is to be understood that minor changes may be resorted to in the commercial adaptation of our invention without departing from the scope of the invention as hereinafter claimed.

What we claim as new is:

1. An apparatus for use in discovering and determining ore bodies, characterized by the provision of two coils the axes of which are out of parallelism, rigidly mechanically connected to each other and in electrical connection with each other.

2. Anapparatus for use in discovering and .determining ore bodies, characterized by the provision of two coils the axes of which are out of parallelism,rigidly connected mechanically to each other andin electrical connection with each other, one of said coils being In testimony whereof I aflix my signature.

HORA E GEORGE ISBISTER WATSON.

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