US1894134A - Parallel conductor system - Google Patents

Description

Jan. 10, 1933. TONKS PARALLEL CONDUCTOR SYSTEM Filed June 17, 1931 Fig.1.

Fig.4.

Inventor":

His Attorney.

Patented Jan. 10, 1933 iinirso LEW'I TONKS, OF SCHENEiITADY, NEVJ YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK PARALLEL CONDUCTOR SYSTEM Application filed June 17,

My invention relates to parallel conductor systems such as those of the Lecher wire type, for example, and it has for one of its objects to provide means whereby these systems are rendered more practical for purposes of electrical measurement, control, etc.

Systems of the type referred to are well known in the art and commonly comprise a pair of conductors of suitable length arranged in parallel space relation at a suitable distance apart. If desired, however, one of these conductors may be made concentric with the other or arranged in any other suitable manner. One end of the two conductors are joined together through means dependent upon the use to which the system is to be applied and the opposite ends may be either left open or joined together as the case may require. The desired measurement or control is then effected by means of a bridge between the two conductors, which may comprise a suitable sensitive current indicating device, and which may be arranged for sliding engagement with the two conductors. If it be assumed that a high frequency electro motive force is impressed upon the two conductors the current flowing in the bridge is dependent upon the position of the bridge upon the parallel conductors and is determined by certain effects, such as resonance, in the conductors on opposite sides of the bridge.

One of the principal objects of my invention is to provide means which may be conveniently employed in connection with a system of the type described whereby the current in the bridge is rendered independent of the characteristics of the system on one side of the bridge while maintaining the sensitivity of response of this current in the bridge to the characteristics of the system on the opposite side of the bridge.

A further object of the invention is to provide an oscillation generator in which the frequency is determined by the position of the bridge on the conductors of a system of the type indicated and in which extraneous influences on the conductors at points beyond the bridge are prevented from afiecting the frequency of oscillations produced.

The novel features which I believe to be 1931. Serial No. 545,059.

characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, and its further objects and advantages may best be understood by reference to the following description taken in connection with the accompanying drawing in which Figs. 1, 3 and 4 represent my invention as applied to parallel conductor systems utilized for different purposes; Fig. 2 represents certain properties of the arrangements shown in Figs. 1 and 3; and Figs. 5 and 6 represent characteristics of the arrangement shown in Fig. 4.

Referring to Fig. 1 of the drawing, I have shown therein a pair of parallel conductors 1 joined together at one end thereof, as indicated at 2, the opposite ends being left open.

A low impedance bridge 3, including a suitable current indicating device which may comprise a thermal sensitive element, for example, is arranged for sliding engagement along the conductors 1. These conductors may have a high frequency electromotive force impressed thereon in any suitable manner as by being placed within the field of a high frequency radiating system, which I have indicated at 4.

As thus described the system comprises a conventional Lecher wire system as used for the purposes of measuring wave length, for so example. The bridge 3 divides the system into two opposite portions and may carry current the magnitude of which is determined by the characteristics of either of said opposite portions. As the bridge is moved along the conductors sharp maxima occur at points spaced a half wave length apart, these maxima being determined by the characteristics of that portion of the system on one side of the bridge and similarly additional sharp maxima occur at points spaced a half wave length apart determined by the characteristics of the opposite portion of the system.

Thus, for example, in F 2 the full line curve represents sharp maxima which occur at intervals of a half wave length along the conductors, the first full line maxima being at approximately that distance from the closed end 2 of the conductors 1. The dotted itcccurves represent inaxinia which likewise occur at intervals of a half wave length along the conductors, the first of these maxiina being spaced approximately a quarter of a wave length from the open end of the conductors, as shown in the drawing. On the drawing I have used the symbol A to designate wave length. It will thus be seen that the interval at which these maxima occur may serve as an indication of the wave length of the impressed electromotive force.

The full line maxima are caused by resonance conditions in that portion of the system at the left of the bridge 3 and they are thus of diminishing amplitude as the bridge is moved toward the open end. In the same way the dotted linomaxinia are produced by resonance conditions in that )ortion of the system at the right of the bridge 3. Thus, at the frequencies employed, the ends of the conductors at the right of the bridge are electrically connected together due to inherent capacitance between the conductors thereby producing the resonance condition as described.

In the use of systems of the type described in which the two sets of maxima occur due respectively to the properties or" the conductors on opposite sides of the bridge, a certain amount of confusion and difficulty is likely to result from the presence of the two sets of maxima. The space relation between the two sets of maxima varies with the frequency and with the length of the conductors. They may coincide, or occur in any other relative position along the length of the conductors. Accordingly confusion results to the operator in that in observing a mavima in the meter A he may be unable to determine whether this maxim-a is produced by resonance in the conductors at the right or at the left side of the bridge, and accordingly considerable trial and experimentation is necessary before a satisfactory determination is made.

In accordance with my invention this difficulty is eliminated by connecting an auxiliary low impedance brid e which I have indicated at 5 across the two conductors at a point spaced from the bridge 3 by a distance of preferably one-quarter of a wave length. This distance may vary, however, by an eighth of a wave length in either dir='=-"tion dependent upon the impedance of the bridge 3. Thus if the bridge 3 is of low impedance the location of this auxiliary bri. 3e may vary over a considerable range whereas if the bridge 3 is of relatively high iin )edance i. e. of a value which is an appreciable fraction of the surge impedance of the sys em, for example, then for best results the bridge 5 should be placed at substantially one-quarter of a wave length from the bridge 3. he auxiliary bridge, however, may be placed at any integral odd multiple of a quarter of a wave length within the range of variations indicated. This auxiliary bridge preferably should constitute a short circuit between the two conductors but it may include any low impedance comprising resistance, inductance, or capacity. If desired, it may comprise a copper bar, as indicated at 5, bearing upon the conductors l and arranged to be moved along the conductors in unison with bridge 3 as by being attached thereto by members 6.

I have discovered that a bridge of this kind across the conductors, as above described. has the effect of entirely eliminating one of the two sets of maxima without affecting the occurrence of the other set. Thus, for example, with the short circuit 5 arranged upon the side of the bridge 3 towards the open end of the conductors the dotted line maxima of Fig. 2 are completely eliminated. \Vith the short circuit arranged upon the opposite side of the bridge 3 the full line maxima are eliminated. In this way the desired measurements are greatly facilitated.

Fig. 3 represents the system described as employed for measuring impedance. This arrangement is similar to that of Fig. l, but differs therefrom in that the conductors are joined at the closed end by means of an impedance Z which is to be measured by the Lecher wire system. It is apparent from Fig. 2, for example, that when the conductors 1 are short circuited at one end thereof the maxima due to resonance conditions in the circuit comprising the closed end of the conductors and the bridge 8 occur at half wave length intervals from the closed end. When these conductors, however, are joined together through an impedance the points at which the maxima occur are all moved either to the left or to the right, dependent upon whether the impedance is inductive or capacitive. If this impedance is made infinite the first maxima will occur at substantially a quarter wave length from the open end as; indicated in Fig. 2, other maxima occurring at half wave length intervals thereafter. Thus the points at which the maxima occur serve as a measure of the impedance connected between the ends of the conductors. Here again it is desireble to eliminate the effects of the conductors on the opposite side of the bridge 3 from the closed end, and ac cordingly the bridge 5 is shown comprising a short circuit between the two conductors spaced at a distance of substantially a quarter wave length from the bridge 3.

In Fig. 4 I have shown a system of the type described, as utilized for control of the frequency of an oscillation generator. In the arrangement of this figure the oscillation generator is one of the split anode ma netically controlled type comprising an electron discharge device having two anode segments 7 arranged in cylindrical formation, and to each of which one of the parallel conductors 1 is connected. The outer ends of the parallel conductors are connected together and to the positive side of a source of anode potential 8 the negative side of which is connected to the cathode of the electron discharge device. The cathode comprises a heated filament 9 extending along the axis of the cylinder comprising the two anode segments 7 and arranged to be energized from. a source of electromotive force 10. A magnetic field within the discharge device and parallel with the axis of the anode cylinder is provided by means of a coil 11 which is energized from a source of electromotive force 12.

As thus arranged the circuit in which oscillations are produced comprises the bridge 3 and the parallel conductors at the left thereof, together with the anode segments and the capacity therebetween. The constants of this circuit are of course varied by movement of the bridge 3 to the left and to the right and accordingly the frequency of oscillations is likewise varied. The magnitude of the oscillations produced is indicated in a general way by the current flowing in the meter A.

It has been found, however, that with an arrangement of the type described with the short circuit 5 omitted, the frequency of the oscillations produced varies with the position of the bridge 3 in the manner shown by the dotted line curves 13 in Fig. 5. Thus, for example, as the bridge 3 is moved from the left-hand end of the conductors toward the right the frequency changes from one of very short wave length to longer wave lengths in substantially linear relation to the movement of the bridge over a certain range after which the rate of change in frequency diminishes, as indicated by the lower dotted line curve 13. At a certain point, however, it is found that the wave length abruptly increases to a considerable extent, as indicated by the left-hand end of the upper curve 13, after which it then again gradually assumes a substantially linear relationship to the movement of the bridge. The current in the indicating instrument A varies with this movement of the bridge in accordance with the curve 14 of Fig. 5, a decided minimum occuring in the neighborhood of the abrupt increase in wave length. I have found that this character of the system can be entirely obviated by use of the bridge 5 spaced as previously described, and that when so employed the frequency of the system varies in direct proportion to the movement of the bridge 3, as indicated by the full line curve 15.

A further advantage resulting from the use of the short circuit bar 5, as indicated at 4;, results from the fact that extraneous influences upon the conductors at the right side of the bridge are obviated. Thus, for example, it may occur that any slight mechanical variation of the position of these conductors,

or of the position of mechanical objects in the neighborhood of these conductors, may greatly vary the current in the meter A and the frequency of the oscillations produced. The change in current in the meter A is shown, for example, in Fig. 6 in which I have plotted the curernt in meter A as ordinates against the position of a short circuit between the two conductors 1 when moved longitudinally thereof as abscissa, the bridge 3 remaining in fixed position. Thus, it will be observed that as the short circuit is moved toward the right the current in the meter A gradually increases and subsequently slightly diminishes to a point at which an abrupt drop almost to zero occurs after which the current again rapidly increases. Thus it is apparent that any external influence upon the conductors at a point such as this is likely to afi ect very greatly the current in the meter A. I have found, however, that effects such as this may be entirely eliminated by use of the short circuiting bridge 5 spaced from the bridge 3, as previously described.

While in Fig. 4 I have shown a particular oscillation generator employed in connection with the parallel conductor system, it is pointed out that the phenomenon explained is due to the action of the parallel conductor sys tem and may occur in connection with any system for exciting the oscillations in the parallel conductors in which the frequency is determined by the constants of the circuit comprising these conductors. This is be lieved to be due to the fact that the parallel conductor system has two degrees of freedom. Thus over a certain range of move ment of the bridge 3 the frequency of oscillations is determined by the constants of that portion of the system on one side of the bridge, whereas at a certain position of the bridge the constants of the opposite portion of the system becomes effective to control the frequency thereby causing the sudden change in frequency above noted.

lVhat I claim as new and desire to secure by Letters Patent of the United States is 1. In a system for electrical measurement or control, the combination of a pair of conductors, means for supplying electromotive force to said conductors, a conducting bridge between said conductors arranged for movement along the length thereof and dividing said system into opposite portions whereby the current in said bridge is dependent upon the characteristics of said opposite portions, and a connection between the two conductors in one of said portions to prevent the characteristics of the conductors of said one portion from affecting the current in said bridge.

2. In combination, a pair of conductors joined at one end, a conducting bridge between said conductors arranged for movement along the length thereof thereby constituting, with the joined ends of said conductors,a closed circuit, means to supply high frequency eleetromotive force to said circuit, whereby current is caused to flow in said bridge dependent in magnitude upon the position of the bridge upon said conductors, and means for'rendering the magnitude of current in said bridge independent of resonance in the conductors on the opposite side of said bridge from said joined ends, said means comprising a connection between said conductors on said opposite side of said bridge.

3. The method of utilizing a Lecher wire system, which includes the step consisting in shortcircuiting the conductors of the Lecher wire system at a point spaced from the conducting bridge thereof by a distance of approximately an odd integral multiple of a uarter of a'wave length of the electromotive 59 orce induced in said conductors.

4. In combination, a pair of parallel conductors, means to supply high frequency electremotive force to said conductors,.a meter connected between said conductors at a point dividing the conductors into opposite portions of such length that resonance conditions at said high frequency occur in said opposite portions and are indicated by said meter as the point of connection of the meter to the conductors is moved along the conductors and a low impedance bridge between said conductors spaced from the point of connection of the meter with said conductors by a distance of'an odd multiple of approximately a quarter of a wave length of said electromotive force whereby resonance conditions in that portion of the conductor in which said bridge is located is prevented from affecting the meter.

40 5. The combination in an oscillation generator of a pair of parallel conductors comprising the oscillatory circuit of said oscilla= tion generator, high frequency exciting means connected to said conductors at one end thereof, a conducting bridge connected between said conductors and movable along the length thereof thereby dividing said conductors into opposite portions, and an auxiliary conducting bridge between said conductors spaced fromsaid first conducting bridge by a distance substantially equal to an odd multiple of a quarter of a wave length of the oscillations produced and on the side of said first bridge opposlte from said exciting means whereby the frequency of oscillations produced is determined entirely by that portion of the system to which the exciting means is connected.

In witness whereof, I have hereunto set my hand.

LEWI TONKS.

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