US1551797A - Artificial line - Google Patents

Description

Sept. 1, 1925;

' O. E. BUCKLEY ARTIFICIAL LINE Filed AUE. 5. 1922 \LlllllllllllllII/IIL J mmmom. l

. 4m l/lIsI/uzce 1mm Jim End f/Vaali r) Oil - Patented Sept. 1, 1925.

UNITED STATES PATENT oFF cE.

OLIV'EB IE. BUCKLEY, or uArLEwoon, new ma am, ASSIGNOB 'ro WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF N YORK.

EW YORK, 11. Y., A CORPORATION or nnw ARTIFICIAL LINE.

Application filed August a, 1922. Serial in. 578,856.

To all whom it may concern: I

Be it known that I, OLIVER E. Buckner, a citizen of the United States of America residing at Maplewood, in the county it Essex and State of New Jerse have invented certain new and usefu Improvements in Artificial Lines, of which the following is a full, clear, concise, and exact description.

The principal object of the invention is to provide an artificial line that shall accu-' simulate a long signaling conductor.-

ratel In t is specification there is disclosed as an example of the invention, a balancing network for the duplex operation of a long high-speed continuously loaded ocean telegraph cable.

Fig. l is a diagram showing the particular-artificial line here disclosed as representing the invention. Fig. 2 is a diagram showing the current in the conductor at various distances from the sending end.

Fig. 3 is a permeability diagram for the loading material. Fig. 4 is a diagram showing the efi'e'ct of variation of air gap on effective permeabilit and Flg. 5 ma diagram showing the e ect on p ermeability of superposed constant magnetizing force. I

In the United States patent application,

Serial No. 492,725, filed August 16, 1921,

(corresponding to British- Patent No. 184,774) in the name of O. E. Buckley, there is disclosed a continuously loaded conductor suitable for use as a long ocean tele- In the specification of that case it is pointed out that the loading of long ocean telegraph cables has heretofore been found of no practical advantage. In

deed, no telegraph cable of length greater than 100 nauts has been loaded for any purpose, and the only loading of shorter cables has been primarily for tele hone use and in some cases secondarily or superposed telegraphy.

A telephone cable of length 100 nauts has been loaded with a wrapping of smalliron wire, but the cable conductor described in the Buckley'patent application is loaded with tape of a special composition called permalloy which is fully described in the specification of that application. I

A suitable form of permalloy is obtained by fusing together iron and nickel in the respective proportion of 21 per centand "7 8 per cent and formin the composition into a tape of suitable imensions. permalloy tape is applied helically to the conductor, with the edges abutting. Thereafter, the taped conductor is given a heat treatment described in the specification'reterred to, which leaves the permalloy tape in a condition of very high permeability for low magnetizing forces, many times higher than for the best samples of iron heretofore in'use. Y I I The high permeability of the loading material gives the loaded conductor a high inductance, thus diminishing the attenuation, and facilitates the transmission of signals at much higher frequency than has been possible -on the unloaded cable conductors heretofore in use. p x

In the operation of long ocean'cables it has been quite usual heretofore to operate them duplex. For this purpose, as is well known, artificial lines are provided "at both ends, each of which simulates the cable elec- ,trically to a practicable degree, .and the actual cable and the artificial line are connected up as arms of a Wheatstone bridge. The matter 'of making and adjusting an artificial line so that it will simulate a long ocean cable with suflicient accuracy has been one of considerable difficulty, even though the cable was not loaded. "In'the United States patent application referred to, the continuously loaded line, is disclosed as be-' ing operated only one way. In the'particular example there considered, the one Way operation was shown to be at about ten times the speed for-the unloaded cable The unloaded cable has its message capacityfinwith which comparison was proper;

This

loaded cable opan five times the difiiculty that maybe noticed. The nonloaded cable has resistance and capacity,

whereas its'leakance and inductance are al-' most negligible. The'loaded cable "has a large amount of inductance "which, of course,

must be simulated in the artificial line, thus increasing the difiiculty of effecting a balance. Moreover, the inductance varies with respect to the current, whereas the factors met inbalancing the unloaded cable, namely, resistance and capacity, are substantially the same for different currents. Still further, the effective resistance of the line is determined, in a measure, by eddy current losses and other effects in t e loading materialso that this effective resistance for the loaded cable varies with chan e of the current, whereas for the non-loa ed cable the efiective resistance is substantially constant.

With the conditions in view for simulating the lon continuously loaded conductor, I have evised an artificial line that is like the cable conductor with respect to all the essential constants involved, and may be used to balance such a conductor for duplex operation, and may be adjusted in a convenientmanner to secure the desired balance.

The fparticular loaded cable considered by way 0 example in the Buckley patent application has a cylindrical copper conductor of diameter 0.168 inch. This is enveloped by a helically wound tape of permalloy of thickness 0.006 inch and width 0.125 inch, which makes the overall diameter of the taped conductor 0.180 inch. When applied in this way, the permalloy tape shows a virtual permeabilit of 2,000 or more, whereas for any grade 0 iron heretofore available the figure would not be over 200. By virtue of this extraordinary property of permalloy, its hi h permeability at low magnetizing forces, t e conductor loaded in this way serves for the high speed telegraph transmission described in the Buckley United States patent specification already identified.

After assembly of the cop r conductor and its loading material, as escribed, they are put through a heat treatment which de velops the high I 'rmeability referred to. Then the cover 0 gutta percha insulation, wires; etc.,is applied. The cable described by way of example has a length of 2,000 nauts. The magnetic properties of the loading material will a pear more fully in connection with the fo owing description of the artificial line.

Referring to Fi 1, the cable already described is indicate at 10. The receiver R is in the cross member of the 'Wheatstone bridge, two adjacent arms of which on one side have the respective interposed equal condensers C. The transmitter T is connected to the apex formed by the junction of the conductors for these two condensers C. The remainin two'ar'ms of the bridge are formed by the ca 'le 10 and the artificial line now to be described in detail.-

For the tgart of the artificial line lying nearest to e bridge, in an electrical sense,

there is employed a series of conductors 11 of the same dimensions and material as the cable conductors, and loaded in the same.

way. The cable conductors are surrounded with gutta ercha or. other suitable insulation, but it 1s not necessa to simulate this condition in the artificial line. The sections of ta d conductor in the artificial line may be 0 different lengths, shorter near the bridge and longer away from it. However, more conveniently, they may be of the same length, say each feet. These sections will be connected in series throu h small adjustable inductance coils 12 an resistances 13.

Condensers 14 are connected on one side to points adjacent to coils 12 and on the other the inductive effects negligible between different parts thereof.

There are four fundamental physical constants in the cable which must first be considered for the pur ose of matching the artificial line to the ca 1e, These are the resistance, capacity, inductance and leakance. Bfy making the conductor of the sections 11 o the same material and cross-section as the conductor of the cable, the series resistance per unit length is matched to a close first approximation. It is well known that cables are manufactured in sections which are spliced together before laying. The manufacturing methods employed necessarily result in small differences for the constants for these sections. Whatever the constants are for the various sections of the cable, it is assumed that they will be made the same for the corresponding sections of the artificial line 11, so that each naut of its 100 nauts will have the same resistance as the corres 0nding naut of the cable. Precision of a justment will be secured by the use of the small interposed adjustable resistances 13.

The portion 11 of the artificial line, has not only the same conductor as the cable, but it has the same inductive material wound helically thereon. Therefore to a close first approxlmation the series inductance of the artificial line 11 will be the same as of the first 100 nauts of the cable, naut for naut, but the small interposed adjustable inductance coils 12 will facilitate making a recise adjustment to secure equality of in notance between the cable and the artificial line, naut by naut.

The distributed shunt ca acity for the cable will be sufiicicntly simu ated in the artificial line by the condensers 14, each with sending one plate grounded'and the other plate connected to the cable at a. sixty foot interval.

Each condenser 14 will have substantially the same electrostatic capacity as a sixty foot kw of the actual cab the effect of the dielectric hysteresis of the cable insulating material be closely sim-i ulated.

The attenuation will determine a current in the actual cable that will be somewhat as shown in-Fig. 2, where the abscissae represent distances in nauts from the sending end and the ordinates represent the currents at the corresponding ints in the cable.- At 100 nauts distance e current will have dropped from its sending value 0A to the value indicated by the ordinate DP. Supposing that the whole arriving current at this point were reflected back toward the end, the current that would get back to the sen end would be only that corresponding to e ordinate D'P'. But, of course, any reflection irregularity will roduce only a small .fraction of a total refiection. It will be apparent that for irregularities in the line further out, that is, say, further than 100 nauts along the cable, the effects due to partial reflections will be comparatively small at the sending end. Thus, it becomes apparent that it is the head end of the artificial line for which the most accurate adjustment is required, and that is the reason why the continuously loaded artificial line 11 has been employed for the head end as shown in Fig. 1 instead of an artificial line with lumped loadin After this continuously loaded artificial e has been carriedto a suitable length, as at the point- 17 in Fig. 1, it is continued in the form of an artificial line made up of lumped elements as will now be explained. I

For the part of the artificial line correspond' to the next few hundred nauts of the cab e, there are provided sets of elements in succession, each set comprising a series inductance coil 19, a series resistance 18 and a shunt condenser 20. To a first approximation, the inductance coil .19 has an inductance slightly lem than a certain definite length of the cable 10; the resistance 18 (with w atever resistance may be in the coil 19) is the same as the resistance of the same length ofthe cable 10, and the condenser 20 has the same capacity as the capacity of that same length of the cable 10.

Associated with each such group of coils Hand 18 and condenser there are also a small adjustable air core inductance coil The 21 in'series and an adjustable hi h resistance coil 30 in shunt to the con euser 20. The function of the resistance 30 is substantially the same as of the resistance 16. The con enser 20 is more nearly perfect than the distributed capacity of the cable, and

the resistance 30 in shunt to the condenser 20 makes the functional likeness more nearly exact. ductance coil 21 will be explained presently.

The magnitudes of the successive resistances 18 and coils 19 may be graded, being made smaller at locations closer to the bridge and thus facilitating closer adjustmentwherethesimulation to the actual line needs'to be more exact. In this case the condensers 20 will be graded in like manner.

The use of the inductive material on the cable causes it to have an inductance L that is not constant but is dependent on the magnitude of the current. This may be pointed out with reference to Fig. 3. The curve 22 is the ordinary B-H curve for permalloy, with ap ropriate'scales for the co-ordinates. H stan s for applied magnetizing force and B stands for the magnetic induction developed in the material. The curve 23 in the same figure is the p.H curve where pzB/H. The values of H involved in cable transmission are low and they fall off vary rapidly with distance from-the transmitting end, so that beyond the first hundred nauts of the cable and in the corresponding part of the artificial line only a narrow range, say from O to X on ig. 3 is involved.

By the application of suitable constant factors of proportionality, the'p.H curve can also be regarded as an LI curve, where L is the inductance and I is the current. roblem of simulating the loaded line may c said to involve the problem of making the artificial line have the same Ll curve as the cable. This means that for corresponding points in the two lines, the LI curve shall be the same for both lines. In addition the hysteresis loss in the artificial line must be the same at each point as for the corresponding point along the length of the cable, but at points far out on the cable, its effect will be practically negligible, and the criterion of matching the LI curves will be sufiicient. If the inductance were constant the LI curve would be a horizontal line but its slope expresses the fact that the inductance is a ratio whose value varies dependently upon the. variation of the current. If the core material is different from permalloy then it must be worked at a flux density to compensate for the difierence and make the LI curve the same for the ermalloy loaded cable and the artificial ine. In. the present case, in order to make the lumped artificial line as nearly as possible like the cable, the same inductive material is employed, that is, the cores of the The purpose of the adjustable incoils 19 are made of permalloy, heat-treated and otherwise prepared in the same way as the permalloy tape wound on the cable itself. By this feature of construction an imp-p111:- tant step is taken to make the artificial e closely simulate the actual line.

cores of the inductance coils 19,

Not only is permalloy employed for the ut in addi tion these coils and cores are designed so that the permalloy is worked at the same magnetic density as in the cable, that is, if a steady current .of a certain number of microamperes flowin duces a certain flux ensity in the material ofthe surrounding tape, then the coils 19 are designed so that the same current flowing in their windings will produce the same flux density in their core material. In this way, the assurance is gained that the same curve 23 in Fig. 3 will be followed for corresponding points of the cable and the artificial line.

In the cable certain losses due to eddy currents in the loading material will be inevitable and accordingly the cores of'the coils 19 are laminated to such a thickness as to make the alternating current losses here the same as in the cable for the same currents in the respective conductors.

Another feature of construction that is employed in connection with the series inductance coils 19 is to make them with air gaps and to make these air gaps adjustable. The purpose of the adjustable air gaps is to adjust the inductance of the coils. An increase of the air gap will diminish the inductance of the coil, and vice versa. However, the same increase of the air gap that diminishes the inductance will more rapidly diminish the rate of variation of the inductance with current strength. In other words, referring to Fig. 4, an increase of the air gap, will change the LI curve from 27 to 28, but if the ordinates are multipliedby a constant-for curve 28, it cannot be brought to coincide with curve 27 but may be brought to such a locus as curve 29. This is shown by the following considerations.

Let

M=magnetomotive force impressed in the circuit,

Rzreluctance of circuit,

B=fiux density at the air gap, lzlength of the iron portion of the circuit,

Z =length of the air gap,

Azcross-sectional area of the air gap,

H =magnetic field intensity in the iron,

The equations of a magnetic circuit comprising a number of 11'011 elements of various along the cable prodimensions and permeabilities, and an air gap, are- M=BA-R (I) and- I h=2 (2) MA: A

Zl,=l

where g. may be considered as the mean permeabllity of the iron. Equation (1) becomes a and can be written in the two forms- H=HX+HRI and where a may be termed the effective permeability of the air gap, is the effective permeability, and H= is the mean magnetic field intensity around the circuit or the actual field intensity in the absence of an air gap. From equation (4) p. can be computed when the value of p. and the dimensions of the air gap are known.

The variation of the effective permeability with impressed field intensity H will now be determined. For small values of H the p.H curve for iron can be written- =no( therefore- B F( l) i =I o i l o l l o l and- Fe whence- This relation can inverted by substitutwhereterms of a, b, p...

(4). Substituting (8) in (6) gives B in terms of H- whence From equations (10) and (11) it is evident that the introduction of an air gap in a magnetic circuit causes 'a' much greater reduction in rate of change of permeability than in the permeability itself. For example, if the air gap is such as to reduce where the initial effective permeability of the circuit to one half its previous value the rate of change of permeability is reduced to oneeighth its former value for small values of H, or the ratio of rate'of change ofpermeability to initial permeability is reduced to one-fourth of its former value.

Having provided for adjustment of the air gap of each coil 19, the foregoing considerations show that this introduces an undesirable change in the ratio of rate of change of inductance to current strength. With the end in view to compensate this efiect, the small series adjustable air core inductances 21 are employed. By means of an adjustable inductance 21, the inductance can be varied Without varying the rate at which the inductance changes with current? so that with the two adjustable'coils 19 an 21, a desired adjustment of both of these factors can be secured.

Farther out on the artificial 'line a dif ferent method is employed for adjusting the inductance of the coils, as shown for the coils .19. These may be made with rmalloy cores like the others, but they 0 not have adjustable air gaps and the adjustable air core coils 21 are not employed. v

and resistances designated 32 in and Around each core for the series artificial line windin s 19 there is a separate conductive win ing 24 and in circuit therewith a battery and an adjustable resistance 25. As shown in Fig. 5, it will be seen that although L varies with I ordinarily as shown by curve 27, yet for a superposed direct current and a narrow range of associated variable current, the apparent value of L 'varies as shown by curve 26. By adjusting the direct current in the winding by means of the adjustable resistance 25 the core is kept at any desired point on the curve 26 of Fig. 5,and since the ordinates of this curve represent inductance it will be seen that an adjustment of inductance is secured bythis-means. w

Still farther out on the. artificial: line, where reflection;irregularitieswwi1l.- be e'xsaid sections and in series therewith.

' 3. An artificial line comprising continuously loaded conductor sections m series, lumped im dance elements between said sections an in series therewith, and shunt lumped impedance elements connected between said sections.

4. An artificial line comprising continuousl loaded conductor sections in series, and umped inductance elements between said sections.

5. An artificial line comprising conductor sections in series, each with uniform inductance in substantial amount, and small adjustable lumped inductances alternating with said sections in series.

6. An artificial line comprising continuously loaded conductor sections in series and small adjustable lumped inductances and resistances between consecutive section in series. I v

7. An artificial line comprising contin-- uously .loaded conductor sections in series, shunt condensers connected between consecutive sections, and high resistances in parallel with said condensers.

8. An artificial line comprising conductor sections continuously loade with a magnetic alloy consisting chlefl of nickel and iron,

adjustable lum in uctancev elements between said sect ons and in series therewith,

umped impedance elements between I tinuously loaded with a magnetic alloy consisting chiefly of nickel and Iron, and an artificial line for balancing said cable comprising two sections of conductor of the same kind as the main cable core and loaded with said alloy in the same manner, an adjustable lumped inductance between said tions, a pluralit of lumped inductance coils in said artificial line more remote from the connection to said cable than said continuously loaded sections, and a core composed of said alloy for each of said coils.

10. In combination, a smooth signaling conductor, transmitting and receiving apparat'us associated with one end thereof and a balancin that end, t e part of said line nearest said end comprising series connected sections of smooth conductor like said signaling conductor in respect to the series impedance characteristics thereof and lumped shunt impedance devices connected in alternation with said sections. corresponding in value withrthe shunt impedance characteristics of the portions of the signaling conductor of the same lengths as the corresponding sections.

11. In combination, a smooth signaling conductor, transmitting and receiving apgaratus associated with one end thereof an a balancing artificial line connected with that end, the part of said line nearest said end comprising series connected sections of smooth conductor approximately like said signaling conductor and small adjustable lumped elements in series between the sections tofacilit-ate exact adjustment.

12. In combination, a smooth signaling conductor, transmitting and receiving apparatus associated with one end thereof, and a balancing artificial line connected with that end, the part of said line nearest said end comprising series connected sections of smootliaconductor like said signaling conductor, condensers connected in shunt between the sections and having substantially the same capacity as lengths of the signaling conductor corresponding to said sections, and adjustable resistances in parallel with said condensers to make the total shunt path at each point between' sections of the same value and character as the distributed shunt path for the corresponding part of the signaling conductor.

13. In combination in an artificial line, sections of continuously loaded conductor, small adjustable inductances and resistances interposed in series between such sections and adjustable condensers and resistances connected in shunt between said sections.

14. In combination, a signaling conductor loaded continuously by means of a certain permeable material, transmitting and. re-

ceivmg apparatus associated with one end artificial line connected with thereof and a balancing artificial line concomprising coils with .the same material sectlons, a shunt condenser between said secf or their cores. 4

,15. In an artificial line to simulate a con- I tinuously loaded'line, inductance coilshaving adjustable air gaps.

16. In an artificial line to simulate a continuously loaded line, inductance coils having adjustable air gaps and in series alternation therewith adjustable air core inductance coils.

17. In an artificial line to simulate a continuously loaded signaling conductor, two

kinds of adjustable inductance coils in series alternation, one with a core of permeable material and an adjustable air gap, the other with an air core and adjustable as to its inductance, whereby, with relative adjustment, the signaling conductor can be simulated.

18. In combination, a signaling conductor continuously loaded with'a certain permeable composition, transmitting and receiving apparatus associated withone end thereof and a balancing artificial line connected with that end and comprising coils with cores of the same said material and with adjustable air gaps, the dimensions of said coils and cores being such that the material isworkedat the same magnetic flux density as on the signaling conductor.

19. In combination, a continuously loaded signaling conductor, transmitting and receiving apparatus associated with one end thereof and a balancing artificial line connected with that end, said artificial line com prising inductance; coils with cores, .said coils and' cores being proportioned togive the same inductance current characteristic in the artificial line as in the signaling conductor.

20. In combination, a continuously loaded signaling conductor, transmitting and receiving apparatus associated with one end thereof and a balancing artificial line connected with that end, said line comprising coils and cores with adjustable air gaps for which the adjustment varies the inductance less than the rate of change of inductance with current, and adjustable air core coils in series by which com nsation may be effected to make the artitib ial line simulate the loaded conductor.

21. In combination, a signaling conductor continuously loaded with a magnetic alloy smooth conductor continuously loaded with said alloy like the signaling conductor and the said line farther out comprising coils having cores composed of said alloy. v

22. In combination, a continuously loaded signaling conductor, transmitting and receiving apparatus associated with one end thereof and a balancing artificial line connected with that end, said line comprising series elements and shunt condensers at intervals, each said condenser having an adustable high resistance in parallel therewith.

23. In an artificial line to simulate a continuously loaded signaling conductor, inductance coils in series and resistances connected in series alternately with said coils,

the values of said resistances being enough,

when taken with the resistances of the inductance coils to simulate the line with respect to both inductance and resistance.

24. In combinatioma continuously loaded signaling conductor, transmitting and receiving apparatus associated with one end thereof and a balancing artificial line connected with that end, said line comprising inductance coils with cores of permeable ma- -terial, auxiliary coils on said cores and adustable direct current sources to energize said last mentioned coils.

25. In an artificial line to simulate a continuously loaded signaling conductor, in-

- ductance coils with cores of the same mate- 27. The'coinbination with a continuously loaded signaling conductor, of an artificial line simulating said conductor including inductance coils with cores of the same material as the loading material, said coils and cores being designed to have an LI curve for each point of the artificial line simulating that of the corresponding point of the signaling conductor and also simulating the hysteresis loss of the loaded signaling conductor.

' 28. The method of producing a balancing impedance in an artificial line equal to the impedance of a signaling conductor eontinuously loaded with magnetic material, which consists in working the magnetic material at each point of the artificial line on approximately the same LI curve as for the corresponding point of the signaling conductor.

29. The method of producing a balancing impedance in an artificial line equal to the impedance of a signaling conductor continuously loaded with magnetic alloy, which consists in working the magnetic material at each point of the artificial line on a proximately the same LI curve as has t e corresponding point'of the signaling conductor and at the same hysteresis loss.

'30. The method of adjusting the inductance of the coils in an artificial line to balance a continuously loaded signaling conductor, which consists in introducing a variable amount of substantially constant permeability substance in the magnetic circuits of at least a portion of said coils.

31. The method of adjusting the inductance of coils in an artificial line to balance a continuousl loaded signaling conductor, which consists in super-posing the field of a local direct current on the cores of said coils and adjusting the magnitude of said direct current.

In witness whereof, I hereunto subscribe my name this 2nd day of August A. D., 1922.

OLIVER E. BUCKLEY.

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