US242092A - Stephen d - Google Patents

Description

(N0 Model.)v

S. D. FIELD. Rheostept.

Patented May 24,1881.

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III/IIIA UNITED STATES PATENT OFFICE.

STEPHEN D. FIELD, OF NEW YORK, N. Y.

RH EOSTAT.

SPECIFICATION forming part of Letters Patent No. 242,092, dated May 24, 1881.

(No model.)

To all whom it may concern Be it known that I, STEPHEN D. FIELD, a citizen ot' the United States, residing in the city, county, and State of New York, have invented certain new and useful Improvements in Rheostats for Duplex Telegraphs, of which the following is a speciication.

My invention relates to certain improvements in apparatus for the transmission ol" independent telegraphic signals simultaneously from opposite ends of the same line.

The object of my invention is to neutralize or prevent the production of the false signals which tend to be manifested upon the receiving-instrument at the transmitting, or, as it is technically termed, the home, station, by the so-called static discharge,7 which consists in the sudden escape to earth of a quantity of electricity stored up or accumulated upon the main line by inductive action during the outward flow of the electric current, which takes place when a telegraphic signal is transmitted.

The invention relates more particularly to an improved construction of the rheostat which constitutes the equating` circuit, commonly termed the artificial line, and it consists in forming the said rheostat of two parallel conductors, placed in close proximity to and insulated from each other, the said conductors being of substantially equal length, but having different resistanees. These are joined together at one end to form a loop, which is inserted n the artificial line and forms the principal portion thereof.

In the accompanying drawings, Figure l is a diagram illustrating the principle upon which my apparatus is constructed. Fig. 2 is a diagram showing the manner in which the length of the artificial circuit may be varied. Figs. 3, 4, and 5 show different modifications in the construction of my apparatus.

In Fig. l I have represented one terminal station arranged for duplex transmission according to the ordinary method, together with aline extending to the earth at the distant station.

K is an ordinary open circuit or three-point key, the rear contact-stop, 3, of which is conn nected directly to the earth, while the front contact-stop, 2, is connected to one pole of a battery, E, the other pole of which is to earth.

m m are the two equal and opposiu helices oi' a differential electro-magnet, M, which actuates the receiviiig-instrument. Then the key K is depressed and brought in contact with its front stop, 2, a current from the battery E passes through the key to the point 1, where it divides, one portion going by the wire 4, through the helix m, over the line L, to the distant station, and thence to the earth at g, returning through the earth to the opposite pole of the battery. In like manner the remaining portion of the current goes, by the wire 5, through the helix m', thence through the artificial line L L2 to the earth at g', and thence returns in like manner to the other pole ot' the battery. This latter branch circuit is technically termed the artificial line in order to distinguish it from the mainline, which eX- tends to the distant station. It' the resistance of the articial line be so adjusted as to be approximately the same as that ot' the main line, the current transmitted by the key will divide at the point l into two equal portions, which will produce equal or opposite electrodynamic effects upon the armature of the electro-magnet M, and the said armature will therefore remain at'rest when the key Kis depressed, notwithstanding that a current is passing over the line L to the distant station. It, however, the distant station transmits a current from its own battery (not shown) at the same time, the strength ot` the current in the main line is augmented by the combined action of both terminal batteries, its electro-dynamic effect overpowers that ot' the current of the artificial line, the armature of the electro-magnet M is attracted, and a signal produced at the home station. Thus it will he understood that the receiving-instrument at the home station responds only to currents or signals comin g from the distant station, and not to those transmitted by the key at the home station, and consequently the two stations, when provided with similar apparatus, can transmit signals simultaneously to each other without interference, the receiving-instrument at each station, although at all times traversed by the current ofthe main line, responding only to the signals produced by the transmitting-key at the other station.

In order to produce the result hereinbet'ore IOO set forth it is obviously essential that the resistance of the artificial line should be as nearly as possible equal to that of the main line. rlhis has heretofore been effected by placing one or more `rheostats in the artificial line. These consist of a suitable length ol" comparatively thin wire, preferably made of some metal which is a poor conductor ot' electricity. A sufficient length of such wire is wound upon one or more spools or bobbins, and so arranged in connec tion with connnutators that any required length ot' it may be included in the circuit of the artificial line. By this means an equal division of the current from the battery E between the main and artificial lines may be readily brought about.

Having thus explained the construction and mode of operation of an ordinary duplex-tele graph apparatus, I will next describe the nature of my present improvement, and the manner ot' its application thereto in the best. man- {lel DOW kllOWll t0 111B.

Itis well known that an insulated telegraphic line-wire of considerable length, whether suspended above the earth or submerged beneath the water, is capable of accumulating or storing up a quantity of electricity while connected with a source ot' electricity. This property of an insulated conductor is termed its inductive77 or electrostatic capacity, andthe electricity so stored up and retained is called the static charge77 ot' the conductor. The electrostatic capacity ot the insulated conductor is a quantity depending upon the extent of its superficial area, and upon the thickness of the non-conducting space which separates it from the earth, or from other conductors in electric connection with the earth, which insulatingspace is called the dielectricl7 Thus in the case of an ordinary telegraph-liuc suspended upon poles in the air the earth and the surrounding objects connected therewithsuch as buildings, trees, and the like-form the outer inductive surface, while the air constitutes the insulating medium or dielectric surrounding the conductor. ln the case of a submarine cable the insulating-coating ot' guttapercha constitutes the dielectric, and the iron armor ofthe cable, or the surrounding water, asthe case may be, the outer ind uctive-surface. It will appear, therefore, from the herein beforementioned considerations, that when a long line of telegraph is connected with the battery by depressing the key at the sending-station, as for the purpose of' transmitting a signal, the line will acquire a considerable static charge. At the completion ofthe signal, when the key is raised, the line is first disconnected from the battery and immediately afterward connected directly to the earth at the home station, whereupon the accumulated induced electricity stored up in the line will suddenly escape to the earth, traversing one coil of the electromagnet M of the home receiving-instrument, and producing what is termed the static disin which it is placed have practically no electrostatic capacity, there will be no corresponding discharge from the artificial line through the opposing coil oi' the electro-magnet M, and consequently an extra or false signal ot' short duration will be produced by the uncompensated action of the static discharge of the main line in the electro-magnet.

I have discovered that the disturbing efi'ects of the static discharge from the line upon the apparatus at the home station maybe compensated or neutralized by an improved construction of the equating-rheostat which constitutes the principal portion of' artificial line, by which method of construction it is placed under electrical conditions corresponding to those of th'e main line.

In Fig. l the main circuit consists ot' a lincwire, L, which we may assume to have a total resistance of, say, tive thousand ohms, extend ing to the distant station, and of the earth G, which constitutes the parallel return-conduc tor, and which has little or no resistance. Now let the artificial line L in like manner be coustructed of a thin wire composed of metal of inferior conductivity, but of sufficient length to otter a resistance of five thousand ohms, and let this bejoined at the pointl to another conductor ot' very small resistance, L2, laid parallel with it and extending to the earth at g or to the other pole ofthe battery. It is obvious that an inductive action must take place between the conductors L and L2 ot' the artificial line, which will correspond in its nature to that which takes place between the main-line conductor L and the earth G beneath it, and that these effects will balance or neutralize each other in the opposing coils m and m of the receiving-magnet M. I avail myself of" this principle in the construction of my improved rheostat, which consists ot' a conductor of great resistance and a conductor of' little resistance, equal in length, placed parallel to each other and properly insulated. The construction and arrangement ot' the rheostat may be modified in various ways, according to circumstances. lt may be rolled up in a flat spiral, as shown in Fig. 3, or upon a bobbin, as shown in Fig. et. I consider it preferable, however, to lay it to and f'ro upon a plane surface, as shown in Fig. 5. The particular arrangement, however, may be varied in many ways, so long as the principle is kept in View.

The electrostatic capacity of the open-air line L varies materially in differentconditions ot' the weather, being much greater in cold or dry weather, when the insulation is good, than in wet or damp weather, when the insulation is poor. It results from this that the efiect of the static discharge upon the home instrument is much greater at some times than at others. As the artificial line is not exposed to these changes in the weather, its electrostatic capacity and the force of its discharge remain practically constant.1 Hence, unless some charge.77 If1 the rheostat andthe artiicial line means are provided for adjusting this, the

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compensation will frequently become very imperfect. I therefore prefer to arrange my rheostat in a greatery or less number of sections, in the manner indicated in Fig. 2, with peg-oommutators or other equivalent devices placed between the sections, as shown at a, b, c, and

' d, whereby the length and resistance of the operative portions of the artificial line maybe varied at pleasure, and its electrostatic capacity likewise varied at the same time in corresponding` ratio.

I do not desire to limit myself to the use of the rheostat constructed substantially as set forth exclusively in connection with the particular form of duplex telegraph hereinbefore described, as it may be employed with equally good results in combination with ina-ny other known forms of such apparatus. The modifications necessary to adapt it to such use will readily suggest themselves to those skilled in the art without further description.

I claim as my invention- An equating-rheostat for duplex telegraphs, constructed, substantially as hereinbefore set forth, of two parallel conductors placed in close proximity to and insulated from each other, having substantially the same length, but different resistances, and joined together at one end to form a continuous conductor.

In testimony whereof l have hereunto subscribed niy name this 31st day of March, A. D. 1881.

STEPHEN D. FIELD.

Witnesses MILLER G. EARL, CHAs. A. TERRY.

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