US1008282A - Selective telephone signaling system. - Google Patents

Description

0,11; NORTH. SELECTIVE TELEPHONE SIGNALING SYSTEM.

APPLICATION FILED 001. 11, 1907. 1,008,282.

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UNITED STATES PATENT OFFICE.

CHARLES H. NORTH, OF CLEVELAND, OHIO, ASSIGNOR TO THE NORTH ELECTRIC COM- PANY, OF CLEVELAND, OHIO, A CORPORATION OF OHIO.

Specification of Letters Patent.

Application filed October 11, 1907. Serial No. 396,933.

To all whom it may concern:

Be it known that I, CHARLES H. NORTH, a citizen of the United States of America,

and a resident of Cleveland, in the county" of Cuyahoga and State of Ohio, have invented certain new and useful Improvements in Selective Telephone Signaling Systems, of which the following is a specification. 4

hIy invention relates to a selective telephone-signaling system, affording for telephone exchanges an improved method of selective signaling, and has for its object the modification of selective signaling methods of the prior art, which shall be an advance in efliciency and eliminate false signals.

More particularly, my invention is ap plicable to telephone systems, wherein selective calling or signaling of a plurality of subscribers upon a given line is required, and my invention has been perfected with this single end in view, whereby signaling currents are impressed upon the line alternatively, which shall avoid the more or less active tendency observed in previous signaling systems to actuate two or more of the selective calling appliances.

Until a compa 'atively recent date, it has been deemed commercially practicable to actuate signaling systems known as harmonicringing systems, by means only of generator currents, which are respectively in step or tune with the signaling appliances used upon the multiple party lines. These currents, by reason of the fact that a single generator outfit was almost universally use(; in practice, operating at a substantially fixed rate of speed, presented in frequency of alternations, multiples of 2, 4, 6 and 8,' corresponding to the respective brushes of the dynamo. In consequence, there existed a coincidence in the electromagnetic impulses, which constantly tended to interfere with the successful working of the system, and produced false signals, particularly for any extended or intermittent period of signaling or ringing. Prior to my application of the, principles of non-coinciding currents to selective signaling, I believe that the undesirable feature just alluded to,

had never been theoretically or practically overcome.

Although I do not deem my invention restricted to particular apparatus, it may most readily be practiced by the employment of interrupters having definite rates of speed, in association with a source of direct current, but commutator devices, one of which I shall briefly advert to, may also be resorted to for practicing my invention, as herein described and claimed.

Before explaining the means for practicing my invention, I may state, in a preliminary way, that the system of telephone signaling herein set forth, is one wherein the signaling currents adapted to beimpressed upon the party line, are of such frequencies that they are non-coinciding in 'efl'ect upon the several translating devices or ringers. In the simple four-party line system, set forth for the exemplification of my improvement, the current frequencies are multiples of '5, 7, 9 and 11, whose respective effects, I shall best be able to explain in connection with diagrammatic representations plotted to indicate the different currents throughout their periods of noncoincidence, and compare them with a diagram similarly plotted to represent the commercial four-party signalingcurrents known to the prior art.

In said drawings, Figure I, represents a telephone system equipped with interrupters and signaling bells assumed to be respectively tuned in accordance with my im provement. Fig. II is a cross-sectional view of a commutator device; and Fig. III is a viewin side elevation of said multiple commutator, which represents other means for applying non-coinciding currents to a tele- Patented Nov. 7, 1911.

phone signaling system. Fig. IV is 3. diag'ammatic representation of the electromagnetic effect of the four partially coinciding signaling currents of the prior art,

and Fig. V is a similar diagram of the the theoretical sine-wave, which the signaling currents approach, but I have employed. straight lines meeting at angles instead of such curves, for making more apparent the peak, or eii'ective magnetic variation of the respective alternating currents ct \dill ercnt frequencies. These same diagrams may be taken, as well to indicate the respective relations between the preferred alternating currents employed in practicing my invention, but this specification may be made a little more direct and clear, by alluding to the diagrams as representative of the magnetic ettiect ant. relations resultant from said currents. Fig. V1 is an enlarged detailed diagram of an interrupter-device.

'lhroughout the several figures of the drawings, 1 have employed the same character oi rt-zfereuce to indicate similar parts, or corresponding diagrammatic representations.

As stated, the alternating currents for selective singnaling, may be arbitrarily varied, so long as substantially the 1101 harmonic or discord relation exists between the respective currents. Thus, for five-party selection, the cycles per second may best range between 30 and 78, being multiples of the odd numbers from 5 to 13 inclusive.

Fig. 1 representing the preferred means for practicing my invention, will be explained in more detail as it embodies novel features in addition to those herein claimed. in said. figure are shown four sets of in terrupters, which are so adjusted with respect to each other as to impress alternating currents when' respectively connected to line, which have frequencies representing substantially the multiples of live, seven, nine and eleven; these'iour being the simplest combination for practically operating selective signaling systems, In this instance, we may further assume that the common multiple is six, which I have found most desirable for practical purposes. Accordingly, the respective intt-irrupters a, a, 0i and a-'* will. be so constructed and justified as resppctively to impress upon the line alter nating currents of thirty, forty-two, fiftyfour and sixtysix alternations per second.

Explaining first the structural features of the interrupter, it will be seen that-the vibrating member or reed a, equipped withv a variable weight a", is designed, undrr. the influence of laterally positioned electromagnates bb, alternatively to engage the contact springs c 0 thereof. These electromagnets each comprise a high and low re sistance coil 17 b shunting each other and terminating respectively in the contact spring 0 c.

In the preferred embodiment of my invention, the source of current, as battery B, has one of its poles connected directly with the tongue or vibrating member 'a of the while the other pole of the batinterrupter, tery is connected directly with the high their respective excitations generate poles of "like sign in each of the magnet cores. The

reed or tongue a preferably is of steel and is polarized, more readily to respond to, the

about the contact springs 0' 0 and their respective associated windings I) b is the condenser e.

As shown in the diagram, Fi 1, the secondary (Z of each converter d, is connected through a resistance lamp cl? with the corresponding contacts e, 6 6 e of an operators selective key, controlling the flow of current to the calling plug p of the cord .circuit, which is shown inserted in the pack p of a four-party selective telephone line. Each station upon said line, connectedbetween conductors l, 2, is designated by a signaling bell f, P, f, y with its'associated condenser the ordinary sub-station apparatus being omitted as unnecessary. Moreover, the customary cord circuit and line signaling apparatus is conventionally indicated in the. diagram, sufiiciently to illustrate the principal application ot the invention, but I do not consider that these features require explanation herein.

Each of the interrupters a, a a a is connected in circuit precisely as explained above, employing converters (1 whereby to transmit current to the signaling circuit, but the reeds or vibrating member of said intcrrupters and their weights, are respectively made stiffer and lighter for the high frequencies, and more flexible and heavier for the low frequencies. sired number of these adjusted interrupters may be employed. \Vith respect to the windings upon the electro-magnetslb b of these interrupters, vided with more turns upon the high frequency interrupter-s than upon the low, while the co-a'cting shunt coils are provided with fewer turns upon the coils of the high freterrupters. Preferably this is found to be desirable in practice, for the reaso'u that with the stitl'er reeds and higher rates of vibration, more work must be done by the high 'lrcqucncy electro-magnets, and as an ex am le of a i )roximatel the referred numl l P excitation of the magnet coils. Bridgedljractically any de-- I quency interrupters, than upon the correspondmg windings of the low frequency 1nthe series coils, are prov Current then flows through windings m i will be. well understood. causes altermiting her of turns for a tour-party line employing twenty-four volts on the primaries, I may say that the highest frequency interrupter will have 100 turns upon its series coil, and

6500 turns upon the shunt coil, while the lowest frequency interrupter will have 4.0 3

turns upon the series coil, and 12,500 turns upon its shunt coil; the windings upon the other interrupters bein intermediate of these two. I have preterably wound the secondaries to generate 160 volts in the .naling circuit, and this I findjis transmitted with relatively small drop in voltage, even to the most distant stations. This is because of the fact that the series coils are energized by the full flow of current and'impart a more powerful vibratory movement to the contact member (1, thereby insuring a longer closure of the respective magnet circuits,

tending to secure approximate magnetic saturation ot' the iron body of the converter, and thereby transmitting the maximum voltage from the secondary winding. This operation probably will be better understood by making further reference to the diagram, Fig. I, and assuming that one of the stations is to be rung, as station 7'. Assuming too.

that the line has been tested, and the calling plug inserted in the proper jack, the operator will actuate her selective key, closing together the contact a. All of the interrupters are in operation under the impulse of their respective shunt windings, but immediately upon the closure of the contacts a, the impedence of the converter connected with interrupter a will at once be reduced, thereby permitting the flow of exciting current through the divided primary windings (2'. Current may be traced from the upper pole of the battery, through the connnon conductor to the. vibrating member a, contact 0, series winding 7/, the right hand portion of the primary winding 1?. and conductor 3 to the lower pole of the battery. The vibratory member is augmented in its motion and is actuated by the series winding out of engagement with contact and into engagement with contact 0, thereby opening circuit with contact and its connected windings, and closing the circuit with contact 4- and the connected windings upon the lc'lt.

thereof, and theleft hand coil of the primary winding (Z' upon the converter. This, as

the sleeve of the plug. the contacts of the operators key, and contacts (1' (assumed to be closed), and conductor 5 to the right hand 1 side of the secondary windings. The bell f, will, ot course, respond to this current ot proper trtapicncy, while the remaining bells upon the line circuit will fail to be actuated, as will be well understood by those. conl versant with the art.

In practice. each of the interrupters. upon installation is connected in circuit as shown. The adjusting screws 1/ are separated to such an extcnt that neither of the contact springs c c is in engagement with the vibratory member (I. ()ne of these screws as 5/ is then turned until the contact spring c is brought into engagement with the contact of the vibratory member. whereupon it will start under the impulse of but a single magnet. This screw then turned back slightly. say to the extent of one quarter turn, aml the opposing screw y is'thcn turned until tln contact I" similarly is brought into engagemcut with the contact of the vibrating member, whereupon this screw is also set in its ad: justed position and the interrupter device will continue normally underthe impulse of its shunt windings. It will be scen, however, that with a slight bias, the vibrating member may be actuated by a single electromagnct, but preterably l employ the arrangemcnt herein set forth. The mechanical features thereof are explained at greater length and claimed in the application of John F. Engle, tiled June 12th, 1907, Serial No. 378,549.

The respective sets of brushes j engage the commutator segments, and the same are arcs provided in their su 'iporting standards From these brushes, the respective alternating currents are taken off in lieu of the. 1 several transformer currents of Fig. I, to which they may correspond in non-harmonic relation. are respectively provided with an increasing number of segments, which are so coupled or connected together between their terminals m by cross wires in disposed. therebetween, as to secure substantially non-harnating currents. This relation is also ads i ustable or alter-able in .large measure by ing supported between the bearings 71. 71

imlividually adjustable within the slotted' The several cominutators 7"y'*' monic relation bet ween the respective altcr- Instead of the interrtmters, I may em-- 'em ploycd moving the respective brushes within their arced paths. The relative number of cycles per second, will, of course, be dependent upon the speed at which the multiple comn'mtator device is rotated, and since substantially constant speed is requirethl do not recommend or rely upon the mechanical features just above explained in practicing my invention. Connnutators or rotary contacts 2' 2', are merely slip-rings engaging the main brushes, and are suitably connected up with the multiple COllllIlllttll'OL contacts.

Iii-order to present my invention graphically and more clearly, I have plotted the diac' arms of Figs. IV and V, the former of which is representative of the standard four-party frequencies of 16%, and 66% cycles per second. The latter is representa tive of the current frequencies, preferably in practicing my invention. It

will be appreciated, that as between the frequencies of 33,, and 50 cycles per second, there exists the relation of a musical fifth, while between all of these current-cycles, excepting only the third, or 50, there exists the octave rcla on, hence the propriety of terming the systems of the art harmonic signaling systems.. The most casual comparison of these two figures, IV and V, demonstrates the vast superiority of the nonharmonic currents for selective signaling. Fig. IV, shows the coincidence of the four harmonicalternating currents, which occurs e: ch .06 of a second, as opposed to the nonharmonic currents which coincide only six times each second, above the zero line. By reason of the necessary coincidence of the harmonic currents, false signals are constantly liable to occur, particularly as between the currents havingrespectively 16%,- and 50 cycles per second, which are in co-' incidence during two-thirds of the time.

' Another frequently observed source of 1nterferences, is the coincidence likely 'to 00- our when the armatures of the bells, responsave to currents having cycles per second,

, are slightly off center, thereby materially employcd upon party phasizing-the disturbing coii'icidencc during half of the swing of said armature. More than this, bells responsive to the lowest frequency, are open to the serious-objection of being. responsive to currents transmitted by the ordinary hand generator, frequently em- When frequencies of substantially 30 cycles per second, or higher, are employed, however, it is impossible'to ring any of the selective bellsby means of a hand generator, for. the reason that it is impossible to turn the generator fast enough -'nanually. it; will he iobservcd, that in the neferred frequcncies, employed in practicing my in vcntion, the lowest. frequency corresponds approximately with the second frequency effects of these currents are employed in the prior art, and the objection last alluded to, is at once eliminated. Considering Fig. V, it is seen that the magnetic non-coinciding above the zero line, throughout the relatively long period of one-sixth of a second, and because of the diversity of these current effects, false signals are rendered impossible with the use of non-harmonic currents. To recapitulate, in comparison" t' these preferred methods of selective sign-aiing, itwill be noted as stated above that the frequencies employed in the non-harmonic system bear the relation of discords to each other, whereas the frequencies employed in the bar nonic system bear, as the name would indicate, the relation of harmonics to each other. For example, reduced to their lowest terms it will be observed that the HOD-lltll'illOlllC frequencies bear the relation to cach other of 7, 9, and 11, while the harmonic frequencies bear the relation to each other of 1, 9, 3, and 4.

One of the chief ditliculties encountered in the operation of the harmonic system has been due to the liability to cross ring. This tendency has been particularly noticeable between the 16% cycle and the 50 cycle ringers. although the other frequencies have not been entirely free from the same charactcrof trouble. Upon analyzing; the waves of the arious cycles or frequencies the reason for this interference is quite obvious. The laws governing the vibration of nonharmonic and harmonic ringers, vibrators or polc changers are the same as those gov erningjthe vibration of musical reeds or springs. lt-iswell known that if a reed of any pitch or frequency is vibrated, all other reeds in close proximity to it, or which are subjected to the same force which actuates the reed in question, in synchronism or harmony with the reed vibrated arealso caused to vibrate. l/Vhen one vibrating reed. in close proximity to another causes the latter to vibrate, it is known as sympathetic vibration.

Sympathetic vil'n-ation is most pro nounced between two synchronous reeds, or reeds vibrating in the same period and as between these two reeds perfect harmony exists. .Next in matter of harmony is the octave, as where one reed vibrates twice as, rapidly as the other. Next follows the fifth with a ratio of two to three. It will boobscrvcd by reference to the ordinary harmonic frequencies that we have the ratio both of octaves and fifths between the sovcral frequencies, and when a current of any -iven t'rta'ptcncy is impressed on the line, it naturally follows that any ringer tuned-in synchronism with the ringing current, will respond. This is as it should he, as this is the principle upon which the system is and which are either are of uniform capacity.

based, but it also follows that any ringer. in l harmony with the impressed current will also respond to a greater or less degree. dependent upon the ratio of coincidence. This latter application of the principles involved is the real root of the cross-ringing trouble experienced in harmonic systems. and it is seen that making one reed of such asystem in harmony with another reed of a different frequency is really a violation ofv the very principle upon which the system is based, and upon which it depends for its margin of safety.

In harmonic systems the margins are so small as to make it necessary to wind the ringers to different resistances. The 16 cycle ringer is wound to 2500 ohms; the 33,, cycle from 500 to 2250 ohms, and the 50 cycle and, 66% cycle ringers are usually wound to 500 ohms each, although the mar gin of safety could be made somewhat wider by aarying these windings somewhat from those usually employed. In the herein described non-harmonie system, all ringers may he wound to the uniform resistance of 1000 ohms, and are in all respects precisely alike with the. exception of the weight on the armature. 'Ihearmatures for the various frequencies preferably are interchangeable. and if it should be desired to change a ringer from one frequency to another the only thing which it is necessary to do is to remove the armature from the ringer 1 and replace it by an arn'iature properly adjusted for the frequency upon ,which'the-ringer is to be used. This makes it unnecessary to keep a stock of ringers for the different frequencies on hand, but instead a supply of these interchangeable armatures alone is required. The margin of safety in the harmonic systcn'i is so slight as to. make extremely accurate adjustment of the ringers necessary. and it is also essential that the condensers used in series with the ringers Vvith the nonharn'ionic system having much wider mar gins, ti extreme care. in adjustment and in the sleetion of condensers is not required. in the case of the foregoing system it will he noticed as stated above, that the frecords to each other, and by using (these fre quencies the element of sympathetic vibrationand consequent cross-ringing is eliminated and the working margin greatly amplified.

Metallic circuit lines affording the best and mostapproved method of practicing my invention, have been considered alone herein, but it will be appreciated that the number of possible party line stations may be doubled with a given number of selective signaling currents. merely by resorting to the expedient of ringing over either limb of the metallic line to ground, in a manner well known in the art.

In the foregoing. I have endeavored to set forth the preferred practical details, and the theories of operation as understood by me, but I do not wish this to be interpreted as necessarily limiting my invention to such detailsfand accordingly claim the following:

1. In a system of the class (lQSCIibGththQ combination with a central telephone exchange, of a plurality of multiple-station telephone-lines connected therewith; each of said lines being equipped with selective-signaling apparatus at the. different stations respectively tuned to respond to currents of different inharmonic frequencies, and the said telephone exchange being equipped with calling-apparatus producing currents of corresponding inharrnonic frequencies, substa'ntially as set forth.

2. In a system of the class described, the combination with a telephone exchange equipped with signaling-apparatus produc ing currents approximately of 30, 4:2 and 54 cycles per second, of a plurality of multiplestation telephone-lines connected with said exchange; each of said lines being equipped with selective-signaling apparatus at the different stat-ions. respectively tuned to respond -to currents of these inharmonic frequencies,

substantially as set forth.

3. In a telephone exchange system, the combination with central-office equipment, including sources'of alternating signaling currents Whose frequencies are substantially multiples of five, seven. and nine, of amultiple-station telephone-line, including at carpi} station a signaling device respectively.

tunedto respond to currents of the different frequencies, substantially as set forth.

4:. In a telephone exchange system, the combination with central-oflice equipment, including a source of current and associated converter and interrupter devices adjusted to supply currents of diflerent non-harmonic frequencies, and a multiple-station telephone-line including at each station a. signaling-bell respectively tuned to respond to currents of the different frequencies, substantially as set forth.

5. The combination with a telephone switchboard, of sources of signaling currents adapted alternatively to be connected in circuit with a called line; said currentsbeing of non-harmonic frequencies, a multiple-station telephone-line connected to said switchboard .and at each station a signaling-bell respectively tuned to respond to currents of distinctive frequency, substantially as set forth.

6. In a telephone exchange system, the

combination with central-office equipment,

rupter devices adjusted to deliver currents of I Signed zit Cleveland, this tenth day of different n0n-lmr1n0nic frequencies, and a October, A. D. 1907, in the presence '01 two plurality of multiplestation telephone lines subscribing Witnesses.

extending to the central-office; and at each CHARLES H. NORTH. 5 station a signaling bell tuned to respond to Witnesses:

currents of one of the n0n-harmonic fre- Jesse A. BUEL,

quencies, substantially as set forth. ALBERT LYNN LAWRENCE.

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