US2373675A - Party line printing telegraph system - Google Patents

Description

L A. GARDNER ErAL l PARTY LIFE PRINTING TELEGRAPH SYSTEM 'A VA17, 1945.

. Find July 19. 1941 'r sneeia-sneet 1 Arron/wv April-17, '1945. 'AL GARDNER Erm. 2,373,675 '.PARTY lm m. PRINTING TELEGRAPn'sY-sTl-:u f Filed July 19,5;941 v' sneetsesneetj z v n i q s Fvg 'fsheetgshet s April?, 1945. L A..GARDNER E'rAL'.

PARTY L .In PRINTING TELEGRAPH -sYs'rEM Filed July 19, i941" `7 Smets-.sheet 4 y PAR'TYLINE PRINTING TELEGRAPH SYSTEM Ap 'l 17, 1945. L A'. GARDNER ETAL PARTY LINE PRINTING TELEGRAPH SYSTEM 7' Sheets-Sheet 5 Filed July 19, 1941' L. A. GAR

MER c/ukos ATTORNEY Ap 17, 194s..

'L.. A. GARDNER ET AL PARTY LINE PRINTING TELEGRAPH SYSTEM Filed vJuly 19,' 194l 7 Sheets-Sheet 6` April 17, 1945. l. A. .GARDNER ETAL 2,373,675

PARTY LN PRINTING TELEGRAPH SYSTEM V Filed July 19, 1941 '7 Sheets-Sheet 7 l l x MUL T/-SEC TION L /NF REPEA TER ATTORNEK Patented Apr. 1 7, 1945 PARTY LINE PRINTING 'TELEGRAPH A SYSTEM Leland A. Gardner, Maplewood, and vKenneth W.

Y Richards, Packanack Lake, N.J.,

assignors of 4one-half to Bell Telephone Laboratories, Incorporated,

a corporation of New York, and onehalf to American Telephone and Telegraph Company,- a corporation of New York Application July 19, 1941, Serial No. 403,116

(c1. ris-z) 11 Claims.

This invention relates to a communication system for transmitting signaling impulses lover telegraph lines or channels and more particularly to a telegraph system for connecting a plurality of outlying telegraph subscriber stations to a central exchange oflice over a single Wire telegraph line, channel or trunk.

The problem with which this invention deals is that of giving a plurality of remote subscribers or remote outlying stations access to and service over a teletypewriter exchange by means of telegraphic trunks or channels less in number than the number of subscribers. The cost per mile of such trunks is great and their more eflicient utilization is highly desirable. This problem has been solved successfully for groups of considerable numbers of subscribers, say fteen to one hundred, by satellite systems; see patent to Lucek 2,228,279, dated January 14, 1941, for disclosure of a typical system. The problem has also been solved for smaller numbers of, say five toten, subscribers in a group; see application of Large,

' Serial No. 37'?, 805, led February 7, 1941. Systems have also been devised to serve two and in some cases three or more subscribers over a single trunk. See Locke 2,225,648, dated December 24, 1940, and Goodwin 2,257,677, dated Sept. 30, 1941, and Knandel 2,306,734, dated December 29, 1942. Therefore, a specific object of this invention is to provide improved and more elcient systems of this class or systems suitable for somewhat diierent service requirements. A copending application of the present inventors, Serial No. 393,324, led May 14, 1941, relates to systems of this kind operating with code ringing, i. e., subscribers must answer only the number or combination of rings identifying their own station; in contradistinction one of the major featuresof the present invention is a semiselective automatic system of ringing whereby only the desired subscribers bell is rung. Except for practical limitations of relay design, etc. and potential delays due to a busy Y) trunk line the number of subscribers or outlying stations is unlimited.

An object of the invention is to improve systems whereby a plurality' of subscriber stations may be provided with teletypewriter switching service over a single wire line, channel or trunk.

Another object of the invention is to provide for improved utilization a telegraph line, channel or trunk of the repeater type as a means of operatively extending through a local control or, switching, centerz any one of a plurality of subscriber stations to a remote central omce thereby giving the subscriber a party line service vover said line, channel or trunk.

Another object of the invention is'to .provide semi-selective ringing in a system which permits at any one time one only of a plurality of stations to be operatively connected at the switching center to a telegraph line extending through one or more repeater stations to a telegraph exchange oiice.

Another object is to provide a system responsive to semiautomatic selective ringing whereby any one of a plurality of subscriber stations may be operatively connected through the switchingy center to a line, channel or trunk to the exclusion of the other of said subscriber stations connected to the same line, channel or trunk.

Another object is to provide an improved system whereby any one of a plurality of subscriber stations may be operatively connected through the` switching center to a multi-section line, channel or trunk. Another object is to provide a system having a plurality of subscriber' stations connected to a switching center with means thereat for operatively connecting any one of said stations to the exclusion of the other o! said stations, to amultisection half-duplex single wire line, channel or trunk extending through a plurality of repeater stations in series and a source of busy signals at said switching center for automatically informing a'subscrlber at one or more of said subscriber stations whenanother of said subscriber stations is operatively connected to said line, channel or trunk.

Another object is to provide a system lin accordance with the preceding objects wherein busy signals to inform a subscriber that the trunk is busy are transmitted in permutation code.

According to an embodiment of the present invention two or more teletypewrlr subscriber stations are connected, in parallel, to a switching center by one or two wires and the switching center is connected to the exchange, or central, oiilce by a single wire. The line between the exchange 1oiilce and the switching center may be multisectional. Semiautomatic selective ringing is providedwhereby the selection of one of said subscriber stations is' made by a first, a second or a third pair of-relays at the switching center, which pairs are respectively'responsive to one, two or three rings by the operator at the exchange olce. A source of busy signals is provided for transmitting to each subscriber station, permutation code signa1s,.such as-a series of "letters" or ,K or

other known characters should asubscriber at.

said station attempt to establish a. connection to the line at a time when the line is in use by a subscriber-at another of said stations. The idle a system wherein each of a plurality of subscriber stationsmay be connected to the switching center by one or two single wire circuits and.

either' of said two arrangements may `be operatively connected over a single wire. Sil181e or multisection lin'e extending to the teletypewriter exchange office, each station of such line being operated half-duplex using polar signals, employing current reversals in one direction and differences of current in the other direction. Multisection lines in the main channel may include carrier. radio or any other suitable links.

The invention will now be described with rspect to the accompanying drawings which illustrate two telegraph systems in which an embodiment of the invention is satisfactorily adapted. The drawings are arranged into two groups respectively identified herein as systems X and Y.

System Xconsists of Figs., 1 to 4, inclusive, and system Y consists of Figs. 6, 7, 8, 3 and 4,. Both systems are equipped to furnish semiautomatio selective ringing for calling subscriber stations. System X comprises subscriber lines of two wires each between each of the subscriber stations and the switching center, and a. single section, onewire line for interconnecting the switching center and a teletypewriter exchange omce, rwhereas system Y comprises lines of one wire each between each of the subscriber stations and the switching center, and a. multisection line interconnecting the switching center and the teletypewriter exchange omce. The teletypewriter exchange oiiice will hereinafter be referred to as the 'I'WX oiilce.

The drawings are as follows:

2,373,675 subscriber stations are locked out, or-prevented,

will be noted that each oi the subscriber stations A', B' and C' is connected to the switching center by a single wire which is utilized for performing three functions, namely, transmission. signaling and controlling. The equipment at this switching center provides for semiautomatic selective ringing for calling the subscriber stations; Fig. 8 shows in schematic form, the equipment at an intermediate repeater point in-a single-wire multisection line circuit with wiring adapted for semiautomatic selective ringing;

Fig. 9 shows the relative arrangement of Figs. 6, 7, 8, 3 and 4.

- SYSTEM X GENERAL Dxsciur'rroN vInasmuch as station A is shown in detail and stations B and C are substantially similar to station A, a description of the equipment employed at station A and the method of operation of such equipment is suilicient for a description and a method of operation of the equipment at each of i stations B and C which are shown in diagrammatic form. Station A is connected to the switching center by two conductors I and |02. StationsV B and C are similarly connected by their respective pairs of conductors |03 and |04 and Fig. 1 shows three toll line subscriber teletypewriter stations A, B and C. Station A is shown in schematic form and each of stations B and C is shown in diagrammatic form;

Fig. 2 shows', in schematic form, the equipmentv at the switching center located in the community of subscriber stations A, B and C. It will be the switching center to a toll line extension circuit terminating equipment located in the distant TWX oice and designed to provide for semiautomatic selective ringing. The terminating equipment includes a repeater;

Fig. 4 shows, in diagrammatic form, the op` erators cord-and position circuits and a local subscribers loop 4vterminating equipment at the TWX oilice and the subscribers teletypewriter set at a local subscriber station connected directly to the TWX omce:

Fig. 5 shows the relative arrangement oi Figs.

1, 2, 3 and 4;

Fig. 6 shows three toll line subcriber teletype` writer stations A', B' and C'. Station A' is shown in schematic form and each of stations B and C n is shown in diagrammatic form;

Fig. 7 shows, in schematic form, the equipment at the switching center located in the community af subscriber stations A', a' and c'. It

HIE and |06. The upper conductor of each pair is for transmitting and signaling and the lower conductor is for controlling the connection established between its respective station and the switching center. 'Ihe equipment at station A includes facilities for providing attended station V service only and is identical with Fig. 1 of United States Patent 2,143,000, granted to W. W. Cramer et al. on January 10, 1939, except that the power switch at station A has an e'xtra pair of contacts for grounding the control conductor |02, and the elements shown therein, such as relays 3l, #i and 02, stopl contacts 05 and condenser 38, are omitted. 'I'hese additional elements in the arrangement of Fig. 1 of United States Patent 2,143,000 provide for unattended station service and therefore are not required in the present invention.

Fig. 2 shows a schematic circuit arrangement of the equipment located at the switching center. Common tov stations A, B and Cis a source 201 of continuous ringing current for calling on a semiautomatic selective basis any one of the subscriber stations, for example, should the switchboard operator desire to call any one of the subscriber stations A, B and C, the ringing key associated with the selected cord circuit, would be operated once for selecting station A, twice for selecting station B land thrice for station C. At the switching center three pairs of relays,'namely, relays 202 and 203, relays 200 and 205, and relays 200 and 201 areprovided to respectively respond to the l, 2 and 3 intervals of ringing current received in response to the operation of the ringing key at the operators switchboard. y The iirst pair of relays 202 and 203 respond to one interval of ringing current and prepare a transmission circuit to station A, the second pair of lrelays 204 and 200 through an operating path closed by the operation of relay 202 responding to two intervals of. ringing current and thereby release relays L202 and 203 and close a transmission circuit through to station B -and the third pair of relays 200 and 201 through an operating path kclosed by the operation oi relay 200 respond to the three intervals of ringing current and thereby release relays 200 and 200 and close a transmission `circuit through to station C. At a subscriber station, the ringing current so applied s from source 23| may be one second on and three seconds oil, until the subscriberresponds. Also common to stations A, B and C is a source of busy signals eected by polar relay 233 over a plurality ofcircuits extending through the armatures, in parallel, of relay 233 and a break contact and a lower armature of each of auxiliary line relays 233, 233 and 231, to the transmission conductorsA |3|, |33 and |33, respectively assol0--ductor 301, through the ,333. r Relay 333, upon operatii 1g,j(l)k connects at its outer left amature and contacts the transmission conductor 333 to. tip conductor of jack 33| and tip conductor o! the calling plug of cord circuit ,332,' the circuit closed being traceable from grounded'positive battery at the marking contact and armatureof polarized receive relay 333, conupper winding of polarized send relay 333, make-before-break contacts of relay 333, through the upper winding rof polarized break lrelay 3|0, outer left-hand armature and contact of relay 303, to the above-'-v ciated with -th'e auxiliary line relays, relay 233 1| mentioned tip conductors; (2) closes at its inner being under control of an interrupter circuit comprising relays 2|3, 2| i, 2|2, 2|3, 2M and 2I3. Relay 233, upon being operated at -predetermined intervals, causes to be produced at the teletypewriter of any one or more subscribers stations a series of "letters signals. The stations receiving said signals are those whereat the subscribers attempt to call by turning on the power switch when the line to the switchboard at the TWX left armature andcontact a circuit for energizing the biasing, or lower, winding of break relay v3H); -(3) closes at its outer right armature and contact a circuit traceable from grounded positive battery 32|,` resistance 322, conductor 323, outermost right-hand amature an'd contact of relay 333, conductors 323 and' 325, resistance 323 v' to one side of thewinding-of rel-ay 321, which is of the alternating current type; a parallelpath oilice is in use by asubscriberat one of the gg extends over conductor 323 to the marking, or

other stations.` Line relays 232, 203 and 203 vare respectively provided for stations A, B and .Wile type and represents the toll line extension circuit arranged for connection through'the conleft-hand, contact and armature of polarized relay 3|6; another parallel path extends thrhlgh dated auxiliary line relay, a connection to its own- 3g of relay 333 to the plate of vacuum tube 33|; still vparticular subscribers station such as A, B or C.

Party, or multistation, line 2|3 is of the singleanother path extends from conductor 323, resistance 333,', conductor 3,33, through resistance 333 to the grid circuit of vacuum tube 33|.

Relay 333, upon operating, (1) transfers lamp trol,` or switching, center of stations A, B" and C. 3l conductor 331 -at its right-hand armature toits Line 2|3 terminates at the I WX cnice in the terminating equipment such as shown in Fig.. 3, the opposite end being connected to jack 33| at the operator's switchboard. Arranged in prox-'- front contact which is connected over conductor m, back contact and outer' right-hand armature of relay 3|3, to grounded battery thereby causing line lamp 333 to lig-lit; (2) prepares `at its leftimlty to jack 33| are operator's cord circuit 332, 30- hand amature and icontact an operating circuit operators position circuit 333, both o f which may Ybe somewhat similar to rig. 2A of UnitedStates' Patent aisalrafgmid to x. E r'itcn on May 16,

i 1939. Another jlack 333 at the operators switchfor relays 33 3 and 333 tol await the operation of When the operator operates the ringing key of cord 'circuit 332 such as shownin United States j Patent 2,158,113, supra, wherein the ringing key designated 23| therein, connects source 3|3 of .f ringing current, overring conductor 333 in a circuit which extends over the contact and outer left-hand armature f relay 333, conductor 333,

n through the winding of relay 331, condenser 333,'

to ground. The operators ringing key is operated once-to chil station A, twice to can stenen B and `three times to call station AC and relay 331 with Operatorsf switchboard and arranged4 for beintg 'u the aid or condenser 333 willbe operated accordthrough the operators cord circuit other subscribers stations (not shown), tance between the TWX oiilce and subscribers 'ssamm A, nidad c is assumed w be considerable yandthexeik'rre requires toll line including. thenecesaryrepeaters. l *Marano or Orniirron Operator calls' i that-a connection is desired with-one" oi' the subscribers', stations A, B and C, the opera# l 'tor at 'the switchboard .cord circuits, such 'as cord'circuit 332 to jack 33| connects one ofl several' and-then connects a ringing key to source 3|3' associatedwith'eordfcircuit '332, say one opera- 4 'The dis." v

ingly, that i's, for the duration of each operation #of vthe key.' Relay 331, upon operating, (l) closes 'vat'its left-hand armature and .contact an obvious operating circuit for relay '3|3 and (2) at its right-hand armature and front contact a circuit 'extending from source 333 of grounded ringing current, conductor 313, front contact and arma- -ture'of relay 3|3, transmission lconductor 2I3,

innermost upper amature and back contact o! 'relay 2|1, through Vthe widing of alternating current relay 2|3, condenser 223, toground; and

over a parallel path extending through resistance 22| and the winding of relay 222 to ground. Relay 3|3, 4uponoperating, disconnects the line ,side

4 'or the terminal repeater from conductor 2|3 and n applies ringing current over conductor 2|3 to operate alternating current relay 2|3.

When the operator releases the ringing key relay 331releases thereby opening the ging cirn cuit and closing a-circuit. from con uctor 2|3, to the sleeve conductor oi' the cord circuits, Refthrough the amature andfront contact of relay lay 332, upon operating, operates relays 333. and' in, armature and back' contact of relay m,

to ground'through resistance 332. The release or relay 351 opens vthe operating path of relay 3|3, butrelay 3|3 being of the slow-tofrelease type does not release immediately but remains operated long enough for resistance 332 to discharge .the line before the line conductor 2|3 is closed back to the line side of the terminal repeater via conductor 333.

Normally, that is during the idle condition, line conductor 2|3 terminates in a ground connection 3|3 via the innermost right-hand armature and back' contact of relay 333. After the operator connects a cord circuit to line jack 33| and relay 333 is thereby operated, the line terminates in potentiometer tap 333 intermediate grounded positive battery 3|| and ground connection III, the

ings, in series, of receive relay 333 and relay 3|3, retardation coil 3|1, conductor 333, to line conductor 2|3. This voltage-is insumcient to operate relay' 3H even though maximum leakage is present on the. line circuit, but ,will operate the sensitive relay 222.

The initialy ringing period (about one second) .will operate relay -2|3 and during the'ringin'g period relay 222 4may or may not releaseand in either case no action takes place. Relay 2|3,

upon operating in `response to the ringing curaavaeu lower armature and iront'contact a ground con'- nection to a circuit traceable over conductor 255 through the winding oi relay 233, conductor 23|, t0 grounded battery at the front contact and inner lower armature of relay 223. Relay 233 is of the slow-to-operate type and is timed to operate in about` ilve seconds, as will be hereinafter explained.

A second ringing period, that is, the reapplicationof grounded battery at the inner lower arf mature and back contact of relay 225 in a circuit extending over conductor 23|, back contact and outer upper armature oi relay 223, inner lower armature and front contact of relay 223, conductor 251, innermost lower armature and back contact of relay 205, innermost lower armature and front contact of relay 203, through the upper winding of line relay 203 to ground, causes the second line relay 203 to operate and lockv up in a circuit traceable from ground, through its upper winding and its contact and upper armature, outer upper armature and back lcontact of relay 201, conductors 228 and 229 to grounded battery at the make-before-break contacts of relay 225. Relay 203, upon operating, closes at 'its inner lower armature and frontcontact a circuit for operating relay 205 which operates and locks up at its inner upper armature and front contact to grounded battery. Also relay 203, upon operating, closes at'its outer lower armature and iront contact a circuit traceable from ground, conductor 255, through the winding of relay. 233, conductor 23|, to grounded battery rent from source 333, closes an operating circuit for slow-to-oper'ate relay 223. Relay 223 operates and closes an operating circuit for relay 223 which also operates. Relay 223, upon operating, I(1) closesa locking circuit for itself over the back contactand inner upper armature of relay 22,3;

and (2) removes ground at its-make-before-break contact so that no subscrlber's station can originate, a connection after the initial ringing impulse. The ilrst operation o! relay 223 closes at its inner lower armature and front contact a cir- Vcuit extending from grounded battery at -the inner lower armature and back contact of relay 225, conductor 23|,

contact and outer upper g armature of relay 223, inner lower armature and front contact of relay 223, conductor 251inner- 'I most lower armature and back contact of relay 205, innermost lower armature and back contact Voi? relay 203, through the upper, or primary, winding of line relay 232 to ground. Relay 232 operates and (1) locks in a circuit extending over its upper armature and contact, conductor 221, contact and outer upper' armature of relay 235, outer upper armature and contact of relay 231, conauctors m and m to grounded battery at the make-before-break contact of relay 223; and l(2) at its inner lower armature and front contact connects ground to a circuit extending through -the winding of and over themake-betore-break contacts of auxiliary line relay 233, conductor 230, back contact and inner lower amature of relay m; and when relay m realms mm1-m1- at the expiration of the ilrst ringing pulee,'

grounded battery is furnished over conductor 23| and over the outer upper armature and back wntact of relay 223. At the expiration of ringing pulse relay 233 operates ami locksirom grounded battery at its upper armature. Also. relay 232, upon operating. connects at its outer y at the back contact and inner lower armature of relay 225. As hereinbefore stated, relay 233 is of the slow-foperate type and therefore has not as' yet operated. Relay 205, upon operating, opens at its outer upper armature and back contact, the locking circuit for relay 202 which now releases and causes the release of relay 203. At the expiration of the second ringing interval, relay 223 releases.

A third ringing interval again causes relay 223 to operate thereby closing a circuit from grounded battery at the inner lower armature and back contact of relay 225, conductor 23|, outer upper armature and back contact of relay 223, inner lower armature. and front contact of relay 223, conductor 25.1, innermost lower arma'- ture and front contact oi' relay 205, through the upper winding oi' the third line relay 206 to ground. Relay 205 operates and locks up in a circuit traceable over the front contact and inner upper armature, conductor 229 to grounded battery at the make-before-,break contacts of relay 225. Also relay 205, upon operating, closes at its lower armature and contact an operating circuit for relay 201, the circuit being traceable through the winding and make-before-break contacts of relay 231, conductor 230, to-the back contact and inner lower armature of relay 223,

outer upper armature and contact of relay 226. conductor 23| togrounded battery at the back contact and inner lower `armature of relay 225.

-R'elay 201 operates and closes a locking circuit the inner lower armature and back contact of .relay 225 is removed at the outer upper and back contact of relay 226, this grounded battery having been used for selecting line relays 202, 203 and 206; Also relay 226, upon operating,

connects at its `inner upper armature and front contact grounded battery to start conductor 232, back contact and armature of slow-to-release relay 2| I, through the winding of slow-to-release relay 2|0 to ground.

Relay 2I0 operates and at its inner upper armature and contact applies grounded battery over start conductor 232, to the winding of relay 2| I. Relay 2| I operates and opens at its armature and contact the operating path forrelay 2|0. Inasmuch as relay 2I0 is of the slow-torelease type, it is maintained operated a short interval after the operation of relay 2|| and then releases to open the operating path for relay 2I I. Inasmuch as relay 2|I is of the slowto-release type, it is also maintained operated for a short interval after the release of relay 2|0 and then releases to reoperate relay 2I0 `which in turn reoperates relay 2|I. This cycle continues as long as the grounded battery is lmaintained at the inner upper armature and contact of relay 226'. 'I'he operation and release of relay 2|0 in recurring cycles applies approximately sixty impulses per minute, to a circuit `traceable from ground at the outer upper armature and contact of relay 2I0, conductor 263, make-before-break contact ofand through the winding of relay 2I2, resistance 234, conductor '235, start conductor 232, to grounded battery at th inner upper armature and contact of relay 226. 'I'he first closure of ground over conductor 263 operates relay 2I2 which locks up at its contacts and upper armature to ground and relay 2|3 remains normal since ground is present on both ends of the winding of relay 2|3. On'the rst open condition of the operating circuit for relay 2I2, ground is remvedfrom one end of thewinding of relay 2I'3, and since grounded battery via conductor 23|l and resistance 236 is present on the otherend, relay 2|3 operates. The second closure ofjgrqundat the outer upper armature and contact of relay 2|0 completes an operating circuit extending through the upper armature andfront contact of relay 2|3 to one end of the winding of relay 2|2 and since ground is present on the other end of relay 2I2, relay 2I2 is shunted and relay 2I3 remains operated on the second release of relay 2 I 0 whereby ground at the outer upper armature and contact is removed, relay 2 I 3 releasing. Subsequent sixty impulses per minute causes relays 2I2 and 2|3 to operate and release as just described. This reduces the sixty impulses per minute ground to thirty impulses per minute furnished to the relays 2|4 and 2I5. Relays 2|4 and 2|5 operate in-a manner similar to relays 2I2 and 2|3, respectively, and further reduce the sixty impulses per minute to one 'second closed and three second open interrupted ground pulses. These pulses are transmitted over conductors 231 and 238,

` outer upper armature and back contact of relay 226, conductor 239, through the winding of relay 240 to grounded battery and relay 240 operates each time a grqund is connected to conductor 238 which is referred to hereinafter as theA interrupted ground conductor. During the one second operate time of relay 240 ringing current from source 20| is connected atV the front contact and armature of relay 240 to conductor 24|, the middle lower armature and front contact of one of the auxiliary line relays 203, 205 and 201, depending upon which one of these relays remains operated at the conclusion of the ringing interval set up by the operator at the switchboard, and then over a transmission conductor, such as conductor |0| for station A, to the ringer at the subscribers station, say ringer |01 at station A. The selected station will be rung automatically at the termination of the ve secondl operating period of relay 2i33. l

Subscriber answers The subscriber in response to the operation of the station ringer, say ringer |01, operates power switch I08. Power switch |08, upon being operated, completes a path from grounded alternating current source |09, conductor |I0, lefthand contacts of the switch| conductor III, through the winding of relay ,I I2 to ground, and

relay ||2 operates. A path parallel to that ex vsend relay |23, retardation coil |24, negative terminal to positive terminal of rectifier ||4, retardation coil |25, marking, or upper, contact and armature of send relay |26, retardation coil |21, to ground connection |26. The energized rectifier supplies a source of potential diierence between its terminals and thus to the lcircuitincluding ground connection |28 and line conductor IOI. Rectifier ||4, upon becoming energized, also causes current to ow in two parallel paths, one extending from the positive terminal of the rectifier through the right-hand and the lefthand biasing windings, in-series, of send relays |26 and |23, respectively, to the negative terminal of the rectifier, and the other from the positive terminal of the rectier, conductor |20, break-key |30, transmittingcontacts |3I, of subscribers teletypewriter set |32, conductor |33, normal contacts of line-in key |34, conductor |35, regulating resistance |36, conductor |31, through the lefthand and the right-hand operating windings, in series, of sendrelays |26 and |23, respectively, to the negative terminalof the rectifier. Printer magnet |40 of subscrlbers teletypewriter |32 is also normally energized by current flowing from rectifier ||4 over a circuit including conductor I4I, through the winding of printer magnet |40, conductor |42, varistor elements |43, retardation coil |44, marking, or lefthand, contact and armature of receive relay A| I3, retardation coil |45 to ground at the lower normal contact of key II1. The biasing, or lower, winding of receive relay ||9 is energized over conductor |46 and resistance |36 and serves to operate receive relay ||9 to its spacing or righthand position when the line |0| is opened'. Re. sistance |38 is of the adjustable type in order iler alone may be used or the rectiiler may be used inl shunt to al condenser.l The purpose of the rectifier is to furnish a resistance that will automatically vary with any change in voltage. For example, the pair of rectiilers shown in the drawings have a very high resistance when relatively low voltages are impressed across the terminals thereof and a relatively low resistance at high voltages. Hence when unduly high voltages appear in the printer magnet circuit the varistor elements as a unit protect the printer magnet against current surges. A further description of the various elements in the circuit shown in Fig. 1 may be had by referring to United States Patent 2,143,000, s upra.

During the'idle condition after switch |06 is operated and the potential applied to the line by rectifier I I4 is of negative polarity and when the cut-through relay 2 I 1 is operated as will be hereinafter described, the negative potential so applied holds the repeater relays through the system in the positions shown. Power switch |08, upon being operated, connects ground at its righthand contact to control conductor |02 of a circuit Which extends over the outermost lower armature and front contact of relay 203 (assuming that relay 203 had been in an operated position when ringing current from source 20| was applied for -transmission over a line conductor such as conductor IOI), conductor 254, through the winding of cut-through relay 2 I 1, to grounded battery. Relay 2I1 operates and at its innermost upper armature transfers line conductor 2 I 6 from. relay 2I3 and 222 to the transmission conductor IOI via the armature and back contact of relay 240 and the back contact and middle lower armature 'of relay 203. Relay 222 releases when relay 2I1 operates. Also relay 2 I1, upon operating, closes at its outermost upper armature and contact an obvious operating circuit for relay 225 which operates. Relay 225 upon operating The yaristor elements |43 mature and back contact of relay 3I3, conductor 3I2, innermost right-hand armature and front contact of relay 303, to potentiometer tap 364 which is of positive polarity. Relay 3I4 operates and polarized relays 3I6 and 306 of the repeaters remain in the positions shown. Relay 3I4, upon operating, closes at its armature and contact a circuit extending from grounded positive battery 32|, resistance 322, conductor 323, outermost right-hand armature and contact of relay 303, conductors 324 and 325, resistance 326, through i the winding of alternating current relay 321, re-

' 366, marking, or left-hand, contact of relay 3I6 (1) transfers interrupted ground conductor 230 a from ringing conductor 233 to conductor 243, condenser 25|, conductor 262, through the upper winding of polarized relay 253 to ground; (2) closes at its inner upper armature and front contact, an operating circuit for relay 203 which operates; (3) releases at its inner/upper amature and back contact relay 224; (4) opens at its inner lower armature and back contact the operating circuit for relay 233 which releases and in turn eiects the release of relay 226; (5) maintains at its inner lower armature and front contact grounded battery to 4start conductor 232, even though relay 226 is released; and (0) transfers4 grounded holding battery for any one of line relays 202, 204 and 206, say in this case relay 202,v from its make-before-break contacts to its outer lower armature and front contact which is oonnected to the front contact and middle upper armature of relay 2|1 which is now in an operated position. Polarized relay 253 is provided to furnish busy signals as will be hereinafter described.

Negative voltage on the transmission line conductor |0l is now impressed on transmission conductors 24|, 242 and 2 I6, armature and back contact of relay 3|3, conductor 363. through the uppermost winding of polar'relay 3I6 and the upper through the winding of relay 3I4, lett-hand arto ground. Relay 321 operates and connects at its armature and contact an obvious operating circuit for relay 3I3 which operates. Relay 3I3, upon operating, opens at its outer right-hand armature and back contact, the operating circuit for call lamp 333 which now becomes extinguished. Relay 3|3, u-pon operating, completes at its outer right armature and front contact the circuit hereinbefore prepared at relay 305 for operating relays 343 and 344 both of which now operate.

Relay 343, upon operating, (l) opens at its inner left armature and contact, a circuit traceable from grounded positive battery 32|, resistances 322 and 345, inner left-hand armature and contact of relay 343, conductorv341, through the middle winding of polar relay 3`I6 and the lower Winding of polar relay 306 to ground at its inner right-hand armature and back contact whereby the idle marking condition is removed from polar relays 3I'6 and 306 of the repeater; (2) at its inner right armature and front contact, closes the artificial line circuit which extends from apex 363, conductor 343, front contact and inner righthand armature of relay 343, conductor 350, through'the lower winding of relay -306 4and the middle winding of relay 3I6, conductors 348 and 341, resistance 310, condenser 352 to ground connection 35|; (3) opens at its outer left-hand armature and contact the operating circuit for relay 351; and (4) prepares at its outer righthand armature and contactthe operating circuit for relay 36|.

Relay 344, upon operating, (l) closes at its right-hand armature and. front contact, the artiilcial line circuit which extends from apex 31|, conductor 354, `right-hand armature and contact -of relay 344, conductor 353, through the lower follows the'signals and relay 3I4 is shunted by `winding of polar relay 306, retardation coil 3I5,

condenser 335, the pathl so closed extending through resistance 312, condenser 356, left-hand armature and contact of relay 344, to tap 313. The action is as follows: During the time that relay 3I6 is on its marking, or left-hand, contact, resistance 326 at one end of the winding of relay 321 is grounded, and groundedv battery through -resistances 322`and 355 and the front contact and left-hand armature of relay 344, charges converses and continues to hold relay 321 operated. During long marking or long spacing signals, relay 3|4 operates to hold relay 321 operated.. The biasing current in the lower winding of relay 3l0 tends to operate the relay to' a spacing, or righthand, contact, but the marking current in the loop or' upper winding of relay 3|0 is twice as great and in the opposite direction so the relay is operated to its marking, or left-hand, contact. Grround connected to the armature and marking, or left-hand, contact of relay 3|0 is impressed on a circuit. extending over. conductors 314 and 335 to maintain condenser 315 discharged during the time the loop to the subscribers circuit is in marking condition. During the normal transmission period, relay 3|0 will follow the transmission signals. The circuit is now ready for communication between the subscriber and the operator at the switchboard. All subscriber stations other than the one answering the'.` call 'are locked out because the operating circuit for their respective line relays is opened by the removal of ground at the make-before-break contacts of relay 224 via a back contact and armature of relay 2I-1.

Busy line indication the lower winding of the relay and to operatethearmature thereof to its spacing, or right hand, contact. This ground that is applied to conductor 243 is connected for about -twenty milliseconds and at the rate about once per second.

With relay 209 operated, this intermittent twenty millisecond ground is applied to conductor 248, contacts and armatures of relay 209, and over back contact and lower amature of the .auxiliary line relay associated with the subscriber station whereat a call is attempted when the toll line is engaged in a connection to one of the other stations. The intermittent ground when applied to a transmission conductor, such as conductors |03 and |05,`will produce a series of letters signals at the teletypewriter of a subscriber who attempts vto call by turning onv the power switch when the line to the switchboard is in use `by a party at another of the stations. These'signals cause a suilicien't amount of current in the properl direction through the line winding of the receiving relay such as relay ||9 at station A, to overpower the biasing current in the lower winding of such relay for a' period of time required to produce the letters signal. initiated the subsequent call, after noting these signals, shuts oi the power and places another call at a later'time.

Subscriber disconnects 4The subscriber turns oil'I power switch. |08 thereby removing grounded negative potential from transmission conductor |0| and ground from conductor |02. The removal of ground from conductor |02 opens the circuit traceable over the outermost lower armature and front contact of relay 203, conductor 254, through the winding of relay 2|1 and relay 2|1 releases.' Relay 2|1, upon releasing, releases relay 225. vRelay 225, upon releasing, removes grounded battery from the start conductor 232 and the interrupter cir,-

' cult comprising relays l2|0, 2||, 2|2, 2|3, 2|4 and 2|5 is restored to normal. Likewise, interrupted ground is removed from conductor 238 whereby the busy, or "letters, signals are discontinued. During the release time of slow-to-release relay 225, which time is about one-half second, the holding battery for line relay 202 is lost because relay l2|1 releases as soon as the power switch |08 is turned off. Line relay 202 and its'associated auxiliary line relay 203 release. Relay 225, upon releasing, causes relay 209 to release.

The removal of negative potential from the transmission conductor |0| causes the release of relay 3|4 and, in turn, the release of relay 321. Relay 321, upon releasing, causes the release of relay 3|3 and relay 3|3, upon releasing, closes at its outer right-hand armature and back contact,-

the operating circuit for lighting supervisory lamp 339 as a signal to the switchboard operator to remove cord circuit 402 from jack 30|. Relay 3|3, upon releasing, also releases relays 3,43 and 344; disconnects conductor 2|8 from conductor 386, and when cord circuit 402 is removed4 and relay 303 releases applies ground at the back contact and left-hand armature of relay 3|3 to a circuit extending through the winding of relay 3 I4, retardation coil 3I5, through` the upper windings, in series, of relays 305 and 3|6, back contact and armature of relay 3|8, transmission conductor 2|6. Relays 343 and 344, upon releasing, apply grounded batteries 32| and 318 to two biasing circuits, one extending over the inner leftfhand armature and contact of relay 343, conductors I 34B, 341 and 348, through the middle winding of relay 3|8 and the lower winding of relay 306 to ground at the inner right-hand armature and back contact of relay 343 and the other from lower winding of relay 308 to ground. When the switchboard operator disconnected from the line terminating equipment by disconnecting the cord The subscriber who circuit relay 305 also released and the circuit restored to normal.

Recall signa@ from the subscriber A recall signal is given to the operator at the switchboardby the subscriber momentarily operating a recall key, such as key 6 at station A, several times. While the key is operated, the line is opened to direct current-and relay 3|4 releases and in-turn relays 321, 3|3, 343 and 344 release.

and furnish grounded Abattery for holding the terminal repeater relays 306, 3|5 and 308 in a marking condition in the same manner as hereinbefore described under disconnect. 'Ihe alter-` nate opening and closing of the line by the operation of the recall key causes supervisory lamp 339 to flash.

Break signal from the subscriber spacing condition so that relay 3|4 continues to hold relay 321 and its associated relays operated. Break relay 3|0 operates to its spacing, or righthand, contact. When the subscriber restores break key |30, negative marking polarity will be applied to the line at the subscriber's station and the terminal repeaters including relay 3 I 0 operate to their marking contacts and the circuit is in condition for the transmission of telegraph signals. If the subscriber sends a break signal exceeding six seconds, vacuum tube 33| will function as hereinafter described under Trouble break but otherwise performs n'o useful function at this time.

Break signal to subscriber charge from grounded positive battery 32|, over conductors 323, 324 and 325 through resistance 330 and over conductor 335. When the loop is closed to marking, relay 3|0 operates to marking and discharges condenser 315 thereby preventing condenser 315 from obtaining enough of a. charge to cause vacuum tube 33| to draw plate current.

-Trouble break Vacuum tube 33| with its associated apparatus is designed to detect a break signal of six seconds or more through the supervisory repeater. With relay 303 operated, the filament of tube 33| lights. As long as relay 3|0 is in marking condition, condenser 315 is discharged and the tube does not draw plate current. If, however, the break exceeds approximately six seconds, condenser 315 has had time to charge from grounded positive battery 32| through resistance 334 to a potential as high as that of the filament. Therefore Athe grid connected through the current limitingresistance 336 causes plate current to 110W and operate relay 333. Relay 333, upon operating,

operates slow-torelease relay 303. Relay 309,

upon operating, (1) connects grounded battery at its outer right-hand armature and contact to a source 319 of interrupted ground such as produced over conductor 238 in Fig. 2, and thesource is connected to a circuit extending over the lefthand armature and contact -of relay 309, c onduc tor 380, outer right-hand armature and contact' of relay 343, conductor 38|, through the winding of relay 36| to grounded battery and (2) transfers the loop transmission lead 382 from the terminal repeater to a path extending over conductor 383 to the inner left-hand armature of relay 36|. Relay 36| operates and releases when the interrupter opens and closes ground to the winding of relay 36| in recurring cycles. When the interrupter closes the operation of relay 36| re' moves grounded negative battery 318 from conductor 383 and closes a loop through to the associated supervisoryrepeater circuit. If the supervistory repeater circuit is still spacing, relay 3|0 remains on its spacing, or right-hand, contact and relaysl 333, 309 and 36| remain operated and the terminal repeater sends a spacing signal out over transmission conductor 2|6 to the subscribers station. Also, relay 36|, upon operating, closes at its right-hand armature and contact a path extending from ground at the armature and spacing contact of relay 3|6, conductor 384, contact and right-hand armature of relay 36 I, resistances 311 and 365, through the winding of relay 321, conductors 325 and 324, outer right-hand armature and contact of relay 303, conductor 323, to grounded battery 32| whereby relay 321 is held operated during the spacing interval. Relay 3|4 is under control of the subscriber's station only when the terminal' repeater sends a marking sig-` nal out on the line. This takes place when relay 36| releases thus opening the holding path of relay 321, leaving it under the control of relay 3|4. Transmission conductor 302 is again connected through the back contact of relay 36| to grounded negative battery v318. This operates send relay 308 of the associated terminal repeater to marking and ground is sent out over transmise sion conductor 2 6 to the subscribers station. If relay 36| is operated and the space signal changes to marking polarity in the loop circuit, relay 3|0 will operate to its marking, or left-hand, contact which discharges condenser 315 thereby cutting oi plate current in vacuum tube 33|. Relay 333 therefore releases which will in turn release relays 309 and. 36| and the circuit will be ready for communication.

If the subscriber disconnects during a 'trouble break, which causes relays 333, 303 and 36| to operate, relary 3|4 will release on the rst marking pulse sent by the terminal repeater and relay 321 will release, thus releasing relay 3|3 which functions as hereinbefore described under Subscriber disconnects. II the loop is still spacing,

the operator receives the disconnect signal, andrelay 333 and 309 will be operated. When the switchboard operator removes the supervisory repeater patching cord, relays 303 and 305 will release and open the operating circuit of the vacuum tube 33| and the biasing windings of lrelay 3|0. Relay 333 will release and open the holding path of relay 303 causing it to release and the circuit will be restored to normal.

The subscriber may send a recall or disconnect signal during the time the line is marking when a trouble break exists on the loop side of the terminal repeater. When this condition exists the line circuit times out after approximately six seconds and causes the repeater to send alternate marking andspacing signals over the line to the subscriber. IThe operator will go in on the circuit and operate'the split key (n ot shown but associated with the cord circuit) in order to determine to which side of the supervisory repeater circuit the trouble is coming. 'I'his will change the loop back to the marking condition and when relay 36| operates on the next spacing pulse, the transmission path is closed through the terminal repeater and relay 3|0 will operate to its marking, or left-hand, contact, and the circuit will func- Een as hereinbefore described under Trouble Operator abandons call Assume that relays 202 and 203 or relays 234 5 and 205 or relays 206 and 201 are operated due to the operator pulsing with ringing current,.as v

hereinbefore described. If the subscriber does not answer after a specified time, the operator removes the ,cord circuit from jack 30| and there-A Y from ground at the lower amature and contact of relay 226, conductor 241, upper armature and contact of relay 222 through the winding of relay 225 to grounded battery. Relay 225 operates and thereby removes the holding battery for the operated line relay of relays 202, 204 and 206. Relay 225 also removes the holding battery for relay 233. Relay 233 releases in about one second after relay 225 operates and the release of relay 233 releases relay 226 thereby causing the release of relay..225 and all relays are now returned to idle'condition. In case the busy, or letters," signal circuits function during the momentary operation of relay 225, no action takes place because at this time the transmission conductor at each subscribers station, such as conductor at subscriber A, is terminated in the ringer and condenser circuit such as ringer |01 and condenser |41 at station A. f

Subscriber calls Assume that the subscriber at station A desires to make a call to the operator's switchboard, power switcli` |00 is operated to its on position whereby the station set is placed in an operated condition as hereinbefore described Vand ground is connected over controly conductor |02 to the outermost lower armature of relay 203. With the subscribers set at station A in an operated condition, negative potential is applied to transmission conductor |0|, middle lower armature and back contact of relay 203, through the lower winding of relay 202, contact and outermost lower armature of relay 2|1, to ground at the makebefore-break contacts of relay 224. Line relay 2,02 operates and 'locks in a circuit traceable from ground at its front contact and upper armature, conductor 221, back contact and outer upper armature of relay 205, outer upper armature and Iback contact Aof relay 201, conductors 228 'and conductor 23|, to grounded battery at the inner lower armature and back Contact of relay 225. Relay 203 operates and locks to grounded battery at its upper armature and front contact. Relay 203, upon operating. completes a circuit hereinbefore prepared when power switch |08 was operated and connected ground to control conductor |02, the circuit being traceable over the outermost lower armature and front Vcontact of relay 203,

conductor 254, through the winding of relay 211 to grounded battery. lRelay 2|1 operates and in conjunction with the operation of relay 203 trans- Amission conductor 10| is connected through to transmission conductor '2?6. The negative potential now impressed on transmission conductor 2|6 extends through a circuit traceable over the armature and back contact of relay 3&8. conductor 363, through the retardation coil 3|1, the

uppermost winding of relay 316 and the upper winding of relay 306, retardation coil 3| 5. through the winding of relay 3|4. left-hand amature and back contact of relay 3|3 to ground at theinnermost right-hand armature and back Vcontact of relay 303'. Relay 3|4, upon operating, connects ,grounded battery 32| to a circuit extending through resistances 322 and 355, conductors 384 and 361, armature and contact of relay 3M, conductor 366, resistance 3,65, through the winding of relay 321, conductor 328, to ground at the marking contact and armature of relay 3 6. Relay 321 operates and closes at its armature and contact an operating circuit for relai1 3 I3. Relay 3|3, upon 'operating, transfers at vits left-hand amature and contact transmission lead 2|6 to the armature of send relayy 308 and closes at its 'outer right armature and front contact, a cir- .cuit extending from .grounded battery over conductor 34|, back contact and right-hand armature of relay 305, conductor 331 to light lamp 339. The operator, upon noting the lighting of lamp 339, inserts the answering plug of cord circuit 402 into jack to complete therestablishment of the connection as hereinbefore described.'

SYSTEM Y A' is shown is schematic form and that Aat each of stations B' and C' is shown in diagrammatic form. The equipment at each of stations B' and C' is identical with that at station A'. Stations A', B' and C' are identical with stations A, B and C 'employed in system X hereinbefore described except that stations A', B' and C' have no control conductors such as conductor |02 at station A, conductor |04 at station B and conductor |05 at station C, the transmitting and signaling conductor at each station of system Y serving for control purposes also. 1

Fig. 7 shows in schematic form the equipment at the control, or switching, center. Common to stations A', B and C' is a source 10| of continuous ringing current for calling any one of the subscribers stations. Also common to stations A', B' and C' is a source of busy signals effected by relays 102 and 103 which are arranged during the establishment of a connection to alternately operate at regular recurring intervals whereby relays 104, 105, 106 and 101 operate in sequential cycles to place Ilterrupted ground on a circuit for operating polarized relay 108. Relay 108, in response to the interrupted ground, transmits current pulses over the transmission conductor extending to a subscribers station at which a call is attempted when the toll line extension circuit is engaged by a subscriber at another station,

these current pulses producing a busy signalv at the teletypewriter of the subscriber attempting to -interfere with a busy line. Line relays 100', 1| 0 and 1|| are respectively provided for stations A',

Y, B' and C and auxiliary line relays 1|2, 113 and is of the slow-to-release type, for providing a closed path for the signals transmitted from Yany one of subscribers stations A', B' and C. The

transmission signals from any one of the subscribers stations reverses the direction of line current in accordance with thel marking and spacing conditions of the line. Relay 1|1 is poled for operation when the subscribers station 'teletypewriter set is marking and relay 1.I8 is poled for operation when the subscribers station teletypewriter set is spacing. Therefore, relay 1I3 which,as hereinbei'ore stated, is slow to release and is operated in response to the operation of either relay 1|6 or 1I1, will remain in its operated position during the transmission to supply the holding ground for relay 1|! which, when operated, furnishes ground for holding relay 120. Holding relay 120 provides grounded battery ior maintaining the interrupted ground relays operating to furnish the busy signals when any subscribers station is connected through to the toll circuit conductor 1|5. Y

. Fig. 8 shows a schematic circuit arrangement of the multisection line'r'epeater conditioned for semiautomatic selective In the idle condition allrelays in the multisection line repeater are in their released positions as shown. At the left-hand side of Fig. 8 polar relay 00| `in the supervisory circuit and polar receive relay 302 in the repeater circuit are held to their marking,

or left-hand, position by a holding current in a circuit extending from grounded battery at the back contact and lett-hand amature of relay 803, through the middle windings, in serios, of relays 802 and 80| vto grounded network 820. When a switchboard operator rings after connecting a cord circuit to the toll line extension multistation circuit, the ringing current 4operates alternating current relay 804 and, in turn,` causes relay 805'to operate. Relayv305, upon operating,

`operates slow-to-release relay 000 and connects source 801 of 2li-cycle ringing current over the operated contacts of relay 803 to transmission polarized send relay 303, make-beiore-break contact of relay 303, through the upper winding of polarized break relay 3|0, outer left-hand armature and contact of relay 303, to the above-mem' tioned tip conductors; (2) closes at its inner left armature and contact a circuit for energizing the biasing, or lower, winding of break relay 3|0; (3) closes at its outer right-hand armature and contact a circuit traceable from grounded positive battery 32|, resistance 322, conductor 323, armature 'and contact of relay 303, conductors 324 and 325, resistance 326 to one side of the winding of relay 321, which is of the alternating current type; a parallel path extends over conductor 328 to the marking, or left-hand, contact and armature of polarized relay 3|6; another parallel path extends `through resistance 330 to the iilament of vacuum tube 33|; another path extends through the winding of relay 333 to the plate of vacuum tube 33|; and still another path extends from conductor 325, resistance 334, conductor 335, through resistance 336 to the grid Y circuit oi vacuum tube 33 I.

Relay 305, upon operating, (1) transfers lamps conductor 331 at its right-hand armature from its back to its front'contact which is connected over conductor 338, back contact and outer rightn conductor 115 to operate the ringing equipment"A in the control circuit as will be hereinafter de-v scribed.`

Figs.3 and4 areused insystemYalsoand represent the toll line extension terminatingA equipment at the operators switchboard in theA TWX cnice. The terminating equipment like that lat the multisection line repeater station is arranged for semiautomatic selective ringing also.

Y METHOD or Orm'rxon Operator calls Y Assuming that a connection is desired with one of the subscribers stations A', YB' and C', the operator at the switchboard connects one of several cord circuits, such as cord circuit 402, to jack 30|, and then'connects a ringing key to source 4|0 associated with cordcircuit 402, say one operation of ringing key for station A', two operations i'or station B' and three operations for station C'.

'I'he operators ,cord circuit 4021upon being inserted into jack 30|.. operates sleeve relays 302 in a circuit traceable through grounded battery connected to the sleeve conductor on-the cord circuit. Relay 302, upon operating, voperates relays 303 and 305.

Relay 303, upon operating, (1) connects at its outer left armature and contacts transmission conductor 304 to the tip conductor of jack 30|,

' tact and armature of polarized receive relay 300,

conductor 301, through the upper winding of hand armature oirelay 3I3 to grounded battery. thereby causingline lamp 339 to light; and (2) prepares at its left-hand armature and contact an operating circuit for relays 343 and 344 which circuit closes when relay 3|3 operates.

When the operator operates the ringing key of cord circuit 402, wherein the ringing key connects source 4 I0 of ringing current, over ring conductor 350 in a circuit which extends over the contact and outer left-hand Iarmature oflrelat7 343, conductor 359, through the winding of alternating current relay 351, condenser 385 to' ground.` The operators ringing key is operated once to lcall station A', twice to call station B' and thrice to call station C' and relay 351 will be operated accordingly. that is, for the duration of each operation of'the key. Relay 351, upon operating, (1) closes at its left-handV armature .and

i contact an obvious operating circuit for relay 3 I8; and (2) at its right-hand armature and front contact a circuitextending .Iromsource 300 of grounded' ringing current, conductor 316, iront contact and armature of relay 3I8, .transmission conductor 833, outermost upper armature and back contact of relay 8|4, conductor 833, through the winding of the alternating current relay 804,

Ycondenser 026.10 ground; and over a parallel path extending through resistance 842 andthe winding of relay 843 to ground. Relay 318, upon operating, disconnects the line side -of the terminal repeater from conductor 833 andV applies ringing current over conductor 833 to operate alternating current relay 804, the operating circuit for which was just described.

when the operator releases the ringingkey,

relay 351 releases and opens the ringing circuit and closes a circuit from conductor 833, through the armature and front contact of relay 3|8, armature and back contact of relay 351 to ground through resistance 302. The release of relay 351 opens the operating 4path of relay 3|3, but relay 3I8 being of the slow-to-release type does not release immediately but remains operated long enough for resistance-382 to discharge line conl ductor 333 before the line conductor is closed back through the line side of theterminal repeater via' conductor 333.

Duringthe idle condition, that is, when the system i's normal, line conductor 833 terminates in a ground connection 3|8 via the innermost right-hand armature and back contact of relay 303. ,After the operator connects a cord circuit to line jack 30| and relay 303 is thereby operated, the line terminates in tap 364 of positive polarity of a potentiometer having grounded battery 3|| at one end and ground connection 3|8 at the other end, the potentiometer having a path to ground extending over the inner right-hand armature and contact of relay 3|3, middle righthand armature and contact of relay 303. The positive voltage at tap 364 is applied to the line over conductor 3|2, back contact and left-hand armature of relay 3| 3, through the winding of relay 3|4 and'retardation coil 3|5 through the upper winding of received relay 308 and the upper winding of relay 3|6, retardation coil 3| 1, conductor 363, to line conductor 833. This voltage is insuiiicient to operate relay 3|4 even though maximum leakage is present on the line circuit but will operate the sensitive relay 043.

The initial ringing period (about one second) will operate relay 804 andduring the ringing period relay 843 may or may not release and in either case no action takes place. Relay 804 responds lto the ringing current from source 360 and closes an operating circuit for relay 805. Relay 805 operates and .closes at its inner upper armature and contact an obvious operating circuit for a slow-to-release relay 806. Relay 806 operates to connect source 801 of continuous ringing current over the front contact and outer upper armature of relay 8,05, front contact and armature of relay 806, transmission line conductor 1|5, which at the control center is connected over the innermost upper armature and back contact of relay 1 I8, through the winding of alternating current relay 12|, condenser 128 to ground. The initial ringing period (about one second) will operate relay 12| and during the ringing period relay 130 may or may not release and in either case no action takes place. Relay 12|, upon operating, responds to the ringing current from source 801, whereby relays 122 and 123 are in turn operated during the ringing interval.

l Relay 122, being of the slow-to-operate type, de-

lays its operation until slightly after relay V'12| pulls up in response to the ringing current. Relay 123, upon operating, (l) closes at its inner lower armature and contact a locking circuit for itself, which circuit extends over the back contact and inner upper armature of relay 1 8 to ground; and (2) removes ground at` its make-beforebreak contact so that no subscriber stationcan establish a connection after the initial ringing impulse has been transmitted. The first operation of relay 122 closes at its inner lower armature Aand front contact a circuit traceable from grounded battery at the innermost lower armature and back contact of relay 1|8, conductor 13| back contact and outer upper armature of relay 124, inner lower armature and front contact of 'relay 122, conductor 132. innermost armature and back contact of relay 1|3, innermost armature and back contact of relay 1|2, through the upper winding of relay 108, to ground and relay 108 operates and locks at its upper armature and contact in -a circuit traceable over the back contact and outer upper arinature of relay 1|3, outer upper armature and'back contact of relay 1|4, conductor 133, to grounded battery at the makebefore-break contact associated with the middle lower armature of relay 1|8.

Relay 108, upon. operating, connects' ground at its inner lower armature and front contact to a circuit extending through the winding and the make-before-break contacts of relay 1|2 to the back contact and inner lower armature of relair 122 and when relay 122 returns to normal at the expiration of the 'iirst ringing pulse, the circuit is extended over the outer upper armature and back contact of relay 124 to grounded battery at the inner lower armature and back contact of relay 1 9. Relay 1 I2 operates and is locked to grounded Y battery at its upper armature and front contact. Also relay 108, upon operating, connects ground at its lower armature and front contactrto a circuit .traceable through the winding of relay 125 to grounded battery at the inner lower armature and back contact of relay 1|9.V` Relay 125 which is of the slow-to-operate type is timed to operate in about lve seconds. The function of relay 125 will be explained hereinafter.

A second ringing period will cause relay 122 to again operate and reapply grounded battery over the inner lower armature and back contact of relay 1|8, through the backcontact and outer upper armature of relay 124, the inner lower armature and front contact of relay 122, the innermost lower armature and back contact of relay 1 |3, the innermost lower armature and front contact of relay 1|2, through the upper Winding of relay 1|0 to ground. Relay 1 I0 operates and locks through its upper winding in a circuit traceable over its upper armature and front contact, outer upper armature and back contact of relay 1|4 to grounded battery at the inner make-before-break contacts of relay 1|8. Relay 1 |0, upon operating,

connects ground at its inner lower armature and" front contact in a circuit extending through the winding and make-before-break vcontact of relay 1 |3 to the back contact and innerlower armature of relay 122 and when relay 122 again returns to normal at the expiration of the second ringing period the circuit is extended over the outer upper armature and back contact of relay 124 to grounded battery at the innermost lower armature and back contact of relay 1I8. Relay 1|3 operates and locks to grounded battery at its inner upper armature and front contact. Relay 1|3, upon operating, opens at its outer upper armature and back contact a locking circuit for relay T09 which releases and causes the subsequent release of relay 1 2.

A third ringing period again causes the operation of relay 122 which, upon operating, again connects grounded battery at the innermost lower armature and back contact of relay H8 to a circuit traceable over the outer upper armature and back contact of' relay 124, inner lower armature and front contact of relay 122, innermost lower armature and front contact of relay 1|3, through the -upper winding of relay 1| to ground. Relay 1|| operates and locks in a circuit traceable over its inner upper armature and front contact to grounded battery at the inner make-before-break contacts of relay 1|8. Also, relay 1| upon operating, connects ground at its lower armature 'and contact to a circuit traceable through the Windnormal after the expiration of a third ringingl period, the circuit is extended over the back contact and outer upper armature of relay 124` to grounded battery at the back contact and inner- Relay-1u 'Y most lower armature oi relay 1| 8. operates and locks to grounded battery atits inner upper armature and back contact. Relay 1 4,

- oirelay 1|3.

upon operating, opens at its outer upper armature and back contact the locking circuit for relay 1I.. Relay 1|0 releases and thereby causes the release Relay 1I I, upon operating, connects ground at its outer upper varmature and front contact to a circuit for maintaining relay 125 energized.

Now that the three ringing. intervals have been completed, sayin ilve seconds, which is the op.- erating time of slow-to-operate relay 125, the relay now becoming suiliciently energized, therefore, operates and closes an obvious operating circuit for relay 124 which operates. During. the operating time (live seconds) of relay 125, the operator must ring l, 2 or 3 to select the desired station and do so only once. At the expiration of the five-second interval, ringing current is impressed on transmission conductors 360|, 602 or 604 depending upon which of subscribers stations A', B and C' is desired in the completion of the connection, the ringing curent so applied being derived from source The ringing current is applied during each one-second operate time of relay 121, and is repeateduntil the subscriber 'at the called station responds. Relay 121 is em ployed for connecting source .10| of continuous ringing current tothe transmission conductor extending to the called subscribers station and this relay is operated by interrupted ground transmitted over conductor-128. Interrupted ground conductor128 is also employed for operating relay 100 which produces a busy signal each timea subscriber attempts to make a call when the toll line is busy.

Assume that the connection desired lby the operator is to station Ai in which event there will,

be only one ringing interval. Relay 103, upon relay 103 and the latter ismaintained operated ifor a short interval after the release of relay 102.

Relay 103, upon releasing, causes relay 102 to re operate, which in turn reoperates relay 103. 'I'his cycle continues as long as grounded battery is maintained at the inner upper armature and contact of relay 124. The operation and release of relay 102 in recurring cycles apply approximately sixty impulses per minute to. a circuit traceable from ground at the outer upper arma.- ture and contact of relay 102,'conductor 135, make-before-break contact of lrelay 104, then through the windingv of relay 104, 4resistance 135, conductors 131, 138 and 139 to grounded battery at the inner upper ,armature and contact of relay 124. The iirst closure of ground over conductor 135 operates relay 104 which locks to ground at its front contact and armature, and relay 105 remains normal since ground is present on both endsof the winding of relay 105. On the first' conductors 131, 13B and 133 to grounded battery.

the other end, relay 105 operates. The second Y closure of ground at the outer upper armature operating, closes at its inner lower armature' and front contact an operating circuit for relay 1I2, the circuit being traced from ground over the inner lower armature and front contact of relay 109, through the winding of relay'1I2, at its make--before-break contact, back contact and inner lower armature of relay 122, outer upper armature and back-contact ofrelay 124, conductor 13 I, back contact and innermost lower armature of relay 1 I 9 to grounded battery, the closure of this circuit being completed when relay 122 returns to normal at the expiration of the ringing lower armature and back contact of relay 1I0.- Relay 125 is of the slow-to-operate type and requires ve seconds to operate.

Inasmuch as there is only one ringing impulse transmitted, relay 125 will wait ve seconds `and will then operate. YRelay 125, upon operating,

closes an obvious operating circuit forrelay 124 which operates. Also relay 124, upon operating,

' connects at its inner upper armature and front contact grounded battery to a circuit traceable over the back. contact and armature of relay 103, through the winding of relay 102 to ground.

Relay 102 operates and at its inner upper armature and contact applies ground tothe winding' of relay 103. Relay 103 operates and opens at its amature and contact the operating path of and contact of relay 102 completes an operating circuit extending through the upper armature and front contact of relay 105 to one end of the winding of relay 104 and since ground is present on the other end of relay 104, relay 104 is shunted and relay 105 remains operated on the second release of relay 102 whereby ground at the outer upper armature and contact is removed. Relay 105 releases. Subsequent sixty impulses per minutc causes relays 104 and 105 to operate and release in regular recurring intervals as just described. This reduces the sixty impulses per minute to ground to thirty impulses per minute rst to the relays 105 and 101. Relays y106 and 101 operate in a manner similar to relays 104 and 105, respectively, and further reduce the sixty impulses per minute to one second closed and three seconds open interrupted ground pulses. These pulses are transmitted over conductorsV 14| and 120, outer upper amature and back contact of relay 1|0, conductor 142, through the winding of relay 121 to grounded battery and rela'y 121 operates each time a ground is connected t0 conductor 123 which is referred to herein as the inter- 'rupted ground conductor. Relay 121 operates and thereby causes relay 144'to operate. During the Y one-second operate time of relay121, ringing currelay 102. Inasmuch as relays 102 and 103 are slow-tolrelease types the formerv is maintained rent from source 10| is connected at the front contact and upper armature voi? relay 121, conductor 132, front contact and upper armature of relay 144, conductor 145, front contact and middle lower armature ci relay 1|0, line conductor 60|, recall key 5I0, upper make contact of key SI1, .armature and back contact of relay 8| 2, through the ringer 301,'condenser 645 to ground and the ringer at station A is rung automatically at the termination of the live-second operating period of relay 125. 1

Subscriber answers The subscriber in response to the operation of station ringer 601 operates power switch 608.

Power switch 608, upon being operated, completes a path from grounded alternating current source 003,- conductor t! 0, contacts ofthe switch, conductor 6I I. through the windingV of relay SI2, to ground. Relay 612 operates. A path parallel to that extending' over1conductor GII extends over conductor 0| 3 through rectiiler 5I4 and printer 622, armature'andmarking, or lower, contact of terminal to positive terminal of rectifier 614, retardation coil 625, marking, or upper, contact and armature of send relay 626, retardation coil 621, to ground connection 628. The energized rectifier supplies a source of potential difference between its terminals and thus to the circuit including ground connection 628 and line conductor 601. Rectifier 614, upon becoming energized, also causes a eurent to flow in two parallel paths; one extending from thepositive terminal of the rectifier, through the right-hand biasing winding of send relay 626 and the left-hand biasing winding of send relay 623, tothe negative terminal of the rectifier and the other from the posi` tive terminal of the rectifier, conductor 629, break key 630, transmitting contacts 631 of subscriber teletypewriter set 632, conductor 633, normal contacts of the line-in key 634, conductor 635, regulating resistance A636, conductor 631 through the left-hand and right-hand operating windings, in series, of send relays 626 and 623 respectively to the negative terminal of the rectier. Printer magnet `6411 of subscribers teletypewriter 632 is operated by current owing from rectiiier 614, in a circuit including conductor 641, through the winding of printer magnet 640, conductor 642, varistor elements 643, retardation coil 644, marking, or left-hand, contact and amature of receive relay 619, retardation coil 645, to ground at the lower normal contact of key 6 I 1. The biasing, or lower, winding of receive relay 819 is energized over conductor 646 and resistance 638 and serves to operate relay 619 to its spacing, or righthand, position when line 601 is opened. Resist-V ance 638 is of the adjustable type in order that it may be adjusted to suit conditions of the line send relay 623, retardation coil 624, negative 7 (3) prepares at its middle upper armature and contact an extension to the holding circuit for re-s lay 109; and (4) opens at its lower armatures and contacts the operating circuit for line relays 109, 110 and 111. Relay 119, uponv operating, (l) completes at its middle lower armature and iront contact the extension of the holding path for line relay 109; (2) closes at its outermost lower armature and front contact an operating circuit for holding relay 120; (3) at its innermost lower arr'nature and front contact connects grounded battery to start conductor 139 and thereby closes an operating circuit for relay 102; (4) closes at armature and contact a path for maintaining grounded battery connected to start conductor 139 and (2) provides at its lower armature and contact a holding circuit for itself and relay 109 in the event relay 119 releases. Relay 126, upon operating, closes at its armatures and contacts the busy signal path extending from the spacing contact of relay 108, conductor 149,- to conductors 150, 151 and 152, in parallel, whereby busy signals may be furnished by relay 108 to any one of subscribers stations A', B and C which attempts to initiate a connection to toll line conductor when such line is at the-time establishing or in an'established connection.

through the control unit to the switchboard at TWX office. A further description of the various elements in the -circuit shown in Fig. l may be had by referring to Fig. l of- U. S. Patent 2,143,000, supra.

During the idle condition after switch 608 is operated and the potential applied to the line by rectifier 614 is of negative polarity and when the cut-through relay 118 is operated as will be hereinafter described, the negative potential so applied holds the repeater relays throughout the system in the positions shown.

Power switch 608, upon being operated, causes marking, or negative, voltage from rectifier 614 to be applied to line conductor 601 which extends in a circuit traceable over the middle lower armature and front contact of relay 112, conduct/or 145,` `armature and back contact of relay 144, `conductors 143 and 146, through the winding of polarized relay 111, resistancel 141, conductor 148, to ground at the make-beforebreak contacts of relay 118. .Relay 111 is poled to operate on marking, negative voltage, and therefore at this time relay 111 operates to close an obvious operating circuit for cut-through re"l lay 118. Relay 118 which is of the slow-to release type, operates (1) to extend transmission conduc- .tor 601 to toll line conductor 115; (2) closes at its outermost upper armature and contact an operating circuit for slow-to-releasev relay 119;

The negative potential of rectier 614 is now applied to toll line conductor 115 which extends over the armature and back contact of relay 806 through winding No. 1, in series, of polarized re.- lay 801 and polarized receive relay 802, resistance 815, retardation coil 8 16, resistance 811, through the winding of relay 806, conductor 836, innermost upper armature and back contact of relay 814 to ground at the armature and back contact of relay 844. Relays 801 and 802 remain in their marking positions as shown Eand relay 808 oper-y ates and closes a circuit extending from grounded battery 812, resistances 811 and 810, conductors 821 and 828, armature and contact of relay 808,

conductor 829, resistance 830, through the winding of alternating current relay 809, conductors 831 and 832, marking contact and armature of relay 801 to ground. Relay 801 operates. Relay 809, upon operating, closes an obvious operating circuit for slow-to-release relay 803. Relay 803, upon operating, operates relay 614 and removes at its back contact and outer left armature grounded battery from the biasing winding No. 2 of receive relay 802 and of relay 801. Also, relay 803, upon operating, completes the other part of the apex circuit which part extends over resistance 819, front contact and outer left-hand armature of relay 803 through the No. 2 biasing winding of relays V802 and 801, in series, to grounded articial line network 820. Relay 814, upon operating, establishes the alternating current path for holding relay 809 operated, while relay 801 is following the signals transmitted from the teletypewriter at,y subscribers station A and the teletypewriter at the operators position, the circuit changing in accordance with the operationI of relay 801. When relay 801 is in its marking position, as shown, the alternating current circuit, as hereinbefore stated, is traceable from ground at the armature and marking contact of relay 801, conductors 832 and 831,v through the winding of relay 809, resistances 830 and 834, condenser 135, contact and middle armature of relay

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