US2138580A - Printing telegraph system - Google Patents

Description

Nov. 29, E93. F. s, KINKEAD PRINTING TELEGRAPH SYSTEM Filed July 1l. 1936 3 Sheets-Sheet 1 v. mbv

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ATTORNEY Nov. 29, 1935. F. s. KNKEAD PRINTING TELE'GRAPH SYSTEM Filed July 1l, 1936. l 3 Sheets-Sheet 3' A 7` TOR/VE V Patented Nov. 29, 1938 UNTE if.

OFIE

PRENTING TELEGRAPH SYSTEM York Application July 11, 1936, Serial No. 90,082

5 Claims.

This invention relates to a printing telegraph system and more particularly to a telegraph system wherein automatic switches are employed for the establishment of channels of telegraph communicaticn.

The invention has for its main object to eiiect the repeating of signals in each of the line circuits in a printing telegraph private'branch exchange system which utilizes automatically and directively operable switches at a central office for establishing telegraphic connections between subscribers stations.

Another object is to eiect transmission in both directions in a circuit established between any one subscribers station and a plurality of the other, or called, stations and to eiect in a circuit so established, transmission in both directions between any two or more of the plurality of called stations ior conference purposes.

Heretoiore in printing telegraph private branch exchange systems wherein were employed automatically operated line-finder and hunting connector switches, the transmitted signals were repeated over a plurality of line circuit groups to receive a broadcast message, by a repeater connected in the connector switch circuit. In such systems two or more subscribers stations connected in a predetermined group, may be connected to a set of terminals in the multiple contact bank of the hunting connector switch, which set may be directively selected in a manner similar to a set used for establishing a connection between individual subscribers stations. A circuit so established, that is to include a predeterined group of subscribers stations is arranged to permit transmission in one direction only, in other words, from the subscribers station originatinor the call to, the plurality of subscribers stations, grouped to receive the call. This type ci circuit is usually known as a b-roadcast circuit wherein the receiving station cannot transmit, although such stations may transmit over other circuits provided for originating calls. In having a single repeater for a predetermined group oi subscribers stations, it was necessary that the subscribers line circuit have equivalent resistance values, regardless of the length o1" the circuit. The resistance values of all line circuits arranged in a predetermined, or broadcast group, were made equal at the time the system was installed and line circuits of this predetermined value oi resistance may be added to or removed from the broadcast circuit without necessarily adjusting the networks that Were originally installed.

According to the present invention, a plurality of subscribers line circuits may be connected in a predetermined group to a set of terminals on the hunting connector switch or establishing a conference circuit. The conference circuit differs from a broadcast circuit in that it, as its name implies, provides for transmission in both directions between the originating station and any one of the stations in the predetermined group and between stations in the predetermined group. This arrangement also provides for separate repeaters in the subscribers line circuit whereby no compensation in the resistance network individual to the line circuit is required to accommodate for the addition or removal of line circuits in a predetermined group.

One feature of the present invention provides supervision and remote control that is not affected by ground potential differences.'

Another feature resides in the introduction of a special repeater in each line circuit whereby grouping of station line circuits for conference connections may be had Without necessitating additional repeating relays and without impairing transmission.

Still another feature is the provision of a connector switch circuit arranged to hunt the rst idle station in one or more predetermined groups, the one or more groups being connected to a single set of terminals in the multiple Contact bank of the hunting connector switch.

The invention will be understood from the following description when read in connection with the accompanying drawings:

Fig. 1 of which, represents at the left a teletypewriter subscribers station circuit SS which connects over a line with a dial ofce line circuit LC, each arranged according to this invention. The line circuit LC is shown connecting with a typical dial office line-finder LF, which is represented in an abbreviated schematic form:

Fig. 2 shows a dial office connector circuit arranged, according to this invention and adapted to cooperate with the circuits of Fig. l;

Fig. 3 shows a conference line circuit CLC arranged according to this invention and interconnected with the line circuit LC of Fig. l and with the line circuit LC of Fig. 3, which cooperates with the line-iinder LF and the teletypewriter subscribers station circuit SS of Fig. 3;

Fig. 4 is a single line layout illustrating in an abbreviated skeleton form the general circuit arrangement of the invention;

Fig. 5 is a block diagram which shows the order in which the circuits of the invention are to be interconnected.

The operation of the invention will now be described in detail. Let it be assumed that the subscriber of station |0| desires to establish a teletypewriter connection with the stations of the conference line circuit CLC, the circuit arrangements of which are shown by Fig. 3. In this arrangement are represented two groups consisting of master stations M1 and M2, with each of which is associated the group comprising subsidiary stations K1, K2, Kn. Station K1 is identical with station ESI, and station K2 with station 304. All circuits for these stations are shown in detail. For the other stations only the apparatus of the conference line circuit is shown. As will appear from the hereinafter given description, the invention provides that the calling station will dial the number of thc conference line associated with station M1. The connection will then be cornpletedif station M1 and at least one of the stations K1, K2, Kn are not busy. If (a) station M1 is busy or (b1) all of the stations K1, K2, K11 are busy then the hunting connector of Fig. 3 will endeavor to establish connection with the conference terminals of station M2. If now M2 and at least one of the stations K1, K2, Kn are not busy, the connection Will then be completed to the conference .group of station M2. If, however, (a) station M2 is also busy or (D) all of the stations K1, K2, Kn are busy then a busy indication Will be returned to the calling station I0|, as Will be hereinafter described.

To initiate the call, start switch |02 is operated which operates the motor control relay |03 in a circuit traced from the source of alternating current power |04, over conductor |05, through resistance |06, contacts of switch |02, Winding of `relay |03 andl resistance |01 to the said current source |04. To facilitate the operation of relay 03, a rectier 08, which may conveniently be of the usual copper-oxide type, is connected in shunt with the winding of relay |03. With this arrangement, one-half of the alternating current wave through said Winding is effectively annulled so that the operating current for relay |03 is thereby made unidirectional. Relay |03 in operating closes an obvious circuit from alternating current source |04 to the teletypewriter motor |09, which is started and to the rectier ||0, which is represented conventionally by a box and may be of any well-known type. The output of rectifier |I0 is delivered over conductors I I to the winding of relay H2 which operates and closes a circuit for operating relay I I3, which is traced from current on conductor |05, through resistance I 06, operated contacts of key |02, lower winding of relay H3, contacts of stop key I I4, lower contacts of relay I |2 and resistance I |5 to current source |04. Relay I i3 in operating short-circuits the contacts of start key |02, thereby maintaining the operating circuits for relays |03 and ||3 hereinbefore traced, after key I 02 is restored to its normal postion. Relay I2 in operating transfers with its battery |30, through the winding of relay |29,

upper outer back contacts of relay |28, resistance l2?, over line conductor H6, through upper operated front contacts of relay ||2, resistance ||8, normally closed contacts |26 of the sending distributor pulsing contacts of dial |25, contacts of break key |24, winding of printer magnet |23, over line conductor I1, through resistance |22, uppermost winding of relay |2| and operated contacts of relay |20 to positive grounded battery I IQ, Relay |2| also operates in this circuit at this time but it has no immediate function. Relay |20 in operating closes an obvious circuit for operating relay |35, which in turn operates relay |36 in a circuit which is traced from ground through the inner, upper, back contacts of relay |28, upper contacts of relay |35 and winding of relay |36 to grounded battery. Relay |36 in operating places a ground on commutator contact |37, thereby indicating that the terminals |38 of the calling line are located on the tenth level of the line-finder* |39, which functions to cause the brushes |40 to establish contact with terminals of terminal set |38. Details of the linender are well known in the telephone art and are omitted since a complete description would not add to an understanding of this invention. When the lower or sleeve brush of brush set |40 contacts the lowermost terminal of terminal set |38, ground |4| is connected to conductor |42v through the winding of a relay, not sh0wnin the line-finder circuit which operates the cutoff relay |28 in a circuit traced from battery through the Winding of relay |28, over conductor |43, through lower operated contacts of relay |35 to the ground on conductor |42. In multiple with the winding of relay |28', through the lower contacts of relay 35, is resistance |44, Whichis used to reduce the resistance of the operating circuit of the before mentioned line-lnder relay, not shown, the winding of which is connected to ground |4l. Cutoff relay |28 in operating, locks through its lower contacts to ground on conductor |42, and with its uppermost contacts releases relay |29, which releases relay I25. Relay I 35 in releasing disconnects with its lower contacts resistance |44, and with its upper contacts opens the circuit of relay I 30, which releases, disconnecting ground from commutator contact |31.

When brushes of set |40 established contact with terminals of set |38 a circuit was closed for operating relay 20| which may be traced from negative battery through the winding of relay 20|, over con-ductor 202, middle brush of set I 40 and middle terminal of set |38 to junction |45, from which the circuit is the same as that followed for relay |2I. As soon as the circuit for relay 20| is established the current through the winding of line magnet |23 of the circuit of station |0| which was previously flowing from the source connected to the high resistance. winding of relay |29 only, is increased so that this magnet now operates, and connects current in Wellknown manner to the last segment of the receiving distributor, not shown, thereby causing the associated distributor arm to stop revolving, which is an indication to the operator at station |0| that the circuit is ready to receive dial impulses. When relay 20| operated as before described, a circuit was closed for operating the pulsing relay 203, which may be traced from grounded battery through the contacts of relay 20I, over conductor 204, through contacts of relay 205, and windingvof relay 2013 to ground. Let it be assumed now to facilitate this description that the directory number of the conference line with which a connection is desired is, for instance 91, and that the corresponding terminals on the connector bank are 206, 201, 203 and 209. On the rst-break of the dial |25, the circuit hereinbefore traced through the windings of relays |20 and |2| is opened. Relay |2| releases due to the biasing action of the current in its middle winding, the circuit of which may be traced from positive battery II9 through operated contacts of relay |20, middle winding of relay |2|, and resistance |46 to ground. Relay |20 remains operated due to the current through its upper winding and relay 20| remains operated dueto the shunt path through the bridging resistance |53. Relay |2| in releasing connects ground through its back contacts to conductor |50, thereby closing a circuit for operating relay 205, which may be traced from grounded battery through resistance 2|4, upper and lower windings of relay 205 in series, over conductor 218, through back contacts 262 of relay 221, over conductor |41, through tip brush of set |40 and tip terminal of set |38 to said ground on conductor |50. Relay 205 in operating releases relay 203. When relay 203 operated it operated relay 2|8 through an obvious circuit. Relay 2|8 is slow to release and holds over the dial pulses. Consequently a circuit is now closed to operate slow-release relay 2l9 and Vertical magnet 220, which is traced from grounded battery through the windings of vertical magnet 220 and relay 2|9, normally closed contacts of vertical off-normal combination 22 I, over conductor 222, through operated upper inner make contacts of relays 2|8 to ground on back contacts of relay 203. On the next closure of the contacts of dial |25 relay 2| reoperates in turn causing the release of relay 205, the reoperation of relay 203, and the deenergization of vertical magnet 220, relay 2|9 being of the slow-release type remains operated at this time. The connector switch, in the well-known manner, now takes one vertical step, causing the VON springs 22| to operate, transferring pulsing conductor 222 from conductor 223 to a path extending through the armature, front contact and winding of relay 2|9 to conductor 224. Immediately after, on the second opening of dial |25, vertical magnet 220 is reenergized and the switch takes its second vertical step, the pulsing circuit now being completed through the front contacts of relay 2|9, which being slow releasing, remains operated during successive pulses of the dial. In this way the switch is stepped upward until the ninth level is reached, which corresponds to the tens digit, of the assumed number, 91. When the dial closes after the ninth pulse, relay 2|9 releases and pulsing lead 222 is now transferred by the back contacts of relay 2 I 9 to conductor 225. This conductor is exten-ded through the upper, outer normally closed contacts of relay 226, contacts 26| of relay 221 to conductor 228. From conductor 228 the circuit is completed through the middle upper contacts of relay 229 and the winding of rotary magnet 230 to grounded battery. Another multiple circuit from conductor 228 is completed through the winding of relay 23| to grounded battery. The connector is now ready for rotary stepping. After the units digit 1 of the assumed number 91 is dialed, rotary magnet 230 causes the switch to rotate horizontally one. step, and brushes 2|0, 2| I, 2I2 and 2|3 contact with terminals 206, 201, 208 and 209, respectively. If the conference line connected to terminals 206, 201, 208 and 209 is not busy, battery potential will be present on sleeve conductor 232, which will operate the cutthrough relay 221 in a circuit which will now be described. After the last rotary pulse, which in this case is assumed to be that due to the units digit 1 of the number 91 relay 203 and 2|8 operate due to the closing of the line circuit and therefore relay 23| releases and rotary magnet 230 is deenergized. The release of relay 23| accordingly closes a circuit from'battery through the winding of relay 30|, back contacts of relay 302, over conductor 232, through terminal 208 and connector brush 2|2, over conductor 233, lower outermost back contacts of relay 23|, over conductor 234, through upper winding of relay 221, upper inner back contacts of relay 226, to ground on the upper, outermost operated contacts of relay 2|8. Relay 221 partly operates; it first closes a locking circuit for itself from battery through its lower winding, contacts 265, over conductor 235 to ground on the lower operated contacts of relay 2|8, and then completely operates on this lower winding. In the. circuit hereinbefore traced for operating relay 221 through its upper winding, relay 30| also operated and connected ground 305 with its lower, next to outermost armature and front contact to conductor 306. For this description it is assumed that station 304, which corresponds to conference station K2 is not busy. Relay 301 is accordingly not operated, since there is no ground on conductor 309 due to the non-operation of the cutoff relay 308 of the regular line circuit 3|0 of station 304. When cut-oli relay |28 of the regular line circuit |48 of station |0| operated, ground was connected to conductor |49 bythe upper front contacts of relay |28, thereby operating relay 3 I5 of the conference line circuit associated with the regular line circuit of station |0I. The aforesaid ground on the conductor 306 is now eX- tended through the lower outermost contacts of relay 3|6, through similar contacts of intermediate relays similar to relays 3I6 and 3 I1, which intermediate relays are not shown, through lower outermost contacts of relays 3|1 and 3|8, armature and front contact of relay 3|5 operated as aforesaid, armature and back contact of relay 301 and winding of relay 3|1 to battery. Relay 3|1 operates and (l) locks through its lower innermost contacts to ground on sleeve conductor 232, (2) connects with its upper armature and contact tip conductor 240 to tip conductor 320, (3) connects with its lower, next to innermost armature and contacts, ring conductor 239 to ring conductor 321, (4) connects ground to conductor 32| with its lower next to outermost armature and contact thereby operating cut-oil. relay 308, which in operating connects ground with its upper inner front contacts to conductor 309, thereby operating relays 301 and 322. Relay 322 in operating transfers conductor 323 from its connection with the winding of relay 324 to a similar connection with the rst succeeding non-operated relay similar to relay 324, thereby making the conference line circuit associated with said succeeding relay available to a call through the line associated with the conference station M2. The aforesaid ground on conductor 32| is eX- tended over sleeve conductor 325 to the sleeve terminal 259 of the regular non-conference connector terminals of station 304 thereby making this set of terminals test busy. With its upper outer armature and contact cut-off relay 308 also disconnects the winding of relay 326, thereby preventingV its operation from station 304 over the tip and ring conductors 340 and 335.

Relay 221 in operating as before described connects ring conductor 236 through'its contacts 2|1 to the lower armature of relay 231, which operated previously, when relay 2I8 operated,- in a circuit from ground on the upper outer armature and contact of relay 2|3 through upper outermost armature and contact of relay 229 and winding of relay 231 to battery. When relay l231 operates a circuit is closed from alternating ringing current source 238, through lower front armature and contact of relay 231, closed contacts 2|? of relay 221, over ring conductor 236, through `connector brush 2|| and associated terminal 201, over ring conductor 239 through lower, next to innermost armature and contact of' relay 3I1, over con-ductor 321, through resistance 328, over line conductor 335 through upper armature and back contact of relay 329, upper winding of relay 303 and'condenser 330 to ground. Relay 303 which is designed to operate on alternating current, now operates and locks on current from the alternating current supply 33|. The apparatus of the circuit of station 304 now functions in the same manner as did that of station circuit |0|, when relay I|3 operated in response to the operation of start key |02. Relay 332 operates and closes a circuit for starting teletypewriter motor 333. and for energizing the rectifier 334. Rectifier 334 supplies current for operating relay 329, which transfers line conductor 335 from the upper winding of relay 303 to the circuit of the teletypewriter of station 304.

ACut-through relay 221 in operating also closes a circuit for operating relay 229 which is traced from battery through the upper winding of relay 229, resistance 242, lower closed contacts 266 of relay 221, to ground on conductor 235. Relay 229 in operating opens, with its upper, out'ermost contacts the operating circuit of relay 231, which releases disconnecting the ringing current source 238 and connecting negative battery 243 to the ring conductor. Current from positive battery 336 now flows through the operated contacts of repeater relay 331, top winding of repeater relay 338, resistance 339, over line conductor 340, through winding of teletypewriter printer magnet 34|, contacts of break key 342, dial 343, and distributor 344, resistance 345 and thence through the upper armature and front contact of relay 329 and the circuit path over the ring conductor hereinbefore traced in connection with the operation of relay 303, to the'aforesaid negative battery 243; Printer magnet 34| is energized and its'subsequent operation depends on the signal impulses that are transmitted from station |0'I. The circuit details for accomplishing this are well known and are not shown here. Repeater relay 338 is also operated due to the current in` its top winding, which predominates over the normal ow of current from positive battery 336 through its middle or biasing winding.

Relay 221 in operating also performs various additional functions. With its contacts 26| it opens the operating circuit of relay 23|, thereby causing the release of this relay after a connection has been established. Transfer contacts 232 transfer tip conductor |41 from the upper winding of relay 205 to tip conductor 2|5 by way of upper` armature and contact of relay 231 and closed contacts 263 of relay 221. Contacts 264 open the release circuit for the connector switch. Contacts 268 disconnect the hunting lead-2I6 so as-.to prevent the operation of. relay 229 after the circuit is cut'through, and contacts261 connect direct ground from conductor 235 to sleeve conductor 233 thereby holding relay 30| operated and making terminal 208 test busy to' other hunting connectors.

The circuit between the calling station I0| and the called station 304 is now complete and with the motors at both stations operating teletypewriter communication in either direction may now begin. In accordance Vwith common practice, station |0| may signal station 304 by operating the upper case S key, thereby ringing* the teletypewriter bell at station 304. When relay 30| operated as before `described it completed connection over leads 346 to a line circuit similar to line circuit 3| 0. Lead 349, however, is disconnected by the lower outermost armature and contact of relay 30| to prevent the operation of relay 302, when the cut-orf relay (not shown), the winding of which is connected to lead 350, operates, due to the ground on` the lower middle armature of relay 30|.

The said line circuit associated with relay 30| is connected to the circuit of station M1, not shown, similar to station 304, which station is accordingly also now ready for teletypewriter communication in either direction.

The operation of the invention will now be described, assuming that the calling station |0I transmits a message to be received by the station 304- and thek station M1 connected over leads 346. When the sending distributor of station |0'| transmitsV spacing and marking impulses repeater relay 52| is actuated correspondingly due to the opening and closing of the circuit through its top and bottom windings. When a spacing impulse is transmitted, relay I 2| releases and connects ground to conductor |50. This ground impulse is now transmitted through the tip terminal |38 and associated tip brush |40k of the line-finder |39, over tip conductor |41, through upper operated contacts 262 of relay 221, upper break contacts oirelay 231, upper operated contacts 253 of relay 221, through connector brush 2|0 and associated terminal 206, over conductor 240, through upper operated contacts of relay 3|?, over conductor 320 to the armature of repeater relay 333, which relay is operated, as aforesaid, due vto the operation of relay 329. The normal flow of current through the bottom windings of relays 336 vand 331 is now increased. Relay 333 continues to hold, but relay 331 releases due to the neutralizing eiect of the increased current in its bottom winding. The release of relay 331 disconnects positive battery 336 from the tip conductor 340and connects negative battery 341 thereto. Negative battery 341 meeting negative battery 243 over the ring conductor reduces the current through the winding of the teletypewriter printer magnet 34| to zero,v which accordingly releases delivering a spacing im.- pulse to the teletypewriter apparatus. When the sending apparatus of station |0| transmits a marking impulse relay 25 reoperates due to the reestablishment of normal current through its top and bottom windings and disconnects ground from conductor |50 which reduces the current through the lower winding of relay 331, allowing relay 331 to operate on the normal current through its upper winding and transmit a marking impulse from positive batery 336 to the station 304.. In this manner the teletypewriter messagey is transmitted from station |0| to station 304. The marking and spacing impulses delivered over the tip conductorV |50 alsopass through the upper operated contacts of relay 301, to the tip lconductor 348 which connects with the armature of a repeater relay similar to relay 333, which repeater relay is in the regular line circuit associated with conference station M1. This causes a repeater relay, similar to relay 331, to operate and deliver spacing and marking impulses to its associated stationv (not shown), negative battery 243 functioning over conductor 239, through lower innermost armature and contact of relay SBI and conductor 348.

The operation of the invention has been discussed for the transmission of a message from station IOI to the station 324 and the conference station M1. A description will now be given for transmission from the called station 324 to station IDI. When spacing and marking impulses are delivered from station 304 relay 33B functions in the same manner as did relay I 2i, ground pulses being delivered to conductor 322 and thence over the tip conductor path, hereinbefore traced, to the armature of relay I2I. These ground pulses hold supervisory relay 221 through resistance 132 and cause relay I 26 to deliver spacing and marking impulses to station I'I, causing the apparatus thereat to print the transmitted message. Simultaneously the ground pulses from relay 38 are also delivered through the top contacts of relay BIII over conductor 348 to the M1 station (not shown) at which station the message from station 304 is also recorded. In like manner, the station M1 may also transmit a message which is recorded at stations IBI and 304. Accordingly the three connected stations can freely intercommunicate with each other as desired.

In the description before given it was assumed that the conference group associated with conference station M1 was not busy,'that is, that the station M1 with at least one of the associated stations K1, K2, K11 was not busy. It will now be assumed that a busy condition is encountered, and in accordance with the operation of the invention that the brushes 2I0, 2II, 2I2 and 2I3 of the hunting connector of Fig. 2 now automatically pass over the terminals 206, 221, 208 and 229 and connect with terminals 244, 245, 246 and 241 connected to the conference station M2 and the conference stations K1, K2, t is assumed that station Mz and at least one of the associated stations K1, K2, Kn are not busy. For descriptive purposes let it be assumed that the non-busy station is K2, as in the before given description.

In reference to the M1 station a busy condition is established if ground is found on sleeve terminal 283. This may be due (l) to ground connected by another connector similar to the connector of Fig. 2 or (2) to ground connected to conductor 232 by the operation of relay SI12. Re.- lay 322 may be operated through its upper winding from ground on conductor 349, connected through the lower outermost contacts of relay 321 to ground on the operated contacts of the associated cut-off relay of the regular line circuit of station M1, which cut-off relay was previously operated due to a connection established through the regular line circuit or the regular connector terminals. Relay 302 may also be operated due to a circuit closed from battery through its lower winding, lower, next to outermost back contacts of relay 36|, over conductor 3135, through lower outermost contacts of relay SIS, similar contacts of intermediate relays between relays SI5 and 311, lower outermost contacts of relays SI1 and 3 I8 and operated front contacts of relays SI5 and 301 to ground on the operated contacts of relay 3I I. Relay 302 in operating also disconnects the winding of relay 351.

When brush 2 I 2 encounters the grounded sleeve terminal 228 a circuit is closed for operating relay 223 which may be traced from battery through the winding of release magnet 248, winding of relay 226, break contacts of rotary magnet 231), (which is now deenergized due to the absence of ground on pulsing lead 222 following the dialing of the units digit 1 of the assumed number 91), iower outermost front contacts of relay 23I before this relay releases, over conductor 233 to the aforesaid ground on the sleeve terminal 228. When the slow-to-release relay 231 nally releases, relay 225 locks up through a circuit traced from ground on the upper outer contacts of relay 2I8, over conductor 252, through upper, inner operated front contacts of relay 223, over conductor 25|, thence through the lower, middle, normally closed contacts of relay 231 to battery over the operating path originally traced. When relay 23I releases it also closes a circuit to operate relay 229, which is traced from battery through the lower winding of relay 229, through resistance 252, lower innermost break contacts of relay 235, over conductor 253, through lower outermost contacts 268 of relay 221' to the ground on the hunting terminal 222 which is connected to the sleeve terminal 293. Relay 229 in operating also locks up under control of relay 226 in a circuit traced from battery through the lower winding of relay 229' and its lower innermost and middle contacts in series, over conductor 254, through resistance 255 and lower outer contacts of relay 226 to ground on conductor 256. When relay 229 operates as before described it closes a circuit for operating relay 231' which is traced from battery -through the winding of relay 23I over conductor 228, through upper contacts 261 of relay 221, upper outer, operated front contacts of relay 226, to ground on the upper innermost contacts of relay 229. When relay 23I operates as aforesaid it connects the winding of rotary magnet 230 in multiple with its own winding by means of its upper, inner make contacts. This causes rotary magnet 23@ to rotate the brushes 2 I II, ZI I7 2 I2 and 213 one step until they contact the neXt terminals 244, 245, 225 and 241, corresponding to the number following the assumed number 91, that is, 92. The operation of rotary magnet 231i opens the operating circuit of relay 225, which releases, thereby opening the circuit of rotary magnet 23u, before traced. When magnet 239 releases the winding of relay 226 is connected from battery on the winding of release magnet 263 to sleeve terminal 246, over the same circuit which was traced when brush 2 I 2 made contact with sleeve terminal 228. In this case, however, by assumption the conference station M2 is not busy, that is, there is battery potential on sleeve terminal 2436 and consequently relay 226 doesv not reoperate. Since the number 92 is the second or last number in the group, the hunting terminal 241 is left unconnected. Consequently, the locking circuit which was formerly established for relay 229 through its lower innermost contacts, resistance 255, lower outermost contacts 228 of relay 221 to ground on hunting terminal 299 is now no longer maintained and accordingly relay 229 releases. The connector circuit now functions as before described when connection was established with terminals 226, 221, 228 and 229. In this case relay 221 operates through its upper winding over conductor 353 in series with the Winding of relay 35|, which also operates. Relay 35! with its lower, next to outermost front contacts connects ground to conductor 354 which is extended through lower outermost contacts of relay 355, of intermediate relays not shown, of relays 324 and 356, operated front contacts of relay 351, back contacts of relay 322 to battery through the winding of relay 324. Relay 324 operates and functions with respect to conductors 3M in the same manner as did relay 3|1 when connection was established to the terminals or" the conference station M1 and relay 35| in operating as aforesaid functions with conductors 360 as did relay 30| with the conductors 34S. Station I2! is now connected through for'conference communication, over tipfand ring conductcrs 358 and 359 to the lines of conference station M2, not shown, and of station 304.

The operation of the invention will now be discussed for the busy condition, that is, when stations M1 and M2 are bothbusy, or all stations K1, K2, Kn are busy. When the brushes 250, 2li, 2! 2 and 2|3 in the hereinbefore given description, encountered the busy terminals 206, 201, 233 and 200, they were automatically stepped to the next and last terminals of the conference group, that is, to terminals244, 245, 243 and 241. By assumption, these latter terminals were assumed to be not busy and the operation of the invention in completing the connection was then discussed. These terminals 244,245, 245 and 241 are now assumed to be busy.

Referring to the previously given description, when sleeve brush 2!2 found battery potential on sleeve terminal 243, relay 221 operated when relay 23l released after the removal of the pulsing ground from conductor 225. With busy ground on terminal 246 relay 220 operates in the same manner as it operated from busy ground on sleeve terminal `203, and locks up to ground Yon the conductor 250. When huntingbrush 2|3 contacts the terminal 241, no circuit is closed since terminal 241 is not connected. Consequently, in this case relay 220 does not operate, when relay 23| releases. Accordingly, relay 23! andconsequently rotary magnet 230 are not operated, relay 226 remaining locked up. Relay 226 in operatingconnects ground 251 with its lower inner contacts to the junction vpoint of the upper and lower windings of relay 205. Relay 20.5, however, does not operate, since the current in the windings acts differentially. A circuit closedthrough the upper Winding of relay 205 may be traced from battery |3|, through resistance |33, bottom windings of relays 20 and |.2 I, operated contacts of relay |2|, over tip conductor |50, through line-finder tip terminal |38 and tip brush |40, over conductor |41, through upper back contacts 262 of relay 221, through upper winding .of relay 205 to the ground connected to the junction of its two windings. This current flow causes the magnetic action of the lower winding of repeater Vrelay |20 to predominate over that ofthe upper winding so that relay |20 operates to its back contacts, causing negative battery I5! to meet negative battery I3! over the line of station !0!, thereby reducing the current ow in said line to such an extent'that teletypewriter printer magnet |23 releases and causes the sending distributor-to run open, which will be an indication to the calling station |0| that a busy condition exists.

The operation of the-invention whereby a disconnect signal is given to theV calling station l0! and all apparatus is` restored tonormal when the conference communication between the stations is completed will now be discussed. When the stop key 35! at station 304 is operated the circuit through the lower winding of relay 303 is opened and this relay releases, releasing in turn relay '332, which opens the circuit of teletype- 2 writer motor 333, which stops. The release of relay 332 also deenergizes rectifier 334 which thereby effects the release of relay 329. All apparatus at station 304 is now restored to normal. When relay 323 releases the circuit through station 304 is opened which causes repeater relay 338 to release thereby transmitting a ground impulse over the tip conductor through to the armature of repeater relay 2l. Relay |20 now releases, as explained in connection with the transmission of a busy signal, and the motor of station i0! runs open indicating that a station or" the conference connection has disconnected. The aforesaid ground impulse over the tip `conductor will in similar manner cause the motor of the:

station associated with the conference station M1 also to run open, if the stop key at this station has not been previously operated. The operator at the calling station I0! will now operate the stop key I4 stopping the motor l 09 and restoring r all apparatus at station |0| to normal. When the circuit of station l0! is opened by the release of relay |42, relay l2! releases and also supervisory relay 20| of the connector circuit. The

release of relay 23| opens the operating circuit of relay 203 which releases, inturn releasing relay 2|3 which removes ground from conductor 235 causing the release of the line-finder |30 and the associated cut-off relay |28. Relay 2|8 in Yreleasing also removes the locking ground from the winding of cut-through relay 221 which also releases. The release of relay 221 closes a circuit for operating release magnet 248, which is traced from battery through the winding of magnet y248,

lower operated contacts of VON combination 22|,

upper break contacts 204 of relay 221, and back contacts of relay 2|8 and 203 .to ground. This causes the connector switch with its VON contacts 22| to be restored to normal. The release of relay 2|8 as aforesaid also removed ground from the sleeve conductor 233. This releases relays 35I, 324 and 308, and also the cut-01T relay (not shown) in the line circuit connected with relay 35i over conductors 350. All apparatus is now ready for another call.

The operation of the invention has been discussed for the establishment of a conference connection wherein the connector of Fig. 2 made connection with conference terminals 206, 201,

'208, 203 or 244, 245, 245, 241. It is t0 be undeistood, however, that a connection may also be established on a non-conference basis. Assum-V the same manner as when operated over conductor 32|. Ringing current will be connected to ring conductor 353 which will operate relay 303 and cause the apparatus of station 304 to function as before. Stations l0! and 304 can now communicate with each other. From station l0! the spac- If the called line is not ing and marking impulses are transmitted by relay 21 over the tip conductors of Figs. 1 and 2 as before, through tip brush 2li) and associated connector terminal 251, over conductor 352 to the armature of repeater relay 338. Relay 331 now repeats the received impulses and actuates the teletypewriter apparatus of station 3M. In like manner spacing and marking impulses are transmitted from station 3% to station EDI, relay i2ll repeating the received impulses.

In the previous description the establishment of connections between stations M1, M2, K1, K2 Kn was discussed. Referring to Fig. 4 it is seen that the regular line circuits of these stations, Lilli, 4t2, 463, 406 and mi are connected over conductors M35, 4G?, M38, i309 and fili) with corresponding conference line circuits il l, 412, i i 3, M4 and M5, respectively. All of the aforementioned stations, accordingly, may call or be called in conference over conference connector terminals H6 and 4I?. The same stations may establish non-conference connections over connector terminals lil, lili), 42B, G2! and $22. In addition to the conference stations there may be other stations such as A1 and A2, the line circuits of which are not cross-connected to corresponding apparatus of a conference line circuit. Any one of these latter Stations may originate a conference connection over terminals dit and lill, but it cannot be called for a conference connection by any other station.

The description of the operation of the invention as before given serves to illustrate an important feature oi the invention, whereby it is feasible to connect together for conference communication different teletypewriter stations, as desired, without the necessity of using compensating resistances in series with the line conductors. In other words it is entirely practical to cross connect for a conference group, any number of lines within the current carrying capacity of the apparatus, without consideration being given to the respective resistance of the individual lines. This result is due to the use of individual repeaters in the line circuit of each line.

Another advantageous feature whichis evident from a consideration of the operating description before given is that supervision and remote control of the various stations is unaffected by ground potential dierences.

What is claimed is:

1. In a telegraph exchange system, a plurality of subscribers stations, each arranged to originate and receive calls and certain of said plurality of subscribers stations arranged in a plurality ci groups for conference purposes, a source of signals at each of said stations, a Imain station, line circuits for respectively connecting said plurality of subscribers stations to said main station, means at said main station for connecting in response to signals from one of said sources the line circuit of the calling subscribers station to one or more other of said line circuits respectively extending to the called subscribers stations, and a signal repeater device in each o said line circuits for repeating signals received from the source at any one cf the interconnected subscribers stations for further transmission.

2. In a telegraph exchange system, a plurality of subscribers stations, certain of said plurality of subscribers stations arranged in a plurality of groups, a main station, circuits for respectively connecting said plurality of stations to said main station, a source of signals at each of said subscribers stations, means in each of said circuits responsive to the source of signals at the subscribers station connected to the particular circuit, for repeating the signals from said source, automatic switching means at said main station responsive to said repeated signals for connecting said subscribers station to any one of the other subscribers stations individually or to two or more of the other subscribers stations collectively in one or another of said groups, and means whereby said repeating means is adapted for repeating signals over its associated circuit in either direction depending on the direction of transmission.

3. In a telegraph exchange system, a plurality of subscribers stations, a certain of said plurality of subscribers stations arranged in groups, a connection initiating device and an impulse sender at each of said stations, printing telegraph equipment comprising a transmitting and a receiving unit at each of said subscribers stations, a source of power at each of said subscribers stations for driving said equipment, a main station, a source of current at said main station for operating said equipment in response to the operation of any one of said impulse senders and any one of said transmitting units, a normally deenergized circuit connecting each of said subscribers stations with said -main station, automatically operated switching mechanism at said main station responsive first to said connection initiating device and then to said impulse sender, aterminal in said mechanism, means whereby said terminal may be selected by said impulse sender at a calling one of said subscribers stations for establishing a connection between said calling subscribers station and any one of said groups of subscribers stations for conference purposes, means whereby said source of power at said calling subscribers station is effective to drive its associated printing telegraph equipment in response to the operation of said connection initiating device at the calling subscribers station and said sources of power at said connected stations being effective to drive their associated printing telegraph equipment upon the establishment of the completed connection, and a repeating device in each of said normally deenergized circuits for repeating impulses of current transmitted by said transmitting unit at the transmitting station to each of the receiving units at the subscribers stations in any one group that is connected for conference purposes.

4. In a telegraph exchange system, a plurality of subscribers stations, a certain of said plurality of subscribers stations arranged in groups, a connection initiating device and an impulse sender at each of said stations, printing telegraph equipment comprising a transmitting and a receiving unit at each of said subscribers stations, a source of power at each of said subscribers stations for driving said equipment, a main station, a source of current at said main station for operating said equipment in response to the operation of any one of said impulse senders and any one of said transmitting units, a normally deenergized circuit connecting each of said subscribers stations with said main station, automatically operated switching mechanism at said main station responsive iirst to said connection initiating device and then to said impulse sender, a terminal in said mechanisrn, means whereby said terminal may be selected by said impulse sender at a calling one of said subscribers stations for establishing a connection between said calling subscribers station and the idle subscribers stations in any one of said groups of subscribers stations for conference purposes, and a repeating device in each ofsaid normally deenergized circuits for repeating impulses'of current transmitted by said transmitting .unit-atthe transmitting station to each of the receiving units at the subscribers stations in any one group-that is connected for conference purposes.

5. In a telegraph exchange system, a plurality of subscribers stations, a main station, printing telegraph equipment and a source of power therefor at each of said subscribers stations,rsaid source being normally disconnected from its associated equipment, a normally opened line circuit connecting each of said subscribers stations to said main station, said line circuit having Varying impedance values, a signal repeating means. in each of said line circuits, switching means at each of said subscribers stations for closing its associated line circuit, pulsing means in each of said subscribers stations for transmitting an intermittent current over its :associated line circuit, automaticallyoperated means at said main station responsive rstzto said switching means and then to said pulsing means for interconnecting one of said subscribers stations with more than one of the other subscribers stations for the establishment of a multiple, or conference, connection prepared for communication in both directions as soon as the connection is completed, relay means responsive to said switching means for operatively connectingA the power source at anyone of said subscribers stations originating a call, and other relay means responsive when said automatically operated means completes a connection vbetween said calling stations and more than one of the other subscribers stations, for operatively connecting the power sources kvat said more than one of the other subscribers stations.

FULLERTON S. KINKEAD.

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