US1895112A - Printing telegraph exchange system - Google Patents

Description

Jan. 24, 1933. G. s. VERNAM PRINTING TELEGRAPH EXCHANGE SYSTEM Filed May 12,l 1930 6 Sheets-Sheet 1 ATTORN EY BY e'.

Jan. 24, 1933.

G. S. VERNAM Filed May l2, 19550 D CONCENTRATION 6 Sheets-Sheet 2 `F swITcHING TRUNK 0* 23e l 20e, 21o 207 QI um S2326 1 -@,243 zowanv 255 2467 225 247 l 215 Q32 @7J 2'3 21a 249 T-@.167 les 7I2 7&1242

E G CONCENTRATION BOARD CENTRAL STATION OPERATORS PRINTER sI-:T PRINTER sET 1577 CALL (RELEASE IIIZ J C J -\'l/ CUSTOMERS STATION Io. M Q I- I4 I 5a |04- II77 IIe I P I T 133 o l l 5 |29l L '5B mles "9) I i Q 59 C .rv 2r f BIF T27 a *q |34 |39 :t I 2 I IAO h`, Ie I35 *|25 INVENTOR 136 |24 HOV. ACW-DC' GILBERT $.VERNAM I` Y .,I37 BY I -ATTQRN E Jan. 24, 1933. G. s. VERNAM 1,895,112

PRINTING TELEGRAPH EXCHANGE SYSTEM Filed May l2, 193C 6 Sheets-Sheetv I5 STATION TO TOLL- UNE CORD a i966 306 mvENToR 32" smsen-r SNERNAM H STATION To STATION CORD B Flc. 3 ATTORNEY Jan. 24, 1933. G. s. VERNAM f 1,895,112

PRINTING TELEGRAPH EXCHANGE SYSTEM Filed May 12, 195s e sheets-sheet 4 f J 73o 7oz Eef \474 I. K 503 ToLL LINE To ToLL LINE coRD L v TOLL BOARD OPERATORS PRINTER SET INVENTOR GILBERT S. VERNAM B FIG. 4

vATT'oRNET G. s. VERNAM 1,895,112

PRINTING TELEGRAPH EXCHANGE SYSTEM Jan. 24, 1933.

Filed May l2, 193C 6 Sheets-Sheet 5 Tou. LINE clac-unI TO M L TOLL BOARD OPERATORS PRINTER SET (9 GILBERT s. VERNAM FIG. 5

Patented Jan. 24, 1933.'

, UNITED STATES PATENT y oEElcE GILBERT S. VERNAM, OF RIVER EDGE, NEW JERSEY, ASSIGNOR TO INTERNATIONAL COMMUNICATIONS LABOBATOBIES,. INC.,

NEW YORK Application led Hay 12,

This invention relates to printing telegraph exchange systems and more particularly applies to manually operated printing vtelegraph exchange systems.

, a toll switch board in the central oice one customers printer may be connected directly to another customers printer in the same city or in a different city. The service provided by this toll switch board will correspond in general, to a toll telephone exchange service.

A feature of this invention is the reduction of line current to a fraction of its usual amperage when the line is idle.

A second feature of this invention is the operation of the toll line circuits full duplex for the purpose of controlling the lamp signals so that the calling and supervisory signals may operate independently in the two directions over the line, with the automatic conversion of the circuit to half duplex operation, when printing connections are made.

A further feature of this inventionis a cord circuit for establishing vfull duplex through connections between two telegraph toll lines at an intermediate switching center with provision for the connection of an operators printer intq this cord circuit so that the operator at the intermediate station can communicate with both terminal stations.

A further feature of this invention is the use of monitoring keys in the cord circuits whereby the toll board operator can readlly cut her printer in or out of any of the cord circuits. A feature closely associated with this one is the use of a splitting key in the toll board operators printer circuit permitting the toll board operator to comprinter with either cord of a A further feature of this invention is the OF NEW YORK, N. Y., A CORPORATION 0F PRDITING TELE-GRAPH EXCHANGE SYSTEM 1930. Serial No. 451,693.

arrangement whereby the customers may advise the concentration board operator by lamp signals as to the nature of the service desired.

A further feature of this invention is an alternative arrangement whereby the customer may, by selective means predetermine where at the central station his call is to be answered.

A further feat-ure of this invention is the association of the signal lamps with the cord circuits rather than with the line circuits, and the arrangement whereby the lamps are lighted only when action is required on the part of the operator.

An additional feature of this invention is the provision of a motor control whereby the printer motors at the customers stations are started when the station line is connected to a printer or to a toll board cord at the central oiiice and the provision for stopping the motor from the central oiice or at the customers station.

Outline of system l Referring to the drawings, Figure 1 shows in schematic form two groups of customers i' `of the form of the invention as illustrated i Figs. 2 to 5.

Fig. 2 shows in detail the circuit of a customers station, and the circuits of various parts of a central station viz. a concentration board, a concentration board operators printer set, a switching trunk and a central station printer set.

Fig. 3 shows in detail the left hand portion of station to toll line cord circuit yI and the circuit of station to station cord H.

Fig. 4 shows in detail the right hand portion of the station to toll line cord circuit I, the toll line to toll line cord circuit K and the left hand portion of the toll board operators printer set circuit L.

Fig. 5 shows in detail in circuit J the apparatus at one end of a toll line, similar apparatus being located at the distant endof the line at station M the direction of which is indicated but which is not shown; this gure also shows the right hand portion of toll board operators printer set circuit L.

Fig. 6 shows in detail the circuit of customers station() similar to circuit C of Fig. 2, and in circuit P a portion of a toll board and two concentration board si al panels at a central station showing their use with a selective call system.

Fig. 1 illustrates in outline, the proposed manual printer exchange system. kWhile for purposes of illustration only `live customers statlons are here shown as associated with central station A there may be a lar e number of such stations and all the circuits have been so arranged that the whole system can be expanded with facility to handle an indefinite number of new customers stations as well as new central stations. Thus the concentration board station connections may be readily increased and the number of concentration board and central stations operators printers can be increased to serve the additional local stations. Also the number of station to station, station to toll line and toll line to toll line cords, may vary in number according to the requirements of the traffi, only one of each type being shown, however, in this fi re. Obviously there may also be any num r of station to station toll lines coming into each toll board. It will therefore be understood that in the description of the system in the ensuing pages typical hook-ups will be presented and no attempt will be made to point out all the connections that might possibly be made.

In regard to the expansion of the system illustrated attention is particularly called to certain specific points 1n the circuits where e ansion may take place. At the following points the ground connections ma be made through auxiliary signal circuits; ig. 2, circuit D, at 724; circuit F, at 710, 711 and y712; Fig". 3, circuit I, at 713; circuit H, at 714; Fig. 4 circuit I, at 715; circuit-K, at 716 and 717 Fig. 5, circuit J at 718; circuit L at 719; Fig. 6, circuit P at 720, 721, 722 and 723. At oint'204 in circuit F, Fig. 2, point 708, in clrcuit J, Fig. 5 and point 709 in circuit P, Fig. 6, additional lamps and jacks may be inserted. In' Fig. 3, circuit H, at points 703 and 704 additional monitoring keys might be inserted for use with additional cord cir` cuits, likewise in Fig. 4, at points 705, 706 'sind 707. No attempt has vbeen made, however, to point out all the specific points at wlhich expansion of the system might take p ace.

Likewise it will be understood that there may be any number of additional central stafi tions with associated local lines, and that these various central stations may be con.- nected one to another over the various toll lines insome cases directly and in other cases through an intermediary central station or several intermediary central stations, and

any one customers station associated with one of the central stations may therebybe connected with any other customer station associated with that particular central station or with any other central station.

In Fig. 1 customers stations 1 to 5, are shown connected by telegraph lines 6 to 10 to the concentration board jacks 11 to 15. Connected to an additional jack 16 on the concentration board is a concentration board operators printer 17 by means of which the concentration board operator may communicate with the toll board operator. Cords 18,

19 and 20 at the concentration board lead to tration board with the toll board for various types of service. They may connect any two of customers stations, 1 to 5 through the toll board by means of station to station cord 35.

They may also be used for connecting one of the customers stations 1 to 5, to a central station other than central station A through station to toll line cord 38, connection with the distant central station being made through one of the telegraph toll lines 39,- 40 or 41 associated with the toll board jacks 42, 43 and 44, respectively, each of which lines may be connected to a different central station. The third cord 45 at the toll board is known as the toll line to toll line cord and may be connected to any two of the toll lines 39 to 41 through plugs 46 and 47. In-the toll board cord circuits 35, 38 and 45, monitoring keys 48, 49 and 50 are respectively inserted. By means of these monitoring keys the toll board operators printer 51 may be connected to any one of the three cord circuits. Central station B together with its customers stations and lines and toll lines, is a duplicate of vcentral station A and its auxiliary rlines and has therefore not been specificall described.

The operation of the system for the pur-v pose of sending telegrams or cablegrams through central station A will be clear if i-t is stated that any oneof the customers stations, 1 to 5, desiring to send a. telegram or cablegram is connected by the concentration board operator with one of the central sta- Lagan ing trunkl such as 27, a station to toll lineV cord 38 and toll line 39, 40 or 41 to the toll board of central station B- and thus in reverse order from the toll board at central station B, over a switching trunk to the concentration board of central station B and so to the customers station associated with central station B with which communication is desired.

Where central station A is used las an intermediate station for connecting two other central stations, connections will be made over two of the toll lines 39, 40 and 41 by -means of a toll station to toll station cord 45 the circuit thus passing through only the toll board ofthe intermediate station.

Umtomers station circuit In Fig. 2, customers station C is shown connected to a concentration board D and associated therewith is shown concentration board printer set E, switching trunk F and central station printer set G.

At the customers station C, polar rela 101 is connected in series with customers telegraph line 102 joining the 'customers station C with concentration board D at the central station. This relay 101 has two windings, connected in series, one of low resistance 103 and one of high resistance 104, and is equipped with a biasing spring 105 which tends to move the relay armature 106 against contact 107. Relay 101l will be released and will close contact 107 on the application of a positive potential to line 102 at the central station. In the normal or idle condition of the customers station circuit, l

through the winding of marginal relay 113y and conductor 114 to normally closed jack contact 115 and thence through resistance 116 and over customers line 102 through windings 103 and 104 of relay 10,1 in series, over conductor 117 through printer-line magnet 118, transmitter 119 and trecall or break key 120 to ground 121. Under these conditions, relay 101 will be operated but marginal relay 113 will not be affected by this strength of current.

In the case of a call, either from a central station circuit of this figure (21, 22 or 23 of Fig. 1) or from the toll board (see Fig.'1), a cord plug will be inserted in one of the line jacks 123 of the concentration board with the result that a positive potential will be applied to customers station line 102. The method of applying this positive potential tothe cord circuits will be described later.

The application of the positive potential reverses the direction of the current in relay 101, which was previously held operated by a negative potential, and it thereupon releases armature 106 which closes contact 107. A current is thereby passed from terminal 124, of a local A. C. or D. C. source Lover conductor 125 through resistance 126, conductor 127, through winding Vof control relay 128, conductor 129, to'back contact 130 of relay 131, across armature 132, conductor 133 to contact 107 and thus through conductor 134, resistance 135 and conductor 136 to the opposite terminal 137 f of the current supply. The

closing of this circuit operates control relay 128 which closes its contacts 139 and 138 there- .by respectively, putting into operation printer motor 140, and short-circuiting high resistance Winding-104 of relay 101. vThe line current now increases to its usual working `value of about 60 milliamperes. Resistance 116 in customers line 102 is included in the circuit to regulate the current to this value and to compensate for variations in the resistances of the line wires to different' stations. Under these conditions, printer signals may be sent from the sending contacts of customers station'transmitter 1'19 or from those of a central oiiice or distant printer, and these signals will operate the respective printers without operating relay 101 since spring 10@ gives the relay a positive bias. If a negative potential is'again applied to the line, however, the reversal of current will operate relay 101 to pull up armature 106 and break the circuit through the control relay -128 at contact 107, causing the control relay 128,to release, thus stopping printer motor 140 and reinserting' the high resistance winding 104 of relay 101 into the line circuit. The circuit is now restored to its original or idle condition and a negative current of approximately 6 milliamneres is passing through the circuit.

.In the case of a call originating at customers station C, the customers operator'operates calling key 141 in a direction to close contacts 142, which short-circuits the high resistance winding 104, of relay 101, thus increasing the line current from approximately 6 to 60 milliamperes. The calling key 141 (prrinter 122 in central station printer that the lever will lock in the calling'position or in the normal position but when operated to the releasing side (for purposes to be described later) the key is non-locking and will restore itself to the normal'position when released by the operator.

If the key is left in the calling position, the increased line current will operate marginal relay 113 at concentration board D, which relay, will in turn operate relay 143 of the concentration board circuit which locks itself through a circuit traced from ground 144 through contact 145, jack contact 146, conductor 147, current source 109 and ground 108. Under these conditions current will be applied to toll lamp 148 at concentration board D over a circuit which may be traced from ground 149, contact 150 of relay 143, conductor A151, front contact 152 of relay 113, conductor 153, conductor 154, current supply 109 and ground 108, lighting the lamp and indicating that a connection with the toll board is d esired.

If, on the other hand, calling key 141 at customers station C is operated to the calling position and then restored to normal, the relays 113 and 143 will operateas described and then relay 113 will release, with the result that the message lamp 155 will be lighted, indicatingr that the customer wishes a connection with a central station printer to record an outgoing telegram or cablegram. In either case, relay 101 of customers station C will not be released until a positive current is connected through the concentration board to customers line 102, as previously described. The insertion of a cord plug into the jack 123 at concentration board D will obviously release relays 113 and 143l by` breaking the operating circuits of these relays at contacts 115 and 146 respectively extinguishing whichever lamp is lighted.

After a connection has been established and relay 101 has been released andc'ontrol relay 128 operated at the customers station the customer may send a disconnect signal to the. central station by operating key 141 momentarily to the release position thus closing contact 156 which closes a circuit commencing at terminal 137 of the local current source and consisting of conductor 136, resistance 135, conductor 134, contact 107, conductor 133, conductor 157, contact 156,

conductor 158, Winding of relay 131, resistance 126, and conductor 125 to the opposite pole 124 of the current source. Relay 131 is thus operated and locks itself through its front contact 159 thus breaking the operating circuit of control relay 128 at contact 130 and releasing said control relay which in turn -stops printer motor 140 by breaking contact 139 and connects the high resistance Winding 104 of relay 101 into the "line circuit by breaking contact 138. The resultant reduction in the current in customers line 102 acts to light supervisory signals in the various cord circuits at the toll board as will be described later. When the circuit is .disconnected at the central otlice, a negative current from source 109 is again applied to customers line 102, relay 101 will be operated and the locking circuit of relay 131 broken at contact 107 of relay 101, thus releasing relay 131 and restoring the circuit to normal.

Central station prt-'Itter set crm't As was indicated in Fig. 1 the central station apparatus and circuits `consist generally of concentration board D, concentration board operators printer set E, switching trunk F, central station printer circuits G, station to station cord circuits H, station to toll line circuits I, toll line circuit J, toll line to toll line `cord circuit K and toll board operators printer set circuit L. Circuit G of Fig. 2 illustrates the circuit of the printer set at the central telegraph office used for sending and receiving telegrams and cablegrams. In the idle condition, all of the relays in this circuit are released asV illustrated .and the printer motor 160 is stopped. To prepare this circuit for the transmission of messages the plug 161 which is located at the central station concentration board, is in serted into jack 123, by the concentration board operator thus connecting the central station printer set circuit G with customers station C through line 102, the control relay 162 willbe operated to start motor 160, light the guard lamp 163, and to supply current for the local circuits of the printer as well as to connect a positive current from current source 164 to the customers station line 102. The circuit for operating the control relay may be traced from ground 108 .at concentration board D through current' source 109, protective resistance 165, conductor 147, jack contact 166, sleeve of jack 123, sleeve contact of plug 161, conductor 169, junction point 199, conductor 170, key 171,

conductor 172, back contact 173 of sleeve relay 174, conductor 175, conductor 176, and

so through winding of relay 162 to ground 177.

' It will be seen that the operation of relay 162 closes Contact 168 which connects current lsource 164 through contact 168 to junction 178 from which current flows through resistance 179 to guard lamp 163 and thus to 102 to customers station C as above indi' cated Where motor 140 is started. v The stations now are ready for the transmission of when it is inserted in the jack is so low that it is impossible for the operator to receive a shock from the circuit, except possibly from an inductive discharge from the winding of control relay 162 or the kwinding of sleeve relay 174 when the cord plug 161 is pulled down. This could be avoided, if necessary, lb connecting a resistance from the sleeve of p ug 161 to the ground. The same general method of preventing shocks is used for all the jacks and plugs on the toll board.

en communication between the stations has been completed, the central station printer operator momentarily operates release key 171. This breaks a connection through conductor 172, contact 173, and armature 175, which short-circuits the winding of sleeve relay 174, thus permitting relay 17 4 to operate in series with the control relay 162 and on being energized, sleeve relay 174 itself opens the short-circuit at back contact 173, so that it will not release when the contacts of release key 171 are again closed. It also shortcircuits the winding of control relay 162 b grounding itself through its front contact 18 and ground 188, thus releasing control relay 162, which opens contact 168 thus cutting olf the current from guard lamp 163 and conductor 181 and stopping the printer motor 160. Sleeve relay 174 also applies a negative current from source 189 through the winding of the marginal recall relay 190 to the station line circuit by means of. conductors 191, front contact 192 of sleeve relay 174 and conductor 185, and vtip of plug 161. This current o erates relay 101 at the customers station to pull up armature 106 which opens a circuit to sto printer motor 140 as previously described. Sleeve relay 17 4 also passes a negative current from current source 189 through resistance 193, conductor 194, contact 195, conductor 196, and disconnect lamp 197 Ato ground 198, which circuit lights disconnect lamp 197 located at the concentration board as a signal to the concentration board operator to pull down cord plug'161. As a negative potential has already been applied to customers line 102 from source 189 with the result that the line current has been reduced to approximately 6 milliamperes by the release of the control relay 128 at customers station C, the marginal relay 113 at concentration board D will not operate when plug 161 is withdrawn at, the concentration board. When this plug is withdrawn, however, negative current from source 109 is cut oli from the sleeve ofv plug 161, sleeve relay 174 is released and by reason of the breaking of the circuit at its contacts 195 and 192, respectively,'negativecurrent from current source 189 is removed from disconnect lamp 197 and from tip of 1p1ug'161, and the circuit is restored to its normal or idle condition.

If the concentration b oard opaerator should be slow to disconnect and the customers operator should wish to place another call, call key 141 at customers station C may be operated to close contacts 142 to increase the negative 6 milliamperes currentto a negative current of approximately milliamperes as previously. described. Under these conditions, the recall relay 190 of printer set G, which is a marginal relay operable on a current of 60 milliamperes but not on a current of 6 ,milliamperes, and which is connected through front Contact 192 of sleeve relay 174 to the customers line, will operate and short-circuit sleeve relay 174 through a circuit traced from junction 199,`through conductor 170release key 171, conductor 172, contact 200, armature 201, conductor 202, Winding of control relay 162 and -ound 177. Sleeve relay 174 having been re eased will disconnect the circuit operating recalnlwrelay 190 through contact 192. Recall relay 190 is shunted by resistance 203 to make it slightly slow to release thereby preventing it from releasing until sleeve relay 17 4 has b een completely released.' The release of sleeverelay 174 also removes the short-circuit from control relay 162 which thereupon operates,

. closes contact 168 which passes a current from currentsource 164 to junction 178 thus lightthrough conductor 181, to start printer motor 160 and also passing a positive current through transmitter 122, conductor 183, contact 184, conductor 185 to the tip of plug 161 and so through customers line 102 to customers station C where, by previously de- The switching trunk circuit is shown at F of Fig. 2, (see also switching trunks 27, 28 and 29 in Fig. 1). This circuit serves to extend lthe connections inl either direction ybetween the concentration board and the toll board. If the toll board has more than one ying theguard lamp 163 and passing a current position, the circuits can be multipled at the toll board as indicated in the drawings, (204 .of circuit fF, Fig. 2). If there are several concentration boards, each board will have its` own group of trunk lines to the toll board,

handle the peak load.

sufficient trunk linesv being provided If the toll, llamp 148 at concentration l board D, which is associated with customers station line 102 vlights'indi'catingl that l(511stomers station C wishes to place a toll call,

loffrom customers line 102 through jack 123,

tip of plug 205, conductor 208, contact 209 of jack 210 through conductor 211, similarly through contacts of jacks at any other toll board positions as indicated by dotted lines v"l at 204 and nally through contact 213 of jack 212, conductor 214 and winding of marginal relay 215, resistance 216, negative current source 217 to ground 218. Marginal relay 215 is thereby operated, closing contact 219 and thus closing circuit from ground 220, through positive current source 221, resist- Aance 222, contact 223, conductor 224, contact 219, conductor 225, call lamps 167 and 226 to I ounds 186 and 227 respectively, thereby are located at the toll board. Relay 206 in operating also short-circuits resistance 228, thus preparing a circuit for later operating the guard lamp 229 located at the concentration board. I

This call 'may `be answered ylay inserting `pug 230 (Fig. 3) of station to station cord or plug 231 (Fig. 3) of station to toll line cord I into the switching trunk jack 210 at the toll board or into the corresponding jack for this trunk at any other toll board posi? tion such as jack 212. The detailsof these -cord circuits will be explained later. The i, insertion of oneof these plugs places ground 40 on kthe sleeve of jack 210 through sleeve of plug 231, conductor 233, winding of relay 451, conductor 452, winding of relay 234 and 'ground 235. From the sleevey of jack 210 the ground isl connected through contact lli 236, conductor 237, contact 238, conductor 239, winding of relay 240, resistance 241, to positive current source 221 and so to ground 220, thus o eratin busy relay 240 of switching trunk F, whicIx, by opening contact 223, .extinguishes call'lamps 167 and 226 and also closes a circuit through busy lamps 242 and 243, traced from ground 220, through positive current source 221, resistance 244, contact 245 of relay 240, conductor 246, to junction point 56 247 and thus over conductor 249 and through busy lamp 242 to ground v248vand from junction point 247 again over conductor 249 through busylam 243 to ground 250 and slmilarly through usy lamps at other 'posiv60, tions as indicated by the multi le connections 'at 204. The insertion of `a cor plug i-nto jack 210 or the corresponding "jack sulch as 212 at another position also opens contacts`209 thus removing ground from marginal relay 215 fwhich consequently releases. The tips of ghting the call lamps 167 and 226 which cord plu 230 and 231 (Fig. 3) are both connecte to positive current sources as will be later detailed. On the insertion of one of these plugs in jack 210, the source of positive potential is applied to the customers line 102 through conductor 208, contact `207, tip of plug 205 and jack 123. As previously explained, this posltive current will start printer motor 140 at customers station C.

In the case of a call from the toll board for a station line, the toll board operator inserts a cord plug 230 or 231'(Fig.'3) into an idle switching trunkl jack such as 210. This closes contact 236 and thus places the ground associated with the sleeve 'of plugs 230 or 231 on conductor 237y and passes it through'resista-nce 228 (relay 206 being unoperated) over conductor 239 and through the windings of busy relay 240, through resistance. 241, source of potential 221 to ground 220. Resistance-228 in this case, so

limits the current from source 221 'that' marginal sleeve relay 234 (Fig. 3) of cord I ormarginal rela 251 (Fig. 3) of cord H, cannot operate. usy relay 240 ron ybeing operated, closes its vcontact 245 and, as previously explained, lights the busy lamps 2/12 similarly through guar lamps at other positions as indicated b the dotted line at 710 to ound 255, thus ighting the guard lamp at t e concentration board advising the'concentration board operator of the out oing call. The toll board operator then in orms the concentration board operator of the number of the called station. This maybe done by using` a separate order wire operating-by telephone, by printing telegraph, by manual telegraph means or the switching trunk cord plug 205 may be inserted into jack 256 ofthe concentration boardprinter set E (see also 17 o'f Fig. 1), the operation of which vwill be obvious to those skilled in the art, and the,

necessary information sent directly over the trunk circuit.

The concentration board operator will then insert the switchin trunk plug 205 into jack 123 of the callecustomers station line, this will apply a negative current from current source 109 at concentration board D to the sleeve of jack 123 which in turn will pass the current throu h the sleeve of plug 205 to the winding o sleeve relay 206 of switching trunk F, thus operating relay 206 which opens contact 254 and thus extinguishes guard lamp 229. Relay 206, by closing contact- 238 shunts resistance 228, placing suicient additional current from source 221, on the coils of marginal relay 234 (Fig. 3) of cord I or 251 (Fig. 3) of'cord H, to operate it, thus applying a positive current from source 437 (Fig. 4) or sourceV 'tomers station C where it will start the y into the line again at jack 210.

motor 140 as previously described.

When the call is completed, the toll board operator pulls down the cord plug fromswitching trunk jack 210 which breaks contact 236, releasing busy relay 240 and closingcontact209 of Jack210 thus re-establishing the circuit through the winding of marginal relay 215 to the negative current source 217. This operates relay 101 and releases relay 128 at the customers station, and as the call.

key 141 is in its normal position, the current 4will be reduced to about 6 milliamperes;

Relay 215 may operate momentarily immediately after the removal of the plug, but it will release when the line current is reduced. As relay 240 is released, and sleeve relay 206. remains operated, the circuit from current source to guard lamp 229 is closed andthe lamp will light.Y Contact 245 beingopened on the release of relay 240 the busy lamps 242 and 243 will be extinguished. Under these conditions, the concentration board operator should pull down the switching trunk cord plug 205, restoring the circuit to normal. However, if the opera-tor at the customers station should operate the call key 141 (closing contact 142) to place a new call, before the switching trunk cord plug 205 has been pulled down, high resistance winding 104 of relay 101 will be removed from the cusomers linecircuit and the Acurrent increased from approximately l6 milliamperes to vmilliamperes and marginal signal relay 215 of switching trunk F will then operate to light call lamps 167 and 226 at the toll board and by opening contact 807 will also extinguish the guard lamp 229, whereupon the toll board operator-will plug Station to station cord circuit stations and that, further', thne front andback plugs 268 and 230 respectively, have been inserted .into the jacks 210 oftwo separate switching trunks, which are extended through the concentrationboard D to station C of the called and calling customers, respectively. Relays-'206 and 240 of switching trunk F (Fig. 2) will, therefore, be energized as well as the control relays 128 at the customers station C (Fig. 2) and the sleeve relays 251 and 259 of the station to stationcordcircuit H will also be operated. The polar repeaing relays 257 and 258 will be energized in a direction to hold their respective, armav tures 259 and 260 against marking vcontacts 261 and 262 respectively.

The two left hand windings 263 and 264 of relay 257 and windings 265 and 266 of relay-258 are differentially connected, windings 263 and 265 being connected to ground through the concentration board and the station line, which circuits may be traced, for winding 263, through conductor 808 through front contact 267 to the tip of plug 268 and so through a switching trunk F (Fig. 2), and concentration board D to customers line 102; for winding 265 through conductor 269,

4contact 270 of monitoring key 306, conductor 271,'front Contact 272 of relay'251, to tip of plug 230, and so through a second switching trunk F (Fig. 2) vand concentration board D to a second cusomers line 102. Windings 264 and 266 are carried to ground through artificial lines 273 and 274 consisting respectively of resistance 275 andV inductanc'e 276 and resistance 277 and inductance 278. From junction point 279 where the artificial lines unite a circuit may be traced over conductor 280 to junction point 282 and through conductor 283 and contact 284 of sleeve relay 259 t0 ground 285. The ,circuits through the windings 263` 264,265 and 266 are not exactly balanced, the current through 263 and-265 being nearly twice that of windings 264 and 266. As long as'both circuits on each relay remain closed, the relay armatures will remain against their marking contacts 261 and 262 respectively, but if the circuits 'ofline winding 263 or 265 is opened by an. open signal impulse sent from its respective cusv tomers station C, the relay armature 259' or 260 respectively, will be moved to its spacing contacts 286 or 287 respectively under the influence of the current in the artificial line winding.

' It i's evident, therefore, that each of these relays will respond to signals sent fromthe station to which its line winding is connected.

When so operated, each relay will repeat these signalsthrough the .windings of the other relay into the other station line, thus, if' the line to which winding 263 of relay 257 is connectedis closed at the called customers station C, (Fig. 2) a current will be sent through a circuit as follows: from ground 290, of station to station cord H through source'of positive potential 291, conductor 292, junction point 293, resistance 294, armature 260,1narking contact 262,A conductor 296, back contact 297 of cut relay 298, conductor 299 to junction point 288 and thus through winding 263 of relayv 257 and through conductor 808, contact 267 of relay 259 to the tip of plug.2 68 and thus through a switching trunk F (Fig. 2), through the concentration board D to customers line 102 and so to ground 121 atcustomers station C. Relay 257 (Fig. 3) will then close its marking contact 261 and cause a current to pass from source of positive potential 291, associated with ground 290, through conductor 292, junction point 300, resistance 301, conductor 302, armature 259, marking contact 261 of relay 257, back contact 303 of cut relay 298, conductor304 to junction point 289 and thus through winding 265 of relay 258, conductor 269, contact 270 of monitoring key 306, conductor 271, contact 272 of relay 251, to the tip of plug 230 and thus over a second switching trunk F (Fig. 2), through concentration board D to a second customers line 102 to the calling customers station-C where the printer magnet 118 will be operated and finally to ground 121. A

Winding 305 of relay 257 and winding 295 of relay 258 havevlessturns than the other two windings of these relays and the currents through them have comparatively small magnetic effects in a direction tending to aid the line windings 263 and 265, respectively, in'

holding the respective armatures against the marking contacts. Thisdoes not interfere with the repeating action described above, but serves to hold the armatures against the marking contacts whenrno current is liowing through either of the other windings. Therefore, when the relay 257, for instance, repeats signals through relay 258, the latter relay will not respond to these signals as its armature 260 is held against its marking contact 262 by winding 295 when windings 265 and 266 are open at relay 257, that is to say, when spacing contact 2,86 of relay 257 is closed, armature 260 is held against marking contact 262 by winding 295 and. when armature 259 reverses and contact 261 is closed armature 260 is still held against contact 262, but this time by winding 265. The inductanoes 276 and 278 associated with rela s 257 and 258, which are in series with arti cial line windingsl 264 and 266 respectively, prevent the current in these windings from rising more rapidly than'in the line windings 263 and 265 when the line circuits are closed, thus balancing the inductance of the printer line 1(1114agnet 118 at -the customers stations C Itg'should be noted that the line circuit from the tip of cord plug 230 to the line winding 265 of relay 258 extends through normally closed contact 270 of the monitoring les key 306. When this key 306 is operated, the sending contacts 307 and line relay 318 of the operators printer in operators set circuit L (Fig. 4) are connected in series. with the line at this point. This circuit can be traced as follows: from junction point 308 (Fig.v 3) of monitoring key 306 through contact 309, conductor 310, contact 311 of monitoring key 312, (also through contacts similar to 311 of monitoring keys for other cord circuits indicated by dotted lines 704 and 705) conductor 313, contact 314 of split key 315 (Fig. 4), conductor 316, winding 317 of polar relay 318, conductor 319, contact 320 of monitoring key 321, (also through contacts similar to 320 of monitoring keys for other cord circuits as indicated by dotted line 706) conductor 322, contact 323 of monitoring key 321, conductor 324, key 325, toll i board operators transmitter 307, conductor 326, contact 327, conductor 328,`- contact 329 of monitoring key 312, conductor 330, contact 331, to conductor 271 in station to station cord circuit H. The contact springs of the monitoring key 306 are so arranged and adjusted that the key can be operated or re` stored to cut the toll board operators printer unit (key 325, transmitting contacts 307, line relay 318 and printing magnet 578) inor out of the circuit without momentarily interrupting the station line circuit. Also if two or more monitoring keys are operatedl together in error, this will not interfere with the communication vbetween the customers,

but the operators printer will be conne/ctedv to the cord circuit whose monitoringkey is nearest to the operators set in the circuit, viz., if the monitoring keys 306-and 312 are both operated at the same time, the operators.

the opening of monitoring key 312. It isA to be noted that a monitoring key associated with a toll line to toll line cord K (Fig. 4) should notbe operated at the same time as that of one of the other types of cords as thi/s would permit signals to be repeated from one cord circuit to another. l

The split key 315 of the toll board operators printer set circuit L (Fig. 4) may be used if the operator wishes to communicate with one customers station C andat the same time cut off the other customers station C. For example, if this key is operated in a direction to open the contact 314 and close contacts 332, 333 and 334, the operators printer will be connected through cord plug 230 of station to station cord H,.sincethe opening of contact 314 and the closing of Contact 332 cutsk off 'the return circuit to relay 258 (Fig. 3)

and instead closes the circuitvthrough consplit keyV 315 (Fig. 4) through conductor 340, Awinding 341 (Fig. 5) of supervisory relay 342, conductor 343, to contact point-344 and through resistance 345, which resistance is. equivalent to that of a station line and' then to ground 346.

The circuit just traced energizes relay 342 which opens contact 347 thus preventing relay 348 from operating. The operator may now communicate directly with the station connected through cord plug 230 (Fig. 3) and these signals will not be repeated through the station connected through cord plug 268 (Fig. 3). The station connected through the latter plug may, however, recall the operator by holding recall key 120 at customers station C (Fig. 2) operated for a few seconds. This will open the line and release supervis-x ory relay 342 (Fig. closing contact 347. After a short interval, relay 348 which is a slow to operate relay will operate over a circuit traced from ground 349 (Fig. 4) of the split key circuit, contact 334, conductor 350, contact 347 ig. 5) through winding 351 of relay` 348 through resistance 352 and through source of positive potential 353 to ground 354. The operation of relay 348 closes the operating circuit of guard lamp 355 at Contact 356 thereby lighting the lamp and relay 348 locks itself at contact 357 to hold the guard lamp lighted until split key 315 is restored to normal.

It the split key (Fig. 4) is operated in the opposite direction to close contacts 358, 359, 360, and open contact 327, the line winding 235 of relay 258 (Fig. 3) will be connected through the operators printer and lthrough resistance`345 to ground 346 while the line circuit operating through cord plug 230 (Fig. 3) will be connected to positive current source 338 (Fig. 5) through Contact 359 (Fig. 4) conductor 701 and winding 361 of relay 342 (Fig. 5). Under these conditions, the operator may communicate through relays 257 and 258 (Fig. 3) with the station connected through cord plug 268, while the station connected through cord plug 230 will be in position to operate guard lamp 355 (Fig. .5) as previously described for the 'reverse-situation.

Referring again to station to station cord H, (Fig. 3) the-action of sleeve relays 251 and 259 will be described. Assuming that a call from a customers station has been extended through the concentration board D (Fig. 2) and over a switching trunk F to the toll board, the toll board operator will then insert cord plug230 (Fig. 3) in jack 210 of the switching trunk F. This will close the circuit from ground 281 (Fig. 3) through the winding of .sleeve relay 251, sleeve of plug 230 and contact 236 (Fig. 2) of jack 210, through winding of relay 240 to current source 221 and ground 220 at the switching trunk F. This will operate relay 240 of the switching trunk which will extinguish call lamps 167 and 226 and lightthe busy lamps 242 and 243 as previously described. It will also operate sleeve relay 251 (Fig. 3) of station to station cord circuit H. This relay current to the line and artificial line windings of the other relay.

The circuit of the line winding of relay 258 extends to calling customers station C (Fig. 2) as previously traced `where by reason of the positive current carried over said line from current source 291 (Fig. 3) of station to station cord circuit H, relay 101 (Fig. 2) is released and printer motor 14() started as previously described.: The circuit of the line winding of relay 257 (Fig. 3) extends through baclli contact 365 of sleeve relay259 and through resistance 366 which is equivalent to a station line.

The operator may now operate the monitoring key 306 and communicate with the calling customers station C as previously described. After ascertaining the number of the called line, cord plug 268 will be inserted into jack 210 (Fig. 2) of an idle switching trunk F. As previously explained in connection with the operation of sleeve vrelay 251, this will extend a ground connection to the relay 240 of switching trunk F throughA the sleeve of cord plug 268 and contact 236 of jack 2,10 but as the circuit has not yet been extended to a called customers station C, relay `206 of the switching trunk. circuit F has not been operated and consequently .c

resistance 228 is still in the circuit and sleeve relay 259 (Fig. 3) will not be operated since insucient current passes through resistance 228 to operate it. Guard lamp 229 (Fig. 2) will be lighted by the operation of relay 240 and consequent closing of contact 252. When the concentration board operator replies, the toll board operator gives her the number of the called station. Whereupon the concentration board operator inserts switching trunk plug 205 into jack 123 associated with the called station line 102, which connection extends negative. current from current source 109 at concentration board D through jack v123 and sleeve of plug 205 to relay 206 of switching trunk F which operates to short-circuit'resistance 228 enabling sufficient current to be passed from current source 221 of the switching trunk through contact 236 and jack 210 of switching trunk F and sleeve of cord plug 268 (Fig. 3) to operate sleeve relay 259 of station to station cord circuit H thereby closing contact 267 and connecting winding 263 of relay 257 with the called customers station. On completion of line connections with the called customers station C, positive current is passed from source of positive current2-91 through conductor 292 to junction point 293, resistance 294, armature 260, marking contact 262,

lconductor 296, contact point 297, conductor 299, Winding 263 of relay 257, conductor 808, contact 267 through the tip of cord plug 268, through switching trunk F (Fig. 2) and so through the concentration board and customers line 102 to the called station C where the motor 140 is started as was previously described whereupon the calling and called customers stations C may now communicate with each other. The toll board operator should restore monitoring key 306 to normal as soon as communication is satisfactorily established.

When the call is completed, the operator at each customers station momentarily operates relay key 141 closing contact 156 which operates to lock relay 131 and release control relay 128 as previously described. This stops station motor 140 and reduces the line current to approximately 6 milliam-peres. Assuming that the calling customers station C connected through cord plug 230 (Fig. 3)

Vof station to station cord circuit H, operates releasekey 141 first, relay 258 (Fi 3) of station to station cord circuit H, wil release but as this opens a circuit at contact 262, to both windings 263 and 264 of relay 257, relay 257 cannot release at this time by reason of the eiiect of winding 305 even though the called station, connected through cord plug 268, also operates its release key 141.

Relay 258 thereupon closes a circuit from its spacing contact 287 as follows: from current source 291 associated with .ground 290 through conductor 292, junction point 293, resistance 294, armature 260, contact 287, conductor 367, resistance 368, winding of relay 363, junction point 370, conductor 371, contact 37'2 of monitoring key 306, conductor 373, conductor 374 through contact 375 of relay 251 to ground 281. Relay 363 is a slow act-ing relay which will not operate on short impulses due to printer signals but will operate when armature 260 of relay 258 remains against its spacing contact 287 for a longer interval. Relay 363 being operated, closes -its contact 376 and thereby places ground 377 in the circuit of supervisory lamp 378 associated with cord plug 230 thus applying current from source 291 to the lamp and lighting it. Relay 363 also closes contact 379, which places ground 380 on the ffgcut relay 298. The cut relay operates, and

closing contacts 381 and 382, applies positive current directly to windings 263, 264 and 265, 266 of f relays 257 and 253 respectively over circuits traced as follows: for relay .257 from ground 290 through vcurrent source 291,

conductor 292, junction point 293, resistance 294, conductor 383, contact pointr382, conductor 299 to junction -point 288 and so through windings 263 and 264; for relay 258 from ground 290Y through current source 291, conductor 292, ljunction point 300, re-

sistance 301, conductor 302, to contact point 5 381, conductor 304 to contact pointl 289 and so through windings 265 and 266 of relay 258. Relay 363 in effect, therefore, cuts the repeater so that a signal sent into one side of the repeater will now have no effect on the line circuit of the other side of the repeater. If the release key 141 (Fig. 2) at the called customers station C, connected to cord plug 268 (Fig. 3) of station to station cord H, has been operated by this time, relay 257 will now release by reason of the insertion of high resistance winding '104 (Fig. 2) into the circuit at the called customers station C and after an intervaly relay 3.62 (Fig. 3) will operate and light supervisory lamp 384 associated with cord plug'268, in the same manner as described for the lighting of supervisory lamp 378. lVhen both supervisory lamps 37 8 and 384 are lighted, the toll board operator will pull down both cord plugs 230 and 268. This will operate relay 101 (Fig. 2) at both customers stations C which action will release relay 131 at both customer-s stations and will light guard lamps 229 associated with customers stations lines at' the switching trunk circuit F, to signal the concentration board operator to disconnect, aspreviously described. The cord circuit relays 251 and 259 (Fig. 3) will also be restored to normal which will remove the ground from the relays 362 and 363 causing them to release and extinguish the supervisory lamps 384 and 37 8.

If, instead of sending a disconnect signal, the operator at either customers station wishes to recallthe toll board operator, the recall key 120 (Fig. 2) at customer-s station C may be opened for a period of time suliicient to allow slow operating relay I362 or 363 (Fig. 3) respectively to operate the corresponding supervisory lamp 384 or 37 8, the supervisory lamp, under these conditions, might be flashed by operating and releasing the' recall key slowly several times in succession.

Telegraph toll Zine circuit One terminal of a telegraph toll line circuit is shown at J of Figure 5 (see also J in Fig. 1). As shown on the drawings, two polar relays are used, so connected as to form a difcapable of transmitting signals in both directions could be used. For example, a metallic two wire line equippedl for duplex operation might be used, or two wires, each arranged to 'send signals in one direction. A full duplex carrier telegraph channel might be used or even a two-way radio telegraph channel. It

Ais thought that the method of arranging this .the winding of the pole changer relay 385 is connected through jack contact 386 of jack 387. Pole changer 385 is also connected by a circuit traceable through contact 386, conductor 388,' (which also extends through contacts similar to 386 of any intermediate jacks which may be placed in the circuit at point indicated by broken line 7 08'-it should also be noted that additional lamps may also be inserted at this point) contact 389 of jack 390, conductor 391, resistance 392, winding of busy relay 393 to ground 394. Busy relay 393 is a sensitive relay that will operate on a small current. It, therefore, remains operated to keep the busy lamps 395 and 396 extinguished while the line is idle and at the same time places a ,ground on winding 398 of pole changer 385. Under these conditions, however, the current from the lower or biasing winding 397 of pole changer 385 is stronger than that in the upper or line winding 398 and therefore the pole changer armature 399 remains against its positive or spacing contact, 400. Current from the positive current source 401 passes through resistance 402 and contact 400 to noise-killer 403, and in parallel through windings 404 and 405 of line relay 406 to line 407 and artiicial line 408 respectively. The line relay 406 is not affected by this current but as the pole changer at an identical station M (not shown), at the distant end of the line, is also against Vits spacing contact, the armature of the line relay at station M corresponding to relay 406 at station J, viz. 406M will also be against its open or spacing contact, and the receiving leg, or in other words, thel conductor 409M leading to the tip of jack 387M will be open.

If the cord plug 412 (Fig. 4) is inserted in toll line jack 387, a current from source 414 will be carried over conductor 410 to sleeve of cord plug 412, in other words, the sending leg of the duplex set will be connected through contact 411 to the sleeve of jack 387, and if the sleeve of plug 412 is connected through a suitable resistance to ground, this ground will be placed o-n winding 398 of pole changer 385 through contact 411 of jack 387 and conductor 410. and

the circuit will he completed through resistance 413, current source 414 and ground 415.

It is to be'noted'that resistance 698 connected between current source 414 and winding 397 of pole changer 385l is of much higher resistance than resistance 413, and it is to be further noted that ground 478 replaces' ground 394 whichis' associated with the'busy relay 393 and that resistance 699. associated' with ground 478, is a. lower resistance than resistance 392 associated .with ground 394. Consequently, with the placing. of ground 478 on winding 398, more current iiows through this winding than through winding 397, and armature 399 is therefore operated against its negative or marking contact 416. This will operate the line relay 406M at the distant end of the line to close the receiving leg 409M which will in turn energize Vcall lamp relay 417M to light the call lamps 418M and 419M. The circuit for operating relay 417M maybe traced as follows: ground 420M, source of potential 421M,fresistance 422M. contact 423M, conl'ductor 409M, contact 424M of jack 387M, conductor 425M, contact 426M of jack- 390M, conductor 427M, winding of relay 417M through resistance 428M to ground 429M. It should be noted that the insertion of the cord plug 412M into iack 387M will release the busy relay 393M breaking jack contact 386M consequently lighting the busy lamps 395M and 396M, over a circuit traced from ground 430M through current source 431M,

conductor 432M, resistances 433M and 434M.Y busy lamps 395M and 396M, conducto-r 435M, contact 436M to ground 394M. It 'will be noted that the insertion of plug 412M into jack 387M will also operate pole changer 385M at therdistant end of the line to send a marking signal back over line 407 to relay 406 in circuit J. The further operation of the toll line circuit can best be explained in connection with the operation of the cord circuits.

Station to toll Zine cord mer is used, it will be necessary for the operator tochange plugs as soon as she finds out that the customer wishes a long distance connection. In either case. cord plug 231 (Fig. 3) of station to toll line cord I will ulti'- mately be inserted into switching trunk jack 210 Fig. 2). The insertion of plug 231 into jack 210 closes contact 236 and, as previously described, places a positive potentialV on the sleeve of plug 231 throughv current source v 221 of switching trunk circuit F. This current is passed from the sleeve ofcord plug 231vover conductor 233 (Fig. 3) through thevv windings of relay 451, through conductor 452 and through the windings of marginal relay 234 to gro-und 235 operating relay 234. Relay 451 will also be operated to close contact 453 which operates a circuit from ground 454 through positive potential 455, resistance 456, contact 453, conductor 457,'contact 458 and so through supervisory lamp 459 to ground 460. Thus the supervisory lanip459 will be lighted immediately on connections being made between cord circuit I and switching trunk F. Relay 234, by closing contact 443 connects a positivel current from current source 437 (Fig. 4) to the customers station line 102 (Fig. 2) through a cil"- cuit traced as follows: ground 438, current source 437, resistance 439, conductor 440, contact 441, conductor 442, contact 443 (Fig. 3) conductor 444, contact 445 of monitoring key 312, conductor 446. contact 447, conductor 448. winding of rel'av 449, conductor 450 to cord plug 231 and so through switching trunk circuit F (Fig. 2), concentration board D to customers line 102. This circuit also operates relay 449 (Fig. 3) which closes contact 461. which places ground 462 on relay 463` which in turn opens contact- 458 to extinguish supervisory lamp 459. The operator at cord I may, however. communicate with the calling customers station by operating monitoring keyv312 if necessary.

Cord plug 412 (Fig. 4) is now inserted into the jack 387 (Fig. 5) of an idle toll line to the desired distant city. Repeating rela-y 464 (Fig. 4) in cord circuit I operates like relays 257 and 258 of station to station cord circuit H. which was previously described and therefore its method of operation need not be described here in detail. lVinding 465 of relay 46 4 correspondsto windings 263 and 265 of relays 257 and 258 respectively, winding 466 of relay 464 corresponds to windings 264 and 266 of relays 257 and 258 respectively, and winding 470 of relay 464 corresponds to windings 305 and 295 of relays 257 and 258 respectively, and the corresponding windings have approximately the same resistances. It should be noted, however, that as line relay 406 of the toll line is released when plug 412 isfirst inserted in jack 387,

the receiving leg 409 (Fig. 5) of the duplex set is open and there will be no current through the two windings 465 and 466 ot relay 464 (Fig. 4) but the relay will be held operated by a current from source 437 passed over conductor 467, through resistance 468, conductor 469, through winding 470 of relay 464 to ground 471. The contact 472 of relay 464 being closed, a circuit may be traced from ground 415 (Fig. 5) associated with pole changer 385 through current source 414, resistance 413, winding 398 of pole changer 385, conductor 410, contact 411, sleeve of cord plug 412 (Fig..4), conductor 473, contact 472, conductor 474, contact 475', conductor 476, through supervisory lamp 477, tol ground478, which will be lighted, indicating to the toll board operator of cord I that the distant toll operator at station M has not yet answered. Supervisory lamp 477 is shunted by resistance 699 so that pole changer 385 will receiveits normal working current of about milliamperes without passing excessive current through lamp 477.

'Since ground is placed on the line Winding 398 (Fig. 5) of pole changer 385 it will operate and send a marking impulse'over line 407 to station M. The marking signal transmitted by pole changer 385 will cause line relay 406M to close contact 423M, thus operating relay 417 M and lighting the call lamps 418M and 419M. The operator at station M will respond by plugging cord plug 412M into toll line jack 387M. In this case, as line relay 406M is opera-ted closing contact 423M, and sleeve relay 234M (Fig. 3) of the station to toll line cord circuit I is not operated, the repeating lrelay 464M (Fig. 4) will be held operated through its righthand winding 465M and through the back contact 479M or relay 234M to ground 480M. Relay 481M also operates over a circuit traced from junc-v tion point 482M through winding 466M of relay 464M, resistance 483M, inductance coil 484M, winding of relay 481M to ground 485M. The operation of relay 481M will close contact 486M to place ground on slow release relay 487M over a current operating from ground 485M to contact 486M, through conductor 488M, winding ot relay 487M, conductor 489M, resistance 490M, conductor 467 M and through source of potential 437 M to ground 438M. Relay 487M willt-hen operate to break Contact 47 5M, removing supervisory lamp 477M from the sleeve circuit of jack 387M (Fig. 5) and replacing the ground .478M (Fig. 4) associated with the supervisory lamp 477M by ground 491M through resistance 492M at contact 493M. The supervisory lamp 477M is thereby extinguished, and pole changer'385M operates.

The operation of pole changer 385M (Fig. 5) sends a marking signal back over line 407 to operate the line relay 406. This closes the receiving leg 409 connecting positive current fromv current source 421, through Contact 423, over receiving leg 409, through jack 387, to tip of plug 412 (Fig. 4) and so to windings 465 and 466 of relay 464. The relays 481 and 487 will be operated as previously explained in connection with the operation of station M, the latter relay extinguishing supervisory lamp 477. Relay 487 will also extend the receiving leg circuit 409 from winding-465 of relay 464, over conductor 702 through junction point 730, conductor 731, contact point 496, conductor 442 and contact point 443 (Fig. 3) and so through monitoring key 312 to the line circuit extending to the calling customers station C.

With the monitoring .keys 312 operated, the toll operators at both stations make contact with each other by printer over the toll line 407 and their conversation will be recorded by the printer at the calling subscribers station.- If it is desired to avoid f having this conversation reported at the calling subscribers station, the outward operator may operate split key 315 (Fig. 4) in a di? rection to operate the right-hand springs, closing contacts 358, 359 and 360 and thus connecting a positive current through relay 342 (Fig. 5) to the calling customers station line 102 and connecting station M through cord plug 412 and the operators printer 307 to ground 346 (Fig. 5) as previously described. s f

After the outward operator has transmitted the number of the called station, the o erator at station M will connect plug 231KI Fig. 3) to an idle switching jack 210M Fig. 2) and establish a connection toA the called subscribers station C in the same manner as previously described for local calls. When the cord plug 231M is inserted into jack 210M, sleeve relay 234M does not operate until switching trunk F at the distant station is plugged up at the concentration board. at which time it does operate to extend the toll line circuit through to the called subscribers station C starting the station motor in the usual manner, as previously described.

The customers stations may now communicate with each other by printer. The outgoing printer signals through each station operating repeating relay 464 (Fig.4) of thel cord circuit I, which will in turn open and close the sending leg circuit at contact 472 to operate pole changer 385. Incoming signals from the toll line 407 (Fig. 5) will operate line relay 406 which will repeat these signals overl the receiving leg circuity 409 directly through the windings 465 and 466 of relay 464 (Fig. 4) to the station line 102 (Fig.

2) without operating relay 464, as previously described in connection with repeating relays 257 and 258 (Fig. 3). It will be seen, therefore,"that relay 464 is in effect a half set repeater and has the effect of converting ,y the full duplex circuit into a half duplex circuit. The operators at the two customers` stations C may both transmit and receive but both cannot transmit at the same time. The toll board Ioperators at the two central stations should cut out of the circuitD by restoring their monitoring keys 312 as soon as communication isy satisfactorily established.

The outgoingsignals will operate marginal relay 449 (Fig. 3) as' previously described, and the incoming signals from the distant station vwill operate relay 481 (Fig. 4) as well as relay 449. Relays 449 and 481 will send impulses through the windings of relay 487 ever, and will not release on printer signals. If the operator at either of the customer s stations should wish to recall his toll board operator, he `may do so by slowly opening and closing the contacts of the recall Vkey 120 (Fig. 2) at customers station C.- This will release marginal relay 449 (Fig. 3) for a suflicient yinterval to allow relay 463 to release and light the supervisory lamp 459, as previously described. vIt will. also release relays 481M (Fig. 4) and 449M at the distant end of the line. This will permit relay 487M to release, closing contact 475M and thus ligblting supervisory lamp 477M. Re-

also connects positive current from source 437M to rela 449M (Fig. 3) throu h resistance 439M (Fig. 4), conductor 440 contact 441M, conductor 442M, contact 443M (Fig. 3) conductor 444M, contact 445M, conductor 446M, contact 447M, and conductor 448M, thus operatin relay 449M. Relay 463M should prefera ly be adjusted to be' Such a local signal may be answered by the o`erator by means of monitoring key 312 ig. 3) and if trouble is being experienced,

` split key 315 (Fig. 4) may .be o erated, if

necessary, to determine whethert e trouble is in the local station circuit' or on the toll line circuit. i

At the conclusion of the call both stations should clear the circuit by restoring their call keys 141 (Fig. 2) to normal and momentarily operating the release portions of keys 141', thus releasing contacts 142 and closing contacts 156. This will lock up relay 131 and release the control relay 128 at each customers station to stop motors 140 and reduce the line current, as previously described, by

los

no l

inserting high resistancewindings 104 of rel lays lOl-into the circuits. The reduction in the line current will release marginal relay 4 l449 (Fig. 3) of station to station toll line cord circuit I. The station which rst disconnects will also release relay 464 (Fig. 4) which will in turn open contact 472 and thus open the sending leg circuit and cause pole changer 385 (Fig. 5) to release and armature 399 to close its circuit at contact 400, thus sending a spacing signal over toll line 407 to the other station. This will release relay 406 at the .distant end of the line with the result that the receiving leg circuit will be opened at contact\423, and thus stopping the flow of current from source 421, through windings 465 (Fig. 4) and 466' of relay 464. Consequently relay 464 will be held operated by winding 470, as previously described. Relays 481 and.487 will release, however, to light supervisory lamp 477, as previously described. The supervisory lamp 459 (Flg. 3) at one station is now lighted as well as supervisory lamp 477 (Fig. 4) at the second station. When the second .station disconnects, relay 449 (Fig. 3) at that point will release and, after an interval, relay 463 w1ll release and light supervisory lamp 459, as previously described. This will have no effeet on the toll line circuit, however, as re lay 464 (Fig. 4) is held operated as prev1- ously described. When both subscribers have cleared out, both supervisory lamps will be lighted at one toll board and supervisory lamp 459 (Fig. 3) alone lighted at the other board. Both operators should then.'pull down their cords, restoring the circuits to normal.

ToZZ Zine to toll Zine coml For establishing through connections between two central stations the toll line to toll line or through cord shown as circuit K (Fig. 4) should be used. The operator will normally answer such calls with the station to toll line cord I, previously described, and on finding that a.v through connection to a distant city is desired ascertains the statlon wanted and then substitutes a through cord Tt will be understoodthat the twocord plugs 494 and 495 of this circuit are, whenthe cordis connected, plugged into jacks 387 (Fig. 5) of two separate toll line circuits J. In this cordcircuit, the tip of cord plug`494 (Fig. 4) is connected to the sleeve of the cord plug 495 and vice versa so that when two toll line circuits are interconnected, the sendln leg of each toll line is interconnected to t e receiving leg of the other toll line, sulicientresistance being included in the cord circuit to lower the current in the pole changer 385 (Fig. 5) to the usual value of about 60 milliamperes. Under these conditions the two duplex sets are connected together so as to form a' full duplex repeater and incoming signals from either toll line will be repeated through tothe other line. It is to be noted that this circuit operates differently from station to toll line cord circuit J which as previously pointed out operates over the same toll line as a half .duplex repeater by reason of relay 464 which will repeat signals only in one direction.

The relays in the cord circuit K are not used for repeating signals from one toll line to the other but serve to enable the local operator to connecther printer into the circuit current when the cord is not in use and to extinguish the supervisory lamps. Relays 496 and 497 serve this purpose. These relays each have two windings, one of low resistance 498 and 49.9 and one of high resistance 500 and 501, and are capable of operating on a low current. The same type of relay as relay 101 (Fig. 2) in the customers stations circuit C may bepreferably used for this purpose, but it is not necessary to use a polar relay if a sufficiently sensitive neutral relay is available. j

Assuming that plug 494 has been plugged into a toll line jack 387 (Fig. 5) over which ya call has been received from a distant central station, current from source 414 associated with ground 415, will be passed through resistance 413, winding 398 of relay 385, conductor 410, contact 411 of jack 387, to the sleeve of plug 494 (Fig. 4) and so over conductor 510 through winding 511 of relay 512 and through windings 498 and 500 of polar relay 496 in series aiding, and so through re-v sistance 520 to ground 521. Relay 496 will be operated but since the high'resistance winding 500`of this .relay and resistance 520 in series with it, hold the current to about of relay 496 contact 538 is closed and ground 521 is resultingly` placed on a circuit traced as follows: from contact,538 to junction 801, conductor 550, winding 549 of relay 522conl ductor 548, winding 547 of relay 523, conductor 546, winding 545of relay 508, 'conductor 544, winding 543 of relay 512, conductor 542,

resistance 541 and lthrough current source' 540 to ground 806. This places a biasing current of about 30 milliamperes on the four relays just mentioned. The closing of con- -tact 538 also closes a circuit traced from cur- 'operating them and closing the two cord circuits at contacts 503 and 517, respectively..

It may be assumed that plug 495 will be plugged into an idle jack 387 (Fig. 5) of an idle toll line connected to the distant called station before slow operating relays 559 (Fig. 4) and 560 (since the operator has ascertained the name or number of the called station before plugging up either plug or cord K) `can operate, in which case the'circuit from the tip of plug 494 to the sleeve of plug 495 will be closed and the circuit from 3 milliamperes relays 385 (Fig. 5) and 512 (Fig. 4) will not operate. AOn the operation

Images