US1480206A

US1480206A - Machine-switching telephone-exchange system

Info

Publication number: US1480206A
Application number: US433026A
Authority: US
Inventors: Henry L Hoffmann
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1920-12-24
Filing date: 1920-12-24
Publication date: 1924-01-08
Anticipated expiration: 1941-01-08

Description

Jan. 8, 1924. 1,486,206

H. HOFFMANN.

MACHINE SWITCHING TELEPHONE EXCHANGE SYSTEM I Filed Dem-.24, 1920 5 Sheets-sheaf; I

aim)

Jan. 8, 1924.

H. L. HOFFMANN MACHINE SWITCHING TELEPHONE EXCHANGE SYSTEM Filed Dec. 24, 1920 5 Sheets-Shaw 2 Wye/770i":

4 a Wm Jan. 8, 1924. 1,480,206

H. L. HOFFMANN MACHINE SWITCHING TELEPHONE EXCHANGE SYSTEM Filed Dec. 24. 1920 5 Eheets-Sheet 4- Hen/y L. Hoff mm 513 WW.-

Jan. 8, 1924. 1,480,206

H. L. HOFFMANN MACHINE SWITCHING TELEPHONE EXCHANGE SYSTEM Filed Dec. 24, 1920 -5 sheet s-sheet s //7l /7 for: Men/"y 1.. #0799361? relay (not shown) to place theoperators telephone set in a monitoring position on the cord. The operator now turns the dial 1) for the first digit of the wanted number. lhe dial in moving out of its normal position short circuits the relay B34 permitting the relay E72 to operate. Relay E-72 in operating locks itself to battery and transfers the tip of the plug TT through the impulse springs of the dial D to the battery. The dial, in returning to normal, interrupts the battery to the tip of the plug causing the impulse relay A.--2 of the trunk circuit of Fig. 2 to operate in termittently, the number of times depending upon the digit involved. This impulse relay, in thus operating, causes the setting of the incoming selector (Fig. 3) at the distant automatic oflice which thereupon automatically picks out an idle trunk in the selected level. This trunk includes the equipment shown in Fig. 3 and terminates in the selector shown in Fig 4;. When the operator has turned the dial for all the digits involved which causes the last switch or con- I replaces his receiver, this lamp again lights as a disconnect signal.

If the called line is busy or if one of the selectors had failed to find an idle trunk, the lamp 100 will flash, the frequency of the flashes depending upon the busy condition encountered. The toll operator in response to the flashing of the lamp removes the plug TT of the trunk and toll end of the cord from the toll switching jack TSJ, but before removing the toll plug T from jack J,

v the operator by .means of her ringing key RK, rings on the toll line terminating at the jack J to notify the distant calling operator that the line is clear. If the distant operator rings first, however, the toll supervisory lamp 101 lights and when the operator actuates listening key LK, or pulls out the plug T, this lamp is extinguished.

If the called subscriber can be reached only over a toll line terminating at a toll position at a distant office, the intermediate toll operator inserts the plug TT of the trunk and toll end in a toll line jack leading to such distant ofice and by means of her ringing key BK rings out over the toll line to signal the distant operator at such office having access to the line of the caller subscribed who then completes the connection.

When the calling toll operator applies ringing current to the trunk at the termination of the conversation, the toll supervisory lamp 101 lights until the listening key Lli is operated or the connection is taken down. The keys K and K serve, when operated, to disconnect either end of the cord from the operators telephone set when the operator is talkingon the other end.

More in detail, when the plug- T of the toll end is inserted in toll answering jack J, relay E156 operates, in turn operating relay B162. Relay B162 opens the circuit of) relay E162 preventing the toll supervisory lamp 101 from lighting. When the plug TT of the trunk and toll end is inserted in toll switching trunk jack. TSJ leading to an incoming selector at automatic office, relay E-99 operates in series with relay E-155 and the right winding of relay 51-156. Relay Fi99 disconnects the busy test equipment of the operators tel ephone set from the tip of the cord and connects the tip of the cord through to the ringing key. Relay E-155 is marginal and does not operate at this time on accountof the high resistance in the sleeve of the toll switching trunk circuit, and thus leaves the calling supervisory relay B4 .3 bridged across the trunk. Ringing current applied by a distant toll operator operates the alter nating current relay A196 which releases relay B162. The latter relay in releasing lights the toll supervisory lamp 101 and operates relay E-162 in parallel with the lamp. Relay 15-162 locks up under the control of the listening key LK and relay E-156 so that the lamp remains lighted after the ringing ceases and the relay 13-162 is re-operated through the back contact of relay A196. The lamp 101 may be extinguished by operating the l stening key which releases relay E-162 or by taking down the connection which releases relays E156 and E-162 Relay 13-162 is made slow in operating to guard against the possibility of lamp 101 being lighted by Morse impulses. Relay ,A.196 may be operated for a short time by Morse impulses and release relay B-162 momentarily. but the slow operating feature of the relay E162 will give relay B-162 time toreoperate before the relay l3l-162 operates and locks. When both ends of the cord. inserted in toll line acks terminating at toll board positions the marginal relay E155 disconnects the calling supervisory relay B43 from the cord circuit. if, on. a through toll connection of this character the splitting key K is operated to disconnect the trunk and toll end TT from the operators telephone set. relay R 4c? bridged across the trunk and toll end so that it will operate when ringing current is received from the trunk and toll end and E 412.795, filed September 25, 19 20.

flash the lamp 100. 'When the splittingkey- K is in its" normal position this bridge for relay B'43 is opened.

Referring" 110W to Fig. 2 which represents a toll switchingtrunli overwhich a connection" is extendedt'o' an automatic exchange, relay C2 operates over its right hand Winding vlieu the operator inserts the plug TT into jack TSJ and by attracting its armature closes a loopcircuit leading to the impulse relay of the incoining selector. at such exchange, which selector being Well known is not shown. It may beat the type shown in application of R. L. Stokely. Serial Tie brushes 300,- 301,-302 and multiples 303, 305, indicate such selector. l Vhen' the dialing ke DK is thrown and the dial is operated, relay Eli-42 operates, connecting relay 1 2 across the loop leadingto the inipulse relay of the incoming selector at the automatic o'ili'ce. Relay I2 in operating causes slow relay to operate, whi chire lay shunts the left-hand winding ofrelay C2 whereupon the latter relay releases the circuit through its right hand Winding being opened when relay'E72; Fig: 1, 013'- e'rate's as the dial is moved out of its normal position. Relay D-2 in operating operates relay E-Q which locks up was ground'at the inner left contact ot relay B2. now energ zed. Relay E 2 at ts vouterlett contact locks up relay D'2, independently of.

its original ene'rgizing circ'uit which leads over the front contact of relay I2. The dial in restoring intermittently operates relays 94-2 and l-Qi relay" A-Q- interniittentlf" opening theflo op circuit to, the hit pulse relayot the incomingflselector. and relay I2 alternately ojpening'aiid' closinga shunt path around'relay D2. If, during the operation of buildingfup a connection, oueot the selectors fails to find an idle trunk in the selected group, it opens the loop circuit including relay I2. Relay I2 in closing its backeontact permanently shunts out relay D-2.- Relay D- 2 infclosngits right hand contact operates. relay Il-2. Relay H2 locks up and connects interrupted battery of inipul'sespenniinute to the Winding of relay C2in shunt of the r sistance F200. 'Relay Bl3in the cord (Fig. 1) follows these impulses and flashes the supervisory lamp lOO-tb', indicate to the operator the tail ure to fin'djan' idle trunk.

in case the called line is busy, interrupter is connected in circuit to flash the lamp 100 at different rate to indicate" to the 0})- crater the busy condition of the selected line.

In case the called subscribers'line'is found to be idle by theconnector 5) this-conditicu causes the 'polar-i zed relay. F'-2 to ope ate and-cause'lamp 100 t'o're'main steadily lighted asaringingsignalwhen the op eraterre'storesthe key..DK. Relay F-2 in operating/alsoenergizes relay ;G2 vhich cuts the trunkthrough, thus disconnecting .the,rela'yfs' C'2and A-2 from the circuit leading baclt to the toll operatofisposition. H'aviiig described in a general manner the op rates. of the system a call will now we traceaui detail. v

The toll-operator, having been informed of'the nuinberof the Wanted line and assiirii'iii g.thislineto be in a nearby auto:- mafia exchange, tests for an idle trunk by touching theltip' of her plug TT to the sle'eveof thejac-k TSJ of the tollsvvitching trunk in" the yvellkno vn manner, and if she does not receive a clic-k in her receiver she inseigts tlie plugzTT into the toll switching t'u'nk ja'ck'TSJ. The following circuit is thereupon closed to--operate relays*E-99q (Fig: 1)iaiid B;2. free pole'of battery; relays E' 99 1 1 -155,- right wind inggpr relay lie-15 6, sleeves of the plugran d j :fck', relay B"2'togroiind.; Relay E155 (lees not; operate in the-circuit, as stated. Relay E-15G is oper'ateddue to plug T being inserted-in jacleJ Relay. Ill-+99 in operating disconnects the operators busy testcircuit from the tip of .cordgancl connects the, two sides ot the ti'p otfthe lineto'gether. 'Relay B-2- (Fig. 2); in]. operating pr'ep'are's certain circuits Wliich'ivill 1 be traced later. This trunk will saw testbusy at the other toll. operators positions due to battery applied to the sleeve v nnltiple's' the sleeve of the plug [1. "The'ins'ertion' of the plug also. closes the following circuit to energizerelay C2: free pole of .battery;;-resistance 200, right hand Windingof relay;C2, conductor 2 01 a'rinature oQ of relay G 2, conductor 203', iiiiieinnoriiialcontact of relay. 130, ring of the" jacl; TSLring ot' thc plug TT,'condu to'ifl 120, lower norrna-l contact or. ringing l: KK, right hand Winding of retardation coil" 121, relay 13 -43," ujlllit'tlll'e and back contempt .relay"l$-155 which is not oper- Whe'nthe plug IT is inserted in a toll trunk switching jack, butonly when it is insertedina toll line leading to a toll positioh at afdistantfofii'ce, left hand Winding of retardation c0il l2l; upper normal contact of ringing ke'y RK, armature and-front contact of relay E, 9, conductor 102, left hand nor'nial contact of relay E72, con-Q followingzl bridge' to operate the impulse relay tr te inc'oiri-ing''selector at the autoni'ati'c" oifice', conductor" 205, conductor 206,

outer left hand armature and back contact of relay H2, conductor 207, armature and front contact of relay C2, left hand winding of relay C2,

conductors

208 and 209, inner right armature and front contact of relay l3-2, conductor 210,v polarized relay F2, conductor 211, conductor 212. The operator now throws the dialing and monitoring key DK, whereupon a circuit is closed to operate relay B34, Fig. 1, which in attracting its armature closes a circuit to connect the operators head set across the cord. She now rotates the dial D for the first digit of the wanted number. The closure of the contact 104 of the dial as the dial moves off normal shunts the relay B34, which permits the marginal relay E72 to operate. Relay E-7 2 in attracting its right hand armature locks itself to ground at a contact of the dialing key DK which when actuated remains in its operated position until manually restored by the operator. Relay E72 in closing its left-hand contact opens the bridge containing relay B43 and connects the free pole of the bat tery through the impulse contact 108 of the dial to the tip of the plug. The opening of the said bridge opens the circuit heretofore traced through the right hand winding of relay C2. Marginal relay A-2 now operates in series with the impulse contact of the dial, the circuit being as follows: free pole of battery, resistance 109, impulse contact 108, left hand armature and front contact of relay E72, conductor 103, tip of the plug TT, tip of the jack TSJ, outer normal contact of relav 130, conductor 131, armature 204 and back contact of relay G2, conductor 213 and relay A-2 to ground. Relay A2 in attracting its left hand armature bridges relay T2 across the tip and ring of the trunk in parallel with the left hand winding of relay C 2. Relay T2 in attracting its armature closes a circuit to operate relay D2 as follows: free pole of battery, resistance 214, conductor 215, relay D2, conductor 216, right armature and front contact of relay I'-2, conductor 217, contact 218 of relay G-2 to ground. Relay D 2 in attracting its left armature short circuits the left hand winding of relay C2 which thereupon releases, thus opening one of the bridges to the impulse relay at the incoming selector and leaving bridged across the circuit only relay 1 2. This bridge may be traced as follows:

conductors

205 and 206, outer left hand armature and back contact of relay H2, conductor 207, conductor 208, relay T-2, left hand armature and front contact of relay A2, conductor 211, conductor 212. Relay D2 at its right armature and front contact closes the following circuit to operate relay E2: free pole of battery, relay E2, conductor 220, right armature and;

front contact of relay D2, conductor 221,

conductors

222 and 228, inner left armature and front contact of relay 13-2 to ground. Relay E-2 in attracting its inner right armature locks itself to grounded conductor 222. The function of this relay will be later described. Dial D, Fig. 1, in returning to normal, interrupts at its impulse contact 108 the circuit of the impulse relay A2, Fig. 2, which at its left armature interrupts the circuit of the impulse relay of the incoming selector a number of times corresponding to the first digit of the wanted number. The incoming selector TS is thus set to the desired level and then automatically picks out an idle toll transmission selector shown inFigs. 3 and 4. The terminals of this selector are designated 303, 304, 305.

The seizure of the toll transmission selector, Fig. 4, with which the relay and repeating coil equipmentof Fig. 3 is asso ciated, causes the closure of the following circuit for impulse relay A-4, Fig. 4, of the toll transmission selector: freepole of battery, right hand winding of relay A4, conductor 400, conductor 306, outer left armature and back contact of relay B-3, conductor 307, contacts of relays F-3, and H-3, conductor 308, upper left-hand winding of repeating coil 309, conductor 325, multiple terminal 303, brush 300, conductor 212, conductor 211, left armature and front contact of relay A2, relay 1-2,

conductors

208, 207, outer left hand armature and back contact of relay H-2,

conductors

206, 205,

brush 301, multiple terminal 304, conductor 326, lower left hand winding of the repeat ing coil, conductors 311, 312, contacts of relays H3 and F-3 and B3, conductor 313, conductor 401, through the left winding of relay A-5 to ground at the lower normal contact of the switch 402 which is operated only on the eleventh rotary step of the transmission selector. The impulse relay A--4 in attracting its right armature energizes slow relay B-4. This relay in attracting its left armature applies a ground over the

sleeve wires

451 and 314 to multiple 305 to cause this trunk to test busy and to hold up the release relay of the incoming selector in the well known manner. When the relay B4 operates it closes at its right hand armature the following circuit for relay D 3 of the relay and repeating coil circuit, Fig. 3: ground, right armature and front contact of relay B-4, conductors 403 and 418, conductor 404, conductor 405, contact 406 of re lay D-4, conductor 407, 315, outer right hand armature and back contact of relay F 3, conductor 316, relay D3 to free pole of battery.

The second operation of the dial by the operator transmits the second digit of the called line causing relay A-2, Fig. 2 to open anclclosethe' impulse-j circuit for therleiy'r A4, which in vibretiiig its right hand? armature transmits impul s'e's over the' fol lowing/ circuit 'to "the vertical magnet" 40 8" oi? the toll transmission selector: "gi 'o lii'iclefi ri ht-armature and back coiit'act of 'relayf far-l, inner armature and froii'thdlitact of relay 13 -4, conductor e09; armature *klOhfitl brick Contact of relay 'D-ge coii clucjtor $411,"- slow relay C4,; magnet 408to"free"pole"off battery. The brushes ofthe toll trimsirii sien selector are thus elevitetl' to' the deeired'j level. When the dial returri's to nor'malaliclf maintains the relay 'A -2 'ehergiz'etl', relity" PLe remains" energizeil and; after e slight inter 1 slow relay C -e releases. l Vhh the relay C 4: op'ereted' o1r'the' ffirstiIhp1ils'e and the selector toolrits fir tfstep', relay" iY'-i operated over "the" follotvin g circui tree pol ofhattery, relay E-'4,-uppe1'-- fc oiitact of 0% norm'elsit itch 415,conclt bt6r 41h, arm. cure anti front contact of relhy-C 4, f COHQJiCtOZ 4:17, con'tl'uotor 4:18, cohductor'lOil" to ground at the'rig'htarmelt ire 'eiicl front Contact of relay Be In attrhctihg its inner armature, re1ay E *4-" locksl itSelf to the upper armature and hzick Contact of slow rela'y 1 -14:, this eirct i't'incli'icling the'hrmer: ture hack contact" 01: rotary megfiet' 419; Upon the 'cessatiohhfthe in'ip'ulees" Mid'th release of the slow relay (3- 'tl1ecir:ctiit er the rotary niegnetiselos'ecl es'ffoll'ows :fr'ee {vole or bzitteryfmaghet' 41 9; outer allfiiittll'' and front contact of relay E'4'.' normal Contact of relzg C l, condi'ictor"417, coIiF opening the circuit of th'e rotary magi-en. If the trunk is busy,reley' E-4 a'g'zuh energizes over the following circuit 2' free poleofbelt tery, relay 13 upper 'cont'ct oh-Switch contact" of re- 1m lL- l conductor 425 'test brush426"to a L 1 h r ground on the testvmu'lti'pie 4:2(5 Relay li 5. in attracting its inner armature agtiihf leeks up through the upper armature and back Contact of relay F-Ainncl atthe other" armature again closesthecircuit 0f retnr y magnet Whichhdvances thei hrhs'heer to the net-1t trunk and at 'theencl ofit'stroke open, the looking; circuit o'hrelay'lfi f "which in retracting its armature opens the circuit of the rotary megnetelfi. V

Asuming now that the 'selehtor' has" failed to find an idle trunk In thateverltoh the eleventh rotary 'step,sWitoh 402is'0pemreaby the shaft of the selector and opens the &

bick coh ct 0f relay 13-4. Relay E-4 is marginal and doesnot operate in this circuit in series with the relay D4. Relay D-4 in attracting its

armatures

431 and 432 extends the talking conductors through to the talking brushes 433 and 434. The attraction of the armature 423 of relay D4 grounds the test brush 426 and consequently test multiple 427 of the selected trunk, causing the same to test busy to other selectors. The contact 435 is made before the contact 406 is broken by the armature 437 of the relay D-4. Consequently relay D3, Fig. 3, in the relay and repeating coil equipment is maintained energized over the following circuit: free pole of battery, relay D3, conductor 316, outer right armature and back contact of relay F'3, conductor 315, conductor 407, contact 435, conductor 438, brush-439, multiple 440, control conductor 441, conductor 500, conductor 501, armature 502 and back contact of relay K-5, conductor 503, sleeve conductor 550, conductor 442, multiple 427, brush 426, conductor 425, lowermost armature and back contact of relay 1 -4, conductor 424, armature 423 and front contact of relay D4, conductor 418, conductor 403, to ground at the right armature and front contact of slow relay B4. Thus, the circuit for relay, D-3 (Fig. 3) is maintained closed as the circuit is extended from switch to switch. As will hereafter appear, relay F+3 is not operated until the desired line is found idle and seized, when it reverses the direction of current flow in the circuit leading back to the toll operators position to li 'ht the supervisory lamp 100 to indicate to her the idle condition of the line, whereupon she will cause the connector to begin the automatic ringing operation. The switch of Fig. 5 to which the connection has been extended is a combination toll and local connectorcontaining multiples of ordinary lines in its bank. This switch is accessible not only to the toll transmission selectors of Fig. 4, but also to the local selectors which are used by the subscribers in building up their own local connections. The seizure of the connector causes the dos ing of the following circuit for the impulse relay A-5: free pole of battery, upper winding of relay A5, conductor 504, conductor- 505, left winding of slow relay J5, conductors 506 and 507, lowermost armature and back contact of relay K-5, ring conductor 546, conductor 443, multiple 444, brush 434, conductor 445, armature 432 and front contact of relay D4, left armature and front contact of relay A-4, ring conductor 446, conductor 318, lower armatures and back contacts of relays K3 and M-3, lowerright hand Winding of the repeating coil 309, resistance 319, inner left armature and front contact of relay D3, resistance 320, outer left-hand armature and front contact of relay D3, resistance 321, upper right hand winding of repeating coil 309, upper armatures and back contacts of relays M3 and K3, tipconductors 322, 447, armature 431, and front contact of relay D4, conductor 448, brush 433, multiple 449, tip conductor 450, conductor 510, upper armature and back contactof relay l5, conductor 511, conductor 512, lower winding of relay A5 to ground. Relays J5 and A-5 operate in this circuit, the former at its innermost right armature closing a locking circuit for itself as follows: free pole of battery, right winding and right innermost armature and front contact of relay J-5, conductor 514, conductor 531, conductor 515 to ground at the armature 516, and front contact of slow relay B5 which is energized upon the energization of the impulse relay A-5. Relay B-5 grounds the sleeve wire 517, leading to the test multiples in the local selectors, this circuit leading from grounded armature 516, conductor 515, to conductor 517. The return of the dial to normal transmitting the tens digit after the operation of transmitting the hundreds digit of the wanted number interrupts the circuit of relay A2, Fig. 2 which in turn interrupts the circuit of the impulse relay A5, Fig. 5 which in vibrating its armatures transmits impulses to the vertical magnet 518 of the connector over the following circuit: free pole of battery, magnet 518, slow relay 519, right contact of off normal switch 520, conductor 521, lower armature and front contact of relay 13-5 to ground at the armature and back contact of the impulse relay A5. At the first step of the connector, the off normal springs 520 are shifted and the succeeding impulses are transmitted by way of the upper armature and front contact of relay 519 and the contact 522 now closed at the off normal springs 520. The selector brushes are thus lifted to the desired level and upon the cessation of the impulses, impulse relay 141-5 remains energized and relay 519 in series with the vertical magnet releases preparing the circuit of the rotary magnet 523. The units impulses pass through the back contact of the impulse relay A-5, lower armature and front contact of relay B--5, conductor 521, off normal contact 522, upper armature and back contact of slow relay 519, conductor 524, left armature and back contact of relay G-5, conductor 525, uppermost armature and back contact of relay 11-5, rotary around into engagement with the desired line.

If this line is idle, potential is present on its test multiple 526 through the cut 01% Wind ing of the line switch in accordance with well-known systems such as that disclosed magnet 523 to free pole of I battery. The connector is thus stepped 1 ,aeegeee in Patent 1,159,855, issued Noveinber 9,1915, to T. G. Martin; and the "followingcircuit" is closed to operate relay 'H+5: n'u'ultiple 526, brush 527, conductor 528, -right hand armature and back" contact of relay v12%5," conductor 529', upper Winding of relay H 5," conductor 580, right hand armature and bac'li' contact of relay Ge-5, conductor 531, conductor 5i5,-arinature 516 of relay B+5"to' ground. Relay H-5 in attractingits. armature 532 locks itself to the groundedsleeve' Wire 550 and extends this gro'unded con-' ductor over conductor 533, middle right armature and front contact of relay J'5, conductor 53% to the relay Relay K-5 in attracting its armature 502 discon-= nects the grounded sleeve Wire 550fro1nthe" control lead 50'O -leading'baclz'to the relay D3, Fig.- 3 of the relay? and repeatingcoil equipment circuit. Re'lay'D'3, therefore releases and in retracting its righthand armature operates relay 1F 3,' FigJ3, over" the following circuit? free pole of battery, relay F3, right armature'and back contact of relay D'3, conductor 323, conductor 450, armature 423 'and' front contact of relay D- i,'conduct0rs 418, 4:03 to ground at the ri htarmature" and frontcontact of relay B Relay F 3 in attracting its outer right armature closes a substitute ground to holdup the slow relay F-5 to prevent ringing'from occurring at this time: grounchrighthand armature of'relay' E3, conductor 321, right armature and back contact of relay B 3, outer right arrriature and front contact of relay Fi3,"control 'conductors 315, 107, contact 2315 o f'r'elay' D l, conductor 438, brush 439', multiplettO, conductor 14-1, conductor eodrmntcontact'and armature and lowerfwinding of relay F-5 to free pole of battery. Relay F5 was energized upon the first impulse to the vertical magnet, this circuit being'as follovvs tree pole of battery, lower 'wi'nd'ingot relay F-5, lower armature and front contact of" slow relay 519,inner1nostright hand arma ture and front contact of relay J 5, conductor 51-1, conductors and 515 toground' at the upper inner armature and front con act of relay B5. VV'hen' energize'drelay F--5 lockedby Way of 'its armature 535; and front contact, conductor 501, armature 502 and back contact of relay K-'5' to" grounded sleeve Wire 550." Consequently," the operation of relay K-5 to cause the re-' versal of direction of the currentfiovifin the loop leading ba'ckto the'toll operators position opened the circuitof sloW'rel-ay 5' and unless a substitute circuit was provided for holding it up" the ringing operation would autornatically take place" This is'prevented by applying a substitute ground as described to the control conductor 500over the circuit traced to" ho'ldthe relay F'5 until the operator, by'depressin-g-a"1 ey' as "tracting' its armatures" operates the last digit, I theopera'tor' restoresher dial 'ing"ke'y DEC whichrele'asesfrelay E-72 as described- Whi'c'h' disconnects the dial from the tip of the" p'li1g,"causing the releaseof the" relay A'2',Fig; 2'and the closure of an energizing circuit for relays C2 and B43, throught'he right hand Winding of relay C 2,re lay 'B'43 and relay A2'. Relay A-2*it Willbe remembered, releases under this-conditibn and in retracting its left'arrna ture" opens the bridge to the distant ofic'e 'includin rela"I+-2'leavin onl the olarized -relay 2 bridged across the trunk froin 'upp'ertalking conductor 212, Fig. 2,

conductor 2ll, polarized relay F2, con

ductoi 210,"iniier right armature andfront contact of relay B' 2, conductor 209, con ductor2 08, left hand vvin'ding of relay C 2, armature and front contact of relay C2,

conductor 207, outer left'arrnat ure and back contact ot relayt H'-2, conductors 206 to lower talking "conductor 205'. The reversal of thedirection er current in the talking conductors due to the operation of relay F3 (Fig. 3) causesthe'relay F-2 to operate, closing the following circuit for relay 'G 2';" o1e of battery,relay G-'2, con

ducto-r' 224, contact 225 of relay F-2, corn 2 ductors"22 6, 227, 228, inner left armature andt'ront contact 'o't'relay B-2 to ground. Relay 'G -2'lock's itself up' o'ver the following'circui't: fre'e'pole'battery, relay G2 conductor224,conductor 229, front contactand armaturejaso, ofrelayi G 2, conductor 231,

conductors

227, 228 to ground at the inner left hand armature of relay I*1elay G-'2 connects the talking. conductors of Fig. 2 through to the talking conductors of Fig. 1'Whereupo1'1 the calling supervisory frelay operates in series Wltll the re lay {t -4, Fig, 4, and lights the supervisory lamplOO asa ringing signal to the toll operator, Relay G 2 Fig. 2 cuts off the bridge including" relays C-2 and A'2. Re-

lay opens the bridge containing; relay F-2. The'operator now operates her ringing" kev RK which impressed alternating current-upon the talking conductors and oper-j atesthe'alternating current relay C-3 in bridge of the trunk which in at-j the relay The polarized relay 8 3 is also bridged across the trunk; Fin. 3, but the low frequency 16 to'20 cycle ringing current open the-bridge containing relay S3. Re-

will irnin'ediately operate relay Which will by 'attrac'tlnp; its outer lett armature tively high frequency alternating current only, say 135 cycles. Relay S3 will not therefore release relay R-3 which is now energized from ground on the sleeve wire 31 1-. Relay R-3 is at this time holding open. the circuit of relay H3 for a purpose which will later appear. To guard against a momentary opening of the back contact of relay S-3 releasing relay 13-3, relay lt-3 is made slow to release as shown. melay lfi3 in attracting its right armature opens the circuit heretofore traced, which has been holding relay F 5, Fig. 5, energized. Relay F5 in retracting its armature 53? connects ringing current to the called line through its own upper windin This ringing current is automatically continued until the called party removes his receiver, resulting in the increase in the current through the upper Winding of relay F-5 causing thesame to operate removing the ringing current. The attraction of the armature of this relay again closes the locking circuit for the same over control conductor 500. The extension of the tip and ring conductors by relay F5 to the called line operates relay A3 over the winding of which talking current is fed to the called line. Relay A3 in operating energizes relay 13-3 which in attracting its right hand armature applies ground to the control conductor 315 to hold up relay F5, Fig. 5. Relay in attracting its left armatures closes a bridge across

conductors

306, 313 to hold up relay 1 1- 1, and opens the connection of battery through the windings of relay A.- 1, Fig. 5, to the talking conductors, leading back to the operators position which causes the deenergization of supervisory relay B 13. This relay in retracting its armature extinguishes the supervisory lamp 100 which notifies the operator that the subscriber has responded. Talking current is fed to the called line over the windings of relay A--3 and the repeating coil 309. This talking circuit is a standard repeating coil transmission circuit used in long distance connections. Talking current is fed to the other line from the distant exchange. Durin conversation the trunk leading from the lett hand windings of repeating coil 309 through the right hand winding of the re peat? g coil (not shown) at the distant office is dry, in accordance with standard practice. The operator may now request the subscriber at the substation'shown in Fig. 5 to deposit the necessary coins in the coin box which may be of the type shown in said Patent 19 13219, issued November 5, 1912 to O. F. Forsberg. These coins in passing tl'irough the box strike go ngs whereby the operator is informed of the denominations of the coins inserted. When she is satisfied that the proper coins have been deposited she picks up her plug P Fig. 1 and inserts it into the jack 133, and closes the leftgcontacts of switch 135 which grounds the ring of the plug, this resulting in the energization of relay 134. Relay 13 1 in operating energizes relay 130. Relay 130 in operating applies high frequency alternating current, which may be of 135 cycles per second, to the trunk 131, 137, which operates the alternating current relay S3, Fig. This relay in operating removes the shunt from about relay (i -3 which in operating grounds conductor 306 leading to the wind-- ing of relay A l, Fig. 1-, which is connected to battery. This is to prevent the release of the connection if the subscriber should hang up his receiver at this time since relay 130, Fig. 1, in operating opens the loop circuit over which the relay AA was held over the cord. Alternating current relay S3 in operating releases slow marginal relay R3, which in closing its back contact energizes relay H3, this circuit including armature and front contact of relay F3 now energized. Relay H3 in at tracting its inner right armature operates relay K3 and in attracting its outer right armature extends the source of 110 volt collect current through the front contacts of the relay K3, to the trunk conductors 322, 318. r his current passes over the talking conductors, Figs. r and 5 to ground through the polarized magnet 1 -5, Fig. 5. .Vheu the polarized magnet T a; operates and collects the coins, it opens the contact 538 in the coin box to remove the polarized magnet from the talking circuit.

If on the other hand the deposited coins are to be refunded, the operator closes the right contacts of switch 135, Fig. 1. This not only grounds the sleeve of the plug P but also the tip of the plug, resulting not only in the operation of the relays 134: and 130, but also relay 150 which in operating bridges a retardation coil 138 across the trunk conductors 131 and 137. As before the high frequency alternating current from the source 136 causes the operation of the relay H3. Due however, to the presence of the bridge containing retardation coil 138, Fig. 1, the shifting relay N3 operates, its circuit including the left-hand arinatures and front contacts of relay E3, the talking conductors, Figs. 2 and 1, and the bridge referred to. Relay N3 shifts the conductor 339 leading to the front contact of the relay H-3 from the collect source of post tive current to the refund. source of negative current. Consequently refund current is transmitted over the line to operate the polarized magnet P-5 in the coin box in the substation in the other direction to refund the coins and open the contact 538. The alternating current relay (3-3 which will be remembered operates to cause the ringing operatlon of the connector to take place, Wlll reac es not operate on the 135 cycle current for the reason that it is mechanically slow to operate and its electrical characteristics are such that it will not respond to such high frequency alternating current.

ssiuning now that the desired line when selected by the connector is busy. In that case the test multiple 526 5 is grounded. lVhen test wiper 527 is set on the buy multiple 526, ground. is extended .over brush 527, conductor 528, contact 5&0 of :relay E5, conductor 54.1, armature 542 and back con tactiof relay 1-1-5, conductor 5&3, relay G 5 to free pole of battery. Relay -G5 energizes and when E5 releases as the units impulses terminate locks itself up over the following circuit: free pole of battery, relay G .5, conductor 543, armature 5&2 and back contact of relay li -5,, conductor 5&1, make before break contact 544 of relay E ;5,, right armature and front contact of relay G-G, conductor 531, conductor 55-15 to ground at the armature 516 and front contact of relay B.5. Relay ,in the case of a local call connects busy tone from the source 5525 to the calling line. In the case of a toll call this lousy :tone is not used, a flashing signal being given to $116 operator instead, as described. Due :to the operation of :relay relay ,cannot operate. Consequently, relay iliI--.5 is not energized to .open the circuit of relay .D3 .3 as described in the case of .an idle line. inasmuch as relay D3 remains energized, relay 1 3, whose circuitis maintained open at the outer right armature and back contact of relay is :not operated and no current reversal in the trunk zleading back to the operator s position ioccurs. Polarized relay Ffi2 Fig. 2, is not operated in this case and relay G 2 remains inert. .Since the relay E-2 is locked 11p .at-this time and relayGr2 is inert, when the operator restores her dialing .key 'DZK .a circuit is closed from interrupter 233 of 120 impulses per minute to shunt out resistance 200 to cause the supervisory relay B--i8 to Jfiash the

lamp

100, 120 ii mes per minute, which indicates to the op erator that the selected line is busy, whereupon. she pulls out the plug TT from the trunk switching jack TSJ which results in the release of all switches and the normal condition of all the apparatus including :the various looked up relays.

During the conversation the called 3511bscriber by moving his hook up and down causes the supervisory lamp 100 at :the ,toll operators position to flash as in manual practice without releasing the switches. This is apparent from the preceding description inasmuch as relay l b- 3 Fig. 3 isin circuit with the called line andeach time it attracts "its armature it operates the relay the supervisory relay ,B43 and puts bridge across-the relay A& to hold it operated. .When the called subscriber replaces his; receiver the lamp 1().O ,at thetoll opere ators position Fig. 1 is lighted. Theoperato-r may rering the subscriber if necessary iif sheicl-esires to recall him by actuating her ringing key BK which-operates relay C to operate which in attracting its right hand armature again releases relay F Fig. 5 which initiates the automatic ringing operation. The; control or this relay,F5;is removed from the relay E-B by the attraction of the right armature of relay when the called subscriber responded and is restored to the relay E3 and consequently to the operator when the called subscriber replaces the receiver and rleenergizes ire'lay B.3.

lWhen the operator desires to break down the connection after the cal-led subscriber has replaced his receiver, she reinovesith-e plug TT from the toll switching jack TSJ. This releases relay A.4 Fig. 4 which causes the restoration ofall the switches. If, however, the operator pulls out the plug while the called subscriber still has his receiver off the switch hook, the switches are not released.

Assuming, however, that the called subscriber has replaced his receive-r, when the operator removes the plug, relay A4 releases, dcenergizing relay B-4-. Relay B?& in retracting its router left armature -removes ground from the sleeve conductor 4:51 leading over the sleeve conductor 314 (to the re lease relay of the incomingselector IS which thereupon causes release of such selector in the well-known manner. The removal of ground from conductor ;&03, by the retraction of right hand armature of relay B4lreleases relay D land the retraction of. the right hand armatures of relay A-4 and inner left armature of relay Be -encloses the circuit of the release 1magnet52 of the toll transmission selector as follows: free pole of battery, magnet 425,10wer contact of off normal switch 415, conductor 41153, back contact and inner left hand armature of relay B4c to ground at the right hand armature and back contact of relay A4 The slow relay F-4 fl fil'lelfig'lZeCl in parallel with the release magnetra-nd opens the circuit to the test brush 426 during restoration at its lowermost armature. At its armature 454 it short cir cui;t s the lefthand Winding of relay A-i. At its upper armatureit closes a locking circuit for itself .which ;is opened when the off -I Q, '1na;l switch assumes its normal position. Hllieopening/of the circuit of the tip and

ring conductors

5 and 546 causes the release of relays A5 li -5, J. 5, Fig. 5 which results in the closure of th circuit of connector release magnet 546 free pole of battery, magnet e46, .lett hand 101 -11- tacttot oil normal switch 520, *backcontact and lowermost armature of relay D 5, lower armatures and back contacts of relays B5 and A-5 to ground. The connector upon reaching normal position restores the oil normal switch 520.

The relay l I S is provided to permit the toll operator to apply ringing current to a selected private branch exchange line to signal the operator thereat. This relay is operated when relay E3 is operated due 'to the actuation of the ringing lrey by the toll operator. In private branch exchange working the called subscriber may hang up his receiver, but due to the'hridge at the P. B. X. operatofis board the relay A l remains operated and thus no disconnect signal is given to the toll operator.

What is claimed is 1. In a telephone system the coinl'iination of subscribers lines, an operatofls position. means including toll switching trunks and automatic switches for extending a call from said position to a subscribers line, a coin box at the substation of said line having a coin disposal magnet, collect and refund current sources associated 'with one of said trunks, a coin current applying relay associated with said trunk, an alternating current source at said position, a manual switch at said position for applying alternating current from said cource to said trunk to cause the operation of said relay to apply current from one of said sources to the connected substation to operate the coin disposal magnet in one manner, a shifting relay also associated with said trunk, and a manual switch at said position for operating said coin current applying relay and also said shifting relay, the latter substituting the other coin current source to operate the coin disposal magnet in another manner.

2. In a telephone system the combination of telephone lines, a connection comprising toll trunks and automatic switches. a coin box at the substation of the COll'l'lBCllQtl line having a coin disposal magnet, a toll operators position, a pair of coin current; sources associated with one of said trunks, a coin current applying relay associated with said trunk, means including a manual switch at said position for operating the same, a shifting relay controlling the association of said sources with said trunk, a circuit for operating the same controlled at alternate contacts or said coin current applying relay and including the trunk leading back to the toll position, and means at said position controlled by the operator for closing the circuit or not, dependent upon which source is to be connected to the connected subscribers line.

3. In a telephone system the combination of telephone lines, an operators position, means including toll trunk lines and automatic switches for extending connection to trunk one of said lines, a coin box at the substation of said line having a coin disposal magnet, collect and refund coin current sources associated with one of said toll trunks, a coin current applying relay associated with said trunk, a shifting relay for controlling the connection of said sources to said trunk, an alternating current source associated with said position, a manual switch for applying alternating current from said source to said to cause the operation of said coin current applying relay to apply current from one of said sources to operate said coin disposal magnet in one direction, a bridge for said trunk, an impedance device therein, and a second manual switch for applying alternating current from said source to said trunk and also closing said bridge thereacross to operate said shifting relay to cause said coin current applying relay to apply current from the other source to said magnet.

4. In a machine switching telephone system, the combination of a number of o'fiices, a. toll position at one office, automatic switches and trunks at another oiiice, subscribers lines terminating in said last office, two-wire interofiice trunk over which said switches are set to complete a connection to one of said lines, coin boxes at the substations of said lines having coin disposal magnets, sources of collect and refund current at said automatic office, a coin current applying relay at said automatic ofice operated from said toll position over said two-wire interoiiice trunk to cause current from one of said sources to be applied to the coin disposal magnet to operate the same in one direction, a shifting relay at the automatic oihce, and means controlled by the toll operator including a circuit over said interoi'lice. trunk for also causing the operation of said shifting relay to cause current from the other source to be applied to the coin disposal magnet to operate the same in another direction.

5. In a machine switching telephone system, the combination with a number of oflices, a toll position at one otlice, automatic switches and trunks at another office, subscribers lines terminating in said last office, a two-wire interoflice. trunk over which said switches are set to complete a connection to one of said lines, coin boxes at the substations of said lines having coin disposal magnets, sources of collect and refund current at said automatic oflice, of a pair of relays at said automatic oiiice, one arranged to shift the connections of said sources, and the other to cause the extension of said connections to the trunk leading to the connected line, a bridge for said trunk, a retardation coil therein, and manual means at the toll office for either applying alternating current to operate said latter relay to cause current from one source to be applied to the connected line, or for applying alternating current and also a bridge containing a retardation coil across the trunk to permit said first mentioned relay also to operate and shift the connections to the other source.

6. In a machine switching telephone system, the combination with a number of of fices, a toll position at one ofiice, automatic switches and trunks at another office, subscribers lines terminating in said last office, a two-wire interofiice trunk over which said switches are set to complete a connection to one of said lines, coin boxes at the substations of said lines having coin disposal magnets, and a source of collect current at said automatic office of an alternating cunrent relay in the trunk at said automatic office arranged when operated to cause the extension of said source to the trunk leading to the connected line, and a key at the toll position for applying alternating current to said interoffice trunk to operate said relay.

7. In a machine switching telephone system, the combination with a number of offices, a toll position at one oflice, automatic switches and trunks at another ofiice, subscribers lines terminating in said last office, a two-wire interoffice trunk over which said switches are set to complete a connection to one of said lines, coin boxes at the substations of said lines, coin disposal magnets therein, and a source of collect current at said automatic ofiice, of an alternating current relay in the trunk at said automatic office, a relay operated thereby to cause the ex ension of said source to the trunk leading to the connected line, and a key at the toll position for applying alternating current to said interoffice trunk to operate said alternating current relay.

8. In a telephone system, an operators position, a trunk, two alternating current relays bridged thereacross, one adapted to respond to high frequency alternating current only, and the other to low frequency a ternating current only, a. coin current charging circuit controlled by one relay, and a ringing circuitcontrolled by the other, sources of current of high and low frequency at said position, and manual means controlled by the operator thereat for impressing current from said sources on said trunk to selectively operate sald alternating current relays.

9. In a. telephone system, an operators position, a trunk, two alternating current relays bridged thereacross, one adapted to respond to high frequency alternating current only, and the other to low frequency alternating current only, a slow-to-release relay, a circuit therefor including a back contact of said high frequency relay, a coin current applying relay, a circuit therefor including a back contact of said slow relay, a relay adapted to be operated by the operation of said low frequency relay tocause ringing current to be applied to the trunk, sources of high and low frequency current at said position, and manual means controlled by the operator for impressing alternating current from said sources to said trunk to selectively operate said alternating current relays.

10. In a telephone system, an operators position, a distant office, a two-wire trunk leading from said position to said distant office, two alternating current relays bridged across said trunk at the distant office, one adapted to respond to high frequency alternating current only, and the other to low frequency alternating current only, a coin current charging circuit controlled by one relay, and a ringing circuit controlled by the other, sources of alternating current of high and low frequency at said position, and manual means controlled by the operator for impressing current from said sources on said trunk to selectively operate said alternating current relays.

11. In a telephone system, firstand second offices, an operators position at said first oflice, a line terminating at said second ofiice, a trunk interconnecting said offices, automatic switches at said second office, means at said first office for controlling said automatic switches over said trunk to interconnect said trunk andsaid line, a source of current, a. coin disposal magnet associated with said line, a source of alternating current at said first office, means. for connecting said alternating current source to said trunk, and a relay responsive to alternating current received over said trunk from said source for connecting said first men tioned source of current to said line to control said magnet.

In witness whereof, I hereunto subscribe my name this 21st day of December A. D., 1920.

HENRY L. HOFFMANN.