US1729857A - Multioffice telephone system - Google Patents

Description

Oct. 1, 1929. R. F. STEHLIK MULTIOFFIGE TELEPHONE SYSTEM 1s sheds-sheet 1 Grginal Filed July 19. 1926 35m .Ehm

Oct. 1,'1929. R. sTEHLlK 1,729,357

MULTIOFFICE TELEPHONE SYSTEI Original Filed July 19. 1926 13 Sheets-Sheet 2 x v.. x, f WN NL.

u SHHUI u QNNMSNSY X kwh M. IHWL m @L myw PEE @Em Imran DIW-f- E'udnllfh F. Ehlzk UCL l, 1929- R. F. STEHLIK MULTIOFFICE TELEPHONE SYSTEM Original Filed July 19, 1926 15 Sheets-Sheet 3 Oct. 1, i929. R. F. STEHLIK 1,729,857

MULTIOFFICE TELEPHONE SYSTEI( original Filed July 19, 1926 1s. sneat-sheet 4 Termina im: Nanna] TCIE' Oct. l, 19429. R, F. STEHLIK 1,729,857 MULTIOFUFICE TELEPHONE SYSTEM original Filed July 19, 1926 15 sheis-sheei 5 ITizUEn m11- Rudnlph F.' Ehhk Oct. l, 1929. R. sTEHLlK MULTIOFFICE TELEPHONE SYSTEM 13 Sheets-Sheet 6 led July 19, 1926 Original F1 Inuen or Eudnlfh F. E'I-e'hhlf Oct. l, 1929. A R. F. sTEHLlK MULTIOFFICE TELEPHONE SYSTEM Original Filed July 19, 1926 15 Sheets-Sheet '7 who@ @SM nu@ n mi Cet. 1, 1929. R, F, STEHLlK 1,729,857

MULTIOFFICE TELEPHONE SYSTEM Original Filed July 19. 1926 13 Sheets-Sheet 8 Prm Eu nl h1? Ehhk oct. l, 1929. R F, STEHLIK 1,729,857

MULTIOFFICE TELEPHONE SYSTEM Original Filed July 19, 1926 15 Shee'tS-She'i" 9 Ill-II Inuen u11 Oct. l, 1929. R. STEHLIK 1,729,857

MULTIOFFICE TELEPHONE SYSTEM Original Filed July 19. '1926 13 Sheets-Sheet 10 Eudzfh F. Efe-511k Oct. 1, 1929.

R. F. s-rEHLlK 729,857

MULTIOFFICE TELEPHONE SYSTEM Original Fld Jlllly. 19. 1926 13 ShejetS-Sheet 11 ILKIA Oct. 1, 1929. R. F. sTEHLlK MULTIOFFICE TELEPHONE SYSTEM original Filed Juiy 19; 192e A15 Sheets-Sheet 12 I'Enfen 1jr NNN Engg/:h E 5mm M TVT riginal FiledA July 19.*' 1926V 13 Shee't'sS'heet 13 .Patented oct." 1, 1929 UNITED STATES PATENT OFFICE RUDOLPH F. STEHLIK, OF CHICAGO, ILLINOIS, A-SSIGNOR T0 AUTOMATIC ELECTRIC INC., OF CHICAGO, ILLINOIS, A CORPORATION OF DELAWARE MULTIOFFICE TELEPEON E SYSTEM Applicationl led July 19, 1926. Serial No. 123,323. Renewed February 27, 1929.

A The present invention relates to multioliice telephone systems, but more particularly to multi-cnice tele hone systems containing both automatic o ces and manual oflices.

The principal object of the invention is the production of suitable circuit arrangements such that the organizations of equipment that are known as directors, and are used to control the operation of the automatic switches, may be used also to transmit series of coded impulses to operate the call indicators in the manual oiices.

A further object of the invention is the production of suitable circuit arrangements whereby the combination directors send call indicator impulses representing subscriber digits onl in case the call is to a terminating manual o ce reached directly from an automatic office, and send, prior to the sending of thev subscriber digit impulses, suitable call indicator impulses indicative of the particular called manual oice when the call is completed to or through a tandem manual office.

In accordance with a further object of the invention, arrangements are provided whereby the talking conductors, at an repeater or trunk holding circuits at whic the talking conductors are inductively coupled, are connected together metallically and cleared of their bridges prior to the sending of the call indicator impulses so as to permit the call indicator impulses to be delivered from the combination directors directly to the call indicator equipment in the manual office, and suitable arrangements are provided for again cutting in the repeaters and the trunk holding circuits after the call indicator impulses have passed through.

There are quite a number of objects and features which are more or less subsidiary to the foregoing main object. These latter objects and features are listed below:

(a) A feature of the invention relates to the provision of suitable arrangements whereby the digits transmitted in code to the call indicator at a tandem manual oice may be assigned at will by makingl suitable cross connections in the director.

(b) A further feature more or less closely connected with the one in the precegding paragraph relates to the novel arrangement whereby the regular sender of the director, which is used ordinarily to transmit impulse series to set the automatic switches, is transformed automatically at the proper time during a tandem manual olice call so that it functlons under the control of the register on which the office digits are recorded to set the registers that are to transmit the call indicator digits indicative of the particular manual office called.

(c) According to a further feature of the 1nvention,wl1`en the call is for a manual office, the regular sender of the director operates in the usual manner to trunk the call forward toward its designation until a trunk line leading to the manual office is reached, but the operator is not signalled responsive to the seizure of the trunk line. When, however, all the registers in the director have been set the director exerts a further controlling influence on the holding circuit to cause the operator to be signalled.

(d) A further feature resides in the arrangement involving the trunking cord circuits at tandem manual oices and the call indicators at such otiices. The arrangement is such that the ringing circuit inthe cord circuit is rendered effective by the call indicator if the setting of the indicator is such as to indicate that the call is a local call, the ringing circuit being such that it is inefective otherwise.

(e) According to still another feature of the invention, arrangements have been provided whereby the indicator sender of the director is caused to automatically skip over the office-digit positions when the call is for a terminating manual office reached directly from an automatic oiice, so as to enable the calll indicator sender to send subscriber digits on y.

(f) Another feature of the invention relates to arrangements emplo ed for automatically terminating the cut-t rough condition of the repeaters and the trunk holding circuits after the call indicator impulses have been transmitted, so as to permit a release of the connection.

There are other objects and features of the 100 invention in addition to the ones mentioned specifically herei-nbefore which can' be un- 4 derstood best from a perusal of the following description in connection with the accompanying drawings. Referring now to the drawings comprising Figs. 1-13 showing circuit diagrams and Fig. 14 showing a la out of Figs. 113, Figs. 1-4 show the trun ing equipment used in setting up certain connections; Fig. 5, shows the call indicator at a tandem manual oliice; Figs. 6-10, show the combination director; and Figs. 11-13, show certain desirable modifications.

More in detail, Fig. 1 shows a trunk comprising conductors 5-7 extending from the line switch banks 2-4 to the selector S-1. The trunk circuit TC-l is inserted in this trunk for the pur ose of controlling the director (of which t ere is a plurality) which may be connected to the trunk by means of the director selector DS. The trunk circuit TG1-1 is arranged to supply talking current to the calling line and to hold up the switches in the calli-ng automatic' oiiice so that repeaters on the outgoing trunks are unnecessary.

Fig. 2 shows the second selector S-2 n the incoming end of the inter-office trunk comprising conductors 75 and 76, together with the repeater R-l associated with the trunk comprising conductors 135 and 136 outgoing to the third automatic orice. This rawing shows also the timer T--l that comes into play, when the talkin conductors at the repeater R-1 are switched straight through, to terminate the switched-through condition after a suitable interval has been allowed to elapse.

Fig. 3 shows the trunk holding circuit TC-2, on the outgoing end of the trunk line comprising conductors 241and 242 extending to a manual oiiice. This holding cir cuit is inserted between the banks of the selector S-3 and the outgoing conductors of the trunk line in order to provide a holding circuit for the selector S-3 and in order to maintain the bridgeacross the conductors 241 and 242 leadin to the manual office open after the seizure o the trunk line and until the trunk circuit is controlled from the director to close the bridge so as to signal the operator.

Fig. 4 shows the cord circuit CC-l on the incoming end of the trunk comprising conductors 241 and 242. This ldrawing shows also the cord circuit CC-2 on the incoming end of a trunk line connecting the tandem manual oliice with the terminating manual oice. The cord circuit CC-l is used to complete the connection 'to a line local to the tandem manual oiice if the call is for such line, and to extend the connection to a terminating manual oice in case the call is for a line in such oliice. A

Fi 5 shows the six-digit call indicator that may e associated with any of the cord circuits in the tandem manual oliice to indicate the called oiiice and to indicate the number of the subscriber in such oiiice. The relays 409-411 are the receivin relays; relays 401 and 402 are switching re ays that switch the contacts of the receiving relays to the four relay-operating conductors in regular rotation as each digit is received; the two rows of relays lying above the center of the sheet are the transfer relays; and the relays below the center of the sheet are the registering relays. The first two groups of the registering relays register the two code digits indicative of the called otlice, and the remaining four groups of registering relays register the thousands, hundreds, tens, and unitsdigitsofthenumber ofthe called line.

The relay 304 of the cord circuit CC-l Fig. 4, is energized over conductor 357 from the call indicator shown in Fig. 5, in case the l call is for a line terminating in the tandem manual oiice. Relay 304 operates to adapt the-cord circuit CC-l so that ringing current will be sent out in the usual manner when the plug of the cord circuit is inserted into the jack of t-he called line.

Referring now t Figs. 6-10 which show the combination director, the portion of the director shown in Fig. 6, includes the inputcontrol sequence switch S and thev outputcontrol sequence switch S, together with the relays 521 and 522 that control the sequence switch S.

Fig. 7 shows the release relay 622 which is energized over the release trunk conductor 37 when the director isseized; the s'witching relay 621 which is operated at the end of the transmission of the number to bring about the switching-through operation at the trunk circuit, and the freeing of the director; relay 623 is the sending relay of the director that controls the sendingof the stepping im ulses that operate the automatic switches an is in turn controlled by the interrupter 626; relay 624 is the pick-up relay that operates at the beginning of the transmission of a series of' impulses; and rela 625 is the stop relay that is operated-throng the stop wi er 649 of the sending switch SS to terminate t e digit being transmitted.

-In Fig. 8, the oliice register OR registers the two oliice digits of any called number and brings its wipers 725 into engagement with the'set of bank contacts assigned to the called oflice. The intermediate distributing frame I. D. F. is provided in order to permit the control exercised by the oiice register OR on the sending equipment of the director to be assigned or varied at will.

Fig. 9, shows the thousands, hundreds, tens, and units registers that register the subscriber digits of the number, and it shows also the code registers CR--l and CR2 that are set in accordance with" the position of the oice re ister `OR by the re ular sender when the ca l is completed to or t rough a tandem manual oiice.4 The up er wiper of eachAof the thousands, hundre, tens and units registers is for the purpose of controllin the regular sending switch SS Fig. 7, and t e two lower wipers of each of these registers, as well as the two lower wi ers of each of the code registers GR-l and R-2 are for the pur ose of controlling the call indicator sender S Fig. 10.

Considering now the equipment shown in Fig. 1Q, relay 901 is pulled up when the setting of the office register OR Fig. 8, indicates that the call is completed to or through a tandem manual office; relay 902 is similarly pulled up, instead of relay 901, if the call is to be completed to a terminating-manual oliice reached directly from an automatic office; relays 903 and 904 send the impulse that is repeated at the repeater R-l to the trunk circuit TC--2 to cause the o erator to be signalled when all the registers ave been set; relays 905-907 are for the purpose of securing the starting of the code sendinv switch SS when the loperator responds; and relay 908 is the relay that closes the restoring circuit of the sender SS in case the same is in an off-normal position when the release of the director occurs. ,J

In Fig. 11, a portion of the director shown in Figs. 6-10, is shown with a certain modification to be hereinafter explained. The trunk circuit 'FC-3 may be used in place of a trunk circuit TC-1 Fig. 1, in case repeaters are used on the outgoing trunk lines, as it is -then unnecessary to incorporate a holding f... uu

arrangement in the trunk circuit ahead of the first selector.

The repeater R-2, Fig. 12, is used to replace the repeater R-l Fig. 2, when the director is modified as in Fig. 11.

The holding circuit TC-4, Fig. 13, is used to replace the holding circuit 'fC-2, Fig. 3, when the modified director is used.v

The invention having been described generally, a detailed description of the operation oi' the apparatus shown will now be given. For this purpose it will be explained first how the director handles a call that is completed to a subscriber of an automatic exchange, and for the sake of simplicity it will be assumed that the called line terminates in the saine exchange as the calling line.

Uall to automatic Zine Assuming that the line switch of a calling subscriber who desires to call an automatic subscriber seizes the trunk lineJ comprising conductors -7 at the terminals 2 4, line relay 10 pulls up over the calling line and closes at armature a circuit for release relay 11. Release relay 11 grounds the release trunk conductor 6 at armature 17 so as to provide a holding circuit for the calling line switch. It will be observed that the grounding of conductor 6 results in the closure of a circuit through the left hand winding of the electropolarized relay 8. Owing to the fact that the cores of the two windings ofu the relay 8 are i connected together by the soft iron yokes as shown, the relay 8 is not operated at this time because the' core of the. r1 ht hand windin serves as a shunt around tie core of the'le t hand winding.

As a further result of the operation or relay 11, a circuit is closed at armature 18 for relay 26 of the director selector DS in series with the stepping magnet 25, and at armature 19 the junction of the relay and magnet is connected through armature 23 and the resting contact and armature 29 to the test wiper 33. If' the director on which the wipers of the director selector DS are standing 1s idle, relay 26 pulls up without being affected by the connection to the test wiper, but, if the director is busy, a ground potential is encountered by test wiper 33. In this case relay 26 is short circuited and stepping magnet 25 operates in the usual buzzerlike manner to advance the wipers of the switch DS stepbystep in search of an idle director. When an idle director is reached, for example, the one shown in Figs. 6-10, t-he stepping action of the selector DS ceases, and relay 26,- being no longer short circuited,

lgulls up in series with stepping magnet 25.

tepping magnet 25 does not operate at this time on account of the relatively high resistance of relay 26. Upon operating, relay 26 disconnects test Wiper 33 from the test circuit and connects it to ground at armature 29, thereby making the seized director busy immediately; prepares the impulse circuit at armature and at armatures 27 and 28 connects the conductors 5 and 7 extending to the selector S-l to the loop conductors 35 and 36 of the director. When this occurs, line relay 51 of the selector S-l pulls up over conductors 35 and 36 through the resting contacts and armatures 635 and 738 Fig. 7, conductor 604 and the resting contact and armature 919, Fig 10. At armature 62, relay 151 closes a circuit for relay 52, which prepares the switch for operation at armature 64 and places an additional ground on conductor 6 at armature 63.

In the seized director, release relay 622 Fig. 7, pulls up over the release trunk conductor 37 when conductor 37 is grounded upon the seizure of the director and opens the normal restoring circuit of the sending switch SS at armature 631; opens the restoring circuit, including conduct'or 507, of the sequence switch S at armature 633; at armature 634 removes ground from the release conductor 502-; and at armature 632 places ground on conductor 608whereupon the release relay 908, Fig. 10, of the sending switch SS operates to open the normalrestoring circuit of the sending switch SS and to prepare at armature 936 and its working contact a swfitch-through circuit over the conductor 'he does so, line relay 10, of the trunk circuit TC-l Fig. 1, falls back once for each interruption produced in the line circuit at the calling substation. Each time it falls back, it closes at armature 16 a circuit through armature 30 and its Working contact, wiper 34, the bank contact on which it is standing, conductor 38, armature 627, Fig. 7, and its resting Contact, conductor 505, distributing wiper 527 and its first contact, the associated conductor, and vertical magnet 727 of the office register OR to battery. By the operation of the vertical magnet, the Wipers of the office register OR are raised step-bystep and they come to rest opposite the desired level of bank contact.

Series relay 521, Fig. 6, operates upon the transmission of the first impulse of current to the vertical magnet, and, being slow acting, remains operated throughout the series of impulses. At its upper armature relay 521 closes a circuit 'for relay 522 which operates and prepares a circuit for stepping magnet 523 of thel switch S." This circuit is closed momentarily when relay 521 falls back at the end of the series of impulses, and the circuit is opened again by relay 522 when it falls back. The result is a momentary energization of stepping 'magnet 522 to advance the Wipers 526 and 527 one step. When the second office digit is dialled, the impulses of current are delivered over the circuit path above traced to wiper 527, Fig. 6. From this point, the impulses of current are delivered through the conductor terminating in the second bank contact of Wiper 527 to the rotary magnet 726 of the office register OR. By the operation of the rotary magnet, the wipers of the office register OR are rotated step-by-step until they come to rest upon the desired set of contacts, which set of bank contacts, it will be assumed, is the set bearing the reference numeral 721.

Whenthe Wipers of the sequence switch S are advanced another step at the end of the rotary movement of the office register OR, the distributing wiper 527 extends the impulse conductor to the conductor leading to the stepping magnet of the thousands register, Fig. 9. At the same time, Wiper` 526 of the switch S connects ground to the start vconductor extending to the first six contacts in the bank of wiper 530. This results in the starting .of the regular sender shown in Fig.

V7 to transmit the code of the called office in l register registers the tens digit; and the units register registers the units digit,

office digit, the ground potential is extended yby wiper 530 of the sequence switch S to .the impulse conductor 509, closing a circuit through the resting contact and armature 644' and the interrupter 626 for the sending relay `623. Relay 623 now cnergizes and deenergizes under the control of the interrupter 626. Upon its first energization, relay 623 closes at armature 636 a circuit for stepping-magnet 647 of the sending switch SS. Magnet 647 operates and moves the associated pawl into engagement with the next tooth in the wiper driving ratchet Wheel, but does not advance the Wipers 648 and 649. At armature 635, relay 623 opens a point in the outgoing control circuitincluding conductorsv 35 and 36, but this is Without effect at this time as armature 635 and itsl resting contact is shunted at the resting contact and armature 638. When relay 623 falls back the first time, it permits magnet 647 to fall back and advance the Wipers one step, whereupon pick-up relay 624 is operated through' wiper 648. At armature 638 relay 624 removes the shunt from around the sending contacts 635, and at armature 639 it prepares a locking circuit for relay 625 and closes, through armature 643 and its resting contact, a circuit over conductor 506 for magnet 528 of the sequence switch S. lMagnet 528 operates over this circuit preparatory to advancing the wipers 529 and 530.

As the shunt is now removed from around the sending contacts 635 of relay 623, each subsequent operation of relay 623 opens the outgoing control circuitnomentarily, Wipers 648 and 649 being advanced an additional step at the termination of each opening in such circuit. As the call is Jfor a subscriber local to the calling exchange, and as the local thousands selectors are accessible from the third level of the selector S-1, Fig. 1, the first contact in the group 721 on which the wipers of the ofiice register OR, Fig. 8, are now standing is cross connected on the I. D. F. to the third impulse stop conductor, and, when the wiper 649 encounters the third impulse stop conductor at the end ofthe third interruption in the .outgoing control circuit, stop relay 625 is operated over the following circuit: from ground by way ofwiper 531, Fig. 6, the first associatedbank contact, the upper Wiper of the office register OR, the

bank contact on which it is standing, the associated I. D. F. jumper, the third impulse stop conductor, the associated contact in the bank of wiper 649, Fig. 7, and relay 625 to battery. At armaturey 644, relay 625-disconnects rela-y 623 before it has had time to operate again; it closes the restoring circuit of the sending switch SS at armature 642 and at armature 643 it closes a locking circuit for itself through the working contact and armature 639, at the same time removing ground from conductor 506. Magnet 528 of the sequence switch S now falls back and advances the wipers 529-531 one step, and wiper 531 removes ground. from the rst wiper of the oilice register OR and places it, on the second wiper. Since one code digit is sufficient in the present case, it is necessary that the remainin code-digit positions of the sequence switch be skipped automatically without any digits being sent corresponding to such positions. Accordingly, the bank contacts on which the remaining wipers of the ofiice register OR are standing, are cross connected to the skip conductor 501. The skip cond'uctor 501 is connected through the selfinterrupting contacts of magnet 528, Fig.- 6 to the said magnet. The result is that magnet 528 operates in its usual buzzer-like manner and advances the Wipers 529--531until the last code-digit position of the switch S has been passed, and the Wipers have landed in their seventh position, corresponding to the thousands digit.

When the restoring circuit of the sending switch SS is closed at armature 642 of stop relay 625, magnet 647 operates through its self-interrupting contacts and advances the wipers 648 and 649 to their normal position, in which position the restoring circuit is opened at the wiper 648, as is the circuit of pick-up relay 624. Relay 624 is slow acting and it remains operated for an interval after its circuit is opened.

After the interval for which it is adjusted, relay 624 falls back and opens at armature 639 the locking circuit of relay 625. Relay 625 is slow acting also, and it remains operated for another interval, after which it also falls back and again connects. up the interrupter 626 at armature 644 to start the transmission of the next digit (in this case the thousands digit). It may be pointed out that the interval required :for relays 624 and 625 to fall back one after the other is sufficiently long to permit a selector to initiate and effect its trunk hunting movement before the next digit is transmitted.

As the wiper 531 of the sequence switch S is now on its seventh bank contact which is connected to the upper wiper of the thousands register, Fig. 9, the thousands digit, Awhich is started when the stop relay 625 falls back as above described, is terminated in accordance with the setting of the thousands register; the

hundreds digit is terminated in accordance with the setting of the hundreds register; the tens digit is terminated in accordance with the setting of the tens register; and the units digit is terminated in accordance with the setting of the units register, the wipers of the sequence switch S bein advanced automatically one step at the en of each di 't and in the manner above described. That eing the case', wi er 531 reaches its last position upon being a vanced another step at the end of the unit digit, and it placesground on the switchthrough conductor 508 in order to bring about the switch-through operation in the trunk circuit TC and the freeing of the director in the manner to be described subsequently.

Considering now the effect of the transmission of the digits. on the automatic switches, line relay 51 of the selector S-l falls back once for each of the three interruptions produced in its circuit when the oflice code digit 3 is transmitted by the director. Each time it 4falls back, relay 51 closes at armature 62 a circuit through armature 64 and its working contact and -relay 53 for the vertical magnet 59. Vertical magnet 59 operates in the usual manner and raises the wipers 72-74 step-by-step op site the first level of bank contacts. 'Sie slow acting series relay 53 operates when the first impulse is transmitted and it remains operated until after the third impulse has been transmitted. At armature 65,.relay 53 closes a circuit in conjunction with the oil'- normal contacts 61, which operated upon the irst vertical step, through the interrupter contacts 60, for stepping relay 54. Relay 54 operates over this circuit and closes a locking circuit for itself at armature 66. At armature 67 it prepares a circuit for rotary magnet 58.

When relay 53 falls back shortly after the end of the third impulse, it closes the rotary magnet circuit at armature 65, whereupon ro-` tary magnet 58 operates and advances the wipers of the selector into engagement with the first bank contact in the third level. Near the end of its stroke, magnet 58 opens the stepping relay circuit at the interru ter contacts 60. Stepping relay 54 falls ackV and opens the rotary magnet circuit, whereupon the rotary magnet falls back and closes its interrupter contacts 60 again. v

From this point on, the o eration depends upon whether the first trun line is busy or is idle. If this trunk line is idle, switchin relay 55 now operates, seizing the trunk. I the trunk is busy, however, relay 55 is short circuited and relay 54 is again operated by the ground potential encountered on the test contact of the busy trunk by test wiper 73.

vRelay 54, therefore, again closes the rotary magnet circuit, and the wipers are advanced another step.

This alternate operation of relay 54 and las conductors extend, according to the label,

to a local thousands selector. When this idle trunk line is reached, relay 55 energizes in series with relay 54, but relay 54 is not operated at this time on account of the relatively high resistance of relay 55. At armature 70, relay 55 removes ground from armature 62 of line relay 51, thereby opening the circuit of release relay 52 and preventing any fur; ther operation of the vertical magnet 59 and any operation of release magnet 57 until relay 55 again falls back; it opens the test circuit and connects test wiper 73 to the grounded release trunk conductor 6, thereb making the seized trunk busy immediate y; and at armatures 68 and 71 it disconnects conductors 5 and 7 from the windings of line relay 51 and extends them through wipers 72 and 74, and the bank contacts on which they are standing to the line relay of the seized thousands selector. The line and release relays (not shown) now operate in the usual manner to prepare the switch for operation and to place a further ground on the release trunk conductor of the partly established connection. A. moment later relay 52 falls back and removes ground from conductor 6 at armature 63, but this is of no eiect at this time as the release trunk conductor is already grounded at two other points.

When the thousands digit is transmitted by the director, the seized thousands selector operates in the usual manner to extend the connection to a hundreds selector in the desired group, the seized-hundreds selector operates when the hundreds digit is transmitted and extends the connection to an idle connector in the desired group; and the seized connector operates in response to the tens and units digits transmitted by the director and extends the connection to the called line and applies ringing current thereto in the usual manner.

Returning now to the director, when wiper 531 of the sequence switch S grounds the conductor 508 at the end of the transmission of the units digit, the two windings of the two step relays 621 Fig. 7, are energized in series, operating the relay. At armature 627 relay 621 disconnects conductor 38 from conductor 505 and connects it to ground, thereby closing a circuit over conductor 38 and through wiper 34, working contact and armature 30, and armature 16 and its lworking contact for switching relay 12. Relay 12 energizes and locks itself to the release trunk conductor 6 at armature 21, releases the switch DS at armatures 22 and 23, and at armatures 20 and 24 connects. the two sections of the trunk line together between the trunk circuit TC-l and the selector S-1. Now, when relay 26 of director selector DS falls back due to the opening of its circuit at armature 22 it disconnects conductors 5 and 7 4from the - conductors 35 and 36 extending to the director, leaving the line relay of the connector involved in the connection held up through armatures 20 and 24, right hand winding of relay 8, and the impedance 9. Relay 8 is not operated at this time, however, on account of the fact that the direction of current in the right hand winding of relay 8 is such that the magneto-motive force generated by the said 'winding assists the flow of magnetism in its original nath, each core of the relay serving as a shunt for the other.

In the director, relay 622, Fig. 7, falls back when the director is freed by the director selector DS, Fig. 1. At armature 631, relay 622 closes the normal restoring circuit of the sending switch SS; it closes the restoring circuit of the switch S at armature 633, whereupon the switch S advances the remaining step to its normal position; and at armature 634 it places ground on conductor 502. When this occurs. the release magnets of the switches S and OR Figs. 6 and 8, and the release mag nets of the thousands, hundreds, tens, and units registers of Fig. 9, operate through their respective olf-normal contacts to release the said switches in the usual manner. For example, magnet l522 of the switch S Fig. 6, is operated through oil-normal contacts 525, and the release magnet 728 of the oilice register OR is operated through eti-normal contacts 729.

When the called subscriber responds to the ringing of his bell by removing his re-I ceiver, the connector switch in use cuts olf the ringing current and substitutes talking current, whereupon the current flow in the calling conductors extending to the connector switch is reversed by the connector switch in the usual manner. When this occurs, the current low in the right hand winding of relay 8, Fig. 1, is reversed, and the magnetism generated by both windings in multiple now operates the relay. At armatures 13 and 14,

relay 8 reverses conductors 5 and 7 as regards their connection to the windings of relay 10, thereby reversing the current flow in the calling line. This may be made use of to operate a meter for any other similar purpose.

Referring now again to the director, the arrangement for supplying ground to the impulse conductor 509, after tle wiper 530 of the sequence switch S has advanced beyond the positions in which ground is supplied from the start conductor, will now be explained. Ground potential is supplied to the seventh and eighth contacts in the bank of wiper 530 over conductor 503, which is grounded through the upper off-normal contacts of the hundreds register when the hun- .conductor 811 and through armatures 909 and` ing to send the thousands and hundreds digits A before they areregistered. In a similar way the sending operation may again be held up when the sequence switch arrives in the position vin which the tens digit is sent if the units register has not gone off-normal to supply ground to the ninth and tenth contacts of the bank of wiper 530 over conductor 504.

4 When the conversation between the calling and called parties has taken placeand has been terminated, the two parties replace their receivers. When the receiver is replaced at the called substation, the back-bridge battery-feed relay of the connector falls back and reverses the current flow to normal in the talking conductors incoming to the con# nector. When this occurs', relay 8, Fig. 1, falls back and reverses the incoming conductors 5 and 7 back to the position shown in the drawing.

When the calling subscriber replaces lisv receiver, line relay falls back and at its upper armature opens the bridge across the conductors 5 and 7 whereupon the line re-V lay vof the connector falls back and opens the circuit of the associated releasel relay. At armature 13, relay 10 opens the circuit of relay 11, which falls back after an interval and removes at'armature 17 the ground potential from the associated release trunk conductor. This operation, however, is of no effect until the ground potential is removed from the-release trunk conductor of the established connection at the connector switch in use. When s'uchremoval of ground potential takes place on the falling back of the release relay of the connector, the thousands and hundreds selectors-release responsive to the removal of ground potential, and the connector switch is released in the usual manner.

calling line switch releases in the usual man` ner when ground 1s removed from the release trunk conductor.

Gall through tandem maf/tual oyice Assuming now that a calling subscriber, desiring to converse with the subscriber at the substation 356, Fig. 4 removes his receiver; that the trunk line shown in Fig. 1 is seized by the callin line switch; and that the d'rector selector S seizes the director shown in the drawings; the director is prepared for operation in the usual manner when'relay 622 Fig. 7 pulls up, and the setting of the office register OR occurs when the first two di its are dialled. Following the setting of t e office register, the four subscriber digit registers shown in Fig. 9, are set in the manner hereinbefore described.

It is assumed that the terminating manual oice in which the line of substation 356 Fig. 4\terminate is represented by the bank contacts 723, Fig. 8. It will be observed that the ca ll must be trunked to the tandem manual oiice, Fig. 4, and that three code digits are necessary to operate the selectors S-1, Fig. 1, S-2, Fig. 2, and S -3, F ig.` 3, these digits being 1, 3, and 8. Accordingly, the first bank contact in the set 723 Flg. 8 is cross connected on the I. D. F. 4to the first impulse stop conductor; the second bank contact is cross connecte-d to the eighthy impulse stop conductor; and the third bank contact is cross connected to the third i'mpulse stop conductor. Accordingly, the code digits 1,3, and 8 are transmitted in the hereinbefore described manner when the sending switch SS is started at the end of the second oilice digit, the sequence switch S being advanced one `stepat the end of each digit. Since the combination director must now opcrate in a different manner to handle.. this call, which is of a different class, relay 901, Fig. 10 must now be operated. This relay is operated responsive to the arrival of wiper 531 Fig. 6, inthe fourth position responsive to the transmission of the third and last code digit 8, the circuit being as follows: From ground by way of the now-grounded fourth wiper of the otlice register OR, the fourth contact in the set 723, the associated I. D. F. jumper, conductor 701, normally-closed contacts controlled by armature 912, Fig. 10, and relay 901 to battery. Upon operating, relay 901 locks itself at armature 912 to the grounded conductor 608, at the same time opening its initial circuit. At armature 913, relay 901 connects conductor 701 with the conductor 702. Conductor 702 terminates in a terminal at the I. D. F., Fig. 8, and is cross connected in the I. D. F. to the skip conductor 501. This results in the operation of the switch S Fig. 6 to now pass over the fourth code-digit positionand come to rest in the fifth code digit position. As a further result of its operation, relay 901, Fig. 10, prepares at armature 911 a circuit for relay 903; joins conductors and 604 at armature 910, so as to shunt the sending contacts 635, Fig. 7, to prevent further impulses from the regular sender from going out; and at armature 909 it removes ground from conductor 607 for a purpose to be hereinafter made clear, and it

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