US1842585A - Automatic telephone system - Google Patents

Description

Jan 26, 1932. T. F. cRocKER AUTOMATIC TELEPHONE SYSTEM Filed May 6, 1927 :5 Sheets-Sheet I'm/en Thomas FEI'UlZkEZ" Jan. 2%,, 1932.. T. F. CROCKER AUTOMATIC TELEPHONE SYSTEM Inuen UT" Thumaa PEP/Jake? Jan. 26, 1932.. T. F. cRocKER AUTOMATIC TELEPHONE SYSTEM Filed May 6, 1927 3 Sheets-Sheet 3 Thczmas F. Eruukezr till Patented Jan. 26, l932 STATES THUMAES l2. CRUUKER, 01" CHICAGO, ILLINOIS, ASSIG-NOR, BY MESNE ASSIGNMENTS, T essocmrnn ELECTRIC LABORATORIES, INC., OPE CHICAGO, ILLINOIS, A CORPORATION QT DELA'WARE AUTOMATIG TELEHONE SYSTEM Application filed May 6, 1927. Serial No. 189,421..

This invention relates to telephone systems in general, but is more particularly concerned with small automatic telephone sy sterns commonly known as private automatlc exchange systems.

The object of this invention, broadly stated, is the provision. of new and improved circuit arrangements for an attendants cabinet and of new and improved automatic switch ing apparatus, which are particularly designed for use in private automatic exchange systems.

A particular feature of this inventlon is that by the momentary operation of a key individual to an incoming trunk from a mam automatic exchange to the private automatic exchange, the attendants telephone equipment including her dial is automatically associated with that particular trunk, after which the attendant may dial over that particular trunk in either direction, the direction being determined by the setting of a common dialing key. The necessity of having a dialing key and associated controlling equip ment for each incoming trunk is eliminated.

Another feature of this invention is that by reason of the new and improved circuit arrangements for the attendants cabinet, it has become practical to remove all the con trolling relays associated with the attendants cabinet from the cabinet, and mount them on frames at any convenient place remote from the cabinet. The cabinet itself need house only the necessary keys and supervisory lamps, making it relatively small and inexpensive.

Another feature of this invention is the provision of a new and improved connector selector repeater designed for giving so-called discriminating service controlled over a discriminating conductor. The connector may be taken into use either by a private automatic evcl'lange subscriber or by the attendant. and when the connector is used by the attendant, the discriminating conductor serves as a signalling conductor for operating a supervisory sinnal at the attendants cabinet.

These features and other features pertaining to the circuits and to the manner inwhichconnections are established and supervised by the attendant, will be described in detail in the following specification with the aid of the accompanying drawings comprising Figs. 1, 2, and 3. These drawings illustrate by means of the usual schematic circuit diagrams a private automatic exchange system and, to be most easily understood, should be placed with Fig. 2' to the right of Fig. 1 and moving in one direction only. The lineswitch other sumlar lineswltches,

LS, together with has access to the group of connector selector repeaters by way of trunk lines, one of which is shown comprising conductors 5 to 8, inelusive, terminating in the connector selector repeater C. (Hereafter the connector selector repeater G will be referred to as merely connector U.)

Mechanically the connector 0 is of the well known Strowger vertical and rotary type, having horizontal rows or levels of bank contacts, which are multipled with those of the other connectors of the group. In a number of levels of the connectors access is had to the lines of the private automatic exchange subscribers, including the line of substation A aswell as the line of substation A. In one particular level in the banks of the connectors access is had to one or more information trunks for extending connections to the attendant. One of these trunks is shown comprising conductors 301, 302, and 303 accessii ticular private I automatic exchange subscribers are permitted service to the main automatic exchange or to the attendant, while the other private automatic exchange subscribers are restricted to local calls within the private automatic system. At the lineof the jumper 11', whereas at the lineswitches of the restricted subscribers, this jumper is omitted. The connector such as connector 0 either extends or prevents the extension of a connection to one of the outgoing trunks or to the attendant depending on whether or not ground potential is supplied to the discrimmating conductor 6 from the lineswitch by which it is seized. These operations will be described more in detail later.

In Fig. 2 is shown the trunk relay group TRG for the outgoing trunk to the main automatic exchange comprising conductors 202 and 204. At the private automatic exchange, this trunk has two branches. One branch as previously mentioned comprises conductors 202, 203. and 204 accessible to the connectors over which calls to the main exchange are extended. The other branch comprises conductors 252, 253, and 254 terminating in the lineswitch LS, Fig. 1, over which calls from the main exchange to a private automatic exchange subscriber are extended, the banks of the lineswitch LS being mnltipled with those of the other lineswitches. The lineswitch LS may be of the same type as the lineswitch LS.

At the main automatic exchange the trunk comprising conductors 202 and 204 terminates in the individual lineswitch LS and is accessible in the banks of connectors such as connector C in the well known manner. The lineswitch LS may also be of the same type as the lineswitch LS shown in Fig. 1, though the wiper for the discriminating conductor is unnecessary, and further the ground conncction to the lower conductor at the contacts of the switching relay is omitted. Thelineswitch LS together with the other line switches of the trunks from the private automatic exchange, has access in its banks to incoming selectors one of which is shown designated S The selector S as well as the connector C may likewise be of the Strowger vertical and rotary type well known in the art. The automatic switches at the main exchange do not particularly concern the invention, and are therefore shown only in skeleton. It should also be noted that the invention is not limited to a main automatic telephone system. The main exchange might also be a manual exchange. In this latter case the trunk lines from theprivate automatic exchange would terminate in jacks in the well known manner.

Within the dotted rectangle in Fig. 3 is shown the attendants telephone set TS and the various keys and lamps of the attendan'ts cabinet. Individual to each of the interexchange trunks are three lamps and a twowa key such as the lamps L L and L an the key K which are individual to the inter-change trunk shown in Fig. 2. For each information trunk (over which the unrestricted subscribers may call the attendant) there is a lamp and a key such as the lamp L and key K of the information trunk comprising conductors 301, 302, and 303. Besides this equipment there is a common dialing key K This key is operated in one direction to dial out over a trunk to the main automatic exchange, and in the other direction while operating the automatic switches in the private automatic exchange. The attendants cabinet is also provided with key K By operating this key to the right, the buzzer B is connected, so that it sounds on all incoming calls, as will be described more fully later. By operating the key to the left a connector switch in the private automatic exchange that has been operated may be released without disturbing the rest of the connection.

The attendants telephone set TS is a regular desk telephone set of the automatic type, except that additional switch hook springs 399 are provided for controlling circuits to be described subsequently.

Inthe left half of Fig. 3 is shown a group of relays two of whichare common equipment while the relay 300 controls the connection of the information trunk comprising conductors 301, 302, and 303', with the attendants telephone set. The conductors 301', 302, and 303' represent another information trunk accessible in the banks of the connectors in the same level as the trunk comprising conductors 301, 302, and 303. The connection of this trunk with the attendants telephone set is controlled by relay 300.

With this general description ofthe features of this invention and the apparatus involved in mind, a detailed description of the operation will now be given. The operations involved in setting up a connection from the main automatic exchange to a subscriber in the private automatic exchange will first be described. For this purpose, then, it will be assumed thatconnection is desired with the subscriber at substation A by some main automatic exchange subscriber and that a connection has been extended to the private automatic exchange over the trunk comprising conductors 202 and 204: by way of the connector C, for example. As soon as this trunk line is seized at the main automatic exchange, a ringing generator is intermittently connected to the trunk at the main automatic exchange and a direct current circuit is closed for relay 207 which extends from ground through the ringing generator at the main exchange or direct ground (depending on the particular time when connection is n-- And established) over conductor 204, contacts 214, through the resistance R through the winding of relay 207, contacts 21 over conductor 202, through the winding of the ring cutoff relay of the conductor C to battery. Relay 207 operates immediately and places ground potential on the release conductor 203 at contacts 240, thereby immediately guarding this trunk against seizure by a connector in the private automatic exchange. The resistance of relay 207 and R is'sufiiciently high to limit this direct current flow to the extent that the ring cut-off relay of conhector is not operated. Upon the first application of ringing current to the trunk conductors, ringing current-responsive relay 209 at the private automatic exchange operates, its circuit including the two trunk condoctors and contacts 214. Relay 209, in operating, closes a circuit for signalling relay 208. Relay 208 operates and closes a locking circuit for itself at contacts 244, this circuit including contacts 237 and 23-2; completes another ground connection to release conductor 203 at contacts 241; and at contacts 243 closes a circuit for the lamp L at the attendants cabinet in series with relay 314, this circuit likewise including contacts 237 and 232. Lamp l lights, which apprises the attendant of an incoming call over this particular trunk. When the attendant is absent from her desk or is attending other duties, she may lreep the key K operated to the right. in that case, the operation of relay 314 closes a circuit for the buzzer B which on sounding gives further evidence of the incoming call.

When the attendant is ready to answer the call, she removes her receiver from its switch hook if it has not been removed previously and momentarily operates the key K to the left. The latter operation, with the receiver removed, closes a circuit for the upper winding of relay 204 which circuit includes the switch hook contacts 399, contacts 310, and contacts 315 of the key K. Relay 204 operates and performs the following circuit changes:

At contacts 227 relay 204 closes a locking circuit for itself through its lower winding which includes contacts 233, winding of relay 313, and switclrhook contacts 399. Relay 313 operates over this circuit and by separating contacts 310 opens the initial energizing circuit of relay 204 and prevents the energizetion of any other relay similar to relay 204 should the attendant inadvertently operate some other key similar to the key K at this time.

At contacts 226 relay 204 closes a circuit for the upper winding of relay 206. Relay 206 operates and prepares a holding bridge at contacts 239, and opens the initial locking circuit for relay 208 and also the circuit of the lamp l1 and relay 314 at contacts 237.

Relay 208 is held operated, however, over the I holding circuit closed at contacts 225' by relay 204. The current flow through lamp L and relay 314 is limited, however, by reason of the resistance R to the extent that lamp L is extinguished and relay 314 is insufficiently energized to maintain contacts 311 closed. As a result the lamp L is extinguished and the circuit of buzzer B (if connected) opened. As a further resultof the energiza-- tion of relay 204 which effects the closure of contacts 223 and 228, andas a result of the closure of contacts 235 and 236 by relay 206, the common conductors 351 and 352 are connected to the trunk conductors 252 and 254 terminating in the lineswitch LS, Fig. 1. The conductors 351 and 352 are bridged by the operators telephone set and therefore the lineswitch LS is caused to operate in the usual manner and select an idle trunk accessible in its banks.

Another result of the operation of relay 204 is the placing of a bridge. across the outgoing trunk conductors 202 and 204 by the closure of contacts 222 and 230, this bridge including the retard coil 312, the common conductors 361 and 362, and relay 201. The re sistance of relay 201 and of the retard coil 312 is comparatively low so that the current flow over the outgoing trunk conductors is increased sufficiently to cause the ring cut-off relay in the connector C to operate and dis connect the ringing generator and itself from the trunk conductors and complete the tallc ing connection to the attendant. Relay 201 now operates from current received through the windings of the hack bridge relay in the. connector C at the main automatic exchange and at contacts 211 closes a circuit for relay 202. Relay 202 operates and completes another ground connect-ion to release trunk conductor 203 at contacts 212, opens the circuit of relay 207 and the resistance R at contacts 214, and closes the circuitof lamp L at contacts 215, this circuit including switch hook springs 399. The lighted condition of lamp L indicates the busy condition of this particular trunk. Relay 202, in operating, also closes a circuit for relay 203 at contacts 213, this circuit including contacts 219, the lower trunk conductor 204, and the lower winding of the back bridge relay of the connector C Relay 203 in operating closes a locking circuit for itself at contacts 218 independent of the lower trunk conductor, and by separating contacts 217 and closing contacts 216 a bridge which is to include relays 201 and 207 and is later to be placed across the trunk conductors is prepared.

As previously stated, the line switch LS is caused to operate and select a trunk accessible in its banks extending to an idle connector by reason of the telephone set being bridged across the conductors 252 and 254. It will be assumed that the connector C is the one selected, and when connection is extended thereto, line relay 11 operates in the usual manner and closes the circuit of the release relay 12. Release relay 12 operates and prepares the impulsing circuit at contacts 28, and places ground potential on the release trunk conductor 7 at contacts 27. As a result ground potential is also connected to the discriminating conductor 6 by way of contacts 33 and contacts 34. This closes a circuit for the supervisory lamp L at the. I attendants cabinet and also another holdlng circuit for relay 208, these circuits extending over conductor 6 through the lineswltch LS", over conductor 253 to the lamp L and through resistance R contacts 243 and 244 to relay 208. As a result the lamp L lights. Resistance R is now in parallel with resistance R but still the current flow through lamp L is insufficient to cause the lamp to light; nor is the current through resistances R and R sufficient to operate relay 314, though this relay may be operated since it operates on all'incoming calls.

All of the operations described after the attendant removed her receiver and momentarily operated the key K to the right have taken place automatically responsive thereto. The attendant is now in talking connection with the main automatic exchange, and asks the calling subscriber the name or number of the party with whom he wishes to speak. After receiving this information the attendant operates the common dialing key K to the right and then dials the number of the i called party. Throwing the key K to the right merely opens the talking circuit from the attendants cabinet back to the main automatic exchange to prevent the calling subscriber at the main automatic exchange from hearing clicks which would be produced by the operation of the attendants dial.

Responsive to the dialing of the first digit of the called number the vertical magnet 20 of the connector C is operated to step the switch wipers 65, 66, and 67 opposite the level of bank contacts in which the line of the substation A is accessible (having assumed that substation A is the called substation). The series relay 13 operates in series with the magnet 20, and being slow-acting maintains its armature attracted throughout the vertical movement of the switch wipers. At the cessation of the impulses produced by dialing the first digit of the called subscriber, relay 13 deenergizes and prepares the circuit for the rotary magnet at contacts 30.

Responsive to the dialing .of the. second digit of the called number, rotary magnet 21 operates and rotates the switch wipers into engagement with the set of bank contacts ter-' minating the called line. Relay 18 operates in parallel with magnet 21, and being slowacting maintains its armature attracted throughout the rotary movement. If the called line is busy at this time, ground potential will be present on the test contact 69.

As a result, before relay 18 has had time to deenergize, busy relay 17 will be ener ed over the circuit including wiper 66', contacts 59, contacts 55 and contacts 63.' Relay 17, in operating, closes a locking circuit for itself at contacts 48 and prepares the busy tone circuit at contacts 46 in the usual manner, the latter circuit being closed as soon as relay 18 releases its arinatures at the cessation of the impulses of the second digit by the closure of contacts 53. The attendant will hear the busy tone in her receiver, indicating to her that the called subscriber is busy, so

whereupon she will inform the calling main exchange subscriber of this fact and then release the connection as will be described subsequently.

It will be assumed, however, that the called subscriber is idle at this time, in which case no ground potential is present on the test contact 69, and relay 17 is not operated. Instead, when relay 18 releases its armature at the cessation of this last-series of impulses, the switching relay 19 will be operated over its upper winding in the usual manner, the circuit thereof extending from ground on the release conductor 7, contacts 47, upper winding of relay 19, contacts 54, contacts 59, wiper 66, bank contact 69, to battery through the winding of the switching relay of the lineswitchLS in the usual manner. Switching relay 19 energizes and closes points in the talking circuit at contacts 57 and' 62, closes a locking circuit for itself over its lower winding at contacts '60, grounds the test contact 69 by the closure of contacts 58, and opens a point in the rotary magnet circuit at contacts 61. The closure of contacts 57 and 62 also completes the ringing circuit which extends from the conductor 99' to which direct ground and a grounded ringing generator are alternately connected, over the lower talking conductor, through the ringer at'substation A, over the upper talking conductor, and through the upper Winding of the ring cut-off relay 16 to battery. The-attendant will hear the ring back tone in the usual manner, indicating to her that the called subscribers line is idle and that thecalled subscribed is being signalled. a

It is unnecessary for the attendant to wait on the line until the called subscriber answers. She may choose, therefore, to disconnect her telephone set from this connection so that she may give attention to other calls. To do this she merely replaces the responding lamps of all other busy trunk lines is extinguished. Thus the unnecessary burning of the busy lamps whenthe receiver on its switchhook is prevented. It should be noted that the indication given by the busy lamps such as if, is necessary only when the attendant wishes to select an idle trunk to make a call, in which case she will remove her receiver, thereby close the circuit of the busy lamps of all busy trunks. These operations will be described more in detail subsequently.

lloth relays 20 i and 313 also deenergize when the attendant replaces her receiverl The separation of contacts 223 and 228 of relay 20a disconnects the attendants telephone set from in bridge of the conductors 252 and i, and by the closure of contacts 229 the bridge including the lower winding of relay 206 is substituted therefore. By reason oi this bridge including the lower winding oi relay 206 the connector (3 is held in operated position. By the separation of contacts 226 the circuit of the upper Winding of relay 206 is opened, but relay 206 is held energized over its lower winding in series with the line relay ll of the connector *6. By the separation of contacts 222 and 230 the bridge including the retard coil 312 across the trunk conductors 202 and 204 is opened, and by the closure of contact 231 another bridge including relay 207 and contacts 216 and 239 and also relay 201 (it being noted that relay 201i was also in the bridge including the retard coil 312) is substituted therefore. Re lay 201 remains energized and incidentally relay 207 energizes. By the separation of contact 225, the initial holding circuit of relay 202 is opened. lFtelay 208, however, is held over the circuit including conductor 253 and resistance ll previously traced.

Relay 313, in deenergizing, again closes contacts 310 thereby making it possible for the attendant to associate her telephone set with any other trunk line by operating the corresponding key similar to key K. At the present time, with the receiver on its switchhook, only lamp l is lighted which indicates that the called private automatic ex change subscriber is being signalled but has not yet answered.

-l l hen the called subscriber answers the call by removing his receiver, the ring cut-oft relay 16 in connector C operates in the usual manner and closes a locking circuit for itself over its lower winding at contacts ac and disconnects itself and the ringing generator from the talking conductors and completes the talking connection by closing contacts 43 and a l. This operation also completes the circuit for the back bridge relay 14, through the windings o-fwhich talking battery is furnished tor the called substation. Relay 14: energizes and by separating contacts 33 disconnects ground potential from the discrim inating conductor 6. The removal of ground commence conversation with the subscriber at the main automatic exchange, the talking circuit extending over the heavy talking conductors including conductors 5 and 8, conductors 252 and 254, condensers 262 and 26st, and the trunk conductors 202 and 204 extending to the main automatic exchange.

[it the termination of the conversation both subscribers will replace their receivers on their respective switch hooks. The replacement of the receiver at the called subscribers substation opens the circuit of the back bridge relay 14 of the connector C. This relay thereupon deenergizes and again connects ground to the discriminating conductor 6 by the closure of contacts 33. Since relay 208 is now deenergized and resistance R2 is shortcircuited by contacts 242, the placing of ground on conductor 253 causes both lamps L and L to light, and also causes relay 314 to operate. The lighting of these lamps at this time indicates to the attendant that the conversation has terminated and that the called subscriber has replaced his receiver. If the key K be operated to the right, the buzzer 13 also sounds, giving further indication that a call has terminated (or that another call is awaiting attention).

It is also possible for the called subscriber to flash the attendant, should he wish to speak with her, by jiggling his switchhook in the usual manner. This operation causes relay 14 to energize and deenergize in quick succession causing lamps L and L to flash. lln response to this signal the attendant may reconnect her telephone set across the tiunk line by again removing her receiver and momentarily operating the key K to the left, causing the operation of: relay 20 i which conmeets her telephone set across the line conductors 252 and 25 i as previously described.

To release the connection after the called subscriber has replaced his receiver as indicated by the lighted condition of lamps L and L the operator merely operates the key K momentarily to the right. This closes a circuit momentarily for relay 205. Relay 205, in energizing, opens the bridge including the lower Winding of relay 206 by separating contacts 234. The opening of this bridge causes the release of the line relay 11 of the connector C whereupon the connector C re stores to normal in the usual manner. Relay 206 likewise deenergizes and-opens the bridge across the trunk conductors 202 and 204 by separating contacts 239. The opening of this bridge permits the connector C in the main automatic exchange to release in the usual manner (the other switches of the main automatic exchange having released responsive 6 to the replacement of the receiver by the calling subscriber). Rela 207 and relay 201 likewise deenergized. elay 201, in deenergizing, opens the circuit of relay 202, which also deenergizes and opens the circuit of re- 10 lay 203. By the restoration of these relays and relay 207 all the relays of the trunk relay group TRG are restored to normal. By the separation of contacts 212 and 240 the trunk line is again marked idle and ready for use in the extension of another connection either to or from the main automatic exchange. The separation of contacts 215 opens a point in the circuit of lamp L so lamp will remain dark upon a removal of the attendants receiver, thus indicating that this trunk is idle.

As previously stated, the private automatic exchange subscribers whose service is restricted to the establishment of connections with any of the other local subscribers of the private automatic exchange, cannot complete connections to the main automatic exchange or call the attendant. The other subscribers, however, whose service is not restricted, may extend connection directly, to the main automatic exchange by dialing first a special digit such as the digit 0 and then dialing the regular directory number of the main automatic exchange subscriber, or these subscribers may first call the attendant and tell her the name or the number of the subscriber with whom they wish to speak, who in turn will set up a so-called tail-to-ta-il connection, obtaining connection first with the wanted main automatic exchange subscriber and then recalling the calling private automatic exchange subscriber. To describe these operations, it will first be assumed that a private automatic exchange subscriber such as the subscriber at substation A wishes to establish a connection with a subscriber at the main automatic exchange himself without the aid of the attendant: To do so he will remove his receiver and dial the digit 0 after which he will dial the regular directory number of the called main automatic exchange subscriber.

Responsive to the removal of the receiver at the substation A the lineswitch LS operates in the usual manner and extends the connection to an idle connector such as the connector C, for example. When the connection is extended to the connector C, line relay 11 operates and closes a circuit for the release relay 12, which in turn operates and connects ground potential to the release trunk conductor 7 and preparesthe impulsing circuit in the usual manner. Responsive to the dialing of the digit 0, vertical magnet operates in series with relay. 13 and steps the switch wipers opposite the tenth level bank contacts in which access is had to'the outgoing branches of trunks extending to the main automatic exchange. The connector C is provided with shaft springs 91 and 92 which close when the shaft is raised opposite the ninth or tenth level of bank contacts. The closure springs 92 close the circuit for relay 15 in series with the upper winding of relay 16. As a result both relays 15 and 16 ener 'ze. Relay 16 locks itself over its lower win ing to the release conductor by the closure of contacts 40, opens the ringing circuit by separating contacts 42 and-45, and closes points in the talking circuit by closing contacts 43 and 44. Relay 15 operates and connects the upper andlower windings of back bridgerelay 14 independent of the exchange battery by separating contacts 36 and 38 and closing contacts 37 and 39. By the closure of contacts 34, before relay 13 has had time to restore, a circuit is closed extending from ground applied to the discriminating conductor 6 by way of the jumper 11 at the lineswitch LS, via springs 91, ofi-normal springs 94 (springs 94 open and springs 93 close whenever the switch wipers are rotated oil of the tenth set of contacts in the ninth or tenth level), contacts 31, contacts 63, through the windings of relay 17 to battery. Relay 17 operates and closes a locking circuit for itself to the release conductor at contacts 48.

Shortly after the cessation of the impulses of this first digit, relay 13 deenergizes and by closing its contacts 32 a circuit is closed for the rotary magnet 21 which extends from ground by way of discriminating conductor 6, contacts 35, springs 91, contacts 94, contacts 32, contacts 49, contacts 61, through the winding of rotary magnet 21 to battery, relay 18 also operating in parallel therewith. The rotary magnet thereupon operates and moves the switch wipers into engagement with the first set of contacts in the tenth level, and opens the circuit of relay 17 by separating contacts 63. Relay 17 thereupon deenergizes and opens the circuit of the rotary magnet 21 by separating contacts 49 thereby permitting ma et 21 to deenergize and again close contacts 63. If the first trunk accessible in the tenth set of bank contacts is busy, ground potential will be present on the test contact with which wiper 66 is in engagement. As a result relay 17 again operates before relay 18 has had time to deenergize over the circu'it which includes wiper 66, contacts 59, contacts 55, and contacts 63. In energizing, relay 17 again closes the circuit for rotary magnet 21 at contacts 49. Rotary magnet 21 will again operate and rotate the swltch wipers into engagement with the next set of bank contacts. In this manner the switch wipers will be successively rotated until they are brought into engagement with the bank contacts terminating an idle trunk, which will be assumed is the trunk comprising conductors 202', 203, and 204. In this case no till are

hit

till

amazes ground potential will be present on the test contact 89 engaged by wiper 66 and conse quently relay it will not be reenergized. lnstead, switching relay 19 will be energized over its upper winding after relay 18 deenergiues from ground on the release trunk conductor 7 over a circuit including contacts ll", the upper winding of relay 19, contacts 54, contacts 59, wiper 66, test contact 89, to battery through the resistance ll". Relay 19 operates and performs circuit changes as previously described and extends the connection to the trunk conductors 202 and 204.

As a result of the extension of the connectionto the trunk conductors 202- and 204: a-

circuit is closed for the line rela of the lineswitch at the main automatic exc iange terminating the inter-exchange trunk comprising conductors 202 and 204: in series with relay 201. This circuit extends from ground by way of contacts 221, conductor 204, over the bridge including the windings of back-bridge relay 1a (its upper and lower windings now being connected at contacts 37 and 39) over conductor 202 through the winding of relay 201, trunk conductor 202, through the winding of the line relay of the lineswitch lLS- to battery. in this circuit relay 201 operates and closes a circuit "for relay 202. Relay 202 operates and opens the A. 0. bridge including the ringing relay 209 normally across the trunk conductors at contacts 214i and closes a point in the circuit of lamp L at contacts 215. New whenever the attendant removes her receiver the lamp T1 will light indicating that this trunk is busy. lttelay 202, in operating, also prepares a circuit for relay 203 at contacts 213.

The energization oi the line relay of the lineswitch LS at the main automatic exchange over the above traced circuit initiates the operation of this lineswitch to select a trunk to an idle selector such as the selector hi As soon as the lineswitch LS has selected an idle selector and extended the connection thereto, the circuit for relay 203 at the private automatic exchange is closed by reason oi ground through the lower winding of the line relay ot the selector S it should be noted that there is no ground connection normally connected to the lower conductor an at the lineswitch LS When the latter circuit is closed, relay 203 operates and closes a locking circuit for itself at contacts 218 and at contacts 220 connects conductor 204' with the trunk conductor i thereby completing the extension of the talking connection to the selector S at the main automatic exchange.

All the foregoing operations described alter the connector t) was seized have taken place responsive to the first digit dialled by the calling subscriber. Responsive to the dialing of the remaining digits otthe called number, the selector S and other selectors and a connector are successively operated in ing each series of impulses and b the usual manner to extend the connection to the called subscriber, the connector C operating as a repeater to repeat the impulses over the inter-exchange trunk. In this case the relay 18 of the connector C also operates durclosing contacts 52 disconnects the bridge lncluding the baclebridge relay 14 and places a direct bridge across the conductors 202' and 204. This bridge is intermittently opened and closed responsive to the digits dialled by the operation of line relay 11 at contacts 26.

When the called main exchange subscriber answers the call by removing his receiver he may commence conversation with the private automatic exchange subscriber. When the conversation is terminated both subscribers will replace their receivers. The replacement of the receiver at the private automatic exchange substation opens the circuit of line relay 11 which in turn deenergizes and opens the circuit of release relay 12. Release relay 12 removes ground from the release trunk conductor 7 and by closing contacts 28 closes a circuit for release magnet which in turn energizes and restores the connector O to normal. The removal of ground from release conductor 7 also opens the locking circuits "for relay l6 and relay 19, causing these relays to deenergize and open the bridge across the conductors 202' and 204. The removal of the bridge across these conductors causes the release of the switches in the automatic exchange in the usual manner, and also opens the circuit of relay 201. Relay 201 deenergizes and opens the circuit of a relay 202, which in turn deenergizes and opens a point in the circuit oflamp L at contacts 215.

Relay 202, in deenergizing, also opens the holding circuit for relay 203 at contacts 213, and removes ground from the conductor 203 at contacts 212, thereby again placing this trunk in idle condition.

its previously stated a private automatic exchange subscriber (having unrestricted service) instead of setting up the connection himself, may call the attendant and request her to set up the connection to the main automatic exchange for him. The operations performed to call the attendant, and the manner in which the attendant setsup a connection to the main automatic exchange and then recalls the private automatic exchange subscriber will now be described. For this purpose it will be assumed that the subscriber at substation A again wishes to speak with some main automatic exchange subscriber and chooses this latter course to obtain connection. To call the attendant, the subscriber atsubstantion A removes his receiver and in this case dials the digit 9. Responsive to the removal of the receiver the lineswitch LS again operates in the usual manner to select a trunk to an idle connector such as the connector C, for example. Responsive to the lllll lllt ' dialing of the digit 9, the connector 0 open ates to elevate its wipers opposite the ninth level of bank contacts, and then selects an idle one of the trunks accessible therein. These operations all take place in substantially the same manner as described above when the connector C was operated to select a trunk to the main automatic exchange, it being noted that the shaft springs 91 and 92 close as the shaft is raised either to the ninth or to the tenth level. I v

It may be assumed that the trunk line comprising conductors 301, 302, and 303 is the one selected, relay 19 operating initially over its upper winding over conductor 303 in series with lamp L and relay 314. Lamp L" lights and again the buzzer B sounds (providing the key K is operated to the right). The lighting of the lamp L indicates to the attendant that a .call has been extended to her, whereupon she will operate the key K as soon as she is ready to take care of the call. To answer the call, the attendant will remove her receiver from the switchhook and operate the key K This closes a circuit which extends from ground at the switch hook springs 399, thecontacts 310, springs of key K through the upper winding of relay 300 to battery. Relay 300 operates and closes a locking circuit for itself through its lower winding in series with relay 313. Relay 313 operates and by separating contacts 310 opens the initial energizing circuit of relay 300 and also prevents the operator from I associating her telephone set with any other trunk at this time. Relay 300, in operating, also places direct ground potential on the release conductor 303 at contacts 306, and by separating contacts 307 opens the circuit of the lamp L. By the closure of contacts 308 and 309, attendants telephone set is bridged across the talking conductors 301- and 302. Current for the attendants telephone set is fed through I impedance coil 331 bridged across trunk conductors 301 and 302.

The attendant may now converse with the.

station A wishes connection. After obta'intelephone set from the trunk over which she' was called. Replacing her receiver separates the switchhook springs 399 thereby opening the circuit of relay 300 and relay 313. These relays then deenergize and restore to normal.

To complete the call to the wanted main automatic exchange subscriber, the attendant again removes her receiver and she momentarily operates the trunk key of an idle trunk to the left (the idle conditionof any trunk being indicated by the non-lighted condition of the lamp corresponding to lamp L after the attendant has removed her receiver). It will be assumed that the trunk line comprising conductors 202 and 204 is idle at this time and is the one chosen. Operating the key K to the left momentarily, the receiver being removed, causes the operation of relay 204 individual to the trunk line. Relay 204 operates and performs circuit changes as previously described, including the closing of a locking circuit for itself in series with relay 313, the placing of the retard coil 312 in series with the relay 201 across the outgoing trunk conductors 202 and 204. The closing of the circuit for relay 206 which relay operates. with the same result as previously described and in conjunction with relay 204 laces the attendants telephone set including er dial across the trunk conductors 252 and 254. The placing of the operators telephone set including the dial across the trunk conductors 252 and 254, initiates the operation of the lineswitch LS which in operating selects an idle connector, but this operation at this time is only incidental as will be shown presently.

After operating the key K momentarily to the left, the attendant operates the common dialing key K to the left and then dials the number of the called main automatic exchange subscriber. Throwin the key K to the left disconnects the attendants telephone set including the dial from in bridge of the conductors 252 and 254 by tacts 321 and 322, and disconnects the retard coil 312 from in bridge of the trunk conductors to the main automatic exchange by separating contacts 323 and 324 and substitutes the operators telephone set including the dial therefore by closing contacts 325 and 326. The disconnection of the operators telephone set from in bridge of the conseparating con-' ductors 351 and 352 allows line-switch LS to restore to normal, its wipers, however, remaining on the bank contacts last selected.

Operatin key K to the left, by closing contacts 32 closes a circuit which extends from ground at contacts 221, over contacts 228', contacts 327, contacts 325, through the operators telephone set, contacts 326, conductor 361, contacts 222, through the winding of relay 201, trunk conductor 202, through the winding of the line relay of line switch LS at the main automatic exchange. Both the line relay of the .line switch LS and relay 201 energize. Relay 202 energizes as a result of relay 201 energizing, performing the same operations as described previously, including the lighting of the lamp L by the closure contacts 215 and the preparation of the circuit of relay 203 at contacts 213. The line relay of the line switch LS, in operating, causes the line switch to operate and extend the connection to an idle selector such as the selector S for example. Relay 203 then op crates in series with the lower winding of the line relay of selector S with the results previously described.

The operators dial is now included in the bridge across the outgoing trunk conductors 202 and 204 to the main automatic exchange, and automatic switches at the mainautomatic exchange respond successively to the diglts dialled by the attendant and extend the connection to the called subscriber in the usual manner. When the called subscriber answers, the attendant may converse with him and inform him that a particular party at the private automatic exchange desires to speak with him, whom she will call while he, the called main exchange subscriber, keeps his receiver to his ear.

The attendant now throws the key K to the right thereby again placing the retard coil 812 in bridge of the outgoing trunk conductors and again placing her telephone set in bridge of the trunk conductors 252 and 254. Again the lineswitch LS operates to extend the connection to an idle connector such as the connector C, for example. It is noted that throwing of the key K to the right merely opens the talking circuit to the main automatic exchange in order to prevent the called subscriber from hearing disagreeable noises which would be produced by the attendants operating the dial to set up the connection to the private automatic exchange subscriber. The attendant now dials the number of the substation A causing the connector C to operate as previously described and extend a connection to the substation A. The attendant, after completing the dialing of the number of the substation A and hearing the usual ring back tone which assures her that the substation A has not become busy in the meantime, may release her telephone set from this trunk as described in the previous connection. She is also informed when the calling subscriber at A removes his receiver by the extinguishing of lamp L and is likewise informed when he replaces his receiver by the relighting of lamps L and L The attendant when so notified releases the connection by throwing the key K to the left momentarily, this initiating the release operation as previously described.

lit remains to be mentioned, that the subscribers at the private automatic exchange who are restricted to service within the prirate automatic exchange and are not allowed to extend connections to the main automatic ernhange and could not extend connections thereto even though they attempted to do so. The manner in which this restriction is given. does not concern the invention. However,

I the manner illustrated in the drawings may briefly be described. As previously mentioncd, to restrict the service of the subscriber at substation A, for example, it is merely necessary to remove the jumper 11 connecting the contacts 9 and 10. If now the subscriber atsubstation A, after the jumper 11 has been removed, attempts to extend a connection to the main automatic exchan e by dialing the digit (or attemptsto o tain connection with the attendant by dialing the digit 9), the connector 0 will again operate and raise its wipers opposite the tenth (or ninth) level. In this case there will be no ground potential present on the conductor 6, but relay 17 will again operate when springs 91 are closed bythe elevation of the shaft to the tenth (or ninth) level, this time in series with the resistance R (before series relay 13 has had time to deenergize). However, magnet 21 is insufficiently energized through the resistance R (after relay 13 falls back) to operate and rotate the switch wipers into engagement in the first set of contacts in the level opposite which the wipers have been positioned. Therefore no connection is established, but the relay 17 remains energized and the subscriber who attempted connection receives the busy tone.

This completes the description of the invention. What is thought to be new and is desired to have protected by Letters Patent is specifically pointed out in the appended claims.

What is claimed is:

1. In a telephone system, trunk lines, a key and a relay for each trunk line, operating circuits for said relays including said keys and a common conductor, a telephone set, means responsive to a momentary actuation of any one of said keys for operating a relay to associate saidtelephone set with the corresponding trunk line, and means for opening said common conductor to prevent the association of said telephone set with any other trunk line by the subsequent operation of any other key.

2. In a telephone system, trunk lines, a key for each trunk line, a telephone set including a switchhook, means responsive to the operation of said switchhook and a momentary actuation of any one of said keys for associating said telephone set with the corresponding trunk line, and means for preventing the association of said telephone set with any other trunk line by any subsequent operation of any other key until the switchhook has been restored and again operated.

3. In a telephone system, a trunk line having an incoming and an outgoing branch, a key, a telephone set, means separate from said key but automatically responsive to a momentary actuation thereof for connecting said telephone set across the conductors of said incoming branch and for connecting a bridge across the conductors of said outgoing branch.

4. In a telephone system, a trunk line having an incoming and an outgoing branch, a key, a telephone set, means automat cally r esponsive to a momentary actuation of said key for connecting said telephone set across the conductors of said incoming branch and for connecting a bridge across the conductors of said outgoing branch, and a key for disconnecting said telephone set from sald 1ncoming branch and for substituting said telephone set for said bridge.

5. In a telephone system, a trunk km, a calling device, a key, means responslve to a momentary operation of said key for associating said calling device with said trunk line means thereafter controlled by said calling device for extending a connection over said trunk line to a called telephone line, means controlled at will for disassociating said dialfrom said trunk line, and means controlled at will for releasing said connection and for also disassociating said calling device from said trunk line in case it is still associated therewith when said releasing means is operated.

6. In a telephone system, a connector accessible to two kinds of lines, a conductor in said connector, means in said connector for causing it to execute an automatic rotary mo-' tion controlled over said conductor when said connector is taken into use over one kind of line, and a signal controlled over said cona o 'ductor when said connector is taken lnto use 0nd line, an automatic switch accessible to said lines, a signal for said first line, means for said second line for-placing a potential on a conductor of said connector to initiate an operation of said connector when said connector is taken into use over said second line, and means in said connector for placing a potential on said conductor to operate said signal when said connector is taken into use over said first line.

8. In a telephone system, trunk lines, a key for each trunk line, a. telephone set, means responsive to a momentary actuation of any one of said keys for associating said telephone set with the corresponding trunk line, means for then locking said telephone set to the corresponding trunk line independent of the key, and means common to all of said trunk lines for disabling said locking means. i

9. In a telephone system, trunk lines, a key for each trunk line, a telephone set, switch hook springs for said set, means responsive to a momentary actuation of any one of said keys with said springs operated or associating said telephone set with t e corresponding trunk line, and means effective only as long as the switchhook springs remain operated for locking said tele hone set to the corresponding trunk line in ependent of the key. p

10. In a telephone system, trunk lines, a relay for each trunk line, a key for each trunk line, a telephone set, means responsive to the momentary operation of any one of said keys for operating the corresponding one of said relays for associating said telephone set with the corresponding trunk line, means for maintaining the operated relay operated independent of the key,- and a com mon relay controlled by said means for opening the circuits of all of said first relays to prevent the operation of any other relay after one is operated.

11. In a telephone system, trunk lines, a trunk relay for each trunk line, an automatic switch terminating each trunk line, a telephone set, means for actuating any one of said relays, means controlled by the actuated relay for associating said telephone set with the corresponding trunk line and for initiating the operation of the switch terminating the corresponding trunk line, and a common relay actuated in series with the particular one of said trunk relays actuated for preventing the actuation of any other trunk relay thereafter.

12. In a telephone system, trunk lines, a

trunk relay for each trunk line,.a key for telephone set with the corresponding trunk line, a common relay actuated in series with the particular one of said trunk relays actuated for preventing the actuation of any other trunk relay thereafter, and separate means for deactuating the actuated trunk relay and the common relay.

13. In a telephone system, trunk lines,'each comprising two inductively coupledsections, a calling device, means for associating said calling device with one section of any of said trunk lines, and a key common to said trunk lines for disassociating said calling device from said one section and associating it with the other section of the same trunk line.

14. In a telephone system, a trunk line extending from a main exchange to a branch exchange, a branch for said trunk line at the branch exchange normally disconnected from the trunk line, a key, and means responsive to a momentary actuation of said key for inductively connecting said branch with said trunk line.

15. In a telephone system, trunk lines, a normally disconnected branch for each trunk line, a first and a second set of talking leads inductively coupled, a key individual to each trunk line, means responsive to the momentary actuation of any key for-connecting the lid first set of talking leads to the corresponding trunk line and the second set of talking leads to the corresponding branch.

16. in a telephone system, trunk lines, a normally disconnected branch for each trunk line,- a first and a second set of talking leads inductively coupled, a key individual to each trunk line, means responsive to the momentary actuation of any key for connecting the first set of talking leads to the corresponding trunk line and the second set of talking leads to the corresponding branch, separate inductive coupling means for each trunk, and means tor substituting the separate coupling means of the corresponding trunk for the first and the second set of inductively coupled talking leads.

17. In a telephone system, trunk lines, a branch for each of said trunk lines, a key for each of said trunk lines, a common link, and means automatically responsive to the momentary operation of the key of any of said trunk lines for inductively coupling the corresponding trunk line with its branch via said common link.

18. in a telephone system, a subscribers station, a trunk line comprising two talking conductors and a third conductor, means including an automatic switch for extending a connection from said trunk line to said subscribers station, means in said switch for connecting ground potential to said third conductor when a connection to said station is extended, for disconnecting the same from said third conductor when the subscriber at the station answers the call, and for reconnecting the same to said third conductor when the call is terminated, a first signal operated by the initial connection of ground potential to said third conductor, and a second signal operated by the second connection of ground potential to said third conductor.

19. in a telephone system, trunk lines connecting two exchanges, an attendants cabinet at one of said exchanges, a telephone set. keys and supervisory lamps in said cabinet, and relays remote from said cabinet and associated with said trunk lines for controlling said lamps and for connecting said telephone set with any of said trunk lines under the control of said keys.

20. in a telephone system, a t 'unk line, an automatic switch, means tor operating said switch to seize said trunk line, an attendants cabinet, a signal at said cabinet, and a relay in said switch energized in series with said signal when said trunk is seized by said switch. r

21. in a telephone system, a trunk line comprising two talking" conductors and a third conductor, an automatic switch, means for operating said switch to seize said trunk line, an attendants cabinet, a signal at said cabinet, and arelay in said switch energized over said third conductor in series with said signal when said trunk is seized by said switch.

22. In a telephone system, an attendants switchboard, an automatic switch, a trunk line passing through said switchboard and terminating in said switch, an attendants telephone set, means for connecting said telephone set with said trunk line to answer calls thereover, and circuit arrangements for supplying current for the transmitter of said telephone set from said switch.

23. In a telephone system, a trunk, an automatic switch terminating said trunk, means for seizing said trunk, other lines accessible to said switch, means for causing said switch to hunt an idle line responsive to the seizure of said trunk, a relay for said trunk operated in series with one conductor of said trunk, a second relay for said trunk, means controlled by said first relay for connecting said second relay to the other conductor of said trunk, and means for operating said second relay when said switch finds an idle line.

24. In a telephone system, a trunk, an automatic switch terminating said trunk, means for seizing said trunk, other lines accessible to said switch,means for causing said switch to hunt an idle line responsive to the seizure of said trunk, a relay for said trunk operated in series with one conductor of said trunk, a second relay for said trunk, means controlled by said first relay for connecting said second relay to the other conductor of said trunk, means for operating said second relay when said switch finds an idle line, and means controlled by said second relay for disconnecting said second relay from the other conductor of said trunk after it is operated.

25. In a telephone system, a trunk line, an automatic switch terminating said trunk line, means for seizing said trunk, said trunk line comprising two conductors, one of which is continuous from the point of seizure to said switch and the other of which has a normally open point between the point of seizure and the automatic switch, means for operating said switch, and means for closing the normally open point in the said other conductor of said trunk line after said switch has been operated.

26. In a telephone system, a trunk line, an automatic switch terminating said trunk line, means for seizing said trunk line, said trunk line comprising two conductors, one of which is continuous from the point of seizure to said switch and the other of which comprises two normally disconnected sections, means controlled over the first section of said other conductor in series with said continuous conductor for operating said switch, and means controlled over the second section of said other conductor for connecting said sections after said switch has been operated.

27. In a telephone system, a trunk line, an automatic switch terminating said trunk line,

a line relay for said switch, means for seizing said trunk line, a second relay operated over one conductor of said trunk line in series with said line relay when said trunk is seized, means for operating said switch, athird relay for said trunk line, circuit arrangements controlled by said second relay for operating said third relay over the other conductor of said trunk line after said switch has-been operated, and means controlled by said third relay for completing a talking circuit over said trunk line.

28. In a telephone system, trunk lines, a key for each trunk line, a telephone set in.- cluding a receiver, means responsive to the removal of the receiver and the operation of any one of said keys for associating said telephone set with the corresponding trunk line, means for preventing the association of said telephone set with any other trunk line by the subsequent operation of any other key, and means controlled by the replacement of the receiver for disabling said preventing means.

29. In a telephone system, an automatic switch, a trunk line terminating in said switch, means controlled, over a conductor of said trunk line under certain conditions for causing said switch to operate in a distinctive manner, a signal, and means in said switch effective under certain other conditions for controlling said signal over said conductor.

30. In a telephone system, a line, a signal for said line, a switch and means for operating it to connect with said line to extend a call, a relayin said switch operated in series with said signal responsive to the connection of said switch with said line, and means responsive to the answering of the call for disabling said signal.

31. In a telephone system, a trunk comprising two talking conductors and a third conductor, a signal normally connected to said third conductor, a switch and means for operating it to seize said trunk to extend a connection, a relay in said switch operated in series with said signal responsive to the seizure of said trunk, and means responsive to the answering of the call for disconnecting said signal from said third conductor.

32. In a telephone system, a trunk line andmeans for seizing it to extend a connection, a relay and a resistance normally bridged across the conductors of said trunk line,

means for operating said relay responsive to the seizure of said trunk line to mark said trunk line busy, means responsive to the answering of the call for opening said bridge, and means for placing said relay in bridgeof said conductors independent of said resistance to maintain the connection.

33. In a telephone system, an attendants position, a trunk line extending through said position, means for extending a call via said trunk line to said position, a signal operated responsive to the extension of a call, means for disabling said signal responsive to the attendant answering the call, means controlled by the attendant for further extending the call to a called station, a second signal operative responsive to the further extension of the call, means for disablingsaid second signal responsive tothe answering of the call, and means for reoperating said first and said second signals responsive to the termination of the call. I

34. In a telephone system, an attendants position, means for extending a call to said position, a signal at the position operated responsive to a call being extended and disabled responsive to the attendant answering the call, means controlled by the attendant for further extending a call to a wanted station, a second signal at the position operated responsive to the further extension of the call and disabled responsive to the call being answered at the wanted station, and

means for reoperating said first signal and said second signal responsive to the call being terminated at the wanted station.

35. In a telephone system, a telephone set including a switch hook, a plurality of trunks of two different classes, a key for each of said trunks, means eflective when the switchhook is actuated and responsive to the momentary actuation of one of said keys for associating the corresponding trunk .with said telephone set, means responsive to the deactuation of the switchhook for disassociating the connected trunk and the telephone set providing the connected trunk is of one class, and means responsive only to the fur ther actuation of the key for disassociating the connected trunk and the telephone set plroviding the connected trunk is of the other 0 ass.

36. In a telephone system, a trunk com prising three normally disconnected sections, a relay energized responsive to a call over said trunk for connecting the first and second sections of the trunk, a second relay having two windings, means for operating said second relay over one of said windings responsive to the operation of said first relay, means for connecting the second and third sections of the trunk responsive to the operation of said second relay, means for deenergizing said first relay, and means for completing a holding circuit for said second relay including the other winding of said second relay bridged across the conductors of said trunk responsive to the deenergization of said first relay.

, 37. In a telephone system a main office, a branch ofiice comprising an automatic exchange, main lines connecting the main oflice with the branch oflice and terminating in the automatic exchange, subscribers telephone lines terminating in the automatic exchange, subscribers stations having telephone appaith ratus associated with said subscribers lines, one of said subscribers apparatus being pro- "vided with means for mediating the incoming trafic from the main oiiice comprising switching means at the automatic exchange for connecting the telephone line of the mediating subscribers apparatus with each of said main lines, circuits for said switching means, keys on the mediating apparatus for operating said switching means over said circuits, and call indicating means on the mediating apparatus for indicating calls from the main ofice.

38. In a telephone system a main oflice, a branch oflice comprising an automatic exchange, main lines connecting the main oiiice with the branch oifice and terminating in the automatic exchange, subscribers telephone lines terminating in the automatic exchange, subscrihers stations having telephone apparatus associated with said subscribers lines, one of said subscribers apparatus being provided with means for mediating the incoming traflic from the main ofice comprising switching means at the automatic exchange for connectin the telephone line of the mediating subscri ers apparatus with each of said main lines, circuits for said switching means, keys on the mediating apparatus for operating said switching means over said circuits, call indicating means on the mediating apparatus, and means for connecting a main line with a subscribers line through the automatic exchange under the control of the mediating apparatus.

in witness whereof, hereunto subscribe my name this 4th day of April, A. D. 1927.

THUS. F. CROCKER.

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