US1809071A - Telephone system - Google Patents

Description

June 9,- 1931. G. E. scHoMAKER E1' AL 1,809,071

TELEPHONE SYSTEM Filed April 28, 192e. 5 sheets-sheet .1

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5 Sheets-Sheet 2 TELEPHONE SYSTEM June 9,- 1931. G. E. scHoMAKER ET AL Filed April 28, 192e m n wad? I O IILI June 9,- 1931. G. E. s'cHo'MAKER ET AL 1,809,071

TELEPHONE SYSTEM Filed April 28, 1928 5 Sheets-Sheet 5 -LInLr E :Deurne l En Y June 9,- 1931. G. E. scHoMAKER ETAL *1,809,071

TELEPHONE SYSTEM Filed April 28, 192e` 5 sheets-sheet 4 was F.' En nld.

June 9,- 1.931.

G. E. .scHoMAKER ET'AI,

TELEPHONE SYSTEM Filed April 28, l192e;

5 sheets-'sheet 5 Imran nrs Eanr'ss E. E chamakar' C005 am: h No. .3o

'En 'E' .Bauli Patented June 9, 1931 UNEEB STATES PTEN'F GFFECE GEORGE E. SCEOMAKER, OF SYDNEY, NEW SQUTH WALES, l'U'STRALIA, ROY F. GOULD, OF' CHICAGO, LLITOS, ASSG-NOBS TO RESERVE HOLDING COMPANY, OF KANSAS GTY, MESSUB, [a CQEPOlD- ATON OF DELLWAEE.

TELEP-QONE SYSTEB Sera The present invention relates to telephone systems in general, but is concerned more particularly with the branch-exchange equipment in a telephone system employing both main and branch exchanges, although several features of the invention are not speciiically limited thereto.

The invention has been applied to an automatic telephone system including an automatic main exchange and an automatic branch exchange having an attendants cabinet located therein to enable an attendant at the branch exchange to complete incoming calls and to set up connections from a branchexchange subscriber to a. main-exchange subscriber when requested to do so.

One object of the invention is the application of the so-called by-pass method of operation to the branch-exchange switching apparatus so that a single connector will suftice, this connector being used merely to operate the lineswitch on the called line to cause it to seize the same trunk previously seized by the calling lineswitch.

A features of the invention lies in the arrangement whereby each of the ten trunks presided over by a master switch is normally connected to the common connector switch, but is disconnected therefrom and connected instead to an individual battery feed and holding relay as soon as a connection has been set up over the trunk.

According to a further feature of the invention, the master switch is arranged so that it does not operate to preselect a new trunk when a call is made, but waits until the common connector has been operated over the seized trunl-z to signal the subscriber on the called line and to operate the lineswitch on the called line to make connection with the calling line through the trunk in use, whereupon the master switch operates in the usual manner to preselect another idle trunk.

Another obj ect of the invention is the provision of a timing device individual to the connector for freeing the connector automatically in case the subscriber has not dialled the complete number and caused the connector to be freed when disconnected from the trunk as above mentioned.

273,469, and in Great Britain August 26, 1927.

According to a further feature of the i11- vention, the above-mentioned timing device is released and started over again after the complete number has been dialled in order to control the application of ringing current and the regular release of the connector.

A special feature of the arrangement is that ringing current is 4transmitted as soon as the connection has been completed7 only a short preliminary ring being given at that time. A moment later, the timing device causes a long ring to be transmitted to the called line. This long ring is useful in a private automatic exchange in order to locate the substation that is being signalled when several substations are located close together, such as, for example, at adjacent desks in an Another object of the invention is the production of suitable arrangements in a system of the foregoing character whereby certain subscribers are permitted to call through to the main exchange, while calls from other substations to the main exchange vare barred.

rnother object of the invention is the provision of arrangements in the connector for preventing the connecting up of a battery supply to a trunk line when a. connection is being made thereover to the main exchange or to a certain local equipment (a code call machine for example) while permitting a battery supply connection to be made in case the call is a regular local call. This permits branch-exchange subscribers to dial mainexchange numbers and special local numbers.

Ano-ther object of the invention is the provision of suitable arrangements in the incoming trunk lines for controlling the operation of they connector so that it will fail to causeY the battery supply to be connected to a local trunk line in case the call is incoming to the branch exchange from the main exchange, the arrangement being preferred wherein the transmitter in the branch exchange is energized from current transmitted over the inter-exchange trunk line from the main exchange.

Another object of the invention is the provision of suitable arrangements for enabling an attendant at an attenda-nts cabinet associated with the inter-exchange trunk lines to answer and extend calls incoming from the main exchange, to answer the calls incoming to her cabinet from the branch exchange, and to set up tail-totail connections betwcenmainexchange and branch-exchange subscribers.

vAnother object of the invention is the provision of a` novel arrangement whereby both busy-tone current and dial-tone current are transmitted to the connector from the tone equipment over the same conductor, arrangements being provided Jfor causing the flow ot tone current to be distinctly different at one time from the iiow of tone current at the other time so as to differentiate between the dial tone and the busy tone.

There are other objects and features of the invention having to do i'or the most partwith the circuitdetails necessary to carry out the objects and features above mentioned. The various objects and features of the invention will be understood best from a further perusal oi' the descripti n in connection with the accompanying drawings.

Referring now to the drawings comprising Figs. l to 5, they shew ey means ot the usual circuit diagrams a suiiicient amount of equipment in a telephone system involvng the features of the invention to enable the same to be understood. More in particular, these drawings show equipment located in a main exchange, indicated at the left in Fig. l, and the essential equipment of a branch exchange interconnected with the main exchange by means of the trunl line TL, Fig. 1, and oth-v ers. The branch exchange may be considered as belonging to the type ordinarily designated as a private branch exchange, an attendant being located at the branch exchange to vcomplete incoming calls byV ascertaining the number desired and controlling the operation at the automatic switching equipment, outgoing calls being completed responsive to the dialling operation on the part of the calling subscriber without the aid of the branchsexchange attendant.

rThe apparatus shown in Fig. 1 includes the portion of the main-exchange equipment at the left, and the trunk circuit TC at the right of the interconnecting trunk line TL. In the lower part of Fig. l there is indicated cert-ain lreys and lamps located at the switchboard of the attendant and individual to the trunk circuit TC.

The remaining portion of the attendants equipment is indicated in Fig. il, which should be placed under Fig. 1 with the interconnecting lines in alignment. The keys and other apparatus in Fig. e are common to the several trunk circuits such as the trunk circuit TC, Fig. 1. Fig. l shows two so-called information trunks extending to the attendants switchboard from the local switching LS2 is individual to the trunk line TL with which it is associated through the medium ot' the trunk circuit TC, Fig. 1, being connected with such trunk circuit by way of conductors 125-l29.

Fig. 3 shows the single connector of the branch exchange having wipers B22-325. This connector, through the common conductors 219*22l, is normally connected to each of the trunk lines accessible to the lineswitches, one et them being the one comprising conductors 226-229, Fig. 2. This connector has access to each of the lines and line switches et the branch exchange. Fig. 3l shows also the control equipment and auxiliary equipment including the l2-position rotary switch and its associated relays, and the inging interrupter.

Fig. 5 shows the code call apparatus including the lineswitches LSB and LSst associated with the code answering and code calling numbers respectively and the code selector having wiper 507. This apparatus is accessible to the connector shown in Fig. 3 through the banl: contact shown at the left of Fig. 5 and is operated in a mannerA to be explained subsequently. The lineswitches LS?) and LS are under the control et the master switch shown in Fig. 2.

Mechanically, the master switch shown in Fig. 2 together with the lineswitohes LS1 and LS2 of the same drawing and the lineswitches LSS and LS1 of Fig. 5 are ot' the usual type, the plungers of the lineswitehes being preferably et theisel-re-storing type; that is, a plunger, when released, returns at once to the control ot the master switch rather than waiting for the master switch to return again to the position from which the lineswitch was plunged.

The connector shown in Fig. 3 is mechanically of the well-known Vertical and rotary type having its bank contacts arranged in horizontal rows or levels.

The apparatus having been described in general, a detailed description of its operation will now be given; For this purpose it will be assumed that the subscriber at substation A desires to converse with another local subscriber.

Local @all from substation A When the receiver is removed at substation A., line relay 203 of the lineswitch LS1 1 y nad energizes over the two conductors of the calling line and the substation circuit in series and closes a circuit through the pull-down winding of the lineswitch by way ot conductor 202, at the same time disconnecting the operating conductor from the succeeding lineswitches. The ground potential on conductor 202 is obtained from the upper contacts of relays 307 and 304: of the connector, Fig. 3, and through the high-resistance lower winding of the delay-relay 201. As long as the high-resistance lower winding on this relay is unshunt-ed, the lineswit-ch is prevented from operating. The delay relay is slow to operate due to the high impedance oft its lower winding which prevents a quick building up of the current and due to the shortcircuited upper winding ot the relay, which winding is on the armature end or tne relay and therefore prevents the magnet hun from reaching the rmature quickly after it is built up. The delay relay is provided primarily to take care of the situation which might arise in case a. lineswitch attempts to reoperate immediately after being released, in which case it might plunge in on a t other than that preselected by the i switch if it were permitted tooperate before it has restored to the position of the master switch. TVhen relay 201 operates it places the low-resistance upper winding in shunt of the lower winding, whereupon the pulldown winding 205 is magnetized sufficiently to operate armatures 206 and 207, closin the connection through from the lineswitch to the trunl: comprising conductors 22-229 and disconnecting` line rela-y 203 and ground from the conductors or" the calling line.

Line relay 305 ot' the connector now operates over the calling line through conductors 226 and 229 oi the seized trunlr and conductors 219 and 221 of the connector. Upon operating, line relay 305 closes a circuit for relay 306, whereupon the release relay 306 operates and closes a ircuit for relay 307,

which relay, at its lower armature. places ground on the release trunk conducto thereby closing a holding circuit throu test wiper of the master switch and over trunk conductor 227 and contacts of the lineswitch LS1 for the bridge-cutoff winding 204 of the lineswitch. This cir-cuit is established before the slow-acting` 203 has time to Jfall baclr and it serves to maiutain the armatures 206 and 207 of the lineswitch operated.

As a further result of the operation of r lays 306 and 30'?` Fig. 3, thelswitch is pr pared for operation b3 Yf e lower armature of relay 306, and ground is removed at the upper armature ot 307 from the delay relay 201, which relay tails baclr in preparati n for the next calla From this it will be seen 4 that no further lineswitches can be operated time beino because ground potential is remove-d from the contact chain of the line relays.

The calling subscriber now hears the above-mentioned dial tone and dials tl e i rst digit inthe desired number, the digit 5, for example, whereupon line relay 305 reti-acts its armature ve times momentarily. Each time it does so, circuit is closed through the lower armature of release relay 30G for vertical magnet 317, the circuit at the time of its first closure including the lower associated' oli-normal spring, the upper spring 315, and the lower contacts of relay 303. By the operation of the vertical magnet, the wipers S22-325 are raised step by step until they stand opposite the ii'th level ot the baul; contacts. Relay 308 isv operated in multiple with vertical magnet 317 upon. the first impulse of current, and, being slow acting,`it remains operated throughout the digit, thereby inaintain'ng its own circuit and that of the vertical magnet intact alter the oli-normal contacts have shifted, as they do upon the first vertical step. At the end of the verticalmovement, relay 308 falls back and transfers the operating conductor from the vertical magnet 31'? to the rotary magnet `When the next digit is dialled, the digit 6 or example, line relay 305 is deenergized sinr times momentarily, transmitting an impulse to rotary magnet 319 each time it deenergizes.

rlhese in pulses are transmitted through the lower armature of relay 306, the two lower oit-normal contacts associated with ott-normal spring` 315, the lower armature, normal, ot relay 308, normally closed contacts controlled by the lower armature of relay 310, and contacts of relay 312. Magnet 319 responds to these impulses and rotates the wipers 322 325 step by step until they come into engagement with the sixth set of bank contacts (not shown) in the ifth level. Relay 311 is energized in multiple with magnet 319 throughout the rotary movement and at its inner upper armature it disconnects test wiper 323 from the test winding of switching relay 312 and connects it instead 'through interruptor contacts 321 to the combined stepping' and busy relay 310, and at its lowerv armature it places a shunt around the associated contacts of relay 310 so as to prevent the interruption ot the rotary-magnet operating circuit during the rotary movement in case relay 310 operates during such movement, due to a ground potential being engaged on a busy test contact by test wiper 323.

At the upper armature of relay 30'?, ground is placed on conductor 370. starting the ringinterrupter to operating as follows: `When the left-hand winding of the operating magnet energizes through the associated resistancery the reed is drawn to the lett,rwhereupon the diterential right-hand winding cnergizes in the opposite direction, causing the magnet to release the reed which swings to the right. rEhe right-hand winding deenergizes and the reed is attractedagain. The intern ittent current flow through the lower contacts of the reed, as it vibrates, passes through the primary winding of the associated transformer and induces the alternating ringing current in the secondary winding.

Ground potential is extended from conductor 370 to the differential to e relay 363 through contacts of relay 312. Relay 368 buzzes at a rather high rate and places a dial tone7 on conductor 221 through condenser 335.

Ground potential is extended also to start relay 367 from conductor 370 through the upper contacts of relay 311 and switch cam 355 in position 1. The timing switch thereupon starts operating in a manner to be later explained.

aZZefZ Zine busy energized over test wiper 323 by a ground' otential when the wipers or" the connector come to rest on the bank contacts of the called line, and when relay 311`falls baci; the circuit ot rotary magnet 319 and its own circuit is opened at the lower contacts oi the relay, thereby preventing further rotary movement of the connector in the case of further opera-Y tion of the calling device at the calling substation. lt will be noted that relay 310 is now locked energized from conductor 370 through its own inner upper armature, and the rotary magnet interrupter contacts 321. It is tobe noted further that it is unnecessary to have the locking circuit of relay 310 controlled by relay 311 to prevent relay 310 from locking up during the rotary movement, as is ordinarily done, because, in this case, the rotary magnet 319 opens the circuit ot relay 310 on each step of the wipers. vWith lousy relay 310 energized, a ground potential is extended 'from the grounded conductor 370 by way of the upper contacts of relays 311, 310 and 308 to the junction of the winding of relay 368 and the associated resistance, by way of the upper contacts of interrupter relay 365. As a result, relay 363 is intermittently short circuited, as relay 365 pulls up and falls back, causing it to give forth an intermittent buzzing sound instead of a continuous buzzing sound heretofore given. This intermittent buzzing sound is recognized by the calling subscriber as the busy signal. Upon hearing this signal, the calling subscriber replaces his receiver, permitting relays 305, 306, 307, and 310 to tall back, and resulting in the release of the connector and of the calling lineswitch LS1. ln this case the master switch does not advance and in the next call takes the same trunk.

alled Zine alle Assuming now that the desired line is idle when called busy relay 310 is not energized at the end of the rotary movement/and relay 312 is operated instead, when relay 311 falls back and connects the upper winding oi'r' relay 312 to wiper 323. The circuit of relay 312 eX- tends from the grounded conductor 370 by way. oit the contacts oi' relay 310 to the upper windingof relay 312, and thence by way of contacts or relays 311 and 312 to test wiper 323. The circuit is comple-ted to battery through the cut-o winding of the called line-switch, which winding is similar to the winding 204; of the lineswitch LS1. The energization of this winding results in the operation orn the cutoil armature, corresponding to armature 206, clearing the called line of its attachments. Relay 312 operates over this circuit and at its inner lower armature locks itselrl to conductor 370, at the same time removing the operating potential from the tone relay 368, whereupon the buzzing operation o1" relay 363 ceases and the application of the buzzing tone to the lower talking conductor no longer talles place. As a further result of its operation, relay 312 disconnects the rotary magnet 319; at its inner upper armature its disconnects test wiper 323 from its own upper winding and connects it directly to ground so as to maintain the cut-off winding of the called line switch operated; and at its upper and lower contacts it connects up the wipers 322 and 325 to the ringing circuit. The lower wiper is connected to the ringing lead 363, and the upper wiper is connected to the upper winding of'ring-cut-oif relay 309. rlheV application of ringing current to the called line is accomplished in a way which will now be explained.

Operation of timing switch It was mentioned hereinbefore that the timing apparatus, including the 12-position rotary switch, is started when start relay 367 operates from conductor 370 through contacts of relay 311 and cam 355 when the switch is seized. `When it operates, relay 367 locks itself to conductor 360 at its inner lower armature, and at its upper armature it starts interrupter relays 366 and 365 operating. Relayl 366 closes a circuit for relay 365. R'elay 365 operates and short-circuits relay 366, which relay then falls back, short-circuiting and open-circuiting relay 365. Relay 365 falls back and removes the short circuit from around relay 366, allowing relay 366 to reoperate. This operation keeps up as long as relay 367 is operated. The operation is slowed down and is steadied by the copper collars on the armature ends ofthe cores of the relays, which are thereby rendered slow to operate and slow to release.

Each time relay 365 operates it closes a circuit from the grounded conductor 360 for magnet 350. Each time magnet 350 falls i back, after pulling up over this circuit, it advances the ratchet device one step, each step representing a separate one ot the twelve positions. The pulses are delivered at a rate of about two per second.

The device is started when the connector is seized so that the connector may be restored to common use at the end or about four and one-haltn seconds in case the second digit has not been dialled in the meantime. Such action results from the operation o ring-cut-otl relay 309 through cam 354 in position 9 of the device and in a manner to be brought out hereinafter.

Now, when relay 311 responds to the second and last series of impulses inthe number, during the rotary movement of connector and just prior to the test which results in the finding of the line idle and the operation of relay 312 just described, it removes ground at its upper armature from the interrupter start conductor 360, whereupon start relay 367 falls back and closes a restoring` circuit for the timing switch by closing a circuit for the stepping relay 364 through cam 352 (positions 2 to 12) and the interruptor contacts 351 of magnet 350. Relay 364 operates and closes at its lower armature a circuit Jfor magnet 350, whereupon this magnet operates and opens the circuit of the stepping relay. The stepping relay falls back and permits the deenergization of the magnet, resulting in the advance of the timing switch one step. When the magnet deenergiz'es the circuit of relay 364 is reestablished. The relay and the magnet operate alternately in this manner until the restoring circuit is opened, when the switch passes beyond position 12 and arrives in position 1. It will be noted that start relay 367 cannot reoperate t0 open the restoring circuit` until the switch arrivesin position 1, owing to the fact that start relay 367, on falling back, opens its locking circuit. When start relay 367 reoperates, either ren sponsive to the timing switch arriving` in its position 1 or to the falling baclf: of relay 311 at the end of the second digit, whichever takes place last, the interrupter relays 365 and 366 start driving the timing magnet 350 again. Now, while-the timing switch is still in position 1, ringing current from the secondary finding of the ringing interrupter is placed on ringing lead 363, projecting ringing current out over the calling line o-ver the lower contacts of relays 309 .and 312, which ringing current returns by way of the upper line conductor, wiper 322, and the upper contactsA of relay 312 and 309 to battery by way of the upper winding of relay 309. r1`he slow-acting ring-cut-o relay 309 is not operated by this ringin@P current, as no flow of direct cur- `ent takes place due to the inclusion of the usual condenser in the ringing` circuit.

The ringing circuit is opened at cam 356 and lead 363 is grounded directly while the timing switch is in position 2, but in positions 3 to 6 the ringing circuit is closed again and a further and longer application of ringing current takes place. The ringing current is applied in this manner so that the particular telephone which is ringing may be readily located when several telephones are mounted close together. The short preliminary ring calls attention to the call and the long ring occurring shortly after enables the correct telephone to be located.

A portion of the ringing current Hows back to the calling line through the small condenser 384, informing the calling subscriber of the ringing operation.

The ring-cut-otl relay 309 may be operated over the called line in case the called subscribed responds after 'the connection has been completed by the switching relay 312. W'hen operated in this way, relay 309 operat-es through its upper winding over the called line and locks itself to conductor 370 at its inner lower armature. It relay 309 is not so operated, it is operatedk automatically by the timing device when it arrives in position 5. The circuit at this time is from ground by way of the'inner lower armature, operated, of relay 312, cam 353 off the timing device, conductor 359, and the lower winding of relays 309 to battery. Upon operating, relay 309 locks itself to conductor 370 at its inner lower armature; opens a point in the master-switch-st-art circuit at its third` armature from the bottom; disconnects the upperand lower wipers at its upper and lower armatures; thereby stopping the flow of current to thecalled line; and at one of its lower armatures it places ground on conductor 224, thereby operating relay 304v to open a `further point in the ground-supply connection to relay 201 (Fig. 2), and placing ground on thev pull-down wiper 324, closing a circuit through the bank contact on which wiper 324 is standing for the pull-down winding of the called lineswitch, similar to wind- 205 of the lineswitch LS1. When this occurs, the lineswitch on the called line operates and connects the called line with the same trunk line with which the calling line is connected, because the master switch is still standing in the same position. As soon as the lineswitch on the called line operates, its upper winding is energized in parallel with winding 204 of the lineswitch LS1 from conductor 227 of the trunk, which winding serves to maintain the lineswitch operated after the current flow through the pull-down winding has ceased. l

As a further result of the operation of relay 309, it closes at its inner upper armature a. circuit from ground through the upper armature of relay 306, through the upper armature of relay 301, the 30 and 00 cam springs,

and over vcut-E conductor 222 and the corresponding` wiper of the master switch for operating the cut-off and battery-feed relays 218 and 217 ofthe trunk line over which the connection has been completed. Relay 218 operates when this circuit is closed and locks itself at its inner' upper armature to the `grounded conductor 227, at the same time CIO opening its initial circuit; it disconnects conductor 226, 228, and 229 of the trunk line from the corresponding conductors 219, 220, and221 of the connector at its upper and' at its two lower armatures; and atits middle upper armature it extends the ground potential to the upper winding of battery-feed relay 217. This relay is marginally adjusted and does not operate if the resistance 320 (Fig. 3) is included in its circuit. Resistance 320 is, however, short-circuited at this time at the associated contacts, with the result that relay 217 operates and locks itself to trunk conductors 226 and 229 at its upper and lower armatures, at the same time opening its initial circuit. Relay 217 now remains energized over the calling and called lines in multiple, supplying talking current to the transmitters through its windings. At its inner upper armature, relay 217 places a multiple ground connection on the holding conductor 227 so as to maintain both lineswitches operated and' so as to maintain a busy test potential on the corresponding contact in the bank of the test wiper of the master switch.

The two subscribers may now converse with each other over their respective lines and through conductors 226 and 229 of the trunk line.

'onnectma release In the connector, line relay 305 falls back when the trunk line is disconnected from the connector by relay 218, and relay 306 falls back shortly thereafter, opening the circuit of relay 307, whereupon relay 307 falls back. The falling back of relay 306 removes ground at its upper armature from cut-off conductor 222 and the falling back of relay 307 removes ground at one point from release trunk conductor 223, leaving the lineswitches held up solely from the ground potential supplied from the conductor 227 of the trunk at the inner upper armature of relay 217. At its upper armature, relay 307 prepares to replace ground on the pull-down conductor 202' 2), at the same time removing ground from the locking and start conductor 370, stopping` 'the operation of the ringing interrupter and the relays associated with the timing switch and resulting in the deenergization of relays 309 and 312. Start relay 367 of the timing switch now falls back and causes this switch to be restored to its normal position in the manner above pointed out.

With relays 307 and 309 deenergized, re-

lease trunk conductor 223 is connected through contacts of these relays to the master switch start conductor 225, with the result that the ground potential encountered by the test wiper lof the master switch, onthe test contact associated with conductor 227 of the trunk line, energizes the start relay of the master switch to cause the master switch to preselect another trunk line, as will be later explained.

Responsive to the deenergization of relay 306 of the connector, releasemagnet 318 operates through the associated oE-normal contacts 316 and contacts of relay 305 and 306 and restores the connector to its normal position in the usual manner. The release magnet circuit is opened at off-normal contacts 316 when the normal position of the switch is attained.

Release of connection energize, whereupon the lineswitches restorel and, due to theirself-aligning plungers, come immediately to the control of the master switch opposite the instant preselected trunk. The connection is now released and the apparatus is in readiness for use in completing subsequent connections. j

Master switch operation The master switch is of the usual mechanical design and advances to preselect trunksunder power supplied by the so-called U- spring shown just below the solenoid of the master switch. The master switch is shown in the position occupied just after the solenoid has operated to align the plungers opposite the tenth trunk line, which is the trunk line shown in the drawings. Now, when the start relay is operated through the test wiper and over conductors 223 and 225, the groundcontrol conductor 224 is grounded at the upper armature of the start relay so as to maintain the relay 304 of the connector operated during the masterswitch operation, and at the lower armature ofthe start relay a circuit is closed for the locking relay, whereupon the locking relay operates and makes a further ground connection to conductor 224 and unlocks the associated segment, permitting the U-spring to advance the master switch to the next trunk line. If the next trunk line is idle,A

the start relay falls back immediately, followed by the locking relay, stopping the master switch on the trunk. If, however, the trunk line is busy instead of idle, the test wiper of the master switch encounters a.

ground potential on the test contact of the trunk line and the start relay is maintained operated, and the advance of the master switch continues.

lVlien an idle trunk line is found, start and loclr relays fall bach, stopping the master switch on this trunk. `With the start and lock relays both deenergized and with ringcut-off relay 309 of the connector deenergized responsive to the preceding release of the connector, the circuit of relay 30st is opened and this relay falls back, reconnecting ground to the pull-down conductor 202 (lT ig. 2) through the delay relay 201. The apparatus remains in this position until another call is made.

Assuming now that the master switch has advanced step by step until it is now standing on the first trunk line, and that a connection is set up involving this trunk line, the start relay operates in the heretofore described manner upon the release of the connector after the connection has been set up. At this time, the trip relay energizes in multiple with the locking relay through the associated linger-controlled contacts, held in engagement by the upper finger of the master switch. Upon energizing, the trip relay loclrs the locking magnet to ground at its right-hand contacts, and at its inner contacts it closes a circuit for the solenoid of the inaster switch, causing the master switch to be operated in a clockwise direction. The circuit of the trip relay is opened as soon as the master switch starts to move, but the springs remain mechanically loclred in their operated position by the locking spring controlled by the lower finger of the master switch, which is now out of engagement with such locking spring.v

When the master switch reaches the position shown in the drawings, the lower finger of the master switch unlocks the mechanically-locked springs of the trip relay, permitting them to open the locking relay and master switch operating circuit. lf this trunlr is idle at this time, the start relay is not operated and the locking magnet falls back.

Outgoing calls l one shown in the drawings and comprising conductors 226*229, for example. TWhen this occurs the connector and other annav 1 L .l ratus shown iii F ig. 3 respond as iiereinbefore described.

1When the calling subscriber dials the prey liminary digit 0, ten impulses of currentare delivered to vertical magnet 317, whereupon the wipers 322-325 are raised step by step until they come to rest opposite the tenth level of bank` contacts. lll/'hen the switch shaft carries the wipers up to the tenth level (the 0 level), the 0-level shaft springs 313 are closed, ovrfierating` relay 303 from the grounded condenser 220 by way ofcontacts of relays 303 and 301 and the 0level contacts 313. ,Conductor 220k is grounded by way of conductor 228 and the corresponding contacts of the lineswitch LS1. Relay 303 operates and at its middle upper armature removes the short circuit from around the winding of relay 301 and extends the grounded conductor 220 by way of the eleventh-rotary-step spring 314 and its right-hand contact,inner upper armature, operated, of the relay 303,

and the interruptor contacts 321 to steping relay 310. This circuit is completed )ust at the end of the last vertical step and while the slow-acting relay 308 is still energized in multiple with vertical magnet 317. Stepping relay 310 operates over this circuit and locks itself to conductor 370 at its inner -i upper armature, at the same time preparing a circuit for rotary magnet 319 at its lower armature. Relay 301 energizes in series with relay 303 responsive to the removal of the short circuit from around relay 301 by relay 303, and removes the shunt from around resistance 320 in the cut-olf lead. lncidentally, relay 301 locls itself at its inner upper armature to battery through the inner upper contacts of relay 306 and the associated resistance, thereby shunting this resistance around relay- 303, but this operation has no particular effect at this time.

Villien the slow-acting relay 3,08 falls back, it opens the initial circuit of relay 310 at its inner upper armature .and completes the cir- .cuit of the rotary magnet through the lower armatures of relays 3i0 and 312. Relay 310 remainsloclred up at its inner upper armature to conductor 37 0 so as to maintain the rotary magnet circuit closed. Responsive to the energization of the rotary magnet 319, the wipers 322-325 are rotated into .engagement with the first set of bank contacts in the tenth level. Relay 311 is energized in parallel with the rotary magnet and transfers test wiper 323 to the 'circuit of steppingy relay 310 at its inner upper armature. lNear the end of its stroke, rotary lmagnet 319, at contacts 321, opens the circuit of relay 310, whereupon relay 310 falls baclr and opens the rotary magnet-circuit, causing the rotary magnet to fall back and close contacts 321 again.

lf the trunk line terminating in the first set of contacts in the tenth'level is busy, ground potential is encountered on the tenth contact of said trunk line by wiper 323, operating the stepping relay 310 again. Relay 310 again operates magnet 319, causing the wipers to take another step. rllhis alternate operation is repeated as long as the wiper 323 engages busy contacts, and if all the trunk lines are busy the operation continues until the wipers have been advanced to the eleventh-rotary-step position, operating spring 314, which opens a point in the rotary magnet circuit and connects the grounded spring to the circuit of relay 310 through contacts 321, maintaining Arelay 310 operated so as to send back the interrupted busysignal from the tone relay 368 after relay 311 falls back, as Y hereinbefore described. The eleventh-rotary-step contacts above and slightly to the left of relay 301 operate to shunt resistance 320 so that the battery-feed relay of the trunk line may operate over conductor 222 in case the calling subscriber does not hang up, but waits until after the switchthrough operation occurs responsive to the .above-described operation of ring-cut-off relay 309 in position 5 of the timing switch.

Assuming now that the trunk line extending from the 0-level bank contacts shown in the drawings through terminals 256-257 to the lineswitch LS2 is found to be idle, wiper 323 does not encounter` ground potential on the corresponding contact thereof and relay 310does not energize again after the wipers have come to rest on the contact set.

ln this case, the deenergization of the slow-A acting multiply relay 311 is followed by the cnergization of relay 312 through its upper winding, over the conductor extending through terminal 256 and the correspondingly numbered terminal of Fig. 2, conductor 127, and the busy lamp shown in Fig. 1 t0 batt-ery. The busy lamp becomes lighted and relay 312 operates, performing` the functions described hereinbefore. With relay 303 operated, the closing of the locking circuit for the lower winding of relay 312 closes a multiple circuit for the lower winding of relay 309 through the upper contacts of relay 303. Belay 309 thereupon operates and performs the functions hereinbefore described including the grounding of the pull-down wiper 324 to cause the lineswitch on the called trunk to operate and grounding the cut-offlead 222'at its inner upper armature.

l/Vhen wiper 324 is grounded, a circuit is closed-through terminal 257 for the pulldown winding 211 of the lineswitch LS2, operr-ting the lineswitch to disconnect the line relay 209 and to make connection with the trunk line comprising conductors 22S- 229. rlhe springs of the plunger arms 212 connect up the grounded B. C. O.` (bridge-cutoff) conductor 126 to the B. C. O. winding 210 so as to hold the lineswitch operated. Vhen switch LS1 operated.

ground is placed on conductor 222, it is obtained through the resistance 320 on account of the fact that relay 301 is now energized, and, although relay 218 of the trunk is able to energize and lock Iitself toconductor 227, the marginally adjusted line relay 217 does not energize when the operating conductor is eX- tended to it because of the presence of the resistance 320 in series with the conductor. Consequently, the battery feed is no-t connected up locally and the calling subscriber is thereby enabled to operate the switches in the main exchange directly by his calling device, as will be subsequently pointed out.

lNith the lineswitches LS1 and LS2 both operated, the bridge of substation A across` the line thereof is effective in producing a current flow over conductors 125 and 129 (associated with the lineswitch LS2) and through the local trunk line conductors 226 and 229. Conductor 129 is connected to ground in the trunk circuit TC through contacts of relays 116 and 117, and conductor 125 is connected to battery in the main exchange through contacts of relay 117 in the trunk circuit TG, relay 114 of the trunk circuit TC, contacts of switching relay 102 of the lineswitch LS at the main exchange, and line relay 101. Series relay 114 operates in this conection in series with line relay 101 and closes a circuit for release relay 115, whereupon relay 115 places a ground potential on release trunk conductor 127 so as to maintain the inter-exchange trunk line busy to the connector. Abranch connection exists through the upper contacts of relays 119 and 120 to the B. C. O. conductor 126, holding ground being thereby extended through contacts of the lineswitch LS2 to the release conductor 227 of the local trunks, maintaining relay 218l of the trunk and the winding 204 of the line- This operation ofrelay 115 occurs, of course, before the release of the connector, initiated by the action of relay 218 in disconnecting the talking conductors of the trunk line from conductors 219 and 221, takes place.

Relay 116 operates over the lower talking conductor and through its own contacts and those of relay 115, and locks itself to ground locally, at the same time switching the lower ktalking conductor through and removing ground from the right-hand section thereof. In the main exchange, the operation' of line relay 101 results in an idle trunk being selected in the usual manner by the lineswitch LS, this lineswitch being operated by the selfinterrupting magnet 103 under the control of test wiper 105. When an idle trunk line is reached, relay 102, which is short-circuited by the `round potential encountered by wiper 105 during the operation of the lineswitch, is no longer short-circuited and energizes in series with the relatively low resistance magnet and switches the connection through to the wipers -1-106. Line relay 101 is disconnected, and the connection is extended through the line relay of the associated selec? for relav 102 before the slow-acting relay 101 has haddtiine to fall back.

In the branch exchange, the master switch is to advance in the hereinbei-ore-described manner when relays and 309 have both fallen back, and another idle trunk line is preselected, leaving the connection established rom the line of substation A to the main exchange through the lineswitches LS1 and LS2 and the trunk line TL.

The subscriber at substation A now dials the various 1listed Vdigits in the number of the desired subscriber, whereupon the main eX- k change switching mechanism operates to complete the connection in the usual manner.

When the subscriber` at subst-ation A replaces his receiver after conversation, the

main exchange connection is released in the f; usual manner and the series line relay 114 in the trunk circuit TC falls back and opens the circuit of release relay 115. Release relay 115 falls back after a sliO-ht interval and removes ground from conductor 127, whereupon theline switches LS1 and LS2 release and cut-off relay 218 falls back.

Attempted 'main exchange caZZ from restricted f il restricted to the restricted class by removing the'jumper associated with the liiieswitch spring which contactsY with the bankl contact connected with discriminating conductor 22S. In this case conductor 228 is not grounded when the lineswitch LS1 is operated upon the removal of the receiver and conductor 220 of the connector is therefore not grounded. Now when the digit 0 is .dialledy relays 301 and 303 operate in series through contacts 313, and relay 303 extends conductor 220 through contacts ofthe stilloperated slow-acting relay S and interrupter contacts 321 to stepping relay 810. Relay 303 places a ground potential on conductor 220 from the grounded conductor 223 through resistance 302 so as to operate relay 310. Relay 310 operates throughresistance 302 and locks itself to conductor 370. Then, when relay 308 falls back to start the rotary `inoif'ement, it transfers conductor 220, at its upper armature, to the rotary magnet 319 through contacts ot' relays 310 and 812. Rotary magnet 319, however, will not operate through resistance 302, andV relay 310 remains "ie of substation A is changed 'from the un-v operated, giving the calling subscriber a busy signal in the hereinbefore described manner.4 The connector is released by the calling subL scriber or by the timing device in casethe calling subscriber does not hang up.`

s Incomz'fngfcall from main circ/imagel Assume that the trunk line TL is seized'in by a connector switch of the usualtype.

Vfhen this is done, the connector places' ground on private-normal conductor 108', op-

erating relay 102 su'tlticiently to cause its up? per armature springs to move out of engagement with their resting contacts, but therelay dces not operate suiiiciently to cause the wipers to be connected up owing to the usual mechanical interlocking arrangement (not shown) between the armature ot relay 101 and the armature of relay 102.

Make-busy relay 111, which isV bridged across the trunk-line conductors through contacts of relay 115 and in series with the high resistance 110, energizes from the battery potential superimposed on the ringing circuit (not shown) so as to make the trunk line busy in the branch exchange by grounding conductor 127, no matter whether the connection is made to the trunk line during the ringing period or during the silent period. The

high resistance 110 limits the current How to such a value that the ring-cut-OE relay (not shown) will not operate. Y'

VVhenringing current is sent over the talking conductors of the trunk line TL by' the connector, it operates the ring-up relay 112 of trunk circuit TC, whose lower winding -is bridged across these conductors through the associated condenser, lower contacts of-relay 112, and the lower contacts oitl release relay' 115. Upon operating, relay 112, at its upper armature, closes a locking circuit for'itself' through contacts of relay 118. At its lower armature, it removes 'its lower winding from in bridge of the talking conductors, and, at its inner lower armature, it operates relay 113, which makes a second ground connection to conductor 127. Thel second connecl' tion to conductor 127 at the upper contacts of rela-y 113, is of utility during the ringing period,'as it maintains conductor 127 grounded uninterruptedly, even though relay 111 lutters responsive to the ringingcurrent.

113 closes a circuit for the call'lamp at the att-endants switchboard at its inner upper armature through contacts of relay 118,*and` at its lower armature it makes certain circuit changes so that the ring-cut-oft operation 'to be later performed in the calling connector will becontrolled over a loop circuit without any local grounded connectionsto the talking conductors. I

1V hen the attendant notes the lighted con- As a further result of its operation, relayyro ' as TC, thereby supplying a ground potential through relay 401 to conductor 137 and through contacts of the relay to pick up conductor 136. The vtalking circuit of the telephone isbridged across the associated talk-` ing conductors. The operator now throws thez combined release and connect key, individual to the trunk circuit TC into connect position, thereby extending ground from pick-.up conductor 136 to the lower winding of connecting relay 117. Relay 117 operates and locks itseli: through its upper winding and through the inner. upper contacts of re.- lay 120 to the common holding conductor 137. Guard relay 401, Fig. 4, new operates in series with theV upper winding of relay 117, Eig, 1, and disconnects ground4 from piel'- up conductor 136, thereby preventing the operator from operatinganother connecting relay such as 117 until such time the op.- eratorV disconnects by hanging up her receiver or releases the connection by throwing the combined-release and connect key into release position. g

The eperator restores the key after she has yoperated it momentarily, leaving relay 1.17 locked up as above mentioned. 1.Vith relay 117 operated, it will be noted that the talking circuit is split and that conductors 125l and 129 extending to the `lineswitch LS1 are connected to common conductors 133 and 134, and that the main-exchange talking conductors are connected at the upper and lower armatures of the relay to commonconductors 130 Vand 131. this time, ccnductor131 is joined to the lower main-exchange talking conductor throughv the lower armature of relay 117 and the v lower armature, operated, of relay 113.

Upon reference to Fig;y 4, it` will be noted that the commen talking conductors 130 and 131` are joined through contacts of the dial key to,` conductors133 and 134 and that the j cined talking conductors vare bridged by the impedance 402 and bythe talking bridge ofl the attendants telephone. The usual ring-v cu-tfoii operation is now performed in the calling connector responsive to current over the upper talking conductor through rela1 114, through impedance 402 and the'attencints telephone in parallel., and back over the lowertalking ccnductor. At the same time, thel usual ring-cut-o relay oi. the seizing connector responds so as to disconnect. The Vusual talking-currentsupply connections are substituted for the ringing connections.

Relays 1714, 115, and 1,16, pull up one after the other (as in the hereinbefore-described outgoing call) as relay 114 receives current in series. with the lett-hand section ot the upper talking conductor.

Relay 113 being operated 118 at its inner ylower armature, whereupon relay 1,18 operates and locks itself at its inner lower armature through the lower contacts of release relay 120. At 'armature 141, relay 118 prepares'a 1circuit for line relay 209 of the lineswitch LS2; it prepa-res a circuit or the supervisory lamp of the trunk circuit at its upper armature; and it extinguishes the call lampl at its inner upper armature by removing the shunt from around the resistance associated with armature 122 of the operated connect relay 117.

Having caused her position equipment to be connected with the trunk circuit TC in the above manner, the operator learns the desired number-'from the calling subscriber and then throws her dialfin key, shown in Fig, 4, thereby disconnectingjthe impedance 402 and the extendedV main exchange talking conductors 130and 131`fron1 the'extended branch @Xchange talking conductors 133 @c1134. leaving her telephone bridgd across conductors 133 and 134. At the upper contacts of thekey, ground is placed on Vconductor 132, closing a.V circuit through armature 141 of relay 118, lower contacts of relay 119, conductor 128, andthe lineswitch cut-olcontacts for line relay 209. Relay 209 pulls up and operates the lineswitch to seize a trunk line, the trunk line comprising conductors 226.-. 229 for example. Responsive to the operation of the lineswitch, the B. C. O, `winding 210 is energized as a holding winding through the associated contacts of the lineswitch from the ground potential placed'on conductor 126 in the trunk circuit TC through the upper contacts of relays 119 and 1 20 from the grounded conductor 127. vAs a further result of the operation of the lineswitch, the grounded conductor 126- is extended through the bank of theV lineswitch tc release trunk conductor227, thereby making the trunk busy in the master switch'hank and closing a circuit over conductor 223 and contacts of relays 307 and 309 of Ythecennector for the start relay of the master switch over` conductor 225. The start relay, being stiiljly adjusted-Y energizing' over conductors 219 and 221 through the attendants telephone which is now connectedto the incoming talking conductors 125 and 129` as above pointed out@ 1n case diiiiculty is experienced in preventing the start relay fromenergizing, its .Circuit may be altered to include an .added'pair of normally closed contacts on delay relay 201.

The operator now dialsthedigits in the desired number, whereupon the conductor is set on the line of the called subscriber, the

line of substation A for example, in which case the substation A is signalled by ringing current, after which the lineswitch LS1 is operated through wiper 324 of the connector and through terminal 253 when the ringcut-oif relay 309 operates. Ground is placed on cut-ofil conductor 222 at the inner upper contacts of ring-cubed relay 309 to operate relay 218, Fig. 2, through the cut-off wiper of the master switch, but battery-feed relay 217 is not operated at this time owing to the fact that the resistance 320 is inserted into the circuit owing to the previous operation of relay 301 ovei conductor 220 from the batl tery connection supplied at the contacts of the lineswitch LS2 for that purpose. Relay 301 is locked at this time through its own contact and the inner upper contacts or relay 306 to the associated resistance, and its initial circuit is opened. The result of this is that the battery supply for talking purposes comes to the called substation A from the main exchange rather than from the branch exchange, this being in accordance with well- '1 established practice.

In case the operator, during the setting up of a local connection, discovers that she has made a mistake in dialling, or, for any other reason, wishes to release the connector and start over again, she presses the releasein key, Fig. 4, opening the line circuit at the lower contacts of the key and grounding coir i ductor 135 at the upper contacts of the key so as to operate the release-in relay 119, Fig. l, through armature 12.3 of relay117. Relay 119 disconnects ground from the lineswitch private normal conductor 126 at itsvvupper armature and opens a point in the line relay circuit at its lower armature. YVhen the key is released, the restored lineswitch ree-peintes and the connector is prepared for operation as hereinbefore explained.

Having dialled the local number, the oper` Aator restores the dial-in key, reconnecting the two sections of the talking circuit together so that the subscribers may converse.

After listening in, either before or after restoring the dial-in key, to make sure thatthe desired subscriber has responded, the operator replaces the receiver on her telephone,

opening the locking circuit of the upper winding of connecting relay 117 of the trunk circuit TC. Relay 117 falls back and connects the two talking sections together and er hangs up. This bridge is effective, in case the operator hangs up right after dialling, to hold the connector inthe branch exchange operated until it is released responsive to the operation of the timing device or to the response ofthe called subscriber. Relay 118 remains locked up through its own inner lower contacts and the lower contacts of relay 120. f When the called subscriber replaces his receiver at the end of the conversation, line relay 114 falls back and opens the cir-cuit of release relay 115, which relay falls back and lights the supervisory lamp through contacts of relay 118. When the calling subscriber hangs up, the connector in use releases (unless it is of the release-by-lastpa'rty type),

permitting relay 102 to restore and connect up line relay 101 of the lineswitch. Line relay 101 does not operate at this time, even though relay 111 is bridged across the talking conductor of the trunk line owing to the fact that there is no operating ground potential connected to the lower trunk line conductor.

When the operator n otes the lighted conrelease-connect key in release position, operating relay7 120, bringing about the release of relay 118. rlhe lineswitches LS2 and LS1 rei lease and relay 218 falls back responsive to the removal of ground potential from the conductor 126 at the upper contact of relay 120. The entire connection is now released and the apparatus involved therein is in-readin'ess to be used in setting up further connections.

Setting up a tail-todae? connect-0n with such trunk is caused to operate to connect such trunk with the calling line. Assum` ing that the number of information trunk #1 is dialled, and that this trunk isidle at the time and is accordingly seized, the call lamp associated therewith is operated over the priV4 vate normal conductor in parallel with the bridge-cut-oft' winding of the lineswitch, corresponding to winding 204 ofthe lineswitch LS1. 1 Upon` noting the lighted condition 'of -the call lamp, the operator respondsby momentarily operating the answering key associated with relay 403, whereupon relay 403 operates throughthe switchhook contacts' ofthe attendant telephone and through contacts of relay 401 and locks itself in series with the said relay. Relay 403 disconnects the private normal conductor from' the call lamp and connects it to ground instead, although theY latter is not essential as the connection is being held up by the battery-feed relay of the trunk inuse, corresponding to battery-feed relay 217, Fig. 2. At its upper and lower contacts, relay 403 connects the conductors of the information trunk to the operators talking circuit, enabling the attendant to converse with the calling subscriber. Upon being informed as to the calling s'ubscribers desires, the operator replaces the receiver on the associated telephone, whereupon relay 403 falls back. The connection set up from the line of substation A is released when the calling subscriber hangs'up.

In order to complete the connection .to the desired main-exchange subscriber, the operator removes the receiver from her telephone and observes the busy lamps associated with the various trunk circuits such as the trunk circuit TC', and throws the connect key of an idle one, the one of trunk circuit TC for es ample, whereupon relays 117 and 118 operate as before described, and relay 117 connects the two sections, respectively, of the trunk to the operatorsset over conductors 130 and 131, and'conductors 133 and 134. When the bridge across conductors 130 and 131 is placedacross the trunk conductors extending to the mainexch'ange, there is a ground potential encountered by conductor 131` through contacts of the operated relay 117, and contacts of the unoperated relays 113 and 116. This ground potential is transmitted over conductor 131 and through imi pedance 402, Fig. 4, to the upper trunk conductor'over conductor 130, to operate the line relay 101 of the lineswitoh LS in the main exchange. Relays 114 and 115 are operated, as before.

through the lower winding of the line relay of the selector is placed on the lower talking conductor of the trunk line TL operating relay116 through its own inner lower contacts, contacts of relay 113, and-armature 142 o of relay 11S. Upon operating, relay 116 locks itself energized independent of the lower talking conductor and joinsthe lower talking'conduct-or of the trunk line TL to the `lower left-hand talking conductor 129, at the Sametime removing the local ground connection fromv the lower talking conductor.

In order to be able to operate the mainexehange switches to set up the connection to .the called line, the operator throws her dialscriber responds to the call,'the attendant in- When an adle selector is seized by the lineswitch LS, ground potential forms him that the subscriber at substation A desired to converse with him and requests him to waita moment while she completes the connection.

The operator thereupon releases her dialout key, throws her dial-in key, causing the lineswitch LS2 to operate in the manner described heretofore, and dia-ls the number of the subscriber at substation A, whereupon the connection is extended to his line in the manner hereinbefore described. It will be noted that the impedance winding 402 associated with the dial key, Fig. 4, is placed across conductors 130 and 131 so as to hold the mainexchange connection while the operator is dialling the local number of the subscriber at substation A.

From this point on, the connection is handled in the manner describedv hereinbefore in connection with the description of the handling of an incoming call.

The 00de @all equipment In explanation of the code call equipment shown in Fig. 5, it may be pointed out that in a private establishment it often happens that there are a number of employees who are called quite frequently and whose work f scriber removes his receiver and dia-ls the code-call number 30, followed by the particular code digit assigned to the person in question. Assuming thatthe calling subscriber is the one at substation A, Fig. 2, the removal of the receiver results in the operation of lineswitch LS1 to seize a trunk line, the one shown in the drawing for example. The common connector shown in Fig. 3 is prepared i for operation in the usual manner; is raised up with the third level of bank contacts when the first digit 3 is dialled; and is rotated into engagement with the tenth set of bank contacts in the third level, Fig. 5, when the second digit 0 is dialled. The contacts associated with resistance 320 and labelledv 30 and 00 are separated at this time by the usual cam arrangement on the shaft ofthe switch, thereby inserting' the associated resistance 320 into circuit with the switching conductor 222 so as to prevent the subsequent operation of the battery feed relay 217. Assuming that the code call number is idle at this time, switching relay 312 of the co1mecl tor pulls' up in the usual manner over test wiper 323 through the bridge-cut-off windingV In order to transmit the calls to pulling up of relay 312 the usual locking circuit is closed for the lower windingthereof from conductor 370 and a parallel circuit is now closed for the lower winding of ringcut-oii relay 309 through the associated cam springs labelled 30 and 00. Relay 309 operates and places a ground potential on wiper 324 thereby closing a circuit through the said wiper and the banlrcontacts on which it is standing for the pull-down winding of the lineswitch LS'c, operating the lineswitch LS4: to extend a connection to the same trunk line with which the lineswitch LS1 is connected. Cut-ofi" relay 218, Fig. 2, is operated in the usual manner, but the marginal relay 217 is not operated owing to the fact that resistance 320 is inserted in circuit at this time by the associated cam springs as above pointed out.

Line relay 501 of the code selector now operates over the associated talking conductors and the corresponding conductors of the trunk line in use by the lineswitches LSA and LS1 and over the line of substation A and closes a circuit for the associated release relay 502 which operates and places ground on the associated release trunk and private normal conductor so as to hold up the two lineswitches and cut-off relay 218. This ground potential is placed on this conductor prior to the removal of ground potential therefrom through wiper 323 of the connector. Relay 502 also prepares the code selector for operation at its lower armature.

Then the calling subscriber dials the code digit assigned to the particular desired person, line relay 501 falls back a corresponding number of times and operates the rotary magnet of the code selector each time it falls back. Relay 503 operatesin parallel with the rotary magnet when the first impulse is received, and, being slow-acting, remains operated through the series of impulses. lVhen relay 503 falls back at the end of the digit it closes a circuit through contacts of relay 504 and through off-normal contacts O. N. for starting the motor of the code generator and for supplying a ground potential through the cam contacts of the generator to the various bank contacts. The motor now operates the cam contacts to generate their respective codes in the usual manner and the selected code is supplied through wiper 507 to the code bells through the contacts on which wiper 507 is standing.

Assuming that the person called fails to respond, the calling subscriber replaces his receiver whereupon line relay 501 falls back followed shortly by the deenergization of relay 502 to permit the release of the connection when it removes ground from the associated release-trunk conductor.

lVhen thed-esired person hears his code being broadcast throughout the plant, he

proceeds te the nearest telephone,

removing the receiver and obtaining control of the connector in the usual manner through the operation of the lineswitch on the telephone in use, dials the code-answering number 39, whereupon the connector connects with the line-switch LS3. The switching relay 312 of the.L connector is operated at this time in series with the B. C. O. winding of vLS3, and connects up Wipers 322-a'nd 325,

ing ground from the start conductor of the code generator as well as operating the release magnet to restore the wiper 507 to normal. The circuit of the release magnet is opened at the off-normal contacts of the switch when the wiper 507 reaches its normal position.

In the connector, ring-cut-o relay 309 energizes at thersame time that relay 504, Fig. 5, energizes and it locks itself at its inner lower armature and performs the functions hereinbefore described, including the grounding of the cut-off conductor 222 to 'cause the cut-olf and battery-feed relays of the trunk in use, corresponding to relays 218 and 217, Fig. 2, to operate to isolate the trunk and to connect up a source of transmitter-supply current.

The conversation now takes place between the-line of substation A and the line used by the called subscriber in answering the code call, the switching apparatus included in the connection being the lineswitch LS1 which is plunged in on the trunk comprising conductors 226-229, the lineswitch LS4 which is plunged on the same trunk, the lineswitch LS3, and the line'switch of the answering line, which is plunged in on the same trunk as the lineswitch LS3.

After the conversation is over, the lineswitch LS3 and the lineswitch of the answering line are both released when the an- EL uc to its normal position. Relay 502 also un- .gronnds the associated release trunk conductor, permitting the lineswitches LS4 andv LS1 to restore, and permitting the cut-ofi' relay 218, Fig. 2, to fall back.

The branch exchange has been described Vhereinbefore as of one V10G-line capacity. The circuits of the connector shown 1n Fig. 3,

however, have been arranged so that they will function in connection with a modified bank arrangement when a private automatic exchange of this character is arranged for a capacity not to exceed fifty lines.

vVhe'n the exchange is arranged to have an `ultimate capacity of one hundred lines the section may be installed, in which case the twol wiper setsare adjustedcloser together, so that when `the bottom set isV opposite the first bank level the top set is opposite the sixth level. The bottom'lwiper set uses the lower half of the bank while the upper wiper setl uses the upper half of the bank. n

In this case only live lirstfdigits are required and it is therefore convenient to assign the digits 2 to 6 rather than the digits 1 to 5, on account of the fact that the digit 1 is often undesirable owing to the danger of preliminary impulses and faulty line conditions giving the 4effect lof the dialling of the digit 1 before the dialling operation starts, this condition being well known and generally understood. The wiper sets are therefore adjusted so that they will come Ophosite the levels 1 and 6 of the bank when the digit 2 is dialled and will not extend a connection to the talking conductors of any called line if raised only one step. The reason is that the wipers 322 and 325 of the connector are the wipers of the lower set and do not engage with any bankcontacts, while the wipers 323 andl 32d ofthe upper setfengage with bank contacts in the fifth level, whichV is the upper levely of the line contactsand are therefore not -connected up, being left dead, as are the O-level contacts of wipers 322 and 325 in Fig. 3. Y In casegthe arrangement were usedin connection .withoutgoing trunk lines that required the line contacts of the bank to be connected up, the wipers 322, and 325 would then be placed in the upper set and wipers 323 and 324 would form the lower set. In

this case, wiper 323 would not engage a bank contact `*when the lirst digit is 17 and switching relay 312 would not operate to connect up wipers 322 and 325.

For many years, it has been standard practice to assign .the digit to trunk lines outgoing from a private` automatic exchange, for which reason it is desirable to assign the digit 0 even in the modified 50-line private automatic exchange above described, even though the dialling of the digit 6 is suliicient to cause the seizure of onev of these trunk lines. In Fig. 3, it will be `noted that the circuit of vertical magnet 317 includes con-k .tacts of relay 303 which is operated through thel associated 0 level shaft springs 313. When the 10U-line vprivate automatic exchange is used, the lower contacts of relay 303 perform no useful function, but, when the private automatic exchange, modified as above outlined, is used, the springs 313 are jarranged to operate when the shaft is raised six steps, whereupon relay 303 operates and opens the circuit of the vertical magnet thereby preventingv the -wipers from advancing above the outgoing trunk level.

Yvlhat is claimed is:

1. In a telephone system wherein each of a plurality of lines is provided with a single individual' line switch, trunk lines accessible to such line switches, means controlled over a calling line for causing the line switch individual to such calling line to seize an idle one ,ofvsaid tru-nk lines, a-nd means including directive switching mechanism normally connected ,multiple to each of saidr trunk lines controlled over the cal-ling line for causing the line switch individual to a desired'called line to complete a talking connection between the calling and the called lines by seizing the same trunk line previously seized by the line switch individual to the calling line. l

2.*In a telephone "system wherein the line switches individual, respectively, to subscribers lines are presided over by a single master switch and have access i-n common to a group of trunk lines, means control-led over any trunk line after such trunk line has been Seized lby a line switch Aof a calling line to complete -a'` talking connection between such calling linel and a desired called one of said lines., by causing the line switch: individual tgosaidcalled line-to seize-the same trunk` line previously seized by the line switch of the calling liner.v

3. Ingfa: telephone 'system wherein the line switchesindividual, respectively, to the lines entering the exchange are presided over by a common master switch which causes them all to normally prcselect singleidle one of a plurality of trunk-lines accessible thereto in common, means for maintaining the master switch and the idle line switches at rest vwhen a line switch is `operated over a calling line to seize the preselected trunk, and means conlll() trolled over the calling line and the seized trunl line for completing a talking connection between the calling line anl a. desired called one of said lines by operating the switch ot the called line to seize the s` trunk line.

4. In a telephone system wherein the line switches individual, respectively, to the lines entering the exchange are presided over by a common master switch which causes them all to normally preselect a single ille one ot' a plurality of trunk lines accessible thereto in common, means for maintaining the master switch and the idle l' ie switches at rest when a line switch is Voperated over a calling line to seize the preselected trunk, means controlled Aover the calling line and the seized trunk line tor completing a talking connection between the calling line and a desired called one of said lines by operating the line switch ot the cal ed line to seize the same trunk line, and meins for thereupon operating the master switch to cause the remaining idle line switches to preselect anotner idle trunl line.

5. In a telephone system, a line having a line switch individual thereto, a 'plurality ot trunk lines'accessible to said line switch, and means for operating said line switch to seize a preselected idle one of said trunk lines to initiate a call outgoing trom'said line and for operating said line switch to seize particular one of said trunk lines to complete a'call incoming to said line.l

6. In a telephone system wherein each line entering a central exchange is provided with a line switch individual thereto, a plurality of trunks accessible to said line switches in common, switching mechanism in the e5;- change, means for operating any line switch either yer the line to which it is indi f'idual or through the said switching mechanism in the exchange to seize one et said trunk lines, and a master switch common to all aid line sv tches for predetermining the trunlclines with which the line switches connect so that the lines of operated'line switches are telephonically connected together in pairs.

In a telephone system wherein switching mechanism is provided tor connecting any one of a number of subscribers lines to any one of a plurality of trunk lines, an automaticV connector switch having access to all said lines and normally in association with said trunk lines in common, means foroperating said connector switch over a calling line and-over one ot said trunk lines to effect a connection between the callingline and another line through said trunk line and independent of the connector switch, and Vmeans for thereupon isolating said trunk line from said connector switch while leaving the other trunk lines in association therewith.

8. In a telephone systeinwherein acht rality et trunk linesniay be by switching mechanism to any one cfa plurality of subscribers lines, a single automatic connector switch normally connected to each of said trunk lines, means tor operating said connector switch overacalling line and over one ot saidtrunh lines to complete a connection, and means for thereupon disconnecting trunk line from the connector switch, leaving the remaining trunk lines connected thereto.

, 9. In combination, a plurality of telephone lines, an automatic connector switch'having access thereto, a plurality of trunk lines each normally connected to sad connector switch, and non-numerical switching means for connecting any calling one ot the first-mentioned lines to any one of said trunk lines.

l0. In combination, a plurality of telephone lines, an automatic connector switch having access thereto, a plurality ottrunlr lines each normally connected to .said connector switch, and non-numerical switching means operative to connect any calling or any called one of said lines to any one of said trunk lines. l

l1. In a telephone system, an automatic connector switch, a trunk' line normally connected thereto, means jor extending a calling line to said trunkY line', means controlled'rover the calling line tor-,operating said connector switch into association with a called line, ns for completing a connection between the calling and called lines over a circuit path independent of the connector, a cut-od relay individual to said trunk line, and means effective upon the sa-idcompletion of the connection for operating said cut-oli" relay to isolate `vsaid 'trunk line from said connector switch. Y Y' f 12.111 a telephone system, an automatic connector switch, a trunk line normally connected thereto, means for extending a calling line to said trunk line, current-supply con nections in said connector switch for supplying transmitter current Yto theV calling line, means cont-rolled over the calling line for operating said connector switch into association with a called line, means for completing a connection between the calling and called lines over a circuit path independent of the connector, a cut-ott' relay individual to said trunl'line, means effective upon the said completion of the connection for operating said cut off relay to isolate said trunk line from said connector switch, a current supply relay in said trunk line, and means for connecting such relay to the trunk line to supply transmitter current atter the trunk line has been disconnected from the connector.

13. In a telephone system, an automatic connector switch, a trunk line normally connected thereto, inea-ns for extending a calling line to said trunlz line, means controlled over the calling line for operating said con-

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