US2056752A - Automatic telephone system - Google Patents

Description

Oct. 6, 1936. J. H. Voss AUTOMATIC TELEPHONE SYSTEM Filed Dec. 29, 1933 7 Sheets-Sheet l Oct. 6, 1936. J. H. Voss AUTOMATIC TELEPHONE SYSTEM 7 Sheets-Sheet 2 Filed Dec. 29,

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Patented Oct. 6, 1936 UNITED STATES PATENT OFFICE'.

AUTOMATIC TELEPHONE SYSTEM Application December 29, 1933, Serial No. 704,465

27 Claims. (Ci. 179-27) This invention relates to telephone systems in general, but is concerned more particularly with small systems of the type commonly known as private automatic exchanges.

Private automatic exchanges are as a rule privately owned by individuals or corporations and are installed in factories or other establishments for providing local service between a small number of local telephone lines and for establishing l connections over trunk lines to the main ofce of the telephone companys network.

The main object of the invention is to provide an improved private automatic exchange system of the type shown in Patent No. 1,888,337, issued l Novemr 22, 1932, to John H. Voss, by simplifying and reducing the cost thereof without sacrilcing any of the desirable operating features.

The three push-buttons and other auxiliary apparatus mounted in the base of the telephone 2O shown in the aforesaid patent is eliminated and replaced in accordance with the present invention by a single push-button mounted either in a standard telephone itself or on the accompanying bell box.

25 Another feature which greatly reduces the cost of this system over the system shown in the aforesaid patent is that in the old system in its simplest form six conductors were required between the telephones and the exchange equip- 30 ment while in the present case only two conductors are required.

Other features of the invention relate to the improved method of answering incoming trunk calls, of transferring trunk calls from one sub- 35 scriber to another, and of holding and guarding such trunk lines.

Another feature of the invention relates to an improved attendants cabinet which may be cut into service when desired to intercept all incom- 40 ing trunk calls.

Other features of the invention relate mostly to circuit improvements which will be apparent from the following detail description of the drawings comprising Figs. 1 to 7, inclusive, which 45 show by means of the usual circuit diagrams a suflicient amount of apparatus to enable the in vention to be described and understood.

Fig. 1 illustrates in its lower lefthand corner a local subscribers telephone S equipped with a 50 push-button PB by means of which the subscriber thereat can make and receive trunk calls, can transfer trunk calls, and can hold a trunk call while making or receiving local calls. Two line circuits, one for information line #0L and 55 the other for line #03, are shown near the center y of Fig. 1.

The wipers and motor magnet of one of the local finders are shown at the right of Fig. l, together with the multiple connections to the other local and trunk finders and connectors. 5

Fig. 2 shows a group of finder-connector relays for controlling the operation of one of the finder and connector switch links, the wipers of which are shown in Figs. 1 and 3, respectively.

Fig. 3 shows the connector wipers of this finder i0 connector link, a subscribers line and substation S', and a trunk distributor together with its associated relays.

Fig. 4 at the left shows a finder connector distributor and its associated relays and at the right shows a transfer distributor and its associated relays.

Fig. 5 at the left shows the equipment at the attendants cabinet and at the right the wipers and motor magnet of one of the trunk nders together with its multiple connections to the connector and local and trunk finders.

Figs. 6 and 7 show the relays of one of the two-way trunks, the associated nder and wipers being shown in Fig. 5. V

Referring now to Fig. 1 in detail, all local subscribers lines, Such as S, are equipped with a standard well-known automatic telephone set comprising a calling device CD, a receiver R, transmitter T, switchhook springs SH, ringers RB, and an induction coil. Non-restricted subscribers entitled to make and receive trunk calls as well as local calls have a push-button such as PB mounted in the base of the telephone or on the associated ringer box. Semi-restricted subscribers entitled to answer trunk calls but not originate trunk calls are similarly provided with a push-button, but such subscribers lines are connected to battery through a resistance, such as Z, over a conductor, such as 29, to its corresponding bank contact accessible to iinder wiper |52.

Restricted subscribers are not provided witha push-button and can only make and receive local calls. Each subscribers line extends to a line circuit comprising a two-step line and a cut-olf relay, such as relay |03. The conductors extending from the subscribers line circuits terminate in the banksof both the local and trunk iinders in the connector banks.

The finder switches are mechanically similar to the well-known rotary lineswitch having no normal position, while the circuits thereof have been altered in accordance with the present invention.

mechanically similar to the finders, but instead of automatically hunting for a marked potential as the finder does, the connector is directlvely controlled from normal position by impulses.

The trunk distributor shown in Fig. 4 is mechanically similar to the finders and automatically hunts for an idle trunk line or a. particular trunk line in use dependent upon whether end to cause such armature to vibrate when the relay releases the armature. Relay 410 in the transfer distributor has a spring 41| with a weight 412 which causes spring 41| to vibrate for a predetermined period when the relay 410 is first energized.

Referring now to the attendants equipment shown in Fig. 5, the attendants telephone circuit is mounted on a base and comprises a calling device CD, a handset HS comprising a transmitter and receiver, monophone springs MS which are closed when the handset HS is removed from the cradle, an induction coil IC, and ringers RB. 'Ihe information key, the hold key, the transfer key, the turn signal key SK, the two release and trunk answering keys, (only one of which is shown), and two supervisory lamps, such as SL, are mounted on top of the base alongside of the attendants telephone. The relays 5|6 and 500 to 540, inclusive, and the buzzer B are mounted inside the base. In case a second trunk answer key is provided then another set of relays, such as relays 500 to 540 are also provided since such relays are individual to a trunk answer key. The buzzer B is used when the `attendant answers all incoming trunk calls while the trunk signals are used when any non-restricted local line may answer incoming trunk calls. There are as many common trunk signals placed throughout the establishment as required to enable the local subscribers to determine when an incoming trunk call is to be answered.

In Figs. 6 and 7, one of a number oi two-way trunk circuits is shown connecting the local private exchange with one of the telephone companys exchanges which may be either manual or automatic. When the trunk circuit, shown in Fig. 7 extends to an automatic exchange, a dotted strap shorting the winding of relay 120 is provided. while this strap is cut when the trunk circuit extends to a manual exchange.

Having described the equipment and apparatus, a detailed description of the operation will now be given. Briefly, local calls are completed in the following manner: The local calling party removes his receiver and, after hearing dial tone, dials the number of the desired station. If the called line is not busy, the called f station will be rung automatically and inter- The connector switch shown in Fig. 3 is subscriber S' shown in Fig. 4. Responsive to the removal of the receiver, switchhook spring SH closes a circuit for energizing the combined line and cut-off two-step relay |03 in its rst step as follows: from ground by way of armature |08, conductor |02, lower winding of the induction coil, transmitter T, through the impulse springs of the calling 4device CDthrough the upper switchhook springs to conductor and thence by way of armature |04 through the upper resistance winding and through the lower winding of two-step relay |03 to battery. Due to the resistance in the upper winding of relay |03, this relay is energized in its rst step to close only armatures and |01. At armature |05 relay |03 marks the line S as calling in the bank of the local finder by connecting. the battery through the lower winding of relay |03 to the fifteenth bank contact accessible to finder wiper |53.

At armature |01, relay |03 grounds the finder start conductor 9 to complete a circuit for the start relay 420 in the finder connector distributor shown in Fig. 4 as follows: from ground by way of armature |06 in its normal position, armature |01 in operated position, common finder start conductor 9, through the winding of slowto-operate start relay 420, armature 422, interrupter springs 404 and through the winding of the distributor motor magnet 405 to battery. Motor magnet 405 is marginal and will not energize in series with the winding of relay 420 or in series with resistance 423. At armature 422 relay 420 removes the obvious short circuit from around resistance 423 for a purpose to be more fully described hereinafter, and at armature 42| completes an obvious circuit for energizing relay 400. At armature 40| relay 400 prepares a point in the circuit for the finder test circuit; at armature 402 and its working contact completes the circuit for energizing slow-to-release relay 4|0; and at armature 403 completes the circuit for energizing the finder motor magnet |68 as follows: from ground by way of armature 205, armature 23| and resting contact, conductor 2| 5, bank contact and Wiper 4|6, armature 403, wiper 4|5 and engaged bank contact, conductor |61, and through the winding of motor magnet |68 to battery.

Magnet |68, upon energizing, positions its pawl preparatory to stepping the wipers of the local finder and at springs |69 completes the circuit for energizing the combined line, stepping and test relay 230 as follows: from ground by way of springs |69, conductor |66, and through the upper winding of relay 230 to bat-y tery. Relay 230, upon energizing, at armature 23| opens the previously traced circuit for motor magnet |68, whereupon motor magnet |68 deenergizes to advance the wipers of the local finder into engagement with their next bank contacts. The deenergization of motor magnet |68 also opens the circuit of relay 230 at springs |69, with the result that relay 230 now deenergizes. The deenergization of relay 230 again completes the previously traced circuit for motor magnet |68 and motor magnet |68 again completes the circuit for energizing relay 230 to cause the latter relay to open the circuit to motor magnet |68 and cause the latter Ato step the wipers into engagement with their next bank contacts. In the same manner as just described magnet 68 and relay 230 operate until test wiper |53 encounters a calling potential of a calling line.

When test wiper |53 encountersr a bank contributor motor magnet 405 as follows:

' nector links.

circuit may be traced as follows: from ground through the lower winding of relay 230, through the normally closed springs controlled by arma- ,ture 226, lower winding of relay 220, conductor 220, bank contact and wiper 4|2, armature 40|, wiper 4|3' and engaged bank contact, conductor |03, test wiper |53 in engagement with the bank contact terminating the test conductor of subscriber S', conductor armature |05, and through the lower Winding of relay |03 to battery. Relay 230 is maintained energized over this circuit and relay 220, upon energizing, at armature 22| completes a circuit for energizing slow-to-release relay 2|0 by way of armature 23| and its working contact; at armature 222 prepares a point in the circuit for energizing relay 280; at armature 223 prepares a point in the circuit for energizing series relay 210; at armature 244 connects ground to the guard lead 221 to make this nder connector link busy; at armature 225 connects ground to conductor |63 to maintain relay |03 in energized position and to busy the calling line in the banks of the finders; and at armature 226 connects the lower Winding of relay 230 to the positive talking conductor and at the normally closed springs controlled by armature 226 opens a point-in its own circuit through its lower winding.

Slow-to-release relay 2|0, upon energizing, at armature 2|| completes the circuit for connecting relay 230 across the calling subscribers loop; at armature 2|2 completes a circuit through the upper winding of relay 220 to maintain this relay in energized position; at armature 2|3 prepares a point in the connector test circuit; and at armature 2|4 prepares a point in the impulsing circuit to the connector motor magnet 351. Relay 230 is now maintained over the calling loop over the following circuit: from ground through the lower winding of relay 230, armature 226, armature 20B, conductor |65, wiper |55, conductor |02 over the calling subscribers loop to conductor |0|, wiper |5I, conductor |0l,`armatures 20| and 2| I, and through the upper winding of relay 230 to battery. Line-cut-o relay |03 energizes over the previously traced circuit to operate armatures |04, |06 and |08 in their second step. At armatures |04 and |08 relay |03 disconnects the windings of relay |03 and ground from the subscribers line conductors |0| and |02 and at armature |06 disconnects ground from common start conductor 9.

When the start conductor 9 is no longer grounded, relay 420 deenergizes and at armature 42| opens the circuit to relay-400. At armature 422 relay 420 again short circuits the resistance 423 to complete a circuit for energizing the disfrom ground by way of the grounded start conductor 221, bankY contacts and wiper 4|4, armature 422, interrupter springs 404 and through the winding of motor magnet 405 to battery. This circuit is the circuit by means of which the finder connector distributor preselects idle nder con- Motor magnet 405 is intermittently energized and deenergized over this circuit as long as wiper 4|4 encounters a grounded bank contact. Relay 400, upon deenergizing, at armature 40| opens a point in the finder test circuit; at armature 403 opens a point in the circuit to the nder motor magnet |68; at armatheir fifth or stop position contact.

ture 402 and its working contacts. opens the cir-v cuit oi.' slow-to-release Arelay 4|0; and at its resting contact completes a circuit by'way of armature 4|| for maintaining the motor magnet 405 in energized position during the interval the slow-to-release relay 4|0 is energized. MotorV magnet 405, upon energizing, Vpositions its pawl preparatory to stepping the wipers of the'distributor and at interrupter springs 404 opens they preselecting circuit previously traced. Slow-torelease relay 4|0 deenergizes after an interval and at armature 4|| opens the circuit vof motor magnet 405 whereupon the motor magnet deenergizes and advances the wipers one step into engagement with the bank contact associated with the next nder connector link.

In case this finder connector link is busy there will be ground on the guard conductor corresponding to conductor 221, with the result that the preselecting circuit tomotor magnet 405 is completed to cause the wipers to be set into engagement with the bank contact of the next finder connector link. Motor magnet 405 is intermittently operated over its preselecting circuit until wiper 4|4 no longer encounters a grounded guard conductor, thereby indicating an idle link. When wiper 4|4 loses ground no circuit is completed for magnet 405 and therefore the wipers of the distributor stop in engagement with the bank contact associated-with an idle finder connector link.

Incase all of the finder connector links are busy then each busy link has removed its individual ground from the common lead 2|6 to lprovide a stop position for the wipers of the distributor to prevent their continuous operation during this busy condition. 'Ihis stop position is shown as the last or fifth position accessible to test wiper 4|4 and such position is normally grounded as long as any one of the iinder connector links is idle. The circuit for grounding this position extends from ground by way of armature 204, armature 2|3 and resting contact, conductor 2|0, to the stop position or fth bank contact accessible to wiper 4|4. This stop position is therefore grounded as long as any one of the links is idle and ground is removed therefrom only when all of the links are busy to provide a stop position for the wipers of the distributor.

Considering now the case in which all of the nder connector links are busy, then the wipers of the distributor would be in engagement with In case a call is initiated at this time start relay 420 is energized over the following circuit: from ground on the finder start conductor 9, through the winding of relay 420', armature 422, interrupter springs 404, and through the winding of motor magnet 405 to battery. Relay 420 alone energizes over this circuit; at armature 42| it completes a circuit for relay 400; and at armature 422 lremoves the short from around resistance 423, thereby inserting this resistance in series with relayl 420. Relay 420 is therefore maintained over the circuit including the resistance 423 as long as the iinder start conductor 9 is grounded.

As soon as one of the iinder connector links becomes idle then the busy common conductor 2| 6 is grounded, with the result that relay 420 is short circuited from ground on the busy common conductor 2|6 extending by way of Wiper 4|4 and ground on the start conductor 9. Magnet 405 is marginal and will not energize in series with resistance 423 from grounded start conductor. When relay 420 deenergizes, said relay at armature 422 completes the circuit for energizing magnet 405 over the following circiit: from grounded busy common conductor 2|6, wiper 4| 4, armature 422, interrupter springs 404, and through the winding of magnet 405 to battery. Magnet 405 intermittently operates until test wiper 4I4 nds the idle connector link.

Considering now the case in which all of the finder connector links are busy and the distributor wipers are in stopping position, it will now be assumedthat one of the links becomes idle at a time when no call is being made. In this case as soonas the busy common conductor 2|6 is grounded the circuit for energizing motor magnet 405 is completed by way of wiper 4|4 and armature 422. Magnet 405 operates in the same manner as previously described until the wiper 4|4 flnds the idle connector link.

Returning now to the link circuit at a time when the calling line is found and relays 220 and 2I0 have been operated, dial tone is connected by the operation of these relays to the calling subscribers line as follows: from dial tone conductor 390, twenty-fifth bank contact or normal position of connector wiper 356 and said wiper, conductor 239, resting contact and armature-253, the tone condenser TC, lower talking condenser, and from thence over the calling substation loop as previously traced for relay 230. When the calling subscriber hears the wellknown dial tone, such subscriber will dial the number assigned to the desired subscriber, which number may comprise one, two, or three digits. Assuming now that subscriber S desires to be connected to subscriber S' shown in Fig. 3, and since the number of subscribers S is 6, the calling subscriber will thereupon dial the digit 6". In response to the operation of the calling device CD in accordance with the digit 6 the circuit to line relay 230 is interrupted six times, thereby causing the line relay 230 to be deenergized a corresponding number of times. Relay 230 thereupon deenergizes for each impulse and at armature 23| and its resting contact temporarily opens the circuit to slow-to-release rlay 2 0, which, however, is slow to deenergize and is therefore maintained energibed during the impulsing period. At armature 23| and resting contact, relay 230 transmits an impulse to the connector motor magnet 351 upon each deenergization. This circuit may be traced as follows: from ground by way of armature 205, armature 23| and resting contact, armature 2|4, armature 252, armature 296, conductor 235, and through the winding of relay 351 to battery. A branch of this circuit extends from armature 296 by way of armature 223 and the lower winding of series relay 210 to battery for energizing the latter relay during the impulsing period.y

Connector motor magnet 351, upon energizing, positions its pawl preparatory to stepping the wipers of the connector. Relay 210, upon energizing, at armature 21| opens a point in the circuit to relay 200; at armature 212 opens a point in the circuit to switching relay 290, and also prepares a point in the circuit for combined busy and back bridge relay 250; at armature 213 short circuits its upper winding to make this relay slow-to-release so that it will be maintained in energized position during the impulsing period; and at armature 214 closes a shunt around armature 252 to prevent the operation of busy relay from opening the impulsing circuit to the motor magnet 351. When relay 230 energizes after each impulse, the circuit to connector motor magnet 351 is opened, with the result that thisA magnet steps the wipers of the connector one step for each deenergization. In response to the six impulses transmitted thereto, magnet 351 steps the wipers of the connector from in engagement with their normal bank contacts into engagement` with ,their sixth bank contacts, or the contacts terminating the called line.

The operation of the finder connector at this time depends upon whether the called line is busy or idle. In case the called line is busy, then ground will be encountered by test wiper 353, with the result that` the combined busy relay and back-bridge relay 250 is energized over the following circuit: from ground on the busy test conductor of the called line, sixth bank contact engaged by wiper 353, conductor 234, armature 212 and working contact, armature 295, resistance 254, and through the upper winding of relay 250 to battery. At armature 25| relay 250 opens a point in the testing circuit extending through the upper winding of switching relay 290 and at its working contact prepares a locking circuit for busy relay 250. At armature 252 relay 250 opens a point in the impulsing circuit to magnet 351 and at armature 253 connects the busy tone to the calling line. Shortly after the impulses cease series relay 210 deenergizes and at the normally closed springs controlled by armature 212 completes the locking circuit for busy relay 250 as follows: from ground by way of armature 204, armature 2|3 and working contact, armature 25| and working contact, through the normally closed springs controlled by armature 212, armature 295, resistance 254, and through the upper winding of busy relay 250 to battery. The busy tone is transmitted to the calling subscriber over the following circuit: from a busy tone, armature 291, working contact and armature 253, tone condenser TC, lower talking condenser, and thence over the heavy talking conductors to the calling line.

When the calling subscriber hears the busy tone, such subscriber will replace his receiver to cause the release of the established connection in a manner to be more fully described hereinafter.

Assuming now that the called line was idle instead of busy, then no circuit is completed for busy relay 250 because the test conductor of the called line is not grounded. Series relay 210 deenergizes shortly after the impulsing period and at armature 212 completes the circuit for energizing the switching relay 290 in series with line-cut-off relay 303 of the called line as follows: from ground by way of armature 204, armature 2|3 and working contact, armature 25| and resting contact, through the upper winding of switching relay 290, resting contact and armature 212, conductor 234, test wiper 353 in engagement with its sixth bank contact, conductor 3|0, and through the lower winding of two-step, line, andcut-oi relay 303 to battery.

Relay 303 energizes over the above-traced circuit and operates its armatures in their second step to disconnect itself and ground from the line conductors of the called line. Switching relay 290, upon energizing, at armature 292 prepares a point in the transfer circuit; at armature 293 completes a locking circuit through its lower winding by Way of armature 283 and grounded armature 2|2; at armature 294 connects direct ground to wiper 353 to mark the called line busy to other connectors having access thereto; at armature 295 opens a point in the circuit to busy relay 250; at armature 296 opens a point in the self-restoring circuit of connector motor magnet 351; at armature 291 opens a point in the busy tone circuit; and at armatures 29| and 298 connects interrupted generator to the'called line. The.circuit for signalling the called subscriber may be traced as follows: from interrupted generator by way of resting contact and armature 263, armature 296, conductor 239, wiper 356 in engagement with its.

sixth bank contact, conductor 302, through the ringer bells RB and ringing condenser at the substation, over conductor 30| and from thence to the sixth bank contact engaged by wiper 35| and said wiper, conductor 232, armature 29|, armature 26| and resting contact, and through the upper winding of ring-cut-off relay 260 to battery.

When the called subscriber answers, ring-cutofi relay 260 is energized over the called subscribers loop, this time including the transmitter T and the upper switchhook springs SH in place of the ringer RB and the ringing condenser. At armature 262 relay 260 completes a locking circuit through its lower winding from grounded armature 2|2 and at armatures 26| and 263 opens the ringing circuit and-at the working contacts of these armatures connects the called line in series with differential relay 244 and relay 250.

Relay 250 is energized over the called subscribers loop as follows: from ground by way of armature 2|2, armature 262, through the lower winding of relay 250, through the lower winding of diilerential relay 244, working contact and armature 263, from thence over the previously traced circuit through the called subscribers loop to armature 29|, armature 26| and Working contact, through the upper Winding of differential relay 244 and through the upper winding of relay 250 to battery. Relay 250 alone is energized over this circuit and furnishes talking battery through both its windings to -the called subscriber. Diierential relay 244 does not energize over the previously traced circuit because the two windings are equal and oppose each other. The talking circuit between the local subscribers lines are noW completed over the heavy talking conductors.

After conversation and responsive to the calling subscriber S replacing his receiver, line relay 230 deenergizes when its circuit is opened at the switchhook springs SH and said relay at armature 23| opens the circuit to release relay 2lb. After an interval slow-to-release relay 2|0 deenergizes and at armature 2H opens a point in the talking circuit to the calling line. At armature 2l3 relay 2|0 connects grounded armature 204 to the busy common conductor 2|6 to prevent the iinder connector distributor from stopping on its stopping position as previously described, and at armature 2|2 opens the holding circuits of relays 290, 260, and 220. Relay 220, upon deenergizing, at armature 224 removes one of the multiple ground connections from guard conductor 221, which conductor at this time is grounded by connector wiper 354 in engagement with its multiple contacts connected to ground. At armature 225 relay 220 disconnects ground from conductor |63 and test wiper |53 to remove the busy guarding potential, and at armature 226 opensa further point in the talking circuit and prepares the circuit through the lower winding of relay 220.

Switching relay 290, upon deenergizing, at armatures 29l and 298 opens points in the talking circuit to the called line and the circuit of relay 250 in case the called subscriber has not replaced his receiver; at armature 293relay 290 opens its own locking circuit; at armature 294 opens the circuit to line-cut-oi relay 303 and removes the busy ground potential; and at armature 296 completes a self-restoring circuit for the connector. This self-restoring circuit may be traced as follows: from ground by way of the multipled contacts engaged by wiper 354, conductor 221, armature 224 and resting contact, conductor 231, interrupter spring 358, conductor 236, armature 296, conductor 235, and through the winding of magnet 351 to battery. At interrupter springs 358 motor magnet 351 interrupts its own circuit to cause the magnet to operate in the same manner as a buzzer to advance the wipers step by step until wiper 354 no longer encounters a grounded bank contact. Since the normal position bank contact accessible to wiper 354 is the only bank contact accessible to this wiper that is not grounded, the wipers of the connector will be advanced step by step by motor magnet 351 until wiper 354 reaches its normal position. When wiper 354 reaches its normal position, ground is removed from guard conductor 21 to permit this finder connector link to be preselected by the finder connector distributor shown in Fig. 4.

The local subscribers are divided into three groups, the rst group having only a single call digit in their telephone numbers, the second group having two call digits in their telephone numbers, and the third group having three digits in their telephone numbers. The first digit in the telephone numbers of all second-group subscribers is the digit 0, and the rst and second digits of the subscribers telephone numbers in the third group are the digits 0-0.

In order to call a subscriber in the second group the calling subscriber initiates the callin the same manner as previously described to cause a nder-connector link to be connected to the calling line. ln response to dial tone the calling subscribed dials the digit "0 to step the connector to the tenth bank contacts, which contacts are dead contacts and do not complete any circuits. Since neither ground nor battery is encountered by test wiper 253, the connector remains in this position until the receipt of the second digit. In response to the calling subscriber dialling the second digit the wipers of the connector are stepped from the tenth bank contacts a number of steps corresponding to the digit dialled and into engagement with the bank contact terminating the called line in the second group. The connection is now completed by the connector in the same manner as previously described. .in order to call a subscriber in the third group the calling subscriber dials the digit 0 for the rst digit, the digit 0 for the second digit, and then the units digit of the called line to cause the wipers of the connector to come to a rest in engagement with the bank contacts terminating the called line.

Incoming calls It will now be assumed that an incoming trunk call is received over conductors 194 and 195 from the distant exchange. When an incoming call is received over conductors 194 and 105, relays and 180 operate. Relay 180 is a very high Wound relay and operates in response to either the ringing current or during the silent period, while relay 110 is an anternating current relay which operates only in response to ringing current. The circuit for energizing alternating current relay 110 may be traced as follows: from generator at the main exchange, conductor 194, condenser and upper winding of alternating current relay 110, resting Contact and armature 113, conductor 694, armature `666, conductor 695, armature 144, conductor 195', back to generator at the main exchange. Relay 180 is energized over the following circuit: from ground at the main exchange, or generator, extending over conductor 194 through the winding of relay 180, armature 144, and by way of conductor 195 back to main exchange battery. At armature 18| relay 180 completes an obvious circuit for energizing slow-to-release relay 150. Relay 110, upon energizing, at armature 11| prepares a point in its own locking circuit; at armature 112 disconnects ground from conductor 314- to mark this trunk as calling in the bank of the trunk distributor shown in Fig. 3; at armaturer112 and working contact grounds conductor 310 to energize relay 3|4 over an obvious circuit; at armature 113 and resting contact disconnects the upper winding of relay 110; and at its working contact bridges the alternating current signalling relay 160 and condenser C across the trunk conductors 194 and 195 by way of armatures 666 and 144 and conductors 694 and 695.

Relay 150, upon energizing, at armature 15| completes a circuit for energizing slow-to-release relay 190; at armature 152 completes a circuit for energizing relay at armature 153 prepares a point in its own locking circuit; at armature 154 completes the locking circuit through the lower winding of relay 110 by way of armatures 623 and 633 and their resting contacts over conductor 628; and at armature 155 prepares a substitute circuit for alternating current signalling relay 160. At armature 19| and its resting contact relay 190 disconnects one of the ground connections from the busy common conductor 316 over which the busy relay 36| is normally held energized as long as one of the trunk lines is idle. At armature 19| and its working contact relay 190 connects ground to conductor 313 to operate the trunk distributor in case the wiper 335 is in engagement with the bank contact terminating in this particular conductor. At armature 192 relay 190 prepares a point in the circuit for energizing relay 630. Relay 130, upon energizing, at armature 13| disconnects relay 120 and prepares a point in the talking circuit; at armature 132 connects another ground to relay 192; and at armature 133 prepares a point in its own locking circuit. Relay 3|4, upon enenergizing, at armature 320 disconnects ground from conductor 31| to remove the busy condition and connects battery through the windings of relays 3|5 and 3|6 to the trunk answering bank'contact No. 8 in the connector bank accessible to wiper 353.

Alternating current signalling relay operates from ringing current transmitted from the main exchange and at armature 162 maintains the circuit of relay 150 independent of armature 18|. At armature 16| alternating current signalling relay 160 connects battery to conductor 624, through resistance 163, to signal the attendant or to operate the common trunk signal lamps located throughout the premises dependent upon whether the attendant signal key SK is operated or at normal. r

Assuming that the key SK is normal, then relay 501 is energized over the following circuit: from ground through the winding of relay 501, normally closed springs of key SK, common conductor 609, resting contact and armature 662, conductor 624, armature 16|, and through resistance 163 to battery. At armature 508 relay 501.A completes the circuit for lighting the trunk signal lamps located throughout the premises to enable the non-restricted subscribers to answer the incoming trunk call.

The trunk distributor shown in Fig. 3 is arranged to normally preselect an idle trunk for use in'an outgoing call, and in case the outgoing test wiper 335 is in engagement with the bank contact terminating conductor 313 of the trunk shown in Fig. '1 when such trunk is seized for an incoming call, the trunk distributor motor magnet 333 is energized as follows: from grounded conductor 313, bank contact and Wiper 335, resting contact and armature 322, armature 328, interrupter springs 334, and through the winding of motor magnet 333 to battery. Motor magnet 333 operates to position the pawl preparatory to stepping the wipers of the distributor and at its interrupter springs 334 interrupts its own circuit. Magnet 333 thereupon deenergizes and advances the wipers of the distributor into engagement with the bank contacts terminating the next trunk line. In case this trunk line is idle, wiper 335 does not encounter a grounded bank contact and the Wipers remain in this position. In case the next trunk line is busy, then ground is encountered by the wiper 335 to again advance the wipers to the next trunk or until an idle trunk is found.

Any non-restricted local subscriber equipped with a push-button, such as PB, may answer this trunk call by removing his receiver and dialling the digit 8 to position the connector of the lnder-connector link on the trunk answering position 8.

In response to subscriber S removing his receiver to answer this trunk call, an idle nder connector link is connected to this subscriber's line and in response to the receipt of dial tone such subscriber will dial digit 8 to answer the trunk call. In the same manner as previously v described the connector wipers are stepped into engagement with their eighth bank contacts and when series relay 210 deenergizes after the impulsing period a circuit is completed for energizing relays 290 and 3|6 in series as follows: from ground by way of armature 204, armature 2|3 and working contact, armature 25| and resting contact, through the upper winding of switching relay 290, resting contact and armature 212, conductor 234, test wiper 353 in engagement with its eighth bank contact, conductor 31|, armature 320 and its working contact, through the winding of marginal relay 3|5 and through the upper and lower windings of relay 3 |6 to battery. Relay 3|5 is marginal and will not operate in series with the lower high-resistance winding of relay 3| 6. Relay 290, upon energizing, at armature 292 prepares a point in the circuit for the local release relay 200 and for marking the line of subscriber S as answering a trunk call in the trunk finder bank. At armature 293 relay 290 again completes its locking circuit and at armature 294 grounds test wiper 353. Relay 3|6, upon energizing, at armature 326 opens the initial energizing circuit for relay 363 to prevent its operation in case an outgoing call is originated before the incoming call is completed. At armature 325 relay 3|6 completes a circuit for shunting out the lower high-resistance winding of relay 3|6 only in case\ relay 363 is not energized in a preceding outgoing call. When the lower Winding of relay 3l6 is shunted by battery at amature 369, marginal marking relay 3|5 thereupon energizes in series with relay 3|6. Relay 3|5, upon energizing, at armature 32| grounds conductor v312 for a purpose to be described`later; at armature 322 switches the test circuit from the outgoing test Wiper 335 to the incoming test wiper 336 Vto cause the trunk distributor to nd the calling trunk. At armature 323 relay 3|5 grounds conductor 386 to prepare a circuit for the local release relay 266 and likewise' marks the line answering this trunk call, or line S, in the trunk iinder bank.

At armature 324 relay 3|5 closes a circuit for energizing relay 3|1 when the calling trunk is found by the trunk distributor.l

Considering now that the wipers of the trunk distributor are in the position shown in the drawings, thenrelay 3|1 is short circuited from ground encountered on the multiple contacts by wiper 336 by way of armature 322 and armature 324. A branch of this circuit extends by Way of armature 328 and interrupter springs 334 through the winding of motor magnet 333 for operating Ithe latter magnet. In the same manner as previously described, magnet 333 steps the Wipers of the trunk distributor and interrupts its own circuit until wiper 336 no longer encounters agrounded contact, or in this case until wiper 336 encounters the contact terminating conductor 314, from which ground has been removed by the operation of relay 116. It should possibly be stated at this time that the motor magnet 333 is marginal and will not energize in series with either resistance 329 or the winding of relay 3|1.

When wiper 336 no longer encounters a grounded bank contact, the short circuit around relay 3|1 is removed, with the result that this relay now energizes over the following circuit: from ground by way of armature 324, winding of relay 3|1, armature 328, interrupter springs 334, and through the Winding of magnet 333 to battery. Relay 3|1 alone energizes over this circuit and at armature 321 completes a circuit for energizing relay 3|8, and at armature 328 removes the short circuit from around resistance 329 to prevent the energization of magnet 333 in case conductor 314 becomes grounded. At armature 336 relay 3|8 completes a circuit for energizing relay 3 I 9 and at armature 33| grounds conductor 629 to energize relay 656 in the trunk. At armature 332 relay 3|9 prepares a point in the circuit for magnet 333. Y

'Ihe circuit for energizing relay 6,56 may be traced as follows: from ground by Way of arma-g ture 33|, wiper 331 in engagement with its sixth bank contact, conductor 629, and through the winding'of relay 656 to battery. At armature 65| relay 656 prepares a circuit for later maintaining relay 616 in energized position; at armature 652 prepares the trunk test circuit for energizing relays 610, 666, and 266 in series; at armature 653 disconnects a point in the transfer circuit; at armature 654 completes a circuit for energizing the trunk finder motor magnet 568;

and at armature 655 prepares apoint in the bridge across conductors 56| and 565. The circuit for energizing magnet 568 may be traced from grounded armature 654 by way of armature 61| and resting contact, conductor 561, and through the winding of trunk iinder motor magnet 568 to battery.

Motor magnet 568 energizes and positions its pawl preparatory to stepping the wipers of the trunk nder and at its springs 569 completes the circuit for energizing relay 616 over the following circuit: from ground by way of springs 569, conductor 566, and through the upper winding of stepping relay 616 to battery. Stepping relay 616 energizes over the above-traced circuit and at armature 61| and its resting contact opens the circuit to the trunk finder motor magnet 568 and at its working contact connects another ground to conductor 692. Motor magnet 568 deenergizes when its circuit is opened by relay 610, and, upon deenergizing, advances the Wipers of the trunk nder one step and likewise opens the circuit of stepping relay 616 at springs 569. At armature 61| stepping relay 616 again completes the circuit for energizing motor magnet 566 and the motor magnet 56B at springs 569 again completes the circuit for stepping relay 616. Motor magnet 568 and stepping relay 616 intermittently operate as described until test wiper 552 of the trunk iinder finds the marked bank Contact, at which time a circuit is completed for energizing relays 266 and 666 as well as maintaining stepping relay 610 in energized position. This circuit may be traced as follows: from ground by Way of armature 323, conductor 386, eighth bank contact engaged by wiper 352 and said Wiper, conductor 233, armature 282 and resting contact, armature 292, lower winding of local release relay 266, conductor |62, Wiper |52 in engagement with its fifteenth bank contact or the bank Contact corresponding to the calling line answering this trunk call, conductor '28, fifteenth bank contact in the trunk nder accessible to wiper 552 and said Wiper, conductor 562, resting Contact and armature 62|, armature 652, through the upper winding of relay 666 and through the lower Winding of stepping relay 616 to battery.

Stepping relay 616 is maintained energized I over this circuit and relays 266 and 666 are energized thereover. At armatures 66| relay 666 completes a circuit by way of armature 65| through the upper winding of stepping relay 616 for maintaining this relay in energized position; and at armature 662 and resting contact opens a point in the circuit for operating the' signal relay 561. At armature 663 relay 666 completes a circuit by Way of resting contact and armature 663 for energizing slow-to-operate relay 696; at armature 664 completes a circuit for energizing slow-to-release relay 636; and at armature 665 connects conductor 693 to conductor 696 to provide another circuit for signal relay '|66 when armatureA 666 disconnects conductor 694 from 695. The circuit for energizing relay 636 may be traced from grounded conductor 692 grounded at either armature 162v or by way of armatures 654 and 61| and thence by Way of armature 664 through the winding of relay 636 to battery. At armature 63| relay 636 closes a point in the upper talking conductor; at armature 632 opens a point in the circuit to relay 646 at armature 633 closesacircuit for maintaining relay 666 energized through its lower winding from grounded armature 623; at armature 634 grounds conductor 564 and wiper 554 to make the line answering this trunk call Vbusy and for holding the combined line and cut-off relay |03 in energized position; at armature 635 completes a bridge across conductors 56| and 565 including the resistance 631 and armature 655; and at armature 636 closes a point in the lower talking conductor.

In the local finder connector link local release relay 200 energizes in series with relay 660 and at armatures 20| and 206 opens the line conductors extending to line relay 230, whereupon the latter relay now deenergizes. At armature 203 relay 200 closes a locking circuit through its upper winding as long as slow-to-release relay 2|0 remains energized; at armature 204 opens a point in the original energizing circuit of relay 290 or the locking circuit of the busy relay 250 if the latter relay is energized; and at armature 205 opens a point in the impulsing circuit and also opens the circuit of relay 2|0. Relay 230 deenergizes and at armature 23| opens a further point in the circuit of slow-to-release relay 2|0. After an interval slow-to-release relay 2|0 deenergizes to cause the deenergization of switching relay 290and causes the connector to release in the same manner as previously described.

When relay 290 deenergizes and at armature 204 removes ground from wiper 353, the circuit to relays 3|5 and 3|6 is opened, causing the latter relays to dcenergize. Relay 3|6 deenergizes and at armatures 325 and 326 allows other trunk calls to be originated and answered. Relay 3|5 deenergizes and disconnects ground from conductor 312. At armature 322 relay 3|5 disconnects the incoming test wiper 336 and connects up the outgoing test wiper 335 to cause the trunk distributor to hunt for and select an idle trunk. At armature 323 relay 3|5 disconnects marking ground from conductor 380 to open the original energizing circuit of relays 200 and 660; and at armature 324 opens the circuit to relay 3 1 which now deenergizes. At armature 321 relay 3|1 opens the circuit of relay 3|8 which now deenergizes and at armature 328 short circuits the resistance 329 to permit the energization of magnet 333. At armature 330 and its working contact relay 3|8 opens the circuit of s1owtorelease relay 3|9 and at its resting contact completes a circuit for energizing motor magnet 339 by way of armature 332 as long as the slow-to-release relay 3|9 is operated. At armature 33| relay 3|8 removes ground from conductor 629 to cause the deenergization of relay 650. Slow-to-release relay 3|9 deenergizes after an interval and opens the circuit of motor magnet 333 at armature 332, thereby causing the magnet upon its deenergization to advance the wipers into engagement with the next bank contact. Since the outgoing test wiper 335 is connected to the grounded multiple contacts at this time, the magnet 333 intermittently operates as previously described to step the wipers of the trunk distributor in search of an idle trunk.

Assuming that the trunk last used, was the last available trunk then ground is disconnected from the busy common conductor 316 to provide a stopping position for the trunk distributor wipers to prevent their continuous operation as long as all of the trunk lines are busy. Assuming, however, that one or more of the trunk lines are idle, then busy common conductor 316 is grounded and the wipers are advanced until test wiper 335 loses ground, such condition indicating an idle trunk. The normally energized alltrunk-busy relay 36| also deenergizes when all of the trunks are busy when ground is removed from. the busy common conductor 316. At annature 364 relay 36| opens the circuit to relays 362 and 363 to prevent their energization when a local subscriber attempts to originate an outgoing call, and at the resting contact of armature 364 grounds the ninth bank contact acces- 318 was not grounded and the connector of a nder connector link switches through to cause the seizure,of the last idle trunk. At the same time, however, the trunk was seized for an incoming call and therefore since incoming calls are given preference over outgoing calls the party originating the outgoing call is given a busy tone over conductor 311.

When relay 630 energizes in response to the operation of relay 660 at the time the trunk nder nds the answering local line, relay 630 rst operates its preliminary make armature 635 before operating its other armatures to close a ring-cut-otf bridge across the upper and lower talking conductors extending to the distant main exchange. This ring-cut-oi bridge, comprisingarmature 63|, resistance 631, and armatures 655, 635, and 636 is only temporarily placed across the trunk conductor to cause the disconnection oi ringing current at the main exchange in the well-known manner and to reduce the click in the answering subscribers receiver, since the subscribers line at this time is also connected in bridge of the trunk line. The operation of armature 633 at its resting contact also opens the locking circuit of relay 110 which deenergizes to open the circuit of relay 3|4 at the working contact of armature 112, and to ground the marking conductor 314 at the resting contact of armature 112. Relay 3|4 deenergizes and at armature 320 opens the circuit to relays 3|5 and 3|6 and grounds conductor 31| to place busy potential on the answering trunk position terminating in the eighth bank contact accessible to wiper 353.

When relay 650 deenergizes in response to the deenergization of relay 3|8 relay 650 at armature 65| opens the circuit of relay 610 which thereupon deenergizes, at armature 652 opens the test circuit through the relays 660 and 610; at armature 654 opens a point in the circuit to motor magnet 56B to prevent its operation; and at armature 655 opens the ring-cut-off bridge previously referred to. Relay 610 deenergizes without result since the circuit to motor magnet 568 is opened at armature 654.

At this time the local finder connector link has released and is available for use in other local calls, while in the trunk circuit shown in Figs. 6 and 7 the following relays are operated: relays 630, 660, 690, 130, 150, 180, and 190. The line of substation S is now connected to the distant main exchange over the following circuit: from the substation S, conductors 0| and |02 terminating in the trunk finder bank, wipers 55| and 555, conductors 56| and 565, armatures 63| and 636, through the upper and lower windings of differential relay 6|4, conductors 6|6 and 691, through the normally closed springs controlled by armatures 10| and105 through the talking condenser and through the upper and lower windings of series relay 1| 3 in multiple, resting contact and armature 123, working contact and armature13l, and over trunk conductors 194 and 195 to the distant main exchange.

Relay 6|4 in the circuit just traced is a differential relay and therefore does not operate its armature when both windings are energized. Series relay 1|3 energizes over the above traced circuit and at amature 1|4 completes the circuit for energizing relay 140. At armature 14| relay maintains relay 196 energized, at armature 142 completes a locking circuitfor relay 130, at armature 143 completes a locking circuit for relay 150, and at armature 144 disconnects relay 180 from in bridge of trunk conductors 194 and 195 to cause the latter relay to deenergize. The deenergization of relay 180 is without effect at this time since relay is now held energized over its locking circuit. Subscriber S now converses with the calling subscriber over the heavy talking conductors and both the calling and the called subscribers receive their talking battery from the main exchange.

The release of incoming trunk connections is under control of the calling main-exchange subscriber or the main-exchange operator. The replacement of the receiver by subscriber S opens 'the circuit of series relay 1|3 which accordingly deenergizes and opens the circuit of relay 140. At armature 144 relay 146, upon deenergizing, reconnects the high resistance relay 180 across the trunk conductors to cause its energization if the calling main-exchange subscriber has not hung up. At armature 18| relay 180 maintains slow to release relay 150 operated to prevent the deenergization of relay 130. If the distant main-exchange operator desires to re-signal subscriberl S she may do so by applying ringing generator to the trunk conductors 194 and 195. The alternating current signalling relay reoperates over a circuit including armatures 155 and 665, but does not operate the general trunk signals because the signalling circuit is open at armature 662. Ringing current transmitted from the main exchange extends over the talking circuit previously traced to the line of subscriber S to operate the ringer RB at this substation and therefore directly signal subscriber S.

When the distant calling subscriber or the distant operator disconnects at the main exchange, relay deenergizes and at armature 181 opens the circuit to slow-release relay 150. At armature 15| relay 150, upon deenergizing, opens one of the circuits extending to relay at armature 152 opens thecircut to relay 130 which now deenergizes; and at armature 155 opens the circuit of alternating current signalling relay 160. At armature 13| relay 130, upon deenergizing, opens a point in the talking circuit and at armature 132 opens the circuit of slowto-release relay '|90 which now deenergizes. At armature 19| relay 190 grounds the busy common conductor 316 and disconnects ground from conductor 313 to allow this trunk to be used in an outgoing call. At armature 192 relay 190 opens the circuit of relay 630 which now deenergizes. At armatures 63| and 636 relay 639 opens a further point in the talking circuit; at armature 633 opens the circuit of relay 660 which deenergizes; and at armature 634 removes the busy ground from the multipled test conductor of the called line and likewise causes the release of the combined line and cut-off relay |03. At armature 662 relay 660, upon deenergizing, reestablishes the signalling circuit for operating Outgoing calls Any non-restricted, local subscriber may originate an outgoing trunk call by removing his receiver and dialling the digit 9 to position the connector ora local finder connector link on the trunk calling position 9. In response to the subscriber S removing his receiver to originate a trunk call, an idle nder connector link is connected to this subscribers line and, in response to the receipt of dial tone, subscriber S dials the digit 9 to operate the connector wipers into engagement with their ninth bank contact in the same manner as previously described.

In case all of the trunks are busy, then busy relay 36| in the trunk distributor is deenergized and ground is connected to trunk call position 9 engaged by wiper 353 to causel the operation of the busy relay in the local iinder connector link. The operation of the busy relay, such as relay 250 in the link shown in Fig. 2, causes the busy tone to be transmitted to the calling line in the same manner as previously.

In case, however, one or more of the trunks are idle, then the busy relay 36| is in energized position and a circuit is completed for energizing the switching relay, such as switching relay 290 in the finder connector link, in series with relays 362 and 363 in case the trunk distributor is not in use answering an incoming trunk call. Relay 362 is marginal and will not energize in series with the upper winding of relay 363. The circuit for energizing switching relay 290 and relay 363 may be traced as follows: from ground by way of armature 264, armature 2|3 and working contact, armature 25| and resting contact, through the upper winding of switching relay 290, resting contact and armature 212, conductor 234, test wiper 353 in engagement with its ninth bank contact, conductor 316, armature 364 and its working contact, through the winding of marginal relay 362, through the lower and upper windings of relay 363, to battery at armature 326.

In case the trunk distributor is in use in answering an incoming trunk call, relay 3|6 is operated and the circuit just traced is not completed until relay 3|5 deenergizes as previously described. At armature 369 relay 363 shunts out the upper high-resistance winding of relay 363 to permit the energization of marginal marking relay 362. In a similar manner the operation of armature 369 prevents'the operation of marginal marking relay 3|5 in case some subscriber subsequently attempts to answer an incoming-trunk call when the trunk distributor is in use. Relay 362, upon energizing, at armature 361 marks the calling line in the banks of the trunk finders over the following circuit: from ground by way of armature 361, conductor 319, ninth bank contact and wiper 352, conductor 233, armature 282 and resting contact, armature 292, through the lower winding of local release relay 200, conductor |62, Wiper |52, conductor 28 multipled to the trunk finders to the fifteenth bank contact accessible to wiper 662. At armature 363 relay 362 completes the circuit for energizing relay 3|1 over the following circuit: from ground by way oi armature 363, winding of relay 3|1,

yarmature 323. interrupter springs 334, and

' has therefore preselected the trunk shown in Figs. 6 and 'I when the outgoing trunk call was originated.

l In case the wiper 336 was in engagement with a grounded bank contact, the relay 3|1 would have been short circuited to prevent its operation and the motor magnet would have operated the wipers oi the trunk distributor until an idle trunk was found. At amature 321,relay 3I1 operates relay 3|9 and at armature 326 opens the short circuit around resistance 329.' At armature 33,6 relay3|6 completes the circuit for relay Ill' and at armature 33| completes the circuit ior energizing relay 666 in the preselected idle trunk as'follows: from ground by way oi.' armature 33|', -wiper 331'in engagement with its nrst bank contact, conductor 629 and through the winding of relay 660 to battery. I

In response to the operation of relay 660,' the trunk finder is operated in the same manner as previously described to rind the marked bank contact. at which time a circuit is completed for energizing the local release relay 290 in thc finder connector link and relay 660 in the trunk aswell as maintaining relay 610 in operated position. The operation of the relay 666 in the same manner as previously described causes the operation of relays 690 and 636; In the local armature 325. At armature 3 61 the ieenex'giza-V finder connector link local release relay 260 is energized and Tcauses the local ilnder connector link to release in the same manner as previously described. When switching relay 290 in the local finder' connector link, deenergizes, ground is removed from wiper 363, thereby opening the circuits of relays 362 and 363. At armature 369 relay 363 now permits any incoming calls to be answered by connecting battery to tion ot relay 362 disconnects marking' ground from conductor 319. At armature 396 relay 362 opens the circuit of relay 3l1 which deenergizes to allow the motor magnet to step the wipers of the trunk distributor in search of an idle trunk.

At armature 33| relay lll, upon deenergizing, opens the circuit of relay 666.

The operation of the trunk relays are slightly dii'ferent dependent upon whether the trunk conductors 194 and 196 extend to a manual or an automatic exchange. In either case, ground is disconnected from trunk conductor 194 at the main exchange, while conductor 195 extends to a signalling relay and negative battery in case oi' a manual exchange or extends through the line relay'of an incoming line switch in case the main exchange is an automatic exchange. In addition, relay 120 in Fig. 'l is permanently short circuited in case the trunk conductors 194 and 196 extend to an automatic exchange. while the short circuit is removed from around said relay ln case the trunk conductors extend to a manual exchange. Y

It will ilrst be assumed that the trunk conductors extend to a manual exchange and thereu tore a circuit may be traced from ground through the winding of relay 120 through the local cainng subscribers loop and from thence through the signalling relay at the main manual exchange to battery. The circuit for energizing relay 120 may. be traced in detail as follows: from ground through the winding of relay 120, normally closed springs controlled by armature 13|, through the upper winding of series relay 1l3,y normally closed springs controlled by armature 10|, conductor 6|6, through the upper winding oi.' diilerential relay 6|4, armature 63|, resistance 631, armature 666, armature '636, varmature 636, through the lower winding of differential relay 6l4, conductor 691, normally closed springs lcontrolled by armature 106, through the lower winding of series relay 1|3, resting contact and armature 123, and over conductor 196 to battery through the signalling relay at the main exchange.

'Ihe calling subscribers loop is also connected across the talking conductors 56| and 565 to assist in energizing relays 120 and 1|3 and to later on maintain series relay 1I3 in energized position after the bridge including resistance 631 and armatures 666 and 636 is opened. The operation of the signalling relay at the main exchange signals the operator thereat in the wellknown manner. Series relay 1|3, upon energizing over the above-traced circuit, at armature 1l4 completes an obvious circuit for energizing relay 140. Relay 120, upon energizing over the above-traced circuit, at armature 12| likewise completes a circuit for energizing relay 140; at armature 122 completes a circuit for connecting battery through resistance 124 through the lower winding of series relay 1|3 before armatures 12| and 123 are fully operated, in order to maintain the series relay 1|3 in energized position when relay 120 subsequently deenergizes. At armature 123 relay 120 connects direct ground to conrluctory |96 to maintain the main-exchange signalling relay in energized position. Slow-torelease relay 140, upon energizing, at armature 14| completes an obvious circuit for energizing relay 190; at armature 142 prepares a point in the circuit for relay 130; at armature 143 prepares a point in the locking circuit for relay 150; and at' armature 144 disconnects relays 110 and 160 from in bridge of the trunk. Relay 190, upon energizing, at armature 19| and its resting contact disconnects one of the ground connections to the busy common conductor, and at its working contact grounds conductor 313 to short .circuit relay 3|1 and cause the trunk distributor 1 to preselect another trunk as previously described.

At armature 192 relay 190 completes a circuit for holding relay 630 in energized position by way ol.' conductor 692 and armature 664.

When the trunk distributor operates in the manner previously described to preselect an idle trunk, the circuit to relay 650 is opened, whereupon sueh relay now deenergizes. At armatures and 662 relay 650 opens the circuit to relay 610 which now deenergizes; at armatureA 654 opens the original energizing circuit oi' relay 690, which relay is now held energized from grounded armature 192; and at armature 665 opens the local bridge across the talking conductors. Series relay 1|3 and slow-to-releaserelay 120 are now held energized over the previously traced circuit through the calling subscribers loop. At armature 61| the deenergization of relay 610 opens a point in the original energizing circuit v of relay 630.

When the manual operator at the main exchange answers the call, ground is connected to conductor 194, thereby completing an energizing circuit; for relay 130 as follows: from ground at the main exchange'by way of conductor 194, normally closed springs controlled by armature 133, armature 142, and through the winding of slow-to-release relay 130 to battery. At armature 13| relay 140 completes a point in the talking circuit and also substitutes the ground at the main exchange for ground through the winding of relay at' armature 132 maintains relay 190 energized; and at armature 133 completes a locking circuit for' itself by way of armature 142 before opening its original energizing circuit. Relay 120, upon deenergizing, at armature 12| opens a point in the circuit of relay 140, which relay is held energized from armature 1I4 on the series relay 1|3; at armature 123 disconnects ground from conductor 194 and completes `the talking circuit; and at armature 122 disconnects battery extending through resistance 124 from the lower winding of series relay 1|3 after armature 123 has completed the talking circuit. Series relay 1I3 is maintained energized from ground at the main exchange extending by way of conductor 194, armature 13|, through its upper winding and from thence over the calling subscribers loop through its lower winding, resting Contact of armature 123 and said armature, conductor 195 to battery at the main exchange. The calling subscriber is now connected to the distant operator and may converse over the heavy talking conductors to inform the distant operator of the desired subscriber. The manual operator at the distant exchange completes the connection to the desired subscriber in the wellknown manner.

It will now be assumed that the trunk conductors 194 and 195 extend to an automatic exchange and therefore the operation of relay |530 completes a circuit for energizing series relay 1 i3 and the line relay of an incoming line switch in the main exchange. This circuit may be traced as follows: from ground over the short circuiting connections of relay 120, normally closed springs controlled by armature 13|, through the upper winding of series relay 1|3, and from thence over the local bridge including the resistance 631, the lower winding of relay 1|3, as previously described, over conductor 195 through the winding of the line relay in the incoming line switch to battery. At armature 1|4 relay 1|3 completes a circuit for energizing relay 140 and relay 140, upon energizing, completes a circuit for energizing relay 190 and prepares a circuit for energizing relay in the same manner as previously described. The operation of relay 190 causes the trunk distributor to preselect another idle trunk, whereupon relay 650 deenergizes as previously described. When the local bridge is opened at armature 655 by the deenergization of relay 650 the series relay 1|3 and the line relay in the incoming line switch at the main exchange are held energized over the calling subscribers loop.

The operation of the line relay at the main exchange causes the line switch thereat to operate in the well-known manner to seize an idle trunk, at which time dial tone is transmitted back over conductors 194 and 195 to the calling subscriber. In addition, ground is connected to trunk conductor 194, thereby causing the energization of relay 130 to complete the talking circuit. At armature 13| relay 130 completes a direct metallic loop including the calling subscribers line to enable the local'calling subscriber to operate the automatic switches in the automatic exchange in response to the operation of his calling device CD.

In response to the calling subscriber S operating his calling device CD, the automatic switches in the automatic exchange are operated in the well-known manner to complete` the desired connection. Relay 1|3 intermittently operates during the impulsing period, but since relay is slow to release the latter relay is maintained in operated position to prevent the deenergization of relay 130. Talking battery for 4both the calling and called subscribers -is furnished from the main exchange. During conversation the following relays are in operated position in the trunk circuit; relays 630, 660, 690, 1|3, 130, 140, 150, and 190. and in response to subscriber S replacing his receiver, the closed loop extending to the distant exchange is opened at the switchhook springs and series relay 1|3 thereupon deenergizes. At armature 114 relay 1|3 upon deenergizing, opens the circuit of relay 140 which deenergizes after an interval. At armature 142 relay 140 opens the circuit of relay 130 which thereupon deenergizes. At armature 132 relay 130, upon deenergizing, opens the circuit of relay which likewise deenergizes and at armature 13| opens a point in the talking circuit. The automatic switches in the main exchange are released in the well-known manner and the trunk line is made available for other calls. In the case where the call extended to a manual exchange the distant main-exchange operator would get a supervisory signal to indicate when the calling subscriber has hung up.

Holding circuit In order to describe how local subscribers equipped with a push-button, such as pushbutton PB, can hold a trunk call while making a local call, it will be first .assumed that subscriber S is connected in a trunk call over the trunk line shown in Figs. 5, 6, and '7. The mainexchange subscriber is advised by subscriber S to wait on the line while she completes a local connection. Subscriber S now operates the pushbutton PB to ground conductors |0| and |02, thereby shunting theupper windings of difierential relay |4 and series relay 1|3. This shunt circuit extends from ground at the main exchange over conductor 194, armature 13|, upper winding of series relay 1|3, normally closed springs controlled by armature 10|, conductor 5|6, upper winding of differential relay 6|4, armature 63|, conductor 56|, wiper 55|, conductor |02, through the substation circuit to ground at the push-button PB. Series relay 1|3 is maintained energized over its lower winding from ground at the push-button PB by way of conductor |0|, wiper 555, conductor 565, armature 63B, lower winding of differential relay 6|4, conductor 691, normally closed springs controlled by armature 105, lower winding of series relay 1|3, armature 123, and over conductors 195 to battery at the main exchange. Differential relay 6|4, however, is unbalanced over the circuits just traced and accordingly operates its armature 6|5 to energize relay 100 in its rst step by way of armature 104 and its resting contact. Relay 100, upon operating in its rst step, operates only armature 103 to prepare a circuit for operating itself to its second step, and also completes the circuit for short circuiting its upper After conversation winding. This vshort circuit extends from ground at armature 6I5, conductor 626, armature 104 and resting contact, upper winding of relay 100, armature 103, normally closed springs controlled by armature 1|2, conductor 621, armature 69|, and through the resting contact of armature 643 to ground.

When subscriber S releases the push-button PB ground is removed from the conductors and |02, thereby again completing the energizing circuit through the upper and lower windings of differential relay 6|4 to cause such relay to deenergize. At armature SI5 diiferential relay 6|4, upon deenergizing, removes the short circuit from around relay 100, thereby causing relay 100 to operate to its second step. This circuit may be traced as follows: from ground at armature 643 and resting contact, armature 68|, conductor 621, normally closed springs controlled by armature 1 I2, armature 103, and through the upper and lower windings of relay 100 to battery.

The remaining armatures (indicated by the Roman numerals II) now operate. At armatures 10| and 105 two-step relay 100 completes a holding bridge including resistance 106 across the talking conductors extending to the main exchange; at armature 102 completes an obvious circuit for energizing relay 680; and at armature 104 prepares a circuit for energizing slow-to-release relay`1|0. Relay 680, upon energizing, at armatures 68| and 685 connects the windings of line relay 6I0 in bridge of the line extending to subscriber S. Atrarmature 682 relay 680 connects conductor |24 to relay 620; at armature 683 opens a point in the circuit of relay 680, which, however, at this time is maintained energized in response to the operation of relay 6|0; and at armature 664 grounds conductor |22.

Line relay 6| 0 is now energized over the following circuit: from ground through the lower winding of relay 6I0, armature 605, armature 685, lower winding of differential relay 6|4, and thence over the calling loop to the line of substations S and back to the upper winding of differential relay 6|4 and from thence by Way of armature 68| and armature 60| through the upper winding of relay 6|0 to battery. At armature GII relay 6|!) connects marking battery through the winding of cut-off relay 600 to conductor |23 and the corresponding bank contacts in the local iinders; at armature 6|2 completes a circuit for maintaining slow-to-release relay 690 in energized position; and at armature 6|3 grounds the local nder start conductor 9 to operate the start relay 420 to cause a nder of an idle local nder connector link to hunt for and find the marking potential connected to conductor |23.

Start relay 420 in the nder connector distributor is energized in the same manner as .previously described and at armature 42| operates relay 400. At armature 402 relay 400 operates relay 4|0, completes the nder test circuit at armature 40| and completes the circuit to the finder magnet |68 at armature 403.v

The finder magnet |68 and line stepping relay 230 operate as previously described to step the wipers of the inder until the marking potential on conductor |23 is found by test wiper |53. When test wiper |53 engages its twentyfirst bank contact, relay 600 energizes in series with relays 220 and 230 as follows: from ground through the llower winding of relay 230, normally closed springs controlled by armature 226, lower winding of relay 220, conductor 228, wiper 4|2,

armature 40|, wiper 4I3, conductor |63, wiper |53, conductor |23, armature 6|I, and through the windingof cut-oil relay 600 to battery. At armature 22| relay 220 again completes the circuit for energizing relay 2|0; at armature 222 completes the circuit for energizing relay 280; at armature 223 prepares the circuit for the 'series relay 210; at armature 224 grounds the guard conductor 221 to cause the finder connector distributor to preselect another idle link; at armature 225 grounds conductor |23 by way of conductor |63 and wiper |53 for maintaining relay 600 energized; and at armature 226 disconnects the lower winding of relay 220 and connects the lower talking conductor to line relay 230. At armature 2|| relay 2|0 completes a circuit including both talking conductors for line relay 230, which is maintained energized; at armature 2|2 maintains relay 220 energized; at armature 2|3 prepares a point in the connector test circuit; and at armature 2|4 prepares a point in the impulsing circuit.

Line relay 230 is now energized over both windings in series over the calling loop as follows: from ground through the lower winding of relay 230; working contact and armature 226, armature 206, conductor |65, wiper |55, conductor |25, armature 68|, through the upper winding of diierential relay 6|4, armature 63|, conductor 56|, wiper 55|, conductor |02, through the substation loop to conductor IOI, wiper 555, conductor 565, armature 636, through the lower winding of differential relay 6|4, armature 685, conductor |2I, wiper I5I, conductor |6I, armatures and 2| I, and through the upper winding of line relay 230 to battery. At armature. 28| relay 280 prepares a point in the circuit used in transferring a call, and at armature 282 prepares a point in the circuit through the upper winding of local release relay 200 to automatically cause the release of the local nder connector link in case the connector is operated to originate or answer a trunk call. At armature 283 relay 280 opens a point in the locking circuit of switching relay 290 to make it release, when operated later, dependent upon the operated condition of the local release relay 200.

In the trunk circuit cut-off relay 600, upon energizing, at armatures 60| and 605 disconnects relay 6|0 from the talking conductors |25 and |2I. At armature 602 relay 600 completes its own locking circuit to grounded conductor |23; at armature 603 connects the grounded conductor |23 through the winding of relay 690 to maintain the latter relay energized; and at armature 604 disconnects ground from finder start conductor 9. Relay .6|0, upon deenergizing, at armature 6|| opens a point in the original energizing circuit of relay 600; at armature 6|2 opens a point in the original energizing circuit of relay 690; and at armature 6|3 opens a further point in the circuit to the finder start conductor 3.

The line of subscriber S is now connected to the local finder connector link shown in Fig. 2 and in response to the operation of the calling device CD in accordance with the telephone number of the desired local subscriber the line relay 230 is correspondingly operated over the circuit just traced. In the same manner as previously described, the connector is operated to complete the connection to the desired local subscriber.

In case subscriber S at this time should attempt to answer another trunk call or originate a trunk call while holding a trunk, then local release relay 200 is operated to automatically release the local nder connector link to prevent such trunk call. If subscriber S attempts to answer another trunk call, local release relay 200 is energized from the marking ground at armature 323 as follows: from ground by way of armature 323, when marginal relay 3|5 is energized as previously described, conductor 330, eighth bank contact and wiper 352, conductor 233, armature 282, armature 21|, and through the upper winding of local release relay 200 to battery. In case subscriber S attempts to originate a trunk call, local release relay 200 energizes from marking ground at armature 361 and marking relay 362 is energized as previously described. This circuit may be traced from ground at armature 361, conductor 313, ninth bank contact and wiper 352, conductor 233, armatures 282 and 21|, and through the upper winding of local release relay 200 to battery. The operation of local release relay 200 at' armatures 20| and 206 opens the circuit ofline relay' 230 to cause its deenergization and at armature 202 opens the locking circuit of switching relay 290 to cause the latter relay to deenergize. The local nder connector link in this case is released in the same manner as previously described.

Assuming now that subscriber S has completed a call to another local subscriber and that subscriber S now wishes to release the local connection and return to the held trunk, in order to return to the held trunk subscriber S pushes the push-button PB, thereby unbalancing the differential relay Y6||l to cause its energization. Differential relay 6|4, upon energizing, at armaturev 6|5 completes the circuit by way of conductor 626 and armature 104 and its working contact for energizing slow-to-release relay 1|0. At armature 1|I relay '|I0 temporarily places a bridge including resistance 6|'I across the talking conductors 56| and 565 to reduce the click in the receiver of the substation set. At armature 1|2 relay 1|0 completes a new circuit for holding two-step relay in energized position from grounded conductor 626. When the push-button PB at substation S is released, diierential relay 6I4 deenergizes and at armature 6|5 disconnects ground from conductor 626, thereby opening the circuit of the two-step relay 100 and slow-torelease relay 1|0. At armatures 10| and 105 two-step relay 100 disconnects the trunk-holding bridge including resistance 106 from across the trunk conductors 194 and 195 and completes the talking circuit to the line of substation S. At armature 102 relay 100 opens the circuit of relay 680, which thereupon deenergizes; at armature 103 opens a point in its own circuit; at armature 104 opens a further point in the circuit of relay 100; and at its resting contact prepares its original energizing circuit. At armatures 60| and 685 relay 680 opens the circuit to line relay 230 in the local nder connector link to cause the deenergization of this relay and the release of the local finder connector link as previously described. At armatures 683 relay 680 opens one point in the circuit of relay 690 at its working contact but at its resting contact completes another circuit from grounded armature 663 for maintaining this relay in operated position. At armature 684 relay 680 disconnects ground from conductor |22 to cause the deenergization of relay 280 in the local finder connector link. Slow-to-release relay 'H0 deenergizes after an interval and at armature 1| opens the bridge across conductors 56| and 565 to permit conversation thereover. At armature 1|2 relay 1|0 prepares a point in the circuit for operating twostep relay '|00 in its second step. The subscriber S and the distant main-exchange subscriber are again connected over the previously traced talking circuit' and after conversation may release the connection in a manner similar to that previously described.

'Irunk lines in use in calls originated by the local subscriber are held while the local subscriber completes a local connection and returned to in the same manner as described for the trunk line in use on incoming calls.

Transfer circuits In order to describe how local subscribers may transfer trunk lines from one local line to another,'it vwill be assumed that subscriber S is connected to the trunk line shown in Figs. 6 and 7 and that subscriber S desires to transfer the call to subscriber S. In the samemanner as previously described subscriber S operates her push-button PB to cause the two-step relay 1'0'0 in the trunk to close the trunk holding bridge and to cause a finder of an idle local finder connector link to be connected to conductors |'2l to |25, inclusive, of this trunk line. After receipt of dial tone subscriber S dials the lnumber of subscriber S to ca use the connector to complete-',the connection to the line of subscriber S' as previously described. The talking circuit between subscriber S and subscriber S extends through ythe local -iinder connector link and trunk circuit as' follows: froml line conductors [0| and |02 of line S, wipers 55| and 555 of the trunk ilnder, conductors l56| and 565. armatures 55| andf6'36, through the upper and lower windings of differentialrelay 6|4 in parallel, armatures 68| and 635, conductors |25 and |2I, wipers |55 and |'5|, conductors |6| and |65, armatures 20|' and 206, armatures 2 and 226, through the upper and lower talking condensers and the upper' and lower windings of diierential relay 244, arg maturesy 26| and 263, armatures 25| and 225; wipers 35|- and 355. and thence over the line conductors 30| and-302 to substation S'.

Subscriber S now informs subscriber 8' that such subscriber is desired on a trunk connection. Subscriber S' thereupon operates his push-button PB to ground conductors 30| and '252 through the substation circuit. Relay 244 in the local nder connector link is a diilerential relay and has both its windings connected in series over the called substation loop as follows: from grounded conductor 264, armature 262, lower winding. of combined busy and back-bridge relay 250, lower winding of diiferential relay 244,

working contact and armature v263, armature 236, conductor 239, wipers 356, conductor 352, and thence through the substation ircuit to conductor 30|, wiper 35|, conductor 2 2, armature 29|, armature 26| and working contact, upper winding of differential relay 244, and through the upper winding of relay '250 to battery. Since both windings of the differential relay are equal and oppose each other, the differential relay 244 does vnot therefore operate.

Now, when the push-button PB at substation S' is operated to ground conductors 30| and 302, the lower winding of differential relay 244 is shunted, thereby causing the differential' relay 244 to. operate its armature 245. At armature 245 differential relay 244 completes a circuit for operating the two-step relay 240 in its first step as follows: from ground at armature 604, conductor |22, wiper |54, conductor |64, amature

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