US2087930A - Telephone system - Google Patents

Description

July 27, 1937. J. voss 2,037,930!

' TELEPHONE SYSTEM Filed July 5 1935 10 Sheets-Sheet 1 LOCAL FINDER .VE ZTICAL BANK VERTICAL WIPER INVENTORY JOHN H. voss ATTORNEY.

July 27, 1937. J. H} voss 2 87,930

TELEPHONE SYSTEM Filed July 5, 1935 '10 Sheets-Sheet '4 TRUNK FINDER INVENTOR. JOHN H. voss A TTORNE Y.

July 27, 1937. J. H. vos's TELEPHONE SYSTEM Filed July 5, 1935 1O Sheets-Sheet 6 INVENTOR. JOHN H. VOSS moi A TTORNE Y.

July 27, 1937. J. H. voss TELEPHONE SYSTEM Fiied July 5, 1935 10 Shets-Sheet 7 BY ATTORNEY.

July 1937- J. H. voss 2,087,930

TELEPHONE SYSTEM Filed July 5, 1935 l0 Sheets-Sheet 8 INCOMING CONNECTOR SPGS ROT- STEP INVENTOR. JOHN H. VOSS A TTORNEY. I

Patented July 27, 1937f PATENT OFFICE TELEPHONE SYSTEM JohnH. Voss, Downers Grove, IlL, assignor to Associated Electric Laboratories, Inc., Chicago, lill., a corporation of Delaware Application July 5, 1935, Serial No. 29,864

' 23 Claims.

nections over trunk lines to one or more offices of the telephone company's network.

The main object of the invention is'to provide an improved private automatic exchange system of the type shown in my copending application S. N. 704,465, filed December 29, 1933, now Patent One of the features of the invention relates to the provision of incoming finder and connector links for selecting and transferring trunk calls to local subscribers lines even if all of the local finder connector links are busy. v

Another feature relates to the provision of a trunk distributor used for two groups of trunk lines on both incoming and outgoing calls over the two groups of trunks.

Another feature relates to the provision of divided ringing arrangement provided in both the incoming connectors in the local connectors whereby the subscribers may selectively ring either one of the two subscribers on the called line.

Another feature of the invention relates to the improved attendants cabinet whereby the incoming connector is arranged to camp on busy called local lines and whereby the attendant may ofier a trunk call to a busy called line.

Other features of the invention relate mostly to circuit improvements which will be apparent from the following detailed description of'the drawings comprising Figs. 1 to 10, inclusive, which show by means of the usual circuit diagrams a suflicient amount of apparatus to enable the invention to be described and understood.

Fig. 1 illustrates at itsleft-hand side a local talking conductor I02 while the other subscriber on this line has his associated ringer connected to the upper or negative talking conductor ll. Two line circuits areshown terminating in the line relays it and I03. The local finder shown to the right of Fig. 1 is a vertical and rotary Strowger switch having vertical motion to find the group the calling line is located in and thenrotary movement to find the particular calling line in the group selected. The polar switching relays such as relay 0 in the local finder are polar relays similar to that described in Patent No. 1,673,884, issued June 19, 1928 to H. C. Pye. The wipers of the local finder have access to the local subscribers lines and to one or more lines terminating in the attendants cabinet. While only one line is shown extending to the attendants cabinet it will be understood that additional lines oil of this same finder level may extend to the attendants cabinet. The local subscriber's line and the attendants line are multipled in the manner shown to the banks of the trunk finders, incoming connectors, and the local connectors.

The lower left-hand corner of Fig. 1 shows the' group-marking and starting circuit arrangement for the local finders.

Fig. 2 shows the local connector end of the finder connector link. The local connectors are vertical and rotary Strowger switches directively operated by impulses to find the called line. The lower right-hand corner diagrammatically illustrates one party line having subscribers S2 and S3 thereon, while the rectangle illustrates the line relay and. circuit connections similar to the connections to line relay l03 for the party line shown in Fig. 1. The local subscribers lines terminate in the first to the ninth levels inclusive while the O-level of the local connectors are used for the purpose of originating outgoing trunk balls, for incoming trunk calls, and forcalling the attendant.

Fig. 3 shows the local finder connector distributor for preselecting idle local finder connector links and for causing the operation of the local finder in response to a subscriber initiating a call.

The switch shown in Fig. 3 is mechanically similar to the well known type of rotary line switch which advances its wipers upon the deenergization of its motor magnet.

Fig. 4 shows one of the trunk finders which is similar in mechanical construction and operation to the local finder and which has access to the local subscribers line and to one or more lines extending to the attendants cabinet.

Fig. 5 shows the two-way trunk which is individual to the trunk finder shown. in Fig. 4. While only one trunk finder and its associated two-way Fig. 6 diagrammatically illustrates the'trunk distributor for use with the two groups of trunk lines previously mentioned. The switch shown in the upper portion of Fig. 6 is mechanically similar to the well known rotary line switch in which the motor magnet advances the wipers of this switch upon deenergization. Wipers 6 I 5 and GIG are respectively used for outgoing trunk calls to the second and first groups respectively. Wiper 6 I1 is used to find the trunk line in use on an incoming trunk call, while wiper (H8 is used to start the trunk finder in operation. The lower group of relays 66I to 668 may be called sequence control relays or marking relays for controlling the different types of calls to the two groups of trunk lines. Relays GM and 662 are used on outgoing calls to the second trunk group, relays 663 and 664 on outgoing calls to the first trunk group, relays 665 and 666 are used when a trunk call is to be transferred from one local subscriber to another, while the relays 661 and 668 are used when there is an incoming trunk call from either group.

Fig. 7 illustrates one of the incoming finders and its associated relays, while Fig. 8 illustrates the incoming connector and associated relays. The incoming finder is mechanically similar to the well known rotary type of line switch and has access to the trunks shown in Figs. 4 and 5. The incoming connector shown in Fig. 8 is a vertical and rotary connector which is directively operated by impulses and has access to the local subscribers lines and to the lines terminating in the attendants cabinet.

The incoming finder connector links are used during the transfer of trunk calls or are used by local subscribers to complete a local connection while the calling local subscriber is holding a trunk call.

Fig. 9 shows a transfer distributor in its lefthand portion and in its right-hand portion shows the incoming distributor. The transfer distributor is used when a trunk call is transferred from one local subscribers line to another, while the incoming distributor is used to allot an idle incoming finder connector link for use. The switches shown in the upper portion of Fig. 9 are mechanically similar to the well known rotary type of lineswitch and advance the wipers on the deenergization of their corresponding motor magnets.

Fig. 9A illustrates the manner in which the various sheets of drawings should be assembled.

All of the local subscribers lines, such as S, SI, S2, and S3, are equipped with a standard well known automatic telephone set comprising a calling device CD, receiver R, transmitter T, switch-' hook SH, ringer RB, and an induction coil. Nonrestricted subscribers entitled to make and. receive trunk calls have a push-button, such'as PB, mounted in the base of the telephone or in the associated ringer box. Semi-restricted subscribers entitled to answer trunk calls but not origi nate trunk calls are similarly provided with a push-button, but such subscribers lines are connected to battery through a resistance such as Z, over an individual conductor to its corresponding bank contact accessible to finder wiper I14. Restricted subscribers are not provided with a pushbutton and can only make and receive local calls.

2,087,980 extending to 'difierent automatic exchanges.

Referring now to the attendants cabinet shown in Fig. 10, the attendants telephone circuit is mounted on a base and comprises a calling device CD, a handset HS comprising a transmitter and a receiver, monophone springs MS which are closed when the handset HS is removed from the cradle, an induction coil 10, and ringer RB. The information key, the hold key, the transfer key, key SK, the supervisory light SL, the two or more release and answer keys, and the common offering key are mounted on top of the base alongside the attendants telephone. The relay I020 is common to all of the release and answer keys, while the remaining relays shown in Fig. 10 are individual to one of the answering positions comprising the conductors I092 to I096, inclusive. The other release and answer keys (not shown) each have a similar group of relays and similar conductors terminating in the banks of the switches. 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 telephone subscribers to determine when an incoming trunk call is to be answered.

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 station will be rung automatically and intermittently. If the called line is busy, the called party will receive the busy tone. The release of the local call is under control of the calling party.

In order to describe a local call in detail, it will be assumed that subscriber S desires to call subscriber S2 shown in Fig. 2. Responsive to the removal of the receiver, switchhook springs SH closes a circuit for energizing the combined line and cut-oil two-step relay I03 in its first step as follows: from ground through the upper winding of relay I03, armature I05, conductor I02, lower winding of induction coil 10, transmitter T, impulse springsof the calling device, upper switchhook springs, conductor IOI, armature I04, and through the middle and lower windings of line relay I03, to battery. Due to the resistance in one of these windings relay I03 operates in its first step to close only armatures I06 and I08. At armature I06 relay I 03 connects negative battery potential from the lower winding of relay I03 by way of conductor I41 to bank contact I42 to mark the line of station S as calling; and at armature I08 connects ground to the No. 1 vertical bank contacts and also completes a circuit by way of the resistance and common start a conductor I09 through the winding of start relay 3I0 in the local finder connector distributor.

Relay 3I0, upon energizing, at armature 3II prepares the circuit for the finder start relay I20 and at armature 3I2 closes the circuit for relay 320 in case the distributor wipers are in engagement with bank contacts terminating an idle finder connector link. The circuit for energizing relay 320 may be traced from ground on the busy common conductors 391, armatures 315,

366, 3, 3I2, relay 320, interrupter springs or the motor magnet 333, and through the winding of motor magnet 333 to battery. In case the wipers of the distributor are in engagement with a busy flnderconnector link the guardconductor 396 thereof will be grounded with the result .that switching relay 320 is short circuited from ground on the guard conductor by way of wiper 386, armature 325 and back contact-to the upperterminalof relay 320. This same ground extends by way of the interrupter springs of the motor magnet 333 and through the windings thereof to cause the motor magnet to stepthe wipers of the distributor until an idle local finder connector link is selected, at which time the relay 320 is energized over the previously traced circuit. Due to the high resistance of relay 320 motor magnet 333. will not energize in series therewith. At armature 32! relay 320'prepares a point in the circuit for the polar switching relay I! 0 in the local finder, at armature 322 prepares the group test circuit for the changeover relay 340, at armature 323 prepares the circuit for vertical magnet I50, at armature 324 prepares the circuit for the finder start relay I20, at armature 325 opens the preselecting circuit and prepares a new circuit for the motor magnet 333, at armature 326 prepares the time-release circuit to the motor magnet 333, at armature 321 completes its own locking circuit, at armature 328 prepares the circuit for relays 360 and 310, and at armature 329 completes the circuit for release relay 360. Release relay 360 energizes over the following circuit:

from ground by way of armature 329, armature 313, and through the upper winding of relay 360 to battery. At armature 36! relay 360 completes the circuit for vertical magnet I50, at armature 362 completes the circuit for the finder start relay I20, at armature 3'63 opens the timerelease circuit to motor magnet 333, at armature 364 completes the circuit for time relay 350, at armature 365 prepares the locking circuit for changeover relay 340 and a holding circuit for the lower winding of relay 360 as well as the circuit ior'time-start relay 310, and at armature 336 opensthe original energizing circuit of relay 320. Relay 350 energizes by way of ground at armature 329, armature 312, and armature 364. The armature 35! iso-perated upon the energization of relay 350 to close its upper contacts and is provided with a weight 352 which, upon deenergization of relay 350, causes the armature to vibrate between. its upper and lower contacts for a predetermined time. At armature 35! relay 350 completes a locking circuit through the lower winding of relay 360 by way of armatures 365, 323, and 35!, and also completes the energizing circuit for the time-start relay 310 through the normally closed springscontrolled byarmature 316. At armature 31! relay 310 prepares a point in the time-release circuit tomotor magnet 333, at armature 312 opens the circuit of relay 350, at armature 313 opens the circuit through the upper winding of relay 350, at armature 314 completes a locking circuit for itself from grounded armature 329, and at armature 315 opens a further point in the circuit to relay 320. Relay 350 deenergizes to cause armature 35! to vibrate for a predetermined time'between its upper and lower contacts. Due to the copper slug on release relay 360 this relay is maintained energized by the vibrating armature 35! fora predetermined length of time.

Finder start relay I20 is'energized over the following circuit: from ground at armature 362 tions from the busy common conductor 391 at its back contact, and at its front contact grounds conductor I93. At armature I22 relay I20 grounds the hold conductor I94 as well as completing a circuit through the lower polarizing vwinding of polar switching relay to enable the and through the winding of vertical magnet I50 to battery. Each operation of vertical magnet I50 operates the shaft and wipers of the local finder one step in a vertical direction. On the first vertical step of the shaft the finder off normal springs I6! and I62 are operated. At off normal spring I6! the circuit to release magnet I30 is prepared and at off normal springs I62 a' circuit is prepared for grounding the guard conductor 396. Each energization of vertical magnet I50 likewise completes a circuit for the stepping relay 330 from contacts I5I, conductor 392, wiper 382, and through the winding of stepping relay 330 to battery. Relay 330 energizes over the above-traced circuit and at armature 33! interrupts the circuit to the vertical magnet I50, which accordingly deenergizes. The deenergization of vertical magnet I50 opens the circuit to stepping relay 330 at armature I5! to cause the stepping relay 330' to deenergize and again complete the circuit for vertical magnet I50. This inter-acting between vertical magnet I50 and stepping relay 330 continues until such time as the vertical test wiper I16 encounters a grounded bank contact at which time a circuit is completed for energizing the change-over relay 340 inseries with the stepping relay 330 follows: from ground at'armature I'IIi'by way of armature I08, v'ertical bank contact I, vertical test wiper I16, conducmr 393, wiper 383, armature 3H and back contact, through the upper winding of change-over relay 330, armature 322 and through the winding of relay 330 to battery. Stepping relay 330 is maintained energized over this circuit to hold the stepping circuit to vertical magnet I50 open and the change-over relay is energized to close its locking circuit at armature 332 through its lower winding from ground at armature 365. At armature 3M relay 300 opens its original energizing circuit and grounds the test lead 393 to prepare the energizing circuit for polar switching relay H0, atarmature 344 opens a further point in the original energizing circuit of relay 320, and at armature 303 transfers the stepping circuit from the vertical magnet I50 to rotary magnet M0. The operation of armature 34!; at its back contacts opens the circuit to stepping relay 330 whereupon the latter relay deenergizes, and at armature 33'! completes the circuit for energizing rotary magnet I40 as follows: from ground by way of armature 36!, normally closed springs controlled by armature 33I, armature 323, armature 333 and front contact, conductor 390, armature I23, armature II5 and back contact, through the winding of rotary magnet I40 to battery. The rotary magnet operates to rotate the wipersof the local finder in the well known manner and at arm'a ture I4I grounds conductor-392 to operate-the deenergizes after an interval.

stepping relay 330 which at armature 33I interrupts the circuit of rotary magnet I40. This inter-action between rotary magnet I40 and stepping relay 330 continues until such time as the line test wiper I13 encounters the marked contact terminating the calling line, at which time the polar switching relay H is energized.

The circuit for energizing the polar switching relay IIO may be traced as follows: from ground by way of armature 32 I, front contact and armature 34I, wipers 383, conductor 393, through the upper operating winding of relay I I0, wiper I13, in engagement with bank contact I42, conductor I41, armature I06, and through the lower winding of line relay I03 to battery. Relay IIO, upon operating, at armatures III and H2 connects up line relay 2I0; at armature II3 opens a point in the circuit to release magnet I30, at armature I I4 grounds wiper I13 to fully operate line cut-ofi relay I03 and to mark the calling line busy, and

at armature I55 opens the circuit to rotary magnet I40 and prepares a circuit to guard conductor 396.

Line relay 2I0 of the local connector is now connected in bridge of the calling line by way of wipers HI and I12 and the heavy talking conductors, and at armature 2II completes the circuit for energizing release relay 250 and vertical series relay 260 by way of the connector off normal springs 2I4. At armature 25I, relay 250 prepares the test circuit for the switching relay 200, at armature 252 grounds conductor I93 to maintain the calling line busy, at armature-253 places another ground on hold conductor I94, and at armature 254 opens a point in the circuit to release magnet 2 I 1 as well as preparing a point in the impulsing circuit. Vertical series relay 260, upon energizing, at armature 26I connects dial tone to the lower talking conductor by way of armatures 26I and 213 and contacts 234, at armature 262 opens a point in the energizing circuit of relay 210, and at armature 263 prepares a point in the impulsing circuit to vertical magnet 2 I8.

Two-step line and cut-off relay I03 is energized from grounded test wiper I13 to operate its armatures through their second step. At armatures I04 and I05 relay I 03 disconnects itself from the calling subscribers line, and at armature I01 disconnects ground from vertical bank No. I and the common start conductor I09 to cause the deenergization of start relay 3I0 in case no other subscriber is calling at this time. Relay 3I0, upon deenergizing, at armature 3 opens the circuit of the finder start relay which At armature I2I relay I20 prepares a point in the circuit to release magnet I30 and at armature I23 grounds the guard conductor 396 by way of finder off normal springs I62. When guard conductor 396 is grounded a circuit is completed for the motor magnet by way of armature 325 and front contact and through the winding of motor magnet 333 to battery. Motor magnet 333 positions its pawl and operates its interrupter springs to open the circuit of switching relay 320 which thereupon deenergizes. At armature 325 relay 330 opens the circuit to motor magnet 333 at its front contact and at its back contact completes the self-interrupting circuit to motor magnet 333, whereupon the motor magnet 333 operates in the manner of a buzzer to step the wipers of the local finder connector distributor in a buzzerlike manner until wiper 386 no longer engages a contact terminating a grounded guard conductor. At armature 328 relay 320 opens the circuit through the lower winding of relay 360 to cause the release of.the latter relay, and at armature 329 opens the locking circuit of relay 310 to cause the latter relay to deenergize. Relay 310 deenergizes first before relay 360 and after an interval relay 360 deenergizes. At armature 365 opens the locking circuit of change-over relay 340 whereupon the latter relay deenergizes.

Assuming now that start relay 3 I 0 is held energized due to the start conductor I09 being grounded by another call. The operation of armature I I5 of relay I I0 completes a circuit for operating motor magnet 333 when stepping relay 330 deenergizes, as follows: from ground by way of armature 36I, normally closed springs controlled by armature 33I, armature 323, armature 343 and front contact, conductor 394, armature I24, armature H5 and front contact, front contact and armature I23, guard conductor 396, wiper 386, armature 325 and front contact, and through the winding of motor magnet 333 to battery. At its interrupter springs motor magnet 33I opens the circuit of relay 320 which accordingly deenergizes, and at the back contact of armature 325 completes the self-interrupting circuit to motor magnet 333 to cause the distributor to select an idle local finder connector link over which this other call may now proceed. Also, if for some reason the local finder does not find the calling line then the shaft and wipers are rotated to their eleventh position, in which position the cam springs I10 are closed to ground the guard lead 396 to cause the distributor to find another idle finder connector link.

If, due to some fault, the change-over relay 340 does not operate, then the time-release arrangement is operative after a predetermined time to cause the distributor to find another local finder connector link. In this case relay 360 is held energized through its lower winding for a predetermined time by the vibrations of armature 35I and after this predetermined time relay 360 releases shortly after armature 35I ceases to make contact with its upper and lower springs. Relay 360, upon deenergizing, at armature 36I opens the circuit to vertical magnet I50, at armature 362 opens a circuit to finder start relay I20, and at armature 363 completes the circuit to motor magnet 333. This circuit may be traced from grounded armature 31I, armature 363, armature 326, and through the winding of motor magnet 333 to battery. The operation of motor magnet 333 at its interrupter springs opens the circuit of relay 320 which thereupon deenergizes. Relay 320 deenergizes with the same result as previously described, and at armature 326 opens the circuit of motor magnet 333 to cause the wipers of the distributor to be operated one step, from which point on the distributor operates over its preselecting circuit to find another idle finder connector link. In the local finder relay I denergizes, and at armature I23 grounds the guard lead 396 to maintain this local finder connector link busy until the same is fully released, and at armature I2I completes the circuit for release magnet I20 by way of off normal springs I6I and armature II3. By the operation of release magnet I30 the finder shaft and wipers are restored to their normal position and the finder off normal springs I6I and I62 are restored to their normal position when the wipers reach normal, thereby opening the circuit to release magnet I30 and removing ground from the guard conductor 396.

Returning new to the correct operation of the local finder connector link and at a time when the calling subscriber S receives dial tone over the heavy talking conductors and such subscriber in response to dial tone will dial the digits 9 and 1 to call station S2. The operation of the calling device CD in accordance with the first digit or digit 9, causes the line relay 2 ill to be deenergized nine times. Each deenergization of line relay 2"] transmits an impulse over' the impulsing circuit to vertical magnet'2l8as follows: from ground by way of armature 2H and back contact, armature 252 and front contact, armature 263 and front contact, armature 226 and back contact, and through the winding ,of vertical magnet M8 to battery. The vertical magnet 2 l8 operates the shaft and wipers of the connector one step for each impulse received, after which the wipers come to rest opposite the bank contacts inthe ninth level. On the first vertical step of the shaft and wipers the connector off normal springs l8l, 2M, and tilt are operated. The operation of off normal springs l8! grounds guard conductor 3%,

the operationof ofi normal springs 2H5 prepares a point inthe circuit to release magnet 2H of the local connector, while on normal springs 2M opens the original energizing circuit of vertical series relay 2N3, but this latter relay, due to its slow release characteristics, is held energized,

through its lower winding from the impulses being transmitted to the vertical magnet. The shaft springs 2H2 close only on the first vertical step of the wiper shaft and are opened in response to the second vertical step'ancl since at this time armature 2-62 is operated the ring reversing relay 222 is not operated. Shortly after the impulsing period relay 2% deenergizes, and at armature 26d disconnects dial tone from the calling line, and at armature 262 prepares the circuit to ring-reversing relay 2m and at armature 262 transfers the impulsing circuit from the vertical magnet 2 i 8 to the rotary magnet 2 E2.

The calling subscriber now dials the second digit, or digit 1, to cause the connector to rotate into engagement with the line of the called substation. Line relay 2H3 again follows the dial impulses and at armature 2H completes the following circuit for rotary magnet 2 ill: from ground by way of armature 2 l l and back contact, armature 252- and front contact, armature 263 and back contact, armature 223, through the winding of rotary series relay 292, armature 229, and through the winding of rotary magnet. 2m to battery. By the operation of rotary magnet 289 the connector wipers are rotated one step into engagement with the first bank contact in the ninth level, or the bank contact terminating the line of substation S2. The rotary series relay 2% energizes in series with rotary magnet 2H] and due to its slow release characteristic maintains its armature attracted throughout the rotary movement. At armature 29i relay 292 closes a circuit to the busy test relay 220, and at armature 292 shunts armature 223'to maintain the impulsing circuit should the busy relay 222 operate during such movement.

In case the called line is busy conductor 269 will be grounded from the busy connection, and the busy relay 222 will be energized from conductor 262 by way of bank contact 266, wiper 226, armature 29! and front contact, armature 205,

and through the upper winding of busy relay 220 to battery. At armature 223 relay 220 opens a point in the circuit to the rotary magnet to prevent the further operation of rotary magnet 2l9' after relay 292 deenergizes, at armature 222 and back contact opens a point in the energizing circuit of switching relay.20il, and at its front contact prepares a locking circuit for itself. At

armature 22! relay 22!] connects the busy tone to the lower talking conductor by way of contact 234 to transmit the busy tone to the calling subscriber over the heavy talking conductors in the well known manner. When the rotary series relay 290 deenergizes after the impulsing period the locking circuit for busy relay 222 is completed from grounded armature armature 222- and front contact, normally closed springs controlled over armature 29E, armature 205, and through the up r winding of busy relay 220 to battery. When the calling party hears the busy tone such subscriber will replace his receiver and release the local finder connector link in a manner to be more fully described hereinafter.

Assuming now that the called line. is, idle instead of busy, then busy relay 222 does not operate and when slow'release series relay 292 deenergizes shortly after the lmpulsing period a circult is completed for the switching relay 2min series with the lower winding of the line and cut off relay, similar'to the relay 12, of the called line. The circuit for energizing switching relay 22 in series with the line and cut-off relay of the called line may be traced from ground at armature 25!, armature 222 and back contact, lower winding of switching relay-222, back contact and armature 226, wiper 226, contact 266, conductor 262, and through the lower winding of the line and cut-off relay of the called line to battery. The line and cut-ofl relay of the called line is energized over this circuit to fully operate all of its armatures, to disconnect itself from the called line, and to open the circuit to the common start conductor tilt. At the armature, similar to armature iilt, the line and cut-off relay connects conductor 26!) to conductor 2tii'to maintain the called line busy in the banks of the local finder. Relay 222 first operates its armature 222 to complete a circuit through. its upper winding from ground at armature 252 to operate its remaining armatures. Armatures 226, 222, and 202 at relay 2m) completes the ringing circuit, at armature 223 completes the ring-back circuit through the ring-back condenser RBCfl at armature 205 opens a point in the circuit to busy relay 222, at armature 226 grounds conductor 269, at armature 208 prepares a point in the circuit to transfer relay 220, and at armature 222 opens the circuit to rotary magnet 2 it. The ringing circuit for oper ating the bell of the called station'S2 may now be traced as follows: from. interrupted generator by way of armature 222, back contact and cam spring 2l2, armature 222 and back contact, back contact and armature 233, armature 22 t, wiper 225, bank contact 285, conductor 258, and through the ringer at substation S2 to ground.

When the subscriber at substation S2 answers by removing the receiver a circuit may be traced for operating the ring cut-off relay 222 as follows: from interrupted generator over the previously traced ringing circuit through the switch-hook springs at the called station, conductor 26?, wiper 224, armature 2M, armature 231i and back contact, back contact and'armature 2H, and through the upper winding of cut-off relay 232 to battery. Ring cut-on relay 23B operates over the above-traced circuit and .closes a locking circuit for itself at armature 232, as well as the circuit for fully energizing its remaining armawas. The locking circuit for ring-cut-ofi relay 230 may be traced from grounded armature 253, armature 232, through the lower and upper windings of ring cut-off relay in series to battery. At armatures 23I and 233 relay 230 opens the ringing circuit and completes the talking. circuit over the heavy conductors. Relay 220 now energizes over the called subscriber's loop from ground at armature 253 by way of armature 232, lower winding of relay 220, front contact and armature 233, armature 204, wiper 225, conductor 268, through the substation loop, conductor 261, wiper 224, armature 2III, armature 23I and front contact, and through the upper winding of busy relay 220 to battery. Talking battery to the called line is furnished through the windings of relay 220 over the circuit just traced while the talking battery to the calling line is transmitted through the windings of line relay 2III.

After conversation and in response to the called party replacing his receiver, relay 220 deenergizes. When the calling party replaces his receiver line relay 2IIl deenergizes and at armature 2 opens the circuit of release relay 250. Release relay 250, upon deenergizing, at armature 252 disconnects ground from conductor I93 to release line and cut-off relay I03 and to free the calling line, at armature 253 removes ground from conductor I94 to cause the release of relays III), 230, and 200, and at armature 254 completes the circuit for release magnet 2 I I by way of armature 2H and connector oif normal springs 2I5. Polar switching relay I I0 deenergizes when ground is removed from hold conductor I94, and at armature II3 completes the circuit for release magnet I30 of the local finder by way of finder off normal springs I6I and armature I2I. Relays 230 and 200deenergize, the latter relay at armature 206 disconnects ground from conductor 269 to free the called line and to deenergize the associated line and cut-oil relay. When the finder and connector are released, the off normal springs open the circuit to their respective release magnets. The finder oif normal springs IIiI again grounds the busy common conductor 291 and the connector ofi normal contacts I 8| disconnects ground from the guard lead 396 to indicate that this local finder connector is now available for other calls.

It will now be assumed that subscriber S calls subscriber S3. Since the ringer at substation S3 is connected to the negative line conductor 26! the calling subscriber must prefix the digit I to the number of his line, or 9|, in order to operate the ringer at the substation S3. The finder and distributor operate inthe same manner as before and in response to the subscriber S dialling the digit I the connector operates its wipers opposite the first level of bank contacts. In this case since the wipers of the connector are opposite the first level, the shaft springs 2| 3 are closed and when vertical series relay 250 deenergizes shortly after the impulsing period, the circuit for energizing relay 210 is completed at armature 262 through the lower winding of ringreversing relay 210. Ring-reversing relay 2'") energizes and at armature 214 completes a looking circuit for itself from grounded hold conductor I94. At armatures 2'" and 212 relay 2'"! reverses the generator connections, at armature 213 opens the dial tone circuit, at armature 215 completes a circuit for reenergizing relay 260, and at armature 215 transfers the impulsing circuit from the vertical magnet to the two-step absorbing relay 280. The circuit for energizing relay 260 at this time may be traced from. ground by way of armature 2| I and front contact, armatures 215 and 282, and through the upper winding of relay 260 to battery. At armature 262 relay 260 opens the original energizing circuitto relay2IIl which is locked to hold conductor I94, and at armature 263 prepares the impulsing circuit for relay 280.

The subscriber S now dials the second digit,or the digit 9.. Line relay 2lIl follows the impulses to operate relay 280 in response to only the first impulse, and the vertical magnet for the remaining impulses of the second digit. In response to the first impulse, line relay 2! completes the circuit for energizing relay 280 in its first step as follows: from ground by way of armature 2H and back contact, armature 254 and front contact, armature 263 and front contact, armature 216 and front contact, armature 283 and back contact, and through the lower winding of relay 280 to battery. Relay 280 is energized over the above-traced circuit to close only its armature springs 28I and in so doing short circuits its upper winding from ground on the hold conductor I94. When line relay 2! energizes the short circuit around the upper wind ing of this relay is removed and the relay now energizes in its second step to operate armatures 282 and 283. At armature 282 relay 280 opens the circuit to relay 260, but this relay, due to its slow release characteristics, is maintained energized during the impulsing period, and at armature 283 and back contact opens the original energizing circuit of 'relay 280, and at its front contact prepares the circuit for vertical magnet M8. The remaining eight impulses of the second digit are now transmitted to the vertical magnet. The vertical magnet is now operated eight times to position the connector wipers opposite the ninth level of bank contacts. From the foregoing it will be seen that relay 280 absorbs the first impulse of the second digit and that the remaining impulses of this digit reoperated the vertical magnet to cause the shaft and wipersto take additional vertical steps to position :the wipers opposite the ninth level. The first digit, if digit I,therefore determines that the ringing current will be transmitted out over the negative conductor,.and such first digit conditions relays. 210 and 280 so that only the first pulse of the next digit to be dialled is absorbed and the remaining impulses then reoperate the shaft to the desired level.

The. operation from here on is the same as before, except that the generator is transmitted over the negative line conductor as follows: from interrupted generator, armature 202, back contact and cam spring 2I2, armature 212 and front contact, back contact and armature 23I, armature 2I1I, wiper 224, conductor 261, and through the ringer at substation S3-to ground. The ringback tone to the calling subscriber is transmitted by way of the heavy talking conductors through the ring-back condenser RBC. When subscriber S3 answers, ring cut-off relay 230 is energized over the previously traced circuit and from thence through the substation of subscriber S3, conductor 268, wiper 225, armature 204, armature 233 and back contact, front contact and armature 2H, and through the upper winding of cut-off relay 230 to battery.

Cam springs 2I2 are operated on the tenth rotary step of the selector and are provided to enable subscribers to connect with a code call switch and dial such switch to transmit a desired code call to operate the code call signals Cir placed throughout the establishment. The impulsing circuit over which the code call switch is operated may be traced from armature 2H and back contact, armature 254 and front contact, armature 263 and back contact, front contact and cam springs 2i2, armature 212 and back contact, back contact and armature 233,

armature 2M, wiper 225, and from thence over the bank contacts terminating the code switch in the banks of the local connector.

Incoming trunk calls It will now be assumed that an incoming trunk call is received over conductors 501 and 508.

Ringing current from the central oilice extends by way of conductor I01, condenser, the A C signalling relay 5M, armature 562, conductor 508 back to the central office. A C sign-allingrelay 5% is energized over this circuit and at armature 505 completes the circuit for signalling relay 500. At armature 50! relay 500 completes a cir-. cuit for energizing relay Hill! in Fig. 10 in case the signalling key SK is in normal position, at

armature 502 completes the circuit for time relay 509, and at armature 503 completes the circuit for operating relay 580. The circuit for energizing signalling relay will extends from ground through the winding of said relay, back contact and middle spring of signal key SK, over the common signalling conductor I09! to armature 50!, and through the resistance to battery. At armature i008 relay i007! grounds the common conductor extending to all of the trunk signals which are placed in different locations throughout the establishment to call the attention of the local subscribers to the fact that an incoming trunk.

call is to be answered. At armature 596 relay 593 prepares a locking circuitfor time release relay 58B. Armature bill is provided with a weight 592 which vibrates between its upper and lower contacts when the time relay 5% is released. Relay 5% is energized over the following circuit: from ground by way of armature Md and back contact, armature $65 and back contact, conductor 529, armature 503, and through the lower winding of relay 580 to battery. At armature 583 relay 5% completes a circuit for energizing busylrelay 5%, at armature 5M and back contact removes ground from conductor 532 to mark this trunk line as calling in the incoming bank of the trunk distributor and at the front contact of armature 5M grounds the incoming start conductor 533 to energize the common. incoming trunk call relay 630. At armature 582 relay 58b completes a looking circuit through its lower winding from grounded conductor 52s by way of armature 59E. Relay 630, upon energizing, at armature GM and back contact disconnects ground from incoming start conductor i536, and from conductor mar. Ground is thus removed from conductor 636 to enable alocal subscriber to answer this incoming trunk call. At the front contact of arma-' ture fi3| the circuit for the incoming relays 66? and 668 is prepared.

Any non-restricted subscriber may answer this trunk call by dialling the answer number, in-this case the digits and 3. -In response to a nonrestricted subscriber removing his receiver and dialling the digits O and 3 m answer the trunk call, the local finder and connector operate in the same manner as before, and when rotary series relay 290 deenergizes after the impulsing period the switching relay 2% is energized in series with relays 661 and 558. This circuit may be traced as follows: from ground by way of armature 25!, I

of relay 200, back contact and armature 29!, wiper 2%, bank contact 255, conductor 835, armature SM and front contact, through the winding of marginal relay 65?, and through the lower and upper windings of relay 668 to battery. Relay 661 being marginal will not operate in series with both windings of relay 668. Relay 200, upon energizing, at armature 206 grounds conductor 8% to busy this position to other connector switcheaat armature 201! completes its locking circuit through its upper winding, and at armature 20B prepares a circuit for transfer relay 240.

In the trunk distributor relay 668 energizes over the previously traced circuit, and at armature 69d disconnects battery from the remaining sequence control relays, and at armature 5M locks itself through its lower winding and causes the energization of marginal relay 657 in. case the trunk distributor is not in use on other calls, in which case either of the armatures 6'85, 630, or 684 may be in operated position. In case the trunk distributor is not in use then marginal relay 661 is energized from ground at armature 2W, wiper 226, conductor 695, armature til, winding of relay 656?, through the lower winding of relay ifitiband by way of armatures 5M, 5M, iidl and 535 to battery. At armature 585, relay as? com pletes the test circuit to enable the trunk distributor to find the trunk line having the incoming call, at armatureiifli completes the circuit for energizing the start relay 6% in case the incoming wiper til i is on an ungrounded bank contact, at armature t8? grounds conductor 6% to mark the answering line in the trunk finder bank by way of the local finder and connector link at armature 688 grounds the conductor Ml to. mark the group the answering line is located in, and at armature the grounds conductor was which is used only when the attendant answers incoming calls.

The operation of the trunk distributor at this time is dependent -upon whether the wiper til is in engagement with a grounded bank contact in which case the start relay 5% is short circuited and the motor magnet M5 is operated in a self-interrupting circuit until the incoming wiper an loses ground. The circuit for short circuiting relay Mil and operating the motor magnet liidmay be traced from grounded conductor, such as conductor 532 extending to the idle trunk line, the bank contact terminating these conductors, incoming wiper Ell, armature 635, resting contact and armature Ml, resting contact and armature tilt, through the winding of relay 6M to' short circuit relay sac, and by way of armature M2, interrupter springs, and the winding of motor magnet 6 I 9 to battery.

As soon as wiper 6H engages a non grounded bank contact or a contact'corresponding to the trunk line having an incoming call thereon, the short circuit around relay Mil is removed and relay Mil thereupon energizes in series with the motor magnet cm as follows: from ground by way of armature 686,'rel.ay 6 W, armature M2, interrupter springs; and the winding of magnet di to battery. Motor magnet 569 is marginal and will not energize in series with the high resistancewinding of relay 640. At armature 6M relay 5% grounds the start lead MS of the corresponding trunk line to operate the start relay Q50 thereof, at armature 642 opens its original energizing circuit and the circuit of rotary magnet M9 but due to the resistance R in bridge of armature 622 the relay 640 is maintained in armature .222 and back contact, lower winding l energized position, and at armature 643 operates the release relay 650. Relay 650, upon energizing, at armature 65I prepares a circuit for the magnet (H9.

The circuit for energizing start relay 450 on this trunk line may be traced as follows: from ground by way of armature 6, start wiper 6I8, start conductor 419, trunk finder off normal springs 469, armature 443,- and through the winding of start relay 450 to battery. At armature 45I relay 450 prepares the circuit for operating winding of the polar-stop relay 410, at armature 452 energizes the polarizing winding of the polar relay 410, at armature 453 opens a point in the circuit to relay 440, at armature 454 completes the circuit for the vertical magnet M5, at armature 455 completes a locking circuit for itself from grounded conductor 419, and at armature 456 opens a point in the circuit to release magnet M1.

The circuit for operating the vertical magnet 4I6 extends from ground by way of armature 454, armature 412 and back contact, normally closed springs controlled by armature 42I, armature 4| I and back contact, and through the winding of vertical magnet M6 to battery. Vertical magnet 4I6 operates the shaft and wipers one vertical step in response to each energization, and at contacts of H9 completes the circuit for operating the stepping relay 420. On the *first vertical step of the wipers off normal springs 461 close to prepare the circuit to release magnet M1, and oil normal springs 469 opens the original energizing circuit of start relay 5 which is now held energized by way of its armature 455, Stepping relay 420 at armature 42I interrupts the circuit to the vertical magnet 4I5 which de energizes and disconnectsground from stepping relay 420 which thereupon deenergizes to again close the normally closed springs controlled by armature 42I to again complete the circuit for the vertical magnet 4| 6. This interaction between the vertical magnet MB and 420 continues until the vertical wiper 428 finds the marked vertical bank contact which has been grounded by the operation of relay 661. When the vertical wiper engages a grounded bank contact the change-over relay M is energized in series with the stepping relay 420 when ground is opened at armature M9 by the deenergization of vertical magnet M6. The circuit for energizing the change-over relay and for maintaining the stepping relay 420 in energized position may be traced as follows: from ground at armature 688, conductor 641, bank contact 251 in the local connector, local connector wiper 228,-conductor I96, finder wiper I15, bank contact I45, conductor I55, and in this case through the first vertical bank No; 1, vertical wiper 428, armature 4, lower winding of relay 0, and through the winding of stepping relay 420 to battery. Relay 4| 0 operates its armature M3 to complete a circuit from ground at the oil" normal springs 468 for maintaining the change-over relay in energized position when it opens its original energizing circuit and the circuit of stepping relay 420 at armature 4. At armature 4II change-over relay 4I0 transfers the stepping circuit from the vertical magnet M6 to the rotary magnet H5, at armature 2 opens a point in the circuit to start relay 450, and at armature 4 opens the circuit to stepping relay 420 which accordingly deenergizes. At armature 42I stepping relay 420 completes the circuit for operating rotary magnet H5, and the rotary magnet 4| at contacts MB completes the circuit for energizing stepping relay 420. The operation of stepping relay 420 at armature 42I opens the circuit to rotary magnet 4I5 whereupon the rotary magnet deenergizes to cause the deenergization of stepping relay 420. Each operation of the rotary magnet 4I5 rotates the wipers of the trunk finder one step in a rotary direction. The above inter-action between the rotary magnet M5 and stepping relay 420 continues until such time as the polar stop relay 410 is energized in response to wiper 425 encountering the marked contact marked by the trunk distributor. When wiper 425. finds the marked contact polar stop relay 410 and transfer relay 240 in the local connection energize in series over the following circuit: from ground by way of armature 681, conductor 646, bank contact 256, wiper 221, armature 208, the lower winding of transfer relay 240, conductor I95, wiper I14, bank contact I43, conductor I53, trunk finder bank contact 415, wiper 425, back contact and armature 44I, armature 45!, and the upper operating winding of polar stop relay 410 to battery. Polar stop relay 410, upon energizing over the above traced circuit, at armature 41I completes a circuit by way of the back contact and armature 404 for energizing recall relay 530, at armature 412 and back contact opens the stepping circuit to the rotary magnet and at its front contact completes the circuit for energizing the switch through relay 460 from grounded armature 454, at armature 413 completes a holding circuit for the switch through relay 460, and at armature 469 removes the short circuit from around the upper winding of time release relay 580 to render the latter relay quick to release. Relay 460, upon energizing, at armatures 46I and 462 connects the talking conductors I02 and IM to both windings of the differential recall relay 5I0 and through the lower and upper windings of line relay 550 to ground and battery, respectively. At armature 463 relay 460 g ounds conductor I00 by way of wiper 424 to maintain the line and cut-oif relay I03 energized and to maintain the answering line busy. At armature 464 relay 460 opens a point in the circuit to relay 430, at armature 465 opens a further point in the circuit to release magnet 4", at armature 466 and back contact opens the holding circuit of release relay 580, and at the front contact of armature 466 connects ground at armature 444 to the polarizing windings of the polar stop relay 410 to maintain this relay in operated position. Relay 530, upon energizing, at armature 53I prepares a holding circuit for the two-step relay 520. The circuit for energizing the line relay 550 may be traced as follows: from ground through the lower winding of line relay 550, the lower left-hand winding of the repeating coil, and thence over the heavy talking conductors by way of the normally closed springs controlled by armature 522, the lower winding of diiferential relay 5I0, conductor 5, armature 462, wiper 423, conductor I 02, through the answering substation loop to conductor IOI, wiper 422, armature 46I, conductor 5I3, through the upper winding of differential relay 5I0, normally closed springs controlled by armature 52I, upper lefthand winding of the repeating coil, and through the upper winding of line relay 550 to battery. The recall relay 5I0 being differential will not energize over the above-traced circuit. Line relay 550, upon energizing, at armature 552 completes the circuit for energizing release relay 560, and at armature 55I bridges the right-hand winding of the repeating c011 across the trunk conductors 507 and 508 to cause the ring cut-off relay in the central omce to operate and disconnect ringing current from conductors 501 and 508. Release relay 560, upon energizing, at armature E6! maintains the busy relay 510 in operated position and at armature 562 disconnects the A C signalling relay 504 from in bridge of the trunk conductors 501 and 508. Relay 5M releases and at armature 505 opens the circuit of signalling relay 500 which deenergizes after an interval. Relay 580 deenergizes when its locking circuit is opened by relay 460 and at armature 58! and front contact disconnects ground from conductor 533 to cause the denergization of the incoming trunk call relay in the trunk distributor in case no other incoming calls have come in, and at armature 588 and back contact grounds conductor 532 to short circuit the start relay Mil in the trunk distributor to cause the same to deenergize. Relay 500 deenergizes a short in-.

terval after its circuit is permanently opened at armature 565, and at armature 5M opens the circuit to relay I901 which deenergized and extinguishes the trunk signal lamps throughout the establishment. .At armature 502 relay Elli? opens because the trunk finder has switched through to its answering local line.

In the distributor the incoming trunk call relay 63H deenergizes only in case a second incoming trunk call has not arrived by this time, and at armature 63E opens the circuit to relays tit? and 688 at its front contact, and at its back contact grounds the conductors Gilt-and iiltl. In case a second trunk call has arrived, relay 63b is maintained in operatedposition and the relays coming wiper til, conductor 532, resting contact and armature-585 to ground. At armature 6M relay t lt opens the circuit to start relay 5% which thereupon deenergizes. t lt closes a self interrupting circuit to the motor magnet tit which is effective after the release of relay 650 in case another call has arrived. At armature M3 and front contact relay t lt opens the circuit of release relay 650 which thereupon deenergizes after an interval and at back contact completes a circuit by way of armature t5! for maintaining the rotary magnet 619 in energized position during the release time of release relay 65!). Relay tt'l, upon energizing, at armature 685'opens the self-interrupting circuit to motor magnet as well as opening the short circuit around relay 6M, and at armature 686 opens the circuit of start relay 620 to insure the deenergization of the latter relay. At armature 681 relay Mil disconnects ground from conductor 6% to remove the marking potential from the finder at the connector banks, at armature 638 likewise removes the marking ground from conductor 64?, and at armature 689 removes ground from conductor i098. Relay 668, upon deenergizing, at armatures 690 and 69| reconnects battery to permit the energization of any of the sequence con- At armature M2 relay trunk distributor is now at normal and may be used for subsequent calls.

Returning to the local finder connector link and at a time when transfer relay 240 energizes in series with the polar stop relay 410. Relay 240, upon energizing, at armature 223 completes a locking circuit through its upper winding from hold conductor I94 and at armatures 2M and 252 opensthe circuit to line relay Zlll. Line relay M0 deenergizes and at armature 2 opens the circuit to release relay 250. Release relay 2%, upon deenergizing, at armature 252 disconnects ground from wiper H3 and conductor ltl which is now grounded by way of con uctor me. At armature 253 opens the holding rcuit of relays it, 220, 2W, 280, 2%, and 280, which nowdeenergize, and at armature 254 completes the circuit for release magnet 2H. By the operation of the release magnet til the local connector wipers are restored to their normal position. The ofinormal springs 2E5 open the circuit to release.

magnet ill, The deenergization of switching relay 26!] at armature rot-o1- the release of the switch wipers disconnects ground from conductor 6% to cause the deenergization of relays G61 and ME in case the same has not by this time deenergized. Relay Mil, upon deenergizing, at armature H3 completes the circuit for the finder release magnet l 39, whereupon the magnet restores the finder wipers and the finder oif'normal spring Mil opens the circuit to the release magnet 530. All of the relays and the apparatus in the local finder connector link are now at normal and may be used on subsequent calls.

In the trunk finder, start relay lhll deenergizes when its circuit is opened in response to the deenergization of start relay t lt disconnecting ground from conductor M9 at armature ttl. At armature 55 relay 850 opens the original operating circuit of relay tilt, at armature i152 disconnects one of the grounded connections from the lower polarizing winding of relay Mil, at armature 353 prepares a point in the circuit to transfer relay tea, at armature t'tt opensthe original'energizing circuit of relay lfill and at armature lifit prepares a point in the circuit to release magnet ii'l. The answering subscriber S isnow connected to the two-way trunk by way of the heavy talking conductors Hit and mi, trunk finder wipers 522 and 423, armatures at! and Q62, conductors M3 and 5M, through the windings of the diiferential recall relay 5 l 0, through the normally closed springs controlled by armatures 524 and 522, and through the windings of the repeater coil and line relay 550 to groundand battery. Talking battery is furnished to the subscriber S over the circuit just traced, while the talking battery for the central office subscriber is furnished at that ofiice.

central ofilce' switches and connections, and at armature 522 opens the circuit to release relay 560. After an interval slow-to -release relay 560 deenergizes to open the circuit to busy relay 510 the trunk conductors Ell! and 508 to release the at armature 56!, and at armature 562 reconnects the A. C. signalling relay 564 in bridge of the trunk conductors. Slow-'to-release relay 516 deenergizes after aninterval to disconnect ground from conductor 534 and to ground the busy common conductor 535 at armature 51!, and at armature 512 opens the holding circuit to relay 466 to cause the latter relay to release. After an interval slow-to-release relay 466 deenerglzes to open the talking circuit at armatures 46! and 462, at armature 463 disconnects ground from conductor !66 to release line and cut-off relay I63 and to free the local line, at armature 456 completes the circuit for energizing the release magnet 4 l1, and at armature 466 opens the circuit through the lower polarizing winding of relay 416 to cause the latter relay to deenergize. Relay 416, upon deenergizing, at armature 41! causes the release of relay 536. The circuit for energizing release magnet 4!1 may be traced from armature 465, armature 456, finder off normal springs 461, and through the winding of release magnet M1 to battery. By the operation of the release magnet 4!1 the shaft and wipers of the trunk finder are restored to their normal position. Ofl normal springs 461, 468, and 469 are likewise restored to their normal positions when the shaft reaches its normal position. At'ofi normal springs 461 the circuit to the release magnet 4 1 is opened, at ofi normal springs 468 the circuit to change-over relay 4!6.is opened, whereupon the latter relay releases, and at off normal springs 469 the circuit is again prepared for relay 456. The trunk finder and trunk are now at normal and may be used on other trunk connections.

In case of fault, such as failure of a trunk finder to find the answering line, or in case the incoming trunk call is not answered the time release is effective to free the trunk and apparatus after a predetermined time. Shortly after ringing current from the central oflice is cut off, signalling relay 566 deenergizes to open the signalling circuit at armature 56!, to open the circuit of time relay 596 at armature 562, and to open the original energizing circuit of time re lease 586 at armature 563. When relay 596 deenergizes armature 59! vibrates between its upper and lower contacts to maintain time release relay 586 energized for a predetermined time. At this time since the upper winding is short circuited by normally closed armature 469, the relay is'rendered slow to release and is therefore held energized by the vibrating armature 59!. When the vibrations of armature 59! are of insufficient magnitude to hold relay 586 energized, this relay thereupon deenergizes. At armature 583 relay 586 opens the circuit 'to the busy relay 516 to deenergize the same, at armature 58! and front contact disconnects ground from conductor 533 to release the incoming trunk call relay 636 and at the back contact grounds the conductor 532 to mark this trunk line as busy for incoming calls in the bank of the trunk distributor. The relay 516 deenergizes after an interval and at armature 51! disconnects ground from 534 to enable the trunk distributor to seize the trunk line for use in an outgoing trunk call, and at the back contacts of armature 51! connects ground to busy common conductor 535 to maintain the busy common relay 636 in energized position. At armature 512'relay 516 disconnects ground from conductor 526 to permit the release ofthe trunk finder in case the same has been operated.

Outgoing trunk calls Any non-restricted subscriber may originate an outgoing trunk call by removing his receiver and dialling the digits 01 or 02, dependent upon which group of trunks is wanted. Assuming now that subscriber S desires to make an outgoing trunk call over the first group of trunks and in response to the removal of the receiver at substation S, an idle local finder connector link is connected to the line of substation S. In response to dial tone subscriber S dials the digits 0 and 1 to operate the local connector wipers into engagement with the connectorbank contacts 234, 235, 236, and 231, in a manner similar to that previously described. In case no other local subscriber is at this time originating an outgoing trunk call then the switching relays 266 in the local connector and relay 664 in the trunk distributor are operated over the following circuit: from ground by way of armature 25!, armature 222 and back contact, lower winding of switching relay 266, back contact and armature 29!, wiper 226, bank contact 235, conductor 635, armature 624 and front contact, through the winding of marginal relay 663 and through the lower and upper winding of relay 664, and armatures 683 and 696 to battery. Relay 663 is marginal and will not energize in series with the upper winding of relay 664. Switching relay 266, in the same manner as before, at armature 261 locks itself energized, at armature 266 grounds conductor 635, and at armature 268 prepares a circuit for transfer relay 246. In the trunk distributor relay 664 energizes in case the trunk distributor is not in use and at armature 686 disconnects battery from the group 2 sequence control relays 66! and 662, and at armature 68! connects battery from armature 615 through the lower winding of relay 664 to cause the energization of marginal relay 663. At armature 616 relays 663, upon energizing, connects the test circuit of the group 1 wiper 6!6 to start relay 646 and motor magnet 6!9. At armature 611 relay 663 prepares the circuit of start relay 646, at armature 618 grounds conductors 639 to mark the calling line in the trunk finder bank, and at armature 619 grounds conductor 645 to mark the group including the calling local line in the banks of the trunk finder. As long as the wiper 6!6 is in engagement with a grounded bank contact the self-interrupting circuitfor motor magnet 6!!! is completed and the start relay 646 is short circuited to prevent its operation. This circuit may be traced from the grounded bank contacts engage by wiper 6!6, front contact and armature 616, to relay 646, and by way of armature 642 and interrupter springs and winding of motor magnet 6l9 to battery. When wiper 6 l6 engages a bank contact terminating a conductor, such as conductor 534, with no ground thereon the short circuit around start relay 646 is opened andthis relay thereupon energizes in series with the motor magnet. The motor magnet being marginal will not energize in series with relay 646. Start relay 646, upon energizing, at armature 64! again grounds conductor 419 to energize start relay 456 in the trunk finder. At armature 642 relay 646 opens the stepping circuit to motor magnet H9, and at armature 643 operates release relay 656. Relay 646 is now heldover a circuit including the resistance R and the interrupter spring and the winding of magnet 6!9.

The operation ofjthe trunk finder is similar to that described for an incoming call, and the various operations will. therefore. be briefly d

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