US1504261A - Telephone-exchange system - Google Patents

Description

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ELLS H. MILLS, OF EAST ORANGE, NEW JERSEY, ASSIGNOR T0 WESTERN ELECTRIC GOMPANY, INCR-PORATED, OF NEW YORK, N. Y., A CORPORATION OF NEVI" YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed December 30, 1920. Serial No. 433,98?.

To all fio/0m t may concern.'

Be it known that l, Ennis H. MILLS, a citizen of the United States, residing at East Grange, in the county of Esser; and State of New Jersey, have invented certain new and useful Improvements in Telephone-EX- change Systems, of which the following is a full? clear, concise, and exact description.

This invention relates to a telephone eX- change system and more particularly tol a system in which connections are established between subscribers lines by means of mechanical switching devices.

ln systems of the above mentioned character a central office sending mechanism is employed which controls the selective movements of the mechanical switching devices in accordance with the directory numbers of desired lines which numbers the calling subscribers cause to be registered on the registers of the sending mechanism through the operation of the impulse dials associated with the substations of their lines. lf the subscribers lines are equipped with coin bores it is desirable to further provide central station means for operating the coin boxes to collect or refund the deposited coins as connections are successfully or unsuccessfully established. Since calling subscribers may set the registers of the oilice sender for establishing all connections listed in the telephone directory it may often occur that subscribers may attempt to obtain connections to which they are not entitled without the deposit of additional coins or coins of larger denominations. On the other hand it may be desirable to permit connections to certain lines without necessitating the deposit of a coin, as, for example, connections to anoperators position, to the police station, fire headquarters, hospitals, etc.

ln order therefore that there may be an automatic supervision of the toll controlling means which automatically functions in accordance with the nature of the established connection or in accordance with its routing, it is proposed to associate the service charging controlling means directly with the office sender so that the setting of the sender by the y calling subscriber may determine whether the attempted connection shall proceed with or without the deposit of a coin, or whether the connection shall be rerouted to an operators position where the deposit of the necessary charge may be properly supervised.

lt is the usual practice in systems of this general character to provide central office sending mechanisms which are available for the use of a group of subscribers lines and to associate an idle mechanism with the me-` chanical switching devices employed to establish a desired connection by means of a suitable switching device for only such a period as is necessary Vto enable the switching devices to be adjusted, and to then disassociate such mechanism and render it available for controlling other connections which may be initiated in the same group of lines. Inasmuch as the charging of the call against the calling subscriber is not accomplished until after it has been determined whether the attempted connection is successful, that is, until after the called subscriber responds, and as at this time the otice sender and associated toll controlling mea-ns are disassociated from the established connection, it is therefore necessary to reassociate an idle sender and toll controlling means temporai-ily with the established connection. rlhis is preferably accomplished upon the termination of the established connection;

It is an object ofthe invention to establish a method of and to provide means for permitting the establishmentk of certain connections without the deposit'of a coin.

A further object of the invention is to provide means for routing connections to an operators position when subscribers attempt to establish certain connections.

A further object of the invention is the provision of means for testing to determine whether the substation service charging device has functioned properly in response to the central office controlling mechanism.

One feature of the invention resides in the provision of coin collecting` and refunding mechanism associated with the oilice sender which is controlled by the operation of the sender in accordance with the nature of the established connection.

A. further feature of the invention resides in the provision of means associated with the oiiice sender for rerouting a connection to an operators position if the calling subscriber attempts to call certain numbers. The oilice sender in accorda-nce with this inventionis provided with a group of code env and numerical registers which are set by the calling subscriber in accordance with the.

' Va translator switch from the setting of the code registers. Certain of the register re lays cause thesetting of a class switch associated with the sender; other relays con: trol the functioning of the sender to control the'settino` of the district and otlice switches and others serve as zoning and routing re- Y lays which operates. special route switch.

rFliese Zoning and routing relays, when operated to advance the route switch, cancel the effect of the districtand ol'ice registra-tion which the calling subscriber has caused to be established and set up a new routing for rerouting the attempted connection to an operators position. Y A still further feature resides in the provision of means associated with the oiiice sender for delaying the operation of the sender immediately prior to its control of units selection until after the calling subscriber has deposited the necessary coin, and the further provision of means comjirising a special lregister' relay for cancelling the effect of the sender delay means when the calling subscriber attempts certain connections, as, for example, to an operateurs position, to the police station, tire headquarters,

etc. in order to permit such connections to be established regardless of the deposit of a coin.

These and other features of 'the invertion may be more readily understood by rer- Y erence to the following description con- CFI sidered in connection with the accompanying drawing in which Fig. l shows one of a group of lines terminating` in a full mechanical cnice of the exchange, and a rotary line switch individual to such line by means of which the subscribers line may be connected to an idle district selector switch 3 Fig. 2 shows a district selector and a sender finder switch together with the circuits and controlling mechanism associated therewith; Fig. 3 shows an oflice selector switch together with the circuits and controlling mechanism associated therewith; Fig. l shows an incoming selector switch provided with mechanism for applying ringing current to the terminals of a called line together with the circuits and mechanism for controlling said switch; Fig, 5 shows the mechanism and circuits of a final selector switch and the line of a subscriber to which the selector switch has access; Fig. 6 shows a time measure switch and translator control sequence switch associated with the central oflice sending mechanism; Fig. .7 shows a portion of the circuit of a sending-.mechanism comprising a stepping` .relay c group of counting relays, a sequence switch 'for controlling the circuits of the sender, and a class sequence switch for altering the circuits of the sender in accordance with the class of the call which is to be established; Fig. S shows the code registers which are set in accordance with the iirst three code ior ollice designation digits dialled by the calling subscriber, and a steering switch which successively associates the code registers and numerical registers shown in Fig. 9 with the impulse circuit extending to the calling` subscribers line; Fig. 9 shows the numerical registers which are set by the calling subscriber in accordance with the numerical designation of the desired line; Fig. l0 shows groups of translator register rclays which are variously operatet by the translator switch and pulse machine shown in Fig. ll in accordance with the setting of the code registers for determining the setting of the class switch shown in Fig. 7, the set-ting of the district selector switch shown in Fig, 3, and for setting the sequence switch of the districtselector to determine the connection of the repeating coil into the talking circuit; Fig. ll. shows a translator switch and a development of the pulse machine drum for setting the register relays; 'Fig'. 12 shows a. time measure switch and associated mechanism for applying collection and refunding current to the calling subscribers line for chargingv the call against the subscriber, and signaling mechanism associated wtih a sender monitors position for supervising the operation of the sender; Fig. 13 shows circuits of a route switch under the control of the translator relays of Fig. 10 for determining the routing of calls and Fig. let is a diagram showing the manner in which the several sheets of the drawing should be arranged to show much of a complete organization of circuits as is necessary to illustrate the manner in which connections may be established. Ilhe calling suliscribefs line K is of the usual type of coin box line provided with a transmit-ter., receivencall bell and coin box, and since the line terminates in a full mechanica-l exchange it is also equipped with an impulse sending dial S of the usual type.

The subscribers line terminates in an individual trunk finding switch of the wellknown rotary stepby-step type, which through a plurality of wipers has access to a group of trunk lines terminating in district selector switches. The switch is provided with a stepping magnet for advancing the wipers over terminals of trunk lines in search of an idle trunk and for advancing the wipers around to normal position upon the release of the established connection.

The district selector, oliice selector, incoming selector, and tina-l selector switches,

lil() diagrammaticfally disclosed in Figs. 1 to 5 inclusive, are of the type shown in the patent to E. B. Craft and il. N. Reynolds, 1,123,696, issued January 5, 1915.

The translator switch TS, shown in Fig. 11, is of the same type as the switch shown in the aforesaid patent but is equipped with ten sets of brushes arranged in live pairs, the brush sets comprising each pair being arrangedl to be tripped together. 1n Fig. 1 1 only one pair of the brushes has been disclosed.

The sender finder switch SF, shown in Fig. 2, the time measure switch TM, shown in Fig. 6, the sender monitors time meas ure switch M, shown in Fig. 12, the register vsteering switch BS, shown in Fig. S, and the registers A, B, C, Tl-l, H, T and U, shown in Figs. 8 and 9, are of the wellknown step-by-step type. With the eXception of sender `iinder switch SF, the wipers of these switches are restored to normal position by being advanced by their respective stepping magnets fo-rwardly to normal position. Finder switch SF has no normal position, the wipers thereof resting in contact with the bank terminals last employed, when the switch is idle.

The pulse machine PM, shown in Fig. 11, comprises a drinn of insulating material in which a plurality of circumferential rows of contact segments are embedded, these segments being connected to a source of current through a common slip ring 1125. A plurality of brushes engage the several rows of segments and are arranged to bev variously connected to the cont-acts in the ten banks of translator switch TS through a suitable distributing frame (not shown) for conducting impulses of current from the several segments of the drum to the bank terminals of the translator switch.

For controlling the circuits associated withV the several selector switches and the circuits of the oihce sender, auxiliary switches are employed. These switches may be Aof the type disclosedin the patent to il. N. Reynolds and C. F. Baldwin, 1,127,808, issued February 9, 1915, and known in the art as sequence switches. Each se uence switch comprises a rotatable shaft (driven from a constantly rotating source of power through a magnetic clutch member and can ries a plurality of circuit closing cams., which, at different radial positions of the shaft, cause the closure of a plurality of contacts. The cam contacts associated with each sequence switch are closed only in the positions indicated by the numerals associated with'each contact, with the exception of the master contacts 201, 301, 401, 501, 601, 701, 751 and 1301 associated respectively with sender switches 200, 300, 400, 500, 600, 700, 750 and 1300, these latter contacts being opened in the positions indicated by the numerals appearing adjacent such con tacts and closed in all other positions.

The diderent pieces of apparatus en ployed in the system having now been briefly described, it is thought that a clearer understanding of the invention may be had from a description of the method employed in establishing various connections from the station of the calling subscriber K. The following connections will be described in the order indicated:

T. The establishment of full mechanical connections in the local area.

TI. The establishment of free connections.

TTT. The attempted establishment of connection outside the local area.

TV. The establishment of a connection for special service, as telegraph service.

V. The establishment of calls for either toll or long distance service.

l. THE Es'rABLisnMnNr or A FULL lilncHAN- .man CONNECTION In LocAi. AREA.

, conductor 10aA to ground at the upper armature and back contact of cuteoft relay 102. rThe line relay energizes in this circuit and closes a circuit for the stepping magnet 105 of the switch 100, which circuit may be traced from grounded battery through the 4winding and armature contacts of magnet 105, conductor 106,- the lowermost armature and back contact or relay 102, the righthand armature and front Contact of relay 101, conductor 107, and thence to ground through the wiper 108 and the normal terminal of the bank to which this wiper has access. The magnet 105, upon energizing in this circuit, advances the wipers 108, 109, 110, 111, 112 and 113 of switch 100 to the second contacts of the respective banks to which they have access. As the second contact which wiper 10S now engages is permanently connected to ground, magnet 105 continues to step the wipers to the third set of contacts leading to the first of the group of trunks to which the switch 100 has access.

Tf the first trunk of the group is busy there will be a ground potential on the test terminal thereof appearing in the lowermost bank of the switch, Vand the switch will therefore continue stepping until an idle trunk is found upon the test terminal, of which battery potential appears. lihen this battery potential is encountered a circuit is closed from battery through the right-hand contact-sof sequence switch ycam 202 of the ductor 115, and thence to ground through both windings oit' relay 102. Relays 101 and 102 are then 'energized inthis circuit. The energization ot relay 102ropens the circuit of the stepping magnet 105-at its lowermost armature and back contact and at its upper armature and front contact and intermediate armature and front contact this relay eX- tends the conductors 103 and 104 of the subscribers line to the Wipers 111 and 113 of the switch 100, and thence to the trunk conductors 116 and 117 leading to the selected *district selector. Relay 102, at its intermedi` ate armature and front contact, closes a circuit extending through the lett-hand winding ot sleeve relay 226 of the district selector switch through the normal cont-acts of the left-hand armature of slow releasing relay 227, the lower right-hand contact of sequence switch cam 203 (1 to 21/2), sleeve conductor 118, wiper 109, conductor 120, the intermediate armature and front contact of Vrelay 102, and thence to ground through the upper' winding of relay 102. The sleeve rela'y Y226 of the district selector switch energiZes in this circuit. v For making the calling` subscribers line busy to all calls incoming thereto, battery ypotential is connected to the multiples of test terminal 121 appearing in the banks of all final selector switches having access to this line, over conductor 122, through wiper 110 and the olii-normal segment 123 to grounded battery. Wiper 112 through the grounded off normaliseginent 124 prepares a circuit extending over conductor 125 preparatory to restoring the finder switch 100 to normal when relay 102 becomes dee-nergized upon the termination of the connection.

Upon the energization of sleeve relay 226 a circuit is established for the line relay 228 ofthe district selector switch 250, which circuit extends from grounded battery through the right-hand winding of this relay, the upper contacts of sequence switch cam 204, the right-hand armature and front contact of relay 226, and thence to gro-und through the upper right-hand contact of sequence switch cam 205 (17 to 15). At its inner lefthand armature and front contact relay 226 connects ground potential to the test conduc- Thel locking circuit of line relay 101 is now opened and the line relay deenergizes.

Relay 228, upon energizing, closes a circuit for driving the sequence switch 200 of the district selector switch out of its normal position 1 into position 2, this circuit extending from grounded battery through the magnet winding of sequence switch 200, thel lower right-hand contact of sequence switch cam 206 (1), the inner right-hand armature and front contact of relay 228, and thence to ground at the upper right-hand contact of sequence switch cam 207 (71 to 6). The sequence switch magnet energizes in this circuit and under the control of master cani 201 drives the sequence switch into position 2, in which position a circuit is closed from grounded battery A through the left-hand winding of relay 227, and thence to ground through the upper left-hand contact of sequence switch cam 205 (2 to 11). Relay 227, upon energizing, closes a locking circuit for sleeve relay 226 extending through the left-hand winding of relay 226, the alternate Contact of the left-hand armature ot relay 227, and thence to the sleeve conductor 11S, over the upper right-hand Contact of se* quence switch cam 203 (1%1- to 16), this circuit being maintained through position 'I6 of the sequence switch or until relay 227 bccomes deenergized. Upon reaching position 2 the sequence switch connects a. new holding ground to the test conductor 114 at the lower lett-hand contact of sequence switch cam 205, which holding ground is main tained through position 1871, ot the sequence switch.

As soon as the sequence switch reaches position 1%, a circuit is closed for the stepping magnet 229 of the sender finder SF cx tending from grounded battery through the interrupter contacts and winding ot magnet 229, the lower left-hand contact'ot sequence switch cam 208, the inner right-hand armature and front contact of relay 223, and to ground at the right-hand Contact of sequence switch cam 207. A circuit is also closed at this time through the winding of stepping` magnet 229, the winding of cut-in relays 230 and 244 in parallel and thence to ground at the upper left-hand contact oit sequence switch cam 209 (2 to 11). Relays 230 and 244 do not energize at this time, however, since their windings are shunted by ground connected through the armature of relay 228.

As soon as sequence switch 200 .leaves position 1 the initial energizing circuit of relay 228 is opened at the upper contacts ot sequence switch cam 204, but this relay remains locked over a circuit extending from grounded battery through its left-hand winding, its left-hand armature and front contact, the lower right-hand contact of sequence switch cam 210 (1 to 6), the lower left-hand Contact of sequence switch cam 211 (1 to 2l), the outer left-hand armature right-hand armature and back contact a circuit for driving sequence switch 200 out of position 2 and into position 3. This circuit may be traced from grounded battery through the magnet winding ot sequence switch 200, the upper lett-hand Contact ot sequence switch cam 206 (2), the inner right-hand armature and back contact ot relay 228, and thence to ground at the righthand contact of sequence switch cam 207.

fils soon as line relay 228 deenergizes, the shunt around the windings of relays 230 and 2liis removed at the inner right-hand armature and front contact of relay 228, and relays 230 and 2411 thereupon energize in series with stepping magnet 229, the current llowing ithrough this circuit, however, not being sullicient to cause the energization et the stepping magnet. Relay 230, upon-tenergizing, closes a circuit extending yfrom ground through the inner right-hand armature and front Contact ot this relay, over wiper 231 and the terminal upon which it is resting, conductor 625, and thence to grounded battery through the lett-hand winding of differential relay ($26u Relay 626 ei'iergizes in this circuit and closes a circuit for advancing the time measure switch Tli/l out of its normal position. This circuit may be traced trom grounded battery through the winding ot stepping niagnet 027, wiper 628 and the normal terminal of the bank with which it is associated, interrupter G29, the outer left-hand armature and back Contact of relay 630, andthence to ground at the armature and front contact ot relay 626. Stepping magnet 627 vadvances the wipers ot the time measure switch into position 2 under the control ot interrupter 629 for measuring ott a suitable time interval before relay 630 becomes energized to apply thedialing tone to the calling subscribers line.

As soon as the time measure switch Til/'l reaches position 2 a circuit is established for relay 630V which may 4be traced from grounded battery through the winding ot this relay, bank terminal 631, wiper 632, and thence, to ground. Relay G30 energizing in this circuit closes a locking circuit for itselt -extending through its winding, its intermediate lett-hand armature and front contact, and thence to ground at the armature and front contact of relay 626. At the hack contact of its outer lett-hand armature relay 630 opens the previously traced steppingcircuit through the stepping magnet 627 ot the time measure switch and closes a new stepping circuit which may be traced 'from grounded battery through the winding'ot stepping magnet G27, the armature and back contact of magnet 027, wiper 633, the second position terminal 63stwith which the wiper 633 is new in engagement, the outer lett-hand armature and front contact of relay 630, and thence to ground at the armature and front contact of relay 026. Stepping magnet 627 is now energized in this circuit and by means of itsownseltinterrupting armature contact advances the wipers ot time measure switch Til/l to nposition in which position the circuitho't magnet G27 is opened at wiper As soon asA the time measure switch leaves its normal position busy ground potential is applied to the test conductor G25 multiplied into the bank terminals of all sender iinder switches Sli1 having access to the seized sender. This busy potential is applied to conductor 625 over a circuit which may be traced from ground through wiper 635, the ell normal terminals et the bank with which wiper is associated, the right-l and ditl'erential winding of relay 626, and thence to test conductor 625, and serves to hold the selected sender busy until the sender is released by its disassociation trom the district selector by which it was initially seized,

Relay 630, upon energizing, also closes a dialing circuit tor associating the registers ot the sender with the calling subscribers line, which maybe traced. from groimded battery through the winding ot stepping relay 800, conductor 801,.the outer lett-hand armatureand bach, Contact ot relay 1200, the outer lett-hand armut ire and bach contact ot relay 1201, conductor 1203, the righthand a nature and front contact ot relav G30, conductor 637, wiper 230, the inner lett'- hand va' n nire and trout Contact ot relay 230, conductor 235, the lon ,r lett-hand contact ot sequence switch cam 213, the winding oit relay trunk conductor 16, wiper 111 ot the trunk finding switch 100, the innermost armature and trout contact ot' relay 102, line conductor 103, through the calling sul; sc1ibe "s sending dial S, line conductor 1011, the upper armature and front contact ot relay 102, wiper 113, trunh' conductor 117, the lower lett-hand contact ot sequence switch cam 212, conductor 233, the outer lett-hand armature and front contact of relay 230, wiper conductor G36, inner lett-hand armature and front contact ot relay G30, conductor 1202, the outer righthand armature and back contact of relayY 1201, the outer right-hand armature and back contact of relay 1200, conductor 1204, and thence to ground through the righthand winding of balancing retardation coil 638. The stepping relay 800 energizes in this circuit and at its left-hand armature and front contact closes a circuit for the slow releasing relay 802, this circuit eX- tending from grounded battery through the -winding of relay 802, and thence to ground through the left-hand armature and front contact of relay 800. A circuit is now closed for sending a dialing tone io the calling subscribers line, which circuit may be traced from ground through the make contacts of the right-hand armature ot relay 802, conductor 803, wiper 804-, normal bank terminal 805, conductor 806, through the left-hand winding of balancing coil 638, and thence to ground through the secondary winding of tone coil 689. rEhe tone current iowing in this circuit is indue-tively transmitted to the substation of the calling subscriber through the right-hand winding'of balancingcoil 638 and over the circuit previously traced.

Upon the initial energization of relay 626 a circuit was also established for initiating the operation of the monitoring time measure switch M. The starting circuit for starting the switch M may be traced from grounded battery through the winding of starting relay 1205, the normally closed contacts associated with its inner lett-hand armature, wiper 1206 of the switch M and the normal bank terminal upon which it is resting, conductor 1207, thence to ground at the armature and front contact of relay 626. Relay 1205 energizing in this circuit establishes la locking circuit for itself independent of the wiper 1206, which may be traced through its winding, the make Contact of its inner left-hand armature, conductor 1208, and thence to ground on conductor 1207. At its intermediate right-hand armature, relay 1205 establishes a circuit for slow to release relay 1209 which may be traced from ground through the intermediate right hand armature and front contact ot relay 1205, ,the inner lett-hand armature and back contact of relay 1210, wiper 1277 of the switch M, the normal bank terminal upon which it is resting, the winding of relay 1209, conductor 1211, the right-hand armature and back contact of the coin translator register relay 1035, conductor 1036, and thence to battery at the outer right-hand armature and back contact of zone relay 1302. Relay 1209, upon energizing, closes a locking circuit for itself extending from conductor 1211, through its winding, its left-` hand armature and front contact, the outer right-hand armature and back contact ot coin collect relay 1212, conductor 1218, the armature and back contactof coin test relay 1214, the inner left-hand armature and back contact oi relay 1215, and thence to ground at the outer right-hand armature and 'liront contact of relay 1205. At its right-luind armature and front contact relay 1209 establishes a circuit for relay 1,216, which may be traced from battery on conductor 121i, through the winding oi relay 1216, and thence` to ground at the right-hand armature and front contact of relay 1209, and a circuit for relay 1210 which ma)v be traced from grounded battery through the righthand winding of relay 1210, wiper 1217 olf the switch M, the normal bank terminal upon which the wiper is resting, and thencel to ground at the right-hand armature and front contact of 'relay 1209. rThe encrgization of relay 1216 is without cii'ect at this time.

Relay 1210, upon energizing, establishes` a stepping circuit for the stepping` magnet 1218 of the switch M, which may be traced from grounded battery through the winding of magnet 1218, the right-hand armature and front contact oi relay 1210, wiper 1217 and the normal bank terminal upon which it is resting, and thence to ground at the righthand armature and front contact ot relay 1209. Stepping magnet 1218 advances the wipers of switch M one step when the energizing circuit of relay 1210 is opened at the switch wiper 1217 and the previously traced circuit through the winding ot steppingmagnet 1218 is opened at the armature contact of relay 1210. lith relay 1210 deenergized and switch M in position 1 a new driving circuit for the switch M is established through the winding of stepping` magnet 1218 and the Slow interrupter 1219, which may be traced from grounded battery through the winding of magnet 1218, the. right-hand armature and back contact ot relay 1210, interrupter 1219, the inner letthand armature and back contact ot' relay 1220, the No. 1 terminal in the bank with which wiper 1277 is associated, wiper 1277. the inner left-hand armature and back con tact of relay 1210, and thence to ground ai; the intermediate right-hand armature and front contact of relay 1205. Under the intluence of the .slow interrupter 1219, switch M is advanced into position 3 measuring oii' time suiiicient to enable the calling subscriber to dial the rst digit. l't the calling subscriber fails to dial the first digit within the time measured by the advance ot switch M to position 3, a circuit is established i'or displaying a signal on the sender monitoring lamp 1221, which circuit may be traced from grounded battery through the lamp 1221, the outer left-hand armature and bat-k l contact of relay 1215, bank terminal 1222. wiper 1223, the outer left-hand armature and back contact of relay 1210, and thence to ground at the intermediate right-hand armature and front contact ol relay 15205.

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f'ltt the same time a signal is displayed by the pilot lamp 1224, the lamp 1224 being illuminated over a circuit which may be traced from grounded battery through lamp 1224, the right-hand armature and back contact ot relay 1220, bank terminal 1225, wiper 12777 the inner left-hand armature and back contact ot' relay 1210, and thence to ground at the intermediate right-hand armature and iront contact of relay 1205. The monitoring operator noting the illumination of lamps 1221 and 1224 takes the necessary steps to ascertain the trouble on the calling line or the reason why the calling subscriber has tailed to commence dialing.

Assuming that the calling subscriber does proceed to dial the first digit oic the number of the desired connection within the specitied time interval, and further assuming that the subscriber desires a connection with a subscribers line L which is listed .in the directory as L l S penard 9582, and that the called line is to be reached through a district selector switch 250, an oi'iice selector switch 350, an incoming selector 450, and a iinal selector 550, the subscriber proceeds to dial three letters corresponding to the otlice designation ot the desired line and then dials tour digits representing the number of the line in such office. ln the case assumed the calling subscriber will dial the letters L l S and will then dial the numerals 9532. The three letters which represent the oiiice code will not only cause the setting` of the district selector switch and oliice selector switch to choose the desired otiice, but Will-also cause the se ii'cttz'ng the code and mnnercal registers.

ln response to the first interruption of the impulse circuit by the calling subscriber in accordance with the first letter ot the ohice designation, the stepping relay 800 dee-nergiaes and closes a circuit tor the stepping magnet 807 ot the irst code register A, which stepping circuit may be traced from grounded battery through the letthand armature and back contact ot' prelimr nary pulse relay 808, conductor 809, the winding of slow release relay 810, conductor 811, the winding of stepping magnet 807, the back contact and outer right-hand armature of relay 808, the'normal bank terminal 812 of the register steering switch RS, wiper 818 normally in engagement. therewith, conductor 814, the upper contacts ci' route switch cam 1303 (1), conductor 1304, 'the lett-hand armature and :trent contact of slew releasing relay 802, and thence to ground through the armature and back coutact ot' stepping relay 800. in response to this impulse the stepping magnet 807 advances the wipers olf the register A one step as soon as the circuit oit the stepping inagnet 807 is again opened upon the reenergization of stepping relay 800, and in response to successive interruptions of the lirst code letter L, the register A advances its wipers into contact with the titth set ci terminals of its banks. To insure that the stepping magnet 807 shall remain energized long enough upon each deenergization of stepping relay 800 to cause a complete step of the register, a circuit is closed through relay 841 in parallel with the winding of stepping magnet 807, which circuit may be traced from grounded battery `through the inner right-hand armature and back contact ot relay 808, the winding' of relay 841, wiper 842, the normal terminal of the bank with which it is associated, the armature and back contact of stepping magnet 807, and thence to ground at the armature and back Contact of relay 800 over the circuit previously traced. Relay 841 energizes in this circuit and closes a locking circuit for itsel'i independent of the armature contacts ot relay 800, which locking circuit extends over the circuit previously traced through the winding et' relay 841, through the armature and back contact of magnetI 807, the outer right-hand armature and back contact et relay 808, bank terminal 812, wiper 818, thence to ground through the lett-hand armature and front contact of relay 841. Relay 841 and stepping magnet 807 are thus maintained energized until stepping magnet 807 has moved its armature to substantially the full extent of its movement; lwhen the circuit through relay 841 is opened at the armature contacts et magnet 807. Relay 841, at its right-hand armature and tront contact, closes a holding circuit for slow releasing relay 802 for holding this relay energized independent of the energization of relay 800.

The slow releasing relay 810, which was also energized in the circuit et steppingmagnet 807 ot the register A, maintains its energization because ot' its slow releasing characteristic until the series of impulses transmitted through the magnet 807 ceases, whereupon this relay deenergizes. Upon its initial energization relay 810 closes a circuit extending from grounded battery through the make contacts of its lett-hand armature and the winding or slow releasing relay 815, and this latter relay through its armature and front contact connects ground potential to the `test conductor 625 indepench vently of the eti' normal contacts and wipe-r G35 of time measure switch TM tor insuring that the otiice sender shall be maintained busy during the setting et register A. At its

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