US1504304A - And warbeit w - Google Patents

Description

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Aug., XL2, 1F51 W. P. ALBERT ET AL TELEPHONE ,EXCHANGE SYSTEM Filed Dec. 22

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WALTER I?. ALBERT, 0F EAST ORANGE, NEW JERSEY, AND 'WARREN W. CARPENTER,

0F BROKLYN, NEW YORK, ASSIGNORS T0 WESTERN ELECTRC COMPANY, INCQR.- PORATED, O'F NEW' YORK, N. Y., fr CORPORATION 0F NEW" YORK.

Application filed December 22, 1920. Serial No. 432,420.

T0 all whom it mary concern.'

Be it known that we, WALTER l?. ALBERT and VARREN 7. CARPENTER, citizens oi the United States, residing at East Orange, in the county oi Essex, State of New Jersey, and Brooklyn, in the county of Kings, State of New York, respectively, have invented certain new and usejul Improvements in Telephone-Exchange Syste-ins, or which the following is a tull, clear, concise, and exact description.

rl`his invention relates to telephone ei;- change systems and especially to those sys tems wherein machine switching apparatus is used for building up talking connections.

ln the system disclosed herein connections to called subscribers lines depend in part for their extension and supervision on operators at the central oiiice. The operators receive the designations of the called lines and manipulate devices at their disposal, in accordance with such designations, which govern the selective movement of the automatic switches to set up the connec tions. The calling subscribers lines are lirst attended by answering or A-operators. These operators may be either in the saine oliice where the selective switches are located or at manual positions in distant olices according as the calling line is a local one or one belonging` to an outlying oliice. there the answering operator is situated in a distant ofiice, her position is usually equipped with outgoing trunks leading to cordless positions at the central machine switching oi'lice. The operator in the .originating oihce answers the calling subscriber and learns, 'for example, that the called line is one which must be reached through the central switching oliice. She thereupon con'nnunicates, over an order wire, the wanted number to the operator at the cordless position and requests the assignment of a trunk to'be used for the connection.

The cordless operator in the central switching ol'lice assigns to the answering operator one of the idle trunks interconnectn ing their positions, and atl they same time brings about the association ot' ay register sending mechanism with this trunk. The cordless operator then sets up the called number on her keyboard which causes 'the positioning ot the switch controlling registers.

The registers of the sender there alter serve to govern the automatic switches to selectively entend the connection through to the called line. The cordless operator having performed these duties ordinarily has no further interest in the call until it its time to release the automatic switches following conversation. She is, however, appraised ot the manner in which the establishment ot the connection progresses by means oi indicating` signals. The answering` operator supervises the calling and called lines and initiates the release when conversation is over by taking down her cord circuit. This gives the cordless operator a disconnect signal and she, in turn, effects a release of the automatic switches.

It happens occasionally, during the' establishment ot the connection, hat one ot the automatic switches iinds all trunks busy in the group over which it is limiting and goes to the overflow position. Further progress being defeated by such a condition, the cordless operators attention should be called to the fact in order that she may restore the apparatus used in the partially completed connection.

The object ci' the present invention is, therefore, to provide, in a system of the tore@ going character, means comprising a time measuring device rendered ei'lfective by the register to actuate a signal at the operatorls position in the event that one or the selective switches finds all trunks busy.

,er feature of the invention relates to means including a time measuring device rendered eilective by the register sender when one olf the selective switches iinds all trunks busy for actuating a signal bel'ore the operator and means dependent upon the release of said switch for retiring the signal,

rllhese and other Afeatures contemplated by this invention will become more readily understood from a consideration of the following description and the appended claims.

leiter-ring to the drawing which forms a part of the application, Figs. l to 5 inclusive when arranged in the order illustrated in the diagram of Fig. 6 disclose a portion of a telephone system of the type to which the invention is applicable. At the lett ot the brolren line in Fig. l there is shown the calling plug of an answering operators cord circuit located in an originating otice. To the lett of the broken line there is also shown the voutgoing end of an interoiiice trunk circuit which leads to a cordless'operators position in the central switching oiiice. The remaining portion of this ligure discloses the trunk circuit at the cordless operators position in the central switching oiiice together with the necessary controlling and supervisory devices.

Fig. 2, at the left, shows a district or first group selector switch in which the incoming trunk circuit terminates. To the right of Fig. 2 is shown `a second group selector Switch.

Fig. 3 illustrates a iinal selector or connector switch located in the same oiiice and serving to complete the connections to called subscribers lines.

Fig. 11 discloses a switching unit made up vof two trunk finder switches which serve to automatically associate an idle register sender with the particular trunk circuit at the cordless operators position that has been taken for use in the extension of a connection. This ligure further discloses an allotter switch for assigning an idle register sender for use. 1

Fig. 5 shows a keyboard consisting otV a plurality of rows of number keys located at the operators position and one of a plurality of register sender units to which the keyboard is common.

General description.

The automatic switches shown in Figs. 2 and 3 are ofthe two motion step-by-step type in which a primary stepping magnet operates in response to series of directive impulses to advance the brushes to select the desired group and then a secondary steppingrmagnet operates to step the brushes over the chosen group to select a set of terminals therein.

The trunk finders consist of single movement rotary'step-by-step switches each made up of a plurality of arcuate rows of terminals and cooperating brushes. A trunk finder unit consists of two of these rotary switches, one of which is designated TF1 and the other is designated T F2. vThe pur-` pose of utilizing two switches per unit is to increase the number of trunk circuits at the operators-position that may be associated with the register sender. Half of the trunks, such as the trunk 107, 108 shown in Fig. 1 at the operators position are apportioned to the first trunk finder TF1 and the remaining half of said trunks are ap-portioned to the second trunk inder TF2. When the operator assigns a particular trunk :for use by the distant operator, the first trunk finder switch commences to rotate. and search `for thisv particular trunk.

test of all the trunks which it serves.. Thereafter, the second trunk linder switch TF: begins to operate and finds the desired trunk. In the drawing the several sets ot terminals and brushes of each ot the trunk iinder switches of a given unit are enclosed within the dotted rectangles. Within the lower rectangle are shown the stepping magnet 108 and the brushes and terminals belonging to the trunk finder TF1. The stepping magnet 409 and the several rows of terminals which comprise the second trunk inder TF1 are shown within the area of the upper broken rectangle.

The operators keyboard shown in F ig. 5 comprises four rows of ten keys each, designated as 500, 505, 510 and 515. By the use of these keys the operator may record any number in an oice whose capacity is 10,000 lines. These keys are of the locking type and any depressed key will remain in its actuated position until released by the energization of an electroniagnet. The release magnets for the thousands, hundreds, tens and units keys are shown respectively at 528, 529, 530, 531 and 532. In addition to the ten number keys there is provided a common contact ior cach row. These contacts, which are identitied by the characters 5657 566, 567 and 568, are closed whenever one of the number keys in their corresponding rows is depressed.

The operators keyboard briefly described above is common to a plurality ot trunk finder and register sender units. One oi the register sender units at the operators position is illustrated in detail in Fig. 5. The registers, of which there are four, one for each of the four digits in a subscribe1"s line number, comprise single motion steplay-step rotary switches. The thousands register 501 is provided with a stepping magnet 502, the hundreds register 506 with a stepping magnet 507, the tens register 511 with a stepping magnet 512 and the units register 516 with a stepping magnet 517, which magnets operate to step the brushes of their respective registers from position to position. The stepping magnets, the brushes and their coacting terminal banks and the other elements pertaining to each of the tour registers are located within the spaces of the corresponding broken rectangles at the right of Fig. 5.

The sender cont-rol switch is likewise of the step-by-step rotary single motion design. This switch consists ot a stepping magnet 555 and a plurality of brushes and terminal rows. The several brushes of the sender cont-rol switch are, for convenience, distributed throughout Fig. 5.

Each of the register sender units is, furthermore, equipped with a time measure switch, the function of which is to regulati` the advance of the sender control switch `from one position to another in such a man1 nerthat the automatic selective switches are given a suliicient time to complete a manimum trunk limiting operation. lhe time measure switch generally designated by the letter WP, comprises a small rotary stepey-step device including a stepping magnet 545 and a plur-ality of brushes and terminal rows. The elements of this switch are all conlined within the area of the broken rectangle in the lower lett-hand corner of Fig. 5.

ln order that a trunk nder and register sender unit may always be allotiefor use when one is idle, and to avoid confusion in apportioning the same, an allot-ter switch AL is provided. The allotter switch likewise consists of a small step-by-step device in which a stepping magnet 424 is designed to move the several switch contacts from one position to another. The several elements belonging to the allotter switch are located within the area oft the broken rectangle shown at the right of Fig. 4.

" Detailed operation.

It is believed that a more thorough understanding of the invention may be had by giving a detailed description oi the method ol operation of the system. To this end let it be assumed that a subscriber in the originating oliice illustrated by the disclosure at the. left of the broken line in Fig. 1 has initiated a call. The answering or A-operator at the originatingotlice attends to the calling line in the usual manner and obtains the desired designation. On learning that the calling subscriber wishes to converse with a subscriber whose line belongs to the machine switching office, she converses with the cordless operator in this latter oilice and informs her of the number ot the called line. The order wire, which is used by the operators for communication with one another, not shown in the drawing, its purpose and function being well-known. The cordlx14 operator selects an idle trunkl circuit such as the trunk 107, 108 incoming to her position and communicates to the operator at the origina-ting otlice the identity oi" the trunk taken for use. rlhe originating operator being given this information, inserts the calling plug of' her cord circuit in the jack 101 ot' the outgoing trunk, assigned to her by the cordless operator. rllhe insertion of the plug in the jack completes a circuit from battery through the winding oit relay 1027 sleeve of plug 100, sleeve of jack 101, left-hand winding of relay 106 to ground at the contact and armature .of the polarized relay 105. winding of relay 106 is also included in series with the winding of relay 102. This latter winding of relay 106 is wound with a high resistance so that the llow The right-hand of' current therethrough is not great enough to permit the energization of relay 102. Since, however, the right-hand winding of relay 106 is shunted out at this time by the direct circuit to ground at the arinarelay 106, conductor 108, lower left-hand l" winding of repeating coil 109, right-hand normal contact oi" relay 111, right-hand winding of relay 110 to ground. Relay 110 operates, but the liow ot current is in such a direction that the relay at the originating oliice fails to energize. Conscquently, the supervisory lamp 103 remains illuminated. Relay completes a circuit from battery through the winding ot relay 114 to ground at the contact and armature of relay 110. Relay 114 establishes a circuit from battery, through the lamp 118, inner right-hand armature and back contact oit' relay 117, left-hand armature and back contact or" relay 120, outermost righthand armature and contact of relay 114 to ground. Lamp 118 illuminates in this crcuit and serves as an indication to the cordless operator that the fir-operator .in the originating otiice has connected the calling i line to the assigned trunk.

At the time the cordless municates the identity of the assigned trunk to the distant -operator, she also depresses an assignment key 126, individual to said trunk. The purpose of this .key is to cause the operation of the allotted trunk iinder to associate an idle register sender with the trunk to which said key is individual. A circuit is completed from ba tterv, through the winding ot relay 125, contacts or key 126, right-hand armature and contact ot relay 122, back contact and right-hand armature` of 'relay 124, closed contacts of key 127 toy ground. Relay 125 operates and locks as follows, beforethe contacts of key 126 open when released by the operator: battery, through the winding and front contact and inner right-hand armature of relay and thence to ground as traced at the left-hand contacts of key 12?. Relay 125 establishes a circuit from ground, through its inner left-hand armature and contact, conductor 135, lower right-hand contact 425 (1) of the allotter switch,

. inter brush 550 o1 the sender control switch,V con tact 569, conductor 442, winding ot relay 406 'to battery and ground. Relay 406 becomes energized and completes a circuit from ground through its outer right-hand armature and tront contact, conductor 433, terminal 570, brush 549, contact and armature and winding of stepping magnet 555 to battery and ground. The said magnet 555 energizes, interrupts its own circuit and vdeenergizes to advance the several brushes ot the sender control switch onto their iirst `position terminals.

lt may be well to note at this time that the sender' control switch, the register switches, the time measure switch, the trunk finder switches and the allotter switch are all designed to advance the brushes from one terminal to anotherl upon deenergization of the stepping magnets.

lith the sender control switch in its irst position, the relay 406 is maintained energized,l the circuittherefor being now closed through the brush 550 and terminal 57.1.

'.lhe stepping magnet 408 oi the iirst trunk tinder TF1 commences to advance the brushes 410, 411, 412, etc., trom position Yto position to search for the calling trunk circuit. `The circuit for operating magnet. 408 may be traced trom battery, through the winding ot said magnet, armature and contact thereof', conductor 443, through the connected terminals with which the brush 415 cooperates, intermediate lett-hand armature and 'front contact ot' relay 406, terminal .444, brush 415 to ground. @n the first operation ot the stepping' magnet 408, the seyeral brushes ot the trunk linder TF1 advance to their lirst position terminals. rlhe operating circuit for the stepping inagnet 408, thereafter leads over the coiuluctor 443 and thence directly to ground through xconnected terminals and brush 415, Since the callingV trunk is not represented in theterminals o1" the iirst trunk linder switch, the stepping magnet 408 will con. tiene to operate. until the brush steps oft the t one or" the series of connected inal and makes engagement with the tei iinal 4e. rlie circuit oi magnet 400 ming-opened Vthe switch comes to rest and stal.,-lished as 'follows' tor operatthe second trunk iinder switch TF2: .rery through the winding and armature and contact ot stepping magnet 409, liront Contact and innermost lett-hand armature of ,relay 406, terminal 446, upon which the brush ot the second trunlr iinder switch is now standing, brush 422, terminal 445, brush 415 to grount. Magnet 409 energizes, iptsf its` own circuit and deenergizes to advance the brushes 417, 418, etc., to the terminals representing the first trunk in the group which Vis seryedby the switch TF2. .ilereaiter, the operating circuit tor the stepping magnet 409 leads i'rom lnittery, through the winding and armature androntact ol said magnet, over the series of connected terminals which brush 422 is now engaging, terminal 445 and brush 415 lo ground. .in parallel to this circuit, a circuit is established from battery, through the winding ot relay 407, innermost left-hand armature and Contact of relay 406, brush 422, terminal 415, brush 415 to ground. Relay 407 energizcs` ior a purpose lncsenl'ly to be eonsidered.

lVhen the brushes of: the second trunl: finder reach the terminals identitying the assigned trunk circuit at the operators position, a test circuit is closed 'lroin battery, through the .winding ot' stepping magnet. 409, front contact and lett-handi arma( ure o l relay 407, winding of relay 402, contact and inner` lett-hand armature of' relay 401, brush 411, terminal 447, brush 41S, terminal 44S, conductor 134, contact and outer left-hand armature oft relay 125 to ground. 'lhe siepping magnet 400 energizes pcrimlnently iu this circuit and the brushes are stopped in engagement with the proper set oi terminals. The relay 402 also becomes energized and establishes a circuit as above traced troni battery, through the winding o'lt magnet 4.05). front Contact and lett-hand arinatiue o E relay 407, thence through the winding and Contact and lett-hand armature of relay 402, conductor 435, brush 547 ot the sender control switch, conductor 434, brush 410, brush 417, conductor 133, contact and outer right-hand armature oi relay 110, winding ot relay 122, right-hand contacts of key 127 to ground. Steppiing magnet 40S), relay 402 and relay 122 are locked in this circuit. Ren lay 402 at its inner right-hand armature closes an operating circuit for the relay 401. Relay 401 closes a holding circuit as iiollows tor relay 407: battery, through the winding and inner right-hand armature and contact of relay 407, outer left-hand armature and contact ot relay 401 to ground. )relay 401 also completes a circuit troni battery through the winding of slow-to-rcleas.rx relay 404, contact and right-hand armature of relay 403, outer lelthand arn'lature and contact oi relay 401 to ground. The tunction et the slow-to-release relay 404 will be taken up hereinafter.

The relay 122 which also energizes in the holding circuit serves to extend the conductors 136 and 187, which constitute the inipulse circuit, from the sender to the first group selector switch. Relay 122 at its rightdiand armature and Contact opens the holding circuit ot relay 125. Relay 125 removes ground from conductor 135, whereby relay 406 releases its armatures. Relay 122, furthermore, completes a circuit trom ground through its outermost lett-hand armature and Contact, winding ot relay 120 to the non-grounded pole of battery. Relay 120 becomes Yenergized and at its lett-hand armature and back contact opens the above traced circuit for lamp 113. VLamp 118, however, remains illuminated in a circuit through the innei` right-'hand armature and back con-tact orn relay 117, left-hand armature and front contact of 'relay l120, back contact and innermostlett-hand armature of .relay 124 to greund.

Registration Of celled itzmter.

lt will be assumed that the number of the called subscribers liine 330, which is communicated by the originating operator over the order wire to the Vcordless operator in the machine switching olice, is-96'10. Accordingly, as tsoon as the cordless operator has assigned the trunk, she records the desired designation by depressing the proper keys in vthe thousands, hundreds, tens and units rows on the keyboard. The keys which she actuates are key 557 in the thousands row, key 558 in the hundreds row, key 559 vin the vtens -ro-w and key 560 in the units row. As soon as a key in each of the four rows has been actuated, the common row contacts are closed. and circuits are established tor the stepping magnets 502, 507,

512 and 517 of the registers. These circuits lead in parallel `Vfrom battery through the windings and armatures a-nd contacts of said magnets, conductor `449, lower lett-hand contact 450 of lthe afllotter switch, conductor 428, common contacts 568, 567, 1566 and 565 to ground. The stepping magnets of lthe registers interrupt their own circuits and ad Vance the brushes from terminal to terminal in search of the depressed keys on the operators keyboard. 'lvlihen the thousand register 501 ylinds the operated ,key 557, a circuit is closed from battery through the winding of magnet 502, winding of relay 503, brush 524 (position 1), brush 504, terminal 561, key 557 to ground. When the register 506 linds the depressed key 558, a circuit is completed Afrom battery through the winding ot magnet 507, relay 508, brush 525 1), brush 509, terminal 562, key 558 to ground. ln a similar manner the circuits are completed through the windings ot magnets 512 and 517 and the corresponding relays 513 and 518 to ground. through the operated keys 559 and 560 respectively. Then the registers reach positions corresponding to these keys, `the magnets are thereby permanently energized, and the brushes brought to rest. After the last register has found the depressed key, a circuit is closed trom ground, through the right-hand armatures and contacts of rela-ys`518, 513, 508 and 503 in series, conductor 572, terminal 573,'brush 548, contact and armature and winding' ot stepping magnet 555 to battery and ground. Magnet 555 interrupt-slits own circuit and advances the sender control switch to its second ,position.

'ln position 2 of the sender control switch, the depressed lkeys on the operators keyboard are released inasmuch as they are no longer needed. The circuit for the release magnets 528, 529 etc., may be traced from battery, through the windings of these magnets in parallel, terminal 574, brush 551 to ground. lV-ith the keys released, the relays 503, 5081 513r and 518, rbecome deenergized and close a series circuit from ground oyer'their left-hand armatures and contacts, terminal 575, brush 548, contact and armature and winding oi' magnet 555 to battery and ground. The stepping magnet 555 again energizes` and advances the sender cont-rol switch into position 3. The register sender has thus received the record of the called subscribers line and is now in condition to transmit series of impulses in accordance with said record to operate the automatic switches to set up the necessary connection. The impulse circuit, which is completed over the left-hand armatures and front contacts of relay 122, may be traced from battery, through the rightehand winding of relay 200 at the first group selector S1 back con- `tact an inner left-hand armature of relay 207, conductor 129, middle left-hand armature and front contact of relay 122, con ductor 136, brush 419, brush 412, back contact and lett-hand armature ot relay 400, contact ,and lefthand armature of relay 403, brush 413, brush 420, conductor 137, front Contact and innermost left-hand armature otl relay 122, conductor 128, outer llett-hand armature and back contact of relay 207, lett-hand windinget relay 200 to ground. Relay 200 energizes and closes a circuit from battery through the windingr` of slow-to-release relay 201, front contact and armature of relay 200, contact and outer right-hand ari'nature of relay 207 to ground. lt will also be noted that the relay 405 is included in a circuit .in parallel to the circuit leading through the contact and lefthand armature ot relay 403. llelay 405, however, remains inert so long as its winding is shunted by the lett-hand Varmature and contact of relay 403.

Operation of #ret group selector.

When the sender control switch reaches position 3, a circuit is established from battery, through the winding of relay 556, conductor 579, brush 544 and normal position terminal 576 of the time measure switch T, brush 536 (position 3) brush 520 to ground. l'lelay 556 becomes energized and closes a circuit from battery, through the winding or' magnet 555, contact and letthand armature ot relay 556 to ground. At the same time, a circuit is closed trom ground through the lOnt contact and in- ,armature of relay 556, lett-hand armature and back contact of relay 554, winding oi relay 553 to battery and ground. Relay 553 operates and completes a circuit from battery through its winding and contact and armature, winding of relay 554, conductor 579 and thence to ground atbrush 520.V Relay 554 does not energize sinee its winding is shunted by the direct circuit to ground at relay 552. As soon as the interrupter 451 opens, however, relay 554 becomes operated andlochs in series with relay r1`he next closure or" the interrupter 451 and the consequent energization of relay 552 results in the establishment of a circuit from ground, through the right-V hand armature and contact of relay 554, outer left-hand armature and contact of relay 552, brush 537 (position 3), winding of stepping magnet 502 of the thousands register 501 to battery and ground. liflagnet 502 attracts ,its armature and prepares to acvance the brushes 504 and 520 to their next position terminals, when its circuit is severed. At theV same time, a circuit is eompleted from ground, through the Contact and inner left-hand'armature ot relay 552, Contact and outer right-hand armature of relay 556, left-hand armature and front contact of relay 554, conductor 430, winding of the stepping relay 400 to battery and ground. Stepping relay 400 attracts its armatures, and opensthe impulse circuit leading to the selector S1, thereby permitting the release of relay 200.

Relay 200 on retracting its armature closes a circuit from ground, through the outer right-hand armature and Contact of Vrelay 207, armature and back contact of relay 200, armature and fronteontact ot relay 201-which remains energized during the transmission of impulses-winding of slow-to-release relay 202, winding of the primary stepping magnet 203' to battery and ground. Magnet 203 operates to advance the brushes 208, 209 and 210 into operative relation with the iirst group of terminals. Relay 202 likewise energizes and establishes a eireuit from battery, through the winding of relay 206, lowerinost springs ot the oli normal Contact 211, armature and iront contact oi relay 202, conductor 13o, middle arn'lature and contact ot relay 120, lett-hand contacts of key 127 to ground. 1t will be noted that the oll' normal Contact 211 is closed the instant the brush shaftt takes its iirst primary step. Relay 20G on energizing locks in a circuit from battery through its winding, lower springs of contact 211, armature and Contact oli magnet 205, contact and outer armature ot relay 206 to ground at the contact and outer righthand armature of relay 207. At the lirst primary step of the selector switch S1, a` circuit is also closed from ground through the upper set of ofi' normal springs 211, conductor 131, winding of relay 124 to battery and ground. Relay 124 at its right-haul armature and front contact provides a substitute ground connection :trom the letthand contacts of key 127 to the conductor 130, so that this conducto] will remain grounded when, later, the relay 120 releases its armatures.

Relay 124 at its innermost left-hand armature and back contact opens the circuit 'tor lamp 118 and this lamp becomes extinguished. Relay 124 in addition completes a circuit 'trom ground through the interruptor 123, middle lett-hand armature and contact ot said relay, iront contact and innermost 'ight-hand armature of relay 120, lamp 121 'o battery and ground. Lamp 121 is flashed this circuit to indicate to the operator .t the establishment ot` the connection is proceeding.

The next opening of nterrupter 451 causes the deenergization of relay 552 and the opening o1 the circuits of magnet 502 and relay 400. The magnet 502 advances its brushes te the nextposition and relay 400 closes the Circuit tor relay 200. Relay 200` in turn, opens the circuit through thi` wiiulings o1' relay 902 and magnet 2013 and recloses the Circuitior relay 201. Magnet 203 deenergi'es, but relay 202 being slow lo release does not retract its armature. For each succeeding closure and opening ot the interrrupter 451, the relay 552 is operated to close and open the above traced circuit-s for the register stepping magnet 502 and the stepping relay 400. The register 501 advances from position to position while relay 0? causes the operation of relay 200, which in turn. causes the stepping magnet 20?,- to advance the. brushes from one group et terminals to another. When all impulses have been sent. the brush 520 ol. the register 501 disengages the last grounded terminal and relay 550 becomes deenergized. Relay 556 opens the circuits of the stepping magnets 555 and 545. Magnet 555 releases the brushes of the sender control switch into position 4 and magnet releases the brushes of the time measure switch to their neat position. released as soon as ground is removed from conductor 579. The time `measure switehis d iven through a complete cycle by means of the interrupter 451, which continues to close and open circuit of rela-y 552. The stepping circuit for advancing the time measure switch i my be traced 'from battery through :the winding ol magnet 545 over he `connected terminals cooperating with brush 542, brush 539, inner right-hand armature and back Contact of relay 556, right-hand arn'iature and contact of relay to ground. The purpose of the time measure switch, as stated hereinbeifora is to delay the advance of the sender control switch for a time somewhat greater than that required by the automatic switches to perform a maximum trunk hunting movement. llence, while the time measure switch T is stepping through a revolution, the first group selector S1 is per-forming its trunk limiting operation.

The stepping relay 400 remains permanentlydeenergized following the completion of the ii-rst'series of impulses and thereby maintains the Venergizing circuity for relay 200. `After an interval, the slow-to-release relay 202 retracts its'armature and a eircuit is closed from battery, through the inner armature and Contact of relay 206, winding of the secondary stepping magnet 205, normal contacts of relay 202 to the grounded conductor 130. Stepping magnet 205 becomes energized and advances the Vbrushes 208, 209 and 210 on to the lfirst set of terminals in the selected group. Magnet 205 at its armature `and contact opens the holding circuit oi relay 206, which thereupon deenergizes and opens the operating circuit of magnet 205. Magnet 205 again becomes deenergized and closeslthe following` circuit, provided the irst trunk in the group is busy at this time: battery, through the winding of relay 206, lower springs ototf normal Contact 211, armature and contact of magnet 205, back contact and inner righthand armature of relay 207, brush 210 to ground on the test terminal 215 of the busy trunk. In parallel to this circuit, a circuit also leads through the winding ot relay 207 to the grounded conductor 130. Relay 207, however, is shunted out by the direct connection to ground at the busy testterminal 215 and cannot operate. Relay 206 operates to close the energizing circuit Jier the stepping magnet 205, which advances the brushes to the next set of terminals. This method ot voperation yobtains until4 an idle trunk is reached, the test terminal of which is identified by the absence ot ground poteni tial. Relay 206, therefore, fails to energize and vthe brushes of the switch are brought to rest. Relay 207 is new energized in series with relay 206 to the grounded conduc- Relays 553 and 554-are also tor 130, butthe resistance of the relay 207 is such that enough current does not flow to also cause the operation ot relay 206. The relay 207 at its front contact and inner righthand 'armature extends the grounded conductor 130 through to test brush 210 and tern'iinafl 215 to render the selected trunli rbusy to other switches. Relay 207 at its lett-hand armatures opens the circuit et relay 200 and extends the talking conductors 128, 129 through to the brushes 208 and 209.

rlhe impulse circuit for operating the sec-- ond group selector S2 is established from battery through the right-hand winding of relay 220, back contact and inner lett-hand armature of relay 216, terminal 214, brush 209, Yfront contact and inner lett-hand. armature of relay 207, conductor 129 thence as above traced through the contact and arma ture of the stepping relay 400 and returning by way of conductor 128, outer lett-hand armature and front contact ot relay 207, brush 208, terminal 213, outer leftehand armature and bach contact out relay 216, left-hand Winding oit relay l220 to ground. Relay 220 energizes and completes a circuit :trom battery through the winding ot relay 217, contact and right-hand arinature et relay 220, conductor 231 to the grounded test terminal 215. Relay 217 operates and loclrs up in a circuit from battery through its Winding and armatlu'e and contact and thence to the grounded conductor 231 independently of the right-hand armature and contact of relay 220. l

Operai/0n of' Second group selec/for.

`When the time measure switch reaches the next to its last position, brush 542 disengages the last oi' the continuously connected terminals and steps on to terminal 57S. A circuit is now completed 'from battery, through the winding of relay 403, conductor 439, terminal 560, brush 541, brush 540 and its fourth position terminal to ground. Relay 4023 operates kto ren'iore the shunt from around the winding of relay 405. rlfhe purpose ot this is to permit the relay 405 to make a test oit the impulse circuit to determine if. the selector switch has succeeded in iinding an idle trunk.` Since in the case assumed, an idle trunlr was found, battery current is connected to the impulse circuit through the windings of relay 220 at the nent switch S2 and relay 405 immediately operates when the shunt removed at the left-hand arn'iature and Contact ot' relay 403. Relay 405 closes a circuit from battery through the winding ot' stepping` magnet 545, conductor 438, contact and right-hand armature of relay 405, conductor 437, terminal 578, brush 542, brush 539 and-thence to ground at the right-hand armature and contact ot relay 552. The time measure switch T advances to its normal position. Relay fsender'control switch is now in position 4 4-03 is thereupon released, the shunt close-l and relay 405 becomes deenergized.

AsV soon as the time measure switch reaches its" normal position, and since the u n n u n v a circuit is immediately established from battery, through the winding of relay 556,1

conductor 579, brush 544, 4terminal 576, brush 536 (position 4), brush 521 ot the "Y hundreds register 506 to ground. Relay 556 relay Relay energizes and prepares a circuit from battery, through its winding and contact and armature and the winding ot the relay 554 to the grounded conductor 579. Relay 554 energizes immediately that the interruptor opens and locks up in series with relay 553. VAt the next closure of the interrupter'451, a Vcircuit is completed from ground, through the right-hand armature and contact ot relay 554, outer efthand armature and contact of relay 552, brush (4), winding of stepping magnet 507 to battery and ground. At the same time the above traced circuit is closed from ground, through the Contact and inner letthand armature of relay 552, contact and outer right-hand armature of relay 556, left- A hand armature and front contact of relay 554, conductor 430 and thence through the winding ot the stepping relay 400 to battery and ground. Stepping magnet 507 is energized in order to advance the brushes 509 and 521 to the next position and relay 400 operates to open'the impulse circuit to cause the release orp relay 220 at the second group selector switch S2. Relay 220 on deenergizing completes a circuit from ground through the outer right-hand armature and Ycontact et relay 216, left-hand armature and contact of relay 220, lett-hand armature and front contact of -relay 217, winding oi slow-to-release relay 219, winding of the primary stepping magnet 221 to battery and ground. The stepping magnet 221 operates and moves the brushes 225,226 and 227 into operative relation with the first group of terminals. The relay 219 also becomes energized and completes a circuit'from battery, through the winding of relay 218, lower springs of the oil normal contact 224- which operates on the irst primary step of the switch armature and front contact of relay 219 to the grounded conductor 231. Relay 218 attracts its armatures and closes a holding circuit for itself from battery, through the Winding of said relay, lower springs of contact 224, armature and .contact of the secondary stepping magnet 223, contact and outer armature of relay 218 to ground at the contact and outer right-hand armature ol relay 216.

' Uponthe neXt opening of the interrul'itcl.' 451, relay 552 severs the energizing circuits of stepping magnet 507 and the stepping relay 400. Magnet 507 releases the brushes et the hundreds register to the next position and relay 400 closes the impulse circuit to cause the reenergization of relay 220. Relay 220 opens the circuit of relay 2,19 and magnet 221, rllhe magnet 221 becomes deenergized, but relay 219 being slow to relase` in character maintains its armature during the transmission ot impulses. For each succeeding closure and opening of the constantly rotating interruptor 451, the stepping magnet 507 advances the brushes of the hundreds register one position and the stepping` relay 400 causes the primary stepping magnet 221 to move the brushes of the second group selector successively to another group ot terminals. lVhen the last impulse of the series, represented by the depressed key 558, has been transmitted to the switch, the brush 521 disengages the grounded terminals and relay 556 becomes deenergized. Relay 556 opens the holding circuits of the stepping magnets 555 and 545. Magnet 555 releases( the brushes of the sender control switch to their fifth position terminals. The stepping ma net 545 advances the brushes of the time measure switch and this switch commences to make a complete rotation.

Following the completion of the impulse series, relay 400 remains deenergized and relay 220 remains energized. After an interval has elapsed, the slo'w-to-relense relay 219 becomes deenergizcd and a circuit is closed from battery, through the inner armature and contact of' relay 218, 'winding of the secondary stepping magnet 223, normal contacts oi relay 219 to the grounded conductor 231. The stepping magnet 222i operates to more the brushes 225, 226 and 227 on to the terminals ol the lirst trunk et the selected group. lriagnct 223 opens the locking circuit of relay 218, which becomes deenergized and in turn opens the energizing circuit of magnet 223. (ln the deenergization ot magnet 223, a eiremt is completed as follows, assuming the lirst trunk in the group to be busy at this time and a ground potential to exist on the test terminal 230: battery, through the. winding of relay 218, lower springs ot the ott nor# mal Contact 224, armature and contat-t o't magnet 223, back contact and inner righthand armature of relay 216, brush 227 to the grounded test terminal 230. lt will he noted that relay 216 is included in a circuit in, parallel with the one just traced, but this relay cannot operate as it is shunted by direct circuits to ground at busy test terminals 230. Relay 218 operates and closes the completes a circuit 'rom battery,

above traced circuit'for magnet 223 hich in turn operates to advance the brushes to the next set of terminals and also to 4open the circuit relay operation continues und an idle trunk is found at imiirh time, the sin it '..3 from the winding of' relay lay operates in series with resistance of relay 216, however to prevent the operati-an o'l rel cuitce" is such as ay 213 and the secondary stepping nagnet l ined open and the brushes oi' the sa itcn are brought to rest on the terminals of the idle trunk. Relay 216 at its inner right-hand armature and eontact extends the grounded third conductor 'through to the test terminal 230 to render the selected trunk busy to other second group selector switches Relay 216 at its left-hand armatures opens the circuit ot relay 220 and extends` the talking conductors through to the connector switch C. The impulse circuit may now be traced 'from battery through the right-hand windin oit relay 300, contact and outer lettdiand armature of relay 304, conductor 326, terminal 9:29, brush 226 thence over the lower talking conductor, thrmigh the contact and armature oit the stepping relay 400 at the sender, returning over the upper talking conductor to lirush 225, terminal 228, conduotor 32:", normal contact at the outer lett-hand armature ot relay 305', lett-hand winding ot relay 300 ground. Relay 300 becomes energized and closes a circuit from battery, through the winding ot relay 301, contact and inner rigl'it-hand armature of relay 300, contact and inner right-hand armature oi relay 304 to the grounded third conductor 3&2?. l-lelan.' 301 loef' in a circuit Ytrom battery, through 'its winding and contact and innermost 'right-hand armature,

contact and innermost right-hand armature oit relay 304 to conductor 327. Relay 300 also completes a circuit trom battery through the winding ot the slofw-torelease relay T, Yfront contact and left-hand aimature oi relay 300, contact and outermost right-hand armature oit relay 305, back contactand middle lett-hand armature oi re* lay 304 to ground.

. Oper/'utrin of connector stretch.

Upon reaching the next to its last position, the time measure switch T stops temporarily and a circuit is closed from battery throuK 'thev winding oi relay 403, conductor `9, terminal 530, brush 541,

brush (position to ground. lRelay 403 removes the shunt in around the i ing oi relay 405 and this latter relay operates in series with the vindings ot relay 300 at the connector switch C. Relay through the winding oit vthe stepping magnet 545,

close the shunt around the winding of relay immediately that the time measure switch reaches its normal position, relay 556 is againenergized in a circuit over conductor 579, brush 544, terminal 576, brush 536 brush 522 of the tens register' 511 to ground. Relay 566 closes the circuits hereinbefore traced tor energizing the stepping magnets 4and 545. On the first closure ot' the interrupter 451, relay 552 energizes and closes a circuit for relay 553, which in turn, completes a circuit for relay 554 as above described. is the interrupter opens, relay 554 energizes in series with relay to the grounded conductor 579. The nexttime the interrupter 451 closes, a circuit is completed as liereinbetore traced tor the steppingrelay 400. A circuit is also closed 'from ground, through the right-hand armature and contact of relay 554, outer lefthand armature and contact ot relay 552, brush (5), winding ot the stepping magnet 519l to battery and ground. lttagnet 512 energizes preparatory to advancing the brushes ot the tens register to their next position.

400 operates to open the impulse on decnergizing completes a circuit from ground, through the middle lett-hand armature and back contact of' relay 304, outermost right-hand armature and contact ot relay 305, lett-hand armature and back contact oi2 relay 300, outer left-hand armature and contact of relay 301, contacts 313 and 315, winding ot slow-torelease relay 302, winding ot the stepping magnet 303 to battery and ground. The primary stepping 'magnet 303 actuates to advance the brushes 319 and 320 of the connector switch into operative relation with the iirst group of terminals. Upon the iirst primary step the switch contacts 313 and 315 disengage one another, but before this occurs, the

Contact 313 makes engagement with contact 314 Consequently, the original energ 9,izing the primary stepping magnet 303 to battery and ground. The next time interruptor 451 opens relay 552`deenergizes and opens the Y circuits Vof the stepping magnet 512 and the stepping relay 400. Magnet 512 advances VVthe brushes of the tens register to their neXt positionV terminals and relay 400 closes the impulse circuit to. permit the energization oi" relay 300. Relay 300 opens the circuit through the slow-to-release relay 302 and stepping magnet 303. The stepping magnet becomes deenergized, but relay 302 retains its armatures during the transmissionof impulses.Av For each succeeding impulse sent out by the register sender, the stepping inagnet 512'operates to advance the brushes one step, while relay 300 operates to causel the primary movement of the connector switch. Following the last impulse of the series, the

brush '522 or" register 511 diseno'afres the last grounded terminal and opens the circuit of relayv 556. Relay 556, in turn, opens the circuitsl of stepping magnets 555 and 545, whereupon vthe sender control switch moves out of position 5 and into position 6 and the time measure switch commences to make complete revolution ot its brushes. Atteithe lapse of the necessary interval, during which relay 300 is .holding its arma-- tures attracted by reason of the fact that the stepping relay 400 at the sender is permanently deenergized, the slow-to-release relay 302 retractsiits armatures. Relay 307 being slow to release remains energized `during the vibration oithe armatures of relay 300.

Then the time measure switch, which commences to rotate upon the deenergization ot relay 556, reaches its sixth position, brush 543 makes engagement with the first one ot the connected terminals 581 and a circuit is established as follows: ground,

through brush 543, terminal 582, brush 543,

contact and armature and winding of stepping magnet 555 to battery and ground. The* magnet 555 operates in this circuit to advance the sender control switch from position 6 into position 7. Upon reaching the next to the last position, the time measure switch completesV a circuit from battery,

through the winding of magnet 545, the

mal, a circuit is closed from battery, through the winding ot relay 556, conductor 579, brush 544, terminal 576, brush 530 (7 brush 523 of the units register 516 to ground. Relay 556 operates to close the circuits for stepping magnets 555 and 545. lVhen the interrupter 451 closes, relay 552 becomes energized and establishes a circuit for the relay 553, which in turn, closes a series circuit tor itself and relay 554 to the grounded conductor 579. Gn the next opening of the interrupter, relay 554 locks in series with relay 553. Following this, the closure of interrupter 451 causes the opera tion ot relay 552 and the above traced circuit is established tor the stepping relay 400. Also, a circuit is closed from ground. through the right-hand armature and contact of relay 554, outer lett-hand ariiiature and contact of relay 552, brush 537 (7 winding of stepping magnetl 51T to battery and ground. Magnet 517 energizes preparatory to advancing the brushes ot the units register to their next position terminals and the relay 400 attracts its armature to open the impulse circuit, thereby causing the deenergization of relay 300 at the con nector switch.

Relay 300 upon deenergizing establishes a circuit from ground, through the middle lett-hand armature and back contact ot relay 304, outer right-hand armature and contact of relay 305, left-hand arn'xalure and back contact of relay 300, outer lett-hand armature and contact of relay 301, conta its 313 and 314, left-hand armature and back contact of relay 302, windingl o'l slow-forelease relay 324, winding ot the secondary stepping magnet 309 to battery and ground. Magnet 309 operates to advance the brushes 318, 319 and 320 into engagement with the first set ot line terminals in the selected group. Relay 324 also energizes in series with the stepping magnet and retains its armatures during the transmission ot the units impulses.k In the manner non' well understood, the stepping relay 400 energizos and deenergizes to send impulses over the impulse circuit and the units register stepping magnet 517 is operated to restore the units register 516 to its normal position. When the last impulse of the units series has been sent, which means that the brushes of the connector switch have been driven to the terminals of the called subscribens line 330, brush 523 of the register disengages the grounded terminals and opens the circuit ot relay 556. Relay 556, in turn. opens the circuits of stepping magnets and 545. Stepping magnet 555 releases the brushes oit the sender control switch out of position 7 and into positon 8 and magnet 545 commences to operate to drive the time measure switch through a complete cycle. Before continuing to describe the manner impulse battery,

retracts its armatures following the last units through the winding .et cut-oli relay 312, terminal 321, brush 320, right-hand armature and back contact ot' relay 32d, Vcontact and innermost left-hand armature orn relay 311, right-hand winding of relay 304, t'ront contact and middle righthand armature ot relay 301, back contact anc middle lettehand armature et relay 3011 to ground. Relay 3011 becomes energized in this circuit. The contacts and armatures ot this relay are soarranged that the inner lett-hand armature makes its front contact slightly in advance of the opening ot the middle lett-hand armature and its baclr contact. Therefore, be- :tore the original energizing circuit of relay 304:,can be opened at the middle lett-hand armature of said relay, the following substitute circuit is closed to hold said relay operated: battery, through the lett-hand winding and trontcontact and inner lefthand armature or" relay 304 to the grounded conductor 327. Relay 304 opens the circuit of relay 300 and also the locking circuit hereinbefore traced for relay 301. Relay 300 on deenergizing opens the circuit ot relay 307, which after an interval retracts its armatures.

The ringing circuit is now established for applying ringing currentvto the called subscribers line and may be traced from the ringing source 328, interrupter 329, letthand winding of relay 3057 back contact and inner lett-hand armature of relay 305, contact and outermost right-hand armature of relay 304, outer right-hand armature and contact of relay 311, brush 319, thenceover the loop of the called line 330, brush 318, back contact and inner right-hand armature of relay 3117 middle right-hand armature Vand, contact of relaya` 3041 to ground at the outer left-hand armature and back contact of relay 305. The relay being marginal does not operate in series with the magnet o the ringer at the called substation. 'iVhen the called Vsubscriber responds by removing the receiver from the switchhook, the resistance of the ringer-magnet is removed and suffic cient current flows through the lett-hand winding of relay 305 to cause the energization thereof. The armatures and contacts ot relay 305 are so arranged that the inner right hand'armature and'contact are closed slightly in advance of the opening of the left-hand armatures and their back contacts. Relay 305 therefore immediately locks up in a circuit from battery, through its righthand winding and contact and innermost right-hand armature, normal contacts of relay 307,'conductor 325,A thence over the upper'tallring conductor through the switches S2 and S1 to conductor 128, innermost letthand armature and back contact of relay r122, back contact and left-hand armature of relay 113, upper right-hand winding of repeating coil 109 to ground. Relay 305 at its lett-hand armatures opens the ringing circuit and completes the talking conductors 325 and 326 through to the called subscribers line. A complete circuit is now established from the called subscribers line to the right-hand windings ot repeating coil 109, battery current being supplied through the winding oi relay 112. Relay 300 which is included in this circuit becomes energized and closes a. circuit for slow-to-release relay 30.7. Relay 30T at its right-hand :uniature lnalre-berpore-break contact opens the above traced holding circuit 'for relay 305 and closes a substitute circuit as follows: battery, through the right-hand winding and contact and innermost right-hand armature of relay 305, front contact and right-hand armature of relay 307 to the grounded third conductor 327. This act removes the right-hand winding of relay 305 from the tip side of the line and connects it to the third conductor.

Relay 112 which also energizes in series with the called subscribers line completes a circuit from battery through the winding of relay 111, contact and left-hand armature oit relay 112 to ground at the contact and armature of relay 110. Relay 111 operates and by means of its make-betore-brealr contacts reverses the connections of the winding or" relay 110 to the trunk conductors 107 and 108. This reversal causes current to liow in the opposite direction through the winding ot the polarized relay at the outgoing end ol the trunk in the originating otlice. Relay 105 now operates and removing the shunt from the right-hand high resistance winding of relay 106, causes the relay 102 to become deenergized. Relay 102 ell'aces the lamp 103 which indicates to the origin ating operator that the called subscriber has answered.

After conversation has ceased and the calling subscriber has hung up his receiver, the operator in the originating olliee initiates release by withdrawing the plug 100 'trom the ack 101. The removal ot the. plug from the jack opens the circuit ot relay at the cordless operators position. Relay 110, in turn, opens the circuit of relay 114i and a circuit is thereupon closed from battery, through the lamp 118, inner right-hand armature and front contact of relay 1.17. innermost right-hand armature. and contact ot relay 114, interrupter 115 to ground. Relay 114 also closes a circuit from battery through lamp 121, inner right-hand armature ,and back contact of relay 120, outer right-hand armature and contact of relay 117, middle right-hand armature and contact of' relay 1111, interrupter 115 to ground. The flashing of lamps 118 and 121 in these circuits informs the cordless operator that the conneclil tion should be taken down. To accomplish this,y she manipulates her disconnect key 127. Key 127 on being depressed opens the ground connection to conductor 130. The removal of ground from conducto-r 130 permits the deenergization or relays 207, 215 and 305. Relay 207 completes acircuit from battery, through the winding of release magnet 204, middle springs of the cti normal contact' 211, back contact and armature of relay 201, back contact and armature of relay 200, contact and outer right-hand armature of relay 207 to ground. The release magnet 204 operates to restore the brushes of the selector switch S1 to their normal position, at which time the ott normal contact 211 opens and magnet 204 becomes deenergized. In a similar manner, a circuit is closed trom battery, through the winding of release magnet 222, upper springs of ythe off normal contact 224, back contact and left-hand armature of relay '217, contact and left-hand .armature .of relay 220 to ground at the contact and outer right-hand armature of rela-y 21.6. It will be noted that re- The re- .lease magnet 222 operates to restore the :brush shaft of the selector switch S2 to its ,normal position. When ground is removed from the third conductor 327 at the connector switch, relay `304 also releases its armatures.

A circuit is now closed from battery,

.through the winding of release magnet 308,

,contacts 317 and 316, back contact and midv.die right-hand armature of relay 301, back ,contact and middle left-hand armature of .re-

lay k3.04 to ground. Magnet 308 energizes and causes the brush shaiit of the Vconnector .switch C to restore to its normal posit-ion.

When the normal position is reached, the oli normalcontacts 3416 and 317 are opened and magnet 308 deenergizes. The entire connection has thus been restored to `its normal position `and the apparatus involved vmar again `be vtaken for use in connection with further calls.

Allotment of register Senders.

A `consideration will now be given to the method of allotting the register sender units for use in controlling the'selective switches.

l.According to the disclosure in this case, the

stops in position 5.

pose of assigning the next idle sender. This advance occurs when the sender control switch reaches position 4. At that time, a circuit is completed from battery through the winding and armature and contact oiA the allotter, stepping magnet 424, upper right-hand contact 427 (1-1-2), to ground through the fourth position terminal and brush 551 of the sender control switch. The allot-ter vmagnet 424 operates to advance the contacts o1 the allotter switch into position 3. lf the. next register sender happens to be lbusy at this time, the allott-er switch continues ,to move into position 5 by means loi a circuit similar yto the one traced tor driving said switch vinto position3. Should the nein. register sender he idle, the a-llotter switch The next time an assignment key 126 is depressedby the cordless operator, the grounded start conductor is extended .by Way kof the upper right-'hand Contact 425 (5),l and thence through the windinoF of a relay, corresponding to relay 406, in ividual to the allotted register sender unit.

'Should all the register senders 'be engaged simultaneously, a circuit is completed from battery through the winding of relay 534, -conductor 432, contact 453, outer right-hand armature and contact of relay 402, thence through the outer right-hand yarmature and rontcontacts of each of the relays corresponding to .relay 402 individual to the other registery senders to ground. Relay 534 becomes' energized and closes a circuit from "battery, through the windings ol' the key release magnets 528, 529, etc., to ground at the front contact and armature of said relay. The release lmagnets are operated to insure ,that none of the Vkeys on the operators hej."- board can be locked ,in their actuated position until one of the register senders .become available for use. Since all ofthe register sendersy are busy, the -allotter switch A424 continues to advance from one allotting position to another by means of circuits similar to the one described in detail, until it reaches vits -pos'ition'13- ln this position, a circuit is completed from battery, through the winding and armature andcontact of mag net 424 to ground on the lower lett-hand contact 427 (1S-H7). The steppingmagnet 424, therefore, continues to operate until the switch reaches position 18, where it comes to rest. vWhen one of the register senders becomes idle, the series circuit through the armatures and contacts of' relays 402 is opened and relay 534 becomes deenergized. Relay 524 at its armature and baclncontact closes a circuit including contact 426 (18) to drive the allotter switch into its first allott-ing position. The idle 4allottel and assigned.

'aZZecZ Zine busy.

It Will be next considered that the called subscribers line 330 is busy at the time the connector switch advances its brushes into engagement with the 'terminals thereof. It, for example, the line 330 is busy as a called line, a ground potential will exist on the test terminal 321 by reason o't the following circuit: ground, through the middle letthand armature and front contact of relay 304, innermost left-hand armature and contact of relay 311, backY contact and righthand armature of relay 324, test brush 320 to the test terminal 321. Consequently, as soon as the brush 320 encounters terminal 321 and before relay 324 has time to release, a circuit is completed from battery, through the Winding of relay 311, front contact and right-hand `armature of relay 324 to the grounded test terminal 321. Relay 311 attracts its armatures and locks up over the following circuit, as soon as the slow-to-release relay 324 becomes deenergized: battery, through the lWinding of relay 311, makebefore-break contact at the right-hand armature of relay 324, back contact and righthand armature of relay 310, contact and outermost left-hand armature of relay 311 to the grounded conductor 327.` Relay 311 at its right-hand armatures opens the talking conductors to prevent the application ot ringing current to the called subscribers line. Upon they first closure of the interrupter 323 following the actuation of relay 311, a circuit is established from ground, through the left-hand winding of the tone coil 322, interrupter 323, inner left-hand armature and contact of relay 324, contact and middle left-hand armature of relay 311, outermost right-hand armature and front contact of relay 301, lett-hand winding of relay 304 to battery and ground. Relay 304 becomes energized and locks up in a circuit through its left-hand winding and contact and innermost left-hand armature to ground7 overthe conductor 327. -Relay 304 hand armature and contact of relay 324, contact and middle left-hand armature` of relay 311, outermost right-hand armature and lback contact of relay 301, right-hand winding of relay 300 to battery andA ground. The interrupted current flowing in this circuit induces a current in the lett-hand wind-- ing of relay 300 which is transmitted over the upper talking-conductor to the windings of the repeating coil 109 and thence to the windings of repeating coil 104 and thence to v4 to ground.

initiates the release. rlheicordless operator.

in turnj eliects a disconnection ol the automatic switches m the nranner already dis cussed.

rlZZ trunks busy.

Coming new to that pliase ol' the system which relates more particularly to the invention, the method oll producing an oyerlowfsignal at the cordless olgieratofs position to noti'ty her that some one ol the automatic switches has tound all trunks busy will be taken up in detail. Consider tirs-i that the lirst group selector switch S1 in performing its trunk hunting` operation fails to lind an idle trunk leading` to the proper group ot selector switchesv S2. ,Xs was explained hereinlietore, the sender con` trol switch passes out ot position 3 and into position 4- iinmediately following the completion ot the transmission ol the Iseries o impulses tor causing` the primary operation of the selector switch S1. lVith the sender control switch in position 4, the relay 403, as above described. is energized in a circuit from battery through the winding ot said relay, conductor 439. terminal 530, brush 541, as soon as time measure switch ,'l reaches the next to its last position` brush 540 of the sender control switch in position Relay 403 attracts its armatures and opens the normally closed shunt circuit around the winding ot relay 105. This includes the windingo t relay A'105 directly in series with the impulse circuit leading to the brushes 20S and 200 et the lirs group selector switch S1. In the normal operation, namely when the selector switch linds an idle trunk, battery current is connected through the windings ol a relay such as relay 220 to the brushes 203 and L00A Consequently, in this case. relay 405 hecomes energized as soon as relay fl-03 operates, but since all trunks in the `group are now busy, the brushes 20S and 200 of the lirst group selector have gone to the oyerliow position and battery current is not connected to the impulse circuit. Under these circumstancesn relay 405 remains inert tollowing the operation ot relay 403 and the above traced circuit lor driving` the time measure switch into its normal position is held Open. After the lapse ol the necessary interval following` the operation of relay 403` the slow-to-release relay 404 becomes deenergized due to the tact that its circuit is severed at the-contact and right-hand armature oit relay 403. Relay 4,04 completes a circuit from ground, through its armature lOl) lll)

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