US1518815A - Machine-switching telephone-exchange system - Google Patents

Description

Dec. 9, 24- 1,518,815

L. POLINKOWS KY MACHINE SWITCHING TELEPHONE EXCHANGE SYSTEM Filed Dec. 28. 1918 '7 Sheets-Sheet 1 Dec. 9, 1 24. 1,518,815

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L. POLINKOWSKY MACHINE SWITCHING TELEPHONE EXCHANGE SYSTEM Filed Dec. 28. 1918 7 Sheets-Sheet 7 F 45.7 T] 3 1. a T4 5;

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Patented Dec. 9, 1924.

UNITED STATES PATENT OFFICE.

LIPA POLINKOWSKY, 0F HYDE PARK, LONDON, ENGLAND, ASSIGNOR T0 WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

MACHINE-SWITCHING TELEPHONE-EXCHANGE SYSTEM.

Application filed December 28, 1918. Serial No. 268,649.

To all whom it may concern:

Be it known that I, LIPA PoLINKoWsKY,

a citizen of Russia, residing at 70 Westbourne Terrace, Hyde Park, London, W1, England, have invented certain new and useful Improvements in Machine-Switching Telephone-Exchange Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to machineswitching telephone exchange systems and more particularly to a telephone exchange system in which calls may be extended between a plurality of exchanges in the system.

A feature of the invention is the provision of means for the automatic advance of a group selector from one stage to another in the progress of the establishment of a connection, if the group selector remains at said stage in its sequence of operations longer than a predetermined length of time.

Another feature of the invention and one relating to the first named. feature is the provision of means, associated with the selectors used in extending a call, and in which a preceding selector of a chain of selectors is controlled in its advance from one stage to another by the succeeding selector, whereby the advance of the preceding selector from said stage takes place automatically if the succeeding selector fails to act within a predetermined length of time.

In telephone exchange systems in which a call is extended over a two-wire trunk line to selectors in a distant exchange and in which a fundamental. circuit becomes extended metallically, free of bridges, etc., to

the chain of selectors in succession,-a preceding selector is brought into condition by the succeeding selector to be controlled from the outgoing end of the trunk line after the completion of the selection.

A further featu e of the invention, therefore, is the provision of means to advance a preceding selector of a chain of selectors into a stage to be controlled from the outgoing end of a trunk line if the advance of a 'succeeding. selector is prevented for a given length oftime. I

A still further feature of the invention and one relating to the last named feature is the provision of means associated with a dead level circuit to advance a selector on the incoming end of a trunk line from one stage to another if the selector remains at said first stage longer than a predetermined length of time.

A still further feature of the invention and one relating to the second last named feature is the provision of means associated with the selectors at the distant exchange whereby the selectors will be prevented from being placed under the control of the outgoing end of a trunk line if the call is not extended because of the trunk hunting or repeated trunk hunting operation of a selector.

A further feature of the invention is the provision of means under the simultaneous and independent control of a succeeding selector and a common timing arrangement for the advance of a preceding selector from one stage to another.

A further feature of the invention is the provision, in telephone exchange systems in which the outgoing end of each of a group of two-wire trunk lines is provided with circuits and apparatus for maintaining the trunk line busy until the incoming end thereof is free, of means including common conductor for rendering the engaged trunk idle responsive to the release of the incoming end of the trunk.

In the drawings.

Fig. 1 shows a subscribers line and a first line finder.

Fig. 2 shows a cord circuit comprising a second line finder and a first group selector.

Figs. 3 and 4: show a register equipment.

In Fig. 5 is shown a second group selector on the incoming end of a two-wire trunk line, and in Fig. 6 a third group selector.

Fig. 7 shows a final selector.

Fig. 8 shows a common arrangement which controls the release of second group selectors on two-wire trunk lines.

In Fig. 9 is shown a dead level circuit.

Fig. 10 shows an arrangement for increasing the time interval of the mechanism illustrated in Fig. 8.

The system disclosed as embodied in the present invention will be best understood from a description of the operation thereof.

\Vhen the line relay 201, in Fig. 1, is energized, the common. starting relays 204 provide a circuit for the energization of the power magnets 211 of the free firstline finders in the group. The brush carriages of these line finders rotate and in reaching terminal 210 of the calling line, test relay 214 of a line finder is energized and the terminal 210 is made busy through the connection of the low resistance winding of relay 214 and the winding of relay 212 in parallel to the high resistance winding of relay 214. Relay 212 disconnects the power magnet 211 and provides a circuit, for the energization of the holding magnet 215 and the common starting relays 216. The brush carriage is arrested, and a circuit is provided for the free second line finders which have access to this first line finder. Thesecond line finders, are divided into pairs and their sequence switches 220 are held either in position 18 or position 1. Only the line finder of a cord, on which the sequence switch 220 is in position 1, is able to search for a calling first line finder. Relay 222 of the cord is a then energized in a circuit over the front contacts of the common starting relays 216. The power magnet 221 is energized in a circuit from battery, through lower contact 290, the winding of power magnet 221, back contact and armature of relay 232, front contact and armature of relay 222 to ground at; the back contact and armature of relay 231 and the brush carriage of the second line finder rotates. On reaching terminal 230 the test relays 234 and 232 are energized, terminal 230 is made busy and sequence switch 220 is energized in a circuit over front contact of relay 232. Sequence switch 220 starts from position 1 and moves into position 4. In position 3 of sequence switch 220 a circuit is established for the energization of relays 235 of the cord, relay 213 of the first line finder and cut-olf relay 207 of the calling line, whereby relay 201 is de-energized and the brush carriages of the remaining free first and second line finders are arrested. The release relay 231 together with retardation coil' 237 is brought into connection with the calling line.

In position 4 of sequence switch 220 the searching. sequence switch 280 of the cord is energized and a free register set is searched. The circuit for sequence switch 280 may be traced from battery through the winding of said sequence switch, upper-contact 291, back contact and armature of relay 232, upper contact 281 to ground at lower contact 282. Assuming the register set in Figs. 3 and 4 free, a connection with this @1'egister set is obtained as soon as sequence switch 280 reaches position 1 or 7. Relays 234 and 232 are thereby energizedin a circuit over conductor 293, contact 322 of sequence switch 320 and right hand winding of relay 323. Sequence switch 280 is arrested and sequence switch 220 is advanced into position 5. The calling subscribers line is brought into connection with the secondary windings of the dialling tone coil 324 and the stepping relay 325 of the register set, the circuit including the back contacts of key 301 at the monitoring position. Relay 323 when energized provides over its front contact its'left hand winding and contact 326 bottom a circuit for the energization of sequence switch 320, which controls the steppingin circuit and connects the registers in succession with the contact of the steppingin relay 325. Sequence switch 320 starts from position 1 and moves into position 3. In positions 2' and 3 of this sequence switch the primary winding of the dialling tone coil 324 is connected over sequence switch contact 332 in a circuit with a common interrupter 333 and the calling subscriber,-

when receiving the sharp dialling tone, winds up the dial to send the first figure of the wanted number. When both contacts 322 and 326 of sequence switch 320 are opened, relay 323 is d'e-energized. The ten thousands register 100 is energized in a circuit over sequence switch contact 328 top-,

lay 329 remains energized until the line circuit is opened at the dial and relay 325" is d'e-energized. Relay 329' in closing its back contact again prepares the circuit for register 100 which receives current as soon as relay 325 is again energized. Over the back contact of relay 329,. the relay 337 is connected in parallel tothe register, and the relay 337, when energized provides over its front contact a shunt around the front contact of relay 325. Relay 337 remains energized until the register reaches itsnext position and its local contact is opened. Onthe last interruption at the dial relay 325 remains ole-energized for a comparatively long time and the slow operating relay 334 is energized in a circuit over back contactsof relays 325 and 323 and sequence switch contact 342 top. Relay 323 is then energizedin a circuit over the front contact of relay 334. Sequence switch 320 is again energized, starts from position 3 and moves into position 6. Relay 325 is energized over the calling line before sequence switch 320 reaches position 5. The ten thousands register is disconnected and the circuit is prepared for thethousands register 110 over sequence switch contact 328 bottom, contact 326 bottom being opened when the sequence" Register switch is moving from position 3 to position 4 after contact 328 bottom is closed. The first energization of register 110 takes place immediately the back contact of relay 323 is closed. Register 110starts from position 0 and in closing its contact 111, the right hand winding of relay 329 is shortcircuited and relay 329 opens its back contact, and the register completes its step under the control of its contact 111 and is arrested in position 1. Relay 337 is new connected in parallel to register 110 and maintains the energiz'ation of relay-329 during the time contact 111 is closed. When the dial is released a second time register 110 is brought to a corresponding 3081111011 and sequence switch 320 is advance from position 6 into position 8 in which the thousands register is disconnected and the hundreds register 120 is now connected in the stepping circuit over sequence switch contact 335, and is set up according to the third series of impulses from the dial. Sequence switch 320 is then advanced from position 8 into position 11 in which the tens register 130 is connected in the stepping circuit over sequence switch contact 336 top, after which sequence switch 320 is advanced from position 11 into position 13 in which the units register 140 is connected in the stepping circuit over sequence switch contact 336 bottom. WVhen the dialling is completed sequence switch 320 is advanced into position 15.

The capacity of the exchange is assumed to be 100,000 lines. First, second and third group selectors and final selectors are therefore provided. The position of the registers determines the translation from the decimal number system of the wanted subscriber line to the system of the switches. The setting up of the selectors takes place during the time the subscriber continues the dialling, and the operation of the trip spindle of the first group selector is delayed until the first impulse series is completed on the dial. This corresponds to sequence switch 320 reaching position 4 in which a circuit is closed for the energization of sequence switch 350 over contact'352 bottom and contact 338 top of sequence switch 320. Sequence switch 350, which controls the connection of the registers in succession for the setting up of the selectors, starts from position 1 and moves into position 3. The left hand winding of relay 359 is energized in a circuit over back contact of stepping-out relay 355 and contact 343 bottom of sequence switch 320. reaches position 3 the fundamental circuit is closed over contact 356 top of sequence switch 350, back contact of relay 357, winding of stepping-out relay 355, common wire 296 and winding of relay 222 at the cord. Both relays 222 and 355 are energized, relay When sequence switch 350 359 is de-cnergized. Sequence switch 220 starts from position 5 and moves into position 6 in which the trip spindle magnet 248 is energized. The trip spindlerotates and produces at its contact 250 top short-circuitings around the winding of relay 355. As soon as the back contact of relay 355 is closed the register 100 is energized in a circuit over contact 102, contact 364 top of sequence switch 350, back contact and right hand winding of relay 359, contact 343 of sequence switch 320 and back contact of relay 355. Simultaneously with the energization of register 100 relay 362 is'also energized and provides over its front contact a bridge to the contact of relay 355. Relay 362 in the circuit for the outgoing impulses has the same purpose as relay 337 in the circuit of the incoming impulses and enables a safe operation of the registers. Register 100 starts and closes its contact 101. The right hand winding of relay 359 is short-circuited so that this relay becomes energized, and the register completes its step under the control of contact 101, after which relay 362 is de-energized. In the meantime trip spindle contact 250 has been opened. The stepping relay 355 leaves its back contact, relay 359 is de-energized. On the following closure of contact 250 relay 355 isagain deenergized and register 100 is energized. When, under the control of relay 355, register 100 reaches position 0 relay 357 and sequence switch 350 are energized on the following de-energization of relay 355 in a circuit over sequence switch contact 363 bottom, contact 104- of register 100 and contact 364 of sequence switch 350. Relay 35'? opens the fundamental circuit. Sequence switch 350 starts from position 3 and moves under the control of its local contact 351 into position 4.

When contact 351 is closed and the right hand winding of relay 359 is short-circuited, this relay maintains its energization over back contact of relay 355. After contact 250 of the trip spindle is opened relay 222 is deenergized. Sequence switch 220 starts from position 6 and moves into position 7 in which the test relay 234 is connected to the test brush 252 of the first group selector. Relay 222 is now energized in a circuit over conductor 293, contact 340 top of sequence switch 320 and back contact of relay 339. The power magnet 241 of the group selector is energized in a circuit over front contact of relay 222. The brush carriage rotates in the well known manner with the brushes along the terminal row determined by the position of the trip spindle. In reaching the test terminal of a tree trunk line, relay 234 is energized in a circuit over test brush 252, resistance 500 and back contact of relay 501. In parallel to resistance 500 the relays 501 and 502 are also connected. Relay 234 of the cord brings its low resistance winding and the Winding of relay 232 in parallel to its high resistance winding and makes the terminal of the trunk line busy. Relay 232 is thereby energized, power magnet 241 is disconnected and sequence switch 220 and the holding magnet 245 of the first group selector are energized, the brush carriage is arrested, and sequence switch 220 starts from position 7 and moves over position 8 into position 9 in which the fundamental circuit is prepared at sequence switch contacts 247 top and 255 bottom to the second group selector pending the closure of the circuit at the register set. Relay 502 when energized maintains at its left hand front contact the closure of the circuit over the test brush 252 independent from the left hand back contact of relay 501. Relay 501 provides for its right hand winding a circuit over its left hand front contact and back contact of relay 503. 1

Sequence switch 350 at the register set remains in position 4 until the second series of impulses at the dial has been completed and sequence switch 320 has left position 6. A circuit is then established for the energization of sequence switch 350 over contact 354 and contact 338 bottom of sequence switch 320. Sequence switch 350 starts from position 4 and moves into position 6. The fundamental circuit is closed at the register set over contact 358 bottom of sequence switch 350, back contact of relay 378 and common wire 297. In the distant exchange the sequence switch 520 ofthe second group Selector on the incoming end of the two-wire trunk line is in its position of rest and relay 522 is connected over sequence switch contact 504 top withconductor 536, while release relay 523 together with retardation coil 524 are connected with the second wire 537 ,of the trunk line over contacts 505 bottom and 506 bottom of the sequence switch. The high resistance winding of relay 523 prevents theenergization of relay 355 in the registerset. Belay523 is energized andprovides a circuit for the energization of se quence switch 520 overcontact 507 top and frontcontact of relay 523. Sequence switch 520 starts from position 1 .and moves under the controlof its local contact 521 into position 2,in whichrelay 522 is connected to wire 53.7 over sequence switch contact 505 top, while wire 536 of the trunk line is connected over sequence switch contact 508 with ground. Relays 522 and 355 areenergized. Belay-359 is de-energized. The magnet 528 of the trip spindle is energized in a circuit over sequence switch contact 509 top and front contact of relay 522. The trip spindle rotates and provides at its contact 510 v,top over sequence switch contact 511 bottom short-circuitings .around the winding of relay 355. Assuming register .11 having bee arrested in position 8, this register is energized in a circuit over left. hand back contact of relay 360, contact 112 of register 110 and contact 361 top of sequence switch 350. After register 110 is brought to position 0 under the control of relay 355, relay 357 and sequence switch 350 are energized on the following de-energization of relay 355 in a circuit over contact 363 bottom of sequence switch 350, contact 104 of register 100, contact 364 bottomof sequence switch 350, contact 114 of register 110 and Contact 3610f sequence switch 350. The fundamental circuit is opened at the back contact of relay 357 while sequence switch 350 starts from position 6 and moves into position 7.

As soon as contact 510 of the trip spindle is also opened relay 522 is de-energized and sequence switch 520 is energized .in a circuit over contact 514 top and back contact of re lay 522. Sequence switch 520 starts from position 2 and moves into position 3. Relay 522 is energized in a circuit over sequence switch contact 511 top and contact 510 bottom of the trip spindle. The set of trip spindle interrupting contacts 510 of switches of this character is so'arranged that all three contacts are opened when the trip spindle is standing in its normal position and such that the upper and middle contacts are opened and the lower and middle contacts in engagement with each other when the trip spindle is moved to any of its brush tripping positions. To accomplish this end the lowermost contact is designed to engage a series of notches in the rotating element of the trip spindle. The notch corresponding to the normal position of the trip spindle is sufliciently deep to permit all three of the contacts to remain open. The notches corresponding to the brush trip positions, however, are more shallow in depth, whereby the lowermost contact is held in engagement with the middle contact, but these notches are not sufliciently deep to press the middle contact intoengagement with the uppercontact. As the trip spindle rotates from one position to another, the lower contact rides over the surface ofthe teeth formed between the notches andall three contacts are closed. The left hand high resistance winding of relay 534 is now connected with the test brush 512 over sequence switch contact 513 bottom, while the power ,magnet 531 of the brush carriage isenergized in a circuit over sequence switch contact 515 bottom and back contactof second test relay 532. The brush carriage of the second group selector ,rotates searching for a terminal of a free third selector in the reaching of which relay 5 34 is energized in a circuit over vtest brush .512,- contacts 567 and 541 ofsequence switch 550 individual to this third group selector and resistance 542. In parallel to resistance 542 is also connected the high resistance ,winding of relay 543. Relay 534 brings over its front contact its right hand low resistance winding and winding of relay 532 into connection with brush 512 and makes the test terminal to the third group selector busy. Relay 532 is energized, disconnects at its back contact the power magnet 531 and provides a circuit for the energization of sequence switch 520 over contact 507 bottom and front contact of relay 532. In parallel to sequence switch 520 the holding magnet 535 is connected over its contact 516 bottom. The brush carriage is arrested, and sequence switch 520 starts from position 3 and moves into position 6 in which terminal 512 is now connected over sequence switch contact 513 top direct with relay 532, providing thereby a short circuit around the right hand winding of relay 534 which is thereby de-energized. In position 6 of sequence switch 520 the fundamental circuit is extended over se quence switch contacts 517 and 518 to relay 552 of the third group selector.

Relay 543 when energized provides over its left hand front contact a holding circuit for its winding independent from contact 567 of sequence switch 550. A circuit is closed for the energization of sequence switch 550 over contact 544 bottom and right hand front contact of relay 543. Sequence switch 550 starts from position 1 and moves into position 2.

Sequence switch 350 remains in position 7 until the third series of impulses is completed at the subscribers dial and sequence switch 320 leaves position 8. A circuit is then established for the energization of sequence switch 350 over contact 370 bottom and contact 341 top of sequence switch 320. Sequence switch 350 starts from position 7 and moves into position 9 in which the fundamental circuit is again closed at contact 358 bottom of sequence switch 350. Relay 552 of the third group selector and relay 355 of the register set are energized and relay 359 is de-energized. Sequence switch 550 is energized in a circuit over contact 549 top and front contact of relay 552. Sequence switch 550 starts from position 2 and moves over position 4 into position 5. The magnet 548 of the trip spindle is now energized in a circuit over sequence switch contact 553 top and front contact of relay 552. The trip spindle rotates and provides at contact 555 top bottom short-circuitings around relay 355. Assuming register 120 to have been arrested in an even position, the register is now restored to its position of rest under the con trol of relay 355 in a circuit over contact 122 of register 120, contact 366 bottom of sequence switch 350 and back contact of relay 359. lVhen't-he register 120 reaches position 0 relay 357 and sequence switch 350 are energized on the following de-energizaand over sequence switch contact 556,

tion of relay 355 in a circuit over sequence switch contact 366, contact 124 of register 120, sequence switch contact 361 bottom, contact 114 of register 110, sequence switch contact 364 bottom, contact 104 of register 100 and sequence switch contact 363 bottom. The fundamental circuit is opened, sequence switch 350 starts from position 9 and moves into position 10.

lVhen contact 555 at the trip spindle is opened relay 552 is de-energized and sequence switch 550 is energized in a circuit over contact 549 bottom and back contact of relay 522. Sequence switch 550 starts from position 5 and moves into position 6 in which relay 552 is energized in a circuit over contact 556 top of sequence switch 550 and contact 555 bottom of the trip spindle, due to the construction of the trip spindle contacts already explained in connection with the preceding switch. The right hand high resistance winding of test relay 564 is connected over sequence switch contact 546 top with the test brush 572. The power magnet 561 of the brush carriage is energized in a circuit over sequence switch contact 547 bottom and back contact of relay 562. The brush carriage of the third group selector rotates with the brushes in the row determined by the position of the trip spindle and on reaching the terminal of a free final selector, the right hand winding of relay 564 is energized in a circuit over brush 572, contacts 440 and 441 of sequence switch 450 individual to the final selector and resistance 442. In parallel to resistance 442 .the high resistance winding of relay 443 is also connected. Relay 562 and the left hand low resistance winding of relay 564 are brought into connection with brush 57 2 over sequence switch contact 554. Sequence switch 550 is now energized in a circuit over its contact 557 bottom and front contact of relay 562. Sequence switch 550 starts from position 6 and moves over position 8 into position 9 in which the fundamental circuit is extended at sequence switch contacts 553 top and 559 top to the final selector. Test brush 572 is now connected over sequence switch contact 566, resistance 570 and right hand front contact of relay 543 to ground. Relay 562 is con-' nected in parallel to resistance 570 over contact 545 top of the sequence switch, whereby relay 562 is maintained energized.

Sequence switch 350 remains in position 10 until the dialling of the fourth figure is completed at the subscribers station and: sequence switch 320 leaves position 11. Sequence switch 350 is then. energized in a circuit over contact 352 top and contact 346 bottom of sequence switch 320. Sequence switch 350 starts from position 10 and moves into position 11 in which the fundamental circuit is again closed at contact 358 bottom of sequence switch 356. Relay of the register set and relay 452 of the final selector are now energized. The sequence switch 450 is energized in a circuit over contact 446 top and front contact of relay 452. Sequence switch 450 starts from position 1 and moves into position 2 in which the magnet 448 of the trip spindle is energized in a circuit over sequence switch contact 447 bottom and front contact of relay 452. The trip spindle rotates and provides at contact 455 top over sequence switch contact 449 bottom shortcircuitings around the winding of relay 355. The tens register 130 is now restored to position '0 under the control of relay 355 in a circuit over contact 132 of register 130, contact 367 top of sequence switch 350 and back contact of relay 359. When register 130 reaches position 0 relay 357 and sequence switch 350 are energized in a circuit including sequence switch contact 370 top, contact 134 of register 130 and sequence switch contact 367 top. The fundamental circuit is opened and sequence switch 350 starts from posit-ion 11 and moves intoposition 12. When contact 455 of the trip spindle is also opened relay 452 at the final selector is de-energized, sequence switch 450 is energized in a circuit over contact 456 top and back contacts of relays 462 and 452. Sequence switch 450 starts from position 2'and moves into position 3.

Sequence switch 350 remains in position 12 until the dialling of the last figure is completed at the calling station and sequence switch 320 leaves position 13. A circuit is then established over contact 363 top of sequence switch 350 and contact 330 of sequence switch 320. Sequence switch 350 starts'from position 12 and moves into position 14 in which the fundamental circuitis closed at the register set at sequence switch contact 358 top. Relay 452 is again energized and provides a circuit for the energization .of sequence switch 450 over contact 446 and front contact of relay 452. Sequence switch 450 starts from position 3 and moves into'position 4 in which the power magnet 461 is energized in a circuit over sequence switch con-tact 446 bottom and front contact of relay 452. The brush carriage of the final selector rotates, producing over contact 457 top and contact 449 of the sequence switch short circuitings around the winding of relay 355. Under the control of relay 355 the units register 140 is now restored to position 0 in a circuit over contact 142 and sequence switch contact 367 bottom. When register 140 is in postion 0 relay 357 and sequence switch 350 are energized on the following de-energization of relay 355 in a circuit over sequence switch contact 370 top, contact 144 of register 140, back contact of relay 374, contact 143 of register 140 and sequence switch contact 367. Sequence switch 350 starts from position 14, 7

1Vhen sequence switch 350 moves over :poe sition 14 a circuitis established for the energization of the left hand winding of relay 339 over contact 327 bottom of sequence switch 320, contact 368 bottom of sequence switch 350, left hand back contact of relay 378 and contact 369 bottom of sequence switch 350. Relay 339opens at its back con tact the circuit of relay 222 of the cord and provides over its front contact a holding circuit for its left hand winding. The de energization of relay 222 causes sequence switch 220 to start from position 9 and to move into position 10 whereby the stepping relay 325 of the register set is disconnected from the calling line which is again brought into connection with relay 231 and retardation coil 237. Sequence switch 220 is in position 10 energized in a circuit over back contact of relay 2'62 and the sequence switch moves into position 11.

The de-energization of relay 325 provides a circuit for the energization of sequence switch 320 over contact 348 bottom and back contacts of relays 325 and 323. Sequence switch 320 starts from position 15 and moves into position 16 in which relay 339 is tie-energized and a circuit is established for the energization of sequence switch 350 over contact 340 bottom of sequence switch 320. Sequence switch 350 testing the positions of the registers moves over positions 16, 17 and 18 into position 1. The cir cuit for moving sequence switch 350 out of position 16 leads from battery through the winding of the magnet of said sequence switch, contact 363 closed in position 16, cont-act 104, contact 364 closed in position 16, contact 114, contact 361 closed in position 16, contact 124, contact 366 closed in position 16, lower contact 340 of sequence switch 320, back contact and armature of relay 339 to ground. Sequence switch 350 moves into position 17 where the following circuit is closed, provided register 130 has reached its normal position: battery, through the winding'of sequence switch 350, upper contact 370, contact 134,contact 367 closed in position 17, and thence to ground at the back contact and armature of relay 339. Sequence switch 350 moves in position 18 and the following circuit is closed to advance the same into position 1, provided the units register 140 has reached its normal position: battery, through the winding of sequence switch 350, upper contact 370, contact 144,

back contact and armature of relay 374, contact 143, lower contact 367 closed in position 18 to ground, as described, at the back contact and armature of relay 339. A circuit is then established for the energization of sequence switch 320 over contact 326 top and contact 369 top of sequence switch 350. Sequence switch 320 starts from position 16. In position 18 the energization of Sequence switch 320 is maintained over con tact 348 bottom and back contact of relay 325. Sequence switch 320 moves into position 1 and the register is free for other calls.

When at the final selector contact 457 of the brush carriage is opened relay 452 is deenergized and causes sequence switch 450 to start from position 4 and to move into position 10. Sequence switch 450 first advances from position 4 into position 6 by means of acircuit from battery through the winding of said sequence switch upper contact 456, back contact and armature of relay 462, and back contact and armature of relay 452 to ground. In position 6 of sequence switch 450, relay 452 is energized in a circuit from battery through the winding of said relay, lower contact 459 to ground. Relay 452 attracts its armature and a circuit is established from battery through the winding of sequence switch 450, upper contact 446, front contact and armature of relay 452 to ground, whereby the said sequence switch advances out of position 6 and into position 10. As soon as contact 441 of sequence switch 450 is opened relay 562 at the third group selector is de-energized and sequence switch 550 is energized in a circuit over contact 547 top and back contact of relay 562. Sequence switch 550 starts from position 9 and moves over position 11. into position 12. Contact 541 is then opened and relay 532 at the second group selector is tie-energized causing the energization of sequence switch 520 in a circuit over contact 515 top and back contact of relay 532. Sequence switch 520 starts from position 6 and moves into position 9 in which relay 523 is again brought into connection with the trunk line over sequence switch contacts 506 top and 505 bottom, and relay 525 and retardation coil 526 are connected over sequence switch contacts 51'. and 518 with the final selector. The time for the energization of relay 339 at the register set and the de-energization of relay 222 at the cord is so selected that sequence switch 220 advances into position 10 and brings relay 262 and. retardation coil 257 in bridge to the trunk line after the sequence switch 450 of the final selector has left position 4 and contact 444 bottom is opened, while relay 231 of the cord in position 10 of sequence switch 220 is energized over the calling subscriber line before sequence switch 520 at the second group selector reaches position 9 so that relay 523 is energized over the trunk line and front contact of relay 231.

When sequence switch 450 passes position 7 terminal 470 of the alled line is tested and if found free relay 454 is energized in a circuit including the cut-off relay of the called. line and sequence switch contact 459 top. Relay 462 and the low resistance winding of relay 454 are brought over the front contact of relay 464 in parallel to the high resistance winding of said relay and terminal 470 is made busy. Relay 462 when energized provides a circuit for the energization of sequence switch 450 over contact 453 top and front contact of relay 462. Sequence switch 450 moves over positions 10 and 11 into position 12 in which an alternating ringing current is immediately sent to the station of the wanted line. Relay 452 is brought into connection with the common interrupter 459 which when closed causes the energization of relay 452 whereby sequence switch 450 is energized in a circuit over the front contact of this relay and moves into position 13. The circuit for energizing relay may be traced from battery through the winding of said relay, lower contact 490, interrupter 469 to ground. Relay 452 is now connected, sequence switch 450 being in position 18, with a further common interrupter 472. The curcuit including interrupter 47 2 is traceable from battery through the winding of relay 452, contact 491 to ground at interrupter 47 2. The two interrupters 469 and 4'72 are continuously operated and are arranged to close the circuit to ground at predetermined time intervals so that sequence switch 450 when reaching position 12 is brought after the lapse of a few seconds over positions 12 and 13 into position 14 in which the direct connection of the ringing current supply is removed and the connection of the subscribers line with the ringing source of current is maintained over a common interrupter 474, which at selected intervals connects in succession the circuit either to the source of ringing current or to ground. The permanent ringing circuit may be traced from the ringing source at machine 474, lower contact 473 thence to the lower tall:- ing conductor of the line and returning by way of the upper talking conductor to the lower contact 457, winding of relay 460 to battery and ground. During the time sequence switch 450 is in position 12 to 14 the primary winding of the tone coil 477 is connected to common interrupter, and the secondary winding of this coil is connected in bridge to the line and the calling subscriber perceives an indication that the ringing of the called party is proceeding. As soon as the receiver is lifted from the hook at the wanted station, ringing relay 460 is energized and causes over its front contact the cnergization of sequence switch 450 which starts from position 14 and moves into position 15 in which a through connection of the called suhscrili er line is made to the transmitter current supply bridge at the second roup selector. Relay is thereby ene "zed and provides a shunt around the high resistance winding of relay 523. Relay :2 at the cord is thereby enerzed and provides over its front contact a for the encrgization of sequence circuit .ister 110.

switch 220 which starts from and moves into position 12.

The translation from the decimal number system of the wanted subscriber line to the system of the switches is so made that if the thousands register 110 when under the control of the dial is arrested in an odd position relay 360 is energized in a circuit over contact 116 of register 110 and contact 379 bottom of sequence switch 350 in position 5. Relay 360 provides a holding circuit for its winding over its right hand front contact and sequence switch contact 3 2 top, while position 11 7 over the left hand contact of relay 360 the circuit for the restoration of register 110 is so modified that in position 6 of sequence switch 350 the circuit for the register is closed over contact 113 and the register is restored to position 9 instead of to position 0, after which sequence switch 350 is energized in a circuit over contact 112 of register 110, left hand front contact of relay 360 and contact 115 of register 110. The trip spindle of the second group selector makes therefore the same number of steps whether the register 110 has been arrested in an even position or in the following odd position. After sequence switch 350 leaves position 6 relay 360 is ole-energized and when in position 9 of sequence switch 350 the hundreds register 120 is restored to position 0 the circuit is first extended over contact 124 of register 120, contact 361 bottom of sequence switch 350, contact 112 of register 110 and left hand back contact of relay 360 to reg- The trip spindle of the third group selectors makes therefore, an addi tional step.

If the hundreds register 120 has been advanced under the control of the dial into an odd position relays 373 and 374 are energized in a circuit over contact 375 of sequence switch 350 and contact 126 of register 120 in position 8 of this sequence switch, whereby relay 373 provides a locking circuit over its front contact and contact 372 bottom of sequence switch 350. During the time sequence switch 350 moves over position 8 the register 120 is energized in a circuit over contact 122, contact 366 top of sequence switch 350 and contact 126 of register 120. The register 120 makes an additional step and takes the same position as if the next higher even figure has been dialled. The trip spindle of a third selector takes, therefore, the same position disregarding whether the third figure of the wanted number was even or odd, and after sequence switch 350 leaves position 12, relays 373 and 374 are maintained energized over contact 146 of register 140 and control the translation of the units impulses for the final selector causing the advance of the brush carriage to the second half of the terminal row.

When the brush carriage of a final selector moves between the first and second half of the terminal arc, the short circuiting contact 457 of the brush carriage is in the well known manner closed for a comparatively long time and, if the wanted number corresponds to the first terminal in the second half of the terminal arc, the long closure of contact 457 delays the starting of sequence switch 450 and the opening of contact 444. In order that sequence switch 220 of the cord shall notmove into position 10 before contact 444 of sequence switch 450 is opened at the final selector the circuit at the register is so arranged that if the terminal of the wanted number is the first in the second half of the terminal arc of a final selector the energization of relay 339 at the register set and in consequence the deenergization of relay 222 of the cord is correspondingly delayed. The first terminal of the second half of the terminal are corresponds to an odd position of register 120 and position 0 of register 140. If, therefore, relay 373 has been energized on an odd po sition of register 120 and if register 140 is arrested in position 0 a circuit is closed in position 13 of sequence switch 350 for the energization of relay 378 over contact 145 of register 140, contact 375 bottom of sequence switch 350, front contact of relay 373, contact 146 of register 140 and contact 369 bottom of sequence switch 350. Relay 378 once energized maintains its'energization over its left hand front contact and sequence switch contact 369. When after the completion of the selection sequence switch 350 reaches position 14 the circuit for relay 339 is maintained open at the left hand back contact of relay 378, and the circuit is closed in position 15 of sequence switch 350 over sequence top, front contact of relay 378 and sequence switch contact 369.

When after the conversation relay 231 is de-energized, sequence switch 220 starts from position 12 and moves over position 13 into position 17, the metering battery 259 is connected to terminal 238 during the time sequence switch 220 passes over positions 14 to 16, whereby the meter 208 at the calling subscriber line is operated. In position 17 of sequence switch 220 the power magnet 241 is energized and the brush carriage rotates until its home contact 269 is reached, whereby relay 232 is energized in a circuit over contact 269. The brush carriage is arrested, sequence switch 220 starts from position 17 and moves into position 18 in which the sequence switch remains until the second cord of the pair becomes engaged with a call.

Relay 523 at the incoming end of the twowire trunk is de-energ'zed as soon as front contact of relay 231 is opened in the outgoing exchange. Relay 522 is thereby enerswitch contact 368 gized in a circuit over sequence switch contact 504 bottom and back contact of relay 523. Sequence switch 520 is energized in a circuit over contact 514 bottom and front contact of relay 522. Sequence switch 520 starts from position 9 and moves into pos1- tion 11 in which the power magnet 531 is energized and the brush carriage is restored to its position of rest, whereby after its home contact 539 is closed relay 532 is energized in a circuit over contact 539, sequence switch contact 516 and holding magnet 535. The brush carriage is arrested, and sequence switch 520 is energized in a circuit over front contact of relay 532. Sequence sw.tch 520 startsfrom position 11 and moves into position 1. hen contact 513 of sequence switch 520 is opened relay 543 at the third group selector is de-energized and causes the energization of sequence switch 550 in a circuit over contact 544 top and right hand back contact of relay 543. Sequence switch 550 starts from position 12 and moves into position 14 in which the power magnet 561 is energized and the brush carriage is restored to its position of rest, whereby after the home contact 569 is closed relay 562 is energized in a circuit over contact 569, sequence switch contact 560 top and holding magnet 565. The brush carriage is arrested, and sequence switch 550 is energized in a circuit over its contact 557 and front contact of relay 562. Sequence switch 550 starts from position 14 and moves into position 1.

When relay 543 opens its right hand front contact, relay 443 of the final selector is deenergized and provides a circuit for the energization of sequence switch 450 over contact 458 top and right hand back contact of relay 443. Sequence switch 450 starts from position 15 and moves into position 17 in which relay 460 is brought into connection with the called line over sequence switch contact 466 bottom, the circuit also including sequence switch contacts 467 and 445. Relay 462 and the cut-off relay of the called line are held energized in a circuit over contact 478 of sequence switch 450 independent from the front contact of relay 443. If the called subscriber has not restored his receiver relay 460 becomes energized and provides over its front contact and over sequence switch contact 440 bottom a circuit for the energization of relay 443. Sequence switch 450 is held in position 17. The circuit is established over back contact of relay 452, front contact of relay 462 and sequence switch contact 453 bottom to a common time alarm, which after the lapse of a given time provides a signal in the exchange. After the called subscriber has also restored his receiver, relay 460 and in consequence relay 443 are deenergized, sequence switch 450 starts from position 17 and moves into position 18, in

which the brush carriage of the final is restored to its position of rest. Sequence switch 450 moves then from position 18 into position 1.

The outgoing end of the two-wire trunk in the first exchange is maintained busy until the second group selector at the incoming end of the trunk line is restored to its position of rest and its sequence switch 520 is in position 1. When the cord is released and sequence switch 220 opens its contact 228 relay 502 is de-energized. A circuit is then prepared over right hand back contact of relay 502, right hand front contact of relay 501, winding of relay 503 and the common wire 529, and as soon as sequence switch 520 in the distant exchange reaches position 1 the high resistance winding of relay 503 is energized in a circuit over wire 536 of the trunk line, contact 504 of sequence switch 520 and relay 522. Relay 503 disconnects on its back contact the right hand holding winding of relay 501, which when de-energized disconnects at its right hand front contact relay 503 and connects at its left hand back contact resistance 500 to battery so that the trunk line is again made free.

If the called subscriber is the first to restore his receiver on the hook, relay 525 at the second group selector is de-energized and opens the shunt around the high resistance winding of relay 523. Relay 262 at the cord is thereby de-energized and sequence switch 220 is energized in a circuit over back contact of relay 262. Sequence switch 220 starts from position 12 and moves into position 13. The brushes of the first group selector are thereby disconnected. The second group selector and the final selector are released, while the sequence switch of the cord remains in position 13 and the calling line is held busy until the calling subscriber restores his receiver and relay 231 is de-energized. The cord is then released and the meter-208 of the subscriber line is operated.

If the wanted line has been found busy and the test relays 464 and 462 have notbeen energized when sequence switch 450 of the final selector moves over position 7, sequence switch 450 is arrested in position 10. The secondary winding of the busy tone coil 477 is thereby brought in bridge to theline and the calling subscriber receives a busy tone. When the subscriber restores his receiver and relay 231 is de-energizeda circuit is established for the energizationof the left hand winding of metering-hindering relay 224. Belay 224 disconnects at itsleft hand back contact the circuit for relays .235, 213 and 207, while over the left hand front contact of relay 24 a holding circuit is provided for its left hand winding. right hand front contact of relay 224 and its right hand low resistance winding a circuit is established for the energization of @ver the I sequence switch 220 which starts from position 11 and moves over positions 12 and 13 into position 17. The second and third group selectors are released as has been described. Relay 443 at the final selector is de-energized, sequence switch 450 starts from position 10 and moves into position 11 in which the brushes are restored to their position of rest, whereby after contact 457 bottom is closed relay 452 is energized. Sequence switch 450 starts from position 11 and moves into position' 1.

Since sequence switch 220 is held in position 11 whether the wanted line is found busy or a ringing current is sent to the Wanted station, relay 224 is energized if the calling subscriber gives up the connection before the called subscriber has answered. The release proceeds, without metering, also if the sequence switch of the final selector is in its ringing position and the called subscriber does not answer.

A connection can be released before the selection is completed if the calling subscriber restores his receiver on the hook, whereby if the call is given up during the dialling and relay 325 remains de-energized for a longer time than on the last opening at the dial, relay 339 becomes energized when sequence switch 320 passes over one of its positions 5, 7 10 or 12%. If the release is started and relay 325 is de-energized after the dialling is completed but before the selectors have been set up under the control of the register set, the de-energization of relay 325 causes the energization of sequence switch 320 in the circuit over contact 348, sequence switch 320 starts from position 15 and opens contact 340. When rela 222 of the cord is ole-energized, sequence switch 220 starts and relay 224 is energized as soon as sequence switch 220 reaches position 8 or position 11. If relay 224 is energized in position 8 of sequence switch 220 the sequence switch is arrested and the brush carriage is first restored to its position of rest, after which sequence switch 220 completes its rotation. Sequence switch 320 is held in position 16 until the registers are restored to their position 0. The back contact of relay 359 is connected over contact 340 bottomof sequence switch 320 and back contact of relay 339 direct to ground, while relay 359 is maintained energized over back contact of relay 355.

. When a release is started and relay 222 in the cord is de-energized at a stage in which sequence switch 220 is in position 7 the brush carriage is restored to its position of rest in position 8 of the sequence switch, during which relay 222 remains connected over sequence switch contact 246 top to wire'293. If the sequence switch 320 reaches position 18 before contact 246 of sequence switch 220 is opened, a circuit is established for the energization of relay 339 over wire 293, contact 322 top of sequence switch 320, right hand windingof relay 339, contact 3430f sequence switch 320 and back contact of relay 355. The left hand winding of stepping relay 325 is then energized in a circuit over sequence switch contact 327 top and front contact of relay 339. Sequence switch 320 is held in position 18 until relay 339 and in consequence relay 325 are de-energized.

When the release begins and the fundamental circuit is opened at the moment relay 522 of the second group selector was energized and sequence switch 520 has started from position 1 but trip spindle magnet 528 was not energized and its contact 510 bottom was not closed, the sequence switch 520 starts from position 2 and relay 522 remaining de-energized in position 3 of the sequence switch, the circuit is maintained over back contact of relay 522 and the sequence switch moves over position 3 into position 5. Relay is energized in a circuit over the home contact 539 of the brush carriage and sequence switch 520'moves over position 5 into position 6 in which the sequence switch is energized in a circuit over the back contact of relay 532. Sequence switch 520 moves into position 11 in which relay 532 is again energized in a circuit over contact Sequence switch 520 then completes its rotation, after which the outgoing end of the trunk line is given free.

if a release is started during the time the second group selector searches for a free third selector, the brush carriage continues to rotate until the terminals of a free third selector are reached and relays 534 and 532 are energized; after which sequence switch 520 movesinto position 6. The energization of relay 543 at the third group selector causes sequence switch 550 to start from position 1 and to move into position 2. Since the outgoing end of the two-wire trunk line is kept busy in the first exchange the fundamental circuit cannot be closed over the third group selector. In order that the second group selector may not be held permanently out of service the circuit is brought under the control of a common timing arrangement such as shown in Fig. .8 and the switches are released after the lapse of a suflicient time. For this purpose in position 2 of sequence switch 550 relay 562 is energized in a circuit over back contact of relay 564, sequence switch contact 545 bottom and holding magnet 565. The right hand winding of test relay 564 is connected over sequence switch contact 546 bottom,-

wire 591 to contact 582 of sequence switch 580. Whenever the sequence switch of a second group selector at the incoming end of a two-wire trunk is in position 6 a circuit is closed for relay 584 of the common timing arrangement over conductor and con tact 519 of sequence switch 520 to a common interrupter 589, whereby each time the common interrupter is closed relay 584 is energized. Sequence switch 580 is advanced one step when relay 584 is energized and another step when relay 584 is de-energized, since sequence switch 580 is energized either over front contact of relay 584 and sequence switch contact 583 bottom or over back contact of relay 584 and sequence switch contact 588 top. Sequence switch 580 is advanced, therefore, at given time intervals from the position in, which the sequence switch happens to stay, and when passing position 9 a circuit. is established for the energization of relay 564 of a third group selector, the sequence switch of which is in position 2. The energization of relay 564 causes the opening of the circuit of relay which is thereby tie-energized. Sequence switch 550 is then energized in a circuit over contact 547 top and back contact of relay 562. Sequence switch 550starts from position 2 and moves into position 4. Contact 582 of sequence switch 580 is opened and relay 564 is de-energized causing the deenergization of relay 562 at the third group selector before sequence switch 550 reaches position 4. Sequence switch 580 continues its movement under the control of relay 584 and after passing position 9 a second time contact 582 is again closed and relay 56-1!- is again energized. Relay 562 is de-energized so that sequence switch 550 starts from position 4'and moves into position 5.

The fundamental circuit of the third group selector can also remain open at the register set if the subscriber for some reason delays thedialling of the third figure. The time sequence switch a cycle of operation is therefore so selected that ample time is provided for any delay at the calling station and only if the calling subscriber holds up the completion of the dialling for any unreasonably long time is sequence switch 550 on the third group selector advanced to a position on which the fundamental circuit is opened. The time sequence switch 580 needs for the completion of a cycle of operation can be shortened by connecting its contact 585 to ground, and for lengthening the time of a cycle relays 586 and 587 are provided in the circuit, whereby the wiring is so changed that front contact of relay 584 is disconnected from contact 588 bottom and connected to the armature of relay 587. The manner in which the front contact of relay 584 is connected to the armature of relay 587 for the purpose of increasing the time interval is illustrated in Fig. 10. When relay 584 closes its front contact relay 586 is energized over front contact of relay 584 and back contact of relay 587. Relay 586 provides a locking circuit for its winding over 580 needs to complete its front contact, the winding of relay 587 and sequence switch contact 588. Relay 587 remains short-circuited as long as relay 584 is energized. After the front contact of relay 584 is opened relay 587 is energized and connects the front contact of relay 584 to sequence switch contact 588 bottom. When relay 584 is again energized sequence switch 580 is energized in a circuit over its contact 588 bottom and front contacts of relays 587 and 584. Sequence switch 580 starts from position 1 and moves into position 2. Contact 588 is opened and relay 587 is de-energized. After relay 584 closes its back contact sequence switch 580 moves from position 2 into position 8 in which contact 588 is again closed. The interrupter 589 must therefore be closed twice in order that sequence switch 580 can move from position 1 into its position 3 and so on.

lVhen sequence switch 550 of the third group selector is in position 5 and the fundamental circuit is not closed relay 552 remains tie-energized and sequence switch 550 moves into position 6. Contact 555 bottom of the trip spindle being opened, relay 522 remains de-energized and sequence switch 550 moves from position 6 into po sition 8 in which relay 562 is energized in a circuit over the home contact 569 of the brush carriage. Sequence switch 550 moves over position 8 into position 9. Relay 562 is thereby de-energized and sequence switch 550 moves over positions 9 and 11 into position 12 in which contact 541 is opened.

l/Vhen a release is started at the time a third group selector is searching for a free final selector the brush carriage of the third group selector continues to rotate until the terminals of a free final selector are reached. Relay 564 is thereby energized over contact 546 top of sequence switch 550 in position 6 as has been described, and sequence switch 550 starts from position 6 and moves over position 8 into position 9 in which terminal 57 2 is made busy over sequence switch contact 566, resistance 570 and front contact of relay 548. Relay 562 is energized in a parallel circuit to resistance 572 over back contact of relay 564, sequence switch contact 545 top, terminal 572 and resistance 442 of the final selector. The right hand winding of relay 564' is again connected over contact 546 of sequence switch 550 to wire 591, and when sequence switch 580 passes over position 9 relay 564 is energized and relay 562 is (Il6-81161gl26d. Sequence switch 550 is then energized and moves from position 9 into position 11. During the time relay 562 is disconnected terminal 572 is maintained busy over resistance 570. After sequence switch 580 passes position 9 a second time, relay 564 is energized. Sequence switch 550 leaves position 11 and moves into llH (ii i position 12. Resistance 542 is disconnected at contact 541 of sequence switch 550 so that relay 532 at the second group selector is de energize'd and sequence switch 520' leaves position 6 and completes its rotation.

l Vhen the release is started and the fundamental circuit'is opened at the tinjie relay 452 of the final selector has already been energized and sequence switch 450 is in position 2, the sequence switch moves into position 3 wliere it is held until the switch of the third group selector under the control of sequence switch 550 leaves positions 9 and 11. whereby the second group selector is released, and after relay 543 is dc-energized the circuit for relay 443 is opened. Sequence switch 450 is energized in a circuit over back contact 0-1 relay 443.

\Vhen the release is started at the time sequence switch 450 of the final selector is in position 4 the deenergization of relay "1 52 causes sequence switch 450 to start from position 4;. After contact 441 is opened relay 562 at the third group selector is de energized, sequence switch 550 moves over position 11. Relay 532 at the second group selector is de energized and sequence switch 520 starts from position 6 and moves over position 9, whereby relay 543 and in consequence relay l1 3 are tie-energized before sequence switch 450 reaches position ll. Relay 462 can thereby not be energized at the terminal of a subscriber line on which the brushes of the final selector happen to stay, the brush carriage is first restored to its position of res after which sequence switch 450 completes its rotation.

The automatic release of a second group selector on the incoming end of a two-wire trunk line after the lapse of a reasonable time together with the arrangement to hold the outgoing end oil? the trunk line busy until the sequence switch of the group selector returns into its position of rest allows each register to control immediately the corresponding selector after the series of impulses are completed on the dial for this register. On an average the setting up of a selector and its connection with a tree trunk line to a following selector is shorter than the time the subscriber uses for dialling the succeeding figure of the wanted number. Counting from the moment the subscriber removes the receiver from the hook, the time required to complete a connection is, therefore, appreciably reduced when each register immediately controls the corresponding selector. It would sutlice to connect the second group selector on the incoming end of a two-wire trunk with the common delay arrangement for the automatic release, in which case spare positions on sequence switch 520 could be provided so as to advance it from position 6, but it sequence was found more practical to control the sequence switch of the succeeding selector from the common delaying arrangement.

In a system in which the impulses from the dial can be accumulated in the register set and the selectors are enabled to continue searching it all succeeding selectors are busy until a trunk line becomes free, the number of trunk lines and selectors in a given group can be in practice appreciably reduced it permitting in exceptional cases during the busy hour the delaying of a connection until a trunk line has become free. If all final selectors to a given group of subscribers were busy and the progress of a selection was delayed because the third group se lector continues to rotate and to search for a trunk line, and should the connection of the timing arrangement for an automatic release be connected direct to the second group selector, the time a call is so kept waiting would have to be added to the time a subscriber may suspend the completion of dialling. Since it may happen that a sequence switch oi a group selector arrives'in the position where it is connected with the timing arrangement at the moment after the common circuit for advancing the sequence switch has been opened, the automatic release of the sequence switch will then take a still longer time and the switches would be held after a 'n'emature release an unreasonably long time. 1

When a figure is'erroneously dialled which causes the advance of the group selector on the incoming end of a two-wire trunk to a dead level; the group selector obtains a connection with a trunk'line such as 'shown'in Fig. 9. Test relay 534s of the group selector is thereby energized in a circuit over terminal 692, resistance 696' and back contacts of relays 699 and 697, and also over the windings of relays69'3 and-694 connected in parallel to resistance 696. Relay 693 when energized connects the windings of relay 695 which are diil'erenti'a'lly wound and the interrupter 690 in bridge to the trunk line. Each time the fundamental circuit at the register set containing rela 1 355 is-clo'sed the interrupter 690 causes energizations of relay 355 and the registers are restored in succession, while relay 695 remains de-energized. After the restoration of the registers is completed relay 222 of the cord is deenergized and the sequence switch 220 advances into position 10. A circuit is established over the left hand winding of relay 695 one wire of the trunk line and relay 262 of the cord. A second circuit is prepared over the right handwinding of relay 695 and retardation coil 257 of the cord. When the interrupter 690 is opened relay 695 is energized and provides on its front contact a circuit for the left hand winding of relay 697 which relay when energized opens its back contact and brings its right hand high resistance'winding in the circuit of terminal 692. Relay 693 line and relay 532 at the second group selector are thereby tie-energized. Sequence switch 520 leaves position 6 and moves into position 9. A circuit for the lamp 698 is established over the front contact of relay 697. An operator in depressing key 680 communicates with the calling subscriber. Relay 699 is thereby energized, lamp 698 is disconnected at the right hand back contact of this relay and a holding circuit is established for the winding of relay 699 over its right hand front contact and front contactof relay 697. At the left hand back contact of relay 699 is the shunt around the winding of relay 697 maintained open. After the calling subscriber restores his receiver on the hook and the switches are released, terminal 692 appears engaged until the key 680 is restored and relay 699 is de-energized. On the other hand if key 680 is restored be fore the switches are released relay 699 is maintained energized until relay 697 is deenergized so that the circuit for the lamp 698 is held open.

If the subscriber has noticed the error and gives up the call the register set and the cord are released as has been described. Relay 697 can, therefore, not become energized, relay 532 at the second group selector remains energized and sequence switch 520 is held in position 6. In order to release automatically the second group selector an arrangement is 'made whereby relay 694 provides over its right hand front contact a connection for relay 684 with common wire 691 which is connected with the common delaying arrangement shown-in Fig. 8. When sequence switch 580 passes over its position 9 relay 684 is energized and provides over its front contact and back contact of relay 687 a circuit for the energization of relay 686. After relay 684 is tie-energized relay 687 is energized in a circuit over the winding and front contact of relay686 and the right hand front contact of relay 694. When sequence switch 580 passes position 9 a sec- 0nd time and relay 684 is again energized a circuit is established for the energization of relay 697 over the front contacts of relays 687 and 684. Relay 532 at the second group selector is then de-energized and sequence switch 520 leaves its position 6.

For a forced release of a local connection from the tollboard over the switching section the test terminal of the subscriber line is for a short time interval connected direct to ground and then made busy. The subscriber wanted for a toll connection can be either the called or the calling party in a local connection. If the wanted subscriber is the calling party terminal 218 is connected to ground. Relay'235 at the cordis de-enat the trunk ergized and provides at its right hand back contact a circuit for the energization of relay 224 over contact 243 top of sequence switch 220 and retardation coil 237. The sequence switch 220 is started and the release of the cord, the second and third group selectors, is completed as has been described. The sequence switch of the final selector is thereby held in its position 17 until the called subscriber restores his receiver on the hook. If the forced release happens at the time sequence switch 220 is in positions 5 to 9 and the cord is connected with the register set, the energization of relay 224 takes lace in a circuit over sequence switch contact 243 bottom, wire 295 and one winding of stepping relay 325. When sequence switch 220 leaves position 9 the stepping relay 325 is de-energized and the register set is released.

When the subscriber is the called party in the connection and terminal 470 is con nected at the switching section to ground. relays 462 and 464 are de-energized and cannot become again energized since terminal 470 is immediately made busy at the switching section. Sequence switch 450-is then energized in a circuit over its contact 456 top and back contact of relay 462. As

soon as the through connection with the called line is opened at sequence switch contact 473 relay 525 of the second group selector, is tie-energized and in opening the shunt around the high resistance winding of relay 523 causes the de-energization of re-- lay 262 at the cord so that sequence switch 220 startsfrom position 12 and moves into position 13, after which, the second; third and final selectors are released. The sequence switch of the cord is held in position 13 until relay 231 is ole-energized.

For obtaining a connection over the first group selector with a distant manual board the subscriber dials two fi ures. When register 100 is advanced under the control of the dial into positions 1 or 0 and when sequence switch 350 is started from position 1, a circuit is established in position 2 of the sequence switch for the energization of relay 378 over contact 105 of register'lOO and sequence switch contact 379 top. Relay 37 8 provides over its left hand front contact a holding circuit for its winding traceable from battery through the winding, front contact. and left-hand armature of said relay, lower contact 369 to ground. In position 3 of sequence switch 350 the trip spindle of the first group selector is set up according to the position of register 100. The brush carriage of the first group selector obtains then a connection with a free trunk line. After the second figure isdialled and sequence switch 350 advances into position 6 a circuit is established for the energization of relay 339 over one wire of the trunk

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