US1167646A - Machine telephone switching system. - Google Patents

Description

F. R. McBERTY.

MACHINE TELEPHONE SWITCHING SYSTEM. APPLICATION FILED JUNE 25. 1913.

limgmfio Patented Jan. 11, 1916.

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Llwfifio Patented Jan. 11, 1916.

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F. R. McBERTY. MACHINE TELEPHONE SWITCHING SYSTEM.

APPLICATION FILED JUNE 25,1913. 1 16x6460 I2 SHEETSSHEET 3.

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F. H. McBERTY. MACHINE TELEPHONE SWITCHING SYSTEM. APPLICATION FILED JUNE 25, I9I3.

11,167,646, Patented Jan. 11, 1916.

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MACHINE TELEPHONE SWITCHING SYSTEM.

APPLICATION FlLED JUNE 25.1913. 1 1167 646. Patented Jan.11,1916.

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F. R. McBERTY. MACHINE TELEPHONE SWITCHING SYSTEM.

APPLICATION FILED JUNE 25| 1913- Patented. Jan. 11, 1916.

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F. R. McBERTY.

MACHINE TELEPHONE SWITCHING SYSTEM. v APPLICATION FILED JUNE 25, 19l3.

1 167 646, Patented Jan.11, 1916.

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F. R. McBERTY.

MACHINE TELEPHONE SWITCHING SYSTEM. APPLICATION FILED JUNE 25, 1913.

LlfiTfiQcfi. Patented Jan. 11, 1916.

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F. R. McBERTY. MACIHENE TELEPHONE SWITCHING SYSTEM. APPLIQATION HLED-JUNE 25. 1913.

1 167 646; 7 Patented Jan. 11, 1916.

IZ SHEETS-SHEET I0- F. R. lVlcBERTY.

MACHINE TELEPHONE SWITCHING SYSTEM.

APPLICATION FILED JUNE 25,.1913.

IL JLGKMGO Patented. Jan. 11, 1916.

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F. R. McBERTYr MACHINE TELEPHONE SWITCHING SYSTEM. APPL'ICATIION FILED JUNE 25. I913.

Patented Jail. 11, 1916.

12 SHEETS-HEET 12.

ymmgman v in the art, to systems of widely varying character, as, for example, to 'fullautomatic FRANK ROBERT MoBER'IY, or 'ANTWEEP, BELGIUM,

ASSIGNOR, BY MESNE ASSIGN- IVIENTS, TO WESTERN ELECTRIC COMPANY, INCORPORATED, A CORPORATION OF NEW YORK.

To all whom it may concern:

Be it known. that I, FRANK ROBERT MCBERTY, a citizen of the United States,

residing at 49 Boulevard Leopold, Antwerp, Belgium, have invented new and useful Improvements in Machine Telephone Switching Systems, of which the following is a specification.

This invention relates to improvements in telephone exchange systems for the interconnection of telephone lines, and has to do more particularly with systems in which the extension of the desired connection from a calling line to a called line is accomplished by automatic selector switches under the control of an operator at the central or switching station. Many of the features to be described,*however, are not restricted to systems of this character, being also applicable, as will'be apparent to those skilled or machine telephone exchange systems and, particularly :those features relating to the connection of a calling line with an operator, to manual telephone exchange systems.

One of the principal features of the in-' vention relates tothe use in a telephone enchange system of alternating current, as well as direct current, for both controlling the establishment of connection and the restoration to normalof the automatic se-v lector switches overwhich the desired connection is established? A further feature involves the use in such control of both relays responding only to alternating current, and

where necessary side by side throughout the system, each performing its proper function in the control of the connection established or being established.

I Another important feature ofthe invention relates particularly to that construction of the system herein disclosed, wherein a connection may be established over a plurality of two-conductor trunk-circuits. A

' further development of this feature involves the establishment of a connection over a p111 rality of such two-conductor trunk circuits in series and in succession.

A still further feature of the invention re lating to two-conductor trunk circuits mvolves the establishment of a connection over two-conductor trunk circuits in both direc- Specification of Letters Patent.

relays ,respondingto direct current; such relays being used MACHINE TELEPHONE SWITCHING SYSTEM.

Patented Jan. ii, rare.

Application filed June 25, 1913. Serial No. 775,645.

also the trunk'circuits leading from such office at which the control is exercised to a second office, or even to a third ofiice, may be of the two-conductor type. 1

A still further feature of the invention relates to improved and novel methods andmeans whereby a successful call may be charged or registered against the calling subscriber and involves in part the location of the apparatus whereby the charging circuit is prepared and controlled in association with the first group selector.

A further feature relating to the registering or charging of a call has to do with such an arrangement of the system that no apparatus at the final selector or line switch or any of the group selectors subsequent to the first group selector is necessary to insure the charging of a call to the calling subscriber, if such call has been successful.

A still further feature of this portion of the invention involves the location. of the subscribers register or toll device by which successful calls are registered or charged at. any office or sub-oilice to which the calling line is directly connected, which oflice may, if preferred, be distant from the office at which the control of the selector switches is exercised and at which the relays hereinbeforexreferred to as controlling the charging of'a successful call, may be located.

Still another feature of the invention relates to an improved, novel and efiicient arrangement and construction of-satell1tes to this feature each central stationjnay have associated therewith one or more sub-central stations or satellites located at a distance therefrom, such satellites being of an improved and novel construction and arrange-. ment of such character that incoming calls may be promptly and efliciently received and outgoing calls accurately and properly completed.

A further feature of the invention relates more particularly tothe satellite in which a called line is selected and involves the immediate restoration of the apparatus at such satellite and the freeing of the trunk line leading thereto in case the called line is busy.

Another feature of the invention relates more particularly to systems in which the establishment of a connection is controlled by what is known as the revertive impulse system of control, that is, in which the selecting operations are controlled and accompanied by impulses established in the selecting or fundamental circuit by the movement of a part of the selector, which impulses affeet the sending or controlling apparatus under the control ofasubscriber or operator until the proper number of impulses have beensent and the proper selection has been accomplished, when the controlling apparatus will in turn so affect the selector under control thatit will stop with the proper se-.' lection made. In systems of this character, 1'

of which, for example, one is shown in the British patent specification No. 21260 of 1911 the impulses, instead of passing from the controlling apparatus to the selector under control, pass from the selector under control to the controlling apparatus.

A feature of the invention, therefore, relates to circuits and arrangements of apparatus whereby in a selecting or fundamental,

circuit these revertive impulses produced in i one portion of the circuit will be reproduced in another and separate portion of the circuit to affect the sending or controlling apparatus.

A still further feature of the invention involves the use of a clear, unobstructed registering control circuit from the first group selector to the called subscribers sub-station,

such circuit having associated therewith no bridges conductive to direct current, and such bridges as are associated therewith being without function with regard to the registering operation.

A further feature of the invention relates to the provisionof positive means whereby, in case the line called and selected is busy, the charging or registering of a call to the calling subscriber will be prevented, such means beinglocated at the first group selector, and belng responsive to means located at the final or line selector operating under after an attempted connection to a busy line, and, further, the simultaneous restoration of all the selectors upon disconnection. after a successful call, whereby the time in which any selector is necessarily out of actual serviceis reduced to a minimum.

'A still further feature of the invention relates to the location of the busy back apparatus, that is, the apparatus whereby the subscriber, or the operator supervising the connection, or both such subscriber and operator, will be informed that the desired line lsbusy at the apparatus associated with the first group seleotor. This feature involves, in addition, the construction wherein the busy back apparatus, although initially controlled by the testing apparatus at the final selector, operates thereafter independently I of such apparatus and the connection, in so far as all apparatus subsequent to the fi group selector is concerned may be immediately restoredto its normal condition.

Another feature of the invention relating particularly to systems in which each calling line is immediately mademanifest before arf operator by a visual signal and such calling lines are automatically connectible oneat a time to an operator when idle, involves means whereby such signal will indicate not only the. existence of the call, but also whether or not the calling line to which it is individual is connected to an operator.

. This result is obtained in the invention herein disclosed by having a calling lamp burn steadily upon the receipt of the call until the line with which it is individual is connected to an operator, from which time, until the operator is disconnected from such line,'

the lamp will intermittently fia sh to indicate such connection.

A still further feature of the invention relat-es to a new and simplified arrangement associated with a non-numerical switch over which a calling line is connected to a connecting circuit at a central oifice, whereby a single means exercises various and different controls in the different stages of the operation. i

Another feature of the invention alsoconsists in an improved circuit arrangement between a supervising office and a distant office at which the call as extended includes automatic switching apparatus and relates to such an arrangement of the trunk circuit between such offices that the control of the automatic switching apparatus may be exercised thereover in one direction, while the control of a signal at the supervising ofiice may be exercised thereover in another direction.

Other noveland improved features, particularly such as relate to the controlling apparatus, the control of the finding operation at the second line finder. that is, the line finder at the controlling station, the connecbut it will be understood that the invention is not limited to the particular form or system shown, and is so shown merely for convenience, and is applicable to systems widely varying in character.

The drawings which comprise 9 figures set forth diagrammatically a system embodying-the invention.

Figure 1 shows that apparatus involved in the connection located at the first or in coming satellite or subcentral station. Figs. 2 and 2 show the connecting circuit and associated apparatus, including a line finder and a first group selector, situated at the controlling central office or station.

Fig. 3 shows a second group selector and the apparatus associated therewith which .is also situated at the controlling central office or station. Fig. 4: shows a third group selector and its associated apparatus including the relays whereby the controlling impulses involved in tens and units selection at the final selector are repeated back to the controlling apparatus at the controlling central office or station, all of which apparatus is located at a second central ofiice or station. Fig. 5 shows the apparatus involved in the con nection including a connecting or line selector'and its associated apparatus located at a second satellite. Fig. 6 shows further means associated with the connecting circuits at the controlling central office orsta-* tion whereby the selection and seizing of an operators equipment is controlled. F ig. 7 shows apparatus also at the controlling central oflice or station associated with the different operators positions to which the calls coming in on the connecting circuit shown in Fig. 2 are connectible. Figs. 8 and 8 illustrate the two register-controlling equipments of one of the operators,

that is, the home operator, showing the A register of such operator in full and indicating sufficient of the B register of such operator to make clear the operation thereof. These figures also show the counting relay apparatus of such A register. Figs. 9 and 9 illustrate the registers themselves of the A register apparatus and the set of manually operable keys by which the controlling operation iscontrolled by the operator.

The figures should be placed as follows Figs. 1, 2, 2 3, 4 and 5 in order from left to right; Fig. 6 under Figs. 2 and 2 Fig. 7 under Fig. 6; and Figs. 8, 8 9, 9% to the left of Figs. 6 and 7 and in order. from left to right.

A connecting or final selector switch such as is diagrammatically shown in Fig. 5 is illustrated in British Patent No. 16,867 of 1911. The apparatus associated with this switch as shown in Fig. 5 is somewhat different, but the structure of'the switch will sufliciently appear from such patent and need not be herein described. The group selectors shown in Figs. 2, 3 and 4 are in structure substantially the same asthat shown in) Fig. 5 and in the British patent referred to. The only substantial difference in the structure of the switches from that shown in the patent is in the brush carriage interrupter devices indicated above the brushes in the several figures. That is to say, instead of the brush carriage interrupter involving two switch devices as in the British patent and Fig. 5 herein, it involves a. single switch device which is closed each time the brush carriage moves from one stage to the next, and is open only when the brush carriage rests with its released brushes centered upon a set of contacts. Of course, in the normal position the interrupter brush rests upon the insulated segments'270, 371, and 471 of the several selector switches and as it moves from normal position into position in which the released brushes will make contact and be centered upon the first set of contacts of the row to which they are individual, the brushes 254, 354, 454 will be connected to earth over the toothed segment and. then opened as the brushes are centered. In every successive movement from one set of terminals to the next this circuit to earth will be again closed and opened as the brushes are centered upon the terminals.

The line finder switches shown in Fig. 1, and to the left in Fig. 2, are of a somewhat similar construction to that of the selector switches above referred to and shown in British Patent No. 16867 of 1911 hereinbefore mentioned. They are fully described in British patent 1912, and will not be herein further described.

The sequence switches which are used throughout the system shown to control the circuits of'the various portions of the apparatus, and which are indicated at 100, 200, 300, 400, 500, 600, 70c, 750,800, and 850, are of the type shown in British Patent No. 20840 of 1909, and since thev are sufficiently shown and described therein will not be further described.

Throughout the drawings the sequence switch springs are not indicated in their structural relation to the mov ng parts of the switch, but are so located as to make most clear the circuits of the system disclosed herein. The positions in which such sequence springs are closedto the contacts shown associated therewith are indicated by the numbers shown a'cent to such springs,

such springs being closed to the contact, shown on the same side of the spring with any given number or numbers, in the position indicated by such numbers. The controlling springs of the respective sequence switches indicated at 101, 201,301, 401, 501, 601, 701, 751, 801, 851 are the springs which insure that the sequence switch when started from any position will be positively driven into its next stopping position. The numbers placed adjacent to these springs indicate the positions in which the springs are open, these springs being closed at all other times and positions. Where these numbers are separated by a minus sign it indicates that the circuit is at all times open between the position indicated by the numbers and is closed only in such positions, whereas where such numbers are separated by the plus sign (-1-) it indicates that the circuit is closed continuously between and in the positions iridicated,for example, the sequence switch spring 114 top is closed in position 3 and in position 8, but is not closed in any other position nor between positions 3 and 8, whereas sequence switch contact 110 bottom'is closed in positions 2' and 18 and continuously while the sequence switch is passing fromposition 2 to position 18.

The set of counting relays shown in Fig.

8 is .of somewhat similar arrangement to that shown in British Patent No. 23508 of 1911. Although the circuits are somewhat different from the circuits shown in the patent application referred to, the operation of the set of counting relays is directly analogous to the operation of the set of counting relays in such specification. In detail the arrangement of the circuit of the set of counting relays shown herein will sufficiently appear from the detailed description of the operation of the system.

The registers shown in Fig. 9 are struc- ,turally precisely like the sequence switches above referred to and shown in the British Patent No. 20840 of 1909. The only difference in their operation is that they have no normal position, and having been used "in connection with one call, remain in such set position until used in connection with some other call.

The manually operable keys shown in Fig. 9 are arranged in a somewhat similar manner to the keys of the ordinary addingmachine; when a key is depressed it is held in such position by the energization of a locking magnet individual to the row of which such key forms a part. A key device of this character is disclosed in British patent application No. 23508 of 1911.

Description of operation-The system is best described by the description of the establishment of a call, and the subsequent restoration to normal of the apparatus inthe line relay 116; the attraction of the armature of the line relay closes a circuit and energizes the pilot relay 117 for the group of line finder switches having access to the calling line, and atthe same time, by the arrangement of such circuit, including the resistances 141 and142, places a selectable potential upon the terminal 121 individual to such calling line. The energization of the relay 117 has closed a circuit through the springs 103 and 104 for the power magnet for each of the idle finders of the group controlled by such relay. The brush carriages of such idle line finders thereupon start in motion and the brushes 122, 123, 124, 125 sweep over the contacts 118,119, 120, 121 of the various lines connected thereto, which contacts appear in multiple upon each of this group of line finder switches. So long as the brushes 125 of the line finders pass over contacts 121 of any non-calling lines, that is to say, over contacts on which there exists no selectable potential as above referred to, the line finders continue in motion. As soon, however, as the brush 125 of the line finder reaches the contact 121 upon which such selectable potential exists, the test relay 126 is energized, and by closing the parallel circuit through its armature and low resistance contact with the terminal 121 will be energized. The line finder, however, which has seized the calling line does not immediately stop, coming to rest only when it brushes are centered upon the terminals of the calling line at which time the interrupter 128 will be open and the test relay 127 will become energized through its left-hand winding. Immediately upon the energization of this relay the circuit of the power magnet 150 is opened at its back contact, the circuit of the holding magnet 151 is closed at its front contact; the brush carriage of the finder switch will therefore come positively to rest with its brushes centered upon the terminals of the calling line. The same operation of the test relay 127 has closed a circuit over spring 113 top to drive the sequence switch 100 out of its first or normal position into its third position. On coming into its second position the sequence switch closes the spring 110, and the circuit is therefore established to energize the cutofl' relay 129 of the calling line. This in the usual manner cuts off the line relay, and ground and battery from such line, and causes the consequent deenergization of such line relay 116 and of the pilot relay 117. In consequence of the deenergization of the pilot relay 117, all of the line finders which are in motion will be brought to a stop. Of course, if some other call had meanwhile been initiated the deenergization ot the line relay 116 would not have caused the de'energization of the pilot relay 117, and the idle line finders would have continued in motion so long as a line remained unseized upon which a call had been initiated. The .circuit'for' the cut-off relay over the spring 110 is maintained until the restoration of all the apparatus at this satellite. Therefore, as the sequence switch leaves its second position the spring 109 may be opened and the test-guard heretofore established on the terminal 121 may be removed. This line, however, will not be selected by any other line finder as its selectable potential has also been removed by the deenergization of the line relay 116 individual to the line. Before, however, the spring 109 is opened the control of the relay 127 is transferred to the calling .subscriber by the closure of the springs 111 top and 112 bottom. The circuit for this relay will be maintained through the sixth position of the sequence switch so long as the subscribers loop-circuit is closed at his substation' This is for the purpose that should the subscriber hang up his receiver before the call has been extended to the controlling central office, the deenergization of the relay 127 will, by driving the sequence switch through its seventh position over the spring 113, produce the restoration of the apparatus at the satellite.

1 On coming into position 3 the sequence switch 100 closes the spring 107. This initiates the operation of the line finder apparatus at the central station to which the trunk line terminating in the terminals- 233, 234 is connected precisely as did the removal of the subscribers receiver from his switclr hook hereinbefore descrlbed 1n1t1ate the opcess to the trunk line upon which the call exists will bestartedg in motion over circuits including the springs; 209 top, 210 top individual to them respectively. As the line finders move the brushes 237, 238, 239 and 240 thereof will sweep over the terminals 233, 234, 235 and 236 individual to the respective trunks appearing in such line finders. When a line finder reaches the trunk upon which the call exists its test relay 241 will be energized and, in the well-known manner, place the test guard upon the terminal 236 of the trunk line. The brush carriage, however, will continue to move until the circuit through the interrupter 243 is opened, when the test relay 242 will be energized, opening the circuit to the power magnet 250, closed over the spring 209 top, and closing the circuit to the holding magnet 251 over the spring 208 top. The finder therefore stops with its brushes accurately centered upon the terminals of the trunk line upon which the call exists. The same operation of the relay 242 drives the sequence switch 200 out of its first and normal position into its fifth position by means of a circuit oversprings 208 top and 203 top. As the sequence switch comes into its second position the circuit is closed over the spring 226 for the cutofi relay 244 and the line relay 231 and the pilot relay 232 will be deenergized precisely as the line relay and pilot relay at the satellite hereinbefore described. As the sequence switch moves through its third and fourth position, alter- 'nating current, the source of which is indicated here and elsewhere on the drawings by a circle including plus and minus signs, is applied to the trunk line by the closure of the spring 225 top and a corresponding ground connection is connected to the trunk line to complete the circuit for said alternating current over spring 224 top. This energizes the alternating current relay 132 at the satellite, the current passing through the condenser 134. This alternating current, while it is capable of passing through the condenser 134 as shown, is of sufficiently low frequency and has such other electrical characteristics that it will be inaudible and unobjectionable to the calling subscriber if by chance it should be impressed upon the circuit leading to his receiver. The energization of the relay 132 at the satellite, by means of a circuit including the springs 114 top and 105 top drives the sequence switch 100 into its 7th position. As this sequence switch comes into its 6th position, the alternating current circuit being by this time open at the springs224 and 225 at the central office, it closes a substitute circuit for the relay 127 through the spring 114 bottom, armature and back contact of the relay 132, spring 106, front contact and armature of the relay 127 and spring 104 bottom so that the restoration of the apparatus at the satellite still controlled by the relay 127 now awaits the energization of the relay 132. Position 7 in which the sequence switch 100 comes to rest is the through or talking position of such sequence switch, and in such position the calling subscribers line is connected through to terminals 233, 234 of the through to the repeating coil 2&6 and current is supplied to such subscribers circuit from the battery included between the windings thereof. The supervisory lamp 263 will not be lighted at this time, although the spring 223 is closed, because the supervisory relay 247 is energized. However, the calling lamp 245 will be lighted due to the closure in this position of the spring 207 top. This will indicate to the operator that a call is waiting upon the connecting circuit to which such calling lamp 245 is individual. If the operator in whose position the connecting circuit shown in Fig. 2 is situated is idle at this time such connecting circuit will be immediately and automatically connected to such operators telephone equipment and to an idle controlling equipment of such operator. Similarly, if such opera ator is busy, but the alternate operator is idle and her helping-out key is closed, the connecting circuit shown in Fig. 2 will be connected to such alternate operators telephone equipment and to an idle controlling equipment of such alternate operator. This is accomplished as follows: Thespring 207 not only closes the circuit for the calling line lamp, but also closes a circuit for the distributing sequence switch 600 over the spring 603 top of such sequence switch. The sequence switch 600 therefore moves into its second position. This is the testing position of this distributing sequence switch. In this position battery is connected to the high resistance winding of the relay 636 individual to the home operator of the position in which the connecting circuit shown on Fig. 2 appears, such relay being also individual to this particular connecting circuit. At the same time the battery is connected to the corresponding windingof the relay 637 appropriated to that connecting circuit but which is individual to an. alter nate or helping-out operator, such operator being, for example, the operator whose position is immediately to the left of the home operator. It will be understood, of course, that an additional helping-out or alternate operator may be provided in the person of the operator to the right of the home operator, but for clearness and simplicity the apparatus of but a single helping-out oper-' ator is shown. Battery connections referred to are provided by the springs 606, 607. If

the home operator is busy," her sequence switch 700 will be out of its normal position and no circuit will be established for the relay 636. If the alternate operator is busy, her sequence switch 750 will be out of its normal position, or if, even though she is idle, her helping-out key 771 is not thrown, y

is idle and her helping-out key 771 is closed,

the relay 636 or 637 appropriated to such operator will be energized and the operation of selecting an operator and an equipment of such operator will begin.

It will be understood that for each connecting circuit of a position there will be a relay 636 of the home operator, the high resistance winding of which is connected to the conductor leading to the top contact of the spring 703, all of such high resistance.

windings being connected in parallel to such conductor. Similarly for each connecting circuit of a position there will be a relay 637 of the alternate operator, the high re sistance windings of which are connected in parallel to the conductor leading to the contact of the helping-out key 771. It may be, therefore, that a plurality of connecting circuits are simultaneously attempting to select and seize an idle operator and an idle equipment of such operator. Immediately that the circuit through the high resistance winding of the relay 636 is closed at the spring 703, such relay and any other similar relay of other connecting circuits on the same position, the distributing sequence switches 600 of which are in second position, will be energized, andclose, by the attraction. of their armatures, circuits through their low resistance windings in parallel and throu h the relay 716 and the high resistance 39. Current in the common circuit will. be sufficient to energize the relay 716 but the current in the parallel branches through the low resistance windings of the relays 636 will not be suflicient to energize two of such relays simultaneously. Theretact of relay 716, as it is energized to drive 4 the home operators sequence switch 700 into second position, the relays 636 connected in parallel will allow their armatures to retract until circuit is closed through but one of them, which will'be the one-the armature of which would be the lastto open the circuit at its front contact. This relay 636 alone will remain energized. There-' fore, when the sequence switch 700 comes into its second position but one of the relays 636 is or remains energized. In this position a shunt is closed around the high resistance 739' through the spring 705 bottom, so that sufficient current will pass through the relay 638 to energize it and the sequenceswitch 600 will move out of its second position and under the control of the relay 636 and the spring 605 move into its eighth position. This operation by which the home operator is selected rather than the alternate operator will take place if the home operator is idle, whether or not the alternate operator is busy or idle. If the alternate operator is busy obviously no circuit will be provided forthe relay 637.

If the alternate operator is idle and her helping-out key 771 is closed, the relay 637 will be energized and the alternate operators sequence switch will have moved, but as the distributing sequence switch 600 will be driven through its positions individual 1101116 alternate'operator, no circuit will be established to hold the alternate operators sequence switch 750 in its fifth osition, and such sequence switch will immediately return to its normal position. If, however, the home operator is busy, the al ternate operator observing the calling lamp 245 to be lighted may close her helping-out key771 (unless it is already closed) and if such operator is idle the same selecting operation will take place with regard to the alternate operator as has been described with regard to the home operator. In this case, however, the distributing sequence switch 600 will only be driven into its third position by the energization of the relay 637 and the closure of the spring 604, top. From position 3 when the alternate operator has been seized, theoperation of seizing an idle register of the alternate operator will take place precisely as will the seizure of an idle registering equipment of the home operator with the distributing sequence switch 600 in the eighth position. For thepurpose of illustration, therefore, it will be assumed that the home operator is idle and the distributing. sequence switch 600 has moved into its eighth position. As the sequence switch 600 comes into its eighth or tenth position, the relay 638 being denergized, it establishes a circuit over the springs 618 and 202 bottom, to drive the sequence switch 200 into its sixth position. In the sixth position of the sequence switch 200 and the third, sixth, eighth or tenth positions of the sequence switch 600, the calhng lamp 245 depends for current on the circuit through the interrupter 626 and the spring 603 bottom. This will cause the lamp to flash, indicating that the connecting c rcuit to which it is individual is the one'iwhlch is now connected to an operators equipment.

Upon the opening of the circuit of the relay 716 at the spring 605' top, this relay is deenergized and the home operators sequence switch 700 driven from its second position. As this sequence -sw1tch comes into its fourth position, the circuit 1s again established for this relay over springs 710 top, 704, 608 top and 212 bottom. This will energize the relay 716 agaln before the sequence switch 700 reaches its fifth position, and this sequence switch will therefore stop in such position. If when the sequence switch 600 comes into its eighth position the A register of the home operator is idle, the relay 638 will be energized over springs 602, back contact of relay 639, springs 206, 610 bottom, 706, 870, 803 bottom and back contact and armature of the relay 8250f the A register equipment. This circuit will energize the relay 638 in the eighth and ninth positions of the sequence switch 600 and such sequence switch will therefore be driven into its tenth position which with the eleventh position are the positions individual to the A register equipment of the home operator on such sequence switch. It will be observed that this circuit depends on the closure of the spring 206, indicating thereby that the connecting circuit is ready to have the connection extended, that it depends on the spring 706 indicating that the home operators telephone set is connected to the seizing con necting circuit, that it depends on the spring 870 which is open in the second, third, fourth and fifth positions of the sequence switch 850 of the B register equipment, and its closure therefore indicates that the B register equipment is no longer using the set of manually operable keys shownin Fig. 9, which are common to the A and B register equipments of the home operator; and finally that it depends upon the spring 803 and the armatureof the relay 825, which together indicate that the A register equipment is idle. If the A register equipment had been busy the circuit traced would have been open at the spring 803. On the other hand, a circuit would have been established over the major portion of such circuit and through the spring 855 top and the high resistance relay 875 of the B register equipment.

In the event that the A register equipment is idle the relay 875 would have been shunted and could not have been energized. If the A register equipment is busy the relay 875 would have been energized, but insuflicient current would have passed therethrough to energize the relay 638, and therefore although the B register equipment would have been seized and its apparatus started in operation, the sequence switch 600 would have remained in the eighth position. On the other hand, assuming the A register equipment to be idle, immediately that the sequence switch 600 comes into its tenth position a circuit will be established for the high resistance relay 825 over the circuitas traced before to the spring 610, but now over the top contact of such spring, spring 707, spring 805 top and relay 825. Vhen this circuit is established, the relay 825 is energized, but insufficient current passes thereenergization of the relay 825 of the A register equipment in the tenth position of the sequence switch 600, a description of such subsequent operations in connection with one of the register equipments will suflice. It will therefore be assumed that the A register of the home operator is idle, and that therefore the sequence switch 600 is in its tenth position and the relay 825 is energized. The energization of this relay 825 drives the A register equipment sequence switch 800 out of its first position and into its second position. This movement immediately opens the circuit of such relay 825, and by its denergization it drives the sequence switch 800 out of its second position, and such sequence switch under control of its spring 801 will move into its fourth position. As this sequence switch,

- however, comes into its third position, a circuit is closed for therelay 825 over the spring 617 top and 805 bottom, so that before the sequence switch 800 comes'into its fourth position this relay is energized and the sequence switch will stop in its fourth position. 4.

'lVhen the sequence switch 600 comes to rest in either its tenth position as described or in its eighth position if the A register is busy (and similarly in positions 3 and 6 if the alternate operator has been seized) a circuit is established over the springs 618 and 202 bottom to drive the sequence switch 200 into its sixth position. At this time the springs 609 top and 621 bottom are closed and also in the sixth position of the sequence switch 200 the springs 220 top and 219 bottom are closed. A circuit is therefore established for the home operators telephone set 719 to the connecting circuit over the conductors d, e (broken in Fig. 2'

for clearness) so that the operator may converse with the calling subscriber and inquire and learn the number of the desired line. When the operator has thus learned the number of the line wanted, she will depress the manually operable keys shown in Fig.

9 to indicate such number thereon in a well understood manner.

In the fourthposition of the register sequence switch 800, the apparatus is ready for the operator to indicate the number of the desired line upon the manually operable keys, shown in Fig. 9, by depressing the appropriate key of each of the groups of digit keys. The preparation of these circuits and apparatus for such act by the operator has, of course, taken place while the operator has been learning from the subscriber the rows of keys; the number 9 or tenth key of the next or 10s row of keys, and the number 2 or third key of the last or units row of keys. Each key as it is depressed will be lockedand held in such position by the locking magnets indicated for the several rows of keys, the energizing circuit for which is closed by the spring 814 in the fourth and fifth positions of the sequence switch 800. It is assumed that the keys will be depressed in order either from the highest digit to the lowest or from the lowest digit to the highest. When, therefore, all the keys are depressed a circuit will be closed through the depressed units key and the depressed 100,000s key, to start the various registers 901, 902, 903, 904, 905, 906 in motion over the spring 809 and also a circuit for the relay 718 to drive the operators sequence switch out of its fifth position. The operator having learned the number desired, and indicated such number upon the manually operable keys, her attention is no longer required, and her teleto the connecting circuit in question during the normal course of the establishment of the connection desired. As the home operators sequence switch moves through position 6 the spring 705 will be closed to drive the distributing sequence switch 600 into its eleventh position in which the connecting circuit will still be connected to the A register apparatus but will no longer be connected to the operators telephone, the springs 609, 610 and 621 being open. The movement of the sequence switch 700 on leaving its fifth position will continue into its eighth position, in which position it will find a circuit closed for the relay 716 over the front contact of the relay 718, spring 709 and spring 710, bottom. This will be maintained until the release of the "keys when the number indicated thereon hasbeen registered upon thefregisters hereinbefore noted when the circuit for the relay 718 will be opened and in consequence the circuit for the relay 716 will be opened and the home operators sequence switch will return to its first and normal position ready to be selected and seized by some other con-'

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