US1259967A - Telephone system. - Google Patents

Description

'A. H. DYSON.

TELEPHONE SYSTEM.

APPLICATION FILED SEPT. 6. I906.

Patented Mar. 19, 1918. 5

1| SHEETS-SHEET A. H. DYSON.

TELEPHONE SYSTEM.

APPLICATION FILED sEPTJB. 190s.

Patented Mar. 19, 1918.

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TELEPHONE SYSTEM.

APPLICATION FILED SEPT.6. 190s.

Patented Mar. 19, 1918.

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TELEPHONE SYSTEM.

APPLECATION FILED SEPLG, I906.

Patented Mar. 19, 1918.

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- APPLICATION FILED SEPLG. I906. 1,259,967. Patented Mar. 19, 1918.

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TELEPHONE SYSTEM. APPLICATION HILED SEPT.6. 1906.

A. H. DYSON.

TELEPHONE SYSTEM.

APPLICATION men sums, 190s.

Patented Mar. 19, 1918. 4

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AJH. DYSON.

TELEPHONE SYSTEM.

APPLICATION FILED sEPL'e. 190a.

. 1,259,967. Patentd Mar.19,19l8.

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TELEPHONE SYSTEM.

APPLICATION FILED SEPT-6. I906.

Patented Mar. 19, 1918.

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TELEPHONE SYSTEM.

APPLICATION FILED SEPT. 6. 1906 Patented Mar. 19, 1918.

n SHEETS-SHEET H A WW1 Ml UNITED STATES PATENT OFFICE.

ALFRED H. DYSON, OF CHICAGO, ILLINOIS, ASSIGNOB, BY'MESNE ASSIGNMENTS, '10 KELLOGG SWITCHBOARD & SUPPLY COMPANY, A CORPORATION OF ILLINOIS.

TELEPHONE SYSTEM.

Specification of Letters Patent.

Patented Mar. 19, 1918.

To all whom it may concern:

Be it known that I, ALFRED H. DYsoN, a citizen of the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented certain new and usetul Improvements in Telephone Systems, of which the following is a specification.

The present invention relates to telephone exchange systems generally, and more par ticularly to that class in which automatic switch mechanism operates in response to the removal of a calling partys receiver from its hook. to automatically establish connection between a calling subscribers line and an idle link-circuit terminating before an operator in manually controlled connecting means by which the circuit of the calling line may be extended to a desired called substation.

In systems of this classheretofore proposed, the subscribers lines have usually been divided into groups and a definite number of operators link-circuits assigned to each group, thereby providing a system in which a given subscriber would have access only to a limited number of operators. With such an arrangement, it is impossible to obtain the maximum efliciency, since at times the operators of one group may be over-worked, while those of other groups may be comparatively idle.

One of the objects of the present invention i to devise a system in which any subscribers line may have access to any operators link-circuit. Generally stated, this is accomplished by a particular grouping of the link-circuits in association with the interconnecting switch mechanism. This switch mechanism comprises a plurality of electricallycontrolled switches which operate, when once set in operation by a calling party, to progressively link together idle link-circuits of the difierent groups until the calling line circuit is extended to the first idle operators link-circuit. In the pre ferred form of my invention. Ido not employswitches individual to the subscribers lines, as has heretofore been proposed; but I make use of an arrangement. heretofore proposed by me. according to which the sub scribers lines are arranged in groups and each group is provided with a plurality of switches which I term line selectors. fewer in'number than the number of lines in the group, and each group of line selectors is controlled by a simple switch mechanism common to the group. These line selectors are connected to an equal number of similar switches called first selectors, which are operated to establish connection through other link-circuits to the first idle ones of certain so-called second selectors which are in turn operated to establish connection with the first idle operators link or cordcircuits. On a basis of ten per cent. trunking, which is that commonly employed, a ten thousand line exchange, equipped in accordance with my invention, may provide means by which any subscriber may obtain connection with the first idle one of a thousand operators link-circuits. In such a system, the ten thousand subscribers lines would be divided into one hundred groups of one hundred lines each, the line and first selectors would be united by one hundred groups of ten link-circuits each, first and second selectors would be similarly united by one hundred groups of ten link-circuits each, while the second selectors would be connected to one thousand manually equipped operators link-circuits, thus requiring one thousand selectors of each type and one hundred control or master-switch mechanisms. With this organization, the single act of removing the receiver from its switch-hook at the calling station causes the successive operation of a line selector, a first selector, and finally of a second selector to establish connection between a calling line and the first idle operators link-circuit.

In such an exchange system, that is, one having ten thousand subscribers lines employing one thousand cords, my invention contemplates dividing these into ten great groups of one hundred cords each. the cords of the first group being assigned in regular numerical order, by tens, to operators one to ten, the cords of the second group to op erators eleven to twenty, and so on.

The cords of the first one hundred cord group are provided each with passive multiple contacts at the banks of one hundred second selectors, which, when operated, test the cords and connect with the first idle one, so that if operator number one has one idle cord among her ten, the second selector will pick out and connect with that cord; if all her cords are busy, the second selector will pass on to the cords of the second operator; and if an idle cord is there found,

will connect with it, and so on to the third and succeeding operators.

Similarly, the cords of the second, thlrd and fourth great groups of one hundred cords each are provided with multiple passive contacts appearing at each of one hundred second selectors; one hundred such switches being assigned to the second group of one hundred cords belonging to operators 11-20; onehundred to the third group of cords belonging to operators 21-30, and so on up.

These second selectors are connected to link-circuits, each link-circuit terminating in multiple passive contacts at the banks of one hundred first selectors; the arrangement being such that each first selector bank includes multiple passive terminals of ten link-circuits extending to second selectors belonging to each great group of cords, aggregating for each first selector one hundred multiple link-circuit terminals. The terminals of link-circuits extending to the second selectors of the first one hundred group of cords-those belonging to operators 1-10are so positioned at the first selector banks as to be first tested when a first selector is operated. If one of them be found idle, the first selector connects with it, and the second selector then selects the first idle cord of its one hundred cord group.

The terminals of link-circuits extending to the second selectors of the second one hundred group of cords-those of operators 11 to 20are so positioned at the first selector banks that they will be tested by the first selector when operated, as soon as the first selector has tested the link-circuits of the before-mentioned first group, provided these have been found busy; and if one of the second group of second selectors is idle, the first selector will connect with it and the second selector will pick out the first idle cord of it's one hundred line group; and so on with the other groups of second selector link-circuits.

The first selectors are provided in num ber, less than the number of lines of the exchange, and need be in number only about ten per cent. of the lines. They are connected to link-circuits terminating in switches called line selectors, there being one line selector for each first selector; the line selectors and first selectors being in permanently united pairs.

By the instrumentality of the line selectors, the first selectors are capable of being temporarily interchangeably associated with diflerent calling lines.

Having assumed an exchange employing one thousand cords, as many as ten thousand lines may be led into the exchange without overtaxing the effective capacity of the cords. These lines would be divided into one him dred groups of one hundred lines each. The

one hundred lines of each group would have their individual passive multiple contacts appearing at the banks of ten line selectors, which would be assigned to them. The lines would, of course, be also provided with multiple jacks in the usual manner. If a calling subscriber of any group removes his receiver, he thereby automatically starts the operation of an idle one of the line selectors belonging to the line group which includes his line. This started line selector seeks out the multiple contacts of his line and connects thereto, thereby of course connecting to the calling line an idle first selector. The idle first selector automatically operates and tests multiple contacts of the link-circuits terminating at secend selectors of cords belonging to operators 1-10.v If one of these second selectors is idle, it means that one or more of these eper-- ators has one or more idle cords. In such case, the first selector stops connected to the idle second selector; and the latter (now inconnection with the calling line) begins its operation, testing first the cords of operator number one; finding one idle, it will connect the calling line to it and signal the operator; finding all busy, it will pass on to operator number two, and so on until it finds and connects with the first idle cord included somewhere before operators 1-10, as tacitly promised by the second selector when it permitted itself. to be selected by the first selector.

Of course, it will be understood that if the first selector, being operated, found the ten link-circuit terminals of second selectors of cords belonging to the group of operators 1-10 all busy, it would pass on and test those of operators 1120; those being all busy, it would pass on and test those of operators 21-30, and so on up until it found an idle second selector.

. Thus it may be stated that a first selector, temporarily associated with a calling line, tests the operators positions of the exchange in groups of ten, connecting the calling line to a second selector representing the first s'uch idle group; and that the selected second selector then tests the operators positions of its group connecting the calling line through to the first idle cordcircuit of the first idle operator's position.

It will of course be understood that the numerical values given are for purposes of a concrete example and may be varied as commercial conditions require.

My invention also contemplates a structure wherein the first selectors are omitted and the individual line selectors areconnected. by their link-circuits, with individual second selectorswhich connect directly with cords. In such case, the one hundred cord selecting switches of cords 1-100 (those belonging to operators 1-10) would be, of

course, connected to one hundred line selec-i tors, which number would be suflicient for one thousand subscribers lines which might be lines 1-1000. The one hundred cord se-, lecting switches of cords 101-200 (belonging to operators 11-20) would be connected to one hundred line selectors which might be assigned to lines 1001-2000, and so on up with the other groups of cords, operators and lines. It will be understood in this case that the calls from subscribers1-1000 would always come in on the one hundred cords of operators 1-10, the first operator receiving all calls until her cords are all busy, when operator number 2 would begin to receive calls, and so on up; while all calls from subscribers 1001-2000 would similarly come in on the onehundred cords of operators 11-20, etc.

I also contemplate an arrangement of cords before the operators, such that operator number one would have before her the first cord from each one thousand line subscribers group; operator number two the second cord from each such group; operator number three the third cord from each such group, etc.

Various arrangements, varying from those suggested. may be readily made Without departing from the spirit of my. invention.

n carrying out my invention, I prefer to: employ mechanical switches whose active contacts are capable of movement in two intersecting planes; the movements in the first plane-being called primary movements, while those in a second plane are called secondary movements. A more rapid operation may be secured by the employment of such switches as each primary movement may be employed to test a group of bank contacts, while the secondary movement may be employed to test the individual contact sets of a group, wherein the preceding group-test has indicated the presence of idle contacts. My invention is, however, not limited to the employment of switches wherein the contacts are groupwise arranged.

Another object of my invention is to provide a system of the character indicated which shall be simple and compact in construction, efiicient in operation, and economical to manufacture, install and maintain.

It will also be understood that in developing the invention along the lines indicated, I provide certain novel features and arrangements which are capable of use in many relations and need not be limited in their application to the system and its modifica tions herein disclosed.

The various features and aspects of the invention will be more fully understood upon reference to the following detailed description taken in connection with the acco mpanying drawings, and the scope of the 'mechanism for the control of the line selector.. Fig. 4 is a side elevation of the same, the inclo'sing cover being shown in section. Fig. 5 is a partial sectional view of a line selector switch, illustrating principally the primary magnet and its associated mechanism, the section being taken on a plane indicated by the line 5-5 of Fig. 7. Fig. 5" is a detail view of an offnormal switch of the line selector. Figs. 6, 7 and 8 are elevations of a line selector, each viewed from a different side. Fig. 9, which includes parts 1 and'2, is adiagram similar to Fig.2 of a three wire system constructed in accordance with the present invention. Figs. '10, 11, 12 and 13 illustrate modifications of that portion of the system shown in part 1 of Fig. 1. Fig. 14 illustrates an alternative operators link-circuit arrangement, which may replace that of Figs. 1 or 2. Figs. 15, 16 and 17 are views of a party line key of the character illustrated diagrammatically in Fig. 14. Throughout these views, like characters refer to like parts.

Referring in detail to the drawing and more particularly for the present to the diagram of Fig. 1, A designates the substation equipment of two lines which terminate at the exchange in multiple contacts of line selectors and in multiple jacks. Connection is obtained between a calling and a called line through the agency of the master-switch mechanism B, line selectors C, first selectors D, second selectors E and the manually operated connecting means F. In practice, on a basis of ten thousand subscribers lines and ten per cent. trunking, as previously indicated, there would be one hundred control switches B, one thousand first selectors D, one thousand second selectors E, one thousand link-circuits L, L uniting the line and first selectors, one thousand link-circuits L L, uniting the first and second selectors, and one thousand manually equipped link-circuits L L. With this apportionment, each subscribers line would be multipled to ten line selectors, each link-circuit L L to one hundred first selectors, and each operators link-circuit L, L to one hundred second selectors. It is of course to be understood that this example is given largely for the purpose of 'ing line contacts are encountered.

making clear'the arrangements of the link circuits and interconnecting switches and that the values given may be varied to suit any required condition.

The operation establishing connection between a calling line and an idle operators link-circuit L L briefly stated, involves the following steps: The calling party removes his receiver and thereby, through the agency of the control or masterswitch mechanism B, sets an idle line selector G into operation to automatically pick out and establish connection with the calling line, thus extending the calling line circuit over the link-circuits L, L to a first selector D. Thereupon the first selector is automatically set into operation to pick out an idle linkcircuit L L extended to a second selector, and in turn the second selector is automatically operated to pick out an idle operators link-circuit L L. A signal is then displayed before the operator and she completes the connection,-after making the usual busy test, by inserting the plug 10, in which the link-circuit strands L L terminate, into a jack 11 of the called line. Supervision is then had in the usual way; and at the termination of conversation, all parts may be restored to normal.

In the form of the invention illustrated in this figure, the control switch ,mechanism B comprises a differential relay 12, which controls the'circuit which is instrumental in starting an idle line selector. It also comprises a relay 13 which is energized after a definite'movement of the first selector to in turn energize a motor magnet 14 to step the wipers 1516 over their associated contacts 17 and 18 respectively.

The line selector switch C comprises the bank contacts 19, 20, 21 and 22, with which the wipers 23. 24, 25 and 26 cooperate in making connection between the link-circuit strands L, L and the limbs T, T of the calling line. The wipers 24, 25 and 26 are given both a primary movement and a secondary movement in response to the energizations and deenergizations of the primary magnet PM and the secondary magnet SM respectively. By the primary movement, these wipers are stepped to that group of bank contacts in which the calling line contacts are located; and by the secondary movement. they are moved over the contacts of the selected group until the call- The selection of the group is obtained through the provision of the passive contacts 19. each of which corresponds to a group of bank contacts, and the wiper 23 cooperates with these in selecting the group in which the calling line contacts are located. Normally, the contacts 19-20 are grounded: but as soon as a call is initiated, the contact 20, corresponding to the calling line, and the contact 19, corresponding to the group in which the contacts 20 of the calling line are located, have their normal grounds removed. Thus in the operation of the switch, all the wipers are stepped around until the wiper 23 engages an ungrounded contact 19; then the secondary movement of the Wipers 24, 25 and 26 takes place and is continued until the wiper 24 engages the ungrounded contact 20 of the calling line, the wiper 23 not partaking of the secondary movements. The bank contacts 19, 20, 21 and 22, as previously indicated, are multipled to the corresponding bank contacts of other line selectors, one set of which is shown at 19, 20', 21' and. 22'.

The first and second selectors D and E are similar in construction and operation to the line selectors C, but their wipers are caused to be moved in a primary direction to a group of bank contacts in which contacts connected with a first idle link-circuit are located; then three of the wipers are moved in a secondary direction until they reach the bank contacts of the first idle linkcircuit. In this way, as soon as the line selector has established connection with a calling line, the first selector associated with it is set inoperation and this selector automatically picks out an idle link-circuit running to a second selector. which in turn is set in operation and establishes connection with an idle operators link-circuit, thereby extending the calling line circuit through idle link-circuits of the different groups of link-circuits to an idle operators linkor cord-circuit.

Considering this operation more in detail, it will be observed that the removal of the receiver 27 from its switch-hook 28 at the substation of the calling party completes a bridge between the two line limbs T and T through the transmitter 29, at the same time interrupting the normally closed bridge between said line limbs through the condenser 30 and call-bell 31. A circuit is then closed from the live pole of the battery B through the protective resistance 32, normal contact 33 of the relay 34, normal contact 35 of the relay 36, line limb T switch-hook 28, receiver 27, transmitter 29, line limb T, normal contact 37 of relay 36, normal contact 38 of relay 34, winding of the relay 39. to ground at 40. The closing of this circuit energizes the relay 39 to attract its contacts 41, 42, 43 and 44. Contact 42, moving to its alternate position. completes a locking circuit for the relay 39 extendin from the live pole of the battery B, through resistance 32, normal contact 33 of relay 34. normal contact 45 of relay 36, alternate contact 42 and winding of relay 39 to ground at 40. thereby preventing interference from the substation. Contact 43,

moving to its alternate position, completes a circuit for the control magnet 46 from the live pole of the battery B, through the winding of said magnet and alternate contact 43 to ground at 40. The magnet 46 is thereby energized to attract contact 47 to remove the normal ground at '48 from the group contacts 19-19 corresponding to the line TT The contacts 20-20, corresponding to this line, are normally grounded over a path extending through normal contact 41 to ground at 50. The contact 41, moving to its alternate position, therefore, removes the normal ground from these contacts 20-20 and also provides a path for current from the live pole of the battery B, through the winding of relay 34, alternate contact 41 and to the contacm 20-20 corresponding to the calling line. The movement of the contact 44 to its alternate position completes a circuit for the winding 51 of the difl'erential relay 12 extending from the live pole of the battery B over conductor 52, winding 51, conductor 53 and resistance 54 to ground at 40. As will appear more fully hereinafter, the contacts 15-16 of the master-switch mechanism B are left, after each operation, upon contacts 17 and 18 respectively, extending to an idle line selector. As illustrated, normally there is no path for current through winding 54 of the relay 12. Consequently the completion of the circuit through the winding 51 energizes the relay 12 sufficiently to move its contact 55 to its alternate position, thereby placing ground at 56 upon the wiper 15 and completing a circuit through the primary off-normal switch contact 57, the winding of the primary relay PR of an idle line selector, through the normally closed contacts 5859 of the heat-coil 60 to the live pole of the battery B. The closing of this circuit energizes the primary relay PR to move its contacts 61, 62, 63 and 64 to their alternate positions. The movement of the contact 61 completes a path for current through the winding 54 of the difl'erential relay 12 extending from battery conductor 52 through said Winding, through resistance and alternate contact of 61 to ground at 66. The resistance 65 in the circuit of the wi'nding 54 balances resistance 54. in the circuit of winding 51 so that one winding substantially neutralizes the other in its magnetizing effects and the contact 55 is allowed to return to normal. The contact 62' of the primary relay PR, moving to its alternate position,'closes current through said relay from the live pole of the battery B through the heat-coil 60, winding of the relay PR, alternate contact 62 to wiper 23. Contact 64 of the primary relay PR, moving to its alternate position, interrupts the normal circuit extending through the secondary relay SR; while the movement of the contact 63 to its alternate position completes a vibratory circuit through the primary magnet PM to ground at 67. The repeated encrgization and deinergization of the mag net PM, by reason of its vibratory circuit and its mechanical connection to the wipers 23, 24, 25 and 26, hereinafter referred to more fully, will cause said wipers to move in a primary direction until the group of contacts, in which the contacts corresponding to the calling line are located, is reached. Upon the first primary movement of these wipers, the off- normal switch contacts 57 and 68 are moved to their alternate positions. The movement of the former interrupts the initial energizing circuit of the primary relay PR; but by reason of the movement of the wiper 23 into engagement with a contact 19, the circuit of relay PR is maintained through said wiper 23, contact 19 and contact 62, in case contact 19 is grounded. Thus the circuit of the relay PR will be maintained as long as the wiper 23 is passing over grounded contacts 19, and it in turn will maintain the vibratory circuit of the primary magnet PM. As'soon, however, as the contact 19, corresponding to the group in which the calling line contacts are located, is reached, the maintaining circuit of the primary relay PR will be interrupted at the attracted contact 47 of the relay 46. Thereupon the circuit of the primary magnet PM will be also interrupted at the then retracted contact 63; and at the same time, the circuit for the secondary relay SR- will be completed at the retracted contact 64. This circuit extends from the live pole of the battery B, through the heat-coil 60, winding of the relay SR, normal contact 69, normal contact 64 and alternate contact 68 to ground at 70. The closing of this circuit will energize the relay SR to move its contacts 71, 72, 73 and 74 to their alternate positions. Contact 71, by 1ts movement, interrupts the circuit of the release magnet RM; and contact 72 by its,

.moved to their alternate positions upon the first primary movement of the wipers of the switch; while the secondary off-normal switch (S. 0. SW.) contacts 69 and 76 are moved to their alternate positions upon the first secondary movement of the wipers.

As soon, therefore, as the wipers have begun their secondary movement, this path to ground for the winding 54 of the differential relay 12 is maintained through alternate contact 73 of the secondary relay SR and alternate contact 7 7 to ground at 78. The movement of the contact 74 to its alternate position closes a vibratory circuit for the secondary magnet SM which extends from the live pole of the battery B, through the heat-coil 60, the winding of the magnet SM, alternate contact 74, alternate contact 79 to ground at 78. The repeated energizations and deenergizations of this magnet, by reason of the mechanical relations of the parts, cause the wipers 24, 25 and 26 to move in a secondary direction over the contacts20, 21 and 22 until an ungrounded contact is encountered. It may be stated at this time that wiper 23 moves along with the wipers 24, 25 and 26 only when the primary movement of the switch is being performed. The

just described secondary movement of wipers 24, 25 and 26 is performed independently of wiper 23, the latter remaining stationary, engaging the ungrounded contact 19 sought out by it. As before indicated, upon the first secondary movement, contact 69 is moved to its alternate position, thereby interrupting the initial circuit of the magnet SR which thereafter maintains its circuit through alternate contact 72, Wiper 24 and contact 20 to ground until an ungrounded contact 20 is encountered. When such a contact is reached, the relay SR is deenergized and its contacts 71, 72, 73 and 74 return to normal, leaving the wipers 25 and 26 in engagement with the passive contacts 21 and 22 of the calling line and thereby extending the calling line circuit through the link circuit strands L-L? to the first selector D pertaining to the operated line selector C. The return of the contact 72 to its normal position again places ground on the wiper 24 and thereby completes a circuit for the relay 34 extending from the live pole of the battery B through the winding of said relay, alternate contact 41 of relay 39, contact 20, wiper 24, normal contact 72 to ground at 75. The

completion of this circuit energizes the relay 34 to cause the attraction of its contacts 34, 38, 80, 49 and 33. By the movement of contact 49, a locking circuit is completed for the relay 34 extending from the live pole of the battery B, through the winding of said relay, alternate contact 49, contact 20, wiper 24, normal contact 72 to ground at 75. The movement of contact 33 interrupts the circuit of the relay 39, thereby allowing its contacts 41, 42, 43 and 44 to return to their normal positions. The return of the contact 44 interrupts the circuit through the winding 51 of the'difi'erential relay 12, while the return of the contact 73 of the relay SR to its normal positionsimilarly interrupts the circuit of the other winding 54 of said differential relay. Since these interruptions of the circuits of the wlndings 51 and 54 occur practically simultaneously, the contact 55 of said relay is not attracted. However, it will be observed that if at any time while they are thus included in circuit, a second call causes the grounding of the conductor 53 through the resistance 54', the flow of current through the winding 51 will exceed that through the winding 54 and the previous balance in said windings will be destroyed and the contact 55 again moved to its alternate position to cause the operation of a second line selector. Of course this cannot occur until the contacts l5 and 16 of the control switch mechanism B have been moved into engagement With contacts 17 and 18 associated With such a selector. This movement, however, occurs as soon as the previous line selector has made its first primary movement, since, by that movement, its primary off-normal switch contact 68 is moved to its alternate posltion, thereby completing a circuit for the relay 13 of the switch mechanism B, which may be traced from the live pole of the battery B, over conductor 52, through winding of relay 13, contacts 1618, and alternate contact 68 to ground at 70. The closingpf this circuit energizes the relay 13 and thereby closes a vibratory circuit for the motor magnet 14 of said mechanism, which may be traced from the conductor 52 through the winding of said magnet, and alternate contact 81 to ground at 82. By reason of the mechanical relation of the parts, the energizations and deenergizations of the motor magnet 14 step the wipers 1'5 and 16 over the contacts 17 and 18 until a contact 18 of an idle switch C is encountered. As soon as this occurs, the circuit of the relay 13 is open at contact 68 of this switch tory circuit of the ma et 14 and cessation of movement of the wipers 15 and 16. Re-

turning again to the consideration of the effect of the energization of the relay 34, it will be seen that (in addition to deenergizing the relay 39) by movement of its contact 80 to its alternate position, battery is connected through the resistance 32 to the sleeve contacts of the jacks 11 associated with the calling line, thereby putting them in condition to indicate the busy condition of the line upon the usual manual test.

By the movement of contact 38 of relay 34, the circuit extending from the substation through the winding of the relay 39 is in terrupted, thereby placing said relay beyond the control of the calling party. The relay 34 thus serves as a cut-off relay to remove the normal substation control of the relay 39 whenever the line with which it is associated is used as a calling line. However, when the line is to be used as a called line, the application of battery to the sleeve of one of the jacks 11, associated therewith, completes a circuit for the relay 36 through the normal contact 80 and the winding of said relay to ground at 83. The energization of this relay causes the movement of its contacts 3745 to their alternate positions. .By the movement of contacts 35 and 37, the substation control of the relay 39 is removed.

Referring now to the first selector switch D, which is associated with the distant ends of the link-circuit L--L it will be seen that it is similar in all essentials to the line selector switch previously described. It is automatically set inoperation upon the return of the contact 71 of the secondary relay SR of the line selector, which completes circuit for the primary relay PR from the live pole of the battery 13 through the winding of said relay PR, normal contact 84, conductor 85, normal contact 71, winding of the release magnet RM of the line selector, alternate contacts 76 and 77 to ground at 78. The completion of this circuit does not cause any effective energization of release magnet RM, the winding of RM and PR being properly proportioned to this end, the latter being relatively high, while relay PR is energized sufficiently to attract its contacts 86-87-88 to cause the operation of the first selector D in a manner similar to that heretofore described in connection with the line selector C. Thus the movement of the contact 87 completes a vibratory circuit for the primary magnet PM through the alternate contact 87 to ground at 89, thereby causing the wipers 2324$25 26 to move in a primary direction along the associated passive contacts 19-20-21f22. The first movement of the wipers in a primary direction moves the primary ofi' normal switch contacts 84-9O to their alternate positions. This movement of the contact 84 interrupts the initial circuit of primary relay PR, but in the meantime the wiper 26 has been moved into en-- gagement with the first contact 22. If the latter be associated with a group of ten contact sets whose switches E are all in use, the contact 22* will be grounded through alternate contact 119 at 120, because each of the ten switches E of a group has its individual relay 114 or 114, etc., whose armatures, when attracted, remove tension from bar 118. When a switch E is in use, its magnet 114 is energized; and when all ten are so energized, all tension is removed from bar 118, and contact 119 is allowed to assume its alternate position- In such case, a locking circuit for relay PR from ground 120, alternate contact 119, contact 226, alternate contact 86 to battery, is completed,

and successive primary steps of the wipers are made until wiper 26 engages a contact 22 which is ungrounded, or in other words,

a contact 22 pertaining to a group'of ten .is energized over a circuit extending from the live pole of the battery B through the winding of said relay SR, normal contact 91, normal contact 88, alternate contact 90 to ground at 92. The energization of the relay SR will move its contacts 939495-9G to their alternate positions. The movement of the contact 98 will interrupt the normal circuit of the release magnet RM The movement of the contact 9% will close a vibratory circuit for the secondary magnet SM extending from the live pole of the battery 13 through the winding of said magnet, alternate contact 94, alternate contact 97 to ground at 98. In this connection it should be noted that the release switch (R. SW.) contact 97 moves to its alternate position upon the first primary movement of the first selector D; and the secondary off-normal switch (S. 0. SW.) contact 91 moves to its alternate position upon the first secondary movement of said selector. The movement of the contact 91 to its alternate position. therefore, interrupts the initial circuit of the secondary relay SR, but its circuit is maintained as long as the wiper 23* engages a grounded contact 19 over a path extending from the live pole of the battery, through winding of said relay SR, alternate contact 93, wiper 23* and contact 19' to ground. Contacts 19", engaged by the wiper 23, when associated with link-circuits L L which are in use, will be connected to ground through a multiple contact 19, a wiper 23 engaging said contact, a normal contact 93 and winding 99 of release magnet RM of another switch D to ground at 100. The winding 99 of release magnet RM and the winding of secondary relay SR are so proportioned (the windings of the latter being high), that'when thus placed in series circuit, the energization of the winding 99 will be so slight as not to cause any effective energization of the release magnet RM, while relay SR will continue effectively energized. As soon, however, as contact 19 of an idle link-circuit in the group is encountered, the maintaining circuit for the secondary relay SR will be interrupted because such contact will be open at contact 102 of its switch E and said relay will be dcenergized. During the energization of relay SR, it will be observed that the attracted contacts 95-96 interrupt the link strands L-L so as to prevent interference with possible conversations existing over the multiple contacts over which wipers 2425 pass. Upon the deenergization of the relay SR the continuity of these link-circuit strands is restored, the circuit of the secondary magnet SM is interrupted and continued motion of the wipers 1n a secondary direction is prevented. Thus, the circuit of the calling line is extended through the link-circuit strands LL wipers 243-25, contacts 20*21 and link-circuit strands L -L to a second selector E.

Having thus extended the line circuit to an idle second selector E, the latter is automatically set in operation to pick out and establish connection with the first idle operators link-circuit. The circuits for this selector are substantially the same as those of the first selector previously described. The second selector thus selected is set in operation by the return of the contact 93 of the first selector secondary relay SE to its normal position, thereby completing a circuit from the live pole of the battery B through the winding of the primary relay PR of the second selector E, normal contact 101 of the primary off-normal switch, contact 19*, wiper 23, normal contact 93, winding 99 of the release magnet RM (without causing any effective energization of RM) to ground at 100. This relay PR attracts contacts 102, 103 and 104. Contact 103 now completes the circuit of the primary magnet PM which moves the wipers 105, 106,107 and 108 in a primary direction along the associated contacts 109, 110, 111 and 112 until the wiper 108 engages the first ungrounded group contact 112, thereby interrupting the circuit extending through the winding of the relay PR alternate contact 102, wiper 108, contact 112 to ground through alternate contacts 141 controlled by magnets 136, 136 individual to the cords F. Upon the first primary movement of the wipers, the primary off-normal switch contacts 101-113 are moved to their alternate position, contact 113 then completin a circuit from the live pole of the battery 2 through the winding of the electromagnet 114 and thence by way of alternate contact 113 to ground at 115. The closing of this circuit energizes the electromagn'et 114 to move its spring retracted armature 116 out of enga ementwith a shoulder 117 carried on a rod 118 associated with the spring contact 119. Each link-circuit of a group is provided with an electromagnet corresponding to the electromagnet 114, one other of which (designated 114) is shown. These electromagnets ointly control the common springv contact 119 which is biased so as to close its normally open contact and thereby ground its associated group contacts 22 at 120 whenever all the link-circuits in the group are busy. As previously pointed out, under these conditions the wiper 26 of the first selector passes to the next group contact and thus continues its movement until the first ungrounded group contact is encountered.

Upon the deenergization of the relay PR the circuit of the primary magnet PM is interrupted and the further primary movement of the wipers discontinued as before. Likewise, as before, the return of the contact 104 to its normal position completes a circuit from ground 115 through the normal contact 121 for the secondary relay SR which, upon being energized, closes a circuit for the secondary magnet SM which extends through the alternate contact 122 of the secondary relay SR and the alternate contact 123 to ground at 124, the release switch (R. Sw.) contact 123 being thrown to its alternate position upon the first primary movement of the switch wipers. At the same time, the link-circuit strands L L are interrupted at the contacts ment of this latter contact to its alternate position also closes a maintainin circuit for the secondary relay SR throng the wiper 105. The ground upon the busy contact 109 is provided by a connection through a mul tiple contact 109 engaged by a wiper 105 of another switch through its alternate contact 127, the winding 128 of its release magnet RM to ground at 129. Secondary movements of wipers 105, 106 and 107 continue until the wiper 105 engages a contact 109 of a first idle cord which will be .open at contact 152, and as before, this interrupts the circuit of the secondary relay SR and causes its contacts to return to their normal positions, thereby closing the path from ground through the winding 128 of the release magnet RM to wiper 105 and the .multiple contacts of the selected cord to render it busy, interrupting the circuit of the secondary magnet SM", and rendering the linkcircuit strands L Lf continuous. Thus it will be seen that the circuit of the calling line is completed through first idle linkcircuits of available oups to the strands L L of an idle lin or cord circuit before an operator, with the exception that so far as we have gone, the link-circuit strand L is interrupted at contact 130. As

' tacts to ground at 143.

pole of the battery B through the sleeve supervisory relay 131, over the strand L and strand L, through the winding of relay 132 to ground at 133. The closing of its contacts 134, will remove the shunt about the winding 128 of the release magnet RM The movement of the contact 135 of the sleeve supervisory relay 131 will complete a circuit for control el ectromagnet 136 from the live pole of the battery B", through the winding of said relay and alternate contact 135 to ground at 137. The closing of this circuit will energize the electromagnet 136 so as to move its spring retracted armature 138 out of engagement with the collar 139 on the rod 140 associated with the grounded spring 141, by which ground is placed upon the group contacts 112 whenever all the linkcircuits in the group are in use,'in a manner similar to that previously explained in connection with the electromagnets 114 associated with the link-circuits L -L.

It will be apparent, of course, that if desired, a givenoperators link-circuit may bev rendered busy by completing a circuit through the winding of the electromagnet 136 at a manually operated switchsuch as 142 to ground as at 143. It will also be apparent that any desired group of linkcircuits may be rendered artificially busy by' grounding the associated contacts 112 by a manually controlled switch such as the switch 142, adapted to connect said con- Similarly, by means of a manual switch 142*, cotiperating with a battery connection 143 and a grounded connection 143", the private contacts 109 associated with the link-circuits of any particular group may be rendered artificially busy by throwing the switch to ground, or the second selector connecting therewith may be released by throwing the said switch to its battery connection 143*, as will more fully hereinafter appear.

As soon as the relay 132 has been energized and the link-circuit strand L completed at contact 130, a path for current will also be completed through the strands LL line limb T through the switchhook at the calling substation, line limb T, strands L'L L through the winding of the ti supervisory relay 144 to ground at 145. he flow of current over this path energizes the relay 144 and thereby moves its contacts 146147 to their alternate positions. Contact 146 will then complete a circuit from the live pole of the battery B through the call lamp 1.48, normal contact 149, alternate contact 146 to ground at 145, thereby lighting said lamp as a signal to the operator that connection is desired. The

operation of contact 134 of relay 132 at second selector E is to be rendered slow as compared with that of contact 130, so that the latter will close before the former opens. The closing of- 134 will thus complete circuit for relay 144 before the short circuit is removed from windin 128 of RM Relay 144 will then open its normal contact 147 while magnet RM is still short-circuited,

thus insuring against a premature operation of RM at the moment of selection. The attraction of the sleeve supervisory relay contact 150 closes the circuit for the supervisory lamp 151; but as the tip supervisory relay 144 is energized, this circuit is interrupted at the contact 146. I

Upon observing the display of the call signal 148, the operator will throw over her listening-key levers 153154 and includeher telephone set S in bridge of the link strands L -L, thereby placing herself in communication with the calling party. At this time, transmission current is supplied from the live pole of the battery B through the'winding of the relay 131 to one side of the talking circuit and from the grounded side at 145 of the battery B through the relay 144 to the other sideof the talking circuit. Upon learning the number of the called line, the operator will test in the usual way, touching the tip contact of plug 10 against the sleeve contact of a jack 11in which the called line terminates. If the called line is busy, a potential above that of ground will exist upon the test contact of the jack, and the touching of the tip of the plug Will result in a flow of current over the strand L through normal contact 155, test relay 156 to ground, attracting contact 157 and completing a circuit through one of the windings of the induction coil 158 of the operators set S and causing the usual click in the operators receiver. If the line be thus found busy, the operator will then inform the calling party, and the restoration of his receiver to its hook will cause the release of the interconnecting switches and their return to normal, as will hereinafter he more fully explained.

If the called line is found to be idle, the operator will insert the plug 10 into a jack 11 and depress her ringing-key levers 159160. The insertion of the plug will result in the completion of a circuit through the winding of the sleeve supervisory relay 161 and the cut-off relay 36 of the called line as follows: from the live pole of the battery B, through the winding of relay 161, sleeve plug and jack contacts, normal contact 80 of relay 34 and winding of relay 36 to ground at 83. The energization of supervisory relay 161, by reason of the attraction of its contact 162, will complete a circuit for the supervisory lamp 163. which may be traced from the live pole of the hat-

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