US1563347A - Automatic telephone system - Google Patents

Description

Dec. 1 1925'- A. H. DYSON AUTOMATIC TELEPHONE SYSTEM 13 Sheets-Sheet 1 Original Filed Aug. 19, 1907,

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A. H. DYSON AUTOMATIC TELEPHONE SYSTEM Original Filed Aug. 19, 1907 13 Sheets-Sheet 2 JUL/52720.2.

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' A. H. DYSON AUTOMATIC TELEPHONE SYSTEM Original Filed Aug. 19, 1907 15 Sheets-Sheet 7 Dec. 1, 1925. 1,563,347

-A. H. DYsoN AUTOMATIC TELEPHONE svsmr Original Filed Aug. 19, 1907 13 sheets-Sheet a Dec. 1 1925- A. H. DYSON AUTOMATIC TELEPHONE SYSTEM 15 sheet-sheet 9 Original Filed Aug. 19, 1907 Z/ 2/272755555: W Q K Dec. 1,1925- A. H. DYSON AUTOMATI C TELEPHONE SYSTEM Original Filed Aug. 19, 1907 gs Sheets-Sheet 10'- a iiillll J iiiiiif JEEHIII Vx K x mum HUgsazz E; 7

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' A. H. DYSION 7 AUTOMATIC TELEPHONE SYSTEM Dec 1, 1925- A. H. DYSON AUTOMATIC TELEPHONE szs'rsu Original Filed-Aug. 19, 1907 13 sheets-Sheet 12 I I e P 223 AL M e lilv' e 1.

FZYBPH- A. H. DYSON AUTOMATIC TELEPHONE SYSTEM Original Filed Aug. 19, 1907 13 Sheets-Sheet 13 warren. s rarss PATENT FFEQE.

ALFRED H. DYSON, 0F MONTCLAIR, NEW JERSEY, ASSIGNOR TO KEIILOGG SWITCH- BOARD AND SUPPLY CQMPANY, OF CHICAGO, ILLINOIS,

NOIS.

A CORPORATION OF ILLI- AUTOMATIC TELEPHONE SYSTEM.

Original application filed August 19, 1907, Serial No. 389,180. Patent No. 1,257,283, dated February 19, 1918. Divided and. this application filed March 2 191.7. Serial No. 152,045.

To all whom it may concern:

Be it known that I, Anrnnn H. Dyson, a citizen of the United States, residing at h lontclair, in the county of Essex and State of New Jersey, have invented new and useful Improvements in Automatic Telephone Systems, of which the following is a specification.

The present invention relates to automatic telephone systems generally, and has to do more particularly with that type in which the well known selector and connector switches of the two dimension type otthe' art are employed in conjunction with similarly constructed line selectors controlled by master switches. In such systems the movable contacts, or wipers, of the two dimension switch are associated with a large number of fixed, or passive, contacts arranged in a bank and the wipers are first given a n'lovement in one direction followed by a movement at an angle thereto, the ii' rmer, or primary, movement bringing the wipers to a desired group of bank contacts and the latter, or secondary, movement causing the wipers to engage desired bank contacts in the selected group. The connections among the different switches will be best understood by discussing a particular case. Thus if one hundred point switches be employed in a ten thousand line exchange system arranged on a basis of ten per cent trunking, there would be one hundred mustebswitohee, one thousand line selectors, one thousand first selectors, one thousand second selectors, and one thousand connectors; each subscribefis line would be multipled to ten line selectors and ten connectors; the lines selectors and first selectors would be united in pairs without. multi pling; the wipers 01" the second selectors would be multipled to the bank contacts of one hundred first selectors and the wipers of each connector would be multipled to the bank contacts of one hundred second selectors. Obviously with different assumptions, values differing from the above would he used, but this specific example will suflice to indicate the character of the system to which my invention lr-elongs. The present application is a divisional application of my application. for Letters Patent, Serial No. 389,180, filed August 19, 1907, Patent No. 1,257,283, Feb. 19, 1918.

Another object of my invention is to devise a novel arrangement by which thedifferent parties on a party-line may be selectively signalled by means of code ringing apparatus. I have devised a novel circuit arrangement, operating in conjunction with a ringing machine having different impulse wheels arranged to make and break the ringing generator current according to the code selected.

A further object or" nay invention is to provide means for insuring that the signalled substation will receive the full selected code, that is, that the signal for the called substation will always begin at the beginning of the code ring.

Another object of the invention is to en tend this simplification of structures to all commercial adaptations of the straight automatic system so as to include trunking between exchange, nickel-in-the-slot service, measured service, party line service of different kinds, as well as unlimited service.

Still another object or" the invention is to devise a novel arrangement of electrical connections between the switches whereby the chances of the calling line finding an idle trunk through which to extend its circuits are greatly increased.

The inventionalso includes other features and details which, together with the above, will be more fully understood upon reference to the following detailed description taken in connection with the accompanying drawing, and the scope of the invention will be particularly pointed out in the appended claims.

Before referring tothe drawings, it may be noted that in developing the invention along the lines indicated, many features have been devised which are capable oi? use in other relations than those herein indi cated and in various telephone systems including manual systems and semi-automatic systems as well as straight automatic systems. 4

Referring to the drawings, Fig. 1, which is the principal figure and includes parts 1, 2 and 3, illustrates diagrammatically an automatic telephone system embodying certain features of the present invention; Fig. 2 illustrates a trunking circuit provided with a repeater and designed to connect cxchanges located at some distance from each other; Figs. 3 and 4c illustrate modified c011- nector circuits, the latter being arranged to automatically select one of a number of trunks running to a given private exchange, or to a group of telephones having a single calling number; Figs. 5, 6 and 7 illustrate connector circuits designed for use with party lines, the latter illustrating in addition a four-party subscribers line; Fig. 8 illustrates a modified slot service substation and line circuit; Fig. 9 illustrates a novel method of interconnecting and trunking between switches by which the chances of a calling party obtaining a desired connection are increased Figs. 10, 11 and 12 are elevations of a line selector viewed from different sides, the switch being also typical of the other. selectors and the connectors employed in the system; Fig; 13 is a plan view of said switch; Fig. l l is a sectional plan of a portion of the same taken on a plane indicated by the line l l14l of Fig. 11; Fig. 15 is a detail view of certain con nector olf normal' contacts; Figs. 16 and 17 are front and side elevations of a mastersw'itch employed in the control of the line selectors; Figs. 18 and 19'are front and sectional elevations, respectively, of a ringing machine employed in connection with oer-- tain" of the party line circuits; Figs. 20 and 21 are front and rear elevations, respectively, of meter mechanism employed for measured service; and Figs. 22 and 23 are front and side elevations respectively, of a ringing switch employed for party line use. Throughout these views like characters refer tolike parts.

lvlAIN SYSTEM.

A ppamtus.

Referring to the drawing, and more particularly for the present to Fig. 1, which may be considered the main diagram, M at the left of the diagram designates a subscribers station provided with slot equipment and united to the main exchange by the line limbs P and S which terminate in multiple contactjsof line connectors and line selectors. At the opposite end of the dia gram, N designates a subscribers equipment which is not designed for slot service and which. is similarly united by line limbs P S to the exchange andthe line limbs are similarly connected to the multiple contacts of connectors and line selectors. Connection is obtained between the line at the left 'and'the lin'eat the right through the agency of a master-switch O, a lineselector Q, aflfiis't selector U, a second selector V and a connector WI suming that the selectors and connectors employed in establishing this connection are provided with one hundred bank contacts, and assuming that there are ten thousand lines in the exchange arranged on a basis of ten per cent trunking, then, the number of switches and their multiple arrangement heretofore outlined will exist. In such case there would be one hundred masterswitches O, one thousand line selectors Q, one thousand first selectors U, one thousand second selectors V and one thousand connectors The subscribers lines would be divided into groups of one hundred, and ten line selecting switches would be assigned to each group, thus enabling each line to be multipled to the corresponding bank contacts on ten different line selectors. Each group of line selectors would be under the control of one masterswi.tch, having a pair of bank contacts assigned to each line selector. Each subscribers line would also be multipled to the corresponding bank contacts of ten connectors. In the diagram, only two of the ten sets of multiple contacts of the line selectors and connectors are illustrated, while but live pairs of bank contacts of the master-switch are shown. The movable contacts, or wipers, of each line selecting switch Q are tied to the corresponding wipers of a first selector U, thus providing one thousand direct connections between the one thousand line selectors and the one thousand first selectors. The wipers of the second selec tors are multiply connected to the bank contacts of the first selectors, and since there are a thousand of each of these switches, the wipers of each second selector are connected to the corresponding contacts of one hundred first selectors. Similarly, the wipers of each of the thousand connectors are connected tothe corresponding contacts of one hundred second selectors. As previously indicated, this apportionment of values may be varied at will to suit the exigencies of any particular case.

In the operation of the parts in establishing connection between substations M and N, the calling party at substation M rcmoves his receiver from its hook and thereby, through the agency of the 1nastcrswitch O sets an idle line selector Q, in operation to automatically seek out and establish connection with his line, thus r1:- tending the calling line rii uit to the first selectorU paired with the actuated line lector'Q. The calling party then, by means of'his calling mechanism, transmits a number of impulses corresponding to the digits of the number of the subscriber wanted. The first series of these impulses opera the connected first selector U soas-to cause it to; picleou't an idle second selector V'assoelated with the" thousand group to which the called line belongs. Thus, if the number of the calling party were two thousand some odd, the first set of two impulses would move the wipers of the first selector to the *cond group of its bank contacts and would then auton'iatically move the wipers over the contacts in this bank until an idle contact was encounter-ed, thereby extending the circuit of the calling party to an idle second selector in the second thousand group. The second series oil impulses would similarly operate the second selector V to pick out and establish conn ction with a connector associated with the hundreds group to which the called line l elong's. Thus it three impulses were transmitted over the circuit, the second selector V would move its wipers to the third group of its haul; contacts and the \i'ipers would then automatically more over the contacts in this haul: until an idle one was selected, thereby extending); the circuit ol' the calling line to a connector having access to the called line. The third series of impulses would cause the connector to more its wipers to that group of ten contacts in which the contacts of the called linewere included, and the final series of iin pulses would cause the wiper to more over the contacts in this group until the contacts corresponding to the called line were encountered, thus completing the connection between the call j and the called lines.

Each line is pr vided at the exchange with a line relay LR which is instrun'iental in closing;- a circuit through the masterswitch O upon the initiation of a call, and a cut-cit relay G0 which is' used to destroy the normal substation control of the line relay and to otherwise any the line connections.

The master-switch O comprises a pair of wipers E20 21 co-operating with banl: conta-ts ri -23 and caused to step over said ontacts by a motor n'lagnct Mill, the coinplcte operation being; controlled by the re lays 2 as hereinafter more fully pointed out.

The line selector includ s the wipers 26, .iit and 99 cooperating with banl: conacts 30, 31, 32, ill-3 and, where the meter ucchanisui I'll is used, with. an additional wiper 3 t. co-operating with bank contacts as will appear from Fin-s. 9 to 13 inclusi 0., described more fully hereinafter. l l ipers 2?, 5 5. 52?; and 34: partake of the two increments oi the switch, that is, the priiuar} and seconda y movements, while wipcr 129 partalrcs 01 j, of the primary movement. The primary movement of the wigers is brought about by primary magnet controll l by a. L airy relay PR, and its secondary n'iorenient is sin'iilarly brought about by a secondary magnet controlled b a secondary relay while the release the switch, which permit it to return to its normal position, is brought about by a release magnet RM controlled by a release relay RR. The switch is also provided with primary and secondary oil-normal contacts PO and St) which are operated respectively upon the first p 'iinary and the first secondary increments of the switch. Although each subscribers line is multiply connected to ten line selectors and ten connectors, two such multiple connections only are shown in the drawing wherein bank contacts al 32 and 83" and cooperating wipers 26 2'5 28 and belong to a second line selector and contacts 36, 36 31 37 38 and 38 are bank contacts of two connectors.

The first selector U includes the wipers 39, 410, il which co-operate with bank contacts 452, 43, in response to the operation ot the primary magnet PM controlled by the primary relay PR, and the secondary inao'net SM, controlled by the secondary relays SR and g lt The wipers in this case all prrtalte of the primary and secondary movements and the switch is released througzh the operation of the release magnet P 1 and the release relay BB 'llho iriinary oil-normal contact-s PG and .econdary oil-normal contacts S0 here, as before are operated upon the first priinziry and secondary n'ioveinents of the wi' ers respectively. The circuit associated with this selector also includes a reversing relay RV i lQr'QlSlllQ: the direction of current sup- 1 lied to the calling line and an associated relay 45, all of which will he niore'fully understood from the subsequent description.

The second selector V omprises wipers do, 4-7, 48 which co-operate with bank contacts 49, 5O, 51 in the same manner as the first selector U. In this arse, the corresponding relay, magnets and olii norinal. contacts are designated by corresponding reference characters having the exponent 2 instead of 1..

The connector l is proridei'l with wipers 553, 53, ci'i-operating with bank contacts 5, 56, 57 and in this instance as before, :hey partake of hi primary and secondary u'r-rweinents in response to the operations of the primary magnet l l" and the secondary magnet f-lhl", respectively, and return. to normal upon the operation or release relay and release magnet llllzl. In this instance, the primary oil-normal switch. contacts are designated l? and the second- 'fr' oil-n 'irinal switch. mi'u'acts Fill. ln addition to these parts, the circuit is provided with a busy relay Bit, a ringing relay HG, a control relay it, a tip relay TH, flip-flop relay FF, and a closing relay all. of which cooperate in the manner hereinafter more fully set forth.

As in the case of the line P--S, the line no P*-S" is provided with a cut-oil relay and a line relay LB,

Lil

re l have also illustrated rec rding the completed connection over each calling line. One of these mechanisms is associated with each line selector and comprises a printing magnet 58, a type wheel actuated "by a motor magnet llllvi con rolled by relays (30, (i1 and wiper 62 rotated with the type wheel 59 and co-o ierating with bank contacts (53 of which there is a number equal to the number of contacts 3.3 on the line selectors.

The equipment at substation n includes the usual switch hook (5-12, receiver 65, callbell (36, transmitter (57, calling mechanism 68, and slot mechanism 69 including a polarized relay TO. The equipment at substation N differs from that at substation ill by omitting the slot mechanism 69.

Obviously, the various subscribers lines entering the exchange will be distributed through the agency of a distributing board which 1 have indicated at the points des ignated DB. Many diit ferent methods of distributing may employed, but I preferably distribute the line limbs and the connections with the three sets of connector contacts, as clearly illustrated in the drawing.

Operation.

Having now given a general description of the character of the apparatus diagrammatically illustrated in Fig. 1, it is believed that the invention will be best understood by entering at once into a description of the operation of the system therein depicted.

Assuming that a party at substation Ill desires to converse with a party at substation N and assuming that the number of the latters telephone 3456, then the calling party first removes his receiver from its hoolr (31- and thereby establishes a circuit which may be traced from the live, or neg ative, pole of the battery B through re sistance Tl, closed cont-act T6 of: cutcll relay CU, line limb S, closed Contact 75, the winding of loci: controlling magnet Tl, switclnhoolr 6st. transmitter 67, closed contacti -l, line limb P, normal contact oi cut-oh. clay 00, normal contact T7 oi linc relay loll, and the winding of said re lay to the grounded or return sine or? the battery. The resulting movement of the contact T? to its alternate position closes a. new energizing circuit for the line relay Lit which may be traced from the live, or negative, pole of the battery l3 through the wniding of relay 2t ot the masterswitch O, closed contact T8 of cut-oil relay CO and alternate contact T7 of line relay lilt through the winding of said relay to ground. The closing of this circuit continues the energization of the line relay and actuates relay 2% so as to close its contact it) to complete a starting circuit [or one of the line selectors Q, as will be hereinafter explained. The movement of contact 80 of line relay LR, removes the normal ground connection from the contacts 3O8O corresponding to the calling line, this ground connection normally existing through normal contact 81 of cut-otl' relay CO and normal contact 80 of line relay LR. In addition to the removal ot this ground which establishes that condition which will cause the line selector wipers to stop in engagement with the contacts of the line after they have been moved to the desired group, the actuated contact 80 of the line relay, grounds the winding of relay 82, which, upon being ener ized, opens its contact 83 to remove the normal ground from those contacts 823-33 etc., which. correspond to the group of contacts in which those of the calling line are located, thereby establishing that condition which will cause the line selector to stop its primary movement at the proper group of bank contacts. The contact oil the line relay upon being attracted, destroys the normal battery connection through the winding of the cut-oil relay C9 to the contacts 363G etc., of the connectors to which the line P-S is connected, and substitutes a ground con.- nection therefor. As will be hereinafter explained, the normal battery connection to these contacts permits connection to be made to the line P-S as a called line, while the ground connection renders the said line busy to incoming calls.

The master-switch wipers -2l are brought, after each operation of a line selector Q, into engagement with contacts assigned to an idle line selector as will be hereinafter explained. Thus, as soon as relay 2% is energized, a starting circuit for such line selector is completed by the closing of battery B through the winding of primary relay PR, primary o'lt-normal contact 85, contacts 2220, closed contact 79, and normal contact 86 to ground, thus energizing primary relay PR to actuate its contacts and thereby complete a circuit from the live pole of the alternating current. generator 87 through the winding of prin'iary magnet PM and alternate conta t HR of primary relay Flt to ground, thus causing the wipers 26, 27, 28, 2?) and llto move in a primary direction. The said group relay 82 has its winding connected to a plurality o1. alternate contacts W), as indicated by the symbol T (which sign serves throughout the drawing to indicate a common ctmnecting point), on as many diliercnt lino relays LR. Thus, in the exai'nplc chosen, thcrc would be one hundred line relay-s and ten group relays for a group oil. one hundred calling lines. Each group relay would then be connected to ten dif ferent line relays. Each of the ten bank contacts 33 therefore corresponds to a diflerent sub-group of ten calling lines. Since the primary oil-normal contacts P are actuated upon the first primary movement of the switch wipers, the initial energizing circuit of the p imary relay PR is interrupted, but in the mea time the closing of contact 8.) of said relay has completed a new 311th through wiper 29 which is maintained so long as said wiper engages grounded contacts The end or the wiper 29 is preferably made broad enough to bridge adjacent contacts so that it will not pass out of engagement with one contact before engaging with the next, thus insuring a circuit at all times except when an ungrounded contact 38 is engaged. It should also be noted that although the wiper 29 is normally out of engagement with contact 2'33, it engages said contact at the time the primary off-normal contact 85 breaks, thus ii'isuring a suitable circuit for the relay PR until the wipers have been moved to that group of bank contacts which included the contacts assigned to the calling line. Just as soon as this group of contacts is reached, the primary movement of the switch wipers will be discontii'iued and the contacts 88-89 olf' relay PR will return to normal. The return of contact 88 will immediately energize the secondary relay SR over a circuit extending from the live pole of battery B through the winding of said relay, a secondary oil-normal contact 90, primary oin-ormal contact 91, which is closed at this time, and closed contact 88 to ground. The movement of contact 92 of relay SR to its alternate position, will at once close an energizing circuit for the secondary magnet SM extending from the live pole or the alternating current generator 93 through the winding of the secondary magnet, alternate conta -t 92, and normal contact 94 of ting release relay HR to ground. The rest repeated cnergications and de-energiiiations of the secondary magnet will cause the switch wipers 26, 22', 28 and 34L to move in a secondary direction over the contacts 30, 31, E32 and 35, respectively, of that group of bank contacts including the contacts of the calling line. Since upon the first secondary movement the contacts of the secondary oil-normal switch S0 are actuated, the initial energizing circuit of the relay bill will be interrupted but in the meantime the closing of its contact 95) will provide a new path through normal contact 96 of release magnet RM to wiper 26, and thence to ground so long as said wiper engages a grounded contact 30. It will be noted in this case as in the case of wiper 29 that adjacent contacts and that although nor-- mally out of engagement with the nearest bank contact, it will engage said contact by the time the secondary off-normal con. tacts are moved from normal. Thus, the secondary movement of the switch Wipers will continue until wiper 26 engages an ungrounded contact. Since the contact 30 corresponding to the calling line has been ungrounded as previously pointed out, the wipers will be stopped in engagement with the contacts corresponding to said line. Since other subscribers lines are multiply connected to contacts over which the wipers 2T28 pass during this secondary movement, and since conversation may be going on over a connection including said contacts, the relay SR is arranged to electrically disconnect the wipers 27-28 from other parts during this secondary movement. This is brought about by contacts 96 97, which in their normal positions, join the adjacent portions of the strands or conductors L lf, but when actuated, separate them, hus disconnecting the said wipers from other parts. Thus, as soon as the wiper 26 engages an ungrounded contact 30, the relay SR is de-energized and the contacts 92, 95, 96 97 return to their normal positions thereby discontinuing the further secondary movements of the wipers and restoring the normal connections of the wipers 2728. The contacts 96 97 of relay SR when in their alternate positions connect the right-hand portions of the strands LL by a bridge which includes alternate contact 96, closed contact 98 of release relay RR and alternate contact 97. The same portions of the strands LL are united by a bridge including normal contacts 99 100 of reverse relay RV, windings of primary and secondary relays PR and SR and batteries bZ These batteries being arranged in series, supply cur-ent over a circuit including'both of these bridges and thereby energize relays PR and SR to actuate their contacts. This prevents the possible closing of the release circuit (when the secondary oil-normal contacts SO are actuated) from battery 13 through the winding of release relay RR, closed contact 101, contacts 102103 of re lays PR and SR and the winding of release relay RR of the first selector U to ground.

The restoration of the contact 92 to normal, since the contact -1 of the secondary oil-normal switch S0 is now closed, immediately completes a circuit which is instrumental in causing the movement of the master-switch O to engage contacts of an idle line selector. This circuit extends from ground at contact 94 0'3 release relay RR through said normal contact 92, closed contact 104, contacts 23-2-1 of the masterswitch, and winding otrelay to the live pole of battery B thus energizing said relay to move its contact 86 to its alternate position and thereby close an energizing c1r- -cuit for the motor magnet MM which includes the alternating current generator 105. Due to the mechanical relation of the parts, the energization and de-energization of this magnet will step the wipers 21 into engagement with the next pair of bank contacts. It the line selector correspondii'ig to this pair is in use, there exists a ground at one point or another, as will be explained, on the corresponding contact 23 which will maintain the relay energized and thereby maintain the circuit for the motor magnet. lls soon, however, as an ungrounded contact 23 is encountered, this energizing circuit for relay 25 will be interrupted. Contact 23 corresponding to a busy line selector will always be grounded, while that corresponding to an idle line selector will be ungrounded, thus insuring the stopping of the master-switch with its wipers in engagement with contacts corresponding to an idle line selector. The ground connection with the contact 23 may exist over the path just traced including contacts lOel, 9'2, 94, or by way oi alternate contact 96, alternate contact 95, closed contact 90, closed contact 91 and alternate contact 88 to ground. Or the said ground may be maintained through the off-normal contact 1526 of the primary ottnormal switch P0 of the first selector U, 01' at other times through closed contact 178 of the reversing relay RV and closed contact in of relay 45.

As soon as the secondary relay SR of the line selector has been de-energized, and the adjacent portions of the conducting strands L-L united, there are at once established circuits for the primary and secondary relays PR and SR in lieu of that previously traced through the alternate contacts 969T of relay SR. Thus a circuit extends from the live, or negative, pole of battery B through the winding of the cut-oil relay CO, contact 106-107 of said relay, bank contacts 31, wiper 27, strand L, normal contact 99 of reversing relay RV, winding of primary relay PR to the live, or positive, pole of grounded battery 5. At the same time, a circuit is completed from the live, or nega tive, pole of battery 5 through the winding of secondary relay SR normal contact 100 of reversing relay RV, strand L including contact 97, wiper 28, contact 32, line limb S, via normal contact 76 and coil 71 to the negative pole of battery 13 prior to the operation of cutofi relay CO and immediately subsequent thereto, over line limb S, contact 75, lock magnet 74, switchhook G l, transmitter 67, contact 73, line limb P, including alternate contact- 72 of cutoflt relay CO, contact 31, wiper 2?, link strand L, including contact 96 normal contact 99 of reversing relay RV, the winding of primary relay PR to the positive pole of battery I). The closing of these circuits maintains the relays PR and SR energized, and in addition energizes the cut-off relay CO and the lock-controlling magnet 74 sociated with the calling line. The movement of contact 72 of the cut-ofi relay to it-s'alternate position continues line limb P to contacts 31-31 and interrupts the initial energizing circuit of the line relay LR- and thus destroys the normal substation control of said relay. The opening of its contact 7 8 likewise interrupts the circuit established through relay 21- of the master-switch and the line relay. The opening of contact 7 6 interrupts the normal connection of battery B to the line limb S. The subscribers circuit is thus completed over the heavily marked lines to the sections of the strands LL lying beyond the condensers l08109. The movement of contact 81 interrupts the path for current over the strand L through the cut-off relay CO, but before said circuit is interrupted, a new circuit is provided for the cut-oft relay G0, which extends from battery 13 through the winding of cut-oil relay, contacts 107, 81, engaged contact 30, wiper 26, normal contacts 96 and 95, and winding of relay 61 of the meter mechanism X, to ground. Thus, the cut-oil relay CO is maintained energized. The guarding circuit to ground for the line selector contacts 30, etc., and for the connector contacts 36, 36 etc., is now furnished through said relay 61 as follows:from contacts 36 via normal contact 84, alternate contact 81 and said contacts 30, 30 etc., and thence to ground through said relay 61 over the circuit previously traced for holding the cutofi' relay CO energized. Upon closing this circuit the meter mechanism X is set in operation to move its wiper 62 and the rigidly connected type wheel to that position corresponding to the calling line TI -S. This is brought about by the energization oi relay 61, which completes a circuit "for the motor magnet MM extending from the live pole of the alternating current generator 109 through the winding of said motor magnet, closed contact 110 of relay 61 and closed contact 111 of relay to ground. The wiper 62 is thus moved over the bank contacts 63 which are equal in number to the line selector bank contact These contacts are preferably arranged in a circle so that the wiper 62 need have but a simple rotary motion. Corresponding contacts and 63 are electrically connected and since wipers 3- and 26 are connected, there exists at this time a potential at the contact 63 corresponding to the calling line, which will be above that of ground and, consequently, as soon as wiper 62 in its movement engages his contact 63, a circuit will he completed from contact 63, through wiper 62, winding of relay 60 and closed contact 61 of relay 61 to ground, whereby relay 60 will be energized and its contact 111 opened to thereby interrupt the circuit of the motor magnet MM and thus discontinue further movement of the wiper. By means of contact 61 the ground connection with wiper 62, and thence to contacts 63, 35 and 30 of the particular switch in use, is removed upon the release of the switch and subsequent improper operation, due to the presence of such a ground, is thereby prevented. From this it will. be. seen that the wiper 62 and the type wheel 59 are moved to a definite position corresponding to that of the calling' line and left in that position. As will appear more fully hereinafter, as soon as the desired connection with the line P -S is complete, the printing magnet 58 will be energized and there will be placed on a recording sheet a type impression corresponding to the calling line, as for example, the number or the calling line. The disconnection, and con sequent de-energization, 01 line relay LR causes the release of the group relay 82 unless there be another line relay, belonging to the same sub-group of ten, energized at this time for the purpose oi? also initiating a call. Assuming no such condition to exist, the release of relay 82 will restore the ground via contact 83 to bank contact and to the other multiple contacts on the nine other line selectors,- thereby permitting wipers Q9 of said other line selectors to rotate past the sub-group containing the calling line whose call has now been picked up. Also the de-energization of said line relay LR causes the release of relay 21 of the master-switch 0 unless there be at that time another line relay belonging to the same group of one hundred subscribers then initiating a call. Assuming there be no such other call existing, the rerelease of such relay 241- will prevent the starting ot another line selector when the master-switch steps its wipers 20-21 around to engage the bank contacts corresponding to the next idle line selector.

lVith the parts in this position, then it remains for the calling party to operate his calling mechanism 68 to send the necessary impulses to extend his circuit to that of the called line. The calling mechanism is diagrammatically represented by a disk having a number of teeth adapted to engage a spring 73 to cause it to break contact upon the return of the disk due to its return spring 112, and a single tooth similarly cooperating with contact spring 75 to cause it to open its contact after the contact '73 has completed its interruptions. The dish is also provided with a pin which en: gcs a spring contact 113 to hold it out or gagement with a similar spring contact and a grounded Contact 115. The disk is normally locked by means of a hook 116 arranged to engage a notch in the disk and normally held in engaging position by a spring and moved out of engaging position by the energizations of the magnet Tl. In operation, the disk is moved against the tension of the return spring until a definite number of teeth have passed below the spring 78, and is then allowed to return to normal with the resulting breaking of con-- tacts 73 and 75. -Were substation equipped in the same manner as substation N, that is withoutthe slot mechanism 69, the calling party would now be lreeto operate his dial to semi the necessary impulses. In the present instance, however, any br ak which migl'it be made by contact 7;) would he bridged by normal contact 116 of the slot mechanism so that there would be no resulting interruption or the line limb P as would be necessary to cause the operation 01 the connected first selector; consequently it necessary for the calling party to deposit a nickel or other token in the slot of the slot mechanism 69. \i hen this is done, the contact 116 is forced by the tolaen to its alternate position. This is accomplished in the present instanre by having a suitable projection from the coniac 116' extend into the slot. As indi lower portion of the subs ion diagram, the pivoted end the switch-hook is pro vided with an upward projection 117 which engages the lower end of a pivoted arm 118 which is adapted to be moved in the slot in order to determine the disposal ot the token. ll hen the receiver 65 is first removed lrom its hook, the projection 11'? allows the arm 118 to move to an intermediate position under the pressrue or sprinn' carried by the arm 118 and be ing a the armature 120 of the polar JOil relay 70, which in normal position hears at ain fixed stop. In case the couneetien pletcd, the polarized relay is energized by a reversal of current, caused by the opera tion of the reversing relay RV, to throw the upper end of the arm 118 to the lclt to col lect the tolren by allowing it to pass (lrm'n- Ward through the right-hand outlet of the slot, into a suitable receptacle. in case the desired connection. is not completed, the token is returned upon the restoration of the receiver to its hook which forces the arm 118 to the right to the position indicated in the diagram, thereby allowing: t e token to pass out of the lel thand outlet of the slot into a suitable holder from which it may be taken by the calling party.

Assuming now that the calling party has deposited his token and thereby interrupted a brid ze about the contact 73, he will be at libertyto operate his calling mechanism in accordance with the number of the tel 'ated upon. the

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