US2137518A - Telephone system - Google Patents

Description

Nov. 22, 1938. J. wlcKsl 2,137,518

TELEPHONE SYSTEM Filed May 15, 1957v 4 Sheets-Sheet 2 ALLOTTER GROUP 1NVENTOR.-

1m www BY M,W,Mvm

ATTORNEYS.

4 Sheets-Sheet 3 ATTORNEYS .7 il Mmm Nov. 22, 1938. J; WICK'S TELEPHONE SYSTEM Filed May 15,v 1957 33m kunt Si om mi In O of, I..

N0v.22,1938. JWICKS 2,137,518

TELEPHONE SYSTEM Filed May l5, 1937 4 Sheets--Sheel'l 4 PRIMARYv PRIMARY DER FINDER INVENTOR Wiley/av ATTORNEY.

Patented Nov. 22, 1938 TELEPHONE SYS TEM fJohn Wicks, Oak Park, Ill., assignor to Associated Electric Laboratories, Inc., Chicago, Ill., a cor-v poration of Delaware Application May 15, 1937', Serial No. 142,779

30 Claims.

The present invention relates to signalling systems and more particularly to automatic switching equipment of the type adapted for use in automatic telephone systems serving a compara- 5 tively small number Yof subscribers lines.

One of the most widely used types of telephone systems yet devised is that employing single movement step-by-step line or finder switches and dual movement step-by-step selector and connector switches of the Strowger type, for setting up Vconnections between the various lines of the system. In such a system the bank 'contacts of the iinal and intermediate selecto-r switches are conventionally multipled in groups, each unit multiple being connected to the trunk line of a connector switch, and the bank contacts of Athe connector switches are multipled in groups, each unit multiple being connected to a subscribers line or an inter-exchange trunk line. With this 20 arrangement a connection may be established between any pair of lines included in the system by` way of the selector switch or switches of a particular group or groups and a connector switch in the group of connector switches to which extends the called subscribers line. While this type of system is perfectly satisfactory in operation, it is uneconomical in first cost when used'in a small exchange, in that a large group of comparatively expensive connector switches Vis necessary if reasonably good service is to be obtained. Moreover, the equipment is costly to install in that large and expensive multiples must necessarily be carried between the bank contacts of the various switches. In addition, and due to the constructural features of the Strowger type of switch, a considerable amount ofspace is necessary to accommodate the switching apparatus.

The `disadvantages of a system of the above character are at least in part overcome by the arrangement disclosed in the prior vPatent No. 1,903,207, Wicks et al., granted March 28, 1933. In the system of this patent, single movement rotary stepping switches are used both as concentration switches and vas numerical switches with a consequent decrease in the cost per unit thereof and a lessened installation cost because of the smaller multiples therebetween. The rotary switches employed are of the fty lpoint line variety having embodied therein six levels of bank contacts and, while a greater number thereof is required than in the system employing Strowger switches, the smaller size thereof more than oiisets the increase in number as regards cost and the space requirements for a given installation.

In the system of this patent, only one set of intermediate selector switches is employed, the incoming lines to the bank contacts of the selector and connector switches being, in each instance, multipled in groups, with each unit multiple of the final intermediate selector switches extending to the-trunk line of a connector switch and each unit multiple of the connector switches extending to a subscribers line. As thus arranged, each particular group of connector switches has access to 'a group of iifty subscribers lines. The control equipment associated with each'of the selector switches is arranged to be responsive to impulses dialed at a substation on a line which has seized the corresponding switch y 4and operates ina manner such that the wipers of leach selector switchare, during the impulses of one series of impulses, driven over their respective associated bank Contacts at the rate lof 'one group of -contact sets for each impulse and, lat Ythe conclusion of the impulse series, stand on the rst contact set of the group of contacts to which extend the trunk lines of the connector switches in the bank contacts of which the particular called line terminates. In each position f of the wipers thev operated selector switch has access to the trunk line and test conductors of two connector switches in the Yselected group and, when the rst series of impulses is ended, the trunk vlines extending to the respective connector switches of this group are automatically and successively tested until an idle switch in the selected group is found. Immediately upon the seizure of an idle connector switch, it is conditioned to be responsive `tofurther series of impulses transmitted from the impulsing device at the calling subscribers substation. f

The connector switches as disclosed in the above referred to prior patent are similar to the selector switches 'in' that the subscribers lines 40 are multipled 'in groups in the bank contacts thereof and the wipers for engaging these contacts when moved to any one of a lplurality of positions to which they are operable have access to two different subscribers lines. Here again the 45 control equipment is so arranged that in response 4to the dialing of a second seriesof impulsesthe Wipers are automatically stepped 'over the bank `contacts at the rate of one contact group for each impulse. At the conclusion of the Vsecond series `50 of impulses Athe control -equipment is conditioned vs0 that in response to a third series of impulses the wipers `are stepped from one contact set to thesucceedingcontact set during each alternate impulsefuntil the wipers engage the contacts of 55 impulse.

the called line corresponding to the number of impulses of the digit dialed. More or less conventional means are provided for applying ringing current to the called line, for applying ringback tone current to the calling line and for applying busy tone current to the calling line in the event the called line is found busy. Similarly, the release of a connection is eect'ed in a more or less conventional manner by the removal of ground potential from the control conductor of the operated line, selector and connector switches when the established loop is interrupted at both the calling and called substations.

While the above-described prior arrangement of the patent noted is entirely satisfactory in operation, the economy resulting from the use of smaller switches and smaller multiples is offset to a certain extent by the fact `that the required operating speed for the various rotary switches used is considerably in excess of the speed attainable by any of the low cost switches of this type now commercially available. Thus, with the arrangement shown, the wipers of each of the switches must, with a standard impulsing rate ranging from 8 interruptions per second to 12 interruptions per second, necessarily travel at a rate ofy fifty contacts per second or more, in order to traverse one group of contacts during each Hence, the system necessarily requires expensive, specially constructed switches in order to operate in a satisfactory manner. Moreover, in the system of the prior patent, the selector and connector switches are practically independent in so far as the operation of the control apparatus included therein is concerned. In addition, the usual auxiliary functions such, for example, as the application of ringing current to a called subscribers line, the application of ringback tone current to a calling subscribers line, the application of a busy tone current to a calling subscribers line in the event a particular called line is found busy, and other similar functions of this nature are under the control of apparatus individually provided in each of the connector switches. Since, with the arrangement disclosed, the small rotary switches necessarily have a limited line capacity, a considerable number of connector units is required, thereby entailing a large amount of duplication in the matter of the control equipment provided for performing the specified auxiliary functions.

It is an object of the present invention, therefore, to provide an exceedingly simple andinexpensive arrangement of the general form briefly described in the immediately preceding paragraphs which does not require single movement rotary switches of special construction for satisfactory operation.

`More specifically, itis an object of the invention to provide such a system which is susceptible of being incorporated in a larger system embodyanumber of exchanges and wherein the auxiliary functions incident to the establishing of a connection between a pair of lines included in the system are concentrated in the selector switches and at least a portion of the control equipment provided in each of the connector switches is susceptible of being controlled from a portion of the control equipment necessarily included in each of the selector switches.

In general, the objects as set forth above are in part attained in accordance with the present invention by providing control means in each of the intermediate selectorV switches, which meansl are operated whenthe. corresponding switcn is seized and during and following the establishment of a connection between a pair of lines in the system, and perform the group of auxiliary functions normally performed in a nal selector or connector switch. These functions, as noted above, comprise the application of ringing current to the called line, the application of ring-back tone current to the calling line, and the applicationv of busy tone current to the calling line in the event a called line is busy at the time a call is initiated thereto. As in the system of the prior patent referred to above, the impulse responsive means in each of the selector switches comprise a pair of relays, one of which operates on each alternate impulse of a series of received impulses. These relays comprise a portion of means for causing the associated selector switch to seize anidle connector switch of a particular desired group and in addition comprise means to which are responsive means in the seized connector switch for causing the lastmentioned switch to seize a desired called line.

The system is arranged to provide selective4 harmonic ringing of particular substations on a party line; that is, the ringing apparatus associated with each of the selector switches includes means responsive to a final digit dialed at a calling subscribers substation for transmitting ringing current to a called line of a particular frequency to which is responsive only the signal device associated with the desired one of the telephones onrthe called line. The ringing operation is interrupted and the talking connection com.- pleted in response to the operation of a ring cut'- off relay included in each selector switch.

The grouping of the lines extending to each of the automatic switches comprising the selector and connector switches is such that the number of contact sets in each group is so proportioned relative to the rate of impulsing that the speed at which the switch wipers traverse the contact sets does not exceed forty contact sets per second. By this grouping arrangement, and by concentrating the auxiliary functions noted in the selector switches, the cost of the system, as installed, is considerably lessened.

The novel features believed to be characteristic vof the invention are set forth with particularity in the appended claims. The invention itself. however, both as to its organization and method of operationrtogether with further objects and advantages thereof will best be understood by reference to the specification taken in connection with the accompanying drawings in which Figs. l, 2, 3 and 4, considered together, illustrate a system of the character briefly described above having the features of the present invention embodied therein.

Referring now to the drawings, there is illustrated an automatic telephone system having embodied therein the features of the present invention and employing exclusively automatic switches of the single movement'step-by-step type for setting up connections between any pair Vof telephone lines of the system. In general,

the system comprises a plurality of telephones or subscribers substations, four of which are shown at A, B, C and D adapted to be interconnected by means including their respective associated lines 5, 2 and 3 and switch trains including the aforementioned step-by-step switches. These switch trains, when established, may individually comprise an operated primary finder switch, an operated secondary finder switch, an operated selector switch and a connector switch finder switches.

amitie accessible to the operated selector switchv and having bank contacts in which the called subscribersline terminates. Thus, in the system sho-Wn, the line terminates at the bank contacts of a primary finder switch I2, which switch is accessible to at least oneV group of secondary finder switches, one of which is shown at I3 The latter switch is, in turn, associated with a selector switch indicated generally at I4 and in comfbination therewith forms a under-selector unit; 'Ihe selector switch I4 has accessto each of the connector switches included in the system, one of these switches being indicated generally at I6 as including bank contacts in which the lines 2 and 3 terminate. In order-that an idle secondary finder-selector unit will always -be started, Without delay, in search of a calling line, there are provided, as shown in Fig. 2, two groups of allotter relays indicated, respectively, at 1'I` and 12. As will be pointed out in detail hereinafter, the operation of these allotter groups is such that when a particular nder-selector unit is seized, the next succeeding idle finder-selector unit is conditioned to be seized by the next succeeding calling line.

It will be understood that the primary nder switches are arranged in groups having their bank contacts multipled in groups to serve particular groups of subscribers lines. With the sys'-V tern shown, each of the secondary finder switches has access to each of the primary nder switches. The connector switches, like the primary nde'r switches, are arranged in groups with each connector switch of each group having its bank contacts multipled to the bank Vcontacts of the other switches included in the same group, so that each group of connector switches serves a particular group of subscribers lines. The switches, individual ones of which are associated with individual ones of the secondary iinder switches, individually have access through their respective banks of contacts to each of the connector switches.

With a system employing apparatus of the type mentioned and designed to provide Ygood service for 400 subscribers lines, approximately fortyeight` twenty-live point primary finder switches, twenty-one twenty-five point secondary nder switches, twenty-one twenty-five point selector switches and forty-eight twenty-five point connector switches are required. The forty-eight finder switches may be divided into eight groups with six switches in each group so thatfeach subscribers line has access to six different primary cndary iinder switches, through thebank `contacts embodied therein, has access to each of the forty-eight primary iinder switches. Similarly, each of the selector switches has access through its bank contacts to each of the forty-eight connectorV switches. The last-mentioned switches, like the primary nder switches7 are" arranged in eight groups cf six each with multiples extending between the corresponding contacts of the switches of each group so that six connector switches are available for completing a connection to each subscribers line.

Each of the rotary primary and secondary nder switches is of more or less conventional i form and is of the non-homing type; that is, of-

the type which is not restored to normal following the release of a switch train in which it is involved.Y Each switch comprises a twenty-five point, six contact set, bank contact arrangement with double-ended wipers for 'engaging the-conselector Each of the twenty-one sec-'- tacts, the opposite ends oi each wiper being offset so that each end engages or traverses the contacts of a diierent set of contacts. Thus, the switch I2 comprises six sets of bank contacts, three of which are shown in the drawings, and doubleended wipers 91, 98 and 99 for engagingthe respective sets of contacts, This switch also includes amotor magnet |31 which in cooperation with a ratchet and pawl mechanism, not shown, is arranged to drive thewipers to engage the respective contacts, anda fast acting relay |40 for interrupting the circuit of the motor magnet when the wipers are Vstepped into engagement with the contactsof the'calling line. The relay Id vis of the electro-polarized type such that energization of its upper winding does not cause the operation'thereof, but only conditions the relay to be exceedingly fast acting when its lower winding is energized. Similarly, the switch I3 comprises six sets of Abank' contacts, three rof whichl are shown, and double-ended wipers 59, GIIand 6I havingtheirrespective opposite ends offset so that, when driven by the motor magnet I 35, theyv engage the contacts Y of 'different sets. 'I'his switch, likethe primary nderA switch I2, includes a fast ,acting relay |35) identicalwith the relay |40 which operates when the wipers of thev switch come into engagement with the bankcontacts corresponding to a. primary nder switch seized by a calling line. The operation of the primary and secondary iinder switches is initiated byline relays individually associated with the subscriberfs lines, such, for example, as the relay |99 associated with the line 5.

' Each of the two allotter groups 1I and 12 comprises a plurality of two-step relays individually associated with each of the secondary finderselector links and a common relaywhich is norm'ally operated but which restores when all of the links associated with .the other relays of the corresponding allotter areV busy. Thus, the group 1I comprises a. number of relays 2I0, 220, etc. and a common relay 238 which is normally operated but which restores when all of the relays 2I0, 228, etc. are restored incident to an allbusy condition of the respective .associated finderselector links. Similarly, the allotter group 12 comprises relays 240, 250, etc. individual to other finder-Selector links of the system and a common relay l2Ii0. Itwill be noted that the relay 2|() is individually*,associated with the nder-selec tor link I3, I4 by means of the conductor 29, this relay ydetermining by the position of its armature 2II whether the indicated link I3, I4 orthe next succeeding idle link will be seized. Seizure of the idle links of each Vgroup is in order and is accomplished through the contacts of the respective relays 2 I9, 220, etc., start conductors 21, 28, 28', etc., and group relays such, for example, as the relay III) associated with the group of lines including the line 5.

Neglecting for the present the arrangement of the selector switch I4 and the connector switch IB, Vthe system as described aboveis more or less conventional in form, .and its operation is well understood `in the art. Thus, assuming that a connection is desired between the subscribers substations A and B on a call from the line 5 to the line 2 and assuming that the switches illustratedare the switches involved in establishing this connection, the operation of the apparatus is initiatedby the calling partyV at the substation A lifting his receiver from its hookto cause the line relay IDD to operate and mark the calling'-line in'thevbank' contacts of the group of primary nder switches including the switch I2. Simultaneously the start relay IIO is energized to mark in the bank contacts of the secondary finder switch I3 the prim-ary finder switches of the group at which the calling line terminates.

The secondary nder switch I3 thereupon opcrates to seize the first idle primary iinder switch in the group including the switch I2; and assuming this particular primary nder switch is seized, it operates to seize the calling line 5. When this occurs, the line conductors I0, of the line 5 are connected directly to the conductors 2|, 22 leading to the selector switch |4. The control equipment of the seized selector switch I4 is thereupon conditioned to be responsive to the rst series of impulses transmitted from the impulsing device at the substation A.

In response to the dialing of the first digit comprising the first series of impulses, the control equipment of the seized selector switch I4 causes the wipers of this switch to be stepped into engagement with the iirst contact set of the group of contact sets to which extend the lines of the respective connector switches in the group of connector switches at which the called line terminates. Thereafter, and at the conclusion of the first series of impulses, the selector switch I4 automatically and in succession tests the line conductors leading to the respective connector switches of the selected group until an idle switch in this group is found, whereupon the idle switch is seized .and the control equipment included therein is conditioned to be responsive to further impulses transmitted from the irnpulsing device at the calling substation A.

In response to the dialing of the second or tens digit and assuming the switch I6 to be the switch seized, the wipers of this switch are stepped into engagement with the last contact set of the group of contact sets preceding the group of contact sets in which is included the contact set corresponding to the called line.` When the third or units digit is dialed, the wipers of this switch are stepped into engagement with the contacts at which the called line terminates.

If the called line is idle at the time the wipers of the connector switch are stepped into engagement with these contacts, ringing current is automatically applied thereto and ring-back tone current is transmitted back over the calling loop to indicate to the calling' party that the called line is idle. In the event the called line is busy,

busy tone current is returned over the loop to the calling subscriber to indicate the busy condition of the line.

As will be pointed out in greater detail hereinafter, the release of a connection established in the above described manner is under the control of the last party to hang up his receiver. Thus, if the party at the calling substation A replaces his receiver. on its hook, the switch train is held operated until the called party at the substation B hangs up. Similarly, if the party at the substation B hangs up first, the switch train is held operated until the connection is cleared out at the calling subscribers substation A.

Referring now more particularly to the details of the selector and connector switches having embodied therein the features of the present invention, each of these switches comprises a bank of contacts arranged in six sets, six double-ended wipers, individual ones of which are associated associated ratchet and pawl mechanism for driving the wipers, and control means comprising a plurality of interrelated relays for controlling the operation of the motor magnet and for completing a talking loop between a pair of subscribers lines once a connection has been set uptherebetween. As will be pointed out in detail hereinafter, each of the selector switchesis, by virtue of the wiper rotating mechanism included therein, operable to a plurality of positions and, through the action of a wiper switching relay, has access to two of the connector switches in each position thereof. Similarly, each of the connector switches is operable to a plurality of positions and has access to two subscribers lines in each position thereof. Each of the selector switches differs from each of the connector switches in that there are provided impulse responsive means comprising a pair of relays, one of which operates during each alternate impulse of a series of received impulses and restores during each of the remaining impulses. The control means in each of the selector switches includes means responsive to the operation of the impulse responsive relays for causing the motor magnet and its associated ratchet and pawl mechanism to step the associated wipers over their associated contact sets at the rate of one group of contact sets for each impulse during a particular series of impulses. The motor magnet of each selector switch is also adapted to be controlled automatically to step the wipers at the rate of one contact set each time the magnet is energized after these wipers have been stepped into engagement with the first contact set of the group of contact sets corresponding to the desired group of connector switches.

'I'he control apparatus included in each of the connector switches is simple in the extreme. Certain of the relays individually included therein are arranged to be responsive tothe one relay of the aforementioned impulse responsive means which operates on each alternate impulse of a series of received impulses.V The control of the switch mechanism is fundamentally the same as that of each of the selector switches in that the wipers are rst stepped over groups of contact sets at the rate of one group of contacts for each impulse, following which, and during a succeeding series of impulses, the wipers are stepped at the rate of one contact set per impulse until they engage the contacts at which the conductors of the called line terminate.

Considering specifically the selector switch illustrated in Figs. 1 and 3, this switch comprises a switch mechanism 90 which includes six sets of bank contacts at which the outgoing trunks leading to the connector switches are terminated, wipers 9| to 96, inclusive, for engaging the respective sets of contacts, a camming element 8| on the same shaft as the wipers 0I to 96, inclusive, a ratchet and pawl mechanism, not shown, for driving the wipers and the camming element, and a motor magnet 308 for causing the actuation of the ratchet and pawl mechanism. The control means included in this selector switch comprises aplurality of interrelated relays |25, |50, |55, |60, |10, |15, |80, |85, |90, 300, SID 320, 330, 340, 350, 360 and 310, their control and controlled circuits, all arranged to cause the switch I4 to operate in the manner brieily set forth above. Of the enumerated relays, the relays 3||3 and 320 comprise the impulse responsive means to-which the actuating means of this selector switch is responsive with each level of contacts, a motor magnet-and and also to which certain of the control relays in any connector switch seized by this selector switch are responsive. As will be pointed out in greater detail hereinafter, the sequence of operationof the two relays is such that the relay 3I0 operates at the beginning of each odd impulse, the relay 32S operates at the end of each odd impulse, the relay 350 restores at the beginning of each even impulse, and the relay 320 restores atthe end of each even impulse. These relays in cooperation with the camming element BI, the cam springsA 16, 11 and 86 and the relays 300,' 340 and 350 comprise the necessary control means for causing the motor magnet 308 to step the wipers 9I to 96, inclusive, into engagement with the first contact set of a desired group of contact sets at the rate of one group for each impulse, and also the means for automatically stepping the wipers over the contact sets of the desired group until a trunk leading to an idle connector switch in the selected group of connector switches` is found. Selective harmonic ringing of a desired substation on a party line is achieved by the provision of a frequency selecting minor switch 3I8 including one set of bank contacts indicated at 324, a wiper326 for engagingthe contacts, a ratchet and pawl mechanism, not shown, for actuating the wiper, a motor magnet 33S for `driving the ratchet and pawl mechanism, and a release magnet 338 for permitting the minor switch to restore to its normal position during the release of an established connection involving the selector switch I4. The control of this minor switch is such that it is automatically connected by means comprising 1 the relay 360 to be responsive to a` nal digit dialed at a calling substation, when the wipers thereof are rotated in accordance with the impulses of this digit to select ringing current of the frequency to which only the particular desired substation on the called party line is responsive.

The connector switch IG is, from the standpoint of construction, substantially similar to the selector switch I4 but differs therefrom in that an added set of contacts is included therein and the camming mechanism is omitted. In brief, the mechanism of the switch indicated at 63 comprises seven sets of bank contacts, double-ended wipers 54 to 1e, inclusive, for engaging the respective sets of contacts, a ratchet and pawl mechanism, not shown, for actuating the wipers,

a motor magnet 431 for driving the ratchet and pawl mechanism, and control means comprising relays 460, 4m, 420, 43@,'448, 450 and ll, their control and controlled circuits for causing the motor magnet 431 and its associated ratchet and pawl mechanism to drive the wipers oi the switch in the manner briefly described above. The control circuits for these relays are so connected and arranged that following seizure of this switch by a selector switch such, for example, as the switch I4, and at the beginning of the second series of impulses, the circuit for the relay 4 IB is completed immediately upon the operation ci' the slow-torelease relay 30D of the operated selector switch and conditions the circuits associated with the relay 42d to operate in accordance with the operation of the impulse responsive relay 3m. These two relays, namely the relays lill and 42B, in cooperation with the wiper 64 and its associated set of bank `contacts specifically comp-rise the means responsive to the operation of the relay 3m for causing the motor magnet 3l to operate, thereby causing the wipers of the switch 63 to be stepped at the rate of one group of contact sets per impulse during the series of impulses, ceinprisingthe second dialed digit. In order to rearrange the control circuit for the motor magnet 431 so thatzthe wipers will be stepped at the rate of one Contact set foreach odd impulse during the third series of impulses, the relay 450 is adapted to operate, when the relay lle restores at the endof the second series of impulses, to prepare an alternative circuit forthe winding of the motor magnet431 such that this magnet is energized andr'deenergized in accordance with the operation and restoration of the relays 3H) and i2-l duringlthe third series of impulses.

' Referring now .more specifically to the operation of the `system. during a call from the substation A, for example, to the substation C, for eX- ample, the `operation of the apparatus is initiated, as wasp'ointed vout above, in responseto the subscriber at the` first-mentioned substation lifting his receiver from its ihook. This operation closes a bridge across thefline conductors I and II of the calling line tov complete a circuit for energizing line relayl in series with the resistor IllI, this'xcircuit extending Yffro-nrifground at the lower winding of therelayi HIL-through this windingand by wayof the armature IM, the line conductor I I, thebridge'at the'calling substation, the line conductor I B, the armature |03, the resistor I 0I' and through the upper winding of the relay 4GB to battery. .Due tothe presence of the resistor IGI lin the `:above traced circuit, relay I only partially operates to Inakeonly the X contacts associated with the armatures Ill! and |02, At the second of these armatures a circuit is cornpl'etedfor .energizing the relay HEI, and at the rst there'of'aipath. is completed for marking the callingline 5 in the control contact banks of the primary finder switches in which the line 5l terminates.' The relay IIil, Yupon operating, closes its armatures lI Il to I I6, inclusive, to their respective associated contacts. When the contacts associated 'with the. respective armatures III to I I5, inclusive, make, each of the group of primary nderswitches at which the calling line conductors I6, Il terminate is marked in the control contact-banks oi the secondary iinder switches. whenthe conta-cts associated with `the armature I I I engagaa path is completed extendingfrom battery at the upper winding of the'frela'y I4' rby vway ofthe conducto-r 25, the

armature HI l l, and the conductor -26 to the fourth control contact'of the switch I3. When the armature `I I6 `is operated to engage its associated contact, it `applies ground to the start conductor 2l', thereby to cause therelays in the allotter 'group 'II to select an idle secondary finder-selector link.

Before'proceeding with the operation of the finderswitches, a brief description of the allotter relays or common 'control-apparatus is 'deemed to be in order. `As 'noted`previously, each of these relays 2IU, 220, 24U and 250, etc. corresponds to oneof the secondary finder-selector links, these relays preferably being divided into two or more groups for ay systemembodying four hundred or more subscribers lines, for the purpose 'of expediting the selection of an idle selector link.

As will be pointed out more specifically hereinafter, when any given link is idle, ground is present on the conductor corresponding to the conductor 29 for the selector switch I4. Thus, when the selector switch I4 is idle, ground extends lfrom the armature .|51 lof the relay |55 by way 'of its associated contact |58, the conductor 31, the' armature 334` and its associated contact 336 to theconductorl. As a result, the lower Q1. active' Windingof the relay ZIII is energized 'ill and all of the armatures of the relay are in their fully operated positions. The armature 2| I, therefore, is closed to its associated contact 2|3 to prepare a circuit for energizing the relay |20. At the armature 2|5, a circuit is completed for energizing the relay 230 which relay, in its operated position, holds interrupted the circuits for energizing the respective primary windings of all the relays common to the group v1| in which the relay 2|0 is included. When a connection by way of the finder switches I2 and |3 is completed to the selector link I4, ground is removed from the conductor 29 at the armature |51 of the relay |55 and hence this relay is permitted to restore. In its restored position the relay 2|0 connects the start conductor 21 by way of its armature 2I| to the conductor, corresponding to the conductor 28, for the next succeeding idle selector link controlled by the allotter group 1|. Thus, if the link corresponding to the relay 220 is idle this relay will be in its fully operated position so that the start conductor 21 is connected over an obvious path to the conductor 26'. In this manner the selector links are successively seized and an idle selector link is always immediately available for a calling line in the group corresponding to the allotter group 1|, so long as all of the selector links thereof are not busy. When the last relay, corresponding to the relays 2|0 and 220, of the first group, is restored, following the seizure of its associated selector link, the operating circuit for the relay 230 is opened at the armatures 2I5, 225, etc., and this relay momentarily restores to complete at its armature 233 the primary circuits for re-energizing the upper windings of the relays 2|0, 220, etc. These latter relays in turn partially operate to close their respective "X contacts. Those of the associated selector links which are idle will, as was pointed out above, have ground on the associated conductor such, for example, as the conductors 29 and 29' and hence, when the X" contacts of the associated allotter relays are closed, these relays will assume their fully operated positions to render available for use all of the selector links not busy and to cause the re-operation of the relay 230. If all of the selector links corresponding to the allotter relays of the group 1| become busy at the same time, the operating circuit for the relay 230 is interrupted because all of the armatures corresponding to the armatures 2|5 and 225 of the relays 2|0 and 220, respectively, are restored. As a consequence, the relay 230. restores to connect, over an obvious path including the arma-v ture 23 I, the start conductor 21 of the first group to the conductor corresponding to the conductor 28 for the first idle selector link available in the group governed by second allotter group 12. The operational sequence of the relays 240, 250, etc., and 260, included in the allotter group 12 is identical with that described above for the relays of the allotter group 1| and hence a description thereof is omitted in the interests of simplifying the description.

Continuing now with the operation of the primary and secondary finder-switches to search for and seize the calling subscribers line 5, and assuming that the selector link I4 is the rst idle link available, when ground is extended by way of the armature ||6, the conductor 21 and the armature 2|| to the conductor 28, a circuit is completed for energizing the relay |20. This relay thereupon operates to complete, at its armature |22, an obvious circuit for energizing the upper winding of the relay|30, thereby to render this relay fast to operate, and to complete, at the same armature, a circuit for energizing the relay |15. The last-mentioned circuit extends from ground at the armature |22 over the conductor I8' through the restored armature |26, over the conductor 46 through the armature 315, over the conductor 45, and through the winding of the relay |15 to battery. In response to its energization over the above traced circuit, the last mentioned relay operates partially to condition the selector switch I4 to be responsive to impulses transmitted from the calling substation A. Thus, upon operating this relay applies at its armature |16, ground to the control conductor 38 thereby to complete circuits for energizing the relays |25 and |60. The first of these circuits extends from ground at the armature |16 by way of the conductor 38 through the winding of the relay |25to battery and the second thereof extends from ground at the same armature over the conductor 38, through the armature 355, over the conductor 39 and through the winding of the relay |60 to battery. When the relay |25 operates it opens, at its armature |26, the previously traced energizing circuit for the relay |15. Before the last-mentioned relay falls back, however,` the relay |60 is operated to close at its armature |64 and associated contact |65 multiple ground to the conductor 38 thereby to hold itself and the relay |25 operated.

Returning now to the operations which occu when the relay |20 operates, it will be seen that this relay in its operated position completes, at its armature |2I, an obvious circuit for energiz-v ing the motor magnet |35. This magnet includes self-interrupting contacts associated with the armature |36 such that it operates buzzer fashion to cause the associated ratchet and pawl mechanism to advance the wipers 59-6I, inclusive, of the switch I3 into engagement with the contacts corresponding to the rst idle primary finder switch of the group at which the calling line terminates, or in the case assumed, to the fourth position corresponding to the primary finder switch I2. When this occurs a circuit is completed for energizing the lower winding of the relay |30, this circuit extending from ground at the armature |22 through the lower winding of the relay |30, the control wiper 60 and itsl associated fourth contact, over the conductor 26, the armature and the conductor 25 and through the upper winding of the relay |40 to battery. The relay |30 immediately opens, at its armature |3|, the operating circuit for the motor magnet |35, connects the conductors 2| and 22, respectively, to the conductors I9 and 20, respectively, at the respective armatures |34 and |33, and short circuits, at its armature |32, its lower winding. The relay |30 remains operated, however, by Virtue of the energized condition of its upper Winding. When the armature |32 isoperated into engagement with its associated contact a direct path from ground is completed for energizing the motor magnet |31 and the upper winding of the relay |40, this path extending from ground at the armature |22 through the armature |32, the control wiper 60 and its associated fourth contact, and over the conductors 26 and 25, where the path divides, one branch extending through the armatures |44 and |38, and the winding of the motor magnet |31 to battery, and the other branch extending through the upper winding of the relay |40 to battery. Energization of the lastmentioned Winding conditions, in a wellknown manner, the relay |40 to be exceedingly a, '137,15 is fast in operating when its lower winding is energized. By virtue of the self-interrupting contacts associated with the armature |38, the motor'magnet |31 in cooperation with its associated ratchet and pawl mechanism drives the wipers of the primary nder switch |2 to a position corresponding to the calling line 5, or, in this case, into engagement with the fourth set of contacts in the contact bank, When this occurs a circm't is completed for energizing the lower 'Winding of the relay and the upper Winding of the relay |00 in series, this circuit extending from ground at the armature |22, over the conductor I8' through the armature |32, the control wiper 60 and its associated fourth contact, over the conductors 26 and 25, and through the lower Winding of the relay |40, the control Wiper98 and its associated fourth contact, the X contacts associated with the armature |0| and the upper winding of the relay |00 to battery. `The relay |40 immediately operates in response to such energization to interrupt, at its armature |44 and associated contact |45, the operating circuit for the motor magnet |31, and to place a shunt around the armature at this same armature and its associated contact |46. The relay |40, upon operating, also connects, at its armatures |4| and |42, respectively, the conductors 2| and 22 to the conductors |0 and respectively, of the calling line 5. At its armature |43, this relay short circuits its lower winding, but remains operated by virtue of the energized condition of its upper winding.

When the relay |40 operates to short circuit its lower winding, a direct path is completed for causing the energization of the upper winding of the relay |00, this path starting at ground on the operated armature |22 and extending through the armature |32, the wiper 60, the armature I43, the wiper 98, the closed "X contacts associated with the armature I0| and the upper winding of the relay |00 to battery. Thereupon, this line relay fully operates to interrupt, at its armature |05, the operating circuit for the relay H0, permitting this relay to restore 'and open the contacts associated with the armatures to I6, inclusive, thereby to release the start conductor 21 and the allotter group 1| for further use. rI'he relay |00, upon operating, also interrupts, at its armatures |03 and |04, and their respective associated contacts, its original energizing circuit. When the relay ||0 falls back it opens, at its armature ||6 and associated contact, the previously traced operating circuit for the relay |20, which latter relay restores to open, at its armature lZl, a further point in the operating circuit for the motor magnet |35. At its armature |22, the relay |20 also removes multiple ground from the conductor I8 but ground is retained on this conductor at the armature |25 and the associated front contact of the relay |25, so that the relays |00, |40 and |30 'are held operated.

With the system in this condition the bridge at the calling substation A across the Vline conductors l0 and is extended to the line conductors 2| and 22 to complete a circuit for energizing the line relay |50, this circuit extending from ground at the lower winding of the relay |50 by way ot the armatures |83 and |03, the conductors 22, 20, I8, I', and through the bridge across the conductors and |0 at the calling substation, over the conductors l0, I4', |1', I9 and 2|, and through the armatures |95,

`|8|, and the upper winding of the relay |50 to battery'I When the line relay 50 operates, it completes, at its armature |5| and associated' contact |52, an obvious circuit for energizing the slow-to-release hold relay |55. The latter relay, in turn, operates to interrupt, at its armature |51 and associated contact |58, the circuit extending by way of the conductors 31 and 29 for energizing the lower winding of the allotter rel-ay 2|0. Thus, this allotter relay is permitted to restore vand prepare, at its armature 2|| and associated contact 2|2, a circuit for energizing the rel-ay corresponding to the relay |20, in the next succeedingidle secondary finder-selector link. The relay |55, at the same armature |51 and its associated contact |59, closes multiple ground to the control conducto-r 38. It is noted that the application of ground to the conductor 38 completes an obvious circuit for energizing the lower winding of the relay 360. This relay is of the polarized type such that it does not operate when its lower winding is energized but is rendered exceedingly fast to operate when its upper winding is subsequently energized. At its'armature |56 and associated contact |58', the relay |55 prepares a circuit extending by way of the `conductor 43 for energizing the slow-torelease relay 300, and a circuit extending by way of vthe conductor 43, the armature 364, and the armature 32| for energizing the impulse responsive means comprising the relays 3|0 and 320.

With the system in this condition the calling line is extended-through the primary finder switch I2 and the secondary nnder switch I3 to the idle selector switch I4, which switch is now in condition nto be responsive to impulses transmltted from the impulsing device at the calling substation A. By way or summarizing, it is pointed out that the allotter group No. 1 is now released and that the relays |00, |40, |30, |25, |50, |55 and |60'are in their respective operated positions, the remaining relays shown in Figs. 1, 3 andV 4 of the drawings being vin their respective restored positions. It is further pointed out that immediately upon the wipers of the primary finder switch |2 coming into contact with the bank contacts corresponding to the line |0, dial tone is returned over the loop to the calling subscriber. Thus, when the relay |25 operates in the sequence of operations thus far described, it completes, at'its armature |28, a circuit including the loop extending to the calling substation, the condenser 50 and the upper winding of the relay |50, for energizing the receiver at the calling substation with dial tone current.

As pointed out previously the control circuits for the-relays 3|0 and 320 are so connected and arranged that 'the relay 3|0 operates at the beginning of each odd numbered impulse, the relay 320 operates at 'the end of each odd numbered lmpulse, the relay 3|0'restores at the beginning of each even numbered impulse, and the relay 320 restores at the end of each even numbered impulsefall in response to the alternate operation and restoration of 'the line relay |50. Thus, at the beginning of the first impulse transmitted from the impulsing device at the calling subscribers substation, the bridge across the line conductors I0 and is interrupted at the calling substation A Vto open the operating circuit for the line relay |50 and permit this relay to restore. At its armature |5| and associated contact |53, this relay completes the previously prepared circuit extending by way of the operated armature |56 and the conductor 43, for energizing the relay 300 and the upper winding `of the relay 3|0,

causing both relays to operate.' When the relay 3|0 operates it closes, at `its armature r3|6, a shunt around the upper winding of the relay 320, this shunt extending from ground on the conductor 38 through the armature 3|6, the upper winding of the relay 320 and the armatures 32| and 364, over the conductor 43 and through the armatures |56 and |5| back to ground. At its armature 3| the relay 3|0 prepares a circuit for energizing its lower winding. At the end of the first impulse when the line relay |50 reoperates to interrupt at its armature |5| the original circuit for energizing the relay 3 0, the'above traced shunt is removed from around the upper winding of the relay 320, permitting thisrelay to energize in series with the upper winding of the relay 3|0. The relay 320 thereupon operates to prepare, at its armature 32| and associated contact 323, a circuit for energizing the lower windings of each of the relays 3|0 and 320.

At the beginning of the second impulse when ground is returned to the conductor 43 at the armature |5| of the line relay |50, the respective lower windings of the two relays 3|0 and 320 are energized. The lower Vwinding of the relay 3|0 is differentially wound with respect to the upper winding thereof and, consequently, causes this relay immediately to restore to interrupt, at its armature 3|6, the original circuit over which the upper winding of the relay 320 was energized. In order to render the relay 3|0 quick to restorethe lower winding thereof is so proportioned relative to the upper winding that the magnetic field produced thereby greatly predominates over .that

" 1 of the upper Winding. At its armature 3| |,-the

i' pulse when ground is again removed lfrom the conductor 43 at the armature |5|, the operating circuit including the lower Winding of the relay 32 8 is interrupted, permitting this relay to restore. Thus, the control circuits for vthe relays 3|0 and 320 are inthe condition which prevailed before the beginning of the first impulse. The same sequence of operations as that described above for the rst and second impulses occurs during each succeeding pair of impulses. From the -foregoing description, it will be seen that the condition of the relays 3|0 and 320 at the lend of a particular digit depends upon the number of kimpulses in the digit. Thus, if the number of impulses is odd, both of the relays 3|0 and 320 are operated,

Whereas if an even number of impulses comprises a particular digit, both of the relays are restored.

Returning now to the operations which occur in response to the impulses comprising the first digit, at the beginning of the first'impulse of this digit and simultaneously with the rst operation of the relay 3|0, the relay 300 operates. Due to its slow-to-release characteristic this relay remains operated during the remaining impulses of the digit. At its armature 30| and associated contact 302, this relay prepares a circuit for energizing the motor magnet 308, this circuit extending from battery at the magnet 308, through the winding of this magnet, the self-interrupting contacts associated with the armature 309, over the conductor 19, through the restored armature 356,

over the conductor 44, through the contact 302 and its associated armature 30|, over the conductor l5, through the vcam spring I6 and the associated lower spring 11, and over the conductor 18 to the armature 3|3. At its armature 30| and associated contact 302, the relay 300 opens a point in the circuit, traced hereinafter, for energizing the relay 350 from battery at the motor magnet 308. This prevents the relay 350 from operating as the test wipers 93 and 04 pass over contacts corresponding to idle trunks outgoing from the selector switch during the trunk group selection. At its armature 304, the relay 300 prepares an alternative circuit for holding the relay |30 operated, this circuit being held open at the armature 355 of the restored relay 350.

Since the relay 3|0 operates simultaneously with the Slow-to-release relay 300, it completes at its armature 3|3 the previously traced circuit for energizing the motor magnet 308. This magnet thereupon, in cooperation with its associated ratchet and pawl mechanism, starts to drive the wipers Sil-96, inclusive, and the camming element 8|. Almost immediately, however, the cam follower portion 82 of the spring 16 is lifted from the depression 83 onto the rst cam projection B4, thereby tointerrupt at the spring 11 the previously traced circuit for energizing the motor magnet 308.

With the camming element 8| in this position the cam follower portion 82 of the spring 16 rests just on the leading edge of the projection 84, and the wipers 9|96, inclusive, are in engagement with the first contact set in the contact bank. Simultaneously with the interruption of the previously traced circuit for energizing the motor magnet 308 an alternative circuit is prepared for this magnet, this circuit extending from ground at'the armature 3|2 by way of the contact 3| 4, the conductor 85, and the upper spring 86 associated with the cam spring 1B to the conductor 15 which leads, over the branch of the circuit described above, through the winding of the motor magnet 308 to battery. This circuit is maintained open until the beginning of the second impulse when the relay 3|0 restores. At the beginning of the second impulse when the relay 3|0 is de-energized, the armature 3|2 falls back and completes this alternative circuit, whereby the motor magnet 308 is again energized to operate buzzer fashion and, in cooperation with its associated ratchet and pawl mechanism, drives the wipers 9|-96, inclusive, and the camming element 8| over an arc including the first group of three contacts and corresponding to one group of six vconnector switches. This driving operation is interrupted when the follower portion 82 of the cam spring 16 falls from the trailing edge of the cam projection 84 into the leading edge of the second depression 83. When this occurs the alternative operating circuit for the motor magnet 308 is interrupted at the spring I6 and the associated spring 86 and the first traced circuit for this magnet is again prepared at the springs 16 and '11.

At the beginning of the third impulse when the relay 3|0 is again energized, the first-mentioned circuit for energizing the magnet 308 is recompleted at the armatures 3|2 and 3|3. The motor magnet 308 thereupon causes the wipers 9|-96, inclusive, and the camming element 8| to be rotated over a second group of contacts and into engagement with the first Contact set of the third group of Contact sets when the follower portion 82 of the spring 16 rides over the leading edge of the second projection 04V of the cammin'gzelement and the operating circuit for the magnet 308 is again opened at the springs 16 and 11.

This inode of operation continues for succeeding impulses, the wipers of the rotary switch 90 being driven over a complete group of contacts for each impulse and engaging at the end of each impulse the rst contact set of the succeeding group of contact sets. During the first impulse the wipers ill-96, inclusive, are` driven into engagement with the rst contact set of the rst group of contacts. In order to secure the abovedescribed operation it will be apparent that the width of the projections 84, 84', etc., and the depressions 83, 83', etc., must be so related to the number of contact sets of each group that at the end of each impulse the Wipers are standing on the rst contact set of the group of contact sets corresponding to the number of the impulse. Thus, the relation is such that at the end of the iirst impulse the wipers rest on the rst contact set of the rst group of contact sets, at the end of the second impulse the wipers rest on the first Contact set of the second group, and so on.

The speed at which the wipers 9|96, inclusive, must travel in order to cover an entire group of contacts during each impulse is determined by the relation between the number of contact sets constituting a group of contact sets and the rate of impuising. As pointed out previously, this speed is great and considerably in excess of the normal speeds of which standard rotary switches are capable when the arrangement requires a standard impulsing rate ranging from eight to twelve impulses p'er second and any considerable number of contact sets per group.

In accordance with one feature of the present invention the number of contact sets for each group and more particularly the number of lines terminating at the respective contact sets of each group are so related to the impulsing rate that the required speed of the switch wipers is well within the maximum speed attainable by standard commercial rotary switches. Thus, with the forty-eight connectorswitches of a four hundred line system divided into eight groups and each group requiring only three Contact sets in the contact banks of the respective selector switches, it will be seen that each wiper need travel over only three contacts to pass from one group of connector switches to the next succeeding group. With a standard impulsing rate of eight to twelve impulses per second this corresponds to a wiper speed of somethingV less than forty contacts per second which is well within the maximum operating speed attainable by standard switches.V In this connection it is pointed out that if the wipers, during any one impulse, travel from one group of contact sets to the first contact of the succeeding group before the impulse terminates, no harm is done since the cam spring 16 automatically opens the operating circuit for the motor magnet 308 immediately upon the wipers reaching the rst contact or the second group and independently of the duration of the impulse. If, however, the speed cf the rotary switch is insuiicient to insure the wipers traveling over an entire group of contact sets false routing of calls results. As pointed out previously, with the above-described arrangement of the connector switches a twenty-five point rotary switch having six sets may conveniently be used as the switch 90. Thus, with three contacts of each set in use for each group of six connector switches only twenty-four contacts will be required, the twenty-fthbeing left for the normal or home position of the wipers.

Returning again tothe operations which occur in response to the dialing of the rst digit, at the beginning of the first impulse of this digit and when the wipersV are stepped into engagement with the rst contact set of the first group, the oli-normal springs 311 are closed. The springs 311, upon closing, complete an obvious circuit for energizing the relay 330, which relay operates and, at its armature 334 and associated contact 336opens a further point in the circuit including the lower winding of the allotter relay 2|0. At this same armature and its associated contact 335, the relay 333 prepares a circuit including the conductors 31 and 32 for energizing the supervisory lamp No, 2, this circuit being held open at theY armature |84 of the battery reversing relay |80. The relay 330, at its armature 332 and the associated contact, alsoI opens a point in the circuit through the off-normal springs 3|1 for energizing the release magnet 338 of the minor switch 3|8. At its armature 333, the relay 330 prepares a circuit, traced hereinafter, for energizing the relay 350 from battery at the winding of the motor magnet 308. The relay 330 also interrupts, at its armature 33|, the application of dial tone to the lbop extending to the calling substation A.

Assuming that the called subscribers line such, for example, as the line 3 leading to the substation C, terminates in the bank contacts of the group of connector switches corresponding to the first group of contact sets of the rotary switch mechanism 90, the rst digit will comprise only a single impulse such that the wipers 9| to 96, inclusive, are each moved into engagement with the first contact of their respective. associated sets of bank contacts and both of the relays 3|0 and 320 are operated. Shortly after the first digit is concluded, the slow-to-release relay 300 restores to prepare, at its armature 30| and associated contact 303, a circuit, traced hereinafter, for energizing the lower winding of the busy relay |13.

With the system in this condition, the selector switch automatically operates to select an idle connector switch in the selected group. Thus, let it be assumed that the iirst four connectors of the selected first group are busy. When this condition prevails, ground is present on the first two contacts of each of the contact sets associated with the test wipers 93 and 94, so that, when the wiper 93 engages the first contact of its associated set, circuits are completed for energizing the wiper switching relay 340 and the motor magnet 308. The first of these'circuits extends from groundY on the wiper 93 through the restored armature 353 and the winding of the relay 340 to battery, and the second of these circuits extends from ground on the same wiper, through the contact 342, the restored armature 34|, the armatures 354, 333 and 358 and by way'of the conductor 18', the contact 301', the armature 332, the conductor 44, the armature 35B, the conductor 1S, the self-interrupting contacts associated with the armature 309, and the winding of the motor magnet 308 to battery. The relay 34il'is constructed and adjusted to be extremely quick acting so that it interrupts, at its armature 34| andassociated contact V342; the'above traced circuit for energizing the motor magnet 338 before sufficient time has elapsed to permit the latter'magnet, in cooperation with itsassociated ratchet and pawl mechanism, tov step the wipers 9| to96, inclusive, off of the first contact set. Since, however, under the conditions assumed, the second connector of this group is also busy, ground is present on the wiper 94 so that the previously traced circuit for energizing the motor magnet 30B is completed from ground on this wiper instead of from ground on the wiper 93 when the wiper switching relay 340 operates. Thus, the motor magnet operates, in response to its energization, to step the wipers 9| to 96, inclusive, into engagement with the second contact set of the rst group. During this stepping operation, the previously traced circuit for energizing the relay 340 is interrupted so that its armature 34| is restored to again engage the contact 342 leading to the wiper 93. Since, however, under the assumed conditions, the second and fourth connector switches of the group are also busy, the circuit for the last-mentioned relay is immediately recompleted upon engagement of the wiper 93 with its associated second contact. As a consequence, this relay operates to complete, at its armature 34| and associated contact 343, a circuit extending from ground at the wiper 94 for again energizing the motor magnet 308, thereby causing the wipers of the switch 90 to be stepped into engagement with the third or last contact set of the rst group of contact sets.

It will be noted that each time ground is placed on the testing armature 34| of the relay 340 by one or the other of the test wipers 93 or 94, a path for short circuiting the winding of the switching through relay 350 is completed, this path extending from ground on the armature noted by way of the restored armature 354, the Winding of the relay 35B and back to ground on the conductor 38. This short circuiting of the winding of the relay 350 prevents the relay from being energized over its operating circuit, traced hereinafter and extending from battery at the magnet 308, until such time as a trunk leading to an idle connector switch in the selected group of connector switches is found. In this connection it is pointed out that the battery potential applied to the test contacts of the sets associated respectively with the test wipers 93 and 94 from the line relays, corresponding to the relay 400, for the connector switch shown in Fig. 4, is so low as not to cause the operation of the relay 350 during the trunk group selecting function and when the wipers 93 and 94 pass over test contacts corresponding to idle connector switches. This potential causes current momentarily to flow by way of the armatures 34| and 354 through the winding of the relay 350 to ground, but the magnitude of the current is insufcient to cause operation of the relay. Thus, the relay 350 is prevented from operating to interfere with the trunk group selecting operations while these operations are occurring. It will also be noted that the winding of the wiper switching relay 340 is normally connected by way of the armature 353 to the test wiper 93. Accordingly, this relay is energized during the primary movement or group selecting operation of the switch each time the wiper 93 encounters the test contact terminating a control conductor leading to a busy connector switch. Such operation of the relay 340 is without effect in the operation of the system.

Under the conditions assumed, the connector switch i6 is idle so that battery from the line relay 490 is present on the directing wiper 93 instead of ground and, consequently, no circuits are completed for energizing the relay 340 and the motor magnet 308. The relay 340, therefore, remains in its restored position such that its armatures 345 and 348 are in engagement with their respective associated contacts 346 and 349 leading respectively, by way of the wipers 9| and 96, to the trunk conductors 410 and 412 of the connector switch |6. The engagement of the control or directing wiper 93 with the third contact of its associated contact set removes the short circuit from across the winding of the relay 350 permitting this winding to be energized over a circuit extending from ground on the control conductor 38 through the winding of the relay 350 and by way of the armatures 333 and 358, the conductor 18', the contact 301 and its associated armature 302, the conductor 44, the armature 356, the conductor 19, the self-interrupting contacts associated with the armature 309, and through the winding of the magnet 308 to battery. The relay 350 operates in response to its energization over the above traced circuit, and at its armature 351 and associated contact 358, completes a holding circuit for itself independently of the relay 300 and extending from battery at the winding of the motor magnet 308 by way of the self-interrupting contacts associated with the armature 309, the conductor 19, the armature 351 and associated contact 358, the armature 333 and the winding of the relay 350 to ground on the control conductor 38. Due to the resistance of the winding of the relay 350 the current through the winding of the motor magnet 308 is insufficient to cause this magnet to operate its self-interrupting contacts 399.

At its armature 354 and associated lower contact, the relay 350, upon operating, completes a circuit for energizing the line relay 400 of the connector switch, this circuit extending from ground on the control conductor 38 by way of the armature 354, the armature 34| and its associated contact 342, the wiper 93 and its associated third bank contact, the conductor 41| and the winding of the relay 400 to battery. It is noted that the application of ground to the control conductor 41| marks the seized connector switch as busy in the bank contacts of the other selector switches having bank contacts to which the trunk line of the seized connector switch extends. At its armature 355 and associated upper contact, the relay 350 removes ground from the conductor 39 thereby to interrupt the previously traced operating circuit for the relay |60 and the circuit holding the impulse responsive relays 3| 0 and 329 operated. All three of these relays restore, but without effect at this time. At its armature 355 and associated lower contact, the relay 350 prepares an alternative circuit for energizing the relay |69 and for holding the relays 3|0 and 320 operated during impulsing, the rst of these circuits being held open at and extending from ground on the armature 304 by way of the conductor 56, the armature 355, the conductor 39, and through the winding of the relay |60 to battery. The second circuit, namely that for the relays 3|0 and 320, is the same except that it branches at the conductor 39 to extend through the upper winding of the relay 320 by way of the armature 3|6.

The relay 350, upon operating, opens, at its armature 352, a point in the circuit for energizing the relay 340 and, at this same armature and the associated armature 353 prepares a locking circuit for the relay 340, the latter circuit being held open at the armature 344. At its armature 356, the relay 350 opens a point in the previously traced circuit leading from the cam spring 16 for energizing the motor magnet 308. At its ar- CII matures 35| and 359, respectively, the relay 350 extends the trunk conductors 410 and 412 of the connector switch I6 to the armatures 36| and 365 of the restored relay 360 further to prepare the connection to the called line. The relay 350, upon operating, also opens, at its armature 359', a point in the circuit for energizing the busy relay |10, this circuit being traced in detail hereinafter.

Before proceeding with the description of the operations which occur upon the dialing of the second and third digits at the calling substation and in order to complete the description, it will be assumed that the fifth connector switch of the first group, namely the connector switch I6, is busy and that only the sixth or last connector switch I1 of this group is idle. When this condition prevails, the relay 340 is energized in the manner noted above immediately upon the wiper 93 coming into engagement with its associated third contact. This relay, upon operating, prepares, at its armature 344, a locking circuit for itself and, at its armatures 34|, 345 and 348 switches the trunk conductors of the selector switch I4 from the trunk conductors 410, 41| and 412 leading to the connector switch I6 to the trunk conductors 88, 89 and 81, respectively, leading to the connector switch I1. Since the last-mentioned connector switch is idle, battery is present on the control conductor 89 so that the short circuit is removed from around the winding of the relay 350 and this relay is energized from battery at the magnet 308 over the exact circuit traced above. The relay 350, upon operating, performs the same functions as are described above in connection with the seizing of the connector switch I 6, and, in addition, completes the previously prepared locking circuit for the relay 340. This circuit extends from ground on the control conductor 38- by way of the armatures 344, 352 and 353, and through the winding of the relay 340 to battery. As a result, the relay 340 is maintained in its operated position so that the desired connection is extended by way of the connector switch I1 rather than by way of the connector switch I6.

Provision is made whereby, in the event all of the connector switches of a selected group are busy and following the testing of the lines corresponding to the connector switches included in the selected group, busy tone is returned to the calling subscriber. Thus, in the event all six of the lines corresponding to the connector switches of the iirst group are tested and found busy, the relay 359 fails to operate. Hence, the rotary portion of the mechanism 90 is actuated by the motor magnet 3538 and its associated ratchet and pawl mechanism, until the follower portion 82 of the spring 16 leaves the trailing edge of the projection 84 and drops into the depression 83 to make contact between the springs 1S and 11. It will be remembered that the relays 3 I0 and 320 are in their respective operated positions so that when the relay 300 assumes its restored position shortly following the end of the first digit, a circuit is completed for energizing the lower winding of the busy relay |10, this circuit extending from ground at the armature 3I2, through the armature 3 I3, over the conductor 18, through the springs and 11, over the conductor 15, through the armature 30| and its associated contact 303, over the conductor 41, through the armature |21, over the conductor 58, and through the lower winding of the relay |10 to battery. In response to the energization of its lower winding,

the relay |10 operates and, at its armature |1I, completes an obvious locking circuit for itself extending from ground on the control conductor 38. This circuit maintains the busy relay operated until the connection as thus partially established is cleared out at the calling substation A. At its armature I 14, the busy relay |10 applies busy tone current to the calling loop which is transmitted through the condensers 49 and 50 and the receiver at the calling subscribers substation to inform the party thereat that a connection can not be completed to the called subscribers line.

In connection with the above described circuits for the busy relay |10, it is pointed out that the restoration of the impulse responsive relays 3|0 and 320 in response to the operation of the relay 350, when an idle trunk is found in -a group corresponding to an odd number of impulses causes the preparation of an alternative circuit for energizing the relay |10, this circuit extending from ground at the armature 3|2 by way of the contact 3|4, and the conductor 85 to the conductor 15. Since, however, the armature 359 of the relay 350 is pulled up before the armature 302 of the relay 300 falls back, this circuit is not completed and the busy relay is not energized.

By way of completing the description it is pointed out that the busy relay is energized to perform the functions noted above in all cases where all of the trunks associated with any selected one of the groups of bank contacts of the selector switch I4 are busy. If all of the group of trunks associated with a group of contacts corresponding to any odd number of impulses are found busy the sequence of operations resulting in the operation of the busy relay |10 are exactly the same as that described above for the trunks associated with the rlrst group of contacts. If, however, the all busy condition exists in .a selected group of trunks associated with a group of contacts corresponding to a digit comprising .an even number of impulses the method by which the busy relay is energized is slightly different. In this regard it will be remembered that the impulse responsive relays 3 I 0 and 320 are both restored at the end of any even impulse and that the follower portion 82 of the spring 15 rides in one of the depressions 83, 83', etc., during the testing of the trunks of a selected group of trunks corresponding to any even impulse.

During the testing of a group of trunks corresponding to any even impulse the springs 16 and 11 are in engagement and the above traced circuit for energizing the lower winding of the busy relay |10 is held open at the restored armature 3|3 of the impulse responsive relay 3|0. If an idle trunk in the selected group of trunks is found the follower portion 82 of the spring 'I6 does not leave the depression in which it rides and, consequently, the lower winding of the busy relay |10 remains de-energized. When, however, all o f the trunks of the selected group are busy the rotary portion of the mechanism 80 is driven until the follower portion 82 of the spring 1B leaves the depression corresponding to the selected group of trunks and rides over the leading edge of the next succeeding cam projection. When this occurs the springs 10 and 80 engage and a different circuit is completed for energizing the lower winding of the relay |10, this circuit extending from ground on the restored armature 3I2, by way of the contact 3|4, the conductor 85, the restored armature 359', the springs 86 and 16, the conductor 15, the restored armature 39! and associated lower contact 303, the conductor 41, the armature |21, the conductor 53 and the lower winding of the relay |10, to battery. The busy relay thereupon operates, locks up, and causes busy tone to be transmitted to the calling party just as in the case described for an all busy condition of the trunks associated with the first group of contacts.

Continuing now with the sequence of operations which occur following the seizure of the connector switch I6, when the relay 490 operates as described above it prepares a locking circuit extending from ground at the armature 40| for the restored relays 440, 450 and 460. It will be recalled that the circuit for energizing the motor magnet 308 is interrupted at the armature 356 upon the operation of the relay 350 so that the impulses comprising further digits dialed at the calling telephone A have no eiect upon this magnet. With the system in this condition, the control relays associated with the connector switch I6 are prepared to be responsive to further operation of the slow-to-release relay 300 and the impulse responsive relays 3|!) and 320. The operation of these relays during further impulsing is exactly the same as that described above; i. e., the relay 3||l operates at the beginning of each odd impulse of each digit, the relay 320 operates at the end of each odd impulse, the relay 3|@ restores at the beginning of each even impulse and the relay 320 restores at the end of each even impulse. At the beginning of the first impulse of the second digit when the relays 300 and 3|0 operate, circuits are completed for causing the operation of the relay |60 in the selector switch |4 and the relays 4|0 and 420 in the seized connector switch I6. The first of these circuits extends from ground on the operated armature 304 by way of the conductor 56, the operated armature 355, the conductor 39 and the winding of the relay |60 to battery. The second of these circuits, namely that for the relay' 4I0, extends from ground through the winding of the relay 4|!! by way of the conductor 458, the contact 442 and associated armature 44|, the conductor 451, the contact 462 and associated armature 46|, the trunk conductor 410, the wiper 9| and its associated third bank contact, the contact 346 and its associated armature 345, the armatures 35| and 36|, the conductor 3|, the restored armature |11, the conductor 35, the armature 305 and associated lower contact 306, the conductor 33, and through the armature |13 and the resistor 80 to battery. The circuit for energizing the relay 420 extends from ground at the operated armature 3|5 by way of the conductor 42, the contact |63 and its associated operated armature |6|, the conductor 4|, the armatures 365 and 359, the armature 348 and associated contact 349', the wiper 96 and its associated third bank contact, the trunk conductor 412, the armature 461 and associated contact 469, the conductor 4|S and the winding of the relay 42.6, to battery. Since the above-traced circuit for the relay 4|0 is maintained completed by the slow-to-release relay 300, it stays in its operated position throughout the impulses comprising the second digit. The relay 4|0, at its armature 4| I, prepares a circuit for the motor magnet 431, which circuit is completed when the relay 420 operates, and interrupts at its armature 4| a point in the release circuit for the motor magnet 431. The first mentioned circuit for the motor magnet 431, which is completed upon the operation of the relay 420, extends from ground at the armature 424 by way of the armature 425, the conductor 428, the wiper 64 and the last or twenty-fifth contact of the associated set of contacts, the conductor 421, the restored armature 456, the conductor 419, the armature 4|l, the conductor 409, the self-interrupting contacts 438 and through the winding of the motor magnet 431 to battery. In response to its energization, the motor magnet 431 starts to operate buzzer fashion but, upon taking a single step, the lower end of the wiper 64 leaves its associated twentyfifth contact and interrupts the above-traced operating circuit for the motor magnet. When the wipers of the switch mechanism 63 take their rst step, the off-normal springs 413 are closed to prepare a circuit for energizing the slow-torelease relay 450 and an alternative circuit for energizing the motor magnet 431 during the release of the switch I6. In this position of the switch, the upper end of the wiper 64 is in engagement with the first contact of the group of three contacts indicated at 13 and the lower ends of other wipers are in engagement with the respective twenty-fifth contact of the other contact sets included in the switch. Hence, the wipers are just ready to be stepped onto the iirst contact set of the group of contact sets corresponding to the iirst group of lines included in the plurality of lines to which the switch I6 has access.

At the beginning of the second impulse of the second digit when the relay 3|0 restores in the manner described previously, the above-traced circuit for the relay 420 is interrupted at the armature 3|5, causing this relay to restore. Upon falling back, the relay 420 completes, at its armature 424 and associated contact 426, an alternative circuit for energizing the motor magnet 431, this circuit being exactly the same as that just described with the exception that the wiper 64 is connected to ground at the armature 424 and associated contact 426 by way of the rst contact of the contact group 13 and the conductor 429, rather than by way of the twentyfifth contact and the conductor 423. The motor magnet thereupon operates buzzer fashion and in cooperation with its associated ratchet and pawl mechanism drives the wipers 64 to 10, inclusive, until the wiper 64 leaves the third or last contact of the irst contact group 13 and stands in engagement with the first contact of the second contact group indicated at 14. When this occurs the alternative circuit for the motor magnet 431 is interrupted. It is pointed out that the wiper 64 is so arranged relative to the other wipers 65-10 that when it stands on the first Contact of its associated set of contacts, each of the remaining wipers stands on the twenty-fifth contact of its associated set of contacts. As a consequence, if the second digit comprises one impulse the wipers 65-10, inclusive, are in a position such that an additional step will cause them to engage the first contact set of the first group of contact sets. In the event the called line terminates at a contact set in a group of contact sets other than the first and corresponding to a digit having more than two impulses, the motor magnet 431 is energized each time the relay 420 operates and restores and drives the wipers 64 to 10, inclusive, over a complete group of contacts. The number of the group of contacts which the wipers traverse during any given impulse is in any instance one less than the number of the impulse in the digit, i. e., during the second impulse the wipers 64 to 10, inclusive,

-response to the restoration traverse the first group of contact sets, during the third impulse the wipers traverse the second group oi contact sets and so on. In this manner the wipers always stand in engagement with the last contact set of the group of contact sets having a number one less than the number of the impulse. In` the present assumed case, wherein the called line C terminates at the third or last contact set of the rst group of contact sets, a single impulse will constitute the second digit so that at the conclusion of the digit the wiper 64 stands on the iirst contact of its associated level and the wipers 64 to 10, inclusive, are ready to be stepped onto the respective rst contacts of their respective associated levels.

From the foregoing description it will be apparent that in the connector switch i6 as well as in the selector switch |4 the number of contact sets in each group of contact sets are so related to the impulsing rate that the required speed of the switch wipers is well below the maximum speed attainable by standard commercial rotary switches. Thus with each of the groups of contact sets including only three contact sets at which six lines terminate and with a standard impulsing rate ranging from eight to twelve impulses per second the required speed at which the wipers must travel is something less than forty points or contact sets per second.

At the conclusion of the second digit and in of the relay 300, the relays |60, 3|0, 320, 4|0 and 420 restore. When the relay 4| 0 falls back, it completes the previously prepared circuit for energizing the relay 450, this circuit extending from ground armature 4|3 by way of the contact'4l4, the conductor 406, the oir-normal springs 414, the conductor 401, the armatures 45| and 465, and through the winding of the relay 450 to battery. The last-mentioned relay upon operating completes, at its armature 45|, a locking circuit for itself, which circuit extends from ground at the operated armature 40| by way of the contact 402, the conductor 441, the armatures 45|, 45| and 465 and through the winding of the relay 450 to battery. At its armature 456, the relay 450 interrupts the previously traced operating circuit extending by way of the self-interrupting contacts 438, for the motor magnet 431. At its armature 452 and associated contact 453, the relay 450 prepares an alternative circuit for energizing the motor magnet 431 independently of the self-interrupting contact 438 and in accordance with the operation of the relay 420 during the impulses of the third digit, which circuit is completed only when both of the relays 4|!) and 420 are operated'. This circuit extends from battery through the winding of the magnet 431 and by way of the conductor 4| 6, the contact 422 and associated armature 42|, the conductor 408, the contact 453 and associated operated armature 452, the conductor 405, and the armature 4|2 to ground at the armature 4|3. The relay 450, upon operating, also prepares, at its armature 455, a circuit for energizing the upper winding of the relay 440, this circuit being completed at the armature 4|5 or the relay 4 I0 when the latter relay again operates.

At the beginning of the iirst impulse of the third or units digit, when the relays |50, 300 and 3iil again operate, the previously traced circuits for energizing the relays 4|0 and 420 are again completed to cause the operation thereof. At its armature 4|5, the relay 4|!) completes the previously prepared circuit for energizing the upper at the winding of the relay 440, this circuit extending from ground at the armature 469 by way of the armature 455, the conductor 439, the armature 4|5, the conductor 446 and the upper winding of the relay 440 to battery. The last-mentioned relay is so constructed that only its armature 444 operates in response to the energization of its upper winding and this armature, upon operating, closes the X contacts associated therewith to short-circuit the lower winding of the relay, the path comprising this short circuit starting from ground at the armature 469 and extending over the above traced circuit for energizing the upper winding of the relay, through the lower winding thereof, the armature 444 and the associated X contacts and ending at ground on the grounded conductor 441. As a consequence, the armatures 44| and 445 are not operated at this time. The relays 4|0 and 420, upon operating, also complete the previously traced circuit for` energizing the motor magnet 431, independently of the self-interrupting contacts 438. At the beginning of the second impulse, when the relay 3|!) restores to cause the restoration of the relay 420, this circuit for the motor magnet 431 is interrupted, at the armature 42| and associated contact 422, whereby the wipers 65 to 10, inclusive, are stepped one step or into engagement with the rst contact set of the rst group of contact sets. Simultaneously, a circuit is completed for energizing the wiper switching relay 430, this circuit extending from ground at the armature 4|3 by way of the operated armature 4|2, the conductor 405, the operated armature 452 and associated contact 453, the conductor 408, the restored armature 42| and associated contact 423, the conductor 4|1 and through the winding of the relay 430 to battery. The relay 430, upon operating, obviously operates its armatures 43|, 432, and 434 into engagement with the contacts to which are connected the conductors of the line terminated at the respective first contacts of the contact sets associated with the wipers 66, 68 and 69. At its armature 433, the relay 430 prepares an obvious locking circuit for itself, which circuit is held open at the operated armature 4 I3 of the relay 410.

At the beginning of the third impulse, when the relay 3|0 again operates to complete the circuit for causing the operation of the relay 420, the previously traced circuit for the motor magnet 431 is again completed and the circuit holding the wiper switching relay 430 operated is interrupted, permitting it to restore. At the beginning of the fourth impulse, when the relays 3 0 and 420 again restore, in the order named, the ratchet and pawl mechanism associated with the motor magnet 431 steps the wipers 65 to 10, inclusive, into engagement with the second contact set of the iirst group of contact sets. During the fth and sixth irnpulses the motor magnet is again energized and de-energized to cause the wipers 65-10, inclusive, to be stepped into engagement with the third set of contacts in the rst group of contact sets. With the wipers in this position, the connector switch I6 has access to either the subscribers line 2 or the subscribers line 3, depending upon the condition of the wiper switching relay 430. It will be seen that if this relay is de-energized the armatures 43| and 434 of the relay are connected to the respective line conductors of the line 2 leading to the substation B, whereas, if this relay is energized, the armatures noted are connected to the respective line conductors of the subscribers .line 3 leading to the called substation C.

The condition of the wiper switching relay 430 at the end oi the third digit depends upon the number of impulses constituting this digit. More specifically, if the number of impulses in the digit is odd, the relay 430 remains de-energized at the conclusion of the digit but if the number of impulses of the digit is even, the relay is energized and locked in its operated position. Thus, assume it is desired to establish a connection to the substation B instead of the substation C. In this case the third digit dialed must necessarily be 5, or odd. At the conclusion of this digit, the relays `4|0 and 420 are in their respective operated positions. With the relay 426 operated, the previously traced operating circuit for the wiper switching relay 439 is open at the armature 42|. Shortly following the end of the fifth or iinal impulse of the units digit the relay 305 restores and interrupts, at its armature 305 and associated contact 396, the previously traced operating circuit for the relay 4|9. Simultaneously, the relay 309, at its armature 364, interrupts the circuit holding the relays |60, 3|0 and 320 operated. The relay 4|0 restores immediately following the restoration of the relay 390, and interrupts, at its armatures 4|2 and 4|3, the previously traced circuit for energizing the relay 436. Simultaneously with the restoration of the relay 4|9, the relay 3|!) restores to interrupt the previously traced operating circuit for the relay 420, which latter relay falls back shortly after the restoration of the relay 4||l to prepare, at its armature 42|, the circuit for energizing the relay 430. By the time the armature 42| engages its associated contact 423, however, the armature 4|2 of the relay 4I0 has restored to normal and, hence, the energization of the relay 439 is prevented. Thus, this latter relay does not operate and the armatures 43| and 434 are connected by way of the wipers and 15 to the line conductors leading to the substation B.

In the present case wherein a connection is desired with the substation C rather than the substation B, the third digit dialed at the calling substation will necessarily comprise six impulses instead of five so that, at the end of the digit, the impulse responsive relay 3|9 is restored and the relay 420 is in the same condition. As a consequence, the previously traced circuit for energizing the relay 430 is completed at the armature 42| and its associated contact 423, the relay 439 is in its operated position and the locking circuit for this relay is prepared at the armature 433. Hence, at the end of the digit when the relay 399 falls back to cause the restoration of the relay 4| 0, this locking circuit is completed at the armature 4|3 and its associated contact 4|4 simultaneously with the interruption of its original operation circuit at the armatures 4|2 and 4|3. Accordingly, the relay 430 is locked in its operated position and the armatures 43|, 432 and 434 are connected by way of the wipers 66, 68 and 69 to the line conductors of the line 3 leading to the desired or called substation C. It is pointed out that the relay 43|! remains locked up until the connector switch I6 is seized during the establishing of a subsequent connection.

Returning again to the operations which occur at the conclusion of the third or units digit, the relay 4|9 upon restoring, opens, at its armature 4|5, the shunt around the lower winding of the relay 449, permitting the last mentioned relay fully to operate. Operation of the relay 449 causes a path to be prepared, at the armature 445, for applying ground to the control conductor 459 from the grounded conductor 441. The operation of the apparatus from this point on depends upon the condition of the called line 3.

If the called line 3 is idle, battery from the line relay associated therewith is present on the wiper 68, whereby the relay 449, upon operating, completes a circuit for energizing the relay 460 and the upper winding of the relay 369 in series, this circuit extending from battery at the line relay associated with the line 3, by way of the wiper 69, the control conductor 459, the lower winding of the relay 460, the conductor 449, the contact 443 and its associated operated armature 44|, the conductor 451, the contact 452 and its associated armature 46|, the conductor 41B, the wiper 9| and its associated third bank contact, the armatures 345, 35| and 36|, the conductor 3|, the restored armature |11 and its associated upper contact, the conductor 35, the restored armature 395 and its associated contact 361, the conductor 34, the restored armature |66 and its associated contact |68, the restored armature |12, the conductor 36, and through the upper winding of the relay 360 to ground. Y

The relay 46B operates in response toits energization over the above traced circuit and completes, at its armature 464, a holding circuit extending from battery through the upper winding of the relay to the grounded conductor 448. At its armature 469', the relay 46D opens a'further point in the previously traced path for short circuiting the lower winding of the relay 446 and prevents the application of ground to the lower trunk conductor 412. At its armatures 46| and 461 and their respective associated contacts 463 and 468, the relay 460 prepares points in the loop extending to the called substation and, at these same armatures and their respective associated contacts 462 and 469, interrupts points in the respective previously traced circuits for energizing the relays 4|9, 420 and 46D. At its armature 466, the relay 460 completes an obvious path for applying ground to the control conductor 459, thereby to mark the called line as busy in the bank contacts of the connector and nder switches to which the called line 3 extends. At its armature 465, the relay 466 interrupts the circuit holding the relay `45|) operated, permitting this relay to restore and complete, at its armature 455, a further point in the loop extending to the called substation. The relay 450, upon falling back, at its armature 452 and associated contact 454, prepares a further point in the circuit for causing the motor magnet 431 to return the lwipers 64 to 19, inclusive, to their normal positions when the connection is cleared out and the switch I6 is released. At its armature 45|, the relay V45!) opens a further point in its locking circuit and, at its armature 456` it pren pares the previously traced circuit extending by Way of the wiper 64 for energizing the motor magnet 431 in accordance with the impulses of the rst digit to which the switch I6 is responsive. With the connector switch |6 in this condition it will be seen that the line conductors of the called line are extended back to the trunk conductors of the selector switch and that the loopl between. the calling and called lines is complete except for the open points existing at the restored armatures 36| and 365 of the relay 366 and the restored armatures 312 and 316 of the relay 310.

When the relay 369 operates simultaneously with the operation of the relay 469, it stays operated by virtue of the energized condition of its lower winding. Upon operating, it short-circuits its upper winding at the armature 363, thereby to render itself slightly slow to release. At its armatures 361 and 365, this relay prepares a Ifurther point in the loop extending between the calling and called lines and, at its armature 362, it completes a path for the transmission of ring back tone current by way of the condenser 319 to the loop extending to the callingsub-scribers substation. The relay 360, upon operating, also interrupts, at its armatures 3131 and 365, further points in the respective circuits for energizing the relays 410 and 420. At its armature 364 and associated lower Contact, the relay 360 opens the circuit leadn ing to the impulse responsive relays 310 and 323 and, at this same armature and its associated upper contact, this relay prepares a.circuit for energizing the motor magnet 339 to cause the step-by-step operation of the minor switch 318.

The last-mentioned switch is` for the purpose of selectively applying in `a well-known manner ringing current of any one of five different free quencies to the loop extending to the called line, whereby the signal device at any one of ve diierent substations connected across the line may be caused to operate to the exclusion of all of the other similar devices. When the relay 360 operates as above described, it conditions the minor switch 318 to be responsive to the dialing of the fourth or final digit. At the beginning of the iirst impulse of this digit, a circuit is completed for energizing the relay 309 and the motor magnet 339 in parallel, whereupon the relay 3110 operates to open at its armature 391 a point in the paths for applying ringing current and ringback tone current to the loops extending, respectively, to the called and calling substations. This is necessary to prevent current of the various frequencies F1, F2, etc., from being transmitted out over the called line during the stepping operation of the minor switch 318. VThe abovenoted circuit for the motor magnet 339 extends from ground at the armature 1'51, by way of the contact 153, the operated armature 156, the contact 158', the conductor 43, the armature 364 and its associated upper contact, the conductor 329 and through the winding of the magnet 339 to ,Y battery. The motor magnet 339 is alternately energized and de-energized in accordance with the impulses of the final digit and, in cooperation with its associated ratchet and paWl mechanism, steps the wiper 326 of the switch 318 to a position corresponding to the number of impulses of the digit dialed. At the conclusion of this digit, the wiper of the switch stands in engagement with a contact leading to an alternating current generator having an output frequency the same as that to which the signal device of the called subscribers substation on the party line is responsive. Assuming the signal device of the called substation D is responsive to current of the frequency the same as that of the generator connected to the second contact of the group of contacts, the final digit dialed will be 2 so that at the conclusion of the digit the wiper 326 stands on its associated second contact of the contact set 324. It is noted here that when the wip-er 326 takes its rst step, the off-normal springs 311 are closed to prepare a circuit -for operating the release magnet 338, this circuit being held open at the operated armature 332 of the relay 331i.

With the system in this condition and when the relay 3D1! restores shortly following the end of the fourth or final digit, ringing current is transmitted over the conductors 336 and 328, the lower winding of the ring cut-oli relay 310 and the conductor 361 to the loop extending to the called substation D causing the signal device thereat to operate .and inform the called party that he is being called. Ring-back tone current is transmitted back over the calling loop to the calling subscribers substation to inform the calling party that the called line is idle.

When the called party answers by lifting his receiver from its hook, a circuit is completed for energizing the lower winding of the ring cut-off relay319, this circuit extending from battery on the wiper 326 of the minor switch 318', over the conductor 328, through the lower winding of the relay 310, over the upper side of the loop extending to the called subscribers substation D including the conductor 413, through the bridge at the called substation, back over the lower line conductor of the loop, and the conductor 365 to ground. The relay 3T3 operates in response to the energization of its lower winding and completes, at its armature 374, a locking circuit for itself extending from ground on the control conductor 38, through the armature 3M and the upper winding of the relay to battery. At its armatures 3'12 and 316, this relay interrupts the application of ringing current to the loop extending to the called substation, the application of ring back tone current to the loop extending to the calling substation and completes a talking loop between the calling and called parties. At its armature 315, this relay interrupts a point in the operating circuit for the relay 1'15 and, at its armature 371, it prepares a point in the circuit for energizing the supervisory lamp No. 1. In response to the completion of the talking loop in the above-described manner, a circuit is completed including this loop for causing the operation of the battery reversing relay 189 which relay operates and, at its armatures 181 and 183, reverses battery back over the loop extending to the calling subscribers substation. At its armature 184, the relay 188 prepares a point in the circuit for energizing the supervisory lamp No. 2, this circuit being held open at the armature 15'1 and associated contact 158 of the hold relay 155. At its armature 182, the battery reversing relay 180 opens a point in the circuit for energizing the supervisory lamp No. l and closes multiple ground to the control conductor 33. With the system in this condition, a talking connection is established between the calling and called parties, which connection is maintained until both of the parties hang up.

Before describing the release of the connection as thus established, and in order to complete the description of the operation of the system, it will be assumed that, at the time the connector switch i6 steps its wipers into engagement with the contacts at which the line conductors of the called line 3 terminate, this line is busy instead of idle. When this condition prevails, ground is present on the control wiper S8 and the control conductor 459 and, consequently, a circuit is completed for causing the operation of the busy relay 1'16. This circuit extends from ground on the conductor 459 through the lower winding of the relay 46B, by

way of the conductor 443, the contact 443 and associated operated armature 441, the conductor 451, the armature 431 and associated Contact 4152, the conductor 4119, the wiper 91, the armatures 345, 351 and 33t, the conductor 31, the restored armature 1'1'1, the conductor 35, the armature 335 and associated contact 307, the conductor 34, the operated armature 63 and associated contact 161, the conductor 5l, and through the upper winding of the relay 170 to battery.

It will be understood that this circuit is completed immediately upon the falling back of the armatures associated with the relay 4|0 and the consequent operation of the relay 440, which operations occur before the restoration of the slow-to-release relay |60. It is pointed out that the current which flows over the above-traced circuit is of the wrong polarity to cause the operation of the relay 460, this latter relay remaining in its restored condition. Immediately upon the completion of the above-traced circuit, the relay operates to complete, at its armature |1I, a locking circuit for itself, this circuit eX- tending from ground on the control conductor 38, over the conductor 55, and through the lower winding of the relay |10 to battery.

The busy relay |10, upon operating, applies at its armature |14, busy tone to the loop extending to the calling subscribers substation, thereby to indicate to this party the busy condition of the called line. At its armature |12, the relay |10 opens a point in the circuit for energizing the upper winding of the relay 360 and, at its armature |13, it applies ground to the conductor 33. The system remains in this condition until the connection is cleared out at the calling subscribers substation.

In the event the called line is found busy and busy tone is returned to the calling subscriber, this subscriber may release the operated switch train, by hanging up his receiver to open a point in the loop comprising a portion of the circuit holding the line relay |50 operated. This relay, upon restoring, interrupts, at its armature |5| and associated contact |52, the operating circuit for the hold relay |55 and simultaneously completes, at this same armature and its associated Contact |53, the operating circuit for the relay 300. The latter relay operates and, at its armature 304, completes the operating circuit for the relay |60, which latter relay also pulls up. The operation of the remaining armatures of the relay 303 is without effect. Shortly following the restoration of the line relay |50, the hold relay |55 restores to interrupt the circuit for the relay 300 and causes the sequential restoration of this relay and the relay |60. With the relays |55 and 30 in their restored positions, ground is removed from the control conductor 38 so that holding circuits for the relays |25, 340, 350 and 400 are interrupted. As a consequence, all of these relays restore.

The relay 350, upon falling back, completes, at its armature 356, a circuit for energizing the motor magnet 308, this circuit extending from ground at the armature |5| by way of the con tact |53, the armature |56 and associated con tact |58', the conductor 44', the armature 33|', the conductor 44, the armature 356, the conductor 10, the self-interrupting contacts 309, and through the winding of the magnet 30B to battery. This magnet thereupon, in cooperation with its associated ratchet and pawl mechanism steps the wipers 9| to 93, inclusive, to their respective normal positions when the off-normal contacts 311 are opened to interrupt the operating circuit of the release relay 330. This relay 333, upon restoring, interrupts, at its armature 33|', the previously traced circuit for energizing the motor magnet 308 with the result that the rotary portion of the switch mechanism 98 comes to rest in its normal position such that the follower portion 82 of the spring 16 just engages the lea-ding edge of the cam projection 84. When the rotary portion of the switch mechanism 90 is returned to its normal position, the elements of the selector switch |4 are all in the condition which prevailed at the outset and before the selector switch was seized.

When the relay |25 restores in response to the removal of ground potential from the control conductor 38, it interrupts, at its armature |26, the previously traced circuit holding the relays |30, |40 and the line relay |00 operated, per-- mitting these relays to restore. Thus, the control equipment associated with the primary and secondary nder switches I2 and i3, respectively, is returned to normal.

The release of the connector switch I6, under the conditions stated, is initiated when the relay 400 restores to interrupt, at its armature 40| and associated contact 402, the holding circuit for the relay 440. When the armature 40| falls back to engage the contact 403 it completes a circuit for energizing the motor magnet 431 by way of the self-interrupting contacts 438, this circuit extending from ground at the armature 40| by way of the contact 403, the conductor 404, the off-normal springs 415, the armature 452 and associated Contact 454, the conductor 409, through the self-interrupting contacts 438 and the winding of the magnet 431 to battery. This magnet thereupon operates buzzer fashion and in conjunction with its associate-d ratchet and pawl mechanism and drives the wipers 64 to 'I 0, inclusive, to their respective normal or home positions at which time the oir-normal springs 414 and 415 are opened. When the springs 415 are opened the above-traced circuit for energizing the magnet 431 is interrupted. The normal position of the Wipers 64-10, inclusive, it will be understood, are attained when the lower half of the wiper 84 rests on the twenty-fifth contact of its associated contact level. When this switch is returned to normal, the elements of the connector switch |6 are in the condition which prevailed before this switch was seized and the switch is in condition for further use.

In the event a talking connection is established between the calling subscribers substation and the desired called substation and both of the parties involved hang up, the operations which occur to release the connection are substantially similar to those described above. Under the condition stated, however, the switch train is held operated so long as either party remains on the connection. In this connection it will be seen that if only the calling party hangs up, the battery reversing relay |80, by maintaining ground on the control conductor 38 at its armature |82, holds the primary and secondary nder switches I2 and |3, the selector switch |4 and the connector switch I6 operated until the connection is cleared out at the called substation. Thus, the only operations which occur following the interruption of the loop at the calling substation are the restoration of the line relay |50, followed by the Operation of the relays |60 and 300, the restoration of the hold relay |55, and the subsequent restoration of the relays |60 and 300. When the connection is cleared out at the called substation to interrupt the circuit holding the battery reversing relay |80 operated, ground potential is removed from the control conductor 38 and the elements of the primary and secondary finder switches, the selector switch I4, and the connector switch |6 restore in the exact manner described above in connection with the clearing out of a connection established to a busy line. It is pointed out, however, that, when the release

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