US2171661A - Telephone system - Google Patents

Description

Sept 193%. H, P. MAHONEY TELEPHONE SYSTEM Original Filed June 11, 1937 5 Sheecs-Sheet A T'l ORNEYS p 1939. H. P. MAHONEY ET AL 2,171,661

TELEPHONE SYSTEM Original Filed June 11, 1937 5 Sheets-Sheet 5 CONNECTOR SWITCH MECHANISM 43 FIG. 5

PRIMARY FINDER SWITCH MECHANISM O INVENTORS, HARRY F? MAHONEY JOHN WICHS ATTORNEY5.

Patented Sept. 5, 1939 TELEPHONE SYSTEM Harry P. Mahoney and John Wicks, Oak Park,

Ill., assignors to Associated Electric Laboratories, Inc., Chicago, 111., a. corporation of Delaware Application June 11, 1937, Serial No. 147,644

Renewed March 2, 1939 36 Claims.

The present invention relates to signalling systems and more particularly to automatic switching units for use in setting up connections between the various lines of an automatic telephone system.

One of the best known methods by which connections are established between the various lines of an automatic telephone system is that of routing each connection by way of automatically operating traflic concentration switches and two or more tandem connected impulse responsive numerical switches. Various arrangements and modifications of the switching apparatus are known to the art. Irrespective of the arrangement, however, economy of system construction and service requirements dictate that; each subsc'ribers line shall have access to or be accessible to a group of trafiic concentration switches, each trafiic concentration switch shall be accessible to or have access to a group of lines, each final numerical or connector switch shall have access to a group of lines, and each line shall be accessible to a group of final numerical or connector switches. Such an arrangement necessarily requires that the conductors of each line be multipled in the bank contacts of a number of switches. Thus, in those arrangements wherein the so-called decimal system of selection is utilized, the plurality of intermediate selector switches corresponding to each digit are arranged in groups with the bank contacts of each switch of each group multipled to the corresponding bank contacts of the other switches included in the same group. Similarly, the final numerical or connector switches are arranged in groups with each switch of each group having its bank contacts multipled to the corresponding contacts included in the banks of the other switches in the same group. Such bank contact multiples are costly to construct, and particularly so when of large size; i. e., when the multiple includes a large number of lines multipled between the bank contacts of a large group of switches. The alternative, in regard to the use of large multiples, is to decrease the number of lines served by a particular group of switches with a corresponding reduction in the size of the swtches and a corresponding reduction in the size of the multiples involved. This alternative, however, entails the use of a larger number of switches with a consequent increase in the cost of the apparatus required for a system serving a given number of lines. It will be understood, therefore, that for a system designed to serve a given number of lines, the type of apparatus used and its arrangement are largely governed by the relative cost as determined by the two factors described above. All other considerations being equal, if an arrangement employing extremely large multiples between certain of the switches thereof is to be justified on a cost basis, the amount of apparatus used, the cost of the apparatus, and the number of switch multiples in the system must necessarily be so reduced as to at least counterbalance, and preferably, outweigh the cost of constructing the large multiples involved. Systems of the prior art employing ex tremely large multiples between the various switches embodied therein have not met this requirement.

It is an object of the present invention, therefore, to provide a signalling system, and more particularly an automatic telephone system, of novel arrangement wherein large groups of lines are multipled between the bank contacts of certain of the switches, no multiples exist between the bank contacts of other switches, and which includes apparatus of extremely simple, compact and economical construction.

It is a further object of the invention to provide, in a comparatively small system of the character briefly described above, a plurality of automatic switching units, each of which is operable independently of the other similar units to set up connections between any pair of lines included in the system.

In general, the objects as set forth above are attained in accordance with the present invention by providing in a system of the form described a plurality of automatically operable, impulse responsive switching units, each operable independently of each of the other units selectively to establish a connection between any pair of lines" included in the system, and allotter means for causing the idle ones of the units to be seized in a definite order. Each of the switching units includes a non-homing primary line finder switch, a non-homing secondary finder switch, an impulse responsive selector switch or line group selecting means, an impulse responsive connector switch or additional line selecting means for selecting a particular called line in a selected group of lines, and a single motor for actuating both the connector switch and the primary finder switch. Since each unit is capable of connecting any line included in the system to any other line of the system, the primary finder and connector switches of each unit have access to each and every line of the system. Thus, each line is multipled in the bank contacts of the primary finder and connector switches of all the units. By virwe of these two large multiples and the fact that each unit is operable independently of each of the other units, no further multiples are necessary. The allotter means comprises one or more groups of sequential operating allotter relays which function successively to select the idle switching units in a definite order, to prevent two subscribers who initiate calls at the same time from seizing the same switching unit, and to prevent a calling line from repeatedly seizing a defective switching unit. The secondary finder switch and the selector switch of each unit comprise rotary stepping switches operable independently of the motor which is provided for driving the connector and primary finder switches.

More specifically, the primary finder switch embodied in each switching unit comprises wipers mounted on one of two shafts adapted to be driven by the motor included in the unit, contact sets associated respectively with the wipers, and control means for the motor. Similarly, each of the connector switches includes the wipers carried by the second shaft, contact sets respectively associated with the wipers, and additional control means for the motor. Each of the connector switches is unique in that it is of the nonhoming type, register means comprising a pair of impulse responsive stepping switches of the minor type being provided for registering the subgroup of lines including a called line and the particular called line in the registered sub-group. This registering operation is performed by the operation of the two minor switches to mark se-' lected contacts in each of two contact sets included in the switching mechanism of the connector switch, and is followed by the operation of means, controlled jointly by the marked contacts, the wipers associated therewith and the minor switches, for causing the switching mechanism of the connector switch to be driven by its driving motor to connect the line incoming to the connector switch to the selected called line in the selected group of lines determined by the marked contacts.

In accordance with a further feature of the invention means are provided for causing the switching mechanism embodied in the connector switch of each unit automatically to select an idle line from a small group of lines following the dialing of a particular number at a substation connected to a calling line. This feature is of particular utility in the automatic selection of an idle trunk line included in a group of trunk lines all leading to a private branch exchange and wherein the exchange is allotted only one directory number. Provisions are also made whereby a clear metallic circuit is established through a seized switching unit following the seizure thereby of a particular line or lines, such, for example, as trunk lines leading to an exchange distant from that including the switching units.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specification taken in connection with the accompanying drawings in which Figures 1, 2, 3, 4 and 4a considered together illustrate the invention as applied to an automatic telephone system, and Figure 5 illustrates the details of certain of the elements embodied in the system of Figures 1 to 4a, inclusive.

Referring now more particularly to Figs. 1 to 4a, inclusive, of the drawings, there is illustrated an automatic telephone system wherein a plurality of the improved switching units briefly described above are utilized for setting up connections between any pair of subscribers lines included in the system. In general, the system there shown comprises a plurality of telephones or subscribers substations, three of which are shown at A, B and C adapted to be interconnected by means including their respective associated subscribers lines II, 442 and I and any one of the plurality of aforementioned switching units. These units individually comprise a primary finder switch for selecting from the plurality of lines included in the system a particular group of lines including a calling line; a secondary finder switch for selecting the called line in the group of lines selected by the primary finder switch; a selector switch adapted to be associated by the secondary finder switch with the calling line and automatically operable simultaneously to select two groups of lines one of which includes a called line; and a connector. switch associated with the selector switch and operable to select the group of lines including the called line, a subgroup of lines in the selected group and including the called line, and finally, the particular called line in the selected subgroup. Thus, in the system shown, the line i l terminates in the bank contacts of a primary finder switch III, which switch is accessible to a secondary finder switch IS. The latter switch is, in turn, associated with a selector switch 20 which has access to a final numerical or connector switch 430, in the bank contacts of which the lines I and 442 terminate. As will be pointed out in greater detail hereinafter, each of the lines included in the system terminates at the bank contacts of the primary finder switch Hi and also in the bank contacts of the connector switch 430. Similarly, each of these lines terminates in the bank .contacts of the finder and connector switches embodied in each of the other switching units. With a system of the form illustrated designed to serve one thou sand subscribers lines, and with each of the lines multipled in the bank contacts of the connector and primary finder switches of each of the units, two extremely large multiples are involved in constructing the system. These two multiples constitute the only multiples of any appreciable size included in the system. The rendition of reasonably good service to the subscribers of a one thousand line system requires that at least twenty-two switching units be used. In order that the idle ones of these units shall be seized in a definite order by the calling lines of the system, there is provided the allotter means shown in Fig. 3.

' Since, in a system of the size designated, namely a one thousand line system, many instances of simultaneously initiated calls are likely to occur, the switching equipment is designed to handle two simultaneously initiated calls, thereby to minimize the time required for the seizure of an idle switching unit. To this end the allotter relays are divided into two groups 8 and 9 so arranged that each group is capable of operating at the same time to allot an idle switching unit to a calling line. Further in accordance with this-plan, the switching units are divided into two groups corresponding to the two groups of allotter relays. While each primary finder switch of each group has its bank contacts connected so that it has access to each of the ,lines of the system, the arrangement is such that the switching units of one group normally serve a portion of the lines embodied in the system and the switching units of the other group normally serve the remaining lines. Provisions are made whereby in the event all of the switching units in either of the two groups become busy at the same time the lines normally served by the busy group of units are allotted idle switching units in the other group. More particularly, with twenty-two switching units of the form shown connected to serve one thousand lines, the lines may be divided into two groups of five hundred lines each, the switching units divided into two groups of eleven each and the allotter relays divided into two groups of eleven relays each. The exact manner by which the switching units of each group are made normally to serve the five hundred lines of the corresponding group is brought out more clearly hereinafter.

Neglecting for the present the details of the finder, selector and connector switches, the allotter means and the control means, respectively, included therein, the operation of the unit as briefly described above is, in general, quite similar to that of the conventional prior art systems as referred to in the opening paragraph but differs therefrom in that the unit is operable to establish a. connection between any pair of lines in the system independently of each of the other similar units. In brief, when a subscriber, such, for example, as the subscriber at the telephone A, initiates a call over the line H to a second subscriber's telephone, such, for example,

as the telephone B, by lifting his receiver from its hook, the allotter means illustrated in Fig. 3 immediately allots to the calling line an idle one of the switching units. Assuming that the switching unit shown in Figs. 1, 2, 3, 4 and 4a is delegated by the allotter means to set up the connection, the primary finder switch l0 operates to select a group of lines including the called line H. Immediately following this line group selection, the secondary finder switch l5 associated with the selector switch 20 is started in operation to select the particular calling line in g the group of lines selected by the primary finder switch Hi. When the calling line is seized by the secondary finder switch l5, it is connected through to the trunk conductors of the selector switch 20; and the control equipment of the lastmentioned switch is automatically conditioned to be responsive to the first series of impulses transmitted from the impulsing device conventionally provided at the subscribers substation A.

In response to the dialing of the first digit at the substation A, the selector switch 20 simultaneously selects two groups of lines one of which includes the called line and, at the conclusion of this digit, conditions the connector switch 430 to perform the remaining line selecting functions. Thereafter and in response to the dialing of the second digit, the selected group of lines ineluding the called line is determined and there this lineis found and seized by the connector switch I, it is automatically tested to determine its idle or busy condition.

The arrangement of the switching unit departs from conventional practice in that practically all of the auxiliary control functions are concentrated in the selector portion thereof. Thus, the testing of the called line, the application of ringing current and ring-back tone current, respectively, to the called and calling lines, and the transmission of busy tone current to the calling substation are governed by control relays provided in the selector switch 20. As pointed out in detail hereinafter, the arrangement of the unit is such that a switch train comprising the same is released only when the connection is cleared out at the substation of the calling party.

An understanding of the details of the switching apparatus comprising the primary finder switch l0 and the connector switch 430 embodied in the switching unit illustrated will be facilitated by considering the circuits of Figures 1 and tin connection with the mechanism shown in Figure 5. Similar reference characters have been used in these figures to identify the same elements. As indicated in Figures 1 and 4 and structurally shown in Figure 5, the finder switch l0 comprises a plurality of sets of bank contacts, which contact sets are arranged in groups each having associated therewith a wiper carried by a shaft 40. Similarly, the connector switch 430 comprises a plurality of sets of bank contacts, the sets being arranged in groups, and each set having associated therewith a wiper mounted on a second shaft 35. Each of the shafts 35 and is adapted to be driven by a motor 4|. While several different grouping arrangements are possible, in that illustrated each group of contact sets terminates a group of fifty lines. Thus, the finder switch l0 includes the group 1 of six contact sets indicated at l4, l4", i6, 16'', I1 and I1", each including twentyfive points or contacts. Associated, respectively, with these contact sets are six wipers indicated at 2|, 2|", 22', 22", 23' and 23", alternate ones of which extend in opposite directions to form in effect double ended wipers 2|, 22 and 23, the oppositely extending ends of which are electrically connected together by conducting seg ments ll, 54, etc. The adjacent wipers 2|", 22'; 22", 23' are insulated from each other and from the shaft 40 upon which they are mounted by insulating members indicated at 85, 85', etc. Connections are made with the respective pairs of wipers, such, for example, as the Wipers 2| and 2|", by commutating brushes, not shown, which individually engage the peripheral surfaces of the conducting segments 84, 84, etc. It will be understood that by this arrangement there is, in effect, provided three fifty point contact sets, l4, l6 and I1, so that the group 1 of contact sets terminates fifty lines. Thus, the contact sets ll and I4" may be considered as one fifty point contact set N having associated therewith the double ended wiper 2|. From a consideration of Fig. 1 it will be apparent that the wipers 2| and 22 and the respective associated contact sets it and I6 comprise line conductor switching means and the wiper 23 and associated contact set comprise test or directing means. It will be further understood that in a one thousand line system, nineteen additional groups of contact sets, similar to the group I, and their associated wipers are required, all of which wipers are mounted on the rotatable shaft 46. As a consequence, with the shaft 46 standing in any given position, the finder switch III has access through its twenty groups of wipers and the contacts engaged thereby to each of the lines in a group of twenty lines. More particularly, the switch has access to each of the lines in two five hundred line groups and when standing in any one of its fifty positions, the wipers thereof are connected to the lines included in two ten line groups, one ten line group being included in one of the five hundred line .groups and the other ten line group being included in the other five hundred line group. The particular switching unit shown is normally connected to serve the lines in the five hundred line group including the line H.

For the purpose of selecting from the fifty ten' line groups comprising the five hundred lines normally served by the switching unit shown, the particular ten line group including a calling line, there is provided the common test or directing means comprising the two twenty-five contact sets l8 and I6" and the associated wipers 24' and 24". The wipers 24' and 24" are connected together by a commutating segment 84" and are insulated from the shaft 40 by insulating members indicated at 85" and 85". With the double ended wiper 24, as thus formed, standing in any one position, a group of ten lines is selected from the five hundred line group. It will be understood that each of the contacts of the contact sets l8 and \I8 is multipled to the corresponding contacts of the corresponding contact sets included in the finder switches of the other switching units. A similar common test or directing means comprising the contact sets 19' and I9" and the associated wipers 26' and 26" is provided for selectively associating the switching unit with the fifty ten line groups of the second group of five hundred lines. The wipers 26, 26" are connected together by a commutating segment 84" to form, in effect, a double ended wiper 26, and are insulated from the shaft 46 by insulating members as indicated at 85"". In the normal use of the switching unit shown to serve only the lines of the first five hundred line group, this latter' test means is inactive, but is rendered active, by the operation of a relay R50, to select the ten line groups of the other five hundred lines when all of the group of units normally serving the other five hundred lines are busy. The relay R50 includes fifty pairs of contacts indicated at RAI to RA5I which serve to connect the contacts of the contact sets corresponding to and including the set 18 of each of the finder switches to the corresponding contacts of the contact sets corresponding to and including the contact set 19. It will be understood that each contact of the contact sets l8 and I9 is multipled to the corresponding contact of the corresponding contact sets embodied in the finder switches of the other switching units.

The switching mechanism of the connector switch 438 is quite similar in arrangement to that I of the primary finder switch l6, not only with respect to the construction thereof, but with respect to the line grouping arrangement. In this switch there are provided twenty groups of contact sets, indicated at 406, 481, etc., and wipers associated respectively therewith. Each of the contact sets has twenty-five points or contacts so that the two electrically connected, oppositely. extending wipers associated with alternate adjacent pairs of contact sets provide, in effect, a

fifty-point contact set. Twelve contact sets and twelve associated wipers are included in each group. More particularly, the group 400includes the contact sets 465' to 416', inclusive, and 465" to 410", inclusive, having associated therewith the wipers Hi to 416', inclusive, and 411" to 416", inclusive. The adjacent wipers 4H, 4H", 412, 412", etc., are electrically connected together by conducting segments 86, 86', etc., each of which has bearing thereagainst a commutating brush, not shown, for making a connection to the associated wiper. The wipers are all insulated from the shaft 35 and the adjacent ones 411", 412; 412", 413'; etc., are insulated from each other by insulating members 81, 81', etc. By this arrangement the fifty-point contact sets 465, 466, 461, 468, 469 and 410 are formed having associated respectively therewith the double ended wipers 41!, 412, 413, 414, 415 and 416.

Referring now specifically to the mechanical construction of the primary finder and connector switches as shown in Figure 5, it will be seen that the motor 4| comprises a rotor including a shaft 65 having at the left end thereof a pinion gear 66 adapted to mesh with a gear 61 slidably mounted on the shaft 46, and at the other end thereof a pinion gear 1| adapted to mesh with gear 12 slidably mounted on the shaft 35. It will be understood that the two shafts noted are journaled in bearing members, not shown, fixedly mounted on the frame carrying the .unit illustrated. The gear 61 which is slidable axially with respect to the shaft 40 has integral therewith a hub 10 including a radially inwardly extending projection, not shown, which engages with a slot 69 provided in the shaft 46 to form. a driving connection between the gear 61 and the shaft 48. This gear is normally biased to the left by a coil spring 68 enclosing the right extremity of the shaft 40 and confined between the gear 61 and a flange 61 extending radially outward from the shaft 46. The bias exerted by the spring 68 is normally overcome by the force exerted by a second spring 18 having one end fixedly mounted as indicated at 19 and the other end connected to an arm 16 pivoted at 11 and having a finger 16' adapted to engage the outer radialsurface of the gear 61. For the purpose of overcoming the bias of the spring 18 to permit the spring 68 to move the gear 61 into engagement with the pinion gear 66, there is provided a magnet M34 having a pole face oppositely disposed with respect to the lower extremity of the pivoted arm 16 and adapted to be energized under the control of the control means provided in the primary finder switch It). It is noted that the spring 18 is a heavy, powerful spring so that when the magnet M34 is deenergized, it snaps the gear 61 immediately from engagement with the pinion 66 to stop the wipers carried by the shaft 40 while they still stand inengagement with the proper contacts of the respective associated contact sets.

The mechanism whereby the gear 12, carried by the shaft 35 upon which the wipers of the connector switch 438 are mounted, is moved into driving relation with the pinion gear 1| is identical with that for the gear 61. This gear 12 has integral therewith a hub including a radially inwardly extending projection, not shown, riding in a slot 14 provided in the shaft 35, thereby to provide a driving connection between the shaft 35 and the gear 12. A spring 13,'corresponding to spring 68, normally biases the gear 12 in a direction to engage the pinion gear 1|, but the force exerted by this spring on the gear 12 is the medium of an arm 88 pivoted at 81 and having a finger 88' engaging the outer radial surface of the gear. The force of the last-mentioned spring is negatived by the energization of a magnet M464 having a pole face oppositely disposed with respect to the lower extremity of the arm 88.

The control means embodied in the primary finder switch 18 comprises, in addition to the magnet M34 and the relay R58, a line relay, corresponding to the relay R188, associated with each of the subscribers lines of the system, relays R118 and R138 for controlling the operation of M34, and the allotter relays included in the two groups 8 and 9.

As mentioned previously, the connector switch 438 is unique in that it is of the non-homing type and includes impulse responsive means for registering the impulses comprising the final two digits dialed at any calling substation. This impulse responsive registering means comprises the two minor switches indicated diagrammatically at 435 and 448, respectively, in Figure 4, the circuits of which are shown in detail in Figure 4a. The minor switch 435 includes two contact sets 411 and 481, of ten points or contacts each, wipers 419 and 489 respectively associated therewith, a

ratchet and pawl mechanism, not known, for

driving the Wipers, a rotary magnet M482 for actuating the ratchet and pawl mechanism, a release magnet M483, and off-normal springs NS484 for controlling the energization of M483. Similarly, the minor switch 448 comprises a. contact set 418 of ten points, a wiper 488, a ratchet and pawl mechanism, not shown, for driving the wiper, the magnet M485 for actuating the ratchet and pawl mechanism, a release magnet M486 and oiT-normal springs ONS488. It is noted that the minor switch 435 comprises the line subgroup register means, and the minor switch 448 comprises the means for registering a particular called line in a registered subgroup of lines. Also embodied in the control apparatus for the connector switch 438 is a relay R268 which governs the energization of the magnet M464 and comprises additional control means for the motor more or less conventional construction and is of the non-homing type. It comprises a twentyfive point, three-contact set, bank contact arrangement with double-ended wipers for engaging the contacts, the contact sets shown being indicated at 21, 28 and'29 having respectively associated therewith the wipers 3|, 32, and 33. These wipers are adapted to be driven by a ratchet and pawl mechanism, not shown, associated therewith and actuated by the motor magnet M36. The control means embodied in the secondary finder switch 15 is, to a certain extent, overlapping with that for the primary finder switch 18 and comprises the relays R118, R138 and a fast acting relay of the self-polarizing type indicated at R128.

Referring now -to the selector switch 28, it is pointed out that this switch comprises a switch mechanism 25 which may be of the well-known rotary type and which includes nine sets of bank contacts indicated at 52, 52', 53, 53', 54, 54', 55, 55' and 56 having associated therewith wipers 51, 51', 58, 58', 59, 53', 68, 68' and 61 respectively, a ratchet and pawl mechanism, not shown, for driving all of the enumerated wipers, and a rotary magnet M62 for actuating the ratchet and pawl mechanism. The control means embodied in the selector switch comprises relays R148, R150, R168, R118, R188, R188, R288, R218, R228, R238, R248, R258, and R218, their respective interrelated control circuits, and the interrelated circuits controlled respectively thereby. Of these relays, all of which are conventionally illustrated according to their respective characteristics, the relay R258 comprises means for applying ringing current and ring-back tone current to established loops extending respectively to a called and a. calling substation; the relay R238 comprises means for applying busy tone current to an established loop extending to a calling subscribers substation; and the slow-to-release relay R218 comprises means operable when the telephone on a called line is answered for interrupting the application of ringing current and ring-back tone current to the loops extending respectively to a called subscribers substation and a calling subscribers substation. The last-mentioned relay also comprises means for connecting a calling line to a called line. It will be noted that such a connection includes the voice frequency coupling condensers 38 and 39.

As mentioned previously, in order to distribute calls between the various units of the system, there is provided the allotter means comprising a plurality of relays arranged in two groups. This means, which is shown in Figure 3, includes the two groups of relays indicated at 8 and 9, which groups correspond to the two groups of lines each including five hundred lines. These two groups 8 and 9 comprise relays of the twostep type, each of which is associated with one of the switching units and a common relay which is normally operated but which restores when all of the units associated with the other relays of the corresponding allotter group are busy. Thus, the group 8 comprises a number of relays, R388, R318, R328, etc. and a common relay R338 which is normally operated but which restores when all of the raleys R388, R318, R328, etc. are fully operated corresponding to an all-busy condition of the respective associated units. Similarly, the allotter group 9 comprises relays R348, R358, R368, etc. individual to others of the switching units and a common relay R318. It will be noted that R388 is individually associated with the switching unit shown by means comprising the conductor C99, this relay determining by the position of RA381 whether the unit shown or the next succeeding idle unit will be seized during a call initiated on one of the lines embodied in the system. Seizure of the idle units in each group of units corresponding to the groups 8 and 9 is in a definite order and is accomplished through the contacts controlled by the armatures of the respective two-step relays noted and start conductors C92, C92, etc. The start conductor 92 is multipled to the corresponding contacts of the line relays respectively associated with the lines of one fivehundred line group and, similarly, the start conductor 92' is multipled to the corresponding contacts of the line relays respectively associated with the lines of the second five-hundred line group. It is this multipling which determines which lines are included in each five-hundred line group.

Referring now more specifically to the operation of the switching unit illustrated during a call from the substation A, for example, to the substation B, for example, the operation thereof is initiated, as was pointed out above, in response to the party at the first-mentioned substation lifting his receiver from its book. This operation establishes a direct current bridge across Cl2 and CI3 to complete a circuit for energizing RI00, this circuit extending from ground at the upper winding of RI00, by way of this winding and the elements RAI02, CI3, the bridge across CI2 and CI3 at the calling substation, CI2, RAIOI, C90, and the two lower windings of RI00 in series, to battery. The upper winding of RI00 is a highresistance winding so that this relay only partially operates to make only the X contacts associated with the armatures RAI03, RAIM, and

' RAI06. With the armatures RA I03 and RAI06 operated, the calling line II is marked in the contact sets I1 and I8 of the primary finder switch I0. Thus, if the conductors of this line: terminate at the respective tenth contacts in the bank contact sets I4, I6 and I1 of the switch l0, battery is applied through the lower winding of RI00, RAI03 and CSI to the tenth contact of the contact set I1, and ground is applied through RAIDG and RAI01 to the tenth contact of the contact. set I8. Operation of RAIM applies ground to the start conductor C92, thereby to cause the relays in the allotter group 8 to select an idle one of the switching units.

Before proceeding with the description of the operation of the'finder switches, a brief description of the operation of the allotter relays or common control apparatus is deemed to be in order. As noted previously, each of these relays R300, R3I0, R320, R340, R350, R360, etc. corresponds to one of the switching units.

When any given switching unit is idle, ground is present on the conductor corresponding to C249 for the switching unit shown. Thus, when this unit is idle, all of the control relays included therein are de-energized and ground is extended from RA229' by way of the elements CH8, RA2 I 9, C269, RAI51, C268 and RAI25 to the conductor C249. As a result, the upper or active winding of R300 is energized, and all of the armatures of this relay are in their fully operated positions. The armature RA30I is, therefore, closed to R0303 to prepare a circuit for energizing Rl30. At RA305 a circuit is completed for energizing R3301, which latter relay, with RA332 operated, holds interrupted the circuits for energizing the respective primary or lower windings of all of the relays of the group 8 in which R300 is included. When a connection by way of the finder switches I0 and I5 is, in the manner described hereinafter, completed to the selector portion of the unit, ground is removed from C249 at RAI25, and, hence, R300 is permitted to restore. In its restored position, R300 connects the start conductor C92 by way of RA30I and RC302 to the conductor corresponding to C99 for the next succeeding idle switching unit in the group of units controlled by the allotter relay group 8. Thus, if the switching unit corresponding to R3I0 is idle,

this relay will be in its fully operated position so that C92 is connected over an obvious path to C99. In this manner the switching units of the group corresponding to the allotter group 8 are successively seized, and an idle unit is always immediately available for a calling line in the group corresponding to the allotter relay group 8 so long as all of the switching units thereof are not busy. When the last relay R320 of the first group 8 is restored, following the seizure of its associated switching unit, the operating circuit for R330 is opened at the armatures RA305, RA3 I 5, RA325, etc.; and R330 momentarily restores to complete at RA332 the primary circuits for energizing the lower windings of the relays R300, R3I0, R320, etc. The last-mentioned relays, in turn, partially operate to complete the X contacts associated with their respective inner upper armatures, and those of these relays which are associated with idle switching units immediately fully operate due to the presence of ground on the conductors extending. thereto and corresponding to C249 for the relay R300 associated with the switching unit shown. Thus the idle switching units are repeatedly rendered available for use. It will be observed that normally no single switching unit is seized by successive calling lines and, consequently, there is prevented the possibility of a calling line repeatedly seizing a defective switching unit. Thus, in the sequence of operations described above when the switching unit illustrated is seized, R300 immediately restores and remains restored until the common relay R330 restores. Hence if this unit is defective and it is twice attempted to make a call over the line I I the second attempt will cause the seizure of the idle switching unit next succeeding the unit shown. If all of the switching units corresponding to the allotter relays of the group 8 become busy at the same time, the operating circuit for R330 is interrupted, since all of the armatures RA305, RA3I5, RA325, etc. are restored. As a consequence, RA330 remains restored to connect, over an obvious path including RA33I and C315, the start conductor C92 of the first group 8 to the conductor corresponding to C99 for the first idle switching unit available in the group of units controlled by the relays of the second allotter group 9. Simultaneously, a

circuit is completed at RA333 for energizing R50,

this circuit extending from ground at RA333 by way 01 C316, C93 and the winding of R50 to battery. The relay R50, upon operating, connects at its fifty armatures RA5I-RA5I' the fifty contacts of the contact set I8 to the corresponding contacts of the contact set I9 thereby to condition the finder switches of all of the units to search'for a calling line in either of the five hundred line groups. Thus, when an idle switching unit in the group corresponding to the group of allotter relays 9 is allotted to a calling line in the five hundred line group including the Zine II it is rendered operative to find the group of ten lines including the calling line.

The sequential operation of the relays R340, R350, R330, etc., included in the group 9 is identical with that described above for the relays of the group 8, and hence a description thereof is deemed to be unnecessary. It is noted, however, that in the event all of the switching units corresponding respectively to the allotter relays of the group 9 become busy at the same time, the operating circuit for R310 remains open, and hence the start conductor C92 lead ng to the second group is connected by way of I and C314 to the conductor corresponding #59 for the first idle switching unit avail ;.b1e i. the group of units controlled by the relay.: of the first allotter group 8. Simultaneously a circuit extending by way of C93 is completed at RA313 for energizing R50, which relay operates to perform the same tended by way of C92 and RA30| to 009, a circuit is completed for energizing R|30. This relay, upon operating, completes at RA|32 an obvious circuit for energizing the lower winding of R|20. The relay R|20 does not operate when its lower winding is energized but is conditioned by such energizaton to be exceedingly fast acting when its upper winding is subsequently energized. At RA|3| the relay R|30 prepares a circuit traced hereinafter for energizing the upper winding of R|20, and at RA|33 it prepares a circuit for energizing the upper winding of RI I0. At RA|35, the relay R|30 completes an obvious circuit for energizing the driving motor 4|, and at RA|34 it compietes a circuit'for energizing M34, this lastmentioned circuit extending from ground at RA|34 by way of the elements C258, RAI l2, RCI II, C98 and M34 to battery. With M34 energized, the shaft 40 upon which the wipers of the primary finder switch are mounted is mechanically connected to be driven by the motor 4|. Thus, the wipers of this switch are rotated until they reach a position such that the wiper 24 engages the tenth contact in the contact set |8, at which contact is marked the group of ten lines including the calling line H. When this occurs, a circuit is completed for energizing the upper winding of RI l0, this circuit extending from ground at RA|06 by way of the elements RA|01, the switch wiper 24, C96, the upper winding of RI l0, C251, RA|33 and the resistor I33 to battery.

It is noted here that if all of the switching units included in the group corresponding to the allotter group 0 are busy and a switching unit of the second group is allotted to the calling line I, the circuit for energizing the upper winding of the relay, corresponding to the relay R| ID, of the unit selected, is completed by way of C94, operated armature RAI, C95 and the wiper 26 and C9! of the unit selected, rather than over the path traced above. It is further pointed out that if a switching unit of the second group corresponding to the allotter group 9 is allotted to the calling line H and a switching unit in the first group corresponding to the allotter group 8 becomes idle before the allotted unit has seized the calling line, this line will be re-aliptted the idle unit in the first group and the operation of the seized unit of the second group will be discontinued. Thus, assume that the finder switches of a switching unit in the second group corresponding to the allotter group 9 is in the process of searching for the calling line H and the unit shown in Figs. 1 to 4, inclusive, becomes idle. It will be remembered that R330 is restored when this occurs so that the primary circuit of the allotter relay R300 is prepared at RA332. When, therefore, ground is supplied to C249, corresponding to an idle condition of the unit shown, R300 fully operates to complete at RA305 the circuit for energizing R330. As a consequence, R330 interrupts at RA33| the circuit holding operated the relay of the seized unit corresponding to R|30. At RA333, the relay R330 interrupts the energizing circuit for R50 whereupon this relay restores to open the multiples between the contacts of the contact sets l8 and |9 and thereby disable the seized switching unit of the second group to find the calling line H. Shortly thereafter the relay of the seized units corresponding to R|30 restores and this unit is released. Simultaneously with the operation of R300, the switching unit shown is seized by the calling line. In this connection it will he remembered that ground is still present on the start conductor C92 by virtue of the partially energized condition of the line relay R|00, which ground is extended by way of RA30| and R0303 to C99 to complete the operating circuit for R|30. Thus, the switching unit shown is assigned to the calling line H to perform the switching functions and the originally seized switching unit of the second group is restored to its idle condition.

Returning now to the operation of the finder switches I0 and IS, the relay R||0 operates in response to the energization of its upper winding over the above-traced circuit, and at RA| l2 and RCI I4 interrupts the operating circuit for M34, thereby disengaging the shaft 40 from the motor 4|. Thus, the wipers of the switch I0 are stopped while standing in engagement with their respective associated contacts connected to the conductors of the group of ten lines including the calling line H. At RAI l2 and RCI I3 the relay R||0 completes an obvious locking circuit for itself, and at RAI it completes a circuit extending by way of the self-interrupting contacts associated with MA31 for energizing M36. The magnet M36 of the secondary finder switch |5 operates buzzer fashion to rotate the wipers 3! to 33, inclusive, until they engage the contacts leading to the wipers 2|, 22 and 23 of the primary finder switch l0. In this connection it is noted that the wiper 23 of the primary finder switch, upon engaging the tenth contact of the contact set marks in the test level 29 of the switch |5 the group of contact sets 1 as the group in which are connected the conductors of the calling line II. This is accomplished by applying battery from the lower winding of HIM to the tenth contact of the contact set 29 by way of the switch wiper 23. When the wiper 33 engages this marked contact, a circuit is completed for energizing the upper winding of HIM, this circuit extending from ground at RA|3| by way of the upper winding of R|20, CH5, switch Wipers 33 and 23, C9|, RA|03 and the lower winding of R|00 to battery. The relay R|20 immediately snaps up its armatures, and at RA|24 interrupts the operating circuit for M36, thereby to stop the wipers 3| to 33, inclusive, while standing in engagement with the respective contacts leading to the wipers 2| to 23, inclusive, of the primary finder switch l0. At RA! 23 the polarized relay R|20 short-circuits its upper winding and extends ground from RA|32 by way of RA|23, CH5, switch wipers 33 and 23, C9| and RA|03 to the left terminal of the lower winding of R|00, thereby directly to energize this winding. It is noted that the short-circuiting of the upper winding of R|20 does not cause this relay to restore, it being held operated by its energized lower winding. At RA|25 the relay R|20 interrupts the circuit holding the upper winding of R300 energized to cause this relay to restore in the manner previously described. At RA|2| and RA|22 the relay R|20 connects the conductors C|2 and C I3 to the conductors Cl I6 and Cl II, respectively, of the trunk line incoming to the selector portion 20 of the switching unit.

When the allotter relay R300 restores RA30I, it associates, in the manner described in detail above, the start conductor C92 with the relay in the allotter group 8 associated with the next succeeding idle switching unit.

When the armature RA30| of R300 falls back, it interrupts at R0303 the above-traced circuit for energizing R|30, which relay remains operated, however, for a short interval following across the upper winding of RI20, opens at RAI34 a point in the operating circuit for RI I0, interrupts at RAI35 the energizing circuit for the motor 4| and interrupts at RAI33 the abovetraced circuit for energizing the upper winding of RIIO. As a result, the motor 4I stops, and RI I0 restores, without effect, its armatures RAI I I and RAI l2.

The line relay RI00 is so constructed that the energization provided by its lower winding greatly predominates. When, therefore, this winding is directly energized over the abovetraced circuit, RI00 actuates its associated armatures to their fully operated positions. When this occurs, the original circuit, over which the three windingsof RI00 were serially energized, is broken at RAIOI and RAI02 and ground is removed from the start conductor C92 and the tenth contact of the contact set I8 at the re-' spective armatures RAI05 and RAI01. It is noted that the application of ground from RAI 32 directly to the control conductor C46 marks the calling line as busy in the bank contacts of each of the connector switches embodied in the various switching units of the system. It is further noted that the restoration of the allotter relay R300 occurs shortly after the full operation of the line relay RI00 so that the calling line I I is prevented from seizing a second switching unit.

The connection of the line conductors CH and CI3 to the trunk conductors CI I6 and CI I1, upon the operation of the polarized relay RI20, completes a circuit for energizing the line relay RI40, of the selector switch 20, this circuit extending from ground at the lower winding of RI40 by way of this winding and the elements 0121, R0205, RA204, 0I29, R0221, RA221, 0H1, RAI22, CI09, switch wipers 32 and 22, 0I3, the bridge across CI3 and CH at the calling substation, CI2, switch wipers 2I and 3|, CI08, RAI2I, 0H6, RA224, R0223, CI28, RA20I, R0202, CH6 and the upper winding of RI40 to battery. When RI40 operates, it completes at RAI4I a circuit extending by way of RCI42 and 0259 for energizing RI50. The slow-to-release hold relay RI50, in turn, operates to apply at RAI52 multiple ground to CI I8. It is noted that the sequential operation of RI40 and R050 occurs before the slow-to-release relay RI30 falls back to remove ground from CH8 at RAI32. Thus RI20 and RI00 are held operated. At RAI54 the relay RI50 prepares a circuit, traced hereinafter, for energizing the slow-to-release relay RI60, and at RAI53 it applies ground to the conductor 0I39, thereby to prepare holding circuits for the relays RI10, RI80, RI90, R2I0, R250 and R260. At RAI51, the relay RI50 opens a further point in the previously traced circuit for energizing the upper winding of the allotter relay R300. At RAI5I the relay RI 50 applies dial tone current to the loop extending back to the calling subscriber's substation A to indicate to the calling party that an idle switching unit has been seized and is conditioned to respondto impulses transmitted from the impulsing device conventionally provided at this substation.

At the beginning of the first impulse of the first digit dialed at the calling substation, when the above-traced circuit for energizing RI40 is interrupted at the impulsing device at the calling substation, RAHI falls back to complete a circuit for energizing RI60 and M02 in parallel. This circuit extends from ground at RAI4I by way of the elements RCI43 and RAI54 to the contact RCI55 where it divides, one branch extending through RIGO to battery, and the other branch extending by way o fthe elements 028i, RAI16, RCI10, CH1 and M62 to battery. The slow-torelease relay RI60 immediately operates to complete at RAIGI a circuit extending by way of RAI12 and RCI13 for energizing the upper winding of RI10. The relay R is so constructed that it operates only RAI15 when its upper winding is energized. The operation of RAI15 completes a path for short-circuiting the lower winding of RI10, this path starting at ground at RAI53 and extending by way of CI39, RAI15, the lower winding of RI10, ROI13 and RAI12, back to ground at RAIGI.

At the beginning of the first pulse when RI40 restores, to complete at RAI4I and RCI43 the above-traced circuit for energizing M62, the lastmentioned element in cooperation with its associated ratchet and pawl mechanism steps the wipers of the rotary switch 25 from their respective normal positions into engagement with the respective first contacts of the contact levels associated respectively therewith. During each succeeding impulse of the first digit dialed at the calling substation, the wipers of this switch are stepped at the rate of one step for each impulse so that, at the conclusion of the digit, they stand in engagement with the contacts corresponding to the impulses of the digit dialed. It will be understood that during such impulsing the relays RI 50 and RI60, due to their slow-to-release characteristics, remain operated. In the present instance wherein the conductors of the called line terminate at contacts in the group of contact sets associated with the wipers "I, 412 and 413, and wherein these wipers are connected tothe respec- I tive fifth contacts of the levels 52, 53 and 54, respectively, the first digit dialed at the substation A will necessarily comprise five impulses, whereby at the conclusion of the digit the wipers 51, 58, 59 and 60 are connected by way of the conductors 1 C282, C284, C286 and 0208, respectively, to the wipers 4', 412, 413, and 414, respectively. When the rotary switch 25 takes its first step, during the above-described stepping operation, a circuit, traced hereinafter, is prepared at the switch 1 wiper GI and the first contact of the associated contact set 56 for energizing M62 by way of the self-interrupting contacts associated with MA53. Thi circuit is completed to cause the switch 25 to restore to normal when the switching unit is 1 released. It is noted that for each oif-normal position of the rotaryswitch 25, the line incoming thereto has access to each line of two groups of fifty lines each. Thus, with the wipers of the switch in their respective fifth off-normal posi- I tions the line incoming to the selector switch 20 may be connected by way of the armatures of R210 and the wipers 51 to 60, inclusive, to the wipers 4" to 414, inclusive, comprising the wiper group 400 of the connector switch 430. With the wipers of the switch 25 in this same position the line incoming to the selector switch 20 is connectible by way of the armatures of'R210 and the wipers 51' to 00', inclusive, to the wipers comprising the group 40I embodied in the connector 1 switch 430. As pointed out previously each of the wiper groups including the groups 400 and 40I has access to fifty subscribers lines.

At the conclusion of the first digit, the line relay RI40 remains operated for a sufficient pe- 7 a. point in 'the above-traced path short-circuiting the lower winding of RI"), causing the upper and lower windings of R110 to be energized in series. When this occurs, R118 fully operates to prepare, at RAHZ and RCI14, a circuit for energizing the upper winding of Rl8ll. At RAIH, the relay R110 interrupts the path applying dial tone current to the'loop extending to the calling subscriber's substation. 'At RAI19 the relay R110 opens a point in the circuit, traced hereinafter, for energizing the release magnets M486 and M483 of the minor switches 448 and 435, respectively. At RAHS and R01", the relay Rl10 prepares a circuit, traced hereinafter, for energizing R160 and M482 in parallel.

At thebeginning of the first impulse of the second digit dialed at the'substation A, Rl40 again restores and the last-mentioned circuit for energizing M482 and R160 is completed. This circuit extends from ground at RAI4I by way of RCI43 and RA|54 to RCI55 where it divides, one branch extending through R168 to battery, and the other branch extending by way of the elements C28l, RAITG, RCI11, RAI85, RCI81, C146 and M482 to battery. The relay RIGO, upon operating, completes at RAIGI a circuit extending by way of RAI12, R0114, RAI8| and RAI82 for energizing the upper winding of RI8IJ. The relay R188 is identical in construction with Rllll so that, when its upper winding is energized, it operates RAI84 to complete a short-circuiting path extending from ground on CBS for its lower winding. The magnet M482, when energized, in cooperation with its associated ratchet and pawl mechanism steps the wipers 419 and 489 from their respective normal positions to their respective first off-normal positions or into engagement with the respective first contacts of the contact levels 411 and 48l, respectively. At the conclusion of the first pulse of the second digit when R|40 reoperates, the above-traced circuit for M482 is interrupted, so that this magnet is tie-energized to prepare the switch 435 for a secone step. During the remaining impulses of the second digit, the wipers 419 and 489 are stepped at the rate of one step for each impulse. so that, at the conclusion of the digit, they stand in engagement with the contacts of their respective associated contact sets corresponding to the number of the impulses comprising the second digit. This operation registers the group of lines in which the called line 442 is included by marking with ground potential particular contacts of the contact set 469. In the present instance, if it be assumed that the called line 442 is included in a group corresponding to the fourth contact of the contact set 411, the second digit will necessarily comprise four impulses, so that, at the conclusion thereof, the wipers 419 and 489 engage the respective fourth contacts of the contact sets 411 and 48!, respectively. At the first step of the minor switch 435, the off-normal springs ONS484 are closed to prepare a point in the above-noted circuit for energizing M483.

At the conclusion of the second digit, Rl40 remains operated for a sufficient length of time to permit RIBO again to restore, thereby to interrupt at RAIGI the short circuiting path for the lower winding of R188. This causes the two windings of Rl88 to be energized in series and the relay to complete its operation. At RAI8I the relay R188 prepares-a circuit for energizing the upper winding of RIM, and at RAI85 and RCI8'I it opens a further point in the previouslytraced circuit for energizing M482. At RA|85 and RCI86, the relay Rl88 prepares a circuit for energizing M485 of the minor switch 448 in parallel with RIGO. Thus, the apparatus is conditioned to be responsive to the impulses comprising the third digit dialed at the calling substation.

At the beginning of the first impulse of the third digit when Rl48 again restores, the abovenoted circuit for energizing M485 in parallel with RIEII is completed at RAI4I, this circuit extending from ground on C28l by way of the elements RAHE, RCI11, RAI85, RCI88, R-Al83, CH5 and M485 to battery. The relay R168 being energized over the other branch of this circuit, operates to complete, at RAIGI, the circuit extending by way of RAI12, R0114, RAI8I, RC|83 and RAI9| for energizing the upper winding of RISII. The relay R198 being identical in construction with the relays RH!) and Rl80, operates only RAI92 to complete an obvious short circuiting path for its lower winding. The magnet M485, upon being energized, cooperates with its associated ratchet and pawl mechanism, to step the wiper 480 from its off-normal position into engagement with the first contact of its associated contact level 418. During this step, the off-normal springs ONS488 are closed to prepare a circuit for energizing the release magnet M486. At the end of the first pulse when Rl40 again operates to interrupt the operating circuit for M485, this magnet is conditioned to step the wiper 488 a second step. During the succeeding impulses comprising the third digit, the wiper 480 is stepped at the rate of one step for each impulse, so that, at the conclusion of the digit, it stands in engagement with a contact corresponding in number to the number of impulses in the digit. This operation of the minor switch 440 is for the purpose of registering the particular called line in the registered group of lines by marking with battery a particular contact in the contact set 418. Thus, if the called line 442 in the registered group of lines corresponds to the fourth off-normal position of the wiper 480, the third digit dialed at the calling substation will necessarily comprise four impulses whereby the wiper 480 is stepped into engagement with the fourth contact of the contact level 418.

An understanding of the exact manner by which the minor switches 435 and 448 operate to register the called line and the subgroup of lines in which the called line is included will be facilitated by a consideration of the circuit arrangement for these switches and a portion of the connector switch 430 as illustrated in Figure 4a. The corresponding elements shown in Figures 4 and 4a are identified by the same reference characters. As explained above, the rotary switch 25 operates in accordance with the impulses of the first digit to select the particular group of fifty lines in which the line 442 is included. It is the purpose of the minor switches 435 and 440 to register the subgroup of ten lines included in the larger group of fifty lines which includes the called line and the particular called line in the registered subgroup of lines, As noted previously, the double-ended wiper 415 of the switch 430 actually comprises two oppositely extending wipers which are indicated in Figure 4a at 415' and 415". The two contact sets 469 and 469" associated, respectively, with the two wipers 415 and 415 have their contacts arranged in five groups or subsets of ten each, these five groups tact set 411, and so on.

being indicated at 490, 49|, 492, 493, and 494 The contacts of each subset orgroup are connected together and to one contact in the contact set 411 associated with the wiper 419. Thus, the contacts in the group 490 are connected to the first and sixth contacts of the contact set 411 by way of the conductor 495. Similarly, the contacts of the second group 49| are connected to the second and seventh contacts of the con- It will be apparent, therefore, that the first subgroup of ten lines in any selected group of fifty lines may be selected by dialing a second digit comprising either one or six impulses and, similarly, that the second subgroup of any selected group of fifty lines may be selected by dialing a second digit comprising either two or seven impulses. The reason for providing an arrangement wherein thesame subgroup of lines may be selected by dialing either of two different numbers will best be understood by returning again to the operation of the selector switch 20. As pointed out above, .with the wipers of the rotary switch 25 embodied in the switch 20 in any given off-normal position, the line incoming to the selector switch 20 has access to either of two selected groups of fifty lines each. In the present assumed case wherein these wipers are operated to their respective fifth offnormal positions, the incoming line to the switch 20 is connected by way of the armatures of R210, the wipers 51 to '60, inclusive, and the conductors C282, C284 and C286 to the group of wipers 400 of the connector switch 430. With R210 operated, however, so that itsarmatures are connected, respectively, to the wipers 51' to 60', inclusive, the line incoming to the selector switch 20 is connected to the wipers comprising the group 40| of the connector switch 430, and by way of the last-mentioned group of wipers has access to a second'group of fifty lines.' Thus, the group of fifty lines ultimately to be selected is determined by the condition of R210. With this relay operated, the line incoming to the selector switch 20 will have access to one group of fifty lines, and with the relay de-energized, it will have access to a second group of fifty lines. The energized or de-energized condition of R210 .depends upon the number of impulses comprising the second digit dialed, i. e., if the number of impulses of this is less than six, the wiper 489 of the minor switch 435 will not be connected to C245, and, consequently, R210 will remain deenergized, with the result that the line incoming to the selector switch 20 is connected to the wipers in the group 400. If, on the other hand, the second digit dialed comprises from six to ten impulses, the wiper 489 of the switch 435 will complete an obvious circuit by way of C245 for energizing R210, thereby to associate the line incoming to the selector switch 20 with the group of wipers indicated at 40I. It will be apparent, therefore, that a second digit comprising one impulse causes the minor switch 435 toselect the first subgroup of lines in the group of fifty lines to which the group of wipers 400 has access; that a second digit comprising six impulses causes the switch 435 to select the first subgroup of ten lines in the group of fifty lines to which the wipers 40| have access'and so on. 7 The reason for including ten connected contacts in each of the contact groups 490 to 494, inclusive, is to permit the selection of a. particular line in each subgroup of ten lines. Thus, the wipers 415, 415", 416 and 416" are all mounted on the shaft 35 and move together and, consequently, unless ten' 1 common positions areprovided for the wipers 415' and 415" corresponding to the ten lines of each subgroup, would be impossible to select the in dividual lines included in the subgroup.

' The marking of a desired called line in a selected subgroup of lines is accomplished through the operation of the switch 440 which responds to the impulses comprising the third digit to move its wiper 480 to one of the ten off-normal positions available thereto. When this wiper is moved to its first off-normal position such that it engages the first contact of the contact set 418, it marks with battery the first, eleventh twenty-first, thirty-first, and forty-first contacts of the contact sets 410 and 410", or contacts corresponding to the first line in each of the five subgroups of ten lines. The contacts noted above constitute a subset of the contact set 410. Similarly, when moved to any of its other nine'ofi-normal positions, it marks other contacts constituting subsets of the contact set 410 and corresponding to the same lines in each of the five subgroups of ten lines.

In the assumed case described above wherein the second and third digits dialed at the calling substation A each consisted of fourimpulses, each of the wipers 419, 489 and 480 rests in engagement with its respective associated fourth contact. At the end of the third digit, therefore, a circuit is prepared for energizing the upper winding of R260, this circuit extending from ground at the switch wiper 419 by way of the fourth contact of the contact level 411, the contacts of the group 493, the switch wiper 415", C246, the upper winding of R260, RA2'63, C241, C241, the switch wiper 416", the ninth contact of the contact set 410", the fourth contact of the contact set 418, and the switch wiper 480 to battery.

Continuing now with the operation of the connector switch 430, when R|40 is held operated for a sufficient period of time to permit RAM to restore, the short circuit across the lower winding of RI is broken at RAIBI, causing the two windings of the last-mentioned relay to be energized in series. Upon completing its operation, R|90 opens at RA|9| a further point in the circuit for short-circuiting its lower winding, and at RA|93 opens a further point in the previously traced circuit for energizing M485 of the minor switch 440. At its armature RA|94, the relay R|90 completes a circuit for energizing R240 and M464 in parallel, this circuit extending from ground at RA|94 by way of C|49, RC266 and RA264 to C|62 where it divides, one branch extending through R240 to battery, and the other branch through M464 to battery. The energization of M464 causes the shaft 35 to be brought into driving relationship with the motor 4|. This motor is energized by the completion of an alternative operating circuit at RA|95 immediately upon the 1 operation of Rl90. The circuit noted extends from ground at RA261 by way of CI59, RA|95 and through the motor 4| to battery. When these operations occur, the shaft 35 is rotated to depend upon whether this called line is found idle or busy: Before describing these operations, it is pointed out that the operations occurring shortly following the end of the third digit dialed at the calling substation are the same irrespective of whether the called line is in a group of fifty lines accessible to the wipers 400 or in a group of lines accessible to a group of wipers, such, for example, as the group l, requiring the operation of R210 for association with the line incoming to the selector switch 20.

Turning now to the operations which occur upon the energization of R240 simultaneously with the energization of the motor 4|, this relay, upon operating, opens at RC244 and RA24I a point in the circuit for energizing the upper winding of R250, and at RA! and RA242 prepares a circuit, traced hereinafter, for energizing the busy relay R230, this circuit being held open at RA26| until such time as R260 operates following the seizure of the called line by the wipers in the wiper group 400. When the wipers 41l to 41.4, inclusive, are rotated into engagement with the contacts leading to the conductors of the called line 442, the circuit for energizing the busy relay R230 is completed providing ground is present on C445, corresponding to a busy condition of the called line 442. It is pointed out that if the called line is idle, battery from the line relay associated with this line is present on the conductor C445 so that the busy relay is not energized. Assuming the called line 442 to be idle, when the slow-to-release relay R240 restores shortly following the seizure of the line 442, it completes a circuit for energizing the upper winding of R250, this circuit extending from ground on CH8 by way of RA232, R0233, Cl66, the upper winding of R250, CiGl, RC244, RA24I, Ci68, RA26I, RA2'll, R0211, the switch wiper 59, C286, the switch wiper 413 to battery on C445. In response to the energization of its upper winding, R250 partially operates to complete at the X contacts associated with RA256, a circuit extending from ground on Cl39 for energizing its lower winding. With its lower winding energized, R250 assumes its fully operated position to complete at RA254 a circuit extending by way of ClilB for energizing the upper winding of R220. It is noted that the upper winding of R220 is of a very low resistance such that R220 will not 0perate with the potential normally provided on a control conductor such as C445 leading to a called subscribers line. The function of this relay is set forth more fully hereinafter.

At its armatures RA25I. RA252, RA253, the relay R250 completes circuits for applying ringing current and ring-back tone current to the loops extending respectively to the called and calling lines. The path of the ringing current extends from one terminal of the ringing current generator at RC2|2 by way of the elements RA2H, CI36. RC222, RA22I, CI96, RA25I, CI98, RAZ'H, R0212, C236. the switch wiper 51, C282, the switch wiper 4', C443, the signal device bridged in series with a condenser across the lines C443 and C444 at the called substation B,

C444, the switch wiper 412, G284, the switch wiper 58, C238, RC2I5, RA2'I4, Cl99, RA252, Cl9l, RA225, R0226, Cl3l, RA2I4, RC2i5, C284, and the upper winding of R2l0 to the other terminal of the ringing current generator. A portion of this current is lay-passed by way of 0 I38 and the loop extending to the calling subscribers substation through the receiver at this substation, thereby to indicate to the calling party that the called line is idle and is being rung.

When the called party at the substation 3 answers by lifting his receiver from its hook, a direct current bridge is placed across theconductors C443 and C444, thereby to complete a circuit, including all of the elements included in the above traced path for the ringing current, excluding the signal device at the substation B, for energizing the upper winding of R2l0, this path starting at ground at RC2I2 and extending through the upper winding of R2l0 to battery. In response to such energization, R21 0 closes the X contacts associated with RAZIB, thereby to complete an obvious circuit for energizing its lower winding. With its lower windmg energized, R2l0 assumes its fully operated position to interrupt at RA2 II and RA2| 4 the circuits for applying ringing current to the loop extending to the called line and ring-back tone current to the loop extending to the calling line and also to interrupt the circuit for energizing its upper winding. At these same armatures and their respective associated contacts RC2l3 and RA2I6, a connection is established between the calling and called lines, thereby to provide a conversational circuit between the calling and called parties, which circuit includes therein the two condensers 38 and 39. At RA2I9, the relay R2l0 interrupts a further point in the circuit for energizing the upper Winding of the allotter relay R300.

In response to the operation of R2l0, a circuit is completed for energizing the battery rovers ing relay R200, th s circuit including the path traced above for energizing the upper winding of R2l0 and comprising the loop extending to the called substation B. The relay R200, upon operating, applies at RA20'I multiple ground to Cl39, and at RA20I and RA204 reverses battery back over the loop extending to the calling subscribers substation, which battery reversal may be utilized for metering purposes, or for coin collection purposes in the event the calling substation is a pay station. With the system in this condit on, the conversational circuit is maintained until the connection is cleared out at the calling subscribers substation.

Before describing the release of the connection as established in accordance with the foregoing description, it will be assumed that the called line 442 is found busy at the time the wipers its 473, inclusive, are stepped into engagement with the contacts at which the conductors of this line terminate. It will be recalled that at the time this occurs the slow-t0- release relay R240 is energized so that a circuit .is prepared for energizing the busy relay R230.

When, therefore, the called line 442 is found busy, this circuit is completed and extends from ground on C445 by way of the switch wiper 413 and the elements C286, switch wiper 59, RCZ'll' RA2'I1, RAZSI, C168, RA24l, RA242, RA255, CNN, and the winding of R230 to battery. When energizcd over the above-traced circuit, R230 operates to complete, at RA232 and R0234, a holding circuit extending from ground at CH8 for maintaining itself operated when R240 restores shortly following the conclusion of the third or final digit dialed at the calling substation. At RA232 and R0233, the relay R230 interrupts a further point in the circuit for energizing the upper winding of R250. At RA23 l the relay R230 applies busy tone current to the loop extending back to the calling subscribers substation. thereby to indicate to the calling party the busy condition of the called line. At RA235, the relay R238 prepares a circuit, traced hereinafter, for energizing M454 and the motor 41, this circuit only being provided and utilized for a particular form of service referred to in detail hereinafter.

Following the receipt of busy tone, the calling party may initiate the release of the switching unit by hanging up his receiver, thereby to interrupt the circuit holding the line relay R148 operated. When R148 restores RA141, the operating circuit for R158 is interrupted at RC1,42 and a circuit is prepared at R0143 for energizing M62 included in the rotary switch 25 of the selector switch 28. This last-mentioned circuit is completed when R158 restores and extends from ground at RA141, by way of the elements R0143, RA154, R0156, C144, RA229, C248, switch wiper 61, the selfdnterrupting contacts associated with MA63 and the winding of M62 to battery. The magnet M62 thereupon operates buzzer fashion and, in cooperation with its associated ratchet and pawl mechanism, drives the wipers of the rotary switch 25 until the wiper 6| thereof is disengaged from the multiply connected contacts in the contact set 56, at which time these wipers stand in their respective normal positions. When such disengagement occurs, the abovetraced circuit for M62 is interrupted at the switch wiper 61 and the last contact of the contact set 56.

At RA153, the hold relay R158, upon restoring, removes ground from C139, thereby to open a point in the locking circuits for the relays R118, R188, R198 and R268 whereupon all of these relays restore. At RA152, the relay R158 removes ground from C118, thereby to open a point in the locking circuits for the relays R188 and R128 causing these relays to restore, The relay R118, upon restoring RA119, completes a circuit. for energizing the'release magnets M486 and M483 incorporated in the minorswitches 448 and 435, respectively. This circuit extends from ground at RA119 to C159, where it divides, one branch extending through ONS488 and M486 to battery, and the other branch extending through ONS 484 and M483 to battery. v The two minor switches noted thereupon restore the wipers 419, 489 and 488 to normal at which time the two sets of oil-normal springs noted are opened to interrupt the circuits of the two re-.- lease magnets. It is noted that, with R128 and R158 restored, a circuit is prepared for energizing the upper winding of the allotter relay R388, thereby to mark the switching unit illustrated as idle in the allotter group 8. With the system in this condition, the connection is entirely cleared out and the switching unit is ready for further use.

The release of a connection following the esfrom C139 and C118, respectively. Ground is retained on C139 at RA281. The removal of ground from C1 18 causes the de-energization and restoration of R128 and R188. When R158 restores RA154, the above-traced circuit for energizing M62 is completed causing the rotary switch 25 to restore its wipers to normal. When this switch takes its first step the operating circuit for R288 is interrupted at the switch wipers 51 and 58 causing this relay to restore RA281 completely to remove ground from C139. As a consequence of the removal of ground from C139, the relays R118, R188, R198, R218, R258. and R260 are de-energized and restore. When R118 restores RA119 the above noted circuit for encrgizing the release magnets M483 and M486 are completed to cause the wipers of the minor switches 435 and 448 to be restored to their respective normal positions. With the system in this condition, the connection as established is completely cleared out and the switching unit is ready for further use.

If the called party is the first to hang up, only the relay R288 restores, this operation serving to remove multiple ground from C139 at RA281. The entire switch train is held operated by virtue of the maintenance of ground on C118 at RA152 and the maintenance of ground on C139 at RA153. Thereafter, and when the calling party hangs up to initiate the restoration of R148 and R158, the switch train is released in the exact manner described above.

It will be noted from the foregoing description that the second control conductor C288 plays no part in the operation of the switching unit to establish a connection betweenthe line extending to a calling substation and a line extending to a called subscribers substation. This conductor, as well as the switch wipers and contact sets associated therewith, namely, the wipers 68 and 414 and the contact sets and 468, are only provided in those instances wherein the'switching unit is required to select an idle line from a group of lines extending, for example, to a private branch exchange. Thus, if the calling party at a substation such, for example, as the substation'A dials the number identifying such an exchange and any of the trunk lines leading thereto are idle, an idle trunk will automatically be selected and a connection established to the called exchange. To secure this mode of operation, the contacts of the contact set 461 connected to the. lines of the group extending to such an exchange are multipled to the corresponding contacts of the contact set 468 so that when the test wiper 413 engages a contact, such, for example, as the contact terminating C445, included in a busy trunk line, a circuit is completed for energizing M464, R248 and the motor 4| in parallel. This busy condition is marked -by the presence of ground on C445 so that the busy relay R238 is energized over the circuit traced above. This relay, upon being energized, immediately pulls up RA235 to complete the above-noted circuit for energizing M464, R248 and the motor 41 in parallel. This circuit extends from ground on C445 by way of the multiple conductor C498, the switch wiper 414 and the elements C288, switch wiper 68, R0218, RA219, C163, and RA235, to C164 where the circuit divides, one branch extending by way of C158 and the motor 41 to battery, the second branch extending by way of R0265, RA264, C162 and R248 to battery and the third branch extending by way of R0265, RA264, C162 and M464 to battery. The relay R248 is thus maintained energized to hold the testing circuit including the busy relay R238 complete. As a consequence of the energization of M464 and the motor 41, the wipers 411 to 416, inclusive, are rotated into engagement with the next succontact sets.

ceeding contacts of their respective associated If the second trunk is busy, R230 will be held operated so that the wipers 411. to 416, inclusive, continue to rotate. of the wipers continues until an idle trunk is found. An idle trunk leading to the private branch exchange is identified by the presence of battery on the control conductor embodied therein and corresponding to C445. Hence, when the wipers 413 and 414 engage the contacts associated with an idle trunk, the above-traced circuit for energizing the busy relay R230 is interrupted. When R230 restores, following the finding of an idle trunk, it interrupts, at RA235, the.

above-traced circuit for energizing M464, R240, and the motor 4| so that the wipers 411 to 416, inclusive, are stopped while in engagement with the contacts connected to the conductors of this idle trunk. The operations which occur following the seizure of the idle trunk are exactly the same as those described above, as are also the operations which occur during the release of the switching unit following the setting up of a connection extended by way of an idle trunk selected in this manner. From the description of this paragraph it will be apparent that the busy relay R230, in combination with the contact sets 55, and 468, the respective associated wipers 60, and 414, and the various conductors interconnecting these elements, comprises means for causing further operation of the connector switch 430 to select and seize an idle one of a small group of lines in a larger group of fifty lines selected by the selector switch 20 following the operation of the connector switch 430 to a position for seizing one of the lines of this smaller group of lines.

It will be observed that at no time during the establishing of the connection just described did the relay R220 operate. Consequently, the established conversational circuit includes therein the voice frequency coupling condensers 38 and 39. In the rendition of certain types of services, such for example, as those cases where the system shown constitutes only a part of a larger system, and impulsing from one section of the larger system to another is desired, it is neccssarythat these capacity coupling elements be eliminated and a through metallic circuit be established. These services usually involve trunk lines terminating at the bank contacts of the connector switches included in the various switching units and extending to selector or connector switches in the distant section of the larger system. Each of the control conductors, corresponding to C445 for the line 442, of such trunk lines is marked with battery potential when the distant numerical switch terminating the trunk line is idle and with ground when the switch is busy. This potential is applied to the control conductors through the windings of relays included in the selector or connector switches terminating the trunk lines and ordinarily is higher in value than that applied to the control conductors of the subscribers lines, such, for example, as the line 442, Assuming that the switching unit illustrated seizes an idle one of these lines, the higher potential on the control conductor of the seized line causes the operation of R220 by virtue of the energization of the upper winding of this relay. As noted previously, the circuit for energizing this winding extends from ground on C118 by way of the winding and the elements C188, RA254, RA261, RA211, RC211', switch wiper 59, C286,

Such rotation switch wiper 413, to battery on the control conductor, corresponding to C445. With this upper winding energized, R220 partially operates to complete, at the X contacts associated with RA228, a circuit for energizing its lower winding thereby to cause its full operation. When the selector or connector switch, at which the trunk seized by the switch 430 terminates, is seized, it operates to apply, by way of the control conductor of its associated trunk line, ground to C286 so that, when R220 operates RA228, this ground is applied to CH8 to form a multiple circuit for holding R100, R120, and itself operated. At RA226, the relay R220 similarly applies multiple ground to C139 for holding the relays R110, R180, R100, R210, R250, and R260 operated independenty of the line relay R140 and the hold relay R150. At RA229, the relay R220 opens a point in the circuit for energizing M62 by way of the selfinterrupting contacts associated with MA63. At RA229, the relay R220 opens a further point in the circuit for energizing the upper winding of the allotter relay R300. At its armatures RA221 and RA225 and their respective associated armatures RA224 and RA221, the relay R220 establishes a through metallic circuit from the calling subscriber's line to the trunk line outgoing from the switching unit to the seized selector or connector switch in the distant portion of the larger system. At RA224 and RA221 and their respective associated contacts R0223 and RC221, the relay R220 interrupts the above-traced circuit holding the line relay R140 energized, thereby to cause the sequential restoration of this relay and the hold relay R150. The restoration of R150 causes multiple ground to be removed from the conductors C118 and C139 at the armatures RA152 and RA153, respectively. Thus, the switching unit is held operated from ground in the seized selector or connector switch in the distant portion of the system.

It will be apparent that the release of a conncction involving the operation of R220 and established in the manner described immediately above follows the release of the seized final selector or connector switch in the distant portion of the system. When this occurs, ground is removed from the conductor C118 to cause the de-energization and restoration of the relays R100, R120 and R220. The relay R220, upon restoring, completely removes, at RA226', ground from C139, thereby to cause the de-energization and restoration of the relays R110, R180, R190, R210, R250 and R260, At RA229, the relay R220, upon restoring, completes the above-traced circuit for energizing M62 by way of the self-interrupting contacts associated with MA63. The magnet M63 thereupon operates buzzer fashion to restore the wipers of the rotary switch 25 to their respective normal positions, at which time th operating circuit of this magnet is opened at the switch wiper 61. Similarly, the restoration of RA1'19 completes the circuit, traced above, for energizing the release magnets M483 and M486, thereby to restore the minor switches 435 and 440 to normal. Thus, the switching unit illustrated is entirely released and is ready for further use.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein without departing from the invention, and it is aimed in the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

We claim:

1. An automatic telephone system comprising a plurality of lines and a plurality of automatically operable impulse responsive switching units for establishing connections between said lines; each of said units comprising a finder switch having bank contacts at which all of the lines of the system terminate, a selector switch for selecting two groups of said lines, a connector switch having bank contacts at which all of the lines of the system terminate and including impulse responsive register means for selecting a particular sub-group of one of said selected groups and a particular line in said selected subgroup, common motor means operable to drive selectively said finder and connector switches: and means controlled by said register means for controlling the operation of said motor means; and allotter means for causing the idle ones of said units to be seized by calling lines of said system in a definite order.

2. An automatic telephone system comprising a plurality of lines and a plurality of automatically operable impulse responsive switching units for establishing connections between said "lines;

each of said units comprising a primary finder switch having bank contacts at which all of the lines of the system terminate, a secondary finder switch, a selector switch for simultaneously selecting two groups of said lines, a connector.

switch having bank contacts at which all of the lines of the system terminate and including impulse responsive register means for selecting a particular subgroup of one of said groups and a particular line in the selected subgroup, common motor means operable to drive selectively said primary finder switch and said connector switch, and means controlled by said register means for controlling the operation of said motor means; and allotter means for causing the idle ones of said units to be seized by calling lines of said system in a definite order.

3. An automatic telephone system comprising a plurality of lines and a plurality of automatically operable impulse responsive switching units for establishing connections between said lines; each of said units comprising a primary finder switch having bank contacts at which all of the lines of the system terminate, a secondary finder switch, a selector switch for simultaneously selecting two groups of said lines, a connector switch having bank contacts at'which all of the lines of the system terminate and including impulse responsive register means for selecting a particular subgroup of one of said groups and a particular line in the selected subgroup, common motor means operable to drive selectively said primary finder switch and said connectorswitch, and means controlled by said register means for controlling the operation of said motor means; and allotter means for causing the idle ones of said units to be seized by calling lines of said system in a definite order.

4. In a signalling system, a plurality of lines including a first line and a second line and a switching unit for automatically connecting said first line to said second line; said switching unit comprising motor means, line group selecting means operable independently of said motor means, means including means adapted to be driven by said motor means for selecting said first line and associating it with said line group selecting means, impulse responsive means for causing said line group selecting means to select a group of lines including said second line, additional line selecting means adapted to be driven by said motor means, additional impulse responsive means for causing said additional line selecting means to seize said second line in said selected group of lines, and means for connecting said first line to said second line.

5. In a signalling system, a plurality of lines including a first line and a second line and a switching unit for automatically connecting said first line to said second line; said switching unit comprising motor means, line group selecting means operable independently of said motor means, means including means adapted to be driven by said motor means for selecting sa d first line and associating it with said line group selecting means, impulse responsive means for causing said line group selecting means to select a group of lines including said second line, additional line selecting means adapted to be driven by said motor means, impulse responsive means comprising means responsive to one series of received impulses for selecting and registering a subgroup of lines in said selected group of lines and means responsive to a succeeding series of received impulses for selecting and registering said second line in said selected subgroup, means controlled by said last mentioned impulse responsive means for causing said additional lne selecting means to seize said second line, and means for connecting said first line to said second line.

6. In a signalling system, a plurality of lines including a first line and second line and a switching unit for automatically connecting said first line to said second line; said switching unit comprising motor means, line group selecting .means. operable independently of said motor means, means including means adapted to be driven by said motor means for selecting said first line and associating it with said line group selecting means, impulse responsive means for causing said line group selecting means to select a group of lines including said second line, additional line selecting means adapted to be driven by said motor means, impulse responsive means comprising a stepping switch responsive to one series of received impulses and operable to any one of a number of positions each corresponding to one subgroup of lines in said selected group of lines, said impulse responsive means also including a second stepping switch responsive to another series of received impulses and operable to any one of a number of positions each corresponding to one line in each of said subgroups, means controlled by said last-mentioned impulse responsive means for causing said additional line selecting means to seize said second line, and means for connecting said first line to said second line.

7. In a signalling system, a plurality of lines including a first line and a second line and a switching unit for automatically connecting said first line to said second line; said switching unit comprising a pair of shafts, wipers mounted on each of said shafs, a motor for driving said shafts, a plurality of sets of contacts at which said lines terminate, each of said contact sets being associated with one of said wipers, primary finder means including the wipers on one of said shafts and the contact sets associated therewith and control means for said motor, said primary finder means being operative to select a group of lines including said first line, line group selecting means, secondary finder means operable independently of said motor for selecting said first line from said selected group of lines and for associating it with said line group selecting means, means operable independently of said motor and responsive to a series of received impulses for causing said line group selecting means to select a group of lines including said second line, additional line selecting means including the wipers associated with the other of said shafts and the contact sets associated therewith and additional control means for said motor, impulse responsive means for causing said additional line selecting means to seize said second line, and means for connecting said first line to said second line.

8. In a signalling system, a plurality of lines including a first line and a second line and a switching unit for automatically connecting said first line to said second line; said switching unit comprising a pair of shafts, wipers mounted on each of said shafts, a motor for driving said shafts, a plurality of sets of contacts at which said lines terminate, each of said contact sets being associated with one of said wipers, primary finder means including the wipers on one of said shafts and the contact sets associated therewith and control means for said motor, said primary finder means being operative to select a group of lines including said first line, line group solecting means, secondary finder means operable independently of said motor for selecting said first line from said selected group of lines and for associating it with said line group selecting means, means operable independently of said motor and responsive to a series of received impulses for causing said line group selectng means to select a group of lines including said second line, additional line selecting means including the wipers associated with the other of said shafts and the contact sets associated therew th and additional control means for said motor, impulse responsive means comprising means responsive to one series of received impulses for selecting and registering a subgroup of lines in said selected group of lines and means responsive to a succeeding series of received impulses for selecting and registering said second line in said selected subgroup, means controlled by said impulse responsive means for causing said additional line selecting means to seize said second line, and means for connecting said first line to said second line.

9. In a signalling system, a plurality of lines including a first line and a second line and a switching unit for automatically connecting said first line to said second line; said switching unit comprising a pair of shafts, wipers mounted on each of said shafts, a motor for driving said shafts, a plurality of sets of contacts at which said l nes terminate, each of said contact sets being associated with one of said wipers, primary finder means including the wipers on one of said shafts and the contact sets associated therewith and control means for said motor, said primary finder means being operative to select a group of lines including said first line, line group selecting means, secondary finder means operable independently of said motor for selecting said first line from said selected group of lines and for associating it with said line group selecting means, means operable independently of said motor and responsive to a series of received impulses for causing said line group selecting means to select a group of lines including said second line, additional line selecting means including the wipers associated with the other of said shafts and the contact sets associated therewith and additional control means for said motor, impulse responsive means comprising a stepping switch responsive to one series of received impulses and operable to any one of a number of positions each corresponding to one subgroup of lines in said selected group of lines, said impulse responsive means also including a second stepping switch responsive to another series of received impulses and operable to any one of a number of positions each corresponding to one line in each of said subgroups, means controlled by said impulse rcsponsive means for causing said additional line selecting means to seize said second line, and means for connecting said first line to said second line.

10. In a telephone system, a plurality of subscribers lines includ ng a first line and a second line, said first line having a substation connected thereto including an impulsing device, and a switching unit for automatically connecting said first l ne to said second line; said switching unit comprising motor means, line group selecting means operable independently of said motor means, means responsive to the initiation of a call on said first line and including means adapted to be driven by said motor means for selecting said first l ne and associating it with said line group selecting means, means responsive to a series of impulses transmitted from said impulsing device for causing said line group selecting means to select a group of lines including said second line, additional line selecting means responsive to further series of impulses transmitted from said impulsing device and including means adapted to be driven by said motor means for selecting said second line from said selected group of lines, and means for connecting said first line to said second line.

11. In a signalling system, a group of lines dividedinto subgroups, animpulse responsive automatic switch having access to said lines and a line incoming to said switch; said switch including a switching mechanism for connecting said incoming line to any selected one of said lines; said switching mechanism including a first set of contacts divided into subsets individually corresponding to a particular subgroup in said group of lines, a second set of contacts divided into subsets individually corresponding to a particular line in each of said subgroups of lines, and wipers respectively associated with said sets of contacts; means responsive to a series of impulses transmitted to said switch for marking a selected subset in said first set of contacts; means for marking a selected subset in said second set of contacts; and means controlled jointly by said wipers, said two last-named means and said marked subsets for continuously operating said switching mechanism to a position for connecting said incoming line to the selected line corresponding to the second-marked subset in the subgroup of lines corresponding to the firstmarked subset.

12. In a signalling system, a group of lines divided into subgroups, an impulse responsive automatic switch having access to said lines and a line incoming to said switch; said switch including a switching mechanism for connecting said incoming line to any selected one of said lines, said switching mechanism including a first set of contacts divided into subsets individually corresponding to a particular subgroup in said group of lines, a second set of contacts divided into subsets individually corresponding to a par-

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