US2171669A - Signaling system - Google Patents

Description

Sept. 5, 1939. J. E. OSTLINE SIGNALING SYSTEM Filed Oct 15, 1957 7 Sheets-Sheet 1 FIG. 2

FIG. 3

IE H

INVENTOR. JOHN E. OSTLINE BY M M ATTORNEY 5 '7 Sheets-Sheet 2 J. E. OSTLINE SIGNALING SYSTEM Sept. 5, 1939.

Filed Oct. 13, 1957 Rm v Emmy A momn ATTORNEYS Sept. 5, 1939. J. E. OSTLINE smmune SYSTEM Filed Oct. 13, 1937 7 Sheets-Sheet 3 INVENTOR. JOHN E.OSTL|NE ,W,MM

ATTORNEY5.

ept.5,1939. .E.OS'TUNE 2mm SIGNALING SYSTEM Fil ed Oct. 15, 1937 'TSheets-Sheet 4 ALLOTTER TO OTHER FINDER-CONNECTOR LINKS I JOHN E.OSTLINE BYWMIMM ATTORNEYS" Sept. 5, 1939. J. E. OSTLINE SIGNALINGHSYSTEM Filed Oct. 13, 1937 7 Sheets-Sheet 6 JOHN E. OSTLINE m M ATTORNEYS.

Sept. 5, 1939. 1.1. E. OSTLINE SIGNALING SYSTEM Filed Oct. 13, 1937 7 Sheets-Sheet 7 maze/E 10.5 6 05.

INVENTOR. JOHN E. OSTLINE BY 49 I ATTORNEY 5.

Patented Sept. 5,1939 V UNITED STATES SIGNALING SYSTEM John E. Ostline, Chicago, Ill., assignor to Associated Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application October 13,

43 Claims.

The present invention relates to signaling systems and more particularly to switching apparatus for use in automatic telephone systems.

In an automatic telephone system of any con-' system. Several types of switching units ion performing the above-noted functions are known in the art. One improved form of unit, which is well adapted for use. in the application noted and which possesses distinct advantages with respect to its features of construction andmode of operation, is disclosed and claimed in the present applicants co-pending application Serial No. 147,810, filed June 12, 1937. Briefly described, this unit comprises a circuit control element having mounted thereon contact segments rotatable with the control element in either of two directions to make or break contact between a multiplicity of wipers or bank conductors. These bank conductors are arranged in twosets so that, when the control element associated therewith is moved or rotated in one direction, the

conductors or wipers of one set are connected to the respective associated contact segments, whereas, if the control element is moved or rotated in the reverse direction, the conductors or wipers of the other set are connected to the contact segments. The arrangement as disclosed in the above-referred to copending application is such that the control elements of the various units are susceptible of being actuated by an operating member common to a group of the units and movable in either of two directions to actuate any controlling element operatively associated therewith in one or the other of its two directions of movement. Normally, the control elements are non-operatively associated with the operating member common thereto, means including clutch magnets individually included in the units being provided for operatively associating the respective elements with the operoperating member is in turn arranged, to be moved in either of two directions by means comprising a pair of operating magnets. When one of these two operating magnets is energized, the operating member is actuated to move any control element operatively associated therewith in a direction to cause engagement between the contact segmentscarried thereby and one set of associated bank conductors. With the other 55 magnet energized any control element operaating member to be actuated thereby. The

' to successively calling lines in a definite order. It

1937, Serial No. 168,726

tively associated with the operating member is rotated in the reverse direction to bring the contact segments carried thereby into engagement with the other set of bank conductors. The form of switching unit noted, together with the apparatus common to a group thereof for selectively operating the units of the group, is of exceedingly small size, is econom cal to manufacture and install, and is entirely reliable in operation.

It is an object of the present invention to provide a signaling system, and more particularly an automatic telephone system, embodying switching-units of the above form and wherein the control apparatus consists primarily of standard rotary switches and relays arranged in a simple manner such that a minimum amount of apparatus is required for a system of a given size.

It is a further object of the invention to provide, in a system of the character described, an improved line-selecting switch having a novel mode of operation such that the amount of apparatus required for a switch of a given size is reduced to a minimum.

It is another and more specific object of the invention to provide, in an automatic telephone system, an improved finder switch comprising switching units of the form just described so connected and arranged that the switch automatically operates to find, in an exceedingly short time interval, a calling line included in a group of lines extending thereto.

It is-a still further object of the invention to provide, in an automatic telephone system, an. improved impulse responsive line-selecting switch having embodied therein switching units of the form briefly described above.

In general, the objects as set forth above are attained in accordance with the present invention by providing, in a system of the character noted, a plurality of-improved finder-connector links for inter-connecting the lines of the system for communication thereover, and allotter means of improved arrangement for assigning the links will be understood that, when the apparatus is used in an automatic telephone system having a plurality of lines, at least a portion of the lines will have individually associated therewith subscribers substations, each including an impulsing device of conventional form. The lines of the system are divided into odd and even numbered groups, and included in each finder switch is means responsive to the initiation of a call on'any one of the lines terminating at the switch for selecting an odd numbered group of lines and an even numbered group of lines, one of which includes the calling line. Each finder switch also includes means for further selecting the one of the two selected groups of lines which includes the calling line and for simultaneously selecting a sub-group of lines in the selected group of lines, which sub-group includes the calling line. 'Ihe units selection of. the calling line is accomplished through the provision of means comprising a rotary stepping switch of standard construction for selecting the calling line from the selected sub-group of lines, which means also'operates to condition the connector portion of the associated link to be responsive to impulses .transmitted from the impulsing device included in the substation associated with the calling line. In the connector switch, forming a part of each finder-connector link, there is pro-- vided means responsive to one series of impulses transmitted from the impulslng device at the calling substation for selecting a group of lines which includes a called line. Thereafter, means comprising a rotary stepping switch are-caused to operate in response to a secondseries of impulses transmitted from the lmpulsing device at the calling substation to select a sub-group of lines in the selected group of lines and including the called line. Finally, means. comprising another rotary switch are causedto operateto select the desired line from the selected sub group of lines. I

More specifically, each of the flnder and connector switches comprises a plurality of switching units of the'form just described. each of which has terminating thereata number of the lines of the system, theline-terminating arrangement being such that when the control element of any'unit is moved or rotated in' one of its two directions of movement the unit selects a sub-group of lines included in an odd numbered group of lines, whereas movement of the control element in its other direction of movement re sults in the selection of a sub-group of lines included in an even numbered group of lines. In the case of a finder switch, the means which respondsto the initiation of a call on a calling line, selects a group of the switching units having extending thereto an odd. numbered group of lines and an even numbered group of lines one of which includes the calling line. Thereafter, the line sub-group selecting means operates to select from the selected group of units the unit to which the calling line extends and to determine, in accordance with the odd .or even number identifying the group of lines including the calling line, the direction of movement of the control element embodied in the selected unit. Following the operation of the sub-group selecting means the control element of the selected unit is moved to connect the lines of the selected sub-group, which includes the calling line, to the bank contacts of the rotary stepping switch, referred to above, and provided for selecting the calling line from the selected subgroup of lines. p

Each of the line group and line sub-group selecting means, as well as the. line units selecting means, comprises a rotary stepping switch of standard construction which conventionally comprises a motor magnet for driving the wipers respectively associated with the various sets of bank contacts embodied therein. These motor magnets-are connected and arranged successively to interact with a relay thereby successively to drive their respective associated wipers. When energized and operatively associated with any one of the motor magnets, this relay includes contacts interrupting the operating circuit of the associated magnet, and, similarly, any one of themotor magnetswhen energized and operatively associated with the relay noted, includes contacts interrupting the operating circuit of the relay; This feature of the invention is designed to reduce the cost of each link by reducing the number of control relays embodied therein.

' 'By virtue of the above described novel method of line selection, each finder switch is rendered exceedingly fast in its operation to find and seize a calling line, all without excessive operating speeds on the part of the various rotary switches involved. In thisconnection, it is men tioned here that in a finder switch of the specific form described hereinafter, designed to have access to one thousand lines, the line group selecting function is completely performed at the end of a maximum of five steps taken by the rotary stepping switch provided for performing the line group selection. Similarly, the line sub group selection is completed when the rotary stepping switch provided for this purpose has taken a maximum of five steps. Further in accordance with this feature of reducing the linehunting time interval, the line units selecting switch is arranged so that in operation it tests the lines of a selected sub-group of lines in pairs. To this end, each sub-group of iines,'as extended to the bank contacts of the last-mentioned rotary switch, are broken down into two smaller sub-groups; the lines of which terminate at different sets of the bankcontacts. A pair of relays, one of which corresponds to one of the small sub-groups of lines and the other of which corresponds to the other small sub-groups of lines, are provided for performing line-testing functions. By this specific arrangement the lines of a sub-group of twenty lines may all be tested by ten steps on the part of the rotary switch. Thus, a combined maximum of twenty steps on the part of the three stepping switches suffices to cause any line of a thousand line plurality to be searched for and selected by any finder switch.

The connector or line-selecting switches are somewhat similar to the finder switches in that each thereof comprises a plurality of switching units having a number of the lines of the system terminating thereat, and the control element of each unlt'is movable in one direction to, select a sub-group of lines included in an odd numbered group of lines and inanother direction to select. a sub-group of lines included in an even numbered group of lines. The first impulse responsive means, as referred to above, functions to select a group of switching units to which extend an odd numbered group of lines and an even numbered group of lines, one of which includes the desired or called line, and, also, to determine the direction of movement of the control elements respectively embodied in the units of the selected group in accordance with the odd oreven number identifying the group of lines which includes the desired line. The means referred to above, which/ responds to the second series of received impulses, normally functions moved in the direction determined by the operation of the selecting means which responds to the first series of received impulses. The lastmentioned operation serves to connect the subgroup of lines including the called line to the bank contacts of therotary switch, mentioned above, which functions to select the desired line from the selected sub-group of lines. In the particular arrangement disclosed, each sub-group comprises twenty lines and in order to adapt this number of lines to the decimal system of selection, conventionally employed, there is provided a wiper switching relay for selectively associating the link line extending vto the connector switch with either of two smaller subgroups, of ten lines each, making up a sub-group of lines extended by way of one of the switching units to the bank contacts of the rotary switch noted. This relay is under the control of the means which responds to the second series of received impulses and the condition thereof is determined by the number of impulses comprising the second series of impulses transmitted,

from a calling subscriber's substation.

Each of the finder-connector links also includes means for testing a selected called line to determine its idle or busy condition, means for establishing a connection between the calling and called lines inthe event the called line is idle, and means for applying busy tone current to the calling line'in the event the called line is found busy. Further features of the invention relate to the specific circuit arrangements whereby the elements of the various means briefly referred to above perform the particularfunctions assigned thereto.

In accordance with a further feature of the invention means comprising the impulse responsivemeans described above are provided for causing the switching units embodied in each connector switch automatically to select an idle trunk line from a small group of such lines upon the dialing of a predetermined two digit number at a calling subscriber's substation. As pointed out more particularly hereinafter, this means operates in a manner such that a. clear metallic circuit is established through a seized link following the seizure thereby of one of the trunk lines.

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 Figure 1 illustrates switching apparatus constructed and arranged in accordance with the invention disclosed in the above referred to co-pending application; Fig. 2 is a'broken side view showing the details of one of the switching units shown in Fig. 1; Fig. 3 is a view, partially in section, taken along the lines 3-3 .of Fig. 2; Fig. 4 is a view illustrating the details of the clutching mechanism incorporated in the switchingunit shown in Figs. 1 and 2; Figs. 5 and 6 illustrate the finder portion of a finder-connector link embodied in an automatic telephone system constructed and arranged in accordance with the present invention; Fig. 7 illustrates the allotter means embodied in the system; and Figs. 8, 9 and 10 illustrate the connector portion of the finder-connector link including the finder switch shown in Figs. 5 and 6.

Referring now more particularly to Fig. 1 of the drawings, there is illustrated the improved switching apparatus disclosed and claimed in the above-referred to co-pending application. In brief the apparatus comprises a frame It, divided into two sections II and I2 for respectively accommodating a plurality of switching units I3, l4, l5, etc., and means common to these units for actuating the various circuit controlling elements thereof. The three units I3, I4 and i5 are shown as being mounted on the frame In within the section II by means comprising bolts I8 and I1 extending through the top and bottom members 8 and 8, respectively, of the frame l0.- It is contemplated that with this arrangement the size of the section II for a frame l0 designed to accommodate the switching units for a particular installation shall be sufficient to accommodate the number of units ultimately required-to serve the maximum estimated line capacity of the apparatus.

The actuating means for the various circuit controlling elements embodied in the several switching units comprises a member I8, slidably mounted in openings provided in the end and intermediate members is, 20 and 2| of the frame I0 and having rigidly supported thereon a magnetic piece 22, which forms the armature for each of two actuating magnets 23 and 24 mounted respectively on the frame members 20 and 2| by means of screws 25 and 28. The actuating member I8 is restrainedin a normal position when both of the two magnets 23 and 24 are deenergized by means comprising coil springs 21 and 28 cooperating respectively with pivoted arms 29 and 30 which bear against opposite sides of the armature piece 22. The arm 29 is pivotaily mounted on the upper member of the frame i0 and is limited in its movement to the left through the force exerted thereon by the spring 21 by a stop pin 3| also mounted on the frame ill in any suitable manner. Similarly, the arm 30 is pivot ally mounted on an extension 32 of the member 2| and is limited in its movement to the right under the force of the spring 28 by a stop pin 33 also supported on the frame l0. It will be observed that the member IB is movable in either of two directions depending upon which of the two magnets 23 and 24 is energized. Thus, if the magnet 23 is energized, it attracts the armature piece 22 to the left against the bias of the spring 28 to move the armature piece to the left. In a similar manner and with the member l8 and the armature piece 22 in the position shown, when the magnet 24 is energized, these two members are moved to the right against the force exerted thereon by the spring 21. It is noted that the frame 10, the member i8 and the armature 22 are all constructed of magnetic material, such, for example, as iron, thereby to provide a low reluctance, substantially closed, magnetic circuit for the flux produced when either of the two magnets is energized and to enhance the force ex-- erted on the armature piece 22 following energization of either of the two magnets.

Referring now more particularly to Figs. 2, 3

v and 4 .,of the drawings, wherein the switching unit of the frame 34. Supiitdzed on and insulated from the shaft 31 by means comprising an insulating tube 33 are a plurality of contact segments 48 alternated with a plurality of insulating washers 4 I. For the purpose of fixedly positioning the segments on the shaft 31, thereis provided a fiber key 42 which is adapted to. rest in a key slot formed in the shaft and to extend through suitably formed keyways cut in the tube 33, the segments 4!) and the washers 4|. The segments 48 and the insulating washers 4| are pressed together against an annular ring 43 by means comprising a nut 44 threaded on the right extremity of the shaft. It will be noted that the ring 43 is fixedly mounted on the shaft 31 (by apin 45 driven into a tapered drill hole extending through the ring and the shaft.

Each of the contact segments 48', is electrically connected to a terminal 46. bya flexible pigtail connector 41, formed of copper braid or the like,

this arrangement, a switching unit of extremelyv small size for a given line capacity is obtained.

As shown more particularly in Figs. 2' and 3, each of the contact segments 40 is roughly triangular in shape, is rounded at its upper end, and is provided with a V-shaped groove, the sides of which form the contacting surfaces for engaging with either of two associated wipers. These wipers form two sets comprising respectively the resilient conductors 5| and-52 arranged in rows with their ends disposed on opposite sides of the contact segments. Preferably, these conductors are constructed of bronze or like resilient material and are supported on the frame 34 by clamping the same at the upper ends 'thereof'between insulating members '53,- 54 and 55. The members noted are clamped togetherand to the frame 34 by screws 56 extending therethrough and threaded into tapped drill holes provided in the frame 3-4. For the purpose of guiding the various wipers intheir movement, there is provided intermediate the upper and lower ends thereof a guide member 51 ofinsulatingmaterial supported on the frame 34 by means comprising spacing members 58, located at each end of the member 51, and clamping screws 68. Each of the wipers 5| and 52 is tensionedor biased into engagement with'this member and moves in a guide slot provided therein when engaged by its respective associated contact segment 40. The lower ends of the wipers 5| and 52 are curved outward to insure a smooth engagement with the respective associated contact segmentswhen the segments are rotated into engagement therewith. It willbe observed that the V-shaped groove pro- .vided in the engaging end of each of the segments insures a two-point contact between the segment and its associated wipers. It will be observed further that during rotation of the segments aslidable engagement occurs between each segment and its respective associated wipers to provide-a self-cleaning action-ofthe contacting surfaces. Normally, the segments are restrained in the position shown in Fig. 3 of the drawings by means comprising a coil spring 6| connected between an arm 62 projecting from the annular mutating segments 40 into engagement with the respective associated wipers 5| or 52 of the two wiper sets. Such rotation of the shaft 31 is accomplished through operation of. the actuating member l8 from the normal position shown in Fig. 1 to one or the other of its two off-normal positions. To this end, and as best shown in Figs. 2 and 4, the member |8is provided with a clutch projection 64 extending from the edge thereof, which projection is adapted to cooperate with a clutching element65, slidable axially along the shaft 31, and normally restrainedto the left out of engagement with the projection 64 by a coil spring 61, interposed between the clutching element and the annular ring 43 and enclosing the shaft 31'. A pin 66, extending through. a drill hole provided in the shaft, engages-the sides of a slot 68 out in the shank portion 69 of the clutch element to form a stop against which the element 65 is normally braced, to guide the element 65 in its'movement axially along the shaft 31 and to provide means for mechanically coupling the element 66 with the shaft 31. The radially extending flange portion of the element 65 has formed at its lowerend two fingers 18 and 1| within which the projectionv 64 on the member |8 is'adapted to extend when the element 65 is moved to the right. It will be noted that the sides of the fingers 10 and for engaging the projection 64 are rounded so that, when the member I8 is moved in either of its directions of movement, free and unrestricted movement of the ment 65 to rotate the shaft 31 is obtained.

For the purpose of moving the clutching element 65 to the right to a position such that the projection 64 on the actuating member |8 extends between the fingers 10 and 1|, there is provided a small relay or clutch magnet 12 mounted on an inturned portion 58 of the frame side memele-.

ber 36 by means of a screw 14. Pivotally mounted at 15 in a slot formed in the member 36 is an armature 16 having mounted thereon an arm material, such, for example, as iron, whereby a. substantially closed magnetic circuit, including the armature 36, is provided for the fiux produced.

when themagnet 12 is energized. For purposes of control, there is mounted on the frame side member 36 'a contact spring assembly 8|, comprising two or more contact springs clamped between in sulating members as shown, and secured to the 11. This arm 11 is slotted at its lower end to form two fingers 19 and which extend over the frame member 36 by a screw 82. 'The making and breaking of contact between the two springs comprising the assembly 7| is under the control of an arm 82 formed integrally with the armature 16 "and provided with an insulating cap 83 for engaging the lower end of the right hand spring included in the spring assembly. In order to hold the shaft 31 and the segments carried thereby operated independently of the condition of the magnet 12 and following the energization of this magnet and one or the other of the magnets 23 and 24, the projection 64 is preferably made of square or triangular cross section and the inner opposite sides of the fingers 10 and 1| are gized to bring the provided with V-shaped grooves for lockingiy engaging the opposite edges of the projection 84. By this arrangement, the clutching element 65 may be held clutched to the projection 61 even though the magnet 12 is deenergized, so long as the energized one ofthe magnets 23 and 24 is not deenergized.

.In the operation of the switching unit described above and with'the elements thereof in the positions illustrated in Figs. 1, 2, 3 and 4, if it be desired to connect the lines outgoing therefrom which terminate at the set of wipers including the wipers'iii, the magnet 12 is first eneractuating member I 8 into driving relationship with the shaft 3?. Thus, when the magnet 12 is energized, it attracts its armaturelt to make contact between the two springs of the assembly 8! and to pivot the arm 17 counterclockwise, thereby to slide the clutching element 65 along the shaft 37 against the bias of the spring 67 until it stands in a position such that the fingers 1c and H of the clutching element 65 have extending therebetween the projection 84 mounted on the actuating member ,I 8.

From a consideration of Figs-3 and i, it will be seen that the contact segments til must be rotated in a counterclockwise direction in order to connect the lines incoming to the unit to the outgoing lines terminating at the wipers 50. This means'of course, that the actuating member it? must be moved to the right from the position shown in Fig. 4 and to the left from the position shown in Fig. 1, and consequently requires that the operating magnet 23 be energized. When this occurs, the finger 68 engages with the finger iii of the clutching element 65 to rotate the shaft 37 in a counterclockwise direction and bring the contact segments 40 into engagement with their respective associated wipers 5!], thereby to con! nect the lines incoming to the unit to the lines terminating at these wipers. The operating magnet 26 is maintained energized so longas the connection between these lines is desired. To restore the elements of the unit to normal, it is only necessary to deenergize the magnet 25,

:whereupon the clutching element 65 is disengaged from the actuating member it under the force exerted by the spring 61 subsequent to the return of the member id to its normal position by virtue of the force exerted thereon by the spring 28. As explained above, when the clutching element 65 is disengaged from the actuating member I8, the shaft 31 and the commutating segments 40 carried thereby are restoned to their normal positions through the force exerted on the shaft 31 by the spring 6|. From the preceding description, it will be understood that, if it is desired to connect the lines incoming to the switching unit to the lines outgoing therefrom which terminate at the wipers 52, the exact sequence of operations described above is followed with the exception that the operating magnet 24 is energized rather than the magnet 23.

As noted previously, the actuat ng member i8 is arranged selectively to operate the circuit controlling elements embodied in all of the switching units mounted within the section II of the frame In. This is accomplished by providing projections, corresponding to the projection B for the unit H, at correctly spaced intervals along the actuating member it, which projections are adapted individually to cooperate with clutching elements individually included in each of the switching units and corresponding to the element 65 of the unit 13, when the units are mounted in their correct line is found busy and for positions within the section ii of the frame l0.

Referring now more particularly to Figs. 5 to 10 of the drawings, there is illustrated an automatic telephone system connected and arranged in accordance with'th'e present invention and having embodied therein switching apparatus of the form just described. In general, the system comprises a plurality of telephones or subscribers substations, three of which are indicated at A, B and C, adapted to be interconnected by means including; their respective associated lines Ht, 220 and 2| I, and finder-connector links of the form illustrated. While these links may be designed to serve any desired plurality of lines, it is specifically contemplated hat the links, corresponding to and including the link illustrated, will have access to and be accessible to one thousand subscribers lines. These lines are divided into ten one hundred line groups, numbered consecutively from one to zero, and, as outlined above and pointed out in greater detail hereinafter, the mode of line selection in both the finder and connector portions 'of each link is predicated on the odd and even numbers identifying the various line groups. The number of finder-connector links to be provided obviously will depend upon the telephone trafiic to be handled over the plurality of lines terminating 'thereat. In any case, it will be understood that each subscribers line is multipled to the corresponding bank conductors of the finder and connector switchesembodied in a plurality of links. For the purpose of allotting the links to successive calling lines in a definite order, there is provided the allotter means illustrated in Fig. 7.

This means, as will be pointed out with greater particularity hereinafter, operates in a manner such that an idle link is always in readiness for instant seizure by a calling line. A further general feature of the arrangement illustrated pertains to the provision of control means in the connector portion of each link for testing any selected called line to determine the idle or busy condition thereof, forapplying busy tone current to the calling line in the event the selected called connecting the calling line to the called line in the event the called line is found idle. An additional general feature of the arrangement is concerned with the provision of means whereby automatic trunk hunting ocours in the connector portion of each link upon the dialing of a predetermined digit at the substation of a calling party having a line terminat' ing at the links.

Neglecting for the present the details of the finder and connector switches, the allotter. means, and the control means respectively included therein, the system as briefly described immediately above is, ingeneral, quite similar to conventional prior art systems, the operation of which is well understood in the art. In brief, when a. subscriber, such, for example, as the subscriber at the telephone A, initiates a call over the line Hi to a second subscribers telephone, such, for example, as the telephone B, by lifting his receiver from its hook, the finder-connector link, previously assigned by the allottermeans illustrated in Fig. 7, is started in'operation to search for and seize the calling line. Assuming that the link illustrated is delegated by the allotter means to set up the connection, the finder portion of the link operates to select the calling line and to connect it through to the link conductors leading to the connector portion of the switch. Whenthe calling line is seized, and extended by way of the finder switch to the associated connector switch, the control equipment of the last-mentioned switch is automatically conditioned to be responsive to the first series of impulses transmitted from the impulsing device conventionally provided at the substation A.

In response to the dialing of the first digit at the substation A, the connector portion of the link operates to select a group of lines including the called line 220. Thereafter and in response to the dialing of the second digit, a subgroup of lines including the called line is selected from the selected group of lines and, at the conclusion of this digit, the control equipment of the connector switch is conditioned to respond to the. third or final series of impulses'dialed at the calling substation. With the link in thiscondition and when the third or final digit is dialed, the connector switch operates to select the called line from the selected subgroup including the same and to test the condition thereof to determine its idle or busy condition.

If the called line is found busy, busy rent is applied to the'loop extending to the calling subscribers substation, whereas, if the called line is idle at the time it is selected, ringing current is automatically applied thereto and ringback tone current is applied to the loop extending to the calling subscribers substation. Finally, the connection between the calling and called lines is completed when the called'substation B is answered. As pointed out in detail hereinafter, the arrangement is such that a link utilized in setting up a desired connection is released only when both the calling and called partieshave restored their respective receivers to the associated hooks.

In the use of the link to select a trunk line terminating in the bank conductors of the connector portion thereof and outgoing to a distant exchange, only two predetermined digits needlbe dialed at the calling substation. The impulses comprising these two digits, when received at the connector portion of the link, cause a subgroup of lines consisting solely of trunk lines to be selected, and condition the apparatus normally operative to select a particular called line tofunction in the manner of a trunk hunting selector switch. Immediately, the series of impulses comprisingthe second digit is concluded, this lastmentioned apparatus is started into operation in search of an idle one of the trunk lines. When an idle trunk is found, the trunk hunting operation is interrupted and the calling line is extended byway of the idle trunk to the terminating apparatus located at the distant end of the seizedv trunk. The arrangement is such that all voicefrequency coupling elements, such, for example,

as condensers, are eliminated from the conversational circuit when this circuit includes oneof the trunk lines. The release of a link involved in a connection extended by way of one of the trunk .lines is under the control of the apparatus at tone cur-- p 5, etc., and clutch magnets, one of which is indicated at M520 for the unit 505. It will be understood from the preceding description that each of the units 505, 506, etc., is identical with the unit described above with reference to Figs. 1 to 4, inclusive, and that the frame 504 corresponds to the frame l0 shown in Fig. 1. Each of the switching units 505, 506, etc., like the correspending unit shown in Fig. 2, includes two sets of bank conductors or wipers oppositely disposed with respect to the contact segments carried by the control element embodied in the unit, and having terminating thereat a number of the lines of the system. It is contemplated that each of these sets shall contain sixty conductors so that twenty, three-conductor lines, may be terminated thereat. Thus, each switching unit has extending thereto forty lines, with the result-that twenty-five units are required in each finder switch for the termination of the one thousand lines extending thereto. It is noted here that the twenty lines extending to one set of blank conductors embodied in each switch are included in an odd numbered group of one hundred lines and that thetwenty lines extending to the other set of bank conductors of the same switch are included in the next succeeding even numbered group of one hundred lines. Thus, the switch 505 has extending to its bank conductors, indicated to the left of the control element 501, thelines numbered from H0 to I20, inclusive, and the group of bank conductors, indicated to the right of the control element 501, have terminated thereat the conductors of the lines numbered from 2l0 to 229, inclusive. As noted above, the conductors of the various lines extending to the finder switch ing two groups containing one hundred lines each. This is accomplished through the operation of means comprising a rotary stepping switch 602 which is responsive to the initiation of a call on one of the lines extending to the finder switch and which functions to select a group of the switching units 505, 506, etc.. to which extend two groups of lines one of which includes the-calling line. More specifically, the operation of the switch 602 is controlled by the line relay associated with a calling line, the gang relay R580 associated with the link illustrated, and certain of the relays included in the allotter means. Selection of the group of units is accomplished through the operation of the switch 602 to prepare circuits for energizing the clutch magnets individually included in the units comprising the selected group.

Selection of the subgroup of lines which includes the calling line is obtained'through the operation of means comprising the rotary stepping switch M2 to select the one of a group of units, selected by the switch 602, to which the calling line extends and to determine the direction of movement of the control element embodied in the selected unit in accordance with the odd or even number identifying the group of lines including the calling line. The switch H2 is, in operation, controlled by certain of the relays embodied in the allotter means, which relays are in turn controlled by circuits extending by lines. These magnets comprise means for actuf ating the operating member EH to move any control element operatively associated therewith in either of its'two directions of movement, which means is, through the control exerted theron by the relays embodied in the allotter means, only operative following the energization of one of the clutch magnets.

As noted above, the proper selection of a particular switching unit, followed by the operation of its control element to the selected off-normal position, causes a subgroup of lines including the a calling line to be selected. These lines are extended by way of the contact segments carried by the control element of the selected unit to the bank contacts of a rotary switch 538,-which forms a part of means for selecting the particular calling line from the selected subgroup of .lines. This switch comprises six contact sets often contacts each, and of these contact sets the three upper sets have connected thereto ten of the contact segment sets of each of the twentyfive switching units embodied in the finder switch and the three lower contact sets have connected thereto the remaining ten contact segment sets of each of the switching units. By this arrrangement, and when a selected switching unit is operated, twenty lines, divided into two small subgroups of ten lines each, are extended to the bank contacts of the switch 538, so that this switch may operate simultaneously to test the lines in pairs until the calling line is found. If the calling line is included in one ten-line group and when this line is found, a polarized relay R510 is caused to operate to switch the line conductors thereof through to the line conductors Cl l7, Cl I 9 of the link line extending to the switch 538. .If, on the other hand, the calling line is included in the second smaller subgroup of ten lines, a polarized relay R560 is caused to operate to connect the line conductors thereof to the link line conductors noted.

The line selecting means embodied in the connector portion of each link is, from the standpoint of the apparatus involved, quite similar to that included in each of the finder switches, as briefly described above. Thus, the connector switch shown comprises twenty-five switching mits i0l3, l0l4, etc., of the form shown in Figs. 2 and 3, mounted in a frame l0l2 and having :ommonly associated therewith an operating nember l0l9 under the control otmeans com- )rising two operating megnets MIOZ0 and Ml030, :orresponding, respectively, to the odd numbered :roupsof lines andthe even numbered groups of ines. Each of these units includes a circuit conrolling element, corresponding to the element 3'! or the unit shown in Figs. 2 and 3, that for the wit l0l4 being indicated at l0l6, normally noniperatively associated with the operating memer IMS and arranged operatively to be associ- .ted' with this member by clutch means comprisng a clutch and a clutch magnet, these two elements for the unit l0l being indicated at l0|8 and Ml0l0, respectively. "Forty subscribers lines are terminated at each switching unit, twenty of these lines extending to the bank conductors of one of the two bank conductor sets embodied therein, and twenty extending to the bank conductors of the other bank conductor set. These two twenty line subgroups terminated at each unit are respectively included in consecutively numbered odd and even groups of lines. For example, the lines extending to the conductor set of the unit i035 indicated to the right of the shaft iilifi are consecutively numbered from 2M to 229, whereas, the lines extending to the conductor set indicated to the left of the shaft i966 are consecutively numbered from lid to me.

For the purpose of selecting a group of one hundred lines which includes a desired called line, there is provided means comprising a rotary switch I042, which responds to the first series of impulses transmitted to the connector switch and functions to selectthe group of switching units to which the lines of the group of lines including the called line extend. Thus, with the wipers oi the switch i032 standing in any oilnormal position, five switching units are tentatively selected by virtue oi the preparation of circuits for energizing the clutch magnets respectively embodied therein. The means noted, namely that comprising the switch M62 further operates, in accordance with the odd or even number identifying the group of lines including the called line, to determine which of the two magnets Millie and Midfid is to be subsequently energized, thereby to determinethe direction of movement of the control element embodied in the switching unit which is ultimately selected.

The selection of the subgroup of lines including the called line is accomplished through the operation of means responsive to the second series of impulses transmitted to the connector switch n and comprising a rotary stepping switch.i002

which functions to select the particular switching unit to which the called line extends by further preparing the operating circuit for the clutch magnet embodied therein. Thus, this switch, through the operation of its" wiper SWIBM to a particular off-normal position, determines the one of the five clutching magnets, selected by the operation of the switch i862, which is to be energized, and thereby selects the one of the switching units which is to be operated upon the subsequent energization of one or the other of the magnets M5620 and Ml030. This switch also functions to control the wiper switching relay R960 in the manner pointed out hereinafter.

The contact segments carried by the control element of each unit are connected to the contacts of the contact sets included in a rotary switch 01 which switch responds to the third series of impulses transmitted to the connector switch and, in conjunction with the wiper switching relay R960, comprises means for selecting a desired line from a selected subgroup of lines. In this connection, it will be appreciated that, with any one of the switching units operated to one of its two off-normal positions, twenty lines will be connected to the bank contacts of the rotary switch 914 so that when this switch is subsequently caused to operate it functions to select the called line from the subgroup of twenty lines extended thereto.

As pointed out above, each of the links further includes means for testing a selected called line to determine its idle or busy condition, for applying busy tone current, to the calling'line in the event the called line is found busy, for applying ringing current to the called line: and

ring-back tone current to the calling line in the event the called lineisidle, and for connecting .the "calling line to. the called line in the event the called line is idle and the called substation is 'answered. This means comprises the. busy relay R940, the-ringing relay R950, the ring cutcharacteristic which it off relay R930, and a slave relay R050, together with the operating. circuits therefor. Additional relays R010,- R020, R830,'R840, R050, R860, R010, R900, and R910 are provided in each link for controlling the operation of the various rotary switches and relays referred to' above, all in the manner described with particularity,hereinafter.

Itis-noted here that each or the relays embodied in the a paratus shown is of standard commercial construction and is conventionally indicated in the drawings in accordance with the operating possesses.

The allotter means, illustrated in Fig. '1, comprises, ln addition to the relays R110, R120, R130,'R1l0, R150, R160, and R110 for controllinggthe operation of any seized finder-connector link; a rotary stepping switch 102 which,'in

' combination with certain of the relays noted,

functions to allot the'links to successive calling lines. This stepping switch, together with the other switches of similar type, corresponding to and including the enumerated switches 530, 602,

6l2, 014, I002 and I042, may be of any standard 3 commercial construction which comprises bank contacts arranged in sets, wipers respectively,

associated with the contact sets, and meanscomprising a motor magnet for driving the asso-. ciated wipers. Certain of these rotary switches,

.namely the switches included in the connector subscriber dials the number 01. This causes the rotary switch 1042 to be operated to its tenth off-normal position and the switch 1002' to opersite to its first off-normal position thereby to cause the rotary switch 914 repeatedly to operate under the control of means comprising the two relays. R910 and R920 until an idle trunk in a groupof trunks outgoing to a distant exchange is found. The finding of such a trunk is followed by the'operation of R800 which stops the trunk hunting operation of the connector switch and switches the calling linethrough by way of the selected trunk to the distant exchange.

Operation of ajlnder switch to find a calling line in an odd-numberedgroup' of one hundred lines Referring now in greater detail to the operation of the apparatus to establish a connection between the lines Ill and 220 on a call from the substation A to the substation B, operation of the finder switch illustrated in Figs. 5 and 6 is initiated when the calling party at the substa tion A lifts his receiver from its hook to complete a circuit for energizing the line relay R500. The circuit noted extends from ground at RA5I2 by way of C100, the direct current bridge across the line conductors C|00 and C101 at the substation A, Cl0l., RM and through the winding of R500 to battery.

When R500 operates in response to its energization over the abovetraced circuit, it marks, at RA50I, the calling line in the bank conductors of the switch unit 505 by extending battery from the cut-off relay R510 to the bank conductor 524.

. At its armature RA502, the relay R500 prepares a circuit, traced -hereinafter, for energizing R150 included in the allotter means illustrated in Fig. 7. At its armature RA503, the relay R500 applies ground to C106 to mark, in the contact set associated with SW600, the contact corresponding to the, group of one hundred lines which includes the calling line Ill. The operation ,of RA503 also completes a circuit for energizing R110 embodied in the allotter means illustrated in Fig. 7, this circuit extending from' ground at M503 by way of CI05, C151, RAHI, the winding of R1I0, MA10I and through the winding of M100 to battery.. Due to the high resistance of the winding of.R1|0, the magnet M100 included in the rotary switch 102. does not operate. The relay R1l0, however, operates to complete, at RA1I2, an obvious holding circuit for itself, and to complete, at RA" 1, a circuit for energizing the upper windings of R150, R150 and R110. The last mentioned circuit extends from ground at RA1H to 0150, where it divides, one branch extending throughthe upper winding of R110 to battery, and the other branch extending through the upper windings of R100 and R150 in series to batt'ery'. The three relays noted are of the polarized type and do not operate in response to the ener- ,extending from ground at RAH; by way of SW103, CIII and the winding of R580 to battery. As noted previously and pointed out in greater detail hereinafter, the rotary switch 102 functions to allot the'various finder connector links to successive calling lines in a definite order. The arrangement is such that SW103 always stands in engagement with an associated contact corresponding to an idle finder connector link. Thus, in the present assumed case, wherein the link illustrated is idle at the time the call is initiated on the line I. and is selected by the allotter as the link for use, SW103 stands in engagement with the contact corresponding to this link so that the link. is seized immediately upon opera-tionof R110. Y

When energized over the above-traced circuit, R500 operates 'to complete at RA583 a circuit for energizing the. respective lower windings of R560 and R510 in series, thereby to render these relays, which are of the polarized type, exceedingly fast to operate when their respective upper windings are subsequently energized. The circuit noted'exten'ds from ground'at RA583 through the two windings notedto battery. Y At its armatures RA58I and RA582 the relay R500 prepares circuits for energizing the respective upper windings of R560 'andR510. At RA594, the relay R580 complete'sa circuit for energizing M500 included in the rotary switch 602, this circuit extending fromground atfRA12l by way of C159, RA15I,-

= switch 602 above-traced circuit, prepares theswitch 602 to step the switch wipers embodied therein one step and completes, at MA001, a circuit for energizing R120. The last-mentioned circuit extends from ground at MA601 by way of C125, RA553, C133 and through the upper winding of R120 to battery. The relay R120 now operates to interrupt; at RA121, the above-traced operating circuit for M600 causing this magnet to be deenergized, whereupon the switch wipers of the switch 602 are stepped one step or into engagement with the respective first contacts of their respective associated contact sets. When M600 is deener-- gized to restore MA601, the above-traced operating circuit for R120 is interrupted so .that the operating circuit for M600 is again completed at RA121. This interrelated operation of R120 and M600 continues until SW6" is moved into engagement with the contact corresponding to the group of switching units including the unit at which the calling line 111 terminates.

In the present case, wherein the calling line is included in the No. 1- group of one hundred lines, terminating at the group of units including the unit 505, the switch wipers-of the switch 802 are stepped only one step. When this occurs, a circuit is completed for energizing R110 included in the allotter means, this circuit extending from ground at RA503 by way of C106, the second contact of the contact set associated with SW608, C121, RA561, C134, and through the lower winding of R110 to battery. The relay R110 immediately operates, to interrupt, at RA111 and R0112, the above-traced circuit for M600 and to complete, at RA111 and RC113, a circuit for energizing M610 embodied in the rotary switch .612. The last-mentioned circuit extends from ground at RA121' by way of C159, RA151, RA161, RA111, R0113, C135, RA590, C126 and through the winding of M510 to battery.

Before describing the operation of the rotary switch 612, it is pointed out that the operation of therotary switch 602 to select the group of units including the unit at which the calling line terminates, completes a path for marking, in the bank contacts of the switch 612, the particular unit of the selected group at which the calling line terminates and for identifying the odd or even number of the group of lines, terminating at the selected group of units, which includes the calling line. This path extends from ground at RA562 by way of 0128, SW609, the second contact of the contact set associated with SW609, C105, RA502, C101, to the second contact of the contact set associated with SW614. The application of ground to the last-mentioned contact identifies the calling line as terminating at the switching unit 505 and further as'being included in the No. 1 group of one hundred lines rather than the No. 2 group of one hundred lines. The

further operates to prepare the operating circuits for the clutchmagnets embodied in the selected group of switching units. Thus, with the switch wipers SW603 to SW601, inclusive, standing in engagement with the respective second contacts of their respective contact sets, circuits are prepared for energizing the clutch magnets of the flve'switching units making up the selected group of units. These circuits extend by way of the conductors corresponding to and including C143 which terminate at the respective second contacts of the contact sets noted.

Continuing now with the operation of the rotary switch 612, when M610 is energized over the above-traced circuit, it attracts MA61I to.

complete a circuit for energizing R120, this circuit being identical with that traced above in connection with the operation of the switch 602, with the exception that it extends from ground at MA611 rather than from ground at MA601 associated with M600. The resulting operation of R120 causes the interruption of the operating circuit for M610, at RA121, in the same manner as was described above for the magnet M600. 'i'hus, R120 and M610 interact upon each other to cause the switch wipers of the sw tch 612 to be stepped until the switching unit included in the selected group of units and having the calling line extending thereto is found. In the present assumed case, wherein the calling line is included in the subgroup of twenty lines terminating at the unit 505 and included in an odd numbered group of one hundred lines, the, switch wipers of the switch 612 will be moved only one step at which time a circuit is completed for energizing the lower winding of R150. This circuit extends from ground at RA592 by way of C128, SW609,

C105, RA502, C101, SW614, C124, RA588, C131, 'RA163 and through the lower winding of R150 to battery. In response to the energization of its lower winding, R150 immediately operates to interrupt, at RA151, the operating circuit for M610, thereby to stop the rotary switch 612. With M600 and M610 deenergized, the operating circuit for R120 is opened at MA601 and MA611 so that this relay also remains deenergized. At this point,

it will be noted that the switching unit 505 at which the calling line terminates is selected and that the direction of movement of its control element 501 to connect the lines ofthe subgroup including the calling line tothe bank contacts of the switch 538, is determined. Thus, immediately upon the operation of R150, a circuit is completed for energizing M520 embodied in the switching unit 505, this circuit extending from ground at RA154 by way of C138, RA501, C123, SW613, SW603, C143 and through the windin of M520 to battery. This magnet, which corresponds to the magnet 12 illustrated in Fig. 2 of the drawings, attracts its armature MA521, thereby operatively to associate the control element 501 of the switch 505 with the operating member 515 through the medium of the clutch 509. Simultaneously with the energization of M520, an obvious circuit is completed at RA152 for energizing the slow-to-operate relay R140 and, short- 1y after the operation of the clutch magnet M520, the last-mentioned relay operates to complete a circuit for energizing M540 associated with the operating member 515. This circuit extends from ground at RA143, by way of RA155, R0156, C139, RA586 and through the winding of M540 to battery.

The magnet M540, upon being energized, attracts to the left the armature carried by the operating member 515, thereby to rotate the control element 501 and bring the contact segments carried thereby into engagement with the contact wipers shown to the left to the control ele- -ment. At MA541, the magnet M540 prepares a holding circuit for itself which is completed upon the subsequent operation of R560 or R510. With the contact segments of the switch 505 standing in engagement with the wipers shown at the left of the shaft 501, the subgroup of twenty lines terminating at these wipers are connected by way of the contactsegments engaging respectively therewith, to the bank contacts of the rotary switch 538, as indicated by the lines 230 and 231. This subgroup of twenty lines includes 7 switch wipers SW an obvious circuit is completed'at RA142 of R140 I for energizing'the slow-to-operate relay R120, and, shortly' after the control element 501 has for energizing M530 embodied in the rotary switch 538. This circuit extends from ground at 'RA12I by way of (H59, RA134, C-l4l, RA584, RA515, RA569' and through the winding of M530 to battery. In response to above-traced circuit, M5 30 attracts its armature wipers of the switch 538lto be stepped until the 532, SW533 by way r RA50I, CI04, switch wiper 524, segment 8, Cl09, SW534, CH2, and through the upper winding of R510 to ground at RA50I. The

relay R510 immediately operates tointerrupt, at'

RA515, the operating circuit for'M530; causing this magnet and R120 to remain deenergized. At

RA568, Cl20, RA513,

of M540 to battery, and holds the magnet noted energized independently of the cluded in theallotter means. RA513, the relay R510 completes a path for shortcircuiting its upper winding and a circuit for noted extends from grou'nd'at R510, back to ground at RA501, and the circuit for energizing the 'cut-ofl relay 'R5l0 extends over i t previously traced v relay R500 and to and RA503, the operating its energization over the apparatus in- At its armature 1 RA503 by way of and the upper winding of to cm to cause the energization of R5l0 also marks the calling line III as busy in the bank conductors of the connector switches to whichthis line extends. The cut-oi! relay R5I0, upon being energized over the above-traced circuit, operates to interrupt, at RA5I| and RA5| 2, the operating circuit for the line shunt, at, RA5 I 3, the armature RA50| of the line relay R500, thereby to hold itself energized when R500 restores. When R500 restores, it interrupts, at its armatures RA502 circuits for the relays R150 and R110 included in the allotter means When R1l0 restores, it interrupts, at

it interrupts the operating circuit for R500, causing this relay to restore. When R150 falls back, it interrupts, at RA'4, the operating circuit for M520 and, at RA152, the operating circuit for R140. Shortly following the restoration of R140 and the resulting deenergization of R130, the lastmentioned relay restores. Thus, all of the relays included in the allotter means are restored to normal. The deenergization of M520 embodied in I CI00, the switch wiper 522, the contact segment 516, CI01, SW532, CHO, RA51I, CH6, R0562, RA56I, CH1, RA 80I, RC802 and through the upper winding of R8l0 to battery. When energized over the above-traced circuit, R8|0 operates to complete, at RAM! and RC8I2, an obvious circuit for energizing the slow-to-release hold relay R830, The last-mentioned re- Operation of a finder switch to find a calling line in an even numbered group of lines I Before describing the operation of the connecerence to the line relay R500 associated with the line Ill.

.The operation of ated with the line 220 also causes a circuit to be prepared by way of the conductor, corresponding to Cl01, for controlling the operation of the rotary switch 6. In the present instance, the

- conductor noted, namely that corresponding to CI01, terminates at one of the contacts included in the contact set associated with SW6|5 instead of at a contact in the set associated with SW6. This difierent termination of the conductor noted identifies the calling line as being included in an even numbered group of lines rather than in an odd numbered group of lines.

Thus, when the switch 602 has completed its operationv to select the group of switching units to-which extend the groups of lines, one of which includes the calling line, and R110 has, as a result, operated, the switch H2 is started in operation, in the manner described previously, in search of the switching unit to which extend the subgroup of lines including the line 220. Since, in the last assumed case, this unit corresponds to the second contact of the contact set associated with SW6I5, acircuit is completed, upon SW6|5 encountering this contact, for energizing R160, this circuit extending from ground at RA592 by'way of Ci20, SW609, Ci05, the relay armature, corresponding to RA502, embodied in the line relay associated with the line 220, the above-noted conductor corresponding to C101, the second contact of the-contact set associated with SW6|5, Cl25, RA589, Ci36, RA153 and through the lower winding of R160 to battery. With its lower winding energized, R160 immediately operates to interrupt the operating circuit for M6l0, thereby to discontinue the interrelated operation of this magnet and R120. At RA164, the relay R160, upon operating, cornpletes a circuit for energizing M520, this circuit being identical with that traced previously for the magnet noted with the exception that it starts from ground at RA164 rather than from ground at RA154. At RA165, the relay R160, upon operating, prepares a circuit ior energizing the operating magnet M550 associated with the operating member l5 and, at RA162, it completes an obvious circuit for energizing R140. The last-mentioned relay operates, after an interval, to complete, at RA143, the above-noted circuit for energizing M550, causing this magnet to operate and rotate the control element 501 to bring the contact segments carried thereby into engagement with their respective associated wipers indicated to the right of the element 501. The circuit noted, namely that for M550, extends from ground at RA143 by way of RA155, RA151, RA165, CHO, RA585 and through the winding of M550 to battery. The magnet M550 not only operates the operating member 5l5 to its right cit-normal position but it also prepares, at MA55i, a holding circuit for itself extending-from ground at RA569, which circuit is completed upon the subsequent energization and operation of R560 or R510.

The relay R140, upon operating, not only completes the above-noted circuit for M550 but also completes, at RA142, an obvious circuit for energizing R130. The last-mentioned relay operates after an interval to complete, at RA134, the previously described operating circuit for M530, embodied in the rotary switch 538. This magnet is now caused to operate and interacts with R120 to cause the wipers of the switch 530 to be stepped until SW531 encounters the associated contact corresponding to the calling line 220; which contact is identified by the pres- -Cil1 and CH9 leading immediately operates to interrupt, at RA563',

the operating circuit for continue the interrelated R120. At RA561, the relay R560 short-circuits its upper winding from ground at RA533' and completes a circuit for energizing the cut-oil relay associated with the calling line 220, this circuit being similar to that traced above for the cut-oil? relayR5l0 associated with the line At RA569, the relay R560 completes an obvious holding circuit for'M550 and at its armatures RA56| and M56! and their respective associated contacts RC563 and RC566, it connects the line conductors of the calling line 220, which have now been extended to the bank conductors of the switch 538, to the link line'conductors to the connector portion of the link. The operations-which occur following the energization of R560 are exactly the same as those described above following the operation of R510 in the assumed case wherein the line I II was the calling line. ized, these operations comprise the operation of R8l0 embodied in the connector portion of the link, followed by the operation of R830 and the application of holding ground to CIZZ, thereby to maintain the finder switch illustrated and the cut-off relay associated with the calling line operated independently of R580 and the apparatus included in the allotter means as illustrated in Fig. 7. The operation of R560 is also followed by the restoration of the line relay associated M530, thereby to disoperation of'M530 and means.

From the foregoing description, it will be ap:

parent that the group of one hundred lines including the calling line is marked by the application of ground to one of the fi ve start conductors Cl06, CI, CH5, CH6 and CH1. If the calling line is in the first or second one hundred line group, ground is applied to CI06; if the calling line is in the thirdor fourth one hundred line group, ground is applied to Cl; if the calling line is in the fifth or sixth one hundred line group, ground is applied to-Cll5; and so on. Strictly speaking, the application of ground to any one of the enumerated start conductors only identifies the calling line as being included in one large group of two hundred lines since it determines the group of five switching units to be selected by the rotary switch 602. The termination of the conductor extending to the line relay and corresponding to Cl01, .however, determines whether the calling line is in the odd oreven group of one hundred lines. Thus, as was pointed out above, if the calling line is included in an odd numbered group of lines, the conductor extending to one of the springs of the line relay associated with the calling line and corresponding to CNN is terminated at one of the contacts of the contact set associated with SW6. If, on the other hand, the calling line is included in an even numbered group of lines, this conductor is terminated at one of the contacts included in the set associated with SW6I5. It will further be apparent, in view of the PIC- ceding description, that the rotary switch 6l2 not only comprises means for selecting from the group of units selected by the rotary switch 602, the particular switching unit to which the calling line extends, but also functions to determine Briefly summarthe direction of rotation of-the control element embodied in the selected unit in accordance with the odd or even number identifying the group orlines which includes the calling line. The sub- ,ora corresponding switch, in one die other; results in theselection-of upof twenty lines including the callandflnally the operation of the rotary g-lin m switch. ,5 8 results :inthe selection of the calling,

-, .line ironrtheselected subgroup of lines.

Operation or a connector switch to select a. called line inc evennumbered group of lines f bontinuing' now with theoperat'ion of the conjnectonportion or the imk illustrated, ,when R830 operates, it completes, at RA834, a circuit for energizing R900, this circuit extending from ground "acme armature noted by way of CI80 and the ,winding'otR900 t e battery. At RA836, the relay R830applies ground to C142, thereby to complete a circuit for energizingM100 included in the rotary switch 102 of the allotter shown in Fig. 7. This circuit extends from ground onthe conductor noted by way of SW104, CI62, RA132, RC183, CI60, MA10I and through' the winding of M100 to battery. Due to theself-interrupting contacts associated with MA10I, the magnet M100 operates buzzer fashion and drives the switch wipers u SW103 and SW104 until the last-mentioned wiper stands in engagement with anassociated contact, corresponding to'an idle one of the links. It will be apparent from thelforegoing that a busy link is identified by the presence of ground on the conductor individually associated therewith and corresponding to CI42, whereas, if a, link is idle,

the conductor associated therewith and corre-,

sponding to CI42 is open-circuited. Hence, when SW104 encounters a contact, corresponding to an idle link, the aboveetraced operating circuitfor M100 is interrupted and the operation of the switch 102 is arrested. With the respective switch'wipers of the switch 102 standing in a position corresponding to an idle link, a circuit is prepared byway of SW103 for energizing the re-,

lay in this link which corresponds to R580 embodied in the link illustrated. As a consequence, this-relay will be energized in response to the initiation of a call on the next succeeding calling line, .thereby to cause the seizure of the selected idle link.

When R900 operates, vfollowing the operation of R830, it applies, at RA90I,'dial tone current to the loop extending to the calling subscribers substation, thereby .to indicate to the calling.- party that the apparatus-embodied in the seized link is conditioned to be responsive to impulses transmitted from the impulsing device located at the substation A. Operation of R900 also prepares holding circuits, traced hereinafter, for the ring cut-off relay R930, theringing relay R950 relay .to restore to complete, at RA8I I, alcircuit or energizing R840-in series with MI040 embodied in the rotary switch I042. This circuit extends from ground at RA8II by way of RC8I3,Q

sequentf-rotation of the shaft embodied in the.

substation.

RA885, CI82, RA958, CI83, thewinding of R840, CI89, RA866,- RC868, RA811, CI88 and through the winding of MI040 to battery. The relay R840,

' upon operating, completes, at RA842, an obvious circuit for energizing R850 and, at RA84I, a circuit extending by way of RA86I and R0862 for energizing the lower winding of R860. The lastmentionedrelay is constructed to operate in two steps; that is, it operates only R864 when its lower winding is energized and assumes its fully operated position only when its upper and lower windings are subsequently energized in series. With R850 operated, the upper winding of R860 is short-circuited over a path extending from ground at RA855 by way of 'RA864, the upper winding noted, RA86 I RC862, and back to ground at RA84I. Thus, R860 remains in its partially operated condition during the impulses comprising the first digit.

When MI040 is deenergized at the end of the first impulse of the first digit,.it steps the wipers of the switch I'042'to their respective first oil'- normal positions,- closes the oil-normal springs I049, closes the off-normal springs 8 I4, and opens the off-normal springs 88I.' The opening of the springs 88I results in the interruption of the circuit over which dial tone current is applied to the calling line and closure of the springs 8I4 results in the application of ground to CI42 independently of- R830. With the springs I049 closed, a circuit is prepared for energizing MI040 by way of the self-interrupting contacts associated with MAI04I. At the end of the first impulse of the :first digit, when the operating circuit for R9I0 isagain completed at the impulsing 4 device of thecalling subscriber's substation, this relay re-operates preparatory to again energizing MI 040. During each impulse of the first digit, R8I0 restores'and-then operates, thereby to cause the magnet MI 040 to step the wipers of the switch I042 until they stand in engagement with the respective associated contacts, corresponding to R840 'and R850 remainin their respective operated positions.

, Shortly .following the end of the first digit dialed at the calling substation'A, R840 restores to open, at RA842, the operating circuit for R850 and to interrupt; at RA84I, a point in the shortcircuiting path for the upper winding of R860. With this short circuit interrupted, the two windings of R860 are energized in series over a circuit extending from groundat the off-normal spring 98I embodied in the rotary switch 914, this circuit extending by way of the off-normal spring 982, CI91, 'RA904, CI18, RA864, and through the upperand lower windings of R860 to battery. Upon completing its operation R860 interruptsat RA86I and R0862, a point in the path, traced previously, for shortcircuiti'ng its upper winding and, at RA86I and R0863, pre-' "I002 in' accordance with the .impulses comprising the second digit dialed at the calling subscriber's 2,171,869 At vthe beginning of the first impulse oi the 1 second dialed digit, when R810 again restores, the above-noted operating circuit for M1000 is completed at RA811, this circuit extending from ground at the armature noted by way of R0818, RA835, C182, RA958, C183, the winding of R840,

C189, RAdGQ, R0861, RAB'M RCB'IB, C181, and

through the winding of M1000 to battery. As a consequence oi the re-energization of R000, this relay again operates to cause the re-operation of R050 and to complete, at RA841, the above-noted circuit for energizing the upper winding oi R810, this circuit extending from ground at the armature noted by way of RA881, R0098 and the upper winding of R810 to battery. The last-mentioned relay, like R0150, is constructed to operate in two steps; that is, it operates only RMH in response to the energization of its upper winding and assumes its fully operated position only when its two windings are energized in series. When RAiili is operated in response to the energization of the upper winding noted, it completes a shortcircuiting path for the lower winding of R010, this path extending from ground on RAMH by way of RABti, R5008, the lower winding noted, RAtli, C109, RA008 and C209 to ground at RA959.

In viewof the preceding description, it will be understood that M1000 is energized and deenergized once during each impulse transmitted from the impulsing device at the calling subscribers substation. Each time this magnet is energized, it steps the wipers of the switch 1002 one step so that, at the conclusion of the series of impulses comprising the second dialed digit, these wipers:

stand in engagement with the associated contacts corresponding to the number of impulses oi the digit. In the present assumed case, wherein the second numeral of the number identifying the called subscribers telephone is 2, the second digit will comprise only two impulses so that, at the conclusion of the digit, the switch wipers SWi003 and SW1001 stand in their respective second offnormal positions. When these wipers are caused totake their first step, the off-normal springs 815 and 5005 are closed. The first-mentioned springs function to apply multiple ground to C102, thereby to insure that the finder-connector link illustrated is marked as busy in the bank contacts of the rotary switch 102 embodied in the allotter means illustrated in Fig. 'I. With the springs 1005 closed a circuit is prepared for energizing M1000 by way of the self-interrupting contacts associated with MA1001.

At the conclusion of the second digit dialed at the calling subscriber's substation, when R810 is held energized for a time interval sumcient to permit the restoration of R840, the path short circuiting the upper winding of R810 is interrupted at RA841. As a consequence, the two windings of R810 are energized in series, and this relay assumes its fully operated position. With R860 and R810 operated, acircuit is completed for energizing M1010, this circuit extending from. ground at RA865 by way of RA813, 3186, SWI004, C221, SW1048, C220, and through ;he winding of M1010 to battery. When enerzized over the above-traced circuit, the clutch nagnet M1010 attracts its armature MA1011, hereby operatively to associate the control elenent 1016 with the operating member 1019 so ;hat; when this member is subsequently moved ;o its right off-normal position by M1030, the

:ontact'segments carried by the shaft 1016 will )e moved into engagement with the wipers illuspositions.

trated to the right of the element 1 010. The re lay R810, upon operating, also completes a circuit for energizing the wiper switching relay R880, this circuit extending from ground at RAB" by way of RA813, C188, SW1003, C208, RA! and through the winding of R860 to battery. Shortly following the operation of R810, the relay R800 restores to complete a circuit for energizing M1030, this circuit extending from. ground at RAB" by way of M812, C100, SWMM, and through the winding of M1030 to battery. When energized, M1080 attracts the armature carried by the operating member H010 to the right, thereby to bring the contact segments carried by the shaft 1016 into engagement with the I wipers or the bank conductors shown to the right of this shaft. This magnet also complete at MA103i, a holding circuit for itself, this circuit extending from ground at M901 by way of 02041, MA1031 and the winding of M60853 to bat tery.

The relay R880, upon operating, completes, at

RA961l, a locking circuit for itself, which circuit extends from ground at RA992 by way of C603, RA880, and through the winding of R900 to bat tery. At its armatures RAilSi, M966 and RA988, this relay associates the link line conductors C182, C195 and C100 with the switch wipers SW918, SW819, and 8110000 so that the line testing apparatus is operatively associated with the three lower contact sets terminating the conductors of thelines iii to 2228, inclusive,

'as extended to these contact sets through the switching unit 4014.

With the finder-connector link in this condition, it is in readiness to respond to impulses comprising the third digit dialed at the calling subscriber's substation. Thus, when the relay R810 operates, it prepares, at nests and RC015, a circuit for energizing the motor magnetlviiiiii of the switch 914 in accordance with the impulses of the third digit. This circuit, which is completed when R810 restores at the beginning of the first impulse of the third digit, extends from ground at HAO by RA835, C182, RA958, C108, the windingof R060, C180, RA806, R0861, Bri id, R8015, C119,

way of R0053,-

RC921, RA926, C199 and through the winding of M910 to battery. Since R0 30 is energized in series with M910, it again operates to cause the operation of R850 and to recomplete the abovetraced circuit for short circuiting the lower winding of R810, but this latter relay remains operated due to the continued energiz'ation of its upper winding. The relay'R850 also completes a holding circuit for R000, these two relays remaining energized during the period of impulsing when the impulses are being transmitted to M910. During each impulse of the third digit. M910 is energized and deenergized and operates to drive the wipers of the switch 0151 at the rate of one step for each impulse. In the present case, wherein the called line is the tenth line in the selected group of ten lines, the third or final digit dialed at the calling substation will necessarily comprise ten impulses so that, at the conclusion thereof, the switch wipers of the switch 814 stand in their respective tenth off-normal When these wipers are stepped to their respective first oil-normal positions, the oil-normal spring 981 is moved from engagement with the associated spring 982 and into engagement with the spring 883, thereby to prepare a circuit for causing M810 to restore the wipers of the switch 914 to normal when the connection

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