US2218850A - Telephone system - Google Patents

Description

Oct. 22, 1940. p MAHONEY ET AL 2,218,850

TELEPHONE SYSTEM Filed March 16, 1938 5 Sheets-Sheet l SELECTOR SELECTOR swncn INVENTORSv HARRY P. MAHONEY CLARENCE E. LOMAX ATTORNEYS Oct. 22, 1940.

H. P. MAHONEY ET AL TELEPHONE SYSTEM Filed March 16, 1938 5 Sheets-Sheet 3 5.2% SE mam Emu r HARRY F! MAHONE'Y BY CLARENCE E.LOMAX M, 1du 7 INVENTORS.

I ATTORNEYS.

1940. H. P. MAHONEY' ET AL 2,218,850

TELEPHONE SYSTEM Filed March 16, 1958 5 Sheets-Sheet 5 m .sEE: @5252 NS a3 is EN.) h @mw QM mm? is -3 m mg mN L Q6 NE 80$ M00 QM.

w E m N3 6? al j 68 BY. I

ATTORNEYS.

Patented Oct. 22, 1940 TELEPHONE SYSTEM Harry Paul Mahoney and Clarence Ernest Lomax, Oak Park, Ill., assignors to Associated Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application March 16,

62 Claims.

The present invention relates to improvements in telephone systems and has iorone of'its objects the provision of improved apparatus for terminatinganultiparty rural subscribers lines in a telephone exchange which utilizes automatic switching equipment for setting upconnections between the various lines of the system.

In the usual arrangement 01' existing installed automatic exchanges, wherein certainoi the lines 0 extending to the exchange are of the rural multiparty type and others are of the single party type, no differentiation is made between the lines as regards the mode of terminating the lines in the automatic switching equipment. As a re- 15 suit, the initiation of a reverting call on one of the rural lines usually results in the seizure of certain of the regular automatic switching equipment provided in the terminating exchange. More particularly, when a reverting call is ini- 20 tiated on a rural line, one of the non-numerical automatic switches provided in the exchange is assigned to the use of the line having the calling condition created thereon and operates to switch the calling line through to one, of the numerical 2.1 impulse responsive switches. In certain instances, the s'eized switches are held operated for the duration of .the reverting call. In other systems, apparatus is provided-for causing the release of the operated switches after a prede- 30 termined time interval has elapsed following the seizure of the switches. In either case, certain of the regular automatic switching equipment is tied up so that it can not be used by the other lines.

'35 It is a further object of the present invention,

therefore, to provide in an automatic telephone system apparatus for preventing any of the regular switching equipment provided in an automatic exchange from. being taken for use by a m line having access to the equipment when a reverting call is initiated on the line.

More specifically, it is an object of the invention to provide in an automatic telephone system an improved arrangement wherein the regular 4,5 automatic switching equipment is only rendered 1938, Serial No. 196,136

efliciency of the line is found to be extremely poor.

It is an additional object of the invention to provide, in conjunction with the regular automatic switchingequipment of an automatic exchange, improved apparatus for controlling the selective signalling'of the substations associated with a multiparty line terminating at the switching equipment having access to the line.

It is. another object of the invention to provide an improved arrangement for guarding the multiparty lines against seizure by the automatic switching equipment having access thereto during intervals when the rural lines are occupied with reverting calls.

In the illustrated embodiment of the invention, the multiparty rural subscribers lines extending to the exchange are terminated at a group of improved numerical or connector switches by way of which connections are routed from the single party lines of the system to the rural lines. The rural lines are also terminated in the bank contacts of a group of auxiliary automatic switches which function to render the regular automatic switching equipment provided in the exchange connected by way of trunk lines to certain of the non-numerical switches located in the exchange. Allotter means are provided in association with the several finder-repeater links for the purpose of assigning these links to successive calling ones of the rural subscribers lines in a definite order. '33 Individually provided at the respective substations associated with the respective rural lines are manually operable magneto generators which are used for signalling between the substations of the lines on reverting calls. The arrange- '0 ment is such that an idle one of the finder-repeater links is assigned to the use of any line when-a call is initiated on the line through the operation of one of the generators provided at one of the substations associated therewith. The

seizure of a finder-repeater link does not, :however, result in the seizure of any of the regular automatic switching equipment, each link being so arranged that it functions to switch the connection through to one of the numerical switches only in response to the transmission of a predetermined series of impulses thereto by way of the calling subscriber's line or, in other words, in response to a predetermined operation of the impulsing device provided'at the calling substation associated with the calling line. .More specifically, there is provided in each link an impulse responsive relay which is adapted to be connected to respond to impulses transmitted by way of a seized calling line and in cooperation with the associated control apparatus functions to condition certain of the automatic switching equipment to respond to further operation of the impulsing relay. This control apparatus is so arranged that an artificial leak impedance is connected across the calling line during the dialing of the preliminary digit, whereby the sensitivity of the impulsing relay is reduced during the transmission of the first impulse series and this relay is tested to determine its responsiveness to the transmitted impulses. In the event it is found that the impulsing relay is not faithfully responsive to the impulses of the first series, the control apparatus functions to prevent any of the automatic switching equipment from responding to further operation of the impulsing relay. If, however, the impulsing relay is faithfully responsive to the impulses of the first series, the control apparatus operates to disconnect the artificial leak impedance from the calling line to enhance the responsiveness of the impulsing relay to further impulses transmitted over the calling line.

A timing device is provided in common association with the several finder-repeater links and, if a call initiated on a rural line happens to be of a reverting nature, this device functions to cause the seized one of the finder-repeater links to be released a predetermined time interval after it is seized. Each link is provided with control apparatus for marking any associated calling line as busy, thereby to prevent its seizure by one of the numerical or special connector switches. When any link is released through the operation of the timing device, the above-mentioned control apparatus functions toremove the busy marking and to substitute therefor a marking identifying the associated line as idle. This apparatus further functions to signal over the calling line that the line is no longer guarded against seizure by one of the connector switches.

In accordance with a further feature of the invention, each of the improved connector or final selector switches at which the rural lines terminate is provided with two operating positions for each of the lines. There is provided in common association with this group of connector switches ringing apparatus which comprises a plurality of ringing current conductors and 9. cyclically operating interrupter switch of improved arrangement for impressing on the ringing current conductors the voltage of the ringing current source for coded intervals which are different for each of the conductors. The arrangement is such that, when any one of the connector switches is operated to one of the two positions corresponding to a particular line, one particular ringing current conductor is connected to project ringing current over the line and, when the switch is operated to the other of the two positions corresponding to the line, a second ringing current conductor is connected to project ringing current over the line. Further in accordance with this feature of the invention, the control apparatus provided in each of the connector switches is arranged automatically to discontinue the application of ringing current to a selected line after the current has been applied to the line for a predetermined number of ringing cycles. More specifically, the cyclically operating interrupter acraaao switch is arranged to apply to a control conductor extending therefrom a predetermined potential at the beginning of each cycle of its operation, and a plurality of relays are provided in each connector switch which are so connected and arranged as sequentially to operate in response to successive applications of the said predetermined potential to the control conductor. The first of these relays to operate functions to connect the particular selected ringing current conductor to the selected line, and the last of the relays to operate functions to disconnect the ringing current conductor from the selected line and to connect the trunk line incoming to the connector switch to the subscriber's line.

Further features of the invention pertain to the particular arrangement of the circuit elements whereby the above and additional operating features are obtained.

The novel features believed to be characteristic of the invention are set forth with particularity inthe appended claims. The invention, 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 to 5, inclusive, illustrate an automatic telephone system having incorporated therein the features of the present invention as briefly outlined above.

Referring now to the drawings, the system there illustrated comprises, in general, an exchange, a plurality of single party subscribers lines, two of which are illustrated at "I and I04, extending to the exchange, and a plurality of subscriber-controlled automatic switches including a line switch I00, two selector switches I20 and I40, and a connector switch I50 for setting up connections between the various subscribers lines. Also extending to the exchange are a group of rural subscribers lines, one of which is illustrated at 600, each of which is of the multiparty type. The rural lines are terminated in the bank con tacts of a'group of special connector switches, one of which is illustrated in Fig. 2, and also in the finder portions of a group of finder-repeater links, one of which is shown in Fig. 4. Each repeat-er is connected by way of a trunk line to a line switch and is operative to render the regular automatic switching equipment accessible to the rural lines. Thus, the repeater illustrated in Fig. 4 is connected by a trunk line I25 to a line switch I30 which has access to certain of the selector switches in the exchange. For the purposeof assigning the finder-repeater links to successive calling ones of the rural subscribers lines in a definite order, there is provided in association with these links an allotter switch forming a part of the common equipment indicated generally at 500. The special connector switches of the group having access to the rural lines have associated'therewith ringing apparatus as illustrated in Fig.3, which functions in a manner such that selective code ringing of any desired substation on a selected rural line may be achieved. It is pointed out that the line switches I00 and I30 and the other similar switches corresponding thereto are non-numerical switches in the sense 2,a1e,aco. I a 3 form particular line selecting functions ,in response to impulses transmitted thereto. 'It will maximum volume of trafllc the particular switch group is required to handle. Further in accordance with conventional practice, each 0! thesingle party subscribers lines is multiplied to the correspdnding'bank contacts of a group.

of connector switches, whereby a plurality of switches are available for setting up connections between each line and any other line of the system., The line switches, on the other hand, are individually associated with the respective subscribers' lines, that terminating the line IOI being indicated at I00.

The end of each subscriber's line remote fromthe exchange terminates in one or more subscribers substations, the arrangements of which are different depending upon whether the line is of the single party type or is one oi! the group of mutiparty rural lines. Two substations of the usual automatic type are diagrammatically illustrated at A and B in association with the lines I M and I04, respectively. In brief, each oi! the single party line substations may comprise the usual hand set type of transmitter and receiver, acradle or hook switch, a ringer, and an impulsing device for transmitting the switch control impulses by way of the associated line to the automatic switching equipment located in the terminating exchange. These substations are of the well-known common battery type. The substations associated with the respective rural lines, on the other hand, are of the local battery type,

,one such substation being illustrated in detail at E in Fig. 5 and two other substations of similar type being diagrammatically illustrated at C and D, respectively.

Each of the line switches I00, I30, etc., is preferably of the well-known rotary type, of which there are several commercial embodiments Each wipers thereof to a position opposite a particular level of bank contacts and then rotated to bring the wipers into engagement witha particular set of contacts in a selected level; vertical, rotary and release magnets; and control relays suitably connected and arranged to control the energization of the various magnets and the line switching in accordance with the particularfunctions of the particular switch. In all fundamental respects, these switches are similar to the connector switch illustrated in detail in Fig. 2. Obviously, the particular arrangement of the control apparatus embodied in the switches of different type is diflerent in each instance, 'depending upon the character 'of'the switch.

Neglecting for the present the details of the apparatus terminating the multiparty rural subscribers line, the system as described above is,

in general, entirely conventional in form and its operation 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 IN to a second subscribers telephone, such, for example, as the telephone at the station B, by lifting his receiver from its hook, a loop circuit is completed by way of the line IOI for initiating the operation of the line. switch m toselect a trunk line leading to an idle selector switch. Assuming, for example, that the selector switch I20 is the first numerical switch selected for the use of the calling line IOI, when the trunk line-leading to this selector switch is found, the loop circuit is extended to this switch and? the switch is conditioned to respond'to the first series of impulses dialed at the calling substation. With the selector switch I20 in this condition, dial tone is returned over the established loop to the calling subscriber to indicate that the dialing operation may be started. When the first digit is dialed at the calling substation, the switch I20 elevates its wipers to a position opposite the level of bank contacts terminating the trunk lines respectively extending to the connector switches having access to the called line I04. Followingvthis operation, the wipers of the switch I20 are automatically stepped over the contacts of the selected level until a trunk line leading to an idle connector switch of the selected group is found. Assuming that the connector switch I is the first idle connector switch available, when the wipers of the switch I20 are stepped into engagement with the contacts terminating the trunk line extending to this connector switch, the subscribers loop circuit is extended thereto, thereby to cause this connector switch to be con-' ditioned to respond to the second and third series of impulses dialed at the calling substation. In response to the dialing of the second digit, the wipers of the connector switch I50 are stepped verticallyto a position opposite the level of bank contacts at which are terminated the lines of the ten-line subgroup including the called line I04. Following this series of impulses, the connector switch is conditioned to rotate its wipers stepby-step in accordance with the impulses making up the third and final digit dialed at the calling substation. When the last digit is dialed, the wipers oi the switch I50 are stepped into engagement with the set of bank contacts terminating the called line I04. In accordance with conventional practice, suitable provisions are made in the connector switch I50 for testing the called line to determine its idle or busy condition, for returning busy tone ,over the established-loop to the calling subscriber in case the called line is busy and for applying ringing current to the called line inthe event this line is idle at the time it is selected. Assuming that the line I04 is idle, the desired conversational connection is completed when the called substation B is answered. Also in accordance with conventional practice, the apparatus is arranged to insure its release when the connection is cleared out at the calling and called substations. Any desired mode of initiating the release of the established switch train may be utilized. For example, the control apparatus embodied in the connector switch I50 may be so arranged thatthe release of the connection is entirely under the control of the calling party. Alternatively, the apparatus may be so arranged that the release of the connection is under the control of the last party to hang up.

As indicated above, each of the substations associated with the rural subscribers lines is of the local battery type. More particularly, the substation E illustrated in Fig. 5 comprises a transmitter 8 which is arranged to be connected in a closed circuit including the primary winding ii I of a .transformer H and a local battery 0l3 through the operation of a hook switch 620. The substation equipment further comprises a receiver 6I5, an impulsing device 630, an alternating current generator 6050f the magneto type, and a signal device in the form of a ringer 603 which is normally connected across the conductors of the line 600 over a path including a condenser 504 and certain of the springs embodied in the hook switch 620. It will be understood that the magneto or alternating current generators individually provided at the substations associated with the line 600 comprise means for signalling between the substations on this line on reverting calls.

Referring now more particularly to the finderrepeater links by way of which connections are routed from the rural subscribers linesv to the regular automatic switching equipment and considering the link illustrated in Fig. 4 as exemplary, this link comprises a finder switch 490 of the wellknown rotary type. In brief, the finder switch comprises four sets of bank contacts 4! to 494, inclusive, wipers 495 to 498, inclusive, individually associated with the respective bank contact sets, a motor magnet 499 for driving the wipers over the contacts of their respective associated sets, and a switching-through relay R4) for connecting any selected calling line through to the repeater portion of the link.

For the purpose of assigning idle ones of the finder-repeater links to the various successive calling ones of the rural lines in a definite order and for the further purpose of controlling the operation of a selected finder switch to search for and seize a calling line, there is provided in association with the finder-repeater links the common equipment 500. This common equipment includes a rotary link allotter switch having five sets of bank contacts to 505, inclusive, wipers 505 to 5l0, inclusive, respectively associated with thebank contact sets, a motor magnet 5H for driving the enumerated wipers over the contacts of their associated sets, a start relay R520, and three relays R530, R540 and R550 for controlling the operation of the rotary switch to find an idle link and for controlling the operation of the finder portion of a selected link to find a calling line.

In order to initiate the operation of the common equipment 500. when a calling condition is created on one of the rural subscribers lines, each line has individually associated therewith an alternating current relay which is operative in response to the operation of any one of the magneto generators provided at the substations on the associated line. Such a relay is indicated at R405 as including a winding normally connected across the line conductors of the line 500. In order to prevent the operation of this relay when the associated line is seized by one of the special connector switches, a cut-off relay R400 is provided which operates to disconnect the upper or alternating current winding of R405 from across the conductors of the line 500 in response to the seizure of the line 600 by any one of the connector switches.

The repeater portion'of the link illustrated in Fig. 4 comprises a repeating coil 412, a line or ,impulse repsonsive relay R4I5, a slow-to-release hold relay R430, an impulse correcting network and a switching-through relay R460 which is under the control of an impulse responsive switch 480-. The relay R450 is a pulsing relay which responds to the operation of R! and functions to'repeat impulses to the switch 480 and to the automatic switches constituting the regular automatic switching equipment. The switch 480 is of the well-known minor type and comprises two sets of bank contacts 48! and 482, wipers 483 and 484 respectively associated with the contact sets 48l and 482, an operating magnet 485 for driving the wipers 483 and 484 over the contacts of their respective associated sets, a release magnet 481, and off-normal springs 486 for controlling the energization of the release magnet. There are also provided in the repeater portion of the link two relays R410 and R415 which function to control the operation of the switch 480.

For the purpose of releasing the link a predetermined time interval after it has been assigned to the use of a line having a reverting call initiated thereon, there are provided three additional relays R560, R510 and R500, the last two of which are under the control of a pulse generator 515. The relay R560 also functions as a device for marking the link illustrated as busy in the bank contacts of the allotter switch and as a hold relay for maintaining the link operated following the extension of a subscribers loop circuit to the repeater portion thereof. The pulse generator 515 may be of any well-known construction which includes means for alternately applying ground pulses to the time pulse leads C551 and C513 at spaced intervals. If desired, it may comprise a commutator driven by a synchronous motor through a speed reducing mechanism and including grounded commutator segments suitably arranged to engage brushes respectively terminating the leads C551 and C513.

Referring now more particularly to the group of improved connector switches by way of which the regular automatic subscribers lines gain access to the rural lines, it is pointed out that the connector switches of this group may be of identical construction and arrangement. For this reason, only the switch illustrated in Fig. 2 will be described in detail, but it will be understood that each of the rural lines is multipled to the corresponding bank contacts of each of the switches of this group. In brief, the switch shown in Fig. 2 comprises a switching mechanism 244, of the Strowger type, which includes a plurality of bank contacts arranged in levels; wipers for engaging the contacts; means comprising a vertical magnet 291 and a ratchet and pawl mechanism, not shown, for translating the wipers to a position opposite a; desired contact level; means comprising a rotary magnet 295 and a ratchet and pawl mechanism, not shown, for thereafter rotating the wipers step by step into engagement with a selected contact set in the selected level; a release magnet 239 for causing the wiper oarriage structure to be returned to normal during the release of the switch, vertical ofi-normal springs 265 and a plurality of control relays for controlling the operation of, the three enumerated magnets and the auxiliary functions of the switch. Of these relays, R200 is the usual line or impulsing relay, R204-is the usual hold relay and is of the slow-to-release type, R2 [0 and R220 are slow-to-release pulse circuit control relays, R230 is a ringing control relay, and R2 is the busy test relay. The-remaining relays illustrated in Fig. 2, namely, R240, R250, R260 and R210, are provided in accordance with one feature of the present invention for controlling the ring cut-oi! operation and the line switching operation in an improved manner. For the purpose of selectively signalling the various substations associated with 7 the rural subscribers lines, coded ringing is utilized. To this end, the code selecting switch 280 is provided in the connector switch and is arranged to respond to impulses transmitted thereto by way of a calling line. This code selector switch is of the well-known minor type and comprises two sets of bank contacts 28I and 232 tions between the regular automatic subscribers lines, there is provided'a repeater 290 which is inserted in and divides into two sections the trunk line incoming to the connector switch illustrated in Fig. 2.

The ringing current conductors terminated at the bank contacts of the code selector switch 280 form a cable 3" extending to the bank contacts of an interrupter switch 300, illustrated in Fig. 3.

- and comprises a plurality of sets of bank contacts 382 to 392, inclusive, wipers 310 to 380, inclusive, respectively associated with the bank contact sets, and means comprising an operating magnet 365 and a ratchet and pawl mechanism, not shown, for driving the enumerated wipers over the contacts of their respective associated contact sets. This switch functions to impress on the respective ringing current conductors the voltage of an alternating current source 325 for predetermined intervals during each cycle of its operation, and the bank wiring of the switch is such that the, coded voltage impressed on each conductor during eash ringing cycle is different in character from that impressed on each of the other ringing current conductors. More particularly, the voltage of the source 325 is impressed on each of the enumerated wipers ofthe interrupter switch by way of a transformer 326 having a primary winding 32! connected across the source and a secondary winding 328 having one terminal grounded and the opposite terminal arranged to be connected to the respective wipers. The contact bank of the switch 300 is wired in an improved manner, described more particularly hereinafter, such that the coding of the ringing voltage applied to the several ringing current conductors is difierent for eachconductor. For the purpose of controlling the operation of the interrupter switch there is provided in association therewith a start relay R3I0 and a group of cyclically operating slow-to-operate relays R320, R330 and R340. Specifically, this group of relays functions to connect the wipers of the interrupter switch to the winding 328 and to energize the operating magnet 365 once during each cycle of their operation.

Operation of the ringing interrupter The operation of the ringing interrupter is initiated when ground is applied to the start conductor C3I B by one of the special connector switches in the group including the switch shown in Fig. 2, to complete an obvious circuit for energizing the start relay R3 I 0. The relay R3 I 0, upon operating, completes, at RA3I3, a path for applying a predetermined potential, namely, ground potential, to the pick-up or control conductor C3I5. At RA3I2, the relay R3I0 prepares a, circuit, traced hereinafter, for maintaining itself energized independently of its operating circuit as traced above and until the interrupter switch has been operated through a complete cycle. The relay R3 I 0 also'completes a circuit for energizing the slow-to-operate relay R320, this circuit extending from ground at RA3I I by way of the winding of R320 and. the resistor 3| 4:to battery.

,The relay R3 0 operates, after an interval, to open, at RA32I, a point in the path normally short-circuiting the winding of R330, permitting the latter relay to be energized over a circuit extending from ground at RA3II by way of 'the winding of R330 and the resistor 320 to battery.

The slow-to-opera-te relay R330 operates, after an interval, to open, at RA33I, a point in the path normally short-circuiting the winding of R340,

permitting this latter relay to be energized over a circuit extending from ground at RA3I I by way of the winding of R340 and the resistor 343 to battery. The slow-to-operate relay R340, in

turn, operates, after an interval, to complete, at

RA342, an obvious path for 'short-circuiting the energized winding of R320, causing the last-mentioned relay to restore. When R320 restores, it

completes, at RA32 I, the path for short-circuiting.

the winding of R330. The relay R330 now restores to complete, at RA33I, the above-mentioned path for short-circuiting the winding of R340. When R340 restores, it opens, at RA342,

the path short-circuiting the winding of R320, permitting this latter relay to again be energized over its operating circuit as traced above. Thus, a second cycle of operation of the three relays R320, R330 and R340 is initiated. During each operating cycle of these three relays, a circuit is completed for energizing the operating magnet 365 embodied in the interrupter switch 300. Thus, when R340 operates, it completes, at RA34I, an obvious circuit for energizing the magnet 365. Assuming the wipers of the switch to be standing in the home position as shown in the drawings, when this magnet is energized, the magnet, in cooperation with its associated ratchet and pawl mechanism, not shown, operates to step the wipers with their respective associated second contacts. It is manifest that, for each succeeding cycle of operation of the three relays R320, R330 and R340, the magnet 365 is energized to cause the enumerated wipers to be moved another step. As

/ pointed out immediately hereinafter, movement of the enumerated wipers over the contacts of their respective associated sets results in the coding of the ringing voltage applied to the various ringing current conductors terminating in the bank contacts of the code selector switch 200.

-This is by virtue of the particular bank wiring 310 to 380, inclusive, one step or into engagement and with difierent spacing intervals therebetween. Thus, as the wiper 310 travels over the first twelve contacts of the set 382, it is connected to the ringing current conductor 32 while standin in engagement with its associated second, third, fourth, sixth and seventh contacts. While in engagement with each of these contacts, the voltage developed across the transformer 328 is impressed on the conductor 32 for a short interval. Thus, with the wiper 310 standing in engagement with its second contact and when R330 operates during the second cycle of operation of the three relays R320, R330 and R340, a path is completed for connecting the upper terminal of the secondary winding 328 to the jumper connection 388', this path extending by way of R0333 and RA332. The jumper connection noted is multiplied between the wipers 310 to 313, inclusive, and between the wipers 318 to 380, inclusive. Hence,

the voltage developed across the secondary winding 328 is 'impressedon any ones of the ringing current conductors which extend to the respective second contacts associated with the enumerated wipers. Since the second contact of the set 382 is connected to the ringing current conductor 32, this conductor has impressed thereon the voltage of the ringing current source when R330 operates. Similarly, the ringing current conductors 3|, 4, 34, 4|, 44., l and 43 have the voltage of the source impressed thereon with the wipers of the interrupter switch standing in the position noted. When R340 operates, following the operation of R330.in the second cycle of operation of the three relays noted, the

magnet 385 is energized to advance the wipers into engagement with their respective associated third contacts. This movement of the wipers, however, does not result in the disconnection of the ringing current conductors from the upper terminal of the secondary winding 328 for the reason that each of the wipers is of the bridging type arranged to bridge two contacts during the transition interval when it is being moved from one contact to another. When R340 operates, however, it causes the rapid sequential restoration of R320 and R330 in the manner pointed out of operation of these relays, the potential of the source is impressed on those of the conductors connected to the fourth contacts of the sets respectively associated with the enumerated wipers, and so on. It will be noticed from an inspection of the drawings that the ringing current conductor 32, for example, is not connected tothe fifth contact of the set 382. Hence, during the cycle of operation of the three relays R320, R330 and R340 to advance the wipers from engagement with their respective associated fifth contacts and into engagement with their respective associated sixth contacts, the potential of the ringing current source is not impressed on this particular ringing current conductor. A spacing interval is, therefore, provided between the first half of the code and the second half. Since the conductor noted,

namely, the conductor 32, is connected to the sixth and seventh contacts ofthe set 382, this second half of the code cycle comprises two additional short ringing periods. From this point on and until the wiper-310 is advanced into engagement with the fifteenth contact of the set 382, the conductor 32 is held disconnected from the rin ing current source.

The arrangement is such that two ringing cycles are completed during movement of the switch wipers over the twenty-five points of the switch. The end of the first cycle is reached when the wipers are advanced into engagement with their respective associated thirteenth contacts, and the wipers are moved to a position to begin the second ringing cycle when they are driven into engagement with their respective associated fourteenth contacts. In order to render the spacing between cycles substantially equal, it is desirable rapidly to move the wipers from engagement with their respective associated thirteenth contacts and into engagement with their respective associated fourteenth contacts. To this end, the thirteenth contact of the set 388 is included in a circuit for energizing the magnet 385 by way of the self-interrupting contacts associated with the armature 388, this circuit being completed when the wiper 314 is advanced into engagement with the thirteenth contact of the set 388 and extending from ground on this wiper by way of C338, the armature 388 and the winding of the magnet 385 to battery. When energized over the above-traced circuit, the magnet 385 operates immediately to advance the wipers into engagement with their respective associated fourteenth contacts independently of the cyclically operating relays R320, R330 and R340. This operation marks the-beginning of the second ringing cycle. During this second cycle, the voltage of the ringing current source is impressed on the various ringing current conductors for coded intervals which are identical with those produced during the first ringing cycle. Thus, during the respective intervals when the wiper 310 is standing in engagement with the fifteenth, sixteenth, seventeenth, nineteenth and twentieth contacts of the set 382, the voltage of the source is impressed on the conductor 32 through the operation of the relay R330. During the interval when this wiper stands in engagement with the eighteenth contact of the set 382, the conductor 32 is held disconnected from the source so that a spacing interval is provided which corresponds to that produced when the wiper is moved into engagement with its fifth contact. When the wiper 310 is moved from' engagement with the twentieth contact of the set 382, the voltage of the source is held disconnected from the ringing current conductor 32 until this wiper is again moved into engagement with the second contact of the set 382 at the beginning of the third ringing cycle.

As indicated above, the coding of the voltage applied to each of the ringing current conductors during each ringing cycle is different in each instance. Thus, considering the ringing current conductor l3, for example, this conductor has applied thereto the voltage of the source for a short interval, followed by three narrowly spaced short intervals which are relatively widelyspaced from the first interval, during each ringing cycle. More particularly, when the wiper 3 is moved into engagement with the seventh contact of the set 383 and when R330 operates, the conductor [3 is connected to the ringing current source.

Thereafter and during the interval when the,

wiper "I is standing in engagement with the eighth contact of the set 303, the conductor I3 is held disconnected from the source. When, however, the wiper 310 is moved into engagement with the ninth contact 'of the set 302, this conductor is connected to the source by way of the Wiper 310. Thereafter, and during the intervals when the wiper 31! is standing in engagement with the tenth and eleventh contacts of the set 383, the conductor 13 is connected to the source for short intervals measured by the time required for R330 to operate and restore. By inspection of the bank contact wiring arrangement, it will be apparent that the same coding of the voltage applied to the conductor 13 occurs during the second ringing cycle or duringthe movement of the wipers over the contacts numbered from IE to 25, inclusive.

It is believed that the mode of applying the voltage of the ringing current source on the remaining ringing current conductors will beapparent from the wiring arrangement illustrated in the drawings considered in light of the preceding description pertaining to the two conductors 32 and I3. It is pointed out, however, that the number identifying each of the ringing current conductors is indicative of the particular coding of the voltage impressed, respectively, thereon. More particularly, during each ringing cycle, the conductor l2 has impressed thereon the voltage of the source for one short interval, followed by a spacing interval which is succeeded by two successive and closely spaced short ringing intervals.

Similarly, the conductor 34 has impressed beginning of each ringing cycle. Thus, if the ringing apparatus is started with the interrupter switch standing in the position shown in the drawings, the path for applying ground potential to the conductor noted is completed when R3|0 operates. This circuit extends from ground as applied to the wiper 315 by way of the first contact of the set 381 and RA3I3 to C3l5. Again, when the wipers are driven over their associated contacts to a position where the wiper 315 engages the fourteenth contact of the set 381, this path is again completed. As the switch continues to operate, this path is completed for a short interval at the beginning of each ringing cycle.

The arrangement of the coding switch and its associated apparatus is such that the operation thereof continues until a ringing cycle which has been started is completed, irrespective of whether the operating circuit for the start relay R3I0 is maintained completed. To this end, an alternative circuit is provided for maintaining the start relay R310 energized independently of its operating circuit. This hold circuit for R3l0 is prepared, at RA3I2, when R3l0 operates, is completed when the wiper 314 is moved into engagement with the second contact of the set 386, and is held completed until this wiper is moved into engagement with the thirteenth contact of the set 386. Hence, when the first ringing cycle is started, R3I0 is held operated until the cycle is'completed. Again, when the wiper 314 is moved into engagement with the fifteenth contact of the set 386 to initiate the second ringing cycle, this holding circuit is again completed and is held completed until the wiper noted'is again moved into engagement with the first contact of the set 386. By virtue of this arrangement, it is not possible for improperly coded ringing current to be projected over a selected subscriber's line.

The release of the ringing interrupter is brought about by the removal of ground potential Operation of the apparatus to extend a. connection to a rural'subscribers substation Referring now more particularly to the opera tion of the apparatus to extend a connection from one of the regular automatic subscriber's lines, such, for example, as the-line IN, to one of the's'ubstations associated with the line 600,' and assuming that the line switch I00 opcrates to extend the connection from the calling substation A to the selector switch i 20, when a predetermined digit is dialed at this substation, the selector switch noted is caused to operate automatically to select an idle one of the special connector switches in the group including the switch illustrated in Fig. 2. Assuming the switch illustrated is the first available idle switch of the selected group, when the subscribers loop circuit is extended by, way of the trunk line l2l to this connector switch, the line relay R200 operates to complete, at RAI and R0202, an obvious circuit for energizing the slow-to-release hold relay R204. The hold relay, upon operating,.removes, at RA205 and R0206, battery potential, as extended by way of the resistor 221 to RC206, from the control conductor CI of the trunk line I2]. At RA205 and R0206, groundis applied over an obvious path to the control conductor noted. Throughthe removal of battery potential from.Cl24 and the substitution of ground potential, the connector switch illustrated is marked as busy, thereby to prevent its seizure by another of the selector switches on another call to one of the rural lines. At RA208 and RC209, the

relay R24 prepares a point in the pulsing circuit, traced hereinafter, for energizing the slowto-release relay R2 l0 and the vertical magnet 291 in series. This circuit is completed, when R200 restores at the beginning of the first impulse of the second digit dialed at the calling substation A and extends from ground at RA20| by way of R0203, RA208, R0209, the oil- normal springs 269 and 2 68,.the winding of R2l0, the contact springs 298, and through the winding of the magnet 291 to battery. Upon being energized over the abovetraced circuit, the magnet 291. attracts its associated operating armature to step the wipers embodied in the switching mechanism 2 one step vertically or to a position opposite the first level of bank contacts. During this first step taken by the wipers; the oiT-normal springs 265 are moved to' the off-normal position to interrupt, at the springs 268 and 269, the above-traced impulsing circuit and to prepare, at the springs 269 and 263', an alternative impulsing circuit. This latter circuit is completed upon the operation of R2l0, which occurs simultaneously with the operation of the magnet 291. At the springs 261 ground is applied to the ringing interrupter start conductor 0M6, thereby to initiate the operation of the ringing interrupter in the manner pointed out above. At the beginning of the sec- 0nd impulse dialed at the calling substation A, the above noted alternative impulsing circuit is completed. Specifically, this circuit extends from ground at RA20| by way of R0203, RA208, R0209, the off-normal springs 259 and 269', RA2I I, R02l3, the winding of R210, the springs 298 and through the winding of the magnet 291 to battery. When energized over the above-traced circuit, the magnet 291 again attracts its associated operating armature to cause the wipers of the mechanism 2 to be stepped a second step vertically or to a position opposite the second level of bank contacts. Thereafter, the magnet 291 is energized once for each impulse of the second digit dialed at the calling substation so that, at the conclusion of this digit, the switch wipers embodied in the mechanism 2 stand in a position opposite the level of bank contacts terminating the lines of the group including the called line '600. During this series of impulses, the relays R204 and R2l0 are held operated due to the slow-to-release characteristics thereof. end of the second digit dialed at the calling substation, the line relay R200 isheld energized for a sufiicient time interval to permit R2l0 to restore. This relay, upon restoring, opens, at RAZI I and R02l3, a point in the alternative impulsing circuit over which R2l0 and the magnet 291 were energized in series and prepares, at RA2|I and R0212, a circuit for energizing the slow-torelease relay R220 and the rotary magnet 295 in series.

The last-mentioned circuit, namely that over which R220 and the rotary magnet 295 are energized, is completed when the line relay R200 restores at the beginning of the first impulse of the third digit dialed at the calling substation. This circuit extends from ground at RA20| by way of R0203, RA208, R0209, the oil-normal springs 269 and 269', RA2I l, R0212, RA2I5, the winding of R220, RA23I, R0232, the springs 29 6 and through the winding of the magnet 295 to battery. When energized over the above-traced circuit, the magnet 295 attracts its operating armature to cause the wipers of the mechanism 244 to be stepped from vertical normal into engagement with the first set of contacts in the selected level of bank contacts. The relay R220, upon operating, completes, at RA22I, a path short-circuiting the armature RA2I5 of the busy relay R2l4, thereby to prevent the above-traced impulsing circuit from being opened when the wipers of the switch mechanism 244 are being moved over contact sets terminating busy lines. At RA224 and R0225, the relay R220 opens a point in the circuit, traced hereinafter, for energizing the ringing relay R230 and, at RA224 and RA222, it prepares a test circuit, traced hereinafter, over which the busy relay R2 may be energized. The rotary magnet 295 is energized once during each additional impulse of the third digit dialed at the calling substation so that, at the conclusion of the third digit, the wipers of the mechanism 244 are left standing in engagement with a set of contacts terminating the called line 600. As indicated above and pointed out with greater particularity hereinafter, two operating positions are provided for At the each of the subscribers lines. Thus, 11? the wipers 245 to 240, inclusive, are stepped into engagement with either the fifth or sixth set of bank contacts in the level illustrated, the connector switch will be connected to the called line 000. Obviously, the one of these two sets selected will depend upon the number of impulses making up the third digit. For example, if the number of impulses in this digit is five, the switch wipers will be rotated into engagement with the contact set including the contacts 2" to 240', inclusive. 0n the other hand, if this digit comprises six impulses, the switch wipers will be rotated into engagement with the sixth set of contacts. The particular reason {or providing two operatihgpositions of the switch for each subscriber's line is pointed out in detail hereinafter.

with the wipers of the mechanism 2" standing in one of the two positions corresponding to the called line 000, the succeeding operation of the apparatus depends upon. whether the called line is idle or busy. Before describing the operation of the apparatus resulting when either one of the two conditions noted prevails, brief reference will be made to the arrangement for preventing any possibility of false operation on the part ofthe wipers of the mechanism'fll and for preventing any noise from being introduced in the talking circuit extending by way of these wipers. To this end, each of the two operating magnets 295 and 291 is so connected and arranged that the speed of the respective associated operating armatures is reduced at the end of each stroke thereof and when they approach their respective oppositely disposed pole faces. More specifically, the armature controlled springs 298 associated with the magnet 291 are arranged normally to short-circuit a resistor 291' and are also arranged to be controlled by a second and relatively light armature, not shown,

carried by the magnet 291. This second armature is so constructed and arranged as to operate to open the springs 290 before the main operating armature of the magnet completes its movement. As a result, the initial energizing path for the magnet 291 is by-passed around this resistor. When energized, however, the magnet 291 attracts the armature controlling the springs 290 to open the path short-circuiting the resistor 291, thereby to reduce the energization of the magnet and cause the speed of the operating armature associated with this magnet to be reduced before the end of its stroke. Thus, the shock incident to the completion of the stroke of the armature is materially reduced, thereby eliminating any possibility of the wipers being falsely operated more than one step and minimizing the vibration of these wipers. An identical arrangement, including the contact springs 296 and the resistor 295', is provided in association with the rotary magnet 295 for the same purpose.

Continuing now with thepperation of the apparatus which occurs following the selection of the called line 600, and assuming that the called line is busy at the time it is selected, this condition is indicated by the presence of ground potential on the control conductor 0909. When, therefore, the wiper 291 is moved into engagement with the contact 241', a circuit is completed for energizing the busy relay R2, this circuit extending from ground as applied to 0003 by way of the contact 241', the wiper 241, RA22I, RA222,RA230 and through the winding of R2! to battery. When the busy relay R2 operates, it prepares, at RA2I6 and R02|6, a holding circuit for itself, which circuit is completed upon the subsequent restoration of the slow-to-release relay R220 shortlyfollowing the end of the third digit, and extends from ground at R0206 by way of RA205, RA2I6, R02l8, R0223, RA222, RA236 and through the winding of R2I4 to battery. At RA2I5, the busy relay opens a point in the operating circuit for R220, thereby to prevent further impulses dialed at the calling substation from effecting operation of R220 and the ringing code selecting switch 280. At RA2I9, the relay R2l4, upon operating, completes a path for conducting busy tone current by way of the established subscribers loop circuit through the receiver at the calling substation. This path extends from one side of the busy tone source as connected to 0221 by way of RA238, RA2I9, the condenser 249, one

side of the subscriber's loop circuit, the receiver at the calling substation, and back over the other side of the subscribers loop circuit and the upper winding of R200 to the other terminal of the busy tone current source. The resulting operation of the receiver at the calling substation gives an audible indication identifying the called line as busy. Following the operation of the busy relay R2l4, no further operation of the apparatus occurs until the partially completed connection is cleared out.

Upon receiving busy tone, the calling sub-'- scriber may initiate the release of the operated switch train by restoring his receiver to its hook to cause the restoration of the line relay R200. This relay, upon falling back, opens at RA20I and R0202, a point in the operating circuit for the hold relay R205. When the hold relay restores, after an interval, it removes, at RA206 and R0206, ground from the control conductor 0124, thereby to cause the release of the selector switch I20 and the line switch I00 in the usual manner. At RA205 and R0206, battery is substituted for ground on the control conductor 0l24, to mark the trunk line l2! as idle. The hold relay, upon restoring, also opens, at RA205 and R0206. a Point in the previously traced holding circuit for the busy relay R2, causing this relay to restore. AtRA200 and R0201, the hold relay completes a circuit for energizing the release magnet 239, this circuit extending from ground at RA20I by way of R0203, RA208, RA201, the off-normal springs 266, and through the winding of the magnet 239 to battery. The resulting operation of the release magnet causes the wiper carriage structure of the switching mechanism 244 to be restored to vertical and horizontal normal in the usual manner. When this occurs, the oil-normal springs 265 are moved to the normal position to. open, at the springs 266, a point in the operating circuit for the release magnet. At the springs 261, ground is removed from the ringing interrupter start conductor 03l6, thereby to cause the operation of this switch to be arrested providing none of the other special connector switches associated with the interrupter switch are operated. With the apparatus in this condition, the partially established connectionis completely released and the switches involved therein are in readiness for insteadof busy at the time itis selected by the connector switch shown in Fig. 2, this condition of the switch is identified by the application of 2,219,950 9 battery potential to the control conductor 0603 thereof through the winding of R400. -When, therefore, the wiper 241 is operated into engagement with the contact 241' terminating the conductor 0603, a circuit is prepared for energizing the relay R230. This circuit is completed upon the subsequent restoration of R220 and extends from ground at R0206 by way of RA205, RA2I6, R02 I 1, the lower winding of R230, R0225, RA224, the switch wiper 241, and the contact 241' to battery as applied to 0603. The relay R230-opcrates, when its lower winding is energized over the above-traced circuit, and completes, at RA235, -a holding circuit for itself, this circuit extending from ground on R0206, by way of RA205, Cl 24, RA235 and through the upper winding of R230 to battery. At RA234, the relay R230 applies ground to the switch wiper 241, thereby to complete a circuit for energizing the cut-off relay R400 associated with the line 600. Specifi cally, this circuit extends from ground at RA234 by way of the switch wiper 241, the contact 241', 0603, and through the winding of R400 to battery. The application of ground to the control conductor 0603 of the line 600 serves to mark this line as busy in the bank contacts of the various other connector switches to which it extends. When R400 is energized over the'circuit just traced, it opens, at RA402, a point in the circuit, traced hereinafter, for energizing the lower winding of the alternating current relay R405, and, at RAI, it disconnects the upper winding of this relay from across the conductors of the line 600. At RA403, the relay R400 extends ground as applied to 0603 to the particular bank contacts of the various finder switch contact banks, which correspond to the line 600, thereby to preclude any of these switches from inadvertently seizing the line 600, during the operation thereof to select another f the rural lines having a calling condition created thereon.

At RA238, the relay R230, upon operating, opens a point in the above-traced path for applying busy tone current to the loop extending to the calling subscribers substation and, at RA231, it prepares a circuit, traced hereinafter, for energizing the first relay R250 of the group of ringing control relays R250, R260 and R210. At RA239, the relay R230 completes a circuit for energizing R240, this circuit extending from ground as applied to the bank contact 248' by way of the switch wiper 248, RA239, and through the winding of R240 to battery. The resulting operation of R240 to move RA24I into engagement with R0243'insures that the selected one of the ringing current conductors will be included in the group terminating at the bank contact set 21" of the code selector switch 280. In this connection, it will be understood that, had the wipers of the mechanism 244 been operated into engagement with the sixth set of contacts of the selected level or to the second operating position corresponding to the called line 600, no circuit would have been available for energizing R240 and, hence, this relay would not have been energized following the operation of R230. With R240 deenergized, the ringing current conductor ultimately selected would necessarily be one of the conductors terminatin at the contacts forming the set 282 of the switch 280 because, in such case, RA24I would remain in engagement with R0242, which contact is-connected to the switch wiper 284.

At RA23I and R0233, the relay R230, upon operating, prepares an imriulsing circuit extending to the' operating magnet 228 of the switch 280. With the apparatus in this condition, the connector switch isconditioned to respond to the fourth and final digit dialed at the calling substation A. At the beginning of the first impulse of this digit, the above-noted circuit for energizing the operating magnet 228 is completed, this circuit extending from ground at RA20| by way of R0203, RA208, R0209, the off-normal springs 259 and 259', RAM I, R02|2, RA2i5, the winding of R220, RA23I, R0233, and through the winding of the magnet 228 to battery. The resulting operation of the magnet 228 causes the switch 280 to be conditioned to step the wipers 283 and 284 to the first off-normal position or into engagement with the first contacts of .their respective associated sets 28! and 282. When the relay R220 operates, it completes, 'at RA22 i, the abovenoted path for short-circuiting thearmature RA2I5 ofthe busy .relay R2 l4. At the end of the first impulse and when R200 restores to open the above-traced operating circuit for the magnet 228, the wipers 283 and 284 are stepped to the first off-normal position to select the two ringing conductors terminating at the respective first contacts of the sets 28!. and 282. When this first step is taken by the wipers of the switch, the offnormal springs 285 are moved to the oil-normal position. At the springs 285, a circuit, traced hereinafter, is prepared for energizing the release magnet 229 and, at the springs 281, a circuit is prepared for energizing the busy relay R2l4, this latter circuit being traced hereinafter and being held open at the operated armature RA225 of the relay R220. For each succeeding impulse of the fourth digit dialed at the calling substation, the magnet 228 operates to cause the associated wipers 283 and 284 to be stepped one step so that, at the conclusion of the digit, one of the wipers 283 and 284 will be standing in engagement with a contact terminating a ringing current" conductor having impressed thereon coded ringing voltage of the particular code which corresponds to the called substation E. As pointed out above, in the particular case under consideration and with R240 operated, the coded ringing current must be conducted to the called line 500 by way of one of the ringing current conductors terminating at the contacts forming the set 28L If it be assumed that the coded signal identifying the substation E corresponds to the code of the ringing voltage applied to the fourth conductor terminating at the contact set 28I, the final digit dialed at the calling substation will necessarily comprise four impulses so that, at the conclusion of the digit, the wipers 283 and 284 will be left standing in engagement with their respective associated fourth contacts.

Shortly following the conclusion of the fourth digit dialed at the substation A, the relay R220 restores to open, at RA22I, a point in the path short-circuiting the armature RA2|5 of the busy relay R2 l4 and to complete, at RA'225, the abovementioned circuit for energizing the busy relay. This-circuit extends from ground at the lower one of the off-normal springs 281 by way of the upper spring of this set, RA225, and through the winding of R2 to battery. The relay R2i4, upon operating, opens, at RA2I5, a point in the circuit for energizing R220 and the magnet 228 in series, thereby to prevent any further operation of the impulsing device provided at the calling substation from effecting further operation of the ringing code selecting switch 280. At RA2I9,

R2l4 prepares a circuit for energizing R250,

which relay functions to complete a path for applying ringing voltage to the talking conductors of the line extending to the called substation E. The .circuit for energizing R250 is completed when the ringing interrupter switch is operated to a position to start a new ringing cycle, at which time a ground pulse is applied to CH5. Thus, if R2|4 operates just prior to the operation of the wipers of the interrupter switch into engagement with their respective associated first contacts, this circuit is completed when the wiper 315 is moved into engagement with its associated first contact and extends from ground at the wiper 315 by way of RA3I3, 0315, RA2I9', RA231, RA255, R0255 and through the lower winding of R250 to battery. The relay R250 now partially operates to complete a closed circuit for shortcircuiting its upper winding, this circuit extending from ground as applied to the control conductor 0l24 by way of RA254, the upper winding of R250, R0255, RA255, RA231 and RA2I9' back to ground on 03 l 5. When ground is subsequently removed from 03|5 through the movement of the wipers of the switch 300 out of engagement with their respective associated first contacts, the above-traced short-circuiting path is opened and the two windings of R250 are energized in series, causing the relay R250 to complete its operation. Upon fully operating, R250 opens, at RA255 and R0255, a point in the above-traced circuit for energizing its lower winding and prepares, at RA255 and RA255', a circuit for energizing the lower winding of R250. At RA| and RA252, a path is completed for projecting ringing current over the conductors of the called line 500. In the present assumed case, wherein the code identifying the called substation E corresponds to that of the voltage applied to the ringing current conductor 2!, the path of this current extends'from the upper terminal of the secondary winding 328 by way of R0333, RA332, the switch wiper 3" of the wiper 312, the conductor 2|, the wiper 283, R0243, RA24I, RA252, R0215, RA215, the wiper 245, the contact 245', the line conductor 050i, the condenser 504, the windings of the signal device 503, the switch springs 52! and 528, 0502, the contact 245, the wiper 245;RA25I and RA21| to the grounded terminal of the secondary winding 328 at R0213. It will be understood that portions of this current are by-passed through the signal devices provided at each of the other stations associated with the line' 500. Due to the particular coding of the current, however, the subscriber at the substation E is in formed that his substation is being called and the other subscribers are informed that the call is not intended for their respective substations. A portion of the ringing current is by-passed by way of the condenser 210, RA253 and through the repeater windings 204 and 203 in series to ground at R0213 to cause ring-back tone current to be impressed on the loop extending to the calling subscriber's substation, thereby to indicate to the calling party that the ringing operation is being performed. a

As indicated above,, one feature of the present invention pertains to the arrangement of the apparatus whereby ringing current is only applied to the called line for a predetermined number of the energization of its lower winding over a circuit extending from ground on C316 by way of RA2I9', RA231, RA255, RC256', RA262, RC2, and through the lower winding of R260 to battery. With its lower winding energized over the above-traced circuit, the relay R260 partially operates to complete, at RA26I, a closed circuit for short-circuiting its upper winding, this circuit extending from ground on the control conductor C124 by way of RA26I, the upper winding of R260, RC204, RA262, RC256', RA255, RA231, and RA2 lilback to ground on C315. When ground is thereafter removed from CH5 through the continued operation of the interrupter switch 300, the above-traced short-circuiting path is interrupted and the relay R260 fully operates to open, at RA262 and R0264, a point in the above-traced circuit for energizing its lower winding and to prepare, at RA262 and RC263, a circuit for energizing R210. This last-mentioned circuit is completed after the second ringing cycle is ended and at the beginning of the third ringing cycle when ground is again applied to the control conductor C3 l 5. In this case, the circuit for energizing R210 extends'from ground on C3l6'by way of RA2I9', RA231, RA256, R0256, RA262, R0263, RA210' and through the winding of R210 to battery. When energized over the abovetraced circuit, R210 operates to complete, at

RA218, a holding circuit for itself, this circuit extending from ground as applied to C! by way of RA218 and the winding of R210 to battery. At RA218, the relay R210 open-circuits the pickup or control lead C3l5, thereby to permit the ground pulses impressed on this lead to be effective in controlling others of the connector switches in the group including the switch illustrated in Fig. 2. The relay R210 opens, at RA21I and RA215 and their respective associated contacts R0213 and RC216, two points in theabovetraced path over which ringing current is projected out over the called line 600 and also two points in the path by way of which 'ring-back tone currents is impressed on the loop extending to the calling subscriber's substation. At RA21I and RA215 and their respective associated contacts R0214 and R6211, the conductors of the trunk line incoming to the connector switch are connected through tothe conductor 060i and C602 of the called line, thereby to complete the.

connection to the called line. More particularly, the talking circuit is completed when the call is answered at the substation E. Thus, when the receiver M5 is removed from its hook, the spring 62I is moved into engagement with its associated contact springs 626 and 621 and the springs 625 are closed. With the switch hook 620 in this position, the receiver GIS is connected across the conductors of the line 600 and the transmitter SM is included in a closed circuit by means of which generated voice frequency currents may be impressed on the line 600 through the transformer 6l0. In this connection, it is pointed out that the battery M3 is utilized in generating voice frequency currents at the called substation, whereas talking battery is supplied to the loop extending to the calling substation by way of the windings of the line relay R200.

The release of a conection as established in the manner described above to the substation E is entirely under the control of the calling party.

Thus, if the receiver M5 is restored to its hook before the connection is cleared out at the calling substation, the only result eflected thereby is the disconnection of this receiver from across the conductors of the line 600 and the inter- 5 ruption of the closed circuit including the transmitter 6. When, however, the calling party restores his receiver to its hook to open the loop circuit by way of which the line relay R200 is held operated, this relay restores to open, at RA20I, the operating circuit for the hold relay R204. When R204 restores, ground is removed from the control conductor CI to cause the restoration of the selector switch I20 and the line switch I00 in the manner pointed out above and to open the respective holding circuits for R260, R260, R260 and R210. The relay R230, upon restoring, interrupts, at RA234, the previously traced circuit for energizing the cut-off relay R400, causing the last mentioned relay to restore. When the hold relay restores, the above-traced circuit for energizing the release magnet 269 is completed. The resulting operation of this magnet causes the wiper carriage structure of the switching mechanism 246 to be restored to normal in the manner pointed out above, at which time the ofi-normal springs 265 are returned to the normal position. When this occurs, the operating circuit for the start relay R3l0 embodied in the control apparatus for the interrupter switch 800 is opened and, assuming that none of the other special connector switches are operated, this interrupter switch is restored to normal in the manner pointed out above. When the hold relay R204 falls back, a circuit is also completed for energizing the release magnet 229 embodied in the code selector switch 200, this circuit extending from ground at RA20I by way of R0203, RA200, R6201, the oiT-normal springs 266 and through the winding of the magnet 229 to battery. The resulting operation of this magnet causes the wipers oi the switch 280 to be re- Operation of the apparatus to extend a connection from a rural subscribers substation to an automatic subscribers substation Referring now more particularly to the operation of the apparatus to set up a connection between the line 600 and the line IN on a call originating at the substation E, the call is initiated through the operation of the magneto generator 606 provided at the calling substation. Before operating this generator, however, the calling party should listen in on the line to determine whether or not the line is busy in connection with another call. This may be done by moving the hook latch 624 to a position for holding the contact springs 625 out of engagement and thereafter removing the receiver 6l6 from its hook to complete a path-by way of which this receiver is connected across the conductors of the line 600. Specifically, this path extends from C60l by way of the impulsing springs 63L the transformer winding M2, the receiver M5, the condenser 616, and the switch springs 621 and 62L It will be noted that this path is interrupted for direct current by the condenser 1| '0". The purpose of inserting this condenser in the path is to prevent a short-circuit from being placed across the conductors of the line which might interfere with the dialing operation being performed at another of the substations associated with the line at the time the line is challenged at the substation E. More particularly, the arrangement of the apparatus at each of the other stations is identical with that of the apparatus provided at the substation E, and it will be apparent that if the impulsing device at the last-mentioned station were being operated to deliver impulses to the switching equipment provided in the exchange and a short-circuit were placed across the conductors of the line 900, the

call would'either be falsely routed to the wrong substation or would fail entirely.

After the line is challenged and when the magneto generator 505 is operated, alternating current is projected by way of the springs 908 and the line conductors C50! and C502 through the upper winding of the alternating current relay R405, causing this relay to operate. Upon operating, R405 completes, at RA'I, a circuit for energizing its lower winding in series with the start relay R520 provided in the common equipment 500, this circuit extending from ground at the lower terminal of the winding of R520 by way of this winding, C522, RA402, RA40I, and

through the lower winding of R405 to battery.

At RAMS, the relay R405 opens a point in the path over which its upper winding is energized and, at RA408, it completes a path for marking the calling line 600 in the bank contacts of the finder switches to which this line extends. More particularly, battery is extended .through the winding of R400 and by way of RA400 to the fifth contact of the contact set 494 in the finder switch 490 and to the corresponding contacts of the other finder switch banks.

The common equipment 500 operates in a manner such that the allotter switch provided therein operates to a position corresponding to an idle one of the finder-repeater links immediately after an assigned link has been caused to seize a calling line. Assuming, for example, that the wipers of this switch are standing in the position corresponding to the link illustrated. that is, in engagement with their respective associated tenth contacts, at the time the start relay R520 operates, this relay initiates the operation of the finder portion of the link to search for and seize the calling line 000. More particularly, when R520 operates, it completes, at RA52I, a circuit for energizing the winding of R540 in series with the winding of the operating magnet 5, this circuit extending from ground at RA52I by way of the winding of R540, RA545, RA555, the armature H2 and through the winding of the magnet 5ll tobattery. Due to the relatively high resistance of the winding of R540, the magnet 5 does not operate. Hence, the wipers of the allotter switch are maintained in the position corresponding to the link illustrated. The relay R540, however, operates to complete, at RA544, a circuit for energizing the operating magnet 499 of the finder switch 490 and to prepare, at RA545, a circuit for energizing R530. At M5, the relay R540 prepares a point in the holding circuit for R550 and, at RA543, it prepares a point, in the circuit for energizing the upper windings of R550. At RA545, the relay R540 opens a point in the path normally short-circuiting theresistor 550 so that this resistor is included in the series circuit over which the. relay R5 is held energized'.

The above-mentioned circuit over which the magnet 455 is energized extends from ground at RA552 by way of R0554, RA544, RAIII, the wiper 551, the tenth contact of the set 502, C524 and the winding of the magnet 400 to battery. When energized over this circuit, the magnet 400 advances the wipers of the switch 400 one step and attracts its armature 400' to complete the above-mentioned circuit for energizing R500, this circuit extending from ground at the contact associated with the armature 400' by way of this armature, C525, the tenth contact of the set i, the wiper .500, RA545, and through-the winding of R550 to battery. When R550 operates, it interrupts, at RA50I, the above-traced circuit for energizing the magnet 490, causing this magnet to restore its armature 490' to interrupt the operating circuit for R555. When R530 restores, it again completes, at RAI, the circuit for energizing the magnet 459, causing this magnet to operate to advance the wipers of the switch 490 a second step and to again complete the operating circuit for R530. The interrelated operation of the magnet 490 and R530 continues until such time as the wipers are moved to the position corresponding to the calling line 500. Assuming that the movement of the wipers is started with these wipers occupying the position indicated in the drawings, five steps on the part of the switch 400 will be required before these wipers .are moved into engagement with the contacts of the upper winding of the slow-to-release relay R550 in series with the winding of R400, this circuit extending from ground at the lower terminal of the upper winding of R550 by way of this winding, RA540, the wiper 500, the tenth contact of the set 505, C525 the wiper 490, the fifth contact of the set 494 RA405 and through the winding of R400 to battery. When its upper winding is energized over the above-traced circuit, R550 operates to complete, at RA55I, a holding circuit for itself, this circuit extending from ground at RC542 by way of RA54I, RA55| and the lower winding of R550 to battery. At RA552 and R0550, the relay R550 opens a point in the above-traced operating circuit for the magnet 499, thereby to arrest the interrelated operation of this magnet and R500. At RA552 and R0553, the relay R550 completes a circuit for energizing the switching relay R4l0, this circuit extending from ground at RA552 by way of R0550, the wiper 509, the tenth contact of the set 504, C520 and through the winding of R4 to battery.

When R4|0 operates, it switches the subscribers loop circuit through to the repeater portion of the link and completes. at RA4i4', a circuit for fully energizing the cut-oi! relay R400, this circuit extending from ground at RA4I4 by way of the wiper 490, the fifth contact of the set 494,

to mark this line as busy in the bank contacts of the connector switches to which it extends. I

At RA402, the relay R400 opens a point in the above-traced circuit for energizing the lower winding of R405 and the start relay R520 in series, causing both of these relays to restore, assuming that none of the other rural lines are waiting to be assigned finder-repeater links. If a second calling line is waiting for a link at the time R400 operates, the start relay R520 will be held energized and only R405 will restore. At RAI, the relay R400 holds the upper winding of R405 disconnected from across the talking conductors of the line 600. Assuming that the start relay R520 restores, it opens, at RA52I, a point in the above-traced operating circuit for R540, causing this latter relay to restore to open, at RA54I, the holding circuit for R550. R550 restores, a point is opened in the abovetraced operating circuit for'R4I0. Before R550 falls back, however, and during the sequence of operations just described, R560 is caused to operate to complete a holding circuit for R4I0.

Thus, immediately the subscriber's loop is extended to the repeater portion of the link, a circult is completed for energizing the line relay R4I5, this circuit extending from ground at the fifth contact of the set 492 by way of the wiper 496, RA4I3, the repeater winding 414, RA4I4, the switch wiper 491, the fifth contact of the set 493, 060I, the impulsing springs 63I, the transcontact of the set 49I, the wiper 495, RA4I2, the

' repeater winding 413, and through the winding of R4I5 to battery. The relay R4I5 operates,

ground at RA42 I, by way of R0422 and the winding of R430 to battery. At RA424, the relay R420 completes a holding circuit extending by wa f th r 424 mint inin 't If.

y 0 e eslstor for a a g 1 Se R460 is operative to connect the conductors of operated independently of the hold relay R430. When the last-mentioned relay operates, it opens, at RA43I and R0432, a point in the above-traced operating circuit for R420, prepares, at RA434, a point in the circuit, traced hereinafter, for en-.

ergizing R450, and completes, at RA435, a circuit for energizing R560, which latter circuit extends from ground at RA435 by way of RA58-I and the upper winding of R560 to battery. When R560 operates, it completes the above-noted-holding circuit for-R4I0, this circuit extending from 'ground at RA56I by way of R0563, 0526 and the winding of R4I0 to battery. As indicated above, the arrangement of the apparatus is such that this holding circuit is completed through the operation of R560 before R550 restores to open the operating circuit for R4I0. When R560 opermark the finder-repeater link illustrated as busy in the allotter switch provided in the common equipment 500.

In the event the start relay R520 remains oprelays R540 and R550 are held operated until R560 operates. When the last-mentioned relay operates. the winding of R540 is short-circuited at RA565, causing R540 to restore to open, at RA54I, the holding circuit for R550. When R550 restores, it completes a circuit for energizing the operating magnet 5 of the allotter switch, this circuit extending from ground at RA565 by way of the wiper 5I0, RA546, RA555, the circuit-interrupting contacts associated with the armature 5I2, and the winding of the magnet 5 to battery. The magnet 5, upon being energized over this circuit, attracts its armature to open its operating circuit and to step the wipers of the allotter switch one step or into engagement with the contacts of the set corresponding to the next finder-repeater link. If this next link is busy, the contact of 'the set 505 which corresponds thereto will also have ground potential impressed thereon so that the magnet 5II such time as the wiper 5I0 encounters a contact.

corresponding to an idle one of the finder-repeater links, th'is idle condition being indicated by the absence of.ground potential on the contact corresponding thereto. Thus, when the link illus-' trated is idle, R560 is deenergized so that the tenth contact is open-circuited. When, therefore, the allotter switchis operated to a position corresponding toan idle link, no further circuit is available for energizing the magnet 5I I, and the stepping operation of the switch is arrested.

Following the operation of R4I5, R420, R430 and R560, the control apparatus embodied in the repeater portion of the link is conditioned to" respond to the first series ofimpulses dialed at the substation E.

As pointed out in the introductory portion of the specification, the arrangement of the repeater portion of each link is such that a preliminary or prefix digit is required to cause a loop circuit to be established between the repeater portion of the link and its associated line switch. More particularly, with the link illustrated, the relay the trunk line I25 across the secondary windings of the repeater coil 412 only following the dialing of a digit comprising ten impulses at a calling substation on a line tu which the link has been allotted for use. An impulse correcting relay network is provided such that the character of each impulse repeated over the trunk line I25 is, within limits, independent of the character of the corresponding impulse dialed at the calling substation. I At the beginning of the first impulse dialed at the calling substation E, the abovetraced loop circuit over which R4I5 is energized is interrupted at the impulsing springs 63 I. During impulsing, the shunt springs 632 of the impulsing device 630 are moved to the oif-normal position to short-circuit the receiver 6| 5 in series with the secondary winding 6I2 of the transformer 6I0. ,When R4I5 restores in response to the interruption of the above-traced loop circuit, it opens, at RA4I9, the circuit over which R420 is held energized and completes, at RA4I6 and R04", a priming circuit 'for itself, this latter circuit extending from ground at RA43I by way of R0433, RAMS, RC4", the resistor 4H and the winding of R4I5 to' battery. When R420 restores, it opens, at RA424, its holding circuit and completes, at RA42I, a circuit for energizing 1 3 erated following the operation of R400, the two the lower winding of R450, which circuit extends from ground at RA42I by way of R0423, RA454, RA444 and the lower winding of R450 to battery. The relay R450, upon operating, short-circuits, at RA452, its upper. winding, thereby to render itself slow-to-release, and completes, at RA45I, an obvious multiple holding circuit for the hold relay R430. At RA454, the relay R450 completes a circuit for energizing the lower winding of R440, this circuit extending from ground at R0454 by way of RA454, the resistor 450, RA425, and through the lower winding of R440 to battery. With R440 deenergized, its upper winding is short-circuited at RA4 3 and, hence, this relay possesses a slow-to-operate, characteristic. It operates, after an interval, however, to open, at RA443, the path short-circuiting its upper windingwhereby it is rendered fast-to-release. At RA444, the relay R440 opens the operating circuit for R450. With R440 operated, and when the line relay R4I5 reoperates at the end of the first pulse, a circuit is completed for again energizing R420, this circuit extending from ground at R0442 by way of RA44I, RA4I9 and through the winding of R420 to battery. The relay R420 now reoperates to complete, at RA424, its abovetraced holding circuit and to open, at RA425, the operating circuit for R440, causing this latter relay to restore. The restoration of R440 does not result in the recompletion of the operating circuit for R450, however, since this circuit is now open at RA42I and RC425. The abovedescribed cycle of operation and restoration of the relays R4I5, R420, R450 and R440 is repeated for each impulse dialed at the calling substation E. Since, in the present assumed case, the preliminary digit dialed at the substation E comprises ten impulses, it will be understood that, during this digit, the cycle of operation of the relays noted is repeated ten times. As indicated previously, R450 is the impulsing relay, and it will be apparent from the foregoingdescription that the relation between the period of deenergization and the period of energization of this relay during each impulse is, within limits, independent of the relation between the corresponding periods for the line relay R4I5. More particularly, the restoration of R4I5 at the beginning of each impulse cycle initiates the operation of the three relays R420, R450 and R440 to repeat the impulse, and the extent of the period during which R450 is energized depends primarily upon the slow-to-release characteristic of this relay and the slow-to-operate characteristic of R440.

During the period of each impulse when the pulsing relay R450 is operated, a circuit is completed for energizing the slow-to-release relay R415 and the operating magnet 485 of the switch 480 in parallel, this circuit extending from ground at RA453 by way of RA464 to RA41I, where it divides, one branch extending through the winding of R015 to battery and the other branch extending through the winding of the magnet 485 to battery. The relay R415 operates at the beginning of the first impulse repeated by R450 and remains operated during the'succeeding impulses and until the digit is completed. At its armature :RA-i'lt, this relay opens a point in the circuit, traced hereinafter, for energizing-R410. Obviously, at the end of the first and each succeeding impulse, the above-traced circuit for energizing the magnet 005 is opened. Each time this magnet is deenergized following its energization, it steps the wipers 403 and 404 one step. Since the preliminary digit comprises ten impulses, the wipers noted will be stepped to the tenth of!- normal position or into engagement with their respective associated tenth contacts. At the beginning oi the first step taken by the wipers of the switch 400, the oil-normal springs 400 are closed to prepare a circuit for energizing the release magnet 401. This circuit is held open for the duration of the call, however, through the continued energization of R500.

If it be assumed that the wipers of the switch 400 are successfully operated into engagement with their respective associated tenth contacts in response to the dialing of the preliminary digit at the calling substation E, shortly following the restoration of R450 at the conclusion of the digit, the relay R415 restores, but without effect. Immediately the wiper 400 is moved into engagement with the tenth contact of the set I, a circuit is completed for energizing R400, this circuit extending from ground at the wiper 400 by way of its associated tenth contact and the winding of R400 to battery, This relay, upon operating, opens, at RA404, a point in the above-traced circuit for energizing the magnet 405 and the relay R415 in accordance with the operation of the pulsing relay R450. At RA450, the relay R400 completes an alternative holding circuit for R500, this circuit extending from ground at RA435 by way of RA400 and the upper winding of R500 to battery. At RA405, the relay R400 opens a point in the holding circuit for R510 and the initial holding circuit for R500. Through this operation, the link release relay R500 is prevented from operating to initiate the release of the link in the manner pointed out more in detail hereinafter. At RAI and R0402, the relay R400 opens a point in the path, described hereinafter, for connecting the artificial leak impedance element 4| I' across the conductors of the line 000.

When the relay R400 operates, it also completes a loop circuit to the line switch I50 terminating the trunk line I25. More particularly, this relay connects a bridge across the line conductors of the trunk I25, this bridge extending from the trunk line conductor CI20 by way of R0401, RA400, RA455, the repeater winding 410, the resistor 450, the repeater winding 410 and RA403 to the opposite trunk line conductor CI 21. When this loop circuit is completed, the line switch I30 operates in the usual manner to extend the connection to an idle one of the selector switches. Assuming, for example, that the selector switch I40 is the first idle switch available, when the loop cir'cuit is extended thereto through the operation of the line switch I30, it is conditioned to respond to the second series of impulses dialed at the calling substation E.

During the dialing of the second digit at the calling substation, the four relays R4I5, R420, R450 and R440 respond in the exact manner pointed out in detail above; that is, R450 operates once during each impulse. Each time R450 operates, it opens, at RA455, the loop circuit as extended to the selected selector switch I40, which selector switch responds to the repeated impulses by elevating its wipers in the usual manner to a position opposite the level of bank contacts terminating the trunk lines extending to the connector switches having access tothe called line I.0I. Thereafter, the selector switch operates automatically to select an idle one of the connector switches in the selected group. Assuming that the connector switch I50 is the first available switch in the selected group, when the wipers of the selector switch I40 are moved into engagement with the contacts terminating the trunk line extending to this connector switch, the loop circuit is, automatically extended to the last-mentioned switch, causing this switch to be conditioned to respond to the impulses making up the third and four digits dialed at the calling substation E. When the third digit is dialed at the calling substation, the connector switch I50 responds to select the group of ten lines including the called line IOI, it being again pointed out that the impulses of this digit are repeated to the operated connector switch I50 through the interrelated operation of the relays R4I5, R420, R450 and R440. Following the selection of the ten-line subgroup, and when the fourth digit is dialed at the substation E, the connector switch I50 operates to select the called line. IOI. In order to insure a faithful response of the seized switches I40 and I50, or of other switches respectively corresponding thereto,

to the operation of thepulsing relay R450, all such I nector switch I50 functions to test the called line to determine its idle or busy condition, to return busy tone over the established loop to the calling substation in case the called line is busy at the time it is selected, and to apply ringing current to the, called line in case the line is idle, is identical to that described above with reference to the connection established between the substations A and B on a call initiated at the substation A. Assuming that the called line is idle at the time it is selected by the switch I50, the desired conversational circuit is completed when the call is answered at the called substation A.

The release of the operated switches I50, I40 and I30 and of theoperated finder repeater link is preferably solely under the control of the calling party. Thus, when the "calling party restores the receiver 6I5 to its hook to return the springs of the hook switch 620 to normal, the loop circuit over which R4I5 is held energized is interrupted at the springs 62I and 621. When R4I5 restores, it opens, at RA4 I 9, the circuit over which R420 is held energized. The last-mentioned-relay now restores to open, at RA42I and RC42-2, the operating circuit for the hold relay R430. This hold relay, upon restoring, opens, at RA435, the hold circuit for R560. When R560 restores, it removes,

at RA565, ground from the contact of the set 505 corresponding to the finder-repeater link illustrated, therebyv to mark this link as idle in the bank contacts of the allotter switch; When R560 restores, it also completes a circuit for energizing the release magnet 481, this circuit extending interrupt the operating circuit for the magnet 081. When, during the restoration of the switch 480, the wiper 483 is moved from engagement with the tenth contact of the set 48I, the circuit over which R460 is held energized is interrupted, causing this relay to restore to open, at RA463 and RA466, the loop circuit which extends reference to a call initiated at the substation A and extended to the substation B.

When B560 restores, it further functions to open, at RA56I and R0563, the holding circuit for R4I0, causing this relay to restore to remove, at RA4I4', ground from the control conductor C603 of the line 600. The removal of ground from the control conductor noted results in the restoration of R400 and, when this relay restores, it reconnects the upper winding of R405 across the line conductors of the line 600 and reprepares the start circuit for energizing the lower winding of R405 in series with the start relay R520. The apparatus is now completely restored to normal and in readiness for further use. In this connection it is pointed out that the finder portion of the link is of the non-homing type; that is, the wipers of the switch 490 remain in the position to which they are operated during a line hunting operation until further operation .of the switch is initiated.

As pointed out in the introductory portion of the specification, one of the features of thepresent invention is concerned with the arrangement of the apparatus whereby a calling rural subscribers line can only gain access to the regular automatic switching equipment provided in the automatic exchange through a predetermined operation of the dialing device at the calling substation on the calling line to transmit a predetermined series of impulses to a seized finder-connector link. It may happen that, due to a faulty condition of the line, the line relay included in the finder-repeater link operatively associated with the calling line will not respond to all of the impulses dialed at the calling substation, but only to a portion thereof. On the other hand, the calling party may, through carelessness, fail to dial the requisite number of impulses. Obviously, in either case, a false call would result if the impulses were dialed directly into one of the automatic switches in-,,

cluded in the regular automatic switching equip--" of the regular switching equipment is tied up due to eithe'rof the two causes noted. Moreover, the arrangement is such that the impulsing conditions of any calling line are tested when the control apparatus of the-associated finder-repeater link is responding to the impulses of the prefix digit dialed at the calling substation. This test is achieved by connecting a leak impedance across the conductors of the calling line during the transmission of the impulses making up the prefix digit, thereby artificially to reduce the impulse transmitting efficiency of the calling line. If the line relay of the operated finder-repeater link faithfully responds to the impulses of the preliminary digit under the adverse impulsing conditions imposed by the leak impedance, this impedance is disconnected from across the line conductors during further operation of the dialing device at the calling substation, thereby to in-' crease the impulse transmitting efliciency of the line. Thus, considering again the operation of the link illustrated to extend a connection from the substation E to the substation A on a call initiated at the first-mentioned substation, when the relay R4I0 operates to extend the subscriber's loop circuit through to the repeater portion of the link illustrated in Fig. 4, it not only completes the above-traced circuit including the conductors of the line 600 for energizing the line relay R4I5, but connects the resistor 4| I in series with the two repeater windings 413 and 414 across the

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