US2224517A - Telephone system - Google Patents

Description

Dec. 10, 1940. F. KEssLL-:R

TELEPHONE SYSTEM Filed April 21, 1959 i 6 Sheets-Sheetl 1 Dec. 10, 1940. F. Kx-:ssLER TELEPHONE SYSTEM Filed April 2l, 1939 6 Sheets-Sheet 2 Dec. 10, 1940. F. KEssLER TELEPHONE SYSTEM Filed April 21, 1939 e sheets-sheet 3 wmf/@m7, M M

ATTORNEYS.

Dec. 10, 1940. F. KEssLER TELEYHONE SYSTEM .Filed April 21, 1959 s sheets-sheet 4 mnlw @QE .S v N Swim @ma Dec- 10. 1940- F. KEssLER TELEPHONE SYSTEM Filed April 21, 1959 6 Sheets--Sh'eerI 5 www; TISS $3 l wl; :l mmm Nm3@ G2@ x A :2% L T N 11\1\/1-:1\1T0R` FRANK KESSLER BY M VMM. a

AUQRNEYS Dec. 10, 1940.

F. KESSLER TELEPHONE SYSTEM Filed April 21, 1939 6 Sheets-Sheet 6 FRANK Hess/.ER

BYM,M, MM

ATTORNEYS).

Patented Een. B it@ 2.22am? 'ranno sfrsraiu Frank Kessler, Villapark, Hi., assignor to Asso-A ciateci Electric Laboratories, Inc., Chicagmlll., a corporation oi Deiana-ire l Application prii 2i, 1939, Serial No. 269,161

45 claims. (ci. ris-eri The present invention relates to telephone systems and, more particularly, to automatic telephone systems wherein a portion of the subscribers lines are of the multiparty type.

As explained in Patent No. 1,267,113--Powell, granted May 21, 1918, in telephone systems of the character indicated, when one or more of the substations associated with a multiparty subscriber-s line is taken out oi service or disconnected from lo the line, it is desirable to provide an arrangement whereby calls intended for the disconnected substation are routed to an operators position so that the calling subscribers can be infomed that the called substation is no longer in service. in

. i tercepting service of this character is also desirable in other instances when calls to substations actually in service are to be intercepted. An improved arrangement for providing call intercepting service of the character just mentioned is dis- 20 'closed in the copending application of Carl O. Wright, Serial No. 267,956, iiled April 15, i939. The system disclosed in this copending application utilizes ringing apparatus of the harmonic type which is so arranged that the ringing volt- 25 ages of diierent frequencies and individually corresponding to the substationsof the multiparty lines of the system are transmitted to the groups of connector switches of the system successively and during different ringing' intervals. In ac- 30 cordance with thev invention therein disclosed, there is provided a relay which is controlled by the ringing apparatus and is arranged to operate only during one of the intervals of each ringing cycle. This relay, in cooperation with a second 35 relay connected to be energized by ringing current of any frequency projected over the line arranged for call interception, functions to initiate the operation of apparatus for routing a connecttion from the calling line to the intercepting op- 40 erators position. More particularly, the firstmentioned relay corresponds only to the substation with respect to which calls are to be intercepted and operates only during those ringing intervals when ringing current for signaling this 45 substation would normally be projected over the associated line. According1y, by arranging the call-forwarding apparatus to operate only when the two relays are both operated, only calls intended for the substation corresponding to the 50 first-mentioned relay are routed to the call intercepting operators position. While this arrangement is perfectly satisfactory in operation when incorporated in a system designed for the wellknown directory method of establishing reverting 55 call connections between the substations associated with the multiparty lines, it is not applicable for use in a system wherein reverting call switches are provided for the purpose of! controlling the rig operations requiredincident to the establishment of reverting call connections. More- 5 over, the arrangement, likeother prior arrangements ofthe same generall character; visconnected to be used only for the purpose of intercepting calls intended for substations'which have been or are associated with the muitiparty lines of the system. Another desirable service frequently provided in automatic telephone systems is that oi routing to an operators position `cal.s which have inadvertently been extended to the inactive contacts forming a dead level of contacts embodied in one of the selector switches of the system. In the usual arrangement, these two services are entirely divorced, separate and independent apparatus' being provided for rendering the services of diderent types.

It is an object of the present invention, therefore, to provide, in an automatic telephone system including one or more subscribers lines of the multiparty type, improved apparatus arranged to perform the dual functions of intercepting and routing to an operators position certain predetermined calls routed to the multlparty lines of the system and calls which have inadv `rtently been extended to the inactive contacts of one of the selector switches embodied in the system.

It is another object of the present invention to provide, in a automatic telephone system includ.- ing one or more multiparty lines and arranged to utilize reverting call switches in completing reverting call connections, improved apparatus of simple and economical arrangement which operates in a new and improved manner to intercept certain calls routed to the multiparty lines and automatically to extend the intercepted calls to an operators position. I

It is a further object of the invention to provide, in a system of the character indicated, im-l proved apparatus for controlling the ringing operations performed incident to the completion of reverting call connections.

'Ihe invention is illustrated in its embodiment in an automatic telephone system which includes an operators position,a plurality oi lines, one or more of which is of the multiparty type, and automatic switching apparatus for setting up connections between'the lines. In order clearly to indicate the utility of the inventionyone of the selector switches embodied in the system is assumed tohave a dead level of bank contacts, that is, a contact level which includes inactive contacts not -connected to trunk lines outgoing from the switch. In accordance with the present invention, there is provided apparatus responsive to a call routed from a calling one of the subscribers lines through the automatic switching apparatus to the rst set of inactive contacts of the above-mentioned dead contact level for extending a connectionfrom the calling line to the operators position, together with means responsive to a call routed from a calling one of the subscribers lines through the automatic switching apparatus to the multiparty line and intended for one of the substations normally associated with the multiparty line for extending to the same operators position a connection from the calling line. More particularly, the operators position has associated therewith lineconnecting apparatus through which the calls of both types are routed. This line connecting apparatus is so arranged that it is only capable of handling one call at a time, lockout means being provided for preventing the operation of the substation call intercepting apparatus when a call is routed through the apparatus provided for dead level call interception and vice versa.

The automatic switching apparatus embodied in the system further comprises a reverting call switch which, in conjunction with the harmonic ringing aplaratus of the system, functions to control the .application of ringing voltage to the multiparty lines incident to the completion of reverting call connections. This reverting call switch is arranged to impress upon any one of the multiparty lines having a reverting call initiated thereon ringing voltages of the frequencies respectively corresponding to the calling and called substations associated with the line. -There is also provided, in association with the ringing apparatus of the system, a plurality of sets of relays which individually correspond to the ringing intervals of each ringing cycle. Each of the sets of relays is operative to divide each corresponding ringing interval into two periods and the arrangement is such that ringing voltage ls'impressed upon any one of the multiparty lines, having a reverting call initiated thereon, through the reverting call switch only during the second period of each ringing interval, the respective first periods of the ringing intervals being reserved for the control of the line connecting apparatus to intercept certain calls routed to the multiparty lines. More particularly, each set of relays has associated therewith a control device which is operative during the rst period of each corresponding ringing interval. Each of the control ldevices may be arranged to initiate the operation of the line connecting apparatus to extend connections from called ones of the multiparty lines to the intercepting operators position when the selected ringing interval, during which ringing current is projected over a selected called line, overlaps the period during which the control device corresponding to the selected interval is operated.

Further features of the invention pertain to the particular arrangement of the apparatus whereby the above and additional operating features are attained.

The novel features believed to be characteristic of the invention are set forth with particularity in the 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 Figs. 1 to 6, inclusive, when combined in the manner shown in Fig. 7, illustrate an automatic telephone system having embodied therein the features of the invention brieily described above. More particularly, Fig. 1 illustrates in schematic form certain of the lines and certain of the automatic switching apparatus embodied in'the system; Fig. 2 illustrates the intercepting operators p osition and the line connecting apparatus associated therewith; Fig. 3 illustrates the harmonic ringing apparatus embodied in the system: Fig. 4 illustrates a reverting call switch which is utilized in the completion of reverting call connections; Fig. 5 illustrates the apparatus for routing a connection from an inactive set of bank contacts of one of the selector switches embodied in the system through 1the line connecting apparatus of Fig. 2 to the intercepting operators position; andl Fig. 6 illustrates the equipment for controlling the line connecting apparatus of Fig. 2 to intercept certain of the calls routed to the multiparty-lines of the system. v

In brief, the system comprises an exchange,

of which is indicated at Il, extending to the exchange, and a plurality of subscriber-controlled automatic switches including line switches indicated at I5 and 2 0, respectively, a selector switch 25, and -a connector switch 3l, for setting up connections between .the various subscribers lilies. The exchange housing the automatic switching equipment also has extending thereto a plur'ality of multiparty lines, one of which is indicated at II as terminating in the line switch I5 and the bank contacts of the connector switch 30. This line has associated therewith a plurality of substations B, C, and D which individually include signal devices in the form of harmonic ringers I2, I3 and I4 bridged across the conductors of the line II in series with the condensers I6, II and Il, respectively. The harmonic ringers bridged across the line I I at the various substations are tuned to respond to ringing currents of diiferent frequencies so that any desired one of the substations may be signaled tothe exclusion of the lcthers by projecting ringing current of the proper frequency over the line II. The endof the line I0 remote from the exchange terminates at a subscribers substation A of the usual common battery type. The line switches I5 and 20 and the other similar switches of the system are non-numerical switches in the sense that they are ineffective to perform any line selecting functions other than those of selecting idle ones of the selector switches. The selector and connector switches, on the other hand, are commonly known as numerical switches in that they are operative to perform particular line selecting functions in response to impulses transmitted thereto. It Will be understood that a plurality of switches of each type, namely, a plurality of line switches, a plurality of selector switches, and a plurality of connector switches, are provided in the system for performing the usual line switching functions. The switches of each type are respectively arranged in groups and, in accordance with universally followed practice, the number oi' switches in each group is determined by the maximum volume of traffic the particular switch group is required to handle. Further in accordance with conventional practice, each of the subscribers lines is multinled between the corresponding bank contacts of a group of connector switches, whereby a plurality of such switches are rendered available for setting up connections between each line and every other line of the system. The line switches, onV the other hand, are individually associated with the respective subscribers lines.

Each of the line switches I5, 20, etc., is preferably ofthe well-known rotary type, of which several commercial embodiments are available. Each of the selector and connectorv switches is preferably of the well-known Strowger type having embodied therein a wiper carriage structure adapted to be translated vertically to bring the wipers thereof to a position opposite a particular' level of bank contacts and then rotated to bring the wipers into engagement with a particular set of bank 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 particular functions of the switch. Obviously, the particular arrangement of the control apparatus embodied in the switches of different type is different in each instance, depending upon the character of the switch.

In order more clearly to explain the operation of the circuits to which the invention pertains, a portion of the relay equipment embodied in the line switch |5 and the connector switch 30 has been shown in detail. More particularly, the equipment of the connector switch 30 comprises a slow-to-operate ringing control relay R|00, a slow-acting ring cutoff relay RI l0, and a ringing frequency selecting switch |20 of the well-known minor type. In brief, the switch |20 comprises a single set of bank contacts |2|, aY wiper |22, means comprising an operating magnet |23 for driving the wiper |22 over the contacts of the contact set |2|, a release magnet |24 for causing the wiper |22 to be-returned to its normal or home position, and a pair of o-normal springs |25 for controlling the operating circuit for the release magnet |24. The line switch I5 includes a line relay R|30 which is illustrated in the drawing in order to facilitate an explanation of certain of the circuits referred to hereinafter.

In order to explain the operation of the call intercepting apparatus to intercept calls inadvertently routed to a dead level of one of the selector switches embodied in the system, the selector switch 25 is illustrated as comprising a level of bank contacts, the contactsof which are not connected to lines outgoing from the switch but are reserve contacts which may be used if trailic conditions are such as to require additional connector switches in the system. This level of dead contacts isindicated as comprising a first set of contacts 26, 21 and 23; these being connected by means of conductors 3|, 32 and. 31, forming a trunk 30, to the control equipment illustrated in Fig. 5.

The equipment provided in the line terminating exchange also comprises cyclically operating ringing apparatus for delivering to the various connector switches ringing currents of flvia d'fferent frequencies. The arrangement of this anparatus is such that the ringing currents nf different frequencies aredelivered to the'different groups of connector switches during different.

intervals of each ringing cycle. For example, the arrangement may be such that during tLe first ringing interval of each ringing cycle, ringing current of the frequency-FI is delivered to a first group of connector switches, ringing current of the second frequency F2 is delivered to a second group of the connector switches, ringing current of the third frequency F3 is delivered to a third group of the connector switches, ringing current of the fourth frequency F4 is delivered to a fourth group of connector switches, and ringing current of the fifth frequency F5 is delivered to a fifth group of connector switches; and during the second interval of each ringing cycle, ringing current of the first frequency is delivered to the third group of connector switches, ringing ourrent of the second frequency is delivered to the fourth group of connector switches, ringing current of the third frequency is delivered to the tors are arranged to deliver ringing current by way of ringlngcurrent conductors to the various connector switches of the system. The ringing current conductors are arranged in groups fespectively extending to the diierent groups of connector switches. One such group of ringing current conductors is illustrated as comprising the conductors C300, C301, C308, C303 and C3I0, which are arranged to deliver ringing currents to the connector switches of the group including the switch 30. To this end, these conductors are connected by way of the cable conductors of a cable 3|| to ,the respective contacts of the contact set |2| embodied in the frequency selecting switch |20 of the connector switch 30. These same conductors are multipled in the cgrresponding bank contacts of the frequency selecting switches respectively embodied in the other connector 'switches of the group including thel switch 30. In a similar manner, the ringing current conductors of the bracketed group 3| 2 are terminated in the bank contacts of the various frequency selecting switches respectively embodled in the connector switches forming the secto 305, inclusive, there are provided ve ringing relays R320, R330, R340, R350 and R360, and a ringing interrupter switch 310 of conventional arrangement. This ringing interrupter switch has extending thereto a start conductor C336 over which the start relay conventionally embodied in the switch is arranged to be energized in response to operation of any one of the connector switches of the system. The interrupter switch 310 also has extending thereto a pick-up conductor C331 by way of which the ringing relays of the various connector switches are controlled to control the application of ringing current of a selected frequency to a selected called line. The ringing interrupter switch 310 is arranged repeatedlyv to operate through identical cycles. .During each cycle of operation, the apparatus embodied in this switch functions to imcession', each thereof functioning. when operated.'

to connect its associated ringing current cond uctors to the iivealternating current generators. Thus, during.'the rst period of eachrringin'g y cycle, the relay R323 operates its arma-ture RA32| to disconnect the ringing conductor C333 from ground and to connect this conductor to the ungroundedterminal ofthe alternating current generator 33|. In a similar manner and at its armatures RA322 to RA323, inclusive, the relay R323 disconnects the four other associated ringing current conductors from ground and connects these conductors to the alternating current generators 332, 333, 333 and 335, respectively. Since the relay R323 is alone operated during the rst interval of each rillinal cycle, only the ringing current conductors associated with this relay are connected to the indicated alternating current generators during such intervals. 'During the second interval of each ringing cycle, the second ringing relay R333 operates its armature RA333 to disconnect the ringing current conduc-` tor C333 from ground and to connect this conductor to the ungrounded terminal of the alternating current generator 333. In a similar manner, the other ringing current conductors associated with the second ringing relay R333 are disconnected from ground and connected to the corresponding alternating current generators during the second interval of each ringing cycle. At the beginning of the third interval of each ringing cycle, when thek relay R333 is operated, this relay, at its armature RA335, disconnects the ringing current conductor C3I3 from ground and connects this conductor to the ungrounded terminal fourth ringing relay R353 is operated, the armature RA352 is operated to disconnect the ringing current conductorv C331 from ground and to connect this conductor to the ungrounded terminal of the generator 332. In a similar manner, the other ringing current conductors associated with the fourthringing relay are disconnected from ground and connected to their respective corresponding generators during the fourth interval of each cycle of operation of the interrupter switch 313. Finally, the ringing relay R333 operates during the fifth ringing interval of each ringing cycle to disconnect, `at its armature RA333, the ringing current conductor C333 from ground and to connect this conductor to the ungrounded terminal of the generator 333. Similarly, the other ringing current conductors associated with the ilfth ringing relay R333 are disconnected from ground and connected to the ungrounded terminals of their respective corresponding generators during the fifth interval of each ringing cycle. 'I'he arrangement of the interrupter switch 313 is such that ground potential is impressed upon the pickup conductor C331 at the beginning of each cycle of operation thereof. From the foregoing explanation, it will be apparent that the ungrounded terminals of the generators 33|, 333, 335, 332 and 333 are connected to the respective ringing current conduc-V tors C333, C333, C3I3, C331 and C333 during suglceeding ringing intervals of each ringing cy e.

The system further comprises an operators position 233 to which certain calls mayautomatically be extended through operation of the improved line connecting apparatus illustrated in Fig. 2. 'Ihe equipment provided at the operators position comprises an operators telephone set 232 of any conventional arrangement. an answer key 23|, a hold key 233, an incoming call signal lamp 233, and a signal lamp 235 for indicating those intervals when the key 233 is operated to its olf-normal position. Each ofthe keys 23| and 233 is of the well-known locking type such that when operated to its oiI-normal yposition it remains in the off-normal position kuntil manually restored to normal.

\\As indicated in the introductory portion of the specication, the system is arranged to Autilize reverting call switches in completing reverting call connections between substations associated with the same lines. One switch provided for. vthis purpose is illustrated in Fig. 4 as comprising a pair of ringing frequency selecting switches 333 and 3I'3, each of which is of the well-known,

minor type. The minor switch 333 is operative in response to a second seriesof impulses transmitted to the reverting call switch toselect .the frequency of the ringing current corresponding to-the substation at which a reverting cali originates. In brief, this switch comprises two sets of bank contacts 33| and 332, wipers 333 and.333 respectively associated with the two contact sets, means comprising a rotary magnet 335 and a ratchet and pawl mechanism, not shown, for operating the enumerated wipers to a desired oifnormal position to select a desired ringing frequency, a release magnet 3 33 for restoring the wipers to normal, and a pair of off-normal springs 331 which are moved into engagement when the wipers 333 and 333 are operated to their respective first olf-normal positions. .The switch 3| 3 is .provided for the purpose of selecting, in response to a ilrst-series of impulses transmitted to the reverting call switch, the ringing current of the particular frequency corresponding to a desired called substation.l This second switch is of identical construction with the switch 333 and comprises two contact sets 3|| and 3|2, wipers 3|3 and 3|3 individually associated with the contact sets, a rotary magnet 3|5 for driving the wipers over the contacts of their respective associated sets, a release magnet 3|3, and a pair of off-normal springs 3|1. For the purpose oi' controlling the two minor switches 333 and 3|3 and of controlling the ringing operations performed incident to the completion of reverting call connections, there is also embodied in the reterting call switch a plurality of control relays. These relays include a line relay R333, a slow-acting hold relay R335, ,a pair of digit transfer relays R353 and R333 arranged to be controlled by a slow-to-release impulse responsive relay R335, a line switching relay R323, a pair of ringing relays R335 and R313, and a pair of ring cutoff and release relays R355 and R333.

Neglecting for the present the details of the apparatus illustrated in Figs. 2, 5 and 6, provided subscriber at the telephone A lifts his receiverv from its hook to initiate a call intended for a assen? second subscribers telephone, such, for example,

as the telephone B, a loop circuit is completed for initiating the operation of the line switch to select a trunk line leading to an idle selector switch. Assuming, for example, that the selector switch is selected by the line switch 20, when the trunk line leading to this selector switch is seized, the calling loop circuit is extended to this selector switchand the switch is conditioned to respond to the rst series of impulses dialed at the calling substation. With the selector switch 25 in this condition, the usual dial tone signal is returned over the established loop circuit 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 25 elevates its wipers to a position opposite the level of bank contacts terminating the trunks leading to the connector switches having access to the called line 'Following this operation and during the interdigit pause between the first and second'digits, the wipers of the switch 25 are automatically stepped over the contacts of the selected level until a trunk line leading to an idle connector switch ofthe selected group is found. Assuming that the connector switch 30 is the rst available idle connector switch in the selected group, when the wipers of the selector switch 25 are stepped into engagement with the contacts terminating the trunk line extending to this connector switch, the subscribers loop circuit is extended to the switch 30, thereby to cause this connector switch to be conditioned to respond to the second series of impulses dialed at the calling substation. When the connector switch 30 is seizedvin the manner just described, certain of the control relays embodied therein, and more particularly the line and hold relays, operate to complete a path for impressing ground potential upon the start conductor C336 extending to the ringing interrupter switch 310, thereby to initiate the operation of the interrupter switch in the event it is not already in operation. When operation of the interrupter switch 310 is initiated, the relays R320, R330, R340, R350 and R360 function, in the manner previously explained, successively to connect the conductors C306 to C3l0, inclusive, to the generators 30| to 305, inclusive, during the diierent intervals of each ringing cycle. When the second digit is dialed at the calling substation the wipers of the connector switch 30 are.

stepped vertically to a position opposite the level of bank contacts at which are terminated the lines of the ten line subgroup including the called line Following this digit and during the interdigit pause between the second and third digits, the connector switch is conditioned to rotate its wipers step by step in accordance with the impulses of the third digit of the directory number designating the called substation. When this third digit is dialed, the wipers of the switch 30 are operated into engagement with the set of bank contacts terminating the called line During the interdigit pause between the third and fourth digits, circuits are prepared for energizing the operating magnet |23 of the frequency selecting switch |20 in accordance with the impulses of the fourth and iinal digit. The indicated operating magnet responds to the impulses of the fourth digit by operating the wiper |22 into' engagement with the contact of the contact set |2| having impressed thereon ringing voltage of the particular frequency required to voperate the harmonic ringer |2 provided at the called substation B. Ii it be assumed, forexample. that the ringer I2 is constructed to respond only to ringing current of the frequency F2, theJ fourth digit dialed at the calling substationiwill comprise two impulses so that at the conclusion thereof the wiper |22,wil1 be left standing in engagement with the contact' tierminating the ringing conductor C301. During the operation of the switch |20 and when the wiper |22 is stepped to its first off-normal posi-f' tion, the oil-normal springs |25 are closed to prepare an incomplete circuit for energizing the release magnet |24, this circuit being held open until the switch 30 is released.

Inaccordance with conventional practice', suitable provisions are made for testing the selected called line to determine the idle or busy condition thereof, for returning the usual busy tone signal over the established loop circuit to the calling subscriber in the event the called line is busy, and for projecting ringing current of the selected frequency over the called line in the event this line is idle at the time it is selected. Assuming that the called line is idle, a circuit is prepared, through operation of certain of the relays embodied in the connector switch 30, for energizing the lower winding of the slow-to-operate ringing control relay RI00. This circuit is thereafter completed at the beginning of the next cycle of operation of the ringing interrupter switch 310 when ground potential is impressed upon the pick-up conductor C331, and may be partially traced as extending from ground by way of C331, the lower winding of R|00, the test wiper of the connector switch 30, the private conductor of the line and through the winding of the cut-off relay conventionally embodied in the line switch I5 to battery. When this circuit is completed, the cut-off relay embodied inl the line switch l5 partially operates to disconnect the windings of the line relay R|30 from the conductors Ils and ||b of the called line thereby to clear this line of the shunt impedance represented by these windings. Completion of the circuit just traced also results in the energization and operation of the ringing control relay R|00. This relay, upon operating, completes, at the X contacts associated with RA|02, a holding circuit for itself, this holding circuit having been previously prepared through operation of certain of the other relays, not shown, embodied in the connector switch 30. At its armatures RA|0| and RA|03,

the relay R|00 completes a circuit for projecting 1 Y ringing current of the selected frequency over the conductors of the line In the present case, the circuit traversed by the ringing current may be traced as extending from the ungrounded terminal of the generator 302 by way of RA352, C301, the second contact of the set |2|, the wiper |22, RA||3, RA|03, the cofnductor IIb, the windings of the ringer I2, the condenser I6, the conductor Ils,- RAIDI, RAI l, the upper winding of RI I0 and the exchange battery to the grounded terminal of the generator 302. Portions of this current are obviously shunted through the harmonic ringers respectively provided at the other substations associated with the line The ringer |2, however, is the only ringer which responds to current of the particular frequency developed by the generator 302. Operation of this ringer serves to signal the called subscriber that he is being called. A portion of the ringing current is also shunted, in the usual manner, over the calling loop circuit to energize the receiver provided at the calling substation,

thereby to indicate to the calling subscriber that the called substation is being signaled. It will be apparent from the foregoing explanation with reference to the ringing apparatusshown in tion B. More particularly, when the receiver at this substation is removed from its supporting hook, a direct current conductive bridge is connected across the conductors II. and IIb of the line II to complete a circuit for energizing the upper winding of the slow-acting ring cut-of! relay RIIII. This circuit may be traced as extending from ground by way of RA352, C301, the second contact of the set I2I, the wiper |22, RAII3, RAI03, the conductor IIb, the bridge across the conductors |Ib and II., the conductor II., RAIIII, RAIII, and the upper winding of RI I to battery. When its upper winding is energized over this circuit, the relay RI|0 operates to close the X" contacts associated with RAI I2,

thereby to complete a prepared holding circuit for itself. Thereafter, the relay RIIO, at its armatures RAIII and RAI I3., and their respective associated resting contacts, opens two points in its operating circuit and two points in the above-traced circuit for projecting ringing current over the line II. vAt these same armatures and their respective associated working contacts, the relay RI I0 completes the desired conversational circuit between the calling and called substations. When the relay RI I0 operates it also functions to open the path, not shown, by way of which ring-back tone current is projected over the calling loop circuit, thereby to terminate the ring-back tone signal in the usual manner.

Preferably, the control relays of the connector switch 30 are so arrangedthat the release of the operated switch train is under the control of the calling subscriber at the substation A. With such an arrangement, when the connection is cleared out at the calling substation, the loop circuit extending through to the operated connector switch 30 is interrupted to cause the release of the line and hold relays conventionally embodied in this switch in the usual manner. When these relays restore, the line and selector switches 20 and 25, respectively, are released and the control apparatus embodied in the connector switch 30 is restored to normal. all in a manner well understood in the art. During the release of the control apparatus embodied in the connector switch 30, the previously traced holding circuits for the two relays RIIO and RIM are interrupted, causing these relays to restore. Also, ground potential is removed from the private conductor of the called line I I, whereby the cut-oil relay embodied in the line switch I is released to reconnect the windings of the line relay RI30 to the conductors II. and IIb of the line II. When ground potential is removed from the private conductor of the line II,

battery potential is impressed upon thisconductor through the windings of the cut-off relay embodied in the line switch I5, thereby to mark the line as idle in the bank contacts of the connector switches having access thereto. When the line and hold relays embodied in the connector switch 30 restore, a circuit is also completed for energizing the release magnet of the Strowger mechanismembodied in 'this switch, thereby to cause the wiper carriage structure of this mechanism to be restored to rotary and vertical normal` Similarly, a circuit is completed 4by way of the off-normal springs |25 for energizing the release magnet |24 of the frequency selecting switch |20, whereby the wiper |22 of this switch is restored to normal. When this wiper attains its normal position, the olf-normal springs |25 are opened to interruptthe operating circuit for the release magnet |24. Thus, the switch train is fully released.

Referring now more particularly to the apparatus illustrated in Figs. 2, 5 and 6, for extending connections to the operators position 200, the line connecting apparatus associated with this operators position is illustrated in Fig. 2 as comprising a. plurality of line relays, one of which is indicated at R220, individually associated with the multi-party subscribers lines with respect to which calls are to be intercepted. This apparatus also comprises a pair of cut-oif relays R240 and R210, together with three control relays R230, R250 and R260, which function in the manner pointed out hereinafter to control the signal lamp 204 and the indicated cutoi and line relays. A slow-to-operate start relay R290 may also be included in this apparatus if required.

Theapparatus illustrated in Fig. 5 and provided for the purpose of routing connections from dead or inactive contacts of the selector switches to the line connecting apparatus shown in Fig. 2 consists of a group of relays including a line relay R500, a slow-acting hold relay R5I0, a line switching relay R540, a slow-to-operate signal lamp control relay R550, and a cutoiI.relay R530.--

As indicated, this apparatus is connected by way of the trunk line 36 to the first set of contacts in the dead level of bank contacts embodied in the selector switch 25.

'Ihe ringing control apparatus illustrated in Fig. 6 is provided for the purpose of preventing inadvertent operation of the line relays associated with the multi-party lines arranged for call interception when reverting calls are initiated on these lines. More particularly, this apparatus functions to divided each ringing interval of each ringing cycle defined by operation of the interrupter switch 310 into two periods; the first period oi' each interval being allotted to control of the line relays associated with the mutiparty lines and embodied in the apparatus illustrated in Fig. 2. The second and predominate period of each ringing interval is allotted to control of the ringing relays R465 and R410 embodied in the reverting call switch illustrated in Fig. 4. With the particular arrangement illustrated in Fig. 6, each ringing interval of one second duration is divided into two parts, the first 'period being of approximately one-quarter of a second. duration and the second period being of approximately three-quarters of a second duration. Specifically, the apparatus shown in Fig. 6 comprises a plurality of sets of relays to 165, inclusive, which individually correspond to the five ringing intervals of each ringing cycle and individually function to split each of the corresponding intervals into the two periods mentioned above. The enumerated sets of relays are arranged to be controlled by the interrupter switch 310 over the conductors C320, C321, C320, C229 and C338 and have individually associated therewith master relays R000, R005, R8I0, RIIB C646. cludes a sensitive relay R666 and a pair of slowy I Y y 3,224,517

and R626. More particularly, the relay set 16| comprises two's'low-acting relays R626 and R636 and a third fast-'acting relay R646, which relays are arranged to causethe operation of the associated master relay R660 during the rst period of each .corresponding ringing interval and to impress ground potential upon the ringing control conductor C646 during the `second period of each ycorresponding ringing interval. In a similar manner the second set of relays 162 comprises acting relays R610 and R616, which relays function to control the master relay R6|6 and the application of ground potential to the first ringing control conductor C646. The fourth set of vrelays 164 includes apair of slow-acting relays R660-I and R695 and a sensitive relay R100. which three relays are arranged to control the master relay 2- 25 R6|5 and the application of ground potential to the second ringing control lead C646.' Finally, the fifth set of relays 166 comprises a sensitive [relay R120 and a pair of slow-acting relays R1|0 and R1I6, which three relays are arranged to control the associated master relay R620 andthe application of ground potential to the first ringing control conductor C646. This iifth set of relays is also arranged to control a pair of additional relays R130 and R140 which function to reverse the connections of the ringing conductors C141 and C148 to the ringing control conductors C645 and C646 'at the end of each cycle of operation of the interrupter switch 310. The two ringing control conductors C141 and C146 are multiplied to the corresponding relay contacts of each of the reverting call switches embodied in the system. For the purpose of operatively associating the relay sets 16| to 166, inclusive, with the interrupter switch .310, there is provided a connect relay R160. 'I'he above-enumerated master relays are arranged in the manner more particularly described hereinafter directly to control the line relays, such, for example, as the relay R220, individually associated with the multiparty lines and provided for the purpose of connecting these lines tothe apparatus .shown in Fig. 2. In order to prevent any one of these line relays from responding to a transient voltage impressed upon the associated line due to a lightning surge or the like, there is provided a slowto-operate. relay R663 which functions momentarily to delay the complete operation of an energized one of the indicated linerelays following its initial energization.

Referring now more particularly to the operation of the apparatus illustrated in Fig. 6, when ground potential is impressed upon the start conductor C336 extending to the interrupter switch 310 to initiate the operation of this interrupter switch in the manner previously explained, a. circuit is completedfor energizing the relay R636 of the ilrst relay-set 16|, this circuit extending by way of the grounded conductor C336, RA16| and the winding of R630 to battery. When energized over this circuit, the relay R630 operates to complete, at RA63I, an obvious circuit for energizing the associated slow-acting relay R626. The

relay R626, upon operating, opens, at RA626. a l point in the path, traced hereinafter. for impressing ground potential upon the ringing control conductor C646. At RA621, the relay R626 prepares a circuit, traced hereinafter, for energizing the relay R600. At RA626, the. relay R626 completes a circuit for energizing the connect re` lay R160, this circuit extending by way of the 6 grounded start conductoi C636, RA16I, RA626, RA121, RA643 and the winding of R160 to battery.- When energized over this circuit, the relay R160 first completes, at the X contacts associated with RA161, an obvious holding circuit for l0 itself. At RA161, the relay R166 also completes a holding circuit for the relay R630, this circuit extending by way of the grounded conductor'C336, RA161, RA643, RA121, RA626 and the winding of R630 to battery. :At its armatures RA162 to l5 Rii166, inclusive, the relay R166 thereafter connects the conductors C326.' C321, C326, C626 and Ckthrough to the relay sets 16| to 166, inclusive, so that the relays embodied in these sets are controlled in accordance with ground pulses 20 impressed upon the enumerated conductors through operation of the interrupter switch316. At RA16I, the relay R160, upon fully operating, interrupts apoint inthe common portiony of its own operating circuit and the operating -circuit 25 for the relay R630. When a ground pulse is applied to the conductor C326 lby the interrupter v 'holding circuit for the relay R630, thereby to initiate the sequential restoration of the relays R630 35 and R640. At RA64I, the relay R640 completes the above-mentioned circuitfor energizing the master relay R600, this circuit extending from ground by way of RA64I, RA621- and the winding of R600 to battery. The relay R600 now oper- 40 ates to complete at its armatures RA60I, RA602, etc.,- paths including the left winding of R603 for impressing ground potential upon the associated terminals .166, 161, etc.; these terminals being" connected to the terminals of the line relays em- 45 bodied in the apparatus of Fig. 2 in the manner more fully explained subsequently. The relay R600 is maintained in its operated position for only a predetermined portion of the time interval during which R640 is operated. Thus, shortly -50 following the operation of R640, the relays R630 and R625 sequentially restore to open at RA621 the operating .circuit for R600 causing the lastnamed relay to restore to disconnect ground from the associated terminals 166, 161, etc.. At RA642, 55

the relay R640, upon operating, prepares a path for impressing ground potential upon the ringing control conductor C646; this path being completed upon the subsequent release of the relay R625 and extending from ground byway of o RA626 and RA642 to the conductor C646. This path is not interrupted until the relay R640 restores subsequentto the release of the relay R626. From the foregoing explanation it will be apparent that during -one portion of the vinterval 65 when the relay R640 is operated, namely, the first ringing interval of-the ilrst cycle of operation of the interrupter switch 310, the relay R600 is operated. During the second period of the interval when the relay R640 is operated, the relay R600 is restored and ground potential is impressed upon the ringing control conductor C645. The relative lengths .of these two periods is `obviously determined by the slow-to-release characteristics of the two relays R630 and R626. Preferably,

This circuit extends by way of the 30 -69 relay R605 operates in response to operation of these relays are so constructed and arranged that the relay R600 is operated for the ilrst quarter of each interval during which the relay R640 is energized, while ground potential is impressed upon the ringing control conductor C645 for the remaining three-quarters of each interval when the relay R640 is energized.

The relay R640, upon operating in the manner explained in the preceding paragraph, also completes a circuit for energizing the relay R655 of the second relay set 162; this circuit extending by way of the grounded start conductor C336, RA151, RA643 and the winding of R655 to battery. At RA644, the relay R640 opens a point in the circuit, traced hereinafter, for energizing the relay R660 at the beginning of the second ringing interval of each ringing cycle. The relay R655, upon operating, completes, at RA656, an obvious circuit for energizing the relay R650. The last-mentioned relay, in turn, operates to prepare a circuit for energizing the second master relay R605 and to open at RA652 a point in the path, traced hereinafter, for impressing ground potential upon the second ringing control conductor C646. At the end of the first ringing interval, ground potential is removed from the conductor C326 and is impressed upon the conductor C321 in the manner previously explained. When this occurs the relay R640 is deenergized and restores to open, at RA64I, a further point in the operating circuit for the rst master relay R600 and to interrupt, at RA642, the above-traced path for impressing ground potential upon the ringing control conductor C645. At RA643, the relay R640 interrupts the above-traced operating circuit for the relay R655. At RA644, the relay R640 completes a circuit for energizing the relay R660, this circuit extending by way of the grounded conductor C321, R`A153l, RA644, and the winding of R660 to battery. Upon operating, the relay R660 completes, at RA66I, the above-mentioned circuit for energizing the second master relay R605, this circuit extending from ground by way of RA66I RA65I and the winding of R605 to battery. At RA662, the relay R660 prepares the above-mentioned path for impressing ground potential upon the second ringing control conductor C646. At RA663, the relay R660 completes an obvious circuit' for energizing the slow-acting relay R615 of the third relay set 163, thereby to cause the sequential operation of the two relays R615 and R610 in the order named. The relay R610, upon operating, prepares, at RA61 I, the operating circuit for the third master relay R6I0 and opens, at RA612, a point in a second path for impressing ground potential upon the ringing conductor C645. At RA664, the relay R660 opens a point in the circuit, traced hereinafter, for energizing the relay R680. 'I'he second master the relay R660 and, at its armatures RA606, RA601, etc., completes obvious paths for impressing ground potential upon the associated terminals 168, 169, etc. A predetermined time interval following operation of the relay R605 and when the relays R655 and R650 sequentially restore, to open, at RA65I, the operating circuit for ringing cycle under consideration, ground potential is removed from the conductor C321 and is impressed upon the conductor C326 to initiate the third interval of the ringing cycle. When ground potential is removed from the conductor C321, the relay R660 isdeenergized and restores to open, at RA662, the above-traced path for impressing ground potential upon the ringing conductor C646; to interrupt, at RA663, the operating circuit for the relay R615, thereby to initiate the sequential restoration of the relays R615 and R610; and to complete, at RA664, a circuit for energizing the relay R690. The last-mentioned circuit extends by way of the grounded conductor C328, RA154,VRA664 and the winding of R660 to battery. Upon operating, the relay R680 completes, at RA66I, a circuit extending by way of RA61I for energizing the third master relay R6 I 0. At RA662, the relay R680 prepares a point in the second path for impressing ground potential upon the ringing control conductor C645. At RA683, the relay R680 completes a circuit for energizing the relay R695 of the fourth relay set 164; this circuit extending by way of the grounded conductor C328, RA154, RA664, RA683 and the winding of R695 to battery. When this circuit is completed, the two relays R695 and R690 sequentially operate in the order named and in an obvious manner. At RA694, the relay R680 opens a point in the operating circuit, traced hereinafter, for the relay R100. The third master relay R6I0, upon operating its armatures RA6I I, RA6I2, etc., connects ground potential to the associated terminals 110, 11 I, etc. A predetermined time interval following operation of the relay R6I0 andwhen the relays R615 and R610 sequentially restore, the operating circuit for R6 I 0 is interrupted at RA61I, and the second path for impressing ground potential upon the conductor C645 is completed; this path extending from ground by way of RA612 and RA692 to the conductor C645.

Atthe end of the third interval of the ringing cycle under consideration, ground potential is removed from the conductor C328 by the interrupter switch 310 and is impressed upon the conductor C329 to initiate the fourth ringing interval of the cycle. .When ground potential is removed from the conductor C326, the relay R690 is deenergized and restores to open, at RA66I, a

further point in the operating circuit for the third master relay R6I0; to open, at RA682, a point in the second path for impressing ground potential upon the ringing control conductor C645; and `to open, at RA683, the above-traced operating circuit for the relay R695, thereby to initiate the sequential restoration of the relays R695 and R690. At RAB, the relay R660, upon restoring, completes a circuit for energizing the relay R100, this circuit extending by way of the grounded conductor C329, RA155, RA684 and the winding of R100 to battery. Upon operating, the relay R100 completes, at RA10I, a circuit extending by way of RA69I for energizing the fourth master relay R6I5, which latter relay, upon operating its armatures RA6I6, RA6I1, etc., impresses ground potential upon the associated terminals 112, 113; etc., over obvious paths. At RA102, the relay R100 prepares a point in a second path for impressing ground potential upon the second ringing control conductor C646. At RA104, the relay R100 opens a point in the operating circuit, traced hereinafter, for the relay R120 vof the fifth l relay set 165. At RA103, the relay R100 completes a circuit for energizing the relay R1I5, this circuit extending by way of the grounded conducof R1 I 5 to battery.

Islow-acting relay R1I0 operate in the order named, the last-mentioned thereof functioning-to prepare an operating circuit for the fifth master relay R620 and to open, at RA1I2, a point in a V third path for impressing ground potential upon the ringing control conductor C645. A predetermined time interval following operation of the fourth master relay Rill and when the relaysA R695 and R690 sequentially restore, the operating circuit for R6I5 is interrupted. The relay R6I5 now restores to disconnect the associated terminals 112, 113, etc., from ground. At RA692, the relay R690 completes the second-path, including the operated armature RA102, for impressing ground potential upon the second ringing control conductor C646.

At the end of the fourth interval of the ringing cycle under consideration. the interrupter switch 310 operates in the manner previously explained to remove ground potential from the conductor C329 and to impress ground potential upon the conductor C333. When the conductor C329 is disconnected from ground, the relay R100 is deenergized and restores to open, at RA10I, a further point in the operating circuit for the fourth master relay R6I5, and to open, at RA102, a point in the second path over which ground potential is impressed upon the ringing control conductor C646. At RA104, the relay R100 comi pletes a circuit for energizing the relay R120, this circuit extending by way of the grounded conductor C339, RA156, RA104 and the winding of R120 to battery. At RA103, the relay R100 interrupts the previously traced` operating circuit for the relay R1 I5, thereby to initiate the sequential restoration of the last-named relay and the.

relay R1I0. The relay R120, upon operating,

opens, at.RA123, a point in the previously traced operating circuit for the relay R640 and opens,

at RA121, a point in the previously traced operating circuit for the relay R150. At RA12 I, the relay R completes the above-mentioned circuit for energizing the i'lfth master relay R620,

this circuit extending from ground by way of RA12I, RA1II and the winding of R620 to battery. When this circuit is completed, the relay R620 operates its associated armatures RA62I, RA622, etc., to connect the associated terminals 114, 115, etc., to ground over an obvious path. At RA122, the relay R120 prepares the third path for impressing ground potential upon the ringing control conductor C645, this path being completed at RA1I2 in response to the subsequent release of the relay R1 I0 simultaneously with the deenergization of the iifth master relay R620. 'I'his fth master relay, upon restoring, opens, at its armatures RA62I, RA622, etc., the paths over which ground potential is impressed upon the terminals 114, 115, etc. At RA 122', the relay R120, upon operating, completes an alternative circuit for energizing the relay R630 of the first relay set 16|, this alternative circuit extending by way of the grounded conductor C336, -RA156, RA104, RA122', RA15I and the winding of R630 to battery. When this alternative circuit is completed, the relays R630 and R625 sequentially operate in the order named and in the manner previously described. At RA124, the relay R120, upon operating, completes a circuit for energizing the slow-to-release relay R130, this circuit extending from ground by way of C336, RA124,

RA125, RA144 and the winding of R130 to battery. When energized over this circuit, vthe relay R130 operates to prepare, at RA13I', a holding circuit for itself, and to prepare, itt-RA132,' a circuit for energizing the relay R140.

At the end of the fifth interval of the ringing cycle under consideration, the interrupter switch 310 operates in the manner previously explained to remove ground potential from the conductor C338. Substantially simultaneously, ground potential is impressed upon the conductor C326 to initiate the nrst ringing interval of a second ring- V ing cycle. When the conductor C33I'isdiscon-- nected from ground in the interrupter switch 314, the relay R120 is deenergized and restores to open, at RA12 I, a further point in the operating circuit for the fifth master relay R620, and to interrupt, at RA122, the third path for impressing ground potential upon the ringing control conductor C645. At RA122', the relay R120 interrupts the previously traced alternative operating circuit for the relay R630, thereby to`initiate the sequential restoration of the last-mentioned relay and the relay R625. At RA123, the relay R120 recompletes the previously traced circuit for` energizing the relay R640. At RA121, the relay R120 reprepares the operating circuit for the relay R150. l At RA and RC126, the relay R120, upon restoring, completes the prepared holding circuit for the relay R130, this holding circuit extending from ground by way of C336, RA13I, RC126, RA125, RA144 and the winding of R130 tobattery. Following the completion of this holding circuit, the relay R120 opens, at its armatures RA124 and RA125, a point in the previously traced operating circuit for the relay R130. At RA124 and its associated resting contact, the relay R120 completes the above-mentioned circuit for energizing the relay R140, this circuit extending from ground by way of C336, RA124, RA132, RA146 and the winding of- R140 to battery. The relay R140 now operates to reverse the connections of the ringing control conductors C645 and C646 to the associated conductors C141 and C143, this reversal resulting from the operation of the armatures RA14I and RA142. AAt RA143 and RA144, the relay R140 interrupts the above-traced holding circuit for R and completes a holding circuit for itself, the last-mentioned holding circuit extending from ground by way of C336, RAMI, RC126, RA125, RA144, RA143- and the winding of R to battery. Substantially simultaneously with the interruption of the initially completed holding circuit for the relay R130, an alternative holding circuit is completed for this relay, this alternative holding circuit extending from ground by way of C336, RA124, RA132, RA146, RA145 and the winding of R130 to battery. Thus, the two relays R130 and R145 are maintained in their respective operated positions during the second relay sets, the reversing relays R130 and R140 are released, these relays yremaining' in their respective restored positions for the duration of each odd numbered ringing cycle. Thus, at the end of the second cycle of operation of the enumerated relay sets and when the relay R120 operates, the previously traced holding circuit for the relay R130 is interrupted at RA124 and its associated resting contact.

Substantially simultaneously an alternative holding circuit is completed for the relay R140, this alternative circuit extending from ground by way of C336, RA124, RA126, RA144, RA143 and the winding of R140 to battery. Shortly following the completion of the last-mentioned circuit, the relay R130 restores to open, at RA13I, a point in the common portion of the previously traced holding circuits for itself and the relay R140. At RA132,

the relay R130 opens a point in another of its holding circuits and a point in the operating circuit for the relay R140. Thereafter, and when the relay R120-restores, the remaining holding circuit for the relay R140 is interrupted at RA124 and RA126, causingthe relay R140 to restore to reverse the connections of the ringing control conductors C646 and C646 to the two associated ringing control conductors C141 and C143. Fo1` foregoing explanation that the relay sets 16| and 165 both function to impress ground potential upon the ringing control conductor C646 during the intervals when these relay sets are operating. From this it will be apparent that in 'the 40 absence of the two relays R130 and R140, connected and arranged in the manner just described, ground potential would be impressed upon one of the two conductors C141 and C143 during each of the rst, third, and fifth intervals of each ringing cycle, while ground potential would only be impressed on the other of the two enumerated conductors during the second and fourth intervals of each ringing cycle. This would, of course, mean that ground potential would be impressed upon one of the two con-l ductors during adjacent intervals at the beginning and end of each ringing cycle. Such operation is undesirable for reasons which will be apparent from the following description with reference to operation of the reverting call switch illustrated in Fig. 4. When`ground potential is removed from the start conductor C336, the operated ones of the relays shown in Fig. 6 are allcaused to restore in lan obvious manner.

Referring now more particularly to theloperation of the apparatus illustrated in Fig. 2, to intercept a call routed by way of the connector switch 30 to the line if it be assumed, for example, that -the substation C has been disconnected from service or that for some other reason calls intended for this substation are to be intercepted, and further, that the ringing current frequency designating the substation C is the frequency FI of the generator 30|, it will be apparent that in an attempt to signal the substation C the wiper |22 of the frequency selector switoh |20 will be operated into engagement with the contact terminating the conductor C306 during the frequency selecting digit dialed at the calling substation. With the wiper |22 ofthe switch I 20 occupying this position, each time the ringing relay R320 operates to complete the circuit for projecting ringing current over the called line the relay R220 is energized by this current. The circuit for ener- 5 gizing the relay R220 may be traced as extending from the ungrounded terminal of the gen- `erator 30| by way of RA32I, C306, the 'wiper |22,

RAI |3, RAI03, the conductor IIb, the condenser 223, the lower winding of R220, thev conductor'lO Ila, RA|0|, RAllL'the upper winding of R||0 and theI exchange battery to the grounded ter-l minal of the generator 30|. During the first period of each interval when the relay R320 is operated, the master relay R600 is caused to 15 operate in the manner just explained toimpress ground potential upon the terminal 166. During each interval when the lower winding of the relay R220 is energized'by the alternating ringing current projectedover the line this relay 20 vibrates its armature RA221 to engage its associated working contact. Since the relay R600 is energized during the first period of each of these intervals, a circuit is completed for energizing the upper winding of Rm in series with '25 the left winding of the relay R603. This circuit extends from ground by .way -of the left winding of R603, RA60I, the terminal 166, C229, RA221, RA225, the upper winding of R220, RA224, Rana-Ram and the resistor 21s to battery. 3U Due to the relatively high resistance of the left winding 4of the relay R603,`none of the armatures controlled by the relay-R220 is operated when this circuit is completed. Shortly following the completion of the circuit Just traced, 35 the slow-to-operate relay. R603 operates to complete, at RA604, an obvious path, including its low resistance right winding, which parallels the high resistance leftwinding of this relay.

. Accordingly, the current flow through the upper 40 winding of the relay R220 is increased sufiiciently to cause this relay to complete its operation. Upon fully operating, the relay R220 completes a holding circuit for itself, which circuit extends from ground by way of RA216, the lower winding 45 of R230, RA226, RA226, the upper winding of R220, RA224, RA223, RA215 and the resistor 210 to battery. Following the completion of this holding circuit, therelay R220 opens, at RA224 and RA226 and their respective associated rest- 50 ing contacts, two points in the previously traced operating circuit for itself. At RA22| and RA222, the relay R220 connects the conductors of the called line I to the trunk conductors C283 and C264 extending to the operators position 200. 55

When its lower winding is energizedl over the above-traced circuit including the upper winding of R220, the relay R230 rst closes the X contacts associated with RA232 to complete an obvious holding circuit for itself. Following the 00 completion of this circuit the relay R230 completes its operation to short-circuit, at RA233, its lower winding, thereby to increase the energization of the upper winding of the relay R220. At RA23I, the relay R230 opens a point in the 35 circuit, traced hereinafter, for transmitting ringback tone current through the receiver provided at the calling substation. At RA234, the relay R230 completes an obvious circuit for energizing the upper winding of the slow-to-release relay 7o R240. At RA236, the relay R230 completes a circuit for energizing the signal lamp 204. this circuit extending from ground by way of RA235, RA263 and the filament of the lamp 204 to battery. At RA233, the relay R230 also prepares 75 a path, traced hereinafter, for short-circuiting the upper winding of the relay R540. The relay R240, upon operating, prepares, at RA244, a holding circuit for the relay R210, and opens, at RA243, one of the multiple holding circuits for the relay R230. At RA242, the relay R240 opens va point in the common portion of the operating circuits for the line relays corresponding to and including the relay R220 and individually associated with the multiparty lines arranged for call interception. At RA24I, the relay R240 prepares the above-mentioned circuit for transmitting ring-back tone current through the receiver provided at the calling substation. Following operation of the relay R240 no further operation of the apparatus occurs until the call is answered at the operators position 200.

To answer the call, the operator attending the position 200 operates the key 20'! to its off-normal position to prepare, at the springs 20B and 20i, a talking circuit extending between the telephone set 202 and the calling subscribers substation. At the contact springs 208, an obvious circuit is completed for energizing the lower winding of the relay R250. The relay R250, upon operating, completes, at RA256, a multiple holding circuit for the operated line relay R220.v At RA251, the relay R250 completes an obvious-circuit for energizing the slow-to-operate relay R260. At RA258, the relay R250 opens a point in the abovementioned path for energizing the signal lamp 204. At RA254, the relay R250 interrupts the previously traced holding circuit for the relay R230, causing the last-named relay to restore. At RA253, the relay R250 completes a circuit for energizing the ring cutoff relay RI I0 embodied in the connector switch 30, this circuit extending from ground by way of the resistor 282, the left winding of the impedance element 280, RA253,

C284, RA222, the conductor lla, RAIOI, RAIII and the'upper winding of the relay RI |0' to battery. The resulting operation of the relay RI I0 causes the ringing operation to be terminated and a loop circuit extending from the connector switch 30 to the trunk line conductors C283 and C284 to be completed. At RA25I, the relay R250, upon operating; opens a point in the circuit, traced hereinafter, for energizing the relay R530.

Shortly following operation of the relay R250, the slow-to-operate relay R260 operates to complete, at RA263, an obvious holding circuit for the slow-to-release relay R240. At RA25I, the relay R260 completes an obvious multiple holding circuit for the operated line relay R220. At RA2B2, the relay R260 completes an obvious circuit for energizing the relay R210. The relay R230, upon restoring in response to operation ofthe relay R250, opens, at RA23 I a point in the above-mentioned path for transmitting ringback tone current to the calling substation, and opens, at RA232, a further point in its own holding circuit. At RA234, the relay R230 interrupts the operating circuit for the relay R240. At RA235, the relay R230 interrupts the circuit for energizing the signal lamp 204 and opens a point in the previously mentioned path for short-circuiting the upper winding of the relay R540. When the relay R210 operates it prepares, at RA21I, a point in the circuit, traced hereinafter, for energizing the relay R530 and interrupts, at RA214 and RA215, the operating'circuit and the initially completed holding circuit for the operated line relay R220. At RA216, the relay R210 opens a point in the previously traced circuit for energizing the lower winding of R230 in series with the upper winding of the relay R220. At RA211, the relay R210 completes a holding circuit for itself, this holding circuit extending from ground at RA244 by way of RA211 and the winding of R210 to battery. At RA218, the relay R210 opens affurther point in the above-mentioned path for short-circuiting the upp'er winding of the relay R540. Finally, at its armaturesRAZlZ and RA2 13, the relay R210 completes the desired talking circuit between the operators telephone set' 202 and the calling substation.

If, following the completion of the desiredtalking circuit in` the manner just explained, the operator attending the position 200 desires to free her telephone set for use in answering another call without releasing the est-ablished conkey 203 is actuated to its off-normal position, an

obvious multipleholding circuit is completed at the springs 209 for the operated relay R250. At the'sprlngs 2|0, an obvious circuit is completed for energizing the signal lamp 205. Following the completion of the holding circuit for the relay R250, the answer key 20| may be restored to normal to open the operating circuit for the relay R250 without initiating the release of the relays of the apparatus shown in Fig. 2. Operation of the key 20E to its normal position also disconnects the telephone set 202 from the established talking circuit extendingto the calling substation A so that this telephone set may be used in handling other calls routed to the operator's position 200 over other trunk circuits. In order to reconnect the telephone set 202 to the established talking circuit extending to the calllished talking circuit and to recomplete, at the springs 208,-the operating circuit for the relay R250. Following operation of the key 20| to its off-normal position, the key 203 may be restoredto normal without releasing the established connection. When the key 203 is restored to normal,

the springs 2|0 embodied `therein are disengaged to open the circuit for energizing the signal The release of the apparatus illustrated in Fig. 2 is entirely under the control of the operator attending the position 200. Thus, if the calling subscriber hangs up before the operator clears out the connection, the operated switch train including the line switch 20, the selector switch 25, and the connector switch 30, is released in the exact manner previously described. During the release of the connector switch 30, the loop circuit extending from this switch to the operators posi-- tion 200 is interrupted and negative battery potential is substituted for ground potential upon the control conductor of the called line I, thereby to mark this line as idle in the bank contacts of the connector switches-having access thereto. Interruption of the loop circuit extending from the connector switch 30 to the apparatus shown in Fig. 2 in no way influences the operated relays embodied in this apparatus. When, however, the operator restores the answer key 20| to normal, the springs 208 are opened to interrupt the operating circuit for the relay R250.- This relay, upon restoring, opens, at RA251, the operating circuit for the relay R250, which latter relay, in turn,

Vthe relay R240. Upon restoring, the relay R200 also interrupts, at RANG, the circuit over which the upper winding of the line relay R220 is being held energized. thus causing the last-named relay to release. When the relay R240 restores, it opens, at RAMI, the holding circuit for the relay R210, causing the last-mentioned relay to restore. Thus, all o! the relays embodied in the apparatus shown in Fig. 2 are restored to normal and this appa- ,ratus is conditioned for use in routing another call to theoperators position 200.

From the foregoing explanation, it will be apparent that'the call intended for the substation C associated with the line I I was intercepted and routed to the operator's position 200 through operation of the apparatus shown in Fig. 2 only because the intervals during which the relay R220 was energized by ringing current projected over the line I I partially overlapped the periods during which the relay R000 was operated. With the circuit connections illustrated, only calls routed to the line II and intended for the substation C will be intercepted and extended to the operators position 200. 'Ihis is by virtue of the arrangement whereby the ringing intervals during which ringing currents of the frequencies corresponding to the other substations associated with the line II are transmitted to the connector switches having access to this line do not overlap the periods when the master relay R600 is operated. Thus, on a call intended for the substation B, ringing current is only projected over the line II to energize the relay R220 during the intervals overlapping the periods when the fourth master relay RSIB is operated. Accordingly, the partial operation of the relay R220 eiected through energization of this relay by the ringing current is ineffective to initiate the operation of the trunk circuit apparatus. It will be apparent, however, that by properly connecting the conductor C229 to the terminals controlled by the other master relays R605, R6I0, R6I5 and R020, calls to any of the substations associated with the line II may be intercepted and routed to the operator's position 200. For example, if the conductor C229 is disconnected from the terminal 166 and connected to the terminal 112, the operating circuit for the relay R220 will oe completed during those intervals when ringing current for signaling the substation B is projected over the line II. As a further example, ii' the conductor C229 is connected to both of the terminals 100 and 112 the operating circuit for the relay R220 will be completed each time ringing current of the frequencies respectively corresponding to the substations B and C is projected over the line I I.

Thus, by appropriately connecting the conductor C229 to the terminals respectively associated with the five master relays, calls to any desired one or ones of the substations associated with the line I I may be intercepted and routed to the operator's position 200.

It will also be apparent from the foregoing explanation that the use of the trunk circuit apparatus shown in Fig. 2 is not Hunted to the interception of calls routed to a single multiparty subscribers line embodied ln the system. On the contrary, this aparatus may be connected to serve any number of multiparty subscribers lines through the provision of additional line relays corresponding to the relay R220 and provided in individual association with the lines with respect to which call interception is desired. In this regard, it will be understood that the windings of these additional line relays corresponding to the lower winding Aof R200 will be respectively bridged across the conductors of their respective associated line. In addition, the bracketed con ductors C239 will be multipled to the contacts oi' 5 the additional line relays respectively corresponding to the contacts of the relay R220 to which these conductors individually extend. Further, the armatures of the other line relays, respectively corresponding to RA221 of the relay R220, will 10 be connected to those of the terminals 166 to 115, inclusive, which correspond to the substations with respect to which calls are to be intercepted. With a second of the additional line relays connected in the manner just explained, if a call to l5 be intercepted is routed by way of the line associated with this second relay the apparatus shown in Fig. 2 will respond to the operation ofthe second relay in the manner set forth above. During the operation of this apparatus and when 20 the relay R240 operates, this relay opens, at RA242, a point in the common portion of the operating circuits for all of the line relays, thus preventing subsequently initiated calls which would normally be intercepted from being routed 25 through the apparatus of Fig. 2 to the operator's position 200 until this apparatus is released. With the arrangement illustrated, no provisions are made for discriminating between two calls which would normally be intercepted and which are 30 simultaneously initiated. In such case the line relays individually associated with the two .ines

to which the calls are routed will both operate so that both of the calls'will be routed to the operators position 200. 'Ihis type of operation is, how- 85 ever, not objectionable since the operator attending the position 200 is easily capable of handling the two calls without confusion.

If all calls to one or more of the lines of the system are to be intercepted, the relay R290 may 49 be connected and arranged to be used in lieu of the apparatus shown in Fig. 6 in controlling the line relays associated with such lines. Thus, if all calls to the line II are to be intercepted, the conductor C229 may be disconnected from the control terminals of the apparatus shown in Fig.

6 and connected through the lower winding of the slow-to-operate relay R290 and the lower winding of R230 to ground at RA210 in the manner indicated by the dotted line conductors. As thus 5o connected, if ringing current is projected over the line II to energize the lower winding of the relay R220 the resulting vibration of RA221 causes a circuit to be completed for energizing the upper winding of R220, this circuit extending from ground by way of RA218, the lower winding of R230, the lower winding of R290, RA221, RA225, the upper winding of R220, RA220, RA242, RA214 and the resistor 219 to battery. Due to the relatively high resistance of the lower winding of R290, the relay. R220 does not operate when energized over this circuit. 'Ihe relay R290, however, operates after an interval to complete, at RA29I an obvious path, including its low resistance upper winding, in multiple with its lower winding. 65

When this path is completed the relay R220 completes-its operation tocause the call to be extended to the operator's position 200 in the manner previously explained. Upon fully operating, the relay completes the previously traced holding circuit for itself which circuit does not -include4 the windings of R290. Accordingly, the relay R290 restores shortly following the complete operation of the line relay R220. i

As previously pointed out, the slow-to-operate asaltar? I relays R200 and R603 are provided for the purpose of preventing false call interception on lines arranged for call interception, due to transient surges impressed upon such lines. For example, if a lightning surge should occur on the line ii the lower winding of the relay R220 would be energized thereby. If 'the surge should occur with ground potential directly impressed upon the conductor C229, the relay R220 would immediately complete its operation to cause a call falsely to be forwarded tothe operators position 200. With the arrangement illustrated, however, the slow-to-operate characteristics of the relays R290 and R603 delay the full energizatlon of the upper winding of the line relay R220 fora period substantially exceeding the duration of transients Aof the character mentioned. Accordingly, the relay R220 is prevented from falsely operating when energized by voltages of unsustained transient character. f

Although the apparatus illustrated in Fig. 2 has been described with reference to the interception of calls arranged for bridged ringing, it will be understood that the circuits are valso adapted for use in association with multipart-.y subscribers lines arranged for divided ringing. In the latter case the alternating current windings of the line relays, such, for example, as the relay R220, individually associated with the lines arranged for ca ll interception, may 'be arranged to be bridged between both sides of their respective associated lines and ground through the provision of impedance bridge arrangements. As thus connected, each of the line relays would be energized by ringing current projected over either side of its associated line. In the line connecting apparatus shown in Fig. 2, provisions are made for operating the ring cutoff relay of an operated connector switch arranged for divided ringing. Thus, in the operation of the apparatus described above, the ring cutoff relay RI I of the connector switch was energized in response to operation of the relay R250 over a circuit including the resistor 282 and the left Winding of the impedance element 280. A similar `circuit would be completed if the connector switch were arranged for divided ringing and ringing current was projected therefrom over the side of a selected called line arranged for connection to the line conductor 0 C283, this similar circuit including the resistor 28| and the right winding of the impedance element 280. Thus, it will be apparent that the arrangement illustrated in Fig. 2 is adapted, without modiilcation, for use in conjunction with au- 5 tomatic switching apparatus arranged to serve lines requiring divided ringing, bridged ringing, or both types of ringing.

With the arrangement illustrated, no provision is made for intercepting a call initiated at one station on a multiparty line and .intended for another station on the same line with respect to which calls are normally intercepted. More particularly, if a vcall initiated at the substation B and intended for the substation D is routed by way of the line switch I5 to the selector switch 25 in the manner` previously explained with reference to the call initiated at the substation A, the substation D is signaled by dialing the three l digits of the reverting call directory number designating this substation. The selector switch 25 responds to the impulses of the first digit by elevating its wipers to a position opposite the level of bank contacts terminating the trunk lines extending to the reverting call switches. At the end of the digit and during the interdigit to select an idleone of the reverting call switches.-

Assuming, for example, that the reverting call switch illustrated in Fig. 4 is the irSt idle switch available, when the wipers of the selector switch 25 encounter the contacts terminating the conductors of the trunk. line 33 extending to this reverting call switch, the calling loop circuit is extended to the last-mentioned switch and the line relay R430 is energized thereover. This relay, upon operating, completes, at RAilSi, an obvious circuit for energizing the slow-acting hold relay R435. Upon operating, the relay R436 opens, at RA436, a point in the path, traced hereinafter, for impressing negative battery potential upon the control conductor 34 of the trunk line ci. At RAllSG and its associated working contact,

25 are prevented from releasing. At RAdB'l, thev relay R035 prepares a'circult for energizing the slow-to-r'elease relay lR045 in parallel with the rotary magnet 4I5 of the minor switch all! during the impulses of the second digit. At RA438, the relay R435 opens a point in the common portion of the circuits, traced hereinafter, for energizing the release magnets 406 and 4l6 of the frequency selecting switches 400 and 4l0 respectively. Each time the line relay R430 restores in response to an impulse of the second digit dialed at the calling substation it functions to open, at RA43I, the operating circuit for the hold relay R435, and to complete the above-mentioned circuit for energizing the relay R445 `in parallel with the rotary magnet 4|5. This latter circuit extends from ground by way of RA43I, RA43'I to RA442 where it divides, one branch extending through the winding of R445 to battery and the other branch extending by way of RA453 and the winding of the magnet 4|5 to battery. The relay R445, upon operating, opens, at RA440, a point in the circuit for energizing the relay R450, and, at RA44I, a point in the circuit for energizlng the relay R440. The relays R435 and R445, due to their slow-to-release characteristics, remain operated during impulsing.

Each time the rotary magnet 4|5 is energized it functions to advance the wipers 4I3 and '4I4 one step so that at the conclusion of the second digit dialed at the calling substation these wipers are left standing in a position corresponding to the frequency of the ringing current required to cause the operation of the tuned ringer I4 provided at the called substation D. The two frequency selecting switches 400 and 4|0 are arranged to seelct the side of a subscribers line tuned to respond to ringing current of the frequency F3 developed by the generator 303, the

may comprise either three or eight impulses. Assuming that a second digit of three impulses is dialed at the calling substation, the wipers 4I3 and 4I4 are left standing in engagement with their respective associated third contacts at the end of the second digit. When these wipers are stepped to their respective rst olf-normal'positions, the oil-normal springs 4I1 are moved into engagement to prepare a circuit for energizing the digit transfer relay R450. This circuit is completed shortly following the end of the second digit when the relay R445 restores. Specifically, this circuit extends from ground by way of the oil-normal springs 4I1, RA445 and the winding of R450 to battery. `Upon operating. the relay R450 opens. at RAI, a further point in the above-mentioned path for impressing negative battery potential on the control conductor 34 of the trunk line 33, and completes, at RA452, a holding circuit for itself, this holding circuit extending from ground by way of the olf-normal springs 4I1, RA452 and the winding of R450 to battery. At RA453 and its associated resting contact, Vthe relay R450 opens a point in the above-traced circuit for energizing the operating magnet 4I5 of the minor switch 4I0. At RA453 and its associated working contact, the relay R450 prepares a circuit for energizing the operating magnet 405 in accordance with the impulses of the thirddigit of the reverting call directory number designating the called substation D. At RA454, the relay R450 prepares the previously mentioned circuit for energizing the release magnet 4 I 5.

Each time the line relay R430 restores in response to an impulse of the third digit dialed at the calling substation, the above-mentioned circuit is completed for energizing the slow-acting relay R445 in parallel with. the operating magnet 405 of the minor switch 400. 'Ihe branch of provided at the calling substation B, is tuned-iloA respond. When the indicated wipers are stepped to their respective first ofi-normal positions, the off-normal springs 401 are closed to prepare a circuit, traced hereinafter, for energizing the relay R440. In the present assumed case wherein the ringer I2 provided at the calling substation B is tuned to respond to ringing current of the frequency F2 developed by the generator 302, the third digit dialed at the calling substation may comprise either two or seven impulses such that one of the two wipers .403 and 404 will, at the end of the digit, engage a contact connected to the conductor 31| extending to the ungrounded terminal of the generator 302. Assuming a third digit of two ixnpuises is dialed at the calling substation, the wipers 403 and 404 are advanced, during the impulses of this digit, into engagement with their respective associated second contacts where they remain until the reverting call switch is released. Shortly following the end of the third digit, the relay R445 restores to complete, at RA441, the above-mentioned circuit for energizing the relay R440, this second digit dialed at the calling substation B circuit extending from ground byfway of the onormal springs 401, RA441 andthe`winding of R440 to battery. Upon operating, the relay R440 opens. at RA442 and its associated resting contact, a point in each of the above-traced pulsing circuits extending through the respective windings of the magnets 405 and 4I5. At RA442 and its associated working contact, the relay R440 prepares a circuit, traced hereinafter, for energizing the line switching relay R420. At RA44I,

the relay R440 opens a further point in the path for impressing negative battery potential upon the control conductor 34 of the trunk line 33. At RA443, the relay R440 prepares the abovementioned circuit for energizing the release magnet 400 of the minor switch 400.

After dialing the third digit in the manner just explained.. the calling subscriber replaces the receiver of his telephone instrument upon its supporting hook or cradle, so that the loop circuit extending through the switches I5 and 25 and over the trunk line 33 to the reverting call switch .is interrupted. As a result, the line relay R430 is deenergized and restores to complete the above-mentioned circuit for energizing the line switching relay R420. At RA43I and its associated working contact, the relay R430 opens the operating circuit for the slow-to-release hold relay R435. 'I'he circuit for energizing the line switching relay R420 extends from ground by way 'of RA43I, RA431, RA442, RA452 and the winding of R420 to battery. Immediately this circuit is completed, the relay R420 operates to complete, at RA425, an obvious holding circuit for the hold relay R435, thereby to prevent the last-named relay from restoring.-

At RA42I, the relay R420 completes an obvious path for impressing ground potential upon the start conductor C335, thereby to initiate the operation of the interrupter switch 310, the operation of the ringing relays shown in Fig. 3 and the operation of the control apparatus shown in Fig. 6, all in the exact manner previously exand RA425, the relay R420 disconnects the line terminals of the line relay R430 from the line conductors of the trunk line 33 and connects the indicated trunk line conductors to conduct ringing current to the line II.

Following the operation of the relay R420, ringing currents of the frequencies F2 and F3 are alternately projected over the line II, thereby alternately to energize the tuned ringers I4 and I2 provided at the called and calling substations, respectively. Thus, when ground potential is impressed upon the ringing control conductor C045 during the second period-of the first interval of the first ringing cycle which occurs following operation of the relay R420, a circuit is completed for energizing the ringing control relay R410, this circuit extending by way of the grounded conductor C045, RA14I, C141, RA422 and the winding of R410 to battery. When energized over this circuit, the relay R410 operates to complete at RA41I. RA412, and RA413 the above-mentioned circuit for transmitting ringing current of the'i'requency F3.

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