US2340555A - Telephone system - Google Patents

Description

Feb. 1,1944.

TELEPHONE SYS TEM' Original Filed Nov. 8 1940 10 Sheets-Sheet 1 90/ |2| LINE RIBO FROM CONN. BANKS u I77 I61 I LINE CIRCUIT 2o I6a-, DISTRIBUTOR lslh ' Q INVENTORL SETH E. PETERSON v ATTORNEYS s. E. PETERSON 2,340,555

s. E. PETERSON TELEPHONE SYSTEM Feb. 1, 1944. 5

Original Filed Nov. 8. 1940 RESTRICTED SERVICE 8 TIME BLOCKING RELAYS 25 10 Sheets-Sheet 2 ATTORNEYS Feb. 1, 1944. s; PETERSON 2,340,555

TELEPHOPIEV SYSTEM Original Filed Nov. 8, 1940 10 Sheets-Sheet 3 3 LINK SWITCH 37:

323E THRU SETH N .5. mum/ byway, ATTORNEYS I Feb. 1, 1944.. s. PETERSON 2,340,555

TELEPHONE SYSTEM ori ina Filed Nov. 8, 1940 10 Sheets-Sheet 4 CONNECTOR 40 INVENTOR E. PETERSON ATTOR NEYS Feb. 1, 1944. s. E. PETERSON 2,340,555

" TELEPHONE SYSTEM Original Filed Nov. 8, 1940 10 heets-Sh'eat 5 06h cad sal cer cs: 1 C62;

CONNECTOR 4O C496 C678 C677 INVENTOR SETH E. PETERSON BY W MM ATTORNEYS Feb. 1, 1944.. 5 PETERSON 2,340,555

TELEPHONE SYSTEM Original Filed Noir. 8, 1940 10 Sheets-Sheet 6 CONNECTOR 4O cam NE swrrcu v FIG.6

INVENTOR SETH E. PETERSON ATTORNE YS Feb. 1,

5 E. PETERSON TELEPHONE SYSTEM Original Filed Nov. 8, 1940 10 Sheets-Sheet 7 LOCK g PULS E C78 3 7 TWO WAY REPEATER 3O 7 BY 16mm INVENTER SETH E. PETERSON ATTORN E YS 5. E. PETERSON TELEPHONE SYSTEM Original Filed Nov. 8, 1940 10 Sheets-Sheet 8 M LlNsfiRsso- \882 841 872:}J P883 785 r E x E an 82: 85i 873' ss4 c706, i- C787: :8 822 874 R840 C7881 c7901 885 079m 831- b A.

g;% -l e39 s42 a4s 0793 84 L A 216 C794] 833 -344 I 34-: 0795 C796 {8f LINE 8l2 2 i if 86 CIRCUIT SLAVE HOLD DIST TO FINDER C7981 82 846 R860 START BANKS 070m 33 c702 36 cTos f 4M? 87 R880 Reno r 36 LOCK P LSE TWO WAY REPEATER 30 J s14 DISTANT AUTOMATIC EXCHANGE INVENTOR.

SETH E PETERSON ATTORN EYS s. E. PETERSON- 2,

TELEPHONE SYSTEM Original Filed Nov. 8, 1940 10 Sheets-Sheet 9 $496 Fl (5.9 I @678 TIMER START CIRCUITS 5o ""1 Tl r 9 grzszo L mo. cW- DIAL PERM susv TICK TONE couvsnsmou TIMER TONE GENERATING TIMER GEN. EQUIPMENT CIRCUIT 5| so v52 53 INVEN TOR. SETH E PETERSON M M m ATTORNEYS Feb. 1, 1944.

FROM CODE SW.

S. E. PETERSON TELEPHONE SYSTEM Original Filed Nov. 8. 1940 10 Sheets-Sheet -1O CODE SELECTING 8 OONVEI R SATION-TIMING SWITCH 45 INVENTOR. SETH E. PETERSON ATTORNEYS Patented Feb. 1, 1944 Li -i555 TELEPHONE SYSTEM Seth E. Peterson, Bogota, Colombia, assignor to Automatic Electric Laboratories, Inc., a corporation of Delaware Original application November 8, 1940, Serial No. 364,824. Divided and this application June 29, 1942, Serial No. 448,961

49 Claims.

The present invention relates to telephone systems, and more particularly to improved automatic line-switching equipment which is con trollable in a simple and reliable manner over lines of difierent types, such, for example, as full metallic lines of both the loop and simplex types, and ground return lines, to provide diiierent classes of service to subscribers paying different rates. The present application is a division of copending application Serial No. 364,824, filed November 8, 1940.

It is an object of the invention to provide in a system of the character described, an improved and exceedingly simple arrangement whereby the regular line-terminating equipment, individual to the lines of the system, is utilized to signal the automatic switching apparatus as to the type or class of the calling lines over which the apparatus is seized.

According to another object of the invention, the line-class signaling circuits are so arranged that extra control paths extending through the outlet contacts of the automatic switches are not required for the transmission of the signals.

It" is another object of the invention to provide in a telephone system of the character described, an arrangement whereby the station selective operati'on of the ringing control equipment provided in the connector switches of the system is in part controlled from the line circuits terminating the calling lines over which the connector switches are seized.

It is another object of the invention to provide in a telephone system of the character described, an arrangement wherein the station selective operation of the ringing control equipment provided in the connector switches of the system is in part controlled from the line circuits terminating called lines seized by the connector switches.

In accordance with a further object of the invention, an improved arrangement is provided whereby the line circuits terminating multiparty subscriber lines of the ground return type are arranged to control the ringing control equipment of the connector switches in a manner such that ringing current transmission over the ground return side of a selected line of this type is positively prevented.

It is another object of the invention to provide in a telephone system of'the character described, automatic switching equipment which is so arranged that one type of ring cut-off is provided for terminating the transmission of ringing current over certain called lines of the system, and

a different type of ring cut-off is utilized in terminating the transmission of ringing current over other called lines of the system.

According to a further object of the invention, the type of ring cut-01f utilized in terminating the transmission of ringing current over a seized line is automatically determined during seizure of the line.

It is a further object of the invention to provide in a line-selecting switch, an improved circuit arrangement whereby the back-bridge relay of the switch functions both as a supervisory signal control relay and as a ringing control relay.

In the illustrated embodiment of the invention there is provided a system which comprises a plurality of subscriber lines, certain of which are of the multiparty type individually having a plurality of substations associated therewith, and

automatic switching apparatus in the form of finder-connector links for setting up connections between the lines of the system. The connector switches of the links also have access to one or more groups of trunks which are provided to serve only the substations arranged for unrestricted service and may extend, for example, to one or more distant suburban or central exchanges. Timing equipment common to the links is provided for conversation timing and for forcibly releasing links held over lines having permanent calling conditions thereon.

The subscriber lines of the system are of several different types and include lines arranged for loop circuit control of the automatic switching equipment, simplex circuit control of the automatic switching equipment, and also lines of the ground return type. These lines are individually terminated in line circuits which conventionally comprise line, cut-oli and lockout relays. In accordance with one feature of the present invention, the cut-off and lockout relays provided in the line circuits terminating lines of the simplex and ground return types, are arranged to transmit a control pulse over the positive talking conductors of the respective associated lines when calls are initiated on these lines. A control pulse of this character, when transmitted to a link assigned to the use of a calling simplex or ground return line, is utilized to condition the relay equipment of the link to be controlled over the metallic side of a ground return line or the two sides of a simplex line in parallel. These line circuit relays, when operated in response to seizure of the associated line through one of the connector switches of the system, function to transmit a control pulse back to the connector switch which serves to control the setting of the ringing control equipment provided in the switch in a. manner such that the transmission of ringing current over the ground return side or positive talking lead of the associated line is positively prevented. Further in accordance with this feature of the invention, the circuit arrangement of the finder-connector links is such that the ringing control equipment of an assigned link is, in

setting up a reverting call connection involving a line of the ground return type, so controlled from the line circuit terminating the calling line that the possibility of ringing current transmission over the positive or ground return side of the line is precluded.

In accordance with another feature of the present invention, the cut-off and lockout relays embodied in the line circuits terminating the subscriber lines are also arranged to control the ringing control equipment of the links in a manner such that one mode of'ring cut-off, i. e., instantaneous ring cut-off, is provided for terminating the transmission of ringing current over a called line of the full metallic loop type; and another mode of ring cut-off, i. e., silent period cut-ofi, is utilized to terminate the transmission of ringing current over a called line of the simplex or ground return type. More specifically, the circuit arrangement of the finderconnector links is such that when the cut-off and lockout relays of the line circuit terminating a called line operate to transmit a control pulse over the positive talking conductor of the associated line in response to seizure of this line, the backbridge relay of the link occupied with the call is conditioned to function as a ringing control relay before'the call is answered, and to function as a supervisory control relay after the call is answered at the called substation.

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 Figures '1 to l0,'inclusive, when combined in the manner illustrated in Fig. 11, illustrate an automatic telephone system having embodied therein the features of the invention briefly outlined above. More specifically, Fig. 1 illustrates the line equipment serving two of the subscriber lines of the system, the link distributor, and, in diagrammatic form, one of the finder switches at which the illustrated lines terminate; Fig. 2 illusrtates a relay network which is utilized for controlling the restricted. service and timing relays of the links; Figs. 3 to '6, inclusive, and illustrate the connector end of the link comprising the finder shown in Fig. 1; Figs. '7 and 8 illustrate the repeater terminating one of the inter-ofiice trunks of the system; and Fig. 9 illustrates, in partially schematic form, the timing and tone equipment common to the link circuits.

Referring now more particularly to the drawings, the telephone lines and automatic switching equipment there illustrated may comprise, for example, a small exchange, commonly known as a community automatic exchange or C. A. X, which is designed to serve a suburban area of limited population and is geographically adjacent a larger city or town served by a central exchange. More specifically, the exchange is illus trated as being connected with a distant central automatic exchange 35 by means of a group of trunks including the trunk 36. This trunk is terminated in the C. A. X exchange in a repeater 30. The subscriber substations served by the automatic switching apparatus illustrated may be arranged for three different classes of service. For example, the line 9, which extends only to the substation A and terminates in the exchange in a line circuit It, may be arranged for unlimited central exchange trunk service, and also for local'calls of unlimited duration. The other illustrated subscriber line l6, which terminates inthe exchange in the line circuit 29, is of the multiparty type, this line being arranged to serve the two substations B and C. These two substationsmay be arranged for either semi-restricted or fully restricted service. For example, the substations B and C may be arranged so that central ofi'lce trunk calls over the restricted trunks are prohibited, but local connections established through the automatic switching equipment of the C. A. X maybe held for unlimited periods. Alternatively, the subscribers at the substations B and C may be prohibited both from routing calls over the restricted central oflice trunks, and also from holding local call connections for unlimited periods. The particular type of service provided for the various substations is determined by the wiring arrangement of the line circuits individual to the lines with which the substations are associated. More specifically, if all of the substations associated with a particular line are to be denied central office trunk service, the line circuit terminating this line is provided with an E. C. marking path extending to the finder E. C. contact bank and having resistance battery potential applied thereto through the winding of one of the relays provided in the restricted service and time blocking relay network 25. If the subscribers served by the line it are not to be restricted as to the duration of local call connections, the E. C. marking path just mentioned is arranged to have ground pulses intermittently applied thereto through operation of the relays in the relay network 25.

The subscriber lines terminating at the exchange may be of several different types. For example, the line 9 and the substation equipment connected to this line may be arranged for either simplex or loop circuit control of the automatic switching equipment, and may be either an extremely long line or'a relatively short line. Further, the substation apparatus provided at the substation A may be of the conventional common battery type or of the conventional local battery type. Similarly, the line It may be of the full metallic type employing two line conductors, or may be of the ground return type utilizing a conductor as one side of the line and ground as the return side of the line. In the illustrated arrangement, the line 9 is shown as being of the full metallic type, and the line I6 as being of the ground return type. In order to adapt the automatic switching equipment for control over the lines of different types, different wiring arrangements are utilized in the line circuits, the particular type of wiring of each circuit being determined by the particular character of the associated line. These line circuits are substantially conventional insofar as the relay equipment embodied therein is concerned. Thus, the line circuit l0 comprises the usual line, cut-on and lockout relays indicated at R130, RlZll and RI it, respectively. Similarly, the line circuit 20 terminating the line I6 is provided with a line relay RI10, a cut-oil relay RI.60; and aslowi-to-operate lockout relay RI 50.

the various lines and trunksterminating thereat, 1

comprises a plurality of finder-connector links each having a contact bank capacity of one hundred lines. The illustrated link is shown as comprising a finder switch 5 I and a connector switch 40. For the purpose of assigning these links to the use of calling lines in. a definite order, there is provided a distributor 22, preferably of the preselective type, which i arranged to initiate the operation of the finder portion of a preselected link to search for a calling line in response to the application of ground potential to the distributor start lead I1. Since the finder switch II and the distributor 22 may be of conventional construction and wiring arrangement, these switching units have been only schematically illustrated in the drawings. The connector switch 40 is illustrated in Figs. 3, 4, 5, 6 and 9 of the drawings as being of the well-known Strowger type, employing a Strowger switching mechanism having its contact field divided into four banks each including ten levels or rows of bank contacts. Preferably, the lowermost levels are reserved for the termination of subscriber lines, branch exchange trunks and one or more central exchange trunk lines extending to a toll operator switchboard in the distant central exchange. The uppermost levels of the connector switch are used to terminate the regular or restricted central exchange trunks over which the subscribers having unrestricted service may route connections to the central oflice subscribers with out the intervention of a toll operator. For example, the tenth level of bank contacts in the connector switch 40 may be reserved for the termination of trunks of the last-mentionedgroup.

Referring now in greater detail to the connector switch 46, the Strowger switching mechanism of this switch comprises the above-mentioned contact field at which the conductors of the lines extending to the C. A, X are terminated; a set of wipers 660 to 653, inclusive, and the usual vertical and rotary magnets 408 and 669, respectively which are operative in conjunction with their associated ratchet and pawl mechanisms, not shown, to impart vertical and rotary movement to the wiper carriage structure. This mechanism is also equipped with vertical off-normal springs 414, M5, M6 and 566, which perform various circuit control operations described with particularit hereinafter. nism further comprises a release magnet 401 which, when energized, permits the wipers of the switch to be returned to vertical'and rotary normal in the usual manner; and normal 'post springs M9 and 368, which are arranged to be moved ofi" normal from the normal positions shown in the drawings in response to elevation of the wipers 660 to 663, inclusive, to one or more predetermined vertical oil-normal positions and perform additional circuitcontrol operations described with particularity hereinafter. The equipment for controlling the vertical, rotary and release magnets of the switching mechanism, and for performing the auxiliary control operations required incident to the setting. up of the various types of connections referred to above, includes a pair of line relays R360 and R640 which are normally connected to be energizedin series over the two talking conductors of the trunk 326 in,- coming to the connector switch 16. This equip- The switching mechatil ment further. comprises a slow-acting holdrelay R310, a. slow-acting hold slave relay R330, a reverting call relay R3I0, a slow-acting control relay R320, a link. release relay R340, a switchthrough relay R350. of thetwo-step type, a calling simplex relay R4I0, a battery reversing relay R420, a lock-pulse relay Rt30, a digit transfer relay R450, a pair of slow-acting pulse controlled relays R460 and R410, and a combined ringing and trunk-hunting control relay R460. Additional control relays embodied in the connector switch and shown in Figs. 5 and 6 of the drawings include a second digit transfer relay R5I0, a slow-to-operate, slow-to-release ring cut-01f relay R520, a busy test relay R560, a ring pickup relay R540, a restricted servicecontrol relay R556, an alternating current ringing control relay R560, a pair of back-bridge relays R510 and R6 I 0, a called simplex relay R520, an idle test relay R630, a slow-to-operate conversation timing relay R640, and a slow-to-operate line-switching relay R650. Selection of the ringing code which is to be utilized in signaling over 2. called multiparty line is accomplished through the provision of a minor switch 45, which also functions as a conversation timing switch after the ringing period is ended and a talking circuit is established through the connector. This switch also functions to determine the side of a selected line over which ringing current is to be projected in signaling over a called multiparty line arranged for divided ringing. More specifically, this switch is of the eleven-point type and includes three wipers I 000, IO0I, I 002, the usual operating and release magnets I004and i001, respectively, and off-normal springs I065 and I606.

The inter-office trunks connecting the exchange illustrated with the distant automatic exchange 35 are of the two-way type arranged to handle calls routed in either direction thereover, and each thereof is terminated in the C. A. X in a two-way repeater. Thus, the trunk 65, which terminates in the repeater 30, has access to the links of the C. A. X over a link line 34 which terminates in a line circuit 3!. the repeater 30 comprises a pair of line relays R120 and R650, a slow-acting hold-relay R820, a slow-to-release hold slave relay R830, and a group of control relays R850, R610 and R060, the first two of which are'of the slow-to--operate type, and the last of which is of the slow-acting type. The relay equipment of the repeater further includes a battery reversing relay R1I6,'a calling simplex relay R130, a slow-acting pulse controlled relay R14il, an electro-polarized backbridge relay R150, a line-switching relay R860, and three lock-pulse relays R150, R and R8I0 which'are provided for impulse correcting purposes. The various enumerated relays are interconnected by control circuits which are de' scribed with particularity hereinafter.

The equipment common to the finder-connector links provided in the exchange includes the usual ringing current generator and a ringing interrupter for interrupting the alternating ringing current in accordance with the various ringing codes. The common equipment also includes tick-tone generating equipment 52, dial and busy-'- tone generators 66, a conversation timer 53 and a permanent timer 5!. These four units may be of conventional arrangement and, accordingly, have been only schematically illustrated in the draw ings. The control circuits for these units are, however, novel in character and, accordingly, the details thereof have been shown. More specifi- Briefiy described,

cally, the control circuit for the permanent timer to the various links.

| and the'tone generator 60 comprises a relay *R9I0 which is so connected and arranged that a single control lead C496 is utilized for the purpose of initiating the operation of the timer. 5i

and for the purpose of transmitting timing pulses Similarly, the control circuit for the tone generating equipment 52 and the conversation timer 53 comprises a slow-tc-release start relay R920 and a pulsing relay R930, these relays being so connected and arranged that a single lead C619 is used for initiating the operation of these two units and for the purpose of transmitting timing pulses to the link circuits.

The equipment common to the links and line circuits further includes the restricted service and time blocking relay network 25. Briefly described, this network includes a pulrality of line relays R240, R250 and R250, which are individual to the lines with respect to which restricted service or time blocking is required, and a plurality of slow-acting relays R2 I I3, R220 and R230, which are common to the lines with respect to which such service restrictions are imposed.

LOCAL CALLs ample, that a call intended for the substation C is initiated at the substation A. In order to ini- .tiate the call, the calling subscriber removes the receiver provided at the substation A from its supporting hook or cradle, thereby to complete a circuit for energizing the line relay R538 in the usual manner. The circuit over which this line relay is energized is different, depending upon the wiring arrangement utilized in the line circuit Ill. Thus, if the substation equipment provided at the substation .A is wired for simplex'control of the automatic switching equipment provided in the exchange, the terminals Mt and I61 are connected together, and the terminals I 4 3 and it are connected together. If the line 9 is of the loop or ground return type, or is of the simplex type and the loop resistance thereof is less than 3500 ohms, the relay RIM! is equipped with windings each having a resistance of 200 ohms. If the line is of the simplex type and the loop resistance thereof exceeds 3500 ohms, the relay RI38 is equipped with windings each having a resistance of 1200 ohms. When the above-described wiring arrangement is used, one branch of the operating circuit for the relay RISK; extends from ground through the springs of the hook switch provided at the substation A by way of the positive line conductor fib, the contacts I22, the strapped terminals M5 and M4, the lower winding of RISU and the strapped terminals Id? and I46 to battery. The other branch of this circuit extends from ground through the springs of the hook switch provided at the substation A by way of the negative line conductor 90;, the con tacts I2I and the upper winding of RISil to battery. On the other hand, if the equipment provided at the substation A is arranged for loop control of the automatic switching apparatus provided in the community exchange, the terminals IE3 and I44 are strapped and the terminals I41 and 38 are strapped. With this wiring arrangement, the operating circuit for the. line relay RI3I3 may be traced as extending from ground by way of the strapped terminals I43 and I44, the lower winding of RISIl, the strapped ter- 'minals I41 and I48, the contacts I22, the conductor 9b, the bridge across the conductors 9b and 9a at the substation A, the conductor 9a, the contacts I2I and the upper winding of RI30 to battery. In order more completely to describe the difierent wiring arrangements of the line circuits, it is pointed out that if the line I6 is of the simplex type or is a relatively short ground return line, the line circuit 20 is wired in the manner described above with reference to the line circuit ID in considering simplex control of the line relay RI30. More specifically, in this case the terminals I88 and I8I are strapped, the terminals I90 and NH are strapped, and the terminals I86 and I8! are strapped. On the other hand, if the substations served by the line I 6 are arranged for loop circuit control of the automatic switching equipment, the terminals I and I 8| are strapped, the terminals I84 and I85 are strapped, and the terminals I88 and I89 are strapped. As a further alternative, if the line I8 is of the ground return type, a wiring arrangement is utilized which comprises the strapping of the terminals I80 and I82, I83 and I85, I85 and I81, and I90 and ISI, respectively. With this wiring arrangement, the relay RITE is energized over a circuit including the grounded conductor Ito, the contacts IfiI and the two windings of RIH! in series when a call is initiated at one of the substations B and C.

Continuing now with the operation of the line circuit It, when the line relay Rl3ii is energized over any one of the circuits traced above, it operates to complete, at its contacts I3I, an obvious circuit for impressing ground potential uponthe private conductor 90, thereby to mark the line 9 as busy in the bank contacts of the connector switches. At its contacts I32, the relay RI30 opens the circuit for energizing the cut-off relay RI2B when-the line 9 is seized through the connector end of one of the links. At its contacts I33, the relay RISE! completes a path including the winding of the relay RI20 and the contacts H2 for impressing negative battery potential upon the marking conductor 9d, thereby to identify the line 9 as a calling line in the bank contacts of the finder switches having access thereto.

the finder switch II are first elevated to a position opposite the level of contacts terminating the line 9 and are then rotated to engage the contacts terminating the conductors 9a, 9b and Sol. When the line 9 is found in this manner by the finder switch II, the control equipment of the finder switch operates to extend the calling circuit through to the connector portion of the link and to connect the marking lead 9d to the control conductor 3260 of the trunk 326 incoming to the connector switch 40. In response to this cutthrough operation of the finder switch II, both of the line relays R350 and R440 are energized. Assuming that the line 9 is arranged for loop circuit control of the automatic switching equipment, the relays R440 and R360 are energized in series over a circuit which extends from ground by way of the winding of Rate, the contacts 413 and 523, the repeating coil winding 493, C55, the contacts 355 and '3l2, the trunk conductor 326b, the positive line wiper of the finder switch II, the conductor 9b, the bridge across the conductors of the line 9 at the substation A, the conuctor 9a, the negative wiper of the finder switch H, the conductor 326a, the contacts 3! I and 352, C63, the repeating coil winding Gill, the contacts 62!, C64 and the winding of R360 to battery. When energized over this circuit, both of the line relays operate. In the event the line 9 is arranged for simplex control of the automatic switching equipment, the line relay R363 is initially energized over a circuit extending from ground at the substation A by way of the conductor to, the negative line wiper of the finder switch H, the conductor 326a, the contacts 3 and 352, C63, the repeating coil winding dill, the contacts 42.", C6 and the winding of R366 to battery. The other line relay R445] is energized in parallel with the positive side of the line 9 and in series with the lower winding of the line relay Rl3fl over clrcuit for the calling simplex relay R llfl The line relay R360, upon operating, closes its conlock-pulse relay R 530, ground by way of the contacts 342, 325 and 36!, ore and the winding of R430 to battery. At its contacts 363, the relay R360 prepares a holding circuit for the hold relay R370. At its contacts circuit for itself.

The lock-pulse relay R439, upon locks to ground over a path including C75, the contacts 36!, CSI, the contacts 433 and the resistor 428. At its contacts 53L the relay R430 the common portion of the ciroperating,

cuit extending tacts 34 2, CBI,

the contacts 432, C83 and the winding of R370 to battery.

The relay R375, upon operating closes its conc ta ts 37!, to complete the operating circuit for 5 the digit transfer relay Rite, this circuit 'egtend ihg from ground by wayof the 'o'ohtacts W2 T 37 LC? L'the contacts "4 the oir normm 458 and the winding of R llifi 't'o'b"tter y. At its contacts Ell, the relay Rtlh a1s'o prepares the operating circuit for the line switching relajy R656 and additional operating 'andlocliihg' cir cults described mere -fiill y hereinafter. At its: contacts 372, the relay completes a path including the contacts 3 32 for-impressing ground potential upon the release conducter 3280, there-- by to prepare certain locking and operating circ'uits subsequently referred to detail. when ground potential is applied to "this eonductona holding circuit is preview for cut-through relay of the finder switch ii, the new-acting control relay R320 is ene en over an eb'vi as circuit, and the cut-off relay R'liti is energized over a circuit including this wiper or the finder switch and the contacts [33 and H2. At its contacts 3%, the relay new further prepares the above ni'entio'ned priming circuit for the line relay R369. At its contacts 374, the rela R379 prepares an operating circuit for the idle test relay Rlieit. At its contacts 375, the relay R37 9 completes ah'obvlolls circuitfror energizing the slow-acting holdslave relay R3 30; At its contacts 376, the relay R371? opens a point in a path traced hereinafter; over which-ground potential may be impressed upon the positive line wiper tfil of the connector-switching mechanism.

The digit transfer relay R456; upon operating, locks to ground over a path including the off normal springs 468, the contacts 3H and 3 12-. At its contacts 45 the relay Reta prepar an v circuit for itself. At its contacts 851 and 378,-

the relay R5527 prepares the above rnentione'dcir cuit for energizing the vertical; I the pulse controlled relay R 279 its contacts 452, the relay R 356 opens one of the alternative circuits for energizing the'pulse cam trolled relay R676. At its contacts 355, the relay R453 opens a point in one of theoperating(air-f cuits for the pulse controlled relay R469. At its contacts 357, the relay "Refit! prepares one of the operating circuits for the trunk-hunting relay RG86. At its contacts 459, the a point in the common portion of the operating circuits for the rotary magnet- W9 and the op H194 of the minor switch &5: At

erating magnet cuitfor energizing the calling simplexre'lay R At its contacts 353',

started The hold slave relay upon" operatifig', mp te gr. t

conductor, the test the contacts 453, C7 and" in parallel. at

relay R459 opens the relay R453 prepares c- I the relayR- fill epeils-';-= point in the circuit for transmitting busy" and: tick-tone currents over the callingengl of the" 1 transmit-ting fil al tone" ts are, are and C8I, the contacts 323,

relay R3I0. At its contacts 33I, the relay R330.

prepares the above-mentioned path for impressing ground potential upon the positive line wiper 66I of the connector switching mechanism. At its contacts 333, the relay R330 prepares a path for short-circuiting the conversation timing relay R640 and the lower winding of the link release relay R340, and prepares another operating circuit for the busy test relay R530. At its contacts. 336, the relay R330 prepares a locking circuit for the link release relay R340. At its contacts 332, the relay R330 completes a circuit for energizing the upper winding of the link release relay R340 in series with the upper winding of the permanent cuit extending from ground through the upper winding of R9I0 by way of the combined time pulse and start lead C490, the contacts 425, C69, thecontacts 332 and the upper winding of R340 to battery. Due to the high resistance of the upper winding of the relay R9I0, the relay R340 does not operate when this circuit is completed. The relay R9I0, however, operates to complete an obvious path for grounding the permanent timer start lead 55, thereby to initiate the operation of the permanent timer 5| in the usual manner. At its contacts 9I3, the relay R9I0 completes an obvious path for grounding the start lead 56, whereby operation of the dial and busy tone generating equipment 60 is initiated.

The slow-acting control relay R320, upon operating, closes its contacts 322 to prepare the above-mentioned operating circuit for the reverting call relay R3I0. At its contacts 32I, the relay R320 prepares one of the circuits for energizing the idle test relay R030. At its contacts 323, the relay R320 further prepares the previously mentioned priming circuit for the line relay R300, and completes a locking circuit for ,1

the hold relay R37 0. The last-mentioned circuit extends by way of the grounded hold conductor ing of R310 to battery. At its contacts 324, the relay R320 opens a point in the common portion of the operating circuits for the release magnets 401 and I001. At its contacts 323, the relay R320 interrupts the previously traced operating circuit for the lock-pulse relay R430. Following the operation of the relays R300, R440, R430, R450, R310, R330 and R320 in the manner just explained, no further operation of the link circuit equipment occurs until the dialing operation is started at the calling substation or the link is forcibly released under the control of the per-- manent timer 5|.

When the cut-off relay RI20 is energized, it.

looks to the grounded release conductor 3260 over a path including the contact I24 and the test wiper of the finder switch II. At its contacts I25, the relay RI20 completes an obvious circuit for energizing the slow-to-operate lockout relay RI I0. At its contacts I2I and I22, the relay RI20 disconnects the windings of the line relay RI30 from the conductors oi the line 9, thereby to clear the line of the impedance represented by these windings. At its contacts I22, the relay RI20 also interrupts the previously traced operating circuit for the line relay R440, assuming the line 9 to be of the simplex or ground return type. When the line relay RI30 is thus deenergized, it restores to interrupt, at its contacts I3I, the initially completed path for grounding the private conductor 90 of the line 9. At its contacts I32, the relay RI30 completes an alternative path timer start relay REID, this cir- 305 and 303, and the windfor impressing ground potential upon this private conductor, which path extends through the contacts I24 to the grounded test wiper of the finder switch II. At its contacts I33, the relay RI30 interrupts the operating circuit for the cutoff relay R920. At its contacts I34, the relay RI30 disconnects the distributor start lead H from ground and opens .a point in, the locking circuit for the lookout relayRI I0.

, In the event the line 9 is of the ground return or simplex type, a path including the make contacts I23 .cf the cut-off relay Rl20,and the break contacts III of thelockout relay RIM, is provided for transmitting a control pulse over the positive talking conductor 32) and the positive side of the trunk 326. This control pulse is utilized to short-circuit the line relay R440. On the other hand, if the line 9 is arranged for loop control of the automatic switching equipment, this pulsing path, controlled by the cut-off and lockout relays individual to the line 9, is omitted from the line circuit I0. When the illustrated circuit wiring is provided, the short-circuiting path just mentioned is completed at the contacts I23 when the cut-cit relay RI20 operates. This path may be traced as extending from ground by way of the contacts III and I23, the positive wiper of the finder switch II, the trunk conductor 3261), the contacts 3E2 and 354, C65, the winding 403, the contacts 423 and M3, and the winding of R440 back toground. When thus short-circuited, the relay R440 is deenergized and restores. In releasing, the relay R440 opens its contacts 443 to interrupt its locking circuit as traced above,

- extending from ground by and opens its contacts 44I to interrupt the previously traced operating circuit for the digit transfer relay R430. At its contacts 444, the relay R440 completes the prepared operating circuit for the calling simplex relay R4I0, this circuit Way of the contacts 451' and 444, the lower winding of R4I0 and the off-normal springs 4I4 to battery. When thus energized, the calling simplex relay R4I0 operates and locks to the grounded release conductor 3260 over a path including its preliminary make contacts 4I12. At its contacts M3, the relay R4I0 interrupts a point in the common portion of the above-traced operating circuit and short-circuiting path for the relay R440. At its contacts 4| I, the relay R4I0 completes the second branch of the circuit for energizing the line relay R360 over the two sides of the line 9II in parallel, in the event this line is of the simplex type. More specifically, this second branch may be traced as extending from ground at the substation A by way of the line conductor 9b, the positive line wiper of the finder switch I I, the trunk conductor 320b, the contacts 3I2 and 354, C65, the winding 403, the contacts 423 and M I, C04 and the winding of R300 to battery. Thus, the resistance of the calling circuit over which the line relay R360 is energized is materially reduced in response to operation or" the calling simplex relay R4I0.

Shortly following the operation of the calling simplex relay R4I0 in the manner pointed out above, the slow-to-operate lockout relay RIIO operates and opens its contacts IN to interrupt the above-traced path short-circuiting the line relay R440. At its contacts II2, the relay RI I0 opens a further point in the operating circuit for the cut-off relay RI20. At its contacts II3, the relay RI I0 prepares a locking circuit for itself. At its contacts II4, the relay RI I0 opens another point in the path for connecting the distributor start lead I1 to ground.

Upon receiving the dial tonesig'nal in the man-i ner pointed out above, the calling subscriber may proceed to dial the three digits of the directory number designating the desired substation C. The first two of these digits are utilized to direct the wipers of the connector switch it into engagement with the contacts terminating the conductors of the called line It, and the third digit is utilized to direct the wipers of the code selecting and conversation timing switch 45 to the position corresponding to the code designating the desired substation C. The line relay R380 and the lockpulse relay R 339 follow the impulses of the three digits and function to repeat the impulses of the first digit to the vertical magnet M58 and the relay Rilt in parallel over the above-mentioned pulsing circuit. More specifically, the relay 12.36%, upon restoring at the beginning of each impulse, opens its contacts 361 to interrupt the previously traced locking circuit for the lock-pulse relay R 530, causing the latter relay to restore. At its contacts 362, the relay R3 Bilcompletes the previously mentioned priming circuit for itself, this circuit extending by way of the grounded hold lead CSI, the contacts 323, 355, 382 and N3, the resistor an, C67, the contacts #121, C86 and the Winding of R369 to battery. This priming circuit is utilized to render the relay R360 exceedingly fast to operate when the calling loop, simplex or single wire circuit is recompleted at the calling substation at the end of the open-circuit period of the impulse. At its contacts-353, the relay R368 opens the locking circuit for the hold relay R313.

The lock-pulse relay R i30, upon restoring at the beginning of each impulse, opens its contacts 432 to interrupt the operating circuit for the hold relay RBiil. Due to its slow-to-release characteristic, the last-mentioned relay remains operated during impulsing. At its contacts 433, the relay Rd3fi opens another point in its locking circuit. At its contacts iti, the relay R136 completes the circuit for energizing the vertical magnet 458 and the pulse controlled'relay R473, in parallel. This circuit extends by way of the grounded hold conductor CSl, the contacts 323 and 355, Old and the contacts l3l to the contacts 453 where it divides, one branch extending through the winding of the magnet N38 to battery, and the other branch of the circuit extending through the contacts #5! and the winding of R570 to battery. When first energized over this circuit, the relay R470 operates to complete, at its contacts 472, an alternative locking circuit for the relay RG56, this alternative circuit extending by way of the grounded hold lead CSI, the contacts 3? I, Cll, the contacts 635, C435, the contacts 412 and 654, and the winding of R658 to battery. At its contacts 41H, the relay R 370 opens a point in one of the operating circuits for the relay R liit. At its contacts 473, the relay R470 opens a point in the common portion of the operating circuits for the busy test relay R530 and the idle test relay R638. At its contacts il i, the relay R476 completes an obvious path for short-circuiting the winding Mil of the repeating coil, thereby to reduce the resistance of the pulsing circuit over which the line relay R356 is energized under the control of the calling device provided at the calling substation A. Due to its slow-to-release characteristic, the relay Rfllfl remains operated during'each digit and restores shortly after the digit is ended.

The vertical magnet 458, upon operating, elevates the wipers 660 to 653, inclusive, to the first vertical off-normal position and closes its contacts. 438 to prepare an alternative operating cirto this movement of the switch wipers, the :oiT-' normal-springs d! are opened further to interrupt the operating circuit for the calling simplex relay R llii, the off-normal springs 415 are closed to prepare or complete a path including the contacts 426 and 32 for short-circuiting the winding of the line relay R456, and the off-normal springs 468 are opened to interrupt the operating circuit and the initially completed holding circuit for the digit transfer relay R459. At the ofi-normal springs All, the previously traced locking circuit for the line relay R tdt is interrupted, causing this relay to restore, if'operated. At the ofi-normal springs tilt, the operating circuit for the release magnet it? is prepared. In restoring, the relay Rddfi opens its contacts 4 23, further to interrupt its locking circuit, and closes its contacts 2 to complete the short-circuiting .path described above. When this short-circuiting .path is completed, the winding of the relay R i iii is excluded from the calling loop circuit over which the other line relay Rittil is energized, therebyto decrease the resistance of the circuit for energizing the latter relay. At its contacts Ml, the relay R ldil opens another point in the operating circuit for the digit transfer relayRdSfl. At its contacts M4, the relay Redd reprepares the operating circuit for the calling simplex relay Rdit From the above explanation it Will be apparent that if the line 9 is arranged for loop circuit control of the automatic switching equipment, the line relay RM! is caused to restore and the winding of this relay is excluded from the calling loop circuit in response to the dialingof the first impulse of the first digit of the directory number designating thev desired substation.

At the end of the open-circuit period of each impulse of the first digit, the line relay R360 .reoperates to complete the above-mentioned alternative operating circuit for the lock-pulse relay R1538, this circuit extending from ground by way of the contacts tilt, Ciii, the contacts 36E, C15 and the Winding of R633 to battery. At its contacts 362, the relay R36fi opens the above-described priming circuit for itself. At its contacts 333, the relay R3353 recompletes the holding circuit for the hold relay Edit. The lock-pulse relay R436, upon reoperating, opens its contacts 43! to deenergize the vertical magnet 1583 and the pulse controlled relay R i'ifi, closes its contacts 432 to recomplete the operating circuit for the hold relay R319, and closes its contacts its to recomplete its own locking circuit. From the above explanation it will be understood that the line relay Riitii, the lock-pulse relay R434] and the vertical magnet 393 interact in the exact mannerjust described during each impulse of the first digit. It will further be understood that each'time the vertical magnet it? is energized, the wipers We to 663 are elevated one step. Accordingly, at the end of the first digit,,these wipers are left standing opposite the level of bank contacts in which the conductors of the called line it are terminated.

During the inter-digit pause between the first and second digits, the line relay R360 and the lock-pulse relay RG39 are held operated for a time interval in excess of the release period of the slow-actingpulse controlled relay Rt'iil. Accordingly, the relay R 570 is caused to restore. In releasing, this relay opens its contacts ill to interrupt the path short-circuiting the Winding 4M of the repeating coil, and closes its contacts All to reprepare one of the operating circuits for the pulse controlled relay R469. At its com cuit for the lock-pulse relay R439- In response tacts 413, the relay R410 reprepares the operating circuits for the busy test relay R530 and'the idle test relay R630. At its contacts 412, the relay R410 opens the above-traced alternative holding circuit for the digit transfer relay R450, causing the latter relay to restore.

, In releasing, the relay R450 closes its contacts 452 to prepare an alternative operating circuit for .the pulse controlled relay R410. At its contacts 451, the relay R450 opens another point in the initially completed operating circuit for the relay R410. At its contacts 453, the relayR450 opens another point in its initially completed holding circuit. At its contacts 454, the relay R450 opens another point in its alternative holding circuit as traced above. At its contacts 455, the relay R450 prepared one of the operating circuits for the pulse controlled relay R460. At its contacts 458, the relay R450 opens another point in the above-traced circuit for energizing the vertical magnet 40B and the relay R410 in parallel. At its contacts 459, the relay R450 prepares a circuit for energizing the relays R460 and R410 in parallel with the rotary magnet 409. At its contacts 451', the relay R450 opens another point in the incomplete operating circuit for the calling simplex relay R410. At its contacts 458, the relay R450 prepares the previously mentioned circuit for transmitting busy and tick-tone currents over the calling end of the connection. At its contacts 459', the relay R450 interrupts the previously traced circuit traversed by the dial tone signal current, thereby to terminate the dial tone signal being reproduced by the receiver provided at the calling substation A. Following the release of the relay R450, the link circuit equipment is conditioned to respond to the impulses of the second digit.

During the dialing of the second digit, the line relay R360 and the lock-pulse relay R430 cooperate to repeat the dial pulses to the relays R460 and R410, and the rotary magnet 409 in parallel. More specifically, the circuit over which current pulses are transmitted to these control elements extends by way of the grounded hold le'ad C81, the contacts 323 and 355, C16, the contacts 431 and 459, C494, the contacts 634, C610 and the contacts 532 and 511 to C493 where it divides, one branch extending through the winding of the magnet 409 to battery, and a second branch extending through the contacts 411' and the winding of R460 to battery. A third branch of this circuit extends from the conductor C610 by way of the contacts 531, C99, the contacts 452 and the winding of R410 to battery. When this circuit is initially completed at the beginning of the opencircuit period of the first impulse of the second digit, the relays R460 and R410 both operate. Upon operating, the relay R410 closes its contacts 411 to recomplete the path for short-circuiting the repeating coil winding 401, opens its contacts 411' to interrupt the initially completed operating circuit for the relay R460, and closes its contacts 412 to complete an alternative circuit for energizing the last-mentioned relay. This alternative circuit extends by way of the grounded hold conductor C81, the contacts 311, C11, the contacts 635, C495, the contacts 412 and 455, and the winding of R460 to battery. At its contacts 413, the relay R410 again opens a point inthe operating circuits for the busy and idle test relays.

The relay R460, upon operating, closes its contacts 461 to complete a path for short-circuiting the. winding of the digit transfer relay R510, this path extending by way of the grounded hold conductor C81, the contacts 311, C11, the contacts 635, C495, the contacts412, 455 and 461, C491, the contacts 519', the winding of R510 and the contacts 529 to the grounded release conductor 3260. At its contacts 463, the relay R460 prepares a circuit for energizing the upper winding of the two-step switching-through relay R350. At its contacts 464, the relay R460 prepares the operating circuit for the busy test relay R530. At its contacts 465, the relay R460 opens a point in the holding circuit for the busy test relay R530. At its contacts 466, the relay R460 opens a point in the operating circuit for the idle test relay R630. At its contacts 461, the relay R460 opens a point in the path for transmitting signal currents over the calling end of the connection. Due to the slow-to-release characteristics thereof, the relays R410 and R460 remain operated throughout the second series of impulses transmitted to the link.

Each time the rotary magnet 409 is energized, it operates to rotate the Wipers 660 to 663, inclusive, one step, and closes its contacts 409' to prepare an alternative operating circuit for the lock-pulse relay R430. This alternative circuit is completed in response to the reoperation of the line relay R360 at the end of the opencircuit period of each impulse. Specifically, this circuit extends from ground by way of the contacts 409', C91, the contacts 361, C15 and the winding of R430 to battery. Each time the lockpulse relay R430 reoperates, it recompletes its holding circuit in the manner previously explained.

From the above explanation, it will be understood that in response to the impulses of the second digit, the wipers 660 to 663, inclusive, are rotated step by step until at the end of the digit they stand in engagement with the contacts terminating the conductors of the called line 16. During the inter-digit pause between the second and third digits, the line relay R360 and the lockpulse relay R430 remain operated for an interval in excess of the combined release periods of the relays R410 and R460. Upon restoring, the relay R410 opens its contacts 412 to interrupt the looking circuit for the relay R460, and closes its contacts 411 to reprepare the operating circuit for the relay R460. At its contacts 413, the relay R410 repreparesthe operating circuit for the busytest relay R530. At its contacts 412, the relay R410 also interrupts the above-traced path short-circuiting the winding of the digit transfer relay R510, permitting the last-mentioned relay to be energized in series with the relay R460 over a circuit which extends by way of the grounded release conductor 3260, the contacts 529, the winding of R510, the contacts 519, C491, the contacts 461 and the winding of R460 to battery. When thus energized, the relay R510 operates and locks up in a circuit including the grounded release conductor 3260, the contacts-512 and the resistor 519. After this locking circuit is completed, the relay R510 opens its contacts 519' to interrupt its operating circuit and thus deenergize the relay R460, causing the latter relay to restore. At its contacts 511, the relay R510 prepares the operating circuit for the ri g pickup relay R540. At its contacts 514, the relay R510 opens a point in the common portion of the paths for short-circuiting the timing relay R640 and the lower windin of the link release relay R340. At its contacts 515, the relay R510 prepares an alternative circuit for energizing the busy test relay R530, this circuit only being uti- 'lized in providing the restricted service facilities described more fully hereinafter. At its contacts i 6, the relay R5I0 prepares the operating circuit for the restricted service relay R550. its contacts 5I1, the relay R5I0 opens a point in the common portion of the above-traced branch circuits 'for energizing the relay R460 in parallel with the rotary magnet 400. At its contacts 5| 8, the relay R5I0 prepares a circuit for transmitting impulses to the operating magnet I004 of the code selecting and conversation timing switch'45. The release of the pulse controlled relay R450 in response to operation of the digit transfer relay R5l0 is without effect at this time.

The impulses of the third digit dialed at the calling substation are repeated by the line relay R360 and the lock-pulse relay R430 to the pulse controlled relay R410 and" the operating magnet I004 of the switch 45 in parallel. In this case, the pulsing circuit extends from the grounded hold conductor C8I by way of the contacts 323 and 355, C10, the contacts 43I and 459, C494 and the contacts 634 to C610 where it divides, one branch extending by way of the contacts 53I C93, the contacts 452 and the winding of R410 to battery, and the other branch extending by way of the contacts 532 and M8,

CS II and the winding of the magnet I004 to battery. When thus energized at the beginning of the .first'impulse of the third digit, the relay R410 again completes the previously traced circuit for energizing therelay R460. The two relays R460 and R410 remain operated until shortly following the end of the digit. Each time the operating magnet I004 is energized over the pulsing circuit just traced, it operates to step the wipers I000, IO0I and I002 one step, .and closes its contacts 1003 to prepare another operating circuit for the lock-pulse relay R430. When the enumerated wipers of .the switch 45 are moved off normal, the oiT-normal springs I005 aredisengaged to open a point in the operating circuit for the release magnet 401, and the off-normal springs I005 are moved into engagement further .to prepare the circuit for energizing the release magnet 1001. In thepresent case, the lock-pulse relay R430 is energized in response to each reoperationof the line relay R360 over a circuit which extends from ground by .way of the contacts I003, 09!, the contacts 135.1,. C15 and the Winding of R430 to battery. This'relay in reoperating, locks toground through the contacts 433 and the resistor 428, and opens its contacts 4.3I to interrupt thepulsing circuit extending to the magnet I004 and the relay RI010. Thus, the magnet I004 is energized once in response 'to each impulse transmitted to the link over the calling line. Accordingly, the wipers of the switch 45 are, at the end of the digit,

"left'in the off-normal position correspondingto the code designation of the desired substation. Busy test At'the end of the third digit, the pulse controlled relays R410 and-R430'restore-in the order named. The operations whichoccur in response to the sequential release of these relays depend upon the idle or busy condition of the calleclline l '6. In this regard it will be noted that if this line is idle, the line, cut-oil and lockout relays or the line circuit 23 are at normal so that the private conductor IEcofthe'line i0 is marked with negative battery potential through the oonductorISd and the engaged make contacts l64:of1the operated cut-oil relay EH30. Assuming that the called line I5 is busy at the time it isselected in the manner explained above, the relay R410, upon restoring at the end of the third digit, completes the prepared operating circuit for the busy test relay R530. This circuit extends by way of the grounded private conduce. tor I00, the private wiper 503, G580, the wiper IO0I C or C08I and the contacts 631, depending upon the. .olT-normal position occupied by the wipers of the switch 45, 030, the contacts413 and 434; C584'and the upper winding of R530 to bat.- tery. When thus energized, the relay R530operates-and closes its contacts 531 to prepare a look.- ingcircuit foritself. At its contacts 53L the relay R530 opens another point in the operating circuit for the relay R410. At its contacts 532, the relay R530 opens a. point in the common portion of theoperating circuits for the rotary magnet 409 and the operating magnet I0041 "Thus, followingaopera'tion of the busy test relay R530, the magnets 408, 400 and H304, and the relays R460 and R410 are prevented from responding to further operation of the calling device providedat'the callingsubstation. At its contacts 533, the relay R530 opens the prepared operating circuit for therestricted service relay R550. At its contacts 534, the relay R530 further prepares the 3 operating circuit for the trunk-hunting relay R480. At its. contacts 535, the relay R530 opens a point in the operating circuit for the idle test relay R030. At; its contacts 536, the relay R530 prepares a locking circuit for the switchingthrough relay R350 and a path for connecting the release conductor 326 0 to the test wiper 063. At its contacts 538, the relay R530 opens 'a point in another of the locking circuits for the switchingthrough relay R350 At its contacts 531', the relay R530'prepares the circuit for transmiting busy tone current over the calling end of the connection. At its contacts 538, the relay' R530 opens a point in the circuits for transmitting ringing current and tick-tone current over the caning end of the connection. At its'contacts 539., the relay R530 prepares an alternative locking circuit for the lock-pulse relay R430, which cir cuit is utilized only in the event furtherimpulses are inadvertently dialed atthe calling substation. Thus, if an additional digit is dialedat thecalling substation after the three digits of the directory number designating the desired substation are dialed, the line relay R300, upon restoring'at the beginning of the open-circuit period of each inipulse, opens thelocking circuit for the lock-pulse relay R430, causing the latter relay to restore.

Thereafter, and when the line relay R300 reoperates, the lock-pulse relay R430 is energized over a circuit extending by way of the grounded conductor CBI, the contacts323 and 355, C16, .the contacts 43I and 450, C494, the contacts 034, C510 the contacts 539', C9I, the contacts 36I and C15 and the windingof R430 to battery. When thus energized, the relay R430 locks to ground through its make contacts 433 and the resistor 428, and then opens its contacts 43I to interrupt the alternative operating circuit just traced.

. Shortly following the operation of the busy test relay R530 in the manner pointed out above, the slowaacting pulse controlled relay R450 rethis path is completed, the cut-ofi relay stores. At its contacts 465, the relay R460 completes theprepared locking circuit for the busy test relay R530, this circuit extending by way of'the grounded release conductor 3260, the contacts 531, C585, the contacts 465, C584 and the upper windingof R530 to battery. At its contacts-461, the relayR460 completes the prepared circuit for transmitting busy tone current over the'calling end of the connection. This circuit parallels that traversed by the dial tone current as traced above, but is derived from the busy tone current source over a path including the conduc-- tor E6549, the contacts 531, C58! and the contacts'458". The reproduction of this signal current by the receiver provided at the calling substation A serves to inform the calling subscriber that the desired line is busy. Themanner in which the operated switching equipment is released when the call is abandoned at the called substation is described with particularity herelnaft'er.

Idletest ,In the event the called line [6 is idle at the time" it is selected, no circuit is provided for energizing the busy test relay R530 when the pulsecontrolled relay R410 restores, the upper wind-- ing' of the busy test relay being short-circuited. in series with the winding" of the cut-off relay Rl 60 when the relay R410 restores. Shortlythereafter, andwhen the pulse-controlled relay R460 restores, a circuit is completed for energizing the lower winding of the idle test relay- R630 in series with the cut-ofi relay Rl60, this: circuit extending .by way of the grounded holdl'.

conductor C8l,' the contacts 374, C82, the lower' Winding of R630, C613, the contacts 535, C583,.

lll

the contacts 466' and- 413, C80 alone or C80 and. thecontacts- 631 and C68l, the wiper l00l, C680,.

the test wiper 663, the private conductor. [60, the:

contacts I72 and the winding of Rl68 to battery. When thus energized, the relay R630 closesits preliminary make contacts 638' to complete a locking circuit for itself. This locking circuit extends by way of the grounded hold conductor, C8l,,the contacts 31!, 01!, the contacts 6382088,. the contacts 32I, C10 and the upper winding oi? R630 tov battery. At its contacts 635, the relay R630 opens another point in the previously traced operating circuit for the pulse-controlled relay R460. .At its contacts 634, the relay R630 opens a point in the common portion of the-previously .traced operating circuits for the relays R460 and R410,.the rotary magnet 409 and the operating magnet I004 of the switch 45. At its contacts 633, the relay R630 opens a point in the'operating circuit for the trunk-hunting relay R480. At its contacts 631, the'relay R630 opens one of the above-traced branches of the series operating circuit for itself and the cut-ofi relay R160. 4% its contacts 63!, the relay R630 prepares the operating circuit for the called simplex relay R620. At its contacts 632, the relay R630 completes the operating circuit for the slow-to-operate line-switching relay R658, this circuitextending by way of the grounded hold conductor C8l, the contacts'3'll, CH, the contacts 632 and At its contacts thewinding of R650 to battery.

path for im- 638, the relay R530 completes a pressing ground potential directly upon the private'conductor 160 of the called-line l6, this path extending from ground as applied to the hold conductor CBI'by way of the contacts 638 and thetest'wiper 663 to the conductor [60.

'lholding circuit for the hold slave relay R330.

The iatteri circuit extends from ground by way of the contacts 639, C86. and the winding of R330 to battery. At its contacts 639, the relay R630 shunts the contacts 539' of the busy'test relay R530, so, that in the event any further impulses are dialed at the calling substation theyare ab;- :sorbed in the mannerexplained above.

At its contacts 636, the relay R630 prepares or completes one of the operating circuitsior "the trunk-hunting relay R480, depending upon the setting of the code-selecting and conversation timing switch .45. The last-mentioned re lay, during the ringing period, serves to determine the side of a selected called line of the loop typeover which ringing current is to be transmitted, and is selectively controlled in accordance'with the odd or even character of the third digit dialed at the calling substation. Thus, if the ringer providedat a called substation isconnected between the negative side of the associated line and groundpa third digit comprising an even number of impulses is dialed at the calling substation. In'this case, the operating circuit for the'relay R480 is completed in response ductor ON, the contacts 638, C680, the wiper |00l bridging even-numbered contacts of its associated contact bank, C68l, the contacts 636, C58l, the upper winding of R480, C498, the contacts 626, C499, the lower winding of R480 and the contacts 4'14 to battery. It will be observed from the wiring arrangement of the contact bank associated with the wiper I88l, that if a ringin digit is dialed at the calling substation which comprises an odd number of impulses, the circuit just traced is not completed through the contact bank of the switch 45 and, accordingly,

the trunk-hunting relay R480 remains in its rostored position. With the relay R480 in its restored position, the ringing current transmission circuits are prepared at the contacts 482 and 483 for the transmission of ringing current over the positive side of the selected called line. With the relay R486 operated on the other hand, these circuits are opened at the contacts 482 and 483, and circuits are prepared at the contacts 48l and 484 for the transmission of ringing current over the negative side of the called line, all-in the manner more fully explained hereinafter.

The line-switching relay R650, upon operating,

closes its contacts and 653 to prepare the ringing current transmission circuits, and opens its contacts 652 to interrupt'the prepared orcompleted operating circuit for-the called simplex relay R620. At itscontacts 654, the relay R656 prepares a circuit for energizing the back-bridge relay R610 over the called end of an established connection. At its contacts 655, the relay R650 prepares a circuit'for energizing the ring pickup relay R540 in accordance with the ground pulses conventionally applied to the pickup lead 658 by the ringing interrupter at the beginning of each code cycle. At its-contacts 656, the relay R650 opens a point in the common portion of the operating and test circuits controlled over the E. C. wiper 662.

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