US2374072A - Telephone system - Google Patents

Description

April 1945. w M. BEAUMONT 2,374,072

TELEPHONE SYSTEM Filed Jan. 12, '1943 I 6 Sheets-Shee t 1 F/Ql r0 n/vpmm LINE $1.!

FIG 6'.

FIG 3. FIG. 5. 7

'lNVENTOR W. M. BEAUMONT a Arm/wry April 17, 1945. ,w. M.- BEAUMONT TELEPHONE SYSTEM Filed Jan. '12, 1943 6 Sheets-Sheet 2 I lNl/EN r01? W. M. BEAUMONT A TTORNEV April 17, 1945. w. M. BEAUMbNT TELEPHONE SYSTEM Filed Jan. 12, 1943 6 Sheets-Sheet 3 Fill Flll -./NVENTOR WM BEAUMONT av A TTORNEV Filed Jan. 12, 1943 C T U KEY CALLING EQUIPMENT 4 zr mvornm STAT/0N FIG. 4

6 Sheets- -Sheet 4 5 m g INVENTOR Q w 3 m/u. BEAUMONT a A from/EV April 17, 1945.

W; M. BEAUMONT TELEPHONE SYSTEM Filed Jan. 12, 1943 6 Sheets-Sheet 5 [NI/ENTOR B m M BEAUMONT & 917K A rr omvm April 17, 1945. w. M. BEAUMONT TELEPHONE SYSTEM 6 Sheets-Sheet Filed Jan. 12, 1945 //v l/EN TOR M. BEA UM 0N T W. ax

A TTORNEV Patented Apr. 17, 1945 ium'reo STATE T E YSTE .7 William M. Beaumont, summ mm J., assign'or to I Bell Telephone 'Iiaboratories; Incorporated; i

New .York, N. Y., a corporation of New York- 5 V; Application January12, 1943, ser a N 312,191" Claims. (01. 179-27! 1 This invention relates to telephone systems and particularly to central ofiice and private branch exchange telephone systems of the type in Which an extension station of-the executivetype is pro vided' with facilities whereby connections to freemr'oitheievee ioh m emm s t m re sion efmeans'atthe secretary station for pickmg up'a c all on the key calling line extended thereto through the private branch exchang and quently called subordinate stations may beQestablished by-the party at the executive station or requiring the assistance of the-private branch I exchange attendant in completing connections between his line and the linesof the frequently called subordinates. Systems of this type, which reduce to 'a minimum the requirements imposed .on an executive subscriber in establishing connectionswto the lines of a particular group of-subordinates; and which render such connection to be completed in an expedit ous manner; necessitate vthe use of auxiliary equipment at the executive station in the nature of a group of line selecting I keys, and also of auxiliary switching apparatus which responds selectively to the actuation ofthe lineselecting keysto extend the execut ve's line to the subordinate line corresponding to the particular line selecting key actuated.

*Itis the object of this invention to providean improved telephone system of the keycallingtype briefly defined. above and to further extend facilities afforded by such a system.

' Th s object is attained in accordancewith feature of the invention by providing the-subscriber at a kev calling stat on w th sec etarial service. More particularly, the object of the invention is attained by correlating the'equipment at a keycalling station w th that atasecreta'rys station "in such a manner that telephone calls originated at or incoming to the key callingstation may be handled by a secretary when conditions warrant such procedure. 'In'accordance with this particular feature of the invention-a call onthe-line' individual to the keycalling station ybe picked up by'the s cretary by the simple act of operating a key at the secretary's station which places the ecretarys tele hone inymultiple with the key: calling station line. An ancillary which w s, "held by thepartyat' the key callin station; '1 v 1;, Y .tt. i t Another feature .of the invention renders itpos; siblej'forjthe ,secretaryto'initiate outgoing exchange calls overtheline of'the key calling station', When the party at'the key calling station wishesl'to extenda call through the private branch exchange atflhich his' line terminates, a particularkey assigned'for. this purpose is actuated after the handset .has been removed from its mountingggilhe actuation of this key' causes a certaincombinationfof positive and negativedirect current pulsesto be transmitted pvera con trolicircuit to. selectively operate a corresponding combination of [register relays "which, vin turn, functionitoefiechthe connection of the key .calling' stationiline'to' the line extending to. the private branch exchange. l In accordance with the featurecf the inyentionunde'r instant discussion, the connectiom'oflthe key, calling station line with theLprivate branch exchangev line maybe effected by the actuation of means. at the-secretarys position,.which.means whenfut'ilized, simulates the operationiof theparticular;key at the key calling station and causes the, operationof the same combination; of greg ister relays and the consequent connection of ,the'vprivate branch exchange line with the lineebnductors of thekey calling station. Thus the secretary has access to the privatebranchpxchange not only, by way of the secretarys; own line butv also byway of the key calling .stationiline, and may originatecalls thereover when conditionswarrant it. A

AQfur-ther feature of the invention provides means whereby the party at thekey calling station may establishakey-initiated call to the line extending to the secretarysstationf Suchaconnection ise s,tablished in the samemannerias direct connections to'any other frequently called private branchextension;- that is, by the actuation of atkey at the key calling station individ ually -assigned to the secretarys line.

A still furtherfeatureof th invention permits calls incomingover the secretarys line to be held?! by the secretary and to be picked, up at .the-key calling station. -In accordance with this particular feature; when a call on the secretarys line is to'be transferred to; the key calling station the secretary-places ya hold-condition on the line and disconnects her telephone therefrom. l The party at the key-calling station after removing the telephone thereat from its mounting actuates a key assigned especially for the purpose of pickin i up a call which is held on the secretarys line.

The actuation of such key automatically places the key calling line in multiple with the secretarys line to thus efiectively connect the key calling station to the line over which the call was extended to'the secretary's line andmaintains such connection in the cut through condition while momentarily opening the connection towards the secretarys station to'automatically remove the 1 hold condition placed on the connection by the secretary. Such a connection may be again picked up by the secretary, in which case the-connection of the secretarys telephone with her line I and the disconnection of the key calling station result in the automatic release of the equipmentthat when the handset IBI is removed from its mounting the switch I00 is actuated to close its several contacts. The switches RI, R2, R4 and R8 are disposed relative to the fifteen key-buttons so as to be operated singly or in combinations utilized in extending the key calling line to the secretarys line.

In accordance with another feature or the invention the apparatus. and circuits areso' arranged that calls may be extended to the key calling station when originated at other key calling stations. Such calls are extended to the key calling station by way oithe private branch exchange line over which all calls directed to the key calling station arrive. When such'a'call is extended to. the key calling station the tip and ring conductors of the said'line are physically separated from their normal terminations at 'the exchange thereby isolating the line, from the exchange. This feature provides secrecy on connections involving two key calling stations and precludes the possibility of 'an attendantfat the exchange effectively associating her telephone set with the connection for the purpose of eavesdropping, Or for any other purpose." ,1

A further feature of the invention';contem plates the assignment of a key at the key calling station to each of a one-way line'circuit to the local exchange and a line circuit extcndingto a distant exchange. Thus the key calling subscriber has accessto the local exchange over a plurality of lines andmay alsocomplete calls to extension lines which terminate at an exchange other than the local exchange. v

These and other features of the invention will be readily understood from, the following description made with reference tofthe accompany? ing drawings, which when assembled in the man ner indicated in Fig. 8 constitute a circuit diagram of a telephone system embodying the pres,- ent invention.

Before 'enterin 'into a detailed'des cription of the methodof operation of the system disclosed in the drawings, a brief reference to the equip ment furnished the'executive'station hand the secretary's station S, and also to the apparatus controlled thereby will beniacie. 'I'heupper portelephone hook switch I00. Thesefelments perform well-known functions. v In practicethe telephone set may assume'tl'ie general appearance of a standard "setand differs therefronlin thatlit has mounted on the base'there'of fifteen key but tons and a designation strip which bearsfadesignation for 'each'key corresponding to the line-'to which it is individually assigned. These key-buttons are manually operable andco trbi'tnegop- 'erationof four rectifier control swianes RI R2,

R4 and R8 andals'oswitches SHYind RA. The

when the key-buttons are actuated. When the switches RI, R2, R4 and R8 are actuated they function to effectively connect the corresponding dry rectifiers I I, 22, 44 and 88 to the line conductors of the line KC. Switch RI serves to complete the ground circuit to the tip conductor T of line KC through rectifier II switch R2 serves the same purpose with respect to rectifier22'; switch R4 serves to complete the ground circuit to the ring conductor R of line KC through recti fier 44; and switch R8 serves 'the'same purpose relative to rectifier 88. At P in Fig. 3 there is shown a source of alternating current which, as will appear more fully in a later description, rm nishes current to the rectifiers II, 22, 44 and 88. The table illustrated in Fig. 7 indicates the man; her in which the rectifier control switches are operated in response to the actuation of each of the fifteen key buttons. v

'A separate manually operable key HA is mounted on the telephone set atstation- A'a'nd acts as a holdkey. When actuated, it connects ground to the point III] or induction coil'ID to cause differenti'al relay DF, Fig. 2, to operate for a purpose to be described in detail hereinafter. The lower portion of Fig. 1 represents a secretary's station S which is equipped with a, telephone set comprising the handset I20, dial I2I', ringer I24 and induction coil I22.

mounted on the base thereof such as key KI, K2,

K3 "and I-IK; the'last constituting" a hold key which functions, when actuated, to place a hold conditionon the secretarys private'branc'h exchange line SL. The key KI serves to connect the secretarys telephone set with the line -SL; the keyKZ' serves to connect the secretarys telephone set in multiple with theline conductors of the key calling station line KC; and the'key K3 serves to associate the secretarys telephone with the line SLI to which the secretary may have access. An auxiliary key CK, known as' a. call key, 'is located at the secretarys station S and functions, when operated, to extend the key'calling station Line'KC to the two way private branch exchange line ZLX (Fig. 4). 'This key serves; the same-general purpose with respect to the scoretarys station S as does the No. 15- key button at station'A which serves to extend the key calling station line KC to the exchange PBX.

' Fig. 2, and the relays ST, LO, B, RLI and RL of Fig. -3 constitute a supervisory circuit which functions to provide all the supervisory, Signaling and other features embodied in the key-calling systemdisclosed, The lower portion-of Fig.1; includes relays I, 2, 4 and 8 which, constitutea register circuit, the said relays operating singly or in combinations under the control of the rectifir control switches RI, R2, R4 and R8 a's'indi- 'cated 'by the table shown in'Fig. 7. Theseiegiste'r relays function to selectively controlth op- 'erationof the connector relays GT2, GT4, GT5,

GTSQGT'I, GT8, GT9 and GTHI, shown at the left of Figs. 4, 5 and 6. Each connector relay, with the exception of relay CTIO, is equipped with upper and lower'sets of armatures, only one of' which sets is effective at a time. Which set is effective is determined by whether or not the switching relay SW shown at the upper right Connector relay GT2 serves the two-way private.

branch exchange line 2LX and the private branch of l the line KG, and at H contact I I 02, it "connects 1 ground potential to the switch RA whichswitch,

extension line XI with which the station I X is associated; relay GT4 serves the one-way private branch exchange line LX and the extension line X2 with which the station 2X is associated; relay GT5 serves the extension line X3 with which the station 3X is associated, and also the multiple extension SX associated with the secretary's line SL; relay GT6 serves the line multiple SXI of the secretarys line SL and the extension line X4 with which is associated the station 4X; relays GT1, GT8 and GT9 serve the extension lines X5, X6, X1, X8, X9 and Xl with which the stations 5X, 6X, 1X, 8X, 9X and IOX respectively,- are associated; and relay CTN) serves the line DPX which terminates at a distant private branch exchange. The various pri- 4 vate branch exchange lines and extension stations are illustrated terminating in jacks at the local manual exchange PBX. It is to be understood that such lines may well terminate in switch terminals at a dial exchange, the manual exchange terminations being shown forthe sake of simplicity of disclosure only.

At the upper right corner or Fig. 4 there is diagrammatically indicated the equipment of another key calling station. This showing contains as ngle connector relay GT which, in practice, would correspond to one ofthe connector relays of the key calling equipment associated with station A. This relay functions to extend a call from another key calling station to station A by way of the two-way private branch exchange line 2LX.

I-laying described, in a general way, the cirwits and apparatus illustrated, the method of operation of the disclosed system will now be described in detail.

Call to private branch exchange line tion removes the telephone handset at station A from its mounting and actuates key-button No. which in the drawings is assigned to the private branch exchange line 2LX.

I When the handset I0! is removed from its mounting at station A, the switch I00 is actu-. ated. This switch efiectively connects the'telephone transmitter and receiver of the handset l0! acrossthe tip and ring conductors'T-andR as hereinbefore mentioned, operates whenever anyof the fifteen key buttons of the telephone set at the key calling station is actuated for the purpose of supplying ground to the rectifier key pulsing equipment indicated at KP; With the telephone set bridged across the line KG, relay L (Fig. 2) of the supervisory circuit operates in a circuit extending from grounded battery, windingof relay L, back contact and third lower armature of relay GO, back contact and second lower armature of relay IG, back contact and middle lower armature of relay TK, ring conductor R of the lineKG, through the closed subscribers loop at station A, tip conductor T of the line KG, outermost upper armature and back contact of relay TK, first-lower armature and back conta'ctof relay IGQto ground by way of the second upper armature andback contact of relay CO; Relay L locks under control of relays TK and 10 in a circuit from grounded battery,

. winding and-first upper armature and front contact of relay L, conductor 200, third lower armature and back contact of relay TK, to ground by way of the back contact and second upper armature of relay IG.

With relay Loperated. relay C (Fig, 2), relay first lower armature of relay GT2, conductors 500 and 2M, front contact and second lower armature of relay L to ground. This circuit also now finds ground-at the first upper armature and front contact of relayB. v

At its second upper and lower armatures relay G, operated, opens the tip and ring conductors to the tripping circuit which includes the lower winding of tripping relay TR. At its first lower armature and front contact, relay Goonnects ground to conductor 204 which serves as a holding ground for the register relays I, 2. 4 and 8, and at its first upper armature and front contact it completes an for relay GO.

Relay PB (Fig. 4) operated, connects battery to the sleeve contact of jack JA which terminates the two-way line-circuit 2LX at the private branch exchangePBX thereby rendering the line busy to the private branch exchange equipment. This battery connection is made by way of the upper armatureand front contact of relay PB and resistance 05L It is to be understood that the jack terminations of the various lines at the exchange, have been illustrated for reasons of simplicity only, and that should such lines terminate in a dial exchange the busy condition produced by relay PB would be 'reflected in the automatic switch thereatto render the key calling, or executives line busy to this equipment. At its lower armature and front COD", tact relay PB places a similar busy condition on the lead 43| which extends to the equipment at another key calling station.

Relay CO, the register connector relay, operated, extends the-tip and ring leads. T and R of the station Ato the conductors 3'01 and 300',

obvious operating circuit v respectively, which connect with the register circuit comprising relays I, 2, 4 and 8. The ring the. middle lower armature and back contact of relay TK; the second lower armature and back contact of relay IG, and the third lower armature and front contact of relay CO, whereas the lead R is connected to the lead 380 by way of tip lead T is connected to the lead 3M by way of the third upper armature and back contact of relay TK, the first lower armature and back contact of relay IC, and the second upper armature and front contact of relay GO. Thus the register circuit is effectively connected to the calling line when the handset at station A is removed from its mounting.

At its fifthupper armature and front contact relay GO connects ground to lead 206 and thence by way of conductor 201, normal contacts 208 of tripping relay TR to the motor startlead 205 which results in the operation of the ringing machine included in the equipment shown schematically at PS in Fig. 2. At its middle upper armature, relay CO completes an obvious operating circuit for relay PR. At its fourth upper armature and front contact and its fourth lower armature and front contact, relay GO completes a circuit from the alternating current source P (Fig. 3), by way of conductors 302 and 394 and full-wave rectifier 353 to the point 305 of the register circuit.- This power source P furnishes-current to the register relays l, 2, 4, and 8, which operate selectively under the control'of the key-buttons at the calling station A.

At. its second lower armature and front contact relay GO prepares an operating circuit for relay LO by connecting one terminal of the relay winding to the lead 306 which terminates inone of the front contacts of power failure relay PF2. It will be observed that the power source P normally furnishes operating current to the winding of relay PF! by way of the full-wave rectifier 301 so that this relay PFI is held operated so long as there is no power failure. This relay controls the operating circuits to relays PF2 and AC so that as long as relay PFI is operated the relays PFZ and A are deenergized. In the event of a power failure, relay. PF! releases its armatures thereby causing relays PF2 and AC to operate, the latter functioning as a buzzer signal to audibly indicate the power failure. Relay PF'2 in operating, connects ground potential to a plurality of leads, such as 386, each of which extends to a different relay LO associated with the supervisory equipment serving different key calling stations. Thus should there be a power failure at the time a key calling station initiates a call, the relay LO corresponding to the calling station would operate over the lead 306 and the corresponding contacts of the relay CO.

Relay LO under the condition of power failure functions to automatically extend the calling line KC to the exchange PBX by way of the two-way private branch exchange line circuit 2LX. More particularly, with relay LO operated due to the power failure, relay GT2 (Fig. 4) 0p- I crates in a circuit extending from grounded battery, winding and normal make-before-break contacts of relay GT2, conductor 40L conductor 335, front contact and upper armature of relay LO, front contact and first lower armature of relay L to ground. At its fifth upper armature relay GT2 causes relay TK to operate which disconnects the register circuit from the calling line KC and extends the latter to the link KL which, with-relay GT2 operated, is-extended to the exchange line circuit 2LX. Relay TK, operated, also opens the locking circuit for relay L which relay restores its-armatures. Relay B, however, does not release since it isnow held operated under control of relay L2 in the exchange line circuit 2LX as will now'be described.

-When the relay GT2 operated to extend the link KL to the line circuit ZLX, relay L2 operated in a circuit which may be traced from grounded battery, winding of relay L2, back contact and. second lower armature of relay SL', winding of relay Ll, front contact and third upper armature of relay GT2, conductor 405, back contact and first lower armature of relay SW, conductor 2I4 of link KL, front contact and second upper armature of relay HR, upper winding of relay DF, first upper armature and front contact of relay TK, front contact and second lower armature of relay TK, ring conductor R of line KC,- closed subscribers loop at station A, tip conductor '1 of line KC, third upper armature and front contact ofrelay TK, front contact and first lower armature of relay TK, lower winding of relay DF, first upper armatureand back contact of relay HR, conductor 246 of link KL, second upper armature and back contact of relay SW, conductor 406, fourth upper armature and front contact of relay GT2, conductor 484, first upper armature and back contact of relay SL' to ground. Relay B is held operated in a circuit extending from grounded battery, winding of relay B, conductor M2, second lower armature and front contact of relay GT2, conductor 4-! I, back contact and second lower armature of relay H2, front contact and second lower armature of relay L2 to ground. Thus relay B is held operated and maintains the circuitsin the outthrough condition. Relay Ll operates inthe circuit traced for relay L2 and maintains the relay HI short-circuited.

Relay L2 at its first lower armature and front contact connects ground to the ring conductor 439, extending to the exchange, by way of resistance 409, and the second lower armature and back contact of relay COL. This ground, as will appear from a later description, brings in a lamp signal at the exchange PBX, or in the case of a dial exchange causes the line switch to start operating in a well-known manner. Thus, in the event of a failure of the power source P, a call which is initiated at station A is automatically extended to the exchange over the two-way line circuit ZLX.

Time out At its first upper armature and front contact relay CO completes an operating circuit for relay S'I which relay in operating performs no useful function at the present time unless the calling party fails to actuate a line selecting key-button within a predetermined period of time following the removal of the handset H from its mounting. The description is continued under the assumed condition of no power failure. 4 a

Should the calling party at station A fail to operate one of the key-buttons within-a given interval after starting a call by removing the handset at the calling station from its mounting, the circuit functions to release the register circuit from the calling line. More particularly, when relay CO operated as described above, an operating circuit for relay RL (Fig. 3) is completed which includes grounded battery 308, resistance 3l3, winding of relay RL, thermistor 310, normal low enough to permit relay RL to operate which,

in turn, operates relay RLI in an, obvious cir cuit. Relay RLI operated connects thewinding ofrelay ST in series with the thermistor 3l0 in at potentiometer circuit. The potentiometer-elm .cuit includes battery 3|5, resistance, 314. to the point 316 where it divides, one branch extending to ground by wayof resistance 399, upper armature and front contact of relay RL and. conduc tor 3,12, another branch including the winding of relay ST, thermistor 310, upper armature and front contact of relay-RL-l, conductorstll and 312, front contact and first upper armature of relay CO, to ground. Thus the current in thermistor 3l0 is reduced and the thermistor will cooloff, increasing its resistance. When this current reaches a certain value relay ST will release causing relay L to operate in a circuit extending from grounded battery, winding ofrelay LO, back contact and armature of relay ST, front contact and lower armature of relay RLI, conductor 204,- iirst lower armature and front contact of relay C to ground. With relay ,LO operated, relay CT2 (Fig. 5) operates in a circuit extending from grounded battery, winding of relay, CTZ, normal make-before-break contactsof relay CT2, conductors 40! and 335, front contact and upper armature of relay LO, to iground by A,

way of the front contact and first lower armature. of relay L. At its second lower; armature and front contact relay LO locksv to ground at .the front contact and lower armatureof relay B. Relay GT2, operated, causes relay TK (Fig. 2 to operate in a circuit which is traced from grounded battery, winding of relay TK, co'nductor 2| I, back contact and third upperarmature of relay SW, conductor 2l2, fifthIupper-arma- 'ture and front contact of relay CTLto ground. .1;

Relay TK, operated, disassociates the tip and ring conductors T and R of the line KC from the conductors 300 and 3M which extend to the registercircuit thereby disconnecting the. register from the calling line. Relay TK also opens-the locking circuit for relay L causing thisrelay to restoreiits armatures. Relay L releases relays B and C. Relay B releases relay L0 and causes. re

lay CT: to be deenergized. The circuit'is thus restored to normal. It is assumed in the preceding description that the party at the station A replaces the'handset before actuating a key-button, in which case the relay L2 would notoperate to hold relay B operated. Otherwise the line KC, is extended to the exchange in the mannerdescr'ibedin connection with a power failure.

Ordinarily the party at the key callingstation will operate one of the key-buttons to completeafcall before the timing circuit releasesrelay ST. In the following description the calling'party is assumed to have operated the No. .15 key-button immediately after removing the handset from its mounting at station A. Obviously then, when relay CO operated, as, hereinbefore described, to

complete an operating circuit for. relay ST, the timing circuit including thermistor 310 will not have sufiicient time to cause the release of. relay STso that this relayremains operated in; a cirextending from grounded battery- 315, resis an e 3 7 n i o e y -S.T.,n rma ak 15 Register relay sho n 'in' Fig. 7, to efiectively connect the rectifiers'll, .22, 44 and88'to the conductors of line KC. 'It' is understood that switch'RA is. closed andv switch. S H is opened whenever an one of the key-buttonsis actuated. In accordance with the tablefsh'own in Fig. 7,.reg'ister relays l', 2, 4 and" Bf'oPe'rateWhen theiectlfielf controlling contactsj'Rl, R2,"R4'ahd' R8 are closed in response to'th'efactuation Of key-button No. 15.' "Due" to the Tclosure'of'rec'tifier controlling'contact "Rl,, register "relay '1 operates in 'a' circuit which may be traced from ground, jswitchhook contact"! 02 at station A; switchRA, rectifier controlling switch Rljpositive' poled rectifier l'l, switchho'ok contacts I05, conductor I06, tipconductjo "jTofline KC,'third upper armature and back contactof relay TK, first lower armature an back 'eontactoffrelay 10, second upper arr nature and irontcontact of relay C0, conductor 30l' lower winding of register, relay I, positive poled rectifiers3l8 and 319, conductor 320', rectifieri32l"of fullfwaverectifier 303, winding of' relay FEW; rectifier 322, conductor 304, front contact and fourth lower armature of relay CO, front contactand fourth upper armature of relay CO,

cond torg 302, alternating current source P to ground Relay I" operates in this circuit on the positivepulses transmitted over the tip conductor" I "of'1ineKC.1 v j I 2 operates in a circuit extendme rical-ground; switchhook contact 102, switch RA re'ctifiercontrolling switch R2, negative poled rectifier 22,- switchh'ook' contacts I05, conductor 403, tip conductor T of line KC, third upper 'armature and-back contact of relay TK, first'lower armature and'backcontactof relay 10, second *upperarmature and front contact of relay CO;

ductor 30!; negative poled rectifiers 323 and lower winding-10f relay 2 to the point 305,

c'onductor 3 20, and thence to ground through the source? by "way of the circuit previously describedin connection with the" operation of rel'a'y l",*-eircept that the'rectifiers 344 andj345 of'full 'wa've rectifier 303 are substituted for rectifiers 32l' a-'nd 322. Relay 2 operates in'this circuit on conductor? of line KC.

- The operating circuitfor register relay 4exthe negative impulses transmitted over the tip --tends froin ground, switchhook contact "I02,

s'witch RA,'-rectifier"controlling switch R4, nega- -tive'poled rectifier 4-4, conductor I08, ring conductor Rof'the line KC, n'iiddle lower armature 'andbackjcontact of relay TK, second lower arm'a "ture an'd -backcontact'of relay IC, thirdlower "armature and front contact'of relay CO, conductor 300;-to'-the point 325, thence through negative poled rectifiers326 and 321,:lower winding. of meister relay "4, 'to the point 305, conductor 320'and :thenceto the grounded source P by wayfof the circuit previously described in connection .with

the operation of register relay l. Relay 4 therefore operates on the negativeimpulse transmitted over the ring conductor R of the line KC.

. linegister relay 8 operates 'in a circuitextending from-ground, switchhook contact I02, switchRA,

: rectifier controlling switch R8, positive poled rec- -tifier- 8, 8, conductor 1 08,: ringcondu'ctor R or the line KC, middle lower armature and back contact of'relay TK, second lower armature and-back contact of relay IC,,third lower armature and front contact of relay CO, conductor 300; to the point 325, thence through the lowerwindin'gof "relay 8, positive poled rectiflers- 329: and 328 to the point 305, conductor 32llyand thence to the grounded source'P by way of the circuit previously traced for relay 2. Relay 8 thus operates on the positive impulse transmitted over thering conductor R of line KC.

Register relays l, 2, 4 and 8 in actuating their respective upper armatures to close contacts 330, 33!, 332 and 333 lock to ground at the front'contact and first lower armature of'relayC by way of'common conductor 20 4. It will be noted that during the period that key-button No, 1515 actuated and the operating impulses traverse'the circuits traced for relays l, 2,14 and f8; relay FW is operated and holds its armature disengaged from its working contact. When the key-button is released and the impulses cease to fiow, relay FW restores its armature to extendfthe' ground at I 335, front contact and second lower armature of relayl, contact 336 of relay .2, contact 33'l'of relay [first lower armature and front contact ofrelay 8, conductor 23!, conductor 334, back contact and armature of relay FW, back contact and upper armature of relay LO, front ,contact' and first lower armature of relay L to ground.

Relay GT2, operated, locks by way of its first upper armature and front contact, conductors 500 and to ground atthe front contact and first upper armature of relay B. At its fifth upper armature andfront contaqt relay C,T2' com pletes an operating circuit forrelay 'I'KlFig. 2) which extends from grounded battery, winding of relay TK, conductor 2| [,back contact v and third upper armature of r'elay SW, conductor 2|2 and the fifth upper armature and frontcontact oi relay GT2 to ground. At its first lower armature, relay GT2 opens the operatingpircuit for relay PB'in the private branch exchange line circuit ZLX causing this relay to restore its armatures. At its third and fourth upper armatures and front contacts relay C I2 extends the link KL (Fig. 2) of the supervisory circuit to theprivate branch exchange line circuit 2L Xwhich, as shown in Fig. 4, terminates at the exchange, PBX

in the jack JA. This line. circuitmay well terminate in the terminals of a lineswitch at an automatic or dial exchange but as hereinbefore explained, it is shown terminated at a' manual office merely to simplify the disclosure. I

With relays TK (Fig. 2) and GT2 (Fig. 5) operated, a circuit may be traced from'grounded battery, winding ofrelay L2, conductor 402, back contact and second lower armature of relay SL, winding of relay Ll, front contact and third upper armature of relay GT2, talk conductordfli, back contact and first lower armature of relaySW, talk conductor 214 of link KL,,backcontact and second upper armature of relay HR, upper winding of difierential relay DF, first upper armature and C, 'CO and the register relays i, 2, 4 and 8.

front contact of relay '1'K,front contact and sec ond lower armature of relay TK, ring conductor R of line KC, through the closed subscriber loop at station A, tip conductor T of line KC,'third upper armature and front contact of relay TK, front contact and first lower armature of relay TK, lower winding of differential relayDF, first upper armature and back contact of relay HR, tip conductor 216 of link KL, second upper armature and back contact of relay SW, conductor 406, fourth upper armature and front contact of relay GT2, conductor 4B4, first upper armature and back contact of relay SL' to ground. Relays L2 and LI operate in this circuit but relay DF, being differential, does not operate at this time. Relay Ll short-circuits the winding of relay HI. When relay L2 operates it completes an operating circuit for line relay 40"! which extends from grounded battery, right winding of relay 401,"first armature and back contact of sleeve relay 40B, ring-conductor 439, second lower armature and back contact of relay COL, resistance 489, first lower armature and front contact of relay L2 to ground. Relay 40'! operates in this circuit and completes an obvious circuit for line lamp 410. a

It is to be understood that the ground applied to the ring conductor 439 would serve in a dial exchange to start a line finder operating in the well-known manner to seize the calling line.

At its second lower armature and front contact relay L2 extends ground over a circuit which includes the second lower armature and back contact-of relay H2, conductor 4H, front contact and second lower armature of relay GT2, conductor, M2 to battery andground through the winding of slow-to-release relay B to maintain relay B operated.

Upon noting the lighted signal 410 the private branch exchange operator would insert plug PA into jack JA associated with the lamp signal 4H) to'handle the call in the usual manner.

When relay TK operated, it caused the release, directly or indirectly, of relays L, ST, RL, RLI,

Relay-B, however, as indicated above, is held oper- -ated.'

---It is to be understood that should the calling line terminate at a dial exchange, the party at station A would proceed to complete the initiated callby-operating the dial 189 in the well-known manner. After the seizure of the calling line by the line-finder in the exchange the operation of the dial would set the automatic switches at the exchange in the well-known manner to extend the calling line to the line of a called subscriber whose telephone designation is dialed by the calling party at station A.

However, when in response to the lighted lamp signal 410 at the manual exchange illustrated, the attendant thereat picks up the call in the manner indicated above, relay S operates from battery on the sleeve of the plug PA, over the sleeve terminal of jack JA, upper armature and back contact of relay PB, first upper armature and back contact of relay COL to ground through the winding of relay S. Relay S, operated, closes an obvious operating circuit for relay SL'. Relay SL' at its first upper and secondlower armatures and front contacts closes the talking circuit from the exchange through to the calling station A and at its second upper armature and front contact it connects ground to the lead 41 I by Way of the second lower arma- 'ture and back contact of relay H2, which ground serves to hold relay B (Fig. 3) operated which, in turn, holds the equipment in the cut-through condition. Relay L2 releases when relay SL operates.

On a manual connection the calling subscriber informs the exchange attendant of the telephone number of the desiredcalled' party and the attendant extends the connection in the usual manner.

The insertionof plug PA into Jack JA of the calling line causes the lamp signal 410 to be extinguished in the well-known and obvious man-' ner. Relay S operated, connects busy battery to the lead 4'3] extending to the equipment at another key calling-station.

At the termination of the call between the key calling station A and the desired private branch exchange extension station the party at station Areplaces the handset ml on its mounting, the private branch exchange automatic equipment or the attendant, depending on whether the exchange is of the dial or manual type, opens the sleeve circuit causing the release ofrel'ay S, which relay, in turn, releases relay SL'. Relay SL' releases relayjB which, at its first upper armature and front contact opens the lockingcircuit to relay CT2 which relay, in releasing, opens the operating circuit for relay'TK thus restoring the apparatus to normal.

The same release operations described above in connection with the manual exchange will be performed in the event the establishd connection tothe called line is completed by way of the automatic switches at a dial exchange and released when the calling partly disconnects.

Holding by key calling subscriber Should the party at the key calling station A, for any reason, desire to hold the connection the completion of which was-described above,

the hold key HA at the key calling station is actuated to its closed position. This key operation connects ground 'by way-oi switchhook- .operate due to the differential action of the re lay coils. However, when ground is connected to the tip and ring conductors of the line at the calling station due to the operation of hold key HA, the current flow in the windings of the differential relayDF is unbalanced an'd the relay operates. .The hold key HA effectively.

shunts one winding of the relay. Transmission relay DF. Due to its being differentially connected there is no transmissionloss. in the relay except by the direct current resistance. V

Relay DF, operated, causes relay H to operate in a circuit extending from grounded battery,

"winding of relay H, conductor 200, front contact "and armature of relay DF, conductor 2H, to

its second upper armature opens the ring conductor 2 to the station A and at its front contact and same armature connects battery "2-18 thereto. At its first upper armature-l and back contact relay HR opens thetip lead 216 and at its I front contact and same armatureconnects ground to the tip lead to'thecalling station. Thus, battery and ground are connected-throughthe. windings of the differential relay DE. to the key calling station tomaintain a balanced line while the hold key is operated and to prevent-the line of'the key calling station being connecte'd'tothe register circuit until the hold key is released; v

' At its contacts 220 relay H connects-the tip lead 2|6 extending towards the private branch exchange 'to the holdlead 222 to-effect the following bridge eircuit: from the tip terminal'of jack JA, back contact and second upper armature of relay COL,.front contact' and first-upper armatureof relay SL3 conductor #04, irontcontact and fourth upper armature "of --relay- GT2,

conductor 406, back contact andsecond upper armature of relay SW,- contacts-1200f relay H,

- second lower-armature andback' contact of relay SW, conductor 222, {secondupper armature and front contact-of relay GT2, conductor-4| 3, winding of relay Hl,resistance 4, third lower armature and front contact of'relay SL', first lower armature andback contact of --relay COL, conductor 439 to .the ring terminal of jack JA. Relay L1 is, of course, deenergized at this time due to the operation offrelay HR." The bridge circuit justtraced serve as a holding bridge to hold the established connection. Relay HI operatcsin this circuit from battery at the exchange-and. at its second upper armature-and front-contact establishes an obvious operating circuit forrelay H2. Relay HI at-its first upper armature and front contact connects its own winding directly across theexchange end of the establi'shedconn'ection. Relay H2'at its secondlower armature and 'back contact removes the ground atithe second upper armature and fronticontactof relay SL' from conductor 4H which, by way of-tthe from, contact and second lower-armature of-relav GT2 and conductor 2 was extended to .theiwind ing of relay B. Thus relay B is deenergized-and battery is furnished the calling station from the exchange through the windings of differential ground byway of the first lower armature and Y releases its armatures.

At its; first .u'pper armature and front contact relay B opens the locking circuit for relay CTZ whichi relayrestores its armatures. Though relayrCTZ at-;its fifth upper armature. and front contact opens: the" original operating circuit for relay TK thisplatterirelay is now held operated under controlof relay HR.

Thus the connection is held dueto the operation I of the hold key HA at station A.

When the hold key HA at station A is released relay 'DF releases due to the differential action o'fits windings and in restoring its armature it opens the operating circuit to relay H. Relay H dition causing the .key calling station to be reconnected to the register circuit so that another call may be made by the party at station A, if

desirable. When the party at the key calling station wishes to release the hold condition and again talk on the connection held, the call is picked up in the regular manner. More particularly, the No. 15 key is again actuatedto cause the selection of. the private branch eXQhange line I i 7, HR in which r919? H perates. Banana-a coming to the key calling station on removing the hold condition previously placed on the connection by the operation of hold keyHA.

Incoming call to lcey calling station All calls incoming to the key calling station arrive by way of the two-way privatebranch exchange line 2LX employed in the description just made of a call originated at the key calling station by the actuation of the No. key-button. When this line is, seized either by the operator at a manual exchange or'by the party at another key calling station, battery potential is applied to the sleeve conductor to cause the operation of relay S and relay SL, the latter causing relay GT2 to operate. The operating circuit for relay CT2 extends from grounded battery, winding, of relay GT2, conductor M6, first upper armature and back contact of relay ICJ' (Fig. 2) conductor 4H, back contact and upper armature of relay'H2 (Fig. 4), third upper armature and front contact of relay SL, conductor 9,1 back contact and second upper armature of relay L '(Fig. 2) to ground- Relay GT2, atits fifth upper armature and front contact, causes relay TK to operate in a circuit previously described. At its second lower armature and front contact relay GT2 completes the following operating circuit for. relay B (Fig. 3): grounded'battery, winding of relay .13, conductor 2, second lower armature and front. contact of relay GT2, conductor 4", back contact and second lower armature of relay H2, second upper armature and front contact of relaySL' to ground. Relay 0T2, operated, locks to ground at the front-contact and first: upper armature of relay B. Withrelays GT2 and TK operated, the ringer III at the called station A is connected directly across the tip and -ringconductors of the connection which 'now includes either the terminals of a connector switch at a dial exchange or, as shown in the drawings, the terminals of jack JA at a manual exchange. In either case the transmission of ringing current over the line is effected in the usual manner to which the ringer I l I at station A responds as a call signal. Transmission battery is furnished by the private branch exchange equipment or by the other key calling equipment at the station at which the call is originated. V I

When the calling party disconnects theattendant removes the plug PA from jack JA and relay SL releases its armatures causing the release of relay B which releases, directly or indirectly, the relays GT2 and TK thereby restoring the circuit to normal. The holding feature described in connection with a call originated at the key calling station applies in the same manner to a call inthe private branch exchange line 2LX.

- Call incoming from another key callingstatio'n At the upper. right of Fig. 4 there is schematically illustrated a single relay CT which is. identified as constituting a part of the equipment at another key calling station. The telephone set at such other station would be'furnished with a keybutton assigned to the key calling station A which, when operated, would cause the associated register relays to operate in a particular combination to effect the operation of relay CT. Any one of the key-buttons other than the No. 15 keybutton at the other key calling station may be assigned to the key calling station A, the No. 15 key-button being reserved for connections established over the two-way private branch exchange line circuit associated with the other ke calling station in the same manner as is the key-button No. 15 at station A reserved.

When a call to station A is initiated at the other key calling station relay CT operates in the manner indicated above and at its first armature and front contact extends battery potential over the sleeve conductor 43L thence over the lower armature and back contact of relay PB to ground through the winding of relay SL. Relay SL in operating under this condition performs the same functions ascribed thereto in extending a. call to station A under the heading Incoming call to key calling station.

It will be observed that on a call to stationA which originated at another key calling station relay COL also operates. The operating circuit for relay COL extends from grounded ioattery, resistance 240, upper armature and back contact of relay S, winding of relay COL, front contact and first lower armature of relay SL to ground. Relay COL, in operating, connects battery by way of its front contact and first upper armature to the sleeve terminal of jack JA by way of the upper armature and back contact of relay PB thus marking the line to the station A busy at the exchange. In a dial exchange a busy potential would be extended to the connector multiple in which the line of station A appears, to render the line of station A busy to the automatic switches. Atits second upper and first lower armatures relay COL opens the station A key calling line to the private branch exchange thus providing a.

secrecy feature which precludes the attendantat the exchange from eavesdropping on such a connection. In this manner the line to station A is not only marked busy at the exchange but the transmission conductors are physically disconnected therefrom to thus render eavesdropping by the attendant or operator impossible.

Incoming call released first by key calling party In case the calling party disconnects first on an incoming call relay SL will release and relay L2 will operate over the closed loop to the key calling station A by way of the back contacts and first upper and second lower armatures of relay SL. The operation of relay L2 holds slow-to-release relay COL operated, in a circuit extending from grounded battery, resistance 440, upper armature and back contact of relay S, winding of relay COL, conductor 422, upper armature and front contact of relay L2, second lower armature and front contact of relay COL to ground. When the handset llll is replaced on its mounting at station A relay L2 releases causing the release of all operated relays and restoring the circuit to normal.

Direct station call mounting and actuates the key button assigned armors to theueslred called station. For descriptive purposes it will be assumed that key No. 2 corre+ sponds to the desired private branchextension line which is identifiedas line X2 on 7'. As

shown on this line corresponds to station 2X and terminates in jack U at the exchange.

I When the handset IOl-at station A-is retrieved from its mounting the. same relays operate as pie viously described-in connection with the exten+ sion of a-call' through-the private branch ex change, and the register circuit comprising relays I, 2, 4 and 8 is connected through to the tip and ring conductors T and R of the calling line KC. The party at station A then actuates the key butfton No. 2 which causes relay2 of the register circult to operatelas indicated by the table shown in Fig, 7', I lylore; particularly, the actuation of key button No, 2 closes the rectifier controlling contact R2,which,"in iturn, connects rectifier 22l to th tip conductor 1 of line 'KC to callsethe transor relay FW, b'ack contact and upper armature or relayrLOrpfront contact and first lower armature or relay L .to ground.

Relay 10 now operatesin a circuit extending from grounded battery, winding of relay 10, com ductor 226, front contactand third upper armature of relay SW, conductor 2l2, to ground by way of the fifth upper armature and front eonmission of an impulse o fapolarity such as to opcrate relay 2, over the tip conductor of the line.

Register relay 2 operates in acircuitextending fromgroundatstation A, switchhook contact I02,

switchRA, rectifier controlling, contact R2, negative poled rectifier 22, switchhook contact I05,

conductor 19$,tip conductor T of line KC, third upper armature and back'contact of relay'IfK, first" lower armature andfback' contact ofrelay 10, second upper 'armatureandlront contact of relay CO, conductor Bill; negative po ledrec'ti fiers 3'23 and' 324,lower winding of relay 2, to the point '3fi5and thence back to the grounded source P over the circuit traced 'hel'einbefore.

IReglst'e'r, relay 2, operated, locks under control of relay, 0 in the mannerpreviously described. Rela'yl'FW operates 'in'thecircuit tracedfdr relay 2 towit'hhold "the connection of ground at the front contact and first lower armature of relay L to -the ope'ratingvwindingol relay CT4 untilthe calling fpartlyat station A releases the No. '2 key button corresponding tothe called station 2X. When this 'key button is 'released relay FW re leases itslvarmatilre to apply g'round potential to the lead 334. w en this'occurs'relays', and j GT4 operate. Relay S'Woperatesin a cheaper,- tendingfrom grounded battery, winding and norinal make-before-break contacts of relay f'SW,

conductor 230, back contact and second lower armature of register relay 8, contact 339 of reg ister relay 2, conductorifl, back contact and armature of relay FW, back contact and upper armature of relay 10, front contact and first lower armature of relay L toground'. It will be observed at this time that relay SW operates only whenlegistenrelety' B is unoperated and only when one of the register relays l, 2 or I tact of connector relay "CTL Relay GT4 operated, locks in 'a' circuit including grounded battery,

winding and from contact and first upper a'rmatil-re of'r'elay 0T4, conductor 500, conductor 2M, rront contact and first upper armature "of relay Band'ass'ociated ground. 5

Relay 16 at its second upper armature/opens the lockingucircuit for relayill. causing relay L to release. Relay-L at its second upper armature releases relay::C "and at its llrst lowerarmature opens the operating circuit I'orrelay GT4. Relay 0 at its lirstlow'er armature releases register relay 2 and at its secondupper and lower armatures connects the tip and ring leads 2.02am 203 to the tripping circuit. Relay 16 at its first and second lower armatures connects battery and ground to the conductors of line KC- through the windings of relay A'.- Relay A" operates 'over the closed 'substation loop and applies ground to the winding of relay B to holdwthis relay operated;

1 and second lower ati'natur''s, relay BY keepsthe is operated. Since, as indicated by the table in Fig. 7, register relay -'8 is operatedonly on the actuation of key buttons 8 to 15 inc'llusive, the relay SW operates only when one of the key buttons 1 to 7 inclusive is actuated; By virtue of this arrangement fifteen station selections may be made by means of'only eight connector relays such as GT2, GT4, etc, one selection being enacted by each of the sets of upper and lower arosecures ofthe connector relays. I Connector relay 0T4 operates in a circuit extending-from ground ed battery, winding and normal make-before break'contacts ofrelay 0T4, conductor L2, front contact'and fourth lower armature of register relay 2, contact 34 l of register relay I, contact 340 of register relay 4, conductor "232; fourth lower armature and front contact of relay SW, 'conduc 'tor23l, conductorstfl; back contact "and armature tip ring conductor's open't the [called sta m h Q ra ngoircmt for relay, BY includes an armatureand-rroritcontact or slow;

to-release 'relayn it 'is apparent that the busy test Of'the called line-is made during therelease sumed busy condition oftheealld line X2 to station 2X, sends busy tone back to the callin station one locksuhdei oona ior relay The path for the busy tone current'extends from the tone supply TS (Fig; 2), conductor 233; condenser 231, front contact and's'eoond u er annature of I relay BY, 'conductor'235, front-contact and second lower armature of relay IC-,;=hack contact and seo- 1 end lower armature of relay ring conductor R. of line KC, through the closed loop at Station A, tip conductor T or line'KC, third upper' armat'ur'e and-back contact' of relay'IfK, firstlower armatureand frontcontact or relay It} to ground through the-upper winding of relay A; Thls'ou'm rent generates a tone signal in the receiver of the ha'nds'et ml at station A, Upon-hearing the busy toue'sighal-in the receiver of 'the hamlsset, theparty at station Awould aball'don the'ca-ll by replacing the handset-cults mounting whereupon the circuit is restored to; normal; The release or thecirolllt results from the release of relay A'- which, when relay 11c; operated was connected directly acrossthe' callih'gend of the connection and whlcmat its armatureand front-contact established an obvious operating circuit {or slow to-releaserelay B. Relay le -releases relay GT4,

When' relay BY operated it locked to battery at the third lower armature and front contact of relay IG and when the call is abandoned relay IG restores its armatures to release relay BY thereby discontinuing the tone signal.

C'aflled Zine idle When relay IC operates as described above it opens, at its first upper armature and backcontact the circuit to connector relay C'IZwhich circuit is efiective in operating relay GT2 on calls incoming to station A, thereby preventing double connections- If the line X2 'to the called station 2X is idle, as is now assumed, relay GO releases due to the release of relay C which relay released when relayL released as above described. While relay C was operated, sloW-to-release relay PR .was operated in an-obvious circuit, and when relay G restores its armatures relay GO releases and opens the operating circuit to relay PR. Relay PR, however, remains operated for a short interval of time due to its slow-to-release characteristic. With relay CO released and relay PR operated, a circuit is completed from the grounded continuous ringing supply GS, front contact and armature of relay PR, normally closed make-before-break. contacts of relay CO, conductor 238, lower winding of tripping relay TR, back contact and first lower armature of relay TR, conductor 234, back contact and-second lower armature of relay BY, second lower armatureand back contact of relay G, conductor 203, back contact and secondupper armature of relay TK, conductor 2! of link KL, first lower armature and front contact of relay SW, conductor 240, second lower armature and front contact of connector relay GT4, through theringer circuit at'station 2X, front contact and firstlower armature of relay GT4, conductor 422, front contact and second upper armature of relay SW, conductor 202, back contact and second upper armature of relay G, first lower armature and back contact of relay BY,.contact 242 of relay TR, front contact and fourth lower armature of relay 10 to ringing ground. Thus the signal at station 2X is energized in a continuous manner so long as relay PR remainsoperated and immediately upon seizure of the line X2 by connector relay GT4. The station 2X therefore is signaled immediately upon seizure of its line, when idle, thereby overcoming the delay in transmitting a call signal by means of machine ringing should the line seizure occur during the silent interval between rings.

When relay PR releases its armature after the time interval following the release of relay CO, machine ringing from the source PS traverses the path just traced for the continuous ringing current. The called station is therefore signaled intermittently after having been signaled continuously for an interval of time corresponding to the release time of relay PR. The signaling of the called station is indicated to the calling party at station A since the signaling current from the source PS is projected over the calling end of the connection by Way of the back contact and second lower armature of relay TR, condenser 210, back contact and second upper armatureof relay BY, conductor 235 and thence over the same circuit traversed by the busy tone current from source TS. Relay GO released, opens the connectionbetween the'power source ;P and the register relays l, 2, 4 and 8. This is accomplished by the upper and lower fourth armatures of relay G which, when the relay releases, disconnect conductor 302 extending from the. power source P from conductor 304 which extends to the register circuit.

The line X2 is marked busy at the exchange by virtue of a battery connection to the sleeve conductor thereof. This battery extends from the back contact and first upper armaturev of relay BY, back contact and third lower armature of relay L, third lower armature and front contact of relay SW, conductor 228, and the third lower armature and front contact of relay GT4.

Called station answers When the party at the called station 2X responds to the incoming call signal, the tripping relay TR operates ina well-known manner due to the closure of the station loop circuit at station 2X. Relay TR disconnects the machine ringing current supply from the called line and at its contact 244, and itsfront-contact and first lower armature connects the windings of relay D to the called station 2X. Transmission battery is supplied to the called station through the windings of relay D. Transmission battery is supplied to the calling station A by way of the windings of relay A. The condensers 250 and 25l serve to couple the calling and called ends of the speech transmission path extending between the calling station A and the called station 2X. Conversation between the parties at the two interconnected stations may now be carried on. Relay TR locks operated under control of relay B,

When the handset at station A is replaced on its mounting at the termination of conversation, relay A releases due to the opening of the substation loop at station A and causes the release of relay B. Relay B, released, causes relay GT4 to release'by removing ground from conductor 20! which served to hold relay GT4 locked perated. At its first upper armature relay B removes ground from the locking circuit to relay TR whereupon relay TR releases. Relay GT4 at its fifth upper armature opens the operating circuit to relay IG causing this relay to release. Relay B in removing ground from the conductor 20! also causes relay PB in the private branch exchange two-way line circuit 2LX to release and opens the locking circuit of relay SW. The circuit is thus restored to normal.

Call from secretcrys station via private branch equipment The secretarys station is, as shown on the lower portion of Fig. 1, equipped with a telephone handset I20 and associated induction coil I22, a dial I2 I, a series of keys Kl, K2 and K3, a hold key HE. and a call key GK. Incoming to the secretarys position are a plurality of lines such as line SL which is the secretarys own private branch exchange line, and line SLI. The purpose of the various keys at station S has been hereinbefore indicated. j

, When the secretary at station S desires to make a call to a subscriber by way of theprivate branch equipment at the local exchange, the handset I203 is removed from its support and key Kl is actuated, the latter operation serving to connect the telephone at station S to the secretarys private branch exchange line SL which terminates, as shown in Fig. 5, in the jack JS at the, exchange. When the handset is removed from its mounting and key KI is operated, the line relay associated with the line SL and located at the exchange is operated to bring in a call s na n e w -kn n. an en. he

aazao'za secretary's. line terminate, in. .a dial exchange the call would be extended. tozthe called station in the usual manner when-the dial I2I at station Sis actuated. However, yin-the illustrated embodiment of the inventionthe line SL. terminates at the manual exchange P,.B. X. and the call would be furtherextended by the operator at the exchange who responds to the call-.signalassociated with. the line Sh: v a

' Incoming call secretary Onan incoming call on line SL theringer would beactuated in the. well-known manner to the line conductors of ,the line SL operates over the closed loop at-the secretary's station from battery at the exchange. Theopera-tionofirelay I25 at this time performsno useful function To hold the connection'the. hold key HK is actuated which results ,in the. opening of one side of the line SL to the secretarystelephone thus causing the release of relay I25. A circuit isnow closed from the exchange, over the tipconductor 254 of line SL,'top winding of relay. I26, outer left a1= ternate contactsof key KI, make contacts of hold key HK through theclosed loop at the station S, middle alternate contacts of key KI, and back to the exchange by way of the :ring conductor 255 ofline SL; I

Relay I25 operates in this circuit to connect'a holding bridge acrossthe'tip and ring conductors the keyv K2 is. actuated .to-connect her telephone set across the. line KC, and the call. key CKis operated The latter operation connects'ground potential to both; the tip and ringficonductors of the line KC which, in effect, isthe ecfuivalent of operating the'No. 15 key button at the key calling station A. --Thus, whentthertelephone'rsetat sta tionS-is cnnectediacross the lineKC and the handset removed from its mounting, the register circuit, including relays I, 2; 4 and-i8, is connected to thelinaKC and register. relays I, izyl-and 8 operate'in response to theactuation of call key CK at station S in the same manner as described in connection-with the origination of a callat station A bytheactuatlon' ofkey button No. 15. The register relays I, 2-; 4'and 8 function to operate relay GT2 which connects thelineKC-to the two-way private branch exchange line '21.)! .in

. the manner previouslydescribed. In this inanof the line-SL. -More particularly, this holding circuit includes the armature andfr'ont contact of relay I 26, bottom winding of relay I26 and thenon-inductive .winding* I 28;- This bridge I soeiated therewith. The arrangement of keys KI K2, K3 and key HK is such thatwhen-the hold key HK 'is operated; the key KI, which was operated when the call on 'line SL'was ofriginally completed; is automatically restored. The res to'rati'o'n of key KI causes the opening of the original energizing circuit for relay I26 by way of it's top winding; The relay I26: is-now'held operated over the'tipandring conductors of line SL byway of its bottomwinding'a'nd its "noninductive winding I28; and*-the station equipment' is disassociated from the line SL."

To again pick up the connection on line SL; the secretary at stations merely actuates the key KI to automatically associate the telephone set [20"With the line SL which causesrelay 125 to reoperate. At its 'front contact and-armature relay I25 short-circuits the bottom'winding of relay I26 'therebycausing relay I26 to release which removes the holding bridge from the line and restores 'the circuit to the talking condition.

Coll lay-secretary over the feet culling}station line make a-call-over the key calling stationiine'KC,

ner thesecre'tar'y not only has access to'regular private branch ie'xcha'nge'service by way of the line SL but also byway of the line KC. The operation oftheCTZrelayserves to bring in a lamp signa'lin the case of a manual exchangeor to I In thiscasethe hold key HK is actuated which opens the tipcon'duetorl to the station S and connects it" to the hold lead which includes the windings of relay I3I so that relay I operates overt-he closed loop at station S, the operating battery'being'iurnished at the exchange. Re lay rarmoperating, appliesground to the tip conductor of line KC 't O cause an unbalance in the'line'current traversing the windings of differential relay DF,;causing this relay to operate to-put-aholdcondition'on the line in the manner previously-described; When the connection is held -in this manner, it may be picked up either by the secretary or by the party at theykeyj'calli'ng stationpa" v l rgmsf'efiring call from key call ng station to p secretary w .Whenthe party at the'key calling station A wishes the secretary at station S to pick up a call which-the former ha originated or received-on' line KC, the secretary is so advised and her telephone is connected in multiple with the key calling station by the actuation, of keyv K2, and the handset1I20 is' removed"from its mounting." If the call'came in over the private branch'exchange equipment-,a hold condition may. have been put on the line before the-secretary was-told to pick upvthev call. In this case the secretary operates the call-key CK which, as hereinbefore indicated, produces the same results in theregister circuit as. key 'No. 15 at the key callingstation A." The circuitsthen function to establishla connection to the. two-way. private branch exchang'eline ZLX Y whichremoves the hold condition and permits the secretary to talk on the connection. The

manner inewhich thehold condition is removed- "fHolding by key calling subsc riber.

v-C'aZlfrom key'cdll'ingstation'to secretary When-Wheparty at the key cam-11g amt wishes to talk to the secretary by telephone, the call is started by removing the handset IIII from its mounting atstation A and by operating the key button assigned to the secretarys line which in the present disclosure is key button No, 1. When the handset at station A is removed from its mounting, the line KC is extended to the register circuit in the same manner described hereinbefore. The operation of key button No. l as indicated by the table of Fig. '7 causes rectifier controlling switch RI of the key calling station key-set to be closed and to connect rectifier I I to the tip conductor of the line KC, whereupon a circuit is completed which may be traced from ground, switchhook contact I021, switch RA, rectifier controlling switch RI, positive poled rectifier II, switchhook contact I05, conductor I05, tip conductor T of line KC, third upper armature and back contact of relay 'I'K, first lower armature and back contact'of relay IC, second upper armature and front contact of relay CO, conductor 3M, lower winding of register relay I, positive poled rectifiers 3 I8 and 3I9, to the point 305, positive poled rectifier 32I, winding of relay F'W, positive poled rectifier 322, conductor 304, front contact and fourth lower armature of relay 00, front contact and fourth upper armature of relay CO, conductor 302, to ground through the alternating current source P. Relays I and FW operate in this circuit on the positive pulse resulting from the actuation ofthe No. 1 key button at station A. Relay I locks operated under control of relay C in the manner previously described. When the key button No. l at station IA is released relay FW releases causing relays SW and GT5 to operate. The operating circuit for relay SW extends from grounded battery, winding and normal make-before-break contacts of relay SW, conductor 230, back contact and second lower armature of register relay 8, contact 342 of register relay I, conductor 334, back contact and armature of relay FW, back contact andupper armature of relay LO, front contact and first lower armature of relay'L to ground. Relay GT5 (Fig. 5) operates in a circuit extending from grounded battery, winding and normal make-before-break contacts of relay GT5, conductor LI back contact and second lower armature of register relay 2, contact 3' of register relay I, contact 340 of register relay 4, conductor 232, fourth lower armature and front contact of relay SW, conductor 23I, conductor 334, back contact and armature of relay FW, back contact and upper armature of relay LO, front contact and first lower armature of relay L to ground. Relay T5 locks to ground and to apply signaling current thereto, if idle, in

the manner described hereinbefore in connection with the testing and signaling of the extension station 2X on line X2. As in the case of the call extended to the extension station 2X, the called secretarys station receive an immediate ringing signal from the continuous ringing current source CS which is followed by an intermittent ringing signal originating at the machine ringing source PS. The ringing signal path may be traced from the grounded continuous ringing current source CS, front contact and armature of slow-to-release relay PR, normal make-before-break contacts of relay CO, conductor 238, lower winding and back contact and first lower armature of tripping relay TR, conductor 234, back contact and second lower armature of relay BY, second lower armature and back contact of relay C, conductor 203, back contact and second upper armature of relay TK, conductor 2I4 of link KL, first lower armature and front contact of relay SW, conductor 240, second lower armature and front contact of relay CT5, corresponding conductor of the link SX, lower armature and back contact of relay El, conductor 254 of the secretary line SL, Winding of relay I25, operating coils of ringer I 24 located at the secretarys station S, conductor 255 of the line SL, winding of relay SY, back contact and first upper armature of relay El, front contact and first lower armature of relay GT5, conductor 422, front contact and second upper armature of relay SW, conductor 202, back contact and second upper armature of relay'C, first lower armature and back contact of relay BY, contact 242 of relay TR, to ground by way of the front contact and fourth lower armature of relay IC. The ringer I24 at the secretarys station S responds in a continuous manner to the current traversing the pathjust traced. This continuous signal ersists just so long as relay PR. holds its armature on its front contact and when the armature is released, the machine ringing source PS is substituted for the continuous ringing source CS to cause the secretarys ringer to operate intermittently. The current from the machine ringing source PS traverses the same path traversed by the continuous ringing current except that it is supplied to thi circuit by way of the third upper armature and front contact of relay IC and the back contact and armature of relay PR. Relay SY may operate on the ringing current. The secretarys line at the exchange is marked busy in the same manner that the line X2 was marked busy as hereinbefore described.

When the secretary at station S responds to the operation of the signal and removes the handset I from its mounting and actuates key KI to pick up the line SL, the tripping relay TR operates to connect battery and ground to the called end of the connection by way of the windings of relay D. When this occurs relays SY and I25 operate over the closed loop at the secretarys position. Neither of these relays performs any useful function at this time. Transmission battery is furnished the secretarys line from the battery associated with relay D while transmission battery is furnished the key calling line KC from the battery associated with the relay A. Th key calling station A is now connected for communication to the secretary's station S and conversation between the parties thereat may be carried on.

It will be observed that relay PB of the twoway private branch exchange line ZLX to the key calling station is operated during direct station tostation calls such as the call from station A to the secretarys station S, just described, and in operating busies the two-way line to the central office equipment thus rendering the line inaccessible to such equipment when the key calling station line is in use. The operating circuit for relay PB include the first lower armature and back contact of relay GT2.

The circuit is restored to normal when the interconnected parties restore 5 the'ifhandsets to" their respective mountings. Callflheld by secretarypickedtip [at key calling station I When the secretary has received acall over her lineSL and'wishes the party atthe .key calling station A'to pickup that call, the secretary-first puts a hold condition on the line'SLwhich disconnects the station from the line and requests ground. 7 Relay SW does not operate at this the party at the key calling station to pickup w the call. r

It will be assumed that the'callincoining to the secretary's station S 'byway" of the line-SI; orig inated at the manual exchange at which the line'SL terminatesinthejack'JS. It is to'be understood that the call may just as well have been extended to the line SL by way of automatic switching equipmentat a dial exchange. In either case the ringer [24 at the station S' is actuated when sig'n'aling'curtent is appliedtoj the line SL at the exchange. In' answer to-this signal, the secretary actuates key Kl to connect the telephone equipment at station S to the'line SL and then removes "the handset T 120 from its mounting; In response to these" operations, relays I25 and SY'ope'rate and perform no usetul functions at, this time. slow-release relay SR operates-as a consequence of the operation of relay SY for a purpose to be hereinafter explained in detail. It willbenoted, however, that the operating circuit for relay SR includes the back contact and second upper armature of relay El. Since the call which the secretary has answered is to be pickedup by the party at the key calling station A, the secretaryope'ratesthe hold key HK which releases the Kl-keywhich disconmeets her telephone set from the line-and then requests the party at station A to pick up the held call. the hold key l-IK is operat'ec l as here- 'operates, the latter 't'o'effectively connect-the bottom winding and the non-inductive winding I28 of relay-I26 across theline 'as a holding bridge. Thus the call on line-5L is held; When thepart'y at station A is advised to pick up the call/ the key button at station A assigned dfor this {purpose is actuated after the handset 101 is removed from its mounting? The key button No. 11 is as sumedto'have been assigned for this purpose and they have-been u y-set f'orth hereinbefore? When the N0. 11- key button is actuated," the rectifier-control switches RI; R2 and R8 are closed as indicated by the table shownin Fig. "7. The closure of switches RI R2 and R8 res'ultsin the operation of register relays I, 2 and B. The circuits in which these relays operate "haye been traced 'hereinbe'fore in connection"with the actuation of key buttonNo; 15 and need not be repeated. It has alsobeen hereinbefore described how these register relays lock, when operated, under control'oi r'elay C. It has sco es-n described how relay 'FW remains "operated so' long as akey lautto'n at station Ais operated Relay 'FW restores its armature when the key '-button" 'is released to complete an op'erating (:ircnit for the connector r'elay corresp nding "to the particular register relay or relays opera-ted. reiays" i, 2 and! operateduconnector relay C'lfB operates in a "circuit extending from grounded battery,

winding and normal make-beforeefbreak contacts time since the key button actuated ishigher in number'tlran'seven. a

Relay C'IB locks operated ina circuite'xtend ing from grounded battery, Winding and front grounded battery, winding oirelay TK, conductor 2 H, back contact and third upper armature'of relay SW, conductor 2'l2,"fifth upper armature and front contact. of relay'CTG to ground. Relay TK' operated, disassociates the tip and ring conductors T and R of the lineKC from the conduc tors 300 and 30 I which extend to the register cir cuit, thereby disconnecting the register from the calling line; Relay 'I'K'also opens the locking circuit -fo'r relay L causing this relay to restore its armatures. Relay B, however, does not release as it is now held'operated in a circuit controlled by the second upper armature and front contact of relay El in the secretary's line circuit BL as will appear presently.

Relay TK at its third upper and first lower armatures and associated front contactsextend's the tip conduct-or T of the line KC to the lower winding of relay DF and at its second lower and first upper armatures and associated frontf'con tacts extends the ring conductor R-of theline KC to the upper winding or relay'DF so that, with the p p 0 subscribers loop'closed at station A by virtue of inbeforedescribed, relay I25 releases and relay I26 the" handset thereat being removed from its mounting, relay. E of the secretarys line circuit SL operates from the exchange battery, which; on the connection to these'cretarys stat on how held, supplied the battery to the secretarys telephone. The operating circuit for relay E maybe traced from one te'r'minal of the exchange battery to the ring'termin'al of jack JS by Way of which the "connection "was extended. to the secretarys line SL, winding-of 'relay E front cont'act'a'nd third upper armature of relay CTB, conductorlfli, ba'c'k *conta'ctand firstlower armature of relay SW, conductor 2l4'of the link KL, 'back contact and second upper 'ar'mature of relay HR, upper armature and front contact of relay TK, front contact and second lowerarmature ofrelay TK,

conductor- I06, fourth upper'armature and front.

contact of relay CTB, to the tip term nal-inf jack IS and thence to the otherterminal of "the ekchange battery (not shown). Relay E operated. e t blishes an obvious operating, circuit for -relay El. Relay El at its second upper armature-and ffron't contact completes the ho'lding'circuit for relay B. above referred to, by connecting ground trithe front contact and fifth. lower armature of relay 0T6 conductor 1H2, winding of relay B to battery and ground. Thus relay B is held operated to maintain the supervisory circuit in the cut-through condition.

With relays 0T6 and TK operated, the key calling lin KC is extended to the multiple extension SXl of the secretarys line SL and is therefor now connected to the calling end of the connection established to the secretarys line SL. It remains now to be described how the hold condition placed on the line by the secretary is removed. This hold condition, as hereinbefore described is efiected by the holding bridge comprising the bottom winding of relay I26 and non-inductive winding l28 which were connected across the conductors 254 and 255 of the line SL when the hold key HK was operated. This holding bridge i the means by which relay SY is operated. When relay El operated due to the operation of relay E as above described, the operating circuit for slow-to-release relay SR is opened. This relay, due to its slow releasing characteristic holds operated for an interval after the operation of relay El. At its first upper and its lower armatures, relay El opens the lineconductors of the secretary' line SL towards the secretary's station S. These line conductors are also opened at the armatures of relay SR until relay SR restores them to reestablish the continuity of the line conductors. Thus, for an interval correspending substantially to the release time of relay SR the secretary line SL is disassociated from its jack terminals so that the exchange battery is disconnected from the line SL causing relay l26 to restore. The restoration of relay I26 removes the holding bridge from the line SL in the manner previously described. When relay SR eventually releases its armatures, the line SL i again extended to the term nals of Jacks JS at the exchange. The party at the key calling station may now converse with the party on the calling end of the connection.

The connection just described is released in substantially the same manner as the connection involving the two-way private branch exchange line hereinbefore described. This connection may be picked up again (prior to its release) by the secretary if such action is required. If theparty at the key calling station wishes to transfer the call back to the secretary, the secretary is told verbally to pick up the call. When the secretary picks up the line SL by actuating the key KI and removing the handset 120 from its mounting. relay 'SY operates from the exchange battery over the closed loop at station S and when the party'at the key calling party station disconnects, relay E releases causing the release of relay El and the operation of relay SR. Relay El at its second upper armature removes ground from the winding of relay B in the supervisory circuit causing this relay to restore its armatures. Relay B opens the locking circuit for relay 0T6 which releases its armatures thereby opening the operating circuit for relay TK and releasing the multiple extension SXl of the line SL. Thus the connection established by the party at the'key calling station is released when the connection is picked up by the secretary and the party at the key calling stat on disconnects.

Outgoing call by way of one-way private branch exchange line I When it is found desirable to furnish a key line is seized in the same manner as areother lines such as the two-way private branch exchange line circuit 2LX or a line extending to one of the frequently called stations. More particularly, a call to the exchange over line LX is initiated at station A by the removal of the handset l0! from its mounting and by the actuation of a key button assigned to the line LX. In

the present disclosure a connection between the key calling station line KC and the one-way branch exchange line LX is completed when key button No. 10 at the station A is actuated after the removal of the handset [M from its mounting. It is believed unnecessary to describe the operation of the supervisory equipment (Fig. 2) incident to the removal of the handset l lll from its mounting since this description has been made previously in connection with a call extended by way of the two-way private branch exchange line 2LX.

When the key button No. 10 is actuated at station A, rectifier control switches R2 and R8 are closed to effectively connect the rectifiers 22 and 88 to the tip and ring conductors T and R, re--.

spectively of the line KC. As shown in the table of Fig. '7 register relays 2 and 8-operate in response to the actuation of key button No. 10. It is believed unnecessary to trace the operating circuits for relays 2 and B of the register circuit at this time since they have been describedin detail hereinbefore. Sufiice it to say that when these relays operate, they look operated under the control of relay C and establish an operating circuit for connector relay GT4. Relay GT4 operates in a circuit extending from grounded battery, winding and normal make-before-break contacts of relay GT4, conductor L2, front contact and fourth lower armature of register relay 2, normal contact 34l of register relay l, normal contact 340 of register relay 4, first lower armature and front contact of register relay 8,'conductor 334, back contact and armature of relay FW (relay FW releases when .the No. 10 key button at station A is restored), back contact and upper armature of relay LO, front contact and first lower armature of relay L. Relay GT4 locks in a circuit extending from grounded bating from grounded battery, resistance 251, back contact and first lower armature of relay SLX, front contact and third upper armature of relay 0T4, conductor 405, back contact and first lower armature of relay SW, conductor 2 l4 of link KL,

back contact and second upper armature of relay HR, upper winding of differential relay DF, first upper armature and front'contact of relay TK, front contact and second lower armature of relay TK, ring conductor R of line KC. through the closed loop at station A.-tip conductor T of the line KC, third upper armature and front contact of relay TK, front contact and first lower armature of relay TK, lower winding of difl'erential relay DF, first upper armature and back contact of relay HR, conductor 2? of link KL, second upper armature and back contact of relax

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