US1588437A - Telephone system - Google Patents

Description

June 1s ,"1926. 1,538,437 Y l R. S. BAILEY TELEHONE SYSTEM Filed NOV 25, 1923 2 Shets-Sheet 1 LTE " ing circuit.

Patented June 15, 192.6.

l UNITED STATESl PzvrEN'l OFFICE.

RAND S. BAILEY, OF MONTCLAIR, NEW JERSEY, ASSIGNOR TO AMERICAN TELEPHONE I AND TELEGRAII-I COMPANY, A CORPORATION O F NEW YORK.I

TELEPHONE sYsTE-M.

This invention relates to telephone systems and more particularly to systems wherein calls incoming to an exchange may be handled by any one of a plurality of operators.

Among the objects of this invention is to provide improved means for concentrating vtraffic incoming to a telephonev exchange.

This object is attained in accordance with a feature of the invention by the provision of a two-movement line iinder having permanently associated therewith a connecting link terminating at an exchange in a plurality of multiple answering jacks. By this arrangement a call originating at anyl one of a plurality of lines accessible to the line finder comes into the exchange over the connecting link and is displayed at a plurality of operators positions by'means of multiple line lamps.

Another feature of` in the provision of a slow releasing relay associated with the linefiinder'which permits an operator to disconnect her connect-`r ing circuit from association with the linev located, and its second movement (rotary) finder without releasing the line finder.

A still further feature resides in the provision of a testing relay in an operators connecting circuit which operates in response to the connection of the connecting circuit to a busy line to short-circuit the answering supervisory relay of the connecting circuit, thereby preventing its operation to eifect the connection of the operators telephone set with the connecting.

circuit.

vision of a group of keys common to a plurality of connecting circuits, the actuation of one of said keys causing the application of ringing current to thecalling end of the connecting circuit, and the actuation of another 'of said keys preventing the application of ringing current to the connect- Heretofore expensive and complicated arrangements have been provided by means of which the connecting lcircuit automatically differentiated between an ordinary line and a trunk and whereby the application of ringing current to the trunk was prevented. By means of the present arrangement a standard method operation is achieved whereby a key of some nature is always operated whether the line connected "i to be a regular subscribers line or a trunk he invention resides plurality of multiple answering jacks at a telephone exchange. The structure ofthe switch or line finder is of they general type disclosed' in the Patent No. 972,874f-fB. Kugelmann-October 18,1910, and is adapted 'in its present disclosure to accommodate a group of one yhundred subscribers` lines. The switch isv atwo-movement switch, y.its iirst movement (vertical) selecting a group of ten lines in which the calling line is selecting the specific line inthe selected group. f

Fig. 2 shows the operators connecting or link circuit .C which is adapted to complete connections between the calling subscribers7 lines such as A and B and a station on the four-party line L. The commonl `ringing 4equipment employed in signaling the various subscribersl on the party line L isalso ,f f y shown in this A still further feature resides in the .pro-

igure.

In the following description, the subscriber at station A will be considered the calling subscriber and any one of the four parties on the line L the called subscriber.

The subscriber at station 'A to initiate a callremoves the receiver from the switchhook, whereupon a circuit is established extending from grounded battery throughV the winding of the start relay 100, winding c of the line relay 101, back contact and 'right-hand armature of cut-off relay 102,

over the subscribers closed line loop, inner armature and back contact of relay 102 to v ground. The start relay 100 is common to a group of ten lines.

Upon operating, he start relay 100 connects, at its contacts 104, ground to the instart lead 103` of the regula-r first choice y selector or line finder F,'provided that this switch is available for use. As indicated on the drawing by the lead 105, the instart lead 103 is adapted to be cutthrough Y yto the nert succeeding switch if the rst Vsvvitch 'isy busy.

Assuming the switch F to be free to handle the incoming call, the stepping relay 106 now operates in a circuit extending from groiuided battery through the Winding of relay 106, armature and back contact ofthe vertical magnet 107, varmature and back contact of the rotary magnet 108, contacts v109 of the oil-normal switch 110, back contact and louter right-hand armature of the oth normal relay 11.1,-in4start lead 103 to ground vat the contacts 10a and armature et' the start relayf100. As soon as thest'epping relay 106V opera-tes, the verticalinagnet 10T operates in `a circuit extending from ground'edv battery through the Winding'of the vertical magnet 107, back contact and right-hand ari'nature of the transfer relay 112, front contact and armature'of stepping relay 106, and thence fio-'ground on the in-start'lead 103 over the circuit hereinbefore traced. The vertical magnet 107 in operating -raises the brushes ofthe switch F vone level, and in addition opens the circuit for the ,steppingrelay 106. The stepping relayA 106 in releasing opens the circuit 4for the vertical magnet 10'?, whereupon this `magnet releases.v Upon the rise of the switch brushes to the 'first level due to the' operation of' the r'vertical 'magnet y 1 0?, the of-normal'svvitch 110 is actuated, whereupon the circuit tor the stepping relay v106 is transferred rfrom ground on the instart llea'd103` to ground at'the back'contact and right-'hand armature of the hunting relayj1f13. y

rThe Winding of the transfer relay 112 is now connected through. the commutator brush 114C tothe lirst commutator segment 115.V It the called 'line is located on the lirstlevel of 'the'switch Yor line finder F, the transfer re- "lay '1t12vvill operate throughthev commutator segment 115 to ground at thecontacts 116 andarmatu're of the start relay'100. In the event thatthe calling lineA is not located on the first level of the switch, the stepping relay 106 and the vertical magnet'107 will continue to' operate alternately, to rthe vgroun d at tthe baclr'contact and rarmature of the fhuntingrelay 113, until the vertical magnet- 10'? vvhais vraised the brushes'to the level in which `the calling-line is located, at Which time' the transfer yrelay 112 will operate through'the grounded coinmutator segment, Vand lock to the baci;A contact ground onthe limiting relay 113. Y

Upon operating, the transfer relay 112 substitutes the rotary magnet 108- for the 'vertical magnet I107 in the stepping circuit with the stepping relay 106. The stepping 4relay 106 and rotary magnet 108 yWill then operate"alternately to cause the Vswitch F to 'to extend `the call.

rotate its brushes 'in the particular level in Search of the calling,r line.

When the line relay 101 operated, it con-v nected 'ground toy the terminal 117 on the -multiple bank, and Vas the rotary magnet Y'l 10S advances the brushes to this line, the hunting relay 113 operates in a circuit extending from grounded battery, through the Winding of relay 113, outer left-hand armature and back Contact of oit-normal relay 3 111, brush 113, terminal 117 to ground over the {Tont'contact land armature oi the line relay 101. Y Y

-Relay 113 in operating Vremoves ground from the rotary stepping circuit to prevent further rotation of the brushes at switch F,

At its ar1natures119' and 120, relay 1 (1'3 conu nects thetip and ring conductors of the'caling line to corresponding'terminals oi the multiple 'jacks 130, 140, 150andl 160. In attracting its armature 121, relayV 113'closes through thesleeve'conductor of theY calling line. v

Relay 122 now operates in :a circuitextending from grounded battery through the left-hand Winding ot relay 122, middle armature and back contact o't' cut-ott1 relay 123, front contact and armaturef oi relay 113, brush 124! and Yterminal' of svvitch F,

over the closed subscribers line loop, tervminal 126 and brush 127 of'svvitch F, armature '119 and front'contact of relay 1:13, back contact and outer armature of Vrelay 123 to ground through'the rightihand Winding of relay 122. The windings of relay 122 are of low resistance andf'the'reore. when this relay is connected to the calling line, the line relay y101 and the start relay'100 are shunted,

whereupon these relays release. Relay 122 in attracting its right-hand karmature establishes obvious 'circuits for the line lamps 131, 1111, 151 and 161 causing these lamps to 'be illuminated. VArt its left-hand armature relay 122 causes the slow releasing relay 123 to operate in a circuit extending 'from grounded battery through the winding of relay 123, left-hand armature and front contact oft' relay 122, to groundat the front con- Vtact and' right-hand armature of relayY 113.

V'Slow releasing relay 123 in operating provides'an auxiliary holding'circuit 'for relai/ the release'magnet 132, the completion which is effected when the hunting relay 113 restores. At its outer lleft-hand armature relay 111 opens the hunting lead,it now being noted that the hunting relay 113 is held operated undery the control of the calling subscriber.

An operator at the telephone exchange, upon noting the illumination of one of the line lamps 131, 141, 151 and 161, and who is free to answer the call, inserts the plug 200 associated with one of her connecting circuits into the jack, such as 130, located at her position, whereupon a circuit is established extending from grounded battery, through the lower left-hand winding of repeating coil 201, winding of supervisory relay 202, ring contacts of plug 200 and jack 130, front contact and armature 120 of relay 113, brush 124, terminal 125, over the closed subscribers line loop, terminal 126, brush 127, armature 119 and front contact of relay 113, winding of supervisory relay 133, tip contacts of jack 130 and plug 200, to ground through the upper left-hand winding of re peating. coil 201. Relay 133 operates in this circuit and establishes' an obvious circuit for thecut-off relay 123. Relay 123 at its two outer armatures disconnects the switch line relay 122 from the talking conductors, and at its inner armature substitutes a new holding circuit for'slow relay 128, it being noted that the original holding circuit 'for relay 128 is opened by the release of relay 122. Relay 122 in retracting its right-hand A armature causes the multiple line lamps 131, 141, 151and 161 to be extinguished'.

Relay 202 also operates in the above traced circuit, preventing the illuminationvof lamp 204 at this time and 'connecting the listening relay 205 to the sleeve conductor of the cord, whereupon this relay operates in a circuit extending from grounded battery, through the winding of relay 205, normal make-before-break contact-sof relay 206, armature and front contact of relay 202, sleeve contacts of plug 200 and jack 130, front contact and armature 121 of relay 113, brush 136 and terminal 135 of switch F, winding of the line cut-oll relay 102 to ground. Relay 205 in attracting its lower armature disconnects ground from. the winding of the test relay 203 and in attracting its other armatures connects the operators telephone set, indicated at O. T. to thev talking Conductors of the connecting circuit C. The cut-off relay 102 operates in the circuit above traced to cut off the subscribers line relay 101 from the calling Vsubscribers line. Although there is an apparent tendency for a race at this time, between the listening relay 205 and test relay 203 (it being obvious that with relay 202 operated the test relay 203 may operate from grounded battery through the winding of relay 205, normal make-be-V fore-break contacts of relay 206, armature and front contact of relay 202, armature 212 and back contact Vof relay 206, winding of test relay 203 to ground at the back contact and lower armature of relay 205) relay 202 is made slow-to-release so that should relay 203 operate at this time and momentarily short circuit relay 202, relay 202 will hold up until relay 205 operates to open the circuit for relay .203.

The operator now ascertains the details of the call from the calling subscriber, and upon learning that a subscriber on the line L is desired, she 'makes the usual busy test on the line L, and finding the saine idle, inserts plug 208 into the jack 207 of the desired line. As a result of the insertion of plug 208 into jack 207, relay 209 operates ina circuit extending from grounded battery through the winding of relay 209, back contact and right-hand armature ofrelay 210,

sleeve contacts of plug 208 and jack l207 to ground. Relay 209 in attracting itsarmature 211 establishes an obvious circuit for relay y206, which relay thereupon operates. In attracting its armature 212, relay 206v rc- Inoves the winding of the test relay 203'from the sleeve conductor of the answering end of the connecting circuit C. l-Atits arma-` ture 213, relay 206 locks up to the sleeve of the calling end of the connecting circuit and at its armature 214'it opens the circuit for the listening relay 205, whereupon this relay releases,` disconnecting the operators telephone set from the connecting circuit, and also connects battery to the answering` sleeve circuit to hold the subscribers cut-oliE relay 102 operated. The current from this battery is not sufficient to operate the message register magnet 166. In attracting its armature 215, relay 206 closes its contacts 216 and 217 for purposes which will hereinafter appear.

Relay 218 now operates in a circuit eX- tending from grounded battery, over the back contact and outer right-hand armature of relay 220, winding ot' relay 213, .tila

Vment of lamp 221, back contact and arma-- ture of relay 222 to ground at the contacts 216 and armature 215 of relay 206. The lamp 221 is illuminated in this circuit. Rclay 218 in operating causes the chargerelay 219 to operate over an obvious circuit, in

order to prepare the .message register mag` net 166 for operation. The magnet 166 automatically operates when a called subscriber answers, as will hereinafter appear.

Should thecalling subscribers request a party h connection, the operator actuates the key M, thereupon connecting ground to its contacts 237, 233, 239 and 242. At the contacts 237 a circuit is established from ground on thecontacts 237, over the con v ductor 243, armature 244 and front contact of relay 209, winding of relay 245 to battery and ground. vRelay 245 operates in this -tures removes the short circuit from the ring-back tone condensers'2-l6 and 2li-7. At its inner loWer armature relay 245 locks in a circuit Whichrnay be traced troni grounded battery, through the Winding, front contact and inner lower armature el relay 245, armature and back Contact of marginal relayA 253 to ground at the .contacts 216 and erniature 215 ot relay 206,. At the contacts 288 of ke f M a circuit is established which Ina be traced from Ground at the contacts 238 E 7 armature 2-19 and front Contact oi' relay V209, Winding oit" relay 252 to battery ,and ground.

Relay 252 operates in vthis circuit and in attracting its right-handv armature locks itself in a circuitV extending troni grounded battery, through the Winding otl relay 252, 'front Contact and ri gilt-hand armature of relay 252, armature and bach Contact o'j marginal relay 253 to ground at the contact 216 and aru'iature 215 of relay 206. Alt its inner left-hand arniature relay 252 prepares a circuit tor relay 251i, which VWill be completed in the `following description. 252prepares a circuit `for tlie'transinission oit a special code of ringing current, as Will :hereinafter appear. rit the contacts ol lrey M a circuit is established trein ground at the contacts 242 of hey M', 'armature 255 andV trent contact ofl relay 209, through th Winding of relay 256-to battery and ground. Relay 256 operates in this circuit and at its right-hand armature locks itself in the saine locking circuit asv hereinbe'l'ore traced for relay 24:5. YAt its inner lett-hand armature Arelay 256 connects ground to the ringconductor of the calling end of the connecting circuit C, and at its outer lett-hand arniature it prepares the tip side oi the connection tor the transmission ot ringing current. At the contacts 239.01" key li/l a circuit is established for the lett-hand Winding of relay 210 by Way of the arinat-ure 59 and front contact of relay 209. Relay 2l() operates in this circuit and locks through its right-hand Windingto ground on the sleeve the calling end of the connectingcircuit C. Relay 210 in operating opens the circuit for the start rela-y 209, which relay thereupon releases, it being nonY understood that the relays 245, 256 and; 252 are locked to .ground at the contact 216 of arinature'2l5 of relay 206. Y

lfvlhile the brush ot' interruptor` 258 is on a conducting segment, current troni battery 25"? flows over the conductor 260, over the nor- Y inal inalre-before-break contacts and Winding of relay 254e to Vground at the liront contact and inner lett-hand armature Yof relay 252. ln attracting its right-hand armature f t its outer lett-hand armature lrelay 'nessus-37 current supply through the interruptor 262, Vconductor 261, front Contact and lett-hand armature otv relay. 254, front Contact vand outer lett-hand Vvarmature ofrelay Y252, letthand armature and back Contact oi' relay 209, Winding otinarginal relay 253, outer left-hand 'armature and front Contact ot relay 256, front contacta'nd upper armature of relay 245, 'tip contacts off plug 208 vand jack 207 to ground through the bells at stations M and J. The current in the circuit j ust traced is not suliicient to' cau'sethe operan tion oi marginal Arelay A253 at this time. Both subscribers at stations M and J hear ythe ringing signal,fbut the "subscriber at station M rrecognizes the codeand answers lthe call, Whereas the subscriber at J does not recognize the signal as his, and does not answer the call. f

Should the calling subscriber ask :tor a connection with the subscriber at station'V J, the operator actuates key J, thereby connecting-ground to contacts 261, 262 and 268. The closure ot' the contacts 261 causes relay 2'fl5 to operate in the Vsaine -inanner as described in connection vwith the 4operation,oit key M. The closure of 'the' contact-S262 causesrelay 256 to operate-in a inanner siniilar to that described in thepreyious connection. The closure olE the contacts causes the sleeve-relay 210 to operate and lool lt Will be noted that lWhen key il is actuated, relays 252 `and 254 'do not enter into the ringing operation. Relays 245, 256 fand'2l0, in operating'per'form the same functions as hereinbetore described in connectionwith the previous signaling opera-tion. A A'circuit for a special code of ringing current'now traverses a path which inay be traced from Vthe ringing current supplythrough'theV interrupter 26a, conductor 265, back Contact' and outer lett-hand'armature fot relay 252, leithand arn'iature and back contact of relay 209, through the Winding of marginal relay 253, outer left-hand armature and liront Contact of relay 256, front contact and upper armature of relay 245, tip contacts ot plug and jack '20'7to 'ground through the bells at the subscribers Vstations M an'diil.

The subscriber at station J lresponds to the signaling'currentat this time, Whereas the subscriber M does'not heed the signa-l.

Upona request fora party liti conncction, the operator actuatestheikey lt, thereby connecting ground lo theY contacts 266, 267 and 26S. The saine relays ,-vhich were opera-ted in 4responso to the actuation oi key ha', withV the exception ot' relay 256, are now operated so that the path for the ringing current may be trac vd fronr the ringing current supply through the interrupter 262, conductor 261, front Contact and lett-hand armaturerof relay 254i, 'front contact and outer left-'hand armature ot relay 252, left-hand arinatme and back. contact ige of relay 209, winding of marginal relay 253, out-er left-hand armature and back contact of relay 256, front contact and lower armature of relay 245, ring contacts of plug 208 and jack 207 to Aground through the subscribers bells at stations R and 1V. Though the bells at both stations R and 1V are actuated in response to this signaling current the subscriber at station R recognizes the code as his signal and answers the call, whereas the subscriber at W does not heed the signal.

Should the calling subscriber request a party 1V connection, the operator actuates key V, thereupon connecting ground to the contacts 270 and` 271 so that only relays 245 and 210 of the ringing relays operate, the circuits for these relays now being obvious. The ringing current path may now be traced from the ringing current supply through the interrupter 264, conductor 265, back contact and outer left-hand .arma-v ture of relayv 252, left-hand armature and back contact of relay 209, winding of marginal relay 253, outer left-hand armature and back Contact of rela-y 256, front contact and lower armature of relay 245, ring contacts of plug 208 and jack 207 to ground through the subscribers bells at stations R and 1V. TheV subscriber. at 1V only, recognizes this code and proceeds to answer the call in the usual manner.

Vhen the desired party at a station, such' as M, in response to the incoming signal removes the receiver from the switchhook, the condenser 272 is shortcircuited and a new circuit for the ringing current is established which may be traced over the original ringing current circuit as far as the subscribers line and then through the transmitter and receiver switchhook con'- tacts to ground on either the ring or tip conductors of the connecting circuit, depending upon whether or not relay 256 was operated. This circuit includes the winding of marginal relay 253, and due to the fact that the condenser 272 is short cireuited, the resistance of this circuit is sufficiently reduced so as to permit this relay to operate. Relay 253 in operating opens the locking circuit for relays 245, V256 and 252, releasing them if operated, thereby restoring the ringing equipment to normal. y.

Vhen the called subscriber responds, a circuit for relay 222 is established which may be. traced from grounded battery, through the lower right-handwinding of repeating coil 201, winding of relay 222, back contact and lower armature of relay 245, ring cony tacts of plug 208 and jack 207, over the closed subscribers line loop, tip contacts of jackl 207 and plug 20S, upper armature and back Contact of relay 245 to ground through the upper right-hand winding of repeating coil 201. Relay 222 in operating opens the left-hand armature andy back contact ofy slow releasing relay 218, front contact vand armaturel of relay 222' to ground over the jcontact 216 and armature 215 of relay 206.`

Relay 218 released when relay 222 operated. Relay 220, operating in the circuit just traced, connects the high voltage battery 275- to its frontcontact and left-hand armature,

whereupon current therefrom flows momentarily over the front contact and armature of the slow to release' charge relay 219, sleeve contactsiof plug 200 and jack 130, front contacts and armature 121 of relay 113, brush 136 and terminal`135 of switch lF-to` ground through .the winding of the message register magnet 166. The magnet 166 inoperating on this momentary pulse causes the' message registering device -to operate to register the call. Relay 220 in operating locks to ground on the contact 216 and armature 215 of relay 206 in order to prevent further registration on thisconiiection. Y out part of its winding and thereby increases the flow of current in the other part .so that hereafter such magnet will remain energized on the cord circuit battery. It

Magnet 1667in operating shunts should be noted that relay 219 is so adjusted Y as to hold operated until relay 220 has closed its contacts.

It will now be assumed that the conversation between the calling and called subscribers has terminated and the subscribers l Y have replaced their receivers on their spective switchhooks. f

When the calling subscriberhangs up the receiver at the termination of the conversation, the circuit for the supervisory relay 133 is opened whereupon this relay releases and opens the circuit for'the cut-off relay 123; Relay 123 in retractiiig its two outer a armatures reconnectsrtheswitch line relay 122 to the switch. At its inner armature, relay 123 opens the holding circ-uit for slow releasing relay. 128, whichrelay after an interval, restores to` normal. Relay 128 in retractiing its armature, opens the holding circuit for relay 113v which relay releases and also opens the original energizing circuit for the off-normal relay 1 11, which relay, however, is held operated to ground at thev contacts 129l ofthe otlnormal switch 110.

Relay 113 in releasing its left-hand armatures, disconnects the tip, ring and sleeve` brushes 127, 124 and 136 of the line' finder F from the multiple answering jacks. At its right-hand armature, relay 113 connects ground to the winding of the release magnet 132 by way of the inner lleft-hand armature and front Acontact of relay 111, whereupon,

the release magnet 132 Voperates to restore the lineY inderto normal position. When the line finder returns to normal, the ofi-k normaly contacts 129. are opened, whereupon relay 11.1 releases disconnecting the release magnet from ground at theright-hand armatureV ot relay 113. 'lllieswitch apparatus and all equipment shown in Fig.' 1 are now in normalposition.

lVhen the calling subscriber hangs up, the circuit for the answering cord supervisory relay 202 is also opened so that the laxnp202is lighted over a circuitextending from grounded battery, armature 214; and

'rontrcontact of. relayY 206, armature and;-

baclr contact of relay 202, iilament of lamp 204, contacts 217 and210 and armature 215 ofrelay 206. The illumination of lamp 2011V at: this time serves as a disconnect sig'nalzto the operator.. Y'

When the; called party` restoresl the. re. ce-iver to normal, the,V circuit for thecalhng supervisory relay 222 1s opened, whereuponV lamp221 is. lighted over a circuit extending from grounded batterythroughthe filament of lamp 221, back contact and armature of' relay 222, to ground over theV contacts 2164 and armature 215 et relay 206.

Upon receipt of a disconnectsignal, the operator may proceedto take downthe connectiong Upon withdrawing plug` 200 from Vjack-130 no cord circuit equipmentis affcct-ed, since the sleeve conductor of the answering end of the cord is opened' by the release ofV relay/'S1202 and' 219 andr by the operation of` relay 206. plug 2081from jack-207 causes the openingof theV locking circuits Yfor relays y210- and 200.y Relay 206 in'a releasing its armatures, opens the circuits for the lamps 20-1 and 221 whereupon these lamps are extinguished and also opens the locking circuitv for relay 220,1

whereuponl this relay releases. rllhe cord circuit equip-nient Vis now Vin normal7 condition. "i

Relay 128 associatedfwith the line finder F is made slow releasing soasto enable an i operator to remove the answeringi plug 200 from the jack; 130 Without causing the release ofthe line finder. Vihen the plug 200` is Withdrawn fromy jack 130 and' when the subscriber atd station A, is on the line, relay 133 releases. and opens the 'circuit for the cut-oli' relay 123, which relayV thereupon re- In retracting its inner.

tracts its armatures. armature, relay 128 opens the holding circuit for relay 128, but at its tWo outer armatures, relay 123-1'econnects the'switclrli'ne relay 122 to the calling linev and thisrelay immediately operates over the closed subscribers line loop, and at its left-handfarmature establishes another holding circuit for relay 128, which relay therefore remains operated and preventsthe release of relay The Withdrawal oli 113 and the subsequent operation of thereleaseinagnet 132. Ait its right-hand armature, relay 122l again causes the illuminaf tiongof the multiple line lamps.A Should the ycalling subscriber flash under this condition7 relay 122 will follow the switchhoolr actuations and cause the vflashing of the line lamps. Relay 128, however, Will remain Operated to prevent the release of the line finder.

If the calling subscriber in the previous descriptions requested aconnection which necessitated the employment ot a trunk. circuitwhereinno application of' ringing cur; rent is required, the operator would insert plug. 208 into the trunk jack 280 of the se-v` lected trunk and actuate the trunlrlrey, T. The same relays which were operated kwhen plr-.g 208was inserted into jack 207 operate uponthe insertion ofl the plugv 208 intolthe. y trunk jack 280. The closure of. contacts 281 of key T causes relay 210. to` operate and' lock to the sleeve oit the calling endfot the connecting circuit, andthe disconnection of of the jack 130 and all the multiple jacks became a busy potential' by reason of the current flow through the winding o-'relay Y205 of the lir'st cord in series with the' Winding of relay 102 in the line circuit.

of the calling line, the :battery on. thesleeve thereolt1 causes thetestrela-y 203 or' the second cordcircuitto operate in a circuit extending. from battery on the-sleeve of jack 140,- sleeve of the answering plug of the secondcord,

armature 212 andbaclr contact of relay 206v of the second cord, Winding of test relay- 203 of the. second cord to ground atl the back contact and lovverr armature of the listening relay 205V of the second cord The second cord test relay 203 thereupon op* erates to short circuit the secondcord supervisory relay 202 and prevent its operation,

Since relay 202 of the second cord cannotoperate, the circuit for the secondcord listeningrrelay 205k is held opened at the front contact ofthe second cord relay 202. Therefore, this relay cannot operate and the Second operators headset cannoty be connected to the calling line. Under such a condition, the operator upon receiving no communica? Upon. the insertionA oft. plug 200V lefhen a 'second operator inserts one` ot Vhe;` answering plugs into the ]acl 140 ics 'f' nectthe calling line to said link circuit,

a relay operated in response to the connection ot' the calling line to said link cincuit for maintaining said line finder in its operated position, and means responsive to the seizure of said link circuit at said telephone exchange for deenergizing said relay and maintaining said line finder in its operated position.

2. In a telephonesystem, a telephone exchange, a link circuit terminating therein Ain a plurality of multiple jacks, a two-Inovement line iinder, a plurality of telephone lines, means responsive to the initiation of a call on one of said lines for operating said line finder to connect the calling line to said link circuit, a relay actuated in response to the connection of the calling line to said link circuit, a slow releasing relay controlled thereby, a cut-oli' relay actuated in response to the seizure of said link circuit at said telephone exchange for deenergizing said iirst relay and controlling said slow releasing relay, and means controlled by said slow releasing relay for restoring said line finder to normal position.

3. In a telephone system, a telephone exchange, a link circuit terminating therein in a plurality of multiple terminals, a twomovement line nder, a group of lines accessible to said line nder, means responsive to the initiation of a call on one of said lines for operating said line finder to 'connect the calling line to said multiple jacks and for placing said line finder under the control of the calling line, means responsive to the lseizure of said link circuit at said telephone exchange for placing said line finder under the control of both the subscribers on the calling line and the answering operator at said exchange, and a slow releasing relay controlled by said last mentioned means for maintaining said line finder operated when said link circuit is released at said telephone exchange.

4. In a telephone system, a telephone exchange, a link circuit terminating therein in a vplurality of multiple jacks, a group of telephone lines, atwo-movement line finder, means responsive to the initiation of a call on one of said lines for operating said line finder to connect the callingline to said link circuit, a slow-releasing relay controlling said line finder, a relay controlled from said calling line and operated in response to the connection of said link circuit with said calling line to cause said slow releasing relay to operate to maintain said line inderin its operated position, and means responsive to the seizure of said link circuit by way of one of said multiple jacks for deenergizing said second relay and substituting a holding circuit for said slow releasing relay, thereby placing said line finder under the control of both the calling line and the telephone exchange, said means being released when said link circuit is released at said telephone exchange to place the line finder-under the sole control of the calling line.

In testimony whereof I have signed m name to this specification this 21st day of November, 1923.

RAND s. BAILEY.

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