US1882753A - Telephone system - Google Patents

Description

Oct'. 18, 1932. BQWNE 1,882,753

TELEPHONE SYSTEM Filed May 29, 1931 5 Sheets-Sheet J O 9 Q5 N l2 INVENTOR L.J. BOWNE 8) W7 Oet. 18, 1932. J, BQWNE 1,882,753

TELEPHONE SYSTEM Filed May 29. 1931 5 Sheets-Sheet 3 'g-"IIIHI INVENTOR L J. BOWNE Y A Tm/PNEY Patented Oct. 18, 1932 U ITED stares PATENT OFFICE LANeEoR-n J. BOWNE, OE HOWARD BEACH, EW YORK; 'AssIGNoR'To BELL TELEPHONE LABORATORIES, INCORPORATED, OE NEW YORK, N. Y; A CORPORATIO OE NEW YORK TELEPHONE SYSTEM Application filed May 29, 1931. Serial NO. 540,839.

nections established by means of a local op-I erators cordbetween a local subscribers line and a line to a distant exchange, when the local subscriber hangs up his receiver on.

the switchhook to disconnect, the connection through the cord is split. Thisis for the purpose of preventing the subscribers station from being signaled in case a call is incoming over the line used in this connection before the operator has removed the cordfrom the local subscribers line. Heretofore', this;

splitting has been done by the Operation of a slow-to-operate relay which operated when the subscriber replaced his receiver on the, switchhook. The operation of this relay was.

made slow in order to prevent it from operating during momentary openings Ofthe connection such as occur when the switchhook is flashed bythe local subscriber or when supervision occurs from the distant ofiice. In modern telephone practice the talking current has been increased in circuits of this ,lrind which made it'more difiicult for this slow-to-operate relay to function with a desired uniformity under all conditions of volt- I variations which may occur due to the different transmission characteristics of the connected lines.

It is a feature of this invention to overcome such variations in the periods of delay of the splitting of the cord by providing a circuit arrangement whereby a slowtorelease relay is maintained operated while the connection is established 'and permitted to release when the subscriber replaces his receiver on the switchhook for the release of the connection. The circuit for this slow-to-release relay is controlled by the usual supervisory relay included in the line connection. By this means the periods of delay in splitting of the distant exchange.

cord are made uniform as they are controlled by the slow'-to-release characteristic of this relay independently of the voltage variations on the line.

i In establishing a connection to a distant exchange over a line the circuit for the above mentioned splittingrelay must be put under control of the supervisory relay when the through connection is finally completed and the call is answered by the operator .at the This supervisory relay, however, operates as soonas the local operator answers the call from the local subscriber for supervisory purposes, it is then momentarily released, and finally transferred under control of the battery and ground connection established over the tip and ring conductor when the operator at the distant exchange answers the call. It is, therefore, a further feature of this invention in order to prevent the false release of the splitting relay during the transfer period to establish circuit conditions whereby the splitting relay 'is operated and held by a local battery and ground connecton in the cord as soon as the connection to the distant exchange line, is established and then transferred to the control by the supervisory relay when this latter relay is finally operated.

When the local subscriber hangs up his so receiver on the switchhook to cause the connection to the distant exchange to, be split, a battery and ground connection is established from the cord to the subscribers line for the purpose of permitting the subscriber. 5 r to make a recall on the connection. Under these circumstances, a surge of current may occur in the circuitdue to the battery and ground connection chargingthe condenserin the subscribers telephone set. It is a go feature of this invention to prevent this surge from'disturbing the established circuit conditions in the cord, such as for example, to falsely establish a bridge across the connection to cause a false signal at the centralv office. To prevent such disturbances acirouit arrangement has been provided forshort-circuiting one winding of the battery feed relay that would initiate such false signaling by its operation, due to its being inconnection, the-connection through the cord is reestablished :by the splitting relay-independently of the supervisory relay in the cord and the splitting relay is not placed under control of the supervisory relay until the supervisory relay isoperatedii'n response to current received overthe established connection from the distant exchanges. Hence in case of along line connection :where the transmission characteristics may cause the operation of the supervisory ,rel-ay tobede- "layed thisdelay ;will notfinterfere with the proper function of the splitting relay in establishing a through connection. This is accomplished by'having the special battery feed relay operate when the subscriber lifts his 'receiver'fromthe switchhook and having this relay shunt the supervisoryrelayto per- ".mit the operation of the splitting relay.

WVh'en'the currentis received from the dis- "'tant exchange thesupervisory relay operates and causes'the control over the splitting re- Llay .to 'be transferred to the supervisory relay.

Another :feature of this invention is an arrangement whereby, when a connection is established to a-centra'l otlice,the subscribers telephone is shunted while the battery and ground connection for the tip and ringconductors is;shift.ed from a supply in the cord to a'supplyatthe central office. This is to jprevent clicks in the subscribers receiver during this transfer. The arrangement is such that when the cord is extended'to the central ofiice trunk a short circuit is placed through the cord circuit. Then when the connect1on is extended in the central oflice to the across'the subscribers 'line, the current sup- "ply atthe cord is then removed and a bridge is placed-across the tlp and ring conductors,

whereupon-the short circuit is removedand the tip, and'ring conductors are connected current supply-thereat thebridge is removed. It is another feature of-this'lnvention to short-circuit the operators receiver for a short interval while the operator answers a callmcoming over'a trunk in response to the operation of'tlietalking keyin the cord and "itheinsertion of the answering plug ofthis 7 cord intothe trunk jack.

It'isanother featureof this invention to short-circuit the operators receiver for a short {interval while she answers a call in comingover the trunk to which a cord is 'already connected. "This short circuit is testab'lished'bythe same means, namely, the

operation of the talking key and the condi- 1neans employed for short-circuiting the receiver'is also used asa means for tripping the ringing at'th'e central ofiice when the operator answers the call on a trunk, regardless of whether the call-is answered over a trunk to :which the cord employed'is connected or not, at the time of the call. This is accomplishedtby the establishing of abridge across the tip and ring conductors of the trunk for a short interval.

It is another feature of this invention to provide an arrangement whereby the same means that is used for 'short-circuiting the receiver while answering acall or for tripping the ringing is employed for short-circuiting the receiver during dialing over a central office connection and for maintaining the receiver short-circuited ashort interval after dialingto prevent disturbances or clicks in the-receiver due'to operations atthe central offfice effected by'the dialing.

Another feature o'f'this invention is an arrangement in tie lines employed in systems of this kind for automatically removing the repeating coil from across tie'lineconductors when ringing isappliedto the line on outgoing calls and thereby remove'the drain on the ringing current. This is accomplished by means of an alternating current responsive relay actuated by the ringingcurrent which relay in turn causes another relay to release and open a connection for the repeating coil and establish through connections for the line conductor to permit the ringing current to pass out on the line.

Another-feature of this invention is an arrangement in tie lines used in systems of this kind that have a separate jack for dialing a distant station, for preventing false impulses or interruptions of the connection through the .tie line to the distant station from occurring when the connection is switched from the .talking jack to the dialing jack. This is accomplished by means whereby the tip and Iring terminals of the dialing jack and the tip and ring conductors of the tie line are short-circuited when a cord circuit is connected to the dialing jack and means whereby Whenthe cord has-been prepared for dialing the following functions are caused to take place in the order named: To disconnect the tie line fromthetalking jack, to remove-the short circuit from the dialing jack terminals, to establish a through connection for the tip conductor, to establisha through connection for the ring conductor and to remove the short circuit from the tip and ring conductors of the tie line.

Another feature of theinvention is an arrangement 1n outgoing trunks employed in I systems of thiskind and in thecord circuit whereby-a ringing bridge normally connected across the tip and ring, conductors of the trunk is automatically removed during dialing. This is accoi'nplished by'haviiig a relay in the sleeve circuit of the trunk operate to remove the bridge when the dial is ofl normal, the off-normal contacts of the dial causinga low resistance shunt around a winding of the usual battery feed relay to be established for the operation 0 the relay in the trunk circuit.

In tie lines for private branch exchange systems of the above type surges may occur on the line to cause momentaryoperations of the alternating current responsive relay used for lighting the line lamp. Means has heretofore been provided for delaying the lighting of this lamp. This'means usually includes a slow-to-operate relay and at slowto-release relay. r

An arrangement of this kind is satisfactory when the voltage ofthe battery supply is comparatively low as the slow-to-operate relay willthen function, properly. In modern telephone service a'higher voltage battery is desirable and the slowto-'operate relay will not operate suiliciently slow under these oircumstancesto delay the operation of the line signal. t is therefore a further feature of this invention to provide an ar-' rangement whereby only slow-to-release relays ai'e employed in the circuit arrangement for delaying theoperation of the-line signal. The operation of the signal may therefore be delayfor the proper interval independent of the characteristics ofthe voltage of the operation current.- I

This invention has oeenillustrated 1n the accompanying drawings in which,

Fig. 1 shows acord circuit A and an associated' operators telephone circuit at a private branch exchange embodying features of and terminating in jacks at the private branch exchange and extending, to other pri vate branchexchanges. The figures may be arranged as shown in 6, i

To explain the various features of this in i vention in connection with these drawings,

descriptions will be made as follows: A call from the calling subscriber of line 1 over cord circuit A. in Fig. 1 and trunk 200 in Fig.2 to a distant exchange, the release of such a connection and a recall bythe subscriberv of line 1 of the operator before this connection has been taken down; second, a call incom 111g over trunk 200 and answered by th 0pand 24 to the operators set 17. [he ring con-- erator; third, an outgoing call from the 0perator over the tie line shown in Fig. 3;

fourth, an outgoingcall over the tie line shown in Fig. 4, and fifth, a call incoming over the tie line shown in Fig. 5. Referring now to the establishing of a connection from the subscriber of line 1 through cord A over trunk 200 to the distant exchange, the calling subscriber by lifting his receiver off the switchliook' causes theli'ne relay 2 to be operated to light the line lam 8 inthe usual manner. This call is answered by the operator of cord A by inserting plug nals of plug 5 and iack 6, subscribers loop,

tip terminals of jack 6 and plug 5, upper contacts of ringing key 12, upper winding of relay 7, upper middle normal contacts of dialing key 11, upper winding of relay 8 to ground at lower outer back contacts of relay 9. Relay 811 operating performs no useful-* function at this time. Relay 7 opens the 011'- cuit for supervisory lamp 15 which was closed in the sleeve circuit to ground onjack 6, when plug 5 was inserted therein. Ifit s assumedthat the talking key 16 has been op-'- 3139 erated before the call was answered to assomate the operators telephone 17 with the cord circuit, the supervisory lamp 18 will not operate in the above mentioned sleeve circuit as the circuit therefor'will be opened due to the operation of relay 19, as will hereinafter be described,

With the operators telephone set connected through plug 5 and jack 6 to the calling subscribers line the operator will now ascertain the desired number and if a connection to a distant exchangeis desired the operator will insertrplug 20 into the jack 201 of the trunk 200 leading to this distant exchange.

The immediate effect of this operation will 11 be the operation of relay 21 from battery,

' winding of relay 203, contacts of jack 201, the

sleeve terminals of this jack and plug 20, upper inner normal contacts of dialing key 11, winding of relay 21 to ground. Relay 203 being marginal in character will not operate in this circuit. Relay ineperating disconnects the calling subscribers line from the talking connection through condensers ductor is connected at the upper outer armature and front contact of relay 21 to the contact of the. upper innerarmature of relay 8 and the front contact of the upper outer armatureof relay 9. Relay'21 also disconnects" 13 sleeve terminals of plug 5 and jack 6 to battery at its upper inner armature and back contact from the upper winding of relay 19 and connects it to the winding of relay 9. Finally, relay 21 opens the sleeve circuit for lamp 18 at the lower inner armature and back contact. The operation of relay 21 closes a short circuit around the windings of relay 7 to cause it to release while relay 8 is maintained operated. This short circuit may be traced from battery, upper inner armature and back contact of relay 9, lower winding of relay 8, upper outer armature and front contact of relay 21, upper inner armature and front contact of relay 8, upper winding of this relay to ground at the lower outer armature and back contact of relay 9. The purpose of this short circuit across the tip and ring conductors is to prevent a click through the calling subscribers receiver which occurs when battery and ground is removed later by the operation of relay 9, and to prevent this relay from operating until relay 7 has released. When relay 7 releases it closes a circuit for relay 9 as follows: tery, upper makebefore-break contact of relay 21, winding of relay 9, upper inner armature and back contact of relay 25, lower makebefore-breakcontact of relay 8, lower armature and back contact of relay 7, sleeve terminals of plug 5 and jack 6 to ground at the lower made contacts of jack 6. Relay 9 in operating disconnects battery at its upper ar1na ture and back contact from the ring conductor of the calling subscribers line and ground at its lower outer armature and back contact from the tip conductor. This relay in operating also connects the lower winding of relay 19 across thetip and ring conductors as connected to the normal inner upper and lower contacts of talking key 16 to the tip and ring conductorsof the plug 20. This will serve as a holding bridge after the connectlon has been established Relay 9 also connects the tip and ring conductors from plug 5 to plug 20; at its upper outer armature and front contact for the tip conductor and at its middle lower make-b'efore-break contacts for the ring conductor. When re]ay 9 operates the above mentioned short circuit for relay 7 and the holding circuit for relay 8 is opened and this relay now releases. When relay 8 releases it permits relay 7 to operate over the loop extending through plug 26 and ack 201 to the battery and ground at the distant exchange over trunk 200. As relay 8 is now re leased relay 25v is operated over a circuit as follows: Battery, upper ma :e-before-break contact of relay 21, upper outer armature and back contact of relay 8, winning of relay 25, lower 1nner armature and back contact of this relay, armature and front contact of relay 7,

ground on jack 6. Relay 25 in operating provides a locking circuit for itself through its 7 lower make-before-break contact and lower armature and front contact of relay 9 to the ground on jack 6' under control of relay 9. Relay 25 in operating opened at its upper outer armature and back contact the holding bridge through the lower Winding of relay 19 and by closing its upper make-beforebreak contacts transfers the control of relay 9 to the sleeve circuit closed by relay 7.

If the call is to be extended to a dial central office the operator will dial the desired subscribers line as follows: As the talking and dial key 16 is operated the immediate effect will be the operation of relays 26 and 27 over a circuit from battery, winding of relay 203, the sleeve circuit of jack 201 and plug 20, upper inner normal contacts of key 11, upper outer made contacts of key 16, lower winding of relay 26, winding of relay 27, lower inner armature and back contact of relay 31 to ground. The relay 27 operates first and short-circuits the receiver of the operators set 17 at its armature and front contact. Relay 26 in operating also shortcircuits the receiver at its upper armature and front contact. The purpose. of this will be described hereinafter. Relay 26 closes a circuit for the operation of relay 29 from battery, winding of relay 29, upper outer armature and back contact of relay 30, upper outer armature and back contact. of relay 31 to ground at the lower armature and front contact of relay 26. Relay 29 in operating opens at its upper inner armature and front contact a circuit for relay 31 and closes a ringing tripping bridge across the tip and ring conductors of the cord circuit at its lower outer armature and front contact through the right hand winding or retardation coil 32 and across the left hand winding of repeating coil 33. This bridge performs no useful function at this time but on incoming calls over trunk 200 it trips the ringing. Relay 29 in operating also closes a circuit for relay 30 from battery, winding of relay 30, lower inner armature and front contact and upper outer armature and front contact of relay 29, upper outer armature and back contact of relay 30 to ground at relay 26. Relay 30 in operating provides a: locking circuit for itself to this ground at relay 20 through its upper make-before-break contacts. Relay 30 also closes a second connection for the above mentioned tripping bridge through its lower outer armature and front contact. Relay 30 also short-circuits the receiver at the lower inner armature and front contact in multiple with the upper armature and front contacts of relays 26 and 27. Relay 30 also opens the circuit for relay 29 at its upper outer armature and back contact armature and back contact of-relay 29, up-

per inner arinature and front contact of reoperate and relay is slow in releasing.

Relay 30 in releasing opens the tripping bridge closed at its lowerouter armature and front. contact, as well as the short circuit for the receiver through its lower inner armature and front contact. The operating times of relays 26, 27 and 31 and the releasing times of relays 29 and 30 are such as to allow the tripping bridge to cause tripping functions at the distant exchange to take place'before the operatofls receiver is connected to the telephone circuit in order to prevent the operator hearing. clicks which may occur due to these operations. Due to the operation of relay 31 and release of relay 30 the operators receiver Wlll now be connected to the talkingkey 16 over the t1p and ring conductors over the trunk 200 and a dial tone will then be heard by the operator when the central office equipment is ready to receive dial pulses.

When, now, the operator actuates the dial the off-normal contacts of thedial open the circuit for relay 31. This relay in releasing again short-circuits the receiver. Relay 27 may be released at this time due to the high resistanceof the upperwinding of relay 26. At the releasejof relay 31 the upper high resistance winding of relay 26 is shunted by the establishing of the connection to ground at the lower inner armature and back contact of relay 31 and relay 27 reoperated. When relay 31 releases relays 29 and 30 are again operated to maintain the short circult for the receiver independent of relays 26 and 31. Relay- 31 in releasing also closes the circuit for the operation of relays 36 .and 37. Relay 36 is operated by a circuit from battery, winding of relay 36, upper outer armature and back contact of relay 38, lower outer armature and back contact of relay 31, ofi-normal'contacts of dial 35 to ground at the lower armature. and front contact of relay 26. The circuit for relay 37 may be traced from battery winding of this relay over the same circuit to ground at relay 26. Relay 37 in operating short-circuits the middle and left hand windings of the retardation coil 32, by closing the connection throughits low-er'outer armature and front contact andopens the connection to ground from the transmitter circuit applied at the lowerouter make contact ofkey 16 through.

the upper outer armature and back contact of relay 37. Relay 37. connects this. ground through this armature and the corresponding front'contact to the connection between the lower winding of relay 26 and the winding of relay 27. Relay 27 is thereby. short ciricuited which causes the operation of the marginal relay 203 in the trunk circuit 200. Relay 203 in operating opens the bridge through the. ringing relay 20 1 to prevent this bridge from interfering with the impulses outgoing over the trunk 200 when dialing again. It will be noted that the relays 30 and 31 while placing a short circuit on the receiver at this time prevent the operator hearing any clicks due to the operation of relays 36 and 37. Relay 36 in operating connects ashortcircuit across the middle winding of the retardation coil 32 to prepare a low resistance bridge across the trunk circuit when the dial returns to normal. This bridge will extend between the, tip and ring conductors through the upper make-beforewbreakcontacts of, relay 36 and. the left hand winding of retardation coil-32. Relay 36 also in operating opens the connection between the plugs 5 and 20 to the tip'and ring conductors at the upper and lower armatures and back contacts. This relayalso connects the tip and ring conductors from plug 5 through these armatures and the corresponding front contacts through the winding of relay 38 to battery and ground. Relay 38 now operates over the loop to the calling station if the receiver is still ofi the hook or through the bridge in the cord circuit established by the operation of relay 9, as hereinbefore mentioned. -Re- I lay 38 in operating opensa circuit at its upper outer armature and back-contact for relay 36 from the off-normal contact of the dial 35 and locks up this, relay through the upper make-before-break contacts toground.

V The dial may now return-to normal opening and, closing theimpulse contact accord ingto the digit selected. The line connection through to the distant exchange closed by relay 37 is thereby interrupted to begin the selection of the desired subscribersline in the usual manner. It should be noted that this connection is free from all encumbrances as the bridge in the trunk circuit is removed from across the line and the repeating coil 33 and retardation coil 32 are short-circuited by the operation of relay 37 and the calling subscribers circuit is removed by the operation of relay 36. \Vhen the dial is restored to normal the off-normal springs open the circuit for relay 37 which now releases and rem-ovesa short-circuit from the left and middle windings of retardation coil 32 and connectsa ground to the transmittercircuit at-its upper outer armature and back contact. The normally closed off-normal springs of the dial 35 now close-the circuit through the contacts of relays 30 and 29 for relay 31*- which operates and opens the short circuit for the receiver applied by relay 26.. A short.- oi-rcuit however is still maintained byrelay 30. Relay 31 in operating closes the same locking circuit for itself and opens the circuit for relay 30 which releases slowly and removes theshort circuit from the receiver. The slow-to-operate characteristic of relay 31 and slow-to-releas-e characteristic of relay 3O prevent the operator hearing clicks due to the dialing operations. Relays 36 and 38 remain operated under contro-l'of the key 16. The calling subscriber may now talk to the operator and to the central office when relay 30 releases, this connection being -estab lished to condensers 39 and 40. The central oflice circuit is held operated by the bridge 7 through the left hand winding of the retaring key 16 is operated. hen the subscriber at'the calling'station again removes the receiver from the switchhook lamp is ex tinguished and the call proceeds in the usual manner. At the end of-a conversation when the lamp 15 is lighted indicating that the calling'subscriber has hung up his receiverthe operator may remove the plug from the trunk and restore the circuits to normal; Then relay? releases to' light lamp 15 the connection through the tip and ring conductors from plugs 5 to 20'is' split and local battery and ground are connected to the tip and ring con ductors leading to the calling subscriber over plug 5 and jack'6 while a bridge isconnected across the tip and ring conductors leading to the distant exchanges through plug 20. This is to prevent the calling subscribers station from being signaled on incoming calls from the central oliice in case the connection has not been taken down immediately after disconnection by the calling subscriber. The local battery and ground is supplied to the calling subscribers line to permit this subscriber to originate anew call after disconnection, When both cords are removed from the jack all relays restore to normal. The operations are as follows: lVhen the calling subscriber hangs up his receiver relay 7 releases causingthe release of relay 9. i This splitsthe cord atthe upper outer armature connects battery at its upper inner armature and back contact to the tip conductor and ground to the ring conductor at its lower outer armature and back contacts through the windings of relays 8 and 7. It should be noted however that the upper winding of re lay 8 is short-circuited through the. upper outer armature and front contact of relay by the above mentioned ground to prevent the false operation of relay 8 when relay 9 is released. At this time a surge of current may occur due to this battery and ground connection charging the usual condenser in the subscribers set at the calling station. This surge of current, which would pass through the lower winding of relay 8 would have the tendencytocause the relay 8 to. operate and thereby cause the release of relay 25 but is prevented from so doing by the short circuit aroundthe upper winding of relay 8. In other words, this short circuit of the upper windingca-used by the operat ed condition of relay 25 prevents the normal circuit through the two windings of rela 8 from being completed on the release of relay 9, while the circuit from battery to ground through the lower winding of relay 8 is not sufiicient to operate this relay.

If now thecalling subscriber removes his receiver from the switehhook under this condition relays 8 and 7 will both be operated. Relay 8 is operated in this case by the current passing through the lower winding of relay 8. Relay 8 in operating opensthe circuit for relay 25 which now releases. Relay 8 in operating also short-circuits as hereinbefore described the calling subscribers line and relay 7'. Relay 9 is then operated, due to release of relays 'Z and 25 and operation of relay 8, from battery, upper inner make-before-breakcontacts of relay 21, winding of relay 9, upper inner armature and back contact of' relay 25', lower make-before--break contacts of relay 8, armature and back contact of relay 7 to ground over thesleeve terminals of plug 5. and ack 6 to-ground. Relay 9 in operating connects the central ofiice battery and ground through the windings of relay 7 and the calling subscribers-loop causing relay7'tooperate and relay 8 to release. Relay 7 in operatingextinguishes the lamp 15 and closes a circuit for the reoperation of relay 25 as hereinbefore described. Relay 25 in operating providesthe usual lockin circuit for itself under control of relay 9 and relay 7 and places relay 9' under control of relay 7. Under these circumstances therefore it is evident that any delay of the operation of relay 7' from the central ofiice source will not interfere with the proper-functioningof relay 9 in establishing the through connection.

If the call is incoming over trunk 200 the ringing relay 204 will be operated; This relay in turn closes a circuit for the operation of the alternating current responsive relay 206. This relay in operating provides a lock- 1ng c1rcu1t for itself through its'upper winding" and upper armature and front contact guishes signal 207. lVhen relay 21 is operated over the sleeve circuit as hereinbefore traced thisrelay opens the tip and ring conductor connection between plugs and 5 through condensers 23 and 24. Relay 9 is now also operated from battery,upper makebefore-break contacts of relay 21, winding of relay9, upper inner armature and back con tact of relay to ground at the lower arl'na ture and front contact of relay 8. Relay 9 in operating disconnects at the lower makebefore-break contacts ground for the tip conductor and battery from the ring conductor leading to plug 5. It also connects "the lower winding of relay 19 across the tip and ring conductors leading to the plug 20 as a holding bridge and connects the tip and ring con ductors from plug 20 to plug 5. Itwill be noted that in order to prevent the operator from receiving clicks while answering this call her telephone receiver will be inonientarily short-circuited due to theoperations of the relays 26, 27, 29, and 31 as hereinbefore described. That is, it will be maintained short-circuit-ed between the operation of relays 26 and 31. same regardless of whether the key 16 is op erated to answer the call before or after the plug 20 is inserted in jack 201. In either case the ringing will'be tripped by the bridge established as hereinbefore described through the right hand winding of retardation coil 32' by the operation of relay 29 and the receiver will be short-circuited to prevent the operator from hearing clicks incident to the answering of the call. When the key 16 is restored to normal the connection is cut through and when plug 5 is inserted into the jack of the desired line, lamp 15 is lighted. When the desired subscriber answers relay 7 is operated to extinguish it and cause the operation of relay 25 as hereinbefore described. Relay 25 in operating provides alocking circuit for itself under control of key 16, and opens the holding bridge consisting of the primary winding of relay 19 from across the trunk 200 and places relay 9 under control of relay 7.

If a connection is established to another private branch exchangeover the tie line 300 shown in'Fi 3 from a subscriber through cord circuit 3; the following operations will take place: The operations in the cord cir- These relays operate the.

l Q f a V cuit are the same as hereinbefore described for the extending of a connection over trunk 200. lVhen plug 20 is inserted into jack 301 relay 302 operates over acircuit from battery, winding of this relay to ground at the lower contacts closed by jack 301. Relay 302 in operating disconnects the jack from the trunk 300 andestablishes a circuit for relay 304 from battery, winding of this relay, lower inner armature and front contact of relay 302 over the sleeve circuits of jack 301 and plug "20 to ground through the winding of relay 21 as hereinbefore described. Relay 304 in operating closes an obvious circuit for the operation of, relay 305. This relay connects battery and ground'through the retardationcoil 306 for the tip and ring condoctors and the left hand windings of repeating coil307. When now the ringing key 40 is operated to ring the distant end of the tie line, the ringing responsive relay 308 bridged across the tip and ring conductors is operated by ringing current applied by key 40. Relay 308 in operating short-circuits relay 302 at'its lower armature and front contact and relay 302 inv releasing causes the release of relays 304 and 305. Relay 302 in releasing also disconnects the windings of the repeating coil 307 from the line at the upper inner and middle arinatures and front contacts and connects the tip and ring conductors through past the repeating coil 30'? at the upper and lower outer armatures and back contacts. The tie line is now cleared from all encume brances so that-ringing willpass through the tip and ring conductors directly out over the tie line. l/Vhen ringing ceases relay 308 is released and relays 302, 304' and 305 reoperated to reconnect the repeating coil 307 in the line for speech transmission;

The operation of the tie line 400 shown in Fig. 4 will now be described in connecti on with'an outgoing call. The operation of the cord circuit A is the same as hereinbefore desc ibed in connection with an outgoing call over trunk. 200. lNhen the plug 20 is in:

serted in the talking'jaclr 401, relay 402 is operated over an obvious circuit closed by jack 401. vRelay 402 in operating connects the relay 403 the upper inner armature and front contact to the open sleeve contacts of the dial jack 405. Relay'406 is connected through the upper outer armature and front contact of relay 402 to the sleeve of jack 401 and relay 403 is operated by an obvious circuit closed through the lower inner armature and front contact to ground. The operation of relay 407 closes a circuit for the lighting of line lamp 408 from battery, lamp 403, upper armature and front contact-of relay 409, upper armature and back contact of relay 407 to ground. 5 Relay 406 now operates over the sleeve circuit in series with relay21 andcloses the circuit for the operation of relay .410. Relay 410in operating. connects battery and ground through the retardation co 1-11 to the tip and ring conductors of the 401 to supply tall 'ng and supervisory battery for the cord le it.

Relay 402 also closes at its lower outer armature and front contact a bridgeacross the tip and ring conductors of line 400outgoing tors telephone set in cord A.

to the distant exchange, through the upper winding of relay 409 and retardation coil'412 to prepare the circuit at a distant exchange for dialing. lVhen the distant exchange is.

ready for reception of dial pulses a dialing tone will be transmitted through the condensers 418 and 414 over acl: 408 to the opera- The operator will then insert a plug corresponding to plug :-of anothercor'd circuit into the dialjach 405 for the purpose of dialing the distant ex change. Relay 403 is thereby operated over tne connection established by relay 402 in series with the relay 21 in the second cord circuit. Relay 403 in operating closes acircuit for the operation of relay 415 from battery, winding of this relay, upper inner iarmature and back contact of relay 416,

armature and front contact of re if nects the midpoint between the two windings of relay 417. at its upper armature and front contact to the tip conduct-or of the dial jack.

' If now relay 21 in the cord circuit has not operated at this time relay 417 will operate .40: a

3 the battery and ground over the tip and ring conductors from the cord circuit causes a difference in potential between the two windings of relay 417. Relay 41'? in operating opens at one poiir the circuit for relay 416 i at its lower armature and back contact to prevent this relay from operatingwhen relay 418 operates to close another point of this circuit. Relay 418 will operate over an obvious circuit closed by the operation ofjrelay Belay 4 8 in operating prepares this operating pah for relay 416 at lower outer armature and front contact and opens a lookingcircuit for relay-410 at its lower inner contacts. Relay 418 also connects a short circuit across the tip and ring conductors of the tie line at its upper armature and front contact the purpose of which will be described hereinafter. Relay 418 further opens the ring conductor of the dial jack from the lower armature and front contact of relay 416 at its upper inner contacts.

These relays now remain operated until the circuit forrelay 4fl6'at its lower armature and front contact. Relay 416 operates and prepares a dialing circuit through the tip and ring conductorsof the dial jack as follows: As relay 41.6 in operating opens the operating circuit for relay 415 at its upper inner armature and back contact relay 415 releases, but as it is slow in releasing the locking circuit for relay 416 controlled by relay 418 is prevented from closing in case relay 416 should be operated momentarily when ground is removed from the tip conductor in the cord circuit before the battery is removed which causes relay 417 to release and reoperate due to the change of potential across its winding. l/Vhen relay 415 releases fully it removes the short circuit from the tip and ring conductors of the dial jack 405 at its lower inner armature and front contact and disconnects relay 417 from the dial jack tip and ring conductors. Relay 415 also opens the circuit for relay 418 and connects the tip conductor of the dial jack to the tip conductor of the line 400 through its'upper armature and back contact and the upper outer armature and front contact of relay 416. Relay 418 in releasing closes the looking circuit for relay 416 to the ground at relay 408 before it opens the operating circuit for relay 416 and closes the ring conductor from the dial jack to the line 400 through its inner upper contacts and the lower armature and front contact of relay 416 before it opens the short circuit across the tip and ring conductors of the line. The action of relay 415 in closing the tip conductor through to the line and the relay 418in closing the ring conductor through to the line before relay 418 removes the short circuit from the line is to prevent the possibility of an open circuit appearing at this time and causing a false impulse to be sent to the distant tie line circuit. Dial tone may now beheard by the operator provided the talking dial'key is operated .on the cord circuit connected to the dial jack; The operator now dials the desired number at the; distant private branch exchange. I

After dialing is completed the operator removes the plug of the cord circuit used for dialing from jack 405 causing relay 403 to release which in turn opens the locking circuit for relay 416. Relay-416 in releasing reestablishes the talking connection over the trunk 400 to jack 401 through the cord circuit connected to this jack. Then the called subscriber answers the call the direction of the current flowing from the distant private branch exchange is reversed causing the operation of polarized relay 409 to extinguish the lamp 408. Relay 407 now locks under control of relay 409 by the circuit established at thexupper armature and front contact of relay 409 to preventlamp 408 from lighting falsely on disconnection at this exchange.

release of relay 409. If this occurs while the I; plug is still inserted in the j ack 401, the line lamp 408 will light asa disconnect signal. If the plug is removed from this jack before the distant exchange disconnects the. short circuit is removed from the lower winding of relay 409 by the release of relay 402 to cause an increase in the resistance of the line and thereby in the usual manner release the connection at the distant exchange. Relays 409 and 407 remain operated to prevent the lighting of the line 1311111408 at this time. i

to a subscriber in the private branch exchange over cord'A. When the distant private branch operator applies ringing current to this tie line relay 501'is operated. This relay closes a circuit forrelay 503.. "Relay 501 vibrates in response to the ringing cure rent and opens and closes the circuit for relay 503 but this relay remains operated steadily because of the shunting resistance504 and capacity 506. The -retardation coil 507 and capacity 506 are used to preventthe buzzing circuit from causing noise on the usual bate tery feeding'systenij Relay 503 'in' operating closes a circuit for the operation of relay 510 from battery, winding of relay 5 10, lower make-before-break contacts of relay 511, upper inner contacts of relay 512 to ground at the armature and front contact of relay 503. Relay 510 closes a circuit for relay 511 from battery, winding of relay 511, lower armature and front contact of relay 510, inner ipper contacts of relay 512 to ground at the armature and front contact of relay 5,03. Belay 511 in operating provides a locking circuit independent of relay 510, the circuit of which is opened by relay 511. Relay510is slow in releasing and therefore delays the. closing of a circuit for the operation ofrelay 512from battery, lower winding of relay 512, upper armature and back contact of relay. 510, upper armature and front contactof relay'511 to ground at relay 503. Relay 511 also closes a momentary locking circuit for itself through its lower armature and front contact to ground at relay 503. This circuit opened on the operation of relay 512 "a n d"as relay 510 opened the original energizing circuit relay 511 will now release. Relay 511 completes the obvious circuit for. lighting s gnal 515 closed by relay 512. Relay 511 is slow in releasing. The purpose ofthe slow-torelease characteristics of relays 510 and511 is to hold the circuit for signal 515 open long enough to prevent the false lighting of this 'a cord circuit,'a relay for controlling the consignal in case relay 501 operates on surges such as may'occur upon disconnection; Relay 512 in operating closes a locking circuit" for 05 itself from battery, resistance 504, upper A description will now be made of aycall' incoming over tie line 500 shown in Fig. 5

winding of relay 512, upper armature and back contact of relay 517, lower inner armature and front contact of relay 512 to ground at the lower outer armature and back contact of relay 511. This is to maintainrelay 512 operated. after the original energizing circuit therefor is opened by the release of relay 511. The relay 512 is held operated between the opening of the original circuit and the closing of the locking circuit by the circuit established by its upper armature and front contact for the lower winding to ground at relay 503. In other words, the

. period'of delay in the operation of lamp 550 depends solely on the slow-to-release characteristics of relays 510 and 511 independent ofthe voltage conditions on the line. To answerthis call plug 20'is inserted into jack 516. This causes the operation of relay 517 over a circuit closed by the jack 516. Relay .517 iii operating opens the locking circuit forrelay 512 and-this relay in releasing opens the circuit for lamp 515. Relay 517 also establishes a connection from ground for the sleeve circuit to provide the "usual supervision on the cord circuit. The establishing of a connection to the desired subscribers line in the private branch exchange may now proceed in the usual manner through the cord circuit A. Y

Although this invention has been disclosed .in connection with but a single system, it

the hanging up of the receiver of. the: telephone set of one line for releasing said re lay to break the continuity of said cord circuit.

2.. In a telephone system, subscribers lines,

a cord circuit,v a slow-t-o-release relay for-- controlling the continuity of said cordcircuit, means responsiveto the establishing of a connection between two lines through said cord CllClllllfOI operating said relay to establislrcontinuity-in the said cord circuit, and.

means responsive to the hanging up of the receiver of the telephone-set of one line. for

permitting the release-of said relay inac- -cordance with its slow-to-release characteristics.

3. In atelephone system, subscribers lines,

lay havinggits windings included in the tip and ring'conductors of the cord circuit, means responsive to the establishingof a connection between two lines through said cord vcircuit for operating said relays independently, means for'transferring the control over the first mentioned relay to the supervisory relay to maintain it operated when the supervisory relay is operated, and means responsive to the hanging up of the receiver of the telephoneset of one line for releasing the supervisory relay to release thefirst mentioned relay to break the continuity in the cord circuit.

4. In a telephone system, lines, trunks, a cord circuit, a relay for controlling the continuity of said cord circuit, a supervisory relay in said cord circuit, means for operating said supervisory relay on the connection of the cord circuit to a line, means for operating said first mentioned relay on the connection of the cord circuit to a trunk, means responsive to the operation of said first mentioned relay for releasing the supervisory relay and for establishing the continuity of said cord circuit, means .for reoperating said supervisory relay, and means for transferring the control of said first mentioned relay to said supervisory relay responsive tothe reoperation ofsaid supervisory relay.

' .5. In a telephone system, lines, a cord circuit, a relay for controlling the continuity of said cord circuit, means responsive to the establishing of a connection between two lines through said cord circuit for operating said relay to establish continuity in said cord circuit, a supervisory relay in said cord circuit, means for transferring the control oversaid first mentioned relay to said supervisory relay, a current supply in said cord circuit, a current supply in one of said lines, means for transferring the control over said supervisory relay from the current supply in the cord circuitto the current supply in said line, and means for preventing the first mentioned relay from releasing during the transfer of control of said supervisory relay from one current supply to the other.

6. In a telephone system, a subscribers line terminating in a telephone set including acondenser, a trunk, means for connecting said line and trunk, a first relay, a current'supply, a second relay having two windings normally connected in circuit between said current supply and line, means for releasing said first relay when said subscriber hangs up his receiver. to disconnect said trunk fromsaid line and connecting the current supply to'the subscribers line through the windings of said second relay, a third relay, 7

means for actuating saidthird relay in response to the establishing of a connection,

means for holding said third relay under control of said second relay, and means for short-circuiting one winding of said second relay under control ofsaid third relay for preventing saidsecond relay from operating from the switchhook for reestablishing a connection through the cord circuitindependent of the supervisory relay.

r 8. In a telephone system, a subscribers line, a cord circuit, a trunk, means for es tablishing a connection between said subscribers line and trunk through the cord circuit, 'a supervisory relay, means for releasing said relay in response to the subscriber replacing. his receiver on the switchho ok, a

splittingrelay, means for releasing said splitting relay to split the connection through the cord circuit in response to the release or" the supervisory relay, and means thereafter responsive to the removing of the receiver from the switchhook for reestablishing a connection through the cord by the reoperation of the splittingrelay independent of the supervisory relay.

9. In a telephone system, a subscribers line, a cord circuit, a trunk, a supervisory relay, means for establishing a connection between said I subscribers line and trunk through said cord circuit under control of said supervisory relay, means responsive to the subscriber replacing his receiver on the switchhook' for splitting the connection through the cord'circuit-under the control of said supervisory relay, means responsive to the subscriber again removing his receiver from the switchhook forreestablishingthe connection through the cord circuit independent of the supervisory relay, a current supply in the trunk circuit, means for connectingthis current supply to the cord circuit after the reestablishing of the connectionthrough the cord circuit, means respons siveto this connection of'the current supply .for operating the supervisory relay, and

means responsive to this operation of the superv sory relay for placing the splitting means under control of said supervisory 10. Ina telephone system, a line, trunks, a cord circuit for connecting a line and a trunk, a current supply in said cord circuit,

means responsive to the connection of the cord circuit to a subscribers line forconnecting said supply to a subscribers line, means responsive to the connecting of the cord circuit ,to a trunk'for short-circuiting said subscribers line, for removing said supply from said cord circuit, for establishing a bridge across the tip and ring conductors of said cord circuit for removing said short circuit, and for connecting the tip and ring conductors of the cord circuit through from the subscribers line to the trunk, a current supply in said connected trunk, and means responsive to the removal of the short circuit and the connection of the ti and rin conductors through the cord circuit for the passage of current therethroug-h from said supply in the trunk for removing the bridge.

11. In a telephone system, lines, trunks, a cord circuit for connecting a line and a trunk, a battery and ground connection, means responsive to the establishing of a connection between the cord and the subscribers line for connecting said battery and ground connection to the tip and tin g conductors of the subscribers line, means responsive to the establishing of a connection between the cord circuit and the trunk for short-circuiting the line, for removing the battery and ground connection from the cord circuit, for applying a bridge across the tip and ring conductors, for removing the short circuit, and for connecting the tip and ring conductors through to the trunk, a battery and ground connection in the trunk, and a relay means responsive to current from said last mentioned battery and ground connection for re moving the bridge.

12. In a telephone system, subscribers lines, trunks, a cord circuit for connecting subscribers lines with trunks, an operated telephone set, means for associating said telephone set with a cord circuit, means responsive to the connection of a cord circuit to a trunk and the association of thetelephone set to said cord circuit for short-circuiting the receiver in said set, for establishing abridge across the tip and ring conductors of the cord circuit and for maintaining said short circuit and bridge for a short interval.

13. In a telephone system, a calling line, a trunk, a cord circuit for connecting said line to said trunk, an operators telephone set, means for opening the connection through the tip and ring conductors of the cord circuit when the subscriber hangs up the receiver on the switchhook to release a connection, means for connecting the operators telephone set to the part of the cord circuit connected to the trunk, means for short-circuiting the operators receiver in response to the connectionrof the operators telephone set to said cord, meansfor establishing a bridge across the tip and ring conductors of the part of the cord circuit connected to the trunk, and means for maintaining said short circuit and said bridge for a short interval thereafter.

14. In a telephone system, a cord circuit, a trunk, means for connecting the cord circuit to the trunk, an operators telephone set,

means for connecting said telephone set to the cord circuit, means responsive to the connection of the cord circuit to the trunk and theoperators telephone set to the cord cirmeans for connecting the cord circuit to the trunk, means responsive to the connection of the cord circuit to the trunk and the set to the cord circuit, for-shortcircuitingthereceiver and for establishing a bridge across the tip and ring conductors of the trunk to operate said ringing trip relay, and 'means for removing said bridge and opening the short circuit a short interval thereafter.

16.In atelephone system, a cord circuit, a trunk, means .for connecting the cord circuit to the trunk, an operators telephone set, a dial, means for connecting said set and dial to the cord circuit, and means thereafter responsive to the operation of the dial for short-circuiting the receiver during the dialing and for a short interval thereafter.

17. In a telephone system, a cord circuit. a trunk, means for connecting the cord circuit to the trunk, an operators telephone set. a dial, means for connecting said set and dial to the cord circuit, means responsive to said connection of the set and dial to the cord circuit for short-circuiting the receiver and establishing a bridge across the tip and ring conductors of the cord circuit for a short interval, and means thereafter responsive to the operation of the dial for short-circuiting the receiver during the dialing and for a short interval thereafter.

18. In a telephone system, a trunk, a cord clrcuit, means for connecting said cord cir cuit to said trunk, a repeating coil in said trunk, means responsive to the establishing of a connection between the cord and the trunk for connecting said repeating coil across the conductors of said trunk, a ringing responsive relay in said trunk, means for applying ringing current to said trunk for operating said relay, and means responsive to the operation of said relay for removing the repeating coil from across the conductors of said trunk.

19. In a telephone system, a tie line having atalking connection and adialing connection, means for establishing the talkin connection to the tie line and means for esta lislringthe dialing connection to the'tie line, means responsive to the establishing of the dialing connection for short-oircuiting it and for short-circuiting the tie line, a dial, means for connecting said dial to the dialing connection, and means responsive to said connec tion of the dial for opening the talking connection, for removing the short circuit from the dialing connection, for connecting the tip conductor through from the dialing connection to the tie line, for connecting the ring conductor through from the dialing connection to the tie line, and for removing the short circuit from the tie line.

20. In a telephone system, a trunk, -a cord circuit, a ringing bridge across the conductors of said trunk, a dial associated With said cord, means responsive to the moving of the dial off normal for removing said ringing bridge from across the conductors of said trunk.

21. In a telephone system, a tie line, a relay in said tie line, a signal, and means responsive to the operation of said relay for actuating said signal a short interval after the operation of the relay, said means including only sloW-to-release relays.

In witness whereof, I hereunto subscribe my name this 27th day of May, 1931.

LANGFORD J. BOXVNE,

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