US2047619A - Telephone system - Google Patents

Description

July 14, 1936.

T. F. CROCKER 2,047,619

TELEPHONE SYSTEM Filed Dec. 29, 1954 4 Sheets-Sheet 2 FIG.1 PART 2 RING LINE

HOLD

INVENTOR. THOMAS F CROCKER ATTORNEY.

Patented July 14, 1936 UNITED STATES PATENT orrics Associated Electric Laboratories, Inc.,

Chicago,

111., a corporation of Delaware Application December 29, 1934, Serial No. 759,643

14 Claims.

The present invention relates to telephone systems in general, but is concerned more particularly with telephone systems including a main exchange and a private branch exchange, and the object of the invention is the production of a new and improved private branch exchange,

system by means of which service may be rendered more rapidly and efilciently, and by means of equipment of relatively low cost.

General description I contains desirable features as follows:

(1) Each trunk line extending between the branch exchange and the main exchange terminates at the branch exchange in a switchboard cord and plug by means of which the operator may connect the trunk line with the jack of a local line to complete an incoming call or to extend an outgoing call, while a transfer jack is associated with each trunk, so that the operator can use a local double-plug cord and temporarily transfer the local line from in connection with the trunk line into connection with another local line, while holding a condition of answered supervision on the trunk line.

(2) Each trunk cord is provided with a differential recall relay, operated from a grounding recall key at the subscriber's station, which controls a pair of recall relays so that the local subscriber of inter-exchange connections can control a recall lamp at will to signal the operator. Relay equipment, controlled from the recall relay, brings about the lighting of the recall lamp upon the first manipulation of the recall button, together with the transfer of the local end of the connection to the transfer jack, while on the next manipulation of the recall button the local connection made through the transfer jack by the operator issevered and the original trunk connection reestablished. This feature enables a branch exchange subscriber to be switched away from a main exchange connection temporarily and into connection with another branch exchange subscriber to obtain additional information, for example, following which the main exchange connection may be resumed.

(3) In order to better facilitate the work of the 5 branch exchange operator in directing incoming calls to the appropriate lines, according to the character of information desired for example, a so-called hold signal or lamp is provided which becomes lighted when the operator first throws her talking key to answer an incoming call and remains lighted until the call has been disposed of, as without this signal there is a tendency for the operator to restore her talking key and then go about procuring information as to the disposition of an incoming call and then have her attention distracted so that she forgets that there is an undisposed-of call waiting on the trunk, as the usual call signal is preferably extinguished when the operator responds. At any rate, the 29 special signal referred to serves to indicate to the operator that she has already conversed with the subscriber whose line is connected with a trunk in association with which the signal is displayed. By throwing her trunk-key handle in the other direction, the operator may extinguish the special signal and return the trunk cord to normal condition in the event that she herself is able to supply the desired information without extending the incoming call to a sub- 30 scribers line.

(4) In order to relieve the operator of the necessity of continuing to signal the called local sub-station at intervals until a response is obtained, circuit arrangements are provided such that the operator may manipulate a ring-start key in her position equipment and start the ringing operation in the cord of which the talking key is thrown, following which the ringing current is automatically thrown and intermittently applied until the called subscriber responds, whereupon the ringing current is automatically disconnected, and the talking circuit established, and answered supervision given.

(5) In order to expedite the taking down of connections, the circuit arrangements are provided so that the release of the line relay in the trunk cord when the local subscriber replaces his receiver at the end of a conversation opens the trunk as regards the inter-exchange conductors thereof, giving disconnect supervision in the main exchange. In this way, disconnect supervision is given immediately to the main exchange.

(6) In order to enable the branch exchange operator to use the trunk cord and plug over which a call has been received to set up a connection to a local line tentatively or solely for the purpose of securing information as to the disposition of an incoming call, provisions are made whereby the operator is able to answer an incoming call and then disconnect the incoming trunk from the associated cord plug temporarily by means of a so-called split relay and then use the plug and cord to make her local inquiry connection while the calling subscriber is telephonically disconnected from the terminating cord and plug, and a state of answered supervision is maintained on the inter-exchange trunk, the split condition being terminated by the operator as soon as she has obtained the desired information.

(7) In order to insure the secrecy of conversations against invasion or eaves dropping" by the branch-exchange operator, arrangements are provided such that a warning tone-signal is transmitted over an established conversational circuit in the event that the operator throws a talking key of a cord over which the conversation is taking place, this arrangement being controlled from the calling supervisory relay through contacts of the associated talking key.

(8) A further feature of the disclosed system is that the branch exchange lines are divided into two classes as regards the establishment of inter-exchange connections. The lines of the unrestricted class terminate in the switchboard jacks of which the sleeve is directly grounded, while the lines of the restricted class each terminate in a switchboard jack having the sleeve element grounded through a resistor which so limits the current flow as to render the marginal sleeve relay of the trunk cord non-responsive. The circuit arrangement is such that the completion of a subscriber-to-subscriber talking circuit through a trunk cord is dependent upon the sleeve relay having been operated.

In connection with this feature, special provisions have been made for preventing the operator from either deliberately or unintentionally thwarting the arrangement by operating a talking key of a local cord and simultaneously a talking key of a trunk cord to permit conversation through her headset conductors from a restricted line to a trunk. This is accomplished by providing separate leads from the operators headset to the local cord and to the trunk cord, in combination with a disconnect relay, operable whenever a talking key on a trunk cord is thrown, to disconnect the talking conductors of the local cord from the operators headset and from the talking conductors of the trunk cord.

(9) Each of the inter-exchange trunk cords is provided with a key which transfers the trunk conductors to a pair of calling device leads, when operated. In the event that the branch exchange is operated in conjunction with a manual exchange no calling device is provided, in which case the said key may be used as a flash key, as it opens the trunk conductors each time it is operated, in the event that no calling device is connected.

(10) The trunk cords are each arranged so that so-called night service may be given to one or more local lines. A night key, when operated, by-passes the repeating coil of the cord thereby extending the trunk conductors through to the plug of the cord, whereby the line into which the cord is plugged may be used to originate and receive calls directly over the associated inter-exchange trunk. The usual operators signals at the trunk cord so plugged up for the night service are disabled pursuant to the operation of the above-mentioned night key. 5

(11) It is contemplated that the private branch exchange system disclosed herein be used in business establishments and the like wherein a night watchman, or other person whose principal duty is something other than to operate the switchboard, is on the premises at times other than during regular working hours, and whose auxiliary duty is to operate the switchboard whenever there is need for so doing. Therefore, an arrangement for sounding a night alarm has been provided which requires no special design of the regular equipment. This night alarm is set oil! responsive to a momentary impulse occasioned by a change in signal current which occurs when a line lamp is lighted. 20

Description of drawings Referring now to the accompanying drawings, comprising Figs. 1 to 5, they show, by means of the usual circuit diagrams a sufiicient amount of 25 equipment in a system embodying the principles of the invention to enable the invention to be understood. More in particular, Figs. 1 to 4 are circuit drawings illustrating circuits used in a private branch exchange having a non-multiple switchboard, while Fig. 5 is a switching diagram which indicates the arrangement employed for interconnecting the lines at the switchboard.

Referring now particularly to Fig. 5, three local substations (A, B, and C) are shown interconnected with the switchboard, whereat they terminate in jacks J I, J 2, and J3. At the switchboard, a number of local cords such as LC are provided, the cord LC having plugs P2 and P3,

which may be inserted into the jacks for the purpose of interconnecting a pair of lines.

The trunk line TL is one of a desired number of two-way trunk lines which extend from the illustrated branch exchange to the main exchange (not shown). the trunk line TL terminates in the trunk cord TC and the plug Pl, which may be inserted into any of the jacks.

The trunk TL is provided also with a transfer jack J 4, which is used in connection with a local cord circuit such as LC to interconnect the plug Pl with another local line when the local subscriber involved in an inter-exchange call wishes to converse with another local subscriber temporarily. 5

Referring now to Figs. 1 to 4, Fig. 1 shows the inter-exchange trunk line TL, terminating at the branch exchange in the trunk cord TC and the plug Pl, together with the line of substation A and the terminating jack J I;

Fig. 2 shows the local cord LC, interconnecting the plugs P2 and P3, together with the lines of substations B and C and the associated switchboard jacks J 2 and J3;

3 shows the pe ator's headset and posi- (H At the branch exchange,

. of contacts of ring-start relay 2|2.

relay 2 operates through registor 201 and ground conductor 25|, whereupon calling supertion with the tone lead. 300, as will be pointed out hereinafter; and v Fig. 4 shows the night alarm circuit including the induction coil 10, thenight alarm key K1,

relays 40| to 403, and the impedance coil 404 and,

night alarm buzzer 405. The night alarm circuit is associated with the cord-supervisory and linesignals by way of current-supply conductor M2, and with the local line circuits by way of'currentsupply conductor 4| I. It is to be noted that conductor 4' is normally connected to the ungrounded negative pole of the exchange battery by way of the upper contacts of the night alarm key, and that the negative pole of the exchange .pf the conductors 3| |-3|6 of the multiple cable ,DETAILED DESCRIPTION The disclosure having been described generally, a detailed description of the operation of the exchange equipment will now be given, in which the foregoing and additional features will becomeapparent. It will be explained first how a local call is set up in the private branch exchange.

Local call Assuming now that the restricted-line subscriber at substation C desires to converse with the subscriber at substation A, for example, the subscriber at substation-C removes his receiver, (not shown) thereby closing the usual circuit over line conductors 205.and 206 for line lamp 208 by way of lamp conductor 4| Upon noting the lighted condition of the lamp 208, the branch-exchange operator inserts the answering plug of an idle'local cord circuit, the plug P2 of the local cord LC, for example, into the jack'J3. The cut-off contacts of the jack J3 clear the calling line of its ground and lamp connections. A circuit is now closed over the sleeve circuit by way of the sleeve resistor 201 for the upper winding of ring cut ofi relay 2| by way Ring-cut-ofi visory lamp 2|! becomes lighted as a supervisory signal, but the answering'supervisory relay 2|6 does not become lighted at this'time because its' circuit is,opened at the contacts of the answering bridge relay 209, which relay is now energized- \ground potential directly to the transmitterpotential to the conductor 30l nergizes the transmitter Tby way of the windings of impedance coil 3 I8 and thelower left-hand winding of the induction coil 10. This provision is made so as to economize on the flow of current; it is unneces sary to have the transmitter energized except during conversation. Since the contacts of the key which energize the transmitter close first, the click which would otherwise be transmitted to the calling line is dissipated by the time the talking conductors are connected up. It may be noted that the shunt condenser -3|9 at the operators headset forms'an alternating-current bypass for the impedance coil 3|8, thus localizing the voice currents generated at the transmitter T, and, in cooperation with the impedance coil 3|8, efiectively prevents flow of voice currents in the current-supply leads connected to the impedance coil 3|8.

The talking key K4 of the cord LC also associates the common ring-start conductor 303 with the ring-start relay 2|2 in the cord circuit; it

connects the tone-relay conductor 304 to the contacts of the calling bridge relay 2|0, both for a purpose which will be explained subsequently.

When the operator converses with the sub scriber at substation C and learns that he desires to be connected with the line of substation A, she is able at once to determine whether or not the line of substation A is engaged by merely looking to see whether or not there is a plug in the jack J I, as this is a non-multiple switchboard. If there is no plug in the jack J the operator inserts the calling plug P3 of the cord LC into the jack J thereby disconnecting the line lamp circuit and applying ground potential to the sleeve conductor of the cordat the second point.

Signalling the called subscriber In order to start the signalling, or ringing,

tors 303 and 3| The application of ground po-' tential to ring-start conductor 303 results in the closure of a circuit, through contacts of the operated talking key K4, for ring-start relay 2|2 in the local cord LC. Upon the closure of this circuit, ring-start relay 2|2 operates and disconnects the upper winding of ring-cut-ofi relay 2 from the sleeve conductor of the cord, whereupon relay 2 restores and closes a locking circuit for relay 2|2 at its inner contacts to the grounded conductor 25| by way of contacts of key K4 and contacts of relay 209 in multiple. This locking circuit serves to maintain the ring-start relay 2 I2 operated after the rifig-startkey K5, Fig. 3, has i been restored.

At its lower armature ring-start relay 2| 2' opens the normal connection between the ring conductor of the plug P3 and the corresponding conductor of the plug P2 and connects the ring conductor of the plug P3 tothe ringing lead 2|8 by way of the lower winding of ring-cut-oif relay 2| At the same time, relay 2|2 at its upper contacts places ground potential on the tip conductor of the plug P3 so as to afl'ord a low-impedance return path for the ringing current.

The ringing current received over, the conductor 2| 0 is preferably, of an intermittent nature,

The operator now restores talking key K4, .thereby disassociati'ng her equipment tromthe cord LC, and removing the shunt from around the armature and front contact of the energized answering-bridge relay 209. The maintenance of the locking circuit of ring-start relay 2I2 to conductor I is thus rendered dependent upon the continued energization of relay' 209, whereby the signalling of the called substation is immediately terminated by the restoration of relay 2 I2 in the event that the calling subscriber repl'aces ,his receiver before the call is answered.

When the subscriber at substation A responds by removing his receiver, theusual direct-cur rent bridge is closedacro'ss the conductors I02 and I03- of his line, closing a direct-current path for the lower winding'of the ring-cut-ofl relay 7 II from the (negative potential superimposed on .t 'e ringing currentreceived over conductor 2I0,

the circuit being completed over. the called line and to ground at the upper contacts of ring-start relay 2I2.

Since the continued energization of relay 2I2 nas been dependent upon the locking circuit esestablished for relay 2I2 at the inner lower contacts thereof following the restoration of the ring-start key K5, Fig. 3, the operation of relay 2 at this time results in the opening of the the plug P3 and jack J l and over the line of the called substation A. Relay 2I0 disconnects the calling supervisory lamp 2" at its lower contacts, thereby extinguishing the lamp to give answered supervision to the operator.

Ring-cut-ofi relay 2 is again energized over the sleeve conductor of the plugs P2- and P3 and through the inner upper contacts of ringstart relay 2I2 to maintain the conductor 25I grounded at its lower contacts, preparatory to lighting the lamps 216 and 2H as disconnect signals. From this it will be understood'that the relay 2 is a combined sleeve relay and ringcut-oif relay in that it controls the termination of the ringing period as above explained and also controls the application of ground potential to conductor 25I for supervisory purposes.

Invasion signal It is is to be noted that the upper contacts of the calling bridge relay2 I 0 apply ground potential to the normally open contact pair of the talking key K4 with which tone-relay-conductor 304 is associated. By this provision, if the operator attempts to invade the secrecy of a conversation by throwing her talking, or listening, key K4 after the called subscriber has responded and energized the calling bridge relay 2 I 0, ground po-. tential is extended from the contacts of relay 2l0 through the contacts of the key K4 to tonerelay conductor 304, thereby operating the tone relay 30l, Fig. 3, to apply an invasion-tone signal. The application of the tone signal is made from the tone lead 300 through contacts ,of relay 30I and resistor 32I to the upper left-hand winding of the induction coil 10. A tone current is generated in the secondary winding of the induction coil IC and is transmitted over the operator's tip and ring conductors and through contacts oi. the

' bridge relays 209 and 2I0 both restore, closing talking key to the talking conductors of the cord circuit LC, thereby warning the subscribers that their conversation is being listened to and also warning the operator that her headset conduc tors are telepho'nically connected with a cord circuit over which a conversation is in progress, so that she may immediately restore the key K4 and thereby disconnect her headset conductors from the conversational path.

Disconnect supervision at the local cord Whenthe conversation has been concluded, the two subscribers replace their receivers, whereupon the answering-bridge and callingcircuits for the supervisory relays 2I6 and 2" from conductor 25I, grounded at the lower contacts of relay 2| I. These lamps now both light as disconnect signals tothe operator. In the event that one subscriber delays in replacing his 20 receiver, the disconnect signal associated with the other subscriber becomes lighted, andthe operator takes down the connectionin either case. When the connection is taken down, the relay 2II restores, extinguishing lamps 2I6 and 26 An incoming call The operations involved in extending an incoming call will now be considered. For this purpose it will be assumed that the trunk line TL is taken for use in the main exchange and that ringing-current is 'projected over the conductors I38 and I39 thereof in the usual manner. The upper winding of ring-up relay 2 isnormally bridged across the trimk conductors I30 and I39 by way of the contacts of the dial key K3, conductors I36 andv I31, contacts of the split relay H3, contacts of relays IIO, III, and H2, and the condenser I40. Ring-up relay II2 therefore responds to the ringing current, and at its lower contacts it closes a locking circuit for itself to ground through contacts of hold relay III and contacts of sleeve relay H2. The lock- 'ing circuit of the lower winding of relay II2 includes line lamp I2I and the common lamp The operator responds When the operator notes the lighted condition of line lamp I2I, she throws her talking key K2 so as to get into telephonic communication with the calling subscriber. The key K2 connects the calling tip conductor of the trunk cord TC to the operators headset tip conductor 3I5, and it connects the calling ring conductor to the operators headset ring conductor SIG. These conductors extend through the cable C2 to the operators headset and position equipment of Fig. 3, conductor 3I5 extending directly to the induction coil IC, while conductor SIG passes through the condenser 3" so as to avoid placing a direct-current bridge across the calling conductors of the trunk cord TC and a consequent spurious operation of line relay I00.

The key K2 also associates the common ringstart conductor 3| I with the ring-start relay I00; connects the common split conductor 3I2 to the upper winding of split relay I I3; places a ground potential on the transmitter-ground conductor III to energize the operator's transmitter; and it closes a circuit from the grounded conductor I5I for hold relay III, conductor I5I being grounded through contacts oi! line relay I08 and contacts of key KI. Hold relay III operates and locks itself to conductor I5I, whereby relay III, having once been operated, remains operated either until line relay I 08 energizes or until the key KI is momentarily operated as a release or clear-out key. It is to be noted that the hold lamp I20 is lighted in parallel with the winding of hold relay III to serve as a signal to the operator that an answered but undisposed-oi incoming call has been received over the trunk cord TC.

Giving answered supermsion to the main exchange At its inner upper contacts, hold relay I I I completes the normally open talking circuit to the right-hand windings of repeating coil II9, by joining conductors I33 and I35, thereby bridging the right-hand windings oi! repeating coil I09 across the conductors I38 and I39 of the trunk line TL to give answered supervision to the main exchange and to bring about a cessation in the applied ringing current. Hold relay III also opens the ring-up bridge at another point at its upper armature, while at its inner lower armature it opens the locking circuit of ring-up relay I I2 to restore the ring-up relay and to extinguish the line lamp I2I.

The operator now converses with the calling subscriber and secures information concerning how the call is to be completed. In order to explain the call-oflering feature of the trunk cord circuit, it will be assumed that the calling subscriber is requesting certain information and is not asking for a connection to a specific local line. It may be further assumed that the operator does not know for a certainty which of the various local subscribers has the desired information. In this event the operator proceeds to get in touch with local subscribers one after another until she discovers the right one. It is thought best that the calling subscriber be rendered unable to hear the conversation taking place between the operator and the successive local subscribers, for which reason cord splitting facilities have been provided, operable at the discretion of the operator.

Splitting the cord TC In order to split the trunk cord TC, the operator, while still maintaining the talking key K2 of the cord TC operated, operatesw the split key K6, 9. locking key. As long as the split key K8 remains operated, ground potential is maintained on split conductor 3I2, closing a circuit through contacts of the talking key K2 for the upper winding of split relay II3. Split relay II3 closes an answering supervisory bridge across conductors I36 and I3! at its lower armature, thereby maintaining a state of answered supervision on the trunk line TL. This relay also disconnects talking conductors I36 and I31 from talking conductors I35 and I34 at the normally closed contacts controlled by the upper and lower armatures respectively of the relay. The trunk line TL is thus telephonically disconnected or split from the trunk cord TC.

Inquiry call to a restricted line The operator may now proceed to make an inquiry connection with a local line, the line of substation C, Fig. 2, for example. She does this by inserting the plug PI into the jack J3, thereby clearing the line conductors 202 and 203 of the ground and line lamp connection. Ground potential on the sleeve of the jack J energizes the sleeve conductor I52 of the cord TC, closing a circuit through contacts of line relay I08 for the calling supervisory lamp II9, by way of contacts of the night key KI and lamp conductor 4I2. At the same time, a circuit is closed from the grounded sleeve conductor I52 through jumper I53 for the marginal sleeve relay 'I I0. Sleeve relay IIO, however, does not operate at this time because the jack J3 has ground potential connected to the sleeve terminal thereof through a resistor 201.

'Having inserted the plug PI into the jack J2 of the line of substation B, Fig. 2, the operator momentarily operates her ring-start key K5, Fig. 3, momentarily applying ground potential to ring-start conductors 3H and 303. The application of ground potential to ring-start conductor 3 closes a circuit through contacts of the talking key K2 of the trunk cord TC for ring-start relay I05. Relay I05 closes a locking circuit for itself by way of contacts of ring-cut-oflf relay I06 to conductor I5I, grounded through contacts of line relay I08 and contacts of the night-key KI.

Ringing currentfrom lead I25 is now applied through the operated lower armature of relay I05 to the ring conductor of the called line, returning to ground over the tip conductor through the upper contacts of relay I05.

When the subscriber at substation C responds, ring-cut-oif-relay I06 is operated in a directcurrent circuit including the called line, and it unlocks ring-start relay I05 and permits it to restore. The ringing operation is thereby terminated. Line relay I08 is now operated over the called line and it disconnects supervisory lamp II9 from sleeve conductor I52, thereby extinguishing the supervisory lamp II 9 to give answering supervision. At the same time, relay I08, at its middle armature breaks one point in the ground connection to conductor I5I to deenergize the hold relay I I I, but the hold relay II I remains operated for conductor I5I is maintained grounded through the inner lower contacts of the operated split relay H3. Line relay I08, at its lower contacts, closes a point in the circuit for giving the invasion-tone signal, indicative oi. the fact that the operator is listening in on the connection, but this circuit does not become effective at this time because of the operated condition of split relay II3, which relay, when operated, precludes conversation between the called local subscriber and anyone else but the operator.

The operator and the subscriber at substation B now converse. It will be assumed that the subscriber at substation C informs the operator that the subscriber at substation A is the one who should give the information to the calling subscriber. That being the case, the operator removes the plug PI from the jack J2 and inserts it into the jack JI. When the plug is removed, relay I08 restores.

Extending the incoming call Relay IIO operates when the plug is inserted into the jack J I, as the sleeve of this jack is directly grounded. Following the insertion of the plug PI into the jack J I, the operator momentarily operates her ring-start key K5, to again operate the ring-start relay I05 to start the signalling of substation A. At this point, the operator restores the split key K5 in her position equipment, thereby permitting split relay II3 in the trunk cord TC to restore and reconnect the formerly disconnected sections of the talking circuit. Also the operator restores the talking key K2, as she has no occasion to converse with the subscriber at substation A when he replies.

Local answered supervision When the subscriber as substation A responds, ring-cut-oif relay I06 operates as before and unlocks ring-start relay I05, whereupon relay I05 restores and terminates the ringing operation. Line relay I08 now operates over the line of substation A. At this time, since the split relay H3 is not operated line relay I08 removes the ground potential normally applied to conductor I5I through contacts of the key KI, opening the circuit of the locked hold relay III and permitting this relay to restore, and the hold lamp I20 to become extinguished. With the relay III r estored, the continued state of answered supervision is dependent upon the continued operation of sleeve relay IIO, as the talking connection between conductors I33 and I35 is now completed only at the upper contacts of relay IIO. As before, line relay I08 disconnects supervisory lamp H9, thereby extinguishing it to give answered supervision.

The subscriber at substation A may now converse over the trunk line TL with the calling subscriber.

Invasion signal It may be pointed out that in the event that the operator (inadvertently or otherwise) operates the talking key K2- while the subscriber at substation A is conversing with the calling subscriber by way of the trunk line TL, the contacts of the key K2 connect tone-relay conductor 3I3 to ground through contacts of the operated line relay H8 and contacts of split relay II3. This brings about an operation of tone relay 302 to cause the warning tone to be applied as hereinbefore described, thereby warning the operator and the subscribers that the operator has invaded the secrecy of the conversation.

A temporary transfer connection For the purpose of explaining the recall and temporary transfer feature of the private branch exchange, it will be assumed now that the subscriber at substation A is unable to supply a certain feature of information desired by the calling main exchange subscriber. Under this condition, the subscriber at substation A requests the main exchange subscriber to hold the line for a mo ment while he secures the desired information from someone else. As the first step in securing this information, the subscriber at substation A momentarily depresses the recall push button IOI, temporarily grounding conductor 102 of his line. This operation unbalances the current flow in the windings of the differential recall relay I01, causing the relay to operate.

Upon operating, relay I01 closes a circuit through contacts of split relay II3 for control relay I I4, through the resistor II 5 to the negative pole of the exchange battery. Control relay Ill locks itself at its lower contacts to ground through the lower winding of split relay H3 and contacts of the operated sleeve relay II 0. But relay II3 does not operate in this locking circuit until the recall button IOI is released and recall relay I01 is restored to open the initial circuit of relay I I4.

Upon operating in series with relay H4, relay 6 H3 prepares a temporary locking circuit for its upper winding by way of the contacts of recall relay I01; disconnects the armature of recall relay I01 from the right-hand terminal of relay Ill and connects it to the Junction of the winding of relay III and resistor II5, preparatory to restoring relay H4; and at its upper and lower armatures and associated contacts it disconnects the trunk line conductors I36 and I31 from the conductors I35 and I3, at the same time removing the shunt normally existing around the tip and ring contacts of the jack J0 and connecting conductors I34 and I35 to the tip and ring contacts of the jack J4.

The conductors I36 and I31 are bridged by the 20 lower armature of relay H3 and its associated contact, thereby holding a state of answered supervision on the conductors I30 and I31 and consequently on conductors I38 and I39 of the trunk line TL, as regards the main exchange equipment.

The recall lamp I I6 is lighted through contacts of'control relay H4 and contacts of the jack J4 to signal the operator. The operator responds to this signal by inserting the answering plug of an idle cord circuit, the answering plug P2 of the cord circuit LC, for example, into the jack J4. The lamp H6 is thereupon extinguished by the opening of the cut-oil contacts of the jack. Answering-bridge relay 209 is energized through contacts of jack J4 and the right-hand winding of repeating coil I09 to maintain answering supervisory lamp 2I5 unlighted. The operator, by throwing the talking key K4, converses with the subscriber at substation A, the calling main-exchange sumcriber being unable to hear the conversation.

Upon learning who the subscriber at substation A desires to converse with, the subscriber at substation B for example, the operator inserts the calling plug P3 of the cord circuit LC into the jack J2, completing the connection between the line of substation A and the line of substation B. The operator causes the subscriber at substation B to be signalled in the hereinbefore described manner.

When the subscriber at substation B responds, the talking connection is completed through the local cord LC from the line of substation C through the jack J 4 to the line of substation A, so that the two local subscribers may converse as desired.

Temporary transfer back to main exchange connection It maybe assumed now that the subscriber at 60 substation A, upon conversing with a subscriber at substation B, discovers that he needs to secure further data from the calling subscriber before the subscriber at substation B can give the complete information. That being the case, 65 the subscriber at substation A requests the subscriber at substation B to hold the line for a moment while he again converses with the calling main-exchange subscriber.

T0 transfer the connection back to the trunk 70 line TL, the subscriber at substation A again momentarily operates his recall button IOI. Recall relay I01 is again momentarily operated to apply ground potential to the middle upper armature of relay I I3. At this time, a temporary lock.

' calling main exchange subscriber, he may again,

ing circuit for the upper winding of split relay H5 is closed at the inner upper contacts of the relay, and a shunt circuit for relay iii andthelower winding oi relay H3 is closed through the middle upperarmature and working contact of relay H3. The resistor i 05 prevents the flow of excessive current in this shunt circuit. Relay lit restores and opens its locking circuit at its lower contacts.

When the recall button i ti is restored and the back to the trunk line TL. It is to be noted that 1 the ring terminal of the jack J4 is now connected to the tip terminal of the jack through the upper armature and resting contact of relay H3, hold-= Transfer back to the local connection As soon as the subscriber at substation A has received the desired additional data from the relay II4 when recall button IOI is restored and recall relay IIl'I restores.

with the connection again transferred from the trunk line TL to the line of substation B by way of the local cord LC and the jack J4, the subscriber at substation A again converses with the subscriber at substation B pursuant to obtaining .the desired information. I

Clearing out the transfer connection It may be assumed now that the subscriber at substation A issatisfied with the information he receives from the subscriber at substation B and" the conversation between the two subscribers is thereby terminated. Under this condition, the subscriber at substation A again momentarily operates his recall button IIJI, bringing'about the successive restoration of control and split relays H4 and H3 ofthe trunkcord TC. At the same time, the subscriber at substation Breplaces his receiver (not shown) whereupon disconnect supervision is given by way of the. calling supervisory lamp 2" because of the restoration of the calling-bridge relay 2III. The operator therefore removes the plug P2 from the jack J 4 and removes When the calling subscriber at substation A replaces his receiver at the end of the conversation with the main-exchange subscriber, line relay I08 restores and closes a circuit for supervisory lamp W H9 through contacts of the key Ki and lamp conductor M2, to light the lamp H9 as a disconnect signal. 1

M9, the operator may either take down the con- 4 nection immediately by withdrawing the plug Pi from the jack 58, or she may again throw her talking key Kl to inquire of the calling main exchange subscriber whether he has completed his transaction with the establishment owningthe private branch exchange. The operator follows one procedure or the other, depending entirely upon her instructions. ceeds in the last mentioned way, the operation of the key K2 reoperates holding relay I ll and relights hold lamp I20. Relay III shunts the upper contacts of sleeve relay IIIJ, permitting the operator to withdraw theplug Pl from-the jack J1 and transfer the incoming connection to any other line.

b At any rate, when the plug PI is finally removed from the jack last used (hold relay I01 has been restored at such time) sleeve relay IIO restores and disconnects conductors I35 and I33, thereby removing the right-hand windings of repeating coil I09 from in bridge of the conductors of the trunk line TL and giving disconnect supervision in the main exchange. 1

Outqoing call from the branch exchange In the event that shepro- The way in which outgoing service from the branch exchange is handled will now be explained. For this purpose it is assumed that the subscriber at substation A, desiring to make .a call to the main exchange, removes his receiver and thereby causes the line lamp I84 associated with the jack J I to become lighted as a calling signal. The operator responds to this signal by inserting the answering, plug of a local cord, such as the answering plug P2 of the local cord LC, into the jack J I, answering the call in the manner hereinbefore described.

I Upon conversing with the subscriber at substation A and learning that he desires to make a -main exchange call, the operator removes the plug P2 from the jack J I and inserts the plug of an idle trunk cord, the plug PI of the trunk cord T0 for example, into the jack J I. The operator does not thereafter need to pay further heed to the outgoing connection in the event that the main exchange is a manual exchange, for the act of inserting the plug PI into the jack J I signals the main exchange operator, as will now be pointed out. Since the receiver is off at the substation A, line relay I08 is energized in the usual way to maintain the. supervisory lamp II9 exv tinguished. Sleeve relay. I III is energized over sleeve conductor I52 and at its upper contacts it places the right-hand windings of. repeating coil I09 in bridge of the conductors of the trunk line TL, closing a direct current circuit over trunk line TL to bring in the usual line signal in the main exchange. I

' When the conversation has been completed, and the subscriber at substation A has replaced his receiver, the restoration of line relay I08 results in the lighting of supervisory lamp -I I9 as a disconnect signal, whereupon the operator may take down the connection.

Withholding main exchange service from re-- striated lines In order to confine the inter-exchange traific more closely to oflicial business calls, it is customary for the management of an organization using a private branch exchange to specify that certain lines shall not be permitted switching service as regards main exchange connections. Provisions have been made in the private branch exchange disclosed herein for enforcing this rule notwithstanding possible collusion between a restricted-line subscriber and the branch exchange operator. The way in which this rule is enforced will now be pointed out more particularly.

The ground connection to the sleeve terminal of the jack of each restricted line is made through a resistor such as theresistor 20'I associated with the jack J3 of the restricted substation C, This resistor has been so chosen and the local cords LC have been so designed that the restricting resistors do not interfere with the putting up of local connections, but the putting up of a main exchange connection to a restricted'line is prevented. It is to be noted that the sleeve terminals on the plugs P2 and P3 of the local cord LC are joined by a sleeve conductor, and that over this conductor the relatively high resistance winding of ring-cut-oflf relay 2 is controlled in the manner hereinbefore explained to control the cutting off of the ringing current and the lighting'of supervisory lamps 2I6 and 2H. Relay 2II operates satisfactorily through a resistor such as 201. On the other hand, the sleeve relay IIO of the trunk cord TC, together with the similar sleeve relays of the other trunk cords, is so wound and adjusted that the relay does not operate in series with a resistor such as 201. Keeping in mind that sleeve relay IIO must be in an energized condition to maintain conductors I33 and I35 joined together after hold relay III has fallen back, it will be seen that no conversation can take place over the trunk line TL and through the plug PI when the sleeve current obtained from a jack is insuflicient to operate the marginally adjusted sleeve relay I I0. It will be recalled that conductors I33 and I35 are initially joined by the hold relay III when 'relay' III operates responsive to the initial manipulation of talking key K2. But relay III is restored by the operation of line relay I00 when the local subscriber answers, unless the operator is making an inquiry call, as hereinbefore explained, in which case split relay II3 prevents the restoration of relay III, but also disconnects the main exchange trunk.

From this it will be understood that the incoming trunk is opened and disconnect supervision is given to the main exchange operator when the local restricted service subscriber removes his receiver to answer'the call which has been negligently or otherwise extended to his line by the branch exchange operator. The trunk is thus freed for further use at the main exchange and- Preventing barred conversation over operator's listening taps It is to be noted that disconnect relay 302, in addition to energizing the operators transmitter, disconnects the local tip and ring listening and talking conductors 305 and 306 from the operators headset conductors and consequently from the corresponding conductors associated with the trunk cords such as TC. This arrangement insures that the operator cannot surreptitiously complete a connection between a restricted service line and a trunk line such as TL over her headset conductors through the use of a local cord plugged into the restricted service line (with the talking key thereon thrown) and a trunk cord plugged into a non-restricted line (with the talking key such as K2 thrown thereon),

.as the disconnect relay 302 under such conditions severs the listening-lead connection between the local cord and the trunk cord.

The foregoing provisions bar restricted lines also from outgoing trunk calls.

matic exchange When the main exchange is an automatic exchange, the branch-exchange operator is required to send the impulses necessary to position the switches in the automatic exchange. She does this by throwing the dial key K3 to transfer conductors I I38 and I33 from the holding bridge through the right-hand windings of repeating coil I09 into association with the calling device CD, which calling device is common to all of the trunk lines such as TL. This calling device is operated in the usual manner to transmit the series of impulses, or interruptions, being provided with a condenser II! and resistor II8 which cooperate to reduce sparking and im-v prove the quality of the impulses. For operation in conjunction with a manual main exchange, the calling device CD is omitted, in which case the dial key K3 may be used as a flash" key, to flash or intermittently signal the mainexchange operator when it is desired to attract her attention during the process of setting up or receiving calls.

Through supervision from a local line to the main exchange sociated with the sleeve relay H0, in which case the connection between sleeve conductor I52 and sleeve relay IIO is controlled by line relay I03. Keeping in mind that the supervisory bridge through the right-hand windings of repeating coil I09 is controlled at the upper contacts of sleeve relay I I0 it will be seen that the immediate restoration of sleeve relay IIO following the restoration of line relay I00 gives the usual disconnect supervision in the main exchange. Line relay I08 is provided with a retarding sleeve, as indicated in the drawings, so as to render the relay slightly slow releasing to guard against false disconnect signals occasioned by inadvertent momentary manipulation of the hookswitch at the local telephone. With the jumper I53 removed, the operations involved in setting up connections through the trunk cord TC are the same as described hereinbefore, except that the inter-exchange trunk holding circuit is opened immediately upon the receiver being replaced at the local substation, as above noted,

In connection with the feature being discussed, it may be pointed out that the local operator is preferably instructed to remove the plug PI from the local jack immediately upon receiving the disconnect signal H9 and without challenging the connection or making inquiries, when the through-supervision feature is used, thereby greatly speeding up the service and minimizing the work of the branch exchange operator. It will be recalled, of course, that the recall jack J4 and lamp I I6 are provided to enable those subscribers having access to main exchange service to recall the local operator without relying on "flashing" the hookswitch. Therefore, if the main exchange connection is to be transferred to another local line, the local subscriber involved may get in touch with the operator by the recall operation hereinbefore pointed out rather than by a flashing of the hookswitch, thereby removing all necessity for the local operator to challenge a disconnect signal before she takes down the connection.

Night service at the branch exchange In order to provide night service for such employees of the organization served by the branch exchange as may be on duty at times other than the regular hours for switchboard operation, the trunk cords such as TC are arranged so that one or more may be plugged into local jacks to give direct service to and from the main exchange. For example, if the line of substation A is to be used during the time when the regular operator is not in attendance at the branch exchange, the plug PI may be inserted into the jack J I, with the night key KI operated. The night key disconnects the supervisory lamp 0 as a current saving feature, and it disconnects the windings of repeating coil I09 from in bridge of the two sections respectively of the talking circuit and joins conductors I3I and I32 directly with the conductors I33 and I34, connecting the tip and ring conductors of the plug PI straight through to the conductors I38 and I39 of the trunk line TL, by way of contacts of sleeve relay H0. The inner lower pair of contacts of the night key KI, shunts the terminals across which jumper I53 is connected, so that sleeve relay H0 is connected to the sleeve of the plug PI with the night key thrown, whether the jumper I53 is in place or not. The sleeve relay H0 is therefore in operated position and maintains conductors I33 and I closed so that ringing current received from the main exchange passes through to the local substation. At this point it may be mentioned that night service cannot be given to a restricted service line, such as the line of substation C, Fig. 2, because sleeve relay IIO will not operate through a resistor such as 201 to join conductors E33 and I35 together.

In the event that the main exchange is an automatic exchange, the local lines plugged up as above for direct night service with the main exchange may be automatic telephones equipped with the usual calling device. This calling device is used in the usual way to call main exchange numbers.

The night alarm system whole time to switchboard operation, it is advantageous to provide a suitable audible alarm circuit to call the attention of the night operator when such attention is needed. The night alarm circuit of Fig. 4 has been provided to give a satisfactory service of this nature in an economical manner.

Previous arrangements for giving night service have made use of a series relay (such as series relay 403 in local lead M2) in a line-lamp lead such as M I, but such a relay requires frequent adjustment when a large number of lines are connected to the branch exchange because of the effect of shunts or line leaks, which are usually negligible as far as a single line is concerned, but which become considerable when a large number of lines are involved. The alarm circuit of Fig. 4 responds to a change of current and is largely independent of the amount of current flowing over conductor 4. v

In order to place the night alarm circuit in receptive condition, the night-alarm key K1 is operated. The upper contacts of the key Kl remove the shunt from around the primary wind- I ing of the induction coil 400; the lower contacts of the key remove the shunt from around series relay 403, and apply energizing potential to the priming winding of the line-pulse relay 40 I; while the middle contacts of the key, arranged to make last, connect the secondary winding of induction coil 400 in series with the operating winding of relay 40I through contacts of auxiliary relay 402. Relay 40I is so designed and adjusted that the current-flow through the lower winding, the priming winding, energizes the relay suficiently to render it near the verge of operating, but not sufficiently to operate the relay. The relay is therefore in a very sensitive condition, awaiting an impulse at the induction coil 400. Any impulse that occurs by the removal of the shunt from around the primary winding of the induction coil 400 at the upper contacts of the key has been dissipated by the time secondary winding of the coil and the upper winding of relay 40I have been connected in the circuit.

With the key Kl operated, the removal of the receiver at a substation, such as B or C, closes a circuit for the line lamp, such as 204 or 208, over conductor 4 in series with the primary winding of induction coil 400. Such current increase change as occurs takes place rather rapidly because of the relatively large amount of current drawn by the filament of a lamp when the lamp is cold (a tungsten or similar filament being preferred). The rise of current in the primary winding causes an induced current to flow in the secondary winding of induction coil 400 through the contacts of the key K1, the line Winding of relay 4M, and contacts of relay 402. The direction of this current is such as to assist the magnetic field already set up by the energization of the priming winding of relay 40I, causing relay 40I to operate. The impulse is soon dissipated, but relay 40I, having once operated, remains operated from the energization produced by the priming winding, this tendency being well known.

Auxiliary relay 402 operates; it first disconnects the line winding of relay 40I to prevent a reverse impulse therethrough; at its middle armature, relay 402 closes a shunt around the primary winding of coil 400 so as to afford a direct lighting circuit for the line lamp at the calling station; and at its upper armature it closes a circuit through the windings of retard coil 404 for the buzzer B. The buzzer B is shunted by the condenser 406, which condenser operates in con- Junction with the retard coil 404 to avoid ripples in the potential of the branch exchange battery occasioned by the action of the buzzer.

The circuits of Fig. 4 remain in this condition, with buzzer 405 operating until the night operator responds to the signal and restores the key K'I.

When the key K1 is restored, the circuit of the lower winding of relay 404 is opened, causing relay 40I to restore and bring about the restoration of auxiliary relay 402, and the consequent cessation of the buzzer signal.

After the night operator has disposed 01 the call, he reoperates the alarm key K! to position the night alarm circuit for further operation.

With the night alarm key K1 in operated position, series relay 403 responds to a flow of current over the local lamp conductor 2 in the event that the circuit of a supervisory lamp such as 2 I6 or 2H, Fig. 2, or the circuit of a line or supervisory lamp such as I2! or H9, Fig. 1, is closed. Relay 403 operates the buzzer 405 attracting the attention of the night operator.

Having described the invention, what is considered to be new and is desired to be protected by Letters Patent will be set forth in the following claims.

What is claimed is:

1. In a private branch exchange served by a manual switchboard and trunk-connected with a main exchange, a trunk cord for interconnecting a main-exchange trunk with local lines, local cords for interconnecting local lines with each other, and means effective when the main exchange trunk line is connected through the trunk cord to a local line for setting up a connection by way of a local cord and through the trunk cord between such local line and another local line.

2. In a private branch exchange served by a manual switchboard and trunk-connected with a main exchange, a trunk cord for interconnecting a main-exchange trunk with local lines, local cords for interconnecting local lines with each other, means effective when the main exchange trunk line is connected through the trunk cord to a local line for setting up a connection by way of a local cord and through the trunk cord between such local line and another local line, and means controlled from the substation on the trunk-connected local line and operable at the will of the subscriber on such line for transferring the telephonic connection of his line from the trunk line to the said other local line through said local cord circuit and for transferring the connection back again from the said other local line to the trunk line, as often as may be desired.

3. In a telephone system including a manual switchboard, a cord circuit through which connections may be extended to and from subscribers lines, means in a cord circuit controlled by the fiow of transmitter current to a. connected line for giving answering and disconnect supervision, a recall device in the cord circuit nonresponsive to control over the line when answering said disconnect supervision is given, means controlled by a subscriber on a line connected with by said cord circuit for placing a special condition on the line to bring about the operation of the said recall device, and means for signalling the operator when the recall device is operated.

4. In a telephone system served by a manual switchboard, a cord circuit for setting up connections between lines, a supply circuit at the cord circuit for supplying transmitter current to a connected line, a differential relay in said supply circuit at the cord circuit non-responsive to the normal balanced condition of the transmitter supply circuit, means operable at the will of the subscriber on a connected line for unbalanclfig his line to bring about the operation or said differential relay, and an operator's signal controlled by said differential relay to inform the operator when the subscriber causes the diflerential relay to be operated.

5. In a telephone exchange served by a manual switchboard, a cord circuit for use in interconnecting the lines, a transmitter-current supply connection in said cord circuit effective to supply transmitter current to a connected line, a disconnect relay and a recall relay connected in said transmitter supply circuit, and means controlled by the subscriber on a connected line for selectively controlling the said relays.

6. In a private branch exchange served by a manual switchboard trunk-connected to the main exchange, a trunk cord and plug at the manual switchboard terminating a trunk line incoming from the main exchange, a hold signal and means for displaying it responsive to the operator having answered an incoming call, and means for maintaining said hold signal displayed until the operator has extended the incoming connection to a local line.

7. In a private branch exchange served by a manual switchboard trunk-connected with the main exchange, a talking key associated with a main exchange trunk and operable to place the operator in telephonic communication with the trunk to answer an incoming call, a hold signal associated with the trunk and means for displaying it responsive to the operation 01' the talking key, and means for maintaining the hold signal displayed after the talking key has been restored and until the incoming connection has been extended to a local line.

8. In a private branch exchange served by a manual switchboard trunk-connected with the main exchange, a talking key at a trunk line operable by the branch exchange operator to enable her to answer an incoming call, locking means controlled by operation of the talking key to place and maintain a state of answered supervision on the incoming trunk line when the incoming call is answered, means eflective alter the operator has extended the incoming connection to a local line and the subscriber thereon has answered for restoring the locking means, means including a supervisory relay controlled over the called line for maintaining the state 01 answered supervision on the incoming trunk line during the conversation between the main exchange subscriber and the local subscriber, and means controlled by the restoration of said supervisory relay when the local subscriber replaces his receiver for transferring the incoming trunk line into a state of disconnect supervision and for giving disconnect supervision to the branch exchange operator.

9. In a telephone system served by a manual switchboard, cord circuits at said switchboard for completing connections from calling lines to called lines, operator's telephone conductors, a talking key at each cord circuit for connecting the operator's telephone conductors to the talking conductors of a cord circuit to enable the operator to converse with the calling subscriber, a supervisory relay in the cord circuit and means for operating it when the called subscriber answers the call, and means controlled Jointly by switchboard, cord circuits through which connections are extended to called lines. a talking key at each'cord circuit operable to place the operator into telephonic communication with a subscriber by way of the cord circuit, a supervisory relay in each cord circuit operated when the called subscriber answers, means controlled jointly by the said supervisory relay and the talka ing key for applying a distinctive audible frequency tone to the talking conductors of the cord in the event that the talking key is operated during the progress of a conversation through the cord circuit, cord splitting means in the cord circuit operable to enable the operator to divide the cord into two sections and converse with the called subscriber without being overheard by the calling subscriber, and means for preventing the said application of distinctive tone current.

while said splitting means is operated.

11. In a telephone system in which connections are set up through cord plugs and line jacks, local cord plugs and a trunk cord plug, a sensitive sleeve relay associated with each, local cord plug, a marginal sleeve relay associated with the trunk cord plug, circuit connections with certain of the local Jacks for enabling either a sensitive or a marginal sleeve relay to energize thereover, and circuit connections associated with the sleeve conductors of certain other jacks over which the sensitive sleeve relays of the local cords may operate. but over which the marginal sleeve relay oi the trunk cord will not operate, and means in the trunk cord for completing an eiiective talking connection therethrough controlled by the sleeve relay, whereby any, local line may be connected telephonically with any other local line and a talking trunk connection may be set up be-' tween the trunk and certain of said lines and not between the trunk and certain of the other lines.

12. In a manual switchboard used to give local service and trunk service to subscribers lines,

certain 01 said lines being restricted to local service while other lines are permittedtrunk service, trunk cords for setting up trunk connections to lines entitled thereto, local cords for setting up local connections, operator's headset conductors, s a separate talking key at each of the cord circuits for connecting the operator's headset conductors to the talking conductors oi the cord to enable .the operator to converse with the calling subscriber, and means eflective whenever the talking key 01' a trunk cord is thrown for disconnecting the operator's leads from the local cords, whereby a restricted line may not be connected with a trunk line through a local cord and a trunk cord in the event that a local-cord talking key and a trtgnk-cord talking key are simultaneously opera d. v v

13. In a branch-exchange telephone system, trunk lines connecting the branch exchange with the main exchange for giving main-exchange 20) service to branch exchange subscribers, a switchboard cord and plug terminating a main-exchange trunk, a normally open point in one of thetalking conductors of said trunk. a supervisory relay controlled through the cord and plug and. over a local line to close said normally open point during conversation to give supervision to the main ,exchange, and means associated with said cord and including a manually operable key for bypassing said normally open point and for transierring the trunk conductors directly through the plug to the connected line, whereby ringing current may be received directly by a local line from the main exchange and supervision may be directly given from the local line to the main exchange.

14. In a private branch exchange, means for extending connections between subscribers in the branch exchange, trunk lines to a main exchange, means for extending connections from and to the subscribers lines in the branch exchange over the trunk lines, means in the trunk line operated by a calling or a called subscriber in the branch exchange for switching the connection from the trunk line to a local connecting means, and for (El thereafter switching the connection back to the trunk line at will.

THOMAS F. CROCKER,

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