US1381456A - Automatic telephone-exchange system - Google Patents

Description

n. DEAKIN. AUTOMATIC TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED APR... II, 1919.

UNITED STATES PA'rsNr OFFICE.

GERALD DEAXIN, OF LONDON, ENGLANDASSIGNOR TO EVESTERN 'ELECTRIC COM- PANY, INCORPORATED, OF NEW YORK, iN. Y., A CORPORATION OF NEW YORK.

AUTOMATIC TELEPHONE-EXCHANGE SYSTEM.

To all whom t may concern Be it known that I, GERALD DEAKIN, a citizen of the United States, residing at London, England, have invented certain new and useful Improvements in Automatic Telephone-Exchange Systems, of which the 4following is a full, clear, concise, and exact description.

This invention relates to telephone exchange systems and more particularly to improvements in full automatic and semi-automatic telephone systems.

The object orn this invention is to provide a new and improved arrangement of private branch telephone exchanges having a plurality ottrunk lines leading from a main central office exchange7 at which oiiice socalled iinalor connector switches are adapted to seize any one of said trunk lines when idle. Private branch telephone exchange trunk lines are usually arranged in groups on the connector' switch terminal banks and a group of such trunks leading to a particular privatelbranch exchange is designated by a single number in the telephone directory. The connectors are adapted to be directly operated to step on to the first trunk terminalsin such a group and, it the associated trunk line is busy, to automatically hunt,- due to this busy condition for the iirst idle trunk line and extend an incoming call to the operator at the private branch exchange.

Each of these trunk linesterminate at the .tocall the central officev and to be called by subscribers through the central ofiice. To this end such private branch exchange lines'are connected with lcertain trunk lines 'by meansoi the usual plug and jack and by manipulating a so-called through service key, these trunlr lines and associated cir cuits are prepared for such through service. It is evident that under suoli circumstances said trunk lines must be the only ones accessible .to the connector switches at the central oiiice,` that is, only thetrunk lines connected directly to the private branch exchange lines Specification of Letters Patent.

Application gled April 11, 1919.

Patented June 14, 1921.

serial No. 289,197.

ber of the trunk line wanted and complete the connection in the ordinary manner.

`ln an automatic telephone exchange, where the trunk lines leading to a private branch exchange are only accessible by means oi automatic connector switches, the

conditions are different and means must be provided to distinguishl between such trunk lines that are connected for night service and those that are not connected. Ordinarily, the last private branch exchange trunk line in a group is provided with a low resistance path to battery in shunt with the high resistance winding of the cut-off relay so that the hunting in the group will cease at such last trunk line. It thistrunlr line is engaged or busy, the connector switch will send a busy signal back to the calling subscriber, but if the'last trunk is idle the connector will seize it in the usual manner and extend the connection and ring the private branch exchange operator. The direct lines are similarly equipped with a low resistance l,path to battery and` will therefore act exactly the same Vas the last trunk line.

One feature of the present invention provides means for rendering a plurality ot private branch exchange trunk lines in a group accessible to a directively operated connector by shunting the cut-off relays of such trunks by a low resistance to battery. .Thesen trunks will thereby be available for through service in the same manner as the last trunk line in a groupand the ordinary direct lines. The numbers of the private branch exchange subscribers connected for .through service may be listed in the telephone directory in the same manner as ordinary subscribers except that they will be designated for night service only. Vfhen any one of these numbers is called, the connector switch will be directed by selecting impulses to the number wanted in exactly the same manner as when a direct line is selected and the trunk line so connected will act as a direct line and the connector switch will thereby be prevented from hunting in the group.

To accomplish this purpose, there is provided an automatic switch that is operated lmanually by the depression of a key to cut ing a limited number of trunk lines, the cutting in of resistanccs may be accomplished by means of a relay or relays in place of `the automatic switch. The usefulness of these arrangements lies in their flexibility as the switch vmechanism or the relays .may be easily arranged to increase or decrease the number of trunk lines controlled and any one of the trunks may be selected for this service. The fact that the control may be exercised at the central office or at the private branch exchange is of considerable advantage.

Another feature of this invention is the lprovision of means whereby the ringing on incoming calls automatically ceases soon after a connector switch is set on an idle trunk line but before the private branch exchange operator answers. This is accomplished by means of relays at the private branch exchange that operate in response to vthe ringing current to connect one of the talking leads to ground for the operation of a ringing cut-olf relay at the connector switch. The trunk lines will thereby be cleared for talking when the private branch exchange operator actuates her listening ke a Y Another feature of this invention is the provision of means whereby, when the calling P. B. subscriber in an outgoing call hangs up and before the P. B. X. operator removes the corresponding plug, the trunk vlineniay be immediately seized by a con- .nector switch on an incoming call and the plug end cu-t off to prevent ringing current Vfrom passing through to the substation.

This is alsoV accomplished by means of the relays operating in response to ringing current from the connector switch. The speed in which one connection with the private branch exchange may terminate and another be established is thereby considerably increased.

Another feature of this invention is the provision of means whereby the storage battery used by lthe trunk lines and associated .circuit arrangements at the private branch exchange is charged from the central oiiice source of direct current, whenever a trunk line is not engaged in a connection. This is accomplished by means of aV battery and an adjustable resistance connected through the line relay at the central office7 and over the tip side of the line, through a contact of the supervisory relay and a resistance'to the storage battery. The plugging through of the trunk to a private branch exchange subscriber for night service does not interfere with the charging, but the charging circuit is cut oil' by the supervisory relay whenever the trunk line is engaged.

This and other features of the invention tending to increase the efficiency and flexibility of the private branch exchange service will become apparent in the following description.

In the accompanying drawing, Figure 1 represents diagrammatically an automat-ic telephone exchange system, a private branch exchange system and an arrangement of trunk lines as involved in this invention. Fig. 2 represents a modification of the trunk line control circuit.

Tn the drawing, the parts designated B represent an automatic telephone exchange system such as is shown and described in the U. S. patent to F rank R. McBerty, No. 1,146,583. For the filial or connector switch has been substituted one having a somewhat different circuit arrangement in order to bring out clearly its connection with this invention7 but as it does notas a whole form a part of this invention only such of its functions as relate to the present invention, will be described; as for the remaining functions reference may be had to the above mentioned patent.

The part designated C represents an arrangement of various groups of trunk line terminals and means for rendering a plurality of trunk lines accessible to directively operated connector switches.

The parts designated D represent a private branch exchange trunk line with suitable circuit arrangement for connecting it to a private branch exchange subscribers line indicated at E. In accordance with the above-mentioned patent, the calling subscriber A, when desiring a connection with a subscriber E at the privat-e branch exchangemay, by manipulating his sending apparatus, send impulses through a line finder switch 1() to a register control and sender equipment indicated at 11 at the central office, which acts as a controller to govern the subsequent selecting operations necessary to extend the connection through a series of selector switches 12 and 13 and the final or connector switch 14 to a groupv of private branch exchange trunk lines.

lt will be assumed that an ordinary day service call is to be set up and that all the 'selecting impulses have been sent to extend trunk line Yis tov begin'. Inasmuch as the 10 tical with the corresponding operationsin operations up to this stage are exactly identhe above-mentioned patent, it is assumed thatthev description of the operation of the connector Switch from this stage on and the subsequent operations necessary to extend the incoming call to a calledl subscriber at the private branchl exchange will be suiiicient to clearly Vunderstand the invention involved.

The trunk-hunting operations of the connector switch begin when the sequence "switch 100 arrives in position 6, in which position the line relay 25 is permitted to be denergized. The selector switch B has access to direct subscribers lines, such as line 32, and also to private branch exchange trunk groups, one of which is shown consisting of the trunks 33, 34 and 30. When the brushes of the selectorswitch are advanced to the first trunk 33 of an exchange group, and such trunk is busy, the vswitch is arranged to` determine this fact` andto continue to hunt over the succeeding trunks in search of an4 idle one. The cut-oif relays, such as relay 102, of4 all trunks preceding the last trunk 30 ofan exchange group are provided with a Ihigh resistance winding. If the iirstV trunk of the group is busy, the potential on the test terminal, applied through the high resistance winding of relay 102, is reduced to such an extent that the test'relay 35 cannot operate to discontinue the movement of the selector switch inthe manner `described in detail hereinafter. Consequently, the switch advancesjto the next trunk, and so on, until :an idle one is found, or until it reaches the last trunk 30 in the group. The switch will stop on the terminals of this trunk regardless of the kbusy or idle condition thereof. To accom- Y plish this feature the winding of cut-off relay 44 is shunted'by a low resistance 43.

Due to the low resistance 43, sufficient potential existson the test terminal 45, even though the trunk is alreadyengaged to permit the energizationof test' relay 35. Relay.35 consequently becomes operated and terminates the hunting movement of the selector switch. The sequence switch 100, as hereinafter explained, advances through position.8, inwhich position a test is made to determine the busy or idle condition of thetrunk 30. ,If the trunk is idle, full potential existson terminal 45, kand the testrelay 57 is operated through its high resistance winding to control the sequence switch 4 100 in a manner to Seize and apply ringing 'current to the tru-nk line. If, however, the

trunk -is busy, the potential on the test terminal 45 is so reduced, notwithstanding the low resistance shunt 43, that relay 57 cannot operate and thev sequence switch 100 is controlled in a different manner to bring about the release of the selector switch and the application of a-busy tone back onthe calling line. Should one of the first trunks in the group, such as trunk 33, be-idle when a test thereof is made, full battery potential is applied throughthe winding of cut-oi relay ,102, and the test relay 35 attracts its armatureto determine the hunting movement of the selector switch B. A d y lConsidering the direct, subscribers line, indicatedat 32, the cut-ofi' relay 101 thereof is provided `with a comparatively low resistanceV winding. In other words, the resistance of relay 101 corresponds to the combined resistance of cut-oif relay 44 and resistance Y43 associated with the last trunk oaA private .branch exchange group. Consequently, when the brushes of the selector `switch are advanced to the terminals of a subscribers line, such as line 32, the switch does not perform a huntingV movement even minals 30 of the last trunk line 31. As theconnector finds the trunks 32, 33 and 34 busy, the private branch exchange relay 35 will not be energized and a circuit for the power magnet 36 will be established as soon as the armature of line relay 25 reaches its back contact.V This power circuit extends from battery, power magnet 36, upper contact of sequence switch contact 38, back contact and armature of relay 40, back contact and armature of relay 25, to ground. This circuit 'keeps the power magnet energized andthe brushes, of the switch are advanced o ver these busy trunk line terminals until they finally land on terminals 30,7whena circuit is establishedl fromv battery 42, resistance 43 in parallel with battery and cut.- offrelay 44through terminal 45, brush 46, private branch exchange relay 35, lower contact of sequence switch contact 48, to ground. This energizes relay 35 and establishes a circuit from battery, resistance 50, armature and front contact of relay 35, test relay 40, front contact and armature of relay 52, to ground, as relay 52 is held up as long as the connectorswitch is engaged. Test relay 40 energizes and breaks the above-mentioned power circuit" so that the power magnet 36 `denergizes and stops the switch. The energization of the test relay 40`establishes a circuit from battery, sequence switch 100, upper contact `of sequence switchcontact 54,

`:front contact and ,armature of relay 40, back contact and armatureof relay 25, to

v5'? will be energized when theV sequence switch passes through position l8 by a circuitestablished from battery 42, resistance 43, terminal 45, brush 46, high resistance winding of relay 57, upper contact of sequence switch contact 48, to ground, andestablish a'locking circuit for itself through its low resistance winding, front contact and armature, test relay 40, front Contact and armature of relay 52, to ground. In this manner relay 40 is held energized, and as the sequence switch contact 54 is closed through Vposition-s 6 to 11, the sequence switch will advance to position 12.

1n position 12 ringinglcurrent is applied from alternating-current ringing source 58, upper contact of` sequence switch contact 59, brush 60, terminaly 61, contacts ofdialing key 62, retardation coil `63, condenser 64, trunk line relay 65, contacts of dialing key 62, terminal. 66, brush 67, lower contact of sequence switch corntact 68, ringing -relay 69, to battery. This circuit operates trunk line relay whic'h` relay locks .up

over a circuit from battery 325, battery cut-oll`` key 95, trunk line cut off relay and holding winding of the Vrelay 65 and its front contact 'and armature, to

Yground at a contact of listening key 72.

This holding circuit energizes the cut-off relay 70, which relay cutsof the trunk leads to ylistening key 72 and extendsthe trunk leads through a condens-er 71 and relay 7 3. Relay 73 is energized over the same circuit asrelay 65 and relayf applies at itsfront contact and armature a ground to the tip side of the line. This ground completes -ajdirectcu'rrent circuit for the ringing relay 69 from battery, ringing-relayf69, lower contact of sequence switch contact 68, brush 67, terminal 66, contacts of dialing key 62, upper armature andfront Contact of cut-off relay 70, to ground at the front contact and armature of relay 73, to energize .ringing relay 69 .which did not respond to the above-mentioned ringing current. The energzaton of 12 and into position 15.

Position 15 is the talking position in which the ringing current is cut oil and the .talking leads are cut through as far as the trunk .line cut-off relay 70 in readiness for the operation of the listening key. As soon as the Vringing current is cut off, the relay 73 denergizes to remove the. ground from the tip side of the line Vin order that there may be no drain on the battery 75 after the ringing period, which is practically instantaneous. W'hen the trunk line relay 65 was locked up,a branch circuit from battery,

relay 76, trunk line lamp 77., the front con-` tact and; armature of relay 65, to ground at the listeningkey 2 was completed and lamp 77 lighted to indicate to the private branch exchange operator that an incoming call was present enthis trunk line.l The operator then depresses the listening key 7 2, the immediateefiect ofwhich is'thattrunk line relay 65 'and cut-off relay 70 are released and the talking leads extended through to the operators telephonie. The 'depression oi' the listening key 72 also establishes a circuit from battery, relay,82,itoground at the listening key 72. VThis energizes relay 82 and a circuit is established from battery, armatureY and back contact of supervisory relay 83, outer armature and front contact of relay 82, supervisory lamp 84, to ground to light this lamp -for supervisory purposes as hereinafter described. The operation of relay 82 also establishes a shunt circuitacross the i, talking leads through retardation Vcoil 63, Vthrough-service key 85, inner armature and fron-t contact ot relay 82'., This shunt circuit is `used for metering purposes that forms-nofpart of this invention and need not be vfurther described.

The private branch exchange operator is operator depresses her ringing key 86 and Vrings until the calledsubscriber answers. Then the called subscriber answers, a talking circuit is completed ythrough supervisory relay 83 and the circuit for supervisory lamp 84 is `broken thereby extinguishing the lamp.l f Y At the'end of the conversation and when the Called. Subscriber hangs up his receiver,

switch to be released when the the calling subscriber hangs up, which act results in the denergizaton of relay 52, as is fully described in theA beforementioned patent.

The denergization of relay 52 establishes a circuit from battery, sequence switch 100, upper contact of sequence switch contact 56, back Ycontact and armature of relay 52, to ground, to move sequence switch-100 out of position 15 into position 17. In position 17, a circuit l, is established from battery sequence switch 100, lower contact of sequence switch contact 54, back contact and amature of relay 25, to, ground, to move sequenceV switch 100 into position 18. In

Vposltion 18 ,a circuit is established from battery, power magnet 36, upper contact of` sequence switch contact 38, back contact and armature of relay 40, back contact and' armature of relay to ground, to operate 4power `magnet 36 and drive the connector switch back to normal position. On reaching normaln position, a circuit is established from battery, relay 25, upper contact oi sequence switch contact 89, normal contact 90, to ground. Relay 25 energizes and establishes acircuit from battery, sequence switch 100, upper contact of sequence switch contact 74, and front contact and armature of relay 25, to ground, to drive sequence switch 100 back to position one.

In preparing the private branch exchange trunk lines for night service, that is, making a number .of trunks accessible for incoming calls, it is only necessary to convert them to direct lines by. inserting a low resistance shunt path to battery in parallel with the high resistance cut-off relay winding to battery. Thel trunks that are to be used for night service are then connected with the private branch exchange subscribers who are to receive or send calls directly during the absence of the private branch exchange operator. In order to prevent the trunk lines from being cut off from the connected private branch exchange subscribers by relay in the manner heretofore described when seized by the connector switch, the throughservice key and battery cutoff key are operated.

A trunk line 32 in the group of trunks at 20 is typical of the ordinary trunk line and trunks 33 and 34 are ytypical of the trunk lines to which a resistance shunt may be added., By switching inA these resistances on trunks 33 and 34, or any other trunk in the group, such trunks will be made available for through service. A sequence switch 200 is used for this purpose having sequence switch contacts, such as 201 and 202, closed in positions 2 to 18,4 to 18, etc., a normal contact 203 closed just after position 1 to just before position 18, and a contact 204 closed in position 1 and position 18. To control the sequence switch 200, key 206 at the private branch exchange and thelrelay 208 at the central ofiice, are provided. To

out in resistances, the private branch ex? change operator depresses key 206 and a circuit is establishedl from battery, relay 208, key 206, to ground. This energizes relay 208 and a circuit is established fromv battery, sequence switch 200, upper ContactA of sequence switch Contact 204, front contact and armature of relay 208, to ground.

This starts the sequence switch 200 whichA completes a circuit for itself through its normal contact 203, to ground, and continues to move or rotate until it reaches the eighteenth position when the circuit is broken and the sequence switch stops. The rotation of sequence switch 200 from position 1 to 18 cuts in the resistance 210 in position 2, resistance 211 in position 4, etc. The resistances 210 and 211 are equal in value to that of resistance 43. Hence, for example, when resistance 210 is placed in shunt around the winding of relay 102 the electrical condition on the test terminal of trunk 33 is changed to conform exactly with that on the last trunk 30 of the group. Conseiop quently, -when Vthe brushes of the selector switch B are'advanced to terminals of trunk the same purpose with respect to the nextA trunk 34. It is evident that all the resistances could be inserted at once but it is often preferable to switch them in succession. Selection of trunks for night service need not be confined to the trunks 33 and f 34 and need not be made in any particular order as Vthe trunks selected may be scattered over the group by removing sequence switch contact, such as 201 or 202, or by f the addition of others.

In Fig. 2 is shown a key 215 that may be substituted for key 206 and relay 208 and` the leads 216 and 217 may be connected at 218 and 219, respectively, to the sequence switch contact 204, in case the control over the night service is to be exercised by an attendant, such as wire-chief at the central a limited number of trunk lines and inV which .night service is confined to two or three trunks.

It is seen by this arrangement of the night and through service that no hunting will take place at the connector switch but that the connectors will be directed toa particular private branch exchange trunk by means .of'selective impulses in the same manner as Vto a direct'line and that there will be no distinction between aprivate branch exchange trunk line connected to a private branch exchange subscriber andthe line leading directly to a regular subscriber. VThe relay 'will immediately be energized when the brushes of the connector are set on a selected private branch exchange trunk, and as here inbetore described, the sequence switch will be driven toward the twelfth position. In case the line is idle, the call will proceed, as already described, but in case the wanted subscriber-is busy, the sequence switch 100 will st op in positie-n 10, for it will be remembered that it depends on the energizationV of relay 57 for maintaining'the relay 40 operated after the sequence switch passes the eighth position. Therefore, incase the line is busy, the rela-y 57 will not be energized` as there will be a low resistance pathV to ground through the test relay 57 of the connectoralready connectedto a multiple of the test` terminals of this trunk. This path to ground is of low enough resistance to prevent a suiiicient current from flowing through the highresistance winding of relay 57 of this connector. Consequently, the sequence switch will stop when it Varrives in position lO as the relay 40 that was denergized already in the eighth position, has broken the energizing circuit for the sequencefswitch 100 at its front contact and armature. In position 10, a busy tone is sent back to the calling subscriber through induction coil 250, the primary circuit being established from busy tone alternating current source 251, upper contact of sequence switch contact 252, primary circuit of induction coil 250, to ground. When the calling subscriber hangs up, due to this busy tone, relay 52 de'e'nergizesV and -a circuit is established from battery, sequence switch 100, upper Contact of sequence switch contact 56,

back contact and armature of relay 52, to

ground, Vto' move sequence switch 100 into .position 11.V InV position 11, a circuit is established from battery, power magnet,

upper contact of sequence switch contact 38, back contact and armature of relay 40, back contact and armature of relay 25, to ground,

to drive the connector switch back to nor-V relay 52, to ground, to drive sequence switch 100 into'position 17. In position 17, a cirf cuit is Yestablished from.Y battery, sequence switch 100, lower contact of sequence switch Contact 5a, back contact and armature of relay 25, to ground, to drive sequence switch 100 into position 18. In position 18, a circuit is established from-battery, relay 25,

upper contact ci' sequence switch contact 89,

normal cont-act 90, to ground, to again energize relay 25 and establish a circuit from battery, sequence switch 100, upper contact of sequence switch contact 74, front contact and armature of relay 25, to ground, to drive sequence switch 100 out of position 18 into normal position. Y

In a call outgoing from a private branch exchange, the private branch exchange subn scriber, by removing his receiver from the hook, lights the lamp 301 and the operator answers by inserting plug 78 in jack 79 which extinguishes the lamp 301. The operator then operates listening key 72 and ascertainsr the number ot the subscriber wanted. rIhe dialing of a number may be done by the private branch exchange operator by operating dialing key 62 which connects the operators sender 305 tothe trunk line and the retardation coil 306 to the plug en d of the trunk line. Vi7hen the operator has finished dialing the number, the dialing key returns to normal andthe connection which has proceeded automatically througha line finder indicated at 310 at the central oflice is extended to the wanted subscriber in the usual manner.

When the trunk ,lines are prepared for through or night service that are connected i io to certain private branch exehangesubscribcrs and the through service key 85 is operat- 1: private branch scribed, therelease of the connector is controlled by the hanging up of the calling s exchange subscribers receiver. A The circuit for charging of the storage battery at 325 extends from battery 7 5, adjustable resistance 326, line relay 327, tip

yside of trunk line 31, contact of dialing key 62, upper armature and back contact of cutoffrelay 70, outer back contact and armature of relay 82, armature and back contact of relay 83 resistance 329, key 330, battery v325 to ground. The charging of the battery is not interfered with at any time, except when the truck circuit is engaged, when the supervisory relay 83 is energized and breaks the battery circuit at its armature and back contact. The plugging up of the trunk line for night service has no effect on the battery charging circuit, as only the battery cut-oli key 95 is operated to cut oi the battery from relays 70 and 82, trunk lamp 77 and alarm relay 7 6.

What I claim is:

1. In a telephone exchange system, subscribers lines, trunk lines, an automatic switch Jfor selecting any of said lines, means for placing a given electrical condition on said subscribers lines, means for placing a different electrical condition on the trunk lines, means responsive to said electrical conditions for controlling the operation of said automatic'switch, and means for automatically changing the condition on said trunks to correspond to the electrical condition on said subscribers lines to render said trunks of the same identity as the subscribers lines.

2. In a telephone exchange system, subscribers lines, trunk lines, an automatic switch for selecting any of said lines, means for placing a given electrical condition on said subscribers lines, means for placing a diHerent condition on the trunk lines,means responsive to said electrical conditions for controlling the operation of said switch, and an auxiliary switch for changing the condition on said trunks to correspond to the condition on the subscribers lines to render said trunks of the same identity as the subscribers lines.

3. Ina telephone exchange system, subscribers lines, an operators position, trunk leading to said position, an automatic switch for selecting said lines and trunks, means `for placing a given electrical condition on said lines, means forplacing a different condition on said trunks, means responsive to said electrical conditions for controlling said switch, and means controlled manually by the operator for changing the condition on said trunks to correspond to the condition on said lines to render said trunk and lines of the same identity.

4. In a telephone exchange system, subscribers lines, trunk lines normally distinguished from the subscribers lines, a switching device operable to engage any one of said lines, automatic means at one end of the trunk for eliminating the normal distinction between a trunk and a subscribers line whereby said trunk may be engaged as a subscribers line, and means at the other end of said trunk for controlling said automatic means.

5. In a telephone exchange system, subscribers lines, trunk lines normally distinguished from the subscribers lines, a switching device operable to engage any one of said lines, automatic means for eliminating in succession Athe normal distinction between said trunks and subscribers lines whereby said trunks may be engaged as subscribers lines, and manual means for controlling said automatic means.

6. In a telephone exchange system, a plurality of trunk lines interconnecting two telephone exchanges, a switching device operable to engage any one of said trunks, means at said switching device for applying ringing current to a trunk, and means at the distant end of a trunk for completing a circuit including only one of the talking leads of said trunk to disconnect the ringing current.

7. In a telephone exchange system, a plurality of trunk lines interconnecting two telephone exchanges, a switching device operable to engage any one of said trunks, means for applying ringing current to a trunk, means at the distant end of a trunk responsive to said ringing current, and means controlled from said responsive means over one side of the talking leads of the trunk to disconnect said ringing current.

8. In a telephone exchange system, a plurality of trunk lines interconnecting two telephone exchanges, a switching device operable to engage any one of said trunks, means for applying ringing current to a trunk, means at one exchange for disconnecting the ringing means, means at the other exchange responsive to said ringing current, and means at said second exchange controlled by said ringing responsive means to operate said ringing disconnecting means over one side of the talln'ng leads of the trunk.

9. In a telephone exchange system, a plurality of trunk lines interconnecting two telephone exchanges, a switching device op-v erable to engage any one of said trunks, means for applying ringing current to a trunk, a relay at one exchange for disconnecting the ringing means, a relay mechanism at the other exchange responsive to said ringing current, and means operated by said relay mechanism for connecting a ground over one side of talking leads to control the ringing relay.

10. In atelephone exchange system, a plurality of trunk lines interconnecting twov telephone exchanges, a switching device operable to engage any one of said trunks, means for applying ringing current to a trunk, means for connecting a subscriber at the distant end of a trunk, and automatic means responsive to the ringing current for cutting off the subscriber from the trunk during the ringing perid.

11. In a telephone exchange system, a plurality of trunk lines interconnectingtwo v telephone exchanges, a switching device operable to engage any one of Vsaid trunks, means for applying'ringing current to a trunk, an operatorspositon at the distant end of a trunk, automatic means responsive to the ringing current for cutting 0E the 0perators position from the trunk, and a mauual means for restoring the connection to the operators position.

l2. In a telephone exchange system, a plurality of trunks interconnecting two exchanges, a switching device operable to engage any one of said trunks, a charging means including an adjustable resistance and a source of direct current at one exchange, an adjustable resistance and storage battery atl the other exchange, and a circuit in-v terconnecting said batteries over one talking lead of a trunk.

In Witnessy whereof, I hereunto subscribe my name this 12th day of February, A. D.,

- GERALD DEAKIN.

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