US1491177A - Telephone-exchange system - Google Patents

Description

TELEPHGNE EXCHANGE SYSTEM Filed March 1920 2 Sheets-Sheet 1' ,sists' in the provision Patented Apr. 2.2, 1924.

tFNETE STATES PATET QFFIQE.

any L. STOKELY, or :cLonxi. PARK, new

' Maui? YORK, ASSIGNOR TO W'TESTEBN ELECTRIC CDMIANY, INCORFORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filcd'march 4,

T aZZ whom it may concern Be it known that I, RAY L. S'roxnL'Y, a. citizen of the United States, residing at Floral Park, in the county of Nassau, State of New York, have invented certain'new and useful Improvements in Telephone- Exchange Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to telephone exchange systems and more particularly to such systems involving two central otlices or two private branch exchanges. More specifically, the invention relates to a systerm in which there is one central office in which both manual and automatic switching apparatus is employed in interconnecting subscribers lines, and another ofiice in which an operator manually completes the connections. Extending betweenthe otlices are trunk lines over which a subscriber at an automatic substation may call the operator at the manual exchange or, the operator at the manual exchange may call a subscriber at an automatic substation or an operator at the automatic exchange. The operator at the first-mentioned exchange has access to the trunk lines extending between the otfices.

An object of the invention is to provide improved signaling means in systems of this nature. I

A further object of the. invention is to provide means for efficiently supervising and handling the tratlic in such a system with a minimum of apparatus.

A feature of the invention consists in utilizing a. slow-to-release relay of a selector switch employed in settingthe switch tor controlling the application of ringing current to the trunk circuit to operate a sig naling device associated therewith.

A further feature of the invention c0nof means for en abling' an operator at change to listen in todetermine the inn portance of conversations over the trunk circuits and for extending connections over the trunk circuit to the operator at the manual exchange when the trunk circuit is idle. 1

his thought that the invention will be best understood from the following detailed description, reference being had to the accompanying drawings.

in the drawings, Fig. 1 shows the subthe automatic ex-' 1920. 7 Serial No. 363,275.

station of an automatic subscriber A whose line terminates in a non-numerical switch, schematically represented as B. Accessible to the non-numerical switch is a selector switch such as (land connector switch (not shown) over which automatic inter-connections may be had with other automatic stations. Accessible to the selector (3, is a trunk circuit extending from the first or automatic exchange to a secondor manual exchange. E shows a portion of a cord circuit by means of which an operator at the first exchange may listen in on the trunk or complete connections over the trunk lead ing to the second exchange. D represents schematically a. non-numerical switch by means of which the operator at the manual exchange may establish a connection with an automatic subscriber or the operator at the first exchange. Fig. 2 shows that por tion of the trunk'circuit at the second exchange. A portion of a connecting cord H is shown by means of which an operator may complete calls to a line terminating at er position (not shown) and a dialing cord 1*: by means of which automatic switches at the first exchange may be controlledover the trunk circuit. For the sake of clearness only one subscribers line selector switch, one trunk and one of each of the cord circuits are shown, it being understood that there may be a plurality of subscriber lines such as A, terminating in non-numerical switches at the first exchange, a plurality of selector switches such as C and a plurality of trunk circuits. There may also be a plurality of cord circuits such as E at the first exchange.

Manual subscribers lines and trunk lines ifrcm other exchanges may terminate at the operators position at the first exchange in jacks in-the well-known manner. Such line and trunk circiiiits are wol known andto avoid complicating the drawing they have Been omitted therefrom. At the second exchange there may be a plurality of cord circuits such as H with a single dialing cord K for each position. Subscribers? lines (not shown) of the wellslrnown type may terminate in jacks at the'operato'fis position at the second exchange.

The system will be best understood from a description of the operation thereof.

It the subscriber whose substation is indicated at A desires a connection with an operator at the manual exchange, he will remove the receiver from the switchhook, whereupon his line will be extended to the first selector C in any well-known manner, it being assumed in the present case that a non-numerical switch, schematically indicated as B, is utilized for this purpose.

As soon as the calling line is extended tothe first selector C, line relay 3 is energized over a circuit extending from grounded battery, lefthand winding of relay 3, back contact and outer left-hand armature of relay 9, terminal 4, brush 5, the loop of the calling subscribers line, brush 7, terminal 6, inner left-hand armature and back contact of relay 9, and righthand winding of relay 3 to ground. The resultant energization of relay 3 completes a circuit from grounded battery through the winding of slow-to-release relay 8, front contact and armature of relay 3 and outer right-hand armature and back contact of relay 9 to ground. When the subscriber operates his impulse sender S to transmit the first series of impulses, line relay 3 will be intermittently deenergized in response to such impulses. Upon the first deenergization of line relay 3, a circuit is closed from grounded battery, through the winding oi primary magnet 10, winding of slow-torelease relay 11, front contact and righthand armature of relay 8, back contact and armature of relay 3 and back contact and outer right-hand armature of relay 9 to ground. Relay 3 being of the slow-tore lease type retains its armatures attracted during the sending of impulses. Relay 11 and magnet 10 are energized in this circuit and the latter causes the brushes of the first selector to be moved in a primary or group selecting direction. The energization of relay 11, completes a circuit from ground, left-hand armature and front contact of relay 8, alternate contacts of relay 11, oifnormal contacts 12, which are closed in response to the sending of the first impulse, and Winding of relay 13 to grounded battery to actuate relay 13 upon the movement of the brush shaft from normal. Slow-'to-release relay 11 retains its armatures attracted during the sending of the first series of impulses in response to which the stepping magnet 10 is intermittently energized to advance the brushes into operative relation with the group of trunks leading to the manual exchange through which a desired line may be reached.

Upon completion of the first series of impulses, line relay 3 remains energized for a comparatively long interval, and relay 11 and primary magnet 10 are deenergized. WVhen relay 11 deenergizes, relay 13 is held up over a path including grounded battery, Winding of relay 13, oil-normal contacts 12, normal contacts of magnet 14. front contact and left-hand armature of relay 13, outer right-hand armature and contact of relay 9 to ground. Relay 11 in retracting its armatures completes a circuit for secondary magnet 14 over a path extending from grounded battery, winding of magnet 14, right-hand armature and front contact of relay 13, normal contacts of relay 11, and front contact and lefthand armature of relay 8 to ground. Magnet 14 in operating steps the brushes one step into engagement with the first terminal in the selected group of trunk terminals, and opens the locking circuit for relay 13 causing its deenergization. Magnet 1& thereupon deenergizes. Should the first trunk be busy, ground will be present on the test terminal 20 thereof, which will maintain the shunt around relay 9 and prevent it from energizing. Relay 13 will then be energized over a circuit extending from ground on terminal 20, brush 17, in ner right-hand armature and back contact of relay 9, back contact and armature of magnet 1 1, off-normal contacts 12, and winding of relay 13 to grounded battery. Relay 13 upon actuation again completes a circuit for magnet 1 1 which moves the brushes another step, whereupon relay 13 and magnet'14c again deenergize. As soon as the test brush 17 encounters an idle trunk having a contact corresponding to 20, upon which there is no ground, a circuit is completed extending from ground, left-hand armature and front contact of relay 8, winding of relay 9, back contact and armature of magnet 14:, off-normal contacts 12, and winding of relay 13 to grounded battery. Relay 9 then operates but relay 13 being marginal, will not operate due to the high resistance of relay 9, and the selector ceases stepping.

Relay 9 in operating disconnects relay 3 from the line and completes circuits for relays 29, 26, and 3+1 of the trunk circuit. Relay 29 in energizing completes circuits for relays and the latter controls the reversing of the current flow over the trunk circuit and the former, the actuation of relays 25 and 24:. The circuit for relay 29 extends from ground, left-hand winding of coil 21., upper left-hand winding of repeating coil 22, terminal 18, brush 15, front contact and inner left-hand armature of relay 9, tern'iinal 6, brush 7, through the substation loop, brush 5, terminal at, outer lefthand armature and front contact of relay 9, brush 16, terminal 19, lower left-hand Winding of repeating coil 22, right-hand winding of coil 21, and winding of relay 29 to grounded battery. Relay 29 upon actuation completes a circuit at its right-hand armature and front contact for slow-to-release relay 23 and at its left-hand. armature and front contact for relay Relay 23 in operating places ground on the test terminal 20 through the right-hand Winding of relay 24 to maintain the selected trunk busy and causes relay 25 to operate thereby rendering the trunk circuit continuous and disconnecting the non-nuinerical switch D from the trunk. The circuits completed by relay 23 may be traced as follows: ground, righthand armature and front contact of relay 23, and thence in parallel, one path extending through the winding of relay 25 to grounded battery and the other through the right-hand winding of relay 24, front con tact and left-hand armature of relay 23 to terminal 20. The instant relay 9 attracted its armatures, a circuit for relay 26 was completed thereby momentarily connecting ringing current from a source to the trunk and projecting said ringing current over the trunk to the manual exchange to actuate a relay 107 thereat as soon as relay 25 operated. The circuit for relay 26 is automatically interrupted as soon as slow to-release relay 8 releases its armatures and relay 24 energizes. Relay 2 1 energizes over the path previously traced and in attracting its right-hand armature short-circuits its right-hand Winding thereby placing a direct ground on the conductor leading to terminal 20. A locking circuit is completed through the left-hand Winding of relay 2& to maintain said relay 24 energized. Relay 26 thereupon deenergizes. Ground at" the righthand armature of relay 23 is substituted for the ground at relay 8 to hold the trunk and selector busy. The circuit for the energization of relays 26 and 34 may be traced as follows: ground, left-hand armature and front contact of relay 8, front contact and inner righthand armature of relay 9, brush 17, terminal 20, and thence in parallel one path extending through the back contact and lefthand armature of relay 2 1, inner left-hand armature and back contact of relay 27 and winding of relay 26 to grounded battery and the other extending through the outer left-hand armature and back contact of relay 27 and the winding of relay 34 to grounded battery. Relay 26 in operating permits ringing current to flow over the line to the manual exchange to display signal 110 thereat. Relay 34 in operating completes a circuit for busy signal 36 at the operators position thus furnishing a'vi'sual signal to the operator that the trunk is busy and at its right-hand armatures connectsground and battery through resistances and 66 respectively, through'the back contact and righthand armature of relay 35 to jack 40 for furnishing a busy test at the jack. The

path for the ringing current may he follows lower source of ringing alternate contacts of traced as current 60,

relay 26, back contact and lower inner armature of relay 30, lower alternate contacts of relay 25, conductor 102, inner normal contacts of relay 105, coil 106, winding of relay 107, condenser 108, back contact and left-hand armature of relay 109, outer normal contacts of relay 105, conductor 100, upper alternate contacts of relay 25, upper normal contacts of relay 30, upper alternate contacts of relay 26 to ground. Relay 107, in operating completes a circuit at its armature and front contact for relay 111 which in energizing locks up under control of re lay 109 over a circuit including grounded battery, winding of relay 111, left-hand armature and front contact of relay 111, back contact and outer right-hand armature of relay 109 to ground. Relay 111 upon actua tion completes a circuit at its right-hand armature and front contact for signal 110.

The operator observing this signal may insert plug 116 into jack 115, whereupon a circuit is completed for relays 109 and 118, extending from grounded battery, winding of relay 118, sleeves of plug 116 and jack 115 and left-hand Winding of relay 109to ground. Relay 109 in operating opens, at its outer right-hand armature and front contact, the locking circuit for relay I 111 which retracts its armatures and extinguishes the signal 110; and at its left-hand armature and front contact establishes a bridge across the trunk conductors 100 and 102, said bridge including retardation coil 106, winding of polarized relay 120, front contact and left-hand armature of relay 109. This bridge across the trunk conductors causes relay 31 to operate over a circuit including grounded battery, winding of relay 31, left-hand winding of retardation coil 32, lower right-hand winding of repeating coil 22, lower alternate contacts of relay 33, upper normal contacts of relays 26 and 30, upper alternate contacts of relay 25, conductor 100, outer normal contacts of relay 105, left-hand armature and front contact of relay 109, Winding of polarized relay 120,

Winding of'coil 106, inner normal contacts of relay 105, conductor 102, lower alternate contacts of relay 25, lower normalcontacts of relays 30 and 26, upper alternate contacts of 'relay 33, upper right-hand winding of repeating coil 22, and right-hand winding of 5 The operator at the manuale-Xchange may then actuate listening key and inquire tors leading to the manual exchange, thereby releasing polarized relay 120, which, in releasing its armature, opens the circult for relay 112, and it, in turn, opens the circuit for relay 125, thereby causing the supervisory lamp 126 to light indicating to the operator that the calling subscriber has disconnected. The operator observing this signal may remove plug 116 from jack 115,

- whereupon relay 109 deenergizes and in so doing opens the circuit for relay 31, which in retracting its armature opens the circuit for relay 23. Relay 23 in deenergizing removes ground from test terminal 20, whereupon relay 9 deenergizes thereby completing a circuit for release magnet 15 over a path extending from grounded battery, winding of magnet 15, off-normal contacts 2, back contact and right-hand armature of relay 8, back contact and right-hand armature of relay 3, and back contact and right-hand armature of relay 9 to ground. Magnet 15 in actuating restores the selector to normal in the manner well-known. Relay 23 in deenergizing also causes the release of relays 24, 25, 34, and busy signal 36.

If the operator at the automatic exchange desires connection with the operator at the manual exchange, plug 41 may be inserted into jack 40, whereupon relay 27 is operated over a circuit extending from grounded battery through lamp 45, resistance 49, sleeves of plug 41 and jack 40, right-hand normal contacts of relay 35, outer right-hand arma ture and back contact of relay 34, and winding of relay 27 to ground. When relay 27 operates, circuits are completed for relays 23 andv 30 as follows: ground, armature and back contact of relay 34, right-hand armature of relay 27, and thence through the winding of relay 23 and the winding of relay 30 in parallel to grounded battery. Relay 23 in operating places ground on the test terminal 20 to render it busy over a circuit extending from ground through the righthand armature and front contact of relay 23, right-hand winding of relay 24, front contact and left-hand armature of relay 23 to terminal 20, and also completes a circuit at its right-hand armature and front contact for relay 25, which in operating renders the trunk circuit continuous and disconnects line finder D from the trunk. Relay 30 in operating connects jack 40 to the trunk conductors and completes a circuit for the en ergization of relay as follows: ground, armature and front contact of relay 23, outer lower armature and front contact of relay 30, and winding of relay 35 to battery. Relays 35 and 25 are held locked up under the control of relay 23.

The operator may then actuate the ringing key 43 of the cord circuit E, Whereupon relay 107 is energized and signal 110 is displayed in the manner heretofore described.

When the operator at the manual exchange inserts plug 116 into jack 115 in response to the signal 110, supervisory relay 42 and polarized relay 120 are operated over a circuit extending from ground, upper right-hand winding of repeating coil 44, upper normal contacts of ringing key 43, tips of plug 41 and jack 40, lower inner alternate contacts of relay 30, lower alternate contacts of relay 25, conductor 102, inner normal contacts of relay 105. coil 106, winding of polarized relay 120, front contact and left-hand armature of relay 109, outer normal contacts of relay 105, conductor 100,

I upper alternate contacts of relays 25 and 30,

rings of jack and plug 41, lower normal contacts of key 43, winding of relay 42, and

lower right-hand winding of repeating coil- 44 to grounded battery. Relay 42 in oper ating causes a shunt to be placed around supervisory signal 45 and relay 120 in operating completes a circuit for relay 112, thereby energizing supervisory relay 125 and extinguishing supervisory signal 126. The operator may then actuate listening key 130, converse with the calling party and upon inquiring for the number desired, complete the connection in the well-known manner.

Upon completion of conversation and removal of the plug 41 from jack 40, relay 30 at the automatic exchange releases and relay 31 operates. Relay 30 in releasing reverses the current through the polarized relay 120, which opens, its contacts, thereby releasing relay 112 and it in turn relay 1255, thereby lighting the supervisory signal 126. The trunk circuit is maintained busy until the operator at the manual exchange removes plug 116 from jack 115 whereupon relay 109 deenergizes, thus removing the bridge from the trunk and permitting relay 31 to release. Relay 31 in releasing opens the circuit for relay 23, which deenergizes, thereby removing the ground at its right-hand armature from the test terminal 20, and releasing relays 25 and 35 and restoring all apparatus to normal.

Should the operator at the manual exchange disconnect before the operator at the automatic exchange disconnects, supervisor lamp 45 at the automatic exchange wil light. Removal of plug 116 from jack 115 before plug 41 is removed from jack 410 will not deenergize relay 112 since relay 112 is held up through the contacts of polarized relay 120. Relay 109 will deenergize, how ever, and a high resistance 1 10 is bridged across the line in series with the winding of relay 120. Relay 120 remains energized but supervisory relay 4.2 deenergizes due to the high resistance of coil 1 10. Lamp 45 then lights indicating t the operator that the operator at the distant end has disconnected. Plug 11 may then be removed from jack 40 whereupon all apparatus is restored to normal.

In a similar manner relay 31 or" the trunk circuit is deenergized by the bridging of the high resistance 1 10 in the circuit, when, a connection exists between an automatic subscriber, such as A, and a manual operator, and the latter disconnects first.

It will be remembered that when a connection exists over the trunk between the subscriber at station A and the operator at the manual exchange, busy signal 36 is actuated apprising the operator thereof. Should it be necessary, however, to use the trunk circuit while it is busy to complete a connection of great importance, the operator may listen in in the trunk by inserting plug 11 into jack to and, it the existing connection is not of great importance, inform the parties that the trunk is desired. Condensers 16 and 1'? through which jack 40 is normally connected to the trunk, prevent battery from flowing from the cord circuit E to the trunk circuit. The connection is not disturbed by inserting plug 41 into jack d0 since relay 3% is operated when the trunk is busy. I

The operator at the manual exchange may call a subscriber at the automatic exchange or the operator at the automatic exchange by inserting the plug 116 of her cord circuit into the jack 115 in which the trunk extending to the automatic exchange terminates and operating the'impulse sender S Insertion of plug 116 into jack 115011 an outgoing call from the manual exchange, ope ates the non-numerical switch I) at the automatic ex change in the well-known manner due to the bridge being placed across the trunk conductors 100 and 102. The non-numericalswitch D in operating will connect ground to the test terminal 20 through the brush 61, thereby rendering the trunk busy to selectors and operate relay 3%, thereby placing the busy test on jack -40 and operating busy signal 36, as heretofore described. The operator then inserts the dialing" cord 135 into jack 136 and operates the impulse sender to send out impulses in accordance with the number of the desired automatic subscriber or if the operator at the automatic exchange is desired, in accordance with the number of a jack (not shown) terminating atthe position of the operator at the automatic exchange.

Insertion of plug 116 into ack 115 energizes relay 109 thereby establishing a bridge from the lower trunk conductor, including coil 106, winding of polarized relay 120, front contact and left-hand armature of relay 109 to the upper trunk conductor. Relay 120 then operates by current flowing over the conductors 100 and 102 from the switches at the automatic exchange, and in closing its contacts completes the circuit for relay 112 whereupon relay 125 is actuated and signal 126 is extinguished. Insertion of plug 135 into jack 136 causes relay 105 to operate, thereby connecting the impulse sender to the trunk conductors 100 and 102. hen relay 105 operates the continuity of the trunk conductors is interrupted and relay 120 deenergizes. After the impulses have been sent plug 135 is removed from jack 136, the continuity of the trunk conductors is restored, and relay 120 again energizes.

Withdrawal of plug 116 from jack 115,

upon completion of conversatioi'i restores all relays at the manual exchange and the relays and busy signal at the automatic exchange to normal.

Vhat is claimed is:

1. in a telcphone exchange system, a calling line, an operators position, a two-conductor trunk circuit, a signaling device associated with said trunk circuit at said operators position, means. including a selector switch for extending said calling line over said trunk circuit to said operators position, a source of ringing current, and electromagnetic means operating independently of said signaling device to cause the momentary connection of said source of ringing current to said trunk to actuate said signaling device upon seizure of the trunk by the selector switch, and a locking circuit for said signaling device completed upon actuation.

2. In a telephone exchange system, a trunk circuit, a signaling device connected thereto, selector switch in which said trunk circuit terminates, means for setting said'selector switch on said trunk circuit, a source of ringing current for actuating said signaling, device, a relay controlling the application of said ringing current to said trunk circuit, and means operating independently of said signaling device for causing a momentary energization of said relay upon the seizure of the trunk by the selector.

3. In a telephone system, a calling line, a

plurality of trunk circuits, a signaling device associated with each trunk circuit, means including a selector switch for connecting said calling line with an idle trunk circuit, a source of ringing current, a relay therefor, and means acting independently of said signaling device and upon the seizure of said trunk circuitfor establishin a transient cir til cuit in which said relay energizes to connect said ringing current to said trunk and cause said signaling device to be actuated.

4. In a telephone exchange system, a first ofiice, a second otiice, a plurality oitrunk lines extending between said otiices, automatic switching apparatus including selector switches at said first oliice for extending connections over said trunk, a signaling device associated with each trunk at the second oiiice, means including a line relay and a slow-to-release relay associated with the selector switch, for automatically selecting an idle trunk, and means controlled by said slow-to-release relay for actuating the signaling device of: the selected trunk.

5. In a telephone exchange system, a first office, a second cities, a plurality of trunk lines extending between said oiiices, automatic switching apparatus including selector switches at said first oiiice for extending connections over said trunk, a signaling device associated with each trunk at the second oflice, means, including a line relay and a slow-to-release relay associated with the selector switch, for automatically selecting an idle trunk, means controlled by said slowto-release relay for actuating the signaling device of the selected trunk, and a locking circuit for said signaling device completed upon actuation.

6. .[n a telephone exchange system, a calling line, a trunk circuit, a signaling device associated with the trunk circuit, means in cluding a selector switch for extending the calling line to the trunk circuit, a relay associated with the trunk circuit adapted upon ene-rgization to project a source of ringing current over the trunk to actuate the signaling device, and means associated with the selector switch for causing automatically the successive energization and deenergization of the relay.

7. In a telephone exchange system, a first and a second oiiice, subscribers lines terminating at each of'tice, a two-way trunk cir cuit extending between said oflices, means including automatic switching apparatus for establishing a connection between the first and second offices, an operators position at the first oiiice, a signal at the operators position at the first office for indicating when said trunk is busy, a jack at the operators position at the first oiiice, an inductive and a metallic path extending from the jack to the trunk circuit, means for enabling the operator to converse with the parties connected to said trunk over said inductive path, and means for enabling the operator to establish a connection over said metallic path to the second oiiice when the trunk is idle.

8. In a telephone exchange system, a calling line, an operators position, a two-way two-conductor trunk circuit, means including automatic switches for interconnecting the calling line and operators position over the trunk circuit, a second operators position, means for permitting the operator at the second position to supervise the connection without interfering therewith, and 'T'-* means for interconnecting the first mentioned and the second operators position over the trunk circuit when it is idle.

9. In a telephone exchange system, a calling line, an operators position, a two-way two-conductor trunk circuit, means including automatic switches for interconnecting the calling line and the operators position over the trunk circuit, a second opcrators position means for permitting the operator at the second position to supervise the connection without interfering therewith, means for interconnecting the first mentioned and the second operators position over the trunk circuit when it is idle, and supervisory signals at each, operators position for indicating disconnection.

10. In a telephone exchange system an automatic subscribers station, an operators position, a two-way trunk circuit, means including automatic switches for interconnecting the station and the operators position, a second operators position, a jack thereat, an inductive and a metallic path extending therefrom to the trunk circuit means for enabling the operator at the second position to overhear the conversation of, and converse with, the parties of an established connection over the inductive path without disturbing the connection, and means for completing a connection from the second operators position to the first mentioned operators position over the metallic path when the trunk is idle.

11. In a telephone exchange system, an automatic subscribers station, an operators position, a two-way trunk circuit, means including automatic switches for interconnecting the station and the operators position, a second operators position, a jack thereat, an inductive and a metallic path extending therefrom to the trunk circuit, means for enabling the operator at the second position to overhear over the inductive path the conversation of, and converse with, the parties of an established connection without disturbing the connection, means for completing a connection from the second operaitors position to the first mentioned operators position over the metallic path when the trunk is idle, and means for rendering the trunk busy when in use by either the subscriber, the first mentioned or the second mentioned operator.

12. In a telephone exchange system, a calling line, an operators position, a trunk line, means including automatic switches for establishing a connection between the calling line and the operators position, a second operators position, a jack thereat, two

paths over which said jack has access to the trunk circuit, one of the paths being inductive and normally connected to the trunk and the other being metallic and normally disconnected from the trunk, a cord circuit at the second operators position, means responsive to the connection of the cord circuit with the jack for preventing interference with signaling over the trunk when the trunk is busy, and for enabling the operator at the second position to listen in and converse with the parties to the connection, and means responsive tothe connection of the cord circuit with the trunk tor enabling the operator at the second position to establish a connection to the first mentioned position when the trunk is idle.

13. In a telephone exchange system, a railing line, an operators position, means including automatic switches and a trunk circuit for interconnecting the same, a second operators position, an operators telephone set thereat, means for connecting the operators telephone set to the trunk circuit, during the existence of a connection thereover, for listening and talking purposes, means for preventing such connection from interfering with talking or signaling over the trunk, and means for completing a connection from the second operators position to the first operators position upon disconnection between the calling line and the operators position.

14. In a telephone system, a calling line, a trunk circuit, a signaling device associated with the trunk circuit, means including a selector switch for extending the calling line to the trunk circuit, a source of signaling current, and means including a slow-to-release relay associated with the selector switch and operable upon the seizure of said trunk by said selector switch for causing the momentary application of said ringing current to said trunk to operate said signaling device.

15, In a telephone system, a calling line,

an operators position, a signaling device at said position, a trunk circuit, means including a selector switch for interconnecting said calling line and said operators po sition by way of said trunk circuit, a source of signaling current, means including a slow-to-release relay associated with the selector switch and operable upon the seizure of said trunk circuit by said Selector switch for momentarily applying said ringing current to said trunk circuit to energize said signaling device, and means at said operators position for controlling the restoration of said signaling device.

16. In a telephone system, a calling line, a trunk circuit, a signaling device associated with the trunk circuit, means including a selector switch for extending the calling line to the trunk circuit, a source of signaling current, means including a slow-to-release relay associated with the selector switch and operable upon the seizure of said trunk by said selector switch for causing the momentary application of said ringing current to said trunk to operate said signaling device, and a locking circuit for said signaling device completed upon actuation.

17, In a telephone system, a calling line, an operators position, a signaling device at said position, a trunk circuit, means ineluding a selector switch for inter-connecting said calling line and said operators position by way of said trunk circuit, a source of signaling current, a slow-to-release relay associated with the selector switch and operable upon the seizure of said trunk circuit by said selector switch for applying said ringing current to said trunk circuit to energize said signaling device, a locking circuit for said signaling device completed upon actuation, and means controlled at said operators position for interrupting said locking circuit In witness whereof, I hereunto subscribe my name this 27th day of February A. D.,

RAY L. STOKELY.

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