US1688689A - Automatic telephone system - Google Patents

Description

Oct. 23, 1928. 1,688,689

T. F. CROCKER AUTOMATIC TELEPHONE SYSTEM Filed Aug. 28,;

Thumas F. Eruckar Patented 0st. 23, 1928.

UNITED STATES PATENT CFFICE.

THOMAS E. CROCKER, OF CHICAGO, ILLINOIS, ASSI G-NCR, BY MESI IE ASSIGNMENTS, TO

AUTOMATIC ELECTRIC INC, OF CHICAGO. ILLINOIS, A. CORPORATION OF DELA- WARE.

AUTOMATIC TELEPHONE SYSTEM.

Application filed August 28, 1925.

This invention relates to telephone systems in general, but more particularly to automatic telephone systems havlng; an operator s position at the automatic telephone exchange at which intercepted calls may be answered and where information and complaint service may be rendered. The object of this invent-ion is the provision of a new and improved operators telephone circuit and associated trunk circuits for an intercepting and information operators position.

It has been common practice in telephone systems to provide means for informing a siibscriber when he has dialled a wrong numher which is not assigned to a subscriber, or a number which has been disconnected or to which service has been denied for some reason or other. This is accomplished by trunking the terminals of the unassigned numbers, and the terminals of the subscribers to which service has been denied, to an intercepting operators position. When the subscriber dials such a number, he is automatically connected to the intercepting operator, but is unaware of the fact until the operator answers. WVhen the operator answers, she informs the calling subscriber of his error or gives him such 1n formation as she deems necessary.

This invention is shown in connection with automatic telephone systems employing the well known Strowger step-by-step switches. In such systems, the final switch that is operated to connect a calling subscriber with a called subscriber is a connector switch. When a called subscriber answers a call in response to the ringing; of his ringer, a ring-cut-off relay in the connector is operated to disconnect the ringing current supply and complete the talking connection. Immediately thereafter, a reversing; relay in the connector is operated to reverse the direction of current flow over the callin line for purposes such as operating the calling subscribefis meter. It is customary not to charge the subscriber for the call if his call he intercepted by an intercepting operator. Means are therefore provided to prevent the reversing relay in the connector from operating when a call is intercepted. by an intercepting operator, thereby preventing the operation of the calling; subscribers meter.

Heretofore certain circuit arrangements Serial No. 53,025.

usually including one or more special relays have been provided individually to each of the trunks terminating at the intercepting operators position to accomplish the above result. A feature of this invention, however, is the provision of means individual to the operators telephone circuit for accomplishing this result; that is, operating the ring-cub otl' relay in the connector to disconnect the ringing current supply and complete the talking connection, without permitting the operation of the reversing relay in the connector. Thus one set of relays individual to the operators telephone circuit displaces the one or more relays individual to each of the trunks terminating at the operators position.

In addition to this feature, the operators telephone circuit has been made to operate as quietly as possible. The usual annoying clicks heard in the operators receiver which are produced by the throwing of keys to connect or disconnect the. op-erators telephone circuit to or from a trunk have been eliminated to the extent that they are barely perceptible.

According to another feature of this invention should a subscriber dial an unequippcd number and be connected to the intercepting operator and should it be necessary for the operator to obtain information for the calling subscriber that would take considerable time, it will not be necessary for the operator to keep her telephone circuit connected to the trunk to Which that subscriber is connected. She may throw a key from a talking position to a holding position which will disconnect her telephone set from the trunk in question and permit her to answer other calls or perform other duties during that time. When she has obtained the information to be given to the first calling: subscriber, she may throw the key to the talking; position to again connect her telephone circuit to the trunk to which the calling subscriber is connected and nive him the required information.

It is possible that the first subscriber may become impatient waiting for information and release the connection to the intercepting operator by replacing his receiver. The operator is given no indication that the subscriber has released the connection, but this fact will become apparent to her when she reconnects her telephone circuit to the trunk and receives no answer. It might happen that after the first subscriber has released the connection and before the operator again connected her telephone circuit to that trunk, a second subscriber dialled such a number as to become connected to the intercepting operator over this same trunk. The operator would be unaware of this second connection and ii no provision were made, she might give out the information intended for the first subscriber to the second subscriber and cause a misunderstanding. According to a special feature of this invention, a talking connection cannot be made to the operator by a second subscriber over a certain trunk when an associated key individual to that trunk is in a holding position.

These features and other features not specifically mentioned will be more fully described in the following specification, reference being had to the accompanying drawing. In the automatic telephone system chosen for the purpose of describing the operation and utility of the present invention,

it is assumed that Strowger step-by-step switches are employed; that the final switch operated to complete a connection is a connector switch, one or more selector switches being previously operated; and that the unequipped terminals in the connector banks are trunked to an intercepting operators position. It is also assumed that the trunks from the unequipped selector levels extend to this same intercepting operators position. In the accompanying drawing the intercepting operators telephone circuit is shown at 0 provided with the usual transmitter 18, receiver 12, and dial 11. The contacts 123 and 124 are one set of unequipped terminals in the banks of connector C (shown in skeleton) and are connected to the operators position by the trunk comprising conductors 121. and 122. Individual to each trunk is a trunk circuit such as trunk circuit TC, a call lamp such as L, and a key such as K. which operated to connect the operatorstelephone circuit 0 to the trunk via the conductors 21, 22. and 24.

Each trunk from an unequipped selector level terminating at the operators position also has an individual. trunk circuit, a call lamp, and a key similar to key K which may be operated to connect the operators telephone circuit to the trunk via conductors such as 302 and 303. This circuit and apparatus is not shown since it is not concerned with the present invention. Any well known circuit for trunks from selector levels to an oporators position may be used.

The operator is also provided with one or more trunks such as the one comprising condoctors 221 and 222 with the associated trunk circuit TC and provided with the line lamp U, the busy lamp L and key K, for making outgoing calls to other substations. These trunks extend to individual primary lineswitches 01' a well known type which in turn have access to selectors as is well known in the art. These trunks also terminate in con nector banks. The trunk comprising conductors 221 and 222 is shown terminating in the rotary line switch LS (shown in skeleton) and accessible in the bank of connector C. Outside subscribers may thus also call the operators position over any one of these trunks by dialling the corresponding number. A description of a suitable lineswitch, and of the selectors and connectors mentioned above may be found in the publication entitled Automatic telephony by Smith & Campbell, second edition, pages 46 to 65.

It may be convenient to have the intercepting operator serve also as an information and complaint operator. An information and a complaint number would in that case be listed in the directory, the dialling of either number by a calling subscriber resulting in the establishment of a connection to this same operator. The trunks reserved for information and complaint service are usually accessible directly from a selector level. A special line lamp is lighted when such a call is extended. The operator then actuates a key individual to the trunk over which the call is being extended to connect her telephone set to that trunk by way of conductors 302 and 303.

If the telephone system be large enough to warrant the employment of several operators to render the services mentioned above, the trunks terminating at one position would be multiplied to the other operators positions. For each trunk from unequipped terminals in connector banks, there would be provided a key such as K and a line lamp such as L for each operators position. An incoming call would. then be answered by the operator first to be ready. For each trunk such as the one comprising conductors 221 and 222, a key such as K a line lamp such as L and a busy lamp L would be provided for each operators position. In this case also, an incoming call would be answered by the first operator that would be ready.

VVit-h this general description of the object and the utility of the invention, and the apparatus involved, the following detailed description of the various operations is offered. For this purpose it is assumed that a calling subscriber dials a number either inadvertently or otherwise, such that a connection to the trunk comprising conductors 121 and 122 is established viawell known automatic switches including one or more selectors and the connector C. After the calling subscriber dials the final digit of the number, relay 103 of the trunk circuit TC is energized by ringing current supplied from a ring ing current generator by way of the Wipers of the operated connector, bank contacts 123 and 12 1, conductors 121 and 122, condenser 116, and through the winding of relay 103. Relay 103 Operates and closes a circuit tor relay 1041 which may be traced from ground by way of the resting contact and armature 107, armature 110 and the working contact, through the winding of relay 101 to battery. Relay 10 1 operates and closes a locking circuit for itself at armature 112 and its working con tact independent of armature 110, short circuits the condenser 115 at armature 111.and the working Contact, and closes a circuit for the line lamp L at armature 113 and the working contact. The lighting of lamp L informs the operator of the incomin call.

As soon the ope *ator is prepare-(i to answer the call. she throws the key K to the talking position. In response to the throwing of the key K to the talking position, the following operations take place; The ring cut-off relay 311 of the operated connector is energized and disconnects the ringing current and extends the talking connection; the reversing relay or bacl q-bridge relay the operated connector is energized insuiliciently to cause its operation; and the operatoi."s receiver is connected across the trunk conductor without producing the usual annoying click in the receiver. These results are accomplished in the following manner: Throwing the key K into the talking position closes a circuit for relay 2 in the operators telephone circuit 0 and the upper winding of the relay 102 in the trunk circuit TC which may be traced "from ground tl'n'eugh the winding of relay 2, normally closed springs controlled by armature 9. springs 131, normally closed springs controlled by armature 105, through the upper winding of the relay 102 to battery. Relay 102 operates and closes a circuit for relay 101 at armature 108 and the working contact, and prepares the talking circuit by closing a. point normally open at armature 109 and the working contact. Relay 2 and relay 101 are both slow acting, but since relay 2 is energized in series with relay 102, relay 2 operates sometime before the operation of relay 101 takes place. in operatii'ig, relay 2 disconnects the receiver at armature 4 and the cs-ting contact, substituting a short circuit at the working contact; places a short-circuiting bridge across the conductors 22 and 2 1 at ar nature 5 and the working contact; and closes a circuit for the st thing relay 3 at arn'iature 6 and the working contact which includes the winding of relay 3 and the resistance 17. Switching relay 3 operates and closes a locking circuit for itself at armature S) and the working contact at the same time opening the circuit for the relay 2 by opening the normally closed springs controlled by this an ture; opens he bridge placed across the cor ictors 22 and 21 by armature 5 and the working contact; and completes the talking circuit at armatures 7 and 8. The resistance of relay 3 and the resistance 17 have such values that the bridge across the conductors 22 and 2 1 at armature 5 and the working contact is closed for a length of time just suiiicient to operate the ring-cut-otl rela 311 in the connector without permitting tne actuation of the reversing relay 312 in the connector since the operation of relay 3 takes place before this reversing relay ias had time to operate. Immediately following the operation of the switching relay 3, before relay 2 has had time to fall back, relay 101 operates and opens the circuit 01' relay 101 at armature 107; closes a high resistance bridge across con doctors 121 and 122 including resistance 11% and the lowerwinding of relay 102, at armature 106 and the working contact; closes a locking circuit for itself at armature 105 and the working contact; and opens the circuit for the upper winding of relay 102 by opening the normally closed springs controlled by arn'iature 105. Relay 102 is maintained operated from current supplied through the reversing relay 312 in the connector. The resistance 114: and the resistance of the lower winding of relay 102 are too high, however, to permit the operation. of the reversing relay. I

During the interval after relay 3 has operated and before relay 2 has released its armature, the condenser 15 becomes charged to the potential existing across the conductors 22 and 2 1. When the relay 2 clease-s its arn'iatures, the receiver 12,is connected across the conductors 22 and 2 1. There Will be no annoying click in the receiver 12 when armature 4 makes contact with the resting contact, since the condenser 15 will already have been charged to the proper potential and no fun ther current flow through the receiver will take place.

After the operation of relay 101 which opens the circuit for relay 101 at armature 107, relay 10 1 deenergizes and opens the short circuit around the condenser 115 at armature 111, opens another point in its looking circuit at armature 112, and opens the circuit for the line lamp L at armature 113.

The operator may now converse with the calling subscriber and give such information as she deems necessary. For the purpose of explaining further operations, it will be assumed that the operator must obtain certain information for the calling subscriber from some source not immediately at hand and that this may take considerable time. She may Wish to disconnect her telephone *ir "ait from this connection and answer other calls that may be terminating in her position during this time. To accomplish this she throws the key K from the talking position to the holding position thereby closing the upper right-hand springs of the key K. This operation disconnects the telephone circuit Ill) lZii

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L from the trunk circuit TC but completes a holding circuit for relay 101 from ground by way of the closed upper right-hand spring of the key K, working contact and armature 105, through the winding of relay 101 to battery. Relay 101 is made sufficiently slow acting to prevent its deenergization during the time that the key K is thrown from the talking position to the holding position.

Vhen the operator receives the informa tion to be given to the subscriber connected to the trunk circuit T C, the operator may again throw the key K into the talking position. Relays 2 and 3 operate as previously described. They perform no function at this time, however, other than to connect receiver 12 across the conductors and 2% without a perceptible click. No short-circuiting bridge is placed across the conductors 121 and 122 at armature 5 and the working contact when re lay 2 operates this time, since the short circuit around condenser 115 has been removed. The operator may then converse with the calling subscriber and give him the required inform atio-n.

At the end of this conversation the calling subscriber will restore his receiver thereby restoring he automatic swltches associated with the connection in the usual manner, and the operator will restore the key K to its normal position. Restoring the key K to its normal position opens the circuit of relay 3 and relay 101. Relay 3 deenergizes and restores the operators telephone circuit to its normal state. Relay 101 deenergizes and opens the high resistance bridge across con ductors 121 and 122 at armature 106. When this circuit is opened, relay 102 is deenergized and restores its arn'iature back to normal.

Should the calling subscriber become impatient waiting for the required information and hang up his receiver, and should a second calling subscriber dial such a number as to obtain connection with the trunk comprising the conductors 121 and 122, the relay 103 will be operated from ringing current in the usual manner but a talking connection with the operator will not be established until she has again restored the key K back to normal. Thus the possibility of the operator unknowingly giving out the information to the wrong party is eliminated. The operation of the trunk circuit TC for accomplishing this re suit is as follows: It is assumed that the key K is in the holding position, maintaining the relay 101 in an operated position. As long as the first calling subscriber maintains a connection to the operator, relay 102 will be maintained operated over the high resistance bridge across the conductors 121 and 122 including resistance 114, lower winding of relay 102, armature 106 and the working contact, and armature 109 and the working contact, the current being supplied through the reversing relay in the associated connector. As soon as this first calling subscriber hangs up his receiver, however, the switches associated with the connection including the connector are released, thereby opening the circuit for relay 102. Relay 102 deenergizes and opens the high resistance bridge across the conductors 121 and 122 at armature 109. Re lay 102 cannot again be operated until relay 101 is allowed to deenergize which can only be accomplished by restoring key K to its normal position. \Vhen the operator throws the key K from the holding position to the talking position, thinking that the first subscriber is still on the line, and attempts to give the information intended for the first calling subscriber, she will receive no answer, which is an indication that the first subscriber has released his connection. The operator will then'restore the key K to its normal position. Immediately thereupon the circuit of relay 101 is opened and this relay releases. If the second calling subscriber is still connected to the conductors 121 and 122, the relay 103 maybe operated from ringing current and will then close a circuit for relay 1 4. Relay 104 operates as previously described and lights the line lamp L The operator may then answer the second call in a manner identical to that described above.

It will now be assumed that the operator wishes to make an outgoing call and chooses the trunk comprising conductors 221 and 222. The operator first throws the key K in the calling position. When the key K is thrown into the calling position, a circuit is closed which may be traced from ground through the winding of relay 2, normally closed contacts controlled by armature 9, closed springs 231, through the upper winding of the relay 202, through the winding of. relay 201 to battery. Relay 202 operates and opens a point in a bridge across conductors 221 and 222 at armature 206. The operation of armatures 207 and 208 perform no useful function at this time. Relay 201 operates and closes a circuit for the busy lamp L at armature 205 and the working contact, and closes a point in the bridge across conductors 221 and 222 at armature 204 and the working contact. It is understood that busy lamps need only be provided when there are several intercepting operators positions at which access is had to the same trunk. The lighting of the busy lamp at the several operators positions notifies the remaining operators that this particular trunk is now in use. These operators will therefore refrain from the using of this trunk should they wish to make The opan outgoing call at this same time.

eration of relay 2 and relay 3 will take place at this time in the manner described above and has no function other than to connect the receiver across the conductors 22 and 24: accomplishing this without producing the usual annoying clicks in the receiver. As a further result of the throwing of key K to the calling position, a direct current bridge is placed across the conductors 221 and 222 which may be traced from conductor 221, *losed springs 232, conductor 22, interrupter contacts of the dial 11, through the winding of the retardation coil 13, conductor 23., closed springs to conductor 222, The placing of this bridge across the conductors 221 and initiates the operation of the line switch LS individual to the trunk to extend the connection to an idle first selector and prepares this selector for receiving the first digit of the number which is to be dialled as is Well known in the art.

The operator now dials the number of the substation with which she desires connection. When the dial 11 is moved off-normal, relay 3 is short circuited by the closure of springs 10. Relay 3 deenergizes and again closes the circuit for relay 2 by allowing the springs controlled by armature 9 to close. Relay 2 op crates and again disconnects the receiver 12 and places a short-circuiting bridge across the conductor 22 and 2d at armature 5 and the working contact. The retardation coil 13 is also short-circuited at armature 8 and the resting contact. impulses are produced by the dial in the ordinary manner to operate the automatic switches to extend the connection to the desired substation. Whenthe connec tion is completed and the subscriber answers in response to the ringing of the bells at his substation, conversation may be begun.

At the termination of the conversation, the called subscriber will replace'his receiver and the operator will throw the key K in its normal position. The key K is so arranged that the springs 231 and 234 open before the springs 232 or 233. Thus the receiver 12 is disconnected from the talking conductor at spring 23st before the current carrying bridge including the retardation coil 13 across the talking conductors 221 and 222 is opened at springs 232 and 233. Since the receiver is disconnected before the current carrying circuit is opened, no click will be heard in the receiver when the key K is deactuated, or when the key K is thrown from the talking position to the holding position, an Operation the utility of which will be'described in the following paragraph. V fhen the springs 231 are separated, the circuit for the relay 3 is opened which deenergizes and disconnects the receiver from the conductors 22 and 24 at arinatures 7 and 8.

A further utility of the key K may be described, again assuming that the operator has established a connection to a subscribers substation, and that the operator then learns of certain information that she must obtain for this subscriber that is not immediately at hand. She may instruct the subscriber to remain on the line and then throw the key K from the talking position to the holding position thereby disconnecting her telephone circuit from the trunk without releasing the connection. When the key it is thrown into the holding position, ground is placed on the unction of the upper winding of relay 202 ar l the windin of relay 20L Relay 202 deenergifzcs and cioses the holding bridge across the conductors 221 and 222 at armature 206 and the resting contact. This bridge serves hold the automatic switches associated with the connection operated. Ground at the junction between the upper winding of relay 202 and the winding of relay 201 supplies the holding circuit for the relay 201 and maintains this relay energized. Relay 201 is sufliciently slow-acting sothat it does not de actuate during the time that the key K is thrown from the talking position to the hold ing position.

When the operator is again prepared to talk to thesul'iscriber connected to the trunk in question, she again throws the key K to the talking position. Relay 202 is again operated over the upper winding in series with relay 2 and relay 201 thereby opening the bridge across conductors 221 and 222 at armature 206. The operatorstelephone circuit is again connected across the condutors 221 and 222 iy the operation of relays 2 and 3 in the previously described manner. Conversation may again be resumed, and when it is terminated, the operator restores her key K and the called subscriber replaces his receiver. The bridge including the retardation coil 13 across the conductors 221 and 222 is opened at the key K allowing the automatic switches associated with the connection to release in the well known manner.

Calls may also be extended to the operator by a subscriber over a trunk such as the one comprising conductors 221 and 222 by dialling the corresponding number. Should a subscriber wish to extend such a call, he will remove his receiver and dial the number assigned to the operators position. In response thereto automatic switches will be operated, theiinal one being a connector which will. rotate its wipers into engagement with the bank contacts 223 and 224 or multiples thereof. Ringing current supplied from the ringing current generator now connected to the wipers of the connector will energize relay 203. The circuit extends from one wiper of the operated connector, bank contact 223, conductor 221, armature 20 i and the resting contact, condenser 211, winding of relay 203, conductor 222, bank contacts 224. to the other wiper of the connector. Relay 203 operates and closes the circuit of relay 202 from ground byway of the working contact and armature 210, through the lower winding of the relay 202 to battery. Relay 202 operates and closes a locking'circuit for itself at armatures 207 which may be traced from ground by way of armature 205 and the resting con tact, armature 207 and the Working contact through the lower winding of relay 202 to battery. A circuit is also closed for the line lamp L at armature 208 and the working contact. At armature 206, a point in a bridge to be placed across conductors 221 and 222 is opened, the function of which will be described later.

In response to the lighting of the lamp L the operator will throw the key K into the talking position. The closure of springs 231 completes a circuit from ground through the winding of relay 2, normally closed springs controlled by armature 9, springs 231, through the upper winding of relay 202, through the winding of relay 201 to battery. Relay 201 operates and at armature 205, opens the locking circuit of the lower winding of relay 202 and the circuit of the line lamp L at the resting contact, and closes a circuit for the busy lamp L at the working contact; and prepares a point in the bridge to be placed across conductors 221 and 222 at armature 204 and the Working contact. Relay 202 is maintained operated overits upper winding, at this time functioning to hold open the bridge across conductors 221 and 222 at armature 206. Relay 2 operates and shortly thereafter causes the operation of relay 3 which connects the receiver 12 across the conductors 22 and 23 a in the manner previously described so as to eliminate the usual annoying click in the receiver. In this type of call no provision is made to prevent the reversing relay of the connector associated with the connection from operating. Therefore, as soon as the key K is thrown into the talking position and the bridge including the retardation coil 13 is placed across the conductors 221 and 222, the ring-cut-ofl' relay of the connector is operated and, since this bridge is permanently across the conductors, shortly after the operation of the ring-cut-off relay the reversing relay of the connector is operated.

This latter operation takes place before the receiver 12 is connected across the line by the release of relay 2; thus no click that might be caused by disturbances on the line due to this operation is heard in the receiver.

The operator will begin conversation. Should the calling subscriber be asking for some information that will require a little time to obtain, the operator may again ask the subscriber to stay on the line after which she may throw the key K to the holding position thereby disconnecting her telephone circuit from the trunk, freeing her to perform other duties during the time that the information is'being collected. The operations following the throwing of key K in the holding position, and the reestablishing of the talking connection by reactuating the key in the talking position have been previously described and need not be repeated. The

holding bridge including resistance 212 serves no special purpose in this case. The busy lamps L at the other operators positions are maintained lighted to indicate the busy condition of this trunk. The operations pertaining to the release of the connection are similar to those previously described.

To obtain general information or make a complaint, a subscriber dials the information or complaint number, asthe case may be. By so doing, a connection is established to the operator over a trunk (not shown) directly from a selector level. The operator is notified of the incoming call by the lighting of a lamp (not shown). When ready to answer the call, the operator throws a key (not shown) to the talking position which connects her telephone set to the calling trunk by way of the conductors 302 and 303. The conductors 302 and 303 are shown connected directly to the receiver circuit, thus illustrating how this telephone set may be.

connected when there is no need for producing a momentary short circuit across the calling trunk as is the case when the trunk extends directly from a selector level and when it is unnecessary to prevent clicks in the receiver.

The invention, its utility and operation having been described, what is considered new and is desired to have protected by Letters Patent will be indicated in the appended claims.

)Vhat is claimed is:

1. In an operators telephone circuit, talking conductors individual to said telephone circuit, a receiver normally disconnected from the said talking conductors, and means in said telephone circuit for placing a momentary short-circuit across said conductors, and for connecting said receiver to said conductors when the short-circuit is removed.

2. In an operators telephone circuit, talking conductors individual to said telephone circuit, a receiver normally disconnected from the said talking conductors, means in said telephone circuit for placing a short-circuit across said conductors, and means automatically responsive a predetermined interval after the actuation of said first'means for connecting said receiverto said conductors.

3. In a telephone system, an operators telephone circuit, a receiver normally disconnected from the talking conductors of said circuit, a trunk line, a key for connecting the talking conductors of said telephone circuit to the conductors of said trunk line, means automatically responsive to the actuation of said key for placing a momentary short-circuit across said talking conductors and for thereafter connecting said receiver to said talking conductors.

4. Ina telephone system, an operators tele' phone circuit. a receiver normally disconnected from the talking conductors of said circuit, a trunk line, a key for connecting said talking conductors to said trunk line, means automatically responsive to the actuation of said key for placing a short-circuit across said talking conductors tor a predetermined interval and for thereafter connecting said receiver to said talking conductors.

5. In a telephone system, an operators tele phone circuit, a receiver normally disconnected from the talking conductors of said circuit, a trunk line, means tor extending a connection to said trunk line via automatic switches, manually controlled means for connecting and for disconnecting said talking conductors to and from said trunk line, means automatically responsive to the initial actuation of said manually controlled means for placing a momentary short-circuit across the conductors of said trunk line, and means individualto said trunk line for preventing more than one occurrence of a short-circuit across the conductors of said trunk line during the continuance of said connection.

6. In a telephone system, an operators switchboard, a trunk li e, a calling line, means for associating said calling line with said trunk line, a key for connecting the operators telephone set to said trunk line, means responsive to the actuation of said key for cstablishing a talking connection from said calling line to said operators telephone set, and means for preventing the establishment of a second talking connection after the first connection is released until the key is again restored to normal and then reactuated.

7. In a telephone system, an operators telephone circuit, a receiver in said telephone circuit normally disconnected from the talking conductors, a trunk line, a key for associating said telephone circuit with said trunk line, and means responsive to the actuation of said key for placing a bridge across the talk: ing conductors of said telephone circuit and for connecting said receiver to said talking conductors a predetermined interval thereafter, said means arranged to disconnect the receiver prior to the removal oii'said bridge when said key is deactuated.

8. In a telephone system, an operators telephone set, means including an automatic connector switch for establishing a connection with said telephone set, a ring-cut-oli relay and-a back-bridge relay in said switch, sa'd back-bridge relay normally responsive to the operation of said ring-cut-oil' relay, and means in said operators telephone set for causing the operation of said ring-cut-oii re-' lay without permitting the operation of said back-bridge relay.

9. In a telephone system, an operators telephone circuit, trunk lines, means including an automatic switch for establishing a connection to said telephone circuit via anyone or" said trunk lines, a ring-cut-ofi' relay in said switch, a back bridge relay in said switch normally responsive to the operation of said ring-cut-oii relay, and means common to said trunks for causing the operation or" said ringcut-ofi relay and for preventing the operation of said back bridge relav.

10. In a telephone system an oper'ators telephone circuit, trunk lines accessible to connector switches of the type in which the sig nailing mechanism is disconnected and an oporation denoting an answered condition is Jerlormed when a connection including one of said connector switches is completed between two subscribers, means for connecting said telephone circuit to any of said trunk lines that has been seized by one of said connector switches, and means common to said trunk lines for c ilconnecting the signalling mechanism without causing the performance of the operation denoting an answered condition when a connection to said telephone circuit is completed.

11. In combination, a trunk circuit having a source of current in bridge thereof, an operato-rs telephone circuit including a dial for setting up connections, means for connecting said telephone circuit to said trunk circuit, said telephone circuit including a receiver and a condenser, the latter of which is charged from said source when the connection is established, and means for cutting said receiver out of circuit while the condenser is being charged and Whenever said dial is moved oil-normal.

12. In a telephone circuit, a receiver and a condenser, a pair of talking conductors, means for connecting said receiver and condenser across said talking conductors, a source of potential across said conductors for charging said condenser, and means for eX- cluding said receiver from the charging circuit for a predetermined interval while said condenser is being charged, said first means being automatically responsive to said second means.

18. In a telephone system, an operators position, means for extending calls to said position, an'operators telephone circuitfor answering calls extended to said position, said telephone circuit including a condenser and a receiver, and relays in said telephone circuit operative when a call extended to said position is answered, means for tripping the ring responsive to the operation of one of said relays and for charging said condenser independent of said receiver responsive to the operation of another of said relays.

14:. In an operators telephone circuit, a receiver, a condenser normally connected to said receiver, said receiver and said condenser belng normally disconnected from the talking conductors of said telephone circuit,

means for disconnecting said receiver from I said condenser, means responsive to said first means for connecting said receiver and said condenser across said talking conductors, and means actuated by said second means for deactuating said first means to again connect said receiver to said condenser.

15. In an operators telephone circuit, a receiver, a first set of talking conductors extending from said receiver, a second set of talking conductors, means for disconnecting said receiver from one of said first talking conductors, and means responsive to said first means for connecting said second set of talking conductors to said first set and for disabling said first means.

16. In a telephone system, an operators position, an operators telephone set for answering calls extended to said position, a receiver included in said set, a relay responsive to the answering of a call for disabling said receiver and for tripping the. ring, and a second relay responsive to said first relay for deactuating said first relay.

17. In a telephone system, an operators switchboard, a trunk line terminating at said switchboard, means for seizing said trunk to extend a connection to said switchboard, a key for connecting the operators set to said trunk, means responsive to the actuation of said key for establishing a talking connection from said calling line to said operators telephone set, and means for preventing the establishment of a second talking connection, in case said trunk is seized to extend another connection after the first connection is released and While said key is actuated, until said key is again restored to normal and then reactuated.

In Witness whereof, I hereunto subscribe my name this 26th day of August, A. D. 1925.

THOMAS F. CROCKER.

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