US1491867A - Electrical switching device - Google Patents

Description

April 29 1924. 4 1,491,867

' G. W. KUHN ELECTRICAL SWITCHING DEVICE Filed July 24. 1920 2 Sheets-Sheet l //4 van 70/: 6, W. K 01/4.

Patented Apr. 29, 1924.

UNHTED STATES PATENT orrre GEORGE W. KUHN, OF NEW YORK, N. Y., ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY,'A CORPORATION OF NEW YORK.

ELECTRICAL SWITCHING DEVICE.

Application filed July 24, 1920. Serial No. 398,698.

T 0 all whom t'r' may concern.

Be it known that I, GEORGE W. KUHN, residing at-New York, in the county of New York and State of New York, have invented certain Improvements in Electrical Switching Devices, of which the following is a specification.

This invention relates to electrical switching devices, and more particularly to a switching device adapted for insertion in a telephone circuit and designed to effect successively a plurality of different electrical connections without rendering discon-v tinuous the connection between the tip and ring sides of the said circuit.

Devices of, this nature heretofore used belonging to that class designed to connect atelephone circuit, such as trunk circuit with an operators telephone circuit, or to bridge across the said trunk circuit a holding coil whose function was to maintain in its operated condition certain apparatus associated with the trunk circuit, consisted usually of a key having two groupsof con tacts, which, for the purpose of description, may be referred to asthe right-hand and left-hand groups, although in practice these groups may occupy other relative positions. The trunk circuit terminated upon certain springs of one of these groups and was looped back or strapped through to the springs of the other group of contacts when the springs of both groups were in their normal non-operated position. The telephone set circuit-was connected with certain springs of the said first group and the hold ing coil circuit was connected with certain springs of the other of the said groups of springs.

Associated with each group of springs were certain master springs adapted to be engaged by the cam of the key and when so engaged, designed to operate the other contacts of the same group with which the operated master springs were associated. Thus, if the cam of the key were moved so as to operate the master springs associated with the right-hand group, contacts necessary to connect the operators telephone set with the line would be made. If the cam were moved so as to operate the master springs of the left-hand group, the incoming circuit would be connected with the circult of the holdin coil. If the cam were left in its norma position, which operatively would be midway between the talking and the holding positions of the said key, the master springs of 'neithergroup would be operated, in consequence of which neither the telephone set northe holding coil would be connected to the incoming line sir-- cuit, and, furtherinore, the circuit between the tip and ring sides of the incoming line would be maintained opened. If the incoming line has associated with it a supervisory relay, the operation of which is dependent upon the maintenance of aclosed circuit between the tip and ring sides of the line, such relay would be released when the cam was in its normalneutral position re-- sulting in the release of switches, where the key is used in a system employing automatic switches, and in the actuation of a supervisory signal where the key is used in a manual telephone system.

Thus, if the operator at the incoming position, after answering thecall, finds it necessary to disconnect her telephone set from the. incoming trunk circuit, but desires to hold the latter, she will move the cam of the key from its right to its left-hand position, which necessitates passing through the normal neutral position of the key, during which time the circuit between the tip and ring sides will be opened. If the key is operated relatively slowly, the supervisory relay may be released, thusreleasing switches in an automatic telephone system, or causing theactuation of a supervisory signal in a manual system, thus giving to the operator a disconnect signal. This inadvertent opening of the line circuit thus results in a disconnection of the parties in an automatic system, or the giving of a disconnect signal to the operator in a manual system, and leads to confusion of operation.

It is the object of the present invention to provide a switching device by means of which the tip and ring sides of the incoming circuit will not be opened when the operator moves the cam of the key from the talking to the holding position, or vice versa. Thisinvention will be better understood from the following description when read in connection with the attached drawings, represented-by Figs. 1 and 2, which show an application of the invention to a manual telephone system, and Fig. 3 which shows an application of the invention to an automatic telephone system.

In Fig. 1 of the drawings L represents a trunk line which, for the purpose oi description, will be assumed to be of that type extending from a switchboard A to a repair clerks desk 13. The line L terminates at the switchboard A in a jack 29 with which is associated the lamp 31 by means of which the repair clerk may signal the operator at A. X represents a portion of a cord circuit which may be of the usual subscribers type located at the switchboard A having associated therewith a plug 30 which is adapted to be inserted in a jack 29. The cord circuit X of which approximately one end is shown, comprises, in part, a repeating coil 1 to which battery is connected in order to furnish energy to the line with which the cord circuit may be connected. Connected with the ring side of the cord circuit is a supervisory relay 40, havingassociated therewith a lamp 41, which servesas the supervisory signal of the cord circuit. At the repair clerks desk B there may be located a telephone circuit X which is adapted to be connected with the springs of the key K Associated with the trunkcin cuit L and located at the repair clerks end of the said circuit, are the relays-32 and 33, and the key K The key K is so designed that the cam thereof is adapted to occupy normally the position represented by the circle It will be seen that when the cam is in this position the master springs and the other springs controlled thereby, included within the right-hand group of springs, are spread apart and all of the contacts of said springs are opened. If the cam be moved to its middle position b, the master springs of the right-hand group and the associated springs will be released, and in returning to their natural position, they will close the contacts of the various adjacent springs of this group. This, as will be seen more clearly, later serves to connect the trunk line L with the telephone circuit X If it is desired to disconnect the telephone set circuit "from the trunk line but to maintain operated the supervisory relay of the cord circuit X the cam may be moved into the position designated c. d When thecam is thus operated, the master springs of the-lefthand group and the springs associated therewith will be moved so as to disconnect the telephone set from and to bridrie the holding circuit across the trunk circuit.

Having in mind the foregoing description of the parts shown in the drawings, thisinvention will be more fullyunderstood from the following description of its modeof operation.

Let it be assumed that the operator at A desires 'to obtain from the repair clerk at the position B certain information. i The operator at A will insert the plug 30 of the cord circuit X jack 29 and will then apply ringing current by means of the key K to the line L which, flowing through the condenser 50- and the right-hand winding of relay 32 will cause the operation of said relay. Relay 32 is locked up over a path extending from ground, the left-hand winding of relay 32, contacts 16 of relay 33 and contacts 4 of relay 32 to grounded battery. By the closing of the contacts 4 of relay 32, current will flow through the outer armature of relay 32 and contacts 4 through contacts 6 of relay 33 and through lamp 43 to ground, causing the lighting of this lamp. The clerk at the desk B, noting the lighting of the lamp 43, will operate the key K by moving the cam into the position b. Helay 34 will then be energized over a path e2;- tending from ground, througl'rthe upper lefthand winding of repeating coil 1, through theupper normal contacts of key K tips of plug 30 and jack 29, contacts '7 and contacts 8 of key K winding of relay 34, contacts 9 and contacts 10 of key K right-hand winding of relay 32, rings of jack29 and plug 30, lower normal contacts of key K winding of relay 40, and lower left-hand winding of repeating coil 1 to groundedbattery. Relay 34, in operating,

completes a circuit at its armature and front contact for relay 3 5. Relay 35, in operating, connects the operators telephone circuit X with the talking conductors 11. The tip and ring sides of the line L are also connected through contacts 12, 14, and 13 and 15 respectively with the talking conductors 11, and, therefore, with the telephone circuit X the operation of key K contact 18 is also closed, thereby causing the operation of relay 33 over a path traceable -from grounded battery, lefthand winding of relay 33, contacts 18 and 60 of key K to ground. Relay 33, in operating, locks up over a path extending from ground, right-hand winding, front contact, and. righthand armature of relay 3 3, sleeves of jack 29 and plug 30 and thence through lamp 41, resistance 45, armature and front contact of relay in parallel to grounded battery. Since the supervisory relay 49 has already been operated by a low of current there-through when key K was moved to position Z), a shunt path was established around the lamp 4-1, said shunt path'including the front contact and armature of relay 40 and resistance 45, so that lamp 41 will. no longer glow. Relay 33, in operating, opens the circuit for lamp 43 at contact 6, thereby extinguishing lamp 43. The lOCl.'- ing circuit for relay 32 is also opened atcontact 16 but relay 32 remains energized due to current flowing through its right hand winding from the battery at repeating coil 1,.through the winding of relay 34.

If the clerk at the desk B desires to disconn h -te phen m h n min line circuit L but does not desire to give tothe opertor at A a disconnect signal, the

springs, the contacts 14 and 15 are opened, V

whereby the conductors 11 are disconnected from the telephone set X thereby permitting the telephone set to be used with other trunk circuits. Contacts 8 and 9 of this group are also opened, but contact 21 is closed. It will be seen, therefore, that the movement of the camto position serves to release relay 34, which in turn releases relay 35. The tip and ring sides of the line L however, remain connected together through contacts 7, 21 and of the key K and the right-hand winding of relay 32. The supervisory relay 40, therefore, remains energized, and the lamp 41, associated therewith, remains extinguished so that the operator at A does not receive a disconnect signal as a result of the movement of the cam key K from it's talking to its holding position. 7

When the clerk at B desires to communicats with the operator at A, he will move the cam back again to the position b,thereby connecting the telephone set circuit X with the line L Upon the completion of the conversation and when the connection is no longer desired, the cam of key K will be moved into position a. This serves .to open all of the contacts of said key and thereby breaks the connection between the tip and ring side of the line if, which results in the releasing )of the relay. 40. The lamp 41, therefore, will be lighted due to the removal of the shunt around it, and the operator at A will accordingly remove the plug 40 from the jack 29 and restore the circuitto normal condition.

Fig. 2 shows a cord circuit X equlpped to give a flashing recall signal and is adapted for use in connection with I the trunk circuit L The cord circuit X a portion only of which is shown, has a plug which is adapted for insertion in the jack 29. This cord circuitcomprises a repeating coil to which a battery for'talking and signaling purposes is connected. Connected to the ring side of the answering cord is the following manner.

X isa key K which is adapted tobridge the operators telephone set (not shown) across the circuit or to apply ringing current to the line, depending upon the direction. in'which the key is operated. I

Having in mind the foregoing description of the parts of the circuit and the function performed by each part, this invention will be better understood by the following description of its mode of operation. I

I Let it'be assumed that the operatoror clerk-at B desires to obtaina certain sub- 'scriber, the; clerk will signal. the operator at A by moving the key K to position 1),

which serves to lightthe lamp 31. The operator atA will insert plug 60 into jack 29 and operate the listening key K which serves to connect her telephone set with her cord circuit 'X plug 60 into jack 29, the lamp 82 would tend to light by a flow of current from grounded battery through lamp 82, resistance 98, sleeves of plug 60 and jack '29, right-hand armature and back contact of relay 33, and resistance 99 to ground. The lamp is, however, prevented from lighting by the operation of relays and 84, which establish a short-circuit around the lamp in It will be recalled from the description of Fig. 1 that when the key K was moved. to position b, the connection was established between the tip and ring sides of the line D, and consequently across the conductors of the cord circuit X This results in a flow of current from the battery [connected to the winding of repeating coil 70, through the winding of supervisory relay 80, causing the operation of supervisory relay 80, whereupon contacts 94 of'supervisory relay 80 are closed. VVhen' the operator inserted the plug 60into the jack 29 in order to take up the call, she operated the key K in a left-hand direction in order to connect her telephone set with the circuit which connected conductor 97 through contact 92 to ground. This established a circuit from grounded battery, ri t-hand winding of relay 84, conductor 9%, and contacts 92' of key K to ground, thereby causing the op eration of relay 84. Relay 84, in operating,

locks up over a path extending from grounded battery, right-hand armature and front contact of relay 84, contacts 94 of the relay 80, front contact and left-hand armature of relay 84,lei"t-hand winding of relay 84, through resistance 98, sleeves ofplug 60 and jack 29, right-handarmatur'e and front contact of relay '33, and right hand winding of relay 33 to ground. This establishes a shunt path around the lamp 82 so that it remains extinguished.

Let us assume that after the desired connection hasbeen established and communi-- Upon insertion of the-- cation thereover has been completed, that the clerk at B restores the key K to the position a momentarily and then moves to position b in order to again signal the operator at A. When the key K was moved to position a, the connection between the tip and ring sides of the circuit was opened and the supervisory relay 80 is deenergized which permits the opening of the contact 94. This results in the deenergization of relay 84 and causes the lighting of the lamp 82. This will indicate to the operator that the parties have disconnected, and unless some different 7 signal is given to her as when the key K is moved to the position b, the operator would take down the cords of the circuit. This is prevented, however, when the key is moved into position b by the inauguration of What is known as the flashing recall signal. Thus, when the key K is in position b, relay 80 will be operated which, when relays 33, '84: and 85 are not energized, establishes a circuit from grounded battery, armature and back contact of relay 85, left-hand winding of relay 83, normal right-hand contacts of relay 84, contact 94, normal left-hand contacts of relay 8%, resistances 87 and 98, sleeves of plug and jack 29, right-hand armature and back contact of relay 33, and resistance 99 to ground. This establishes a shunt path around lamp 82, which extinguishes the lamp. The flow of current through the left-hand winding of relay 83 energizes this relay, and if the contacts of the interrupter 90 are in a position to stablish a connection to ground, current will flow from grounded battery, winding of relay 85, right-hand Winding of relay 83, front contact and armature of relay 83, through interrupter 90 to ground. Relay 85 will be energized thereby, and at its armature and front contact, a circuit will be closed for buzzer 91, and, at the same time, the shunt path will be removed from the lamp 82, thus permitting said lamp to light. It will be seen, therefore, that by means of this arrangement the interrupter 90 causes the intermittent energization of relay 85 and the intermittent lighting of lamp 82 whereby a flashing signal is given to the operator which indicates that the party whose line is connected with that cord desires to recall the operator.

In the arrangement of key switches heretofore used in which the cam passed through a neutral position between the talking position and the holding position whereby the connection between the tip and ring sides of the line was momentarily opened, there was switching device of the type embodying the principle o'l this invention, it is possible to transfer the trunk circuit from the telephone set to a holding circuit and vice versa without opening the circuit of a supervisory cord relay and thereby causing an involuntary operation of the said supervisory relay which would produce a false disconnect signal.

.In Fig. 3 of the drawings which represents an embodiment of the invention as applied to an automatic telephone exchange system, there is shown a trunk line L extending from a repair clerks desk or operators position B to an automatic telephone exchange. The trunk line L terminates at the operators position in the key K and has associated therewith a lamp 133 by means of which the operator may be signaled on incoming calls from the automatic telephone exchange. An impulse sender S g is provided for the operator at position B for the purpose of controlling switches at the automatic exchange 011 outgoing calls to stations of said exchange. The trunk line L terminates at the automatic exchange in a nonnumerical switch N and is multiplied to contacts of a connector switch, such as C. The non-numericalswitch N and the connector switch C are schematically represented only, since they form no part of the present invention, the inventive idea of the disclosure being capable of adaptation to any wellknown .automatic telephone exchange. Switches of the type herein indicated are fully disclosed and described in the patent of F. A. Stearn et al., No. 1,395,977, granted November 1, 1921.

Having in mind the foregoing description of the parts shown in Fig. 3 of the drawings, the invention will be more fully understood from the following description of a call from the operators position to a station of the automatic exchange, and a call from a station of the automatic telephone exchange to the operator. 7 Assuming that the operator or clerk at position B desires a connection with a station such as H, at the automatic telephone exchange, the operator at B by moving the key K to position causes the ene'rgization of relays 136 and 134 of the trunk circuit over a path extending from grounded bat- .tery, left-hand inding of relay 134;, winding of relay 136, contacts 118 and 160 of key K and contacts 152 of sender S to ground. Relay 136 in operating short circuits condenser 137, and places a bridge across the trunk conductors L said bridge including the right hand winding oi relay 135 and con tacts of relay 136 thereby causing the operation of line relay .101 of the non-numerical switch N over a path extending from ground, upper normal contacts of relay 102, righthand winding of relay 135, contacts of relay 136, lower normal contacts of relay 1.02 and right-hand winding of relay 101 to grounded battery. Relay 131 of the operators telephone set circuit is also energized over a path extending from ground, through the upper normal contacts of cut-oil relay 102, contacts 112 and 114 013 key K upper talking conductor 111, coil 130, winding of relay 131, back contact and armature of relay 132, contacts 151 of impulse sender S, lower talking conductor 111, contacts 115 and 113 of key K lower normal contacts of cut-off relay 102, and right-hand winding of relay 101 to grounded battery. Relay 101, of the non-numerical switch N, in I energizing, closes a circuit for a stepping magnet (not shown) under the control of which the brushes 108, 109 and 110 of switch N are advanced. As soon as the brush 110 passes off of normal contact 125 and into engagement with segment 123, battery potential is connected to the multiple test terminal, such as 182, appearing in the banks of final selectors having access to the line, over conductor 122, brush 110 and segment 123 to grounded battery, and relay 138 of the trunk circuit L is energized over a path extending from grounded battery, segment 123, brush 110, and the winding of relay 138 to ground. Under control of the stepping magnet (not shown) of the non-numerical switch N, the brushes 108, 109 and 110 are advanced until the terminals 192 and 19 1 of an idle switch, such as C, are reached, whereupon cut-off relay 102 is energized and the line L is extended through to the switch 0. It will be understood that there may be a number of selector switches interposed between the nonnumerical switch N and the connector switch l/Vhen relay 131 of the operators telephone set was energized, it completed a circuit through its contacts for relay 190, said circuit including contacts 152 of'sender S. Relay 190 in energizing telephonically connects the operators telephone set to the conductors 111.

The operator at position B may now actuate the impulse sender S to control the setting of the connector switch C upon the terminals of a desired station, such as H, in the well-known manner. Upon the initial move ment of the impulse sender, contacts 150 are closed and remain closed during the'movement of the sender. The closure of the contacts 150 completes a circuit for the energization of relay 132. Relay 132, in energizing, bridges coil 130 directly across the tip and ring conductors of the trunk circuit L and opens the circuit for relay 131, which in dialing.

retracting its armature opens the circuit for relay-190; Rela'y 190 opens the operators from across the trunk conductors L during,

dialing. As the impulse sender returns to normal, the bridge across the conductors 111, including coil 130, front contact and arma-- ture of relay 132 and contacts 151 of im- -pulse sender S, is intermittently opened thereby conveying impulses to the connector switch. C at the automatic telephone exchange in the well-known manner. At the end of each series'of impulses, the contacts 150 of impulse sender S are opened, thereby permitting the deenergization of relay 132. The contacts 152 of impulse sender S are closed at the end of each series of impulses thereby connecting the bridge, consisting of the right-hand winding of relay 135, the armature and front contact of relay 136, across thetrunk conductors L After sending a suflicient number of impulses to set the brushes 161, 162 and- 163 or the connector switch C upon the terminals 164, 165 and 166 respectively, and if the line at such station has been found idle, ofi'-normal contacts 167 will be closed thereby placing the busy test upon the terminal 166 of the desired sta-' tion. Station H may then be signaled in the well-known manner and after the re sponse of such station, the operator at position 13 and the converse.

party at'station H may If the operator at the desk B desires to disconnect the telephone set from the trunk circuit L and does not desire to'release the connection, the said operator will now move the cam ofthe key K into position 0 By the operation of the master springs in the left-hand group of springs, the contacts 114,

and 160 are opened and contacts 121 are closed. The opening of contacts 114 and 115 disconnects the tip and ring conductors from the telephone set :X thereby permitting the telephone set to be used with other trunk circuits. The closure of contacts 121 holds relay 136 energized when contacts 160 are opened,'thereby maintaining the bridge across the tip and ring conductors of the 'Upon completion of the conversation and when the connection is no longer desired,

the cam of key K will be moved into'position a This serves to open all the contacts of the right-hand group of the key. K

whereupon relay 136 is released and the of the trunk circuit and cut-off relay. 102

of the non-numerical switch associated with the trunk circuit L will be energized over a path extending from groundedbattery, contacts 167, brush 163, terminal 182 conductor 122 and thence in parallel, one path extending through the winding of relay 138 to ground and the other path extending through brush 110, normal contacts 125, lower and upper windings of ClltrOfi relay 102 to ground. Ringing current may be projected over the terminal 180, conductor 148, through the right-hand winding of relay 135 and condenser 137, which are normally bridged in series across the trunk conductors L and conductor 147 to terminal 181. Relay 135 is thereupon energized and locks up over a path extending from grounded battery, right-hand armature and back contact of relay 134, the inner armature, front contact and winding of relay 135 to ground. At the front contact and outer armature of relay 135, a circuit extending through the left-hand armature and back contact of relay 134 is completed for lamp signal 133.

The operator at position B noting the signal 133, will actuate the key K by moving the cam into position 6 whereupon a circuit for relays 136 and 134 of the trunk circuit L will be completed over a path extending from ground, contacts-152 of sender S, contacts 160 and 118 of key K and windings of relays 136 and 134 to grounded battery. Relay 136 is energized, and in attracting its armature short circuits condenser 137 and bridges the right-hand winding of relay 135 directly across the tip and ring talking conductors thereby causing the tripping of the machine ringing in the well known manner and the advancement of the connector into the talking position. Relay 134 is also energized and in attracting its lefthand armature, interrupts the circuit for lamp signal 133 thereby extinguishing said signal and at its right-hand armature and front contact completes a locking circuit for itself over a path extending from ground, armature and front contact of reoperated lay 138, the right-hand winding, front con- .tact and armature of relay 134 to grounded battery. Belay 134 in energizing also interrupts the locking circuit forrelay 135, but

this relay does not retract its armatures since.

it is maintained energized over a path extending from ground, upper right-hand winding of repeating coil 170, brush'161, terminal 180, conductor 148, right-hand winding of relay 135, armature and front contact of relay 136, conductor. 147, termi nal 181, brush 162, winding of relay 175 and lower right-hand winding of repeating coil 170 to grounded battery.- When the operator at position B operated the key K by moving-the cam into the position b coil 130 and winding of relay 131 in series with the back contact and armature of relay 132 and contacts 151 of impulse sender S of the operators telephone set circuit were also bridged across the talking conductors of the trunk circuit. Relay 131 associated with the operators telephone set X is then energized over a path extending from grounded battery, upper right-hand winding of repeating coil 17 0 associated with the connector switch, brush 161, terminal 180, conductor 148, contacts 112 and 114 of key K coil 130, winding of relay 131, back contact and armature of relay132, contacts 151 of'impulse sender S, contacts 115 and 113 of key Kflconductor 147, terminal 181, brush 162,

winding of relay 175 and the lower right- 7 111 and-the operator'at position B may now converse with the calling station.

If, after conversation with the calling station, the operator at desk 13 desires to disconnect the telephone set X from the trunk circuit L but does not desire to re leasethe switches at the automatic exchange, the said operator will move the cam of the key K* into position 0 By the operation of the master springs in the lefthand group of springs, the contacts 114 and 115 are opened whereupon-the tip and ring conductors of the trunk circuit L are disconnected from the telephone set X thereby permitting the telephone set to be used with other trunk circuits. the left-hand group are also opened, but contacts-121 are closed before contacts 160 are opened thereby maintaining relay 136 and consequently maintaining the bridge across the talking conductors of trunk circuit L The telephone set is thus disconnected and free for use but the switches at the automatic exchange are held by the bridge of relay 135 and contacts of relay 186. The switches are thus not released as a result of the movement of the cam K from the talking to the holding switches.

When the operator at the position B deires to converse with the calling station, the said operator will move the cam back into the position 19 thereby connecting the telephone set circuit X with the line trunk circuit. 7 v

Upon completion of conversation and when the connection is no longer desired, the cam of key K will be moved into position 0, This serves to open all contacts of the right-hand group ofkey K thereby removing the bridge from across the tip and ring conductors of the trunk circuit L and causing the release-of the switches at the automatic exchange in the well-known man- 'JIQI. The circuit is then ready for the next call. 7

What is claimed is:

1. In a signaling system, acircuit having associated therewith a supervisory relay, a

holding circuit connected to said first circuit, a third circuit, and a single switch for transferring the connection of the said first circuit from the said holding circuit to the said third circuit and vice versa., Without opening the circuit embracing the said relay.

2. In a signaling system, a circuit having associated therewith a relay, a supervisory signal controlled thereby, a holding circuit connected to said first circuit, a third circuit, and a single switch for transferring the connection of the said first circuit from the said holding circuit to the said third circuit and vice versa, without opening thecircuit embracing the said relay and preventing the indication of a disconnect signal.

3. In a telephone system, a circuit having a supervisory relay, a holding circuit associated with said first circuit, a telephone circuit, and a single switch associated with said first mentioned circuit designed in its normal position to maintain open the circuit of said supervisory relay but arranged to close the circuit of said supervisory relay when the said circuit is connected to said telephone circuit, and to maintain the said supervisory relay circuit closed when the said circuit is transferred from said telephone to said holding circuit.

4. In a telephone system, a circuit having a supervisory relay, a holding circuit, a telephone circuit, and a single switch associated with said first mentioned circuit designed in its normal position to maintain open the circuit of said supervisory relay but arranged to close the circuit ofsaid supervisory relay when the said circuit is connected to said telephone circuit, and to maintain the said supervisory relay circuit closed when the said circuit is transferred from said telephone to said holding circuit and vice versa.

5. In a signaling system, the combination of a line circuit having associated therewith a supervisory signal adapted to indicate circuit conditions, a telephone circuit, a holding circuit, and a single switch designed normally to maintain open the circuit of said supervisory signal but adapted to close the supervisory signal circuitwhenever the said line circuit is connected to the said telephone circuit, and to maintain the said supervisory signal circuit closed when the said line circuit is transferred from" said and having a supervisory. relay associated therewith, a second circuit, a third circuit, and a slngle switch for connecting sald first circuit with elther said second or said third circuit without opening the connection be-.

tween the sides of the said first circuit, whereby the said supervisory relay may be maintained in its operative position.

7. In a signaling system, the combination with a circuit having connected therewith, a cord circuit containing a supervisory relay, of a holding circuit connected to-said first circuit, a third circuit, and a single switch for transferring the connection of the said line circuit from the said holding circuit to said third circuit without opening lay, of a telephone circuit, a second circuit.

including a relay controlling said telephone circuit, a holding circuit and a multi-position switch adapted in one position to connect said supervisory relay in circuit with said second mentioned relay whereby said relays operate and said telephone circuit is connected to the cord circuit, and in another position to interchange said second circuit and said holding circuit to maintain said supervisory relay operated and to disconnect said telephone circuit from said cord circuit.

9. In a signaling system, the combination with a trunk circuit, a cord circuit equipped with a supervisory relay, aholding circuit for said relay, and a switching device having a normal and two successive operative positions, said device being adapted in its normal position to disconnect said trunk circuitfrom said cord circuit, in one of its operative positions to connect said trunk circuit with said cord circuit, and in its other operative position to connect said cord circuit with said holding circuit.

10. In a signaling system, a first circuit having a supervisory device therein, a second circuit to be associated with said first circuit, a holding circuit to prevent the deenergization of said supervisory device, and a switching device comprising a key having a normal and a plurality o1 successive operative positions whereby said first circuit and said second circuit will be normally disconnected, said first circuit and said second circuit will be connected when said switching device is moved to one of its operative positions, and said first circuit and said holding circuit will be connected when said switching device is moved to another of its operative "positions.

nect said set to said circuit, to disconnect said'set from said circuit, and to substitute said second circuit.

13. An operators telephone set, a circuit, a second circuit, a switch having contacts in said first circuit, and connections for saidswitch whereby said operatorstelephone set and said second circuit may be interchangeably connected to said first circuit without 7 said supervisory circuit disassociated when a said trunk is seized at one of said positions, in another position to associate said telephone circuit with said supervisory circuit, and in another position to disassociate said telephone circuit and said supervisory circuit and to substitute a holding circuit for said telephone circuit, thereby maintaining said supervisory circuit closed. v

15. In a signaling system, the combination with a trunk circuit, a cord circuit equipped With'a supervisory relay, a telephone circuit, a relay for connecting said telephone circuit with said trunk circuit, and a switching device having a normal and'two successiveoperative positions, said device being adapted in its normal position to maintain said telephone circuit disassociated from said trunk circuit, in one of its operative positions to establish a circuit for said relay whereby said telephone circuit is connected to said trunk circuit and said supervisory relay operated in series with said relay, and in its other operative position to disconnect said relay and said telephone'circuit from said trunk circuit and to substitute a holding circuit'for said supervisory relay.

In testimony whereof, I have signed my name to this specification thi's'22nd dayof July 1920.

GEORGE W. KUHN.

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