US1541196A - Telephone system - Google Patents

Description

Jun 9, 1925.

A. B. SPERRY TELEPHONE SYSTEM H n A a I h e e H .F wan m8 m v m Q r. w w

QQ AM M l A. h a WP =m m l d m g LI .wl xkq June 9, 1925. 1,541,196

A. B. SPERRY I TELEPHONE SYSTEM Filed Feb. 15, 1923 4 Sheets-Sheet 5 MARGINAL I Ar/hu/ 5 Sperry June 9, 1925.

A. B; SPERRY TELEPHONE SYSTEM Filed Feb,

15; 1925 4 Sheets-Sheet 4 hven/br I Ar/hur 5. Ska/r] I Patented June 9, 1925.

UNITED STATES PATENT OFFICE.

ARTHUR B. SPERRY, 0F NEXV YORK, N. Y., ASSIGNOR TO WESTERN ELECTRIC COM- PANY, INCORPORATED, OF NEW YORK,

N. Y., A CORPORATION OF NEW YORK.

TELEPHONE SYSTEIi/L Application filed February 15, 1923. Serial No. 619,086.

To all whom it may concern:

in it known that I, ARTHUR B. Srnmir, a citizen of the United States of America, residing at New York, in the county of New York and State of New York, have invented certain new and useful Improvements in Telephone Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to telephone systems and more particularly to systems wherein connections are established by means of machine switching al'iparatus.

In machine switching systems it. is customary to connect blank bank terminals, or

terminals of a line from which former scrvice has been discontinued, to special trunks leading to a special operators position, sometimes called an intercepting operators position, so that a subscriber or operator whose connection has been extended to such blank terminals may be informed that the number of the called station has been changed, or service on the line of the called subscriber has been discontinued. In such cases'it is necessary to prevent the operation of a n'iessage register or coin collect device at the calling end of the circuit if the call, which has been extended to the intercepting operator is from a subscriber and it is also desirable to provide supervision back to the originating end of the call if the call, which has been extended to the intercepting operator, is from a toll operators position.

An object of the invention. is therefore to provide an improved arrangement for ena..' ling an operator to answer calls incoming over blank or unequipped terminals of a selector switch without causing a charge to be registered against the calling subscriber.

Another object of the invention is to provide an improved cord circuit to be used in connection with trunk circuits connected to blank terminals for answering calls from either a subscribers station or a toll operators position.

A. feature of the invention consists in providing a cord circuit, for answering calls incoming over trunk circuits, with means for discriminating between calls incoming from the toll operators position and calls incoming from a means functioning in one case to control a supervisory signal and in the other case subscribers line, said to prevent the operation of the call charging device.

This and other features of the invention ranged consecutively with Fig. 1 to the left,

show one embodiment of the invention.

Fig. 1 of the drawings shows a portion of a cord circuit at a toll operators position and a portion of the outgoing .end of a trunk circuit to which the cord circuit has access. Fig. 2 shows schematically the incoming end of the toll trunk circuit, a portion of a toll transmission selector circuit and a subscribers station having access to a line switch and a selector switch. Fig. 3 shows a combined toll and local connector. The combined toll and local connector has access to the subscribers station B and to scribers station A together with its asso-.

ciated switches shown in Fig. 2, are fragmentary portions of the drawings shown in the copending Stokely, Serial No. 412,795, filed September 25, 1920. The same reference characters have been employed in this application as are employed in the Stokely application so that the elements of this disclosure may be readily found in the aforementioned ref erence.

A call from station A for a subscriber at station B will first be described. Upon the removal of the receiver by the calling party at substation A, the line of substation A is automatically extended in the well known manner by the lineswitch LS to a first selector switch SL. The subscriber now operates his dial 90 to set the first selector opposite a group of trunks having access to a plurality of connector switches, whereupon the selector switch automatically seizes one of these switches such as F0. The line relay A-G of the connector switch now operates over a circuit extending from ground, through the lower winding of relay A6, upper normal contacts of relay D45, terminal 34, brush application of Ray L.

till

30, terminal 44, brush 40, thence through the calling substation loop, brush 4L1, termina 45, brush 31, terminal 35, lower inner normal contacts of relay D-6 and upper winding of relay A6 to grounded battery. Relay A6 in operating completes an obvious cirouit through its alternate contacts for slow to release relay 13-45. Relay B6 in at tract-ing its armature 616 grounds test terminal 36; its uppermost armature connects ground over lead 650 to the test terminal 527 of the toll selector switch TTS, for the purpose of rendering the connector FC busy at the selector switch TTS; and in, attracting its lower armature prepares a circuit for slow to release relay 619 and the vertical magnet 618 over a path extending from grounded battery, through the winding of magnet 6'18, winding of relay 619, right-hand contacts oi cit-normal switch 620, lower alternate contacts of relay B-6 and normal contacts of relay A6 to, groui'id. The subscriber now turns the dial .ior the tens digit and the relay A6 transn'iits impulses over the said circuit to the vertical magnet 618 to raise the brushes ot' the con nector to the desired level. The first impulse for the vertical magnet passes over the path previously traced by way of the normal contacts of the oil-normal switch 620; the succeeding impulses pass by way of contact 622 of the oit-norn'ial switch 620 and the upper armature and trout contact of slow to release relay 619, which relay is energized at the first impulse of the tens series and remains energized during this series.-

\Vhen the 'npulses cease, relay 6l9 rcleases, connecting the rotary magnet 623 to the back contact of the impulse relay li6 over a. circuit extending from the back con tact of relay A-6, through the lower alternate contacts of relay B-6, contacts 622 of cit-normal switch 620, normal contacts of relay 619, inner left-hand contacts oi relay G6, conduct-or 625, uppermost contacts of relay H6 and winding of rotary magnet 623 to grounded battery.

The operator now turns the dial for the units digits. At each deenergiza-tion oi the line relay A6, in response to the dialing of the units digits, the impulse circuit for rotary magnet 623 is closed thereby advancing the brushes of the connector switch a number of steps corresponding to the d' it transmitted. Relay E6 is also energ d,

in parallel with magnet 623. when the first units impulse is transmitted. Relay l l6 which is slow to release remains operated during the impulse period. An interval after the last impulse is transmitted, relay E6 releases.

Assuming that the number dialed corresponds to the number of the station l; and that the brushes ot the connector have been applied to the station B. The circuit for operating relay l-l-6 may be traced from ground, through the upper inner contacts of relay l36, conductors 615, and 631, righthand normal contacts oi relay G6, upper winding of relay H-6, conductor 629, outer right-hand normal contacts of relay l'l6, brush 627 to grounded battery at terminal 78. Relay l-l6 in operating locks to ground at the contacts of relay J6 under control of relay B6. The path for the ringing current may be traced follows: ground, through the ringing machine 680, upper winding of relay F-6, back contact and armature 637 of relay F-6, armature 681 and front contact of relay H-6, brush cs4, terminal 77, through the bell of station 3, terminal 76, brush 683, upper inner contacts of relay l-l6, upper normal contacts of relay l*6, to grounded battery. 7

l' v hen the party at station B answers,

relay F6 will energize due to an increase in the amount of current flowing through its upper winding. Relay F6, in operating, disconnects ringing current from the called station, renders the tip and ring tallt- 7 ing of relay D6, contacts 690 of relay K 6, upper alternate contacts of relay F-6, upper inner contacts of relay l*l6. brush 683, terminal '76, through the loop of station B, terminal '77, brush 684., front contact and armature 681 of relay ll6. mature 637 and Front contact of relay F-6, contacts 691 of relay K6 and lower winding of relay D6 to ground. Relay D-6. in operating, reverses the flow oi current over the calling end of the connector circuit and causes the operation of the message register oi the calling substation A in the manner well understood in the art.

Assuming that the called suliistationis busy, ground potential will be present on the test terminal 78 or" the called stat-ion l3 and when brush 627 arrives at terminal 78, relay H+6 will not be operated. Relay G6 will operate over a circuit extending from grounded battery, through the winding of relay G6, back contactand armature 642 of relay l-l6, contact 640 of slow hand cont acts forlamp 152."

lighting indicates to the intercepting opera-'v to release relay E6, conductor 628, brush 627, to ground at terminal 78. Relay G-6 in attracting its outer left-hand armature connects a. source of busy tone 645 to the calling station to indicate that the called subscriber is busy.

Upon the completion of conversation, the restoration of the receivers of the calling and called stations tothe switchhoolcs releases relays A6 and D6. Relay A6 in releasing, releases relay B- 6. An obvi ous circuit is then completed for release magnet 686 through the lett-hand contacts of off-normal switch 620, whereupon the connector switch is restored to normal position.

A call by the subscriber of station A for a number of a line to Which no station is connected will now be described. The terminals of such numbers are connected to trunk circuits such as I T leading to the intercepting operators position. If the subscriber at station A dials a number corresponding to the trunk IT, the connector FC will be set on the trunk terminals 93, 94 anc 95 in a manner similar to that previously described, after which ringing current will be automatically applied to the trunk to light the lamp 152 at the inter ccpting operators position, an indication that a calling line is connected to the trunk 1T. The path of the ringing current may be traced as follows: grounded battery, through the upper normal contacts of relay F-6, upper inner contacts of relay H6, brush 683, terminal 93, condenser 101, right hand winding of relay 153, outer left-hand contacts of relay 154, terminal 94, brush 684, armature 681 and front contact of relay H-6, armature 637, back contact and upper winding of relay F6 and source of ringing current 680 to ground. Relay 153 operates in this circuit and locks over a circuit],

including the outer contacts and the left.-

left-hand contacts of relay 154, and completes an obvious circuit through lts left- Lamp'152 in tor that a calling line is connected to the trunk I'T.

The operator will thereupon insert plug 106 into jack 107 whereupon relay 110 will be operated over a path extending from grounded batter through the right-hand nomal contacts of relay 112, winding and left-hand normal contacts of relay 110, lower normal contacts of relay 114, rings of plug 106 and ack 107, and right-hand nor mal contacts of relay 154 to ground. Relay 110, in operating, completes a circuit for relay 154 of the trunk circuit over a path extending from ground, through the winding of relay 154, sleeves of jack 107 and plug 106, left-hand alternate contacts and windcuit -K continuous.

ing of relay 110 and right-hand normal contacts of relay 112 to grounded battery. Relay 154, in attract-ing its inner left-hand armature, opens the locking circuit for relay 153 which releases, extinguishing the lamp 152, and in attracting its right-hand armature renders the ring conductor of the trunk circuit IT continuous. Relay 110 in attracting its outer right-hand armature completes an obvious circuit for slow-to-pull-up relay 117. Relay 117 in operating completes an obvious circuit for the energization of slowto-pull-'up relay 114.' Relay 114 in attracting its lower armature, renders the ring talking conductor of the cord cir- Be'tore the relay 114 operates, however, to render the ringing conductor of the cord circuit K continuous,-

the ringing current is tripped over a circuit extending from ground, through the inner right-hand contacts of relay 110, lower normal contacts oi": relay 114, rings of plug 106 .to-pull-up to insure that ringingcurrent will be tripped before the operator can connect her head set to the trunk circuit so as to avoid disagreeable clicks in the operators t1. Relay 114, in operating, closes a high resistance bridge across the tip and ring conductors of the cord circuit over a path extending from the tip conductor of the cord circuit K through retardation coil 130, windings of relay 131 and polarized relay 132, right-hand normal contacts of key 133 to the ring conductor of the cord circuit K. The polarized relay 132 is a test relay which determines whether or not the intercepted call is from a toll operator. If the call is not from a toll operator, but from a subscribers line, the flow of current through the winding of relay 132 is in such a direction as to prevent the operation of relay 132. The circuit under these conditions is as follows: from battery through the upper wind- I Cdl tery is connected to the tip conductor of the cord circuit K. Hence, relay 132 does not operateat this time, and relay 135 there- :toreremaills normal. Under these circumstances, the back-bridge relay D6 ot' the connector switch EU will not. operate due to the high resistance of the winding of the polarized relay 132 in series with it; Relay 131, however, operates over the circuit traced in series with relays 132 and D6, thus opening at its armature, the circuit through the winding of relay 112 to ground at the upper alternate contact of relay 11st. Relay 112 is made slow-to-pultmo so that it will not operate during the time interval between the operation of relays 1.14 and 131 and furnish a false disconnect signal by lighting lamp 138. Since relay D-6 does not operate, the currert is not reversed over the calling line and consequently the message register of the calling line will not be operated.

The operator after inserting plug 106 into jack 10'. will actuate key 139 thereby connecting; the operators telephone set 0 in operative relationship with the calling line. The operator may then converse with the calling; party and inform him that service has been discontinued on the line which he has called or give him any other information which he desires.

Upon the completion of conversation, the restoration of the receiver to switchhook at stat-ion A causes the release of automatic switches in the manner well known. The removal of the current from the talking condnctors of the trunk circuit IT when the 7 Relay 112 in attracting its right-hand armature opens the circuit and causes the release of relay 110. The release of relay 110 opens the-circuit of slow-to-pull-up relay 117 which releases, in turn-releasing relay 11%. When relay 1 12 operates, a circuit is completed to operate relay 115 oi the cord circuit K over a path extending from ground, through the winding otrelay 154; sleeves otjack 107 and plng106, windingof relay 115, and righthand alternate contacts of relay 112 to through the winding of relay 112,

grounded battery, Relay 115'. operated closes a circuit to maintain relay 112 operated after relay 114: releases. Relay 115 hasahigh. resistance winding, sothat relay 154; new releases thereby rendering the ring conductor of the trunk circuit I T discontinuous and connecting the alternating current relay 153 across the trunk circuit. It will thus be seen. that, if the operator fails to remove the plug 106 from the jack when the disconnect. lamplEiS is lighted, the trunk circuit. T T is nevertheless available for recall. it before the plug. 106. is. removed -from the jack 107, a recall signal is received, it is necessary for the operator to momentarily remove the plug 106 from the jack:

10?, so as to. restore the opera-ted relays of the cord circuit K to normal so as to pre pare these relays; for. another cycle of operation.

A. call by the toll operator for. a. station to which the connector FC has access but on. whichthe service has been discontinued will now be described, It will be assumed that the trunk- I T isconnected to the terminals correspondingto the number of the station desired.

Extension of the connection from the operators position to the connector switch FC is established in the manner described in detail in the copending application heretofore mentioned and a detailed description of the-operation of the connector switchiwill only be given herein. The operator atter inserting the plug TT into the jack TSJ (F 1) and after actuating the dialing key D1; proceeds to, operate the dial D to send sets of impulses corresponding T011118 number desired, whereupon the selector switches SS and TTS will be set to select the terminalsof the connector switch F6 to which-the trunk l--T is connected. At this time, re-

D-4 ill- 43, D. '5, .B5, 13-43. and J6 will be energized in the manner fully set forth in the above mentioned application.

,T he seizure of the connector causes the closing of the following circuit for the inipulse relay A6: grounded battery, upper winding of relay A}6, conductors 60a and 605, left hand winding of relay J(3, conductors 606' and 607, lowermost arn'iature and back contact of relay K.6, ring condnctor 64 6, terminal 54A, bruslr 5341, conductor 5&5, front contact and armature 532 oi'i relay left-hand armature and trout contact of relay A5,.ring conductor 54:0, lower right-hand; winding of repeating coil 406, resistance 4e60, conductor e22, lett-hand armature and front contact of relay D4r, resistance 423, conductor 4:24, resistance e01, upper right-hand winding of repeating coil. 406, conductor 54,71, armature 531and; "front contact of relay D5, conductor 548, brush 533, terminal 549, conductor- 610, upper arll ll lit) lit":

ill)

mature and back contact of relay K6, conductor 61'1, conductor 612, and lower winding of relay A6 to ground. Relays A6 and J-6 operate in this circuit, the latter at its innermost right-hand arma ture, closing a locking circuit for itself as follows: grounded battery, right-hand winding and inner right-hand armature and front contact of relay J6, conductor 614, conductor 631, conductor 615 to ground at the armature 616 and front contact of slowto-release relay B6, which operated upon the energization of the impulse relay A6. Relay B6, in operating, grounds the sleeve wire 617 leading to the testmultiple terminals of the local selectors, this circuit extending from ground, armature 616 and front contact 1'elav,B-6, conductor 615, to conductor 617. The return of the dial to normal in transmitting the tens digit interrupts the circuit of relay 'A2 which in turn interrupts the circuit of the impulse relay A5, which in vibrating its left armature causes the impulse relay A6 of the connector to transmit impulses to the vertical magnet 618 of the connector over the following circuit: grounded battery, magnet 618, slow-torelease relay 619, right-hand normal contacts of the off-normal switch 620, conductor 621, lower armature and front contact of relay B6 to ground at the armature and back contact. of the impulse relay A-6. At the firststep of the connector, the springs of the off-normal switch 620 are shifted and the succeeding impulses are transmitted by way of the upper armature and front contact of relay 619 and the contact 622 of the off-normal switch 620 now closed. The. connector brushes are thus lifted to the desired level and upon the cessation of the impulses, impulse relay A-6 remains energized and relay 619 in series with the vertical magnet 618 releases thereby preparing the circuit for the rotary mag net 623.

The units impulses pass through the back contact of the impulse relay -A6, lower armature and front contact of relay B6, conductor 621, off normal contacts 622, armature and back contactof slow-to-release relay 619, conductor 624, inner left-hand armature and back contact of relay G-6, conductor 625, uppermost armature and back contact of relay H-6, and winding of rotary magnet 623 to grounded battery.- The connector is thus stepped into engagement with the terminals of trunk IT.

If the trunk I-T is idle, grounded battery will lee-present on the test terminal 95 and the following circuit will be closed to operate relay H6: grounded battery, at test terminal 95, brush 627, conductor 628, righthand armature and back contact of relay E6, conductor 629, upper winding of relay H6, conductor 630, right-hand armature and back contact of relay G-6, conductor 631,-conductor 615, and armature 616 of relay B6 to ground. Relay H6, in attracting its armature 632, looks itself to the grounded sleeve wire 650 and extends this grounded conductor over conductor 633, middle right-hand armature and front contact of relay .J6, conductor 634 to the winding of relay K6. Relay K6, in attracting its armature'602, disconnects the grounded sleeve wire 650 from the control lead 600, leading back to the relay D4 releasing the latter relay. Relay D4, in retracting its outer right-hand arn'iature, operates relay'Flover the following circuit: grounded battery, through the winding of relay F4, conductor 428, outer right-hand armature and back contact of relay D4, conductor 429. armature 523 and front contact of relay D5, conductor 518 and conductor 503 to ground at the right-hand armature and front contact of relay 13-5. Relay F4, in attracting its outer righthand armature, closes a substitute ground to hold up the relay F 6 to prevent ringing current from being transmitted out over the connector at this time. This circuit may be traced from ground, through the right-hand armature and back contact of relay 13-4, conductor 430, right-hand armature and back contact of relay B4, outer right-hand armature and front contact of relay F4, control conductor 414, contacts 535 of relay D 5, conductor 538, brush 539, terminal 540, conductor 600, front contact and armature 635 of relay F-6, lower winding'of relay F6 to grounded battery. The operation of relay K6, to cause the reversal of the direction of the current flowing in the loop leading back to the toll operators position, would cause the deenergization of relay F-6 and unless a substitute circuit is provided for holding relay F6 the ringing operation Vwould automatically take place. This is prevented by applying ground to the control conductor 600 over the circuit traced to hold the relay F6 until the operator by depressing the ringing key, as will be explained hereinafter, releases relay F6 to start the automatic ringing operation. The release of the relay D-4 and the energization of relay F4, as described, reverses the direction of current flow in the talking conductors leading back to the toll operators position.

After having turned the dial for the last time the operator restores her dialing key DK which disconnects the dial from the tip of the plug causing the release of the relay A2 and causesthe closure of an energizing circuit for the right-hand winding of relay C-2, and for relays B-43 and A- -2. Relay A-2 being marginal, releases under this condition and in retracting its left-hand armature deenergizes relay I2, which, in

releasing, causes the release of relay D-'2. The polarized relay F2 is now bridged across the trunk circuit, the bridge extending from the upper talking conductor 212, conductor 211, winding of polarized relay F 2, conductor 210, inner right-hand arinature and front contact of relay B2, conductors 209, left-hand winding of relay C2, armature and front contact of relay C2, conductor 207, outer leftihand armature and back contact of relay 1 2, conductor 200, to the lower talking conductor 205. The reversal of the direction of current in the talk iiig conductors due to the operation of relay F 1 causes the relay F2 to operate closing the following circuit for relay G2: grounded battery, winding of relay G2, conductor 22 1, contact 225 of relay F2,

front contact of relay B2 to ground. Relay G2 locks over the fell wing circuit: grounded battery, winding of relay G2,

conductors 224-. and 229, front contact and armature 230 of relay G2, conductor 231, to ground at the inner left-hand armature of relay B2. Relay G2 connects the talking conductors 212 and 205 through to the talking conductors of the cord circuit whereupon the trunk and toll relay l3-4-3 operates in series with the relay A5 and liglits the supervisory 12111119100 as a ringing signal to the toll operator. RelayG2 disconnects the 'bridge including the relay C2iand A2 from the talking conductors 212 and 205. r

The operator now actuates her ringing key 311K which impresses alternating current upon the talking coiuluctors, to operate the alternating current relay C--L which in attiacting its armature operates the relay This rela' in ZIlQtL'RCtID its arn'iature opens the circuit heretofore traced for holding relay F6 energized; fllclay "0 thereupon releases and in retracting its arn'iature 03? connects ringing current to the selected trunk through the upper winding of relay F-0 and causes'the operation of a signal at the intercepting operators position in the manner previously described. This ringing current is automatically continued until the intercepting operator connects to the trunk over which the call has been received. p

The intercepting operator noting the lighting of lamp 152 inserts the plug 106 into'thejack 107, whereupon the ringing current is tripped and relays 110, 117, 11 1- and 15 i are operated and the bridge including retardation coil 130 and relays 131 and 132 are placed across the cord K in the man ner previously described. A circuit is now closed to operate relays 131 and 132 as follows: grounded battery, through the winding of relayA-d, (which being marginal does not operate) 'b'aek contact and left-hand armature ofrelay D-ie, conductor 122, resistance 4160, lower right-hand winding of repeating coil 106, front contact and lefthand armature of relay A5, arn'iature 532 and front contact of relay D-5, conductor 132 and 131 and coil 130, tips of plug 106 and ack 107, terminal 93, brush (583, upper 1nner contacts of relay H6, upper alternate contacts of relay F6, upper alternate conductor 226, inner left-hand armature and 1 contacts of relay K6, conductor 610, ter- 111111211 5 19, brush 533, upper inner contacts ance 401, conductor 4% and inner righthand normal contact and armature of relay D& to ground. In the circuit traced'the positive side of the battery is connected to the tip conductor ofthe cord circuit "K hence the direction of the current flowing through the winding of the ,polarized relay 132 is in the proper direction to cause this relay'to operate. Relay 131 operated, prevents the operation of relay 112 and the subsequent lighting of'tl e lamp 138 at this time in the manner previously described.

Relay 132, in operating, closes an obvious circuit for relay 135. Relay 135, in operating, locks over a path includinggrounded battery, winding and left-hand contacts of relay 135 and outer right-hand contacts of. relay 110 to ground. Relay 135, in operating, closes a short circuit around the winding of relay 132 thereby reducing the resistance in series with relay A-- 1'to such an extent as to permit the operation of relay A1. Relay A- l, in operating, completes an obvious circuit for relay B'-l'. Belay Bt,in attracting its i'iglit hand armature, applies ground to the conductor 41st to hold relay F6 energized independently of relay Relay Bl, in attracting its lefthand arinatui'es, ClISCODHQCtStlIG battery and ground supplied through the windings oi" relay A 5 to the talking conductors 107 and 4108 leading back to the operators position which causes the deenergization of relay B 13. Relay A. 5 remains operated through itsJVindings in series under the control of relay 13-4. Relay l5-43 in retracting its armature extinguishes the supervisory lamp which notifies the operator that I the intercepting has sponded.

After the completion of conversation heoperator retween the toll operator and the intercepting operator, the intercepting operator may remove plug 106 from jack 107 whereupon relays A4 and 13-4 release. The release of relay B1- again connects battery and ground through the windings of relay A5 to the conductors 407 and 408 causing relay Bet3 to operate and lamp 100 at the toll operators position to light as a disconnect signal. The operator noting this signal may remove plug TT from the jack TSJ. The circuit for relay A5 is thereby opened whereupon said relay A-5 retracts its armatures. Relay A5 in releasing causes the restoration of the selector switch TTS to normal in the manner 'fully described in the aforementioned application. lVhen the toll transmission selector TTS restores to normal, the circuit for relays A6 and B 6 and J6 are opened which results in the closure of the following circuit for the release magnet 686 of the connector circuit: grounded battery, winding of magnet 686, left-hand contacts of the cit-normal switch 620, back contact and lowermost armature of relay D6, and lower armature and back contact of relays B6 and A-6 to ground. Magnets 686 in operating restores the connector switch FC to normal in the manner well known in the art. Connector switch FC upon reaching normal position restores the oii-normal switch 620.

A key 133 is provided at the intercepting operators position to enable the intercepting operator to flash the toll operator. Actuation of key 133 opens the bridge across the cord circuit K whereupon relays A-4c and B l are in turn deenergized. The release of rela B-t 21"2Ll1'1 )laces rela 1 A--5 y as l .3

111 circuit with relay B l3 which operates lighting lamp 100. It will thus be seen that by repeatedly actuating key 133, lamp 100 may be flashed thereby intorn'iing the operator at the toll position that the intercepting operator desires her attention; Con. densers 165, 166 are provided in the cord circuit K to prevent varying the resistance of the high resistance bridge, which would occur due to the shunt formed by the telephone set O, or in case two listeningkeys were operated simultaneously due to the parallel combination which would be formed.

lVhat is claimed is:

1. In a telephone system, a subscribers line, a call charging device associated therewith, an operators position, a signal thereat, a trunk circuit, means including an automatic switch for extending a connection from said line or said operators position to said trunk circuit, a connecting circuit for answering calls incoming over said trunk circuit, and means in said connecting circuit to discriminate between calls over said trunk circuit, said discriminating means serving to prevent operation of said call charging device when a call from said subscribers line is answered and serving to con trol said signal when a call from said operators position is answered.

2. In a telephone system, subscribers lines, call charging devices associated therewith, an operators position, a signal thereat, a trunk circuit, means including an automatic switch for extending a connection from said line or said position to said trunk circuit, means including said automatic switch for extending a connection from one of said subscribe-rs lines to another, means for automatically operating the call charging device of the calling line upon the response oi the called subscriber, a connecting circuit for answering calls over said trunk circuit, means operative when said trunk has been selected by a calling subscriber for preventing the operation of said call charging means, and means operative when said trunk has been selected from said position for causing the operation of said signal.

3. In a telephone exchange system, a subscribers line, a cord circuit, a trunk circuit, a link circuit, switching means for extending a connection from said line or said cord circuit to said trunk circuit, means con nected across the trunk circuit when said trunk circuit is seized for controlling the application of current to the line or the cord circuit, and means eitective upon the connection of the link circuit to thetrunk circuit to operate said second named meansi't the call originatedfat said cord circuit, but ineffective to operate said second'named means if the call originated at said subscribers line.

l. In a telephone exchange system, an operators position. a calling subscribefis line, a second operators position, a cord circuit thereat, a trunk line'extending to said second position, switching means tor cxtending a connection from said sitbscribefls line or said first mentioned operator's position to, said trunk line, current controlling means connected across said trunk line when a connection is extended to said trunk line, and means in said cord circuit effective in response to the connection of the cord circuit with the trunk line to operate the current controlling means it the call is from said first mentioned operators position, but ineffective in response to the connection of the cord circuit with the trunk line to operate the current controlling means it the call is from said subscribers line.

5. In a telephone system, a cord circuit, a subscribers line, a trunk circuit, a connector switch, means including said connector switch for extending a connection from said cord circuit or said subscribers line to said trunk line, a back bridge relayconnected in' circuitwith said trunk line when a connection is extended to said trunk line, an operators link circuit, means in said link circuit operative to operate said back bridge relay if a call originating at said cord circuit is answered, and means in'said link circuit for preventing the actuation of said back bridge relay if a call originating at said subscribers line is answered.

6. In a telephone system, a trunk circuit, a connector switch for extending a subscribers line or a toll operators position to said trunk circuit, a back bridge relay connected across the talking conductors of said trunk circuit when a connection is extended thereto, a cord circuit, a bridge of variable resistance for the cord circuit, means in the cord circuit responsive to the linking of said cord circuit with said trunk circuit for automatically bridging all of said resistance across the cord circuit, means for maintaining the resistance of said bridge unchanged to prevent the actuation of said back-bridge relay it a call originates at said subscribers line, and means serving to automatically reduce the resistance of said bridge across said cord circuit to permit the operation of said back-bridge relay if the call originates at said toll operators position.

7. In a telephone system, a calling line, an operators position, a trunk circuit, means including automatic switches for extending a call from said calling line or said operators position to said trunk circuit, a cord circuit for answering incoming calls over said-trunk circuit, a bridge of either high or low resistance for said cord circuit, and means in said cord circuit for automatically maintaining said bridge across said cor-d circuit at high resistance or for reducing it to a low resistance bridge dependent upon whether the call is from said subscribers line or said ope 'ators position.

8. In a telephone system, a calling line, an operators position, a trunk circuit, means including automatic switches for ex tending a call from said calling line or said operators position to said trunk circuit, a cord circuit for answering incoming calls over said trunk circuit, a bridge of either high or low resistance'for said cord circuit, and a polarized relay in said cord circuit for reducing the resistance of said bridge across said cord circuit from high to low dependent upon Whether the incoming 'call is from said subscribers line or from said operators position.

9. In a telephone system, a subscribefis line, a call charging device associated therewith, an operators position, a signal thereat, a trunk circuit, means including an automatic switch for extending the connection from said line or said operators position to said trunk circuit, a connecting circuit for answering calls incoming over said trunk circuit, means in said connecting circuit to discriminate between calls over said trunk circuit, said discriminating means serving to prevent the operation of said call charging device when a call from said subscribers line is answered, and serving to control said signal when a call from said oper'ators position is answered, a disconnect signal in said connecting circuit, and means responsive to the breaking down of an established connection by the calling subscriber or operator for displaying said disconnect signal.

10. In a telephone exchange system, a subscribers line, a call charging device associated therewith, an operators position, a supervisory signal thereat, a trunk circuit, a trunk signal associated therewith, means including an automatic switch for extending a connection from said line or said operators position to said trunk circuit and for displaying said trunk signal, a'connecting circuit for answering calls, means responsive to the answering of a call incoming over said trunk circuit for restoring said trunk signal, means in said connecting circuit to discriminate between calls over said trunk circuit, said discriminating means serving to prevent the operation of said call charging device when a call from said subscribers line is answered and serving to control said signal when a call from said operators position is answered, a disconnect signal in said connecting circuit, means responsive to the breaking down of an established connec tion by the calling subscriber or operator for displaying said disconnect signal, and means responsive to the extending of a second connection to said trunk circuit for again displaying said trunk signal, irrespective of the relationship then existing between said trunk circuit and said connecting circuit.

In witness whereof, I hereunto subscribe my name this 6th day of February A. D, 1923.

ARTHUR- B. SPERRY.

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