US1337782A - Telephone-exchange system - Google Patents

Description

A. yE. LUNDELL. TELEPHONE ExcHANGE'sYsTEM.,

' APPLICATION FILED MAY I7, 1918. 1 ,337,782. Patented Apr. 20, 1920.

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TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED MAY I?, 191s. 1,337,782. Patented Apr. 20, 1920.

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A. E. LUNDELL. TELEPHONE EXCHANGE SYSTEM.A

APPLICATION FILED MAY1r,1918. E v Patented Apr. 20, 1920.

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TELEPHONE EXCHANGE SYSTEM.

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A. ELLUNDELL. TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED IVIAY I7. I9I8 Apr. 20,

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.ALBEN E. LUNDELL, OF NEW YORK, N. Y., ASSIGNOR TO WESTERN ELECTRIC COMPANY, lNCORPORATED, OF NEW YORK, N. Y., fi CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed May 17, 1918.

To all whom t may concern:

Be it known that I, ALBEN E. LUNDELL, a citizen of the United States, residing at New York, in the county of Bronx, State of New York, have invented certain new and useful improvements in Telephone- Exchange Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to improvements in telephone exchange systems, and more particularly to improvements in telephone systems in which means are provided for indieating the designation or character of calling lines.

l he object of the present invention is to simplify the apparatus and circuit arrangement employed to control the establishment of connections between calling and called lines.

To attain this object, according to this invention, the switching means by which telephonie connections are established is controlled in its operation by a switch operated in accordance with the character or designation of the calling line. This switch isv preferably of the well-lrnown sequence switch type, although circuit controlling devices of a widely varying character may be employed without kdeparting from the spirit of the invention. Depending on the character or designation of the calling line, a certain predetermined number of impulses are sent to an impulse receiving device, such as a set of counting relays. The impulse receiving device operates the switch in a manner characteristic for the line calling. rThe various operations of the switch will determine the manner in which the calling line should be charged for the service. ln view of the fact that this same switch is utilized for controlling the interconnection of the calling and called lines, controlling devices, such as relays, that were heretofore used for this purpose will be saved.

Obviously, instead of the specific apparatus and circuits disclosed, other devices well xncwn in the art may be employed in practising this invention. The invention is applicable also to semi-automatic telephone systems in which switching means, dilfering from those (calling plug and sequence switch) exemplified in the herein disclosed embodiments of the invention, are used.

Specification-of Letters Patent.

Patented Apr. 20, 1920.

sensi No. 235,090.

vThe various features of the invention will more clearly appear from the following description of the preferred embodiment of this invention, and the appended claims.

Figure 1 illustrates three telephone lines with their central oliice terminal connections and identifying circuits; Fig. 2 illustrates a line linder and cord finder circuit for extending a calling line, Figs. 3, 4 and 5 illustrate a cord circuit terminating in a plug, a called line terminating in a spring jaclr into which the plug may be inserted, and a part of the operators circuit; Fig. 6 illustrates the part of the operators circuit that has to do with determining the identity of a calling line with respect to its class of service; and Figs. 7, 8, 9 and 10 show details of the common identifying device or commutator and its connections.

ln the particular embodiment of the invention illustrated in the accompanying drawings, l have shown three lines adapted for different classes of service extending from their respective stations 100, 101 and 102 to switch terminals at the central ollice. 100 may be assumed to be a private branch exchange message-rate station, 101 a party line coin-collector station, and 102 an individual 'dat rate station. The character and arrangement of apparatus at such stations is well lrnown, and l have not thought it necessary to illustrate it specifically. Cutofxc relays 103, 104, 105 and line relays 106, 10.7, 108 are associated with the three lines in the usual way. The line from station 100 being a message rate line, also has associated with it at the central oliic'e a message register 209.

Fach of the lines has four conductors, two being the ordinary line conductors, and the other two, 110 and 111, being conductors local to the exchange. The local conductor 110 of each line has included in it a winding of the associated cutoff relay, while the conductor 111 in each case extends to the common identifying device or apparatus for producing the characteristic electrical conditions which serve to identify the varicus lines. This device is represented` diagrammatically at 112 in the drawing, and is illustrated as comprising nine paths ex tending from the free pole of the central battery to nine terminals which are common to the lines of the exchange, and to one or another of which the conductor 11] its three current impulses.

of each line circuit is extended, depending upon its class of service. l shall hereinafter particularly describe the type of identifying` apparatus which l have found it convenient to employ. For the present, it is sufficient to say that this apparatus is arranged continuouslyV to modify current that may flow in each of the paths so as io produce trains of impulses, the impulses of each train being divided into groups and Ysubgroups and the number of impulses in each group and subgroup being varied so as to produce different and characteristic combinations. The duration of the groups and subgroups in each train is determined and limited by pick-up impulses. Each of the subgroups consists of one or more impulses of current, as determined by the action of circuit changing contacts in the va rious paths. A single interruption in one of the subgroup periods divides the current flow-in that period into two impulses, and two interruptions in the subgroup period divides the current flow in that period into To meet the requirements of. the present embodiment of my invention, 1 have found it only necessary to provide a maximum of three impulses in each subgroup period, the various combinations of one, two or three impulses in each subgroup of a group affording nine different characteristic combinations of current impulses-` As diagrammatically illustrated at 112 in the drawing, path 1 has one impulse in each subgroup period; path 2 has two impulses in the first period and one in the second period; path 8 has three impulses in the first period and one in the second; path 1i has one impulse in the first and two in the second; path 5 has two in the first and two in the second; path 6 has three in the first and two in the second; path 7 has one the first and three in the second; path S has two in the first and three in the second; and path 9 has three in the iirst period and 'three in the second. The marks X placed upon the nine conductor paths indicate interruptions, and the broken lines extending transversely of the paths indicate the division of the resulting impulses into groups and subgroups by the piclcnp impulses. rilhc classification which l have found it desirable to provide for in this embodiment of my invention is a division of the lines into three classes with respect to the character of the line', Vand into three classes with respect to the nature of the charge that is made for the use of the line. rlhe lines are thus classified as indivifglual, party line and. private branch exchange or l). lines, and the classification of the 'lines with respect to the charge divides them into fiat rate, message rate and coin collector lines. There are nine possible combinations in this classification, for each of which ccmbination there is Va path through the identifying device which provides a characteristie identification for that class of line and service. Thus path 1 may have branches to and identify all the individual flat rate lines; path 2 in like manner may identify all of the party flat rate lines; path 3 may identify the private branch exchange flat rate lines; path il, the individual message rate lines; path 5, the party message rate lines; path 6, the private branch exchange message rate lines; path 7, the individual coin collector lines; and path 8, the party coin collector lines. private branch exchange coincollector lines, if there were any such; but as it is not the practice to provide this class of service, path 9 is spare, in the present embodiment, and may be used for identifying some other class of service, if desired.

0f course7 it will be understood that the scheme of identification outlined above is purely arbitrary and may be altered as desired to identify any other classes of service that may be provided. lt will also be understood that by merely increasing the number of subgroups, or the number of impulses in each subgroup, or both, identification may be furnished for as many classes of service or as many line characteristics as may be desired.

When any line calls, it is extended, as shown in the present embodiment, by means of a line finder switch 200 and a cord nder switch 201 to a connecting cord circuit which terminates in a connecting plug 400 that is adapted t0 be inserted by the operator into any spring jack 401 in order to complete the connection between the calling and the called telephone lines. Then the cordfinder switch 201 finos thepconnecting cord circuit that is to be used in completing the connection, the calling line is automatically extended by way of the connecting cord circuit to the telephone set and controlling switches of the operator at whose position the selected connecting cord circuit is located.

Ainong the conductors of the connecting cord circuit that are extended to the associated operators circuits when the connecting cord is selected, there are five, 500, 111, 502, 503 and 50at which are particularly concerned with the operation of the apparatus that has to do with the identification of the line with respect to its class of service. .fill conductors lead to the classot-service indicating device with which the operator is provided, conductor 502 being the wire over which the class-of-service indicating device starts a sequence switch 505, conductor 111 being the identifying wire of the line that is calling, conductor 500 being Y the wire over which the class-of-service re- Path 9 would identify O 'sponsive apparatus is brought into or out of action as the operators circuits are connected with or disconnected from the connecting cord circuit, conductors 503 and 504 being the `Wires through 'which the class-ofservice responsive device exercises control over the sort of current that is applied to the calling line by means of the operators charge key. rlhe sequence switch 505 is individualto an operators cord circuit and controls inits contacts the operation of a sequence switch 102, and the relays associated With the operators cord circuit for effecting the operations required for the class or the particular line calling.

IThe class-of-service responsive device to which the conductors 500. 502, 503, 50e and 111 lead, comprises in the present instance, six lamps arranged in two groups of three lain is each, and groups of relays for controlling the illumination of these lamps and for controlling the electrical condition of the two conductors 503 and 504; which have to do With the control of the operators charge circuit. Before describing the circuits in detail, l shall outline briefly the manner in which the identifying device and the class-ofservice responsive device coperate to identify the extended line with respect to its class of service.

rlie extension of a calling line to a connecting cord, and thus to the associated operator, operates a relay 600, associated with the class-of-service responsive mechanism, which relay in its operation makes this mechanism responsive to subsequent identifying impulses. rlie identifying device continuously operates switch contacts which produce pick-up impulses, these impulses being of two sorts and having a denite, time relation to the identifying impulses produced by the device. iclr-up in pulse No. 1 is transmitted at the beginning of each cycle or train of identifying impulses, and pick-up impulse No. 2 is produced in the middle of each cycle to divide the group determined by consecutive piclup impulses No. 1 into subgroups. For convenience and clearness in illustration, the coinniutator parts of the identifying device which produce the pick-up impulses are diagrammatically shown at 635 and 636 in 6 in connection with the class-of-service respcnsive mechanism at the operators position.

ln outline, the operation subsequent to the energization of the relay 600 is as follows: The first pick-up impulse No. 1 operates the relay 601 and extends the identifying conductor 111 to the relay 602. rJ'he termination of pick-up No. 1 impulse permits the relay 603 to operate, this relay acting to s f'itch pick-up No. 1 circuit to relay 604, and pick-up No. 2 circuit to relay 605. The impulse of identifying current Which flows by Way of conductor 111 as soon as relay 601 operates, operates relay 602, and this relay in turn causes the operation of relay 606. The first interruption in the identifying conductor 111, assuming that a second impulse is transmitted in the first subgroup period, causes the denergization of relay 602 and the energization of relay 607, relay 606 remaining energized. Vhen the circuit of the conductor 111 is again closed in this same subgroup period, relay 602 operates and brings about the operation of relay 608, and the subsequent interruption of the circuit leaves 608 up and operates 609 also, 609 in its operation denergizing 606 and 607. lf there is still another closure of the identifying conductor 111 in the first subgroup period, relay 602 is again operated, thus operating the relay 610, and upon the subsequent termination of the impulse, relay 611 is operated, and relay 610 remains up, relay 611 in its operation denergizing relays 606 and 609. Thus, depending upon the number of impulses of current produced during the irst subgroup period, relays 606 and 606, relays 608 and 609, or relays 610 and 611 of the group of impulse counting relays are left up, their locking circuit being by Way of a conductor which is closed as long as relay 600 remains operated. Relay 606 of the first pair controls the circuit of lamp 612, Which in the particular system of identification shown, is the individual line lamp; relay 608 of the second pair controls the circuit of lamp 613, Which is the party line lamp; and relay 610 of the third pair controls lamp 614, which is the private branch exchange line lamp.

rlhe first subgroup period is terminated by the production of pick-up impulse N 2. Relay 603 having remained operated, this impulse causes the operation of relay 605, which relay, in turn, causes the operation of relay 615. Relay 605 opens the path of pick-up impulse No. 2 and locks itself up, subject to the control of relay 600; While relay 615 completes the circuit of the particular lamp 612, 613 or 614, Which has been selected in the first subgroup period, and also gives relay 602 control over the group of counting relays 616, 617, 61S, 619, 620 and 621.l The impulses which are produced during the second subgroup period bring about the operation of the second group of counting relays 616, 617, 618, 610, 620 and 621, in the same Way as described in connection with the operation of the first group of counting relays 606, 607, 606, 609, 610 and 611; that is, the first impulse causes the first pair of relays 616 and 617 to be left operated; the second impulse leaves the second pair of relays 618 and 61) operated; and the third impulse leaves the third pair of relays 620 and 621 operated, the locking circuit for Whichever pair is left operated being controlled in contacts of ren lay 600. Relay 616 of the first pair in the second group controls the circuit of lamp 622; relay 613 o f the second pair controls the circuit of lamp 623; and relay 620 of the third pair controls the circuit of the lamp 624. In the particular embodiment of my invention described, the lamp 622 is used as the flat rate lamp, lamp 623 as the message rate lamp, and lamp 624 as the coin collector lamp.

The termination ofthe second subgroup, and, therefore, the termination of the cycle with respect to the train of identifying im pulses, is brought about by the :production of another pick-up impulse No. 1. Inasmuch as relay 603 has remained energized, having a locking circuit by way of relay 600, the second pick-up impulse No. 1 flows through relay 604, and the resultant operation of that relay opens the circuit of conductor 111 through relay 602, thus removing the class-of-service responsive mechanism from further control by the class-ofservice identifying device over conductor 111. Relay 604, in operating, also closes a holding circuit for itself under the control of relay 600, and completes a circuit which causes the lighting of the particular lamp 622, 623er 624, which has been selected, by the impulses during the second rsubgroup period. In its outer armature the relay 604 controls the movement of sequence switch 505 out of position 1 and into position 3. Thus, the operation of the relay 600 causes the operators class-of-service apparatus to be responsive to the identifying device during one cycle of its operation, during which cycle one of the lamps of the three in each group is lighted to apprise the operator of the class of service of the calling line. As long as relay 600 remains operated, the associated responsive mechanism is maintained in its operated condition, and the lamps that have been selected are kept lighted. 1When the relay 600 is denergized, the responsive mechanism is restored to its normal condition, in readiness to register another indication whenever the relay 600 is again operated.

Associated with relays 618 and 620 of the second and third pairs, respectively, of the second group of relays, are two relays 625 and 626. These two relays control, through the medium of the conductors 503 and 504, the circuits that are completed by means of the operators charge key. lVhenever relay -618 is operated, relay 625 is also operated to close the circuit of conductor 503, and moves the sequence switch 505 out of position 3 and into position 5. Upon the actuation of a calling supervisory relay 403, this sequence switch is moved into position 6 and connects battery through a low resistance relay 508, a branch of a conductor 509 through which the operator applies current to the third or sleeve conductor 110 of the line for the Operation of the message register 209 of the line andthe position register 510 of the operators equipment. Vhenever relay 620 is operated, it causes the actuation of relay 626 which closes the circuit of conductor 504 to move the sequence switch 505 into position 7. Upon the energization of relay 403, the sequence switch is moved into position 8 and connects a high voltage current generator 511 to conductor y512 to supply coin collecting current to the calling line, in case it be a line with a coin box, when the Operator operates her charge key 405. i

A type of device which may be employed for producing the identifying and piclcup impulses that serve to identify the various classes of lines is illustrated in Figs. 7, 8, 9 and 10. This device, in the form particularly illustrated, consists of ten cam-operated switches 627, 628, 629, 630, 631, 632, 633, 634, 635 and 636, each switch having an associated cam for operating it, the ten associated cams being mounted upon a common shaft 637, which shaft is constantly driven by a suitable source of power. The shaft and associated cams may be driven to rotate at a rate of, say, 120 revolutions per minute. Switches 627 to 634 inclusive are normally closed, and are Operated by their associated cams to be opened momentarily once in each revolution. Switches 635 and 636 are normally opened, and are arranged to be closed once'in each revolution. The cams are cut away to produce the operation of their associated switches at any one of sixpoints sixty degrees apart in the rotational cycle. These points or positions are indicated by the Roman numerals I, II, III, IV, V, VI. The cams associated with switch springs 635 and 636 are cut away to produce the momentary closure of the switch contacts at positions I and IV, respectively, in the cycle of rotation of the cam shaft. These switch springs are those which deter mine the pick-up impulses, switch 636 con-A trolling pick-up impulse No. 1 and switch 635 controlling pick-up impulse No. 2. The cams associated with switch springs 628, 630 and 633 are cut away at position II of the cycle; the cams associated with switch springs 627, 629 and 634 are cut away at position III of the cycle; the cam associatedwith the switch631 is cut away at position V of the cycle; and the cam associated with switch 632 is cut away at position VI of the cycle. Thus the complete rotation of Y the cam shaft with its cams involves the momentary closure of pick-up No. 2 switch 635 at position IV, the momentary. openingof switch 631 at position V and the momentary opening of switch 632 at position VI.

The eight switches 627 yto 634 inclusive GII Cre

are connected in dilierent combinations in the identifying paths 2 to 9 inclusive. Path 2 includes the contacts of switch 628; path 3 includes the contacts oil switches 628 and 627; path Ll includes switch 631; path 5 includes switches 631 and 63o; path 6 includes switches 631; 630 and 629; path 7 includes switches 631 and 632; path 8 includes switches'631; 632 and 633; and path 9 includes switches 631; 632; 633 and 63e. Path 1 is adapted to remain closed in positions Il; 111; V and Vl; and; therefore; does not include any of the switches that are operated in these positions.

The result of the above described arrangement of cani switches in the conducting paths of the identifying device is that these paths have produced in them the distinctive combinations of interruptions illustrated diagrainmatically at 112 in Fig. 1 of the drawing; the impulses produced by the interruptions being divided through the medium of the pick-up impulses Nos. 1 and 2 into groups and subgroups. The various identifying device paths; thus adapted to produce trains or impulses divided into distinctive groups and subgroups; terminate upon connectors :troni which connection may be made with the fourth or identifying conductor 111 of any line that it may be desired to identify; the connector to which the identifying conductor ot the line is led depending upon the classiiication oi the line with respect to whether it is an individual line; a party line or a private branch eX- change line; and whether it has a flat rate or a message rate; or is equipped with a coin bo-X or collector.

Inasmuch as the present invention is not particularly concerned with the character o'j the circuits over which the calling line is extended to the operators position; and over which the calling line is extended to the called line after the operator has obtained such identification of the calling line and such intorrnation concerning the called line as may be necessary tor her purpose; these intermediate circuits and apparatus will he described only to the extent that they are involved in the operation which has particularly to do with the disclosure orp the invention. rllhe organization chosen tor the purpose of showing a specific embodiment of the invention is one which utilizes automatic nder switches for finding a calling line and Jfor extending the calling line to a connecting cord circuit that is at the time idle and available; and which utilises a plug terminal for the connecting cord circuit; which plug terminal is inserted by the operator into the spring-jack of the wanted line. Such systems; with their automatic iinder switches; sequence switches and control circuits; are well known; and this specification need not he burdened with a particular detailed description ot such a system. An example of such a system is shown in the patent to lllilliams; No. 1;30-l; 641; issued May 27; 1919.

ln the operation of the particular embodiment ci the invention illustrated; when one of the lines calls; the associated line relay 106; 107 or 108; as the case may he; is energized; and in closing its contacts closes a circuit which iserl ctive; through intermediate circuits and apparatus that need not here be particularly describen; in permitting current to liow; by way of conductor 202; through one winding oi a relay 203 associated with the line and cord finder circuit. This relay closes its Contact 20e and coiniletes a circuit by way of contacts 205l and 207 of a sequence switch 208 to cause the line finder switch 200 to connect with the terminals et the calling line. rifhe sequence switch 208 is adapted to rest in positions 1; 2; 3; 4; 6; 7; 8; 9; 11i; 15; 16 and 17. @i these positions; the following are oi interest in connection with this description:

Position 1-Normal- Position 2-Awaiting starting circuit.

Position %llunting calling line.

Position 9Hunting cord circuit.

Position 1li-Talking.

It is not necessary to show the connection of `the circuit last traced with the motor magnet ot the line iinder switch; nor th path over which the finding of the calling 'line results in the sequence switch 208 being advanced through the intermediate stages until it reaches position 9; which is the position in which the connecting cord circuit hunted. The circuits for accomplishing this are well known in the art.

When the brush 211 et the line linder 200 comes into engagement wth the corresponding terminal of the calli line; a circuit is completed that includes battery; resistance 213; sequence switch contact 21d; hrush 211 and its cooperating line contact; and the cutoff relay 103; 104- or 105 of the ca ling line. rllhis energizes the cuto'iil rela-y and causes it to disconnect the associated line branch Atroni the line.

lil-.Then the sequence switch nieves into position 9; the motor magnet of the cord iinding switch 201 is made active; over circuits which need not be described; to cause the brushes 215; 216; 217 and 218 of the cord linder switch to engage corresponding contact terminals ot an idle connecting cord. lWhen the idle connecting cord is found; the sequence switch 208 is moved; by the closure oi' circuits that it is unnecessary to describe; into position 1e; which is the talking position. ln this position or" the sequence switch the two talking conductors 219 and 220 of the finder circuit are connected through from brushes 209 and 210 oi' the line linder switch to brushes 215 and 216 of the cord finder switch, by way of contacts 221 and 222 of the sequence switch, which contacts are closed in position 14. The third cone ductor 110 of the circuit is closed, in this position, from brush 211 of the line iinder switch to brush 217 of the cord finder switch by way of contact 214 of the sequence switch, one or' the windings of relay 203 and contact 225 of the sequence switch. rPhe fourth or identifying conductor 111 is closed from brush 212 of the line finder switch to brush 218 of the cord finder switch by way of contact 207 of the sequence switch, contact 204 of relay 203 and contact 205 oi the f sequence switch.

lt will be noted that the motor magnet of the sequence switch, while the switch is resting in the talking position 14, is under the control of contact 228 of the relay by way of contact 229 of the sequence switch closed in position 14; so that in the talking position relay 203 acts as a holding relay the denergization of which causes the sequence switch to move to its neXt position.

The circuits of the connecting cord are governed by a sequence switch 402 which has live resting positions, as determined by a master contact 406, these resting positions being as follows:

Position l-Normal.

Position 7-Listening-in.

Position 10-Ringing.

Position 15-Talking and listening-out.

Position 18-Release.

When the cord circuit is connected with by the cord finder switch 201, the sequence switch 402 is in its normal or No. 1 position. The engaging of brush 218 of the cord finder switch with the corresponding contact of the idle cord circuit, advanced the sequence switch 208 of the iinder circuit from its No.9

- or hunting position to its No. 14 or talking position by well-known circuits which need not be particularly illustrated or described and as soon as sequence switch 208 leaves its No. 9 position, it completes a circuit which may be traced from ground through resistance coil 230, the right-hand contacts of sequence switch cam 225, brush 217 and its corresponding cord circuit contact, conductor 110, resting contact 407 of the charge key 405, conductor 408, the upper contact of sequence switch cam 514, conductor 515 and the winding of relay 409 to grounded battery. The relay 409 becomes energized and closes acircuit from grounded battery through the primary winding of a repeating co'il 410, the winding` of an answering supervisory relay 411, the upper right-hand and lower lefthand contact of sequence switch cam 413, the left-hand armature and front contact of relay 409, sequence switch cam 414, conductor 415, the winding of relay 300, conductor 301, the upper contact of sequence switch cam 416, the right-hand armature and front igss'mse contact of relay 409, the left-hand contacts of sequence switch cam 417, conductor 219 and the primary winding of the repeating coil 410 to ground. The relays 300 and 411 become energized and cause the connection of the operators telephone set 302 to the talking conductors 219 and 220. The relay 411 closes a circuit from ground through its armature and front contact, conductorl 517, the lower contact of sequence switch cam 518, conductor 519, the lower contact of sequence switch cam 419, and the power magnet of sequence switch 402 to grounded battery, for moving the sequence switch 402 out of position 1 and into position 7. Thus immediately upon the seizure of an idle cord, the operator may converse with the calling part While the sequence switch 402 is passing through position 1% and until it moves out of position 8, a constantly rotating interrupter 424 is connected through the righthand back contact and armature of relay 425, the upper contact of sequence switch cam 420, conductor 520, a lamp 521, and a 90 resistance 522 to grounded battery, causing the flashing of lamp 521 which indicates to the operator that a call is awaiting attention at her position. Vhile the sequence switch 402 is moving from position 2 to position 6, ground is connected, through the left-hand contacts of cam 430 and conductor 312 to the lower left-hand contacts of all the cams 419, the controlling sequence switches of which are in position 7. Vhen the sequence switch moves out of position 5, the above traced circuit for relays 411 and 300 is opened. These relays, however, are maintained energized and talking battery is supplied to the operators and subscribers telephone sets from grounded battery through the primary winding of repeating coil 410, winding of relay 411, the conductor 220, the upper contacts of sequence switch cam 413, conductor 308, the inner front contact, armature and the winding of relay 300, conductor 301, the upper contacts or' sequence switch cam 417, conductor 219, and the primary winding of the repeating coil 410 to ground. This circuit is maintained 115 closed until the sequence switch 402 moves out of position 8. Vhen the sequence switch 402 reaches position 6 and until it moves cut of position 8, the above traced path including contact of relay 409 and leading to the 120 operators telephone set, is substituted by a path including the normal contacts of keys 303, 304 and 305, conductors 306 and 307 and sequence switch cam 420 and 421 for maintaining the connection between the op- 125 erators telephone set and the talking conductors 219 and 220.

The movementv of the sequence switch 402 into position 7 brings J:he operatcrs receiving mechanism into association with the cir- 130 cuit. This is accomplished by the closure of a path from ground through sequence switch cam 427, conductor 500 and the winding ci relay 600 to grounded battery, and the connection of conductor 111 through the lefthand contacts of cam428 to the armature of relay 601. ln response to the operation of relay 600 the class-of-service indicating apparatus is automatically caused to operate and thus the operator is apprised of the characteristics ofthe calling line with which the apparatus has just connected her. In response to the operation of relay 600, a path is closed over which the next pick-up No. 1 impulse may operate the relay 601.

rlhis path is as follows: Ground, commutator switch 636, contact 638, back contact 639 of relay 603, and the winding of relay 601 to battery. When the first pick-up No. 1 impulse flows, after relay 600 is operated, relay 601 operates and closes a lccking circuit for itself through its contact 640. When the contact 640 closes, a path is completed for the flow of current through the winding of relay 603 to ground, by way of contact 641 of relay 600. As long as the pick-up No. 1 impulse persists, no current fiows through the winding of relay 603, because this path is short-circuited by the direct path from the winding of relay 601 to ground by way of the pick-up commutator 636. But the termination of the piel;- up No. 1 impulse and the opening of the direct path to ground at 636, permit the current through the winding of relay 601 to be diverted into the path including the winding oi' relay 603 and contact 641 of relay 600. rlhus, upon the termination of the first piclo up No. 1 impulse, relay 603 is operated, and thereafter relays 601 and 603 remain locked up as long as contact 641 of relay 600 remains closed. The opening of the back and closing of the front contact of relay 603 transfers the path through the pick-up No. 1 comi'nutator 636 from relay 601 to the winding of relay 604 by way of normally closed Contact 642 of the last mentioned relay. The closing of contact 643 of relay 603 connects the commutator switch 635 of pick-up No. 2 with the winding of relay 605 by way of normally closed contacts 644 of that relay. Relay 603 thus operates to make ready the paths over which the pick-up No. 2 impulse and the second pick-up No. 1 impulse subsequently operate to control the operation of the indicating device. Y

The actions described in the foregoing are those which follow immediately upon the extension of the calling line to the operators circuit and the receipt of the first impulse from pick-up No. 1. The indicating apparatus is now in condition to receive the impulses of the first subgroup. The iirst impulse over conductor 111 after the operation of relay 601 flows by way of contact 645 of relay 601, through the winding of relay 602, and through the back contact and armature of relay 604 to ground. This impulse causes relay 602 to complete a circuit from battery through the winding of relay 606, the back contacts and armatures of relays 607, 611, 609, 607 and 615 and front contacts of relay 602 to ground. Relay 606, in operating, closes a locking path for itself to ground by way of the winding of relay 607 resting contact 646 of relay 609, and contact 641 of relay 600. The previously traced path from the winding of relay 606 to ground closes in the front Contact of relay 602, short-circuits the path last traced; but at the interruption in the flow of current which marks the end of the rst impulse, relay 602 becomes denergized, thus breaking the short-circuit pathv about relay 607 and causing that relay to operate. Thereafter relays 606 and 607 constituting the first pair of the selected relays, are held operated, subject to the control of the resting contact 646 of relay 609, and the contact 641 of relay 600. Relay 606 in its operated position closes a path for the flow of current to the irst lamp 612 of the first group of three lamps, subject to the control of normally-open contact 647 of relay 615, which contacts are closed at a later stage of the operation by the passage of the pick-up No. 2 impulse, as will hereinafter be described.

Relay 607, in operating, switches the circuit controlled by relay 602 from the winding of relay 606 to the winding of relay 608. Therefore, the second impulse of current that flows over conductor 111 in the first subgroup period and operates relay 602, closes a path for the energization of relay 608 that may be traced from battery through the winding of relay 608, front contact of relay 607, back contact of relay 615, and front contact of relay 602 to ground. The flow of current over this path operates relay 608, which relay closes a locking circuit for itsel.c by way of its front contact, the winding of relay 609, resting contact of relay 611 ard contact 541 of relay 600 to ground. flurrent is diverted from the path last traced by the short-circuit path completed by way of the back contact of relay 615 and the contact of relay 602. Upon the termination of the impulse this short-circuit path is interrupted and relay 609 is operated. Thereafter relays 608 and 609 are both held up, subject to the control of the back contact of relay 611 and contact 641 of rel/y 600. Relay 608, in operating, closes in its contact a path for the subsequent flow of current through the second lamp 613 of the first group, under thelcontrol of contact 647 of relay 615, which is closed at a later stage of the operation. Relay 609, in operating, breaks the locking circuit for the previously operated pair' of relays 606 and 607 and permits those relays to fall back. The falling back of relay 606 opens the circuit of lamp 612, so that that lamp will not be lighted when contact 647 of relay 615 is subsequently closed; and relay 607 in falling back disconnects relay 608 from the controlling circuit and connects in its place relay 610 by Way of the back contact of relay 607 and front contact of relay 609, which is one relay of the pair that is now energized.

The above described operation places relay 610 of the third pair in position to be energized by the closure of the front contacts of relay 602 resulting from a third impulse of current over the conductor 111. lVhen relay 602 closes its contacts upon receipt of the third impulse, a path, like that previously traced for the operation of relay 606 and 608, is closed for relay 610 of the third pair; and relay 610 closes a locking circuit for itself through the Winding of relay 611 and contact 641 of relay 600. Relay 611 is short-circuitcd and prevented from operating as long as the shortcircuiting path by vWay of Contact 647 of relay 615 and the contact of relay 602 is closed, in the manner previously described, and is operated as soon as the shortcircuiting path is broken. Relay 610 in operating closes a path for the flow of current through the third lamp 614 of the first group, subject to the closure of the contact 647 of relay 615; and relay 611 in operating opens the locking circuit for the previously operated pair of relays 608 and 609, and permits these relays to fall back and open the path prepared for the low of current through the second lamp 613.

The first subgroup period is terminated by the production 'of pick-up No. 2 impulse by the momentary closure of contacts 635 of the commutator. It Will be remembered that relay 603 had previously been locked up to prep are a path for the flow of the pick-up No. 2 impulse by way of the winding of relay 605. Upon the passage of the pick-up No. 2 impulse, relay 605 operates, closes a locking circuit for itself by Way of its make contacts 644, subject to the control of contact 641 of relay 600, and also closes a circuit for relay 615. Relay 615, in operating, disconnects the circuit controlled by the contact of relay 602 from the path leading to the relays 606, 607, 608, 609, 610 and 611 of the first group, and connects it to the path which leads to the relays 616, 617, 618, 619, 620 and 621 of the second group. 1t also closes the `circuit for the floW of current over Whichever of the lamps 612, 613 or 614 of the iirst group has its circuit left closed in the contacts of the associated relay 606, 608 or 610. 4 c

Assuming that three impulses of current are caused to pass tothe second group of relays by Way of the path controlled in the front contact 648 of relay 615, the selective operation of these relays by the successive impulses is the same as has been described in detail for the first group of relays, and needs no further description. The only point which needs to be noted in connection with the action in the second group of relays, as distinguished from the action in the iirst group, is that relays 618 and 620 operating do not prepare directly the circuits for the subsequent illumination of their associated lamps 623 and 624, respectively, but close the circuits of these lamps through the medium of the relays 625 and 626, which are operated When their associated relays 618 and 620, respectively, are operated, and which relays 625 and 626 also control circuits governing the operation of message rate and coin collector apparatus, which circuits will be traced hereinafter.

rPhe second subgroup period and the cycle are terminated by the production of a second pick-up No. 1 impulse in switch contacts 636 of the commutator. This impulse flows by Way of contact 638 of relay 600, front contact 649 of relay 603, resting contact 642 of relay 604, and through the Winding of the last mentioned relay. Relay 604 is thus operated, closes a locking circuit for itself, and completes a path for the illumination of Whichever lamp 622, 623 or 624 of the second group is held in circuit by the energiza-V tion of its associated relay 616, 618er 620. Relay 604, in operating, also in opening its back contact, opens the path for the flow of current through relay 602, so that that relay thereafter is unresponsive to the opening and closing of the identifying circuit associated with the calling line. The completion of the cycle or group period of the identifying device thus leaves the circuit of the identifying conductor 111 open in the back contact 650 of relay 604, the path of pick-up No. 1 impulse open in contacts 642 ofA relay 604, the path of 'pick-up No. 2 impulse open in contacts 644 of relay 605, and relays 601, 603, 604, 605 and 615 locked up subject to the control of contact 641 of relay 600. 1f it be assumed that there were three impulses in each subgroup period, it also leaves relays 610 and 611 of the first group and relays 620 and 621 of the second group locked up over the locking circuit controlled in contact 641 of relay 600, and the associated lamps 614 and 624 burning. 1t also, under the same assumption, leaves relay 626 held operated by the energization of relay 620, and the coin collector controlling path 504 closed to ground by Way of the front contact of relay 604. This condition persists and lamps 614 and 624 continue burning as long as relay 600 remains energized. W'hen that relay is denergized the various locking circuits referred to are opened and the apparatus is restored to its normal position.

The actions described above were under the assumption that each of the two sets of counting relays received three impulses in its respective subgroup period. l shall now describe briefly the action that would take place if only one or two impulses were received in a subgroup period. In such a case, the flow of current through identifying conductor 111, following the passage of the first pick-up No. 1 impulse acts, through the medium of the relay 602, to close the energizing circuit of the relay 606. But, assuming that there is but a single impulse in the first subgroup period, this. flow of current continues and the front Contact of relay 602 is held closed throughout the whole of the first subgroup period, and while this condition continues relay 607 is short-circuited and cannot pull up. The passage of the pick-up No. 2 impulse at the end of the first subgroup period actuates relays 605 and 615 as previously described, and relay 615, in operating, removes the short circuit from relay 607, and terminates the first subgroup period with relays 606 and 607 locked up and lamp 612 lighted. If there are assumed to be two impulses in the first subgroup period, the opening of the contact of relay 602 marking the end of the first impulse removes the short circuit from relay 607 and permits it to operate; and relay 607, in operating, prepares the path for the energization of relay 608 by the second impulse.

.Relay 609 of the second pair is kept shortcircuited, as already described, during the passage of the second impulse; but the short circuit is removed and relay 609 operates when pick-up No. 2 impulse operates relay 615 to open its resting contact at the end of the first subgroup period. In operating, relay 609 opens the locking circuit of the first pair of relays 606 and 607, so that two impulses during the first subgroup period leave the second pair of relays 603 and 609 locked up and their associated lamp 613 illuminated, and the other two pairs of relays denergized and their associated lamps dark.

The actions in the second group of counting relays, which follow the receipt of only one or two impulses in the second subgroup period, are exactly the same as the actions described above as taking place in the relays of the first group. The result is that the lamp which is left lighted in each of the two groups corresponds with the number of impulses which are received vduring that subgroup period, the operator being informed by the particular lamp lighted in the first group whether the calling line is an individual line, a party line or a private branch exchange line, and by the particular lamp lighted in the second group whether the line receives flat rate, message rate or coin collector service. Thus, when the operators set 302 is automatically connected with the cord circuit to which the calling line is emended and the relay 600 is operated, the class-of-service indicating apparatus is made operative to cause the calling line to indicate to the operator, by means of the particular lamps lighted, the class of service for which the calling line is adapted. Thus informed, the operator is enabled to write such tickets or memoranda or give such service as her instructions require for this sort of line.

Upon the energization of relay 604, a circuit is closed from ground through the right-hand outer armature and front contact of relay 604, conductor 502, contact 528 and the power magnet of sequence switch 505 to grounded battery. The sequence switch 505 is moved out of position 1 under the control of its master contact 529 into position 3. When the sequence switch 505 leaves position 2g, the above traced energizing circuit for relay 409 is opened in the upper contact of sequence switch cam 514, but this relay is maintained energized by current flowing from grounded battery through its winding, conductor 515, sequence switch cam 530, conductor 531, the upper contact of sequence switch cam 453, conductor 464, resistance 462, the upper contact of sequence switch cam 455, and the lower back Contact and armature of relay 441 to ground.

In position 3 of sequence switch 505 and position 7 of sequence switch 402, the setting of sequence switch 505 is determined by the class-of-service indicator. Depending on the setting of the sequence switch 505, the calling line will or will not be charged for the call. The controlling positions of this sequence switch are as follows:

Position l-Normal.

Position 3-Flat-rate ringing.

Position i-Flat-rate talking.

Position -Message flat-rate ringing. Position G-Message flat-rate talking. Position 7-Coin collect ringing. Position S-Coin collect talking. Position Q-Free call ringing. Position 10-Free call talking.

lf neither the relay 625 nor the relay 626 is energized, then the sequence switch 505 remains in position 3.

lf the relay 625 is energized, then a circuit is closed from ground through the lefthand armature and front contact of relay 604, the left-hand front contact and armature of relay 625, conductor 503, the lefthand contact of cam 543, conductor 544, sequence switch cain 431, conductor 545, and the power magnet of sequence switch h 505 to grounded battery.V Under thereonvground through its lower trol of this circuit, the sequence switch is driven out oit position 3 and through position 4 into position 5.

lf relay 626 was energized, instead ot the position 5 or position 'i' and the called lineV is a free call line, z'. e. one to which calls may be extended free 01"' charge, the operator depresses key 546. rEhe relay 54.7 becoines energized and locks up througl'i conductor 548 and sequence switch cani 429. il circuit is then closed from ground through the lett-hand liront contact and armature ot relay 547, the upper contact of cam 543. conductor 544, earn 43l, conductor 545.r and the power magnet of sequence switch 505 to grounded battery. The sequence switch 505 moves out ot position 5 or 7 into position 1When the operator inserts the plug4 400 into the multiple jack 40l olf the called line, a. circuity is closed from grounded, battery, through the winding of' relay 41 i, the sleeve contacts ot plug 400 and jack 401, and the winding ot the called lines cutoff relay 400 to ground.

The relay 44l opens in its back contact the last traced lenergizing circuit ot relay 409, this relay, however. remains locked up through a circuit extending` from grounded battery, through the winding ot relay 409, conductor 515, sequence switch cam 530.

conductor vthe upper contact or. se- 7 Li quence switch cam 453, the lett-hand trent contact and armature ot relay jl-09, the right-hand contacts ot sequence switch cam 456, resistance 4l8, the lett-hand back contact and armature ot relay 435.,` the righthand contact of sequence switch cam 420 conductor 310, the normal right-hand contacts of lreys lll l R and lill in series to 7 .5 ground. rlhe relay 441 closes a circuit i' front contact, conductor 442, the lower let vliand cont-:ct ot serpience switch cam the right-hand trent contact and armature oi relay 409, the right-hand contacts of sequence switch cam 454, the right-hand armature and back contact of relay 450 and the winding of magnet 449 to grounded batt-ery.` The magnet 449 becomes energiZed and actuates an operators `position meter which indicates the number .of calls handled through the particular operators position. The magnet 449 closes also a circuit irom ground, tl'irongh its front contact and arnniture, lower lett-hand contact ot' cam 419 and the power magnet of sequence switch 402 to grounded battery. The sequence switch 40?; moves out of position T and into position l0. The magnet 449 becomes denergized. llhen the sequence swl "h moves ont or position t?, the locking tact ot cam 420, conductor 47:2, and theV lower contact ci cam 538 to ground. The current flowing through this circuit causes the lamp to burn steadily which indicates to the operator that she may proceed to complete the desired connection as will be hereinafter describen. Upon the energize! tion oit' the calling supervisory relay 403, the sequence switch is moved into some positi .n in which the lower Contact ot cani is open.V For this reason, when the calle-'L subscriber answers, the lamp is extinguished. Y

i further result ot the quence switch 402 out ot position is the denereization of relay 600. This relay opens in its lett-hand front Contact the lochmovernent ot' sen 9. the

ing circuits ot all he energized relays orn the class-ot-service indicator, and restores this device to normal. l

rihe means by which ringing current is appliedrto the called line is of the wellknown type ot machine provided with various commutator segments. The commutator indicated at 465 is arranged to produce two rings within a certain period et time and the commntator 456 is arranged to produce one ring within the set period of time. A comniutator indicated at 46T is arranged to produce an impulse during the silent7 Jeriod of the ringing machine.

Zi rl`he production oit an impulse during the silent period results in the energization ot relay 459. by current flowing through the baclr contact and winding ot elay 452 and the right-hand. contacts ot sequence switch 459 to ground. The relay 452 becon'ies energized and locks up through righthand armature and 'front contact. Vln its letthand front Contact, the relay closes a circuit .trom ground through the lett-hand contacts of sequence switch cam 454, and the pow-er magnet ot sequence switch 402 to grounded battery to move the' sequence switch'out otposition'lO `and into posi.

tion 15.

lli)

When the sequence switch leaves position 10 and opens the right-hand contact of cam 459, the relay 452 becomes denergized. As soon as the sequence switch 402 reaches position 11, the following circuit is closed for controlling the ringing of the called party: from ground through the lower armature and front contact of relay 441, conductor 442, lower left-hand contact of sequence switch cam 443, the armature and back contact of the marginal ringing relay 444, the back contact and armature of the relay 445, the winding of relay 446, and resistance 447 to grounded battery. The relay 446 becomes energized. The relay 445 that is included in a parallel branch of this circuit cannot become energized because its winding is shunted through the path including the armatures and back contacts of relays 445 and 444.' Upon the energization of relay 446, a ringing circuit is closed from ground through the back contact and inner armature of relay 434, the upper armatures and front contacts of relay 446 and relay 441, the tip contacts of plug 400 and jack 401, the bell at the called substation, the ring contacts of jack 401 and plug 400, the lower armature and front contact of relay 446, outer armature and back contact of relay 434, the winding of the marginal relay 444, the inner right-hand armature and back contact of relay 435 and the ringing commutator 466 to ground. Under the control of the commutator 466, the substation bell will be rung and when the called subscriber removes his receiver from the switchhool, the relay 444 becomes energized and thus by opening its back contact removes the shunt from the winding of relay 445. The relay 445 becomes energized, and closes through its right-hand armature and front contact, a shunt around the winding of relay 446, whereupon this relay becomes denergized. Through a branch of the above traced ringing circuit extending through the left-hand back contact and armature of relay 445 and condenser 422 to conductor 219, a ringing tone is sent to the calling subscriber informing him that the called station is being signaled.

Upon the denergization of relay 446, the calling supervisory relay 403 becomes energized and closes a circuit from ground, through its armature and front contact, conductor 542, the contacts of sequence switch cam 536, and the power magnet of sequence switch 505 to grounded battery. Depending on the setting of the sequence switch 505 under the control of the class-of-service indicator, this sequence switch moves now into positions 4, 0, 8 or 10. 1n any one of these positions of the sequence switch, a circuit is closed from ground, through the left-hand contact of cam 538, a calling supervisory lamp 549, and resistance 522 to grounded battery. As long as the relay 403 is energized, the lamp 549 cannot light up because a shunt circuit exists through resistance 550, cam 541, conductor 542, and the front contact and armature of relay 403 to ground.

After the successful establishment of the connection the operator actuates the charge key 405. lf the sequence switch 505 is standing in positions 4 or 10, a circuit is closed from grounded battery, through the winding of relay 552, lower left-hand contact of sequence switch cam 551, conductor 509, contact 470 of the key 405, conductor 110 (Figs. 4, 2 and 1) and the windings of the calling subscribers meter magnet 209 or cut-off relay 103 or 104 to ground. Relay 552 becomes energized but in view of the relatively high resistance of the winding of this relay 552, the meter magnet 209 cannot become energized. Thus, if a line entitled only to message rate service calls a free call line, the meter associated with such calling line will not register the call. rlhe relay 552 causes the operation of magnet 510, which in turn operates a registering device indicating the number of calls handled through the cord circuit shown in Fig. 5.

lf the sequence switch is standing in position 6, the circuit for the calling subscribers meter magnet extends through the lower rightdiand contact of sequence switch cam 551, and the winding of relay 508 to grounded battery. `The winding of relay 50S is of relatively low resistance and for this reason both the relay 508 and the meter magnet 209 become energized. rlhe former operates the magnet 510, and the latter the calling subscribers toll charging device.

ln positions T to 8 of the sequence switch 505, the actuation of the charge key results in the closure of a circuit from ground, through a current generator 511, lamp 553, the winding of relay 554, cam 555, conductor 512, contact 471 of key 405, conductor 219, and then through a coin collecting net at the substation (not shown) to ground. The coin collecting magnet and the relay 554 become energized. The former causes the depositing of the coin in the coin box,

and the latter lights the lamp 556 and thus apprises the operator of the fact that the toil has been collected. 1f the call has been initiated from a pay-station and it becomes necessary to refund the coin, the operator depresses the key 305 and connects a generator of high voltage current 439 through a sequence switch contact 440, conductor 321, the make contact of key 305, conductor 306, sequence switch contact 420.v conductor 219 and then to the magnet of the coin box controlling the refunding of the coin.

Then the calling and called subscribers restore their receivers to the switchhool, the supervisory relays 403 and 411 become denergized. These relays, by releasing their armatures permit the supervisory lamps 525 and 549 to light up. The operator, seeing the two supervisory lamps lighted, removes the plug 400 'from the jack 401, whereupon relays 441 and 450 become dee'nergized. The relay 441 opens the circuit oi relay 445 and closes a circuit from ground through its lower armature and back contact, the upper Contact of cam 455, resistance 462, conductor 404, the upper contact of cam 453, conductor 531, cam 530, conductor 515, and the winding or' relay 409 to grounded battery. 1delay 409 becomes energized and locks up through its lefthand front contact and armature, the lower contactsof cam 413 and resistance 403 to ground. ,fr circuit is 'then closed from ground, through the right-hand Contact of cam 416, the right-hand armature and front contact of relay 409, the lowercontacts or cam 417, conductor 537, the lower contact ot cam 536 and the power magnet of sequence switch 505 to grounded battery.Y The quence switch 505 is moved out from the position it was standing in, and into position 1. The lamps 521, 525 and 549 are extinguished and a circuit is closed from ground, through cani 532, conductor 533, the right-hand contacts of cam 42S, and the power magnet of sequence switch 402 to grounded battery. rlhe sequence switch 402 is moyedout of position 15 into position 18. rllhe relay 409 becomes denergizedand closes a circuit from ground, through the right-hand contact of cani 416, the righthand armature and back contact ot' relay 409, the upper left-hand contact of cam 19, and the power magnet of sequence switch 402 to grounded battery. rEhe sequence switch 402 moves out of position 18 and into position 1.

lVhile the sequence switch $05 was standing in some position between 2 and 11, the relay 203 and the cutoif relay of the calling line were maintained energized by current liowing from grounded battery, through a resistance 557., the lower contact of cani 514, conductor 408, contact 407 of key 405, conductor 110, wiper 217, cani 225, the lefthand winding of relay 20,3, cani 214, wiper 211, conductor 110, and the winding ci the cutoff relay to ground. lil hen the sequence switch 505 is moved out ot position 11, this circuit is opened and the relays included therein become denergized. The rela),7 203 Y closes a circuit from ground, through its contact 228, contact 229 and the power niagnet of sequence switch 208 to grounded battery. The sequence switch 208 is moy-ed out of position 14 into position 15, whereupon the switches 200 and 201 are restored to normal,

.lt the. signaling, 0f a muy line SubStf tion is desired, then, depending upon the designation of the station, thel operator depresses one of the keys W, J, R or M. Assuming that party W is called, the operator momentarily depresses the key W before inserting the plug 400 into the jack 401. ln order to insure the holding up of relay 409 while the key VV is depressed, should the operator insert the plug 400 into the jack 401 during the time she has the key depressed, ground is supplied to the winding of this relay through the right-hand normal contact-s of keys M, R and J, the righthand active contact of key 57, conductor 322, the lower Contact of cam 455, resistance 462 and conductor 464. The actuation or" the key W is without any result on the party line ringing control relays and for this reason the current is applied to the called line in the same manner as in the above assumed case, that is to say, one ring is applied to' the ringing side of the line. To indicate that the party Wis being signaled, the lamp 323 is lighted by current flowing through a cireuit extending from grounded battery through this lamp, the outer back contact and armature ot relay 315, the back contact and armature of relay 317, conductor 319 and sequence switch cam 437 to ground.

It the ringing of the party J is desired, the key J is momentarily depressed. Due to the actuation ot this key, a circuit is closed from ground through the lett-hand resting contacts of keys M and R, the letthand make contact ci key J, conductor 313,V

the Contact oi sequence switch cam 432, the windings ot relays 433V and 434, resistance 45T, conductor 535 and sequence switch cam to grounded battery. T he relays 433 and 434 become energized. fi/*hen the keys M and W are in their normal position, the relay 409 is locked up in a circuit extending from ground through the normal rightfhand contacts oi the party line ringing keys, conductor 310, upper right-hand contact of sequence switch cani 430, back contact and left-hand armature of relay 435, resistance 418, right-hand contacts of sequence switch cam 456, left-hand armature and contact of relay 409, upper lett-hand contact ot sequence. switch cam 453,-sequence switch cam 530, conductor 515, winding ot relay 409 to battery and ground. As far as the resistance 418 this circuit is parallel by a circuit extending from ground, the normal leftV liand contacts of the party line ringing keys,

conductor 324, upper left-hand contact or' sequence switch camright-hand ture and back contactof relay 433 to resistance 418. It any one of the keys is depressed both of these grounds are removed, but the relay 409 is held by the ground at thle back contact Vof the lower armature of re 441, or incase 'the lplug'400` isv inserted in the ack 401 while any one of the keys is depressed, the relay 409 is held by a ground on conductor 322 as hereinbefore described. When the key J has been depressed and again restored, relay 433 is locked up and the holding ground, other ,than that supplied by the armature of relay 441, extends from ground through the right-hand normal contacts of the party line ringing keys, conductor 310, the upper right-hand Contact of sequence switch cam 430, left-hand armature and back contact of relay 435 and thence over the circuitpreviously traced. Upon the insertion of the plug 400 into the multiple jack of the desired line, the relay 441 becomes energized and in turn causes the operation of magnet 449. The sequence switch is moved out of position 7 and into position 10. After the restoration of key J, the relays 433 and 434 are locked up through a circuit including the right-hand front .contact and armature of relay 433, the left-hand contact of sequence switch cam 459, conductor 324, and the left-hand resting contacts of the party line ringing keys to ground. When the sequence switch moves out of p0- sition 8, a substitute ground is supplied for this locking circuit through the upper rightliand contact of cam 459. In response to the energization of relay 433, a circuit is closed from ground, through the left-hand armature and front contact of relay 433, sequence switch contact 468, conductor 316, and the winding of relay 317 to grounded battery. The relay 317 becomes energized and closes a circuit from grounded battery, through a lamp 325, the inner back contact and armature of relay 315, the front Contact and armature of rel'ay 317, conductor 319, and the sequence switch contact 437 to ground. The lighting of lamp 325 indicates to the operator that she has depressed the J key.

As above described, during a silent period of the ringing machine7 relay 452 becomes energized and causes the movement of the sequence switch 402 out of position 10 and into position 15. The above-traced ringing circuit is now closed. However, in view of the fact that the relay 434 is energized, the commutator 466 of the ringing machine is connected to the tip strand 219 instead of the ring strand 220 of the cord circuit.

If the ringing of a party R is desired, the key R is momentarily depressed. A circuit is closed from ground, through the righthand resting contact of key M, right-hand make contact of key R, conductor 326, the contact of sequence switch cam 436, the winding of relay 435, resistance 457, conductor 535 and sequence switch cam 534, to grounded battery. The relay 435 becomes energized and locks up through the upper right-hand contact of cam 430, conductor 310 and the right-*hand resting Contacts ot the keys. The relay 435 closes a circuit from ground, through its right-hand outer armature and front contact, sequence switch cam 469, conductor 314 and the winding of relay 315 to grounded battery. The energization ot relay 315 results in the establishment of a circuit from grounded battery, through lamp 318, the outer front contact and armature of relay 315, the back contact and armature oi' relay 317, conductor 319 and the sequence switch contact 437 to ground. The burning of the lainp 318 indicates to the operator that the party R has been selected. The relay 409 is maintained energized in the above described manner, the conductor 322 being grounded through the lett-hand active contact oi key R, and the locking circuit closed through the righthand back conta-et of relay 433. In view ot the fact that the relay 434 is denergized, and the relay 435 is energized, when the sequence switch 402`moves into position 10, the commutator 465 is connected to the ring strand 220 Jfor signaling the desired party line station.

If the key M is momentarily depressed, two circuits are closed, one circuit from ground, through the left-hand make contact of key M, conductor 313, sequence switch contact 432, the winding of relays 433 and 434; and the other circuit from ground through the right-hand make Contact oi key M, conductor 326, cam 436, the winding of relay 435; and then through resistance 457, conductor 535 and sequence switch contact 534 to grounded battery. Relays 433 and 435 and 434 become energized, when the sequence switch 402 movesinto position 10, the ringing generator 465 is connected to the tip strand 219 Jfor ringing the desired party line station. The relays 433, 434 and 435 are locked up in the above described manner. The locking circuit of relay 409 extends through the left-hand front contact and armature of the relay, the lower contact of cam 456 and then in series with the circuit including` relays 433, 434 and 435.

The lamp lighted in response to the selection of the desired party line ringing current is extinguished when the sequence switch 402 moves out of position 7 If for any reason the operator desires to listen in on a connection, she depresses the key 461 and thus closes a circuit through the upper right-hand contact of sequence switch cam 419 for driving the sequence switch 402 out of position 15 and into position 10. The sequence switch 402 is immediately driven out of position 18 and into position 1, the driving circuit being closed from ground, through the lower right-hand contact of cam 416, the right-hand armature and back contact of relay 409, the upper left-hand contact of @am 419 and the power magnet of se

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