US2187186A - Telephone system - Google Patents

Description

Jan. 16, 1940. B A WALLACE 2,187,186

TELEPHONE SYSTEM Filed Nov. 4, 1937 4 Sheets-Sheet 1 InuerTlT: ETTH. allac'e K HEJI'TIEH.

Jan. 16, 1940. B, WALL 2,187,186

TELEPHQNE SYSTEM Filed Nov. 4, 1937 4 Sheets-Sheet 2 InLFEz-HTT": hE fiTfi. Wallace Jan. 16, 1940. B WALLACE 2,187,186

TELEPHONE SYSTEM Filed Nov. 4, 1937 4 Sheets-Sheet 3 lI'lLIET'lZUI"! 2-2 M u EET'T Fl. Wallace.

H [DI-TIE Jim. 16, 1940. B Aj gLL cE 2,187,186

7 TELEPHONE SYSTEM Filed No 4, 1937 lumen [F .gzzTl'fi. Wallace Patented Jan. 16, 1940 UNITED ,STATES PATENT OFFWE' TELEPHONE (SYSTEM Bert A.,Wallace, Oak Park, Ill., assignor to Kellogg Switchboard and Supply Company, Chicago,Ill., a corporation of Illinois Application November 4, 1937, Serial No. 172,680

17 Claims. (cine-17) r Mydnvention relates to automatic telephone systems of the two wire or metallic line type, in which means located at the central exchange are operated in 'response to a series of rapid interruptions of the subscribers line circuit to connect the calling subscriber to the contacts of the line being called. In the usual system of this.

type a subscriber removes his receiver to initiate a call, a line finder switch connects his line to a selector, whereupon he receives a dialing tone. He then operates his dialing device to step the switch, wipers of a rotary selector switch into engagement with contacts leading to a connector switch; whichin turnis operatedto cause its switch wipers to connect to thecontacts of a desired line.

It is an object of my invention to provide an improved circuit arrangement including a line finder switch, but using a plurality of counting .2 relays in the selector circuit and a plurality of relays in the connector circuit to eliminate the use of switches and their associated banksof contacts.

A feature of my invention is the inclusion in such a system ofmeans whereby a calling subcalledline is busy; ,automaticstarting of inter- 40 rupter and tone machine andpole changer.

.Another feature is the provision in an. automatic telephoneexchange of a relay type connectorarranged for handling revertive calls, the control of which does not require additional bank r 45 contacts or bank wiring and which will function This through any numberof selector stages.

control is accomplished over theftip and ring conductors of theline and consists of a momentary reversal ,of supervisory battery current on the calling lineat, the time a busy test is made.

of the called line. Ifthe connection is to the same line at both ends,;the link is switched-for handling the revertive call so as to ringthe called partywhen the calling partyhangs up 535 c v -,A hiehlr sis a e po i e r lay 'theinstant the busy test is made.

is bridged across the tip and ring conductors on ,the calling end of the link and this relay controls the operation of a slow release secondary relay which provides for locking in the revertive call switch when the momentary reversal of battery current is encountered on the called line at This type of revertive call connector is not limited to use with the circuit shown herein but is equally adapted,

.fOr use withother automatic systems. 110

Other features will become apparent upon a further perusual of the specification and together with the features pointed out will, be explained fully hereinafter, referencebeing had to the accompanying drawings, comprising Figs. 1 to 4, 15. inclusive, in which: a 1

1 is a schematic drawing of the apparatus and circuit connections therefor, comprising the line circuit and line finder switch of my invention;

Fig. 2shows the connector circuit;

Fig.3 shows the selector circuit; and

Fig. 4 illustrates the connecting relays circuit. The present invention will be best understood from' a consideration of the following detailed 25 description, taken in connection with the accompjanying drawings forming a part of this specification, with the understanding, however, that the invention is not confined to any strict conformity with the showing or the drawings go but may be changed or modified so long assuch changes and modifications mark no material de- ;parture from the salient features of the inven tion as expressed in the appended claims.

Referring particularly to Fig. 1 of the draw-,

, ings,;the line conductors l and 2 at theleft of the drawing connect the subscribers station A,

l which is equipped with the usual automatic sub station equipment, such asis well known to those skilled in the art, to an automatic exchange l where they terminate in a line circuit L which consists of a line relay LR and a cut-off relay ,CO which control the usual line finder switches one of which is shown as FS. Conductors la and '20, extend the line to multiple connections and the group of conductors MC extend the lines through multiple connections to the other line finder switches of the group.

The line finder switch apparatus comprisesa motor magnet. MM, which automatically oper-wo ates when a call is initiatedby a subscriber to step the wipers 3, l, 5, and 6 over the bank contacts "l, 8, 9, and H] to select the contacts ofthe .calling line. A bridging relay BG is provided, wh u ersi swwh i e calling i s by the switch FS to open the circuit of motor magnet MM to prevent further advancement of the wipers 3, 4, 5, and 6 and to connect the calling line to the selector mechanism of switch SS. The sleeve relay SL energizes upon the actuation of relay BG to extend the starting conductor H to the next finder switch FS (not shown) of the group. A polarized reversing relay POL, which is the revertive call testing relay, and a polarity reversing relay PRR, and a revertive call control relay RCC are provided to permit a calling subscriber to be directly connected to another party on the same line without the necessity of dialing another number. A supervisory relay SR supplies talking battery to the subscribers line and is alternately energized and deenergized when the subscriber actuates his dialing mechanism to cause the actuation in succession of the counting relays shown in Fig. 3. provided to cause the operation of an associated part of the groupbusying means and to start a tone machine operating, as is well known in the art. This machine also connects dialing tone tens locking relay TLR, a units locking relay ULR, and a unit switching relay USR, which switches the locking conductor from the tens relays ground to the units relay ground. The party line switching relay PTS, which permits the calling subscriber to select ringing current of the proper frequency for summoning the desired party, ringing control relay RCR, ringing cut-off relay RC0, and ringing interrupter relay RI cooperate to control the application of ringing current to the called line. A busy test relay BTR operates, when the called line is busy, to cause the operation of relays PRR and RCC in Fig. 1 andthe revertive call-locking relay RCL in Fig. 2. A cut through-relay CTR operates to extend the conductors of the calling line through to the conductors of the called line and a called supervisory relay CSR operates when the called subscriber lifts his receiver from its switch hook to answer a call. f

Fig. 3 discloses a switching relay SW, sequence relays SQA, SQB, and SQC, and counting relays A to H. Certain of these relays operate three times in each connection; the first operation energizes a tens relay, which selects a group of tens lines; the second operation actuates a 'units relay, which selects the individual line in the group of tens previouslyselected, and the third operation selects generator current of the proper frequency to operate the ringer at the called station.

The apparatus shown in Fig. 4 comprises two of the counting relays of the counting chain and also shows certain of the tens and units switching relays. Only two of the tens relays,

Tl and TH] are shown, but it is to be understood that one of these relays is provided for each group of ten lines in a one hundred line system. Each of these relays is provided with a locking contact and thirty other-contacts, which A busying relay ER is' are divided into groups of three, which are connected to the tip, ring, and sleeve conductors of ten lines. When the relay Tl operates, the ten lines from 10 to 19 are connected to conductors leading to units relays. Ten units relays are provided but only three are shown in the drawings. Each of the units relays has a locking contact and three contacts, which extend the tip, ring, and sleeve conductors of the switching apparatus to corresponding contacts associated with the tens relays. When the unit relay UO operates it connects the tip, ring, and sleeve conductor of the switching apparatus to the tip, ring, and sleeve conductor of the first line associated with the tens relay which is operated. A connection is established by first selecting the tens relay having the desired line within its group and then selecting the proper units relay to select the individual line desired in that group and then connecting the proper ringing current to that line.

Having described in general the circuit of the apparatus used in my invention, I will next describe the operation of the same in establishing the different connections.

If the subscriber at station A whose line terminates in Fig. l desires to converse with another subscriber whose line also terminates at the private branch exchange, he will remove his receiver from its switch hook thereby establish- -M1Vl to operate to step the wipers 3, 4, 5 and 6 into engagement with the first set of contacts I, 8, 9 and it. The energizing circuit of motor magnet MM may be traced from battery, resistance R, conductor 22, motor magnet MM, normally closed contact 34, contact 36 of the off normal springs ON, conductor 31, normally closed contact 38 of sleeve relay SL, conductor H, the ground at alternate contact 29 of relay LR. The circuit or" the motor magnet MM is opened upon the first step of the wipers 3, 4, 5 and 6 due to the opening of contact 36 of the oii normal springs ON which assume their alternate position upon the first movement of the wipers 3, 4, 5 and 6. The closure of alternate contact 53 of ON establishes an illuminating circuit for an off normal pilot'lamp OFL. This oii normal pilot lamp remains illuminated during the time the switch is hunting the calling line and if the switch does not find the calling line the burning lamp will indicate to an attendant which switch is giving the trouble.

A substitute circuit for the motor magnet MM is established if the first set of contacts 1, 8, 9 and 10 are not the contacts of the line of the calling subscriber. This circuit may be traced from battery, resistance R, motor magnet MM, closed contact 34, alternate contact 39 of the off normal springs ON, conductor 40, normally closed contact 41, conductor 42 to ground at normally closed contact 36 of the bridging relay BG. The contact 34 of the motor magnet MM is moved to its alternate position upon the energization of the motor magnet MIM-andthus opens the eneragie'lneo "-gizing circuit of the same which immediately releases its armatureand again closes the contact 34 to establish another energizing circuit for the magnet MM to step the wipers 3, 4, 5 and Binto alternate opening and closingofthe contact 34 i engagement with the next set of contacts. The

causes thewipers to be stepped over the contacts I, B, 9 and H! in search of the contacts of the calling line. Condenser :r is bridged across the motor magnet MM to prevent sparking during the rapid opening and closing of the contact 34.

l The instant wiper 5 engages the contact 9 associated with the calling line, a shunt circuit for 3 the motor magnet MM is established and prevents the further operation of the. motor magnet so i that the wipers remain in engagementwith contacts I, B,'9and ll) of the calling line. This shunt. l circuit which is also an energizing circuit for the bridging relay BG may betraced from battery through resistance R, lower winding of the relay BG, conductor 44, normal closed contact 45 of the' relay BR, conductor 46, normal closed contact 5 41 of the sleeve relay SL, Wiper 5, contact 9, to

ground at alternate contact 29 of relay LR. 5 Due to the relative resistances of MM and BG the flow of current through MMwill be insufficient to energize MM and the wipers will remain in engagement with the contacts of the calling line. 5 Upon energizing, bridging relay BGalso opens the circuit of the motor magnet MM at its contact 30 and establishes an energizing circuit for the sleeve relay SL, and the cut-off relay CO 5 which circuit may be traced frombattery, through the upper winding of relay SL, conductor 48; alternate closed contact 49 of relay BG, conductor 50, wiper 4, contact 8, conductor 5|, through the winding of relay CO to ground. The cut-oil relay CO energizes andopens its contacts 32 and 33 to opens the deenergize relay LR which restores contact 29 and thereby removes ground from contact 9 and starting conductor ll. iromcontact 9 allows the wipers of another finder switchof the group to pass. over the line of this. calling subscriber shouldanother finder, switch The removal of ground of the group be operatedduring the present connection.

The heavily marked talking conductors TC and TC are closed at alternate contacts 52 and 53 of the bridging relay BG to extend the talking circuit through to the connector circuit. The closing of alternate contact 54 of the relay SL and also establishes a locking circuit for the said relay which may be traced from battery through the lower winding of the relay SL, alternate contact 54, conductor 55, to ground at alternate contact 56 of the off normal springs ON. This circuit maintains the sleeve relay SL in its energized position until the on normal springs ON are restored to normal which restoration does not take place until the wipers 3, 4, 5 and 6 have been restored to their normal position by the operation or the release magnet RE. The conductor H is a common starting conductor and is associated with the contact 29 of all the relays LR of the group. Upon the energization of relay SL its 5 contact 38 assumes its alternate position to exi tend the common starting conductor ll through will cause the line of subscriber A to test busy .should it be seized as a called line during the to the next finder switch of the group by way of connection 7: Battery potentialon conductor 3a connection.

.Uponthe. closure of alternate contacts 52 and it 53 of BG an energizing circuit is established fcr through the machine. m

circuit of the off normal pilot lamp OFL the supervisory relay. SR which circuit may be traced from battery through the. lower winding ofrelaySR, conductor 51, alternate contact 53 .of relay BG, wiper B and contact l0, over the subscribers line and back through contact I and =wiper 3, alternate contact 52 of BG, conductor 58, through the upper winding of relay SR to ground. Relay SR energizes and closes its alternatecontact 59 which; establishes an energizing circuit for busying relay BR. This circuit may be traced from battery,through the relay BR and alternate contact 59 to ground. The opening of contact 41 of relay. SL interrupted the original energizing circuit of the bridging relay BG but as the relay BG is slow to release a substitute circuit is closed through alternate make-beforeand tone machine (not shown) which supplies :2

ringing current, a dialing tone, and-a busy tone.

This circuit can be traced from ground at alternate contact SI of BR, conductor [5 l normal contact 180 of CSR to connection MS and then Dialing operation As soon as the relay BG operates to connect the finder switch PS to the selector switch SS the calling subscriber will receive a dialing tone which informs the subscriber that the dialing may be started. This dialing tone circuit may be traced from conductor 65 which leads to the dial tone connection DT of the tone machine and is common to the switch group, normal contact 65 ,49

of relay RCO of the selector circuit, normal contact I33 of CTR, over the heavily marked talking conductor TC, alternate contact 53 of relay BG, wiper 6, contact l0, conductor I to the subscribers receiver. Upon receiving this signal the calling,

subscriber will know that the apparatus is in con dition for the dialing operation.

Assuming that the called subscribers number is 412, the calling subscriber will operate the calling device CD to dial the number 4 and thereby interrupt the talking conductors four times in" the usual manner. Upon the first interruption of the talking conductors the supervisory relay SR will restore to normal. and close its normal contact 59. The relay BR will remain in its operated. position due to the copper slugs which make it slow acting, thus grounding the dialing conductor DC and closing the energizing circuits for the switching relay SW, and the first dialing or counting relay A. The circuit for the switching relay.

SWmay be traced from battery through the wind-' ing of the relay SW, to the conductor DC; the one for the counting relay A from battery through the winding of the relay A, through normal contacts 93, 94and95 to the dialing conductor DC. ,,65

which dialing conductor is connected to ground at normal contact 59 of relay SR through alternate contact 14 of relay BR.

The switching relay SW remains energized during the rapid interruptions of the line, due

toits slow-to-release construction. The counting relay A establishes a locking circuit for itself and an energizing circuit for the sequence switching relay SQA. This circuit may be traced from grounded battery through the winding oi. re1ay A, alternate contact IOI of A, conductor I02, through the winding of relay SQA, normal contact I03, locking conductor LC to ground at the tens locking ground TLG of relay TLR. The next succeeding impulse causes the operation of counting relay B. The initial energizing circuit being traced from grounded battery through the winding of relay B, alternate contact I04 of A, alternate contact 93 of SQA, normal contacts 94 and 95, dialing conductor DC to ground at alternate contact 59 of'relay SR. Counting relay B energizes and establishes a locking circuit for itself and an energizing circuit for sequence switching relay SQB. These relays are maintained operated by current flowing from grounded battery through the winding of relay B, al-

- ternate contact I 01, conductor I06, winding of relay SQB, normal contact I01 of SQC, the look-- ing conductor TLC to ground at contact TLG. The opening of contact I03 of SQB causes the deenergization of relays SQA and A. The next impulse causes the operation of counting relay C by current flowing from grounded battery through the winding of relay C, alternate contact I042) of relay B, alternate contact 94 of relay SQB, normal contact 95 of SQC to ground over the dialing conductor DC. The closing of alternate contact IIJIc establishes a locking circuit for the relay C and an energizing circuit for sequence switching relay SQC. These relays are held operated by current flowing from grounded battery through the winding of relay C, alternate contact I Ic, conductor I08, winding of relay SQC, normal contact I09 of SQA, locking conductor LC to ground TLG. The operation of relay SQC opens the holding circuit for the relays B and SQB'at its alternate contact I01 and these relays accordingly restore their contacts to their normal positions. The fourth interruption of the line by the dialing contacts causes the operation of counting relay D, which is operated by current flowing from grounded battery, alternate contact I040, alternate contact 95 of relay SQC to ground over the dialing conductor DC. The closure of alternate contact IOId of relay D establishes a locking circuit for the relay D and an energizing circuit for the relay SQA. The circuit for these relays can be traced from grounded battery through the winding of relay D, alternate contact IllId, the winding of SQA, normal contact I 03 of SQB, locking conductor TLC to ground TLG. Relay SQA operates and opens its contact I09 to interrupt the holding circuit for counting relay C and sequence relay SQC, which relays restore to normal. At the end of the impulses the relay SR in Fig. l remains energized and ground is removed from the dialing conductor DC a sufiicient length of time to permit the deenergization of switching relay SW. The restoration of normal contact IIO of SW closes an energizing circuit 'for the tens relay T4 associated with a group of ten lines in which the desired line is located. This relay is not shown in Fig. 4, but its circuit is similar to that of relay TI. This circuit to be traced from grounded battery through the winding of relay TI, makebefore-break contact III, conductor cI0 (in the case of relay T l, this conductor will be conductor 040), alternate contact M of relay D, conductor H4, normal contact H5 of relay TLR, conductor IIIS, alternate contact In of relay SQA, normal contact IIO of relay SW, conductor I GI alternate contact 6| of busying relay BR in Fig. 1 to ground. The relay T4 establishes a. locking circuit'for itself through its alternate contact which in this case is I.

III, common locking conductor CLC, winding of relay TLR, conductor I6I to ground at alternate this circuit and it opens its contact TLG to remove ground from the locln'ng conductor LC which causes the restoration of counting relay D and sequence relay SQA.

The subscriber A next dials the second digit, The supervisory relay SR deenergizes to place ground upon the dialing conductor DC. The switching relay SW will be energized and the dialing relay A will also be energized over a circuit previously traced. The

unit switching relay USR of Fig. 2 is energized by current flowing from grounded battery through the winding of relay USR, alternate contact H8, conductor II9, alternate contact IIO of relay SW, conductor IBI to ground at busying relay ER in Fig. 1.

ing circuit for the sequence relay SQA over the locking conductor LC, alternate contact I to ground at unit locking ground ULG of relay ULR. As there is but one interruption of the ULR, alternate contact I of relay U SR, con-- ductor H6, alternate contact I II of SQA, normal contact IIO of SW and conductor I6I to ground at alternate contact GI of relay BR. Unit relay UI establishes a locking circuit for itself through its alternate contact I26 and unit locks? ing conductor ULC, winding of relay ULR, conductor IOI to ground at alternate contact 6| of relay BR.

The energization of unit relay UI connects the tip, ring and sleeve conductors T, R and S of the switching apparatus to the line desired which, in this instance, is line 4I. These conductors are extended through alternate contacts I 2'! of relay UI and I28 of relay T4 (not shown). Units locking relay ULR will be energized over the previously traced circuit and will open normal contact ULG which removes the unit locking ground from the locking conductor LC and causes the restoration of relays A and SQA, which were used in selecting the desired unit relay. Relay;

ULR closes its alternate contact I29 to connect test battery TB to the sleeve conductor S of the line. Current flows from test battery TB, resistance RA, alternate contact I29 of ULR, conductor S, alternate contact I2! of U1 and alter:

nate contact I28 of relay T4 (not shown) to all the multiple contacts of line II. This battery potential being on the sleeve conductor S of the line will cause it to test busy should any other switching apparatus be connected thereto, as will be described later. The cut-through relay CTR is operated by current flowing from grounded battery through the winding of relay CTR, normal contact I30 of ringing cut-off relay RCO, alternate contact ULG to ground. The relay CTR closes its alternate contacts I3I and I32 to extend the talking conductors TC and TCI through to the calling line. The opening of contact I33 removes the dial tone from the calling uartysline.

The dialing relay A estab- .lishes a locking circuit for itself and an energizconductor TC to the subscribers station and Selection of ringing current, I

Next the operator dials the third digit which selects ringing current of the proper frequency to operate the ringer at the station of the desired itself up over a circuit previously described.

The party line switching relay PTS operates after the first impulse over a circuit traced from grounded battery through the winding of PTS, alternate cont-act I34 of ULR, conductor I35, alternate contact I36 of SW, conductor I6I to ground at alternate contact 6| of relay BR. Relay PTS closes its alternate contact I31 to lock itself up overconductor I6I and alternate contact 6I of relay BR. At the end of the impulses "the switching relay SW reenergizes. The ringing control relay RCR is then energized by current flowing from grounded battery through the winding of relay RCR, alternate contact I38 of relay PTS, alternate contact I of USR, conductor H6, alternate contact II 1 of SQA, normal contact III) of SW, conductor I6I, alternate contact 61 to ground. Relay RCR energizes and opens its alternate contact I39 to interrupt the dialing conductor DC, opens alter nate contact I40 to interrupt the circuit of the polarizcdrelay POL and closes its alternate con- ,.,tact IM to establish an energizing circuit for the ringing interrupter relay RI. This circuit can be traced from grounded battery, alternate contact I42 of ringing cut-01f relay RCO, alternate contact I4I of relay RCR, winding of relay RI to ground through a constantly rotating incow 'terrupter not shown but connected to connection INT. The ringing interrupter relay RI is alternately energized and deenergizedover this circuit. Each time it is energized its contacts I43 and I44 move to their alternate positions to open the talking conductors TC and TCI and to apply ringing current to the line of the called party. This ringing current can be traced from one side of the generator source, alternate contact I451) of counting relay B, through normal contacts I450, I45dand I45e, conductor I46, al-

ternate contact I43 of relay RI, alternate contact I32 of CTR over the heavily marked conductor R, alternate contact I21 of relay UI, alternate contact I28 ofrelay T4 over the subscribers line and back through alternate con gized. Due to the construction of relay RTR it is slow to release and therefore remains energized a short period after theringing interrupter relay RIis deenergized, however, it does restore between each ringing period. The ringing tone "relay RTR closes its alternate contacts I48 and I49. The closing of alternate contact I49 connects a ringing tone from a ringing tone machine (not shown), which is connected to connection RT. This ringing tone travels from connection RT to alternate contact I49of relay RTR over informs the subscriber that ringing current has been applied to the called line. The closing of alternate contact I48 of relay RTR connects the talking conductors together through conductor I52. This connection is momentarily maintained after relay RI restores and serves to discharge the residual ringing current on the called line I to prevent any kick back of the current into the finder switch circuit.

If the called subscriber removes his receiver during a ringing period, no action will take place until the end of that ringing period, at which time the ringing interrupter relay RI deenergises. Ringing tone relay RTRremains energized momentarily to discharge the residual ringing current on the called line and then closes normal contacts I48 and I49. The closing of these contacts establishes an energizing circuit for the called supervisory relay CSR. This relay I is energized by current flowing from grounded battery through the winding of relay CSR, normal contact I49, over the heavily marked talking conductor through the receiver at the subscribers station, back over the other side of the line to normal contact I48 of relay RTR and the upper winding of relay CSR to ground. The relay CSR closes alternate contact I62 to establish an energizing circuit for the ringing cut-off relay RCO, which relay is energized by current flowing from grounded battery, alternate contact I62 of relay CSR, conductor I63, the winding of relay RCO to ground. Relay RCO energizes and closes alternate contact I42, which opens the energizing circuit for the ringing interrupter relay RI which will remain deenergized and close normal contacts I43 and I44 to complete the talking circuit. The closing of alternate contact I42 establishes a locking circuit for the ringing cut-01f relay RCO which may be traced from grounded battery, alternate contact I42, conductor 63, alternate contact 62 of relay BR, conductors 64 and I63 to ground through the winding of the relay RCO. The cut through relay CTR remains energized through its alternate contact I64 and alternate contact I3IJ of relay RCO. The relay CTR is slow to release andremains energized during the movement of alternate contact I36 from its normal to its alternate position. When the called supervisory relay CSR operated and closed alternate contact I80 it interrupted the energizing circuit of the Disconnection Upon the termination of the conversation the subscribers replace their receivers upon their respective switch hooks. The replacing of the receiver at the-calling station A will open the energizing circuit of the supervisory relay SR, which relay will restore its contact 59 to its normal position, thereby opening the energizing circuit of the busying relay BR, which relay will also restore its contacts to their normal position. The opening of contact will cause the deenergization of the bridging relay BG which will open its contacts 52 and 53 to open the talking conductors at that point. The opening of contact 49 breaks the energizing circuit of cutoff relay CO which restores and also removes batteryxpotential from test conductor 3a which will permit line A to test idle. The closing of normal contact 30 establishes an energizing circuit for the release magnet RE, which will be operated by current flowing from grounded battery through the winding of release magnet RE, alternate contact M of relay' SL, conductor 42 and normal contact 30 of relay BG to ground. The release magnet RE energizes and restores the switch wipers 3, 4, 5 and 6 and the off-normal contacts ON to their normal positions. The opening of the off-normal contact 56 breaks the locking circuit of the sleeve relay SL but relay SL does not restore due to ground at contact I80 of CSR being connected to conductor I6I.

When the relay BR restored, it opened contact 62, which interrupted one energizing circuit of the ringing control relay RCO. Relay RCO does not open the energizing circuit for the cut through relay CTR as it is held operated over another circuit. The remaining apparatus is held under the control of the called subscriber.

When he replaces his receiver the energizing circuit for the called supervisory relay CSR is opened and it restores its contact I62 to open the second energizing circuit of the ringing control relay RCO. Relay CSR removes the holding ground from the conductor I6I and causes the restoration to normal of the sleeve relay SL in Fig. 1, the party switching relay PTS, the unit locking relay ULR, the unit switching relay USR, the unit relay UI in Fig. 4. The operated tens" relay T4 is also deenergized and the called line is severed from the connection and the apparatus is in condition to establish another connection.

If called line is busy If the called line is busy when it is seized by the operation of the relay UI its S conductor will have a battery potential thereon. The oper" ation in establishing a connection to a busy line is exactly the same up to the point where the unit relay UI operates. If the battery potential is present on the S conductor an energizing circuit for the busy test relay BTR will be established. This circuit can be traced from ground through the winding of relay BTR, normal contact I29 of relay ULR, conductor S, alternate contact I21 of relay UI and I28 of relay T4 over the sleeve conductor and the multiple contacts and through operated contacts of a tens and unit relay in the connector circuit of the established connection over the sleeve conductor S of that connector, through alternate contact I29 of the relay ULR in the other connector to the test battery. An alternative circuit is present when the busy line is a calling line. In such instances the circuit for relay BTR is through conductor S, conductor 3a in Fig. 1 of the busy line, contact 8, wiper 4, conductor 5D, alternate contact 49, upper winding of SL to battery and ground. The busy test relay BTR energizes and establishes an obvious energizing circuit through its alternate contact I64 for the ringing cut-off relay RCO, which operates to prevent the connection of ringing current to the called line, which in this instance is busy. The closing of alternate contact 66 of relay RCO connects a busy tone to the line of the called subscriber and he is thereby informed that the called line is busy. He will thereupon replace his receiver and cause the restoration of the apparatus to normal, as previously explained.

Connection between subscribers on same line If, however, the calling party is calling another subscriber located on the same line, the calling subscriber will not replace his receiver at this time. The energization of busy test relay BTR closed its alternate contact I65 to establish an energizing circuit for the polarity reversing relay PRR in Fig. 1. This relay will be energized by current flowing from grounded battery, winding of PRR, conductor 266 and alternate contact I65 of relay BTR to ground. The operation of relay PRR closes alternate contacts I66 and I61, which reverses the polarity of the battery on the talking conductors and causes the operation of the polarized relay POL. This circuit can be traced from grounded battery, lower winding of relay SR, make-beiore-break contacts 3| and I66, conductor 58, over the talking conductor, wiper 3, con tact I, conductor 2a, multiple contacts and through the alternate contacts I28 of the operated tens relay, alternate contacts I21 of relay Ul the talking conductor, to normal contact I3! of relay CTR, conductor I68, upper winding of polarized relay POL, conductor I59, normal contact I48 of relay RCR, conductor I10, lower winding of relay POL, conductor I'II, normal contact I32 of relay CTR, the talking conductor, alternate contacts I21 and I28 of UI and T4, multiple contacts to conductor Ia, contact I0, wiper 6, talking conductor to alternate contact 53 of relay BG, alternate contact I61, upper winding of relay SR to ground. The polarized relay POL energizes over this circuit and closes an energizing circuit for the revertive call relay RCC. This relay is operated by current flowing from grounded battery through the winding of relay RCC, alternate contact I12 of POL, conductor I13 to ground at PLG of relay PTS. Relay BTR is operated only while the units relay is not energized; as soon as relay ULR energizes contact I29 opens the energizing circuit of relay BTR which then deenergizes. Relay BTR is provided with a copper sleeve and is therefore slow in releasing but when it does release relay PRR releases and restores normal polarity to the line conductors from battery through the winding of relay SR. Polarized relay POL releases contact I12 which opens the operating circuit of relay RCC. Relay RC6 is also slow to release and maintains its contact 20I closed a suificient time to cause the energization of the revertive call locking relay RCL by current flowing from battery, normal contact I 52 of CSR, winding of relay RCL, alternate contact 20I of RCC, normal contact I12 of POL, conductor I13 to ground at PLG of relay PTS. Relay RCL locks up through its own contacts 202 and 203 to ground. The closing of alternate contact 203 keeps ground MG on lead IGI to hold the calling line end of the circuit during the period that the calling subscriber replaces his receiver to permit the application of ringing current to the line.

The busy test relay BTR and the polarity reversing relay PRR operate each time the link circuit selects a busy line and the polarity of the current is reversed in the calling and of the link each time but this reversal of current has no effect except when both ends of the link are connected to the same line.

The calling party, having tested the line to determine its busy condition at the time he initiated the call knows that the busy signal is caused by his operation of the connector switch and will proceed to dial to connect the proper generator current to the line to operate the call bell at the station of the desired subscriber. In our assumption, 2 was considered the last digit of the called line number. The subscriber will dial the digit 2, which will interrupt the line conmittently connect the generator current from the are-Inca ductors two times to cause the supervisoryrelay SE to deenergize and energize twice. 'As previously explained, the grounding of the dialing conductor DC causes the operation of the switching relay SW and of the dialing relay A. The sec- 0nd time the relay SRfalls off the dialing relay B is operated and locks up through its alternate contact ltlb to ground at PLG of relay PTS. After the subscriber has dialed he will replace his receiver upon its switch hook, which operation Will cause the restoration tonormal of the finder switch FS, as previously explained, with the ex ception that thesleeve relay SL will not restore due to the fact that there isa ground at contact MG of relay RCL. 'The deenergization of busying relay BR opens the lockingcircuitof the ringing control relay RCO, which relay closes its normal contact M2 to establish an energizing circuit for the ringing interrupter relay RI through alternate contact 'HH of ringing control relay RCR. RCO releasing cuts off the busy tone and also establishes an energizing circuit to operate relay CTR. Ringing interrupter relay RI is' alternately energized and deenergized to interalternate contacts of relay B out over the line.

lhe removal of the receiver at. the station, of l either the called or calling party, establishes an energizing circuit for the called supervisoryrelay CSPJ, which relay energizes to again operate the ringing cut-off relay RCO to stop the application of ringing current to the line andto connect the subscribers into a conversational circuit in which talking current is supplied through-the windings ground from the conductor 18! and permits all the relays to restore to normal to again place the connecting apparatus in condition for the establishment of another connection. 1

Having describedmy invention, what I claim new and desire to secure by United States Let-;

ters'Patent is x 1. A telephone system including anexchange, a plurality of lines terminating at said exchange,

a plurality of stations on certain of said lines, link means at said exchange for interconnecting any of said stations, a source of battery current associated with said link means, means for rendering any ofjsaid lines busy, means responsive to the engagement of said link with a busy line for immediately reversing the flow of said battery current. w v l v v 2. A telephone system including a subscribers line, a plurality of stations on said line, a link circuit having an answering end-and a calling end for interconnecting any of said stations, a source of current connected to said line, and means responsive to the connection of'both of said ends to said line to reverse immediately the polarity of said current on saidline,

3. A telephone system including a subscribers line, plurality of stations on said line, an automatic link circuit having an answeringjend and a calling end for interconnecting any of said stations, a source of current connected to said link circuit, means responsive to the cormection of both of said ends to said line to reverse immediately the polarityof said current on said link, and secondary means comprising a polarized relay responsive to said polarity reversing means.

l. A telephone system including an excl'la'nge,

a plurality of subscribers lines, a. plurality of stal tions on certain of said lines, a two-ended link circuit for interconnecting any ofsaid stations,

a source of current connected to said link circuit,

means responsive to the connection of both of i polarized relay for holding said link circuit.

against disconnection.

5. A telephone system comprising an exchange,

a plurality of subscribers lines terminating thereat,a plurality of stations on certain of said lines, a link circuit at said exchange for interconnecting any ofsaid stations, a pair of talking conductors for said link, a source of current connected across said conductors, means for con necting both ends of said link to the same line and means responsive to said connection to reverse immediately the connections between said conductors and said source of current.

6. A telephone system comprising an exchange,

a plurality of subscribers lines terminating thereat, a plurality of stations on certain of said lines. a link circuit at said exchange for interconnecting any of said stations, a pair of talking conductors for said link, a sourceof current connected across said conductors, means for connecting both ends of said link to the same line, means responsive to said connection to reverse the connections between said conductors and said source of current,

and relay means responsive to said reversal forpreventing the disconnection of said line and link. 7 A telephone system comprising an exchange,

a plurality of lines terminating thereat, a plu rality of stations on certain of said lines, a link circuit at said exchange for interconnecting any of said stations, an answering end and a calling end for said link, a source of current connected to said answering end, current reversing means operable when said ends of said link are connected to the same line and means associated with thecalling end of said link and controlled by said. reversing means for preventing the disconnection of said line and link.

8. A telephone system comprising an exchange,

a lineterminating thereat, a calling stationand a called station on said line, a link circuit for said exchange, means in said link for connecting said line to both endsof said link, a source of current associated with said link, signaling means under the control cfthe calling station for signaling the called station, means for reversing the connections of said link and said source of current,

means responsive to said reversal of current for maintaining the connection of the link and line line; V l

'9. A telephone system including an exchange, a

w andfor connecting said signaling means to said plurality of lines terminating thereat, a plurality 1 of. stations on certain of said lines, a link circuit having an answering end and a calling end for interconnecting any of said stations, a source of current connected to a calling line, means responsive to the connection of both of said ends to the same line to reverse immediately the polarity of said current, and means preventing the operation of said last means when saidends of said link are connected to difierent lines, one of vvhich is idle. n

10. A telephone system includingan exchange,

.a plurality of lines terminatingat said exchange,

a plurality of stations on certain of said linesya link circuit for interconnecting any of said stations, a source of current associated with said link circuit, means responsive to the connection of both ends of said link to the same line to reverse immediately the polarity of said current,

'2 and secondary means responsive to said polarity reversing means.

11. A telephone system comprising an exchange, a plurality of lines terminating thereat,

a plurality of stations on certain of said lines, an interconnecting circuit comprising a plurality of automatic switches for interconnecting any of said stations, a course of current connected to said circuit, and means responsive to the connection of both ends of said circuit to one of said lines for immediately reversing the connections between the said source of current and said circuit.

12. A telephone system comprising an exchange, a plurality of lines terminating at said exchange, a plurality of stations on certain of said lines, a link circuit for interconnecting any of said stations comprising a finder switch and a connector switch, a source of current connected to said link, means responsive to the connection of said finder switch and connector switch to the same line for immediately reversing the connections between said source of current and said link.

13. A telephone system comprising an ex- -:ohange, a plurality of lines terminating at said exchange, a plurality of stations on certain of said lines, a link circuit for interconnecting any of said stations comprising a finder switch and a connector switch, a source of current connected to said link, means responsive to the connection of said finderswitch and connector switch to the same line for immediately reversing the connections between said course of current and said link, and relay means responsive to said reversal for holding said connector switch connected to said line.

14. A telephone system comprising an exchange, a plurality of lines terminating at said exchange, a calling station and a called station on .one of said lines, a link circuit for interconnect- 'ing said calling and called stations, circuit controlling means at said stations, a finder switch in said link responsive to the circuit controlling means at said calling station to connect one end ofsaid link to the calling station, a connector switch for connecting the other end of said link to the line of the called station, a source of current connected to said link, means responsive to the connection of said connector switch to said line for reversing the connections of said link -"'and said source of current.

15. A telephone system comprising an exchange, a plurality of lines terminating at said exchange, a calling station and a called station on one of said lines, a link circuit for interconnecting said calling and called stations, circuit controlling means at said stations, a finder switch in said link responsive to the circuit controlling means at said calling station to connect one end of said link to the calling station, a connector switch for connecting the other end of said link to the line of the called station, a source of current connected to said link, means responsive to the connection of said connector switch to said line for reversing the connections of said link and said source of current, relay means in said link circuit responsive to the circuit controlling means at the calling station for disassociating the finder switch from said line.

16. A telephone system comprising an exchange, a plurality of lines terminating at said exchange, a calling station and a called station on one of said lines, a link circuit for interconnecting said calling and called stations, circuit controlling means at said stations, a finder switch in said link responsive to the circuit controlling means at said calling station to connect one end of said link to the calling station, a connector switch for connecting the other end of said link to the line of the called station, a source of current connected to said link, means responsive to the connection of said connector switch to said line for reversing the connections of said link and said source of current, means at said exchange for signaling the called station, relay means in said link responsive to the circuit controlling means at the calling station for connecting said signaling means to said line.

17. A telephone system comprising an exchange, a plurality of lines terminating at said exchange, a calling station and a called station on one of said lines, a link circuit for interconnecting said calling and called stations, circuit controlling means at said stations, a finder switch in said link responsive to the circuit controlling means at said calling station to connect one end of said link to the calling station, a connector switch for connecting the other end of said link to the line of the called station, a source of current connected to said link, means responsive to the connection of said connector switch to said line for reversing the connections of said link and said source of current, relay means in said link circuit responsive to the circuit controlling means at the calling station for disassociating the finder switch from said line and means at said exchange for signaling the called station, relay means in said link responsive to the circuit controlling means at the calling station for connecting said signaling means to said line.

BERT A. WALLACE.

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