US2094140A - Telephone system - Google Patents

Description

E DUARD WOCHINGER ATTORNEY.

Sept. 28, 1937. E. wocHlNGER 2,094,140

TELEPHONE SYSTEM y Y Filed July 8, 1935 A 4 sh'ts-sheetA s WLSO 4Go F142 y INVENTOR.

` EDUARD WOCHINGER ATTORNEY.

Patented Sept. 28, 1937 UNiTE AET TELEPHONE SYSTEM Eduard Wochinger, Berlin, Germany, assigner to Siemens & Halske Aktiengesellschaft, Siemensstadt, near Berlin, Germany Application July 8, 1935, Serial No. 30,378 In Germany July 13, 1934 10 Claims. (Cl. 179-18) The present invention relates to telephone in the main exchange which is switched round systems with main and subsidiary exchanges and according to the characterizing number dialled automatic operation `and the object is to proso that either a. call is set up over the connecting duce a system which will enable connections to devices of the main exchange, or the auxiliary be set up between subscribers oi the same subselector LWL-ld in the subsidiary exchange can 5 sidiary exchange (internal calls) in a more be set on the desired subscribers connection. simple and positive manner. In the present embodiment the characterizing is This is achieved in that two speaking lines are arranged so that by dialling the digit l an outprovided between the main and subsidiary exgoing call is characterized, while by dialling the changes, of which one is provided in the subsubscribers number directly, i. e., any digit ex- 10 sidiary exchange with a double purpose selector cept I an internal call and thereupon the subused for exchange calls and for the outgoing scriber desired in the internal call, is charconnecting path for internal calls, and the acterized. second with a nal selector for use with internal The characterizing digit for the outgoing excalls. change call is not taken up by the connecting 15 It is particularly advantageous for a telephone devices in the main exchange, but only by the system to enable internal calls in a subsidiary characterizing switching device and the auxiliary exchange to be set up without unnecessarily selector LWS@ provided in the subsidiary exwithdrawing the local connecting lines within change.

the main exchange from traflic or necessitating In the normal condition of the system all of 2O the dialling of a special characterizing number. the selectors in the subsidiary exchange and also This is attained according to the invention in the switching devices in the main exchange and that a characterizing selector is associated in the in addition all the relays, are uninuenced,

main exchange with a connecting line running between the main and subsidiary exchanges, omgomg Calls 25 which, corresponding to the number of impulses When a subscriber takes up his receiver and of an impulse train determining the desired call momentarily depresses the key, for example key direction, either prepares the influencing of sub- B2 in the case of subscriber A2, earth is consequent selectors in the main exchange used for nected to lead al of the connecting line leading setting up exchange calls, or initiates the estabto the main exchange. In the main exchange 30 lishment of an internal call over a selector of relay X38 energizes over the circuit: earth, the subsidiary exchange. battery, resistance Wil, wiper 031130, winding I In Figs. 1 and 2 a system with a main and subof relay X36, contacts tail, Slicml), 35ilc30, sidiary exchange is illustrated as an embodilead al, winding I of relay Utl, wiper ai of sement of the invention, while Figs. 3, 4, and 5 are lector DB3@ in position O, key B2, earth. Relay 35 a modification thereof. The arrangement illus- X33 locks up over its winding II on closing its trated in Figs. l and 2 in addition to the outcontact 'lx. Contact 345x339 disconnects batgoing and incoming calls enables connections to tery from the lead al of the connecting line. be set up between subscribers of the same sub- Contact 331x311, however, connects battery to 40 sidiary exchange. For this purpose, in addition the bl lead. The following circuit is then set 40 to selector DB3() which serves for setting up up: earth, magnet WSl, contact 3iJ9u3l, bl lead outgoing and incoming calls (exchange calls) of the connecting line, contacts 335c3d, 3373230, and thus works as a double purpose selector, a 339e30, 342y3, relay battery, earth. In second selector LWB@ is provided in the subthis circuit the magnet Wl energizes in the sidiary exchange which serves to set up insubsidiary exchange and relay Kiii in the main 45 ternal connections within the subsidiary exexchange, so that selector DB3@ in the subsidiary change. This auxiliary selector is connected exchange advances one step. Similarly the over an auxiliary line (a2, b2) between the subswitching device influenced by the magnet D35! sidiary exchange and main exchange to the ccnin the main exchange is advanced one step, after necting line leading to the main exchange which this magnet has been energized over Contact 50 is seized by calling subscribers. 3l6lc3. On the energizing of this magnet, con- In order to differentiate between the different tact M8023@ is closed and thus relay Y30 is call directions i. e. outgoing exchange calls and switched on over resistance Wid. This relay internal calls, an additional switching device is opens its Contact 32y30, among others, so that 55 provided (magnet DiSiB, wipers diI3li--diIV30) the operating circuit of magnet W3! and relay K30 is broken, so that these are both deenergized. By the opening of contact 3101630 magnet d30 is also deenergized which again results in the opening of contact 3I8d30 and hence the deenergizing of relay Y30. Contact 342y33 is again closed and thereby the operating circuit for magnet W3I and for relay K30 is set up afresh, so that selector DB30 in the subsidiary exchange and the switching device in the main exchange which is influenced by relay K30, advance a further step.

Since the calling subscriber A2 is connected to the second contact of selector DB30, on reaching this contact, after relay Y30 has operated as before after the completion of the second switching step, the following circuit is set up: earth, battery, relay P30, contacts 3411/30, 3463230, 348an30, 350030, lead aI of the 'connecting line, winding I of relay U3I, wiper al of selector DB30 in position 2, subscriber A2, wiper bl of the same selector in position 2, winding II of relay USI, contacts 301u3I, 30011232 (I-I1) (mechanically operated by LW30), earth. It should be noticed that the connection of the testing relay P30 to lead aI by relay Y30 takes place after each step of the switching device in the main exchange. By the closing of contact 3|9p30 relay Y30 is held energized so that by the opening of contact 342y30 further transmission of impulses for advancing the switching device is prevented. Earth is connected to lead bl over contact 340y30 and the choke DTSI, so that after opening contact 301u3| and closing Contact 308u3l the following locking circuit is set up for relay U3I, energized in the above testing circuit: earth, choke coil Dr3l, contacts 3llk30, 33m/30, wiper dIV30 in position I-II, contact 335030, lead bl of the connecting line, contact 308u3I, winding II of relay U3I, wiper bl of selector DB30 in position 2, subscriber A2, wiper al of selector DB30 in position 2, winding I of relay U3I, lead aI of the connecting line, contacts 350c30, 30an30, 34Sm30, 34Iy30, relay P30, battery, earth. At contact 3541030 a loop is closed for the connecting devices of the main exchange so that, just as in the case of a subscriber having an individual line, preselecting device, for example a call finder, is set in operation. After the setting of such a preselecting device, if the calling subscriber is connected to a free connecting device he receives a signal from the exchange.

Since it is an outgoing call which is being set up in the present case, the subscriber must dial the characterizing digit 1. It should be added that relay J 30 was energized over contacts 32430 and 3261130 and also over wiper dzIII30 in position 0, so that contact 3541930 which was closed by the testing relay P30 which operates as the impulse relay during the numerical selection, is shunted by contact 3557'30. The selection of the characterizing digit 1 is accordingly not transmitted to the connecting devices of the main exchange. On the rst impulse, i. e. on the first deenergizing of relay P30, the magnet di30 of the characterizing switching device is operated in the main exchange over contacts 324:c30, 3211130 and 3281'30, and relay V30 is operated in parallel with the magnet; moreover, by the transitory closing of Contact 3151130, battery is connected over contact 314f30 to the b2 lead of the auxiliary connecting line and hence magnet W32 of the auxiliary selector LW30 is operated. By means of relay V30, energized during the impulse emission, the choke coil D-r30 is short circuited by the closing of Contact 3521130, and by the opening of contacts 35Iv30 and 353v30 the condensers in the speaking leads are disconnected so as to ensure a more clear impulse emission. After the one impulse has been given relay V30 deenergizes on account of the prolonged opening of contact 3211330, so that relay J30, which after one step has been made can hold up over wiper diIII30 in position I and over contact 3251230, is deenergized. The short circuit of impulse contact 3541930 is accordingly removed by the opening of contact 355530 so that the next impulse trains can be transmitted to the connecting devices of the main exchange. The magnet W32 in the subsidiary exchange, which previously displaced the auxiliary selector LW30 one step, can no longer be effected since the corresponding impulse circuit is broken at contact 314730.

When the desired subscriber is reached, after testing on the contact in the normal way, ringing current is transmitted and the speakingk connection is established on the desired subscriber replying. When the conversation has nished a metering impulse is transmitted to the c-lead in any desired manner which does not concern us here. This is extended to the meter SM2 in the main exchange corresponding to the calling subscriber of the subsidiary exchange. The connecting of the corresponding meter takes place on the setting of selector DB30 in the subsidiary exchange by the switching device in the main exchange controlling this selector.

By the switching on of winding II of relay Y30 in the c-lead, which relay assists in sending out the control impulses, the existing connection is prevented from being released during this metering even when the calling subscriber replaces his receiver and thereby releases relay P30 which lies in the circuit of speaking current. When the metering is completed and the calling subscriber replaces his receiver relays P30 and U3I deenergize. Since a locking circuit no longer exists for relay Y30 in the c-lead it is disconnected by the opening of contact 3I9p30 so that it deenergizes. At contacts 3421/30 and 309u3l the operating circuit through magnet W3I and relay K30 in series is now closed again, so that now, in the same Way as for the setting of selector DB30 on the calling subscriber, this is again controlled synchronously by the switching device in the main exchange. If the selector DB30 thus moves on to a subscribers line in which the subscriber has just taken up the receiver, seizing can at once take place again, since both the selector in the subsidiary exchange and the switching device in the main exchange are both in the same switching position, so that the meter in the main exchange corresponding to the calling subscriber is also connected up when the switches are brought to rest. If such a call does not occur, a selector DB30 and the controlling switching device in the main exchange accordingly reach position II, relay E30 energizes in the main exchange over: earth, battery, relay E30, wiper dIII30 in position Il, contact V32430, earth. Relay E30 establishes a locking circuit for itself over its contact 363630. The operating circuit passing over the bl lead is broken by contact 339e30, and also battery is connected to lead b2 of the auxiliary connecting line, so that now magnet W32 of selector LW30 Which stands in position I is influenced in series With relay K30 of the main exchange. The impulse circuit previously operating magnet D30 is correspondingly opened at contact 3I2e30 and is lswitched over to magnet D230 of the characterizing selector by the closing of contact 3l3e30. The auxiliary selector LW30 is accordingly switched on one step, and through the energizing of relay K30 in the same circuit magnet D130 is operated over contact 3l6lc30, and likewise advances the characterizing selector one step. Relay Y30 is operated by the closing of contact 3ldz30, and by opening contact 32y30 breaks the operating circuit for the magnet W32 and relay K30. Contact 3l6lc30 is accordingly opened, so that by the disconnection of magnet Dz'3 and the associated opening of contact 3 l'idz'3, relay Y30 is deenergized and the operating circuit for magnet W32 and relay K3 is again closed. This alternating play is repeated until the characterizing switching device has reached position l l. When this occurs relay H30 is operated over wiper m130 and contact 36111130, and hence contact 3Ih30 is opened which now breaks the impulse circuit for magnet D133 and connects relay Y30 directly in this impulse circuit. Relay K30 deenergizes on the opening of contact 3'l2h30. The auxiliary selector LWB@ is moved on further by means of impulses from the main exchange, but there the characterizing switching device does not move with it. The switching device LWB continues to be advanced until it reaches position I7. In this position earth is connected to the lead a2 over wiper a2 of the switching device LW30. Thus relay U32 is energized in the following circuit: earth, wiper a2 of switching device LW3 in position I l, winding I of relay U32, lead a2 of the connecting line, contact 344h30, resistance Wilt), battery, earth. By the opening of contact 302u32 the switching magnet W32 is disconnected and also the circuit of relay K30 is broken. The current is cut oi from relay Y3l by the opening of contact 3l6k30 so that this relay opens contact 36?@130 and deenergizes relay H30. Contact 3llllh30 is opened and the energizing circuit of relay U32 described above is broken down. Contact 302u32 again closes the operating circuit for magnet W32 and relay K30, so that selector LW30 in the subsidiary exchange advances one step and likewise the magnet Di30 energized over contact 3l6lc30 advances the characterizing switching device in the main exchange by one step. Accordingly both switching devices accomplish the last step into the normal position together. In the position 0 of wiper @i130 relay E30 remains energized over contacts 36471.30 and 335e30 until, since relay Y30 is energized over contact 3lldi30 through the last switching step, relay H30 is again energized over: earth, wiper m130 in position contacts 335e30, 3585c3, 361y3, relay H3, battery, earth. By the opening of contact 36llh30 the locking circuit for relay E30 is broken and this relay therefore deenergizes. Relay H30 holds up, after the opening of contact 365630 over contact 3Ilh3. After contact 3lldi3 has opened relay Y30 again deenergizes. By the closing of contact 339630 relay KSB is furthermore again connected to the bl lead of the connecting line and also preparation is made for switching in the magnet D30 of the switching device in the main exchange in the impulse circut already descrbed, over contact 3l2e30. Thereupon only magnet W3l is operated in series with relay K30. The latter causes relay Y30 to energize over contact 3l67c30, so that this opens the energizing circuit of magnet W3I by opening contact 342y30. By the alternate play of these relays the switching magnet is influenced until the selector DB30 reaches position I1. In this position the following circuit is set up: earth wiper al of selector DB30 in position l'l, winding I of relay USI, lead all of the connecting line, contacts 35c30, 34l8an30, 3451-30, 344h30, resistance Wz'lS, battery, earth. Relay U3l energizes and by opening contact 309u3l disconnects the magnet W3l. Relays K30 and Y30 then also release so that now relay H30 is deenergized by the opening of contact 361v30. Through the closing of contact 3|4h3 the switching magnet D30 in the main exchange is connected up while the energizing circuit just described for relay U3! is broken down at contact 3llh3. The operating circuit for magnet W3! and relay KSB is accordingly closed again at contact 39u3l. The selector DB30 is thus Vadvanced one step and moves into the normal position. At the same time magnet D30 is also inuenced by the closing of contact 3l6h30 so that the switching device in the main exchange similarly makes one switching step which takes it into the normal position. Since the wiper dIV30 of this switching device has now left contact segments I-ll further advancement of the switching device is not possible. All the devices both in the subsidiary and also in the main exchange are now again in the normal position.

Incoming trafic If a subscriber of the subsidiary exchange, for example A2 is called from the main exchange a iinal selector, which is not shown, is set by the corresponding numerical selection. If the connecting line leading to the subsidiary exchange is already seized the wiper dI3! is not in the normal position, so that the final selector cannot test over the c-lead (c2) corresponding to the desired subscriber. The wiper (Z130 remains away from the normal position as long as any of the switching devices of the connecting line either in the main exchange or in the subsidiary exchange are displaced from the normal position. Seizing the connecting line over a nal selector is only possible when all these switching devices have reached the normal position. In the present case the final selector tests over the lead c2 corresponding to the subscriber A2. The circuit passes over resistance Wz'20, contact 358111130, relay A1130, wiper 11133 in position 0, Contact 360an30, resistance Wz22, battery, earth. Relay An3 energizes in this circuit and locks up independently of wiper dI30 over contact 35.911.113. At contact 3480.713() battery is disconnected from the al lead of the connecting line, so that no seizure of the connecting line can take place from the subsidiary exchange. At contact 333an30 battery is connected to lead bl of the connecting line through relay K30. The following circuit is thus set up: earth, magnet W3l, contact 39u3l, lead bil of the connecting line, contacts 335030, 335an30, 339630, 3423/30, relay KSB, battery, earth. By the alternate play between magnet W3! and the magnet D30 in the main exchange operated by relays K30 or Y30 (as described in the case of outgoing traiic), the selector DB30 in the subsidiary exchange is now advanced synchronously with the switching device in the main exchange operated by magnet D3. This -advancement is continued until the wiper 1130 has reached the lead c2 seized by the final selector. At this moment the selector DB30 has also reached the second contact, to which subscriber A2 is connected. When this occurs relay C3 tests over contact 36|cm30 and by opening contact 335030 prevents both the switching devices mentioned from being further advanced. At contacts 334030 and 349030 the speaking leads of the connecting line are switched over on to the speaking leads of the final selector. Relay An30 now holds up over contact 351030. Ringing current can now be sent from the final selector, which is not shown, to the desired subscriber A2 of the subsidiary exchange in the known way. When the desired subscriber replies the ringing current is disconnected in the final selector in any manner with which we are not now concerned. Relay U3l is operated over the subscribers loop by the feeding current connected in the nal selector, so that the bl lead of the connecting line is switched through at contact 308u3l, and magnet W3| is disconnected at contact 30911.3l. The subscriber A2 is now connected to the final selector of the main exchange just as a normal subscriber having an individual line.

When the conversation has finished the c2 lead is disconnected in the iinal selector, relay C30 being thus deenergized. Contacts 334030 and 349030 open and break the circuit for the feeding current, so that relay U3| deenergizes. One effect of this is that the operating circuit for magnet W3! and relay K30 is closed through the closing of contact 309u3l. Through the alternate play of the corresponding relays the selector DB30 in the subsidiary exchange is advanced synchronously with the switching device in the main exchange. Thus, in the same way as was explained in the case of outgoing traino, the selector in the subsidiary station is iirst advanced synchronously with the switching device in the main exchange until position Il is reached. Then it is moved on as far as position I1 alone by means of impulses from the main station, whereupon it completes the final step into the normal position together with the switching device of the main exchange. During the release motion of the switching devices seizing cannot take place again until the two switching devices have returned to the normal position, since, in the case of an incoming call, relay X30 which takes up the initiation of a call is otherwise not energized.

Internal calls Seizing of the connecting line leading to the main exchange by the calling subscriber attached to the subsidiary exchange takes place in the same Way as has already been described in the case of outgoing traic. While in the case of outgoing traiiic (exchange calls) the subscriber had to dial the characterizing digit 1, in the case of internal calls he must now dial the number which the desired subscriber has for internal calls, immediately. Since the digit 1 is employed for outgoing traffic, the internal numbers of the subscribers are limited to the numbers 2 to 10. Thus in this case 9 subscribers can be attached to the subsidiary exchange.

As described above, relays J30 and V30 are energized during the dialling, while relay P30 is intermittently deenergized by the impulses, so that if for example, the calling subscriber A2 desires a connection to subscriber A3 and accordingly dials the digit 3, magnet W32 receives three impulses over the lead b2 and contacts 314730 and 3152330 (impulse contact). The auxiliary selector LW30 is thus set on the third contact. The characterizing switching device is advanced synchronously by its magnet Di30 to the third contact. After the dialling relay V30 is deenergized,

relay Z30 is influenced over: earth, battery, relay Z30, contact 3661230, wiper diI30 in position 3, earth. Since the impulse contact 3541730 in the main exchange loop is shunted during the dialling, by contact 355:1'30, the connecting devices of the main exchange are not set. By the opening of contact 356230 the preselecting device in the main exchange is now no longer seized. Since relay J 30 remains energized over: earth, contacts 32y30, 322730, 32|p3l, wiper dz'III30, relay J30, battery, earth, relay R30 is operated over: earth, battery, relay R30, contacts 3697'30, 3'l0z30, 3 seconds switch. Subscriber A3 is called by ringing current transmitted from the main exchange: ringing current source, contacts 3301'30, 332230, 3331330, lead a2 of the connecting line, winding I of relay U32, wiper a2 of the auxiliary selector LW30 in position 3, subscriber A3, wiper b2 of the auxiliary selector LW30 in position 3, winding II of relay U32, contact 303u32, earth. Since relay R30 is iniiuenced over a 3 second switch ringing current is transmitted to the desired subscriber every 3 seconds. The calling subscriber receives part of this ringing current as a free signal over contact 3l0r30.

If the desired subscriber replies within a pause in the ringing i. e. at a moment when relay R30 is deenergized the following circuit is set up: earth, contact 303u32, Winding II of relay U32, wiper b2 of the auxiliary selector LW30 in position 3, subscriber A3, wiper a2 of the auxiliaiy selector LW30 in position 3, winding I of relay U32, lead a2 of the connecting line, contacts 3331130, 332230, 33h-30, winding I of relay P3l, battery, earth. In this circuit relays P3 I and U32 energize. Since contact 303u32 is opened on the energizing of relay U32, the earth necessary for holding relays U32 and P3| energized is connected through contact 3| |p3l and winding II of relay P 3 l, after the lead b2 of the connecting line has been switched through. Meanwhile relay J 30 is deenergized by the opening of contact 32lp3| and relay R30 is deenergized by the opening of contact 3697'30, so that further transmission of ringing current is prevented. The feeding current for both subscribers is supplied from the main exchange. For Subscriber A2 the circuit runs from the battery connected to lead al and relay P30, to the earth connected through the choke coil Dr3l and lead bl, while for subscriber A3 current is fed from.

the battery connected through winding I of relay P3| to lead a2 of the connecting line, to the earth connected through winding II of relay P3l to lead b2.

Metering of internal calls takes place by the meter SM2 of the calling subscriber A2, connected vthrough the switching device of the main exchange (wiper dII30) being iniiuenced over contacts 362230, 3237'30, 3201/30, and earth.

On the termination of the conversation, when the calling subscriber replaces his receiver relays P30 and U3I deenergize. Contact 3|3p30 opens and the relay Y30 is thus deenergized, while by the opening of contact 3331730 relay P3| is deenergized. By the closing of contact 342y30 battery is connected to the bil lead of the connecting line over relay K30, so that the magnet W3| of selector DB30 in the subsidiary exchange is energized. By the alternate play which has already been described above, the selector of the subsidiary exchange `is advanced synchronously with the switching devices of the main exchange so that both switching devices are stepped round as far as position H. In position ll relay E30 again energizes and causes the auxiliary selector LW30 in the subsidiary exchange to be advanced in the manner already described, under the influence of the corresponding magnet W32. The characterizing switching device is switched on together with this selector. When these two switching devices reach the normal position by the switching operations described above, the selector DB33 of the subsidiary exchange is moved on automatically under the control of relays K3@ and YS@ in the main exchange until it reaches position li, It then completes the final switching step into the normal position together with the switching device in the main exchange.

This short description of the release motion should sufiice, since a detailed description has already been given of the release in the case of an outgoing call.

If the called subscriber of an internal call does not reply, relay P33 releases when the callingr subscriber replaces his receiver, while relay J3i) is only released after the release of relay Y33. Accordingly the earth is disconnected from the metering circuit by contact 3231/3@ before contact 353233 closes so that in this case metering does not take place.

Special circuits If selector DB3() in the subsidiary exchange is displaced from the normal position by hand, earth is connected over contact 33h03! to lead a2 over wiper a2 of the auxiliary selector LWSD, so that relay X30 is energized in the main exchange and locks up over contact 3333633. Battery is connected to the bil lead over contact 33111230 and thus the magnet WSI in the subsidiary exchange is iniiuenced in series with relay K3 in the main exchange. The selector DB3!) is now held until magnet D33 in the main exchange has been switched on through the closing of contact 3l3k3 whereupon both switching devices are advanced synchronously as in the case of a subscribers call, until they reach position Il. In this position relay E33 energizes, as in the case above, and causes the auxiliary selector IiW30 in the subsidiary exchange and the characterizing selector (rotary magnet Di) to advance synchronously to position il, whereupon the auxiliary selector continues to advance alone into position il in precisely the same way as in the case of the release of an outgoing call, the last step into the normal position being executed together with the characterizing switching device. After this selector DB3@ is advanced into position i'i and then iinally into the normal position the last step being made together with the switching device or" the main exchange, if the magnet W32 of the auxiliary selector is displaced from the normal position by hand, Contact 30511232 (l-l'l.) connects earth over the wiper ai of the selector DB3@ to the ai lead of the connecting line, sothat relay X33 is again influenced. In a manner corresponding to that above, selector DB3!) and the switching device in the main exchange which is operated by magnet D33, are again advanced, whereupon after reaching position l l, the magnet W32 of auxiliary selector LW33 is influenced synchronously with the characterizing switching device Di33. The release motion thus takes the same course as is described above. If both selectors in the subsidiary exchange are displaced from the normal position simultaneously, then since contacts 3 and l are connected together in the auxiliary selector, earth is connected to the a2 lead of the connecting line over contact 33lw3|l so that again relay X3!) is operated and the release motion described above takes place.

If the switching device in the main exchange which is operated by magnet D33 is displaced from the normal position by hand, battery is connected to lead bl over wiper dIV3D, and hence the selector DB3 in the subsidiary exchange and the switching device in the main exchange are advanced by the known interaction. All other operations take place as above. In contrast with the movements described above, the connecting line cannot be seized during this return motion, because relay X33, which prepares a circuit for the testing relay P30, is not energized. If the characterizing switching device which is operated by magnet D233 is displaced by hand from the normal position, relay E30 energizes over wiper diIV3ii, and through contact 338633 completes a circuit for magnet W32 in the subsidiary exchange and relay K3@ in the main exchange, so that now the characterizing switching device in the main exchange and the auxiliary selector LWS@ in the subsidiary exchange are advanced synchronously by the interaction as above. If, for example, at this moment seizing takes place on the part of the final selector in the main exchange, relays An3 and C30 can be energized but the selector DB33 in the subsidiary exchange can only be set when the characterizing selector D233 is in the normal position, so that relay E33 releases and by closing contact 339630 connects battery to the bil lead of the connecting line. Each seizure is indicated by the lighting up of the seizing lamp L Seizing can also be recorded. If seizing in the incoming and outgoing directions is to be recorded separately the contacts 372MB and 37 Ian3il can be led separately to a recording device.

In Figures 3, 4, and 5, a modified system with main and subsidiary exchanges is illustrated as an embodiment of the invention, Fig. 3 showing the devices arranged in the subsidiary exchange, and Figs. 4 and 5 those in the main exchange. The switching arrangements of the system enable the establishment of outgoing and incoming calls (exchange calls) and also of internal calls. In order to be able to set up these calls, in addition to the selector DB4@ which serves as a call nder for outgoing calls and as a nal selector for incoming calls, an auxiliary selector LWM] is provided in the subsidiary exchange which is used as a final selector on setting up internal calls. This selector is in connection with the main exchange over a special connecting line and is there connected to the connecting line seized by the calling subscriber when an internal call is set up. The differentiation between outgoing calls (exchange calls) and internal calls results from dialling special characterizing numbers which so operate a characterizing switch in the main exchange that this switch is operated from the normal position by each impulse train.

Outgoing trame X/Vhen the subscriber Al removes his receiver and operates key Bil the following circuit is set up: earth, key Bl, wiper al of selector DBM), winding I of relay UM, lead al of the connecting line, contacts M5033, lilgan, 502x453, winding I of relay X36, wiper dII in position 0, resistance Wi3l, battery, earth. Relay X4!! locks up over its contact 392x453. By closing contact 4|840 the following circuit is completed: earth, magnet W38, contact 334ml, lead bl, contacts 4I3c40, liix, 33h43, 336mm, relay KM), battery, earth.

In this circuit the magnet W4! and relay K40 energize. The selector in the subsidiary exchange thus makes one switching step. By the closing of contact 4401c40 magnet D40 (wipers 1140- dIV40) is also operated so that the selector in the subsidiary exchange and the switching device in the main exchange take one switching step synchronously. Relay Y40 is switched on over contact 444d40 of magnet D40 and interrupts at contact 4361/40 the energizing circuit for magnet W4! passing over the b-lead. Moreover relay K40 is also deenergized, so that by opening contact 4407c40 magnet D40 is also deenergized. By the opening of contact 4440140 relay Y40 is deenergized and thus a new energizing circuit is set up for magnet W4! in the subsidiary exchange. Through the reenergizing of relay K40 magnet D40 is also now energized once more. The mutual interaction continues until the calling subscriber is reached through selector DB40 in the subsidiary exchange. Since in the present case the calling subscriber is connected to the first contact, both the switching devices are only advanced one step. By the energizing of relay Y40 which occurs after each switching step relay P40 is connected each time to lead al, so that on reaching the calling subscriber the following circuit is set up: earth, battery, relay P40, contacts 5041/40, 503x140, 4l0cm40, M5040, lead al of the connecting line, winding I of relay U4l, wiper al of selector DB40 in position I, subscriber Al, wiper bl of selector DB40 in position I, winding II of relay U4l, contacts 40211.41, 4001042 (I-|'!) earth. By closing its contact 4372340 relay P40 holds relay Y40 energized so that no further iniluencing of the switching device can occur. In the testing circuit described above relay U4! also energizes in the subsidiary exchange and at contact 403u4| switches through the connecting line to the main exchange, while through opening Contact 404u4| magnet W4l is disconnected. By the closing of contact 4561040 relay J40 is energized. By the closing of contact 422x230 the loop to the connecting devices in the main exchange is closed thus causing a connecting device to be seized by a pre-selector as in the case of an individual subscribers call. When the calling subscriber receives dialling tone he can begin to dial.

On operating the dial, relay P40 in the main exchange, which serves as a testing relay in setting selector DB40, is deenergized according to the impulses, whereupon the impulses are transmitted to the connecting devices of the main exchange through Contact 422fo40. On the rst deenergizing of relay P40 relay V40 is energized over contact 40h24!) and holds up during the impulse train since it is a slow acting relay. The choke coil Dr42 is short circuited by the closing of contact 4202140 so that by the simultaneous disconnection of the condensers in the speaking leads by the opening of contacts M6040 and 42|v40 the impulse emission is maintained free from distortion. It should be noticed that throughout the emission of the impulses relay U41 in the subsidiary exchange and relay Y40 in the main exchange are kept energized.

Until it has been established that an outgoing call is proceeding the characterizing switching device (wipers dz'I40-dzIV40) operated by the magnet D is operated in step with the setting of the connecting devices in the main exchange, magnet D140, since during the impulse emission relay J40 is kept energized over contact 4461240, being operated over the following circuit: earth,

battery, switching magnet Dz'40, contacts 459540, 450240, 4511740, 4553140, earth. If now, for example, the digit first dialled is different from the internal characterizing digit, relay V40 deenergizes and opens contact 4451140 thus deenergizing relay J 40, so that now relay F40 is operated over` wiper cizIV40 (earth, battery, relay F40, contacts 464ML 465740, wiper dz'IV40 (I-l l), earth). Contact 445140 prevents relay J 40 being operated again when the next impulse train is transmitted, so that the characerizing switching device is brought to rest.

The further impulses are extended in a similar way from relay P40 through contact 422p40 to the connecting devices in the main exchange, but now the characterizing switch in the main exchange is no longer influenced. After setting the connecting devices the desired subscriber may be rung by any desired means, with which We are not concerned, and conversation thus established.

On terminating the conversation a metering impulse is transmitted to the meter of the calling subscriber, which is connected up in the main exchange through wiper dII40 of the switching device in the main exchange which is moved synchronously with the selector DB40 in the subsidiary exchange when the latter is set. During the metering impulse occurring over the c-lead the connection is maintained, even when the calling subscriber replaces his receiver, in that relay Yliil which is connected in the c-lead is maintained energized over its winding II during the metering. The circuit flowing over the c-lead is only broken after the metering has been completed. It may be broken in any desired way. Relay Y40 thus can dcenergize, and after the receiver has been replaced at the calling station, which causes relay U4! to deenergize and hence inter alia contact 40411.11! to be closed, the follow ing circuit, serving to advance selector DB40 in the subsidiary exchange, is closed by the closing of contact 4301/40: earth, magnet W4, contact fliufll, lead bl of the connecting line, contact M3640, wiper dIV40 in positions l-l I, contacts 432e40, 436y40, relay K40, battery, earth. Selector DB40 in the subsidiary exchange makes one switching step and by the closing of contact 4407640 the magnet D40 in the main exchange is operated so that this switching device is also advanced one step. As in the case of setting up the connection of the calling subscriber with the main exchange, the switching device in the main exchange controls the switching device in the subsidiary exchange. Both advance to position l i under the inuence of relays K40 and Y40. In this position relay E40 is operated over wiper CZIII40 and contact 4'l5m40. By closing contact 43le40 relay E40 is connected to lead b2, it being disconnected from lead b! by the opening of contact 432840. By the opening of contact 430640 the magnet D40 is disconnected from the automatic impulse circuit, and the magnet D140 of the characterizing switching device is connected to the latter by the closing of contact 43Se40. The magnet W42 of the auxiliary selector LW40 is now energized over lead b2, whereupon relay K40 is influenced simultaneously in the main exchange. The magnet Di40 thus receives an impulse over contact 440Ic40 so that by closing contact 443dz'40 relay i740 is energized and the advancing circuit for the auxiliary selector LW40 in the subsidiary exchange is again opened at Contact 4361/40. By this interaction both switching devices are advanced synchronously to position l l. In this position relay I-Ili is now energized over: earth, wiper dzIflii in position l I, contact l'GyGG, relay H6, battery, earth. By the opening of contact iitii winding I of relay Xliil is disconnected, and by the opening of contact Mlh d the magnet Did@ o1 the characterizing switch is disconnected from the automatic impulse circuit. The magnet W52 in the subsidiary exchange is now operated alone, without the magnet Dill@ in the main exchange being operated, through the reciprocal play oi relays Kll and Yl, in a corresponding way, until the wiper a2 in the subsidiary exchange reaches position il. In this position earth is connected to the a2 lead, so that the following circuit is set up: earth, wiper al? of auxiliary selector' LWli in position il, winding I ci relay Ut?, lead cl2 of the connecting line, Contact 555MB, resistance Wz'i, battery, earth. Relay UiZ energizes and disconnects the magnet lli/'ft2 at contact lilluil. This is associated with the deenergizing of relays Kliil and Ydll, so that by the opening of contact ilyiil relay I-Ilii is deenergized. By the opening of contact 5ii5h winding I of relay ULI? is deenergized, and by the closing of Contact lil-film@ the magnet Did!! of the characterizing switch is again connected to the circuit which is inuenced by contact dfllc. The magnet Wfl? connected over contact lllluZ is now operated, as is also the magnet by Way of relay Kdo, so that both switching devices make one switching step and thus move together into the normal position. Through relay Ylld, which is operated after the switching step over contact lififdilil, relay is again operated after the switching step has been taken over the circuit: earth, wiper d'iIi? in position B, contacts ltlileli, liillil, lilxflil, relay Hilo, battery, earth. The locking circuit is then completed over: earth, contacts EiEhilB, llyllil, relay HMI, battery, earth. By the opening of contact li'ihfid relay Eil@ is deenergized so that by contact figell the magnet Dit@ is disconnected and thus the connection of magnet Dlii) is prepared at contact 533655. Then after the deenergizing of relay Yll@ on account of the opening of contact liiiiikll selector D213@ in the subsidiary exchange is advanced into position il, in that magnet Ei is energized in series with relay Kill) over: earth, magnet W contact diltul, lead bl, contact lcllp wiper tZIVi, contacts diedl, 235269, relay Kl, battery, earth. Relay K4@ again operates relay over contact dribble?, so that by the opening of contact lifyl@ both relay K/il and the magnet W-'li are deenergized.

lirough this interaction the selector DBM is thus advanced to position il. In this position earth is connected to lead (1,! over wiper ai, so that relay Ulli encrgizes over this lead and by opening contact cifilllli deenergizes the magnet Will and relay Kitt. On account of contact dliikt? eing held open is deenergized and hence also relay HG@ (contact Vital-'5). By the closing or" contact magnet Dil@ is ccnnected to the automatic impulse circtut. Meanwhile relay Uii is again deenergized by the opening of contact Silhiii so that over the bl lead the selector DEfi in the subsidiary exchange takes the last switching step together with the switching device, which is operated by magnet DSE. Since wiper dIViil has now left the segment i-l i, further advancement is prevented. Only now can a new seizure of the connecting line take place.

Incoming traffic If a connection with a subscriber of the subsidiary exchange is desired from the main exchange, seizure of a connecting line leading to the subsidiary exchange by a iinal selector of the rnain exchange over the testing lead (ci, 2 etc.) corresponding to the desired subscriber is only possible when Wiper dIli is in the normal position. In this case the nal selector tests, assuming that subscriber A! is wanted, over the test lead ci, resistance Wz'l, contact ilcl-lll, relay Andi?, wiper dIiil in position contact rlfiianllii, resistance Wide, battery, earth. Relay Anw energizes in this circuit and by closing contact M30/,nfl locks up independently of wiper (ZIM). By the opening of contact tisana@ battery is disconnected from the ci lead so that a seizure of the connecting line on the part of the subsidiary exchange is prevented. Relay K4!) is connected to the bl lead of the connecting line at contact Haude and hence the following circuit is set up: earth, magnet Wfii in the subsidiary exchange, Contact @dai/d, lead bl, contacts M304, Hlm/sdb, 4329MB, @36e/llt, relay Kilo, battery, earth. Magnet Wfil and relay Kli are energized in this circuit. By the interaction, as has already been described in the case o1" outgoing traic, a synchronous advancement of the selector DBlil by magnet WVM in the subsidiary exchange, with the switching device in the main exchange by magnet D12-ii which is operated over contact llioit, is eiected. Both switching devices are advanced until relay Clil, which is connected to wiper dIfl@ over contact llzmllll, reaches the test lead ci seized by the nal selector. In the case considered this happens after the rst switching step. By the energizing of relay CM) a further operation of magnet WM is prevented by the opening oi contact M304, and hence also, since relay K4@ cannot energia-o again, magnet Dl in the main exchange is prevented from being iniluenced. Leads al and bi are switched over onto the speaking leads of the nal selector by the closing of contacts lilclii and ilillc'll. Relay Anil is locked up, by the closing of contact @59046, over the following circuit: earth, resistance Wiil, Contact liti-lelie, relay Anw, Contact li'iamliil, resistance W, battery, earth. The

ringing current for calling the desired subscriber may be transmitted from the final selector of the main exchange in any desired manner. When the desired subscriber replies relay Ui!! energizes over the leads ai and bl and the potential at the nal selector, and switches the bl lead through over contact Ringing current is cut oir in the known way. The desired subscriber is now connected to the final selector of the main exchange just as a normal individual subscriber.

When the conversation has finished the cl lead is cut off from the final selector in any desired way, so that relay Clil deenergizes. By opening contact @Nol-i3 relay Andi) is also deenergized. In the subsidiary exchange relay Ufsi is deenergized so that the magnet Wii is again connected to bl lead oi the connecting line over contact Milla-ll. The return of the switching devices to the normal position now takes place in the same way as has been described in the case of the release of outgoing traffic.

Internal calls The seizure of the connecting line leading to the main exchange by the calling subscriber Al is accomplished in the same way as has been described for outgoing traiiic. In order to reach a subscriber attached to the same subsidiary exchange the subscriber A! must dial the complete normal number of this subscriber. In the present example the number 2,419,572 is chosen as the number of the desired subscriber A2. As mentioned above, after connecting the calling subscriber A! to the connecting line by the energized relay P40, relay J40 is energized over contact 4561140, wiper d1`III40 in position 0 and Contact 45511140, and holds up during the individual impulses over contact 4561140 of relay V40 which is energized during the impulses.

Subscriber A! thus first sends out two impulses, and hence by the operation of the corresponding contacts of relay P40, which previously operated as testing relay, magnet D140 (impulse Contact 4511140) is energized twice and yaccordingly advances the corresponding switching device by two switching steps while the seized connecting device of the main exchange likewise receives two impulses through contact 4221040. When relay V40 deenergizes at the end of the impulse train, relay J 40 holds up over: earth, battery, relay J 40, contact 445;'40, wiper diIII40 in position 2, contacts 5017142, 4537143, 4527144, winding I of relay H4l, earth. In this circuit H4! energizes and operates relay F40 over contact 403714! and also locks up over its winding II by closing contact 466714I. By the closing of contact 402140 magnet D140 receives an impulse, so that the characterizing switch takes one switching step. Hereupon magnet Di40 opens its contact 46Id1'40 so that relay F40 deenergizes. After the switching step has been taken and magnet D140 is again deenergized by the opening of contact 452140 so that contact 46 Id1'40 is again closed, relay F40 is again operated and causes the characterizing switch to be advanced again. This stepping is continued until the characterizing switch has reached the zero position, since in this case wiper diIV40 has left the contact segment !-!I and hence relay H4! is deenergized. Relay F40 is prevented from energizing by the opening of contact 4037141. In the zero position of the characterizing switch relay J40 again energizes over wiper (1111140. This operation just described occurs during the pause between two impulse trains. It may also be mentioned that in position I I of wiper 4111140, during the advancement of the characterizing switch, relay H42 is operated and locks up over contacts 4847142, 489p4! and 4901/40. Thus after the return of wiper 0711140 to position 0, relay U40 is operated over contact 5007142, and is held in a locking circuit independently of wiper 11H40 by closing contact 491u40.

By dialling the second digit 4 the characterizing switch is brought to position 4. After the opening of contact 440114 relay J40 holds up over: earth, battery, relay .140, contact 445140, wiper diIII40 in position 4, contacts 5057142, 4537143, 4527144, winding I of relay Hdl, earth. Relay H4! energizes in this circuit, locks up over contact 466714! and, as has been described above, causes the operation of the magnet D140 of the characterizing switch. This is then brought to the normal position by the alternate operation of relay F40. When wiper dz'II40 again comes to position relay H43 is operated over: earth, battery, relay H43, contacts 4817144, 5l4u40, wiper diII40 in position earth. By the closing of contact 4887143 relay H43 locks up. Relay U40 is deenergized by the opening of contact 50|7143.

When the 'calling subscriber dials the third digit which consists of one impulse, the characterizing switch stands on the iirst contact after the train has passed. The following circuit is set up: earth, battery, relay J40, contact 445140, wiper d1'III40 in position I, contacts 4547143, 4527144, winding I of relay H4!, earth. By the energizing of relay H4! relay F40 is again operated and brings the characterizing switch into the zero position again. During this motion, when wiper (11H40 is in position relay H44 is operated over: earth, battery, relay H44, contacts 4827143, 5! |7145, 5081140, wiper d1'II40 in position earth. By closing contact H44 relay H44 completes a locking circuit for itself independent of wiper d1II40. In position 0 relay U40 is again operated over contacts 4097144, 40071.45 and wiper 6711140 in position 0 and locks up over contact 491u40.

In a similar manner, through the fourth impulse train (9 impulses), after relay H4! has been operated on the 9th step, relay H45 is energized on the advancement of the characterizing switch into the normal position, by relay F40 in position ii, the circuit being: earth, battery, relay H45, contacts 4807144, 5011140, wiper :11H40 in position ll, earth. By the opening of Contact 4987145 relay U40 is deenergized. The characterizing switch has again reached position 0.

After the fifth digit has been dialled, which consists ci ve impulses the characterizing switch stands on the fth contact, so that after relay H4! has energized in this switch position, relay F40 is again energized and the characterizing switch is returned to` the zero position. During this motion relay H46 is energized over wiper 0111140 in the following circuit: earth, wiper (11H40 in position ll, contacts 5081140, 5007145, relay H45, battery, earth. By closing contact 4807146 this relay locks up. Meanwhile the characterizing switch reaches the zero position. After the dialling of the sixth digit which consists of seven impulses and hence moves the characterizing switch round seven steps so that its wiper reaches position seven, relay Z40 is operated over: earth, battery, relay J40, contact 445140, wiper diIII40 in position 1, contact 441h46, winding I of relay Z40, earth. By closing contact 408240 relay Z40 locks up over its winding II. By the opening of contact 458.240 further influencing of the characterizing switch by numerical impulses is prevented. Moreover it cannot be brought back to the normal position since relay H4! is not operated.

When the calling subscriber dials the last digit, in the present case the digit 2, since contact 420240 is now closed this is transmitted, with the help of contact 4281140 to magnet W42 over lead b2 and thus the auxiliary selector LW40 in the subsidiary exchange is set on the contact of the desired subscriber. The transmission of this impulse train to the connecting devices in the main exchange is preventedin that contact 423240 has opened the impulse circuit and moreover has thereby released the connecting devices in the main exchange. Relay R40 is brought under the iniiuence of a switching device over contacts 400240 and 485140 every three seconds, and is thereby energized, so that every three seconds ringing current is transmitted to the desired subscriber over lead Ax12 by the closing of contact 425140. of this ringing current over contact 5!0r40 as an indication that the line is free.

When the called subscriber replies, relay P4! energizes in the ringing pause over: earth, battery, resistance W2'28, contacts 420240, 4211240,

The calling subscriber receives a portion F winding I of relay PM contact li2rllil, lead a2 of the connecting line, winding I oi relay U42, wiper a2 of the auxiliary selector LWllil in position 2, subscriber A2, wiper b2 oi the auxiliary selector in position 2, winding II of relay U42, contact lllutil, earth. Through relay Pill relays H42 to H46 are deenergized on account of the opening of contact flplli, so that by the opening of contact ll'lhfl relay Jill] is also deenergized. Accordingly relay Ri cannot be further energized over Contact figiy'fi, so that the transmission of ringing current is interrupted. In the circuit closed when the desired subscriber replies relay Ull energizes as well as relay Pll and by closing contact letzt-42 switches lead b2 through to the main exchange. Both subscribers are connected together over contacts di lpfll and 2plll, and current is fed from the main exchange. For the calling subscriber the current passes over relay P4B and the choke coil Drill, and for the called subscriber over windings I and II ci relay Pill The internal call is metered in that the meter SM! connected over wiper dl@ corresponding to the movement of the switching device DBM in the subsidiary exchange, is energized over contacts 'llc, lilly'l and dyi@ on the reply ci the desired subscriber.

When, after ending the conversation, the calling subscriber replaces his receiver, relay Pi@ which is influenced over the subscribers loop deenergizes. Thereupon relays Yll and Z493 and also relay Pal are deenergized. Relays Uitl and U42 also deenergize. By the closing of contacts $351,113@ and lilfiutl the operating circuit for the magnet Wll in the subsidiary exchange and for relay Kil@ in the main exchange is closed, and thus the switching devices are released in a similar manner to that already described for the case of outgoing calls.

Had the desired subscriber not replied, relay Yli and then relay Ztl@ would have deenergized when the calling subscriber replaced his receiver before contact .5i-9671i@ had been closed by the deenergization of relay Jflfl, so that in this case no metering would have taken place.

Special circuits If the selector DB/i in the subsidiary exchange is displaced from the normal position by hand earth is connected to the a2 lead over contact 551ml and wiper a2 of the auxiliary selector LWlil in position il, and hence relay Xie is energized in the main exchange, so that, as in the case of a subscribers call. an Operating circuit is completed over contact lixlll for magnet Wll in the subsidiary exchange and for relay Keil in the main exchange. The selector DB4@ in the subsidiary exchange is prevented from being released, by magnet Will being held energized in this circuit until relay Kll also iniiuences magnet DM! in the normal way and so also advances this switching device by one step. Relay Yli! is then again cut off from the operating circuit as in the case of setting up an outgoing call, so that the selector in the subsidiary exchange and the switching device in the main exchange are then advanced synchronously to position ll. In this position, as in the release motion for outgoing traiiic, the magnet W42 is operated and brings selector LWLlii to the zero position with the characterizing switch Dite, whereupon selectorDBil is advanced to position il independently and then moves to the zero position together with the switching device controlled by magnet D40.

If the auxiliary selector LWli is displaced from the zero position by hand, earth is connected over contact llw (I--l'l) to the zero position of wiper al of selector D Bilil, so that in this case, as in the case of a subscribers call, relay X40 is influenced in the main exchange. In this case also both switching devices rotate in the same Way as has been described for the case of release. In order to prevent a subscriber, on removing his receiver, from causing the seizure of the connecting line, which in the case of dialling an internal call must result in a wrong selection since the auxiliary switch LWQ@ is displaced, earth is cut off from contact lieti/.l by contact ililwllZ (I--ID so that the testing relay Pliil in the main exchange cannot test on the subscribers contact.

If both switching devices in the subsidiary exchange are displaced from the normal position by hand, earth is again connected to the a2 lead so as to energize relay X43, over contact ll'lul, since obviously relay Kil@ must be energized for every release oi the switching devices in the subsidiary exchange because otherwise no control of these can take place over the main exchange. In this case also the earth is disconnected through contact illwd (l--ll).

'Ihus as soon as the synchronism between the switching devices in the subsidiary exchange and the switching devices in the main exchange is destroyed, setting on a calling subscriber is no longer possible.

If the switching device in the main exchange operated by magnet Dd@ is displaced from the normal position by hand the operating circuit for magnet Wel and relay K135i over lead bl of the connecting line is completed over wiper dIVMl in positions l-l l, so that the switching devices return to the zero position as above described. Seizure of the connecting line by a subscriber who removes his receiver at this moment cannot occur because relay Xd@ is not energized and accordingly the testing relay Pil@ is not connected to lead al of the connecting line.

If on the other hand the characterizing switch is displaced from the zero position by hand, relay E45 energizes over wiper dz'IVll positions I-I I, and connects a negative potential to lead b2 of the connecting line through contact tlcll and relay Kflll, whereby magnet EQ2 is energized as Well as relay Klll. Both switching devices are then brought to the zero position synchronously, as described above. Since relay E4!! is energized during this motion, even if relay X is energized' due to a new call occurring during this motion, the selector DEQ@ in the subsidiary exchange can only be set after the return to the normal position, sincefor the moment contact 43294!) is still open.

In the main exchange each seizure of the connecting line can be indicated by the lighting of the seizing lamp L. They can also be recorded by a special device. If it is desired to record incoming and outgoing seizures separately the contacts @92321130 and lltcmd can each be connected separately to a recording device.

Having described the invention, what is consid'- ered to be new and is desired to be protected by Letters Patent will be set forth in the following claims.

What is claimed is:

l. In an automatic telephone system, a main and a subsidiary exchange, a pair of trunk lines extending between said exchanges, a selector switch in one of the trunk lines operated to establish calls between the subsidiary and the main exchange and also operated to prepare a connecting path for local calls between two subscribers in the subsidiary exchange, and another selector switch in the other of said trunk lines operated to complete said local calls over a path including both of said trunk lines.

2. In an automatic telephone system, a main and a subsidiary exchange, a pair of trunk lines connecting said exchanges together, a separate selector switch in each of said trunk lines at the subsidiary exchange, means for operating one of said selector switches to establish a call from the subsidiary to the main exchange over the trunk line associated with said selector switch, means for operating the other one of said selector switches to establish an internal call in the subsidiary exchange including the trunk line associated with said other selector switch, said flrst switch and its associated trunk line also operated to provide a connecting path for said local call.

3. In an automatic telephone system, a main and a subsidiary exchange, two trunk lines connecting said exchanges, a selector switch in each of said trunk lines at the subsidiary exchange, means for operating one of said switches for extending calls between said exchanges including only the trunk line associated with the selector switch, means for operating the other of said selector switches for extending calls local in the subsidiary exchange including the associated trunk line, said rst selector switch also operated to provide an outgoing path over its associated trunk line for the local calls.

4. In an automatic telephone system, a main and a subsidiary exchange, two trunk lines connecting said exchanges together, a selector switch at the subsidiary exchange in each of the trunk lines, means for extending calls between said exchanges over one of said trunk lines and its associated selector switch, and means for completing calls between calling and called subscribers in said subsidiary exchange over both of said trunk lines and both of said selector switches.

5. In an automatic telephone system, a main and a subsidiary exchange, two trunk lines connecting said exchanges together, a selector switch at the subsidiary exchange in each of said trunk lines, means for establishing calls between said exchanges over one of said trunk lines and its associated selector switch, means for establishing local calls in the subsidiary exchange over both of said trunk lines and both of said selector switches, and means in said main exchange for connecting said two trunk lines' together when a local called subscriber in the subsidiary exchange answers.

6. In an automatic telephone system as claimed in claim 4, switching means in said main exchange connected to said trunk lines, said switching means controlling the operation of both of said selector switches.

'7. In an automatic telephone system as claimed in claim 4, a driving magnet for each of said selector switches, and a single control relay for each of sai-d driving magnets connected in the associated trunk line.

8. In an automatic telephone system, a main and a subsidiary exchange, a pair of trunk lines extending over both of said selector switches and their associated trunk lines, and means controlled by said characterizing selector as determined by the impulses transmitted by a calling subsidiary subscriber for preparing the further extension of a call in the main exchange or for operating the selector switch in the other of said trunk lines to extend the call to another local subscriber in the subsidiary exchange.

9. In an automatic telephone system, a main and a subsidiary exchange, two trunk lines connecting said exchanges together, a selector switch in each trunk line at the subsidiary exchange, a characterizing selector at the main exchange associated with the first of said trunk lines, means controlled by a calling subsidiary subscriber for transmitting a particular seri-es of impulses over said rst trunk line to extend a call to another subscriber in the main exchange, means responsive to a -diierent series of impulses transmitted by the calling subscriber to extend a local call to another local subscriber in the subsidiary exchange including both of said trunk lines, said characterizing selector operated responsive to the inter-exchange call to control the further extension of the connection and responsive to a local call to control the selector switch in the second of said trunk lines, an impulse repeating contact in the circuit for further extending the interexchange call, and means for preventing the further extension of a call by short-circuiting said contact on local calls and removing the short circuit by transmitting a particular seri-es of impulses characterizing an inter-exchange call.

l0. In an automatic telephone system, a main and a subsidiary exchange, two trunk lines connecting said exchanges, a selector switch in each trunk line at the subsidiary exchange, a characterizing selector switch at the main exchange associated with the iirst of said trunk lines, means for establishing exchange calls from a subsidiary exchange subscriber to a subscriber in the main exchange over a connection including said rst trunk line and associated selector, means for establishing local calls from one subsidiary subscriber to another over a connection including both of said trunk lines and their associated selector switches, means controlled by said characterizing selector switch for determining whether the call is to be extended to a local subscriber or main exchange subscriber, the establishment of the local and exchange calls being controlled by the transmission of series of impulses from the calling subscriber, and an impulse relay in the main exchange controlled by the impulse series for completing the calls.

EDUARD WOCHINGER.

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