US2236798A - Telephone system - Google Patents

Description

April 1, 1941. w. KUSCHE TELEPHONE SYSTEM Filed Oct. 31, 1938 5 Sheets-Sheet l 0G 06 4 m L TELAG EQ MN QQQQQ Him ' INVENTOR: WALTER KUSCHE %Z @4 ATTQRNEY.

April 1, 1941. w. kuscHE TELEPHONE SYSTEM Filed Oct. 51, 1938 5 Sheets-Sheet 2 INVENTOR:

WA LTE R KUSCHE ATTORNEY.

April 1, 1941. w. KUSCHE TELEPHONE SYSTEM 5 Sheets-Sheet 5 Filed 001:. 31, 1938 INVENTOR: WALTER KUSCHE ATTORNEY.

April 1, 1941. w. KUSCHE TELEPHONE SYSTEM Filed Oct. 31, 1938 5 Sheets-Sheet 4 m bw MW DW INVENTOR:

WALTER KUSCHE 2% %ZM4 ATTORNEY.

3 8 1 3% m6 3mm P Q Haw ww Patented Apr. 1, 1941 TELEPHONE SYSTEM Walter Kusche, Berlin-Steglitz, Germany, assignor to Fides Gesellschaft fiir die Verwaltung' rind Verwertung von gewerblicheii Sch'utzrec'hten m. b. H., Berlin, Germany Application October 31, 1938, Serial No. 237,807 In Germany November 22, 1937 19 Claims.

The invention relates to a circuit arrangement for distance communication in particular telephone installations with party lines in which a selection is accomplished by impulses in alternative directions.

The invention concerns the doubling of the number of selectively callable branch sets in such systems without increasing the number of contacts on the selectors used at the branch sets. In order to accomplish this it is lmown to use a number of group selectors, and in this way in spite of the use of selectors with a small number of contacts, a large number of subscribers may be called. The present invention concerns an increase still further in the number of branch sets which can be called, in those cases in which the contact positions of the selector have already been used to their fullest extent. This is attained in that differential polarized receiving devices are provided at the branch sets according to the group, in such a way that the selectors controlled .by the receiving devices are alternately stepped on one after another by a selective operation at the branch sets of one group by a number of impulses in one direction (-1-) and at the branch sets of another group by a number of impulses in the other direction The arrangement according to the invention has the advantage over the arrangement in which the selector is stepped on by impulses in one or i the other direction only by means of the alternate use of impulses in both directions, that the positive control of the receiving relay is ensured. Relay selectors can be used at the branch sets equally with stepping mechanisms.

The arrangement can thereby be such that switch mechanisms are provided at the branch sets controlled by the polarizing relays only initiate the call to the desired branch set in dependence on the pause characterizing the desired branch set. This pause is, according to the invention, produced by an impulse setting the receiving relay in its operated position and terminated by an impulse setting the receiving relay in its normal position. In this way the receiving relays in the branch sets control the desired group characterizing relay which can come into effect in accordance with the setting of the associated selector on the characterizing contacts of the associated branch sets and prepare the call circuit. .On the other hand in the branch sets of the groups which are not required, whose selectors are also in their associated characterizing pauses, control switch means which prevent the characterizing relay from coming into eifect.

The characterizing relay is preferably connected in all branches on the initiating of each selecting operation and is only disconnected again to characterize the selected set and the disconnection of this characterizing relay is maintained until the end of the selector operation.

In order to initiate the call the call circuit prepared during the characterizing pausein the desired branch set, is closed during a further interruption of the impulse series actually by the setting of the selector on the call contact. This call contact is arranged differently at the selectors of the various groups since the selectors are set differently in the call pause corresponding to the alternate stepping on by positive or negative impulses. The call pause like the characterizing pause is thus initiated by an impulse setting the receiving devices the group of the desired set in their operated position and terminated by an impulse in the opposite direction. In this way at the branch sets in the groups which are not required the stepping on selector magnet is maintained connected over receiving relays which in these groups are in their normal positions.

In order to avoid complicated switching arrangements at the sending station each impulse series is arranged to begin always with an impulse in the opposite direction to the last. Each impulse series is begun with an impulse which is always in the same direction independently of the group which is to be selected and ended with an impulse in the opposite direction. In this way it is arranged that an impulse in one direction will always be succeeded by an impulse in the other direction, and this is particularly important in systems with inductively transferred rectified impulses. -Since at thetermination of each impulse series more impulses are sent out than are necessary to move the selector to its operated position, .a further effective control of the associated receiving relay by further impulse up to the end of the selector operation is prevented once the selectorhas reached its normal position. This result is obtained intha't when the zero position of the selector is reached the winding of the polarized relay in the opposite direction is connected which prevents an effective operation of the receiving relay on the receipt of further impulses up to the end of the selector operation.

In order to send the impulse in a positive and simple manner the impulse series together with the necessary characterizing and call pauses for the calling of a desired set are caused to be sent out automatically from the sending station in dependence on a selector controlled by a characterizing means in connection with control relays. The arrangement is preferably such that when the contact position characterizing a desired subscriber is reached switch means come into effect, which, by interrupting momentarily the stepping on circuit for the selector prevent the sending out of selector impulses while after the contact position has been reached characterizing the call position the selector is stepped on, but the sending out of selecting impulses is prevented. For characterizing the calling pause therefore no special switching devices are necessary, but the selector arranged in the sending station is used for the purpose andis stepped on as in the preceding operations whereby switch calling subscriber is determined by the pause bea tween the first impulse serving for seizing purposes and the next impulse bringing about the stepping on of the selector. Thus, time switches which are connected to all branch sets on all groups having the same operating periods, are preferably connected to all branch sets under the influence of a seizing impulse and on a succeeding long pause prepare the calling circuit at the branch sets which are characterized by such a pause while at the remaining branch sets the completion of the calling circuit for the selecting operations is prevented. This means that the time switches which for example can be slow relays, prepare the calling circuit at the branch set of one group (with longer characterizing pause) when they are operated and at the branch set of another group (with a short characterizing pause) when they are not operated.

The arrangement can be such that the time switches at the branch sets prepare a called circuit in dependence on the varying length of the pause connected in the selecting impulse series in order to difierentiate a selected subscriber. The time switches which are connected at all branch sets, on the initiating of the selector operation, are operated by the pause in the selector impulse series characterizing the desired set and by a longer pause are restored, and thus they prepare the calling circuit at the branch set of the desired group, while they prevent a call being made at a branch set of the remaining groups. Also, the time switches do not restore with shorter characterizing pauses, and thus they prepare the call at the set determined by a short characterizing pause while they prevent a call being made at the remaining branch set. The mass production of the switching devices is made easier if the time switches at all branch sets have the same operating period. It is then only necessary to arrange the contacts of the time switches in the called circuits at the branch set as operating contacts in one kind of group and back contacts in the other kind of group.

The sending out of selecting impulse series with the characterizing pause necessary for selecting the desired group is preferably brought about from a sending station automatically in dependence on the switch means controlled by the characterizing means so that for characterizing a calling set a group switch means determining its group is connected which controls the group characterizing pause. Time switches are then controlled by the group switch means which, only after they have come into effect, allow the chain of relays controlling the further course of operation of sending out the impulses, to take place.

In systems in which the selection is performed by rectified impulses transmitted inductively the time switches are preferably brought into effect in dependence of the duration of the pause between the first half wave of current in one direction serving for seizing purposes and the following half wave of current in the opposite direction serving to step on the selector. When in such systems for the purpose of simplification and for ensuring the control of the receiving devices each impulse series begins with an impulse in the same direction independently of the group of the subscriber to be selected, the operation of each of the relays controlling the sending out of the impulses is, according to the invention, momentarily interrupted in dependence of the group characterisation by the group characterizing switch means either at the sending out of the first or on the other hand only after the sending .out of the second impulses.

Further details of the invention are described in the following.

In the accompanying drawings, embodiments of the subject of the application are shown, to which however the application is not limited.

In Fig. l and 8 a diagram of the arrangement of the selecting impulse series for selecting subscribers of the individual groups, is indicated.

Fig. 2 shows the circuit arrangement of the central station sending out the selecting impulses.

Fig. 2a shows the circuit arrangement of a modified central station impulse sender, and

Figs. 3-7 a. diagram of the circuits at the branch sets to receive the selecting impulses.

The selection of the branch sets is performed in the embodiments from a central station, e. g. at an operators position by means of cord lines. Several such sending stations can be provided, however communication between the branch sets themselves is not cOnsidered but is possible in known manner.

In the accompanying drawings all that is not necessary for the understanding of the invention, details of branch sets and sending stations which are known, are not shown.

As an embodiment a system of 240 branches is chosen. When 36 part selectors are provided at the branch sets, the branch sets must be arranged in 8 groups. Thus in this way, in a simple manner, use is made of the invention described. Differentiation is at once made between the branch sets (groups I, III) whose polarized receiving relays are only operated by impulses in one direction (e. g. and branch sets (groups II. IV) whose polarized receiving relays are only operated by impulses in the other direction In each of these groups a further differentiation is undertaken according to the invention, in that branch sets of the groups I and II may only be called when the seizing impulse falls directly on the first stepping on impulse while in branch sets of groups III and IV the call can only take place when between these two first impulses a longer pause (group characterizing pause GP) is interposed which serves for the group characterization. (see Fig. 1). In this way it is possible to' reach 4 groups each containing 30 subscribers. Then according to the invention a further increase of the groups is obtained, in that for 4 further groups (V-VIII) which are otherwise constructed in the same way as groups I-IV, the characterizing pause is arranged to be particularly lon (see Fig. 8). Then at all branch sets according to the embodiments shown in Figures 3-6 the inclusion of a special time switch (N) is necessary (see Fig. '7).

When smaller selectors are to be used for branch sets it is possible by the insertion of the further group characterizing pause to increase the number of groups when decreasing the number of subscribers in the system.

The selection is performed by rectified impulses in alternate directions sent out over the party line. In this way it is possible to send out these rectified impulses either as induction impulses over the line,or to connect the rectified impulses of the particular direction directly to the line in the sending station. A diagram of the arrangement of the selecting impulse series for selecting subscribers of the four different groups is shown in Fig. 1; the impulses are indicated schematically. The selecting impulse series begin with a positive impulse in every case. In group I the polarized relay set to a positive impulse i immediately operated by the first seizing impulse sent out over the line and by the following negative impulse the stepping on or" the selector results. A pause is arranged in the selecting impulse series for characterizing the required subscriber after the sending out of the necessary number of impulses for setting the selector on the calling contact (individual characterizing pause EP, e. g. the subscriber T3 after the setting of the selector DM3 at step 3). The selecting impulse series which is continued at the end of the individual characterizing pause undergoes yet another interruption (calling pause RP) which is set according to the number of impulses (for groups I and III after contact 33 has been reached) which is the same for all sets. During this period the calling current is connected to the selected set. At the end of the calling pause the selector is moved on to its normal position. Details of the operations in the central station and in the receiving station are described in the following.

In branch sets of group II the polarized receiving relay, e. g. P33 is only operated by the first negative impulse as a seizing impulse. ping on of the selector at the branch sets of group II on to step i results therefore only on the second positive impulse which is on the party line. The individual characterizing pause and the call pause are provided in the corresponding way to this for the subscribers sets of group I but according to negative impulses.

Receiving devices of the branch sets of group III are operated by the first positive impulse in the same way as group I. Since, however, between the seizing impulse (positive) and the first stepping on impulse the long pause (group characterizing pause GP) is provided, then for the selection of the subscriber of group I a special time switch comes into effect, which in spite of the agreement in the setting of the selector, makes it possible to close the calling circuit only at the branch sets of this group III.

The selecting impulse series for selecting a branch set of group IV corresponds to that for The step-- one branch set of the party line.

the selection of the branch sets of group II with the only exception that between the seizing impulse (first negative impulse) and the first step.- ping on impulse (second positive impulse) a larger pause is arranged than in the case of the selection of the group II. Therefore, in the same way as for group III a special switching device characterizing group IV comes'into effect and makes it possible to make a call at the branch sets of this group.

The selecting impulse series for selecting the groups V-VIII corresponds to that of groups I-IV with the difference shown in Fig. 8 e. g. for group V the duration of the characterizing pause is greater than for the selection of the branch sets of group I.

I. SENDING DEVICES The sending device (Figs. 2 and 2a) consists of a key set of which one key is associated with In the embodiment only one sending device is shown for branch sets so that a subscriber of the groups I-IV may be called. For the subscribers of groups VI-VII corresponding group keys are added which ensure operation in a manner which is not described in detail and bring about the extension of the characterizing pause beyond the period provided for groups I-IV.

It is possible to reduce the number of keys in known manner, when a set of keys is provided of the numerical sender kind with decade divisions; it is also possible to provide for example 30 keys for individual characterizing and 4 group keys. Of the keys mentioned above only the keys Tl, T3l, Tfil, T9l; T3, T33, T63, T93 and T30, T60, Till Tl2il are shown in order to indicate the key set. This key set is connected with a selecting device which is in the form of a five-part selector. Further series of relays are provided which effect the sending out of the selecting impulses in a manner which is necessary for controlling the receiving devices at the branch sets. The method of operating this sending device is as follows:

(a) Selection 0 a subscriber of group I Should a subscriber of group I, for example subscriber T3 be required the key T3 in that central station is operated. In this way the circuit for the relay GI is completed: earth, battery ZB, relay GI (windingI) key Tl,-earth. The relay GI operates and connects the relay C over: earth, battery ZB, relay C, contact lgl, earth. The relay C connects the relay V over contact 20 and over its contact 30 connects the relay Si over: earth, battery ZB, resistance Wii, relay V (windings II and I), contact 2c, earth and: earth, battery ZB, relay SI (winding I), contacts M2, 30, earth. By the operation of the relay V the winding I of this relay is short-circuited over contact 5v. Further, over contact 117 the relay H is connected: earth, battery ZB, relay I-I, contactiiq, 9p, lllpl, H94, and l2:z:, I30, 111, 6c, earth. The relay H operates and holds over contact 14h and contact Bq. On. the operation of the relay H the sending out of the first impulse to the party line takes place.

In Figs; 2 and 2a two embodiments of the sending devices are shown, in Fig. 2 (upper left hand corner) the embodiment for sending out inductive impulses to the party line and in Fig. 2a (upper right hand corner of Fig. 2) an embodiment for the direct sending out of rectified impulses. In the arrangement according to Fig. 2 by the energizing of the relay H the contact 15h is closed and the contact 16h opened. Since the contact 110 is already closed an impulse of a particular direction (e. g.+) is formed in the secondary circuit of repeater UEZ by the operation of the contacts h and I6 and the resulting opening and closing of the primary circuit of the repeater and the impulses effect the party line over the contacts 2ls1 and 2291 in the following circuit: a-conductor, of the party line, contacts 1891, His, 200, repeater UEZ, contacts 2181, 2291, b-conductor of the party line GL. By the operation of contacts 1891 and 2201 the speaking. device Sp if the central station is disconnected during the selection.

In the arrangement according to Fig. 2a the operation of the relay H the contact 23h is opened and 2412 closed. The current therefore flows over the party line in the following manner: a-conductor of the party line, contacts 2591, 26s, 21h, 280, battery SB, contacts 29h, Mb, 3031, 3101, b-conductor of the party line. Current of positive direction is therefore sent out over the aconductor of the party line. The manner in which this current effects the branch set is elucidated in detail later; here, only the operation in the central station is described.

As already mentioned in dependence on the relay V the relay H is operated and brings about the sending out of the first impulse to the party line. At the same time as the sending out of the first impulse the rotary magnet D of the directly controlled switch mechanism of the central station, is brought from its zero position to the initial position: earth, battery ZB, rotary magnet D, contacts 321), 33h, earth. Parallel to the rotary magnet D the relay M is connected over the rest contact 34q and the relay A over its back contact 35a. Relay A holds over its contact 35a. The relay M operates the relay Q over its contact 36m and this relay, by opening its contact 34q disconnects the relay M again. The relay Q holds over its contact 3'1q and over its contact 38q and the contact 39112 in its normal position connects the relay 0. By the release of the relay M the holding circuit for the relay H extending over contact 48m is finally interrupted so that relay H restores. Thereupon contacts 15h and 16h are again operated to their initial positions so that in the secondary of the repeater UEZ a further impulse is produced which this time is in the opposite direction to the first impulse which is sent out over the party line. In the embodiment according to Fig. 2a a circuit is closed by the release of the relay H in such a manner that the sending battery is only connected to the party line in the reverse direction. The current extends thereby over: a-conductor of the party line, contacts 2501, 26s, 23h, 41a, sending battery SB, contacts 280, 42h, 31ls1, 3191, b-conductor of the party line.

On the release of the relay H by the opening of contact 33h the circuit of the rotary magnet D is further interrupted and by the opening of the contact 14h the holding circuit of the relay Q is also broken. When now the contact 8q is again closed the original energizing circuit for relay H is interrupted by means of contact 130. Only when after the release of the relay Q by the opening of contact 38q, the relay 0 is disconnected and the contact 130 restored, is the relay H energized again. It operates again therefore, and connects the rotary magnet D in the manner already described as well as the relay M. The selector of the central station is therefore moved from its initial positions to the setting 1.

Inthis setting over the wiper 43d, the junction line is connected to the keys T1, T31, T61, and T91 so that when a further key is operated the circuit can be completed over this wiper. Since, however, the key T3 is operated, the stepping on of the selector to this contact position takes place while two further impulses are sent out at the same time in the manner already described.

The rotary magnet D can now on the fourth operation of the relay H move its wiper on to the fourth step, i. e. in setting 3 where it remains. On the fourth operation of the relay H in the manner already described the relay M is energized again, at the same time as rotary magnet D. Therefore, the following test circuit is completed: earth, battery ZB, resistance Wz'2, contact 44m, relay .P, contact 4591, wiper 43d, on contact 3, key T3, earth. The relay P operates and holds independent of relay M over its contact 4612. Further a circuit for the rotary magnet D and the relay M is interrupted at contact 32p. Since the relay Q is energized over contact 36m and holds over contact 3Tq, after the release of relay M and opening of contact liim the previously existing holding circuit for relay H is interrupted, A new holding circuit is formed however over the contacts 41p and 4891 which prevents the release of the relay H and hence the sending out of a negative impulse to the party line. There is therefore a pause in the selecting impulse series actually the individual characterizing pause EP which prepares the completion of the connection to l the called party T3.

The duration of the characterizing pause is determined by the following series of operations of the relays: On the operation of the relay P the relay M is disconnected which connects the relay 0 in the manner already described for relay Q (over contacts 38q, 39m). Relay 0 now shortcircuits the winding 11 of relay V over contact 490 and 50p so that this relay restores after a time. After the release of the relay V the relay P is short-circuited over contact 512; so that this also restores. Therefore, on the one hand relay V is operated again and on the other hand by the opening of 41p the holding circuit for relay H is interrupted. Relay H releases accordingly and in the manner already described brings about the sending out of a negative impulse to the party line as well as the successive disconnection of the relays Q and 0.

After the release of the relay 0 the relay H operates again and in the manner already described brings about a further energizing of the rotary magnet D and hence the stepping on selector in the central station on to contact position 4 etc., until finally contact 33 is reached. At the same time asthe connection of the rotary magnet D the positive impulse is sent out to the party line. In the position 33 a circuit for the relay S is completed which prevents the sending out of further impulses to the party line: earth, battery ZB, relay S, contact 5291, wiper 53d, position 34, and earth. The relay S operates and opens its contacts 19s and E'is, and in Fig. 2a, contact 26s. Therefore, the impulse series in the central station is cut-off from the party line so that in spite of the operation of the contact controlled by the relay H, no impulses reach the party line. The stepping on circuit of the rotary magnet D controlled by the relay H in conjunction with the relays M, Q and 0 remains in operation, however, so that'the selector in the central station is stepped on in the same rhythm as trolled by the relay H are again transmitted to the party line. The first impulse is a negative impulse since the relay S only releases when the relay H is already operated. The interruption in the sending out of selecting impulses during the stepping on of the selector from the 34th to the Mith bank contact serves to produce a large pause (call pause RP) in which calling current is connected to the selected branch set.

The selector in the central station is stepped on in the same rhythm. When it reaches position 49 a circuit is prepared again for the relay S which is closed when the relay H, working in conjunction with the relays M, Q and O, restores: earth, battery ZB, relay S, contacts 52gl', 54h, wiper 53d on contact position 49, earth. By the operation of the relay S the sending out'of further impulses to the party line is prevented. The chain of relays H, M, Q, 0, now operates again andbrings about the stepping on of the rotary magnet D from the 49th bank contact to the home position. In this position the holding circuit in the relay S is again interrupted.

In contact position 49 the release magnet, not shown, for locking the keys is energized and frees the keys already operated so that relay GI restores and hence also relays C, A and V. By the release of these relays the energizing circuit for the stepping on devices of the rotary magnet D is interrupted so that the sending device is again in its normal position.

(b) Selection of a subscriber of group II If the subscriber of group II for example subscrib-er T33 is to be called the key T33 in the central station is operated. In this way, the circuit is completed for the relay G2: earth, battery ZB, relay G2, (winding I), key T33, earth. The relay G2 operates and over its contact 55g2 connects the relay C. In the first place the same stepping operation takes place as results from the operation of the key T3 i. e. sending out of impulses in alternate directions and hence also the simultaneous stepping on of the switch mechanism D in the central station, until the switching mechanism reaches with its wiper 43d the contact 3 associated with the operated key T33. In this position. as described previously in connection with the selection of the subscriber's set T3, the relay H is energized which over its contact 33h has connected the rotary magnet D and eiiected its stepping on to bank contact 3. Simultaneously with'the rotary magnet D the relay M is also connected and connects the relay Q over its contact 36m on the one hand and on the other hand the relay PI over its contact Mm the latfer holding in the following circuit: earth, battery ZB, resistance WiZ, contact 44m, andSEpI, relay PI, contact 5192, wiper 43d in position 3, key T33, earth. On the operation of relay Q relay M is again clisconnectedby the opening of the contact 34q so that the holding circuit for relay H extending over contact 43m is interrupted. Y

In contrast to the selection of a subscriber of group I in which the relay Hin spite of the reconnected: earth, battery ZB, relay X, resistance by the relay P and hence causes the initiating of a pause for'the particular characterizing by means of a positive impulse, in this case since the contact dip is opened the relay H restores so that a further negative impulse is sent out to the party'line, which causes the insertion of the particular characterizing pause.

The duration of the particular characterizing pause is determined by the interaction between the relays Q, 0, V and PI.

On the release of the relay M the relay 0 is operated and over its contact 490 and the contact 58pl, the relay V is short-circuited so that this relay restores after a time. On the operation of the relay 0, the relay Q, is disconnected by the opening of the contact I30 and this restores the relay 0. When the relay V restores after some time it short-circuits the relay PI over contact 5h) so that this relay again reaches its normal position; thus the short-circuit for the relayV is, again removed.

Over the contacts IIipI, I30 andTIu the relay 'H is operated again and in the manner already described controls the stepping on circuit for the rotary magnet and the sending out of the selecting impulses, This takes place until the wiper 53d of the rotary magnet D in the central station reaches the contact position 34. In this contact position the circuit for the winding I of relay SI; which up till now was energized over wiper 59d and contact 30 during the whole series, is interrupted. The relay SI holds however until the release of the relay H over its winding II and the contact GBsI and. Mh, so that the beginning of the calling pause is brought about by means of a negative impulse (by the release of the relay H). Only then does the relay SI restore and open its contacts Zlsl and MM, so that independently of the stepping on of the rotary magnet in the central station and of the coming into eiTect of the relay H no impulse can r'each the party line.

Only when the wiper 59d of the switching mechanism D reaches the contact position 41 and the relay 0 in the relay chain is energized, i. c. When relay H has already restored, does the relay SI operate again: earth, battery ZB, relay SI (winding I), wiper 59d on contact position 41, contact Silo, earth. Relay SI holds therefore independently of relay 0 over its own contact IiIsI and later over contact 30. The first effective impulse is a positive impulse on the operation of the relay H again. The further impulses which are sent out to step on the rotary magnet D to its normal position are transmitted to the party line in the manner already described. The stepping on of the stepping devices of the central station to their normal positions'res'ults as described for group I.

(0) Selection of a. subscriber group III If a subscriber of group III for example sub scriber T63 is to be called the key T63 in the central station is operated. In this way, a circuit is completed for the relay G3 and winding II of relay GI.

Both relays operated, over relay GI in the manner already described, the relay C is energized which brings about the connection of the relays V and SI. Further in dependence on the relays G3 over contact 6293 the relay X is contacts 62g3, 2c, earth. The relay X only operates however, after a considerable delay as a result of the parallel connected condenser lease of the relay M holds over the contact closed 75: KI. Meanwhile over contact Iv the relay H is connected and there follows in the manner already described the stepping on of the rotary magnet D in the central station to its normal position A and at the same time the sending out of positive impulses to'the party line. Relay H which in the manner already described connects the relay chain M, Q, does not restore immediately although the contacts 8:; and 40111. are opened since the following holding circuit exists: earth, battery ZB, relay H, contacts 63:0, 6493, To, 60, earth. Relay H holds until finally the relay X operates and contact 63a: is opened. Only then does the relay H restore and the release of the relay chain M, Q, 0 become possible. Therefore, between the first positive impulse and the first negative impulse a characterizing pause occurs in the selecting impulse series by which group III is differentiated from the subscribers of group I. The further switching operations at the end of the selecting operations relay X also restores after the release of relay D.

((1) Selection of the subscriber of group IV If for example the subscriber T93 is to be called, key T93 in the central station is operated. Then the circuit is completed for the relay G4 and for the winding II of relay G2. The relay G2 causes the operation of the switching mechanism in the central station in the same way as'in selection of a subscriber of group II. When the switch mechanism D in the central station reaches its initial position a and the sending out of the first positive and first negative impulse results then after the release of the relay H, in contrast to the operations occurring in the selection of a subscriber of group II an exceedingly long interruption in the energizing circuit of the relay H results in the following manner:

After the operation of the relays C and V the relay X is connected over its winding II; earth, battery ZB, contact 63g4, relay X (Winding II) contacts 653 11), 6c, earth. The relay X now operates and opens its contact I2x. Since now contact g4 is also opened by the operation of the relay G4, after the sending out of the first positive and first negative impulses (operation and release of relay H), the relay H is not operated again as before since its energizing circuit is open. Only when the slow relay Y connected over its contact and 66g4, to which the condenser K2 is parallel, operates in the contact 65y opened, and the holding circuit for relay X interrupted. Over the contact I2x set back in its normal position the relay H is operated. Therefore, between the first negative impulse which influences the switch device of group IV for its first selecting operation and the second positive impulse a long pause occurs in the selecting impulse series. This pause effects a group characterization at the receiving device as will be described in detail later. After the operation of the relay H the stepping on of the rotary magnet D in the central station and the sending out of selecting impulses over the party line follows in the manner already described in the selection of a subscriber of group II.

The manner in which the selecting impulse from the central station affects the receiving stations follows from the description of the receiving device shown in Figs. 3 to 6.

II. RECEIVING Dnvrcn In Figs. 3 to 6 receiving and selecting devices are shown at the subscribers sets, T3, T33, T63 and T93. The devices of the four subscribers groups described are the same in their fundamental circuit arrangement. They differ only as regards a few contact alterations. The receiving devices in these embodiments are connected over repeaters to the common line. For this purpose a polarized relay is provided at each branch set which for the subscribers of the subscribers groups I and II is operated by positive impulses and for the subscriber of the groups II and IV by negative impulses. Further, at all branch sets a rotary magnet of a stepping mechanism is provided. Then again at each sub scribers set two slow relays R and S are provided whose release periods are arranged to be different so that the group characterizing pause falls between the first selecting impulse bringing the first polarized relay to its operated position and the following impulse in the opposite direction.

(a) Selection of the subscriber T3 If the subscriber T3 is to be called impulses are sent out to the party from the central station in the manner already described (see Fig. 1, group I). The first positive impulse operates the relay P3 at the branch set T3 over its winding I so that the circuit is closed in the relay S3: earth; local battery 0133, relay S3 (winding I) wiper ldm3 in zero position, contact 203, wiper 3dm3 in zero position, contact 4123, earth. The relay S3 operates and connects relay 03 over contact 5s3 and 6dm3. Both relays hold independently of relays P3 over contact 103. The relay R3 connected parallel to S3 is energized but it is not operated immediately since its operating period is arranged to be very large by means of a parallel condenser Kr3. Since now after a short period the negative impulse is sent out over the party line the relay P3 is again brought to its normal position so that relay R3 does not operate in this selecting operation. By means of the short pause between the two first impulses and the resulting non-operation of the relay R3 the selection of the subscriber in group I is characterized. As a result of the contact 4p3 being again in its normal position the circuit is completed for the rotory magnet DM3: earth, battery 0B3, rotary magnet DM3, contacts 803, 4103, earth. The rotary magnet DM3 operates and brings its wiper on to position I in the contact bank. In this way by means of wiper 3dm3 the energizing circuit of the relay R3 is finally interrupted for this selecting operation.

On receipt of further impulses of alternate direction the stepping on of the rotary magnet DM3 from contact to contact takes place. After the setting on contact 3, the following results by the receipt of the four successive positive impulses:

The contact 4123 is operated and interrupts the circuit in the rotary magnet DM3, so that this restores and opens contact 9dm3. Since the wiper Idm3 rests on the contact position characterizing the subscribers set T3, the energizing circuit for the relay S3 dependent on the .two contacts of the stepping on magnet is interrupted at both contacts. The relay S3 which is a slow relay is now restored so that during the normal pause between two selecting impulses it may remain energized since a large pause is inserted bythe central station in the impulse series between the fourth positive impulse and the fourth negative impulse in order to characterize the desired subscriber. This pause is larger than the release period of the relay S3. Relay S3 closes its contact l0s3 and this prepares the circuit for the bell Wk3. At the same time the contact s3 opened and remains opened during the further selecting impulse series so that the relay S3 can no longer energize in this selecting operation. The relay C3 holds, however, owing to its larger release period determined by the parallel condenser, which period is longer than the duration of the individual characterizing pause.

When now after determination of the individual characterizing pause the fourth negative impulse follows, the rotary magnet DM3 is energized again and connects the wiper on to the contact 4. The further stepping on of the rotary magnet DM3 takes place under the influence of impulses sent out from the central station until the 34th positive impulse is sent out from the central station and the switching mechanism in the central station reaches the contact 33. Then in the manner already described the call pause is interposed and is only completed after a longer period by the sending out of the 34th negative impulse. In this call pause the call is made effective in the desired setting and this takes places as follows: By the 33rd negative impulse the switch mechanism. DM3 of the desired branch set reaches contact position 33. On the following 34th positive imp'ulse the relay P3 is again operated, then relay magnet DM3 restores and over contact Edmii the holding circuit for C3 is maintained. Hence the circuit is completed for the bell W7c3 of the desired set: earth, battery 0133,

bell WkS, call controlling repeater U23, contacts i333, llr3, wiper l2dm3 on contact 33, contact 103, earth. The bell sounds; the operation of the bell is transmitted over the repeater Ue3 and the contacts l3c3 and 23s3 to the sending station. When at the end of a call pause further impulses follow the rotary magnet DM3 is stepped on from the setting 33 and finally reaches its normal position.

(s) Selection of subscriber T33 If the subscriber T33 is to be called the polarized relay P33 remains in its rest position when the first positive impulse is sent out of the party line. As it is only operated by negative impulses I the first positive impulse over the party line is therefore without influence on branch sets of group II. The first negative impulse following directly on the first positive impulse, first operates the polarized receiving relay at the branch sets of group II by the closing of contact 4p33 a circuit is completed for the relay S33: earth, local battery OB33, relay S33 (winding I), wiper loin i3 in zero position, contact 2033, wiper 311111.33 in zero position, contact 41233; earth. Relay S33 operates and over its contact 5333 and contact $d77t33 connects the relay C33. This relay holds and also keeps up the relay S33 over its contact 1033. At the end of the first negative impulse and on the receipt of the second positive impulse acircuit is completed over contact 3033 for the rotary magnet DM33. The switch mechanism DM33 therefore reaches its contact setting on the second negative impulse.

In corresponding manner the switch mechanism is stepped on until after the sending out of the fourth positive impulse, the switch mechanism reaches the third contact (see Fig. 1, group II). Since now the individual characterizing pause (E'P) is connected for the purpose of calling the subscribers set T33 in the sending station after the sending out of the fourth negative impulse, the rotary magnet DM33 is restored, since the contact 31033 is operated; further since the wiper ldm33 is directly on the insulated contact 3 the relay S33 at the calling set is also restored. The relay S33 prepares a connection for the bell Wk33 over its contact H1833.

At the end of the characterizing pause the impulses sent out from the central station control the rotary magnet DM33 further, until under the influence of the 35th positive impulse it reaches contact 34. Since now on the sending out of the 35th impulse the switch mechanism reaches contact 34 and thus after the sending out of the 35th negative impulse the setting of the calling pause is brought about, the relay P33 is operated by this negative impulse and disconnects the rotary magnet DM33. Therefore, bell Wk33 .op-

crates: earth, battery OB33, bell Wk33, repeater U633, contacts H3833, T33, wiper 'l2dm33, on to contact 34, contact E033, earth. The bell sounds until the call pause is ended and the switch mechanism is stepped on by further impulses into its home position.

(0) Selection of subscriber T63 The polarized receiving relay at the branch sets of group III is connected in the same way as at the branch sets of group I, i. e. the polarized relay is operated by positive impulses. The particular differentiation between the branch sets of group I and III consists in that, at the branch sets of group III the cont-act of the relay R in the bell circuit is an operated contact and not as in group I a back contact.

If the subscriber T63 is to be called the following operations take place:' By the first positive impulse sent out over the party line the relay P53 is operated and connects the relay S63 and parallel there-to the relay R33 which is a slow action owing to the condenser K1153. Since now in the sending station between the sending out of the first positive impulse and the first negative impulse, a longer pause characterizing the group of the calling subscriber is made, in addition to relay S33 the relay R63 also operates on set T63. This relay holds over its contact B1163 and contact 1063, which after the operation of relay C63 connected by relay S83, is in its operative position. The further switch operations'are now the same as described inconnection with subscriber T3 1. e. in the individual characterizing pause following on the set on step 3 the relay S63 restores so that the bell circuit is prepared. The bell Wk63 is connected when the selector DM63 has reached the setting 33: earth, battery 0363, bell Wk53, repeater Ue63, contact Ills53, r63, wiper i2d1nfi3, contact setting 33, contact 1063, earth. The stepping on to the normal position takes place as in the case of subscriber of group I.

( 1) Selection of subscriber T93 The receiving relays of group IV are operated by negative impulses in the same way as those of group II. Also in this case in order that the branch sets of group IV shall be differentiated from those of group II, the contacts of the relay III. AVOIDANCE OF FALsE CALLS It is important that in the selective calling of a subscriber of the party line the operation of the bell in the case of a subscriber who is not required shall be prevented. This is done as follows:

When for example the subscriber T3 is called the first negative impulse follows directly on the first positive impulse which is sent out over the line. By the direct following on of these two impulses the very much delayed operating relays R, e. g. relay R63, which can only be connected in the normal position of the rotary magnet DM63 is not energized in branch sets of group III. Therefore the called circuit remains interrupted by the contact r63 remaining in its normal position even when the relay R63 preparing a call circuit is restored by setting the contact 3. Thus there is a positive differentiation between branch sets of groups I and III.

The differentiation between branch sets of groups I and II is arranged in that the switch mechanism at the branch sets of group Iis stepped on by means of negative impulses sent out over the line while at branch sets of group I it follows by means of a corresponding positive impulse. When now in the call of a subscriber set T3 after the setting of the rotary magnet DM3 and the sending out of the fourth positive impulse, a pause is inserted, then at the branch sets of group II, i. g., T33 the rotary magnet DM33 reaches the contact setting 3, the contact 4123 is however in its normal position (under the infiuence of the positive impulse sent out over the line) and maintains the circuit of the rotary magnet DM33. As a result when the wiper Idm33 also reaches the insulated contact 3 and thus interrupts the circuit of the relay S33, this relay S33 is still maintained energized over the contact 9dm33. Therefore a call circuit is not pared at set T33.

It is then only necessary for care to be taken that when the selector DM33 reaches contact setting 33 in which the call circuit is closed during the call pause at branch sets T3, the circuit of the relay C33 holding rotary magnet DM33 connected during this period shall be maintained energized since the contact Bdm33 maintaining the circuit of relay C33 is opened as a result of the connection of the rotary magnet DM33 during the call pause (by means of contact 4p33 in its normal position). This is done by closing the following circuit for relay C33 in the setting 33 corresponding to the group I independently of contact 6dm33: earth, battery OB33, resistance, relay C33, wiper l2dm33 on contact 33, contact 1033, earth.

The operation of undesired branch sets of group IV on the selection of relay subscriber of group I is prevented in the same way as for group III by the relays R, e. g. R93, remaining operative.

.When the subscriber set T33 (group II) is called, the calling of another undesired subscribers set which is also connected to contact 3 pre- of this selector must be avoided. In the calling of subscriber set 33 the individual characterizing pause follows after the 4th negative impulse, i. e. at a time in which the switch mechanisms are set on the 4th contact in group I as well as in group II, when, however, the receiving relay of group II is in an operated position the polarized relay at the branch sets of group I is in the normal position i. e. at the branch set T4, not shown, but corresponding to the branch T3, the rotary magnet DM4 is connected over the contact 804 and the contact 4214 in its normal position. As a result relay S4 whose seized circuit is interrupted over the wiper ldm4, still remains energized so that the calling circuit at subscriber set T4 cannot be prepared. At the branch sets of groups III and IV the preparing of the call circuits is prevented by the failure of the relays R, e. g., R63 to operate, as a result of the direct following on one after another of the two first impulses controlling the receiving relays and thus the calling circuit is held open.

In the selection of the subscriber's set T63 (group III) after the first positive impulse a pause occurs in the selecting impulse series characterizing group III in which the slow to operate relay R63 is energized at the branch set T63 and prepares the call circuit for its group. At the branch sets of group I, e. g., T3, a long pause between the first impulses has the effect that in addition to the relay S3 the slow to operate relay R3 shortcircuited by the condenser Kr3 energized and by opening its contact r3 interrupts the calling circuit during this selecting operation. At the branch sets of group II, c. g., at the subscriber's set T33, a pause between the first positive and first negative impulse characterizing group III in general has no effect since the polarized receiving relay remains in its normal position on the first positive impulse and is only operated by the first negative impulse which completes the pause. False calls are, however, not possible even at branch sets of this group since the characterizing pause in the selection of subscriber T83 follows a positive impulse and finds the receiving relays of group III, e. g., T33 in the normal position. Therefore the rotary magnet DM33 is connected so that relay S33 cannot restore. The same takes place in the branch sets of group IV.

If the subscriber T93 is called, the rotary magnet DM33 is operated in group I by the first negative impulse which is followed by the longer group characterizing pause and remains energized until the next positive impulse, since the relay C3 rendered slow to respond by means of the condenser does not restore. Relay R3 is not energized since the selector is already in position I. In spite of this, false calls cannot occur since the characterizing pause begins with the negative impulse in which the polarized receiving relays (P3) and the subscribers sets of group I are in the normal position and holding the stepping on magnet (DM3) connected. In branch sets of group II after the first negative impulse, e. g., in subscriber's set T33, the polarized relay P33 is operated so that in view of the following group characterizing pause the relay R33 operates and with its contact 733 interrupts the calling circuit. During this operation at branch sets of group III the group characterizing pause following on the first negative impulseis ineffective since the selector is held in position I; but if moreover the polarized receiving relay after the entering relay is in rest position, and holds over contacts 41063 and 8c63 the rotary magnet DM63 is energized.

IV. Srnrrmc on TO THE Home POSITION Since the switch mechanism of groups I and II are stepped on by negative impulses and the switch mechanism of groups II and III by positive impulses, care must be taken that the receiving devices reach their rest position in all groups at the end of the selecting operation, This is done as follows;

In the selection of a subscriber of group I, e. g., T3 after a call pause the switch mechanism is stepped on in such a manner that finally, by means of the 37th negative impulse which brings the polarized receiving relay into its normal position, the rotary magnet DM3 is connected and opcrates its wiper from setting 33 to zero setting.

It thus maintains the switch mechanism of the branch set of groups I and II in their normal position. Switching mechanism of the groups II and IV are, however, still on the 36th contact. It is,

therefore, necessary to send out a further positive impulse over the line by which the selectors at the branch sets of the groups II and IV shall also be brought to their normal positions. The sending out of a positive impulse over the party line, however, would bring the receiving relays at the branch sets of the groups I and III to operate again; this is prevented in that in the zero position, e. g., in set T3 over the wiper |4dm3 and the contact 15dm3, a second winding of the relay P3 is connected which has an opposite effect to the winding I. In the same way at the subscribers sets of group III, e. g., T63 there follows the connection of winding II of P63 over: wiper avoid the effects of resonance in the repeaters of the receiving devices when the directionof the selecting impulse sent out by one selecting operation is opposite to the direction of the last selecting impulse. In order to avoid complicated switching devices which ensure such an impulse succession in the various selection operations all the selecting operations are begun with a positive impulse. It is therefore necessary to end each selecting operation with negative impulse, i. e.,

after the last positive impulse, by which the receiving device in the branch sets of groups II and IV are restored to normaL. a finalnegative impulse must be sent out. The problem exists of preventing the receiving devices of groups II and IV from operating again due to this last negative impulse. This required result is obtained in the same way as in the case of the branch sets of groups I and III, for example over the wiper Hiatm33 in its normal position and the contact 15dm33 in its operated position, winding II of relay P63, over MdmQB and 15(lm33, the Winding II of relay P93 is energized and its effect is opposite in direction to that of the winding I influenced by the selecting impulse. The last negative impulse is therefore inefiective at the branch sets of groups II and IV, while at the branch sets of groups I and III the polarized receiving relay in its normal position is in general not operated. The selecting and receiving devices at all branch sets are now in their normal positions.

|4dmfi3 in zero position and contact 15dm63 in its operated position. The last posi- When by means of some impulse the polarized receiving relay is momentarily operated and then restored, then at the branch set concerned, the relay C is connected in addition to relay S and. holds in the first place over contacts 103 and 6dm3 and then after the delayed operation of the rotary magnet DM3, is restored; rotary magnet DM3 then also restores. Thus in order that the selecting devices of these branch sets shall not remain on the positions reached by means of the disturbing influence a self-interrupting circuit is completed which brings about the stepping on of the switch mechanism to its home position and winding II of relay S3 is energized over the contact 103 in its normal position, and the wiper 1Gdm3 on contact segments 136 and over 11111113. The relay S3 operates and connects the rotary magnet DM3 over contact 1883. The r0- tary magnet operates-and moves forward by one step and thereby interrupts the energizing circuit for relayS3 at contact "(11223 which relay opens its contact 1333 and disconnects the rotary magnet DM3. Over contact 11dm3 in its normal position relay S3 is energized again over winding II and again connects the rotary magnet. This interaction between the two magnets is repeated until the wiper 16dm3 reaches its 0- position.

V. SELECTION or SUBSCRIBERS or Gaoors V-VIII In order'to select a subscriber of groups V-- VIII e. g. T123, a key Ti23 not described in. de-

tail, associated with one of these sets is operated in the sending station (Fig. 2). Thearrangement can be such that in addition to the switching devices coming into effect on the operation of the corresponding key T3 (for sub scriber T2) a group switch means T5 is connected which increases the length of the characterizing pause till it is longer than that for groups I-IV, by means of a delay device, e. g. a relay coming into effect on the operation of the test relay P.

The switch operations at the branch set T123 to be selected are as follows:

On the arrival of the first positive impulse sent out over the line the polarized relay P123 to be is energized so that contact 410123 is operated. In this way the circuit is closed for the relay S123 (winding I): earth, battery OBlZS, relay S123 (winding I) wiper 1dm123 on the contact segment 0-2, contact 20123, wiper 3dm123 in zero setting, contact #40123, earth. The relay S123 operates and connects relay N123 over contact 21sl23. At the same time over contact 5si23 and contact 6dm123 still in its normal position, relay C123 is energized. This operates and over its contact 10123 forms a holding circuit for its relays S123 and N123.

On the following impulse the stepping on 0!.

the subscriber T123 is inserted in the selecting impulse series then the selector DM123 rests with its wiper on contact 3. Since the polarized relay Pl23 has operated its armature the rotary, magnet DM|23 is disconnected so that the energizing circuit for the relays Sl23 and Nl23 is also interrupted over contacts 9dml23 and 23dml23. When now the characterizing pause before the receipt of the next impulse is sufiiciently long then not only does the relay Sl23 restore, but also the relay N123. Therefore at the set T|23 the call circuit for the bell Wlcl23 is prepared over contacts M23 and 22nl23.

The further switching operations are the same as already described in connection with the subscribers set T3, i. e., on the setting of the selector DMI23 on the contact 33 the call circuit is closed and the bell is connected for the duration of the call pause. At the end of the call the selector is stepped on to its normal position.

When the subscribers set T3 is called a false calling of the set Tl23 is prevented, in that after the receipt of the fourth positive impulse the selecting impulse series is interrupted by a short characterizing pause and only the relay SI23 restores, and over contact 2ls|23 the energizing circuit for the relay Nl23 is interrupted and the relay N|23 remains operated over contacts 5s|23 (normal position), M23 and 23dml23, and thus, by keeping its contact 2212i 23 open, maintains the call circuit for the bell W7c|23 interrupted.

Even now false calls occur at the branch set T3 when the set T|Z3 is called. Therefore at the set T3 the contact 22n3 (not shown) con trolled by the relay N3, must be so arranged that when it is closed (in Fig. 7 indicated by dotted lines) it prepares the call circuit. When, therefore, the set Tl23 is called and as a result of the long pause, the relay S3 in addition to the relay 53, then at the set T3 the call circuit is interrupted by means of the contact 22n3 which has reached its normal position.

In a similar way as in group V the selection of branch sets of groups VI to VIII takes place and so this is not described in detail in the embodiment since its switching devices correspond to those described in detail at the branch sets in groups II-VI; it is only necessary-as follows from the above-to have the special relay (N) at all branch sets in order to lengthen the characterizing pause which is arranged in the same way as shown in Figure '7 for all branch sets.

What is claimed is:

1. In a telephone system, a party line, two groups of stations on said line, a selector at each station of one group responsive only to impulses of one polarity transmitted over the line, a selector at each station of the other gnoup responsive groups of stations on said line, a selector at each station of one group responsive to impulses of one polarity, a selector at each station of the other group responsive to impulses of a different i polarity, means for transmitting over said line 'a train of impulses alternating in polarity to operate the selectors of said two groups alternately, means for introducing a characterizing pause between any two successive impulses in said train,

and means controlled by the selectors for selectively signalling a particular station depending upon which two impulses said pause is introduced between.

3. In a telephone system, a party line, means for transmitting over said line a train of impulses alternating in polarity, two stations on said line, a polarized receiving device at one of said stations responsive only to the impulses of one polarity in said train, a polarized receiving device at the other of said stations responsive only to the impulses of the other polarity in said train, said two devices thereby operated alternately during transmission of said impulses,

means for introducing a characterizing pause between two of said impulses, and means controlled by said devices in accordance with the polarity of the impulse immediately preceding said characterizing pause for selecting one or the other of said stations.

4. In a telephone system, a party line, means for transmitting over said line a train of impulses altemating in polarity, means for introducing a characterizing pause of variable length between two of said impulses, a plurality of stations on said line each having a polarized receiving device and timing means, and means controlled by said receiving devices and said't-iming means in accordance both with the polarity of the impulse immediately preceeding said characterizing pause and the length of said pause for selecting a particular one of said stations.

5. In a telephone system, a party line, one station on said line having a receiving device responsive only to current transmitted over the line in one direct-ion, another station on said line having a receiving device responsive only to current transmitted over the line in the opposite direction, and means for transmitting alternating current over said line to operate said devices periodically and alternately to select one of the stations.

6. In a telephone system, a party line, one station on said line having a receiving device responsive only to current transmitted over the line in one direction, another station on said line having a receiving device responsive only to current transmitted over th line in the opposite direction, means for transmitting alternating current over said line to operate said devices alternately, means for then interrupting the transmission of said alternating current for an interval of time, and means controlled by said devices in accordance with the direction in which said alternating current last flows over said line before said interruption for selectively signalling one or the other of said stations.

7. In a telephone system, a party line serving two stations, a step-by-step selecting device at each of said stations, and means controlled over the line for stepping said devices at the two stations alternately to select one of said stations.

8. In a telephone system, a party line serving two stations, a step-by-step selecting device at each of said stations, and means controlled over the line for stepping said devices at the two stations concurrently but in a predetermined outof-pha-se relationship to select one of said sta tions.

9. In a telephone system, a party line serving a plurality of groups of stations, a step-by-step selecting device at each of said stations, and means for stepping said devices concurrently and in a predetermined phase relationship to select one of said stations, said relationship being such that the devices at all stations of each group are stepped in unison and that the devices at stations of different groups are not stepped in unison.

10. In a telephone system, a party line serving two stations, a step-by-step device at each of said stations, means controlled over the line for stepping said devices at the two stations alternately, and means at each station for selecting that station when the device thereat has been stepped to a particular position.

-11. In a system of the kind described, a plurality of relays, means for energizing said relays, a holding circuit individual to each relay and maintainmg that relay energized, a line, means controlled over said line for transitori-ly interrupting each of said holding circuits in turn, said interruptions normally being of such length as not to permit said relays to release, and means for prolonging any of said interruptions thereby to release the relay whose circuit interrupted.

12. In -a telephone system, a party line, a plurality of stations on said line, a selector relay at each of said stations, means for energizing said relays, a local circuit at each station maintaining the relay thereat energized, a step-by-step device at each station, said devices responsive in unison to impulses transmitted over the line and effective to transitorily interrupt each of said local circuits in'turn, said interruption normally being of such length as not to permit the relay whose local circuit is interrupted to restore, and means for introducing a selecting pause between two of said impulses transmitted over the line thereby to prolong the interruption of one of local circults and permit the corresponding selector relay to restore.

13. In a telephone system, a party line, a plurality of groups of stations on said line, means for transmitting a train of spaced impulses over the line, means for introducing between any two successive impulses of said train an additional spacing of variable length, means including a selector at each station for selecting one of said groups of stations in accordance with the length of said additional spacing and selecting a particular station of that group in dependence upon which two impulses of said train said additional spacing is introduced between.

14. In asystem of the kind described, a line, a plurality of stations on said line, a selector at each of said stations, means for transmitting two trains of impulses concurrently over said line to operate said selectors to select a station, the impulses o-i said two trains being in such timed relationship that each impulse of one train is followed by an impulse of the other train, one of said selectors responsive only to th impulses of one of said trains and another of said selectors responsive only to the impulses oi the other of said trains, said two selectors thereby operated alternately during said selecting of the stationl 15. In a system of the kind described, a line, two stations on said line, a selector at each of said stations, means for transmitting a train of impulses over said lin to operate said selectors to select one of said stations, one of said selectors operated by alternate ones of the impulses in said train and the other selector operated by the remaining impulses in said train, said two selectors therebyopera ted alternately during said selecting oi the station.

16. In a telephone or like system, a party line, a plurality of stations on said line, a step-bystep switch at each of said stations, means opelated whenever it is desired to call any of said stations to transmit impulses over said line to operate all of said switches a predetermined number of steps, said number being the same regardless of the station wanted, means for varying the spacing of said impulses in accordance with the station wanted, and a device at each station operated over the switch at that station after same has been stepped said predetermined number of steps only if the impulses transmitted over said line were spaced in a particular way.

17. In a telephone or like system, a party line, a plurality of stations on said line, means for selecting any one of said stations, said means including an impulse transmitter operated during the selecting of the station to transmit a predetermined number of impulses over the line, said number being th same regardless of the station being selected, means controlling said impulse transmitter to introduce a characterizing pause between two of said impulses, an impulse counting device at each of said stations, and means controlled by said devices to select a particular one of said stations depending upon which two impulses said pause is introduced between.

18. In a telephone system, a party line, means for transmitting over said line a train of impulses alternating in polarity, means for introducing a characterizing pause between two of said impulses, a plurality of stations on said line each having a polarized receiving device and impulse counting means, and means controlled by said receiving devices and said counting means in accordance both with the polarity of the impulse immediately preceding said pause and with the number of impulses in said train for selecting a particular one of said stations.

19. In a telephone or like system, a line, a plurality of stations on said line, means for transmitting two trains of impulses concurrently over said line, means at certain of said stations for counting only the impulses in one of said trains, means at others of said stations for counting only the impulses in the other of said trains, and means controlled by said countmg means in dependence upon the number of impulses in said trains for selecting a particular one of said stations.

WALTER KUSCHE.

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