US1772472A - Automatic telephone system - Google Patents

Description

. Aug. 12,- 1930. J. wlcKs AUTOMATIC TELEPHONE SYSTEM 10 Sheets-Sheet 1.

Original Filed Aug. 26, 1926 & Mg S \Q g g mm w John Mmks J. WICKS 1,772,472

10 Sheets-Sheet 2 -ImrEn m" I John Mmks Aug, 12, 1930.

AUTOMATIC TELEPHONE SYSTEM Original Filed Aug. 26, 1926 Aug; 12, 1930.

' J. WICKS AUTOMATIC TELEPHONE SYSTEM 10 Sheeis-Sheet 3 Original Filed Aug. 26,1926

John Mmks Aug. 12, 1930. 7 J. WICKS AUTOMATIC TELEPHONE SYSTEM Original Filed Aug. 26. 1926 10 Sheets-Sheet 4 J. WICKS AUTQMATIC TELEPHONE SYSTEM Original Filed Aug. 26, 1926 John Inluzks M 1 mg.

J. WICKS AUTOMATIC TELEPHONE SYSTEM Aug. 12, 1930.

Original Filed Aug. 26, 1926 10 Sheets-Sheet 6 FITITT:

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AUTOMATIC TELEPHONE SYSTEM Original Filed Aug. 26, 1926 10 Sheets-Sheet 8 Qisk Juhn Inlmks Aug. 12, 1930. J. WICKS 7 AUTOMATIC TELEPHONE SYSTEH Original Filed-Aug. 26, 1926 10 Sheets-She et 9 m m W Nam Aug. 12, 1930. J w c s AUTOMATIC TELEPHONE SYSTEM Original Filed Aug. 26, 1926 v 10 Sheets-Sheet 1O atented An. 12, 1930 JOHN WICKS, DE UAR PARK, ILLINOIS, ASSIGNOR '10 AUTOMALKIC ELECTRIC INC., 01? GHICAGO, ILLINOIS, A CORPOTION OF DELAWARE AUTOMATIC TELEPHONE SYSTEM Application filed. August 26, 1926-Serial No. 131,575. Renewed hecember 1e, 19%.

This invention relates to telephone systems in general, but is more particularly concerned with automatic telephone systems in which connections are. established through 5 the medium of subscriber controlled automatic switches. In such a system, automatic switches such as a first selector, one or more intermediate selectors, and a connector are successively operated under the control of a dial at the calling station. This invention further pertains especially to that kind of automatic telephone system in which the motor magnets of the automatic switches aredirectly operated by current impulses produced by the line relay'of the first selector, the line relay of the first selector being operated by impulses produced by the dial of the calling statifin.

An automatic telephone system of this kind, known as a direct pulsing system, is disclosed in the inventors copending application Serial No. 8,343, filed Febfll, 1925. In the system disclosed in the above application, the current impulses for operating the motor magnets of the automatic switches are produced by the line relay of the first selector (better termed, the first selector repeater) and are transmitted to the magnets of the first selector repeater and to the magnets of so the succeeding switches over one of the talking conductors of the extended trunk line. While this method of control is entirely satisfactory for switch operation in a single exchange, loop control (control over the two conductors of the trunk line in series) is recognized as being most preferable for controlling switch operations, especially when connections between exchanges are extended. In the former case the difference in ground potential between any two exchanges,

which may vary between wide limits from time to time, constantly threatens proper switch operation when such operation is controlled overa single conductor. In the pres- 5 ent invention, the possibility of this condition causing trouble is entirely eliminated, for

the reason that the control of the magnets of the switches is affected over the two trunk conductors in series.

The main object of this invention, therefore, is the provision of new and improved automatic switches for use in a direct puls ing automatic telephone system. The main feature resides in the circuit arrangement whereby the current impulses for operating the magnets of the switche produced by the line relay of the first selector repeater, are transmitted to the magnets of the switches over the two sides of the extended -trunk line in series.

Other objects are accomplished and various features are contained in the invention which will be fully described in the body of this specification with the aid of the accompanying drawings.

Referring now to the accompanying drawings comprising Figs. 1-12, Figs. 1-1O show by means of the usual schematic circuit diagrams a sufficient amount. of the apparatus in a multi-ofiice telephone system embodying the principles of this invention to enable the invention to be clearly described and understood.

Fig. 11 is a diagram showing how the drawings upon which Figs. 1-8 appear are to be arranged, (Fig. 8 to be substituted for Fig. 3 as directed hereinafter) to be most intelligently understood in connection with the descriptions of the establishment of certain connections to be given. Fig. 12 likewise is a diagram showing how the drawings upon which Figs. 2, 8-10 appear may be arranged (Fig. 10 to be substituted for Figs. 2 and 7 as directed hereinafter) to be best understood in connection with the descriptions of the establishment of certain other connections to be given also. The following paragraphs give a brief description of each of the above figures.

Fig. 1 shows the subscriber substation A whose line terminates at the exchange in the individual lineswitch LS, and is accessible to a group of connectors by way of conductors 101'103'. The lineswitch LS, with other similar lineswitches has access to a group of first selector repeaters of which the selector repeater SR is one. In the banks of the selector repeaters access is had to the outgoing trunks to the other oifices in the system, a group of trunks to each ofiice being accessible in a separate level; in one certain level access is had to a roup of reverting call switches, and in anot or level access is had to a group of local second selectors. The dial tone machine DT, for producing a dial tone current supply, the supervisory equipment, comprisin relays 181 and 182 and lamps LL an the subscribers meter M, are also shown in Fig. 1. The substation A is of the usual automatic type- The lineswitch LS is of the well known rotary type having no normal position and moving in one directlon only, being advanced upon the back stroke of the associated step ing magnet. The selector repeater SR mec anica-lly is of the usual Strowger vertical and rotary type. The circuits of selector repeater SR form a particular part of this invention and will be described in detail in later paragraphs.

Fig. 2 shows the local second selector S and the local third selector 8*. The selector S is one of the group of local second selectors accessible in a certain level in the banks of the first selector repeaters. In the banks of this group of second selectors, access is had to the various groups of local third selectors, the selector S being one of a certain roup. In the banks of third selectors access is ad to the various groups of connectors. It is also assumed that the exchange in question has a sub-office. Trunks to the sub-office are accessible in a certain level in the local second selector terminating thereat in incoming third selectors, similar to incoming selector IS, Fig. 4. p

The selectors S and S are identical in mechanical and circuit details and are of the well known Strowger vertical and rotary type. The circuits of these intermediate selectors are modified to meet the requirements of the invention and will be described in detail hereinafter.

Fig. 3 shows the connector C which is one of a certain group ofregular connectors accessible in the banks of the group of third selectors containing selector S (and also in the banks of the group of toll transmission selectors containing toll transmission selector TTS, Fig. 6). In the banks of the connector C access is had to a group of lines extending to substations, the line to substation- A" being one of these. This line also terminates in the individual lineswitch LS Below the connector C the ringing equipment, comprising the generator G and interrupter T, the ground interrupter I, and the busy machine BM are shown.

Mechanically the connectorC is of the well known Strowger vertical and rotary type. The circuits of the connector also form a part of the invention and will be described in detail in following paragraphs. The substation A" and the lineswitch LS are in all respects like the substation A and lineswitch. LS, shown in Fig. 1, except that in lineswitch the system. The incoming trunks from the other ofiices likewise terminate in similar incoming second selectors. The banks of the incoming second selectors are directly multipled with the banks of the local second selectors, and the incoming second selectors are thereby given'common access to the various groups of local third selectors.

The incoming selector IS mechanically is also of the Strowgervertical and rotary type. The circuit arrangement, forming a particular part of this invention, will be described in detail hereinafter.

The right-hand half of Fig. 5 shows the incoming toll selector TS. This ,toll selector terminates one of the toll trunks 'incomin from the ofiice in which the main toll boar is located. As many incoming toll trunks, terminating in similar incoming toll selectors, are provided as are necessary to carry the traflic to the ofiice in question. In the banks of the'incoming toll selectors, access is had to groups of toll transmission selectors, and also to a grou of trunks extending to the sub-oflice of the 0 co in question these trunks also terminating at the sub-office in similar toll transmission selectors.

The toll selector switch TS is of the ordinary Strowger vertical and rotary type and is operated according to. the well known two wire system of control. Special off-normal springs are provided however, to adapt it for use in the system being described.

The left-hand half of Fig. 5 shows the toll operators cord CO by means of which toll connections are established over trunks ex-' tending to the various ofiices in the system, each trunk terminating at the toll board in a jack such as jack J. This cord is of standard type and forms no particular part of the invention itself. The circuit thereof will be described only in so far as is necessary to fully describe other apparatus controlled by means within the cord.

Fig. 6 shows the toll transmission selector TTS, which is one of a certain group of toll transmission selectors accessible in the banks of the incoming toll selectors. The banks of the toll transmission selectors are directly multipled with the banks of the local third selectors, and the toll transmission selectors and local third selectors are thereby given common access to the connectors.

Mechanically, the toll transmission selector TTS is also of the Strowger vertical and rotary type. The circuit arrangements, however, have been modified to meet the requirements of the invention and will likewise be described in detail hereinafter.

Fig. 7 shows the frequency selecting connector FSC which is in all respects like connector C, Fig. 3, mechanically and in the method of operation, except that it is provided with an individual frequency selecting mechanism FS which is operated responsive to "a digit to select-the frequency of ringing current to be applied to the called line. In

its banks access is had to party lines. The

frequency selecting connector FSC is one of a group of frequency-selecting connector-s accessible in the banks of a certain group of local third selectors multipled with the banks of a certain group of toll transmission selectors, which in this case will also be assumed to be the same group having access to the group of regular connectors containing connector C. One party line, accessible to connector FSC, serving substations A'-A-', and terminating at the exchange in the lineswitch LS is shown. The substation A shown in full, and also the other substations, only the bells of which are shown, are in all respects like the substation A, Fig. 1, except that the ringers are normally connected from one or the other side of the line to earth instead of being normally bridged across the line conductors. Lineswitch LS is in all respects like lineswitch LS Fig. 3. A description of the operation of connector FS'C will be given in so far as it differs from the operation of connector C.

Fig. 8 shows the rotary connector RC, which is also like the connector C, Fig. 3, except that it performs an automatic rotary hunting movement after completing its rotary directive movement. In its banks, access is had to groups of lines extending to private branch exchanges with the number of the first line assigned as the call number of the entire group. The rotary connector RC is one of a group of rotary connectors accessible in the banks of a certain group of local third selectors multipled with the banks of a certain group of toll transmission selectors, which in this case will be assumed to be the same group having access to the group of connectors containing connector C. The first and last trunk-of a group extending to the private branch exchange X, accessible to connector RC, are shown. minates in an individual lineswitch such as LS at the main exchange, and in a ack such as jack J 8 at the branch exchange. The lineswitch LS is in all respect like lineswitch LS shown in Fig. 3. A description of the operation of connector BC in so far as it differs from the operation of connector C, Fig. 3, will also be given.

Fig. 9 shows the first selector repeater SR which is very similar to the first selector repeater SR, Fig. 1, the difierence in the two cases residing in the mannerin which the operation of the subscribers meter is controlled. The first selector repeater SR is adapted to control the operation of the subscribers me- Each trunk terter over a fourth conduct-or, while the first selector repeater SR is adapted to control fourth wi er is omitted in lineswitch LS", and

the meter 9 is connected to the private normal conductor 902' and is marginally adjusted.

Fig. 10 shows the reverting call switch RV, which, with other similar reverting call switches, is accessible in a certain level-in the banks of the first selector repeaters. The reverting call switch RV is also of the Showger vertical and rotary type, its circuits being modified, however, to meet the requirements of the invention, as will be described in detail in later paragraphs.

In the lower right-hand corner of Fig. 10 the special ringing equipment is shown, comprising the five ringing generators (which may be the same generators indicated in Fig. 7), the interrupting relay 7 4 and interrupter T. The interrupter T comprises two commutators with conducting and insulating segments as shown, and wipers for each rotating on the same shaft.

With this general description of the ob jects of the invention, the features, and the apparatus used, in mind, a further understanding and appreciation of the invention may be gained from a detailed description of the operations performed in the establishment of various connections between subscribers. For this purpose it will first be assumed that the suscriber at substation A wishes to establish a connection with the subscriber at substation A", (drawings to be arranged as shown in Fig. 11).

Gall from. substation A to substation A" To initiate a call, the subscriber at substation A first removes his'receiver. Removing the receiver at the substation A places a bridge across the line conductors 101 and 103,

thereby closing a circuit for the line relay 1 trunk upon which the switch wipers are posifrom ground onthe test contact engaged by battery.

" idle trunk line.

- switching relay 105 is prevented from operthe test wiper 118, armature 110 and the resting contact, armature 114 and the working contact, interrupting contacts 115 through the-winding of the stepping magnet 108 to Accordingly stepping magnet 108 operates in a buzzer like manner to advance the switch wipers 117120 in search of an During this operation ating by reason of the ground potential on both ends of its winding.

7 When an idle trunk line is reached, stepping magnet 108 ceases to operate, and relay 105, being no longer short circuited, energizes in series with the stepping magnet 108.

tepping magnet 108 does not operate over this circuit due to the relatively high resistance of the Winding of relay 105. In operating, relay 105 prepares a circuit for the subscribers meter M at armature 111, prepares'a holding circuit for itself at armature 110 and the working contact, and at armatures 109 and 112 disconnects the line conductors from the line relay 106 and ground, and extends the talking connection by way of these armatures and their working contacts, wipers 117 and 120, conductors 121 and 124, normally closed contacts controlled by armatures 137 and 141, normally closed contacts controlled by armatures 155 and 156, through the lower and upper windings of the line relay 126 tov battery and ground, respectively. Line relay 126 operates and closes a circuit for the release relay 127 at armature 142 and the working contact. Release relay 127 operates and performs the following circuit changes: At armature 144 ground potential is placed on the release conductor 122, thereby marking the trunk to first selector repeater SR busy and also completing a holding circuit for line relay 106 of the lineswitch LS, this taking place before the slow acting line relay 106 has had time to release its armatures. At armature 147 a circuit for the lower winding of holding relay 128 is prepared. At armatures 145 and 146' an initial energizing circuit for holding relay 128 is closed, which may be traced from ground by way of armature 150 and the resting contact, working contact and armature 145, normally closed springs controlled by armature 162, armature 160 and the resting contact, armature 146 and the working contact, resistance 136, through the upper winding of relay 128, armature 158 and the resting contact, resting contact-and armature 141, normally closed springs controlled by armature 164, through the upper winding of series relay 129, through the winding of vertical magnet 133 to battery;

Relay 128 operates over this circuit and by the actuation of armatures 148 and 152 establishes a new ener 'zing circuit for itself. Th1s circuit exten s from round at normally closed contacts control ed by armature 129, through the winding of vertical magnet 133 to batteryoi At armature 150 a circuit is closed for the lamp L in series with relay 181. Lamp L lights and relay 181 operates. The purpose of the lamp L and relay 181 will be described later. By the operation of arma-' ture 150, direct ground is removed from release conductor 122', ground now being supplled thereto through the upper winding of relay 125,

The first selector repeater SR is now in condition to receive the'first series of impulses to be dialed by the calling subscriber, all the above operations having taken place responsive to the removal of thereceiver at the calling substation. Furthermore, as soon as the wipers of the lineswitch LS are rotate'd into engagement with the trunk extending to the then idle first selector repeater SR, a dial tone is transmitted to the calling subscriber from the dial tone machine DT to which conductor 193 is connected. Hearing this tone indicates to the calling subscriber that he may commence dialing the number of the desired subscriber. I

In response to the dialing of the first. digit of the called number, the loop across the line conductors 101 and 103 is opened a corresponding number of times, thereby opening the circuit and causing a corresponding number of deenergizations and reenergizations of the line relay 126. Each time that relay 126 releases its armature 143, the resistance 136 and the upper winding of relay 128 are short circuited. The resistance of the upper winding of relay 128 is relatively high compared to the resistance of the upper Winding of re lay 129 and the resistance of the winding of vertical magnet 133. The short circuiting of resistance 136 and the upper winding of relay 128 therefore permits an increase in the current flow through the vertical magnet 133 suificient to cause the operation of the magnet each time the said resistance and winding is short circuited. Thus vertical magnet 133 operates to step the switch wipers opposite winding of relay 127 to battery and also to.

battery over a parallel circuit including arma ture 142 and the resting contact and resistance 136'.

Series relay 129 is also energized in series with vertical magnet 133, and by reason of its slow acting characteristic is maintained operated during the operation of vertical magnet 133. In operating, relay 129 closes an initial energizing circuit for stepping relay 131 which extends from ground on release conductor 122, working contact-and armature 153, armature 163 and the resting contact, ofi-normal-springs 166 which are closed upon the first vertical step of the switch wipers, through the winding of the stepping relay 131 to battery; Relay 131 operates and closes a holding circuit for'itself at armature 160 which may be traced from ground through the upperwinding of relay 125, working contact and armature 145, normally closedsprings controlled b armature 162, armature 160 and the wor ing contact, interrupting springs 165, off-normal .sprin s 166, through the winding of relay 131 to a ttery. The circuit of the stepping magnet 134 is also prepared at armature 159.

At the termination of the impulses of the. first digit, relay 129 deenergizes and opens the initial energizing circuit of relay 131 at armature 153. This armature, in releasing, allows the springs controlled thereby to close and complete the circuit for stepping magnet 134. Magnet 134 o crates and rotates the switch-wipers 1711 3 into engagement with the first set of bank contacts in the selected level and also opens the holding circuit for stepping relay 131 at interrupting springs 165. Relay 131 deenergizes and in turn opens the circuit of stepping magnet 134 at armature 159, also opening its own locking circuit at armature 160. Magnet 134 deenergizes and again closes interrupting springs 165. It the trunk terminating in this set of bank contacts is busy at this time, ground potential will be present on the test contact upon which the wiper 172 is positioned. A circuit will again be closed for stepping relay 131 from round on this test contact, wiper 172, armature 162 and the resting contact, interrupting springs 165, off-normal springs 166 through the winding of relay 131 to battery. Relay 131 will again operate to close the circuit of stepping magnet 134, which thereupon energizes and rotates the switch wipers into en-' gagement with the next set of bank contacts as previously described. This stepping operation is repeated until an idle trunk is found, which is indicated by the absence of ground potential on the associated test contact.

It will be assumed that the first idle trunk in the selected level at this time is the trunk comprising conductors 174-176. When the switch wipers 171-172 are rotated into engagement with the set of bank contacts 17 4-176' terminating this trunk, no circuit is closed for the stepping relay 131. Consequently the switch wipers are arrested in. this position. Furthermore, since no ground potential is applied to the upper terminal of theswitching relay 132, the following circuit becomes effective to cause the energization of the switching relay 132; ground through the upper Winding of relay 125, working contact and armature 145, through the winding of relay 132, interrupting contacts 165, 011- normal springs 166, through the winding of relay 131 to battery. The current flow in this circuit, limited by the comparatively high resistance of relay 132, is insuflicient to cause the energization of relay 131. Relay 132 operates, however, and performs the following circuit changes: Ground potential is supplied to the release conductor 175 of the selected trunk by way of upper winding of relay 125, working contact and armature 145, working contact and armature 162, and wiper 172, and the test contact 17 5 to which the conductor'175 is connected. A point in the circuit for operating the subscribers meter M is closed at armature 163, At armatures 161 and 164 the control circuit is extended by way 3 of Wipers 171 and 173, bank contacts 174 and 17 6, conductors 17 4 and 176 to the local second selector S The normal ground and battery connections to the upper and lower talking conductors are disconnected at the springs controlled by armatures 161 and 164. The control circuit now extends from ground at normally closed springs controlled by arms. ture 208 of second selector S conductor 174, bank contact 174', wiper 171, armature-161 and the working contact, armature 137 and the resting contact, armature 148 and the working contact, armature 146 and the working contact, resistance 131, upper winding of relay 128, working contact and armature 152, resting contact and armature 141, working contact and armature 164, wiper 173, bank contact 176, conductor 17 6, normally closed springs controlled by armature 211, winding of relay 202, through the winding of vertical magnet 204 to battery. The application of ground potential to release conductor 17 5 closes a circuit extending by way of the normally closed contacts controlled by armature 209 through the upper winding of the two-step relay 201 to battery. The energizetion of the upper winding of relay 201.causcs the operation of armature 21.0 only. This operation merely opens a point in the circuit of release magnet 206 and prepares other circuits to be described later.

In response to the next digit dialed by the subscriber at substation A, resistance 136 and the upper winding of relay 128 are again short circuited a corresponding number of times. I This causes the operation of the vertical magnet 204 in a manner similar to the way in which vertical magnet 133 of the first selector repeater SR was operated. In operating, ma net 204 steps the wipers 221-223 opposite the level of bank contacts corresponding to the digit dialed. Relay 202, which operates in series with the vertical magnet 204 and due to its slow-acting characteristics remains operated during the transmission of this series of im ulses, closes a circuit which may be traced from ground by way of armature 210 and the working con,- tact, working contact and armature 212, offnormal springs 218 which are closed upon the first vertical step of the switch wipers, through the winding of stepping relay 203 to battery. Stepping relay 203 operates and closes a holding circuit for itself at arma ture 213-and prepares a circuit for stepping magnet 205 at armature 214. At the termination of this series of impulses series relay 202 deenergizes and, by permitting-the closure of the springs controlled by armature 212, closes a circuit for stepping magnet 205. Magnet 205 operates and rotates the switch wipers 221223 into engagement with the first set of bank contacts in the selected level, and also opens the holding circuit of stepping .relay 203 at interrupting springs 215. Stepping relay 203 deenergizes and opens a circuit of the stepping magnet 205. In releasing, stepping magnet 205 again closes interrupting contacts 215. If the trunk terminating in this set of bank contacts is busy, ground potential will be present on the test contact engaged by test wi er 222, and a circuit will again be closed or relay 203 from ground on said test contact, wiper 222, armature 209 and the resting contact, interrupting contacts 216, interrupting contacts 215, off-normal springs'218, through the winding of relay 203 to battery. The alternate operation of the stepping relay 203 and magnet 205 now takes place in a manner identical to the way in which stepping relay 131 and stepping magnet 134 of the first selector repeater SR operated,- thereby causing the selector S to position its wipers on the first set of bank contacts terminating an idle trunk line, an idle trunk line again being indicated by the absence of ground potential on the test contact. During this time, relay 201 is prevented from operating in itssecond step by reason of the ground potential on both terminals of its lower winding.

It may be assumed that the trunk line selected is the one comprising conductors 224-226. Since wiper 222 encounters no ground potential, the circuit which may be traced from ground on the release conductor 17 5, through the lower winding of relay 201, interrupting contacts 215, off-normal springs 218, through the winding of the stepping rela 203 to battery, becomes eflective to cause re a 201 to operate in its second step. Due to t e high resistance of the lower winding of relay 201, the current flow in the circuit is'insuflicient to cause the operation of relay 203. Relay 201, in operating to its second step, causes the full operation of all its armatures with the following results: At armature 209 ground potential is supplied to the release conductor 225 of the local third selector S by way of ground on release conductor 175, working contact and armature 209, wiper 222, and the test contact 225 to which conductor 225 is connected. The circuit for the upper winding of relay 201 is at the same time opened by the separation of contacts controlled by armature 209. At armatures 208 and 211 the control circuit is extended to the selector S, ound now being supplied to the upper talking conductor at springs controlled by armature 208,-and battery to the lower talking conductor through vertical magnet 204 in series with relay 202' at s rings controlled by armature 211.

The se ector S is identical in all details to the selector S and operates responsive to the next series of impulses dialed by the calling subscriber in a manner identical to the way in which selector S operates, positioning. its wipers opposite the level of bank contacts corresponding to the digit dialled and then selecting an idle trunk in this level.

It may be assumed that the trunk selected is the one comprising conductor 234236 terminating at the connector 0. Thus,when this trunk is seized a circuit is closed for the upper winding of the two-step relay 301 from ground supplied to release conductor 235, resting contact and armature 313 through the upper winding of 301 to battery: Relay 301 operates in its first stage operating armature 312 only, opening a point in the circuit of release magnet 308. A circuit is also closed for switching relay 305 from ground on conductor 235 through the normally closed vertical off-normal springs 333, through the lower winding of relay 305 to battery. Relay 305 operates and prepares a holding circuit for itself at armature 328, and at armature 326 connects the vertical magnet 306 in series with the series relay 302 at the same time disconnecting the rotary magnet 307. Relay 305 at this time functions as a change-over relay as will be further described later. Seizure of the trunk also causes the control circuit to be extended to the connector 0, ground now being supplied to the upper talking conductor at springs controlled by armature 311, and battery to the lower talking conductor through vertical magnet 306 in series with relay 302 at springs controlled by armature 315.

Responsive to the dialing of the next digit b the callin subscriber, resistance 136 and t e upper winding of relay 128 are again short circuited a corres onding number of times thereby causing the operation of the vertical magnet 306 to position the switch Wipers 341-343 opposite the corresponding level of bank contacts. Series relay 302 operates in series with the vertical magnet 306 and due to its slow-acting characteristic remains operated during the transmission of the series of impulses. 'At armature 317 and the Working contact, the holding circuit for relay 305 is completed to maintain this relay operated during the vertical movement of the switch wipers, the initial energizing circuit for the lower winding of rela 305 eing opened on the first vertical step 0 the switch wipers at vertical off-normal spring 333. The operation of armature 316 at this time is without effect. At the end of this series of impulses, relay 302 dcenergizes and opens the holding circuit of the lower winding of relay 305 at armature 317. Relay 305 deenergizes and reconnects the rotary magnet 307 in series with the relay 302 at armature 326 at the same time disconnecting the vertical magnet 306.

Responsive to the next series of impulses dialed by the calling subscriber the rotary magnet 307 is operated to rotate the switch wipers into engagement with the set of bank contacts corresponding to the digit dialed, this set being the one terminating the line of the called substation A, namely bank contacts 344-346. Relay 302 again operates during the transmission of this series of impulses, this time in series with the rotary magnet 307, and prepares the testing circuit for the test relay 304 at armature 316 and the working contact. The remaining operations of the connector C now depend upon whether the called line is busy or idle at this time.

If the line to substation A" is busy at this time, ground potential will be present on the back contact 345, and the engagement of wiper 342 with contact 345 completes a circuit for the test relay 304 from ground on contact 345 by way of wiper 342, armature 316 and the working contact, resting contact and armature 327, through the winding of test relay 304 to battery. Relay 304 operates and opens a point in the ring back tone circuit at armature 323, closes a point in the busy tone circuit at armature 322, and prepares a locking circuit for itself at armature 321. Shortly after the termination of this series of impulses, relay 302 deenergizes, this time closing a locking circuit for test relay 304 by permitting springs controlled by armature 316 to close. A circuit for the lower winding of two-step relay 301 is also closed by the release of armature 317 which may be traced from ground on release conductor 235, rotary ofi-normal springs 331 closed upon the first rotary step of the switch wipers, armature 317 and the resting contact, vertical olfnormal springs 332 closed upon the first vertical step ofthe switch wipers, through the lower Wlnding of relay 301 to battery. The energization of the lower winding of this relay causes this relay tooperate in the second step, causing the full operation of all the armatur'es of this relay with the following results: At armature 313 the circuit for its' upper winding is opened, and at armatures 311 and 315 the ground and battery supplied to conductors 234 and 236 are disconnected.

The disconnection of ground and battery.

from the conductors 234 and 236 causes the deenergization of the holding relay 128 in the first selector repeater SR. In deenergizing, relay 128 opens the circuit of the supervisory relay 181 at armature 150, at the same time placing ground potential on the release trunk directly. Bythe release of armature 151, the lower winding of battery feedrelay 130 is connected to the lower talking conduc tor. By the release of armatures 148 and 152 a talking circuit is completed from the substation A to the connector C,.so that the calling subscriber may hear the busy tone from the busy machine BM, a busy tone potential being supplied to the lower talking conductor from the common busy tone conductor 391, resting contact and armature 319, armature 322 and the Working contact, to conductor 236 from where it is transmitted to the calling substation. Hearing this tone notifies the calling subscriber that thedesired line is busy at this time, whereupon he will replace his receiver with the intention of calling some later time. Replacing his receiver initiates the release of all the operated switches, this operation being fully described in later paragraphs.

Returning now to the point where further operations of the connector were determined by the busy or idle condition of the calling line, it may now be assumed that the line to.

substation A" is idle at the time connection relay 304 is not operated, no ground potential being present on thebank contact 345. In this case, when relay 302 falls back at the termination of the impulses, a circuit is closed which may be traced from ground on release conductor 235, armature 321 and the resting contact, through the upper winding of relay 305, resting contact and armature 316, wiper 342, bank contact 345 through the winding of the switching relay 361 of the lineswitch LS", interrupting contacts 369, through the winding of the magnet 363 to battery. Relays 305 and 361 operate in this circuit, but due to the high resistance of the switching relay 361, the current flow is insuflicient to cause the operation of magnet 363. Relay 305, in operating, closes a locking circuit for itself at armature 328, places ground potential on the bank contact 345 at armature 325 by way of wiper 342, thereby marking the line of substation A" busy, and

at armatures 324 and 329 closes the signalling circuit to signal the subscriber at substation A". The signaling circuit may be traced from ground by way of the resting contact and armature 318, armature 324 and the working contact, wiper 341, bank contact 344, line conductor 371 through the balls of the substation A", line conductor 372, bank contact 346, wiper 343, working contact and armature 329, armature 320 and the resting contact, through the lower winding of ring cut-otf relay 303, common signalling conductor 390 to which battery superimposed ring ing ccurrent from generator G and direct battery are intermittently connected. Relay 361 in energizing, disconnects the normal ground and battery connections from the line conductors without connecting up the switch wipers 380-382, this being due to the usual mechanical interlocking mechanism between relays 361 and 362. The bells at the substation A" now operate responsive to the ringing current until the subscriber at substation A" answers. Obviously, relay 301 is again operated in its second step at the end of the last series of impulses, the circuit for its lower winding being closed by the release of armature 317, after which relay 128 in the selector repeater SR is deenergized, preparing the talking circuit by releasing armatures 148 and 152 as reviously described.

When the su scriber at substation A" removes his receiver to answer the call, a direct current bridge is placed across the line conductors 371372 which closes a direct current circuit for the ring cut-off relay 303. Ring cut-off relay 303 operates and closes a locking circuit for its upper winding at armature 319' which may be traced from ground on release conductor 235, armature 319 and the working contact, through the upper winding of relay 303,. resistance 309 to battery. At armatures 318 and 320 the ringing circuit is disconnected and the talking circuit between the subscribers at sub station A and substation A is finally comacross the called ine.

pleted. The release of armatures 148 and 152 bridges batter feed relay 130 directly Relay 130 operates and disconnects one terminal of relay 128 from the lower talking conductor at armature 158; reverses the ground and battery connections to the calling line at armatures 155 and 156; and at armature'157'closes a circuit for the magnet 116 of the subscribers meter M in parallel with the lower winding of relay 129. The meter M operates to register the callf Relay 129 operates andlocks to the release trunk at armature 153, and functions to maintainthe circuit of magnet 116 closed u'ntil'the connection is released. In :"this way the meter M is prevented from being falsely operated by the jiggling of the receiver switchhook at the called station.

The reversing of the battery and ground conthe line, talking batter nections to the calling line performs no function in the present connection. This operation may be used to cause the collection of a coin when a call is initiated from a pay station, and is therefore shown here for the purpose of illustration. The calling and called subscribers may now hold conversation, relays 125 and 130 being the only brid es across being urnished through the windings of relay 125 for the calling subscriber and through the windings of rela 130 for the called subscriber.

At the end of the conversation both subscribers will replace their receivers. lVhen the called subscriber replaces his receiver, the direct current bridge across the line conductors is opened thereby causing the deenergization of the battery feed relay 130. Relay 130 deenergizes and restores its armatures to normal. The direction of current flow to the calling substation is restored to normal by the release of armatures 155 and 156, and-a circuit for the supervisory lamp L and relay 182 is closed at armature 157. When the calling subscriber replaces his receiver, the direct current bridge across the line conductors 101 and 103 is mterrupted thereby opening the circuit for the line relay 126. Relay 126 deenergizes and opens the circuit of release relay 127 at armature 142. Relay 127 deenergizes and releases its armatures with the following results: At armature 144 ground potential is removed from the release conductor 122, and a circuit, which-includes the off-normal springs 168 closed upon the first vertical step of the switch wipers and armature 138, is closed for the release magnet 135. "In operating, magnet 135 restores the switch wipers 171-173 to normal. The removal of ground from release conductor 122 also opens the holding circuit for the lower winding of relay 129, and removes ground otential from the meter conductor123. Reays 129 and 105 thereupon deenergize and restore their armatures to normal; magnet 116 of the subscribers meter M restores to normal.

By the release of armature 145, ground potential is removed from the release conductors 122, 225, and 235, which are serially connected, extending through the first selector repeater SR, second selector S third selector S and connector C. The removal of ground from these respective conductors causes the deenergization of switching relay 132 in the selector repeater SR, switching rela 201 in the second selector S switching re ay 201 in the third selector S and switching relay 301 in the connector 0. The deenergization of the above mentioned switching relays efi'ect the closure of the following release circuits: A circuit for release magnet 206 is closed from ground by way of armature 210 and the resting contact, Vertical 011- normal springs 217 closed upon the first vertical step of the wipers 221-223 of selector S, through the winding of release magnet 206 to battery. Release ma net 206 operates and causes the restoration of the wipers 221 223 of the selector 8. Similarly, a circuit is closed for release magnet 206 of the third selector S which magnet operates to release wipers 231233 of the selector S to normal. A circuit is also closed for release magnet 308 which may be traced from ground by way of the resting contact and armature 312, vertical ofi-normal springs 330 closed upon the first vertical step of the connector C, through the winding of the release magnet 308 to battery. Magnet 308 operates and causes the restoration of the wipers 341-343 of the connector C to normal. The removal of ground potential from the release conductor 235 also opens the holding circuits for the ring outofi relay 303, and switching relay 305. These relays thereupon deenergize and restore their armatures to normaL- All apparatus used in establishing the above described connection has now beenrestored'to normal and is ready to be used again to establish other connections.

Uall from distant o fice t0 substation A use of outgoing repeaters is entirely obviated,

the trunks extending from one exchange to another being accessible directly in the banks of first selector repeaters of the type shown in Fig. 1 (or Fig. 9, to be described later) and terminating directly in incoming selector repeaters such as shown in Fig. 4. To describe the operations performed in establishing a connection from a subscriber in one office to a subscriber in another office, it will be assumed that a certain subscriber 1n some distant oflice desires connection with the sub-u scriber at substation A, (drawings to be arranged as shown in Fig. 11)

Toestablish this connection, the subscriber in the distant oflice removes his receiver and dials the directory number of the substation A. In response-to the removal of the receiver at the calling substation the individual lineswitch of the said substation operates to select a trunk to an idle first selector repeater, which ma be identical to the first selector repeater s own in Fig. 1.' Responsive to the dialing of the first digit of the called number, the first selector repeater operates as described above and positions its wipers opposite the level of the bank contact in which trunks to the oflice serving the subscriber at substation A are accessible, and

then automaticall select an idle one of'these trunks. It may eassumed that the'trunk selected is the one comprising conductors 401 and 402 terminatin in the incoming second selector IS, Fig. 4. hen this trunk is seized,

. a circuit is closed which may be traced from ground by way of the resting contact and armature 419 in the incomin selector IS, through the winding of line re ay 403, trunk conductor 401, over a loop including a resistance and the holding relay of the selected firstselector repeater similar to resistance 136 and relay 128 of selector repeater $18., over trunk conductor 402, armature 420 and the resting contact, through the upper winding of the marginal-1y adjusted impulse relay 405 of the incoming selector IS to battery. The resistance of the above traced circuit is sufiiciently high to prevent the operation of relay 405 at this time. Relay 403 is partially shunted by the-ground connection by way of resting contact and armature 418 and resistance 440 but nevertheless operates over the above traced circuit and performs the following circuit changes: At armature 415 an obvious circuit is closed for release relay 408. Relay 408 operates and at armature 428 opens a point in the circuit of release magnet 413 and connects ground potential to release conductor 450. Relay 403 in operating also closes a circuit which may be traced from ground by way of the normally closed springs controlled by armature 431, armature 416 and the working contact, armature 417 and the resting contact, resistance 441, through the windin of the holding relay 406, normally close vertical off-normal springs 436, normally closed springs controlled by armature' 435, resting contact and armature 449, through the winding of series relay 409, through the winding of vertical magnet 412 to battery. The current flow in this circuit is insufficient to cause the operation of magnet 412 and series relay 409 at this time, but holding rela 406 energizes and at armature 424 shunts t e ofi-normalsprings 436 which are opened upon the first vertical step of the switch wipers, prepares the holding circuit for stepping relay 407 at armature 423, and at armature 425 prepares a deenergizing circuit for impulse relay 405. p

Responsive to the next series of impulses dialed by the calling subscriber, the resistance and relay in the selected first selector repeater at this oiiice similar to resistance 136 and relay 128 of selector SR, Fig. l, are short circuited by contacts on theline relay a number of times corresponding to the 2 digit dialled, as previously described. Each time that this resistance and relay are short circuited, the current flow in the above traced circuit includingthe two trunk conductors in series is sufficiently increased to cause the operation of the marginal relay 405. Marginal relay 405, in operating, closes a circuit for the lower winding of relay 405 at armature 422 which may e traced from ground by way of armature 422 and the working contact, armature 425 and the working contact, resistance 442, normally closed springs controlled by armature 419, through the lower winding of relajy 405 to battery. Marginal relay 405 is di erentially wound with the windings so proportioned that the magneto motive force produced by the current in the upper winding when the resistance and winding of the impulsing relay in the first selected repeater are short circuited, is greater than that produced by the lower winding. For this reason relay 405 remains operated dur ing the time the resistance and the impulsing relay of the first selected repeater are short circuited. But when the short circuit is removed from the said relay and resistance, the current flow in the upper winding of relay 405 is reduced so that the magneto motive force produced by the current in the lower winding is greater than that produced by v the current in the upper winding. Relay 405 therefore immediately deenergizes and in so doing opens the circuit of its own lower winding at'armature 422. In this manner, the impulse relay 405 operates in positive syn chronism with the line relay of the first se-- lector repeater. Each time relay 405 operates, resistance 441 and relay 406 are short circuited. This causes impulses of increased current in the circuit of magnet 412 and series relay 409. As a result magnet 412 is operated to raise the wipers 451-453 of the incoming selector IS opposite the level of bank contacts corresponding to the digit dialed. Series relay 409 operates in series with the magnet 412, remaining operated continuously during the transmission of the series of impulses by reason of its slow acting characteristic, and closing a circuit for the stepping relay 407. This circuit may be traced from ground by way of armature 428 and the working contact, working contact and armature 429, armature 434 and the resting contact, ofi-normal springs 437 closed upon the first vertical step of the switch wipers, through the winding of stepping relay 407 to battery. Stepping relay 407 operates and closes a holding circuit for itself at armature 426 which may be traced from ground by way of armature 423 and the working contact, armature 426 and the working contact, interrupting springs 439, off-normal springs 437, through the winding of relay 407 to battery. .At armature 427 a circuit is prepared for the rotar magnet 414.

t the termination of this series of impulses, series relay 409 de-actuates and closes a circuit for magnet 414 which may be traced from ground by way of armature 428 and the working contact, normally closed springs con trolled by armature 429, working contact and armature 427 through the winding of rotary set of contacts is busy, ground potential will be present on the test contact engaged by wiper 452, and relay 407 will again be energized. Thus stepping relay 407 and magnet 414 operate alternately and cause the switch wipers to be moved into engagement with a set of bank contacts terminating an idle trunk, in the well known manner.

When the contacts terminating atthe idle trunk are reached, which may be assumed to be the trunk comprising conductors 454456, no ground potential will be encountered by wiper 452, and the circuit which may be traced from ground by way of armature 428 and the working contact, through the winding of relay 411, interrupting contacts 439, ofi'-norn1al springs 437, through the windin Y of stepping relay 407 to battery, becomes e fective to energize switching relay 411. Due to the resistance of switching relay 411, the current flow in this circuit is insuflicient to cause the operation of stepping relay 407. Switching relay 411 operates, however, and performs circuit changes as follows: At armature 433 ground potential is supplied to release conductor 455 by way of armature 428 and the working contact; a circuit is prepared for switchover relay 404 at armature 432; the initial energizing circuit of relay 407 is opened at armature 434; and at armature 431 and 435 ground and battery via magnet 412 is disconnected from the heavy talking conductors by the separation of the normally closed springs controlled by these armatures step, thereby preparing the selector for operat1on.,

Responsive to the next series of impulses dialed by the calling subscriber, relay 405 is again operated a corresponding number of times, short circuiting relay 406 and resistance'441 the same number of times, which causes the operation of the verticalmagnet

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