US1607782A - Automatic telephone system - Google Patents

Description

Nov. 23 192a. 1,607,782

A. J. RAY

- AUTOMATIC TELEPHONE SYSTEM Filed April 17, 12 22 '10 Sheets-Sheet 1 F1 IE 1 A. J. RAY

l0 Sheets-Sheet 5 b fiTiThur l B Z.

Filed April 1'7, 1922 Nov. 23 1926.

AUTOMATIC TELEPHONE SYSTEM Nova 23 1926.

A. J. R AY AUTOMATIC TELEPHONE SYSTEM 10 Sheets-$heet i;

Filed April 17, 1922 Nov. 23 1926. 1,607,782

A. J. RAY

AUTOMATIC TELEPHONE SYSTEM Filed April 17, 1922 10 Sheets-Sheet 6' if! ZK/ I Ty.

A. J. RAY

AUTOMATIC TELEPHONE SYSTEM Nov. 23 1926.

Filed April 17, 1922 10 Sheetsh 9% '7 Imran 0rur i135 Nov. 23 1926.

A. J. RAY

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A. J- RAY AUTOMATIC TELEPHONE SYSTEM Filed April 17, 1922 10 Sheets-Shjeo' 9 HUT" Nov. 23 1926. 1,607,782

A. J. RAY

AUTOMATIC TELEPHONE SYSTEM Filed April 17, 1922 10 Sheets-Sheet 10 Jfmen ur fiffhur 152g art- Patented Nov. 23, 1926.

UNITED STATES ARTHUR J. BAY, OF CHICAGO, ILLINOIS,

PATENT OFFICE."

ASSIGNOR, BY MESNE ASSIGNMENTS, TO

AUTOMATIC ELECTRIC INC., OF CHICAGO, ILLINOIS, A CORPORATION OF DELA- WARE.

AUTOMATIC TELEPHONE YSTEM.

Application filed April 17, 1922. Serial No. 553,677.

The present invention relates in general to automatic telephone systems of the multioflice type, but is more particularly concerned with systems of this character in which the main offices of the system have several smaller exchanges subsidiary to them, the latter being commonly known as sub or satellite exchanges; and the object of the invention may be said to be the provision of sub-office switching equipment embodying new features and novel circuit arrangements which are better adapted than those heretofore used to meet the service requirements of the present time.

More specifically, one of the principal ob jects is to produce a novel device referred to hereinafter as a switching discriminator. This device introduces a considerable saving in the inter-oflice trunks, and also decreases the number of switches required in certain classes of connections.

There are other objects of the invention not now specifically mentioned which together with those enumerated above will be described thoroughly hereinafter, reference being hadto the accompanying drawings forming part of this specification.

Referring now to the drawings, Figs. 1 and 2 show maps of certain of the exchanges in the system about to be described. Fig. 3 shows the manner in which certain figures of the drawings are to be placed in order that the description of the operation of the system may be followed. Fig. 4 shows a general trunking layout of the system accord ing to the map shown in Fig. 1. Figs. 5-12, inclusive, when placed in the relative positions indicated in Fig. 3, show by means of the conventional circuit diagrams the detailed circuits of the various apparatus and the manner in which the novel results set forth above are accomplished.

The invent-ion is, of course, applicable to various sizes of multi-oflice telephone systems; however, in the present case it has been illustrated in connection with a six digit system, or one the ultimate capacity of which does not exceed a million lines.

The system disclosed in the present case has ninety main exchanges each having an ultimate capacity of ten thousand lines, and sub-exchanges or satellites varying in size from fifty or one hundred lines to one thousand. In a six digit system of this character well as with the first.

the first two digits dialled select the particular main exchange desired. The third digit determines to which group of one thousand lines a call is going, while the fourth digit selects the particular group of 100 lines which contains the desired called line. Since the sub-exchanges may vary in size from one hundred to one thousand lines, the third or fourth digit, as the case may be, determines the particular satellite exchange called.

In a system of the character outlined above, it often occurs that two or three of, these satellite exchanges will be located close together, at some distance from the main exchange to which they are subsidiary and that a second main exchange is situated quite close to the sub-exchanges. Under these conditions there will, in all probability, be trunk l nes connecting one or more of the sub exchanges with the second main exchange as These additional groups of trunk lines may be provided because there is a great deal of trafiic from one or more of the sub-offices in the direction of the second main exchange, which makes it' more economical to install additional groups of trunk lines from these sub-offices to the second main exchange rather than route the calls which go to points in the general direction of the second exchanges thru the main exchange with which the suboifices are associated. Under these conditions, all outgoing calls which finally terminate at an exchange located in the general direction of the aforesaid second main, exchange will be routed thru that exchange, while all calls in the other direction will be routed through the first main exchange. All incoming calls will be handled thru the first exchange.

In describing the drawings, the general layout of the system will first be explained with reference to the maps of the exchanges, Figs. 1 and 2. In Fig. 1 there is shown a main oifice designated by the refernce character 91 which represents the number of this office in the numbering scheme ofthe system. The main offce 91 has the subsidiary satellite ()fTlGGS 912, 913, and 9181 associated with it. The first two mentioned sub-ofiices each have an ultimate capacity of one thousand lines, while the last mentioned sub-office is of one hundred lines capacity. At 92 is shown another main office located in fairly close proximity to the sub-exchanges but at some distance from the main office 91. The lines connecting the various exchanges illustrate the trunk lines in the system and the arrow heads indicate whether connections may be handled in both directions or only in one direction over these trunk lines, thus, the three sub-exchanges 912, 913 and 9181, are connected to the main exchange 91 by trunk lines which are used for calls in the direction of the main exchange and in the direction of the sub-ofiices and in addition the 913 sub-ofiice is connected with the exchanges 912 and 9181 by trunk lines which are used for calls in either direction. All the above trunk lines may be of the so called two way type or may be two groups of one way trunk lines depending upon what is considered the most advisable in each case. The sub-oilice 913 is also connected, by means of a group of one way trunk lines, to the -main exchange 92 so that calls in the general direction 01 the main oitice 92 may be extended without taking a trunk line to the main exchange 91 and thereafter a trunk line from exchange 91 to exchange 92.

in Fig. 2 is shown another situation in which two sub-otfices are associated with the main exchange 91 and the trunk lines are so arranged that, in order to call exchange 912 from exchange 918, it is unnecessary to go thru the main exchange 91.

Referring now to the trunking diagram shown in Fig. l, the various trains of switches involved in typical connections in the trunking situation shown in the map, Fig. 1, are illustrated. To give a general understanding of the operation of the invention, the manner in which calls are extended from the sub-oiiice 913 to the various other exchanges will be given with reference to Fig. 1.

F or the purpose oi": the description it will first be assumed that the subscriber at substation A in .sub-office 913 desires to call a subscriber at substation A in the main ex change 91. In order to accomplish this result he will remove his receiver and operate his calling device for the six digits 91826X, the letter K as used in this combination of digits, and as it will be used subsequently, simply indicating that any digit from 1 to 0 may be dialled as the final digit so far as the trunking diagram is concerned, the individual bank contacts of the connector levels not being shown. .Vhen the receiver is removed at substation A the primary line switch (1 is caused to select an idle trunk line leading to a secondary line switch such as C. The secondary line switch C is thereupon operated to select an idle trunk line extending by way of a repeater such as R to an incoming first selector E in the main exchange. An idle finder switch such as F is started in operation as soon as the primary trunk line is seized in order to reearse associate a switching discriminator SD with the seized trunk line. In response to the first digit dialled by the calling subcriber the first selector E in the main exchange raises its wipers opposite the ninth level of bank contacts. The selector E then operates to automatically select an idle trunk line leading to a second selector such as E. The element N of the switching discriminator SD is operated in synchronism with the selector E in the main exchange and operates to raise its wipers to the level of bank contacts corresponding to the digit dialled. lihen the calling device at sul station A is operated in accordance with the second digit 1 of the called number the second selector E is caused to raise its wipers opposite the first level of bank contacts. Thereafter the second selector E is operated to select a trunk line leading to an idle third selector switch which we will assume is the selector E In the switching discriminator SD the element N responds to the digit 1 and rotates its wipers in on the level of bank contacts to which it was raised by the first digit, that is, the first contact in the ninth level. In response to the third digit- 8 the third selector E raises its wipers to the eighth level of bank contacts and then automatically operates them to select a trunk line leading to an idle fourth selector such as E The element M of the switching discriminator SD, in response to the third digit 8, raises its wipers to the eighth level of bank contacts. When the next digit 2 is dialled the wipers of the fourth selector E are operated to the second level ot bank contacts and are then rotated to select a trunk line leading to an idle connector switch which it will be assumed is the connector H. In the switching discrin'iinat-or SD the element M responds to the fourth digit oi": the desired number and rotates its wipers into engagementwith the second bank contact on the eighth level. inasmuch as the digits 9182 determine that the connection is going to the main exchange and not over any one of the by-paths accessible thru the line switches C, C, C, U, and C the switching discriminator PS1) has no function to per form and is released. In accordance with the next two digits 6X dialled by the subscriber at substation A the wipers of the connector H are raised vertically to the sixth level and then rotated into engagement with the bank contacts in which is terminated the line of the desired subscriber at substation A It will now be assumed the subscriber at substation A desires to call a subscriber at substation A" in the hundred line sub-exchange 9181 whose number is 91817X. In response to the first three digits 918, the first, second and third selectors such as E,

E and E in the main exchange are operated in a manner similar to that described in the preceding connection. The elements N and M of the switching discriminator SD are operated in the same manner as before in response to the digits 918. The fourth selector E is raised to the first level in response to the fourth digit 1 and automatically operates to select an idle trunk line leading to an incoming connector in the sub-exchange 9181 thru a repeater such as R The element M of the switching discriminator SD also responds to the fourth digit 1 and rotates its wipers into engagement with the first set of bank contacts on the eighth level. It will be noted from the trunking diagram shown in Fig. 1 that the sub-exchange 9181 is located a point midway between exchanges 913 and 91 and also that the exchange 918 has trunk lines extending to exchange 9181. Therefore, in order to reduce the length of trunk lines used, the switching discriminator SD causes line switch C to be automatically 0perated to select an idle trunk line leading to an incoming connector in the sub-exchange 9181 thru a repeater such as R line seized by the line switch G extending to the main exchange and the selectors E,- E, E and E therein are released as a result of this operation, as is the switching discriminator SD. In response to the last two digits 7X, an incoming connector such as H is operated to complete the connection to the line of the desired substation A It will now be assumed that the calling subscriber atsubstation A desires to communicate with the subscriber at substation A in the thousand line sub-exchange 912 whose number is 91278X. hen the receiver is removed, the primary line switch C operates to extend the calling subscribers line to an idle secondary line switch such as C. The line switch C then operates to select a trunk line extending to an idle incoming first selector such as E in the main exchange. When the primary trunk line is seized an idle finder such as F is operated to associate the discriminator SD with said trunk. In accordance with the first two digits 91 a first and a second selector such as E and E are operated in a manner similar to that above described and the connection is extended to a third selector such as The element N of the switching discriminator SD is operated in response to the digits 91 raising its wipers to the ninth level of bank contacts and then rotating them into engagement with the first contact in that level. hen the third digit is dialled the third selector E in the main exchange is operated to raise its wipers to the second level of bank contacts and then to rotate them in search of an idle trunk line leading to an The trunk incoming fourth selector in the sub-exchange 912. The element M of the switching discriminator SD is operated to the second level in response to the digit 2 in the manner before described. The number 912 determines that a subscriber in the sub-exchange 912 is being called and, as there are trunk lines extending from the sub-exchange 918, in which the call is originated, to the subexchange 912, the switching discriminator SD causes the line switch C to extend the call over an idle trunk line to an incoming fourth selector such as E in the sub-exchange 912. The trunk line extending to the main exchange, the switches operated therein, and the switching discriminator SD, are immediately released. In accordance with the three remaining digits 78X the fourth selector E and a connector such as H are operated to extend the connection to the line of the substation A.

It will now be assumed that the subscriber at substation A in the sub-exchange 913 desires to call the subscriber at substation A in the other main exchange 92. In order to do this the calling subscriber will remove his receiver and operatehis calling device for the digits 9255651. W hen the receiver is removed the primary line switch 0 and a secondary line switch such as C operate to select a trunk line extending to an idle incoming first selector switch in the main exchange and an idle finder such as F operates to connect a switching discriminator SD with the selected primary trunk line. In response to the first digit 9 the wipers of the first selector E are raised opposite the ninth level of bank contacts and are then automatically rotated main exchange 92 by way of the repeater R The element N of the switching discriminator is also operated in accordance with the digit 2 and, as there are trunk lines extending from sub-exchange 913 to the main exchange 92, the line switch C is operated to select one of these trunk lines and the connection to the main exchange is released as is the switching discriminator SD. hen the next four digits 556K are called, an incoming third selector such as E a fourth selector such as IE and a connector such as H, are operated in the main exchange 92 to extend a connection to the line of the substation A The manner in which connections are extended to subscribers in the various eX- changes adjoining the exchange 913 having been described, the way in which a local connection is established will now be explained. For this purpose it will be assumed that the calling subscriber at substation A desires to call a subscriber at substation A whose number is 9l3 l6X. Vlhen the receiver is removed, the line switch C and a secondary line switch C are operated in the usual manner to select a trunk line extending to an idle first selector which it will be assumed is the selector E in the main exchange. By the operation of an idle finder such as F the switching discriminator SD is associated with the seized primary trunk line. In response to the first two digits 91 of the called number the first selector E and a second selector E in the main or change are operated to extend the connection to an idle third selector such as The element N of the switching discriminator SD operates to register the first two digits in the same manner as before described. lVhen the third digit 3 is dialled the third selector in the main exchange responds and operates to raise its wipers to the third level of bank contacts and then seizes an idle incoming fourth selector E in the subeXchange 913. As the first three digits determine that the connection is going to a local line, the operation of the element ill of the switching discriminator SD for the digit 3 causes the line switch C to be operated to seize an idle trunk line extending to a local fourth selector such as The trunk line extending to the main exchange, the operated switches therein and the discriminator SD are released as before.

In response to the three remaining digits 46X, the selector E and a connector H are operated in the usual manner to complete the desired connection to the sub-station A.

It will be assumed that the subscriber at substation A desires to call the subscriber at substation A on his own line. In order to accomplish this result the subscriber at substation A will remove his receiver and operate his calling device for the digit O. In response to the removal of the receiver the line switch C and a secondary line switch such as C operate as before described. By the operation of an idle finder F, when the primary trunk is seized, a switching discriminator SD is associated with the said trunk. lVhen the digit Q is called on the calling device, the selector is operated to raise its wipers to the tenth level. As the tenth level is dead the trunk selecting operation of the first selector is without function. As the element N of the switching discriminator is operated in accordance with the digit 0 which determines that a subscriber on the same line as that of the substation A is being called, the line switch C is operated to select an idle ring back device K and the connection to the main exchange and the switching discriminator SD are released. The subscriber at substation A vill now replace his receiver upon the switch-hook. By this operation the ring back apparatus K starts functioning and the signals at substations A and A are rung alternately. When the called subscriber at substation A answers, the subscriber at substation A is informed of this fact as he is no longer si nalled and he will remove his receive and converse with the subscriber at substation A.

From the above it will be seen that the greatest economy in the length of trunk lines used in various connections is effected, the shortest route to the exchange in ich the called subscribers line is terminais employed in extending connection to that subsc ber.

llefcrr' now more particularly to the detailed circuit drawings Figs. 5-12, inclusive, in Fig 5 there is shown a party line in the upper left hand corner of the drawing in the substations A and A thereon. The substation A is of the automatic type hari g the usual talking instrumentalities and a calling device S. The substation A is similar to the substation A in every respect except that its bell is connected from the opposite side of the line to the ground. The party line comprising conductors 11 and 12 terminates at the exchange in the individual line or trunk selecting switch C.

The line switch C is of the usual rotary type whose wipers have no normal position, always standing in engagement, when idle, ith the bank contacts associated with the trunk line last used. The line switch C, in common with a plurality of other line switches of the group, has access to trunk lines leading to secondary line switches, such as the line switch C. The line switch C is of the usual rotary type, similar to the line switch C, and has access to trunk lines extending to the main exchange by way of repeaters such as the one shown at B, Fig. 6.

Associated with each of the trunk lines to which the line switch C has access, is a relay group similar to the one shown in the drawings at HG. This relay group is adapted to control the starting of an idle finder switch such as 1!, Fig. 9.

The finder switches, such as F, are of the usual rotary t pe, and function to associate switching discriminator, such as the one shown at SD, with the seized primary trunk line.

The starting of an idle finder switch is controlled by a distributor switch, such as the one shown at D, Fig. 9, which is also of the same general mechanical construction as the switches C andF. The primary trunk line, in addition to terminating in line switch C, has associated with it the rotary line switches C, C, C, C and 0 Fig. 10. The rotary line switch 0* has access to local fourth selectors, such as the selector E shown in Fig. 12. The trunk lines accessible to the line switch C extend to the ring back apparatus, such as K, Fig. 11. The line switch C has access to trunk lines which extend to the second main exchange via the repeater B, Fig. 11. The trunk lines accessible to the line switch G extend by way of repeaters, such as R to a small sub-exchange of one hundred lines where they terminate in incoming connector switches. The line switch C has access to trunk lines extending to another nearby sub-exchange of one thousand line capacity where they terminate in incoming fourth selectors by way of repeaters, such as R The switching discriminator SD, Fig. 9, is made up of two switches M and N of the usual Strowger vertical and rotary type.

These switches differ slightly from the regular Strowger switches in that they are provided with a vertical bank and associated wipers. The vertical bank is so arranged that each vertical bank contact is opposite a level of the usual bank contacts. The switching discriminator SD is operated in response to the impulses sent over the trunk line to the main exchange and determines whether any of the line switches such as C*C inclusive, will be operated and the connection to the main exchange released.

The repeater R, Fig. 6, has the function of repeating impulses over the trunk line comprising conductors 139 and 1 10 to the main exchange switches, and also to send impulses back to control the switching discriminator such as SD.

A number of repeaters such as repeater R, Fig. 6, are accessible to the secondary line switch C and similar switches and are adapted to be connected with only when all the trunks, such as the one comprising conductors 139 and 1410, extending to the main exchange are busy. The repeater R operates to control the switching discriminator in the same manner as the repeaters such as R so that if all the trunks to the main exchange are busy the calling subscriber will not be precluded from extending a call over one of the other paths as provided by the line switches C*C inclusive.

The selector E, Fig. 6, is of the usual Strowger two wire type and has access to trunk lines extending to second selector switches such as the one indicated at E, Fig. 7.

\Vhile the second selector E is merely indicated in the drawings it will be understood that it is similar to the selector E in all respects except that the circuits are so arranged that immediately upon a connection being extended to this switch ground. is placed upon the release trunk conductor 178 in order to maintain the preceding selector switch in its operated position. The selector E has access to trunk lines extending to third selector switches such as n in the main exchange and to trunk lines extending by way of repeaters such as the one shown at R to incoming third selector switches. in the second main exchange.

The selector switch E is similar to the selector switch E and has access to trunk lines extending to fourth selector switches such as E in the main otlice and to trunk lines extending by way of repeaters such as those shown at R andlEt to the one thousand line sub-exchange tributary to the main exchange. The trunk lines extending through the repeater R are shown terminating in a fourth selector F1 Fig. 12, in the sub-ofiice in which the call is originated. The trunk lines extending through repeaters such as the one illustrated at R terminate in an incoming fourth selector, in the other one thousand line sub-office.

The fourth selectors in the main exchange such as the one indicated at E Fig. 7 have access to trunk lines leading to local connector switches such as the connector H and to trunk lines extending by way of repeaters such as R to incoming connector switches in the one hundred line sub-office tributary to the main exchange.

The repeaters R R R and R are similar to the repeater R previously described.

The connector H is a switch of the usual Strowger type and has access to local subscribers lines in the main exchange, one of these being shown in the drawings terminating in the bank contacts $423-$415, inclusive, and having associated with it the substation A The substation A is similar to the substation A already described.

The ring back equipment K, Fig. 11, enables a subscriber on a party line in the sub-oflice to call another subscriber on his own line, I

The repeaters R, R and R are similar to repeaters which have already been described.

The local fourth selector FF, Fig. 12, has access to connector switches such as H in the sub-exchange in which the substation A is located.

The. incoming fourth selector E Fig. 12, is similar to the selector E, Fig. 6, already described and has its banks multiplied with those of the local fourth selectors such as E The connector H, Fig. 12, is identical in all respects to the connector H, Fig. 8, and has access to the lines of the local substations in the sub-exchange, one of these being that of the substation A The substation A is similar to the substation A, described before, and its line terminates at the exchange in the rotary line switch G Throughout the drawings, the relays which have slow acting characteristics are denoted by the shading on the lower ends of their cores or else by the solid black portion on the upper ends of their cores. The relays which have cores shaded on the lower end are the usual so-called slow acting relays and are slow to fall back but notnoticeably slow to pull up. On the other hand, the relays which have the upper ends of their cores shown solid black are slightly slow to pull up, in addition to being slow to fall back.

Having described the drawings and the general manner in which connections are established from the subscriber at substation A to subscribers in the various other exchanges, the detailed circuit operation when these connections are extended will now be described with reference to Figs 5---12 inclusive, these drawings being laid out in the manner shown in Fig. 3. In order to describe these operations, it will first be assumed, as in the general description, that the subscriber at substation A in the subeXchange 913 desires to call a subscriber at the substation A in the main exchange, whose number is 91826X. In order to do this the calling subscriber will remove his receiver and operate his calling device S in accordance with the above digits.

hen the receiver is removed at substation A a circuit is completed over the line conductors 11 and 12 for the line relay let of the individual line switch 0. Relay 14;, upon energizing, at its armature 25 closes a circuit for the switching relay 13 in series with the motor magnet 15 and at its armature 24 connects the test wiper 27 to the above circuit at the point midway between the switching relay and the said motor magnet. The operation of the rotary line switch C now depends upon whether its wipers 2628, inclusive, are associated with a busy trunk line or not. Assuming first that the associated trunk line is busy ground will be connected to the test contact engaged by the test wiper 27, the switching relay 13 will be short circuited, and the motor magnet 15, being supplied with direct ground via the said test wiper, will operate as a buzzer to advance the switch wipers step by step in search of an idle trunk line. However, it will be assumed in the present case that when the receiver is removed at substation A the wipers of the line switch C are associated with an idle trunk line and it will be assumed further that this trunk line is the one shown in the drawings terminating the bank contacts 2931, inclusive. Under these conditions the switching relay 13 is energized immediately after the energization of the line relay 14L. Belay 13, upon operating, at its arn'iature 19 connects ground to the test contact 30 of the seized trunk line in order to prevent the said trunk line from being used for another call, and at armaturcs 1S and 20 disconnects the line conductors 11 and 12 from the winding of the line relay 14: and from ground, respectively, and extends them by way of wipers 26 and 28, bank contacts 29 and 31, armatures 47 and 19, and their back contacts, armatures and 7 4 and their back contacts, and thru the winding of the line relay 66 to battery and to ground, respectively, in the secondary line switch G.

Immediately upon the extension of the calling subscribers line to secondary line switch C, as above described, the line relay 66 thereof is energized. Relay 66 at its armature 77 closes a circuit for the switching relay 65 and the motor magnet 67 in series, at armature 76 connects the test wiper 81 to the above circuit at a midpoint between the switching relay and the motor magnet and at armature places ground upon the release trunk conductor 7 8, thereby establishing a holding circuit for the primary line switch C. This holding circuit may be traced from ground on release trunk conductor 78 by way of normally closed springs controlled by armature 48, test contact 30, test wiper 27, armature 19 and its front contact, thru the winding of the switching relay 13 and thence thru the winding of the motor magnet 15 to battery. This holding circuit serves to maintain the switching relay 13 energized throughout the connection and it will be understood that it is established before the slow acting line relay 14: has had time to deenergize. A branch 01' this holding circuit also extends by way of the private normal conductor 22 to multiply connected test contacts in the banks of con nector switches which have access to the line of the substation A whereby the said line is protected from intrusion during existence of the connection The energization of the line relay 66 of the secondary line switch C causes the trunk selecting operation of this switch to take place in substantially the same manner as that of the primary line switch C.

It will be recalled that when the switching relay 13 of the primary line switch C energized ground was placed upon the test contact 80. This ground causes the energization of the relay 40 in the relay group HG associated with the seized trunk line. Relay 40, upon energizing, removes ground from the conductor 57 thereby rendering the trunk line in use having the multiple test contacts such as 461 accessible to the finder switches such as F. Another result of the energization of the relay 40 is that a circuit is completed extending from ground by way of armature 46 and its back contact, front contact and armature 44-, conductor 55, wiper 442 of the distributor switch D, bank contact 480 and thence thru the winding of the starting relay 409 of the finder switch 13 to battery. Relay 409, upon energizing, at its armature 425 closes a circuit for the switching relay 408 in series with the motor magnet 442-3 and at armature 426 connects the test wiper 469 to the above circuit at a point midway between the switching relay and the said motor mag not As the test contacts such as 461 are normally grounded in the banks of the finder switches such as F and this ground potential is removed only when a primary trunk line is seized as is the case when ground is removed from the test contact 461, a motor magnet 448 of the finder switch F will operate as a buzzer to advance the switch wipers 4ti8475, inclusive, until they are rotated into engagen'ient with the set of bank contacts 4504G7, inclusive, associated with the primary trunk line in use. During the operation of the motor magnet 443, the switching relay 408 is maintained short circuited by ground upon the successive test contacts and consequently does not energize. Immediately upon the trunk line terminating in bank cont-acts 460-467, inclusive, being seized, the short circuit is removed from relay 408 and the said relay energizes. Upon energizing, relay 408 at its armatin'e 421 opens the circuit of the release magnets 447, 450 and 485 of the switches M, N and S of the switching discriminator SD, at front contact of this armature places ground upon the contact 481 in the bank of the distributor switch D, at armature 422 places ground upon the bank contact 460, at armature places ground upon the test contact 461 in order to render the trunk line seized by finder F inaccessible to other finders which may be subsequently started, at armature 424 prepares an impulsing circuit for controlling the switching discriminator SD. The connection of ground to bank contact 481 of the distributor switch I) causes the motor magnet 490 of that switch to be operated. This operation causes the distributor switch wipers 441 and 442 to be brought into asso ciation with an idle finder switch. The distributor switch I) performs the function of extending the common starter wire 55 to an idle finder switch similar to the finder F. The operation of the distributor switch D opens the circuit of the starter relay 409 which cleenergizes. However, after the energiza-tion of relay 408 and before the deenergization of relay 409 a circuit is com pleted extending from ground. by way of armature 425 and its front contact, front contact and armature 422, back contact and armature 427, wiper 468, bank contact 460, conductor 56, and thru the winding of the relay 41 to battery. The relay 41 is energized over this circuit and, upon operating, at its ar nature 45 opens the circuit of the relay 40, at the front contact of this armature establishes a locking circuit for itself and places ground on the conductor 56 in order to maintain. the switching relay 408 energized after the deenergization of relay 409, at its armature 46 removes ground from starting wire and at front contact of this armature places ground on the conductor 57.

Returning now to the operation of the secondary line switch C, it will be remembered that the energization of the line relay G6 initiates its trunk hunting operation. When an idle trunk is found which, we will assume, is the trunk line terminating the bank contacts 8487, inclusive, there will be no ground potential present upon the test contact 85 engaged by the test wiper 81 and the switching relay being no longer short circuited, is energized in series with the motor magnet 67. The motor magnet, of course remains inoperative on account of the high resistance of relay 65. Relay 65, upon operating, prepares a controlling circuit for the switching discriminator SD at armature 78, at armature 7 2 places ground upon test contact 85 in order to busy the seized trunk line, at armature 71 prepares a holding circuit for the relay 41 of the relay group RG and the switching relay 18 of the line switch C, and at armatures and 74 extends the calling subscribers line by way of wipers and 88, bank contacts 84 and 87, trunk conductors 96 and 99, thru the left hand windings of the repeating coil of the repeater it to the upper and lower windings of the line relay 180 of said repeater.

Tlhe line relay of the repeater .is energized over the calling subscribers line and, upon operating, at its armature 132 completes a circuit for the slow acting relay 131, and at its armature 133 closes a bridge or repeating circuit across the trunk conductors 1.89 and extending from the sub exchange 913 to the main exchange 91 where they terminate in an incoming first selector switch E. Relay 131, upon operating, at armature 136 prepares a point in a controlling circuit'for the switching discriminator SD, at its armature 184 closes a point in a certain chain circuit which will be described later and at its armature 135 places ground upon "the release trunk conductor 9? thereby establishing a holding circuit for the secondary line switch C. This holding circuitmay be traced from ground on trunk conductor 97 by way of bank contact test wiper 81, to armature 72 and its front contact where the circuit divides one path extending thru the winding of the switching relay and the winding of the motor magnet 67 to battery, and the other path joining a previously traced holding circuit for the relay ll of the relay group RG and the relay 13 of the line switch C.

Upon the closure of the above mentioned repeating circuit in the repeater R, the line relay 150 of the incoming first selector E in the main exchange is energized over the trunk conductors 139 and 1 10 in series. Helay 150, upon attracting its armature 160, closes the circuit of the slow acting relay 151. The latter relay, upon energizing, at ari'nature 162 opens the circuit of the release magnet 155, at the front cont-act of this armature prepares the impulsing circuits of the selector E and at armature 161 prepares a circuit for the relays 153 and 1541.

It will be noted that the lower winding of the line relay 150 of the selector E is connected thru the secondary transformer winding of tone machine T to ground. Thus immediately upon the previously mentioned repeating circuit being closed, the calling.

subscriber is given an audible signal in order to inform him that he may now operate his calling device. lVhen the calling device is operated in accordance with the first digit 9, nine interruptions are no duced in the circuit of the line relay 130 of the repeater R and this relay deenergizes a corresponding number of times in response thereto. At each deenergization of the line relay 130 the previously mentioned bridge across the trunk conductors 139 and 140 is opened. The nine interruptions produced by the calling device S at substation A are in this manner repeated to the line relay 150 of the selector E. At each deenergization of the line relay 150 a circuit is closed for the vertical magnet 157 of the selector E in series with the slow acting relay 152. Magnet 157 operates to raise the switch wipers 171173, inclusive, step by step until they are placed opposite the ninth level of bank contacts. The slow acting relay 152 is energized in series with the vertical magnet and, upon the first vertical step of the switch, when the off normal springs are shifted, a circuit is completed extending from ground by way of front contact and armature 161, armature 164 and its front contact, working contact of off normal spring 163 and the said spring, back contact and armature 180 and thence thru the winding of the stepping relay 153 to battery. Relay 153, upon operating, at its armature 165 establishes a locking circuit for itself and at armature 166 prepares a circuit for the rotary magnet 156. At termination of the vertical movement of the selector E the slow acting relay 152 deenergizes and at its armature 164l completes the circuit of the rotary magnet 156. Magnet 156 operates to rotate the switch wipers into engagement with the first set of bank contacts on the ninth level and at its armature 180 opens the locking circuit of the stepping relay 153. Relay 153 deenergizes thereby opening the circuit of the rotary magnet 156 which deenergizes also. Assuming that the trunk line associated with the first set of bank contacts on the ninth level is busy, there will be a ground potential upon the test contact engaged by the test wiper 172 and the stepping relay 153 will again be energized. Relay 153 operates to establish a locking circuit for itself at armature 165 and to close the circuit of the rotary magnet 156 at arma ture 166. Magnet 156 rotates the switch wipers into engagement with the next set of bank contacts on the ninth level and at armature 180 opens the locking circuit of the stepping relay 153 which deencrgizes and opens the circuit of the rotary magnet which deenergizes also. The alternate operation of the stepping relay 153 and the rotary magnet 156 continues until the switch wipers are brought into engagement with a set of bank contacts associated with an idle trunk line, which, we will assume, are the bank contacts 17 1-17 6, inclusive. As soon as the wipers 171173, inclusive, are brought into engagement with this set of bank contacts, the switching relay 15 1, which has been short circuited during the operation of the selector E, is energized in series with the stepping relay 153. However, the latter relay is not opera ed at this time on account of the comparatively high resistance of the switching relay 15 1. Relay 1541, upon energizing, at its armature 168 places ground upon the test contact 175 in order to make busy the seized trunk line, at armature 169 opens the circuit of the slow acting relay 151, at armatures 167 and 170 disconnects the windings of the line relay 150 from the trunk conductors 139 and 140, and at the front contacts of these armatures extends the said trunk conductors by way of wipers 171 and 173, bank contacts 17 1 and 176, trunk conductors 177 and 179 thru the windings of the line relay of the second selector E.

The second selector E is similar to the first selector E in all respects except that the release trunk is extended back in a manner that has been completely shown in the fourth selector E Fig. 12. Thus, when the connection is extended to the line relay of the selector E this relay immediately energizes and closes the circuit of its associated slow acting release relay. The latter relay operates in the usual manner to prepare the operating circuits of the second selector and to place ground upon the release trunk conductor 178 in order to establish a holding circuit to maintain the first selector E in an operated position.

Adverting back to the operation of the repeater R, when the first digit 9 is dialed, an additional result of the deenergizations of the line relay 130 is that at each retraction of the armature 132 an impulse of current is sent over the following circuit: From ground by way of the said armature and its back contact, armature 136 and its front contact, trunk conductor 98, bank contact 86, wiper 82, front contact and armature 73, conductor 58, bank contact 462, wiper 470, armature 424 and its front contact, thru the winding of the slow acting low resistance relay 407, wiper 440 of the sequence switch S in its first position and thence thru the winding of the vertical magnet 449 of the element N of the switching discriminator SD to battery. Magnet 449 operates to raise the switch wipers 437 and 438 step by step until they are brought opposite the level of bank contacts corresponding to the first digit dialed which in this case is the digit 9. The slow acting relay 407 is energized in series with the vertical magnet 449 and, upon attracting its armature 420, closes the circuit of the slow acting relay 406. At the termination of the vertical movement of the element N the slow acting relay 407 deenergizes and opens the circuit of the slow acting relay 406. After the deenergization of relay 407 and before the deenergization of relay 406 an impulse of current is sent to the operating magnet 486 of the sequence switch S. The sequence switch S is a simple rotary switch having an operating magnet 486 and ,release magnet 485, the rotary magnet 486 being adapted to actuate the wipers 439 and 440 upon each energization. Therefore, as an iinpluse of current is sent to the rotary magnet 480 of the said switch, it operates to advance the wipers 439 and 440 into their second position.

lVhen the calling device at substation-A is operated in accordance with the next digit 1 of the desired number, an interruption is produced in the circuit of the line relay 130 of the repeater 1%. Relay 130, upon retracting its armature 133, repeats the digit to the line relay of the second selector switch E. The line relay of the second selector E controls the operation of the vertical magnet in stepping the switch wipers 200 202, inclusive, opposite the first level of bank contacts. The trunk selecting operation of the second selector is now initiated and takes place in a manner similar to that described in connection with the first selector E. Vhen an idle trunk line is found, which, we will assume, is the trunk line terminating in bank contacts 206-208, inclusive, the switching relay of the selector E is oper-' ated to disconnect the line relay of the said select-or and to extend the trunk conductors 177 and 179 to the line relay of the third selector E The third selector E is identical with the second selector E. Thus, immediately upon the extension of the trunk line to the line relay of the third selector, the said relay is energized to close the circuit of its associated slow acting release relay. The latter relay operates to prepare the impulsing circuits of the third selector and to establish a holding circuit for the selectors E and EU Referring now to the operation of the repeater B, when the second digit 1 is dialed, an impulse of current is sent to the element N of the switching discriminator SD over the same circuit as was traced in the first instance. However, inasmuch as the sequence switch S has been operated this impulse of current actuates the rotary magnet 448 and causes the wiper 438 of the element N to be rotated into engagement with the first contact of the ninth level. The slow acting relay 407 is energized in series with the rotary magnet 448 and at the termination of the rotary impulse causes the sequence switch magnet 486 to operate, the latter operation stepping the wipers 439 and 440 into their third position. Upon the deenergization of the slow acting relay 407, a circuit is completed extending from ground by way of back contact and armature 419, wiper 438, bank contact 91 of the element N, and thru the right hand winding of the relays 401, 403 and 404 in multiple to battery.

The relays 401, 403 and 404 are of the shunt field'type. That is, they do not attract their armatures until both their windings are energized simultaneously.. This is due to the fact that when only one winding is energized a magnetic short circuit exists so that the magnetic circuit does not include the relay armature. However, when both windings are energized together the magnetic circuit includes the relay armature which is then attracted. Therefore it follows that even though the circuit of the right hand windings of the relays 401, 403 and 404 are closed these relays are not energized. The movement of the wipers 439 and 440 of the sequence switch S into their third position transfers the impulsing circuit from the rotary magnet 448 of the element N to the vertical magnet 446 of the element M.

In response to the next operation of the calling device S at substation A for the digit 8, eight interruptions are produced in the circuit of the line relay 130 of the repeater R, and by the operation of this relay are repeated to the line relay of'the third selector switch E in the 'main'exchange. The line relay of the third selector switch causes the vertical magnet to-operate thereby stepping the switch wipers 210212, inclusive, to the eighth level of bank contacts. The trunk selecting operation of the selector E now takes place in the usual manner. Assuming that the trunk line shown in the drawings terminating in bank contacts 219 fitU 221, inclusive, is the one selected, the connection is extended to the fourth selector E The line relay of that switch is energized and closes the circuit of its associated release relay. This relay, upon operating, in addition to establishing the usual holding circuit for the precedingly operated selector switches, prepares the operating circuit of the fourth selector.

In the repeater R, the eight deenergizations of the line relay 130 cause eight impulses of current to be sent to the vertical magnet 446 of the element M of the switching discriminator SD. The magnet 446 operates to move the wipers 435 and 436 to the eighth level of bank contacts. As be fore, the slow acting relay 407 is energized in series with the vertical magnet 446 and at the termination of the magnets operation causes the sequence switch wipers 439 and 440 to step into their fourth position, thereby transferring the impulsing circuit from the vertical magnet'446 of the element M to the rotary magnet 445.

The calling subscriber at substation A may now operate his calling device for the fourth digit 2 of the number of the called substation A By this operation two interrup tions are produced in the circuit of the line relay 130 of the repeater It and are repeated in the usual manner to the line relay of the fourth selector switch E The vertical magnet of the selector E raises the wipers 225-227, inclusive, of the switch, opposite the second level of bank contacts under the control of the line relay. At the termination of the vertical movement of the switch E its trunk hunting movement is initiated and takes place until an idle trunk line is associated with its wipers, which, we will assume, is the trunk line terminating in the bank contacts 228230, inclusive. As soon as the idle trunk line is found the switching relay of the fourth selector E is energized to extend the connection to the connector H.

Immediately upon the extension of the connection, as above described, the line relay 301 of the said connector is energized and operates to close the circuit of the release relay 302. Upon operating, the relay 302 at armature 314 opens the circuit of the release magnet 335, at the front contact of this armature prepares the operating circuits of the connector H, and at armature 313 places ground upon the release trunk conductor 235, thereby establishing a holding circuit for the selectors E, E, E and E At the repeater R the two deenergizations of the line relay 130 cause two impulses of current to be sent to the rotary magnet 445 of the element M of the switching discriminator. The wiper 436 thereof is accordingly rotated into engagement with the second bank contact of the eighth level. As this contact is dead there is no further armature 427 operation of the relays in the relay group RG, The slow acting relay 407, which is energized in series with the rotary magnet 445, at the termination of the rotary operation causes the wipers 439 and 440 of the sequence switch S to be advanced to their fifth position. As there has been no operation of the relays of the relay group RG, as soon as the sequence sw'"ch wiper 439 is advanced to its fifth position, a circuit is completed extending from ground by way of thesequence switch wiper 439 in its fifth position, back contact and armature 416, armature 417 and its back contact, and thru the winding of the relay 410 to bat tery. Relay 410, upon energizing, at its opens the circuit of the switching relay 408 of the finder F. Upon deenergizing, the relay 408 completes the circuit of the release magnets 447, 450 and 485 of the elements M and N, and the sequence switch S, respectively. By the operation of these release magnets the various switches mentioned are restored to their normal position, the release magnet circuits being opened by oli normal springs of the respective switches when they return to their normal position. By the deenergization of relay 403 all the circuits of the finder F and switching discriminator SD are restored to normal and this equipment reverts to common use so that it may be used for another connection. The release of this apparatus is brought about on account of the fact that the particular combination of digits dialed by the calling subscriber have determined that the call going to the main exchange, or that it is necessary to complete the connection thru the main exchan e and not by way of any one of the by-pat is accessible to the line switches C, C C, C or l i hen the calling device at the callin substation A is operated in accordance witn the next digit 6 of the desired number, six interruptions are produced in the circuit of the line relay 130 of the repeater B. By the operation of the armature 133 of the relay 130, these interruptions are repeated to the line relay 301 of the connector H which deenergizes a plurality of times in response thereto. At the first deenergization of the line relay 301, an impulse of current is sent to the vertical magnet 33' over va circuit extending from ground thru armature 312 and its back contact, armature 314 and its front contact, off normal springs 316 and 315, thru the winding of the slow acting relay 3, and thence thru the winding of the vertical magnet 336 to battery. The above is the circuit over which the first impulse to the vertical magnet is sent. However, upon the first operation of the switch shaft, the off normal springs are operated and the remaining vertical

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