US1542958A - Automatic telephone system - Google Patents

Description

June 23, 1925. 1,542,958

A. J. RAY

AUTCMATI C TELEPHCIEv SYSTEM .Ehur Half CJ. Mrz? June 23, 1925.

A. J. RAY

AUTOMATIC TELEPHONE SYSTEM Filed Jan. 21,. 1921 4 Sheets-Sheet 2 Elm- Ehur l Ea ETV.'

June 23, 1925.

A. J. RAY

AUTOMATI C TELEPHONE SYSTEM 4 Sheets-Sheet 4 Filed Jan.Y 2l, 1921 mu wfmqmtmf@ I HS m .Mkm QQ Q \w\ IL u k. NBN n@ NN I; WMM im N EZT:

Patented .lune 23, 1925.

- UNITED STATES PATENT OFFICE.

ARTHUR J. RAY, OF CHICAGO, ILLINOIS, ASSIGNOR TO AUTOMATIC ELECTRIC COM'.-

PANY, OF CHICAGO, ILLINOIS,

A CORPORATION OF ILLINOIS.

AUTOMATIC TELEPHONE SYSTEM.

Application filed January 21, 1921. Serial No. 438,985.

To all whomy z't may concern.'

Be it known that I, ARTHUR J. RAY, a citizen of the United States of America, and a resident of Chicago, Cook County, and State of Illinois, have invented certain new and useful Improvements in Automatic Telephone Systems, of which the following is a specification.

The present invention relates in general to automatic telephone systems, but more particularly to such'systems as comprise main and branch exchanges; and the object of the invention is to provide a new and improved method for completing branch exchange connections locally, branch to main and mam to branch trunk lines not being used for such connections, without departing from or in any way modifying the standard numbering arrangement.

Systems in which this result is accomlished have been designed before, notably in the following U. S. patents, which are referred to as indicating the state of the art: Lubberger No. 1,295,181 Feb. 25, 1919; Willis and Martin, No. 1,306,825 June 17, 1919; Hershey, No. 15,073, reissued March 29, 1921.

The present invention provides a number of circuit improvements and-other refinements, especially in the switching selector repeaters at the branch exchange, these being the switching mechanisms used to eliminate the inter-exchange trunk lines on local calls. The new features will be pointed out and explained fully in the course of the general description of the invention which will now be proceeded with.

Although the invention is applicable to systems of different sizes, it will be assumed for convenience that we are dealing with a system that has an ultimate capacity of 100,000 lines. IVe will assume further that only 90,000 lines are in use and that they are divided into nine main oliices of 10,000 lines each, at least one oice having a branch exchange of 100 lines. IVe may also assume that the toll recording operator occupies the position that would otherwise be taken by the tenth oflice, that is, she is reached by calling 0. In a 100,000 line system the first digit dialled determines to which group of 10,000 lines the call is going. The second digit determines to which group of 1,000 lines, while the third digit determines the particular group of 100 lines for which the call is intended. Now since the branch exchange has only 100 lines in it and the third digit dialled picks out the hundreds group, we must have in the branch exchange switching selector repeaters capable of switching on the third diglt.

The general trunking arrangement is not novel and consequently is not shown, the drawings showing only so much of the equipment as will be used to explain the novel features of the invention. Figs. 1, 2, and 8 show by means of the usual circuit diagram the apparatus required to enable the subscriber at substation A (Fig. l) in a branch exchange to extend local calls, or extend calls to an operators position 0 (Fig. 8) in the main exchange, or to a called station A in the main exchange. Figs. 3 to 7, inclusive, show the different arrangements of the wiring in the banks of the switching selector repeaters in the branch exchan e.

The substation A shown in Fig. l an the substation A (Fig. 8) are ordinary automatic substations. Suhstation A is one of a hundred similar substations that terminate in the branch exchange. Each substation line may terminate at the branch exchange in a rotary line switch or trunk selector of the usual type, the line switch in which the line of substation A terminates being indicated by the reference character C. The line switch in which substation A terminates is also a rotary line switch and is indicated b v the reference character C. The line switches in the branch exchange have common access to a group of perhaps ten switching selector repeaters, one of which is shown in Fig. 2 and is indicated by the reference character D.

The switching selector repeater D is a vertical and rotary switch of the usual Strowger type so far as mechanical construction is concerned, having special relays and circuits added. however, that enable-it to function as a repeater. In this case the selector functions of the switch D are those of a third selector for it operates on the third digit to pick out an idle connector switch when used for local calls.

There is a secondary line switch, such as the line switch indicated by the reference character E, associated with each switching selector repeater, whose function is to pick out an idle trunk line leading to the main exchange for the purpose of completing the call to main in case the call is to go there or to any other main oliice, or in fact anywhere except to the local branch exchange. One of the trunk lines to the main exchange to which the line switch E and other secondary line switches have common access is the trunk line comprising conductors 138 and 139. These conductors extend to the main exchange and there terminate in the incoming first selector switch F. lThe tenth level' of the first selector F gives access to a toll recording operator as is clearly shown in Fig. 8. The toll operator is at the toll oilice, or exchange, which may be some distance away from the main exchange in which the selector F is located. The third level of selector F gives access to second selectors such as the second selector G in the same exchange; while the other levels (not shown) give access through repeaters and associated trunk lines to incoming second selectors located in the various other main exchanges.

The so called repeater L shown in Fig. 8 is provided to establish a holding circuit for any selector which is operated to establish connection with the trunk line associated therewith. This is in accordance with the usual practice and is done primarily to avoid the necessity of having three conductors between oflices.

In Fig. 8 there is shown at 0 the relays and equipment individual to each trunk at the toll recording operators osition, together with the operators hea set.

To complete the general description of the system, it may be stated that calls from the main exchan to the branch exchange may be complete by way of a group of trunks that terminate in incoming connectors in the branch exchange. f

The foregoing aragraphs will serve to give a, general un erstanding of the character of the apparatus, and the system of trunking which is employed. The new improvements, and the precise circuits, however, used in accomplis ing the objects of the invention, cannot be readily understood without a more detailed explanation of their operation. Such explanation will now be iven. For this purpose we will assume that the 345 hundred group of lines is located in the branch exchange, or in other words oonnection to a branch exchange connector is obtained by callin 345. We will further assume that the su scriber at substation A desires connection with a subscriber whose telephone number is 34567 and whose line, therefore, terminates in the branch exchange.

When thel receiver is removed at the calling substation A a circuit is completed over the conductors 11 and 12 for the line relay 15 of the line switch C. Upon energizing, relay 15 closes a circuit at its armature 20 which includes the winding of the switching relay 14 and the stepping magnet` 16 in series; and at its armature 21 connects test wiper 26 to the above circuit at a point midway between the said switching relay and the stepping magnet. The operation now depends upon whether the trunk line with which the line switch wipers are associated is busy or idle. If the trunk line is busy there is a ground potential upon the test contact with which the test wiper 26 is in engagement; the switching relay 14 is short circuited and the stepping magnet 16, which interrupts its own circuit, is operated in the manner of a buzzer to advance the switch wipers in search of an idle trunk line. However, we may assume in the present case that when the call is initiated the trunk line upon which the wipers of the line switch are standing is idle. Under these circumstances when the line relay 15 is energized the switching relay 14 is not short circuited and the stepping magnet 16 is not operated because of the high resistance of said switching relay. The latter relay, however, is energized, grounds the test wiper 26 at armature 18, and at armatures 17 and 19 disconnects the line conductors l1 and 12 from the windings of relay 15 and fromv ground, respectively, and extends them by way of wipers 25 and 27, and bank contacts 28 and 30, conductors 31 and 33, armatures 54 and 58 and their restin contacts, and normally closed contacts of t e electro polarized reversing relay 44 to the upper and lower windings of the line relay 35 of the switching selector repeater D. The line relay 35 immediately energizes, ground being dsupplied to its lower winding through the left hand Winding of the induction coil associated with the trunk tone machine T, normally yclosed contacts controlled by armature 73, and normally closed contacts controlled by armature 77, and when it does so it closes at armature 57 the circuit for release relay 36. Release relay 36, upon operating, closes at armatuurJ 61 a.Y holding circuit extending from ground through the lower winding of induction coil I, working n .of private normal conductor 13 to multiple test contacts in the banks of the connectors, thereby guarding the line against intrusion in the usual manner. In the switching se-Y lector repeater D a branch of the holding circuit extends from grounded conductor 32 through the upper winding of electro-polarized relay 44 to battery. This winding is of high resistance and few turns and, therefore, cannot operate the` relay until it is assisted by current in the lower winding. The switch D is now ready for the usual vertical impulses, but before proceeding with this it will be necessary to consider circuits that were closed for the secondary line switch E.

"hen the line relay is energized a bridge is closed across trunk line conductors 101 and 105 which is effective in operating the line relay 119 of the secondary line switch E. The circuit for line relay 119 is as follows: from ground through line relay 119, resting contact of armature 125 and said armature, conductor 105, armature 93 and its working contact, eleventh rotary step cam spring 53, operated by cam 94, and resting contact of said spring, lower winding of electro polarized relay 44, relay 38, resting contact of armature 66 and said armature, conductor 101, armature 122 and its resting contact, resistance R3, common conductor 146, armature 145 and its resting contact to battery. The line relay 119 and the relay 38 both energize over this circuit, but the current that flows in the lower winding of relay 44 opposes that in its upper winding and consequently it does not energlze. However, at the same time that the circuit for line relay 119 is closed a circuit is closed at armature 57 of line relay 35 of switch D for release relay 36 as has been described. The two relays operate practically simultaneously and relay 36 of switch D at armature 62 closes the following circuit: from ground through armature 62, eleventh rotary step cam spring 49, operated by cam 94, and its resting contact, conductor 102, relay 118, and stepping magnet 117 to battery. Vith line relay 119 energized, it is seen that test wiper 132 is connected to the above circuit at a point between the switching relay and the stepping magnet. These circuit conditions `are substantiallyfthe same as those that were described in connection with the operation of line switch C, and it necessarily follows that the secondary switch E operates as a trunk selector to select an idle trunk line to the main exchange. Assuming that the trunk line comprising conductors 138 and 139 is the first one found idle, when the test wiper 132 arrives at test contact 136 the rotar movement ceases, no ground being found liv test wiper 132, and

the switching relay 118 is energized. As

a result, the conductors 101 and 105 are dis- 139, and armatures 168 and 171 and their resting contacts to the upper and lower windings, respectively, of the line relay 151 of the first selector F in the main exchange. There being a bridge closed across the conductors 101 and 105, as already explained, the line relay 151 of the selector F energizes and operates the release relay 152 in the usual manner thereby making the selector F ready for the usual vertical impulses. Before going further certain circuit details in the secondary line switch E will be con-I sidered.

When the switching relay 118 energized the original energizing circuit of the line relay 119 was broken, but when armature 124 operated it opened the test circuit and closed a locking circuit for the slow acting line relay, before it had time to deenergize, extending from the Working contact of armature 124 and said armature through armature 127 and its working contact, and stepping magnet 117 to battery. Stepping magnet 117, being wound with few turns and having a stiff adjustment, does not energize at this time. As a further result of the energization of switching relay 118, armature 121 closes a circuit that extends from grounded conductor 102 through relay 120 tobattery. Relay 120 energizes and places ground on test contact 136 and its multiples in the banks of other secondary switches, in order to make the selected trunk busy, and at armature 140 it closes a point in the circuit of relay 144. The function of relay 144 will be fully ex lained later.

The explanation may now be proceeded with. The calling line has been extended to the switching selector repeater D and a branch from the said switch has been extended by way of the seconda line switch E to the first selector F in xtile main ex change. With these facts in mind the results ensuing from the calling of the first digit will be easily grasped. The first digit to be called is 3, and when the calling device S at substation A is operated, three interruptions are produced in the circuit of the line relay 35 of switch D. At each interruption the line relay 35 deenergizes and sends an impulse of current through the vertical magnet 47 over the following circuit: from ground through armature 60 and its resting contact, armature 57 and its resting contact, armature 63 and its working contact, normally closed contacts controlled by armature 69, slow acting relay 40, and vertical magnet 47 to battery. The slow acting relay'40 is energized in series with the vertical magnet and retains its armature attracted during the vertical movement. The slow acting relay 37 is energized in parallel with the slow acting relay 40 and the vertical magnet and it also retains its armatures attracted during the vertical movement. Upon the first upward step of the shaft the vertical oil' normal springs 51 and 52 come into contact with their working contacts. The operation of off normal spring 52 closes the circuit of the vertical off normal relay 39 which energizes and at armature 69 transfers the impulsing circuit so that it passes through the working contact of armature 69 and said armature, armature 74 and its working contact, and over previously 'traced circuit to the vertical magnet 47.

The operation of vertical magnet 47 raises the switch shaft and wipers three steps and consequently they stand opposite the third level of contacts in their associated banks (shown in Fig. 3).

Returning now to the line relay 35, the deenergization of this relay not only brings about the operation of the vertical magnet 47 as described, but also produces interruptions in the bridge across conductors 101 and 105, these interruptions being produced at armature 93. As a result the line relay 151 of the distant selector F is deenergized three times and the wipers 172-474. inclusive, of the selector F are raised until they stand opposite the third level of contacts in their associated banks. In brief, the line relay functions in the same manner as the line relay of the well known automatic repeater and thus repeats the impulses or interruptions in its circuit to the circuit of the line relay of the selector F. As a result, the switch D and the selector F are operated practically simultaneously. It will be noticed that while the impulses are being repeated the relay 37 is energized, and at its armature 66 closes the bridge across conductors 101 and 105 by way of a more direct path that excludes the windings of relays 38 and 44. This is the usual expedient made use of to obtain a first class switch control circuit.

We shall now go into the details of the operation of selector F. Each time the line relay 151 deenergizes due to the open ing of its circuit at the switching selector repeater D it operates the vertical magnet 156 in series with slow acting relay 153 over the following circuit: from ground through the resting contact of armature 170 and said armature, armature 161 and its resting Contact, armature 163 and its working Contact, relay 153, and vertical magnet 156 to battery. By the operation of the vertical magnet the switch shaft and wipers are raised step by step until they stand opposite the desired level of bank contacts. elay 153 operates and retains its armature attracted throughout the vertical movement of the shaft and upon the closure of the vertical olf normal springs 159 completes a circuit for the stepping relay 154. Upon energizing, relay 154 prepares the circuit for the rotary magnet 157 at armature 167 and at armature 166 establishes a locking circuit for itself. At the end of the vertical movement of the shaft the slow acting relay 153 deenergizes and completes the circuit for the rotary magnet which thereupon energizes to advance the wipers 1724174, inclusive, into engagement with the first set of bank contacts in the level opposite which they are raised. The rotary magnet also breaks the circuit of the stepping relay 154, at interrupter contacts 160, which deenergizes and breaks the circuit of the rotary magnet, which thereupon deenergizes also and again closes its interrupter contacts. The operation now depends upon whether the test contact with which the test wiper 173 is in engagement is busy or idle. If the test contact is busy it has a ground potential on it, and the stepping relay energizes again and the same cycle of operation is repeated over and over until an idle or ungrounded test contact is reached. l/Vhen an idle set of contacts is reached the switching relay 155 energizes in series with the stepping relay 154 over the following circuit: from ground through working contact of armature -16'2 and said armature, switching relay 155, interrupter contacts 160 of rotary magnet 157, vertical off normal springs 159, and stepping relay 154 to battery. Relay 154, however, due to its relatively small number of turns,y does not energize over this circuit. It is assumed that test contact 176 is the first one found idle. ln this case the energization of relay 155 switches the connection through to the trunk line terminating in bank contacts 175-177. inclusive, and leadiner to selector G. Before the slow acting re ease relay 152 has had time to fall back and remove ground from the circuit of the switching relay 155, the line and release relays `(not shown) of the selector G pull up in the well known manner to ground the release trunk leading back to test contact 176, thereby establishing a holding circuit for the switching relay 155.

Returning again to the switching selector repeater D, we find that at the end of the vertical movement of the shaft and wipers the slow acting relays 37 and 40 deenergize. The former at armature 66 replaces the relays 38 and 44 into the bridge across the conductors 101 and 105, while the latter at armature 74 transfers the impulsing circuit from its working contact to its resting contact. It may be said here that the springs 97 and 98 are so placed on the switch that they are operated by the shaft when it is raised upward three steps and, therefore, are now operated.

Briefly stated, the result of the operation of the calling device S in accordance with the first digit 3 ofthe desired-number iszthat the winers 251-254, inclusive, of switch D are raid until they stand opposite the third level of their associated banks and that the wipers 172-174, inclusive, of the first. selector F in the main exchange have been raised to the third level and rotated to pickl out an idle lineassunied to bethe one terminating in bank contacts 175177. inclusive, and leading to a second selector represented by the rectangle G.

The calling subscriber may now operate his calling device in accordance With the second digit 4 of the desired number. In response to the interruptions in the line thus produced the line relay is deenergized four times and as before repeats these interruptions to the trunk line comprisingr conductors 188 and 189 leading to the main exchange. In response to these repeated irn-v pulses the second selector G raises its Wipers step b v step until they stand opposite the fourth level of its banks and rotates them to pick out an idle trunk line assumed to be the trunk line leading to the third selector H. The operation ofthe second selector G is exactly the same as that of the first selector F and hence need not be explained any further.

At the same time that the line relay 35 of the switch l) repeats .the impulses to the main exchange it operates the rotary magnet 46 over the following circuit: from ground over the previously described impulsing circuits to the armature 74 of relay 40 and thence through the resting contact of said armaturel` shaft controlled spring 97 and its working contact, resting contact of armature 99 and said armature` and rotary-magnet 46 to battery. The rotary magnet receives four impulses over this circuit in multiple with slow relay 37 and accordingly steps the wipers 251-254, inclusive, into engagement with the fourth set of contacts in the level opposite which they ive/re previously raised. At theend of the series 'ofim pulses slow relay 87 deenergizes and when it does so it completes atarrnature 65 a circuit for relay 43 as follows: from grounded contact 255 (Fig. 3) through wiper 251, con* ductor 95, resting contact of armatureA 65 and said armature, and relay 43 to battery.V

Relay 43 energizes and at armature 8G closes a c1rcuit for the release magnet 48 as -follows: from ground over the previously traced circuit for relay 48 to the Working contact of armature- 86 and thence through said'armature, workingcontact of armature of vertical otinormal relay 89 and-said armature, armature `79rand itsy resting contact, and release magnet 48 -to battery. f Release magnet 48 accordingly energizes and Athereby restores the switch shaft and wipers to normal. In order that the wiperY 251, when it in releasing moves off of contact 255,

net 48. Abranch of .thisicircuit exte'ndsby way of armature 86 and` its-@working convtact to relay 43. 'lVh'en the=shaft reaches its normal position it forcesrthe'of'normal spring .52 away from itsA working contact which yopens thecircuit 'of the Voff-normal relay 39. -The off normal relay"39^deen rect ground from `the circuit of the release magnet 48 .and in so doing it. leaves the* release `magnet 48 and the lower Winding of Arelay 42 connected in series overthe following circuit: rfrom vground through armature 84 and its working contact, lower winding of relay 42. armature 79c and its resting contact-and release magnetfv48 `to battery. Owing to` the relatively high resistance of thealowcr winding lof 4relayf42 the -releasefmagnet -48deerre1'gi-zes while .the relay .42 energizes'and attarmature 82 locks" itselffto grounded release trunk'conduotor .82 by means of its upper Winding. 4This is accomplished bysozadjusting t-he -relay .42 that armaturer 82fvmakes.contacti-With its working contact ybefore armature 79=breaks away from its resting contact. `#Returning to the release mag-net 482I we.findithatr when itAv deienergizesy Vits 1f armature lbre-aks'i the .circuit of -relav'43f whichaecordinglysdeenergizes and breaks the. circuit of the lower4 Winding of the relay 42,ibut since relay 42 has already energizedfandl loek'edf'itself by means of its upper Windingthisf-has no effect on it.

Summing it upythe'etfectofathe.oallingof the second digithas -beenitorraise'the wipers of the second selector Gr-zin ;the=.main vexchange .to the fourth'leveliand rotate' `them to pick out an idle trunkflinecleading-toian idle' third selector assumed''toffbe-:the'` :third selector represent-ed `by the t4rectangle H. :In the bra nch exchange the fswitchiug' selector repeater l) rotated its wipersffour steps: and upon its Wiper. 251cfindingl afgroundred-fcon- `tact in its associated :banksio-perat'ed the-ref calling device forV the. :third digit 51 :tfhefive pimpulses are repeated toth'ird'selector `H lin them-ain exchange whiiclrfstepsitswipers UP Vt0 the fifth level andwrotates'them infv bank contacts.

Search of an idle trunk line. We will assume that the trunk line terminating in bank contacts 197, 198, and 199 is the first one found idle and consequently the one selected. Since this trunk line is reached by calling 345 it must give access to the branchv exchange. Accordingly it leads to a repeater and from there to an incoming connector located in the branch exchange.

At the same time that the switching selector repeater D in the branch exchange repeats the five impulses to the selector H in the main exchange it operates its vertical magnet 47 over the same circuit and in the same manner it did when the first digit was called. The vertical magnet in this case operates step by step to raise the switch shaft and wipers until the wipers 251-254, inclusive, stand opposite the fifth level of The vertical off normal springs close and complete the circuit ofoff normal relay 39 which energizes as before. In-this case when it energizes it completes at armature 72 the following circuit: From "f2 ground through the armature 62 and its working contact, armature 64 and its Working contact, resting contact of eleventh rotarystep cam spring 50 and said spring, armature 72 andits working contact, resting contact of armature 85 and said armature, working contact ofarmature 80 and said armature, and stepping relay 41 to battery. .Relay 41 energizes over this circuit and at armature 76 establishes the followinglocking circuit for itself. From ground through armature and its resting con. tact, working contact of armature 76 and said armature, resting contact of the armature of rotary magnet 46 and said armature, and thence over previously traced circuit to relay 41. At the end of the vertical movement the slow acting relay 37 deenergizes and at armature 64 closes a circuit for rotary magnet 46 as follows: From ground through armature 62 and its working contact, armature 64 and its resting contact, armature and its working contact, and rotary magnet 46 to battery. Rotary magnet 46, upon energizing over this circuit, steps the wipersl 251-254, inclusive, into engagement with the first set of contacts in the fifth level of their associated banks and at the same time operates its armature to break the locking circuit of stepping relay 41. Relay 41 accordingly deenergizes and at armature 75 breaks the circuit of rotary magnet 46 which, upon deenergizing, allows its armature to come into contact with its resting contact. The operation now depends upon whether the first trunk is busy or idle. If the first trunk is busy there is a ground on the private conductor terminating in test contact 265 completing a circuit extending from Contact 265 through test wiper 252, conductor 96, armature 88 and its resting contact, armature 59 and its resting contact, armature 81 and its working Contact, resting contact of the armature of rotary magnet 46 and said armature, and over the previously traced circuit to relay 41. Relay 41 accordingly energizes and at armature 75 closes again the previously traced circuit for rotary magnet 41 which operates to step the wipers over to the next set of contacts. This cycle of operation is repeated over and over until an idle trunk is reached. Then an idle trunk is found, ground is not present on the test contact thereof and the switching relay 45 energizes in series with the stepping relay 41 over the following circuit: From grounded conductor 32 through switching relay 45, resting Contact of the armature of rotary magnet 46 and said armature, and over previously' traced circuit through relay 41 to battery. Relay 41, however, due to its relatively small number of turns does not energize in series with relay' 45. However, we shall'assume in the present case that the trunk line terminating in the first set of contacts is idle. Under these circumstances when the wipers reach the first set of contacts the test wiper 251 finds, no ground and the switching relay 45 is accordingly operated as before explained and when it does so it connects test wiper 252 to conductor 32 by way of armature 59 and its working contact, and at armatures 54 and 58 disconnects the incoming line conductors from the upper and lower windings of line relay 35 and extends them by way of conductors 91 and 92, wipers 253 and 254, and bank contacts 256 and 257 to trunk line conductors 259 and 260 understood to extend to and terminate in the line relay of a local connector switch, as previously explained. The line and release relays of the connector are accordingly energized and the latter grounds the release trunk conductor 258. This ground extends back to conductor 32 and its multiples and by means of it relay 14 of the line switch C and relay 45 of the switch D are maintained energized and thus hold lthe switches C and D in their respective operated positions. It is understood that this holding circuit is established before the slow acting release relay 37 has had time to deenergize. As to the secondary line switch E and the connection through it to main, the latter connection is released by the permancnt deenergization of the line relay 35 of switch D following the operation of the switching relay 45. The slow acting relay 36 deenergizes soon after the deenerglzation of line relay 35 and at armature 62 disconnects -ground from holding conductor 102 thereby breaking the circuit of relays 118 and 120. Relay 118 immediately deenergizes Vand breaks the circuit of relay 119.

Relays 119 and 120, however, being slow acting do not release immediately and the stepping magnet 117 is energized and steps the Wipers of the line switch into engagement with the next set of bank contacts. The object of stepping the wipers ahead one step upon the release of the switch is not only to secure a better distribution of the calls, but also to prevent the tying up of a call by a defective trunk line. Suppose the trunk line comprising conductors 138 and 139 is defective for some reason, one of the conductors perhaps being open or grounded or the distant selector F being out of order. In such a case a party might try repeatedly to get a main exchange number without success, for on each attempt he might get the same defective trunk line. VViththe arrangement shown, howeventhe first attempt would be unsuccessful, if the connection was attempted by way of the defective trunk line, but when the calling party disconnected to try the number over again he would get a new trunk line, and ultimate success would be assured, even if it should be necessary to try all of the available trunks.

The connection under consideration has now been extended to a local connector in the branch exchange and the trunk line to the main exchange which was tentatively connected with during the first three digits has been restored to common use by its release and the release of the secondary line switch E. The calling subscriber may now go ahead and call the remaining two digits 6 and 7 of the desired number, with the result that the local connector to which the call has been extended is operated to complete the connection to the desired called line. This part of the operation is old and need not be further considered. Y

Ve shall now assume that the same subscriber makes another call and that this time he desires connection with a subscriber whose number is 34,467 and whose line accordingly terminates in the main exchange. IVe shall assume that in this case as before the switching selector repeater D is the one connected with and that the connection at the end of the second digit 4 is exactly the same as it was at the end of the second digit 4 in the preceding case, the first two digits being the same in both cases. The condi tions in this case as in the preceding one at the end of the second digit are as follows: At the main exchange the connection has been extended by way of selectors F and G to the third selector H, While in the branch' exchange the switching selector repeater D has been stepped up to the third level of bank contacts and rotated in to the fourth set and upon finding ground on contact 255 released back to normal position and in so doing relay 42 has become energized and locked to release trunk ground. With these facts in mind, the effect of calling the third digit 4 will be readily appreciated. When the calling subscriber operates his calling device in accordance with the third digit 4 of the called number the line relay 35 of the switch D repeats the impulses over the trunk line comprising conductors 138 and 189 to the third selector H in the main exchange which steps its Wipers up to the fourth level and rotates them to select an idle trunk line leading to a connector switch. ive will assume that the trunk line leading to connector switch M is the first one found idle and consequently the one taken for use. The line and release relays 182 and 183 immediately energize and the latter grounds the release trunk conductor in the usual manner to hold the switches back of it in their respective operated positions. In the branch exchange the switch D raises its wipers to the fourth level and rotates them into engagement with the first set of contacts in that level. It will be noticed upon examining Fig. 3, that the contact-s in the fifth level which wiper 251 came into contact with in the previous call are not wired, that is, they are left dead. However, the corresponding contact 261 in the fourth level is grounded. Now when the switch D rotates its Wipers into engagement with the first set of contacts in the fourth level of its banks as previously explained, test wiper 252 will engage the dead contact 262 and the wipers will be rotated no further but before the switching relay 45 can energize, its circuit is broken at armature 85 of relay 43, said relay energizing over the following circuit: from grounded contact 261 through test wiper 251, conductor 95, resting contact of armature and Said armature, and relay 43 to battery. When relay 43 energizes it closes at armature 87 a multiple point in its circuit so that it will not be deenergized when relay 37 operates armature 65 when the next digit is called.

It will/be seen that as a result of the calling of the third digit 4, which finally de- .terminesthat the call is going to the main exchange, the switching selector repeater D stepped its wipers up to the fourth level and rotated them into engagement with the first set of contacts in that level, thus operating relay 43 which prevents the further operation of the calling device from causing any mechanical operation of switch D. However, the switch D can still function as a. repeater to repeat the impulses to the main exchange. In the main exchange we have the selectors F, G, and H operated and the connection extended to the connec tor M. The calling subscriber may now operate his calling device in accordance with the last two digits 6 and 7 of the desired number and when he does so the connector M lifts its Wipers to the desired level and rotates them into engagement with contacts 192, 193, and 194, in which the desired line terminates. This part of the operation is old and need not be considered in detail. Only so much of the connector M is shown as is needed to make the present invention perfectly clear. lVhen the called subscriber answers in response to the ringing of his bell he raises the receiver from its hook thereby completing a direct current circuit for back bridge relay 131. Relay 181 aecordingly energizes and by means of armatures 184 and 185 reverses battery in the trunk circuit extending back to switch D. This reverses the direction of the current flow in the lower winding of reversing rclay 44 of switch D. The two windings of relay 44 which have heretofore been opposing each other now assist each other in operatingrelay i4 which energizes and upon so doing reverses the direction of current flow in the calling subscribers battery loop.

This operation has no function in the present disclosure but on account of its being standard practice the circuits are shown in this way. Conversation may now take place over the heavy talking conductors. After the conversation is finished the subscribers will hang up their receivers and release will take. place in the usual manner.

We shall now assume that the same subscriber makes a third call. This time he calls for a subscriber whose number is 35567 aud whose line, therefore. terminates in the main exchange. Since the second digit of this number is not thesame as the second digit of the numbers of lines fermi hating in the branch exchange. the second digit called will determine that the call cannot be intended for the branch exchangel and consequently the switching selector repeater D will not need to move its wipers after the second digit is called. ive will assume that the subscriber at substation A has removed his receiver and has called the digit 3 and he has obtained connection with the same switches or in other words comlitions are exactly the same at the end of the first digit'3 in this case as they were at the end of the first digit 3 in the preceding case. Summing it up then the switching selector repeater D has stepped its wipers up until they stand opposite the third level of bank contacts. Spring 97 is operated so that it is in Contact with its working contact and the switch is ready to rotate under control of the calling device. The first selector F in the main exchange in response to the calling of the first digit 3 raised its wipers up to the tnird level and rotated them to pick out an idle trunk leading to the second selector G. With the call thus extended the subscriber at substation A operates his calling device for the second digit 5 of the desired number. The result in the main exchange is that the selector G raises its wipers step by step` until they stand opposite the fifth level of bank contacts and, upon rotating them, picks out anr idle trunk line leading to a third selector (not shown).

At the branch exchange the switching selector repeater D rotates its wipers step by step until they rest on the fifth set of contacts in the third level. As soon as the slow acting relay 3T deenergizes the following circuit is completed: from ground through resistance R (Fig. 3) bank contact 263, wiper i251. conductor 95. resting contact of armature (i5 of relay 37 and said armature, and relay 43 to battery. Relay 43 energizes and loc :s itself at armature 8T and its working contact independent of armature (l5 and at armature S4 closes a circuit for relay 4:2 extending 'from ground through armature 34 and its working contact. lower winding of relay armature T9 and its resting contact. and release magnet 43 to battery. Relay 42 energizes and just before armature 79 breaks away from its resting contact armature 32 makes on its working contact` thereby locking relay 42 by means of its upper winding to the grounded release trunk conductor y32. Armature 99. upon operating. opens the circuit of the rotary magnet to prevent further rotation of the switch when the calling device is again turned. Release magnet 48 having` a winding of few turns and having also a stift` adjustment does not energize at this time.

The calling of' the remaining digits 5. 6. and 7 produces no movement of the wipers of the switch D. The switch D acts merely as a repeater to repeat the impulses to the main exchange where. by means of switches that are not shown. the call is completed. After the termination of the ensuing conversation the subscribers hang up their receivers and the switches automatically release themselves in the usual manner.

Now we will assume that the subscriber at substation A removes his receiver for another call and as' before obtains connection with switch D which through switch E gives him connection to switch l" in the main exchange. le will assume that the call is for a subscriber whose directory number is 44567. However. as a matter of fact any number not beginning with the digit 3 would serve the purpose as well as the one chosen. Since the first digit of all numbers local to the branch exchange is 3, it is easily seen that any number the first digit of which is anything but 3 cannot be a branch exchange number. Consequently we shall expect no further movement of the wipers of the switch D after the first digit is called.

Yhen the calling subscriber operates his calling device for the first digit 4 of the desired number the switch D operates in the usual manner to step its wipers up to a position opposite the fourth level of its associated banks, while the selector F in the main exchange steps its Wipers to the' fourth level and rotates them to pick out an idle trunk leading to a repeater (not shown) and thence to an incoming second selector in the particular office of which the numbers all begin with the digit 4. Since the spring 97 in the switch D is operated only when the Wipers are stepped up to the third level it is, therefore, not operated in this case when the first digit is' four and consequently the circuit of the rotary magnet is open at that point. This being the case the switch D can function only as a repeater. lVhen the calling subscriber at substation A operates his calling dvice in accordance with the remaining digits 4, 5, 6, and 7 of the called number the switch D acting as a repeater repeats the impulses to the repeater in the main exchange which repeats them again to the switches 1n the particular main office to which the call has been trunked with the result that the subscriber at substation A obtains connection with the subscriber for whose number he operates his calling device. This part of the operation is old and need not be further considered.

In the foregoing, in order to obtain connection with a local connector in the branch exchange a subscriber must dial three digits of which no two are the same. In actual practice, however, in case of additions or other changes as are continually taking place in a growing system a condition sometimes arises that makes it imperative that two or sometimes all three of the first digits be the same,` that is, instead of the first three digits being 345 they may be 333, 343, 444. or in fact any oneI of a number of combinations in which at least two of them must be the same. lvithout a special arrangementwhen the first digit is the saine as the third a difficulty' arises which is as follows: The level of contacts d) which the switch wiper 251 has access in the second digit is determined by the first digit and at the end of the second digit these contacts with the exception of one must have ground on them through a resistance and the excepted one must be grounded direct. However, at the end of the third digit, in case the number diallcd is that of a local subscriber, the contacts passed over by wiper 251 must not be grounded because if they are the wiper 251 upon coming to rest on one of them will complete a circuit for relay 43 as explained in connection with the example in which the subscriber at substation A called the number 34467, and relay 43, upon energizing, will open the circuit of switching relay 45 at armature This would prevent the switching selector repeater 'from switching the call through locally, and there` fore, defeat the very purpose for which it is intended. In order to overcome this difliculty, the grounded armature 83 is added to relay 42 of switch D and conductor 271 is connected to the resting contact of said armature at one end and at the other end it is connected directly to one of the contacts on'which the wiper 251 stops at the end of the second digit of a local number, while it is connected through a resistance to the other nine contacts on which the wiper 251 may stop at the end of the second digit in case the first digit called is that of local numbers. In order that this arrangement may be made perfectly clear we will assume that the connectors in the branch exchange are reached by calling 333. In this case the bank shown in Fig. 4 will be substituted for the top or private section of the bank shown in 3, and the wiring shown on the fifth level of the lower section of Fig. 3 is moved down to the third level of the same section. It will now be readily seen that ground is on the third contact in the third level of contacts wiped over by wiper 251 while ground through resistance R2 is on all the rest of the contacts in that level. For the first two digits that is exactly what is desired. If the first digit called is three the wipers are raised to the third level and when the second digit is called the wiper 251 is rotated over the contacts in question and stops on the one for which the calling 4subscriber turns his calling device. If we assume that the first digit is three and the second digit is three then the wiper 251 upon reaching the grounded contact Q64 will complete a circuit for the relay 43 with the ultimate result that the switch is released, relay 42 energized and locked' up to the release trunk, and relay 43 is allowed to deenergize. This all happens as explained in the example in which the subscriber at substation A calls the subscriber whose telephone number 34567 and accordingly need not be explained again. Relay 42 upon energizing disconnects ground from conductor 271, hence, if the next digit called is 3 the switch can rotate over the third level to pick out an idle trunk, for the contacts wiped ,over by wiper 251 will be dead. It will now be seen that the local numbers are not limited to any particular combination.

It will be understood from the foregoing that a plurality of levels of the switching selector repeater may be used for local switching instead of only one level, provided the size of the branch exchange rcquires it. For example. if there are 200 lilies in the branch exchange, two groups of local connectors will be provided instead of one, the trunks to the additional group of connectors being taken from any level other than the level used Afor the first group. Assuming that the fourth level is assigned to the second group` the first contact in the fourth level of the bank associated with wiper Q51 is disconnected from ground, so that if a calling subscriber dials the digit 3, followed by the digit 3 again, the connection will be switched to a local connector in the second group if the next digit dialled is the digit 4. Following the same plan, another group of trunks could be taken from the fifth level to a third group of connectors in order to increase the capacity to 300 lines.

The foregoing part of the explanation will now be supplemented by a` more. detailed consideration of some of the circuit refinements that have been incorporated in the circuits of switches 1) and E. In the lower part of Figure 2 is shown a so called trunk tone machine indicated by the reference character T. The ,purpose of this machine is explained as follows: 'hen a subscriber lifts his receiver to make a call the line switch in which the calling line terminates may be standing on the first of a number of busy trunks and accordingly will have to rotate over several contacts. Now if the subscriber starts to dial the first digit before the line switch has found an idle trunk, obviously, he will not obtain connection with the number for which the calling device is operated. In order that a subscriber may know when to begin operating his callingr device, the positive winding,r of the line relay 35 of the switch D is normally connected to ground through the secondary winding of trunk tone. machine T. The subscribers are instructed to listen for this tone before calling the first digit. Ordinarily in the case` of a telephone system that is not equipped with switching selector repeaters but has selectors instead, the first `selectors, only are arranged to give out the so called trunk tone and when the connection is extended to a second selector the line is quiet again. Now in order to simulate this condition. in the switching selector repeater the olf normal relay 39 which operates iu response to the calling of the first digit is arranged to place direct ground on the lower winding of line relay 35 and at the same time disconnect said winding from the trunk tone machine T. This is done at armature 73d and in a manner that is readily seen and needs no explanation. When switch D releases as it does on the second digit of local numbers the off normal relay 35 falls back and restores the trunk tone to the lower winding of relay 35. but relay 42 is immediately operated as has been previously explained and at armature 77 applies ground to and removes trunk tone from the lower Winding of relay 35.

In a system of this sort, a. subscriber in the. branch exchange should be notified when he cannot get a connection to main on account of all the trunks to main being busy. It will readily occur to one skilled in the art that we. need only apply the well known busy signal in such a manner that it would be heard by any subscriber who obtains connection with a switching selector repeater during the time when alltrunks to main or busy. If that is done the subscriber hears the busy signal when all trunks to main are busy even though he may intend to call a local number. and unless he knows whether the number he wants is a local number or not he has no way of determining whether or not the busy signal he hears means that. he cannot obtain the desired connection.

In the prese-nt. invention when a branch exchange subscriber initiates a call that must be completed by way, of a, trunk line leading to the main exchange when all trunks to main are busy, the applied busy signal cannot be heard by the calling subscriber until he has called such digits as determine definitely that the call is not intended for a local subscriber. Upon referring to Fig. 1, it becomes evident that when all trunks'to main such as the trunk line comprising . conductors 138 and 139 are busy all relays such relays 120, 142. and 143 are energized and thus complete a. circuit extending from ground by way of the work- -ing contact of armature 140 and said armature. and the corresponding contacts and armatures on relays 142 and 143 to battery through relay 144. Relay 144, upon energizing, removes battery from common conductor 146. In case all the trunks to main are busy when the subscriber at substation A makes a call by way of switch D the energization of line relay 35 closes a bridge across conductors 101 and 105 but since battery is removed from common conductor 46 the relay 119 of switch E cannot energize. Switching relay 118, however, does energize and contrary to the usual practice pulls all the way up, even though the line relay 119has not been energized. It will be understood from this that the usual mechanical interlocking arrangement between the armatures of the line and switching relays is omitted, and this omission causes no harm to result. due to the revised circuit arrangement which includes the normally open contacts in the line conductors controlled by the line relay. If desired the same circuit arrangement could be used on the primary line switches, such as the line switch C, Fig. 1, but because of the great number of primary switches the mechanical device is usually preferable on account of its cheapness. The calling subscriber now operates his calling device for the Erst digit of whatever number he may desire. If this is any digit other than three or if it is not the first digit of local numbers the shaft operated spring 98 will not be forced away from its resting contact and a. circuit will be closed extending from the secondary winding of the busy machine B, armature 71 of ofi' normal relay 39 and its working contact, spring 98 and its resting contact, conductor 104, resting contact of armature 128 and said armature, working contact of armature 122 and said armature, conductory 101, armature 66 and its resting contact and thence by way of upper talking condenser back to the calling subscribers telephone set. rI"his produces the well known busy signal and the subscriber upon hearing it will know that he cannot obtain the connection he desires.

If, however, the first digit called for is three there is no way of knowing whether the subscriber desires a connection with a local subscriber or with one to .vhich the call must be extended by way of the main exchange. In this case the spring98 is forced away from its resting contact and opens the circuit so that the calling subscriber cannot hear the busy signal. Assuming that the first digit called is 3 and that the bank wiring shown in Fig. 3 is the wiring that is used` if the second digit is anything except 4 it will determine that the call is intended for the main exchange and relays 43 and 42 will pull up and lock as has been previously explained. Relay 42.. upon energizing, closes ashunt around spring 98 and its associated contact at armature 78 and its working contact and the subscriber will hear the busy signal as explained before. However, if the second digit is 4 the switch D releases as has been previously described and when it does so the off normal relay 39 upon deenergizing breaks the busy signalling circuit at armature 71. lf the switch releases at the end of the second digit and if the third digit is anything but 5 the switch rotates onto the first contact and remains there until the connection is released and obviously the calling subscriber hears the busy signal, but if the third digit is 5 the switch rotates to find an idle trunk on the fifth level of its bank contacts leading to a local connector, and when it does so the switching relay 45 energizes and at armatures 54, 58 and 59 extends the connection through to the selected connector and consequently severs the connection between the llausy signalling machine .B and the calling Upon referring to the drawing it will be noticed that the switch D (Fig. 2) has apparentlyv three cams all indicated by the numeral 94. n actuality all theI springs 49, 5d and 53 are grouped together and operated by a single cam. They are shown divided in the drawing for convenience only. The purpose of these springs is to give the calling subscriber a busy signal when he calls a local number and finds all local trunks busy and also to release the secondary line switch E and the connection that has been extended through it to' the main office. If this were not done a subscriber might call for a local number, and upon finding all local connectors busy, fail to hang up immediately and thereby tie up a trunk line to main, a first, a second, and a third selector in the main oflice and also a trunk line from the main office back to the branch exchange. This possibility is entirely eliminated in the present invention in a manner that will now be explained. lVhen the switch D is used in making a call that is intended for a local subscriber it steps up, upon the calling of the third digit, to the level corresponding to the third digit of local numbers and rotates its wipers over this level in search of an idle trunk line leading to a local connector. If an idle trunk line is not found the wipers are rotated until they pass off the last set of contacts in that level and when they do so the cam 94 secured to the shaft operates springs 49. 5l) and At spring 50 the circuit of switching relay 45 is broken to prevent said relay from energizing and opening the circuit of line relay 35. Spring 53 opens the bridge across conductors 101 and 105 and thereby releases the connection to main, while spring 49 opens the holding circuit for switch E which steps to the next contact and assumes normal condition thus leaving the trunk to main free for another call. Spring 53 in addition to opening the bridge across conductor 101 and 104 also closes a circuit from busy signalling machine B to the lower talking condenser and thence back to the calling subscriber to inform him that he cannot obtain the desired connection until a trunk becomes idle and that he must call later in order to do so.

It will be seen from the above that when a local number is called that the trunk to main is released whether the local connection is obtained or not.

The practice of reserving the tenth level of first selector switches iii automatic systems for connection to the toll recordin operator has been used quite extensively and as has been explained before is used in the present case. ln the drawings, Fig. 8, shows one level assumed to be the tenth of the first selector F leading to the repeater L said repeater being arranged to give access by way of the trunk line comprising conductors 220 and 221 to a toll recording operator. In a system of this sort the toll recording operator must know whether the calling subscriber is entitled to toll connection or not and if so what kind. This is usually accomplished by the use of the so called discriminating tone. In Fig. 1 of the drawings the discriminating tone machine is shown and is indicated by the reference character N. This tone machine is arranged to give out tones of different character according to the kind of service to which the calling subscriber is entitled and is connected onto the private normal of the calling line switch through a condenser. Since arrangements of this kind are well known in the art it is not deemed necessary to go any further into detail concerning the discriminating tone machine. In the selector repeater D there is laced an induction coil indicated by the re erence character I. This induction coil is connected in the circuit in such a manner that the toll recording operator, upon throwing a key'preparatory to answering, hears the kind of tone if any that is placed on the rivate normal of the calling line switch.

e shall now assume that the subscriber at substation A desires a toll connection in which case he calls the toll recording operator. We shall assume further that when he removes his receiver he obtains connection with the switching selector repeater D as has been explained before, and that through the secondary line switch E he obtains connection with the trunk line comprising conductors 138 and 139 which also has been previously explained.

When the calling subscriber operates his calling device for the digit 0 the switching selector repeater D raises its wipers to the tenth level and at the same time repeats the ten impulses to the first selector F in the main exchange which steps its wipers up to the tenth level and rotates them to pick out an idle trunk line leading to the toll recording operator. The operation of the selector F has been previously explained and consequently need not be explained again now. We may assume in the present case that the trunk line terminating in bank contacts 178-180, inclusive, is the lirst one found idle and consequently is the one selected. Such being the case, when the switching relay 155 operates it extends the connection by way of armatures 168 and 171 and their working contacts, wipers 172 and 174, bank contacts 178 and 180, and conductors 200 and 202 to the upper and lower windings of line relay 210 of repeater L. The line relay 210 and release relay 211 of the repeater L accordingly energize. The latter grounds the release trunk conductor 201 at armature 217 in order to establish a holding` circuit for the selector F in the well known manner. Line relay 210 closes at armature 215 a circuit extending from ground through impedance 212, working contact of armature 215 and the said armature, trunk conductor 220, spring 230 of key K and its resting contact, and the upper winding of relay 223 to battery. Relay 223 energizes over the above traced circuit and lights the lamp 240 over a circuit extending from ground through the working contact of armature 227 and said armature, armature 226 and its resting contact, and lamp 240 to battery. In order to simulate the practice that has come into extensive use in automatic systems of indicating to the calling subscriber when the called subscribers bell is being rung, relay 223 closes at armature 237 lsprings 230-232, inclusive, and when she does so relay 222 is energized over a circuit extending from ground through the working contact of spring 231 and said spring, and relay 222 to battery. Relay 222, upon energizing, opens the circuit of lamp 240 at armature 226 and locks itself to ground by way of armatures 226 and 227. A branch of the energizing circuit for relay 222 extends by way of spring 235 of key K and its resting contact to battery through the lamp 241 which accordingly becomes lighted. As soon as the key K is thrown as above explained, the circuit ot the upper winding of relay 223 is shifted so that it includes relay 213 of repeater L instead of impedance 212 and may be traced as follows: From ground through armature 214 of release relay 211 and its working contact, relay 213, trunk conductor 221, spring 232 of key K and its working contact, and the upper winding of relay 223 to battery. It may be stated here that key K is so adjusted that spring 231 makes contact with its working contact before either spring 230 or 232 breaks away from its resting contact. Relay 213 energizes when its circuit is completed as explained and opens at armature 218 the circuit of line relay 210 allowing it to deenergize and break the circuit to release relay 211 but a multiple circuit for relay 211 is closed at armature 219. The opening of the circuit of relay 210 stops the fiow of current in the loop extending back by way of selector F and the trunk line comprising conductors 138 and 139, to the switch D in the branch exchange and thereby allows the relay 38 of switch D to deenergize and when it does so it removes direct ground from release trunk conductor 32 at armature 68 thereby introducing the lower winding of induction coil I in the circuit. With this condition existing the discriminating tone current placed on the private normal 13 of the calling line switch C Hows by way of the working contact of armature 18 and said armature, test wiper 26, test contact 29, release trunk conductor 32, armature 61 of relay 36 and its working contact, and lower or primary Winding of induction coil I to ground. The fluctuations of this current in the primary are reproduced in the secondary of induction coil I. A path for this reproduced fluctuating current extends froin the right. hand end of the upper or secondary Winding of induction coil I through the associated condenser, resting contact of armature 67 and said armature, resting contact of spring 53 and said spring, working contact of armature 93 of relay 35 and said armature, positive talking conductor of the established connection, spring 232 of the operators key K and its lower working contact, the operators head set, working contact of spring 230 and said spring, negative talking conductor of the established connection, armature 128 of the line relay 119 of the secondary line switch E and its working contact, and conductor 103 to the left hand end of the secondary winding of induction coil I. The operator hears the discriminating tone and after ascertaining the kind of service to which the calling subscriber is entitled throws her key over to the opposite or answering position. When the key is thrown the circuits in the repeater L and consequently the switch D are restored to the same condition they were in before the key was first thrown. The operator can now converse with the calling subscriber in the usual manner. When the conversation is finished the calling subscriber replaces his receiver upon the switch hook, thereby Ieleasing the connection.

In the foregoing description 'it has been assumed that the switching selector repeater D is used in a hundred thousand line system and that the branch oflice is not above a few hundred lines and that the branch office connectors are accessible from the banks of the switching selector repeaters. It has been explained before that under these circumstances the switching selector repeaters must be capable of switching on the third digit called. Then used in a ten thousand line or four digit system in which one hundred lines are located in the branch exchange the switching selector repeater must be capable of switching on the second digit for in such a system it is the second digit called that determines to which group of 100 lines the call is going. For this reason when the switch D is operating in a four digit system the two terminals 90 are 'umpered together and spring 97 is so ad- ]usted that it cannot touch its working contact. lVe shall assume that it is the 45 hundred group of lines located at the branch exchange or in other words, connection to a branch exchange connector is obtained by calling 45. In this case the upper or private bank section shown in Figure 3 will be replaced by the private section shown in Fig. 5. When the calling subscriber operates his calling device in accordance with the first digit of the desired number the switch D operates to raise its wipers a like number of steps and since the terminals 90 are jumpered together the circuit conditions for the stepping relay 41 are the same as thev were at the end of the digit 5 in the case' in which the subscriber at substation A called the subscriber whose number is 34567. That being the case, as soon as the slow acting relay 37 deenergizes armature 64 completes the circuit for the rotary magnet 46 which energizes to step the wipers onto the first set of bank contacts in the level opposite which they were raised. If the digit that is called is anything but 4 the wiper 251 encounters a contact that is grounded through either resistance R4 or R with the result that relays 43 and 42 energize and lock themselves in the same manner as described when the second digit 5 was called in the case in which the number 35567 was called, and when the remainder of the digits are called the switch D acts merely as a repeater to repeat impulses to the main exchange.

If we assume that the first digit called is 4 the wiper 251 upon being rotated onto grounded contact 273 completes the follow-` ing circuit for relay 43: from ground through contact 273, wiper 251` conductor 95, resting contact of armature 65 and said armature` and relay 43 to battery. Relay 43 energizes and at armature 86 completes a circuit for release magnet 48 as follows: from ground over previously traced circuit for relay 43, working contact of armature 86 and said armature, working contact of armature 7() and said armature, armature 79 and its resting contact, and release magnet 48 to battery. Release magnet 48 energizes andrestores the wipers to normal. In orda r that its circuit will not be broken by wiper 251 when it leaves grounded contact 273, release magnet 48 operates its armature to complete a locking circuit for itself and relay 43 as has been explained liefen ll'hen the switch reaches normal, relay t2 is energized and locked to grounded release trunk conductor 32 at armature 82, and relay 43 is allowed to deenergize. lf the next digit called is 5, wiper 251 engages contact 275 which is now dead, armature 83 being operated, and since the circuit of test wiper 252 is closed at armature 81 of relay 42, the switch operates to pick out an idle connector and when it does so the connection to main is released and the call is completed locally through the seized connector in the usual manner. If the second digit had not been 5 then the wiper 251 would have engaged a contact that is grounded either directly, or through resistance R. When wiper 251 engages a grounded contact relay 43 operates and at armature 85 opens the circuits of relay 4l and 45, thus preventing the remaining digits from causing further movement o? the wipers.

Bank wiring similar to that shown in Fig. 5 is satisfactory only so long as the first and second digits of local numbers are different. We shall now assume that they are the same, we shall assume further that the first two digits of local numbers are 55. In that case the private section of the bank shown in Fig. 6 is substituted for the top, or private section shown in Fig. 3. Since all the contacts upon one of which wiper 251 must come to rest at the end of the first rotary step after the calling of any digit, except 5, are connccted to ground through resistance R5, the calling of any first digit other than 5 has the same effect as the calling of any first digit other than 4 in the preceding case, and accordingly the switch does not release but acts during the calling of the remaining digits only as a repeater, however, if the first digit called Vis 5 wiper 251 comes into engagement with contact 274, which being connected to conductor 271 is grounded at armature 83 of relay 42 and consequently release takes place in the usual manner and at the end of the releasing operation relay 42 energizes and becomes locked up as has been explained before. Relay 42, upon energizing, disconnects ground from conductor 271 at armature 83, thereby removing ground from contact 274. It is easily seen that if the second digit is five that the switch D will operate in the usual manner to select an idle trunk leading to a local connector. It is also easily seen that if the second digit is anything but 5 that the wiper 251 engages a contact that is grounded through resistance It*s and relay 43 operates in the usual manner and locks itself at armature 87 and its working contact while at armature 85 it breaks the circuit of relays 41 and 45, thereby preventing further movement of the shaft and wipers when the remaining digits are called.

It has been explained how the switching selector repeater D operates to switch on the third digit called and also on the second digit called. It will now be explained how it can be made to switch on the first digit called. For this pur-pose we shall assume that we are dealing with a ten thousand line or four digit system in which two thousand lines are located in the branch exchange,

IVe shall assume further that it is the fourth and fifth thousands that are located in thc` branch exchange. In the branch exchange we will have two groups of second selectors which will be seized from the fourth and fifth levels respectively, of the switching selector repeaters. These selectors in turn operate to pick out idle connectors in the proper group. In this case we shall substitute the private bank section shown in Fig. 7 for the top or private section in Figure 3, while the lower section shown in Fig. 7 will have its fourth level wired also. In this case the switching selector repeater D is left exactly as it was for switching on the second digit called except that the terminals 89 are jumpered together. lith this done it is easily seen that as soon as the switch is seized relay 42 energizes by means of the upper winding and the switch is in exactly the same circuit condition as it was in the preceding case after it had released upon the calling of the first digit of local* numbers. lVith this condition existing the first digit called determines whether the call goes to main or not. If the first digit called is 4 or 5 the switch D rotates in the usual manner to select an idle trunk and when one is found the connection to main is released and the call is completed in the usual manner; but if the first digit called is other than 4 or 5, the wiper 251 engages a grounded Contact and relay 43 operates and the switch functions as a repeater during Ythe remaining digits and repeats the impulses to the main exchange where the call is completed in the usual manner.

Having fully described and ascertained my invention, what I consider to be new and desire to have protected by Letters Patent will be pointed out in the appended claims.

What I claim is:

1. In a telephone system, main and branch exchanges, means including a switching selector repeater for connecting a calling branch subscriber with a called subscriber in either exchange. a rotary line switch permanently associated with said selector repeater, trunk lines to the main exchange accessible to said lin(` switch, means for operating said line switch to select an idle trunk line whenever the said selector re peater is taken for use, means for giving the calling subscriber a busy signal in case all of said trunk lines are busy, and means for rendering said last mentioned means inoperative until the calling subscriber has called such digits as determine definitely that the call in order to be successful must be completed by way of one of said trunk lines.

2. In a telephone system, main and branch exchanges, means including a switching selector repeater for connecting a calling branch subscriber with a called subscriber in either exchange, trunk lines to the main exchange, means for associating one of said trunk lines with the said selector repeater when the latter is taken for use, means for giving the calling subscriber a busy signal in case all of said trunks are busy, and means for rendering said last named means inoperative until the calling subscriber has called such digits as determine definitely that the call in order to be successful must be completed by way of one of said trunk lines.

3. In a telephone system, main and branch exchanges, means including a switching selector repeater in the branch exchange for completing connection from a calling branch exchange subscriber to a called subscriber in either exchange, means responsive to the initiation of a call by a branch exchange subscriber for extending his line to said switching selector repeater, said repeater being adapted when taken from use to give out a distinctive tone to indicate to the calling subscriber that he may proceed with the call. an ott normal switch for disconnecting said tone when said selector repeater is operated, means for releasing said selector repeater in case the same is operated to call a branch subscriber, and means for preventing said tone from being again applied to the calling line when such release takes place.

4. In a telephone system, main and branch exchanges, means including switching selector repeaters for completing connections between calling branch exchange Subscribers and called subscribers in either exchange, means responsive to the initiation of a call by a calling branch exchange subscriber for extending his line to one of said switching selector repeaters, said repeaters so arranged that when taken for use they give out a distinctive tone to the calling subscriber to indicate that he may proceed with/the call, and means responsive to the calling of the first digit of the desired number for rendering said tone inoperative, said last means being rendered inoperative responsive to the calling of the second digit, and additional means for rendering said tone inoperative responsive to the calling of the second digit.

5. In a telephone system, main and branch exchanges, branch to main exchange trunk lines, switching .selector repeaters in the branch exchange, means responsive to the initiation of a call in the branch exchange for connecting the calling line with one ot said switching selector repeaters and also with one of said trunk lines, said repeaters arranged so as to give out a distinctive tone when they are connected with to indicate to the calling subscriber that he may proceed with the call, means for giving the calling subscriber a busy signal it all of said trunk lines are busy, and means for rendering said busy signalling means inoperative until said distinctive tone is removed.

6. In a telephone system, main and branch exchanges, a plurality of subscribers lines of different character terminating in saidt exchanges, means including a switching selector repeater for extending any branch exchange line when calling to an operators position by way of the main exchange, means for operating and releasing said selector repeater during the setting up of the connection, and means for giving the operator a distinctive tone indicative of the character of the calling line.

7 In a telephone system, main and branch exchanges, means including a switching selector repeater in the branch exchange for completing connection between a calling branch subscriber and a called subscriber in either exchange, said switching selector repeater having primary and secondary movements controlled respectively by the first and second digits called, means responsive to the calling of the first digit for rendering the secondary movement operative only when the first digit called is a particular one, and means responsive to a secondary movement of a predetermined extent for releasing said selector repeater to render the same responsive to a third digit.

8. In a telephone system, main and branch exchanges and interconnecting trunk lines, automatic switches in the main exchange, a switching selector repeater accessibleto a calling branch subscriber and adapted to repeat impulses over an interexchange trunk line to operate i series of main exchange switches, local connectors accessible to said selector repeater, means for operating said selector repeater in its primary movement responsive to the first digit in the called number, means for operating said selector repeater in its secondary movement responsive to the second digit in the number, means for then automatically releasing said selector repeater, means for reoperating said selector repeater in its primary movement responsive to the third digit in the number, means for automatically operating said selector repeater in its secondary movement to select an idle local connector, means for switching the calling line through to the selected connector. and means for releasing the partially' established connection in the main exchange.

9. In a telephone system, main and branch exchanges and interconnectingr trunk lines, automatic switches in the main exe change, a switching selector repeate accessible to a calling branch subscriber and adapted to repeat impulses over an inter-ex change trunk line to operate a series of main exchange switches, local manna-,tors acces sible to said selector repeater, means for llfi operating said selector repeater in its primary movement responsive to the first digit in the called number, means for operating said selector repeater in its secondary movement responsive to the second digit in the number, means for then automatically releasing said selector repeater, means for reoperating said selector repeater in its primary movement responsive-,to the third digit in the number, means for automatically operating said selector repeater in its secondary movement to select an idle local connector, means for switching the calling line through to the selected connector. means for releasing the partially established connection in the main exchange, and circuit arrangements such that in case a. digit is called which finally determines that the called line is in the main exchange further selective movement of said selector repeater thereafter is prevented, and the said selector repeater is caused to function solelyv as a repeater to complete the required connection via the switches in the main exchange.

10. In an automatic telephone system. main and branch exclianges varying in size, a switching selector repeater for use in branch exchanges, means in said selector repeater for switching any branch exchange call from the main exchange to the branch exchange when suthcient digits have been called to determine its destination, and means for causing said selector repeater to switch on either the first, second, or third digit in a called number. whereby the said selector repeater may be used in branch exchanges of different sizes.

11. In a telephone system. main and branch exchanges, means including a switching selector repeater in the branch exchange for completing a connection from a calling branch exchange subscriber to a called subscriber in either exchange, means responsive to the initiation of a call by a branch exchange subscriber for extending his linel to Said switching selector repeater, said repeater being adapted when taken for use to give out a distinctive tone to indicate to the calling subscriber that he may proceed with the call. a relay for use in controlling the switching operations in accordance Wiin the exchange in which the called subscriber is located, and contacts on said relay tor disconnecting the tone circuit from the calling line.

12. In a telephone system, main and branch exchanges, means including switching selector repeaters for completing connections between calling banch exchange subscribers and called subscribers in either exchange, means responsive to the initiation of a call by a calling branch exchange subscriber for extending his line to one of said switching selector repeaters, said repeaters so arranged that when taken tor use they give out a distinctive tone to the calling subscriber to indicate that he may proceed with the call, and contacts operated responsive to the tirst step of said switching selector repeater responsive to the calling of the first digit of the desired number for rendering said tone inoperative.

13. In a telephone system, main and branch exchanges, a plurality of subscribers lines et different character terminating in said cx` changes, means including a switching selector repeater for extending any branch exchange line when calling to an operator-s position by way ot the main exchange, and means for giving the operator a distinctive tone indicative ot' the character of the call' ing line. said means including a truni; l :a extending to the operator`s position, a relay in the selector repeater energized over the trunk line. and means for opening the circuit of said relay to deenergize the same and complete the tone circuit.

14. In a telephone system, main and branch exchanges and interconnecting trunk lines, automatic switches in the main exchange, a switching selector repeater accessible to a calling branch subscriber and adapted to repeat impulses over an inter-exchange trunk line to operate a series of main exchange switches, local trunk lines accessible to said selcctf repc xtec means for operating .Caid selector repeater in its primary moviimir responsive to the rst digit in the called number, means for operating said selector repeater in its secondary movement responsive to the second digit in .the number. means for then auteanatically releasing said selector repeater. means for reoperating said selector repeater in its primary movement responsive to the third digit in the number, means for automaticaliy 'operating said selector repeater in its secondary movement to select an idle local tiunlt line, means for switching the calling line through `to the selected local trunk line. and means t'or releasing the partially established connection in the main exchange.

15. A snitching selector' repeater for uSe. in branch exchanges. said selector repeater comprising means tor switching a call originating in the branch exchange in which it is being used vfrom the main exchange to the said branch when sufficient. digits have been called to determine the destination of the call, and comprising also means whereby the switching operation may be caused to take place on either the lirst, second, or third digit ot the called number, thus enabling the said device to be used in branch exchanges of different sizes.

16. In a telephone system, main and branch exchanges, a plurality of subscribers lines of diticrent character terminating

Images