US1688150A - Signors - Google Patents

Description

Get. 16, 1928. 138mm R. MERCER ET AL TELEPHONE SYSTEM Filed Sept. 1924 8 Sheets-Sheet l fill lrmlll llHll ljflll In; W

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Oct. 16, 1928.

R. MERCER ET AL TELEPHONE SYSTEM Filed Sept. 6, 1924 8 Shtseet '7 ImrE'n 01'' Richard MEPEEP- Frank T211021 W 5-- Oct. 16, 192E. msmso R. MERCER ET AL TELEPHONE SYSTEM Filed Sept.6,'l924 8 Sheets-Sheet 8 1W5? Emhard PIEPEEP Frank Teach Err-g I Patented ea. is, 1928.

warren stares "earner GFFHCE.

RICHARD MERCER, OF HARROW, AND FRANK TENCH, OF LONDON, ENGLAND, AS-

SIGNORS, BY MESNE ASSIGNMENTS, T0 AUTOMATIC ELECTRIC INC, OF CHICAGO,

ILLINOIS, A CORPORATION OF DELAWARE.

TELEPHONE SYSTEM.

Application filed September 6, 1924., Serial No. 736,354; and in Great Britain September 18, 1923.

' The present invention concerns improvements in or relating to automatic telephone systems, more particularly systems of the type in which the automatic switches are directly controlled by the subscriber. Since the subscribers dial has usually ten finger holes the switching in such systems will normally be on the decimalprinciple, i. e. the number of contacts upon which the switches can be set by impulses will be a power of 10. Such a system if used without any modification is apt to be uneconomical in the case of small exchanges of say, from 1000 to 5000 lines or in small networks having less than five exchanges since a large proportion of the first selector bank is unused. Accordingly the object of the present invention may be stated generally to be the provision of improved switches and improved trunking arrangements whereby a more efiicient utilization of the switches is possible and in the case of exchanges of from 1000 to 4000 lines capacity a switching stage may be entirely saved. the switches employed are of the type known as large capacity switches i. e. they have more than one set of wipers and a corresponding number of banks, the particular set to be used being selected according to requirements.

The feature of the invention broadly stated is the more efficient or economic utilization of switches owing to the superior efficiency of large groups of trunks which additionaleificiency is attained by means individual to the switches and independently of any increase in the number of leads between the switches of one stage and the switches of a preceding stage. Moreover very slight alterations are necessary to the switches and there is no radical departure from the main features of construction and operation which have been proved to give reliable service.

According to one feature of the invention,

' a plurality of means of access are provided to one or more groups of subscribers" lines, the switch or switches affording each means of access being subjected to a different directive control. This arrangement may be rendered possible because one or more exchanges work are or-o ded with a plurality Some of.

ElZOS access used being dependent upon the value of the exchange selecting digit or digits dialled, in which case the connection proceeds in the ordinary way, or according to another feature of the invention, means may be provided for discriminating between connections established in response to diifercnt digits so as to enable these connections subsequently to be resolved in accordance with said different digits.

The objects of the invention may be attained by the use of specially modified autoiatic switches which are not effectively operated in response to the first digit but in which this first digit is recorded upon relays,

the switch then operating in the usual manner in response to subsequent digits.

The operation of the relays may be effected tion taken in conjunction with the accompanying drawings. It should be understood however that the embodiments described are by way of example only and that considerable modifications could be made in the circuit details without exceeding the scope of the invention.

The main object of the invention, to permit the use of large groups of trunks whereby the economy always associated with large groups can be attained, is achieved by two methods either or both of which may be employed as desired, firstly, by special slight though important modifications of the standard switches which are known to oper ate reliably and secondly, by the application of the principle of grading which will be more fully described hereafter.

Referring now to the drawings, Figs. 1 to 9 and 18 are layout diagrams showing schematically various proposed arrangements of the switches in systems of different Figures 10., 11, 12, 13, 1e, 16 and 17 are de' {DZ glut diagrams n e the invention, while Fig. 15 indicates a single contact bank showing how the connections are made when gracing is resorted to.

In each of Figs. 1 to 9, and 18 it is assumed that a connection is set up from the subscriber A over the primaryline switchC to the subscriber A having a similar line switch C Dealing first with Fig. 1, this represents the switching plan of a10,000 line exchange in which all the switches are of the so-called large capacity type, having. two sets of wipers and corresponding banks and thus having access to 200 lines. Both the first and second selectors are arranged for simultaneous hunting, but whilethe second selector E has 10 groups each of 20 lines outgoing from it, the first selector ,D comprises only 5 gronpseach o't' lines since the two banks oileach switch are multipled together in a special manner. This multipling may conveniently be between levels 1.t0 5 in the lower bank and levels (3 to 0 respectively in the upper bank, orbetween levels 6 to 0 in thelowerbank and levels 1 to 5 respectively in the upper bank, but other arrai'igements may equally well be employed. In the above case it the subscriber dials either 1 or Ghe obtains access to the same group of 20 trunks; consequently it is necessary to provide some means of discriminat on between the digits 1 and 6, as in general they will be required to produce a different final effect.

"Thisdiscrimination is effected by connecting a special potential momentarily to one of the speaking leads before the succeeding series of impulses, and. this potential is re peated through the second selector and operto detcrminoiwhich set of wipers of the connector H shall be used. lVith the arrangement shown in Fig. 1 the benefit of large groups or? trunks is obtained in both the first and second selecting stages, s': co the second selectors are of the 10-level Ell-trunk type and exceptfor the provision for repeating the discriminating potential are identical with those described in BritishPatent No. 170,385 granted Oct. 19, 1921. It may be preferable however in some cases to use. see- 0nd selectors of standard type having groups of ten lines; the desirability in any particularinstance will be determined by the special circumstances. of the case. Detailed circuit diagrams corresponding to are given in Figs. 10, 11 and 12.

The arrangement. shown. in Fig. 2 is very sim lar except that in this case the first selector D is standard and the combination into large groups takes place at the second selector E which isnow similar to the first selector 1) shown in 1. The. connector H again has two sets of wipers, one or other oi": which is selected in response to the receipt or non-receipt of the discriminating potential, which in this case is transmitted direct from the second selector E Fig. 3 shows an arrangement again applied to a 10,000 line exchange, and very similar to Fig. 1. The first selector D in this case is identical with that shown at D .inFig. 1,]ont the second selector-F instead of .a standard switch ,or he ngarranged tor. simultaneous hunting overl th banks as in Fig. 1, responds to the discriminating potential to select one or other of its two sets of wipers, and connect ons are then made from enact. the twohanks to separate groups granted F eb. 26, l-920 in which the wipers are only operated by the odd impulses, while the even impulses perform a switching oper ation. In the specification mentioned it 'will be remembered, the switch had two banks and sets of wipers, the second set-be-' ing brought into use if an even number of impulses was received and the switch was adapted to respond to as many as 20 impulses. As applied to the present invention however the switch would only respond to ten impulses and would thus take a maximum of 5 steps. Accordingly the two sets of wipers will be in parallel and spaced five steps apartr and arrangements will be provided for simultaneoushunting. 'The bank wiring will be such that leyels 1 and 6 lead in the same direction, levels 2 and 7 lead in. the same different direction and similarly levels 3 and 8 and so on. In order to obtain the required discrimination in this case, the odd impulses are arranged to produce the actual movement of the switch wipers as before while the even" impulses operate a relay which controls the con nection of discriminating potential ovcr the line at the righttime in the manner previously descr bed. .Second selector E is standard except for means for repeating the Y discriminating potential and connec'torlFP issimilar to connectors H and H It will be apparent that any of the arrangements shown in Figs. 1 to 1 may be applied to a 1000 line exchange with suitable modifications, i. e. in general the elimination of the second selectors so that the discrimlnating potential is transmitted direct -from the "first selector to the connector.

Inthe case of a 5,000 line exchange, the ordinary numbering scheme aIi(l"'standaI'(l bank wiring is used something like half the bank is wasted owing tothe first digit being only oneof a possible five numbers. The

systemof bank wiring for the first selector shown'in 4, may advantageously he used to attain greater economy in, this case,

messiah being then'of the type shown in Fig. 10 with two sets of wipers spaced five steps apart and a'ranged for simultaneous hunting. Since in this instance, there is no combination of two different digits, it is unnecessary to send any discriminating potential and the second selectors and connectors may be or" the standard type, or standard large capacity second selectors may be employed as in Fig. 1.

Figure 5 shows an arrangement suitable for a i000 line exchange and its use enables the first selectors normally used to be eliminated entirely. This is attained by arranging the first selectors such as F to respond to the first series of impulses to register the digit dialled anl then to be operated in the usual manner response to the second digit. The registering of the first digit may be effected either by causing the switch to step up, maize a suitable record and then drop back as in the switch shown in Fig. 18 or b allowing the first series of impulses received to operate relays direct as in the switch shown in Fig. l i. in order to secure the necessary discrimination, the selectors such as F, and connectors as H will each have two sets of wipers and according to the first digit dialled appropriate selection is made between the various sets of wipers,there being clearly tour choices available.

Figure 6 shows a similar principle applied to a 400-line exchange, in which case obviously one switch such as the connector H impulses, in which case a connector shown.

in 17 operating on the principle shown by the selector in Fig. 14: may be used.

The application of the same principle to a 2,000 line exchange follows at once and is depicted in Figs. 7 and 8. In F igure 7 the first selector F "is set in accordance with the first digit and after responding to the second digit sends a discriminating potential to the connector H to determine which set of wipers is to be used. In Fig. 8 the first digit is employed to determine which set of wipers of the nrst selector F shall be used and two separate groups of connectors such as H and H may then be employed each of stand ard type.

Figure 9 is concerned with a network in which there are only a small number of exchanges, say less than ten. In this case instead of only one level of the bank of the first selector G being allotted to each exchange as has been usual practice hitherto, each exchange of such size as to warrant it is llotted two or, perhaps three levels and by this means a large group of trunks may be obtained and the usual saving incidental thereto gained. The second selector E and connector H may now be standard in all respects. The combination of two or more levels to form a large group of trunks is effected by applying the principle or grading, for instance, as indicated in Fig. 15.

Suppose for instance that from the switch of which a single bani: is shown in 15, one rather larger exchange is accessible over levels 2, 3 and l and a somewhat smaller exchange over levels 6 and 8, while the remaining exchanges in the network are each acces sible over one level only. It may not, however, be desirable to proi ide the full trunks to lead to the medium sized exchange and in this event the first tour contacts, say, in each of levels 6 and 8 may be individual while the remaining six contacts in each level are multipled together, so that a total of A trunks is then provided. Similarly in the case oi the larger exchange it is assumed that 20 trunks will be suflicient and hence the first 5 contacts in each of levels 2, 3 and 4 are individual, while the remaining 5 in the 3 levels are multipled together so that a total of 20 is obtained.

This arrangement of grading may also be employed with advantage in a number of the cases mentioned above, notably, in the systems shown in Figs. 1, 2 and 3, in fact in allcases in which simultaneous hunting takes place with discriminating means provided. In Fig. l the first selector may then be of standard type, with grading between corresponding levels such as l and 6, 2 and 7, 3 and 8, and so on. This arrangement will also apply to the similar switches shown in Figs. 2 and 3. Under these circumstances the trunk lines from individual contacts will extend to ordinary selectors which will he in two different groups corresponding to the two different portions of the bank. Only the trunks associated with the contacts which are multipled between a number of levels need then lead to the modii' ed second selectors and connectors shown in Figs. 1, 2 and 3. By this means a substantial proportion of the advantages of simultaneous hunting may be obtained without the disadvantages or additional wipers and increased complexity; all that is necessary is to employ a special arrangement of bani: wiring.

A'specially advantageous arrangement on these lines is possible in the case of a 10.000 line exchange in which the st um bers are distributed substantially unirormly from 1000 to 9,999. In this case it is an ranged that these number which have the first digit even also have the last digit even andthose that have the first digit odd have the last digiu odd also, or vice versa. Grading may then be applied to the pairs 01" levels throughout the first selector bank and since 10 discrimination is necessary succeeding swi hes as wellaas the first selectors may be of sta dard type.

An alternative construction for these switches whenugrading is not employed but simultaneous hunting is, 1S toprovide only one bank as in the ordinary course, but three sets of wipers soaced five steps apart. The upper and lower of wipers .are then. multipled together toform one set while. the middle wipers form the other set. It will obviously be necessary inthis case to provide sittlicient clearance above and below and between the banks and the resulting increase in the overall height of the switch may in some cases be a disadvantage. This construction is diagrammatically illustrated inl ig. 18.

The general princigles involved and the improved trlmlting scheme incorporating them having been described, a detailed delit = upper bank. with post springs which are operated on halt per bank and the levels 6-0 in the lower bank are multipled to levels 1-5 in the The switch is also provlded the number of levels i. e. 5, although it is immaterial whether they are operated on five consecutive levels or otherwise, for instance on alternate levels. The circuits of this switch as wel as that shown in Fig. 11 are very similar to those disclosed in British Patent No. 170,385, previously referred to, it being arranged that simultaneous hunting takes place over both banks and that the connection is then established with the first idle line encountered by either set of wipers.

The selector in Figure 11 is also arranged :tor simultaneous hunting but in this case there is no mnltiphng between the banks so that access is obtained to a dili'e'rent group of 20 trunks on each level. Furthermore the switch is not provided with post. springs but has means for repeating the discriminatf ing potential which may be momentarily connected to one of the speaking leads from the first selector.

Figure 12shows a connector adapted to be used with either of the switches shown in Figures 10 and 11 and this .is also provided with two banks and two sets Oil wipers. In tiis case the selection of the bank to he used determined by the .receiptor.nonsreee ipt of the discriminating potential referred to-in connection with Figure 11.

It is assumedthat a subscriber has access to the switch shown in Fig. 10 overa primary andpossibly a secondary line switch in the usualway. Vhen the speaking leads are switched through at the line switch, a circuit completed over the loop and conductors 1 and 2 for the line relay .4, which thereupon operates .andv at armature 5 and its front contact completes a circuit for release relay 6 from earth at armature and its back contact, andarinature 11 andits .baclccontact. Relay 6 upon energizing at armature 7 prepares the impnlsing circuit, armature 8 connects earth to release trunk conductor 3 and at armature .9 prepares the discriminating potential circuit. The subscriber will now proceed to dial the first digit in the required number whereupon a number of interruptions will be produced in his loop and line relay 4 will .deenergize momentarily a corresponding number of times. On each deenergization of the relay't a circuit is completed as follows: earth, armature 10 and its back contact, armature 11 and its back contact, armature 5 and its back contact, armature 7 and its front contact, winding of series relay 14, winding .of vertical magnet 15 to battery. The vertical magnet is thus operated to raise the switch wipers a number of steps corresponding .to the digit dialled and series-relay. 14 is energized and being slow'to release remains energized throughout the series of impulses. At armature 1.6 the following circuit is completed for the shunt field relay 19 as soon as the switch steps ofi'normal and the ofi normal springs 17 and 23 are closed; earth, battery, interrupter contact 24, off normal contact 23, left hand winding of relay 19, armature 16 and its front contact and parallel. thereto through the right hand winding. of relay 19 and normally open contact controlled by armature .16, off normal springs 17, armature 8 and its front contact to earth.

The .shunt field relay 19 is thus energized over bothits wmdmgs and consequently 0peratos; at .armatures 20 and 21 completes a locking circuit for itselt and at armature .22 prepares a circuitfor the rotary magnet 25. At the endof the train of impulses,

series relay 14: deenergiizes andreleases the armature 16 whereupon a circuit is completed from earth, front contact andarmature 8, off normal springs 17 normally closed contacts controlled by armature 16, armature 22 and its front contact, rotary magnet 25 to battery. The rotary magnet thereupon operates to rotate the wipers one step into engagement with the first set of bank contacts, at the'samc time opening its interrupter contact 24 whereby the circuit of the shunt field relay 19 is opened.

.Assume for convenience of description that both the sets of wipers are now in engagement with busy lines so that both wipers 39 and will find earth. In these cireumstances a circuit may be traced from wiper 39, armature 30 and its back contact, right hand winding of relay 19, off normal contact 2, interrupter contact 24 to battery, and a similar circuit from wiper 40, armature 28 and its back contact, left hand winding of relay 19 to battery by way of contacts 23 and 24- as before. In these circumstances relay 19 again energizes and the rotary magnet is again connected up over the circuit previously traced and the switch moves another step.

Suppose now that only wiper 39 finds earth on the contact with which it is now in engagement. Since relay 19 only operates its armature when both its windings are energized it will not now do so but a circuit may be traced as follows: battery, interrupter contact 24:, off normal contact 23, left hand winding of relay l9, winding of relay 26, armature 31 and its back contact, off normal contact 17, armature 8 and its front contact, earth. Relay 26 operates in this circuit, at its armature 29 opens a point in the circuit of relay 27, at its armature 10 opens a point in the circuit of the release magnet, at armature 28 connects the release trunk conductor through to wiper l0 and at armatures 34 and 35 disconnects line relay i and connects the speaking leads through to the line wipers 43 and 4.4.

It should be mentioned that to provide for the case in which both the test wipers encounter free trunks at the same instant, the adjustment of the relays 26 and 27 is so arranged that one, say relay 26, will always pull up slightly before the other and thus open its circuit at armature 29. It should also be mentioned, that the springs 17 and 18 are not off normal springs of the ordinary type operated by the switch shaft, but are closed when the vertical magnet energizes and opened when the release magnet energizes.- This provision is made to obviate the possibility of relay 19 energizing and locking up in case both test wipers should encounter busy trunks simultaneously during the release motion.

Suppose that in the present instance the post springs 38 have been operated: in this case on the operation of relay 26, earth is connected to the lower speaking conductor and wiper A by way of post springs 38,

armature 9 and its front contact, front contact and armature 32, armature 35 and its front contact. t will be seen that this connection is only momentary since it will be removed as soon as relay 6 releases and opens armature 9.

As soon as relay 26 switches through, a circuit is completed for relay 45 of the second selector Fig. 1l as follows: battery,

as before.

upper winding of relay lf), back contact and armature 58, back contact and armature 52, contact with which the wiper 43 is in engagement and said wiper, front contact and armature 34, lead 1, over subscribefls loop,

the lower winding of relay 19, at armature 69 prepares the impulsing circuit and opens a point in the circuit of the release magnet .73 and at armature 7O prepares a circuit for repeating the discriminating potential to the succeeding switch. It will be observed that owing to the connection of earth to thelower trunk conductor, relay 49 is short circuited and hence does not operate. In response to the dialling of the next series of impulses, vertical magnet 7 2 is operated to step the wipers to the proper level. Series relay 4''? is operated throughout the series of impulses and at its armature 71 completes the circuit for the shunt field relay 48 as soon as the off normal contacts 7% close. When the normally closed springs controlled by armature 71 are again closed a circuit is completed by way of armature 7 8 and its front contact for rotary magnet 79 and the hunting movement takes place lVhen a free line is encountered by either wiper 82 or wiper 83, one or other of relays 50 and 51 will operate.

Suppose in the present case that relay 51 operates; at its armature 59 it connects release trunk conductor 8% through to test wiper 82, at its armature 60 opens the circuit of the releasemagnet Q 3 extending over the off normal contacts 75 which are now closed, at its armature 61 opens a point in the circuit of relay 50, at armature 62 connects up the discriminating potential to the lower speaking conductor and at armatures 58 and 63 disconnects line relay 45 and connects the speaking leads through to wipers 76 and 77.

When this occurs a circuit completed for the line relay of the connector in Fig. 12 (which is assumed to be seized over wipers 76, 77 and 82) as follows: battery, upper winding'of relay 86, contact on which wiper 76 is resting and said wiper, upper speaking lead, front contact and armature 58, back contact and armature over the subscribe'rs loop, armature 62 and its front contact, armature and its back contact, armature and its front contact to earth. Relay 86 energizes inv this circuit and at its armature 87 completes a circuit for release relay 88 which energizes also. Relay 88 .70 lead 2, armature 32 and its front contact,

upon operating, at armature 89 connects earth to the release trunk conductor 85, at armature 90 prepares the testing circuit, at armature 91 connects up the lower winding of relay 86 at the same time disconnecting the lower winding of relay 118 and at armature 92 prepares the impulsing circuit.

When the subscriber dials the next digit, relay 86 is de-energized a corresponding number of times and on its first de-energizati'on completes the following circuit: earth, armature 8'7 and its back contact, armature 92 and its front contact, spring 94 and spring 95 with which it is normally in engagement, winding of series relay 93, vertical magnet 98 to battery. The series relay is energized in this circuit and at its armature 97 serves to maintain its own circuit and that of the vertical magnet intact when the off normal springs shift as occurs on the first step of the switch.

At the end of the train of impulses, re-

lay 93 de-energiz'es and releases armature 97 so that on receipt of the following train of impulses, a circuit is completed for the rotary magnet 102 as follows: earth, armature 87 and its back contact, armature 92 and its front contact, off normal springs 92k and 96, armature 97 and its back contact, back contact and armature 105, armature 109 and its back contact, rotary magnet 102 to battery. A branch of this circuit extends through the winding of relay 99, which being slow to release, remains energized throughout the train of impulses. Relay 99 at armature 101 connects the busy relay 103 by Way of armature 120 and its resting contact to test wiper 125 and at its armature shunts armature 105 so that the circuit of the rotary magnet is not interrupted in case the busy relay 103 operates during the rotary movement. This will happen if wiper 125 should pass over busy lines whereupon relay 103 in addition to operating armature 105 will at its armature 104- prepare a locking circuit for itself. If the called line is busy, relay 103' will be energized when the switch comes to rest and upon the de-energization of relay 99 will be locked up in the circuit; earth, armature 90 and its front contact, armature 104 and its front contact, normally closed springs controlled by armature 101, winding of relay 103 to battery. In this case the operation of arma ture 116 will connect busy tone to the line so that the calling subscriber is notified and hangs up his receiver thereby releasing the connection. It will be assumed however that the called line is idle hence relay 108 will not be energized when relay 99 de energizes and instead the following circuit will be completed when armature 101 engages with its back contact: earth, armature 90 and its front contact, armature 10 1 and its back contact, upper winding of relay 106,

back contact and armature 101, armature 120 and its back contact, wiper 125, cut oil relay and driving magnet associated with the called subscribers line switch to battery.

The cut oil relay operates in this circuit to clear the line of its normal battery and earth connections and relay 106 also operates, at armature 108 completes a locking circuit for itself to the release trunk conductor, at armature 109 opens the circuit of the rotary magnet so that any further impulses' which may be sent will be ineffective, at armature 107 places direct earth on test wiper 12a and at arn'iatures 110 and 111 connects the ringing generator RG and the upper winding of ringing trip relay 112 respectively to the subscribers line so that he is rung in the usual manner. Vhen he replies relay 112 is operated by direct current over hisloop, at its armature 113 com-' pletes a locking circuit for itself and at armatures 114 and 115 disconnects ringing current and completes the speaking leads. The back bridge relay 117 is now energized and operates at armatures 130, 131 to reverse the current flow over the calling subscribers line for metering or like purposes. The subscribers may now converse and at the end of the conversation the connection is released when the calling subscriber hangs It may be desirable at this oint to explain the sequence of operations in case the post sirings 88 in Fig. 10 are not operated. In this case when relay 26 switches through, the lower winding of relay 19 which was previously short circuited is now operative so that the relay energizes and at armature 64:

completes a locking circuit for itself to release trunk conductor S l and at armature 65 opens the circuit for repeating the discriminating potential to the succeeding switch. Similarly when relay 51 switches through, owing to the absence of discriminating potential. on the lower trunk conductor, relay 118 is operated over its lower winding and at armature 119 completes a locking circuit for itself and at armature 121, 120 and 122 disconnects the normal set of wipers and connect-s up the second set. It will thus be seen that outgoing from the first selector there were five groups of twenty trunks instead of the usual ten groups of ten trun {S with which arrangen'ient an appreciable saving of second selectors is possible, and that the combination which took place at the first selector is resolved at the connector by means of the dis-- criminating potential which is repeated over the second selector.

Referring now to Figure 13 this indicates a circuitof a selector suitable for use in a layout such as that indicated. in Figure 5, i. e. the case of a 4,000 line exchange. Accord.- ing to this arrangement upon receipt of the first digit the switch is operated in the usual manner but is then immediately released whereupon it is enabled to respond to a further digit, after which an automatic hunting operation takes place. In response to the first movement, however, suitable post springs are operated so as to energize either or both or neither of two relays,by which means the first digit, it one of a possible four, can be recorded. This switch also has two sets of wipers one or other of which is used accordin; to the operation or non-operation of one of the said relays, while the other relay controls the connection of a momentary discriminating potential to the line. The operations involved will now be described in detail. I

1V hen the switch is taken into use, for instance in known manner over an individual line switch associated with a subscribers line, the following circuit is completed: bat tery, upper winding oi line relay back contact and armature 236, conductor 201, over the subscribens loop, conductor 202, armature 23S and its. back contact, lower 'inding of relay 20% to earth. Relay 201 operates and at its armature 205 completes a circuit for the release relay 206. Relay 206 upon operating, at armature 207 connectsearth to release trunk conductor 203 and prepares a holding circuit for relay 214i and at armature 208 prepares the impulsing circuit. When the subscriber dials the first digit, the relay 204 is deenergized a number of times and at each deenergization the following circuit is completed: earth, armature 205 and its bac; contact, armature 208 and its front contact, winding of series relay209, vertical magnet 211 to battery. The switch is thus raised to the level corresponding to the digit dialled and the series relay 209 being slow to release remains energized throughout the train or" impulses. Suppose for the sake of example, that the digit 1 has been dialled and that on the fourth level both the post springs 215 and 218 are operated.

Accordingly when relay 209 deenergizes a circuit is completed from earth on armature 207 and its front contact, armature 210 and its back contact, armature 225 and its back contact, post springs 215, normally closed contacts controlled by armature 216, winding of relay 21 1 to battery and parallel thereto, post springs 218, normally closed springs controlled by armature 22,0, winding of relay 219 to battery. Relay 214 upon operating, at armature 216 completes a locking circuit for itself dependent upon armature 207 and at armature 217 prepares the connection of the discriminating potential to the lower trunk conductor. Relay 219 upon operating at armature 220 completes a locking circuit for itself and at armature 221, 222 and 223 disconnects the first set of wipers and connects up the second set.

A circuit is also completed on the doomergization of relay 209 which extends from earth on armature 207, armature 210 and its back contact, oil normal springs 212, armature 228 and its back contact, release magnet 213 to battery. A branch of this circuit also extends by way of the normally closed springs controlled by armature to the winding of relay 224. The release magnet therefore operates in this circuit to restore the switch to normal, and relay 22a is encrgized. Upon operating at its armature 225 it opens a point in the circuit for relays 21% and 219, so that if these have not been already operated they cannot be operated on the succeeding vertical movement of the switch, at armature 226 locks itself up to release trunk conductor 203, at armature 228 opens its circuit for the release magnet and at armature 227 prepares a circuit for the stepping relay 231. The switch is thus re leased after respon d'ng to one digitwhatever the value of that digit.

The subscriber will now proceed to dial the next digit, whereupon the number of interruptions are again produced in the circult of line relay 201 and it deenergizes accordingly. Upon each de-energizatiou a circuit is completed as previously traced and the vertical magnet 211 of the switch is stepped up to the corresponding level. As soon as the oil normal contacts 229 close, a circuitis completed from earth on release trunk conductor 203, armatnre 210 and its front contact, interrupter contact 230, off normal contacts 229, armature 227 and its front contact, winding of stepping relay 231 to battery. Relay 231 at armature 233 prepares a circuit for the rotary magnet 23 1 and at armature 232 completes a locking circuit for itself dependent upon the interrupter contact 230 of the, rotary magnet, At the end of the train of impulses when relay 209 releases, a circuit is completed from earth on release trunk 203, armature 210 and its back contact, front contact and armature 233, winding of rotary magnet 23% to battery. The switch wipers are thus moved one step into engagement with the first set of contacts. The operation of the rotary magnet 23-1C opens nterrupter contact 230 so that stepping relay 231 is deenergized. If test wiper 240 finds earth on the contact with which it is in engagement, a circuit for relay 231 will be again completed and it will energize thereby closing contact 233 and causing; rotary magnet 23 1 to advance the switch wipers turther step. This operation continues until the test wiper 2 10 engages a contact which is not earthed, whereupon switching relay is no longer short circu ted and energizes in the follow ing circuit: battery, winding of relay 231, front contact and armature 227. oil normal contacts 229, interrupter contact 230, winding of relay 235 to earth on release trunk conduct-or 203. Stepping relay 231 is not energized in this circuit owing to the high resistance of relay 235. This latter relay, however, operates and at armature 237 connects release trunk conductor 203 to test wiper 240, at armatures 236 and 238 connects the speaking leads through and disconnects the line relay -1 and at armature 239 connects discriminating earth on armature 217 to the lower trunk conductor 202. lVhen relay 20d deencrgiZes the circuit of relay 206 is opened and it deenergizes also thereupon releasing its armature 207 so that the circuit of relay 21-1 is opened; the connection of earth to lowcr trunk conductor by way of armature 217 i s thus only momentary. This connection of earth may operate a connector such as is shown in Fig. 12 in the same manner as was described in connection with this figure, and the connection is completed in a manner which will be readily a jzpreciated from the description already given of Fig. 12.

The circuits of a switch 01 a similar kind are illustrated in Fig. 14, this switch however being arranged so that its wipers are not moved in response to the first d git as in the case of the switch in Fig. 1.3, but instead the number received is'set up on relays d rect. As before it will be assumed that the first digit transmitted to this switch is four. \Vhen the switch is taken into use, for instance over the subscribers line switch, a circuit is completed over the subscribers loop and armatures 3 10 and 344- and their back contacts for the line relay 300. This relay upon operat ng completes a circuit for the release relay 302, which at armature 303 connects earth to release trunk conductor 299 and at armature 1 prepares a locking circuit for relay 333. Relay 302 moreover at armature 305 prepares the impulsing circuit and at armature 306 prepares a circuit for transmitting a discriminating potential v to the next switch it necessary.

The subscriber now dials the digit 4 and in response to the first interruption in the loop, relay 300 is deenergi ed and a circuit is then completed from earth, back contact and armature 3 12, armature 301 and its back contact, armature 305 and its front contact, winding of relay 309, armature 337 and its back contact, armature 321 and its back contact, lower winding of relay 319 to battery. It should be mentioned at this point that the relays 319, 325 and 333 are each of the twostep variety arranged to operate a light armature when current traverses their lower windings only and to operate all their armatures when they are energized Over both windings in series. In response to the first impulse therefore, relay 319 operates only its armature 320 whereby earth is connected to the other terminal of its upper winding over back contact and armature 335 and back contact and armature 329. hen

armature 301 leaves its back contact on the termination of the impulse, the upper winding of relay 319 is no longer short circuited and the relay operates fully, thereby at armature 321 transferring the impulse lead to relay 325 by way of armature 328, at

armature 322 preparing a locking circuit for relay 333 and at armatures 323, 324. and 325 disconnecting the normal set of wipers and connecting up the second set. Relay 309 is energized in the impulsing circuit and being slow to release, remains energized throughoutthe train of impulses; at armamature 310 it opens a point in the circuit of the rotary magnet 313, at armature 311 prepares a circuit for the stepping relay 314, which circuit is, however, inellective during this train of impulses since the offnormal contacts 318 do not close, and at armature 312 opens a point in the locking circuit of relay 333.

\Vhen relay 300 next deenergizes the impulsing circuit extends as previously traced to armature 321 and thence over its front contact and armature 328 and its back contact through the lower Winding of relay to battery. Relay 325 operates its light armature 327 at this time and on the termination of the series of impulses operates fully; thereupon at armature 331, another point is closed in the circuit for connecting up discriminating potential, at; armature 329 the locking circuit of relay 319 is opened so that it deenergizes, at armature 328 the impulsing circuit is transferred to relay 333, and at armature 330 another point is prepared in the circuit of relay 333. The succeeding impulse extends over the same circuitas did the first since relay 319 is now deenergized again; for this reason no circuit is now completed for relay 333 since armature 321 has released. Relay 319 therefore operates all its armatures with the same results as before, its locking circuit now extending over the front contact of armature 329; thus both relays 319 and 325 are now energized. Upon the succeeding deenergization of relay 300 it again completes the impulsing circuit which now extends over armature 321 and its front contact, armature 328 and its front contact lower winding of relay 333 to battery. This relay at once operates its light armature 33-1 and on the termination of the impulse operates all its armatures; thereupon at armature 335 the locking circuit of relays 319 and 325 is n1omentarily opened, so that they both deencrgize, and at armature 337 the impulsing lead is transferred to the vertical magnet 338. The final result therefore with a train of four impulses is that relay 333 only is operated and is held locked up to earth on arma ture 304. Hence the normal set of wipers of the first selector will be used and since no discriminating potential will be sent over the line, the normal set of wipers of the connector also will be used.

Upon the dialling of the succeeding digit the impulsing circuit as explained now extends to the Tertiral magnet and consequently the switch shaft and wipers are raised a number of steps corresponding to the digit dialled. The circuit for the stepping relay 314 is completed as soon as the off-normal contacts 318 close and upon the release of relay 309 the switchcommences to hunt in known manner. \Vhen it finds a free line, relay 339 is operated and disconnects the line relay and switches through the speeding leads at armatures 340 and 344 and at armature 343 closes another point in the circuit for connecting discriminating potential to the lower trunk conductor.

As mentioned above in the case in question since neither of the relays 319 or 325 remains operated, the first or normal set of wipers is used and no discriminating poten-. tial is sent out to the next switch. In case hon-ever, the first digit dialled is 1 instead of 4, relay 319 would be energized as before and relay 309 would then deenergize since no further impulses are being sent. When this occurs a locking circuit for relay 319, is closed over an alternative path by way of back contact and armature 311 and a circuit is also completed from earth, armature 312 and its front contact, armature 322 and its front contact, both windings of relay 333 to battery. Relay 333 therefore at once operates all its armatures with the results previously described except that since the circuit of relay 319 is now maintained intact over armature 311, relay 319 remains energized. When the succeeding impulses are sent for operating the vertical magnet relay 319 is *iaintained energized over the front contact 335 of relay 333 during the operating of rela 309.

If a train of two impulses had been sent relay 319 would first have been energized and then relay 325, relay 319 being deenergized by the operation of relay 325. On the ibsequent deenergization of relay 309 a circuit would have been completed for relay as before and in this case clearly the final result is the energizationof relay 325 so that the first set of wipers would have been. used and no discriminating potential would have been sent.

Should the first digit be 3, both relays 319 and will be energized and in this case since their locking circuits are completed at armature 311 and its backcontact before armature 335 is operated they both remain energized. In this case therefore, the second set of wipers is used and discriminating potential is sent out to the next switch, This discriminating potential (earth) is connected up when the switching relay 339 operates and extends over front contact and armature 343, armature 306 and its front contact, front contact and armature 331 to the lower speaking lead. Since the circuit of the line relay 300 is opened when relay operates and this then opens the circuit of the release relay 302, the connection of earth to the lower trunk conductor is only momentary. The arrangements for responding to it can be similar to those provided for responding to the similar operation in the case of the switch shown in Figure 10, i. e. a connector of the type shown in Figure 12. Thus the switch shown in Figure 14 as well as that shown in Fig. 13 is adapted to respond to the first digit received by in without any effective movement of its wipers, the said first digit however being arranged to selectively determine the ultimate destination of thecall.

Refer now to Figure 17 in which is shown the circuit of a connector suitable for use in a layout such as that indicated in Figure 6, i. e. the case of a 400 line exchange. According to this arrangement upon receipt of the first digit the switch is operated in the usual manner, but is then immediately released whereupon it is enabled to respond to two more digits. In response to the first movement, however, suitable post springs are operated so as to energize either or both or neither of two relays, by which means the first di 'it, if one of a possible four, can cause tne wiper set having access to subscribers of the desired hundred .to be connected for use. Since the principle of selecting wipers is the same as that shown in Fig. 13 a detailed description of operation is thought unnecessary.

The circuits of a switch of a similar kind are illustrated in Fig. 16, this switch however, being arranged so that its wipers are not moved in response to the first digit as in the case of the switch in Fig. 17, but instead the number received is set up on relays direct. This switch uses the same principle of selecting wipers as the selector shown in Fig. 14 and in view of the previous description a detailed description is therefore thought unnecessary.

It should be mentioned that though in all the examples described with the exception of the arrangement shown in Fig, 9, a local connection has been assumed i. e. one entirely within a single exchange, it must not be as sumed that the improved trunking schemes are limited to such arrangements. On the contrary, the invention may also be applied to trunking between exchanges or standard trunking may be used between exchanges and the improved arrangements for the local portion only. In case repeaters should be required for inter-exchange working, these can be arranged to repeat the discriminating potential by the provision in the second selector in Fig. 11 or the connector in Fig. .12.

It should also be mentioned that though connections have been described asextended direct from a calling subscriber, the im proved switches will clearly work equally well in response to impulses sent from a register translator; probably in this case, however, it would be preferable to use standard switches and effect the necessary changes in the register translator.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be per formed, we declare that what we claim. is:

1. In an automatic telephone system a switch train responsive to the digits of a call number to extend a connection, a plurality of wiper sets on the last switch of said train and means controlled by the first of said digits forcontrolling the application or non-applicationof a discriminating poten: tial to said last switch for determining the wiper set to be used by said last switch.

2. In an automatic telephone system, a switch train responsive to the digits of a call number to extend a connection, a plurality-of wiper setson the last switch of said train,-and means in the first 01. said switches controlling the application or non application of a potential to said last switch for determining'the wiper set to be ,used by said last switch.

3.; In an automatic telephone system, a switch train responsive to the digits, of a call'number to extend a connection, a plurality of wiper sets on the last switch of said train, means in the first of said switches responsive to the first of said digits for directivelyoperating said switch and means also in 'the first. said switch and controlled by said directive operation for controlling the application or non-application of a potentialfto said last switch for determining the wiper set togbe used by said last switch.

4. In an automatic telephone, system, a switch train comprising a switch responsive to the first, a switch responsive to the second, and a switchresponsivc to the last two digits of a call number to extend a connection, a plurality of wiper sets on the last said switch, means in-said second switch for selecting the wiper set to be usedby said last switch and means in said first :switclnfor controlling said selecting means,

5. In arr-automatic telephone system, a switch train comprising a switch responsive to the first, a switch responsive to the second, and a switch responsive to the last two digits of a-call number to extend a connectioma plurality of wiper sets on the last'said switch, a relay in said second switch arranged to apply a discriminating potential-to said" last switch to select the wiper set to be used, and means in said first switch for controlling-saidrelay.-

6. In an automatic telephone system, a a switch train comprising a switch responsive to the first, a switchresponsive to the sec.- ond, and a switch responsive to the last two digits of a call number to extend a con nection,-a plurality of wiper sets on the last saidswitch; means in said second switch for 1 tion,..a plurality of :wiper sets on the last 7 said switch, a relay. in second switch arranged to apply a discriminating potential tosaid last switch to select the wiper set to be .used, .anda shaft operated spring set in said first switch for controlling said .relay.

8. In an automatic telephone system, a plurality Oil serially related switches used in establishing a connection, the first of said switches being accessibleiover a plurality of trunk routes, a plurality of trunk routes leading front a-scond of said switches, means a for seizing said first switch and operating it into connective relationwith said second switch'and means dependent upon the trunk route over which said first switch was'seized for determi-ningthe trunk route selection of said second switch.-

9.111 an automatic telephone system, a plurality of serially related directive switches used in -extending a talking connection,-a plurality of wiper sets on -a second oneof said-switches, means for operating of first of said switches into connective relationwith saidsecond switch, means in saidfirst switch for then sending a directiveimpulse over one side of said connection to determine the wiper set to be used by said second switch, and means for then directively operating said second switch to complete said connection.

10. In an automatic telephone system, a switch train comprising a first, second, and a last switch, a plurality of wiper sets on said last switch, a plurality of trunk paths over which said second switch is accessible. to said first switch in accordancewith first digits of difl'erentvalucsand means determined by the path over which said second switchiisseized for determiningthe wiper tet to-be used by said last switch.

11 In an automatic telephone system, a switch train comprising a first, second, and a lastv switch, a plurality of wipers on said last switch, means for extending a talking connection through said switches, means in said first switch for momentarily applying a directive potential to one side of said connection to said second switch, means in said second switch responsive thereto to apply a similar potential to one side of said connection to said last switch and means in said last switch controlled by said potential to select the wiper set to be used in completing said connection.

12. In an automatic telephone system, a switch train comprising three switches, the second switch accessible to the first over a plurality of paths responsive to digits of different values, a plurality of wiper sets on said third switch, and means controlled by thevalue of the route selecting digit re ceived by said first switch for determining the wiper set to be used by said third switch.

13. In an automatic telephone system, a switch train comprising a connector having a plurality of wiper sets, and intermediate selector switches thru which said connector is accessible to a first selector switch, said selectors responsive to the digits of a call number for extending a connection to said connector, and means dependent upon whether the first digit of said series is even or odd for determining the wiper set to be used by said connector.

14. In an automatic telephone system, a connector switch having a plurality of wiper sets, a selector switch having access to said connector, a shaft on said selector, magnets for operating said shaft, a register, circuit means for directing the odd impulses of a digit to operate sazd magnets and the even impulses of said digit to operate said register, and means controlled by said register for determining the wiper set to be used by said connector.

15. In an automatic telephone system, a connector switch having a plurality ofwiper sets, a selector switch having access to said connector a shaft on said selector, magnets for operating said shaft, a register, circuit means for directing the odd impulses of a digit to operate said magnets and the even impulses of said digit to operate said register, said magnets operating said switch into connection with said connector and means controlled over said connection by said register for determining the wiper set to be used by said connector.

16. In an automatic telephone system, a connector switch having a plurality of wiper sets, a selector switch having access to said connector, a shaft on said selector, magnets for operating said shaft, a register, circuit means for directing the odd impulses of a digit to operate said magnets and the even impulses of said digit to operate said register, said magnets operating said switch into connection with said connector, said register momentarily applying a selecting potential Ill to on side of said connection to select the wiper set to be used by said connector.

17. In an automatic telephone system, an automatic switch having access to second automatic switch, a plurality of wiper sets on said second switch, means responsive to a digit received by said first switch for operating its mechanism, means responsive to said operation for registering said digit and for returning said mechanism to normal, means for then operating said mechanism into connective relation with said second switch and means dependent upon said registering digit for determining the wiper set to be used by said second switch.

18. In an automatic telephone system, a plurality of serially related autoi'natic switches having a. plurality of wiper sets, means in a first one of said switches for registering the first digit received thereby to determine the wiper set to be used by that and a succeeding switch, and means l'or sub-- sequently moving the selected wipers of said first switch into connection with a second one of said switches.

19. In an automatic telephone system, a switch train comprising switches having a plurality of sets of wipers, a register relay in the first of said switches operated by the first digit received to thereby determine the wiper set to be used by said first switch, means for operating said switch into connection with a second sw h, and means controlled over said connection by said relay for determining the wiper set to be used by said second switch.

20. In an automatictelephone system, a switch train comprising switches having a plurality of sets of wipers, a register relay in the first of said switches responsive to the first digit received thereby to determine the wiper set to be used by said first switch. means for operating said switch into connection with a'second switch, said relay con trolling the application of a directive impulse to one side of said connection to select the wiper set to be used by said second switch.

21. In an autoi'nati-c telephone system, a switch train comprising switches each having a shaft carrying a plurality of sets of wipers, a register relay in the first of said switches, shaft operated means for controlling said relay, means for operating said shaft into engagement with said controlling means and for then releasing the shaft, means for subsequently operating said switch into engagement with a. second switch, the switch selected and the wiper set of the second switch to be used being controlled by said register relay.

22. In an automatic telephone system, a selector switch having wipers, means in said switch for registering a digit for a call number without moving said Wipers, means responsive to a subsequent digit for moving said wipers .to extend a connection to a second switch, and means controlled by said registered digit to control said second switch.

23. In an automatic telephone system, a. selector switch having wipers, relays in said switch for registering the first digit received thereby without moving said wipers, and

means responsive to a subsequent digit for moving said wipers to extend a connection to a second switch, and means controlled by said registered digit to control said second switch.

24. In an automatic telephone system, a selector switch having a plurality or wiper sets, a relay group in said s itch for registering the first digit received thereby without moving said wipers, said group comprising a relay arranged to select a set of said wipers, and a relay arranged t connect a discrimi nating potential to the line.

25. in an automatic telephone systenna switch having" wipers thru which other switches are reached, means for re 'isteriug the first digit received by said swr h without moving said wiper said registering means preparing circuit fo subsequently repeating a special code to t a distinc tive setting of said second itch.

26. In an automatic telephone system a group of selector switches divided into a plurality of sub groups, a plurality of trunk lines accessible to said switches and multiple connections such that certain of said trunk lines are individual to each of said sub groups and other of said trunk-lines are common to said group of switches, directive switches terminating said individual and said common trunks, and means for operating said switches through said selector.

2?. in an automatic telephone system, a calling line and a switch accessible thereto, 1 bank containing a plurality of groups of contactsv associated with said switch, a plurality oi? wiper 's on said switch, trunk groups leading to said contacts, the number of trunk groups being less than the number of said contact groups, and multiple connections between said contact groups such that certain of said trunks are accessible to said calling line thru di'ii'erent ones of said wiper sets responsive to two or more values of digits dialled from said callingline.

in an automatic telephone system, a switch. train comprising a switch responsive to the first, (i switch responsive to the second,

and a switch responsive to the last two digits or a call number toextenc a connection, a plurality of wi mr sets of said last switch, and 1 ms in. said first switch for selecting the wiper set to be used by said last switch.

29. in an automatic telephone system, a group of switches divided into two subgroups, a plurality of wiper sets on each of said switches, a second switch having access to said first sw1tches, .a plurality of wiper sets on said second switch, each of the.

call number to extend a connection, a plu rality of wiper-sets on each of said switches,

means for operating a first position switch of said train, means in said switch for extending a connection to a second position switch cv a wiper set of the first switch end switch, and meansin said first switch --determinin r the wiper set to be used by second switch irrespective of the wiper set used by the first switch.

31. In an automatic telephone system, a switch having two sets of wipers, a group of switches accessible to said first switch through oneor the other of said two sets of wipers,

means for operating said first switch into connective relation with said group of switches, means in said first switch for simultaneously hunting for an idle one of said group ofswitehes and for connecting with said idle: one through the wiper set engaging it, a plurality of wiper sets'on said second switches and means in said first switch for applying a discriminating poten tial to said connected second switchirrespectire of the wiper set used by the first switch to determine the wiper set to be used by said second switch.

32. In an automatic telephone system, a switch train comprising three serially related switches,- a plurality of wiper sets on each of said switches, means for operating the first switch into engageu'ient :withthc second and the secoudinto engagement with the third, automaticmeans, dependent upon trunk conditions for determining the wiper sets to be usedi by said-first and second switches, and means in said first switch for determining the wiper set to he used by said thirdswitch irrespective of the wiper sets used by the first and second switches.

Signed by me, atLondon, England, this 22nd day of August,192 -l.

RICHARD MERGER.

Signed by me at London, England, this 22nd day of August, "1924. 7 v

FRANK TENCH.

selected by the busy or idlecondition of said

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