US1942462A - Telephone system - Google Patents

Description

Jan. 9, 1934. J. wlcKs TELEPHONE SYSTEM Filed July 16, 1932 S'SheenS-Sheetl l Jan. 9, 1934. J. wlcKs TELEPHONE SYSTEM Filed July 16, 1932 8 Sheets-Sheet 2 -Imren Dr- Jul-m Mieke Ma/4W Jan. 9, 1934. J. wlcKs TELEPHONE SYSTEM Filed July 16, 1932 8 Sheets-Sheet 3 @mdk H SS Q Jan. 9, 1934L J. wlcKs 1,942,462

TELEPHONE SYSTEM Filed July 16, 1932 e sheets-sheet 4 mm H? Jan. 9, 1934. J. wlcKs TELEPHONE SYSTEM Filed July 16, 1952 8 .Sheets-Sheet 5 MS o @I WS G@ El@ m. .FL SQ d '-'Inuen CJP- John .Mck

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Filed July 16, 1932 8 Sheets-Sheet 6 www Inman m"- Jn hn Mi: ks

Jan. 9, 1934. J. wlcKs TELEPHONE SYSTEM 8 sheets-sheet 'I Filed July 16, 1932 Jan. 9, 1934. J. wxcKs 1,942,462

TELEPHONE SYSTEM Filed July 16. 1932 8 Sheets-Sheet 8 P05/HUN' John Mlcks Patented .an.9, 1934 TELEPHONE SYSTEM John wicks, oak Park, n1., assignr to Automatic Electric Company, Limited, Liverpool,

England Application July 16, 1932. Serial No. 622,909

41 Claims.

The present invention relates in general to telephone systems, but is concerned more particularly with automatic telephone systems, and the object of the invention is to produce a new and improved automatic telephone system employing suitably controlled single-motion rotary stepby-step mechanisms.

GENERAL DESCRIPTION Following the general recognition of the Strowger, automatic, vertical-and-rotary switch, together with systems incorporating this switch for use in setting up connections between calling and called lines, many attempts have been made to replace the vertical-and-rotary Strowger mechanism with a mechanism having a rotary motion only, on the theory that a switch mechanism which has only a single motion is inherently simpler and more economical to produce than one which has two coordinate motions. Further, these attempts have been based partly on the belief that more eXibility is secured with a rotary mechanism, as regards the allocation of contacts to trunk groups, as the division of the contacts in the trunk groups in a rotary mechanism may be made along purely arbitrary lines, whereas with the Strowger mechanism (as commonly employed) the grouping is rather rigidly determined in accordance with the separate levels of contacts.

Whereas the group selection is determined by a primary, or group selecting7 ordinate` motion in a Strowger switch, bringing the wipers of the switch opposite a desired level of bank contacts directly responsive to received incoming impulses constituting a series; in the case oi a switch mechanism having a rotary motion only, with all of the contact sets arranged in one row or level, the advance of the wipers into association with the desired group of contacts must be made by a hunting movement, and this hunting movement must be controlled by an impulse responder or register oi some suitable form, and the wipers are subsequently rotated over the contacts in the group in a trunk-hunting operation, or in response to the inal digit in the number, as in the case of a connector or final selector.

As an alternative to the above-described method of bringing about the group positioning of the rotary switch, a so-called register sender may be employed at a point more or less remote from the switches, in which register sender the digits of a desired number are stored, following which the serially related rotary switches are successively positioned by revertive control, somewhat after the fashion of the power driven automatic switches.

For the purpose of combining economy with reliability both of the above-enumerated methods of positioning the rotary switches are made use of in the system herein disclosed; the connectors, or nal selectors, are positioned, in tens selection under revertive control, while the group selectors are positioned by a hunting operation.

A feature of the system disclosed herein in that apparatus common to the several groups of switches is provided for the purpose of enabling the individual switch mechanisms and relay apparatus to be simplified and abbreviated as much as possible.

A further feature of the present disclosure is that the common-apparatus unit for a group of selectors includes what is termed a by-pass Selector, which is arranged to quickly iind an idle trunk in a selected group and to extend a dialling connection immediately thereto so that the next digit dialled will be delivered to its proper destination, while the associated conversational switch is caused to hunt for and connect with the same trunk line engaged by the by-pass selector, whereupon the connection is made through the conversational switch, and the by-pass selector and associated common equipment are released.

The invention includes a number of features of novelty in a system such as brieyoutlined above, and will appear more fully hereinafter.

Description of drawings Referring now to the accompanying drawings, comprising Figs. 1 to 9, they show by means of the usual circuit diagrams a suficient amount of the equipment in a telephone system embodying the invention to enable the invention to be understood. More in particular, Figs. V1 to 4, show switching apparatus through which a connection may be set up from the line substation A, Fig. 1, to the line of substation B, Fig. 4; Figs. 5 to 8 show certain common controlling equipment which is taken into use temporarily while the connection is being established but which forms no part of the established talking connection; and Fig. 9 shows an overflow circuit, the utility for which will be made apparent hereinafter.

The invention has been illustrated in connection with a ten-thousand-line system, one employing three orders of numerical switches. `The rst order of numerical switches is represented by the first selector FS--L Fig. 2 (a thousands selector); the second order of switches is ,represented by the penultimate selector PII- 1, Fig. 3, (a hundreds selector); and the final order of switches is represented by the connector, or nal selector C-l, Fig. 4.

The non-numerical trunking, the trunking between calling lines and the first selectors, is accomplished by finder-secondary links, one of which is .illustrated in Fig. l as the nder F and the secondary switch SS. As regards calling, the subscribers lines are divided into groups of approximately one hundred lines each. The line finders, of which the nder F, Fig. 1, is an example, may each have access to a total of 102 lines, having for this purpose six semi-circles of bank contacts, nity-one contacts in a semi-circle, with a single ended wiper for each semi-circle of bank contacts, as illustrated. The wipers are divided into two groups as shown, and positioned so as to stand in diametrically opposite positions. The Wipers are interconnected in pairs, giving the effect of three wipers having access to 102 bank contacts each.

v'Ilrie finder F is provided with a single operating magnet, magnet 114. This magnet is arranged to be operated in a buzzer-like manner through the control of its associated interrupter contacts, and it advances the wipers 10-113 one step each time it restores after having been operated.

The secondary switch SS is of similar construction to the finder F, but it is provided with only lthree semi-circles of bank contacts of twenty-five contacts to each semi-circle and with three cooperating double-ended wipers, actuated by the operating magnet 1341-.

, In order to provide an economical distribution of traffic, the distributing frame DF is interposed between the nders, such as F, and the secondary switches, such as SS, so as to allow the calls originated in a single finder group to be distributed throughout a numb-er of groupsof secondary switches. Each secondary switch has access to twenty-five iirst selectors, such as the first selector FSL Fig. 2. The first selectors are ordinarily mounted and bank wired in groups of ten. Therefore, a group of secondary switches, such `as SS, have their banks connected in multiple and connectedk to two and one-half groups or shelves of rst selectors. The next two and one-half shelves of first selectors are accessible to a second group of secondary switches, and so Keeping in mind that the finders, such as F, are provided in suflicient numbers in each case to handle the maximum estimated trafc from the associated group of calling lines, it may now be pointed out that the distributing frame DF is utilized about as follows. The terminals corl responding to the first finder in a group may be cross-connected on the distributing frame DF to a secondary switch in the first secondary group; the second finder in the same group may be crossconnected to a switch in the second secondary group; and so on. Other groups of finders are connected tothese secondary groups in a similar manner. In this way, a given secondary group receives calls from a large number of finder groups, whereby the traffic amongst the several secondary groups is substantially equalized, a1- though the traiiic furnished by the several primary or finder groups may differ from group to group at any given time. Y

For the purpose of controlling the finder switches and secondary switches, a pair of distributors is provided for each finder group. The distributors D1 and D2, Fig. 5, are the distributors provided for the iinder group containing the finder F, Fig. l. These distributors are controlled over the start wire 150 common to all of the lines accessible to the finder F and associated finders. Each distributor comprises a rotary switch mechanism having eight doubleended wipers, with twenty-five contacts in each semi-circle of bank contacts. Ordinarily, there are only from ten to fteen finders in a group, in which case the unused contact sets are passed over by the distributor because the test contacts of the unused sets are connected to ground. The distributors D1 and D2 are arranged so that they operate concurrently, each of them taking a second finder secondary link for use pursuant to linking the calling line to an idle rst selector, and the rst to complete this operation causes the other distributor to stop, unless a second line is calling, in which case the second distributor continues its operation to cause the second calling line to be linked with an idle first selector.

The rst selectors, represented by the first selector FSl, Fig. 2, are each similar to the nder F, Fig. l, except that eight pairs of wipers and eight fifty-one contacts of semi-circles are provided, as there are four conductors in the bank multiple of the selectors instead of three, as in the case of the finders. The selector has access to approximately one-hundred trunk lines, which are ordinarily divided into ten groups averaging ten trunk lines to a group, although the sizes of the groups may be assigned so that some groups contain only a few trunks, while other groups contain more than ten, depending upon traffic requirements and other practical considerations.

As mentioned before, the first selectors are ordinarily mounted in groups of ten, called a shelf. A pair of by-pass selectors, the by-pass selectors, such as BPS-1 and BPS-2, Fig. 6, are provided for each shelf of ten selectors. A permanent bank multiple is provided which multiples together the bank contacts of all the selectors in a shelf and the bank contacts of the two by-pass selectors of the same shelf. Whereas the selectors through which the conversational connections are established are provided with single-ended paired wipers and have no normal position, the by-pass selectors, such as the selector BPS-L Fig. 6, are provided with double-ended wipers and have a normal position, corresponding to the fifty-first set of bank contacts.

The ten selectors of a shelf are divided into two sub-groups of five selectors each, with a separate one of the two by-pass selectors associated with each of the two sub-groups. Each of the ve selectors of a sub-group is normally connected to the associated by-pass selector, whereby when a selector is taken for use the remaining idle selectors in the same sub-group are rendered temporarily busy to the switches having access to them. Following this, the by-pass selector receives the digit in accordance with which the selector is to be positioned and selects an idle trunk line in the corresponding group, following which the selector used is caused to hunt for and conviding the ten selectors of a shelf into sub-groups corresponding to the two by-pass selectors BPS-1 and BPS-2, Fig. 6, is to assign the first selector FSl, Fig. 2, and each of the odd-numbered selectors to the by-pass yselector BPS-l andl to assign the selector F52, Fig. 2, and each "C lill) of the even-numbered selectors of the shelf to the by-pass selector BPS-2, Fig. 6. This is the arrangement indicated in Figs. 2 and 6. Interference between simultaneous position tests being performed in two sub-groups of a shelf is prevented by the arrangement whereby the switches in one sub-group test for the position assumed by the associated by-pass switch by searching for one pole of the exchange battery, while the switches in the other sub-group of the shelf test for the other pole of the exchange battery.

The register RS associated with the by-pass selector BPS-1 is a ten-point rotary switch having the double-ended Wiper 641, driven on the forward stroke by the operating magnet 642. Wiper 641 normally stands on the tenth bank Contact, with the off-normal contacts 643 in open position, as shown. The timer switch TS-l is a similar mechanism, and is provided for the purpose of freeing the by-pass selector in the case of delayed dialling, as will be pointed out subsequently.

The disclosed system being a ten-thousand line system, the first or thousands selectors are succeeded by penultimate or hundreds selectors, the circuits of the penultimate selector PIT-1, Fig. 8, being shown in full. Mechanically the penultimate selectors are somewhat more complicated` from a circuit standpoint because they supply talking current to the two lines of an established connection and supply ringing current to the called line.

The arrangement of the penultimate selectors into shelves and sub-groups is the same as described in connection with the rst selectors, with two by-pass or directing units assigned to the even-numbered and odd-numbered selectors, respectively, of a shelf-group of ten. The common units for the selector shelf containing the penultimate selectors PU-l and PIT-2 of Fig. 3 are the directors DR-l and 13R-2, Figs. 7 and 8. The term director has been applied to a cornmon controlling unit such as the DR-l, Figs. 7 and 8, because this unit serves, not only as a bypass selector for the associated penultimate selectors, but also as a register controller to position any connector taken into use by an associated selector.

The director DR--l includes a by-pass selector BPS-3, Fig. 8, similar mechanically to the mechanism of the by-pass selector BPS-1, Fig. 6. The director DR-l, however, has additional relay equipment and other apparatus to enable it to position any selected connector, as will hereinafter appear.

The connector C1, Fig. 4, is a nal selector (or connector) in one of the groups accessible to the selectors, such as PU-l, Fig. 3. This connector is similar mechanically to the selectors, but it diers from a circuit standpoint in that it is caused to return to normal position after each use thereof, with the lower wiper set on the i'ifty-lirst set of bank contacts. This diiferent arrangement is employed at the connector because the connector is positioned b-y a directive control operation instead of by a hunting operation, as in case of the selectors, such as PU-l.

Detailed description The system having been described generally, a detailed description of the operation of the apparatus shown will now be given. For this purpose it will be assumed that the subscriber at substation A, Fig. 1, desires to converse with the subscriber at substation B, Fig. 4, in which case the subscriber at substation A removes his receiver and dials the digits in the number assigned to the subscriber at substation B.

Call from substation. A to substation B (1166); starting the distributors When the subscriber at substation A removes his receiver to call the subscriber at substation B, Whose number it is assumed is 1166, line relay 105 of the line circuit LC energizes over conductors 101 and 103 through the upper and lower contacts of cut-oli relay 106. Upon operating, line relay 105 disconnects the private normal conductor 102 from cut-off relay 106 and connects it to ground, thereby guarding the line oi sub-station A from seizure by way of any one of the connectors having access to it. At its middle armature, line relay 105 connects the low-resistance element 104 in parallel with the winding of cutoff relay 105, thereby marking the line of substation A as calling in the banks of the nders, such as F. At its lower armature, relay 105 places ground on start conductor 150, thereby cnergizing the common start relay 501 to start the distributors D1 and D2 into operation. It will be understood, of course, that both distributors respond by going through substantially similar operations, but the detailed operations of the distributor D1 only will be described.

In the distributor Dl, start relay 502 now opcrates in series with resistance element 509. At its lower armature, start relay 502 prepares a locking circuit for switching relay 504 and closes a poiaring circuit for electropolarized test relay 507; at its upper armature it connects the operating magnet 508 with the test wipers 521 and 526 by Way of contacts of the switching relay 504, so as to close a self-interrupting circuit for magnet 508 incase the wipers of the distributor are standing on three contacts associated with a busy link circuit (such as the one shown in Fig. l) at its inner-upper armature it closes a local stepping circuit for magnet by way of the upper contacts of the group-test relay 503 and -ie upper contacts of the electro-polarized trunktest relay 507; and at its inner-lower contacts it connects up the group-test relat7 503 to the grouptest wiper 527.

As will be explained more fully shortly, operating magnet l508 is now operated in a buzzer-like if;

manner, either because of ground potential being obtained through the linlt-J st wiper 521 or wiper 526, or in a local circuit through contacts of the group-test relay 503, until an idle link circuit is reached having its secondary switch associated with a secondary group in which there is an idle rst selector. The linlr test made by Wipers 521 and 526 is a test for an absence of ground potential on the test conductors, such as conductor 154, of an idle link, While the test group test made through wiper 527 is made for ground potential and over group-test conductors, such as i58. The nature and purpose of the group test will now be explained a little more fully.

Since it would be futile to take a nder-secondary link for use and operate the secondary switch thereof in search ci an idle first selector when there is no idle rst selector accessible to the secondary switch, there is a common-test or group-test conductor, such as conductor 135, eX-

The group- T test conductor 135 is normally grounded by way of each of the ve common apparatus units associated with the iive sub-groups of first selectors forming the secondary group. It is normally grounded by way of contacts of switching relay 201 and conductor '221 Yextending to the by-pass selector BPS-1, and the upper contacts of release relay 603, Fig. 6. When the by-pass selector BPS-l is in use, ground potential is removed `at the upper contacts oi release relay 603 from conductor 221, thereby ungrounding conductor 135 at one point. If all the by-pass selectors of the same secondary group are in use at one time, it is obvious that ground potential is removed at all points from the group-test conductor 135. Also, when the rst selector FS-l is in use, it breaks one connection between the kgroup-test conductor 135 and conductor 221, so that if all switches in a shelf-sub-group of iive are in use, ground potential for that sub-group is thereby removed from the group-test conductor 135, instead of at the by-pass selector.

From the above-discussion, it will be seen that there is idle-indicating ground potential on Vthe group-test conductor 135 at all times, except when there are no trunk lines available in the associated secondary group of twenty-five trunks, at which time there is no ground potential ton conductor 135. A similar conductor is provided for each of the other secondary groups.

Se'zeing an idle )imiter-secondary Zink Referring now again to the distributor D1, Fig. 5, the buzzer-like operation of magnet .508 takes place, either through the local circuit controlled bythe contacts of group-test relay 503 or through the link-test wipers l521 and 526, advancing the wipers 521-527 step-by-step in search of an idle link circuit in a secondary group containing one or more idle trunk lines, until an idle link circuit is reached related to a secondary group in which there is at least one outgoing trunk line.

It is to be noted that group-test relay 503 energizes each time it encounters a ground potential on a test contact, indicative of a link :associated with a secondary group vcontaining an idle selector, and that relay 503 :falls back each time wiper 527 engages a contact associated with a link circuit in a busy secondary group. With relay 503 operated, a circuit is prepared for switching relay 504 and the local driving circuit for relay 508 is opened, rendering the further driving of the distributor dependent upon the grounded or' ungrounded condition of the test contacts engaged by wipers 521 and 526. It will be assumed that the nder-secondary link composed of the finder F and the secondary switch SS, Fig. 1, is idle and that there is a ground potential on the grouptest conductor 135 of the secondary group, indieating that one or more trunks are idle in the secondary group. Under this condition, when the wipers 521-527 land on the contacts associated with conductors 152-158, the driving oircuit through wipers 521 and 526 is open on account of conductors 154 and 157 being ungrounded; and group-test relay 503 is operated through wiper 527 and over the local branch 158 of the group-test conductor 135, by way of contacts of relay 115, the flexible spring 116 and the associated jack contact, and a jumper on the distributing frame DF. The driving operation now ceases. Under this condition, a circuit is completed for switching relay 504 through the armature of the operated group-test -relay 503 and in series with operating magnet 508. Relay 504 thereupon operates vin series with magnet `508, but magnet 508 is Ynot operated at this time because of the relatively :high resistance of relay 504. Upon operating, relay 504 closes a locking circuit for itself at its inner-lower armature by way of thelower armature of start relay 502; disconnects the link-test and line-test wiper `521 from the circuit of stepping magnet 508 -and prepares to extend it by way of contacts of trunktest relay 507 to the -upper winding of line-test relay 506; at its lower armature it disconnects test -wiper 526 Vfrom the magnet circuit and connects it to ground to -guard the link by way of conductor 157 against seizure .by the second distributor; at its middle-lower armature it connects trunk-test wiper 524 to trunk test relay 507; and lat its inner-upper armature it closes van operating circuit by way of wiper 522 and-conductor 156 for operating lmagnet 134 of 'the secondary switch SS.

Seiziny an idle first selector The Wipers V1.31-133 of the secondary switch SS are :now 'driven by 4the 'buzzer-like action of magnet `134 until `the wipers come into engagement with an idle `trunk line, which trunk line it will be assumed is the one comprising conductors 136-138 and extending tothe first selector FSl, Fig. 2. The Iidle conditionof this trunk line is indicated bythe application of battery potential to the release-trunk `conductor 137 thereof, by way of the iiexible test-jack spring 212 associated with the first selecto-r FSl, contacts fof switching relay 201, conductor 222, yupper armature, normal, of relay 603, flexible test-jack 11o spring 637, contacts of relay 602, and resistance element 638. When wiper 132 -encounters the battery potential thus placed on conductor 137, a circuit is closed for the upper winding of `trunktest relay 507 in the distributor D1 by way of 1115 wiper 524, conductor 153, contacts of relay 115, a jumper von 'the vdistributing frame DF, wiper 132, and conductor 137, to battery over the circuit previously traced through resistance element l638, Fig. 6.

It may be pointed out that electro-polarized relay 507 is a Pye polarized relay, the construction and operation of which is explained -in the patent to Pye, 1,673,884, granted June 19, 17928. Relay 506 is of the same type vas relay 507. This polar'rzed ltype of `test relay is used so as to avoid an operation of the relay in case so-called booster battery is encountered, which has an opposite polarity with respect to ground from the regular exchange battery. With the two windings of 130 relay 507 energized in the same relative direction, relay 507 operates and closes a circuit for the polarizing winding of electro-polarized -relay 506 at its inner-lower armature; places ground potential directly on wiper 524 at its lower arof the nder F. By this operation, the second- TZ c ary switch SS is stopped, and the finder F is .start-ed into operation to find the calling line.

It is to be noted that relay 507 removes ground at its middle-upper armature from the yarmature of the group-test 'rel-ay y503, thereby finally u 506 to restore.

terminating the group test. This ground potential is allowed to remain on the upper armature of relay 503 after switching relay 504 has energized and locked itself at its inner-lower armature so that in case all the trunk lines in the selected secondary group become busy before an idle trunk in the group has been found, as indicated by the energized or non-energized condition of relay relay 503 falls back and starts the link testing operation again, as it closes a direct circuit again for magnet 508 under the assumed condition and thereby short-circuits and deenergizes relay 504. With relay 50'? now energized, however, the ground potential is removed from the armature of group-test relay 503 as above pointed out, and the group-test is thereby eiectively terminated.

Finding the calling Zine The finder F now operates responsive to the buzzer-like action of magnet 114 until wipers 108-110 reach the contacts vassigned to the line of substation A, whereupon the upper winding of the line-test relay 506 in the distributor D1 is energized in series with resistance element 104 in the line circuit LC, through contacts of the energized line relay 105 and contacts of the nonenergized cut-o relay 106, wiper 109, conductor 154, wiper 521, and contacts of the energized relays 504 and 507. Upon operating, relay 506 opens the circuit of operating magnet 114 at its upper armature, thereby terminating the advance cf the under F; it closes a shunt around the winding of start relay 502 at its lower armature; and at its inner-lower armature it grounds the switching-relay wiper 525, thereby closing a circuit over conductor 155 for switching relay 115 of the illustrated iinder-secondary link. Switching relay 115 now operates and joins the wipers of the nder F with the wipers of the secondary switch SS. Relay 115 also opens the group-test circuit at its lower armature, and it prepares a locking circuit for itself at its inner-lower contacts, thereby extending its initial energizing ground potential by way of wiper 109 to cut-off relay 106. When cut-oir relay 106 operates, it opens the associated branch of the start circuit at its middle-lower armature; disconnects resistance element 104 at its inner-lower armature,

and at its upper and lower armatures it disconnects the line relay circuit from conductors 101 and 103, whereupon line relay 105 falls back and joins test conductor 102 to the cut-ofi relay again.

In the distributor D1, group-test relay 503 restores when the group-test circuit is opened at the lower contacts of relay 115. Moreover, start relay 502 restores following the elapse of a short interval after its winding is shunted at the lower contacts of the line-test relay 506. When it falls back, relay 502 opens the circuit of switching relay 504 and test relay 50'7 at its lower armature, whereupon these relays restore, and relay 507 opens the circuit of relay 506, causing relay When relay 506 restores, the distributor is in normal condition in readiness to be operated again. Ordinarily, the common start relay 501 has restored by the time relay 506 restores, but in case another call is waiting, relay 501 remains operated and relay 502 immediately reoperates to start the distributor D1 into operation for the next call.

With the deenergization of the common start relay 501, the distributor D2 stops operating and clears out.

Preparing the first lng-pass selector for operaufionl With switchingrelay 115, Fig. 1, and .cut-ofi relay 106, both energized, the calling line is now freed of attachments and extended through to the first selector PS1 by way of conductors 136 and 138. Conductors 136 and 138 are connected through contacts of switching relay 20 1 to the common- line conductors 224 and 225, with the lower winding of the connecting relay 202 of the first selector in series with conductor 225. Conductors 224 and 225 are connected through contacts of switching relay 603 to line relay 606 in the by-pass selector. VThe upper winding of line relay 606 is connected directly to the ungrounded pole of the exchange battery, while the lower Winding of line relay 606 is connected with the grounded poleof the exchange battery by way of contacts o relay 601 and the dial-tone conductor 636. Accordingly, line relay 606v of the icy-pass selector BPS- 1 now operates over the calling line, and the calling subscriber hears the dial tone impressed on conductor 636, notifying him that he may now manipulate his calling device in accordance with the digits of `th desired number. I

It is to be noted that the winding of release relay 603 is normally shunted through the contacts controlled by the armature of linelrelay 606. When relay 606 operates, it closes a circuit for relay 603 through-resistance 639,` and opens the above-mentioned shunt path. 1 Line relay 606 also disconnects the operating magnet 642 of the register switch RES-.1. Relay 603 now operates in series with resistance element 639 and closes a self-locking circuit at its inner-upper armature; it connects the commontirne-impulse lead 630 to the operating magnet 634 of the timing switch TS-l at itslower armature, and opens a point in the self-restoring circuit of the operating magnet634 at its inner-lower armature; at its middle-upper armature it removes ground potential from the common-test conductor 221 and connects ground potential to the local locking conductor 623; and at its upper armature it disconnects common release trunk conductor 222 from battery by way of resistance element 638 and connects it to ground, thereby providing a holding circuit through lthe contacts .of switching relay 201 of the iirst selector FS-l and jack spring 212 for relays 115 and 106Fig. 1. This circuit, it will be understood, is established before the slow-releasing start relay 502 of the distributor Dl falls back as before described.;

In the rst selector FE1, connecting relay 202, the lower winding of whichis connected in series with the common line conductor 225, energizes in series with line relay 606 of the by-pass selector BPS-1. At its inner-upper armature, lineA relay 202 closes a locking circuit for its upper winding over the grounded common release trunk conductor 222; it by-passes its lower winding at its inner-lower contacts; it prepares a trunk-test circuit at its upper armature; and at its middlelower and lower armatures it prepares circuits for operating magnet 203 and switching relay 201.

walling the fmt digit 1) When the subscriber'at substation A manipulates the dial of his calling device in accordance with the rst digit in the desired number, a corresponding series of interruptions is produced in the calling line. Each time the circuit over the calling line is interrupted, line relay 606 in the by-pass selector BPS- 1 restores. Each time it restores, line relay 606 closes a circuit for operatingr magnet 642, by reconnecting they operating magnet' to the operating circuit at its lower armature andby replacing the shunt around release relay 603 at the normally closed contacts controlled by its inner armature. Series relay 605 operates. in. parallel with resistance element 639v and operating-magnet 642 when the iirst impulse is deliveredto, magnet 542, andv it remains operated` throughout the series ofY impulses becauseit is a slow-actingr relay, andv also because of= the shunt circuit for it throughV thel resistance element 639; Release relay 603 remains operated throughout the series of impulses, as it is rendered slow-releasing by the shunt circuit beingf placed around it at the contacts controlled by the innerv armature of line relay 606. By the operation of magnet 642, wiper 641` of thev register switch RS-l is advanced step-by-step until it comes to reston the bank contact correspondingto the dig-it dialled.

Group selection at the luy-pass selector When series relay 605, operates responsive to the rst impulse, it locks itself at its4 lower armature'in multiple with resistance element 639 and independent ofi` the normally. closed contacts controlledf byv armature 622; opens points. in, the test circuit of relays 608 and; 609l afty its inner-lower and middle-lowerarmatures; prepares a startingcircuitfor operating magnet 610 at its upper armature; andat its inner-upper armature it closes' acircuit fromconductor 629. (grounded at themiddle-upper armature ci release relay 603,) for release-control relay 6011. Relay 601 now opcrates andmakes-a multiple ground connection to conductor 222 at its upper armature; substitutes direct ground potential forI ground potential by Way of the dial-tone` conductor 636 atY armature 621i, therebyV terminating the application ofl dial tone ourrent; it connects resistance element 640 in shunt of'releaserelay 603 and` opens the initial',

circuit of"` series rel'ay605l at armature 622, for a pur-pose tobehereinafter explained; opens a point in thecircui-tof'relay 602 at its inner-upper armature; opens a point in the restoring circuit of the register RS--l atY its lower armature;- at its inner-lower` armature prepare a special= con-- troly circuit for the lower winding of relay 602 inthe event of anoverfiow condition in theselected trunk group; and at armaturev 6232 it com'- ple-tes a circuit from, the grounded conductor 629 by Way of the operated upper armature of series relay 605, contacts of relays 604', 608; and 609,

' andthe associated self-interrupting contacts-for operating magnet 610.

Qperatingv magnet 6.10 now starts to operate in aV buzzer-like manner to rotate the wipers 6121--6202 of the by-pass selector in search` of the trunk groupindicated by the-assumed position of wipcr'64'l of the register RS-V-l.- It will be` understood, off course, that thegroup-hunting operation ofthe'by-pass selector is produced concurrentlyf with the stepping of theregister- BES-1, as relays 605 and 601 energize successively responsive to the first impulse to start the operation of magnet 610-. Under ordinary conditions, the Wipersll to-620ladvanceover the contact groups at about theA same rate that the wiper 641 of the register RSV-f1 advances from one contact to the next,v and the group-test relayy 604 may operate andrestore-a number of times during the receipt of@ ther digit and the positioning of the by-pass selector. A-t anyr rate, when. the wipers 611 to 620 advance to their iirst oil-normal position (they normally stand on the fty-rst set of bank contacts) wiper 620 places ground on' the group of contacts in its bank corresponding to the first trunk group, thereby closing a circuit for the group-test relay 604 through wiper 641' on the iirst contact, to which it was advanced responsive to the rst impulse. When relay 604 operates,l it opens the circuit of magnet 610 at its upper armature to halt the group-hunting operation'. Then, when wiper 641V advances tothe second contact, responsive to the second received impulse, relay 604 deenergizes and closes the driving circuit ofk magnet 610 again, which driving circuit remains closed until wiper 620 again catches up with. wiper 641 and brings about' the reoperation of the group-test relay 604.

In the present assumed example, the received digit is the digit l, represented by a single impulse. Therefore, wiper 641 advances to the rst contact in its bank and remains there, causing the group-hunting operation of the by-pass selector to be terminated with the wipers 611-620 in association with the trunk lines in the-iirst trunk group.

With line relay 606 in an energized condition atthe end of the dialled digit,.the impulse-series` relay 605 shortly falls back to mark the end ,of the digit. Relay 605 is adjusted so as not to hold up with the current flow through it in multiple with resistance element 639, with the two connected in series with. relay 603. However, with the current flow through relay 605 and resistance element. 639 increased by the additional'. current flowing through resistance element, 640, now connected in. shunt of the winding of relay 603 through, armature 622 of the operated relay 603 and resting` contacts. of the group-test relay 604' (assuming that relay 604 hasnot yet operated), relay 605 remains operated as long as resistance element 6 40 remains connected in shunt of relay 603. By. this arrangement, relay 605 does notfall back toY mark the end of the digit and thereby start the trunk hunting operation untilV relay 604 operates to indicate that. the group indexed by the called digithas been located by theV by-pass selector. The valuer of` resistance element 640J is so related to the-windings oi relays 603 and 605 that the current ow through, relay 605 with resistance element 640 in circuit is just sufficient to. holdV therelay operated, Therefore, when. relay 6044 operates (in. the event that the operation of relay 604- is delayed beyond the time when relay 605. would normally fall back), relay 605 restores almost immediately, thereby introducing a minimum delay between the end of the digit and the starting of the trunk-hunting operation.

Trunk hunting When series relay 605 restores at the end of the digit as above pointed out, it opens the initial' circuit of release-control relay 601 at its innerupper armature, leaving relay 601 locked up at its inner-upper armature to conductor 629 by way'of contacts of relay 607'. At its lower armature relay 605 disconnects itself and magnet 642, from the operating circuit (relay 601 being inoperated condition) at its upper armature it extends ground potential from conductor 629 by way of the operated armature 623 to the operated innerlower armature of the group-test relay 604; and i at its inner-lower and middle-lower armatures it extends the ground potential from the nowgrounded working contact of the inner-lower armature of the operated relay 604 tothe test windings of the switching and wiper-switching lll@ relays 608 and 609, thereby enabling these relays to test for idle trunk lines in the selected group.

At the same time that relay 605 extends ground potential at its upper armature to the inner-lower armature of the group test relay 604, relay 604 being operated the ground potential is extended through the upper armature of relay 604 and the contacts of switching relays 608 and 609 to the operating magnet 610. Magnet 610 now drives the Wipers in search of an idle trunk.

For the purpose of halving the number of hunting steps required to be taken by the wipers 611-620 of the by-pass selector, the wipers 611, 612, and 614-619 are divided into two'groups, with the directing wiper 620 and the restoring Wiper 613 common to both gro-ups. The Wipers 611, 612, 614, and 615 constitute the rst group, While Wipers 616-619 constitute the second group. Each group contains a pair of line Wipers, line wipers 611 and 612 for example; a trunk test Wiper, wiper 614 for example, and a position-test Wiper, Wiper 615 for example. By this arrangement, each off-normal position of the by-pass selector corresponds to two trunks. Now, keeping in mind that the driving circuit for operating magnet 610 is now closed through contacts of relays 608 and 609 and that the test circuits for relays 608 and 609 are now closed at the contacts of series relay 605 and through test Wipers 614 and 618, respectively, it Will be understood that one (or both) of the relays 608 and 609 operates in case one (or both) of the trunk lines now engaged by the two wiper sets of the oy-pass selector is idle, While ii both of the trunk lines are engaged neither relay 608 nor relay 609 operates, and the wipers 611-620 are driven step-by-step by the operation of magnet 610 until a pair of trunk lines is reached, at least one of which is idle.

Trunk seizure It will be assumed that the iirst pair of trunk lines reached in which at least one trunk line is idle` is the pair comprising conductors 231-234 and 241-244. It Will be assumed further that the` trunk line comprising conductors 241-244 is in use at this time, and that it is the trunk line comprising conductors 231-234 which is idle. Under this condition, there is no idle-indicating battery potential on conductor 243, and so Wiperswtching relay 609 does not operate'. Since the trunk comprising conductors 231-234 is idle, there is an idle-indicating battery potential on conductor 233, causing relay 608 to operate through contacts of of Wiper 614. The idle indicating potential for operating relay 608 is'obtained over conductor 233 by way of test-jack spring 309 of the penultimate selector PU-l, Icontacts of relays 303 and 308, the common release-trunk conductor 346 associated with the director DR-l, Figs. 7 and 8, inner- `lower armature and resting contact of release relay 801, inner-lower armature and resting contact of relay 707, test-jack spring 712, and resistance element 713.

relay 609 and by Way Vthe common release-trunk conductor 346, opens a point in the test circuit of relay 609 to prevent relay 609 from operating subsequently and thereby interfering With the connection established by relay 608 through armatures 655 and 656; at L.

in the desired number, by Way or" Wipers 611 and 612 of the by-pass selector BPS-1, Fig. 6.

In the meantime, line relay 606 fallsb-ack responsive to being disconnected at armatures 651 and 652. The operating magnet 642 of the register RS-l does not operate again at this time because relay 601 is operated and locked at its inner-upper armature through the contacts o position-test relay 607. At the normally closed contacts controlled by its inner armature, relay 606 places a shunt around release relay 603, causing release relay 603 to restore. The restoration of relay 603 at this time does not cause any harm to result, as release-trunk conductor 233 has by now become grounded by the director DR-l (as will be explained later) With relay 608 operated and relay 609 non-operated, as is now the case, conductor 629 receives ground potential from release-trunk conductor 233, maintaining relays 608 and 601 operated. Relay 601 maintains the common release-trunk conductor 222 grounded at its upper armature, thereby maintaining the 'I by-pass selector BPS-1 and the remaining idle associated conversational switches guarded for the time being.

Positioning the first selector FS-1 Relay 608 also closes a circuit from ground, on the grounded conductor 629 and through contacts of the position-test relay 607, over conductor 226 for operating magnet 203 of the first selector FS-l, by Way of contacts of the connecting rei lay 202. The operating magnet 203 of the first selector FS-l now starts to operate in a buzzerlike manner to advance the wipers 204-211 in search of the trunk line selected by the by-pass selector BPS-1.

The Wipers 204-211 of the rst selector FS-l V I continue to be operated by magnet 203 until Wipers 204-207 arrive on the conductors 231-234, constituting the trunk line which has been seized by Way of the wipers of the by-pass selector BPS-1. When the wipers 204-207 arrive on these conductors, Wiper 205 extends a ground potential (obtained through resistance element 212 and the upper contacts of connecting relay 202) over conductor 232 to the position-test ,y

relay 607 by Way of Wiper 615 and contacts of the non-operated Wiper-switching relay 609. The position-test relay 607 immediately operates and opens the driving circuit of operating magnet 203 of rst selector FS-l, thereby terminating the movement of the wipers. At the same time, relay 607 connects the grounded conductor 629 to the switching conductor 223, thereby closing a circuit through contacts of connecting relay 202 for switching relay 201 of the first selector PS1. H5:

Switching relay 201 noW operates and connects the incoming release-trunk conductor 137 with test wiper 206, at'the same time locking itself to the release-trunk conductor; it disconnects the incoming release Atrunk conductor 137 fromV the common release-trunk conductor 222 at its innerconnection to the trunk comprising conductors 231, 233, and 234 and extending to the penultimate selector PU-l is thus changed over to include the conversational switch FS--1 instead of the by-pass switch BPS-L Restoring the by-pass selector BPS-1 I-n the Icy-pass selector BPS- 1, relay 601 now restores because its circuit was opened upon the energization of relay 607, along with the opening :of the driving circuit of the first selector FS-l.

When it restores, relay 601 closes the restoring circuit of the register RS-l at its lower armature and by way of off-normal contacts 643. The register RS-l is now operated in a step-by-step manner by the buzzer-like action or" operating magnet 642 until it arrives in its normal position, whereupon the operation ceases because oit-normal vcontacts 643 separate. Relay 601 also removes ground potential from conductor 222 at its .upper armature, whereupon the remaining idle conversational switches associated with the bypass selector are rendered idle, and connecting relay 202 of the rst selector FS-l is unlocked and restores. Moreover, relay 601 at its inner-lower armature connects restoring wiper 613 to operating magnet 610. Operating magnet 610 now operates in a buzzer-like manner to drive the wipers 611-620 until they reach normal condition. As soon as the wipers start to move, ground .potential received by wiper 614 over conductor 233 is disconnected, permitting the operated relay 608 to restore. Relay 602 is operated -from wiper 613 through armature 624, normal, and disconnects magnet 642 from relay 605, preventing relay 4605 vfrom reoperating during the restoration period and reoperating release-control relay. The group-test and position test relays 604 and -607 are restored responsive to the movement of the wipers.

Preparing the director DR-1 ,for operation Responsive to the seizure of the penultimate selector PU-1, which seizure is rst accomplished by the by-pass selector as hereinbefore explained and then taken over by the conversational switch FS-l, the calling loop extended to conductors 231 and 234 causes connecting relay 307 in the penultimate selector to be energized in series with line relay 711 in the director DR-l. It is to be noted that line conductor 234 is grounded by way of the lower armature of relay 303, and that relay 307 has its upper winding connected between the common negative line conductor 345 and the incoming'talking conductor 231, by way of the upper armature of relay 303.

When connecting relay 307 operates in series with line relay 711, it locks itself to the common release trunk conductor 346 at its inner-lower armature; it places a shunt around its upper winding at its inner-upper armature; and at its remaining contacts it prepares the penultimate selector PU-l for operation in conjunction with the director 13R- 1.

In the director, when line vrelay'711energizes,

it opens a point in the magnet operating circuit at its upper armature, and at its inner armature it applies ground potential to conductor 720 and removes a shunt from around the winding of release relay 801, whereupon relay 801 operates in series with series relay 802. Series relay 802 does not respond at this time because of the relatively high resistance of release relay 801. Upon operating, relay 801 places an additional ground potential on conductor 720 at its upper armature, thereby closing a locking circuit for itself; it places ground potential on the common-release trunk conductor 346 at its inner-lower armature, thereby closing a holding circuit for the previously established portion of the connection before the previously explained deenerg'ization of relay 601 of the by-pass selector BPS-1 has occurred and removed ground potential from release-trunk conductor 222; and at its remaining armatures, relay 801 completes the preparation of the director DR-l for operation.

Dialling the hundreds digit (1) When the second digit (the hundreds digit) o1 the number is dialled, line relay 711 of the director DR-l falls back a corresponding number of times. Each time it restores, line relay 711 replaces the shunt around the winding of release relay 801 at the contacts controlled by its inner armature, and at itsv upper armature it completes valcircuit for operating magnet '812 of the register switch RS-2, from the grounded conductor 720 by way of armatures 730 and 732. By the operation oi magnet 812, wiper 810 is 'advanced step-by-step in a counter-clockwise direction to mark the Contact corresponding to the value of the received digit.

Series relay 802 responds to the rst shunting of release relay 801, when the 'rst impulse is received, and it remains operated throughout the series of impulses. Upon operating, series relay 802 opens points in the test circuits of relays 807 and 808 at its inner-lower and middle-lower armatures; it prepares a driving circuit for operating-magnet 810 at its inner-upper armature; and at its upper armature it connects resistance element 809 in shunt of release relay 801 by way of contacts of the group-test relay 804, so as to maintain the series relay operated until the group-test has been completed, as explained more fully in connection with series relay 605 of the by-pass selector BPS-1, Fig. 6.

Group selection at the penultimate lZig-pass sevlector When the wiper 813 of the register switch RS-2 is advanced responsive to the rst impulse, it closes a circuit for the group-test relay 804 through wiper 830 in its normal position on its fty-rst associated Contact, whereupon relay 804 operates and opens a point in the driving circuit at its inner-upp-er armature, while at its lower armature it closes a circuit from the grounded conductor 720 for the hunting-control relay 709. Relay 709, thereupon operates and locks itself to conductor 720 at armature 741, by way of armature 735 of relay 710,; it prepares a test circuit for relays 807 and 808 vat its lower armature; and at armature 742 it closes a point in the driving circuit of magnet 810, so as to start the group-hunting operation as soon as the group-test relay 804 falls back responsive to the second step of wiper 813 of the register switch RS4-2.

Whenv wiper 813 is advanced through its second step and comes upon its second contact, group-test relay 804 deenergizes and closes the driving circuit, which circuit extends from the grounded conductor 720, through armature 742 of the operated relay 709, inner-upper armature of the o-perated series relay 802, inner-upper armature of relay 804, armature 834, contacts of test relay 808, and the Seli-interrupting contacts of magnet 810, to the winding of the said magnet. This circuit remains closed until the Wipers 821--830 have been driven in a clockwise direction until wiper 830 overtakes wiper 813 of the advancing register RS-2, whereupon relay 804 is again operated to break the driving circuit at its inner-upper armature.

When the impulse series has ended, and the wipers of the by-pass selector BPS-3 have been rotated to the position corresponding to the one assumed by wiper 813 of the register RS-2, and group-test relay 804 has become energized to terminate the group-hunting movement, series relay 802 restores because it is unable to remain operated for more than a short interval of time in series with release relay 801 when release relay 801 is not shunted by resistance element 809. When it restores, series relay 802 closes points in the test circuits of the lower windings of electro-polarized relays 807 and 808 at its inner-lower and middle-lower armatures, and at its innerupper armature it completes the driving circuit for magnet 810 through the operated inner-lower armature of group-test relay 804, whereupon the trunk-hunting operation starts.

Trunk hunting In the assumed call, the digit received at the register RS-2 is the digit 1, in which case the wipers S21-880 have not been rotated at all as a result of the digit being received as they are normally in position to start rotating over the first group of trunk lines and need not move over this trunk group during the dialling of a digit unless this digit has a value greater than one. Therefore, the wipers are now driven out of their normal position on the fifty rst set oi bank contacts and are rotated in a clockwise direction until test wiper 823, associated with relay 808, encounters an idle-indicating battery potential on the release-trunk conductor on an idle trunk line.

Trunk seizure In the present case, it will be assumed that the rst trunk line found to be idle is the one comprising conductors 829-332 and the one cornprising conductors S33-336, simultaneously encountered by wipers 826-829, is in use. Under these conditions, the wiper-switching relay 808 is not operated, but switching relay 807 is operated because the upper terminal oi its lower winding is supplied with ground potential through the lower armature of the operated relay 709 and through the inner-lower armature of series relay 802; the lower terminal of the lower winding of relay 807 is connected through contacts of wiper-switching relay 808 to the test wiper 823. The test circuit over conductor 331 is complete to battery by way of test-jack spring 405 of the connector C-1, Fig. 4, and resistance element 406. Upon operating, relay 807 by-passes its lower winding so as to place a guarding ground potential on the release-trunk conductor o the seized trunk; opens a point in the test circuit of relay 808 and its lower armature so that relay 808 cannot now operate in case the alternate trunk line of the pair becomes idle; at its innerupper armature it interrupts the driving circuit of magnet 810, thereby stopping the wipers on the selected trunk; it opens an additional point in the driving circuit and prepares a circuit for transfer and connector-start relay 710 at armature 833; and at its upper armature it extends ground potential from the grounded conductor 720 through the contacts of the position-test relay 800 and over conductor 347 to the operating magnet 310 of the penultimate selector Pil- 1, by way of contacts of the connecting relay 307.

Positioning the penultimate selector PU--1 The operating magnet 310 of the penultimate selector PU-l now starts to operate in a buzzerlike manner to drive the wipers 321-328 in a clockwise direction until contact is made With the trunk line which has been selected by the by-pass selector BPS- 3 of the director DR-l, Figs. 7 and 8.

When the wipers 321-924 arrive on the set of bank contacts in which the conductors S29-332 terminate, wiper 322 extends a ground potential (obtained through contacts of connecting relay 307) over conductor 830 and by Way of wiper 822 and the inner-upper armature of relay 808 to the position-test relay 806. Position-test relay 806 thereupon operates and interrupts the driving circuit of magnet 310, stopping the wipers or" penultimate selector PU--l on the previously selected trunk line.

DiaZZtng the tens digit (6) When the tens digit is dialled, the digit 6 in the assumed example, line relay 711 of the director DPW-1 is deenergized momentarily six times. Each time it restores, line relay 711 closes the previously traced circuit from ground on conductor 720 by Way of armatures 730 and 732 for the operating magnet 812 of the register RS--2, thereby causing the register to take six steps from the first oir-normal contact. This contact, it will be recalled, is now marked with ground potential because Wiper 830 of the by-pass selector BPS-3 is now standing on the group of multiple contacts corresponding to the digit dialled. In this case, since the digit one was the digit dialled, then wiper 830 is now standing on one of its rst ve contacts, the third contact to be exact, because the third trunk in this group is the idle trunk selected. The dialling of this digit, it will be understood, may begin while the penultimate selector PU-l is searching for the position assumed by the by-pass selector BPS-3.

When the rst impulse is deliveredto operating magnet 812, series relay 802 is operated, as before, through the contacts controlled by the inner armature o1c relay 711, and it remains operated throughout the series of impulses. It is to be noted that resistance element 809 is not shunted around relay 801 at this -time as the shunt path through this resistance element is open at the upper armature of the operated relay 807.

As soon as wiper 813 takes its first step, responsive to the nrst impulse in the tens digit, the circuit oi the group-test relay 804 is opened, whereupon relay 804 restores, thereby closing a circuit through the operated armature 834 for the upper winding ofl test-control relay 805, by way of contacts of relay 803. This circuit includes the inner-upper armature of the operated series relay 802, armature 742 of the operated relay 709, and the grounded conductor 720. When relay 805 operates, it closes a locking circuit for itself at its upper armature through contacts of relays 803 and 801; it opens a point in a subsequently used energizing circuit for the already energized-and-locked relay 709 at its lower armature; and at its inner-lower armature it disconnects the now ungrounded wiper 813 fromthe deenergized relay 804 andy prepares a circuit for its own lower winding in series with relay 803.

With relay 804 now restored, and with switching relay 807 operated, when series relay802 restores at the end of the tens digit, it closes a circuit through the middle armature of relay 804 and by way of the operated armature 833 for the transfer and connector-start relay 710. When relay 710 operates, it opens the locking circuit of hunting-control and tens-cut-off relay 709 at armature 735, whereupon relay 709 restores and operates relay 704 at armature 741; prepares a circuit for relayk 703 at its lower armature; and at armature 730 and 729 it disconnects operating magnet 812 of the register switch RS-2 from the operating circuit and substitutes operating magnet 721 of the register "RS-3, preparatory to the unitsdigit being received by the register RS-3.

Dz'allz'ng theum'ts digit (6) When the units digit is dialled, the digit 6 in the assumed example, line relay 711 restores six times. Each time it does so, it closes a circuit from the grounded conductor 720 through the operated armature 729 and armature 731 for operating magnet 721. Magnet 721 advances wiper 723 six steps in a clockwise direction.

Series relay 802 is operated again during the units digit and remains operated until the end of the digit. Upon operating, relay 802 closes aV circuit at its lower armature from ground by way of the grounded conductor 720, and the'lower armature of the operated relay 710, for relay 703, by way of the inner-upper contacts of relay 702. When relay 703 of the counting pair comprising relays 702 and 703 operates at its lower armature and its upper armature, it closes two locking circuits for itself. The rst locking circuit is from the grounded conductor 720 by way v of armature 741 of the now-deenergized relay 709, and armature 733; and the second locking circuit is from ground by way of the grounded release-trunk conductor 346 and the winding of relay 702. Relay 702 does not operate at this time because it is supplied with ground potential at both terminals.

When relay 802 restores, at the end of the units digit, it leaves relays 703 and 710 operated and locked to conductors 346 and 720.

Group selection at the connector C-I When the combined transfer and connectorstart relay 710 operates responsive to relay 802 restoring at the end of the impulses constituting the tens digit, in addition to transferring the operating circuit from the register RS-2 to the register RS-3 at armatures 730 and 729, relay 710 connects the revertive pulse relay 708 to wiper 821 of the by-pass selector at its upper armature, by way of the upper armatures of relays 709 and 707, and at armature 737 it connects groundv potential (from the grounded conductor 720 by way of the resting contacts of armature 742) towiper 824 of the by-pass selector BPS-3. As a` result, the revertive pulse relay 708 is now connected by way of wiper 821 to conductor 329 leading to the connector C-l, and ground potential is now placed on conductor 332 by Way of the associated wiper 824. At the same time, relay 710 prepares a circuit at armature 736 for the lower winding of the tens-test relay 803 in series with the lower winding of the energized test-control relay 805, while at armature 730 it closes a control circuit for operating-magnet 812 of the register RS-Z, which circuit includes armatures 732 and 730, inner-upper armature of relay 709, normally closed contacts controlled by thev inner armature ofthe revertive-pulse relay 708, inner-upper armature of relay 710, and the inner-upper armature of the release-control relay 707. As a result, operating magnet 812 now energizes and advances the wiper 813 one step pursuant to the revertive control of the connector C-l, under the control of the revertiVe-pulse relay 708.

In theconnector C-l, start relay 403, the lower winding of which is connected to incoming oonductor 332 by way of contacts controlled by armature 421, and the lower armature of relay 401, operates in response to the ground potential placed on the incoming conductor 332, as above explained. Upon operating, relay 403 at its upper armature locks itself to the grounded release-trunk conductor 331 by way of the upper winding of relay 402, but relay 402 does not operate for the time being, because it is supplied with ground potential at both terminals; it connects the incoming conductor 329 through its own upper winding to wipers 410 and 414 at its inner-upper armature, at the same time disconnecting wipers 410 and 414 from the lower winding of relay 401; and at its lower armature it opens a point in the restoring circuit of magnet 404 and closes a local self-interrupting circuit for magnet 404 through the lower armature of the non-operated relay 402. Magnet 404 now starts to operate in a buzzer-like manner to advance the wipers 408-415 in a clockwise direction over the associated contact bank. It is to be noted that wipers 412-415 are advanced 01T the last contact set in the associated bank upon the first step, while wipers 408-411 are advanced onto the first set of associated bank contacts on the same step of the switch. The advance of 130 the switch continues without any particular immediate eiect until the fth step of the wipers occurs, whereupon wiper 410, encounters the grounded fth contact in the first encountered line-group. When this happens, a circuit is 135 closed from ground by way of wiper 410, the upper winding of the operated relay 403, the innerupper armature of the same relay, through the contacts of relay 401, and over conductor 329, for the reVertive-pulse relay 708 in the director 140 DR-l. This circuit, it will be recalled, includes the upper armature of the release-control relay 707, and the upper armatures of relays 710 and 709. When relay 708 operates, it opens the circuit of operating magnet 812 at the normally 145 closed contacts controlled by its inner armature, whereupon magnet 812 restores preparatory to advancing the wiper 813 an additional step.

The correspondence between the tens groups or lines or contacts (considered in consecutive 150 order from normal position), the number of rcvertive impulses sent back in reaching the groups, and the tens digits, is as follows:

Revertive impulses Tens digits In any case, the number of revertive impulses transmitted back to the revertive-pulse relay 708 is the complement of the tens digit, with respect eleven. In other words, the number of impulses in the tens digit added to the number of rcvertive impulses always equals eleven.

The contacts accessible to wipers 410 and 414 are divided into groups of ten, conductor 420 being connected to the iirst four contacts in each group of ten, while ground potential is connected to the last six contacts in each group. As a result, a revertive pulse is initiated each time wiper 410 arrives on the fifth contact in a group and is terminated when wiper 41 0 leaves the tenth contact in the group. The particular number of contacts in a group to which conductor 420 and ground potential are connected is in some measure arbitrary, but the assignment of iour and six has been found by experiment to be quite satisfactory.

W hen wiper 410 leaves the nal contact in the first group, it engages an ungrounded contact in the second group (connected to conductor 420), thereby opening the circuit through the upper winding of relay 408 for revertive-impulse relay 708 in the director 13R-1. Relay 708 `thereupon restores and again operates magnet 812 for the second control step.

As this operation continues, wiper 813 is advanced one additional step each time wiper 410 passes off the last grounded Contact in a new group. Keeping in mind that the tens digit dialled is the digit 6 and that wiper 813, therefore, has been advanced siX steps beyond the position marked by wiper 830 consequent to the trunk hunting operation of the by-pass selector BPS-3, it will be seen that the wiper 813 has again arrived on the marked contact when four additional, control impulses have been imparted to magnet 812. Magnet 812 receives one impulse, it will ce recalled, before the rst revertive impulse to relay 708, and an additional impulse at the end of each revertive impulse, when relay 708 restores.

'Ihe fourth control impulse is delivered to magnet 812 just as wiper 410 of the connector terminates the third revertive impulse, and enters the fourth consecutive group. At this time, a circuit is closed through wipers 830 and 813 in series for the lower winding of the operated test-control relay 805, in series with the lower winding of the tens-test relay 803, by way of armature 736. Relay 808 is thereupon operated to open the locking circuit of the upper winding of relay 805 at its inner-upper armature and close a locking circuitI for itself. Relay 805 remains operated for the time being through its lower winding. Relay 803 also prepares a circuit at its lower armature for reoperating relay 709 as the tens-cut-off relay, while at the same time it prepares a shunt circuit for relay 709at its upper armature.

Now, when wiper 410 engages the nrst grounded contact in the fourth associated group, revertive-pulse relay 708 is again operated to againl open the circuit of operating magnet 812. Then, when wipers 408-411 leave the last contact set in the fourth group, and wipers 412-415 arrive on the rst contact in the fifth tens group, the circuit of revertive pulse 708 is opened again, and relay 708 restores and again reoperates magnet 812, whereupon wiper 813 is stepped orf the contact marked by the wiper 830, opening the circuit through the lower windings of relays 803 and 805. Relay 803 remains operated and locked, but relay 805 restores because its locking circuit has been opened by relay 803. When it restores, relay 805 closes at its lower armature a circuit through the lower armature of the operated relay 803 for relay 709, but relay 709 does not now operate because it is shunted by ground potential supplied to the upper terminal of the associated current supply resistance element, in parallel with the now-operated magnet 812, through the upper contacts of tens-test relay 803.

When the revertive-pulse relay 708 next operates, responsive to wiper 410 of the connector C-l encountering ground potential in the :dfth consecutive contact group, it opens the circuit of operating magnet 812, allowing this magnet to deenergize, at the same time removing the shunt from around the winding of relay 709, which shunt was previously established through the normally closed contacts controlled by the inner armature of relay 708, upper armature and resting contact of relay 709, and the upper armature of relay 803. When the shunt is removed from around itswinding, relay 709 operates through the lower armatures of relays 803 and 805. Upon operating, relay 709 at its upper armature opens a point in the circuit of relay 708, leaving relay 708 operated for the time being through its own upper armature and the upper armature of relay 702; it removes ground potential from the positive wiper 824 of the by-pass selector BPS- 3 at armature 742; and at armature 741 it opens the main branch of the upper locking circuit or" relay 703, leaving this locking circuit closed through an armature of series relay 704.

In the connector Cl, when ground potential is removed from the incoming conductor 382 at armature 742 of relay 709, Fig. 7, the upper winding of 402 in the connector C-l is no longer shunted, and relay 402 operates in series with the lower winding of relay 403, from ground potential encountered on release-trunk conductor 331 by way of the upper armature of relay 403. When relay 402 operates, it disconnects the lower terminal of its upper winding from relay 403 and closes a locking circuitvfor its two iwindings in series, which locking circuit includes the upper contacts of relay 402. Relay 408 does not restore at this time because is held operated through its upper winding and over conductor 329 in series with the revertive pulse relay 708. At its lower armature, relay 402 shifts the circuit of operating magnet 404 to wiper 410, so that the further operation of magnet 404 dependent upon the continued supply of ground potential on wiper 410. In this way, the local circuit of l operating magnet 404 has been opened responsive to wiper 410 arriving on the first grounded one of six successive contacts, and the time of six steps of magnet 404 is allowed for the consequent above-described operations to take place and change over the circuit of magnet 404 to the group-test Wiper 410 so as to avoid over-running the rst contact in the desired group.

Since the iifty-rst set of contacts accessible to wipers 408-411 is not needed, this contact set is unused and the contact thereof in the bank ofV wiper 410 is grounded, as indicated,'causing wipers 408-411 to advance over this contact set also.

The wipers of the .connector C-1 now come to rest because neither wiper 410, nor the corresponding wiper (414) of the lower wiper set now encounters ground potential. In addition, the circuit through the Winding of relay 403 for revertive-pulse relay 708, Fig. 7, is new open, permitting relays S and 403 to restore. When relay 403 restores, it connects operating magnet 404 at its inner-lower armature, through the operated armature 421, and the lower armature of relay 401, to the incoming conductor 332, preparatory to the final positioning (with wipers 412- 415 standing on the rst contact set in the associated bank, the first set in the sixth consecutive group) of Wipers 412-415 on the contacts of the called line.

in the director, when relay 703 now restores, it opens the revertive-control circuit at its upper armature, while at its inner armature it opens the locking circuit of slow-acting series relay 704 and the upper locking circuit of relay 703, so that, in case series relay 802 has fallen back at the end of the units digit and opened the initial circuit of relay 703, relay 702 now ensrgizes in the lower locking circuit in series with relay 703. Its circuit is from ground potential supplied from release-trunk conductor 345, through. the lower contacts of relay '702. Upon operating, relay 703 disconnects the'revertiVe-pulse relay 708 at its upper armature; disconnects operating magnets 721 and 812 at armatures 731 and 732; opens a further point in the upper locking circuit of relay 703 at armature 733; prepares an impulsing circuit at armature 734 for operating magnet 721, while at an adjacent armature it connects the units interrupter relay 701 to ground by Way of the inner-upper armature of relay 709, normally closed contacts controlled by the inner armature of relay 708, inner-upper armature of relay 710 and the inner-upper armature of relay 707, causing relay 701 to operate,

Final positioning of the connector C'-1 When relay 701 operates, it closes a circuit for relay 708, whereupon relay 708 operates and at the contacts controlled by its inner-upper armature it opens the circuit of relay 701. Relay 701 shortly restores and opens the circuit of relay 708, whereupon relay 708 restores and again closes the circuit of relay 701. This interaction between relays 701 and '703 continues until the release-control relay 707 is operated through the wiper 723 when the predetermined number of digit impulses has been transmitted to the connector C-1 to bring about the units setting thereof.

Each time relay 703 energizes under the abovedescribed control of the units-interrupter relay 701, it closes a circuit at its inner armature through the middle-upper armature of relay 707, and armature '734 for operating magnet 721 of the register R-S-B. Each time relay 701 operates, it closes a circuit for the lower winding of relay 704 and a circuit over Wiper 824 for operating magnet 404 of the connector C-1.

Series relay 704 operates upon the first of these operations of relay 701, (in case it has restored) and remains operated throughout the series of impulses delivered to the connector. The circuit for operating magnet 404 includes the lower armature, normal o relay 401, armature 421, and the inner armature oi' relay 403. Operating magnet 721 energizes and advances wiper '723 each time it receives an impulse, and operating inagnet 404, energizes each time it receives an impulse, and it advances the wipers 408-415 one step each time it deenergizes following an impulse.

Since the units digit stored on the register switch RS-S is a 6 wiper 723 has been advanced six steps from its normal position as shown in the drawings. As a result, wiper 723 must be advanced four additional steps to return again to its normal position. Therefore, when the fourth control impulse has been delivered to magnets 721 and 404, wiper 723 is returned to its normal position, whereupon the units-test or releasecontrol relay 707 is energized from ground by way of the grounded conductor 720, the lower armature of relay 710, and the lower armature of relay 702. Upon operating, relay 707 opens an additional point in the circuit of the units-interrupter relay 701 at its inner-upper armature, thereby terminating the series of impulses. When the iinal impulse (the fourth impulse in the series) is thus terminated, operating magnet 404 of the connector C-l restores and advances the wipers 412-415 from the third set to the fourth set of contacts in the rst contact group in the associated lower bank semi-circles. This is the contact group associated with the line of substation B, telephone number 1166.

Testing the called line With slow-acting series relay 704 energized as above pointed out during the final setting operation of the connector C-l, busy relay 705 is connected through the resistance element 714 and the upper armature of series relay 704 and the upper armature of relay 707 (as soon as relay 707 operates), to the trunk conductor 329 leading to the connector C-l. In the connector C-l conductor 329 is now connected through the upper contacts of switching relay 401, innerupper armature, normal, of relay 403, and the upper winding of switching relay 401, to the test wipers 409 and 413.

The called line busy When test wiper 413 arrives on the test contact of the called line, at the end of the final impulse in the series, a ground potential is encountered on the test contact of the called line by test Wiper 413 in case the called line is busy. In case ground potential is encountered, a circuit is closed through the upper winding of relay 401, as previously traced, through resistance element 714 for the two-step relay 705. Busy relay 705 is operated through its rst step to close its lightly adjusted, first-step, lower armature, but the marginally adjusted switching relay 401 is not operated because of the current-limiting effeet of resistance element 714.

After a slight interval, relay 704 restores and closes a locking circuit for busy relay 705 at its lower armature to the grounded release trunk conductor 346, while at its inner-upper armature it transfers the test circuit to idle relay 706, which relay is prevented from operating at this time because it is connected so that it requires

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