US2190140A - Telephone system - Google Patents

Description

Feb. 13, 1940.

FROM SELECTOR LEVELS R. TAYLOR ET AL.

TELEPHONE SYSTEM Filed July. 22, 1937 4 Sheets-Sheet i was GILL/N65 TTQ INVENTORS REGINALD TAYLOR GEORGE THOMAS BAKER Feb.'l3, 1940. R. TAYLOR ET AL TELEPHONE SYSTEM Filed July 22, 1937 4 Sheets-Sheet 2 luvs/woes REGINALD TAYLOR GEORGE THOMAS BAKER 5 CHARLES GILL/N65 Feb. 13,1940. T Y R' 2,190,140

TELEPHONE SYSTEM Filed July 22, 193'; 4 Sheets-Sheet s INVENTORS REGINALD TAYLOR GEORGE THOMAS BAKER CHARLES GILL/N65 ATTY Feb. 13; 1940. TAYLOR ETAL 2,190,140

TELEPHONE SYSTEM Filed July 22," 1937 4 Sheets-Sheet 4 4 r h h7 1 INVENTORS REGINALD TAYLOR GEORGE THOMAS BAKER Z 5 CHARLES GILLINGS Patented Feb. 13, 1940 M TELEPHoNssYsTE Y' 1 w Reginald 'llaylor and George Baker,

Liverpool and Charles Gillings, London, Engiland, assignors to Associated Telephone and "tionof Delaware {Application iinyea, 1937,? Serial N 3 155,014

- In Great Britain August 11, 1936 The present invention relates to telephone systenis ranti while particularly concerned with systems employing final selector or two digit group-"selector switches "of the up and around 5 or two motion type is also applicable; to group selectors of "other kinds and constructions.

Arrangements have already been suggested whereby after the'setting operation a switch.

nisadapted to "hunt for an idle line in a group. In case the 'groupov'erflowsgon to other levels due to all lines in the first levelhaying been found lousy a further level is liuntedeover which is reached as a result oi alevel hunting opera-= tion. With this arrangement it was. necessary stance; OlltIE'ESQD aleyelgior any one group had to be successive and in case a igroup required more than one level,thepverflowmutlets of the group had to be accommodated on the firstand -suhsequent -successive outlets of the further level required. Incrder to cater for extension; :one or more spare outlets were allottedatthe end of each gmup hut if 'it was desired to extend group above thepredetermined maximum it" 5 was necessary to make a somewhat complicated change to the/switch or even -to remove the group to. another" switch with a consequent:

v alteration of the exchangenumberallocated to: the group. One of theobjects of the invention is therefore to provide an improved switch which permits of the utilisationjof spare outlets inan'y position on any levelwhenit is desired to extend a group.-

' Accordingto'one ie'atureof the invention an I auxiliary :sw. ch preferably of theuniselector type isa'ssociatedr with a finallselector or group "selector switchand is arranged/afterthe final same): or group jselectory has tested a line or group or linesand found them to be busy to *:contr'ol the selectorso that it hunts to find 2131-, i

other line or 'lines of thegroup first tested under the control or the unisel'ectoi" distinct from the previous arrangements which resetting of the switch was effected by impulsing. According to a'n'other feature of the invention switch provided with twoflor more sets :of.

wipers is arranged initially to test a group of lines accessible to onesetof wipers only as 'determined by the" route over which the switch was takeninto but: is arranged in testing over other lineso'f thegroup to test over either set of wipers according to the position of the additional lines or the group. v

w j'A'ccordingto a'third i eature of the invention the switch when the wipers/are passing over moraine. (o1. use-1s) 'peatedly.

plioable up and around switches can he; con- 1 trolled by a uniselector so asto, repeatedlytest a group of lines. 1 I

to groupgthe, lines in special Imannerior in-.

contacts is operated by a sel-finterrupted .cireuit except when it ispassing over outlets' in; the

s n,.;b.ine te e v. I i

According to; a iour th feature o f the invensection of -the group it is adapted to simultaneously i' f tfoutlets accessible to two orgrnore sets fiw p s 1 e a 1 According ,to yet a fifth feature of the invention single 1ines,'adjacent lines forming a jsingle e11 group andlines of a group havingiaplurality of sectionswith one or more lines of the group in each section are adapted to,,be tested re- The invention being particularly apv These and other issues or the ma s @111 [be [better l in derstoodj ironr the; following description of two methods of} carrying it, into gg effect -reference jloein'g had to Figs, 1 and; 2 and Figs; 3 and fl, which should be arranged side by side to form circuit diagrams' of a ZOO outlet i P. 2 4? .fi-ne vee end e fi i l is selector respectively. Both switches are of;the; 5 longitudinal-and rotary type and employ-, two I m n eh n sms Qf..-ihe t d o e i "Patent No. 2,028,689, granted, January 21,1936, i to R. N. SaXby,while each switch has associated with it an auxiliary uniselector s h I x 1 30 Referring now to Figs. 1 and iz' -it will firstfb'e assumed that an auxiliary uniselector is not fitte d fin which casetheswitch is arranged to perform the functionsofa standard 200 outlet iinal selector with facilities for P". B. groups; ,r 5 up to 10 lineson both hundreds of the Z OO total "outlets. :This is effected by strapping terminals.

K, it L and l /[wand terminals- G, J and ;E"together' and by making the following cross connections to thejoddand even hundreds banks 'Pziiandmo P22 asfol'lows; H y Terminal A'to the first line in each R B. X.

group and terminal B to all other lines in each "PUB. Xqgroup except the last. i

switch is taken lTltOllSG] over the odd hundreds set of. conductors negative :1,.p'ositive 1 and P l in which'case' 'the operation does not involvethe energisati'onof the wiper switching relay 'WS.

' When'the 'speakingieads are looped lrelay A50 Voperates and brings up relayB which thereupon I v at" armature bl extends a guard earth on to'the I incoming Pl conductor and at armature bfif op crates relayC QVer itsflIight handwinding in series withresistance YD. 'Relay, C finlloperatgs ing at armature cl prepares the impulsing circuit via its left hand low resistance winding to the vertical magnet VM, the magnet being, however, non-operative in series with the Winding or v relay B.

sponding to the digit dialled. During the im pulse trainrelay B is intermittently shortcin,

cuited at armature al, but this relay remains operated due to the slugging effect of the short circuiting. The presence of the metal'rectifier MRB in the energising circuit of relay B pre vents the slowing down of the magnet opera: tion which would otherwise result by the direct connection of the comparatively low valuenon- "inductive resistance in parallel with its winding.

It will be readily understood that neither'the vertical magnet nor'relay C will hold operated in series with relay B and moreover the inductance of the latter relay is such that it has no appreciable effect on the magnet performance; J

v On the first vertical step the off normal springs N are mechanically operated and at contacts N4.

extend an earth from armature bz' toshort circuit the right hand winding of relay C to enable the relay to hold satisfactorily during impulsing also'to enable it to release when impulsing ceases. v

At the end of the train of impulsesrelays A and B remain steadily operated and after a short period relay C releases whereupon relay E is operated in series with the magnet VM and at armature e2 it transfers the impulsing circuit to the rotary magnet RM and at armature el removes the earth shunt from the right hand Winding of relay C thereby enabling it to 'reoperate.

Thesecond digit is similarly repeated by'relay .A through the winding of relay C to therotary magnet RM which accordingly advances the Wipers into engagement with the required linen On the first rotary step. the rotary off normal springs NR are mechanically operated and at contacts NR2 again short circuit the right hand winding of relayC.

Atthe end of the digit relay C releases after a short interval and at armature 04 opens the mences to release slowly. At armature 03 an earth is now extended over armatures r k4, b4 and 108 2, and the upper winding of relay PA in series with the lower winding of relay HA on to the odd hundreds group test wiper P11 and assuming that the wipers have been positioned into engagement with the first line of a P. B. X group the odd hundreds test wiper P21will encounter an earth by way of the 'strappingbetween the bank contact on which it is resting and terminal A, armatures c5, rkZ, hi1, 71b4, M14, 1! and b2 whereupon relay PA will be operated over its lower winding. Relay PA in operating at armature pal operates relay HT from the same earth and this relay thereupon looks over armature htl, contacts rm and .armature ht2. Relay HT in operating completes an operatingcircuit for relay HS from earth over. armatures e3 and M6 and operated oiT normal contacts N2 and at armature h 1 it disconnects the operating circuit for relayPA.

whilst relay PA will release. relay PA an energising circuit is completed for 5 If the first line of the P. B. X group is engaged wiper PI1 will encounter an earth or disconnection thus preventing the operation of relay HA On the release of the rotary magnet RM as followsz-earth by armatures b2, 1 I, had, hbd, hi2, ph3, 11:13, hsl, ofi normal contacts N3, armatures ha! and 71271,

magnet RM to battery and accordingly the wipers are advanced to the nextposition while at the 10 same time the opening of the rotary magnet interrupter contacts rm opens the holding circuit of relay-HT. Relay HT thereupon releases and at'armature htZ disconnects the magnet energising circuit while at armature kill it extends 15 earth to terminals A and B byway of armatures M2, 05. and 11.85. The cross connection from terminal'A is now ineirective since the wipers have been steppedofi the first line of the group but the earth isnow extended over terminal B 0 and cross connection to the intermediate lines of the group in the P21 bank and it thereupon re-energises relay PA over its lower winding.

Relay PA'in operating again operates relay HT which as before locks and prepares the rotary Z5 magnet energising circuit and disconnects the lower winding of relay PA. Should the PI1 wiper again encounter a busy outletrelay HA will not operate and relay PA will. release as before, whereupon the rotary magnet is again ener- '30 ised and the cycle of operations continues until the switch reaches a free outlet in the group or alternatively the switch will rotate to the 1th position. I Relay E will have released after its slow release period at some instant during the rotary search and in so doing it re-operates relay C on its right hand winding by removing the short circuit therefrom while it disconnects the impulsing circuit for the rotary magnet at armature e2 to io prevent its energisation in case the subscribers dial is accidentally operated. Relay HS is provided with a slug to enable it to hold operatd during the'interaction between relays HT, PA and the rotarymagnet. 7 415 As soon-as Wiper Pli encounters a free outlet in the group which is indicated by a battery potential extended iromthe cut'oif relay of one of the subscribers in the group, relay PA will remain will operate.

Relay HA in operating at armature ha t locks over its upper winding to the earth via armatures fl and b2, at armatures hat and 7W2 connects-'55 up wipers +l and -l, at armature ha3 it extends an earth over the Pli'wiper to guard the selected outlet and to operate the called subscribers cut-off relay; at armature had it disconnects the holding circuit for relay HT and co at armature ha! it disconnects the magnet driving circuit. Relay HT in releasing opens the holding. circuit of relay HS which releases after a short interval and thereupon completes an operating circuit for relay J as follows: earthf fi armature b2, contacts N4 and NR2, armatures 71.88, and M5, winding of relay J to battery, and this-relay in operating at armature 7'4 thereupon applies ringing current over common conductor Hi through the winding of relay F onto the selected line, the ringing current finding a return path by way of resistance YB to the ringing return battery connected to common lead l6. At armatures a I and 1'2 a ring-back tone transformer connected to common lead I4 is extended to the middle winding of relay A whereupon a tone is 1 applied by induction from the middle to the ill outer windings on the incoming speaking conductors in a balanced circuit so as to inform the calling party thatthe call is proceeding satisfactorily and that the wanted party is being rung.

When the called subscriberreplies relay F operates and at armature f3 and f4 disconnects the ringing current and at the same time switches the incoming speaking conductors through, where- .upon relay D operates over the called partys loop and contacts ft and fl in series with the cur-. rent limiting the resistance BRA. Further at armature fi relay F inserts its lower winding in series with the "upper winding of relay HA and thus provides a locking circuit for itself while at armature it it disconnects the ringing tone to the calling subscriber. Relay D in operating at armatures di and (52 provides the usual supervision by reversing the current to the calling side of the circuit while it completes an operatingcircuit for relay E from earth, armature b2, contacts N4, winding of relay armatures.

c4 and :13, vertical magnet VM (non-operative in this condition) to battery. Relay E thereupon at'armature e' l locks independently of the arma ture (Z3 and atarmature e8 connects booster batteryt'o'the incoming release trunk conductor over armature 9'3 to operate the subscribers meter in l the wellknown manner. At armature e5 relay J is disconnected and its slow release time determines the, duration of application of the booster metering pulse after which earth is reconnected to the release trunk conductor at armature 7'3. Rectifier MIRAserves to maintain a guard earth to the 'P conductor during the transit times of armatures 7'3 and 66. Clearly if relay D flicks during its operation due 'to clumsy removal of the receiver by the called party relay E will hold op- .erated due to its slug and there will be no false and during its'release time relay HA will operate over its lower winding over the P11 wiper to the called p-artys cut-oii relay when the cir cuit operation will proceed. as described previ-' Should all the lines in the groupbe engaged relay HA will not operate in the last position of" the wipers and hence on release of relay HS after its slow release period a self-interrupted driving circuit for the rotary magnet RM is completed as follows: earth, armature b2, contactslN i and NR3, arrna'tures 7138', ed, hat, 71.73%, b5

hti, rotary magnet interrupter contacts rm, ar-

' matures p133, p023, and hs i, vertical magnet interrupter contacts om, armatures T101 and b3, strapping between terminals K and 'L, contacts N3, armatures hal and hill, rotary magnet RM to battery. Accordingly the switch rotates its wipers to the 11th; step position and on reaching this position the wiper P21 encounters an earth by way of the multlp-led 11th step contacts, the cross cone nections between terminals J'and .E, armature htl to the earth whereupon relay PA quickly operates overits lower winding and opens the cirmagnet drive until the switch reaches the 11th.

cuit of the rotary magnet. Relay PA in. operating thereupon extends "an earth by way of its upper holding winding in series with the lower winding of relay I-IA on to the "P11 wiper wherewv upcnrelay I-IA operates in series with resistance YC. Relay HA inoperating locks up infthe normal manner, further disconnects the rotary magnet circuit, short circuits and releases relay PA and operates relayJ. Relay P will thenbe con nected up to the negativea'nd positive wipers but ll) since these wipers are standing in the 11th position which is unwired this relay will not be operated. The 11th step cam springs S are also mechanically operated thereby connecting relay A contacts Si and S2 in circuit with the busy flash l and tone cam assemblies BF and BT which are connected to commonlleads lfi and t3 respectiveiy, Busy tone is thereupon returned tothe calling party in a balanced circuit, the busy flash arrangement serving in a well known manner to flash the supervisory lamp if the call has been set up by an operator. The arrange'ments'of the windings of relay A are such that this relay is maintained operated under all positions' of the busy flash cams. 525

During the rotation of the switch to the 11th position itwill be seen that there is no possibility of switching to a free line in another group on the same level since the resting armature hs5 prevents earth from being extended to terminal B while the A terminal is disconnected by the oper atedar'rnature 05, so that no circuit can be cornpleted to operate relay PA and thereby cut the position.

Assuming now that the switch is taken into use over the even hundreds set ofrconductors negative 2, positive 2, and P2,'the operation will continue in a normal manner until'relay E isfoperated on release of relay Cat the end of the firstoio digit when the low resistance left hand winding of relay WS is inserted in the incoming positive line ancithis relay operates. On the first rotary step made in response to the second digit, the r0 tary on normal springs N7" are operated ,and'at Z contacts NR3 short circuit the'operatingwinding of relay WS which, however, remains operated on its right hand winding by way of contacts NR2 and Nil, and armature 122 to earth; Relay W S in operating disconnects the operating earth'forlhfi the odd hundreds test and switching relays PA i and. HA and transfers it over to the even hundreds relays PB and HB which are associated with the test wipers P22 and Plz respectively; at the same time at armature wsflthe normal operating 5 circuit for relay PA is disconnected whilst theu'ppe'r winding of relay PB is connected up towiper P22. {The circuit operation will now proceed in a nor-; mal manner except that the testing will be performed overthese wipers and when a free outlet W0 is encountered relay I-IB will be operated to switch the speaking leads through to the negative 2 and positive 2 wipers. i l I In case the switch is set by the dialled impulses on to an intermediate line of a P. B. X gronpfl onrelease of relayC there'will be no earth extended to operate the test relay PA 01. PB as the case may be, since terminal 'A is cross connected only to the first line of a group. Relays HT and HS will not therefore be operated and if the line is free relay HA or I-IB will operate according to whetherrelay WS is operated orsnoawhen theoperation will proceed in a normalmanner. \If the line is engaged the switch will not rotate further to test other lines in the group but in this caseb i7 5- release of relay E after its slow release period a self-driving circuit will be completedfor the rotary magnet as follows: earth, armature b2, contacts N4 and NR2, armatures hs8, 25, has, M76, 115 and htl, interrupter contacts rm, armatures 10b3, m3 and hsd, interrupter contacts cm, armatures Tkl and b3, strapping between terminals K and L, contacts N3, armatures ha! and hbl, magnet RM to, battery. Accordingly the switch wipers will be advanced to the 11th position where busy tone will be returned in the normal manner.

Should it be desired to extend any P. B. X group advantage may be taken of spare outlets in any of the odd or even hundreds levels. By the way of example, assume that a P. B. X group whichis situated on the first seven outlets of level 3 in the odd hundred groups is to be extended to 14 lines. Due to the relative congestion of the switch it will be further assumed that the group of 14 lines must be made from 4 sections situated on various levels as follows:

" (a) The first seven odd hundreds outlets on -1evel3.

*(b) The last two even hundreds outlets on level 3.

(c) The last two odd hundreds outlets on level 8.

(d) The last three even hundreds outlets on level 8. To enable the switch to perform a hunting operation over this widely scattered group it is necessary to utilise an auxiliary uniselector represented by banks Id, 2d, 3d and 401 which serves will mark further outlets in the group on the level dialled (inthis case level 3) by means of a cross connection between contacts of the P21 and P22 banks corresponding to outlets in subsequent sections of the group on this level and terminel P.

Terminal R is cross connected to the next level of the vertical'bank to which the switch must be raised to continue the hunting operation, in'this' case level 8. On finding all outlets and subsequent sections of the group if any, on level 3 busy the switch will restore to normal and then drive vertically until it reaches level '8 whereupon the uniselector will be stepped to the next position.

In this position wiper 2d will mark the succeeding level to which the switch must be raised while the outlets in the section or sections in the group on level 8 will be marked by wiper Gd or alternatively if there is no further vertical hunting required there will be no strapping from the contact on which wiper Ed is now resting whilst the contact on which wiper 3d is resting will be cross connected to terminal G in order to return a busy tone to the calling subscriber in case all outlets in the group are engaged. Terminal A will be connected as before to the first outlet and terminal B to all other outlets in the first section of the'group except thelast whilst terminals K, L

and M and E,G and J will be connected as shown and not strapped as previously described, it being understood that when the operations previously described require the employment of circuits including the strapping connections other such circuits will be replaced by means involving the use of appropriate banks and wipers of the uniselector under, the conditions to which such circuits relate.

In order to secure access to the first line of the first section of the group the switch will have to be taken into use over the odd set of conductors. On dialling digit 3 the switch will be raised vertically to level 3 in the usual manner while on the reception of digit 1. the wipers will be advanced into engagement with the first line of the P. B. X group. At the end of this digit relay C releases after a-short interval and disconnects relay E which remains operated for a further short interval while an earth is extended over terminal A and P21 bank and wiper'to operate relay PA in the normal manner. Relay PA in operating closes a circuit for relay HT which in turn operates relay HS and disconnects the operating circuit for relay PA. Should the line be engagedrelay PA will release and thereupon the magnet RM and relays PA and HT will interact in the normal manner until the switch reaches an idle line or the last line in this section of the group.

If the last line is also busy, then, since an earth is not encountered by wiper P21 to operate relay PA in this position due to the fact that there is no cross connection between terminal B and the last outlet in the first section, relay HT is not operated and therefore the rotary magnet is not re-energised. No further operation ensues until relay HS releases after having previously been held operated during the rotation due to its slug, when a self-interrupted driving circuit for the 'magnet DM is completed as follows: earth, arma ture b2, contacts N4 and NR2, armatures M8 and e (relay E having released by this time), armatures hat, hbfi, b5 and htl, interrupter contacts rm, armatures 10b3, m3 and hs l interrupter contacts um, armatures 17c! and b3, bank id, uniselector magnet interrupter contacts dm, magnet DM to battery.

' Accordingly the Dm switch wipers are rotated until wiper 3d encounters the position which is strapped to the last outlet of the first section. Relay PA then operates quickly to earth over wiper 3d and the cross connections on to the P21 bank and opens the driving circuit at armature p113 and at armature pa! re-operates relay HT. This relay at armature ht3 operates relay RK which at armature rlcl locks independently of armature hi3 and completes an operating circuit for relay HS over armatures Th6 and hi5 and contacts N2. Relay HT in operating disconnects the operating circuit of relay PA at armature ht! and as it has been assumed that the lastoutlet in the section was engaged and that it is still engaged relay PA will release and at armature p113 will again prepare an energising circuit forthe rotary magnet RM and relay HT will be released.

On release of relay HT at armature htl a selfinterrupted driving circuit is completed for the rotary magnet RM over earth, armatures 112, l, hafl, hM, Th8, e5, her-6, 71b6, b5, htl rotary magnet interrupter contacts rm, armatures 12b3, pa3, hs4f, off normal contacts N3, armatures hctl, hbl, winding of rotary magnet to battery and the wipers are thereupon rotated until they reach the 9th position, that is, the first outlet of the second section of the group, when an earth will be extended over operated armatures Th2 and hsfi, terminal D, wiper and bank 4d, and cross connection to further outlets of the group on the P22 bank to operate relay PB on its upper winding by way of armature TM.

.l'Jue' however Relay PB in operating'opens the magnet circuit and reoperates relay HT which in turnopens the operating circuit of relay PB which then releases. if it is assumed that the even hundreds wiper Pig is in engagement with a busy outlet. On release of relay PB the rotary magnet is again energised to step the wipers to position 10 and if this second outlet is engaged-the magnet will be again energised to step thewipers to the 11th position. Since the wipers are now out of engagement with the group there will be no earth I positionwhereupon they fall androtate below the banks under spring tension back to their normal position where the oil" normal contacts N3 open and disconnect the driving circuit. Preferably the rotary. magnet is mechanically prevented from opening its interrupter contacts during the vertical release movement so that there is no tendency for it to chatter. 1 J

It will be noted that armatures 1K3 andrkfi in the operating position providean alternative circuit to the armatureswsfi and wst respectively of relay W S so that whenever hunting takes place in an overflow group in which'ca'se relay RF. is always operated the outlet canbe over either set of wipers although normally without overflow the outlet is over the set of wipers determined by the incoming leads.

In the normal position the rotary off normal and the oil normal springs NR and N are restored to normal and at contacts N2 the holding circuit for relay HS is disconnected. This relay thereupon releases after a short interval and completes a self-interrupted drivingcircuit for the verticalrnagnet VM as follows: earth, armatures 212, ii, ha l, hbt, 1R8, e5, hail, hbla, b5 and mi, contacts vrm, armatures p123, 120,3 and had, vertical magnet interrupter contacts 'vm,

armatures rlcl and hit, vertical magnet VM to battery, and accordingly the wipers are raised vertically whilst at the same time an energising circuit Dlvl from earth over armatures 7706, hit and hsZ. to thereverse drive action of the unisel ector switch the wipers are not advanced to the next position. until subsequently the magnet DM is ole-energised.

On reaching level 8, on which are situated the sections 0 and d of the group an earth is extended over armatures T102 and hsli, 2d wiper and bank and the cross connection to operate relay PA which thereupon opens the driving circuit and at armature pal operates relay I-IT. Relay ET in operating locks up over armatures htl and hit, at armature htl opens the operating circuit of relay PA which then releases since its upper winding is in an open circuit, and at armature hi4 further opens the driving circ' t of the 'rnagnetVivi. The energising circuit of the magnet DM is opened at armature. ht5 whereupon fthenniselector wipers arestepped to the next position whileat "75 armature hi5 earth is ezktended over armaturerlct to, re operate relay HS. In

is completed for the uniselector magnet.

resting is unwired since it is not desired tomark any further levels to which the switch mus'tbe raised to continue hunting while the 'contact on which wiper 3d isresting willbe wired to termi- Y nal G for a purpose'which will be understood later. Relay HS inoperating extends earthover ainiatures hi2, pat'and hs hcontacts N3'a nd ariuatures ital and hb l to energise the rotary magnet RM andthe uripe'rs are thereupon adthis position the contact on which wiper 2d is vanced'into engagement with "the'first outlet, on

level il while relay HT is dc-energised by the operated contacts rm. However as the wipers'are not set into engagement with an outlet of the gup there will he no circuit to operate relay PA and hence on release of relay HT the magnet l-"tlvi will self-drive until'the wipers reach position 3 which is the first line or" section 01 of the group. In this position since an even outlet has been utilised an earth will be encountered over the id wiper and cross connection to the P22 bank; thereby operating relay PB. This relay in operating at armature. poi re-operates relay HT- which in turn releases relay PB if the outlet is engaged whereupon the switch will he stepped to positionlfl Since there" are odd and even outlets in the groupin thisxposition, on release of relayHT'both relays PA'an'd PB will be operated over wiper and bank 3d and cross connection to banks 21 and P22 respectively and at armatures pal and phi relay HT will be re-operated.

If the odd outlet isfree relay PA will hold and relay HA will operate to switch connection through in the normal manner, while if the even outlet is. free relay PB will hold and relay HB will switch the line through. If both outlets are freeboth relays PA and PB will hold butrelay HA in operating will cut ofi relay HB at armature hail thereby giving priority to the odd set 01.

wipers.

If bothoutlets are engaged relays PA and PB will releaseand will cause the magnet RM to advance the'wipers to position 10 in which are situated the lasttwo outletsin the groups If Tooth the outlets in this position are engaged the wipers will be advanced to the 11th position.

. In this position a circuitis completed to operate relay PB over :a connection made between the contact on which wiper 3d is resting and terminal G since this is the last level to be hunted over and at armature plat the driving circuit is opened whilerelay HE is operated from earth, armature p322 and the windings of relays PB and HR to battery resistance YC whereupon relay J will be operated in the normal manner to return busy tone to the callingsuhscriber.

Should the switch be set by the dialled im-.

pulses, on any of the lines ,in the group except the first, the switch will test this line only and i will not perform a hunting operation if it is busy.-

Thus on release of relay C there Willjbe no earth extended to operate relays PA and PB since terminal A is only connected to the first lineof the group and therefore relaysI-IT and HS will not be operated to prepare for further rotary hunting. If the desiredline is free relay HA or rm will operate according towhether relayWS is operated or not, when the operation will proceed in a normal manner. If, however,=theline is'engaged, on release of relay Efollowing that of relay C, a seli interrupted driving circuit will be completedior the uniselector magnet DM as follows: earth, armature o2, contacts N4 and NR2, armature hsll, armatures e5, haB, hbS bE and MI contacts rm, armatures M3, 3 and hsA,

contacts om, armatures rk'i and b3, bank Id, uniselector interrupter contacts dm, magnet DM to battery. This switch thereupon self-drives to the home position 1 where relay PA is operated over wiper and bank lid to open the drive circuit and at thesame time operates relay HT which in turn tacts N4 and NR2, armatures hst, e5, hat, hbS,

b5, and htl contacts rm, armatures 12b3, p113 and 7284, contacts N3, armatures ha? and hbl, magnet RM to battery. The wipers are thereupon rotated to the 11th position where an earth marking is extended over wiper and bank 4d to operate relay PB which cuts the drive in a normal manner. Relay HE is then operated in series with resistance YC andin turn operates relay J when busy tone will be returned to the calling subscriber. It should be mentioned that a similar condition is brought about when a call is made to a group comprising a single line, that is to say, -on release of relay E. a driving circuit will be completed for the uniselector magnet DM and the operation proceeds as above described.

On release of the connection at the conclusion of conversation, when the calling party hangs up relay A releases and releases relay B and other relays previously. held operated are released in turn.. A circuit is then completed from earthed delayed alarm equipment which is connected up over common lead ll via the resting contacts of all relays and bank and wiper id to home the uniselector and when this reaches the home position 1 a circuit is then completed to self-drive the magnet RM which advances the wipers to the 12th position where they are restored to normal in the manner previously described.

A substantially constant initial unguard period which is represented by the release time of relay C is provided on the incoming release trunk conductor to enable the preceding switches to be restored to normal with the minimum of delay. When the switch reaches normal the restoration of. the off normal springs removes the guard earth from the incoming P conductor at con tacts N I.

A buzzer connected to common lead H in conjunction with test jack springs T! and armature hb5 enables the set of wipers in use during conversation to be readily determined without removal of the dust cover from the switch.

If the calling party should fail to restore his receiver after the called party has hung up earth will be extended over armatures d4 and f2 to light the lamp LP in series with delayed alarm equipment connected to common lead 12.

Referring now to Figs. 3 and 4 these show a circuit diagram of a 200 outlet group selector which is adapted, by the provision of an auxiliary switch of the uniselector type to perform repeated hunting operations at predetermined intervals over single lines, adjacent lines forming a single group and lines of a group having a plurality of sections distributed over various levels. After a predetermined number of researches arrangements may be made to stop the hunting and to return busy tone to the calling party. Facilities are also provided whereby any pair of odd and even hundreds outlets in the group except the first may be dialled when busy tone will be returned if they are both found to be engaged, no

distributed anywhere over the levels of the.

switch, the only limitation being that a pair of odd and even outlets on any level must belong to the same group. A maximum of twenty-two outlets on each level is available, due to the inclusion of the 11th step busy contacts which are normally used in such switches for returning busy tone to the calling party and the switch has therefore a maximum capacity of 220 outlets.

For the purpose of description it will be assumed that a particular group comprises thirty outlets, twenty-two of which occupy the whole of level 3 and of the remaining eight, four occupy the first two and four occupy the last two odd and even outlets on level 8. repeated hunting. over this particular group may take place the cross connections shown in the drawings between banks GM2, 3 and t and terminals A to E are necessary. Terminal A connects with all contacts on the SW bank which represent the position of the odd and even outlets making up the group, while terminal B connects with a contact on the M bank representing the position of the first pair of outlets in the group and which is therefore in this example connected up to contact I in level 3. The connections to the other terminals can be seen from the drawings, whilst the purpose of the cross connections to the GM banks will be appreciated in the ensuing description.

Considering now the circuit operation, on seizure the loop extended over the incoming negative and positive conductors operates relay A which vthereuponin turn operates relay B. Relay B in operating at armature b2 operates relay In order that the C on its lower winding and at armature b3 re-' places the idle resistance battery marking potential normally extended on to the incoming P conductor by a guard earth, while at armature b5 a dial tone transformer is connected up over common lead 1 l to the middle winding of relay A to extend dial tone in a balanced circuit to the calling party.

On dialling the first digit 3 relay A responds and impulses the magnet VM and accordingly the switch wipers are raised vertically to level 3.

On the first vertical step the off normal springs N are operated and at contacts N2 prepare an operating circuit for relay E, whilst at contacts N3 a circuit is prepared for the rotary magnet RM. Contacts N2 also disconnect the energising circuit of relay C but this relay remains held on its low resistance upper winding due to its slug during the impulse train, while similarly relay B remains held due to the slugging efiect produced by the short circuiting of its winding on each release of armature al.

At the end of the train of impulses relay C releases after a short interval and at armature cl operates relay E and this relay thereupon locks at armature el independently of the armature cl, re-operates relay C on its lower winding at armature eZ and at armature e6 prepares the impulsing circuit for the rotary magnet RM. On re-operation of relay C at armature 03 an enermagnet VM tobattery and accordingly the switch wipers are raised vertically while at armature 03 the magnet GMM is agains'energized and at armature 05 the winding of relay-PA is connected to the vertical bank VB in preparation for arresting the vertical motion of the switch atthe next level to be hunted over, in this case level 8. On the first vertical step theN springs are again operated and'at contacts N2 open the energising circuit of relay C which however remains held during the vertical motion on its upper winding due to its slug. i When the switch reaches level 8 earth is extended over wiper and bank GMZ and cross connection to terminal C, vertical bank VB, wiper VW and armature 05 to battery via the winding of relay PA which accordingly quickly operates and opens the driving circuit. After a further short interval relay Creleases and at armature 03 it de-energises the magnet Glmvl whereupon the GM wipers are advanced to position 12., In this position the outlets in the group on level 8 are marked over wiper GM i whilst the wiper GM2 marks level 3 so that in this case if all the outlets in the group onlevel 8 should be found busy the switch on restoring to normal would again step vertically and cut-in on the original level dialled" whereupon the cycle of operations would recommence. Should the group overflow to a still further level the GM2 wiper in position 12 would mark the next level to which the switch should be raised to continue the search. Relay C in releasing also at armature c5 releases relay PA when a self-interrupted driving circuit is completed for the rotary magnet RM from the earthed lead Ill, armatures 1102, m3, slat and c2, interrupter contacts rm, armature e5, hb2, hyl, 71:12 and haul, ofi normal contact N3, magnet RM'to battery. During the rotary hunting operation whilstthe switch is passing over contacts of the group an earth feed is supplied to relays HX and HY over the SW wiper and bank so that if a disengaged outlet in the group is encountered one'or other of these two relays will be operated to cut the drive.

If all outlets in the group on level 8 are engaged the switch will rotate to the 12th position and will restore to normal. In the normal position relay C is again operated and initiates the vertical hunting. On reaching level 3 relay PA is operated to the marking extended over wiper GM2 in position 12 and arrests the vertical motion and .on the subsequent release of relay C a driving circuit .is completed for the rotary magnet BM in a normal manner whilst the GM magnet which has been previously energised during the vertical motion is now released and advances the GM wipers to position 13. In this position wiper GlVM extends an earth marking to terminal B which connects with the first line of the group on the M bank whilst an earth is extended over wiper GM2 and cross connection to terminal E to operate relay RS which locks at armature rs2 and at armature r34 prepares a circuit to release relay SK. On the first energisation of the magnet RM the wipers are cut in to the position to which they were set by dialled impulses but there is now no operating earth extended to relays HX and HY since there is no strapping connection from contact l3 on the GM bank and terminal A. Earth is however extended over armature sk5, GM i, wiper in position 13, cross connection to terminal B and bank and wiper M tooperate relay PA which at armature pa2 armature slcii whilst at armature 3702 a circuit is completed to operate relay E over armature cl,-

contacts N2 and armature 272 to earth whilst at armature ski) the earth lead Hi is now transferred to wiper and bank GM! whereupon the GM switch self-drives to the home position 1 where the driving circuit is opened. Earth is new extended over armature e l, wiper GM3 in position i and armature rst to relay TP which is connected up to common lead it extending to time pulse equipment. that a pulse of battery potential is applied to this lead at predetermined intervals which might be, for example, of the order of 12 seconds and henceion reception of the next pulse relay 'IP is operated and at armature tpl it energises the magnetGMM and at armature tp2 it energises the magnet 5PM of a small stepping switch SP whilst at armature i103 it opens the circuit of relay RS which releases after a short interval. On release of relay TP the magnets SPM and GMM are de-energised whereupon the wipers are advanced to position 2. The GMi wiper in this position now completes a self-driving circuit for the magnet GMM and the wipers are thereupon rotated until they again reach original position 11 where the earthed wiper 6M3 extends a marking to operate relay PA which cuts the drive. At armature pal relay SK is now re-operated and this relay at armature $102 releases relay E, at

armature slcii extends earth to relays HX and HY and at site completes a driving circuit for the It will be understood magnet RM on release of relay PA by the armature at. The whole cycle of operations now recommences and is repeated at predetermined intervals until a free outlet in the group is found.

The switch SP is advanced one step before each researching operation and it is arranged that if no free outlet in the group is found after a predetermined number of such operations a circuit is completed from earth, armature sic5,

wiper and bank SP1, to'battery via relay RN. This relay in operating at armature m3 opens the earth feed to the driving magnets while at armatures mi and m2 busy tone and flash is connected up over common conductors l2 and I3 respectively to the windings of relay A and thence to the incoming speaking leads to inform the calling subscriber or operator that all outlets in the group are engaged.

If the switch should be set by the dialled impulses on to any line of a group except the first, relay PA will not be connected up to the bank GM3 since the cross connections thereto are only made from first lines of groups. The Gm switch will therefore rotate until it reaches the last position when an earth will be extended over armature ed, wiper and bank GM3, and armature rsl to operate relay PA and cut the drive. Relay PA in operating operates relaySK in the usual manner when an earth will now be extended over armature slc5 and wiper and bank GM i to operate relay RN which further opens the driving circuit at armature m3. In the meantime if one or other of the pair of outlets on to which the outlets were found to be busy they will have failed v to operate and thus on operation of relay RN busy tone will be returned to the calling party over the resting armatures of relays HB and HA;

When the parties clear at the end of conversation earth is removed from the release trunkconductor thereby releasing either relay HA or HE.

A self-interrupted driving circuit islnow completed for the rotary magnet RM from the earthed lead l0, armatures pa2, m3 and slcfi,

the uniselector is generally wiper GMI in the home position 1, armature b4.

SP switch cit-normal contacts SPNi, rotary magnet interrupter contacts rm,, armatures e5, hbZ', 'hyl, heal and haul, contacts N3 and magnetRM to battery, and accordingly the wipers are rotated clear of the banks from where they restore to normal when the off-normal contacts N3 in restoring open the driving circuit. The restoration of the contacts N4 now extends a resistance batterypotential over armature b3 on to the incoming P conductor to renderjthe switch available for further use. p

A buzzer connected to common lead M in conjunction with test jack springs TI and armature 71b6, readily enables the set of wipers in use during conversation to be determined without removal of the cover.

In the arrangement described sumed that a uniselector is provided individual to each switch but the invention also contemplates making the uniselector common to a numberof switches, it being borne in mind that the uniselector is only in use for short periods of time. t 'f The invention is not necessarily limited to the employment of a uniselector as a two motion or up and around switch might be used in its place as will be readily understood. A'uniselector is usually of small capacity and as the invention in the majority of cases will. only require the use of a small capacity switch, it will be seen that of contacts arranged in levels accessibleover two different paths, a plurality. of lines accessible to said switch through groups of adjacent contacts of non-adjacent levels, means for setting said switch to one of said groups, means for testing the lines associated therewithand means efl'fecit has been, as-

speaking the more tive when all of a group ofadjacent contacts is found busy and 'whenthe, switch is seized over a certain one of said paths only to cause the switch,

to be'reset to another group of said plurality of lines. v

2., In an automatic switching arrangement, a two-directional hunting switch having access to groups of lines divided into non-adjacent subgroups, means for settingsaid switch toa certain sive theretoior testing lines 'of the sub-group and causing the switch to be advanced, when a sub-group of a particular grouppmjeansresponbusy line is encountered, and means effective in one instance when the last line of a sub-group is found busy to cause the switch-tobe resetfto another sub-group of said particular group and without resetting the switch. J v

3. An automatic switching: arrangement .a

sub-group is found busy to cause the switch to be reset to said certain sub-group; l I 4. Inan automatic switching arrangemehhfia divided intosub-groups accessible to said switch,

means for settingthe switch to test the lines of 30 I a certain 'oneof said sub-groups, an auxiliary switch associated with said hunting switch operated when all the lines of a sub-group are busy v to'control the resetting of said huntingswitch to the next sub-group, said auxiliary switch operj ated when all lines of said group are busy to controltheresetting of saidhunting switch to available and means responsive to thetestingof said group of lines aplurality of times for, ren-r 'deringsaid signalling means efiective. i 5. An automatic switching; arrangement as claimed in claim 2, whereinan auxiliary switch is included in said last-named. means to mark the position to which said hunting switch is to be 5 1 reset.v i

6. An automatic switching arrangement as,

claimed in claim 4, wherein the "encounterof an idle line, during any of .thetesting operations is l effective to restore said auxiliary switch and said lastnamed meansto normal.

; my EGiNAiD TAYLOR.

'GEORGETHOMAS BAKER."

jcrmRLEs-GILmNGs.

r35 said certain sub-group, means "for repeatedly t I testing saidsub-groups, signalling means for indicating that'noneof the lines of thegroup are 25 two-directional hunting switch, a group of lines

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