US1821998A - Circuit arrangement for automatic and semiautomatic telephone exchange systems - Google Patents

Description

Sept. 8, 1931. E. P. G. WRIGHT- 1,821,998

CIRCUIT ARRANGEMENT FOR AUTOMATIC AND SEMIAUTOMATIC TELEPHONE EXCHANGE SYSTEMS Filed March 28, 1930 5 Sheets-Sheet 1 4 Ass FIG. l-A

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ATTORNEY Sept. 8, 1931. E. P. G. WRIGHT 1,821,993

CIRCUIT ARRANGEMENT FOR AUTOMATIG AND SEMIAUTOMATIG TELEPHONE EXCHANGE SYSTEMS Filed March 28, 1930 5 Sheets-Sheet 2 CC C:

'r In} INVENTOR ESMOND EC. WRIGHT WM'M- ATTORN EY E. P. e. WRIGHT 1,321,998 T FOR AUTOMATIC AND SEMIAUTOMATIC.

Filed March 28, 1930 5 Sheets-Sheet 3 INVENTOR ESMOND PG. WRIGHT ATTORNEY w h o v v n nlinL 'WT X v 33 E In. I x v .3 1 mxm w It! E n23 E nmfiw WIN |.fl|||v Mn; I u xw l QUE a m n w v n m Sept. 8, 1931.

cmcun' ARRANGEMEN TELEPHONE EXCHANGE SYSTEMS n1- H L hmx L, g1 v. I"... r 8m: 9? Elm: I nT- 1. mm: wwx M h G3 NOE Sept. 8, 1931. E P wm 1 821,998 C CIRCUIT ARRANGEMENT FOR AUTOMATIC AND SEMIAUTOMATIC TELEPHONE EXCHANGE SYSTEMS Filed March 28, 1930 5 Sheets-Sheet 4 INVENTOR ESMOND FPG. WRIGHT BYZ/WWQ ATTORN EY G. WRIGHT 1,821,998

OMATIC AND SEMIAUTOMATIC Sept. 8, 1931. E. P.

CIRCUIT ARRANGEMENT FOR AUT TELEPHONE EXCHANGE SYSTEMS Filed March 28, 1930 5 Sheets-Sheet 5 INVENTQR ESMOND PG. WRIGHT 8Y7 ATTORNEY ofiice and to two or more groups of local trunk lines.

Fig. 2 shows a first conversation group finder switch for use in calls local to the main olfice.

Fig. 3 shows an incoming conversation group finder switch for use at the incoming end of a two-wire junction from the satellite ofiice.

Fig. 4 shows a control circuit which is common to one or more local first group finders as shown in Fig. 2 and one or more incoming group finders as shown in Fig. 3. The control circuit comprises a control switch R1 equipped with wipers and banks 4, 5, 6, 7, 8 and 9 and a bye-path switch R2 equipped with wipers and banks G, M2, M1, T2, T1, +2, +1, 2, 1. Certain positions of the switch R1 are used for effecting a marking in the bank of the bye-pass switch R2, contacts in the bank 9 in these positions being suitably strapped to the terminals in the control bank 0 or" the switch E2, whilst other positions are used for operatively associating the control circuit with a particular local or incoming group finder switch over banks 4:, 6, 7, 8, 9. Bye-path conductors extend from the terminals of the banks 1, 2, +1, +2 of the switch R2 to control circuits at the succeeding switching stage and bye-path test wires extend from the terminals of banks T1, T2 to conversation finder switches at the succeeding switching stage. The terminals in the marking banks M1, M2 are multipled to corresponding terminals in the marking banks of the associated conversation switches.

Fig. 5 is a schematic layout diagram showing the apparatus involved in difierent types of call and the relative positions of the apparatus illustrated in Figures 1 to 4. The apparatus located at the main ofiice is shown above the broken line whilst that at the satellite ol'lice is shown below this line.

Figure 6 is a schematic diagram illustrating a further application of the invention.

A brief general description will first be given of the operation of the system shown in Fig. 5.

Assuming a subscriber S2 in the satellite ofiice B removes his receiver to make a call his line is extended over first and second line finders SLFl, SLF2 to a free switching selector repeater SGF associated with a free control circuit SBP. The switching selector repeater SGF selects a unction J terminating in an incoming group finder JGF having associated with it an idle control circuit lBP at the main exchange A. The first digit is repeated over the junction J and also advances the switch R1 of the control circuit SBP, and if this digit is not one signifying a call local to the satellite ofiice B, the control circuit SBP is released and subsequent digits are repeated over the junction J. It the first digit corresponds to that signifying a local call, the control circuit SB]? is held and the switch R1 responds to the second digit which is also repeated over the junction J. If this digit is not one of those allotted for local calls the control circuit SBP is released and the switch SGF functions solely as a repeater. If however the second digit is one of those which in combination with a particular first digit signifies a local call, the switch R1 of the control circuit marks a group of trunks in the bank of the switch R2, which advances to this group and hunts for an idle final finder switch SF F having an idle associated control circuit SF BP On the engagement of such a final switch the switch R1 is again advanced to connect the control circuit SBP with the selector repeater SGF which is then advanced to the trunk selected by the switch R2. The third and fourth digits are repeated over a wiper of the switch R2 and a byepass conductor to the switch R1 of the control circuit SF BP which marks a wanted line S3 in the bank of the switch R2. When this line is engaged by the switch R2, the switch R1 associates the control circuit SFBP with the final finder SFF and a test is made of the condition of the wanted line in the control circuit SFBP. If the wanted subscriber is engaged, a busy signal is given from the switching selector repeater SGF whilst if the line is free the final finder SFF-is advanced to it and ringing current is supplied from the selector repeater SGF. The control circuit SBP is released when the R1 switch of the control circuit SFBP has picked up the final finder SFF. The release of the control circuit SBP brings about the release of the control circuit SFBP. Talking current is supplied to both the calling and called parties from the selector repeater SGF.

Assuming that the call was to a subscriber S1 in the main ofiice A the first digit dialled sets the switch R1 of the control circuit lBP which marks the wanted group in the bank of the switch R2, which commences to ad- Vance immediately the impulses start arriving. The switch R2 searches for an idle second group finder 2GF having an idle associated control circuit 2BP and at the same time the switch R1 hunts for-the first group finder JGF which is to replace the bye-pass. The group finder JGF is then set on the trunk selected by the switch R2. Meanwhile a second digit is passing over the bye-path switch R2 to the control circuit 2BPat the second switching stage, which operates in similar manner to the first stage selecting circuit. The control circuit lBP at the first stage is released when the control circuit 2BP at the second stage has become operatively connected to the predetermined finder switch 2GB over the wipers of the R1 switch at that stage. The finder switch 2GF is then ad vanced to the trunk selected by the R2 switch associated with the control circuit 2BF. At the final selecting stage the R1 switch of the selected control circuit 3BP responds to the tens and units digits and marks a Wanted line S1 in the banks of the R2 switch. When the wanted line is engaged by the R2 switch, the R1 switch associates the control circuit 313]? with the selected final finder FF and a test is made of the condition of the wanted line in the control circuit 3131 If the wanted line is busy, a busy signal is given from the switch QGF, whilst if the line is idle the finder S3 is advanced to it and ringing current is applied from the switch QGF. The control circuit 2BP is released when the R1 switch of the control circuit 313]? has picked up the final finder FF. The release of the control circuit 2B1 brings about the release of the control circuit 8131?. Talking current is supplied to the calling and called parties from the switches SGF and QGF respectively.

In the case of a call from a main exchange subscriber S to another main exchange subscriber S1, the calling line is extended over first and second line finders LFl, LF2 to an idle local first group finder lGF associated with an idle control circuit 1131 The control circuits lBP are associated with both local group finders lGF and incoming group finders JG-F the proportion of one to the other being governed by traffic requirements. The connection is extended over a second group finder QGF and a final finder FF as described in the previous paragraph. Talking current is fed to both parties from the switch QGF.

The circuits will now be described in detail with reference to typical calls.

Local call within satellite ofiice The satellite selector repeater, Fig. 1A. with its associated control circuit Fig. 1-13, is taken into use from a preselector circuit and is tested through the wire T, contact (151 and 7281 of the selector and contacts 61, the home contact and wiper 1- of the switch R1 of the control circuit through a protective resistance to battery. If the circuit is found to be free by the preselector circuit that circuit will reduce the potential on the common point between contacts Z)81 and b1 and consequently cause the control circuit to test busy to other preselector circuits. When the preselector circuit has completed connection to the calling subscriber ground will be placed on the wire K causing the operation of relay KS. A circuit is also completed for relay AS from battery and the lower winding of relay AS over the subscribers loop to the upper winding of relay AS and ground. Relay AS completes the obvious circuit for relay BS and at the same time the following circuit is completed for relay B :Battery and winding of relay B contacts 7L1, .21, K83, asl, to ground. Relay BS closes a circuit at conr tacts 682 for the left-hand winding of a shunt field relay 11S. R'elay B completes the circuit for the conversation switch magnet 'S through its interrupter springs M2, 7686, m l, b8, '02, #3, and Z96 toground, and at contacts 62 closes a locking circuit for relaye KS via contacts 22, c2, (and g in parallel) and RS2. At the same time a testing circuit is prepared for relay V through its righthand winding and contacts M2, K87 to the test wiper T of the selector repeater. Each of the 1 outgoing junctions from the satellite ofiice to the main oifice is allotted a pair of relays J B and J T and when relay B of the control circuit operated a ground potential was placed over contact 67 and the winding of the common relay G0 on one side of all the relays J B which are normally connected to the negative sides of the respective junctions. All junctions which are engaged will be characterized by the fact that the J Trelay is op- @5 erated and in consequence if the junction is in use there will be no circuit for relay J B since its circuit will be open at contacts jtl. Referring now to Figs. 3 and 4 which for the present case should be placed Fig. 3 above E30 Fig. 4, the negative line will be connected (if the incoming conversation group finder is free) through contacts 2Ks1, Fig. 3 and 2M1 to the test wire 3 of the control circuit Fig. 4 and if the latter circuit is free there 935 will be a battery potential applied tothis test wire via Qttl, 2tt3, 2391, 291, 2611, 265 which will cause the operation of relay J B in the satellite ofiice. Relay G0 which is marginal will. also operate from battery in the 2100 control circuit associated with the incoming selector switch. Relay GG is so adj ustcd that two of these relays will not operate in multiple should a call be made simultaneously from a second satellite office having unctions terminating in incoming selectors associated with the same control circuit. Relay J B at contacts y'bl prepares a circuit for relay J T over which relay V in the control circuit is operated over a common lead, contacts gcl to battery when the test wiper of the selector repeater reaches an idle junction as indicated by the energization of relays JB and GC. Relay V in operating opens the driving circuit of the selector S at 02 and closes a locking circuit for itself via its left-hand winding and contacts 411, H3, 66. Relay J T which operates in series with relay V, holds over a circuit through contacts y'tQ when the relay J3 rest-ores and a parallel circuit is closed through the right-hand winding of relay V and contacts 65, 113, 94, R89 to relay Hs which also operates in series with relay V. Contacts hsS, places a ground potential from Z983 on the test wiper T and also completes a loop over the negative and positive wires through 7:84, Z89, (188, upper winding of relay Is, Z83, right-hand winding of relay DS, Z36, lower winding of IS, Z912 and he?) causing the operation of relay QKS in the incoming conversation finder, Fig. 3 from battery on the test wire 3. Qhsl, 21081, negative line through the loop at the satellite selector repeater to the positive line, contacts 27682, winding of 2K8, contacts 2Hs4 to ground. Relay QKS will operate and close its light contacts 2KS5 thereby completing a locking circuit for its lower winding. The negative and positive wires are switched through at contacts 27ml, @7682 respectively to the control circuit associated with the incoming conversation switch where relay 2A operates and closes an obvious circuit for relay 213. here necessary this control circuit may be arranged to feed back dialling tone which will be transmitted over the junction and through the satellite selector repeater to the calling subscriber.

If all the junctions are busy the selector continues stepping until it engages the first idle local outlet beyond them, when relay V energizes in series with relay G over the circuit right-hand winding of V, $252, Rsi', wiper T and test contact of selector, wiper and contact of bank 8 of switch R1, and relay G. All the contacts of this bank 8 are strapped together except those in the positions corresponding to local calls. Relay G opens at contacts 4 the circuit of relay HS which relapses, and at contacts 1 opens one parallel path in the locking circuit of re lay KS.

If the digits dialled indicate that the call is for the main office relay Z operates as already described and at contacts Z2 opens the other parallel path in the locking circuit of relay KS, the relapse of which disassociates the control circuit. Busy tone is applied to the negative line over lead RT and contacts 7681, hsl.

If the digits dialled indicate that the call is local to the satellite the switch R1 is stepped to a position in which the circuit of relay G is opened at bank 8 and this relay relapses before the release of relay C. Relay Z does not respond and the call proceeds in the usual manner.

lNhen the calling subscriber commences dialling the relay AS responds and at each impulse a circuit is made from the magnet R1, contacts b3, 63, ml, winding of relay C, k5, RS4, Z284, cs2 to ground causing the switch R1 to take one step for each of the impulses. The relay O is of the slow releasing type and remains up during the impulses. The forward loop to the incoming group finder. Fig. 3 interrupted at contacts cs3. Relay CS is energized in parallel during impulsing and at contacts 082 short circuits relays IS, DS to improve the impulsing loop condition. If the first digit dialled is not one signifying a local call the wiper 4 of the switch R1 will come to rest in a position to complete a circuit for the relay Z through contacts 205, bank contact and wiper 4 of the switch R1, the interrupter springs RINT2 of the switch R2 contacts '01 to ground. Relay Z in operating opens at contacts 21 the circuit of relay B which at 62 opens the locking circuit of relay KS causing the latter to release. Relay KS disconnects the control circuit and the relapse of relay C closes a restoring circuit for the switch R1 over ]L3, be, off-normal contacts and wiper of bank 3, interrupter springs RINTl and 01. The satellite selector now acts solely as a repeater repeating the impulses at contacts cs8 over the forward loop.

If the first digit corresponds to that signifying the local call, in case illustrated the digit 3, the switch R1 or" the control circuit, Fig. 1-13 is advanced to a corresponding posltion and on the relapse of relay C completes a circui for the relay through contacts 103 ank contact and wiper 4 of the switch R1 interrupter springs RINTQ of the switch R2, contacts 01 to ground. Relay W locks u through 204, the oli' normal contacts and wiper 8 of the switch R1, the interrupter springs RINTl of the switch R1, contacts 01 to ground. A circuit is also closed for the magnet of the switch R1 through contacts 7L3, Z23, 102, the off normal contacts and wiper of the bank 3, interrupter springs RINTI of the switch R1, contacts 01 to ground, which will cause the switch to stop until it reaches position 12, in which position the contact in bank 3 is not strapped to the other contacts since contacts 105 are open. In this position also the locking circuit for relay is opened causing that relay to release. The second of impulses will cause the switch R1 to step before and if the second digit is not one signifying a local call the relay Z will be operated and cause the release of the control circuit as already described. If, however, the second digit corresponds with a second digit allotted to local calls, in the present instance the digit 5 or 6, a circuit will be completed for the magnet R2 through contacts 7L6, g2, m1 bank contact and wiper 4-, the illterrupter springs RINT2 of the switch R2, contacts 01 to ground. The switch R2 will continue stepping until its wipers arrive at the beginning of a group of outlets marked by the switch R1 where a circuit is completed for the relay M through contacts #5, wiper C of switch R2, marking wire to bank 7 of the switch R1, '04, e7, protective resistance to battery. When relay M operates the circuit for the magnet R2 is opened at 0721 and a circuit is closed for the relay E which operates via m2 and bank 4 of the switch R1 and locks to ground through 63 and 66. The operation of relay E opens a circuit for relay at 67 thus restoring the driving circuit of the magnet R2 which continues stepping and testing each outlet via the following circuit :-Ground 52, 5/3, right-hand winding of relay H, (26 to the test wiper TO. A free ion a ground potential on the test wiper TC to mark that outlet busy to other control circuits. Relay H opens at b6 the circuit of the magnet R2 and at 71 1 a circuit is closed for the magnet R1 through contacts t2, interrupter springs RINTl of the switch R1, contacts 01 to ground causing the magnet to step round until the relay T is operated through contacts 61, wiper and contact 2 of bank 2 of the switch R1, K82, g1, 62, to ground. Relay T besides opening the driving circuit of the switch R1 at 752 closes at 251 an obvious circuit for relay TT. l/Vhen the relay F operated the circuit or relay HS was opened at and [L83 removes the ground from the test wiper T making relay JT dependent upon the circuit over the grounded winding of relay V and contactstti, R87. When relay TT operates the circuit for both windings of relay V is opened at contacts i232 and tt3 and both the relays V and JT release. The operation of TT also closes the circuit for the magnet S of the selector through contacts hSQ R86, m4, ]L9, 64 and ttl to ground, causing the selector to again commence stepping. The bank contacts of the selector engaged by the wiper M are multipled directly with the control bank contacts of the control switch R2 and when the selector reaches the terminal on which switch R2 is standing a circuit is completed for relay M through tt6, wiper and contact of bank 6 of the switch R1 and wiper and contact of bank M of the selector, bank contact and wiper MG of the switch R2, to protective resistance and battery. Relay M opens at m4 the circuit of the selector S and places a ground poten tial through ttl, 64, 72 9, m4 and R87 on the test wiper T. During this time the remain ing digits will be passed forward to the final'selector control circuit over the following impulse circuit :-a81, R83,- 21, b2 and negative wiper of switch R2. The final selector which is identical with that shown in Fig. 4. of the copending application referred to, extends connection to and tests the wanted line as described in'that specification. If the required subscribers line is busy the final selector control circuit will remove the ground which it placed on the test wiper TC and cause the release of the relay H but no ground potential will be fed back to the test wiper T of the satellite selector and consequently when relay H releases relay KS will also release and busy tone will be fed out to the calling subscriber through contacts R81 and ksl. Relay KS disassociates the control cir cuit from the selector and the relapse of relay H closes a restoring circuit for the switch R1. The switch R2 is a non-homing switch. If, however, the called subscribers line is free before the relapse of KS and H there will be a ground potential fed back over the test wiper T which will be extended through K87, M8, [L8, 412, M4 through wiper and contact of bank 5 of the switch R1 to the relay LS which will operate and look through Z810 and B86 to ground. Relay LS will close an obvious circuit for relay HS which at h81 disconnects busy tone. The ringing circuit is now completed through contacts f84, Z88, hs, positive line through the subscribers loop to the negative line, contacts ILS5, Z811, f86 to ringing relay lead RR. hen the called subscriber answers relay FS operates and locks up through f82 and 683 to ground. The calling subscribers loop is extended through f83 and fs5 to a transmission feed provided from contacts Z84 and Z85 through the windings of the relay IS. The operation of IS closes the circuit to the subscribers message register through contacts Z82 and 2'82 and wire M. At the end of the conversation when the calling party hangs up, relays AS and BS release. The release of relays LS, IS, FS, HS follows and the homing circuit for the magnet S is closed through the interrupter springs, contacts 7Ls2 K85, and wiper N and oil normal bank contact to ground. A circuit is also closed for relay CS through contacts 685 to ground through the wiper N. Relay CS remains operated until the switch has gone back to normal. Relay CS opens the incoming test circuit at CS1.

If all the outlets of a wanted group available to the switch R2 are engaged the wiper C closes the circuit for the relay G on the last contact of the group through the contacts e8. Relay G operates in series with the relay M which opens the driving circuit of themagnet R2 at m1. Relay 9 opens the test circuit at 3, at 94 unlocks relay HS and at 91 opens the locking circuit of the relay KS which releases, disconnects the control circuit and connects busy tone to the calling line, as already explained.

. OaZZ from sateZZz't-e office to main ofice 2 1, 2191, 2M3, 261, to ground. At the first impulse, relay 2A releases but relay 2B being of the slow release type, remains operated and completes a circuit for the magnet 2R1 through 263, 252-, winding of relay 2C and I 2a1 to ground. At the end of the impulse relay 2A reoperates and the switch 2R1 steps into posltlon 2. In position 2 the circuit for relay 2M is opened by the wiper 9 and when "1 operation of the former.

2H releases a circuit is completed for the magnet 2R2, through its interrupter springs, 267, 22221, wiper and home position of the bank N2 of switch 2R2, 2G1, and 261, to ground. The switch 2R2 takes a step and continues stepping by means of its own interrupter springs and the off normal contacts of the bank N2, to ground at 265 until relay 2M reoperates. The switch 2R1 takes one step for each impulse received from the subscribers dial and the strapping between the banks 9 and 2C is so arranged that the circuit for 2M is completed whenever the 28-2 switch reaches the commencement of the group corresponding to that on which the 2R1 switch is standing. hen the digit is completed, relay will release after a period and when relay 2M operates due to the switch 2R2 hav ing reached the position indicated by the bank 9, relay 2M will operate as already described and a circuit will then be completed for relay 2E from battery and winding of relay 2E, 293, 203, 2762, wiper and off normal contacts of the bank N2, E5 to ground. Relay 2E will close its light contact 2610, and lock over its second winding to ground at 261. 2611 opens the circuit for relay 2M which releases and recloses the driving circuit of the 2R2 switch through 267, 2127.1, wiper and ofi normal contacts of the bank N2, 264, 1, 2291, 26253, to ground at 261. Contacts 2613 and 2614 close the testing circuits for relays 2(1); and 2P respectively, and one orboth of these relays will operate it the outlets on which the wipers are resting are free. It relay 2P alone operates the driving circuit of the switch will be opened at 2191 and at 2192 a circuit will be closed for relay 2H which will lock up via 2H5 through 22363 to ground at 261. I1 relay 2g operates a driving circuit of the switch will be opened at 291 and at 292 a circuit will be closed for relay 2J which will operate and closes at 271 a circuit for relay 2H which will also operate. 265

will provide a locking circuit for both the 291, 2721, 2223, 261 to ground.

Relay2M will open the driving circuit of the switch 2R2 at 27221 and close at 2m2 a circuit for relay 2G through 267. Relay 2G is of the slow to operate type and will not operate during the period when both relays 2E and 2M are operated during the initial However, on the last contacts of the group the circuit for relay 2G is maintained and this relay will eventually operate and connect at 299 the busy tone over wire BT to the calling subscriber.

1; RVhen relay 2E operated a circuit was completed for the switch 2R1 through 262, the interrupter springs, and 261 to ground. This will cause the switch 2R1 to continue stepping until the relay 2T operates through wiper and bank contact 4, and contacts 2K83, 2684. It will be understood that there is no more than one finder accessible to this control switch with a ground potential on a contact in bank 4. When relay 2T operates the obvious circuit is closed for the relief relay 2TT. At contacts 2222 a locking circuit is provided for relay 2T. When both relays 2TT and 2H are operated due to the fact that the switch 2R2 has found a free outlet in the required group and the switch 2R1 has found the finder which it has been predetermined will complete the call, a circuit is completed for the finder magnet 28 through bank contact and 7, 27223, 2225, and 268 and at the same time a ground is extended through 2666 and the wiper and bank contact 9, to the finder wiper 2M and when the finder wipers stand on the outlet corresponding to that on which the switch 2R2 has switched through, the ground on the finder wiper M will be extended to the control wiper M2 or m1, 274, 2j5, 2613, to relay 2M. The operation of 2M opens the circuit for magnet 2S at 2m3 and closes the circuit for the relay 2G via 267, 2m2 the off normal bank N2, 264, 291, 2191, 2223 to the ground on the testwire. Relay 2G will operate and close the circuit for relay 2HS through bank contact and wiper 6, 291, 2964, 26235, 268, to ground. Helay 2HS will operate and 2686 will extend ground over the H wiper to the H wire of the succeeding finder in order to mark that switch to the succeeding control. Contacts 26 82 and 2683 will prepare the permanent circuit to replace the bye-path. The control switch does not release until the ground potential is removed from the T wire by the succeeding control circuit. When the relay 2H operated the circuit for relay 2A was opened and relay 2B released also after a short period. Relays 2E and 2T were maintained, however, over 232, 269, 2013 or 2j3, 2612, 2014, by the ground potential on the test wire which is maintained by the succeeding control circuit under the control of the calling subscribers loop. WVhen the succeeding finder removes ground from the T wire, relays 2T and 2E release and subsequently relays 2TT, 2M and 2H release. When relay 2H releases the homing circuit for the switch 2R1 is completed through 263, 263, 266, off normal contacts and wiper of bank 5, interrupter springs, 2t1, to ground. In a similar way the homing circuit for the switch 2R2 is completed through 267, 27221,

wiper and off normal contacts N2, 265, to ground. \Vhen both these switches have returned to their home positions, the battery is re-connected to the test wire through 265.

Should it happen that the subscriber fails to dial, a circuit will be completed from ground on the pulse lead A through the home contact and wiper of the bank 6, 293, 2126, 2227, to the relay 2G which will lock up to 294:, 202, 261 to ground. After some predetermined period a second pulse will be received over the pulse wire B, wiper and home contact of bank 10 of the switch 2R2, 292, to relay 2E. Relay 2E on operating will lock through 2010 to ground at2b1 and open the circuit for relay 2G at 266. Relay 2P will operate from ground at 261, through 297,2h11, 2e14, wiper and home contact of the T1 bank to protective resistance and battery. Relay 2P will cause the operation of relay 2H and the subscribers loop will be switched via 2h1 and 2h3, 2j6 and 2y'8 through the home contacts of the banks 1 and +1 298 and 261, back to the relay 2A. WVhen relay 2E operated, it closed the driving circuit of the magnet 2R1, as already described and this switch will step forward until relay 2T operates. Relay 2T will close a circuit for the relay QTT, as already described, for the finder magnet 2S. lVhen the finder has been driven to the terminals corresponding to those on which the switch 2R2 is standing (that is the home terminals), relay 2M will operate and a circuit will be closed for relay 2G through 267,27722, wiper and home contact of the bank N2, 2M4, 2H5, and 2h8 to ground. 291 closes a circuit for the relay QHS which is maintained through 2hs6, H wiper and home contact of the finder S, home contact and negative wiper 2hs2, subscribers loop 2h83, positive wiper and home contact, to ground. The operation of 298 opens the circuit for relay 2A which releases and opens the circuit for relay 2B. Relay 2B in turn opens the circuit for relays 2E,

2G, 2H and 2T causing the switch 2R1 to return to normal. The finder relay QHS is maintained operated over the subscribers loop until the subscriber releases.

The connection is extended over a penultimate group selector and a final selector in the manner described in British application No. 3264:8/28 with reference to Figures 3 and 4 of that specification.

It will be seen that the relay QKS Fig. 3 remains locked up until relay 2H8 operates. In the case of a premature release therefore provision must be made to ensure that the relay 2H8 is operated.- The contacts 2X84 holds the control circuit, Fig. 4, engaged by providing a holding circuit for relay 213 so that if the calling party releases prematurely the control circuit is held until the conversation finder has been advanced and the switching relay QHS is energized.

Call between two subscribers in the main ofiic'eA The calling line is extended over first and second hne finders in known manner a local first group finder Fig. 2 with its associated control circuit Fig. 4 being tested over the wire T, Fig. 2 contacts hsQ, conductor 3, Qtzfl, 2M4, pl, 91, 2e11, the wiper and home contact oi the bank 9 of the switch R1, the home contact and wiper of bank C of the switch R2, 265 to protective resistance and battery. It the circuit is found to be free by the preselector circuit, that circuit will reduce the potential on the common point between hs2 and 2tt1 and consequently cause the control circuit to test busy. When the preselector circuit has completed connection to the calling subscriber, a ground potential will be placed on the wire K causing the operationof relay KS. A circuit is now com pleted for relay 2A from battery and one winding of relay 2A, 2712, conductor 1, K82, negative wire, subscribers loop, position wire K88, conductor 2, 27A, second winding of relay 2A to ground. Relay 2A completes the obvious circuit for relay 213 over 2a2 and relay 2B opens the testing circuit at 265 and closes a locking circuit for KS through Qbl, conductor 4 and K85. Relay Ks grounds the hold wire H over contacts K84 and K81.

The control circuit, Fig. l, receives the dialling impulses and controls the extension of the connection over the group finder, Fig. 2,

as described for the previous call, the switching relay HS operating when the line selected by the R2 switch has been found and switching through the talking wires and grounding the hold wire H at contacts hs5 preparatory to the removal of the ground over the conductor 4 when the control circuit is released.

The remainder of the operations in extending the connection are similar to those described in the previous call.

It will be appreciated that the method of testing for idle junctions terminating in incoming finders with free control circuits may also be applied in arrangements where incoming group finders at the incoming ends of junctions from two or more distant ofiices are associated with the same control circuits. Figure 6 shows such an arrangement in lay- 'out.' A number of junctions A from one office terminate in incoming group finders AGF similar to that shown in Figure 3 and a number of junctionsB from another office terminate in incoming group finders BGF also similar to that showniin Figure 3. The finders AGF and BGF are associated with a number of control circuits BF comprising the usual R1 and R2 switches, each control circuit serving a number of junctions from each of the ofiices A and B. In this manner the junctions are arranged in large groups with respect to the control circuits Bl? this arrangement permitting the use of fewer control circuits than would be the case. if control circuits were provided individual to the junctions from the respective offices.

WVhat is claimed is:

1. In or for an automatic or semi-automatic telephone system one ormore conversation selector switches for use at the incoming end of a two wire junction from a distant oflice, one or more conversation selector switches for completing local connections and one or more common control circuits associated with and arranged to control the operation of both the incoming and local conversation selector switches.

2. In or for an automatic or semi-automatic telephone system, one or more conversation selector switches for use at the incoming endof a two-wire junction from a distant oflice one or more conversation selector-switches for use at the incoming end of a two-wire junction from a second distant oflice and one or more common control circuits associated with and arranged to control the operation of the selector switches at the incoming ends of the junctions from both oilices.

3. In a circuit arrangement comprising a selector switch having access to a group of junctions terminating in incoming selector switches which are operated under the control of common control circuits means operated on the seizure of said selector switch for first making a simultaneous test of said junctions and control circuits whereby idle junctions terminating in incoming selector switches associated with idle control circuits are marked selectable and means for causing said seized selector switch to conduct a hunt for one of said marked junctions.

4. The combination with a plurality of conversation satellite office selector switches having access to oflice junctions and to local trunks of a control circuit comprising discriminating means adapted to respond to one or more digits and if such digit or digits are indicative of a local call to cause a switching device associated with said control c rcuit to select an idle local trunk and provlde a bye-path for succeeding impulses! 5. In or for an automatic or semi-automatlc telephone system a plurality of conversatlon satellite otfice selector switches having access to oiiice junctions and to one or more groups of local trunks, a control circuit common to said conversation selector switches and provided with means for testing said local trunks, means for causing a conversation selector switch to make a search for an idle ot'ice junction when taken into use, and thecriminating means in said control CIICUIt which responds to one or more digits and either causes said control circuit to be freed or causes a switch in said control circuit to select an idle local trunk and to provide a bye-path for succeeding impulses.

V 6. A telephone system comprising a dlstant oiiice, a local office, two wire junctions extending between said offices and incoming selector switches, local selector switches and common control circuits for said switches at said local oflice and means adapted to prevent the selection of a two wire junction to an incoming selector switch or a trunk to a local selector switch when the control circuit associated with the incoming or local selector switch has been taken for use with another associated incoming or local selector switch.

7. A telephone system comprising a plurality of distant oiiices, a local office, two wire junctions extending between the local office and said distant otiices, incoming selector switches and common control circuits therefor at said local office and means adapted to prevent the selection of a two wire junction from either of the distant ofiices when the control circuit associated with the incoming selector switch has been taken for use with an other associated selector switch at the incoming end of a junction from either of said distant ofiices.

8. A telephone system comprising a distant oflice, a local oflice, two wire junctions extending between said oiiices, and incoming selector switches, local selector switches and common control circuits for said switches at said local office wherein a switch comprised within one of the common control circuits is adapted under the control of received impulses to select a trunk which serves as a bye-path for succeeding impulses until a predetermined associated selector switch has advanced to the selected trunk.

9. A telephone system according to claim 8 having a relay in said control circuit wherein said selected trunk is adapted to be marked in the bank of said predetermined associated selector switch over a wiper of the switch in the common control circuit and wherein said predetermined associated selector switch is adapted to be advanced to said marked trunk under the control of said relay.

10. A telephone system comprising two otiices, two wire unctions extending therebetween, selector switches and common control circuits therefor at one of said oiiices and means adapted to test said junctions and said control circuits simultaneously.

11. A telephone system comprising a plurality of oflices, two wire junctions extending therebetween, incoming selector switches and outgoing selector switches in which said unctions terminate and means whereby the free or engaged condition of said junctions is not indicated in the banks of the outgoing selector switches until one of the latter is taken into use.

12. A telephone system comprising a plurality of oiiices, two wire junctions extending therebetween, incoming and outgoing selectors in which said junctions terminate and common control circuits therefore wherein a battery potential is adapted to be normally applied to one of the talking conductors of a junction from the control circuit associated with an incoming selector if both said selector and control circuit are free, a relay having its winding normally connected to said conductor at its outgoing end and means adapted to connect a ground potential to said winding when an outgoing selector is taken in use, said relay being adapted to apply a selectable potential to a test contact in the bank of the outgoing selector.

13. A system in accordance with claim 12, wherein said ground potential is adapted to be applied from a common control circuit associated with the outgoing selector switch.

14. A system in accordance with claim 12 having a second relay, wherein said selectable potential is adapted to be applied over a winding of said second relay, and wherein said second relay is adapted to be operated when the corresponding junction is selected and to disconnect said first mentioned relay from the junction to hold the junction busy from its outgoing end.

15. A system in accordance with claim 4 wherein said control circuit is provided with a switch, said switch being adapted to respond to one or more digits to bring about the release of said control circuit.

16. A telephone system comprising a main oflice, a local office, junctions extending therebetween, main oflice and local oflice selectors at said local ofiice having common control circuits associated therewith, one of the control circuits for the main office selectors having two switches, one of said switches adapted to respond to one or more digits to cause the second of said two switches to select an idle trunk to an idle local oflice selector which has associated therewith an idle control circuit which is adapted to control the setting of the selector at the next selecting stage.

17 A system in accordance with claim 16 wherein in the case of a local call said first mentioned switch is adapted to mark a wanted group of local trunks in the contact bank of the second mentioned switch, causing the latter to select an idle trunk therein.

18. A system in accordance with claim 16 wherein said first mentioned switch after responding to a first digit is adapted to move to a predetermined intermediate position and wherein, in response to a second digit said switch is adapted to be advanced to a further position in which a group of trunks in the contact bank of said second mentioned switch vanced to the selected trunk under the control of said relay.

20. A system according to claim 16 wherein said selectors are each provided with an impulse responding relay which is adapted to repeat impulses directly to the stepplng magnets of the first mentioned switch of said two switches comprised within the control circuit.

21. A telephone system comprising a main office, a satellite oifice, local selectors and control circuits therefor at the satellite olfice wherein talking current is fed from a local selector for a talking connection set up between two subscribers associated with said satellite ofiice.

In witness whereof I hereunto subscribe my name this sixth day of March 1930.

ESMOND PHILIP GOODWIN WRIGHT.

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