US1901940A

US1901940A - Telephone exchange system

Info

Publication number: US1901940A
Application number: US495062A
Authority: US
Inventors: Esmond P G Wright
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1929-12-18
Filing date: 1930-11-12
Publication date: 1933-03-21
Anticipated expiration: 1950-03-21

Description

Mam? 1933- E. P. e. WRlGHT TELEPHONE EXCHANGE SYSTEM Filed Nov. 12, 1930 9 Sheets-Sheet l nvz/avmi? E19 6. WRIGHT 77IMM ATTORNEY March 2-1, 1933- E. P. G. WRIGHT TELEPHONE EXCHANGE SYSTEM Filed'Nov. 12, 1930 9 Sheets-Sheet 2 N Gt INVENTOR 5. a. WRIGHT ATT RNEV v March 21, 1933. E, P. G, WRIGHT 1,901,940

TELEPHONE EXCHANGE SYSTEM Filed NOV. 12, 1930 9 Sheets-Sheet 3 INVENTOR P.G.WR/GHT ATTOR EV March 21, 1933- E. P. cs. WRIGHT v 1,901,940

TELEPHONE EXCHANGE SYSTEM Filed Nov. 12, 1930 9 Sheets-Sheet 4 IN VE N TOR E.P. G. WRIGHT BY A T TORNEY E. P. G. .WRIGHT TELEPHONE EXCHANGE SYSTEM -March 21, 1933.

9 Sheets-Sheet 5 Filed Nov. 12, 1930 lllllll INVEN 70/? 5P. 6. WRIGHT By A TTDR/ME) March 21, 1933- E. P. G. WRIGHT 1,901,

TELEPHONE EXCHANGE SYSTEM Filed Nov. 12, 19,30 9 Sheets-Sheet 6 l l l I 8 8 //vv/v TOR 1 P. G. WRIGHT March 21, 1933. E, "P. G. WRIGHT 1,901,940

TELEPHONE EXCHANGE SYSTEM Filed Nov. 12, 1930 9 Sheets-Sheet '7 //v l ENTOR E. P. G. WRIGHT A TDR Y March 21, 1933. E. P. (5. WRIGHT TELEPHONE EXCHANGE SYSTEM Filed Nov. 12, 1930 9 Sheets-Sheet 8 08: l l l l l l l l I l I l 000:8 I u I I I l I l I I l uaoo ve ill l ill .lllll llllli Ooneeool II II. \lllI-l Ill llllll ooooooo l I I cuuo IN VEN TOR E. R a. WR/GH r ATTOR Y March 21, 1933. E. P. G. WRIGHT TELEPHONE EXCHANGE SYSTEM Filed Nov. 12, 1930 9 Sheets-Sheet 9 lNl/ENTOR '.P. G. WRIGHT BY WPB m 9m ATTORNEY Patented Mar. 21, l3 3 ESIVIOND E.

WEIGHT, OF CROYDON, ENGLAND, ASSIGNOR '10 VIESTEBN ELECTRIC COMPANY, INCGBPOBATED, OF NEW YORK, N. Y., A CORPORATION OF HE /V YORK TELEPHONE EXCHANGE SYSTEM:

Application filed November 12, 1930, Serial No. 495,062, and in Great Britain December 18, 1929.

This invention relates to telephone exchange systems and more particularly to measured service telephone systems in which metering is effected automatically in accordance with the zone within which the called subscribers station is located with respect to the calling subscribers station.

The object of this invention is to provide simple and efidcient means for determining and registering the charge to be made on calls to different points all of which are reached in part over a single group of trunks.

According to this invention means are provided for controlling the operation of a selector switch so that the brushes are advanced to the same group of trunks in response to pulses corresponding to any one of a plurality of digits. For instance on calls completed in part over a single group of trunks to a tandem point the dialing of any of several different digits is effective to cause selection of this group of trunks.

Another feature of this invention resides in an arrangement whereby a single group of trunks is selected in response to impulses corresponding to any one of a plurality of digits, these impulses being at the same time effective to determine the charge to be made for the establishment of the call, the charge being varied according to the number of impulses received. Thus in extending calls to and through a tandem oilice the transmission of any one of several dili'erent digits causes the selection of the same group of trunks to the tandem oi'i'ice but the charge to be made for each call depends upon its destination beyond the tandem other: and this is indicated by the number of impulses received.

The features of this invention will be better understood from the following description of a telephone system in which the invention is applied. This system, which is shown diagrammatically in the drawings. is a controller bye-path system equipped with a register-translator for use on certain classes of calls. It is understood, however, that modifications and other applications of the invention will readily occur to one skilled in the art.

Referring to the drawings:

Fig. 1 shows a subscribers station A and line circuit LC, a primary finder LFl, a secondary finder LFQ, a group and start unit G, and a pre-selector D.

Fig. 2 shows a first selector stage comprising a conversational switch CS1 with which the secondary tinder of Fig. 1 is permanently associated, and a bye-path control unit 01 which is common to a group of conversational switches including the one shown. The conversational switch is separated from the control unit by the broken line.

Figs. 3 and 4 show a second selector stage comprising a conversational switch CS2 and a second stage bye-path control unit G2 which is common to a group of switches including the switch CS2. The broken line separates the conversational switch from the common control unit.

Figs. 5 and 6 shows register-translator unit RT which is common to a plurality of second stage control units including the unit C2.

Figs. 7 and 8 show an intermediate selec tion stage comprising the conversational switch CS3 and a bye-path control unit G3 which is common to a group of switches in cluding the switch CS3. The broken line separates the conversational switch from the control unit.

Fig. 9 shows an outgoing trunk repeater 'Tll i for use on calls to tandem oflices.

Fig. 10 indicates how Figs. 1 to 9 are to be placed to form the complete system to which this description relates.

Referring to Fig. 1, A represents a subscribers station which is equipped with a subset of the usual type having a dial for use in automatically establishing telephone con nections. The line from this station terminates at the exchange in a line circuit LC, in the banks of primary finders, such as LFl,

' and also in the banks of connector switches,

which are not shown. The line circuit LC includes the usual line and cut-ofi relays and also includes a message register. The subscribers lines are divided into groups and there are as many lines in a group as there are sets of terminals in the banks of the primary line finders. The primary finder switches comprise 100 point single-motion step-by-step switches of the no-normal type having two sets of wipers arranged 180 apart, each wiping over an arc of 50 terminals during one complete revolution of the switch shaft. The finder LFl includes a stepping magnet and the brushes numbered 11, 12 and 13 together with corresponding banks of terminals.

The lines in each group are mnlt-ipled to the banks of as many primary finders as are required to handle the trailic from that group. 1; group unit is associated with each group of lines; this unit includes a start relay 6 for starting an idle pie-selected secondary finder in search of a primary finder whenever a call is originated over any of the lines in the group.

Zhe secondary finccr switches are similar to the primary finder switches; the finder LE2 includes a step ing magnet and brushes numbered ll t 46 inclusive together with corresponding banks of terminals. The secondary finders are linked to conversational switches of a first selecting stage and are divided into groups each of sufiicient size to handle the trailic which will be directed through them. Each secondary group is arranged to search for a differentprimary finder in each of the primary groups. Associated with each group of secondary finders is an allotting and controlling switch D which pre-selects an idle secondary finder linked witl a first stage selector and having an associated control circuit which is also idle. Preferably, therefore the number of pre-selecting switches is equal to the number of groups of secondary finders and to the number of primary finders in each group. The pie-selector D which include the stepping magnet 20 and the brushes numbered 21 to 28 inclusive together with corresponding terminal banks. is also a single-motion step-by-step switch having no normal position.

hen a subscriber originates a call, the starting relay in the associated group circuit marks all the primary finders serving the group in which the call originates, and starts a set of secondary finders, which have been preselected by the switches D, in search of an idle primary finder. These secondary finders hunt until two of them have reached marked primary finders; and those two primary finders then hunt until one of them finds the calling line.

The conversational switch CS1 of the first selecting is a 100 point single-motion stcp-by-step switch having a stepping magnetand wipers 51 to 54; inclusive. together with corresponding banks of terminals. The control unit C1 comprises a control s vitch 1L, a bye-path switch and an associated group of relays. The control switch R1 is a 50 point step-by-step single-motion switch, the terminals being strapped so that in one complete revolution of the switch there are as which the calling line is connec many cycles of operation as the capacity of the switch permits; this switch includes the stepping magnet and wipers numbered 61 to 65 inclusive together vith corresponding banks of terminals. The bye-path switch R2 is a 100 point single-motion step-by-step switch having a stepping magnet and wipers numbered Tl to 76 inclusive together with corresponding terminal hanks. There are two sets each of the wipers designated 71, 72, 73 and 74, both sets being eil ective to simultaneously wipe over corresponding banks of terminals. Certain groups of po sitions of the switch 1 .1 are used to effect a marking in the bank of the byepath switch R2, the terminals in these positions of the bank 65 being connected as required to the terminals in the control bank 75 01" switch Qther groups of positions of switch R1 are used for operatively connecting the control circuit with a particular conversational switch to which a calling line has been er;- tendcd a id through which the control circuit is receiving impulses created by the opcration of the chat. at the calling subscribcrs station; the terminals in these ions of marking banks 74- are multipled to corresponding terminals in the marking ank oi all the conversational switches s the control unit C Outgoing talkin r ductors extend from the ban I the conversational switches of the switching stage. Correspoi ding l test conductors extend from the ban] 4 and 73 of bye-path switch to the svxi t hes of the succeeding switching Holding conductors extend irom tl e terminals in the bank 53 of switch CS1 to the conversatioinil switches of the succeeding switching stage.

The c ntrol switch is advanced under control of the impulses created by the dialing ot the first digit of the called number to corresponding position; whereupon the byepath switch P1 is advanced to the groupof terminals thus marked in the banks T l. The switch is then advanced automatically to select a set of terminals in the marker the test terminal of which is connected through an idle conversational switch oi the succeeding selecting stage to an idle control unit. The incoming impulse leads are thus immediately extended through brushes 71 and 72 to the succeeding bye-path control circuit. The R1 switch is then again i vanced until it finds the terminals of the versational switch of the first selectin group.

lVhereupon the switch CS1 is advanced un its test brush 54; makes contact. wi .11 t marked terminal corresponding to the set terminals selected by the bye-path switch Both the control and conversational connections are thus extended to the succeeding lecting stage.

The conversational switch CS2 of the second selecting stage, shown in Fig. 3, is similar to the switch CS1 of the first selecting se; it includes the stepping magnet 100 and the brushes 101, 102, 103 and 104 together with corresponding banks. The control unit C2, shown in Figs. 3 and l, includes the control switches and El /l3 and the byepath switch RM2. The control switch Rlvll is sim lar to the control switch R1 of the ing stage; it includes the stepg magnet 110 and the brushes numbered 111 to 119 inclusive, together with corresponding banks of terminals. The bye-path switch B l is similar to the hye-path switch R2 or" the first selecting stage; it includes the stepping magnet 120 and the brushes numbered 121 to 126 inclusive together with corresponding banks of terminals. The control switch REE?) is similar to the bye-path switch 3M2: it includes the stepping magnet 140 and the brushes numbered 141 to 148 inclusive together with corresponding banks of terminals.

T he register-translator unit RT, shown in igs. 5 and 6, includes a finder switch RF *v means of which the register-translator may be connected to any one of the group of second stagecontrol units with which it is associated. It also includes a code switch a num rical switch NS, three sets of e. clays, and a sender switch SM. The

' a single-motion step-byhaving no home position; it has magnet 200 and brushes numbered 0 inclusive, together with correbanlrs of terminals. The code singleunotion step-by-step normal position; it has a tenning magnet 220 and brushes numbered nn l i 221 to 225 "ml sive, together with corres nc'inp oanlis of terminals. The numerica switch I? S is a single-motion step-bystep switch having a normal position; it has stenpin. magnet 2&0 and brushes numbered 24'! inclusive, together with correg )anks of terminals. There are sets or register relays numbered rec-ively from 251 to 25% inclusive, from to 264- inclusive and from 271 to 27 1 in- These sets register respectively the n hundreds, and tens digits of a number in accordance with corrending advances or" the numerical switch The units digit of a called number is istered by the numerical switch and does need to be transferred since all of the mpulses have then been received. The

r switch SM is single-motion stepswitch having a normal position; it eppinsr nagnet 280 and brushes num- I o 285 inclusive together with cording banlts of terminals.

The second stage control unit receives the second and third digits of the office code, and

luring receipt of the third digit a starting signal is extended to a number of registertranslators causing their various finder switches RF to search for the control unit from which the starting signal was received. The second office code digit is stored by the EM3 switch under control of switch 3M1, and the bye-path switch Rh/l2 selects the corresponding outgoing trunk group under control of switch RM3. Switch El /l2 then automatically selects an idle set of terminals in this group, the test terminal of which leads to a conversational switch of the succeeding selecting stage. The third office code digit is stored by the RM3 switch.

If the call is a local call the register-translator is released as soon as the connection is extended through the bye-path switch RM2 to a succeeding local selecting stage. If the call is an interofiice call reached over direct trunks and an idle trunk is immediately avail able, the register-translator is also released as soon as the connection is extended through the bye-path switch 3M2; but it an idle trunk is not found before the next digit is dialed, the numerical digits are stored in the registertranslator and retransmitted by its sender switch to complete the connection. If the call is one which may be completed over alternative routes,that is, either over a direct trunk selected by the bye-path switch RM2 or over a trunk selected at the intermediate outgoing selecting stage, the register-translator is released if an idle direct trunk is immediately available. But, if all direct trunks are busy, the ofice code digits are retransmitted by the control unit C2 to the register-translator at the same time that the numerical impulses are being received; the control unit C2. then operates to advance the bye-path switch RM2 to a group of terminals connected to an intermediate outgoing selecting stage, and the completion of the connection is controlled by the register-translator. If the call is one which is completed only through the intermediate selecting stage, the oliice code and numerical digits are received by the register-translator and the bye-path switch RM2 advances to the group of terminals leading to the intermediate selecting stage. If the call is one which is completed through a tandem ofice, the intermediate selecting stage is effective to select the group of trunks which lead to this tandem oliice although the impulses transmitted by the register-translator to control the selection are varied in accordance with the particular called office to be reached through the tandem point.

The intermediate selecting stage, shown in Figs. 7 and 8, comprises a conversational switch CS3, a bye-path control unit C3, and a metering control switch Z. The control unit C3 comprises a control switch and a byepath switch IE2. The switches CS3, IE1 and IE2 are similar to the switches CS1, R1 and R2 of the first selecting stage shown in Fig. 2.

The switch CS3 has a stepping magnet 300 and brushes numbered 301, 302, 303 and 304 together with corresponding banks of terminals. The switch 1R1 has a stepping magnet 320 and brushes numbered 321 to 327 inclusive, together with corresponding banks of terminals. The 1R2 switch has a stepping magnet 350 and brushes numbered 351 to 355 inclusive, together with corresponding banks of terminals. The Z switch is a single-motion step-by-step switch having no normal position; it has a stepping magnet 370 and brushes numbered 371 to 374 inclusive, together with corresponding banks of terminals. The selecting operation of the outgoing stage is completed in response to impulses received from the register-translator of the second switching stage in a similar manner to that in which the selecting operation of the first stage is completed in response to the impulses created by the dialing of the first digit of the ofiice code. The IE1 switch is also effective to operate the charge control relays 307 and 308 of the switch CS3 according to the position to which the P51 switch is advanced by the impulses from the registertranslator. lVhen the superv ory relay 306 of the switch CS3 operates 1 consequence of the answer of the called subsc r. a starting signal is transmitted to the charging switch Z whereby this switch, which is common to a group of conversational swi ches such as CS3, hunts for and connects to the particular switch whose supervisory relay has operated. The charge control circuit is then effective, under control of

relays

307 and 308 of the conversational switch to operate the calling subscribers register the required number of times.

The outgoing truck repeater TR shown in Fig. 9 transmits the remaining impulses sent out from the register-translator RT over the outgoing trunk to the distant tandem oi'iice T. The tandem oiiice may be equipped with any of the well known types of automatic telephone apparatus which responds to incoming trains of impulses corresponding to the number of a called station.

The selecting stages for completing local calls or for completing calls which do not make use of the intermediate selecting stage are not involved in the description of this invention and therefore they are not illustrated in the drawings. For the same reason reference to the operation of the second selecting stage and register-translator on these types of calls will be omitted, as far as possible.

The operation of the system shown in Fi 1 to 9 inclusive will now be described, giving detailed attention to a. call which is routed through a tandem oflice.

When the subscriber at station A removes the receiver to originate a call, an obvious circuit is closed over line 1 for operating the line relay 2. Relay 2 connects the windings of the cut-oil relay 3 over conductor 5 to mark the sleeve terminal of the line 1 in the banks of the associated group of primary line-finder switches. Relay 2 also closes a circuit for operating the start relay 6 in group circuit G.

Relay (3 connects the windings of relay 7 over conductor 9 to the marking terminal in the bani-ts of all secondary finders in the asso ciated secondary group. Start relay 6 also connects ground at its outer front contact, through the outer back contact of relay 7, over conductor 8 to operate the start relays such as relay 31, of all the idle distributor switches. One of these operating circuits is traced from conductor 8 through the normally closed contact of the left-hand continuity springs of relay 3d, left-hand back contact of relay 36 to the winding of start relay 31. Relay 31 closes a circuit for operating relay 32, from ground at the right-hand bacl: contact of relay 35, through the right-hand front contact of relay 31, winding of relay 32, brush 27 of the distributor switch, ver conductor 48, eft-hand back contact of relay 55, over conductor (37 to the common control unit- C1, through the outer left-hand back contact of relay conductor 93, back contacts of relays S6 and 87, conductor 92, inner right-hand back contact of relay 85, brush 65, and normal terminal of switch R1, normal terminal and brush 75 of switch R2, right-hand back contact of relay 82, and through resistance 79 to battery. As soon as this circuit is closed the drop in potential across resistance 79 is suiiicient to prevent the selection of any conversational switch in the associated group by another preselector, similar to D, which is hunting for an idle secondary finder as hereinafter described. Relay 32 closes a circuit from battery through the winding and interrug iter contacts of the stepping magnet l-O of switch LFQ, brush 26, right-hand front contact of relay 32, inner right-hand back contact of relay o6, inner left-hand back contact of relay 34, to ground at the back contact of relay Thus relay 32 and the corresponding relay, of each of the distributor swftches which is connected to an idle secondary line-finder, the control circuit of which idle, close the energizing circuit for the stepping magnet of the associated secondary line-finder switches. Relay 32 also connects ground through its outer left-hand front contact, the neXt-to-th -outer righthand back contact of relay 36, winding of test relay 33, and through brush 23 of the distribntor switch to brush 45 of the secondary line-finder switch with which the preselector D is connected.

T he secondary line-finder LF2 is advanced under control of the stepping magnet -l0 from one terminal to another until the brush 45 reaches the marking terminal to which conductor 9 is multipled, whereupon test relay i for operating relay i tact of relay 3?. inner righthand I e left-hand front a t. isconnecti grcun 3 from tne winding of relay 31.

d o 'ated to the ground at th co L of relay Rewill not operate in relay 33, but when rolled by another dis- 'es the marked pritwo test relays 31 ate and dis the It apparent, therefore, 7 finders continue to hunt 111 have sci' ed primary finders yin recess to the calling line. he secondary finder stops on the terof a prii. a, tinder which is already engaged, the relay 3 operates in a circuit ich may be trace. fronrbattery through wii'iding, neXt to the inner right-hand back contact of relay 36, inner left-hand front w contact of relay 32, brush of distributor switch D brush 44- of finder LFEZ terminal the ousy primary line-under, through the tiple wiring to the correspondlng ternal in the bank of another secondary lineiinder which has alreac y ectahlished connec- 1 this primary finder, over a conducspanning to conductor 47, to ground nt cont-act of the relay correspondthe secondary finder switch condvance. A primary finder will be 'nto use, however, if it is idle even if ng on a busy line, since in this case the brush d lwill not be connected to ground at a busy conversational switch.

aforementioned operation of relay 3% c oses a circuit for the stepping magnet he primary find-er LE1. This circuit e traced from battery through the windi and interrupter contacts of magnet l0, te mal and brush 46 of line-finder L1 2, terminal and brush of banl: 21 of thdistributor switch D, through the outer right-- front contact of relay 34, to ground at the left-hand back contact of relay 35. When t in ay b 5/ one of the two hunting primary finders engages the terminals of the calling lines, a circuit is closed from battery through the windings of cut-ofi relay 3, in parallel with the winding of the message register l, over conductor 5, through the terminal and brush 13 of line-finder LFl, terminal and brush 43 of line-finder LFQ, terminal and brush 22 of distributor swit D, and through the lefthand winding of relay to ground at the neXt-to-the-inner right-hand front Contact of relay Relays 3 and 35 are operated by the current in this circuit but the message register a is marginal and does not operate at this time. Gut-off relay 3 releases line relay 2 by disconnecting its Winding from the line 1. Relay 2 in turn causes the release of relay 6 unless this relay is held operated due to the origination of call over one or more of the other lines in the group. Relay 35 looks in a circuit from battery through its righthand winding, and through thenent-to-thv outer right-hand front contact of relay 34, to ground at the left-hand front contact of relay 35. Belay 35 opens the circuit for operating the stepping magnet of the primary finder LFl, opens the circuit through tae winding of relay 32, and closes a circuit from battery through the winding of relay 36, through the middle right-hand front contact of relay 34.- to ground at the left-hand front contact of relay 35 lhe primary finder IE1 is thus stopped on the terminals of the calling line, relay 32 releases, and relay 36 operates. Relay 36 opens the circuits through the windings of relays 31 and 33 to cause their release; and relay 31 cannot thereafter reoperate if the origination of another call in the same group should cause ground to be reconnected to conductor 8. Relay 31 opens the circuit through the winding of relay 34; and with relays 32 and 34 released, relay 36 is held operated through the normally closed contacts of the right-hand continuity springs of relay 3%, inner right-hand front contact of relay 36, over conductor 29 to ground at the back contact of relay 32. The release of relay 34 causes the release of relay 35. Relay 36 closes a circuit for operating relay 56 of the conversational switch CS1 associated with the secondary line-finder used in extending this connection this circuit may be traced from battery through the winding of relay 56, over conductor l9, through the terminal and brush of bank 28 of distributor switch D, and through the middle left-hand front contact of relay 36 to ground at the right-hand front contact of relay 35.

The aforementioned release of relay closes a circuit from battery through the winding and interrupter contacts of step ingina enet 20 of distributor switch B, through the left-hand front contact of relay 36 F l ir-to-theanner lert-hand hacl: contact or 34, over conductor 29 to gro'und at the left-hand back contact of relay 32. The distributor switch D is thereby advanced to preselect an idle secondary finder whose control circuit is also idle in readiness for the next call. lVhen the terminals of such a secondary finder are reached, relay 32 operates in a circuit from ground at the right-hand back contact of relay 35, outer left-hand front contact of relay 36, winding of relay 32, brush 27 and terminal of switch D, over conductor 48, through the back contact of relay 55 of the associated conversational circuit, over conductor 67 to the associated control circuit, and thence to idle battery in av similar manner to that hereinbefore described for the operation of relay 32 upon the origination of a call over line 1. Relay 32 opens the circuit for stepping magnet 20 and opens the locking circuit for relay 36. The release of relay 36 in turn ca'uses the release of relay 32. Should the distributor switch D engage a secondary finder which, although idle, has been preselected by another distributor switch, relay 37 is operated, l eiore relay 36 releases, in a circuit from battery through he winding of relay 37, next-to-the-inner right-hand front contact of relay 36, brush and selected terminal of bank 24, through the brush 2% of the preselector which has already selected this secondary finder, to ground at the outer righthand front contact of the relay which corresponds to relay 36. Relay 37 connects ground from the outer right-hand front contact of relay 36 through the right-hand front contact of relay 37 to conductor 29 to hold relay 36 operated and thus continue stepping the preselector brushes past this terminal. Relays 32 and 37 release when the br'ushes are advanced so that the preselector continues to hunt until another idle secondary finder is reached.

The aforementioned operation of relay 56 extends the connection from the calling line 1, through brushes l1 and 12 of primary finder LFl and brushes $1 and 42 of secondary finder LF2. right-hand front contacts of relay 56, conducc (3S and outer left-hand back contacts of relay 88, to the windings of impulse relay 81 of the control unit Cl. Relay 81 operates thereby closing an obvious circuit for operating relay 32. Relay 56 also connects ground throi its left-hand from contacts, through brush of line-finder LF2 and brush 13 of line-finder LFl to hold the cut-off relay 3 of the calling subscribers line operated, and thus prevent release of the connection. Relay 82 connects ground at its outer left-hand front contact to conductor 93, thereby locking relay 56 through its winding and right inner front contact. Relay also opens the test circuit over conductor 6. and through resistance 7 9, so as to prevent the seizure of any other conversational switch associated wi h the control unit C1. Relay 8% now operates in a circuit which may be traced from battery through its winding, right outer back contact of relay 88, next-tothe-inne right front contactof relay 82, brush and normal terminal of bank of switch B2, normal terminal and brush (35 of switch R1, inner right back contact of relay 85, over conductor 92, through the back contact of relays 8'? and 86, over conductor 93 to ground at the left outer front contact of relay 82. The secondary winding of transformer 30 connected through the mid :lle left back contact of relay 85, in parallel with the leftnand winding of relay 81 so that dial tone 1S transmitted to the calling subscribers station as an indication that dialing of the called number may be in.

i l en the calling subscriber dials the first i reeases and reoperates each time the line circult is opened and closed at the dial contacts. Relay 82 is a slow-to-release relay and res operated during the receipt of the ntire train of impulses. The release of relay 1 closes a circuit from battery through the OOKD winding of magnet 60 of switch R1, through tie left outer back contact of relay 85, left inner front contact of relay 82, winding of relay 83, to ground at the right-hand bacl: contact of relay 81. Magnet (30 and relay 83 both operate in this circuit. Relay 83 is also a slow-to-release relay and holds operated during receipt of the entire train of impulses. The reoperation of relay 81 causes the release of magnet 60, thereby advancing the switch into position Belay releases when the brushes of switch R1 advance from position 1, the normal position. Each release and reoperation of relay 81 thus causes the peration and release of magnet 60 thereby advancing the brushes of switch R1 to a position which corresponds to the digit dialed.

The aforementioned release of relay 8i, when the brushes of switch R1 are advanced from position 1 to position 2, closes a circuit from battery through the winding of stepping magnet 70 of switch R2, middle right hand back contact of relay 88, interrupter cont-acts of magnet 70, right-hand back contact of relay 8st, brush and normal terminal of bank 76 of switch R2, front contact of relay 83, and through the back contacts of relays 87 and 86 to ground on conductor 93. When magnet 70 operates, the circuit through its winding is opened and magnet 70 releases, thereby advancing the brushes of switch R2 to position 2. lVith switch R2 in any position other than its normal position the connection from the winding of magnet 70 to brush 76 is extended through the off-normal terminals of bank 76 to ground at the right outer back contact of relay 85. Switch R2 is thereafter advanced under control of its own interrupter contacts until relay 84 reoperates as hereinafter described. The terminals in bank 65 of switch R1 are connected lit) to the terminals in bank of switch R2 in such a manner that the circuit for reoperating relay 84 is completed whenever the R2 switch reaches the beginning of the group which corresponds to that on which the R1 switch is standing after all of the impulses created by the dialing of the first digit have been received( The circuit for reoperating relay 84: may be traced from battery through its winding, right outer back contact of relay 88, right outer front contact of relay 82, brush 75 and terminal of switch R2, the corresponding terminal and brush of bank 65 of switch R1, inner right back contact of relay 85, over conductor 92, and through the back contacts of relays 87 and 86 to ground on conductor 93. When relay 8% reoperates in this circuit, it opens the circuit for operating magnet 70 to stop the brushes of switch E2 on the first set of terminals in a group which corresponds to the first digit dialed by the calling subscriber.

The reoperation of relay 84 closes a circuit for operating relay this circuit may be traced from battery through the left-hand winding of relay 85, left outer back contact of relay 91, left-hand back contact of relay 83, right-hand front contact of relay 84, brush and terminal of bank 76 to ground at the right outer back contact of relay 85. Relay 85 closes a locking circuit through its right-hand winding and inner right-hand front contact to ground over conductor 93 before the circuit through its left-hand winding is opened at its outer right-hand back contact. The operation of relay 85 causes the release of relay s4 and connects the windings of test relays 86 and 87 to test brushes 78. If the first set of terminals of the selected group are idle, one or both of test relays 86 and 87 operate, depending upon which of the brushes 73 is in contact with an idle set of terminals. The circuit for operating relay 86 may be traced from ground on conductor 98, through the right outer back contact of relay 91, winding of relay 86, left inner back contact of relay 88, neXtto-the-outer right-hand front contact of relay 85, lower brush 7 3 and first terminal in the selected group, over conductor 98, left outer back contact of relay of the selected conversational switch CS2 in the next switching stage, over conductor 106 to the associated control unit C2, through the left-hand back contact of relay 189, normal terminal and brush 111 of switch RMl, right outer back contact of relay 130, upper brush 12 1 and the normal terminal of the corresponding bank of switch RM2, and through resistance 127 to battery. The circuit for operating relay 87 may be traced from ground on conductor 98 through the winding of relay 87, middle right-hand back contact of relay 91, neXtto-the-inner left-hand back contact of relay 88, middle right-hand front contact of relay 85, through the upper one of test brushes 7 8 and the first terminal of the selected group, thence over a conductor similar to conductor 98, to battery in a control unit in the same manner as already traced for the operation of test relay 86. The operation of either or both of relays 86 and 87 prevents the further advance of the brushes of switch R2 since the circuit for operating magnet 70 passes through the back contacts of both of these relays. If the first sets of terminals in theselected group are busy, stepping-magnet (O is reoperated in a circuit which may be traced from battery through its winding, middle right-hand back contact of relay 88, interrupter contacts of magnet 70, right-hand back contact of relay 83, brush 76 and terminal with which it is in contact, right outer front contact of relay 85, conductor 92, and through the bac r contacts of relays 87 and 86 to ground on conductor 98. The brushes of switch are thus advanced until an idle set of terminals is reached and either or both of relays 86 and 87 operate or until the brushes reach the last of terminals in, the selected group. If relay 86 operates it closes an obvious circuit for operating relay 88; and relay 88 looks through its inner righthand front contact to ground on conductor 93. If relay 87 operates, and relay 86 is not operated, it closes an obvious circuit for operating relay 89;-and relay 89 closes an obvious circuit for operating relay 88. Relay 88 looks to ground on conductor 98; and relay 89 is looked through its inner left-hand front contact and the inner right-hand front contact of relay 88 to the same ground. Relay 89 controls the connections to brushes 71, 72 and 76% trender either the upper or lower of these brushes effective, to the exclusion of the others, dependin upon whether the selected set of terminals 15 located in the upper or the lower of the corresponding banks. In the following description we will assume that the selected terminals are located in the lower one of banks 71, 72 and 73 so that relay 89 is not operated. Test relays 86 and 87 are released by relay 88 after it has locked operated.

If all of the terminals of the selected group are busy, a circuit is closed from battery through the winding of relay 8%, right outer back contact of relay 88, outer right-hand front contact of relay 82, brush and last terminal in the selected group of bank 75, nextto-the inner right-hand front contact of relay 85, conductor 92, back contacts of relays 87 and 86, to gro nd on conductor 93. Relay 8% opera es in this circuit, to prevent the further operation of stepping magnet 70. Relay 8% closes circuit from batte v through the winding of of relay 85, 11"1 -hand front contact of relay 8%, brush and of-norinal terminals of bank 76, through the outer right-hand front contact of relay 85, over conductor 92, and thence to ground as hereinbefore traced. Relay 91 is a slow-to-operate relay so that it will not operate in this circuit during the intervals that both relays 84 and 85 were operated at the time of the initial operation of relay 85; but on the last set of terminals in a group the circuit for relay 91 is maintained so that relay 91 eventually operates and connects busy tone through the secondary winding of transformer 90, right inner front contact of relay 91, middle left-hand front contact of relay 85 in parallel with the left-hand winding of relay 81, so that the all-trunksbusy signal is transmitted to the calling subscriber.

The aforementioned operation of relay 85, at the time of the completion of group selection by switch R2, was also effective to close a circuit for operating stepping magnet of switch R1 so as to advance the brushes of switch R1 into engagement with the set of terminals through which itis connected to the conversational switch CS1. The circuit for operating magnet 60 may be traced from battery through its winding, through the outer left-hand front contact of relay 85, interrupter contacts of magnet 60 to ground at the back contact of relay 66. The stepping magnet 60 is therefore alternately operated and released and the brushes of switch R1 are advanced one step by each release of the magnet 60. When brush 61 makes contact with the terminal associated with switch CS1, relay 66 operates in a circuit which is traced from battery through its winding, brush and terminal of bank 61, right inner front contact of relay 56, over conductor 93 to ground at the left outer front contact of relay 82.

VVit-h relays 66 and 88 both operated (due to the fact that the R2 switch has found an idle set of terminals in the required group, and that the control unit C1 is connected through the brushes of switch R1 to the conversational switch CS1), a circuit is completed for operating the stepping magnet 50 of the conversational switch CS1; this circuit is traced from battery through the wind ing and interrupter contacts of magnet 50, terminal and brush of bank 64 of switch R1, left-hand back contact of relay 84, and through the outer right-hand front contact of relay 88 to ground at the lefthand front contact of relay 66. Relay 66 also connects the ground on conductor 93 through the back contacts of relays 86 and 87, conductor 92, right-hand front contact of relay 66, and through the brush and terminal of bank to the test brush 54 of switch CS1. Magnet 50 advances the brushes of switch CS1 until the test brush 54 comes into contact with the terminal in its bank which is connected to the terminal of the selected set in the bank 74 of switch R2, thereby extending the ground on test brush 54 through brush 74, the middle right-hand back contact of relay 89, and through the neXt-to-the-outer right-hand front contact of relay 88, to the winding of relay 84. Relay 84 operates, thereby opening the circuit for operating the stepping magnet 50 so as to stop the brushes of switch CS1 on the terminals of the outgoing eonversational switch which was previously s lected by the byepath switch R2. Belay 84 closes a circuit for operating relay 91; this circuit is traced from battery through the winding of relay 91, left inner front contact of relay 85, right-hand front contact of relay 84, brush and terminal of bank 7 6 of switch R2, right outer front contact of relay 85, conductor 92, back contacts of relays 87 and 86, to the ground on conductor 93. Relay 91 closes a circuit from battery through the winding of relay 55 of conversational circuit CS1, terminal and brush of bank 63 of switch R1, left outer front contact of relay 91, left-hand front contact of relay 84, right outer front contact of relay 88, to ground at the left-hand front contact of relay 66. Relay 55 locks through its right outer and left inner front contacts and through the outer left-hand front contact of relay 56 to ground at the inner left-hand front contact of relay 56. Relay 55 extends the talking connection, from

brushes

41 and 42 of line-finder LF2, through its inner right-hand front contacts, through brushes 51 and 52 of switch CS1, over trunk 99 to the conversational switch CS2. It also extends the ground at the inner left-hand front contact of relay 56, through the left outer front contact of relay 56 and the left inner front contact of relay 55, through brush 53 of switch CS1 over the sleeve conductor of trunk 99 to mark the associated conversational switch CS2 in the bank 118 of switch RMI in the control unit C2.

The aforementioned operation of relay 88, after switch R2 finds an idle of terminals in the selected group, is effective to disconnect the windings of line relay 81 from the calling line and to extend the connections from the calling line through its outer left-hand front contacts, the inner and outer right-hand back contacts of relay 89, through the lower brushes and selected terminals in banks 71 and 72, over conductors 96 and 9?, to the control unit C2 of the succeedin selecting stage. Relay 88 also extends conductor 93. through the left-hand back conta ct of relay 89, the inner left-hand front contact of relay the neXt-to-thc-outer right-hand front contact of relay 85, through the lower brush and terminal of bank 7 over conductor 98 to the control unit C2. Relays 81 and 8:2 release in consequence of the operation of rela but relays 56, 85 and 88 (also 89, if operated) are held operated by ground connected to conductor 98 as is hereinafter explained.

lift

. mal.

Impulses created by the dialing of succeeding digits of the called number are, therefore, transmitted through control unit C1 to control unit C2, until the control unit C2 5 disconnects this ground from conductor 98, at which time relays 56, 85 and 88 are released. Relay is held operated through its right outer front contact and brush 53 of switch CS1, over the sleeve conductor of 0 trunk 99 to ground in control unit C2 as is hereinafter described. The release of relay 56 cause the successive release of relays and 84 and the release of relay 66 closes a circuit for advancing the R1 switch to nor- The circuit for operating stepping magnet is traced from battery through its winding, left outer back contact of relay 85, left inner back contact of relay 82, right inner back contact of relay off-normal 0 terminals and brush 62 of switch R1, interrupter contacts of magnet 60. to ground at the back contact of relay 66. The release of relay 84 closes a circuit for advancing the R2 switch to normal; this circuit is traced 5 from battery through the winding of stepping magnet 70, middle right-hand back contact of relay 88, interrupter contacts of mag net 7 O, right-hand back contact of relay 8%, brush and elf-normal terminals of bank 76, to ground at the right outer back contact of relay 85. With both of switches R1 and R2 in their normal positions, the control unit C1 is made available for use with another of the associated conversational switches since the 5 test conductor 67 is new again connected through resistance 79 to battery.

JVhen the connection from the calling line is extended through brushes 71 and 72 of switch R2 of control unit C1, line relay 131 Q of control unit C2 is operated in a circuit which may be traced from battery through the right-hand winding of this relay, right outer back contact of relay 165, next-to-the outer right-hand back contact of relay 166, 5 over conductor 96, through the lower bank and brush 71 of switch R2 in control unit C1, outer right-hand back contact of relay 89, outer lefthand front contact of relay 88, conductor 68, outer right-hand front contact of 0 relay 56, brush d1 of line-finder L1 2, brush 11 of line-finder LF1, line 1 and the calling subscribers sub-set, brush 12 of line-finder L1 1, brush 42 of line-finder LF2, middle right-hand front contact of relay 56, conduc- 5 tor 69, neXt-to-the-outer left-hand front con tact of relay 88, inner right-hand back contact of relay 89, through the lower brush and terminal of bank 72 of switch R2, conductor 97, next-tothe-inner right-hand back 0 contacts of relays 166 and 165, through the left-hand winding of relay 131 to ground. Relay 131 closes an obvious circuit for operating the slow-to-release relay 131. Relay 132 closes a circuit for operating relay 130, from battery through the winding of relay 130, right outer back contact of relay 166, over conductor 129, to ground at the front contact of relay 132. Relay 130 opens the aforementioned test circuit through the brush and normal terminal of bank 124 and connects ground through its left outer front contact, the left outer back contact of relay 139, conductor 106, the left outer back contact of relay 105, over test conductor 98, terminal and lower brush 7 3 of switch R2 of control unit C1, neXt-to-the-outer right-hand front contact of relay 85, left inner front contact of relay 88, left outer back contact of relay 89, to holding conductor 93 of control unit 01; this ground is effective to prevent the release of

relays

55, 56, 66, 8t, 85 and 88 as hereinbefore mentioned.

When the calling subscriber dials the seeone digit, this being one of the digits of the office code, line relay 131 of control unit C2 is alternately released and reoperated as many times as its operating circuit is opened by the contacts of the dial. The release of relay 131 closes a circuit for operating the stepping magnet 110 of switch RMl and relay 133 this circuit is traced from battery through the winding of stepping magnet 110, right inner back contact of relay 136, right inner frontcontact of relay 130, winding of relay 133, to ground at the back contact of relay 131. VJhen relay 131 reoperates, the stepping magnet 110 releases but relay 133 is a slow-to-release relay and it remains operated until all of the pulses corresponding to the second digit have been received. Since relay 132 is also a slow-to-release relay it remains operated during receipt of this train of impulses. The brushes of switch RMl are thereby advanced by the alternate operation and release of mag net 110 to a position which corresponds to the second digit dialed by the calling subscriber.

hen the switch Rlvll reaches position 2, a circuit is closed for operating the stepping maknet 140 of switch 3M3; this circuit is traced from battery through the winding and interrupter contacts of magnet 1 10, brush and normal terminal of bank 145, over conductor 128, through the second terminal and brush of bank 111 of switch Rllll, middle right back contact of relay 136, over conductor 129 to ground at the front contact of relay 132. Stepping magnet 120 of switch RM2 is also operated when the brushes of switch RMl enter position 2, since the winding of magnet 120 is then connected, through its interrupt-er contacts and through the brush and normal terminal of bank 126, over conductor 128 to the second terminal of bank 111 of switch El /l1. The release of magnets 140 and 120 when their circuits are opened by their own interrupter springs causes the advance of switches RM2 and RM3 from their normal position to position 2. The terminals of bank 112 of switch RMl are connected in pairs to ice the terminals of bank 148 of switch RM3; to illustrate,

terminals

2 and 3 of bank 112 are connected to terminal 2 of bank 148, and terminals 4 and 5 of bank 112 are connected to terminal 12 of bank 148. lVhen, therefore, the brushes of switch RM3 are advanced into position 2, a circuit is completed from battery through the winding of, relay 134, brush and terminal 2 of bank 148, through

terminal

2 or 3 and brush of bank 112 of switch Rldl, right-hand back contact of relay 139, to ground at the left inner back contact of relay 158. In operating, relay 134 prevents the closing of another operating circuit for the stepping magnet 140 so that switch RM3 remains in position 2 until switch RMl has advanced beyond position 3. If, and when the brushes of switch RMl are advanced beyond position 3 in response to impulses received by line relay 131, relay 134 releases; and the circuit for operating magnet 140 to cause the further advance of switch 3M3 is traced from battery through the winding and interrupter contacts of magnet 140, brush and oil-normal terminals of bank 145, back contact of relay 134, to ground at the left-hand back contact of relay 136. When the brushes of switch RM3 reach position 12, the circuit for operating 134 is again closed; and the operation of relay 134 prevents the further advance of switch RM3 until the brushes of switch RMl have been advanced beyond position 5. The stopping

positions

2, 12, 22, etc. of switch RM3 represent the first terminals of different routing groups in the banks 141 and 142. The first and succeeding terminals of each group of terminals in banks 141 and 142 are connected to the first terminal of a corresponding group of terminals in bank 125 of switch RM2. The first terminal of each group in bank 125 is thus continuously marked while the brushes 141 and 142 are engaging the corresponding terminals in their respective banks. This arrangement prevents the advance of switch RM2 beyond the first terminal of the group marked by switch RM3. The winding of relay 149 is connected to

terminals

3, 5, 7, 9, and 11 of bank 111 of switch RMl so that this relay is operated, through brush 111 in each of these positions; to the ground on conductor 129, but the operation of relay 149 during the receipt of the impulses created by the dialing of the second digit is without effect since at this time brush 142 is continuously connected through the right outer back contact of relay 136 and the left-hand back contact of relay 168, to ground at the right outer back contact of relay 158.

Having advanced from normal to position 2 the further advance of switch RM2 is controlled by relay 135, this relay being connected to operate when brush 125 of switch RM2 engages the terminal marked by brushes 141 and 142 of switch RM3. The circuit for operating relay 135 may be traced from battery through its winding,'right outer back contact of relay 162, brush and marked terminal of bank 125 of switch RM2, terminal and brush of bank 141 or 142, through the left inner front contact of relay 149 or the right outer back contact of relay 136, and through the left-hand back contact of relay 168, to ground at the right outer back contact of relay 158. The circuit for operating magnet 120, after the brushes of switch RM2 have been advanced to position 2, may be traced from battery through its winding and interrupter contacts, brush and off-normal terminals of bank 126, left inner back contact of relay 162, back contacts of

relay

135, 157 and 156, to ground at the middle lefthand back contact of relay 162. If and when the brushes of switch RM3 are advanced beyond the first group, as controlled by the setting of switch RMl, the stepping magnet of switch RM2 will be again energized due to the release of relay 135; and the brushes of switch 3M2 will be advanced until they engage the next terminal which is marked by brush 141 or 142 of switch RM3, at which time relay 135 reoperates in the circuit iereinbefore traced. Vfith both of relays 134 and 135 operated and with relay 133 released, a circuit is completed for operating relay 136. This circuit may be traced from battery through the left-hand winding of relay 136, front contact of relay 134, right-hand back contact of relay 133, front contact of relay 135, back contacts of

relays

157 and 156, to ground at the middle left-hand back contact of relay 162. Relay 136 closes a locking circuit through its right-hand winding and neXt-to-the-inner right-hand front contact, to ground at the left inner front contact of relay 130. Relay 136 opens the circuit for operating magnet 140 of switch RM3, disconnects the back contact of relay 131 from the magnet 110 of switch RMl and connects the back contact of relay 131 to magnet 140 of switch RM3 in readiness for storing the next train of dial impulses.

If switch R-Ml stopped in one of

positions

3, 5, 7 9 or 11 so that relay 149 is operated and if the circuit for operating relay 135 passes through brush and bank 142 instead of through brush and bank 141, relay 135 releases when relay 136 operates and relay 149 is locked through its right-hand front contact and the right outer front contact of relay 136, to ground on conductor 129. The release of relay 135 again closes the circuit for operating magnet 120 of switch RM2 so as to advance the brushes of this switch until they reach the terminal which is marked by brush 141 instead of brush 142 of switch RM3. Relay 135 then reoperates to stop further advance of switch RM2. Thus relay 149 controls the marking circuit through brushes 141 and 142 depending upon the first digit dialed. In the following description we will assume relay 14.9 to be normal so that brushes 142, 14a and 1 1-? are operatively effective to the exclusion of brushes 1e11, 1 13 and 146.

To sum up the operation due to the dialing of the second oflice code digit relay switch 3M1 is advanced to a position which corresponds to the number of impulses received. Switch EMS is thereby advanced to a corresponding routing group in order to marl a group terminal in the bank of switch E1112. Switch 3M2 is thereupon advanced under control of switch 3M3 to the first terminal of a group which leads toward the exchange or exchanges indicated by the second oilice code digit. Relay 13%- operates when switch El /l3 has been advanced to the terminal marked by switch EH1 and relay 135 operates when switch EH2 has been advanced to the terminal marked by switch R113.

The aforementioned operation of relay 136 also closes a circuit for operating stepping magnet 110 of switch Eli l1 to advance the brushes of this switch to connect with conversational switch CS2; this circuit may be traced from battery through the winding of magnet 110, right inner front contact of relay 136, back contact of test relay 137, and interrupter contacts of magnet 110 to ground. The brushes of switch RMl are thereby advanced by the alternate operation and release of magnet 110 until the terminals associated with the conversational switch CS2 are reached, at which time a circuit is completed for ogerating test relay 137. Relay 13d releases when switch RMl advances. The circuit for operating test relay- 137 may be traced from battery through the winding of relap 13?, resistance 138, brush and terminal of bank 118, back contact of the continuity springs of relay 105, over the holding conductor of trunk 99, through the terminal and brush 53 of switch CS1, the left inner front contact of relay 56, and through both left front contacts of relay 55 to ground. Relay 13? opens the operating circuit for magnet thereby preventing the further advance of switch Rldl. Relay 137 also closes an obvious circuit for operating relay 139. Relay 139 disconnects the ground at the left out-er front contact of relay from test conductor 98 and connects this ground hrough the left outer front contact of relay 139, through the brush and terminal of bank 118, back contact of the continuity springs of relay 105 over the sleeve conductor of trunk 99, through brush 53 of switch CS1 and the right outer front contact of relay 55 to the winding of relay 55 to hold this relay operated after relay 56 is released. Relays 56,66, 84, 85 and 88 of the second selecting stage release when the ground over conductor 98 is thus disconnected by the operation of relay 139 from conductor 93 of control unit C1, thereby causing the return of this control unit to normal as hereinbefore described. The impulsi'ng circuit from line 1 is now traced through the inner right-hand front contacts of relay 55, brushes 51 and 52 of conversational switch CS1, over the talking conductors of trunk 99, through the terminals and brushes of banks 116 and 117 of switch RMl, the left inner front contacts of relay 139, the back contacts of the right-hand inner continuity springs of relay 166, and through the outer r ht-hand back contacts of relay 165 to the windings of line relay 131.

When the calling subscriber dials the next digit (the third digit of the ofiice code), relay 131 is alternately released and reopera'ed in response to the impulses thus cretet. The first release of relay 131 closes a circuit for operatingmagnet of switch T1113 and slow-to-release relay 133; this circuit may be traced from battery through the winding of magnet 140, middle left back contact of relay 159, outer left back contact of relay 162, neXt-to-the-inner left-hand back con 'act of relay 166, inner left front contact of relay 136, right-hand front contact of relay 130, winding of relay 133, to ground at the back contact ofrelay 131. The operation of relay 133 closes a circuit for operating relay this circuit may be traced from battery through the winding of relay 150, left outer front contact of relay 136, next-to-theouter left-hand back contact of relay 166, left outer front contact of relay 133 to ground on conductor 129. Relay 150 locks in a circuit from battery through its winding, the left outer front contact of relay 136, right outer front contact of relay 150, left outer back contact of relay 158, and through the normally closed contacts of the left-hand con tinuity springs of relay 166, to the ground on conductor 129. Relay 150 sends a starting signal to all of the register-translators associated with the control unit C2 by connecting the ground at the outer back contact of relay 170, through the left outer front contact of relay 150, to conductor 180. Relay 150 also connects battery through the windings of relay 170, the middle left front contact of relay 150, left outer back contact of relay 159, to the test terminal associated with control unit C2 in the bank 209 of the register-translator RT and the corresponding terminals in the banks of the other associated register-translators.

The alternate operation and release of magnet 140, in response to the impulses received by relay 131 from the dialing of the third digit, causes the advance of the brushes of switch RM3 to a corresponding terminal in the previously selected routing group. 17 hen relay 133 releases after all of the im pulses corresponding to the third digit have been received, a circuit is closed for operating relay 151; this circuit is traced from battery through the winding of relay 151, outer lefthand back contact of relay 133, neXt-to-the- SOY