US1772561A - Automatic telephone system - Google Patents

Description

Aug. 12, 1930. s'r u 1,772,561

AUYOIM'IC TELEPHONE SYSTEM Filed Ma 14, 1928 14 Sheets-Sheet 1 I ""'I"'nven n1" Rudolph Frank ET'a'hlik WW2? L Aug. 12, 1930. R. F. STEHLIK AUTOMATIC TELEPHONE SYSTEM Filed May 14. 1928 14 Sheets-Sheet 2 w, w) M hlik In E T f'U n n Rudulph Frank Aug. 12, 1930.

R. F. STEHLIK AUTOIATIC TELEPHONE SYSTEI Filed llay 14. 1928 14 Sheets-Sheet 3 Aug. 12, 1930. R. F. STEHLIK 61 AUTOMATIC TELEPHONE SYSTEM Filed May 14. 1928' 14Sheets-She9t 4 RRG 1 .9 7 L 5 //5 I93 90 87 40 I80 46 Rush]. 11 Frank Elih'lik Aug. 12, 1930. R. F. STEHLIK AUTOMATIC TELEPHONE SYSTEM Filed May 14, 1928 14 Sheets-Sheet 5 Iaur Rudd 11 Frank ST'e'hlik 42- Aug. 12, 1930. R. F. STEHLIK 1,772,551

AUTOHATIC TELEPHONE SYSTE- Filed May 14, 1928 14 Sheets-Sheet 6 llllllllll l5 TRG U- Rudol h FPZZZ 515mm Aug. 12, 1930. R. F. STEHLIK AUTOMATIC TELEPHONE SYSTEM Filed May 14. 1928 14 Sheets-Sheet 7 Aug. 12, 1930. R. F. STEHLIK AUTOMATIC TELEPHONE SYSTEM -14 Sizeets-Sheet 8 Filed May 14, 1928 Rudul h Frank E'lFhZik Aug. 12, 1930. R. F. STEHLIK 1,772,561

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Aug. 12, 1930. R. F. STEHLIK AUTOIATIC TELEPHONE SYSTEI 14 Sheets-Sheet 12 Filed May 14, 1928 mm m 5 3mm m n 5 SR wF h 11K M mam N m u. R

Aug. 12, 1930.

R. F. STEH LlK AUTOMATIC TELEPHONE SYSTEM Filed May 14, 1928 14'Sheets-Sheet 13 Inuen n1" Ruiz H h Frank E'Tfihlik 511-51 Patented Aug. 12, 1930 BUDQIJBHIFRANK STEHLIK, OF CHICAGO, ILLINOIS, ASSIGNOR TO RESERVE 'HOLDIN G COMEPAN'Y, 'OF KANSAS CITY, MISSOURI, AGORPOR-ATION OF DELAWARE AUTOMATIC TELEPHONE SYSTEM Application fllGd May 14, 1928, Serial No.

'The present invention relates to improvements in or relating to automatic telephone systems and more particularly concerns small exchange systems such as are used in private ofiices'or'in villages or-the like.

Gne ,of-the objects of the present invention is to'provide a small'exchange sys'temhaving a capacity of up to five or ten speaking circuits and employing only line switches and switches.

The line switches according'tothis feature of the invention may be either of the rotary type inwhich the Wipers are operated step I by step over a single level by a pawl and rat'ehet mechanism or of the plunger type audit is 'believed to be novel to employ "line switches'in this manner.

Another feature of the invention relates to are'layeounting and storage arrangement in which the tens "counted on a set of counting relays less in'number than the maxi- 11111111 .nun'iber oft impulses in a series to be eourrted and then transferred to the Storage relays which are also less in number than the maximumnumber of ilnpulsesina series to be;cui1ted and thenutilizin'g the counting relays to count the units digit; the storage relays and counting relays the'n'j'ointly control an .o'era'tion such as the operation of a ealledsu s'cribers line switch.

Anotherifeature ofthe invention relmesto the sefttingup ofealls from a small exchange to ainain exchange by which the "trunk line is connected'to the trunk relay group by dif- "ferent leads hutin a manner similar to that in which ,a called suhscrihers line is connected'to-the trunk relay group "on a local call.

These and other features of the invention will be better understood by referring -to the accompanying drawings, Figs. 1-15, which show bymeans-of the usual-eireiiittha rams suificient of the apparatus employed in the {present invention to enable the description 277,525, and in Belgium October 8, 1927.

to be followed. It Will be understood, how ever, that various modifications maybe made in the circuit details by those skilled in the art Without departing from the spirit of the inventlon.

Referring now 'tot'he accompanying drawings, Fig. '1 shows'the line switch of a subscriher together with the bank' of ten sets of contacts that-are available for the plunger arm of hisline switch to operate. T he lower part of the figure shows the circuit of the master switch which is used to control the alignment of the freeplun'ger arnisof the line switches oi-allthe subscribers. The p'lungers employed are of the self aligning type'iitted with spring c'ont'rol so that when a plunger is released 'by the de-en'ergization of a plunger magnet at the-end ofa conversation,

itis automatically brought into line with the remaining "free plunger-s u'ntier-thecontrol oil the master switch.

Fig. 2 shows a b'attery feed relay group s'how'n in connection with the line switeh of "subscriber 22 in '1; similar relay roups are represented by rectangles mai kec TRG 25 in Fig. 1.

Fig.3 sho'wstheline switches o'f-subscr-ibers 52 2.116 56 so 'thatthe operation of the master switch in conjunction "with the line switches maybe more easily followed.

i'g. 4 shows one of the two recorders in which the chain of c'ountin'g relays shown in the top left-hand corner' isused first 'to count the tens digit; "this digitie then transferred to the storage relays WV, X, Y, Z and the counting relays are then used to count the units digit.

Fig. 5 shows the marker, the seven tens marking relays being shown on the left-hand side-and the units marking relay on the righthand side.

Fig. 6 shows a general layout of another modification of'theinvention employing rotary line switches.

'Fig. 7 shows callingand called subscribers line switches.

Fig. '8 show-s a trunk relay group.

Fig. '9 shows a recorder and recorder finder.

Fig. shows a main trunk relay group used in connection with calls incoming from and outgoing to the main exchange.

Fig. 11 shows a battery feed group used for converting the ordinary subscribers impulses into battery impulses.

Fig. 12 is a trunking diagram of connections with the main exchange.

Fig. 13 shows circuit details of a trunk line switch used for setting up calls outgoing to the main exchange.

Figs. 14 and 15 show an arrangement for subscribers line switches alternative to that shown in Figs. 1 and 3. In this case each subscriber has two line switches, one of which operates on outgoing calls and the other of which operates on incoming calls.

An alternative form for exchanges having a larger capacity and permitting of two speaking circuits is described with relation to Figs. 14 and 15. In this case each subscriber is provided with two line switches, for instance, subscriber No. 22 is provided with an outgoing line switch OLS22 which serves for outgoing calls and an incoming line switch ILS22 which serves for incoming calls. Similarly subscriber No. 56 is provided with line switches OLS56 and ILS56. Further, subscriber No. 52 is provided with line switches OLS52 and ILS52. The line switches OLS22, OLS56, OLS52 have access to the inlet ends of ten trunk relay groups such as that shown in Fig. 2, while the line switches ILS22, ILS56, have access to the outlet ends of the same trunk relay groups. Two separate master switches OMS and IMS are provided; the master switch OMS controlling the outgoing switches such as OLS22, OLS56 and OLS52, While the master switch IMS controls the incoming line switches ILS22, ILS56 and ILS52. The only alteration between this arrangement and that de scribed with reference to Figs. 1, 2, 3, 4 and is that the line switches are altered and Figs. 14 and should be substituted for Figs. 1 and 3. The outgoing master switch OMS is of substantially standard construction and design, while the incoming master switch IMS has been specially designed to operate in the manner which will be described.

In order that the invention may be better understood a description will be given of the setting up of a complete connection and it will be assumed that subscriber No. 22 wishes to make connection with subscriber No. 56. When subscriber No. 22 lifts his receiver to initiate a call he completes a circuit as follows; battery line relay LR22, contact 11, line 12 of the subscribers loop through the subscribers instrument and back over line 13, contact 14 to earth. Line relay LR22 therefore picks up over this circuit and closes contact 15, whereby a circuit is completed for the pull down winding of the plunger magnet PM22 as follows; battery, upper or pull down winding PDC of PM22, contact 16, cont-act 15, conductor DM, contact 100 to earth. That is, assuming contact 100 is closed, which normally is except when the master switch MS is hunting, plunger magnet PM22 energizes and causes the plunger to engage with the contact bank so that contacts 1'7, 18, 19 and 20 are closed and thereby lines 12 and 13 are connected forward to lines 21 and 22 respectively, wnile earth is connected over contact 19 to the contact of the bank of the master switch corresponding to the magnet PM22 (this contact is given the reference 23). The closure of a circuit over contacts 17 and 18 causes a circuit to be completed over the subscribers loop for the line relay LR in the battery feed relay group Fig. 2, line relay LR energizes and. at contact 25 completes a circuit for release relay RR. Release relay RR therefore energizes and closes contact 24,

thereby connecting earth back over the release trunk 26, contact 20, lower winding BCO of the plunger magnet PM22 to battery. It should be mentioned that when magnet P3122 energized it opened contacts 11 and L1, thereby permitting- LR22 to de-energize. LR22 is, however, a slow to release relay and therefore does not fall away for some little time, so that contact 15 remains closed until the circuitfor the lower winding of the plunger magnet has been completed. The current through this winding is sufficient to hold the contacts 17, 18, 18 and 20 closed and to hold open the contacts 11 and 14. Relay RR on energizing, in addition to closing contact 24 closes contact 27, whereby a circuit is completed as follows; earth, contact 27, contact 28, conductor 29, contact 30 of switching relay SR1, contact 32 of switching relay SR2, recorder test relay RTR- to battery. RTR energizes and closes contacts 31 and 33, there by completing a circuit over contact 31 as follows: earth contact 34, contact 31, upper winding of relay SR2 to holding conductor 35; and a circuit over contact 33 as follows; earth on contact 36, contact 33, upper winding of relay SR1, conductor 37, relay HRl of relay recorder grou RRGl to battery conductor 35 leads to re ay recorder group RRG2. If relay recorder group 1 is busy, earth will be connected directly to contact 158 over con tacts in the trunk relay group which has taken RRGI into use, similar to contacts 27 and 28 in TRGl. If relay recorder group REG]. is

busy the upper winding of SR1 is merely short-circnited when earth is connected to its lower terminal by the closure of contact 33. This has no effect on relay SR1 which is locked energized at contact 157. The closure of contact 31 places earth on the lower terminal of the upper winding of relay SR2 and if relay recorder group RRG2 is free, relay SR2 will energize and connect the relay recorder group RR-G2 to trunk relay group TRGl. If, 011 the other hand, the relay recorder group RRG'l is free and RRG2 is busy,

(ill

relay SR1 will energize in series with relay HRl over the following circuit; earth, contact 36, contact 33, upper winding of relay SR1, conductor 37, holding relay HR1 to battery; relay HRl will energize in series with the upper winding of relay SR1 and close contact 38 and 39. At contact 38 a circuit closed as follows: earth, contact 38, contact 81, storage connector relay SCR to batt The operation of relay SCR, however. has no immediate effect. Relay SR1 on energizing closes a locking circuit for itself at contact 157 as follows: battery, lower winding of relay SR1, contact 157, conductor 29, contact 28, contact 27, earth. i 'he circuit of relay RTR is broken at contact 30 and relay RTR falls back opening contacts 31 and thus cutting off relay SR2. At contact 158, relay SR1 closes a maintaining circuit for relay HRl and at contact 51 extends the iinpulsing conductor 43 to the relay recorder group RRG'L If, however, both RRG]. and RRGQ had been busy, then neither SR1 nor SR2 would operate and when dialling commenced the busy signal would be given to the calling subscriber in a manner which will be described later.

The subscriber now commences to dial the first digit five. In this case it will be assumed first of all that both RRGl and RRG2 were busy. In this case as soon the line relay LR Fig. 2 falls back a circuit would be completed as follows: earth, contact 40, contact 41, contact 42, impulsing conductor 43, contact 44, contact 45, (relays SR1 and SR2 both being de-energized), busy test conductor 46, upper winding of busy relay BR to battery. Busy relay BR accordingly energizes and locks energized over contact 47 to the release trunk 26 and at contact 48 connects up the busy tone to the conductor 49 which passes via condenser 50, conductor 22, conductor 13 to the calling subscribers line and back over conductors 12 and 21 through the upper winding of relay LR to battery; when the subscriber listens and hears the busy tone, he knows that he cannot complete the connection.

If, however, relay recorder group RRGl is idle a circuit will be completed on the transmission of the first impulse of the series as follows: earth, contact 40, contact 41, contact 42, conductor 43, contact 51, conductor 52, contact 53, contact 54, contact 55, contact 56, counting relay FR] to battery. Relay FRl accordingly energizes and closes cont acts 57 and 58. A branch circuit for the first impulse also passes through change-over relay CH1, and relay CH1 accordingly energizes and closes contact 59. thereby energizing relay ACHl. Relay ACl'll energizes and closes contact 60 thereby n'eparing a locking circuit for relay FRI as follows: earth, contact 60, contact 61, relay FRlA contact 57, relay FR1 to battery. This locking circuit however is not effective until earth is removed from the upper terminal of relay FR1 over conductor 52 on the termination of the impulse. Consequently when the first impulse ends, relay FRlA energizes in this locking circuit with relay FRI, thereby opening contact 56 and closing contact 62. Relay FRlA operates other contacts the purpose of which will be clear later.

Relays CH1 and ACHl are both slow to release and consequently remain energized during the train of impulses, and accordingly the next operation which takes place occurs on the transmission of the next impulse when relay LR deenergizes a second time. Relay LR closes a circuit which this time may be traced as follows: earth, contact 40, contact 41, contact 42, conductor 48, contact 51, conductor 52, contact 53. contact 54, contact 55, contact 62, relay FR2 to battery. Relay FR2 accordingly energizes and closes contact 63, thereby preparing a locking circuit for itself as follows; earth, contact 66, contact 64, relay FR2A, contact 63, relay FR2 to battery. This locking circuit however does not become effective until earth over conduo tor 52 is removed from upper terminal of relay F R2 on the termination of the impulse. \Vhen this occurs relay FR2A ener; the locking circuit of relay FR2 and opens contact 61 thereby enablin relays FRlA and FRI to release. At the same time it opens contact 55 and closes contact 65. The next impulse may be traced over the previously described circuit including contact 54. but this time it passes over contact 65 iruiteadi of contact 55 to relay FRB and battery. Relay FR3 energizes, closes contact 66 whereby a locking circuit for itself is prepared as follows: earth, contact 60, contact 67, relay FR3A, contact 66, relay FR3 to battery. This, as before, only becomes effective when earth over conductor 52 is removed from the upper terminal of relay FRS, on the termination of the impulse whereupon relay FR3A. energizes and opens contact 64, therel y releasing relays FR2A and FR2. At the same time relay FR3A opens contact 54 and closes contact 68. The fourth impulse n be traced over the previously described cuit, including contact 53 but instead of passing over contact 54, it now passes over contact 68, contact 69, relay FR4 to battery. Relay FR4 energizes and prepares a locking circuit for itself as follows: battery, relay FR4, contact 70, relay FR4A. to earth on contact 60. As soon as the fourth impulse terminates earth over conductor 52 is removed from the upper terminal of relay FR4, and accordingly the locking circuit becomes effective and relay F R4A energizes opening contact 69 and closing contact -71. It also opens contact 67, thereby opening the locking circuit of relay; FP3A and FR3, which relays accordingly deenergizes, and closes contact 72. The fifth til Ire

impulse will now pass over contacts 54, and 56 to relay FRl and battery, since relays FRlA, FR2A and FR3A have restored to normal. Relay FRl accordingly energizes, prepares a locking circuit for itself as before over contact 57, relay FRIA, contact 81, contact 60, to earth, but contact (31 is this time shmt-circuited by contact 72. This is of no importance seeing that at the present time we are only transmitting five impulses but the purpose of it will become apparent later when more than live impulses are generated. ()n the termination of the fifth impulse, relay FRlA energizes in series with relay FRl as before. Since the fifth impulse terminates the series, relay CH1 will now (lo-energize. This will be followed shortly after by relay ACHl but in the meanwhile a circuit may be traced as follows; earth contact, 73, contact 74, contact 75, contact 188, relay FR4 being energized, contact 77, relay FRlA being also energized, contact 78, conductor 79, contact 80, lower winding of relay Y, lower winding of relay Z to battery thus causi1 1 g storage relays Y and Z to energize. Relays Y and Z on energizing complete locking circuits for themselves as follows; earth contact 38, contact 84, contact 83 and thence for relay Z over contact 82 and the upper winding of relay Z to battery, and for relay Y over contact and the upper winding of relay Y to battery. As mentioned above, relay ACHI de-energizes shortly after relay CH1 falls back, and consequently contact 84 opens shortly after the events just described, thereby removing a short-circuit from the disconnect relay DR so that the locking circuit for relays Y and Z instead of passing over contact 84, now passes as follows: earth, contact 38, relay DR, contacts 82 and 85 and upper windings of relays Z and Y respectively to battery. Relays Y and Z are therefore locked energized through their upper windings, relay DR energizes and opens contact 83, thereby preventing relay DR being de-energized in the next series of impulses, when contact 84 is again closed. Relay DR opens contact 81 to enable relay SCR to release and open contacts 87 to 92 inclusive; and also opens contact 75 and closes contact 86 to enable an impulse to he sent at the end of the next series over a different circuit for a purpose to be described later.

\Vhen ACHl released it also opened contact 60, thereby opening the locking circuit of relays FR l, FR LA, FEl, FRlA, so that these relays restore to normal and everything is now in readiness for the transmission of the next series of impulses. The next series of impulses as regards Fig. 2 operate the same as before and the impulse may be traced from; earth, contact 40, contact 41, contact 42, conductor 43, contact 51, conductor 52, contact 53, contact 54, contact 55 contact 56,

relay FBI to battery, while a branch circuit also extends over relay CH1 to battery. Relay CH1 energizes as before, opens contact 73, and closes contact 59. Relay ACHl also energizes as before and closes contacts (30, 84 and 74 and opens contact 144. At contact 60 it prepares a locking circuit for relay FRlA as follows: earth, contact 60, contact 61, relay FRlA, contact 57, relay FRl to battery. This, however, only becomes effective at the end of the first impulse when earth is removed from the upper terminal of relay FRl. When this impulse terminates, relay FRlA energizes in series with relay FR1, opens contact 56 and closes contact 62, thereby preparing an energizing circuit for relay F 12. which as previously described energizes at the beginning of the second impulse and is locked energized in a locking circuit as follows: battery, relay FR2, contact (33, relay FRQA, contact (34, contact 60 to earth. At the end of the second impulse, relay FR2A energizes; on ti 1e third impulse relay FR?) energizes at the beginning and relay FR3A at the end as previously described; and on the fourth impulse, relay F114 energizes at the beginning and relay F R414 at the end. As will be recollected from the previous circuit, each succeeding relay opened the locking circuit for the previously energized relay so that at the end of the fourth impulse, relays FR4 and Flt-1A were alone energized and these remain energized d uring the remainder of the impulse series. Relays F111 and F 1. 1 are energized at the end of the fifth impulse as previously described. relays F114 and FR4A remaining energized. The sixth impulse may now be traced as follows: earth, contact 40, contact 41, contact 42, conductor 43, contact 51, conductor 52, contact 53. contact 54, contact 55, contact 62, relay FRQ to battery. Relay FRQ energizes and prepares a locking circuit for itself over contact 63 in series with relay FRQA, contact 64, con tact 60 to earth. At the end of the sixth impulse relay FR2A energizes in series with relay FR2 in this locking circuit and opens contact 61. telays FRl and FRIA, however, are not de-energized since they are locked energized over contact 72 independently of contact 61.. Consequently at the end of the sixth impulse relays and FRQA remain energized and the following; relays are all energized at this time: F114. FR4A. FR2, FR2A. FRl. FRlA, and all these are dependent upon earth at contact 60. At the end of the series of impulses. relay CH1 de-energizes and is followed after an interval by the de-energization of relay ACHl but in the interval thus produced an extensive train of operations takes place as will now be described.

Upon the de-energization of relay CH1, a circuit is completed as follows: earth, contact 73, contact 74, contact 86, relay SDR to IOU battery. Relay SDR accordingly'energizes, opens contact 53 to prevent further impulses affecting the counting relay chain and closes a locking circuit for itself at contact 93 as follows: battery, relay SDR, contact 93, contact to earth, and relay SDR therefore becomes solely dependent upon the holding relay HRL At contact 111, relay SDR closes a circuit from battery, relay ACHl, contact 11 1, contact 110 to earth for maintaining the relay ACHl energized until the 1 master switch has completed its hunting operation as will be seen later. Relay SDR also closes contact 94, thereby connecting earth over the conductor 95 to energize the start relay SRM of the master switch. The master switch start relay SRM therefore operates and-closes contact 99 thereby completing a circuit for open main relay OMB which onergizes and disconnects earth at contact 100 from the open main conductor BM thereby preventing the operation of any subscribers plunger magnet it he shouldremove hisreceiver while the master switch is hunting. At contact 90 relay SRM completes a circuit for the lower Winding of the differential locking magnet as follows: earth, contact 96, lower winding of the locking magnet L'Mto battery. The locking magnet LM accordingly energizes and closes contact 97. At contact 97 it connects earth to relay ORM, this however is without effect since earth will be supplied at contact-99 by relay SRM which remains energized until the master switch has finished its hunting operation; contact 97 is provided for the case when the master switch is hunting for the inlet'end of a free trunk relay group in which case the relay SRM is not energized. An auxiliary circuit for the upper winding of the locking magnet, which is wound in .the opposite direction to the winding just energized in circuit with contact 96, is now connected in a circuit extending as follows earth, contact96, upper winding of locking magnet LM, contact 101, contact 102, wiper 103 of the master switch to the contact With which the Wiper is engaging. This circuit is therefore dependent upon the potential at the contact on whichthe Wiper 103 happens to be resting. The locking magnet as is well known, on energizing releases the master switch so that it moves allthe idle plungersaround,-at the same timemov ing the wipers 103 and 606. Consequently as soon as the Wiper 103 rests on a contact conuected to battery, the windings of the locking magnet LM are energized in opposition to each other and the locking magnet de-energizes, the master switch is then'loeked, and the contact 97 opened. Itzwill be seen later that the hunting operation of the master switch has taken'place between the falling back of relay CH1 and the'falling back of relay ACHi and that in this interval relays SDR, 81R and FR have energized-in succession. W-hen relay ACHl then falls back a circuit is completed for relay SR of the trunk relay. group {-TRGl which in turn completes a circuit for relay COR which cuts oil the relay recorder group. Relay SDR tie-energizes and removes earth from conductorB-fi, relay SRM falls back and opens the circuit of relay OMB which releases after a short intervaland ClOSESQCOIHbflCtlOO. It will: also beseen later that the operational the plunger arm Pnfifi-occursat the: same instant as the operation of relay FR in the relay recorder group RRGl. It is ofcourse necessary for the master switch to set all the idle plungers adjacent to the outlet or answering end of the trunk relay group over which the call for subscriber 56 has been initiated, and battery Was accordingly connected t0'contact105 over conductor 104 by the operation of relay SDR at the instant of the termination of the second digit; contact 105 corresponding in position to the connection ,of'the outlet end of the trunk relay groupinzthe bank of the line switches. The connection of batterycto conductor 104 may be traced as follows: battery, selection initiating relay SIR, contact 108, conductor 107, contact 106, conductor 1'04, contact 105, Wiper 103, contact 102, contact 101, upper Winding of differential locking magnet LM, contact 06, to earth; and since only one circuit such as that just described can be closed at a time and consequently only one relay such as SIR can be energized at a time; then assuming that the relay SIR (which, as has been described, is associated with the recorder which in turn is associated with the trunk relay group T RG1) is operated it will be seen that all theplungers have been aligned opposite the springs connected to the outlet end of the relay group TRGl shown in Fig. 2. Relay SIR energizes over this circuit and closes contact 109 for a purpose to be described later,'opens Contact 110, thereby opening the maintaining circuit for relay ACHl, which had extended over contact 111. At contact 124 relay SIR closes a circuit for the-units relav as will be described later, and at contact 112 closes a circuit for one of the tens relays. When relay SIR closes contact 112 a circuit is completed as follows: earth, contact 112, contact 1130f relay Z, which it will be recollected was energized after the transmission of the'first'digit, contact 114 of relay Y, which was also'energiaed, conductor115,

relay TD5 to battery. Relay'TDli'is provided individual to subscribers whose first digit is five, and consequently is operated every time a subscriber having one of these numbers is called. Since, in tlire'prescntexample, subscriber 56 'isibeing called,=-relay TDE). energizes and closes contacts 116 to 122 inclusive. Earth is connected over these contacts tooach of seven conductors Such as conductor 123 which receivesits earth conneo tion at contact 121 and then proceeds directly to the line switch of subscriber 56; similar single conductors connect each of the other of contacts 116 to 122 inclusive to one of the line switches of subscribers whose numbers have five as their first digit.

The connection of earth to conductor 123 causes a circuit to be completed for relay UCR56 as follows: earth, contact 121, conductor 123, contact 600, winding of relay UCR56 to battery; relay UCR56 energizes, thereby opening contact 602 and closing contact 603.

It will be seen that the earth connected to conductors similar to conductor 123 closes a circuit for each of the relays such as relay UCR56, i. e. relays UCR5155 and UCR57 provided that the corresponding line switch is not busy; if any of the line switches of subscribers 5157 are busy the relay corresponding to relay UCR56 will be cut off at a contact corresponding to contact 600.

In the further example illustrated, yiz.

line switch of subscriber 52, if the line switch 1 is idle a circuit is closed for relay UCR 52 over the following circuit; earth, contact 117, conductor 98, contact 601, relay UCR52 to battery; relay UCR52 energizes thereby opening contact 604 and closing contact 605. If the line switch had been busy the circuit of relay UCR52 would have been open at contact 601 which is maintained open during a call by the lower winding of relay PM52.

Relay SIR in addition closes contact 124,

:3 thereby completing a circuit as follows:

earth, contact 124, conductor 125, units relay UR to battery; relay UR energizes and closes contacts 126 to 132, inclusive. Of these, contact 127 is connected to conductor 133 which connected to contacts such as 603 of the relays UCR of the line switches of each of the subscribers whose numbers have six for the second digit. Each of the other six contacts such as 127 is connected to a corresponding 5; set of seven contacts. In the further example No. 56 and that magnet only as follows: bat

tery, upper winding of. relay FR, contact 109. contact 188, contact 77, contact 134, contact 135. conductor 136, contact 127, conductor 133, contact 603, pull-down winding of magnet PM56 of the line switch of subscriber No.

56 to earth. The pull-down Winding of ma gnet PM56 accordingly energizes and causes the plunger of the subscribers line switch to plunge closing contacts 137, 138 and 139, thereby establishing connection with the trunk relay group TRG]. If subscriber No. 52 is free. relay UCR52 will operate and close contact 605, but no circuit will be completed for magnet PM52 since conductor 630 is only connected to the upper winding of relay FR when the units digit 2 has been registered on the chain of counting relays FR1 to FR4. The operation of the relay PM56 also opens contacts 140 and 141, thereby cutting off the line relay LR56. The circuit of relay UCR56 is opened at contact 600 but the relay remains operated for a sufficient time to allow PM56 to lock energized over its lower winding before the circuit of its upper winding is broken at contact 603. The magnet PM56 energizes over its lower winding, contact 138, release trunk conductor 143, to earth on contact 24.

t will be noted that earth is already Waiting on release trunk conductor 143 so that a circuit is completed for the lower winding of relay PM56 as soon as contact 138 is closed. If the called line were busy, no circuit would be completed for relay FR in series with the pull-down winding of relay PM56, and accordingly relay FR would not energize. It should be understood that all the foregoing operations have taken place in between the dcenergization of relay CH1 and deenergization of relay ACHL It will be remembered that the circuit of relay ACHl was opened when a circuit was closed for relay TD5 at contact 112. Relay ACHl, however, owing to its slow release feature was held operated for a short time until relay FR had energized after the plungers of idle line switches had been aligned opposite the outlet end of the trunk relay group under consideration, trunk relay group shown in Fig. 2). If relay FR has not energized before relay ACHl releases. the following circuit is completed: earth. contact 73, contact 144, contact 145, contact 146, conductor 147. contact 148, conductor 46, upper winding of relay BR to bat tery. Relay BR accordingly energizes and gives the busy signal as previously described. 1

()n the other hand, if subscriber No. 56 had recn idle. the pull-down winding of magnet P1156 would have energized and relay FR would have energized, relay FR would open contact- 146 and close a locking circuit for itself over contact 149 and contact 39 to earth so that on relay ACI-Il de-energizing relay FR would be locked up and no circuit would be completed for the busy relay. Relay ACHl. on opening contact 60, releases the relays FR4, FR4A,FR2,FR2A,FR1, FRlA, so that all the counting relays are restored to normal. Relay ACHl on de-energizing when relay FR is energized also completes a circuit as follows: earth, contact 73, contact 144, contact 145, contact 640, conductor 150, contact 151, switching relay SR to battery. SR accordingly energizes and is locked energized over the following circuit: battery, switching relay SR, contact 152, contact 153

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