US1846466A - Telephone system - Google Patents

Description

Feb.` '23, 19132. J. i. BELLAMY TELEPHONE SYSTEM Original Filed March 17, 1928 5 Sheets-Sheet Feb. 23, 1932. u `1. `l. BELLAMY 1,845,466

` TELEFHONE SYSTEM Original Filed March 17, 192,8 3 Sheets-Sheet 2 SEND/NG Inl-m I. EEHamH MVM/Qi@ x. l. BELLAMY L46166 TELEPHONE SYSTEM Originl Filed March 17, 1928 3 Sheets-Sheet 3 Patented Feb. 23, 1932 Unirse erstes PAE'NT OFFICE JOHN I. BELLAMY, OF BROOKFIELD, ILLINOIS, ASSIG-NOR, BY MESNE ASSIGNEENTS, TO

.ASSOCIATED ELECTRIC LABORATORIES, INC., OF CHICAGO, ILLINOIS, A CORPORA- IION F DELAWARE TELEPHONE SYSTEM:

Original application filed March 17, 1928, Serial No.

The present invention relates to telephone systems in general, but is concerned more particularly with automatic telephone systems employing register senders, although certain p of its features are not conlinedV specifically thereto.

A further object is the production of a new and improved trunking arrangement for using a plurality of levels per Oroup at selectors that have only a few outgoing trunk groups, thereby ,decreasing the tratic per selector per level so as to enable trunk economy to be eiiected owing to the increased multipling flexibility. i5 @ther objects and features, for the most part more or less incidental to the foregoing, will appear upon a further perusal of the specification in connection with the accompanying drawings comprising Figs. 1-4.

This application is a division ot my application tiled March 17, 1928, Serial Number 262,575.

Referring now to the drawings, they show by means of the usual circuit diagrams a suiiicient `amount ot apparatus in a telephone system embodying features of the invention to enable the invention to be understood. Fig. 1 is a schematic diagram indicating how two shelves of ten selectors each vwith their wipers suitably readjusted may be multipled together and with other selectors in order` to iform a flexible and economical trunling arrangement. Figs. 2-4 show a complete register sender and a part of a switch train with which the register sender co-operates to eX- tend connections.

In Fig. 2 there is shown a selector S (also indicated in Fig. 1) having access to two groups of trunk lines, one trunlr line of each group being shown. rlhe trunk circuit TC is inserted in the trunk line comprising conductors 201-203 extending to the selector' S and has associated therewith the register-sender selector RSS. The trunk lines such as the one comprising conductors 201-203 may be seized by calling lines through line switches or finder switches in any well known ordesired manner. A feature of the present disclosure is that the usual release relay and the usual switch- 262,575. Divided and this application filed May 17,

Serial No. 453,357.

4ing relay of the trunlr circuit preceding the iirlst selector have been combined into a single re ay.

Figs. 8 and 4 taken together show the register sender, together with the common inter` mediate distributing trame I. D. F .F ig. 4, which is common to a plurality ot' register sender. rlhe apparatus shown in Fig. 3 comprises the registers A, B, C for registering the three initial letters of called oiiice names, the thousands, hundreds, tens, and units registers for registering the subscriber digits in called numbers, the sending switch, and the relays 311-315.

The portion of the director shown in Fig. 4 includes the input control switch having wipers 411 and 412, the output control switch having wipers 404 and 405, the'impulse generating and correcting relays 40G-409, the translating switch TS, and the associated relays 401, 402, 414, 415, 439, and 44E-445.

The apparatus Yhaving been described in general, a detailed description of its operation will now be given. For this purpose it will be assumed that the trunk line comprising conductors 201- 203, Fig. 2, is seized incidental to a call to a line terminating in the oiiice whose designating digits corresponding to the three initial letters of its name, are 3, 4, and 2.

TWhen the trunk line is seized, the conductors of the calling line are extended to conductors 201 and 203, whereupon line relay 204 of the trunk circuit TC operates over the calling line and places ground at its middle upper armature on release trunk conductor 202 so as to maintain the connection and to render the trunk line busy. At its inner upper armature relay 204 closes a circuit for relay 206 and stepping magnet 207 of the registerselecting switch RSS in series, and at its upper armature it connects test wiper 209 of the switch RSS to the junction of stepping magnet 207 and relay 206. As a result, relay-206 is short circuited and stepping magnet 207 is operated by a ground potential in case the register sender on which the wipers of the switch RSS are standing is busy. Operating magnet 207 operates through its self-interrupting contacts and advances the wipers 208- inn 211 step by step in search of an idle register sender. Assuming that the register sender shown in Figs. 3 and 4 and reached over conductors 212-215 is the first one found to be idle, the wipers of the switch RSS come to rest when they reach the bank contacts associated with this register sender, due to the absence of ground potential on conductor 213. At this point, relay 206, being no longer short circuited, operates in series with magnet 207. Magnet 207 does not operate at this time due to the relatively high resistance of relay 206. Upon operating, relay 206 places a multiple ground connection on release-trunk conductor 202 at its upper armature so as to maintain the trunk line guarded during the impulsing action of line relay 204, which is subsequently to take place; it opens a point in the test circuit and grounds wiper 209 at its inner upper armature thereby grounding conductor 213 so as to guard the seized register sender; and at its remaining armatures it connects up wipers 208, 210, and 211.

Line relay 221 of the selector S now pulls up over conductors 214 and 215 and wipers 210 and 211. Upon operating, relay 221 closes a circuit for relay 222 through the upper winding of series relay 223 and vertical magnet 226. Relay 222 operates in this errcuit but relay 223 does not operate due to the relatively high resistance of relay 222. Vertical magnet 226 fails to operate for the same reason. It will be noted that while the contacts of relay 221 are in mid position there is a shunt around the high resistance relay 222 through the lower resistance winding of relay Relay 223 and vertical magnet 226 would operate as a result of this condition ex cept for the fact that the condition exists during only an extremely short time as the contacts pass from one position to another. Upon operating, relay 222 makes a multiple ground connection to release trunk conductor 202 at its upper armature, and at its lower armature it opens a point in the circuit of release magnet 227 and locks itself to battery through the vertical magnet 226, thereby shunting the upper winding of relay 223.

In the register sender, release relay 312 Fig. 3 operates over release trunk conductor 213 when the said conductor is grounded as above described, and prepares the register sender for operation by ungrounding restoring conductors 302 and 304 of the output control switch in Fig. 4 and release conductor 30G of the input control switch of Fig. 4 and of the registers in Fig. 3.

IVhen the calling subscriber dials the first oflice digit 3, line relay 204 of the trunk circuit TC falls back three times momentarily. Each time it falls back, relay 204 opens the circuit of slow acting relay 206 at its inner upper armature, but relay 206 is sufiieiently slow to release that it remains operated throughout the series of impulses. As a fur ther result of each deenergization of relay 204, a circuit is closed at the lower armature of the relay, through the lower contacts of relay 206, wiper 208, conductor 212, series relay 415, Fig. 4, wiper 412 and the bank contact on which it is standing, and the associated conductor to the operating magnet of the register A, Fig. 3. In response to the three impulses received over the above traced circuit, the operating magnet of register A advances the wiper of the register three steps into engagement with the third off-normal bank contact. Series relay 415, Fig. 4, operates when the first impulse current is trans mitted through it, and, being slow acting, remains operated throughout the digit. Upon operating, relay 415 operates the slow acting relay 414, with the result that a circuit is closed, when relay 415 falls back, through contacts ofl relay 414 for operating magnet 410 ot' the input-control switch. This circuit is opened a moment later when slow acting relay 414 Jfalls back again. Wiper 412, on advancing from its first contact to its second contact responsive to the operation of magnet 410, shifts the impulse conductor from the operating magnet of register A, Fig. 3, to the operating magnet of register B, and wiper 411 closes an operating circuit for the preliminary start relay 443 associated with the translating switch TS, whereupon the operation of the translating switch may start in a manner to be subsequently described.

IVhen the second ofiice digit 4 is dialled, the four impulses are transmitted over a circuit as hereinbefore traced to wiper 412 and then by way of the second back contact thereof to the opera ing magnet of register 1);, Fig. 3, whereupon the wiper of register B is set in accordance with the digit 4.

The input control switch of Fig. 4 advances another step following receipt of the second ofiice digit with the result that the third digit is directed to the operating magnet of the register' C, which register records the third office digit 2. In a similar way, the thousands, hundreds, tens, and unit digits are recorded on the corresponding registers shown in Fig. 3, the input control switch of Fig. 4 being advanced one step at the end of each digit- At the end of the units digit, wiper 412 lands on a. dead Contact and the wipers remain in this position until the register sender is released.

Returning now to the point at which relay 443 is first operated at the end of the registration of the first ofce digit due to the advance of wiper 411 of the output control switch, relay 443 connects up relay 442 to the wiper of register A at its upper armature, and at its lower armature it prepares a circuit for operating magnet 438 of translator switch TS. At this point it may be pointed out that the circles to the left of the tapped battery,"loc-ated tothe leftrof the interme diate distributing iframe IDF and numbered l to 11, represent terminalsto which other terminals represented by similarly numbered circles in F ig. 3 are to be connected. The inter-connecting conductors have been omitted in the drawings in order to avoid undue coinplication and to render the drawings easier to follow. .Vith this in mind, it will be noted that the presence ot the wiper of register A on its third off-normal Contact in connection with the conductor connected to the No. 3 battery tap extends the potential ot this battery tap through the upper Contact ot relay 443 to the right hand terminal of test relay 442. Relay 442 will operate atthis time if its lett hand terminal'is connected to any potential other than that to which its right hand terminal has been connected by register A'. Assuming now that wiper 437 is standing on a bank contact cross connected to some battery tap other than No. 3, relay 442 operates due to the difference in potential at its two terminals and closes a circuit for stepping relay 439. 'Relay 439 operates and closes a locking circuit tor itself at its inner upper armature through contacts ol' operating magnet 436. Relay 439'also closes a circuit for operating magnet 438 at Aits lower armature and at its three upper arinatures it disconnects relays 4405-442 so as to prepare for the next step. Relay 442 falls back. When the operating magnet 433 has completed its stroke, it opens the circuit of relay 439, whereupon relay 439 falls bach and opens the circuit of the operating mag net, at the same time connecting up relays 440 442 again. W'hen the circuit of the operating magnet is opened, the magnet falls back and advances the wipers 431-437 one step. lf the potential now Vplaced on the left hand terminal of .relay 442 through wiper 437 of the translating switch and the bank contact on which it is standing is ditterent than the potential placed on the right hand terminal of: the relay, the relay operates again, whereupon the translating switch is advanced another step.

llhen the wipers of the translating switch Aarrive Yupon the contacts assigned to an office whose first digit is 3, relay 442 fails to operate again because the same potential is now on both terminals, and the translating switch remains inert until the second digit is dialled, as hereinbefore described, whereupon relay 444 is included in the circuit in se "ies with relay 445 when wiper 411ot1 the input control switch advances to its third contact at the end of the second digit. Relay 444 connects up test relay 441 to the wiper of register B, Fig. 3, with the result that relay 441 operates and closes a circuit for stepping relay 439 to bring about a further advance of the switch, in case the potential encountered by wiper 436 rot the translator'switch TS and placed on the left hand terminal of the relay is unlilre a potential previously placed on the right hand terminal of the relay when register B was set on its fourth oli-normal contact. rlhere be in practice a number of othces all having the common iirst digit 3. Ordinarily, only a few of these oiilces will have the digit 4 as the second digit, and the translating switch will now be further advanced until the wiper 436 encounters the iirst bank Contact cross connected to the No'. 4 battery tap;

Upon the receipt of the third digit and the setting of the register C in the manner herein before described, the output control 'switch includes relay 445 in series with relays 443 and 444 through contacts olthe transfer relay 446, whereupon relay 446 operates and connects up test relay 440. rlhe righthand terminal of test relay 440 has previously been connected to the No. 2 battery tap by the wiper of the C register upon the response of this register to the third eilice digit 2. As a result, relay 440 operates and causes a further stepping action of the translator switch TS until the wipers 431-437 varrive upon the bank cont-act set 342 shown in the drawings. ln this position only, the potentials supplied to the lett hand terminals of the relays 440-442 are, respectively, the saine as the potentials supplied to the right hand terminals of the relays, and no one of the three test relays can operate. Under this condition no further advance of the translator switch takes place and the stiily adjusted transfer relay 446 operates due to the Jfailure o stepping relay 439 to operate. lt will be noted that the circuit of relay 446 is prepared upon the operation of relay 445, at the end of the registration ot the third ollice digit, and that the circuit of relay 446 is closed each time the stepping relay 439 is deenergized. Relay 446, being stitliy adjusted, does not operate until relay 439 remains deenergized for an appreciable length of time. Upon operating, relay 446 locks itself to the grounded banlr of wiper 411 at its upper armature, at the same time opening the circuit of relays 443-445, whereupon these relays fall back and disconnect the test relays 440-442. At its lower armature relay 446 eXtendsground' over start conductor 447 to relay 407 of the impulse generating relays 406 and 407 so as to start the retransmission of impulses.

lVhen ground is placed on start conductor 447, relay 407 energizes and closes a circuit for relay 406, at the saine time placing ground on impulse conductor 443. Relay 406 energizes and opens the circuit of relay 407, with the result that relay 407 shortly falls back and opens the circuit of relay 406 and removes ground from impulse conductor 443. Relay 406 falls baclr and recloses'the circuit of relay 407, whereupon relay 407 operates again. This operation continues in this manner as long as there is a ground potential on start conductor 447. The copper collar on the core of relay 407, as indicated by the black upper portion of the relay core, is placed on the armature end of the relay rather than on the heel end of the relay so as to render the relay slightly slow to operate, in addition to being slow to release. The operation may be further varied by giving relay 406 a relatively stiff adjustment so that it will not operate until the core becomes practially fully magnetized responsive to its circuit being closed.

Each time ground is placed on impulse conductor 448 impulse-correcting relays 408 and 409 energize in series. Relay 408, being lightly adjusted, operates first and closes a locking circuit for itself and for relay 409 at its lower armature, and at its upper armature it prepares to ground impulse conductor 303. Then relay 409 operates, shortly after relay 408 operates, it completes the grounding of conductor 303 at its upper armature; short circuits relay 408 at its lower armature; and at its inner upper armature it closes a circuit for its two windings in series. The closure of this circuit is without immediate effect, however, owing to the fact that the upper winding of relay 409 is short circuited through the lower contacts thereof by the ground potential on conductor 448. After it is short circuited at the lower contacts of relay 409, relay 408 receives no current from the circuit including the exchange battery, but there is a circulating current set up through its winding and through the lower contact of relay 409 due to the receding magnetism in its core, which renders the relay slow to release as is well known. Assuming first that the impulse delivered by relay 407 over conductor 448 to relays 408 and 409 is shorter than a standard impulse, rela 407 falls back before relay 408 falls back, but relay 409 remains operated through the lower contacts of relay 408 until relay 408 falls back, maintaining the ground potential on impulse conductor 303. lf, on the other hand, the impulse delivered by relay 408 is longer than a standard impulse, relay 408 falls back while relay 407 is still operated,

i and relay 409 remains operated through the lower armature of relay 407 for the duration of the impulse. In any case, relay 408 falls back, following its short circuiting at the lower contacts of relay 409, after a sufficient time has elapsed to transmit an impulse of standard length over conductor 303. lVhen it falls back, relay 408 terminates the impulse at its upper armature, and at its lower armature it removes ground from impulse conductor 448.

lVhen the ground potential is removed from impulse conductor 448 at the last point, either at rela-y 407 or 408 depending upon the adjustment of relays 406 and 407, the short circuit is removedfrom the upper Awinding of relay 409, whereupon the two windings are energized in series. The upper winding is differential with respect to the lower winding and preferably has more turns than the lower winding, with the result that the relay falls back almost instantly in preparation for the next impulse.

The foregoing operation of correcting relays 408 and 409 is repeated each time a ground potential is placed on impulse conductor 448.

Itis to be noted that the impulses delivered by relay 408 will be independent of reason able variations in the potential of the eX- change battery owing to the fact that relay 409 is adjusted to operate when the current fiow through its windings reaches a. predetermined value. If the potential of the exchange battery is high, this predetermined value is reached more quickly and relay 409 operates sooner following the closure of the circut through relay 408 and the lower winding of rela-y 409, whereas if the voltage of the exchange battery is low relay 409 does not operate so quickly, but waits until the current value through the circuit of the two relays reaches the same point as before. It will be understood of course that in either case relay 409 operates within a very small fraction of a second in the embodiment herein disclosed. It will be noted further that the variation in the time required for relay 409 to operate does not affect the length of the impulse delivered over conductor 303, because, while the circuit is prepared by relay 408, it is not completed until relay 409 operates to short circuit relay 408.

Return now to the point at which the impulses begin to be placed upon the impulse conductor 303. Responsive to the first impulse on this conductor, operating magnet 316 of the sending switch Fig. 3 operates through contacts of stop relay 314 and, upon subsequently deenergizing when the impulse is terminated, advances the wipers 317 and 318 one step. Although, at its left hand contacts, operating magnet 316 opens the bridge across the outgoing impulse conductors 214 and 215, there is a substitute bridge at this time closed through the upper contacts of pick-up relay 313. Upon each succeeding impulse, magnet 316 operates again and advances the wipers 317 and 318 one step upon deenergizing at the end of the impulse. Upon the first step of the wipers 317 and 318, wiper 317 encounters a grounded bank contact, closing a circuit for pick-up relay 313. Relay 313 prepares the outgoing impulse circuit by removing the local shunt at its upper contacts, while at its inner contacts it closes a circuit through contacts of stop relay 314 and over conductor 301 for the operating magnet 403 of the output control switch, Fig. 4. Magnet 403 operates-and prepares to advance thewipers 404 and 405 when it subsequently deenergizes.

With pick up relay 313 operated, each operation of magnet 316 results in an opening of the bridge across conductors 214 and 215, each such interruption being termed an impulse. I Referring now tothe cross connections at the IDF, Fig. 4, it will be noted that the bank contact on which the iirst-digit wiper 431 ot the translating switch is standing is cross connected to the sixth battery tap. This connec tion predetermines that the first digit transmitted will be the'digit. 6.

At the end ot the iirst impulse transmitted over conductors 214 and 215 at the left hand contacts of operating magnet 316, the test wiper 318 is advanced one step to the No. 2

vbattery tap. By this arrangement, if vthe digit to be terminated is` the digit 1, current of the correct polarity flows through the polarized test relay 315 operating the relay to terminate the digit. In the present case, however, the digit to be sent is 6 and the potential placed on the left hand terminal of the polarized test relay 316 isl the potential of the siXth battery tap causing current to flow through the polarized relay in the direction opposite to `that in which it must How in order to operate the relay. This current iiow is overa circuit path including the lower contacts of stop relay 314, conductor 305, wiper 405 of the output control switch, wiper 431 of the translating switch TS, the bankcontact on which it is standing, and the associated jumper on the intermediate distributring frame IDF to the .No 6 battery tap. Upon the next step of the wipers ot' the send ing switch, wiper 318 encounters theV No. 3 battery tap, whereupon a current tlow in the same direction as before, but of a lessened intensity` flows through the test relay. The

which time no current flows through the polarized test relay due to the fact that it is connected to the same battery tap at both terminals. However, upon the neXt step of the wipers, wiper 318 encounters the No. 7 battery tap, whereupon the current of the correct polarity flows between the No. 7 and the No. 6 battery7 tap through the polarized test relay over Vthe circuit path above traced. The polarized test .relay 315 now operates and closes circuit for stop relay 314, whereupon stop relay 314 operates to terminate the digit. At its upper contactarelay 314 places a short circuit across conductors 214 and 215; at its lower armature it disconnects conductor 305 from the polarized test relay 315 and transfers it to the polarized skip relay 311; at its inner upper armature it opens the impulse circuit of magnet 316 and closes its restoring circuit through its self-interrupting contacts 5 and wiper 317 and at its middle upper armarupter contacts and advances the wipers 317 and 318 to their normal positions, whereupon the buzzing action stopsdue to the fact that wiper 317 encounters an ungrounded contact in its normal position. At this time the circuit of pick up relay 313 is opened, and the relay shortly falls back and opens the locking circuit of stop relay 314. Relay 314 falls back after a slight interval and reestablishes the circuit tor transmitting the second code digit.

Wiper 405 of the output control switch is now standing on its second bank Contact, eX- tending conductor 305V to the second code wiper 432 of the translating switch. The bank contact on which wiper 432 is now standing is connected through an IDF jumper to the tenth battery tap, predetermining that the nent digit will be'the digit 0, corre-A spending to ten impulses. It will be understood of course that the value ot the various code digits may be assigned arbitrarily at the IDF in order to lit the trunking system that exists from the calling oice to the called oflice. Since thelDF connection is to the tenth battery tap, the sending switch of Fig. 3 continu-es to operate without reversing the current flow through the polarized test relay 315 until wiper 318 lands upon thecontact connected to the eleventh battery tap, atter the tenth impulse has been sent out. When this occurs, relay 315 operates and terminates the digit in the previously described manner. y

The advance of the output control switch from its second to its third position takes place in the manner described above, whereupon wiper 405 renders effective the third code' wiper 433 ot the translating switch. Since this wiper is standing on a bank contact cross connected to the seventh battery tap, the sending switch of Fig. 3 sends out the code digit 7, whereupon the output controlswitch is advanced another step.

When the output control switch advances at the end of the third digit, wiper 405 engages the bank contact connected to wiper 434 of the translating switch whose present associated bank contact is cross connected to the skip conductor, or the grounded pole ot the exchange battery. The advance of the output contro-l switch, it will be remembered,

y occurs just at the end ot the digit and respon-A sive to the operation of stop relay 314. It will be recalled also that relay 314 at its lower armature disconnects the sending control conductor 305 from test relay 315 and connects it instead to the polarized skip relay 311. rllhe upper terminal ot' the skip relay is connected to the No. 1 battery tap and the relay is polarized so that it will operate only when the lower terminal is grounded, the connection to any battery tap ot a more negative polarity serving merely to send current through the skip relay in the reverse direction. lVhen the skip relay operates at this time due to the cross connection at the DF, it grounds conductor 304, closing a circuit through the fourth contact in the bank of wiper 404 and the saine wiper and the seltinterrupting contacts of the operating magnet of the output control switch for advanc ing the output control switch through the remaining code-digit position. It will be noted that the output control switch may be advanced through two or more code digit positions, provided the corresponding contacts in the bank of the translating switch are connectedV to the grounded terminal of the exchange battery.

Upon being advanced through the Jfourth position, wiper 405, in its ifth position, eX- tends the control conductor 305 to the wiper ot the thousands register of Fig. 3. Ordinarily, the calling subscriber dials the complete number without hesitation, in which case the thousands register is operated before the code digits have been sent out, and the retransmitting operation does not catch up with the registering operation. However, in case the calling subscriber has hesitated and has not yet dialled the thousands digit, the sending operation is held up because the stop relay 314 is maintained energized, after pick up relay 313 falls, back over a circuit through the rst contact in the bank of the wiper or" the thousands register by potential supplied through skip relay 311 from the No. 1 conductor to the wiper of the thousands register through the lower armature, operated, of stop relay 314 and over conductor 305 and wiper 405 of the output control switch. In this case, the stop relay remains energize@ and holds up the testing operation until the thousands register is operated. Since the output control switch has advanced beyond vthe influence of skip relay 311, it is immaterial whether this relay responds or not.

Assuming now that the subscriber has dialled the number without hesitation. the sending operation continues and the thousands digit is terminated in accordance with the setting of the wiper of the thousands register to which the lett hand terminal ot the polarized test relay 315 is connected after stop relay 314 falls back.

The usual advance of the output control switch takes place following the termination ot the thousands digit, whereupon the hundreds, tens, and units digits ar-e retransmitted in the same manner.

ldlhen the output control switch advances another step at the end of the units digit, wiper 405 encounters its last bank contact, placing a potential on conductor 212 which is obtained over conductor 305 through contacts ot stop relay 314 from the No. 1 battery tap and through skip relay 311. The placing of this potential on conductor 212 closes a circuit through wiper 208 of the register selector RSS and through contacts of relays 206 and 204 for switching relay 205 of the trunk circuit TC. Switching relay 205 operates and locks itself to the grounded release trunk conductor 202 at its inner lower armature, and at its upper and lower armatures it disconnects conductors 201 and 203 from line relay 204 and extends them to the corresponding conductors oi' the selector S, thereby placing the maintenance ot the established connection under direct control of the calling subscriber.

Relay 204 falls back responsive to its disconnection by relay 205 and it opens the circuit of slow acting relay 206. Relay 206 talls back aiter a slight interval and frees the register sender by disconnecting` the wipers 208-211 of the register-sender selector.

In the register sender, release relay 312 falls back when the register sender is treed and it grounds release conductors 302, 304-. and 30G, causing the operated apparatus of the register sender to restore to normal. The restoration to normal of the output control switch is accomplished through the last contact` in the bank of wiper 404 and the seli interrupting contacts of the operating 1nag net 403.

The restoration to normal of the input control switch is accomplished by release magnet 413 which. operates from conductor 306 through the associated off-normal contacts. The registers Shown in the lower part ot Fig. 3 restore to normal in the same manner. It will be noted that conductor 304 grounded by relay 312 so as to insure the advance of the output control switch to its seco-nd, third and fourth positions in case oi' a premature release due to the calling subscriber hanging up his receiver while the sending operation is in progress. vlease ot the input control switch results in wiper 411 opening the locking circuit ot relay 446, whereupon relay 446 ungrounds start conductor 447, permitting the relays 40G-400 to cease their operation.

Now, when the first train oi impulses, reoresenting the digit 6, is transmitted to the selector S over conductors 214- and 215 from the sending switch, line relay 221 of the sclector S falls back momentarily sii: times. Each time it falls back, relay 221 shunts relay 222 by connecting the lower winding of relay The re- 223 in parallel with the winding ot relay 222. It is to be noted that the upper winding of relay 223 is open circu'ited at this time to permit the current flow to buildup quickly in relay 223. Relay 222 is maintained operated while 'shunted by relay 223 due to the circulating current through relay 222. Relay 223 and 'magnet 226 roperate in series. y

lach time relay 221 reoperates, it removes the shunt from around relay 222, after replacing the upperwinding of relay'223 in a closed circuit through ycontacts ot relaysv222 and 225. lllhen this occurs', magnet 22S/falls back due tothe high resistance ot relay 222, but relay 223 remains operateddue to the circulating current in--its Aupper winding. lach time relay 221 releases again, vertical magnet 226 operatesV again and anotherV current flow takes place through the lower winding ,of relay 223. j f

llt the end of the vertical movementof the selector, wipers 229-231 have been raised opposite the sixth level ot bank contacts by the six operati-ons ci vertical magnet 226, and relay 223 shortl' Yfalls back owing to Vthe cessation of the circulating current in its upper Winding, starting the hunting o1n the selector. The circuits are prepared for hunting action of the selector upon the irst oil-normal movementof the selector when relay 224 operates through the contacts of the operated relay 223the associa-ted offnormal contacts, and the interrupter contacts of rotary magnet 22S.Y Relay 224 locks itselie to release trunk conductor 202 at its upper armature and prepares a circuit .tor

rotary magnet 228cat its lower armatures. Then, when relay 223 falls back at the end ot the vertical movement, the prepared circuit of the rotary magnet is closed whereupon the rotary magnet operates, advancing the Wipers 229-231 onestep into engagement with the i'irst set of bank contacts in the sixth level. Near the end of its stroke,l magnet 228 opens its interrupter contacts."-

whereupon stepping relay 224 falls back and opens its own locking circuit and the rotary magnet circuit. The rotary magnet now falls back and closes its interrupter contacts again.

The further operation ofthe selector depends upon whether the trunk line terminating in the first set of bank contacts is busy or idle. lf thev irst set ot contacts tests idle, switching relay 225 now operates, seizing the connected trunk line. lf th irst tests busy, relay 225 is short circuited by the ground potential encountered on the busy test contact by test wiper 230 and does not operate. This saine ground potential is extended through the olf-normal contacts or" the selector and the interrupter contacts or" therefore seized.

- grounded `responsive to being disconnect 225, and places the lower winding of' relay advance' byiclosing the rotary-magnet circuit.

This alternate operation of rotary magnet 223 and stepping relay 224;;continues until an idle trunk line is reached. lt will be assinnedn that the trunk line comprising conductors '232-234.- is found to be idle and is When this trunk line is reached, switching relay,"T 225 is not short circuited and it operates from the grounded release trunk conductor 202 in series with stepping relay 22a through the associated oilenormal and interrupter contacta Relay 22% does not operates in series with relay 225 owing to the relatively high resistance'o'f the latter. -Upon operating, relay 225opens the vertical magnet'operating circuit and a point in the release magnet circuit at its inner lower contacts, leaving relay `222 energized through contacts of relay 221 andthe upper winding of relay 223. n t its inner upper contacts, relay'225 opensa' point in the testfcircuit and connectsA wiper 230 to rthe release trunk r conductor 202, thereby making the seized trunk busy immediately. At its upper and lower armatures, relay 225 disconnects the incoming talking conductors from relay 221 and entends them through wipers 229 and 231 andthe bank contacts on which they are standing to conductors 292 and 234 respectively of the seizedY trunk line. The line relay of the seizedV trunk line (not shown) now operates and causes the associated release trunkconductor to be grounded in the usual manner so as to-hold up' the 'connection tromthe seized trunkline. Linerelay 221 fallsback by relay 223 in shunt of. the winding ot relay' 222,`at the same time opening tne initial energizing circuit of relay 222. SinceV the locking circuit of relay 222 now open at the inner lower contacts otrelay 225, no further current lows through this relay from the eX- change battery, but the relay does not fall back immediately due to the circulating `current through its winding in series with the lower winding or" relay 223. fitter an interval, relay 222 falls back' and prepares acircuit for the release magnet at its lower armature. removing one ground connection 'from conductor 202 at its upper armature.

Responsive to the remaining trains of irnpulses retransmitted by the sending switch as hereinafter described, the connection is eX- tended to the desired ohce and is completed therein to the desired line. The called party is signalled in the usual manner. When the called partyl replies the conversation may take placeas desired. rl`he connection is released in the usual manner when the receivers are replaced upon the termination of the conversation. The release of the selector-S takes place relll) \ Vany assigned office.

sponsive to the removal of the ground potential from release trunk conductor 233 of the trunk line, which results in the deenergization of switchingl relay 205 of the trunk circuit TC and in the deenergization of switching relay 235 of the selector S. When relay 225. falls back it closes at its inner lower contacts a circuit through the lower armature of relay 222 and the associated off-normal contacts for release magnet 227, the operating current being obtained from the lower winding of relay 223 through the normally closed ycontacts of line relay 221. The release magreached, the release magnet and relays 223 and 224 fall back. Relay 224 ungrounds conductor 202.

Referring now again to Fig. 4, it will be noted that the spare set of bankcontacts shown in the bank of the wipers 431-437 of the U. translator switch TS has one contact (the Contact in the bank of wiper 437 associated with the A register, Fig. 3,) connected to the grounded terminal of the exchange battery, it is impossible for the translating switch TS 2 to stop onl this set of bank contacts because no setting of the A register will satisfy the required condition for stopping because there will be a potential difference across test relay 442 regardless of which position the register A is set in. Spare sets, it will be understood, may exist when there are fewer offices in the system than there are sets of contacts in the bank of the translator switch.

It will be noted that the upper set of contacts shown in connection with the translator switch is labelled, Unassigned-office set. This set of contacts is reserved for disposing of calls wherein' the setting of the A, B, and C registers, Fig. 3, does not correspond to The contact in this set which is wiped over by the test ywiper 437 associated with test relay 442 is connected to the grounded terminal of the exchange battery so as' to prevent the translating switch from stopping on the unassigned-office set. The relays 401 and 402 are provided to dispose of the call when the unassigned-otlice set has been passed over the second time. If` the setting of the A, B, and C registers is in accordance with any assigned office, the translating switch will stop without making more than a single complete revolution. Tf the switch makes more than one revolution and therefore passes the unassigned-office set twice, the A, B, and C registershave been incorrectly set and the call should be cleared out from the register sender without further delay. In order to accomplish this, there is a ground potential through contacts of relays 446 and 445 and the associated resistancef Wiper 431 engages the upper contact of the unassigned-office set each time the wipers of the translator switch pass over this set. Upon this ground potential heilig placed on this contact by wiper 431, relay 402 operates through contacts of relay 401, locking itself energized and opening a point in the special switch-through circuit at its lower armature. At its upper armature relay 402 operates relay 401 from the grounded release trunk con- Vhen the wiper 431 passes off the bank contact in question, the circuit of relay 402 is opened whereupon relay 402 falls back and opens a further point in its own circuit, leaving relay 401 locked up to conductor 213.

lVhen the upper contact of the unassigned-f oilice set is again grounded upon the next passage of wiper 431, the ground potential fails to operate relay 402, because relay 401 is operated, and av circuit is closed through contacts of the non-operated relay 402 andr sa through contacts of the operated relay 401 and over conductor 212 as above traced to the switch-through relay 205 in the trunk circuit TC. Relay 205 operates and switches the connection through, cutting off relay 204,VV

which releases relay 206 to free the register sender.

It will be apparent that the above switchthrough operation takes place with the selector S non-operated because no digits can be sent out in any case until after the translating switch TS has completed its operation. Under this condition, the incoming conductors 201 and 203 are extended through to line relay 221 of the selector S, which line relay is ordinarily disconnected by the usual operation of the selector before the switching relay 205 operates. In this case, a .special tone from the tone source through the transformer 212 is placed on the calling line through the lower winding of relay 221, informing the calling subscriber that the number is unobtainable and that he must replace his receiver and try again.

In order to prevent the possible completion of the connection to a. subscribers line in case the calling subscriber should disregard' the tone and continue to dial, the operating circuit of the vertical magnet 226 opened at the upper contacts of relay 205 so as to prevent the vertical. magnet from responding to deenergizations of line relay 221. The connection to the selector is released when the calling subscriber replaces his receiver.

Referring now` particularly to Figs. 1 and ten, each group being called a shelf',there being a multiple from each contact in the bank of one switch to the corresponding contacts of adjacent switches, a connecting rack is provided common toa plurality of shelves and a cable known as a bank cable is run from each switch shelf to the frame. This cable contains as many wires as there are'contacts in a switch bank. Each shelf is represented on the connecting frame by a set of contacts, to which the corresponding bank-cable wires are connected, and as many shelves as desired are multipled together as regards their several levels and are appropriately connected to trunk cables representing trunks extending to the next order of local switches'or to inter office trunk lines as the case may be.

ln case there are ten similar trunk groups accessible to a group of selectors, the grouping is fairly simple, as the banks of ten shelves may be multipled together and connected to ten groups of outgoing trunk lines, one group per level. 10() switchesrinvolved and there are 100 outgoing trunks.

Assume now that the tra-flic on one level ofV the group of selectors is slightly heavier than the traliic on any onev of the'other levels, the ten trunks carrying the load from that one level may become overloaded, in which case it is necessary to rearrange the multipling so that ten trunks will carry the load of possibly 8 or 9 shelves as regards the level in question. Tf the trafic were rstill heavier on the level in question ten trunk lines might be ablel to handle traffic from only three or four shelves. Under such circumstances, with the level load as heavy as assumed, the addition of the traffic of another shelf onto a trunk group increases the total number of calls delivered into the group quite materially, and it is difficult to secure a fine distribution of the traffic in `order to keep each trunk group working efficiently without being overloaded.

Tt may be pointed out that the condition such as outlined above of abnormally heavy traiiic per shelf, per trunk group is rarely encountered when ten full levels of a group of selectors is working, because in that case the calls are ordinarily distributed more or less evenly over the various levels of the shelves, with the result that a level of a large number of shelves can be multipled together to, send traffic into a group of ten trunks as Vgro up is increased Tn this case there are above outlined. In case, however, there are only a small number of groups of trunks accessible to a selector, two for example, a given shelf of switches will send approximately half the traffic into a given trunk group if the calls are equally Vdivided and more than half its traflic in onec'ase if the traffic to that trunk group is heavier. The same condition obtains but to a lessening degree as the number of trunk groups per selector from two up toward the full number.

llt may be pointed Vout further that it is usually in the inter-@flee portion of the trunking system that selector groups are encountered having access to only a small number or trunk groups. This is due ofcourse to the fact that inter-ol'lice trunking is laid out along the lines necessary to secure the most eflicient use of the outside cable system rather than from the standpoint of the economy of switching equipment. Now, if the register senders could be arranged to send their calls systematically to all levels of a selector group having only two groups of trunks outgoing therefrom, half the levels could be multipled into one group and half the levels into another groupwith the result that a line distribution of traffic could be obtained.

The grouping of Figs. 1 and 2is made under the assumption that there are only two trunk groups accessible to the first selectors in the office in which the equipment shown is located. Of these groups, the one including the trunk comprising conductors 232-23l is an outgoing group, while the group including the trunk comprisingV conductors 2%237 is assumed to lead to local thousands selectors. Assuming that the local traffic is substantially equal to the outgoing traffic,

vthe calls will be fairly equally divided between the twogroups. The outgoing'group is arranged to receive traffic. from the upper five levels of the selectors, while the local group is arranged to receive tralic from the lower live levels. In order to direct the traffic into the various levels, the register senders are arranged to send out the digit 6 if the call is outgoing and to send out the digit 1 if the call is a local call. In order to complete the distribution, the wipers of the several switches on a given shelf, for example, s ielf 1 of F ig. 1, are set in various positions. F or example, Lthe wipers of selectors 1 and 2 of Fig. 1 have their wipers set in the normal way, one step below the lowerbank level; the wipers of selectors 8 and 4 of this shelf are set opposite the first level; the wipers of selectors 5 and 6 are set opposite the second level; the wipers of selectors 7 and 8 are set opposite the third level@ and the wipers of selectors 9 and 10 are set opposite the fourth level. As a result, when the digit 1 is sent, the selector used may be operated to connect with a trunk line in any one of the lower five levels, depending upon the selector used, while it the digit (i is sent the selector used may connect with any one of the upper live levels, depending upon which selector is used. lt will be seen, therefore, 'that the traiiic from two selectors of the shelf of ten is sent out on each of the upper live levels to the outgoing group and sent out on each of the lower live levels to the local group. The traliic therefore has been reduced to small units, while eaving the shelf multipling standard.

ln Fig. l it will be noted that a trunk sub-group (Si, containing ten trunks as indicated by the label 10'l`.) receives traliic from the upper live levels ol' shelil and from the ninth and tenth levels of shelf 2, making a total of seven shelf levels supplying trailic to ten trunks. lt will be noted further that another su -group of ten trunks receives trai'lic from the lower live levels oic shell l and liroin levels l and or, shelf r`l1e thirc sub-group of ten trunks receives traiiic 'from levels 6, 7, and 8 of shell 2, and there is a juniper extending down trom this trunk group indicating that it receives traiiic trom `tour slielic levels of the next shelf of the series. rl`he same is true tor the subgror-.p S4. From this it will be seen that either the local group (comprising sub-groups S2, Se, etc.) or the outgoing group (comprising sub-groups Sl, S3, etc.) can handle more than half of the total trai'lic, but this is ordinii-ily necessary, due to the tact that the peak load on the outgoing group and 'the peak load on the local group do not ordinarily occur simultaneously.

lf calculations or observations show that the formed groups of trunks can handle more t aliic than is being` directed to them or that they are overloaded,the jumpering can be suitably rearranged and the adjustment can be finely made due to the relatively small trai'iic per shelf level offered by the improved arrangement hereinbefore presented.

As an alternative way or' handling' the situation described and ot securing substantially the saine results, the wipers of the shelves such asl and 2 could be all set one step below the first level in the usual way instead olf the staggered arrangement illustrated and au approximately equal distribution ot trallc could be made by dividing` the register senders into five groups. rhe register senders in group #l would send traliic out over the irst and sixth levels by merely retransmitting the digits l and 0, all the directors do in the arrangement above described; the register senders in group 2 would send out the digits 2 and 7 instead; the register senders in group wouldsend out the digits 3 and 8; and so tort-h.

Although the arrangemento Fig. l has been described as of particular utility in connection with a multi-oilice telephone system employing register senders, this arrangement may often be used to advantage in other systems not containing register senders. For example, in a QOOO-line system the lirst selectors are thousands selectors. lv'ow, if the digits l and 6 are assigned tothe two thousand-line groups, respectively, the calls will be scattered throughout the ten levels of the selectors provided the wipers are readj listed on switches 2 to l0 ol each shelf shown in Fig. l.

t is to be understood oi course that the arrangement is not limited to the lirst selectors but may be applied to any order of selectors as the occasion may arise.

lt is to be understood that, although the arrangement has been described in detail in connection with selectors having only two outgoing trunk groups accessible thereto, the same arrangement may be applied to selector groups having any number of outgoing trunk groups up to live. For example, there are live trunk groups accessible yto a group 01"' selectors the first five switches may have their wipers set in the normalway one step below the Vfirst level of contacts, while the second tive switches of vthe shell' have their wipers standing just below the secondlevel 01"' bank contacts. ln this case-the digits assigned to the outgoing trunk groups are the digits l, f5, 5,7, and 9. The lirst live switches on the shelf send their trallic out over the levels l. 53, 5,'7, and 9, while the remaining switches send their tra'l'lic out overfthe levels 2, il, 6, 8, and l0. As an alternative arrangement, the wipers of the second five switches of the shell"A 10 may be set just below the `sixth level instead oit just'below the second level, in which case the digits assigned to liveoutgoing groups are the digits 1-5, respectively. This results in the Afirst live switches sending their traliic out over the lirst `live levels of the bank and in the last live switches sending .their traflic out over the upperlive levels of the bank. ln this case levels 1 and 6 belong to the same trunk group; likewise 2 and 7, etc.

As an arrangement alternative to the one shown in Fig. l, the digits 1 and 2 may be assigned instead of the digits l and G. In this latter case the wipers of the selectors ot a shelf are fet as follows: switches l and 2 below the lirst level, il and 4- below the third level, 5 and G below the fifth level, 7 and 8 below the seventh level, and 9 and 0 below the ninth level. In this case, when-the digit l is dialled the call may be sent out over either ot the odd-numbered levels, while if the digit 2 is dialled the call maypass out from any one of the even-numbered levels, depending upon which switch handles the call.

Referring again to the impulse-correcting device shown in Fig. il and comprising relays 408 and 409, it will be apparent that, although thisis shown in connection with an arrangement for `transmitting impulses to l islam the sending switch of a register' sender, it isA` readily applicable to impulse repeaters used` cess to two groups of outgoing trunks, thereV being separate digits assigned to the two groups, respectively, the wipers of said selectors being differently set so that they stand normally in such a position so that calls are directed to a'plurality of levels inV response to the digit assigned to one group and are directed to a separate plurality of levels in response to the digit assigned to the other group, and multiple connections between the respective levels of each group such that the calls reach the correct trunk groups.V

2. In a telephone system `wherein multilevel trunk-hunting selectors have twice as many levels as there are separate trunk groups accessible to a group of such selec'- tors, means for sending calls from said selectors to each outgoing trunk group over twoselector levels.

3. In a telephone system, a plurality of multi-level trunk-hunting selector switches` wherein the contacts in the banks of the wipers of the several switches aie multipled together contact for Contact, means whereby the bank level over which a. call is transmitted from a selector is controlled jointlyA in accordance with the digit received by such selector and in accordance with the selector receiving suchk digit.

4. In a telephone system, a group of mult-i-v level 'trunking selector switches, a group of trunks accessible through a plurality of levels of said selector switches and having a digit assigned thereto, said switches being variously adjusted with respect to their bankcontact levels so that the level of contacts` with which connection is made in response to the said assigned digit is dependent upon the switch to which the digit is sent.

5. In combination, a plurality of selector each having a bank of contacts and a shaftoperated wiper, the wipers being differently positioned on the shafts so that a given moveinentof a shaft brings the wiper thereof into relationwith a portion of the Contact bank depending upon the selector whose shaft is moved, and conductor groups connected`V in regular multiple to all of the contact banks.

6. In a telephone system, a group of selectors having bank contacts connected in multiple with each other, each contact bank be ing divided into contact groups, each of said selectors having a wiper, and means in each selector responsive to a received digit for bringing the wiper thereof into relation With v the contact group in thefselector bank which corresponds to the -received digit, the wipers Jof the selectors `being differently adjusted with respect totlieirrespective contact banks so that -the sainefdigit received by two selectors causes the respective wipers thereof to be brought into relation with different groups intheir respective contact banks.

7. In combination, selectorf'b'anks, groups of' trunk lines having thesame digit desig- V Vnations and connected in multiple to corres'pondingly` positioned groups of contacts in all said banks, selectors associated with said banks, and wipers for saidselectors having different normal positions so that the same digit received at different selectors will cause the-selectionof different groups oftrunk lines. Y

8. Iii combination, selector banks each having contacts arranged in groups, conductor groups connected to corresponding groups of contacts in all banks, and selector mechanisms associated with said banks, respectively, and having wipers with different normal settings relative to the. respective contact banks, whereby the conductor group with which a wiper is associated upon a given movement being imparted theretoby the associated selectorniechanism depends Aupon the selector mechanism and wiper used.` l

9. The method of regulating the number of selector switches -in a multipled Y group of 'switches which 'extend connections to a given sub-group of trunks which consists in differently vadjusting the wipers of the selector switchesV so that the same imparted movement at two selectors bringsthe respective wipers into association with diiferent sub-groups of trunks.

10. In a bank-multipling arrangement for group-selector switches as used in automatic telephone systems,` a connectingL rack, switches arranged in shelves, each shelf comprising a number lof switches with corresponding bank contacts of each group of contacts of each switch in the shelfmultipled together 'and to corresponding terminals of said connecting rack, different sub-groups of bank contacts allotted to the same main group, and means for apportioning the traflic offered by a shelf of switches between subgroups of bank contacts which are allotted to the same main group, whereby the terminals on the connecting rack may be connected to different sub-groups of the same main'group in such a manner as to enable the traiiic to be suitably apportioned to each sub-group.

1l. In a bank-multipling arrangement as claimed in claim 10, certain of the switches of a shelf being mechanically modified so that in response to a predetermined control they obtain access to differently-located groups of baril; contacts than the other switches of the shel claimed in claim 10, the wipers of some of the various switches of a group being normally placed in different positions relative to their respective Contact banks so that in response to the saine control they obtain access to different sub-groups of multipled contacts.

13. In a telephone system, sets of bank contacts, each set being divided into groups,

`witches having access to said sets of bank contacts, respectively, each switch being adapted to select a different group of contacts resoonsive to the same digit, and a group of trunk lines connected in multiple to all said groups of bank contacts. Y

14. In a telephone system, two groups of multi-level trunk hunting switches, two groups of trunk lines extending to the same numerical group of the exchange, multiple connections whereby the first trunk group is accessible to the switches in the first switch group via two levels of bank contacts and is accessible to the switches in the second switch group by way of one of said two levels of bank contacts, and multiple connection-s whereby the second trunk group is accessible to the switches in the second switch group via the other of said two levels of bank contacts.

15. In a telephone system as claimed in claim 14, the switches in each switch group having diierent adjustments so that in respense to a digit of a given value some switches hunt over one of said two levels, while other switches hunt over the other of said two levels.

16. In a telephone system as claimed in claim 14, register controllers arranged to control all of said switches, said register controllers being divided into two groups, means in the register controllers of one group for causing the switches to hunt over one of said two levels with a given setting of the registering apparatus, and means in the register controllers of the other group for causing the switches to hunt over the Other of said two levels.

In witness whereof, I hereunto subscribe my name this 25th day of April, A. D. 1930.

JOHN I. BELLAMY.

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