US1805726A - Automatic telephone system - Google Patents

Description

y 1931. N. H. SAUNDERS AUTOMATIC TELEPHONE SYSTEM Filed May 8, 1929 9 Sheets-Sheet 1 m WI v QE m @m w wt 6E w wt 92m R at m I u H at H RMNNSQ 1mm? Nbrman H. Saunders y 1931. N. H. SAUNDERS AUTOMATIC TELEPHONE SYSTEM Filed May a. 1929 9 Sheets-Sheet 2 v 3R mum WWW um WE 1mm Mai-"man H 531m HXU 223 03 N* E WwN k wt mmm N. H. SAUNDERS ,805,726

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N. H. SAUNDERS AUTOMATiC TELEPHONE SYSTEM Filed May 8. 1929 9 Sheets-Sheet 7 FIG. 6

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N. H. SAUNDERS AUTOMATIC TELEPHONE SYSTEM 9 sheets-sheet 9 Filed May 8, 1929 InUEnl-Ur Norman H.5aunders lineswitch releases open. new trunk is taken.

. arrangement for ringing when a reverting call is ma ists of lesser importance in Patented I. May 19, 1931 UNITED STATES PATENT OFFICE COMIPANY, OF CHICAGO,

NORMAN H. SAUNDERS, OF HOMEWOOD, ILLINOIS, ASSIGNOR TO RESERVE HOLDING ILLINOIS, A COBZPORATION DELAWARE AUTOMATIC TELEPHONE SYSTEM Application filed May 8, 1929. Serial No. 361,311.

- The present invention relates to automatic telephone systems in general, but is concerned more particularl with the development of a small unattende exchange designed to serve a small town and the surrounding community; and the broad, general object is the production of new and improved circuit arrangements whereby the apparatus is simplified and improved.

A further object is the provision of suitable circuit arrangements for notifying an attendant at a nearby attended exchange when an abnormal condition arises within the unattended exchange of sufiicient gravity to warrant the dispatching of a repairman to the unattended exchange to make an ads justment or to perform a repairing operation. It is a further object to provide suitable arrangements for giving the attendant at the attended exchange a distinctly different signal in case an abnormal condition exthe unattended exchange. Itis a feature of the arrangement that both indications may be given over a trunk line between the attended and unattended exchanges while ceeding over the trunk line without interfering with the conversation.

A further object is to provide an arrangement such that a connector accessible to the lineswitch of a calling line is not used in case it is out of order.v This object is realized plunger line automatically by the use of switches of the so-called self-aligning type. When the individual fuse of a connector is blown the line relay fails to respond and the because the trunk tests Since the plunger is self-aligning a In case the defe at in the connector consists 1n its sticking in an oilnormal position, special arrangements are provided for causing the trunk leading to the connector to test open so as to cause the lineswitch to release and automatically realign on a new trunk.

A further object is to bagk on party lines A further object is to provide a simplecombination one-digit and two-digit connector a conversation is pro-.

' its operation will provide a simplified which is operated in accordance with two digits when a subscribers line is being called and is operated in accordance with only one digit in making certain other calls to be hereinafter explained.

It is a further object to make provisions for preventing the tying up of all calls to a trunk group by an open or other defective condition of the first trunk of the group In addition to the foregoing, there are other objects and features of the invention which will be understood best upon a further perusal of the specification in connection with 4 General description Figs. 1 to l show certain -switching apparatus m an attended manual exchange an in an unattended communit automatic exchange (abbreviated C. A. changes are interconnected by the trunk'line TLl extending between Figs. 1 and 2; Figs. 5 to 8 show certain apparatus known as power and supervisory apparatus auxiliary to the switching apparatus in the C. A. X.; and Figs. 9 and 10 show a desirable modification of the apparatus of Figs. 3 and 4, respectively; Fig. 11 shows the code sent out by the code interrupter apparatus of Fig. 7; Fig. 12 shows the sheets on which Figs. 1 to 8 are drawn should be placed; and Fig. 13 is a layout of Figs. 9 and 10.

Detailed clescajption A general description of the apparatus having been given, a detailed description of now be proceeded with. For this purpose it will be assumed that the subscriber at substation'Al desires to converse with the subscriber at substation A2.

Local call in the 0. A. X.

When the receiver is removed at substation A1, line relay 304 of lineswitch LS1 operates over conductors 301 and 303 and places The two ex-v the accompanying drawings comprising Figs. 1

2 Qrsomae ground on the private normal conductor 302 at itsupper armature, at the same time closing a circuit for the pull-down winding of the magnet 305 at its lower armature; By

5 the ground potential on conductor 302, the

line of substation A1 is made. busy immediate] to the connectors, and,-by the closure 7 of t e circuit through the lower winding of magnet 305, the plunger arm 306 is operated to force the bank contact springs into engagement. This extends the conductors 301303 into engagement with conductors 308310, respectively. As a further result of the operation of the plunger arm 306, thelocal contact springs thereof connect the upper winding (the bridge-cutoff winding) of magnet 305 to the grounded conductor 302 r to form a holding circuit for the lineswitch.

Upon the operation ofthebridge-cut-ofi' arm 307, which occurs responsive to the energization of magnet 305 by either winding,

line relay 304 and ground are disconnected from conductors 301 and 303, respectively. Relay 304, being slow acting, does not fall back immediately. p

Responsive to the extension of the grounded conductor 302 to conductor 309, start relay 311 of'the master switch MSl operatesthrough test wiper 312 and over a branch of conductor 309 and preselects an idle trunk in the usual manner. a

In the local connector L01, line relay 323,

whose lower winding is connected to conductor 310 by way of contacts of relays 322 and 321 and whose upper winding is connected to conductor 308 by way of oil-normal contacts 332 and contacts of relays 322 and 321,

operates over the calling line and closes a circuit for release relay 324 in series with 40 the vertical magnet 335. The vertical magnet does not operate ate/this time owing to the relatively high resistance of release relay 324. Release relay 324 operates and places ground on the release trunk conductor 309 at 1ts upper armature, closing a holding circuit for the lineswitch LS1 through the upper winding of magnet 305 by way of the local contact springs of plunger arm 306. This circuit is closed before the slow-acting relay 304 has had time to fall back.

.As a further result of the operation of relay 324, oil-normal contacts 332 are shunted at the inner-upper contacts of the relay and ground is placed on locking conductor 344 65 at the middle-upper contacts. This prepares a locking circuit for relays 326, 330, and 331 and closes a circuit through oil-normal contacts 334 for the upper winding of relay 326. Relay 326 operates and prepares an operating circuit for vertical magnet 335 at its inner-lower armature. r

At the lower armature of relay 324, a point in the circuit of release magnet 336 is opened and ground potential is extended to the tonestart conductor 621 which extends to Fig. 6,

operating the tone-start relay 809 by way of conductor 623, with results to be pointed out hereinafter. Thisground potential is supplied through the low-resistance shelf relay 376, common to a shelf of connectors. Relay 376 does not operate because of the relatively high resistance of the tone-start relay 809. The connection having been extended from the line of substation Alto the. connector LCl, and relay 326 having been operated, dial-tone current now passesirom conductor 811 to the lower talking conductor through contacts of relays 330 and 326 and from thence to the calling substation, informing the calling subscriber that he may now dial he desired number.

lVhe'rFthe calling device (not shown) at substation A1 is manipulated in accordance with the first digit 8 in the desired number, the line circuit is interrupted a corresponding number of times and line relay 323 of the connector LCl falls back momentarily each time the line circuit is interrupted. Each time it falls back, line relay 323 opens the initial circuit of relay 324 and short circuits relay 324 by grounding its lower terminal. Eac time relay 324 is short circuited, a direct circuit is closed for the Vertical magnet 335 by way of the inner-lower contacts of relays 321, 324, 327 and 325, and the inner lower armature, operated, of relay 326.

Each time the short circuit is removed from relay 324 upon the reoperation of relay 323, the vertical magnet 335 restores.

By the operation of vertical magnet 335, the wipers 339-343 are raised step by step to the desired level of bank contacts. Although shortcircuited. momentarily each time the line relay falls back, relay 324 remains operated due to the circulating current through its winding. Relay 329 operates in multiple with the verticalmagnet 335 each time relay 324 is short circuite-d and it remains operated throughout the series of impulses in series with relay 324, but it is unable to remain operated indefinitely in series with relay 324 owing to the relatively high resistance of the latter and owing to the shunting effect of magent 335. Therefore, relay 329 falls back shortly after the, termination of the vertical movement. While operated, relay 329 maintains a locking circuit for relay 326 at its inner-upper armature through the upper armature of remagnet 338, the wipers 339-342 are rotated Upon 'er the called line is busy or idle.

into engagement with the set of bank contacts in the eighth level in which the line of substation A2 terminates. This bank contact set is shown in the drawings as the first contact set in the eighth level. Accordingly, thc second digit dialled is the digit 1. The vertical wiper 343 is rotated out of engagement with its contact bank, with which it makes sliding engagement during the vertical movement.

Relay 329 is again operated during the rotary movement, this time in parallel with the rotary magnet. 'At its upper armature it closes a circuit for the auxiliary relay 328. Upon operating relay, 328 disconnects test Wiper 340 from the test windings of relays 321 and 330 and connects it instead to the winding of busy relay 327, while relay 329, at its middle lower armature, places a shunt around the inner lower contacts of busy relay 327 so as to prevent the circuit of relay 329 from being interrupted prematurely by the operation of busy relay 327 during the rotary, movement in case test wiper 340epasses over grounded test contacts.

The operation following the termination of the rotary movement depends upon wheth- Assuming first that the called line is busy, busy relay 327 is operated when the wipers come to rest on the bank contacts ofthe called line, and, when the calling subscriber finishes dialing and listens, he hears the busy tone caused by an application of busy-tone current from the busy tone conductor. 810 through contacts of relay 330 and 327 to the lower talking conductor.

With relay 327 operated and relay 329 at normal, the circuit of relay 329 is opened a so that relay 329 cannot operate again.

Relay 328 falls back responsive to the de-- energization of relay 329 and completes a locking circuit for the bus relay 327 to the locking conductor 344 y way of the middle upper. armature of relay 327.

earing the busy tone, the calling subscriber is expected to replace his receiver andbrin'g about the release of the lineswitch and the connector. "Assuming now that the line of substation A2 is idle when called, the busy relay 327 is not energized when the wipers come to rest on the contacts of the called line and the deenergization of relays 329 and 328 is followed by the energization of relay 330. The circuit of relay 330 is-from ground by way of the grounded conductor 344, through the middle-upper armature, normal, of relay 327, ninth-level shaft spring 333 and its lefthand contact,-lower winding of relay 330, upper armature of relay 328, middle-upperarmature of relay 330, test wiper 340, and thence by way of the bank contact on which wiper 340 is standing, to battery through the cut-off winding of the lineswitch (not shown) associated with the line of substation A2. The bridge-cut-oii relay of the lineswitch associated with the called line now optraced circuit, it lock itself to conductor 344 at its inner-upper armature, at the same time preparing a locking circuit for relay 326 independent of the upper armature of relay 329. At its middle-upper armature, relay 330 disconnects wiper 340 from the test circuit and connects it directly to ground; it prepares a circuit for pick-up relay 331 at its upper armature; it shifts the operating circuit from the rotary magnet 338 to the operating magnet 354 of the associatedcode selector CS2; it prepares to place ground on the common interrupter start conductor 622 at armature 356; at armature 357 it opens a point in the busy-tone circuit so as to prevent the busy tone from being applied to the line upon the operation of busy relay 327, when it occurs after the code switch is operated; and at its lower armature it opens a point in the dial-tone circuit so as to prevent the dial tone from being heard after the ring-cut-ofi relay 326 is subsequently operated.

When the next and last digit, the stations digit, is dialled, the resulting impulses are delivered now to the operating magnet 354 of the code switch CS2, owing to the operated condition of the inner-lower armature of relay 330, with the result that the wipers 351 and 352 of the code switch CS2 are advanced to a position corresponding to the code of the called substation. It may be pointed out here that the code switch is arranged to signal any one of ten parties on a called line, it being assumed that half the ringers are connected between one conductor of the line and ground and the other half connected between the opposite conductor of the line and ound. In this way, ten parties may be signalled by means of five codes, the selected code being applied to one conductor or the other depending upon the station called. 'In

wiper 352 on its fifth contact to the lower' winding of ring-cut-ofl relay 326. The completion of the two connections just described is of course dependent on the subsequent operation of pick-up relay 331.

When the wipers of the code switch CS2 come to rest and relay 329falls back, relay 327 is operated through contacts of relay 329 and through the off-normal contacts 3530f the code switch CS2. Upon operating, relay 327 places ground on the common interrupterstart conductor 622 at armature 346 through contacts of relays 330 and 322; at its innerlower armature it opens the operating cir cuit; and at its upper armature it connects the ick-up conductor 713; topick-up relay,

331 y way of the upper contacts. of relay 330. The ringing interrupter'of Fig. 7 and:

the tone equipment of Fig. 8 -are now operating in a manner to be hereinafter described,

and during the operation of the ringing inthe called line by way of wiper 351, signal-' ing the subscribed at'substation A2..-

When the subscriber at substation A2 responds, a loop is closed across the conductors of his line, whereupon the lower Winding of relay 326 is energized over the called line, the current flowing to the called line by way of the fifth contact in its bank, and Wiper 352, contacts of relays 326 and 331, and wiper 342. The return circuit to ground is similar except that it follows the upper conductor of the called line and wi ers 339 and 351 and is completed by way 0 #5 code conductor. Upon operating, ring-cut-ofi relay 326 completes its locking circuit at its inner-up- I per armature from the grounded conductor 344 by way of the inner-upper armature of relay 330.

At its upper and middle-lower armatures, relay 326 opens the ringing circuit and completes the talking circuit. Back-bridge relay 322 now operates over the called line and reverses the incoming line conductors as regards their connections with the windings of line relay 323, for the purpose of metering or the like. At its lower armature, relay 322 disconnects ground potential from the common interrupter start conductor 622, while atits upper armature it makes a second application of ground potential to the release trunk conductor 309 so as to prevent the release of the line switch LS1 while the connections to the linerelay are reversed.

The conversation may now take place. When the conversatlon is terminated, the

two subscribers replace their receivers. vOn

the assumption that "the subscriber at substation A2 replaces his receiver first, back-bridge relay 322 fallsback and again reverses the connections of the line relay to their normal condition, at the same time removing the and the oil-normal contacts multiple ground connection from conductor 309' and again applying a ground potential to the interrupter start conductor 622.

When the receiver is replaced at the calling substation, line relay 323 falls back and short-circuits release rela 324, With the re sult that relay 324falls ack after a slight interval. Upon so doing, it permits the lineswitch LS1 to release by removing ground potential "from conductor 309 at its upper armature, and it removes ground at OIN point from conductor 344, but this conductor is now maintained grounded through the oilnormal contacts 353 of the code switch CS2, and contacts of relays 329, 328, and 327.

At its lower armature,relay 324 removes ground from the tone-start conductor 621 and closes acircuit for the release magnet 355 of the code switch CS2. The circuit of this magnet includes contacts of relays 321, and 324, and armature 345, operated, as well as the associated release signal relay 376, common to a shelf of connectors. When the release magnet of the code switch CS2 operates, the wipers 351 and 352 are restored to normal,

353 open, allowing relays 327, 330, and 331 to release. When rela 327 releases it disconnects the release condiictor from release magnet 355 and connects it to release magnet 336 by way of the off-normal contacts associated therewith. 9

Upon the operation of magnet 336 the wipers 339342 and 343 are restored to their normal position in the usual manner, and the various off-normal contacts of the connector restore to their normal condition. Upon the falling back of relays 327 and 330 the interrupter? start conductor 622 is again ungrounded.

The connection is now released and the apparatus involved therein is in readiness to be used in establishing subsequent connections.

Reverting call on' the line of substation A1 It will be now assumed that the subscriber at substation A1 desires to call another subscriber Whose substation is on the same line. In order to do this,the subscriber at substation A1 removes his receiver and obtains dial tone from a local connector in the usual manner, following which he dials the digit 9, followed by thestations digit of the calling station and then the stations digit of the called station. When the digit 9 is dialled, the local connector in use is operated to the ninth level and seizes a ring-back switch, such as the ring-back switch BB1, Fig. 4, in a manner to be described more in detail hereinafter, and the ring-back switch responds to the two stations digits and conditions itself to perform the signalling operation after the calling subscriber hangs up.

It will be assumed that the local connector LCl of Fig. 3 is the one seized by the lineswitch LS1 when the receiver is removed at substation A1, in which case the connector is lli) prepared for operation in the manner hereinefore described by the- operation ofrelays 323, 324, and 326.

When the first digit is dialled, the wipers 339-342 are raised opposite the ninth level of bank contacts: The arrangement involving the vertical wiper test 343 is for the purpose of causing the local connector LCl to act as a single digit connector when a reverting call is made. Since the wipers are now raised to the ninth level, wiper 343 encounters the ninth associated bank contact, which is grounded as may be seen in the drawings.

This places a ground potential on the rotary test wiper 341 and also places a ground potential on the regular busy test wiper 340 on account of the fact that the wiper 343 contacts also with the bank contact immediately below the contact on which it is standing, the eighth bank contact in this case. It will be recalled that relays 326, 328, and 329 are in operated condition at the end of every vertical movement. In this case, since wiper 340 is'grounded by way of the vertical wiper 343 from ground on its ninth contact and by way of its eighth contact, busy relay 327 is operated and at its inner-upper armature it connects the resistance 337 in parallel with relay 328 so as to form a path for circulating current tomake relay 328 slow acting. Relay 328 is ordinarily not slow acting so as not to delay the switching operation when an idle line is reached.

When relay 329 falls back at the end of the vertical movement and opens the circuit of relay 328, relay 328 is slow acting and does not fall back immediately owing to the fact that the resistance 337 is in shunt of it at this time. With relay 328 thus operated, and with relay- 329 restored and ground potential encountered by the vertical wiper 343, a circuit from ground is closed for relay 325 by way of wiper .343, the interrupter contacts of rotary magnet 338, and contacts of relays 329 and 328. Upon operating when this circuit. is closed, relay 325 closes a locking circuit for itself at its lower armature through the interrupter contacts of the rotary magnet" closes a circuit at its upper armature to relay 328 operated; and at its inner- 1101i lower armature it disconnects the rotary magnet 338 from in parallel with relay 329 and closes a circuit for the rotary magnet to ground. The rotary magnet operates'and it rotates the wipers 339-342 and 343 one step. Near the end of its stroke, magnet 338 opens the circuit of relay 325, whereupon relay 325 falls back and opens the circuit of magnet 338 at itsinner lower armature. Obviously, relay 325 opens a point in its locking circuit at its lower armature and opens the circuit of the now slow-acting relay 328 at its upper armature. v has been rotated away from engagement with its vertical set of contacts with the result that the further operation depends u on whether the "trunk lme leadin toathe rst ring-back switch is busy or id e. If it is busy, wi er 341 encounters a grounded contact wit the result that relay 325 operates again thereover and busy relay 327 remains operated over the encountered grounded contact and maintains relay 328 shunted by resistance 337 so as to maintain it slow acting. In this case the rotary magnet 338 is operated again and the wipers advance another step. This alternate operation of relay 325 and magnet 338 continues until an idle trunk line is reached, whereupon relay 325 fails to operate again and relay 327falls back. When relay 327 falls back, the shunt 337 is removed from around the, winding of relay 328 and this relay immediately falls back and connects up the test wiper 340.

With relays 327 and 328 both deenergized, a test circuit is closed from ground on conductor 344 to battery on the release trunk conductor 365 by way of wiper 340 and the bank contact on which it is standing. This is under the assumption that the ring-back switch RBl is idle when tested and is, therefore, seized. The test circuit at this time includes the test winding of switch-through relay 321 instead of the test winding of switching relay 330 on account of the fact that the ninth-level shaft spring 333 is now shifted to its alternate position. The complete circuit for the upper winding of relay 321-is as follows: from ground by way of the grounded conductor 344 (grounded as hereinbefore pointed out at the middle upper armature of relay 324), middle-upper armature, normahof relay 327 ,spring 333 and its right-hand contact, upper winding of relay 321, resting contact and upper armature of relay 328, middle-upper armature of relay 330, test wiper 340, the bank contact on which 'it is standing, conductor 365, lower armature,

normal, of relay 402, Fig. 4, jumper 429, upper armature, normal, of relay 425, and resistance 430 to battery.

Upon operating, relay 321 closes a locking circuit for its lower winding at its inner-upper armature to the groiinded release conductor 309, and at the same time it joins release conductor 309to the test wiper 340 by way of contacts of relays 328 and 330. At its inner-lower armature, relay 321 opens a "point in the operating circuit; it opens a further point in the release circuit at its middle-lower armature and closes an alternative tone-start circuit; and at its upper and lower armatures it disconnects the incoming conductors 308 and 310 from the talkin circuit (including the front and backbrldge relays 323 and 322) and extends them directly to the wipers 339 and 342. When this is done, line relay 424 of thering- back ductors 364 and 366 through contacts of relay 421, operates over the calling line and through the wipers 339 and 342 of the local connector LCl and closes a circuit for release relay 425 through the operating magnet 433. Release relay 425 energizes and prepares the switch for operation at its lower armatures and closes a holding circuit for the connector and line-switch at its upper armature by placing a holding ground potential on conductor 365. Since conductor 365 is now joined, as above pointed out, to release trunk conductor 309 of the local connector LCl, the line switch LS1 remains operated and relay 321 of the connector LCl remains energized through its lower winding.

When line relay 323 is cut off by the operation of the upper and lower armatures of relay 321, it falls back and short circuits relay 323, with the result that relay 324 falls back after an interval, but the connector LCl does not release owing to the fact that relay 321 is operated.

. The calling subscriber now dials the digit corresponding to his own station suffix, whereupon the line relay 424 of the ring-back switch BB1 falls back a corresponding number of times. Each time it does so, it closes at its make-before-break contacts a circuit for the operating magnet 433 of the digit register DB1 as follows: from ground by way of the resting contact and middle-lower armature of relay r428, contacts controlled by line relay 424, inner-lower armature of release relay 425, inner-lower armature, normal, of relay 428, and the inner-lower armature, normal, of relay 427 to battery by way of the operating magnet 433. By the operation of operating magnet 433, wipers 435 and 436 are positioned on the contact set corresponding to the suflix assigned to the calling substation. It will be noted that relay 425 is short circuited on each impulse delivered to the operating magnet but this 4 relay remains operated in the manner pointed out in connection with release relay 324 of the local connector LCl. Relay 426 operates in multiple with the operating magnet upon the first closure of the circuit to the latter and it remains operated throughout the series of deenergiza-tions of relay 424 for the reason pointed out in connection" with relay 329, Fig. 3.

'When relay 426 falls back at the end of the stations digit assigned to the calling station,

the lower winding of transfer relay 427 is energized through the off-normal contacts 432 of the digit register DB1 and through the normally closed contacts controlled by the armature of relay 426.

The calling subscriber now dials the digit assigned to the desired station on the calling line, whereupon line relay 424 is again deenergized a corresponding number of times. Each deenergization occurring at this time results in the closure of a circuit for the operating magnet 438 of the digit register DB2 owing to the operated condition of the rela 427, which transfers the operating circuit from magnet 433 to magnet 438 at its inner lower armature. It will be noted that, when relay 426 operates at the beginnin of the second series of impulses, the initia circuit of relay 427 is opened, but an alternate circuit is closed for the relay through its upper winding by way of its upper contacts.

When relay 426 falls back at the end of the digit,it completes a circuit for the lower winding of relay 428 through ofl'-normal contacts 437, and again completes the initial circuit forthe lower winding of relay 427. Belay 428 disconnects the operating circuit from magnet 438 at its middle-lower armature and transfers it instead to relay 421 by way of the normally closed contacts controlled by the inner-lower armature of relay 422. This extension of the operating circuit, it will be noted, is made to the upper terminals of relay 421, whose lower terminal is connected to battery through the operating magnet 433. Belay 421 isaccordingly connected in series with the operating magnet 433 and relay 425, but is short-circuited at the armature of relay 425.

It will be noted that the ground potential is removed at the lower armature of relay 428 from the spring combination controlled by the armature of line relay 424. This is done so as to prevent relay 425 from being short circuited upon the nextadeenergization line relay 424.

Having dialled the required stations digits, the calling subscriber at substation A1 replaceshisreceiverto allowthe ring-back process to take place. When this is done, relay 424 falls back and removes the short circuit from around relay 421. Belay 425 is now held operated in a circuit including its own inner lower armature, inner-lower armature, operated, of relay 428, normally closed contacts controlled by the inner-lower armature of relay 422, relay 421, and operating magnet 433. Belay 421 now operates in this holding circuit in series with relay 425 and at its lower armature places ground on the "interrupter start conductor 622; it connects the pick-up conductor 713 to pick-up relay 423 at its inner-upper armature,and at its two uppermost armatures it disconnects the incoming conductors 364 and 366 from the windings of line relay 424 and connects them instead to the ringing circuit.

When the ringing interrupter of Fig. 7, which is started responsive to the grounding of interrupter start'conductor 622 by relay 421, 1

arrives in its pick-up osition and grounds the pick-up conductor 7 13, pick-up relay 423 operates through contacts of relay 421 and locksitself to ground through the inner-upper armature of relay 425, at the same time openlower winding of ring-cut-ofi' relay 422 to their contact banks.

- the lower right-hand ing coil 431 by way coil 431 to one sent back over ing its initial circuit. At the middle-upper armature of relay 423, a ground potential is7 appliedto the lower left-hand repeating-coil terminal through contacts of relay 421, and at the upper contacts of relay 423 the connection is completed from conductor 364 through the wiper 440. At its three lower. armatures, relay 423 connects up the first and third and fifth code conductors to the bank of the digit registers DB1 and DB2. These conductors are normally open so as to prevent sparking occasioned by the passage of the wipers of the digit register DB1 and DB2 from contact to contact.

The ringing current now sent back to the line of substation A1 depends upon'the relative setting of the re isters DB1 and DB2. In case the ringers of t e calling and called stations are connected to opposite sides of the line, it is necessary to send out the code of the calling station on one side of the line in addition to sending out the code of the called station on the other side of the line so that the calling man will know, by the cessation of his code, when the called man has responded, but if both ringers are connected between the same side of the line and ground, it is necessary to send out only the code of the called substation, as this code is then heard at both substations. Assume, for example, that both ringers are connected between the upper line conductor and ground. In this case, the last two digits will be from one to five in both cases and the wipers of the digit registers DB1 and DB2 will be set on the first half of In this case, the position of wiper 440 directly determines the code sent to'the line through the upper talking conductor, as it directly contacts with one of the live code conductors, while the wiper 441 extends terminal of the repeatfive contacts in its banks to wiper 436. This terminal is not further extended by wiper 436, however, onaccount of the fact that the first fivecontacts in its bank are left dead.

If it is assumed that the ringer of the calling station is connected between the lower conductor of the line and ground, the stations digit assigned thereto is any one from six to 0, with the result that the dialling of this digit-results in the digit register DB1 being set on a bank conta ct set ofthe second half. In this case, the wiper 436 extends the lower right-hand terminal of the repeating of the code conductors. s a result, the code of the calling subscriber is the lower talki gconductor, owing to the repeating action of t e repeating coil 431, at the same time that the code of the called party is sent back over theupper conductor. It is the necessity for the simultaneous signalling over both conductors that gives rise to the repeating coil 431, which is station on the calling line.

of any one of the first one of the code conductors directly used in order that a battery potential may be present at all times on the lower talking conductor so as to form a circuit for the lower winding of the ring-cut-ofl? relay 422 at any time that the receiver may be removed at any It will be noted that, in case the digit used to set the digit registers DB2*is any one from 6 to O. the wipers 440 and 441 are set on .the second section of the banks and it is the lower conductor upon which the ringing current is impressed by wiper. 441 through the medium of the repeating coil 431, while whether or not ringing current is impressed upon the uppersconductor by Wiper 440 depends upon the specific setting of wiper 435. If the digit register DB1 is set on the second section of its bank, the wiper 435 merely encounters the ground potential for completing the circuit of the ring-cut-ofi relay and no ringing current passes out overthe upper talking conductor, because both ringers are connected between the lower conductor of theline and ground and both the calling and the called party hear called substation. On the other hand, if the calling substation is one whose ringer is connected between the upper line conductor and digit register DB1 is set in ac- 1 to 5 and the ground, the cordance with a digit from upper conductor is extended to .a code conductor by wiper 435 in the first half of its contact bank. 1.,

At any rate, the calling party hears his own code transmitted back to the calling line over the conductor to which his ringer is connected, and at the same time that the other code is transmitted back over the other side of the line, or else he hears only the code of the called substation in case both ringers are connected between the same side of the line and ground.

Assuming first that the called party does not respond, the calling subscriber removes his receiver and to clear out the ringing equipment and cause the connection'to be released in a manner to be hereinafter described.

Assuming now that the subscriber at the called substation responds, a circuit is completed for the lower winding of ring-cut-ot'f relay 422 to ground by way of wiper 440 and or through wiper'435 and one of the code conductors or through wiper 435 and ground directly. The return path for the operating circuit of relay 422 is to battery by way of the upper ing, relay 422 closes alocking circuit for its upper winding at its inner-upper armafor relay 425 at-its" lower armature; and at again replaces it in order the code assigned to the 3 Winding of repeating coil 431. Upon operaty it "prepares again the shunt 4 its inner-lower armature it, connects relay f 426 (in parallel with operating magnet 438 3 through the inner-lower armature, operated net 433 in series. This-leaves a holding cir-" cuit established for relay 425 through its own inner-lower armature, the inner-lower armature, operated, of relay 427 and the operating magnet 438. 4

Relay 421 falls back at this tinie and removes ground from the interrupter-start conductor 622 at its lower armature, at the same time short circuiting relay 425 through its lower armature and resting contact, corresponding armature of relay 422, 'middlelower armature of relay 428, and the contacts of the armature of relay 424. 1 The placing of this short circuit around relay 425 closes the usual operating circuit for relay 426 and the magnet 438. This operating circuit is usually opened, however, before the relay and magnet have had time to operate and in a manner to be now described: At its two uppermost armatures relay 421 transfers conductors 364 and 366 back to the windings of line relay 424, whereupon line relay 424 again operates and establishes the regular circuit for relay 425 in series with operating magnet 433, removing the short circuit from around relay 425. v

The two subscribers may now converse with each other in the usual manner, the transmit,- ters at the two substations being supplied with talking current through the windings of relay 424.

It may be pointed out that, in case the ring-back switch RBI is used in connection with a connector or other first switch in the train which does not employ a dial tone, the jumper 429 is removed from between the associated terminals, with the result that, when ring-cut-ofi relay 422 operates, it removes ground from the holding conductor 365 and brings about the immediate release of the connection. The line switch LS1 of the calling line releases in that case and takes a new trunk line and the transmitter current is supplied from the line relay of the first switch of the train. In the present case, however, since dial tone is supplied to the calling line by the connector LCl the jumper is left in place, as the dial tone would interfere with the conversation. 7

When the two subscribers replace their receivers at the end of the conversation, line relay 424 falls back and again short circuits release relay 425 through contacts of relays 428, 422, and 421 as above pointed out, incidentally operating relay 426 and the magnet 438. After an interval, relay 425 falls back and removes the holding ground from conductor 365 at its upper armature, opening the circuit of relay 426 and magnet 438 at its inner-lower armature.- At its lowerar-mature, relay425 removes ground from'the tonestart conductor and closes a circuit through the associated shelf-supervisory relay for release magnet 434 of the digit register'DRl magnet 439 operates and causes the digit register DR2 to restore. Off-normal contacts 437 open and deenergize relay 428, which falls back and opens the circuit of release magnet 439 at its lower armature. The common release-signal relay is, of course, energized in series with either of the release magnets and falls back when the circuit of the: last release magnet is opened.

In the local connector L01, relay 321 falls back when the ground potential is removed from release-trunk conductor 365 of the ringback switch RBl and closes the release magnet circuit at its lower armature through contacts of relays 324 and 327. When this occurs, release magnet 336 operates and restores the connector to normal position in the usual manner.

Operation of the trunk-Maytag relays I times happens thata ring-back switch such as the ring-back switch RBI becomes defective and does not operate properly, or that one of the conductors leading thereto becomes open. Since this ring back switch is first choice to the several connectors, repeated attempts during light traflic to make a reverting call may all fail if the same ring-back switch is taken for use in each case. On the other hand, if there is an alteration so that the first call takes the first ring-back switch and a second call must take the second ringback switch before the first is again rendered available for service, the second attempt to make a reverting call results in the second choice switch being taken for use over the conductors 367369.

In order to accomplish this result of alternating between the first two ring-back switches the relays 402404 are provided, and they operate as follows: When the ringback switch BB1 is taken for use and the release trunk conductor 365 is grounded, a cir- 404. This locking circuit does not become eifective and no current flows through it as long as the ground potential is maintained on conductor 365. When, however, the ground potential is removed from conductor 365 401 at the same time opening t e circuit of relay 403. After a slight interval, relay 403 falls back and applies a guarding potential to conductor 365 at its lower armature through the lower armature of relay 402. The delay in the application of this guarding potential to conductor 365 is of sufficient 1nterval to permit the connector involved in the connection to restore. With relay 402 operated and relay 403 restored, relay 404 is connected to the release trunk conductor 368 of the ring-back switch BB2 through contacts of relays 402 and 403. 7

When the next reverting call is made, the trunk line comprising conductors 367-369 leading to the ring-back switch BB2 is seized on account of the fact that the trunk line leading to the switch BB1 is made artificially busy, as above explained. When this trunk line is seized, relay 404 operates and opens the circuit of relay 402 whereupon relay 402 falls back and removes the guarding potential from the conductor 365 to permit the next call to come in to the ring-back switch BB1. It will be understood, of course, that there may be other ring-back switches in addition to the two shown,, in which case one of the remaining switches is taken any time a reverting call is made when the first two are in use.

Hall from the 0. A. X. to the manual ewahange It will now be assumed that the subscriber at substation A1, Fig. 3, desires to converse with a subscriber whose line terminates in'a manual exchange, a part of, the equipment of which is shown in Fig. 1. It will be assumed further that the line switch LS1, upon operating when the receiver is removed at the calling substation, seizes the local connector LC1 in which case the connector LCI is prepared for operation in the usual manner. When the first digit 0, of the number 01 assigned as the call number of the manual ofiice, is dialled, the wipers 339-342 are raised opposite the .tenthlevel of bank contacts, and wiper 343 contacts with the tenth associated bank contact. Wiper 343 also bridges from the ninth contact tothe tenth contact, causing wipers 340 and 341 to be both grounded as in the case of a reverting call. Relays 328 and 329 are energized as before, and,'as soon as relay 329 falls back at the end of the vertical movement, it completes the circuit for stepping relay 325 from 'the' grounded wiper 341 through contacts of relay 328. The first rotary step is accordingly taken to advance the wipers 339-342 onto the first set of contacts in the tenth level and to cause the wiper 343 to disengage the vertical contact strip.

The rotary movement continues beyond the first bank contact set or stops, depending upon whether the first trunk line is busy or idle. It will be assumed that the first trunk line is idle and that the movement accordingly stopxs. In this case, the busy relay 327 falls bac as does relay 328, and relay 330 is energized throu h its lower winding as pointed out hereinbe ore in-connection with a-call between substation A1 and substation A2. The energizing circuit at this time includes the test wiper 340, as before, and is completed now to battery over the first contact in the tenth level, test conductor 371, contacts of relay 262, release trunk conductor 209 of the incoming connector I0, upper armature, normal, of relay 224, the associated ofi-normal spring and its lower contact, and the lower winding of rela 221 to battery. Upon energizing over t is circuit, relay 330 disconnects the operating conductor from the rotary magnet 338 at its inner-lower armature and extends it to theoperating magnet of the code switch CS2 with the result that, when the calling subscriber dials the next digit 1,

the code switch CS2 is operated to enable ringing current to be transmitted over the trunk ine TL1 associated with the incomin connector IC.

11 the mcomlng connector IC, relay 221 operates as a cut-off relay and disconnects conductors 208 and 210 from the'portion of the talking circuit including the front and back-bridge relays 222 and 223, so as to clear the line for ringing current. With ground otential applied to conductor 209, a current fiows through the upper winding of the electro-polarized relay 204, but the relay is not operated by either winding alone'due to the design of the windings of the relay.

When the ringing current is applied to the wipers 339 and 342 of the connector it passes over conductors 370 and 372 to the right-hand windings of the repeating coil associated with the alarm circuit ALCKT. The ringing current is repeated into the left hand windings of the repeating coil, and passes over the conductors of the trunk line TL1 to the manual oflice and is again repeated through the repeating coil there and operates the ring-up relay 107 through contacts of the cut-off relay 106. Upon operating, the ring-up relay locks itself operated mechanically under the control of the cut-off relay as is common practice in connection with the ring-up and cut-ofi air. The ring-up relay closes a circuit for t e answering lam 108.

When the operator notes the light condition of the answering lamp she inserts the plug of a cord circuit (not shown) into the line ja'ckLJ, whereupon the sleeve relay 106 operates "over the sleeve of the jack from a battery potential applied to the sleeve of the plug of the cord and mechanically unlocks the ring-up relay 107 and permits it to restore. At its upper armature, relay 106 reand 372 are reversed between the bank mulassists the current flow in the upper winding on account of the fact that conductors 370 'tiple and the conductors 208 and 210 as shown. Upon operating, relay 204 shifts the connection to relay 205 so that the high resistance upper winding is included in series with the low resistance lower winding. ThlS I decreases the current flow over the trunk line TL to such an extent that relay 104 is unable to operate and complete the circuit of the supervisory lamp 109, which is prepared by relay 105, energized through the lower armature of relay 106.

The operator now converses with the calling subscriber and extends the connection to the desired line in the usual manner.

When the ensuing conversation is terminated, the subscriber at substation A1 replaces his receiver whereupon the connector L01 and the line switch LS1 release in the usual manner and the ground potential is removed from conductor 371. When this occurs, relays 204 and 221 fall back. Relay 204 increases the current flow over the trunk line TL by shifting the connections of relay 205 back to normal, whereupon relay 104, Fig. 1, operates and closes a circuit for supervisory lamp 109 so as to cause the lamp to become lighted as a disconnect signal.

When the operator perceives the disconnect signal, she pulls down the connection, whereupon relays 104106 fall back and relay 205, Fig. 2, falls back as a result of the opening of the circuit over the trunk line.

In the interval between'the replacing of the receiver by the subscriber at substation A1 and the pulling down of the connection by the operator, a circuit is closed for line relay 223 of the incoming connector 10 with the result that the connector is prepared for operation in the usual manner, but this op-, eration is merely incidental and its chief function is to guard the trunk line from seiz ure in the O. A. X. as long as the operator has the connection up in the manual exchange.

e connector is restored to .its normal condition when the relay 205 falls back.

It will now be assumed that the operator in the manual ofiice receives a call to be comleted to the line of substation A2 in the O. A. El. Assuming that the trunk line TL1 is idle, the operator may insert the calling plug of her cord circuit in use into the line ack LJ, resulting in the energization of relays 106 and 105 and the energization of relay 104 over the trunk line TL1. Lamp 109 becomes .li hted as a supervisory lamp.

.tion in a manner explained in connection with the local connector L01 and in addition short circuits the resistance 244 at its inner-lower armature. It may be pointed out at this time that the incoming connector IO and the code switch CS1 taken together are almost identical with the local connector LCl and the code,

switch CS2, and that they difier only in slight details to be fully explained. For this reason it will be considered unnecessary to repeat the description of the operation of the incoming connector 10 in all its details.

In the manual oifice, the o erator inserts the plu of the dial cord D into the dial jack D after she has taken the trunk line for use, and she proceeds to operate the calling device CD in accordance with the three digits in the number of the line of substation A2.

When the calling device CD is first turned off-normal, a circuit is completed through the ofl'-normal contacts thereof and over the tip of the plug and jack for relay 101. Relay 101 disconnects the simplex leg of the trunk line TL1 from ground through relay 104 and connects it instead to ground through the ring contacts of the ack and plug and the impulse contacts of the calling device CD. As a result, each time the impulse contacts are opened on the return movement of the calling device CD the circuit of the repeating relay 205, Fig. 2, is opened. Relay 205 falls back a number of times corresponding to the digit dialled and repeats the interruptions produced in its circuit into the circuit of line relay 223. As a result of this vertical magnet 235 is operated in the manner described in connection with vertical magnet 335, Fig. 3, and the wipers 239242 are raised opposite the desired level of bank contacts.

When the next digit is dialled, rotary magnet 238 is operated to advance the wipers 239-242 into engagement with bank contacts in which the line of substation A2 terminates,

and, if the line is idle, relay 230 operates to seize the line and to extend the operating cirthe result that th called line'is signalled.

cuit to the operating magnet 254 of the code switch CS1.

When the stations digit is dialled, the code switch CS1 operates in the manner'described in connection ,with the code switch CS2 with When the calle subscriber answers, ringcut-ofi relay 226 operates and removes the ringin current and completes the talking circuit. ack-bridge relay 222 operates at this time and reverses the incoming conductors 208 and 210 in regard to their connection with the windings of line relay 223, whereupon'the.

electro-polarized relay 204 operates and gives 5 answering supervision to the calling operator by causing relay 104 to fall back and open the circuit of supervisory lamp 109. L Upon perceiving the disconnect-- signal I when relay 104 operates again under control ,differs from the connector LC1 will now be explained. The 'ofl-normal spring located above relay 222 is for the purpose of guarding the connector 10 from seizure'by a connector such as the connector LCl while the connector IC is releasing. At this. time relay 224 is at normal, but the oif-normal spring mentioned abgve is in engagement with its grounded upper contact, placing a guarding ground potential on conductor 209 by way of the upper armature of relay 224. When the normal position is reached, the said olfnormal spring moves into the position' shown 0 inthe drawing, rendering the connector idle.

Since the connector cannot release until the code switch CS1 releases and permits relay 227 to fall back, the connector is held guarded in case either it or the switch CS1 is unable to release.

The resistance 244 is provided to prevent 23 sufficient current flow through magnet to cause eventual damage in case the conductor 208 becomes grounded just sufiiciently to cause the'armature of line relay 223 to move over against its contacts, but not enough to move it all the way. In this case relay 224 remains short circuited and'resistance 244 is not shunted as it is when relay 224 operates.

With reference to the trunk busying relays 262-264, these relays operate in'the same from the manual oflice alon with the local connector LC1. The multip e is left intact between the incoming connector and the local connector LCI on the ninth and tenth levels so that the operator in the manual ofiice can test the ring-back'switches and themanualto-automatic trunk lines.

Giving trouble alarms- In case an abnormal condition arises within the P. A. X., such as the failure of one or the other charges to start, thefailure of the ringing machine, or the sticking of a connector in an oil-normal position or'the blowing of afuse, it is necessar that an alarm be given or that the conditlon be indicated so that the defect may be remedied. In case the trouble consists in a fuse of a local connector being blown or "the connector stuck in an oil-normal position, there is no emergency existing and there is'no need of sounding an alarm to get the same prompt action :as would be required in case of the failure of the ringing current, for example.

This difi'erence in the importance of the various trouble conditions is recognized in the present disclosure in the division of alarms into two-classes, regular alarms and emergencyalarms.

The relays lar-alarm relays, and the. relays 556-560 manner as relays 402-404, Fig. 4, in order to make the trunk line extending to the incoming connector IC artificially busy, after 0 it has been used, until'the trunkline TL2,

which is the second trunk of the group, has been used.

It will be noted IC has access to the ring-back switches of as Fig. 4 and also to the trunk' lines incoming that the incoming connector are the emergency-alarm relays.

More in particular, relay 554 of the first group is the one which eventually operates in case there is aregular alarm existing-and relay 559 is the relay of the second group which operates tosound an emergency alarm. The way in which these relays'are operated will be explained more-in detaiP-hereinafter. At this time it will be merely assumed that relay 554 operates to indicate a sci-called regular-alarm condition such as the failure of a connector to release, in'which case it closes a circuit at its lower armature for relay 562. Relay 562, upon operating, closes a circuit at its upper armature for the local buzzer 531 which signals an attendant in case one is present. making a repair, for example. At its lower armature, relay 562 closes a -circuit for relays 563 and 564 in series with the associated resistance. Relay 563 is normally short circuited by the contacts of relay 564 and relay 564 operates 'first and removes the short circuit from around relay 563. Relay 563 then operatesand short circuits relay 564, causing relay 564 to'fall back and again short circuit relay 563. This action continues with the relays 563 and 564 alternatin Each time relay 564 operates itopens t e circuit that is normally closed through contacts of relay 561 from battery through resistance 565 and over conductor 547 to the normally energized relay 201 i in the] alarm circuit AL.CKT. When relay 201 ,falls back, it closes at its lower armature a circuit for the buzzer 202 in 551-555, Fig. 5, are the regu-

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