US2099429A - Automatic telephone system - Google Patents

Description

Nov. 16, 1937. J. E. ns1-LINE AUTOMATIC TELEPHONE SYSTEM '7 Sheets-Sheet l Filed May 7, 1934 rrr:

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7 Sheets-Sheet 2 J. E. osTLlNE AUTOMATIC TELEPHONE SYSTEM Filed May '7, 1934 Nov. 16, 1937.

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. Nov. 16, 1937. J. E. OSTLINE AUTOMATIC TELEPHONE SYSTEM Filed May 7, 1954 7 sheets-sheet 3 Nov. 16, 1937. J. EOSTLINE AUTOMATIC TELEPHONE SYSTEM Filed May 7, 1934 7 Sheets-Sheet 4 NVE/vra@- do//N E. 05u /NE rrr.'

Nov. 16, 1937. .1. E. OSTLINE AUTOMATI C TELEPHONE SYSTEM Filed May 7, 1954 7 Sheds-sheet 5 Filed May '7, 1954 Nov. 16, 1937.

7 Sheets-Sheet 6 .dou/v .OST/.INE

md Bm J. E. @s1-LINE 2,099,429

AUTOMATIC TELEPHONE SYSTEM Filed May 7, 1954 7 sheets-sheet 7 Nov. 16, 1937.

Patented Nov.. i6, 1937 PATENT OFFICE 2,099,429 AU'roMA'rrc TELErnoNE srsrEM John E. O stline, Berwyn,`I1l.,-asslgnor-to AssociatedrElectrlc Laboratories, Inc.. Chicago, lll., a corporation of Delaware Application May 7, 1934, Serial No. '124,238

18 Claims. (Cl.v 179-17) The present invention relates in general to automatic telephone systems, but more in particular to systems suitable for installation in small towns and villages. An automatic system of this type is generally known as a community automatic exchange or C.A.X. In these systems it is the usual practice to provide for multi-station party lines having either bridged or grounded ringing circuits, or combinations of each and lo the subscribers are signalled by means of code ringing equipment. The Aexchanges are also usually unattended, but are provided with trunking facilities' to distant exchanges.

I One of the objects of the present invention is to economically provide a telephone system oi this character capable of serving a community requiring a system of a capacity of as many as two hundred lines and trunks. n

One of the outstanding features of the lnvention relates to the employment of nder connector links oi' a novel type common to all lines and trunks of the system and employed to connect any calling line or trunk through to a desired called line.

Other features have to do with the novel manner in which a ilnder connector link is employed to establish local, reverting call, PBX. and toll trunk connections, respectively.

The invention is disclosed in seven sheets of drawings, numbered Figs'. 1 to '1, respectively. The drawings should be arranged with Fig. l to the left of Fig. 2, Fig. 3 to the right of Fig. 2, Fig. 6 immediately below Fig. 3, Fig. 5 to the immediate left of Fig. 6, Fig. 4 below Fig. l, and

with Fig. '7 'to the left of Fig. 1, and with the corresponding lines of the various adjacent iigures in'alignment. With the drawings so arranged they diagrammatically disclose suicient circuits and apparatus to enable the invention to be understood when considered in conjunction with the description which follows. y

Considering the drawings more in detaiLvFig. 1 shows a calling party line and its individual line equipment SLE, and the line equipment 'ILE of a trunk line which is substantially like the subscribers line .equipment SLE. To the right of the trunk and subscribers line equipment shown are bank contacts and the wipers of a ilnder portion of apparatus and equipment constituting one 5 of a plurality of 'finder connector links of the system. The operating and release magnets of the flnder are shown inthe lower central portion of the gure.

Fig. 2 discloses the central portion oi? the finder connector link and at the bottom of the figure are grouped the operating and release magnets and the special rotary control bank and wiper oi' the connector mechanism of the link.

Fig. 3 shows the remainder of the link circuit, the wipers and certain of the bank contacts oi 10 the connector, and-in the lower portion of this figure discloses the operating and release magnets and the/wipers and banks of the class and code switch CC of the link. The equipment to the right of the figure comprises a subscribers line 15 equipment SLE and its associated party line, and also an alarm line equipment ALE which may be seized by a toll operator for obtaining supervision of possible trouble conditions existing in the community automatic exchange. 20

In Fig. 4 is shown an allotter comprising an vallotter control relay group designated generally ACR and a second'group of link selecting relays designated LSR. In the lower portion of the figure are two other relay groups, one comprising 2 a group of group markingrelays GMRA and the other comprising a group of finder control relays FCR.

The equipment in Fig. 5 in the main consists of a combination of code interrupter relays CI 30 employed in generating the codes required to signal the various stations on party lines. In the lower part of this figure there are also a number of relays designated generally as ARG which function under certain abnormal conditions to 35 register alarm conditions in the alar'mline equipment ALE of Fig. 3.v

Fig. 6 shows the ringing equipment RE employed.

In Fig. 7 the majority of the circuits shown 4f! comprise a trunk TR and its associated equipment terminating in a distant exchange. In the lower rightfhand corner of this figure, however, is shown a group of time cut-ofi relays 'TCOy 1 employed to prevent various pieces of equipment 45 being held for an undue period.

Throughout the drawings numerous types of relays, well known in the automatic telephone art, are shown. Slow-to-operate relays are shown having a fullfblack upper section. Slow-release relays are shown having a cross-hatched section.

in a shunted magnetic circuit. The subscribers' line relays are of this type. These relays only operate when both windings areenergized. A number of three-pole relays of the type covered by Pye Patent No. 1,673,884, issued June 19, 1928 are also employed, and these are designated with a core equipped with a bar magnetically separating the two windings of the relay. These relays only operate when both windings are energized, but will then hold through one winding. 'Ihe test relay |15 is an example of this type. The nder and connector switch mechanisms, respectvely, are of the Well known Strowger type arranged with two sets oiv wipers giving these switches access to two groups of lines each. 'I'he switch employed as a connector is also provided with an auxiliary rotary control bank RCB and an associated wiper RCW which are employed to produce an automatic trunk hunting movement of the connector when the switch is positioned opposite P.B.X. and toll trunk levels of its bank contacts.

The class and code switch mechanisms shown in the lower portion of Fig. 3 are of the well known pawl and ratchet type arranged to advance its wipers in a step by step manner when i its operating magnet is intermittently energized, and to restore its wipers through the medium of a spring, tensioned during the advance, upon operation of the release magnet of the switch.

In brief, the operation of the system is as iollows:

When a calling subscriber initiates a'call the test conductor of the calling line is marked with 'calling potential and the group in which the calling line is located is marked on the contact of one of the group marking relays GMR associated with the allotter, and the connecting relay |65 of the link operates to cause the finder control relays FCR, also associated with the allotter, to interact with the vertical magnet of the finder oi the link to cause the finder to elevate its wipers opposite the group in which the calling line is located. The finder control relays at the same time operate the group marking relays GMR in a definite sequence, and when the one is operated which has a potential on one of its contacts the control of these relays by the finder control relay ceases and a change-over relay of the finder control relay group operates .to bring about the line hunting or rotary movement of the finder. When the marked line is found the test relay |15 operates to stop the finder and to cut the calling line through to the link circuit. The calling subscriber now receives dial tone and proceeds to transmit the digits constituting the called subscribers number. The subscriber dials four digits to complete a connection to the called line. I'he first digit transmitted operates the class and code switch CC to determinein which hundred group the called line is located and to also determine on which side of the line the ringing current is to be transmitted. The class and code switch is then released. 'I'he next two digits transmitted position the wipers of the connector into engagement with the desired line. 'I'he fourth digit transmitted then positions the class and code switch CC to determinethe code to be transmitted to the called line. The equipment for generating the code is obviously disclosed in Fig. 5 and the code actually transmitted ofthe system will now be given.

is determined by the position of the wipers lll and 3|1 of the switch CC.

Incoming trunk calls come in over line equipment the same as provided for local subscribers lines and connections are established in the same manner except that on this type of calls the called line instead of receiving talking potential from relays in the link is cut through to relays i'n the trunk circuit.

. On outgoing trunk calls tc a distant exchange the single digit 8, 9 or 0 is dialled and the lmpulses of. this digit operate` the class and code switch seven steps after which a relay in the link operates and switches the remaining impulses of the digit to the vertical magnet of the connector of the link to connect the switch wipers opposite the desired trunk level. The switch then automatically rotates under control of its rotary control wiper to connect with the nrst idle trunk. i

On P. B. X. trunk calls the connector switch, after having its wipers positioned on the contacts of the first line of the P. B. X. group by the transmitted impulses, rotates under control oi' its rotary control wiper to nd an idle line as in outgoing trunk calls.

In establishing reverting calls the subscriber dials the regular four digit number of the called station and upon receipt of the busy tone hangs up his receiver. During the ringing operation of the called station the calling subscriber receives a characteristic ring back tone or hears the same code as is being received at the called station, and upon cessation of the ringing of his own signal is advised that the called subscriber has responded. In reverting call connections the link circuit releases as soon as the called party responds and the calling and called subscribers on the y same line receive talking battery from the line relay of such line.

A more detailed description ofthe operation Local connections In order to describe in detail the operation of the system it will rst be assumed that the subscriber at station 595| desires to establish a connection with a party at station 2645. When the subscriber at'station 595| removes his receiver a circuit for the line relay |3| is completed. This circuit extends from ground through the left winding of relay |3|, through the contacts |36 of cut-off relay 35, line conductor |28, the station equipment, line conductor |29, the contacts |31 of the cut-olf relay |35 and through the righthand winding of line relay |3| to battery. The line relay |3|, upon operating, at its armature |33' disconnects the cut-oi relay |35 from the test lead oi' the connector multiple of the calling line and instead connects ground potential thereto, thereby rendering the calling line busy to other subscribers. The relay |3|, also, at its contact |32 connects the cut-oil relay |35, via contacts |42, to the test terminal |60 of the nder bank to mark #595| as a calling line, and at contacts |34 applies ground potential to start conductor 4|0 via armature |43 and its resting contact, thereby marking the group 'in Which-the calling line is associated in the allotter.

The ground potential applied to the start conductor 4|0 extends via conductor 451, resistance cuit for itself excluding the contacts 482'. 'I'his circuit includes conductor 408, thelower contacts of relay i423, and conductor 4001. v

The inclusion of relay 400| in a locking circuit excluding contacts of relay 4002 preventsa premature release of relay 400| which might otherwise occur should a succeeding call be initiated over a line of the first hundred group immediately following the operation of relay 400 I. When a call is initiated by a line of the first hundred group relay 4002 is operated instead of relay 400| and at its contacts 482 prevents a subsequent calling line of the second hundred group from interfering with calls initiated over the rst hundred group.

The relay 400|, at armature 4004 transfers the connection of the winding of relay 482 from associatlon with group marking relay contacts of the first hundred group of calling line start conductors and associates it with the contacts of the group marking relays associated with the second hundred group of start conductors. The relay 400| also, at contacts 4005 prepares a point in the operating circuit of wiper switching relay |14, and

l l at contacts 4006 closes a circuit for the allotter control relay 4|8. This circuit extends from ground, supplied throughthe contacts 4006, conductor 4009, contacts 4|1 of slow-release relay 4|4, the contacts 460 of all` link busy relay 43|, and through the lower winding of relay 4|8 to battery. The relay 4|8, upon energizing, at

contacts 420 applies ground potential to conductor 462 to maintain the slow release relay 435 energized independently of armature 434, at armature 42| applies ground potential to the .conductor 463, and via contacts M5 to relay 4H of the timing relays 4M, M3 and 4|4, and at its contacts 422 applies ground potential via contacts 429 to conductor 055, extending to the connectlng relay of the link at the time associated with the allotter. In the present example the circuit extends via contacts 440, conductor 402 and through the winding of connecting relay to battery.

Upon an inspection oi' Fig. 4 is will be observed that the present system is assumed to be provided with twelve link circuits andv that only the first, second, and twelfth link selecting relays have been shown. The rst of the twelve links is the one shown in the drawings to have been preselected at the time the call under consideration was initiated. As long as one or more of the link circuits are idle, the all link busy relay 43| is energized over the common all link busy conductor 403, from ground supplied from one or more oi the multiple circuits extending from the idle -link circuits. One of these circuits may be traced from grounded armature |50 and its resting contact, conductor |2|, contacts 244, off-normal spring ON22 at its resting contact, conductor |20, ofinormal spring ON|2 and its resting contact, the busy keys springs, contacts |85, the all link busy conductor 403, and the winding of relay 43| to battery. Since a like circuit extends via each idle link and intoconnection with the all link busy conductor 403 the relay 43| only deenergizes at such time as all of the links are busy. The relay 43| at contacts 433 closes a point in a circuit including the guard conductor 40| of the preselected link and which later becomes effective in case the calling line is not found within a predetermined time, as will' be described later. The relay 43| at contacts 460 closes a point in the pick-up circuit for relay 4| 8, at armature 434 removes ground from the timing conductor 463 so as to place this conductor and the timing relays 4||,

4| 3, and 4| 4 under control of relay 4|8, and connects ground to conductor 462. This ground potential, extends to the winding of slow release relay 435, through the lower winding of relay 438, the break contacts of this latter relay, to the lower break contacts of link selecting relay 446, the contacts 444 of relay 439, and the lower winding of this relay, in multiple with resistance R45. Relay 435, upon operating at its contacts 431, opens the initial operating circuit of linkselecting relay 439, and at contacts'436 prepares a locking circuit for relay 438. The relay 439 is initially energized from ground on the front contact of armature 434 supplied to the upper winding of relay 439 vla contacts 431 and conductor 453 and through the upper winding of relay 421, contacts 432, conductor 454. 'Ihe relay 439 at contacts 440 closes a point lnl the operating circuit of the link connecting'relay |65, at its contacts 442 prepares break contacts oi relay 446, conductor 45|, the

break contacts of relay 438, the lower winding of this relay, the winding of slow release relay 435, and the contact and armature 434 of relay 43| and ground. Upon completion of the circuit the relay 435 operates and at its contacts 431 breaks the initial operating circuit of relay439 and at its contacts 436 prepares a locking circuit for relay 458.

Since the first link is the one preselected, clue to the link selecting relay 439 being in energized position, the relay M8, upon energization, com'- pletes, in this case, the circuit for energizing the link connecting relay |65. This circuit extends from ground through contacts 422 of relay M8,

contacts 429, conductor 455, contacts 440, start conductor 402, and the winding of relay |95 to battery. The start relay 4| 8 at its contacts 42| grounds conductor 463 to energize the timing ren lay 4H; at contacts 420 applies ground to conductor 402 so as to hold relay 435 and the link selecting relay 439 energized independent of the all link busy relay 43| should the link selected be the last idle one of the group; and at contacts 4|9 completes a circuit for itself independent of the contacts 450 of relay 43|, and also'independent of the contacts til of timing relay 4|4. The relay 4H operates and, after an interval, completes the circuit of slow to operate relay Il |3 and this relay in turn completes the operating circuit of slow release relay 4M. The relay 4|4, upon operating, at its contacts 4|5 interrupts the circuit of relay 4|| which accordingly deenergizes, and at contacts 4&6 closes a point in a link selecting circuit which will be completed later if the selected link fails to find the calling line within a predetermined time. The relay 4|4 also,` at its` 4||, upon restoring, causes its weighted spring to vibrate and in sodoing alternately opens and closes the circuit of slow to operate relay 4|3. Due to its slow to release characteristic the relay 4|3 remains operated dur-ing the vibration of' armature 4|2. When vthe armature 4|2 nally comes to rest, in its deenergized position, relay 4|3 restores. If the nder has not by this time succeeded in finding the calling line or some other line has in the meantime effected the grounding of conductor 4008 relay 4|8 will still be energized. Under these circumstances the relay 4 |3 completes a circuit from ground at contacts 42| of the start relay, through the armature and resting contact of relay 4|3, contacts 4|6, 433, 442, conductor 448, the upper break contacts of relay 441, guard conductor contacts 443, the upper winding of link selecting relay 446, conductor 454, contacts 432, and the upper winding of relay 421 an'd resistance R48 in multiple to battery. The relay 446, -upon operating, at its lower break contacts interrupts the locking circuit of the link selecting relay 439, which accordingly restores and disassociates the first link from operative relation with the allotter. The relay 446, at its lower make contacts now cornpletes a locking circuit for itself, at its contacts 443' prepares a point in the operating circuit of the next link selecting relay of the group, at contacts 442 closes a point in a circuit including the guard conductor of the second 'ofthe links, at contacts 44| opens a point in the guard conductor of the subsequent or thirdlink, and at contacts 440 connects the start lead of the second link to the common start conductor 455.

In the link circuit the relay |65, upon becoming energized over the previously traced circuit, at contacts |24 and |66 applies ground potential to the test and polarizing windings of test relay |15, at contacts |64 applies ground potential to conductor |01, and at contacts |61 closes a point in the operating circuit of Wiper switching relay |14. The relay |65 also, at contacts |68, closes a point in the operating circuit of cut-through relay 423, at armature |69 removes ground potential from conductor |2|, and applies ground potential to conductor 406 and through the contacts 495 of interrupter relay 48'2 and the Winding of relay 48| to battery. The relay |65 iinally, at its contacts |10 applies ground potential to conductor 403 to replace that removed therefrom asv a result of the operation of armature |69, to hold the all link busy relay 43| operated until the calling line is found if this is the last of the idle links; and at contacts |1|, |12, and |13 operatively associates the verticaland rotary magnets |26 and |25 and the associated control conductor |21 with leads 408, 405, and 401, extending to the nder control relay group FCR.

Relay 48|, upon operating, at its contacts 496 applies ground potential to the holding conductor 486 and over an associated branch conductor 486|. The ground potential on the branch conductor extends via armature 4862 and its back contact, conductor 489, the break contacts of relay 466, and the winding of group marking relay 461 to battery. The relay 48|, at its contacts 465, opens a point in the operating circuit of rotary magnet |25 of the finder, and at contacts 464 completes the initial operating circuit of vertical magnet |26. This circuit extends from ground supplied through contacts 48 of interrup'ter relay 413, the armature 493 and its resting contact contacts 464, conductor 408, contacts |1|, and the winding of vertical magnet |26 to battery. The vertical magnet |26 accordingly operates, and in the well known manner, moves the wipers |41, |49, |5|, |59, and |6| of the nder up one step opposite the rst level of the associated bank of contacts in which the calling lines terminate. Near the end of the armature stroke of the Vertical magnet |26 it applies ground ingly restores to normal.

vresting contact and armature 46 of relay 414,

the upper winding of relay 415, the armature and its resting contact, and the resistance to battery. Relay 413 finally at its contacts 48 opens the circuit of vertical magnet |26, which, in turn, removes ground potential from conductor |21 and from the initial operating circuit of relay 413.

The relay 415, upon operating, at its contacts 43 prepares an operating circuit for relay 414, and at its armature 4| interrupts the locking circuit of relay 413. The relay 415 also at its armature 4| breaks the traced locking circuit of interrupter relay 413. This latter relay accord- Relay 461, which it will be recalled had its circuit completed upon operation of relay 48|, at its break contacts opens a point in the locking circuit of relay 41|, at its outer upper make contacts closes the obvious operating circuit of relay 466, at its inner upper make contacts complete a locking circuit for itself extending through the'upper break contacts of relays 468, 469, 410, 41|, to the grounded conductor 486. The relay 461 also, at its inner lower make contacts, prepares a point in the operating circuit of relay 468, and at the remainder of its contacts closes points in the rst and seventh group control circuits of each 100 line group, but which are ineffective so far as the present operation is concerned. Relay 466, upon operating, at its uppercontacts completes a locking circuit for itself, and at its lower contacts breaks the initial circuit of 461.

The relay 413, upon restoring, completes an operating circuit for relay 414, from ground on conductor 486 applied through armature 492 and its resting contact, through contacts 43 of relay 415 and through the lower winding of relay 414 to battery. The relay 414, upon operating, at its contacts 44 completes a locking circuit for itself excluding the armature 492, at its armature 41 breaks a second point in the traced holding circuit of relay 413, at its armatures 45 and 46 interrupts the operating circuit of relay 415, and at the front contacts of these armatures connects the upper winding of this relay in series with the upper Winding of relay 414. Finally, the relay 414, at armature 4862 removes ground from the initial operating circuit of relay 461 and at its front contact applies ground to conductor 488, through the `inner lower make contacts of relay 461 and the winding of relay 468 to battery. The relay 468 accordingly operates and at its break contacts interrupts the previously traced locking circuit of relay 461 which accordingly restores. The relay 468 also, at itsv inner upper make contacts completes a locking circuit for itself similar to the one previously traced for relay 461, at its inner lower make contacts prepares an operating circuit for relay 469, and at the remainder of its make contacts closes points in the second and eighth group control circuits of the rst and second hundred groups, not involved in the present connection.

with wipers |81, |89 and |8|, having access to subscribers' lines of the second hundred group.

The change-over relay 482, upon operating, at

for itself including its upper winding, conductor 408 and the iront contact and grounded armature of relay |88, contacts |80 of test relay |18, and

|89 "of relay |88, and at its amature 483 interruptsapoint in the operating circuit of the vertir cal magnet |28 and prepares a point in the oper- Y ating circuit of rotary magnet 28. An' instant later the relay 48| restores and at its contacts 488,

removes ground potential from the holding conductor 488 thereby bringing about the deenergization of any operated ones of the group marking relays GMR and of either oi.' the relays 414 or, 418 which lmay happen to be operated at this time, and at contacts 488 completes the operating circuit of rotary magnet |28. This circuit extends from ground supplied through the contacts 48 of relay 413, amature 483 and its front -contact, contacts 488, conductor 401, contacts |13 the winding of the rotary magnet |28 to battery. The rotary magnet |28, upon operating, rotates the associated nder wipers into engagement with their rst set of bank contacts in the level in lwhich the calling line terminates, in the present example the ninth. -The rotary magnet near the end of its operating stroke applies ground potential toconductor |21 as did the vertical magnet |28. 'I'he interrupter relay 413 oi the allotter accordingly becomes energized and at its interrupter contacts 48 opens the circuit of the rotary magnet. Since the conductor 488 is no longer grounded, owing to the deenergized condition of change-over relay 48|, the interrupter relay 413 no longer exerts any influence over the group marking relays or over the finder control relays 413, 313, or 418. The rotary magnet |28, upon restoring, interrupts the operating circuit of relay 413 and this latter relay vaccordingly restores to again establish the operating circuit of the rotary magnet. It will be obvious, therefore, that the rotary magnet |28 and the finder control relay 413 operate alternately, and that the wipers of the nder are in this manner rotated over the selected group of bank contacts until contacts oi the calling line, or in case the calling line is not found until the last contacts of the contact bank K arev encountered.

In order to prevent the ilnder of some link from continuously hunting should a call be initiated from a line havingv an open test contact y the following circuits are provided: Each under is provided with an eleventh rotary bank contact |80 in each of its levels. lThe ten revertive control relays |4| to the lines of a level have their upper windings connected in se'ries. The winding of the last relay is terminated to battery and the winding of the ilrst relay is terminated on the eleventh step test contact |80.

If, for instance, line 888| has an open test lead, and the line is taken for use or becomes short circuited, a nder will be Started to hunt for this line. Due to the fact that the test contact is open the finder will continue hunting in a. rotary direction until it reaches the eleventh step test contact |80. At this point the test wiper will encounter battery in series with the windings of all of the relays |4| ofI such level and they will operate. As soon as the relay |4| of line 898|, at its armature |43 closes its make contact it will immediately lock itself from ground supplied through the contacts |34 of the operated line ref lay |3|. The relay |4I, of the line calling, will at its amature |43 also open up the start conductor `4||l and thereby prevent this calling line from starting another ilnder while the receiver remains oii its hook. Y

-We will now` return to a consideration of the operations which follow the ilnder test wiper encountering the test contact of a calling line having calling potential thereon; When this occurs -an operating circuit, is completed including the cut-ofi' relay |38 of the subscribers line equipment and the upper winding of the test relay |18 of the link circuit. This circuit extends from the ground supplied through contacts |24 of the relay |88, the upper winding of test relay |18, conductors |88 and |08, armature |88 and its iront i, contact, the test wiper |8I, test contact |80, the

' to' battery, and via a second branch including the contacts |38 of re1ay|38 and resistance RI to battery. VIhe relay |38, upon operating, at its contacts |38 disconnects the resistance RI and the associated battery from the traced operating circuit of relay |18, at its armature |40 opens a point in the permanent alarm circuit which will be 'described later, at the front contact ol this armature completes a circuit through the lower winding of slow. releasev relay |4|, at contacts |38 closes a holding circuit for itself independent of contacts |42, and at contacts |38 and |31 disconnects the line relay |3| from in bridge of the line. The line relay |3|, upon restoring, at its armature |33 disconnects direct ground from conductor l at its working contact and at its resting contact substitutes the ground now supplied through the working contact and armature ,A

|24 of relay |88, the contacts |13 of test relay |18, conductors |89 and |08, armature |88 and its working contact, wiper |6I, the associated bank contact |60, the contacts |38, andthe contact and armature |33, so as to maintain con-V 'moves ground from the start conductor 4|0.

The relay |18, upon operating, at its contacts |80 interrupts the circuit, of rotary magnet |28 and thereby prevents further movement of the nder wipers, at its contacts |18 shunts out its upper winding so that the ground supplied through the contacts |24 and |88 will be effective to replace that formerly derived through the front contact and armature |33 of line relay |3|, as previously explained. The relay |18, at contacts |18 and |11 connects the talking conductors of the calling line through to conductors |02 and |03 of the link, and at its contacts |19, completes an operating circuit for the cutthrough relay 423 of the allotter control relay group ACR. The circuit of relay 423 includes contacts |88 of relay |68 and the cut-through which is ineffective at this time, at contacts 425 places a shunt circuit about the lower winding of 'with the talking conductors |02 and |03 of the link, at contacts |16y and |11. When this occurs an operating circuit is completed for the link line relay 245. This circuit extends from ground through the relay 245 through -,the contacts controlled by armature 25|, conductor 202, through contacts controlled by armature 34|, the con- 'ductor |02, contacts |16, armature |53 and its front contact, wiper |51 and its associated bank contact |56 to the line conductor |28, through4 the substation equipment, line conductor |29, the bankcontact |56 and the associated wiper |59, the front/ contact and armature |54, contacts |11, conductr |03, through contacts controlled by armature 340, conductor 204, contacts controlled by armature 252, conductor 206, and the lower winding of relay 349 to battery and over a second branch in multiple with relay 349 and extending via contacts 258 and resistance R2| to battery. The resistance R2| is low compared to that of relay 349 and therefore 349 does not operate over the traced circuit `so long as resistance lR2| is included therein. The relay 245, upon operating, at its upper contacts closes a pointin acircuit effective an instant later by operation of armature 241., and" at its lower contacts completes an obvious operating circuit for the relay 246. The relay 246, upon operating, at its contacts 248 applies ground potential to conductor 221 vla the resistance R22, but which is ineffective at this time,v and at armature 241 removes ground potenti al from conductor I3 and atthe front contact of this armature applies ground potential over conductori |4 to and through the winding of slow release relay |94 to battery. 'Ihe relay |94, upon operating, completes an obvious operating circuit for the relay |90. The latter relay, upon operating, at its armature |9| separates conductors |05 and'l |06 and connects ground potential to the conductor |06 to replace that being applied to it by the contacts |24 of the connecting relay at contacts 93 appliesground potential, via the springs controlled by armature |83,

`to conductor ||9 and to the lower winding of the test relay |15 in substitution for the ground being applied by the contacts |66 of the connecting relay 65, and at contacts |92 completes an obvious operating circuit for the slow release relay |95. The latter relay, upon operating, at its contacts |96 closes a point in the operating circuit of time release relay 8|, at its contacts |96 closes a point in a circuit including the operating magnet 320 of the class and code selecting switch 'CC and of the series relay 263 in multiple, which circuits will be traced subsequently. 'I'he relay also, at its uppermost contacts. connects dial tone to talking conductor |03 by way of conducto-r |0|, contacts 280, 281, the back contact and armature 234, conductor 20|, contactsv 361,

condensers C3| and C32, conductor 204, and the contacts controlled by armature 340 to conductor |03. The relay |95 also, at its contacts |91 comt pletes a circuit extending over conductor ||6 and through the lower winding of vrelay 235 to battery. Thevrelay 235, upon operating, at its contacts 238y completes a locking circuit for itself including the conductors 5, |99 and the previously grounded hold conductor |06; lat contacts, controlled by its armature 239, removes direct ground from the wnding of relay 246 and substitutes therefor ground potential supplied through resistance R22 and contacts 248 oi' relay 246. The relay 235 also, at its contacts 236; supplies ground potenti-al to conductor |01 in order to maintain the wiper switching relay |14 energized independently of contacts |64 of the connecting relay |65, at its contacts 243 applies ground to conductor4 223 for a purpose having utility ,only when outgoing trunk calls are being set up. and at its armature 24| removes ground potential from the class and code switch release conductor 224 and connects this conductor to the conductor terminating at armature 289 of the relay 284. The relay 235, furthermore,'at contacts 240 applies ground potential to conductor 1, through contacts |89, time start conductor 109, contacts 151 of relay 156 of the time cut-oil.' relay group TCO and through the winding of solenoid of this group to battery, and via a branch conductor 109', the armature and back contact of relay TCI, to the winding of slow release relay 15| and battery. Finally, the relay 235 at its contacts 242 applies ground potential to the guard conductor 40|, through contacts -443 of the link selecting relay 439, the upper winding of relay 446 of this group, the conductor 454, contacts 432 of relay 43|, and through the upper wind'ng of relay 421 to battery.I

The relay 421, upon operating, at its contacts 430 completes a locking circuit for itself including its lower winding and contacts 424 of the cutthrough relay, at its contacts 429 interrupts the previously traced circuit of the connecting relay |65 in the link circuit, and at its contacts 428 places low resistance R48 in multiple with its upper' Winding, thereby increasing the current flow over the traced circuit suiiiciently to enable the operation of the link selecting relay 446, and the consequent association of the next idle link with the allotter.

The relay |65, upon restoring, at its armature |64 opens the initial locking circuit of relay |14, but without effect at this time since ground is now being supplied to the locking winding of this relay vla contacts 236 of relay 235, as previously explained; and at contacts |66 removes ground potential at this point from the winding of test relay |15, but without effect because of the previously substituted ground potential through contacts |93 of relay |90. The relay |65, also, at its contacts |69 interrupts the circuit of change-over relay 482 of the i'lnder control group FCR, which accordingly restores, at its contacts |10 removes ground potential from one of the twelve multiples extending by way of conductor 403 to the all link busy relay 43|, and at its contacts |68 interrupts the previously traced circuit of the cutthrough relay 423. The relay 65 also at its contacts |13, |1|, and |12, disconnects the vertical and rotary magnets and the control conductor |21 from association with the allotter.

The link selecting relay 446, upon operating, at its lowermost break contacts interrupts the locking circuit of relay 439 causing it to restore; at its inner lower make contacts completes a locking circuit for itself including the lowermost break contacts of the third link selecting relay (not shown) thereby maintaining the slow release relay 435 energized. "I'he relay 446, at its contacts 443', prepares an operating circuit for the next link selecting relay of this chain, at its contacts 442 closes a point in the guard 'circuit of the associated link, at its contacts 440 connects the start conductor of such link to the common ccnseries. The relay 439, upon restoring at contacts 440 disconnects the start conductor 462 of link I from conductor 455, at its contacts 44| closes another point in the guard circuit of link 3, at its contacts 442 opens a point in the guard circuit of link l, at contacts 443 opens the initial operating circuit of relay 446 and 421, atits contacts 444 interrupts its own locking circuit at a second point, and at its contacts 445 prepares a locking circuit for the relay 441.

Upon the restoration of the cut-through relay 423 as a result of this circuit having been opened at contacts V|68 of relay |65; the relay 423 at its contacts 424 opens the locking circuit of relay 421, permitting that relay to restore, and at its contacts 425 again prepares a point in the locking circuit for relay 4|8 which is independent of the all link busy4 relay 43|, and at -its contacts 426 opens the shunt previously placed about the marginal relay 438. The relay 423 also, at its lowermost contacts, opens the locking circuit of relay 400| which accordingly restores and removes ground from the start lead 4008, providing no other lines have in the meantime initiated a call. The relay 421, upon restoring, atits con-k tacts 429 again prepares the conductor 455 for receipt of ground potential when the relay 4 I8 becomes energized consequent to the initiation of another call.

The removal of the shunt circuit from about the lower winding off' relay 438 by relay 423 is without eiect so far as the operation of relay 438 is concerned, unless due to some abnormal condition, current is supplied to it from more than one of the link selecting relays, such as 439. Should this occur, for example, as a result of a maintenance man working on the contacts of these relays, the relay 438 will become energized and at its lower contacts interrupt the locking circuit of any operated ones of the link selecting relays, and at its upper contacts 'will become locked energized through the contacts 436 of the slow release relay 435. Since these locking circuits both include the slow release relay 435 the latter relay after a slight delay will'deenergize, and at its contacts 431 establish an operating circuit including the conductor 453, the upper winding of relay 439, the contacts 432 of all link busy relay 43| and the upper winding of relay 421 to battery. The relay 421 will accordingly operate followed by the operation of relay 329 to again preselect a link circuit. The slow release relay 435 upon restoring also breaks the locking circuit of the marginal relay 438 and accordingly the relay 439 will become locked upthrough the break contacts of the relay 438 and the winding of the slow release relay 435. The latter relay will accordingly again become energized and in so doing at its contacts 431 will again interrupt the initial operating circuit of the relay 439.

In case all of the link circuits become busy all of the circuits such as described for the all link busy relay 43| will be interrupted and this relay will accordingly restore. This relay, upon restoring, at its contacts 460 interrupts the operating circuit of start relay 4|8, so as to prevent relay 4|8 being-operated when a subscriber initiates a call at a time when no idle links are available. The relay 43|, at its contacts 432, opens a point in the operating circuit of relay 439 which might otherwise be completed following the operation of the last link selecting relay 441 of the chain, even though the link circuit associated with the relay 441 is already in use, at its contac-ts 433 opens the controlling path extending from the timing relays 4| 4|3, and 4|4, and at its armature 434 removes ground potential from the common locking circuit of the link selecting relays and from the operating circuit of relay 435, and applies this ground via the contacts 4|5 and the timing relay 4I to battery.

As soon as one of the links becomes idle the all link busy relay 43| again becomes energized to again establish the operating circuit of relays 4|8 and 421 and the link selecting relay of the then idle link. These relays accordingly operate as before followed by the operation of relay 435- which again is included in the locking circuit of such link selecting relay, after which the circuits will be in the condition in which they are shown, providing the link which became idle is the one associated with relay 439.

When the calling subscriber hears dial tone he proceeds to operate his calling device `in the usual manner to transmit the digits of the called number. If the rst digit transmitted simply comprises a preliminary impulse, relay 245 at its lower contacts interrupts the circuit o1' repeating relay 246 only once, and the latter relay, in turn, at its `armature 241 and its back contact transmits one impulse out over conductor 3, through contacts |96, conductor ||2, to the winding of slow release relay 263 and battery, by way of armature 259 and its back contact and contacts 264 to the upper winding of relay 210 to battery, and also by way of armature 218 and its back contact, the lowermost armature of relay 296 and its back contact, conductor 226, to the winding of rotary magnet 320 of the switch CC to battery. The relay 246 also at its contacts 248 opens its own locking circuit. The magnet 320, however, near the end of its armature stroke applies ground potential direct to conductor 221, thereby'enabling relay 246 to operate from this direct ground as soon as the lower contacts of line relay 245 again close.

The relay 263, upon operating, at its contacts 264 closes an obvious circuit through the lower winding of relay 210. The circuit traced through the upper winding of relay 210 including its own break contacts 254 assists the relay 263 in the quick operation of relay 210. The contacts 254 of this relay are arranged to break after all other contacts of the relay have been actuated.

Upon the termination of the transmission of the rst series of impulses, in the present example simply a. preliminary impulse, thev line relay 245 remains energized as does also the pulsing relay 246. The prolonged removal of ground potential from the pulsing circuit permits the deenergization of slow release relay 263, which has remained operated throughout the impulse series. This relay at contacts 264 interrupts the circuit of relay 21|), permitting that relay to also restore to normal. With the wiper 3|8 of switch CC in engagement with its rst contact; the relay 210, upon restoring, at its armature 214 and its back contact completes a circuit including the release magnet 3|9 of the switch CC causing it to restore. This circuit extends from battery through the magnet 3|9, the oi normal springs ON3, closed upon the initial movement of the wipers of switch CC off normal, conductor 224, first bank `contact and' wiper 3|8, conductor 225, contacts v288, 282, and 214, resting e r21|), upon restoring, at itsarmature 214 and its back contact now completes an operating.l circuit spring ON2 Iand its resting contact, back contact and armature 214, contacts. 282. 288, conductor 226, the wiper 3|8 of the class and code switch CC, and its second bank contact, and the conductor 2|8 and winding oi' relay 211 to battery. 'I'he relay 211, upon operating, at its contacts 28| com-` pletesthe circuit of the release magnet 3|8 of the class andsl code switch. This circuit extends from ground on the conductor |81 and its branch y 281| through contacts 28|, the back contact and armature 288, the front contact and amature 24 I, conductor 224, the off normal contacts ON3, closed upon the initial movement of the wipers of switch CC, and the magnet 3I8 to battery. The switch CC accordingly restores, and upon reaching its normal position, again opens its contacts 4ON3. The relay 211 at its contacts 283 completes a locking circuit for itself independent of the switch CC via contacts 268 and 28| to the grounded conductor 2|1, at its contacts 282 opens a point in its initial operating circuit; at its armature 218 transfers the impulsing circuit from association with the magnet 328 of switch CC into association with the operating circuit of vertical magnet 234 of the connector switch of the link, via the resting contact and armature 283 of relay 284; and at its contacts 288, interrupts the dial.

tone circuit.

The operation of only the relay 2.11 determines that the link will select a line in the first hundred group and that the code signal transmitted out over the called line will comprise one of the iirst ten codes and will be transmitted over the ring conductor 382 of the link. If the first digit dialled is. three, the ground potential supplied over the wiper 3|8 and its third bank contact, following the deenergization of relay 218 at the conclusion of the impulse series, extends through the lower winding of relay 332 to battery. The relay 332, upon operating; at contacts 321 and 328 transposes the generator and ground connections of the link, and thereby determines that the called line is one of the ilrst hundred group and that it will be signalled by one or the first ten codes transmitted over the tip conductor 383 of the link. The relay 332 also, at contacts 328v completes a circuit for relay 211, from battery through the winding of this relay, conductor 2|8, contacts 328, conductor 2 I8, contacts 26| and over the previously traced circuit to ground, and at-its contacts 33| completes a locking circuit for itself including the contacts 356 and the grounded conductor 2|1.

If the first digit transmitted is four, the wiper 3|8 will be in engagement with its fourth bank contact and will complete a circuit through the windings of relay 326. The relay 326, upon operating, at contacts 328 completes the circuit of relay 211 as did relay 323, at contacts 33|' completes a locking circuit for itself, and at its lowermost armature prepares the link for signalling aline in the first hundred group with one of the second ten ccdes over the ring conductor 382. l

If the first digit transmitted is ve', the wiper 3 8 completes a circuit through the lower winding of wiper switching relay 368. 'I'he relay 368, at its armatures 312, 313 and 314 determines that the line called will be one of the second hundred, at its contacts 369 completes a locking circuit for itself, and at its contacts 3282 completes the circuit of relay 211. Since the relay 328 is not operated it isdetermined that the selected line in the, second -hundred group will be signalled over the ring conductor 382 by one of theilrst ten codes.-

If the first digit transmitted is six, ground on 4 the wiper 3| 8 completes the circuit through the upper windings of relays 368 and 332 in series. Obviously, relay 211 also operates. The relay 388 lagain determines that the called line will be one of the second hundred, while the relay 332 again determines that ringing will occur over the tip conductor 383 of the link. j

The relay 218, upon restoring, following the transmission of the first digit, in all instances,

completes the previously traced circuit through the release magnet 3|8, causing the switch CC to restore to normal.

If the first digit is greater than seven the link is prepared for a call to the toll voperater, as will be explained subsequently.

In the connection at present being described,

the first digit transmitted is two, accordingly, the

link is prepared as previously described to transmit signalling current of one of the first ten codes over the ring conductor 382 of the link.

Upon the transmission of the second digit, in-

springs ON2I, 22 and 23 operate on the ilrst movement of the wiper shaft; at 0N23 place a multiple ground on the guard conductor 48| from the armature |68 and its resting contact over conductors |2| and |22, to hold the link busy until the connector switch returns to normal; and at contacts 0N2| interrupt the initial circuit of relay 211. The vertical magnet 234 supplies ground potential, upon each operation, to the conductor 221 to supply operating ground to the relay 246 in the same manner as did the magnet 328 of the class and code switch CC.

At the termination of the transmission of the second digit of the called number the relays 263 and 218 restore as before. The relay 218 now', at `its armature 215 and its back contact, completes an operating circuit for the relay 284. This circuit extends from ground on conductor 2|1, through contacts 28|, oil normal spring ON2| and its working contact, armature 215 and its resting contact, and the winding of relay 284 to battery. The relay 284, upon operating, at contacts 281 opens a second point in the dial tone circuit, at its contacts 286 closes a point in the circuit of test relay 228, at its armature 285 transfers the pulsing circuit from .the vertical magnet 234 of the connector switch to the rotary magnet 233 thereof by way of the lower winding of relay 266, at its contacts 283 opens another point in the initial operating circuit of relay 211, at its inner lower make contacts completes a locking circuit for itself including contacts 28| and the grounded conductor 2|1, and at its armature 288 opens a second point in the previously traced circuit of release magnet 3|8 of the switch CC and at the front contact of this armature pre.

and the lower winding of relay 266. The rotary magnet 233 at its front contact' applies ground from contacts 243 through conductor 233 to the conductor 221 to control the circuit of relay 246 in the same manner that it was previously controlled by magnets 320 and 234. The relay 266, upon operating, at its contacts 261 completes a locking circuit for itself including its upper winding and the contacts 231 of relay 235, at its contacts 268 opens a point in the operating circuit of relay 296, and at contacts 268 interrupts the formerly traced operating circuit of relay 211. The relay-211, however, remains energized until after relay 210 deenergizes following the transmission of the third digit of the called number, by ground supplied to it from conductor ||6 through contacts 265, 266|, and 283.

Following the termination of they transmission of the third impulse series, the relay 263 at its contacts 265 interrupts the circuit of relay 211 and the latter relay accordingly restores. The relay 211, upon restoring, at its armature 218 interrupts the impulsing circuit to the rotary magnet 233 and at its back contact, reestablishes the impulsing circuit extending to the operating magnet 320 of the switch CC.

Ringing code selection Upon the transmission of the fourth or final digit of the called number relays 263 and 216 operate as before, while the ve impulses transmitted in the present example, cause the magnet 320 of switch CC to position its wipers ino engagement with their tth bank contacts to, by means of the position of wipers 3I6 and 3|1, determine the code to be transmitted to the called line.

Following'the transmission of the final impulse of the fourth series, the relay 216, upon restoring, atarmature 21| and its resting contact completes an operating circuit for relay 253 which includes its upper winding, the front contact and armature 289 and battery supplied over the previously traced release circuit including'the magnet 3| 9 of switch CC. Owing to the high resistance of relay 253 compared to that of the magnet 318 only v253 operates over this circuit. The relay 253,

Cir

upon operating, at contacts 256 closes a locking circuit for itself including its lower winding and the grounded conductor |01|. The relay 253 at its contacts 255 places a shunt about the upper or holding winding of relay 266, causing it to restore: at contacts 259 opens a point in the impulsing circuit to prevent further operation of the class and code switch when the circuit of relay 246 is again interrupted; at its contacts 256 removes the resistance R2| and battery from in shunt of relay 349, thus allowing this relay to operate over the calling line loop; and at its-contacts 268 prepares a locking circuit for relay 349. The relay 349, upon operating, at its inner upper contacts completes the prepared locking circuit for itself and which includes contacts 341 I, conductor 2 |6| and the contacts 266 of relay 253. The relay 349 also, at its upper armature opens a point in the operating circuit of relay 336 and closes a point in the operating circuit oi relay 341. The relay 353 in addition to producing the foregoing circuit changes,resulting in the operation oi relay 349, at its contacts 251 completes an operating circuit for the test relay 228 providing the called line is idle. -This circuit extends from battery through the winding of the cut-off relay 393 of the called line, the break contacts of the line relay 391 of the called line, conductors 389. test contact 366, wiper 365, the contact and armature 312, test conductor 2|8, contacts 219, the .armature 212 and its resting contact, contacts 251, armature 34 and its resting contact, contacts 286, and through the upper winding of the test relay 228 to ground. If the called line is busy while the impulses are being transmitted to the code switch the test wiper 265 will encounter ground potential and in so doing cause the busy relay 239 to operate, then at the end of the impulse series if the line has become idle the relay 226 will operate over a momentarily established circuit including contacts 266, back contact and armature 293 front contact and armature 34 and over the previously traced circuit to battery. Under these circumstances, the relay 226 at contacts 24 breaks the circuit of relay 230, permitting it to restore. The relay 253, upon operating, also at contacts 266 completes the circuit of slow to operate relay 290 via contacts 268 of relay 266. Relay 290 operates and at contacts 292 closes a point in the circuit of pick-up relay 258. The relay 290 also, at contacts 29| opens the locking circuit of relay 284, which now restores.

The relay 228, upon operating; at its contacts 2| completes a circuit for .the Eenerator start relay 626 by way of conductor 22|, contacts 351, conductor 3|5, and contacts 639; at its contacts 23 applies ground potential to conductor 2|9 and through ,the amature 312 and its resting contact, wiper 365 to the test contact 386 of the called line to maintain the same busy to other calling subscribers, and at its contacts 24 opens a point in the operating circuit of the busy relay 230.

The cut-oil relay 393 of the called line, upon operating, at its contacts 394 and 395 removes the associated line relay from in bridge of the line, at its inner upper break contacts removes battery and resistance R from in multiple with the relay 393, -at its contacts 396 extends ,the ground potential on conductor 369 via the break contacts of the line relay 391 into connection with the finder multiple test conductor 396, and at its armature 399 opens a point in the alarm circuit to be described later and completes an operating circuit through the lower winding of relay 34|'. 'I'he operation of this latter relay is Without effect at this time.

Rf'naina At the beginning oi' the rst ringing code cycle following the energization of relay 226 a ground impulse is transmitted ,to the pick-up conductor PU in a. manner which will subsequently be described. When this occurs a circuit for the pickup -relay 356 is completedthrough the break contacts and upper winding of this relay, contacts 348, conductor 2|5, back contact and armature 291, contacts 292, and through the front contact and armature 22 of relay 226 to battery. The relay 358 at its contacts 359 completes a locking circuit for itself including its lower winding, contacts 356 and the grounded conductor 2|1; at contacts 366 connects the lower winding of the ringing relay 343 to the wiper 3|6 of switch CC; and at contacts 36| connects the upper winding of relay 343 to the wiper 3| 1 of switch CC, via

:sol

contacts 36|' and bank contact and armature' quently described extend via ythe wipers 3|3 and 3i1 andoperate the ringing -relay343as required to produce the desired ringing code. The relay 343. when operated, at its armatures 344 and 345 closes the ringing circuit to the link conductors 302 and 303 to the called line; and at its contacts 343 closes the ringback tone circuit.

Since the relay 332 is at normal ground con-- nected generator current from the generator lead GEN. extends through the associated resistance, contacts 323, back contact and armature 328.` front contact and armature 345, and contacts 333 to the ring conductor 302 to the ringers and condensers on the ring conductor of the called line to ground in the case of a divided ringing line such as shown or back through the tip conductor 303, contacts 335, armature 344 and its front contact and armatures 321 and 322 and their back contacts to ground in the case of a bridged ringing line.

Had/the relay 332 been operated the ringing current on a divided ringing line would have been transmitted to the tip conductor 303 and through the ringers on that conductor of the called line to ground. e

In the present example ringing current is applied to conductor 302 through armature 314 and its resting contact, the wiper 33|, bank contact 382, conductor 331, through the switchhook-contacts oi' station 2645 and the associated ringer to ground. The relay 343 also at contact 343 connects the generator lead, by way of the front contact and armature 361, condensers C3| and C32, conductor 204, through contacts controlled by armature 340, to conductor |03 to transmit ring-back tone to the calling subscriber.

Immediately preceding the removal of each ground. pulse over the combination lead and wiper 3|3 and for a short interval thereafter, the drain lead DRI is grounded as will hereinafter be explained, to close a circuit through the lower winding of relay 333, which accordingly, operates. The rel'ay 343, upon restoring, at the end ofthe ringing pulse over the combination or mask conductor, connectsthe ring lead 302 via armature 335 and its working contact and through the associated resistance to battery, and the tip lead 303 via armature 334 and its working contact and the associated resistance to ground, to discharge the condensers in series with the ringers on the called line. When ground is removed from the drain lead DRI relay 333 restoresand transfers the conductors 303 and 302 to the relays 220 and 341, respectively, to prepare the link for cutting oil the ring.

When the called party hears his code signal and answers, either during a silent period or be t" tween codes a circuit is completed through the subscribers loop for energizing the ring cutoff relay 341 and back bridge relay 223 as follows: from ground on holding conductor |01, through th'e winding of ring cut-ofi' relay 341, the front contact and armature of relay 343, contacts 334, 344, 355, talking conductor 303, to and through the Acalled station apparatus and back over conductor 302, contacts 363. armature 345 and its back contact. armature 335 and its back contact, conductor 203. armature 33 and its back contact, and the winding of back bridge relay 223 to battery. .The relay 341, upon operating, at its contacts 348 completes a locking circuit for itself, at its contacts 353 interrupts the locking circuit of the pick-up relay 353 permitting it to restore, at contacts 343 opens a point in the pickf up circuit of the pick-up relay 358, to prevent it from reoperating when the pick-up lead PU deenergization of generator start relay 320, if no` other link is maintaining it operated at this time; at itsv contacts 350 opens a point in the locking circuit of relay 230, at its contacts 341| opens the locking circuit of relay 343 which, however, remains energized over the calling line loop; and at its contacts 353 and 354 connects the back bridge relays |33 and 223 in bridge of the talking co'ndfuctors 302 and 303 extending to the called line. The back-bridge relay 223 is connected by way oi' the resting contact and armature 33, conductor 203, and contacts 354 to the conductor 302, while the relay |86 is connected by way of conductor |04 and contacts 353 directly to the conductor 303.

`'I'he relay |83, upon operating, at its contacts |31 closes a point in the circuit of reversing relay 250 completed only when the call is extended from a paystation line, at contacts |83 disconnects the time pulse lead 101 lfrom the lower winding of relay |8|, and at contacts |33 removes ground from the time startvlead 103 to prevent the automatic disconnection of the link. The relay 223, upon operating, at its contacts closes points in circuits employed only during the establishment of reverting call connections, and which are described hereinafter.

Talking battery is supplied to the calling subscriber through the windings of relays 245 and 343, and to the called subscriber through the windings of relays |86 and 229. 1

After conversation and in response to the called party replacing his receiver, relays |83 and 223 restore. The restorationof -relay 223 is without effect atthis time. at its contacts |83 again vcloses the circuit of the solenoid 150 and of its associated relay 15|, so as to start the timing operation; and at contacts |83 connects the relay |3| to the time pulse lead 101 to insure the release of the link should the calling subscriber fail to replace his receiver.

When the calling subscriber replaces his receiver the circuit to line relays 245 and 343 is broken and these relays accordingly restore. The restoration of relay 343 is without eiect. The relay 245, however, upon restoring at its lower contacts interrupts the circuit of relay 246 and at its upper contacts interrupts one oi" the two multiple ground paths to slow release relay |34. The relay 243, upon restoring, at contacts 248 opens a point in its holding circuit, and at armavture 241 interrupts the circuit of relay |34 and transmits a pulse of current to the slow release relay 263 in the same manner as when a dialled impulse is being transmitted. The operation of relay 263 at this time, however, is without effect.

Upon the restoration of slow release relay |34, the circuit for the associated slow to release relay The relay |86, upon restoring'.

|30 is interrupted. This latter relay, upon restoring, at its contacts |32 interrupts the circuit of relay |35; and at its armature |3| removes ground potential from the conductor |06, and accordingly from conductors |33 and ||5.

'I'he relay |35, upon restoring, at contacts i3 opens the circuit of relay 233, which now restores, 'and at contacts |33 disconnects the lower winding of the time release relay |8|.from the time pulse lead 101.

The removal of ground potential from conductor |03 is also effective tobring about the de energization of the cut-off relay |35 of the calling line. The cut-oir relay accordingly restores and reestablishes the Acircuit of the calling line to a normal non-calling condition.

The removal o f ground potential from conductor ||5, and also from conductor ||8 resulting moves ground potential from guard conductor 40| so as to mark the link as being again available or use, and at contacts 240 removes ground potential from the lead ||1 extending via contacts |89 and time start conductor 109 to the time start solenoid 150 and its associated relay 152 so as to stop this equipment from functioning in view of the fact that release is taking place in the normal manner. The relay 235 also at its contacts 236 removes ground potential from the hold conductor |01 thereby interrupting the locking circuit of relays 253, 341, 368 and |14 which accordingly restore; and at its contacts 244 completes a circuit to the release magnet 23| of the connector magnet which may be traced as follows: from ground at the armature |69 and resting contact of relay |55, conductor |2|, contacts 244, cif-normal spring ON22 and its working contact, and the Winding of release magnet 23| to battery. The connector mechanism and its associated wipers accordingly restore to normal in the usual manner. When the off-normal contact spring ON22 encounters its normal contact a circuit is established to the releas'e magnet |30 of the finder mechanism of the link. This circuit extends from ground on conductor |2|, through the contacts 244, off-normal spring ON22 and its resting contact, conductor |20, off-normal spring ON|2 and its working contact, and the winding of the release magnet |30 to battery. The finder mechanism and its associated set of .wipers are accordingly restored to normal position in the well known manner.

Called line busy y Having explained the operations which occur when an idle line is called, a description will now be given of the operations which occur when the called line is busy. It will be recalled that during the receipt of the impulses of the third digit the relay 246 repeated impulses over a circuit including the relay 266 and that this relay operated and at its contacts 269 shifted the locking circuit of operated relay 211 from its control to the contacts 265 of relay 263, so that following the transmission of the third series of impulses the relay 263, upon restoring, interrupts the circuit of relay 211. Now, with the called line busy, upon transmission of the fourth series of impulses, the relay 210, upon operating, at its armature 212 and its working contact completes an operating circuit for the busy relay, from ground supplied over the test conductor 2|0, to contacts 219, the armature 212 and its working contact, contacts 24 of the test relay 228 and through the winding of relay 230 to battery. The relay 230, upon operating, at its contacts 39 applies busy tone by way of the working contact and armature 294 and over the previously traced circuit to the calling line, and at contacts 33 prepares a locking circuit for itself extending from the grounded hold conductor |01 through contacts 350, conductor 209, contacts 33, contacts controlled by armature 212, and contacts 24. The relay 230 also at its other contacts makes circuit changes employed in the course of setting up a reverting call connection which will be described hereinafter. An instant later relay 210 restores and at contacts controlled by armature 212 closes the locking circuit of relay 230 and opens the operating circuit thereof.

The calling subscriber, upon hearing the well known busy tone, replaces his receiver and in so doing opens the circuit oi the line relays 245 and 349. The restoration of relay 349 is without eifect at this time. The relay 245,however, upon restoring, is effective as before to interrupt the circuit of relay 246. This latter relay restores and at armature 241 interrupts the circuit of relay |94 which, accordingly, restores. The relay |94 opens the circuit of relay |90. Relay |90, upon restoring, at contacts |93 opens the circuit oi relay |15, which restores and frees the line from the link; at its contacts |92 opens the circuit of relay |95 and at its contacts |9| removes ground potential from the test conductor |08 and from the branch conductors |99/and H5, thereby interrupting the locking circuits oi' relays 235 and |35, which accordingly restore. The relay. 235, upon restoring, at contacts 238 removes ground from the hold conductor |01, thereby interrupting the locking circuits of relays 230. 888 and |14 which accordingly restore; and at contacts 244 initiates the operations previously described which bring about the restoration of the switch CC and of the finder and connector wipers of the link.

Pay station connections Subscribers lines equipped with paystations are grouped together and have their lines terminating in a particular level of the ilrst hundred group of finder bank contacts. When a inder elevates its wipers opposite such a level it closes its normal post springs NP, and in so doing prepares an operating circuit for the reversing relay 250. This circuit extends from ground on the normal post springs NP, through contacts |81 and |62, conductor and the winding of relay 250 to battery.

In such a connection, when the called subscriber answers, the back bridge relay |86 at its contacts |81 completes this circuit. The relay 250, accordingly, operates to reverse the normal battery and ground connections with respect to the calling line and to thereby operate the paystation mechanism of the calling station to collect the deposited coin in the usual manner.

Revertzng calls A description will now be given of the operations which take place when a subscriber calls another subscriber on his own line. For this purpose it will be assumed that the subscriber at station 595| desires to communicate with a subscriber at station 5958 and, accordingly, removes his receiver and proceeds to dial the digits of the called station. During the testing stage of the connection, since the called line is also the calling line, the busy relay 230 will be actuated the same as if any other busy line is being called.

When the calling subscriber hears the busy tone he will replace his receiver, thereby opening the circuit of the link line relays 245 and 3,49 peracca-isa mitting these relays to restore. The relay 245, upon restoring, at its lower contacts interrupts the circuit of relay 246 and this relay accordingly also restores. These two relays, upon restoring, at their upper armatures remove ground potential from'conductor ||4 extending to the slow re lease relay |94. The relay 246, also, at its armature 241 and its resting contacts again connects ground potential to they slow release relay 263. 'Ihe relay 263 accordingly operates and at its contacts 265 extends ground potential on conductor |I6 via front contacts and armatures 290| and 34, contacts 251, the back contact and armature 212 and contacts 219 to the test conductor 2| 0 nowconnected via the wiper 319 with the connector normal conductor tof the calling line. This ground potential extends through the armature |33A and its resting contact to the winding of cut-oil' relay |35 and via contacts |33 to the finder test terminal |60. The relay |94, upon restoring, interrupts the circuit of slow release relay |90. The relay |90, upon restoring,'at its contacts |92 opens the circuit of slow release relay |95; at contacts |93 opens the circuit of relayl15, which restores; and at its armature |9I and its resting contact now completes an operating circuit for relay 229. This circuit extends from vtheground Just traced to test contact |60, armature |9I and its resting contact, conductor |05, contacts 3.6 of busy relay 230, and the winding or relay 229 to battery.

Relay 229, upon operating, at conctacts 26 closes the circuit of generator start relay 620; at contacts 25 connects battery supplied through resistance R24, and through the armature 22 and resting contact of test relay 226 to conductor 2|5, to preparey the pick-up relay 356 for operation under control of the code interrupter in the same manner as when some other line is called; and at its contacts 21 completes a holding circuit for slow release relay |95 before this latter relay has had time to restore consequent to the opening of contacts |92. This holding circuit extends from battery through the winding of relay |95, conductor |09, contacts 21 and 35, conductor |08, to the grounded contacts of armature |63.

It will be observed that since the calling line is one of the second hundred group the wiper switching relay 366 will have been operated following the transmission of the first digit 5 of the called number. This circuit extends from battery through the lower windingof the relay 366, the fth bank contact and wiper 3|6 of switch CC, conductor 225, contacts 266 and 262, armature 214 and its resting contact, resting contact and off normal spring ON2I, and contacts 29| to the grounded conductor 2|1. The relay 368, upon operating, at its armatures 312, 313 and 314 connected the connector end of the link with the wipers 315, 311, and 319, having access to the second hundreds group of lines, at its contacts 369 completed a locking circuit for itself, at its contacts 3292 closed a point in a holding f circuit for relay 211 which is independent of contacts 29| of the slow to operate relay 290, and at its contacts 31| opened a point in an automatic trunk hunting circuit which will be described hereinafter.

In response vto the operation of the generator start relay 620, consequent to the operation of relay 229, the ringing equipment of Fig. 6 and the one long ring.

with bine code combination selected by the pntioning of the switch CC in response to the trans- .mission of the last digit of the called number.

Since in the present example 6 is the last digit ytransmitted the wiper 3 |3 is connected with mask conductor 3| and the wiper 3 I6 with combination conductor C6. Referring now to ,the ringing combination chart. it will be seen that the code transmitted will consist of four short rings followed by During the establishment of a reverting' call connection to the reverse signal relay 32| is periodically operated over a circuit which extends from battery through the winding of relay 32|, vconductor 2|4, contacts 3| of the busy r llay 230, conductor y2 I3, contacts 392, to reverse si al` REVBIG. which is periodically conductor grounded as will be subsequently explained! The relay 32 I, upon operating, at its contacts 322 and 323 reverses the generator connection and opens the generator return circuit for bridged ringing lines, to prevent. givingflthe reverting call'si'gnal on bridged ringing or ground return lines, at armature 324 and its front contact completes a circuit including the lower winding of drain relay 333, and at its front contact and armature 325 closes a circuit through the upper winding of the ringing relayl 343. The ringing relay 3,43, upon operating, at this time. owing to the energized condition oi relay 32|, transmits ringing current out over the line to actuate the ringers which are connected to the line conductor opposite the one to which the ringer of the called station is connected so that if the ringer of the calling station is not on the same side of the line as is the ringer of the called station the calling subscriber will be signalled by operation of ringing relay 343, while ,relay 32| is operated, to notifyhim that the called station is being signalled. The relay 32| is only actuated during silent periods of the code as will be subsequently explained.

From the foregoing it will be appreciated that a subscriber making alreverting call who also has his ringer connected to the same line conductor as the called station, will hear the code signal. However, should the ringer of the called station be connected to the other conductor, instead of hearing the code signal he will receive a succession of short rings as Along as the called party is being signalled.

The drain relay 333,v which, during the signalling operation of a called line, which is not also a calling line. is operated solely over the drain lead DRI is now also operated over the circuit including contacts of relay 32|. Also, Just before ground is removed from the reverse signal lead REV.SIG. ground is supplied'over the drain lead DR2 and through contacts 32 of the busy relay to the upper-winding of relay 333 to battery to hold relay 333 operated for a short interval after relay 343 restores. When ground is removed from the reverse signal lead REV.SIG., the circuit to relay 32| is opened.- Relay 32|, upon restoring, at its armature 325 transfers the lower winding of relay 333 from ground to the drain lead DRI, thus'interrupting the .'*rcuit of this relay; at armature 325 transfers the upper winding -of relay 343 from ground'to the selected mask conductor 3I| or 3|2, thus opening the circuit of relay 343; and at armatures 322 and 323 reverses the generator connection and prepares a generator return circuit for bridged ringing lines. lRelay 343,l upon restoring, as in" the= previous description of its operation, removes generator current from the called line, and connectsground

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