US2149646A - Automatic telephone system - Google Patents

Description

March 7, 1939. -J H. Voss AUTOMATIC TELEPHONESYSTEM 3 Sheets-Sheet 1 Filed Oct. l, 1936 March 7, 1939. J, H. Voss AUTOMATIC TELEPHONE SYSTEM Filed Oct. 1, 1956 3 Sheets-Sheet 2 IN VENTOR.

ATTORNEY.

March`7,` 1939. .1. H. voss AUTOMATIC TELEPHONE' SYSTEM 3 Sheets-Sheet 3 Filed oct. 1, 1956 T0 FINDER BANKS .wxm .220v OF v mov.

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Patented Mar. 7, 1939 UNITED s'rATE-s PATENT oF-FlcE 2.149.646 AUTOMATIC rnLErnoNE SYSTEM .lohn H. Voss, Downers Grove, lll., assignor to Associated Electric Laboratories, Inc., Chicago Ill., a corporation of Delaware VApplication October 1, 1936, Serial No. 103,490`

' `v21 Claims; (Cl. 179-18) I. The present invention relates in general to automatic telephone systems and more in particularv Vto small automatic telephone systems which are adapted for use i'n rural communities.

An automatic system of this type is generally known as a community automatic exchange or C. A. X. In systems of this kind it is the usual practice to provide for multi-station party lines having either bridged or grounded ringing circuits, or combinations of each, and the subscribers are signalled by means of code ringing equipment. -lt is also customary to provide trunking facilities for extending connections to distant switching centers which maybe eithermanual or automatic exchanges. The object of the invention may be stated to be the provision of a new and improved telephone system of this character.`

One of the features of the invention relates to .an improved link circuit comprising a nonnumerical line-finder switch for nding a calling line, and a Anumerical connector switch for extending a connection to a called line, or to an idle trunk line to a distant exchange. 'I'he link V`circuit is arranged to operate directly into a manual or automatic switching center without the use of a repeater.

A further feature .is in the arrangement used to p'rovide a holding circuit for the link when a call is extended to a distant manual exchange or a distant automaticexchange. The release of the link circuit is controlled by the operator, when a call is extended to a manual exchange, and by the called subscriber, when a cal-l is extended to a distant automatic exchange.

A still further feature of the invention relates to a new arrangement for assigning a diierent link circuit on successive calls by subscribers.

'I'he foregoing objects and features of this invention together with others not specifically mentioned at this time will be described hereinafter with reference to the accompanying drawings, which show by means of the usual circuit diagrams suiiicientof the' apparatus involved to enable the invention to be readily understood.

Referring to the drawings, Figspl, 2, and 3, when placed in alignment, show the equipment for extending a connection from a calling subscriber to a called subscriber. Fig. 4, on the same shows a full metallic common battery party line and the associated line circuit at the C. A. X. 'I'he ysubscribers station A represents one of a plurality of subscribers stations ,that can be concode ringing, half the ringers being connected from one side of the line to ground, and the'.

other half being connected from the other side of the line to ground.` It will be understood that various other types of lines may be connected to the C. A. X., such as individual lines and party lines with bridged ringers. Lines of this kind will be described later on in connection with the operation of the systems.

Connections between the various subscribers lines in the system and connections from a subscribers line to an outgoing trunk line are established by means of finder connector links. One of these links is shown in Figs. 1, 2, and 3 of the drawings. It comprises a finder switch, Fig. l, which is indicated by the designation Finder; a code-selecting switch and a connector switch,

Fig. 3, which are indicated by the designations Code switch and Connector, respectively. These switches are preferably rotary 25point switches and are similar to the switch disclosed in Patent 1,693,027, granted to John Erickson, November 27, 1928. These switches are of the step-by-step type in which the wipers move in a forward dlrection only, and in which the wipers are advanced when the stepping magnet retracts its armature rather than\when it attracts its armature. The link also comprises a number of relays which are shown in Figs. l, 2, and 3, and a repeating coil shown in Fig. 2.

The allotter circuit shown in Fig. 1, comprising a start relay and two link selecting relays, controls the starting and selection of the finderconnector link. The allotter is common to two link circuits in this particular system and is ar.- ranged to start both idle links to ind a calling subscribers line or to start the idle link if one of the links is busy. The allotter is also arranged to assign a diierent'link circuit lto nd a calling subscriber-s line circuit on successive calls.

As mentioned hereinbefore, Fig. 4s shows a A trunk line to a distant exchange terminating in a regular subscribersline circuit which comprises the usual line, cut-off, and lock-out relays, together with a start relay and a battery-reversing relay. When a call is extended over the trunk line fro-m the C. A. X. to the distant automatic exchange, the battery reversing relay is held operated, thereby holding the link circuit in the C. A. X. in an operatedl position. The release of the connection is under control of the called subscriber at the distant automatic exchange.

The operation of the system will now be described, it being assumed for this purpose'that the subscriber at station A desires to call a subscriber at station B. When the subscriber at station A removes his receiver a circuit is comductor 28, station equipment A, line conductor 29, lower winding'of line relay I, armature 20 of cut-oi relay 2 to ground. Line relay I operates, and at armature 23 it connects ground `to' the private normal conductor 3l, thereby rendering the calling line busy in the banks of the connector switches. At contact 22, line relay I connects the cut-off relay 2 to conductor 32 in the nder bank. This operation marks the line as calling to the banks of the iinder switches, the other terminal of cut-oi relay 2 being connected to battery. In addition, line relay I places ground on the allotter start conductor 30 at armature 24. f

The ground potential applied to conductor 30 causes the allotter start relayl to energize. At armature 33, allotter start relay 4 places battery on link #l start conductor 40. and at armature 35`p1aces battery on link #2 start conductor 4I. Start relay 4 also connects battery by way of armature 34, and the normally closed contacts of armature 31 on relay 5, to the upper winding of relays 5 and 6, to ground. In addition, battery is also connected by way of armature 39 through the lower portion of relay 6 to ground. Link #2 selecting relay 6 does not operate because its windings are in opposition to each other. However, #l link selecting relay 5 operates by way of the above described circuit and locks itself up to battery by way of armature 31. At armature 36, link-selecting relay 5 opens part of the stopping circuit of cthe iinder in link #2.

The four conductors AI B I, A and B, extending to link #2, are designated A, B, AI, and BI, re-

spectively, extending to link #1, as is shown to the right of the allotter. The conductors designated `A, B, AI and BI of link #2 are reversed as they extend to link #l so that conductors A and B of link #2 connect 'to conductors AI and BI, respectively, of link #1; also, conductorsAI and BI of link #2 connect to conductors A and B, re

spectively, of link #1. The reason for this reversal in conductors between links #1 and #2 will be understood from the detail description ofthe operation.

The placing of battery on the link-start conductor 40, due to the operation of start relay 4 in the allotter, completes a circuit for start relay I in link #1, from battery on conductor 40, winding of start relay I0, armature 42, amature 43, conductor 44, bank contact 303 of the connector portion of the link I, wiper 304, to ground. Relay I0 operates, and at armature 46 opens the stopping circuit to the finder in link 2. At armature 41, start relay I0 completes a circuit for the roltary stepping magnet 1. This circuit is completed from battery at the rotary stepping magnet 1, armature 58, armature 41, armature 42, over two paths to the grounded conductor 44, one of which is through armature 48 on start relay I0 and the other of which is on armature 43 oi supervisory timer relay I5. In addition, at armature 45 start relay I 0 also prepares a stopping circuit for the finder switch. This circuit includes the lower winding of switching relay 9, conductor B, armature 38 of the relay 6 of the allotter, conductor A, lower winding of stepping relay 8, and wiper 60 of the finder switch. At armature 44, relay I0 prepares a circuit which will be described later, and at armature 43 completes a circuit for line relay I9, which includes resistance 50 and the upper windingof line relay I9. Line relay I9 operates, and at armature 6I completes a circuit for lock-pulse relay I2 which may be traced from battery through the winding of lock-pulse relay I2, armature. 6I, amature 51 on relay I1, to the normally closed contacts controlled by armature 6I,

to ground. In response to the closing of this circuit th'e lock-pulse relay I2 operates and at ar- .mature 52 completes a circuit for the operation i iary release relay I1 is operated over the following circuit: ground at the normally closed contacts controlled ,by armature 6I, contacts at armature 54, conductor 12, armature 2I2, armature 213, conductor 1I, winding of auxiliary release relay I1, to battery. Another path for the circuit for relay I1 may also be traced by way of contact 63 of reverting call relay II. Auxiliary release relay I1 operates, and at armature 56 grounds the interrupter start lead by way of armature I 0I, conductor 69, armature 2I5, and at armature I00places a ground potential on conductor 9|. At armature 55 it connects the supervisory timer relay I to the time-pulse conductor TP.

The timing equipment momentarily grounds conductor TP at the beginning of eachy timing cycle and completes a circuit for supervisory timer relay I5 over the following path: conductor TP, normally closed contacts controlled by armature 64, armature 55, armature 65, conductor 66, armature 2| 4, conductor 69, winding of supervisory timer relay I5, to battery. Relay I5 operates and completes a locking circuit for itself at armature 64 and its front contact; replaces `the ground at the normally closed contacts controlled by armature 6I to the CO conductor from the timer, which is grounded during the timing cycle, at armature 6I and its front contact; and at armature 43 opens the circuit of start relay I0, to prevent the linkfrom being seized during the ringing period on reverting calls. The ground potential is maintained on the cut-off conductor CO for atleast two minutes. After this period of time has elapsed and the calling subscriber has 4not dialled, or if the called subscriber has not answered, or if there is av permanent on the line which would cause the operation of the equipment, the ground is removed from conductor CO. When this occurs all relays locked to the C0 conductor will release thereby causing the entire link to restore to normal.

The operation that has taken place has been due to the grounding of the start conductor 40, and it should be understood that the same operations have taken place in link #2. By referring back to the operation of the rotary magnet 1, a description will be given of the stepping action of the flnder switch portion of the link #l in its search for the callingline.

f In response to the operation of the rotary magnet 1, contacts |04 are closed and stepping relay 8 is energized. The energization of the rotary magnet I also prepares for the advancement of wipers 60, |02, and I 03, to the next bank contacts of the nder switch. 'I'his action takes place because of the operation of stepping relay 8, which at armature 58 opens the operating circuit of rotary magnet 1, thereby causing the advancement ofthe wipers to the next set of bank contacts.A `At armature I04, rotary magnet `1 also opens the circuit for the stepping relay 8, which falls back and at armature 58 again completes bank contacts.

the energizing circuit for rotary magnet 1. The interaction between stepping relay 8 and rotary magnet 1 continues, thereby advancing the wipers 60, |02, and |03, over the bank contacts oi' the nder switch.

When the wipers encounter the bank contacts of the'calling line, a circuit is completed from battery at thev winding of cut-oi! relay 2, armature 26, amature 22 of the operated line relay I, conductor 32 and its associated bank contact, wiper 60, lower winding of stepping relay 8, conductor A, armature 38, conductor B, lower winding of switching relay 9, armature 45, yto ground. Cut-oil relay 2 in the line circuit, stepping relay 8, and switching relay 9, all operate in series. The operation of stepping relay 8 prevents further advancement of the wipers because vthe circuit for the rotary magnet is held open at Aarmature 58. Switching relay 9 locks up from battery by way of its upper winding, amature |05, armature |08, armature and lower contact 54, armature 6|, to ground on the cuto conductor CO. At armature |01, switching relay 9 places a ground potential on conductor 30 of the allotter to maintain start relay 4 in an energized position. This circuit is' completed to maintain start relay 4 of' the allotter in an operated position until start relay |0 in the link falls back, dueto the opening of armature 42 by the operation of switching relay 9. It should be noted that the ground potential which is used in the locking circuit for switching relay 9 also extends by way of armature |08 and wiper 60 of the nder switch to the cut-ofi' relay 2 in the line circuit. When switching relay 9 operates and closes amature and contact |08 to insure 'the operation of cut-olf relay 2, stepping relay 8 releases slowly because of the ground potential connected to both sides of the lower winding over the following circuit: ground on cutoi conductor CO, armature 8|, armature 54 and its front contact, armature |08, lower winding of stepping relay 8, conductor A, armature 38, conductor B, lower winding of relay 9, armature 45 to ground. 'Ihis slow action in releasing of stepping relay 8 prevents contacts 58 from closing before start relay I0 has had time to fall back. Switching relay 9 also' connects the subscribers line conductors 28 and 29 through to the line relay I9 in the link circuit, by way of its armatures |09 and 0.

Referring back to the operation of cut-off re-` lay 2 of the line circuit, it will be noted that at armatures and 2| line relay 2| is disconnected from the subscribers line conductors 28 and 29. However, battery and ground potential is now supplied to the calling subscriber by way of the winding of line relay |9 of the link #1. At armature 21, relay 2 completes a locking circuit for itself by way of the grounded conductor 32, and when line relay l falls back, this ground potential is extended by way of armature 23 of line relay to the private' normal conductor 3|, to maintain a busy condition on the connector In addition, cut-off relay 2 at armature 20, completes an energizing circuit for lockout relay 3. Lockout relay 3 on energizing, opens the initial operating circuit for cut-oil relay 2 at armature 26, and at armature 25 opens a point in the start circuit over conductor 30 to the allotter.

Referring back to the start relay I0 in the link whose circuit was opened by the operation of the switching relay 9. Relay 0 falls back andA at armature 44 removes ground potential from the start conductor 30, which allows'relay 4 in the alloter to deenergize. I'n addition, start relay |0, upon falling back," opens the circuit at armature 45 through the lower winding of switching relay 9 which is of no avail because relay 9'is locked in an energized position by way of its upper winding. It prepares a stopping circuit forl the flinder in link'#2 at armature 46; it prevents the operation of the rotary magnet `I after stepping relay 8 is released at armature 41; and at armature 49 prepares a circuit for the pick-up pulse from the code interrupter. 'Ihe removal of'ground from the upper winding of line relay I9, due to the deenergization of start relay |0. does not affect relay I9 at this time, because it is held in an operated position over a circuit including both of the windings and the calling subscribers station.

A description will now be given of what happens in the allotter circuit in response to the restoration of start relay 4. At armatures 33 and 35 start relay 4 removes the battery potential from the start conductors 4|! and 4| of links #1 and #2, respectively. Since link #1 has already been positioned and is connected to a calling line, the removal of battery from link start conductor is of no consequence. link start conductor 4| causes link #2 to cease operating. The relays in link #2 are restored to their normal position. However, it might be well to point out that the wipers controlled by the rotary magnet in link #2 remain engaged with the bank contacts of the finder to which they were positioned in response to the last deenergization of the rotary magnet. In other words, the wipers of the nder switch do not Ahave a normal or home position, and therefore, retxnain in engagement with the set of bank conac s. Y

Referring again to the release of start relay 4 of theallotter, it will be noted that at armature 34 battery is removed from the lower winding of link #2 selecting relay 8. Relay 6 now operates by way of a circuit including its upper winding and armature 31 since there is no current owing in the opposing lower winding. At armature 38, relay 6 opens the stopping circuit for link #l by disconnecting the A and B conductors, and at armature 39 prepares a circuit for the lower winding of link #l selecting relay 5.

If another subscriber in the C. A. X makes a call, a line relay similar to line relay of the line circuit shown in Fig. 1 operates and grounds the allotter start conductor 30, causing the operation of start relay 4. Start relay 4 again connects battery to conductors 40 and 4| to start both ilnderS, and at armature 34 closes a circuit to the lower winding of link #l selecting relayl 5. This causes relay 5 to release. With relay 5 in its normal position, and relay 6 operated, the start relay in link #2, which is the same as the start relay |0 in link #1, willopen-the stopping circuit for link #1. The stopping circuit for the finder in link #2 is now closed at' armature 35 of the allotter due to the restoration of relay 5, so that the calling line will be connected through link #2 when it is found. When the second calling line has been found by the nder in link #2, start relay 4 of the allotter will restore to norf mal. When relay 4 releases, battery is removed from the upper winding of link #2 selecting reV lay 6, thereby causing `relay B to restore to its normal position. With link selecting relays 5 However, the removal of battery from j ferent link will be assigned to the calling lines ron successive calls.

When the link #l was rst seized and relay I0 operated, among other operations already explained, release relay I6 and auxiliary releaseV relay I1 wereoperated. At armatures |00 and |I| a ground potential was applied to conductor 9|, by the operation of relays I6 and I1, and at armature 56 ground was extended by way of armature IOI, conductor 69, armature 2I5, to the interruptor start conductor to start the code interrupter machine. The ground potential applied to conductor 86 at armature III2 has no eiect at this time. However, the ground potential applied to conductor 9| by the closing of armatures I0|I and I II completes a circuit over one path including the wiper 309 of the code switch and its associated bank contact and the lower winding of unit series relay 2| 0 by way of conductor 2I6. The circuit over the other path includes the wiper 305 of the connector switch and its normal or home bank contact, conductor 2I1, and the upper winding of the` tens series relay 208 to battery. 'I'he operation of the tens series relay 208 connects the dial tone to the calling subscribers line over the following path: dial tone conductor DT, armature 2 I8, condenser, armature 221, armature 231, upper right-hand winding of the repeating coil, armature 238, normally closed contacts controlled by armature 24|, lower winding of back-bridge relay 205 to ground. The dial tone is induced in the upper left-hand winding ofthe repeating coil over the upper'line conductor to the calling subscriber. At armature 22|, the tens series relay 20B prepares a locking circuit for itself and at armature 220 prepares a circuit for operating the rotary magnet 30| of the connector portion of link #1. The opening of Icontacts 2I9 by the relay 208 opens apoint in the restoring circuit for the rotary magnet 30| which will be explained more in detail later. f

In response to the operation of unit series relay 2|0, auxiliary relay 2II is operated from ground at armature 224; a holding or locking circuit is prepared at armature 222 for the upper winding of relay 2I0; and at armature 223 a circuit is prepared for the ring cut-off relay 206 which is eiective only when the wipers of the connector switch are controlled by a calling subscriber who desires to make a call over the trunk.

Upon operating, auxiliary relay 2II disconnects the busy tone conductor BC from thelink circuit at armature 258; prepares an operating circuit for the rotary magnet 302 of the code switch at armature 259; connects the busy 'relay 209 through tothe wiper 306 of the connector, thereby preparing the line busy test at armature 260; at armature 26| opens a point in the circuit for restoring the wipers of the code switch to their normal or home position; `and at armature 262 opens a point in the circuit for the #l pulse timer relay I4.

The link circuit now is in a position to receive the impulses transmitted in response to the operation of the calling device or dial by the calling subscriber. It will be assumed that the subscriber at station A desires to talk to the subscriber at station B whose number is 45. It may be well to mention at this time, that the subscribers line number consists of two digits. 'I'he rst digit controls the connector switnh in the link circuit to select the-line,l and -the second digit controls the code switch in the link to select the ringing code to be transmitted over the line.

Whenthe subscriber at station A operates his calling device for the iirst digit 4, the circuit for line relay I9 in the link is interrupted momentarily four times by the impulse springs of the calling device ,in the usual and well known manner. The operating circuit for line relay I9 is from ground,lower winding of relay I9, normally closed contacts controlled by armature |I3, con-- ductor 11, lower left-hand winding oi the repeating coil, conductor |32, armature |I0, wiper |02 of the iinder switch, conductor 29, substation A, conductor 28, wiper |03 of the finder switch, armature |09, conductor 16, upper left-hand winding of the repeating coil, conductor 19, 4normally closed contacts controlled by armature III, upper winding of line relay I9, to battery. The line relay I9 is maintained in an operated position over this loop circuit, and each time this circuit is momentarily interrupted by the impulse springs of the calling device at station A,'1ine relay I9 falls back and momentarily completes a circuit at the back contact of armature 5I and by this same action momentarily opens the circuit to the lock-pulse relay I2. Each time relay I2 falls back, a circuit is completed through the back contact of armature |I6 for operating the' rotary magnet 30| of the connector switch and a holding circuit by way of the lower winding of the tens .series relay 208. This circuit is'from ground on cut-oi conductor CO, armature 6I of the timer relay I5, front contacts of armature 51, back contacts of armature IIS, conductor 19, over one path including the front contacts of armature 22| and the lower winding of tens series relay-208 to battery; and over the other path including armature 220, conductor 2132i, winding of rotary magnet 30|, to battery. Seies relay 208 is maintained in operated position over this circuit. The rotary magnet 30| upon operating, completes a circuit from ground, armature 3|3, conductor 8|, armature 5I and its resting contact. resistance |I5, armature III, resistance 50, upper winding of line relay I9 to battery. Line relay I9 is only partially energized over this circuit due to the resistances 50 and ,I I5 and does not energize sufiiciently to operate its armature |5I. The reason for this partial energizing circuit of relay I9 is provided so that the line relays will operate faster when its circuit, including the upper and lower windings, is closed again by the impulse springs of the calling subscribers dial. When the .impulse springs of the dial are closed again, line relay I9 operates and at armature 5I again completes the circuit from ground at the cut-o conductor CO to the lock-pulse relay I2. Lock-pulse relay I2 upon energizing completes a locking circuit for itself at armature 53 by way of the resistance 62 and armature 5I of the line relay,vand at armature H6 and its -back 4contact opens the circuit for the tens series relay 208 and the rotary magnet 30| of the connector. When the rotary magnet 30| falls back, wipers 30B to 308, inclusive, are advanced one step. In response to the dialing of digit 4, line relay I9 and lock-pulse relay I2 fall back four times thereby controlling the rotary magnet 30| so that its wipers 304 to 308, inclusive, are advanced into engagement with the fourth set of bank contacts of the connector switch.

It should be noted that each time a circuit is completed for the rotary magnet the circuit is also completed to the lower winding oi' the tens series the circuit is opened for the rotary magnet 80|,

due to the fact that' the ,copper sleeve around its `core makes itslow to release. Auxiliary relay |6,

"which is maintained in 'an energized position from ground at armature 52 of the lock-pulse relay, is also a slow-to-release relay due to the sleeve around its core and does not fall back during the momentary interruption of the lock-pulse relay |2.

When wipers 304-308, inclusive, of the connector switch are advanced into engagement with the calling line in response to the first digit dialled, a battery potential would be encountered on conductor 3M if the line is idle, and a ground potential would be applied thereon if the called line is busy. The ground or battery potential, as the case may be, is applied fromthe linecircuit of the called subscribers line. 1f the line is busy the ground potential on conductor 3M compltes a circuit for the busy test relay 209 by way f wiper 306 of the connector switch, conductor 248, armature 260 and its front contact, windingvof busy test relay 209 to battery. The busy test relay operates at this time but the busy tone applied to conductor BT by the tone relays is not connected to the calling subscriber's` line until the release of auxiliary relay 2|| after the code switch has been set by the .dialling of the second digit. If the called line is idle, battery potential on 3| 4 does not have any eiect on the busy test relay, therefore it does not operate. However. the busy test relay is connected to the called line by way of armature 260 of the'auxiliary relay 2|| during the dialling period required to set the code switch. c

After the first series of impulses has been completed, the slow-to-release tens series relay 208 falls back, and at armature 22| and its resting contact prepares the circuit for the rotary magnet 302 of the code switchand the slow-to-release unit series relay 2|0. In addition, dial tone is disconnected from the calling subscribers line at armature 2|8; the circuit for restoring the wipers of the connector switch to normal is prepared at armature 2 I9; and at armature 220 the impulsin circuit for the rotary magnet 30| is opened.

The subscriber at station A now dials the second digit of the wanted subscribers number, which is in this case, the digit 5. Each time the line relay I8 falls back in` response to the interruption in its circuit bythe impulse springs of the dial, lock-pulse relay |2 falls back as has been described before. At armature ||6 the circuit for rotary magnet 302 of the code switch and the 4circuit for the unit series relay 2|0'is completed as follows: from the grounded cut-off conductor CO, armature 6| and its -front contact, armature 51 and its front contact, armature ||6 and its back contact, conductor 19, armature 22| and its resting contact, over one path including armature 222 and the upper winding of series relay 2&0 to battery; and over another path including armature 259, conductor 252, winding of rotary magnet 302 of the code switch to battery. Atv armature 3|5, rotary magnet 302 .grounds conductor 8| in the same manner as described in connection with the operation of rotary magnet 30| of the connector switch. Ground on conductor 8| operates lock-pulse relay |2 as soon as the line relay I9 operates at the termination of the first pulse. Lock-pulse relay |2 opens. the circuit for the rotary magnet 302 of the code switch, causing it to release, thereby advancing its wipers 309-3I2, inclusive, into engagement with theilrst set of bank contacts.

The operating circuit for units leries relay 2|0 over its lower-winding, is opened as soon as wiper 308 is advanced from the normal orfhome position of vthe codex bank. However, relay 2|0 is slow to release and ismaintained in an ener--4 gized position due to the momentary circuit completed over its upper winding each time lock- 'pulse Lelay |2'falls back. Thecircuitfor the line relay I9 and lock-pulse relay I2 is momentarily opened in response to the dialling of. 'digit 5 by the calling subscriber. Consequently, rotary magnet 302 of the code switch advances wipers 309-8 l2, inclusive, into engagement with the fth set of bank contacts of the code switch.

It will be assumed that the subscriber at station B whose number is 45 is busy. Therefore, the ground potential on conductor 3|4 has caused the operation of the busy 'test relay 209 as vhas been described. On completion of the dialling of the last dig/it, unit series relay2|0 releases, and at armature 224 opens the circuit for auxiliary relay 2||. When auxiliary relayf2|| falls' back the circuit `for the busy `test relay 209 is trans-A ferred from the front contact of armature 260, to the resting contact controlled by the front contact of armature 260. When this transfer in the circuit for the busy testfrelay is made relay 'thereby causing the release of the entire connection.

It will be assumed now that the called line was found idle. Under this condition, conductor 3M of the called line will now be grounded when the wiper 306 engages the bank contact, and the busy test relay 209 will not operate.v In view of the fact that the busy relay 209 is not oper` ated and auxiliary relay 2|| has fallen'back, a circuit iscompleted from the grounded cut-olf .conductor CO, armature 6| and its front contact, armature 51 and its front contact, conductor 82, armature 258 and its resting contact, armature 260 and its resting contact, conductor 248, wiper 306 of the connector switch and its associated fourth bank contact, conductor 3M, to the cut-off relay in the called line circuit to battery. The grounding of conductor 3|4 causes the wipers of the code switch to their normal or homeposition. The release of the unit series relay 2|'0 completes an energizing circuit'for the pick-up and switching relay 201 at armature 225.- The circuit for the pick-up' and switch- 'ing relay 201 may be traced over the following path: battery, upper winding of relay 201, armature 225, armature 259, conductor 93, armature 1 |20, armature 49, pick-up conductbr PU, tothe interrupter machine, or code interrupter relays, as the case may be, the codeinterrupter momentarily grounds the pick-up lead PU thereby operating the pick-up and switching relays201. Relay 201 operates and locks itself in an energized position to the grounded conductor 9| `by way of its lower winding and armature-23|. At armatures 226, 228, 228, andk 230, pick-up and switching relays 201 prepare the ringing circuit to the called subscribers line. The code inter# rupter now transmits ringing code over conductors I to 5, inclusive. It will be assumed that code 6, connected to conductor 3I6, is the ringing code of the subscriber at station B. The ringing circuit is as follows: code interrupter machine, conductor 8I6, wiper 8H of the code switch, conductor 258, armature 228, amature 284, armature 228, conductor 244, wiper 301 and its' associated fourth bank contact, conductor 3I1 of the called subscribers line, through the ringers of all subscribers stations whose ringers are connected through conductor 3I1 to ground. The code ring transmitted over this circuit rings all the bells connected to conductor 3I1, but the ringing code transmitted indicates to the subscriber at station B that he is wanted. It should be noted that a portion of the ringing current passes through condenser 260, through the repeating coil, over the called subscribers line, and gives the calling subscriber an audible ringing tone as an indication that the bell at the called station is being rung.

When the subscriber at station B answers` the call, the grounded code ringing current which was extended over the circuit just traced, is connected to conductor 3I8 of the called subscribers line in response to the removal of the receiver at station B. This circuit is extended, due to the removal of the receiver by the subscriber at station B, over conductor 8I8, bank contact and wiper 308 of the connector, conductor 243, armature 226, armature 233, armature 230, conductor 254, wiper 3I2, and the associated fth bank contact of the code switch, 4conductor 255, lower winding of ring cutoff relay 206 to battery. Armature 260 of the ring cut-oi relay 206, is adjusted to make its X contact rst, thereby completing a circuit from grounded conductor 9|,- armature 260, upper and lower windings of relay 206 to battery. The grounded ringing code circuit over which ring cut-off relay 206 was initially operated over its lower winding has suflicien-t resistance in its circuit to prevent its shorting out oi' the upper winding of relay 206. Relay 206 locks up over the circuit just described, and disconnects the ringing current from the called subscribers line at the back contacts of armatures 233 and 234, and at their front contacts connects the called subscribers line through the repeating coil and backbridge relay 205. The opening of armatures 2I2 and 235 by relay 206 does not affect the circuit operation at this time.

The back-bridge relay 205, which was connected to the called line when the ring-cut-oi relay operated, is energized over the following circuit: battery, upper winding of back-bridge relay 205, the normally closed contacts controlled by arma- Iture 242, armature 26|, lower right-hand winding of the repeating coil, armature 234, and its front contact, armature 228, conductor 244, Wiper 301 and the associated fourth bank contacts of the connector, conductor 3I1 of the called subscribers line,station B, conductor 3I8 of the called subscribers line, wiper 308 and associated fourth bank contact of the connector switch,` conductor 234, armature 226, armature 288 and its front contact, armature 231, upper right-hand winding of the repeating coil, arm'ature 288, normally closed contacts controlled by armature 24|, lower winding of back-bridge relay 205 to ground. In

response 4to the operation of back-bridge relay 205, supervisory relay I8 is operated from ground at armature 262.

Supervisory relay I8 performs several operations. At armature 65 it disconnects the supervisory timer relay I5 which restores to normal, thereby disconnecting the link fromthe timer equipment. The ground normally suppliedv from the cut-off conductor CO of the timer equipment is now supplied from the Vnormally closed contacts controlled by armature 6I. At armature IOI, supervisory relay I8 opens the start circuit to the code interrupter, and at armatures I I3 and II4 causes the reversal of current in the calling subscribers line. The operation of other armatures controlled by supervisory relay I8 is of no importance at the present time. The reversal of current on the calling subscribers line may be used for either metering or for supervision when either of lthese services are required.

The required connection has now been completed. The calling `line is supplied with talking current through the windings of line relay I8 and the left-hand windings of the repeating coil. The called line is supplied with talking current from the back-bridge relay 205 and the righthand windings of the repeating coil. The talking circuit has been drawn in by means of heavy lines and will therefore be readily traced.

The release of local call connections, similar to the call described, is under control of the calling party. However, it will be assumed in this case that the called subscriber hangs up his receiver rst. When the subscriber at station B replaces his receiver on the switchhook the circuit for the back-bridge relay 205 is opened. Back-bridge relay 205 accordingly falls back and opens the circuit ior supervisory relay I8 which also restores to normal. At armatures II3 and II4, relay I8 again causes the reversal of battery to the calling line for supervision. It grounds the interrupter start lead at armature IOI, and at armature 65 prepares the circuit for the supervisory timer relay I5. As has been explained before, the supervisory timer relay I5 operates at the beginning of a time cycle from the timer when the time pulse lead 'IP is momentarily grounded. When this occurs, time-pulse relay I5 operates and locks itself up at armature 64. The release of the connection is now under control of the timer which will remove the ground from the cut-oil? conductor CO after a predetermined time interval has elapsed.

For the purpose of describing the release of the connection under control of the timing equipment, it will be assumed that the calling subscriber has failed to hang .up his receiver after the called subscriber has released the connection. It may be well to mention at this time that the timing equipment would also control the release of the link circuit if a calling subscriber should fail to dial after having removed his receiver to make a call; or if there is a permanent or a short on the line; or if a called subscriber fails to answer a call within a predetermined time interval..`

When the timing equipment has operated through a complete-cycle, ground is removed from the cut-01T conductor C0. Accordingly, cut-oir relay 2 of theline circuit which waslocked up over a circuit including the grounded CO conductor falls back. Relay 2, upon restoring, agairrconnects the line relay I to the linen Line relay I operates over the previously traced circuit including the Y calling subscribers equipment at station A, and

at amature 24 completes a locking circuit for the lockout relayf3. Lock-out relay k3 is a slow-torelease relay and falls back slowly when its initial energizing circuit is opened bythe release of cutoil' relay 2. vThe line relay I also grounds the conductor 3| v to make the line busy at the test contacts of the connector bank. The line circuit of the calling subscribers line is now locked out from the link. Consequently, the subscribers on the same line with station A cannot make calls nor can they receive'calls. The line' circuit will remain locked out until such time as the subscriber at station A replaces his receiver or, if the line is shorted, the short is removed. When this occurs, the line relay I restores to normal, thereby removing the ground from conductor 3| and also opening the locking circuit for lockout relay Referring again to the removal of ground from the cut-01T conductorv CO by the timer, it will be noted that the previously described holding circuit for the upper winding of the switching relay 9 is also opened. Switching relay 9 falls back, and at armatures |09 and IIO opens the energizing circuit of line relay I9, and at armature opens points in the circuit from the pick-up conductor PU. In addition, at armatures I2I and |22 and their respective bank contacts, switching relay 9 also prepares a self-interrupting circuit for the rotary magnets of the connector and code switch of the link. Line relay |9, upon falling back, opens the circuit for the lock-pulse relay .I2 which also falls back, thereby opening the III, release relays|6 and I1 remove ground from conductor 9| thereby causing the release of ring- .cut-oif relay 206 and pick-up and switching relay'20'I. When pick-up and switching relay 201 restores to normal it completes the self-interrupting circuit for controlling the rotary magnet of the connector and rotary magnet `302 of the code vswitch to advance their respective wipers to the normal or "home position of the respective bank contacts.

Referring now to the bank contacts of the connector and also to the bank contacts of the code switch, it will be noted that wipers 304-308, inclusive, of the connector andwipers 3093|2, inclusive, of the code switch are shown in engagement with the normal or home bank contacts of the switch.l If the wipersiof the connector switch were advanced twelve steps they would again engage another normalor home bank on the same switch.v Therefore, the second ap" contact. The same is true of the code switch,

, however the code switch onlyneed advance its pearance of the bank contacts of the connector switch'has Vnot been shown since it is a direct multiple of wha/t is shown in theA first appearance.

The multipling of the bank contacts of the code switch between the first and second group is the same asL described in connection with the connector bank contacts.

Since the wipers 304-308, inclusive, of the connector are in engagement with the bank contact to which line is connected, and since wipers 309-3I2, inclusive, ofthe code switch are inengagement with the set of bank contacts to which conductor 3I6 is connected, the following circuit for restoring the wipers of the code switch to normal may be traced.y Grounded wiper 304 of the connector switch, conductor 96 which is multipled to the contacts engaged by wiper`304,

alteration in the multipling of the bank contacts of which wiper 3|0 of the code switch has access, the rotary magnet 302 continues to operate and break its own circuit at armature 3I9 until wiper 3|0 engages the same contact to which conductor 25| is connected. The circuit of the rotary magnet 302 is now transferred from conductor 249 to conductor 25|. The wipers 309-3I2, inclusive, of

the code switch have now been advanced to their normal or home bank contacts, and are in a position to be controlled by a calling subscriber to again select a desired code ring.

The previously traced circuit from the grounded wiper 304 of the connector, to wiper 3I0 of the code switch is now extended by way of conductor 25|, armature 2|9, conductor 245, armature 320v of the rotary rmagnet 30|, winding of rotary magnet 30|,to battery. Rotary magnet 30| operates over this circuit and at armaturev320 opens the energizing circuit for itself. Upon releasing, rotary magnet 30| advances its wipers 304-308, inclusive, to the next set of bank contacts. The set of wipers continue to advance over the bank contact of the connector, under control of the self-interrupting circuit of the rotary magnet 30|, until the wiper 304 leaves the bank contacts which are multipled to conductor 96 and engages the bank contact connected to conductor 95. The transferring of the circuit from conductor 96 to conductor 95 does not affect the self-interrupting circuit for the rotary magnet 30|, because the circuit is now maintained over the back contacts of armatures I2I and |22 of the switching relay 9. Therefore, the rotary magnet 302 `continues to advance its wipers 304- 308, inclusive, until wiper 304 engages the normal or home. bank contact. When wipersV 308-308 engage the home bank contact the circuit for the rotary magnet 30| is accordingly opened. .The link circuit is now at normal and may besused to find another calling subscribers line and to ex-A tend a-connection.

In lthe description of the release of the link,

it was assumed. that the called subscriber hung up his receiver first and that the calling subscriber failed to hang up his receiver, and that thelrelease of the connection was under control of the timer equipment. If the calling subscriber had released the connection ilrst, by restoring his receiver, the release of the link is substantially as has been described with the exception that the line circuit of the calling subscribers line is not locked out. When the calling subscriber hangs up his receiver the line relay I9 falls back and lopens the circuit for lock-pulse relay I2. Lockpulse relay I2 opens the circuit of release relay I6. Release relay I6 falls back and disconnects the grounded cut-off conductor CO of the timer at armature 54. When'this ground is removed switching relay 9, auxiliary release relay I1, and cut-.off relay 2 of the line switch, are all restored to normal. Line relay I of the line circuit is now bridged across the line, but does not energize because the loop circuit including the subscribers line is now open. VLock-out relay 3 of the line circuit is also released. The remaining portion of the link circuit is released in the same manner as has been described previously. n

A description will now be given 'to explain how a subscriber, such as a subscriber at station A, calls for another subscriber on his own line. That is what is commonlytermed a reverting call.

When the receiver is removed at station A, the same operations take place as have been described, with the result that the calling line is picked up by the finder switch of the link. Assuming that the link shown on the drawings is used, the nder switch will establish a connection to the calling line, and circuits will be completed automatically for placing the connector portion of the link under control of the calling subscribers dial. The calling subscriber now dials the ilrst digit of the wanted subscribers number,

. thereby controlling the connector portion of the finder switch to advance its wipers to select the wanted line. The subscriber now dials the last digit of the number, thereby controlling the code switch to advance its wipers. Following the operation of-the code switch, the called line is tested in the manner hereinbefore described, and of course it is bound to be busy. This, it will be understood, is because the called line is also the calling line.

Upon receiving the busy signal, the calling subscriber hangs up his receiver. The subscribers on party lines have special instructions, and therefore, such a subscriber knows that when he calls a party on his own line he can expect to get the busy signal and that the proper procedure in such a case is to hang up his receiver and walt a sufiicient length of time for the signalling operation to take place.

When the receiver is replaced at station A, relay I9 falls back, followed by the falling back of lock-pulse relay I2. Accordingly, the slowacting release relay I6 deenergizes. Relay I6. upon deenergizing, removes the ground potential from the wiper 60 of the finder switch and the upper winding of switching relay 9 at armature 54, but prior to thisa circuit has been connected up in a manner which will now be explained. When lock-pulse relay I2 falls back it closes a circuit, at armature |I6 and its back contact, from the grounded cut-off conductor C0, armature 6|, armature 51 and its front contact, armature ||6 and its back contact, armature 22|, armature 259, armature 263, conductor 248, to test wiper 306. The test wiper is now in engagement with a test contac't to which the private normal conductor 3| of the calling line is connected, so that ground is extended by way of conductor 3|, back contact of armature 23,01 line relay i, Fig. l, armature 21 of the cut-oil? relay '2, conductor 32, to test wiper 60. 'I'lius ground is maintained Ion` conductor V32 and wiper 6|)V touhold cut-ot! relay 2, switching relay 9, and auxiliary release relay |1 energized so as to maintain the 'connectionafter the calling party hangs up his receiver. .A When the release relay I9 falls back, it completes 'a circuit at the back contacts of armature 54, which extends from the grounded test wiper 60 of the nder, by way of amature |09, armature 54 and its back contact, conductor 94, armature 264 of the busy relay 299, armature 235, conductor 95, winding of reverting call relay II, to battery. Reverting call relay II operates, and due to its adjustment closes armature |25 and its X contact rst to transfer theV grounded conductor including wiper 60 from armature |08 of the switching relay 9. When the reverting call relay is fully energized, the circuit for switching relay 9 is opened at armature |06; the initial energizing circuit for relay Il is opened at the back contact of armature 50 63; and at the front contact'of armature 69 a locking circuit is completed for relay II.` At armature |24, reverting lcall relay connects the pick-up lead through to the pick-up and switching relay 201. When switching relay 9 falls back it removes the line relay I9 from the line wipers of the iinder portion of the link circuit and prepares the self-interrupting circuits for the rotary magnets of the connector and code switch portion of the link.

When the code interrupter is in a position to pick-up relay 201 at armature 221 disconnects the busy tone from the calling subscribers line in order to prevent theringing current from backing up on the busy leads, which may at this time be connected,up in the other link circuit. This condition only occurs on reverting calls, since it is only on a call of this kind that the busy lead is connected up during the ringing operation, this is due tothe fact that in arevertive call the. busy relay 209 is energized.

l When the called Subscriber answers his telephone, the removal of the receiver closes a circuit in the previously described manner for operating ring-cut-oil! relay 209. The ring-'cut-oii.' relay connects up the back-bridge relay 205 to the line which accordingly operates, and at armature 262 completes the operating circuit for supervisory relay I9. At armature 2|2, ring-cutoff relay 206 opens .the circuit of auxiliary release relay I1. Relay I1, upon falling back, opens the previously traced circuit for. grounding the private normal conductor 3| `of the line circuit at armature 51. When ground is removed from the normal conductor 3| by the deenergizat'ion o! auxiliary release relay I1, cut-oil relay 2 of the line circuit falls back. The relays of the link circuit and the wipers of the connector and code switch portion of the link circuit are Arestored to normal in the same'manner as described in con; nection with making local calls.

Considering now the eil'ect on the line circuit when ground is removed from the normal conductor 3| and cut-oil' relay 2 falls back. This' The ringing code of the called subscriber s 2,149,646 connects up line relay I, which promptly encrat armature 24 of the line relay, and it also mainnormal conductor 3| at armature 23 oi' the line relay I.

Talking battery is fed to the4 line through the winding of line relay i, and the line equipmentl .'is therefore the only apparatus that is in use during conversation on a call of this character. The link circuit which was used toset up the connection has been restored to normal as has been previously described and may be used in another connection.

'l'.'he subscriber at substation A in the callwhich has just1been described, knows` when the called subscriber on his line answers, because the ringer at s'tation'A has stopped ringing. Since the bell at station A is connected to the same side of the line as the bell of the called subscriber, both bells will ring in parallel and when his own bell stops ringing the subscriber at station A knows that the subscriber he has called has answered. If a station is called, at which the bell is connected to the other side oi' the line, the subscriber at 'substation A will not hear the ringing, but he will wait, according to instructions, a long enough timetopermit the wanted subscribers ybell to be rung several times, when he will remove his receiver.

'I'he operations which take place in setting up a connection tov a subscriber in a distant automatic exchange will now be described. Certain contacts in the bank of the connector portion of lthe link circuit, have been set aside for trunk lines extending to a distant automatic exchange. Forthe purpose of this description it will be assumed that the trunk line composed of conductors TI and T2 extending from the exchange herein described to a distant automatic exchange with which service is to be Igiven. The trunk line conductors Ti and T2 may be connected to a regular subscrlbers line equipment, similar to the subscribers line equipment shown in Fig. 4. The

A, automatic switches at the distant exchange may be similar to the switches and circuits of the John E. Ostline application, Serial No. 724,238, led May 7, 1934. j

Since two trunk lines are provided for handling calls to the automatic exchange in question, the connector portion of the link shown in the drawings must be arranged to operate as a rotary automatic selecting connector. This merely means that the subscriber in calling the distant exchange will dial the number of the rst trunk line in the group. If this trunk line is idle it will be seized and the connection will be extended thereover. If the rist trunk line is busy,` however, the rotary magnet will automatically advance the wipers of the connector to the next trunk line. If the second trunk line is busy the calling subscriber will receive the busy signal indicating that the trunk lines to the distant exchange are in use.

It willbe assumed now` that the subscriber at station A, Fig. 1, desires to 'extend a connection to the distant automatic exchange, shown in part on lllg.v 4. A:,.In order to accomplish this, the subscriber must dial a preliminary number 01, followed by the'regular number of the desired subscriber in the distant automatic exchange. When the receiver is removed at station A, the previousfly described operations'take place, by means of which, the calling' line is `picked up by an idle link circuit. It will be assumed that the link circuit shown inliigs. 1, 2. and 3 of the drawings is used. When-the subscriber dials the first digit 0, ten impulses are transmitted to the rotary magnet 30| in the same manner as has been described in connection with local calls. The wipers 304-308,'inc1usive, of the connector, advance to the contacts of the connector banks to which the rst trunk line is connected, in other words, the tenth set of bank contacts. When wiper 304 engages its tenth bank contact,`a circuit is completed from ground at Wiper 304, conductor 95, armature |2| and its front contact, conductor 94, armature 233 and front contact of 4the operated units series relay 2|0, both windings ofthe ring cut-oi relay 206 in series, to battery. Ringcut-off ,relay 206 operates, thereby preventing the contact to which conductor 246 is connected. f

If the trunk line to the distant automatic exchange is busy when the Wipers'of the connector switch engage the trunk line, test wiper 306 encounters a ground potential on conductor 32|. A circuit isthen completed for the busy test relay 209, from grounded conductor 32 i, wiper 306, conductor 248, armature 260 and its front contact, winding of busy test relay 209, to battery. Relay 209 operates and at armature 266 prepares a selfinterrupting circuit for the rotary magnet 30| of and advances its wipers 304-308, inclusive, tothe next set of bank contacts. Wiper 305 has now been disengaged fromtheself-interrupting oircuit for the rotary magnet 30|, thereby preventing the rotary magnet from energizing again to advance its wipers, if the second trunk in the trunk group is busy.

If the second trunk in the group is also busy, ground potential will be encountered by the test wiper 306 of the connector, thereby maintaining the busy relay 209 energized. Busy relay 209 prevents relay202 from operating at armature 265, and at armature 259'prepares a busy circuit to the calling subscriber. After the dialling of the second digit, relays 2|0 and 2| fall back, as has been described hereinbefore, and completes the locking circuit for the busy relay 209. When auxiliary relay 2|| falls back the busy tone is transmitted receiver. Thevlink circuit is restored to normal and is available for another connection. If the calling subscriber should fail to hang up hisv receiver the time equipment will complete its pre- It will be assumed now that the"`tr1mk line is4 found to be idle, and for convenience vthe first trunk of the group as indicated on the drawings is selected. Therefore. test wiper 306 of the con-v nector does not encounter ground potential 'on conductor 32|, and busy test relay 209 is not energized.

The calling subscriber may now dial the digit 1.

The rotary magnet 302 of the code switch is operated as before, advancing its wipers 309-3 I 2, inclusive, one step. Since the ring-cut-off relay 206 has disconnected the circuit for transmitting ringin'g current to the trunk line, -the advancement of the wipers by the code switch to select the ringing current is not important at the present time. After the dialling of the second digit, unit series relay 2I0 fallsy back and opens the circuit for auxiliary relay 2| I. At armature 223 and its back contact, unit series relay 2I0 upon falling back, completes a circuit for the change-over relay 202. This circuit may be traced as follows: battery, winding rof relay 202, terminal M jumpered to terminal N, armature 265, armature 223, conductor 94, armature I2I, conductor 95, tenth bank contact and wiper 304 of the connector, to ground.

Since the call being described is to an automatic exchange, the change-over relay 20| which is used on toll calls to a manual exchange is disconnected and the change-over relay which is u sed on toll calls to automatic exchanges is connected. In

addition, relay 2|0 prepares the circuit for pickup and switching relay 201 at armature 225. 'Ihe pick-up and switching relay 201 is operated when the pick-up conductor PU is grounded and locks itself up at armature 23| to the grounded conductor 9|. At armatures 226 and 228, relay 201 connects the trunk line through to both windings of the repeating coil. When relay 202 operates.' it opens the circuit for supervisory timer relay I5 at armature 2|4, thereby preventing the link circuit from being released under control of the timer equipment. When auxiliary relay 2II falls back ground is forwarded at armature 260 over conductor 248 and test wiper 306 to the private normal condition 32| to operate the cut-01T relay in the line circuit of the trunk line and also to make the trunk busy at the connector bank terminals of the second link.

Referring again to the operation of change-over relay 202, it will be noted that at armature 239 ground is placed on conductor 99 in order to place the release of the link circuit under the control of both the calling and called parties, and at armatures 26| and 238 it disconnects the back-bridge relay 205 from the trunk line, and at the same time at armature 238 and its front contact completes a loop circuit over the trunk line, which will be described later. At armature 240, relay 202 completes a circuit from the grounded conductor 9|, armature 240, lower winding of pick-up and switching relay 201, to battery. This circuit is completed to insure the operation of relay 201 to cut the trunk line through to the automatic exchange. It is quite possible that the pick-up conductor has not been grounded before relay 202 operates. Therefore, relay 201 is operated even if the pick-up conductor PU has not been grounded.

' selects the calling line.

When change-over relay 202 operated it completed a loop circuit over the trunk for the line relay 405 of the line equipment in the distant automatic exchange. The circuit for line relay 405 is as follows: battery, upper winding of line4 ,armature 234 and itsfront contact, lower righthand winding of the' repeating coil, resistance 261, armature 238,'upper right-hand winding of the repeating coil, conductor 15, amature |36,

, armature |35, conductor 13, armature 233 and its'front contact, amature 226,` conductor 243, wiper.308 'and its associatedtenth bank contact of the connector portion of the link circuit, trunk line. conductor TI, normally closed contacts controlled by armature 401, conductor 4|2, lower winding of line relay 405. armature 4|6, to ground.` 'I'he two relays, shown to the left of the dash line in Fig. 4, are provided in the trunk line to prevent lthe release of the C. A. X. link circuit until the called subscriber has released the connection. Therefore, when line relay 405 operates, a circuit is completed from ground at armature 4I0, armature 4|3, winding of start relay 402, to battery. Start relay 402 operates and grounds the finder start conductor to the allotter at armature 409, and at armature 4I0 prepares a circuit for the battery reversing relay 40|. Line relay 405 prepares a circuit for cut-olf relay 404 at armature 4|9, and at amature 420 completes an energizing circuit'for battery reversing relay 40| and by the same operation grounds the SN conductor to busy the calling line in the banks of the connector switch. Relay 40| operates and at armature 409 completes a locking circuit for itself from the ground at amature 420 of the line relay. The reversal of battery at armatures 406 and 401 by the operation of relay 40| has no effect at this time due to the fact that the circuit for the hold relay 203 of the C. A. X. link circuit is opened at amature |36 by release rela-y I6. Therefore it will nsl be understood that the hold relay 203 cannot v operate' until release relay I6 is deenergized. Due to the grounding of the nder start lead by the operation of relay' 402 of the distant automatic exchange, a finder in the link eventually When this takes place, ground on conductor S, which is connected to the finder bank, is extended by way of armature 419, armature' 4I4, and winding of cut-off relay 404, to battery. Cut-olf relay 404 operates over this circuit and locks itself tothe grounded S conductor. At armatures 4I5 and 4I6, cut-olf relay 404 opens the circuit for line relay 405, and at the front contact of armature 4I6 completes an energizing circuit for lock-out relay 403. Lockout relay 403 operates and opens the circuit to start relay 402 at amature 4I3, which accordingly falls back.` When line relay 405 deenergizes, it opens the initial energizing circuit relay in the link circuit 'is operated over the' loop' in the'same manner'that the line re1ay 405 of the line equipment was operated. The automatic switches in the distant exchange are now in a position to receive the impulses transmitted by the operation of the calling device atv sta-- first time this circuit is opened the lock-pulse relay I2 falls back. The operation of the line relay I9 and the lock-pulse relay I2 during the dialling period has been described in detail hereinbefore. When lock-pulse relay |2 fallsback a circuit is now completed for the #l pulse timer relay I4 from ground at either armature |00 or armature I||, amature |26, conductor 90, armature 262, conductor 89, armature |40, lower winding of #l pulse timer relay I4, to battery. Relay I4 operates and completesfa locking circuit for the vslow-to-release relay I6 at armature |33, it completes the circuit for the lower Winding of #2 pulse timer relay I3 at armature |30, vand at Y armature opens the circuit for the line relay oi' the link in the distant automatic exchange. The short circuit around the upper winding of relay I4, completed at armature |34, makes the relay slow to release. timer relay I3 is completed from ground at amature III, armature |30, amature |21, lower winding of relay I3 to battery. Relay 'I3 has a short circuit around its upper winding and is consequently somewhat slow to operate. Upon oper--y ating relay I3 completes a locking circuit for itself at armature |29, from ground at armature III, and at armature |40 opens the initial energizing circuit for the lower winding f relay I4, and at armature |28 prepares the operating cir- 'cuit for the lock-pulse relay I2. Relay I4 ialls back, and at armature |35 again closes the loop circuit over the trunk liner to the line relay in the link circuit at the distant exchange. When the impulse' springs at the calling subscribers dial are closed again, line relay I9 operates and completes the circuit for operating lock-pulse relay I2. Relay I2 operates and completes a locking circuit for itself and at armature |21 opens the circuit for #2 pulse timer relay I3. At armature |26, relay I2 opens a point in the energizing circuit for relay I4.

Line relay |9, lock-pulse relay I2, and the pulse timer relays I3 and I4 go through the above described cycle of operations during-each interruplscriber .and the automatic switches at the distant exchange are connected to the wanted sub- Y scribers line in the well known manner.

The wanted subscriber is signalled by the ringing The circuit for #2 pulse y lower resistance.

equipment inthedistant automatic exchange, and

answers his telephone.

When the conversation between the calling and called subscriber has been completed they will hang up their receivers. It will be assumed that the subscriber at station A replaces his receiver first, thereby opening the circuit 'for line relay I9 of the link circuit. Line relay I9 opens the circuit for lock-pulse relayY I2, which also falls back. When lock-pulse relay I2 falls back, the

previously described operating cycle of the pulse `timer relays I3 and I4 will be again closed, and

the momentary opening of contacts |35 will transmit another impulse over the trunk line tothe distant automatic exchange. However, this is of no consequence at this time since the Aimpulse transmitted will not ailect the switches at the distant exchange. Pulse timer relay I3 remains energized over a circuit including armature |29 and opens'the circuit for relay 4. Release relay I6 now falls back and completes a `:ircuit for the hold relay 203at armature |36 and at the front contact of armature |36 the loop circuit, over which the line relay in the distant automatic exchange is maintained operated, is opened. The line relay referred to is not the line relay 405 shown in Fig. 4, but is the line relay of the link circuit that receives the impulses transmitted over the trunk line. The circuit for energizing hold relay 203 is as follows: from ground, winding of relay 203, armature 236, conductor 14, armature I36, armature |35, conductor 13, arma.- ture 233, armature 226, conductor 243, wiper 309 and its associated tenth bank contact, trunk line conductor TI, armature 401 and its front contact, conductor 4I I; over the negative conductor by way of the finder switch wiper, -to the winding of theline relay, to battery. The winding -of the hold relay 203 is of a high resistance, and the winding of the line relay in the link circuit at thegdistant exchange is of considerably operates'but the line relay does not operate. Upon operating. relay 203 completes a circuit from ground aty its upper armature, armature 2I3, and conductor 1I to maintain auxiliary re- Therefore,l the hold relay 203 lease relay I1 in an energized position. As long as auxiliary release relay I1 remains operated the link circuit at the C. A. X. will notA release. Since the called subscriber at the distant automatic exchange has hung up the receiver to release the connection, the Aequipment at the distant exchange restores to normal. When the switches at the distant exchange have been released,

ground is removed from the S conductor, thereby opening the locking circuit for cut-off relay 404, and battery reversing relay 40| in parallel. In addition, ground is removed from the SN'conductor extending to the connector banks, thereby removing the busy condition from the test contacts in the banks of the connector.- Relays 404 and 40| fall back when ground is removed from the S conductor, and at armatures 406v and 401 the reversalmaintained over the trunk conductors TI and T2 is restored to normal. Therefore, the battery potential applied to conductor 4I| and trunk conductor TI to maintain the hold relay 203 in the C. A. X. operated, is now disconnected from trunk conductor TI and connected to trunk conductor T2. The circuit to the hold relay 203 is`no longer maintained, and it accordingly restores to normal. The deenergization of cut-oli relay 404 of the line equipment in the distant automatic exchange permits lockout relay 403 to fall back, and at armatures 4|6 and 4|5 .tant automatic exchange.

again connects the line relay 405 to line conductors 4|| and 4|2. When the holdrelay 203 in the C. A. X. falls back, it opens` the circuit for the auxiliary release relay I1, which upon deenergizing permits the link circuit in the C. A. X. to restore to normal in the same manner as described before.

From the description of the above connection it will be understood that 'when a subscriber in the C. A. X. extends a connection over the trunk line to a distant automatic exchange, that the release of the equipment in the C. A. X. is under the control of the'called party. This particular arrangement is provided to prevent another subscriber in the C. A. X. from seizing a trunk to a distant automatic exchange when the equipment thereat has. not completely restored to normal.

By holding the C. A. X. equipment in an operated` condition, under control of the equipment at the distant automatic exchange, a subscriber in the C. A. X. is unable to select the trunk in use because of the busy condition maintained on the test contacts in the banks of the connector.

A call which is extended from a calling subscrber in the C. A. X. to a subscriber in a manual exchange will now be considered. It will be assumed for this purpose that the calling subscriber is the subscriber at station A. It will also be assumed that the trunk line conductors Tl and T2 shown between Figs. 3 and 4 of the drawings, terminate at a distant manual exchange in equipment similarto trunk TR shown ,on Fig. '7 in the John E. Ostline application, Ser. No. 724,238, f

fied May 7, 1934.

When the receiver is removed by the subscriber atstation A, a link circuit is taken for use in the' manner previously described. It will be assumed that the link circuits shown on the drawings is the one which is connected to thecalling subscribers line after the removal of his receiver. It should be clearly understood that two trunk lines, which may be connected to the banks of the connector portion of the link circuit, Will either terminate in a distant automatic exchange or a distant manual exchange.

'I'he calling `subscriber dials the number 01 and thereby controls the link circuit to select the trunk line to the distant manual exchange. A detailed description of the operation of the link circuit in selecting an idle trunk line has been described hereinbefore, in connection with establishing a connection between a local subscriber in the C. A. X. and a subscriber in a dis- Therefore, it lwill be assumed that the trunk line to the manual exchange in this case is idle, busy relay 209 has made the test and has fallen back, and after the dialling of the second digit the .unit series relay 2|0 and auxiliary relay 2|| have fallen back. When lthis occurs, a circuit is completed for the change-over relay 20| which is now connected [jup by a jumper from terminal N to terminal O rent from the trunk line, and pick-up and switching relay 201 has been connected by way of its upper winding, armature 225, armature 259, conductor 93, armature |20, armature 49, to the pick-up conductor. When the pick-up conductor` PU is grounded the pick-up and switching relayY 201 operates and locks itself, by way of armature 23|, to grounded conductor 9|. At armatures 226 and 228, relay 201 connects the trunk line through to both windings of the repeating coil anc'. the windings of the back-bridge relay.

By referring again to the operation of the change over relay 20|, it will be noted that a circuit `is completed for the reversing relay 204. This circuit may be traced from battery, winding of relay 204, armature 268, conductor 80, armature H6, amature 51 and its front contact, to the grounded cut-off conductor CO of the timer equipment. In addition, a circuit is completed at armature 21| for transmitting a ringing tone to the calling subscriber. The ringing current is transmitted from the code machine by way of contacts on the code switch, conductor 251, tone condenser, armature 21|, conductor 98, armature |39, over the calling subscribers line. 'I'he ringing tone, received by the calling subscriber, is an indication that the operator is being signalled. Relay 204, at armatures 24| and 242, reverses the battery in the trunk lines TI and T2 causing the operation of a polarized relay in the manual exchange. The polarized relay, upon operating,

completes a circuit to signal the operator at the interval between ground pulses over the pick-up conductor. The back-bridge relay 205, which furnishes talking battery over the trunk line to the manual exchange, is not operated over the loop circuit including both conductors of the trunk, because of a high resistance of one of the windings of the polarized relay at the manual exchange.

The operator at the distant exchange plugs in on the calling line when the signal is noted, r

and completes a circuit for shunting out the high resistance winding of the polarized relay. Sufficient current will now ow over the trunk conductors to permit the back-bridge relay 205 to operate. Back-bridge relay 205, upon operating, closes an obvious circuit for supervisory relay I8. Relay I8 operates and opens the circuit of supervisory timer relay I5 at armature 65, thereby disconnecting the timing equipment from the link circuit, and at armature |31 completes a locking circuit for release relay I6. In addition, relay I8 reverses battery over the calling subscribers line for metering or supervision when that type of service is required, and at armature |39 disconnects the ringing tone from the calling subscribers line, thereby indicating to the subscriber that the operator at the distant manual exchange has Ianswered. The calling subscriber now gives the operator the number of the subscriber at the distant omce.

, hook isdepressed, the calling line circuit is broken and line relay I9 falls back, followed by the lock- Relay I2, -upon deenergizing,

at armature IIB. The current flow over the trunk line Vto the polarized relay is again reversed, causing the polarized relay to restore to normal, and again signal the operator. `When the switchhook at the calling subscribers starmanual operators position.

tion is released, the line relay I9 and lock-pulse relay I2 are again energized, and at armature IIS the circuit is again completed for the reversing relay 204. When the reversing relay 204 operates again the current iiow over the trunk line is again reversed so that the polarized relay at the distant exchange s again operated. During the momentary operation of line relays I9 and I2 the release relay is held operated from the change-over relay 20|, thereby preventing the release of the link circuit. These operations may be repeated several times as the subscriber momentarily depresses his switchhook, resulting in the interrupted operation of the signal at the In view of the arrangement for recalling the operator which has just been described, it will be understood that the release of the connection is under the control of the operator. When the calling subscriber has completed his conversation with the wanted subscriber in the manual exchange and replaces his receiver, the described operations result in the operation of the signal at the operators position. The operator will supervise the call and will ascertain whether the parties are through with the connection. She will then remove the plug from the jack. When the plug is removed from the jack, the short circuit around the high resistance winding of lthe polarized relay is removed, thereby causing the release of the back-bridge relay 205 in the link circuit of the C. A. X. Upon deenergizing, backbridge relay 205 opens the circuit for supervisory relay I8 which also deenergizes. Relay I8 opens the circuit for release relay I6, at armature |31 and the remaining portion of the link circuit restores to normal in the same manner as has been described hereinbefore.

The invention having been described, what is considered to be new will be pointed out in the appended claims.

What is claimed is:

1. In atelephone system, a plurality of subscribers lines, a plurality of finder-switches, an allotter common to all vof said lines and said switches, means responsive to the initiation of a call by a subscriber on one of said lines for controlling said allotter to start all of said switches searching for the calling line, and means in said allotter for selecting one of said switches for connecting with said line and for preventing another switch from finding the calling line.

2.A starting arrangement for controlling the starting of a plurality of devices comprising, a start relay and a plurality of selecting relays, `means for energizing and deenergizing said` start relay, a rst circuit for energizing one of said selecting relays in response to the irst energization of said start relay, a second circuit for energizing a second selecting relay responsive to the first deenergization of said start relay, and a third circuit for deenergizing the first selecting relay responsive to the second energization of said start relay.

3. vA combination as set forth in claim 2, characterized by the provision of means controlled by the start relay in response to its second deenergization for deenergizing the second kselecting relay.

4. In a relay allotter, a start relay, means for energizing and deenergizing said start relay, two diierentially wound selecting relays, means controlled by the operation of saidstart relay for operating one of said selecting relays and for preventing the operation of the second of said selecting relays, means controlled by the operation of said first selecting relay for operating said second selecting relay responsive to the restoration of said start relay, and means controlled by said second selecting relay for restoring said iirst selecting relay to normal responsive to the reoperation of said start relay.

5. In a switching system., a pair of switching devices, an allotter common to said devices, a

starting mechanism in said allotter, means responsive to the operation of said starting mechanism for starting said devices for continuous operation, means in said allotter controlled by and responsive to the operation of said starting mechanism for permitting one of said devices to cease operating and for causing the other device to continue to operate after said one device has ceased its operation.

6. In a telephone system, subscribers lines, two finders for nding any one of saidlines, an a1- lotter common Ato said nders and said lines, means in said allotter responsive to the initiation of a call over one of said lines for simultaneously starting both of said finders, means in said allotter for determining vthe nder that shall nd the calling line, and means responsive to the nding of said line by said determined iinder for stopping both iinders.

7. In a telephone system, subscribers lines, two iinders for finding any one of said lines, an allotter common to said nders and said lines, means in said allotter for starting both of said nders, said means responsive to the initiation of a call over one of said lines, means in said allotter for determining the iinder that shall iind the calling line, means responsive to the finding of said line by said determined finder for stopping both finders, and means responsive to the initiation of another call over one of said lines for restarting the idle finder to iind said other line.

8. In 'a telephone system, a pair of nder switches, subscribers lines, an allotter common to said switches and said lines, means responsive to the initiation of a call over one of said lines for simultaneously starting said finders in their line finding operation, means in said allotter for connecting only one of said switches to iind said calling line, and means in said allotter and said connected finder switch for connecting the remaining iinder switch to iind successive calling lines as long as one-switch is in use.

` 9. In a telephone system, a lpair of switches, subscribers lines, an allotter for alternately selecting said switches to find a calling subscribers line', means for operating the selected switches to seize calling lines, and means controlled by a switch 'which has seized a calling line for connecting an unselected switch to lnd a calling line irrespective of the selection of said allotter.

10. In a telephone system, a trunk line,` a first for connecting said second switch to the other end of said trunk line for establishing a. telephone connection from a calling subscriber to a called subscriber over said switches and said trunk line, means controlled by said second switch for reversing the current over said trunk line responsive to said connection with said trunk line, a hold relay connected to one conductor of said trunk line when said calling subscriber-replaces his receiver, said hold relay responsive to the reversed current supplied over one conductor of said trunk for preventing the release of said rst switch until said current reversing means is restored to normal. i

11. In a telephone system, a trunk line to a distant automatic exchange, a switch for establishing connections over said trunk line, a calling subscribers line connected to said switch,

means in said switch controlled over one con-` ductor of said trunk line operated responsive to the release of said line by a calling subscriber for preventing the disconnection of said switch from said trunk line, and means at said distant exchange for releasing said switch.

12. In a telephone system, a trunk line to a distant automatic exchange, a switch for seizing said trunk line and extending a call thereover, a calling subscribers line connected to Said switch, means controlled over one conductor of said trunk line for preventing the release of said switch when said calling subscribers line is disconnected, and current reversing means at the distant automatic exchange for controlling the release of said switch. y

13. In an automatic switch, a line relay, a stepping magnet, a pulse relay controlled at a front contact of said line relay, a circuit for said stepping magnet controlled at the back contact of said pulse relay, a circuit including contacts on said magnet for priming said line relay, and contacts on said line relay for disconnecting said priming circuit.

14. In a telephone system, a trunk line, a switch for extending connections over said trunk line, a loop circuit from said switch including said trunk line for controlling automatic switches at the distant end of said trunk line, a pulse timer in said switch for interrupting the circuit operating and for selecting one of said test cir- Y cuits, 'means controlled over said selected test circuit for stopping the operation of both of said switches and forl connecting the switch connected to the selected test circuit to said lcalling line, and means in said allotter responsive to successive operations of said starting circuit for alternately selecting said test circuits to alternately connect said switches to the calling line.

.subscribers line is v sponsive to vthe initiation having a normal position 16. In a telephone system, a subscribers line, a pair of switches for finding said line, an allotter, a test circuit for each of said switches, means responsive to a call over said line for controlling said allotter to start both of said switches and for controlling said test circuits so that only .one of said switches can select said calling line,

and means responsive to successive calls over said line for alternately controlling said test circuits so that said switches are alternately controlled to select said line.

17. In atelephone system, a trunk line to a distant automatic exchange, a switch for seizing said trunk line and extending va call thereover, a calling subscribers line connected to said switch, means controlled over one conductor of said trunk line and operated when said calling disconnected for preventing the release of said switch, and means at the `distant automatic exchange for controlling the release of said switch.

18. In a telephone system, a plurality of subscribers lines, a plurality of switches for nding l one of said lines, a start relay in each of said nder switches, a connector switch associated with each of said iinder switches, means in one of said connector switches for preventing the operation of the start relay in the iinder switch associated with said one connector switch, and means in said nder switch for connecting another of said finder switches for operation reof a call overone of said subscribers' lines when said start relay is prevented from operating.

19. In a telephone system, a plurality of subscribers lines, a pair of Linder switches for lfind- 1 ing one of said lines, an allotter for selecting one of said finder switches, a connector switch associated with each of said nder switches, and means in one of said connector switches effective in an o-normal position of said one connector switch for preventingthe selection of the nder switch associated with said one connector switch irrespective of the selection of said allotter.

20. In a telephone system, a plurality of sub- ,scribers` lines, a pair of finder switches for linding one of said lines, an allotter for alternately selecting said nder switches to nd a calling subscribers line, a Aconnector switch having a normal position associated with each of said finder switches, means in one of said connector switches eiiective in an off-normal position of said one connector switch selection of the nder switch associated with said one connector switch, and means in said i'lnder for selecting the other `of said nder switches irrespective of the selection of said allotter.

21. In a telephone system, a plurality of subscribers lines, a first under-connector link, a second finder-connector link, an allotter for selecting one of said links, means in the connector portion of one of said links effective during the existence of an unstandard condition of the connector of said one link for preventing the selection of said one link, and means in said link and said allotter for selecting the other `said link for operation responsive to the initiation of a call over one of said subscribers lines irrespective of the selection by said allotter.

JOHN H. VOSS.

for preventing the

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