US2370335A

US2370335A - Allotter

Info

Publication number: US2370335A
Application number: US350222A
Authority: US
Inventors: Bert A Wallace
Original assignee: Kellogg Switchboard and Supply Co
Current assignee: Kellogg Switchboard and Supply Co
Priority date: 1940-08-03
Filing date: 1940-08-03
Publication date: 1945-02-27
Anticipated expiration: 1962-02-27

Description

Feb. 27, 1945. B. A. WALLACE 2,370,335

ALLOTTER Filed Aug. 3, 1940 5 Sheets-Sheet 1 7375.7 M14. l H2227' Feb. 27, 1945. B, A WALLACE 2,370,335

ALLOTTER Filed Aug. 3, 1940 3 Sheets-Sheet 2 /P//VG//V G TONE Fell 27, 1945- Y B. WALLACE ALLOTTER Filed Aug. 3, 1940 3 Sheets-Sheet 3 m mmm WML Patented Feb. 27, 1945 UNITED STATES PATENT OFFICE ALLOTTER Bert A. Wallace, Chicago, Ill., assignor to Kellogg Switchboard and Supply Company, `Chicago, Ill., a corporation of Illinois Application August 3, 1940, Serial No. 350,222

15 Claims. (Cl. 179-18) The present invention relates in general to automatic telephone systems, and more in particular to automatic telephone systems of the relay type, which connections between calling and called lines are established solely by means of relays. The general object of the invention is to provide a new and improved system of this character.

The system disclosed herein is a two-digit system, having a maximum capacity of one hundred lines. Connections are established bymeans of link circuits, each link comprising a finder which has access to calling lines and a connector which is directively controlled over a calling line which has been connected with by the .associated nder to complete the connection to the called line. Since the links are provided on a` percentage basis and are common to all the lines, means must be provided for assigning idle link circuits to calling lines in a systematic manner, to the end that any calling line may be given theexclusive use of a link circuit to complete the call, so long as idle links are available.

A device for assigning link circuits as mentioned in the foregoing is commonly referred to as an allotter, and a special object of the invention is tc provide a new and improved allotter, consisting entirely of relays, and adapted for use in larger systems as well as in the small system disclosed herein.

Other objects and features of the invention will be brought out in the course of the ensuing description, reference being made to the accompanying drawings, Figs. 1, 2, and 3, which show by means of the usual circuit diagrams sufficient of the apparatus and circuits involved to enable the invention to be explained and understood.

Referring to Fig. l of the drawings, the reference character A indicates a, subscribers station, which may be of any suitable automatic type, including a dial or calling device. The sub-station A is connected with the exchange over a line comprising conductors 2 and 3. At the exchange the line is Provided with the usual line and cut-oli relays 5 and 6.

A second subscribers station is indicated at B and is connected to the exchange'over the line conductors l0 and Il. The line and cut-olf relays for the line of station B are indicated at I3 and I4.

As previously mentioned, the maximum capacity of the system is one hundred lines. It is customary, however, to use the digit 0 for calling an operator, which reduces the capacity of the operators equipment is not shown herein, it may be assumed that the digit 0 is reserved for the purpose stated and that there .are accordingly only ninety subscribers lines. These lines are divided into nine groups in accordance` with the rst or tens digits of their telephone numbers. Thus the lines numbered from 1l to 10 constitute the first group, the lines numbered from 21 to 20, the second group, and s0 on.

The two lines shown in Fig. 1 are both lines of the first group. The line of station A is the nrst line of the group, and accordingly the telephone number is 11. The line of station B is the sixth line of the first group, and its telephone number is 16.

Associated with the rst group 0f lines are three

control relays

22, 23, and 24. Relay 24 may be referred to as a group control relay and is common to all the lines of the group. Relays 224 and 23 may be referred to as subgroup control relays. In explanation of this, it may be stated that each group of lines is divided into two subgroups, one comprising the rst rive lines of the group, and the other the last ve lines of the group. Relay 23 is common to lines 11 to 15, constituting the rst sub-group, while relay 22 is common to lines 16 to 10, constituting the second sub-group. l

Each of the other groups is provided with a. similar set of control relays. The drawings show the group control relay 21 and sub-group control relays 25 and 2B, which are associated with the ninth group of lines. The group control relays are interconnected by guard circuits which are not readily understood from the showing of the rst and last group control relays, and accordingly the drawings also shows the group control relay of an intermediate group. This is relay 28, associated with the second group of lines. Fig. l also shows a iinder which constitutes part of one of the link circuits used for establishing connections. This finder comprises nine tens relays such as relays 3| and 32, five units relays such as 4I and 42, a. switching relay 49, and two relays 54 and 551 The tens relay 3| is associated with the rst group of lines, and is providedwith ten sets of contacts by means of which the ten lines of the iirst group may-be connected to a set of ten intermediate trunks. The drawings only show two sets of contacts on relay 3l, being the sets in which the lines of stations A and B are terminated. The line of station A, vfor example, comprising line conductors 2 and 3, also the test system to ninety subscribers lines. Although the 55 conductor 4, terminates at the contact set desig- The drawings show two of the ten intermediate# trunks above referred to, one of them being designated by reference numerals 36, 31, and 38. These trunks are multipled to the contact sets of the nine tens relays, as indicated in the drawings, and extend to contact sets on the units re-Y lays. The rst and sixth intermediate trunks extend to the rst units relay 4|, the second and` seventh intermediate trunks extend to the. secv ond units relay 42, and so on.

Each units relay is adapted to extend the two intermediate trunks terminating therein to a pair of intermediate trunks which terminate in the switching relay 49, one trunk of the pair being the one comprising conductors 4G, 41, and 48. The intermediate trunk comprising conductors 46, 41, and 48 is normallyv connected through contacts of relay 49 to the trunk line comprising conductors 56, 51, and 53, which leads to the connector which is ass-ociated with the finder being described. The otherintermediate trunk of the pair may be connected to the connector trunk by energization of relay 49.'

Relays 54 and 55 are provided for temporarily connecting up the marking conductors over which the tens and units relays and relay 49 of the finder are initially energized during the establishment of a connection.

The connector is shown in the lower half of Fig. 2 and in Fig. 3, and comprises the connector control relays i3 to |22, Fig. 2, the counting relays 30| to 3|0, Fig. 3, with the two common establish connections to the ten lines of the .'rstk group and has ten sets of contacts, of which only the two sets assigned to the lines of stations A and B are sho-wn in the drawings.

The allotter is shown in the upper half of Fig. 2 and comprises relays to 2|5. The relays 20| to 2|2 are individual to the link circuits, respectively, relays-M3 and 2|4 are control relays associated with the odd and even individual relays, respectively, while relay 2|5 is a common control relay. Since twelve individual relays are shown, it will be understood that twelve link circuits such as the link circuit shown are provided for.. The number may, however, be in-creased or decreased to suit varying'trac conditions.

The operation of the system will nowbe described, it being assumed for this purpose that the subscriber at station A desires to call the subscriber at station B. The connection is established by removing the receiver at station A and.

When the receiver is removed a bridge is closedacross the line conductors 2and 3 in known manner and a circuit is completed for the line-relay 5. Upon energizing, relayA 5 grounds the-individual marking conductor `|58 and also grounds conductor 20, which is common to lines 1 to 5 of the first group. The grounding of conductor 20 completes a circuit for the group control relay 24 of the rst group which may be traced from ground by way 0f contact 1, conductor 20, contact 60, winding of relay 23, winding of relay 24, contacts controlled at 6|, conductor 62, contact 63, conductor 64, contacts of all intermediate group control relays such as contact 65 of relay 28, contact 66, and resistance 61 to battery. Relay 24 is energized over the above circuit and locks itself at contact 6|. At contact 66 relay 'i4-.disconnects batteryl from conductor 62, which prevents all, the other group control relays such as21-and.ZB'rOm'energizing responsive to calls that may be initiated in other groups. At contact 12 relay 24 places ground on the tens marking conductor 1|, thus preparing for energizing the rst tens relay such as 3| of the finder in the link circuit to be used.

Thel sub-group controlrelay 23 is'energized in series with relay 24,` and at contact 13 disconnects conductor 2|, common to lines 6 to 0 of the rst group, from the sub-group control relay 22, thus preventing relay 22 from energizing responsive to a call being initiated on one of these lines. Relay 23 also connects the ve individual marking conductors such as conductor 68 to ve common units marking conductors such as 69. Since conductor 68 is grounded, this operation prepares for energizing therst units relay such as `4| in the iinder which will be used for the call.

Attention may now be directed to the allotter which is shown in Fig. 2. The operation of this device will be described in detail later on, but for the present it will be suflicient to state that one of the relays 20|to 2|2 will be in energized p0- sition, thereby assigning the associated link circuit as the one to be used on the next call. It may be assumed that the rst link'circuit, the one shown in the drawing, is idle and is the next one t0 be used. Accordingly, relay 20| of the allotter will Ibe in energized position, as shown.

Returning now to the call under consideration, when the group control relay 24 energizes it grounds th'e common conductor 15 at contact 14'," thereby establishing a circuit for relays 54 and 55 which may be traced over said conductor 15 to Contact 2|6 of relay 2|5 and thence by Way of contact 2|9 of relay 20|, conductor 16 (individual to the rst link circuit), and windings of relays 54 and 55r to battery. Upon energizing, relays 54-and 55A connect the common marking conductors through -to the tens and units relays of the iinderl of the rst link circuit.

.As the result of the extension of the marking conductors, asdescribed inthe preceding paragraph, the tens relayi3| isenergized over the tens marking conductor 1|, and-the units relay 4| is energized` over the units marking conductor 69. These relays prepare locking circuits for themselves at contacts `39 and 11, respectively;` Relay 4| also disconnects battery from the other four units relays such as-42 at contact 18, thereby preventing anyof these other units relays from energizing in case one of the lines 12 to15 of the rst; group is calling at this time.

The energization of relays 3| and 4| extends the line of station A to the line relay in the connector ofthe rst link 'circuit over a' path which includes-contactsV 33 -and,34 `of relay 3|, intermediate trunk conductors 36` andv31, contacts 43 and 44-of relay 4| conductors 40 and'41, normally closed contacts of re1ay'49, trunk conductors 56 and 51, and the upper and lower windings of the line relay |2|, these windings being connected to ground and battery, respectively. The line relay |2| is accordingly energized, and at contact |26 closes a circuit for the slow acting release re-` lay |22.

Upon energizing, relay |22 grounds the local holding conductor |45 at contact |24 and also places ground on the holding conductor 58 of the incoming trunk from the inder. The grounding ofy conductor 58 extends ground over conductor 58' to complete the previously prepared locking circuits for relays 3|y and 4|. A circuit for the cut-off relay 6 is also completed, said circuit extending from the grounded holding conductor 58 by way of normally closed contacts of relay 49, conductor 48, contact 45 of relay 4|, conductor 38, contact 35 o-f relay 3|, conductor 4, and winding of cut-oli relay 6 to battery. On energizing, relay 6 disconnects the line conductors 2 and 3 from ground and from the line relay 5, respectively, which causes the line relay to deenergize. The deenergization of the line relay breaks the circuit of

relays

23 and 24, and these relays accordingly deenergize also. Ground on conductor 4 is also extended over conductorS to the connectors, whereby the line of station A is made busy to incoming calls.

When the release relay |22 energizes, it opens its contact |23 and thus disconnects battery from the conductor 25| leading to the allotter, thereby bringing about certain operations in the allotter, including the temporary energization of relay 2|5, the deenergization of relay 20|, and the energization of another relay such as 202 in order to assign another link circuit for the next calling line. These operations will be described presently, but for the moment it will be suflicient to note that the circuit of relays 54 and 55 is broken at contact 2|6 of relay 2|5 and also at contact 2|9 of relay 20|. Relays 54 and 55 accordingly deenergize and disconnect the marking conductors from the iinder of the first link circuit. It will be noted that the circuit of relays 54 and'55 is broken at the allotter, even though the group control relay 24 may remain energized due to another call and thus maintain ground on the common conductor 15.

As the result of all the foregoing, the calling line has been extended to the connector, where the line and release relays |2| and |22 are energized. A connection may now be traced from the dial tone source by way of conductor |46, contact |41, contact |39, impedance |48, condenser |49, contact |33, contact |29, and condenser |8|, to the trunk conductor y56, whereby a dial tone signal is transmitted to the calling station A, notifying the calling subscriber that dialling oi the called number may begin. The number of the called subscriber is 16, and therefore the dial is rst operated in accordance with the digit 1.

When the rst digit is dialled, a single interruption is produced in the line circuit and the line relay |2| is deenergized momentarily a single time. The release relay |22 does not fall back when its circuit is broken momentarily, due to its slow releasing characteristic. On deenergizing, the line relay transmits an impulse to the slow acting relay ||4 over a path extending from ground by way of contactL |26, contact |25, contact |31, contact |42, conductor |65, and winding of relay ||4 to battery. On energizing, relay ||4 When the line relay |2| falls back momentarily, I

it also sends an impulse to the rst counting'relay 30 Fig. 3, over a path which extends from ground by way of contact |26, contact |25, contacts |31 and |42, conductor |61, contact SI5, winding of relay 30|, and through the serially related chain contacts on relays 302 to 3|0, inclusive, to battery. On energizing, relay 30| prepares a circuit for counting relay 302 at contact 3|8, and closes a locking circuit for itself at contact 311 which extends from the grounded holding conductor |45 by way of contact |64, conductor |10, contact 3H, winding of relay 3| winding of relay 30|, and the chain contacts of relays 302 to 3|0, inclusive, to battery. This locking circuit includes relayl 3| l but is ineiective to energize said relay until the impulse from the line relay has terminated, whereupon relay 3| energizes. Relay 3H breaks 'the initial energizing circuit of relay 30| at contact 3|5 and further prepares the circuit of relay 302 at contact 3 6. As the digit l was dialled, only the counting relay 30| is energized at this time, but the Adescription of the call will not be interrupted, since an opportunity of completing explanation of the operation of the counting chain will be affordedwhen the results following the dialling of the second digit are discussed.-

A short interval after the line relay has come to rest after the dialling of the rst digit, the slow acting relay ||4 falls back, followed by relay ||5. The function performed by relay ||5 during dialling is to prevent two subscribers lines from being momentarily connected during thel operationv of the counting relays. It performs this function by disconnecting the talking conductors |13 and |68 from their branches |14 and |69, respectively, at contacts |55 and |58. This operation is, of course, unnecessary when the digit dialled is the digit l, but is essential on other digits because each counting relay except the i'lrst is energized before the preceding relay is deenergized, as will appear from the subsequent description.

Continuing Awith the call, when relay ||4 deenergizes, it places ground on the two marking conductors |1l and |12 and completes a circuit for the first tens relay 32|, the circuit extending from ground on conductor |45 by way of contact IBI, resistance |80, contact |62, conductor |1|, contact 3|9 on relay 30|', and winding of relay 32| to battery. On energizing, relay 32| locks itself over a circuit extending from ground on conductor |45, winding of relay H3, conductor |15, lower contact of relay 32|, and winding oi" relay 32| to battery. In energized position, the tens relay 32| extends connections from contacts of the ten counting relays to the ten lines of the rst group.

Relay ||3 is energized in series with relay 32| and at contacts |62 and |63 disconnects the two marking conductors |1| and |12. These conductors are separated at this time to prevent the false operation of another tens relay when the next digit is dialled. Relay ||3 also disconnects ground from conductor |10, thereby bringing about the deenergization of relays 3H and 30|.

The calling subscriber may now dial the second digit of the called number. The second digit is the digit 6, and accordingly a series of six interruptions is produced in the line circuit, causing the line relay 12| to momentarily deenergize six times. At each deenergization the line relay sends an impulse to relay ||4, which energizes and remains in operated positionl duringetheee ries of impulses. Relay is alsov energizedras. before. When relayvr |I4j enex'gizes,` itrepla'ces ground on conductor |-at'contactll6lgrtherebyt' promptly preparing the; locking circuit foruthe!` rst counting relay 30|'. Relay: I`I4falso closes: a circuit for relay I I6,y extending-fromfground bnl. conductor |45 by way. of contact |64,` contact. |60, and Winding of'relay H612 to battery. On. energizing, relay ||6 locksfitself'atcontact |5'|;.. and at contact I52fp`1aces' ground-0n" conductor |10 independentof` the contact onr relay I=|4i in'. order that conductor |10' may' bel malntalned` grounded after relay I |4 has deenergized.v Relay` ||6 also disconnects dial-tone from" the calling line at contact |41. l

While the line relay issending impulses-to -re'- lay I|4, it also sends-impulses to the counting' relays. The rst impulseenergizes relay 301i over a circuit which includes conductorV |61-, con

tacts of relays 302 to 3|0, inclusive, to battery;

On energizing, relay preparesa' circuiti'cr'A relay 302 at contact 3 I8, and locks itself at' con; tact 3I1 over a previously traced circuit which includes conductor |10 and relay 3| thelatter relay energizing at the termination of theilrst impulse. Relay 3|I disconnects the'ir'npulse con'L ductor |61 from relay 30| and other. odd'A` counting relays at contact 3| 5, and at'co'ntact'3l Giurther prepares 4the circuit of relay302.

On receipt of the second 'impulsefrom the line relay, the second counting relay- 302" en'ergizesv over a circuit extending over 'conductor ltT'and by way of contact 3I3, winding of-relay'302, con; tact 3|8, contact 3I6, and resistance`330' to battery.' On energizing, relay"302"'lock`s lts'elf in' a new circuit which extends from gro'unded'conductor |10 by way of Contact 733|, winding of re'- lay 3|2, Winding of relay 302, contact 333;. and" chain contacts on relays` 303' to 3|0, inclusive; to battery. In addition; relay 302" partly pre' pares a circuit for relay 303 at contactv 332' and' breaks the locking circuit o'f relays`30`| and 3| I"` at the chain contacts associated' .with contact aecomoer'gized. responsivetoz the last impulse andv locks. itselfinseries with relay 3|2 at contacts 33.1y and1333,.relay 3|2 energizing at the termination of theA impulse. The operation of relay 306 selects the sixth line in the group of ten lines that Relayy has-.been selected` by4 the tens relay 32|. 32| is the rst tens relay. and accordinglyline 16., or the line4 of station B, hasbeen selected.

and thenceitofthe test conductor` I2 of the called:

line', Fig. l. Relay III-also breaks the circuit of relay II5; but relay |5is slow to deenergizefandl eholds' uplongf enough for the called line to beV tested 'over the circuit described.

Assuming that'the'called line is busy, there will be a ground potential on conductor |2` and the test relay |I1 in the connector will energize, locking itself atzcontact,` |40. At contact |42 relay ||1 breaks4 the impulsing circuit, and at contacts. |4| and |43" it' breaks the circuits of relays IIB' and? ||9,' respectively, preventing these relays from energizing when relay I I5? falls' back. Finally, at contact |30, relay I |1 connects a source Yof busy signalling current with the calling line; thus giving the calling subscriber a busy signal. The. calling subscriber will then replace his receiverLand the equipment in use will be restored to normal in a manner to be :presently described.

333, whereupon these tworelays'deenergize; 'Rev lay 3.|2 energizesin series with relay 302 at the" termination of the Second' impulse, disconnects' the' impulse conductor |61l from" relay'` 302 andl other even counting relays atcontact 3|3 and completes the preparation of the circuit" of re'- lay4 303 at contact 3I4.

In response to the third impulse relay'30'3en`- ergizes over a circuitv extending over conductor" |61 and by way of contactj 3|5', windingof relay' 303, contact 332, contact 3|4, andresistan'ce 330 to battery. Relay 303 locks itself over a circuit extending from' the' grounded conductor' |10'by way of contact 334, winding of relay 3H', Winding of relay 303, contact 336, and chain contacts of relays 304 to 310,` inclusive, to battery'. Relay 303 also prepares the circuit of relay 304" at con*- tact 335, and breaks the circuit ofV relays 302anjd 3|2 at 336 by disconnecting theserelays" from the chain circuit to battery.'v Relays 302" and 3'I2` explanation, and need not be describedl in" de tail; It will suffice to say that relay 3061s en= Assumingnow that the called line is idle, there will'be no ground potential on the test conductor I2 'when' the'test, circuit is completed by the de energization'ofv relay ||4', and the test relay ||1 will'not be energized. When relay I l5V falls back,

therefore, a circuit will be' completed for relayv |I8, extending from grounded conductorY |45, contact I6|, contact |56, contact |53, contact |411, and winding'of relay ||8 'to battery. On energizing, relay. ||8 disconnects'the test circuitI from the test relay ||1 and connects it to ground' at contact |34; therebyv grounding conductors I8 and". |2fto make the calledline busy and completing' a circuit-l for the cut-off relay I4. Onfenergizing, relay? I4 clears the called line of itslnormal batteryI and ground connections.

In additiony tothe foregoing, relay I|1 breaks` the impulsing circuit at contact |31, and at contact. |3511; opens another point in the circuit over' which battery is normally applied to the conducy torl 25| extending to thev allotter. Finally, atv contacts. |33 and |38 relay ||8 completes the connection4 to thecalled line, said connection ex-Y tending frornthe incoming trunk conductors 56- and. 51, by way of the condensers I8| and |82;

conductors

342 and 343, contacts 345 and 346and conductors |6 and |1 to lineconductors I 0' and' ofthe called line.y

The ringingl interrupter machine connects groundl intermittently to. the conductor |83, thereby operating the ringing relay- IIS at intervals overa circuit extending over said conductor |83'an'dby way of contact |51, contact |54,.con tact |43, and winding of relay I9 to battery. On energizing, relay I |51l breaks the connection tothe called line and'. connects the called line to the ringing. current' generator over conductors I|l4` and |85, therebyrlnging the bell at the called station. At the same time a source of ringing tone signalling current is connected to the calling line by way of conductor |88 and contact |28,

thereby notifying the calling subscriber that the ringing operation is proceeding. It should be noted also that each time relay ||9 deenergizes it momentarily connects ground and battery to the called line at contacts |38 and |3|. These contacts should break later than the ringing contacts |25 and |32, and are eective to dissipate the charge on the line and in the condenser at the called station that may remain after the ringing circuit is broken. The object of this operation is to prevent a false operation of the back bridge relay |20.

When the called subscriber answers, the back bridge relay |28 is energized over the called line in an obvious manner. Relay |28 will energize at once if the receiver at the called station is removed during an interval between ringing periods, or as soon as relay ||9 deenergizes ii the receiver is removed while the bell is ringing. On energizing, relay |20 closes a circuit for the test relay ||1 at contact |21. On energizing, relay H1 functions as a ring cut-off relay, breaking the circuit of the ringing relay ||9 at contact |43. Relay l1 also breaks the initial energizing circuit of relay HB at contact |4| but closes another circuit `for said relay including its locking contact |36 before it can deenergize.

The connection between the calling and called lines is now complete and conversation can proceed. The talking circuit includes the condensers |8| and |82. Current for the transmitter at the calling station A is supplied through the windings of the line relay |2| while the transmitter at the called station B is supplied through the windings of the back bridge relay |28.

When the conversation is finished the subscribers will replace their receivers and the connection is released. The circuits are so arranged that the calling subscriber controls the release of the finder while the release of the connector is controlled by either the calling or the called subscriber, depending on which subscriber last replaces his receiver.

When the receiver is replaced at the calling station A the circuit of the line relay |2| is bro-ken and said relay deenergizes, breaking the circuit of the release relay |22. After a brief interval relay |22 deenergizes and removes ground from the holding conductor 58, thereby permitting relays 3| and 4| to deenergize. This restores the finder to normal. The removal'of ground from conductor 58 also opens the circuit of the cut-off relay 6, which. deenergizes and re-connects the line conductors 2 and 3 to ground and to the line relay 5, respectively, thus placing the line of station A in normal condition.

At the connector the back bridge relay |28 remains energized until the called subscriber hangs up and maintains ground on the holding conductor |45 by way of contact |21 and the locking contact |40 of relay H1; Relay ||8 maintains battery disconnected from conductor 25| after relay |22 has restored in order to maintain the link in unselectable condition at the allotter.

When the receiver is replaced at the called station B, relay |20 falls back and breaks the cir- Thev Accordingly, relays H3, H6, H8, 30B, 3|2,

the test conductor of the called line and the cutoff relay |4 is deenergized, thereby placing the called line in normal condition.

The connection described in the foregoing is typical of connections established by calling lines 1 to 5 in all groups. Calls'made by lines 6 to 0 in the various groups are the same, except that relay 49 of the nder in use is energized on such calls. For example, if an outgoing call is made from the line of station B, which is the sixth line in the iirst group, the operation of line relay |3 grounds conductor 2|, and the sub-group control relay 22 is energized instead of sub-group control relay 23. Then when relay is energized, assuming that the rst link circuit is used for the call, a circuit is completed for relay 49 at the same time that the circuits are completed for relays 3| and 4|. Relay 4S energizes and the line of station B, line 16, is connected to the connector trunk instead of the line of station A. It will be noted that whenever relay 49 is energized it becomes locked to the holding conductor 58' at contact 18. l

Reference Will now be made to Fig. 2 for a more detailed explanation of the allotter. From what has been said before it will be understood that conductor 15 incoming to the allotter is common to all the subscribers lines and may be grounded by any calling line. Also, conductors 16 and 25| outgoing from the allotter are individual to the rst link circuit, conductor 16 extending to the finder and conductor 25| extendingv to the connector. The allotter is provided with as many pairs of outgoing conductors as there are link circuits.l Thus

conductors

242, 243, and 244 extend to the finders in the second, third, and fourth link circuits, and there are eight similar conductors which extend to the finders in the other eight link circuits. Conductors 252, 253,'and 254 extend to the connectors in the second, third, and fourth link circuits, and there are eight similar conductors extending to the connectors in the other eight link circuits. The conductors such as 16, 242, etc., are control conductors over which the relays such as 54 and 55 are energized to connect the marking conductors to the finders, while conudctors 25|, 252, etc., are test conductors by means of which the allotter determines whether the link circuits are busy or idle.

One of the relays 20| to 2|2, inclusive, of the allotter is normally energized, and for convenience it has been assumed that Athe energized reand the rst link vcircuit is thus assigned for use on the next call. f

When the next call is made, conductor 15 is groundedin the manner already explained, andA relays 54 and 55 are energized over conductors 15 and 15, whereby the marking conductors are connected up and the nder of the first link circuit is operated to connect with the calling line. The line and release relays of the connector are then operated and the latter relay opens at contact |23 the previously traced .circuit of relay 20| 13o-battery through'resistancet". This-operation'removes the-:shunt Tfrom vrelay 2|3 and said relay energizes ineseries'i withL relay" 20 I.

AOn energizing, relay `f2|3 A'closes :a circuit for relay `2 I5, lwhich energizes .f and vopens conductor I5` at contact 2|6. 'Relay 2 I3 also 4closes acircuit for relay i202 extending `from l ground by lway Yoi contact-2|?, contact22I, winding of relay202, andl conductor "252 to battery in" the' connectorl of the second link circuit,=assumingfthat'thislink circuit is idle. On-energizing, relay202 closes a locking circuit-for itself'atfcontact221, prepares a circuit for relay'203'at contact-228, and 'connects-uprelay '2 4 at contact 5229. Re1ay'f2 I 4 is shunted by the circuit to Vbattery overvconlductor :2521 and is'not'operated. Relay 202 'also breaks the circuit of relays-20| and S2 |13 iatits chain contactscontrolled by contact' 221.' and said relays are "deenergized, theilatter relay breaking the circuit'of relay 2I5. 'Relay- 2I5=`shouldfbeslow 'to deenergize in orderto aiordf'ample 'time for the operation of the allotterbetweenfsuccessive calls. When relay 2I5 falls back, itiextends the vcommon conductor`i by way of contact' 2 |46, con- 'tact 2|'9 of the now deenergized relay 120| and r"contact 226 of the'energized Are1ay2'2II2,fto'con ductor'242. `The latter conductorextends tore- `lays such as 54 and '355 in" the Afiinder of the 1second` link circuit, which .is therefore fassigned' for luse on the next call.

When the nextcall is'made,'battery is 'removed from rconductorf252 in'the 4connector of :theisecond vlink circuit and relay 12H '-isfenergized yin series vwith relay i202. On energizing, relay 3'2I'4 closes :a circuit "for relayIS, which operates againand opensconductor`'5. 'Relay 112|'4 ialso Vcloses/a circuit for-relay203- 'Assumingithat the thirdf link circuit is busy, 'there wllllbe' 'no'battery potential on conductor253'in 'the connector, and the lcircuit 'of relay"`203wvill extend: from ground by 'way of contactf2I-8, lcontact-"228,f-vvinding of relay 203, normally `closed contacts :associated `with -contact 1233, andf'the resistance P238 fto `battery. On energizing, relay `203flocks 'itselff-at contact 23| andat thelassociated chain 'contacts'breaks the circuit of vrelaysl'202 A and "214, which A deenergize. 'Relay 203 'preparesfacircuit 'for relay 204 at contact 232, and atfcontact'2i33it=substitutes relay 2 |-3 forthe resistance5238.

Relay 2|3 accordingly energizes in series-with -relay 203 and closesl anothercircuit for relay'e2l5, thus maintaining this relay energized. Relay? 2 |13 also closesv a vcircuit for relay 204 `which extends from ground'by 'way' of contact "2 i1, vlcontact '232, winding of relay '204,l and conductorf254 (assuming that the fourth link `circuit is; idle) Lto battery in the connector `of the 'fourth-link circuit. 'On energizing, relayl204 locksitself at contact 235 and atthe lassociated chain contacts breaksthe 'circuit of relays 203 and`2I-3,' which deenergize.

Relay 204 also prepares'a circuitfor relay '-205 at contact 235,-and "at contact 23T it connects up relay 2|4, Whichdoes not -'energizefhoweven because' it` is-shunted by the circuit'over conductor 254'to battery at'the connector.

AFollowing the deenergization of'relay2 I 3,`1elay 2 I5 is deenergizedfand 'thecommon'conductor l5 is extended 'byway'of contact 2I6, Vand contacts `2|!I, 226, 230, and 234,"tc conductor 244. "The 'lattericonductor isindividualtothe fourth link Acircuit which isthus' assigned for use on' thenext call.

In response to `succeeding callsyrelays' 205 to `i2 I2," inclusive; will be :energized successively in a Vmanner which willbe readily understood `from'the preceding explanation. When relay 2|2 is ener- `g'ized,iitxlor'sksitself at contact :265 and at the @associated contactsbreaksthe circuitlof relays 12H fand 2l3.

The-locking circuit of relay 2I2 Vextends vfrom groundfby way of contact 265, conductor 26B, contacts controlled at contact 220 of .relay 20|, conductor261, winding of relay. 2I2,

and conductor 262 to battery at the connector in -the twelfth linkcircuit, assuming that this link circuit is idle.

When the twelfth link circuit is takeninto use,

yrelay 2|4 `energizes in series Withrelay 2I2 and closes a'circuit for relay 20|, extending from :ground by way of `contactr2l, contact "284, chain sgize. l-'telay l2I2 breaks the locking circuit of 'relay E20 I at vcontact 265, Vand yalso breaks the `initial energizing circuit of this relay at contact 264, but at thefsame time it replaces ground on the chainz circuit and thus establishes the previously traced Vcircuit over which relay'i20|.is.maintained energizedfwhile the first link circuit is waiting for afcall.

It will be seen'fromthe' foregoing that the link .circuits lareztested and assigned for` use by the allotter inzreguiar vrotation, thereby equalizing the'trafiic .between the! link circuits. :the link `.circuits becomebusy, rthe allotter will :operate continuously, testing the link circuits one In case all after the .'otherluntil'onefof them is'iound idle `and is "assigned for the next call. During such testing operation ftherrelay -'2I5 is 'maintained -energized and' is `only permitted to deenergize Y-aiterianidle llink 'circuit has been vfound and fassignedifor use.

It'will :bei'seen further that fno' link circuit can ybeiassigne'd unless'there isfa'batterypotential on its :associated test conductor. "In case a concalls-will itest busy to' the allotter= andlwill not be aassignedffor useby callinglines until the'fuseis replaced.

The testing arrangement'alsolends itself with Ifacility to .the articial Vhusying of'the link cir- -cuits.

Each of vthe test `conductors 'such `as '25 I, 252,.etc., is preferably provided with a'busykey In the explanationof' the setting up oi a confnection" from station Af to station B the allotter lwas described'as being operated to test-for another link circuit when theline relay was operatedover the calling line, the line relay operating o5 "relay I 22 and the latterrelayremoving 'connector 'may be considered as'the normal operation of the `batteryfrom conductori25 I 'at contact |23. This system. However, it is usually desirable as a aftemporary'bridge is closed across the vtrunk 'conductors 56 and5'I when v'relay 55 energizes. 'The closure Aof this bridge insures the energization of the lineand'release relays of the connector even though there'may be a defective contact `at'one vofthe-relays in the iinder, which would prevent the line relay in the connector from energizing over the calling line. The possibility of such a case of trouble is remote, but if it did occur it would tie up the system ,until the calling subscriber replaced his receiver. The arrangement described prevents such result by insuring the operation of the allotter regardless of whether the calling line is properly extended through to the connector or not.

The invention having been described, that which is believed to be new and for which the protection of Letters Patent is desired will be pointed out in the appended claims. i

What is claimed is:

l. In an automatic telephone system, a plurality of connectors, an allotter for assigning said connectors to successive calls, relays in said allotter, individual test conductors extending from the allotter relays to the respective connectors, means in each connector for maintaining a potential on its test conductor while the connector is idle, circuits for the allotter relays whereby one of the relays is held energized by the idle potential on its associated test conductor, means in each connector controlled by thecalling subscriber when the connector is taken into use for a call to remove the potential from said test conductor, and means controlled by the called subscriber for replacing the potential on said test conductor.

2. The combination, with a plurality of links, of an allotter comprising a plurality of link selecting, relays, two control relays, means for energizing said selecting relays successively in search of an idle link, circuits for the odd and even selecting relays including said control relays, respectively, whereby said control relays are energized alternately during the searching operation, link assignment circuits controlled by said selecting relays and including a common conductor, and means controlled by said control relays for holding said conductor open during the searching operation. l

3. In an automatic telephone system, a plurality of link circuits, an allotter comprising a like plurality of link selecting relays, test conductors extending between the selecting relays and their respectively associated links, circuit arrangements whereby one of said relays is normally maintained in energized condition over its associated test conductor, and a circuit prepared by the energized relay for allotting the associated link to the next call.

4. The combination, with a plurality of links, of an allotter comprising a plurality ,of link selecting relays, means local to the allotter for energizing said relays successively to search for an idle link circuit, and means for preventing the energization of each relay, said means comprising a conductor individual to the preceding relay to which a potential is applied at the associated link if the link is idle.

5. The combination, with a plurality of links, of an allotter comprising a plurality of link selecting relays, means for energizing said relays successively to search for an idle link, said means including two control relays common to the odd and even selecting relays, respectively, and shunt circuits including conductors individual to the links for preventing the energization of the associated control relay when an odd or even selecting relay iinds an idle link.

6. In an allotter, a series oi selecting relays, a series of test conductors, one for each relay, a normal energizing circuitfor each relay includlill ing its test conductor,l an auxiliary energizing circuit for each relay which is effective in case the normal energizing circuit is inoperative, two relays which are common to the odd and even selecting relays, respectively, for controlling said energizing circuits, and circuit connections for controlling said common relays over said test conductors.

7. The combination, with a plurality of link circuits, of an allotter comprising a like plurality of link selecting relays, test conductors extending between said selecting relays and their respective links, means in each link for maintaining a potential on its associated test conductor While the link is idle, local means in the allotter for energizing said relays successively in search of an idle link until a relay associated with an idle link is energized, a circuit for the last energized relay including its associated test conductor, and a connection to said test conductor which prevents saidlocal energizing means from operating the next selecting relay until the potential on said test conductor is removed.

8. rlhe combination, with a plurality of link circuits, of an allotter comprising a relay individualv to each link circuit, a normal energizing circuitl for each relay including a conductor individual to the -associated link, a common energizing circuit for said relays including a resistance, a locking circuit for the odd relays including a control relay for the even relays, and a locking circuit for the even relays including a control relay for the odd relays.

9. The combination, with a plurality of link circuits, of an allotter comprising a like plurality of link selecting relays, means for energizing each relay over a conductor individual to the associated link if the link is idle, a common circuit for energizing any relay when its associated link is busy, two control circuits common to the odd and even relays, respectively, contacts on each relay for disconnecting it from said common circuit and for connecting it to one of said control circuits, and relays in said control circuits for controlling said energizing circuits.

10. The combination, with a plurality of links, of an allotter comprising a selecting relay individual to each link, means for energizingy one of said relays over a circuit extending to the associated link, whereby the associated link is selected for the next call, means in the said selected link for opening said circuit when the link is taken into use, a relay energized in series with the energized selecting relay responsive to the opening of said circuit, and a circuit for the next selecting relay controlled by said last mentioned relay.

1l. The combination, with a plurality of links` of an allotter comprising a like plurality of relays, a circuit for energizing a first one of said relays including a branch local to the allotter and a parallel branch which is open if the associated link is busy, means for closing said cir cuit to energize the said first relay over both said branches or the local branch alone, a third branch of said circuit which is substituted for said local branch upon energization of said rst relay, a control relay in said third branch energized in series with said first relay in case said parallel branch is open, and a circuit for the second of said plurality of relays closed by said control relay.

12. In an automatic telephone system, a plurality of link circuits, each comprising a relay type finder and a connector, marking conducv-tors, -a relay: individual to-.;each..link circuit4 Afor connecting-said marking conductors to itsinder, a common operating conductor for said individ- .ual relays, yan allotter, relays in-said allotter controlled from said connectors,circuits Whereby'one like plurality of link selectingrelays, .test con-- :duotors extendingk between the said selecting-relays and their respectively associated link circuits, means including the test conductor of .an

idle link circuit for maintainingthe correspond- .ing selecting `relay energized. a circuitprepared 20 by the energized selecting relayv forallotting-...the associated link circuit to the next call, and means responsive to the -seizure of such link circuit on the next call for successively `energizing the other selectingV relays untila-selecting relay associated with another idle link circuit isv energized.

114.2In an :automatic telephone system, eplurality of link circuits, .an allottercomprislng'a :like yplurality of linkselecting relays, vmeansfor ,maintaining a random one of said relays ener- .g'ized to assign the associated link circuit to the vnext call, and Imeans responsive to saidr callin case'the assigned link circuit is the only idle link circuit for successively energizing all said selecting relays in search of an idle linkcircuit.

15.1In lan automatic telephone system, a plurality of link circuits, an allotter comprising-a like plurality of link selecting relays, test conductors extending from said selecting relays to their respective associated link circuits, means in .each link circuit for maintaining a test potential '.onitslassociated test conductor-when theiink circuit. is'idle, Ameans responsive to -a .call for operating 4a plurality of said relays successively to pass :by busylink circuitscharacterized by the absence-'of potentials on their test conductors, theoperation continuing until a selecting relay corresponding to an idle link circuit lisv energized,

and .a -switch vindividual to each link circuit for Aopening its test conductorto make the link cir- 25 cuit busy.

BERT AfWALLACE.