US2358237A

US2358237A - Telephone system

Info

Publication number: US2358237A
Application number: US469778A
Authority: US
Inventors: Benjamin F Lewis; William A Malthaner
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1942-12-22
Filing date: 1942-12-22
Publication date: 1944-09-12
Anticipated expiration: 1961-09-12

Description

Sept. 12, 1944.

B. F. I Ewls ETAI.

TELEPHONE SYSTEM Filed Dec. 22, 1942 12 Sheets-Sheet l /NL/EwmffsfsQ S'ept. 1,2, 1944. B. F. I Ewls ET Al.

TELEPHONE SYSTEM l2 Sheets-Sheet 2 Filed Dec. 22, 1942 III, ||I|I IIII Il. III llllllll .lIl

||II| I IIIIIII IIIIIIIIHH HH HH Il e f Ems www0/:5; 14./ A. MAL THA/VER y Sept. 12, 1944. B. F. I Ewls ET Al.

TELEPHONE SYSTEM Filed Dec; 22, 1942 12 Sheets-Sheet 3 F. Ew/s MUM/VER I/VVENTORS! W A Arkon/vw sept. 12, 1944.

B. F. Ll-:wls ET AL 2,358,237

TELEPHONE SYSTEM I Filed Dc. 22, 1942 12 SheefS-Sheet 4 A .stfLEW/s /NVENTO/ n/.AMALTHANER ATTORNEY Sept. 1 2, 1944. B. F. L Ewls ET Al. t .2,358,237

` TLEPHONE SYSTEM :Filed Dec. 22, 1942 12SheeLS-Sheet- 5 /NVEA/ro/es:

FIG. 5

f? EW/5 ,4.

B W. MALTHANE/P ATTORNEY Sept. 12, 1944.4

B. F. LEw|`s ETAL 2,358,237

TELEPHONE SYSTEM l Filed Dec. 22, 1942 12 sheets-sheet e Afro/MEV Sept. 12, 1944. B. F. LEWIS ET AL TELEPHONE -SYSTEM Filed Dec. 22, 1942 l2 Sheets-Sheet 7 ELEW/s www 14./ AUHANER ATTORNEY Sept. 12, 1944. B. F. LEWIS ET AL 2,358,237

A TELEPHONE SYSTEM Filed Deo. 22, 1942 12 Sheetsfsheet 8 L/NK CONNECTOR /2.

MAL'HANER BV l Sept. l2, 1944. B. F. LEwls ETA. 2,358,237

TELEPHONE SYSTEM Filed Dec. 22. 1942 12 sheets-sheet 9 TRANS/.A TOR CC 7:

y /NvE/vrO-Rs: BfLEW/S WA. THANER BV i ArToR/Ey Sept. 12,' 1944. B. F. LEwls ETAL TELEPHONE SYSTEM v12 Sheets-sheet 11 Filed D66. 22, 1942 AT TURA/EV sept. 12, 1944. a. F.' pms., TAL

Y 2,358,237 TELEPHONE sYs'rEM A ,y

12 sheets-sheath Filed Dec. 22. .1942.

/M/Nr'ons arf-.LEWIS ATTORNEY Patented Sept. 12, 1944 TELEPHONE SYSTEM Benjamin F. Lewis, Bayside, and William A. Malthaner, New York, N. Y., assignors to Bell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application December 22, 1942, Serial No. 469,778 .5 claims. (ol. 17a- 27) This invention relates to telephone systems and particularly to small capacity telephone systems of the private branch exchange type (P. B. X) in which cross bar switches are employed. More particularly, the invention is in the nature of an improvement over the small capacity telephone system disclosed inu Patent 2,300,951, issued to W. A. Malthaner on November 3, 1941, in which means are provided whereby the telephone lines or stations equipped with Ydifferent types of call sending devices may operate common apparatus by which to set up desired connections such as, for instance, between a station that utilizes a dial sender to transmit a series of impulses designating a called number and a station that utilizes an alternating current generating device to operate and -transmit combinations of different frequencies to designate the called number.

In some P. B. X exchanges of the above type in which the P. B. X subscribers are also provided with facilities for establishing direct connections to the main central ofce over trunks interconnecting the oflice and the switching element of the P. B. X, the lines privileged to establish trunk connections are provided with a key for each trunk which must be operated to connect the associated trunk with the line upon the initiation of a call. When the branch exchange contains both privileged and non-privileged lines, the non-privileged lines being restricted to local branch service only, circuit complications arise to distinguish and keep separate the two classes of lines.

According to the present invention the privileged lines are not provided with trunk keys, and a feature of 'the invention is the provision of an arrangement whereby all outgoing and incoming trunk calls clear through what may be called a control station at which the trunk keys and other necessary equipment are concentrated, all lines desiring trunk connections being required to dial or key the control station and requestl the desired connection of the attendant thereat. The control station attendant then asks the calling party to restore, dials the outside number over an available trunk and, when the wanted outside party answers, dials the number of the station originating the request. The trunk is then automatically extended back to this party without any further assistance on the part of the control` station operator. A trunk lamp associated with the engaged trunk apprises the control station operator that the call is established and the controlY operator thereupon restores his receiver to eiect a breakdown of the local connection between the control station and party originating the call. The trunkV is thereafter under the direct control of the originating party and when he restores, the trunk is restored to normal, proper signal facilities being provided to apprise the control station'operator that the trunk is then again available for service.'

A more specific feature of the invention is, therefore, a circuit arrangement in a P. B. X of the class described in which, on j an outgoing trunk connection between the control station and the trunk and the subsequent dia-ling of the calling line' by the control operator, the trunk is automatically caused to be extended 'back to said line to establish thereby a talking connection thereover.

The invention is illustrated in connection with the following drawings in which:

Fig. 1 shows two of the twenty stations in the P. B. X, station A having a line designation of 39 and provided with an alterating current or key pulsing generating device LG, land station B having a line designation 20 and provided with a dialing device LD. In the present embodiment of the invention, station B isutilized as the controlstation throughV which all outside connections to and from any other station in the P. B.'X may be established, said control station being always provided with a dialing device LD,

while thev other nineteen stations inthe P. B. X-

may be provided with either a dialing device LD or a key pulsing device LG;

Figs. 2 and 3 show diagrammati'cally a cross bar switch frame vof known construction having ten horizontal outlets and twenty verticals to each of which vertical is connected a subscribers line.' The rst vertical is designated as vertical 20 and is assigned to control station line 2li (station Bi), the last vertical is designated as vertical 39 and is assigned to line 39 (station A), while theV intermediate verticals 2| to 38 are each respectively assigned to a similarly designated line;

Fig. 4 in the left portion thereof, shows a link allotter circuit, while the rest of this gure and Fig. 5 show the call allotter circuit;

Figs. 6, '7, 8, 9 and l0 show the details of the link circuit;

Fig. 11 shows, in diagrammatic form, two other links and a power generating, tone and alarm circuit; v

Fig. 12. shows one two-way trunk in detail, said trunk interconnecting the P. B. X with the central oflice, and three other trunks, conven- A; secondly, in respect to the operations neces-, sary to set up an outside call to the central olce' from station A, and, thirdly, in respect to the operations necessary to establish an incomingr connection from the central olice` tostation A.

Before describing the detailed operation of the invention, however, it is desirable to call attention to the fact that the illustrative embodiment of the invention is being shown in connection with a small oflice having a maximum capacity of twenty'lines, each station of which, with the exception of the control station B, is equipped either with'a dialjLD or a'generator'LG for transmitting VvCH3, which form a link allotter circuit. Relays CHI and CH2 are shown in an operated position while relay CH3 is shown in an unoperated posicalled line designations, said control station B being always provided with a dial Each line appearsY on one of the twenty verticals of the cross bar switch, conventionally shown in Figs. 2 Vand 3,-and each line; for simplicity, has been given a numerical designation corresponding to the vertical torwhich it is assigned.

The-dial LD visY the ordinary impulse dial well known ,in automatic telephony, and its manipulation `interrupts 'the'line to produce a series of pulses the number of which, in Ya series, correspends Vtothe digit from nwhich the dial is pulled over to the stop attachment prior to releasing it for its return to normal, inthe course of which the train or series of impulses is produced. The deviceV LG, on thel other hand, is an alternating current generator which, for example, may be of ,the type-shown'in Patent No. 2,147,710 granted to R. F. Mallina on February 21, 1939. It comprises 'a number of reeds which may be plucked in pairs toproduce vibrations within a magnetic field and thereby cause the production of currents having frequencies determined by their respective physi- 'cal periodicities. A These currents are transmitted over the" link into registers therein for use in causinguthe link to complete the connection to the-desired line. Y

A For' the quantity of internal trafc which may arise ywithin the twenty lines of the system, only three links are provided each occupying two 'horizontal outletsof thecross bar switch,`link I (the circuit structure of which lis Yshown in detail in Figs 6 to 10, inclusive) occupying theV two uppermost outletscontrolled, for selective purposes, by select-magnets 8 andS; link 2 occupying the two horizontal outlets immediately below those of link -I and controlled by

select magnets

6 and 1, while link `3 occupies the two horizontal outlets immediately below those of link 2 and controlled by

select magnets

4 and 5. The remaining four outlets of the switch are reserved for four interolne trunks, trunk I (Fig. 12) being wired to the third horizontal outlet controllable for selective purposes by select magnet 3,

whiletrunks

2, 3 and 4 are each wired to horizontal outlets 2, I and 0, respectively. It is to be observed that the horizontal outlets for the links extend straight across the frame, thereby giving each verticalV access to eachlink. The horizontal outlets for the four trunks, on the other hand, are not continuous. The upper group of trunk conductors designated USl'and UH are connected only to the cross-point of vertical 20on the third horizontal tion. These three relays control the sequential allotment of an, available link to a calling line and 'the function of the relays CHI and CH2 in the condition shown is to route the start conductor I to the first available link in the oice. As stated before, in the present embodiment of the invention itis assumed that the quantity of traine from and between the various lines of the office, including the control station B, may be properly handled by the use of only three links so that the relays CHI, .CH2 and CH3 serve to route a calling line to one of the three links depending upon which one is free in the order of allotment. The operated condition of relay CHl indicates that the link to which it provides access is in an idle condition, the locking circuit of said relay extending from battery through the winding thereof, contacts of key 'KYL conductor 2, No. 1 back contacts of relay B of link No. 1 (Fig. 5), conductor 3, No.3 front contacts of relay CHI to ground. The locking circuit of relay CH2 which controls access to link No. 2 is traced over a path which extends from battery through its winding, contacts of key KYZ, conductor 2' in the bracket line 4, through the No. 1 back contacts of relay B in link No. 2 A(saidilink being diagrammatically indicated in Fig. 10), conductor 3 in the bracket line 4, No. 6 contacts of relay CH2 to ground.

On the other hand, the operating circuit of relay CH3 which provides access'to link No. 3, while traceable over the contacts. of its associated key KY3, conductor 2 within bracket `line 5, through the No. 1 backcontacts of relay B in link No. 3 (said'link being diagrammatically shown in Fig. l0) and conductor 3 within bracket line 5, terminates in the No. 3 normal contacts of relay CH3 and also in the No. 3 open contacts of relay CHI.v

In other words, for a calling line to have accessibility to link No. 1, relays CHI and CH2 must be operatedJ and relay CH3 must be normal. It will be shownthat, as each link is allotted in rotation, the circuits of relays CHI, CH2 and CH3 are changed to provide for the advancement of start conductor I from one link to the next in the order Vindicated by the numerical indication of each of the three links.

Bearing in mind that relays CHI, CH2 are operated and that relay CH3 is normal, it may now be assumed that a call is originated at control station B (line 20). The telephone instrument is removed from its cradle at said station and key L is operated. A circuit is now completed for relay L20 of said line which extends from battery over the upper normal contacts of the hold magnet H020 associated with vertical 20, winding of relay L20, ring conductor R, over the station loop, tip conductor T, No. l normally made contacts of relay L20 to ground on the No. 1 contacts of cut-01T relay C020. Relay L20 operates. Over its No. 1 front contacts, the'ground terminal of its circuit is switched from solid ground on the No. 1 contacts of relay C020 to ground through the secondary winding of-'transformer LBT to the primary winding of which is connected a source of distinctive tonewhich, as Will be described shortly, is transmitted to the calling line in the event that no linkis available for completing the connection. Y

Over its No. 2 and No. 3 contacts, relay L29 causes a circuit to be completed for relay LO20 of the call allotter circuit (there being one relay LO- for eachV line) and relay ST of link No. l which, since relays CHI andCHZ of the allotter are assumed to be operated and relay CH3 is assumed to be normal, is the preferred link in the order of selection. The circuit for the relays ST and L20 is traced as follows: Ground through the No. 1 contacts of relay El, winding of relay LO20, conductor 6, No. 3 contacts of relay L20, the No. 3 set of contacts closed by the telephone instrument cradle, serially through normal contacts of the trunk keys TKI, TKZ, TK3 and TKII, contacts of key L, No. 2. contacts ci relay L20, start conductor I, No. 3 contacts of relay CH2, No. 1 contacts of relay CHI, conductor 1, winding of relay ST to battery. Both relays LO20 and ST operate in this circuit. Relay LO20, upon operating, completes a circuit for relay N the path of which may be traced from ground on the No. 1 contacts of relay L029, conductor I0, No. 1 back contacts of relay M, No, 4 contacts of relay MS, winding of relay N to ground. Relay N operates and completes a circuit for relay M which extends from ground on the No. 2 contacts of relay N, No. l back contacts of relay MS, winding 01|?l relay M to vbattery. Relay M operates, opens the circuit of relay N at its No. l back contacts and causes the latter relay to release. The release of relay N opens the circuit of relay M but this relay, however, remains locked to ground on conductor I0 under the control of the No. `1 contacts of relay MS and its own No. 2 contacts. When relay MS operates as described below, relay M releases. This cycle for operating relays M and N ordinarily performs no useful function but will perform an emergency function that will be explained in due course. LO20 completes a circuit for relay E which may be traced from ground on the No. 1 contacts of relay El, No. 2 contacts of relay LO20, conductor 8, serially through the No. 1 back contacts of the individual link relays LK3, LKZ and LKI in the Y allotter, conductor 9, winding of relay E to battery. Upon operating, relay E locks to ground on the No. 1 contacts of relay LO20 and, at the same time, closes a circuit Vfor relays EI and E2 extending from ground on its contacts traced thereto from No. 1 contacts of relay LO20, No` 2 normally made contacts of VArelay MS, the Windings of relays El and E2 in parallel to battery. Relays EI and E2 operate but relay LO20, which operated from ground on the No. 1 contacts of relay El, now holds locked to battery through relay ST of the selected link, as previously traced, to conductor 6, winding of relay LO20 and its At the same time, relay- No. 1 contacts, conductor 8 as traced to conduc-,f

tor 9, contacts of relay E to ground on the No. 1 contacts of relay LO20. Hence with the operation and locking of relay LO20 individual to control station B, and with the operation of relays EI and E2, all other lines may not receive service if calls are initiated thereat during the time when station B is having a link assigned to it since, with relays EI and E2 operated, no ground is available for completing the circuit of the relays L0- of the respective calling lines.

When relay EI operates, it completes a circuit for relay MS, said circuit being traced from ground on conductor I0, No. 14 contacts of relay EI, winding of relay MS to battery. Since relay MS has slow-operating characteristics, it operates after an interval, opens thereby Fthe locking path of relay N, supplies holding ground over its No. 2 contactsior relays EI and E2 and, over its No. 3 contacts, applies ground on conductor I0 to conductor II. Ground on conductor II is used to complete the circuit or the link select magnet 9 in virtue of operations which will be shortly described and which have been taking place in the link as a result of the operation of relay ST therein.

In the event that, due to some trouble condition, relay E of the link allotter fails to operate, relay MS cannot operate and ground will not be applied to conductorv II over its No. 3 contacts. Under these cir-cumstances it is desirable, if possible,rto complete the connection and so emergency means are provided for applying ground to conductor I I when relay MS fails to operate. It will be remembered that upon the operation of relay LO20 a circuit was completed for relay N, and that prior to the operation of relay MS, relay N caused the operation of relay M. Now when relay M operates, it opens the circuit of relay N, but relay M remains naked over its No. 2 contacts to ground on conductor I0, and it will be observed that, with relay N normal and relay M operated, ground on conductor I0 is applied to conductor VII via the No. 1 front contacts of relay M and the No. 1 contacts of remy N.

Returning, now, to the operation of relay ST of allotted link No. 1, a circuit is completed for select magnet 9, the path of which may be traced from battery through the winding of said magnet, conductor I1, No. 2 contacts of relay B, No. 4 contacts ofY relay ST, conductor Il, to the afore- `traced ground thereon. Select magnet 9 operates and conditions the group of cross-points on the ninth horizontal level .for selection, including cross-point 9 on vertical 20 through which the calling loop will be extended into the link as shown hereinafter. Select magnet 9, upon operating, completes a contacts and common conductor I8.to the common windings of`relays S and SI causing said relays to operate and complete a circuit for cutoilE relay C020, the circuit of said relay being traced from ground on the No. 3 contacts of relays S and SI, No. 3 contacts of relay L029, conductor I 9, winding of relay C020 to battery. Relay C020 upon operating closes an obvious circuit for hold magnet H020 of the vertical 20 .tol which line 20 (station B) is connected and, because select magnet 9 is operated, operates cross-point 9 on Vertical 20. This cross-point 9 remains op No. 2 contacts of said relay, No. 1 contacts of recircuit from ground over its lay T2, conductor SL'No. 3 "contactsV of crosspoint 9 on vertical 20 to ground.

Furthermore, although the release of relay L020 opened the original operating circuit of cutoi relay C020, said relay now remains locked under the control of the No. 3 contacts of the station telephone instrument and the contacts of key L, said locking circuit being traced from ground on the No. 2 contacts of relayCOZIJ, No. 3 switchhook contacts, serially through the normal contacts of the tr-unk keys TKI to TK4, contacts of key L, No. 4 contacts of cross-point 9 on vertical 20, winding of relay C020 to battery. Thus relay C020 is maintained in an operated position, in turn holding operated magnet H020l which keeps cross-point 9 closed.

Since cross-point 9 is operated, the line tip and ring conductors T and R are joined to the link tip and ring conductors LT and LR, respectively, over the No. 6 and No. 5 contactsof the operated cross-point 9, respectively, and this joining of conductors completes an operating path for relay A of the link which may be traced from battery through the lowerwinding of said relay, No. 2 back contacts of relay HS, conductor LT, No. 6 contacts of cross-point 9, line conductor T, over the calling line loop, line conductor R, No. 15 contacts of cross-point 9, conductorLR ofthe link, No. 3 back contacts of relay HS, upper winding of relay A to ground. Relay AV operates andY completes a circuit for relay .B which extends from ground on conductor SI, front contacts of relay A, No. 4 normally made continuity contacts of relay B, winding of relay B to` battery. Relay B operates and locks over its No. 4 front contacts to ground on conductor SI. Relay B, at its No. 2 contacts, opens conductor I'I thereby causing the release of the select magnet 9. However, since the hold magnet H023 is operated, cross-point 9 on vertical 23 remains closed. Relay B further completes a circuit from ground over its No. 8 contacts to a relay (not shown) in the power charge circuit IIJII by means of which, when the relay is operated, circuits are closed thereby that will increase the charging rate to the link power supply during the time that the link is being used and, over its No. and No. 6 contacts, connects ground to holding conductors 20 and 2I for holding and operating certain other relays as noted below. Over its No. 1 contacts, relay B opens the locking circuit of relay yCHI in the allotter circuit which, upon releasing, advances the common start conductor I over the No. 3 contacts of relay CH2, No. 2 contacts of relay CHI, No. 1 contacts of relay CH2 to conductor 'I' which further extends to relay ST of link No. 2.

It is now evident that if, at the time the call was initiated at station B, `link No. 1 is busy or otherwise unavailable, relay CHI individual to the link in the link allotter circuit would have been normal, and the start wire I with ground applied thereto would have been joined to conductor 'I' of link No. 2 to cause the operation therein of relay ST inthe same manner as that of relay ST in link No. 1 as already described. 0n the other hand, if both links No. 1 and No. 2 are busy or otherwise unavailable, relay CH2, as well as relay CHI, would be normal since their respective locking circuits would be opened at the No. 1 contacts of relay B of their respective links. However, as soon as relays CHI and CH2 are both normal, a circuit is completed for relay CH3 which extends from battery through its winding, contacts of key KY3, conductor 2", No. 1 con- -tacts of relay B of link No.3, conductor' 3', to

ground over the No. 1 normally made contacts of relay CHI. lRelay CH3 operates and, with relays CHI and CH2 normal, indicates that links No. 1 and No. 2 are unavailable but that link No. 3 is. If a call is now initiated at a line station as, for example, station B, ground on start conductor I is extended to conductor 'I" which is connected to the winding of relay ST of link No. 3, the path being from ground on conductor I, No. 4 contacts of relay CH2, No. 2` contacts of relay CH3, conductor 1", to the winding of relay ST of said link causing its operation and the connection of link No. 3 tothe calling line.

If all three links are unavailable,.relay CH3 will be normal as well as relays CHI andVCHZ. Under these circumstances, the initiation of a call will cause ground on the start conductor I to be applied to conductor 22 via the No. 4 contacts of relay CH2, No. 1 contacts of relay CH3, No. 2 contacts of relay CHI, No. 2 contacts of relay CH2, 4to conductor 22. This conductor extends (through bracket line I3) to the power, tone and alarm circuit III) and closes a circuit therein which causes a distinct link busy tone to be applied to the

conductors

23 and 24 extending to the primary winding of the link busy tone transformer LBT. Since the secondary winding of this transformer is connected to ground and is completed into a circuit over the line loop to battery through the upper normally made contacts of the hold magnet HO- and through the winding of the line relay the subscriber at the calling station will hear the tone as an indication that, due to unavailable links, the connection cannot be established. I

As soon as a link becomes available, say link No. l, then a circuit is completed for relay CHI which extends from battery through its winding, thence as traced to conductor 3, No. 5 contacts of relay CH2 to ground; Relay CI-II operates and locks to ground over its No. '3 contacts to reestablish the path of start conductor I to the winding of relay ST in readiness for seizure on the next call. If link No. 2 becomes available, relay CH2 operates over a circuit traceable from battery through its winding, thence as traced to conductor 3 to ground on the No. 3 normally made contacts of relay CH3.

Returning, now, to the operation of relay ST of link No. 1 assumed to have been taken into use, ground on the No. 3 contacts of said relay completes a circuit for relay LS! of its private link connector and this circuit is traced from ground on said contacts, conductor 58, winding of relay LSI, serially through the No. 2 normally made continuity contacts of relays LS2 and LS3 (the former being individual to link No. 2 and the latter to link No. 3) to battery. Relay LSI operates, connects operating battery to its winding through its own No. 2 front contacts and, over its No. 1 front contacts, completes an obvious circuit for cut-in relay LCI which operates in consequence thereof.

The object in operating relays LSI and LCI at this time is to connect the common alternating current pulse receiver and translator shown in Figs. 10 and 9, respectively, to the link taken into use and, when the former circuit is so connected to the latter, the signal for the consummation of the connection being the operation of relay LSI, said receiver must be made unavailable to other links. This is done by removing the operating ground for relays LCZ and LC3 at the No. 1 back contacts of relay LSI so that if either relay LS2 or LS3 should have its operating circuit established by relay ST of its correlated link, the circuit of relay LC2 or LC3 will be cut off at the'No. 1 back contacts .of relay LSI.` On the other hand, if the rst calling link happens to be either link No. 2 or link No. 3, then the corresponding operation of either relay LS2 or LS3 will cut oi the operating circuit of relay LSI at its respective No. 2 normally made continuity contacts. Under these conditions, if link No. 1 is seized in the meanwhile, the failure of relay LSI to operate .will prevent the operation of relay LCI and thereby prevent the simultaneous .connection of the common alternating current receiver and translator to two calling links.

The alternatingcurrent,receiver of Fig. is adapted to receive alternating current impulses from a calling stationV equipped with an alternating current generating device such as, for example, the device LG at station A (line 39).- Since the P. B..X exchange will contain tele phone stations equipped with either a, device LG, as at station A, for producing alternating frequency pulses designating the wanted line, or with the usual dial LD, as at station B, for producing a series of direct current pulses indicative of the Wanted line, the link must be equipped to serve both types of stations although at the time it is connectedto a, calling line the seized link has no way of telling which type of station is making the call. Hence the link must be prepared, initially, to receive either direct current pulses from aV dial LD or alternating current pulses from a generating device LG. Since the link itself is normally arranged with a register to receive direct current pulses, as will be shown shortly, the alternating current receiver common to all links must be connected to a .calling linkV before the calling subscriber can be advised, by an appropriate Warning tone, to transmit the called line designation. Accordingly, when relay LCI operates, a circuit is completed for relay GR in the translator which extends from ground 'on conductor ZI, No. l1 back contacts ofrelay C, conductor '15, No. Ll. contacts of relay LCI, cnductor l, winding wof relay GR to battery. Relay GR operates and disconnects ground from conductors 'H and '.FQ'WhiCh, as will be shown, areV connected to the callingloop by the operation of relay ON. lA circuit is also completed for relay ON .which may be traced from ground on the No. 5 contacts of relay LCI, conductorll, winding of relay ON to battery. Relay ONYoperates and, over its No. `1 contacts, closes through a circuit for a low frequency tone derived from thetone oscillator 'I0 through adjustable resistance pad 62 and transformer 6I. The path of` this circuit is traced as follows: From the lower terminal of the secondary winding oi transformer 3|, conductor I4, No. 1 contacts of relay ST, conductor I5, No. 6 contacts of relay LCI, conductor IB, No. 3 contacts of relay RR, No. 2 contacts of relay RA, No. 1 contacts oi relay ON, conductor I2, through' the low-pass filter 33 to the upper Aterminal of the secondary winding of transformer 6I. The tone frequencies produced by Vthe oscillator 'I0 are thus induced over the secondarycircuit above traced.

Through a transformer arrangement (not shown) in the low-pass filter 63, the low frequencies are induced inthe closed circuit comprising the transformer`68,`a transformer in said low-pass lter and, a transformer in high-passY filterSfI. Beyond thelsecon'dary winding of the transformer 'in the`lter 64 'ar S able filter networks which are designed to pass only frequencies within the signal frequency band of the Vfrequencies that are produced by 'the station generator LG when the same is operated. Hence the tone frequencies produced by oscillator "I0 will notV pass into the volume limiter Q35 or into the enabler 80. They will, however, be induced into the secondary winding of transformer vElisir said secondary winding is closed into an electrical system, which it isbecause conductors lI and 'I2 are but extensions of the line conductors Tand R into the link and the alternating current receiver connected thereto. The path is traced as follows: From the left side of the secondary winding of transformer 68, conductor ll, No. 2 contacts of relay ON, conductor l, No. 7 front contacts of relay LCI, conductor 5ft, condenser C2, No. 2 back contactsoi relay HS, conductor LT, No. 6 contacts of cross-point 9 on vertical 20, conductor T, over` the loop of station B, con- .ductor R, No. 5 contacts of cross-point 9 on vertical 2), conductor LR, No. 3 back contacts of relay HS, condenser C3, conductor 55, No. 8 front contacts of relay LCI, conductor lil, No. 5 contacts of relay ON, conductor 'I2 to the right terminal of the secondary winding of transformer G8. Inasmuch as the receiver of the telephone instrument of station B is included in the above closed circuit, vthe tone-induced thereover is heard by the attendant at station B, which he understands as a signal to proceed with dialing the wanted number.

The control station attendant, upon receiving a tone, operates the dial LD to transmit the called line designation. In the present embodiment of the invention, it is assumed, as said before, that the capacity of the office isy twenty lines and that the numerical designation of each of said lines extends from 20 to 39, inclusive, it being further assumed that the control `'station B has a

numerical vdesignationof

2,3 and that station Ahas a numerical designation of 39, the intermediate stations, equipped either with the dial LD or the device LG, bearing the numbersY Y 2| to 38, inclusive. The calling subscriber there- Y fore dials a wanted designation by dialing two digits, the rst of which may be a 2. or a 3 and the second of which may be any digit from 0 to 9.

Since it has been assumed that control station B is to be connected to the called line A, the attendant at station B will rst'operate his dial to transmit three pulses forthe tens digit and thereafter nine pulses for the units. digit.

Asis well known, the operation of the dialLD makes and Ibreaks the ,calling line .loop as many times as required .to produce the impulses called for. by the digits. Hence, upon dialing the digit 3, three impulses are produced andv the same will cause three successive releases of relay A. When relay A releases on the first pulse it completes a circuit for relay PI which extends from `ground on conductor SI, the back contactsv of relay A, No. 3 contacts of relay B, No. 2 contacts of relay E, biackcontactslof relay P2, No. 2 back contacts of relay P3, winding of. relayjPIjto bata tery. Through the No. l back contacts of relay P3, the circuit further extends'to the Winding of slow-release relay C. Both Yrelays PI and C oper-- ate and short-circuit the lower winding of relay P2, ground to one side of this winding beingsupplied over the No. 2 contacts of. relaysC .and

ground on the other side being supplied overthe No. 1Y contacts of relay PI to the Ybackcontacts Y of relay A. With the operation ofj'r'e'lay'PI, a

e Connected suitcirfcuitis completed for relay SW .which extends from battery through its upper winding and the No, 2 normally made contacts, No. 5 back contacts of relay T2, No. 2 front contacts of relay PI, conductor 23, No. contacts of relay RT, conductor 24, No. 1 front contacts of relay C to lground on conductor 2 I. Relay SW operates and locks over its upper winding and No. 2 front contacts to ground on the No. 1 front contacts of relay/C. When relay A operates at the termination of the rst pulse, the short-circuit around the lower winding of relay P2 is removed and this -relay operates in series with relay PI over a circuit path which may be traced from ground on the No. 2 contacts of relay C, lower winding of relay P2, No. 1 contacts of relay PI, No. 2 contacts of relay P3, winding of relay PI to battery. Hence, after the rst pulse is terminated, relays PI, P2 and SW are operated, the latter being locked," as said before, to ground on conductor 2I through the No. 1 front contacts of relay C which, being slow releasing, ,remains in an operated condition between pulses.

On the beginning of the second pulse, relay A releases again and completes' a circuit path for Vrelay P3 which extends from ground on the back contacts of relay A, No. 3 contacts of relay B, No. 2 contacts of relay E, front contacts and upper winding of relay P2, winding of relay P3 to battery. vRelay P3' operates and releases relay'PI subsequent to which a circuit is completed for relay T2 which extends from battery through the upper winding of said relay and its No. 3 normally made contacts, No. 4 front contacts of relay SW, No. 2 back contacts of relay PI, conductor `23, and thence, as previously traced, to ground on the No. 1 front contacts of relay C. Relay T2 operates, locks over both of its windings in series through its No. 3 front contacts, conductor 28, No.5 contacts of relay HS, conductor 20 to ground on the No. 5 contacts of relay B and opens the locking circuitv of relay ST which releases. The release of relay ST at this time, however, results in no other function.

At the termination of the second pulse, relay A reoperates and relays P2 and P3 release so that,

l at the termination of the second pulse, relays PI,

P2 and P3 are normal, relay C is in an operated position due to its slow-releasing characteristics, while relays SW and T2 are' locked. l

At the beginning of the thirdpulse, the release of relay A again causes the operation of relay PI vand relay P2 is again short-*circuited but, in this case, a circuit is also completed for relay T3 which extends from battery through its upper Winding and No. 2 normally made continuity contacts, No. 1 contacts of relay DC, No. 5 front contacts of relay SW, No. 5 front contacts o f relay T2, No. 2 `front contacts of relay PI, conductor 23, and thence, as already traced, to ground on the'No. 1 front contacts of relay C. Relay T3 operates and, through its No. 2 front contacts, locks serially over both windings tov previously traced ground on conductor 28 from 'the No. 5 contacts of relay B. At the end ofthe pulse, relay A reoperates and relay P2 operates in series with relay PI, as previously described. However, since this is the third and last pulse ofthe tens digit, there will be a relatively long interval before the transmission of the first pulse of the units digit, an interval which is sufcient to cause the release of relay C, followed by the release of relay SWand the release of relays PI and P2 which hold to ground over the No. 2 contacts of relay C. Y

'1t win be observed that the dialing cf the-numeral 3 as the tens digit of the called number has resulted in the operation and locking of relays T2 and T3. If they tens digit had been a 2 instead of-a 3, the result would have been the operation and locking of relay T2 only. No provision has been made in the link for registering any tensdigit other than a 2 or a 3` since the capacity of the exchange is assumed to be limited to twenty lines each having a numerical designation from 20 to 39. However, it is evident that if other numerical designations were to be used, or if the capacity of the exchange were to be increased to include more thanvtwenty lines,A the link circuit could easily be changed by any one skilled in the art to cause the registration therein of any or all other values of the tens digit.

Prior to the dialing of the second or units digit, relay A is operatedV and relays PI, P2 and P3 are normal. Upon theiirst interruption of the line loop for the series of pulses of the second or units digit, relay A will release followed by the operation of relays PI and C as previously described, while a circuit is now completed for relay CI-which extends from battery through resistance RS, the Winding of said relay, No. 4 normally made continuity contacts thereof, conductor 25, No. 10 backV contacts of relay RT, conductor 26, No. 4 contacts of relay T2, No. 1 contacts of relay SW, conductor 24, to ground on the No. 1 front contacts of relay C. Relay Cl Voperates in this circuit and locks over its No 4 front contacts, No. 5 contacts of relay HS to ground on conductor 20; AV circuit is now Y completed for relay CX, which extends from battery, resistance CR, the winding of said relay and 'its No. 3 normally made continuity contacts, No. 5 front contacts of relay CI, to ground on the No. 5 contacts of relay B. Relay CX operates, locks to operating ground over its No. 3 front contacts and, at its No. 1 contacts, opens Y the circuit of relay LSI which releases to release lbaclrcontacts of relay SW, No. 5front contacts 'of-relay T2; No.2 front contacts of relayPI and thence as traced to ground on the No. 1 front contacts of relay C; Relay I operates and locks with both of its windings in series through its No. 5 front contacts, serially through the No. 4 continuity contacts of relay II, No. 5 continuity contacts Aof relay III, No. 4 continuity contacts Vof relay IV, No. 5 Ycontinuitycontacts of relay V, conductor 28, No.r 5 contacts of relay HS to ground on conductor 20,y Upon the termination of the pulse, relayA reoperates and relay P2 is operated serially with relayiPI.

On the secondpulse, relay Areleases, relay P3Aoperates in series with relay P2 in consequence thereof, while relay PI releases as previously described., A circuit is vnow completed for relay II extending fromv battery through its upper winding, No. 4 contacts of relayI, conductor 29, No. fijlback contacts o f relay SWT-,Nd 2 back t contacts ofrrelayPI to, ground, as Y previously vtraced'tothe No. 2' front contacts of relay C.

a previously traced ground through the continuity contacts of relays III, IV and V. On the break of its own No. 4 continuity contacts, relay II releases relay I which thereby restores to normal. At the termination of the second pulse,

relay A reoperates and relays P2 and P3 releaseI as previously described.

At the beginning of the third pulse, relay PI reoperates and a circuit is completed for relay lII which extends from battery through its upper winding, No. 3 front contacts of relay II, No. 4 contacts of relay V, No. 3 contacts of relay IV, conductor 21, No. 5 back contacts of relay SW, No. 5 front contacts of relay T2, No. 2 front contacts of relay P I, conductor 23 to ground as previously traced. Relay III operates on its upper winding, locks serially with its lower winding and No. 5 front contacts to a previously traced ground through the No. 4 and No. 5 continuity contacts of relays IV and V, respectively, while, upon the break of its own No. 5 continuity contacts, it releases relay II which thereby restores to normal.

On the fourth pulse, relay PI will be in a nonoperated position and, therefore, a circuit will be closed for relay IV which extends from battery through its upper winding, No. 4 contacts of relay HI, conductor 29, No. 4 back contacts of relay SW, No. 2 back contacts of relay PI to ground as previously. traced. Relay IV operates on its upper winding and then locks in series with its lower winding and No. 4 front contacts, through the No. 5 continuity contacts of relay V, to ground as previously traced. Upon the break of its No. 4 continuity contacts, relay IlI releases and restores to normal.

On the fth pulse, relay PI will loe Operated and a circuit will be closed for/relay V which extends from battery through its upper Winding, No. 3 front contacts of relay IV, conductor 21, No. 5 back contacts of relay SW, No. 5 front contacts of relay T2, No. 2 front contacts of relay Pl to ground. Relay V operates on its upper winding and locks in series with its lower winding through the No. 3 contacts of relay I, its own No. 5 front contacts to ground as previously traced on the No. 1 front contacts of relay C. When it breaks its own No. 5 continuity contacts it releases relay IV which thereby restores to normal.

On the sixth pulse, relay PI will be in a nonoperated position whereupon a circuit will be completed for relay VI which extends from battery through its upper Winding and No. 5 continuity contacts, No. 1 contacts of relay V, conductor 2S, No. 4 back contacts of relay SW, No. 2 back contacts of relay Pl to ground. Relay.VI `operates on its upper winding and locks serially through its lower winding and No. 5 front contacts to ground as previously traced on conductor 28. Relay V, however, will remain locked since its own locking circuit is independent of the operated condition of relay VI.

On the seventh pulse, relay Pl will be in an operated position whereupon the previously traced circuit for relay I will be established and relay I will operate in said circuit, locking thereafter in series with its lower winding and No. 5 contacts and through the previously identified contacts of relays II, III and IV,Y and the No. 1 contacts of relay VI to ground on conductor 28. Relay V is released upon the operation of relay I.

On the eighth pulse, relay PI will be unoperated and a previously traced circuit for relay l1 will be established, which relay, upon operating,

eration of relay II, the locking circuit of relay I is opened at the No. 4 continuity contacts of relay II and relay I thereby restores to normal.

Relay VI remains locked toV ground on conductor 28.

On the ninth pulse, relay Pl will be operated and a previously traced circuit for relay III is established causing said relay to operate on its upper winding and then lock in series with its lower winding and No. 5 contacts, No. 4 continuity contacts of relay IV, No. 5 contacts of relayV to ground on conductor 28. Upon the operation of relay III, relay II restores. locked to ground on conductor 28.

On the last or zero pulse, relay Pl will be normal and a previously traced circuitI will be established for relay IV which operates thereover on its upper winding and then locks serially through its lower winding and No. 4 continuity contacts, No. 5 continuity contacts of relay V, to ground on conductor 28.

On the last or zero pulse, relay Pl will be nor? may and a previously traced circuit will be established for relay IV which operates thereover on its upper winding and then locks serially through its lower winding and No. 4 continuity contacts, No. 5 continuity contacts of relay V, to ground on conductor 28. Relay VI is still locked to ground on conductor 28.

Thus the pulses of the second or units digitare registered in the relays I-VI .of Fig'. '1, the relay, or relays, operated depending upon the number of pulses received. The relationship between the number of pulses and the relays operated to correspond thereto is shown in the following table:

Relay op- I tt.

It has been assumed that the called subscribers number is 39 and therefore in respect to the units digit, relays III and VI will have been operated.

At the end of the last pulse of the second digit with relay A reoperated, relay C will release and a circuit is then closed for relay DC which eX- tends from battery through its lower winding and No. 5 continuity contacts, conductor 39, No.2 contacts of relay Cl, conductor 15, No. 1 back contacts of relay C to ground on conductor 2l. RelayDC operates on its lower winding and locks through its No. 5 front contacts in series with its upper Winding to ground as previously traced on conductor 28. Relay DC, upon operating, completes a path for relay SW extending from bat-V tery through its upper and lower windings in series, No. 2 front contacts of relay DC to ground on conductor 28. Relay DC also connects batterythrough the lower winding of relay BY to a conductor which, depending upon the numerical register relays in Fig. '1 which have been operated in response to the units digit, extends to an armature of the hold magnet of the vertical associated with the called line which, in this case,

Relay VI remains will be hold magnet HO39. This path istraced as follows: Battery through the lower winding of relay BY, No. 4 continuity contacts of said relay, No. 1 front contacts of relay CI, No, 4 contacts of relay DC, No. 1 front contacts of relay T3,v

conductor 3D, No. 4 front contacts of relay VI, conductor 3|, No. 6 contacts of relay DC, conductor 32, No. 6 contacts of relay llL'conductor 33, lower armature and contact of hold magnet H039 to the winding of relay C039. The object of this circuit is to test for the idle or busy condition of the called line. Should this line be busy, hold magnet H039 will be operated, whereupon it will apply ground to conductor 33 through its lower front contacts and causethereby the operation of relay BY which then locks through its No. 4 front contacts serially through its upper winding, No, 5 contacts of relay HS to ground on conductor 29. Relay BY applies ground through its No. 1 contacts to conductor 34 extending to the power, tone and alarm circuit |I whereby circuits are closed therein to apply a busy tone source tovconductor 35. This conductor extends over the No. 2 contacts of relay BY to one side of condenser C2 through which the tone current passes over the No. 2 back contacts of relay HS, conductor LT, over the loop previously traced to conductor LR, No. 3 back contacts of relay HS, upper winding of relay A to ground. The busy tone thus furnished the calling station 20 indicates to the attendant thereat that the called line is busy, whereupon he Yrestores the telephone instrument upon the cradle and thereby opens the circuit of relay A, the release of which initiates the restoration of the apparatus as dey scribed hereinafter.

Assuming, ho-wever, that the` called lineis not busy, then hold magnet H039 willA loe normal and relay BY will not be caused to operate. In this case a circuit is closed for relay LKI of the link in the call allotter, whichY circuit extends from battery through the winding of said relay, conductor 33, No. 3 contacts of relay BY, No. 3 contacts of relay SW, No. 3 contacts of relay CI, conductor 3l to ground on the No. 11 contactsof relay EI. Relay LKI operates, completes a cir-V cuit for relay BI in the call allotter, Ywhich circuit extends from battery through the winding of relay Bi, conductor 38, No. contactsofrelay LKI, conductor 39, No. 2 contacts ofY relay CI, conductor '15, No. l back contacts of relay C to ground on conductor 2l, and: opens the serial locking path oi. all relays LO- which, should any of them operate in response to the initiation of a call during the time that a link is setting up the terminating end of a connection,V will be prevented from locking at the time relays EI and E2 operate in the manner previously described; The failure of a relay LO- to lock will then prevent ground from being` applied to conductor lI over the contacts of relay MS. In this manner, a line which calls during the setting up of a connection will be preventedfrom. interfering and, of course, willA also be denied service until the previous connection has been set up; Relay LKI also completes a circuit for relay EA of the call allotter which traces from battery through its winding, conductor 9, No. 1 front contacts of relayLKi, conductor 3l, to ground on the No. 1l contacts of relay El. Relay lil'` now operates relays El, E2 and MS as previously describedA and, when relay MS operatesa circuit iscompleted` for select magnet 3 which extends from battery through theV winding of said magnet, backy contacts of relay TKLI, conductor 49NQQ6 contacts of relay LKI conductor 4|, No. 1 contacts of relay BI, conductor Il, No. 3 contacts of relay MS, conductor I9, toV ground on the No. 3 contacts of relay LKI. Select magnet 8 operates, conditions the horizontal cross-points on the eighth level for selection. and completes a circuit from ground through the contacts of said magnet, conductor la, windings of relays S and SI in parallel, to battery, causing said relays to operate. The operation of relay S connects ground through its No. 2 contacts, conductor 42, the No. 4 contacts of relay LKI, conductor 43 to the common terminal of resistance RS and the winding of relay CI causing the release of the latter. Upon the release of relay CI, ground is applied to conductor 33 which, as previously traced, is connected to the Winding of relay C039 of the called line A. Relay C039 operates and completes an obvious circuit for. hold magnet H039 which operates toY close cross-point 8 on Vertical 39. The operation of the hold magnet H039 disconnects operating ground for relay-C039, but this relay now holds over the No. 4 contacts of cross-point 8 of vertical 3.9, conductor S, No. 3 `back contacts of relayV E, No. 7 contacts of relay B, front contacts of relay A (which is lbeing held over the calling line loop from station B) to ground on conductor Si as previously traced thereto. Operated cross-points 8 and 9 on verticals 39 and 2D, respectively, eiect therconnection between the calling contro-l station B and the called station A.

Ground on conductor S2 applied thereto by the closure of the No. 3 contacts of cross-point 8 on vertical 39 completes a circuit for relay SP, the path of which may be traced from ground on said conductor, No. 2 front contacts of relay T2, No. contacts of relay BY, winding of relay SP to orattery. Relay SP operates and connects ringing current applied' to conductor 41 within the bracket line I3 from the power and ringing circuit IID, through the No. 3 contacts of relay RTR and lower winding thereof, No. 3 front contacts of relay SP., conductor 48, No. 5 contact of crossfpoint 8 of vertical 39, ring conductor RI of; the called station A, over the loop of said station, tip conductor TI, No. 6 contacts of said cross-point 8, conductor 49No. 2 front contacts vofVV relay SP, conductor 5i] within the bracket line I3 to ground applied thereto in the power and ringing circuit IIIl. Ringing current is thus applied to the called subscribers line and an audible ringing tone is provided for the calling station, the circuit of saidtone extending from one side. of -ringing tone circuit (not shown) in the power and` ringing circuit III), conductor III within bracket line I3, No. 5- contacts of relay SP, condenser C6, condenser C2, and-thence as traced over the calling loop to ground through the upper winding of relay A. 'The control operator at station B thus hears the ringing tone. When the call is answered, relay RTR operates and locks over its upper winding and No. 2 contacts to ground on the No. 4 front contacts of relay SP, and furtherv completes a circuit for relay HS which extends from battery through its winding,

conductor 5I, contacts VI and 2 in cross-point 8 e of vertical- 39, Vconductor 52,l No. 1 contacts of relay RTR to ground on conductor 2 I. Relay HS operates and, by-opening its No. 5 contacts, disconnects the ground `Which holdsrelays SW, T2, T3, DC and the register relays III and VI operated. The release of relay T2 releases relay SP which, in turn, releases relay R'IR'andl connects the supervisory relay E to the called line.` The circuit of relay E is follows: Batteryfthrough