US2277586A - Telephone system - Google Patents

Description

March 24, 1942. c. R. GRAY TEI/JEPHONE SYSTEM' Filed oct. 16, 1940v Patented Mar. 24, 1942 TELEBHONE SYSTEM Cecil R. Gray, Morristown, N. J., assigner to Bell Telephone Laboratories,

Incorporated; Newy York, N'. Y., a corporationof New York Application October 16, 1940, Serial.No-. 3(i-1,380

5 Claims. (Cl'. 179-18) This invention: relates'to; telephone systems and particularly tosystems comprising impulse controlled switches for; establishing connections between calling and called lines.

ItV isf an objectk of' the invention to. provide a more reliable impulse repeating arrangement and; to,l otherwise improve the impulse repeating arrangement in, branch omcef selector-repeaters.

The invention; is an improved: impulse repeatngarrangementl in a branch, ofce-selector-repeater. The impulses are received by an impulse receiving relayI which directly repeatsv these impulses; to the selector switch` ofthe selector-repeater, orY to succeeding` Selectors in the' branch office, and cont-rolsga repeatingfrelay whichtransmits corresponding*impulses-.over a trunk to the main cnice in two separatey grounded circuits, each comprising one; off the conductors of the trunk. The impulse receiving relay is adjusted for response@ to impulses received from` calling lines; andthe impulse. repeating rela-y is adjusted and has its releasing; time. controlledto;` transmit impulsesl ofJ a character-which insures satisfactory operati-on ofV impulse receiving means at the distant end; of; the; trunk, they requiredv character being dependentI upon the resistance and capacity ofthetrunkz.

A feature ofthe invention. is; an impulse repeating arrangement of; the aiorementionedcharacterfin a branch oiceZ selector-repeater in which closure of thel impulse repeatingk circuits; over the conductors of a trunk to the', main o'iee and closure of the supervisory4 bridge across the conoluctors of; the4 trunky are contrclled by a relay which is initially operated upon seizure of the l,

selector-repeaterprior.- to they receipt of a nrst train of impulses and thereafterV operated, in respense, to the rst; impulse of. each; succeeding train of impulsesl The operationl of thisA relay immediatelyV upon seizure insures against? releasing ofthe relay during receipt' of.y the -rst train ofA dialv impulses,` i

A further feature is-the: provision off an auX- iliary' relay' in a; branch; ofce; Selector-repeater of the-aforementioned characterfor controlling the connection of dial tone to, the. calling line. According to; this,` feature; one.: of thev conductors of a calling line. is; connected througha talking condenser to oneof thefconductors of a trunk to the main oilice'im-mediatelyupon seizure of the selector-repeater and selection of a, trunk to the main office, the connection between the other conductor of the calling linel and other talking condenser being; even, at, a contactl of the auxiliary relay so that; thisfcendensel: will not interferewith the transmission of dial tone to; the callingl line. When thev rst dial impulse-is received from a calling station, the; auxiliary relay operates, to terminatethe transmission of dial tone and to: connect the other conductor ofthe calling line through the other talking condenser to the other conductor of the trunk, the-connection of both, of the talking condensers between the conductors ofthe calling lineL andthe conductors of the; tru-nk to ther main oiiice being effective to prevent bell tapping at the calling station during dialingi The drawing which forms a part of this specication shows, schematically; a system and circuit arrangement ink which the invention and its features are embodied. The invention is not, however, limited in-.itsapplication to the particular system shownV in the drawing butis generally applicable to impulse? controlled switching and signaling systems.

The drawing, whichy consists of a single ligure,

represents a system comprising a branch office and a mainoce. The branch office is represented bysubscribers stationsA and B, lines Ll and L2',a liney finder LE, a selector-repeater SR, a. service codey selector SCS, and a connector BC; andthe main oice is representedk by anincoming selectorIS. I The subscribers stations are of the common battery-typeI and include dials/or other impulse senders for control-ling the automatic switches through` which connections between calling and called lines; are established. The line-finder switch LF, selector switch S; service code selector switch SCS; connector switch BC'and incoming selector switch ISareof the Well-known twomotion step-by-step type. Reference may be had to Automatic Telephony, second edition, by Smith-and Campbell, pages 53 `to 65, inclusive, for a description of the structure ofsuch switches andv their operation whenr used asv selectors and connectors. Reference may,I behad to'the'patent toyR, L. Stokely, 1,799,654 of April 7, 1931, for a descriptionof the operationr of a two-motion stepby-step finder. The line finder LF' is represented bya set of brushes and one set of terminals.; the connector BC is represented by-its. brushesv and one set of terminals;- the. selector SCS. is represented by its, line and release. relays in. addition to its. brushes 6I, 62, 634 and, 64,k andv a single set of terminals; and theA selector IS is represented by its. brushes, one set. of, terminals and its. line relay. l

'I,he;`selector-repeater4 is represented the drawing by the brushes. 6J., 62.. 6.3, and` 6,4. and

one set of terminals, the vertical stepping magnet 1I, release magnet 13, the vertical off-normal springs 14 and the 11th rotary step springs 16 of the selector S; by the brushes 91 and 38 of the trunk hunting switch TS; and by a line relay 41, release relay 42, dial tone control relay 51, impulse repeating relay 45, repeating control relay 53, switching relay 40, supervisory relay 44, and the contacts of other relays which are included in the arrangement for repeating impulses, received by the line relay 41 from a connected calling subscribers line, over a trunk to the main oflice and to succeeding selector and connector switches in the branch oiice. Reference may be had to the copending application of H. Hovland, Ser. No. 361,365, iiled on Oct. 16, 1940, for a complete disclosure of this selector-repeater together with various main and branch oilice trunking arrangements in which the selector-repeater may be used. The same reference characters are used for the various elements of the selector-repeater shown in the drawing of this .application as are used for the same elements in the aforementioned copending application of H. Hovland.

Assume now that a call is originated at station A and that the line finder LF is operated to connect the calling line L| to the selector-repeater SR in usual manner. Upon connection of line Ll to the selector-repeater SR, line relay 41 is operated in a circuit which is traced from battery through the upper Winding of relay 41, upper back contact of relay 44, a lower back contact of relay 4U, middle brush of line nder LF, through line Ll and the station A, upper brush of line finder LF, upper back contact of relay 4B, a lower back contact of relay 44, lower winding of relay 41. back contact of the 11th rotary step springs 16, a back contact of relay 43, a back contact of relay 51, and through a winding of dial tone transformer 58 to ground. At its inner lower front contact, relay 41 closes a circuit for operating relay 42 and a circuit for operating relay 53. Relay 42 connects ground to conductor 33 to hold the line finder LF. As described in the aforementioned copending application of H. Hovland, the trunk hunting switch TS is operated to select an idle trunk to the main oiiice at the same time that the line nder LF starts hunting for the calling line; and, when an idle trunk is selected, relay D is operated. When relayk 54 operates, it closes a circuit for operating the repeating relay 45 and a circuit for energizing the upper polarizing winding of relay 44. With relays 53, 50 and 45 operated, battery is connected through resistor 54, inner lower front contact of relay 53, upper front contact of relay 45, brush 91, one conductor of the selected trunk T to the main oiice, and through the right winding of line relay 233 of selector IS to ground; and ground is connected through resistor 5|, front contacts of relays 53, 45 and 50, brush 93, other conductor of trunk T, and through the left winding of relay Zilli to battery. R'elay 250 is thereby operated to prepare the selector IS for response to dial impulses. 1t is to be noted that the operation of relays 45 and 5U also connects the conductors of the trunk to the main oiiice to one side of the talking condensers 59 and 60, the other side oi' condenser El! being connected to one of the conductors of the calling line; but the connection between the other side of condenser 59 and the calling line is open at a contact of relay 51 to prevent interference with the transmission of dial tone to the calling station.

' rst impulse, magnet 1| releases.

When the calling subscriber dials the first digit of the number of xthe called subscribers station with which connection is desired, line relay 41 is alternately released and reoperated as many times as there are units in the digit dialed. The release of relay 41, at the beginning of the rst dial impulse, closes circuits, including the lower front contact of relay 42 and back contacts of relays 49 and 43, for operating the vertical stepping magnet 1| and for operating relay 51. Relay 51 closes a locking circuit to conductor 33 before it opens its operating circuit, disconnects the dial tone transformer 58 from the calling line, and closes the connection between the calling line and the talking condenser 59. The connection of condensers 59 and 60 to the calling line during the repeating of dial impulses over trunk T is eiective to aid the transmission of these impulses and is also effective to prevent bell tapping at the calling station during dialing. When relay 41 reoperates at the end of the The release and reoperation of relay 41 in response to each succeeding impulse of the train causes a corresponding operation and release of the vertical stepping magnet 1|, the brushes being thereby advanced to the level corresponding to the digit dialed. The vertical off-normal springs 14 are actuated when the shaft moves out of normal position due to the rst operation of stepping magnet 1|, the winding of relay 53 being thereby connected, through a back contact of relay 44, in parallel with the stepping magnet 1| and under the control of the back contact of relay 41 instead of in parallel with relay 42 and under the control of the front contact of relay 41. Being slow in releasing, relay 53 remains operated until after relay 41 reoperates at the end of the last impulse. Relay 42 is also slow in releasing and remains operated during dialing. The release of relay 41 in response to each dial impulse opens the operating circuit of repeating relay 45, the release of relay 45 being delayed for a desired interval of time by the charging of condenser 4B. When relay 41 reoperates at the end of each impulse, relay 45 reoperates.

The release and reoperation of relay 45, in response to each impulse, opens and closes the two ground return circuits over the conductors of trunk T to cause a corresponding release and reoperation of the line relay 20|), the brushes of selector IS being thereby advanced to a level corresponding to the digit dialed.

The selector-repeater SR. is arranged to absorb one or more digits by return of the brushes of selector S to normal after advance to a level corresponding to the digit to be absorbed, to release the trunk to the main ofce on calls to subscribers in the branch office, and to trunk hunt in a selected level either after the trunk to the main office has been released or prior to the dialing of enough digits to determine whether the called line is in the main office or in the branch office. The operation of the selector-repeater SR on various types of call and in various trunking arrangements is set forth in detail in the aforementioned copending application of H. Hovland.

If the rst digit dialed indicates that the call is for a subscriber in the main oiiice or is one which must be completed through the main oice, th'e brushes of selector S are held opposite the selected level without trunk hunting, the impulses created by the dialing of the remaining digits of the called number being repeated by relays 41 and 45 over the trunk to the main oice to .contr'ol; theswitches through whichnthezdesired connection isF completed: in this:X case; relayfiil` is operated to open theY short' circuit. around resistor 31 to prevent the further operationv of vertical stepping magnet 1I in= response to.x dial impulses.

If' the first. digiti does. notA determine that the call is to be completed over-the selected' trunk to the main. oice, the-digit' is absorbed'by a return of.- the brushesI of' selector S to normal. The brushes are-'then advanced by the impulses created' by` the dialingA of the second digitl tov aV corresponding level; and these impulses are repeated' by relay 45, in the manner hereinbefore described', over the trunkv to the mainv oce. Iithev secondi digit indicatesthaty the'` call' is for a subscriberl in the mainl oiiice, relay 431 is op'- era-ted, the selector S is notl released, and: succeeding" trains of impulses are reptated to the main office without further operation of; the vertical stepping magnet 1 I.

If the second digit indicates that the called line is in the branch oiice, relay 48 is operated to release the trunk to the mainl oice. Trunk hunting may occur in the level corresponding to the second digit or ina levelI selected inf response to thev impulses for a succeeding digit. When an idle trunk is found relays Il!)`v and 4U are operated, as described in they copending-Y application of H. Hovland. The operation'of relay 4l.' causes the release of relays 41 andV 45, and connects` the call-'ingA line through brushes 6| and 62y to the next switch in thev branch cnice;

K and the impulses created by the dialing of the remaining digits of the called subscribers num- I- ber control the switches in the branch olice through which connection with the called line is established.

If the second digit'does notV finallyv determine whether the call is a mainl ora branch oiiice call, the brushes of selector S may or may not be restored to normal to absorb this digit, depending upon the particular trunking arrangement and the value of the digit. If the second digit is absorbed, the third digit may indicate that the call is a main office call; in which case relay 43 is operated and impulses created by further dialing are repeated over the trunk to the main omce. But if the second digit is not absorbed, the brushes of selector S are advanced .f

additional digits are required to indicate whether th'e call is a main or a branch office call, the impulses created by the dialing of the third digit are repeated by relay 45 over the trunk to the main office in the manner hereinbefore described; and these impulses are also repeated by relay 41 over the trunk engaged by the brushes of selector S. This trunk may be connected to a service code selector, other branch ofce selector, or to a connector. In the drawing, the bank of selector S is represented by two sets of terminals, one set connected to a service code selector SCS and the other connected to a connector BC. Assuming the selection of a trunk leading to a service code selector SCS, the circuit for repeating the third train of impulses includes the windings of -line relay IUI, brushes 6| and 62, and front contacts of relay 41 and 49. If the third or a succeeding train of impulses finally indicates that the call is to be completed in the branch oince, relay 40 is operated in the manner Cil described; vinl the. copendngv application of H. Hovlanda to.4 connect, the; callingV line directlyv totheibrushes; 6I; and 62:.,l If, however, the thirdor a succeeding train. ofV impulses: iinally determine that thecall is to be completed overv the trunk tov themainy ofhce, relay 43t isoperated andl relay 49.- isy released', therebyv causing the release of the selector SCS; and, ify additional digits are dialed, the; impulses are repeated onlyV over the trunk to the-main oiiic'e.. f

Ona call completed by switchesrin the branch oiice, the connection is held under control of the calling subscriber by ground potential connected tothe terminal engaged by test brush 63. The disconnection of this holdingspotential when the conversation is ended causes the release of relay 4t andthe return of the selector S and line finder- LF to normal in thef manner described' inthe copendi-ngapplicationI of H.' Hovland. On a call completed over a trunk to the main oilice relays 41, 45 and' 42r are held under control of they calling subscriber, thei talking condensers 59 and G being included in the talking connection between the calling line and the trunk to the main cnice. Whenr the calling subscriber restores the station to normali,` relays 41, 45'? and' 412 re-V lease succession. eiectii-lg'the return of the. selector repeater SR and' line finder LF to normal? and' opening vthe bridge across the trunk tothe main oli-ice to effect the return ofv the switches in the main oice to normal. y

It isparticularly` to be noted that the provision of a separate repeating relay 45 for repeating impulses to the main ofli'ce permits the adjustment'of` this relay according to the length and'` character ofthe` outgoing trunks without affecting the response of the impulse receiving relay- 41 toy dial; impuls-es from the calling line.

What is claimediis:

1. In combination, a line, an impulse receiv.- ing relay connected' to" said lineand responsive to current impulses therein, a trunk line, means comprising said impulse receiving relay and an impulse repeating relay for controlling an imi. pulse repeating circuit over the trunk line, the

repeating relay being adjusted according to the resistance and capacity of the trunk line, an operating circuit for the repeating relay controlled by the impulse receiving relay, and a condenser connected to the Winding of the repeating relay so as to render said relay slow in releasing and thereby increase the length of each closure of the impulse repeating circuit during the repeating of impulses.

2. In combination, a line, an impulse receiving relay yconnected to said line and responsive'to current impulses therein, a trunk line, impulse receiving means connected t0 said line, means comprising said impulse receiving relay and an impulse repeating relay for repeating impulses in said line to said trunk line, each` of the conductors of the trunk line being included in a separate circuit for repeating the impulses t0 said impulse receiving means, the repeating relay being adjusted according to the resistance and capacity of the trunk line, an operating circuit for the repeating relay controlled by the impulse receiving relay, and a condenser connected to the winding of the repeating relay so as to render said relay slow in releasing and thereby increase the length of each closure of the impulse repeating circuit during the repeating of impulses.

3. In combination, a rst line, an impulse receiving relay connected thereto, a circuit including said line for operating said relay, a tone source included in said circuit, means for transmitting impulses in said circuit to said relay, a second line, means comprising saidV relay for repeating impulses from said first line to said second line, an auxiliary relay, a circuit for operating said auxiliary relay closed in response to the rst impulse received by said impulse receiving relay, circuit means for maintaining the operation of said auxiliary relay, a condenser, and contacts actuated by the operation of said auxiliary relay for removing said tone source from the operating circuit of the impulse receiving relay and for closing a talking connection including said condenser between said first and second lines.

4. In a branch oice selector-repeater comprising an impulse controlled group selector and a non-numerical trunk hunting switch, a line relay, an impulse repeating relay controlled by said line relay to repeat impulses in a separate grounded circuit over each conductor of a trunk selected by said non-numerical switch, a supervisory relay for connection across the conductors of a selected trunk, a slow-to-release relay having normally open contacts in said impulse repeating circuits and normally closed contacts in the connection between said supervisory relay and said conductors, means comprising a front contact of said line relay for operating said slowto-release relay prior to the receipt of dial impulses to prepare said impulse repeating circuits, means including a contact of said line relay for operating the group selector to select a group of terminals corresponding to a train of impulses incoming to said line relay, means including contacts actuated upon'movement of said selector out of normal position to transfer the control of said slow-to-release relay from the front contact to a back Contact of said line relay, whereby said slow-to-release relay is held operated until all of the impulses in the first' train incoming to said line relay have been received and is reoperated upon release of said line relay in response to the iirst impulse of each succeeding train of impulses.

5. In a branch oice selector-repeater comprising an impulse controlled group selector and a non-numerical trunk hunting switch, a line relay, an impulse repeating relay controlled by said line relay to repeat impulses in a separate grounded circuit over each conductor of a trunk selected by said non-numerical switch, a supervisory relay for connection across the conductors of a trunk selected by said non-numerical switch, a slow-to-release relay having normallyopen contacts in said impulse repeating circuits and normally closed contacts in the connection between said supervisory relay and said trunk conductors, means comprising a front contact of said line relay for operating said slow-to-release relay prior to the receipt of dial impulses to prepare said impulse repeating circuits, means including a contact of said line relay for operating said group selector to select a group of terminals corresponding to a train 0fV impulses incoming to said line relay and to select a set of terminals therein connected to an idle trunk, means comprising a contact of said line relay for repeating a train of impulses incoming to said relay after selection of an idle trunk by said group selector to said trunk, means including contacts actuated upon movement of said selector out of normal position to transfer the control of said slow-torelease relay from the front contact to a back contact of said line relay, whereby said slow-torelease relay is held operated until all of the impulses in a rst train incoming to said line relay have been received and is reoperated upon release of said line relay in response to the rst impulse of each succeeding train of impulses.

CECIL R. GRAY.

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