US2152769A

US2152769A - Telephone system

Info

Publication number: US2152769A
Application number: US165607A
Authority: US
Inventors: Neal D Newby
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1937-09-25
Filing date: 1937-09-25
Publication date: 1939-04-04
Anticipated expiration: 1956-04-04

Description

April 4,1939- k 'N. D. NEWBY 2,152,769

TELEPHONE SYSTEM "Filed Sept. 25, 1957 v 5 Sheets-Sheet 1 INVENTOR N. D. NEWBY A TTORNEV April 4, 1939. N. D. NEWBY 2,152,769

' TELEPHONE SYSTEM Q Filed Sept. 25, 1937 5 Sheets-Sheet 2 FIG. 2

7'0 NEX T l. INK

INVENTOR' MDnNEWBY,

I ATTORNEY April 4, 1939.

N. D. NEWBY TELEPHONE SYSTEM Filed Sept. 25, 1957 5 Sheets-Sheet 4 N. D. NEWBY ATTORNEY April 1939- I N. p. NEWBY 2,152,769

" TELEPHONE SYSTEM Filed Sept. 25, 1957 5 Sheets-Sheet 5 ATTOkA/EP Patented Apr. 4, I939 UNITED STATES PATENT OFFICE Telephone Laboratories, Incorporated,

New

York, N. Y., a corporation of New York Application September 25, 1937,Serial No. 165,607

11 Claims.

This invention relates to automatic telephone systems and particularly to communication facilities furnished by small community dial oflices at which a plurality of party telephone lines terminate.

It is the object of this invention to simplify and improve the facilities of such ofifices and to facilitate the extension of connections between lines terminating thereat as well as between stations of the same line.

The invention is embodied in an organization of circuits and apparatus comprising a plurality of link circuits, each of which is accessible to any station on any of the party lines terminating at the central office, for the purpose of extending connections between calling and called lines and also between calling and called stations of the same line, and a selector switch, individual to each link, having certain terminals of a single bank of terminals allotted to the line circuits and which is controlled by the calling dial at the subscribers stations.

In accordance with a feature of the invention, a single relay per line per link is used to perform the combined functions of the line, cut-off and cut-through relays heretofore relied upon in the establishment of automatic telephone connections. This relay, as a line relay, is normally connected to the line circuit and responds to receiver switchhoo-k operations when a call is initiated; as a cut-off relay it cuts off the line circuit from the normal battery supply and associates it with the battery supply normally associated with the windings of the link calling supervisory relay and as a cut-through relay it operates on an incoming call to cut the link circuit through to the called line circuit.

Another feature of the invention resides in the use of a calling supervisory relay in the calling end of a link circuit which follows the interruptions of the dialing mechanism at a subscribers station and controls the operation of a pulsing relay accordingly, and in the provision of means for transferring the calling supervisory relay from the calling end of the link circuit to the answering end thereof on revertive calls, for the purpose of permitting ringing code impulses to be sent out over the calling line with which the called station is associated.

A further feature of the invention resides in the use of a timing relay in the link circuit which is controlled by the answering supervisory relay and functions, when a called party, on a nonrevertive call, delays answering an incoming call for a predetermined interval of time, to release the link circuit and place the call on a revertive basis. This feature renders it impossible for a link circuit to be unnecessarily tied up for too long a period of time and places a busy condition on the calling line.

A still further feature of the invention resides in the interposition of a relay chain circuit intermediate the link pulsing relay and a stepping magnet controlling the selector switch which serves to convert each combined open and closure of the line circuit effected by the actuation of the dial at a subscribers station into a single controlling impulse. This halving of the transmitted pulses permits the use of all terminals on the selector switch, instead of alternate ones, for the line terminals and precludes the necessity for a special dial for controlling the stepping magnet.

These and other features of the invention will be readily understood from the following detailed description made with reference to the accompanying drawings, in which:

- Figs. 1 and 2 placed side by side, with Fig. l to the left of Fig. 2, illustrate three groups of subscribers stations and a line circuit per group, each line having access to each of a plurality of link circuits;

Figs. 3 and 4 each illustrates a link circuit and associated selector switch which are utilized to extend connections between the line circuits shown in Figs. 1 and 2;

Fig. 5 shows the code ringing circuit which controls the application of ringing current to a called line. A single code ringing circuit serves an oflice, and

Fig. 6 illustrates the manner in which the several figures are to be associated to effect a complete system. 1

It is believed that, the invention will be best understood from a detailed description of the operation of the system disclosed and to this end the following description is directed to the operations effected'when the subscriber at station D on line A initiates a call to the subscriber at station F on line B and the link allotter circuit has marked link L as the next link to receive a call.

The link allotter circuit comprises relays Sol, 602 and 603. Relays fifll and 602 each serve a pair of linlis, relay 601 serving links L and L which are illustrated in full, and relay 602 serving two other links one of which is represented diagrammatically by the block identified as L. Relay 603 allots calls to the pairs of links alternately if calls are being handled one at a time. These relays are of the polarized type and are adjusted so that the armatures will remain on the contact when the relays are deenergized. This feature allows a circuit design which draws no current from idle links. The windings of the relays are poled so that current flowing from grounded battery through the left-hand winding of a relay to ground causes the armature to close the lower contact. While current is flowing through both windings the position of the armature is indeterminate. When only one call at a time is in progress the links are assigned in rotation. This feature insures the calling subscriber of getting a working link on the second attempt if the first link seized should be inoperative due to a trouble condition.

The allotter circuit illustrated will serve four links. If current is flowing through the righthand winding of relay 603 to two links (assuming links L and L to be busy) and to only one link through the left-hand winding, the armature is moved to the lower contact. If all four links are busy the position of the armatures is indeterminate but no error in assignment results due to no ground being supplied to the armature of relay 603 from the lead 604 which is common to all four links. When one link of each pair is busy the positions of the armature of relay $03 is also indeterminate but no error results due to there being an idle link available for either the upper or lower contact.

In the following description it has been assumed that the link allotter circuit has marked link L as the next link to receive a call. 7

The subscriber at station D removes the receiver from its switchhook whereupon line relay 9 which is individual to the line A and link L operates its preliminary contact in a circuit. extending from grounded battery 5 associated with the all links busy circuit shown in the upper half oftheblock L in Fig. 4 which diagrammatically rep-resents another link circuit, conductor 6, back contacts'and second lowerarmatures of relays 4', 8, 9, and I I, through the closed subscribers line loop at station D, upper armature and back contact of relay H1, first upper armature and back contact of relay 9, corresponding armatures and back contacts of relays 8 and 4, conductor 2, upper winding of relay 9, link allotter lead I3, conductor 605, upper contacts and armatures of relays Bill and 603, conductor Gil i, conductor l5, back contactand inner left-hand armature of relay 16 to ground.

- Relays 9, 8 and l are of the well-known type which operate a preliminary contact (first lower make contact) on a small operating current. The closure of this preliminary contact then supplies suflicient power to the relay windings to operate the entire spring pile-up. v

Relay 9 operates its preliminary contact in this circuit and then completely operates and holds operated in a circuit extending from grounded battery, lower winding and first lower armature and front contact of relay 9, hold conductor [8, normal. make-befo're-break contacts of relay-l6, conductor l9, through the link' allotter circuit as just described, to ground at the back contact and inner left-hand armature of relay Hi to ground.

Relay 9 completelyoperated, connets'the calling supervisory relay 20 of link L (Fig. 3) across the calling line so that this relay now operates in a circuit extending from grounded battery, upper winding of relay 20, back contact and innermost upper armature of relay 23, tip conductor 24, front contact and inner upper armature of relay 9, back contact and upper. armature of relay ll, through the closed subscribers line loop, second lower armature and back contact of relay l I, second lower armature and front contact of relay 9, ring conductor 25, innermost lower armature and back contact of relay 23, lower winding of relay 29 to ground. In operating, relay 9 also cuts off the battery 5 from the line circuit A and substitutes therefor the battery associated with the windings oi the calling supervisory relay 26.

By the operation of relay 9 the calling line A is connected to the calling end of the link circuit L shown in Fig. 3.

At its armature and front contact relay 20 causes pulsing relay 26 to operate. Relay 26, by way of its left-hand armature and front contact connects ground to the winding of slow-torelease, relay l6, which relay operates. At its innermost right-hand armature and front contact relay l6 connects ground direct to the hold conductor l8 to hold line relay 9 operated. Ground on the left inner armature of relay I6 is transferred from the normal contact to the front contact thus indicating to the link allotter circuit that link L is no longer idle, but busy. Relay Iii holds operated for the duration of the call under control of the calling supervisory relay 21) which controls the operation of relay 2%.

The subscriber at station D may now dial the code assigned to the called station F on line B. This code for descriptive purposes will be assumed to be made up of the numerals 0-4-6-0-3 in the order indicated.

The selector switch lfil which is individual to the link circuit L is of the general type commonly used in railway train dispatching. 7 Such a switch is shown in J. C. Field Patent 1,343,256. In the present case the switch differs from that shown in the patent primarily in that it uses a single bank of forty-one terminals and the hold pins characteristic of the Field device are omitted. The regular telephone dial functions in such a manner that in dialing the digit 1 the line circuit is opened and closed once; in

, dialing the digit 2 the line circuit is opened and closed twice and so on. If the selector magnet 3i were to be controlled directly from the pulsing relay it is apparent that, for each combined open and closure of the line circuit eifected by the dial, the magnet would be operated twice and would advance the selector two steps. In other words, the dialing of the digit 1 would advance the selector two steps; dialing oi the digit 2 would advance the selector four steps, etc. Such functioning reduces the capacity of the selector switch in that only every other terminal may be used. To permit the use of all terminals of the selector, it is necessary to either employ a special dial or else provide some means for halving the pulses effected by the dial, that is,

combining each line circuit open and closure so as to produce a single selector operating impulse. Applicant has interposed a relay chain circuit, comprising relays 2? and 32, which functions as a pulse halving circuit and which renders it possible to employ the dial in common use today without sacrificing any of the selector terminals. The manner in which this pulse halving circuit functions will appear presently. V

Actuation of the dial 1 at station D causes the line circuit A to be interrupted in the wellknown manner so that the calling supervisory relay 20, included in the line circuit, follows the dial pulses. Pulsing relay 26, being controlled by relay 29 also follows the dial pulses but relay I6, being slow-torelease, remains operated during pulsing.

The selector switch |ll| is controlled by the selector magnet 3|. As illustrated, the selector magnet functions each time relay 2'! of the pulse halving circuit operates or releases due to the fact that the two right-hand windings are energized when relay 2'! is in its released position and the two left-hand windings are energized when the outer armature of relay 21' is moved to engage its front contact. For each operation of the magnet 3| the brush of the selector is advanced one step in a well-known manner. It will be noted, therefore, that for each operation of relay 21 and for each release thereof the selector advances one step.

The selector switch |0| as hereinbefore mentioned includes a single bank of forty-one terminals. The first terminal a is called the off-normal terminal or postion to which the selector brush is moved when relay 20 first operatesupon connection of the link circuit L to the calling line A. Beginning at the next terminal the succeeding terminals may be numbered 1 to 40. Terminals l to 9, inclusive, 11 to 19, inclusive, and 21 to 28, inclusive, are called line terminals being allotted to the line circuits to be served by the selector;

terminals

10 and 20 are rest terminals; terminal 9 may be assigned to a trunk circuit to an operator if desired; terminal 29 is used for revertive calls; terminal is the cut-through terminal and the remaining terminals may be used for code ringing purposes.

As hereinbefore described, calling supervisory relay 20, pulsing relay 26 and slow-to-release relay |6 operate when the link circuit L is connected to the calling line A by the operation of relay 9. A circuit for the right-hand windings of selector magnet 3| is also completed to ground at the innermost right-hand armature of relay I6 by way of the back contact and outer armature of relay 21, conductor I00 and the back contact and outermost lower armature of relay23. The selector magnet 3| operates in this circuit and moves the selector brush to off-normal terminal a.

Relay 32 of the pulse-halving circuit also operates as a consequence of the operation of calling supervisory relay 20, in a circuit extending from grounded battery resistance 28, winding of relay 32, normal make-before-break contacts of relay 32, conductor I02, front contact and righthand armature of relay 26, conductor Hill and thence to ground at the front contact and innermost right-hand armature of relay l6 by way of the back contact and outer armature of relay 23. In operating, relay 32 locks directly to conductor I60 which finds ground at the front contact and innermost right-hand armature of relay l6.

From the description so far given, relays 28, 26, I6 and 32 operated when the link L was connected to the calling line A and the selector |0| was advanced one step to the off-normal position. The subscriber at station D now dials the digit 0 of the code number 0-4-6-0-3 which we have assumed is assigned to the called line B. When the line circuit is opened due to the actuation of dial I at station D, relay 20 releases and opens the circuit to relay 26 which relay, in releasing its right-hand armature, opens the path to ground on conductor l6 which ground had been shunting the operating battery of relay 21 through the back contact and inner armature of relay 2'! and resistance 29, thus preventing its operation. Now with this shunt removed, relay 21 operates in a circuitextending from grounded battery, resistance 29, winding of relay 21, front contact and armature of relay 32 to ground on conductor I06. Relay 2| operated causes the lefthand windings of selector magnet 3| to be energized to cause the selector to be advanced to terminal No. l which immediately succeeds offnormal contact a on the selector bank.

When the line circuit A is closed again to complete the first pulse, relays 20 and 26 reoperate, the latter causing relay 32 to release. This. release results from the fact that, with relays 21 and 26 both operated, the winding of relay 32 is shunted by ground from lead I06, through the right-hand armature and contact of relay 26 and left inner armature and front contact of relay 21. Though the line circuit A has experienced a break and a closure, the stepping magnet 3| was operated but once and advanced the selector but one step.

When the dial opens the line circuit for the second time during the dialing of the numeral 0 relays 20 and 26 again restore their armatures to normal. Operating ground supplied the winding of relay 2'! from lead I60 through the righthand contact of relay 26 is removed. Relay 2? accordingly releases so that both relays 32 and 21 are now in the released position, the latter relay completing an energizing circuit for the right-hand winding of the selector magnet 3|. The selector |0| thereupon experiences another advance movement and its brush now engages contact No. 2. When the line circuit is again closed by the dial, relays 20 and 26 again operate causing relay 32 to operate. This relay holds operated when relay 2! reoperates upon the following line circuit opening, causing the selector magnet 3| to be again energized and to step the selector to position No. 3. It is believed unnecessary to describe any further operation of the pulse halving circuit upon receipt of succeeding ground pulses from relay 26. Suflice it to say that for each combined line circuit opening and closure effected by the dial, the selector advances one step and that advancement occurs only on the line circuit opening, the closure being rendered inefiective in stepping the selector. In other words though each break eifected by the dial be comes two pulses, only one of the pulses is efiective in operating the selector.

In the connection described it was assumed that the code required to signal the subscriber at station F on line B is 0-4-6-03. The digit 0 leaves the selector on a rest terminal, the digit 4 selects the line B, the digit 6 positions the selector brush on the twentieth terminal which is a rest terminal, the digit 0 positions the selector brush on the thirtieth terminal to cut the link circuit through into a ringing condition and the last digit 3 sets the ringing code circuit to send out the ringing code assigned to the station F.

Relay 29 is operated during the pulsing of each digit under control of the left-hand armature of pulsing relay 26. Between digits, it releases. and places ground through the marginal low resistance relay 33 on the brush of the selector ||l| to cause the operation of a line relay I65 as a connect relay and operates relay 3| as a ringing cut-through relay as will appear presently.

In the connection described, the selector brush rested upon terminal No. 10 upon the dialing of the digit 0. As this terminal is a rest terminal no circuit functions are performed. On the second digit 4 the brush rested upon the fourteenth terminal identified on the drawings by the letter b. A circuit accordingly exists which may be traced from grounded battery, lower winding of line relay I05 (Fig. 1), seventh lower armature and back contact of relay E05, conductor} which extends across Fig. 2 and down along the right-hand margins of Figs. 2 and 4 and thence to terminal I) and brush of the selector switch I0 I, conductor I2, back contact and armature of relay 20, conductor 30, left-hand normal make-before-break contacts of relay 3i, armature and back contact and winding of marginal relay 33. Relay 505 operates in this'circuit and in attracting its seventh lower armature transfers the grounded lead I from the lower winding of line relay I05 to lead I3I which is connected to the upper winding of relay I09 by way of the normal make-before-break contacts of that relay so that relay I09 operates. Relay I05, however, upon operating locks in a circuit extending from grounded battery, lower winding of relay I05, first lower armature and front contact of relay I05, to ground on. the hold lead I8.

It will now be observed that, due to the operation of relays I05 and I00, the called line B is connected to the conductors I28 and I20 which are connected to the outer upper and second lower armatures of relay 30 which, by way of their front contacts are connected to the outer upper and lower armatures, respectively, of relay 4| which relay controls the application of ringing current from the source I00 to the called line.

If the line B had been busy on a revertive call or is the called line on another connection, relay i 09 would have been operated so that battery I01 would be connected to the conductor I by way of the front contact and third lower armature of relay I 00, outermost lower armature and back contact and seventh lower armature of relay I05 whereupon marginal relay 33. would operate as: a buzzer. The transfer contact of relay 33 takes the inductive kick when the operating circuit to relay 33 is opened and places it on conductor I I I g which is connected to the tip conductor 24 by way of the back contact and innermost upper armature of relay 23 as a busy'indication to the calling subscriber at station D on line A. If line B is busy asthe calling line on another connection (therefore, relay I09 is normal) the line relay in link L (relay 408) or the line relay in link 3 (relay 404) would be operated. Assume relay 408 in link L operated. Battery I01 through front contact, lower outer armature relay 408, lower outer armature, normal contact and lower seventh armature and normal contact of relay I05 to the terminal on switch IOI will operate marginal relay 33 as a buzzer. The.

line B in this description is assumed to be idle.

- back contact and armature of relay 20, conductor armature of relay I6. At its left-hand armature relay 3| transfers the lead 30 associated with the selector brush from" the winding of relay 33 to the lead II5 which is connected to the inner upper armature of relay 39 which, by Way of its associated back contact is connected to the upper winding of relay 39, conductor 30, back con tact and-outermost upper armature of relay 23 and thence to the ring start lead H3 which finds ground at the outermost lower armature and front contact of relay I09 by way of the fifth lower armature and front contact of relay I05.

When the last digit 3 is dialed by the calling subscriber the selector brush engages the third ringing terminal (the thirty-third terminal) whereupon a circuit is established extending from battery H6 associated with the ringing code circuit (Fig. 5) outer right-hand armature and back contact of slow-to-operate relay 200, conductor II'I, back contact and. second right-hand armaeture of relay 203, conductor I I9, back contact and second right-hand armature of relay 208, conduc tor I2I, back contact and second right-hand. er

mature of relay 209, conductor I23, back contact.

and second right-hand armature of relay 250, conductor I25, thirty-third terminal of the selector switch WI and the selector brush, conductor I2, back contact and armature of relay conductor 30, front contact and left-hand armature of relay 3|, conductor I I5, inner upper armature and back contact of relay 30, upper winding of relay 39, conductor 36, back contact and.

outermost upper armature of relay 23, ring start" lead I I3, front contact and'fifth lower armature of relay I05, front contact and outermost lower armature of relay I00 to ground. Relay 39 operates in this circuit. Relay 30 looks in a circuit extending from grounded battery, lower winding of relay 39, first lower armature and front contact of relay 30, conductor 35, back contact and outermost lower armature of relay 23, to ground at the front contact and innermost right-hand armature of relay IGJ In attracting its inner upper armature relay 39 transiers the selector brush lead I'I'5 from the upper winding of relay 39 to the winding of relay 0i and at its fourth lower armature and front contact connects ground at the innermost right-hand armature and front contact of relay It to the lead I21 which serves to start the ringing code. circuit functioning. At its outer upper and second lower armatures and front contacts relay 30 connects the ringing tip conductor I28 and the ringing ring conductor I20 of the link circuit L to the two outer armaturesof relay ii which relay, when operated connects the ringing current source I00 to these armatures.

The operation of the code ringing circuit shown on Fig. 5 will now be described.

The code ringing circuit shown on Fig. 5 in cludes a pulse generating portion consisting of slow relays I40 and MI. When ground potential is applied to the lead I21 as describedin the preceding paragraph, relay I4I operates in a circuit including the left-hand armature and back contact of relay I40. Relay I40 now operates to ground on the lead I2! by way of the left-hand armature and front contact of relay I4I. Relay I40 opens the operating path to relay I4I causing this relay to release. When relay I4 releases, the ope-rating path to relay I40 is opened and this relay releases thus restoring the circuit to normal for another cycle. Relays I40 and MI of the pulse generating circuit continue to operate in this manner as long as ground potential is applied toconductor I21.

During the release of relay I4! ground potential supplied through the right-hand armatures and front contacts of relays MI and I 40 causes the chain of counting relays 200 to 2II to make one step as follows: Ground through the righthand operated contacts of relays MI and I40 is transmitted over conductor I42, left-hand armature and back contact of relay 2II, conductor I44, normal make-before-break contacts and winding of relay 200, conductor I46 togrounded battery I41. Relay 200 is slow-to-operate and operates in this circuit.

During the operate time of relay 200, ground from conductor I44 is transmitted to the lefthand winding of relay 20 I by way of the left-hand armature and back contact of relay 200 so that relay 20I operates in an obvious circuit. Relay 200 is held operated by ground on the ring hold lead I21 through the second right-hand armature and back contact of relay 2, conductor I49, inner right-hand armature and front contact and winding of relay 200 to grounded battery I4! by way of conductor I46.

After the operation of relay 200, one of the relays 20I to 2II is always operated causing the chain circuit including the lefthand armatures of these relays to be broken. This circuit is used, however, to hold momentarily the operated relays in the chain as they count up but not when they count, down since relay 2! I is then operated as will appear presently.

With relay 200 operated and relay 20I locked in the path just described, the pulse of ground which operated relay 20I now causes the operation of relay 202 in a circuit extending from lead I44 (grounded), left-hand armature and front contact of relay 200, left-hand alternate makebefore-break contacts of relay 20I, left-hand winding of relay 202 to grounded battery I41 by way of lead I46. Relay 202 operated, opens the holding circuit for relay 20l which relay starts to release. As will be described later, the interval of time during which relays 20I and 202 are both operated is used to time an impulse of ringing current in the connected link circuit L.

The pulse of ground which operated relays 20! and 202 will have terminated by the time relay 20I is released. When the next pulse of ground is supplied, relay 203 operates in a circuit extending from ground on lead I44, left-hand armature and front contact of relay 200, back contact and lefthand armature of relay 20I (released), alternate make-before-break contacts of relay 202 (operated) left-hand winding of relay 203 to grounded battery 141 by way of conductor I46. Relay 203 looks in a circuit similar to that in which relay 20! locked as already described. At its left-hand armature relay 203 opens the holding circuit for relay 202 which relay releases. The operating circuit for relay 204 is opened until relay 202 re leases. While relay 202 is releasing another ringing impulse is timed.

Pulses of ground from relays I40 and I II step up the remaining

relays

204, 205, 206, 201, 208, 209 and 2I0 in a manner similar to that already described in connection with the operation of relays 20I and 202, until relay 2II is operated in a manner now apparent.

Relay 2II is held operated from. ground supplied by conductor I2! through the second righthand armature and back contact of relay 20I, (the first in the chain) through the first righthand armature and front contact of relay 2H which is arranged to close before the left-hand normal contacts are opened. Relay 2, operated, opens the holding circuit for relay 200 and for the left-hand winding of relay 2 I 0, but immediately provides a holding path for the right-hand winding of relay 2I0 extending from grounded battery I41, conductor I46, right-hand winding of relay 2I0, front contacts and first right-hand armatures of relays 2I0, 209, 208, 201, 206, 205, 204, 203, 202, and 20I, conductor I99, front contact and second right-hand armature of relay 2| I to ground on ring hold conductor I21. Relay 2I0 is therefore not released until relay 209 is reoperated.

The pulse of ground which operated relay 2| l, or the succeeding pulse, will operate relay 209. The circuit for relay 209 extends from grounded battery I 41, conductor I46, right-hand winding of relay 209, alternate make-before-break contacts of relay 2I0, front contact and left-hand armature of relay 2, conductor I42 to ground by way of the right-hand armatures and front contacts of relays I40 and MI. Relay 209 operated, opens the holding circuit for the right-hand winding of relay 2I0 whereupon this relay releases.

With relay 209 operated and relay 2I0 released the circuit is in condition to operate relay 208 on the next ground pulse. The relays 2I0, 209, 208, 201, 206, 205, 204, 203, 202 and 2M are stepped down one at a time, beginning at the top of the chain, by the use of the right-hand make-before-break contacts in the same manner that they were stepped'up by the use of the lefthand make-before-break contacts. When relay 20I is operated, holding ground for relay 2 is removed at the second hight-hand armature and back contact of relay 20I causing relay 2 to release,.which relay in turn opens the holding path for relay 20I which relay releases at the end of the pulse of ground supplied from the pulse generating circuit including relays I40 and MI.

The first nine of the ringing codes consist of two groups of equal length ground impulses with a short silent interval between groups. The impulses per group vary from one to three. A tenth code consists of six impulses in one group. As the above described chain of relays steps up, the code is generated and as the relays step down the waiting interval between codes is measured.

Each code starts with a pulse from battery I I6 to set up a ringing condition in the link circuit as already described. This causes the link to always start ringing at the beginning of the code even though it should be connected while the ringing circuit was engaged in generating a ringing code for another link.

With all relays in the chain circuit normal, battery H6 is connected to lead I (small numeral) Fig. 5 by way of the outer right-hand armature and back contact of relay 200, conductor H1, back contact and second right-hand armature of relay 203, conductor H9 and the back contact and second right-hand armature of relay 208. Battery is further extended to lead 2 (small numeral) by way of the back contact and second right-hand armature of relay 209 and thence to lead 3 (small numeral) through the back contact and second left-hand armature of relay 2I0. Battery is similarly connected to leads 4, 5, and 6 (small numerals) through the outer right-hand armature and back contact of relay 200, back contact and second right-hand armature of relay 202, conductor I98, and'back contacts and third right-hand armatures of

relays

208, 209, and 2I0. Likewise battery is connected to leads I, 8 and 9 (small numerals) through the outer right-hand armature and back contact of relay 200, back contact and third righthand armature of relay 20I, conductor I91, and the back contacts and fourth right-hand armatures of

relays

208, 209, and 2 I0. Battery is connected to lead I0 (small numeral) through the outer right-hand armature and back contact of relay 200, back contact and third hight-hand armature of relay 20I, conductor I91, and the back contacts and third right-hand armatures of

relays

204, 205, 206, and 201.

As mentioned above, each pulse of ground in the ringing code is measured while one of the relays in the chain is operated while the preceding relay is releasing. Code 1, for example, (lead I small numeral) consists of two pulses of ground separated by an interval measured by the time required to operate relays I52, I53 and I54.

The codes in table form areas follows:

Code Code Code Code Code Code Code Code Code Code 10 The ground for each code is supplied from the fourth right-hand armature and back contact of relay 2| l. Codes 1, 2 and 3 are generated as follows: Ground from the outermost right-hand armature and back contact of relay 2I I, by way of conductor I96, second right-hand armature and front contact of relay .204, front contact and second right-hand armature of releasing relay 203, conductor II9, back contact and second right-hand armature of relay 208 to lead I (small numeral) gives the first pulse of ground. This pulse of ground is also delivered to leads 2 and 3 (small numerals) through the back contacts and second right-hand armatures of relays. 209 and 2I0, respectively. The time required for operating

relays

205, 206 and 20! is used to separate the two groups of impulses. Another pulse of ground is then delivered tolead I (small numeral) through the front contact and second right-hand armature of releasing relay 20'! and front contact and second right-hand armature of relay 208. This pulse of groundv is also placed on leads 2 and 3 (small numerals) by way of the back contacts and second right-hand armatures of relays 209 and 2I0.

Lead 2 (small numeral) has an additional pulse delivered to it from ground through the front contact and fifth right-hand armature of releasing relay 208 and the front contact and second right-hand armature of relay 209. This pulse of ground also reaches lead 3 (small numeral) through the back contact and second right-hand armature of relay 2I0.

Lead 3 (small numeral) receives a third impulse of ground in the last half of the code, as shown in the above table, through the front contact and fifth right-hand armature of releasing relay 209' and the back contact and second right-hand armature of relay 2I0. With this description the circuit operation for the remain ing codes should be easily followed; however, the operation for code 7 will also be described. Ground through the front contact and fourth and front contact.

right-hand armature of relay 202, through front contact and third right-hand armature of releasing relay 20 I, conductor I9'I, through the back contact and fourth right-hand armature of relay 208 gives the first pulse of group one of the codes '7, 8, and 9. The second pulse of the first group is generated by ground through the front contact and fifth right-hand armature of relay 203 and through the front contact and third righthand armature of releasing relay 202 and con- In the present description we have assumed that code No. 3 is assigned to the substation F on line B. In the manner described, therefore, the code ringing circuit functions to transmit over the conductor I25 a single ground pulse which, after a pause, is followed by three successive ground pulses. Relay II in the link circuit responds to these ground pulses in a circuit extending from grounded battery, winding of relay 45, front contact and inner upper armature of relay 3S, conductor H5, left-hand armature and front contact of relay 3I, conductor 3G, armature and back contact of relay 29, conductor I2, brush of selector IOI and the thirty-third terminal thereof, conductor I25 which corresponds to lead 3 (small numeral) of the ringing code circuit. Relay 4| accordingly follows the pulses of ground supplied from the ringing code circuit and, by way of its outer upper and lower armatures and front contacts cnnnects the 20-cycle ringing current source I06 with its superimposed battery to conductors I28 and I28 which, due to the operation of relays I05 and I09 are connected to the called line B. The signaling equipment at the stations on line B is accordingly actuated and the subscriber at station F, recognizing her code, answers the call. The use of the gas discharge tube in series with the bell serves to ground the bell and line only when superimposed ringing voltage breaks down the tube.

After each ground pulse from the ringing code i.

circuit relay 4! releases and connects the answering supervisory relay 44 to the conductors I28 and I 29 now'associated with the called line B. When the called subscriber responds to the in coming ringing signal, relay 44 operates over the closed (called) subscribers loop and establishes an obvious energizing circuit for relay 23. Relay 23 operates and allows relays 3i, 33, ill, 32 and the selector IOI to release and cuts the left-hand windings of repeating coil 50 into the calling end of the link L. Relay 23 looks to ground from relay I6 through its own second lower armature I The release of relay 39 releases the code ringing circuit.

The stations D and F of lines A and B, respectively are now connected for communication. The calling end of the connection may be traced from grounded battery, upper winding of calling supervisory relay 20, front contact and. second upper armature of relay 23, conductor I0, upper The one pulse in the second groupleft-hand winding of repeating coil 50, front contact and innermost upper armature of relay 23, tip conductor 24, front contact and inner upper armature of relay 9, back contact and upper armature of relay II, through the closed line loop at station D of line A, second lower armature and back contact of relay II, second lower armature and front contact'of relay 9, ring conductor 25, innermost lower armature and front contact of relay 23, lower left-hand winding of repeating coil 50, to ground through the lower winding of calling supervisory relay 20. The answering end of the talking circuit may be traced from grounded battery, upper winding of answering supervisory relay 44, upper right-hand winding of repeating coil 50. back contact and outer upper armature of relay II, back contact and outer upper armature of relay 39, tip conductor I28. front contact and outer upper armature of relay U 5, front contact and upper armature of relay Hi9, closed line loop at station F of line B, second lower armature and front contact of relay I09. third lower armature and front contact of relay H35. ring conductor I29, second lower armature and back contact of relay 39, third lower armaure and back contact of relay II. lower righthand winding of repeating coil 50 to ground through the lower winding of answering supervisory relay 44.

At the termination of conversation between the subscribers at stations D and F the receivers at the stations are replaced on their respective switchhooks. The calling and answering ends of the link circuit are therefore opened and the supervisory relays 20 and 44 restore their armatures. Relay 20 released, releases relay 26 which in turn opens the circuit to relay I6, which relay releases and removes ground from its innermost right-hand armature thereby causing relays 23, E and N35 to be deenergized. Relay I05 opens the locking circuit for relay I99 and this relay releases. The circuit is accordingly restored to normal.

Revertive call If the call originating at station D. for example, of line A is to another party on the same party line, that is, a revertive call, a special codeis used. The calling subscriber, noting that the first four digits of the code are the same as his own. is instructed to dial the special code with the last digit of the called partys code. Usually, the subscriber is provided with a bulletin listing the parties on his line with the codes to be used for each.

In the present description it will be assumed that the subscriber at station D desires to converse with the subscriber at station E, both stations being on the same line A and link L has been marked by the link allotter as the next link to be used.

Removal of the receiver at station D causes line relay 9 to operate in the manner already described to connect the calling line A to an idle link circuit L. Relays 20, 26 and I6 operate upon connection of the link circuit L to the calling line in a manner previously described. The subscriber at station D now dials a special code such as 0-0-9-1-9. The selector IOI follows the dial pulses through the pulse-halving circuit consistingof relays 21 and 32, in the manner previously described. Dialing the digits 0, 0, places the selector brush on two rest terminals so that no circuit functions are performed. Dialing the third digit 9 positions the brush on the twenty-ninth terminal which is connected to the upper winding of relay II by way of conductor 12 whereupon relay II operates in a circuit extending from grounded battery, upper winding of relay II, conductor I2, twenty-ninth terminal on the selector bank, selector brush, back contact and armature of relay 29, conductor 30, normal left-hand make-before-break contacts of relay 3|, armature and'back contact and winding of marginal relay 33 to ground. Relay II operates in this circuit and locks in a circuit extending from grounded battery. lower winding, front contact and first lower armature of relay II, back contact and third outer armature of relay 23 to ground at the front contact and first right-hand armature of relay I6. At its inner upper armature and front contact relay II connects ground to conductor 13 and thence through the front contact and fourth lower armature of line relay 9, normal make-before-break contacts of relay I I to battery and ground through the upper winding of relay I I. Relay H operates in this circuit and locks in a circuit extending from grounded battery, upper winding of relay II, front contact and first lower armature of relay II, conductors I4 and I5, sixth lower armature and front contact of relay 9, conductors I6 and TI to ground through the lower winding of relay II Relay II remains locked up for the duration of the connection as will be shown presently.

Relay II in attracting its upper second and third lower armatures, connects the calling supervisory relay 20 to the answering end of the link circuit L which is the end which is now connected to the calling line A due to the operation of relays 9 and II. The supervisory relay 2!) which controls the operation of the selector switch I0! is now controlled by the dialing mechanism at station 1 over the answering end of the link. The contact arrangement of relay II is such that movement of the second upper armature and the lower third armature cause a makebefore-break sequence of the associated contacts.

Dialing of the fourth digit 1 causes the selector brush to reach the thirtieth selector terminal which is connected to the winding of relay 3| by way of conductor 34. Relay 3|, accordingly, operates to ground through marginal relay 33 and performs the same functions as it did when 0perated in the previous description.

The counting relays 45 and 46 are now connected to the code end lead I95 of the code ringing circuit by way of conductor I8, front contact and fourth lower armature of relay 'II, and the front contact and third lower armature of relay 39. The purpose of

relays

45 and 45 will be described presently.

Upon dialing the ringing code 9 which is assigned to the called station E, relay 39 is operated as was previously described and two groups of three ground pulses (see code table) are sent out over lead I25 (connected in this case to the ninth ringing code terminal of the selector bank) from the lead 9 (small numeral) of the ringing code circu t. These ground pulses cause the relay 4| to operate in a manner previously described to connect the 20-cycle current source I06 to the leads I23 and I29 of the link circuit in a manner indicative of the code being transmitted. As relay 4i operates to follow the ringing code, the circuit to relay 20 is broken and relay 2!! releases while ringing current is connected to the line. Relay 26 does not release, however, as it is held operated by ground from the front contact and upper third armature of relay TI through the iront contact and lower outermost armature of relay 39. The lead I28 is connected to the tip conductor of the line A by way of the front contacts and outer upper armatures of relays 9 and I I, whereas the lead I29 is connected to the ring conductor of the line A by way of the front contact and third lower armature of relay 9 and the front contact and second lower armature of relay i i. The subscribers bells at the stations on line A are sounded accordingly and the subscriber at station E, recognizing the code as her own, answers the call.

In the description of the code ringing circuit shown in Fig. it was shown that after each code was transmitted, relay 2 operated to connect ground to code end lead I95. This ground as above mentioned is connected to the counting relays 95 and 46 due to the operation of relays ii and 39. This ground causes relay 45 to operin a circuit including its normal make-before-break contacts and resistance '89. The winding of relay 46, however, is shunted due to the connection of the grounded lead 18 to a point between the relay winding and resistance 8| by way of back contact and inner armature of relay Relay 45 accordingly operates and relay 46 remains released. The relay 45 locks in a circuit extending from grounded battery, resistance 89, winding of relay 45, front contact and right-hand armature of relay 45, conductors 8| and 35, back contact and outermost lower armature of relay conductor I8 to ground at the right innermost armature and front contact of relay I6. In attracting its left-hand armature relay 45 prevents the operation of relay 23 upon the operation of relay 46.

When relay 2| I in the code ringing circuit releases after the first transmission of the code, ground is removed from the lead I95 and therefore from. lead 18, thus removing the shunt from relay 45 so that this relay now operates in a. circuiu extending from grounded battery, resistance 82, winding of relay 46, front contact and righthand armature of relay 45 to ground by way of the locking circuit for relay 45 just traced. Relays and 46 accordingly are now operated in parallel.

The code ringing circuit continues to function to repeat the signal tothe called station and at the end of the repeated signal, relay 2H again operates to again. place ground potential on lead 695 and accordingly, on lead I8 whereupon relay is shunted by virtue of the fact that relay 46, by way of'its inner armature and front contact connects the grounded lead I8 to a point between the winding of relay 45 and resistance 80'. Relay releases and upon its release, with relay 45' still operated, a circuit is established extending from grounded battery, upper winding of-relay 23,

conductors

82 and 83, left-hand armature and back connection to the calling supervisory relay 2i], 7

which relay releases due to the fact that the tip and ring leads 24 and 25 are open at the upper and second lower armatures of relay II.

Etelay 29 released,iopens the circuit to relay 26, which relay releases and causes relay I6 to release. Relay I6, released, opens the locking cirremoves ground from. the hold lead I3 which to relay causing this relay to release and causes line relay .9, which was held operated by ground on the lead I8 to release. The contact arrangement of relay 9 is such that the contacts X and Y close before contact Z opens when the relay releases so that the locking-circuit for relay l I which includes the sixth armature and contact Z is maintained closed for an interval of time after the contacts X and Y are opened. The relay i I is accordingly held operated until a circuit for its operation over the closed line loop is established by the release otrelay 9. This circuit extends from grounded battery, upper winding of relay II, conductor 3, back contacts and outer upper armatures of relays-4, 8 and 9, front contact and upper armature of relay II, closed line 100p, second lower armature and front contact of relay II, third lower armatures and back contacts of relays 9, 8 and 4, conductors 22 and TI toground by way of the lower winding of relay I I. The release of relay 9 frees the link circuit L and the subscribers at stations D. and E converse over the line A to which nothing but the windings of relay Ii and the associated battery are connected, as just described.

It will be noted that when all links are busy as evidenced by the operation of relay I6 of link L,

relay I6 of link L, relay I6"- of link 3 and relay IS' of link L, relay 2I2'of the all links busy circuit operates in a circuit extending from grounded battery, winding of relay 2 I 2, back contact and armature of relay 2I2, conductor 2I3, front contacts and outermost right-hand armatures of relays I6,'I6, I6 and 5'. Relay 2I2 operates in this circuit as a buzzer to place an inductive kick on lead 2I4 which is connected to the tip conductors of all the line circuits by way 'of the back contacts and inner upper armatures of the line relays, such as relays 4, 8, and 9 of the line A and of corresponding relays of lines B and C to indicate to a calling subscriber that no links are available.

If the time interval between the connection of a link to a line and the answer of the called subscriber, or the completion of a revertive call, or the time interval between the hanging up of the called party and the calling party is greater than a predetermined interval, the link circuit functions similarto a revertive call so as to free the link and hold the calling line on its associated relay, such as relay II or relay I69. The operation is initiated by the operation of the timing relay ll which may be of the well-known dashpot type. This relayis operated from ground on the normal contact of the answering supervisory relay 44, the normal contact and second right hand armature of relay I6 through the Winding of relay ii to grounded batteryi Relay I'I operated, connects ground through its right-hand inner armature and front contact to the lower winding of relay 39 which relay operates and looks as previously described. Ground is also connected to the upper winding of relay ll through theleft-hand armature and front contact of relay I I. Relay I I also operates and looks as previously described' With relays-t9 andII- *operated,"the link functionsas on a revertive call to count two repetitions of the ringing code. Relay M is, however, not operated. At the end of the second a repetition, if the calling subscriber has not, in the meantime, hung up, the link functions as previously described for a revertive call. An alarm 4135 is actuated when relay I I. operates on a nonrevertive call. 7

When the calling party on a nonrevertive call hangs up first the link releases as previously described for a normal call. However, when the line relay associated with the called line (such as line 3) is released and the windings of relay I09 are thereby connected to the loop, relay I09 is held operated until the called subscriber on line B hangs up and thereby prevents a link from being seized as for a new call.

What is claimed is:

1. In a telephone system, subscribers line circuits, a link circuit, a selector switch individual to said link circuit and having a terminal for each of said line circuits, and means comprising a relay for each of said line circuits responsive to the actuation of the switchhook on one of said line circuits for extending said one of said line circuits to said link circuit, said relay operating also upon the actuation of said selector switch to the terminal individual to the said one of said line circuits in response to the initiation of a call on another of said line circuits to cause the connection of said link circuit to the said one of said line circuits.

2. In a telephone system, a subscribers line circuit, a source of current normally connected to said line circuit, a link circuit, a source of current normally connected to said link circuit, a line relay energized by current from said first source in a circuit including said subscribers line circuit when the subscriber thereon initiates a call, and contact means controlled by said relay when operated in response to the initiation of a call, for transferring said line circuit from said first source of current to the source of current associated with said link circuit and for establishing a locking circuit for said line relay independent of said line circuit.

3. In a telephone system, a line circuit, a plurality of stations on said line circuit, a dialing mechanism at each of said stations, a link circuit having calling and answering ends, a selector switch individual to said link circuit, means for controlling said selector in response to the actuation of the dialing mechanism at one of said stations, said means being normally connected to the calling end of said link circuit and means controlled by said selector when actuated by said dialing mechanism in accordance with a prearranged code for transferring said selector controlling means from the calling end of said link circuit to the answering end thereof whereby any further actuation of the dialing mechanism after the transfer causes the operation of said selector controlling means by way of the answering end of said link circuit.

4. In a telephone system, line circuits, a calling station and a called station on one of said line circuits, a dialing device at said calling station, a link circuit for extending connections between said line circuits and having calling and answering ends, a selector switch, selector control means control means for connecting said source of signaling current to said one of said line circuits to cause the operation of said signal means.

5. In a telephone system, line circuits, a pair of relays for each of said line circuits, 2. link cir cuit having calling and answering ends, means responsive to the initiation of a call on one of said line circuits for causing the operation of one of the associated pair of relays to cause the connection of the line circuit to the calling end of the link circuit and means responsive to a call incoming to one of said line circuits for causing the conjoint operation of the associated pair of relays to cause the connection of the line circuit to the answering end of said link circuit.

6. In a telephone system, a line circuit, a sub-. scribers station on said line circuit, a link circuit having a calling end and an answering end, means comprising a relay normally connected to said line circuit and responsive to the removal of the receiver at said station for connecting said line circuit to the calling end of said link circuit and means also comprising said relay and responsive to a call incoming to said line circuit for connecting said line circuit to the answering end of said link circuit.

7. In a telephone system, a calling line, a called line, a link circuit having calling and. answering ends, a line relay for each of said lines, a second relay for each of said lines, a selector switch individual to said link circuit, means responsive to the initiation of a call on said. calling line for operating the line relay associated therewith to cause the calling line to be connected to the calling end of said link circuit and subscriber controlled means on said calling line for actuating said selector switch to cause the conjoint operation of the line relay and the second relay associated with said called line whereupon said called line is connected. to the answering end of said link circuit.

8. In a telephone system, a line circuit, a dial station on said line circuit, a link circuit, a selector switch individual to said link circuit, means responsive to the removal of the receiver at said station for connecting said line circuit to said link circuit, a stepping magnet for said selector, a control circuit for said magnet, a pulsing relay responsive to the operation of the dial at said dial station for repeatedly opening and closing the control circuit to said magnet and a relay chain interposed between said pulsing relay and said magnet for causing said magnet to step once for each combined open and closure of said control circuit.

9. In a telephone system, a subscribers line circuit, a dial station on said line circuit, alink circuit, a selector switch individual to said link circuit, means responsive to the removal of the receiver at said station for connecting said line normally connected to the calling end of said circuit to said link circuit, a stepping magnet link circuit, means responsive to the initiation of a call at said calling station for connecting said one of said line circuits to the calling end of said link circuit, means responsive to the actuation of the dialing mechanism at said calling station in accordance with a prearranged code for transferring said selector control means from the calling end of said link circuit to the answering end thereof and for connecting said one of said line circuits to the answering end of the link circuit, signal means at said called station, a source of signaling current and means responsive to further actuation of said dialing mechanism subsequent to the transfer of said selector for said selector, a control circuit for said magnet, a pulsing relay responsive to the operation of the dial at said dial station for repeatedly opening and closing the control circuit to said magnet, a relay included in said control circuit adapted to step said magnet in both its operate and release positions and means cooperating with said relay and included in said control circuit for causing said relay to step said magnet only when said control circuit is opened and to hold the magnet operated during the closed period of said control circuit.

10. In a telephone system, a calling line, a called line, a link circuit having calling and answering ends, a supervisory relay associated with the answering end of said link circuit, means responsive to the initiation of a call on said calling line for connecting the calling end of said link circuit to the calling line and the answering end to the called line whereby said supervisory relay is connected across the called line to be operated upon the response of a subscriber on the called line, and means controlled by said supervisory relay and operating a predetermined interval of time after the connection of the supervisory relay to the called line and before the response of a subscriber thereon for effecting the release of said link circuit from the called and calling lines.

11. In a telephone system, line circuits, a calling and a called station on one of said line circuits, a dialing device at said calling station, a link circuit for extending connections between said line circuits and having calling and answering ends, a selector switch, selector control means normally connected to the calling end of said link circuit, means responsive to the initiation of a call at said calling station for connecting said one of said line circuits to the calling end of said link circuit, means responsive to the actuation of the dialing mechanism at said calling station in accordance witha prearranged code for transferring said selector control means from the calling end of said link circuit to the answering end thereof and for connecting said one of said line circuits to the answering end of the link circuit, a code ringing circuit, means responsive to a further operation of said dialing mechanism subsequent to the transfer of said selector control means for connecting said code ringing circuit to said link circuit whereupon said code ringing circuit functions to transmit a definite ringing code over the answering end of the link circuit, means for causing the code ringing circuit to repeat the ringing code, and means controlled by the code ringing circuit and automatically eifective after a repetition of the ringing code for releasing the link circuit.

NEAL D. NEWBY.