US1575334A

US1575334A - Telephone system

Info

Publication number: US1575334A
Application number: US682416A
Authority: US
Inventors: Robert W Harper
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1923-12-24
Filing date: 1923-12-24
Publication date: 1926-03-02
Anticipated expiration: 1943-03-02

Description

March 2 1926.

r 1,575,334 I R. w. HARPER TELEPHONE SYSTEM Filed D09. 24, 192:

9 Sheets-Sheet 1 //11/e/1/0r. Hake/f W fiarper March 2 1926. 1,575,334 R. w. HARPER TELEPHONE S YSTEM Filed Dec. 24, 1923 9 sheets sheet 2 f l am mwy March 2 1926. 1,575,334 R. W. HARPER TELEPHONE SYSTEM Filed Dec. 24, 1923 9 Sheets-Sheet 5 Maj-ch 2 1926,

1,575,334 R. w. HARPER TELEPHONE SYSTEM Filed Dec. 24,

9 Sheets-Sheet 4 Q ks March 2 1926. r l 1,575,334

R. W. HARPER TELEPHONE SYSTEM Filed Deb. 24, 1923 9 Shets-Shet 5 March 2 1926. 1,575,334

R. W- HARPER TELEPHONE SYSTEM Fi Dec. 24 1923 /wer VIZ/70,70 5, WA)

March 2,1926. 1,515,334

R. W. HARPER TELEPHONE SYSTEM Filed Dec. 24. 192:

R. w. HARPER TELEPHONE SYSTEM March 2 1926. 1,575,334

Filed Dec. 24, 1923 9 Sheets-Sheet 8 Patented Mar. 2, 1926.

UNITED STATES crates.

ROBERT WV. HARPER, OF EASTORANGE, NEW JERSEY, ASSIGNOR TO WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

SYSTEM.

Application filed December 24, 1923. Serial No. 682/116.

To all whom it may concern Be it known that 1, ROBERT W. fianrnn, acitizen of the United States of America, residing at East Orange, in the county of Essex and State of New Jersey, have invented certain new and useful Improvements in Telephone Systems, of which the following is a. full, clear, concise, and exact description.

This invention relates to telephone systems and particularly to systems employing automatic switching apparatus for setting up connections.

The object of the invention is an improvement in automatic telephone systems of small capacity whereby the manner of establishment of connections is simplified and the efliciency of the system in general is increased.

According to one feature of the invention there are provided a plurality of relay connecting devices for interconnecting calling and called lines, together with two separate sets of countingrelays responsive to successive series of impulses for selectively closing the operating circuits of said relay connecting devices.

Another feature relates to a controlling mechanism consisting of a series of counting relays wherein the first relay of the series operates and releases either when an accidental impulse is to be absorbed or when the first selective impulse is immediately followed by succeeding impulses. In case the first selective impulse is followed after an interval by a single impulse said r lay remains operated to effect the desired circuit connection.

The drawings disclose a representation of a preferred means of carrying out the invention. The several figures when arranged in the manner shown in Fig. 11 foym a complete circuit diagram.

Fig. 1 shows a number of subscribers lines arranged in groups. In conjunction with these lines are shown two groups of multi-contact relays with cooperating links. Connected to certain of these relays is shown one of a number of incoming trunks by means of which calls may be extended from the central ofiice to any station. In this figure are also shown two mult'i-contact connecting devices, each of which is associated with a group of the first mentioned multi-contact relays for controlling the operation thereof.

Fig. 2 shows one of a number of central office trunks with associated controlling aparatus by means of which a subscriber may obtain connection with a central otficc "In this figure is also shown an attendants line together with a number of keys to be used by the attendant, as well as a number of lamps for signaling the attendant under certain conditions.

Fig; 3 shows the attendants register sender consisting of a number of counting relays whose operation is controlled by the attendants dial for purpose of select ng a set of the mnlti-contact relays shown in Fig. 1. Fig, 3 also shows certain controlling equipment.

Fig. 4 shows a plurality of central oilice trunks, one of which is shown terminating in the contacts of a set of multi-contact relays. Arranged to cooperate with these contacts are a plurality of links. The sub scribers lines are connected to the contacts of another group of multi-contact relays.

In this figure is also shown trunk CulltlOlling apparatus for; controlling the operation of the several groups of nulti-contact relays. l p y i Fig. 5 shows common apparatus for supplying ringing current and busy tone, as well as a buzzer circuit for giving an audible signal to the attendant.

Fig. 6 shows the attendants line circuit with circuit controlling and signaling apparatusl Fig. 7 shows groups of multi-contact relays, one of these groups of relays acting as a line connector and the other groupacting as line finders. Terminating in certain contacts of these relays are shown a number of intermediate links. Arranged. to cooperate with these intermediate links are other sets of horizontal links. The hori zontal links appearing in the line finder ated primary, secondary and intermediate links. Fig. 9 also shows besides the line and cut-off relays, a group starting circuit for allowing but one calling line to be connected with an intermediate link at a time. There is also shown an emergency starting circuit and a portion of the allott-er mechanism.

Fig. 10 shows a register sender which is associated with an intermediate link for registering the designations of called lines and controlling the operation or" the connector relays.

From an examination of the several fig ures it will be seen that the subsribers lines are arranged in groups, two of such groups being shown. Each group of lines has associated with it a number of multicontact relays, as re ays 110. 410, 710, 715, etc. Each line of a group has an appearance in separate sets of contacts in each of these multi-contact relays. In Fig. 1 is shown schemetically by means of the dotted rectangle 104, a second set or". multi-contact relays similar to relays 110. 111, 112, etc., and also an incoming trunk 121 similar to trunk 120. The dotted rectangle represents a second set of multi-contact relays similar to relays 410, 4111, 412, etc., and an outgoing trunk 421 which is similar to trunk 420. The dotted rectangle 900 shows schematically a second line connector mechanism similar to that, shown at 700 in Fig. 7, while rectangle 901represents a second line finder mechanism similar to that shown hen a calling subscriber removes the re ceiver for the purpose of conversing with another local subscriber, the operation of the line relay causes a particular group relay as 905 to operate and to lock in series with the common relay 906. This prevents a subscriber whose line is in another group causing interference by initiating a call be fore the first calling line has been connected with an intermediate link through the line finder relays. If the intermediate link 907 is busy, an allotter' relay 909 associated therewith, is operated and a circuit will be closed to operate a conecting device 7 03, thus causing the operation of multi-contact relay 715 which is individual to the group of lines in which the calling line is located. A relay as 708 which corresponds to the units digit of the calling line is next operated. The calling line is thus connected by means of a primary link as 712 with an intermediate link 720.

The calling subscriber neXt dials the tens 7 1001 and 1002 should the calling subscriber inadvertently dial a tens digit of one, The numbers ofthe subscribers lines are so arranged that all tens digits are greater than 1. It the tens digit is greater than 5, however, transfer relay 1003 operates and allows the same register relays to be used for recording tens digits greater than 5 as are used for recording tens digits less than 5. hen the tens digit is recorded, a circuit is closed to operate the proper one of the multi-contact relays as 710 which corresponds to the tens digit as recorded on the register 1000. The calling subscriber next dials the units digit of the called line. If this digit is 3 or less, a relay as 1004 is operated. If it is greater than 3, the transfer relay 1005 opcrates, thus allowing three register relays to be used for recording the units digits 1 to 5. The subscribers numbers are so grouped that there is no units digit greater than 5. The recording of the units digit on register 1010 causes the operation of the proper multi-contact relay as 725. The calling line is then connected by means of a primary link 711, an intermediate link 720 and a secondary link 727 with the called subscribers line, ringing current having been applied to the line by the ringing mechanism 500.

Should the called line be busy, relay 802 is opera-ted and busy tone is transmitted from the tone source 550 back to the calling subscriber.

hen a subscriber desires to talk to the attendant the operation is similar to that already described as far as the point where the subscriber is ready to dial. In this case the circuits are so arranged that the digit 0, when dialed, causes the operation of a relay as 803 which connects the calling line by means of a primary and intermediate link with the attendants line 601, causing a lamp 602 to light, thus signaling the attendant. The attendant thereupon operates a key 603 which places a talking set 605 in communication with the calling subscriber.

hen a subscriber dials a special code,

in this case 11, for the purpose of obtaining connection with the central office, the

operation is similar to that described in connection with a local call as far as the p'lint where the impulses are recorded on registers 1000 and 1010. In this case a trunk relay 804 operates and in turn causes the operation of a multi-contact relay 410 which corresponds to, the tens digit of the calling line and also operates another multi-contact relay 4-12 which corresponds to the units digit of the calling line. The operation of relay 80st opens the circuit of slow release relay 1006 which supplies holding ground for the finder relays st and 715. 'lVhen relay 1006 operates, therefore, the finder relays release, thus disconnecting the intermediate link 720 from the calling subscribers line. l.he calling subscribers line is now connected directly through "contacts of relays L10 and 412 with an outgoing central oiiice trunk as 420. The subscriber may proceed to dial the central ofiice number, in the case of mechanical ofiice, or give thenumber verbally in the case of a manual oificc.

- In the case of restricted service with regard to a local subscriber calling a central ofiice, a key 910 individual to the subscribers line is operated, thus moving the ground for operating the trunk connecting relays are and 412 thereby preventing the subscriber from obtaining connection with the central office.

On calls incoming from the central office,

as soon as the central office operator applies ringing current to an incoming trunk shown in Fig. 2, a line lamp 201 lights for the purpose of signaling the attendant who answers by operating a key 212. If the incoming call is for a station, the attendant receives the number from the central office operator and throws a stations key 202-3 causing her talking set to be disconnected from the central oflice end of the trunk and transferred to the local end by means of the operation of relay Meanwhile, a bridge is placed across the trunk to hold the connecting apparatus at the central ofiice. lhe attendant next dials the designation of the wanted station which is recorded on the register sender shown in Fig. 3 consisting of a tens register 800 and a units register 301. When the record has been established, the proper 1nulti-contact relays as 110 and 113 are operated. The former corresponding to the tens digit of the required station as recorded on register 300, while the latter corresponds to the units digit as recorded on the register 301. When relay 113 operates, the attendants sender (Fig. 3) is released. Busy tone and ringing current are applied to the line in the same manner as for a local call. When the attendant releases the listeningkey 202 and the stations key 203, the called subscribers line is connected directly with the central office trunk.

Should the called line be busy when the attendant connects thereto she may break in on the connection by operating key 205.

The release of this key will cause the incoming trunk to wait on the busy line and ring it when it becomes idle. The attendant is provided with a release key 206 which, when operated, allows the transfer of an incoming call from one station to another. A disconnect key is' provided by means of which the attendant can give a disconnect signal to the central office when a station cannot be connected with. As soon as the attendant answers an incoming call, lamp 908 lights and remains lighted until the local subscriber answers. i

The attendant is also provided with a line circuit 610, by means of which she canoriginate calls to the central office onto any local subscriber.

. Detailed description of'local call.

The description of'how a local connection completed will .now be given. For this purpose, assume that the subscriber of line 101 desires totalk with subscriber of line 102 whosenumber is 33. W ien the calling subscriber removes his receiver from the.

armature and back contact of relay 911. The operation of relay 90% connects ground at its right armature and front contact through the right hand winding of group relay. 905 to battery at the back contact of the common relay 900. Relay 905 closes a of the calling line to ground at the outer locking circuit for itself from the above.

traced ground through its left windingand the left inner armature and front contact to battery through the winding of relay 906 which operates. The operation of relay 90-3 removes the battery for energizing other group relays similar to relay 905. Thus, if'a subscriber whose line is in another group now initiates a call, his line will not be connected to a line finder until the previous calling line has first been connected. If two subscribers, whose lines 'are in different groups initiate calls simultaneously, the subscriber whose line is in the lower numbered group will have his line extended first, since the operation of the lower numbered group relay opens at its left inner armature and, front contact the locking circuit for all succeeding similar relays.

At this point, it will be noticed that each intermediate link as link 907, Fig. 9, has ass ciated with it two allotter relays as 909 912. Similarly, intermediate link 720, Fig' 7, has associated with it allotter relays 705 and 706. Once an intermediate link has been used the allotter relays associated therewith remain locked until the last intermediate link has functioned. 'l he operation of the allotter relays associated with the last moving the locking ground from all the .armature and front contact of relay 909,

conductor 950, left armature and back contact of relay 705, to battery through the winding of 1c.ay 7 03 which operates. Relay 703 closes a locking circuitfor itself from battery throughits w iding locking armatureand contact, conductor 952, winding of relay 914': to grounc. as above traced. Relay 91% does not operate at this time since its winding is shunted by ground through the left arn'ia'ture and front contact of relay 909. The operation of relay 703 closes a circuit for energizing the particular multi-contact finder relay as 7 08 which corresponds to the units digitof the calling line, and also a particular group finder relay as 715 which corresponds to the group in which the calling line is located. The circuits for the purpose are as follows; From battery through the winding of relay 708, armature and contact of relay 703, conductor 750, left armature and front contact of relay 90s to ground at the left outer armature and front contact of relay 905. Relay 715 operates from battery through itswinding, contacts of relay 703, conductor 951 to ground at the right outer armature and front contact of relay 905.

The operation of tinder relays 708 and 715, connects the calling line 101 through primary link 712 with the intermediate link 720. Belay S01, thereupon operates from battery through its winding, tip conductor of .the link 720, contacts of relay S and re lay 715 to the tip side of the calling line through the calling subscribers set, back over the ring side of the calling line, contacts of

relays

715 and 708, ringside of link 720 to ground through the winding of relay 801. The operation of relay 801 causes the operation of the holding relay 1006 from battery through its winding, conductor 1050, leftouter armature and back contact of relay 80 1, left armature and contact of relay 801, conductor 850 to ground through the winding of low resistance relay 551, which operates to start the tone mechanism 550.

Relay 1000, in operating, performs the following functions 1. Connects ground throughits left mature and contact, conductor 1.051, resist

ances

722 and 723 in parallel to the arma- 705 transfers the starting circuit to the next link.

3. Connects ground through its right armature and contact to conductor 1053, sleeve conductor of intermediate link 720, contacts of

relays

708 and 715, sleeve conductor of the calling line to battery through the windng of cut-off relay 911. Relay 911 operates in this circuit and renders the line 101,

busy to other calling lines.

When relay 705 operated it removed the shunt from the \vinding of relay 91 1- which now operates and prevents this same calling line becoming associated with another intermediate link through the left armature and front contact of relay 705. The operation of cut-off relay 91.1 causes the release of line, relay 1 and group relay 905. The release of relay 905breaks the holdin circuit for relays 914 and 703 which now release and render the starting circuit and allotter mechanism available for use in connection with another calling line.

The calling subscriber now dials the tens digit of the wanted line. Relay 801, Fig. 8, uponthe transmitting of the first impulse will release. The release of relay 801 removes the short circuit from around the winding of relay 805 which operates from battery, left armature and contact of relay 808, retardation coil 806, winding of relay 305, right armature andcontact of relay 808 to grounded conductor 1053. The operation of relay 805 connects the battery at,

the left armature and contact ofrelay 808 through the armature and contact of relay 805, winding of slow-release relay 807, conduct-or 852, left armature and back contact of relay 1007, left inner armatures and back contacts of

relays

1008, 1009, 1011, 1012, in series, and thence through the winding of relay 1013 to the grounded conductor 1053.

Relays

1013 and 807 operate in this circuit. After the transmission of the first impulse relay 801again operates, thus causing the release of relay 805. Relay 805 on releasing removes the short circuit from around the winding of relay 1012 which now operates in series with relay 1013. The operation of relay 1013 closes a circuit for operating relay 1002 from grounded conductor 1053, winding of relay 1002, right inner armature and contact of relay 1001, left armature and contact of relay 1013,

right-armature and back contact of relay 1017, normal contacts of relay 1003, conductor 105%, to battery at the left armature and contact of relay 808. At the termination of the first impulse, relay 1001 operates in series with relay 1002 in a manner similar to that described in connection with relay 1012. Relay 1002 closes a circuit from ground at the left outer armature and contact of relay 1003,.right armature and contact of relay 1002, Winding of relay 1018, conductor 105 1, to battery atthe armature and contact of relay 8.08. Relay 1018 closes a locking circuit for itself in series with the winding of relay 1007 to grounded conductor 1053. Relay 1007 does not operate in this circuit since its Winding is shunted by the abovetraced groundand by ground at its right inner armature and back contact. The transmissionof the next impulse in the tens train-causes relay 805 to again operate and connect battery through itsarmature and contact, Winding of relay 807, conductor 852, left armature and back contact of relay 1007, left inner armature and back contacts of relays 1008, 1009, 1011 in series, left inner armature and front contact of relay 101.2 to ground through the winding of relay 101 1 which operates and locks in series with relay 1011 in the manner already describe-d. The operation of relays 1011 and 101 1 causes the release of

relays

1012, 1013, 1001 and 1002. In a similar manner the transmission of'the third and last impulse of the tens series causes the operation of relays 1009 and 1015 and the release of relays 1011 and 1014. In; the comparatively long interval following the train of tens impulses, relay 807 releases. The release of relay 807 removes ground from the conductor 805 thus allowing relay 1007 to operate and lock in series with lay 1018.

The operation of relay 1007 connects ground through its, right outer armature and contact, right armature and back contact of relay 1003, right inner armature and front' contact or relay 1009, conductor 1055,

Winding of relay 709 to battery. Group connecting relay 7 09 looks in a circuit from battery through its winding, armature and locking contact, resistance grounded sleeve conductor of intermediate link 720. 1

At this point it will be observed that th locking circuit of counting relays 1017 and 1019 is different from the locking circuit of other counting relays, the circuit comprising the left normal contacts of relay 1003. This is for the purpose of recording a tens digit greater than In such a case the transmission of the sixth impulse causes counting relay 1013 to operate 'roin grounded conductor 1053, winding of relay 1013, left inner armature and back contact traced battery.

716 to

theof relays

1012, 1011, 1009, 1008 in series, left armature and back contact of relay 1007, conductor 852, to battery through the Winding of relay 807. As soon as relay 805 releases at the end of the sixth impulse, relay 1012 operates in series With relay 1013 as 7 before described. As soon as relay 1012 operates acircuit is closed to operate a group transfer relay 1003 from grounded conductor 1053, Winding of relay 1003, left inner armature and front contact of relay 1019, left outer armature and front contact of relay 1012, conductor 105 1 to battery at the armature of relay 808. 1003 locks from grounded conductor 1053,

Transfer relay through its Winding, left inner amature and front contact, conductor 1054 to the above The operation of relay 1003 therefore causes the release of counting relays 1017 and 1019. The ground for operating the connector relays shown inFig. 7 is now transferred to the right armature and front contact of relay 1003 and the outer right armature and front contact of the operated counting 'relay. Thus by means of transfer relay 1003 tens digits greater than 5 may be recorded on five sets of counting relays and the proper corresponding connector relay energized.

Returning to the point Where relay 1018 locked in series with relay 1007, subsequent to the termination of dialing of the tens digit, the calling subscriber next manipulates the dial to transmit the units digit, in this case 3. The release of relay 801 on the first impulse causes the operation of relay 805 as already described and a circuit is closed from battery through the left armatune and contact of relay 808, armature and contact, of relay 805, Winding of relay 807, conductor 852, leftarmatureand front contact of relay 1007, left inner armature and back contacts of relays 1022 and 1004:111 series, through the Winding of relay 1020 to ground at the right armature and contact of relay 1006. hen relay 805 releases on the termination of the first impulse the short circuit is removed from the Windingof relay 1.004: Which IlO-W operates in series with relay 1020. In a similar manner the trans mission of the second impulse causes the operation of relays 1021 and1022 and the release of

relays

1004 and 1020. Since the number of the called line is assumed to be 33, three units impulses Wlll be sent and relays 1023 and 1024Will operate, causing the VVhenthe subscriber has finished dialing the units digit, the slow relay 807 releases and connects groundthrough its right normal contacts, conductor 860, right armature and Contact of relay 1018, resistance 1025, left outer, armature and back contact of relay 1005, right armature and contact of relay 1024, conductor 1056 to battery through the winding of units connector relay 717. With group connector relay 709 and units connector relay 717 operated, a circuit is closed to energize the slow operating relay 808 from the grounded conductor 1058, winding of relay 808. conductor 853 to the armature and locking contact of connector relay of primary link 712, intermediate link 720 and secondary link 713with the called subscribers line and a test thereof is made prior to ringing. It will be noted'that when relay 1018 operated subsequent to the dialing of the tens digit, a circuit was closed from battery through the right hand winding of test relay 809, conductor 854, left outerarmature and contact of relay 1018 to the grounded conductor 1053. If the called line is busy the sleeve conductor 718 will be grounded in a manner similar to that already described in connection with rendering the calling line 101 busy. Test relay 809 will, therefore, remain locked from battery, through its left winding, normal contact-sof relay 802, left inner armature and front cont-act of relay 809, thence to the grounded sleeve conductor of the called line. Relay 802 will also operate from battery through its winding and normal contacts to the above traced ground and will lock through the left outer armature and contact of relay 809 tothe grounded sleeve conductor of intermediate link 7 20. The operation of relay 802 causes a busy tone to be sent from the tone source 550, conductor 552, condructor 855 right armature and front contact of relay 802, condenser 810, ring conductor of the intermediate link and thence over the calling subscribers line notifying him that the called line is busy. This busy tone is cut off from the wanted line by relay 812 which operated as soon as relay 809 closed its left outer armature and front contact. 0

If, however, the called line is idle there will be no ground on the sleeve conductor 718. hen relay 1018 releases, test relay 809 will also release. The release of relay 809 will connect ground through its left inner armature and back contact and thence to the sleeve of the conductor 'of the called line, thus rendering the called line busy to other calling lines. In this case relay 802 will not operate, but relay 812 will remain locked from battery through the winding of relay 501, conductor 560, left winding of relay 812, left armature and contact thereof, left outer armature and back contact of relay 802, armature and contact of relay 813 to the groundedsleeve conductor of the link. Re lay 501 operates in this circuit'and starts the ringing mechanism 500 in the manner to be described hereinafter. This causes ringing current to be induced, in the winding 502 of the ringing transformer thence over conductor 530, winding of relay 813, right outerv armature and back contact of relay 809, right outer armature and front contact of relay 812 to the ring side of the called line, through the called subscribers ringing apparatus, back over the tip side of the line, right inner armature and front contact of relay. 812, right inner armature and 'back contact of relay 809, conductor 561, thence to ground at the winding 502 of the ringing transformer.

lVhen the called subscriber removes his receiver the resistance of the circuit including relay 813 is reduced. Relay 813 operates and at its armature and back contact opens the locking circuit for relay 812 and ringing start relay 501, the latter cutting off the ringing mechanism. The release of relay 812 extends the tip and ring conductor of the calling line to the tip and ring conductors of the called line. Relay 814; operates and supplies talking current to the called subscriber. The operation of relay 814 places ground on the sleeve conductor of the intermediate link to holdthe link and connector relays after the callingsubscriber has disconnected.

Disconnection.

When the calling subscribe-r replaces his receiver on the switchbook, relay 801 releases, in turn releasing relay 1006. WVhen relay 1006 releases it opens the holding circuit of finder relays 708 and 715 and cut-off relay 911. However, the remainder of the connection is under control of the called subscriber.

lVhe'n the called subscriber replaces his receiver relay 8141 releases opening the holding circuit for connector relays 717 and 709 which release. If the key 707 is operated the release of relay 81 1 will cause the release of allotter relays 705 and 706, thus'rendering intermediate link 720 selectable by another calling line. However, if key 707 is normal, allotter relays 7 05 and 706 will remain locked and intermediate link 720 will not be selectable until all succeeding links have functioned. I

Emergency start circuit.

that intermediate link 907, Fig. 9, is idle.

Therefore, allotter relays 909 and 912 are released. If, however, intermediate link ill 907 is not associated with the calling line within a certain time, the emergency start circuit functions to allot another idle intermediate link and connect the calling line thereto. For this purpose the emergency start circuit begins to function immediately that a group relay as 905 operates. Relay 916 operates from battery at the normal contacts of relay 917, winding of relay 910 to the grounded conductor 915. The operation of relay 916 closes an obvious circuit for relay 917 which is slow to operate. YVhen relay 917 has operated relay 916 starts-to release. Relay 917, in operating, closes a circuit from batter 7 throu h the left WlllCllIl of relay 913, winding of relay 918, left inner armature and back contact of rela 913 left'armature and contact of relay 917 to the grounded conductor 915. Relay 918 operates in this circuit out relay 913 does not. in turn, releasing relay 917. When relay 917 releases a circuit is closed from battery, through the left winding of relay 913, winding of relay 918, right hand winding of relay 913, right armature and contact of relay 913 to the grounded conductor 915. Relay 913 operates in this circuit. Another cycle of operation of relays 916 and 917 occurs. Gn the second operation of relay 917, relay 913 locks, but relay 913 is shunted and releases. lVhile relay 916 is releasing the second time, a circuit is closed from the grounded conductor 915, left middle armature and'front contact of relay 913, left inner armature and back'contact ofirelay 918, left armature and back contact of relay 912 to battery through the right hand Winding 'of relay 909.

Preliminary pulse circuit.

The registermechanisms shown iii-Figs. 3 and 10 are so arranged that if a comparatively long interval ensues between the first impulse transmitted and subsequent impulses, the first impulse will not be counted. If, however, the first impulse is one of a train of impulses, the preliminary pulse circuit does not function. it will be remem bored in connection with the recording of the first impulse on register 1000, preliminary pulse relay 1002 operated in conjunction with counting

relays

1012 and 1013. If,

After an interval relay 916 releases,.

therefore, an interval intervenes between this first impulse and the next succeeding impulse, relay 807 will release and open the holding circuit for counting

relays

1012 and 1013*Which also release. At the same time the shortcircuit'is removed from the Winding of relay 1001 which now operates in series withrelay 1002. 'The operation of relay 1002 prevents the operation of relay 1007and a consequent shifting to the units register 1010, since relay 1007 is shunted by ground at the left armature of, relay 1003. On a subsecuent impulse which may be assumed to be the first normal impulse,

relays 1012 and 1013 re-operate to record this as the first impulse, subsequent impulses being recorded in the usual manner. This absorption of a preliminary impulse is made use of in dialing the central ofiice code, namely 11, in'such a manner that the first pulse is recorded on the preliminary pulse relays 1001 and 1002 and thesecond impulse is recorded on the relays 1012 and 10.13 without operating any relays of the units register 1010. The combination of

relays

1001 and 1012 causes the operation of a trunk relay 804: as described later in connection with an outgoing trunk call.

Trunk circuit outgoing cells.

When a local subscriber dials the special code 11 with the purpose of communicating with the central oilice, the operation is similar to that already described in connection with a. local call as far as the point where the number is recorded on the register 1000. In this case, since there is a units digit of 1,

the firstimpulse will cause the operation of" v relays 1001, 1002, 1012 and 1013. When relay 807 releases after this impulse, countingrelays1012 and 1013 release, but relays 1001 and 1002 remain operated. The subscriber then dials the units digit 1. This causes the re'operation of

relays

1012 and 1013. However, when relay 807 releases following the dialing of the units digit, counting

relays

1012 and 1013 remain operated from grounded conductor 1053, windings of

relays

1013 and 1012 in series, right armature and front contact of relay 1013, right outer armature and front contact of relay 1001, conductor 1054, to battery at the armature of relay 808. s I With counting relay 1012 and preliminary'pulse relay 1001 operated, a circuit is closed to operate trunk relay 804 from battery at the armature and contact of relay 815, right hand winding of relay 80 1, conductor 862,"left armature and contact of relay 1001, right inner armature and front contact of relay 1012, conductor 860, right normal contacts of relay 807, to the grounded conductor 1053. Relay 80-1": closes a locking circuit for itself from grounded'com ductor 1052, left inner armature, front contact and left winding of relay 804, to battery through the winding of relay 815 which operates and prevents the operation of other trunk relays similar to 804. When relay 804 operated,-it opened at its left outer armature and back Contact the holding circuit for relay 1006, which is slow to release.

Immediately that relay 804 operated, it

Y front contact of relay 406, conductor-751,

left outer armature and front contact of relay 804, left armature and contact of relay 801, conductor 850, to ground through the winding of relay 551. The operation of relay 405 closes a circuit for operating a trunk group relay 410 corresponding to the group in which the calling line is located, and also a trunk units relay 408 which corresponds to the units digit of the calling line. The circuit for relay 410 is from battery through its winding, lowermost armature and contact of relay 405, conductor 450, contacts of finder group relay 715, conductor 752, right outer armature and contacts of relay 804, conductor 863 of the intermediate link, contacts of finder relays 708 and 715, to ground at the key 910. In *the case of restricted service, there will be no groundat key 910 and thecalling subscriber will be unable to obtain connection with the central oflice.

The circuit for operating units relay 408,

' armature and contact in parallel through resistances 413 and 414 to provide locking circuits for the operated trunk units andtrunk group relays 408 and 410 respectively.

After an interval when slow relay 1006 has released, groundgis removed from the conductor 1051, thus causing the release of

finderrelays

708 and 715. The release of these latter relays disconnects primary link 712 and secondary-link 720 from the calling line, causing the release of relay 801, which in turn causes the release of relay 405. The

lVhen relay 415 operated subsequent to e the connection of line 101 with trunk 420, ground at the outer armature andfront contact of relay 415 was placed on the tip side of the trunk, causing the operation of the line relay at the central oflice and giving a signal to the operator. When the central oliice operator answers, relay 409 operates since it is bridged across the trunk. Relay 409 closes an obvious circuit for slow-release relay 417. The operation of relay 417 closes a circuit from battery through the winding of relay 418, right armature and contact of relay 416, to ground at the left armature and contact of relay 417. Relay 418 in operating, connects the calling line directly withthe central otlice trunk and releases relay 415. At the sametime, supervisory relay 419 operates, in turn closing an obvious circuit for relay 428. Relay 423 opens the operating circuit of relay 409 and provides a substitute holding circuit for relay 417. W hen relay 415 releasedit removed the short circuitfronr around the winding of relay 407, which now operates to render outgoing trunk 420 busy, and to extend the starting conductor 453 to the next idle link. y

Should all the central office trunks be busy when the calling subscriber dials the central ofiice code, a circuit will be closed from the grounded starting conductor 751, through the left armatures and front contacts of all relays similar to 407, conductor 451, left hand winding of relay 816, tobattery at the right inner armature and front contact of relay 804. A tone will then be transmitted from the tone source 550, conductor 552, conductor. 855, left inner armature and front contact of relay 816, condenser 810, and thence to the ring side of the calling line, notifying the calling subscriber of the busy condition.

lVhen the calling subscriber replaces the I receiver on the switchhook, relay 419 releases, causing the release of relay 423. The remainder of the connection is under the control of the central ofiice operator by means of relay 409 re-operating upon the release of relay 423, thus providing a holding circuit for relay 417 and maintaining the units and group connector relays energized. \Vhen the central office operator disconnects, relay 409 releases, in turn releasing relays 417, 418, 416 and the connector relays 408 and 410. Relay 407 also Iii releases. and renders trunk 420 selectable by other calling lines.

[ ncoming calls.

When a central ofiice operator plugs in on an incoming trunk, as shown in Fig. 2, relay 209 operates from a source of ground at the central oflice, (not shown) ring side of the trunk, left middle contacts of key 207, windings of relay 209, right normal contacts of key 233, inner normal contacts of relay 204, tip side of the trunk, right normal contacts of key 207, to battery (not shown) at the central oflice. Relay 209 closes an obvious circuit for slow release relay 210,- which causes the lamp 202 to be lighted as a signal to the attendant. lVhen ringing current is applied to the trunk, relay 213 operates since its left hand winding is bridged across the trunk in series with condenser 2 i. Relay 213 closes a locking circuit for itself from battery, through its right hand winding, right outer armature and contact of relay 216,1eft inner armature and contact of relay 213, to ground at the armature of relay 210. Line lamp 201 lights from battery through the winding of relay 560, conductor 253, lamp 201, to round through the left outer armature and front Contact of relay 213. Relay 560 operates in this circuit, causing buzzer relay 561. to vibrate, thus giving an audible signal to the attendant. The attendant answers by operating listening key 212, which connects her telephone set across conductors 263 and 26st and thence across the central office trunk .through the normal contacts of relay Relays 219, 220 and 221 also operate at this time over obvious circuits. After receiving the number of the desired station, the attendant operates stations key 203 and dials the desired number. Assume that the number of the wanted line is 23. llnniediately that the key 212 is thrown, relay 216 operates over an obvious circuit and closes a circuit from the grounded conductor 250, left normal contacts of'relay 217, left inner armature and back contact of relay right inner armature and contact of relay 216. to battery througl'i the guard lamp 208 which remains lighted until the called subscriber has answered. The operation of relay 216 also connected retardationcoil 218 in parallel with the right hand high resistance winding of relay 209. The operation of relay 216 also opened the looking circuit of relay 213, causing the line lam-p 201 to be extinguished.

Whenthe attendant operated stations key 203, ground was connected through the right.

middlecontacts of key 212, left contacts of key 203, in parallelcircuit to battery through the windings of relays 204C and 217. Relay 2041 transfers the talking set from the outgoingendof the tri-i-nk to theloc'al end,

thereby operating relay 222. Relay 217 closes a circuit from battery through the winding of relay 103, conductor 150, right outer armature, and contact. of relay 217, right armature and contact of relay 223, left outer armature and front contact of relay 217, to ground at key 206. Relay 103 operates in this circuit and extends the above traced ground through its lower armature and front contactover conductor 1.57 to battery through the winding of relay 303.

The attendant now dials the tens digit of the desired station. The release of relay 222 on the transmission of the first impulse, removes ground at its left armature and contact from the conductor 251, and con ductor 351, thus allowing relay 302 to operate from battery at the. armature and contact of relay 303, retardation coil 304:, winding of relay 302, to grounded conductor 350. a

This same battery is extended tln'oughthe right armature and front contact of re 302, winding of slow-release relay 305, ri t armature and back contact of relay 306, right outer armatures and back contacts of

relays

307, 308, 309 and 310 in series, windinn relay 31-1, to the grounded conductor 350. The operation of relay 311 closes a armature and back contact of relay 312, right armature and front contact of relay 311, left armatureandl back contact of relay 319, left normal contacts of relay 316, conductor 35 1, to battery at the armature and contact of relay303. At tl'ietermination of the first impulse, ground isagain applied to conductor 351, causing the release of relay 302 and the removal of the short circuits from around the windings of

relays

310 and 312, which now operate. The operation ofrel-ay 313 closed a circuitfrom battery at the armature and contact ofrelay 303, winding of relay 315, right armature and front contact of relay 313, to

ground at the left outer armature and contact of relay 316. Rela 315 looks in series with the winding of relay 306, but relay 306 does not operate since it is shunted by the above traced ;r1o11n l. of the called line is assumed to be 2, the transmissionof the second impulse causes the operation of counting relays 309 a nd 3111 and the release of

relays

310, 311, 312 and 313.; Following the dialing of the tens digit, relay 305 releases and removes the short circuit from around the. winding of relay .306, wl'iiclrnow operatesin series. with relay 315% the. grounded conductor 350.

The operation .of relay; 306' extends the tactof relay 300,;cotlda'1ictdf- 353, contacts mg of preliminary pulse relay 313, right Since the tens digit 1 circuit from grounded conductor 350, wind conductor of. the busy line.

condenser 2 'and front contact 'ofrelay 20f, left lnner of relay 103, to battery through the winding of group connector relay 110. Relay 110 closes a locking circuit for itself from battery through its winding and locking contact, conductor 152, left outer armatureand front contact of relay 217, to ground at key 206.

lVhen relay 306 operated, it also transferred the impulsing circuit to the 'units register 301 and the recording of the units digit is similar to that already described for a local call. In the case assumed relays 317 and 318 remain operated at the end of the units dialing. lVhen relay 305 releases at the termination of the units series, a circuit is closed from battery through the winding of units connector relay 113, contacts of relay 103, conductor 153, left inner armature ant front contact of relay 317, left armature and back contact of relay 820, resistance 321, right arniature and front contact of relay 315, left normal contacts of relay 3-05, to the grounded conductor 350. Re lay 113 closes a locking circuit from battery through its winding and locking contact, conductor 1, winding of relay 223 left outer armature and front contact of relay 217 to ground at key 206. Relay 223 operates in this circuit and opens the holding circuit for relay 103, which releases. Relay 103 causes the release of

relays

303, 315, 806 and the operated counting relays. The 'attendants sender is thereby released for use in connection with another call.

The testing of the called line is accomplished in substantially the same manner as described for a local call. Test relay 22 perated when relay 315 closed its left arma ture and front contact. If the called line is busy, relay 22 1 will remain locked through its right hand winding, normal contacts of relay 225, left outer armature and front contact of relay 224, to the grounded sleeve lVhen relay 224 closed its leftinn-er armature and front contact relay operated through its right hand winding. At the same time a circuit '*as closed for relay 225 from battery at the right armature and contact of relay 234:, winding of relay 225, left normal contacts of relay 225, to the above tracedground.

Relay also'locks to ground at key 206 and a busy tone is transmitted to the attendant from a tonesource 550, conductor 552, right armature and front contact of relay lower outer armature contacts of key 212 conductor 26f throu 'h the attendants set,'coi1ductor 263, left outer contacts of key 212. lower in'ner armatiu'e and front. contactof relay left normal left hand winding of relay By means ofkey 205, the central office can be automatically conuected'to a busyliue tact of relay 236, left outer armature and front contact of relay 224, to the grounded sleeve conductor of the busy line. Relay 23 1 looks through the left outer armature and front contact of relay 224: to the sleeve of the busy line. This condition exists until the called station becomes idle, at which time ground is removed from the sleeve, re

leasing relays 234 and 224. As soon as it becomes idle the desired station is therefore rung in the manner hereinafter described and without further action by the attendant.

Ifthe called line is idle", relay 224 will release after the units dialing but relay 226 will remain locked from battery through the winding of relay 501, left hand winding of relay 226, left inner armature and contact thereof, left inner armature and contact of relay 225, right armature and contact of relay 227, left outer armature and front contact of relay 217, to ground at key 206. he operation of relay 501 starts the ringing mechanism 550 and ringing current is transmitted over conductor 502, winding of relay 227, right outer armature and back contact of relay 224, right outer armature and front contact of relay 226, ring side of the trunk, thence over the ring side of the calling line through the subscribers ringing apparatus, back over the tip side of the calling line, tip side of the trunk, right inner armature and front contact of relay .226, right inner armature and contact of relay 22*1, conductor 511, to ground at the winding 502 of the ringing transformer. The attendant may now restore her keys. The restoring of'key 212 releases relays 204 and 217.

Vvhen the called subscriber answers, relay 227 operates, opening the holding circuit of relays 501 and 226, which release. Relay 501' stops the ringing mechanism, and relay 226 connects the called line to the contacts of relay 228, thus operating relay 222. this time. relay 230 operates from battery through its winding, left inner arn'iature and back contact. of relay 217, left armature and contact of relay 223, left outer.

armature and contact of relay 226, to ground at the left armature of relay 222. Relay 280 closes an obvious circuit for relay 23 Art the same time. a circuit was closed from contacts of. relay 228. to ground through the ground at the left armature and contact of relay 210. left aramature and front contact of relay 230, right contacts of key 203, left-contacts of key 3, a: battery'threugh the windings of relays 228 a ncl 229 in parallel. Relays 228 z 1'11d'229" locfk to ground at the armeture of relay 210, and reley 230 releases. The eperatio'l'i of r lay 228 com pletes the connection of the calling line with the central ollic'e trunk and releases feltty 222. Relay 229 closes a circuit from battery through the winding of relay 232 right inn'er arnmture and front contztct of relay 229, left inner arm'ziti'i're and frer'it contact of relay 221, left armature and back 0011- t-ziict of relay 230, to ground at the left arnittitre of: relay 210. Relay 232 locks in if, circuit trom battery through its winding and locking contact left noriii'al contacts of relay 217, to groi'in'd at the right armature O't relay 210. Relay 232 in ape-ratin cittlses guard lamp 208 to be extinguished as e signal to the attendant that the called subscriber has answered.

When the called subscriber hel' gs the receiver en the hook, lfeltys 219, 220, 221, 230, 228, 229, 231 and 21e1-e1ease Relay 232, however, remains locked; The release of the connector relays 110' and 113 is under control of the central ofltee by means of relay 210, which is operated through the Contact of the bridging relay 209. The" called sue scriber may recall the attendant by operating his sw'i'tcjl'i-hook, thus ausing the ree eraitiionof 1':elztys'219, 220 incl 221, and closing a circuit from battery throu h the right hand winding of relay 213 right outer in n iziture and contact of relay216, right inner ern'iatiire and contact of relay 232, left inner armature ztnd back Contact of relay 216, right outer ermature and contact Otrela'y 323, to ground at the left armature of relay 220 thus causing line lgnnp 201 to light and signal the attenclzi-ntllVhen the central 0ffi ce disconnects, relay 209 releases, in turn releasing relay 210 which causes the release of the remainder of the connection.

( ells t0 the attendant.

en" intermediate link with the ett'encla nfis line circuit 601. Ringing ciurcnt is applied to the line 601 in the manner previously described, thus causing relay 604' to operate anal the consequent lighting of lamp 002.

-ersj by operating akey The attendai'it an v (303 which is associatedwithlelnrp 602 and thereby connects her tel in'g set GO5if1direct connection Wit-lithe calling line. Should the attendant reswre key 603' while the Cell to battery.

scriber, in the nianner described for at local call.

Tone circuit.

lVhehever' rela 801 of an iiiterinecliate link circuit or relaly 222 of a trunk circuit operated, relay 551 Operites, in turn 0p- Relay 557 in operating", 7

eralting' relay 557. removes the short circuit from the high 1"e sistances and 554, thus causing the release'of relay 557. This process is continued, resulting in a tone. Relay 551 also closes an operating circuit for slmi releese relay relay 555 hi turn operztting relay 556. Relay in'operatieg, releases relay 555. Each time relzty' 556- o'pe'rates, it coiir jlete's the tone circuit through its right armature and Contact to" the tone leed 552. From this it will be seen that by 'neztfis 'o't cycle of operations of relays 555 and 556-, tone current is applied for 21 certain period and (l-isconnected for another period from the conductor 5'52.

Ringing circuit. 1

Whenever any link or trunk circuit is in the ringing condition, relay 501 operates, closing en ebyions circuit for slow-release relay Relz y 503" connects ground through its right a rinature anc f contact to operate" relay 506. Relay 506 in turn operates relzty 507;- lleliijy 507 causes the release of relay 506. By 11168115 of" the selfinterrupting characteroii' relays 5'06entl 5'07, grotrncl is intermittently connected :it the right armature and back contact of relay 507 to the Winding 510 of the ringing trans form-er.

Rela' y 503 also connected ground tlllOfigh its left arm-limit and contact, winiiling of relay 5'12' ,1 'i ;1it nor n'ail contacts on; relay 513, Relz'i-y512 operates and extends this sani'efg'rouncl through its left ktl'lllzltlllO and front contact to operate relay Relay after an interval (ip'eifi-tes and opens the o era-ting circuit of relay 512 which begi-itsto mie'asez- \Vhile relay 5121s reles-sing, gfoul'id (it the left uri'iitrt i ire of iel-ey 503 is connected through-the left zi iineture and. contact of relay 513 lelt {ii ture and back COIHEECU of relay 514-, left winding of relay 5T8, telnet vtl'irough the left Windi" of relay 11; A ey 51 8 6p hes" in t ll-1.2 ciircuit, b t relay 514 does not When relay 513 ieleiise's', ee-mid is coniiecte'd through the i""ght iiifier zilIlTitfil-H arid front contact of may 518', bothwindi gs-10f rel-11y 518- in series; to birttery through the left win me