US2241158A - Automatic telephone system - Google Patents

Description

May 6, 1941. w.'r. POWELL AUTOMATIC TELEPHONE SYSTEM- 9 Sheets-Sheet 1 Filed Sept. 21, 1939 I N VE N TOR w/A/heso TROWELL ORNEY.

y 1941- w. T. POWELL AUTOMATIC TELEPHONE SYSTEM 9 Sheets-Sheet 5 Filed Sept. 21, 1939 m2 m mh\ 3 o M I m m 93 vw S W I I III E Ro m \Q m? w M 1| I w ma Q 1 3 A I I I I l I I I I L 2 g1 W M Q NQ II A. A. A. A L JQQ 93 .1 L 1* 1- I I T II I Ill M may L m A A vvl L1 Yb II-r l I I I I I l.- I I I I 2 mm Si :2 3? m2 ATTORNEY.

w. T. POWELL 2,241,158 AUTOMATIC ,TIEILEPHONE SYSTEM Filed Sept. 21, 1939 9 Sheets-Sheet 4 Q Q L w I 9 \h 3 T: I. I Q Q Q Q Q Q Q Q I kQ T i T T Y N MM I L (I L QN\ B w m mw I r. L I TI v I I Li- I i IT I I I I T I I I I I I I I I ll .l

May 6, 1941.

I I I I l I I I I l l I I l I I I l I I I I I I I I l I I I I L:- LI- L I I m I 2 :3 I I I I I I I I I I INVENT OR. WIN/EEO T POWELL ATTORNEY.

W.IT. POWELL 2,241,158

AUTOMATIC TELEPHONE SYSTEM Filed Sept. 21, 1939 I 9 Sheets-Sheet a W/NFEED I POWELL ATTORNEY.

May 6, 1941.

May 6, 19 41.

w. 'r. POWELL AUTOMATIC TELEPHONE SYSTEM Filed Sept. 21, 1939 Sheets-Sheet 6 INVENTOR.

. B MtE 45m m WINFRED T. Fol/ELL ATTORNEY.

May 6, 1941.

w. r. POWELL' AUTOMATIC TELEPHONE SYSTEM Filed Sept. 21, 1939 9 Sheets-Sheet 'T ATTORNEY.

y6,1941 w. T. POWELL 2,241,158

AUTOMATIC TELEPHONE SYSTEM ATTORNEY.

y 1941- w. 'r. POWELL AUTOMATIC TELEPHONE SYSTEM 'Filed Sept. 21, 1939 9 Sheets-Sheet 9 TUTUTGTUT LfirUrUrUw U TU TU TU T mummm INVENTOR. Wl/VFRED TJPOWfLL BY A ATTORNEY.

INN

Patented May 6, 1941 S PATENT OFFICE AUTOMATIC TELEPHONE SYSTEM Winfred '1. Powell,

Rochester, N. Y., minor to The Stromberg-Carlson Telephone Manufacturing Company, Rochester, N. Y., a corporation of New York- Application September n, 1939, Serial No. 295,925

11 Claims.

This invention relates to telephone systems and more particularly to automatic telephone systems.

In automatic telephone systems of the type in which relays are employed as switching means a for completing a part or all of the telephone connections, provision must be made for completing trunk calls to and from a distant exchange. In such an arrangement provision mustpalso be made at the local exchange for transferring a trunk call originating at a distant exchange from one substation at the local exchange to any other desired substation thereat, the trunk in use being held during the transfer operation. Provision must also be made for releasing a connection from a calling substation to a busy called substation while signalling the calling substation of the busy condition.

The present invention ha for its purpose the improvement in such automatic telephone systems by the provision of novel circuit arrangements for meeting the above-mentioned conditions.

The drawings diagrammatically represent a telephone system when Figs. 1, 2, 3 and 4 are arranged end to end in order, reading from left to right, and when Fig. is placed below Fig. 4 and with Figs. 5, 6, '7, 8 and 9 placed end to end and arranged to read from right to left.

In these drawings Fig. 2 represents a call substation and its telephone line, and

Fig. 2a represents a portion of employed in a code call arrangement;

Fig. 3 represents a portion of a trunk circuit which terminates at a distant exchange represented by the dotted rectangle;

Figs. 4 and 5 when taken together indicate a call substation at a telephone line as well as a relay connector and certain oi the common equipment;

Fig. 6 represents a counting relay arrangement in which impulses dialed by the calling subscriber are counted and by which a relay connector is selectively operated;

Fig. 7 represents the major portion .of a link connector utilized in extending a telephone connection;

the circuits Figs. 1 and 8 represent a relay finder arrangement for connecting the telephone lines to links and to trunk circuits; and

Fig. 9 represents a lock-out arrangement whereby originating ,calls are. extended in sequence. This figure in the lowerright hand corner thereof, also illustrates a relay allotter which functions to assign idle link circuits for use in sequence. It is believed thatthe invention will best be understood by describing the operation of establishing a connection from a calling subscribers line such as that designated #11 (Fig. 2) to a called subscriber's line herein designated #41. When the calling subscriber removes his receiver from the switchhook to initiate a call, a circuit is completed for the line relay 5 of this line. This circuit is traceable from the negative pole of battery, winding of the line relay 5 (Fig. 9), conductor 6, back contact and armature of relay l, inner back contact and armature of the cutoff relay 8, telephone line conductor 9, thence through the calling substation circuits of the calling subscriber, telephone line conductor ll, outer armature and back contact and cutofi relay 8 to positive pole of battery. The line relay 5 when energized completes a lockout circuit whereby all of the remaining telephone lines of the group are disabled from making a connection until a link is extended to the calling telephone line and whereby a finder of the relay type extends a link to the calling subscribers line. The operation of the relay type finder is completed in a very brief interval of time so that the looking out of the remaining lines of .the group is not seriously objectionable. It will be appreciated that the lock-out arrangement is provided in order that two simultaneously originated calls will not be coupled to the same link.

The mentioned lock-out circuit is completed for the tens lock-out relay l2 and for the units lock-out relay l3. It will be appreciated that the tens lock-out relay i2 is common to all telephone lines of .the group having the numeral one as a tens digit designation, whereas the units lock-out relay I3 is common to all telephone lines of the group having the numeral one as a units digit designation. The operating circuit for the units lock-out relay i3 and for the tens lock-out relay i2 is traceable from the positive pole of battery, continuity spring and back contact of the relay l2 and thence thru the corresponding continuity springs and back contacts of the remaining tens lock-out relays of this group, namely relays l6, l5, l6 and I1, conductor l8, inner back contact and continuity spring of the relay l2, winding of this relay, conductor 19, front contact and armature of line relay 5, conductor 20, winding of the units lock out relay I3, its inner continuity spring and back contact, conductor 2i, outer back contacts and continuity springs of units lock-out relays 22, 23, 24, 25, I3 and resistance to the negative pole to the battery. The lock-out relays l2 and I3 are energized in this circuit and complete a locking circuitfor themselves from the negative pole of battery, inner armature, front contact and winding of the unit lock-out relay l3, conductor 28, front contact and armature of the line relay 5, winding of the tens lock-out relay I2, its inner front contact armature to the positive pole of the battery. While the tens lockout relay l2 and. the units lock-out relay l3 are thus held energized no other lock-out relays of the group can be energized since their energizing circuits are interrupted at the outer continuity springs and back contacts of the relays l2 and I3. T

As soon as the lock-out relays I2 and I3 are energized, the relay'2'l (Fig. 9) of a link allotter of the relay type is energized from the negative pole of battery, winding of the relay 21,- back contact and armature of the relay 28, conductor 23, front contact and armature of the look-out relay l2, conductor 38, armature and front contact of the relay l3, to the positive pole of battery. The allotter relay 2'! when thus energized, completes circuits for operating the tens finder relay 3| (Fig. 8) and the units finder relay 32. The circuit for the relay 3| is traceable from the negative pole of battery, winding of the relay 3|, conductor 33, armature and front contact of the relay I2, conductor 34, armature and back contact of the relay 28, uppermost front "contact and armature of the relay 21 to the positive pole of battery. The units finder relay 32 has lts circuit likewise traceable from the negative pole of battery, winding of the relay 32, conductor 35, armature and front contact of the units lock-' out relay l3, conductor 36, armature and back contact of relay 38, inner front contact and armature of relay '2'! to the positive pole of battery. With the tens finder relay 3| and the units finder relay 32 energized, the tip conductor 31, the ring conductor 38 and the sleeve conductor 33 are extended thru the contacts of the units finder relay 32 and the tens finder relay 3| to the corresponding conductors 48, 4| and 42 of the allotted trunk or link circuit. The extension of the calling line conductors 31 and 38 to the link conductors 48 and 4|, completes a circuit including these conductors in series with the upper and lower windings of the differentially wound relay 43 (Fig. '7) and of the calling bridge relay 44 which also serves as an impulse relay. The relay 44 is energized in the circuit but the differentially wound relay 43 is not operated at this time. On the operation of the relay 44 the slow releasing relay 45 is energized from the negative pole of battery, winding of this relay, middle front contact and armature of the relay 44, conductor 46, back contact and armature of the trunk release relay' 41 to the positive pole of battery. When the relay 45 is operated it closes an obvious operating circuit for the relay 55. Also as soon as slow releasing relay 45 is operated, it closes a locking circuit for the tens to the positive pole of battery. The operation of the relay 45, thru its armature 52 and front line to an allotted link circuit.

contact, connects .the positive pole of battery through the winding of the relay 53, to the sleeve conductor 42 of the link. This sleeve conductor, on the'operation of the relay finder is connected to the sleeve conductor 39 of the calling line and this last-named conductor is connected thru the right-hand armature and back contact of the r y 1 (Fi 2), winding of the cutofl relay 8 to the negative pole of battery. The cutofl relay is thus energized and thru its innermost front contact and armature completes a locking circuit for itself independently of the control of the relay 1. The operation of the cutoff relay 8 also disconnects the line relay 5 from its related telephone line. Relay 5 thereupon releases and efiects the release of the look-out relays l2 and i3 so that they are again in readiness to cooperate in extending another telephone calling Although the operations just described in extending a calling line to a link appear rather involved, they are effected in a matter of a fraction of a second. As soon as the cutoff relay operates, the slow releasing relay I is energized from the negative pole of battery, righthand winding of this relay, front contact and armature of cut-off relay 8 to the positive pole of battery.

It will be recalled that the relay 2! of the link allotter was operated following the initiation of the call to effect the operation of the tens finder relay 3| and the units finder relay 32 in order to connect the calling line to the link. On the operation of the relay 55, which was efiected as soon as the slow releasing relay 45 was energized, a circuit was completed for operating the number one allotter relay 28. This circuit extends from the negative pole of battery, lower winding of relay 28, conductor 56, lower front contact and armature of relay 55 to the positive pole of battery. Relay 28 when thus operated is locked actuated in a circuit from the negative pole of battery,'upper winding of this relay, its inner front contact and armature, back contact and armature of relay 51, which is the number 4 allotter relay of the series, to the positive pole of battery. Thus, on the next originating call, the relay 58' (Fig. 9) which is individual to the number two link will respond in a manner similar to the operation of the relay 21 which operated as previously described to extend the calling line to the number one link. It will be understood that the relays 59 and 60 will operate and lock in succession to allot the next link circuits in the groupfor connection to other telephone lines. However, when the relay 5! associated with the last link of the group is operated, it interrupts the locking circuits of the previously operated allotter relays so that they allot their individual link in succession.

As soon as the relay 45 was energized in response to the completion of the connection of the calling line to the allotted link circuit, the relay 5! (Fig. 6) associated with the counting relays of theconnector was energized. The energizing circuit for the relay 5! is traceable from the negative'pole of battery, winding of the relay 51, innermost lower back contacts and armatures of the counting relays 58 to 63 inclusive, conductor 64, upper armature and back contact of relay 55, conductor 66, upper armature and back contact of relay 49, conductor 81, back contact and armature 88 of relay 69, conductor 18, upper front contact and armature of relay 45 to the positive pole of battery. When the relay 5! is operated it applies a dial tone thru its front nected to an idle link circuit in the manner described and has received the dial tone, the calling subscriber operates his dial impulse sender to transmit several series of code impulses corresponding to the respective digits of the wanted party's line. Let it be assumedthat the called subscribers line is designated number 4|. The calling subscriber first operates his impulse sender to transmit four impulses, that is, the line circuit will be interrupted four times and after a pause it will be interrupted once to transmit an impulse corresponding to the units digit one. In response to each of the four tens impulses, the calling bridge relay 44 releases and attracts its armature four times. However, the slow releasing relay 45 remains operated during the sending of this series'oi impulses.

When the impulse relay 44 releases in response to the first interruption of the line circuit corresponding to the first impulse of the tens digit,,the relay 44 releases. This causes the energization of the number one counting relay 58, from the negative pole of battery, windin of this relay, conductor 1i, uppermost front contact and armature of relay 51, conductor 12, armature and back contact of the pulse lock relay", conductor 14, uppermost front contact and armature ofrelay 55, uppermost armature and back contact oi'relay 44, conductor 15, up-

per armature and back contact of the release relay 49, conductor 81, back contact and armature 88 of the cut-in relay 88, conductor to the positive pole of battery at theupper armature and front contact of relay 45. The number one counting relay when thus energized, closes a locking circuit for itself from of battery, its winding, its innermost, lower front contact and armature and thru the innermost back contacts and armatures of the counting relays 58 to 63 inclusive, conductor 64, back contact and armature of relay 65, conductor 56, armature and back contact of relay 49, conductor 61, back contact and armature 68 of relay 69, conductor 10 to the positivepole of battery at the front contact and armature of relay 45. A locking circuit is also completed for the relay 51 from the negative pole of battery, winding of this relay, its inner front contact and armature, conductor 16, front contact and armature of relay. 55, back contact and armature of relay 44, conductor 46, backcontact and armature of slow releasing relay 41 to the positive pole of battery. "When'the impulse relay 44 operates after the first impulse just described, the relay 51 is released since its holding circuit is interrupted at the armature and back contact of the mentioned relay .44. The number one counting 'relay 58 however remains energized since its holdering circuit is independent of the relay 44.

When the impulse relay 44 is again deenergized in response to the second impulse of the tens digit, the number two counting relay 59 is energized from the negative pole of battery, winding of this relay, conductor 11, front contact and armature of relay 58, uppermost back contact and armature of relay 51, conductor 12, back contact and armature of relay 13,

conductor 14, uppermost front contact .and armature of relay 55, uppermost armature and back contact of relay 44, conductor 15, armature and back contact oi relay 49, conductor 81,-back the negative pole 'ture of the relay 41.

contact and armature 58 of the cut-in relay 69, conductor 10, front contact and armature of relay 45 to .the positive pole of battery. The number two counting relay 59, when thus energized, closes a locking circuit for itself from the negative pole oi battery, winding of this relay, its innermost lower front contact and armature, innermost lower back contacts and armature of relays 60 to 88 inclusive, conductor 64, back contact and armature of relay 55, conductor 66, upper armature and back contact of relay 49, conductor 51, back contact and armature 68 of relay 69, conductor 10 to the positive pole of battery at the upper front contact and armature of relay 45. The locking circuit for the relay 58 is now interrupted at the innermost lower back contact and armature of the relay 59 but before the number one counting relay 58 releases, a substitute locking circuit is closed for itself from the negative pole of battery, winding oi the relay 58, its innermost upper front contact and armature, inner back contact and armature of relay 51, conductor 16, front contact and armature of relay 55, back contact and armature of relay 44', conductor 46 to the positive pole of battery, at back contact and arma- This last-described circuit locks .the number one counting relay in operated condition until the relay 44 is again energized at the conclusion of the number two impulse of the tens digit, at which time it releases.

In response to the third impulse of the tens digit, the number three counting relay 60 is operated and locked operated in the manner previously described while the number two counting relay will be held operated until the impulse relay 44 is again operated at the conclusion of the third impulse, at which time it releases. Similarly, in response to the fourth ten series of impulses.

impulse, the number four counting relay 6| is energized and is locked operated over circuits similar to those already described. When the impulse relay 44 is operated at the conclusion of the fourth impulse, the number three counting relay 60 releases but the fourth counting relaytl is maintained operated at this time. In the course of the transmission of the four impulses corresponding to the tens digit, the relays 51, 58, 59, 60 and GI are operated and releasedin turn, with the exception of the number four counting relay 6! which is held operated until the tens connector relay is operated in the manner to be described. It will be noted that there are no time margins or marginal relay operations in this counting circuit since each relay is operated in turn in response to the transmission of each impulse from the dial sender at the subscriber's station and during the closed circuit intervals between impulses, a preceding counting relay of the series is released to close a break point in the operating circuit for the next counting relay in the series to be operated by the next impulse.

The change-over relay 11 is operated in response to the first impulse of the tens digit and owing to its slow releasing characteristics is maintained operated during the sending of the The circuit for thus operating change-over relay 11, extends from the negative pole of battery, winding of this relay, conductor 14, uppermost front contact and armature of relay 55, uppermost armature and back contact of the impulse relay 44, conductor 15, upper armature and back contact of relay 49, conductor 61, back contact and armature 68 of relay 68, conductor 18 to the positive pole of battery at the front contact and armature of relay 46. At the conclusion of the sending of the four impulses corresponding to the tens digit as a result of which the number four counting relay 6| has been operated and locked operated, the impulse relay 44 will be energized for a suflicient period so that the change-over relay 11 will release, its operating circuit being interrupted at the uppermost armature and back contact of the impulse relay 44. v

As soon as the change-over relay 11 releases, a circuit is completed for operating the fourth tens connector relay 18. Since the number four counting relay has beenoperated, the operating circuit for the connector relay 18 extends from the negative pole of battery, winding of this relay, conductor 18, lowermost front contact and armature of the number four counting relay 6|, lowermost back contacts and armatures of the relays 68, 68, 68 and 61, back contact and armature of relay 88, conductor 8|, armature and back contact of change-over relay 11, conductor 82, back contact and armature 68 of relay 68, conductor 18 to the positive pole of battery at the front contact and armature of relay 46. The connector relay 18 when thus operated closes a locking circuit for itself from the negative pole of battery, winding'of this relay, its inner front contact and armature, conductor 83, inner front contact and armature of relay 46 to the positive pole of battery. Also as soon as the connector relay 18 is operated, a circuit is 'closed for the lease of the relay 66interrupts the initial operating circuit for the transfer relay 88, which circuit extended thru its upper winding. However, the relay 88 is now locked operated thru its lower winding, but the' change-over relay 11 releases.

Also as soon as the relay 66 releases, a circuit is closed thru the back contacts and armatures of counting relays 68- to 63 inclusive, for operating the relay 61 which circuit is identical with that previously described as completed prior to the sending of the tens series of impulses. With the relay 61 again energized, the series of counting relays are in readiness to count the series of impulses corresponding to the units digit.

Since it has been assumed that the units digit is one, the impulse sender at the calling subscriber's station transmits one impulse in response to which the impulse relay'44 retracts its armatures. When this takes place, the number one counting relay 68 is operated and locked operated over circuits identical with those previously described in connection with the counting of the tens digit series of impulses. It will be recalled that the operating circuit for the numher one counting relay extends from the negative 'pole of battery, winding of this relay, conductor winding of this relay, its lower front contact and ture of relay 18, conductor 85, to the positive pole of battery. The operation of the relay 66, at its armature and back contact, interrupts the previously described circuit which has been holding the number four counting relay 6| operated so that this counting relay now releases and the series of counting relays is in readiness for operation in counting the impulses corresponding to the units digit. The release of the number four counting relay 6|in the manner just described completes a circuit for operating the transfer relay 88. This circuit extends from the negative pole of battery, winding of the change-over relay 11, conductor 14, armature and back contact of relay 18, conductor 12, armatures and back contacts of relays 61 to 63 inclusive, conductor 86, upper winding of the transfer relay 88, front contact and armature of relay 66, conductor 66, armature and back contact of release relay 48, conductor 61, back contact and armature 68 of relay 68, conductor 18 to the positive pole of battery at front contact and armature of relay 46. Change-over relay 11 is also energized in this circuit with the transfer relay 88, but the operation of the change-over relay 11 performs no useful function at this time. The transfer relay armature and through the lower back contacts and armatures of relays 68, 68, 8|, 62 and 63 and thence to the positive pole of battery over the conductor 64 as previously described.

With the number one counting relay 68 thus operated and change-over relay 11 released, a

circuit is completed for the number one units connector relay 81, from the negative pole of battery, winding of the relay 81, conductor 86,

front contact and armature 88 of relay 68, back contact and armature of relay 61, middle front contact and armature ofjthe transfer relay 88 :inow operated) conductor 8|, armature and I back contact of change-over relay 11, conductor 82, back contact and armature 68 of relay 68, conductor 18, front contact and armature of relay 46 to the positive pole of battery. Connector relay 81 when thus energized is locked operated from the negative pole of battery, winding of this relay, conductor 88, front contact and armature I of relay 81, conductor 83, front contact and armature of relay 46 to the positive pole of battery. The release relay 66 is now operated, from the negative pole of battery, winding of this relay, armature and front contact of relay 88, conductor 8|, front contact and armature of relay 81, conductor to the positive pole of battery."As soon as the release relay 65 is operated it opens the locking circuits of the counting relays which have been operated, in this case the number one counting relay 68.-

As soon as the tens connector relay 18 and the unitsconnector relay 81 are operated, the called line #41 (Fig. 4) has its tip conductor 82, its ring conductor 83; and its sleeve conductor 84 extended thru the contacts of these relays to the corresponding tip, ring and sleeve conductors 86,

-86 and 81 of the called and of the link circuit connect the ringing current, Also when the which was seized by thecalling telephone line. The test-of the called line #41 is now made. it be assumed that this line is idle at this time. Under this condition the change-over relay 11 (Fig. 7) is actuated from the negative pole of battery, winding of relay ll, conductor 14, armature and back contactof relay I3, conductor 12, armature and back contacts of relays 51 to 63' inclusive, conductor 96, upper winding of relay 99 (Fig. 6), front contact and armature of relay 65, now operated, conductor 66, armature and back contact of release relay 49, conductor 61,, back contact and armature 98 of relay 69, conductor 19, front contact and armature of relay, to the positive pole of battery. The

operation of the change-over relay ll completes a circuit for operating the cut-in relay 69. This circuit extends from the negative pole. of battery, winding of the relay 69, its continuity spring and back contact, armature and front contact of relay 11, conductor 9!, front contact and armature of relay 81, conductor 85 to the positive pole of battery. The relay 69 when operated closes a locking circuit for itself thru its continuity spring and armature, conductor 79 to the positive pole of battery, at the armature and front contact of relay 45. The operation of the cut-in relay 69 interrupts the energizing circuits of the changeover relay H and of the transfer relay 99 which circuits, it will be recalled, extend thru the back contact and armature 9B of relay 69. The cut-off relay of the called line is operated over the sleeve conductor 94 of this line, sleeve conductor 91 of the called end of the link connected thereto, front contact and armature 68 of relay 99, conductor 79 to the positive pole of battery at the armature and front contact of relay 45. the sleeve conductors 91 and 99 provide a busy potential for rendering thecalled line busy.

It has been mentioned that the change-overrelay H is slow-releasing and therefore before it retracts its armatures, a circuit is completed for the ringing relay 99, from the negative pole of battery, resistance, winding of this relay, front contact and middle armature of the change-over relay ill, sleeve conductor 91, which it will be recalled is now connected over conductor 19 to the positive pole of battery at the armature and front contact of relay 45. The ring relay 99 as soon as it is operated, closes a locking circuit for itself thru its lower front contact and armature, holding conductor 10 to the positive pole of battery at the armature and front contact of relay 45.

On the operation of the ringing relay 99, in terrupted ringing current is applied to the tip and ring conductors 95 and 99 of the called end of the link circuit in use'and thence to the corresponding conductors of the called line which include the ringer of the called line. The conductors 95 and 9B are connected to the-ringing generator thru armatures and front contacts of the cut-in relay 99 and ringing relay 99. It will be understood that ringing circuit leading to the ringing, generator (not shown) includes the ringing trip relay E99. Interrupted ringing cur rent is applied to the ringer (not shown) at the called substation over the circuit 'just described, until the called party responds by removing his receiver from the switch hook. When this takes place the marginal trip relay I is operated and at its armature and front contact closes a shunt circuit about the ringing relay 99 causing this last-named relay to release and thereby dis- The positive battery thus applied to ringing relay 99 releases, the battery feed relay NH of the called end of the connection is connected in series with the differentially wound relay )2 to the tip and ring conductors 95 and 98 of the called end of the link.

The release of the telephone connection just completed is efl'ected by the calling subscriber when he replaces his receiver on its switch book. This act opens the line circuit at the switch hook contacts and thereby effects the release of the impulse relay 44 and in turn the slow releasing relay 45. It will be recalled that the relay 45 when operated applied the positive pole of bat! tery to the holding conductor I0. Thus when the positive pole of battery is disconnected from the holding conductor 19, the tens connector relay 78, the units connector relay 81 and the tens finder relay 3| as well as the units finder relay 32 are released. The relay 45 also opens the sleeve conductor 42 of the calling line and therefore efiects the release of the calling cut-oil relay 8. Likewise, the release of the relay t9 effects the release of the relay 55 as well as the cut-off relay of the called line because the circuit of this last-mentioned relay which extends to the positive pole of battery over the sleeve conductor of this line, is interrupted'at the front contact and armature of relay t5.

- In the event that the called line was busy at the point in the operation when it was tested, then the positive pole of the battery would be connected to the sleeve conductor of that line either over a conductor similar to conductor ti,

and calling end of the link to the positive pole of battery at the armature 52 and front contact of relay 45, or over a conductor similar to the sleeve conductor 91 of the called end of the link and thence over the holding conductor it to the positive pole of battery at the armature and front contact of relay 45. Referring back to the time when the units connector relay 9? was operated, a circuit is closed for operating the relay 990i the link circuit. The operating circuit for the relay 49 extends from the positive pole of battery on the sleeve conductor of the called line which extended thru the armatures and contacts of the units connector relay 8! and the tens connector relay-18 to the sleeve conductor 97 of the link, armature and back contact of the change-over relay 11, conductor I09, back contact and armature of relay 69, back contact, continuity spring and winding of the release relay 49, conductor I94, winding of the busy relay I09 (Fig. 2) to contact and armature of the cut-0E relay 8 and thence thru the calling subscribers receiver at the calling station and then over the telephone line conductor II to the positive pole of battery at the armature and back contact of the cut-oi! relay 8. r

It should be pointed out that the change-over relay 1! cannot be energized to initiate the selection of the called line now'assumed to be busy, inasmuch as the change-over relay circuit is now open at the back contact and armature of the release relay 49. 'Since the change-over relay 11 cannot be operated under the conditions asthe conductor 9 s'umed, the cut-in relay 69 and the ringing relay 99 will not be energized to eflect the application of ringing current. holding circuit of the tens finder relay 3| and the units finder relay 32 include the conductors 48 and 50 which are normally connected in series thruthe lowermost armature and backcontact of relay 49. Therefore when the release relay 49 is energized the holding circuits for these finder relays are interrupted so that they release to disconnect the calling line from the selected link. The cutoff relay 8 (Fig. 2), of the calling line which was maintained operated over the sleeve conductor 39 of the calling line and the sleeve conductor 92 of theselected link also has its circuit interrupted when the finder relays disconnect the calling line from the link. In addition the disconnection of the link from the calling line interrupts the operating circuit of the impulse relay 44 which releases and in turn effects the release of the slow releasing relay 45. Relay 45 on deenergizing effects the release of the various operated relays of the link in the manner previously described.

When the cutoff relay 8 releases in the manner just mentioned, the calling line circuit including is extended thru the armatures and back contacts of the cutofi relay 8, armature, front contact and lefthand winding of the relay 1 and thence thru the righthand winding of the busy relay 185 which is common to a group of lines. The busy relay m9 connects busy tone current to the calling line and the relay 1 remains operated to maintain the calling line disconnected from its line relay so that this line relay cannot now connect the calling line to another link circuit. It will be appreciated that the cutoff relay 3 cannot be energized while the receiver at the calling substation is off of its switch hook since the initial operating circuit of the cutofi relay is maintained open at this time at the righthand armature and back contact of the relay 1. The energization of the busy relay I85 starts the busy tone machine and the busy tone current is applied to the calling line by being induced from the lefthand winding of 'the relay Hi5 into the It will be recalled that the digit impulse, the system operates as previously described to effect the operation of the number one counting relay 58. At the end of the tens series of impulses the number one tens connector relay I01 is operated and locked operated in a manner similar to that already described. In response to the single units impulse the number one counting relay 58 is again operated andin this instance is effective to complete a circuit as previously described for operating the number one units connector relay 81. The energization of these last-mentioned connector relays extends the link circuit, which is connected to the calling line, to the code call unit shown in Fig. 2a. The positive pole of battery is connected at this time to the sleeve conductor I08 of the code call unit, which conductor includes the winding of the start relay I09 and is connected to the negative pole of battery. The start relay ")9 at its front contact and armature completes a circuit for starting the code call current generator (not shown). It will be noted that the tip conductor H0 and the ring conductor III of the code calling network are connected thru the impedance coil H2 so that this closed circuit across these conductors actuates the trip relay I90 to prevent ringing current from the link being applied to the code call network. If the calling party does not hear a busy tone signal in his telephone receiver at this time, he knows that the code call is idle, and he then proceeds to dial the code of impulses assigned to the party wanted. For example, he may dial the digit two twice in order to give two short rings or he may dial 0 twice to righthand winding thereof to which winding the a calling line is connected. When the calling subscriber replaces his receiver on its switchhook the telephone line circuit is opened whereupon the slow releasing relay 1 releases and all of the circuits employed in the telephone connection under consideration are restored to their normal condition.

The present system is arranged so that a party at any station of the system can establish code call conditions whereby signals such as bells or lights or both may be operated according to predetermined codes in order to locate various persons in a plant where the system may be used. In effecting the code operation of the system, a party desiring to initiate code call signals, is instructed to dial a predetermined number. In the system herein disclosed the predetermined number is assumed to be #11. It will be understood that the use of #11 for the code call prevents the use of this number for a subscribers line. The subscriber, after removing his receiver from the switchhook and after receiving the dial tone indicating that his line has been connected to an idle link circuit, first operates his dial sender to transmit one impulse corresponding to the give two long rings. of cours it will be understood that various codes of long and short impulses may be assigned for use in signalling various parties. The core call impulse circuit extends from the negative pole of battery, winding of the relay H3, conductor il' i, front contact and armature of the units connector relay 81, front contact and armature of the tens connector relay ifi'l, conductor H5, uppermost armature and front contact of relay Nil, conductor lit,

back contacts and armatures. of the counting relays 92 to 51 inclusive, conductor 16, front contact and armature of relay 55, back contact and armature of the relay impulse i l, conductor 66, back contact and armature of the trunk release relay 91, to the positive pole of battery. Thus on each deenergization of the impulse relay 44 in response to each of the code impulses transmitted by the calling subscriber, an impulse is transmitted over the last-described circuit to the pulse relay H3. It will be noted that the relay 3' is slow releasing and will remain operated during a series of properly timed impulses. Thus it will remain operated for a comparatively long interval of time when the #0 digit is dialed and will remain operated for a comparatively short interval of time when the digit two is dialed. The operation of the relay H3 applies generator current thru its armatures and front contacts to the conductors H1 and H8 across which the code call signals such as l'l9 are connected in multiple. Thus the signals herein shown illustrated as bells ring the predetermined code at their various locations. When the wanted party hears his code on the common code bells H9 he answers by dialing a predetermined number, e. g. the number 12. The party answering, of course, goes to the nearest telephone'and removes the receiver from the switchhook thereat, which results in connecting this line to a second link cirto .the single tens cuit. The desired party thereupon sends impulses-according to the number 12 which, of course, operates first the number one counting relay associated with the link circuit connected to his line and the operation of this relay'efiects the energization of a number one tens connector relay similar to II". In response to the units digit #2 the counting relay 59 is likewise oper- 'ated in the manner already described. The operation of this counting relay causes the operation of a number two units connector relay similar Ito I20. The operation of the mentioned tens and unit connector relays extends the line #12 to the link circuit thathas been used by. the calling party. As soon as this connection has been established positive potential on the sleeve conductor I2I energizes the make busy relay I22 which relay at its armature. and front contact connects the positive pole of battery to the sleeve conductor I08 connected to the link used by the calling telephone line, thereby maintaining the code call number busy until both parties to the connection have replaced their receivers on the switchhooks. The tip and ring conductors at the calling end of the link used by the answering party are thus connected to the tip and ring conductors of the calling end of the link used by the calling party because these are common to the code call circuit.

Thus a talking connection is established between the callingand the called parties. The release of the connection used by the callin party releasesthe link and the other apparatus used by him and a link and apparatus used by the answering party is similarly released when the answering party hangs up. The release of both of these connections restores the code call apparatus to normal condition.

In accordance with the present invention it is proposed to provide for trunk call connections from the present system either to a distant manual telephone ofiice or to a distant automatic telephone office by means of two-way trunks between the present system and. a central ofllce of either of the mentioned types. lines in the present system may be arranged to have restricted or unrestricted connection to the mentioned trunks, that is certain of the telephone lines can obtain connection to these trunks while other lines of the system are so arranged that they cannot be connected to said trunks. Let it be assumed that a calling party on a tele- The telephone phone line arranged for unrestricted service, de-

sires connection to a trunk leading to a distant ofice. This subscriber is instructed to dial a predetermined number, for example, #55, to select the first idle trunk leading to the central oflice (Fig. 3). However, in the case of incoming calls from the distant central ofilce, the central omce operator plugs into an idle trunk and ringing current applied to this trunk is effective to operate one or more bells in the present automatic exchange. Any person hearing these bells can answer the incoming trunk call by removing the receiver from the switchhook of any telephone line in the system and dialing a predetermined number, for example, the #66.

Let it be assumed that it is desired to initiate a call from an unrestricted telephone line in the system to a distant exchange. The subscriber does this by removing his receiver from its switchhook and as soon as he hears the dial tone he dials the predetermined trunk number 55. On removing the receiver from the switchhook, the apparatus operates to extend the calling line to an idle link circuit thru the operation of a tens finder relay and 2. units finder relay in a manner previously described in extending a call between local subscribers. As soon as the linkis connected to the calling line, the dial tone is applied to this line and the subscriber operates his dial sender to transmit five tens impulses; In response to these five impulses the counting relays are operated in a manner already described to energize the #5 counting relay B2. In response to the operation of this relay the tens connector relay I23 is operated in manner similar to that already described. The calling subscriber then transmits five units impulses corresponding to the units digit of the predetermined number 55. In this instance the counting relays of the selected link will attempt to count the five units impulse of the second or units digit but the counting will be stopped and the corresponding counting relay will be locked operated at the first idle trunk in the group of five trunks leading to the distant ofiice. In other words if trunk number one is idle, only one of the five units impulses will be effective to operate the counting relays and the remaining four impulses will be ineffective. However, if trunk number 5 is the first idle trunk then all of the five impulses oi the units digit will be counted and the number 5 counting relay 62 will be operated and locked. If all five trunks of the group are busy then all of the five units impulses will be counted but a busy circuit will function to signal the calling party that all of the trunks in the group are busy.

Let it be assumed that the trunk illustrated in the drawings (Fig. 3) is the number one trunkand that this trunk is idle.- Under this condition when the subscriber transmits five impulses of the units digit the impulse relay 44 will release five times after which it will remain energized. The first release of the relay M in response to the first impulse is efiective to operate the number one counting relay 58 at which time the relay 5'! releases when the relay 44 operates at the end of the first impulse. Since the trunk number one is assumed to be idle the relay I3 is now operated from the negative pole of battery, winding of relay I3, armature and front contact of the number one counting relay 58, conductor I25, front contact and armature of the tens connector relay I23, conductor I26, back contact and armatur of the make busy relay I21, conductor I28, back contact and armature of the slow releasing relay I 29 (Fig. 3) to the positive pole of battery. This operation of the relay I3 opens the circuit including the conductor I2 so that the remaining counting relays of the series will not be operated in response to impulses, that is the remaining four impulses are of no effect. In the event that the first four trunks of the group of five trunks are busy, the relays similar to I29 thereof will be energized so that no circuit will be completed for operating the relay I3. When however, the fifth units impulse is recorded on the number five counting relay 62, the relay I3 will be operated in a circuit similar to that described but in this instance will be complete from the back contact and armature of a relay similar to I29 at the fifth trunk of the group.

Since it has been assumed that the first trunk is idle and only one units impulse effectively registered, the units connector relayii'i will be operated over a circuit as described so that the trunk #1 will be selected although the number 55 has been dialed. At the conclusion of the operation of the counting relays, the release relay 65 is operated over the conductor 9i, its circuit being completed at the front contact and armature of the connector relay 81. With the relay 65 energized, the operated counting relay, in this instance the number one counting relay 58, is released since its holding circuit is interrupted at the armature and back contacts of relay 65. Thechange-over relay 11 is now operated fromthe negative pole of battery, winding of this relay, armature and back contact of the relay 13, conductor 12, armatures and back contacts of relays 51 to 63 inclusive, conductor 86, upper winding of the relay 80, front contact and armature of release relay 65, conductor 66, armature and back contact of relay 49, conductor 61, back contact and armature 68 of relay 69 and thence over the holding conductor 19 to the positive pole of battery at the front contact and armature of relay 45. When the change-over relay 11 operates, cut-in,relay 69 and the ringing relay 99 are operated as previously described. A circuit is now completed from the negative pole 'of battery, resistance, back contact and armature of the make busy relay I21 (Fig. 3), conductor I30, armature and front contact of the units connector relay 81, conductor I3I, lefthand winding of the relay I99, conductors I32 and I33, front contact and armature of the number five tens connector relay I23, conductor I34 and conductor 91, front contact and armature of relay 69 and thence over the conductor 18 to the positive pole of battery at the front contact and armature of relay 45. in turn operates the finder marking relay I35 (Fig. ,3). This circuit extends from. the negative pole of battery, winding of the relay I35, conductor I36, front contact and armature of the relay I99, armature and back contact of the relay I31 which is common to the group of trunks, to the positive pole of battery. With the finder marking relay I35 operated the trunk marking Relay I99 operates and relay I38 is energized in a circuit from the positive pole of battery, winding of this relay, conductor I39, armature and front contact of the units connector relay 81, conductor I48, armature and front contact of relay I99, conductor I4I, front contact and armature of relay I35, conductor I42, righthand winding of the relay I99 to the negative pole of battery. This circuit operates the trunk marking relay I38 and holds the relay I99 operated.

At this time the tens finder relay I44 (Fig. l) and the units finder relay I of the number one trunk are operated to connect this trunk to the calling line number II. Relay I44 is operated in a circuit from the negative pole of battery, winding of this relay, armature and, front contact of the trunk marking relay I38, armature and front contact of the finder marking relay I35,

conductor I46, and 33, frontcontact and armature of tens finder relay 3|, conductor 48, back contact and armature of the release relay 49, conductor 58, front contact and armature 5I of the slow releasing relay 45 of the link. Similarly the units finder relay I45 is energized in a circuit from the negative pole of battery, winding of this relay, armature and front contacts of relays I 38 and I35, conductors I41 and 35, front contact and armature of units finder relay 32 and thence over conductor 48 and the remainder of the circuit already described to the positive pole of battery at the front contact and armature 5| of relay 45. The operation of the tens and units finder relays I44 and I45 extends the tip, ring and sleeve conductors 31, 36 and 39 of the subscribers line #11 to the tip, ring and sleeve conductors I46, I41 and I98 of the trunk, thence thru both windings in series of the relay I48 (Fig. 3) of the trunk, conductors I49 and I59, back contacts and continuity springs of the holding relay I5I thru both windings in series of the differentially wound relay I52 from whence one side of the circuit is extended thru the continuity spring and back contact of the relay I53, Winding of the relay I54 to the positive pole of battery. The other side of this circuit is extended from the lower winding of the differential relay I52, back contact and inner armature of relay I54, trunk line conductor to the distant office, armature and backcontact of the cut-off relay I55 associated with the operators trunk circuit, winding of the line relay I56 also associated with the trunk circuit, to the negative pole of battery. Differential relay I52 does not operate at this time but the line relay I56 operates to signal the operator who plugs in an idle cord circuit to the related trunk. The relay I 48 is also energized in this circuit and at its inner front contact and armature it completes a circuit for operating the slow releasing relay I5 1. The relay I51 at its inner upper front contact and armature completes an operating circuit for the slow releasing relay I29. Relay I29 on operating, completes a circuit from the positive pole of battery, its armature and front contact, conductor I58, armature and back contact of relay I 18, armature and front contact of the tens finder relay I44 and winding of this relay to the negative pole of" battery and in multiple therewith thru the armature, front contact and winding of the units finder relay I45 to the negative pole of battery. These last-described circuits function to lock the finder relays in operated condition.

Referring back to the point in the description moves positive battery potential from the relays such as I99, I60, I6I and I62 to prevent the operation of other finder mar king relays such as I35,'at the same time in the event that several trunk calls are initiated simultaneously. Trunk release relay 41 (Fig. '1) is now operated from the negative 'pole of battery, winding of this relay, conductor I63, front contacts and armatures of finder marking relay I35 and of trunk marking relay I38 as well as of the tens finder relay I44 and the units finder relay I 45, to the positive pole of battery. Trunk release relay 41 when operated locks itself in this condition thru its inner front contact and armature, front contact and armature of relay 45, to the positive pole of battery. However, the operation of the trunk release relay, at its uppermost armature and back contact, interrupts the energizing circuit including the conductor 46 leading to the slow releasing relay 45. When the relay 45 releases, it removes the positive potential which has been holding the relays 3|, 32 (Fig. 8) of the finder and relays 55, and 53 of the link, tens connector relay I23 and the units connector relay 81, as well as the cut-in relay 69, the ringing relay 99 and the finder marking relay I35, thus all of these relays also release. Trunk release relay 41 also releases because its holding circuitis openedat the relay disconnects the link in use, from the calling line and thus the impulse relay ll releases. Relays I38 and I89 are also released by the release ofher cord circuit into the trunk jack, the contacts of which are designated I6I and I62, the'cut-off relay I55 of this trunk is operated in the wellknown manner to disconnect the line relay I66 and to extinguish the trunk signal (not shown). Current from the cord circuit (not shown) at the central office is now applied to the tip contact I6I of the plug, back contact and continuity spring of the relay I53, conductor I63, front contact and armature of relay I51, conductor I66, winding of the relay I53 to the negative pole of battery. Relay I53 is thus operated and its continuity spring and armature completes a locking circuit for itself independent of the battery supply at the operators cord circuit. With the relay I53 operated it interrupts'the circuit of the relay I54 which releases.

From the foregoing it will be seen that the link circuit originally connected to the calling line to establish this connection is released and that the calling line is ,connected directly thru the contacts and armatures of the finder relays I and-I65 to the trunk circuit leading to the central office.

When the subscriber at the localstation designated #11 terminates the connection by replac-.

ing his receiver on its switchhook, the tip and ring conductors leading to the central office are opened and this effects the release of the relay I48 of the local trunk circuit. This gives the central office operator disconnect supervision, also the release of the relay I48 causes the slow releasing relay I51 to deenergize. Relay I51 on releasing, opens the locking circuit of the relay I53 and connects the high resistance relay I65 across the trunk. Thus relay I53 releases and relay I65 operates. When therelay I65 operates, it closes a circuit for holding the slow releasing relay I29 before it has had time to release, following the'release of the relay I51. Since relay I29 is thus held operated, the trunk still tests busy and the cut-off relayB of the local line #11 is still held operated. The operated make busy relay I21 (Fig. 3) keeps this trunk busy by disconnecting the negative pole of battery at its back contact and armature. It will be understood that the make busy relay I21 is locked operated thru its inner front contact and armature, conductor I66, front contact and armature of relay I29 to the positive pole of battery. When the, central oillce operator disconnects by removing the plug of her cord circuit from the jack which includes the contacts I6I and I62, the trunk circuit is opened which allows the high resistance relay I65 to release. This relay in turn effects the'release of slow releasing relay I29 and relay I29 then eifects the release of the tens finder relay 3|, the units finder relay 32 and the make busy relay I21. The tip and ring conductors of the local line #11 are now opened because the finder relays I44 and I45 of the trunk are released.

In the case of a call originated at the distant central oilice and intended for a subscriber at the local automatic exchange, the operator at the central oflice'plugs her cord circuit into the trunk jack of the first idle circuit leading to the local automatic exchange. As a result of plugging into this trunk jack, battery connected at the cord circuit taken for use is applied across the trunk conductors for operating the high resistance relay- I65. When the operator applies ringing current to the trunk to signal the local automatic exchange, this alternating ringing current operates the relay I61. The slow releasing relay I29 is operated as a result of the operation of either of these last-mentioned relays. The relay I29 makes this trunk busy to outgoing calls because it removes positive potential from the conductor I28. However, this trunk is selectable at the local exchange by the local substation which is assigned to answer such incoming calls.

This trunk is rendered selectable because the relay I28 applies positive battery, at its armature and front contact, to the conductor I66 which it will be noted is extended thru the inner armature and back contact of the make busy relay I21. The operation of relay I61 by the ringing current intermittently connects local uninterrupted generator current to the common bell circuit for signalling the attendant who is assigned to answer incoming calls. I

The party at the local automatic exchange who is responsible for answering calls from a distant ofiice now removes the receiver from the switchhook and operates the dial sender at the substation to transmit impulses corresponding to #66. The removal of the receiver from the switchhook causes the telephone line of this assigned party to be selected by the first idle link circuit. On the completion of this connection of the link to the mentioned line, a dial tone informs the party that he can proceed with dialing the number 66. In response to the six .impulses corresponding to the tens digit #6 the counting relays 58 to 62 inclusive are operated and released while the number 6 counting relay 63 is operated and is maintained operated at this time. The operation of the number 6 counting relay 63 causes the operation of the number 6 tens connector relay I68 (Fig. 4). At the close of the-tens series of impulses and after the operation of the tens connector relay I68, the counting relays are restored to their normal position as previously described, in readiness to receive the impulses corresponding to the unit-s digit of the number 66. In response -to these units impulses the number one counting relay 58 is operated and as soon as this takes place the relay 13 is operated from the negative pole of battery, winding of this relay, front contact and armature of the counting relay 58, conductor I25, front. contact and armature of the tens connector relay I63, conductor I69, back contact and armature of the make busy relay I21, conductor l66, front contact and armature of the circuits then function in the previously described manner, for selecting this trunk after which the trunk connects itself to the calling line by way of its finder relays and the link is released. Supervision and release operations are now controlled in the manner describedior an outgoing trunk call.

The above description relates to a local telephone line which is equipped for non-restricted service, that is, it can make calls over a trunk to ple with the high resistance such as I10 (Fig. 2)

In the case of such a line which is equipped for only limited service, the marginal relay 53 of the selected link will not operate. In such a case when the trunk number 65 is dialed, positive battery at the armature and back contact of relay 53 is extended over conductor IH, armature and front contact of the tens connector relay I68, conductor I34 to the sleeve conductor 91 of the link. Thus when change-over relay 11 releases at the close of the series of impulses, the

circuit including conductor 91 is extended, thru the armature and back contact of relay 11, conductor I03, back contact and armature of the cut-in relay 59, back contact, continuity spring and winding of the release relay 49, conductor I 3, winding of the busy relay I85. The release relay 69 is energized in series with the busy relay I05. Release relay d9 when operated efiects the disconnection of the calling line from the link which it has seized. The calling line is now connected to the winding of its associated relay 7, and busy tone is supplied to this lineuntil release, as previously described.

. Provision is made in the present system so that either an outgoing trunk call'or an incoming trunk call can be transferred by certain of the substations of the local automatic exchange to other local lines. In order to effect such trans- .fer the local substation must be provided with a push button such as I1I enabling one side of the calling line to be connected to ground. For convenience in describing the operation of this transfer feature, it will be assumed that the calling line number II is connected to a central office trunk which connection has been completed in the manner already described. It will further be assumed that the party connected to the trunk circuit at the distant exchange finds that his connection should be transferred to line number I5. It will be remembered that with the line number II connected to the first trunk, namely trunk number 5I, tens finder relay I44 and the units finder relay I45 will be operated.

Also the relays I48, I51, I29, I53 and I21 of the trunk will be operated in the manner already described. Each of the trunk conductors to the distant ofiice will be energized thru the plug contacts I6I and I62. However, at this time the relays I54 and I65 are not energized. Now when lines.

the subscriber at substation number II, receives button I'II momentarily and then dials the num ber I5. The actuation of this bush button grounds one side of the telephone line circuit which is effect/iveto unbalance the differential relay I52 of the trunk so that this relay operates. When the relay I52 operates it closes a .short circuit across its upper winding so that when once energized, it will remain operated even though the push button III is released. The upper contact and armature of the differential relay I52 connects the conductors I12 to I13 leading to the lookout circuit for the several By this arrangement, the differential relay I52 acts in the same mannera a line relay of the telephone lines, and thus causes the'operation of the tens lock-out relay I1 and the units lock-out relay I3. These two lock-out relays when operated, cause the allotter repeater relay such as 58 of the first idle link, to be operated which is assumed to be link number 2. The operation of the relay 58 causes the tens finder relay I15 and the units finder relay such as 32 of the second link to operate to connect the tip, ring and sleeve conductors of trunk number 5| to the tip, ring and sleeve conductors of link #2. The impulse relay similar to 44 of link #2 is energized over the tip and ring conductors of the calling line circuit. Relay M in'turn causes relays similar to 45 and 55 of this link to be operated. On the operation of the relay 35, relay I5I of the trunk is operated, because the sleeve conductor of the trunk is connected to positive battery at link number 2 and is extended thru the finder relays and thence by the sleeve conductor of the trunk to the Winding of the holding relay IEI. Relay I5i at its make before break contacts connects a resistance coll I16 across the trunk conductors leading to the central omce, for the purpose of holding this trunk and for providing supervision. If the push button I'II has been released by this time, then the opening of the back contact and armature of the holding relay I5I establishes a balanced circuit through the windings of the differential relay I 52 for causing this relay to release. When the relay I5? is thus released it opens the operating circuit of the tens lock-out relay I1 and the units lock-out relay I3. However, the trunk is still held because the holding relay I5I is still operated. The conductors I16 and I11 leading from the relay I68 of the trunk are extended thru the units finder relay such as 32 and a tens finder relay such as I15, to the corresponding tip and ring conductors 40 and 4| of the second link, which last-named conductors are connected in series thru the upper and lower windings of the differential relay 43 and the impulse relay 44 respectively to the negative and positive poles of battery. The party at station number I I now dials the number l5 corresponding to the number of the substation to which the call is to be transferred. In response to each of the series of impulses corresponding to the digits of the number 15, the impulse relay 44 successively operates the counting relays so that the tens connector relay I01 and the units connector relay I84 are operated to connect the line of substation number I5 to this second link. Ringing current is then supplied to the telephoneline number I5 and when the subscriber thereat answers by removing his receiver from its switchhook, the ringing current is disconnected and the subscriber at station number I5 is in telephonic connection with the subscriber at station number II. This last-named subscriber advises the subscriber at ture of a tens finder relay similar to I15 to the positive pole of battery. It will be recalled that station number I5 that a call is waiting him on the trunk. This latter subscriber then operates his push button similar to that shown at I" to ground one side of the telephone connection. This operation is effective to unbalance the differentially wound relay. I02 ofthe second link causing this relay to operate. When relay I02 is operated, a circuit is completed for operating the trunk release relay 41. This circuit is traceable from the negative pole of battery, winding of relay 41, front contact and armature of the relay I02, front contact andarmature of the relay IOI (now operated) back contact and armature of the differential relay 43, conductor I83, front contact and armature of a tens finder relay similar to I15 which relay has cooperated in connecting line number II to line number I5.

Trunk release 41 when operated locks itself in this condition at the innermost front contact and armature of relay 45, to the positive pole of battery. The release relay I18 of the trunk is now energized from the negative pole of battery, winding of this relay, conductor I19, armature and front contact of the units finder relay such as 32, armature and front contact of a tens finder relay similar to I15, conductor I80, front contact and armature of differential relay I02, back contact and armature of differential relay 43, conductor I83, front contact and armature of a relay similar tov I15 to the positive pole of battery. The operation of the relay I18 opens the locking circuits for the finder relays I44 and I 45 of the trunk circuit so that the telephone line number II is disconnected from the trunk and is transferred back to its own line circuit. It will be recalled that at this time the relay 1 is locked-energized in series with telephone line number II. Since the cutoff relay 8 has been released by the disconnection of the line number II from the mentioned trunk, relay 1 while thus operated, maintains busy potential over the sleeve conductor 39 to maintain this line busy until the subscriber thereat replaces his receiver on its switchhook. As soon as the relay 1 is operated it applies a busy tone to the telephone line number II which continues to sound in the receiver at substation number II until the subscriber thereat replaces his receiver on the switchhook at which time the circuit of relay 1 is opened. This is effective to remove the busy potential from the sleeve conductor 39 and also disconnects the busy tone current from this line.

As soon as the telephone line number II is disconnected from the mentioned trunk by the operation of the release relay I18, the relay I48 of the trunk circuit deenergizes but the slow releasing relay I51of this trunk has a substitute circuit completed for itself at this time at the front contact and armature of relay I5I, Also when the release relay I18 energizes it disconnects the telephone line number II from the calling end of the second link circuit so that the impulse relay 44 thereof deenergizes.

When the push button similar to Hi at sub-- station number I5 is operated and thenreleased, the differential relay I02 of the second link retracts its armatures thereby closing a circuit for operating the transfer relay I8I of this link. A circuit for operating the relay I8I (Fig. 8) extends from the negative pole .of battery,-winding of this relay, armature and front contact of relay 41, conductor I82, back contact and armature of relay I02, front contact and armature of relay IOI, back contact and armature of differential relay .43, conductor I83, front contact and armawhen telephone line number I5 was selected by substation number II, a tens connector relay similar to I01 and a units connector relay similar to I84 was operated, Corresponding finder relays I44 and I81 of the two-way trunk are now operated to extend this trunk to telephone line number I5. The circuit for operating the tens finder relay I44"of the trunk is traceable from the negative pole of battery, winding ofthis relay, conductor I85, armature and front contact of relay of a units finder relay such as 32, armature and front contact of a tens flnder relay such as I15, armature and front contact of transfer relay I8I, conductor I85, conductor I81, inner front contact and armature of tens connector relay I01, conductor 83, front contact and armature of slow releasing relay 45 to theposltive pole of battery. The number 5 units finder relay I81 is also energized from the negative battery, winding of this relay, conductors I88 and I89, armatures and front contacts of relays 32 and I15, armature and front contact of transfer relay IBI; conductor I90, conductor I9I,.front contact and armature of the number 5 units connector relay-I84, conductor 83 to the positive pole of battery at the front contact and armature of slow releasing relay 45. The finder relays I44 and I81 when thus operated are held looked over a circuit including the conductor I58 which extends to positive battery at the front contact and armature of relay i29. This selection and operation of the trunk finder relays is of course made before the finder relays of the link and the transfer relay I8I release.

Also when the push button similar to "I at substation number I5 isreleased, the release of the differential relay I02 effects the release of the slow releasing relays similar to 45 and 55 at the second link because one circuit of relay 45 is opened at a front contact and armature of the differential relay I02. The other branch oper ating circuit of the slowreleasing relay 45 is opened at the back contact and armature of trunk release relay 41 since this relay is now operated. The release of relay 45 effects the release of relay 55. The relays I15, 32, I01 and I84 of the second link are released by the release of relay 45 at the second link. The relay 41 also deenergizes because its locking circuit is opened at the relay 45. However, relay 41 is slow releasing. Relay I8I is also releasedwhen the relay 41 deenergizes. The holding relay I5I of the trunk circuit is released because the relay 45 removes positive potential from the sleeve conductor leading to this ground. The trunk circuit is now connected to line number I5'and since the holding relay I5I is released, line number I5 is in telephone connection with the trunk. Line number I5 is thus in control of the release I and of the supervision of the-trunk circuit in the manner previously described to telephone line number II,

A further feature of this invention enables the transfer operation to be effected among a series of telephone lines in succession provided each of these lines has a push button similar to Hi and a ground connection at its substation. The repeated transfer among the series of telephone lines in succession is effected. in exactly, the same manner as already described since the transfer of the trunk from a first line such as line number II to a second line such as number I5 places line number I5 in exactly the same condition as

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