US1625624A

US1625624A - Call-distributing system

Info

Publication number: US1625624A
Application number: US370142A
Authority: US
Inventors: Winfred T Powell
Original assignee: STROMBERG CARLSON TELEPHONE
Current assignee: STROMBERG CARLSON TELEPHONE; STROMBERGCARLSON TELEPHONE MANUFACTURING Co
Priority date: 1920-03-31
Filing date: 1920-03-31
Publication date: 1927-04-19
Anticipated expiration: 1944-04-19

Description

April 19, 1927. 1,625,624

W. T; PQWELL CALL DISTRIBUTING SYSTEM Filed Marchfil. 1920 4 ts-Sheet J CDFFiCE *2 FKE. 1

TELEPHONE SET.

ENJENTOE WIHFRED T POWELL ATTGRNEY April 19 1927.

FIG. 2

W. T. POWELL CALL DISTRIBUTING SYSTEM Filed March 31. 1920 4 Sheets-Sheet. 2

B POSVHON POSITKSH RELEfiSE KEV l a f P i 1 I I I I I P I 8 l l l ,9 INVENTOR &5 WINFQED T. POWELL \AJW 0 BY ATTO EY April 19 1927. 1,625,624

w. T. POWELL CALL DISTRIBUTING SYSTEM Filed March 51. 1920 "4 Sheet-Sheet s BPOSITI Fig.2. A

Pos wl n B PO5\T\OH, RELEASE KEY.

TRurmka f3 INVENTOR 5 wmFRED TPOWELL nun ATTORNEY April 19,1927. 1,625,624

W. T. POWELL CALL DISTRIBUTING SYSTEM Filed M arch 31. 1920 4 Sheets-Sheet 4 OPER m-o Rs SET.

FlGS

INVENTQR WHiFRED T POWELL ATTORNEY Patented Apr. 19, 1927.

UNITED STATES PATENT OFFICE.

WINFRED T. POWELL, OF ROCHESTER, NEW YORK, ASSIGNOR TO THE STROM BEFRG- CARLSON TELEPHONE MANUFACTURING GOMIANY, OF ROCHESTER, NEW YQRK,

CALL-DISTRIBUTING SYSTEM.

Application filed March 31, Serial No. 370,142.

This invention relates to telephone sys tems, and more particularly to. telephone systems in which automatic switches are employed to distribute calls to. various operators.

In manual telephone systems of relatively large size it is necessary in the case of certain calls that the connection be completed through two or more ofiices. In accordance with the practice formerlyemployed, for such cases a so-called order wire extending between the two oifices serves as a means over which the operator at the first oiiice, known as the A operator, was able to repeat the wanted number to the operator atthe second office who, is known as the B operator. I I

Briefly the operation of extending a call in such a manual system, involves the connection of the answering endof the A operators cord circuit to the calling line, and this operator receives the designation of the wanted line. She thereupon instructs a B operator at the wanted office of the number of the wanted line over an order wire, and the B operator instructs the A operator over the same order wire of the number, of the trunk to be used. The A operator then inserts the calling end of the cord circuit into the jack of the trunk circuit designated.

In the present invention the order wire has been omitted and in its stead a series of trunks and automatic switches are employed. In the present system on the initiation of a call the A operator inserts the answering end of her cord circuit into the jack of the calling line and receives the designation of the wanted line. She thereupon inserts the calling end of her cord circuitinto any one of a plurality of jacks of trunks leading to the wanted oifice. A trunk selecting switch then selects an idle trunk leading to the wanted oliice where primary and secondary switches select idle trunks to connect the calling line to a B operators position. While these switching operations are taking place, a tone is transmitted to the A operators telephone set to inform her that the B operator is not in readiness to receive the call. When, however, the tone is discontinued, the A operator repeats the designation of the wanted line and the B operator after testing the wanted line and finding it idle, inserts the calling end of her cord circuit into the jack of the wanted line. The

signaling of the wanted line and the other claims.

The drawings with Fig. 2 placed at the right of Fig. 1 diagrammatically represent a telephone system having one or more B operators" positions and in which a predetermined number of calls are apportioned to each B operators position, and when this predetermined number of calls are unanswered at this B position no other calls can be extended thereto. In Fig. 1 there "is diagrammatically represented anoflice designated #1 and part of a second office #2. In oflice #1 there is represented a calling subscribers line and its associated equipment. A cord circuit at the A operators position is also indicated, and the circuits of the trunk selecting switch for selecting anidle trunk to a wanted office are shown at the left of the dotted line. At the right of the dotted line there is shown the equipment of 05cc #2 for selecting an idle B operators position. In Fig. 2 there is shown one plug ended trunk circuit individual to this position, as well as other equipment be low the dotted line common to all trunk circuits of this position. At the upper right hand corner of Fig. 2 there is shown a telephone line, herein referred to as the called line. Figs. 2 and 3 when substituted for Fig.- 2, represent a modified form of the invention, in, which overflow positions are Shown. its many of these positions will he provided as are necessary to care for traliic which cannot he handled by the regular B operators positions. Corresponding parts of Fin". 9 are designated by the same reference characters as are used in Fig. 2.

The switches of the present invention may he of the structure substantially similar to that disclosed in the patent to Clement, #1,107,153, patented rcugust 11, 1914.

It Will he understood that the equipment of ollice :g'il, such as the operators cord circuit as well as the operatofis telephone set, Will be of the character of those now in use in manual common battery telephone systonne.

Several of the relays, notably 10, 525 and 33 have contacts designated X which indicates that these contacts close before other contacts on the associated relay are operated.

It is believed the invention will best be understood by descrihinp; the method of extending a call from a calling substation, such as A to a called substation such as B, and subsequently explaining the method of extenliling; the calling line to a second called suhstation, such as C.

l l hen the calling: S iiscriber at A initiates a call by removing; his receiver from itn switchhoolt, the line relay LR individual to his line, is energized over a circuit controlled at back contacts of the cut-oil relay CO, and this relay is actuated to li ht the lamp a sociated with the anion c jack (3 of the calling line. The operator on noting that lamp 5 is lighted, inserts her answering plug 7 into the jack ll. This operation causes the cut-otl' relay CO to he energized, which deenergizes the line relay lull, which in turn extinguishes the lamp The operator thereupon depresses her lis-iteninp; hey LK which counccts her telephone set in ln'idge of the n utering end of her cord circuit and ascer Kaine from the calling party the deF'guation ot the wanted otlicc and the desired line term inatingr thcrcat. The operator then inserts the calling; plug: 3 oi the cord circuit which she has taltcu tor use into onc oi a group oi jacks fl, thr uc'h which the wanted oliicc may he reached. oon an the plug 5'? is; inserted into the jaclt the relay loll is operated in a circu t clcwezgl troui oroundwinding Oil the relay l l. elecrc at the jzu-l' ll, sleeve of the plug ti, winning ol re; ll which control;

a supervirory relay (not shown) to grounded battery. The re ay ll) attracts llt-E armatures, and a; its middle armature connects a tone ovcr conductor 12, inneuniost upper back contact and armature of relay through the lower side oi the cord circuit, the operators telephone set. upper ride of the cord circuit to ground, through the supervisory relay 14-. This tone or a similar tone Will he applied to the A oncrators headset until the P) operator is ready to receive the designation of the wanted line.

At the iuner-nurt armature ol relay in, a circuit in closed l'rom grounded battery, rceistance, winding, nrn'ialure and haclc contact oi: the motor magnet 15 of the distributor switch, lower back contactand armat urc of relay 3, inneranost trout contact and armature of relay to ground. Under the control of this circuit, the dietrilnitor au'itch advances its brushes progressively until its; tcet brush l6 encounters the test terminal oi an idle trunk leading to the wanted ollice. This idle condition indicated by the pros-:- euce of: ground potential on its test terminal.

liJGt it he assumed that the first idle trunk circuit tested lift the distributor switch is the one Whose conductors are designated. 17 and ltl in Fin. 1. As noon 8?} thiu t'lllllli' is tested, a circuit completed troin ground, outer armature and hacl: contact of relay 19, teat terminal o'l this trunk, test ln'ush 16, upper winding ot relay l which has low resistance outer-moat trout contact and arn'iature of relay 1t), resistance, to grounded battery. This circuit shunts the SlifllflDlllg n'iagnetof the dietrilinitor ewitch to stop the Fame and also energizes the switching relay This last named relay attracts its arniatures, and at its lower armature and :lront contact closes a holding circuit for itself through its high resistance Winding, from ground, innermost armature and trout contact 0t? relay ltl, armature, tront contact and Winding o't relay 13, holding hrush 20, over the holding terminal of the eelected trunk and Winding of relay 19 to grounded battery. At the upper arnnilurcs ot the switching: relay 13, the callinp; line l'a extended to the wanted otlice. At the outer armature and back contact of relay it), a guarding condition is placed on the teat terminal ot the selected trunk. it the inner front contact and arn'iature of relay 19, a hreal; point: in the conductm ill is closed. This conductor ll extends a circuit for relay but this relay short circuited by ground at the armature-i and back contacts of relays similar to l9 associated with idle truulc ot the ,ca-onp. l l ou'ever, as soon a: all the trunks these various eluiutiup; circuits are removed and the relay 53:2 attraij tn its arniiat-ures to control the opera tion. ot': the meter 2?) and ot a visual aigual 24- at the poieition to notify the A. operator that all the outgoing trunks,- of a particular group are in use. As soon as the conductors l7 and l8 ot the selected trunk are extended to the Wanted otlicc, relay in operated in a circuit traceable lrom grounded battery, left hand Winding of this relay, upper-most hack contact and arunituro of relay 26 to ground, through the winding of the relay 1 lot the A operators cord circuit. At the left hand armature and trout contact ol relay a tone is extended over of th group arc ong agei'l.

fill

llO

conductor 27. This second tone is applied to the A o] )erators headset as soon as the first tone is removed so she will know that the B operator is not ready to receive the wanted number. At the outer-most armature and front contact of relay a circuit is closed from ground, back contact. armature and winding of the motor magnet 28 of a distributor switch which will be designated a primary switch, resistance, to grounded battery. Under the control of the motor magnet 28, this primary switch advances its brushes until its test brush 29' encounters the test terminal of an idle trunk.

Let it be assumed that the trunk whose conductors are designated 30 and 31 is the first idle trunk tested. A circuit will thereupon be closed from grounded battery, re sistance, inner armature, front Contact and winding of relay 25, upper winding of relay 26, test brush 29, conductor 32, outer left hand armature and frontcontact of relay 33 to ground at the armatures and back contacts of a group-busy relay 34 to stop the primary switch and operate relay 26. As soon as the relay 26 attracts its armatures, it closes a holding circuit for itself from ground, its lower winding, lower armature and front contact, holding brush 35, winding of relay 33 to grounded battery. As soon as the relay 33 is operated, it extends a tone to the A operators headset over conductor 36 and its inner left hand contact and armature, and at its outer left hand armature applies a busy condition to the selected trunk. At the outer right hand armature and front contact of relay 33, a circuit is closed from ground, lower-most armature and back contact of relay 37, armature, back contact and winding of the motor magnet 38, resistance, to grounded battery. Under the control of this motor magnet, the secondary distributor switch herein called the secondary switch advances its brushes to find an idle trunk circuit leading to a final connecting operator. The idle condition of the trunk will be indicated by the'presence of ground on its test terminal applied over conductor 58 and controlled at the outer right hand front contact and armature ofrelay 69, so that when the test brush 41 encounters an idle test terminal a circuit will be closed through the lower winding of relay 37. innermost right hand front contact and armature of relay 33, resistance, to grounded battery. This circuit energizes the relay 37 and shunts the motormagnet 38 to stop the secondary switch. Relay 37 when energized, closes a locking circuit from grounded battery, its upper winding, lower-most front contact and armature, outer-most right hand front contact and armature of relay 33 to ground. At its upper armatures and front contact the A operators telephone setcis connected to a trunk circuit terminating in armature and back contact of relay ary switches.

a plug at a B operators position. At the upper back contact and armature of relay 37, the tone is no longer communicated to the A operators headset, thus informing her that the B operator is now ready to receive the wanted number. As soon as the last mentioned trunk is seized, its relay 42 is energized over a holding brush 43, innermost, lower'front contact and armature of relay 37, holding brush 35, lower front contact, armature and winding of relay 26 to ground. A relay similar to 42 is provided for each trunk ofthe group to which the secondary distributor switch has access. As soon as the A operators cord circuit has been extended over the trunk conductors 43 and 44, the relay 45 of Fig. 2 is energized over the two sides of the link circuit and operators cord circuit in series, through the winding of relay 14 to ground and to grounded battery (not shown). The relay 45 attracts its armature and closes an op erating circuit for the slow releasing relay 46, which attracts its arinatures to close cir cuits hereafter described. At the left hand armature and front contact of relay 46, a circuit is closed for actuating the slow releasing relay 47.

Simultaneously with the operation of the relay 45, the relay 48 is operated in a circuit closed from grounded battery, winding of this relay, inner lefthand back contact and armature of slow releasing relay 49, conductor 50, over the remainder of the circuit in multiple with the relay 42, to ground through the lower winding of relay 26 of Fig. 1. The relay 48 is operated in this circuit and at its left hand'armature and front contact closes a circuit which will flash the lamp 51 in a circuit-including the interrupt-er 57. The flashing of the lamp indicates to the B operator that a call is coming to her position and that she should be in readiness, to care for the same. At the inner right hand front contact and armature of relay 48, a circuit is closed from grounded battery, over conductor 58, conductor 67, left hand winding of the relay 59 to ground which operates to place a guarding potential temporarily on all idle trunks of the position, so that no other calls can come to this operators position until she has completed the call which waiting attention. This is accomplished by the openlng of the test circuit at the inner left hand The relay 59 at its outer left hand contact closes a circuit including conductor 68, lower winding of relay 34 of Fig. 1 to grounded bat tery. Relay 34 attracts its armatures and removes ground potential from the test terminals of idle trunks from the primary switch terminating at this group of second All of the trunks out from the secondary switch will be blocked at this time (though not busy) because they all go to this position which is temporarily engaged.

In the event that all the trunks terminating at the secmulary switch are busy, all the relays 4-2, one of which is individual to each trunk leading from the secondary switch are operated to remove a short circuit [real the upper winding of relay El -l: and to close av holding circuit troin grounded battery, resistance. iront contacts and arinatures of relay a, and upper winding of relay il -l to ground. it will be understood tha; when any trunk of this group extending from the secondary switch hccoines idle, that its associated relay 42 will he (lo-energized and again short circuits the upper winding ot relay Illso that the primary switch can -function again. The group relay B l: oi Fig. 1 will also be operated whenever there is no operator at the position under consideration. At this time the relay ll!) which is in series with the opemtors trainuuitter circuit is tie-energized because the operator on leaving the position will disconnect her telephone set. Relay 69 on (lo-energizing will extend ground over conductor (38 to operate the relay 31 in the manner previously described.

As soon as the relay 4-6 attracted its armatures a circuit "as closed from ground, inner armature and back contact ot relay 55, outer right hand front contact and armature of relay -"l-6, winding of slow releasing relay 54, right hand armature of relay 49 and its back contact, and winding of relay to grounded battery. Belay 52 attracts its arinatures and connects the B operators telephone set to the trunk circuit over which the call is being extended. The 13 operator thereupon receives the designation of the wanted line and inn'nediately makes her position available to other calls by depressing the position release key 60, or she can proceed to insert her calling plug into the multiple jack of the wanted line attcr which this operators position will be automatically made a *ailable to other calls.

'lwo meters (323 and (l?) are provided, the 11st to indicate the number of times that uicralur s position is unblocked by de-- pres-dug the hey (ll) which is th method that the operator instructed to l'ulluw s nce it insures more rapid. haiulling of calls. and the serord meter (3?: shows the total number of calls completed at this position. l y comparing the rmu'lings on the two meters a supervisor can determine whether the operator is following instructions.

it will he assumed that the operator depresses her position release hey till to render -ailablc her position to succeeding calls. As soon as key is depres ed. a circuit is closed from ground. left hand winding of, relay (ll, right hand winding o l relay ill. in

mars al series, outer right hand armature and front contact oi? relay 4E8, continuity spring 62 and winding o't relay 4-9 to grounded battery. These relays are energized in this circuit and the relay 61 completes a locking circuit for itself and closes an operating cir cuit for the meter magnet (33 through its outer left hand front ccmtact and armature, its lett hand winding, ari'natrne and trout contact tocground. Relay 4-9 on ei'ie'rgizalion closes a locking circuit for itself through its continuity spring (32, its right hand armature and winding of relay 54c, outer right hand armature and trout contact of relay 46, inner back contact. and armature ot' relay an to ground. At the inner left hand arnuuure and bacl; c n1tact of relay if). the actuating circuit of relay 48 is opened. causing this relay to de-energize, and thereby disconnect the lamp 51 from the interrupter and extinguishing the same until the lamp 5i is again lighted at the time o l? diwounectiou as will be further described. lit the outer left hand armature and bacl; contact at relay 419 a break point is opened in the conductor 58 which would otherwise complete a test circuit at the right hand armature and back contact of relay 48. The opening of this test circuit renders the trunl: in use unselectable.

Z'The deenergization of relay 4.8 also opens at its inner right hand armature and front contact the operating circuit of the relay 59 which has previously been energized to hold the ope 'ators' p r-;i.tion unselectable.

As soon as the operator received the designation oi the wanted line and while the several operations just described have been taking place, she touches the tip of her plug to the sleeve of the wanted line to ascertain whether or not this line is idle. It busy, this lastinentioned operation will cause a distinctive click in her headset since the busy condition of the called line will be indicated by battery potential on the sleeve o'li its jack, and this potential will be extended through the righthand armature and hacl: contact of relay to ground, over conductor 56 which has included therein a coil intlucl'ircly connected, to the operato1"s receiver.

Let it he assumed that the wanted line. is idle in which orcnt the operator will insert her plug l into the jack .l of the wanted line. In response to this operation, the sleeve relay 5:) will be operated in series .wilh the cut-oli' relay oi the wanted line. These relays a re thus energized and attract their armatures. At the right hand armature of relay to. the test conductor 56 is opened and at the inner left hand armature and trout contact oi? relay 55, a circuit is closed 'lroni ground, winding of the relay (i l, conductor 70. and winding of the relay {l to grounded battery. The relay 64 is ltll) contact and ari'nature of slow releasing relay 54, winding of the meter magnet 65 to grounded battery. This meter as has been described, registers the number of completed calls. Vith relay 64 operated, a circuit is cloied from the ringing generator, middle armature and contact of relay 47,

armature and back contact of relay 71, winding of the trip relay TRIP, front contact and upper arn'iature of relay 64, tip of the plug through substation circuits and. bell of the wanted station, ring contact of the jack and plug, inner armature and front contact of relay 64, and resistance to grounded battery. The called party is thus signaled over this circuit and the calling party receives ringing induction through the resistance 72 to inform him thatthe called'party is being signaled. When the called party responds the marginal trip relay operates, and at its armature and front contact short circuits the relay 64 which deenergizes to close a break pbint in the ring conductor of the trunk inuse and also to short circuit resistance 72.

The calling subscriber receives talking battery through the windings of relays 160 and 161 while the called party receives talking battery through the windings of relay 71. Relay 71 is energized in this circuit and places a short circuit about the high resistance winding of relay 45 which may have a resistance of 12000 ohms.

\When the calling party terminates the call, the answering supervisory signals are lighted in the well known manner, and when the called party replaces his receiver on its switch hook, relay 71 de-energizes and removes the short circuit which exists about the left hand or high resistance winding of relay 45. With this high resistance included in circuit'including conductors 43 and 44, the calling supervisory signal is lighted. After receiving these disconnect signals by the lighting of these supervisory lamps the A operator withdraws the plug 7 from the jack of the calling line and the plug 8 of her cord circuit from the jack of the selected trunk. As soon as this takes place, the relav 45 tie-energizes and interrupts the oper ating circuit of the slow releasing relay 46. This last mentioned relay releases and the supervisory lamp 51 of the B operators position is caused to glow steadily in a circuit extending from grounded battery, lamp 51, left hand armature and back contact of relay 48, outer left hand armature and front contact of relay 55, inner armature and back contact of relay 46 to ground through resistance 81 which may be a pilot'relay common to the .POSJIOD. The operator on notlng that lamp 51 is burning steadily knows that the conversation has been completed and removes the plug P from the jack J of the called line. The apparatus at the B operators position is thereupon restored to its normal position and becomes available in handling a succeeding call.

When the A operator removes her calling plug 8 from the jack 9 of a selected trunk, the relay 10, the circuit of which was controlled through the sleeve of the jack 9 and plug 8 tie-energizes and at its inner armature and front contact opens the locking circuit of the switching relay '13. The relay 13 die-energizes to release the trunk finder switch at oiiice #1 and effects the de-energization of relay 19 which has maintained.

a guarding potential on the trunk whose conductors are designated 17 and 18. The brushes of the trunk finder switch at office #1 remain in engagementwith the terminals of the trunk last used, but the brushes of the switch are severed from the conductors of the trunk that terminates therein at the armature and front contacts of the relay 13. The conductors of this trunk are also opened at another point by the removal of the plug 8 from jack 9. The release of the trunk finder switch opens the line conductors extending between ofiice #1 and oliice #2 with the result that the relay 45 of Fi 2 deenergizes and retracts its armature. Shortly afterward the slow releasing relay 46 deenergizes, but before the slow releasing relay '47 has had time to retract its armatures, a

circuit is closed from ground, armature and back contact of relay 46, inner armature and front contact of relay 47, conductor 50, brush 43, armature and front contact of relay 37, winding of relay 33 to grounded battery, which shunts the relay 26, causing it to retract its armawtures. At the upper armatures of relay 26 the brushes of the primary switch are disconnected from the conductors of the trunk that terminate therein, and at the lower armature of this relay'its locking circuit is opened. This primary switch after releasing alsoremains with its brushes in engagement with the terminals of the trunk last used. A short time after the relay 46 retracts its armatures, the slow releasing relay 47 de-energizes and opens the circuit which shunted the relay 26 and held energized the relay 33, permitting this relay 33 to retract its armatures. At the outer right hand armature and front contact of relay 33, the locking circuit of the switching re lay 37is opened and this relay retracts its armatures to release the secondary switch whose brushes likewise. remain in engagement with the terminals of the trunk last used.

Referring to the modification shown in Figs. 2 and 3 when the overflow positions one of which is shown in Fig. 3 are employed, each secondary line switch will be provided with one or more sets of overflow terminals indicated at 125, 12?, 127 and 162 of l? 1 and the regular trunks from these switches, instead ot extending only to one operators position, are distributed among a group oil 1% operators positions. Furthermore, the group relay 3% of Fig. 1, is made common to a plurality of 13 operators positions, instead of being individual to one B position. l l hen this overt-low arrangement is used in case all of the B operators pesitions, such as shown in Fig. 2 become simultaneously busy, this condition will be in di *ated by a guarding potential on the test terminals such as -10 of all trunks leading to these positions. Under such conditions it a call is extended to olliee #2, it will be further extended to overflow positions irrespectire ot' the number 01 *alls awaiting completion at these positions. The method of extending a call when the overflow position arrangement is used, is substantially similar to that previously described.

Let it be assumed that a subscriber at A desires to converse with the subsc 'iber at C. The A subscriber will initiate the call by removing his receiver from its switch hook, and this will effect the lighting of the lamp 5 at the A operators position. The A operator then inserts the plug 7 into the jack (3 and thereafter presses the listening key LE to connect her telephone set to the calling line and to receive the designation of the wanted line. The operator then inserts her plug 8 into the jack 9 01" a trunk leading to an idle trunk selecting switch at ollice #1 and this switch selects an idle trunk leading to a primary switch at o'llice it which it is assumed is the wanted ollice. The primary switch now selects an idle trunk leading to a secondary switch, and since it has been assumed that all of the li operators are busy, this secondary switch will not seize any of the trunks leading to these positions, owing to the busy condition on their test terminals, such as 10 of Fig. 1, but will seize an idle overflow trunk like that shown in F g. 3 leading to an overflow position.

As soon as the test brush all of the secondary switch reachcs the test terminal 121' of this idle overflow trunk, a circuit is completed tor the switching relay 3? extending from grounded battery, resistance, inner right hand arn'iature and contact of relay 33. lower winding ot switching relay 3?, test brush ll, test terminal 1'37, test conductor 128, armature and back contact of relay 11 0, conductor 130. armature and trout contact of relay 19.9 which energized it this operator is at her position. conductor 131. arms ture and trout contact o l relay 1352 to ground. It will he noted that his relay 132 is not operated until all the regular ll operators positions are engaged at which time the relays 59 at these positions will be actualcd to remove a short circuit which has previously existed about relay 1132.

soon as the secondary switch has seized overflow trunk, the conductors 133 and 13-1: of this trunk will he serially included inv a circuit completed through the winding ot' the supervisory relay 11 at the A operators position and including both windings oi the relay 101 of l ig. 3. The relay 101 is operate-d in this circuit and at its armature and contact closes an operating circuit for the slow releasing relay 102, and the energiza tion of this relay ell'ects the actuation of the slow rcleasing relays 102-3 and 10-1: for purposes to be described. As soon as the switching relay 37 attract its armatures, a holding circuit for this relay is closed from grounded battery, upper winding oi. relay 3i, its lower-most :lront contact and armature, ()lltEFlllOS'l; :l rout contact and armature o1 relay 3:3 to ground. Also the holding circult of the relay 215 is now extended through its high resistance winding, its lower armature and front contact, holding brush 35, inner lower a rniaturc and front contact of relay 23?, holding brush =53, holding conduc tor 13.5, lower winding of relay 100 to grounded battery. The relay 100 is energized in this circuit, and at its upper armature opens the test conductor 128 01 the overllow trunk in use and at its lower armature closes a circuit to light the signal lamp 111, to inform the operator that a call is await- Eng attention. The circuit for the lamp 111 is traceable from grounded battery, through the lamp, armature and liront contact of relay 100, conductor 136, armature and back contact 0t relay 105, conductor 137, contact 112 of the operatofls listening key, contact. 113 and the interrupter to ground. Under the control of this interrupter the lamp 111 is flashed to inform the operator that a call is "aiting at her position. The operator at the overflow position throws her listening key Lli to inductively coiniect her telephone set shown at the lower right hand corner of Fig. 2}, to the trunk conductors 132:3 and 134. leading to the A operators position. As in the case where the overflow position is not used, as soon as the secondary switch has seized an idle trunk leading to the overflow position the various tones disappear from the line and the i l. operator knows that it is time to give the designation of the wanted line. This designation is received by the overflow position operator.

The operator then tests the line leading to the substation at C by touching the tip oi the plug P to the sleeve ol the ack J. This operation connects the sleeve of the jack ,1 to the operators headset over conductor 118. It at the time the plug P is connected to the sleeve of the jack, a guarding potential was present on the sleeve, a distinctive cliel:

will be heard in the operators headset which informs her that the wanted line is engaged. Let it be assumed that the wanted line is idle, the overflow operator thereupon inserts the plug P into the'jack J of the Wanted line. This operation completes an energizing circuit for the relay 105, closed from grounded battery, upper winding of the relay 100, relay 105, sleeve of the plug P, sleeve of the jack J, through the cutoff relay herein represented as resistance 115 to ground. Relay 105 attracts its armatures and at its left hand armature opens the flashing circuit forthe lamp 111 to prevent this lamp from being flashed again on the same call, but at its left hand'armature and front contact closes a supervisory circuit in which .this lamp will be steadily lighted at the close of conversation as will be described. At the right hand armature and front contact 'of relay 105, a break point is closed in the conductor 139 of the trunk that termi nates in the plug P. At the outer right hand armature and front contact of relay 105, a circuit is closed from ground, conductor 141, winding of relay 106, resistance to grounded battery. Relay 106 is energized in this circuit and attracts its armatures to close a ringing circuit which extends from the ringing generator, conductor 118, inner front contact and armature of relay 103, armature and back contact of relay 109, winding of trip relay 108, upper front contact and armature of relay 106, tip of plug P, through the substation circuits and bell of the substation C, ring of the jack J, ring of the plug P, inner upper armature and front contact of relay .106, resistance to grounded battery. The resistance 120 causes a tone to be transmitted to the subscriber at A to indicate that his party is being signaled. 'As soon as relays 105 and 106 are actuated an operating circuit is closed from grounded battery, winding of meter magnet 107, inner front contact and armature of relay 104C, armatures and front contacts of relays 106 and 105 to ground. This meter indicates the number of calls completed at this overflow position. When the called subscriber at Canswers, the trip relay 108 attracts its armature which places a short circuit from grounded battery, resistance, armature and contact of relay 108, outer right hand contact and armature of relay 105 to ground about the relay 106. Relay 106 thereupon deenergizes and retracts its armatures. As soon as this takes place a circuit is completed for the relay 109 serially including both of its windings and the

conductors

139 and 140. With relay 109 operated the ringing circuit previously described is interrupted to prevent the reapplication of ringing current to the wanted line during the call just completed. At the left hand armature and front contact of relay 109, the high resistance left hand winding of the relay 101 is eliminated from the circuit including the

conductors

133 and 134 to control the supervisory means associated withthe A operators cord circuit. When the calling subscriber at A and the called subscriber at C terminate the connection, the answering and calling supervisory lamps (not shown) of the A operators cord circuit are lighted in a manner previously described to indicate to her that the call has terminated. She thereupon removes the plugs 7 and 8 of her cord circuit from the jacks with which they were in engagement. This causes relay 10 to de-energize and interrupt the holding circuit of the switching relay 13. This relay deenergizes and interrupts the holding circuit of the relay 19, which removes the guarding condition from the test terminal of the trunk that has just beenoin use. With the

conductors

133 and 134 opened, relay 101 retracts its armature and after a short interval the relay 102 retracts its armatures. This effects the steady lighting of lamp 111 at the overflow operators position in a circuit completed from grounded battery, lamp 111, armature and front contact of relay 100, conductor 136, left hand armature and front contact of relay 105, inner armature and back contact of relay 102, the winding of pilot relay to ground. The lighting ofthis lampinforms the operator that the connection has been terminated and she removes the plug P from the jack J with which it has been in engagement.

The trunk just used of the overflow position is not in condition to receive another call until the relay 100 deenergizes. This occurs when the B operator at the overflow position removes the plug P from jack J after the A operator has released her cord circuit. It will be understood that the energizing circuit of the upper winding of relay 100 is broken at the plug P.

At the time that the A operator releases her cord circuit, relay 102 de-energizes while the slowreleasing relay 10 3 is for a short time held operated. This places a ground potential on conductor 135 through the outer front contact and armature of relay 103, and the left hand armature of relay 102 to short circuit and release relay 26. Relay 26 controls the release of the primary and secondary switches. With these switches released the energizing circuit for the lower winding of relay 100 is interrupted. The apparatus and circuits are now in condition to receive a second call.

In Figs. 2, 2-"- and 3 there are provided release relays 16 i and 166 and release keys 165 and 167. It will only be necessary to explain the function and operation of the release relay 16 1 and release key 165, since the function of relay 166 and key 167 are identical therewith. These relays and release keys are provided to care for the condition that arises when the Jr operator momentarily inserts the plug 8 into the jack 9, and then removes this plug trom its jack. Under this condition the line switch at oilice :ijrl seizes a primary line switch and this in turn seizes a secondary line switch at the second oi'lice. The primary and secon1lary switches at oll'ice #2 will remain opcrated, and the supervisory lamp at will continue to flash. it some means like the release relay ltil and key use were not provided, it would be impossible to release the primary and secondary switches operated in this way. When an occasion arises sin'iilar to that just described, the l) operator on connecting her telephone set to the trunk (lc;-;- ignatcd by the lamp 5i. and on discoveringthat the call has been abandoned inserts the plug P into the jack associated with the re lease relay ltll. This energizes relay int and causes it to attract its armature. The operator then depresses key 165 and connects ground to the release trunk 50, and this ctfects the release 01 the primary switcl as as in the case oi a normal call.

\Vhat I claim is:

1. In an automatic telephone 5 ear, a pin 'ality of incoming lines, primary trunk selecting switches for said lines, each switch being provided with movable brushes including a test brush and a holding brush, contacts for each switch arranged to be on gaged by its brushes, primary trunks terminating in the contacts of said prin'iary switches, each trunk having a test conductor and a holding conductor, means for chaactcrizing the test conductors of select able trunks by the presence of potential and for characterizing unsclectable trunks by the absence of potential, means for operating the brushes oi the primary line switch of an incoming circuit to move its brushes over the contacts of said primary trunks, means responsive to the engagementof the test conductor ot a selectable trunk for stop ping said primary trunk selecting switch, a holding circuit thereupon completed including the holding conductor of the selected trunk for holding said primary line switch in its operated condition, a secondary switch in which each primary trunlr terminates, secondary trunks terminating in said secondary switches, means for characterizing sclcctablc secondary trunks by the presence of potential and for characterizing unselectable trunks by the absence of potential. and means responsive to the seizure oil a primary trunk by the prin'iary line switch :lor causing the secondary switch to seize a secondary trunk distinguished by the presence of potential.

9. In an automatic telephone system. a

eeaeaa plurality of incoming lines, primary trunk selecting switches for said lines, each switch being provided with movable brushes includiug a test brush and a holding brush, contacts for each primary switch, to be engaged by the various brushes, primary trunks terminating in the contacts or said primary switches, cach trunk having a test conductor and a holding conductor, means for characterizing the test conductors of selectable trunks by the presence of potential and for characterizing the test conductors of unselcctable trunks by the absence of potential, means for o 'ieratin the brushes ol the primary line switch or an incoming circuit to more its brushes over said prin'iary trunks, means responsive to the engagement of the test conductor oi a selectable trunk by its test brush for stopping said primary switch, a holding circuit thereupon completed through the holding brush of said primary switch including the holding conductor of the selected trunl; for holding said primary line switch in operated condition, a secondary line switch in which each primary trunlr terminates, secondary trunks terminating in said secondary line switches and means re spousive to the seizure of a prin'iary trunk by a primary switch for causing the secondary line switch to seize an idle secondary trunk. v

ll. in an automatic telephone system, a plurality of incoming lines, a plurality of prnnary trunks terminating in said primary trunk selecting switches, means for characterizing unseleeti ble prin'iary trunks by the absence oi potential and for characterizing selectable trunks by the presence of potential, means for operating a primary trunk selecting switch of an incoming line to select a primary trunk characterized by the presence of potential, a secondary trunk select-- .iug switch for each primary trunk, secondtrunks terminating in said secondary switches, means for operating the secondary switch oi the selected trunlc to seize an idle secondary trunk and means for preventing the selection of a prii'nary trunlr when all the secondary trunks are in an miseiectable condition.

1:. In an automatic telephone system, a plurality of incoming lines, primary trunk selecting switches for said lines, a group of primary trunks terminating in said primary trunk selecting switches, means for characterizing unselectable primary trunks by the absence of potential and for charactcrizimr selec able trunks by the presence of potenon. said means inclmling a relay common to said group of primary trunks, said relay being provided with sets of contacts less in number than the number ol primary trunks in said group. means for operating the primary trunk selecting switch of an incomterized by the absence ot potentia lpa second:

ary switch foreach primary trunk, a group of secondary trunks tcrm' ting inrsaidsecondary switches, means .101 operating; the seconc cry switch of the selected trunlc to" y-ti'unlt and means etseize. an idle se'conth. tfective when all the group of secondary trunks are m an uuselectable conditlon .t'or

causing said relay to characterize all of said primary trunks unsclectable.

5. in an automatic telephone system, incoming lines, primary trunk selecting switches for said lines, a group of primary trunks terminating in said primary trunk selecting switches, means for characterizing unsclectable primary trunks by the absence of potential and for characterizing selectable trunks by the presence of potential, said means including a relay common to said group of primary trunks, means for operating the primary switch of an incoming line to select a primary trunk characterized by the presence of potential, at secondary trunk selecting switch for each primary trunk, secondary trunks terminatin in said secondary switches, means for operating the secondary switch of the selected primary trunk to seize an idle secondary trunk, a relay for each secondary trunk arranged to be operated when its associated trunk is seized, and means for disabling said common relay when the relay of any of the secondary trunks is in an inert condition. I

(3. in an automatic telephone system, incoming lines, primary trunk selecting switches for said lines, a group of primary trunks terminating in said primary trunk selecting switches, means including a test conductor for each primary trunk for characterizing unselectable primary trunks by the absence of potential and tor characterizing selectable trunks by the presence of potential, a relay common to said group of primary trunks, said relay when operated removing potential from the test conductors of the group of primary trunks, means for operating the primary switch or an incoming line to select a primary trunk characterized by the presence of potential, a secondary trunk selecting switch for each primary trunk, secondary trunks terminating in said'secondary switches, means for operating the secondary switch or" the selected primary trunk to seize an idle secondary trunk, a relay tor each secondary trunk arranged to be operated when its associated trunk is seized, and means for disabling the common relay when any of the relays ofthe secondary trunks are in an inert condition.

7. In an automatic telephone system, incoming lines, primary trunk selecting switches for said lines, a group of primary trunks terminating in said primary trunk selecting swi-tches ameansctor characterizing unseleetable-=prnnary tiainles :by; the absenceof potential and forcharaeterizingselectable trunksbyith -:pre'sence of potential, ,said means including; a relay common --toi :said group of primary trnnks,:- means for oper ating aida'relay; to remove potentialL-from! tie primary group of trunks, means for operating the primary switch of an incoming line to select a primary trunk characterized by the presence of potential, a secondary switch for each primary trunk, secondary trunks terminating in said secondary switches, means for operating the secondary switch of a selected primary trunk to seize an idle secondary trunk, a relay for each secondary trunk arranged to be operated when its associated trunk is seized, and means for disabling the operating means of the common relay when any of the secondary trunks are in an inert condition.

8. In an automatic telephone system, a phirality of incoming, lines, primary trunk selecting switches for said incoming lines, means for characterizing selectable trunks by the presence of potential and for characterizing unselectable primary trunks by the absence of potential, means for operating the primary switch of an incoming line to select a primary trunk characterized by the presence of potential, a secondary trunk selecting switch for each of said trunks, a second set of trunks accessible to said seoondar 1 trunk selecting switches, said secondary set of trunks including one or more over-flow trunks, and means preventing the seizure of the over-flow trunks when the remaining secondary trunks are idle.

9. In an automatic telephone system, a plurality of incoming lines, primary switches for said incoming lines, each switch having sets of contacts and brushes including a test brush for engaging said contacts, primary trunks terminating in said contacts, each primary trunk having a test conductor terminating in one of said contacts, operating means for advancing said brushes over said sets of contacts to seize a selectable primary trunk,- a relay common to said primary trunks for normally applying potential to the test conductors of said primary trunks to render them selectable, means for removing said potential from the test conductor of a selected primary trunk, a secondary switch for each primary trunk, secondary trunks terminating in said secondary switches, means for operating said secondary switches to seize a selectable secondary trunk, a relay for each secondary trunk arranged to be operated on the selection of its associated trunk, and. means effective on the operation of all of the relays of the secondary trunks for operating said common relay.

10. In a telephone system, incoming lines,

a plurality 01 operators positions, means including automatic switches for extending said incoming lines to said operators positions, a plurality of recording; devices at each operators position, means for rendering an operators position unseleetal'ile, two releasing means for rendering said operators posi tion selectable, and means including said recording deviees for determining which releasing means has been employed. 10 In witness whereof, I hereunto subscribe my name this 29th day of March, A. D.

WINFRED '1. POWELL.