US1540420A

US1540420A - Automatic telephone system

Info

Publication number: US1540420A
Application number: US473483A
Authority: US
Inventors: Winfred T Powell
Original assignee: STROMBERG CARLSON TELEPHONE
Current assignee: STROMBERG CARLSON TELEPHONE; STROMBERGCARLSON TELEPHONE MANUFACTURING Co
Priority date: 1921-05-28
Filing date: 1921-05-28
Publication date: 1925-06-02
Anticipated expiration: 1942-06-02

Description

June 21925.

w. T` POWELL AuToMATIc TELEPHONE sYsTEM .h1-ne Z, 1925.

FINDER'.

BRIDGE.

BRlDGE ALLOT TER.

`F|NDER ALLOT TER INVENTOR BY www ATTORNEY WINT-'RED 'E POWELL Patented June 2, 1925.

UNllTE PATEN \VINF'RED "1. POWELL, '0F ROCHESYER7 NEW' 'YORK, "A'S'SIGNG'R 'T0 TEE 'STROMBERG- CARLSON TELEPHONE MANUFACTURING GCMPANY, "F MCHESTER, NEW YORK, A

CORPORATION OF 'N EW YORK.

AUTQMATIEC TELEPHONEFSYSTEM.

Application filed May 28, 192i. `Serial JNO. MSABS.

To `all 107mm it muy concern.' V

Be it known that I, lVINrnED T. PownLL, a citizen of the United States, residing at Rochester, in the county of Monroe and State of New York, have invented cert-ain new and vuseful Improvements in Automatic Telephone vSystems (Case #89), of which the following is a full, clear, concise, and eX- act description.

rThis invention relatos to .telephone systems and more particularly to telephone systems `employing 4automatic switches fin establishing telephone connections.

The main features :o-t this invention reside -Vin novel circuits tor setting :automatic switches and for releasing the same, The various features will appear from the detailed description and f'appendingg claims.

The drawings with Figure 1.and Figure 2 arranged in the .order named represent so much of a telephone system as is necessary for .an understandin-g of the present invention. est the le'l't ot the dotted line of Figure 1 there are -iiepresented two substations and telephone lines leading from` these substations to t-he brushes of :a line switch individual to these two lines. At the right of this dotted line 'there are represented two secondary line switches which are effective to select bridge :or trunk circuits. In the upper lett hand corner et Figure 2 and to the lei et the dotted line there is represented a briV ge or trunk circuit which is comparable to an ope-rators :cord circuit in a manual telephone system. At the letthand side ot this ligure there also appears a bridge allotter switch which functions to `assign idle bridges 'tor use in succession. At the upper right hand corner of this figure a group of multi-contact relays `are represented while only three of 'these relays are shown, it will bc understood that in the present sys-tem such relays are employed. At the lower right hand corner a register sender comprising a tens register and a `units register' is shown while near the center of this ligure there appears -a tinder switch which functions Vto connect its associated regi-ster sender to a selected bridge circuit. lt is to be understood that :there .are as lmany register senders and associated inders as there are simultaneous `calls in the process et' being established. oit .this ligure there is represented a linder it the lower lett hand-corner allotter which functions to vassign ya finder l be understood by describing the 4method rot establishing `a telephone connection from a calling substation indicated at A to La called substation indicated at B. Vhen the calling subscriber `at A remo-ves his receiver 'from its switch hook to initiate such a call, a circuit is closed for the line relay 5 from grounded. battery wind-ing oit this relay, inner upperV back contact and armature of the ycut -o'f rei lay 6 over the .lower side ofthe calling line and through the substation circuitsin series over the :upper side of the calli-ng line and through fthe uppermost aranature and back Contact ot the .cut off relay to ground. rIfhe line relay is actuated in this circuit and closes an operating circuit tor :the motor magnet 7 extending from grounded battery, resistance, back contact, larmature and winding yot the motor magnet 7, Auppermost front contact and arma-ture ofthe line relay, uppermost armature. and back contact of the cutoff relay 6 to l(freund. Under thecontrol oit this `circuit the brushes 18` t-o 15 inclusive of the primary line switch are fad Vanced until the test brush 1'()A locates a test terminal of a pair of idle trunks leading to a pair of idle secondary line switches. Let it be assumed that the itirst pair `ot idle trunksltested are those shown .in Figure 1 at which time the test termi-nal 16 of this trunk will be characterized fby the presence ot' `ground potential indicating .its idle condition. As 4a result of this test, the cut oil' relay 6 and the -cut ott relay 17 are .operated in series in a circuit traceable from grounded battery, resistance, back contact, :armature of the vmotor magnet 7, lowerrfront `Contact and armature of the line relay f5, lower wind.-

ing ot. the cut olf rel/ay 17, lower winding ot' the cut oli relay `6, test `brush 1.0, test terminal 16, contact 18 and armature of relay 19, contact and armature oi relay 21, up-A ico ` effect its deenergization. At its uppermost armature and back contact it opens the operating circuit of the motor magnet 7. It will be noted that the initial energizing circuit of the cut oill relay 6 and cut oil relay 17 is interrupted at lower armature and 'ront Contact of line relay 5 but these cut off relays are slow releasing so that they remain energized for an appreciable interval of time thereafter. At the uppermost armatures and front contacts of the cut off relay 6 the calling line is extended through the brushes 8 and 9 of the primary line switch to ground at the uppermost armature of the relay 24 and to grounded battery through the inner upper armature and back contact of the relay 24 and lower winding of relay 22. The relay 22 is energized in this circuit and closes a holding circuit for the cut off relays 6 and 17. This circuit may be traced from grounded battery, upper windings ot relays 6 and 7 in multiple, inner upper armature and front Contact of relay 17, holding brush 13, holding conductor 25, contact 26 and armature of relay 22, lowermost back contact and armature of relay 19 to gro-und. It will be noted that the closure of the contacts of the relay 17, connects the upper winding of relay 23 in series withthe selected primarytrunk and the paired calling line but this circuit is incomplete at theV switch hook of substation B.

As soon as the relay 22 attracts its armatures, it closes an operating circuit Jfor the motor magnet 27 of the primary line switch shown at the upper part of FigureJ 1, this circuit being closed from grounded battery, resistance, back contact armature and winding of the motor magnet 27, Contact 28 and armature of relay 22, uppermost armature and back Contact of relay 24 to ground, and if the brushes 29 to 33 inclusive of this secondary line switch are not resting in engagenient with the out-going terminals of the allotted bridge circuit, this operating circuit will actuate the motor magnet causing it to advance rthe brushes of the secondary line switch until its test brush 30 engages the test terminal of the allotted circuit.

Let it be assumed that the allotted bridge circuit is that appearing in Figures 1 and 2 and when the test brush 30 of the secondary line switch engages the test terminal 34 of this allotted bridge ci-rcuit the relay 24 is energized to stop the operation of the moto-r magnet 27. The operating circuit of relay 24 extends from grounded battery, resistance, back Contact, and armature of magnet 27, upper low resistance winding of relay 22, its upper front contact and armature, upper with the upper winding of the relay 24 in f the circuit ust described, while at the armatures and front contacts ot relay 24 the calling line is extended through the secondary line switch brushes 32 and 33 conductors 4() and 41 through both windings in series of relay 42 to ygrounded battery. Relay 42 is operated in this circuit and at its upper armature and front contact closes an operating circuit for the slowv releasing relay 36. While the operation of this relay completes a holding circuit for the secondary line switch which extends from ground atthe upper armature and front contact of relay 36 and conductor 43, holding brush 31, contact 44 armature and winding or" relay 24 to grounded battery. At the lower armature and back contact of relay 36 the initial energizing circuit of relay 24 is interrupted with the result that relay 22 deenergizes.

As soon as the relay 22 is first operated, a

vcircuit is closed for starting an allotted linder switch to associate its register sender with a bridge circuit which is allotted for use. This is eii'ected by the operation oi relay 45-and a circuit is closed from ground, lowermost armature and back contact of relay 19, armature and contact 46 of relay 22, conductor 47, winding of relay 45, upper armature and back contact of relay 48, outer right armature and back contact ot relay 38, armature, contact, and winding of the motor magnet 49 of the bridge allotter to grounded battery. The motor magnet 49 is not operated in series with the relay 45 but this relay is caused to attract its armatures and at its outer armature and front contact closes a circuit trom ground, brush 50 of the finder allotter, winding oi the motor magnet 51- ot the linder, through the resistance, back contact and armature of relay 52 to groundedvbattery. Under the control of this circuit the motor magnet 51 advances the brushes 53, 54, 55, 56, 57 and 83 of the finder switch until the allot-ted bridge circuit is located at which time the motor magnet 51 is shunted by a circuit closed from grounded battery, upper armature and back contact of relay 52 resistance, winding of relay 58, finder brushv 53, allotter brush 59, outer front contact and armature of relay 45 to ground. This circuit stops the operation of the motor magnet 51 ci' the finder switch and operates relay 58. As soon as the relay 58 is operlhil lill

ated, it closes a locking cire-uit t'or itself from grounded battery, at the lower armature and back contact of a relay similar to 52 at an idle finder switchA ot the series, winding` ot relay 52, innermost armature, i'ront contactand right-hand windingl oit' relay 58, finder brush 54, outermost back contact and armature ot relay 60, inner lower bach contact and armature of relay 6l, winding' oi' relay 62, conductor t8 to ground at the upper iront Contact and armature of relay B6. ln the event that all the finders oi `the system arein use all the relays similar to 52 will be actuated so that at this time the last described circuit will extend trom grounded battery through the winding oit the relay 23), with the result that the relay 31) operated to interrupt the operating,l circuit ot the motor magnet 63 of the finder allotter to prei/ent its useless hunting ttor an idle linder switch, however, iii' an idle iinder switch is available as soon as the rela 512 is energized, it closes a circuit from grounded battery at its upper armature and Yliront contact, finder allotter brush 64 windini),l of relay eltlto ground. Relay 48 is actuated and eil'ects the deenergization or" relay whereby a circuit will then be conipleted from ground, outer armature and hack contact ot relay 45, lower armature and front contact oi.l relay d8, armature and back conta-et ot relay 39, haelt contact armature and winding` oi the motor magnet 63 to grounded battery. Under the control ot thiS circuit the motor magnet. 63 advances the brushes 56 and 64 of the finder allotter until the brush 6ft ot this allotter engages the test terminal ot an idle finder switch which` is characterized by the absence of battery potential due to the fact that its relay 52 is deenergized. lWhen such an idle iinder is located, relay i8 deenergizes and opens the operating' circuit 'for the magnet 63.

lroin the foregoing description of the adran-cingot the `finder allotter switch it will be that this switch is not advanced until the calling; line has been Vextended to the allotted bridge through a primary and ak secondary line switch and until the allotter llinder switch has'connected its associated register sender to the ientioned bridge. The iii-st ot these operations is indicated by the inergir/.ation ot relay 36, while the completion ol the linder operation is indicated pletes an actuating circuit tor slow releas ing relay 65, extendingl trom grounded battery, winding or" this relay, lower armature and front contact ot relay 62, conductor 66, and through a multiple conductor 67 to ground at the lett hand baelrcontact and armature of a relay similar to at an idle bridge circuit. However, it' all the bridge circuits are in use this last described circuit instead ot being completed at the armature and back Contact ot some relay 65 will extendthis circuitthrough the winding ot relay 238 to ground. Relay 65 indicatesthat associated bridge cireuitis engaged and completes a circuit from ground, its lett hand armature and front contact, brush68 oil the bridge allotter, outer armature and back contact ot relay 38, bach contact armature and winding ot the motor magnet 49 to grounded battery. Under the control et this circuit the bridge allotter advancesits

brushes

37, 59,68 and 70 until an idle bridge Y circuit is located at which time the operating` circuit ot' the motor magnet is no longer completed. ln the event thatthe relay 38 is operated due to the tact that all the bridge circuits are in use, the operating circuit ot the motor magnet will be interrupted at the outer bacl: contact and armature oi relay 38 to prevent a needless operation ot the bridge allotter. Also when relay 36 attracts its armatures `it closes a circuit from rvround, upper armature and -ifront contacter' relay 86, conductor 7l, windingv ot slow releasing relay 72, resistance to grounded battery.

'As soon the relay 62 is operated it dis-v connects the upper winding ot the `relay l2 troni its connection to grounded battery at the bridge .cuit and extends the in'ipulse circuit to the register sender. This circuit may be traced 'from grounded battery,y winding` of the motor magnet 75 its back cont-act and armature, contacts Y6 ot the otiiiornial switch, bzclr contact and continuity spring ot change over relay 7"?, tens register brush 78 in its normal position, inner bach ctmtact.. continuity siliringijs and winding of impulse relay 79, finder brush 56,` conductor 80, upper armature and continuity spring` oil relay 62, throueli conductor L'il and the two sides in series o' 'the selected. pri iry trunl:` circuit and ot the calling line, through the conductor l0 and loiier winding of relay vl-S2 to ground. Under the control oit this circuit the impulse relay 59 energized and at .its outer :trout Contact closes a circuit lor motor magnet i5 to advance the tous register into position 2. Relay 79 also closes a` lockingcircuit tor itself whichertends through continuity springv and armature oi" relay' "t9, secondary winding; et the 'induction coil to grounded battery. rEhe primary winding of this induction coil is connected to a source ot tone current and this tone transmitted to the calling subseribers station indicating to him that the apparatus is in condition to receive the impulses corresponding to the wanted line. Y

Let it he assumed that the designation of the wanted station is #32 under which assumption the subscriber at A first operates his impulse transmitter to effect three interruptions of the impulse circuit corresponding to the tens digit of this numher. In response to the first of these interruptions the locking circuit for the impulse relay 7 9 is opened and it deencrgizes to close an operating cir cuit for the motor magnet 75 extending from grounded battery, winding of this motor magnet, its hack contact and armature, through the contact 76 of the off-normal switch, register brush 78 in its first position, outer baclr contact and armature of the impulse relay to ground. The change-over relay 77 is also energized in a circuit in multiple of that just ldescribed yand attracts its armatures. At its left hand armature and continuity spring it closes a'loreak point in the operating circuit of the motor magnet so that this circuit is now independent of the control of the off-normal contact 76. At the inner right hand armature and front contact of relay77, the operating circuit of the motor magnet of the units register is interrupted to prevent its operation during the transmission of the tens series of impulses, while at the outer right hand armature and front contact of relay 77, a circuit is closed from ground through conductor 82, finder brush 88, conductor 84, inner front contact and armature of relay 62, winding of the relay to grounded battery. Relay 85 attracts its armatures and at its contact 86 closes a substitute holding circuit for the relay 36, while at contact 87 of this relay the impulse circuit is extended to ground independent of the lower winding of the relay 42. y

As soon as the register brush 78 reaches Vposition two and the line circuit is closed by the dial, the impulse circuit is again com.- pleted through the Winding of the impulse relay 79, this relay energizes and locks itself operated through its armature and continuity spring. At the outer armature and front contact of this relay a circuit is closed from ground, register brush 78 in its second position, continuity spring and armature pf relay 77, and winding of the motor magnet 77 to grounded battery which advances the register into its third position.

In response` to the second interruption of this tens series, the impulse relay 79 retracts its armatures and through its outer armature and hack' contact, and register brush 7 8 in its third position, it completes an operating circuit for the motor magnet 7 5 which advances the tens register brushes into their fourth position, in this position, the impulse relay 79 is again actuated and closes the mentioned locking circuit through its continuity spring and armature. At the outer armature and front contact of this relay an operating circuit is again complete for the motor magnet 75 which advances rthis register into its fifth position. In response to the third and last interruption ot the tens series, the impulse relay 79 retracts its armatures and completes yan operating circuit, for the motor magnet to'advance the tens register into its sixth position. Here again the impulse relay is actuated and advances the tens register into its seventh position. At the close of this series of impulses the change-over relay 77 has its operating circuit interrupted for a relatively long interval so that it deenergizes and at its left hand armature and continuity spring opens the mentioned operating circuit of the motor magnet associated with the tens register and at its right hand armature and baclr contact it closes a break point in the operating circuit of the motor magnet 88 of the units register. f

As soon as the relay 77 deenergizes after the impulse relay 79 is operated, an actuating circuit is closed for the'motor magnet 88 of theunits register, from grounded battery, winding' of this magnet. its back contact and armature, contacts 89 of the off-normal switch, back contact and continuity spring of the change-over relay 90,`

innerv armature and back contact of relay 77, contacts 91 of the ofi-normal switch now closed, units register brush 92 in its normal position, outer front contactyand arma-turc of impulse relay 77 to ground. Under the control of this circuit, the motor magnet 88 advances the units register into its first position in which it is in condition to receive the 'impulses corresponding to the units digit of the wanted number which are two in number. In response to the first interruption of the impulse circuit the impulse relay 79 has its reciting circuit opened and' it dcenergizes to close an operating circuit for the motor magnet 8S through its outer hack contact and armature and units register brush 92 in its first position. Under the control ofthis circuit, the units register advances into position two where the operating circuit ofthe impulse relay 79 is again closed. This relay closes its locking circuit and through its outer front contact and armature coniplctes an operating circuit to advance the units register into its third position. In response to the next interruption, the impulse relay deenergizes and advances the units register' in position four, and when the impulse relay is again operated it advances the units register into its fifth position. Here the impulse relay 79 cnc Zes and remains op'- erated for a relatix yly long interval which opens the operating circuit oi the units il il series to ground at the bach contact anc continuity spring of relay 95. Relays 93 and 95 are operated in this circuit and close breakpoints in the test circuit ot the wanted line. The relay 95 onactuation opens the operating circuit to the other similar relay-s such as 96 and 97V at their finder switches which will prevent the simultane-V ous testing ot other lines. At the right hand armatureV and back contact ot relay 95 the energizing circuit of relay is opened but .since it is slow releasing it will hold its armatures attracted tor a relatively short period thereafter. Y

lt the called line is idle, the test circuit will then be complete from ground at the middle armature and `:trent contact otrelay 58, right hand armature `and trent contact ot relay 95, armature and liront contactot relay 98, winding et relay 99, tensregister brush 100 in its seventh position, contact 101 ot relay 93, conductor 102 which extends through the uppermost armature and back contact ot the cut otlq relay 17 ot Figure 1 through the winding of the line relay 5 to grounded battery. In the event that the brushes ot the primary line switch were not in engagement with terminals ot idle primary trunk circuits, the line relay 5 will complete an operating circuit for the motor magnet 7 to advance the brushes ot the primary switch to idle prim-ary trunks. This operation ot the primary line switch is the same as when one of this pair ot tele-phone lines originates a call, and when the prin'i-ary switch reaches an idlevr aair ot teun-les the cut-oiln1 relays such `as 0 and 17 are `operated Vto seize this pair ot" trunks thereupon the test conductor 102 is extend-y ed to lthe line switch brush 12 as will presently be described. Under the condition -a-ssumed, the brushes of the primary line switch are already in engagement with an idle primary ltrun'li circurt and the out oit relay 17 is already operated to extendk c-onductor 102 through the brush 12 .of the 'primary switch, the uppermost armature and back contact ot relay 103, upper winding` ot relay 2 to grounded battery. Relay 21 operated in this circuart and at its upper armature and front contact closes a multiple energizing circuit tor the relay 23.

This relay when energized effects the operation o'i `the motor magnet. 104l-ot the seccalling line hasrbeen extended. Vhen this trunl circuit is reached the relay 103 is operated in a circuit` completed from grounded battery, resistance, back contact and `armature ot motor magnet 104,. lower winding, front contact and armature ot relay 23, lower winding of relay 10.3, lower armature and liront contact ot' relay 21, test brush 109 in engagement with testconductor 110, allotter brush 55, front contact and arn'iature of relay 99 toground Relay 103 is thus energized and at its lower back contact and armature, opens the operating circuit for the motor magnet -1, while at its lower front contactsand armatures it extends the-called lines to conductors of the allotted bridge circuit. At` the uppermost armature and back contact of relay 103 .the test circuit including conductor 102 is interrupted which causes the 4deenergiza-tion ot the relay 99 -o'l the finder switch which has previously been locked operated but the relay 103 hasa holding circuit closed from grounded battery, upper winding and upper armature and front contact ot relay 103, 'holding brush 107, holding conducto-r 111, winding of ringing rela-y to ground at the lower trentV contact and armature ot relay 72. Y

The ringing relay 00 is actuated and closes a signaling circuit from the source ,of ringing current through the lower winding ot relay 112, right 'ha-nd trent contact and armature ot relay 00, conductor- 113 of the bridge circuit and throng-h the primary and I V72 `to ground. lRinging current is intermit tently applied yover this circuit in the well known manner until the called party respo-ndsY at which time the trip relay 112 is actuated to short circuit the ringing relay 60 causing 'it to deenergizem The ytrip vrelay is then locked ope-rated from ground applied through its upper winding, troutv contact and armature, inner bach contact and armaV ture ott relay 00,` lowerV front coin-tact and armature o'l' relay 7 2 to ground.

yll'lhen the ringingrelay 60 attracts its arn'iatures it opens ythe locking circuit tor the relay 58, causing this relay to deenergize. Relay controls the vrelease of the register sender and at its middle armature and back contact closes a circuit from ground, oil' normal contacts 115 ofv the oil-normal switch, armature, back contact and winding of the motor magnet 7 5 to grounded battery. This circuit causes the restoration of the tens register to normal. At the outer armature and back contact of relay 58 a restoring circuit tor the units registeris closed through off-normal contacts 116. It will beremem- ,bered that the relay 52 is energized in series with relay 58 so that relay 52 also deenergizes to render the linder under consideration accessible for use in a succeeding call. Talking battery is supplied to the calling line through the windings of relay 42 while talliing battery is supplied to the called line through the windings of relay 119.

In the event that there are no; bridge circuits vailable, relay 38 is operated and it no finder switch and its associated register sender is available relay V39 will be operated so that ground potential is applied over conductor 117 to causethe calling line to select y the overflow trunk `shown at the eXtreme right o Figure 1. lhen this trunk is seized, relay 118 is operated to apply a busy tone to the calling line. This tone is applied through the lower winding of relay 118 as long as the calling subscriber holds his connection, while relays 88 and 39 are energized.

Let it be assumed that the called line was busy when the mentioned test was made, under this assumption the conductor 102 will be open at the uppermost `back contact and armature of relay 103 sothat relay 99 of liigure 2 will not be operated. The test relay 61 will therefore be operated over a circuit traceable from grounded battery, winding of this relay its continuity spring and back contact, finder brush 57 back contact and armature of relayy 99, back contact and armature olf' relay 98, right hand Jfront contact and armature ot relay 95, middle liront contact and armature oi relay 58 to ground. Relay 61 is thus actuated and closes a locking circuitV Jfor itselfthrough its continuity spring and armature to ground at the upper front contact and armature of relay A source ot busy tone current is thus applied through the lowermost armature and frontv contact ot relay 61 to the calling station. I v

At the termination of the connection when the calling party replaces his receiver on its switch hook, relay 42 deenergizes and shortly afterwards the holdingrelay 86 retracts its armatures. This removes .ground from the holding conductor 43 to permitthe deenergization oi. the relays 19 and 24. The deenergization ol relay 19 elifects the release of the cut onl relay Gand since the primary'and secondary switches are olf Vthe type which remain in engagement with the trunk lines last used, this is all that is necessary to release them lhen the called party restores his receiver to itsswitch hook the relay 119 is deenergized and at its front contact opens the holding circuit of slow releasing relay 72 in the event that the callingl party has already released. H', however, the calling party still maintains the connection when the slow releasing relay 72 deenergizes the trip relay 112 releases and opens the holding conductor 111. This permits relays 21 and 103 to release and the deenergization of relay 21 causes the release of relay 17. -The release of this last mentioned relay places the secondary and primary line switches in condition for use on a succeeding call.

In the connection ust described, it so happened that the calling and called lines both terminated at the same primary line switch.` However, in the event that line A. terminated in a different line switch from the called line its associated line will be extended to idle secondary line switches and if this associated line is not calling a selected secondary line switch will remain inactive. ciated calling line originates a call during the periodthatline A is calling the secondary line switch to which the associated line is connected will be operated in the same manner as the secondary line switch already described. Likewise the line associated with the called line B will be connected to an idle Vsecondary line switch which switch willy reprogressively movable switches, magnets 'foradvancingthe same, and operating circuits for said magnets completed alternately at saidnormally open and said normallv closed contacts. l'

2. In an automatic telephone system, reg` ister switches, eachhaving a progressively movable brush and a motor magnet including a winding, a pair of conductors leading to said register switches, and operating circuits for each register switch including its brush,fa motor magnet winding, and said conductors.

3. In an automatic telephone system, register switches, a magnet for each switch for advancing the same, an impulserelay having normally closed and normally open sets ol contacts, means for causing a series of operations of said impulse relay, and operating circuits for said magnets closed through said` contacts in response yto the operations of saidrelay.

4. In an automatic telephone system, regi 14. In an automatic telephone system, pairs of telephone lines, primary and secondary automatic switches, each havingfixed and movable contacts, said movable contacts being arranged for rotary movement to engage said Xed contacts succes- Sively, each pair of telephone lines terminating in movable contacts of a primary automatic switch, trunk circuits extending between Said primary and secondary switches, link circuits, a register Sender common to vsaid telephone lines, means responsive to the initiation of a call on one of said telephone lines vfor extending said tele- V phone line through its prima-ry automatic switch, a trunk circuit and a secondary automatic switchl to a'link circuit and to said register sender7 said register sender being controllable over the calling` telephone line to record the designation of a Wanted telephone line, a starting circuitfor the called telephone line for causing a primary and a. secondary line switch to extend the called telephone line to the link circuit to which said calling telephone line has been oonneoted7 and means including said register sender for completing the starting circuit of the called telephone line.

In Witness whereof, I hereunto subscribe my name this 26th day of May'A. D. 1921.

WINFRED T. POWELL.