US1564020A - Automatic telephone system - Google Patents

Description

Dec. 1, 1925. 1,564,020

W. T. POWELL,

AUTOMATIC TELEPHONE SYSTE M INVENTOR Wl N FRED 'l'. POWELL ATTORNEY Dec.- l, 1925- l 1,564,020

w. T. POWELL AUTOMATI C TELEPHONE SYSTEM Filed MarchA 14 1922 2 Sheets-Sheet 2 F\G E CONNECTOR INVENTOR ATTORNEY WINFRED n POWELL,

, Patented Dec. 1, 1925.

t LStILUZ UNITED STATES PATENT OFFICE.

WI-NFRED T.` POlvVIjlLL, O15'A ROCHESTER, NEW YORK, ASSIGrNORr TO THE STROMBERG- CARLSON TELEPHONE'MANUFACTURING COMPANY, OF ROCHESTER; NEW `YORK, A

CORPORATION F NEJ'V YORK.

AUTOMATIC TELEPHONE SYSTEM:

Application filed March 14, 1922;

To zZ/ wlw/n i?? may concern Be it known that I, lVINrnnD' T. POWELL,

a citizen of the United States, residingI at Rochester, in the county oi' Monroe and State of New York, have invented certain ne and useful improvements in Automatic Telephone Systems, of. which the following 'is a full, clear, concise, and exact description` This invention relates to telephone systems and lmore particularly toitelephone systems en'iployingl automatic switches in completing some portion ot a telephone conne@ tion. Y

In automatic telephone systems in which the automatic switches are directively controlled by directive impulses as distinguished tl'rom those controlled by revertive impulses, it frequently happens that the time interval between the various series of impulses exceptth-ose corresponding to the tens and units digit ot the wanted number, are of such short duration that. it does not permit a long enough period for the trunk hunting;` operation ot the various selector switches. Il" 'a series otAA impulses is transmitted bei'ore a select-or switch has completed-k its trunk hunting operation it results that the call is elther mutilated, resulting in the calling 'ot unfong part-ies, or else the call is lost altogether. Under either condition one or more trunk circuits are uselessly held busy until the calling' subscriber abandons' the call, although these trunks are ot no use to the subscriber' after the mutilation or the call. This condition is particularly aggrar 'rated in periods oi' heavy trailic when the selectors rotate more, with the resultthat numerous trunks are uselessly withheld 'from service t'or a brietperiod.

It is the purpose ofthe present invention to provide ior the` immediate release of all; the operated selector switches and their 21S- sociatedtrunks, as soon as a connection; tails, because a seriesof impulses has been trans` mitted te a selector switch. before it has completed its trunk hunting operation.

The dawing's with Figs 1 and 2 in.- the order named diagrannnatically represent a portion of a telephone system including the present invention. The portion et the drawingl oit Fig. 1 at the left of the dotted line represents the calling` subscribers line with substation circuits connected thereto, as Well Serial No. 543,697.

as an individual line switch of this line, while that portion of the drawing at the right of Fig. 1 diagrammatically represents the operating circuitsoi1 a selector switch.

At the left of the dotted line ot Fig. 2

there are represented the operating circuits of a connector or final numerical switch, while at the extreme right ot' this tigure there is represented a. called telephone line trnd the substationv circuits connected to this The line switch herein referred to may be substantially similar to that disclosed in the patent to Clement #1,107,158 patented August 11, 1914, while the selector switch and the connector switch herein referredto may be substantially similar to those switches disclosed in the patents to Keith, EricksontbErickson #815,321 and #815,176 issued March 13, 1906. lVhile these last mentioned numerical switches are arranged for operation in a; s'o-called three-wire system, it will be readily understood. how they may be modified to operate in a so-called rtwo-wire system such as that disclosed in the present application.

lith this brief outline of the mechanical structure of the system used, it is believed that the system will best be understood by describingthe method of establishing a telephone connectionfrom a calling substation indicated at LA to4 acalled substation indicated at B.

Then the calling; subscriber at-A removes his receiver from its switch hook the line relay 5 is energized in a circuit closed from grounded battery, winding` of this relay, upper backcontact and armature of the cuto1i` relay\6,-.over the, upper side of the callin g line and: through the substation circuits in series, over the lower side of `the calling line, inner upper armature and back contact of cut-ot relay 6, outer armature and back contactof relay 7 to ground. As a result of the energia-ation ot the line relay 5, anl operating` circuit. is closedy for the motor` magnet S traceable from grounded battery, windingbackContact and armature ot this magnet, front Contact and armature of line relay 5, inner lower bafckcontact and armature ot relay 6, left hand armature and back contact of relay 7, conductor 9, test brush 10 and a test terminal Similar' to 14 of busy trunks, which are characterized by the presence of ground potential applied at the right hand armature and front contact of relay 15 or over the holding conductor 16 as will be hereinafter pointed out. Under the control of this circuit the motor magnet 8 advances the brushes l() to 13 inclusive until the test brush 10 encounters the test terminal of a trunk which is characterized by the absence of potential. Let it be assumed that the first idle trunk tested is that shown in Fig. 1. This failure of the test brush 10, to further engage a busy test terminal, results in the discontinuingof the operating circuit of the motor ymagnet 8. During the period that the motor magnet is operating, a circuit is completed for the cut-oft' relay 6 closed from grounded battery, winding, back contact and armature oi the motor magnet 8, winding of relay 6, back contact and armature of relay 7, left hand front contact and armature of relay 5 to ground. This circuit is not effective, since the cut-ott1 relay 6 is shunted until the operating circuit or' the motor magnet 8 is no longer completed. Then the circuit described ior the cut-off relay 6 becomes eiectiveY and this relay attracts its armatures to extend the two sides of the calling line through its upper armatures and front contacts through the line switch brushes 12 and 13 and thence throughthe windings of the impulse relay 19 in series, through the upper armatures and back contacts of the switching relay 18. The impulse relay 19 is thus energized and completes an energizing circuit for the slow releasing relay 15 extending from grounded battery, winding of this relay, front contact and armature oi relay 19, middle bacl contact and armature of relay 18 to ground. Relay 15 is energized in this circuit and completes a holding circuit for the cut-ott1 relay 6 traceable from ground, at Jdie front contact and armature of relay 15, test terminal 14, test brush 10, conductor 9, back contact and armature of relay 7 inner lower armature and front contact of relay 6, inner armature and back Contact of relay 7, winding o't' cut-ott relay 6,.armature, back contact and winding o't motor magnet 8 to grounded battery.v

The selector switch is now in condition to receive impulses corresponding to the first digit of the wanted number. In response to each of these impulses the impulse relay i9 vibrates its armature and closes an operating circuit for the primary motor magnet 20 from grounded battery, winding ofthis magnet, winding of the'change-over relay 21, contacts 22 ofthe oit-normal switch which remains closed until the secondary movement of the selectorv switch is started, front contact and armature of relay 15, back contact and armature of relay 19, back contact and middle armature of relay 18 to ground. In response to each of these directive impulses this circuit is closed and the primary motor magnet 2O advances the selector switch brushes 23, 24C and 25 one step in their primary movement to select a wanted group of trunks. At the irst completion of the operating circuit of the motor magnet 2O the slow releasing change-over relay 21 is energized and holds its armatures attracted until the close of this series of impulses. Also after the first primary step of the selector switch, the relay 26 is operated in the circuit extending from grounded battery, winding of this relay off-normal contacts 27, armature and continuity spring of relay 21, armature and front contact of relay 15 to ground. VVhen'the change-over relay 21 deenergizes atthe close of this series of impulses the relay 26 is locked operated from grounded battery, its winding, off-normal contacts 27, conductor 29, back contact and armature of secondary motor magnet 28, outer front contact and armature of relay 26, middle back contact and armature of relay 18 to ground.

With the relay 26 operated and with the change-over relay 21 deenergized, an operating circuit is closed for the secodnary motor magnet 28 from grounded battery, windA ing of this magnet, inner front contact and armature of relay 26, back contact and continuity sprine` of relay 21, armature and front Contact ot relay 15 to ground. In response to the closure of this circuit the motor magnet- 28 advances the brushes 23, 24 and 25 one step, into engagement with the terminals of the irst trunk of the selected group. At this time the rotary oH-normal contacts 22 are opened and the contacts 30 are closed. As soon as the motor magnet 28 operates, it opens the lockingcircuit of the relay 26, but if the trunk with which the selector brushes are in engagement is busy, a condition indicated by the presence of ground potential on its test terminal suoli as 81, then the relay 26 will be again operated in a circuit from grounded battery, its winding, ott-normal contacts 27, conductor 29, back contact and armature of magnet 28, conductor 82, hack Contact and armatm'e olE relay 18, conductoiy 16, test brush 25, test terminal 31 te ground. When relay`26 is again operated the secondary motor magnet 28 will advance the selector switch brushes an additional step to bring them into engagement with the terminals of the second trunk circuit.

Let it be assumed that the iirst idle trunk circuit tested, is the one shown at the right of Fig. 1, leading to the connector switch et Fig. 2. It will be noted that duringthe period in which the selector switch is operating, a circuit is completed for the switching relay 18 from grounded battery, winding of relay 26, o'H-normal contacts 27, conduct-or 29, back contact andV armature ofY magnet 28, conductor 32, winding of relay 18, armature and front contact of relay 15 to ground. This circuit, however, is inetl'ective to operate the relay 18 owing to the tact that it is short circuited by ground applied through conductor 1G. Then an idle trunli is reached however, this short circuit is removed and the relay 18 is operated to extend the calling line through its upper armatures and trent contact, through selector brushes 23 and 24 and both windings oit the impulse relay 33 in series, through the back contactsand continuity springs ot' relay 3a. The impulse relay 83 is energized in this circuit and closes a circuit tor energizing the slow releasing relay 35. This last mentioned relay closes a locking circuit tor the rela-y 18 traceable Jfrom ground, left hand armature and 'trent contact oit' relay 35, conductor 36, test terminal 31, testv brush 25, inner armature and trent contact ot relay 18, wind ing of this relay, conductor 32, armature and iaclr contact ot magnet 28, conductor 29, ott"- normal contacts 2, windingl oit relay 2G to grounded battery. The relay 2G does not remain energized in series with relay 18.

.During busy periods when many oi the trunks are busy it frequently happens that the trunk limiting operation is ot relatively long' duration, and it', as frequently happens, the calling subscriber dials a succeedingl ser-- ies of impulses closely 'following the itirst, then the selector switch will not .have time to complete its operation. in the mutilation ot' a call, and since it then becomes necessary to start the connection anew, circuits are provided which will ini-- mediately release the portion of the connection established. Let it be assumed that while the secondary motor magnet 28 is advancing the brushes 28, 24 and 25 the subscriber at A. sends a second series or iinpulses. it this time relay 18 will not be operated so that this series ot impulses is transmitted to the impulse relay 19. ln response to the tirst oit this second series ot' impulses the relay 19 will retract its armature and a release circuit is closed from `ground, middle armature and back contact ot relay 18, armature and back contact oit relay 1S), armature and Atront contact ot' relay 15. ott-normal contacts 30, new closed, terminal 3T, brush 11 of the line switch, lowerw most iront contact and armature ot relay tl,

:tor the release magnet 38 troni grounded battery, winding` etl this magnet, oi'ii-iioriiial cont-acts 89, bachv contacts land armatures et rThis will result relays 15, 19 and 18 to ground. The operation of the release magnet 38 is effective to restore the selector switch to its normal position. Then cut-oit' relay 6 retracts its armatures the line relay 5 will again be energized since the calling subscriber at A is still on the line but this time the circuit ot' the line relay is closed through the outer trent contact and armature ot relay 7, wind-- ing olf the induction coil to ground. llfith' the line relay 5 energized a locking circuit is closed 'tor the slow releasing relay 7 coinpleted from grounded, battery, winding ot this relay, its front contact and armature, 'tront contact and arma-ture ot' line relay to ground. Atthe outer right hand arn'iature and front contact ot relay 7, a source ot' busy tone current is applied to the callingl line to inform the subscriber that a connec tion cannot be completed. llt should be noted that 'the operation ot the relay i" opens the operating circuit ot the motor magnet 8, so that this magnet will not operate and the circuit tor the relay G is opened to prerent the seizure ot any trunk circuit.

lt this arrangement is used in a large system, one or more selector switches ot' the saine character as that shown at the right ot Fig. 1 will bc interposed at the points where the heavy line conductors are shown broken, so that it the iii-st selector has completed its operation to select a second selector but this second selector is improperly operated due to the hurried dialing ot the series oit impulses, then the lirst and second selector' switches as well as the line switch will be released in the manner already described. it will oit course, be understood that any number ot' selectors or trunk limiting switches may be employed in a connection and as has been indicated, e ch oi these switches will be provided with the tentures ot this invention.

lt has already been pointed out how the calling line is extended through the line switch brushes lf2 and 18 and the selector brushes 23 and Q-l to the windings oi the impulse" relay 3S ot the connector switch. lt has al-ffso been shown that the impulse relay Sli-l is thus actuatezil to operate the slow releasing relay 35. The connector switch circuits are therefore in condition to receive a series ot impulses correa-spondiug to thc tens digit ot' the wanted number. In respense to the impulse oit the tens series ot impulses, an operating circuit is closed tor the priu'iary motor magnet L10, trom grounded battery, winding oi this magnet, winding ot the change-over relay ll1. otl normal contacts 4t2, outer trontco'ntact and armature ot relay back contact and armature oi relay 83 to ground. Under the control ot this circuit the primary motor' magnet advances its brushes 118, let and one step in their primary direction, causing lift) the contacts 42 to be opened, 'and closing the contacts 46. lt will be noted that the changc-over relay 4l is energized in series With the primary motor magnet and in response to the remaining impulses of this series the primary motor magnet is operated in a circuit new traceable from grounded battery, Winding ot this magnet, Winding or' the change-Over relay 41, its front contact and armature, ott-normal contacts 46, outer trent Contact and armature of relay 35, back Contact and armature o't relay 33 to ground. ln response to each oit these impulses the connector switch continues to advance its brushes in their primary direction.

At the close of the tens series of impulses, the change-over relay 41 deenergizes and prepares an operating circuit tor the secondary motor magnet 47. In response to the impulses of the units series of impulses relay 33 yibrates its armature and closes a circuit from ground, armature and back contact ot this relay, armature and front contact ot relay 35, ott-normal contacts 45, armature and back contact oit relay 4l, inner back Contact and armature of relay 48, armature 49 and back contact of relay 30, Winding of the secondary motor magnet 47 to grounded battery. ln response to cach ot these impulses, the motor magnet 47 advances the brushes 43, 44 and 45 in their secondary direction over terminals of the lines oli' the selected group. It. should be noted that the slow releasing relay 5l is energized in a circuit in multiple with that just described for the motor magnet and when once operated closes a locking circuit for itself, through its lett hand armature and :trout contact, which circuit is maintained during the units series et' impulses. lit the close otI this series ot impulses when the selector brushes are in engagement with the terminals oit the Wanted line, but before the slow releasing relay 5l deenergizes, the test ot the wanted line is made.

lit' the Wanted line is busy, its test terminal 52 will be characterized by the presence otv ground potential thereon and the test relay 48 will be operated in a circuit traceable 'troni grounded battery, Winding ot' this relay, lou'ermost armature and bach contact ot relay 80, continuity spring and armature of relay 5l', test brush 45, and test terminal 52 to ground at the connector, that has previously seized the wanted line, which ground is applied through a multiple terminal similar to 52 and a test brush similar to and an armature similar to and its front contact to grou-nd. ylie relay 5l deenergizes and the test relayv 48 is then locked operated in a circuit t ending trein grounded battery, Winding et this relay, lowermost armature and bacl; Contact ot relay 80, continuity spring and back contact ot relayy 5l, right hand trout contact of relay 48, conductor 56, lett hand 'liront con tact and armature ot relay 35 to ground. This last mentioned circuit is maintained until the connection is disestablished. At the outer armature and front contact ot relay 48, a source of busy tone current is applied to the calling line to inform the calling subscriber that the Wanted line is busy.

Let it be assumed that When the test of the called line is made that it is idle, under Which condition, battery potential will be present on its test terminal 52, this Will prevent the operation ot the test relay 48 but the switching relay 8O Will be operated in a. circuit closed from grounded battery, cut-ott relay 54 of the Wanted line, test ter minal 52, test brush 45, armature and back contact ot relay 5l, conductor 55, upper Winding ot relay 80, armature and back Contact oi relay 48, conductor 56, trout contact and armature or' relay 35 to ground.

Relay attracts its armatures to complete a'ringing circuit and also locks itself operated in a circuit including grounded battery, its loWermost Winding, front contact and armature, conductor 57, inner front contact and armature of relay 35 to ground. Ringing current is now applied over a ringing circuit closed from the ringing generator (not shown) through the upper armature and back contact of the trip relay 58, inner, upper front contact and armature of relay 80, connector brush 44, over the loiver side of the Wanted line and the called bell of the substation circuits, over the upper side o't the Wanted line, connector brush 43, uppermost armature and front contact of relay 80, upper Winding` of trip relay 58 to grounded battery. Ringing current is supplied over this circuit until the called party responds at which time the trip relay is operated to disconnect the source of ringing current from the Wanted line. The trip relay 53, when operated, locks itself in this condition through its lower front contact and armature, over conductor 57 to ground. It should be noted at this point that the uppermost contact of the trip relay 58 is adjusted so that; the locking circuit is completed. before this Contact is opened. lVhen the trip relay operates it closes a set ol" break points in the called subscribers portion oi' the connection.

Talking current is supplied to the called subscriber through windings ot relay 34, Which causes this relay to attract its armatures and reverse the direction ot current being supplied to the calling party. rlhis rcversal o't current. is effective for controlling message charging devices or for other similar purposes. Talking battery is supplied to the calling subscriber through the Wind ings oit the relay 33.

At the termination ot the conversation When the calling subscriber replaces his rellt) lit)

ceiver on its switch hoolg, the impulse relay 33 cle-energizes and shortly afterwards the slow releasing relay 35 deeners'izes. This opens the holdinr` conductor 36 which permits the switching' relay A18Min Fig'. l to deenergi'ize and close an operating;circuit for the release magnet 38, this circuit is closed from grounded battery, winding' of release magnet 38, off-normal contacts 39, baclr contacts and armatures of relays l5, 19 and 18 to ground. i-ilso the opening,` of conductor 36 permits the release ot the cut-off relay 6 which causes the line switch to revert to its normal condition.

rlfhe release of the connector switch iscontrolled by the subscriber of theconnection that hangs up his receiver last. In the event that the calling` subscriber is the lastto hang up his receiver, the impulse relay 33 deenergizes and shortly afterwards the relay 35. rit this time relay 34 is `deenergized so that an operating' circuit is closed tor the release magnet 59 ot' the connector switch, 'troni grounded battery, winding' of this magnet, oil-normal contacts 60, back contacts and armatures of relays 34, 35 and 33 toA ground. The release mafi'net 59 on energization restores the connector switch to normal condition. In the event that the called subscriber is the last to hang' up his receirer, at this time the impulse relay 33 and the slow releasing' relay 35 are .deenen gized and the connection is lnow controlled by the relay 34: which has a substitutehold ing` circuit for itseltI through lits right hand winding, inner, lower front Contact -and armature of the trip relay 58, outer Vfront contact and armature of relay Sil, lowermost "r'ront contact and armature of relay 5,8, contact 61 and armature of relay 80 to ground. It will also be noted that the locking circuits tor the trip relay 58 and switching' relay 80 are completed in multiple with that just described. When the called subscriber replaces his receiver on its switch hoolr, the relay 34rdeenergizes which opens the locking' circuits of the relays 80, 58 and A `but closes the energizing' circuit for the release magnet 59 4'from grounded battery otlfnormal contacts '60,baclr contacts and armatures of relays `34, Slaud 35 to ground. This apparatus isnow in Aits normal condition in readiness to be used in the next call.

`That is claimed is z l. In an automatic telephone system, a plurality of telephone lines, a plurality of primary trunks, an automatic switch for connecting a calling telephone line to any idle primary trunk, a numerical switch for each primary trunk arranged for directive movement in response to impulses and trunk hunting' movements, secondary trunks terminating-in said numerical switches. means for sending several series or impulses over said telephone line, means responsive to the. `[irst series of impulses for directiyely operating said numerical switch, means operating at the terminationy of the first series of impulsesy tor causing' said numerical switch to hunt lfor an idle trunk, means effective to release said'numerical switch if a second series ot' impulses is transmitted over said telephone line before said numerical switch has completed its trunk hunting' operation, and mea-ns for notifying' the calling' subscriber ot the release kof said numerical switch.

2. In an automatic telephone system, a plurality of telephone lines, a' plurality of primary trunks, a primary switch for con,

necting` a calling telephone line to an idle primary trunk, a numerical switch for each primary trunk, secondary triuilrs terminating in said numerical switches, means associated with each telephone line for transmitting several series of impulses, means for operating each numerical switch directiyely in response to a series of impulses and automatically to perform a trunk hunting' operation, a holding circuit extending,l` from said primary switch to the selected numerical switch on the seizure of the same, and means associated with said primary switch lor opening said holding circuit it the second series of impulses is transmitted over said telephone line during the trimk hunting period of said numerical switch.

3. ln a telephone system, a plurality o' telephone lines, a plurality of trunk circuits,

means including a non-numerical switch and numerical switches together with said'tr'unlr circuits tor extendinga telephone connection y from a calling telephone line in the direction of a wanted telephone line, means associated with the calling telephone line for transmitting several'series ot impulses to control said numerical switches, and means for releasing all the switches in the connection i'lf one ot said series ot impulses is sent prematurely and 'for preventing' temporarily the operation of lsaid non-numerical switch.

el. ln a telephone system, a plurality ot telephone lines, a plurality 0i trunk circuits, means including; non-nun'ierical switches and numerical trunlr hunting" switches together ,with said trun'lr circuits tor extending a telephone connection from a calling telepnone line in the direction ot a wanted telephone line, meansassociated with the calling` telephone line for transmitting several series ot impulses to control said numerical switches and means for restoring all the switches in the connection if one of said series of impulses is sent prematurely, and means for notifying' the calling subscriber olf such restoring operation.

5. 'In a telephone system, a plurality ot telephone lines, a plurality ot trunks, a primaryV switch for extending' a calling te'lephone line to an idle trunk, a mm'ierical trunk hunting switch individual to each trunk, secondary trunks terminating in said Cil numerical switches, an impulse relay associated with each numerical switch, said relay being controlled over a calling telephone line and a selected trunk in series, means for ope-rating a selected numerical switch directirely and subsequently automatically in its trunk hunting movement, means responsive to the seizure of an idle secondary trunk by said numerical switch for removing the impulse relay from the con- -trol or' said telephone line, and a relay -at said primaryv switch and a circuit for the same ex- 'tending` through contacts of said impulse relay, said relay when operated effecting the restoration ot the primary switch and the selected numerical switch.

6. In a telephone system, a plurality ot telephone lines, a plurality of primary trunk circuits, automatic switching means for extending` a calling' telephone line to an idle primary trunk, a numerical trunk limiting switch for each primary trunk, secondary trunks terminating in said numerical switches, a holding conductor extending between said switching means and a selected numerical switch as soon as said selected numerical switch is seized, an impulse relay at each numerical switch responsive to inipulses from the calling telephone line, means for disabling said impulse relay when its associated switch has seized a secondary trunk, a relay for interrupting the holding circuit of said switching means and said numerical switch, and a circuit for said relay controlled by the operation of one of said impulse relays during the trunk hunting operation of said selected numerical switch.

7. In a telephone system, a plurality of telephone lines, impulse senders associated therewith, a plurality of primary trunk circuits, automatic switching means for extending a calling telephone line to an idle primary trunk, a numerical trunk limiting switch 'for each primary trunk, secondary trunks terminating` in said numerical switches, a holding conductor extending between said switching means and a selected numerical switch as soon as the saine are connected together, a relay for interrupting the holding circuit of said switching means and said numerical switch, and a circuit for said relay closed responsive to one or more impulses from an impulse sender during the trunk limiting operation ot said numerical switch.

8. In a telephone system, a plurality of telephone lines, means associated with each telephone line for transmitting several series of impulses, a plurality oi primary trunks, switching means for interconnecting a calling telephone line with an idle primary trunk, a numerical trunk hunting switch for cach primary trunksecondary trunks terminating in said numerical switches, means including other numerical trunk hunting switches and trunks for further extending a telephone connection, means at each of said numerical switches for directively operating its numerical switch in response to impulses from said impulse transmitting means, means also located at each numerical switch for causing said switch to be advanced automatically to select idle trunks, means associatedwith one of said switches functioning if the same is prematurely operated to restore the switches of the portion of the connection already established, and means for notifying the calling subscriber of suc'li restoring operation.

9. In an automatic telephone system, a plurality of telephone lines, a plurality of primary trunks, automatic switching means for interconnecting a calling telephone line and an idle primary trunk, means at each telephone line tor transmitting series of iinpulses, a numerical trunk limiting switch for each primary trunk, secondary trunks and trunk hunting switches individual thereto, tertiary trunks with numerical trunk hunting switches individual thereto, means for directively and automatically operating said numerical switches in succession, restoring means associated with said switching means, a circuit for said restoring means eX- tended in succession to said numerical switches' on the seizure of the same, means operating in response to impulses during they trunk hunting operation ofr any numerical switch of a connection for actuating said restoring means, and means operating temporarily to prevent the connection ot the calling line toa primary trunk.

f 10. In an automatic telephone system, a plurality of telephone lines, means associated with each telephone line for transmitting series of impulses, a plurality of primary trunks, a non-nunierical switch for each telephone line ior extending the same when calling to idle primary trunks, a motor niagiiet for advancing each non-numerical switch, a line relay energized over the calling telephone line, a cut-olil relay ordisconnecting said line relay from said telephone line, a control relay at said linel switch, an operating circuit for said control relay, means eiiective on the seizure of an idle trunk for operating said cutoff relay and for maintaining the same operated dui'- ing the connection, a numerical trunk-hunting switch for each primary trunk, secondary trunks terminating in said numerical switches, and means at each numerical switch for operating said switch in response to impulses from an impulse transmitting device and for subsequently operating said numerical switch independently of impulses to seize an idle secondary trunk, said control relay being effective to restore the line lll) switch of the calling line and the selected numerical switch in response to a premature series ot impulses.

ll. In an automatic telephone system, a plurality of telephone lines, an impulse sender tor each telephone line, a plurality of primary trunks, switching means for eX- tending a calling line to an idle primary trunk, a numerical trunk limiting switch tor each primary trunk, secondary trunks terminating in said numerical switches, operating means lor each numerical switch responsive to a series ot impulses to select a wanted group of secondary trunks, means for subsequently causing the selected numerical switch to hunt for an idle trunk in a selected group, an impulse relay controlled over a selected primary trunk and a calling line and responsive to impulses tor controlling the directive operation of said numerical switch, a switching relay at said numerical switch :for disabling said impulse relay on the seizure ot' an idle secondary trunk,` a sequence relay for disabling the trunk limiting mechanism ot said numerical switch during the directive operation otl said impulse relay to control the operation ot' said switch, an oit-normal switch associated with said numerical switch, and means eliective on the receipt of impulses by said impulse relay while said switching relay and said sequence relay are deenergized and when said ott-normal contacts are closed, for eil'ecting the release of the portion ot the connection already connected.

l2. In a telephone system, a plurality of telephone lines, primary trunks, switching mechanism for extending` a calling telephone line to an idle primary trunk, a numerical switch Yfor each primary trunk, secondary trunks terminating in said numerical switches, each of said primary and secondary trunks including a pair of talking concluetors, a combined test and holding conductor tor maintaining the connection already established, a` fourth conductor, and means controlled over said fourth conductor responsive to the receipt of a premature series of impulses for disabling said holding conductor.

13. In a telephone system, a plurality of telephone lines, an impulse sender for each telephone line, a line switch for the use of each telephone line, trunks terminating in said line switches, a numerical trunk hunting switch for each primary trunk responsive to a series of impulses from an impulse sender, a motor magnet for advancing the line switch of the calling line to seize an idle trunk, a line relay controlled over the two sides oit' the calling line in series on the initiation of a call, a cut-oit' relay and a control relay associated with said line switch, a circuit 'for said motor magnet extending tlu'ough contacts of said line relay and said control relay, means responsive to the seizure oli an idle trunk for actuating said cutotf .relay to discontinue the operation et said line relay, a circuit for said control relay extending to the selected numerical switch through contacts oit said cut-oill relay, means at said nunierical switch operating in response to a premature series ot impulses tor closing the circuit oli said control relay,

locking circuit tor said control relay completed ou its energisaation,means responsive to the operation of said control relay for restoring the associated line switch and selected numerical switch, and means including said control relay for preventingv the operation ot said cut-oil'l relay.

l-l. In an automatic telephone system, a plurality ot telephone lines, an impulse sender for each telephone line, a plurality o'l" primary trunks, switching means for extending a calling line to an idle primary trunk, a numerical trunk hunting switch lor each primary trunk, secondary trunks terminating in said numerical switches, operating means for each numerical switch responsive to a series of impulses to select a wanted group of secondary trunks, means tor subsequently causing the selected numerical switch to hunt 'for an idle trunk in the selected group, an impulse relay associated with the selected numerical switch and controlled over the selected primary trunk and a calling telephone line, said impulse relay being responsive to impulses from said impulse sender for controlling the operating means ot' said numerical switch, means responsive to the operation of said impulse relay during the trunk Ilimiting operation ot said selected numerical switch for interrupting the connection including the calling telephone line and the selected primary trunk, and means responsive to said interruption ttor releasing said operated switching means and said selected numerical switch.

15. .ln an automatic telephone system, a plurality oit telephone lines, impulse senders associated therewith, a plurality of primary trunks, automatic switching means tor extending a calling telephone line to an idle primary trunk, a numerical trunk hunting switch tor each primary trunk, secondary trunks terminating in said numerical switches, a relay associated with the operated automatic switching means for effecting the release ot' said switching means and the selected numerical trunk hunting switch, and means associated with said selected numerical trunk hunt-ing switch and operated responsive to the receipt ot' directive impulses at said selected numerical switch during its trunk limiting operation for actuating said relay.

16. In au automatic telephone system, a plurality ot telephone lines, impulse senders associated therewith, a plurality of prin'iary trunks, automatic switching means for eX- tending a calling telephone line to an idle primary trunk, a numerical trunk hunting switch tor each primary trunk, secondary trunks terminating in said numerical switches, a relay associated with the operated automatic switching means ior causing the release ot' said switching means and the elected numerical trunk hunting switch, means associated with said selected numerical trunk hunting switch and operated responsive to the receipt of directive impulses at said selected numerical switch during its trunl: hunting operation for operating said relay, and means controlled by said relay for signaling said calling telephone line.

1T. In an automatic telephone system, a plurality of telephone lines, a plurality of trunks, means including a non-numerical switch for interconnecting` a calling telephone line with an idle trunl on the initiation of a call, a numerical switch for each trunk, means associated with the calling telephone line for sending series of impulses to control said numerical switches, and

means for releasing all the switches of the connection if a'certain series of impulses is sent prematurely, and for preventing the calling telephone line from being connected to a trunk circuit again until said calling telephone line terminates the call.

18. ln an automatic telephone system, a telephone line, an impulse sender associated with said telephone line, a line relay operable over said telephone line, a control relay, a plurality of trunks, means including nonnumerical and numerical switches tor eX- tcnding said telephone line when calling to one of said trunks, said impulse sender heing operable to directively cent-rol said numerical switches, releasing means for said switches governed by said control relay, `means for operating said control relay in response to a premature series of impulses, and a locking circuit for said control relay completed at said line relay.

In witness whereof, I hereunto subscribe my name this 9th day of March A. D. 1929.

INFRED T. POVELL.

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