US1506054A - Telephone system - Google Patents

Description

Aug. 26 1924..

H. M. FRIENDLY TELEPHONE SYSTEM 1921 5 Sheets-Sheet 2 Filed May 20.

IIII Aug. 26 1924.

H. M. FRIENDLY TELEPHONE SYSTEM Filed May 20. 1921 5 Sheets-Sheet 5 Aug. ze, 1924. 1,506,054

H. M. FRIENDLY TELEPHONE SYSTEM Filed May 20, 1921 5 Sheets-Sheet 4 InvEnTDF- WQLM Qms.

5 Sheets-Sheet 5 InvEnnr-f VI Il Filed May 20. 1921 HErbErI-Ml'lendl Patented Aug. 26, 1924.

UNITED STATES PATENT vOFFICE,

HERBERT M. FRIENDLY, F PORTLAND, QBEGON.

TELEPHONE SYSTEM Application filed May 20, 1921. Serial No.v 471,165.

matic and semi-automatic telephone systems.y The invention in the specific form chosen,v

for the illustration herein, contemplates a so- 'called two-wire common battery automatic telephone system as has been widely used, the present invention 'occasioning certain departures from equipments heretofore known so far as I am aware, in attaining the new objects, while retaining certain operative functions which are known. y e

The exampled form of the present invention chosen to illustrate it, contemplates its adaptation to a comprehensive automatic telephone exchange system. Ithas'the fol-4 lowlng and other objects a. 'To provide means-in an automatic selector (first or succeeding) whereby if controlling impulses are applied before the selector Y has completed its automatic functioning it y nectionto be established. In the event that c will be caused to lock and thereby render the circuits non-responsive to` succeedin impulses which mlght cause a misdlrecte con-v the call has been vitiated, so that a new at-y tempt can be made to eiect the connection.

i The means is also provided to record through level or group as busy.

` b. To rovide means in an automatic cona meter device the number of times the selector encounters all the trunks in Aa certain n ector w ereby when it encounters a called line and iindsit` busy it will,in addition to applying a busytonejt'o its' leading-in conductors audible to the callin subscriber, apply 'alspeclal tone briey audi le-along the line leadmg to the called subscriber and to vthe line telephonically related therewith. That is to say, where a telephonie conncc- -lines in a group) for service.

tion is established between a calling and a called subscriber and a new call to one of the said subscribers is attempted not only will the subscriber directing the new call receive a tone indicating the busy state of the line called, but the two parties in telephonic relation will vbe apprised that an attempt is being made by a third arty to reach one of the.

lines in the establis ed connection `between the subscribers. l

c. To provide means in an automatic group-selecting connector whereby if all the accessible to the connector has been found usy by the connector, abusy tone will beapplied to its leadin -in conductors, audible to the calling su scriber, and in addition, a brief, special tone will be applied, audible to lall the parties in teleph-onic relation over the lines of the oup. That is to say, should the group-se eating connector test a plurality ofgoutgoing lines (which may be termed trunk lines, possibly extending to a private branch exchange switchboard) and finds all of them busy, a

nected thereto are busy, a special tone will be applied audible to parties telephonically related to theseibusy' lines, indicati'n condition. A meter device is provi ed at ition has ensued.

the rivate branch exchange to integrate the num er of times this con -the That is to say, the meter .will indicate the total number of times all but one of the group of lines has been busy and, therefore,

leaving but one idle line open and available There are other objects of the present in'- Avention which will appear. I

Referring further to`paragrap I automatic telephone exchange operatlon where selector switches automatically function follopving the directed selection of a' trunk group and where, thereafter, a. number of busy trunks are encountered and passed over in seeking a disengaged trunk,

tta.

' digit series sent involves a plurality of imthe period of automatic selecting function ing is, in instances, prolonged beyond the period that the calling subscriber waits before initiating the transmission of the succeeding series of impulses constituting the next following. digit of the number being called. It will thus appear that under this condition the calling subscriber (or a mechanical calling means functioning automatically from a set-up condition) will have started a series of impulses before the selector has found and seized a leading-out trunk extending to a succeeding switch.- Under this condition the call will be vitiated. In instances wherein the premature pulses, the selector" will have had time to have found and seized an idle leadingout trunk before all of ythe `'impulses constituting the digit being sent by the calling subscriber will have transpired, and therefore one or more impulses of the series intended to operate a switch on the remote end of the properly seized line will be effective to the hunting selector. It will, under the last assumed condition, be manifest that a less number of impulses than intended will reach the selector on the remote end of the seized trunk. This will mean that a wrong trunk group, as indicated by a smaller number of directive impulses received, will be step-by-step selected by the said remote selectorand an idle trunk there* of connected with. A call from this point on, in the direction of a called subscriber may proceed normally responsive to theimpulses transmitted from a calling device in control of the calling subscriber, but it, of course, will be manifest that a wrong called subscriber will be reached. Conditions such as this are annoying to both parties of the established connection and tend to create a distrust in automatic switching means, and

perhaps prompt service complaints 'to be made entailing costs to the operating company in making investigations, the seat of trouble of which can-not be definitely placed. The function of the selector of the present invention will definitely forestall the possibility of establishing a wrong connection where such conditions are that of the calling subscriber dialing a succeeding digit series too quickly has ensued, and moreover, will apprise the calling subscriber that it will be fruitless to go ahead with the call until he has replaced his receiver and has re-initiated the call. It will appear that subscribers will soon accustom themselves to the fact that too rapid dialing will not always be effective, and will therefore, adjust the calling to the practical considerations of the equipment.

The second feature under paragraph va." that of metering the number of times selectors of a group encounter all trunks of a certain level or group busy, has its convenience in\ exchange systems by enabling an automatic observation to be madeto ascertainl if ample trunking facilities have been provided to certainv divisions of the exchange. The selectors of a group can lbe adjusted at will to record the number of times a busy condition has been found inv any particular trunk group or level, and therefore absolute records are made, regardless of the number of times selectors of a group may find a busy condition in other accessible trunk groups not concerned with the particular observation being conducted.

Referring further to paragraph b: In automatic exchange systems, wherein there is no operator to inform the parties to a telephonie conference that a third' subscriber is calling for one of the connected lines, a telephonie conversation acts to bar the subscribers premises against all callers regardless of the relative importance of the call under way to the call which is sought to function involved in the present invention,

therefore, affords an element of convenience and security to users in that they willknow immediately that there is someone seeking connection with one of the lines involved in the telephonie conference so the conversation ensuing ma be terminated as promptly as is expedlent to enable the party attempting the connection to re-initiate the call presently with a reasonable certainty of successfully completing it. pear that this function will serve not only a convenience-to. all subscribers concerned, but that it will forestall complaints being lodged to seek the assistance of the operating company in getting the subscribers holding a prolonged conversation, perhaps, to release their connected lines.

Referring further to paragraph c: In automatic telephone exchange operation wherein groups of trunk lines (or other lines) extend from a main branch exchange of an operating company to the premises of a subscriber, it has been found that the number of trunk lines subscribed for are often 'fewer than the traffic requirements warrant.

Under these conditions calling subscribers more or less often find themselves barred by lreason of all trunks testing busy because of the trunk being connected to a line, or

" by reason of the calling, following the initiation of a call on the trunk not having been completed simply. This entails a delay to calling parties and occupies exehan e It will thus apholding the trunks hearing the tone they will be prompted of the condition and terminate the conversations as quickly as possible so as to relieve the condition, or it will prompt 'the subscriber that he has not provided for, or subscribed for enough trunk lines to take care of the traiiic demands between the exchange system and his establishment.

Referring further to paragraph b: Subl scribers using a plurality of trunk lines, for

care of his traiiic requirements.

example, as contemplated in the foregoing paragraph c, wish to avoid the condition wherein the calling subscriber will find his establishment barred by reason of finding all trunks busy. The subscriber is interested in having his employes make as brief use of the lines as possible in conversation, and further, wants lines constantly available for outgoing traffic from his establishment. It will be manifest that the present. invention operates towards forestalling the saidl undesirable condition from ensuing. ,by reason ofthe fact that when all but one of the trunk lines are busy, regardless of any demand, a tone will be briefly applied, audible along each and every one of the connections over the engaged trunks which will apprise those using them, or any oneholdl ing one simply, of the condition and, therefore, prompt the release of the trunk as soon as possible. From the operating companys viewpoint, this functioning forestalls busy trunk conditions being encountered with the attendant delays, annoyances and undesirable conditions enumerated.' To the subscriber it will influence his employes to thebriefest consistent use of the trunk lines and conduce to maintaining an open way to and from his establishment at all times, and it will also serve to keep himl posted as tol whether he' has provided .for or subscribed for a sufiicient number of, trunks to take The present invention, in view of the foregoing general statements and the specific descriptions to follow, has wide adaptations, and moreover would in many instances involve a different application for the Same nominal use in :an exchange. It will also appear that other usesV more or less equivalent to those enumerated may be made of the present invention without departing vvfrom its scope, in view of the subjoined\`claims.

In accordance with this invention as ap' plied to the system chosen for itselucidation, each line terminates in a lineswitch\ (also termed a pre-selector herein after), and

the latter have common access to a plurality of first selectors. The first Selectors have common access to a plurality of groups of connectors, which latter groups vhave common access to certain groups ofvsubscrib-A ers lines. Other connector oups have access to certain groups of su scribers lines.

In the accompanying drawings Fig. 1 shows a subscribers automatic telephone T leading to a pre-selector PS, and the latter, in common with other pre-selectors not shown, are in selective relation to 'a selector A of the present invention.

Fig. 2'shows a connector B of the present invention, together with an accessible subscribers line leading to a telephone T2. The `telephone T2 is similar to telephone T.

Fig. 3 shows a calling telephone Ta which is similar to telephone T. The telephone T"s leads to a pre-selector PS3 which is similar to pre-selector PS.l The pre-selector PS3, in common with other pre-selectors not shown, have common access to4 first selector FS3 which is similar to selector A. First selector F S3, in common with other first selectors not s hown, have common access t connector GUNS. Y Connector CONS has common access with connector B, and other connectors not shown, with telephone T2- Telephone T2 has' its leadingfout lines terminating in a pre-selector similar to PS indicated simply by the cut-off relay C, it

not being thought necessary to show all the pre-selectors in detail in the present descriptions.

Fig. 4 shows a group-selecting connector C, well known in the art, having access to a group of trunks disposed in the manner contemplated in the present invention. Also, a pre-.selector PS* connected with oneof the trunks of the group. It -is similar to PS.

Fig 5 shows certain novel equipments at the private branch exchange endsl of the trunks, shown as leading out from the bank contact group shown in Fig. 4. Telephone T5 thereof is similar to T.

Fig. 6 shows a schematic detail of the arrangement of bank and co-operating wipers shown in H of Fig. 5.

Fig. 7 shows thel arrangement of the vari- .ous indicated figures in one organization of the equipments in'the present invention, which4 will be detailed hereinafter.

Fig. 8 shows an arrangement of the varil ous indicated figures in a second organization of-equipmentsin the present invention, which will be detailed hereinafter.

Fig. 9 shows a cord-pair for use with the springjacks shown in Fig. 5.

Referring to certain of the various;

In Fig. 1, T is the usual series type of automatic telephone having a calling device 121 of the general class as shown in British patent to Dicker, No. 29,654 of 1910. The

pre-selector PS is of the general class as shown in U. S. patent to Lamb, No. 1,193,- 160 granted A'u 1st 1, 1916.,v The first selector A is of t e general class shown in U. S. patent to Keith'& Erickson, No. 815,- 321 granted March 18, 1906, of course, modi# fied 1n mechanicaland circuit details to opdependent sources throughout, wherever erate on the well. known so-lcalled two-wire principle and in accordance with the present invention.

In Fig. 2, B is a connector of the general class as shown in U. S. patent to Keith & Erickson, No. 815,176 granted March 13, 1906, ofcourse, modified in mechanical and circuit details to operate on the well known yso-called two-Wire principle and in accordance with the present invention.

In Fig. 4, C is of the general class as is connector B in Fig. 2, and is known in the art as a group-selecting connector. The novelty relating to it as regards the present i invention is in the bank connections and tails of which may be assumed as similar to that `shown in the said cited patent to Lamb, or the pre-selector PS, bearing in mind that it is preferred, though not necessary, for the stepping or advancement of the wipers of element H to be responsive to the de-actuation of motor-magnet M rather4 than directly upon its actuation.

To simplify the drawings and descriptions, battery and ground are shown as ina plied, but it is to be understood that tlie system is of the common batterytype. In the descriptions, when a circuit is traced to a winding, the opposite terminal of which is shown applied to grounded battery or to ground, the described circuit is to be considered as traced to ground through 'the winding to battery, or direct to ground as indicated;

The` performance of the equipments will be detailed under different assumed operative conditions, bearing in mind that the equipment elements may be variously organized in the assembly of a system. n Referring to the accompanying 4draw- 1ngs:- f

Assume a call from telephone T to telephone T2, 1s 211. The figures will be assembled as shown in Fig. 7. Upon the calling subscriber at telephone T initiating the call b v removinv` the receiver-from the switchhoov of telephone T the pre-selector PS will function in the well known manner and extend the` connection to the first selector A, which latter is assumed to be the first seizable first selector of a group accessible to the pre-selector PS. A circuitexists after the seizure of A from grounded battery, upper winding -of relay 101, armature 102, conducylower winding of relay 101, eleventh-ro- .124 will actuate consequent upon the first 'of vertical magnet 125 set forth, a circuit the telephone number of which tor 103, wiper 104, of pre-selector PS, conductor 105, telephone T, conductor v106,l wiper 107, conductor 108, armature 109,

tary7 cam-spring 110 to grounded kspring 7 112, relay 101 actuating. Anoperative circuit can now betraced from the winding of slow-releasin' relay 114 to grounded armature 115. A so, grounded contact 116 will apply ground to conductor 117 and through wiper 118 to thewinding of cut-olf relay 119, thus maintaining the pre-selector, and guarding the line leading to telephone T against intrusion, all in the well known manner.

Upon the calling subscriber operating the calling device 121 in accordance with the first digit 2 of the called number, the energizing circuit of relay 101 heretofore traced will be opened two times and relay` 101 will therefore, de-actuate and re-'actuate two times resultant thereto. Upon each retraction ofarmature 1,15 an operative circuit can be tracedfrom'said armature, armature 122, armature 123, winding of slowreleasing rela 124, upper armature of the right-hand re ay to the winding of the vertical magnet 125. The slow-releasing relay current impulse being established, and it is sustained over the lapsel between the impulses and for its period after the final impulse. The vertical ma et will operate two times vand raise the s aft carrying wipers 127, 128 and 129 two vertical steps into alignment with Vthe second level of bank contacts. At .the time relay 124 first attracted its armature 131, bearing in mind the operation is established from grounded battery through winding of shunted relay 132, olf-normal spring 133, armature 131, conductor 117 to grounded contact 116, relay 132 actuating.

At the expiration of the period of relay 124, whereu on its armature 131 retracts, a circuit'can betraced from the winding of the rotary magnet 134, armature 135, armature 131, conductor4 .117 to grounded contact.- 116, the rotary magnet actuating and advancing the wipers 127, 128 an 1.29. one rotary position into engagement with the 11 .first set of bank contacts 136, 137 and 138 respectively. Incident to the first rotary movement rotary off-normal springs RON will engage, however to no operative purpose at this juncture, but to prepare a c1rcu1t the purpose of which will appear presently.

It'will be assumed that the first set of bank contacts are those of a busy trunk and, therefore, that bank contact 136 will constitute ground potential. Them upon the retraction 4of the rotary magnet armature 139, a circuit is established from grounded battery through the winding of relay 132, spring 133, armature 139, conductor 140, armature 141, conductor 142, wiper`127 to assente tute ground potential the same operativev function will transpire las described and cause the Wipers to be advanced a second rotary step, this cycle of operations continuing until a bank contact not constituting ground potential is engaged by Wiper 136.

It will now be assumed that this nongrounded contact finally engaged by Wiper 127 is the `first contact 136 of the level. The operation of the selector upon encountering said 136 as ungrounded, about' to be described Will be the same as had it encountered one or more grounded'contacts and then encountered a non-grounded one. Upon Wiper 127 engaging ungrounded contact 136-there will be no energizing circuit reestablished for relay 132. The resistance and adjustment of relay 132 i's such that it will not actuate when its winding is included in series relation with the Winding of relay 143. 'Bearing in mind the nongrounded condition' of Wiper 127, a circuit can now be tracedv from grounded battery, winding of relay 132, spring 133, armature 139, conductor 140, Winding of relay 143, spring 144, conductor 117 to grounded contact 116, relay 143 actuating and relay 132 remaining un-actuated. A. circuit can now be traced from grounded contact 116, conductor 117, armature 141, conductor 142,

Wiper 127 to bank contact 136, applying ground potential to the said 136, thereby guarding its trunk a ainst intrusion by other selectors J accessi le to it through a multipled bank contact sets. The foregoing general operation of selector A is Well known in general principle, but it will appear there are other features introduced into this selector.

It will now be assumed that while the selector Wi ers 127, 128 and 129 are being RON to the winding of relay rotated, see ing an idle trunk, thatthe callingl subscriber operates the callin device 121 1n accordance with the 4second dlgit 1.

Bearing in mind -that^ relay 143 is in nor-` mal position durinu the said rotation, it

caused to'de-actuate and re-actuate one time. U on its de-actuation acircuit will be esta lished from grounded armature 115, armature 122, rotary onormal springs, 145, causing it to actuate. A locking clrcuit will be established for the said 145 through its armature 146, conductor 117, to ounded contact 116. A closed path will e established consequent to the operation of relay 145 from grounded armature 147 to conductor 142,l thus applying a false busy condition etective as if Wiper 127 is encountering grounded bank contacts and it will, therefore, continue to rotate until its carrying shaft is blocked by encountering the eleventh-rotary cam-spring CS. Under this condition ground potential is maintained on both Winding terminals of relay 143 so vit is inoperative to its armatures, and relay 101 and its dependent relay 114 will continue to remain in control of the calling subscriber at telephone T.,V A circuit can now be traced from grounded s ecial tone source 150, armature 151, con uctor 152, spring 110, lower Winding of relay 101, armature 109, through the described path including telephone T, armature 102, upper winding of relay 101 to battery. The tone Will thus be audible to the calling subscriber at T and it Will indicate to him the the Wipers 127, 128 and 129 having rotated oit the last operative set of banky contacts, of which there would usually be ten, and would, therefore, have no operative relation `with a successive switch `which might be affected by manipulations 'of the calling device 121 Were it inadvertentl reason of the calling subscriber not listening for the tone. However, no operative effect will have occurred by reason of the transmitting of impulses after relay 145 actuates. f

Upon the callingsubscriber replacing the receiver, opening the described energlzmg circuit to relay 101, it is caused to de-actuate followed by its vdependent relay 114 and the restoration of the pre-selector PS in sequence. An operative circuit can now be traced from grounded armature 115, arma- 'turev 122, armature 123, onormal spring 154 to the Winding of release magnet 155 causing it to actuate and restore the selector A.

Assume that 4the set of springs SCS are adjusted to be engaged by a cam on the shaft when it attains the eleventh-rota position when the shaft is functioning wit the wi ers inl registry with the third bank level, fin' example, the selector having been operated accordingly. This condition would ensue 'if the trunks leading from this level continued by wereall found busy. 1t is to be understood y will be manifest t at relay 101 will ben'n this connection that the cam designed to gard 'to the cam-springs corresponding to 0f course, all selectors in a le at will so that the selector Vcan be read-v yconductor 152, spring 110` (bearing ldrum 161 are of a well known loperative bank contact co-operative thereto SCS on the various selectors respectively. Under the conditions of the cam-spring SCS operating, a circuit will be closed from grounded tone source 156, winding of meter drive-magnet 157, common conductor 158, spring 159, conductor 160, armature 151, in mind that eleventh-rotary cam-springs (JS are operated under all eleventh-rotary conditions regardless of levels), lower windin of relay 101 over the described path inclu ing telephone T, upper winding of relay 101, to grounded battery, causing the said 157 to operate and step the meter drum 161 theaugular distance representing one unit. The tone emanating from source 156 will manifestly be audible to the calling subscriber. The meter magnet 157 and its co-operating form of electro-magnetic meter device, in which a plurality of drums are in correlation, each drum .representing a numerical order, progressively. The meter electro-magnetic core is slowereleasing to preventJ it from deactuating and re-actuating by a short lapse of current, such as mi 'ht be introduced by calling device 121, an thereby registering falsely.

Conductor 158 is a common conductor leading to the meter magnet 157, which is also common. The said 158 is common to a group of selectors having access to the sama. group ofy trunks on the third level, So that one meter serves a plurality of selectors. 1t

will be manifest, therefore, that the number of times the selectors of a group have rotated ofi the operative bank contacts into the eleventh-rotary osition on the lthird level will be indicate on the meter drums.

Should the wiper 127 rotate oit the ,last

in normal operation on a level not elective to the spring set SCS, the set of springs CS Vwould be the only' set operated; Under this condition a circuit can be traced from grounded tone source 156, cam spring 163, spring 159, conductor 160, armature 151, conductor 152, spring 110., lower winding of relay 101 over the traced path includingthe telephone T and the upper winding of relay 101 td grounded battery, the tone from tone source 156 being audible to the calling subscriber at T, and the ground through the said tone source 156 replaces the ground on spring 112 disengaged when spring 110 is engaged so that relay 101 is maintained until the subscriber at telephone T replaces the receiver.

The operation of Fig. 1 being now clear,l the description will be continued from the instant that relay 143 actuated consequent to wiper 127 encountering ungrounded bank` contact 136. A circuit can now be traced from grounded battery through the upper winding of relay 201, spring 202, conductor 203, bank contact 137, wiper 128, conductor 166-armature 102 over the described path including telephone T to armature 109, conand to bank Contact 136 before the period off vrelay 114 has expired following the actuation of relay 143 and, therefore, no lapse of ground occurs to conductor 142, so that relay 143 and relay 119 will be maintained from connector B.

Upon the calling subscriber at telephone T operating the calling device 121 in accordance with the second digit 1 relay 201 will be caused to de-actuate and reactuate one time, responsive thereto. A circuit will be established upon the re-t-raction of armature 208 from it through armature 212,l armature 213, series winding of slow-releasing relay 214, Winding of vertical magnet 215, sideswitch wiper 216 in irst position to grounded battery. Relay 214 will attract its grounded armature217 and thepvertical magnet "215 will step its shaft carrying wipers 220, 221 and 222 one vertical step, aligning with the rst level of bank contacts. Upon the attraction of armature 217 a circuit is closed therefrom to the winding ot' private magnet 223, causing it to actuate and incidentally attract its armature 224 l against its co-operating 'grounded contact 225. The mechanical detalls relating to the private magnet 223 are well known in the art so that it is sutlicient to say here that upon the expiration of theperiod of relay t '214 following the re-attractiony of relay 201 the private magnet 223 will deactuate and permit the sideswitch wiperl 216 and its compamon wiper ond position. y

Upon the calling subscriber at telephone T operating the calling device .121 in accordance wlth the thirddigit 1, relay 201 will de-actuate and re-actuate one time in 218 to advance into their sec-l m accordance therewith as before, this time, f

however, grounded armaturev208 applies its ground through armature v212, armature 213, winding of relay 214, armature 226,'winding of rotary magnet 227 sideswitch wiper 216l in second position yto grounded battery.v

rea

be (le-energized to permit the sideswitch 5 pre-selector -connector CON@N for example.

wiper 216 and its companion wiper 218 to advance into their third position, however, this advancingof wipers 216 and 217 will depend upon whether wiper 220 finds ground potential von bank contact .230, as

will appear presently.

Assuming that bank contact 230 does not constitute ground potential, upon the private magnet de-energizing and the said wipers 216 and 218 advancing to their third position, a circuit can be traced from ground, wiper 218, winding of relay 235, wiper 216 to grounded battery, relay 235 actuating. Also, from ground, wiper 218, wiper 220 to bank contact 230, serving to energize the cut-oil' relay and guard the line leading to telephone T2 against intrusion through other connectors accessible to it, as A circuit can now be traced from grounded interrupted ringing current source 236, armature 237, armature 238, wiper 222, bank contact 232, line conductor 239, condenser 240, signal device 241 at telephone'l`2, line conductor 242, bank contact 231, wiper 221, armature 243, armature 245, inside winding of relay 246 to grounded battery. The relay 246 is so designed that it will be inoperative to the signaling current emanating from source 236 and traversing the signal device 241, due to a condenser 240 being included therewith, but is operative to direct currents such as would., traverse the said insidr` relay 246 were it energized over a conductiveJ path rather than the inductive path involved in condenser 240.

Upon vthe called subscriber at telephone T2 removing thereceiver and closing the conductive path therethrough, the winding of relay 246 will operatively energize it so that. its armatures will be attracted. A- circuit can now be traced from grounded off-normal spring 248, armature 249, through the lower winding of relay 250, conductor 251, armature 237, armature 238, wiper222, bank contact 232, line conductor 239, received atl-telephone T2, line conductor 242, bank @ontact 231, wiper 221, armature 243, armature 245, conductor 252, upper winding ofrelay 250 to grounded battery, relay 250 actuating?. A l c ing circuit to maintain armatures of relay- 246' attracted will-be completed from grounded battery, through outslde winding of relay 246, armature 249, to grounded spring 248, insuring that the armatures of relay normal spring 248 is freed. the off-normal' springs being operated on the first off-normal movement of the shaft. It is manifest that the attraction of armatures 2 53 and 254` .will serve to transpose fthe relation of the lwinding of,

246 will remain attracted until lofftelephone 'I'a operating the from the cal ing subscriber'at telephone T in the direction of the called subscriber over the traced circuit to conductors 203 and 204. and through condenser 256 to conductor 252 and over the traced circuit Yincluding the receiver of called telephone T2, conductor 251, condenser 257 to conductor 204, transmission current being supplied to the calling telephone T from the winding of relay 201 and to the called telephone T2 from the windings of relay 250. The disposition of the said relays 201and 250 is not new in connectors, as generally applied. The restoration of connector B occurs upon the last party to the conversation replacing his receiver, as yis well known in this general type of connector, and forthat reason will not be detailed.

The'pr'esent invention as it is applied in connector B involves the following: The special grounded tone source 260, armature 261 and its co-operatin contact 262 on release magnet 263, conuctor 264, leading from said armature l261, armature 265 on relay 207, conductor 266 leading from the resting contact co-operating with armature 265 to armature 267 on the busy relay 268, conductor 269 leading from the working contact of said armature 267 to telephonie con- 'ductor 270 leading to wiper 222. It will -thus appear that upon the attraction of armature 267` the special tone -will be .applied from ground to one limb of the telephonie i .conductor leading to wiper 222. The functioning of selector B with f particular reference to the present inveny ltion will be,taken up more fully presently.

It will be assumed'that a calling subscriber at `telephone T3 initiates a call by removing the receiver from the switchhook 301, whereupon pre-selector PS3 will automatically function in the manner well known and 'attain connection with the first available first-selector FSP in the manner well known. Assumel further that the calling subscriber at telephone Ta is calling subscriber at telephone T2 the telephone number of which, as was stated hereinbefore, is

211, accessible to connector B and con 3 nector CON and lother connectors. It, of course, a different group to thetelephone Ts and, therefore, the respective pre-selectors of' is manifest that the telephone T is inthe lines leading to the said telephones T l, and T8 are in access to different groups of first selectors, selector A being in one group and selector `FSs being-.in another group. Telephone T3 now being in control of selector FS, upon the calling subscriber at calling device 302 in accordance with the rst digit 2 of the desired telephone line, the wlpers of first selector FSS will be caused to be raised to the calling subscriber at telephone T8 calling the last two 4digits 1 1 of the desired telephone line the wipers 315, 316 and 317 will e caused to be raised one vertical step into alignment with the first bank level of the connectorl and thenl directedl rotated-in into engagement and seizure o the first set of bank contacts 318, 319 and 320 respectivelythe connector GONE, projecting ringing current and otherwise functioning as fully set lforth in the description relative to connector B in effecting connection to telephone T2, and the cut-ofi relay 271 will be energized dueto the sideswitch wiper 321 being in its third position, in the manner well known and as detailed with respect-to connector B. The subscriber at telephone T2 will respond as before.

' Under the condition ensuing, that of a telephonie circuit existing between calling telephone T3 and called telephone T2, the telephone T, pre-selector PS, selector A and connector B are in their normal positions and bank contact 230 constitutes ound po-l tential and thus serves to guard-[the telephonie circuit established between telephone T3 and telephone T2 against intrusion by connector B or other connectors that may have` access normally to the line leading to telephone T2. p

It will now be assumed that the calling i Subscriber at telephone T has established a telephonie connection in the direction of telephone T2 as has been heretofore fully described and that when lwiper 220 engages bank contact'230, it now encounters thebusy ground potential assumed due to the established connection between telephone T3 and telephone T2. lBearing in mind v the described functioning of connector B up until the wiper 220- engaged bank contact 230 wherein sideswitch wipers 216 and 218 were in their second posltlon,

it will be manifest that the ground otential now found on bank contact 230 wi at this instant be applied over wiper 220, sideswitch wiper 218 in second position, conductor 272,

spring 273, winding of relay 268, spring 2?,

` winding of private magnet 223to ground battery, thus maintaining the private magnet 223 ener 'zed after the retraction of armature 217 t e period of relay 214: after the impulse to the rotary. magnet 227 was imparted by way of advancing wiper" 220 into,

engagement with bank contact 230. Bearing in mind that as long as the private magnet 223 remains energized the sideswitch wipers 216 and 218 are not .permitted to advance into their third position, it will ape'ar that the described energizing circuit or relay 235 will notl befestablished and, therefore, it will not attracty its armatures 243 and 238. y way of completing the telephonic circui from the calling telephone T to the wipers 221 and 222 which are in electrical engagement with bank contacts 231 and 232 respectively.

At the time the winding of relay 268 became energized it attracted its armatures andestablished a locking circuit` from grounded battery, winding of the rivate 268, armature 275, to grounded spring 248,

ymagnet 223, spring 274, winding o relay thus maintaining private magnet 223 and the relay 268 locked actuated. This circuit will not be opened until the shaft of the connector restores to normal.

Under the locked condition last described, a circuit can be traced from grounded busy tone source 276, armature 277, ytelephonie conductor 251, condenser 257, conductor 204; over the described path, including calling telephone T, to conductor 203, condenser 256upper winding of relay 250 to grounded. battery, the tone being audible to the calling subscriber at telephone Tand `indicates to him that the connector B has encountered a busy line, that-is, the line leading to telephone T is busy. In view of the locked condition of the private magnet and relay 268, no selective operation of connector B can follow. However, the calling subscriber at telephone T can replace his receiver and open the hereinbefore described energizing circuit for rela 201 -.causing 1t to de-actuate followed by its dependent relay 207 in sequence. Bearing in mind that relay 250 has not yetactuated, a circuit can nowpbe traced from grounded armature 209, p

off-normal spring 278, armature 279 to the winding of the release magnet 263, causing it to actuate and restore Athe shaft of connector B, carrying vthe wipers 220, 221 and 222 to normal.

The armature 265 of relay 207 is adjusted to make its co-operating-resting contact upon retractionl before the armature 209 makes its'co-operating resting contact upon- ,retraction Also, the release magnet 263, which carries an electrical armature 261, and a co-operating resting contact 262, is given electrical and mechanical properties which produce a retarded eect upon the armature261. That is to say, the armature 261 will vnot disengage its resting contact l262, which may follow the armature over a portion of its movement, until after an ap' preciable interval elapses after the energithe electro-magnet, or `by introducing anecdota zation of the said release magnet 263. The object of this characteristic will appear. It is not new t0 retard the operation of magnets for an appreciable period after the energization by the so-called slugging of 'dashpot devices that require a prolonged torque to overcome.

In light 0f the foregoing it will appear that for an appreciable time following the establishment of the described rcircuit from grounded armature 209 to grounded battery through the winding of the release magnet 263, a circuit can be traced from grounded special tone source 260, resting contact 262, armature 261, conductor 264, armature 265, conductor 266, armatur 267,

.conductor 269, conductor 270,4 wiper 22,

bank contact 232 to conductor 239.` From conductor 239, which in View ofthe established co-nnection between telephone T3 and telephone T2, is common to the two said telephones, and bearing in mind the relationship of the front and back bridge relays'in connectors CON?, it vwill be manifest that the tone traced to conductor 239 will traverse the receivers of the said telephone T3 `and T? and reach ground in connector GUN3 through the lower winding ofthe 'back1 bridge relay and through the telephonic condenser corresponding to 257 inl .connector B and upper winding of the front bridge relay corresponding to 201 in connector B to grounded battery. The said -tone applied audible to the calling subscriber at telephone T3 and the called subscriber at telephone T2 will endure until armature 261 attracts from its resting contact 262. It will thus be clear that upon the calling party at telephone T rep-lacing his receiver to restore the connection fol-- lowing his receiving a bu signal when attempting to complete a ca ing the condition is applied for an interval audible to the subscriber on the line called and also audible t0 the subscriber on the line in telephonie relation with it through the exchange apparatus. This apprises them that some one is attempting to reach one of their lines so that they may terminate the service and render the lines seizable as soon as expedient.

yularl reference to t In the foregoingl description, with particarmature 280, and to enable conductor 266 to be removed from the contact upon which armature 265 rests and attach 1t sponsive a circuit traced throug l, a tone indicate special tone source 260,v

connection as has been set forth), for ay period equal to the period of relay 207. That is to say, that the prompting tone applied to conductor 270 will now traverse the path from grounded tone source 260, resting contact 262, armature 261, conductor 264, armature 280, resting contact 281, conductor 266, armature 267, conductor 269, to said conductor 270. It will be manifest that this circuit will be established for the period or rela 207 before it de-actllates and energizes t e release magnet 263, so that the prompting tone 4will have a duration of aplication to conductor 270 correspondingly onger than described where the prompting tone path included armature 265 in lieu of Iarmature 280 and its resting contact 281.

lIt will be apparent under the latter arrangement that should the calling subscriber at telephone T operate his calling device 121 and thereby cause relay 201 to operate rethereto (however to no operative purpose net 215 or the rotaryV magnet 227 due to the sideswitch wiper 216 being in the second position 'and armature 226 on relay 268 being attracted), the established prompting tone h armature 280 and resting contact 281 will become established lupon each de-actuation of relay 201, and, therefore, a series of prompting tone4 applications will be 'made to conductor 270, audible through the telephones T3 and T2 corresponding to the digit called by the calling subscriber at telephone T. Of course,\.-if no manipula- Y tion of the dial 121 is made and the calling and moreover, it may be desirable to change the method of operation in this detail from time to time.

It is also preferred to provide an extra set of normally disengaged off- normal springs 286 and 287 lto enable conductor 264 toybe disconnected from armature 261 and applied to spring 286 and to disconnect the conductor leading to resting contact 262 and apply it to spring 287. This change would be made by the attendant vif for any traiie or other reason it were desired to prolong the application of the prompting tone to conductor 27 0- from the .time armature 265 retracts until dependent upon the vertical magy 4 the connector B has its shaft restored to normal, and not have the tone disconnected from conductor 270 upon the attraction of armature 261 which is an appreciable time before the shaft has started to restore. Of course, where thes rings 286 and 287 are operative and used t e armature 261 and its `co-operating resting contact 2621 have no operative Under t e condition wherein springs 286v urpose.

, and 287 are operatively employed, upon the retractionf of armature 2654 (or 280, depending upon which amature is operatively used) the special tone will be applied from be borne in mind that the promptingr tone. vwill not be audible along conductor239 after the wiper 222 disenoages from bank contact 232 consequent to the operation of the release magnet 263 in effecting the restoration, and moreover, the tone standing on wiper 222 while restoring will be momentarily applied to cpo-operating bank contacts corresponding to bank Contact 232 which may be assed over in releasing, in case the wiper as been rotated in past the first contact. The duration of this latter falsely applied prompting tone will be so brief as to not ordinarily be discernable.

Referring now to Fig. 8 for the assembly of figures in the organization of equipments illustrating other features of the present invention as a plied in the exampled tele- -phione system i lustrative of it. It will now i,

phone T manipulatin the calling device 121 e assumed that the calling subscriber at telephone T desires to effect a telephonie connection to telephone T", located in a private exchange on the lpremises of a 'subscriber. It-will also be assumed that there are four trunk lines accessible to a groupselecting connector C (of vwell known type as has been stated at the outset) on its rst bank level, and, therefore, calling the same nominalte'lephone number will insure that the rst accessible trunk of the group of four will be automatically selected and seized. Terminating each one of the said four trunks at the 'private exchange end is a springjack 501 and also a calling signal' dev1ce,-as will appear presently. Terminating each one of the "local lines, as` for eX- ainple the line leading to the 'said telephone i T, is, a springjack 502 and a pre-selector PSW.I The loperation on the part of the calling subscriber at telephone T1, is therefore connection to the to establish a primar l detailed presently,

springjack 501 as shall gain the response of theI operator at the private branch exchange through the said 501, and then be connected by the operator through the agency. of a connecting or switching cord-pair, as shownl in Fig. 9, from the springgack 501 to springjack 502.

lThe operator will signal the called subscriber at telephone T5 and the lconnection be manipulated in accordance with thefirstl digit 4 of the called number, whereupon, the selector A will function in the manner as hereinbefore detailed, however, this time the wipers thereof 127, 128 and 129 rotating-in and hunting and seizing a first disengaged trunk onthe fourth bank level, which will be assumed to be the trunk leading from the first set of bank contacts 175, 176 and 177 leading over conductors 178, 179 and 180 respectively to connector'C.

A circuit can now be traced from grounded battery 'upper -winding of relay 401, spring 402, conductor 179, bank contact 176, wiper 128 over the hereinbeforev described path including the telephone T, wiper 129,

ank contact 177, conductor 180, spring 403, lower winding of relay 401 to ground, relay 401 actuating. An operative circuit can now be traced fromV the `winding of slowreleasing rela 405 to grounded armature 406. Upon t e calling subscriber at telee caused to e raised one vertical step into.

alignment with the'rst level of bank contacts shown in the drawing. Uponthe calling subscriber at telephone T'manipulating the calling device 121 in accordance with the third (and final digit 1 ofthe telephone number of t e,called trunk oup, the said wipers 407 to 410 (inclusive will be caused to be controllably step ed'one rotary position into engagement with the first set ofbank contacts 412 to 415 respectively. The connector C being well known in the art, `will not require detailed description here. Suffice it to say, however, that should the wiper 408 have encountered ground on bank contact 413 it would have automatically rotated or advanced a step, thesaid wipers 407 to 410 then engaging the bank ycontacts 416 to 419, and should the wiper on bank contact 417, the said wipers 407 to 410 would be caused to b'e automatically rotatedor advanced a step to the next rotary position. This automatic functioning will continue until the wiper 408 engages a bank contact that does not constitute ground potential, or until the Wiper 407 engages a bank contact constituting ground potential.-

In this connection it may be stat-ed that it is wellknown in the art to have the bank contacts engageable by wiper 407 of all but the last trunk of a group free of operative attachments and, therefore, not subject to constituting ground potential, however, to have the last bank contact of a group engageable by wiper 407 tied to the last bank contact of the group engageable by wiper 408. And, therefore, if the lastA bank contact of the firoup which is engageable by the wiper 408 should constitute ground potential the last bank contact of the group engageable by wiper 407 will constitute ground potential. It is well known that if wiper 407 encounters ground potential theautomatic rotation of the connector C will be stopped thereby, and a tone indicative that the entire group of trunks'(of which there may be one only or more), are bus From this it follows that thelast pair o contacts of each group have the companion contacts engageable by companion wipers 407 and 408 electrically itied. yIn practice a single level may constitute a group or it may be single lines extending therefrom. In the latter case, the bank contacts thereof engageable by companion wipers 407 and 408 will be electrically tied so that in the event that the bank contact engageable by wiper 408 constitutes ground potential by reason of its being busy, the companion bank contact engageable by Wiper 407 will also constitute ground potent1al, causing the connector testing to be set in its busy-testing condition upon' its wiper 407 resting on'the grounded bank contact at the. instant of test, and, therefore, will` not rotate into an irrelevant group.

By reference to Fig. 4,- it will be noted that the last companion contacts 421 and 422 of the group 'of four trunks engageable by companion wipers 407 and 408 are tied together electrically, the circuit including the winding of slow-releasing relay 425.

Heretofore, so far as I am aware, the tying of these contacts has been -direct and have not included an electro-magnetic energizing circuit of an operative device such as relay 425. However, the resistance of the winding of said relay 425 does not offer enough obstruction to operatively affect the normal functioning of connector C, should somevof the groups of trunks accessible to-said connector C have the last companion contacts bank contacts 413, 41 426 and 422 will function as follows, bearing in mind that because of bank Contact 422 constituting ground potential bank contact 421 will also constitute ground potential. Bearing in mind also, that sideswitch wipers 427 and 428 are in their second position during the time wipers 407 to 410 are rotating in the operation of hunting for anidle trunk of a group. When wiper 407 encounters ground potential on bank contact 421 (being the last trunk position of the group) this ground potential will be conducted over conductor 430, spring 431, armature 432, winding of relay 433, sideswitch Wiper 427 to grounded battery, relay 433 actuating. A locking circuit for relay 433 can now be traced from off-normal grounded spring 437, conductor 438, armature 439, spring 431, armature 432, winding of relay 433, sideswitch wiper 427. to ygrounded battery. The armature '444 being attracted, the rotary magnet 445 is incapacitated.` During the time relay 433 is energized a circuit can be traced from tone source 446, conductor 447, armature 448, telephonic conductor 449, condenser 450, conductor 180 over the described path including telephone T, conductor 179, condenser 451, upper winding of relay 452 to grounded battery, the said tone being audible to the calling subscriber at telephone functioning of connector C can take place until after it is restored to normal by his replacing the receiver as setA forth.

The round potential found -by wiper 407 on ank contact 421 ensued, perhaps, by reason of some other accessible connector having its wiper corresponding to 408 in seized relation to the bank contact co-operative thereto corresponding to bank contact 422 and which is in multiple relation to 422, it being understood that in practice there would ordinarily be a .plurality of connectors similar to C in a group in access to groups of multiple bank contacts in ycorresponding relation to the' said connectors so that a call can vbe completed toa trunk group in -a similar manner regardless of whatconnector is functioning.

In this connection it may be stated when 'a connector rotates on to a set of bank contacts of an idle trunk, which in this instance ywill be assumed the fourth or last trunk of the group, wiper 407 and also wiper 408 not finding ground potential or either bank contact 421 or 422, the private magnet 455 will be de-energized, permitting t the sideswitch wipers 427 and 428 to move into their third position, whereupon conductor 456 leading to wiper 408 will constitute ground potential (received through sidev switch wiper 428) and applies it to bank contact 422 and its multip es, and of course, to the companion contacts, as 421, thereto. It is now manifest that the ound potential derived through wiper 40% and conductor 430 which caused relay 433 to actuate was derived through the winding ofrelay 425` (which is comnggn to one group),\cvaus ring vit to attract its armatures. Also, ldue to the attraction of armature 439 on relay .433 the traced circuit, including conductor 430,- was opened forthwith after the said operative establishment of a circuit including it, consequently deenergizing relay 425. However, due to the slow-releasing characteristic of rela 425, it will remain actuated for a period a ter its de-energization. During the time relay -425 has its armatures attracted, grounded tone source 460 is applied through the -said latter armatures 'overconductors 461, 462, 463 and 464 to bank contacts 415, 419, 465 and 466 respectively. 'It is manifest that `the said bank contacts 415, 419, 465 and 466 are in electrical con, tinuity with the lower limb of the trunks `one to four respectively, and bearing in mind that since they are in a bus condition either by being in 'seized relation with a connector similar to C, or is in a seized relation through a pre-selector as PS4. The conductors 467,468 and 469 of PS4 lead to a first selector A in whichvthe said lat-.. tcr conductors correspond toconductors 117,

spending to 101 of selector A of first selector similar to A (if thc selector has .not seized), the winding of a relay corresponding to relay 201, of a connector similar to B, or through the winding of a battery supply relay such as 960 in a cordpair similar to Fig. 9; all dependingl upon whether each trunk concerned is busy due to the fact lan outgoing call to the private branch exchange through a connector as C has been` made, or whether the busy condition is due to a call having been initiated at the private branch exchange as will be detailed presently and, therefore, involves a pre-selector as PS4, and possibly a cooperating rst selector as A and avconnector successive to the said selector. v

It is to beremembered in this connection that it is contemplated that each trunk of the four in a group shown as leading to theright margin in Fig. 4 is equipped for two-way service, as is the first trunk, and that, therefore, each trunk has a preselector connected thereto similar to PS. The first trunk only of the group is shown connected to a pre-selector, being pre-selector PS, in order not to unduly complicate thedrawings. The group of first selectors companion to A accessible to the pre-selectors PS4 and PS has likewise been omitted froml the drawings to avoid unduly complicating the drawings. But in view of the statement that conductors 467, 468 and 469 Aof pre-selector PS1 correspond to conductors 117, 103 and 108, which latter conductorsare accessible to wipers 118, 104 and 107 respectively, it is -not thought necessary to detail these selectors companion to A in order 'to convey a comprehensive understanding of the system contemplatedunder 'the present invention, and, moreover, it is old in the art to complete connections from a pre-selector through successive switches in the direction of a called subscriber in a telephone system.

It is now manifest, in view of the foregoing, that if a connector encounters a called trunk group in which all the trunks thereof are busy, either by reason of the service thereon .being initiated from a calling telephone in the main exchange, or by reason of the service thereon be'ng initiated from the private bitanch exchaiige, not only will the calling subscriber in the main exchange f attempting to effect a connection to the pri'- vate branch exchange receive the customary busy tone as heretofore known in the art, but the function contemplated under the present invention will be brought into requisition wherein a brief special tone will be applied over the telephonie conductors of all the busy trunks of the group, audible to subscribers in telephonie relation thereto, regardless of which end of the trunk is the initiating end. This tone will indicate to all auditors that a call has been attempted direeted towards one of the group of trunks leading between the private branch exchange and the main exchange and that it has not been' completed due to finding all the trunks busy. t

Referring now to Fig.l 5 wherein four individual sets o-r pairs of trunk terminatin equipment units are indicated. To avoi unduly involving the drawings, the first trunk of the group 0f four heretefore re ferred to as leading from bank contact sets accessibe to connectors as C, is the only orio shown in schematic detail though enough has been shown of the corresponding equipment of the succeeding three trunks in the group .to clearly show the details of operation and construction.

In order to impart a complete understanding of the operation at the private branch yexchange, a call will be assumed as completed over the first trunk of the group, that is, that wiper 408 does not encounter ground potential when it engages bank contact 413 (bank contact 412 being clear of attachments and having no o-perative ob-` ject under any condition). As is well known, sideswitch wipers 427 and 428 arein the second position when the wipers 407 to 410 are advanced into engagement-with bank contacts 412 to 415 respectively, and due to armature 475 being attracted incident to the wipers being driven the first step, the inside winding ofprivate magnet 455 will be energized and, therefore, restraining the sides \vitch wipers 427 and 428 from moving into their third position. However, upon the retractionL of armature 475, the private magnet 455 will de-energize, and therefore is will permit the wipers 427 and 428 to advance rinto their third position. This would not have occurred hiad wiper 408 encountered ground potential on bank contact 413, and communicated it over conductor 456, wiper 428, through the outside winding of p-rivate magnet 455 t-o grounded battery. Inasmuch as wipers 427 and 428 have now advanced into their third position, a circuit can be traced from grounded sideswitch wiper 428, conductor 456, wiper 408 to bank contact 413, thus applying ground potential to said 413 and its multiples. The circuit from conductor 456 can be traced through the winding of relay 476, wiper 427 to grounded battery, relay 476 actuating. A circuit can vnow be traced from interrupted ringing current source 477, armature 478. armature 479, spring 480, wiper 409, bank contact 414, conductor 481, armature 503 to tip spring 504 of-springjack 501 and through the upper winding of slow-releasing relay 505 to ground. The relay 505 is designed to be operative to the said source of ringing current 477. Y v

Relay 505 will attract its grounded armatures 506 and 507. Calling lamp 508 will glow, indicative that a call has been completed over the first trunk of: the group and `that a calling subscriber is awaiting the response of the attendant at the private branch exchange. A circuit can now be traced from grounded armature 506 to the sleeve thimble 509 of springjack 501 and through armature 510 to the winding of relay 512, relay 512 actuating. A circuit can now be traced from grounded contact 513 to private bank contact 514 and bank contact f of element H; also, winding of relay 515 will be disconnected from bank contact 514 and other connections in multiple relation thereto'byv reason of the attraction of armature 516. Lt will be noted in this connection that a non-operative circuit path can be tracedJ from the grounded battery through lower winding of relay 505 ring spring 517 of springj ack 501, armature 518, conductor 519, bank contact 415, wiper 410, armature 482, armature 483, through the inside winding of relay 484 to grounded battery. The polarity of the grounded battery sources at the opposite endsI of the traced path are of the same and have the same voltage and, therefore, `will exert no effect upon relay 505.f

It will be assumed now tendant at the private branch exchange observing the glowing of lam 508, the said attendant will insert switching plug 902 into springjack 501, whereupon the windings of relay 505 will become disconnected 'from the traced paths. A circuit can now be traced from ground through the winding of relay 903, sleeve 904 of plug 902, vsleeve .thimble 509 of springjack 501, armature 510 to the winding of relay 512, the windings of relays 903 and 512 being in series relation. Relay 512 will be maintained actuated and relay 903 will actuate. A circuit can now be traced from interrupted ringnig current source 477 over the described t path to spring 504, thence to tip 905 of plug 902, spring 906 of dialing key 907, spring 908 through the winding of the polarized relay 909, spring 910, spring 912, ring 913 of plug 902, spring 517 of springjack 501, armature 518, conductor 519, bank contact 415, wiper 410, armature 482, armature 483, inside winding of relay 484 to grounded. battery. Relay 484 has the same characteristics as' were Idefined in relation to relay 246 of connector B and, therefore, it will actuate.

The direction of the winding on polarized relay 909 is such that with current traversing it derived as traced through the inside winding of relay 484 it will not move its armature 914 from the normal position shown in the drawing, but should the current be reversed in direction it will operate vits armature 914 to disengage its resting contact 915. A circuit can now he traced from grounded armature 916, armature 914, resting contact 915 clearing' lamp 917 to grounded battery, the said lamp 917 vglowing. lt is to be borne in mind that the described circuit, includin the winding of polarized relay 909, endures very brlefiy, only until relay 484 actuates, whereupon the circuit traced fromv armature 478 to armature 483, and including the winding of polarized relay 909, is now continued from that upon the atarmature 478 over conductor 485, upper y lwinding of relay 452 to grounded battery,

, v923, spring924 to tip 925 of p and from armature 483,l conductor 449, lower winding'of relay 452, conductor 487, armature 488, conductor 438 to grounded off-normal spring 437, relay 452 actuating.' The direction of current traversing the wmdmg of polarized relay 909 being Vthus reversed from that first described, its armature 914 is caused tobe attracted from its restin contact 915, lam 917 extinguishing; t will be noted in tV is connection that a locking circuit is established for relay 484 from outside winding conductor l487, armature 488, conductor 438, to grounded off-normal.

spring 437 and that this locking circuit will be maintained until the connector has been released to normal in a manner well understood, and generally as has been set forth in connection with connector B.

The telephonie circuit now exists -from` 'from conductor 180, condenser-450, conductor 449, armature 483, armature 482, wilder 410, bank contact 415, conductor 519, armature 518, rin spring 517 of springjack 501,

ring 913 of p ug 902', spring 912, spring 910, condenser 927, conductor 928, spring 929, spring 930 to rin`g`931 of plug 926. Listening key 935 will be manipulated, completing a circuit from telephonie 'conductor .,921

through the operators receiver 936 second-l ary winding of induction coil 937 to telephonic conductor 928, the calling subscriber at telephone T and the private branch exchange attendant being thus in telephonie communication.

It will be assumed that the calling subscriber at telephone T requests the connection extended to telephone T5. The private exchange attendant will now insert switching plug 926 into springj ack 502. A circuit can now be traced from 'ing of relay 945, sleeve 946,101? plug 926 to sleeve thimble 521, conductor 522, winding of relay 523 in pre-selector PS5, armature 524 of motor magnet M5 to grounded battery. The mechanical adjustment between the armatures of-relay 523 and relay 525 of pre-selector PS5 is well known,- so it will be understood that armature 526 operates to disassociate the winding of relay 525, and

. that armature 527 operates to disassociate grounded contact 528, but that no 'other voperative effect is produced by armature 526, or by the lower armatures i of saidrelay 523. Relay 945 is now operated due tothe g 926, and v ound 'through windt establishment lof the traced .circuit including its winding, so that a vcircuit can now be ltraced from grounded armature 950 armature 951, clearin lamp 952 to grounded battery, lamp 952 g owing. The attendant will now briefiy depress self-restoring key 923 whereupon ringing current from source 953 will be applied from spring 954, spring 924, tip 925 of plug 926, spring 527 of spring- .jack 502, line conductor 528 through condenser 529, signal bell 530, line conductor 531, spring 532 of springjack 502, sleeve 931 of plug 926, spring 930, spring 955 to the opposite pole of the ringing source953, signal bell 530`0perating to summons the called subscriber at called telephone T5. Upon the called subscriber at telephone T5 responding i by removin vthe receiver from the switchhook, a con uctive circuit for direct current will be established between conductors 528 and 531 including the receiver, calling device 533, and transmitter 534 so that\the telephonic circuit previously traced to'tip 925 and ring 931 of plug 926 is now extended tov and includes telephone T5. A circuit can also be traced from grounded battery, upper winding of relay4 960, conductor 921, over thel describedl path, including telephone Ts (key 923 being normal),y conductor928, lower winding of relay 960 to ground. The current derived through the windings of relay 960 will serve as a battery supply for Athe telephone T5 and will also cause armature 951 to be attracted, extinguishing lamp 952, indicating that the called subscriber at telephone T5 responded and has the receiver thereat eff the switchhook. The attendant 4 at the private branch exchange switchboard can restore the listening key 935 at any time .afterf receivin the instructionsl from the callingvv subscri er, or the said attendant can listen in on the established telephonic connection between the calling andthe called subscriber. f

It will now be assumed that the yconversation has terminated, and the called subscriber at telephone T's replaces the receiver first. Under this condition relay 960 will de-actuate and 're-establish the current in flamp 952, causing it to glow. to indicate to (and in factplug 902), may be wit drawn, and the service terminated. If plug 902 is withdrawn, from sprin'gjack 501 the windin s of relay` 505 become lre-associated vin bridge relation between conductors 481 and 419. Bearing in mind that the calling subscriber at telephone T is still holding the receiver, 'relay 401 and its dependent relay 405 will remain actuated and, therefore, no circuit can be tracedv to ground from the winding of slow-releasing relay 490, it having remained normal up to this time. Under this condition relay 505 will re-actuate as it will derive current over the traced path including/ the attendant the condition, so that lug 926' conductors 481, 519, and the windings of relay 452 which originally energized it as described. This, of course, will cause the calling lamp 508 to re-glow and apprises the attendant at the private branch exchange that the calling subscriber has not replaced his receiver and in all probability desires a further, new connection extended within the private branch exchange. The private branch exchange attendant can re-respond and complete a connection in the manner as before described. However, the private branch eX- change attendant would not ordinarily take down the connection completely, in 4so far as withdrawing plug 902 from springjack 501,

until after a clearing signal indicated by p the glowing'of lamp 917 ensued to indicate that the calling subscriber at tele hone T had replaced the receiver, as will be escribed presently. So, in light of the foregoing, 1f the attendant withdraws plug 926 from springjack 502 and then does not observe lamp 917 glowing, it will indicate that the calling subscriber at telephone T has not replaced his receiver, and perhaps wants further attention. p

It will now be assumed that the calling subscriber attelephone T replaces his receiver. This, regardless of whether the called subscriber at telephone-T5 has replaced his rceiver or that the attendant has withdrawn plug 926 from springjack 502, Upon the calling subscriber replacing his re'- ceiver and thereby opening the described energizing circuit of relay 401, dependent relay 405 will de-actuate. It will be borne in mind here that relay 452 will be maintained either through the Winding of polarized relay 909, provided the plug 902 is in springjack 501, or through the windings of relay 505, provided said plug 902 has been withdrawn. A circuit can now be traced from grounded armature 440, spring 441, armaturc 442 to the winding of relay 490, relay 490 actuating. Armatures 491 and 492 will be attracted against their respective make-v before-break springs. It will now be seen that the conductive relationship between armatures 47 9 and 482 and wipers 409 and 410 will be transposed, and that, therefore, the direction of current derived from the windings of relay 452, including conductors 481 and 519, will be reversed and the direction of current traversing the winding of relay 909 (assuming plu 902 to be in spring jack 501) will be such t at armature 914 will engage" contact 915 and re-establish the glowing of lamp 917. The glowing of lamp 917 will indicate that the calling subscriber at telephone T has replaced his receiver. The attendant will now Withdraw the plug 902 from springjack 501. I

Bearing in mind that relay 490 is actuated, a circuit path can be traced from the upper winding of relay 452, conductor 485, arma- 'ture 478, armature 479, armature 492, wiper voltage is at opposite ends of the path last traced and, therefore, .relay 505 is not-energized and it remains normal. We may also trace the path from ground through upper winding of relay 505, spring 504, armature 503, conductor 481, contact 414, wiper 409, armature 491, armature 483, conductor 486,

lower winding of relay 452, conductor 487, l

armature 488, conductor 438, to grounded spring 437. There being no energyin -the ath last traced no electromagnetic efect .will be exerted upon relay 505, so that lamp 508 will not re-glow if plug 902 is withdrawn from springj ack 501 upon the attendant noting the glowing of lamp 917.

At this instant relay 452 not being energized, an operative circuit can be traced from the windin of -release magnet 443, armature 442, spring 441, to grounded armature 440, causing the connector C to be re stored to normal. At this juncture, ground potential being removed from bank contact 413 by reason of wiper 408 disengaging, the

energizing circuit, of relay 492 will bev o ened and the winding of relay 493^reap p ied to armature 494 and to conductor 519, and also ground on contact 495 will be reapplied to armature 496 and to conductor 481 in the well known manner, restoring the first trunk into normal condition in readiness for service originating from either end. It will be assumed now, that the attendant at the private exchange desires to initiate a call on the first trunk of the group and extend it tpward a subscribers line in the main exchange. Plug 902 would 'be inserted in springjack 501, whereupon a circuit can be traced from grounded battery thro-ugh winding of relay 493, armature 494, conductor 519, armature 518, spring 517 of springjack 501, ring 913 of plug 902, springs 912 and 910, winding of relay 909, springs 908 and 906, tip 905, spring 504, armature 503, conductor 481, armature 496 to grounded contact 495, The direction of current traversing' relay 909 is such as to energize it and hold armature 914Vinto engagement with contact 915 and, therefore, maintain lamp 917 glowing. Pre-selector PS4 will function in the well known manner and seize'

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