US1688161A - stehlik - Google Patents

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US1688161A
US1688161A US1688161DA US1688161A US 1688161 A US1688161 A US 1688161A US 1688161D A US1688161D A US 1688161DA US 1688161 A US1688161 A US 1688161A
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relay
armature
magnet
finder
circuit
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q3/00—Selecting arrangements

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  • the presentinvention relates in general to telephone systems, but is concerned more particularly with telephone systems of the type in which so-called finder switches, that is, backward hunting switches, are employed to connect aY calling line with an idle trunk line; and a special object of the invention is the production of a new and improved .sending arrangement to be used in connectionwith finder systems of the directive-finder type whereby there is no loss of time between the two directing digits transmitted to a finder and between the second of the digits and the switching-through operation.
  • finder switches that is, backward hunting switches
  • a vertical marking wiper is provided on the first sender to mark the level to which the finder is raised and to render the sec-ond sender controllable from lines in that level only so as to prevent possible. calling lines in the other levels from interfering with the operation of the second sender to stop the finder on the wrong set of contacts.
  • a further feature of the case relates to the provision whereby the secondary switch which is used to connect a finder with a first selector is rendered preselecting as soon as the finder is allotted.
  • lt is a special feature of the case', however, that the preselected trunk ⁇
  • this drawing shows the automatic substations A and A.
  • the lines associated with the substations terminate in the banks of the finder F as well as in the connector banks shown at-the left. These lines are provided with the usual line and cut-ofi' relays 2 5.
  • the finder F also shown in Fig. l, is controlled, when allotted by the finder allotter F A, from the sending mechanism Ishown in Figs. 3 and l to connect with any one of the 100 lines to which it has access.
  • The, secondary hunting switch SS, Fig. 2 is used to connect th-e finder F vwith an idle first selector, such as FS, and it is connectedA to the finder F, Fig. l, through the medium of the intermediate distributing frame IDF which is employed in order to enable the desired cross-connection between the various primary lgroups in which thc finders are located and the various secondary groups in l which the secondary switches are located to be control the operations of the finder allotter FA Fig. 11 switch S associated' with the'r'elay 201 which is used to close a circuit for the relay 201 when it is desired to energize this relay to disconnect the controlling4 relays 221-229, from the finder allotter iA Fig. 1, and to connect it instead to the spare allotter (not shown).
  • This operation is performed, it will be understood, in case an attendant? wishes to test or adjust the finder allotter FA. In this way the ser-vice. is not interrupted at such times.- v
  • Fig.- 4 s-howst-he vertical sender VS' which is usedl to control? theiinders in their vertical operation; ⁇ its shows the rotary sender RS which is used to control the finders in their rotary operation; andv it shows also the sequence switchv SE whichis employed for the purpose of controlling the sequence or opera tions or the two senders VS and RS, andv to effect the switching-through operation at the end of the operation of the rotary sender RS.
  • finder F and the iirstselector" FS are f both of the well known vertical and rotary type of switch, havingbank contacts arranged in horizontal rows or levers.
  • the :tinder F is modified in that its wipers, in-y stead of standing one step below the iirstlevel of the bank contacts Vasin the ordinary case,
  • the finder allotter FA is, as shown, a simple rotary switch of the well knowntype in which the wipers areadvanced step by step by an associated stepping magnet and in which the wipers are advanced upon restoring stroke of the armature, rather than upon the operating stroke.
  • v A Y Relay 221 is the iirst-level control relay.
  • This drawing shows also the' It is energized responsive to a call over a line terminating in the first'- level or the finders and it operates to prevent the operation of the vertical magnet or' the allotted iinder by open ing the vertical magnet circuit at armature 241, and to prevent the operation of the vertical sender VS, Fig. 4, and to operate the sequence switch SE right away by shifting the cont-rol circuit at armature 243.
  • Y It is energized responsive to a call over a line terminating in the first'- level or the finders and it operates to prevent the operation of the vertical magnet or' the allotted iinder by open ing the vertical magnet circuit at armature 241, and to prevent the operation of the vertical sender VS, Fig. 4, and to operate the sequence switch SE right away by shifting the cont-rol circuit at armature 243.
  • Relay 222 is the secondary-line-switch switching relay, so called because it occupies the same position in the circuit as the switching relay of an ordinary rotary line switch. This relay pulls up when the secondary line switch' finds an idle trunk in case relay 226 is energized. f
  • Relays 223'and 224 are the emergency stcp' ping relay and the regular stepping relay, respectively.
  • Relay 224 is controlled over conduct-or 7 9 to 'open the impulse circuit as soon asthe magnet to which the impulse circuit i's connected operates.
  • Relay 223' is slow to pull up. Its circuit is closed each time the impulse circuit is closed, but does not ordinarily have suihcient time to operate before the regular stepping relay 224 is pulled up, but, in case the contacts of thel magnet fail'to close (dueto had adjusti-nent or to dirty contacts, etc), the emergency stepping relay 223 pulls up after an interval which is slightly longer than the time required for the average magnet to operate and termi'- nates the impulse'being delivered.
  • Relays 225 and 226 are the auxiliary start relay and start relay, respectively.
  • - Relay 225 is provided primarily as a circuit closing relay on account of the great number or con- Sti lou
  • Relay 227 performs several functions and is called the guard relay because the upper winding of this relay is energized in a branch circuit with the magnet 77 or the iinder allotter FA, Fig. l. to maintain the start relay 228 disconnected during the hunting operation of the finder allotter, and because the lower wind-ing of the guard relay 227 is energized from armature 264 ofthe series guard-control relay 228, which remains energized during the restoration to normal of the vertical sender VS and thc rotary sender RS.
  • Relay 228 is the busy relay and' it energizes through resistance 230 when ground is removed from conductor 88 responsive to the condition or all finders such as F being busy or otherwise unavailable.
  • Line relay 3 thereupon energizes and, in iddition ⁇ to grounding the start conductor 12 at armature 8, closes certain control circuits at armatures G and 7.
  • rEhe control circuit closed at a mature 7 is the second-level verti al-control circuit and is used to control the finder to bring its Wipers opposite the second level ot' bank contacts.
  • the circuit closed at armature 6 is the llo-25 rotary control circuit and is used to guide the Wipers ot the i'inder into engagement with the ii'ith set ot banl; contacts in the second level after they have been raised opposite that level.
  • Mafmet 104 is not operatively engined at this time on account ot' the relatively nigh resistance oi the switching ⁇ relay 222.,1 Fig. 3.
  • Relay 222 upon energizing. closes a second point in the cut-throiw'h circuit at armature 244, and at arn'iature 245 it opens the connection which gneviously eX- isted between, the steppingniagnet 10 the secondary switch SS and the test ivf V102 anu places ground on test wiper 102 through armature 205 and its resting contact, conductor S2, Wiper'fl ot the finder allotter FA, the lirst associated bank contact, and the ⁇ jumper 54. rThe result of this latter operation is to guard the preselected lirst selector FS. 2, from seizure.
  • the auxiliary start relay 225 places a local ground on the start conductor 12 at armature 251 so as to maintain the start relay A220 energized independent ot the calling line until the common controlling ⁇ apparatus has gone through its complete sequence oi' operation.
  • relay 225 places a shunt around the self-interrupting contacts 78 otl the Finder allotter stepping magnet 77 for a reason which i 7ill become ap'- parent upon a :tui-ther perusal ot the description.
  • the auxiliary start relay 225 at armature 253 disconnects the lirst-level-control the vertical magnet operating conductor 2T armature 241v and its restingl Contact, armature 203 and its resting Contact, conductor 80, Wiper 71 of the finder allotter FA, and
  • vertical magnet 84 to battery.
  • Vertical mao-A net S4 is thereupon energized and it rais the Wipers 31-33 troni their normal position opposite the lirst level ot bank contacts to a position opposite the second level oit bank contacts.
  • the placing ol ground upon conductor 270 by armature 254 ot the auxiliary start relay 225 also extends a Iground potential through armature 249 and its resting contact to the sender impulse distributing Wiper 312 ot the sequence switch SE.
  • This ground potential is extended through Wiper 812 in its first position, conductor 277, armature 243 and its restino ⁇ contact, and conductor 271 to the stepping magnet 301 of the vertical sender VS. Accordingly, stepping magnet 801 energizes preparatory to advancing the Wipers 807--309 on its restoring stroke When its circuit is subsequently opened.
  • ground potential is extended to' theterminal 321 which is a common connecting point, it may be pointedvout, for the vertical'control conductors such as the vertical control conductor 16 oi the second level) lll) ol all the levels with the exception ol the first level.
  • a circuit is novv closed from the grouni'led terminal 321 over conductor 1G, armature 7 and its working contact, conductor 17, terminal 292 which corresponds to the second level oil bank contacts of the tinders, lirst contact in the bank ot wiper 30G and the said wiper, and the first contact in the bank oit Wiper 311i and said Wiper for stepping n'iagnet 303 ot the lequence itch SE.
  • magnet 3025 energizes in mlltiple with stepping magnet 301 ol the ver( lal sender VS and in multiple with vertical magnet 3ft ot the inder F, preparatory to advancing Wipers S12-314 to their second position to terminate the vertical movement and to initiate the rotary movement as soon as the lirst impulse terminated.
  • magnets 301 and A303 tall back and advance their respective associated Wipers one step, and vertical magnet 3st ot the :tindcr F falls back and removes ground trom conductor T9, whereupon stepping relay 224, Fig. 3,. again falls back to transmit the next impulse. y
  • Wiper 314 has advanced from the l'irst contact, which is associated with the vertical control Wiper 308 ot the vertical sender VS, to its second contact, which is associated ⁇ with the rotary control wiper 311 of the rotary sender RS, the Afurther advance of the sequence switch SE to tern'iinate the second digit to be transmitted to the allotted iinder is under the control of the rotary-control' Wiper 311.
  • the sender impulse distributing. Wiper I 312' has disconnected the. sender impulse conductor 27S) from conductor 277 leading to. stepping magnet 301 oi the vertical sender by way ot armature 243 and its resting contact and conductor 271, and has connected it instead to stepping magnet 302 of the rotar sender RS.
  • the impulse lead which Wiper 309 terminates is connected to terminal 295 common to all lines in the second level to the exclusion of terminals such as 204i common to the other levels, respec-r tively. Accordingly, 1t may be seen that the Y lli cuits of rotary magnet of the iinder F and stepping magnet 302 of the rotary sender RS, respectively. Stepping magnet 302 now falls back and advances the wipers 310 and ⁇ 311 one step, whereupon wiper 311 disconnects ground from the lirst rotary control conductor and connects it instead to the second rotary control conductor.
  • magnet 77 does not fall back responsive thereto owing to the fact that contacts 7 8 are shunted by armature 252 audits working Y contact of relay 255 through a connection which included armature 210 and its resting contact and conductor 87.
  • Relay 36 energizes over the above traced circuit unless the line of substation A has become busy during the time elapsingv between the removal of the receiver and the arrivaloi:l the tinder F due to a call being extended to the line through the connector bank terminals shown at the left. Assuming the line to be still in the idle calling condition, relay 36 pulls up and extends the line conductors orp the calling ⁇ line by the way of working contacts of and armatures l2 'lit andY 46 over the heavy talking conductors shown to the first selector FS Fig. 2.
  • Relay 36 at armature 43 also disconnects the test .wiper 32 from the junction of resistance 3S relay 3 from the line of substation A.
  • Line relay' 3 new falls' back and separates conductors 18 and 19 and conductors 16 and 17 at armature 6 and 7, and at armature 8 removes ground trom the start conduct-or 12, leaving this conductor grounded in the common equipment at armature 251 oit the auxiliary start relay 225, Fig. il.
  • this relay7 locks itself to the grounded release trunlf. conductor 72 at armature 44, and at armature 415 opens a. further point in the circuit of release magnet 39.
  • line relay 121 energizes responsive to the tina-l extension of the calling line at relay of iinder F, as above .pointed out, and closes at armature 131 a circuit for release relay 122.
  • Release relay now energizes and at armature places ground on release trunk conductor 109 so as to maintain the connection between the first selector and the calling line through the finder F and the secondary switch SS independent oit the common controllingr equipment which is to be shortly associated with another finder-secondary link.
  • release relay 122 As a further result of the energization of release relay 122, it opens a point in the circuit et release magnet 126 at armature 134: and closes a point in the circuit of vertical magnet 128, and at armature 132 closes a point in the circuit of the common chain relay 106 for a purpose which will be later pointed out.
  • the first selector is now in readiness to be operated in accordance with the first digit ot' the desired number. The description ot this operation, however. will be deferred until the description et the opera-tion ot the common controlling apparatus has been completed.
  • relay 228 resides through the low wound series gu ardcontrol relay 228. Accordingly relay 228 impuls/es when the restoring circuits are clos-cd and it remains energized until they are both opened on account of the 'fact that it is slow acting and is able therefore to maintain its armature attracted notwithstanding the interruption in its circuit. It may be pointed out that relay 22S at armature 26-1- closes a circuit through the lower winding of the relay 227 so as to maintain this relay energized and the restoring circuits of the switches VS and RS intact at armatures 262 until the restoring operation is completed. At armature 265, relay 228 closes a circuit through the resistance 266 and through the switch-room supervisory relay 231 so that an attendant may be informed in case the restmfing circuits are not opened within a reasonable length of time.
  • relay 226 disconnects the combined cuttlhrough and test conductor (new grounded at the rst selector FS) from the cut-through circuit and connects it back to the test circuit again; it opens the circuit ot lthe secondary switching relay 222 at armature 25S, and again .closes a point in the circuit of busy relay 229, whereupon the relay 222 'falls back, but without any particular result at this time; and at armature 257 it opens the circuit or' the auxiliary start relay 225.
  • relay 225 tails back and removes the local ground from the start conductor l2 at arniature 251; reconnects conductor 221 to the terminal 26S) atarmature 253; and at armature removes ground from wiper 312 of the sequence switch .
  • the upper winding ot rcla .fV
  • Vhen stepping magnet 77 of the finder allotter FA tails baci it advances the wipers 'le-76 one step.
  • the finder allotter FA busy wiper 75 engages a grounded bank contact with the result that the :ircuit over conductor Se, lfor the upper winding ot th' Vhereinbetore pointed out) Vtails bacl; ai
  • sequence switch E as well as the remainingg,l part ol the common equipment is ready to be used in handling anothercall.
  • Relay 123 is energized in series vvith vertical magnet 12S and, being slonv acting, maintains its armature attracted throughout the series ot impulses.
  • llt armature 135, relay 123 prepares a circuit liorstepp'lng relay 121,'ivhicli is completed oil normal contacts i upon the first upward step ot the .yitch, and which includes, in addition, the interrupter 152 of the rotary magnet 12"?.
  • Relay 121 energizes When this circuit is clesedanc it tat armature 13G, and at armature 13?' prepares a circuit lor rotary magnet 127.
  • relay 125 is short circuited by the ground potential encountered on the busy test contac" by test Wiper 111eL and it does not energine.
  • Relay 1241 energizes trom this same ground potential and again closes at armature 187 the circuit ot rotary magnet 12?'. vVhen this occurs rotary magnet 127 pulls up rfhis alternate operation ot relay 12-l ant magnet 127 continues as described until an idle trunk is reached, which trunli, it will be assumed, is the one comprising conductors 1019-151 and terminating ⁇ in bank contacts 145-1118.
  • relay 125 removes ground from armature ariiiature 141, tlierel" f opening the circuit ot' the slouv acting relay 122; it closes a niultiipile point in the chain circuit at armature 139; it opens the testcircuit and prepares the holding circuit at armalture 1110; and at armatures 138 and 1&2 it
  • the subscriber at substation A replaces his receiver, whereupon theground is removed in the usual manner from release trunk conductor 150 ot lthe trunk seized by the first selector FS,
  • the decnergization oiE relay 125 results in the closure ot the circuit at release magnet 126 through armatures 141, 131, and 134, and through the oil normal contacts 129. Release magnet 126 thereupon energizes with the result that the wipers 143-145 are restored to normal position in the usual manner. The circuits of magnet 125 is opened at oil normal contacts 129.
  • relay 3G upon falling back, removes ground ii'rom wiper 32, whereupon cutoil relay 2 falls back and again connects up ground to one line conductor and line relay 3 to the other.
  • Relay 36 also completes the circuit ot release magnet 39 at armature 45.
  • the circuit includes armature 48 and its resting contact, arn'iature 45 and its resting Contact, and oif normal spring 51 at itsupper contact. Release magnet 39 now'encrgizes with the result that wipers 3,133 are restored to normal position in the usual manner, whereupon the circuit of release magnet 39 is opened at off normal spring 51.
  • relay 221 Upon energizing, relay 221 closes a locking Acircuit for itself and opens its initial circuit at armature 242; opens a point in the vertical magnet operating circuit at armature 241 so as to prevent the usual magnet circuit from being closed at this time as the wipers are already opposite the first level of bank contacts; and at armature 243 it opens the circuit for advancing the vertical sender VS and prepares over conductor 281 a circuit for automatically advancing the sequence switch SE, Fig. 4, from its first position to its second position.
  • wiper 313 closes the usual circuits at its armatures ductors 279 and 280 to the sender-impulse and the linder-impulse distributing wipers Y 312 and 313.
  • the ground potential placed on wiper 313 is extended through conductor 277, armature 243 and its working contact, conductor 281', and the self-interrupting contacts G tothe stepping magnet 303 of the sequence switch SE. Accordingly, magnet 303 operates and opens its own circuit, whereupon the wipers 313-314 are advanced one step from the vertical sending position to the rotary sending position.
  • the ground potentialvon wipers'312 and 313 is now extended in the usualmanner to the rotary magnet of the finder F and to magnet 302 of the rotary sender RS in the manner hereinbefore described, and stepping relay 224 is controlled over the common stepping' conductor 79 to interrupt the circuits at armatures 248 and 249 in the hereinbefore described manner, thereby advancing the rotary sender RS and the linder F simultaneously.
  • v Y Y At the end of the fourth stepzof the finder F and ot' the rotary sender RS, the wiper 311 oi" the rotary sender RS is standing' on the li'lth 'associated bank contact.
  • Start relay 226 also, it will be noted, shunts the resting contact and armature 260 at armature 256 so as to maintain the connection between the test wiper 102 and the stepping magnet 104, 2, independent of the restingl contact and armature 260 of the guard relay227.
  • the release-guard conductor 83 is extended through the wiper 74 and its first associated Contact to the release guard relay 37 of the finder F. Accordingly, when the release guard conductor 83 is grounded vat armature 250 of the auxiliary start relay 225, as hereinbefore pointed out, the release guard relay 37 pulls up and remains up as long as the auxiliary start relay remains energized. It will he noted that the cut-through conductor 84 is extended through the cut-through wiper to olf normal spring 50 and that as soon as the release-guard re-y lay 37 pulls up a ground potential is placed at armature 48 on.
  • the finder F is maintained busy to the finder allotter FA subsequent to the falling back of the release-guard relay 37 as soon as the common controlling apparatus is through setting the finder F, not from the release trunk conductor 72, but from the local ground through the resting contact and armature 47, and through the upper contact and off normal spring ⁇ 50. Accordingly, this ground potential is available for guarding the finder F until the olf normal springs shift back to their iormal position shown in the drawings when the finder is finally released.
  • this relay is slow to pull up and it does ,not therefore have time to pull up in the ordiand armature 263, and armature 247 and itsA resting contact for the auxiliary stepping relay 223, is effective in energizing this relay in a kperiod of time somewhat longer than ordinarily required for energizing the operating magnet of the finder.
  • relay 223 closes at armature 246l a local circuit for 'stepping relay 224, whereupon relay 224 energizes to open the impulsing circuit at armatures 248 and 249 and to open the circuit of the auxiliary stepping relay 223 at armature 247.
  • Relay 223 now falls back fairly quickly, notwithstanding the copper slug on the armature end of its core. owino; to its stiff adjustment, and at armature 246 opens the circuit of stepping relay 224 which thereupon falls back to send the next impulse.
  • this relav is normally included in the circuit from ground through armature 258 and its resting contact, relay a Ad resistance 28() to butg tery.
  • the normally grounded conductor 88 which is ⁇ commtm to all the af'- sociated 'inders, is connected at ne junction of relay 229 and resistance 239.
  • Conductor 88 is grounded in the linder F through armature i8 and its resting contact, armature l5 and its resting contact, and oil normal spring 5l and its lower contact.
  • a two-motion finder switch In a telephone system, a two-motion finder switch, a calling ⁇ line terminatino in the banlrthereof, prim ary and secondary m. nets for driving said finder in its respective movements, means toi' sendino a s.' idle train of impulses to said finder, and means independent ci control by said impulses for diverting the first part oit said series to said primary magnet and for diverting the remaining part tosaid secondary magnet, whereby said finder is set upon the bank contacts ot' the callingl line.
  • an impulse generator' In an electrical controlling system, an impulse generator', a path for the impulses generated thereby, and means comprising a step-hy-step switch operated by only one or' the impulses transmitted over said path for barring further impulses from passing over said path.
  • a finder controlling arrangement comprising an impulse generator, a primary motion counting switch having progressively movable wipers, a secondary motion counting' switch having progressively movable wipers, and a counting-switch-control sequence switch having progressively movable wipers.
  • a register associated with the sendingmechanism for registering the extent of the primary operation of an operated .linder to place the further operation of the sending apparatus under the exclusive control of calling lines in the group selected by the primary operation of the finder.
  • an impulse generator for generating two series of impulses, two counting switches for counting said series, respectively, connections con-V operating magnets of the finders, an allotter n for connecting said Contact to an idle finder, and means controlled by the operating magnets of the allotted finder for controllingY said relay to operate said Contact.
  • a relay having ⁇ a Contact for transmitting impulses to the operating magnets of the iinders, an allotter for connecting said contact to an idle finder.
  • ll. ln a telephone system employing finder switches, numerical switches, a secondary line switch connected to each finder switch, means for allotting an idle finder switch for use before a call is received, and means for thereupon causing the secondary switch connected with the allotted finder to select an idle numerical switch.
  • a telephone system employing finder switches, numerical switches, a secondary line switch connected to each finder switch, means for allotting an idle finder switch for use betore a call is received, means for thereupon causing the secondary switch connected with the allotted inder to select an idle numerical switch, and means responsive to a call for rendering the selected numerical switch busy to other econdary switches.
  • an electrical controlling system an impulse generator tor generating a series oi evenly spaced impulses, a counting switch having wipers and a magnet, said magnet being energized by said impulses to advance said wipers to count said impulses, contacts engaged by said wipers, means for marking a certain one of said contacts to deline a group of said impulses, a plurality of paths for said impulses, i cans controlled through said n'iarked contact and counting switch wiper which engages it, ior ending said group by diverting the remaining impulses of the Eeries to another or" said paths.
  • the method ot preventing number scrambling, oit simultaneous calls received by a control mechanism, by registering the level designations of the calling lines in a level selecting control, by preparing circuits for registering the contact designations of the lines in a contact selecting control, and by closing said circuit after said level selecting control has been positioned, to register the contact designations of only those calling lines which are in the selected level.
  • a group of inder switches having banks, a plurality of groups of lines terminating in said banks each oi' said groups comprising a level in said banks, a. common control mechanism comprising a. senderptor delivering impulses to said finders, a plurality ot counting switches and a sequence switch, means individually associated with each of said lines and responsive to a call thereon to start said control equipment functioning, to mark the level containing the line in one of said counting switches and to prepare a.
  • 1mpulsing device which consists ot closing circuit to the magnet which is to be impulsed and of closing a pulse terminating circuit b contacts closed by that magnet when it i in its fully operated position.
  • a @groep ot lir a group of finder switches having' aceethereto, secondary switches coiuected to sait finder switches, a group oi numerical switches accessible to said secondkt ,ry switches7 a control eqnii'nnent common to said iinder switches, an allotter l'or a i-iociating said c" trol equipment with one oi said finde; switches7 start relay in said control equipment energized in ,spense to a call on one et said lines to start said equi ifnent 'tanctioning to position the allettet ,Finder on that line and te establish a connection therewith, means associated.
  • a secondary magnet for moving said Wipers to select a line in a selected leveh control means responsive to the initiation of a call on one oi said line for operating); said magnets in turn, to position said Wipers on. the contacts of said line1 and a rela;7 energized in response to the initiation ot a call in the level opposite which said Wipers normali)7 rest for removing said primary magnets from said control means and operating said secondary magnets to position said Wipers on the contacts of Asaid calling; line.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Investigating Or Analyzing Materials By The Use Of Magnetic Means (AREA)
  • Relay Circuits (AREA)
US1688161D 1925-06-04 stehlik Expired - Lifetime US1688161A (en)

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Application Number Priority Date Filing Date Title
GB14485/25A GB257661A (en) 1925-06-04 1925-06-04 Improvements in or relating to telephone systems

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US1688161A true US1688161A (en) 1928-10-16

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US (1) US1688161A (enrdf_load_stackoverflow)
FR (1) FR613558A (enrdf_load_stackoverflow)
GB (1) GB257661A (enrdf_load_stackoverflow)

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FR613558A (enrdf_load_stackoverflow) 1926-11-24

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