US1491323A - Telephone-exchange system - Google Patents

Description

April 22 1924.

D. l.. TEMPLE TELEPHONE EXCHANGE SYSTEM Filed April 5.

1921 3 Sheets-Shea; l

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April 22, 1924. 1,491,323

D. L.. TEMPLE TELEPHONE EXCHANGE SYSTEM Filed April s. 1921 3 sheets-Sheet 2 .n ,M 3. l M |-....L N m m m Il :n 1, L j e "umf @nu uvm n\"` --.Ilm l s MQ@ Ta SW in lu a N .w l s www QQ J m W @S 0 R. M w. a E m m. v. bh. n E, 1 m M 5. w mdb, T w n. Mn VJ X m ma. n .0 .Tm A SQ, D. W M h d NRL- P .1 .Tm F hg rd Patented pr. 22, 1924.

uNITi-:n STATES maleza PATENT OFFICE.,

DAVID L. TEMPLE, OF FLORAL :PARKl NEW YORK, ASSIG'NORy TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW' YORK, Y.. A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed April 5,

7'0 @ZZ wiz/0m t 'may concern.'

Be it known that I, DAVID L. TEMPLE, a citizen of the United States, residing at Floral Park, in the county ofNassau, State of New York, have invented certain new and useful Improvements i in Telephone-EX- change Systems, of Which the following is a full, clear, concise. and exact description. Thisr invention relates to `a telephoneexchange system in which connections are extended by means of machine switching mechanism, and more particularly, to apparatus in manual terminating ofiices of such an exchange for transmitting busy signals to calling subscribers if desired lines are busy. y

In a large telephone exchange during the transition period from a manual to an automatic operating basis, many ofiices of the exchange are operated upon a manual basis as to calls local to the office and are arranged to terminate calls originating in mechanical offices of the exchange by means of plug ended trunks. The numbers of lines desired by calling subscribers in mechanical `oiices are displayed before operators in the manual office by means of call indicating devices. Subscribers lines in such manual offices may also be called from other manual ofiices of the same exchange in the Well-known manner.

Vhen a desired line in such a manual oiiice is tested and found to be busy, it then becomes necessary to apprise the calling subscriber of that fact. In order that no confusion shall arise it is desirable that a. busy signal of the same character be employed throughout the exchange regardless of whetl'ier the calling subscriber is a subscriber Whose line terminates in an office equipped for manual or automatic operation or Where the desired line terminates.` It is further essential that the character of the busy signal. if universally employed throughout the exchange, shall be such as will flash supervisory lamps at originating manual offices,

but will not operate call charging mecha-r nism associated With the switching mechanism of mechanical offices.

lle-retofore this result has been accomplished through the provision of two groups of busy back jacks at such manual oiiices, outx group being employed in connection with terminating trunks extending to origiating manual offices and the other group 192]..` Serial No. 458,659.

in connection with terminating trunks extending to originating mechanical offices. As the provision of two groups of busy back jackstends to confusion and the false charging of calls to calling subscribers in mechanical offices through the inadvertent employment of a busy back jack of the Wrong group, and since it is further necessary to trainthe operators in the proper use of the twofgroups of jacks, it is desirable to provideasingle group of jacks which may be used for calls incoming from both manual and mechanical offices. It is therefore au object of `this invention to provide a busy back jack and `associated circuits which is arranged for use with terminating trunks extending from either a manual or a mechanical office. f

A Lfurther object of the invention is the provision of means for rendering the busy back circuit inoperative and for giving an alarm should the circuit become unstandard to such an extent as would cause false call charging if employed to transmit a busy signal to 'asubscriber in a mechanical office.

A still further object of the invention is the provision ofmeans for giving an alarm in case the tip and ring contacts of any busy back jack of a. group of jacks become shortcircuited. i

Further features of the invention will be apparent from the following description taken in connection With .the accompanying drawings, in Which-Fig l shows apparatus at a mechanical oli'ice of an exchange. comprising one of a plurality of subscribers lines terminating in such mechanical oflice, a line svi/itch.individual to the subscribers line, ay district selector for extending a connectionfrom the subscribers line to interoflice trunks extending to other offices of the exchange or to other switches of the same-office, and an oiiice sender shown diagrammatically Within the dotted rectangle for controlling the operation of the district selector and the apparatus in other exchanges of the o'fiice to which a connection may be-extended` Fig. Qshows one of a group of interoftice `trunks terminating at an operators position O in a manual office` a subscriber-s line terminating in such manual o'liiffe and a busy back jack for associating the busy jack mechanism shown in Fig. 3 With the interotlice trunk, in the event that the desired subscribers line is found to be busy. A relay call indicator is also indicated by the small rectangle in the lower left-hand portion of Fig. 2 for indicating to the operator the designation of the line desired by the calling subscriber.

Fig. 3 shows the circuits of busy back mechanism associated with the busy back jacks shown in Fig. 2 together with alarm circuits for indicating' an unstandard condition ot the busy back mechanism.

F ig. et shows diagrammatically circuits for extending connections to the operators position 0 of a manual office directly from a mechanical otiice through a district selector, or indirectly from a mechanical oiiice through a special operators position 02, and also circuits for extending` a connection to the manual of'ce from another mann ual olice or' the same exchange, also the line of a manual subscriber 'terminating in the manual oHice and busy back jacks for cooperation with the terminating circuits ot the manual oiiice for transmitting' a busy -`:ignal to a calling subscriber in either a mechanical or manual originating oliice.

The line switch 106 is oit the welll-known step-by-step type controlled in its step-bystep movement by the stepping magnet 102. rPhe district selector 150 is of the so-called panel type shown in the patent to E. B. Crait and J. N. Reynolds 1,123,696, issued January 5, 1915, but has been disclosed herein in an abbreviated form for the pur* pose o'll simplifyingthe disclosure of this invention. The switch has been illustrated as having` but a single set 147 of brushes, the switch being set to a. desired group of terminals by a single selectiveA movement under `the control of the updrive inagnet 143.

The sequence switch 198 associated with the district selector is of the well-known type disclosed in the patentto J. N. Reynolds and C. F. Baldwin, No. 1,127,808, issued February 9. 1915. The otlice sender disclosed in the dotted rectangle is of the type disclosed in the patent to F. A..Stearn and F. J. Scudder, No. 1,395,977, issued November 1, 1921, only so much of this sender being disclosed herein as is -considered necessary to an understanding of this invention.

The relay call indicator, shown in the Ismall rectangle on Fig. 2, may be of the type disclosed in the application of A. E. Lundell and E. H. Clark, Serial No. 887,531. tiled June 9. 1920, but since a complete disclosure of the circuits of this indicator is not essential to an understanding of this invention they have not been disclosed herein.

Having now briefly described the invention and the apparatus employed, it is thought that a clearer understanding ofthe o Il invention may be had from a more detailed description of the manner in which connections are established. It will first be assumed that `the calling subscriber A in a mechanical otIice of the exchange desires a connection with the subscribers line B which terminates in a manual oiiice of the exchange and that the line of the desired subscriber is at the time free. The calling subscriber to initiate the call removes his receiver from the switchhook, whereupon a circuit is established for the line relay 100 extending through the armature contacts of the @nooit relay 101, over the calling line loop. Line relay 100, upon energizing, establishes a circuit for the stepping magnet 102 which in the well-known manner advances the wipers 103, 104- and 105 of the line switch 106 over the terminals of trunk lines extending to district selector switches. As soon as an idle district selector is found, a circuit is established for the cut-O' relay 101 of the calling line which may be traced from battery through the operating winding of relay 110, cam contact 111, bank terminal 109 and test wiper 105 of line switch 106 and to ground through the windingof cut-oit1 relay 101 and the winding of a message register magnet 112. Relays 110 and 101'energize in this circuit, but magnet 112 being marginally wound does not not receive sufiicient current at this time to energize. Upon the energization of cut-ofi' relay 101, the circuit of the subscribers line relay 100 is opened and the advance o1 the line switch is thereupon arrested.

` Relay 110, upon energizing, closes a circuit for advancing sequence switch 198 of the selected district selector 150 out of position 1 and into position 2, which circuit extends from battery through the magnet winding of sequence switch 198, cam contact 113 (1) and to ground at the right-hand armature contact of relay 110. With se quence switch 198 in position 2,. a circuit is established forthe stepping magnet 11G of the sender finder switch SF for advancing the sender finder in search of an idle otlice sender. The circuit of stepping magnet 116 may be traced from battery through the winding` and armature contact of magnet 116, cam contact 117 (2) and thence to ground at the left-hand armature and contact of relay 118. During the hunting movement of sender finder SF. the test wiper 119 advances over test terminals oi oliice senders until the wiper 119 engages the test terminal of an idle sender. when a circuit is established for relay 118 extending 'from battery through the winding oi this relay` wiper 119 and terminal 120 to ground. Relay 118, upon energizing. opens the previously traced circuit of stepping magnet 116 thereby arresting the movement of the sender finder and closes a circuit for advancing sequence switch 198 into position 3, which circuit extends from battery through the magnet winding of the sequence switch, through cani contact 121 and to ground at the armature contact of relay 118.

Upon the association of an idle oflice sender with the selected district selector, an inipulsing circuit is established between the oflice sender and the calling lineA over which circuit the ralliiig subscriber is enabled through the operation of hiscalling dial S to register thc number of the desired line upon the registers of the sender. This iinpulsing circuit may be traced from battery through the register stepping relay 123, wiper 124, conductor 125, the left-hand contact of cam 126 (1 to 3), baul; terminal 108 and wiper 104 of line switch 106, thence over the calling subscribers line loop and through his calling dial S, tiipcr 103 and bank terminal 107 of line switch 106, the lower contact of cam 127 (1 to 3), conductor 128, wiper 129 and thence to ground.

lilith sequence switch 198 in position 3, a fundamental circuit is established between the district selector 150 and the selected oflice sender, which i'nay be traced from battery through the vv'inding of control relay 131, cam contact 132 conductor 134-., ipen135,the winding of sender stepping relay 13(3,tl1econtact of cani 130 which cani is assoc'ated with a sequence switch (not sho-wn) :associated with the ofice' sender, the armature and bach contact of counting relay 137, wiper 138, conductor 139 and thence to ground at cani contact 140 (3 to 4). Relays 138 and 131 energize in this circuit, relay 131 closing a locking circuit for itself through its left-hand armature, cam contact 133 (3 to 4) and thence to conductor 134 and over the fundan'iental circuit previously traced, and at its righthand armature closingl a circuit extending through cam contact 142 and conductor 141 for advancing sequence switch 198 into position 4.

lith sequence switch 198 in position 4 a circuit is now established for the updrivc magnet 143 for advancing the brush set 147 of the district selector 150 in search of a group of trunk lines extending to the office of the e'changc in which the desired line B tern'iinates. The circuit of magnet- 143 may be traced from battery through the winding of magnet 143, cam contact 144 (4) and to ground at the right-hand arma-- turc of relay 131. Magnet 143, upon energizing, n'esses the depending portion of switch shaft 145 against the constantly rotating updrive roller 146, whereupon the switch shaft and the attached brush set 147 is driven upwardly.

the brush set 147 approaches a position "civ beneath the first group of bank r, shaft wiper 148 engages a conducting through wiper 148.

portion of comniutator 149, where` upon a circuit is closed in shunt of the winding of the sender stepping relay 13G which may be traced from battery, through the winding and left-hand armature and Contact of control relay 131, the cani contact 133 (3 to 4), cani contact 151 (4), conductor 152, commutator 149 and thence to ln response to the establishment of this shunt circuit, sender stepping relay 13G deenergizes and in the well-known manner controls the circuits of the sender to count one impulse on the counting relays of the omce sender.

As the switch shaft 145 continues in its upward movement, the shaftwiper 148 engages an insulating portion of commutator 149 and the previously traced shunt circuit is thereupon opened, again permitting the energization of sender stepping relay 136. Thus, during the continued upward movement of the switch shaft, the sender stepping relay 136 is intermittently energized and deenergized, until the 0 counting relay 137 becomes energized when the office sender will be satisfied with respect to the oiiice registration of the desired subscribers line. Upon the energization of relay 137,

the previously traced fundamental circuit is opened, thereby opening the circuit of con-y trol'relay 131. As soon following the opening of the fundamental circuit as the brushes of brush set 147 are centered upon the lowermost set of bank terminals in the selected group, shaft wiper 148 will engage an insulating portion of commutator 149 and relay 131 will become deenergiaed, opening the circuit of updrive magnet 143 to arrest the upward movement of the switch shaft and closing `a circuit extending through cam'contact 153 (4), and over'con ductor 141 for advancing sequence switch 198 into position.

With sequence switch 198y in position 5 the circuits of the district selector are prepared for controlling the district selector in its limiting movement for selecting an idle trunk in the selected -group of interoflice trunks.' A circuit is now established for relay 131 extending from battery through the winding yof the relay, cam contact 132 and to ground at cam contact 154 and at its right-hand armature contact closes a circuit extending over cani `contact 142 and conduct-or 141 for advancing` sequence switch 198 into position 6.

Under the assumption that the first trunk of the selected group, upon the 4bank terminals of which the brush. set 147 is now resting, is at the time busy, relay 131 is maintained locked after sequence switch 198 leaves position 5 over a circuit extending through the left-hand armature of relay 131, cam contact 133 (5 to 6), cam Contact 155 (535 to 10), test brush 156, testrterininal 157, thence over multiples of test terminal ground the oi'iice sender functions in the well-known manner to transfer the line number registered upon its numerical registers to the re lay call indicator mechanism for indicating to the operator at position 0 the number of the line desired.

Upon the energization of relay 224 and the association of the relay call indicator-mechanism with the conductors 205 and 206 of the trunk circuit, the circuit previously traced for relay 200 is opened at the armature contacts of relay 224 and relay 200 deenergizes, opening the locking circuit of relay 212. The previously traced circuit of lamp 216 is now opened and since at this time relay 221 is energized, a new circuit for lamp 216 is established, extending from battery through the lamp, over conductor 283, conductor 284 and to ground through interrupter 285 for causing the lamp 216 to flash. This lamp continues to flash during thesetting of the relay call indicator and until the operator inserts the plug P in which the selected trunk circuit terminates, in the jack of the line indicated by the illuminated lamps of the indicator. Upon the dee'nergization of relay 212, the initial energizing circuit of relay 223 is opened, but relay 228 now remains locked over conductor 229 and to battery through the winding of relay 228, thereby causing the energization of relay 228.

Following the completion of the setting of the relay call indicator, relay 260 associated with the indicator energizes in the manner fully set forth in the aforesaid application of A. Lundell and E. H. Clark, :1nd opens the circuit of relay224. The relay call indicator is now disconnected from the conductors 205 and 206 of the trunk circuit and the circuit of relay 200 is again established. Relay. 200 upon reenergizing closes a locking circuit for relay 228 over conductor 210 and establishes a direct shunt to ground around the winding of relay 228. Relay 228 thereupon deenergizes.

The operator noting the flashing of lamp 216 and the illumination of lamps of the call indicator, takes up the plug P of the trunk circuit corresponding to the flashing lamp 216 and in the well-known manner tests the sleeve of the jack of the line indicated by the indicator to determine if the desired line is idle and free to receive the desired connection. Under the assumption that the desired line B is idle, the operator inscris the plng- P in the jack J of the line, whereupon a circuit is established which may be 'traced from battery through the winding of relay 241, conductor 240, conductcr 289, conductor 238, the winding of rr' `r)20, conductor 87, `sleeve contacts of pli. l) and jacl; l and thenceto ground throlugh the winding of cut-olf relay 286 of the line B. Relays 236, 220 and 241 energize in this circuit, relay 220 establishing the continuity of the tip strand of the trunk circuit and opening the locking circuit of relay 218. Relay 218, upon deenergizing, now opens the circuit of relay 221, which in turn, opens the circuit previously traced eX tending through lamp 216 and interrupter Disconnect lamp 242 is not illuminated at this time as it is shunted by the winding of relay 241. y

Since at this time the oflice sender has completed its functions, advance relay 171 becomes energized in the manner set forth in the patentto F. A. Stearn and F. J. Scudder hereinbefore referred to, removing the shunt around resistance element 176. The current now Aflowing through the winding of relay 168 is reduced to such an extent that this relay de.-nergizes, opening the circuit of relay 181, which upon deenergizing, closes a circuit extending over cam contact 153 (7 to 8) and conductor 141 for advancing sequence switch 198 into position 10. The oflice sender is now restored in the well-known manner and disassociatedfroin the district selector switch 150, whereupon it is rendered available for use in establislr ing other connections.

y Vllith sequence switch 198 in position 10, relay 200 of the selected interotice trunk is energized over a circuit which may be traced from battery through its right-hand winding, conductors 201 and 202, the upper left-hand widing of repeating coil 208, conductors 204 and 205, bank terminal 167 and brush 165 of the district selector 150, cam contact 177 (10), the upper right-hand winding of repeating coil 178, the winding of polarized relay 179, the lower right-hand winding of repeating coil 178, cam contact 180 (10), brush 164 and bank terminal 166 of district selector switch 150, trunk conductors `206 and 207, the lower left-hand winding of repeating coil 203, conductors 208 and 209 and thence to ground through the left-hand winding of relay 200. Current flowing in this circuit while in such a direction as to energize relay 200, does not flow through the windings of polarized relay 170 in such a direction as to cause its effective energization.

The operator to call the subscriber B now depresses the ringing keyr 242 for connecting the source of ringing current 250 to the called line. In response to the application of ringing current, the called subscriber removes his receiver from its switchhook thereby establishing a circuit for the supervisory relay 243 which may be traced from battery through the lower right-hand winding of repeating coil 208, the winding of relay 243, conductor 244, the lower normal contact of ringing key 242, the ring contacts'of plug P and J, thence over the subscribers line loop, through tip contacts of jack J and plug P, the upper normal contacts of ringing key 242, conductor 245, conductor 246 and thence to ground through the ripper right-hand winding of repeating coil 203. Relay 243, upon energizing with relay 241 energized, establishes a circuit for reversing relay 247 which extends from battery through the winding of relay 247, conductor 248, conductor 249 and thence to ground at the armature contact oit' relay 241. Relay 247, upon energizing, reverses the connection ot the windings of relay 200 to conductors 205 and 206, respectively, whereupon current flows through the windings ot' polarized relay 179 in such a direction as to cause its effective energization. A circuit is now established at the district selector or relay 181 which may be traced from battery over contact 182 of the circuit interrupting cam 183, the winding of relay 181, cam contacts 183 and 184 of sequence switch 198, closed in position 10 and thence to ground at the contact of polarized relay 17 Relay 181, upon energizing, closes a locking circuit for itself independently o1 cam contact 182 and prepares a circuit for charging relay 168 which is etl'ective as soon as cam 183 moves to such a position as to cause the closure of its contact 185. Relay 168, upon energizing, closes a locking circuit for itself extending over the upper contacts of cam 169 and to ground through its own right-hand armature contact, and at its left-hand armature contact prepares a circuit over conductors 190 and 191 which is eiective for charging a call on the calling subscribers message register 112 following the termination of the conversation and the movement of the sequence switch 198 into position 17.

The calling subscriber A is now connected in a conversational circuit with the subscriber B over the conductors shown in heavy lines in Figs. 1 and 2, the calling subscriber receiving talking current through the lefthand winding or' repeating coil 178 and the called subscriber receiving talking current through the right-hand winding oit repeating coil 203. During the continued. establishment of the talking circuit, the supervisory relays 186 and 248 are maintained energized. Upon the termination of the conversation, the subscribers restore their receivers to their respective switchhooks, whereupon relays 186l and 248 become deenergized. Relay 186, upon deenergizing, closes a circuit extending over conductor 187 and cam contact 188 to 16) for advancing sequence switch 198 out of position and into position 16. As soon as sequence switch 198 leaves position 16.1-, the previously traced circuit for relay 110 is opened at cam contact 111, but relay 110 is maintained energized over a circuit extending from battery through its right-hand operating winding, conductor 191, the lefthand armature contact of relay 168, conductor 190, cam contact 189 (17), bank terminal 109 and wiper 105 of line switch 106 and thence to ground through the windings otl cut-ofi' relay 101 and message register magnet 112. Booster battery current is also connected through the winding of message register magnet 112 from booster battery, through cam contact 193 (17), cam contact 19J (17), the left-hand armature contact and lett-hand non-inductive winding of relay 110, conductor 191, the left-hand armature Contact ot relay 168, conductor 190 and thence to ground through the winding ot magnet 1.12 over the circuit previously traced. Magnet 112 now receives sutlicient current to cause its energization, thereby causing the registration ot a call on the calling subscribers message register.

)Vith sequence switch 198 in position 17 a circuit is now established for relay 131 which may be traced :trom battery through the winding ot' relay 131, cam contact 152 (17), and thence to ground through cam contact 154 (17). ltelay 131, upon energizing, closes a circuit over cam contact 142 (17), and conductor 141 for advancing sequence switch 198 out or' position 17 and into position 18. As soon as sequence switch 198 leaves position 17, the circuit previously traced through the windings ot' cut-olil relay 101 and the message register magnet 112 is opened at cam contact 189 and the circuits associated vwith the calling subscribers line and individual line switch are thereby rcstored to normal condition in the wel1-kno\\'n manner. lith sequence switch 198 in position 18 a circuit is now established tor thc downdrive magnet 194 extending through cam contact 195 (18) for energizing the downdrive magnet 194. This magnet upon energizing presses the depending portion o1 switch shaft 14o against the downdrive roller 199, thereby causing the downward movement of the switch shaft into normal position. As soon as the switch shaft reaches its normal position, shaft wiper 1-18 engages the normal commutator segment 196 anda circuit is established 'from ground ou sli-att wiper 148, through segment 196, cam contact 197 (18)` and over conductor 1-1-1 tor advancing sequence switch 198 into normal position. The circuits of the district selector are now in normal position.

As soon as sequence switch 198 leaves position 17, busy potential is removed 'from test terminal 158 o1 the selected interollice trunk and this trunk is made available tor other calls. Upon the movement ot the district selector switch 198 out ot position 10. thc circuit previously traced through the winding of trunk relay 200 is opened at cam contacts 1.77 and 180 and relay 200 deenergizes, opening Athe locking circuit of relay 228. Re-

lay 223, upon deenergizing,disconnects relay 2dr-1 trom the circuit` previously traced over the sleeve conductor 237 of the trunk in shunt ot the disconnect lamp 242 and the lamp now becomes illuminated over a circuit extending from battery through the lamp, the winding ot" relay 220, conductor 237, sleeve contacts ot plun- 1 and jack J to ground through the winding of relay 23o. The operator in position0 noting the illumination of lamp 242 removes the plug P from the jack J, whereupon the lamp 242 becomes extinguished and relays 220 and 236 become deenergized. All or' the` apparatus at the manual oiiice enualoyed in the establishment ot the connection is now restored to normal position.

1t at the time the operator at position 0 tests the jack ot the desiredline she finds the line busy, she inserts the plug P of the trunk circuit in a busy-back jack J of a group of jacks at her position tor the purpose of transmitting a busy back signal' to the calling subscribers line. Upon the insertion of the plug P in the jack J. a circuitis established from battery through the Winding of relay 241, conductor 240, conductor 239, conductor 238, the Winding of relay 220, sleeve conductor 237, the sleeve contacts of plug P and jack J, conductor 249 `and to ground through the Winding oi' relay 300. Relay 300, upon energizing in this circuit, establishes a circuit for the busy-backrelay 302 extending from battery at the armature contact of relay 305, over conductors 304e and 303. through the Winding of relay 302 and to ground through'y the busy-back interrupter 301. Busy-back relay 302 is intermittently operated in this circuit and at its left-hand armature and alternate contact establishes a connection from ground through the secondary Winding of tone coil 306 to the ring contacts of all busy-'back jacks of the group.

The circuit closed over the ring contact ofthe jack lf upon the operation of relay 302 may be tracedV from `ground through the secondary Winding of tone coil 300, the outer left-hand armature and contact of relay 302, ring conductor 307, ring` Contact of jack Ji, ring contact of plug P, the lower normal contact. .of ringing key conductor 244, the Winding of relay 243. the loiverright hand Winding ot repeating coil203 and thence to battery and ground. The intermittent closure ot this circuit through the operation ot. relay 302 causes the intermittent operation vof relay 24.3' and the intermittent reversal ot current through the Winding ot polarized relay 179 `at the district selector 1.50. Tone current which is also transmitted trom thei primary ot the tone coil 306 inductiyely into the circuittraced through the lower right-handwinding ot repeatingcoil-r203 ,is inductively transmitted over the interotlice trunlr through the righthand `Winding ot repeating coillTS and thence inductiif'ely to the calling subscribers line to apprise the calling subscriber ot the fact that the desired line is busy. y

The circuit closing periods ot the busybacl interriu'nter 301 are so designed that the intermittent periods during u iich polarized relay 17S) closes tue circuit ol" relay 181 at the district selector are ot such short duration that the circuit closing cani 183 does not havetinie to close the circuit@ or; charging relay 103 before relay 181 becomes unlocked and deenergized and thus the call i charging circuits ot the subscribcrs district selector are not conditioned tor charging'a. call on the subscribers message register.

rAt the busy-back circuit, relay 303 `is in.-

termittently operated through the rotation "f4 armature contact ot relay 303, conductor 3111, the Winding ot relay 313. conductor 312, conductor 311 and thence to battery, through the armature contact of relay 3107 which latter relay operates during a ringing interval ot' the ringing currentinterrupter 309. The energizing circuit of relay 310 may be traced from ground through the Winding of the relay, condenser 331, the ringing interrupter 300 and thence to ground through the ringing generator 319. Upon the energization ot relay 313 a circuit is established for relay which may be traced from battery throughthe Windingof relay 315, the right-hand armaturen and contact ofrelay 313,` the Winding ot relayv 313, conductor 3111. the armature and contact of relay 303 and thence to the permanent ground. Relay 315 noW prepares a circuit for relay 305 which may be traced 'from ground through the lettdiand armature and contact ot relay 313. the winding oit relay 305, conductor 316, the armature and alten nate contact of relay 315. conductor 311 and to the front. contact of relay 310 Which circuit is-closed upont-he next ringing period of the ringing interrupter 309.

Bela-32305, upon energizing. closes a locking circuit for itself.z extending from batteryithrough its right-hand armature vcoutact and Winding to ground at the lefthand armature and contact ot 4relay 313 and at its left.-liand armature and normal contact opens the circuit extending through thebusy-back relay 302 to prevent the operation of relay 30,211.14' the ei'entcthat an operator plugs into a busy-back jack of the group during the time that the busy back circuit is unstandard by reason of the permanent ground. By thus rendering the busy back circuit inoperative, a steady ground connection over the sleeve contact ot the busy-back jack is prevented and thus the false operation of a calling subscribers message register is obviated.

Instead of employing the ringing current interrupter 309 for timing the operation ot the chain ot relays 305, 313 and 315, any other Suitable timing device as a chain of slow acting delays might be employed.

Relay 305 upon energizing also closes a circuit from battery extending over conductor 318 to ground through the winding of alarm relay 317 for the purpose ot operating an alarm signal 322 at the chief operators position, an alarm 321 at the wire chiefs desk and for ringing a bell alarm 320 at the wire chiefs desk. The circuit for alarm bell 320 may be traced from ground through the bell magnet windings, the lefthand armature and contact of relay 317, the ringing current interrupter 309 and from ground to the source of ringing current 319. This inoperative condition of the busy back circuit is maintained through the operation of relay 305 until the proper steps have been taken to clear the trouble, when the circuit is again placed in operative condition.

Should a cross connection appear between the tip and ring contacts of any busy back jack of the group, then when an operator plugs into such jack thereby causing the energization of busy-back relay 302, a circuit is established for relay 324 which may be traced from ground through the winding of relay 324, the right-hand armature and contact of relay 302, the tip and ring contacts of the defective jack, the ring contact of plug P, the lower normal contact ot ringing key 242, conductor 244, relay 243 and thence to battery and ground through the lower right-hand winding of repeating coil 203. Relay 324, upon energizing, establishes a circuit for relay 325 which may be traced from ground through the armature and contact of relay 324, the winding of relay 325, condenser 332, ringing interrupter 309, and thence to ground through the ringing current generator 319. Dtelay 325 is intermittently operated in this circuit and at its armature and contact establishes an intermittent energizing circuit for relay 317, which in turn, causes the lamps 321 and 322 to be liashed. In response to these flashing signals, operators at either the chiel" operators position or wire chiels desk take the proper steps to have the trouble at the defective jack cleared. It is obvious that a permanent cross between the tip and ring contacts of the busy-back ack would cause a steady operation of relay 243 at the operators terminating trunk, which in turn, would cause the registration of a call on the calling subscribers message register.

Should a false ground exist on the ring conductor 307 ot any ack ol the group due to any cause such as a cross connection between the sleeve and ring or ring and tip contacts o't such jack, then when the operator plugs into one of the jacks this ground potential while el'ective to cause the energization ot' relay 243 irrespective of ground applied through the energization of relay 302, is ineffective to cause the continued operation of the supervisory relay 243 of the trunk circuit and the false charging of a call since at -this time and upon each deenergization otl busy-back relay 302 the ring conductors 307 of the jacks are connected to battery through the winding oi low resistance relay 353. The winding of relay 353 being of low resistance and being in shunt of the winding of relay 243 shunts the current away from relay 243 and prevents the continued energization thereof during the intervals that busy-back relay 302 is deenergized. Relay 353 energizes however and closes a circuit over conductor 354 for causing the intermittent operation of relays 325 and 317 and the flashing of signals 321 and 322. The flashing of signals 321 and 322 indicates that there is trouble on one of the busy-back jacks.

It a connection is extended to a trunk circuit at the operators position 0 through a semi-mechanical operators position, such as shown at 02 in Fig. 4, the op.- eration oit the busy-back relay 302 under the control of busy-back interrupter 301 causes the intermittent operation of the polarized relay 375 at the semi-mechanical position, which in the well-known manner, causes the flashing of a supervisory signal at the opzerators position 02. Likewise, it a call has been extended to the manual office from an originating manual office over a plug ended trunk circuit terminating in the terminating office at the operators position 0, the connection of such trunk circuit at such position 0 with the busy back circuit causes the intermittent operation of the busy back relay 302, which in turn, causes the flashing of a supervisory signal in the originati-ng office in the well-known manner. In the diagran'l in Fig. 4, the manner in which ,these three types of connections may be established to a terminating manual olhce havebeen sche-- matically disclosed. A calling subscriber, for example, may obtain connection directly with the terminating manual ofce over a line switch 106, district selector 150 and trunk circuit 205, 206 as illustrated in detail in Figs. 1 andf2, or through the district selector 150, the trunk circuit 350 and 351, the semi-mechanical cord circuit at the special liti Leonesa Q A operators position 02 and the district selector 352 in which the semi-mechanical cord circuit terminates. f

l/llhzit is claimed is:

l. ln a `telephone exchange system, calling subscribers lines, called subscribers lines, means comprising automatic switching .mechanism and plug ended trunk circuits ii'or establishing conncc ons between said lines, call charging means associated with said calling lines, and mechanism common to said til-unir circuits and associable therewith over the plugs thereoiC for trai'isinitting a busy si giial to a calling line if the called line is busy, said mechanism being ineffective to cause the operation ot the call charging n'ieaiis of said callingl line.

@..ln atelephone exchange system, a callin@ subsrribers line, a call charging device a tion, a trunk line extending to said position, a second operators position, a supervisory s' nal atvsaid latter position, a called subsci ecris line terminating in said rst operators position, means for extending a connection. lroin either said subscribers line or said second operatorie position to said called subscribers line, a busy baci; jack at said rst operators position and busy-back mechanism yassociated with said jack for transmitting a busy signal to said calling subscribcs line or to said sexond operators position iii said called vline is busy, said mechanism being' eiiective to operate said sional il' the connection is extended from id second operatorls` position4` but inefctive to operate sai call charging device kZ') l associated with said luie comprising a timed operating` mechanism, an operators position,

a trunk line terminating in said position,

a second opeiatons position, a called subcribci"s lineterminating in said iirst operatorie position, means for extending a conncction from either said subscribeils line or from said second opeiators position to said called subscribers line, a supervisory signal at latter operators position, a busy jack at said first operatorls position, and busy baci; mechanism `associated with said jack ifor transmitting a busy signal back over the established `connection if said called line is busy and tov intermittently completing an operating circuit for either said timed operating mechanism or said supervisory signal for periods sulhcient to operate said signal but iiisulicient to operate said call charging device.

e. ln a telephone exchange system, a call ing subscribers line, a called subscribers line, means comprising a plug ended trunk circuit for establishing a connection between viociatf-wl with said line, an operators posi-` eaid lines,y call charging means associated with said' calling line, group of lousy back jacks, a source of tone current, a relay associated with said jacks, means for intermittently operating said relay When said trunk circuit kis associated with one of said jacks foi' intermittently associating said source of tone current with said jacks and with said calling line, said intermittent application of said source ci tone current beineiective to operate said `call charging means.

, ln a telephone exchange system, a callsiibscribers line, a call charging device ociated with saidl line, an `opei'atoi"s lll 'po.ition, means for extending a connection from said line to said operators position, a Ualled subscribers line terminating in said opeiators position, busy back mechanism orassociation with id established connection it said called line is busy for transmitting a busy signal to said calling line and means for rendering said mechanism inoperative to transmit said signal if said mechanism in such an unstandaid condition as would erroneously operate said call charging device.

6. ln a telephone exchange system, acalliiig subscribers line, a `called subscribers line, means comprising a plug ended trunk circuit for establishing a connection between said lines, a call charging device associated with said calling line, means responsive to the answer of said called subscriber 'for preparing said call charging device for operation, a group of busy back jacks, a source of tone current, an interrupter, a relay associated with said jacks, means for causing said relay to be intermittently operated by said interruptor when said trunk circuit is associated with one ot said jacks for associating said source of tone current with said jacks and said calling line for periods of insufiicient duration to operate said call charging device and means for renderingr said relay inoperative to transmit said sig ual it a condition prevailsy at said interrupter such as would maintain said busy tone current associated with said calling line for a period suiiicient to operate said call charging device. y

7. ln a telephone exchange system, a calling subscribei"s line, a called subscribers line, means comprising a plug ended trunk circuit for establishing a connection between lines, a call charging device associated with said calling line, means responsive to the answer of said called subscribei1 for preparing eall charging device tor opera tion, a busy baci; mechanism for association with said trunk circuit fory transmitting a busy signal to said callingline if said called line is busy, but ineffective to operate said call charging device, means for rendering said mechanism inoperative to transmit said said icc

lll@ i signal if said mechanism is in an unstandard condition and means for giving an alarm signal until said unstandard condition is removed.

8- In a telephone exchange system, a calling subscribers line, a call charging device associated with said line comprising a timed opera-ting mechanism, a called subscribers line, means comprising a plug ended trunk circuit for extending a connection between said lines, means responsive to the answer of said called subscriber Jfor operating said call charging device, a busy back mechanism for association with said trunk circuit for transmitting a busy signal tosaid calling line if said called line is busy, but for periods less than the operating time of said timed operating mechanism and timing means effective upon an unstandard condition of said busy back mechanism to disconnect said busy baclr mechanism after a period less than the operating time of said call charging operating mechanism.

9. In a telephone exchange system, a calling subscribers line, a called subscribers line, means comprising a plug ended trunk circuit for establishing a connection between said lines, a call charging device associated with said calling line, means responsive to the answer ofsaid called subscriber for preparing said call charging device for operation, a busy-back jack, a source of busy tone current, a relay, means for causing said relay to be intermittently operated when said trunk circuit is associated with said jack for intermittently associating said source of current with said jack and said calling line an alarm device and means eiiective upon the operation of said relay if the tip and ring contacts of said jack are cross connected to operate `said alarm device.

l0. In a telephone exchange system, a calling subscribers line, a called subscribers line, means comprising a plug ended trunk circuit for establishing a connection between said lines, a call charging device associated with said calling line, a. relay associated with said trunk circuit responsive to the answer of said called subscriber for preparing said call charging device for operation, a group of busy back jacks, a source of busy tone current, a relay associated with said group y of jacks, means for causing said relay to be intermittently operated when said trunk circuit is associated with one of said jacks for intermittently associating said source of current with said jacks and with said calling line, and a low resistance relay adapted to be connected in shunt with said first relay and to be operated by a false ground on the ring contact of any one of said jacks for pre.- venting the operation of said call charging device.

1l. In a telephone exchange system, a calling subscribers line, a called subscribers line, means comprising a plug ended trunk circuit for establishing a connection between said lines, a call charging device associated with said calling line, relay associated with said trunk circuit responsive to the answer of said called subscriber for preparing said call charging device for op` eration, a group ofbusy back jacks, a source of busy tone current, a relay associated with said group of jacks, means for causing said relay to be intermittently operated when said trunk circuitis associated with one of said jacks for intermittently associating said source of current with said jacks and with said calling line, a low resistance relay adapted to be connected in shunt with said first relay and to be operated by a false ground on the ring contact of any one of said jacks for preventing the operation of said call charging device, and a signalling device under the control of said last named relay for indicating an unstandard condition of one of said jacks.

12. In a telephone exchange system, a calling subscribers line, a call charging device associated therewith comprising a timed operating mechanism, a called subscribers line, means comprising a plug ended trunk circuit for extending a connection between said lines, means responsive to the answer of said called subscriber for operating said call charging device, a busy-back mechanism for association with said trunk circuit for transmitting a busy signal to said calling line if said called line is busy but for periods less than the operating time of said timed operating mechanism, and a chain oi relays operative to disassociate said busybacl mechanism after a period less than the operating time of said call charging operating mechanism if said busy-back mechanism becomes permanently grounded.

In witness whereof, I hereunto subscribe my naine this lst day of April, A. D., 1921.

DAVID L. TEMPLE.

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