US1356164A - Telephone-exchange system - Google Patents

Description

A. E. LUNDELL] TELEPHONE EXCHANGE SYSTEM. APPLICATION FILED JULY 14, 1917.

In venfo/afl/brn f. L unde/L A. E. LUNDELL.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED JULYM, 1917.

' Patented Oct. 19, 1920 3 SHEETSQSHEET a.

Alb; E. unde/L ALDEN EL LUNDELL, OF NEW YORK, N.

comrm, INCORPORATED, or new Yonx. a

Y., ASSIGNOR TO WESTERN ELECTRIC YORK, N. Y., A CORPORATION 02' NEW TELEPHONE-EXCHANGE SYSTEM.

Application filed July 14,

To all whom it may concern:

. Be it known that I, ALBEN E. LUNDELL, a citizen of the United States, residing at New York, in the county of Bronx and State of New York, have invented certain new and useful Improvements in Telephone- Exchange Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to a semi-automatic telephone exchange system in which stepby-step switches are utilized for the purpose of extending a connection from the calling to the called line, which switches are controlled by means of a sending device-operated by an operator in accordance with-the designation of the desired line. Switches of this .general character are well known and the-type which it is preferred to employ in connection with this invention 1s disclosed in an application of O. F. Forsberg filed February 5,1915, Serial No. 6,302, issued as Patent No. 1,252,420, Jan. 8, 1920. The sending device is also of a well-known character and the. type which it is preferred to use in connection with this invention is illustrated in U. S. patent to F. R. McBerty No. 1,075,430, patented October 14:, 1913.

.The control between the switchesand the sending device is preferably of the character known as the revertive impulse control, that is, impulses are impressed upon a circuit-extending between the sending device and the switch under control, which circuit is generally known as a fundamental circuit,

such impulses being produced in the movement of the switch under control.

When the proper number of impulses have been impressed on the fundamental circuit, the sending device is operated to sever such circuit and terminate the selecting movement of the switch. In addition to the selector switches and the sender, automatic Specification of Letters Patent.

1917. Serial no. 180,594.

ergization, or once for each deenergization.

or once for each energization and denergization of the stepping magnet.

The present invention has to do. more particularly with improvements in systems of the character outhned above, which improvements are directed to simplifying the circuits and reducing the amount of apparatus employed.

In accordance with a feature of the in vention, therefore, certain apparatus is arranged to perform in addition to its normal function, the functions heretofore performedby addition-a1 apparatus. In accordance with this feature of the invention, a relay, usually termed a line relay, is provided WhlCll, in addition to controlling the setting and selecting operations of a selector switch, 1s also arranged to render the release magnet of. the switch inoperative until the connection extended to suchswitch is disconnected, a function heretofore formed by an additional relay termed the trunk-keep relay.

In accordance with a further and related feature of the invention, a test relay is provided at a selector switbh, which relay is adapted to discriminate between busy trunk lines leading to private branch exchanges and busy direct lines. In the case of busy direct lines, such relay is ada ted to intermittently operate a si a1 be ore an operator indicating such act, whereas in case of busy trunk lines to intermittently operate a. stepping magnet to cause the switch to step to the next set of contacts.

Other features not s cifically mentioned will-appear from the ollowing description and claims. V

In the drawings, Figure 1 represents diagrammatically a portion of the equipment and circuits at. operators position includselector circuits; and Fig. 3 represents a Patented oct. 19, 1920.

.ing a cord' circuit and associated selector switch; Fig. 2 represents second and final sender circuit and cord finder for associatin such sender with a cord circuit.

The invention will best be understood by a description of the operation of extending a connection from a calling to a called line.

It will be assumed that a subscriber at the substation indicated at the left of Fig. 1 desires to communicate with the sub scriber Whose substation is indicated at the right of Fig. 2, and Whose number may be assumed as 1234. When the subscriber calls, the usual call lamp (not shown) is illumi nated, thus notifying the operator that a call is awaiting attention. The operator thereupon inserts a plug, such as 100, in the jack 101, such plug being 1nd1v1dual to one of several cord circuits associated with such operators position. As soon as the plug is inserted in the jack, the relay 102 which is associated with the sleeve of the plug, is energized in series with the cutoff relay 101, which is assoclated with the sleeve of the jack. The relay 102 closes a circuit for the sequence switch 103 extending from battery, through the motor magnet of sequence switch 103, contact 104 (position 1), front contact and armature of relay 102 to ground. There is one sequence switch of this character associated with each cord, and as such sequence switch serves to connect the operators telephone to the cord it is known as the listening key sequence switch. There is also associated with all the cords of the operators posi tion a common relay indicated at 105, the purpose of which is to prevent the simultaneous association of the operators telephone with a plurality of cords. The seuence switch 103 is arranged to stop in i our positions indicated as positions 1, 2, 4 and 7.

Position 4 is the so-called listening-in position because the operators telephone set is connected to the cord in such position at the contacts 106 and 107; and position 7 is known as the listening-out position because when the sequence switch reaches position 7, the operators telephone is disconnected at the contacts 106 and 107. There is also provided a listening-out key 108' and a listening-in key 109. When the sequence switch 103 is started in motion from position 1, due to the operation of relay 102, it will continue into position 4 provided the relay 105 is not energized, as the following circuit will then be established: From battery, through the motor magnet of se uence switch 103, contact 104 (position 23, backcontact and armature of relay 105. As the circuitof the relay 105 is multipled to contacts such as 110 on each of the listening-key sequence switches, if such listening key sequence switches are in positions 4 to 5;}, the relay 105 will be energized and all of the other sequence switches such as 103 will be be ond osition 2.

t wil be assumed, however, that the relay 105 is not energized and that the operators telephone is not connected to another cord, so that the sequence switch 103 will continue in movement until position 4 is reached, in which position the operators telephone set is connected to the cord at contacts 106 and 107, enablin the operator to communicate with the callmg subscriber in order to ascertain the number of the desired line. As soon as the sequence switch reaches position 4, however, a circuit is established or side-switch magnet 300, which is associated with the cord finder shown in Fig. 3. This articular side switch is arranged so that t e arms thereof are stepped forward oneste for each energization, and one step for eac deenergization of the side-switch magnet 300; therefore, when the circuit is established from battery, through the sideswitch magnet 300, conductor 111, contact 112 (position 4), slde-switch arm 113 (position 1), to ground, the cord-finder side switch is moved into position 2. In position 2 of the cord-finder side switch, a circuit is established for the motor magnet 301 of such cord finder, which circuit extends from battery, through the motor magnet 301, armature and back contact of such motor magnet, side-switch arm 302 (position 2), back contact and left-hand armature of the test relay 304 to ground. The side-switch magnet 300 is maintained energized over a circuit extending from battery, magnet 300, arm 303 (position 2), back contact and armature of test relay 304 to ground. The cord finder may be any well-known t pe of step-by-step switch which is adapted to be stepped either in a rotary or vertical direction over terminals associated with the cord circuits of a position. The motor magnet 301 when energized interrupts its own circuit at its armature and contact, and causes the stepping of the switch brushes indicated at 305, 306, 307 and 308 over the stationary terminals until a set of terminals such as 309, 310, 311 and 312 individual to the cord circuit which has been taken for use is encountered, in which case the test terminal 309 will be electrically distinguished from other similar test terminals, and the following circuit will be established for test relay 304: from battery, through the two windings of the relay 304 in series, right-hand armature and back contact of release magnet 313, brush 305, terminal 309, conductor 114, contact 112 (positions 2 to 6), side-switch arm 113 (position 1) to ground. The side-switch arm 113 forms a part of the first selector side switch, the actuating magnet for which is indicated at 115. The relay 304 is energized in this circuit and opens at its left-hand armature and back prevented from moving contact the previously traced circuit for the motor magnet 301, and thus stops the cord. finder with the brushes 305 to 308 thereof in contact with the terminals 309 to 312 of the particular cord which has been taken for use. In the meanwhile the operator having ascertained the number desired, has depressed the No. 1 key of the thousands row; the No. 2 key of the hundreds row; the N o. 3 key of the tens row, and the No. 4 key of the units row of her key set, and also depresses the start key indicated at 314. The operation of these keys will be without effect until the cord has been found,.and consequently the relay 304 has been energized.

Assuming that the cord finder has found the cord and the relay 304 has been energized,.the following :circuit will be established for the sender sequence switch 315: from battery, through the motor magnet of sequence switch 315, contact 316 (position 1)., contacts of the start key 314, conductor 317, front contact and left-hand armature of the relay 304 to ground, whereupon the sequence switch 315 moves into position 2. In position 2 of the sequence switch 315 the sideswitch magnet 115 of the first selector switch and the stepping magnet318 are included in series inthe so-called fundamental circuit, which circuit may betraced from battery, through the left-hand winding of the sideswitch magnet 115, contact 312, brush 308, sequence switch contact 319 (position 2), stepping magnet 318, back contact and outer armature of the No. 0 countin relay, sequence switch contact 320 (posltion 2) to ground. The first selector side switch is arranged so that it will be stepped forward only upon the denergization of the sideswitch magnet 115, so that the initial energization of the magnet 115 will not move the side switch. The side-switch magnet 11,5, however, closes at its right armatureand front contact a circuit for the rotary or brush choosing magnet 116 of the first selector, which circuit extends from battery, through the magnet 116, side-switch arm 117 (position 1), contact and righthand armature of the magnet 115, through remain energized, .but will intermittentl for each rotary stepof the brush sha shunt the stepping magnet 318.

As the No. 1 thousands key has been operated, upon the first energization of the stepping relay 318 through .the fundamentalcircuit, the No. 1 counting relay will be energized over a circuit which extends from battery, No. 1 counting relay, armature and back contact of the No. 1 countlng relay, the

- No. 1 thousands key, contact 122 (position 2) armature and contact of the stepping relay 318 to ground. The No. 1 counting relay closes a locking circuit from ground, through the right hand contact of sequence switch cam 321 and the windings of counting relays 1' and 1, to grounded battery. The winding of counting relay 1', being shunted through a path including the key contacts, contact 122 and the contact of relay 318, this counting relay does not become energized by the current flowing in the above traced looking circuit until the relay 318 becomes de- .energized and opens the shunt path. The

conductor leading to the contact of the #1 thousands key is now extended through the armature and front contact of counting relay 1' to the winding of counting relay 0. For this reason upon the next energization of relay 318 the counting relay 0' becomes energized and operates in thesame manner tact, also 'establishs a circuit extending from I battery, through the motor magnet of the sequence switch 315, contact 316 (position 2), contact and inner armature of the No. 0 counting relayto. ground, to drive the sequence switch 315 into position 4. In passing from position 2 to position 4, the contact 321-is opened, thus deenergizing all of its counting relays and restorlng the same to normal. In the meanwhile, as soon as the side switch of the first selector reaches po sition 2, a circuit is established for the sideswitch magnet 115, which-extends from battery, through left-hand winding of such magnet, through the side-switch arm 122 (position 2), vertical normal contact 123 to ground. The energization of the magnet 115 closes at its right-hand armature a circuit extending from battery, throu h vertical magnet 124, side-switch arm 11 (position 2), contact and-right armature of the magnet .115, through the interrupter 121 to ground. As soon as the switch has thus taken its first vertical step and the test brush 125 thereof is brought into contact .with the test terminal 126, if the trunk, to

which the test terminal is individual, is in use, a ground will be found upon such con-v the side-switch arms associated therewith to position 3, and in the opening of the previously traced circuit for the vertical magnet 124. As soon as the brushes 127 and 128 come to rest upon the terminals 129 and 130 of an idle trunk, provided the sender se-- uence switch has reached osition 4, the iundamental circuit is exten ded to the second selector switch, including the step ing magnet 318 and the relay 200 in series. his circuit may be traced from battery, through the relay 200, which at this time functions as a line relay, back contact and left armature of the side-switch magnet 201, side-switch arm 202 (position 1), the resistances 203, side-switch arm 204 (position 1), terminal 129, brush 127, side-switch arm 132 (position 3) terminal 310, brush 306, contact 320 (position 4), back contact and outer armature of the No. 0' counting relay, stepping magnet 318, brush 307, terminal 311, sideswitch arm 133 (position 3), brush 128, terminal 130, side-switch contact 205 (position 1), resistances 206 to ground. The relay 200 is energized in this circuit and at its lefthand armature and contact connects itself to the fundamental circuit, independent of the contacts of said switch magnet 201. At its right-hand armature the relay 200 closes a circuit for the side-switch magnet 201, which may be traced from battery through the right-hand winding of the side-switch magnet 201, side-switch arm 207 (position 1), right armature and contact of line relay 200, back contact and left-hand armature of relay 208 to ground. The side-switch magnet 201 is arran ed so that the sideswitch arms are'stepp d forward upon the release of such magnet so that the sideswitch arms will be unaffected by the initial energization of such magnet in .the circuit just traced. The magnet 201, however, closes, at its right-hand armature and contact, a circuit for the rotary magnet 209, which circuit extends from battery, through the magnet 209, side-switch arm 210 (position 1), contact and right-hand armature of the side-switch magnet 201, interrupter 211 to ground. The magnet 209 isintermittently energized in this circuit, and rotates the brush carrying shaft of the second selector switch, and at the same time, at its right-hand armature, placesa ground upon the fundamental circuit between the relay 200 and the stepping magnet 318, thus, for every rotary step of the brush shaft, the stepping magnet 318 is shunted, and, hence, deenerglzed. As, in the case assumed, the No. 2 hundreds key has been operated upon the initial energization of the stepping rela 318, the No. 2 counting relay is energize and after three shuntingsof the stepping magnet 318, the counting relays will operate in the well-known manner, until No. 0 counting relay is ener ized which, at its outer armature, opens the fundamental circult. When the fundamental circuit is opened, the relay 200 releases and causes the side-swltch magnet 201 to also release, which, in turn, moves the side-switch arms into position 2. In position 2 of the side switch a circuit is established for the side-switch magnet 201, which extends from battery, through right-hand windin of the sideswitch magnet 201, side-switc arm 212 (position 2), vertical normal contact 213 to ground. The side-switch magnet is energized in this circuit, and as soon as theswitch makes the first vertical step, is maintained energized, through the test brush 214, and test terminals 215 of busy trunks to ground.

Therefore, as long as the brush 214 makes contact with test terminals of busy trunks, the side-switch magnet 201 remains energized, and at its right-hand armature and contact maintains a circuit for the vertical magnet 235, and the brush carrying spindle continues to step vertically, but when a contact individual to an idle trunk is found, the side-switch magnet ping the side switch to position 3 and also opening the previously traced circuit for the vertical magnet 235 and hence stopping the switch. In the meanwhile, due to the energization of the No. 0 counting relay, se quence switch 315 is driven to position 6 over a circuit which extends from batte motor ma st of se uence switch 315, contact 316 position 4 inner armature and contact of the 0' countin relay to ground. When leaving position 4 t e sequence switch 315 opens the locking circuits for the countingI relays and restores them to normal.

'11 the particular system disclosed, means are provided for selectively signaling the plurality of stations on a single line. The selection of the proper ringing current is controlled in the brush choosin movement of the second selector switch. 7 e detailed operation of the second selector switch and apparatus associated therewith for accomplishing this function will be hereinafter described when the point of operation has been reached where it is necessary to signal the called party. Returning now to the operation 0 extending the call, as soon as the second selector side switch reaches posit1on 3, the slde-swltch magnet 201 is again 201 releases, step- I energized over a circuit which extends from battery, through the right-hand winding of cuitmay be traced from battery, relay 216,

outer left-hand armature and contact of the side-switch magnet 217, arm 218 (position 1, terminal 219, brush 220, conductor 221, arm 204 (position 3), terminal ,129, brush 127, arm 132 (position 3), terminal 310, brush 306, contact 320 (Position 6), outer armature and contact-o the 0 counting relay, stepping relay 318, brush 307, terminal 311, arm 133 (position 3), brush 128, terminal 130, arm 205 sition 3), resistances 206, to round. he relays 216 and 318 are energized in this circuit. In response to the energization of the relay 318, the No. 3 countlng relay is energized throu h the contacts of the operated tens key. Ihe relay 216 when energized closes at its up er armature and contact a circuit for itsel to the fundamental circuit, independent of the armature and contact of the side-switch magnet 217. At its lower armature-and upper contact the relay 216 closes a circuit for the side-switch magnet of the fi'nal selector switch 217, which circuit extends from battery, right-hand winding of the magnet 217, arm 221' (position 1), upper contact and lower armature of the relay 216 to ound. This side switch is arranged, owever, to step the arms-thereof forward only on the release of the side- 40 switch magnet so that the arms do not move at this time. The side-switch magnet 217, however, "closes a circuit at its inner lefthand armature for the rotary or brush choosing magnet 223, which circuit extends from battery, magnet 223, arm 224 (position 1), contact and inner left-hand armature of magnet 217, interrupter 225, to ground; Upon each operation of the rotary magnet 223 a ground is'placed on the fundamental circuit at the armature and contact of such magnet, short-circuiting the stepping magnet 318. In response to these repeated short-circuitings, the stepping magnet is energized and denergized, operating the counting relays in the usual manner until the No. 0 counting relay is operated, which relay opens the fundamental circuit at its outer. When the fundamental circuit is armature. opened the relay 216 is released, opening the magnet 217, causing it to release to step the final selector side switch in position 2. At the same time the No. 0' counting relay has closed at its inner armature and contact '65 a circuit to drive the sequence switch 315 previously traced circuit for. the side-switch into position -8, which circuit extends from battery, through the motor magnet of sequence switch 315, contact 316 ition 6), contact and inner a'maizure of di countin reaytogroun. n assmg' from si on 6' to position 8, thd sequence 'swi c h 315 opens the locking circuit at the counting relays and restores them to normal. As soon as the No. 0' counting relay is redored to normal and the sequence switch 315 reaches sition 8, the fundamental circuit s established identically as before, includmg the relay 216 and relay 318 in series. The relay 318 when energized at this time closes the circuit of the No. 4 counting relay throu h the operated units key; the relay 216 clbses a circuit bv way of its armature and contact, independent of the contacts of the side-switch magnet 217 and the sideswitch magnet 217 is also energized as before, through the u per contact and lower armature of the re ay 216, and the sideswitch arm 221 in position 2. In position 2 of the side switch the magnet 217 closes a circuit for the vertical magnet indicated at 226, which circuit extends from battery vertical ma et 226, arm 224 (position 2), inner le -hand armature and contact of 217, interrupter 225, to ground. Vertical magnet 226 is intermittently operated in this circuit, stepping the brushes vertically and at each operation, at its armature and contact, connects a ground to the fundametal circuit, short-circuiting the stepping relay 318. This operation continues until the counting relays have been operated in the usual manner, when the No. 0' counting relay is energized, opening the fundamental circuit and releasing the relays 318 and 216. The releave of the relay216 causes the release of the side-switch magnet v217, causing the final selector.side-switch to move into position 3.

As the function of the sender has now been completed before describing the further operation of the final selector switch, the release of the sender will be described. The No. 0' counting relay when energized closes a circuit to drive the sequence switch 315 out of'position 8 back to normal, which 115 circuit extends from battery, motor magnet of sequence switch 315, contact .316 ition 8),-inner armature and contact oi tlie No. 0 counting relay, to ground. In leaving position 8, the sequence switch 315 opens 120 a contact 319,'over which, from positions 5 to 8, the side-switch magnet 115 of the first selector has been maintained energized, over a circuit which extends from battery, through the left-hand winding of the side- 125 switch magnet 115, terminal 312, brush 308, contact 319 (positions 5 to 8), to ground. The release of the magnet 115 moves the side-switch arms into position 4. As soon as the first selector side switch reaches posi- '180 tion 4 the holding circuit for the relay 304 is interrupted at the arm 113, causing the relay 304 to release. As soon as the relay 304 falls back a circuit is established for the release magnet 313 of the cord finder, which circuit extends from battery magnet 313, arm 302 (position 3), back contact and lefthand armature of the rela 304, to ground, thus restoring the cord nder to normal, and disconnecting the sender from the operators cord circuit.

Returnin now to the final selector. When the final selector side switch moves into position 3, the side-switch magnet 201 is released, provided the relay 237 is not energized as will presently be described as the energizing circuit therefor is opened when the arm 231 leaves position 2. The release of the magnet 201 steps the second selector side switch into position 4. With the side switch of the final selector in position 3 a circuit is momentarily established for the relay 216 and the test relay 233, which circuit extends from battery, relay 216, contact and outer left-hand armature of 217, arm 232 (position 3), left-hand winding of the test relay 233, arm 234 (position 3), lower contact and lower armature of the relay 216, to ground. Relay 216 looks itself up through a circuit which extends from battery, rela 216, contact and upper armature thereo arm 236 (position 3), terminal 215, brush 214, arm 212 (position 4), to ground. Energization of relay 233 closes a circuit for side-switch magnet 217 extending from grounded battery, right winding of magnet 217, side-switch arm 221 in position 3, outer armature and. front contact of relay 233, contact 241 of relay 237, front contact and lower armature of relay 216, to ground. When the brushes of the final selector have been brought to the contacts of the desired line, any one of three conditions may be found upon the test terminals of such line, depending upon the character of the line. If the line is an ordinary direct line and is idle, battery potential will be found upon the test terminals thereof. If the line is an ordinary line and is busy or the last trunk of the group assigned to a private branch exchange, reduced battery potential will be found upon the terminals. If the line is an idle trunk leading to a private branch exchange an intermediate potential will be found on the terminal.

Assuming first that the line tested is an idle line or an idle trunk leading to a private branch exchange, the relay 233 will release as will also the side-switch ma et 217, and the relay 237 which is marginal will not be energized. Under these conditions the final selector side switch will be stepped into position 4 and the side-switch magnet 201 will also be released, stepping the side switch of the second selector into position 4. In the particular system diaclosed an arrangement is provided for signaling either direct lines or one party of a four-party line. The second group selector, as shown in Fig. 2, has access to two groups of final selectors. The party lines are multipled in both groups of final selectors so that if the connection is established to a given party line through one group of final selectors a different character of ringing current is impressed upon such party line from that which is impressed upon the same line when reached through the other cup of final selectors. Therefore, the particular brush chosen in the second selector in response to the designation set up on the sender determines the character of ringing current impressed on that line. This is accomplished as follows: the second group selector spindle is provided with an arm 250, which in the rotary movement of the brush carriage spindle passes over contacts and in alternate positions, as shown, makes contact with contacts associated with the ringing current, selecting relay 251. Thus, if the arm 250 is in contact with a contact such as 252, the following circuit is established for the relay 251: from battery, relay 251, contact 252, arm 250, side-switch arm 253 in position 4 to ground. This relay then locks up at its right armature and contact direct to the ground at the side-switch arm 253. If the arm 250, however, rests on any other contact than a contact such as 252, then the relay 251 is not energized.

Assuming then that the arm 250 is stopped in the position shown in reaching the particular line under consideration, then as soon as the side switches of the second group selector and final selector are in position 4, signaling current is projected on the line of the character necessary to signal the particular party on that line. In the case assumed this will be an alternating current superposed on positive intermittent current, and will extend from such source of ringing current, winding of the ringing cut-ofi' relay 254, left armature and back contact of relay 251, lower armature and upper contact of the relay 255, side-switch arm 228, position 4, brush 229, contact" 230, sideswitch arm 231, in position 4, brush 256, contacts of the line, throu h the bell on such line, back to the brush 25 side-switch arm 218, in position 4, terminal 219, brush 220, side-switch arm 258, in position 4, upper armature an d front contact of the relay 255, to ground. The relay 255 is energized when the side switch of second group selector reaches position 4 as follows: the relay 259 is operated in position 4 of the side switch over the following circuit: from battery, relay 259, upper left-hand winding of the repeating coil, side-switch arm 204 osition 4, terminal 129, brush 127, side-switc arm 132 tact and armature of the relay 259, to.

ground.

When the called subscriber responds the resistance of the ath of the ringing current is reduced su ciently, so that the relay 254 operates. The relay 254 in opening its contact removes the shunt normally existin around the relay 261 and permits such re ay to operate. The relay 261 in operatmg at its front contact shunts out the relay 255 and places the relays 260 and 261 in series.- As soon as the relay 255 is released, the talking circuit is extended to the called line, and the supervisory relay 262 is energized, and as the relay 260 is now energized a circuit is established for the supervisory relay 151 of the cord circuit, extinguishing the ordinary supervisory lamp 153 associated with the cord circult. The parties are now-connected for conversational purposes.

At the termination of the conversation, if the called subscriber hangs up first, the relay 262 is deenergized, opening the circuit of the relay 151 and in releasing lights the supervisory lamp 153, notifying the operator to take down the connection. on the operator takes down the connection the relay 102 is released, and in releasing closes a. circuit for the release magnet 149 of the first selector switch, which circuit extends from battery, through the release magnet 149, the off-normal spring 154, side-switch arm 155, in position 4, sequence switch contact 156, in positions 7 and 8, back contact and armature of the rela 102, to ground. This causes the releaseo the first selector switch and the restoration of the apparatus associated therewith to-normal. As the relay 260 at the second selector switch is still energized, the relay 208 at such selector switch is energized over a circuit which extends from battery, through the left-hand armature and front contact of the relay 260, relay 208, to ground. The energization of the relay 208 has resulted in the energization of the relay 200 over a circuit which extends from battery, relay 200, front contact and left-hand armature. of the relay 208, to ground, and in position 4 of the side switch, the relay 200 is maintained energized-over a circuit which extends from battery, relay 200, contact and left-hand armature of the relay 200, side-switch arm 202 in position ,4,

to ground. When, however, the first selector switch is restored the energizing circult of the relay 259 is interru ted, opening the previously traced circuit or the relay 260.

The relay 260 in releasing releases the relay 208. With the relay 208 released and the re lay 200 energized, a circuit is established for the release magnet 263 of the second selector switch, which circuit extends from battery, winding of relay 263, side-switch arm in position 4, contact and right-hand armature of the relay 200, back contact and lefthand armature of the relay 208 to ,und. This causes the release of the secon selector. hen the second selector releases the looking circuit for a'line and trunk keep relay 216 of the final selector is broken,.causmg such relay to release. When this occurs a circuit is established for the release ma net264 of the final selector, which exten s from battery, through the release magnet 264, off-normal contact 265, side-switch arm 234, in position 4, to ground. This restores the final selector to normal and all of the apparatus utilized in establishing the call is now restored to normal.

If the particular line to which the final selector has been directed had happened to be a trunk leading to a rivate'branch exchange, and such trunk ad been busy, an

intermediate potential, as before explained, would have been present uponthe test contacts. As the relay 237 is marginal, it will not be energized under these conditions, but the relay 233' will be maintained energized over a circuit which extends from battery, through the right hand winding of such relay 233, right-hand winding of the relay 237, the front contact and inner armature of the relay 233, side-switch arm 238, in position 3, test brush 239, terminal 240 through a resistance to ground. The side-switch magnet 217 will also remain energized over a circuit which extends from battery, through the right-hand winding of the side-switch magnet 217, side-switch arm 221 (position 3), outer armature and contact of the relay 233, contact 241 of relay 237, lower armature and upper contact of rela 216 to ground. Therefore, the side switc will remain in position 3', and as the side-switch I magnet 217 is energized, the following circuit will be established for the vertical mag net 226 of the final selector: from battery,

through the magnet 226, back contact and right-hand armature of the relay 237, sideswitch arm 224, in position 3, inner lefthand armature and contact ofthe magnet 217 interrupter 225, to ground. Therefore, the final selector will continue to step vertically until a contact is reached individual to an idle trunk leading to a private branch exchan e, or until the last of such trunks is reache If an idle trunk is encountered the test relay 233 will release and will release the side-switch magnet 217, and the final selector will be stopped, and ringing will take place identically as described in connection with an idle line. If, however, no idle trunk is available the same condition will exist on the terminals of the last private branch exchange as exists upon the terminals of a busy directline, and the operation of the system will be the same as though the test brush of the final selector had been directed to a busy directline, so that it is only necessary to describe this operation in connection with a busy direct line, which will now be done.

If a line is a busy direct line, the lowest potential will be present upon the test terminal, and the relay 237 will operate in series with the test magnet 233, it being remembered that the side switches of the second selector and. of the connector are then in position 3. The side switch of the second selector, however, will be held in position 3 momentarily over a circuit which extends from battery, through the side switch magnet 201, side-switch arm 228, in position 3, brush 229, terminal 230, side-switch arm 231, in position 3, front contact and right hand armature of relay 237, side-switch arm 224 in position 3, inner left-hand armature and contact of the side-switch magnet 217,

' interrupter 225, to ground. The magnet 237 when once energized, due to the reduced potential on the test terminal of busy lines, will be maintained energized over a locking circuit closed at its left-hand armature and front contact, which circuit extends from battery, through the right-hand winding of the side-switch magnet 217, side-switch arm 221, in position 3, left-hand winding of the relay 237, left armature and front contact thereof, the upper contact and lower arma-F ture of the relay 216, to ground. Therefore, upon the first opening of the interrupter 225, the side-switch magnet 201 will release, and the side switch of the second selector will be moved into position 4. As the side-switch magnet 217 and the magnet 237 are maintained energized as long as the relay 216 is energized, a circuit is established for the supervisory relay262, which circuit will extend from battery, repeating coil, to the lower right-hand winding of the repeating coil, relay 262, lower contact and armature of the relay 255, side-switch arm 228, in position 4, brush 229, contact 230, side-switch arm 231, in position 3, front contact and righthand armature of the relay 237, side-switch arm 224, in position 3, inner left-hand armature and contact of the side-switch magnet 217, interrupter 225, to ground. The intermittent operation of the relay 262 causes, over the circuit previously traced, the intermittent operation of the relay 151, which causes the flashing of the lamp 153, notifying ,the operator that the line is busy. The

operator thereupon repeats this information to the calling subscriber and removing the plug 100 from the jack 101 releases the connection and apparatus identically as in the previously described case, with the exceptlon that the release of the relay 216 after the release of the second selector causes first the release of the side-switch magnet 217 and the relay 237, stepping the final selector side swltch into position 4,. in which position the release magnet 264 is energized, restor in thefinal selector.-

hat is claimed is: 1. A telephone exchange system comprising a plurality of link circuits over which a connection may be extended to an automatlc selector switch, a control circuit for sa d selector switch including said link circuits, a motormagnet and a release magnet for such selector switch, a control relay normally included in said control circuit for the purpose of controlling said motormagnet, and means for placing said control relay under the control of apparatus associated with one of said link circuits independently of said control circuit for the purpose of controlling the release magnet of the selector switch.- A

2. An automatic telephone exchange system comprising a plurality of link circuits adapted to be associated for the purpose of extending a calling line to a selector switch associated with oneof said link circuits, a pair of conductors included in such link, circuit over one of which a selector switch is adapted to be controlled, a control relay at such selector switch, means for associating such control relaywith one of the conductors of Such link circuits for the purpose of controlling the selective operation of the selector switch, and means for associating such control relay with an additional conductor of such link circuits for the purpose of controlling the release of the selector switch.

3. In an automatic telephone exchange system, a selector switch having access to direct lines and to trunk lines leading to a private branch exchange, a motormagnet for said selector switch, a testing circuit associated with such selector switch, a relay included in such test circuit, said relay being arranged to respond only to the electrical potential on the test terminal of busy trunk lines leading to private'branch exchanges and test terminals of busy direct lines, and means controlled by the response of said relay for intermittently operating a busy signal and by the non-response of said relay for intermittently operating the motormagnet of said selector switch.

4. In a telephone exchange system, an automatic selector switch, a motormagnet and a release magnet for said switch, a control device, a control circuit extending from said control device to said switch, a relay at said switch normally included in said control circuit and adapted to be energized when said control circuit is established, a circuit for the motormagnet of the switch established when such relay is operated, means conqing said relay, and means controlled by the trolled in the operation of the motormagnet release of said relay for removing it from the to impress impulses on said control circuit control circuit and for placing said release 10- at a point between said relay and said conmagnet under the control of said relay.

5 trol device to operate-said control. device, In witness whereof I hereunto subscribe means forming a part of said control device my name this 11th dag of Jul -A. D. 1917. for opening said control circuit and releas- ALB N E. L NDELL.

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