US1278245A - Telephone-exchange system. - Google Patents

Description

A. B. SPERRY.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED MAR 11:.

1,278,245. Patented Sept. 10,1918

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A. B. SPERRY.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED MAR. 30. I917. 1 ,278;245. Patented Sept. 10,1918.

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A. B. SPERRY.

TELEPHONE EXCHANGE SYSTEM.

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ARTHUR B. SPERRY, OF NEW YORK, N. Y., ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW/V YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed March 30, 1917.

To all whom it may concern:

Be it known that I, ARTHUR BRUCE SPERRY, a citizen of the United States, residing at New York, in the county of New York 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.

.his invention relates to telephone exchanges wherein line finders are apportioned to calling lines by an extended starter wire, and its object is to provide a circuit arrangement wherein when the starter wire is extended to the next idle finder through offnormal contacts associated with the intermediate busy finders, the restoration of such finders by the disestablishmentof the connections in which they are involved will not disrupt any starting circuit which v may at that time extend over such contacts to such idle finder.

In accordance with this invention a relay is associated with each finder, and the starter 7 leads to the stepping mechanism of such finder circuit over a back contact of such relay. Upon the initiation of a call and the consequent grounding of the starter wire, such stepping mechanism is operated to cause the finder to seek for and connect with the callin line. Upon making connection with the calling line a circuit is closed to operate said relay, which thereupon at its front contact extends the starter wire to the stepping mechanism of the next idle finder. To prevent the brea ing down of connections in which the intermediate finders and their corresponding relays are involved, over the front contacts of which relays the starter wire is extended to the stepping man-net of the finder being set, from deene Zing said relays and disrupt ing the starting circuit, each relay is provided with a locking winding connected to such front contact, and adapted to. hold such relays up as long as the starter wire is grounded, and since this ground is only removed when the finder being set reaches the calling line and operates its cut-relay, inter ference with the starting circuit by the re lease of intermediate finders is prevented.

Figures 1, 2, 3 taken together show a com-v pleted connection between a calling and led subscribers station;

Specification of Letters Patent.

Patented Sept. 10, 1918.

Serial No. 158,561.

A detailed description of the operations involved in setting up a connection will first be described, after which those parts of the circuits with which the invention is particularly concerned will beconsidered.

Upon the removal of the receiver at sub. station A, line relay 1.00 is energized. In attracting its left armature it creates a calling condition upon the multiple 101 of substation A in the finders in which suchline appears. In attracting its right armature, it energizes relay 102 over the following circuit to start a line finder in search of the calling line: free pole of battery, relay 102, armature and back contact of relay 10d, conductor 103, right armature and front contact ofrelay 100, conductor 161, to ground at the armature and back contact of relay 162, the function of which will hereinafter appear. Relay 102, in attracting itsupper armature, locks itself to conductor 103, independently of the right armature and back contact of relay 10 1, and in attracting its lower armature, applies ground to multiple segment 105 individual to the group of lines to which substation A belongs, and also closes the circuit of the primary magnet PM of the line finder as follows: ground, lower armature and front contact of relay 102, conductors 106, 107, armature and back contact of relay a, conductor 6, side-switch arm 110 and its first contact, armature and back contact of magnet PM, magnet PM, free pole of battery. This magnet makes and breaks its own circuit, thus rotating the finder brush shaft 153. The attraction of the lower armature of relay 102 also closes a circuit for relay 111 in parallel with that traced for magnet PM: ground, lower armature and front contact of relay 102, conductors 106 and 107, armature and back contact of relay a, conductor 113, relay 111, free pole of battery, Relay 111 connects the group brush 11 1- to the finder side-switch escape magnet ESC and interposes a break in the circuit of finder release magnet RM. At this time, however, the escape magnet does not operate since it is shunted over the path traced including the armature and back contact of magnet PM. Magnet PM energizes in the circuit traced and near the end of its stroke opens the shunt about the escape magnet, at which time the brush 114- is. in contact withgrounded group segment 105 and the escape magnet becomes energized over the following circuit: free pole of battery, magnet PM, magnet ESC, conductor 115, left armature and front contact of relay 111, conductor 116, brush 114, segment 105, to ground at the lower armature and front contact of relay 102. The escape magnet is V constructed to release the side switch from position 1 to position 2 upon its energization. In position 2, the escape magnet is maintained energized over the following circuit: free pole of battery, magnet PM, magnet ESC, armature and back contact of relay 117, arm 118 and its second contact, conductor 119, conductors 200, 201, left armatuge and back contact'of relay 202 to ground. In position 2, arm 110closes the following circuit for magnet SM to step the positioned finder brushes 120, 121, 122 over the multiples 123, 124 and 101 of the group to which substation A belongs: free pole of battery, magnet SM, its armature and back contact, armature and front contact of magnet ESC, arm 110 and its second contact, conductor 6, to ground at the lower armature and front contact of relay 102. When the test brush 122 reaches the multiple 101 of substation A, the following circuit is closed to operate test relay 117 to stop the line finder on the calling line: free pole of battery, left winding of relay 160, the function of which will hereinafter appear,

armature and back contact of said relay, left armature and front contact of relay 100, conductor 126, multiple 101, brush 122, relay 117 to ground. Relay 117 opens the circuit traced for magnet ESO, which becomes deenergized, and in retracting its armature, opens the circuit of magnet SM to'stop the finder on the calling line terminals. Magnet ESC, in deenergizing, releases the side switch into position 3. In position 3 arm 118 energizes the cut-off relay 127 over the following circuit: free pole of battery, right or left winding of relay 127, depending upon whether the substation A is a restricted or a non-restricted line, as will hereinafter more fully appear, conductor 126, contact 101, brush 122, arm 118 and its third contact, conductors 119, 200, 201, left armature and back contact of relay 202 to ground. Relay 127, in operating, deenergizes relay 100. The retraction of the left armature of relay 100 removes the calling condition from ductor 132, arm 133 and its third contact, conductor 134, arm 135 and its third contact, brush 121, terminal 124, through the telephonic apparatus at substation A, terminal 123, brush 120, arm 136 and its third contact, conductors 137, 138, left winding of relay 131, ground. Relay 131, in operating, energizes a slow relay 139. Relay 139, in attracting its right armature, interposes a break in the circuit of finder release magnet RM. This break is interposed before the relay 111 has retracted its left armature. In attracting its left armature, relay 139 closes the following circuit to energize slow relay 202 (Fig. 2) ground, left armature and front contact of relay 139, conductors 140, 203, 204, first selector sideswitch arm 205 and its first contact, relay 202, free pole of battery. Relay 202, in at tracting its left armature, closes the following circuit for release relay 206 which, in operating, connects the primary magnet PM to the back contact of the stepping relay 131. This circuit extends from ground, left armature and front contact of relay 202, conductors 261, 233, right armature and back contact of relay 221, contact and upper armature of release magnet RM, winding of relay 206 to free pole of battery. 'When the finder side switch moves into position 3, a distinctive tone is transmitted over the following circuit to the calling line to indicate to the calling party that the central ofiice apparatus is ready to receive impulses: free pole of battery, secondary windin 223 of tone source 224, relay 218, conductor 222, left armature and back contact of relay 221, conductor 220, .arm 219 and its first contact, lower armature and back contact of relay 209, conductor 225, right winding of relay 208, free pole of battery. This tone is transmitted by induction through the windings of relay 208 to the calling line over the following circuit:

ground, left winding of relay 208, conduc-.

tor 226, upper talking conductor 227, con denser 245, conductor 144, arm 136 and its third contact, brush 120, terminal 123, through the telephonic apparatus at substation A, terminal 124, brush 121, arm 135 and its third contact, conductor 134, arm 133 and its third contact, right winding of relay 131, free pole of battery.

The calling party now operates his sender S to transmit the first digit of the wanted number. In returning to normal, the sender interrupts the circuit traced a number of times, corresponding to the digit involved. Upon each retraction of the armature of relay 131, an impulse is transmitted to first selector stepping magnet PM over the following path: ground, primary off-normal contact PON, armature and back contact of relay 131, right armature and front contact of relay 139, arm 142 and its third contact, conductors 143, 207 (Fig. 2), left armature and back contact of relay 208, slow relay 209, arm 210 and its first contact, eonductor 211, left armature and front contact of relay 206, magnet PM, free pole of battery. Magnet PM, in response to these impulses, steps the selector brushes 212, 213, 21 1 into operative relation with the desi ed group of trunks 215, 216, 217. Relay 209, being slow to release its armatures, is maintained energized during the transmission of the impulses. In attracting its lower armature, this relay closes the following circuit for relay 218: ground, lower armature and front contact of relay 209, arm 219 and it's first contact, conductor 220, left armature and back contact of relay 221, conductor 222, relay 218, free pole ofbattery. Relay 218, in operating, closes the following circuit for the escape magnet 228 of the first selector, which magnet is constructed to re lease the side switch from position to position upon its deenergization: free pole of battery, magnet 228, arm 229 and its first contact, conductor 247, spring 248 and armature of relay 218 to ground. lVhen the sender S restores and maintains relay 131 energized, relay 209, after a slight interval, becomes deenergized, opening the circuit of relay 218, which, in denergizing, opens the circuit of the escape magnet 228, which, in releasing its armatures, passes the side switch to position 2 to initiate the trunk hunting operation. In position 2, escape magnet 228 is again energized over the following circuit: free pole of battery, magnet 228, arm 229 and its second contact, spring 230, now closed to its lower contact, to ground. Magnet 228, in attracting its armature, closes a self-interrupting circuit for the secondary stepping magnet SM of the first selector: free pole of battery, magnet SM, its armature and back contact, armature and front contact of magnet 228, arm 231 and its second contact, conductor 232, left armature and back contact of first selector release magnet RM, armature and back contact of relay 221, conductors 233, left armature and front contact of relay 202 to ground. Magnet SM thus steps brushes 212, 213, 21 1 over the selected group in search of an idle trunk. Test multiples 217 of busy trunks are grounded, as will hereinafter appear. Upon the first secondary step of the brushes, contact 230 is opened and the escape magnet is dependent for its continued energization upon the grounded test terminals 217 of busy trunks. When the first idle trunk is reached, the ungrounded condition of its test multiple 217 causes the deenergization of the escape magnet, which opens the' stepping circuit, thus stopping the selector upon such trunk, and in denergizing, passes the side switch to position 3.

1n position 3 ground is applied to the test multiples 217 of the seized trunk over the following circuit: brush 21 1, conductor 236, arm 237 and its third contact, right armature and front contact of relay 202 to ground. The application of this ground energizes release relay 300 in the connector (Fig. 3), which, in attracting its outer right armature, connects primary magnet 1 M of the connector to the upper talking conductor 301 to receive the tens impulses, and in attracting its left armature, interposes a break in the circuit of the connector release magnet E M The calling party now operates his sender S to transmit the tens digit of the wanted number. Upon each retraction of the armature of the stepping relay 131, an impulse is transmitted over the following circuit to the primary stepping magnet P M of the connector: armature of relay 131, now grounded, and its back contact, right armature and frontcontact of relay 139, arm 1 12 and its third contact, con ductors 1&3, 207, left armature and back contact of relay 208, relay 209, arm 210 and its third contact, conductors 23 1, 115, arm 14:6 and its third contact, conductors 147, 235, brush 212, terminal 215, conductors 301, 302, outer armature and front contact of relay 300, arm 303 and its first contact magnet P M free pole of battery. Magnet PM thus steps the brushes 304:, 305, 306 into operative relation with the group of terminals containing those of the wanted line 307, 308, 309. The slow relay 209 in the circuit traced for the primary magnet, became energized upon the first impulse, and remained energized during the transmission of the impulses. In attracting its lower armature, this relay closes the following circuit for the escape magnet 310 of the connector, which releases the connector side switch from position to position, upon its deenergization: ground, lower armature and front contact of relay 209, arm 219 and its third contact, conductors 238, 148, arm 1&9 and its third contact, conductors 150, 239, brush 213, terminal 210, conductors 311, 312, arm 313, upper armature and back contact of relay 314, escape magnet 310, free pole of battery, When the sender restores and maintains im' 1 else relay 131 energized, the slow relay 209, after a slight interval, becomes inert, opening the circuit traced for the escape magnet 310 which, in releasing its armatures, passes the connector side switch to position 2. In position 2, arm 303 substitutes the secondary magnet $9 M for the primary magnet P M in the stepping circuit. The calling party now operates his sender S to transmit the units digit of the wanted number. Upon each retraction of the armature of relay 131 an impulse is transmitted. over the circuit traced to the side-switch arm 303, thence to the secondary magnet S M free pole of battery, and as before, the slow relay 209, in attracting its lower armature, energizes the connector escape magnet 310 over sideswitch arm 313 and now by way of its second contact. The magnet S M steps the brushes 304, 305, 306 into engagement With the multiples 307, 308, 309 of the desired line. If the line is busy its test terminal 309 Will be grounded over a. brush 306, arm 316 and its third contact, and the left grounded armature of the relay 315, or such arm and its fourth contact and the right-hand lowresistance winding of the relay 315 to ground. In such event the left-hand highresistance Winding of relay 315 of the testing connector is shunted and does not attract its armatures. In passing out of position 2 connector side-switch arm 317 opens the circuit of relay 300. This relay thereupon becomes inert, and in retracting its left armature, closes the circuit of connector release magnet R M? as follows: free pole of battery, magnet R 17 conductor 318, left armature and back contact of relay 300, primary off-normal contact 319 to ground. The release magnet in energizing restores the connector to its normal position and also restores the side switch. Before contact 319 opens, however, as the brush shaft is restored, contact 320 closes, which results in a locking circuit being provided for magnet R M as follows: free pole of battery, magnet R M left armature and back contact of relay 300, conductor 321, contact 320, resistance 322, conductor 323, right armature and front contact of magnet R 1 release con ductor 325, terminal 217, brush 214k, conductor 236, arm 237 and its third contact, right armature and front contact of relay 202 to ground. Magnet R M at its left armature and front contact, closes the following circuit to produce a busy tone in the calling line to indicate to the calling party that the line desired is occupied: ground, secondary winding of source of busy tone current 326, left armature and front contact of magnet R h/ arm 327 and its first contact, condenser 328, arm 329 and its first contact, conductors 330, 311, terminal 216, brush 213, conductors 239, 150, arm 1&9 and its third contact, conductors 148, 238, arm 219 and its third contact, lower armature and back contact of relay 209, conductor 225, right winding of relay 208, free pole of battery. An induced current is created in the secondary winding of relay 208 included in the calling circuit. This circuit is the same as that traced for the dial tone. The calling party, upon hearing this busy tone, replaces his receiver. The replacement of the receiver deenergizes relay 131, Which, in retracting its armature, opens the circuit of slow relay 139. This relay after a slight interval releases its armatures. The retraction of the right armature closes the circuit of finder release magnet RM as follows: free pole of battery, magnet RM, conductor 151, right armature and back contact of relay 111, conductor 152, right armature and back contacts of relays 139, 131, contact PON to ground. The release magnet, in addition to restoring the finder brush shaft 153, also restores the side switch. The retraction of the left armature of relay 139 deenergizes relay 202. Relay 202, in retracting its left armature, opens the circuit of relay 206, which, in retracting its right armature, closes the circuit of first selector release magnet RM as follows: free pole of battery, magnet RM, right armature and back contact of relay 206, contact PON to ground. Magnet RM, in addition to restoring the selector brush shaft, also restores the side switch. When the shaft reaches its normal position, contact PON opens and deenergizes the magnet RM. The retraction of the right armature of relay 202, removes ground from conductor 236, which results in the de'elnergization of connector release magnet R M The apparatus is now all restored.

Assuming the selected line to be idle, full potential is present upon the multiple 309 thereof, and the test relay 315 becomes energized over its left-hand high-resistance winding, in the third position of the side switch. This circuit is as follows: ground, left high-resistance winding of relay 315, arm 316 and its third contact, brush 306, terminal 309, cut-oft relay of the selected line, free pole of battery. Both the cutoff relay and the relay 315 become energized in this circuit, the former removing the control of the line relay from the selected line in the well-known manner and the latter connecting the test multiples 309 directly to ground over its left armature to cause the selected line to test busy to other connectors. The attraction of the right armature of re lay 315 maintains slow relay 331 energized over the following circuit, this relay having been energized in position 2 over connector side switch arm 332 in parallel with the escape magnet 310: free pole of battery, relay 331, arm 332 and its third contact, right armature and front contact of relay 315, right-hand low-resistance Winding of relay 315 to ground. Relay 331, in attracting its armature, closes a locking circuit for relay 300 as follows: free pole of battery, relay 300, its right armature and front contact, conductor 333, right armature and front contact of relay 331 to the grounded third Wire 325. This circuit isclosed before the circuit including the arm 317 and its second contact is opened, as the side switch passes out of position 2. Thus the relay 300 holds its left armature attracted to maintain the connector release circuit open. In parallel with the relay 331 the escape magnet 310 is energized to apply ringing current to the selected line. The ringing circuit is as follows: free pole of generator 334, ringing cut-off relay 314, inner armature and front contact of magnet 310, arm 335 and its third contact, brush 305, terminal 308, bell 336, terminal 307, brush 304, arm 337 and its third contact, outer armature and front contact of relay 310 to ground. A portion of the ringing current flows over the following circuit to indicate by a characteristic tone to the calling party that the selected line is being signaled: ire-e pole of generator 334, relay 314, inner armature and front contact of magnet 310, conductor 338, arm 327 and its third contact, condenser 328, arm 329 and its third contact, conductors 330, 311, terminal 216, brush 213, conductors 239, 150, arm 149 and its third contact, conductors 148, 238, arm 219 and its third contact, lower armature and back contact of relay 209, right-hand winding of relay 208, free pole of battery. This tone is transmitted by induction through the windings of relay 208 to the calling line as before described.

When the called party removes his receiver, marginal ringing cut-off relay 314 becomes energized, opening the circuit of escape magnet 310 which, in deenergizing, passes the side swltch to position 4. In position 4 arm 316 connects the test multiples 309 to ground through the low-resistance right-hand winding of test relay 315 to maintain such line busy. Arm 332, in passing out of position 3, opens the circuit of slow relay 331. Before this relay retracts its right armature, however, arm. 317 reaches position 4 and reconnects release relay 300 to the grounded third conductor 325 to prevent release of the connector. The arm 329 reaches its fourth ontact before the right armature of relay 331 is retracted, which results in an impulse being transmitted over the following circuit to energize the called supervisory relay 208: ground, left armature and front cc. are; of relay 331, arm 3.99, and its fourth contact, conductors 330, 311, terminals 216, brush 213, conductors 239, 150,'a-rm 149 and its third contact, conductors 148, 238, arm 219 and its third contact, lower armature and back contact of relay 209, conductor 225, right winding of relay 208, free pole of battery. Relay 208. in attracting its right armature, closes the following circuit for the first selector escape magnet 228 1 ground, right armature and front contact of said relay, conductors 246, 240, left armature and back contact of relay 241, conductor 242, arm 229 and its third contact, magnet 228, free pole of battery. lVhen the impulse ceases and relay 208 retracts its right armature, the escape magnet in releasing its armatures, passes the side switch to position 4 in which position the called supervisory relay 208 is energized over the called line circuit as follows: free pole of battery, right winding of relay 208, conductor lower armature and back contact of relay 209, arm 219 and its fourth contact, conductors 238, 148, arm 149 and its third contact, conductors 150, 239, brush 213, terminal 216, conductor 311, arm 335 and its fourth contact, brush 305, terminal 308, through the telephonic apparatus at the called substation, terminal 307, brush 304, arm 337 and its fourth Contact conductor 301, terminal 215, brush 212, conductors 335, 147, arm 146 and its third contact, conductors 145, 234, arm 210 and its fourth contact, arm 244, conductor 226, left winding of relay 208 to ground. Relay 208, in attracting its left armature, permanently interposes a break in the impulse circuit to prevent the calling party from thereafter transmitting impulses to the magnets, and in attracting its right armature, closes a substitute circuit for slow relay 202 as follows: ground, right armature and front con tact of relay 208, conductor 246, arm 205 and its fourth ontact, relay 202, free pole of battery. Since relay 202 controls the release of the first selector and connector as described, the release of these switches is now controlled by the called party. The parties may now converse, talking current being supplied to the calling line over the windings of relay 131 and to the called line over the windings of relay 208, and the calling and called ends being inductively connected by condensers 245, 273.

Upon the termination of the conversation and the replacement of the receiver by the calling party, the finder is released as already described. The replacement of the receiver by the called party deenergizes rclay 208, which, in retracting its right armature, opens the circuit of relay 202. The retraction of the left armature of this relay deenergizes relay 206 as described in connection with a busy call, the deenergization of this relay causing the release of the first selector. The retraction of the right armature of relay 202 removes ground from the third wire 236, with the result that relay 300 becomes inert', and at its left armature and back contact closes the circuit of release magnet R M of the connector as described in connection with a busy call.

It is desirable in private branch exchange working to restrict some of the subscribers to local service and the circuit arrangement shown is such that when a restricted subscriber attempts to set up a call to a distant office, the selector switches are automatically released when set by such a subscriber in operative relation to the trunk group leading to such oflice. The cut-off relays of the restricted lines have a lower resistance than those of the non-restricted lines, and when, upon the removal of the receiver, one of the restricted lines has become extended to a first selector (Fig. 2) the marginal relay 262 thereat becomes energized and prepares the circuit of the release magnet of the first selector. The circuit for the relay 262 is as follows: free pole of battery, left-hand low-resistance winding of relay 127, conductor 126, terminal 101, brush 122, arm 118 and its third contact, conductors 119, 200, relay 262 to ground. WVhen the slow relay 209 releases its armature upon the termination of the first set of impulses, and the side switch moves into position 2, the grounded right-hand armature of relay 202 is extended over first selector side-switch arm 237, conductors 265, 2 50, brush 251 on first selector brush shaft 252, segment 253, with which it is now in contact and which corresponds to the selected outgoing trunk group, arm 254: and its second contact, armature and front contact of relay 262, conduc' tors 264, 263, release magnet Rl free pole of battery. The first selector is thus released when a restricted subscriber attempts to set up a prohibited connection- If the calling party sets the selector brushes in operative relation to the extra trunk group to which segment 9 belongs, the circuit of the release magnet is closed as described except that it leads from brush 251 to conductor 267 and thence to the front contact of relay 262.

Referring to that point in the operation when the calling line has been extended to an idle first selector, as shown in Fig. 2, it will be recalled that as the finder side switch moves into position 3 when the brushes of the line finder are stopped upon the calling line terminals the relay 131 becomes energized over the calling line circuit, and operates relay 139, which in turn operates slow relay 202, Fig. 2. The attraction of the'left armature of relay 202 energizes relay a, Fig. 1, to extend the starter wire (Z to the next idle finder. The circuit for relay a is as follows: ground, left armature and front contact of relay 202, conductors 261, 165, right armature and back contact of magnet RM, right winding of relay a, to free pole of battery. Relay a, in attracting its left armature, extends the starter wire (Z to the left armature of relay 0 of the next idle finder. This relay corresponds to relay a. Conductor I) connect left armature and front contact of relay, a, conductor 164-, left armature and back contact of relay a, conductor 7), side-switch arm 110 of such idle finder, primary magnet PM thereof, free pole of battery. This finder is thus started in motion and seeks the calling line in the manner described.

The conductor 164 is shown dotted to indicate a connection between the left hand winding of relay a and the left hand armature of relay a similar to the connection be tween the left hand winding of relay a and the left hand armature of relay a. In other words this connection, shown for convenience as a direct connection, in reality includes an armature and back contact of a group relay similar to 102 with which the relay a is normally associated.

In parallel with the circuit for the stenping magnet traced, the circuit referred to including the left winding of relay (0 is closed. Since this circuit will remain closed until the line is found or, in other words, as long as the starter wire (Z remains grounded, the relay a will be held up and will maintain the continuity of the stepping circuit independently of the circuit through the right winding of said relay, which circuit may be opened at any time by the deenergization of the relay 202 of the connecting circuit to which it belongs, due to the subscribers to such connection replacing their receivers. Upon the operation of the impulse relay 131 of such finder, and the resultant energiZ-ation of the slow relay 202 of the first selector 100 associated therewith, the relay (0 is energized over its right winding, and extends thestarter wire 164 to the left armature and back contact of relay 6& and conductor 71 leading to the primary stepping magnet of 105 the next idle finder. Thus, the starter wire is always maintained associated with an idle finder and the locking windings of the relays a of busy finders connected to the starter wires d, 16 1 so as to be held up by a call passing to a finder beyond, and until such finder is fully set, irrespective of any subsequent change in the condition of the con neoting circuits to which such intermediate finders belong. It may happen, however, that all the finders are in use when a call is initiated. In that event if the right armatures of the line relays 100 of the lines were connected directly to ground, as has been the practice heretofore, the initiation of such call would operate a starting relay 102 to ground starter wire (Z, which would look up all the relays a, a, etc., and so prevent any of such relays from releasing, so long as the subscriber initiating such call maintains his receiver off the switchhook. This circuit would in'that case be as follows: grounded conductor d, in parallel through the left windings of the relays a, a, etc., to free pole of battery. To prevent this, the slow relay iii) 162 is provided, and ground is connected to the right armatures of the line relays 100 through an armature and back contact of this slow relay. Vhen all the line finders are in use, a circuit is closed for relay 162 in series, through the right armatures and front contacts of relays a, a, etc. Relay 162, in attracting its armature, removes ground from the right armature of all line relays 100, thus preventing the operation of any such relays from operatingthe starting relay 102 which would close the locking circuit referred to. With the arrangement shown, and assuming all the finders are busy, the first connection broken down releases the corresponding relay a, which, it. retracting its right armature, deenergizcs slow relay 162. The right armature of said relay a, leaves its front contact before the armature of relay 162, which is slow to release, reaches its back contact, at which time only can the starting relay 102 be energized to ground the starter \116 (Z. But by this time the left armature of the said relay /1 has already reached its back contact and associated such starter wire with the primary magnet thereof.

lVhena connection is broken down, the relay 202, in deenergizing, opens the circuit through the right winding of relay 0:, as stated. The relay does not immediately deenergize, however, due to a substitute circuit closed at the right armature and front contact of the release magnet RM of the finder. This circuit is only opened when the finder fully restores, since the release magnet is locked up until such time over the primary oif-normal contact PON and its left armature and front contact. Thus, the starter wire (Z is not connected to conductor 6, and the finder cannot be started in operation until such finder has reached its normal position. Inasmuch as the selector is permanently associated with the finder. it is desirable that this switch be completely restored also, before the finder can be set in operation, and to accomplish this purpose the relay a is energized over the following circuit until the first selector has fully restored: free pole of battery, right winding of relay a, armature and back contact of magnet RM, conductors 165, 261, 233, lower armature and front contact of magnet RM eff-normal contact PON to ground.

The relay 160 is provided for the purpose of giving an alarm, in case the third wire 169 over which potential is applied to the multiples 101 becomes accidentally ground.- ed. When the line relay 100 energizes, upon the initiation of a call, and applies potential to the test terminal 101 through the left-hand low-resistance winding of relay 160, while this relay momentarily operates when the finder connects with the line over the circuit traced including side-switch arm 118 and its third contact and the left armature and back contact of relay 202 (Fig. 2), its circuit is immediately opened by the operation of the cut-off relay 127. In this event relay 160 is not energized long enough to cause the operation of a time alarm connected to conductors 166, 167. This time alarm may consist of any of the well-known arrangements. In case conductor 169 becomes accidentally grounded, relay 160, in attracting its left armature, will, after a predetermined interval, cause the operation of the alarm signal. This time alarm also is operated if the finder fails to connect with the calling line within a predetermined interval, the circuit for operating it in that event leading over the left armature and front contact of group relay 104. This relay is operated upon the initiation of a call due to the operation of group relay 102-, but the line is normally reached and the cut-off relay operated, and consequently relays 102, 10 1 rendered inert, before such predetermined interval has elapsed. In attracting its armature, it opens the shunt about its right-hand high-resist ance protecting winding, thus including the same in series with the low-resistance left winding.

What is claimed is:

1. In a telephone exchange system, the t combination with telephone lines, automatic finder switches, an extended starter wire, means for maintaining said starter wire extended to an idle finder, said means including an electromagnetic responsive device for each finder adapted when operated to advance the starter wire, a circuit for operating the device completed when connection is made with the calling line, and a locking circuit for said device including a front contact thereof and the starter wire.

2. In a telephone exchange system, the combination with telephone lines, automatic finder switches, an extended starter wire, means for maintaining said starter wire extended to an idle finder, said means including an electromagnetic responsive device for each finder adapted when operated to advance the starter wire, a circuit for operating the device when completed when connection is made with the calling line and maintained pending the connection, and a circuit prepared by the operation of said device and including a winding thereof and the starter wire to maintain the same energized and the starter wire extended, independently of the disestablishment of the connection involving the finder to which said device belongs, and means for closing said circuit upon the initiation of a call.

3. In a telephone exchange system, the combination with telephone lines, automatic finder switches, an extended starter wire, means for maintaining said starter wire extended to an idle finder, said means ineluding an electromagnetic responsive de vice for each finder adapted when operated to advance the starter wire, a circuit for op erating the device completed when connection is made with the calling line and maintained pending the connection, and a circuit prepared by the operation of said device and including a winding thereof, means for grounding the starter wire upon the initiation of a call, such grounding when such circuit is so prepared closing the same and maintaining the starter wire extended until the calling line has been found.

4. In a telephone exchange system, the combination with telephone lines, automatic finder switches, an extended starter wire, means for maintaining said starter wire extended to an idle finder, said means including an electromagnetic responsive device for each finder adapted when operated to advance the starter wire, circuits for operating said devices completed when connection is made with calling lines and maintained pending the connection, and circuits prepared by the operation of said devices and including windings thereof, means for grounding the starter wire upon the initiation of a call, such grounding when such circuits are so prepared closing the same in parallel with each other and with the stepping magnet of the finder to which the starter wire is extended to maintain the starter wire tended to such magnet until the calling line is found.

5. In a telephone exchange system, the combination with telephone lines,'means for interconnecting the same, including automatic finder switches, an extended starter wire, means for maintaining said starter wire extended to an idle finder including a relay for each finder adapted when operated to advance the starter wire, alternative circuits for said relay, means for closing one circuit when connection is made with the calling line by the finder to which such relay belongs and for maintaining the same closed pending the connection, the other circuit including a front contact of the said relay and the starter wire, means for closing the same upon the initiation of a call and for starting the next idle finder, and means for opening the circuit when the finder connects with the calling line.

6. In a telephone exchange system, the combination with telephone lines, means for interconnecting the same including automatic finder switches, an extended starter wire, means for maintaining said starter wire extended to an idle finder including a relay for each finder adapted when operated to advance the starter wire, said relay having two windings, alternative circuits for said relay, one closed when connection is made with the line by the finder to which such relay belongs and maintained closed pending the connection, and the. other including a front contact of the operated relay and the grounded starter wire. i

7 In a' telephone system, automatic finder switches, an extended starter wire, means for grounding the same upon the lllltliltlOIl' tablished, and a circuit including the starter wire, the stepping mechanism of the next idle finder and a front contact and the other winding of said relay, said circuit being prepared when said relay operates when con nection is made with the calling line.

8. In a telephone exchange system wherein an extended starter wire is employed to apportion idle line finders to calling lines, such wire being maintained in association with the stepping mechanism of an idle finder through normally open contacts associated with intermediate finders, the combination with the finders, the extended starter wire and a single means associated with each finder adapted to extend the starter wire and to maintain the same extended irrespective of the restoration of the intermediate finders.

9. In a telephone exchange system wherein an extended starter wire is employed to apportion idle line finders to calling lines, such wire being maintained in association with the stepping mechanism of an idle finder through normally open contacts of intermediate finders, the combination with the finders. the extended starter wire and a relay associated with each finder adapted to' 10. In a telephone exchange system, the

combination with telephone lines, a connecting circuit including an automatic finder switch having a release magnet, a relay as sociated therewith, a starter wire extending through a front contact of the relays of busy finders to an idle finder, means for operating said release magnets to disestablish the connections, and means for maintaining the relays energized until the finder brush shafts are fully restored.

11. In a telephone exchange system, the combination with telephone lines, automatic finder switches including release magnets, an extended starter wire, means for maintaining said starter wire extended to an idle finder including a relay for such finder adapted when operated to advance the starter wire, a circuit for operating said relay completed when connection is made with the calling line, and an auxiliary circuit for said relay including an armature and front contact of said finder release magnet.

12. In a telephone exchange system, the combination With telephone lines, means for interconnecting the same including an automatic finder and a selector switch, an extended starter Wire, means for maintaining said starter Wire extended to an idle finder 10 including a relay for each finder adapted When operated to advance the starter Wire, a circuit for operating the same completed When connection is made With the calling line, and auxiliary circuits for said relay including the armatures and front contacts of the release magnets of said finder and selector.

In Witness whereof, I hereunto subscribe my name this 29th day of March, A. D. 1917.

ARTHUR B. SPERRY.

Copies of this patent may be obtained for five cents each, by addresslngthe commissioner of Patents, Washington, D. 0.

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