US1471017A - Telephone-exchange system - Google Patents

Description

Oct. 16 1923.

S. B. WILLIAMS, JR

TELEPHONE EXCHANGE SYSTEM Filed Nov. 25 1919 4 Sheets-Sheet 2 W F N ma/enior Oct, 16 1923. 1,471,017

5. B. WILLIAMS, JR

TELEPHONE EXCHANGE SYSTEM 7 Filed Nov. 25. 1919 4 Sheets-Sheet a 4y 7 Any Get. 1.6 1923.

S. B. WILLIAMS, JR

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UNITED STATES PATENT OFFICE,

SAMUEL B. WILLIAMS, JR, OF BROOKLYN, NEW YORK, ASSIGNOR '10 WESTIERN iELEC- TRIC COMPANY, INCORPORATED, OF'NEW YORK, N. Y., .A. CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed November 25, 1919. Serial No. 840.542.

To all whom it may concern Be it known that I. SAMUEL B. WILLIAMS,

Jr.-, a citizen of the United States, residing at Brooklyn, in the county of Kings, 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 telephone exno change systems employing machine switch ing, and more particularly to private branch installations wherein connections may be made between stations within the private branch installation, or between'such stations 1 and a central ofiice.

In many business houses where the greater part of the calls are made between substations within the private branch exchange, the number of central ofiice calls is not sulficient to occupy the full time of an operator. It is, however, desirable to have provision made for answering incoming central oifice calls, for iving information to persons calling WitlilIl the branch exchange, and for supervising certain outgoing central ofiice calls. Toprovide such service has in the past required either a switchboard and operator at the branch exchange or else a far greater number of central oflice trunk circuits than the number of calls between branch exchange stations and central ofiice stat-ions warranted.

It is the object of this invention to pro vide such serviceat the branch exchange without either a full time operator or an unnecessarily large number of central ofiice trunk circuits.

According to one feature of the invention one or more substations hereinafter termed receiving stations, having no special equipment, are designated to provide operator service. These substations may be those of certain clerks whose incidental duty it is to answer calls either from the central ofiice or from stations within the branch exchange when information is desired. Inasmuch as it requires only a small portion of the time of one of these clerks and as she need have no special equipment other than an ordiiary telephone subset provided with a simple cal ing device, it is possible without undue expense to have an intelligent personanswer incoming central oflice calls, which is a great advantage to a business.

According to another feature of the invention a trunk circuit is provided which terminates in four places, namely an operators position at the central ofiice, a nonnumerical switch having access to receiving stations, the bank termlnals of branch exchange final selector switches and the brushes of companion final selector switches at the branch exchange.

Still another feature of the invention is y the provision of a trunk circuit terminating in only three of the previously named points, all within the branch exchange, namely, a non-numerical switch having access to receiving stations, the bank contacts of final selector switches and the brushes of companion final selector switches.

Referring to the drawings, Figs. 1, 2 and 3, with Fig. 2 to the right of Fig. 1 and Fig. 3 above Fig. 2, show diagrammatically the c1rcu1t-s employed in completing connections between various substations within the branch exchange and between such stations and a central ofiice.

Fig. 4 shows partly schematically and partly diagrammatically all the possible types of connections in this systemwhen the number of branch exchange substations is small; and Fig. 5 is a simplified diagram of the connections in a system of this character when the number of branch exchange substations is great enough to re uire the use of first selector switches in addition to final selector switches.

To the left of the dotted line in Fi .1, a substation ,A and a line finder switc 100 with circuits therefor are shown. In the dotted left-hand lower corner of Fig. 1 are shown relays individual to the group of line finders which have access to the substation A. To the right of the dotted line in Fig. 1 and to the left of the dotted line in Fig. 2, is shown a final selector switch 200 with the three types of circuit terminals on which it may be set. To the right of the dotted line in Fig. 2 isa trunk circuit linking the final selector terminals with a nonnumerical or hunting switch 25 and a comnumber of lines in the exchange.

panion final selector switch 20. In Fig. 3 is another trunk circuit similar to the one in Fig. 2, but also leading to multiple jacks at a central office, one of which is indicated within the dotted rectangle.

Figs. 6 and 7 represent a detail of the circuit of Fig. 1 and show the alternate connections of the cut-off relay. Fig. 6 represents the connection when the associated line is a restricted service line and Fig. 7 represents the connection when the service of the associated line is not restricted.

The receiving station F shown in Fig. 3 is provided with a cordless board but it will be apparent from the description hereinafter that it performs no function which may not be done just as well by a station such as E.

The structure of the line finder, final se lector, and companion final selector switches may be of the type fully disclosed in the patent to Forsberg No. 1,252,420 of January 8, 1918, but it IS understood that these switches might be of any well known type.

In Fig. 4 are shown banks of terminals divided into levels 400, 401, 402, 403 and 404 to which substations A, B, C, D and receiving stations E and F are connected. Additional levels of bank terminals, not shown, may be provided in accordance with the Each heavy dot, 31, 32 represents a set of terminals and each line 405, 406 represents a set of conductors making up trunk circuit.

. Line finder switches 100, final selector switches 200, and two kinds of companion final selector switches 20 and 300 are arranged to engage with their brush sets one of the multiple terminal sets of any line in any level. Non-numerical or hunting switches 25 and 30 are arranged to hunt over the level 402 which leads to receiving stations E and F.

It willthus be seen that any subscriber may by initiating a call have his line picked up by a line finder 100. By operating his calling device he may set a final selector 200 in its primary movement so that one of its brush sets 407 or 408 will be ready to travel over a group of terminals in any level of the bank. If he has chosen a level 402, 403 or 404 he may then direct the switch 200 in its secondary movement to any line in that level when a call will be complete to the wanted subscriber. If the subscriber sets the final switch 200 in its primary movement on level 400 it will in its secondary movement hunt an idle central office trunk 406. If he has chosen level 401, however, the switch 200 will in its secondary movement automatically select an idle trunk 405 and the hunting switch 25 will select an idle receiving station E or F. If the calling subscriber desires the call extended, the receiving subscriber operates his calling de vice to set the companion final se ector switch 20 on any desired level of terminals. The switch 20 may be set directively on the terminals of any station in the branch exchange, or it may be directed in its primary movement to the central oflice level 400, when in its secondary movement it will antomatically select an idle trunk 406.

Provision is made for restricting certain substations to interior calls, so that if a subscriber at one of these stations should set a final selector 200 on level 400, a connection would be completed through auxiliary brush 201 and the commutator segment 202, individual to the central ofilce level, to restore the switch. All subscribers may have unrestricted connection with a receiving station however, and the receiving subscriber may at his discretion extend such connections either within the exchange or to the central office.

Incoming calls from the central oflice go 'over the trunk circuit shown in Fig. 3 to a hunting switch 30 which connects them with an idle receiving station F. The receiving subscriber having inquired and found out what is wanted, may then set the companion final selector switch 300 to complete the connection with a desired substation. As soon as the companion final selector switch is set the switch 30 is restored to normal leaving the receiving station ready for the next call.

In Fig. 5 are shown the possible connections in a branch exchange employing both first and final selector switches. Either an ordinary substation A or a receiving station E will, upon the initiation of a call, be seized by a line finder 100 and connected to a first selector 500. The subscriber, by operating his calling device then sets the selector 500 in its primary movement on either a level 401 leading to a trunk circuit such as that shown in Fig. 2, a level 400 leading to a trunk circuit such as that shown in Fig. 3, or on the particular level 501 leading to final selectors 200 in whose banks are terminals of the wanted line. If he has chosen a level 501, an idle final selector 200 is automatically selected in the secondary movement of the switch 500. By operating his calling device the subscriber may then directively control the final selector 200 in both its primary and secondary movements to complete a connection with the wanted subscribers line within the branch exchange. If he has chosen a level 400, the selector 500 will in its secondary movement select an idle gunk circuit 406 leading to the central of- If the subscriber A sets the first selector 500 on level 401, an idle trunk circuit 405 will be selected in the secondary movement of the switch 500,. whereupon a hunting switch 25 will pick out an idle receiving subscriber E. The receiving subscriber by operating his calling device may then set another first selector 500 on either of the three levels 501, 400 or 401. If the switch 500 is set on a level 501, the connection will be completed to any wanted substation within the exchange through a final selector switch 200 in the same manner as when the calling subscriber made such a call without-the intervention of a receiving subscriber. When the switch 200 has been set the hunting switch 25 releases to leave the receiving subscriberxready for the next call.

Calls coming in from the central office cause a hunting switch 30 to select the line of an idle receiving subscriber E who answers the call. Having found that an extension of the connection is desired he operates his calling device to set the first selector switch500 on terminal 501 and then re-opcrates the calling device .to set switch 200 on the terminals of the wanted subscribers line. The hunting switch 30 releases as soon as the switch 200 is set.

Having described the general circuit arrangements it is believed that the invention will be readily understood from a detailed description of the setting up of the various possible connections.

I m'tz'atz'o'n; of a call by a private branch ea:- change .mbscm'bcr and the primary settz'ng of the final selector switch.

When the subscriber at A lifts his receiver off the hook he operates a line relay 101 over a circuit from grounded battery, right-hand winding of relay 101, back contact and inner armature of relay 114, conductor 115, substation A, outer armature and back contact of relay 114, left-hand winding of relay 101 to ground. Relay 101 in attracting its left-hand armature creates a calling condition upon the multiple 116 of substation A in the finders in which such line appears. In attracting its right-hand armature, relay 101 completes a circuit from ground, its right-hand armature and front contact, conductor 104, back contact and armature of relay 102, through the winding of relay 103 to grounded battery. Relay 103 is energized in this circuit, and locked up from grounded battery through its winding, front contact and left-hand armature over the circuit previously traced. Relay 103, in energizing, places a ground on commutator segment 105 individual to the group of lines of which substation A is a member. A circuit is now completed from grounded battery, righthand winding of release control relay 120, conductor 121, side switch arms 122 and 123, first position, conductors 124, 109 and 108, back contact and left-hand armature of relay 107, conductor 106 to ground at the right-hand armature and front contact of relay 103. Rela I 120 is energized in this circuit and is 100 ed up over a circuit from grounded battery through the right-hand winding, armature and front contact of relay 120 over conductor 108 and the circuit just traced to ground at the right-hand armature of relay 103. A circuit is also completed from ground, front contact and right-hand armature of relay 103, conductor 106, left-hand armature and back contact of relay 107, conductor 108, conductor 109, side switch arms 110 and 111, first position, back contact and arma ure of magnet 112 through the winding of primary magnet 112 to grounded battery. Primary magnet 112 interrupts its circuit and steps the brushes 117, 118 and 119 around until the group of lines containin station A is reached. When the finder brus es reach the group in which the call originated, a circuit is completed from ground, spring 125, commutator segment 105, brush 113, conductor 126, back contact and right-hand armature of relay 107, side switch arm 127, first position, conductor 128 through the windings of the slowto-release escape magnet 129 and slow-torelease primary magnet 112 to grounded battery. Magnet 129 is shunted at this time by ground at the armature of primary magnet 112, but when this armature opens near the end of the step, magnet 129 is energized to advance the finder side switch to position 2. The circuit for primary magnet 112 is now broken at side switch arm 111 and the switch stops with a brush set in position to traverse the calling group of lines.

Magnet 129 is held energized in position 2 of the side switch over a circuitleading from grounded battery, winding magnet 11.2. winding magnet 129, conductor 128, side switch arm 127, second position, back contact and armature of relay 130 to ground; but magnet 112 is marginal and will not en-- ergize in this circuit. A circuit is now completed from grounded battery, winding of secondary magnet 131, armature and back contact of this magnet, conductor 132, inner left-hand armature and front contact of relay 120, side switch arms 123 and 122, second position, conductor 128 in parallel with the circuit for magnet 129 previously traced to ground at the back contact and armature of relay 130.

Secondary magnet 131 in energizing interrupts its circuit and steps the brushes 117 118 and 119 to the terminals 116, 133 and 134 of the calling line. \Vhen this line is reached a circuit is completed from grounded battery, resistance 135, front contact and left-hand armature of relay 101, conductor 136, terminal 116, brush 117 side switch arms 111 and 110, second position. through the windingof relay--to ground. Relay of relay &

previously traced for escape magnet 129. This magnet in releasing passes the side switch arms into position 3.

In position 3 of the side switch the cut-off relay 114 is operated over a circuit from grounded battery through the left or both windings of relay 114 (see Figs. 6 and 7), according as the line A is a restricted or a non-restricted line as will appear more fully hereinafter, terminal 116, brush 117, side switch arms 111 and 110, third position, through the winding of relay 196 to ground. Relay 114 in energizing opens the circuit of line rela 101; Relay 101 in retracting its left-han armature removes the calling condition from the terminals 116 of the line A, and in retracting its right-hand armature it breaks the circuit of relay 103 which thereupon is deenergized. The circuit for relay 102 is broken at the right-hand armature oi relay 103, and the line finder starting relays are ready forthe next call.

In position 3 of the side switch a circuit is also completed for stepping rela 137 from grounded battery, left-hand winding of said relay, side switch arms 123 and 122 third position, conductors 138 and 139, brush 118, terminal 133 through the apparatus at substation A, terminal 134, brush 119, conductors 140 and 141, side switch arm 142, conductor 143, right-hand winding of relay 137 to ground. Relay 137 in being energized completes a circuit for slow-to-release relay 150, from grounded battery, winding 150, front contact and armature of relay 137, through primary off-normal spring 151 to ground. Relay 150 in attracting its right-hand armature completes a circuit from ground, right-hand armature and front contact of rela 150, conductor 157, back contact and 1e -hand armature of slow-to-release release magnet 158, conductor 159, contact spring 160 of relay 145, conductor 161 throu h the righthand winding of relay 162, si e switch arm 163, first position, lefthand windin of rela 162 to grounded battery. Circuits are a so completed at this time from grounded battery through the right-hand winding of relay 107, and from rounded battery through the lefthand winding of relay 120 in parallel with the circuit just traced, to ground at the righthand armature of relay 150. Relays 162 and 107 are energized in these circuits, and relay 120 is held up after its locking circuit is broken due to the energization of relay 107. Relay 107, in being energized, connects the in-starter wire 164 over conductor 106 to the out-starter wire 165, to permit operation of other line finders in the group to which the finder 100 belongs.

The calling subscriber now receives a distinctive dial tone over a circuit which ma be traced from ground through the secon ary winding 144 of tone source D. T. outermost right-hand armature and back contact of relay 145, side switch arm 146, first position, conductor 14?, condensers 148 and 149, side switch arm 122, third position, thence in parallel with the circuit of relay 137 over the talking conductors, through the substation apparatus and back over the talking conductors through the right-hand winding of relay 137 to ground. The subscriber, hearing this tone, now operates his sender S to transmit the first digit of the wanted number. In returning to normal the sender interrupts the circuit of the stepping relay 137 a number of times corresponding to the digit involved. Each time relay 137 retracts its armature, a circuit is completed from ground primary oil-normal spring 151, armature and back contact of relay 137, lefthand armature and front contact of relay 150, side switch arm 152, third position, conductor 153, through the winding of slow-torelease relay 1 54, conductor 155, side switch arm 156, first position, conductor 204, through the windin of the primary magnet 205 of the final se ector switch, conductor 206, middle right-hand armature and back contact of relay 145 to grounded battery. Relay 154 is operated in this circuit, but being slow-to-release remains ener ized throughout each series of impulses. fielay 150 being slow-to-release also remains energized during the sending of impulses. Primary magnet 205, in response to these impulses, steps the brushes 207, 208 and 209 to the grou of terminals in which the line desired by t e calling subscriber appears. At the end of this series of im ulses, rela 137 holds its armature attracte for a su cient time to allow relay 154 to be deenergized. When relay 154 was energized it completed a circuit from round, outer armature and back contact 0 the final selector release magnet 213, conductor 214, front contact and right-hand armature of relay 154, conductor 166, back contact and armature of relay 167 through the windin of selector escape ma net 168, to grounde battery. Magnet 168 is energized in this circuit, and when this circuit was broken by the deener ization of relay 154, magnet 168 became eenergized to pass the selector side switch arms into position 2.

Establishment of a connection to another private branch exchange station.

previously traced through relay 154, conductor 155, side switch arm 156, second position, conductor 215, through the winding of the selector secondary magnet 216, to grounded battery. Secondary magnet 216 is operated by these impulses 'to'step brushes 207, 208 and 209, into engagement with the terminals 210, 211, 212 of the wanted line. Belay 154 and escape magnet 168 are also operated in the impulse circuit and at the conclusion of the im ulses, relay 154 in being deenergized brea s the circuit of escape magnet 168 to allowit to become deenergizcd. Magnet 168 in being deenergized passes the selector side switch'into posmon 3. If the called line is busy, ground potential will be found on its test terminal 212. This ground being applied through brush 209, conductor 169, side switch arm 170, third position, innermost left-hand armature and back contact of relay 171 through the right-hand winding of relay 172, and side switch arm 163, third-position, will shunt the right-hand winding of relay 162 which'is also connected over conductor 161 and the circuit previously traced to ground at the front contact and right-hand armature of relay 150.

Relay 162 will therefore become deenergized and close a circuit from grounded battery through the winding of relay 145, conductor 173, back contact and armature of relay 162, conductor 174, outermost lefthand armature and back contact of relay 171, conductor 175, selector primary 0E- normal spring 17 6 to ground. Relay 145 in being energized completes a circuit for release magnet 213 from grounded battery,

winding of release magnet 213, conductors 177 and 178, innermost right-hand armature and front contact relay 145, to ground through primary off-normal spring 176. The

release magnet 213 is energized in this circuit and locks up over a circuit from grounded battery through its winding, front contact and inner armature and conductor 175 to ground at ofi normal spring 176. The energization of the release magnet restores the selector switch to normal.

When relay 145 was energized it completed a locking circuit for itself from grounded battery through its winding, lefthand armature and contact spring 160, conductor 159, left-hand armature and back contact of magnet 158, conductor 157, front contact and right-hand armature of relay 150, to ground. When the selector switch reaches normal, the subscriber at A will receive a busy tone which is transmitted over the following circuit: ground, secondary winding 179 of tone source B. T. outermost right-hand armature and front contact of relay 145, side switch arm 146, first position, conductor 147, condensers 148 and 149 and thence over the circuit previously traced for the dial tone over conductor 143 to ground through the right-hand winding of relay 137. The subscriber hearing this tone trfplages his reeiverh on its svfvitch-hool ere ym rru ing t ecircuit o relay 13 Relay 137 in becoming deenergized opens the circuit of relay 150. After a short interyal this relay is deenergized and opens at its right-hand armature the circuits for relays 120, 107 and 145. Relay 120 in being dcenergized 4 completes a circuit from grounded battery through the winding of finder release magnet 158, outer left-hand armature and back contact of relay 120, conductor 180, back contact and armature of relay 137, spring 151 to ground. The release magnet 158 is energized in this circuit and locks up from grounded battery through its winding, front contact and right-hand armature and spring 151 to ground. The release magnet 158 restores the line finder switch 100 to normal, at which time spring 151 opens to break the locking circuit of magnet 158 and the systern is ready for the next call.

f, however, substation B is found idle when the selector side switch passes to position 3, a circuit is completed from grounded battery through the winding of cut-ofi relay 216, terminal 212, brush 209, conductor 169, side switch arm 170, third position, innermost left-hand armature and back contact of relay 171, through the right-hand winding of relay 172, side switch arm 163, third position, right-hand winding of relay 162, conductor 161, contact spring 160, conductor 159, left-hand armature and back contact of relay 158, conductor 157, front contact and right-hand armature of relay 150 to ground. Relays 172 and 216 are energized in this circuit and relay 162 is maintained energized. Relay 172, in being energized, connects ground over its front contact and right-hand armature, contact and innermost left-hand armature of relay 171 and side switch arm 170, third position, over brush 209 to test terminal 212 to render the called line immediately busy. This ground also shunts the right-hand windings of re.- lays 172 and 162 but they are not deenergized since a substitute circuit is completed immediately from grounded battery through the left-hand winding of relay 162, side switch arm 181, third position, left-hand winding, left-hand armature and front contact of relay 172, conductor 155, side switch arm 156, third position, to ground. The-es cape magnet 168 is energized over a circuit from grounded battery, through winding of magnet 168, armature and back contact of relay 167, conductor 166, over the circuit just traced to ground at side switch arm 156, third position. Magnet 168 in being energized completes a circuit to apply ringing current to the called line which may be traced from a source of ringing current 11 through the winding of ringing cut-ofi relay 167, side switch arm 182, thir tion, ont contact and inner left-hand armat re of magnet 168, conductor 147, s1de switch arm 183 third position, conductor 184, side switch arm 185, third position, conductor 186, brush 208, terminal 211, through the bell (not shown) substation B, term nal 210, brush 207, conductor 187, s1de switch arm 188, third position, conductor 189, s1de switch arm 190, third position, conductor 191, outer left-hand armature and front contact of magnet 168, to ground. Belay 167 is marginal and will not be energlzed in the circuit just traced until the called subscriber answers. When the called subscrlber answers he lowers the resistance of the ringin circuit by shunting the bell with his swltc hook, and relay 167 is energized. In belng energized, relay 167 opens the circuit previously traced for escape magnet 168, and

escape magnet 168 is deenergized to pass the selector side switch into position 4.

Substations A and B are now connected over conductors 140 and 141, side switch arm 142, third position, condenser 193, Side switch arm 190 fourth position, conductor 189, side switch arm 188 third position, conductor 187, brush 207, terminal 210, substation B, terminal 211, brush 208, conductor 186, side switch arm 185 third position, conductor 184, side switch arm 183, fourth position, condenser 149, side switch arm 122 third position, conductors 138 and 139, brush 118, terminal 133, conductor 115, through substation A, terminal 134 and brush 119 to conductor 140. Talking current is supplied to the calling line through relay 137, and to the called line from grounded battery, through the left-hand winding of impedance coil 192, side switch arm 183 fourth posit-ion and side switch arm 185 third position, ring conductor 186, thence through substation B, tip conductor 187 side switch arm 188 third osition and side switch arm 190 fourth position, through the right-hand winding of impedance coil 192, to ground. Relay 162 is held energized throughout the conversation over a circuit from grounded battery, left-hand winding relay 162, side switch arm 163 fourth position, right-hand winding relay 162, conductor 161 and over the circuit previously traced to ground at the right-hand armature of "relay 150. Ground is also applied to the sleeve terminal of the called line through side switch arm 170 fourth position, conductor 169, brush 209, and terminal 212 to hold cut-ofi' relay 216 energized, and to furnish a busy test at the multiples of line B in other switches. At the conclusion of the conversation, the calling subscriber in placing his receiver on its switc'hhook, opens the circuit of relay 137 which becomes deenergized to open the circuit of relay 150. Relay 150, in being deener ized opens the circuit of relays 120 and 16%; finder release magnet 158, and seearner lector release magnet 213 are energized to release the finder and selector switches in the manner described when line B was foun to be busy.

Establishment of a connection to a central ofice trumk.

If the subscriber at station A desires a central ofiice connection, 11 on hearing the dial tone when the finder si e switch reaches position 3, he operates his sender to set selector switch 200 on a level 400 in the final selector bank which leads to central ofiice trunks. The operation of the finder switch and the selector switch in its prima movement is the same as when a ticu ar station B was desired. At the end of the first series of impulses however, auxiliary brush 201 will be in engagement with commutator segment 202 which is individual to the central oflice level. Upon the deenergization of relay 154 at the conclusion of the first set of impulses, magnet 168 is deenergized to pass the side switch into position 2, and ground is applied through spring 176, conductor 175, lefthand armature and back contact of relay 154, conductor 194, brush 201, commutator segment 202, conductor 195, to the armature of relay 196. If the substation A is restricted to branch exchange calls, its cut-off relay 114 will be connected to terminal 116 through the left-hand winding only, and relay 196 will be energized over a circuit from grounded battery, left-hand winding relay 114, terminal 116, brush 117, side switch arms 111 and 110, third position through the winding of relay 196 to ground.

The ground of sprlng 176, appearing at the armature of relay 196 will therefore be extended over conductor 177 through the winding of release magnet 213 to grounded battery. Magnet 213 will be energized and locked up in the same manner as before and release of the selector switch will take place precisely as though selector 200 had been set on the terminals of a busy substation within the branch exchange. The calling subscriber will receive a busy tone as before and will hang up to release line finder 100 as before.

If, however, substation A is a non-restricted station, its cut-off relay 114, will be connected to terminal 116 through both windings in series, and relay 196 being marginal will not be energized. in the circuit previously traced. The ground on the armature of relay 196 will therefore be extended over the back contact of relay 196, side switch arm 197,- second position, through the winding of relay 171 to grounded battery. Relay 171 is energized, and locks up over a circuit from grounded battery through its winding, right-hand armature and front con a conductor 198 and conparductori161 over the circuit previously traced for relay 162 to ground, at the right-hand armature of relay 150. A circuit is thereupon completed from grounded battery through the winding of magnet 168, armature and back contact of relay 167, middle left-hand armature and front cont-act of relay 171, conductor 199, secondary ofi-normal spring 10, which is. closed until the secondary movement of the selector switch begins, spring 176 to ground. Escape magnet 168 is energized in this circuit and held up over a circuit through side switch arm 170, second position, conductor 169, and brush 209 to ground on busy terminals 219 of central ofiice trunks after the secondary movement of the selector switch opens contact spring 10. A circuit is also completed from grounded battery through the winding of secondary magnet216, conductor 215, side switch arm 156, second position,conductor 155, conductor 220, back contact and armature of magnet 216, conductor 221, side switch arm 146, second position, inner armature and front contact of magnet 168, side switch arm 182, second position, innermost left-hand armature and front contact of relay 171, conductor 198 and thence in parallel with the locking circuit of relay 171 to ground at the right-hand armature of relay Stepping magnet 216, makes and breaks this circuit at its armature and back contact, and steps the brushes 207, 208, 209, over the terminals of central oflice trunks until an idle trunk, indicated by battery potential at test contact 219, is found. At this time, escape magnet 168 is shunted by the battery potential applied through brush 209, side switch arm 170, second position, middle left-hand armature and front contact of relay 171, and back contact and armature of relay 167. Escape magnet 168 is deenergized to pass the selector side switch into position 3, and to open at its inner lefthand armature the circuit of the secondary magnet 216.

In position 3 of the selector side switch, a circuit is completed for finder escape magnet 129 from grounded battery through the winding of magnet 112, winding of magnet 129, conductor 128. side switch arms 127 and 197, third position, right-hand armature and front contact of relay 171, and thence in parallel with the locking circuit of relay [71 over conductors 198 and 161 to ground, at the right-hand armature of relay 150.-- Escape magnet 129 is energized in this circuit and advances the finder side switch to position 4.

In position 4 of the finder side switch the circuit of stepping relay 137 is interrupted at side switch arms 123 and 142, fourth position, and this relay is deenergized to open the circuit of relay 150. Relay 150, however, is slow-to-release and is not deenergized at once, but maintains the circuits of relays 171, 120 and 107, and completes a circuit in parallel with said circuits from round at the right-hand armature of reay 150 over conductor 157 the circuit previously traced to conductor 198, front con tact and innermost left-hand armature of relay 171, side switch arm 170, third position conductor 169, brush 209, terminal 219, conductor 222, through the winding of relay 301 to grounded battery. Relay 301 is energized in this circuit and completes a circuit to energize relay 303 which may be traced as follows: ground, right-hand armature and back contact of relay 302, left-hand armature and front contact of relay 301, winding of relay 303 to grounded battery. Relay 303 in being energized completes a circuit from ground, front contact and outer right-hand armature of relay 303, through the winding of relay 304 to grounded battery. Relay 304 is energized and connects the trunk conductors 223and 224 to the armatures of relay 305. In being energized, relay 303 also completes a circuit from ground, front contact and left-hand armature of relay 303, conductors 306 and 307, outer right-hand armature and back contact of relay 308, through the winding of. relay 305 to grounded battery. Relay 305 is energized to complete a circuit from grounded battery through the right-hand winding of relay 309, front contact and inner armature of relay 305, front contact and outer armature of relay 304, ring conductor 223, terminal 218, brush 208, conductor 186, side switch arm 185, fourth position, conductor 139 through the finder brushes and apparatus at substation A, back over tip conductor 140, side switch arm 188, fourth position, conductor 187, brush 207, terminal 217, conductor 224, inner armature and front contact of relay 304, outer armature and front contact of relay 305, through the left-hand winding of relay 309 to ground. Relay 309 is energized in this circuit and closes a circuit from grounded battery through the winding of slow-to-release relay 302, front contact and right-hand armature of relay 309 to ground. Relay 302 in attracting its armatures applies ground through its lefthand armature and front contact to conductor 222 to take the place of the ground formerly applied through the right-hand armature of relay 150 to hold up relays 301, 171, 107 and 120.

When relay 309 was energized it also completed a circuit, from ground, left-hand armature and front contact ofrelay 309, conductors 310 and 317, through the winding of relay 311, conductor 312, armature and back contact of relay 313 through the winding of relay 314 to grounded battery. Relay 314 is energized in this-circuitbut relay 311 is marginal and will not be energized in series with relay 314 which is high wound. Line relay 314 in being energized completes a circuit for call lamp L at the central ofiice operators position. The operator seein lamp L lighted inserts the plug 315 of 181 cord circuit in jack 316 of the line calling. A circuit is thereb completed from .grounded battery, le t-hand lower winding of repeating coil 318, winding of supervisory rela 319, ring 320, contact Spring 321, con uctor 312, through the winding of relay 311, conductors 317 and 310, front contact andleft-hand armature of relay 309 to ground. The resistance of supervisory relay 319.is relatively low, so that both marginal relay 311 and relay 319 are energized in this circuit. Relay 319 in being ener 'ized extinguishes the calling supervlsory amp (not shown). When the operator inserted plug 315 into jack 316, a circuit was also completed from grounded battery (not shown), through the sleeve of plug 315 and jack 316 and the winding of cut-ofi' relay 313 to ground. Cut-oflt' rela 313 was energized to extinguish the cal lamp L. Relay 311 in being energized completes a circuit from ground, armature and front contact of relay 311 through the winding of relay 308 to grounded battery. Relay 308 is energized and at its outer righthand armature breaks the circuit of relay 305. At its left-hand armature it closes a low resistance shunt circuit to provide a path for voice current around relay 311 through conductor 322, resistance 323, front contact and left armature, of relay 308, back to the ring conductor 317. Resistance 323, however, is not small enough to' cause relay 311 to be deenergized. Relay 305 in being deenergized. connects the talking conductors 224 and 223 through to the contact springs of relay 324 and interrupts the circuit of relay 309. Relay 309 in,being deenergized breaks the circuit of relay 302,

but this relay is slow-to-release and stays' up until a substitute circuit is completed as will appear hereinafter.-

Relay 308, in attracting its inner right-hand armature completed a circuit from ground, inner right-hand armature of relay 308,

through the winding of relay 324 to grounded battery. Relay 324 is locked up over a circuit from grounded battery through its winding, front contact and right-hand armature over conductor 306, left-hand armature and front contact of relay 303 to ground. A circuit is also completed from grounded battery through the winding of slow-to-release relay 325, front contact and outer right-hand armature'of relay 308, conductors 307 and 306 to ground at the front contact and lefthandarmature of relay 303.- Relay 325 in attracting its armature completes the substitute circuit for holding up relay 302 from grounded battery through thetw'inding of relay 302, front contact and armature of relay 325 to ground.

A talking circuit is now completed from substation A over the conductors shown in heavy black to the central ofiice. The central ofiice operator, by depressing a listening key (not s own) may inquire the number desired by the callin subscriber and may thereupon complete t e connection to the wanted subscriber in any well known man ner.

The release of the connection will occur upon the deenergization of relay 311. At the close of the conversation the calling party in replacing his receiver on its hook breaks the circuit through supervisory relays, 311 and 319. Relay 319 in being deenergized lights the calling supervlsory lamp (not shown) before the operator who removes plug 315 from jack 316. Relay 311 in being deenergized opens the circuit of relay 308 which retracts its armatures. At its outer ri ht-hand armature relay 308 breaks the circuit of relay 325 which retracts its armature to break the circuit of relay 302. Relay 302 in being deenergized, removes ground from conductor 222 thereby opening the circuits of relays 303, 171, 107 and 120 which relays become inert. Relay 303 in retracting its armatures opens the circuits which had held up relays 304 and 324, and the trunk circuit is now in normal condition. Relay 171 in being deenergized completes a circuit for release control relay 145 which may be traced from grounded battery, relay 145, conductor 173, back contact and armature of relay 162, conductor 174, outer-most left hand armature and back contact of relay 171, conductor 175, through off-normal spring 176 to ground. Relay 145 attracts its armatures and completes the previously traced circuit for selector release magnet 213. This magnet causes release of the selector switch in the same way as described for a call between station A and station B. Relay 120 in being deenergized com pletes the previously traced circuit for finder release magnet 158 which is energized to release the finder switch in the manner previously described and the system is now ready for another call.

Establishment of a connection to a receiving subsem'be'rs station.

pulses to set the selector switch on level arm 197, second position, through the wind-- ing of relay 171, to grounded battery. Relay 171 is energized and locks up through its right-hand armature and front contact 7 and conductor 1.98 to ground at the righthand armature of relay 150 over the circuit previously traced. A circuit is then completed from ground through off-normal contact 176, secondary off-normal contact 10 closed until'the initiation of secondary movement, conductor 199, middle left-hand armature and front contact of relay 171, back contact and left-handarmature of relay 167 through the escape magnet 168 to grounded battery. Magnet 168 is energized in this circuit and after the switch has taken its first secondary step and the off-normal con tact 10 is opened, is maintained energized in a circuit from battery, winding of magnet 168, armature and back contact of relay 167, front contact and middle left-hand armature of relay 171, arm 170, second position and brush 209 to ground on busy test terminals 229 of receiving subscriber-s trunk lines. A circuit is also completed from grounded battery through the winding of secondary magnet 216, conductor 215, arm 156, second position, conductors 155 and 220, back contact and armature of magnet 216, conductor 221, arm 146, second position, inner armature and, front contact of magnet 168, arm 182, second position, innermost left-- hand armature and front contact of relay 171, and thence in parallel with the locking circuit of said relay to ground at the righthand armature of relay 150. The secondary magnet 216 makes and breaks this circuit at its left-hand armature and passes the se lector brushes over terminals 227, 228 and 229, until an idle set of terminals is reached. The idle condition of these terminals being denoted by absence of ground on sleeve terminal 229, the locking circuit of escape magnet 168 is broken and magnet 168 is deenergized to pass the selector side switch into position 3. In opening its inner arma ture, magnet 168 permanently opens the circuit of secondary magnet 216 to stop the brushes 207, 208 and 209 in engagement with the idle set of terminals. 1

In position 3, of the selector side switch a circuit is completed for finder escape magnet 129 from grounded battery through the winding of magnet 112, magnet 129, conductor 128, arms 127 and 197, third position right-hand armature and front contact of relay 171, and thence in parallel with the locking circuit of relay 171 to ground at the right-hand armature of relay 150. Escape magnet 129 is energized in this circuit to advance the finder side switch to position 4. In position 4 of the finder side switch the circuit of stepping relay 137 is interrupted at side switch arms 123 and 142, fourth position, and this relay 137 is deenergized to open the circuit of relay 150. Relay 150, however, is slow-to-lease and is not deenergized at once, but maintains the circuits of relays 171, 120 and 107 until a substitute ground is provided from the selected trunk circuit. With the finder side switch in position 4, and the selector side switch in position 3, a circuit is completed from grounded battery through the righthand winding of line relay 230, back contact and innermost left-hand armature of relay 231, terminal 228, brush 208, conductor 186, arm 185, fourth position, conductor 139, brush 118, terminal 133, through the apparatus at station A, terminal 134, brush 119, conductor 140,-arm 188, fourth position, conductor 187, brush 207, terminal 227, middle left-hand armature and back contact of relay 231 through the left-hand winding of relay 230 to ground. Relay 230 is energized and completes an energizing circuit for slow-to-release relay 232. Relay 232 in attracting its armature applies ground to terminal 229 to replace ground formerly applied at the right-hand armature of relay 150 for providing a busy test, and holding up relays 171, 107, and 120. A circuit is also completed from ground, armature and front contact of relay 232, conductors 233 and 234, side switch arm 235, first position, right-hand armature and back contact of relay 236, back contact, armature and winding of motor magnet 237 to grounded battery. Magnet 237 makes and breaks this circuit at its left-hand armature and steps brushes 238, 239 and 240 of the hunting switch 25 over terminals 241, 242 and 243 of receiving subscribers lines. Busy lines are denoted by ground on their test terminals 243 which shunts the right-hand winding of test relay 236 over brush 240. When an idle line is reached, a circuit is completed from grounded battery through both wind ings of cut-off relay 244, terminal 243, brush 240, right-hand winding of test relay 236, arm 235, first position, conductors 234 and 233 to ground at the front contact and armature of relay 232. Relay 236in being energized interrupts the circuit of magnet 237 to stop the switch on the selected set of terminals, and at its left-hand armature completes a circuit from grounded battery through the winding of relay 245, left-hand winding, front contact and armature of relay 236, thence over the circuit previously traced to ground at the armature of relay 232. This circuit energizes relay 245 and holds up relay 236 after its right-hand winding has been shunted by the attraction of its ri 'ht-hand armature to provide a busy ground at terminal 243. Relay 245 in attracting its right-hand armatures completes a circuit to ring the call bell if the receiving subscriber is equip ed with the type of apparatus shown at or to energize its re ay 326 if the station has the equipment shown at F, which circuit may be traced from a source of ringing current through the right-hand winding of relay 246, back contact and inner right-hand armature of said relay, front contact and inner right-hand armature of relay 245, brush 239, terminal 242 through the call hell or relay, according to the equipment at the receiving station, terminal 241 brush 238, outer right-hand armature and front contact of relay 245, outer right-hand armature and back contact of relay 246 to ground. Relay 246 is marginal-and will not be ener gized in this circuit until the resistance is lowered when the called subscriber answers in the case of station E, or throws his answering key 327 in the case of station F.

At this time relay 246 attracts its armatures to interrupt the calling current and com pletes at its left-hand armature a holding circuit for itself which may be traced from grounded battery, left-hand winding of relay 246, left-hand armature and front contact of said relay, front contact and lefthand armature of relay 245 to ground. In attracting its right-hand armatures, relay 246, also completes a connection between the calling substation and the (receiving' substation, talking current being supplied through both windings of relay 230. Supervisory relay 247 is energized in the talking circuit. 7

Transfer 0 a call from a receiving subscribers statzon to a regular private branch exchange station.

The calling subscriber may now obtain any information he desires from the receiving subscriber. In case it is desired to extend the connection to a substation within the branch-exchange such as that shown at C, the receiving subscriber operates his calling'device to lnterrupt the circuit through supervisory relay 247. When relay 247 was first energized it completed a circuit from grounded battery through the winding of slow-to-release relay 248, conductor 249, front contact and armature of relay 247 to ground. When relay 247 becomes deenergized in response to the first impulse caused by the operation of the receiving subscrlbers sender, a circuit is completed from. ground,

armature and back contact of relay 247, normal contact 250 of relay 251, inner righthand armature and front contact of relay 248, through the winding of slow-to-releasa relay 252, side switch arms 253 and 254, first position, front contact and inner armature of relay 255, through the winding of primary magnet 256 to rounded battery. Relay 255 was energized when relay 232 first attracted its armature, over a circuit from grounded battery, right-hand winding of relay 255, arm 259, first position, lefthand winding of relay 255, conductor 257, back contact and armature of release magnet 258, conductor 233 to ground at the front contact and armature of relay 232. Magnet 256 steps the brushes 260, 261 and 262 of companion final switch 20, over the termi nals in its bank. In case the called substation is not in the first group of terminals, the receiving subscriber in operating his calling device will send more than one primary impulse. In response to the first impulse, slow-to-release relay 252 is energized and remains operated throughout each series of impulses. Relay 252 completes at its lefthand armature an energizing circuit for relay 251 from ground, left-hand armature and front contact of relay 252, through relay 251 to grounded'battery. A'circuit is also completed from grounded battery through the winding of companion final escape magnet 263, armature and back contact of relay 264, conductor 265- to ground at the front contact and left-hand armature of relay .252. When relay 251 was energized it com leted a circuit for relay 266 from groun ed battery, right-hand windin relay 266, front contact and inner leftand armature of relay 251, thence over the talkingflconductors through the a paratus atY-I su s tation E, and back throng left-hand armature and front contactof relay 251 and left-hand winding of relay 266 to ground. Relay 266 in attracti its armature provides a substitute circuit to hold up relay 248 after relay 247 has retracted its armature during the first'impulse. In response to succeeding interruptions caused bv t e operation of the sender at substation I l,

relay 266 vibrates its armature. Each time the outer that the armature of relay 266 is retracted,

. to the terminals of the desired line.

relay 252 to become deenergized; Relay 252 in being deenergized opens the circuits previously traced for relay 251 and for the escape magnet 263. Magnet 263 in being deenergized steps the"-- companion final side switch into position 2. Relay 251 in being deenergized again completes the circuit from relay 230 through the substation E which operates relay 247.

The receiving subscriber now sends a series of lmpulses to set the switch 20 on the terminals of the desired line. In response to the first of these impulses, relay 247 is deenergized to complete a circuit from grounded battery through the winding: of the secondary magnet 267, arms 254, and 253,.second osition, through the winding of relay 252, ront contact and inner righthand armature of relay 248,- normal contact 250 ofrelay 251 to ground at the back contact and armature of relay 247. Relay 252 is energized in this circuit and operates relay 251 and the escape magnet 263 in the same manner as during the primary impulses. The secondary magnet 267 steps the brushes 260, 261 -and'262 of switch 20 one step in their secondary movement. In case more than one impulse is sent, relay 266 is againincluded in thecircuit with the sender at substation E and vibrates its armature to complete the circuit for sec ondary magnet 267 from ground, armature and back contact of relay 266, righthand armature of relay 251 and contact lever of normal contact of relay 251, inner right-hand armature and front contact of relay 248 and thence over the path traced for the first impulse through the winding of secondary magnet 267 to grounded battery. Magnet 267 in response to these impulses steps the brushes of the switch 120 t the conclusion of this series of impulses, relay 266 remains energized to break the circuit of relay 252, and after a short interval this relay retracts its armatures to open the circuits of relay 251 and escape magnet 263. Magnet 263 in being deener-.

' gized, passes the "side switch into position 3. Relay 251, in retracting its left-hand armatures again completes the circuit between station A and station E to energize relay 247. Relay 248 being slow to release remains energized as long as the receiving subscriber holds his connection, since it is energized over a circuit from grounded battery through its winding to ground at either the armature and front contact of relay 247, or of relay 266 since one of these relays is energized at all times until station E is disconnected from the line. Relay 248 at its leftha.nd armature provides a substitute circuit for holding up relay232 in case the calling subscriber should, by abandoning the call, open the circuit of line relay 230. Release is therefore under the control of the receiving. subscriber while line is busy, ground on its test terminal.

will be connected through brush 262 and arm 272, third position, to the left-hand winding of relay 271 to shunt this relay which is also connected to ground through the outer left-hand armature and back contact of relay 273, arm 259, third position, left-hand winding of relay 255, conductor 257, back contact and armature of magnet 258 and conductor 233 to the front contact and ground at armature of relay 232. As no circuit is now completed for relay 255, it retracts its armatures to complete a cir cuit for magnet 258 which may be traced from grounded battery through the winding of magnet 258, outer armature and back contact of relay 255 through rimary ofiirormal spring 274 to ground. l .elease magnet 258 is energized in this circuit and restores the companion final brushes and side switch arms to normal, at which time-ofinormal spring. 274'opens to break the Circuit through 'magnet 258. In attracting its armature, magnet 258 completes a circuit ,from grounded battery through the winding of relay 27 5, front contact and armature of magnet 258 and conductor 233, to ground at the front contact and armature of relay 232. Relay 275 is energized in this circuit and locks up over a circuit from grounded battery through its winding front contact and right-hand armature and conductor 276 to ground, at the front contact and armature of irelay 247. In attracting its left-hand armature, relay 275 completes a circuit from ground, through the secondary. winding of busy tone source 287, front contact and left-hand armature of relay 275, inner left-hand armatureand back contact? of relay 277 throughthe condenser 278 and tip conductor 279 throu h the receiving subscribers substation thence back over the ring conductor through the innermost armature and back contact of relay 231 to the right-hand winding of relay 230 and grounded battery.

The receiving subscriber hearing this busy tone informs the calling subscriber that the called line'is busy and may then, by operating his sender, reset the companion final switch 20 in accordance with the desire of the calling subscriber, or he may release the entire connection by replacing his receiver on its hook. The operation of resctting the companion final switch is the same as when this switch was first set and need not, therefore, be described. If the subscriber does-not desire any further COTI nection'; the receiving subscriber in replacing his receiver on its book interrupts the circuit for relay 247, and relay 266 being inert at this time, relay 248 is deenergized to break at its lcft-hand armature the sub stitute circuit for relay 232. When thecalling subscriber hangs, up his receiver he breaks at his switch-hook the circuit for relay 230, In becoming deenergized, relay 230 interrupts at its armature the circuit for relay 232 whichthereupon is deenei' gized. Relay 232 in becoming deenergized removes the holding ground from terminal 229 thercby interrupting the circuits of relays 171 and 120. Relays 171 and 120' are deenergized to cause the restoration of the selector and finder switches in the manner previously described when a central ofiice call was made from station A. Relay 232 in being deencrgized also completes a circuit from ground, armature and back con tact of relay 232, outermost left-hand armature and back contact "of relay 231 through spring 280 closed when hunting switch 25 is off-normal, through the winding of magnet 281 to grounded battery.

Magnet 281 is energized to restore hunting. switch 25 to normal position at whlch time spring 280 opens to render magnet 281 inert. The system is now ready for the next call. v

If the line C, when tested, is found to be idle, no ground will appear on its sleeve terminal 27 0, and a circuit will be completed from grounded battery through the winding of cut-off relay 282, terminal 270, brush 262, arm 272, third position, through the left-hand winding of relay 271, back contact and outer left-hand armature of relay 273, arm 259, third position, through. the left-hand winding of relay 255, back con;

tactand armature of magnet 258 over con-- ductor 233 to ground at the front contact and armature of relay 232. Cut-off relay 282 and test relay 271 are energized in this "circuit, and release control relay. 255 is maintained energized. Relay 271 in attracting its left-handarmature connects a dead ground to terminal 270 to provide a busy test and to shunt the left-hand winding of relay 271. Relay 271 is not deenergized however, since a substitute-circuit is completed from grounded battery .to the righthand Winding of relay 255, arm 283, third position, right-hand winding, front contact and armature, of relay 271, conductor 257 to ground at the armature of relay 232 over the circuit previously traced. Relays ing its armatures closes a circuit to ring the call bell at substation C which may be traced from a source of ring current through the winding of ringing trip relay 264, inner armature and front contact of magnet 263, arm 284, third ,position, brush 261 terminal 269, through the apparatus at station (J, terminal 268, brush 260, arm 285, third position, outer armature and front contact of magnet 263 and arm 286, third position, to ground. Relay 264 is marginal and will not be energized in this circuit until the subscriber at C lowers the resistance of ,the ringing circuit by removing his receiver from its hook. Relay 264 thereupon is energized and breaks at its armature the circuit of escape magnet 263. Escape-magnet 263 in becoming deenergized passes the companion final side switch into fourth position; Stations A and C are now connected through companion final brushes 260, and 261, arms 285 and 284, fourth position, selector terminals 227 and 228, selector brushes 207 and 208, arms 188 and 185, fourth position, and the conductors shown in heavy black. In fourth position, release control relay 255 is held energized over a circuit from 'grounded battery through the right-hand winding of relay 255, arm 259, fourth position, left-hand winding of relay 205, conductor 257, back contact and armature of magnet 258, and conductor 233, to ground at the armature of relay 232. Ground is connected through the right-hand armature'and back contact of relay 277, arm 272, fourth position, and brush 262 to terminal 270, to provide busy potential and to hold cut-off relay 282' en-- ergized, Talking current is supplied through both windings of relay 230. Side switch arm 235 in passing to fourth position interrupts the holdingcircuit for relays 245 .and 236. Relay 245 when deenergized interrupts at its left-hand armature the circuit for relay 246, and at its right-hand armatures the circuit for relay 247. Relay 247 in being deenergized breaks the circuit to be busy and the receiving station E is ready for the next call.

When the subscribers at A and C complete their conversation, and hang up their receivers, they interrupt at their switch-hooks the circuit of relay 230. Relay 230 in being deenergized opens the circuit of relay 232 which retracts its armature. Ground being removed from conductor 233 and terminal 229, release control relay 255 retracts its armature to complete a circuit formagnet 258. Relays 171 and 120 also retract their armatures, and release of switches 100, 200 and 20 takes place in the manner described when substation C- was found to be busy.

lz'stablz'slzment of a connection from a restricted service station to a central .ofice trunk.

pose of-getting information. The hunting switch 25 picks an idle receiving subscriber in the manner previouslydescribed and substation A is then connected to a receiving station such as E. The calling subscriber informs the receiving subscriber of his desire for a central ofiice connection, and the receiving subscriber may, at his discretion, extend the call to the central, ofiice. To do this, the receiving subscriber operates his sender to set the companion final brushes 260, 261, and 262 in their primary movement on a level 400 in which appear terminals of central oflice trunks. The operation of the final switch in its primary movement is accomplished in the manner previously described when a call was being extended to a substation C within the exchange, except that at the end of the primary movement auxiliary brush 288 will rest on commutator segment 289 individual to the central office level. WVhen relay 252 is deenergized at theend of the primary impulses, a circuit is completed from grounded battery through the winding of relay 273, conductors 290, 291 and 292, commutator segment 289, brush 288, conductor 293, back contact and righthand armature of relay 252, conductor 257,

back contact and armature of magnet 258,

hand armature and front contact of relay 27 3, conductor 257, and thence over the circult just traced to ground at the right-hand armature of relay 232. Release control relay 255 is held up in first and second osit1ons from grounded battery rightand winding of relay 255, arm 259, iirst position, left-hand winding of relay 255, conductor 25? to ground at the armature of relay 232.

When relay 252 became deenergized it also interrupted at its left-hand armature and inner front contact, the circuit for escape magnet 263. Magnet 263 in being deenergized passes the side switch into second ositlon. In second position of the side swltch, escape magnet 263 is again energized over a circuit from grounded battery through the winding of magnet 263,'armature and back contact of relay 264, conductor 265, front contact and outer right-hand armature of relay 273, conductor 294, arm 272, second position, and brush 262 to onnd on terminals 219 of-busy central 0 cc trunks. Magnet 263-in attracting its outer armature completes a circuit from -grounded battery through the winding of secondary magnet 267, arms 254 and 253, second position, armature and back contact of magnet 267 inner right-hand armature and front contact of relay 273, outer armature and front contact of magnet 263, arm 286, second position, conductors 257 and 233 to ground at the armature of relay 232. Secondary magnet 267 makes and breaks this crcuit at its armature and back contact, and steps the brushes 260, 261 and 262 over the terminalsof central ofiice trunks. When an idle set of terminals is found, absence of ground potential on test terminal 219 opens the circuit which has been holding up magnet 263, to allow this magnet to be deenergized. Magnet 263 in being deenergized passes the side switch into third position and at its outer armature breaks the circuit of secondary magnet 267 to stop the brushes 260, 261 and 262 in engagement with terminals 217, 218 and 219 of the selected trunk line.

Relay 277 was energized in parallel with relay 273 and had a holding circuit provided from grounded battery through the winding of relay 277, conductors 291 and 290, inner left-hand armature and front contact of relay 27 3 and thence in parallel with the locking circuit of relay 273 to ground at the armature of relay 232. When the side switch reaches third position, ground', is therefore applied to terminal 219, through the armature of relay 232, conductor 233, back contact and right-hand armature of relay 231, contact springs 296 of relay 277, arm 272, third position, and brush 262 to energize relay 301 and to provide busy poture and back contact of relay 264, conductors 265 and 297, arms 253 and 254, third position, front contact and outer left-hand armature of relay 277 to ground. A circuit is thereupon completed from' a source of ringing current, through the wind1ng of relay 264, front contact and inner armature of magnet 263, arm 298, third position, back contact and left-hand armature of relay 275, inner left-hand armature and front contact of relay 277, resistance 299, conductor 22, outer armature and front contact of magnet 263, arm 286, third position to ground. Resistance 299 is low enough to allow relay 264 to be'energized in this circuit thereby interrupt'nl'gi-the circuit previously traced for the escape'ma net 263 which is deenergized to pass the si e switch into fourth position.

With the side switch in fourth position a circuit is completed to energize relay 231 which may be traced from grounded battery, winding of relay 231, side switch arms 254, and 253, fourth, position, conductor 290, inner left-hand armature and front contact of relay 273, and thence in parallel with the locking circuit of relay 273, to ground at the armature of relay 232. Belay 231 in attracting its left-hand armatures breaks the circuit of relay'230 which in being deenergized opens the circuit of relay 232. Relay 232 is slow-to-ielease and does not therefore retract its armature until ground has been applied to conductor 233, from relay 302.in 'the'selected trunk circuit. Relay 301 which it will be remembered was energized immediately upon the seizure of the trunk when the companion final side switch was in third pos tion. is held energized after the side switch passes to fourth position over a circuit from grounded battery through the winding of relay 301, conductor 222. terminal 219. brush 262. arm 272, fourth position, right-hand armature and contact springs 296 of relay 277, right-hand armature and front contact of relay 231, and thence in parallel with the circuit just traced for relay 231 to ground at the armature of relay232.

The ener ization of relay 301, causes the same operation of the relays in the trunk circuit as was described when the selector switch 200 was set direct on terminals of such a trunk circuit, and need not be described in detail here. When line relay 309 attracts its armatures to energize relay 302, relay 302 at its left-hand armature applies ground to conductor 222 and thence through terminal 219, brush 262, arm 272, fourth position, right-hand armature and contact springs 296 of relay 277, right-hand armature and front contact of relay 231, arms 254 and 253, fourth position, conduct-or 290, inner left-hand armature and front contact of relay 273, conductor 257, back contact and armature of magnet 258, conductor 233 to terminal 229. Relays 255, 273, 277 and 231 of the companion final switch are held energized in this circuit throughout the remainder of the connection. Relays 120, 107 and 171 are also held up over this circuit. \Vhcn the companion final side switch passed into fourth position, the receiving subscriber at station E was disconnected and the switch 25 was restored in the same manner as was described when a call was completed between station A and station C.

The central ofiice operators call lamp L, Fig. 3, is lighted in the same manner as was described when a direct central office call, without the intervention of a receiving subscriber,-was made and the operator inserts her plug 315 in jack 316, thereby energizing relays 311 and 308 in the manner previously described. and depresses her listening key (not shown). A talking circuit is now completed between the operators head set (not shown), and substation A, energy being supplied over a circuit from grounded battery lower left-hand winding of repeating coil 318, supervisory relay 319, ring 320, spring 321, conductors 312 and 322, resistance 323, front contact and left-hand armature of relay 308, inner left-hand armature and front contact of relay 324, back contact and inner left-hand armature of relay 305, front contact and outer right-hand armature of relay 304, conductor 223, terminal 218, brush 261, arm 284, fourth position, terminal 228, brush 208, conductor 186, arm 185 fourth position, conductor 139, brush 118, terminal 133, through the apparatus at substation A, terminal 134, brush 119, conductor 140, arm 188, fourth position,'conductor 187, brush 207, terminal 227, arm 285, fourth position, brush 260, terminal 217, conductor 224, inner armature and front contact of relay 304, outer armature and back contact of relay 305, front contact and outer left-hand armature of relay 324, conductor 328, spring 329, tip of plug 315, upper left-hand winding of repeating coil 318 to ground.

The operator inquires the number desired by the calling party and completes the connection in the usual manner. At the conclusion of the conversation when the calling subscriber replaces his receiver on its hook, he interrupts the circuit just traced which has been holding supervisory relays 311 and 319 energized. Relay 319 in being deenergized lights its associated supervisory lamp (not shown) and the operator removes plug 315 from its jack. Relay 311 in being deenergized opens the circuit of relay 308. Relay 308 in retracting its armatures closes the circuit of relay 305 from grounded battery through the winding of relay 305, back contact and outer right-hand armature of relay 308, conductors 307 and 306, lefthand armature and front contact of relay 303 to ground. In case the calling subscriber at station A desires another central ofiice connection immediately, he does not leave his receiver on'its hook, but immediately removes. it, thereby completing acircuit from grounded battery through the righthand winding of relay 309, front contact and inner armature of relay 305, front contact and outer armature of relay 304, conductor 223, terminal 218} brush 261 and thence over the circuiflpreviously traced through the apparatiis at substation A, and back through brush 26(), terminal 217, conductor 224, inner armature and front contact of relay 304, outer armature and front contact ofrelay 305 through the left-hand winding of relay 309 to ground. Relay 309 at its right-hand armature completes a circuit to hold up slow-to-release relay 302 when sl'ow-to-release relay 325 is deenergized due to the retraction of the outer right-hand armature of relay 308. In attracting its left-hand armature, relay 309 operates central ofiice line, relay 314 to light the call lamp L in i the manner previously described. The operator again inserts her plug 315 in jack 316 thereby operating relay 311 over the circuit previously traced. Relay 311 in attracting its armature completes a circuit for relay 308 which attracts its armatures to cut-off relay 305. Relay 305 in being deenergized completes the previously traced talking circuit between substation A and the central ofiice.

In casethe subscriber at station A did not desire any central oflice connection, he would leave his receiver on its switchhook, so that no circuit would be completed for relay 309, and shortly after the deenergization of relay 308, relay 325 would retract its armature to open the circuit of relay 302. Relay 302 in being deenergized removes from conductor 222 the ground which has been holding up relays 255, 273, 277, 231, 171, 107 and 120. Relays 255, 171 and 120 in being deenergizcd cause the release, respectively, of the companion final switch 20, the selector switch 200 and the line finder switch 100, in the manner described for the release of connection between substations A and C, and the system is now in normal condition ready for other calls.

Establishment of a call from the central 077506 to the private branch emclumge.

On calls from the central oflice to the private branch exchange, the operator inserts her plug 315 in a jack 316 of an idle trunk circ'uit leading to the private branch exchange. A circuit is thereupon completed from grounded battery through the lower left-hand winding of repeating coil 318, supervisory relay 319, ring 320, spring 321, conductor 312, winding of relay 311, conductor 317, left-hand armature and back contact of relay 308, through the winding of re'ay 330, conductors 353 and 328, spring 329, tip of lug 315 through the upper lefthand win ing of repeating coil 318' to winding of relay 301, conductor 222, front, 1

contact and left-hand armature of relay 302 to ground. Relay 301 in attracting its right-hand armature closes a circuit from ground, right-hand armature and front contact of relay 301, conductor 331, armature and back contact of magnet 332, side switch arm 333, first position, through the lefthand winding of relay 334, arm 335, first "position, conductor 336 through the ri hthand winding of relay 334 to grounded attery.; Relay 334 is energized in this circuit and locks upfrom grounded battery through its right-hand winding, conductor 336, arm 335, first position, 1eft-hand winding front contact and armature of relay 334, back contact and armature of magnet 332, and conductor 331 to ground at the right-hand armature of relay 301. Belay 302 in applying ground to conductor 222 also renders multiple terminals 219 of this trunk line busy.

After the operator inserts her plug 315 in the jack of the trunk line, ringing current is impressed on the calledlinefrom a source of ringing current (not shown),

through ring 320, spring 321, conductor 312,

winding of relay 311, inner left-hand armature and back contact of relay 3 24, condenser 337, back contact and outer left-hand armature of relay 324, conductor 328, spring 329, tip of plug 315, upper left-hand winding of repeating. coil 318 to ground. As the resistance of this path is low, relay 311 is energized to operate relay 308. Relay 308 in attracting its arniatures completes a circuit from ground, front contact and inner right-hand armature or relay 308,

through the winding of relay 324 to grounded battery. A circuit is thereupon completed from grounded battery through relay 302 being slow-to-release remained up until its substitute circuit was completed. Relay 338 in being energized completes a locking circuit for itself from grounded battery through its winding, left-hand armature and front contact to ground at the right-hand armature of relay 30 2. Relay 324 is locked up over a circuit from grounded batter through its winding, front contact and right-hand armature and conductor 306 to ground at the right-hand armature and front contact of relay 338. In attracting its left-hand armatures, relay 324 interrupted the ringing current circuit to cause relay 311 to be deenergized, thereby breaking the circuit of relay 308, which in retracting its armatures completes the previously traced circuit for relay 330, and opens the circuit of relay 325. Relay 302 is held up by ground at the armature of relay 330 and relay 338 is held up over its locking circuit after relay 325 retracts its armature. In retracting its outer right hand armature relay 308 completed an energizing circuit for relay 305 which may be traced from grounded battery through .the winding of relay 305, back contact and outer righthand armature of relay 308, conductors 307 and 306, and the right-hand armature and' front contact of relay 338, to ground.

In attractin its right-hand armature, relay 338 comp eted a circuit from ground, front contact and right-hand armature of relay 338, left-hand armature and back contact of relay 303, conductor 339, arm 340,

first position, right-hand armature and back contact of relay 341, back contact and armature of magnet 342 through the winding of said magnet to grounded battery. Magnet 342 makes and breaks this circuit at its armature and back contact and steps the brushes of the hunting switch 30 over the terminals leading to receiving subscribers stations. Busy terminals are denoted by ground on sleeve terminal 343 which shunts the right-hand winding of relay 341. When an idle terminal is reached, a circuit is completed from grounded battery through both windings of cut-off rel-a 344, terminal 343, brush 345, right-hand Winding of relay 341, arm 340, first position, conductor 339, back contact and left-hand armature of relay 303 to ground at the right-hand armature and front contact of relay 338. Relay 341 attracts its armatures, at its right-hand armature opening the circuit of magnet 342 to stop the switch 30 on an idle set of terminals, and applying ground from the front contact and right-hand armature of relay 338 to test terminal 343 to provide a busy test. At its left-hand armature relay 341 completes a circuit from grounded battery through the winding of relay 346, left-hand winding, front contact and armature of relay 341, and thence in parallel with the circuit of relay 344 to ground at' the right-hand armature of relay 338. Relay 346 is energized in this circuit and rela 341 is held up after its right hand win ing has been shunted. Relay 346 in attracting its righthand armatures, completes a circuit from a source of ringing current through the righthand winding of relay 347, back contact and inner right-hand armature of said relay, front contact and inner right-hand armature of relay 346, brush 348, terminal 349 through the left-hand winding of relay 326, condenser 350, terminal 351, brush 352, outer right-hand armature and front contact of relay 346, outer right-hand armature and back contact of relay 347 to ground.

Relay 347 is marginal and will not be energized in this circuit at this time. Relay 326 however attracts its armature completing a circuit from grounded batter through lamp 354, right-hand winding, ront eontaet and armature of relay 326, normal contact of answering key 327, to ground. Lamp 354 lights and informs the reeeivin subscriber that a call is awaiting attention on his associated line. The receiving subscriber thereupon throws his answering key 327, breaking the circuit for lamp 354 which goes out. In operatingthe answering key a low resistanceshunt circuit is completed in parallel with the circuit through the lefthand winding of relay 326 and relay 347 is now energized. In attracting its left-hand armature, relay 347 completes a locking circuit for itself, while in attracting its righthand armatures relay 347 interrupts the ringin circuit and closes a circuit for relay 309, w ich may be traced from grounded battery through the right-hand winding of relay 309, front contact and inner armature of relay 305, conductor 356, relay 357, spring 359 of relay 358, front contact and 1nner right-hand armature of relay 347, front contact and inner right-hand armature of relay 346, brush 348, terminal 349, lowest spring of key 327, through the apparatus at substation F, top spring of key 327 terminal 351, brush 352, outer right-hand armature and front contact of relay 346, outer righthand armature and front contact of relay 347, inner left-hand armature and back contact of relay'358, outer armature and front contact of relay 305, through the left-hand winding of relay 309 to ground. Relay 309 is energized and in attracting its left-hand armature completes a circuit from grounded battery, through the lower left-hand winding of repeating coil 318, winding of relay 319, ring 320, spring 321 conductor 312, winding of relay 311, conductors 317 and 310, front contact and left-hand armature of relay 309 to ground. Relays 3'19 and 311 are energized in this circuit, relay 319 0 erating its associated supervisory lamp not shown) to inform the central oflice operator that the call has been answered, and relay

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