US1308554A - Call-xistribtjtina system - Google Patents

Description

R. L. QUASS.

CALL DISTRIBUTING SYSTEM.

APPLICATION FILED OCT. 8. 1917.

5 SHEETS SHEET l. 4

Patented July 1,1919,

R. L. QUASS. CALL DISTRIBUTING SYSTEM.

APPLICATION FILED OCT. 8. I917.

Patented July 1, 1919.

5 SHEETS-SHEET 2- yew far fia/p/ A. 04/4755.

R. L. QUASS. CALL DISTRIBUTING SYSTEIVIfQ' APPLICATION FILED OCT. 8' I917.

mmwfimm Patented July 1, 1919.

5 SHEETS-SHEET 3.

Fez/ ab L. Quass.

H. L QUASS. CALL DISTRIBUTING SYSTEM.

APPLICATION FILED OCT. 8. I911.

Lwg m v Patented July 1, 1919.

5 SHEETS-SHEET 4.

I R. L QUASS. CALL DISTRIBUTING SYSTEM.

APPLICATION FILED OCT. 3. I917.

IPfl'IGllIJGdI July I, 1919. 5 SHEETS-SHEET 5 'mwwm UNITED STATES PATEN oFFIo [men L. QUABS, or mwrnonnn, new mnsnm ssszenon TO wesem snnornrc I llll lid

0mm, INCOBPOBATED, OIN EW YORK, N. Y.,"" A CORPORATION OF NEW YORK.

To all whom, it may concern I 5136 it. known that '1, Rem x; L. Qrmsah citizen of, the United States,v residing at tributih Systems, of which the followin is a full, c ear, concise, and exact descri tion.

This invention relates to telephone ca dis-- tribnting systems of the type in whichthe calls orginated by the lines of the exchange are automaticall distributed to o craters positions at w ic connection with t e called subscribersulines is completed. The invention has primaril to do with the provision of means for sa eguarding such a system against failures of operation which mi ht result from careless manipulation of t e, ap paratus on the part of the operators, or which might arise from the improper operation of the apparatus itself, the ob ect being to-improve and render more eflicient and reliable the operation of the system.

Generally stated, the system of the preferred embodiment of the invention herein disclosed provides a plurality of operators positions each equipped with a number of plug-terminated connecting circuits for completmg connection with called subscribers lines, The connection between these connecting-circuits and the calling subscribers lines is effected throu h the medium of a number of finder circuits, each of which has an automatic switch at one end for finding and connectin with any subscribers line that may be calli at the other end for selecting an available operators position and then connecting with an idle connecting circuit at that position. The connecting circuit to which the connection is extended terminates in a plug, and the o erator completes connection with the called subscribers line by inserting the plug into the spring-jack of that line.

lln the selection of an .operators position by the finder circuit certain devices are operated that render the position inaccessible to other incoming calls, and the position remains inaccessible until certain other apparatus operates to restore its accessibility. Similarly, the selection of an idle connecting circuit by the incoming call renders that connecting circuit inaccessible to other cells until the accessibility of the circuit is restored by taking down the connection.

f Specification of Letter! Patent. Application filed October a, 1917. semi Ho. issue.

ng,-and an automatic switch been extended.

- ioamnisrnrsvmo svsrun.

Patented July 1 1919.

The idle oraccessible condition of a concircuit, in the potential battery with the test conductor associated with the connecting circuit. One

of the ob e'ctS of the present invention is so to organlze the system that when, by the nectigg present system, is indlca by'the connectlonof relatively high accidental grounding of one of the test conductofe or-otherwise, an abnormal electrical cond1t1on o: E the testing circuits of an operators posltionis created, that position is I automatlcally made inaccessible to incoming calls, while at the, same time the ability of the operator to supervise existing connections is not interfered with. Another object of the invention is to provide means for signaling theoperator of the selection of her osition' the instant the selection occurs, and or withdrawing the signal after a predetermined time interval, or at the instant the connecting circuit is seized if the seizure takes place before the ex iration of that timeinterval. Another ob ect of the invention is to provide means for preventing holding the operators position unselectable for more than a predetermined interval in the event of an abnormal operation of the apparatus which controls t e connection of the operators telephone with a connecting circuit when the operator listens in on that circuit. Another object of the invention is to prevent an unintended release of the callingillme from the connecting circuit to which it as been extended in case the operator happens to insert the calling plug into the spring-'jackof the called subscribers'line in such a way as momentarilyto break the connection as the plu moves into the spring jack. Another obJect 0f the invention is to give an operator a characteristic signal or indication when she inserts into the springjack of a line the calling plug of a connecting circuit to which a calling line has not of the system.

' mm the relationshi between them, Fig. 3 shows two cord s ector 'switchesof one frame with their associated selection controlling apparatus and circuits, together with similar apparatus and circuits for the cord selector switches (not shown) of another frame; and Figs. 4 and 5 show the position circuit may be connected. The figures taken together, and arranged side by side in the or er indicated by the lines that extend to the margins of the sheets, illustrate as much of a complete organization as is necessary to gain an understanding of the construction and mode of operation of the system.

The telephone lines are indicated in each of the two groups shown in Fig. 1, it being understood that each group may comprise a large number ofsuch lines. The practice is to give the finder swltch brushes access to the terminals of five hundred "lines, these lines being arranged in ten groups of fifty lines each. Each of the lines has associated with it at the central ofiice a line relay 12 and a cut-off relay 11. Each line is also provided with one or more spring-jacks 14 by means of which connection may be made with the line when it is a called line. The lines represented as calling lines in Fig. 1 and the line shown as a called line in Fig. 5 may be lines of the same sort, similarly equipped and located at the same exchange; or the lines may be located at different offices. In the present instance, the called line shown in Fig. '5 is indicated as being provided with connections by means of which it may have control over finder'switch mechanism 1n the mannerillustrated in connection with the lines of Fig. 1, Each group of lines, LG and LG, has associated with it certain group apparatus consisting of two relays 19 and 24, a common protective relay 250, and a timing sequence switch 100. There is also provided apparatus common to all of the line groups, comprising the relays 22, 23 and 33.

The groups of lines have access to groups of connecting circuits through the medium of finder circuits F, F, F, which terminate upon the brushes of pairs of finder switches of which twosets, LF and CS and LF and CS, are shown. Each of the groups of connecting circuits is associated with a particular operators position, of which the apparatus of one is shown at O and the apparatus of the other is partially shown at 0.. In the particular svstem illustrated, it is the practice to provide each operators position with twenty-five connecting circuits extending to multiple groups of terminals upon the cord selector switches, and to give the merely dia brushes of each cord selector switch access to the terminals of twenty such g"oups of connecting circuits".- But one of the connecting circuits is shown complete, the other connecting circuits in the associated group and in the other groups being similarly organized and connected. Multiple connections of'the connecting circuit with the terminals of the cord selector switches are shown in the case of the connecting circuit that is indicated and the one that is completely illustrated; and in like manner multiple connections of the tele hone line with the terminals'of the line fin er switches are shown in the case of the lines that extend from the two stations shown. The multiple connections that exist between corresponding sets of switch terminals and the other connecting circuits and telephone lines are omitted to avoid confusing the drawing. A number of groups of cord selector switches like the group illustrated in Fig. 3 may have access to the same groups of connecting circuits and their corresponding operators positions. This is indicated in Fig. 3. Each of the oups of cord selector switches has associated with it certain selection controlling apparatus, that associated with the cord selector switches shown in Fig. 3 appearing under the caption Frame 2, and that associated with the cord selector switches of the other group that is not shown appearing under the caption Frame 1. The selection controlling apparatus for each frame or group of cord sclcctor switches comprises a set of relays 77 93, and 94 for each operators groups, CG, CG, to which the cord selector has access, and a group of relays 54, 55, 61 and 63 common to all of the first mentioned groups.

As the line finder switches LF and LF, and the cord selector switches CS and CS in themselves are not novel, they are shown ammatically. These switches be substantlally like the switch illustrated and described in the patent to James L. Mc- Quarrie, No. 1,177,044, issued March 28, 1916. The line finder and cord selector switches are alike in all substantial respects.

Each comprises a longitudinally movable shaft 1 carrying as many sets of brushes 2 as there are groups of stationary terminals to be engaged. To move the shaft up, an extension at the lower end of the shaft is brought into engagement with the con- 120 stantly rotating power member 3 by means of an idler Wheel operated by the up-drive magnet 32; and to move the shaft down, tho. extension is brought into engagement with the power member 4 by means of an idler wheel operated by the down-drive magnet 62.

Normally the brushes of .each of the sets 2 are held apart, so as to clear the associated terminals, by means of a separating 130 eeann cam located between the innermost brushes lit of the set. The com 5 is rotatably mounted, and when rotated in one direction, releases the brushes and permits'them to engage the associated terminals. The tripping or releasing of the brushes is controlled ya number of trip- magnets 16, 17. Each of these when energ1zed rotates an associated trip rod 6 that extends transversely. to the sw1tch shafts 1 and carries as man tripping yokes l as there are finder swltc we in the group. The trip rod,-in rotatmg, brings all oi its tripping yolres 7' into position to .o

crate the rush controllin came 5 of t e corresponding sets of brushes on all oi the switches, so that whichever ot the finder switches is caused to move uphas that set oi brushes tripped that corresponds with the particular trip magnet 16, 17, that is at the time energized, When the finder switch that has been in use is returned to its. nor mal position, any of the associated controlling cams 5 that has been tripped is engaged and rotated in'a reverse direction to separate its switch sorings again and thusrender them inactive.

as :in the various stages oi the upwardnuove tit Roch oi the line finder and cord selector switches has associated with it a commutator which comprises a number ct stationary commutator segments and a set of movable brushes carried at the top oi the switch shalt land cofiirating with the stationary i 's commutator serves to u ment of the switch shaft. I a

For controlling thecircuits of the organization, there are employed a number oil sequence switches which are shown at dliierent points and are designated 100, 9200,

300, e00 and 500, res ectively. Thesedse e 1suence switches'may e of the t c osed in Patent 1,127,808 issued'lie rua 0, 1915, to Reynolds and Baldwin. Rae consists of an electromagnetically controlled motor or driving mechanism and'a number of associated switch cams. The switch cams associated with each of the sequence. switches 100 are designated 101 to 103 inclusive; those associated with each of the sequence switches 200 are designated 201 to 223 inclusive; those associated with each of the sequence switches 300 are designated 301 to 310 inclusivegthose associated. with each of the sequence switches 400 are designated 401 to 416 inclusive, and those associated with each of the sequence switches 500 are designated 501 to 519, inclusive. To each of the contacts associated with the various sequence switch cams are a plied certain numerals. These numerals n the caseof the cams 101, 201, 801, 401 and 501 indicate the only positions of the associated sequence switch in which these particular contacts are open; the numerals applied to all of the other contacts of each sequence switch indicate the only ositions of the particular associated switc in which the associated, contacts are closed.

The sequence switches 100 merely act as timing switches and have only one resting position. The resting positions of the other sequence switches, and the stages of operation with which these positions are associated, are as follows:

' Sequence switch R00.

1. Normal. 1 2. Awaiting starting circuit.

3. Awaiting startin circuit release. A. Hunting calling 'ne.

0. Awaiting precedin finder circuit.

l. Awaiting operators selecting circuit. d. Releasing operator s selecting circuit. 0 Hunting cord circuit.

. Talking. Line finder at tell-tale. Cord selector at tell tale.

Line finder return.

. Cordselector return.

Sequence switch 300.

1. Awaiting a call. 4-. Position vacant. Position busy.

Sequence switch 400. 1. Normal. 7. Listening in.

. Listening out...

dogmat c switch Z5110. Normal.

. Awaiting listening they sequence switch. N I

@ Selective ringing operations.

13. Ringing called line. 16. Awaiting supervisory relay. 17. Talking.

. Themanner in which the system is organized will appear from the description of its operation which follows. It w1ll be assumed that the subscriber at station A initiates a calL. When the tele hone receiver is taken from the switchhoo a circuit is closed that extends by way of both windings of the line relay 12 and both limbs of the telephone line, and is completed in the-contacts of the switchhook at the subscribers station. The flow of current in this circuit energizes the line relay 12, which in operating applies at its right-hand armature and contact, a ground to the conductor 18. This causes current to How from battery through the winding of the relay 19, sequence switchcontact 103 (18% to 1 conductor 18 and ground at the contacts of the operated line relay 12. The relay 19 attracts its armature and closes a circuit that extends from battery through the right-hand winding of the associated relay 24, front contact of relay 19, back contact {of relay 22 and lower armature and back contacts of relay 32 to ground. Relay 24 operates and closes at its left-hand front contact a circuit that extends from battery by way of the winding of the associated group trip magnet 16 and the left-hand winding of the relay 24, in parallel, to the front contact of that relay, and thence by way of conductor 58, the winding of the relay 22, and the lower arms ature and back contact of therelay 23 to ground.

Current flowing in the circuit traced above operates the trip magnet 16 of the group in which the calling line is located, locks up the relay 24 of theassociated group and operates the relay 22 common to all of the groups. The tri magnet 16 rotates its associated trip rod to bring all of the yokes into position to tri the corresponding set of brushes of whic ever of the line finder switches is started. The group relay 24 breaks, at its left-hand back contact, thecircuit of the conductor 58 to the corresponding relays 24 of the succeeding groups of the series.

The relay 24, at its right-hand front contact, also completes a circuit that extends from battery through the motor magnet of the sequence switch 100, and contact 102 (18% to 1%) of that switch. In moving out of position 1, sequence switch 100 closes its contact 101 and opens its contact 103. As contact 101 is closed in all positions excepting position 1 of the sequence switch, the switch is caused to make one complete rotation; and as contact 103 of the sequence switch is open in all positions excepting positions 18% to 1%, the conductor 18 is held open while the sequence switch is making its revolution and until it gets back to position 1. The time required by the sequence switch to make one complete rotation is so regulated as to be greater than that occupied by the line finder switch in finding the terminals of any calling line. The action, therefore, is such as to interrupt the group conductor 18, and hold it open until after the line relay 12 of the callin line has been released as a result of the line.

The relay 22, common to all the groups, in

zation of the associated relay 24 and ti ending of that operation of the correspondin trip magnet, the interruption of this con uctor insures the operation of only one trip magnet and the tripping of only one set of brushes on a started line finder switch.

The common relay 22, when it operates, applies ground to the starting conductor 29 to start a finder switch huntin for the calling line. The starting con uctor 29 has branches extending to like sequence switch cams 206 of all of the finder circuits terminating upon the line finders that have access to the callin line. But, for reasons which will hereina r be explained, the sequence switch 200 of only one of these finder circuits is standing in its 2 position. Assuming that this is the sequence switch of finder circuit F, when the relay 22 is actuated by the calling line, as already described, a circuit is completed that extends from battery through the left-hand winding of relay 30, sequence switch contacts 206 (2), conductor 29, front contact and armature of starting relay 22, lower armature and back contacts of relay 23 to ground. The right-hand winding of relay 30 is at this time also in cluded in parallel with the left-hand winding of the relay in the energizing circuit, the parallel branch being from battery through resistance coil 56, sequence switch contacts 217 (2 to 9) right-hand winding of relay 30, se uence switc contacts 220 (2) and (1 to 13 thereafter joining the conductor that extends from the left-hand winding of relay 30, and to ground over the circuit already traced. The effect of this is to give the relay 30 the benefit of the energizing action of both windings.

As a result of the closure of the circuit traced above, the relay 30 is energized and closes a circuit that causes the associated sequence switch 200 to move out of position 2. This circuit extends through the motor magnet of the sequence switch 200, sequence switch contact 202 (2) ri ht-hand front contact and armature of 're ay 30, sequence switch contact 208 (2 to 7), conductor 79, commutator segment M of the associated cord finder switch CS, and to ground by way of the brush that is in engagement with this commutator segment. Relay 30, in attracting its armatures, also closes a locking circuit for itself that extends from battery by way of the resistance coil 56, sequence switch contacts 217 (2 to 9), the right-hand winding of the relay 30, sequence switch contacts 216 (2 to 4) and (2 to 9), front contact and left-hand armature of the relay 30, and armature and back contact of the relay 37 to ground.

As a result of the closure of its motor magnet circuit in the right-hand front contact of the relay 30, the sequence switch 200 moves out of position 2 and comes to rest in position 3. In position 3 of the switch, a

circuit is closed that extends from battery by way of the up-drive magnet 32 ofthe corresponding line finder switch LF, con-, ductor 59, sequence switch contact 207 (3 to a), front contact and ri ht-hand armature of relay 30, sequence switch contact 208 (2 to 7)., and to ground by way of conductor 7 9 and the commutator segment M and associated brush of the corresponding cord finder CS. The energization of theupdrive magnet 32 starts the upward movement of the corresponding elevator rod with its associated sets of ushes. At the outset of the u 'ward movement of the elevator rod, all the brush trip levers are moved past the corresponding trip yokes. The only trip magnet that is energized in this case is the magnet 16 which corresponds with the group in which the callin line is cats and, consequently, the on y tri yoke in position to engage a tri lever on t e elevator rod is the one w ich controls the brushes 10, 41, 42 and 43 that are adapted to engage the terminals of that particular roup of lines. This set of brushes, thereore, is released and made 0 erative, and the other sets are held clear 0 theirassociated line terminals.

As soon as the set of brushes corres onding with the calling line is tripple the group apparatus, by means of w 'ch the ines control the brush trippin finder starting operations, may 6 returned toits normal condition. The first step in this restoring operation is eflected by the closure of a. circuit which is completed by way'of the K segment of the line finder commutator immediately after the brushes are tripped. This circult extends from battery in parallel branches through the relays 23 and 33 see Fig. 1), conductor 26, sequence switc contact 209 (2:1 to 3 conductor 68, and to ground by way of t e K segment of the line finder commutator and its associated brush. The energization of the relay 23 interrupts, at the lower back contact of that relay, the reviously described circuit that has up to t is time maintained the ener ization of the trip magnet 16, the group re ay 24 and the common starting relay 22. Relay 23, at its upper front contact, closes a locking circuit for itself and the associated relay 33 that extends by way of conductor and the se uence switch contacts 210 (2% to 1) of al of the finder circuits in series, to ground at a point beyond the last switch of the series.

As has already been stated, normally there is only one of the finder circuits wit bit osition 2 awaiting the finder circuits are in position to close their contacts 210. The locking circuit. for the relays 23 and 33 is, therefore, held closed until another one of the finder circuits has its sequence switch moved into position 2. This is accomplished by relay 33, which, in operating, conductor 28 to move the sequence switch of another finder circuit out of position 1 and into position 2 and which also applies a ground to the conductor 27 to move the sequence switch of the appropriated finder circuit out of position 3.

Assuming that the sequence switch of finder circuit F is in position 1 and that the sequence-switch of finder circuit F is in some position between 4 and 17, that finder circuit being assumed to be in use, the operation of the relay 33 completes the fo1- lowing circuit: from battery, through the motor magnet and contact 203 (1) of the sequence switch of finder circuit F, conapplies a ground to tacts 211 (1) of the same sequence switch,

contacts 211 (3 to 17 and (4 to 17) of the sequence switch 200 of finder circuit F contacts 211 (3 to 17) and (3 to 3%) of the sequence switch 200 of finder circuit F, conductor 28, lower contact and armature of the relay 33 to ground. This causes the sequence switch of finder circuit F to move into position 2. and 11118..

If by any chance the sequence switch of finder circuit F should'failto be moved into the call-awaiting osition 2 when the relay 33 operates, it will be moved into that position when the sequence switch of the appro-,

priated finder circuit F moves into position 5 at a slightly later stage in the operation. The circuit by which this result would, under the circumstances, be accomplished extends from battery throu h the motor magnet and contact 203 (1 of the sequence switch of finder circuit contacts 211 (1') of that sequence switch, sequence contacts 211 (3 to 17 and (4-to 17) of finder circuit F (assume to be in use), and thence by we of contacts 222 (5 to 1) of all of the fin er circuit sequence switches in series to ground. In other words, at any time that the finder circuit sequence switches are all standing in position 1 or in osition 5 and beyond, a ground is applied y way of the 222 cams in series that moves one of. the switches into osition 2, and thus laces the associated fin er'circuit in its cal -awaiting condition. The sequence switch of finder circuit F is moved out of position 3 by the closure of a circuit that extends from battery throu h the motor magnet and contacts 203 (3) o the sequence switch of that circuit, conductor 27 and upper contact and armature of relay 33 to ound. As'soon as the sequence switch oE finder circuit F moves into position 2, it opens at its contact 210 the circuit by way of conductor 25 armatures.

which has been maintaining relays 23 and 33 energized and these relays release them I ela 23, in releasing, reconnects to ground t e circuit which extends in branches 57 and 58 through its various sets of group relays, thus again giving the groups access to the starting circuit.

At this Stage of the operation of the system, the sequence switch of the appropriated line, the test relay 37 of the finder circuit is connected with local conductor 253 of that line. This local conductor has two branches, one or the other of which is closed depending upon the condition of the line relay 12 of the associated line. If the line relay is inert, as it is when the line is not calling, or when the line has been connected with and its cut-ofif relay operated, the local conductor 253 of the line is connected with ground by way of an identifying device 252 and a relatively low potential battery. If

the line relay 12 is energized, as it is when the line is calling and is not connected with, the local conductor 253 of the line is connected with ground by way of the righthand back contact and armature of the protective relay 250 common to a group of lines,-

the energizing winding of this relay, and a relatively high potential battery 251. Therefore, as the elevator rises and the brush 43 engages the corresponding terminal 47 of each, of the lines of the group in which the calling line is located, a circuit is completed as each line terminal is engaged that extends, either by way of the low potential battery, the device 252, and the left-hand back contact and armature of relay 12 to the local conductor 253 of the line; or by way of the high potential battery, the winding of common relay 250, the right-hand armature and back contact of that relay and the left-hand front contact and armature of relay 12 to the local conductor 253; and thence by way of line terminal 47 brush 43, conductor 51, finder sequence switch contacts 204 (1 to 8) and (2% to 4), and winding of relay 37 to ground.

The relay 37 is so adjusted that it will respond only to the current flow produced in the circuit by the high potential battery, and not to that produced by the low potential battery. As the line relay 12 of the calling line is energized, thus connecting the high potential battery to the associated local conductor 253, the test relay 37 respends when the brush '43 engages the terminal 47 of the calling line. The response of the relay 37 causes that relay to interrupt in its back contact the previously traced circuit by way of the left-hand armature and front contact of the relay 30, sequence switch contacts 216, and right-hand winding of relay 30, which circuit had been holding the relay 30 locked up from the moment that the relay was first energized upon the re eipt of the call.- Relay 30 in releasing its armatures breaks its own locking circuit, and also breaks the previously-traced path, including sequence switch contacts 208, right-hand armature and front contact of the relay 30, and sequence switch contact 207, over which current has been flowing to energize the updrive magnet 32 of the line finder. Therefore, the operation of the relay 37 upon the finding of the calling line acts to efiect the instant deenerglzation of the up-drive magnet 32, and thus to stop the brushes upon the terminals of the calling line.

In order that the brushes may always be stopped in registration with the line terminals, the locln'ng circuit of the relay 30 has an alternative path to ground by way of sequence switch contact 215 (2 to 4), conductor 66, the C segment of the line finder commutator and the corresponding brush to ground. The C segment of the commutator is so formed and related to its brush that the connection between the two is interrupted only when the corresponding line brushes on the elevator rod arein engagement with corres onding sets of line terminals. The unloe of the relay 30, and the consequent stopping of the upward movement of the elevator rod, can therefore occur only when the line brushes are in proper relation to the terminals of the calling line. I When the relay 30 is deenergized, as a result of finding the calling line, it also completes a circuit that extends from battery through the motor magnet and contact 202 (3 to 4) of the finder sequence switch, righthand back contact and armature of the relay 30, sequence switch contact 208 (2 to 7), conductor 79, and M segment and corresponding brush of the cord selector CS to ground. The closure of this circuit moves the sequence switch out of position 4. When the finder sequence switch reaches position 4%, it closes a path for the flow of current through the cut-off relay 11 of the calling line by way of resistance coil 64, sequence switch contact 212 (4% to 1211;), conductor 50, brush 42, line terminal 46 and conductor 53.. The flow of current in this circuit operates the cut-oif relay 11 to, disconnect the relay 12 from'the circuit, and that relay in releasing its armatures disconnects the high potential test battery from the local conductor 253 and disconnects ground from the common conductor 18. The disconnection til) of ground from conductor 18 occurs before the timing sequence switch 100 has completed its cycle of rotation and reconnected conductor 18 with role 19.

The brushes of the line finder switch are now at rest in enga ement with the termi nals of the calling line, the sequence switch 200 of finder circuit F is at position 6, the group starting circuit represented by the conductors 57 and .58 and the associated relays 22, 23 and 33 has been released and is in readiness to respond to another callm line, and the sequence switch of another der circuit has been moved into position 2, and thus brought into operative relation with the starting conductor 29.

When the sequence switch of the finder circuit over which the call is being extended has reached position 6, the finder circuit is brought into operative relation with the operators selecting circuit. When the finder sequence switch reaches position 6, it awaits the closing of a circuit, the completion of whichis deg-indent upon the condition of the other der circuits of the associated group. This circuit extends from battery through the left-hand winding of the relay 30, contact 219 (6) of the appro- "priated circuit sequence switch contacts 219 (9 to 4:) of the sequence switches of the associated finder circuits preceding 1t 1n the series, conductor 76, outer armature and back contact of relay 54, and right-hand back contact and armature of relay 61 to ground. A branch path for the energizer tion of relay -.30 also exists at this time, this branch path extending from battery-through resistance 56, sequence switch contacts 217 (9, to 9), right-hand winding of relay 30, sequence swltch contacts 220 (6) and (1 to i 13), and contact 219 (6) of the appropriate finder circuit sequence switch, from which point it extends to ground at the righthand back contact and iarmature of the relay ()1 over the path already traced. This circuit for the energization of relay 30 is open either in the cam 219 of a preceding finder se uence switch in the series, or in contacts 0 the relay 54 or 61 as long as any sequence switch of the series is in positions 4 to 9. Th'at'is, it is open from the time the line finder switch of any associated finder circuit finds a calling line until the cord finder switch of that circuit has moved far enough to trip the brushes corresponding with the selected operators position, as will be described. Not until this has occurred will the above-traced circuit of the awaiting finder circuit be closed. When the circuit is closed, the relay 3O attracts its arinatures and completes a circuit that extends from battery through the motor magnet and sequence switch contact 202 (6 to 7) of the sequence switch 200, right-hand front contact and armature of relay 30, sequence switch contact 208 (2 to 7), conductor 79 and segment M and corresponding brush of the cord selector commutator to grou d. The completion of this circuit moves finder se uence switch out of position 3.

hen the sequence switch 200 reaches position 6% it closes a circuit that extends from battery by way of the winding of relay 55 (Fig. 3), conductor 71, sequence switch contact 218 (6:2 to 8), conductor 67, andsegment M and corresponding brush of the line finder commutator to ground. The operation of the relay 55 applies ound to the conductors 81 extending to al of the 0 erators positions. At each of the positlons where the operator is at her station and is in readiness to receive a call the associated relay 91 (Fig. 4) is inert, and the operators telephone sequence switch 300 is in its 1 position. Consequentl at each of such positions, a circuit is c osed' that extends from battery, through the winding of the asso ciated relay 92, left-hand armature and back contact of relay 91, sequence switch contact 304: (1), conductor 81, armature and front contact of relay 55 to ground. The relay 92 of each available osition therefore attracts its armature and c oses a circuit that extends from battery, throu h the front contact and armature'oi the re ay 92 to the conductor 82, and thence to ground by way of the windings of the relays 77 corresponding to that operators position at the various cord selector frames. X

When the finder sequence switch 200 reaches position 7, in which position it comes to rest, 1t closes a circuit that extends from battery through the winding of relay 54, left-hand back contact and armature of relay 61, conductor 73, finder sequence switch contact 218 (7 to 8), conductor 67, and segment M and corresponding brush of the line finder commutator to ground. Relay 54 attracts its armaturesand completes a branch of the circuit traced above, which branch extends from conductor 73 1) way of the armature and back contact '0 the relay 63, front contact and inner armature of rela 54, armature and front contact of relay 77 (which relay is energized, as previously described, as a result of the corres onding operators position being in readiness to receive a call), right-hand back contact and switch spring of relay 93 of the corresponding group, winding of associated relay 94,

and resting contact of relay 93, ,con uctor 83, left-hand back contact and armature of relay 95 at the 0 operators osition to battery. Upon the closure of t e above-traced -branch circuit, group relays 93 and 94 are.

energized in parallel withthe relay 54. Relay 93 in operating disconnects its own energizing winding and that of relay-94 from the previously traced path to battery by way of the left-liandback contact and armature of relay 95, and connects them in a path which extends to battery by way of conductor 84 and the winding of the relay 95. This causes the relay 95 a so to be energized and to interrupt in its left-hand armature and back contact the path by way of conductor 83 over which the relays 93 and 94 were initially energized. V

Relay 94 in operating closes a circuit from battery through the winding of the trip magnet 20 corresponding to the selected operators position, and to ground by way of the right-hand armature and front contact of the relay 94. This relay also closes a eucuit that extends from battery through the winding of the relay 63 and the left-hand armature and front'contact of the relay 94 to ground. The relay 63 in operating closes a branch that extends from the conductor 7 3v (grounded by way of contact 218 (7 to 8) of the line finder sequence switch) through the armature and front contact of relay 63,

conductor 72, sequence switch contacts 220 (7) and (1 to 13), and left-hand winding of relay 30 to battery. A branch energizing path for relay 30 also extends from conductor 72 by way of sequence switch contact 220 (7), right-hand winding of relay 30, se quence switch contacts 217 (2 to 9), and resistance 56 to battery. Relay 30 attracts its armatures and closes a circuit that extends from battery through the motor magnet and sequence switch contact 202 (6 to 7), front contact and right-hand armature of relay 30, sequence switch contact 208 (2 to 7), conductor 79, and segment M and corresponding brush of the cord selector commutator to ground. The closure of this circuit moves sequence switch 200 out of position 7. Furthermore, relay 30 in operating is locked up over a circuit that extends from battery through resistance 56, sequence switch contacts 217 (2 to 9), right-hand winding of relay 30, sequence switch contacts 216 (7 to 9) and (2 to 9), front contact and left-hand armatureof relay 30 and armature and back contact of relay 37 to ground. When the sequence switch reaches position 8 it closes a circuit that starts the upward movement of the brush-carrying rod of the cord selector switch, this circuit extending from battery through the up-drive magnet34 of the cord finder, conductor 89,

sequence switch contact 207 (8 to 9), righthand front contact and armature of relay 30, sequence switch contact 218 (8 to 9) conductor 67, commutator segment M of the line finder and corresponding brush to ground. Y

At the outset of the upward movement of the cord finder brush rod, the tripping levers of the various sets of brushes are brought simultaneously into operative position with respect to the corresponding tripping yokes,

mosses energized. In the present instance, it is assumed that this is the trip ma et 20 associated with the terminals of t e group of connecting cord circuits extending to the O operators position. Immediately after the set of brushes is tripped, the common operators selecting circuit is restored so as to be available for the use of other cord finder switches. This is effected through the medium of a circuit that is completed by the grounding of the K segment of the cord finder commutator, this segment being so located as to be engaged by its brush immediately after the tripping levers of the sets of brushes pass the associated tripping yokes. The circuit referred to extends from battery through the winding of relay 61, conductor 74, sequence switch contact 221 (72 to 8), conductor 80, cord finder commutator segment K and its corresponding brush to ground. Relay 61 in operating opens, at its left-hand back contact, the previously-traced circuit by way of conductor 73 which, up to this time, has been holding energized the relay 95 at the O operators position and the relays 93 and 94 for responding to this position on the cord finder frame. The release of the relay 94 decnergizes the corresponding trip magnet 20 and the common relay 63. The deenergization of the relay 93 reestablishes, subject to the release of relay 61, the control of other finder circuits over the brush tripping mechanism of the associated cord finder frame. Relay 61, in operating, closes a locking circuit for itself by way of conductor 73, sequence switch contact 218 (7 to 8), conductor 67 commutator segment M of the line finder and corresponding brush to ground. It also completes a circuit that extends from battery through the motor magnet and contact 205 (8) of the sequence switch 200, conductor 7 5, right-hand front contact and armature of relay 61 to ground. The closure of this circuit moves sequence switch 200 out of position 8. In moving out of position 8, the sequence switch opens its contacts 218 (7 to 8), thus denergizing relay 61 and again extending conductor 73 to the relay 54 and the conductors over which the operators selection is effected. In closing its right-hand back contact upon release, relay 61 also restores the continuity of con ductor 76 and makes it available for moving out of position 6 the sequence switch of some other finder circuit which may be waiting for access to the operators selecting circuit.

After the cord selector switch CS passes the brush-tripping position, it continues its upward movement until the brushes are flow of current is completed from high potcntial battery 251 (see Fig. 4), through the winding 0t common protective relay 197, armature and back contact of that 'relay, lower back contact and armature of relay 134, conductor 128, right-hand armature and back contact of rela 119, lower back contact and armature of relay 155, contact 404 (1) of the listening key sequence switch,

conductor 88, test terminal 118 and brush 114 of the cord selector, conductor 99, finder sequence switch contacts 206 (8 to 9) and the winding of relay 37 to ground. Relay 37 thereupon attracts its armature and opens the previously traced locking circuit that has been holding relay 30 energized. Relay 30, in releasing its armatures, opens at its right-hand front contact and armature the 'ener zing circuit for the up-drive Ina net 34, t us stopping the brushes of the cor selector switch in engagement with the terminals 01 the selected connecting circuit. lln

engaging its back contact, the right-hand armature of relay 30 closes an energizing circuit for the motor magnet 01 the finder sequence switch which extends by wa of cam 202 (8 to 9), back contact and rlghthand armature of relay 30, cam 218 (8 to 9),

a connecting cord sequence switch conductor, 67, and the M segment and corresponding brush of the line-finder commutator to ground. The closure of this circuit moves sequence switch. 200 out of position 9, whereupon the switch continues to move until it reaches position 14, where the talking circuit is completed at cams 213 and 214.

An instant after the finder sequence switch leaves position 9, it closes a circuit that extends from battery through the windings of relays 151 and 154-(see Fig. 5) in parallel, contact 505 (1), listening key sequence switch contact 405 (1), left-hand back contact and armature of relay 152, conductor 87, cord selector switch terminal 117 and corresponding brush 113, conductor 98, and finder sequence 'switch contacts217 (92 to 14) and (9% to 11) to ground. Relay 154 in operating closes a locking circuit for itself and relay 151 that extends by way of its left-hand front contact and armature, connecting cord sequence switch contact 506 (1) and listening key sequence switch contact 406 (1 to 6) to ground. Relay 154 also closes a circuit that extends from battery through the motor magnet and cam 403 (1) of the listening key sequence switch, contacts 507 (17 to 8) and (1) of the connecting cord sequence switch and right-hand frontcontact and armature of relay 154 to ground. The

closure of'this circuit causes the listening key sequence switch to move out of position 1, and, in doing so, to open the test conductor 88 at sequence switch contact 404 (1), and also to open at sequence switch contact 405 (1) the path over which the relays 151 and 154 were first energized.

Relay 151, associated with relay 154, in I operating closes a circuit that extends from battery through the winding of relay 152 and outer front contact and armature of re-' lay 151t0 ground. As a result relay 152, prior to the moving of the listening key sequence switch out of position 1, has disconnected conductor 87 from connection with battery by way of sequence switch contact 405 1) and the windings of relays 151 and 154, and has connected it with an alternative path to battery by way 01" the left-hand front contact of relay 152 and winding of relay 155. The relay 155 in operating closes at its upper front contact and armsture a normal break in talking conductor 86, and at its lower back contact and armature opens the path of test conductor 88. When the listening key sequence switch reaches position 2, an additional path to ound for holdin the relay 152 energized, 155 closed by wa 0 sequence switch contact 407 e energization of relay 151 at the instant the cord is seized also brings about the closure of a circuit that extends from battery through the winding of the common relay 134, conductor 129, contact 502 (1) of the connecting cord sequence switch, and inner front contact and armature of relay 151 to ground. Relay 134 in o crating opens at its lower armature and bac contact the circuit over which the potential of the high voltage test battery 251 is applied to the test seized by a cord selector is withdrawn from the selected cord and also from its associated cords at the instant of seizure, and is not reapplied to such of the cords as may be in condition to be selected until the common relay 134 is deenergized. The deenergization of relay 134 occurs when the relays 1'51 and 154 are released by the opening of their locking circuit at cam 406 when the listening key sequence switch moves beyond position 6.

When the listening key sequence switch 400 is moved out of positlon 1, in the manner described above, it continues its movement until it reaches position 7. In position 7 the cams 408, 409, 410 and 411 of the listening key sequence switch interrupt the talking strands of the connecting circuit and include between their severed ends a loop that has connection by way of conductors 135 and 136 with the operators telephone set 147. This puts the operator in communication with the calling subscriber. At the same time the operator is informed of the identity of the connecting cord over which the call is being extended by the flashing of the lam 161 associated with that cord, the circuit or illuminating this lamp extending from battery through the reslst-ance 163, lamp 161, calling cord sequence switch contact 514 (1 to- 2), listening key sequence switch contact 412 (12- to 18-1), and interrupter 162 to ground.

As has previously been explained, when the sequence switch of an appropriated finder circuit reaches position 63-, it operates a trip magnet on the cord selector frame that corresponds with a waiting operators position, and at the same time operates the relay 95 associated with the apparatus at that operators sition. When the relay 95 at the operators position attracts its armatures, it closes a circuit which extends from battery through the winding of the relay 142, conductor 121, right-hand front contact and armature of relay 95, and right-hand front contact and armature of relay 125 to ground. Relay 142 in operating closes a ocking circuit for itself that extends to ground by way of the inner front contact and armature of relay 142, operators sequence switch contact 305 (16% to 15) and the right-hand front contact and armature of relay 125. The relay 142 in operating also closes a circuit that extends from battery through the motor magnet and contact 303 (1 of the operators sequence switch, outer ront contact and armature of relay 142, contact 306 (1 to 9) of the operators sequence switch and right-hand front contact and armature of relay 125 to ground. The closure of this circuit causes the operators sequence switch to move out of position 1 and to continue its movement until it comes to rest in position 17. By causing the relay 95 to control the movement of the operators sequence switch 300 out of position 1through the medium of the locking relay 142, thls movement of the operators sequence switch is made certain, even though there is only a momentary energization of the relay 95 in the selectlon of the operators position. As the locking circuit of the relay 142 is controlled in the contact 305 (16%} to 15) of the operators sequence switch, the locking circuit is broken and the relay 142 released the moment the sequence switch 300 passes beyond position 15 in its movement to its resting position 17.

The left-hand windlng of the relay 91 is connected in parallel with the winding of the relay 142; and as a result the instant relay 95 attracts its armature, the relay 91 opens, at its left-hand armature and back contact, the path over which the relay 92 is energized when the operators position is to be selected. This path is also opened at sequence switch contact 304 (1) an instant later when the operators sequence switch is moved out of position 1 by the encrgization of the locking relay 142. Thus the operators position is made inaccessible to other calls the instant it is selected, and is maintained inaccessible until the operators sequence switch returns to position 1 and the relay 91 is de'energized.

When the relay 95 operates upon the selection of the operators position, it closes a circuit that extends from battery by way of the left-hand armature and front contact of relay 95, conductor 120. and thence through two parallel paths, one of which extends through the winding of the relay 195 and the right-hand front contact and armature of relay 125 to ground, and the other of which extends through the winding of the relay 145, upper back contact and armature of relay 153, operators sequence switch contact 302 (18% to 15) and the right-hand front contact and armature of the relay 125 to ground. The relay 145 in operating closes at its front contact and armature an alternative path for supplying current for main taining the energlzation of the relays 145 and 195 after the relay 95 has released its armatures at the conclusion of the selecting operation. The relay 195 in operating effects certain circuit changes the object of which will be described hereinafter. The relay 145 in operating closes a circuit that extends from a source of call-tone current 143 through a condenser 144, right-hand front contact and armature of relay 145, and a winding of the operators induction coil 146 to ground. Thus a call-tone is produced in the operators telephone receiver the instant the relay 95 operates upon the selection of the position. s the energizing circuit for the relay 145 which controls the application of the call-tone is controlled at the upper back contact and armature of relay 153 and at the operators sequence switch contact 302 (18"; to 15) the call-tone continues until the relay 153 is energized, or until the operators sequence switch, which is independently actuated by the relay 95 at the instant of selection, as has been described, moves past position 15 in its movement from position 1 to position 17 The energization of the relay 153 is effected by the closure of the circuit that extends from battery through the winding of the relay 153, conductor 129, and upper front contact and armature of relay 134 to ground. The relay 134, as has already been described, is energized by the energization of the relay 151 at the moment the circuit by way of conductor 87 is closed upon the seizure of the connecting cord of the cord selector switch. Thus the relay 153 is energized to dei nergize the relay 145 to withdraw the call-tone upon the seizure of the connecting cord at the selected operators position. As the continued energization ofthe relay 195 is under the warning of the selection of her 1position by ciated with that cor position has been made inaccessible to other hearing thecallrtone inher ,te phone receiver, and that a few moments later she is apprised of the connecting cord that is to be used by the flashin of the lamp 161 assod. In the meanwhile the incoming calls by the operation of the relay 91 and the movement of the operators sequence switch 300 out of position 1, and the operators telephone apgaratus has been connected with the selecte connecting cord by the movement'of the connecting cord sequence switch to position 7. The 0 erator now being in communication with t e calling subscriber, inquires the number of the line that is wanted, and upon bein informed completes connection with that me by insertlng the calling plug 170 into the corresponding spring-jack 14, first testing the line by touching'the tip of the plug to the sleeve of the spring-jack. 1f the line is busy, the potential that exists upon the sleeve of the spring-jack causes current to flow by way of the tip of the plug, the right-hand armature and back contact of relay 175, conductor 133, and winding of relay 184 to ground. Relay 184 in o crating closes a circuit that extends from atterythrough the retardation coil 18,5 and the test winding of the operators induction coil 146 to ground. This causes a click in the operators telephone receiver that tells her that the line is busy Assuming that the line isfree for connection, the insertion of the plug 170 closes a circuit that extends from battery through the coils of the relays 119 and 175 in series, and thence by way of the registering sleeve contacts of the plug 170 and spring-jaclr 14 to ground by way of the -winding of the cut-0d relay 11. The cut-ofi tip of the plug from the conductor 133 ex-' tending to the operators busy test relay 184, and connects it instead with the tip strand of the talking circuit. lRelay 175 also closes a circuit that extends from battery through the motor magnet and contact 503 1) ofthe calling cord sequence switch, contact 413 (7) of the listening key sequence switch, and left-hand front contact and armature of relay 175 to ground. The closure of this circuit energizes the motor magnet and moves the call cord sequence switch out of position 1. When the calling cord sequence switch reaches position 2 it comes to rest and completes a circuit that extends from battery switch, and right-hand bac through the motor ma et and contact 403 (7) of the listenin e sequence switch, contact 515. (2) of the callin cord sequence contact and armature of relay 154 to ground. When the llstening key sequence switch 400 moves out of position as the result of the closure of this clrcuit, it completes a circuit that extends from battery through the motor magnet and contact 504 (2) of the calling cord sequence switch, contact 413 (8 to 15) of the llstening key sequence switch, and left-hand front contact and armature of relay 175 to ground, The closure of this circuit moves the calling cord sequence switchout of position 2..

As the listening key sequenpe switch 400 movesbeyond position 8, it operates its cams 408, 409, 410 and 411 to disconnect from the connecting cord circuit the loop that extends to the o erators telephone circuit by way of the con uctors 135, 136, 165 and 166 and con meets the talking conductors 85 and 86 of the connecting cord circuit directly through to the left-hand windings of the'repeating coil 169. Furthermore, it interrupts the branch of the energizing circuit of the cord circuit holding relay 152 that had been completed to ground by way of listening key sequence switch contact 407 (2 to 7) and leaves the continued energization of the holding relay dependent upon a path to ground that extends by way of the right-hand front con- 1 tact and armature of relay 152 and contact 508 (1 to 181) of the calling cord sequence switch.

After the calling cord sequence switch 500 is moved out of position 2 by the movement of thelistening key sequence switch out of position 7 as described above, it moves through its various stages (under the control of the circuit which extends to ground by way of calling cord sequence switch contact 504 (4 to 13) and the right-hand back contact and armature of relay 180) until it reaches position 12, at which point a circuit is closed that extends from battery through the winding of relay ture and back contact of relay 178, armature and back contact of relay 177 sequence 180, left-hand arma- 15), and sequence switch contact 516 (3 to 13) to ground. The closure of this circuit energizes relay 180 and causes it to open at its right-hand armature and back contact the circuit by way of contact 504 (4 to 13) of the calling cord sequence switch which theretofore had maintained the energization of the motor magnet of that switch. As the cam 501 of the calling cord switch is cut so as to keep the energizing circuit of the motor magnet closed in position 12 of the sequence switch, the switch continues to move until it reaches position 13, where it comes to rest.

In position 13 of the calling cord sequence switch, ringing current is applied to the connectingcord circuit to ring the bell at the called subscribers station. This is effected through the medium of a circuit which has two branches alternately closed in the rotation of the commutator 182, one of the branches including the battery and the other including a source of ringing current 181. From the commutator 182 the circuit extends by way of sequence switch contact 517 (13), winding of relay 177. left-hand armature and front contact of relay 180, sequence switch contact 519 (13), ring contact of the calling plug 170, ring spring of the springjack 14, and thence over the corresponding side of the line to the called subscribers station and to ground by way of the sub-station condenser and bell. At the same time the other side of the called subscribers line is connected directly to ground by way of sequence switch contact 518 (13). The closure of this circuit causes the bell at the sub-station to ring intermittently, and also by the diversion of a small part of the alternating current by way of the condenser 183 and the winding of the repeating coil 169, causes the ringing current to be heard by the calling subscriber. When the called subscriber in responding to the ringing of the bell takes his telephone receiver from its hook, the resultant closure of the relatively low resistance path across the limbs of the line causes an increase in the current flow over the circuit just traced, and brings about the energization of the relay 177. This relay is preferably so constructed and adjusted, in any well known way, as to make it insensitive to the alternating current flow that passes through it during the ringing of the hell but responsive to the current flow that takes place when the telephone receiver is taken from its hook.

When the relay 177 operates, it opens the short circuit that normally exists about the winding of the relay 178, which relay is included in the path previously traced through the relay 180 and cams'507 and 516 of the calling cord sequence switch. The removal of the short circuit causes relay 17 8 to attract its armatures. The opening ofthe left hand armature and back contact of the relay 178 prevents the reestablishment of the short circuit about the relay 178 when the annature of relay 177- falls back after a momentary attraction. Engagement of the righthand armature of relay 17 8, with its front contact closes a path from battery including a resistance coil 17 9, which path is in parallel with the, path from battery including-the relay 180. The resistance of the coil 179 and the winding of the relay 180 are so proportioned that the relay 180 is shunted and releases its'armatures. The left-hand armature of relay 180 in falling back opens the previously traced path over which ringing current was applied to the conncctin cor circuit. The right-hand armature o relay 180, in releasing and closing its back contact, closes a circuit that extends from battery through the motor magnet and contact 504 (4 to 13) of the calling cord sequence switch. This causes the sequence switch to move out of position 13.

When the calling cord sequence switch leaves position 13, it moves to position 16. In this position a circuit is completed that extends from battery through the lower right-hand winding of the repeating coil 169, calling supervisory relay 187, sequence switch contact 519 (16 to 17), engagin rin contact surfaces of the calling lug 1 0 and called line spring-jack 14, tl fence to the called subscribers station over one limb of the line, through the sub-station apparatus and back over the other limb of the line to the engaging tip contact surfaces of the spring-jack 14 and calling plug 170, righthand armature and front contact of rela 175, sequence switch contact 518 (14 to 17) and upper right-hand windin of the repeating coil 169 to ground. The current flow in this circuit energizes the calling supervisory relay 187 and causes it to close a circuit that extends from battery through the motor magnet and contact 503 (16) of the calling cord sequence switch, and armature and front contact of relay 187 to ground. This moves the sequence switch out of position 16, whereu on it moves to position 17, which is the ta ing position.

Up until this moment, the lamp 161, which, as described, was caused to flash when the call first came in, has been burning steadily as a ringing lamp, the circuit for its illumination being to ground by way of contact 516 (3 to 16) of the calling cord sequence switch. When the sequence switch moves out of position 16, this circuit is interrupted and lamp 161 is extinguished. At the same time, a circuit is closed from battery throughresistance coil 188, and thence by way of two branches, one of which extends through the calling supervisory lamp 189, left-hand front contact and armature of relay 119 and sequence switch contact 513 (17) to ground, and the other of which extends by way of resistance coil 190, sequence switch contacts 514 17 and armature and front contact of relay 187 to ground. The resistance in the latter branch is low, as a result of which the calling supervisory lamp 189 is shunted out as long as tlcile calling supervisory relay 187 is energize When this stage has been reached in the operation of the system, the talking circuit is complete between the calling subscriber and the called subscriber, the finder circuit sequence switch 200 is inposition 14, the

called subscribers line.

calling cord sequence switch 500 is in position-i17, and the listening-key sequence switch is in position 15, the listenin out position. In this condition of the circuit,

the calling subscriber has control over the answering supervisory: lamp 172 through the medium of the answering supervisory relay 171, and the called subscriber has control over the calling supervisory lamp 189 through v'isory relay 187. As long as both subscribers havetheir telephone receivers oil the switchhooks, these lamps are dark. When either one of the-subscribers hangs up, 'the corresponding lamp is lighted. When both lamps light at the same time, the operator knows that the conversation is at an end and takes down the connection.-

The operator disconnects by removing the calling plug 170 from the *rmg-jack of the his act permits relays 119 and 175 of the connecting cord circuit and the cut-off relay 11 of the calledsubscribers line to fall; back. The cut-off relay 11, in falling back, reconnects the line relay 12 with the called 'subscribers line. Relay 119 in releasing its right-hand armature reconnects the high potential battery I 251 with the test conductor 88 of the cord is not entirel established, and the cord cir-- circuit. But the continuity of the connection of the test conductor 88 with battery cuit is there' ore not made selectable until the relay 155 has released itsa'rinatures and the listening sequence switch contact 404 has been closed by the return of the sequence switch to position-1. The relay 155 at its-lower armature opens the test conduetor 88 Whilethe talking circuit is established and thus revents any. possible interference of the Eighpotential test battery 251 with the set of class of service impulses common to the exchange. The other armature of the relay 119, in disenga ing its front cont-act, exting ishes the cal ing supervisory lamp 189.

' Relay 175 in releasing completes a circuit that extends from battery through the winding of-relay 157, sequenceswitch contacts 512 (2 to 17), and left-hand back contact and armature of relay 175 to ground. Helay 157 in operating closes a locking circuit for itself that extends by we of sequence switch contacts 512 (2 to 17), inner armature and front contact of rela .157, and sequence switch contact 510 2 to 17) to ground: Relay 157 also closes a circuit that extends from battery through the motor magnet and contact 503 (2 to 17) of the calling cord sequence switch, outer front contact and armature of relay 157, and sequence switch contact 511 (2 to 18) to ground. The closure of this circuit moves the callin position 1 whereupon it-continues to rotate the medium of the calling supercord sequence switch 500 out of until it reaches and comes to rest in position 1, its normal position.

An instant after leaving position 17, the sequence switch 500 opens, atits contact 508 (1:1 to 18%), the path over which, up to this tune, the holding relay 152 has been main- .talned energized. The relay 152 releases its armatures and brings about the return to normal of the finder circuit and its assoclate'd apparatus in a. manner presently to be described. When the calling cord so quence switch 500 reaches position'l, it completes a circuit that extends from battery through the motor ma et and contact 403' (15) of the listening-file} sequence switchy contact'515 (1) of the ca lin cord sequence switch and r1ght-hand bac contact and --armature of, relay 154 to ground. This moves the listening-lie sequence switch 400 out of position 15 an permits it to return to normal under the control of its cam 401. When the holdingrelay 152 of the connectlng cord circuit becomes inert it breaks at its left-hand armature and. front contact the circult by way of conductor'87 of the connecting cord circuit, conductors 98 and 50 of the finder circuit and conductor 53 of the callingline, including windings of relays 155 of the cord circuit, 30. of the finder circuit, and '11 of the calling line; Consequently these three relays release their armatures. Thecu-tofi' relay 11 of the callmg line. in releasing its armatures reconnects the line relay 12 with the line conductors 58 and 39. Relay 30 of the finder cir- 100 cult 1n releasing closes a circuit fromlbattery through motor magnet and cam 202 (1 1) of the finder sequence switch, lefthand back cont-act and armature of relay 30, and armature and back contact of relay 37 to ground. Thls moves the finder sequence switch out of the talking position 14. When -the finder sequence switch reaches position 15 a circuit is closed for the energization of the relay 30 that includes in parallel branches both windings otthat relay. One branch of this circuit extends from battery through resistance 56, sequence switch coli- -tacts 217 (15 to 16) and (12 to 16), righthand winding of relay 30, sequence switch contacts 220 (15) and (11 to 16) to conductor 67; the other branch extends from battery, through the left-hand winding of relay- 30, and sequence switch contacts 220 (15) and (11 to 16) to conductor 67; thence both branches extend by way of conductor 07. and M segment and corresponding brush of the line-finder commutator to ground. He lay 30 in operating closes a branch path to ground for maintaining its energizatiomthis 12 Relay 30' in operating also closes a circuit that extends from battery, through motor magnet and contact 202 (15) of the finder sequence switchfiight-hand front contact 5 and armature of relay 30, sequenceswitch contact 218" (15), conductor-67, and" M segment and corresponding brush of the line-' the path to ground by way of conductor 67 and the M segment of the line-finder com-. mutator; the energization of the relay being maintained in position 16 of the sequence switch by we of the branch that includes its right-ban winding, com 216, left-hand contacts of relay 30, and resting contacts of relay 37. This circuit isheld closed and relay 30 is kept energized until the cord circuit through which the call was extended has returned to its normal condition. When this occurs a circuit is closed that extends from high-potential battery 251, through the winding and contacts of common relay 197 (see Fig. 4:), armature and back contact of relay 134, conductor 128, armature and back contact of relay 119, lower back contact and armature of relay 155, sequence switch contacts 404' (1), closed when the cord circuit returns to normal, conductor 88, cordselector contact 118' and corresponding brush 114, conductor 99, sequence switch contact 208 (16), right-hand armature and front contact ofrelay 30, sequence switch contacts 204 (9 to 17) and (16 and winding of relay 37 to ground. The closure of this ciru cuit energizes relay 37, which attracts its armature and opens the previously traced .holding circuit of the relay 30. Relay 30 in releasing its armatures closes a circuit't-hat extends from battery through the winding of down-drive magnet 62 of the line-finder switch, conductor 60, sequence switch contacts 22-3 (1-6 to 16%) and (16 to 7), lefthand back contact and armature of relay 30, and armature and back contact of relay 37 to ground (the energizing circuit of relay 37 having been interrupted at the right-hand front contact and armatureof relay 30 when that relay released). As a result of the closure of this circuit, the brushes of the line- -finder switch are returned to normal. As the line-finder brushes reach normal. a circuit is closed that extends from battc through the motor magnet and contact 20% (16) of the finder sequence switch, conductor 69, and Y segment and corresponding brush of the line-finder commutator to ground. When the finder sequence switchmoves to position 17, as a result of the closure of the amaze hand winding of relay 30, and also opens" above-traced circuit, a cu'citit is completed 'that extends from battery through the winding of the down-drive magnet 35 of the cord selector, conductor 90, finder sequence switch contact 218 (17), conductor 67, and M segment and corresponding brush of the line-finder commutator to ground. The closure of this circuit returns the cord selector switch to normal; and as the brushes reach normal, a circuit is closed that extends from battery through the motor magnet winding and contact 205 (17) of the finder sequence switch, conductor 31, and Y segment and corresponding brush of the cord selector commutator to ground. The closure of this circuit causes the finder sequence switch 200 to return to its normal position. As has hereinbefore been explained, the operators position is selectable by an incomin call only when the'operators. sequence SWltCh 300 is standing in position 1. When the relay 95 is ener 'zed upon the selection of the position, t e operators sequence switch is moved to position 17 in the man ner hereinbefore explained, and thereafter remains in that osition until it is returned to position 1. T e circuit for returning the operators sequence switch from position 17 to position 1 extends from battery through the motor magnet and contact 303 (17) of theoperators sequence switch,and is completed to ground by way of the upper armature and front contact of the relay 192 of the associated positionwhen that relay is operated. The energizing circuit of each of the relays 192 at the various operators positions extends from battery through the winding and lower switch spring and resting contact of that relay, the right-hand urmature and back contact of the associated relay 91, and contact 307 (15 to 18) of the associated operators sequence switch to a conductor 140 which is common to the energiz ing circuits of all of the positions, this conductor 140 extending to ground by way of 110. the series of operators sequence switch contacts 308 ('2 to 18) one of which is associated with the sequence switch of each operators position. Consequently when the sequence switches 300 of the entire series of operators positions have been advanced to position 2 or beyond by the selection of these positions by incoming calls, or otherwise, as will be explained, the path to ground by way of the conductor 139 is closed, all of the relays 192 the paths of which are completed to the conductor 140 are energized, and the operators sequence switches at such positions are moved out of position 17 and come to rest in position 1. Thus these positions are again rendered available for receiving incoming calls. In order to insure the closure of the energizing circuit of relay 192 for a suliiciently long interval to effect the movement of the associated Sequence'switch, the relay 13o in operating closes a locking circuit for itself to ground by way of operatorssequence switch contact 310 (15 to 8), this locking path being opened to release the rela when the sequence switch moves beyon position 18.

It may at times be necessary for the operator to supervise or listen in on an estabhshed connection. In order that the operator may bring her telephone apparatus into connection with a clrcuit upon which connection has been established, it is necessary that the associated listening key sequence switch 400 be moved from' its listening-out position 15 to itslistening-in position 7. This is accomplished by pressing the associated listening-in key 191, which closes a circuit that extends from battery through the motor magnet and contact 402 (15) of the listening key sequence switch, right-hand contact and switch spring of listening-in key 191,

conductor 130, ri ht-hand armature andback contact of re ay 195, right-hand back contact and armature of relay 95, and righthand front contact and armature of relay 125 to ground. As a result of the closure of this circuit the listening key sequence switch moves out of position 15. Upon reaching position 1, it is moved through this position by a circuit that extends from battery through the motor ma net and contact 402 (1) of the listening key sequence switch, and contacts 511 (2 to 18) of the calling cord sequence switch to ground. Consequently the listening key sequence switch continues to move until it reaches position 7, in which position the operators telephone apparatus is again connected with the circuit through the medium of the listening key sequence switch, cams 408, 409, 410, 411. Having supervised the connection, the operator may disconnect her telephone apparatus from the circuit by pressing the listeningout key 186, which is common to all of the connecting circuits of her position. This closes-a circuit that extends from battery through the motor magnet and contact 403 (7) of the listening key sequence switch, and. contacts of the master listening-out key 186 to ground. As a result the listening key seqnence switch is caused to move out of posi-- tion 7 and again come to rest in position 15. Or the operator may listen out on one connection by listening in on another. This is effected through the multiple connections which exist between the contacts 402 (7) and the contacts 406 (2 to 6) of all of the listening key sequence switches. When any listening key sequence switch is standing in position 7, the movement of the listening key sequence switch of any other connecting circuit through positions 2 to 6 afi'ords an energizing path to ground for the motor magnet of the listening key sequence switch that is standing in position 7.

When the operator presses a listening-in ke' 191 to supervise the connection establis ied on the corresponding circuit, it is desirable that in doing so that she shall render her position unselectable by an incoming call if her sequence switch 300 is standing in its waiting position 1; and also, if her sequence switchis standing in position 17, that she shall prevent it from being returned to position 1 by relay 192, as described, in which-position the operators position would again be selectable. To accomplish this, the depression of the listening-in ey 191 completes a circuit that extends from battery through the lefthand winding" of relay 91, left-hand armatureand back contact of relay 195, conductor 138, listenin key sequence switch contact 414 (9 to 16? and left-hand contact and switch spring of the listening-in key 191 to conductor 130, from which point the path to ground is as has already been traced. If the operators sequence switch is standing in position 1, the

relay 91, in attracting its armatures as a result of the closure of this circuit, opens at its left-hand armature and backcontact the energizing circuit for relay 92, which relay, as has already been explained, controls the selection of the position. If the op erators sequence switch 300 is standing in position 17 when the listening-in key 191 is pressed, the energization of the relay 91 opens, at the right-hand armature and back contact of that relay, the path over which the relay 192 receives its energizin current from conductor 140 when all of tie operators sequence switches 300 of this group of operators have'been moved out of position 1 and-are standing in position 17, or in some position between 2 and 18. Therefore, if the operator presses her listening-in key 191 an instant before the last of the series- "of sequence switch contacts 308 (2- to 18') is closed, her sequenceswitch 300 will be prevented from being restored to position 1. where it would render the position immediately accessible to an incoming call which,

'when it seized a connecting cord, would automatically disconnect the operators telephone from the cord circuit she was attempting to supervise.

In moving from the listening-out position 15 to the listening-in position 7 as a result

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