US1450321A - Party-line revertive ringing system - Google Patents

Description

Hy. A

, 1,450,321 A.,E'. LUNDELL ET AL PARTY LINE REVERTIVE RINGING SYSTEM gli? mma June leso by Mx l pr. 3, 1923.

1,450,321 A. E. LUNDELL ET AL PARTY LINE REVERTIVE RINGING SYSTEM Filed June 4, 1920 '7 sheets-sheet 2 /H sua/fors fq/ben f. L unda/l Apr. 3, 1923.

A. E. LUNDELL ET AL PARTY LINE REVERTIVE-RINGING SYSTEM Filed June 4, 1920 '7 sheets-sheet 5 Apr. 3, 1923. 1,450,321

A. E. LUNDELL ET AL PARTY LINE REVERTIVE RINGING SYSTEM /ben EL Lande/l fo/'7e Thompson 'by my.

A. E. LUNDELL ET AL PARTY LINE REVERTIVE RINGING SYSTEM Fll'ed June 4, 1920 '7`sheets-sheet 5 Apr. 3, 1923. 1,450,321

A. E. LUNDELI. ET AL PARTY LINE REVERTIVE RINGING SYSTEM Filed June 4, 1920 '7 sheets-sheet 6 Patented pr. 3, 1923.

UNHTED STATES insana rsrsnr carica.

ALBEN E. LUNDELL, OF CHICAGO, ILLINOIS, .AND GEORGE THOMPSON, OF MOUNT VERNON, NEW YORK, ASSIGNORS TO WESTERN ELECTRIC COMPANY, INCORPO- RATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

PARTY-LINE REVERTIVE RINGING SYSTEM.

Application led .Tune 4,

T o all 'whom 'it cna-y concern Be it known that we, ALBEN E. LUNDELL and (l1-:Ouen THOMrsoN, citizens of the United States, residing at Chicago, in the 5 county of Cook. State of Illinois, and at Mount Vernon, in the county of Westchester, State of New York, respectively, have invented certain new and useful Improvements in Part -Line Revertive Ringing Systems` of which the'following is a full,

clear` concise, and exact description.

This invention relates to automatic telephone exchange systems and more particularly to full mechanical systems of large capacity.

It is the object of this invention to provlde an improved revertive ringing system.

A feature of the invention is an arrangement whereby a calling subscriberl may, under the control of his impulse sending device` establish conditions such that he may signal a subscriber on his own party linel without the necessity of obtaining the assistance of an operator.

A further feature of the invention is the provision of an organization such that no selective switches need be positioned in order to accomplish the desired ringing operations` it being merely necessary for the calling subscriber to establish connection to a register sender.

In order to accomplish revertive ringing Ou a party line it has usually been necessary to provide special apparatus at the calling substations so that extra manipulations by the calling subscriber are relluired. or else it has been necessary for him to set numerical switches to establish a connection to an operator who then instructs him to replace his receiver, whereupon the desired ringing current is supplied under the control of such operator. An additional scheme which is sometimes used is one wherein certain of the numerical selector switches are provided with a special group of contacts to which ringing generators of varying characteristics are connected, and if these numerical switches are then directively positioned,v the proper ringing current is then supplied to the party line.

The present system provides many advantages over any of the above arrangements. The operation of the system in general is as follows. Since the invention has been 1920. Serial No. 386,517.

' call is to be made, the oflice designation to be dialed is always the same, regardless of what office the party line appears in, and each subscriber on each party line is provided with a list of the names of the subscribers whose stations appear on his line. The numbers and office designations which are given to him individually will, of course, be different from the numbers and office designations which appear in the regular directory.

The subscriber upon initiating a call will seize an idle trunk leading to a numerical switch which normally controls the selection of a desired olice. A register sender is then automatically associated with his line and he will dial in the usual manner and position a set of registering devices. If hefirst dials the code which has been taken for use in connection with revertive calls, theregisters which normally controlthe selection of the desired oiiice will be positioned in sucha way that no selections take place but instead ringing apparatus will be connected to the calling line. As soon as the calling subscriber replaces his receiver, which he will be instructed to do when initiating a call which is to be revertive on his own line, this ringing apparatus is put into operation and will alternately signal the substation of the called subscriber and theV substation of the subscriber who initiated the call. The selection of the proper kinds of ringing current will be controlled by the numerical registers which would normally operate to control the numerical switches to select the desired line in the selected oliice.

A complete understanding ofthe invenshows the circuits of a district selector switch and a sender selector switch. 3 shows register controlling equipment and an associated sequence switch. Fig. 4 shows the ringing apparatus. The sequence switch contacts shown at the right of Fi are controlled by the sequence switch o Fig. 3. Figs. 5 and 6 show the registerlng devices and the various contacts controlled by them, the contacts controlled by each register appearing verticallyl above such register in Figs. 5 and 6. Fig. ,7 shows the counting relay sending device with lts associated ste ping relay and controlling sequence switc The operation of the system when a nonrevertive call is put through will first be described.

The subscriber at substation 1 desiring to initiate a call will .remove his receiver from the switch-hook, whereupon a circuit is completed from grounded battery, left-hand winding of line relay 2, upper middle armature and back contact of cut-off relay 3, conductor 4, through the apparatus at the substation, conductor 5, the outermost upper armature and back contact of cut-off relay 3, right-hand winding of line relay 2 to ground. Relay 2 is energized in this circuit and completes a circuit from grounded battery, resistance 6, armature and back contact of stepping magnet 7, armature and front contact of line relay 2, conductor 9, normal contact 10 and its associated brush 11, and the winding Aof stepping ma et 7 to ground. Magnet 7 is energized in t is circuit and advances the line switch Wipers one step. As soon as the line switch wipers engage thc second set of terminals in the arc served by them, .a self interrupting circuit is completed for stepping magnet 7, this circuit extending from grounded battery, resistance 6, armature and back contact of magnet 7 conductor 8, lower armature and back contact of cut-oit relay 3, oit-normal conducting segment 12, brush 1'1 and the winding of magnet 7 to ground. Under the influence of this circuit magnet 7 continues to interrupt its own circuit and advances the line switch wipers until an idle trunk is found whereupon the circuitl just traced will be broken due to the energization of cut-off relay 3. The test terminals associa-ted with busy trunks leading to district selector switches will be characterized by the absence of potential while the test terminals kassociated with idle trunks will be characterized by ground potential thereon. soon, therefore, as test brush 13 engages the terminal of an idle trunk, a circuit is completed from grounded battery, resistance 6, armature and back contact of magnet 7 (which deenergized to cause the advance of the switch),arma.ture and front contact of relay 2, lower winding of relay 3, test brush 13, Contact 14, conductor 15, left-'hand contacts of sequence switch spring 101, conductor 102, righthand armature and back contact of relay 103, lower right-hand contact of sequence switch spring 104 to ground. Cut-off relay 3 is energized in this circuit and permanently interrupts the circuit of stepping magnet 7. Cut-ofi' relay 3 upon energization also opens the circuit of relay 2 and this relay deenergizes. Relay 3 upon energization also completes a. locking circuit for itself extending from grounded battery, winding of relay 103 (Fig. 2), upper righthand contacts of sequence switch spring 105, conductor 107, terminal 16 and its associated brush 17, innermost upper armature and front cont-act of relay 3, upper winding of relay 3 to ground.

Relay 103 is energized in the above-traced circuit and by its right-hand armature removes ground fro-m the test terminal of the trunk selected in order to render this trunk non-selectable to other hunting line switches.

Relay 103 upon energization also completes a circuit extending from grounded battery, winding of stepping magnet 108 of the sender selecting switch. armature and back contact of magnet 108, winding of relay 109, conductor 110, sequence switch spring 169, right-hand armat-ure and front Contact of relay 103, lower right-hand contact of sequence switch spring 104 to ground. Relay 109 is energized in this circuit and connects through the various controlling leads to the sender. The resistance of relay 109 is sufficiently high to prevent the operation of stepping magnet 108.

rThe sender selector switch is a. step-bysteprotary switch which is advanced under the control of stepping magnet 108. Magnet 108 maintains this switch with its wipers upon the terminals of an idle sender at. all times that the district is not in use. The seizure ot' the sender is accomplished as soon as relay 109 is energized and any sender selecting switches which are rest-ing on thc terminals associated with the sender, which has just been seized are caused to be advanced by means of a circuit extending from grounded battery, windings of magnets cor-- responding to magnet 108, armatures and back contacts of magnets 108` conductors 114, outer left-hand armatures and back co-ntacts of relays 109, brushes 113 to the grounded terminal 112. The magnets 108 of sender selectors associated with other districts will then be energized and interrupt their own circuits to cause the advance of the sender selector brushes into engagement with the terminals individual to another sender, and will continue in mo-tion until an idle sender has been found at which time they will remain in enga-gement with the terminals of such sender until it is seized by some district.

Referring to the operation of the circuits shown, the energization of relay 109 completes a circuit from grounded battery, winding of relay 201 (Fig. upper lefthand contact of sequence switch spring 202, conductor 203, terminal 115 and brush 114 associated therewith, the inner left-hand armature and front contact of relay 109, conductor 116, lower right-hand Contact of sequence switch spring 105, conductor 107, terminal 16, ibrush 17, inne'r upper armature and front contact of relay 3, upper winding of relay 3 to ground.

Relay 201 is energized in thls clrcu-it and completes a circuit from grounded battery, winding of the power magnet of sequence switch 200, upper right-hand contact of sequence switch spring 257, left-hand armature and front contact of relay 201, to ground, for moving this sequence switch out of position 1 and into position 2. As soon as relay 109 operates, the subscribers impulse leads are connected through to the line relay by way of the left-hand armatures of relay 109. The line circuit toarmature and front contact of relay 109, conductor 131, lower contact of sequence switch spring 130, conductor 22, terminal 21, brush 20 and thence over the loop of the calling su scribers line, returning to brush 19, terminal 18, conductor 129, upper Contact ot' sequence switch spring 128, conductorv 127, outer left-hand armature and front contact of relay 109, conductor 126, brush 125, terminal 124, conductor 217, inner right-hand armature and back contact of relay 215, conductor 218, upper right-hand contact of sequence switch spring 219, conductor 220, to ground at sequence switch spring 241. Line relay 212 is energized in this circuit.

With sequence switch 200 in position 2 and with relay 109 energized, circuits are completed for advancing sequence switch 100 out of position 1 and into position 2. This is accomplished by energizing relay 117 over a circuit extending Jfrom grounded battery, winding of relay 117, lower contacts of sequence switch spring 118, conductors 119 and 120, b'rush 121, terminal 122, conductor 204, lower left-hand Contact of sequence switch spring 205, righ-hand armature and front contact of relay 212 to ground. Relay 117 is energized in this circuit and completes a circuit from grounded battery, power magnet of sequence switch 100, upper left-hand contact of sequence switch spring 135, right-hand armature and front contact of relay 117 to ground, for moving'this sequence switch out of position 1 and into position 2.

1n position 2 of sequenceswitch 100, rela 103 completes a locking circuit for it.- self exclusive of the contact of sequence switch spring 105. This circuit extends by Way of the left-hand armature and front contact of relay 103, the lower contact of sequence switch spring 136, to grounded conductor 107.

As soon as se uence switch 200 reaches position 2, the su sc'riber is free to dial the characteristic designation of the wanted line in order to set the registers shown in Fig. It is obvious that the time elapsed before'the subscriber is free to dial, is very small, since all that is required is that relay 109 operates to cause the operation of relay 201,I which moves sequence switch 200 out of position 1 and into position 2.

' The selector switches used in establishing the connection are of the type whose structure and Inode of operation is similar to that of the switches shown in Patent No. 1,168,319 issued January 18, 1916, to A. E. Lundell. These switches are each of fivehundred-line capacity. In the present arrangement, registers are provided which will be set in' accordance with imfpulses transmitted on a decimal basis in accordance with the digits of the number of the called subscriber. The registers will then translate these impulses to control the selective operations of the switches on a nondecimal basis. As shown in the present disclosure, provision is made to have a call extended through four switches. each of five-hundred lines capacity. In accordance with the well-known grouping arrangement, by means of the latter two switches of the train 10,000 lines may be served. There= Jfore, the rst two switches of the train will be utilized to select an oliice ot 10,000 lin'e capacity. The first switch of the train will select a district and the second switch of the train will then he operated to select a particular olice. By varying the number of trunk lines in a group at the district and ollice selector switches, an exchange capacity ranging from 4,000,000 to 25,000,000 lines may be obtained. For instance, if each brush of the district selector has access to four groups of twenty-five trunks each, any one of twenty districts may be selected by the district selector with twenty-five lines running to each district. If the grouping arrangement at the oiiice selector is the same, any one of twenty oiiices may be selected by the oice selector. Therefore. connection may be extended by means of a district selector and an oiiice selector to any one of four hundred oiiices, each one of 10,000 line capacity. This would provide a system of 4,000,000 lines. 1f each of the brushes at the district selector has access to ten groups of trunks of ten Vlines each, a call may be extended to any one of fifty c listricts. and if the office selector grouping arrangement is the same, the call may then be further extended to any one of fifty' offices by means of an ofiice selector, so that a call may be extended by means of a district selector and an office selector to any one of twenty-five hundred ofiices, each of 10.000 line capacity. As a result, this groupA Ain a -final connector switch. At the final connector switch each of the five brushes has access to ten roups of ten lines each, each of these leading to a subscribers station.

In order that the' calling subscriber may not have to carry in mind a large number of digits, it is proposed to designate the desired oflice number by means of letters of Y the alphabet and three series of impulses will be sent to setthree registers to control the first two switches of the train. These three registers will control brush and group selection at the district selector and brush and group selection at the office selector. An impulse-sending device of any wellknown type will be used, being arranged merely lto cause a desired number of circuit interruption in response to the operation of a finger wheel. The sender dial may be lettered .so that in addition to a finger hold` for each digit, the hold characterized by the No. 0 which would be arranged to send one impulse, may also bear the letter A. The No. 1 finger hold may bear the characterizations B and 1. In this way the lettering on the 'dial plate complete would be A-0, B-1, C-2, D3,. E-4, F-, G-6, H7, I\-8, J-9.

Under the conditions assumed in the present design of the system, the code to be dialed for a revertive call would necessitate -an office characterization comprising the three letters J-J-J. Since we are at present not considering a revertive call, it will be assumed that the calling subscriber desires to establish connection with a subscriber whose number is 3456, in an office characterized by the three letters D-E-F. The subscriber will proceed first to operate his impulse dial to send four impulses, then to send five impulses, and then to send six impulses, after which he will proceed to send the digits constituting the desired num ber in the selected ofiice..

The registers employed in this system are of the well-known power-driven type and are of a mechanical construction similar to that shown in Patent #1,127,808, issued` February 9, 1915 to Reynolds and Baldwin. The register 400, which receives the first letter of the ofhce code willbe hereinafter designated as Athe A register' the register 401 will be designated as the register and receives the second letter of the office code; register 402 will be designated the C register and receives the thir letter of the office code. Registers 403, 404, 405 and 406 respectivel take up the registrations of the thousan s, hundreds, tens and units digits, respectivel The sequence switch springs shown in igs. 5 and 6 are associated with nthe various registers, the springs above and below any given register being controlled thereby.

In order that the setting operationv of the registers may be understood, it should be noted that all the register contact springs designated by the letters B, F and G are so arranged that in the odd positions of the register switch with which they are associated, the upper contacts will be closed,

while in the even positions of the switch the lower contacts'will be closed. In each case the normal position of the switch. will be considered as an odd osition.

In response .to the rst series of impulses the circuit of line relay 212 is intermittently. interrupted. Upon the first deenergization of relay 212 a circuit is completed fram grounded battery, right-hand armature and back contact of relay 228, conductor 232, upper left-hand contact of sequence switch spring 235, conductor 236, upper" contacts of sequence switch spring 414, which are closed since this is a Gr spring, 4conductor 237, left-hand winding of relay 222, lefthand armatureA and back contlact of relay 212, to ground.

Relay 222 is energized in the above traced circuit and completes a circuit from grounded battery, power magnet of register 400, upper contacts of register spring 412, which is closed-since lthis is a B spring, conductor 415, upper left-hand contact of se uence switch springl 238, conductor 239, le -hand armature and front contact of relay 222 to ground, for moving this register out of its normal position and into posi tion 0.

Relay 222, upon energizing, completes two locking circuits for itself by way of its right-hand armature. The first of these extends from grounded battery, right-hand armature and front contact of relay 222,1eftvhand winding of relay 222, armature and back contact of relay 212 to ground, and` ino maintainsl this relay energized untilline relay 212 is energized in response to the completion of the first interruption of line ductor, 240, upper contacts of register spring 416, which are closed in the odd position of the register, conductor 417 upper left-hand contact of sequence switch spring 233, to ground at sequence switch sprlng 241. y

The locking circuit through the righthand winding of relay 222 is broken as soon as register 400 moves into an even Aposition due to the opening of the circuit at the upper contacts of spring 416. When the line circuit is again completed and relay 212 becomes energized, the circuit through the lefthand windlng of relay 222 is broken and the relay deenergizes.

In response to the next deenergization of relay 212, with the register 400 in position 0, a circuit is completed from grounded battery, right-hand armature and back c'ontact of relay 222, conductor 223, upper lefthand contact of sequence switch spring 224, conductor 225, lower contacts of 'register spring 416, conductor 227 ,left-hand winding of relay 228, left-hand armature and back contact of relay 212 to ground. Relay 228 is energized and completes a circuit from grounded battery, power magnet of register 400, lower left-hand contact of register spring 412, conductor 413, upper left-hand contact of sequence switch spring 229, conductor 230, .left-hand armature and front contact of relay 228 to ground, for moving the register out of position 0 and into position 1.

Relay 228, upon energization` completes two locking circuits for itself through its right-hand armature, one of these circuits extending from grounded battery, righthand armature and front contact of relay 228, right-hand winding of relay 228, conductor 231, lower contacts of register spring 414, closed in the even position of the register, conductor, conductor 234, upper lefthand contact of sequence switch spring 233, to ground. The other locking circuit extends from grounded battery, right-hand armature and Jfront 4contact of relay 228, lefthand winding of relay 228, left-hand armature and back contact of relay 212, to ground. As before, when the line circuit is again closed, the resultant energization of relay 212 opens the locking circ-uit l through the left-hand winding of relay 228,

Vance register 400 out of osition 1 and into position 2 over circuits i entica'l with those circuits previously traced for moving the register out of its normal position and into position 0. Locking circuits of relay 222, identical with those previously described in the description of the operation of this relay, are also completed and interrupted in the same manner.

In response to the fourth interruption of the line` circuit, relay 228is again energized to move register 400 from position 2 to position 3, inthe lsame manner as described for moving it from position 0 to position 1, the cycle of ope-ration of relay 228 in this case fbeing the same as when it was previously' brought into use.

It will thus be seen that for each interruption of the line circuit the register 400 will be advanced one position. At the termination of the first series of impulses, at which time four interruptions of the line circuit will have occurred, the register 400 will have advanced four steps into position 3. Relay 228 is energized in response to the last deenergization of linel relay 212.

It is to be observed that as soon as register 400 left its normal position, a circuit was completed for relay 242 (Fig. 3), this circuit extending from grounded battery, winding of relay 242, lower contact of sequence switch spring 243, conductor 244,/ upper4 right-hand contact of sequence switch spring 418, lower contacts of register springs 419, 420, 421, 422, 423, and 424 in series, conductor 425, left-hand armature and front contact of relay 212 to ground. This circuit is completed momentarily each time relay 212 is energized during the sending of the first series of impulses. Relay 242 is, however, designed to be slow to attract its armature and, therefore, these momentary circuit closures will not allow its armature to close its contact. However, after register 400 has been positioned and during the interval between the sending of the iirst and second. series of impulses, relay 212 remains energized Jfor a relatively long time and as a result, relay 242 attracts its armature, thus completing a circuit from grounded-battery, power magnet of sequence switch 200, upper right-hand contact of sequence switch spring 245, conductor 246 to ground, for'moving this sequence switch out of position 2 and into position 3. When sequence switch 200 leaves position 2, the energizing circuit of relay 242 is broken at the lower contact of sequence switch spring 243, and relay 242 deenergized. i

In position 3 of sequence switch 200 the second series of impulses may be received. Five impulses will be sent to advance register 401 live steps into position 4. At this time, relays 222 and 228 function to control the advance of register 401 in a manner substantially similar to that previously described. At this time, however, the energizing circuit for relay 222 extends through thev upper right-hand contact ot' sequence switch spring 235, conductor 247, upper contacts of register spring 426, conductor 237, and thence to ground as previously described. The energizing circuit of relay 228 extends by way of the upper right-hand contact of sequence switch spring 224, the lo-wer contacts of register spring 427 and conductor 227, to ground as previously described. The operation of setting register 401 41s fundamentally similar to that ot setting register 400 and it is thought need not be described in detail.

After the second series of impulses has been sent, relay 212 will remain energized a comparatively long time and will complete a circuit for relay 242 from grounded battery, winding of relay 242, upper contact of sequence switch spring 243, conductor 248, upper contact of register spring 419, and thence through the lower contacts of register springs 420, 421, 422, 423 and 424 in series, and conductor 425 to ground as described. This circuit has beeny intermittently closed upon each short actuation of relay 212 but does not become effective until after the sending of the series df impulses. When re lay 242 is energized, a circuitis completed from grounded battery, power magnet of sequence switch 200, upper right-hand contact of sequence switch spring 245, conductor 246, armature and front contact of relay 242, to ground for moving this sequence switch out of position 3 and into position 4.

The subscriber continues sending series of impulses, and as a result register 402 will 'be set in position 5, register 403 will be set in position 3, register 404 will be set in position 4, register 405 will be set in position 5, and register 406 will be set in position 6.

Upon the completion of the setting of register 402, the energization of relay 242 will advance sequence switch 200 from position 4 to position 5, the completion of the setting of register 403 will advance sequence switch 200 into position 6; the completion of the setting of register 404 will advance sequence switch 200 into position 7; the completion of the setting of register 405 will advance sequence switch 200 in position 3, and when the last register 406 is positioned, sequence switch 200 will be advanced out of position 8 and into position 9.

Vhen sequence switch 200 reaches position 4, at which time registers 400 and 401 will have been positioned, these being the regis` ters which control the district selector switch shown in Fig. 2` a circuit is comple-ted from grounded battery, power magnet of sequence switch 300 (Fig. 7), lower right-hand contact of-sequence switch spring 301, conductor 302,

contact of sequence switch spring 249 to ground, for moving this sequence switch out ofnosition 1 and into position 2.

n position2 of sequence switch 300 the fundamental circuit is completed to control selection at the district switch. A circuit is completed from grounded battery, winding of relay 117 (Fig. 2) upper contacts ot sequence switch spring 118, conductors 137 and 138, brush 139, terminal 140, conductor 250, armature and back contact of relay 304,

Iwhich is in parallel with the 0 cqunting relay, winding of stepping magnet`305, upper contact of sequence switch spring 306, conductor 307, through the contactsof register springs 428 and 429 in parallel, conductor 430, lower right-hand Contact of sequence switch spring 205, conductor 204, terminal- 122, brush 121, conductor 120, upper righthand and lower left-hand contacts of sequence switch spring 141, resistance 142 to ground. Relay 117 is energized in this circuit and locks up to conductor 137 through its lett-handarmature and front contact.

It is to be observed that, if both registers 400 and 401 are in position 9, which corresponds to the sender designation J, the fundamental circuit would not havebeen completed, since both register springs 428 and 429 would have been open. It is therefore obvious that in case the revertive ringing. oice code has been sent, which comprises the letters JJJ, the relay 117 would not have been energized and would not have advanced the district as will now be described. The

operation of the system in connection with aarmature and back contact of the No. 2

counting relay, conductors 308 and 431, lower left-hand contact of sequence switch spring 432, conductor 433, upper left-hand contact of sequence switch spring 309, conductor 310 to ground at the armature and front contact ot' stepping relay 305. The No. 2 counting relay is energized inythis circuit and preparesa circuit Jfor the No. 2 counting relay which does not become effective until the stepping relay is deenergized to remove the shunt about the winding ot f:

the No. 2 counting relay.

In position 3 of sequence switch 100, a circuit iscompleted from grounded battery, winding of up-drive magnet 143, right-hand contacts of sequence switch springs 144,

right-hand armature and front Contact of relay 117 to ground. Magnet 143 is energized and causes the brush shaft to be moved upward in a brush selecting movement. As Soon as commutator brush 152 engages a conducting segment of commutator 146 the holding circuit of relay 117 is extended directly to ground at the district selector, this circuit extending from grounded battery, winding of relay 117, left-hand armature and front contact of relay 117, upper lefthand Contact of sequence switch spring 118, upper left-hand contact of sequence switch spring 147 conductor 148, commutator 146 and brush 152 to ground. Stepping relay 305 is shunted down in this circuit and allows the No. 2 counting relay to become energized. When brush 152 engages an insulating segment ofcommutator 146, relay 305 again becomes energized and causes the energization of the No. 1 counting relay. Stepping relay -305 is intermittently actuated as the brush shaft moves upwardly until, on its third deenergization, the 0 counting relay and relay 304 are energized. Relay 304 opens the lower.branch of the loc-kino' circuit of relay 117 and when, a moment ater, brush 152 engages an insulating portion of commutator 14 at which time the brush shaft will be properly positioned to trip the third set of brushes, the locking circuit for rela-y 117 is completely broken and this relay deenergizes and opens the circuit of the up-drive magnet, thus bringing the brush shaft to rest. The deenergization of relay 117 also completes a circuit from grounded battery, power magnet of sequence switch 100, lower right-hand contact of sequence switch spring 135, right-hand armature and back contact of relay 1,17, to ground, for moving this sequence switch out of position 3 and into position 4.

In the sender, the energization of the 0 counting relay completes a circuit from grounded battery, power magnet of sequence switch 300, upper left-hand contact of sequence switch spring 301, armature and front contact of the 0 counting relay to ground, for moving this switch out of position 2 and into position 3. Since relay 290 (Fig. 3) is not energized at this time, due to conditions which will be subsequently described, sequence switch 300 is immediately moved out of position 3 and into position 4, due to the completion of a circuit extending from grounded battery, power magnet of sequence switch 300, lower left-hand contact of sequence switch spring 311, conductor 312, armature and back contact of relay 290 to ground.

With sequence switch 100 in position 4 and sequence switch 300 in position 4, the fundamental circuit is again completed to advance sequence switch 100 out of position 4 and into position 5 by means of circuits identical with. those previously traced for moving this sequence switch out of position 2 and into position 3. v 4

In position 5 of sequence switch 100Atl1e district brush shaft is moved upward in a group selecting movement due to'the closure of a circuit from grounded battery, winding of up-drive magnet 143, left-hand contacts of sequence switch spring 144, right-hand armature and front contact of relay 117 to ground. It is to be observed that as soon as sequence switch 100 reaches position 4, a circuit is completed from grounded battery, winding of trip magnet 149, Contact of sequence switch spring 150, lower left-hand" contact of sequence switch spring 151 to ground. The resultant energization of magnet 149 operates the trip rod 180 so that upon subsequent upward movement of the brush shaft the third set of brushes will be released into engagement with the terminals served by them.- i

TheA first energization of stepping relay 305 completes a circuit from grounded battery, winding of the No. 2 counting relay, armature and back contact of the No. 2 counting relay, conductors 308 and 434, lower left-hand contact of sequence switch spring 435, upper contact of sequence switch spring 436, conductor 437, upper right-hand contact of sequence switch spring 309, conductor 310, armature and front contact of relay 305 to ground. Stepping relay 305 is intermittently shunted down as the brush moves upwardly due to the engagement of commutator brush 152 with commutator 153 which supplies holding ground directly to relay 117 by way of the upper left-hand contact of sequence switch spring 147 and conductor 148. Upon the third shuntingv down of the stepping relay the 0 counting relay and relay 304 are energized in parallel. Relay 304 permanently opens the lower branch of the locking circuit of relay 117 and when, a moment later, the brush 152 engages an i11- sulating segment of commutator 153, relay 117 deenergizes and completes a circuit from grounded battery, lower' right-hand contact of sequence switch 135, right-hand armature and back contact of relay 117 to ground for moving this switch out of position 5 and into position 6. The deenergization of relay 117 opens the circuit of up-drive magnet 143, and brings the brush shaft to rest with the selected set of brushes in operative relation to the selected group of trunk lines.

In the sender, the energization of the 0 counting relay completes a circuitl from grounded battery, winding of the power magnet of sequence switch 300, upper lefthand contact of sequence switch spring 301, armature and front contact of the 0 count-l -ing relay to ground, for moving this seout of position 5 and into position 6 due to the closure of a circuit for its power magnet extending from the lower left-hand contact of sequence switch spring 311 by way of conductor 312 to ground at the armature and back contact of relay 290.

In position 6 of sequence switch 100, a circuit is completed 4from grounded battery, left-hand winding of test relay 155, lower right-hand contact of sequence switch spring 156, conductor 157 to ground, at the righthand armature and back contact ot relay 117. Relay 155 is energized in this circuit and locks up through its right-hand winding over a circuit extending from grounded battery, right-hand winding of relay 155, up-

per contacts of sequence switch spring 158, right-hand armature and'front Contact of relay 155, conductor 160, test'brush 159 and its associated terminal 161 to ground, provided that the first trunk in the selected group is busy, it being understood that busy trunks will be characterizedby the presence of ground potential on their test terminals, while no potential will be found on the terminals of idle trunks.

Relay 155 upon energization also completes a circuit from grounded battery, power magnet of sequence switch 100, upper left-hand contact of sequence switch spring 135, left-hand armature and front contact of relay 155 to ground, for moving this sequencet switch out of position 6 and into position 7.

In position 7 of sequence switch 100 the selected set of brushes is moved upward in a trunk selecting movement due to the closure of a circuit from grounded battery, winding of up-drive magnet 143, right-hand contacts of sequence switch spring 144, left-hand armature and front contact of relay 155 to ground.

As soon as test brush 159 encounters the terminal of an idle trunk the locking circuit through the right-hand winding of relay 155 is opened. Relay 155 does not immediately deenergize, however, dgue .to the existence of a circuit from grounded battery, left-hand windin of relay 155, upper right-hand contact o sequence switch spring 156, conductor 162, commutator 163, commutator brush 176 to ground. When, an instant later, brush 176 engages an insulating segment of commutator 163, at which time the brush set will be accurately centered on the terminals of the selected trunk, relay 155 deenergizes and opensr 'the circuit of up-drive magnet 143 to bring the selected brush set to rest on the terminals of an idle trunk leading to the oiice selector. The deenergization of relay 155 also completes a circuit from grounded battery, power magnet of sequence switch 100, upper lefthand contact of sequence switch spring 165,

left-hand armature and back contact of relay 155 to ground, for movin" this switch out of position 7 and into position 10. 1

The fundamental circuit is now completed from grounded 'battery at the office selector associated with the seized trunk, over conductor 166, terminal 167, brush 168, upper contact ot' sequence switch spring 169, conductor 138, brush 139, terminal 140, conductor 250, armature and back contact of relay 304, winding of stepping relay 305, upper contact of sequence switch spring 306, through the upper contacts of register springs 428 and 429 in parallel, conductor 430, lower right-hand Contact of sequence switch spring 205, conductor 204, terminal 122, brush 121, conductor 120, upper contact of sequence switch spring 170, brush 171, terminal 172, conductor 173, to ground at the oilice selector through the usual switching devices at the oiiice selector. The updrive magnet at the office selector Vis then brought into service and brush selection takes place in substantially the same manner as described in connection with the district selector. The office selector in this movement will cause interruptions of the flow of current to the stepping relay 305 by means of an interrupting commutator corresponding to commutator 146 and brush 152 at the district selector.

The closure of the fundamental circuit causes the energization of relay 305. Upon the energization of stepping relay 305 a circuit is completed from ground, armature and front contact of relay 305, conductor 310, lower right-hand Contact of sequence switch spring 309, conductor 313, contact of register spring 438, upper contact of register spring 439, upper left-hand contact of register s-pring 440, conductors 441 and 308,

armature and back contact of the No. 2V

counting relay, andthe winding of the No. 2 counting relay to grounded battery. The No. 2 counting relay prepares a circuit for the No. 2 counting relay in the well known manner. The movement of the ofce selector operates the counting relays until the 0 counting relay and relay 304 are energized. Relay 304 opens the fundamental circuit, thus opening one branch of the circuit of the relay which controls the otiice selector and causing the subsequent stopping of the office selector in a position to trip the third set of brushes.

The energization of the 0' counting relay closes a circuit from grounded battery, power magnet of sequence switch 300, upper lett-hand contact of sequence switch spring 301, armature and front contact of 0 counting relay to ground, for moving this sequence switch out of position 6 and into position 8. In passing from position 6 'to position 8, the holding circuits of the counting relays are opened at sequence switch springs 314 and 315 and the counting relays are deenergized.

In position 8 of sequence switch 300, the fundamental circuit is again closed 'through to the office selector and again causes the energization ot' the up-drive magnet at the oflice selector. Groupl selection will now take place. As the switch shaft, is elevated relay 305 is again intermittently shunted by means of a circuit Jfrom a colrunutator similar to coinmutator 153 at the district selector. The first energization of stepping relay 305 completes a circuit from ground, arma-ture and Jfront contact of relay 305, conductor 310. lower left-hand contact of sequence switch spring 309, conductor 314, contact of register spring 442, upper 'contact of register spring 443, upper left-hand contact of register' spring 444, conductors 445, and 446, armature and back Contact of No. 5 counting relay and the Winding of the'No. 5 counting relay to grounded battery.

As the ofiice selector switch moves upward in the group selecting movement the counting relays will be successively actuated in the same manner as above described. As soon as relay 304 is energized the Jrundamental circuit is opened, thus stopping the selected set of brushes of the oflice selector at the bottom of the fourth group of terminals served thereby. The energization of the 0 counting relay completes the above traced circuit for moving sequence switch 300 out of position 8 and into position 10.

Meanwhile trunk hunting takes place at the ofiice selector in a manner substantially like that described in connection with the district switch, and upon completion of trunk hunting, the ofiice selector will have seized a set of terminals leading to an idle incoming switch in the desired oflice.

Since the operation of the incoming and final switches are well known in the art. it is not believed to be necessary to describe the operation of the sender in connection with the setting of these switches. In positions 10 and 12 of sequence switch 300, brush selection and group selection, respectively, at the incoming switch will be controlled. The incoming switch will then trunk hunt to pick anidle final switch, whereupon the fundamental circuit will be again completed and in position 14 of sequence switch 300, final brush selection will be accomplished. In position 16 of sequence switch 300, group selection of the final will take place. and in position 17 of sequence switch 300 final line selection will take place. The called line will be tested and if idle will be signaled in the well known manner.

Since the number of the line wanted was 3 4 5 6, the second brush and third group of the incoming switch will-have been selected, and at the final, the fifth brush, sixth v the final switch, the energization of the 0 counting relay operates to advance sequence switch 300 out of position 17 and into position 18, in the usual manner. y,

As soon as sequence switch' 30.0 reaches position 18, a circuit is .completed from .grounded battery, power magnet of sesol quence switch 200, Fig. 3, upper right contact of sequence switch spring 251, conductors 253 and 254, closed contacts of reg-` ister spring 447, conductor 448, upper righthand contact of sequence switch spring 351 to ground, for moving sequence switch 200 out of position 9 and into position 13.

In position 13 of sequence switch 200, a circuit is completed from grounded battery, left-hand winding of relay 155, (Fig. 2) lower left-hand contact of sequenceswitch spring 156, conductor 176, brush 177, ter# minal 178, conductor 255, lower4 left-hand" contact 'of sequence switch spring 256 to. ground. Relay 155 is energized in this cirf cuit and completes a circuit from grounded battery, power magnet of sequence'switch 100, upper left-hand contact of sequence switch spring 135, left-hand armature and front contact of relay 155=to ground, for moving this sequence switch out of position 10 and into position 14. It is to be ob# served that relay 155 upon energization locks up through its right-hand winding and the upper contacts of sequence switch spring 158-, the left-hand 'armature and front contact of relay 155 and the upper right-hand and lowerleft-hand contacts of sequence switch spring 104, until sequence switch 100 leaves position 13'. Relay 155 is then deenergized and allows the sequence switch to come to rest in position 14.

As soon as sequence switch 100 leaves position 134, the impulse leads into the sender 'are opened at sequence switch springs 128 and 130, and line relay 212 is allowed to deenergize. At the same time the circuit lof relay 109 is opened at sequence switch sequence switch springs 128 and 130 respectively. Current flow over the subscribers line causes the energization of relay 181 which becomes energized and causes in turn the energization or' relay 182 over a circuit extending Jfrom grounded battery, winding of relay 182, armature and front contact of relay 181, right-hand armature and front contact of relay 103 to ground, at the lower lefthand contactot sequence switch spring 104. The energiz'ation of relay 182 completes a circuit from grounded battery, power magnet of sequence switclr 100, lower left-hand contact ot sequence switch spring 135, armature and front contact of relay 182 to ground, for moving this sequence switch out of position 14 and into position 15.

Referring now to the register controlling circuit shown in Fig. 3, it will be noted that when sequence switch 100 left position 11, the upper branch of the locking circuit of relay 201 was broken at sequence switch Spring 105, and when sequence switch 100 leaves position 13% to cause the deenergization of relay 109, the subsequent deenergization of line relay 212 opens the lower branch of the locking circuit of relay 201. Relay 201 thereupon deenergizes and completes a circuit from grounded battery, power magnet of sequence switch 200, upper left-hand contact of sequence switch spring 257, left-hand armature and back contact of relay 201 to ground, for moving this sequence switch out of position 13 and into position 15.

In position 15 of sequence switch 200, the various registers shown in Fig. 5 are restored. The first register to be restored is register 406, by means of a circuit extending from grounded battery, power magnet of register 406, upper right-hand contact of register spring 449, conductor 450, lower left-hand contact of sequence switch spring 219, conductor 220 to ground at sequence switch spring 241. Register 406 rotates until it reaches its normal position at which time the driving circuit just traced will be opened at the upper contact of register spring 449. As soon as register 406 reaches its normal position, a circuit is completed for restoring register 405, extending from grounded battery, power magnet of register 405, upper contact of register spring 451, lower left-hand contact of register spring 449, conductor 450 to ground over the path described. Register 405 is then advanced into its normal position where it is brought to rest and at the same time completes the circuit for restoring register 404. In this manner the restoration of the registers continues until all the registers have returned to their normal position whereupon a circuit is completed from grounded battery, power magnet of sequence switch 200, upper left-hand Contact of Sequence switch spring 251, conductor 258 and thence through register springs 452, 453, 454, 455, 456, 451 and 449 respectively, as soon as the. lower contacts of these register springs are closed in the normal positions of the registers, and thence to ground over conductor 450 over the path described. The completion of this circuit advances sequence switch 200 out of position 15 and into position 18.

As soon as sequence switch 20() reaches position 18, a circuit is completed from grounded battery, power magnet of sequence switch 300, upper lett-hand contact of se quence switch spring 811, conductor 316, upper right-hand contact of sequence switch spring 259, conducto-r 220 to ground at sequence switch spring 241. Completion of this circuit advances sequence switch 300 out of position 18 and into position 1.

lVhen sequence switch 300 reaches position 1, a circuit is completed from grounded battery, power magnet of sequence switch 200, lower right-hand contact of sequence switch spring 251, conductor 260, lower right-hand contact of sequence switch spring 351 to ground, for moving this sequence switch out of position 18 and into position 1. The various registers, the sender and the register controlling equipment have now all been restored to their normal condition and are ready for reuse. It is to be noted that after relay 109 releases and removes from its'outer left-hand armature the ground which was maintaining the sender busy, the sender is protected against seizure until it is fully restored by meansbf ground supplied to test terminal 112, from sequence switch spring 241, Fig. 4, by way of conductor 220, the upper left-hand Contact of sequence switch spring 259 Iand conductor 261. W hen sequence switch 200 reaches position 1, this ground is removed and the sender may again be selected for reuse.

Conversation takes place in position 15 of sequence switch 100. Upon complet-ion of the conversation the calling subscriber re places his receiver upon the switchhook, thus opening the line circuit. Relay 181 deenergizes and causes the release of slow release relay 182. Relay 182 upon deenergization completes a circuit from grounded battery, power magnet of sequence switch 100, lower left-hand contact of sequence switch spring 165, armature and back con tact of relay 182 to ground for moving this sequence switch out of position 15 and into position 18. i

In position 18 of sequence switch 100, a circuit is completed from grounded battery, winding of'down-drive magnet 173, and the lower contacts of sequence switch spring 151 to ground. Magnet 173 is energized and causes the restoration of the district selector. When the brush shaft is fully returned to its normal position, a circuit is completed from grounded battery, winding of power magnet of sequence switch 100, lower contact of sequence switch spring 174, commutator segment 175, brush 176 to ground, for moving sequence switch 100 out ot position 18 and into position 1.

As soon as the district selector brushes 168, 171 and 159 leave the terminals of the trunk leading to the office selector, restoration of the oflice selector is started. The oiice selector, incoming, and final switches are restored in the usual manner.

When the sequence switch 100 leaves position 18, the holding circuit of the cut-off relay 3 is broken and this relay deenergizes and causes the restoration of the subscribers individual line switch, by completing a circuit from grounded battery, resistance 6, armature and back contact of stepping magnet 7, conductor 8, lower armature and back contact of cut-oit' relay 3, off normal segment 12, brush 11 and the winding of stepping magnet 7 to ground. Stepping magnet 7 interrupts its own circuit and cont-inues to do so until the switch has been advanced through a complete revolution and back to its normal position, at which time brush 11 will leave segment 12 and permanently open the circuit of magnet 7. During the return of the switch, the wipers will pass over busy and idle trunks without stopping, since line relay 2 is not energized at this time. All ot the apparatus has now been restored to its normal condition and is ready for reuse.

The conditions which arise in case the calling subscriber abandons the call, either before dialing to set any of the registers or after he has dialed to set some of the registers but not all of them will now be described.

It will first be assumed that a subscriber abandons the call without operating his dial at all. In this case his initial removal of the receiver will cause his line switch to pick an idle district as previously described. 'preselected sender will then be connected to the district and advanced into position 2 as described. The district sequence switch will also be advanced into position 2. Assuming now that the calling subscriber replaces his receiver at this time, line relay 212 willbe deenergized and will cause register 400 to be advanced one step into its 0 position. Line relay 212 will now remain deenergized and will allow relay 262 to become energized over a circuit extending from grounded baittery, winding of relay 262, lower contact of sequence switch spring 263, right-hand armature and back contact of relay 212 to ground. This circuit is normally completed upon each interruption of the line circuit during the sending of the series of impulses. Relay 262 is however designed so as to be slow to attract its armature and therefore does not become energized during the normal operation of the system. In case of an abandoned call however, relay 262 becomes deenengized4 and completes a circuit from grounded battery, power magnet of seguence switch 200, upper lefbhand contact o sequence switch spring 245, arma'- ture and front contact of relay 262 to ground, for moving this sequence switch out of position 2 and into'position 9. Since only one of the registers has been advanced out of its normal position, a circuit is then.

at once effective to advance sequence switch 20() out of position 9 and into position 13. This circuit extends from grounded battery, power magnet of sequence switch 200, lower left-hand contact of sequence switch spring 251, conductor 252 through the lower contacts of register springs 457, 458, 459, 460, 461 and 462 in parallel to ground. Since sequence swich 200 does not come to rest in position 4 at this time, but passes directly through it, sequence switch 300 is not moved out of position 1, since ground is closed to lead 302 for an insufficient period of time to allow this sequence switch to advance.

When sequence switch 200 reaches position 13, a circuit is completed from grounded battery, winding of relay 117, Fig, 2, lower right-hand and upper left-hand contacts of sequence switch spring 118, conductors 137 and 138, brush 139, terminal 140, conductor 250, right-hand contact of sequence switch spring 256 to ground. Relay 117 is energlzed in this circuit and completes a circuit from grounded battery, power magnet of sequence switch 100, upper left-hand contact of sequence switch spring 135, right-hand armature and front contact of relay 117 to ground, for moving this sequence switch out of position 2 and into position 3. Since sequence switch 200 is in position 13, sequence switch 100 is immediately moved out of position 3 and into position 4 by means of a circuit extending from grounded battery, power magnet of sequence switch 100, lower right-hand contact of sequence switch spring 135, contact of sequence switch spring 183, conductor 176, brush177` terminal 178, conductor 255, lower left-hand Contact of sequence switch spring`256 to ground, When sequence switch 100 lreaches position 4, since the district selector has not been put into operation, a circuit is completed. from grounded battery, power magnet of sequence switch 1 00, contact of sequence .switch spring -=174, v'noirmall commutator 4segment 175 and brush 176 to ground, for moving this sequence switch out of position 4 and into. position 15. Since the call was abandoned, relay 182 will not have been energized and therefore a circuit it at once completed from grounded battery. power magnet l"of sequence switch 100, lower lefthand Contact of sequence switch spring 165, armature and back contact of relay 182 to ground, for moving sequence switch 10() out of position 15 and into position 18 from which position it is at once moved into 1 by means of the previously traced circuit eX- tendingthrough the contact of sequence switch spring 174- and normal commutator segment 175 and its associated commutator brush 176 to ground. y

The release of the district selector causes the release of relay 201, Fig. 3, which advances sequence switch 200 out of position 13 and into position 15, wherein register 400 is restored to its normal position. With all the registers in their normal positions, circuits identical with those previously traced are completed to advance sequence switch 200 into position 18, from which position itis advanced into position 1 as previously described. l

If the subscriber abandons the call after withoiit completing the full registration, the restoration of the registers and various controlling apparatus is substantially similar. In case the first three registers have been set, the fundamental circuit will have been completed and the various selective operations will have been started at the time the call is abandoned. The continued deenergization of relay 212 at this time will cause the energization or" relay 262 and sequence switch 200 will be advanced into position 9 as previously described. Since some one, or perhaps several, of the registers are in their normal positions at the time sequence switch 200 reaches position 9, a circuit will again be completed for advancing sequence switch 200 by way of the lower left-hand contact of sequence switch spring 251 and conductor 252.

Meanwhile the district switch will complete its selective operations and sequence switch 100 will come to rest in position 10, A circuit is then completed from grounded battery, left-hand winding of relay 155, lower left-hand contact of sequence switch spring 156, conductor 176, brush 177, terminal 178, conductor 255, lower left-hand contact of sequence switch spring 256 to ground. Relay 155 is energized and at its left-hand armature and front contact completes a circuit for moving sequence switch 100 out of position 10 and into position 14.

A circuit is then completed Jfrom grounded battery, winding of down-drive magnet 17 3, lower contacts of sequence switch spring 151 to ground. Magnet 17 3 is energized and causes the restoration of the district selector brush shaft. When the district brush shaft reaches its normal position sequence switch 100 is advanced out of position 1 4 and into position 15, and thence into position 1 as previously described in connection with an abandoned call.

.As soon as the district selector brush set dialing a number of series of impulses, but.

leaves the terminals of the trunk leading to the oiiice selector, the incoming selector and any succeeding switches in the train are released in the well known manner.` Under the conditions assumed, sequence switch 20() is advanced into position 18 as previously described whereupon a circuit is completed Jfrom grounded battery, power magnet of sequence switch 300, upper left-hand contact ofV sequence switch spring 311, conductor 316, upper right-hand contact of sequence switch spring 259, conductor 220 to ground at sequence switch spr-ing 241. The completion ofthis circuit advances the-sender sequence switch 300 out of whatever position it happens to be in, into position 1, whereupon sequence switch 200 is advanced out of position 1S and into position 1. The apparats is now all in its normal condition.

The operation of the system when used by a subscriber on a party line in making a revertive call to a stationon the same line will now be described.

The invention has been shown applied to a system in which revertive ringing may be accomplished on a fourpart line of the type in which a desired one o the four stations may .be selectively rung by applying ringing current superimposed on lplus or minus battery to either the tip or the ring side of the line. Since the systemcould easily be adapted to operate with any type of party line ringing system, whether ar-.

ranged for two or four party lines, it is not to be restricted to the specific embodiment shown, which merely illustrates one form of carrying out the principles involved.

As previously stated any party line sub` scriber in the system, regardless of which oiiice he is in will dial a characteristic office code when he desires to make a revertive call. To accomplish this, each party line subscribed will be supplied with the names of the subscribers who are on his own party 1 line, since these numbers will have no relation to the numbers appearing in the regular directory. The directory numbers will, of course, be used by any other subscribers who desire to converse with a subscriber on a given party line, provided that they are not on the same line.

As just stated by first dialing impulses corresponding to the letters JJJ the sender registers will be set in positions to accomplish revertive ringing. The thousands, hundreds, tens and units registers will then be positioned and determine which substa tion on the party line will be rung.

Briefly the general operation is as follows: The subscriber initiating a call will dial JJJ and then dial the number which corresponds to the particular party line station on his own line which he desires to signal. He will then replace his receiver I on the switch-hook. The sender vand special revertive ringing apparatus will then be operated to ring first the called subscribers station and then the station of the originating subscriber. The ringing of the bell at the originating subscribers station informs him that the system is operating satisfactorily and that the called subscriber has not yet answered. When the called subscriber removes his receiver from the switchhook ringing current is disconnected, and the bell at the originating station ceases to ring, thus informing the calling subscriber -that\ the called party has answered. He will then remove his receiver from the switchhook and may converse with the called subscriber.

- Battery for "the conversation is supplied out of its normal position.

from the district switch which is held byy `the calling subscribers line switch. The

district switch, however, does not advance Referring now to Fig. 6, thousands register spring 464, hundreds register springs 466 and 467, tens register spring 469 and units register springs 471 and 472 are the springswhich determine which two parties shall be signaled in the case of a revertive call. In the case of all of these four registers the digits 2 and 1 are the only ones which are used to control the ringing selections.

It will be assumed that the subscriber whose substation is signaled by ringing current superimposed on plus battery applied to the ring side of the line desires to talk with a subscriber on the same party line whose substation may be signaled by ringing current superimposed on minus battery applied to the tip side of the line. He will consult his individual card showing the substations on his own party line and will learn that the number he must dial is J J J 1221.

The. calling subscriber thereupon removes his receiver from the switchhook and his individual line switch selects anidle trunk to a district switch in a manner identical with that described in connection with a non-revertive call. He will then dial J J J 1221 to set the A register in position 9, the B register in position 9, the C register in position 9, the thousands register in position 1 the hundreds register in position 2, the tens register in positionv 2 and the units register in position 1. The operation of the district circuits and the register controlling circuits in Fig. 3 is identical with that previously described and it is thought that no further description is necessary.

After the registers have all been set the district sequence switch 100 will be in position v2, the register controlling sequence switch 20,0 will be in'position 9 and the sender sequence switch 300 4will have been It is to be observed that when sequence switch 200 reaches position 4, however, the fundamental circuit including 'line relay 117 (Fig. 2) is not completed. This circuit extends from grounded battery, windin of relay 117, lower right-hand and upper i hand contacts of sequence switch spring 118, conductors 137 and 138, brush 139, terminal 140, conductor 250, armature and back contact of'relay 304, winding of stepping relay 305, contact of sequence switch spring 306, conductor 307 to register springs 428 and 429 inl parallel. `Since the A and B registers'are both in position y9', in the case of a revertive call, springs 428 and 429 are both openand the fundamental circuit is not completed to start selection at the district switch. The district sequence switch there- 2, the shunt path about relay 290 is reino-ved, since this shunt is now open at each of the register springs 411,472, 473, 463, 465, 468 and 47 0, at any one of which it would normally be in existence provided any designation other than JJ J had first been dialed or 1n case' any one of the numerical registers has not been advanced beyond its zero position. The relay 290 is now included in the line circuit which extends from grounded battery, winding of relay 212, winding of relay 290, conductors 263 and 214 left-hand armature a-nd back contact of relay 215, conductor 216 'and thence through the calling substation to ground as previously described.

Relay 290 responds in series with line relay 212 since the line circuit is closed immediately following the termination of the last series of impulses. Relay 290 upon energization completes a circuit .from grounded battery, power magnet of sequence switch 300, left-hand contacts of sequence switch spring 320, conductor 321, armature and frontv contact of relay 29() to ground, for moving sequence switch 300 out of position 2 and into position 3.

The calling subscriber will then replace his receiver and await the ringing of the called subscriber. The resultant` interruption of the line circuit allows relays 212 and 290 to be deenergized. The deenergization of relay 290 completes a circuit from grounded battery, power magnet of sequence switch 300, lower left-hand contact -of sequence switch sp-ring 311, conductor

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