US1342823A - Telephone-exchange system - Google Patents

Description

A. E. LUNDELL AND E. H. CLARK.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILE!) N0v.2, 1917.

Patented June 8, 1920.

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TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED NOV. 2, 191?.

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A. E. LUNDELL AND E. H. CLARK.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED NOV. 2, 1917.

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A. E. LUNDELL AND E. H. CLARK.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED NOV. 2. 1917.

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A. E. LUNDELL AND E. H. CLARK.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED may. 2, 1911.

1,342,823. Patented June 8, 1920.

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TELEPHQNE EXCHANGE SYSTEM.

APPLICATION FILED Nov. 2, 1917.

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TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED NOV- 2,1917- Patented June 8, 1920.

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A. E. LUNDELL AND E. H. CLARK. TELEPHONE EXCHANGE SYSTEM. APPLICATION FILED N0V.2I I917.

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TELEPHONE EXCHANGE SYSTEM. APPLICATION FILED NOV. 2, 1917.

1,342,823. PatentedJune 8,1920.

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Thausa nds A. E. LUNDELL AND E. H. CLARK.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED n0v.2,1917.

Patented June 8, 1920.

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TELEPHONE EXCHANGE SYSTEM.

APPLICAHON FILED NOV. 2, 1917.

Patented June 8, 1920.

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A. E. LUNDELL AND E. H. CLARK.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED NOV. 2. 1917.'

Patented June 8, 1920.

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AI|BEN E. LUNDELL AND EDGAR H. CLARK, OF NEW YORK, N. Y., ASSIGNORS 'IO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A

CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Specification of Letters Iatent.

Patented June 8, 1920.

Application flied November 2, 1917. Serial No. 199,888.

To all whom it may concern:

' Be it known that we, ALBEN E. LUNDELL and EnoAu H. CLARK, citizens of the United States, residing at New York, in the county of Bronx and State of New York, and at New York in the county of New York and State of New York, respectively, haveinvented certain new and useful Improvements in Telephone-Exchange Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to telephone exchange systems of the semi-automatic type, and more particularly to systems in which tandem trunking is required.

It is the object of this invention to provide a system in which subscribers calls may be extended through a plurality of offices in tandem and to accomplish this end in a rapid and efficient manner.

In accordance with this object a switchin center is provided, there being provided at this point an operator corresponding to a B operator, who will receive calls from outlying offices and who will then operate automatic switching mechanisms under the control of a ke set to extend the calling line to a desire( outlying ofiice. From this outlying office the call may be extended by means of mechanical switches, or an indicator may be operated at this point to inform the operator at the tandem point of the number of the desired line. If the call is to be again trunked from this point through another distant office in tandem, the indicator will also inform the tandem point operator as to the office to which the call is to be trunked.

In the present disclosure it has been assumed that all calls will be extended to a tandem point operator who will trunk to an outlying office, it being obvious that if the call is for a number located at her own office she could readily complete the connection, and that in this case the indication of the last office would be omitted.

No disclosure has been made of the method by which calls may be completed at an outlying office provided with automatic switches for completing this type of connection, since this form of connection is well understood in the art.

A feature of the invention is the method of providing metallic supervision for the various operators concerned in setting up the connection.

A further feature of the invention resides in an improved method for performing the operations necessary in handlin the overflow condition, that is, the condition which arises when all the trunks of a selected group are busy.

Another'feature of the invention resides in the provision and method of controlling two allotters which control the assignment of senders to the operator controlling the switching center.

A still further feature of the invention is provided by a novel test which is made by the sender to determine whether or'not the operator at the tandem point has removed her plug from the jack, the object of this test being to delay the operation of the impulse sending device which controls the call indicating mechanism at such office until such operator is ready to receive a call.

An added feature of the invention is the provision of means to delay operation of the sender, when connection is being established to an interdistrict ofiice selector, until such selector has arrived at its normal position and is ready for reoperation.

A further feature of the invention is an arrangement by which the stepping relay, that is, the relay which controls the successive operations of the counting relays in the sender, is used only on calls to a distant office; that is, if the office selector is local, the counting relays will be directly controlled from the commutator of the switch being operated; but if the call is extended through an interdistrict ofiice, the stepping relay is utilized to insure greater accuracy.

Other features will appear from the following description and appended claims.

It is thought that the invention will best be understood from the following detailed description, reference being had to the accompanying drawings.

In the drawings, Figures 1 to 13 inclusive indicate diagrammatically a telephone exchange system embodying the principles of the present invention. Fig. 14 is a plan showing with what relation to one another the various sheets of drawings should be laced, it being understood, however, that igs. 3 and 4 are interchangeable,

switch contacts shown tended through a local 'ofiice selector or an interdistrict oflice selector. 1

Fig. 1 shows a" calling subscribers substation and a cord circuit at an A ope'rators position, as well as the outgoing-end ofa trunk to the cordless o erators position at the switching center; ig. 2 shows the-01rcuits of a district selector, all the sequence in this figure being under the control of the sequence SWICCh shown at the bottom of the figure, w1th the exception of the contacts withm the dotted lines, which are utilized for overflow slgnaling under the control of the sequence swltch shown in such dotted rectangle; Fig. 3 shows the circuits of a local oflice selector; F1 4 shows the circuits of an interdistrict o ce selector; Fig. -5 shows the circuits of an 1ncoming trunk at a tandem pomt, together with the cord circuit of a manual operator at an outlying oflice and the substation apparatus of a called subscriber; Fi 6 shows the circuits of a cord finder, w ile 1n the dotted rectangles are shown the circuits for controlling two allotters, there being a seuence switch associated with each ailotter or controlling thecontacts associated with it within the dotted lines; Figs. .7, 8 and 9 indicate sender circuits for re istering a desired number and for transmltting suitable impulses for controlling the extension of the call; Figs. 10, 11, 12 and 13 show the circuits of the relay call indicator which controls the indication of the designation of the desired outlying oflice and of the desired line number.

spring 19, conductor 20,

The subscriber at substation 10 desiring to initiate a call removes his receiver from the hook, causing a line signal to be displayed before the A operator, one of whose cords is indicated at 0. The operator on observing this signal, inserts the plug 11 into answering jack 12 associated with the line signal of the calling subscriber and inquires the number of the wanted line. The operator at 0 by means of an order wire which may be of any well-known type, converses with the operator at the switching center, whom we shall hereafter designate as the cordless operator, and upon being advised to use the trunk outgoing from jack 13, inserts plug 14 into jack 13 and extends the calling line to. the operators position shown in Fig. 2., When plug 14 is inserted into jack 13 a circuit is completed from grounded battery, lamp 15, resistance 17, sleeve conductors of plug 14 and 'ack 13, windingof relay 18, to ground. Iielay 18 is energized in this circuit and lamp 15 is lighted.

A circuit is now completed from ground, lower right-hand contact of sequence switch lower windin of relay 21, lower right-hand winding 0 repeatmg coil 22, armature and front contact upper ri-lght-hand wmdingof repeating coi not shown, but

of relay 18, winding of polarized relay 23i 22, trun conductor 24, upper windin of relay 21, upper right-hand contact 0 sequence switch spring 25, to grounded battery. Flow of current in this clrcult is in such a direction as not to energize polarized rela 23, but relay 21 is energized, completmg a circuit from ground, armature and ront contact of rela 21, upperright-hand and lower left-han contacts of sequence switch spring 26,- lamp 27 togrounded battery. Lamp 27 is lighted to inform the cordless operator that the A operator has plugged in on the assigned trunk. The cordess operator then momentarily depresses non-locking assignment key 28, whereulpon a circuit is completed from grounded attery, power magnet of sequence switch 29, upper contact 0 sequence switch spring 30, closed lower contacts of key 28, to ground. Sequence switch 29 moves from osition 1 to positon 2 under the control 0 its normal contact 31.

It is to be observed at this point that if at the time the assi nment key is depressed the ,sequence switch; associated with any other district selector is standin in position 2, it will be immediately move out of position 2 and restored to its normal position,

when the sequence switch shown in Fig. 2 arrives in osition 2. This would occur as follows. he relay corresponding to relay 32 associated with such other selector would .be enellgized over a circuit extending from and front contact of relay 32, left-hand con-.

tacts of a sequence switch spring corresponding to sequence switch spring 35, to ground. This,relay would then complete a circuit from grounded battery, power magnet of its associated sequence switch, lower right-hand contact of a sequence switch sprmg corresponding to sequence switch spring 30,1eft-hand armature and front con-.

tact of relay 32, lower right and upper left contacts of a sequence switch spring corresponding to sequence switchspring 26, to ground, for moving its associated se uence switch through positions 2 and 3. T e relaly corresponding to relay 32 is deenergized w on the associated sequence switch leaves soon as the sequence switch arrives in position 6, a circuit is completed from grounded battery, power magnet of such sequence switch, upper right-hand contact of a sequence switch spring corresponding to sequence switch spring 37, commutator segment 38, commutator brush 39 to ground, for moving this sequence switch into its first or normal position.

Returning now to the regular operation of the system, when sequence switch 29 arrives in position 2, a circuit is completed from grounded battery (Fig. 6), right-hand winding of relay 40, conductor 41, upper contacts of sequence switch spring 42, conductor 43, lower right and upper left con tacts of sequence switch spring 35, to ground. Relay 40 is energized in this circuit and completes a circuit from groundedbattery, winding of power magnet 44 of the sequence switch associated with the cord finder, upper right-hand contact of sequence switch spring 45, right-hand armature and front contact of relay 40, to ground, for moving this sequence switch out of position 1 and into position 3. WVhen sequence switch 44 leaves position 2, the original energizing circuit of relay 40 is broken, but this relay remains energized over a locking circuit extending from ,grounded battery, righthand winding of relay 40, conductors 41 and 46, left-hand armature and front contact of relay 40, upper contact of sequence switch spring 47 finder brush 48, conductor 49 and lower contact of sequence switch springs 50 associated with undesired selectors, to ground. It is to be remembered that only one district selector sequence switch can be in position 2 at a given time, and therefore only the district selector with which the sender is to be associated can be seized by the cord finder. When sequence switch 44 arrived in position 3, a circuit was completed from grounded battery, winding of updrive magnet 51, lower contact of se quence switch spring 45, right-hand armature and front contact of relay 40, to ground. This caused the cord finder brush set to be moved upward in search of the terminals of the link circuit with which a sender is to be associated. As explained, relay 40 is main-- tained energized as long as the finder is passing over the terminals associated with district selectors whose sequence switches are in any other position excepting position 2. When brush 48 encounters a terminal associated with the link circuit with which a sender is to be associated, the locking circuit of relay 40 is broken. This relay does not immediatel deonergize, however, since an alternate olding circuit extends from grounded battery, left-hand winding of relay 40, right-hand contacts of sequence switch spring 52, commutator 53, brush 54, to ground. When brush 54 engages an insulating segment of commutator 53, at which time the finder brush set will be accurately centered v onthe terminals of an idle trunk, this second holding circuit for relay 40 is broken and this relay denergizes and opens at its right-hand contact an armature the driving circuit of magnet 51, bringing the finder brushes to rest on the terminals associated with the desired district selector. When relay 40 is denergized, a circuit is completed from grounded battery, winding of power magnet'of sequence switch 44, lower left-hand contact of sequence switch spring 55, to ground at the right-hand armature and back contact of relay 40, for moving this sequence switch out of position 3 and into position 4.

When the cord finder sequence switch arrives in position 4 a circuit is completed from grounded battery, power magnet of sequence switch 29, lower right-hand con tact of sequence switch spring 37, conductor 56, terminal 57, finder brush 58, conductor 59, lower left-hand contact of sequence switch spring 60, conductor 61, upper left-hand contact of sequence switch spring 62, to ground, for moving this sequence switch out of position 2 and into position 3.

0 With sequence switch 44 in position 4, a circuit is completed from grounded battery, right-hand winding of relay 40, upper right-hand contact of sequence switch spring 106, to ground. Relay 40 is energized and completes a locking circuit for itself from grounded battery, right-hand winding of relay 40, conductors 41 and 46, left-hand armature and front contact of relay 40, lower contact of sequence switch spring 47, brush 107, terminal 108, conductor 109, lower left-hand contact of sequence switch spring 50, to ground. The energization of relay 40 completes a circuit from grounded battery, power magnet of sequence switch 44, upper right-hand contact of sequence "switch spring 45, right-hand armature and front contact of relay 40, to ground, for moving this sequence switch out of position 4 and intoposition After the cordless operator depressed the assignment key, she depressed keys in a key set to control the registration of the desired line. Assuming that the desired substation is No. 8888 and is not on a party line, and

that the outlying oflice throu h which it may be reached rom the tan em ointto WhlCh connection will be extende by automatic switches is represented by the code number 323, the operator will then depress the tandem hundreds key No. 3, a tandem tens key No. 2 and a tandem units key No. 3, a key N0. 8 in each of the thousands, hundreds, tens and units columns, respectively,-and will also depress the start key 63, since no stations impulses are to be sent.

If the outlying ofiice to be reached is one to which a great many calls are to be made, it may be possible to accomplish the tandem registration by depressing a single dis trict key indicated at 64, it being observed,

as will appear presently, that the depression of this single key will have the same efi'ect on the registers controlling the outlying ofice selection as the depression of the tandem hundreds, tens and units keys Nos. 3, 2, 3, respectively.

Assumin that the upper allotter 153 shown in ig. 6 is standing in position 1 to assign the sender shown in the accompanying drawings, the operation of setting the registers is as follows. As soon as the tandem hundreds key. No. 3 is depressed, a circuit is completed from grounded battery (Fig. 7), conductor 65, winding of relay 66, winding of relay 67, closed contacts of tandem hundreds key No. 3, windingof relay 68, conductor-69, conductor 70, upper right-hand contact of sequence switch spring71, winding of relay 72, conductor 73, upper lefthand contact of sequence switch sprlng 74, to ground. Relays 66, 67, 68 and 72 are energized in this circuit, relay 72 looking itself to ground at its left-hand armature and front contact. In response to the closure of tandem tens key No. 2, a circuit is completed from grounded battery conductors 65, 75 and 76, closed contacts of tandem tens key No. 2, winding of relay 77, conductor 69, to ground over the path described. In response to the operation of tandem units key No. 3, circuit is completed from grounded battery, conductor 78, winding of relay 79, closed contacts of tandem units key No. 3, conductors 80 and 69, to ground over the path described. It is thus apparent that in response to the setting up ofthe number 323 on the tandem keys or the depressionof district key 64, relays 66, 68, 67, 77, 79 and 72 have been energized. The energization of start relay 66 completed parallel circuits for the power magnets of the sequence switches controlling the class, district brush, district group, ofiice brush and ofiice group registers, respectively, it being borne in mind that the cord finder sequence switch is at this time in position 5. The circuit of the class register power magnet may be traced from ground at the armature the magnet of the armature and back contact of relay 81,

power magnet of class register sequence switch 82, conductor 83, upper I left-hand contact of sequence switch spring 84, to grounded battery. The circuit of the power district brush register may be traced from ground at the armature and front contact of relay 66, right-hand armature and back contact of relay 85,=powe r magnet 86, conductor 87, upper right-hand contact of sequence switch spring 88, to grounded battery. The circuit of the district group register sequence switch may be traced from ground at the armature and front contact of relay 66, right-hand armature and back contact of relay 89, power magnet 90, conductor 91, lower right-hand contact of sequence switch sprin 88, to grounded battery. The circuit of %he ofiice brush register sequence switch may be traced from ground at the armature and front contact of relay 66, right-hand armature and back contact of relay 92, power magnet 93, conductor 94, upper right-hand contact of sequence switch spring 84, to grounded battery. The driving clrcuit of the office group register sequence switch may be traced from ground at the armature and front contact of relay 66, righthand armature and back contact of relay 95, power magnet 96, conductor 97, lower right-hand contact of sequence switch spring84, to grounded battery.

Under the influence of the above traced circuits, the registers are caused to rotate from the positions they had last assumed until brought to rest under the control of the test relays 81, 85, 89, 92 and 95, respectively, associated with them. When the class register reaches position 8, a circuit is completed from grounded battery, conductor 65, winding of relay 81, class register spring 98 (position 8), closed contacts of tandem hundreds key No. 3, conductors 99, 100, 101, 80, 69 and 70, to ground over the path described. The energization of relay 81 opens at its right-hand armature the driving circuit of power magnet 82, and this causes the class register to be brought to rest in position 8. When the district brush register arrives in position 1, a circuit is completed from grounded battery, conductor 65, winding of relay 85, district brush register spring 102, closed in position 1, armature and front contact of relay 68, conductors 69 and 70, to ground over the path described; The resultant energization of relay 85 causes the district brush register to come to rest in position 1. When the district group register arrives in position 3, a circuit is completed from grounded battery, conductor 65, relay 89, district group register spring 103, closed in position 3, armature and front contact of relay 67 conducdescribed, causlng the district group register to come to rest in position 3. When the office brush register reaches position 2, a circuit is completed from grounded battery, winding of relay 92, office brush register spring 104, closed in position 2, armature and front contact of relay 77, conductors 69 and 70 to ground. The resultant energization of relay 92 causes the ofiice brush register to come to rest in position 2. l/Vhen the office group register reaches position 3, a circuit is completed from grounded battery, conductor 65, winding of relay 95, office group register spring 105, closed in position 3, armature and front contact of relay 79, conductors 69 and 70, to ground as described, causing the ofiice group register to come to rest in position 3.

As soon as the class and district brush registers have been set, as indicated by the energization of relays 81 and 85, cord finder sequence switch 44 is moved from position 5 to position 6 over a circuit extending from grounded battery, power magnet of sequence switch 44, conductors 110, 111 and 112, upper left-hand contact of sequence switch spring 113, conductor 114, left-hand armature and front contact of relay 81, left-hand armature and front contact of relay 85, to ground at the armature and front contact of relay 66. As soon as the district group register is positioned, as indicated by the energization of relay 89, cord finder sequence switch 44 is moved outof position 6 and into position 7 by a circuit extending from grounded battery, power magnet of sequence switch 44, conductors 110, 111 and 112, upper right-hand contact of sequence switch spring 113, conductor 115, left-hand armature and front contactof relay 89 to ground at the armature and front contact of relay 66. As soon as the office brush and oflicegroup registers have been positioned, as indicated by the energization of relays 92 and 95, sequence switch 44 is moved out of position 7 and into position 8 over a circuit extending from grounded battery, power magnet of sequence switch 44, conductors 110, 111 and 112, upper right-hand contact of sequence switch spring 55, conductor 116, left-hand armature and front contact of relay 92, left-hand armature and front contact of relay 95 to ground at the armature and front contact of relay 66.

The method of setting the number and stations registers will now, be described. As soon as start key 63 is depressed, it being understood that the stations. keys are so Wired that if stations impulses are to be sent the depression of a stations key will perform the same starting function as the start key, a circuit is completed from grounded battery (Fig. 9). winding of relay 117, closed contacts of start key 63, conarmature and back contact of relay 120,

power magnet 121, conductor 122, lower left-hand contact of sequence switch spring 123, to grounded battery. The circuit of the units register sequence switch may be traced from ground at the right-hand armature and front contact of relay 117, right-hand armature and back contact of relay 124, power magnet 125, conductor 1126, lower right-hand contact of sequence switch spring 123, to grounded battery. The circuit of the tens register sequence switch may be traced from ground at the righthand armature and front contact of relay 117, right-hand armature and back contact of relay 127, power magnet 128, conductor 129, upper right-hand contact of sequence switch spring 123, to grounded battery. The circuit of the hundreds register sequence switch may be traced from ground at the right-hand armature and front contact of relay .117, right-hand armature and back contact of relay 130, power magnet 131., conductor 132, lower left-hand contact of sequence switch spring 133, to grounded battery. The circuit of the thousands register sequence switch may be traced from geound at the right-hand armature and front contact of relay 117, right-hand armature and back contact ofrelay 134, power magnet 135, conductor 136, lower righthand contact of sequence switch spring 133, to grounded battery. The number and stations registers; now rotate and continue to rotate until they arrive at the positions determined by the keys depressed. ,lVhen the thousands register reaches position 8, a circuit is completed from grounded battery, conductor 137, winding of relay 134, thousands register spring 138, closed in position 8, closed contacts of the thousands key No. 8, conductors 119 and 70, to ground over the path described. The resultant energization of relay 134 opens the driving circuit of the power magnet 135 and the thousands register is brought to rest in position 8. By means of similar circuits, relay 130 is energized in position 8 of the hundreds register to cause this register to stop in such position. Similarly, relay 127 causes the tens register to stop in position 8 and relay 124 causes the units register to stop in position 8. When the stations register arrives in position 0, a circuit is completed from grounded batens ,to assign another sender.

tery, tvinding of relay 120, stationsre 'ster spring 139, closed in position 0, close contacts of start key 63, conductor 140, normal contacts of stations key No. 1 -(used to indicate the 10,000 digit .when the number of the desired line is more than 10,000), conductor 119, to ground over the path described. The resultant energization of .relay 120 causes the stations register to come to rest in position *0. As soon as all the number registers and stations register have been positioned, as indicated by the energization of their associated controlling relays 134, 130, 127, 124, 120 respectively, a circuit is completed for moving sequence switch 44 out of position 8 and into position 9, this circuit extending from grounded battery, power magnet of sequence switch 44, conductors 110, 111, lower right-hand contact of sequence switch spring 55, conductor 141, in series through the left-hand armatures and front contacts of the re lays 134, 130, 127, 124 and 120 respectively, to ground at the right-hand armature and front contact of relay 117.

With the cord finder sequence switch in position 9, parallel circuits are completed to the key release magnets 142, 143, 145, 146 and 147 in parallel, these circuits being traceable from, grounded battery, upper lefthand contact of sequence switclr spring 88, conductor 148, winding of magnet 142, to ground; also from grounded battery, lower eft-hand contact of sequence switch spring 88, conductor 149, winding of magnet 147. to ground; also from grounded battery, upper left-hand contact of sequence switch spring 133, conductor 150, through the windings of magnets 143 and 145 in parallel to ground; and from grounded battery, upper right-hand contact of sequence switch spring 133, conductor 151, winding of magnet 146, to ground. The magnets 142, 143, 145, 146 and 147 control the release of all the keys which have been depressed, and these keys should now be released. If all the keys are successfully released, the locking circuit of relay 72 will be broken when the last key is released, and this relay will deenergize, completing a circuit for moving sequence switch 44 out of position 9 and into position 10, this circuit extending from grounded battery, power magnet of sequence switch 44, conductors 110, 111 and 112, lower right-hand contact of sequence switch spring 113, lower contact of sequence switch spring 152, left-hand armature and back contact of relay 72, to

I ground.

With sequence switch 44 in position 10, a circuit is completed for advancing the upper allotter sequence switch 153 into a position This is accomplished by means of a circuit extending from grounded battery, power magnet of sequence switch 153 conductors 154, 155, 156, lower contacts ofi sequence switch spring 42, conductors 157, 158, lower contact of sequence switch spring 159, conductor 160, left-hand contacts of sequence switch spring 161 associated with the bottom allotter 163, the upper right-hand contact of spring 162, closed in the normal position of the foot clutch, to ground.

' It might be well'to' describe at this time the interaction of the two allotters which assign senders, these allotters being of the sequence switch type, one being indicated at 153 and the other at 163. Assuming that in the beginning allotter 163 was resting in position 18and that allotter 153 was in position 1, upon the completion of the operation up to the point described, allotter 153 will be advanced out of position 1 andinto position 2, as described. In position 2 of allotter 153, a circuit is completed from grounded battery, resistance '169, upper left-hand contact of sequence switch spring 71, winding of relay 72, upper right-hand contact of sequence switch spring 159, conductor 160, to ground over the path described. If one of the three finders which is assigned by allotter 153 is idle and in a position to beassigned, relay 72 is not energized in this circuit, since it will be shunted by a circuit extending from grounded battery, resistance 169, upper and lower left-hand contacts of sequence switch spring'71, conductor 170, upper right-hand power magnet of sequence switch 153, conductor 154, upper contact of sequence switch spring 152, to ground at the armature and back contact of relay 72.

As long as all the cord finders are busy and until one of them is ready for allotment, as indicated by its arrival in position 18, no keys can be depressed, since relay 72 by its energization supplies battery to the release magnet conductors 148, 149, 150, 151 by way of allotter spring 171 and the right-hand armature and front contact of relay 72, and therefore no number can be set up on the operators key set until a sender has been assigned. As soon as a sender becomes idle, relay 72 is shunted and the allotter is moved out of position 2 and into position 3, as described.

Provided that the manually operable" key 164 associated with allotter 153 is in its normal position, the allotter will at once he moved out of position 3 and into position 6 by means of a circuit extending from grounded battery, power magnet of allotter 153, upper right-hand contact of sequence switch spring 165, normally closed contacts of key 164, to ground. In position 6 the I allotter assigns the next sender and after this sender has been operated, is moved into position 12 by similarcircuits to those just described. After this third sender has been used, the allotter is moved into position 17 by means of circuits just described. When allotter 153 arrives in position 17, a circuit is completed from grounded battery,- winding of the power magnet of allotter 163,

upper left-hand contact of sequence switch spring 166, lower left-hand contact of se quence switch spring 167, to ground, for moving allotter 163 out of position 18 and into position 1, whereupon it will assign its first sender which we shall refer to as the fourth sender. IVith allotter 163 in position 1, a circuit is completed from grounded battery, power magnet of allotter 153, lower left-hand contact of sequence switch spring 165, upper right-hand contact of sequence switch spring 168, to ground, for moving this allotter out of position 17 and into position 18. where it will rest until allotter 163 has assigned its lastsender and moved into position 17, whereupon allotter 153 will be moved out of positionl8 and into position 1, to reassign the first sender.

The cord finder sequence switch remains in position 18 after completing its operation and awaits reassignment. The cord finder shown in the drawing is to be allotted in position 1 of allotter 153. Therefore, with sequence switch 44 in position 18 and allotter in position 1, a circuit is completed from grounded battery, power magnet of sequence switch 44, conductors 110, 111 and 112, lower left-hand contact of sequence switch spring 113, conductor 158, lower left-hand contact of sequence 'switch spring 159, conductor 160,

left-hand contacts of sequence switch spring 161, to ground at the normal contact of the foot clutch 162. This moves sequence switch 44 into position 1 ready for operation when another district sequence switch moves into position 2. In case the allotted cord finder is busy, in which case its sequence switch will not be resting in position 18, the operation will be delayed until it arrives in some position between 9 and 18. In positions 10 to 17 of the cord finder sequence switch which would normally be the next to be allotted, a circuit is completed from grounded battery, power magnet of allotter 153, conductors 15-1, 155 and 156, lower contactsof se quence switch spring 42, conductors 157, 158, lower left-hand contact of sequence switch spring 159, to ground over the path described, which would move the allotter from position 1 to position 2, and it would then advance into position 6, as described, to assign the next cord finder.

Assuming that it is desired to eliminate the senders assigned by allotter 153, these senders can be cut out of service by depressing locking key 164, it being further assumed that at the time this key is depressed allotter 153 is standing in position 1. The allotter may then be moved out of position 1 as usual and will not effect the operation of the first sender. The allotter stops in position 3 and allows allotter 163 to become independent; that is, to reassign senders 4, 5 and 6. In this case, with the key 164 depressed, lamp 172 has a circuit extending from grounded battery, operated contacts of key 164, resistance 173, the normal contact of the foot clutch spring 174, resistance 175, lamp 172, to ground, but it is shunted by a path extending by way of resistance 176, conductor 177,-lower right-hand contact of sequence switch spring 106, to ground. When the assigned cord finder sequence switch arrives in position 18, this shunting circuit is removed and lamp 172 is lighted. At this point the foot clutch, controlling springs 162 and 174, is operated. In this case, ground contact supplied from the lower right-hand contact of clutch spring 162 and conductor 178 to the lower right-hand contact of allotter spring 166 prevents allotter 163 from stopping in either positions 17 or 18, and therefore this allotter will keep on assigning senders Nos. 4, 5 and 6. When the foot clutch is operated, the allotter 153 associated with it is ineffective, because the ground feed at the upper right-hand contact of clutch spring 162 is open. The allotter 153 may now be revolved and any tests or repairs which it was desirable to make may be made without affecting the opera tion of the system. When the allotter 153 is to be again out into service, it must beleft in position 18. Key 164 may now be released and lamp 172 will not be lighted until allotter 163 is in some position included in the positions 1 to 14. This circuit extends from grounded battery, normal contacts of key 164, conductor 179, upper and lower righthand contacts of allotter spring 161, conductor 180, lower and upper contacts of allotter spring 181, resistance 182, lower contact of clutch spring 174, resistance 175, lamp 172, to ground, causing the lighting of this lamp. At this time the foot clutch may be restored to its normal position, and the allotter 153 will be moved out of position 18 and into position 1 when allotter 163 arrives in position 17, as usual. The circuits of the locking key and foot clutch associated with allotter 163 are identical with those described for allotter 153.

In case both allotters get into a position for assigning senders; that is, in case both these allotters are in a position included between positions 1 and 14, neither is effective and an alarm is given. The alarm circuit extends from ground, lower left-hand and upper rigl1t-hand contacts of sequence switch spring 183, conductor 184, normal contacts of key 164, upper and lower right-hand con-

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