US1736259A - A copabtnership consisting of charles a - Google Patents

Description

NOV. 19, 192.9. J. E. GARDNER 1,736,259

AUTOMATIC TELEPHONE SYSTEM Filed'May 11. 1927 4 sneetsheet 1 ATTORN EY Nov. 19, 1929. r n J. E. GARDNER v 1,736,259

AUTOMATI C TELEPHONE SYSTEM Filed May ll-,- 1927 4 Shevelzs-Shf-zexll 2 INVENTR ATTORNEYS .N0v.'19,1929. y @.EGARDNER 1,736,259

AUTOMATIC TELEPHONE SYSTEM Filed May 11, 1927 4 Sheets-Sheet 3 www v sb D NVENTOR j@ g. Y

ATTORNEYS Nov. 19, 1929. J. E. GARDNER AUTOMATIC TELEPHONE SYSTEM Filed May ll, 1927 4 Sheets-Sheet 4` INVENTOR #e m. Y

ATTORNEYS Patented Nov. 19, 1929 mam "Unirse STATES, PATENT OFFICE.

JOHN GARDNER, or CHICAGO,V ;t r. 1.i1 rors,V AssrGNoR To BROWN, minorenni?.k a DIEN- Nnn, or CHICAGO, iLLiNOrs, A ccPAnTNnn-snrr CONs'IsTINC or CHARLES- A. BROWN, Ammin n. Bonrrcnna; ANDv JOHN A. DIENNEB,

AUToMATiC TELEPHONE SYSTEM Application filed May 1.1,

My invention relates in matic telephone systems.

One of the objects of my inventionis to provide a novel method for directively controlling the automatic'switching equipment in the central exchange irom the subscriber-s station. p,

Another object of my invention is to pro'-y vide means for increasing the speed at which the switching mechanism in the central oiiice may be Operated.

general to auto Another object is to provide means for directively controlling( switching equipment in Another object is to Vdo away with all slow-acting relays in the central oiiice switching equipment and to provide a positiveL means of controlof the switching equipment by meansof quick-acting relays.

Another Object is to reduce the amount of `centi-al olice switching equipment needed Another object is to provide a novel methody of. directively controlling the central oflice switching mechanism from the' subscrihers substation which is different from tral Oiiice switching mechanism from the subscribers 'substation which renders it impossi'blefor the subscriber. to sendaso-called preliminary impulse. y p

4v A:.urther object is to provide a new and im moved 'calling device or permitting or 1927. seran No; 190,397.

controlling the'v operation of theicentr'al office equipment ata muclr higher rate of speed.

A further object is to provide a new and improved circuit for the subscribers individual line switch.

. Another object is to'provide a new and improved circuit for the selector switches* in the central oiiice switchingequipment.

Another object. is to provide a new and improved repeater circuit.

Another Objectis provide an improved connector circuit.A

A still furtherobj'ect is to provide means for instantaneously releasingfthe switching equip-ment used in an established connection at the central o'ice when' thel subscriber hangs up. f

The most modern automatic telephone systems of the present day employ what is known as the two wire principle, whether the system uses the so-called Strowger switchingequipment, the panel type switching equipment or relay selecting'equipment, or not.l The fundamental principle of this socalled two wire operation is timing relays.

The central oiice yswitching ymechanism is operated from thesubscribers substation by the subscriberv operating .a calling device which produces-a series of openings in the line. l During-this period of successive openings, a quick acting relay at the central oiiice responds, while a slow acting relay is maintained energized. ,'lheV Yquick acting relay serves to operate the selecting mechanism by sending out a series of impulses. slow'acting relayis maintained energized by this series of impulses. When the dial is restored to normalv after one operation, the line is closed fora comparatively .long period of time, the quick acting relay remains enerthe impulses sent outby the quick acting relay, is deenergized to cause the automatic trunk selecting movement of the directively controlled switch,fso that the next stage of selecting operation maybe performed. The switches are successively operated iii this mannen until the desiredl connection is estab-1V lished. VvAfter the conversation is completed, the conneton is usallyreleased by the 'calls yso gized7 and the slow acting relay, energized by, Y

ing subscriber hanging up. This operation permanently opens the line until the next call. rIhis opening of the line causes the quick acting relay under the subscribers control to deenergize. A short interval of time after this deenergization, the selecting equipment is released upon the deenergization of the slow acting relay whose circuit is opened by the deenergization of the quick acting relay under the control of the calling subscriber.

Another great diiiieulty encountered in the practical operation of the two wire system, is the production of one or more openings of the line when the receiver at the calling telephone is removed from the switch hook. These openings cause the operation of the selecting equipment at the central oilice. This invariably causes a wrong number. Many attempts have been made to overcome this, the one that is used in practice involves the use of ten percent of the selecting equipment and still does not cure the difficulty entirely. The usual practice is to trunk the calls which start with the digit l to an operator who informs the subscriber to call again. In this case no number can be used starting with the digit l. Not only is this method unsatisfactory, but it provides no solution of the problem where two preliminary impulses occur.

In view of the fact that the proper operation of the selecting equipment at the central office is dependent upon the functioning` of fast and slow acting relays, it is highly iinportant that these openings in the line circuit brought about by the manipulation of the subscribers calling device be properly timed both as to duration and speed of occurrence. It is essential that the subscriber refrain from interfering with the return, or impulse producing movement of the calling device dial in any manner whatsoever.

It will be seen that any interference with this backward movement will so slow the action of the impulse sending, that the central o'lce switching equipment will fail to operate properly. If the movement of the dial is interfered with so that the line is maintained open too long, the selecting equipniient will be released. If the movement of the dial is stopped with the line closed, the trunk selecting movement of the switch occurs at an improper point. In addition, if the dial is forced in backward movement, impulses will switches at the central office are directively controlled by applying theground connection to either one or the other oflthe lines leading to the subscribers substation. The impulses sent to directively control the switchin mechanism by successively grounding the vertical side of the lines a plurality of times. The automatic trunk selecting movement is initiated by momentarily groundine' the rotary side of the line. rlhe release or the selecting equipment is secured by grounding both sides of the line simultaneously. It will be seen that the three wire system had many advantages over the two wire system which was later adopted, since all the functioningl of the selectingequipment was positively controlled. However, the ditiiculties arising in providing a ground connection at the telephone substation and the troubles arising therefrom, such as varying ground potentials, was great enough to overcome all the advantages of the three wire system.

As before stated. many attempts have been made to incorporate the advantages of the three wire system into the two vire system. Se far as I know, all these attempts have proved unsuccessful. @ne of these attempts was simpiy to eliminate the use of the slow acting relay in the two wire system without deviating from the principle employed. This consisted in supplying condensers in the impulsing circuit of the relays which, in the two wire system, were made slow acting, but which, in thi system, were quick acting. The period between the impulses was taken up by the condenser discharging into the circuit: to maintain the quick acting relay energized during this interval of time.

Another attempt consists in employing a modification o'l' the calling device which, at the end of the impulses, son ds a series of high frequency impulses to which the usual quick action relay at the central ollice would not respond, but a special relay in circuit with it would respond. This special relay in responding initiated the trunk selecting or switch over action of the selecting equipment at the central o'tlice, VThis was termed thc socalled Zing` impulse system.

In another attempt the switch over was ohtained by the slow acting principle above discussed. but the release was soniowhat different. rifhe subscribei"s substation circuit i 7as modified so that the calling device. instea d of opening the line, simply removed the short circuit from a resistance at the subscribers station. The usual quick acting relay at the central oliice was adjusted to respond to this opening of the line for removing tho shunt around the resistance. IIowevcri there was another relay at the central station, which controlled the release, that was maintained energized in series with the comparatively iigh resistance at the station. After the conection was completed and the subscriber iunej up, the line was completely opened so that this relay which was maintained oper-- ated during the impulsing would be deener gi ed to release the selecting equipment. This Lacasse.

was anattempt toeliminate' the diiiiculty pulse?.

Obviously, these 4attempts to obtain the adn` vani'age's ofthe' t i ee wire system inthe two wire'. were uns ucc-ees lul and did not go tothe root of the: trouble. The. present invention is designed to: obviatc` all the disadvantages of the two wire syslem and still to. maintain a great advantage over the three "wiresysteiny thav of having no ground connection at the subscribers station. In addition, the present inv'enti'onnroif'ides means wherebv the cen-.

vral ottico switching equipment may be directively controlled at a much greater speed than has l'iit'herto been the case. It also provides means or'controlling the central o'liice-equipment much more positively and in a manner entirely different than that which ,has hitherrlhat principle also one of the most eliicient and accurate circuit prinfciil-es-that has yet been devised.

There are many other objects than those mentionedin the `foregoing.; which, together with the above, wil be described in the de'- tailed specification which is to follow, taken in conjunction with the accompanying drawings, forming part of this specification.

Vfhile lha-ve shown my invention applied to an a oniati'c tell, ione system, it will be obv? s that the Aselecting princiole employed is equal y applicable fin any selecting system such as those employed inl any telegraphy,

supervisory control, train control and, in

' the su'bseriber; A

the line until the dial restoresto normal,

fact, in any selecting systemy where it is neces to control the positioning of a device.

In practicing my invention, Iprovide a4 special type of calling device at the subscribers station. rFhis calling device is adapted to throw a: certain amount of resistance in a: line, depending upon the digits dialed by This resistance remains in whereupon it is withdrawn. Associated with the central oihce switching mechanism is a similar resistance.

switching' equipment. lVhen the'subscriber removes 'the receiver, the usual automatlc,

'Y trunlrselecting or line tindingtalres place, `by

, operates the calling device, a resistance is;

j, first selector.

unich the subscribers line is connected to a the circuit oi'one winding of the diilerential relay permitsthis relay toroperate. `VThe1-e^ upon, an automaticmovement of ,the switch' A differential relay is,v employed to control the operation l oft' the rIhe diHerent-ial relay in theVv occurs. As this movement takesy placefre-` sistance is. introduced step by step in the circuit of the other winding of the dierential the diii'erer'iti-al relay. retracts its armature` and the stepping movement of the` switch ceasesl The selecting switch is now in a posi; tionjcorresponding'to the digit :dialed by the subscriber. Inasmuch Vas this .movement of the switchf occurs over `a circuit local to the switch and is merel-y controlledfby the bal-v ancing action, it will :occur very rapidly. It will be seen-that the switches of the central oiiice are controlled from thesubscribers station by a' balancing arrangement. ThisA is very accurate and corresponds to what might be termed a potentiometer method of control.

Vhile in the drawings the invention has been shown and described as applied to the so-called Strowger type of automatic telephone equipment, it will be understood that it may be'applied equally well to the so-called panel type, relay type, and, in fact, to all types ot automatic telephone apparatus.

Referring now to the drawings, comprising Figs. l to' 10, inclusive,1suiicient apparatus and circuits have been shown by means of the usual conventionaldiagrams to enable my invention to bev readily explained and understood. 4 f

- Reterring.now to the drawings Figs. l to '6 show the mechanism of my improved callingI device vat the subscribers station;V

Fig. 1 is a top plan view of my improvedy calling' device; Y

Fig: 2 is a medial cross-section Vof the same; 'Y l Fig.; 3 is a section along line 3.-x3 of Fig.

2 looking in the direction of the arrows showing certain mechanism that .has to do with the backward movementot the calling device dial;

IFig. 4 is a section along the line 4,-4 of Fig. 2v looking in the'direction of the arrows showing the'manner'in which the resistance is cut into the line;

5 lis adetail section along the lineof'Fig. 3, looking in the direction of the 'arrows and showing the so-called shunt springs;

` Fig. 6 is an enlarged crosssection along the line 6i-6 of Fig. 4 showingY cert-ain details of construction; Y v

Figs. 8 andi) show the necessary circuits to Villustrate the operation of the apparatus. Fig. 10 is a diagrammatic view of the subscribers telephone substation circuit;v

i InFig. 7 the substation A isof the type shown diagrammatically in Fig. 10.

V'Thejline switch Cisfof the usual rotaryv typepbeing-provided with three wipersV 724Y to 126, inclusivegeach adapted to engage Va series ot 25 bank contacts, such as 727 to 729,

Y'inclusive.''` The jline switch() is provided FIJI with the usual type of switching relay 710, line relay 711 and motor magnet 712. A special type yot line relay 711 is provided having a low resistance lower winding which is adapted to maintain the relay energized in series with the relay 710 and motor magnet 712. rl`he wipers 724L to 726, inclusive, are adapted to be advanced by the operation ot the motor magnet 712 upon its deenergization. The motor magnet 712 interrupts its own circuit and operates as a buzzer, to advance its wipers into engagement with the bank contacts associated with an idle trunk.

The selector switch D is one of a plurality ot such switches accessible to the individual subscribers line switches, such as C. The selector D is of the usual Strowger type having a directively controlled vertical movement and an automatic rotary trunk selecting movement. The selector switch is provided with wipers 7 63e765, inclusive. These wipers are adapted to be moved vertically by the operation of the vertical magnet 737 and are adapted to be rotated into engagement with the bank contacts, such as 770 to 772, inclusive, the terminals of an idle trunk in the level selected, by the rotary magnet 736. ln addition to the usual wipers 763 to 765, inclusive, the selector is provided with a vertical wiper 766. This wiper 'is adapted to be operated into engagement with vertical bank contacts, such as 7 68. rlhere is one such vertical bank contact for each level of the switch. 'lhe vertical bank contacts are connected to a. resistor 767 that is similar to the resistor 705 in the substation A. rlhe vertical bank contacts are connected to the resistor 767 in such manner that the iirst vertical bank contact is connected to the same corresponding point in the resistor 767 that the bank contact, such as 706, in the subscribers station, such as A, is connected to. The selector switch D is adapted to be released by the operation et the release magnet 735. For contro'ling the selector switch such as D, relays such as 730 to 734, inclusive, are provided. 'llhe relay 7 30 is of the differential type. Relay 7 31 is a quick acting release relay. Relay 732 is an interrupter relay. Relay 733 is a switching relay, and the relay 734 is a con trollin relay.

The trunk lines accessible to the selector switch D may terminate in second selectors or in connectors, dependinsT upon the size of the system. It the trunk rines terminate in .aj ond selectors and there is more than one exchange in the system. certain et' these trunk lines lead to repeaters in order that two wire trunk lines may be used tor interconnecting the various exchanges.

ln the present case, the trunk line leading from the bank contacts 770 to 772, inclusive, extend by way ot the conductors 773 to 77 5, inclusive, to the repeater R (Fig. 8). Re-

- peater R comprises the relays 301 to 806, in-

elusive. The relay S01 is an electropolarizcd relay having` an upper polarizing winding and a lower low resistance winding 'for operating the relay. The upper winding ot the relay 801 is connected to battery in series with a fairly high resistance. rl`he operation oi the relay is such that the relay will not attract its armature until the curr .it flow in both windings is in the same direction. lVhen the current flow in the same direction, the rclay is energized. Upon energizing, the rclay is adapted to cut out the resistance in series with its polarizing winding. rlhe relay 803 is a dii'lerential control relay. rllhe relay 804 is adapted to supply battery to the calling line. The relay 806 is a dillerential relay. There is a minor switch such as M associated with each repeater such as l. rlhe minor switch M is ot' the usual construction having two wipers S and 831, each adapt-ed to engage in their rotation a series of ton bank contacts. The wipers ot the minor switch nre adapted to be rotated by the stepping magnet 807 and released by the operation of the rclease magnet 803. There is a resistor 832 connected to the various bank contacts accessible to the wiper 830 so as to provide tor a variation in resistance in the circuit et the lower winding ot the differential control relay 803 corresponding to the change in resistance occasioned in the circuit of the upper winding by the operation ot the calling device. Similarly, there is a resistor connected to the bank contacts accessible to the wiper 831 so that movement of this wiper may control the selectin g mechanism in the distant exchange in the same manner as if the switching mechanism were controlled from a calling subscribers telephone.

rllhe trunk line comprising conductors 840 and 841 extending from the repeater lt terminates at another exchange in an incoming selector D1. This selector has a circuit that is similar to the selector l) and is ot the usual Strowgcr type. rllhe second selector ,lll has access to the trunk lines liading to connector such as H (Fig. 9).

rl`he connectors, such as H, are of the usual vertical and rotary type. 'lhe connector ll is provided with vertical and rotary magnets 910 and 911 and a release magnet 909. rlhe vertical and rotary magnets are adapted to operate the wipers 966 to 963, inclusive. lrst in a vertical and then in a rotary direction. rlhe connector switches H are also provided with vertical wipers such as 964-. These 1vipers are adapted to engage a vertical bank ot ten contacts, such as 965. ln addition, all the connector switches have an entre. wiper, such as at 962, for controlling the rotary movement of the switches. rll his wi per and the associated bank contacts are identically the same as those employed on the sof-called rotary connectors manniiactined by the Automatic Electric Co. .A resistor, such Yle ' ing talking battery t0 vthe called lin-e. This relayl is also adapted'toKV attract its armatures o The connector switch H as 967, is' connected toL the verti'ca-l bank contacts in the manner shown, and to the rotary. bank contacts,A corresponding rotary contacts' atl-various llevels are; multiplied together.

, The connector switches-H are provided withV 903; is what is known as atwosstep relay. W hen the upper Winding of the relay 903 is energized, onlyfthe armatures 923, and 926 are operated. r`When both the upper and lower windings et the relay 903 are energized, all the armatures of this relay are operated. 'The relayQOet is an interruptor rela The relay 905is` vcut-H rela-y. The relay 906 is a back bridge relay forsupplywhen its lower winding is energized in series with theresistance 940. rEhe relay 907 is a busyV control relay.V TherelayS/Qis a switch,-

or cut-in relay. .l i l c r o access to called subscri'bersrlines, suclif as vthe line of'k the subscriber at the substation A15.' The substation A1 is similar to' the substation A previously:

described.v The `line'switcl'r C1` is. the called subscribers line switch and is similar to the line switch C previouslydescribed.

- `lhecalling subscriber' issupplie'd with a busy tone fromv thebusy machine BM in the event that'th'ev called line is busy, while the called subscribe'rls substation isrung inter-l mittently by the ringing current furnished bythe ringing equipment RI'. These devices are of the.` usual type and neednot be described in detail. V r n v`Referring newvv taFigs. 1 to 6', inclusive,

and-Fig. 10,lff'sliall now describe the novelv v calling device adapted for' use in my ini'- provedrsystem. Likerelierence characters4 in the various figures refer to similar parts.

'A The novel calling device consists of the usua'lbase plate 10, finger hold dial 11 carry-V ing on its 'underneath side a pawl 12 adapted to engage thecrovvn ratchet 1'3`that is adaptedito operate the usual governor mechanism 14 .through the gears 15, 16 and 17. The

tric Company 'of' -Chicago. AV finger stop li's .mounted upon ashaft 19 by aboss- 9. The shaft 19^is supported'between the base plate` vl() and a subbase plate 20. The

"subba'se plate' 20 isheld'invspaced relation tothe base plate 10 by means ofv bolts 25,

26 and 27 passing through holes vin 'the periphery oft-he subbase plateand the hollow spacersQl, 22 and 23 and threaded into holesin the baseplate 1:0.- Mounted below the subbaseipl-ate `is a series of ten bank 'contacts 24, these bank contact-sare of the usual construction and may be mounted on a fai-r-A 'lyf thick circular insulatingy'ri-ng 8 by means of screws. rlhe bankcontact assembly is held in .spaced relationwith respect to the su-bbase plate by passing the bolts 25, 26' and 27 through holes 2 8, 29" and 301m the; insulating rin-g 8. The shaft 3l has an enlarged end spacing portion (randl is attached tothe dial 1&1 by means of the screw A7. The shaft 31 extends at its lower end into a recess 33 in the `shaft34- The upper portionot the shaft 34 is screwed into the centering or locking cam 35 which is provided w-it'l' i-l the shoulders 36 adapted to rest against the base, plate 2O under tension` of a spring 3'?, one end of which lis attached vto the subbase plate 2(1'and' the other end to the shaft 3'4. The lower end of the shaft 34 -is threaded; to .receive the wiper mounting carrying the' wiper 38'. The wipery 38 is insulated from the shaft 34 in any well known or approvedI manner. This wiper may be adjusted bymoving the nuts 3901i the threadedv end ofY the shaft 34, whereby the -wh01e=wiper as sembly is moved up or down. `The wiper- 38 is adapted to engage the bank contacts-`v i 24 when rotated. The wiper is so-plositi'oned with respect to the bank contacts-t at,l when the dial is operated for the dig-it 1, the wiper- -is moved intoengagement with the first bank Contact.,l A releasing member 40- is attached to the shaft-31 by' means'of a boss v41. The'` rotatable shaft 19 andvv the inger'sto'pr 18" carries an arm 44' that is adapted to operate the spring- 45 to open the contacts 47 and to close the contacts 46;-thislatter operationY performs certain functions in telephone substation circuit as 'wwill'appearr 'The spring member assembly is mounted inposition on the base plate by two screws 49.A 'lhewhole kspring assembly is, of course, insulated froml the basefplate in any Welli-knownfor'proved manner. The shaft 19 carries Aanfarm v50 that is adapted to operate thecenteringpawl 52through the link member The centen ing pawl 52v is pivoted at 53 and is normally held in its inoperative position by the spring .54. lVheu the shaft V19 -is rotated the pawl 52 is adapted 'to engage the centering wheely 35. `A number of' notches 55 are cut in the periphery of this centering Wheel. These notches are ten innumber, corresponding to the'ten positions ofthe calling .device dial. Then the shaft 19 is rotatedA by the operators fingers striking the stop l18, the pawlf52 is adjacent to one of these notches and is forced into engagement therewith. This action: serves toy center vthe wiper 38 `in engage, ment with the proper bank contact. The centering Vwheel 35 is rotated when the shaft 31 is turned by the memberj40 engaging a pin 55 imbedded Vin the wheel 35; The'movement of they wheel 35 causes the rotation of the wiper 38 and the tensioning of the spring ico 37. The pawl 52 is held in this operated position by the toggle mounting of the spring e. Thus the wheel 35, as well as the wiper 38, are locked in their proper positions until the dial restores to normal, whereupon, the member 40 engages the end of the pawl f 2 and it is released from its locking position. The vcentering wheel is permitted to restore to normal under the action of the spring 37. Restoration of the centering wheel 35 also brings about release ofthe wiper 38 as they are mounted together.

Having described the mechanical construction of my calling device, T will now explain i the manner in which the various elements function when the calling device is operment of the calling device dial 11 the pawl 12 rides over the surface of the crown ratchet and this ratchet remains stationary. The shaft 31 attached to the dial 11 is, of course, rotated, thereby tensioning the spring The arm 40 engages the member attached to the centering wheel 35 and the centering wheel 35 is thereby rotated, carrying the wiper 33 into engagement with theV fifth bank contact. The movement of the member et@ also permits the locking member or pawl 52 to be operated when the shaft 19 is rotated by the finger of the calling subscriber engaging the finger stop 13. When this oc` curs the pawl 52 is forced into engagement with the fifth notch in the centering wheel 35 whereby wiper 33 is centered into engagement with the fifth bank contact. The locking pawl 52 is held in this position by the action of the spring 54. The rotation of the shaft 19 also causes the movement of the member 4a from engagement with the spring 15, whereby this spring is permitted to engage the spring 4:6 and break the electrical connection previously existing between the spring 47 and the spring 46. This operation serves to open the transmitter and rcceiver circuit in the telephone substation.

l/Vhen the calling subscriber removes his finger from the finger hold, the dial 11 is free to return to normal under the influence of the spring 32. The pawl 12 now engages a tooth in the crown ratchet 13 and turns this ratchet which in turn operates the governor through the gears 16 and 17. In the present instance the governor does not slow down the dial very materially.. Tt is only provided to prevent the dial 11 from snapping back rapidly and causing injury to the equipn'ient. inasmuch as the centering wheel 35 is locked by the pawl 52, the wiper 38 remains in engagement with the fifth bank contact since the shaft 31 is revolving in the opposite direction the member 4L() has no connection with the locking wheel 35. Just before the dial reaches its normal position the member L10 strikes the end of the pawl 52 and withdraws it from engagement with the locking wheel 35, thereby permitting this wheel, together with the shaft 34, to restore to normal, thus carrying the wiper 38 to its normal position. The pawl 52 is maintained in its normal position by the action of the spring 54. The shaft 19 is rotated to its original position at this time and maintained there by the action of the spring 5t; the rotation of the shaft causes the member Ltf1- to operate the spring 15 to its original position, whereby the telephone substation circuit is restored to normal. Substantially the same operation occurs when any other digit is dialed.

Tt will be noted that the function of the caliing device briefly is to position the wiper 3S in engagement with the proper bank con tact at the end of its forward movement and permit it to remain there until the completion of its backward movement. The wiper 38 is locked in engagement with the proper bank contact until the dial 11 is restored to normal. Thus, so far as the operation is concerned, the calling subscriber may interrupt the backward rotation of the dial, bring it forward, or force it backward all without causing any different operation of the calling device. Tf the subscriber holds the dial from returning, the wiper 38 remains positioned until he does permit it to restore. if he moves the dial forward and attempts to rotate it beyond the point at which it is set, he cannot because the wiper is locked.. Therefore, nothing the subscriber can do without actual violence can affect the prescribed operation of the calling device. The manner in which the circuit is designed prevents any false operations occurring under the above conditions and permits the proper number to be obtained in spite of it. This will appear fully hereinafter.

Tn Fig. 10 I have shown a diagrammatic view of a telephone substation equipped with my improved calling device. This substation consists of the usual transmitter 75, receiver 76, bell 77, ringing condenser 78, and hook switch 79. The calling device is of the type just described. The wiper and bank contacts and springs for controlling the telephone substation circuit only have been shown. It will be seen that the bank contacts are connected to a resistor 80. Thus, when the wiper is operated into engagement with a bank contact, a certain amount of resistance in placed into the line circuit. The points on the resistor to which the bank contacts are connected are determinined by the average resistance of the line. Another determining factor is the springs controlled by armature 7 51, upper winding of diiterential relay 730, and armature 742 and its front contact to battery.

The results o'r the operation of the relay 731 are: that at armature 741 a circuit is completed that extends vfrom ground by way of armature 7 38 and its back contact, armature 741 and its front contact, resistance 747, back contact and armature 769, back contact and armature 7 62, armature 761 and its bach contact, and relay 782 to battery; to connect the battery to the midpoint of the ditferential relay 730 at armature 742, to open one point in the release circuit at armature .743 and to connect ground to the vertical wiper 7 06 at the front contact of this armature. The relay 7 32 is energized to open a point in the ground connection to the release trunk at armature 748, to establish a locking circuit tor itself at armature 749, and to complete a point in the circuit ot' the vertical magnet 737 at armature 750. All these operations occur responsive to the removal ot the receiver from the switch hook at the calling substation.

In automatic telephone systems the voltage of the battery is usually maintained between 46 and 52 volts. ln order that the operation of my invention may be more readily understood and explained, it will be assumed that the voltage of the battery at the main exchange is 100 volts. It will be understood, of course, that any desired voltage may be employed.

F or the best operation of the system, it is desirable that the resistance of the subscriberslines, in any given exchange, be substantially alike-` This result may be obtained by the insertion of a resistance in the subscribers line at the main exchange so that the resistances ol' the shorter lines may be brought up to substantially the same as those or" the longer lines. This is not altogether essential, as will appear from a consideration of the invention in the subsequent description. All that is necessary is that the difference in resistance between the shortest and the longest lines be considerably less than the change in resistance made by the steps of the calling device. For the moment, we will disregard the resistance of the line. The resistance of the upper and lower windings of the differential relay in the selector switches, such asl), will be assumed to be 250 ohms each. The resistance of the windings of the relay 731 in the various selectors will also be assumed to be 250 ohms. Thus, when the receiver in removed at the calling station, there will be 500 ohms in series with the battery in addition to the resistance of the line and the transmitter and receiver at the calling substation. The maximum current flow in milliamperes over any line will, therefore, be 200 milliamperes. The amount of resistance that can be used in the calling device depends upon the sensitivity of a diil'erential relays, such as 730. ln the present instance l have assumed that a change in current liow in one winding of the differential relay of 10 mills will be sufficient to maintain the armature oil the relay attracted. Obviously, this is a very simple matter, `for, with the dili'erential relay energized, there is a closed magnetic circuit, and only a fraction ot the current low is necessary in its windings to maintain the armature attracted of what would be required to originally attract the armature.

Tn View of the fact that the more resistance there is in any circuit, the greater the amount of resistance that will have to be thrown into the circuit to bring about a constant current change which, in this instance, is desired to be 10 milliamperes. Tt is therefore preferable to work with as much resistance in a line, S5 as possible, so as to make the system immune to any change in line conditions. Under the above conditions, it will be ii'ound that it the total resistance of the line and the resistance included for the digit 0 is 5000 ohms, there will be 20 milliamperes of current lowing in the line circuit. For 30 milliamperes of current in a line circuit, the total resistance of the line and relays will be 3332 ohms; lor 40 milliampere current iiow. the resistance will be 95 3000 ohms; for 50 milli ampere current iiow, 2600 ohms; for a milliampere current llow, 1606 ohms; for milliampere current liow, 1428 ohms; for an milliampere current iow, 1250 ohms; for milliampere current liow, 1110 ohms; ior milliampere current flow, 1000 ohms; and for milliampere current flow, 908 ohms.

li we assume that in the exchange under discussion the resistance oli the average line is substantially 200 ohms, then we have the figure of 700 ohms for the combined resistance of the upper winding of the differential relays, such as 73 and for the relays, such as 731, plus the line resistance of 200 ohms. New, if we deduct 700 ohms from the various resistances given above, we will have the point on the resistor. to which the various contacts ot the calling device bank must be connected. Below is a table giving the points on the rell sistor for the calling device For digit 1 bank cbntact 1 is connected to the resistor at a point where 208 ohms are thrown in a line.

Ohms 2 500 3 410 4 550 `tliel most' satisfactory manner of" control y it is possible to' disregeidthe line iesisteiiee cient to Cause c 'urrentyariation in the'V line vcircuit oil()` inilliz'mp'eie's lfor each successive position.

Theorie-Citi@ of selection employ/tedepend's upon thev changes or yariationsin the conductivity ofthe circuitcausingchanges in current How.' It obyious'that by, changing -aiiyeleetiicei eimrcteristies ofl avpeirouit in 'definite order, it is possible' to controiiselecting Y apparatus as desired.` However, it is Well known that aJ change' in conduetiyitlylis Y me a-,deyicesuch as a telephone switch so' the present priuoiple has' been employed. It will be obvious after an understanding of `the pi'eseiit'invention is had how the desired results niay be obtained by Varying any other eleciri(zalI c'liajracteristi'eV or characteristics of the lirfe circuit such as thejimpedance, capaci'- tanee, arid inductance orreactance, and 'pro- Viding uieans in the central ofce switching equipment-U to" respond to 7such" ya'rietions either by b'laneing, as in thepresent'xealse, or measuring the olangein the characteristic and o'ontroliing the selecting device in accordance with the Value me"asured`.V l y e 'iii tlfeide'scription 0f the proges ofthe present call, it Willbe assumed that the call'- ing subscriber' operates his' calling de'v'ice in aceordaiiee with thehiiinber' ofl thecal'led subseriber at' substation: A11, and it Willkb'eA asj suiued' `further that this 'number .eoiisists v` of I theaigitsoeee. l

Cil

When the Calling device isoperated inV ,eoi'danice With the first digit 5, 'the Wiper 701 ottlie callingdevioe placed in engagement with the fitth bank Contact, whereupon, when 'the' sliunt'springs 02 and 7 Qii're'operated,

the transmitter and ijec'eiverfare 'disconnected from the calling line circuit, a rcertain amount of resistance is'y thrown in tli'ef-line. In this instance, 728i ohms. e .A 'y

Referring now to the operation of theselector siviteh D, when vthe relay 731energi'zed it completed a Circuit for the upperand lower win dinfijs o??? the diierentialfrelay 7 3G at armatures 742 and 743. 'The operation of the relay 731 takes place immediately upon the selector Dv being seized by the line switch C.

circuitY completed for the upper Winding of theV differential relayv 730, andthe differeiitial relay 730'is 'eiieifqized4 through its lower Wind- Howeiier, its operation underthese conditions is Without iunctionyexcept to open the circuit of the relay 732 at armature 728. When the line relay711 is deenergized, a

circuit'is Completed for the upper Winding oli vthe differential relay, which 'seryes'to blance Vvthe' Current flow through its lower Winding,

end'periits the retraction of the armature 738 to eonipiete the. revijousiy traced eireuit for the relay 732'. he resstor 7780i the se- 'Yleetor switch D yserves to balance the resistente of the calling. line and `that of the transmitter and reeeiver. A

Now', Vwhen the telling device isv operated in accordance with' the digit 5,- theutransmitter and receiver at the substation A is cut out of the line circuitA as before described.y Tooompensate for the remoyeljof the resistance of the transmitter-arid the receiver', the resistance 7 0 9 is substituted ifiseries with the resistor 705 that is oormeeted tothe various bank contacts. With the values' of line; 'resistance assuinedithere are milliamperes of Ycurrent fiofwig through the line and' tbe upper wiiifrdingofthe relay 730 at this time. In the `lower4 winding" of the differential relay 730,

there are Y approximately 14B ki'ioiili'a-niperes of Aeurreibtflowing.A The re-ley 730 there-fore o-p'eratesfto' attract thearmeture 7 38 and 739.

B y the rop'eatiofrr of the 'armature' 7 38 point ithefcircuit of thereiay 732 is opened,.while fronlt Contact 'of thev armature 7 38 there is a circuit established for making another ground lconneation tothe release trunk.- B y the operationv of thev arr'nalti'ire,739,` a point in the circuit'of the rotary magnet 736` is opened, WhileVat" the 1front contact otthis armature, there is* a'. circuit Completed that 'extends from groud by way of said armature and its front,contaevertieei magnet 737 and front "Contact agndi armature 750, to battery. The vertical nia-'gnet737- is energized to raise the switeh shaft, carrying vertical wiper 7 66 and the Wipers' 763 'to'v 76`55'i'1`1elu`sivfe, opposite the first ie'ig'eliY of baril; contacts. Theoperaition of -t'he Vertical' magnet 737 also interrupts the looking circuit of 'the relay 732 .at armature 7 62. The relay 732 is .dee'nergized to open another' point in its Iookingfeireuit at armature 74.9,aiid toy open the orcuitofl the vertical magnet at armetore 750,;md' to complete a point in'. the ground eonrieotioii to the rei-ease trunk-Yatarma'ture v748,; Tievertieaif magnet 737 will be en 1igizedto position its pewi and tofeoriiplete sfoireuirt' at err-,nature 7612 for the relay 732; A Tbiv f reu'it extends frornfgrouiid Way of efrrrmture757 and its beek contact,

.mim-tire 738 Contact; Upon ico l Yizo the first vertical step of the switch, the verticali wiper 766 is shifted into engagement with the second vertical bank contact. By this o-peration, a certain amount of resistance is placed in the circuit of the lower winding of the differential relay 7 30. The value of this resistance is equal to the value that is placed in the circuit of the upper winding of `the relay 731 by the operation of the calling device at the calling station in accordance with the digit 1, whereby the wiper 701 is operated into engagement with the first bank contact. rlhis is not suticient to balance the dilferential relay 730 and it remains energized.

rlhe relay 7 32', upon operating, again completes a locking circuit for itself at armature 749, and at armature 750 completes the circuit of thevertical magnet over a path that extends from ground by way of armature 739 and its front contact, vertical magnet 737, and front contact and armature 750 to battery. The vertical magnet 737 is operated to advance the switch shaft carrying the switch wipers 763 to 765, inclusive, opposite the second level of bank contacts. The vertical wip- Ver 7 66 is also shifted into engagement with the third vertical bank contact. By the latter operation more resistance is inserted into the circuit of the lower winding of the diferem tial relay 730, in this case 300 ohms. This is notsuiiicient to balance the relay and the differential relay remains operated.

The vertical magnet, upon operating, also opens the locking circuit of the interruptor Vrelay 732 at armature 762. The interrupter 723 ohms resistance are inserted in series with the circuit of the lower winding of the dierential relay 730. Under these conditions, the same amount of current is flowing in both the upper and lower windings of the differential relay 730, and this relay is balanced, and, therefore, immediately retracts its armatures 738 and 739. By the operation of the armature 739, the circuit of the vertical magnet 737 is opened, and the vertical movement of the switch cases. rEhe interrupter relay 7 32 is energized, of course, over the circuit through the 0E normal spring 745 previously traced.

By the release of the armature 738 of the differential relay 7 30,`the direct ground connection is removed from the release trunk. There is a ground connection to the release trunk to maintain the relay 710 in the line meente switch C energized over a path that extends from ground by way of armature 7 43 and its front contact, relay 734-, and front contact and armature 740 to the release trunk. The relay 734 is therefore energized. This relay has not been previously energized because it has been short circuited by the ground through armature 7 33 and its front contact. In order to insure that the relay 732 is operated before the relay 7 34 is energized, there is a short circuiting ground connection to the release trunk that extends from ground by way of armature 757 and its back contact, back contact and armature 752, back contact and armature 7 48, and front contact and armature other point in this short circuiting ground connection at armature 757, to open one point in the circuit of the relay 7 32 at arnnitin'e 769, to establish a locking circuit for itself at armature 753 exclusive of the armature 740 and its front contact, to prepare a point in the circuit of a relay corresponding to relay 7 3V in the next succeeding switch at armature 760, and to complete a circuit for the rotary magnet 736 at armature 759 over a path that extends from ground by way of arn'iature 739 and its back contact, armature 759 and its front contact, rotary magnet 736 and armature 7 50 and its front contact to battery.

The rotary magnet 736 is immediately energized over this circuit and operates to rotate the switch wipers one step. In addition, the rotary magnet 736 opens the circuit of the interrupter relay 732 at armature 761. This relay is therefore deenergized to open a point in the circuit of the rotary magnet. The rotary magnet is also deenergized.

If the wipers 763 to 765, inclusive, are in engagement with the bank contacts of an idle trunk, the switching relay 733 is energized. However, it will be assumed that the wipers are in engagement with a busy trunk. ln this event, there will be a ground potential present upon the private bank contact that is engaged by the private wiper 764-. A circuit will therefore be completed from grouml by way of the private wiper 76st, armature 753 and its back contact, back contact und armature 762, armature 761 and its back rontact, and interruptor relay 7 32, to battery. The interruptor relay 732 is .immediately energized to establishing a locking circuit for itseltl at armature 7 et?, and to complete a circuit for the rotary magnet 736 armature 7 50. The rotary magnet 736 is cnergized to rotate the switch wipers another step and to open the circuit of the interruptor rtlay 732 at armature 761. The interruptor relay is deenergized to open the circuit ofthe rotary magnet. rihe interruptor relay 732 and the rotary magnet 7 36 continue to operate.

.alternately until the wipers 763 to 765, in

elusive, engage the bank contacts associated with an idle trunk.

1 S0 740. The relay 734 1s energized to open anitil) is in engagement.

It will be; assumed that the bank contacts Y770 to 772,'inc`lusive, are the bankcontacts associated with an idle trunk- Under these conditions; when the wipers of the selector switch D engage these bank contacts, there will benoground present upon the bank contacts 771 with whichthe private wiperl 764 Under 'these conditions there is a :circuit completed for the switching relay 733. The circuit for energizing `the relay 733' extends from the ground by way of armature 743 and its frontcontact,

Y Vrelay 734, front contact and armature 758,

working Contact of Voil normal spring 746 and said spring, ,relay 7 33, back contact and armature 762, armature 761 and its yback contact, and relay 7 32l to battery. The vrelay 733 is energized'over vthis circuit thoughl the relay 732remains deenergized. This is true because of the relative high resistanceof the winding of the .relay 733. Upon operating,

.the relay 733 opens a point in thecircuit kof -the release ymagnet735at armature 755k to close a maintainingcircuit for'itself at' armature 754 to makeV itsl own circuit. independent 'of the deen'ergization of the relay 731, to

Iprepare a holdingcircuit 'for itself at armature 753, vto lopen a point at the Vpreviously f mentioned shunting circuit. atarmature .7 52, T3() to op'en'the circuit of the 'relay k731and the `upper windingof 'the diierential relay 730 at armatures 751 vand 756 and to extendthe conductors of the calling line to the vrepeater R whichhasbeen selected'bythe trunkselecting operationof theseleot'orD. V

' The relay 731 is deenergized tofopen the Acircuit of the diierential r'elay730at armature 742,.-to open one point'inthe circuit of l the relay 733 atarin'ature' 7 43, andtol prepare a releasecircuit at .theback contact of this armature.

When the calling vline is extended Vto the repeater R in the manner `described-.there is a*circuit'completed-for the relay 804 over a path that extends' from ground vthrough the upper' Winding of 'said relay, 'normally closed springs controlled by armature 812 `ofre lay"8()1, trunk conductor-'775, `bank contact 772, wiper 765, rontcontactand armature 760, "and armature l7.55 and its armature"758-,"to'open apointinthe circuit "of 'the rotary magne't736 at armature 7 59,

tofopen the previously tracedv eircuitffor'the relay 804 at armature 760,' fand toy establish another circuit for this-relay at .its normally closed springs over afpa'th that extends from ground, upper windingv of relay 804, normally closed springs controlled by armature .812, trunk conductor- 77 5, bank contact 772,.

normally closed springs controlled by armature 760, armature 7 56 and its frontv contact, bank contact 729, wiper 726., normally closed springs controlled by armature 723, liront contact and' armature 719, overfthe calling line, armature 716 and its ffront contact, wiper 724, bank contact 727, front 'Contact and armature 751, wiper 76,3, bank contact 770,

l trunk conductor y77 3, normally closed springs controlled vby armature 814, :upper Winding. 'of dierential relay 803, armature 822 and its front contact to battery. The relay 804 is maintained energized over this circuit.

It will be seen thatthe'direetively controlled movement of Vthe vertical magnet 737 takes place under the control offthe differential relay 730. Thevertical magnet 737 isV operated together with relay 732 over a localfcircuit to raise the switch shaft vertically. Y It Willfbe appreciated that this vertical Jmovement takes place veryfrapidly andis only limited'by the mechanical constructionandadjustments off the switch. iThe-speed ofethisvertical movement is comparable to the: speed-of. a finder switch.

In fact Atheisele'ctor switche'operatesfin 'identif callythe same mannerasV a -inder inl both 'its vertical and rotary-movements. Sincefthe directively controlled 4'speed of the selector switch isso great lit lvis possible to adjust Ithe calling device so ythat the digit constituting the number willbe sentent very" much more rapidly. In facuthe dial may be permitted to comeback very, very rapidly. I'f'the vdial `should be i adjusted to *a :relatively 'slow backward: movement, the `selector- A switchfmay com- 1 `Splete'this vertical movement and trunk selecting movement before the wiper 701 oftlre rcalling device'isA restoredto'normal. Under Vthese conditions,ri't special `provision is vnot made, a false operation `wou'ld'ibe the result. 'Thisistrue becauserthere will be a vcertain amount 'of' e resistancel Iinserted. in the calling line When'the'next' selecting'device'is connect- Ved with. AThe mannerin'whichthis is taken -Icare 'of will noiwirbedescribed. -ln theevent 'Itha'ta trunk-lineleading to 1asecend selector "switchfis selected instead oil faftrnnkline lead- :ingtothe repeater R, the result of such procedure, i'fthe calling device is not yet restored to normaL/will be considered. This second selector will-be identically -the samefas the 'selectorD and wefwill consider the oper-ation with respect `tothe selector D. When t-he second selector switchisseized, a relay? simiflar tothe relay 731 is energized to throw the vdixerler-1lti alrelay'730 into thel'ine'circuilt. -Ilf the calling device has not been -restoredfto normal, the dil'erential relay is energized, Vconsequentlythere isno circuit for the relay 732. 'Until' therelaysuch as 732 is energized,

.lig

no vertical operation of the switch can occur. rlhe resistance 747 is inserted in series with the relay 782 to make it slower to operate. rlhe armature Tel is also adjusted to engage its Contact after the other armatures have contacted with their front contacts so to give the relay 730 time to operate befcre the circuit for the relay 782 is closed. llVhen the calling device restores to normal the resistance is removed from the line circuit and the relay such as 780 in the second selector will retract its armature. This operation brings about the energization of the relay such as 782 in the second selector. rlhereafter, the selector switch may be operated in the same manner as before described with respect to the operation of the selector switch D. Thus, should the selectorl such as D select the next switch before the dial of the calling device has restored to normal, no false operation of the selected switch Will occur.

At this point it will be well to discuss the operation of the selector switch D should the calling subscriber interferewith the backward movement of the dial of his calling device. From the description of the operation of the calling device, it will be recalled that the only effect of interference with the return movement of the dial is to change the time period during Which the resistance is placed in the line circuit. 1t is obvious that if the subscriber retards the return movement of the dial, the resistance placed in the line circuit by the calling device remains there until the dial is permitted to restore to normal. lt will be apparent from the description of the effect of thel selector D, seizing the next switch before the calling device dial restores to normal, that this does not in any manner effect the progress of the call except to increase the time necessary to establish the connection.

New should the calling subscriber force the dial of the calling device during its backward movement, the result, if any, is merely to reduce the time during which the resistance is placed in the line circuit. Since the dial returns very rapidly of its own accord, the effect of this is negligible on account of the speed of the selecting apparatus. However, by reason of the construction of the calling device, an attempt to force the dial in the return movement is controlled by the governor therein7 since the governor will have greater braking effect when the dial is forced.

Referring new to the operation of the repeater R to which We have progressed in the description of the connection about to be made by the subscriber at substation rl. Other results of the operation of the relay 801i in the repeater R are that battery is connected to the mid-point of the differential relay 808 at armature 822, a circuit is prepared for the relay 805 at armature 820, a point in the circuit of the release magnet 808 is completed at armature 830, a circuit for the lower win l ing of the electropolarized relay 801 in bridge of the trunk conductors 84:0 and 841 is conipleted at armature 887, and the relay G is placed in bridge of the trunk conductors 82110 and 841 over circuit that extends from the trunk conductor 840, normally closed springs controlled by armature 810, upper winding of relay 808, wiper 831, in engagement with its normal bank Contact, and front contact and armature 828 to the conductor 84:1. The relay 806 is then energized over this circuit to prepare a locking circuit for the relay 805 at armature 827 and to open a point in the circuit ofthe release magnet 808 of the minor switch lvl at the back contact of this armature and open a point in the circuit of its lower differential winding at armature 826.

lf the calling device at the substation A has not yet restored to normal the dil'l'erential relay 803 is operated immediately after the operation of relay 804- and the high impedance relay 805 is not energized. No further operations occur until the calling device restores to normal, whereupon, both windings of the relay 803 Will have the same amount of current flowing through them and the armatures thereon will be retracted. A circuit is thereby completed for the relay 805 over a path that` extends from ground by Way of armature 819 and its bach contact, armature 820 and its front contact, normally closed springs controlled by armature 824- and high impedance relay 805 to battery. The relay 805 is energized to prepare a circuit for the relay 802 at armature 825. Another result of the operation of the relay 805 is to open its original energizing circuit at armature 8211 and to establish a locking circuit for itself at this same armature to ground upon the release trunk.

When the calling device at the calling substation A is operated in accordance with the next digit 4l, the Wiper 01 of the calling dcvice is moved into engagement with the fourth bank contact. By this operation, a resistance of 550 ohms, with assumed values given before, is thrown into the line circuit of the dierential relay 808. rlhe dilferential relay 808 is thereupon operated to open the circuit of the lower winding of the relay 801, which is in bridge of the trunk conductors, at armature 818, to open another point in the circuit of the relay 805 at armature 819, and to complete a circuit at the front contact of this armature that extends from ground, by way of armature 819 and its front contact, front contact and armature 825, armature 889 and its back contact, relay 802, and normally closed springs controlled by armature 811 to battery.

The relay 802 is energized over this circuit to open a point in the circuit of the lower Winding of relay 806 at armature 817, and to complete a circuit at armature 810 that exlill) tends from ground by way of armature 821 and itsfront contact, armature 815 Vand its ture 839 the circuit of the relay 802 is lopened and this relay is deene'rgized.v Upon-the first movement of the minor switch, the oft' normal springs 828 and 829 are shifted, whereby the circuit of the lower winding of the relay 801 is opened, while a circuit is prepared for the lower winding ofthe relay 806. l I

It will be seen that there is-a resistor connected to the bank contacts accessible to both the wipers `830 and 831. These resistors correspond to the resistor 7 06 in the calling device at the substation A and to the resistor 767 ofthe selector D. By the operation of tbe wiper 830 certain resist-anceis connected in circuit .with the lower winding of the Vditerential'relay 803. In this case the resistance is 20,8 ohms, however, the relay 803 still remains energiaedbecause ofthe unbalanced current iow'in the two windngs.- By the movement'of the wiper 831 a certain amount of resistance is thrown in the cirouitextendv ing in bridge ot the trunk conductorsA 840 and 841 which may be traced vfrom conductor 840, normally closed springs controlled by armature 810, upper winding ofrelay 806,y

second bank contactY engaged by'wiper 831,v said wiper, .and front. contact andarmature 823,Y to trunk conductor 841.

the differential. relay, such as 730m the selector D1, which is the'incoming selector at the second exchange. `This initiates the operation ofthe selector D1 in identically the same malle ner as has been described with respect to' the selectorD.-y t

The relay 802 in repeater R is deenerg-ized to open its locking circuit at'armature 838, to prepare'a circuit for the-lower lwinding of the relay 806 at armature 817 and openV the circuit at the stepping magnet V807 at armature 816. Stepping magnet 807 is de-V energized to complete a circuit for the relay- 802. `The relay 802 operates. to close the cir-v cuit for the stepping magnet 807. The a lter,v nate operationoi the relays .802 and the stepl,

ping magnet 807 continues .until the wipers 830 and 831 of the minor switch M are moved relay 803,: and the same amount of current then'ilows in each winding? of: the 'difieren- The cjormectfL ing of this resistance in bridge ot the trunk conductors 840 and V841 serves-to unbalance tial relay 803 in opposite directions. The relay 803-is immediately deenergized to open the circuit of the relay 802. lVhen the relay 802` deenergizes to open the circuit of the magnet 807, t-he wipers 830 and 831 are in e'ngagement with their respective fifth bank contacts. There is no urthermovement ot the wipers 830 and 831 for the present.

`By the movement of the wiper 831 into engagement with the fifth bank contact, the same amount of resistance is placed in bridge of the trunk'conductors 840 and 841, as was' Y inserted in the circuit of the upper winding ofthe differentialI relay 803 by the operation of a calling device of substation A in accordance with the. digit 4. A

`The'incoming second selector D1 is thereby operated until it has positioned its wipersopposite the fourth level of bank contacts in identically` the same manner as has been described with respect Ytothe operation oiv the selector D. When this occurs the differential'relay, similar to the relay 730, in the. selector D1 is deenergized to initiate the rotary movementof the switch. Now, when the vertical movement of the selector switch D1 ceases, the relay similar to the relay 734 similar` tothe relay 902 in the connectorY switchH is operated, the trunkline Vcomprising conductors 840 and 841 is opened to the connector switch H at a point in the selector switchDl.

The relay 8,06 inthe repeater R is` thereby deenergized, since its circuit is opened. Upon deenergizlng, the relay 806 opens. the locking circuit of the relay 805 at armature' 827 and completesv a circuit for the release magnet 808' atthe back conta-ct ot this armature. .f Another result of the operation oct the relay 806 is that at armature 826 a circuit is established for maintaining the armatures of the relays 806' in a normally Vinoperative condition. This is true because there 1s a circuit come` pletedfextendingfrom ground by waypof back contact and armature: 817, ott' normal spring 829. and its yworking Contact, back contact and armature 826 and lower winding orelay 806 to battery. The relay806k cannot be ener-- gizedV by current lowthrough its upper wind- Y ing-inl the samedirection as before, for the reason that. the lower winding of this relay is wound softhat the. magnetic field set up by this winding neutralizes the magnetic field. 'set up by the current `flow on the other winding.-A The relay 805 is deenergized to opena point inthe circuit ofthe relay 802, and to establish a' point in its original energizing circuit. [The relay 806 is also adjusted s()` that the current flow through its lower wind-V ing' iS vliotsuicientto :operate Yits armatures.

leil- The release magnet 808 of the minor switch M operates to restore the Wipers 880 and 881 to their normal position. The off normal springs are thereupon shifted and the relay y.806 may be operated ivhen the relay such as 784 in the selector switch D1 is deenergized to complete the line circuit to the connector H It will be assumed that the operation of the incoming selector switch l)1 has been such as to select the connector switch H.

`When the calling device at substation A is operated in accordance With the next digit of the calling subscribers number, namely 8, a certain amount of resistance is placed in the circuit of the upper Winding of the differential relay 808 in the repeater R. In the present case, the value of this resistance is 410 ohms. The differential relay 803 is thereupon operated. It Will be recalled that the minor switch M of the repeater R Was released by the operation of the relay 806. The operation of the relay 806 also brought about the deenergization of the relay 805. ln addition, by the operation of the armature 827 on the relay 806, the circuit was closed for the release magnet 808 of the minor svvitcli M. The restoration of a Wiper 880 to normal removes the resistance from the lower Winding of the differential relay 803. ln the event that the calling device at the substation A had not yet returned to normal, the relay 803 would be energized. The energization of the relay 808 at this time is of no particular function, for the reason that the relay 805 is noW deen-ergized. When the calling device restores to normal the relay 805 is energized over a previously traced circuit to prepare a circuit for the interrupter relay 802 at armature 825 and to complete a locking circuit for itself at armature 824. This locking circuit is established when the relay 806 is again energized at the time that the off normal springs 828 and 829 are shifted to their normal positions upon the release 1 of the Wipers 830 and 831 to their normal position.

New, when the resistance is inserted into the calling line by the operation of the calling device at substation A, the relay 808 is again energized. Since the relay 805 is now operated, a circuit is completed for the interrupter relay 802. YThe interrupter relay 802 serves to establish a locking circuit for itself at armature 838, and to complete a circuit for the stepping magnet 807 at armature 816. 'lhe stepping magnet 807 is operated to open the cir-cuit of the interrupter relay 802. The alternate operation of the relay 802 and the stepping magnet 807 continues until the switch Wipers 880 and 831 are advanced into engagement with the fourth set of bank contacts. In this position the Wiper 880 has placed a resistance in the circuit of the lovver Winding of the differential relay 803 Which corresponds With the amount of resistance Maaate" placed in the upper Winding by the operation of the calling device at substation A. The differential relay 808 is thereupon deenergized to connect the lower winding of the electric polarized relay 801 in bridge of the trunk conductor 840 and 841.

By the operation of the Wiper 881 of the repeater R, a resistance corresponding to the resistance connected in the circuit of the upper Winding of the differential relay 808 is placed in bridge of the trunk conductors 840 and 841.

lJVhen the relay 902 in the connector ll is energized in the manner before described, the operation of this relay serves to connect ground to the release trunk at armature 918, to connect battery to the mid-point of the differential relay 901 at armature 919 to coniplete a circuit at armature 920 that extends from ground by Way of said armature and its front contact, armature 916 and its back contact, armature 926 and its back contact, back contact and armature 947, resistance 940 and lower Winding of the relay 906 to battery. The relay 906 is energized, to prepare a circuit for the upper Winding of the relay 902 at armature 987, to connect ground to armature 915 of the differential relay 901 at armature 938, to establish a locking circuit for itself at armature 989, and to prepare ann other point in the circuit of the relay 902 at armature 941.

TWhen the Wiper 881 in the repeater lt is operated to place the resistance in bridge of the trunk conductors 840 and 841, the diil'erential relay 901 in the connector ll is unbalanced and attracts its armatures 915 and 916. By the operation of the armature 916 a circuit is completed that extends from ground by Way of armature 920 and its front contact, armature 916 and its front contact, bacl; contact and armature 984, and relay 907v to battery. The operation of the armature 9.15 serves to complete a circuit which extends from ground by Way of armature 950 and its bachy contact, front Contact and armature 988, armature 915 and front contact, back contact and armature 954, back contact and armature 929 and relay 904 to battery.

The operation of the relay 907 serves to complete an additional circuit for he lower Winding of the relay 902 over a path that c2'- tends from ground by way of armature 9.18 and its front contact, normally closed spri controlled by armature 956, normally closed springs controlled by armature 955, front contact and armature 946, to one terminal of the lower winding of the relay 902. This circuit is closed in order to maintain the relay 902 energized after the oil- normal springs 966, 967 and 968 are shifted, which occurs upon the first off normal step of the switch.

The relay 904 is energizedL to establish a locking circuit for itself at armature i over a circuit which extends from ground upon remeegaan' lease trunk conductor 849armature 930 and its front contact, back contact and* armature 954, bac'l'eon'tactand armature 929, and rc.- `lay 904L to battery. Another resultof the operation of the relay 904 is that at armature 931 a circuit is completed that extends from A jtical magnet 910 is operated` to raise the switch shaft carrying thel switch Wipers 960 to 963, inclusive, opposite the first level of bank contacts'. By this operation also, the

vertical wiper 964 is raised into engagementV with the second verticalv bank contact.

Another lresult ofthe operation of the vertical magnet 910y is that an armature 929, the lockv ing circuit ofthe relay 904 is opened and thisrel-ay isdeenergilz'ed to open the circuit ofthe vertical magnet v910. The vertical magnet 910 is deenergized to posi-tion its pawl andV to complete a circuit for the relay' 904. The operation of the vvertical wiper 964 serves to insert-a resistance into the circuit of the lower windingof the differential relay 901. This resistancel isvinsuiicient to balance the currentllow in the two windings of relay 901 and it remains' energized to again complete a circuit for'l the relay 904. The interrupter relay 904 andthe vertical magnet 910 are alterfourthvertical bank contact. By the operati'o'nA ofthe vertical wiper 964- sufticient resistance 'is inserted into the jcircuit of the lower winding ofthe-'relay 901 so that the current flow in both windings of this relay is j' equal.y "In the present instance the operation ofthe vertical wiper 964 into-'engagementwith the fourth vertical bank Ycontact causes theinsertion of approximately V410 ohms resistance into the circuit ofthe lower winding of-the differential relay 901. 'This resistance vcorresponds to'theresistance that has been Y inserted into the circuit of the upper windingof the relay 901 bythe repeater R.v

The relayI 901 is thereupon deenergized to lopen the circuit of the interruptor relay904.

lThe `vertical operation ofthe switch wipers ceases. YBy the operation of armature 916 of the relay 901, the circuit ofthe relay 907 is opened andthis relay is VTdeenergized, and at thel bach contact of this armature al circuit isY prepared for energizing the relay 906. kBy the operation 'of the armature f9-15-there is a circuit completed which 'extends 'fromfground by way of varmature- 950fan'd its "back contact,V

front lContact andarmature938, armature 915 and its'backecontact, working contact of olf normal spring 966 and said spring, and the upper winding of lthe two-step krelay 903 vto battery..kv The 'energization the upper `wind-- of'therelay1903 serve'stoa't-tract the armas tures' 923, 924 and 926; The operation of the armature 926 of the rela-y 903 serves to open a point inf the original energizing circuit of therelray 906. The operation of the armature 923of`the relay 903'opens-the locking circuit ofV the relay 906, whereupon the relay 906 is deenergized'. The operation of the armature 9240i the relay 903 serves to open the circuitV vofthe lower winding'of the differential relay y901 through vertical wiper 964, to complete-V a new circuit for the lower winding of relav7 901 over a path that extends from' ground' by way of armature 920 and its front Contact, front contact and armature 924, resting contact of rotary off normal spring 957, lower winding of relay 901, and armature 9.19 to battery, and to establish a circuit for the lowerwirrding of the relay 903. The rotaryof'nermal springs 956 and 957 are of the usual construction and are adapted to be operated upon the first rotary step of the switch. It will be noted that the circuit for the lower winding of the relay 903 is ineffective at the present time for the reason that it is short circuited by the- `circuit previouslyvtraced for its upper winding. Consequently, the armatures 921, 922, 925` and 927 of the relay 903 remain in their normall position for the present. By the dee-nergizationof the relay 907, the armature 946 of this relay is retracted to open the circuit of the lowerI winding of the relay 902. The relay 902 is not deenergized because there isaeircuit completed for its upper winding overa paththat extends from ground upon release trunk conductor 849, normally closed springs controlled by armature 956, normally closed springs controlled by armature 955,normally closed springs controlled by armature 946, and the Lipper winding of relay902 to battery.

The opening of the .circuit of .the lower winding of the relay 902 serves to open the circuit ofthe relay 806 in the "repeater R.

Thev results following thev deenergization of thisirelay will be described hereinafter. The relay 906'isideenergized to open its locking circuitlat armature 939 and to remove ground from armature '915 of the relay 901 at armature 938. This latter operation bringsabout the openingofthe circuit ofthe upper` windingofthe relay 903. The relay 903'is now energized overa circuit that includes both itsf upperfand'lower .windings in series. As -a result of this, allv the armatures of the. relay are attracted. The operation of the armature 92,1 serves to' reestablish a circuit for the re ture-:925 serves to prepare a circuit for thev rotary magnet 911, v'as well as 'to `open the ciricuit of the vertical magnet 910. The operation of the armature. 927 of the relay 903 serves to prepare a circuit for the relay 906, while the operation of the armature 928 opens the original energizing circuit for the upper winding of relay 903. In the present instance the relay 906 is energized because the current flow in both the upper and lower windings of the relay 901 is equal, and this relay is deenergized. This is true, because of the functioning of the repeater R responsive to the deenergization of the relay 806. The relay 906 is energized over a circuit which eX- tends from ground by way of armature 920 and its front contact, armature 916 and its back contact, armature 927 and its front contact, back contact and armature 947, resistor 940, and the lower winding of the relay 906 to battery. The relay 906 is energized to conuect ground to the armature 915 of the relay 901 at armature 938 and to establish a locking circuit for itself at armature 939.

Referring now to the repeater R, when the relay 806 is deenergized there is a circuiteS- tablished for its lower winding over a path which extends from ground by way of armature 817, olf normal spring 829 and its working contact, back contact and armature 826 and the lower winding of relay 806 to battery. This circuit is to maintain the relay 806 inoperative. The operation of the armature 827 of the relay 806 serves to open the locking circuit of the relay 805 and to complete a circuit for the release magnet 808 of the minor switch M. The restoration of the minor switch M serves to prepare the repeater to receive the next digit from the calling subscribers substation. The remaining operations in the repeater R occur in substantially the same manner as has been before described following the deenergization of the relay 806.

When the subscriber at substation A operates his calling device in accordance with the last digit 2 of the called subscribers number, a certain amount of resistance is inserted into the circuit of the upper winding of the differential relay 803 of the repeater R. For the values given, this resistance is 300 ohms. The relay 803 in the repeater R is thereupon operated to bring about the interaction of the relay 802 and the stepping magnet 807 to advance the switch wipers 830 and 831 into engagement with their third set of bank contacts. When this occurs, the wiper 830 has inserted into the circuit of the lower winding of the differential relay 803, the same amount of resistance that has been inserted in the circuit of the upper winding of this relay by the calling device at substation A. The relay 803 is thereupon deenergized to stop further movement of the switch wipers.

By the operation of the wiper 831, a certain amount of resistance is inserted in bridge of the trunk conductors 840 and 841, correspending to the amount that has been inserted in the calling subscribers line by the operation of the calling device thereat. The insertion of this resistance into the line enn tending between the repeater R and the connector fl, serves to unbalanee the differential relay 901, since its circuit has been previously completed by the operation of armature 921 of the relay 803. rlihe relay 901 is energized, the operation of the armature 916 serves to open a point in the original energizing circuit of the relay 906 and to complete a circuit at the front contact of this armature for the relay 997. The operation of the armature 915 of the relay 901 serves to Complete a circuit which extends from ground by way of arma ture 950 and its back contact, front contact and armature 938, armature 915 and its front contact, back contact and armature 954, back contact and armature 929, and relay 904 to battery. rlhe relay 907, upon energizing, connects the private wiper 961 to the lower winding of the relay 905, prepares a circuit for the rotary magnet 911 at armature 951-4, prepares a circuit for itself exclusive of the armature of the relay 905 at armature 945, and at armature 946 serves to prepare an alternative circuit for supplying ground to the lower winding of the relay 902. rlhe relay 904, upon energizing, establishes a locking circuit for itself at armature 930, and at armature 931 completes a circuit which extends from ground by way of armature 981 and its front contact, armature 925 and its front contact, armature 944 and its front contact, and rotary magnet 911 to battery. The rotary magnet 911 is energized to rotate the Switch shaft carrying the switch wipers 960 to 963, inclusive, into engagement with the first set of bank contacts on the third level. Another result of the operation of the rotary magnet 911 is that the locking circuit of the relay 904 is opened at armature 954. rlhc relay 904 is deenergized to open the circuit of the rotary magnet and the rotary magnet is deenergized to position its pawl and to complete another circuit for the interruptor relay 904. rlhe relay 904 is energized to complete the circuit of the rotary magnet which operates to advance the switch wiper 960 te 963, inclusive, into engagement with the second set of bank contacts into third level, which it will be assumed are the terminals of the line of the called substation A1 in the connector H designated by the bank contacts 970 to 973, inclusive. Upon the rst rotary step of the switch, the oit normal springs 956 and 957 are shifted, whereby one ground connection is removed from the lower winding of relay 902 at spring 956 and the circuit of the lower winding of the relay 901 is shifted to the wiper 962 at spring 957. By the operation of the wiper 962, a certain amount of resistance is placed in the circuit of the lower winding of the differential relay 901. As the

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