US2598695A - Impulse sender with relay distributor - Google Patents

Description

June 3, 1952 H. E. HILL ETAL 2,598,695

IMPULE SENDER WITH RELAY DISTRIBUTOR Filed Sept. 10, 1949 5 Sheets-Sheet 1 PERMANENT A ONE! H. E. HILL wve/vrgf 0,5. PARK/NSON fz/Ja 3. M

AT TORNE V June 3, 1952 H. E. HILL ET AL 2,598,695

IMPULSE SENDER WITH RELAY DISTRIBUTOR Filed Sept. 10, 1949 5 Sheets-Sheet 2 FIG. 2

" H. E. HILL MENTOR; 0. B. PARK/NSON AT TORNE V June; 3),, 1952 H. E. HILL ETAL IMPULSE SENDER WITH RELAY DISTRIBUTOR 5 Sheets-Sheet 3.

Killed Sept. 10,,

FIG. 5

H. E. H/LL IN VE N TORS 0.8. PARk/NSON Maw Z W.

A T TORNE Y H. E. HILL ETAL IMPULSE SENDER WITH RELAY DISTRIBUTOR June 3, 1952 5 Sheets-Sheet 4 Filed Sept. 10, 1949 H.E.H/LL igf aamem/vsou WMJW,

June 3, 1952 H. E. HILL ET AL IMPULSE SENDER WITH RELAY DISTRIBUTOR 5 Sheets-Sheet 5 Filed Sept. 10, 1949 PULSE POSITIONS ASA FUNCTION OF TIME DIG/TS I234567090 TIME MIL L [SECONDS PHASE 0 V TIME- PHASE A FHA 55 a TIME- Phil :5 4

PHAJE a TIME PHA SE .4

FIG. I28

GENERATION 0F PULSES REPRESENTING DIG/T I 3 m mm mm x m m m am am M W I Hm I nm F A F 4 RE RE 59 R w." w.. an 0R F I 6 I25 THE sum PULSES AND PULSES REPRESENTING THE 0/011 2 AS APPL IED TO THE LINE DURING ONE C YCL E OF THE E XL! 714 7/ ON C URREN T H. E. H/L L 'WENTORS 0.8.PARK/NSON ATTORNEY Patented June 3, 1952 IMPULSE SENDER WITH RELAY DISTRIBUTOR Henry E. Hill, Livingston, N. 3., and David B. Parkinson, Cleveland Heights; Ohio, assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a-corporation of New York Application September 10, 1949, Serial No. 115,016

6 Claims. 1

This invention relates to an improved telephone subscribers station apparatus and more particularly to improved calling and supervisory equipment employed in an automatic switching telephone exchange system.

The object of the present invention is to provide an improved subscribers station calling equipment and supervisory means' for control thereofwhich is preset in accordance with the entire number to be called before the call is initiated and which operates at high speed after the call is initiated and transmits identifying signals repeatedly until the signal transmitting equipment is stopped by the supervisory means under control of equipment at the central station. As in previous systems of the type set forth in a patent application of Parkinson Serial No. 39,015, filed July 16, 1948, which issued on March '7, 1950 as Patent 2,499,606, each digital position of the called subscribers station designation is represented by pulses wherein the identity or character of the respective digits or magnitude thereof is determined by the time elapsing between the two pulses. As set forth in the aboveidentified Parkinson application a plurality of impulse coils are employed to generate the pulses transmitted to the central station under control of an alternating-current wave received from the central ofiice. In addition, a manual selector device is provided to permit the subscriber to select the character of the symbols or digits in the various digital positions of the calling subscribers identification.

In the subscriber station in the prior art, however, a stepping switch or rotary device has been required to transmit the signals representing the various digits in sequence. Such equipment is difficult to maintain and tendsto be expensive. It requires considerable skill in ad justing it and maintaining it." Furthermore, appreciable powermust' be applied from the central office to satisfactorily-operate or step such devices;

v The object of the present'invention is'top'iovide an" improved stepping or commutator-arr'angem'ent which is small, lightweight and which may be readily operated by power transmitted from the central office overthe subscribersline because the operating powerrequired is very small. Furthermore, except for' certain sealed contacts the stepping arrangement employs no moving parts, thus greatly reducing the maintenance required and at the same time improving the reliability and service'oif'ered to the telephone subscribers.

A feature of this invention relates to a plurality of reed-type contact structures enclosed in glass or other suitable envelopes of the type disclosed in United States Patent 2,245,391, granted to Dickten, Jr. June 10, 1941, and United States Patent 2,264,622, granted to Ellwood November 25, 1941.

Another feature of this invention relates to operating a distributor by a plurality of such relays controlled by the same alternating current which controls the impulse coils. The distributor is advanced solely by means of the relays and' rectifiers or non-linear elements connected between the windings and contacts of these relays and the source of alternating current provided for operation of equipment at the s'ubs'cribers station.

A feature of the invention relates to appara tus and equipment for setting up all of the relays in a predetermined position upon the initiation of a call by a subscriber each time the subscriber initiates such a call. Novel features of the relay stepping or commutator arrangement disclosed but not claimed herein are claimed in our copending divisional application. I

Novel features of the switching arrangement for switching from calling or dialing to talking disclosed herein but not claimed are claimed in a copending application of Dunlap and Malthaner Serial No. 116,068, filed on September 16, 1949.

Another feature of this invention relates to control networks for controlling the impulse coils and also the distributor relays from the same source of alternating current supplied over the subscribers line from the central station.

In an exemplary embodiment of this invention set forth herein in detail, specific circuits have been arranged to cooperate with the system set" forth in detail in a patent application of Malthaner and Vaughan, Serial No. 115,961,

filed on September 16, 1949. I

The foregoing and other objects and features of this invention maybe more readily understood from the following detailed description of an the called subscribers, number.

Fig. 6 shows a partial section view along the;

broken line 6-6, Fig. Fig. '7 shows the right-hand end view of th finger operated setting device shown in Fig. 5;

Fig. .8 shows a bottom view of the subscribers station equipment shown in Fig. 2 t V Fig. 9 shows a partially broken away view of the subscribers station equipment, along the.

broken line 99 of Fig. 3; V

Fig. 10 shows a right-hand elevation of the equipment shown in Fig. 8 along the section line III-l0;

Fig. 11 shows the supervisory and switching control equipment Which is manually operated but released under control of the central office equipment; and j 1 Figs. 12, 12A, 12B, 12C, 12D, and 12E illustrate typical wave forms of the applied alternating current or fluxes produced thereby and typical wave forms of pulses generated by the equipment made in accordance with this invention and. located at the subscribers station. I i I Fig. 1 shows the over-all schematic of the subscribers station equipment. 7 As, shown inFig. l:

the subscribers station equipment includes a handset 2| which when resting upon the support or cradle depresses the pins 22 and causes the bell cranks [9 to actuate contacts 24 to the right and contacts 23 to the left as shown in Fig. 1.

Contacts 24 are controlled solely by the position of the handset 2| while the contacts'23 arecon: trolled jointly by the handset through the pinf22 andbellcrank 19 and also a magnetic locking or holding device 41 which includes the windings 21, 28. 'In addition the usual induction coilhaving windings 32 and 33 is provided for'transmission of the voice currents.

1 A. group of saturable magnetic impulse coils 40 and; to 59 are'provided for generating a start pulse and ten stop pulses to represent each possible identity orcharacter of each of the digitsof V The secondary winding of these coils is connected to a manually controlled switching or dialing arrangement-l3fl "which'permits the subscriber to selectthedesignation or'number of the called.subscribers.sta tion. The manual switching or selector device I30. is in turn connected to a plurality of electromagnetic-reed-type relays of the type disclosed in the above-identified patents'to Ellwoodand Dickten. These relays are arranged to successively close their contacts and thus provide 'a distributor arrangement for transmitting the pulses representing the identity of the variou digits of V the called subscribers number in succession. A

group ofrectifiers or unilateral conducting'devices1l56 through Hi3, inclusive, and I80 through {93, inclusive, are provided to control the relays of the distributor as will be described hereinafter.

Although'any'suitable source of alternating current-may be employed to actuate the equipment at the subscribers station, in the specific embodiment described herein the alternating-current power for actuating the-subscribers station apparatus issupplied to the subset equipment. over the subscribers line from a source at a remote or distant point which remote or distant point is usually the central oilice.

In addition phase-splitting networks comprising inductances 4!, 42 and condenser 43 are provided for applying alternating currentsin quadrature to the two sets of primary windings of the impulse generating coils 40 and 50 through 59, inclusive. An isolating and phasing network comprising inductance 35 and condenser 31 is provided to isolate the circuits of the distributor comprising relays 10! to 1 Hand the impulse generating coils 40 and 55 through 59, inclusive. This network suppresses transients due to the operation of the distributor relays lfll through H4 and thus prevents these transients from interfering with the operation of the impulse coils 40 and 50 through 59 or with the operation of the receiving equipment at the central ofiice. In addition, this network is employed to properly phase the controlling currents supplied to the distributor relays and the impulse coils.

In the exemplary embodiment shown, provision is made for the generation of pulses representing eight different digital positions or characters representing the called 'subscribers station during each complete cycle of operation of the calling apparatus and these pulses are repeatedly generated as long as the excitation current is applied. In addition in the specific embodiment set forth herein pulses representing four additional digits are transmitted during each cycle of operation of the calling apparatus which additional. pulses maybe employed toidentify the calling station for charging purposes or for other reasons. When these extra digits are not required they will be omitted. Pulses representing any arbitrarily chosen number of digital positions or characters (within reasonable limits) may be generated by properly designed signaling apparatus. Eight digital positions or characters have been selected for this disclosure for I representing the called subscriber's station since eight character calling numbers are in common use in telephone systems. It will be understood that these characters may be digits or letters or a combination of the two as commonly used in designating telephone calls. Each of the digits 0 to 9 will be represented by a difierent combination of two pulses, the pulse combination representing the digit '2 will also represent the letters A, B and C; the pulse combination representing the digit 3 will also represent the letters D, E and F; and so on. Hereinafter, each combination of eight "characters will be referred to as each called number irrespective of whether the combination comprises digits or letters and di its. a 7 I -In accordance with an exemplary embodiment of this invention, each of the pulses generated is of about 1 millisecond in duration. When pulses of this duration are transmitted over various types of voice frequency communication paths encountered in telephone systems, about 3 milliseconds are required for the longest transients to'die out sufliciently so that the succeeding pulse may be accurately recognized without interference from the transient caused by the previous pulse. In otherwords each transmitted pulse of approximately 1 millisecond duration is in efiect lengthened to a decaying alternating current of ap proximately 3 milliseconds duration. At the end of this 3-millisecond period or any time thereafter a second pulse may be transmitted.

. The signaling systememployedin this embodiment of the invention comprises a start pulse of 1 millisecond duration for each character, the

start pulses being generated at about. llemillisece 0nd intervals as long as the pulsing transformers are energized, and a stop pulse of 1 millisecond duration for each character,. each stop pulse reaching its peak value during the 3.5 to 7.44- millisecond intervalof timeafter the'start pulse hasreached its peak value; In .order to provide suflicient margins of safety to permit-reliable signalin over .35. milliseconds. are allowed for the decay of each pulse and the. times of the start of transmission assigned to stop pulses representingdigits of successive magnitudesdifierby .444 millisecond. Thus. digit 1 is represented by a start pulse followed by a stop pulse which reaches its peak value about 3.5. milliseconds after the start pulse reachesits peak value, digit 2 is represented by a start pulse followed by a stop pulse which reaches its peak value about 3.80; milliafter the start pulse reaches its peak value, and so on. It. will be observed that the stop p lse for the digit 0 reaches its peak value 7.44 milliseconds afterits start pulse and 3.5, millieconds before the next succeeding start pulse. Thus. there is required an increment of timeof 3,5, milliseconds for the decay of the start pulse, 9 increments of timeof .44/1 millisecond eachfor the generation of a pulse at any one of the ten times necessary to represent. the various di its, and a last increment of time of 3.5 milliseconds, all of the latter being required to permit a Stop pulse to decay only if it should occur at the end of the ninth increment of time. Consequently, about 11 milliseconds of time elapse between the start pulses of succeeding digits, from which. it

follows that 11 milliseconds are required in this exemplary system to transmit each digit or character designating the called number.

In order to indicate the starting point of the transmission of a called number, a time interval of approximately 22 milliseconds during which no pulses are tr nsmittedis pr ided at the be inni of orbetween groups of pulses representing a called number. Thus, a time interval of 111 millisecondsris required to transmit-each eight-digit called number and the corresponding no-signal or. blank period. ,When the subsetis arranged to transmit extra digits to identify the calling (or called) stationthe time of the cycle of the calling apparatus is correspondingly xtended.

In accordance with this exemplary embodiment of the invention the signaling pulses are generated by saturation-typ pulse g neratin t nsformers. There are eleven pulsing transformers, onefor each of the numerals 0 to 9 and one for the start or reference pulse. Thev excitation cur,- rent for the apparatus may be obtained local y at the subscribers station or, as in the exemplary embodiment set forth herein, the excitation current for the pulse coils is transmitted from the central ofiice over the line which interconnects the si naling station with the central ofiice. This current is an alternating current of substantially inusoidal wave form, and at the signaling station the current is passed through a phase shifting network so that the current is converted tc a twophase source in which the two, current are 90 degrees out of phase.

Each of the. pulse-generating transformers has a sin le winding secondary and two primary windinss. Th p mary w d n s of; th t ans orme are serially interconnected and. connected with thetwo phases of the excitation current so --that one, phase, of the excitation current is applied'to one prim ry winding of ach transform r 'andrso that other phase of the excitation. c rrent is 6 applied to the other primary winding of each transformer. The secondary windings of the transformers are connected across the line through a selector switch and distributor.

The magnetic core of each transformer is de signed to be saturated except for very small values f mp re-tur s, nd an l ctr c p ls i g ne ated in the se ndary windinglof ach trans former w en he flux i chan ed. ir'om sa uration at o e polarity to saturation at the. other'polar y- The flux generated in the coreof each trans. former with two primary windings depends upon the number of turns in the. two primary windings of th transformer and up n th current. flowing n each w d n In th s embodime t f them: vention the maximum value of the currents. in the circui s associated with each phase a e e u Thl s. theflux, generated in the core of each trans: rmer w th tw pr ma y wind n s depend upon the number of turns in the prima y w nd n s o the transformer and upon the time-phase..re1a= on h p tween the cu re s flowing i ho p i' mary, winding .v Th pulse attains a maximum value when the flux becomes zero,

For this signaling system it is necessary that allpuls s be substantia ly a ike as. to wave form amplitude and that. each combi ation 0.1 O pulses repres ntin a. d git b o the ame polarity, Th area under a v lt ge time curv represent ng t pul is proportional t he total change. in.

fl x and to the. number of tur sin-th condary windin High intensity ener a ionwil produce a hi h. short pulse, while lower energizatio n. will produce a wider pulse having the Same area Thus, if all pulses are to be alike the total maxie mum ampe ern n ch core mu be qualhs um n qual maxima in the cu ren s f'the two phases and a SUI-degree phase displacement t e or pu s s of q a amp itude and, hape the terms Nsand N of the twb primary windingsoj each of the transformers must be such that where NA NA etc. are the number of turns in the primary winding of the transformers which is connected to phase A of the excitation current and-N3 Ne etc. are the number of turns in the other primary winding of the same transformers which is connected to phase B of the excitation current. If these conditions are met and if the cores and secondary windings ofall the trans- .formers are alike the pulses will be suitable "for must be satisfied at the time the pulse is a. maxi, mum wher A and B. ar asdefin d above. and IA and IB are the currents through Na and Ne, respectively. If each phase of the excitation current is of sinusoidal wave form and both phases of equal maximum amplitude, then the timing is'deterrnined by the turns ratio as follower 14 .10 COS wt. B= o sin wt and substitution gives.

' M1 sin wt--NBIo c s wt=o Or? I V -tanwt V where IA, IB, NA and NB are as defined above; I is the maximum current supplied by each phase of the excitation currents equals the frequency the time in seconds.

jfIhus' when the angular position of the desired pulse is fixed in relation to each half cycle of the excitation current, the number of turns and the polarityfof the winding are given by these equa- I tions.

QSince, the magnetic flux in each transformer is reduced to zero two timesjduring each cycle of the excitation current, it follows that a combination of two pulses representing a digit must occur during each half cycle of the excitationcurrent and thateach combination of two pulses repre senting a digit are of opposite polarity to the preceding two pulses.

Fulsing transformers and 50 through 59 inelusive are interconnected sothat the A windings or the transformers are connected in series and connectedto the excitation current through phase of the transformers are connected in series and,

connected to the excitation current through phase shitting networks 42 and .43. The phase shifting: networks are of conventional design and serve to apply aiialternating current to the A windings of the transformers which is displaced 90 degrees inj time -phase relationship from the alternating currentfapplied to the B windings of the transformers. Transformers and 50 through 59 inclusive'contain two primary windings and these transformers serve to generate the stop or digit pulses;

As discussed hereinbefore, each of the transformers 40' and 50 through 59 inclusive is designed so that its core is saturated except for very small values offlux Thus, a short pulse is generated in the secondary winding of each transformer when; the flux in the core of that transformer passes through zero magnitude. These pulses are inaeh transformer will equalthe summation ie ba'a i e ie-ium eeeereeee y. h ehese winding. As discussed hereinbefore, since the maximum value of the current in each phase is equal and since the time-phase relationship between the, two alternating currents is fixed, the time at which the summation of the ampereturns and consequently the. flux in eachtransi'ormerpasses through zero magnitude is gov- Lerned by. the number. ofyturns ineach phase winding. e Fig. 123 indicates the ampere-turns gcneratedin each phase winding of transformer 5| as a function of time and shows the timephase relationship between the stop pulses representing the digit 1 and the ampere-turns generated in each phase winding Figs.'12C and in cycles per. second multiplied by'21r, and t is I 12D' indicate the time-phase relationships for the generation of 'stop' pulses representing the digits 2 and 0, respectively. In each case the stop-or digit pulse voltage is induced'in the output winding when the summation of theamperethe'preceding pulse as induced by the same transformer." It' will be'apparent that the particular phase. relationships indicated are arbitrary and that otherrelationships' would serve equally well. 'As'shown inFig;I1,' each'pulsin'g transformer isconn'ected tolines' 13 and" 14 through condenser 12. This condenser is proportioned to the iterative impedance or: the line and to the impedancs ofi'the' secondary windings of coils 40 and 50 through 59, inclusive, so that each halfcycle pulse as generated bya transformer is applied through condenser 12' to the line as a complete cycle of'alte'rnatingcurrent of sinusoidal waveform," and the period of each :complete cycle of alternating'current is equal to the time required for each half-cycle pulse as generated bythe transformers; 'i i Fig. 12E indicates the start pulses-and pulses representing the digit 2 as 'applied to the line during "one cycle of the -excitation'current.-- Fig; 1212: in conjunction with Figs; 12Aand 12C indi cates the relationship between the pulses' as generated' in the transformers and the pulses as applied'tothe line. y Y 1 1 e .I T An excitation current which "alternates at cyclesper second is employed for -thisembodiment of the invention. 'Howev'er, it will reap parent that other frequencies would serve: equally n v m 1 g f The primary" windings of each of the-transformers through 59; inclusive} 'a'rpro rtioned so that each transformerlgene'rates a stop pulse corresponding to the digit assigned to that transformer. each of these transformers generates a pulse "which reaches its' -p'eak value at 'a" time during the -millisecond 'interv'al assigned to" stop or digit pulses and" there is'f'a -millisecond time interval between the-' peak values of each pulse generated.

During the time that the excitation isapplied to the pulsing transf orinersfa pulse is'generated in f the secondary of each of the "transformers during eachh'alf cycle ofthe" excitation current. In order to apply thefp'ul'se's tofth e line cdmprising conductors 'l 3' and 14 in conformity with the caned'nuinber whicliit'is desired to transmit,

'SIctor sw th 1'30 "and the; distributor are employed to; interconnect" the transformers with the line; e 1' v 'A" s'eleetor switch serves toiiitei'C nneCt the pulsing ftransjformers' witl'r 'the line through the V distributor. Thus; I pulses repr senting any or the :dig'its 0 w 9 'lmaylpeiimpressed"acrossthe telephone line in" accordance with the {settin r the'seiector switch? Figs. 5," 6 "and 7 indicate one embodiment of the selector switch. It is enclosed'incase 190. and-selector dials H tols'andraeaselever I33 are access'ibl'to an 'operator;;" The selector dials are made of 'a" non-conducting material such as hard rubber or plastic, and each dial is provided with ten indentations 'aloiigits outer periphery.

Each indeiitation': designated by "a letter or h mper com e ing to? the" telephone signaling system', "and eachus of suitabl'e' confi'guration to permit an operator's finger to engage and move the dial. The selector dials are separated by spacers III to I" which are attached to case I36. As indicated in Fig. 6, each dial is attached to an individual support I66 so that each dial may be moved approximately onefourth of a revolution about shaft 26. The inner surface of each dial is provided with ten grooves which correspond to the finger indentations on the outer periphery of the dial. The grooves on eachdial serve to engage with a detent pawl to secure each dial in one of the ten possible positions as selected by the operator. As indicated in Fig. 6, detent pawl 36 which cooperates with dial I6 is pivoted about shaft I36. Spring 46 is attached between support I66 and pawl36 so that pawl 36 is normally forced against'dial I6, thereby securing the dial in a fixed position by engaging with one of the ten grooves. Spring 46 also serves to apply a continuous force to support I66 which tends to rotate support I66 and dial I6 in a clockwise direction about shaft 29. The grooves on the dials and the detent pawls are shaped and positioned so that by pressing upon the finger indentations in a dial an operator can move the dial in either direction and so that the ratchetaction of the pawl against the grooves secures the dial in any one of the ten positions to which it may be moved. The rotary movement of the dials is limited to about one-fourth of a revolution by stop I3! and insulator HI. I

Release arm I 36 is connected with release lever I33 through lever I34 and is provided with slots to engage each detent pawl. When'lever I33 is in its normal position, arm I38 permits each detent pawl to engage with a groove in the corresponding dial. When lever I33 is depressed; arm I38 is moved in a clockwise direction about shaft I36 and the detent pawls are disengaged from the.

lays I6I to I I4, of the type disclosed in the aboveidentified patents to Ellwood and to Dickten and each of the relaysin the specific embodiment set forth herein comprises an individual coil I6l surrounding two normally open reed relay contacts. These reeds are made of magnetic material and sealed in a container which may be of glass or other suitable material. The reeds are polarized by means of one or more permanent magnets so that reeds normally remain open.

However, when a current of one polarity within the operating range flows in the winding the contacts will not close but when a current of the same or smaller magnitude of the opposite polarity flows through the winding surrounding these contacts the contacts will close. When the current through the winding is then reduced to zero, the

contacts remain closed until current of a predetermined substantial magnitude flows in the reverse direction through the windings at which time the contacts open and remain open until Insulator I9I supports the various the current again flows through the winding in the operating direction. In addition a common winding 38 is provided for all of the relays and surrounds all of the reeds and their associated polarizing magnets in such a manner that, when a current of sufiicient magnitude is passed through the winding, the reeds of a predetermined one of the relays will be actuated in the opposite manner to that which the' reeds of all the other relays are actuated. This behavior may be accomplished by reversing the sense of polarity. of the polarizing magnet and of the operating winding of the one relay from the sense of the polarity of the polarizing magnet and operatin winding of all the other relays.

It is to be notedthat the right-hand reed in each of the relays is employed to interconnect successive ones ofthe digit selectors I I through I8 of the selector switch I36 with the common conductor 39, whereas the left-hand reeds are employed to control the operation of the relays of the distributor. I

Assume now that the relays are positioned with the reed contacts in relay I69 closed while the reed contacts of all the other relays are open. Further assume that controlling frequency for controlling the reeds is applied between conductors 48 and 49. 'If the alternating current between the conductors 48 and .49 is in such a'direction that the upper conductor 48 is negative with respect to 49 at the time thecontacts of the relay I69 are closed then a path is completed by the closure of the left-hand contacts of the relay I69 from conductor 46 through winding of relay I68 to conductor 49. Current flows in the above path in such adirection as 'to maintain the reed contacts of relay I68 open. This is indicated diagrammatically by the arrow shown within the relay I68 which indicates the direction which the current must flow between the windings of this relay to cause its contacts to close. When the current flows in the opposite direction the relay will open the contacts as described above. When the alternating current changes polarity so that the upper conductor 48 becomes positive and the lower conductor 49 negative then current ceases to flow through the winding of relay I68 and flows from the upper conductor 48 through the left-hand reed of relay I69 and through the rectifier I68 at this time and through the winding of relay H6 in such a direction as to close its contacts. Upon closure of the left-hand contacts of relay II6, current also flows from the upper conductor 48 through the left-hand contacts of relay II6 through rectifier I58 and the winding of relay I69 to the lower conductor 46. This current flows in such a direction as to open contacts of the relay I66 and interrupt the current flowing through the winding of relay III). The contacts of relay II6 however remain closed at this time so that current continues to flow through the winding of relay I66 in such a direction as to maintain the contacts of this 'relay open. When the upper conductor 46 again becomes negative current flowing through the left-hand contacts of relay I I6 reverses and flows through the winding of relay III and rectifier I56 instead of through the Winding of relay I69 and rectifier I56. The direction of flow of current through this Winding is such as to cause the reed contacts of this relay to close and complete a-circuit through the left-hand contacts of relay I II and rectifier I89 through the winding of relay I I6 in the reverse direction thus causing tors 48and 4a;

1 contacts 23 are also switched or right-hand position.

cycle of the alternating current between conduc- 'Furthermore,- upon each reversal of the voltage between these conductors 48 and 49 the reed contactsof the succeeding relays are closed and the reed contacts of the previous relays are opened.

The circuits asshown in Fig. lare in their 1 normal or'idle condition. At this time the ringer 1 30 is connected in series with condenser 3| across thev tip and ring conductors 13. and 14 extending to the central oifice. batteryis normally connected to one of these conductors and ground to the other conductor 1 thus placing acharge upon the condenser 3|.

.If the subscriber is called, ringing current will be applied to these conductors at the central ofiice and, cause the ringer 30 to ring and call the'subscriber. When a subscriber answers, he i will pickup the handset 2| and allow pins 22 to rise.

As a result, the contacts 24 will be movedfto their left-hand position as shown in I Fig. 1... .As" shown in Fig. 11, the pins 22 in 3 rising cause the bell cranks l9 to rotate in a clockwise direction. As a result, the contacts 1 24 close and; the member 'H counter-clockwise direction away from thearmature 25 of themagnetic lock or'relay 41. The 1 polarity of the voltage applied to the tip and i 3 ring conductors l3 and 14 at the central ofiice is rotated in a is in such a direction at this time as to move the armature25 to the right as viewed in Fig.

ljand also'in Fig. 11' with the result that the to their opposite Withboth contacts 23 and 24 actuated to through I I4 inclusive are disconnected from'line conductors l3 and 14 and the transmission apparatus and circuits including the transmitter 1 and receiver of the handset 2| and windings 32- and 33 of the induction coil and condenser 34 are connected to the tip and ring conductors .13 and 14 extending to the central office toprovidethe usual subscribers transmission 3 circuit and to supply necessary battery to the transmitter of the handset 2|.

At the central oflice their operated positions, the signaling equipment at the subscribers station comprising the impulse coils 40 and 53 through 59, the selector switch 130- and the distributor relays The circuits then remain in this condition so 1ong..as the subscribers are talking over the established circuits. It should be noted that 3 throughout this time a direct-current path exists between the conductors I3 and 14 extending from conductor 13 through the-left- 33,-',the transmitter of the handset 2| and the Variations in the transhand operated set of contacts 24, the righthand operated set of contacts23, induction coil duce -curents in the secondary windi'ng32 of the inductioncoil which currents flow in arcincuit-whichextend from the commonlconnection betW een -thetransmitter and receiver through the left-hand winding 32 of the induction coil,

through the central set of operated: contactsoi a'group of contacts 23, and through'thereceive'r and back to the .common' points betweenthe receiver and. transmitter. --i

vVoice currents arriving over conductors I3 and 14 transmittedi over the above-described circuit; including the winding: 33 .of induction coiliand the transmitter of thehandsetinduce currents in the-:left-hand' winding .32 connected to the receiver in the'manner described'above.

The condenser 34 ismconnecte'd' betweenithe upper terminal. of winding 32 and theqtransmitter ;and increases the transmission efficiency oflthe handset in the .usual manner.

At'rthe termination of the call, the subscriber willireplace the handset 2| upon 'thecradle or supporting members and-cause pins, 22' to be depressed. As a'result,-the group of contacts designated 24 willbe-actuated to the right as shown in Fig. '1, while the contacts 23 will be actuated tothe left. In addition the armature 25 of the switchingirelayr i'l is also; actuated to the left. At this, time the direct-current 'path between conductors l3 and'M isVinterrupted and the ringer 30 and condenser -3 reconnected 'betweenithe'tip and ring; and/the normal battery potential applied to the conductor at the central oflice thus restoring the charge on condenser 3| to its normal value. When a, subscriber at the substation described herein in detaildesires to make acall, he will first ascertain the number or designation of the subscriber with which hewishes to communicate. The subscriber will then set the selector switch I30 of Fig. 1, which is also shown in Figs. 2, 3,4,5, 6, 7, 9 and l0by placing his finger over the desired letter or numeral for each digit in the ratchet wheels-II to I8 and then moving these wheels downward to the guide or stop member, which may form a part of the front of the case of the subset as indicated: at I39 in Figs. 3, 4, 5, 6 and '7.

' After the subscriber has moved each one of these dials or wheels in this manner, he may check the setting of the instruments to be sure that it is set in accordance with the designation of the desired subscribers station. ,At this time this designation appears in the first line above the stop or guide member I39.

If thesubscriber has made an error in setting these selector discs, he may correct the error in either. of two ways. (1) He may adjust the setting of. the individual discs that are not set as he desires, or (2) he may release them all byoperation of button I32. shown in Figs. 2 and 3 which depresses the lever |33, shown in Figs. 2, 5 and 7, which lever then moves the link member 34 downward and rotates the latch control plate I38 in a clockwise direction and is viewed in Figs. (Sand 7 The member I38 then'engagesthe pawls or latches 33 associated with each of the selector discs and rotates these latches in a clockwise direction, thus disengaging these pawls and latches from the notches on the inside of the discs as shown in Fig. 6 andpermits these discs to be restored to their original or zero position after which the subscriber may again set them'in accordance with :he designation of the desired subscribers sta- After the'subscriber'has set these discs and checked the accuracy of the setting, he is ready to place a call. It should be noted that in setting each disc, a brush 26 carried or supported by each of the discs passes over a group 'of' ten contact bars Bl to 10 and makes contact with one of these bars depending upon the position in which the disc is set by the subscriber. Thus the brush 26 attached to each of the discs makes contact with a corresponding one of the contact bars when the subscriber has set the disc in accordance with the desired number. Such contact arrangement'is represented graphically by the selector member I30 in Fig. 1 wherein the brushes attached to the discs are designated H through I8. These'brushes are moved in engagementwith the horizontal bars or conductors as shown in Fig. 1 and represented by the bars 6! through 70 in Figs. 6 and 7.

After having set these discs, the subscriber will then pick up the handset 2| which will allow the pins 22 to rise. The bell crank l9 then rotates and permits both groups'of contacts 23 and 24 to be actuated to their operated position. Contacts 24 do so move and'are actuated to their left-hand position as shown in Fig. 1 However, the armature 25 of the relay or magnetic holding device 41 maintains the set of contacts 23 in their normal or operated position at this time due to residual magnetic attraction between the armature and left-hand polepiece-as shown in Fig. 1.

The contacts 24 in being operated to their left-hand position connect the condenser 31 across the terminals of the common winding'38 surrounding all of the'reeds of the reed relays NH through H4. The condenser 3| discharges in this circuit and in discharging closes the reed contacts of one of the relays and opens the reed contacts of all of the other relays-which may be closed. Assume, for example, the contacts of I Ware closed and the contacts of all 'of the other relays are opened.

- As described hereinabove, the permanent magnet associated'with the reeds of relay H will then maintain these contacts closed until opened by the reversed magnetic field due to a reverse current'fiowing through its winding.

Contacts 24 in moving to their left-handposition also connect conductor 13 through the lefthand operated contacts 24 and right-hand'normal-contacts 23 to the upper terminal of winding 27', and connect conductor 1'4 through the righthand operated contacts 24 and the left-hand normal set of contacts 23 to the lower winding terminal of'winding 23. The other terminals of'windings 2!- and 28 are connected together andto the network comprising inductor 35- and condenser 31. Thus, the windings of relay 2?- provide a direct-current path between conductors Hand 14 at this time and provide a path from each of these conductors to the network comprising the elements 35 and'3'l.

At this time, a circuit also extends from conductor 14 through the right-hand operated contacts 24 and the left-hand normal contacts 23 to the left-hand terminal of the secondary winding of the impulse coil 40. This circuit may be also traced through this winding of coil 40 to the common conductor 15 extending to a terminal of a secondary winding of each of the saturable pulse coils Sit-through 59. The circuit will later extend then' through various ones of these coils and theselector switch [-33 to the right-hand set of reed contacts of the respective 14 relays 19] through I 08 or to'the corresponding contacts of relays Hi9 through H2, independent of the selector switch I35. The circuits then extend from the contacts of relays lflithrough H2 to common conductor 39 and then through condenser 12, the right-hand break. contacts of TABLE The equipment at the central oflice responds to the current flowing over'conductors. 13 and 14 and through the windings 21' and 28- and causes the line at the central ofiice to be-con nected to a receiving and registering circuit. Upon connection of the line to this-circuit at the central ofiice, the central oflice equipment will be conditioned to respond to the; calling signals transmitted fromthe subscribers station. In addition, the equipment at the central ofiice interrupts the supply of' direct currentto the conductors 13 and 14 and applies alternating current between both ofthese conductorsand ground. The armature of relay 25, however, still remains in the. position shown. due'to' the residual magnetic induction of the permanent magnets employed in this'device. The alternating'current applied to both conductors '13v and mat the central ofiice flows. over these con-.- ductors and throughthe two windings 21 'andr23 in opposition so that itdoes not produce any appreciable magnetic efiect' upon the magnetic look-- ing device 41; The alternating current then-flows to the network comprisingelements 3.6fand 31. This network is provided to suppressswitching transients which may arise due": to the-operationoft. the distributor relays andthus'prevents these transients fromwadversely afiecting the operation of the pulsecoils andSO through 59. The suppression of these transients also prevents. said transients from. interfering with the operation of the equipment at the central exchange. This network also controls;themag nitudeLand phase of the alternating voltagebetween conductors 48 and 49 so that a voltage suf ficient to operate therelays at the required speed isprovided across theseconductors, whichxvoltage' has a phasesuch that the distributor relays advance. oneach half cycle before therpulses from coil 40 are generated during each half cycle. This current consequently flows from the conductor 49 through the winding of relay. I09, rectifier orunilateral conducting'device I58? and leftehand reed'contacts'of relay I [0- to conductor 48, assuming that thefirst half cycle oi the alternating current applied to conductors to and 10' is of the negative polarity. From" conductor 48; the alternating current. flows. through the phase? shift networks comprising inductors. 4| andi42 and c'onde'nser43 and: then throughz/the two sets'of primary windingsrof the saturable impulse coils 40 and 50 through 59, inclusive; Thereafter the alternating currents now through the resistors 44 and to ground.- As described hereinbefore, thetwo phase shifting: networks 1 4I and42 and condenser-43 cause the alternating currents flowing through the two primary As described ary' windings of each of; these impulse coils. 1

3 These pulses are generated at different times in the manner described above. The pulses are first generated in the secondary or output windings 1 of the start coil 40 and thereafter in the output windings of each of the successive saturable magcycleof the applied alternating current. Thus, if

Furthe'rmorepthere may be'some traner generation of these pulses at this time so I netic coils 50 through 59, inclusive. Such a pulse 1 is generated by each of the coils for each half 1 that these first pulses are generally ignored. 1 However, when the alternating current reverses, after the first half'cyclewhich, as assumed above is negative, or if the first half cycle applied to l the specific subset described herein in detail is positive then currentfiows from the conductors I3and "14 and through-the windings 21 and 28 in opposition to conductor'49 and then through operated reed contacts of relay H0 to conductor 48, and then through the impulse coils and phase shift networks to ground as described above.

The direction of flow ofwcurrent' through the winding of relay III at this time causes its-reed 1 contacts to'close and in closing, theJleft-hand reed contactscomplete a circuit from conductor 49 through the winding of relay III], rectifier or 1 unilateral conducting device I89'to conductor 48, I through the left-hand operated reed contacts of relay I II and then'to ground in the manner described above; Thedirection .of flow of ."current 1 through the winding of relay H0 at this timeis in such adire'ction'as' to cause its contacts to open.' Thereafter the contacts of this relay remain open until the relay is again actuated.

During this half cycle'the pulses will be gen-,

erated by each of the impulse coils as described above. a

During the next succeeding half cycle of the alternating current, 'acircuit is completed from conductor '49 through the winding of relay 3 I I2 andunilateral' conducting device I9Il to conductor 48 through the left-hand operated reed contacts of relay III and then to ground as de- 1 135 1 the winding of relay III, rectifier ISEL-left-hand scribed above. Current is flowingthrough the sion ci-rcuit as will he describedhereinafter.

However, as pointed out above, the-equipment at the central office will usually be designed to'employ these first few pulses for conditioning the equipment to accurately respond to the succeeding pulses. I

- Under the assumed conditions at the'beginning of the next'half cycle the contacts of relay H3 will close and cause the contacts of relay H2 toopen. The closure of the right hand contacts of relay H3 at this time connects conductors I3 and 14 together in a circuit which extends from conductor "through the right-hand operated contacts 2 4, through the left-hand break contacts 23 and the operated right-hand contacts of relay H3 to conductor 39, and then through condenser 12 and through the. righthand break contacts 23 and the left-hand operated contacts 24 to conductor I3; thus-in effect short-circuiting the line through the condenser 12 and the operated contacts H3. Asaresult, the output of the impulse coils are in efiect disconnected or short-circuited at this time. Consequently, no pulses will be transmitted over lines 13 and I4 even though such pulses are generated during this half cycle by the various coils'40 and 50 through 59, inclusive; likewise, at the beginning of the next half cycle of the alternating current, the contacts of relay I I4 close in a manner similar to the operation of the previous relays, and the contacts of relay'l I3 open. During this half cycle, the right-hand contacts of relay II4 similarly short-circuit or connect the conductors I3 and I4 together through condenser 'I2 and prevent the transmission of pulses to the central office.

These two half cycles during which no pulses are transmitted constitute a blank interval and are recognized at the central ofiice as indicating the termination of pulses representing a subscribers designation has been transmitted and that pulses representing the succeeding transmission or repetition of the designation is about to be started. The central office circuits respond to the blank interval by conditioning the received circuits so that they will respond to the next succeeding pulses and record these signals if they are properly received as described in the above-identified application of Malthaner and Vaughan filed on an even date herewith.

During the next half cycle of the applied alterhating current, contacts of relay III] are closed and the contacts of relay I I4 open. At this time the brush II of the selector switch I30 hasbeen positioned in contact with one of the conductor bars BI through I0 as shown in Figs. 6 and .7. Assume for a purpose of illustration that it has been moved to engage the No. 2 or third conductor bar from the bottom of Fig. 1 as shown by the dotted half circle. In other words,'the brush arm 26 attached to the first selector disc engages the conductor 68 as shown in Figs. 6- and 7 indicating that the first letter designation of the called subscribers station. is an A, B or C. Assume, for example, that it is a C. During this half cycle, the right-hand contacts I2I of relay IOI are closed and connect the brush arm II to the common conductor 39. Consequently, when the start pulse coil 40 generates a pulse, this pulse is transmitted over the following path to conductors I3 and 14 to the central office. This pathmay be traced from conductor 13 through the left-hand operated contacts 24, the righthand break contacts 23, condenser I2, common conductor 39, right-hand contacts I2I of relay IIlI, brush arm II, the No. 2 horizontal conduc- 17 tor of the selector switch I30, the secondary windingof the impulse coil 52 and the second= ary winding of the start pulse coil 40 and through the left-hand break contacts 23 and the righthand operated contacts 24 to conductor I4. v

It is noted that the windings 2! and 20 of the polarized relay or locking device 41 are also shunted across these conductors as described above. However, these windings offer high 1m pedanc-e to the pulses transmitted to the central office and thus do not materially interfere with the transmission of these pulses.

A short time later during the same half cycle and in the position indicated in Fig. 12 for the No. 2 or C character of the digit or symbol of the called subscribers number, a pulse is generated in the secondary winding of the impulse coil 52 which pulse is likewise transmitted over the conductors I3 and 74 to the central office over the same circuits described above with reference to the start pulse generated in the secondary winding of coil 49. These two pulses as explained above, identify the character of the first digit or symbol of the called subscribers number. The condenser I2, together with the secondary winding of coil 52, for the start pulse and condenser 1'2, together with the secondary winding of the coil 46 for the stop pulse, comprise a pulse-shaping or filter element which tend to eliminate the high frequency components of these pulses and cause the pulses transmitted over the line to the central office to have a wave form approximating' a single cycle of a sine wave.

During the next half cycle the reed contacts of relay I02 will close and cause the contacts of relay IOI to open. Closure of the contacts of relay I02 and the opening of the contacts of relay I| occur very near the beginning of the half cycle. Gonsequently when the start pulse is generated by coil 40 it is transmitted over a circuit extending from conductor I4, the righthand operated contacts 24, the left-hand break contacts 23, through the secondary winding of coil 54, the selector disc brush I2 which is assumed to be positioned in contact with No. 4 segment as shown in Fig. 1, the left-hand closed reed contacts of relay I02 to common conductor 39 and then through condenser 12 and through the right-hand contacts of contacts 23 and the left-hand operated set of contacts of contacts 24 to the conductor I3, extending to the central oifice.

A short time later the stop or digit pulse is generated in coil 54 which is likewise transmitted through the same circuit to conductors I3 and I4 extending to the central office. It is to be noted that the pair of pulses transmitted during the time the contacts of relay IOI are closed has one given polarity while the pair of pulses transmitted during the time the contacts of relay I02 are closed has the opposite polarity. The reversal of polarity of the successive pairs of pulses is illustrated in Figs. 12, 12A, 12B, 12C, 12D and 12E in which the successive pulses transmitted during successive half cycles are shown to be of Opposite polarity.

As shown in Fig. 1 by the dotted lines the selector switch I30 has been set to transmit a number assumed to be CH3I0|40. Consequently, during the second half cycle after the blank interval, pulses will be transmitted from coils 40 and 54 designating G, H or I which we have assumed to be H. During the third half cycle pulses will be transmitted from coils 4B and 53; during the fourth half cycle pulses will be transmitted by coils '40 and 5| and will be transmitted through the contacts of relay I04. Thus during each half cycle following the blank interval a pair of pulses is transmitted under control of one of the brush arms I I through I 8, inclusive as positioned by the selector 'cliscs designating the number of the called subscribers station. Consequently, during each half cycle a pair of pulses is transmitted designating each one of the digits or symbols of the designation.

Each pair of pulses is transmitted during the time successive ones of the distributor relays IOI through I08 is operated. During the ninth half cycle and the succeeding three additional half cycles the relays I09 through I I2 operate and transmit four additional pairs of pulses. These pulses are transmitted to identify the calling subscriber's station. As shown in the drawing the left hand reed contacts of these relays are connected to output windings of coils 51, 55, 53 and 52, thus indicating that the last four or any other specified group of digits of the calling subscribers designation comprise the number .7532. Consequently this information is also available to the equipment at the central ofiice for switching purposes as well as charging purposes if and when it is desired. Thus during the ninth half cycle the pair of digits identifies the numeral I while the pair during the tenth half cycle identifies the numeral 5, etc.

At the end of the twelfth half cycle and at the beginning of the thirteenth half cycle, relay II3 will again be operated and effectively shortcircuit the line conductors 13 and I4 to the pulses so that no pulses will be transmitted during this half cycle. During the fourteenth half cycle relay I I4 likewise operates and causes relay II3 to release. Relay II4 as described above also prevents transmission of any pulses to the central office. These two intervals during which no pulses are transmitted comprise a blank intervalas described above to indicate that a complete designation or calling code has been transmitted and that a succeeding one will start following this blank interval. Thereafter the above cycle of operation of the calling equipment at the subscribers station is repeated until the circuits at the central office function to change the connections of the subscribers station.

The equipment at the central ofiice in responding to fine or morecomplete sets of signals or portions thereof will establish switching paths through the switches from the calling subscribers line towards the called subscriber's line.

When the connection has been extended to the called subscribers line the central ofiice equipment is arranged to interrupt the alternating current applied between both of the line conductors and I4 and ground and apply a direct=current voltage between these conductors cf reversed polarity.

The details of the operation of the central cffic'e equipment in response to the calling signals transmitted frcm the subscribers station and alsc the details of the arrangement for interrupting the application of the alternating current to the line conductors I3 and 14 at the central office and the application of a direct-current voltage of the reverse polarity between them at this time is described in detail in the aboveidentified application of Malthaner and Vaughan which application is made a part of this application to the same extent as if fully set forth and repeated herein.

Interruptionj of the alternating current stops the-operation of the impulse. coils .40.. and B throughid and also stops the operation of the distributor'relays llll through 4.

The application of the direct-current voltage between conductors 13 and 14 in the reverse di- 1 re'ctioncauses the armature of the magnetic relay or holding .device 25 to operate to its righthand positionland' thus permit contacts 23 to be operated. At this time both contacts 23 and 24 are operated and thus as described above the transmitter and receiver of the handset 2| are connected to the windings 32 and 33 of the induction coil and to the line conductors I3 and extending to the central ofiice. At this time Upon the completion'of the call the handset v 2| willbe placed upon its supports and the pins 22 depressedwhereupon both sets of contacts 23 and 24 are actuated to the positions shown in the drawing. Likewise the armature 25 of the magnetic holdingdevice 41 is moved to its lefthand position as shown in the drawing where the circuits to the subscribers station are returned to their normal or idle condition ready to respond to a call from the central office or to be utilizedin making a call to another subscriber in themanner described above.

It is to be understood that the above-described arrangements are illustrative of an application of the principles of this invention. Numerous other arrangements and modifications may be devised by those skilled in the art without departing from the spirit and scope of the invention. V

What isclaimed is:

1 1. A telephone dialin system, apparatus for: generating a start pulse and a plurality of stop pulses designating the identity of the numerals of a called designation, an ,output'circuit, a manually operable selector switch, a plurality of relays, apparatus for actuating said relays one after the other in succession, interconnecting circuit means for interconnecting said manually operable selector and said apparatus for generating pulses and said relays for extending a difcircuit for a; selected one of said stop pulses during the actuation of each of a plurality of said relays, apparatus for applying alternating current to said relays for advancing them one relay for each half cycle of said alternating current.

2. In combination in a telephone system calling apparatus comprising a subscribers line, a plurality of impulse coils for generating calling pulses, an energizing circuit for supplyin alternating-current power to said coils, means for selectively interconnecting said coils one at a time with said line, a" manually operable selector switch, a plurality of relays, an actuating cir-v cuit for actuating said relays one at a time in response to alternating-current power, connections between said line, said impulse coil energizing circuit and said actuating circuit for said relays for supplying power from said line to actuate said relays and energize impulse coils.

3. In combination in a telephone system callingi apparatus comprising a subscriber's line, a plurality of impulse coils .for generating calling pulses; means for selectively interconnecting said coils one a time with said line comprising a manually operable selector switch and. a pluralityofrelays, connections between said line, said impulse coils and said relays for supplying alternating-current power from said line to actuate said relays one at a time and to energize said impulse coils and a. filter network connected in said connections to prevent interference between said coils and relays.

4. In combination in a telephone system callin apparatus comprising a subscribers line, a

ferent pulse transmission path to said output plurality of impulse coils for generating calling pulses, input and output circuits for each of said coils, means for selectively interconnecting said line and said output circuits one at a time comprising a manually operable selector switch and a plurality of relays, an actuating circuit for actuating said relays one at a time in response to each half cycle of an applied alternating current, connections between said line, said impulse coils and said relays for supplying alternatingcurrent power from said line to actuate said relays and impulse coils, a phase control network included in said connections to control the relative times of operation of said relays and the output pulses from said impulse coils.

5. In combination in a telephone system calling apparatus including a subscribers line, a plurality of impulse coils for generating calling pulses, means for selecting said pulses comprising a manually operable selector switch and a plurality of relays arranged in succession, a winding individual to each of said relays, a set of contacts individual to each of said relays for controllin the circuits of the windings of said relays, a plurality of unilateral conducting devices connected between'said controlling contacts and said windings, connections between said windings and said contacts and said line for conveying alternating current from said line to said windings for operating one of said relays and restoring another of said relays in response to each half cycle from said alternating-current source, and connections-from said line to said impulse coils for supplying alternating current to said impulse coilsya phase control network included in said connections to control the relative times of said operation of said relays and the output pulses from said impulse coils.

6. In combination inra telephone calling system apparatus including subscribers line terminals, a plurality of impulse coils each havinga put windings and said line terminals for supplying alternating current of two different phases to said input coils from said line terminals for inducing in said output circuit a pulse during each half cycle of alternating current from each of said cores, selecting means for selecting said output pulses comprising a manually operable selector switch and a plurality of relays arranged in succession, a winding individual to each of said relays and a set of contacts individual to each of said relays for controlling the circuits of said windings of said relays, a plurality of unilateral conducting devices connected between said controlling contacts and said windings, and connections between said windings and said contacts and said line terminals for applying alternating current from said line terminals to said windings for operating one of said relays and restoring another of said relays in response to each half cycle from said alternating-current source, a phase control network included in said connections to control the relative times of operation of said relays and the output pulses from said impulse coils.

HENRY E. HILL.

DAVID B. PARKINSON.

REFERENCES CITED The following references are of record in the file of this patent:

Number UNITED STATES PATENTS Name Date Cummings Aug. 8, 1911 Hargan Apr. 14, 1925 Smith Jul 14, 1931 Stacy July 28, 1931 Burger Mar. 24, 1942 Cooper Aug. 25, 1942 Roberts Mar. 23, 1943 Dohle June 29, 1943 Goff Sept. 14, 1943 Guenther May 8, 1945 Mallina Feb. 12, 1946 Parkinson Mar. 7, 1950

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