US1762963A - Means for synchronizing rotary devices - Google Patents

Description

June 1o, 1930. A. D. Down 1,762,963

MEANS FOR SYNCHRONIZINGl ROTARY'DEVICES Filed April 26,l 1928 3 ySheets-Sheet 1 June 10, 1930.

A. D. ADOWD l MEANS FOR SYNCHRONIZING ROTARY DEVICES Filed April 26, 1928 5 Sheets-Sheet 2 Arm/Mfr lJune 10, 1930. -A. D. DowD MEANS FOR SYNCHRONIZING ROTARY DEVICES 3 sheets-sheet s Filed April 26. 1928 .www5

Arron/vir ANDREW D. DOWD, OF .'HOBOXEN', NEW 'I'FRSIEIY,v ASSIGNOR TO 'WESTERN ELECTRIC Patented .lune l0, 1930 UNITED STAT-Es PATENT OFFICE COMPANY, INCORPORATED, OF NEW YORK,v N-i .A CORPORATION OIF NEW YORK MEANS FOB vSYNCH'RONJZZING ROTARY-DEVICES Application led April 26, 1928, Serial 170.272,90), vsind in Great Britain October 31, 192?. I

Thisinvention relatesto means for-synchronizing a plurality of rotary members and is particularly intended and adapted for use in so-called synchronous ltelegraph or signaling systems though alsov applicable for other apparatus, as for-example, thesynchronizing of picture transmitting' apparatus. i

An object-of the invention is to maintain in -synchronism rotary distributors at .terminal stations in a simplex telegraph system having an intermediate station arranged to repeat signals in opposite directions on long submarine cables.

A more speciiicobject of the invention is to automatically correct in both forward and backward directions the speed of the dis-l tributors at the repeatingand the receiving stations during each receiving interval when such'distributors -pull out of phase with the l distributors at the sending station.

A preferred embodiment of 'the invention is shown and described herein as being adaptable to a multiple-x printing submarine ca le telegraph system such as disclosed in U.S.

Patent No. 1,689,328 granted to A. M. Curtis* l on Oct. 30, 1928,l and therefore a brief description of this system will( facilitatea clear understanding of the present invention. l In this system a number of separate printing telegraph transmitting and receiving mechanisms at both ends of the'cable are connectedV in rotation so that each transmittingl circuit at one end is momentarily connected over the cable to its corresponding receivingcircuit at the other end. The amount of time alotted to each circuit is equal to thetotal transmis-y sion time divided by the number of separate sets of circuits. The cable operation is simplex, that is, messages are transmitted in one direction only during a given interval of time and the direction of i transmission is l reversed automatically at statedintervals in order to' handle traiiic in bothf directions over one cable. In other words, .the transmission mechanisms at one end of the able are con-4` nected to the receiving mech nisms at the opposite end of the cable forza ertainvperiod andthen reversed so that thai-transmitting mechanisms at the'opposite ondere-connected .beenset to the ldesired proportions of time.

The mechanisms for transmitting and receiving consist of' so-called rotary distributors comprlslng 'transmitting rings, receiving ringsandcorrecting rings. vThe correcting rings, whlch are .mounted on each of the `senderv distributors, are arranged to be orientable -in relation to the other rings on -,theirrespective distributors whereby the system may be adjusted before the actual transmission of messages begins to establish synvchronism between the vsender distributor at one end of the .cable and the receivingvdistributor yat the other end when such distributors` are interconnected for the transmission of messages. `In this manner, differentl amounts of time lag due to the transmission characteristic of the cable may be compensated. The distributors have a tendency to drift out of synchronism and phase during the intervals when the reversals of direction and transmission take place. Means for cor- .to the receiving mechanisms at the origin'atrecting this loss of synchronism and phase are disclosed in detailin U.. Si'Patent'No.

1,670,461, issued to G. A. Locke-on M ay 22,

1928, whichmeans are particularly adapted t'o systems-*having lonly two stations .inter- -correction is generally made in a forward direction, that is, in the direction .of-rotation of the distributor brushes and, .if it shouldbe desirable at any time to eil'ectgthe correction in. a backward direction, aman.- ually operatedtwo-position switch which is" .provided for this ,purpose must be operated to its alternate positionin order to shift the correcting ap aratus for backward movement of the d1stributor brushes.

I According to the present invention, correcting means somewhat, similar to those disclosed in the Locke patent, supra, are employed for restoring synchronism and phase 1n a system in which two terminal stations and an intermediate station are interconnect- 1 ed by-a long submarine cable, but the proposed method of correcting rovides for corterminal station and the intermediate sta-Q tion fall out of synchronism and phase with the distributor at the sending terminal station, the correction can be applied at the receiving terminal station and the intermediate station practically simultaneously.

This invention will be better understood by reference to the following detailed description taken in connection with the accompanying drawing in which Figs. 1 and 2 represent a diagrammatic layout of a multiplex submarine cable telegraph system which includes an inland terminal station A, a land line, a shore te'rminal station B, a submarine cable, an intermediate, or repeater, station C, another submarinev cable, and another terminalstation D, all connected in series. Fig. 3 shows the correcting mechanism used in connection with the apparatus at the terminal station D. f f

Inasmuch as the invention relates principally to a method and means `for malntaining in synchronism and phase the distributors at thc various stations, such parts of the system as are not directly concerned with the problem, for example, such apparatus as the transmitting and receiving distributors, impulse transmitting and printin devices, driving motors, storing relays, an amplifier units: are merely indicated by enclosures, while of the direction of transmission control apparatus, only the cams and spring contacts essential for the switching of the line for transmission in one direction or the other have been indicated. C n the other hand, the

lst

speed correcting or synchronizing means at the terminal station D have 'beenshown in considerable dctailand this will be taken as being representative of similar means used inconnection with the receiving e uipment at stations A and C. For a full understanding of the system, reference can be made to the Curtis patent, supra, as the following description will be confined principally to such portions of the system as are connected with the synchronizingproblem.

` Referring to Fig. -1 there is shown at the inland terminal station A, a transmitting distributor 100 with its associated impulse transmitting device 101 and a receiving distributor .102 with its printing device 103 connect- Aed to contacts actuated by cam 104, which valternately connect said distributors to a land line.105. which extends to the shore 'terminal station B. Correcting rings 106 with their associated correcting apparatus 107 `are shown connected to the contacts of a twoposition correction control relay 108 at sta- -tion B. Relay 108 is shownconnected in series with the line relay 109 in the output of amplifier 110 the latter being connected to the submarine cable 111 whlch extends to the repeater station C.

` The equipment at station B comprises av receiving distributor 112 and its associated storing relays 113 from which the signals arev retransmitted through the transmitting distributor 114 to the submarine cable 111. Of

the direction control apparatus vat this station, only transfer relay 115 and the cams 116 and 117 for controlling contacts )zo switch from reception to transmission, and vice versa, have been shown. VAt this station, signals received from line y105 are repeated to cable 111 through the receiving distributor 112, storing relays 113, transmitting distributor 114, while the signals from the cable 111 are amplified through the amplilier 110 ,tovactuate line relay 109 whichdirectly controls the lretransmission of signals to the land line 105 through the contacts actuated by cam- 116.

The corrector control relay 108 responds to they signals `incoming from cable 111 and thereby causes the necessary correction in the receiving distributor 102 through the correcting rings 106 and correcting apparatus 107. The correcting rings 106 are mounted on the sending distributor 100, and the correcting apparatus 107, which is for producing angular shiftsof the brushes traveling overthe faces of the distributors 100and 102,

is located between the motor (not shown). for driving the distributors and the distributors themselves, as will hereinafter be explained. The distributors at station B are driven in synchronism with the distributors of vstation A by mea-ns of the distributor arrangement 118 at station A whereby impulses are sent over a separate line 119 to the driving motor arrangement 120 at station B. .These arrangements are shown and described in detail in the Curtis patent, supra. No4 correcting rings or apparatus are required for station B because` the distributor thereat is driven from the same source as the distributor at station A.

The submarine cable 111. terminates at repeater station C at which the equipment for receiving signals-includes an amplifying device 200, line relay 201, receiving distribupeated to the correcting rings 207 for thef operation vof the correcting apparatus 208 to.

rection control relay206 is in series"withthe line relay 201- and controls the impulses vreelfect the necessary. correction in the dis-- tributors 202 and 204. Repeating signals in the o posite direction, that is, from station D to i; through station C is accomplished by transfer relay 209 and cam 210 and transfer.

relay 211 and cam 212, all of which are under the control of the direction control apparatus (not shown) cable 205 are received and amplified .by the amplifying device 213 and li'ne relay 214.'

Relay 214 repeats the amplified signals to receiving distributor 215 and storing relays 216 and these repeated signals are retransmitted through sending distributor 217 over cable 111 and land line 105, to'station'. The correction lcontrol relay 218 is in series with the line relay 214 to control the impulses repeated to the correcting rings 219 for operating correcting apparatus 220. to effect the necessary correction` in the distributors 215 and 217. Two sets of distributors with separate correcting apparatus are provided at station C to handle traic in both directions, the correcting-apparatus'208 being located between the motor (not shown) for driving distributors 202 and 204 and the distributors themselves, and the correcting apparatus 220 being located betweenthe motor (not shown),- 'for' driving , distributors 215 and 217 and the distributors themselves. .4 The correcting rings 207 and 219 are respectively mounted on the sender distributors 204 aud`217.

' Submarine cable 205 terminates at station- D `at which the equipment for receiving signals consists of an amplifying device 221, line relay`222, receiving-distributor 223 and the printing apparatus 224. The correction con-v trol relay 225 is in series with the line relay 222 tocontrol the correcting apparatus 226 through correcting rings 227. Transmission from station D is directed by-impulse trans'- mitting devices 228 through the sending distributor 229 to cable'205 and the directionv control cam 230 causes throu h the operation offtransfer relay 231, the shifting of opera- `tion over the cable 205 from the receiving to thef sending apparatus, and vice versa.

f The correcting apparatus 226v and correct- Fig. 3 and respectively designated therein by ing rings 227 in Fig. 2 are shown in detail in characters 326 and 327. The correcting rings are made up of a continuousring and a segmented ring, the latter ring consisting ef ten segments for each channel employed in the f system.- For example,in afive-channel system such as described in the Curtis patent, supra,

the segmented ring consists of fifty segments.

' tures-of thls invention, a description will now be made of the vmethod of bringing the dis-v These iugs are interconnected by a rotatable brush' 332 which, as 'it passes over each segment is arranged to complete a circuit for operating an auxiliary correction relay 333.

The signals incoming from diiferentlal beveled gear' arrangement 337` posite directions.

i 'f Relay 333 is al three-position relayand controls the'operation of acorrecting mechanism 334. This mechanism is located between the motor (not shown) for driving the distribu. tors 323 and 329 andthe distributors themselves. The shaft'335 is driven by themotor -and the shaft 336 drives the arms on whichthe brushes, such as 332, for `thedistributors aremounted. These armsiare arranged to drive the brushes over the various distributor faces in a manner well known in the art.'

he correcting'mechanism 334 consists of a disposed between the motor shaft 335 and the brush shaft 336 and the gears that link these two Shafts together are mounted on a supporting frame 338 secured to a worm pinion 339 that meshes with a worm 340. Any

change in the angular position -of the worm.

pinion 339 changes the angular osition of the linking gears and this in turn c anges the vangular posltion of the brush shaft 336 with respect to the motor shaft 335. The worm 340 is rotatable to shift the angular position of the worm pinion a small angle by means ofcorrector magnets 341 and 342 in one-direction or t-he other. The ratchet wheel and pawl mechanisms 343 and 344, respectively,

. TRAB- are operated by these magnets so that upon the operation of either one of the magnets, an angular shift of the distributor brushes in onedirection or the other is effective.A In

order to hold the worin 340 firmly while the magnets are not rotating it, a separate-ratchet wheel 345 and a pawl 346 is provided. This wheel and pawl alsolimits the movement'o'f theworm 340 to one step each time a corrector magnet operates.v The automatic corrector mechanism 334 is therefore camhla 'nf Shin;-

tion of rotation of the brushes. It is seen,

therefore, that this mechanism corrects in either direction and can be eective while the distributor brushes are being rotated by the motor and in this way synchronizing effects maybe produced between the brushes of the distributors at thediff'erent stations, as will hereinafter bem'ojlfef fully explained. The i automatic correctin'ggapparatus at stations A and C are identical with that shown in Fig. 3,

two sets being provided for station C in order to correct for .synchronism and phase in op- To more fullyset lforth the' various' fea- 12oA l tributors at the various stations into synchro'- at stations B, C and D may be regulated in` accordance with the determined speed of the distributor at station A. That is to say, the fundamental speed will be set at station A although it should be remembered that during the transmission of messages the station from which transmission takes place at any given time sets-the pace at which the receiving station distributors will opera-te. As previously mentioned,the speed of the distributor at `station B is controlled by the distributor drive rings 118 at station A and will not be described herein in detail as their arrangement is well known'in the art. `It is sluiicient to say that the speed of the motor fordriving the distributors at station B lis entirely controlled from the impulses received over the line 119. If, therefore, the' distributors of station Aare setto a certain speed and the motor atstation B is regulated so that the distributors at station B are traveling at the same speed, the next step will. be to vtransmit so-called phasing signals from the sending distributor 100 over line 105 to the receiving distributor 112 at sta' tion B. The brushes of the receiving distributor 112 must now be set in phase with the 'brushes of the sending distributor v100 at station A. This is done by means shown anddescribed in detail in thelCurtis patent,y supra, and is described in generalin the Locke. patent, supra. When this phase relation is attained, the signals received from station A are permitted to be retransmitted through storing relays`113 and the sending distributor 114 over the submarine cable 111 to. station C. TheseV retransmitted signals are now used by the operator at station C for determining the speed at which the distributors at station C shall travel and, as.

far as transmission `of signals between stations A and'C are concerned the presence of\station B ma be disregarded in the following description of the method of. synchronizing.

The operator at station C now proceeds in a manner similar to that of the operatory at station'B is phasing the brushes of the receiving distributor 202 and, when this phase relation has been obtained, the correcting apparatus 208 is switched in to be cont-rolled by the impulses produced Aby the corrector control relay 206. rlhe correcting apparatus will function to automatically correct the positions of the distributor brushes in both for-v ward and backward direct-ions for any loss of synchronism or phase occurring thereafter.

The signalsl received at station C are retransmitted through storing relays 203, sending. distributor 204 over su marine cable 205 to station D. These signals are used by the operator at station D for determining the speed at whichthe distributors at station D shall travel. The operator at station D also proceeds in a manner similar to that ofthe operator at station B and, when the brushes of the receivin distributor 223 are broughtinto phase wit the brushes of sending distributor 204 at station C, the operator at station D switches in the correcting apparatus 226 to 'be controlled by the impulses produced at the correction control relay 225 in response to the incoming signals. Correcting apparatus 226 will likewise function to automatically correct the positions of thel distributor brushes at station D in both forward and backward directions forlany loss of synchronism or phase.

In order to reverse the direction of transmission and reception so that messages may be transmitted from station D, the direction control cams 104, 116, 117, 210, 212 and 2 30 are actuated -by a timing device (not shown). This timing device is merely a means for actuating the above mentioned cams at certain intervals to make'them perform thisdesired switching of the circuits atpredeterminedj -close the connections between the receiving distributor 102 and the line 105. Similarly, 'cam 116 opens the connections between the receivingdistributor 112 and line 105 and closes connections between line 105 andthe armature of line relay 109.1l The cam 117 closes a circuit for the operation'of relay 115 to open the connection between the submariney cable 111 and the sending distributor 114 andto close. a connection between this cable and the amplifying device 110. Signals incoming 4over cable 111 will therefore now passas previously stated through the amplifyingdevice 110, line relay 109 and correction control relay 109. The operation of cam 210 closes a circuit for the operation of transfer relay 209 to cause this-relay to'actuate its armature to a position opposite to that shown in the drawing, thereby opening the connection between cable 111 and the amplifying device 200 and closing a connection between the cable and the sending distributor 217 .f Cam- 212, upon operating, lcloses a circuit for the operationof transfer relay 211l to cause this relay to open the connection between the cable 205 and the sending distribu-v tor 204 and to close a connection between the cable and amplifying device 213 at which de- 15. tion C, B and A to the speed of the distribuand storing relays 216 for retransmission stations C and B to station A may now begin vses through sending distributor 217. The operation of cam 230 operates transfer relay 231 to open the connection' between cable 205 and receiving apparatus at station D and to close a connection between the cable andthe sending distributor 229.

When the operations of the aforementioned cams are completed, the transmission of phasing signals from station D through repeater for-'synchronizingof the distributors at stator at station D. It will be recalled that the arrangement of the system is such that the sending station is a pace-setting .station -although the distributors at all four stations are operating at the one speed..v When the phasing is accomplished at each station in turn, the ,correcting apparatus at the re eating station C and the receiving station are connected for maintaining the distributors at their respective stations in synclironism and phase.

lF ig. 3 shows the equipment at -station D more in detail than Fig. 2, different characters heilig used for corresponding elements to avoid confusion in referring to the two figures. The correcting rings 327 are shown connected through the continuous, or upper, ring to the ,contacts of the correction control relay 325. Relay 325 is atWo-position polarized relay having an armature arranged to remain iii4 one position while signals of one polarity arebeing received and to move to its alternate position when the polarity of the signals is reversed. The segmented ring of ring set 327 is arranged in two groups of alternate segments, vone group A being connected in a circuit extending through the left-hand winding of auxiliary correction relay 333 and the other group R connected ina circuit extending through the right-hand winding of relay 333. Relay 333 is a threeposition polarized relay having an armature arranged to be normally in a neutral position tributors '229 and 223 in Fig. 2 in either av but effective to engageeither of two associated contactsl in response to a current flowing through either of the above mentioned windings. When the armature of relayV 3331engages either of its associated contacts, one or the other of the corrector magnets 341and 342 operates to move the brushes on the disforward or a backward direction, the direction depending on whic vwindin of relay 333 is energized. When rotatable rush 332, .which interconnects the rings of ring set 327, 1s in contact with an A segment at the instant relay 325 moves from one contact to the other,

the left-hand winding oferelay 333 becomes energized, operating corrector magnet 341 to 'handwinding of relay 333 to negative move the brushes in a forward direction and when the brush is in contact vwith an R segment the right-hand winding of relay 333 becomes-energized and the magnet 342 opcrates` to move the brushes in a backward brush correction is in a forward or a backward-direction-according as the brush 332 is in contact with an A (advance) or R (retard) segment; and if, as will be the case if. the distributors'of station D are in perfect phase relation with the distributors of station C, the brush 332 is passing over one of the' insulated spaces between an A and an R segment at the instant ofthe actuation of relay 325, no circuit Will be completed to either of the windings of relay 333. Assuming that the brushes of the distributor of station D are lagging behind the brushes of the distriby utor at station C taking iinto consideration the characteristic lag of the cable 305, brush 332 will be' in contact with an A segment as shown instead of in contact -with the insulated space following it, and a circuit` is therefore closed, traceable from positive battery 347, armature and right-hand contact of relay 325, condenser 348 and high resistance 349 in parallel, conductor 350, continuous ring, brush 332, andan segment of ring set 327, conductor 351, back contact and armature of magnet 341, conductor 352, left-hand winding of relay 333,*t'o negative battery 353,

direction. It will be seen, therefore, that the but not enough currentwill flow in this circuit at this time because of the high resistance in parallel to the condenser 348. At the next reversal of polarity of the incoming signals, the armature of relay 325 moves to its alternate position and closes a circuit extendingfrom the positive battery 347, armature and left-hand contact of relay 325, condenser 354 and high resistance 355 in parallel, conductor 350 over the same path just traced-to the negative battery 353. A surge of current is produced in the circuit including condenser 354 at the moment the armature and -left- 343 to shift, through the corrector mechanism 326, the'sh'aft 336 for a small angular distance in a forwarddirection in relation to the rotation of the shaft. This shifting of shaft 336 causes the brushes of the receiving distributor 323 and brush332 of the correcting rings 327 to move forward a correspondingangular distance. When relay 333 operates,

it closes'at its left contact and armature` a 1 locking circuit for itself extending over con'- ductor 357, resistance 358, through the leftbatl tery 353, and this locking circuit prevents the release of the relay until magnet 341 has reached its fully operated position. When magnet 341 reachesits fully operated position, a circuit is closed extending from positive battery 356, armature and left contact of relay 333, conductor 357, resistance 358, armature 'and front contact of magnet 341, conductor 359, to negative battery 3 53, and this circuit shunts the left-hand winding of relay 333 which now releases its armature, thereby causing the release of magnet y.341. In this manner relay'333 is prevented from operating 'in response to another ,impulse received from the correcting rings unt-il the magnet 341 is fully restored to its normal position. At

l the next reversal of polarity of' the incoming signals passing through the windings of relay 325, a brush will again be in contact with an A segment if synchronism or phase has not been restored, and the relay armature will move toits right-hand Contact to send another-impulse from positive battery 347 through the left-hand Winding of relay k333. Relay v333Willl again operate and cause the correcting mechanism 336 to move the distributor brushes another step in a forward direction. `Resistance 358 is of a value such that the holding current passing therethrough and through the left-hand winding o--relay 333 is not suiiicient to prevent the release of the reposition, to operate corrector magnet 342 overY Thus,` animpulse of positive current is sent on each reversal through the condensers 348 and 354 alternately and through an R segment, providing relay 333 is in its normal a circuit extendingfrom positive battery 347,

y through either condenser 348 or 364 and an R segment, backl contact and armature of magnet 342, conductor 360, through the righthand winding of relay 333 to negative bat tery 353. vRelay 333 operates and interconnects its armature and right-hand contact to close a circuit extending from positive battery 356, armature and right contact of the relay, conductor 361, through the winding of magnet 342 to negative battery. Magnet 342 eoperates 'and actuates the pawl and 'ratchet mechanism 344 to shift the shaft 336 for a small angular distance in a backward direction in relation to thel rotation of the shaft. This shift ofthe shaft causes the brushes of the receiving distributor 323 and brush 332 of the correcting ring 337 to move backward a corresponding angular distance.

impulses from positive battery 347 until magnet 342 hasbeen restored toits normal position. `The resistance 362 is the same value as resistance 358 and the holding current passing therethrough and the left-hand winding of relay 333 is not suflicient to prevent the release of the relay when the armature of magnet 342 engages the front contact of the relay. i

Inasmuch as the correcting apparatus at stations A and C areliden'tical with that shown in Fig. 3, their operations. will be the same as those for the apparatus at station D. No further description will be necessary. By this method of correction the motors at all the stations in the system may be operated at the one speed, and for any loss of synchronism or phase which may occur in the intervals at reversals in transmission to reception and vice versa, when no impulses are being transmitted, the correcting mechanisms at the receiving stations may automatically shift the brushes of their respectivelyassociated distributors in-both forward and backward directions during each receiving interval.

What is claimed is:

1. .In a synchronous telegraph system,a transmission -line,.distributors and brushes therefor connected to opposite ends of said line; synchronizing means for said distributors controlled by the distributor at the sending end of' said line, means for stepping the brushes around the distributor at the receiving end `in both forward and backward directions withrespect to the direction of tributors and rotating brushes therefor arrangedto operate at the one speed, a transmission line interconnecting said stations,

-means for automatically reversing the direction ofptransmission from time to time, lsyn-l chronizing means at each of said stations comprising a plurality of correcting clock- '1'otation, automatic' means for eiecting the change of brush stepping from one direction hand mechanisms for stepping the .distribu-.

tor-brushes in bothforward and backward directions with respect to the 'direction of rotation,in response to the current reversals of the incoming signals should the distributors at the receiving stations pull out of phase with the distributor at the sending station and automatic means for reversing the brush stepping operation should the brush be stepped beyond its desired phase.

3. In a synchronous telegraph system, a transmission line, a rotary distributor comprising a continuons and a segmented ring and associated with said line, a rotatable brush interconnecting said rings, two electri cally controlled clockhand mechanisms for stepping -said br-ush in responseI to reversals of current of the incoming signals in forward and backward directions with respect to the direction of rotation while it is rotating, to vary the speed of sai/d brush in accordance with the speed of the incoming signals, autolnatic means .for changing the direction of said stepping operation and means for pre-4 venting the further operation of either mecl1` anism until such mechanism is positively restored to its normal position.

4. In a synchronous telegraph system, a transmisison line adapted for simplex operation, a rotary distributor comprising a continuous and a-segmented ring associated with said line, a rotatable brush interconnecting said rings, two electrically controlled clockhand mechanisms for automatically stepping said brush in response to reversals of current of the incoming signals, in both forward and backward directions with respect to the direction of rotation `While it is rotating, to Vary the speed ot' said brush in accordance with the speed of the incoming signals, a twopo .sition relay in series with said line andresponsive to current reversals of the incoming signals, a three-position relay for operating either of said mechanisms. a circuit for operating the second mentioned relay should said brush be out of phase with the incoming signals, and means in said circuit for preventing the reopcration of said second relay until said mechanisms are fully restored to their normal positions.

In witness whereof, I hereunto subscribe my name this 25th day of April A. D., 1928.

ANDREW D. DOWD.

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