US2367042A - Signaling apparatus - Google Patents

Description

Jan. 9, 1945.

J. T. NEISWINTER SIGNALING APPARATUS Filed Dec. 23, 1941 INVENTQR JZT/V/ezswzner BY TTORNEY .signed to him. i

Patented Jan. 9, 1945 STATE-S1, -PAT-EN'T OFFICE I v 2,367,042 e SIGNALING APPARATUS I f v James T. Neis winter, South Orange, N. J., as-

si'gnor to American Telephone and Telegraph Company, a corporation ofN ew York V Application Dec mber 23, 1941', Serial- No. 424,105 12 Claims. r01. n -38 0) 7,- This invention relates signaling systems and,

more particularly, tosystems employing apparatus for producing modulated currents to be trans mitted to various partiesrconn ected to a telephone line for ringing or other purposes.

. One form of ringing system in use :at present for ringing any oneof a plurality of partieszconnected to a telephone line involves the transmission of a ringing current consisting of a predetermined I number'of dots and dashes which are simultaneously transmitted toall of the parties, the'ringing current-beingrendered audible signaling'apparatus, but the apparatus for producing speech or like signals as well as apparatus for, responding to the speech or like signals will not be shown.

Referring. to the drawing, one of a number of subscribersistations is shown including, among other things, a dial D-having a contact'which is shown in its normal or closedjposition. The subscribers station'is connected bya telephone cirat each partys station. The combination of dots and. dashes assigned to any one of the partiesis different from that assigned to any other. party.

Each party will therefore hear every ringing signal transmitted over the line toany oitheother parties and the only party who willansw'er the call will be the onewhose ringingcode has been received. This form of ringing system which cuit E'to the central ofiice; At the central ofiice there islocated a filter F, a vacuum tube amphfier VD, a relay V0, one of the windings of which is connected to the plate circuit of the vacuum tube'VD -a relayvi which is connected to one of the contacts'of the'relay Vothrough a circuit including a condenser; CA and a resistor Za, and

, includes a condenser CM, a gas tube VM, a relay may be arranged so that any party may be rung by any one of the other parties or by the central ofiice operator requiresall of the parties ,tolisten to all of the codes received so that each party may be ready to. respond only to the code, as-

office to respond to the manipulations'of the dial I at anysubscribers offices. In the proposed arrangement, each dial may be'operated a'predemoreselective and posi termined number of times, each dial operation being employed to produce a number of clicks or.

pulses on the telephone circuit, the number of clicks or pulsescorresponding-to the number dialed. At thecentral office a predetermined harmonic, of the pulses produced by the dial will be selected and caused to operate a relay for an interval of time which isdiiierent for ,the numbersto be dialed; If'the number 0 is dialed, for

example, the relay will be operated fora longer interval of time than if the number 5 is dialed. The repeated operations of the relay may then be caused tooperate a selective circuit for ringing any one of the various parties to the exclusion of all of the other parties.

This invention will be better understood from the detailed description hereinafter following, when read in connection-with the accompanying two parallel circuits which are connected to the two' contacts of the relay V1. One of these parallel circuits includes a condenser CS, a gas tube VS, and a relay S. The other parallel circuit a condenser CL, a gas tube VL and a relay L.

The-winding'of relay L is also connected to one of the contacts of the relay S which is in the other"parallelbranchJ The upper terminal of condenser CL is connected to another of the contacts of relay S. Relay L may be employed to control a relay N.

When the dial D at the subscribers station is operated in the usual way fordialing, let us say, numbers 5 or 0, the arrangement will act in response' to the dial. operations to energize the winding of the relay L at the-central oln'ce, the relay L being operated for either of the numbers dialed. The circuit may be adjusted so that the operation of the relay L when'the digit 5 is dialed will take place for an interval "of time as, for example, two-tenths of a second. The relay L will be operated for about seven-tenths of a second when the digit 0 is dialed.

When dialing No. 1, for example, the primary circuit or transformer A will be opened once and closedonce bythe contacts of dial D. Upon the of transformer A upon the closure of the primary circuit. Each of the two surges of current in the primary of transformerA will produc a comdrawing which illustrates thedialing apparatus at each subscrib'ers station and apparatus at the central omce whichwill respond to the dial oper'ations.-Thedrawingshows only the dial or plete and independent pulse of current in the secondaryof transformer A. Thus by dialing No. 1, two complete pulses of current will be transmitted by transformer-,A to line E. Hence by dialing No. 5, ten complete pulses .of current will be transmitted over line E. Furthermore,

by dialing No. (which is the equivalent of dialing a No. twenty complete pulses of current will be transmitted over line E. These pulses of current are, of course, not pure sine waves, but transients. 'As the dial D is of the type which is generally timed to produce these twenty pulses in about one second, the transients produced and transmitted over line E occur at the rate of twenty per second. Similar transients are produced upon dialing any other number. However, 10

the number of transients produced and transmitted over line E will simply be twice the number dialed by dial D. Hence when dialing N055, ten transients will be produced and transmitted over line E, and these ten transients'will occur} within about one-half of a second. v

The filter F at the central ol'fice may comprise one or more anti-resonant circuits similar to the one shown, the anti-resonant circuit orcircuits being tuned to, for example, 1000 cycles-which may becon'sidered to be the fiftieth harmonic of the 'pulses'produced by the dial. The vfilter F will transmit the 1000 cycle harmonic to the tube-VD to be amplified thereby. The :upper winding of relay V0 which is a. polar relay will receive the 1000 cycle current which is interrupted at the cycle rate by the dial contact and the armature of the relay V0 will therefore operate and release at the 20 cycle rate in accordance with the 1000 cycle current which traverses its Winding.

Thus the relay Vo will operate and release once for each dial click or pulse. Inasmuch as two clicks orpulses are produced for each unit of the number dialed, as already stated, the relay V0 will operate twice for each unit ofthe number dialed. It will be shown hereinafter that the circuit interconnecting the armature of relay V0 and the winding of relay L is set up. so that the dial clicks or'pulses may operate the relay L for .difierent intervalsof time, the intervals depend ing upon the number dialed. The interposed circuit is also arranged so that speech and other extraneous voltages will be unable to actuate the relay L.

During the idle condition of the circuit the l contact'of the dial D is closed and no current will be flowing over the telephone circuit Relay V0 will be held released by the bias current con tinually traversing thelower Winding of relay V0, the armature of relay V0 resting upon its contact 1 S asshown inthe drawing. No current will be flowing through the winding of the relay V1, its armature also resting against its contact S. .The condenser CS will -however, be charged to the voltage of the battery 131.. This voltage wi11=be hi her than that required to ionize the gas between the input or control electrodes of the tube VS and, hence, the gas between these electrodes will be ionized. The relay S will be energized by the flow of current from battery 32 through a circuit completed through the armature and contact S of relay V0, the winding of relay S, the armature designated I of relay S and its make contact and ground. With the winding of relay S energized, ground will be connected to theanode of tube VS by armature l' of relay S and, hence, no current will flow through the output circuit of tube 'VS. The operation of relay S transfers the flow of current from battery 32 (through the winding of relay S) to ground so electrode will be connected toground through the armature 2. of relay S and its make contact.

- With condenser CL discharged, the tube VL will be deionized and, therefore, the relay L will be released. I Relay N will also be released and lamp P extinguished. Both tubes VM and VL are deionized for the further reason that plate voltage -from batteryT-Bncannot reach these tubes, the

" tactof armature 30f relay S.

During the idle condition of the circuit, more- Assume now that the dial D of the subscribers station is rotated in a clockwise direction for dialing. any. desired .digitzand thatit is then released so that the dial may rotate in a counterclockwise idirection to open and close its contact several times dependingon the number dialed. As thedial': contact opens, it produces a click which interrupts the currentflow over the primary winding of transformer A. The interruption of-the primary circuit will induce a current in the secondary circuit which is of a frequency dependent upon the constants of the dial apparatus. as already stated. With .a standard dial the secondary ofthe transformer. of the circuit will have induced therein a 20 cycle current along with itsnumerous harmonies.- The fundamental andall harmonics will be suppressed by the filter F except/the fiftieth harmonic which is of 1000 cycles, .the .latter current being then transmitted to the vacuum tube VD and'amplified thereby. The amplified current will flow throughithe upper or operating' winding-of the relay V0. This current will produceia'magnetic effect in the upper or operating'winding of relay V0 to' overcome the opposing magnetic effect of the biasing current flowing throughthelower-winding of relay V0 and therebycause the armature of the relay to move to its contact M. The closure of contact M bythe'armature of relay Vo will then allow current toflow frombattery B2 through the impedance Zr and through the winding of relay V1, thereby causingthe: armature of relay V1 to close its contact M. At the same time the relay S will become releasedldue tothe opening of the circuit between battery B2 andthe winding of relay S 'denserCS will be grounded and the condenser will then. discharge so that the gas between the input or control electrodesof'. tube VS will become deionized. Moreover, the-removal of ground from the upper plate-0f condenser CM upon the operation -.of relay Vi will allow condenser GM to become charged bycurrent supplied by battery Ba. Upon the release .of the relay S the positive potential of-battery B4 will be applied through the (armature 3 .of the relayS and th Winding of relay M .totheanode of tube VM. However, the charge'on condenser CM will not be raised to the value required to ionize .the gas between the input electrodes-of tube VM unless relay V1 operates for a longer timethan the time required for one click orypulse of a standard dial. Hence relay M will remain unoperated. The release of relay S also removes ground from the upper plate of condenser -.C L theretofore provided throughthe armature .2 ofrelay'S, thereby allowfurther described.

ing condenser CL also. tocharge. A positive potential is likewise applied by battery B4 to'the anode of tube VL through the winding of relay L, but for similar reasons tub VL will not be fired and relay L will therefore remain released.

: At the termination of the first click or pulseof the dial, current will cease to flow through the primary winding of transformer A and, hence,

and insufficient to overcome the biasing effect of the current traversing the lower winding of this relay and hence relay V will'remain released. While relay V0 is released, battery B2 will be disconnected from the winding of relay V1, thereby releasing relay Vi, the armature of relay V1 then a closing its contact S. At the same time the positive potential of battery B2 will be applied to the anode of tube VS through the armature and contact S of relay V0 and the winding of relay S. As

the armature of relay V1 also leaves its'contact M the condenser CS-will then be charged by current supplied by battery B1, but the tubeVS will remain deionized because the voltage on condenser CS will be insufficient in the time after the first click or pulse to reach the value re- F quired to ionize the gas between the input electrodes of tube VS.- Also the condenser CM will be discharged through the circuit provided by the armature and contact S of relay V1. v

As the dial contact becomes closed at the end of the first unit of the number;dialed,'the dial remaining in rotation thereafter, another click or pulse will be produced. This will result in the transmission through the filter F of a'similar 1000 cycle current. The armature of relay'Vo will again move to its contact M and the cycle of events similar to that already described for the opening of the dial contact which produced a like current will be repeated, but this need-not be The same series" of events will take place with each? opening and closure of the contacts of the dial D as the dial rotates in a counter-clockwise direction after it is released. It will be observed, however, that the relay S, though normally operated in the idle condition, becomes released as the dial rotates to close its contact and relay S stays released throughout the movement of the dial.

After a predetermined intervalof time as, for

- example, about three-tenths of, a second after the dial D has first opened its contact, the condenser CL will reach a voltage upon charge whichis suflicient to ionize the gas within the control gap of the'tube VLF This time interval is dependent upon the size of the condenser, the potential of the battery B5 and other circuit constants. vAfter the tube VL becomes fired the relay L will become operated due to the flow of current from battery B4 through the circuit established by armature 3 of relay S after relay S has become released. The relay Lwvill remain operated until dial D has come to rest and finally closed its contact. v

Upon the operation of relay L, relay N will be operated, current being'supplied to the winding.

of relay N fromv battery B7 throughthe lower armature and its front contact. In. operating, relay N becomes locked in its operated position, the-locking circuit comprising battery E8, the upper armatureand make contactof relay N, coninafter.

tact X1 of jack J,.the winding of relay N and ground- The armature of relay N may also be used to complete a circuit to lamp P to apprise the operator that the subscriber has signaled her.

The operator may then insert her plug into jack J toconnect her cord to line R. The insertion of her plug into jack J momentarily breaks the holding circuit for relay N and, therefore, the latter relay releases, extinguishing lamp P, The

subsequent'reoperation of relay N makes possible a recall signal by re-illuminating lamp P while the operators plug is still in jack J.

When the dial D closes'its contact at the end of its rotation, the relay V0 will thereafter become released, which in turn will cause the relay V1- to become released. The relay of relay V0 will allow the positive potential of battery B2 to be applied through the armature and contact S of relay V0 and the winding of relay S to the anode of tube VS. As the charge on'condenser CS reaches a sufiicient value, the tube VS will become ionized, the ionization occurring after a predetermined interval of time as, for example, about 35 milliseconds after the dial has come to rest. As the tube VS becomes ionized current will flow through the winding of relay S, causing its operation. But as relay S operates, it connects the anode of tube VS to ground through its armature I and itsmake contact The armature of relay S then opens the circuit between battery '34 and the anodes of tubes VL and VM, causing both tubes to become deionized. As tube VL becomes extinguished, the relay L will become released and remain released thereafter. Thus the circuit arrangement will be returned to its idle condition.

M It will be observed that the arrangement at the central oflice includes a filter F which is tuned to about'lOOO cyclesand a network interposed between the filter F and relay L which acts like a 20 cycle filter. This combination of circuits is designed to prevent voice currents from operating the relay L, as will be explained here- The network interposed between filter F and relay Ldistinguishesbetween the series of clicks or pulses produced by dialing the number 5, for example, and the series of clicks or pulses produced by dialing 0, the distinction being based upon the fact that the first series of clicks or pulses-which may be approximately five-tenths of a second longmay operate relay 'L for, let us ,say, about two-tenths of a second, while the second series of clicks 0r pulseswhich may last about one second-may operate the relay L for about seven-tenths of a second.

It has been pointed out hereinabove that relay V1 is operated in response'to each operation of relay V0. The condenser CA is interposed be tween the armature of relay Va and the winding of relay V1 as already noted. This condenser in discharging holds the relay V1 operated for a few milliseconds after relay V0 has released. The value of the hold-over feature is such that if the relay V0 operates faster than say 25 times per second, the winding of relay V1 will then receive suflicient current from condenser CA to remain in an operated condition during the repeated releases of relay V0. For vibrations of the armature relay V1 will fix the lower limit of thefilter net-' work as will be explained hereinafter.

- per second, the interval betweenthe clicksduring which time, the relay V1 is released-Will be long enough to permit the condenser CS to be charged by current from battery B1 to a voltage sufficient to ionize the control gap of the tube VS. When this happens the relay S will become operated, thereby grounding the condenser CL through the armature 2 of relay S. Hence for clicks or pulses of such a slow rate the relay L will remain released.

The arrangement is thus tailored to fit the series of pulses transmitted over the telephone circuit E and applied to the operating winding of relay V0. Whenever the interval between the clicks or pulses is too long'the tube-VS Will become ionized and prevent relay L from operating. On the other hand, whenever the durations of the clicks or pulses are too long, the tube VM will become ionized and likewise prevent relay L from operating. Whenever the Spaces between the clicks or pulses and their durations are both too short-Which will be the case for a fast dial or for any low frequency effect induced in the telephone circuit Ethe relay V1 will remain operated and tube VM Will become ionized. This will result'in maintaining relay L released.

When voice currents reach the telephone circuit it will happen in practically all cases that the pause between the syllables will be long enough to cause tube VS to become ionized. On the other hand, one of the syllables of the speech currents may be so prolonged as to cause the tube VM to become ionized before the interval of .time such as three-tenths of a second, which is required to elapse before relay L operates. In either case relay L Will not become operated.

It has been shown hereinabove that with each operation of the dial the relay L will be operated for an interval of time which is either long or short depending upon the number dialed. If the dial were operated four times, for example, the relay L will then be operated four times and in each case the duration of the operation of relay L will depend upon the number dialed. Thus the dial may be successively operated to produce any desired combinations of long and short pulses.

The condenser CM and tube VM in the upper branch of the arrangement are employed to prevent currents derived from the clicks or pulses from operating relay L if these currents last longer than about 20 milliseconds. The condenser CS and tube VS in the lower branch of the arrangement are employed to prevent pulsesderived from the clicks or pulses from operating relay L if the intervals between the clicks or pulses last longer than about 35 milliseconds. Relay L is thus protected againstall pulses except those derived from suitable dial clicks from which 1000 cycle current interrupted about 20 times per second is derived.

shown) which may be connected to conductors y1y2, the voltage being applied for an interval I of time depending upon the length of the operation of relay L. In the latter situation relay N and its related circuits maybe omitted. Apparatus for responding to any such series or combinationof three, four, or more pulses-s-which may be any desired combination of long and short pulses-are shown and described in applicants copending applications, Serial Nos. 373,573 and 373,574, filed January 8, 1941, and Serial No. 399,782, filed June '26, 1941, now respectively, Patents 2,334,574, 2,334,575 and 2,300,003 and the selecting or switching circuit there shown may be considered as part of this specification. The selecting or switching circuit will be connected to conductors 111 and 112.

The arrangement of this invention may therefore be used either to respond to dial clicks or pulses to operate relays L and N and illuminate lamp P to apprise the central office operator that a call is being transmitted or (Without relay N and lamp P) to apply voltage a number of times to conductors 111 and 212 to produce pulses to operate a selective circuit for connecting the subscriber to any one of a plurality of diiTerent lines. In either case the control of the circuit is practically entirely exercised by the subscriber in manipulating the dial.

.While this invention has been shown and described in certain particular embodiments merely for the purpose of illustration, it will be understood that the general principles of this in-. vention may be applied to other and widely varied organizations without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

1. In a signaling system, the combination of a pulsing device, a source of direct current, a transformer having its primary winding connected in series with said source of current and said pulsing device, means responsive to the operation of said pulsing device to produce in the secondary Winding of said transformer a series of pulses of alternating current of a frequency which is harmonically related to the number of current spurts produced by said pulsing device in 'the primary winding of said transformer, one

pulse of said alternating current being produced in the secondary winding by the interruption of the flow of current from said source in the primary winding and another pulse by the reconnection of said source to said primary winding, means responsive to the ulses of alternating current in the secondary winding to produce a pulse of direct current, said latter means including means to prolong the pulse of direct current so that its length corresponds to the number of alternating current pulses in the secondary winding, and -a translating device responsive to said pulse of direct current.

2. In a signaling system, the combination of a dial having a contact which may be repeatedly opened and closed, a source of direct current voltage, a transformer having its primary winding connected in series with said dial-and said sourceof voltage'so that a plurality of'spurts of current may flow in the primary winding with 'each operation of said dial, means responsive to the repeated opening and closing of the contact of said dial to derive fromsaid spurts of current a seriesof pulses of alternatingcurrents said alternating currents being harmonicallyre lated to the number of said spurts of current produced by said dial device, means responsiveto the pulses of alternating current in the secondary windingto obtain a single pulse of direct current of a duration which corresponds to the number of alternating current pulses, and apparatus controlled by said pulse of direct current.

3. Ina signaling system, the combination of a dial having a contact which may be repeatedly opened and closedf a source of unidirectional voltage, a transformer having its primary winding connected in series with said source of voltage and said dial so that a plurality of spurts of current will traverse the primary winding with each operation Ofsaid dial, means responsive tothe repeated operations of said dial to derive '5. In a signaling system, the combination of i a dial having a contact which may be opened and closed one or more tim'es'during each operafrom said spurts of current a plurality of groups of pulses of alternating current of a frequency which is.a harmonic of the number of said spurts of current per second, a pulse of alternating current being producedin the secondary winding 01 said transformer by the interruption of the flow of current from said source of voltage to said primary winding and another pulse being produced in said secondary winding by a reconnection of said source of voltage to said primary winding, means responsive to eaclr group of pulses of alternating current to obtain a pulse of direct current, and a circuit controlled by said pulse of direct current.

' 4. In a signaling system, the combination of a dial having a contact which may be opened and closed during each operation of the dial, a

source of unidirectional voltage, a transformer having its primarywinding connected in series with said dial and said source of voltage so as to produce a plurality of spurts of current in the primary winding of said transformer with each.

operation of said dial, each operation of said dial opening and closing said contact one or more times, means responsive to the repeated operations of said dial to produce in the secondary,

winding of said transformer a plurality of groups of pulses. of alternating current of a frequency which is harmonically related to the number of said spurts of current per second, a pulse of alternating current being produced in the secondary winding upon the interruption of the flow of current from said source of voltage through the primary winding of said transformer and another of said pulses being produced in the secondary winding of the transformer by the resumption of the flow of current from said source through the primary winding of said transformer, the number of pulses of alternating current in each group being determined by the number of times the dial contact is opened and closed in each operation of the dial, means responsive to.

of current in the primary winding of said transformer with each operation of said dial, said. spurts of current in-the primary winding ofsaid transformer producing a plurality of pulses of alternating current in the secondary winding of said transformer, a pulse of alternating current being produced in' the secondary winding of said transformer upon each interruption of the flow of current from said source through said primary winding and another pulse being produced upon each reconnection of said source with said primary winding, meansfor obtaining from said pulses of alternating current in the secondary winding of said transformer pulses of a predetermined harmonic of said alternating current in the voice frequency range, and means responsive to the pulses of said harmonic current to obtain a pulse of direct current of a length which is proportional to the number of pulses of the harmonic current.

6. In a signaling system, the combination of a dial having a contactv Which may be opened and closed one or more times during each operation thereof, a source of unidirectional voltage, a transformer having a primary winding connected in series with said dial and said source of voltage so as to produce a plurality of spurts of current in the primarywinding of said trans: former with each operation of said dial, said spurts of current in the primary winding of said transformer producing a plurality of pulses of alternating current in the secondary winding of said transformer, a pulse of alternating-current being produced inthe secondary winding with each opening of the circuit of said source of voltage and said primary winding and another pulse of alternating current being produced in the secondary winding with each reconnection of said source of voltage and said. primary winding, meansfor-obtaining from said pulses of alternatingcurrent in the secondary winding of said,

transformer pulses of a predetermined harmonic of said alternatingcurrent within the voice frequency range, means responsive to the pulses of.

said harmonic current to obtain a pulse of direct current of a length which is proportional to the number of pulsesof harmonic-current, and a circuit controlled by said pulse of direct current.

, 7; In a signaling system, the combination of a subscribers station, a central omce, and a line interconnecting said subscribers station and said central ofiice, the subscriber's station including a dial having a contact which may be opened and closed one or more times during each operation thereof, a source of unidirectional voltage, and a transformer having its primary winding connected in series with said source of voltage and said dial so as to produce a plurality of spurts of current in the primary winding of said transformer with each operation of said dial, the secondary winding of said transformer being connected to said line, said spurts of current in the primary winding of said transformer producing in the secondary winding of said transformer pulses of alternating current of a frequency which is harmonically related to the rate at which said spurts of current are produced in the primary winding Q said transformer, the number of pulses of V alternating current being determined by thevnumber of times-the contact of said dial is opened and closed during any operation thereof, said pulses of alternating current being transmitted over said line to the central oifice, said central ofiice including means responsive to received pulses of alternating current to Obtain a pulse of direct current of a length which is proportional to the number ofpulses of alternating current, and a circuit controlled by said pulse of direct current.

8. In a signaling system, the combination of a dial having a contact which may be opened and closed any desired number of times, means res sponsive to each opening and closing of the dial contact to produce two. pulses of alternating current, first and second condensers, means for charging the first condenser to a predetermined voltage whenever each pulse lasts longer than a predetermined interval of time, means for charging the second condenser to a predetermined voltage when the intervals between the pulses exceed a predetermined interval or time, a circuit to which voltage may be capplied,and means for preventing said voltage from being applied to said circuit whenever the charge on either of said o nse s eac es s d red te mined a e- 9. n a gna n s s em, he m n n of a dial having a contact which may be opened and closedany desired number of times, means responsive to each opening of said dial contact to produce a pulse of alternating current, means responsive to each closure of the dial contact to produce another pulse of alternating current, first and second condensers, means for charging the first condenser to a predetermined voltage whenever any pulse lasts longer than a predetermined interval of time, means for charging the second condenser to a predetermined voltage whenever the intervals between the pulses last longer than a predetermined interval of time, a translating device, means for operating said translating device only when the voltages on said condensers do not reach the predetermined values, and'means for preventing'the operation of said translating device'whenever the voltage on either condenser exceeds the predetermined value.

10. In a signaling system, the'eombination of adevice'having a contact which may be opened and closed any desired number of times, means responsive'to the operation of said device to'produce a plurality of pulses of alternating current,

: means for operating said translating device in response to said pulses of alternating current, and means for preventing the operation of said translating device whenever either of the gas tubes has been fired.

1.1. In a signaling system, the combination of means for producing a predetermined number of direct current pulses in regular succession, a transformer having its. primary winding connected in series with said pulse producing means, a pulseof alternating current being produced in the secondary winding of said transformer from each direct current pulse together with the harmonies of said alternating current, a line connected to the secondary winding of the transformer for transmitting said alternating current pulses and the harmonics, afilter for selecting from. the received pulses only those pulses which are of a predetermined harmonic of the alternating current to the, exclusion ,of all other ourrents, a relay, means for actuating said relay in response to the receipt of said selected harmonic, and means interposed between said filter and said relay to prevent the operation of said relay in response to currents other than pulses of the selected harmonic.

12. The combination of means for producing alternating current interrupted at regular intervals, first and second condensers, first and second gas tubes controlled respectively by said condensers, means responsive to the length of each pulse of alternating current to charge said first condenser, means for firing said first gas tube when the chargepn said first condenser exceeds a predetermined value, means responsive to the interval between successive pulses of alternating first and second condensers, first and second gasa.

for firing said second gas'tube when the charge on said second condenser exceeds a predetermined value, a translating device, means responsive to the pulses of alternating current to operate said translating device, and means responsive to the-firing of either gas tube. for preventing the operation of said translating device.

JAMES T. NEISWINTER.

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