US1991082A - Television apparatus - Google Patents

Description

Feb. '12, 1935. F. CONRAD 1,991,082

I TELEVISION APPARATUS Filed Jan. 1s, 1929 5 sheets-sheet 1 A'TTORNEY Feb: 12, 1935. F CONRAD TELEVISION APPARATUS Filed Jan. 18, 1929 5 Sheets-Sheet 2 INVENTOR Fra/7,? Conrad.

ATToRNEY Feb.- 12, 1935. F. CQNRAD TELEVISION APPARATUS Filed Jan. 18, 1929 5 Sheets-Shea?l 3 2 Seconds v INVENTOR Y Frank Conrad.

\ AT'TORNEY 1 Feb. 12, 1935. F, CONRAD TELEVIS IION APPARATUS 5 sheets-shet 4 Filed Jan. 18, 1929 i-IIMII'IIIIIIF v QI L INVENTOR 777mm? Conrad.

f BY

AT'TORNEY W WQ 2 gmk.

AS r Feb-#12., 1935. F. CONRAD 1,991,082

TELEVI S ION APPARATUS Filed Jan. 18, 1929 5 Sheets-Sheet 5 aa fl INVENTOR Fran Conrad.

`ATTORNEY Patented Feb. 12, 1935 l i l i TELEVISION ArrARn'rUs o Frank Conrad, Wilkinsburg, Pa., assignor to West- 1 inghouse Electric & Manufacturing Company, a corporation of Pennsylvania Application January 18,`

lMy `invention relatesto television and more Y particularly to a radio transmission system fork causing `distant images to appear upon a screen. yThe object of my invention is to'provide im.-`

5 proved apparatus for synchronizing the scanning discs" in a system ofthe above-mentioned Ype- `A further object of my invention is to provide a receiving apparatus for yprojecting the transmitted image upon a screen. v i

i `A still further object of my invention Iis to provide an improved scanning-disc structure. r f A still further object of my invention is to pro-4 vide an improved system for simultaneously transmitting images from ajplurality of widely spaced transmitters.

In practicing my invention, I employ scanning discs at transmitting and receiving stations, the

scanning discs being driven by synchronous mo-l tors controlled by a single source of alternating current having a comparativelyhigh `frequency, o

preferably a frequency `near the upper limit of` the audio frequency range utilized in broadcasting musical programs. The frequency of the is multiplied and the current transmitted from the transmitting stations as a carrier wave. The v alternating current is maintained at aconstant frequency by means of a system including an electric clock and a synchronous motor which, periodically, applies heat to a tuning fork, as will be more fully described hereinafter.`

Instead of employing a synchronous motor of the usual type for driving a scanningdisc, a softiron ring, having teeth `on its outer edge, is `attached to the'scanning discso that the scanning disc itself constitutes a part of vthe rotor of the synchronous motor.

By employing a mercury-arc `lamp or a gas lamp, such as a neon lamp, connected to the output of the receiving apparatus through a specially designed circuit, a light of sufficient inten sity is obtained to throw a View of the transmitted image upona screen. In thisV way, a picture of larger dimensions is obtained than has been possible with most systems formerly constructed. f f i Other features and advantages of my invention f will appear from the following description, taken 0 in connection with the accompanying drawings in which:

'.Figure l isa diagrammatic view of the apparatus and electrical connections employed in` a system constructed in accordance with my in- \vention;"

current from the same alternating-current source `pling meansi andradiated.'I Thepicturefcur 1929, serial No. 333,374

Fig. 2 is an end elevational view "of a scarl-ffA ning disc and a synchronouslmotor constructed; inaccordance with my invention;

rig. e is a diagram to aid in describingftnei* operation of the constant-frequency,generator; Fig, `'l is a diagrammatic viewy of ,theheatingr box and heating apparatus Aforthe oonstant-fre` quency-generatorjtuning fork;

Fig. 8 is anend elevational View of fork and its holder and driving.mechanisn 1`;'` Fig; 9 is a sectional View, taken 'alonga linef; corresponding to the line IX-IX of Fig. 8.

`Referring to Fig. 1, the system comprises two; widelyspaced transmitting stations-station1`A` 25" and station B-With .their ,correspondingfreceivf, ing stations-stationl andstaton B.` l.

A carrier wave of frequency ,fz is supplied from` a source `1 of alternating current having a suby i stantially constantfrequency, `prefer bly above 36' the range commonlyI utilized when' transmitting i musical programs, anda frequency multiplier The frequency` employed in the example being de'- f scribed is 5000` cycles l"per second.' The frequency of the. Sooo-Cycle currentis multiplied tothefre; 35" jf quency fzby anysuitable frequency multiplier andfthe current `then supplied to an amplifiereV modulator 3. ",An .example of a frequency "multi-f@ plier which may be employed in my system de-f` scribed in Patent 1,646,438- granted` October 2.5.j40 l l92'toH.`A.Affel. ,A q The picture current, containing a rangeoof freiy j quencies representedby fp, is also supplied toY the ampliiier-rrodulator 3,` andthe resulting :nod

lated carrier,` represented by favfzifp, is supplied"L "i:

to a" transmitting antenna 4`by any suitablecoul rent of frequency fp is obtained by `means 'o'fapfv 1 paratus including aj scanning disc Gand 'aphotojf' i electric cell17. The scanning'dsc 6`is'ofa Well 50 known type having holes located inja `spiral,

around its periphery, as shown in detail in FigsQzZ". and 3i., n beam of light from a light source; 8' is" passedl through these holes uponthe imagejgtow `be transmitted' and isreflected'to the photoelec-r 55 the tuning` V261 the modulated carriervvavef1, f1i5000.

tric cell 7, the current output of which varies in accordance with the lightintensity. The scanning disc 6 is rotated at a high speed by means of a synchronous motor 10 of the phonic-Wheel 5 type connected to the 500G-cycle source 1 by means of a metallic line 11 and amplifiers 12 and A carrier current f1 is modulated by the 5000- cycle current land radiated from an antenna as The apparatus for transmitting the'modulated carrier wave f1, f1i5000 comprises an amplifiermodulator 14 to which is connected anV oscillatorgenerator 15, supplying a current of frequency f1, and the 500G-cycle generator 1.' The amplifier-modulator 14 i's connected -to an antenna 15 by any suitable coupling means 17.

The receiving station A', comprises a scanning disc 18, similar to that at the transmitting stav tion, and a source of light 19, the intensity of which is varied in accordance With the modulated carrier wave j2.'1hemodulated carrier Wave f2 r isvpicked up Vby thereceiving antenna 20, demodu-V lated by a detector 21`, and theresulting picture current fp 4ampliiied'by a vacuum-tube amplifier 22"andA impressed'upon a mercury-arc lamp 23 through. a step-down transformer24 and a condenser 25.' The mercury-arc vlamp 23 is connected to adirect-current supply through an in- 30.l Yd'u'ctance 26, aresistance, 27 andra connection 28.

The scanning. disc y18V is driven by a synchron'iu'sV motorl 29,` similar to motor l0, connected to aV circuit' dwhich `receives and VVcle'zn'odulates the modulated carrier Wave f1. By means ofthis 35, circuit, the carrier` Wave fris picked up by the antenna 31, demodulated by adetector 332, and the iresulting 500G-cycle current passed ythrough an amplifier 33`and' 'a50`00-cycle iilter 34 to the synchronous motor, 29.. Consequently, thescan- 4a.,ningdisc 18, at the-receiving station, is run in synchronism withf the scanning disc 6 at the transmitting station, and a reproduction of the imageappearson a. screen 35. Obviously, the scanning` discs 6'and18 will remain in synchro- 4lnis'mso. that the, image Will'be reproduced even "though the frequency of the constant-frequencygenerator'output varies slightly.

The lutilization ofa mercury-arc lamp 23, as illiistrated,` is desirable" since it isr possible to .caus`e. a Wide' variation in the light intensity` by means of' a comparatively small energy output from theamplifier 22 in the radio-receiver circuit. 1 This' is possible because the characteristic of "a mercury=arc lamp is such that the voltage E-...impressed across the, tube electrodes remains ""nearlyfconstant'even though the Value of the currentA passing through the tube varies Widely. For.example, if' the. current consumption of a tube is `4`amperes, 4with' a. direct-current voltage offi'f'volts impressed upon.. the tube electrodes, th'curren't throughthe tube may be decreased f to ,3..amperes or increased to 5 amperes by a change of1 only 1 or 2 'voltsin the applied directcurrent voltage. Accordingly, by employing the .stfep-.d`own transformer 24, a comparatively high secondary current'having a small voltage variation can beobtainedfrom the thermionic-tube amplifierj22'and'employed to produce large current.`changes inthemercury-arc lamp 23. 7d'.-- Since gas lamps, lsuch as the neonlamp, have characteristics similar tothe mercury-arc lamp, tlieymaybe substituted for the mercury lamp, ifld'sirdj. l

IA svtepedown-transfo'rmer ratioof 20 to 1 has 75,` been .-foundfsatisfactcry, .f although, obviously, the

ratio may vary within wide limits and should be determined by the characteristics of the particular lamp being employed. The Values of capacity, inductance, resistance and direct-current-voltage supply employed in the circuit, like- Wise, are not critical. The following values have been found satisfactory: condenser 25, 300 microfarads; inductance 26, 3 henries; resistance 27, ohms; and D, C. voltage supply, 110 volts.

The transmitting station `B is employed for broadcasting the image 9 located at the station A o-ver a section of the country remote from the Y, section covered by station A. Station B transmits on a carrier Wave having the same frequency as that transmitted from station A. This carrier wave is obtained by receiving the modulated carrier Wave f1 on an antenna 36, demodulating it bya detector 37, and multiplying the frequency of the resulting 500G-cycle current by a frequency multiplier 38. The resulting carrier Wave f2 is impressed upon an ampliier-modulatorBB, modulated by the picture current fp vwhich is supplied to the amplifier-modulator 39 fromvthe station A over a metallic line 40, andtransmitted from an antenna 41. A radio repeater .station 42, located in the vicinity of station B, broadcasts a carrier Wave f3 l modulated by the 500G-cycle current, represented by fs, fai-5000, fordriving the scanning discs at1 the receivingstation B' located inthe-vicinity of station B. The repeater station 42 is-Of theV Well known type which receives a modulated carrier Wave'of one frequency, amplifies it, changes the frequency of the carrier Wave and re-radiatessitt ln the circuit illustrated, the modulated carrier f1 is picked up by a' receiving antenna 43,'transmitted to the amplifying and frequency-changing unit` 44 through a transformer or other couplingl device 45 and re-radiated from a transmitting antenna 46.

The receiving' station B', Whichreceives the4 image 9 transmitted from station B, identical With receiving station A', except for the fact that the receiving circuit is tuned to the carrier-'Wave frequency vf3 instead of tothefre-V quency f1.

One of the main reasons `for choosing a frequency of 5000 cycles per second for driving` the scanning discs is that it is a frequency lto which radio-broadcast receivers are comparatively insensitive, while, at the same time, it is a frequency Which can be transmitted overa high grade telephone line and through the repeater apparatus associated therewith. The metallic line 1i connecting the 500G-cycle supply 1 `to the View of this fact, it is both economical andconvenient to have a system in which existing `55 synchronous motor 10 at station A may be severalmiles in length, since the studio or the event toV telephone lines andtheir associated apparatus` may be utilized, either without modication or with the associated apparatus only slightly modified. i

The fact that the frequency of 5000l cycles per i pear in the output When it is desired to receive ,K

used for.:` effective, transmission. frequencies in the `neighborhood `of 5000 cycles and demodulate i a different carrier frequency modulated by speech or music. The 5000-cycle frequency, however, is so high that it is above the- `frequencies of undesirable noise. For this reason,

many radio receivers and loud speakers are designed to cut-off at a frequency below 5000 cycles per second. i

per` second snot so high but what it can be transmitted over a telephone line designed fortransf mitting musical programs. Even though the tele. phone linemay not eciently transmit a current ofthis frequency, sufficient amplification may be Furthermore,

per second arelow enough so that a telephone line can easily bemodified, if necessary, to transl tations-has further advantages in that it permits 5511 adapted for the `double use of synchronizing `the havingapproximately the same diameter as that of the scanning disc. This makes possiblethe i use of a synchronous motorhaving so many rotor l f teeththat it may slip one rotor tooth and yet not shift the image toomuch to one side on the screen. f .i

Itaalsc permits the utilization of the frequency of 5000 cycles persecond,the harmonics of which may be employed forchecking the carrier frequencies of broadcast stations-these carrier frequencies being spaced kilocycles apart.` While the harmonics of `certain frequencies below 5000 cycles per second (of the frequencies of 1000 and 2000 cycles per second, for example) would in-` clude frequencies equal to those of the broadcast carrier waves, the harmonics would be so closetogether that they could not be readily identified. On `the other hand, the frequencies above 5000 cycles per second, which have harmonics suitable for checking broadcast carrier Waves, are too .high to be transmitted over a telephone line. For'these reasons, the 5000-cycle frequency is peculiarly scanning disc in a television system of the type above-specied and of checking `the frequencies,

of broadcast carriers.`

Referringto Fig; 4,'which shows thestructure `employed at transmitting station A, the scanning vingfconnected to the scanning disc 6 by a belt 51 and by means of asynchronous motor 10. `The motorv may be of any type the speed of `which caribe adjusted to drive the scanning disc 6'at` approximately the correct speed. The object in employing the motor 50` is to reducethe power which mustbe furnished by the synchronous motor 10. The synchronous motor 10 has a rotor which comprises a laminated iron ring 52 having teeth on its periphery and so bolted ort riveted to the scanning disc 6 thatthefdisc forms part `teeth `63 projecting from its periphery.

nous motor 10are wound on soft-iron pole pieces supportedby a member 54bolted `to one ofthe i of `.the rotor. The Vstator coils 53 of the synchro-5` supports 48. This motor is of the phonic-wheel i type and is1 shown in detail in Figs. 2 and 3.

A vibration dampener 55 for reducing the effect of hunting ofthe synchronous motor 10 is employed. The dampener comprises a balance wheel ,which the scanning disc 6 comprises a disc ofi i i ;v i i metalor any other suitable material having 60 Atthe same time, a frequency of 5000 cycles i holes locatedI around its periphery in the form 4`cfa spiral., Because ofthe difficulty of making` square holes `of thegdesired smallness in a disc` .over the large holes 59 and held in position by,

Square holes 61 are punched in the i screws 62. thin plates 60 in order to give the maximum amountof light with maximum detail. After the thin plates 60 have been mounted on the disc 6,- thesquare holes 61 are lined up exactly by optical..

The synchronousmotor 10 for driving thescani ning disc Siincludes'the scanning .disc itself,"as i partof the rotor, and a rotor element riveted `or bolted to the scanning disc.- `This element comprises a laminated ring 5,2 of soft iron having i InY the example illustrated, the rotorhas 300 teeth andra `synchronous speed, therefore, of 1000 R.` P. M. when the 5000-cycle supply 1 is .connected lto it` `through a vacuum-tube amplier.- It will be ynoted that the synchronous speed of the motor is one-halfl the value it `would be if the `5000--Vv cycle current were supplied to it without a directcurrent component,` since such a component prepieces v(i5-.adjacent to the rotor teeth 63.` The llaminated aro 64 is supported by a member `54 attached `to the support 48. `A coil 66V is wound on eachstator pole 65,'and the coils 66 are con-i.4

nected in Aseries in such direction that, atlany instant, the adjacent poles are of unlike polarity. In order to provide space for thestator coils 66, there is only one stator pole to every three rotor teeth` thesynchronous speed of the motorfbe-` ving determined bythe number of rotor teeth.

Obviously, the stator may comprise a longer or:

a shorter laminated arc 64 than the one illustrat-` ed Vor, if desired, it may .comprise two or more laminated arcs. The modification illustrated is; `one of the preferred forms, since the structure necessary for supportingthe stator is simple and` compact. i Y

In Fig. 2a amodied arrangement of the rotor structure is shown. In this modification. a soft-l iron ring 52, having the projecting teeth 63, is

mounted outside the spiral of holes 61 in the disc volve'd in employing the modified 4structure is thatgin order to obtain a picture of the same siz'e and havingthe same detail as is obtained when using the other structure, the scanning v holes must be placed in a circumference having the same diameter as that 'of the holes in that structure; In some cases, therefore, an unduly largelv disc would be required. A synchronous motor constructed in the manlo'ne'r above-specified lprovides an economical and efcient means for driving a plurality of scanningvdisos in synchronism.

The structure and electrical 'connections of the 5,000-cycle generator 1 employed in the system `fdescribed above are shown in Figs. 5, 7, 8 and 9. While a generator which will supply an output having -a substantially constant frequency is not essential for synchronizing purposes, it is essential Vfoi" checking the carrier frequencies of broad- 1ca`st`stations. The apparatus indicated in Fig. 5

by vthe legend heater and fork is shown schematically in Fig. '7. It comprises a heat-insulated bo'x 67 within which' are locatedtwo electric heaters 68 and 69. The upper heater 68 is con- --`Vnected to a source of current through a thermostatic relay 70 of the bimetallic type. A condenser '71 is shunted across the relay contacts to reduce'sparking. The 'interior of the heater box L 1 is maintained at substantially a constant tem- "fperature by means of the heater 68 and thermostatic relay 70. The heater 69, which may be an ordinary flat-iron heater, is provided iior applying heat directly to the tuning fork holder 72, the famount of heat which is applied being con- `tro1led by means of the circuit shown in Fig. 5.

The elements 73 and 74, connected to the conductors '75 and '70, respectively, are electro-magnet-icdevices for driving the tuning fork. Tleconstruction of the tuning- fork holder 72, 40"'iftuning fork, and electro-magnetic driving means '73`and '74 can best be understood by referring to Figs. 8 and 9. The holder 72 comprises two solid metallic blocks 77 4and 78, preferably of l brass, each havinga vertical hole '79 drilled off ""center, therein. Each block has a larger threaded hole, drilled at right-angles to the vertical ho1e'79 and communicating with it, in which one oftheelectromagn-etic driving units '7B and 74 is t supported. The two blocks 77 and 78 are clamped 'li'together lby means of bolts 80, with their thin walls adjacent to each other and with a sheet of ymagnetic material 81 therebetween. In thisway, two well portions '79 are formed, separated by a thin partition of magnetic material 81 and ""1'1on-magnetic material 82. A square notch 83 is cut in themiddle of the upper edge of this partition. The tuning fork 84 is clamped, by means of' bolts 85, between two solid metal blocks 86 Eand 87,`preierably of brass. Blocks 86 and 87 are i1`secured by tous se to me mocks 77 and 'is in such position that a portion of the tuning fork 84is`loca`ted within thevnotch 83 cut in the partition, while the prongs 99 are located within the tvs-:ills 79. A clip 100 is attached at the top` of the block for holding a thermometer 101. The tuning-fork-driving elements 73 and .'74 comprise telephone-receiver units having poles adjacent to the prongs 99 of the tuning fork 84. 700 These poles'are soft-iron pieces attached to the poles of a permanent magnet 102. They have coils 103 mounted thereon which are connected to' the binding posts 104. The driving elements w `are held-in place by means of set screws 105. 75141 The` partition above-specified is provided for vlay contact.

ture 125 of the polar relay 124 rests against the i left-hand contact, the armature'llS of the relay i 114 is pulled up to connect the fork heater 69` electrically" smeidng the drivingfeiements 73ans j 74V from eachother. f

Since the tuning fork 84 `vis in Vcontact with the brass blocks 86l and 87 which are good heat conductors, the temperature of the fork 84 may be controlled by varying the amount of heat applied to these blocks. This is done by setting the fork holder '72 upon an electric heater 69, as shown in Fig. 7, and by controlling the' amount f driving element '73 is connected to the output of .K

the-ampliner 106 by conductors '75. By means of this arrangement, the fork 84 is driven at its natural frequency bythe energy supplied from the amplifier 106, and a current of this frequency can be obtained from the ampliner output.

The frequency of the current' generated is controlied by varying the amount of .heatisuppledl through the heater circuit 107-v tothe forkA heater 69. The amount of heat supplied tothe fork 84 is controlled by meansof a synchronous motor. .i

108 (preferably of the phonicv wheel type) con-i nected to the forlr-'ampliner output through an amplier 109, and by means of an electric clockf.'

When a current of the desired frequency is .being generated, the synchronous motor 108 connects the fork-heater circuit 107to a `source of.

current at regular intervals, while the electric clock 110 disconnects the heater circuit10'7 from Y the source at like intervals. heater 69' is alternately connected to, Vand disconnected rom, the source of current, which, in the example illustrated, isa 110 voltfalternating-current supply. The circuit connecting the current supply to the fork heater 69fmayV be traced from one terminal of the 1101volt source,

through a conductor 111, a'resistor 112, the'armature 113 of a relay 114, a contact of relay 114,` an ammeter 115, a second resistance 116, an .indicator lamp 117 and `resistance l118 in parallel, a conductor 119, one conductor` of line 107, the fork heater. 69, the other conductorof line 107 In this way, the fork.

and the conductor 120, back tothe other terminal of the alternating-current supply. The wind-V ing of relay 114, which pulls up the armature 113 and thereby connects the fork heater 69 to the alternating-current supply, has one terminal connected to :ground and the other terminal connected, through a resistance 121 and a'conductor 122, to one terminal of a battery 123, the other terminal of the battery 123 beingconnected. to

ground.

A polar relay 124, having an armature '125 connected to ground, is Vprovided for connecting theright-hand terminal of the winding of 'relay' 114 to ground through' the conductor 126 and re- It is evident that, when the armato the 110 volt supply. When the armature 125 of the polar relay 124 rests against the righthand contact, lthe winding of the relay 114 is short circuited and the armature 113 drops down, thus disconnecting the fork heater 69 `from the 110 volt supply. l

The armature. 125Lof .thepolar relay .1241150 `a driving coil.

r pulled overto the left, to 'connect the fork'heater U69 to'the110` volt supply, `each time the upper terminal of the left-hand winding 127 lof said relay is connected to ground by means of the synchronous motor 108 through the conductor 128,

brush 129, contact element 130, shaft 131, ring 132A and brush 133. The shaft 131 is connected to the synchronous motor 108 through a gear reduction unit so that contact between element "5130 and brush 129 is made once every two sec- 'onds if the tuning fork -proper frequency. i

' 1 The polar relay armature 125 is pulled against 84 is vibrating at the the right-hand contact, to disconnect the vfork heater 69 from the 110-volt supply, each time the 108 and the electric clock 110 are so adjusted with respect to each other that they alternately connect and disconnect the fork heater 69 and the current supply. The electric clock 110 is, preferably, of the type described and claimed in my copending application, Serial No. 176,061, filed March 17, 1927, in which the pendulum is driven by charging and discharging a condenser through Y The coil of the polar relay 135 is connected in series with this driving coil.

When the armature 134 is pulled against the left-hand contact, a circuit is completed froma battery 136, through a resistance 137, a conductor 138, a relay winding 139, a conductor 140, the relay armature134, and the left-hand contact, back to the battery 136. This pulls the relayarmature 141 against the upper `contact and connects the upper terminal of the right-hand winding 142 of the polar relay 124, toground through conductor 143 and armature 141. The armature 125 of the polar relay 124 is then `pulled against the right-hand contact, and `relay armature 113 drops, thereby disconnecting the heater 69 from the current supply.

A special circuit is provided for passing current through the polar relay vwindings 127 and 142 in response to the closing of either the synchronous motor or the electric-clock contacts. The circuit comprises the battery 123 which is connected, through a conductor 144, a resistance 145 of a few hundred ohms and a second resistance 146 of several megohms, to one terminal of a condenser 147. The other terminal of the condenser 147 is connected to the other terminal of the battery 123 through ground. A circuit is likewise completed from one terminal of the bat-1 sistance 146, a'condenser 149 similar to condenser 147, and through ground, to the other terminal of the battery 123.

By means of the circuit described above, the i condensers 147 and 149 are kept charged. Ac-

cordingly, when the upper terminal'of either polar relay` Winding 127 or winding 142 is connected to A'shortly after it is pulled'aganst it, since the rush of currents lasts a very short time-"Therefore,

the armature of therelay may be pulledaway from a relay contact even though the contacts of the synchronous motor 108 `or electric clock'` 1105i 5 e whichrpull the armature 125 against thel relay contact are still closed.

The condensers150 and resistances l51`are em'-` ployed to reduce sparking atthe relay contacts. The `followingvalues of capacity, resistance,

`and voltage have been foundsatisfactory although, obviously, other values may be employed if,` desired: `resistances 146 `and `1,4'8`eqi'1a1 5 fme'gohms; resistance 145 equals 1000 ohms; resistance 112 equals'50 ohms; resistance k116 equals 800 ohms; resistance 118 equals 20 ohms: condensers 147 and 149 equal .25 micro-farads; resistance 121 equals 10,000 ohms;` and voltage` of battery 123 equals 350 volts. Theoperation of the-circuit will be more fully understood byrreferrin'gtolthe diagramof Fig. 6 which greatlyv exaggeratesV the rapidity-[with which changesin the' fork 'frequency ioc'cur.' In

this diagram, the current applied to the yfork heater 691' is plotted' against time in seconds.

From zero to four seconds, the generator is supplying a current ofthe proper frequency, that is, 5,000 cycles per second. `Accordingly, the fork heater 69 is alternately connected to, and ldisconnected from, the current supply at one-second intervals. When thefork 84 begins to vibrate too slowly, the synchronous .motor 108 slows down,

and, after the heater 69 has beerrdisconnected` from the current supply (as after the four-second interval) it is not again connected to the current supply until a longer time than one second. The

electric clock 110, however, is not affected by` quency will` increase.` In the diagram, the fork frequency begins to increase after the ten-second interval. After the twelve-second interval, the fork 84 begins to vibrate too rapidly, and the synchronous motor 108 speeds up. This results in heat being applied to the fork 84 an instant sooner than it would be if the fork were vibrating at the 500G-cycle frequency. The temperature of the fork 84 is, iaccordingly, increased and its frequency is changed the desiredamount.

It will be noted that, at the sixteen-second interval, the fork 84 is vibrating so rapidly that the synchronous motor 108 connects the heater 69 to the current `supply `as soon as it is disconnected by the electric clockllo. It is evident that, if the fork 84 vibrates still more rapidly, the synchronous motor speed will be so high that its contact connects the fork heater 69 tothe current supply just before the contacts of relay 139 are closed by the electric clock 110 to disconnect the current supply fromthe heater. When this happens, less, instead of more, heat is applied to the fork 84 than is applied when it runs at the proper frequency, andthe system will not correct the fork frequency. In such a case, a manual adjustment must be made to increase the yfork Ldi,sconnects the fork heater 69 from` the curren l, .onnects the forkHheater-,GQ to thecurrent e\r,ery.10,000 ,cyc1es,- ,While-,the electric clock 110 1.1..,In television apparatus, a `scanning device ,co prising agdisc/and means comprising a plu- -.,-2. In televisionapparatuafafscanning device comprisinga yrotatabledisc and arotor element of a synchronous motor `disposed coaxially ,V'With @aid-disc andvsupportded thereby.

.A In television rkapparatus, a scanning ldevice' comprising a rotatable element and a rotor ele- E 1nent, cfa .synchronous motor .directly supported 1f thereby.

.,5 y, television apparatus, a scanning device Supply peripheraLprojections adapted to cooperate with Various modifications maybe made 4inmy in- Ypprojections disposed in circuiarformation 545 on said vdisc ,whereby the discnfunctions as a part Iof the-rotor of a.synchronous,V motor.

n agarose comprising a disc; the Idisc `being :provided with a eldvvinding to provide motive power for said disc.

5. In ytelevision apparatus, aV scanning `device comprising a disc which is rotatable about its axis and which has light-transmitting openings disposed thereinnear its periphery, and a syn-'- chronous-,motor rotor comprising a circular mag- .netic element havingteeth projecting from its periphery, said rotor being supported bysaid disc and disposed with its teeth a. greater distance from the axis=of said dise than are said openings.

6. In television apparatus, a scanningdeVice comprsinga rotatable disc, a rotor 'of a synchronousrnotor disposed coaxially with saiddiscand` supported thereby, said rotor comprising a' circular element of magnetic material having teeth projecting fromits periphery,.and a synchronous 20 motor ,stator comprising polessupported incooperative rela-tion With saidtrotor for a portion only ofv its circumference.

FRANKCONRAD. 25

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