US1907986A - Frequency control device - Google Patents

Description

May 9, 1933. D. G. LITTLE 1,907,985

FREQUENCY CONTROL DEVICE Filed July 15 1927 INVENTOR @ana/0 Z///Q 4 ATT'ORNEY Patented May 9, 1933 l #UNITED STATES PATENT OFFICE D ONAL'JILGP.l LITTLE, OP EDGEWOOD, PENNSYLVANIA, ASSIGNOR TO 'WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA i I FREQUENCY CONTROL DEVICE Application filed July 15, 1927. Serial No. 205,889.

- My invention relates to frequency-control devices, and it has particular relation to devices comprising piezo-electric crystals.

One object of my invention is to provide a piezo-electricecrystal-holding device whereinthe undesirable eects of the electrodes 0n ,the free vvibration period of the crystal are entirely vobviated.

lAnother object of my invention is to provide a piezo-electric-crystal-holding device wherein the crystal is not subject to wear when in use.

Another object of my invention is to providey a piezo-electric-crystal-holding device whereinthe crystal may be utilized for any period desired with full assurance that the original calibration of the crystal will not change.

It has been found by experience that piezoelectric-crystal sections, when utilized for frequency-control of a thermionic-tube oscillation generator, are subject to a detrimental amount of wear by reason of their contact with the supporting electrodes. The crystalsection vibrates violently,- when electrostatic lields of the proper period are impressed thereacross, and tends to so move about on the lower, electrode that the surface of the crystal in contact therewith is being constantly abraded to a more or less extent. In the case of large crystal sections utilized to control loscillations at relatively low frequencies, the wear is not particularly disadvantageous, since the percentage change in the oscillation frequency of the crystal caused thereby is relatively small.

' The situation is different, however, when the crystal-sections are utilized to control the generation of extremely high frequencies. The vibration period of a piezo-electric crystal, such as a disc of quartz, is principally determinedby its physical dimensions, as is well known in the art. For extremely high frequencies, the thickness of the crystal, measured in a direction perpendicular to the face thereof in contact with the supporting electrode, may be of the order of only a few millimeters. In such event, even the slightest wear will cause a relatively large percentage change in the oscillation frequency of the crystal and, consequently, a relatively i large shift in the frequency of the oscillations generated by the thermionic-tube device associated therewith.

In accordance with the present invention, I dispense entirely with the physical contact between the crystal and the lower supporting electrode that has been deemed necessary, according to the teachings of the prior art, and suspend the crystal section by filamentary means in the space above such electrode.

An important feature of my invention lies in the choice of that portion of the piezoelectric oscillator with which the lamentary supporting means makes contact. In general, it may be stated that crystal sections, of the types commercially utilized for frequency control of thermionic-tube oscillation generators, are so arranged that they oscillate symmetrically about a plane that is parallel to one of the cooperating electrode faces. The regions of the crystal defined by the intersection of such plane with the faces thereof are consequently nodal points, and, by so` arranging the supporting means that it contacts such nodal points only, wear on both crystal and supporting means is minimized.

Among the features that I consider characteristic of my invention are those set forth with particularity in the appended claims. rThe invention itself, however, both as to its organization and its method of operation, together with further objects and advantages thereof, will best be understood by reference to the following description, taken in connection with the accompanying drawing, in which:

Figure 1 is a view, partly in elevation and partly in section, illustrating a preferred embodiment of my invention.

Fig. 2 is a sectional view taken along a line corresponding to the line IIII of Fig. l.

Fig. 3 is a sectional view of a piezo-electric oscillator taken along a line corresponding to the line III-III of the F ig. 2.

Fig. l is a view, in perspective, of the piezoelectric crystal and a supporting frame there-v for.

As shown in Figs. l and 2, a boxlike, rectangular container 1, preferably made of bakelite, hard rubber, or other insulating material, comprising a. top 2, a bottom 3, an a plurality of sides 4, 5, 6 and 7, carries a 5 frame-device 8 centrally positioned in the interim` thereof.k frame 8, lwhich is shown in detail infFig 4, may -besu ported by a plurality of brackets 10 arrangeidiagnnelly of the corners of the container, or may 10 be supported in any other appropriate manner.

The frame 8 preferably comprises a rality of sides 11 and is preferably cu or molded from a single piece of insllating matenel- Ahook`12, provided at one end Vwith an eyelettl', is mounteden each side 11 of the frame, the eyelets extending toward the center of the space enclosed by the frame and being ari ranged to'liein a. lane paralleltothe plane dened by the anger surfaces ef the fnamemembers 11. The opposite ends of the hooks maybe anchored in small holes 14 drilled in the'frame-members, as shown in Fig. 4. f l5 ',Apezo-.electric-crystal section 16, substantialflfy-a rectangular parallelopiped in shape, has small notches 16 cnt into certain of the comers thereof, asshown in Fig. 3. A cord Hfpwferably ofsilk er other good insulating i. materieel, eneircles the crystal section and is in position by the said notches. The cord I?, intermediate the points where it lies imthenotches, entendsthrough and is held hythe eyelet portions 1'3 of the hoek devices l5 mythes supporting the crystal section with urpperandlowerfaoesparalleltcthe lane delned iby the under surfaceof the Yame flieftop 2 ofthe container has a. threaded 4 openingextending therethroiph, and, in .this

epen'mg is mounted a metallic yadjusting screw H) havngia lmnnled lziaadf2ll.v The hr lower end of the adjusting screw is provided enlarged circular portion 22that is Matably mounted in a recess in the upper and a metallic rectangular Steuerelement 23 which carries an electrode 24. A. rectanguiar guide 25 is axed te the nncrsurface ofthe top of the container .and surrounds the stem 28 to prevent rotation thereof while perthe said stem to move toward and fnomthe top, under the influence of ,the acljusting screw.

y'illhe `.bottom 3 of the container is provided withan .adjusting screw 26 which actuates a stem 27 carrying an electrode 28 analogous to the upper electrode 2A.

Suitable electrical connections (notsholwn) are .provided ,for the velectrodes 24 and 28, l0 whgrabythey may ibe conductively, or otherwise, associated with a thermienic device.

'The opposing I:smi-faces of theelectrodes are parallel to each otherland are also parallel to the lower Surfaces of the frame members. fr

45 The crystallin; sosupportedin thefts-me that its faces are parallel to the lower surface of the frame members and, consequently, the said faces are parallel to the electrode surfaces.

The crystal, when subjected to an electro- 7 static field, at its natural frequency, tends to symmetrically with respect toa lane .which is parallel to the faces thereo and which is snbstantally midway between the sald faces. The notches which en e the "5 supportin string or thread are so p ac d that they in lthe said plane. The crystal, therefore, when vibrating does not tend to exert my .weer ,upon the said supporting means, inasmuch as the oints in which the 3 supporting means touch crydalane nodal points and-move to'onslyfan extent jlwilljertthe crystal is 1 The spacing between die e andithe two electmasmay be made as small lade, U sizable-by moving the said` inami out. Preerab1y,the distance between iam of the crystal and the` ,assaulted therewith should he anoddnumher of wave l5 1.11.8113 Dflhe Stillifrdilllw hen in mxerannfxyephysical mlmb'nn of the crystal is in no way lntelliered Hill! by theelectmdns,4 and, by reason oftxhe tact that thegystal is supported Onlygt :1118181 pomtsy-itns. fme ,to ivibrate with respect it@ such paints with-maximum amplitude.

Inaddit'mm there is, ofrwaursc, n0 am" upon the crystal, since vibrating f., '.r theqfdc not ymalle .Contact with@ e ai ilfhetcasliindgitc @www :man:` o. ank I have found ,that thengfaeqnency of gag. tal, nihenmounted according fte In ilman-` tmn, is `abxniutely,conatant ipridedy au' rounding atmosphere is .kept lat .a constan! u temperature, and the likalihQOd 0f ,om

..1s manlmlzed. Although il have and mi# @niv a single specite fevgacf any1-.inseam medxcatxs thereof will Lbs apparent ,te theskled in .the art. My4 iayeatipn ahem# fue ,is noting), excennliefar .asis necassaultedy prior anta. Y -l .the misfit. of thaappendadfcleixna I claimras my invention:

1. In combinatiop, a frame provided mit@ attaohingldemcesm wameleettiraE-F. PS- cillatemmaansfnraupwtmgeid BE' inem saldllevllgs E? fmntiwt with. w

rshtyefelmtrpdsan means when y ses@ frame lhe a9 carsadby .sa atractivas than .the ssidnscillatqr .1s .snap ad between oacntt mthfsaad electnqge tb w n camine. on, @semanal e fr. l attaching @mesa @www12 )1 l my), .a empara structure ear i i plurality; eff remise y .adiustble Slam w and means whereby said frame may be so carried by said structure that the said oscillater is suspended between and out of Contact with said electrodes.

In testimony whereof, I have hereunto subscribed my name this 11th day of July, 1927.

DONALD G. LITTLE.

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