US2639315A - Variable high-voltage electrical condenser - Google Patents

Description

Patented May 19, 1953 UNITED STATES PATENT OFFICE VARIABLE HIGH-VOLTAGE ELECTRICAL CONDENSER Application June 15, 1949, Serial No. 99,203

8 Claims.

1 This invention relates to electrical condensers, such as those generally used in radio, television, or similar electrical circuits.

More particularly, this invention relates to variable electrical condensers which are capable of withstanding high voltages. The purpose of such variable high voltage condensers is generally to provide a capacity whose value can be regulated at will and which is capable of being used in circuits having a high impressed voltage, either D. C. or high frequency. Condensers of this type find wide application in the output loading ciredits of almost any radio transmitter having an output greater than a few watts. Heretofore, such high voltage variable condensers have been available in a wide variety of physical sizes and electrical capacities, but none of those currently available combine a high electrical rating with a small physical size.

Heretofore, variable air condensers have generally been fabricated from a plurality of interleaved electrodes, so arranged that the metallic sheets constituting the electrodes could be moved together or apart by the actuating means. In each case, the dielectric was usually a r, although sometimes compressed gases and even liquids have been used satisfactorily. However, the dielectric constant of all gases, and of all liquids which are otherwise satisfactory, is very low; hence, a large amount of dielectric must be employed to obtain a given capacity rating. Attempts have also been made to introduce solid dielectrics between the electrodes, but the results have not proven generally satisfactory. Difiiculty has been encountered as a result of the mechanical wear arising from the relative movement of electrodes against the dielectric, which movement must neeessarily take place in a variable condenser. This wearing action may cause particles of the metal electrodes to become embedded in the dielectric, or may cause the dielectric to score the electrodes, or may create such a diminution in the dimensions of one or the other or both, that the capacity at a given dial setting is no longer constant. Particularly in the case of high voltage condensers, the above wearing action is very serious, since corona effects may be stimulated, resulting in highly erratic operation and eventual total destruction of the unit. Furthermore, in

the case of precision condensers (such as are now 2 is extremely serious. The obvious method for overcoming this difiiculty is to provide an intervening layer of air between the dielectric and the relative moving electrode. However, this, in turn, raises other difliculties, particularly insofar as this scheme requires the use of mechanically precise bearings in order to bring the intervening air layer down to dimensions which are practical since, obviously, if the intervening air layer is not kept small, the result will degenerate to what is essentially an ordinary air-dielectric condenser.

Other schemes for overcoming the above objections have similarly been proposed. A typical example is Patent No. 2,219,921, which shows a variable condenser in which the dielectric is split, so that the relative movement takes place between lapped halves of the dielectric rather than between the dielectric and electrode. While this may overcome the difliculties arising from the sliding of dielectric against electrode, nevertheless, such a condenser is costly to manufacture, is large and bulky for a given capacity rating and will vary so much that it cannot qualify general- 1:; as a precision component.

It is a principal object of this invention to provide a variable high voltage electrical condenser of simple construction which shall be considerably smaller than existing devices of this type of equivalent electrical rating.

5: turization, both of components and complete assembly.

'(2) Variable high voltage condensers which shall be easier and cheaper to manufacture than existing devices of equivalent electrical rating.

(3) Variable high voltage condensers which will withstand the adverse effects of operation at low atmospheric pressure, such as that encountered in aircraft transmitters when the aircraft is operating at high altitudes.

(4) Condensers having a structure which a1- lo-ws complete electrostatic shielding.

(5) High voltage condensers in which the defects and limitations associated with the use of air gaps as dielectric elements are eliminated at the same time that abrasive wear of moving components and the attendant instability in electrical characteristics of the condensers is not introduced.

(6) High voltage condensers having relatively moving parts constructed so that an electrically precise structure is provided Without recourse to precision bearings or similar units generally employed for this purpose.

Still further objectives and the entire scope of applicability of the present invention will be-- come apparent from the detailed description given hereinafter; it should be understood, how ever, thatthe detailed description, while indicating a preferred embodiment of the invention, is given by Way of illustration only, since various changes and modifications within the spir t and scope of the invention will become apparent to those skilled. in the art from this detailed description.

A more complete understanding of the structure involved with this invention may be hadby reference to the accompanying drawing.

It will be understood that this is a preferred arrangement of parts, but other arrangements, including other means for adjusting the moving parts; can be employed. The novel features of this invention do not reside solely in the particula-r layout of parts in this illustration of a s e ci'ali zed 2-section condenser.

In the drawings: Figure 1 a. longitudinal cross sectional view of a 2-section variable high voltage condenser incorporating-the features of this invention;

Figure 2 is a cross-sectional View along line 2 -;2-ofFigure-1;

Figures 3 andxl are electrical diagrams of the equivalent circuit.

Referring first toil 'gure 1-, the Z section c denser has two-- .ato-r electrodes it it t are insulated from themes and from. each ot by mounting means "25, fit, it and hereinafter described in greater detail. The movable electrodeconsists of the single nickel block w'hicht is electrically common to both sections and which is also grounded to the case it by reason of -the"conch'ictivit'y of its actuating means, which "actuating means comprise preliminarily the outside threaded shaft Elli and associatedfit tirigsfi'i' Stated otherwise, this ccnd has two electrical terminals and iifl'each rep resenting one sweet one of two variable condensers", the other side of which common to both'units'andgrounded. The latter groan ed el'erhen t furthermore acts an electrosta shield for the entire unit.

The electrodes it and constitute opposed lectrostaticel'e "rodes of the onesecti'on of the condenser; the dielectric elements H, M, Is and 3''! constitute a composite dielect of cc'- operating parts-the part it having no in'heren variable feature, while the parts .t, if, and ill pab'le'of relative movement one to the other. The sameis"true'of"the'other section of the denser. The importance of this is more i'ully explained hereinafter in connection with Figuresfi and-4 or" the drawing.

The electrode. it of the stationary capacitive elerhent'is showirconveniently as a length of'lrol low cylindrical tube. 'lhiselectroi'le is permanently and coaxiaily embedded in ceramic'cyl inder ll whichiscomposed of a ceramic having a-high'-dielectricconstant and a high dielectric strength. An'example of such a ceramic is a mixture of titanium dioxide, and silica, which available With a dielectric constant of 108 and witheicellentdis ipation factor and high dielec-- tric'strength; The choice of this or some other suitable material is dictated by the requirements of theparticular condenser which. is to be built, and this selection, which may be done by anyone skilled in the art, is not the subject matter of this invention. However, as far as is known to the inventor, there is no material electrically suit able for the cylinder H which can be rubbed in contact with a metallic electrode without adversely affecting either the metallic surface or the cylinder H or both, thereby eventually destroying the condenser as a Whole. In this invention, the outer surface of the cylinder H and the mating surface of the moving metallic block 30 are treated so as to produce, on the mating surfaces, an entirely different substance which is capable of fricticnally o crating against itself indefinitely without any deleterious effects. This treatment, described below in greater detail, results in the achievement of the objectives out lined previously,

'lhe cylinder H may be any ceramic or other dielectric material capable of withstanding term peratures of at least 1000" F. This is first given a coating of nickel on at least the external cylindrical surface. While there are many Ways of accomplishing this nickel plating, such as by electro deposition, electrophoresis, chemical deposi-- tion, metallic evaporation techniques, or cathode sputtering, the preferred method is to use a proccss known as gas plating d'escribedin consider abledetail in :5. Letters Patent No. 2,332,309 and No. 2,34,138, and British Patent-No. 487,854 of June 1938. It enough for the purpose of describing the present invention to state only that the process consists of immersing the cerainic cylinder '5 5, previously heated to a tem perature of about 350 F2, in an atmosphere of nickel carbonyl. At thisternperature, the gaseouslNflCOn decomposes into carbon monoxide and pure nickel, the latter beingdeposited on the surface of the heated cylinder ii. The decoinposition of nickel carbonyl under these conditions has been known since about 1890 and the application of these phenomena for plating purpose has been successfully exploited for a number or years.

After the nickel plating has been accomplished, the entire cylinder H is heated in an oxidizing atmosphere so as to convert the coating f2 entirely into nickel oxide. The process for doing this is described at length in my previous application for U. S. Letters Patent, Serial No. 49,022, filed September -13, 1948, now abandoned. In brief, the process consists in heating the nickel to a temperature of 1000" to 2500 F. in-a current of gas containing oxygen, and subsequently allowing the nickel to cool. The heating, tiining, and cooling inust be under controlled conditions, the details of which will'be found in the aforementioned'application'serial'No. 49,022. In general, the process as previously disclosed resulted in the formation of a tightlyadherent layer (comprised of a mixture of 'th' ""ri'ous oxides of nickel) over a base of the 0' al metallic nickel. In thepresent invention, h w'eve'r, the entire layer of nickel previously depositedby the'ga's plating. process is'converted'to alnixtureof nickel oxides by the high temperature oxidation process. Stated otherwisathe entire layer i2 is converted to nickel oxide, there remaining no metallic nickel in this layer upon completion ofth'e oxidation process. Obviously, the times and conditions of the gas plating process must be properly correlated with the times and conditions of the oxidation process in order that this conversion may be efiected completely. -Whileit is not. possible to define explicitly the precise times and conditions required to achieve this result, previous experiments indicate that the layer I2, when in its metallic state prior to conversion to the oxide, should preferably have a thickness of the order of magnitude of .0002" to .002".

It will be noted that the gas plating process is equally applicable to other metals having metastable carbonyls, such as iron, cobalt, chromium, and the like, although nickel is presently the pref erred material for carrying out my invention, because of the hereinafter described desirable properties of its oxides.

In a similar manner, the cylinder II is provided with a coating I2.

The other electrode is composed of the nickel block which is fabricated to a shape best illustrated in Figure 2. This block has two holes which are very slightly larger in diameter (about .0005") than the completely processed cylinders II and II. This block is first completely fabricated to the desired dimensions, including not only the two holes previously mentioned but also including facilities for actuating it (which facilities may consist of the threaded portion 32 for moving it laterally and also the outer surfaces 33, 34, and 36, of which two or more may be used to guide the block 30 and prevent it from twisting in the case when the shaft is rotated). After fabrication, this entire block is heated to form an oxide on at least the interior surface CH and 3| of the two holes. process is also carried out in accordance with my previously mentioned application for U. S. Letters Patent, Serial No. 49,022. The oxide will tend to form all over the block 30, although it is required only on the interior cylindrical surface 3! and 3|. It may be removed elsewhere if this is desired and, in particular, it may be removed from the interior threaded surface 32 in order to make the block 30 electrically conductive to the shaft 50, although other means for bringing out the connection to movable block 30 (such as by a flexible lead) are obvious.

Electrode 30 may also be fabricated of some base metal which is subsequently nickel-plated unusual properties and gives rise to some results which might not be expected, were it not for my discovery of these properties in the course of experimenting with this material. First, the cylinder I I engages with the block 30 in such a way as to provide a very freely running fit, even when the clearance between the two units is as little as .0003". Ordinarily, a fit as close as this, between two metallic surfaces or between a metal and a ceramic or glass, would be classified as a push or force fit and obviously unsuitable for this application. But, when mating surfaces of oxide, previously described, are run together with such small clearance, there is in effect provided a bearing which may be run dry and which will exhibit the properties of a jewel bearing.

The unusual properties of a nickel oxide mixture itself are set forth in detail in my previously mentioned application, Serial No. 49,022.

The unusual properties of this oxide-on-oxide This oxidizing bearing are further disclosed in my application for U. S. Letters Patent, Serial No. 83,494, filed March 25, 1949. The latter application discloses a condenser fabricated from two metallic electrodes (preferably of nickel) which are subsequently oxidized at their mating surfaces. In the present application, only one of the mating parts (30) is fabricated from metal and subsequently oxidized, whereas the other (I I) is fabricated from a non-metal (such as the aforementioned titanium dioxide and silica ceramic) which is then metal-plated, and this metal-plating is then oxidized in its entirety, so that the plated layer is completely converted to a non-conducting layer of oxide and so that no metallic material remains.

Returning again to Figure 1, it will be noted that the small clearance between block 30 and cylinders II and II will require that the latter be mounted in such a way, that no conflict will result between the position of these cylinders as defined by the mounting means and the position as defined by the mating block 30, when it is in various stages of engagement with the blocks Ii and II. In brief, cylinders II and II should be floated within the block 30 in such a way that they can yield so as to conform to any minor eccentricities or wobble in the actuating means 32 and 5B. If this is not done, then obviously the entire mechanism must either be made to prohibitively close dimensional tolerances or else, the entire unit will bind. It is possible to so suspend the cylinders I I and I I that they are rigidly positioned in the axial direction, while still being yieldably positioned in the orthogonal or radial direction.

In the present invention, this is accomplished by providing a cantilever wire 2|, preferably of spring steel, beryllium-copper, or Phosphor bronze, or other suitable metal, which engages with the far end of sleeve-electrode I0 by means of a metallic element 22 (which may be a block of solder poured into the internal cavity of sleeve I0 approximately to the depth indicated in the figure and then allowed to harden). A generous clearance is provided between the internal dimension of sleeve l0 and the external dimension of cantilever wire 2|, so that the former may wobble a considerable distance in all directions, except axially, at either end without permitting the internal surface of I0 to contact the external surface of ii. This type of mount functions smoothly and efiiciently in connection with the rest of the condenser mechanism; particularly it cooperates well with the close fit between surfaces 12 and 3I. A similar arrangement 2 I and 22 is provided for the other electrode Iii. Thus the end fitting plate 2% may be manufactured to ordinary machine tolerances insofar as the positions of 2| and El are concerned; furthermore, this insulating end plate may be retained in the case 40 simply by crimping the end thereof as shown at 4!.

Considering now the resulting electrical condenser, each section may be regarded as a circuit consisting of two condensers effectively connected in series. The first condenser comprises the metallic electrode It and the ceramic II, but the other electrode of this condenser does not actually exist as such, and may be referred to as a phantom electrode. The second condenser consists of the electrode 30 and a dielectric comprising the two layers of nickel oxide 3| and I2 (together with a negligible airgap I3 therebetween) and the same phantom electrode for the other side. This equivalent circuit is shown in Figure 3.

acsaeic Equivalent condenser I is effectively the high; voltage section, and across itappears virtually all of the voltage drop between working electrodes and '30. Condenser l'lhas relativelydittle effect on the equival'eiot electrical 1-circuit since it is o a uch larger capa i than.s c e ser, As is known, a series c-ircui t consistmgpta large a da m 1 c mr i l h trarfia ac tr very nea ly equal to t o t small pacit row r J-z bis thec pa wr I whi hri es eni e o provid n he. mech c vs l b e chara eri t c o th s in l me a n. s se o u m tsl c ns der tions of th s n aent c it r tt e of. thev m reesed Ease item 10 0, v answers-acro s the-d lect i com o ed o 1.2 w a s l o Th s me e e ib r l beca at com o i e id eqtr c ot-sesam withstanding very high voltages, being limited to a maximum ot under i000 volts. ahn s equivalent condensers lend I-I cooperate in such a manner that; provides the high voltage condenser which is to be -varied whereas Il provides the means of accomplishing this variation, the two together cooperating so as to provide a variable condenser which may be operated above, say, 10,000 volts ln yaryi-ng the condenser it must be remembered that electrode l landthe phantom electrode must be moved together rela :tive to electrode t0, as noyariation could occur if the phantom electrode remain-sstationary.

Retnrningnoy/to Figure i, it willbe seen that the device illustrated grits {this requirement, pron w o c u e tha t e l s r 1 2 i totall m sorted .to the dielectric consisting of a mixture 0f the oxides of nickel and that no metallic niclgel is allowed to -remain in this layer. Thus, ithe equivalent circuit may be iurther reduced to that shown in Fig-ure which schematically illustrates condensers land 11 effectively connected in series and ganged together insuch a manner, that they a togetherin l. l

h ab v descrip i n'o t ci c t srre t solely for the purpose of exposition and illustration of What isaccomplishedby tnyinventionin order that this may vbe more readily comprehe ded by the reader. The i nvention itself, however, is not to be construed as narrowly limited to the me e connection of two condensers inseries (this being lmown in thelart), but rather asdefined bythe scope-of the claims which will be appended below. r Anqtherfeature which may be incorporated in this invention is the provision of meansforovercoming thermal variations in the capacity of the unit. As a first approximation the condenser may be made vby fabricating the case lil and the shaft of the same material,:e. g., nickel as the block 30. Further improvementvmay be had by a judicious choice .of these materials, together with the choice .of material for the cantilever electrode 2t and 2i". Likewise; certain elements, such as the closed end 42 of case 40, maybefabric'ated of blmeta'l'li'c elements. In the design of these temperature compensating means; consicls erable advantage maybe taken of thefact that Cyjinde'r 1;: has a very low :coelficient of thermal expansion, whereas block -30 has-quite;a large such coefiicient; although in both cases; the layer of nickel oxide (12 and 31) is so tightlyadherent of the underlying material, that there is no danger of it separating therefrom.

As will be apparent from the discussion given above, ni'c'lrel is the preferred metal from which the important metallidportions elementsjfl and 30, of these new condensers .Shflllld be fabricated andalso the metal irom which the oxide coatings 12v and. 531 should be formed, Howeyen other metals .may be used the formation of the tubes I 0 and the element 30, such :as silver, brass, aluminum or any other similar inert, electrically ndu tin m ta A so o r m als besides nickel be .used to dorm theox-ide coatings 1 1,2 at, including the metals: rhodium, .inr idimn, osmium, ruthenium, cobalt, molybdenum, and

rom um v by While the disclose of the present -inyentiqn is directed toward high voltage ,tran n tter condensers, and while furthermore their seintransm to is pr ab y th m tlike y appli a f h s c ndensers, t e a lica io 611 1 35 me yoltage yariable condensers is not limited to this field alone.

-I. a =v x 1. A high voltage -variable condenser compris ed by s i u in one oi s i el m t b in w ch v tag e ement-o t b a shape commie ing an internal metal tube, :a surrounding tubular body's-f ceramic material carried by said metal t e n a h r nt er cons st n o a s ble m tal ox ov r yi i c r mic mat rial, th second element being a low voltage element comprising-a metallic member having a tubular opennat nof a specorr nd na to aid hi h oltage element, butslightly largerin size, where,- by said highvoltase element may slide axially within said opening, said opening having a surfQcCBEDTlI-fid of a layer of stable metal oxide and means carried by S9i hi0l1$ih for moving said elements relative to one another.

2. .A condenser as claimed in cla-imyll wherein said high voltage element is mounted ,upon :one end of a compliant cantileyer wire whichextends axially within said element, said wire :beingmigid- 1y fastened at the other end to a portion of said u in -.7 v.

3. A condenser as claimed in claim v1,avvlieiiei-n said ceramic body .is greater indepth than the c mbined epthf aid sta le m ta oxide coatings and the ;ai-r apzbetween said coatings.

, Aco d sera l i-medl ns aim 1, whe e said element moving :meanscomprises an outside t e de memb arr e bread-n inees a topermit free rotation ithout 10 ndina'l tion- ,said outside threaded member being threaded into an inside threaded sectiononL-said 10 voltageelement. M Y U H ,5. A ariable condenser as claimed-in claim 1 wherein ,one of said elements is mounted on m n i 7, a curat y p it oni g, the el ments rigidly in the direction of said motion responsible or th v r a i n in lect os at c -caiaa t whi yieldably ,lpositioni-ng the element all other directions, whereby a tree-sunning fit between said relatively movableelements provided.

6 A variable condenser as claimed in claim ,1; in which .said second element comprises a pair of layers of .an oxide of .a metal selected from the group consisting of rhodium, ,iridium; osmium, ruthenium, cobalt, molybdenum, chromium and niche'lsaid layersbeingcapableof rlative' nova. me il, one past the other, while in contact with each other. 2

7. A high voltage variable condenser comprising apex-lilac housing, two high zvoltagecapacitive elements comprisin'ganinside me al -tube,;a surrounding ceramic tubulanbody carried, by -said mea tim n s la e i eeea sies a laying e i .se a i a qdr sachet ai mamas being carried within said housing substantially ins a u ng, apa r-o ap ci ye lem ntscarparallel to one another upon a wire which extends centrally down said inside metal tube with the tube being fastened to one end of the wire and the other end of the wire being rigidly supported by said housing, a low voltage capacitive element slidably carried within said housing comprising a block-like metallic member having two tubular openings therethrough corresponding in shape to said high voltage elements into which high voltage elements extend, an inside threaded section in said low voltage element, an outside threaded member fixed against longitudinal motion while being allowed to rotate in an opening in said housing, said outside threaded member being threaded into said inside threaded opening, whereby said low voltage element may be moved relative to said high voltage element by rotation of the outside threaded member.

8. A high voltage variable condenser comprising a housing, a pair of capacitive elements carried by said housing, one of said elements being a high voltage element of tubular shape comprising an internal metal tube, said high voltage element being mounted upon one end of a compliant cantilever wire which extends axially within said element, said wire being rigidly fastened at the other end to a portion of said housing, a surrounding tubular body of ceramic material carried by said metal tube and an adherent layer consisting of a stable metal oxide overlaying said ceramic material, the second element being a low voltage element comprising a metallic member having a tubular opening therein of a shape corresponding to said high voltage element, but slightly larger in size, whereby said high voltage element may slide axially within said opening, said opening having a surface formed of a layer of stable metal oxide and means carried by said housing for moving said elements relative to one another.

ROBERT P. GUTTERMAN.

References Cited in the file of this patent UNITED STATES PATENTS

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