US2273522A - Adjustable slidable-electrode condenser - Google Patents

Description

Feb. 17, 1942. A. HOROWITZ ETAL 2,273,522

" ADJUSTABLE SLIDABLE-ELECTRODE CONDENSIERY Filed Sept. 50, 1939, 2 Sheets-Shae? 1 eram/c INVENTORS ALEXANDRE HoRow/Tz BY Ill-R l/V/A ATTORNEY Feb. 17, 1942. 'A. HcRowlTz ETAL 2,273,522

I ADJUSTABLE SLIDABLE-ELECTRODE CONDENSER Filed Sept. 30, 1939 2 Sheets-Sheet 2 27 43/3 was 9 INVENTORS ALE/(ANDRE HOROW/TZ HERRE N BY 7 t M'UM/ ATTORNEY Patented Feb. 17, 1942.

UNITED STATES PATENT OFFICE ADJUSTABLE SLIDABLE-ELECTRODE CONDENSER Alexandre Horowitz and Herre Rinia, Eindhoven, Netherlands, assignors, by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application September 30', 1939, Serial No. 297,299 In Germany October 18, 1938 3 Claims, (Cl. 175-41.5)

able electrodes of a s idable-electrode condenser respectively to at 1 ast one carrier extending in the direction of adjustment, and to support the carriers against a common constructional part. Such aslidable condenser has proved to be satisfactory from the point of view of construction, though it has been found that the adjusted capacity of such condensers is dependent upon the ambient temperature.

The latter point results, for example, in the oscillatory circuit, in which such a condenser is interposed being gradually detuned when the set is put into operation in the cold state and this until the moment at which the internal part of the set has attained the highest working temperature. Consequently, when the set is exactly tuned immediately after being switched on, the tuning will no longer be correct after some time has elapsed so that afterward the exact tuning has to be ascertained once again.

'As iswell-known, the aforementioned detuning of the oscillatory circuits of an apparatus originates in most cases not only from the tunwhich is oppositely directed to the variation in initial capacity produced by expansion of the electrodes with temperature variations. The temperature coefllcient of the intermediate part or support may particularly be chosen so as to bring about a temperature dependency of the initial capacity of the condenseror condensers which is equal to the variation in initial capacity produced by expansion of the electrodes with temperature variations.

Thus a; temperature independency of the condenser or'condensers may be obtained; as is required in many cases.

The invention, together with its advantages will be more clearly understood by reference to the accompanying drawings showing, by way of example, a few embodiments of condensers according to the invention.

ing condenser, but also from the other parts ofthe oscillatory circuits such, for examp e, as the coilsand the trimmer condensers and the like. These circuit parts as well as the tuning condenser normally have a positive temperature coefiicient, i. e. an increase in temperature results in an increase in capacity and inductance of the circuit parts. The temperature dependency becomes manifest as Darticularly interfering for' high frequencies of the tuning range.

The invention relates to a particular con- 'structional design of a slidable condenser by which the disadvantages stated above are reduced or substantially obviated.

' According to the invention, the carrier or carriers of at least one electrode comprises or comlows a certain pre-determined regularity.-

The temperature coeflicient of the intermediaterpart or support is preferably chosen so as to brin about a temperature dependency of the initial capacity of the condenser or condensers,

Figs. 1 and 2 represent a multiple 'slidable condenser in longitudinal section and in cross section, of which the carriers of the fixed electrodes are provided with intermediate parts, Figs. "3

and 4 each shows a multiple slidable condenser wherein the carriers 91 the fixed electrodes and the carrier of the movable electrodes are or is supported according to the invention agalnst the common constructional part by means of a separate part. Fig. 5 shows one embodiment in which the carrier of the movable electrodes is supported against the common constructional part by means of a part belonging to the adjusting de- =vice. Equivalent parts are designated by equal references in the figures.

Figs. 1 and 2 represent a triple slidable condenser; the electrodes I, 2, 3, 4, 5 and 6 of which are helically formed. Each of the electrodes comprises a bottom plate II, I2, I3,'I4, I5 and I6 and a centering bush 2I, 22, 23, 24, 25 and 26 fastened in the bottom plate. Each of the movable electrodes I, 3 and 5-is fastened to a carrier or shaft 1, which is movable for the purpose of adjusting the capacity of the condensers in the direction' of the shaft, by soldering to the shaft 1 the ends of the centering bushes 2|, 23 and 25 which are remote from the corresponding fixed electrodes 2, 4 and G. The shaft 1 is movably mounted in the centering bushes 22, 24 and 26 of the fixed electrodes 2, 4 and 6, the latter being fastened to carriers 8 and 9, which are symmetrically arranged with respect to the shaft I, in such manner that the carriers are passed throughthe recesses in the bottom plate I2, I 4 and I6 and connected thereto by soldering. All of the carriers 1, 8 and 9 are supported against a common constructional part, in the present of the constructional parts required for adjusting the capacity, which are constituted by a rotatably mounted bush 30 in the casing wall ll comprising a pin 3| which engages the screw thread 20 provided in the shaft 1, and the carriers 8 and 8- are supported by soldering to the casing wall ll. To avoid an inadmissible great play of the shaft 1 in the direction of adjustment, a spring I8 is provided which is arranged in the casing wall l8.

For a better understanding of the explanations following hereinafter it is supposed for the time being that temperature variations do not affect the mutual position of the points of fastening of the electrodes at'the carriers (points of suspension). Consequently, the distance between the bottom plates of two electrodes of a condenser (for example the bottom plates i3 and distance between the electrodes adjacent to one a another decreases, for example when the electrodes, as is shown, are completely separated from one another.

The invention has in the first place for its purpose to obviate the undesirable temperature coeflicient originating from expansion of the electrodes, particularly to eliminate it substantially completely, if required, or to change it to a negative coeflicient.

This is achieved by providing means by which the carriers of the fixed and movable electrodes and consequently also the fixed and movable electrodes are subjected, due to temperature variations, to a displacement of a certain magnitude with respect to one another.

According to the invention, intermediate parts 28 and 29 are arranged to this end in the carriers of the fixed electrodes. If, for example, the carriers consist of ceramic material, as is desirable in view of a mutual insulation of the electrodes, the intermediate parts are preferably made of metal such, for example, as ,brass or zinc.

The influencing of the capacity of the condensers through the intermediate parts due to temperature variations will be motivated by the following.

As already mentioned, all carriers 1, 8 and 9 are supported against the casing wall ll. Since in the construction shown in Fig. 1 the carriers I, 8 and 9 are substantially supported directly points A, B and B, the carrier ends supported against the casing w'all II will not be mutually displaced in the direction of adjustment due to temperature variations. When now the carrier parts between the supporting points of the car riers at the casing wall I! and the points of suspension of two electrodes, for example 3 and 4, of a condenser, i. e. the carrier parts AF, BG and B'G are also taken into account with temperature variations, the result is as follows. If the carriers 1, 8 and 9, except the intermediate parts 28 and 29, consist of ceramic material, the ansion of the carrier parts consisting of cerami material may be practically neglected in view of the very low expansion coefficient of ceramic material. Consequently, the length of the part AF is not influenced by temperature variations and the bottom plate I3 of the movable electrode 3 will not be displaced with respect to the casing wall II. On the other hand, the length of the carrier parts BG and B'G is influenced by temperature variations, since these carriers comprise the metal intermediate parts 28 and 29. If due to an increase in temperature by one degree the increase of the length 0 of the intermediate parts is Ac, the distance, from the bottom plate H of the fixed electrcde 4 to the casing wall I1 and consequently also to the bottom plate i3 of the movable electrode 3 will be increased by the amount Ac per degree temperature difference. This displacement in the direction of adjustment of the electrodes 3 and 4 with respect to one another, of course, brings about a variation in capacity of the condenser concerned, i e. a temperature increase brings about a decrease in capacity. In the construction shown in Fig. 1, the intermediate parts 28 and 2! in case of temperature variations consequently bring about a variation in capacity which is oppositely directed to the capacity variation originating from expansion of the electrodes. If therefore, the initial capacity ofthe condenser should be independent of temperature variations. the expansion Ac of the intermediate parts in the direction .of adjustment must be equal to the total expansion (Aa-i-Ab) of the two electrodes 3 and l, i. e. v- AC=AG+Ab If, however, a negative temperature coefiicient of the initial capacity of the condenser is required in view of thepositive temperature coefficient of other circuit parts, for example of a trimmer condenser, of the oscillatory circuit in which the condenser concerned is to be interposed, the expansion of the intermediate parts must be greater than the total expansion of the electrodes, 1. e.

Ac Aa+Ab By choosing the expansion of the intermediate parts, i; e. by choosing their lengthand expansion coeflicient, the temperature dependency of the initial capacity of the condenser may be adapted to the conditions imposed in each particular case.

In connection with the foregoing it must still be mentioned that if the condenser is capacity linear, as practically applies for the illustrated form of the electrodes, the capacity variations brought about by temperature variations are equally great for each adjustment of the condenser. If, however, the condenser is not capacity linear but, for example, frequency linear, the expansion of the intermediate parts 28 and 2! is preferably so chosen that the initial capacity of the condenser, together with the capacity of the trimmer and of the wiring exhibits the desired temperature dependency, since in general any undesirable variations to this total capacity become manifest as very interfering, if the electrodes of the condenser are entirely or substantially entirely separated from one another, because in this case the relative variation of the total capacity is greatest.

In the arrangement shown in Fig. 1, the intermediate parts 28 and 29 will influence with equal independent of temperature, whereas the third should have a negative temperature coefficient, this may be achieved by arranging in the carriers another intermediate part of appropriate length .and this between the points of suspension of the and 33 (which correspond to the intermediate parts 28 and 29 in Fig. 1) which are used to obtain a certain temperature dependency of the condensers, serve for supporting the carriers 8 and 9 of the fixed electrodes 2, 4 and 6 against the casing wall IT. The parts 32 and 33 are of a tubular form and their one ends are secured by soldering (points B and B) to the casing wall I I and their other ends (points C and C) to the carriers 8 and 9.

For obtaining a temperature independency of the initial capacity of the condensers, the expansion Ac of the tubes 32 and 33 between the points of fastening BC and BC', is to be chosen, as previously, so as to be equal to the total expansion Aa+Ab.

In this case, as in Fig. 1, the temperature dependency of all condensers is equal if the expansion of the carriers 1, 8 and 9 is neglectably small. It will be clear, however, that the latter applies only approximately.

The invention permits such a construction that the expansion of the carriers 1, 8 and 9, even when it is comparatively great, substantially does not influence the initial capacity of the condensers. This is achieved by choosing the carrier parts between their supporting point and the point of suspension of the electrodes of equal length. The supporting points of the carriers 1, 8 and 9 are designated by A, C and C. The points of suspension of the movable electrodes are indicated by D, F, H and the points'of suspension of the fixed electrodes by E, E; G, G; J, J.

The arrangement has now been chosen such that the following relations apply:

A temperature variation of the 'abovementioned carrier parts will in this case bring about,

respect to the casing wall l1; since, however, the electrodes of each of the condensers are displaced by the same amount and in the same direction with respect to the casing wall, the mutual position of the electrodes of a condenser is not influenced and a capacity variation is not pro-, duced. In the foregoing it was assumed that all carriers consist of the same material. It is evident that it is also possible to use different materials for the carriers. In this case the expansion of the parts corresponding to the carrier parts constituted above must be equal to the expansion of the other parts corresponding to the carrier parts constituted above.

The latter measure, of course, also applies to the construction of the condenser shown in Fi 1.

i Fig. 4 shows one form of construction of a condenser in which the part which is provided for obtaining a certain temperature dependency it is true, a displacement of the electrodes with serves to support the carrier of the movable electrodes I, 3 and 5 against the casing wall IT. The carrier 1, which consists of ceramic material, has at one end a bore in which is screwed an attachment of a metal shaft 7. The shaft 1, as in the previous figures of the carriers 1, is provided with screw thread 20 and supported against the casing wall H. The portion 34 of the shaft which is passed through the bottom plate l2 of the fixed electrode 2, has its diameter reduced and is covered by a tube 35 which consists also of ceramic material for obtaining at the same time a bearing of. the shaft 1 in the centering bush 22 of the fixed electrode 2 and an insulation of the shaft with respect to the centering bush.

The temperature dependency in this case is determined by the portion AK of the shaft which extends between thesupporting point A of the shaft I against the casing wall I! and the supporting point K of the carrier 1 at the portion 1 of the shaft. the construction was chosen such that the expansion of the carriers has substantially no importance for the capacity of the individual condensers, for the following relations apply:

If the construction should satisfy the above conditions, the length of the shaft portion AK is thus ascertained and only the expansion coefiicient with respect to the temperature dependency tobe obtained can, of course, be freely chosen.

If the temperature dependency of the initial capacity brought about by the carrier 1--| and the variation of the initial capacity brought about by expansion of the electrodes with temperature variations are to be oppositely directed, the fixed electrodes 2, 4 and 6 must be arranged in Fig. 4, in contradistinction with the arrangement in the-previous figures, between the casing wall I! and the corresponding movable electrode I, 2 or 3.

In conclusion, Fig. 5 shows one embodiment in which the carrier of the movable electrodes is supported against the casing wall I! by means of a part belonging to the adjusting device and this by means of the bush 30 which is rotatably mounted in the casing wall l1 and provided with a pin 3| which engages in the thread 20 of the movable carrier i.

The bush 30 is made of a much greater length than in the previous examples. This results in the supporting point of the carrier 1 at the bush 3!] not being situated approximately in the plane of the casing wall I! (see, for example, Fig. 1, point A), but at the point C. The supporting point of the bush 30 at the casing wall I! is situated at the point A and consequently the part AC of the bush 30 is decisive for the temperature dependency of the condenser capacity.

In the arrangement of Fig. 5' one end of the carriers 8 and 9 of the fixed electrodes is soldered directly to the casing wall II. It is evident, however, that in addition to the particular shape of the bush 30, these carriers may also be supported against the casing wall I'Lif required by means In this case also, like in Fig. 3,

Finally it may be mentioned that in the arrangements shown it is advantageous to secure the carriers fastened in the casing exclusively in the casing wall 11 and to mount these so as to be movable in the casing wall I8 so that, as has been set out in detail in the copending application, Ser. No. 280,515, filed June 22, 1939, the carriers of the casing II) are not hindered in their free expansion.

What we claim is:

1. An adjustable slidable condenser, comprising a housing having a pair of end walls. a. plurality of pairs of cooperating fixed and movable electrodes contained within the housing, an operating shaft extending through one of the end walls carrying the several movable electrodes, at least one carrier rod for supporting the several i fixed electrodes extending in the direction of adjustment and having one end aflixed to the end wall through which the operating shaft extends and the other end freely mounted within the other end wall, at least one of the electrode carriers having at its end adjacent to the end wall through which the operating shaft extends a metallic part whose temperature coefficient is such that the temperature dependency of the initial capacity of each of the several pairs of cooperating electrodes follows a certain predetermined regularity.

2. An adjustable slidable condenser, comprising a housing having a pair of end walls, a plurality of pairs of cooperating fixed and movable electrodes contained within the housing, said electrodes each consisting of a base plate and a helical sheet member having one of its edges affixed to the base plate, the free edges of a pair of cooperating electrodes being adjacent one another to permit the electrodes to be interleaved on with the other, an operating shaft extending through one of the end walls carrying the several movable electrodes through the intermediary of their base plates, at least one carrier rod for supporting the several fixed electrodes through the intermediary of their base plates extending in the direction of adjustment and having one end vaffixed to the end wall through which the operating shaft extends and the other end freely mounted within the other end wall, said carrier rod for the greater part being of ceramic material and the remaining part which is affixed to the end wall being of metal, the temperature coefficient of said metal part being such as to bring about a temperatur dependency of the initial capacity of each of the several pairs of cooperating electrodes which is substantially equal to the variation in initial capacity produced by the longitudinal expansion in opposing directions of each pair of cooperating electrodes with temperature variations.

3. An adjustable slidable condenser, comprising a housing having a pair of end walls, a plurality of pairs of cooperating fixed and movable electrodes contained within the housing, said electrodes each consisting of a base plate and a hellcal sheet member having one of its edges amxed to the base plate, the free edges of a pair of cooperating electrodes being adjacent one another to'permit the electrodes to be interleaved one with the other, an operating shaft extending through one of said end walls carrying the several movable electrodes through the intermediary of their base plates, at least one carrier rod for supporting the several fixed electrodes through the intermediar of their base plates extending in the direction of adjustmentand having one end affixed to the end wall throughwhich the oper- ALEXANDRE HOROWITZ.

HERRE RINIA.

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