US2315330A - Adjustable slidable electrode condenser - Google Patents

Description

March 30, 1943. 'HORCwn-z ET AL 2,315,330

I ADJUSTABLE SLIDABLE ELEGTRODE CONDENSER Filed Sept. 30, 1939 7. b 8 Z ll 2 .w sw RR mw HE E vm WN ATTORNEY great stableness trode 2, i. e. the point of attachment of the centering bush l on the shaft I, than to the point B where the intermediate member is secured to the eleotrode 3.

When also considering the expansion of the intermediate members (whose length is denoted by c) in the directionof adjustment it'will be evident that due to an increase in temperature and the ensuing expansion of the intermediate members the fixed electrode 3 is moved away from the movable electrode 2. If for each degree of the increase in temperature the expansion of the intermediate member is Ac and that of the electrodes 2 and 3 in the direction of adjustment amounts to na and Ab respectively the initial capacity of the condenser is not infiuenced by variations in temperature when the expansion of the intermediate member is equal to the total expansion of the two electrodes in the direction of adjustment, i. e. consequently when When, in view of' the positive temperature coefficients of other elements of the circut, e. g. a trimmer condenser of the oscillatory circuit, part of which is formed by the tuning condenser shown, a negative temperature coeificient of the initial capacity of the condensers is desired, the expansion of the intermediate members must exceed the total expansion of the electrodes and therefore The expansion of the intermediate members 1 and 8 may `be arbitrarily chosen within wide limits according to the requirements which are each time to be complied with since the length of the intermediate members and the material of the latter (i. e. consequently their coeflicients of expansion) may be chosen at will. If a very of the condenser is required, it is advisable to utilise shortv intermediate members; they are therefore preferably made of a metal having a high coefiicient of expansion such, V

for example, as tin or zinc. If a very great stableness is not absolutely necessary it is simpler from the standpoint of construction to make the intermediate members and that portion of the electrode `(the base plate l I) to which the intermediate members are secured, from one piece of sheet metal as is shown in Fg. l. The choice. of the material depends in this case on the requirements to which the base plate H has to satisfy. When, for example, the electrode consists of a spirally wound strip of copper or brass which is secured by soldering to the base plate ll, .the latter should preferably also consist, in view of the soldering of the strip, of copper or brass and the expansion of the intermediate members can only be controlled by the choice of their'length. In order to ensure temperature-dependence of the condenser the length c of the intermediate members, measured in the direction of adjustmustbechoseninthiscasesoastobeequal to the total of the lengths (a+b) of both electrodes.

In connection with the above explanations it por-ts, when may finally be obscrvedv that when the condenser is capacity-linear, as practlcally occurs with the shown construction of Variation brought about by variations in temperature, which capacity Variation may be zero, may be equal in value for any adiustment of the condenser. If, however. the condenser is not capacity-linear but is, for example, frequencylinear, the expansion of the intermediate members 1 and I should preferably be so chosen that the initial capacity of the condenser together with the capacity of the trimmer and of the wiring exhibits the desired dependence on temperature since in general any possible undesired Variation of this total capacity becomes manifest in a very disturbing manner when the electrodes of the tuning condenser are telescoped completely or substantially completely out of one another since in this case the relative variations of the capacity are greatest.

In the foregoing it was -assumed that in the case of temperature variations the supports neither expand (or that their expansion is unimportant) nor are displaced relatively to one another. This supposition approximately holds good when the supports consist, for example, of

ceramie material having a very low coefiicient of expansion and the supports are supported, for example from the easing Il, in such manner that reiative displacement of the supports due to said supporting does not occur, as will hereinafter be shown fully.

Fig. 3 represents a ganged slidable-electrode condenser according to the invention. A shaft l2 which is slidable in the axial direction for the purpose of adiusting the capacity has mounted on it movable electrodes l3, 15, and |1. Fixed electrodes ll, ii and I! are secured, by means of intermediate members 19, 2|; 2|, 22; 22, 2|, to supports 25, 21 which are carried by a casln 25. A bush 29 provided witha pin 30 is rotatably mounted in the wall 28 of the casing. The bush 29, which is actuated, for example, by the adiusting device, is mounted in such manner that axial displacement cannot occur. The pin 3B engages a screwthread 3| and, upon rotating of the bush 29, it brings about a displacement "of the shaft |2. In order to avoid an amount of play of the shaft [2 with respect to the wall 28 of the casing there is provided a spring 32. Metallic partitions 28' are provided in the casing ll in order to screen the separate condensers from one another.

As may be seen from the figure thesupports 26 and 21 as well as the support |2 are supported by the wall 28 of the casing in such manner that the points of support D, E of the supports 2| and 21 and the point of support F of the support I! are located approximately in a plane perpendicular to the axial direotion of the condenser rectly by the wall 2| of th of support therefore does not give rlse, in thecase of temperature variations, to a relatlve displacement in the direction of adjustment of the supparts 25, 21 and Il. attachment of the diate members of the separate condensers. for example G. H and I, as well as the supportinx points of the supports are located in a plane perpendicular to the direction of adjustment. This particular situation of the points of attachmmt ,has the advantage that expansion of the supthe latter consist, for example, of the same material, does not bring about a varithe electrod the capacity practically di- Furthermore, the points of electrodes and the intermeation in' the capacityof the condensers, so that the coefllcient of expanslon 'of the material of `the supports is in itself unimportant since the marks also apply, of course, to the relative position of the electrodes |5, IS and I'l. I! since the points where these electrodes are secured to the supports are also located :'or each pair Ofrelectrodes substantially in one plane perpendicular to the direction of adjustment.

Although the intermediate members by means Of which the fixed electrodes H. IS and i' are secured to the supports 26 and 21, have in Flg. 3 all of them the same length, it is evident that, if required, it is also possible, Of course, for the intermediate members, for example for those Of one of the fixed electrodes, to have a different length. Another temperature-dependence of the capacity of the condenser in question is thus obtained as may be required, for example, in view of the elements of the oscillatory circuit into which the tuning condenser has to be connected.

i Fig. 4 represents a single condenser Of a ganged slidable-eelectrode condenser the two electrodes of which are secured to the supports with the aid of an intermediate member according to the lnvention; As in the preceding examples th'e fixed electrode 33 is equipped' with acentering bush 35 which is provided .in a base plate 3.4 and in which a shaft 3,5 is mountedso 'as to be slidable.

The base. plate '33' of the movable electrode 31 has secured in it one'end of a centering bush 39. In contrast with the preceding examples the centering bush 30 is nOt shrunk on to the shaft 33 but that end Oflthe bush 33 which is directed towards the fixed electrode 33 is secured to the shaft 3| by soldering (at the point K). Whereas in the preceding examples. the point where the movable electrode is suspended from its supportis located approximately in the plane of the base plate (see for example Fig. 1 point ;A and- Flg. 3 point G), the point of Suspension K of the movable electrode 3'I is located in this case in appreciably closer proximity to the fixed electrode 33. The centerlng bush 39 thus acts as the intermediate member by means Of which the condenser acquires a pre-determined temperature-dependlarly suitable when, in view of a negative tem- ,whilst, in addition, the construction is very stable. This construction is therefore particuperature coefiiclent of the condenser, the total length of -the intermediate members has to be taken 'comparatively large.

What we claim is:

1. An adjustable slidable-electrode condenser, comprising a pair of cooperating .electrodes, one fixed and' the other movable, a support for each electrode and an intermediate member' serving solely as a conneeting member interposed between each of'said electrodes and its support, the point where the intermediate member of one electrode is secured to the support being located, measured in the direction of adjustment. in closer proximity tothe point of Suspension of the other electrode than is the point where the intermediate member is secured to said one electrode and said electrodes having a predetermlned length and the combined lengths of the intermediate members. z

measured in the direction of adjustment, being substantially. equal'to the combined lengths of the two electrodes.

2. An adjustable condenser of the slidableelectrode type comprising fiired'and movable electrodes which areadapted to be interleaved one with the other, a suqobl operatmg shaft 'having the movable electrode aflixed thereto at a predetermlned point, a carrier rod disposed in parallel to the Operating shaft having the fixed velectrode aflixed thereto at a predetermlned point,

said predetermined points of electrode suspension in the minimum capacity position of the elec- -trodes being aligned in a plane substantially at right ang'les to the Operating shaft.

3. An adiustable condenser of the slida bleelectrode type comprising fixed and movable electrodes Of predetermlned length which are adapted to be interleaved one with the Other, a slidable Operating shaft. a bushing mounted on said shaft having the lmovable electrode amxed to one end thereof, the other end of the bushing ence since, as in the preceding examples, the

point K where the intermediate member 3| is secured to the. support 36 is located, measured inthe direction of adiustment; in close: proximity to the point of Suspension M of the fixed electrode, 33 than to the point L where the intermediate member 33 is secured to the movable electrode u. 'rhe nxed electrode a is'seouree to its supv vadvantagcous to choose the total length of the intermediate members 3| and ll, 4|, measured i in the 'directionof adjustment (B+W) soas to be equal tothe sum of the lengths of-both electrodes 33'and 31.

In order to ensure temperature-dependenoe of the condenser. the total ex'pansionof the intermediate members 33 and", li must now be being aihxed to the shaft, a carrier rod disposed in parallel to the Operating shaft, and a second' bushing mounted on said rod having the fixed electrode aflixed to one end thereof, the other end of the bushing being aflixed to the rod, said i bushings being of a combined length substantilly equal to the combined length of the electrodes. w

4. An adjustable condenser of the slidablei' electrode type comprising fixed. andv movable 4electrodes of predetermlned length which are adapted to be interleaved one with the other, a slidable Operating shaft, a bushing of substantially the same length' as the movable electrode mounted on the shaft and having one end amxed :to the electrode and the other end to the shaft.l a carrier rod disposed in'paraliel to the Operating 1 shaft,'and a bushing of substantially the same length as the flxed electrode mounted on the rod vand hving One end aflixed to the electrode and the other end to the rod, the emu ot the bushings to which are respectively connected the shaft and the rod being,v in the minimum capacity i position ofthe electrodes, aligned in a plane sub-` stantially at right angles to the Operating shaft.

` ALaxsNpan noaowrrz- HERRE RINIA.

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