US2115916A - Electric condenser - Google Patents

Description

M.v osNos 2,115,916

Mxipy 3, 1938.

l ELECTRIC CONDENSER original Filed May 5, 19:52

' INVENTOR MENDEL 05 5 BY /fmw Patented May 3, 1.938

ELECTRIC CONDENSER Mendel Osnos, Berlin, Germany, assigner to Telefunken Gesellschaft fr Drahtlose Telegraphie m. b. ll., Berlin, Germany, a corporation of Germany Application May 5, 1932, Serial No. 609,401. Renewed July 25, 1936. In Germany July 2, 1931 3 Claims'. (Cl. F15-41.5)

This invention relates to an improved electric condenser whose capacity varies very markedly with the temperature. A condenser of this invention is particularly adapted to use in a circuit for tuning the capacity of a vacuum tube transmitter, especially when short-waves are employed, and is to be controlled from a remote point or else for the purposes of stabilizing frequency of a valve transmitter controlled by the agency of a piezo-electric crystal.

According to the invention a. vcondenser of this kind is created so that it active surface or its inter-electrode distance, or else both, are adjusted or regulated by a fluid possessing a large temperature coeflicient of expansion or else by a gas (say, air) or a combination thereof. It is then feasible to heat the liquid or the gas or a combination of both, for example, by means of electric .heating to a more or less high degree, with the result that the capacity of the condenser is regulable or adjustable at will at anyv desired rate.

A number of practical embodiments are shown in the drawing, of which,

Fig. 1 is a vertical cross section of the improved condenser having double walls;

Fig. 2 is a vertical cross section of a simple modification of this condenser;

Figl 3 is a vertical cross section of another modification of this condenser;

Fig.k 4iso. Wiring diagram of the heating system.

Referring to Fig. 1, I and IA denote a doublewalled (jacketed) glass vessel of cylindrical form whose space between the lateral walls is very small (say, 1/2 to 1 mm. in radial direction) but comparatively large between the bottom or4 end surfaces. f

'Ihe space or cavity between the bottoms of the two cylinders is filled entirely by a suitable liquid 2 such as mercury, for instance. The space between the shells is not filled at all or only up to a certain height or level h; but the entire space between the shells is suitably exhausted. The inner and the outer shell starting at a certain level ho is coated with a highly conducting metal il, and 3A say, tinfoil.

The entire vessel is supported by a coil body 9, preferably made of metal which carries a winding 1 heated by current. y

When the temperature of the liquid mercury increases its level will rise in the space between the lateral Walls and there is formed a capacity between the liquid and the tinfoil coat.

It can be proved that the change in capacity of such a condenser is directly proportional to the variation in the temperature, indeed, it is possible to write with close approximation:

whereTo and Ca the temperature and capacity. respectively when the level of the column of the liquid between the lateral walls is flush with the lower edges of the tinfoil coats or slightly above them, T a higher temperature and C'a correspondingly increased capacity, Vo the volume of the liquid at temperature To, K a constant which is a function of the nature of the liquid and of the dimensions of the container.

If the liquid consists of mercury having a coefficient of thermal expansion of say 0.000181, if the distance between the surfaces of the shell: 1 mm., the wall thickness 1 mm., and if a kind of glass is used having a dielectric constantz'l, then with close approximation:

where C in cm., Vn in cm. cu., and T in degl'. C.

For short waves the capacitive reactance (capacitance) between the liquid and the metal plate 9 is `very low so that the capacity according to Equation (2) comes to be close to that between. the contacts 8 and 5.

Another simpler, though somewhat less favorable, embodiment is shown in Fig. 2, where l is a glass jar or bottle having a base or bottom considerably larger in area than the cross-section of the neck, and 2| a metallic electrode which can be screwedby means of a screwthread 4 on the collar ring or flange 22 so as to be at the correct distance above the liquids level (mercury) Y Now, if the liquid mercury -ls heated by means of the heater windingv 'i wrapped around the body 9 the liquid will be caused to expand, the distance the sheet-metal casing would occasion seriousl losses where short waves are dealt with.

Now, this drawback can be obviated by that the major part thereof is outside.

What follows further-from Formula I(2) is that C-Co T Tow .(3)

In practice it will befound advisable to make the quantity --T To=l (4) But it Will be noted that Vo even in the limiting case must be equal to 500 cu. cm. Assuming that the liquid is mercury, the weight thereof would be as much as 0.5 13.6=6.8 kilos. volume of the conductive liquid may be appreciably reduced if for the actuation of the mobile electrode recourse is had to the thermal expansion of a liquid or gaseous substance which, while being non-conducting or but slightly conductive, possesses a high coefficient of thermal expansion. An embodiment of this kind is shown in Fig. 3. The constituent parts of the device are as follows: f f 3| is a-space within the glass vessel I which is filled either with liquid or with a gas (air) or with both, which though not conducting electricity, possesses a high coej'icient of thermal expansion; 2 is a conducting liquid mercury, 3 and 3a tinfoil coats, I the cylindrical glass vessel with a double wall being open inside a short distance above the bottom, 35 a cover being e' mented on the' glass vessel I, 9 a heater body, 31 insulated lead-ins to the heater body, 38 terminals for the latter, 39 a seal for the lead to the liquid electrode, 30 lead to the liquid electrode, 34 cementing of the cover 35, i2 space above the conducting liquid between the shells of the two cylinders. 'Ihe space is either evacuated or contains a gas (air) of lower pressure than the pressure inside space 3|; optionally also a heater coil I3 for heating the space I2.

If the heater element 6 is heated electrically, the pressure inside space 3| will rise and thus also the mercury in space I2, and thus alter 4the capacity of the condenser.

If space I2 is' small enough compared with space 3l it can be proved that the capacity of the condenser is nearly proportional to the temperature in the space 3|, if space I2 is evacuated. But if the space I2 is not exhausted then the capacity of the condenser is proportional to the temperature and pressure difference between spaces I2 and 3|.

Instead of the space 3| it would be possible also to heat the space I2, and then the capacity decreases with increasing heating current. It would also be feasible to heat both spaces though at dierent temperature, for it will be understood However, the.

that the change in capacity, as already pointed out, is predicated only upon the temperature differences of the two spaces.

'I'he difference in the temperatures of the two spaces may be regulated, for instance, by means of a bridge arrangement according to Fig. 4, where, as previously, 6 and I3 the heater resistors of the spaces 3| and |2,vwhi1e Il denotes a potentiometer located at the control point whose voltage division ls regulated by a slide contact I5. In case of dierential heating the resistances and the cooling conditions of spaces 3| and I2 may be so chosen that the temperature of the ambient will exercisevno influence upon the capacity so that the capacityis merely a function of the position of contact Il (Fig. 4).

I claim: L

l. An electric condenser comprising an insulating cylindrical casing having a double wall, said double wall having a relatively small internal space in the radial direction but a substantially large space between the bottom of one of said walls\and the top ofthe other wall, a metallic coating on the upper outside surface of each wall, a mobile electroderwithin said walls, and an external electric heating element comprising a disk-like coil body having a heater winding and located below said container to control the level of said mobile electrode.

2. An electric condenser comprising an insulating cylindrical casing having a double wall, said double wall having a relatively small internal space in the radial direction but a substantially large space between the bottom of one of said walls and the top of the other w`all, a metallic coating on the upper outside surface of each wall, a mobile electrode located within the lower portion of said walls, the space in the upper portion ofsaid walls being evacuated, and an external electric heating element` comprising a disk-like body having a heater winding and located below said container to control the level of said mobile electrode.

3. An electric condenser comprising an.in sulating cylindrical casing having a double wall, said double wall having a relatively small internal space in the radial direction but a substantially large space between the bottom of one of said walls and the top of the other wall, a metallic coating on the upper outside surface of each wall, a mobile electrode of mercury within the lower portion of said walls, the space in the upper portion of said walls being evacuated, and

an external electricheatlng element comprising a disk-like body having a heater winding and located below said container to control the level of said mobile electrode.

' MENDEL OSNOS.

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