FR2619914A1 - Electrical capacitor whose capacitance varies as a function of temperature, pressure and inclination - Google Patents

Abstract

The present invention relates to a variable-capacitance electrical capacitor used as a temperature, pressure and inclination sensor and whose capacitance depends on these physical magnitudes. The device of the invention consists, on the one hand, of a container 1 made of borosilicate or of ceramic or of any other refractory material, containing mercury 2 in which an electrode 6 is immersed; the mercury 2, acting as a moving armature (core), can expand or slide through a dielectric tube 4 and a thin sheet of varnished copper 8, used as a stationary armature (plate), is adhesively bonded against the tube 4. In addition, the varnished copper sheet 8 is roughened at one of its points 9, to which an electrode 7 is soldered. The device according to the invention can be employed as a precision thermometer, densimeter, dosimeter, inclinometer and is simple and reliable.

Description

the present invention relates to an electrical capacitor with verifiable capacity used as a temperature, pressure and inclination sensor and whose capacity depends on these physical quantities
Electrical capacitors with variable capacitance are particularly required for placing part or all of metallic reinforcements side by side around a same axis (trimmer). However, these devices are not directly sensitive to temperature or pressure and, moreover, they require an external mechanical action to adjust their capacity to the desired value.

Fluid dielectric variable capacitors are known (DE-AS
5I9) and (2 537 772) and a variable capacitor (Ds-OS 22 39 220) comprising chambers filled with a fluid dielectric, and which is constituted by a dielectric cylinder coated with an electroconductive layer on a part of the surface of the outer envelope which forms a first. capacitor frame, and a movable piston axially inside the dielectric cylinder and which forms the second armature of the capacitor; however, no indication of the formation of an electrical capacitor with variable capacitance as a function of temperature or pressure or inclination is given in these documents
The object of the invention is to provide an electrical capacitor with variable capacitance, as described at the beginning, which is of simple construction and inexpensive
According to the invention, the aim is achieved in that the fixed first frame of the capacitor is an electroconductive layer coated by the surface of the outer casing of a borosilicate dielectric cylindrical tube or any other refractory material, hermetically cradled by one of its bases and whose other base is integral with the opening of a reservoir into which the end of an electrode, the other end of which exits through the upper base of the tube, , as we have already said, is hermetically closed
Said reservoir is filled up to its throat with mercury of such dewlap that when the temperature or the pressure rises in the reservoir, the mercury rises in the tube thus behaving as the second mobile armature of the capacitor according to The space between the mercury free surface and the rest of the tube is vacuum; the section of the tube is sufficiently small and the tank volume large enough that the slightest variation in temperature or pressure can cause a significant variation in the height / column of mercury in the tube.

The advantages provided by the invention more particularly consist in a simple construction of an electrical capacitor with variable capacity as a function of temperature, pressure and even the inclination in which the presence of a mechanical part mobile is not essential. thus, mechanical wear can be avoided as occurs in known capacitors
The invention will be better understood from the following description of a preferred embodiment of the variable capacity device according to the invention, with reference to the accompanying drawings in which:
Figure I shows a section of the device according to the invention.

 Figure 2 shows a section of the device according to the invention provided with a screw system that adjusts the capacity to the desired value.

 Figure 3 shows a form of association of two devices according to the invention.

selon l'invention particulièrement adaptée à la mesure d'inolinaison).Figure 4 shows a form of association of two devices

according to the invention particularly suitable for measurement of inolinaison).

 FIG. 5 represents an electronic diagram in which the device according to the invention is used as a temperature, pressure or inclination sensor.

mercure monte dans le tube\4 comblant dans le même temps une partie de 1' espace vide 5
4 particulier une façon de faire varier la pression à l'intérieur du réservoir I consiste à le plonger dans un récipient contenant un liquide ou à l'introduire dans une atmosphère gazeuse servant de pneumostat.Referring to Figure I, the reservoir I, serving as a support for the entire device, is filled with mercury 2 to its groove 3
When the temperature or pressure rises in the tank I, the

mercury rises in the tube filling at the same time part of the empty space
In particular, a way of varying the pressure inside the tank I consists of immersing it in a container containing a liquid or introducing it into a gaseous atmosphere serving as a pneumostat.

tact électrique va. extrémité de l'électrode\o dont l'autre extrémité plon

ge\dans le réservoir à mercure I, et le point de contact électrique VB,
dont l'autre extrémité est extrémité de l'électrode 7 soudée, à la couche électroconductrice 8 revêtue de verni, en un point 9 que l'on a pris soin de gratter au préalable, est donnée par la formule approchée du condensateur cylindrique::

où Ao désigne la permittivité du vide
Ar la permittivité relative apparente du diélectrique du condensateur
désigne l'épaiseur du tube 4,
R le rayon de la gaine de l'électrode 6 et h = h(T,p) désigne la hauteur de la colonne de mercure dans le tube 4, avec l'origine des hauteurs prise à la base inférieure de la couche conductrice cylindrique 8.The capacitor capacitor C value seen between the point of con

electrical tact goes. end of the electrode \ o whose other end plon

in the mercury tank I, and the electrical contact point VB,
whose other end is the end of the welded electrode 7, to the electroconductive layer 8 coated with varnish, at a point 9 which has been carefully scratched beforehand, is given by the approximate formula of the cylindrical capacitor ::

where Ao denotes the permittivity of the vacuum
Ar the apparent relative permittivity of the capacitor dielectric
denotes the thickness of the tube 4,
R the radius of the cladding of the electrode 6 and h = h (T, p) denotes the height of the mercury column in the tube 4, with the origin of the heights taken at the lower base of the cylindrical conductive layer 8 .

On the other hand, at ordinary pressure, the melting temperature of the mercury being equal to -38.87 degrees Celsius, and the boiling point of the mercury being equal to 356.9 degrees Celsius, when the temperature of the tank I is comprised Strictly between -38.87 degrees Celsius, with a certain margin of safety, the isobaric dilation formula of mercury around the ordinary pressure makes it possible to write

Or denotes the coefficient of cubic expansion of mercury,
Y the interior volume of tank I and h. (p) the height of the mercury column in the tube 4 when the reservoir I is heated to zero degrees oelsius at a constant pressure p '
Therefore, for e <1, the capacity of the capacitor according to the invention is expressed by the formula:

 The electrode 6 is firmly retained by a base 10a which hermetically closes the upper part of the tube 4 thus sealing the entire device according to the invention.

 FIG. 2 represents a section of the device according to the invention provided with a non-electroconductive tight screwable sleeve 10h to which is welded one end of a non-electroconductive rod II whose other end is an ellipside of lateral dimensions smaller than the diameter cylindrical tube 4 and including a lead spherule 12.

In this way, when the sleeve lob is unscrewed fully, that is to say when said sleeve 10b occupies the highest position relative to the tube 4, the end of the rod II encompassing the lead spherule is found totally outside the tank I
On the other hand, when the sleeve 10b is screwed down completely, that is to say when said sleeve 10b is brought into contact with the upper part of the tube 4, the end of the rod 11 encompassing the lead apheresis is immersed. at the maximum depth in mercury 2 contained in the tank I.

 Due to the Archimedean firing when the lead ephule I2 is immersed in the mercury 2 contained in the tank I, there is an elevation of the level of the mercury column in the tube 4. As a result, the composite system by the sleeve 10b, the rod Il and the lead spherule I2 makes it possible to adjust the capacity of the device according to the invention to the desired value.

 FIG. 3 represents a cross-section of two identical devices according to the invention, the respective reservoirs 1a and 1b of which are connected by a non-electroconductive linear conduit 13. The behavior of this combination of two devices according to the invention is understood by the principle communicating vessels.

FIG. 4 represents the device according to the invention, as shown in FIG. 3, and placed in equilibrium on an inclined plane I4, the device as shown in FIG. 4 makes it possible to deduce the angle D that said inclined plane makes. with the horizontal plane by measuring capabilities
CI and C2 respectively seen on the one hand between the electrical contact nips VAI and VBI, and on the other hand between the electrical contact points VA2 and VB2; 1 denoting the distance separating the tubes 4a and 4b, the following formula is established:

au point de contact électrique VAI, d'autre part à une extrémitd d'un interrupteur 20 dont l'autre extrémité est reliée à un capacimètre 21. Les interrupteurs I8 et 20 sont agencés de telle façon qu'ils fonctionnent systématiquement en opposition, c'est-à-dire que quand l'un est ouvert 1' autre est fermé et vis versa
De plus un bâtonnet de ferrite 22 flotte dans le mercure contenu dans la conduite non-électrocenductrice I3 et les réservoirs la et Ib présentent à leurs gorges respectives des goulots d'étranglement 23 et 24 qui empê- chent la ferrite 22 de pénétrer dans lesdits réservoirs 1a et Ib; et une bobine d'auto-induction 25, dont la conduite non-électroconductrice 13 sert de mandrin, est enroulée de telle façon que son centre coïncide avec le centre de la conduite non-électroconductrice I3 et que sa longueur soit égale à celle du bâtonnet de ferrite 22. Referring to Figure 5, the device according to the invention as shown in part in Figure 4 is connected by its ends VB2 and V31 to ground, by its end VA2 at one end of a switch I5 whose the other end is connected on the one hand to an end of a coil I6 of inductance L whose other end is connected to a generator 17, on the other hand to an end of a switch 18 whose other end is connected to the electrical contact point VAi of the device according to the invention as shown in FIG. 4 A variable capacitor (trimmer) 19, one electrode of which is held to ground, is connected by its other electrode

at the point of electrical contact VAI, on the other hand at one end of a switch 20 whose other end is connected to a capacitance meter 21. The switches I8 and 20 are arranged in such a way that they function systematically in opposition, c that is, when one is open the other is closed and vice versa
In addition, a ferrite rod 22 floats in the mercury contained in the non-electrocenductive line I3 and the tanks 1a and 1b have at their respective grooves bottlenecks 23 and 24 which prevent the ferrite 22 from entering said tanks. 1a and Ib; and a self-induction coil 25, whose non-electroconductive pipe 13 serves as a mandrel, is wound so that its center coincides with the center of the non-electroconductive pipe I3 and that its length is equal to that of the rod ferrite 22.

teur opérationnel monté en amplificateur suiveur. La capacité\CX est alors remise à zéro Farad; ce qu'on vérifie à l'aide du capacimètre 21 lorsque l'interrupteur 20 est fermé.The device according to the invention as shown in FIG. 4 is set as follows
When the device according to the invention as shown in Figure 4 is placed on a horizontal plane, that is to say for D reduced to the zero angle, the ferrite 22 is then completely inside the coil Whose ductance becomes maximum and can then resonate with a capacitor of known and fixed capacitance which forms with the coil 25 an auxiliary circuit connected to the generator I7 by means of an amplification.

Operator mounted as a follower amplifier. The \ CX capacity is then reset to Farad; this is verified using the capacimeter 21 when the switch 20 is closed.

 After this preliminary adjustment, the device is ready for measuring the angle D that makes a plane inclined with the horizontal plane.

The switch 18d being closed
First, the switch 13 is closed, the switch 18b remains open and the frequency t of the generator is varied to the resonance. The capacitance seen between the terminals VA2 and VB2 is equal to C2, then the resonance condition

ainsi obtenue, on ouvre l'interrupteur 15 et ferme l'interrupteur 18b, l'interrupteur 20 butant par conséquent ouvert; on cherche alors, en faisant varier à la fréquence donnée V la capacité CX du condensateur 19, La nouvelle condition de resonnance qui / s'écrit par conséquent:

Then working at this frequency

thus obtained, the switch 15 is opened and the switch 18b is closed, the switch 20 therefore abutting open; it is then sought, by varying at the given frequency V capacitance CX capacitor 19, the new condition of resonance that / is written as:

 The comparison made between the two resonance conditions thus obtained therefore goes as follows: CX I C2 - CI.

from where

Thus, the measurement of the capacitance CX of the capacitor I9, which takes place by closing the switch 20 / and opening the switch 18a, makes it possible to determine the angle D sought. In particular, for small inclinations, the following linear relationship is drawn between D and CX:

Claims (5)

 I - Electrical Capacitor with variable capacity as a function of temperature, pressure and inclination, characterized in that it comprises capacitance measuring means, a tank (I), in which is bathed an end of an electrode (6) held stationary by a sealing gasket (3) or a weld on a base (10a) containing mercury (2) as a movable armature of said electrical capacitor being able to mount in a dielectric tube (4) coated on its outer surface by a conductive layer (8) which is then the fixed armature of said capacitor and on which is welded an electrode (7).  2 - capacitive electric capacitor according to claim I, characterized in that a screw-and-seal sleeve (10b) is integral with a rod (II) of lateral dimensions smaller than those of the opening of the dielectric tube (4), the other end of which contains a spherule of lead (12) is capable of wetting in the mercury reservoir and thereby raising the level of the mercury column (2) in the dielectric tube (4).  3 - electrical capacitor with variable capacity according to the inclination according to claim I, characterized in that two variable electrical capacitors according to the invention coupled by placing in communication their respective tanks (1a) and (Ib) by the intermediate of a non-electrically conductive conduit (13) together form an electric capacitor with variable capacitance, depending on the temperature, the pressure and the inclination, very suitable for the measurement of inclination.  4 - variable capacitance electric capacitor according to one of claims 1 or 3, characterized in that a ferrite rod (22) is in eéré in the non-electroconductive conduit (I3), that bottlenecks (23) , 24) are placed at the ends of the pipe (13) integral with the reservoirs (1a, 1b) and that a coil (25) is centered on the non-electroductive pipe (13) which serves as a mandrel.  5 - variable electric capacitor according to one of claims I, 3 and 4, wherein said means for tilt measurement comprises a sinusoldale voltage generator (17) in series with a coil (16), deur devices according to the coupled by a non-electroconductive conduit (13), switches (15, 18 to 18b /, 20), a variable capacitance (I9) and a capacitance meter (21).