DE2456384A1 - SENSING ELEMENT FOR ELECTRIC MEASUREMENT OF INCLINATIONS - Google Patents

Description

Dipl.-Ing. H. MITSCHERLICH Ο —8 MUNICH

DipL-ing. K. GUNSCHMANN S * in-.dorfstrasse

Dr. rer. not. W. KÖRBER ^ r «·» «» Dipl.-Ing. J. SCHMIDT-EVERS

PATENTANWÄLTE ' ^2δ · NOV .. 197.4.

Dr.Kö / Ne

CONTRAVES AG.
Zurich, Switzerland

Schaffhauserstr. 58o

Patent application

. Sensing element for electrical measurement of inclinations

The invention relates to a level or sensing element for electrical measurement of inclinations or for determining the true perpendicular for bodies at rest and the apparent perpendicular for moving bodies. In particular concerns the Invention a sensing element for determining the perpendicular by measuring an electrical that changes as a function of the tilt Impedance between flat electrodes that are connected to a liquid contained in a container are in contact and each connected to an externally contactable electrode connection.

There are such sensing elements are known in the form of tubular vials for displaying the inclination in only one Direction and in the form of circular vials for indicating the inclination in all directions. It is known for the production of such sensing elements in combination with electrodes made of highly conductive material to use an electrolyte solution of good conductivity

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the, for example a solution of an alkali halide in an alcohol, and the container with this solution partially to fill, leaving a gas bubble, the position of which defines the streamlines between the electrodes and thus determines the measured impedance; the change in impedance between two electrodes will depend on the Tilting of the sensing element due to the change in the equilibrium position of the liquid or gas bubble generated in the container. It is also known to let electrodes in an electrically insulating wall of the container and the side of this structure facing the liquid as a section of a hollow spherical or ring-shaped surface to shape. A so-called base electrode is often attached to an opposite wall, with the walls provided with electrodes have at least one common plane of symmetry that is vertical in the normal position exhibit. The individual electrode connections are connected to the corresponding electrodes by cables, which are passed through the walls, unless the electrode, line and electrode connection consist of a single part that lies cemented in the wall and traverses it.

The requirements regarding the geometric shape and position of the electrodes "and the walls are in directly related to the desired precision of the inclination measurement and are particularly due to the trend tightened for the miniaturization of the sensing elements. as Sensing element characteristic, d. H. as a variation of the measured impedance depending on the tilt, a predetermined, mostly linear function is sought, whereby it is difficult to determine the deviation of the characteristic from the Linearity as well as the influence of temperature, which over the expansion of the liquid the dimension of the

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Keeping the gas bubble as small as possible. In addition ■ Requirements for tightness, corrosion resistance, mechanical resistance, etc. come in view of all these requirements are the insertion and cementing of the electrodes in the walls and that Grinding these structures to the required precise shape rather difficult and costly manufacturing operations, in which, despite all the measures, a high reject rate and an inadequate reliability rate of the product are to be accepted.

It is known to be made by inserting and cementing of the electrodes in the walls and the grinding of these structures to avoid the difficulties that arise, that the electrodes are formed from layers applied as paste or lacquer, e.g. B. from plotted accordingly Platinum or silver layers. this makes possible indeed, from one and the same layer each one electrode, one associated electrode connection and to form a connecting conductor track, the conductor tracks from the inside of the container to the outside Adhesive points are passed through, at which the components of the joined together to form a container The sensing element are in contact. In this solution · is but disadvantageous that in certain applications, for. B. in the military to level a gun the Required geometric precision of the sensing element because of the layer thickness and roughness of the paste or Electrodes applied to varnish are far from attainable; this applies to both the precision of the 3? orm of the inner Wall of the container in the area of the electrodes such as the precision of joining the container to the Bonding points in the area of the conductor tracks. Another-

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on the other hand is also disadvantageous that the adhesive strength of the The applied layers, among other things, do not meet the requirements for the application mentioned.

The object of the invention is to provide a novel construction of a sensing element which is an essential allows cheaper manufacturing processes and not only meets existing requirements more satisfactorily, but also the adaptation of the sensing element characteristic to the application by a free choice of the electrode shape improved.

It has been found that the solution to this problem is made easier by using what is known as thin-film technology will. Under thin layers, such as those in the Manufacture of electronic components are used, one understands those layers that are on a " Underlay are formed, the layer thickness usually below 5 μ and usually in the range of 0.01 up to 1 a. remain. Those used to form thin layers in Processes to be considered are, for example, vapor deposition, sputtering, electroplating and chemical Deposition, the application of paste, whereas other, state-of-the-art processes are by no means excluded, such as anodizing to form insulating thin layers on certain Metals. On the other hand, the so-called thick layers are excluded from this, which are caused, among other things, by the application of Paste or varnish e.g. B. formed by screen printing, and their thickness typically in the range of 20 u lies.

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According to the invention, a sensing element is characterized in that at least one of the liquid facing, electrically insulating surface of a wall of the container as an electrode. this superficial applied thin layer is formed.

Such electrodes applied as a thin layer are not substantially raised above the surface of the wall; the elevation occurring around the thickness of the electrode layer the electrode surface has essentially no effect on the equilibrium position of the liquid or the gas bubble.

In a preferred embodiment of the electrodes applied as a thin layer, these are made of multiple layers. On the outer side of the multilayer, facing away from the wall The electrode structure is a vapor-deposited, electrochemically active black layer, which is advantageously electroplated after the vapor deposition.

With such electrochemically active black layers, better wetting by the dragonfly liquid can be achieved and to achieve a reduction in the contact resistance between the electrodes and the liquid.

In a vial with electrodes made according to this training, these consist, for example, of a) one to to about 0.2 η. thick adhesive layer of 50:50 Hi-Cr alloy; b) one up to about 0.06 u. "thick protective

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layer of gold; and c) one up to about 1.1µ thick Layer of gold black. The adhesive layer and the protective layer are vapor-deposited under conventional vacuum conditions. The vapor deposition of the gold black layer takes place in the presence of nitrogen or helium residual gas in the Pressure range from 0.1 to 2 Torr with high evaporation rate. The gas is also z. B. Argon can be used, and the black coverings can be made of other precious metals such as gold instead of gold. B. platinum, iridium, rhodium, Osmium etc. or from certain transition elements such as z. B. antimony, bismuth, etc. and their alloys.

In another embodiment, the electrodes consist of a) an adhesive layer and b) a protective layer as in FIG previous example, also from c) a vapor-deposited or formed by sputtering metallic Plastin layer, and d) an electrodeposited platinum black layer up to about 1 u thick. The metallic platinum layer under c) can also be formed galvanically with a thickness of up to about 1 u.

In all of these examples, the total thickness of the thin-film electrodes remains essentially below 5 V--

With the electrodes applied as a thin layer, the The advantage achieved is that the properties to be demanded of the wall material and of the electrode material are mutually exclusive are independent, so that the choice of materials is not restricted by any requirement for compatibility will.

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The material of a "wall is advantageously used before application of the electrodes brought to the desired geometric shape, so it is only homogeneous material too ■ edit and not, as with known designs, an inhomogeneous structure made of insulating, electrode and cement material. The mechanical processing will be accordingly easier and cheaper. It is known to use an electrically insulating material for the material of a wall To use substance on which the electrodes according to the invention are applied: it will mostly Tempered glass applied that is commercially available as Pyrex or Duran is well known. By applying according to the invention. an electrode as a thin layer is also the variant allows, after which a wall is formed from electrically conductive material, for example from a corrosion-resistant metal such as tantalum or stainless steel, or made of silicon.

In this production method, according to the invention, one is off electrically conductive material existing wall of the sensing element at least on its "facing the liquid" Surface covered by an electrically insulating material applied as a thin layer, whereby a wall with an electrically insulating surface is created.

The application of such insulating materials is well known in thin-film technology. Are used z. B. that Sputtering oxides in a high-frequency field or oxidative sputtering of suitable oxide-forming metals. If tantalum and silicon are used, an extremely thin but highly insulating oxide layer can be anodized are formed. Layers of plastic can also be applied.

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The advantage of this inventive variant is that for the material of the wall a substance due to its durability, easier or more precise processing and similar properties can be selected without restriction on the basis of electrical behavior. To the The material of the wall is advantageously given the desired geometric shape first, and only then the surface facing the liquid is provided with an insulating layer on which the optionally required number of electrodes is applied.

Thanks to the inventive application of the electrodes to the electrically insulating surface of the walls of the Container, the shape of the electrodes can be optimized to achieve the desired characteristic.

It is known that the steepest possible steepness is a linear characteristic is achieved with an electrode set, which consists of a base electrode and, for each, directly canting plane to be detected, consists of a pair of electrodes designed approximately as circular areas, wherein on the one hand the pair of electrodes and on the other hand the base electrode symmetrically about a common plane of symmetry are. With this approximately circular shape of the electrodes, it is disadvantageous that a temperature-related change the gas bubble dimension has a strong effect on the steepness of the characteristic curve.

It is also known to give the electrodes a rectangular outline, each with a pair of sides of a rectangle runs parallel to a plane of symmetry of the sensing element. In so far this outline is a narrow strip

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equals, its longitudinal direction in the to be detected The canting plane lies and its ends are relatively wide away from the demarcation line between the gas bubble, the electrolyte solution and the container, is the Characteristic of the. Sensing element pretty much independent of the geometric outline of the strip in the area of these ends; thereby these ends can in a known manner any, e.g. B. rounded shape can be given. The disadvantage of this solution is that it affects the dimension of the sensing element has requirements that are in contrast to the requirements of miniaturization: the Influence of the gas bubble dimension and the deviation from the linearity of the characteristic curve are only kept small if when the width of the electrode strips is small compared to their length and compared to the gas bubble dimension.

It has been found that a linear characteristic is achieved with a different, special shape of the electrode surfaces can be, with this particular shape the influence of the gas bubble dimension on the three steepness of the Characteristic is very reduced.

According to the invention, at least two flat electrodes are in a sensing element in a manner known per se as symmetrical about a normal vertical plane Pair associated with each other, and the outline of an electrode surface is the outline of a flat quadrangle projected vertically onto the surface, the wall from a rectangle having sides parallel to the plane of symmetry by inserting circular arcs with the Plane of symmetry facing concavity instead of said one Pages is derived.

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Preferably order the outlines in a pair of electrodes of the electrodes from the projection of two symmetrical quadrilaterals, the arcuate sides of which as equal arcs of two equal circles intersecting on the plane of symmetry are formed ..

In such an embodiment of the sensing element according to the invention the impedances are expediently between the base electrode and one electrode of the Electrode pair detected as a member of a bridge balanced in the normal position, and the one caused by the tilt Adjustment error corresponds to 'the characteristic curve of the sensing element. A characteristic that is as linear as possible and a The lowest possible dependence of the characteristic on the gas bubble dimension is achieved when the gas bubble is in Normal position covers about half of each electrode. The sensing element can be tubular with a single pair of electrodes and a base electrode as well Can-shaped with two pairs of electrodes and a base electrode be formed, the sensing element in the former case one, in the latter case two perpendicular to each other Has planes of symmetry; Variants with three or more electrode pairs and planes of symmetry are not particularly useful, but not excluded.

With the application according to the invention of the electrodes as thin layers on the electrically insulating surface of the walls of the container, it is also possible to use different electrode outlines to create various non-linear To achieve characteristics, for example and depending on the application, square, logarithmic and other Characteristics. Thanks to the precision of the electrode outlines that can be achieved with thin-film technology, not only

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opens up the new possibilities mentioned, including the The reproducibility of the products is considerably facilitated and improved compared to the known designs. ·

Another gate part of the application according to the invention the · electrodes as thin layers are used to improve their adhesive strength and corrosion resistance the electrodes can be multilayered in a manner known in thin-film technology. It's practical all known combinations of an adhesion-improving agent lower layer and an electrically and chemically advantageous upper layer applicable; for example a thin layer is applied to a hard glass wall, those made of a lower layer of nickel-chromium alloy and a top layer of gold or platinum. There are many insulating plastics known that are not injured by the application of certain thin layers, for example made of aluminum or gold so that, among other things, these metals can be used as a lower layer for the application of electrodes to improve plastic-coated walls and the application of such surface-insulated walls to facilitate. ".

As already mentioned, in the known designs a sensing element the individual electrode connections connected to the corresponding electrodes by cables, which are carried out through the walls or at points of adhesion, which relates to difficulties on the manufacturing cost, precision and reliability of the sensing elements and in some Cases the application of electrically conductive material

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for the walls of the container practically excludes. It has been found that the solution to these problems is also facilitated by using thin-film technology.

According to the invention is an electrode with an associated .Elektrodenanschluss in a known manner by a Conductor track electrically connected as a thin film in a known manner on electrically insulating Surface parts of assemblable to a container components of the sensing element is applied.

This has the advantage that the conductor tracks thanks to their low layer thickness, can be passed from the inside of the container to the outside at gluing points, at which the components of the sensing element assembled to form a container are in contact without affect the precision of the sensing element.

It is advantageous, although not absolutely necessary, that the conductor tracks and the electrodes are made of the same thin layers exist. Also, the conductor tracks can either be exposed or in a known manner through one thereon applied, electrically insulating thin layer be covered. In the latter case, the conductor tracks come not in contact with the liquid, and they do not add to the electrode area. In the former case, when the partial area of the conductor tracks in contact with the liquid in relation to the area of the corresponding electrodes is small, covering is not necessary; this particularly favorable embodiment is achieved with short and narrow conductor tracks.

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By, the application of thin film technology is still, a different, new construction of a sensing element possible. It is known in thin-film technology "by. Application of certain alloys such as B. nickel-chromium alloys to create layers on the surface between any two places a significantly greater electrical resistance can be measured than between two equally located points on the surface of a good conductor, e.g. B. a thick copper layer. That The same result can be achieved by applying an extremely thin layer of a good electrical conductor will. When manufacturing resistors using thin-film technology, both parameters, the Layer composition and layer thickness, used usefully.

It has now been found that in a sensing element, advantageously, a considerable electrical resistance in the electrodes is localized and these electrodes of a relatively good conductive liquid on a variable Proportion of their area are contacted, this proportion being practically short-circuited.

In this production method, a sensing element is according to the invention characterized in that in the absence of the liquid the electrical resistance between two Place an electrode surface is much larger than when contacting these points through the liquid speed.

Mercury can be used as the liquid, but certain metals such as gold and silver are used for the

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Formation of the electrodes are excluded - If the specific sheet resistance of the electrodes is high enough can also be a known sensing element liquid as a liquid, z. B. an alkali halide solution used in an alcohol. Depending on the intended use of the sensing element, the organic Solutions and mercury have differences in specific gravity, viscosity, and wetting power etc. to choose one or the other liquid, creating a new possibility for optimal customization of the sensing element is given to the application.

The invention is illustrated in the drawing and explained below, for example. Show it:

Fig. 1 shows a first embodiment of a sensing element, in section, with consisting of thin layers Provide electrodes, conductor tracks and electrode connections;

FIG. 2 shows the cuvette of the sensing element according to FIG. 1, in section, with very much for better illustration enlarged layer thickness of the thin layers;

Fig. 3 shows the cover of the sensing element according to Fig. 1., in Section, with the layer thickness of the drawn in very enlarged for better illustration Thin layers;

Fig. 4- The cover of the sensing element according to Fig. 1, in Top view showing a first embodiment of the electrodes;

Fig. 5 shows the cover of the sensing element according to Fig. 1, in Top view showing a second embodiment of the electrodes;

6 shows a second embodiment of a sensing element,

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in section, with electrodes, conductor tracks and electrode connections consisting of thin layers Mistake.

In the following, Example I refers to Pig. 1, 2, 3 and 4; Example II specifically relates to Pig .. 4; Example III relates in particular to FIG. 5. Examples IV and V also correspond to FIG Fig. 5; and example IT specifically relates to FIG. 6. In all drawings, the same elements are interpreted with the same reference numerals.

Example I.

According to Fig. 1, 2, 3 and 4-, there is a sensing element in the Form of a circular level from a cuvette 1 and a cover 2, which are joined together and cemented the container of the sensing element, in the normal position the cover is above the cuvette and essentially comes to lie horizontally. Both parts are made of hard glass (plastic glass). The cuvette is almost a Cylindrical hollow body with a bottom, the diameter of which is 24 mm on the inside and 28 mm on the outside. At one point the Connection between cylinder 11 and base 12 is. a fusible filler neck 3 is provided. The floor 12 is about 2mm thick. The upper edge 13 of the cylinder 11 is just sanded. The cover 2 is approximately a flat cylinder, the upper side 21 of which is flat and its lower side 22 as a spherical section of 360 mm Radius is ground and polished. Measured at the cylindrical edge 23, the height is 3 mm · the diameter is 28 mm, so that cuvette 1 and cover 2 fit together exactly in terms of their outer diameter.

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All electrodes 40, 44 consist of two layers applied one above the other by vapor deposition, a lower one about 0.15 V * thick layer 41 of 50:50 M-Cr alloy and an upper approximately 0.02 .mu.m thick gold layer 42. The conductor tracks 43, 45 consist of the same thin-film material and are not covered. The base electrode 44 extends over the entire floor 12 ' inside the cuvette 1 and a 1 mm wide conductor track leads from the base electrode along an inner surface line of the cylinder 11 over the edge 13 and along one outer surface line up to a spot 46 of 5 mm diameter located about halfway up, which serves as the electrode connection serves. Four circular electrodes 40 of 7 mm in diameter are on the lower side 22 of the cover 2, in a square with a distance of 7 mm from the center of an electrode to the center the cover. From each electrode 40 a 1 mm wide strip conductor 43 runs radially outward and extends over the corresponding surface line of the edge 23 and over the "upper side 21 of the cover 2 up to a spot 47 of 5 now extends diameter, which is used as the electrode connection serves.

The cuvette 1 and the cover 2 are cemented to one another by conventional epoxy resin 5 (araldite). The one from it formed container is with a 1.5% solution of LiCl in ethanol 6 filled, leaving a gas bubble 7, which at room temperature has a diameter of about 14 mm in diameter. In an optimal bridge circuit, at room temperature and at a Supply voltage of 1 volt (400 Hz) typically achieves a linear characteristic of 50 mV / mrad + 10%.

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Example II

According to Pig. 4- is a sensing element of the one in example Γ described sensing element differing in that the diameter of the four applied to the cover Electrodes is 5 ma and the diameter of the gas bubble is about 16 mm. A linear characteristic curve of 140 mV / mrad + 10% is typically achieved.

Example III

According to FIG. 5, a sensing element differs from the sensing element described in Example I in that a different electrode shape is used for the four electrodes applied to the cover. These electrodes are derived from the vertical projection of a flat square which has two straight and parallel sides 6 mm long and 4 mm apart and two circular arc-shaped sides 7 mm in radius. The greatest distance between two opposing electrodes is 8 mm, so that the front circular arc-shaped side of one electrode lies on the same circle as the rear circular arc-shaped side of the opposite electrode. The diameter of the gas bubble is about 14 mm at room temperature. A linear characteristic curve of 60 mV / mrad + 10 % is typically achieved.

Example IV

One sensing element is from that described in Example III Sensing element differing in that other dimensions of the electrodes are used. The length of the straight sides is 4, 1 mm, so that the circular arc-shaped sides

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the electrodes do not come to rest on the same circles. It will typically have a linear characteristic of 160 mV / mrad + 10% achieved.

Example V

A sensing element is of that described in Example IV Sensing element differing in that the cover is made of silicon, which is 0.2 u thick, thermally generated, electrically insulating oxide layer is coated. The results are the same as in the Achieved Example IV.

Example VI

Referring to Fig. 6, a sensing element is different from that in the example III described sensing element differing in that the base electrode and the conductor tracks are made of pure Nickel, while the four electrodes applied to the cover are made from a 0.01 µm thick layer of one 80:20 Ni-Cr alloy, and the liquid used is mercury. Comes in normal position the cover 2 to lie below the cuvette 1. The mercury forms a liquid drop 8 about 14 mm in diameter on the cover. It will be a approximately linear characteristic curve of 50 mV / mrad is achieved.

Patent claims:

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Claims (1)

Claims Λ.) Sensing element for determining the plumb bob by measuring an electrical impedance, which changes depending on the tilt, between flat electrodes which are in contact with a liquid contained in a container and are each connected to an externally contactable electrode connection, characterized in that at least one of the liquid facing, electrically insulating surface of a wall of the container (1) an electrode (40, A4) is formed as a thin layer applied to this surface. 2. Sensing element according to claim 1, characterized in that that a wall of the sensing element made of electrically conductive material at least on its the surface facing the liquid of an electrically insulating layer applied as a thin layer Material is coated, creating a wall with an electrically insulating surface is. Sensing element according to Claim 1, characterized in that that at least two flat electrodes (40) dm is known to be assigned to one another as a pair which is symmetrical about a normal vertical plane are, and the outline of an electrode surface on .die surface of the wall projected perpendicular The outline of a flat quadrilateral is made up of one having sides parallel to the plane of symmetry Rectangle by inserting circular arcs 5 09827/0804 -20- is derived with the plane of symmetry facing concavity instead of said sides. 4. sensing element according to claim 3i, characterized in that that in a pair of electrodes the outlines of the electrodes (4-0) from the projection of two symmetrical squares exist whose circular arc-shaped sides as the same arc of two equal ', are on the plane of symmetry intersecting circles are formed. Sensing element according to Claim 1, characterized in that that an electrode (40) with an associated electrode connection through a conductor track (43) electrically is connected, which as a thin layer on electrically insulating surface parts of to a container assemblable components of the sensing element is applied. 6. Sensing element according to claim 1, characterized in that in the absence of the liquid the electrical Resistance between two points of an electrode surface is significantly greater than when making contact these spots through the liquid. 7. sensing element according to claim 1, characterized in that that at least one thin-film electrode (40, 44) is multilayered and that on the outer side of the multilayer electrode structure facing away from the wall has a vapor-deposited, electrochemically active black layer is located. 509827/0804 - 21 - 8. Sensing element according to claim 7> characterized in that that the electrochemically active black layer is galvanically treated after the vapor deposition. The patent attorney 5098 27/0804